Plant Flow Measurement and Control Handbook [1st ed.] 9780128124383

Table of contents :
Cover......Page 1
Plant Flow Measurement and Control Handbook......Page 2
Copyright......Page 3
XI -
Flow Conditioning Computation and Control......Page 4
Foreword......Page 5
Index......Page 6
Acknowledgments......Page 8
1.0.0 INTRODUCTION......Page 9
1.0.1 DISCUSSIONS COVERED IN THIS BOOK......Page 11
1.1.0 Flow Measurement Basics......Page 13
1.1.1 BASIC CHARACTERISTICS AND ASSOCIATED TERMS FOR FLOW METERS......Page 16
1.1.2 PHYSICS ON FLUID PROPERTIES......Page 17
1.2.1 IMPORTANT TERMS RELATED TO INSTRUMENTATION......Page 27
1.2.2 TERMS RELATED TO THE PROCESS......Page 30
2.0.0 BASIC FLUID MECHANICS......Page 39
2.1.2 BERNOULLI'S EQUATION FOR FLOW CALCULATIONS......Page 42
2.1.3 FLOW EQUATION IN TERMS OF PIPE GEOMETRY......Page 43
2.1.4 DISCHARGE COEFFICIENT......Page 44
2.1.6 RELATED DISCUSSION TERMS......Page 45
2.1.8 MEASUREMENT AND FLOW COMPUTATION......Page 46
2.1.9 PRESSURE/TEMPERATURE COMPENSATION FOR FLOW......Page 49
3.0.0 FLOW MEASUREMENT TYPES AND PRINCIPLES......Page 50
3.1.0 Fluid Flow Measurement Types and Principles......Page 51
3.1.1 INFERENTIAL FLOW METER TYPES AND PRINCIPLES......Page 52
3.1.2 POSITIVE DISPLACEMENT FLOW METER TYPES AND PRINCIPLES......Page 60
3.1.3 VELOCITY AND FORCE FLOW METER TYPES AND PRINCIPLES......Page 65
3.1.4 MASS FLOW METER TYPES AND PRINCIPLES......Page 79
3.1.5 FLUID FLOW MEASUREMENT IN AN OPEN CHANNEL......Page 85
3.2.0 Solid Flow Measurement Types and Principles......Page 91
3.2.1 SOLID FLOW METERS BASED ON FORCE AND DEFLECTION PRINCIPLES......Page 92
3.2.2 SOLID FLOW METERS BASED ON LOAD SPEED/TIME PRINCIPLES......Page 97
3.2.3 NONCONTACT TYPE SOLID FLOW MEASUREMENT......Page 102
3.3.1 MAJOR CHARACTERISTIC FEATURES OF SLURRY FLOW AND ITS EFFECTS......Page 105
3.3.2 FLOW METER TYPES FOR SLURRY FLOW......Page 106
3.4.0 Multiphase Flow Measurement Types and Principles......Page 107
3.4.1 APPROACHES FOR MULTIPHASE FLOW METERING......Page 108
3.4.2 TYPES OF METERING PHILOSOPHIES......Page 109
3.4.3 MFM TECHNOLOGIES......Page 112
4.0.0 SELECTION OF FLOW METERS......Page 117
4.1.0 General Discussions on the Flow Meter Selection Process (Closed Pipe)......Page 119
4.2.1 PROCESS ISSUES FOR FLOW METER SELECTION......Page 121
4.2.2 SELECTION PROCESS RELATED TO THE FLOW METER......Page 124
4.4.0 Cost and Approval Considerations for Flow Meter Selection......Page 129
4.5.0 Flow Meter Selection Matrix......Page 130
5.0.0 DISCUSSIONS ON PERMANENT PRESSURE LOSS AND ALLIED ISSUES......Page 133
6.1.0 Principles and Good Practices for Installations......Page 135
6.2.0 Principles and Good Practices for Calibrations......Page 138
6.2.1 FLOW METER CALIBRATION ISSUES......Page 140
7.0.0 CRITICAL OR SONIC NOZZLE......Page 142
7.3.0 Functional Details of Sonic Flow Nozzles......Page 143
8.1.1 AEROFOIL WORKING PRINCIPLES......Page 144
8.2.0 British Thermal Unit Measurement......Page 145
8.2.2 SENSORS USED IN BRITISH THERMAL UNIT MEASUREMENT SYSTEMS......Page 146
8.3.1 THEORY OF OPERATION......Page 148
8.3.3 DISCUSSIONS ON CROSS-CORRELATION MEASUREMENT......Page 151
LIST OF ABBREVIATIONS......Page 152
REFERENCES......Page 153
FURTHER READING......Page 156
1.0.0 POSITIVE DISPLACEMENT METERS: GENERAL DISCUSSIONS......Page 340
1.1.1 GENERAL REQUIREMENTS AS PER ISO 5167-PART 1......Page 158
1.1.2 GENERAL DISCUSSIONS ON INSTALLATION (ISO 5167-1:2003)......Page 159
1.1.3 The Étoile Straightener......Page 160
1.2.2 Types of Corrosion Process......Page 1137
1.3.0 Volume and Mass Conversion Factor......Page 161
2.3.0 Pipe Flow of Slurries......Page 162
2.2.0 Tapping Point Installations and Mounting......Page 169
2.5.0 Specification of Hall Sensors......Page 939
3.2.3 Operation Part of IEC 61511......Page 171
2.2.3 ORIFICE PLATE MOUNTING......Page 172
2.2.4 IMPULSE LINE INSTALLATION......Page 175
2.2.5 UPSTREAM/DOWNSTREAM STRAIGHT PIPE REQUIREMENTS......Page 179
2.2.6 PERMANENT PRESSURE LOSS......Page 180
3.1.0 Solid Flow Characteristic Features and Essential Properties......Page 1134
2.3.2 Slurry Flow in a Vertical Pipe......Page 181
2.5.2 Straight Length Requirement and Flow Conditioners......Page 182
2.4.1 LIQUID FLOW METER CALIBRATION: GENERAL DISCUSSION......Page 183
2.4.3 ORIFICE PLATE CALIBRATION......Page 186
3.2.1 Elbow and PCHB for Flow......Page 188
2.5.3 INTEGRAL ORIFICE ASSEMBLY......Page 191
2.5.4 SENIOR ORIFICE ASSEMBLY......Page 192
2.4.0 Material Selection, Sizing, and Flow Range......Page 416
5.3.1 Features of Digital Local Flow Meters......Page 955
3.0.0 FLOW NOZZLE......Page 195
3.1.0 Description of the Construction Details and Features: Flow Nozzles......Page 196
3.3.0 Rectangular Weirs......Page 199
3.2.1 TAPPING STYLES......Page 200
3.2.2 TAPPING DIAMETER AND SOURCE POINT......Page 201
3.2.3 FLOW NOZZLE MOUNTING......Page 202
3.2.4 Major Application Areas......Page 444
3.3.0 Discussions on ISO 5167-3:2003 Standard......Page 206
4.4.4 EMFMs in Paper Plants......Page 662
7.2.2 Installation Requirements of Paddle Type Flow Switches......Page 208
3.5.0 Specification/Data Sheet......Page 209
4.7.2 PULL CHORD SWITCH......Page 782
3.6.1 SONIC FLOW PRINCIPLES......Page 211
3.4.0 Meter Size, Selection, and Performance......Page 213
4.2.1 TAPPING DETAILS......Page 216
4.2.4 STRAIGHT LENGTH REQUIREMENTS......Page 217
4.2.5 PERMANENT PRESSURE LOSS......Page 218
4.3.1 GENERAL DISCUSSION......Page 220
4.5.0 Specification/Data Sheet for Venturi Tube......Page 221
5.1.1 Description of Direct-Flow Gages......Page 950
5.1.1 FLOW ELEMENT DESCRIPTION AND APPLICATIONS......Page 224
5.2.0 Dall Tube......Page 225
5.2.2 CHARACTERISTIC FEATURES AND APPLICATIONS OF DALL TUBES......Page 226
6.0.1 BASIC PRINCIPLES OF PITOT TUBES......Page 227
6.0.2 FLOW CALCULATIONS......Page 228
5.0.0 Wedge Flow Element......Page 229
6.1.4 PITOT TUBE SPECIFICATIONS......Page 231
6.2.1 DESIGN AND CONSTRUCTION DETAILS......Page 232
6.2.3 MOUNTING AND INSTALLATION......Page 234
6.2.4 SPECIFICATION OF AN AVERAGE PITOT......Page 235
6.2.5 AIR AND FLUE GAS MEASUREMENT BY AN AVERAGE PITOT TUBE......Page 236
6.3.0 Krell Bar......Page 237
7.1.1 DESCRIPTION......Page 238
7.2.0 Flow Element Calculation......Page 240
7.3.3 PRESSURE AND TEMPERATURE MEASUREMENT AND COMPENSATION......Page 241
7.4.3 TRANSMITTER CONNECTION......Page 242
7.5.2 SPECIFIC DATA......Page 244
8.1.1 WORKING PRINCIPLES......Page 246
8.1.2 SIZING AND FLOW EQUATION......Page 247
8.1.4 DESIGN DETAILS......Page 248
8.1.5 MOUNTING AND INSTALLATION......Page 249
8.1.7 SPECIFIC DATA......Page 251
8.2.1 CHARACTERISTIC FEATURES OF ELBOW TAPPING FLOW ELEMENTS......Page 252
9.1.1 BASIC PRINCIPLES OF OPERATION OF A ROTAMETER......Page 253
9.1.2 ROTAMETER FLOW SIZING......Page 255
9.1.4 ROTAMETER TYPES......Page 256
9.1.5 ROTAMETER DESIGN DETAILS......Page 258
9.2.0 Other Variable Area Flow Meters......Page 260
LIST OF ABBREVIATIONS......Page 262
FURTHER READING......Page 263
APPENDIX
VI - Enclosure Electrical Protection......Page 1136
1.0.0 BASIC PRINCIPLES AND GENERAL DISCUSSION......Page 265
1.0.1 APPROACHES FOR OPEN CHANNEL FLOW MEASUREMENT......Page 266
2.3.2 MEASUREMENT ACCURACY......Page 272
1.0.3 SELECTION FOR OPEN-CHANNEL FLOW MEASUREMENT......Page 276
2.4.2 FEATURES AND ADVANTAGES......Page 278
1.1.0 Fluid Mechanics of Open Channels......Page 279
2.4.2 Applications in Flow Measurement......Page 938
1.1.2 CONSERVATION OF ENERGY......Page 280
1.1.3 MOMENTUM FORCE AND VELOCITY DISTRIBUTION......Page 281
2.2.1 Homogeneous Flow......Page 282
1.1.6 FRICTION EQUATIONS AND ROUGHNESS COEFFICIENT......Page 283
1.1.7 SPECIFIC ENERGY......Page 285
1.2.0 Properties of Open Channels......Page 288
2.0.0 DISCUSSIONS ON METER TYPES USED IN CUSTODY TRANSFER......Page 289
2.1.2 EXPLANATION OF FLUME GEOMETRY......Page 290
2.1.4 SITE CONDITIONS AND ASSOCIATED TECHNICAL ISSUES......Page 291
2.1.5 SUBMERGENCE AND MODULAR FLOW......Page 292
3.1.2 Positive Displacement Meter Complex Flow Measurement......Page 647
2.1.7 HEAD SENSING TECHNOLOGY......Page 293
2.2.0 Venturi Flume......Page 294
2.2.1 DIFFERENT VENTURI FLUMES......Page 295
2.3.0 Parshall Flume......Page 297
3.1.5 Ultrasonic Meter for Complex and Slurry Flow Measurement......Page 652
2.3.2 PARSHALL FLUME INSTALLATION DISCUSSIONS......Page 300
2.4.0 H Flume......Page 301
2.5.0 Cutthroat Flume......Page 302
3.0.0 DISCUSSIONS ON PROVER SYSTEMS AND MASTER METERS......Page 303
2.8.2 Gas Turbine Flow Meter......Page 305
3.1.2 SUBMERGED FLOW IN A WEIR......Page 306
3.1.4 SILTATION IN WEIRS......Page 307
3.1.4 Meter K Factor and Performance......Page 308
3.2.0 V-Notch Weir Details......Page 309
3.4.0 Trapezoidal or Cipoletti......Page 311
3.5.2 DESCRIPTION OF BROAD-CRESTED WEIRS......Page 312
5.2.1 Use of DP Type Meters......Page 1101
3.5.3 DESIGN BASIS FOR BROAD-CRESTED WEIRS......Page 313
4.6.0 Motor Speed Control......Page 780
4.0.0 SECONDARY INSTRUMENTS FOR OPEN-CHANNEL FLOW MEASUREMENT......Page 315
3.3.0 General Design Details......Page 316
4.1.2 STAFF GAGE......Page 322
4.2.6 Pressure Loss for Thermal Dispersion Mass Flow Meters......Page 609
4.1.4 ONLINE PRESSURE SENSOR/TRANSDUCER......Page 325
4.1.5 ULTRASONIC LEVEL SENSING SYSTEM......Page 327
4.1.6 BUBBLER TYPE LEVEL MEASUREMENT......Page 330
4.2.1 TRANSMITTER DESCRIPTION......Page 333
4.2.2 SPECIFICATION......Page 334
4.2.3 MOUNTING AND INSTALLATION......Page 335
LIST OF ABBREVIATIONS......Page 337
REFERENCES......Page 338
FURTHER READING......Page 339
1.1.0 PD Meter Working Principles......Page 341
1.2.1 Power Supply in a Current Loop......Page 1213
1.3.0 Unit Conversion for Power......Page 342
1.1.2 BELT CONVEYOR......Page 691
1.4.1 FACTORS INFLUENCING VOLUME DISPLACEMENT IN PD METERS......Page 343
1.2.1 Viscoelasticity......Page 634
1.4.3 PERFORMANCE CRITERIA FOR PD METERS......Page 345
1.5.1 MAJOR APPLICATION AREAS FOR PD METERS......Page 346
1.5.2 SELECTION GUIDELINES FOR PD METERS......Page 347
1.7.1 CALIBRATION ISSUES FOR PD METERS......Page 350
1.7.4 SOME IMPORTANT PD METER ISSUES......Page 352
1.9.0 Custody Transfer Applications......Page 353
C......Page 1241
2.1.3 SIZING AND SELECTION OF NUTATING DISCS......Page 354
2.1.4 PRESSURE DROP......Page 355
2.1.4 Multivariable Transmitters......Page 356
2.4.1 FLOW METER IN GRAVITY PRESSURE INSTALLATION......Page 357
2.5.2 General Installation Discussions......Page 572
2.4.3 FLOW METER IN UTILITY APPLICATIONS......Page 359
2.0.1 Risk Frequency......Page 1173
3.1.2 DESCRIPTIVE DETAILS FOR OVAL GEAR METERS......Page 360
3.1.3 PRESSURE LOSS......Page 361
3.2.1 MAJOR FEATURES AND ADVANTAGES......Page 362
3.3.1 ELECTRICAL SECTION......Page 363
3.4.1 METER SIZE AND RANGE SELECTION......Page 364
3.4.2 METER PERFORMANCE AND K FACTOR......Page 365
3.5.0 Specification of Oval Gear Meters......Page 366
3.6.1 METER ORIENTATION......Page 368
2.3.1 THEORY OF OPERATION FOR IMPACT SCALE SOLID FLOW METERS......Page 716
4.1.2 DESCRIPTIVE DETAILS OF ROTATING PISTON METERS......Page 370
4.1.3 PRESSURE LOSS IN THE METER......Page 372
3.6.3 Specification......Page 459
4.3.0 General Design Details......Page 373
6.3.2 Major Flow Instruments Used......Page 374
7.2.0 Constant Mass Flow Controllers......Page 1060
4.4.2 OVERALL PERFORMANCE......Page 375
6.5.0 Specification of Noncontact Type Nucleonic Solid Flow Measuring Systems......Page 793
5.0.0 ROTATING VANE METERS......Page 377
7.3.1 CAPACITANCE TYPE SOLID FLOW MEASUREMENT......Page 797
5.1.2 DESCRIPTIVE DETAILS OF ROTATING VANE PD METERS......Page 378
5.2.0 Features and Applications of Rotating Vane PD Meters......Page 380
5.3.1 PHYSICAL/MECHANICAL DESIGN DETAILS......Page 381
5.4.1 METER SIZES FOR SELECTION......Page 382
5.5.0 Specification of Rotating Vane PD Meters......Page 383
5.6.0 Installation Details......Page 384
1.1.0 Discussions on Mechanical Equipment for Solid Flow......Page 688
6.1.1 PRINCIPLES OF OPERATION......Page 385
6.1.2 DESCRIPTIVE DETAILS OF ROTATING VANE PD METERS......Page 386
9.2.0 Speed Sensor......Page 387
6.5.0 Specification of Reciprocating Piston PD Meters......Page 388
6.6.0 Installation Details......Page 390
7.1.2 OPERATING CONDITIONS AND AVAILABLE SIZES OF LOBED IMPELLER PD METERS......Page 391
5.1.2 METER DESCRIPTION......Page 783
7.2.1 OPERATIONAL DETAILS......Page 392
7.3.1 OPERATING PRINCIPLES OF GEAR PD METERS......Page 393
7.4.2 BRIEF SPECIFICATION OF ROTARY METERS......Page 394
6.3.1 RADIATION SOURCE......Page 790
8.3.0 Shutoff Valve......Page 395
8.6.0 Local and Remote Register......Page 396
9.1.0 Hall Effect Sensing......Page 397
9.2.0 Hall Effect Flow Sensors......Page 399
LIST OF ABBREVIATIONS......Page 400
6.0.0 NONCONTACT TYPE NUCLEONIC SOLID FLOW METERS......Page 401
2.1.0 Theoretical Background of Hall Effect......Page 403
1.3.0 Oscillating Type Flow Meters......Page 404
3.2.0 Enclosure Classes......Page 405
2.1.2 Description of a Turbine Meter......Page 406
2.1.3 Pickup Types......Page 408
1.1.4 DUST Cloud Measurement......Page 410
2.1.6 Brief Technical Details for Gas Turbine Flow Meter......Page 412
2.2.2 Application of TFMs......Page 413
2.3.2 Rotor Assembly and Some Other Meter Internals......Page 414
2.3.3 Turbine Flow Meter Bearings......Page 415
2.5.6 CORIOLIS METER DISCUSSIONS......Page 1164
3.2.1 PIPE PROVERS......Page 1075
2.4.2 Meter Sizing and Flow Range......Page 417
2.3.5 Foreign Materials and Medium Quality......Page 419
2.1.2 PHASE FRACTION MEASUREMENT......Page 421
2.7.1 Installation Discussions......Page 422
2.3.1 Air Flue Gas Flow Measurements......Page 423
2.8.1 Insertion Type Turbine Flow Meter......Page 424
2.8.3 Double-Rotor Turbine Flow Meter......Page 428
2.9.0 Other Inferential Flow Meters......Page 431
2.1.3 FEATURES AND APPLICATION DETAILS......Page 709
2.9.2 Woltman Flow Meter......Page 432
3.0.0 Vortex and Swirl Type Flow Meters......Page 433
4.0.0 Foundation Fieldbus......Page 1228
4.0.0 Oil and Gas Applications......Page 435
3.0.4 Swirl/Vortex Precision Meter......Page 436
4.0.0 SIF, SIL, and SIS......Page 1183
3.1.1 Principles of Operation......Page 438
3.1.2 Description of Vortex Meter......Page 439
3.1.3 Bluff Body and Sensor Description......Page 441
4.2.2 Thermal Dispersion Mass Flow Meter Characteristics Issues......Page 446
4.2.0 Multiphase Flow Meter Specification Issues......Page 923
3.2.2 Application Area......Page 447
3.3.1 Sensor and Converter Design......Page 448
3.3.3 Flow Range and Sizing......Page 452
4.5.3 Wedge Flow Element in Alumina Plant-Red Mud......Page 665
7.4.2 Specification of Variable Orifice Flow Switches......Page 614
5.5.1 Element Orientation and Alignment......Page 675
3.5.1 Mounting of Vortex/Swirl Meters......Page 456
3.5.2 Meter Installation Discussions......Page 457
4.1.0 Basic Theory of Measurement......Page 460
4.2.1 Meter Categories, Features and Applications......Page 463
4.1.1 DISCUSSIONS ON OPERATING PRINCIPLES......Page 464
4.3.1 Range Limits and Accuracy......Page 465
5.4.0 Specification Details for Wedge Elements......Page 673
4.4.1 Range Limits and Accuracy......Page 466
5.0.1 Basic Theory of Measurement......Page 467
5.0.2 Parameters and Constraints......Page 468
5.0.3 Induced Voltage Measurement......Page 469
5.0.4 Magnetic Field Characteristics......Page 470
5.0.6 Noise Issues......Page 472
5.1.0 Descriptive Details of Electromagnetic Flow Meters......Page 473
3.6.8 MAGNETIC RESONANCE IMAGING......Page 917
4.2.4 BELT SCALE/BELT WEIGHER SELECTION GUIDE......Page 761
5.1.3 Operating, Environmental Parameters, and Protection for Flow Meters......Page 474
5.1.4 Meter K Factor and Performance Data......Page 475
5.2.1 Features of Electromagnetic Flow Meters......Page 477
8.0.0 Signal Processing in Smart Transducers and Converters......Page 1061
5.3.0 Part Details and Design Aspects of Electromagnetic Flow Meters......Page 478
5.3.1 Electrodes and Associated Design Issues......Page 479
5.3.2 Magnetic Field and Field Excitations Discussions......Page 480
5.3.3 Electromagnetic Flow Meter Grounding......Page 483
5.3.4 Noise and Electronic Design Improvements......Page 484
5.3.5 Secondary Device (Transmitter)......Page 485
5.3.6 Flow Ranges, Meter Sizing, and Selection......Page 488
5.3.7 Material Selection Guide......Page 490
5.4.0 Specifications of Electromagnetic Flow Meters......Page 491
5.5.0 Installation Discussions......Page 492
5.7.0 Insertion Type Electromagnetic Flow Meters......Page 495
6.0.0 Ultrasonic Flow Meters (USFMs)......Page 498
6.0.1 Basic Theory of Operation of Doppler Type USFMs......Page 499
6.1.1 Descriptive Details of Doppler USFMs......Page 501
6.1.2 Descriptive Details on Transit Time USFMs......Page 502
6.1.3 Description of Other Types of USFM......Page 504
6.1.4 Transducers......Page 505
6.1.5 Secondary Electronics for USFMs......Page 508
6.2.0 Meter Performance and Associated Factors......Page 510
6.2.2 Installation Effects......Page 511
6.3.1 Features of USFMs......Page 512
6.3.2 Application Area of USFMs......Page 513
6.4.1 Specification of Doppler Type USFMs......Page 514
6.4.2 Specification of Transit Time Type USFMs......Page 516
6.5.0 Inline USFM......Page 518
6.5.2 Components of Inline USFMs......Page 519
6.5.4 Minimum Back Pressure for Inline USFM in Liquid Applications......Page 520
6.6.0 USFM Installation Discussions......Page 521
6.7.0 Discussion on Meter Selection Process (Within the Same Meter Category)......Page 522
6.7.2 Requirements and Constraints......Page 523
6.7.3 Selection Discussions......Page 524
6.9.0 Concluding Discussions and Recent Developments......Page 525
7.1.1 Cup Type Mechanical Anemometer......Page 526
7.1.2 Vane Type Mechanical Anemometer......Page 527
7.2.1 Features of Thermal Hotwire Anemometers (HWA)......Page 528
7.2.2 Descriptive Details: Hotwire Anemometers (HWA)......Page 529
7.3.0 Doppler Effect Anemometer (Anemometry)......Page 531
7.3.2 Laser Doppler Anemometry Principles......Page 532
7.3.4 Specification for Laser Doppler Anemometers......Page 534
8.1.2 Target Meter With Deflection......Page 535
8.2.1 Features of Target Flow Meters......Page 536
8.3.1 Descriptive Details of the Target Variable Area Flow Meter......Page 537
8.4.1 Specification for Target Flow Meters......Page 538
8.4.2 Specification for Target Variable Area Flow Meters [45,46]......Page 539
9.1.1 Volumetric Flow......Page 540
9.2.1 Features......Page 541
9.3.0 System Specification [49]......Page 543
List of Abbreviations......Page 544
References......Page 545
Further Reading......Page 546
1.0.0 Introduction and General Discussions......Page 547
2.0.0 Coriolis Mass Flow Measurement......Page 548
1.1.1 Installation Problems and Solutions......Page 549
2.1.2 Theory of Operation of Coriolis Flow Mass Flow Meter......Page 552
2.1.3 Descriptive Details of Coriolis Meter and Design Issues......Page 554
2.1.4 Coriolis Meter Characteristics......Page 559
2.1.5 Operating and Environmental Conditions......Page 561
2.4.5 PROVING LIQUID ULTRASONIC FLOW METERS......Page 562
2.1.8 Materials of Construction and Process Connections......Page 564
2.1.9 Performance Data......Page 565
2.2.2 NONMETALLIC ELASTOMERIC MATERIALS......Page 566
2.3.2 Temperature Effect......Page 567
2.3.7 Other Conditions......Page 568
2.5.0 Coriolis Mass Flow Meters Installation Discussions......Page 571
2.6.1 Zero Checking and Calibration......Page 573
3.0.0 Impeller Turbine Mass Flow Measurement......Page 574
4.0.0 Thermal Mass Flow Measurement......Page 576
4.0.1 Theoretical Background of Heat Transfer Mass Flow Meters......Page 577
4.0.2 Theoretical Background of Thermal Dispersion Mass Flow Meters......Page 580
4.1.0 Capillary (Bypass Heat Transfer) Thermal Mass Flow Meters......Page 583
4.1.1 Formula Derivation for Capillary Thermal Mass Flow Meters......Page 584
4.1.2 Descriptive Details of Capillary Thermal Mass Flow Meters (TMFM)......Page 586
4.1.3 Operating Conditions and Performances of Thermal Mass Flow Meters......Page 589
4.1.5 Gas Conversion and Allowed Gases......Page 590
4.1.6 Specification of Thermal Mass Flow Meters......Page 591
4.2.1 Formula Derivation for Thermal Dispersion Mass Flow Meters......Page 593
2.3.2 DESCRIPTIVE DETAILS OF IMPACT FLOW METERS......Page 719
4.2.4 Thermal Dispersion Mass Flow Meter Design Issues......Page 603
4.2.5 Specification of Thermal Dispersion Mass Flow Meters......Page 607
3.3.3 NEUTRON ACTIVATION ANALYSIS PROCESS......Page 889
4.2.8 Installation and Adjustments for Thermal Dispersion Mass Flow Meters......Page 610
4.3.2 Limitations of Thermal Mass Flow......Page 615
4.3.4 Digital Meter Configuration......Page 616
List of Abbreviations......Page 617
Further Reading......Page 618
Preamble......Page 1169
A......Page 620
1.0.1 Fluid Classification by Rheology......Page 622
1.0.2 Discussions on Fundamental Terms in Rheology......Page 624
1.1.0 Rheology and Viscosity......Page 629
1.1.1 TERMS AND DEFINITIONS......Page 811
1.1.2 Non-Newtonian Time-Independent Viscosity......Page 631
1.1.3 Non-Newtonian Time-Dependent Viscosity......Page 633
1.2.4 Current Loop Types......Page 1214
2.1.1 Terms Frequently Used for Slurry Flow Measurement......Page 636
2.1.2 Objective and Classification of Slurry Flow......Page 637
2.2.0 Solid-Liquid Flow Regime......Page 639
2.2.2 Heterogeneous Flow......Page 640
2.3.1 Slurry Flow in a Horizontal Pipe......Page 641
3.0.1 Meter Types......Page 642
3.0.2 Meter Selection Guide for Complex and Slurry Flows......Page 644
3.1.1 DP Method in Slurry Flow......Page 646
3.1.3 Turbine Meter for Complex and Slurry Flow Measurement......Page 648
3.1.4 Electromagnetic Meter for Complex and Slurry Flow Measurement......Page 649
3.1.8 Slurry Flow Measurement and Electrical Resistance Tomography......Page 653
1.7.0 Custody Transfer Measurements and Legal Issues......Page 655
4.0.0 Instrumentation for Selected Slurry and Complex Flow Applications......Page 656
4.1.2 Ash Slurry and Limestone Flow Meter......Page 657
4.2.0 Cement Slurry Flow Measurement......Page 658
4.1.1 Different Major Flow Instruments Used in Oil and Gas......Page 1084
4.3.2 Purpose of Drilling Fluid and Types of Drilling......Page 659
4.3.3 Coriolis Meters in Drilling Operations......Page 660
4.4.0 Pulp and Paper Slurry Flow Measurement......Page 661
4.4.5 SONAR in Paper Plants......Page 663
5.3.0 PROFIBUS Configuration and Communication......Page 1233
4.5.1 Alumina Plant and Red Mud......Page 664
4.6.0 Complex Fluids in Food and Beverages......Page 666
6.2.3 Mass Flow Meters......Page 667
5.1.3 Discharge Coefficient......Page 668
5.1.4 Wedge (H/D) Ratio......Page 669
5.2.2 Operating Conditions and Flow Capacity......Page 670
5.2.3 Performance Data......Page 671
5.3.1 Special Features of Wedge Elements......Page 672
5.5.2 Instrument Connection and Transmitter Types......Page 676
7.3.3 Sonar Type Flow Metering in Aluminum Manufacturing......Page 1114
5.5.4 Mechanical Steps for Installation of Wedge Elements......Page 677
List of Abbreviations......Page 678
References......Page 679
Further Reading......Page 680
1.0.0 INTRODUCTION: AN OVERVIEW OF SOLID FLOW MEASUREMENT......Page 682
1.0.1 DISCRETE MASS DELIVERY WEIGHING SYSTEMS......Page 683
1.0.3 IN-MOTION WEIGHING SYSTEMS-DISCRETE MASS WEIGHING SYSTEM-WEIGHBRIDGES......Page 686
1.1.1 FEEDING ARRANGEMENT FOR SOLID FLOW......Page 690
1.1.3 ROTARY FEEDER......Page 692
1.1.5 DRAG CONVEYOR AND APRON FEEDER......Page 693
1.1.6 VIBRATING FEEDER AND TABLE FEEDER......Page 694
1.1.7 BUCKET CONVEYOR......Page 695
2.1.3 Link RS (EIA) 485......Page 696
1.2.0 Material Characteristics for Solid Flow......Page 697
1.2.1 FORCES AND STRESSES IN BULK SOLIDS DURING FLOW......Page 699
1.2.3 PROPERTIES FOR FLOWABILITY OF BULK SOLIDS......Page 700
1.2.4 FACTORS INFLUENCING FLOWABILITY OF FINE BULK SOLIDS......Page 701
2.1.0 Metals and Alloys......Page 1139
1.3.1 COMPARISON OF VARIOUS WEIGH FEEDER TYPES......Page 703
1.3.2 COMPARISON OF VARIOUS SOLID FLOW METERS......Page 704
1.4.2 DISCUSSIONS ON SOLID FLOW MEASUREMENT SYSTEM CHOICES......Page 705
1.4.4 MATERIAL CHARACTERISTIC AND CONSTANT PARAMETER ASSUMPTION......Page 706
2.1.1 THEORY OF OPERATION......Page 707
1.6.2 Mass Flow Rate Conversion Factors......Page 1131
2.1.5 INSTALLATION......Page 710
2.2.0 Coriolis Solid Flow Meter......Page 711
2.2.1 THEORY OF OPERATION......Page 712
2.2.3 FEATURES AND APPLICATION DETAILS......Page 713
2.2.4 SPECIFICATION OF CORIOLIS SOLID MASS FLOW METER......Page 714
2.3.0 Impact Scale Solid Flow Meter......Page 715
2.3.3 FEATURES AND APPLICATIONS OF IMPACT FLOW METERS......Page 720
2.3.4 SPECIFICATIONS OF IMPACT SCALE SOLID MASS FLOW METERS......Page 721
2.3.5 INSTALLATION AND CALIBRATION DISCUSSIONS FOR IMPACT SCALES......Page 722
3.0.0 GRAVIMETRIC FEEDER AND LOSS IN WEIGHT......Page 723
3.1.1 PRINCIPLES OF OPERATION FOR GRAVIMETRIC FEEDERS......Page 725
3.1.2 FEATURES OF GRAVIMETRIC FEEDER WITH DESCRIPTIVE DETAILS......Page 728
3.1.3 APPLICATION AREAS OF GRAVIMETRIC FEEDERS......Page 729
3.2.0 Loss-in-Weight Measurement......Page 735
3.2.1 PRINCIPLES OF OPERATION OF LOSS IN WEIGHT......Page 736
3.2.2 DESCRIPTIVE DETAILS FOR LOSS-IN-WEIGHT MEASUREMENT......Page 739
3.2.3 FEATURES AND APPLICATIONS OF LOSS-IN-WEIGHT MEASUREMENT......Page 742
3.2.4 SPECIFICATION OF LOSS-IN-WEIGHT MEASUREMENT......Page 743
3.2.5 LOSS-IN-WEIGHT MEASUREMENT WITHOUT A LOAD CELL......Page 745
4.0.0 BELT WEIGHING SYSTEM......Page 747
4.1.0 Weigh Feeder Systems......Page 748
4.1.2 DESCRIPTIVE DETAILS OF WEIGH FEEDERS......Page 749
4.1.3 FEATURES OF WEIGH FEEDER (ALSO BELT SCALE/BELT WEIGHER)......Page 753
4.1.5 SPECIFICATIONS OF WEIGH FEEDERS......Page 754
4.1.7 WEIGH FEEDER DISCUSSIONS......Page 756
4.2.1 FUNCTIONAL ASPECTS OF THE BELT SCALE/BELT WEIGHER......Page 757
4.2.2 DESCRIPTIVE DETAILS OF BELT SCALES/BELT WEIGHERS (ADDITIONAL DETAILS)......Page 758
4.2.3 SPECIFICATIONS OF BELT SCALE/BELT WEIGHERS......Page 759
4.3.0 Load Cell and Sensing Electronics......Page 762
4.3.1 DESCRIPTIVE DETAILS OF LOAD CELL MEASUREMENT......Page 765
4.3.2 LOAD CELL DISCUSSIONS......Page 768
4.3.3 LOAD CELL SPECIFICATION......Page 771
4.4.1 DESCRIPTIVE DETAILS OF SPEED SENSING......Page 773
4.4.2 SPECIFICATION OF SPEED SENSING......Page 775
4.5.1 FUNCTIONAL DETAILS OF WEIGHING ELECTRONIC INTEGRATOR AND CONTROLLER......Page 776
4.5.2 FEATURES AVAILABLE FOR WEIGHING ELECTRONIC INTEGRATORS AND CONTROLLERS......Page 777
4.5.3 DESCRIPTIVE DETAILS OF WEIGHING ELECTRONIC INTEGRATORS AND CONTROLLERS......Page 778
4.5.4 SPECIFICATION OF WEIGHING ELECTRONIC INTEGRATORS AND CONTROL SYSTEMS......Page 779
5.3.0 Specification of Microwave Solid Flow Instrument......Page 784
6.1.0 Principles of Operation for Nucleonic Mass Solid Flow Meters......Page 787
6.2.1 CONFIGURATIONS FOR SOLID FLOW MEASUREMENT IN PIPES......Page 788
6.3.0 Descriptive Details of Nucleonic Solid Flow Measuring Systems......Page 789
6.3.2 RADIATION DETECTION......Page 791
6.3.3 INTELLIGENT COMPUTING AND EVALUATION UNIT FOR NUCLEONIC FLOW METERS......Page 792
7.1.1 OPERATIONAL DETAILS OF SCREW WEIGH FEEDERS......Page 795
7.1.3 TYPICAL FEATURES OF SCREW WEIGH FEEDERS......Page 796
7.4.0 Force Flow Type Solid Weigh Meters......Page 798
8.0.0 PROCESS BATCH WEIGHER......Page 800
8.2.1 GAIN-IN-WEIGHT METHOD......Page 801
9.0.0 CONCLUDING DISCUSSIONS ON SOLID FLOW MEASURING SYSTEMS......Page 802
9.4.0 Conveyor Accessories......Page 803
LIST OF ABBREVIATIONS......Page 804
P......Page 1255
FURTHER READING......Page 806
1.0.0 INTRODUCTION: CONCEPT OF MULTIPHASE FLOW-AN OVERVIEW......Page 807
1.1.0 Fundamentals of Multiphase Flow......Page 810
1.1.3 MULTIPHASE CHARACTERISTICS AND FLOW REGIMES......Page 815
1.2.0 Two-Phase Flow Measurement......Page 823
1.2.1 UNDERSTANDING TWO-PHASE FLOW......Page 824
1.2.2 TYPES OF TWO-PHASE FLOW PHENOMENA......Page 826
1.2.3 VOID FRACTION AND VOID FRACTION MEASUREMENT IN TWO-PHASE FLOW......Page 829
1.2.4 TWO-PHASE FLOW SENSING AND SENSORS (CORIOLIS MASS FLOW, US, PIV, AND LDA)......Page 838
1.2.5 WET GAS METERING......Page 845
1.2.6 WATER CUT METERING......Page 850
1.3.0 Multiphase Flow Metering Philosophy and Well Testing......Page 851
1.3.2 MULTIPHASE FLOW COMPUTATIONAL REQUIREMENTS......Page 852
1.3.3 MULTIPHASE METER IN OIL AND GAS......Page 853
1.3.4 WELL MONITORING......Page 854
1.3.5 WELL TESTING......Page 856
2.0.0 MULTIPHASE FLOW MEASUREMENT ESTIMATION AND TYPES......Page 859
2.1.1 PHASE FLOW OR VELOCITY MEASUREMENT......Page 860
3.2.0 IEC 61511 Safety Lifecycle......Page 863
2.2.1 DP METHOD (DP ELEMENTS: VENTURI, V CONE, ORIFICE)......Page 864
2.2.2 NON-DP WET GAS MEASUREMENTS......Page 865
2.2.3 WET GAS FLOW METER (COMBINATION)......Page 866
2.3.0 Water Cut Meter......Page 868
2.3.1 WATER CUT METER WORKING PRINCIPLES......Page 869
2.3.3 WATER CUT METER SPECIFICATION......Page 871
2.3.4 WATER CUT METER DISCUSSIONS......Page 872
2.4.2 BASIC PROCESS OF A VIRTUAL METERING SYSTEM......Page 873
2.4.3 ANALYSIS OF VIRTUAL METERING SYSTEM RESULTS......Page 875
3.1.2 Flange Face Types......Page 1151
3.3.0 Flange Dimensional Details......Page 878
3.2.0 Microwave Measurements in Multiphase......Page 879
3.2.1 ADVANTAGES AND DISADVANTAGES OF MICROWAVE MEASUREMENT TECHNOLOGY......Page 880
3.2.2 THEORETICAL BACKGROUND FOR MEASUREMENT......Page 881
3.2.3 RESONATOR TYPE SENSING......Page 883
3.2.4 CHANGE OF FREQUENCY TYPE MEASUREMENT......Page 884
3.2.5 ABSORPTION TYPE MEASUREMENT......Page 885
3.3.1 GAMMA RAY ABSORPTION METERING......Page 886
3.3.2 NEUTRON ACTIVATION ANALYSIS-BASIC DEFINITIONS OF TERMS......Page 888
3.3.4 PROMPT GAMMA-RAY NEUTRON ACTIVATION ANALYSIS (PGNAA)......Page 891
3.3.6 NAA AND OIL EXPLORATION......Page 892
3.4.1 WIRE MESH TYPE MEASUREMENT FUNDAMENTALS......Page 893
3.4.2 ELECTRICAL MEASUREMENT OF CONDUCTIVITY TYPE WIRE MESH......Page 895
3.4.3 ELECTRICAL MEASUREMENT OF CAPACITANCE TYPE WIRE MESH......Page 896
3.4.5 ELECTRICAL IMPEDANCE METHOD (GENERAL: LOCAL MEASUREMENTS)......Page 898
3.4.6 SOME RECENT DEVELOPMENTAL WORK IN ELECTRICAL IMPEDANCE MEASUREMENTS......Page 899
3.5.0 Needle Probe (Local Void Fraction)......Page 901
3.5.1 OPTICAL TYPE NEEDLE PROBE......Page 903
3.5.2 THERMAL TYPE NEEDLE PROBE (COMBINED)......Page 904
3.5.3 ELECTRICAL TYPE NEEDLE PROBE (COMBINED)......Page 906
4.5.0 Coriolis Mass Flow Meter in Cryogenic Applications......Page 909
3.6.1 GENERAL TOMOGRAPHY PROCESS......Page 910
3.6.2 X-RAY TOMOGRAPHY: X-RAY CT......Page 911
3.6.3 GAMMA RAY TOMOGRAPHY......Page 912
3.6.4 NEUTRON/POSITRON TOMOGRAPHY......Page 913
3.6.5 ELECTRICAL IMPEDANCE TOMOGRAPHY......Page 914
8.2.3 Mass Flow Measurement of Cement for Reduced Chromatic Concrete......Page 1118
3.7.1 BACKGROUND THEORY FOR MR RESONANCE MEASUREMENT......Page 918
3.8.1 PRINCIPLES OF OPERATION......Page 920
4.1.1 GENERAL REQUIREMENTS AND EXTERNAL CONDITIONS FOR METER SELECTION......Page 922
4.2.3 OUTPUT SPECIFICATION REQUIREMENTS......Page 924
5.2.0 Brief Multiphase Commissioning Discussions......Page 925
6.0.0 MULTIPHASE FLOW METERING-TESTING AND CALIBRATION......Page 926
4.0.0 Ingress Protection......Page 927
REFERENCES......Page 928
FURTHER READING......Page 930
1.0.0 Introduction......Page 931
2.0.0 Hall Effect Sensing and Flow Measurement......Page 932
2.2.1 Analog Type Sensor......Page 934
2.2.2 Digital Type Sensor......Page 935
2.3.2 BIPOLAR Magnetic System......Page 936
3.1.1 Magnetic Pickup Working Principles......Page 940
3.1.3 Installation of Magnetic Pickup......Page 941
1.3.3 Installation Effect on Ultrasonic Flow Meter......Page 942
4.0.0 Cryogenic Flow Measurement......Page 943
4.1.1 Constraints of Various Cryogenic Flow Meter Types......Page 944
4.1.2 Selection of Flow Meter in Cryogenic Applications......Page 945
5.2.0 Protection Standards With Comparison......Page 946
4.2.0 Instruments Used in Production Oil Separators......Page 947
4.6.0 Ultrasonic Flow Meter in Cryogenic Applications......Page 948
4.7.0 Processing Electronics in Cryogenic Applications......Page 949
5.1.3 Specification for Direct-Flow Gages......Page 952
5.2.0 Sight Flow Indicator......Page 953
5.2.4 Sight Flow Indicator With Spinner......Page 954
5.1.0 Major Challenges and Aims of Flow Measurement......Page 1100
6.1.1 General Design Details for Water Meters......Page 956
6.1.2 Domestic Water Flow Meters......Page 957
6.1.3 Irrigation, Agriculture and Fertilizer Water Flow Meter......Page 959
6.2.1 Mechanical Oil Flow Meters......Page 961
5.2.3 Use of Ultrasonic Flow Meters......Page 963
3.0.0 Safety Lifecycle......Page 1179
7.0.1 Definitions and Terminologies With Explanations......Page 964
7.0.2 Flow Switch Types......Page 967
7.1.0 General Requirements of Flow Switches With Explanations......Page 968
7.2.1 Descriptive Details of Paddle Type Flow/No-Flow Switches......Page 969
7.2.3 Specifications of Paddle (Vane) Type Flow Switches......Page 970
7.3.1 In-Line (Piston) Flow Switch......Page 971
7.3.2 DP Type Flow Switch......Page 973
7.4.1 Working Principle of Variable Orifice Flow Switch......Page 974
7.5.0 Thermal Dispersion Type Flow Switch (Monitor)......Page 976
7.5.1 Theoretical Background of Thermal Dispersion Flow Monitors......Page 977
7.5.2 Description of Thermal Type Flow Switches......Page 978
7.6.0 Discussions on Miscellaneous Flow Switches......Page 979
7.7.0 Discussions on Solid (Bulk) Flow Monitors......Page 980
7.7.1 Microwave Type Solid Flow Monitors......Page 981
7.7.2 Electric Charge Type Flow Monitors......Page 984
List of Abbreviations......Page 986
Further Reading......Page 987
Preamble......Page 988
1.0.0 Flow Conditioning......Page 989
1.1.0 Flow Straighteners......Page 990
1.1.1 Tube Bundle Flow Straightener......Page 991
1.2.0 Flow Conditioners (True Flow Conditioners)......Page 992
2.1.2 Cast Iron and Carbon Steel......Page 993
1.3.0 Discussions on Flow Conditioning......Page 995
1.3.2 Swirl Effect on Some Selected Metering Types (Volume Flow)......Page 996
1.3.4 Some API Requirements......Page 998
2.0.0 Flow Transmitters (DPT and MVT) and Converters......Page 999
2.1.0 Basic Transmitter Theory, Technologies and Selection......Page 1000
2.1.1 Signal Transmissions and Smart Transmitters......Page 1001
2.1.2 Transmitter Measurement Loop......Page 1002
2.1.3 Transmitter Components and Accessories......Page 1004
2.1.1 Pipe Specifications......Page 1149
2.2.1 Wetted Parts......Page 1006
2.3.1 Accuracy and Its Significance......Page 1007
2.3.2 Other Miscellaneous Effects and Responses......Page 1008
2.3.2 Mill Air Flow Measurements and Control......Page 1009
2.4.2 Specification of Multivariable Transmitters......Page 1010
2.5.0 Mounting and Installation of DPTs and MVTs......Page 1011
3.1.1 Working Principles and Types of Peristaltic Pump......Page 1013
4.2.3 Link Device, Gateway and Communication Stack (Link Active Scheduler)......Page 1231
3.1.3 Parts and Technical Details of Peristaltic Metering Pumps......Page 1015
3.2.0 Piston-Operated (With/Without Diaphragm) Metering Pumps......Page 1016
3.2.1 Description of a Direct Piston-Operated Metering Pump (No Diaphragm)......Page 1017
3.2.3 Technical Data......Page 1019
3.2.5 General Discussions on Diaphragm Pumps......Page 1020
3.3.0 Metering Pump in Dosing Control (Application Example)......Page 1023
4.0.0 Energy Flow Computation and Metering......Page 1025
4.1.0 General Discussions on Energy Flow and Its Requirements......Page 1027
4.2.1 Important Terms for Fuel Gas in Combustion......Page 1030
4.2.2 Use of WI for Heat Flow......Page 1031
4.2.5 Energy Flow/BTU Meter Discussions and Specification......Page 1032
4.3.1 Boiler Efficiency Calculation With Energy Computation Unit......Page 1034
4.3.2 Boiler Efficiency Formulation and Measurement Points......Page 1037
5.1.1 Definition of a Flow Computer......Page 1038
5.1.3 Density Computation and Variation Issues for Compressible Fluids......Page 1039
5.2.1 Description of Flow Computers......Page 1040
5.2.2 Features of Flow Computers......Page 1041
7.2.2 Electromagnetic Flow Meter Applications......Page 1042
5.3.0 Various Display Units and the Operator Interface......Page 1043
6.1.0 Flow in Batch Control......Page 1044
6.1.1 Functional Details of Flow in a Batch Process......Page 1046
6.1.2 Flow Meters in Batch Process Operations......Page 1048
6.1.3 Features of Batch Controllers......Page 1050
6.1.4 Specification for Batch Controllers......Page 1051
6.2.0 Filling Machines......Page 1052
6.2.1 Standard Issues Related to Filling Machines......Page 1053
6.2.3 Description of Typical Filling Machines and Systems......Page 1054
6.3.1 Volumetric Dispensing......Page 1056
6.3.2 Gravimetric Dispensing......Page 1057
7.1.1 Constant Volume Flow Controller in Gas Applications......Page 1058
8.1.0 Standard Transmitters......Page 1062
8.2.0 Smart Converters......Page 1064
References......Page 1065
Further Reading......Page 1066
Preamble......Page 1067
1.1.0 Issues Related to Industrial Dusts......Page 1068
1.1.2 Use of Purge Rotameters and Other Types......Page 1069
1.1.3 Other Gas Flow Meter Types......Page 1070
1.2.1 Diagnostic Features in Ultrasonic Flow Meters......Page 1071
1.2.2 Fouling Effect on Ultrasonic Flow Meters......Page 1072
1.2.3 Vortex Meter and Associated Issues......Page 1073
2.2.0 ATEX Method of Protection......Page 1141
1.3.1 Profile Distortion......Page 1074
2.1.1 Main Steam Flow Measurement......Page 1076
3.2.3 Field Intrinsically Safe Concept (FISCO)......Page 1078
2.2.2 Conventional Coal Flow Measurement and Controls......Page 1079
2.2.3 Pulverized Coal Flow Measurement......Page 1080
2.3.0 Air and Flue Gas Flow Measurement......Page 1081
2.4.0 Flow Meters for Abrasive Fluid Handling in a Flue Gas Desulfurization Plant......Page 1082
D......Page 1083
4.1.2 Use of Instruments at Different Stages in the Oil and Gas Process......Page 1086
4.3.0 Flow Metering Standards......Page 1088
4.4.1 Gas Metering System (Station)......Page 1094
4.4.2 Liquid Measuring System (Station)......Page 1095
4.5.1 Advantages of USFM for Leak Detection......Page 1096
4.5.2 Descriptive Details of the Leak Detection System......Page 1097
4.7.0 Petrochemical Application......Page 1099
2.1.0 Risk Analysis and Assessment......Page 1174
5.2.2 Use of Magnetic Flow Meters......Page 1102
5.2.4 Use of Vortex......Page 1103
5.2.6 Sonar Flow Meters in Pulp and Paper Plants......Page 1104
6.1.0 Instrument Types Used in Pharmaceutical, Food, and Beverage Industries......Page 1105
6.2.2 Turbine Flow Meter Applications......Page 1106
6.3.1 General Process Requirements in Food and Beverage Industries......Page 1107
7.1.1 Integrated Steel Plant Process Outline......Page 1109
7.1.2 Aluminum Production Process Outline......Page 1110
7.1.3 Coal Mining and Methane Recovery Process......Page 1111
7.2.1 DP Type Flow Metering......Page 1112
7.4.1 Methane Gas Flow Measurement......Page 1115
8.1.0 Brief Cement Making Process......Page 1116
9.1.2 Flow Meter Types and Selections......Page 1120
9.2.0 Energy Consumption in Biogas......Page 1121
9.4.0 Flow Measurements in Breweries......Page 1122
9.4.2 Flow Metering in the Brewing Process......Page 1123
List of Abbreviations......Page 1125
References......Page 1126
Further Reading......Page 1127
1.1.1 Explanation of Pressure and Various Definitions......Page 1128
1.3.1 Volume Conversion Factor......Page 1129
1.4.2 Density Specific Gravity of a Few Selected Materials......Page 1130
3.2.2 Implementation Part of IEC 61511......Page 1182
1.0.1 Explosion Triangle......Page 1189
1.0.2 Range of Explosion......Page 1190
3.2.0 Flowability for Solid Flows......Page 1135
2.1.3 Hastelloy Types......Page 1140
3.2.0 Differential Pressure Transmitter......Page 1142
4.0.0 Material Compatibility......Page 1143
Further Reading......Page 1146
1.2.0 Temperature Class......Page 1147
1.4.0 Unit Conversion for Energy......Page 1148
2.1.2 Tube Specification......Page 1150
2.4.3 APPLICATION AREAS......Page 1153
4.0.0 Gasket System......Page 1155
1.1.0 Explanation of Custody Transfer......Page 1156
1.3.0 Measuring System for Custody Transfer......Page 1157
1.5.0 Role of AGA and API in Custody Transfer Metering......Page 1158
1.6.0 Meter Selection for Custody Transfer Metering......Page 1159
2.2.0 Positive Displacement (PD) Type Flow Metering......Page 1160
1.1.1 Class Division Classifications......Page 1161
2.4.1 PRINCIPLES OF OPERATIONS......Page 1162
2.5.1 PRINCIPLES OF OPERATION......Page 1163
3.2.0 Prover Types......Page 1166
3.3.0 Proving Conditions......Page 1167
FURTHER READING......Page 1168
1.1.0 Definitions and Explanations of a Few Related Terms......Page 1170
1.2.0 Discussions on BPCS and SIS......Page 1172
2.1.1 Risk Register......Page 1175
2.1.2 Risk Matrix......Page 1177
4.1.1 SIL Categories......Page 1184
4.2.0 SIL Determination Techniques......Page 1185
List of Abbreviations......Page 1187
1.0.3 Components for Explosion......Page 1191
1.1.0 Electrical Area Classification......Page 1193
1.1.2 Zone System-ATEX Directive......Page 1195
2.1.0 NFPA Method of Protection......Page 1197
3.1.0 Explosion Protection Principles......Page 1200
3.3.0 Intrinsic Safety (IS)......Page 1203
5.1.0 Enclosure Markings......Page 1207
. List of Abbreviations......Page 1210
References......Page 1211
1.1.1 Current Loop and Selection for 4-20mADC......Page 1212
1.3.0 Other Hardwire Signal Types......Page 1215
2.1.2 Link RS (EIA) 422......Page 1216
2.2.0 MODBUS Protocol......Page 1217
2.2.1 Transaction Methodology......Page 1218
2.2.2 Implementation Methods......Page 1219
2.3.1 HART Protocol Features......Page 1220
2.3.2 HART Protocol Characteristics......Page 1221
2.3.3 WIRELESS HART PROTOCOL......Page 1222
3.0.0 Fieldbus System and Safe Fieldbus......Page 1223
3.2.1 IS Barriers in Fieldbus......Page 1224
3.2.6 Fieldbus Nonincendive Concept (FNICO)......Page 1226
4.2.2 Technical Description of H1 Bus......Page 1229
5.2.0 PROFIBUS Structure......Page 1232
5.3.3 Networking......Page 1235
5.4.0 PROFINET......Page 1236
. List of Abbreviations......Page 1238
References......Page 1239
E......Page 1245
F......Page 1246
H......Page 1249
I......Page 1250
L......Page 1251
M......Page 1252
N......Page 1254
R......Page 1258
S......Page 1259
T......Page 1261
V......Page 1263
W......Page 1264
Z......Page 1265
Back Cover......Page 1266

Citation preview

Plant Flow Measurement and Control Handbook Fluid, Solid, Slurry and Multiphase Flow

Swapan Basu

Academic Press is an imprint of Elsevier 125 London Wall, London EC2Y 5AS, United Kingdom 525 B Street, Suite 1650, San Diego, CA 92101, United States 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom Copyright © 2019 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www. elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-12-812437-6 For information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Jonathan Simpson Acquisition Editor: Kostas KI Marinakis Editorial Project Manager: Joshua Bayliss Production Project Manager: Surya Narayanan Jayachandran Cover Designer: Victoria Pearson Typeset by TNQ Technologies

Dedicated to Gurudeb, whom I trust and to my parents and Kakamoni and my loving wife and children

Foreword Flow is a part of life. In our everyday life, it is difficult to imagine a physical system where there is no scope for flow. Even the simplest of systems over time require some form of exchange, which can be perceived or represented as flow. Measurement and control of the flow rate of physical materials are extremely important for mass balance and economic reasons and can never be overestimated. Given the wide variations of physical media having a variety of physical and chemical properties, it is natural that there will be a need for dedicated flow meter and/or flow-metering device types to suit specific needs. One of the unique features of this book is that it caters to all types of flow: fluid, solid, slurry, and multiphase; and details treatise on measurement, communication, and controls. The book in each section is dedicated to the description, specification, installation, calibration, and custody transfer (where applicable) of different types of flow meters, flow devices, flow converters, along with fieldbus communication. The inclusion of modern communications systems, applications of these meters in safe as well as hazardous conditions, safety lifecycle and flow meters, as well as flow converter enclosure details have also enriched the book. Although there are books that have covered these areas separately, there was no single book to cover all these types of flow-metering devices with required details mentioned above in a single volume. Starting with basic flowmeasuring principles it covers head type flow meters, open channel flow measurement, PD flow meters, velocity and force type flow metering, mass flow meters, slurry flow measurement, solid flow meters, multiphase flow meters, special flow metering devices (including cryogenic flow

measurement), flow conditioning along with the application of different flow meters in different plants over twelve chapters and seven appendices. I felt that the book offers a fine balance between fundamental details, theoretical analysis with required mathematical details and formula, and practical issues related to design, installations, and calibration custody transfer (as applicable). The book offers detailed applications not only to plants of different types and sizes but for flow meters in other applications also. The author of this monumental work, Mr. Swapan Basu, has a rich industrial experience in instrumentation and control engineering in India and abroad, with myriad process design and commissioning exposures to his credit, and maintains a continuing interest in the latest developments in his field. I truly feel that the book which developed, often drawing from the author’s personal industrial experiences, would be extremely helpful to practicing engineers as well as for freshers in the field. This book is extremely helpful for civil, mechanical, and process engineers dealing with flow systems in plants and processes. I am delighted to know that this book has been selected by IChemE in their series of publications. I wish the author all the success for the book from his efforts. Dr. Dipak C. Patranabis M.Sc. (Tech.), Ph.D., M.I.E., F.I.E.T.E., M.I.S.A. Former Professor and Head, Dept. Instrumentation and Electronics Engg. Jadavpur University Kolkata 700092

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Preface In our daily life we always flow in one form or the other. The most common forms of flow are flow of air and flow of water. It is difficult to imagine a physical process or system without flow. The physical and chemical properties of physical media have wide variations, giving rise to different kinds and types of flows. Some media may be lighter or some may be heavier, and some may be highly viscous, while some may have high turbulence. In the case of solid flows there will be variations with respect to flowability depending on the bulk density and other properties of solids. Depending on the rheological properties there will be variations in slurry flow measurements. In the case of multiphase flow, depending on the fractions of solids, liquids, and gases, there will be differences in flow measurement principles. While the majority of fluid flows are Newtonian, there will be some flows which are non-Newtonian. In order to cater to all these requirements there will be different kinds of flow meters working on different measuring principles and technologies. This book covers design details, sizing calculations, specification, installation, calibration, and application notes for each of the flow meter types. In Chapter I, flow measurement principles along with the basic technology behind different kinds and types of flow meters pertinent to fluid, solid, slurry, and special flows, along with multiphase flow meters, have been discussed. While discussing this, a detailed account on the basic theory of measurement with mathematical deductions & equations, and physical and mathematical details on the mechanics of flow metering have been covered. Special emphasis has also been put on the methods of selection of flow meters which can cater to the requirements for various applications. Discussions have been put forward on calibration needs and methods also. Chapter II has been dedicated to head type flow measurement and variable-area flow meters. The discussions include different kinds of primary flow elements, along with detailed discussions on fluid mechanics. The pros and cons of various differential flow elements along with their applications have been covered. Open channel flow metering, with details of hydraulic design, are used for measurement of large flows of water, such as in rivers/dams. Chapter III, dealing with

open-channel flow measurement, discusses in detail various hydraulic structures meant for open-channel flow measurement. Details covered here include sizing and design calculations for these structures with design formula and measuring methods. A number of sensors covering both mechanical as well as electronic types, such as US types, have been included in this chapter. A wide range of PD meters is available for measurements of different fluid types, especially for highly viscous fluids like those found in oil and gas applications. Chapter IV has been dedicated to PD meters to cover almost all types of PD meters available, with their application areas. Velocity and force are commonly used parameters for fluid flow measurement. Turbine meters, electromagnetic flow meters, ultrasonic flow meters, vortex/swirl metera, and fluidic meters, such as Coanda effect meters, are examples of velocity type flow meters covered in Chapter V, which also includes target flow meters based on the forcemeasuring principle. Apart from volume measurements of fluids discussed above, mass flow measurement based on Coriolis principles and twin-turbine flow meters have been covered in Chapter VI. This chapter also discusses why and how mass flow measurement is accurate and true flow measurements for fluids. Rheological properties of fluids actually govern slurry flow. There are different techniques, such as wedge meters, along with special types of conventional meters redeployed for slurry flow measurement. Some fluids, which are nonNewtonian, need special attention. In Chapter VII these have been covered. Solid flow measurement and their requirements are quite different from those applicable for fluid flow measurement. Chapter VIII has been dedicated to account for the same. Starting from standard weight measurements such as centripetal, impact scale, weigh feeder, and belt weigher, detailed discussions have also been presented on Coriolis type flow measurement, gravity-filling machines, road vehicle weighing, and railway weighing. Also, noncontact type measurements, such as microwave type flow meters and radiometric flow meters have also been described. Multiphase flow is quite commonly encountered in oil and gas fields, and many other areas demand completely

xvii

xviii

Preface

different kinds of measurement techniques. There is a wide range of technologies involved in the measurement of multiphase flow measurement, these are: gamma ray, PIV, LDA EIT (including virtual measuring systems), tomography types including gamma/X-ray, neutron/positron, optical, ultrasonic electrical impedance with computerized tomography (CT), to name a few. Detailed accounts of these, along with conventional measurement types, and their applications depending on multiphase fluid conditions have been enumerated at length in Chapter IX. Chapter X is dedicated to various flow sensing types, flow gages, flow switches (for solid flow also) types, along with standard mechanical meters, such as water meters. Detailed discussions have been presented on cryogenic flow measurement and various kinds of flow pickups used in flow meters. Flow-conditioning devices are basically accessories for flow measurement used for accurate fluid flow measurements. DPTs and MVTs are major devices for flow measurement with head type flow measurement. Various flow-computing devices, controllers, batch controllers, and dispensers are used in flow measurement systems as secondary devices. In Chapter XI, discussions on these, along

with energy flow metering and metering pumps have been included to complete the discussions on flow measurement systems. Detailed discussions on flow measurement problems and plant-specific issues in various power, process, and industrial plants have been discussed in Chapter XII. Engineering unit conversions, material selections, and mechanical details of flow meters and their accessories are very important for flow meter applications. All these required data and design details have been appended to this book. The importance of safety lifecycle, hazardous applications, and enclosure details for flow measurement cannot be overestimated, so required details have been appended to this book along with discussions on device communications. An attempt has been made to maintain the delicate balance between theoretical and mathematical details and the author’s research work on the subjects through global industrial plant experiences over nearly four decades. The efforts of the author make the book suitable for practicing engineers in industries as well as for budding engineers and advanced students.

Acknowledgments At the outset the author wishes to put forward his thanks and gratitude to the International Electrotechnical Commission (IEC) and IChemE. The author is thankful to IEC for granting permission to use some of their figures from IEC 61508 and 61511 in the book and would like to acknowledge the following: The author thanks the International Electrotechnical Commission (IEC) for permission to reproduce information from its International Standards. All such extracts are copyright of IEC, Geneva, Switzerland. All rights reserved. Further information on the IEC is available from www.iec.ch. IEC has no responsibility for the placement and context in which the extracts and contents are reproduced by the author, nor is IEC in any way responsible for the other content or accuracy therein.

In addition, the quotation from IEC Standards should include the following footnotes: IEC 61508-1 ed.2.0 “Copyright © 2010 IEC Geneva, Switzerland. www.iec.ch” IEC 61511-1 ed.1.0 “Copyright © 2003 IEC Geneva, Switzerland. www.iec.ch”

The author is extremely thankful to the Institution of Chemical Engineers (IChemE) for selecting the book in their series of publications. The author is grateful to M/S. Emerson for allowing the use of the image of Daniel-Senior-Orifice-Fitting in the book (courtesy of Emerson: e-mail dated 13th Nov. 2016) and Krohne D.E. for allowing use of the image of the external and internal view of M Phase 5000 in the book (courtesy of Krohne D.E.: e-mail dated 16th Oct. 2017). The author would like to pay tribute and thanks to Professor

Dr. Dipak C. Patranabis (JU) who spared time to go through the book and agreed to write the Foreword for the book. The author is indebted and would like to thank M/S. Ajay Kumar Debnath, Jyotish Sarkar, and Ashoke Chakraborty who spent their valuable time in going through the write up and coming up with valuable suggestions and sharing lot of information with the author, to enrich the content of the book. The author is also thankful to M/S Jawahar Bahttachrya, Sugato Banerjee, Manab Ray, and Pradip Kumar Chakraborty for their suggestions on various chapters. The author is thankful to Rajlaxmi Basu for her suggestions in developing the book, especially in the device communication part. The author is extremely thankful to Mr. Deb Kumar Basu for guiding and developing the cover design, with good suggestions which were extremely helpful in developing various figures in AUTOCAD. The author would also like to thank the entire team at Elsevier, the publisher, who took all the pain out of the creation of this book. Last, but not the least, the author would like to thank his children Idai (Raj) and Piku (Deb) for their continuous inspiration and support and he would like to convey special thanks to his wife, Bani Basu, for managing the family with care within limited resources and encouraging the author when writing book. The author feels great pain in the sudden demise of his uncle (the late K.K. Basu), who was responsible for bringing the author to this position, and so the author acknowledges his immense contribution for all his works. The author sincerely acknowledges the support he has received, without which it would have been impossible to publish the book.

xix

CHAPTER I FLOW METERING: GENERAL DISCUSSIONS (AN OVERVIEW)

Chapter Outline 1.0.0 Introduction 1.0.1 Discussions Covered in This Book 1.0.2 International Standards and Regulations 1.1.0 Flow Measurement Basics 1.2.0 General Relevant Terms and Discussions 2.0.0 Basic Fluid Mechanics 2.1.0 Bernoulli’s Equation for Pipe Flow Measurement 3.0.0 Flow Measurement Types and Principles 3.1.0 Fluid Flow Measurement Types and Principles 3.2.0 Solid Flow Measurement Types and Principles 3.3.0 Slurry Flow Measurement Types and Principles 3.4.0 Multiphase Flow Measurement Types and Principles 4.0.0 Selection of Flow Meters 4.1.0 General Discussions on the Flow Meter Selection Process (Closed Pipe) 4.2.0 Specific Discussions on the Flow Meter Selection Process (Closed Pipe) 4.3.0 Open System Flow Meter Selection 4.4.0 Cost and Approval Considerations for Flow Meter Selection 4.5.0 Flow Meter Selection Matrix

1 3 5 5 19 31 34 42 43 83 97 99 109 111 113 121 121 122

1.0.0 INTRODUCTION I still remember the interview day of my first job, I was asked by one of the interviewers, “What are the major parameters measured for boiler monitoring?” As a fresh engineer and without thinking through the question, I immediately replied “steam flow” (probably as it was a boiler, steam came into my mind). One of the interviewers (probably) was surprised! He stared at me and asked “How come you thought of steam flow first?” Then it was my turn to be surprised with the counter-question. I really had no answer! Hopefully I could guess now, after so many years in the process industry, why there was a counter-question. Of the four major parameters, i.e., pressure, temperature, level, and flow, normally measured in all process

5.0.0 Discussions on Permanent Pressure Loss and Allied Issues 6.0.0 Principles and Good Practices of Installation and Calibration 6.1.0 Principles and Good Practices for Installations 6.2.0 Principles and Good Practices for Calibrations 7.0.0 Critical or Sonic Nozzle 7.1.0 Features and Advantages of Sonic Flow Nozzles 7.2.0 Applications of Sonic Flow Nozzles 7.3.0 Functional Details of Sonic Flow Nozzles 8.0.0 Miscellaneous Flow Measurement Systems 8.1.0 Aerofoil in Air/Gas Flow Measurement 8.2.0 British Thermal Unit Measurement 8.3.0 Cross-Correlation Flow Measurement List of Abbreviations References Further Reading

125 127 127 130 134 135 135 135 136 136 137 140 144 145 148

control instrumentation, flow measurement is the most complex, as there is no direct means to measure it. For flow measurement one has to depend on one or other of the related parameters, which vary with the associated conditions. The historical background of flow measurement has been illustrated in Fig. I/1.0.0-1. From elementary physics it is known that there are three states of matter. These include the following. l

Plant Flow Measurement and Control Handbook. https://doi.org/10.1016/B978-0-12-812437-6.00001-9 Copyright © 2019 Elsevier Inc. All rights reserved.

Solids: The molecules of a solid are usually closer together and the attractive forces between the molecules of a solid are so large that a solid tends to retain its shape. Fluids: In the case of fluids, the attractive forces between the molecules are comparatively 1

2

Plant Flow Measurement and Control Handbook

The concept and understanding of “FLOW” comes after the publication of “Hydrodynamica” in 1738 by the Swiss physicist and mathematician Daniel Bernoulli (17001782). He actually framed famous fluid equation. However earlier days also people had some concept of flow, Aristotle viewed the motion which involves a medium that rushes in behind a body to prevent a vacuum. Bernoulli introduced the concept of the conservation of energy for fluid flows. So when a restriction is put, there will be increase in fluid velocity hence kinetic energy but there will be loss in static pressure, hence energy.

FIGURE I/1.0.0-1 Historical background of the concept of fluid flow.

l

l

much smaller and do not retain their shapes. A fluid may be either a gas or a liquid. Gas: The molecules of a gas are much farther apart than those of a liquid and the force of attraction is weak. For this reason a gas is very compressible, meaning that upon removal of all external pressure, it tends to expand indefinitely. Liquid: A liquid has molecules closer than a gas and the force of attraction is greater than in a gas. A liquid is relatively incompressible— meaning that upon removal of all external pressure except its own vapor pressure, the liquid does not expand indefinitely. Vapor: A vapor is a gas whose temperature and pressure are such that it is very near the liquid phase. Thus steam is considered a vapor because its state is normally not far from that of water.

Naturally, flow measurement of each of these phases and mixing of them requires technical approaches which shall be dealt with in detail in this handbook. Again of the fluid flow measurements, compressible fluid flow measurement is comparatively more complex than for noncompressive fluid/liquid. Similarly, flow measurement of multiphase and slurry is much more complex. According to B.G. Liptak “No industrial measurement is more important than the accurate detection of the flow rates..” Naturally the following question comes to mind “Why?” On account of the following reasons, the importance of flow measurement in industrial as well as social applications has grown exponentially: l

l

accounting purposes and leakage management; custody transfer from supplier to consumer (especially in the oil and energy sectors);

l

essential in any process and manufacturing plant, including quality management in batch processes, dosing, etc.

As a result, efforts have been made to improve the quality and performance requirements from flow-metering devices demanding higher or better accuracy, linearity (as applicable), and a better turndown ratio. The safety life cycle is now becoming a part of any devices or systems leading to demands for higher stability, reliability, and safety on these flow devices. Also, in order to match with the development of electronics (especially embedded electronics and micro controllers) and communications, additional demands have been placed on flow devices to support software and communication facilities. Various points discussed so far a few examples of generic issues, in specific there could be wide variations in the fluid properties between two measurements (even in the same plant, e.g., air flow, coal flow, steam flow, and feed water flow in power plants) even in the same plant and/or in various industries. The material may be solid, liquid, or gas and single or multiphase. The material may be abrasive, corrosive, explosive/ flammable, or toxic, etc. The flow could be in an open channel or in a closed pipe or a duct. There can be large variations in the size (and geometry) of the pipe/duct or channel (e.g., a few mm to a few meters). There can also be wide variations in pressure (from a vacuum to a few hundred kg/cm2) and temperature (cryogenic to a few hundred degrees Celsius). Some fluids may be conductive (water) and some are very much less conductive (oil). In some cases volumetric flow measurements are acceptable, e.g., in gas fuel stations—a car filling X liters of petrol or in irrigation XXX

Flow Metering: General Discussions (An Overview) Chapter | I

cusec of water release. On the other hand, in a few cases it is necessary that flow measurements are in mass, e.g., XXX tons of coal per XXX MWH energy, or XXX tons of gypsum per XXX tons of cement production. From the above discussions it is evident that measuring instruments need to have at least the following qualities [1]: l l l l

l l l l l

high overall accuracy; well-understood functionality; better design and easy sizing; established installation procedure with less dependency on pipe straight run; easy operation and maintenance; testability even without a test bench; self-monitoring and diagnostics; suitably developed for safety life cycle; communication ability.

In order to cater to these requirements there are quite a good number of technologies that have been developed and are available for flow measurements. Therefore, the task of the designer in selecting a flow meter for a particular service is becoming more and more complex. This is clear from a simple example: Steam flow measurement, with which the discussions started, can be measured by head type flow measurement technique, vortex meter, turbine meter, or Coriolis mass flow meter, to name a few of the seven technologies used for steam flow measurement. The question is which one will be best suited for an application. Even within head type measurement there are choices of flow elements, such orifice plate, flow nozzle, etc. Therefore, it is extremely important to see which is best suited for a particular application as well as being economical. Overview discussions have been put forward in this book to guide proper selection of flow-measuring, computing, and controlling devices. Emphasis has been put to look into the sizing, design calibration, and installation aspects of each type of flow device. Also, short discussions have been put forward to cover commissioning and operation and maintenance (O&M) of these flow devices. Other important issues in connection with flow measurements are various international standards and units and unit conversions. In order to understand the implications of these standards in flow measurements it is essential to have some fundamental

3

knowledge of fluid mechanics and physics. In this book short discussions on these are given.

1.0.1 DISCUSSIONS COVERED IN THIS BOOK Prior to moving to technical details discussions in this book have been arranged to ensure that the reader is well aware of detailed content of the book. 1. Chapter I: This chapter gives initial discussions to portray an overview of basic material characteristic properties and flow metering technology. The coverage includes relevant parameters in general that affect flow measurement, fluid mechanics, and physics, and flow profile—laminar flow turbulent flow. An overview is provided of various flow-measuring principles, with short discussions on the pros and cons. Types of flow meters and their applications for selection, requirements for good practices of calibration, and installations are the main issues discussed here. The discussions cover both fluid and solid flow measurements and controls including slurry/complex fluid and multiphase flows also. Major terminologies and common issues mostly have been covered in this chapter so as to help to go through subsequent chapters. 2. Chapter II: Head type flow-measuring flow elements covering Bernoulli’s theorem and flow calculations. Also covered are specification sheets, sizing, constructional details, straight length requirements, pressure loss, etc. for orifice plates, flow nozzles, Venturi tubes, Dall tubes, Pitot tubes, Annubar, Krell’s orifice, V cone and elbow type flow measurement. Wedge flow device although operate in in head type measurement principles yet as it is more connected with slurry flow measurement it is discussed in chapter VII. Although variable area flow metering does not work in head type flow measurement principles yet same has been covered here. 3. Chapter III: Open channel flow measurement: Design and sizing of weirs, Parshall flumes, other open channel flow metering elements and level-sensing instruments. Design drawing

4

Plant Flow Measurement and Control Handbook

4.

5.

6.

7.

8.

specifications, installation, and calibration of the above devices and elements. Chapter IV: Positive displacement instruments: Working principles, pros and cons, design details, specifications, calibration, installation details, pressure loss, and tips for Operation and maintenance (O&M) for positive displacement (PD) flow meters such as nutating discs, oval gear, rotating pistons, rotating vanes, reciprocating type, helical gear bi/trirotors, etc. to name a few. Chapter V: Force/velocity type measurement: Working principles, pros and cons, design details, specifications, calibration, installation details, and tips for O&M for each of the meters including: turbines, paddle wheels, vortices, electromagnetic, target, Coanda effect and momentum exchange, and ultrasonic (transit time, Doppler). This chapter also accounts for some sensing types. Although not velocity type flow measurement but this chapter includes discussions on Target type flow meter also. Chapter VI: General discussions on volumetric versus mass flow, and density issues. Working principles, pros and cons, design details, specifications, calibration, installation details, pressure loss, and tips for O&M for Coriolis and other mechanical mass flow meters as well as thermal mass flow meters. Chapter VII: This chapter has been dedicated for slurry and complex fluid flow measurements. Rheology Newtonian and non Newtonian fluid types and associated fluid mechanics have also been covered. It covers both various flow meters and their applications in industries as well as various plant applications and use of flow meters there have been covered here. Chapter VIII: Solid flow measurement: General discussions and solid flow-measuring techniques and associated physics. Working principles, pros and cons, design details, specifications, calibration, installation details, and tips for O&M for each of the meters including: Coriolis solid FM, microwave and nucleonic solid flow meters, load cells and speed sensors, impact scale, loss in weight and gravity feed, belt scale/belt weigher, weigh feeder.

9.

10.

11.

12.

Discussion on Gain in weight (GIW) and Loss in weight (LIW) have also been covered so as to meet the requirements for various filling and dispensing machines discussed in chapter XI. Chapter IX: Multiphase flow measurement: Multiphase flow-measuring concept, twophase flow measurement, wet gas flow measurement, miscellaneous flow-measuring techniques, multiphase flow measurement with special reference to oil and gas applications. In each case working principles, pros and cons, design details, specifications, calibration, installation details, and tips for O&M are covered. This chapter covers detailed on various measurement technologies such as various tomography principles to name a few —used in flow measurements of multiphase flow measurements, well testing separators etc. Chapter X: Special flow meters, flow gages, and switches: Working principles, pros and cons, design details, specifications, calibration, installation details, and tips for O&M for Hall effect flow meters, flow meters in cryogenic applications, different metering pumps and special flow instruments. Chapter XI: Flow computation and control: This chapter is dedicated to various flowcomputing devices from DPTs to MVTs. This also includes metering pumps, energy calculators, dispensing machines, batch controllers, bottling machines, batch controllers, flow computers (density compensation, flow management computer), flow controllers (alarm, ON, OFF, and PID), signal conditioning unit, PLC/DCS interface, rate flow indicator, as well as totalizer. For each case a detailed description, specifications, design data, electrical connections, and interface are given. Chapter XII: Plant application and problems: This chapter is dedicated to general common problems for various plants and plantspecific issues pertinent to thermal power plants, nuclear power plants, oil and gas industries (offshore/upstream, midstream, and downstream), paper and chemical plants, food and pharmaceutical plants, steel and metallurgical plants, cement plants etc.

Flow Metering: General Discussions (An Overview) Chapter | I

13. Appendix I: Unit conversions and flow regimes. 14. Appendix II: Material selection guide. 15. Appendix III: Mechanical and piping data. 16. Appendix IV: Custody transfer. 17. Appendix V: Safety life cycle discussion. 18. Appendix VI: Enclosure electrical protection (class). 19. Appendix VII: Device communication.

1.0.2 INTERNATIONAL STANDARDS AND REGULATIONS There are a number of international standards followed in flow measurements. A short list of these standards is presented in Table I/1.0.2-1 for the reader to go through as required. During the discussions in this book these will be referred to with the correct standard reference. The reader is advised to refer to the latest revision of the applicable standard.

5

1.1.0 Flow Measurement Basics As indicated in Fig. I/1.0.0-1, It was physicist D. Bernoulli who first introduced the concept of conservation of energy in fluid flow. From fundamentals of energy conservation it is known that energy associated with any given amount (mass) of material under given conditions is fixed. Fluid mechanics discussed here is concerned with the transformation of pressure energy into velocity and conversely conversion of velocity back to pressure energy. Here pressure energy means the pressure which is capable of creating both kinetic energy (KE) and potential energy (PE) [2]. When any restriction is put in a closed pipeline the velocity of the flowing liquid increases, because the volume in the upstream side must be equal to the volume at the downstream, otherwise there will be an accumulation or dearth of liquid! However, this is never noticed. On account of restriction, the area decreases, so there must be a

TABLE I/1.0.2-1 Some Relevant International Standard Details* Standard No.

Application Area

ANSI/ISA 84.00.01

See IEC 61511 (modified)

ANSI/ISA 88

Batch control

ASME 19.5

Flow measurementdperformance test code

ASME PTC6

Flow nozzle

DIN 19559

Measurement of flow of wastewater in open channels and gravity conduits

EN 29104

Methods of evaluating the performance of electromagnetic flow meters for liquids

EN 60529

Specification for degrees of protection provided by enclosures (IP code)

EN/IEC60529

Specification for degrees of protection provided by enclosures (IP code)

EN/IEC 60079

Explosive atmosphere

IEC 61158

International communication network

IEC 61508

Functional safety of electrical/electronic/programmable electronic safety-related systemsdsupplier community

IEC 61511

Functional safety of electrical/electronic/programmable electronic safety-related systemsdprocess plant end user

ISA RP 31.1

Turbine flow meter

ISO 10790

Measurement of fluid flow in closed conduits. Coriolis flow meter

ISO 11605

Calibration of variable-area flow meters

ISO 14511

Measurement of fluid flow in closed conduits. Thermal mass flow meter

ISO 15769

Hydrometrydacoustic velocity meters using the Doppler and echo correlation Continued

6

Plant Flow Measurement and Control Handbook

TABLE I/1.0.2-1 Some Relevant International Standard Details*dcont’d Standard No.

Application Area

ISO 2714

Liquid hydrocarbonsdVolumetric measurement by displacement meter.

ISO 2715

Liquid hydrocarbonsdVolumetric measurement by turbine meter systems

ISO 31000

Risk management principles and guidelines

ISO 31010

Risk managementdRisk assessment techniques

ISO 4359

Flow measurement structuredFlumes

ISO 4360

Hydrometry open-channel flow measurement using triangular weir

ISO 5167 1

Measurement of fluid flow by means of pressure differential devices. General principles and requirements

ISO 5167 2

Measurement of fluid flow by means of pressure differential devices. Orifice plate

ISO 5167 3

Measurement of fluid flow by means of pressure differential devices. Nozzle and venture nozzle

ISO 5167 4

Measurement of fluid flow by means of pressure differential devices. Venturi tube

ISO 6416

Ultrasonic flow measurement

ISO 6817

Measurement of conductive liquid flow in closed conduits

ISO 6817

Measurement of fluid flow in closed conduits. method using electromagnetic flow meter

ISO 9104

Measurement of fluid flow in closed conduits

ISO 9300

Measurement of gas flow by means of critical flow Venturi nozzles

ISO/TR 12764

Measurement of fluid flow in closed conduits. vortex shedding flow meter inserted circular cross-section conduit running full

ISO1100 1

Liquid flow in open channel

NEMA

For enclosure class

NORSOK I105

Fiscal measurement systems for hydrocarbon liquid

Before moving to technical discussions it is advisable that for any doubt on unit conversions standard books on units and measurements in any standard physics book (graduation level) may be consulted to avoid any confusion. *Not exact title mentioned here.

corresponding increase in velocity, so that the volume flow rate matches. Again an increase in downstream velocity means there will be some acceleration. From Newton’s second law it is known that for any acceleration there must be some impressed force which, in this case, comes from higher pressure at the upstream. An increase in velocity downstream means that downstream fluid will have higher kinetic energy. From a conservation of energy point of view, there must

be a corresponding reduction in energy in another form, which has been transformed into kinetic energy. This transformation comes from pressure energy. Therefore, downstream there is increased velocity of liquid, i.e., higher kinetic energy at the cost of a decrease in pressure, i.e., pressure energy. From the discussions, it is clear that a flow restriction causes an increase in the flowing velocity at the cost of pressure of the flowing fluid as shown in Fig I/1.1.0-1.

Flow Metering: General Discussions (An Overview) Chapter | I

UPSTREAM SIDE TAPPING DISTANCES FROM A FLOW (PROVIDED IN TABLE BELOW) ELEMENT P

D

FC

THICKNESS

7

DOWNSTREAM SIDE TAPPING DISTANCES FROM A (PROVIDED IN TABLE BELOW) CF

D

P

PIPE ID (D)

PIPE ID (D)

A

FLOW

NOT IN SCALE 0.35-085D dp PERMANENT

dp Vena contracta

UNSTABLE REGION

VENA CONTRACTA

NOTE: IN THE TABLE BELOW ALL DISTANCES ARE MEASURED FROM UPSTREAM FACE OF FLOW ELEMENT (A).

TAPPING

TAPPING

UPSTREAM

DOWNSTREM

SYMBOL

STYLE

DISTANCE

DISTANCE

REMARKS

C

CORNER TAP

APPLICABLE

FOR D < 50mm

F

FLANGE TAP

APPLICABLE

FOR D > 50mm

D

D D/2 TAP

APPLICABLE

FOR D > 150mm

P

PIPE TAP

D

2.5D

D/2

8

FIGURE I/1.1.0-1 Concept of fluid flow measurement.

8

Plant Flow Measurement and Control Handbook

As shown in this figure the highest pressure drop will be slightly away in the downstream side. This point where the pressure drop is the maximum is referred to as the vena contracta. Pressure at the vena contracta is Pvc. In head type flow measurements the differential pressure between upstream and downstream of the restriction is measured to compute flow (discussed at length in subsequent chapters). A few typical tapping styles have been depicted in Fig. I/1.1.0-1. When downstream tapping is placed at the vena contracta it is known as vena contracta tapping. Coming back to the main issue, from Fig. I/1.1.0-1 it can be seen that after having the highest pressure at the vena contracta, there will be pressure recovery. However, it never reaches the original upstream pressure. This means that there will be some permanent pressure loss (PPL). This permanent pressure loss through various flow elements can be expressed as a percentage of the total pressure drop. Prior to proceeding further preliminaries of typical characteristics expected of flow meters and the basics of a few other details normally encountered in flow measurements are discussed. This will help to grasp the details in subsequent chapters for flow measurements. 1.1.1 BASIC CHARACTERISTICS AND ASSOCIATED TERMS FOR FLOW METERS There are a few basic desirable characteristics of flow metering devices. However, this does not mean that all these characteristics need to be

present in all flow metering devices. Some of the most important characteristics are listed below. 1. Wide operating flow range, temperature, and viscosity; 2. Less sensitivity toward flow profile and related properties; 3. Smaller permanent pressure loss; 4. Suitability for a wide range of media (material, fluid); 5. Suitable construction material to withstand corrosive and abrasive damage; 6. Simpler calibration; 7. Easy installation; 8. Less maintenance; 9. Immunity to vibration and other mechanical disturbances; 10. Higher sensitivity, reliability, and overall accuracy; 11. Suitable safety life cycle study; 12. Safety issues and safety integrity level (SIL) as required; 13. Suitable output and device communication capability; 14. Suitable output signal for easy integration. In view of the above it is clear that there need to be judicious applications borne in mind while selecting a flow meter for a particular application. These will be discussed at length in Section 6.0.0 of this chapter. A brief idea of the measurement accuracy (see Subsection 1.1.2.1) of a few flow meter types is illustrated in Table I/1.1.1-1 [3,4].

TABLE I/1.1.1-1 Flow Measurement/Meters (Typical for Idea Only) Meter Name

Accuracy % FSD

Meter Name

Accuracy % FSD

Orifice plate

2

Flow nozzle

1.5

Venturi

1

Pitot tube

0.5

Ultrasonic flow meter

1

Electromagnetic

0.5

Vortex

1

Cross-correlation

1

Rotameter

1 (of reading)

Hot wire

2

Positive displacement

0.1 (TD 70:1)

Turbine

0.1 (for TD100:1)

Mass flow

0.1 (TD 100:1)

Open channel

2%

FSD, full span division; TD, turndown (ratio); highest possible accuracy.

Flow Metering: General Discussions (An Overview) Chapter | I

1.1.2 PHYSICS ON FLUID PROPERTIES Fluid properties shall be discussed here. For basics & explanation standard book on thermodynamics should be referenced. Density and viscosity are two fluid properties which directly influence fluid flow. Density is more important when mass flow computation is desired. Also, both density and viscosity influence Reynolds number (discussed later) which determines flow types, e.g., laminar/turbulent flow. While on the subject, it is better first to define what density is. The density r of a fluid is its mass per unit volume, i.e., m/V ¼ r. There is another important term here, specific weight, which is defined below. Specific weight Y of a fluid is the weight per unit volume, i.e., specific weight g represents the force exerted by gravity on a unit volume. So, density and specific weight are related by Y ¼ 1$r$g or Y [ rg, where g is acceleration due to gravity. The most important fluid property is viscosity. 1. Physical significance of viscosity and velocity profile: The viscosity of a fluid puts resistance to the flow, or resistance to any object passing through the fluid. It can be conceived of as the thickness of the fluid. Certain fluids, like water and gasoline, flow rapidly when

compared with the flow of honey or motor oil. Since honey or motor oil are thicker, they do not flow rapidly. One must remember that this is not due to density as oils a lower dense than water but flows slowly. This is due to viscosity. This means that thicker fluids like honey/motor oil have more viscosity. Fluid flow may be considered as a collection of moving plates, one on top of the other, when a force is applied to the fluid, shearing occurs and the viscosity is a measure of the resistance offered by a layer between adjacent plates [5]. This is like sliding these moving plates relative to one another, with the center plate moving fastest and the outermost one at rest. The viscous force between the two plates opposes sliding. This is the reason that it is also referred to as internal friction. The layer of fluid near the surface is nearly at rest with respect to the surface, whereas the speed of the fluid layer at the center will be the highest, as shown in Fig. I/1.1.2-1. Also, there is no slipping at the center. Such slips occur due to viscosity. Thus it is seen that viscosity has an impact on the velocity profile and hence flow measurement.

HIGHEST v AT CENTER

ZERO AT SURFACE

MAXIMUM SPEED FROM CENTER IN %

100

ZERO AT SURFACE

80

60

40

20

0

0

9

20

40

60

80

100

DISTANCE FROM CENTER TO LIQUID BOUNDARY IN %

FIGURE I/1.1.2-1 Velocity profile of viscous fluid inside a pipe.

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Plant Flow Measurement and Control Handbook

Another important issue obviously comes into mind that if the velocity varies from the wall to the center, which velocity should be considered for flow calculation. It is normally the average velocity that is taken for flow calculations. Therefore, in order to keep the flows going one needs to apply greater pressure at the back of the flow than at the front of the flow, e.g., as when squeezing toothpaste or a ketchup sachet [2]. In a liquid, the cohesive forces between the molecules give rise to viscous force. In the case of compressive fluids, e.g., gas, it comes from collisions between the molecules. From the above discussions it follows that layers move relative to each other. The velocity at which the layers move relative to each other is therefore the shear rate. Shear rate is proportional to shear stress: Shear ratefShear stress or Shear stress ¼ m$Shear rate. This proportionality constant is referred to as absolute or dynamic viscosity. It is important to note that the discussion in the case of Newtonian fluid (refer to Subsection 1.1.2.5 in this chapter) viscosity is independent of shear rate. Here discussions are presented only on Newtonian fluids. Further generalized details on viscosity are presented in Section 1.1.0 of Chapter VII. Viscosity is highly dependent on temperature. In the case of liquids, with temperature the cohesive force

Viscosity

Oil

Water

Gas

Temperature

FIGURE I/1.1.2-2 Variation of viscosity with temperature.

reduces, and so viscosity falls. In contrast, with an increase in temperature the collision increases in compressible fluid so viscosity increases, as shown in Fig. I/1.1.2-2. There is another way to express viscosity. Kinetic viscosity is the ratio of absolute (or dynamic) viscosity to density, a quantity without involving any force. Kinematic viscosity can be expressed as: n ¼ m=r

(I/1.1.2.1-1)

where n ¼ kinematic viscosity (m2/s), m ¼ absolute or dynamic viscosity (N s/m2), and r ¼ density (kg/m3). 2. Viscosity and Reynolds number: Related to viscosity there is another important factor— Reynolds’ number. Even at constant flow, if the Reynolds number changes, the meter reading will also change. Therefore, it is necessary to calculate the Reynolds numbers at flow extremes (maximum and minimum) to ensure that the corresponding change in flow coefficients is within the acceptable error limits. Now the question is how the Reynolds number is related to viscosity. The Reynolds number is a ratio of inertia force and internal friction or viscous force. It is often expressed as: Re ¼ rvdh =m ¼ vdh =nðnuÞ

(I/1.1.2.2-1)

Re ¼ rvd=m ¼ v$d=nðnuÞ

(I/1.1.2.2-2)

where kinematic viscosity n(nu) ¼ m/r; r ¼ density, dh ¼ hydraulic diameter (discussed later), and v ¼ velocity based on the actual cross-section of the duct/pipe (rather than average velocity). For full pipe hydraulic diameter is equal to full diameter hence both equations equate. These terms are discussed in the next main section. Eq. (I/1.1.2.2-2) is a generalized equation, e.g., circular pipe flow. 3. Measuring variables: Flow rate measurement is the measurement of amount passed per unit time— and this could be in the volume flow rate or mass flow rate. From basic physics it is known as an intrinsic property, so, mass flow rate is the ideal measurement value as it

Flow Metering: General Discussions (An Overview) Chapter | I

11

Definitions of NTP and STP: NTP: Normal Temperature pressure is defined as air at 20°C (293.15K) and one atm (101.325 kN/m 2, 101.325 kPa) Density 1.204 k/m 3. In FPS it is T: 68oF & P: 14.7psia STP: Standard Temperature and pressure is defined by IUPAC as air at 0°C (273.15K) and 105 Pascals. Earlier definition of STP to 273.15K and 1atm (101.325 kPa) has been discontinued. In FPS it is T: 60oF & P: 14.696 psia

FIGURE I/1.1.2-3

Definitions of NTP and STP.

is independent of pressure and temperature. However, at times, the volume flow rate is more convenient to measure. The flow rate for coal is normally expressed in tons per hour, whereas air flow rate is expressed in Nm3/h. Mass flow rate qm is expressed in Mass/time in kg/s, T/h, etc. and volume flow rate qv (or only q) is expressed in volume/ time in L/s, m3/s, m3/h, and Nm3/h. In cases of volume flow one needs to mention the same at a specified temperature, because the density of materials varies with temperature. For this reason even for noncompressible fluid temperature compensation is often called for (when there are wide variations in temperature, e.g., temperature compensation for feed water flow measurements). In the case of a compressible fluid the situation is totally different. From the ideal gas law it is known that PV ¼ nRT

(I/1.1.2-1)

where R is the universal gas constant, and may be 0.08206 (L$atm)/mol$K, when pressure is expressed in atmospheres, volume in liters, and temperature in degrees Kelvin. Here P stands for pressure, T stands for temperature, n stands for mole, and V stands for volume. From Eq. I/1.1.2-1 it can be seen that volume is dependent both on operating pressure and temperature. Therefore, for compressive fluid flow measurement both temperature and pressure compensation are necessary to take care of density variations. Also, for expressing the volume flow of a compressive fluid, the corresponding operating pressure and temperature

need to be known. In order to circumvent such problems usually such volume flow is mentioned at a standardized pressure and temperature. There are two such standard pressure/temperature conditions. These are normal temperature pressure (NTP) and standard temperature pressure (STP) as detailed in Fig. I/1.1.2-3. Therefore, compressible fluid flow is expressed as, e.g., 90 Nm3/h. As indicated in the above section, density (r) is expressed as mass/volume in kg/m3, g/cm3, etc. The discussion presented above is for instantaneous flow rate but not on the total quantity delivered. Therefore, to get total flow one needs to compute the following equation normally done in a totalizer. Z t2 x dt where x ¼ qv Qv ¼ (I/1.1.2-2) t1 for totalized volume Z

t2

QM ¼

y dt where y ¼ qm t1

(I/1.1.2-3)

for totalized mass Now with this introductory discussion complete, it is time to go deeper into the systems and to define a few terms and their requirements, starting by exploring compressibility and noncompressibility. 4. Compressibility and noncompressibility: Compressibility of any substance is the measure of its change in volume under the action of external forces, e.g., due to pressure as shown in Fig. I/1.1.2-4. It is the fractional change in

12

Plant Flow Measurement and Control Handbook

P

so that,

P +dp P P +dp

Cp ¼

v-dv

v P +dp P P

P +dp

FIGURE I/1.1.2-4 Compressibility of fluid.

volume of fluid on account of unit change in pressure. Now let us look at this issue from a density point of view. On application of pressure when there is negligible or no variation in density in the flow domain, this is an incompressible fluid. Of course, there will be some variation of density with temperature (as there will be change of volume due to temperature). Obviously, this is true for liquids. On the other hand, compressible fluid flow defines “variable density flow” [6]. Combining the two aspects together for perfect gas the following equation holds good. If r ¼ density; P ¼ operating pressure, and T ¼ operating temperature in Kelvin P ¼ rRT;

(I/1.1.2-4)

where R is the gas constant variable with gas and is given by R ¼ Ṝ/M where Ṝ is the universal gas constant 8314 J/kg$K. Like pressure and temperature, heat and energy are important issues. Therefore, it is necessary to look at them calorically. In order to limit this discussion, details of thermodynamics are not covered and readers are advised to consult any standard book on thermodynamics. Here only relevant details are discussed. Specific heat at constant pressure Cp and specific heat at constant volume Cv are related by the following equation Cp  Cv ¼ R; specific heat ratio Y ðor Kappa k sometimes usedÞ ¼ Cp =Cv ; (I/1.1.2-5)

YR Y Cv ¼ Y1 Y1

(I/1.1.2-6)

Eqs. I/1.1.2-5 and I/1.1.2-6 are very relevant for flow element sizing. Now applying the first and second laws of thermodynamics one finally arrives at the isentropic relationship given by ðP2 =P1 Þ ¼ ðr2 =r1 ÞY ¼ ðT2 =T1 ÞðY=Y1Þ ; (I/1.1.2-7) Eq. (I/1.1.2-7) has been established to show the relationship of density, which has a direct impact on flow measurement, with a variation in pressure and temperature in the isentropic process. In the isentropic process, entropy is constant and the process is reversible and adiabatic (consult any standard book on thermodynamics). Another important parameter is the Mach number, which is the ratio of local velocity (V) to the speed of sound (c), i.e., M ¼

V ; c$

(I/1.1.2-8)

If M < 0.3 it is subsonic incompressible and if 0.3 < M < 0.8 it is subsonic compressible flow. M < 1 is subsonic flow and M > 1 is supersonic flow. So from here one gets to know that significant velocity change, pressure, and temperature give variations in fluid density in compressible fluids. Compressibility (k) is a reciprocal of the bulk modulus of elasticity (E) and compressibility can also be defined as k ¼

1 dr r dp

i.e. dr ¼ rkdp;

(I/1.1.2-9)

There are two types of compressibility, namely, isothermal compressibility kT and isentropic compressibility kS. k and E depend on the nature of the process. From Mach number one can define transonic (0.8 < M > 1

Flow Metering: General Discussions (An Overview) Chapter | I

or 1.2) and supersonic shock waves (1 or 1.2 < M < 3). These are stated here because compressible fluid has an important impact on flow such as: choked flow is flow in a closed pipe/duct that is limited by sonic condition. A pressure ratio of 2:1 can cause sonic flow. Noncompressible fluid: if the flow velocity is small compared to the local acoustic velocity, the compressibility of gases can be neglected. Considering a maximum relative change in density of 5% as the criterion of an incompressible flow, the upper limit of Mach number becomes approximately 0.33 [7]. 5. Non-Newtonian and Newtonian flow: At the start of Section 1.1.2 it was stated that density and viscosity have an immense impact on fluid flow. From Subsection 1.1.2.4 it has been established that a variation in density actually divides fluid into noncompressible and compressible fluids. It has been observed that flow velocity is also an influencing factor. From the kinetic theory of gas it is established that molecular velocity gives rise to pressure and hence affects density. PV ¼ 1=3 Nmc2rms ;

(I/1.1.2-10)

where P ¼ pressure; V ¼ volume, N ¼ number of molecules crms ¼ RMS velocity; m ¼ molecular mass. Amongst the various materials available around the world, there are wide variations in viscosity, e.g., when air has viscosity in the order of 105 viscosity units, molten glass has viscosity in the order of 1012 of the same viscosity units [8]. As viscosity goes on increasing, the fluid tends to become a solid (e.g., glue). So, for argument sake, one can consider a solid as a fluid with viscosity tending towards infinity. This stands to signify that as viscosity increases materials loses their flowability. Similarly, viscosity is another impacting factor which divides fluids into Newtonian and non-Newtonian fluids depending on variations in viscosity (at constant temperature) with shear force normally encountered in, e.g., a pump. This is clear from Fig. I/1.1.2-5.

13

Newtonian fluids behave according to Newtonian law; shear stress is linearly proportional to the velocity gradient or rate of shear strain. So, if shearing stress is s, and m is dynamic viscosity, then dc (I/1.1.2-11) s ¼ m ; dy Thus, for Newtonian fluids, the plot of shear stress against velocity gradient is a straight line through the origin. On the other hand, for non-Newtonian fluids, Eq. I/1.1.2-11 is not valid. On account of the fact that they do not follow the linear relationship of Newtonian law of viscosity these fluids are referred to as non-Newtonian fluids, e.g., major polymers, adhesives, and ketchup, to name a few that show non-Newtonian fluid behavior. A detailed account for Newtonian and nonNewtonian fluids is presented in Section 1.0.0 of Chapter VII. l Newtonian fluid: From Fig. I/1.1.2-6 it can be seen that in the case of Newtonian fluids there is a linear relationship between stress and strain. This is because Newtonian fluids viscosity remains unchanged at constant temperature, no matter the amount of shear applied. Also, in Newtonian fluids viscosity is independent of shear rate. This has been very clearly shown in Fig. I/1.1.2-5. l Non-Newtonian fluid: As is seen in Fig. I/ 1.1.2-6, in a non-Newtonian fluid, the relationship between the shear stress and the strain rate is nonlinear, and it can even be time-dependent also. Therefore, a constant coefficient of viscosity cannot be defined. From Fig. I/1.1.2-6 it can be seen that there are two kinds of nonlinear curves, for two types of non-Newtonian fluids. These cases are described below. ○ Dilatant: In this case viscosity increases with shear stress, hence n > 1, e.g., quicksand. These are also termed as shear-thickening. ○ Pseudoplastic: In this case viscosity decreases with shear stress, hence n < 1, e.g., ketchup.

VISCOSITY

AT CONSTANT TEMPERATURE

VISCOSITY INDEPENDENT

VISCOSITY VARIES

OF STRESS

WITH STRESS

NEWTONIAN

NON NEWTONIAN

VISCOSITY

e.g. WATER

STRESS

TIME INDEPENDENT VARIATION

TIME DEPENDENT VARIATION

TWO

TWO

TYPES

TYPES OVER TIME DECREASES e.g. GLUE THIXOTRO PIC

DECREASES

VISCOSITY

e.g. QUICK SAND

D

PSEUDO PLASTIC INCREASES

VISCOSITY

T AN T A IL

WITH STRESS

RHEOPECTIC

OVER TIME INCREASES WITH STRESS e.g. CREAM

WITH STRESS e.g. KETCHUP

STRESS

STRESS OVER TIME

FIGURE I/1.1.2-5 Non-Newtonian and Newtonian flow types.

1 Ideal Solid

n1

Ideal fluid dc/dy

n signifies varia on nature, n=1 constant, 1: increasing nature –shear thickening

FIGURE I/1.1.2-6 Stressestrain relationship for fluid types. Based on an idea from Fluid Mechanics, IIT Kanpur, http://nptel.ac.in/courses/112104118/lecture-1/1-11-cause-of-viscosity.htm#DemoCausesofViscosity.

Flow Metering: General Discussions (An Overview) Chapter | I

○

○

The above two cases of non-Newtonian fluids are cases where the change in viscosity is independent of time as shown in Fig. I/1.1.2-5. However, there are cases where it is dependent on time, e.g., glue. Time-dependent variations in viscosity with stress also have two categories, as shown in Fig. I/1.1.2-5, and these are described here. Rheopectic: Like dilatant (n > 1), in rheopectic fluids viscosity increases with stress but is time-dependent, e.g., cream, gypsum. Thixotropic: Fluids with thixotropic properties decrease (n < 1) in viscosity when shear is applied, but this is timedependent, e.g., glue, paint. For a non-Newtonian fluid, the viscosity is determined by the flow characteristics. This has been depicted in Fig. I/1.1.2-7 for a velocity profile showing how various types change the profile. Fig. I/1.1.2-1 shows the velocity profile for a particular fluid, whereas in Fig. I/1.1.2-7 variations in velocity for different types of fluid have been highlighted to show how, with a change in fluid type, the velocity profile changes. Discussions on non-Newtonian and Newtonian fluid types are now concluded and we now look at change of flow types with Reynolds number mainly for Newtonian fluids. Discussions of the

15

same for non Newtonian fluid has been covered in chapter VII. 6. Fluid flow types and Reynolds number: Osborne Reynolds is considered as the pioneer in investigating the variations in flow types. In Subsections 1.1.2.1 and 1.1.2.2 short discussions about the physical significance of dynamic viscosity and Reynolds number have been established. The Reynolds number (in Eq. I/1.1.2.2-1 or Eq. I/1.1.2.2-2 for a circular pipe) is primarily responsible for classifying various flow types. So, we get Re [ rvd/m (for meaning of symbols Eq. I/1.1.2.2-2 should be referenced). Irrespective of the pipe diameter, type of fluid, or velocity based on Reynolds number fluid flows can be classified as [5]: laminar flow for: Re < 2300; (ReCr) transitional flow for: Re [ 2300e4000; turbulent flow for: Re > 4000. From the foregoing it can be seen that, in addition to viscosity, Re is also dependent on density. For liquids (incompressible), the density varies with temperature. However, for gases, the density depends strongly on the temperature and pressure. l Laminar flow: Laminar flow is normally encountered when dealing with a small pipe and low flow velocity. In laminar flow, fluids flow in parallel layers without mixing [9]. This means that the fluid particles move in well-ordered adjacent sliding layers. The velocity distribution shows that

NON NEWTONIAN

SHEAR THINNING (n1)

NEWTONIAN

FIGURE I/1.1.2-7 Velocity profile for fluid types.

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Plant Flow Measurement and Control Handbook

l

the frictional forces at the stationary pipe wall exert the highest retarding force and that from layer to layer the velocity increases to its maximum value, at the middle of the pipe [1]. At low velocities and high viscosities the fluid flows in layers, this is known as laminar flow in which the layers do not mix with one another. This is well depicted in Fig. I/1.1.2-8A with velocity profile. There are two types of laminar flow: (1) stable laminar flow (stable against imposed external disturbance) and (2) unstable laminar flow (when imposed external disturbance is amplified). Turbulent flow: Turbulent flow is noticed in high flow or in large pipe flow for Re > 4000. Since Reynolds number (Re) takes into consideration the essential factors, velocity v and viscosity n (nu), so, it is an evaluation criterion. When the velocity increases or the viscosity decreases an additional motion is superimposed on the

axially oriented movement throughout the flow stream. Flow vortices, wakes, and eddies make the flow unpredictable and cause movements in all directions in a random manner and affect the flow streamlines in such a way that there is a uniform velocity profile. However, at the wall or nearby, a boundary layer is formed on account of its adhesion to the wall. Therefore, the velocity must accelerate from zero to u. Thus, the velocity profile in the outer region is not steady. This is very clearly depicted in Fig. I/1.1.2-8B. Turbulent flow is characterized by rapid mixing and cross-currents flow perpendicular to the direction of motion and threedimensionality [10]. Having gathered some knowledge on the two main types of flow, it is better to compare them to observe their changes. For this Table I/1.1.2-1 gives a comparison of laminar flow and turbulent flow.

(A)

U

d

VELOCITY

LAMINAR FLOW

VELOCITY PROFILE

(B)

TURBULENT FLOW

VELOCITY PROFILE

FIGURE I/1.1.2-8 Flow types and velocity profile. (A) Laminar flow and velocity profile. (B) Turbulent flow and velocity profile.

Flow Metering: General Discussions (An Overview) Chapter | I

TABLE I/1.1.2-1 Comparison of Laminar and Turbulent Flow Point of Comparison

Laminar Flow

Turbulent Flow

Reynold’s number

Re < 2300

Re > 4000

Velocity profile

Parabolic (Fig. I/1.1.2e8A)

wRectangular (Fig. I/1.1.2e8A)

Pressure drop

Small

Appreciable due to friction

Average velocity (vavg)

vavg ¼ 0.5 max. velocity vmax (wide variation)

vavg ¼ 0.5 max. velocity vmax (less variations)

Transitional flow: Reynolds number 2300 is also referred to as the critical Reynolds number. 2300 (ReCr) is very important as from this point there is the probability of mixing, i.e., the critical Reynolds number 2300: ReCr defines with reasonable accuracy the transition point. Transitional flow is the mixture of the two above types of flow with the center being turbulent and the edges laminar. 7. Various media flow measurement: Fluid flow measurement in multiphase and slurry l

applications needs special attention on account of the complexity in flow measurements in these applications. Again, solid flow measurement is quite different from fluid flow measurement. l Slurry flow: Slurry flows are very important for mineral, metallurgical, pulp and paper, and food process engineering. The material transport in these plants takes place as slurry and/or complex fluids (commonly encountered in food and beverage industries e.g. Mayonnaise/chocolate). The most important characteristics of slurries are defined by their rheology described in Fig. I/1.1.2-9, which actually explains the nature of flow of matter. For any basic system design it is essential to understand the rheology of slurries. For further discussions on the same Section 3.3.0 in this chapter & Chapter VII may be referenced. l Solid flow measurements in dynamically feeding bulk materials (namely, clinker, raw meal, or fine materials) need a few considerations to attain high-accuracy measurements. There are a few “weighing basics” that allow for extremely sensitive and reliable recognition for both material load and belt speed—the two fundamental

Rheology: The term first was coined way back in 1920 Keeping in mind Greek quota on "panta rei" meaning everything flows. By defini on, Rheology is a branch of physics and engineering which deals with the deforma on and flow of ma er, especially the non Newtonian fluids and plas c flow of solids. It is concerned with study of flow of ma er mainly liquids, but also so solids, solids which flows rather than deform. In real life applica on Rheology is concerned with applying and extending classical discipline of Elas city and Newtonian fluid mechanics to special materials whose behavior cannot be described with classical theory. FIGURE I/1.1.2-9

17

Rheology.

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Plant Flow Measurement and Control Handbook

measurements to provide accurate and repeatable gravimetric feeding [11]. The following are major issues necessary to be considered for having a highperformance (high accuracy and repeatability) systems such as weigh feeder. ○ Minimal belt reaction error: This is a function of the belt; associated issues include the amount of inherent belt tension and the alignment of the weigh suspension. ○ Efficient scale design: This is to ensure the proper transfer of the load sensed by the weigh suspension to the load reaction device. ○ A high-performance load reaction device: These are the transducers that transform the sensed material load to a digital signal for the feeder’s control system. Overall system accuracy and repeatability require that the speed determination be of a reliable source and of sufficient resolution as well as the weighing measurement issues discussed. There are several ways and means for solid flow measurements, a major few major systems have been listed below. ○ Platform scale. ○ Hopper weighing system. ○ Belt scale/belt weigher. ○ Weigh feeder. ○ Impact scale. ○ Loss in weight method. ○ Batch system. ○ Filling machines. ○ Nucleonic system. (A)

l

In most (with the exception of noncontact types) of the cases of solid flow measurements, mechanical construction and mechanical arrangements are very important. In fluid flow measurements, in most cases the measuring instrument (may be with associated control) is a self-contained unit. In solid flow measurements mechanical feeding arrangements are a major part of the measurements where instrument sensors with control systems carry out flow computation. So, in those cases close coordination with mechanical/ process engineers is essential for accurate results. For detailed discussions Chapter VIII may be referenced. Multiphase flow: A multiphase flow measurement is the measurement of flow of each of different components found in a mixed form—especially oil, water, and gas. This measurement is a complex phenomenon producing a variety of flow regimes whose distributions, in both space and time, differ from each other [5]. There are mainly three variations in flow regimes, i.e., bubble type, stratified type, and slug type, as shown in Fig. I/1.1.2-10. The major use of multiphase flow measurements is in oil and gas area. There is a wide variety of instruments, starting from conventional DP type measurement to sophisticated instruments like Neuron and X-ray CT (computerized tomography) available for such measurements. Chapter IX is dedicated to multiphase flow measurements.

(B)

GAS

(C)

OIL

WATER

FIGURE I/1.1.2-10 Multiphase flow types. (A) Bubble type. (B) Stratified type. (C) Slug type.

Flow Metering: General Discussions (An Overview) Chapter | I

1.2.0 General Relevant Terms and Discussions In the above discussions, some relevant factors which influence flow measurements have been discussed in terms of their physical significance which will be helpful for understanding flow measurements. After completing short discussions on over view of flow measurement from this point onwards detailed discussion on flow measurement systems shall be discussed. These terms and some others are now looked at in more detail. 1.2.1 IMPORTANT TERMS RELATED TO INSTRUMENTATION A few relevant terms for flow measurements and flow-measuring instruments are discussed in this subsection. These are relevant for instruments their selection of instruments. 1. Accuracy and accuracy measurement: The dictionary definition of accuracy is “freedom from error.” However the ISA defines accuracy as “In process instrumentation, degree of conformity of an indicated value to a recognized accepted standard value, or ideal

(IN)ACCURACY IN % ACTUAL READING

(A)

19

value.” Also, as per ISA, it is measured in terms of positive and negative deviations observed during testing under specified conditions and procedures. According to B.G. Liptak “When an instrument is specified to have 1% accuracy, people do not expect it to have 99% error! The intended meaning of that statement is 1% inaccuracy or a 1% error relative to some reference standard” [12]. According to ASME, the “accuracy” of flow measurement is the degree of freedom from error, or the degree of conformity of the indicated value of the instrument to the true value of the measured quantity [13]. 2. Accuracy discussions: One important criterion in flow meter selection is accuracy, which highly depends on the turndown (TD) ratio. However, installation, e.g., straight length, plays a role in attending accuracy in flow measurement. Often people specify accuracy in terms of % of full-scale division (FSD), often also referred to as full scale (FS). Also, it is quite common to specify accuracy in terms of percent of actual reading (AR). In connection with this, Fig. I/1.2.1-1 may be (B)

5 ERROR AS % FULL SCALE VARIES AS SHOWN

4

3

ERROR AS % ACTUAL READING IS CONSTANT ERROR AS % ACTUAL READING IS CONSTANT

2

1 ERROR AS % FULL SCALE VARIES AS SHOWN

0

0

20

40

60

80

ACTUAL FLOW IN %

100

1% FS ERROR FOR 100 AS FS IS 1 AT 20% FLOW INACCURACY DOES NOT HAVE SAME EFFECT AS THAT AT 60% FLOW.

FIGURE I/1.2.1-1 Error and performance of measurement. (A) Error in terms of % actual reading. (B) Error as full scale and actual reading.

20

Plant Flow Measurement and Control Handbook

referenced. As FS is always larger than the calibrated span (CS), a sensor with percent FS performance will be less accurate than one with the same percent CS specification, e.g., an instrument with a range of, e.g., 1000 units and a calibration span of 500. Therefore, 1% FSD will be a 10-unit error but for 1% CS, the error will be 5 units. So, for comparison, it is advisable to convert all quoted accuracies in terms of percent of AR units [14]. The issue will be clear from an example. Suppose a meter has a full scale of 100 units. Therefore, an accuracy of 1% FSD means that the error will be 1 unit. Now when the actual flow is 20 units it may show 19 or 21 units. Similarly at 80-unit flow it may show 79 or 81 units. Naturally, the effects of such an error at 20% and 80% are not same. In contrast, a 1% reading has a constant impact at all flow ranges. This has been shown in detail in Fig. I/1.2.1-1B. Also refer to Subsection 1.2.1.5 below for guaranteed accuracy. 3. Error and uncertainty: According to ISA it is the algebraic difference between the indication and the ideal value of the measured signal and can be obtained by making an algebraic difference between the two values. The uncertainty of a measurement represents the doubt about the validity of the result of the measurement. This is related to the instrument calibration system. From ASME one gets “uncertainty of measurement” as the range within which the true value of a measured quantity can be expected to lie with a specified probability and confidence level [13]. 4. Range: According to ISA it is the two extreme limits within which a quantity is measured, received, or transmitted. This is expressed specifying the upper range limit (URL) and the lower range limit (LRL). 5. Rangeability/turndown: Rangeability is also commonly referred to as the turndown ratio or span ratio. Though it is described

as rangeability, this is in terms of the span of the instrument. It indicates the span in which a flow meter or controller can accurately measure the fluid. In other words, it’s simply the high end of a measurement span compared to the low end of measuring span, expressed in a ratio of maximum flow:minimum flow, e.g., if a given flow meter has a 50:1 turndown ratio the flow meter is capable of accurately measuring down a 1/50th of the maximum flow. There lies the fallacy, suppose an instrument is specified as having an overall accuracy of 0.075% FSD accuracy and turndown ratio of 400:1. What does this mean? This means that for this instrument you can set a span of, e.g., 0e1 kg/cm2, or you can even set the instrument as a 0e400 kg/cm2 span. However, the maximum accuracy is also available as 0.075% FSD. However, it NEVER specifies that both happen at the same time. For this reason, manufacturers provide the accuracy variation curve. This is similar to the guaranteed accuracy that may be achievable for a TD of, e.g., 6:1. 6. Repeatability: As per ISA it is the closeness of agreement among a number of consecutive measurements for the same value of the input under the same operating conditions, approaching from the same direction, for full-range traverses. Another term often encountered is “reproducibility,” which is similar except that in this case the approach is from both directions. In this connection, the ASME definition may be interesting. According to ASME, “repeatability” for flow measurement is the closeness of agreement among a series of results obtained with the same method on identical test material, under the same conditions (same operator, same apparatus, same laboratory, and short intervals of time), whereas “reproducibility” for flow measurement is the closeness of agreement between results obtained when the conditions of measurement differ, e.g., with different test apparatus [13].

Flow Metering: General Discussions (An Overview) Chapter | I

7. Span: Span can be defined as the algebraic difference between the upper- and lowerscale values within which the instrument is supposed (or calibrated) to work. Normally, for instruments, the minimum and maximum spans are specified. This indicates that one cannot calibrate the instrument lower than the minimum span (0.05kPa i.e. Kilo Pascal) and or more than the maximum span (max value of URL 1kPa). However, within these span limits any span can be selected and can be set at any point within the range as shown in Fig. I/1.2.1-2 with suitable example. 8. Range: This can be defined as the lowest and highest readings the instrument can measure. Therefore, range refers to the capability of the instrument. Normally, the lower range limit (LRL) and upper range limit (URL) are specified, e.g., an instrument (say one DP transmitter, e.g., 265DS of ABB) with a range 1 kPa means it can measure LRL ¼ 1 kPa and URL ¼ 1 kPa (refer to Fig. I/1.2.1-2). 9. Linearity: Linearity is a measure of the proportionality between the actual process variable (being measured) values to the instrument output within the calibrated span. In the case of flow measurement by a rotameter it is linear but for a head type measurement with the help of a differential

10.

11.

12.

13. 14. 15.

21

pressure (DP) transmitter (DPT) it is nonlinear. Drift: Drift is the change in the reading of an instrument of a fixed variable with time. There may also be drift due to temperature also. Hysteresis: Hysteresis can be defined as the different readings noted when an instrument approaches a signal from opposite directions. This means that the path followed by instrument reading ascends from the lower to the upper range may not be the same when the same instrument reading descends from the upper to the lower range. There will be a gap which signifies hysteresis. Sensitivity: The sensitivity of an instrument is the ratio between the changes in the output of an instrument to the corresponding changes in the measured variable. The higher the ratio, the greater will be the sensitivity of the instrument—a desirable feature of the instrument. Resolution: This is the smallest difference in input (process) variable to which the instrument is capable of responding. Offset: The offset of an instrument represents the reading of the instrument at zero input variable. Zero/span adjustment: An instrument with an offset needs adjustment. Such an

0 ARC TO INDICATE INSTRUMENT RANGE

CALIBRATED SPAN (CS)

e. g. 1K Pa

(CAN BE SET ANY WHERE WITHIN RANGE) MIN. SPAN < CS < MAX SPAN MAX SPAN MIN. SPAN MIN. SPAN e.g.= 0.05KPa

MAX SPAN e.g.= URL=1KPa

FIGURE I/1.2.1-2 Range and span of instrument.

e. g.

+ 1K Pa

22

Plant Flow Measurement and Control Handbook

adjustment is known as zero adjustment. Therefore, a change in zero is often called bias error or DC offset or zero shift. Any ideal linear device has the following relationship: Output Y1 ¼ m1X þ 0; if the instrument responds as follows: Y1 ¼ m2X þ C, then the instrument needs adjustment. The adjustment of setting C to zero is called zero adjustment. Meanwhile the adjustment m2 to m1 (i.e., of gain) is referred to as span adjustment. In this connection Fig. I/1.2.1-3 may be referenced. From the above some idea of zero and span adjustments is gathered. For further details, Ref. [15] may be referred to. With this the discussions on instrument characteristics are concluded and we move on to understand how various physical parameters affect flow and their physical significance. 16. Vector product: It is known that of the various physical quantities a few are scalar, such as speed and work done, and a few are vector quantities, such as magnetic or electric field and velocity. When these physical entities interact with one another the products can also be scalar or vector quantities. It is known that each force and displacement is a vector quantity but work done, which is computed from force and displacements, is a scalar quantity. This is because in this case the dot ($) product of these two quantities is computed to get work done.

On the other hand, in the case of voltage developed in an electromagnetic flow meter is computed by cross-product of fluid velocity and magnetic field (both vector quantity). So, in generalized way it can be: ! for two vectors, namely, ! a and b with angle q between them will have: ! dot product: ! a $ b [ a$b$cosq—this is a scalar quantity, whereas, ! cross-product ! a 3 b [ a$b$sinq (here the modulus of a, b should be used) and the direction of the resultant vector will be ! orthogonal to both ! a and b . The direction will be obtained by the right-hand rule from a to b. Naturally the cross-product of ! ! ! b  a will not be same as ! a  b (the direction will be different). 1.2.2 TERMS RELATED TO THE PROCESS Here a few terms already discussed and a few new terms and their relevance in measurements will be discussed. 1. Hydraulic diameter (Dh): characteristic length (in meters): The hydraulic diameter can be considered as the characteristic length used to calculate the Reynolds number (Re). In the case of a circular pipe (completely filled) it is the same as the diameter but in case of a noncircular pipe/duct it has a separate significance. This uses the perimeter and the area of the conduit to provide the diameter of a pipe which has proportions such

Curve (2): Actual value ideal curve. Equa on: Y = MX + 0

Actual Value % Output

1 2

3

% Input

Curve (1): Calibra on shi ed: (-ve) zero shi and (+ve) Gain/span shi . Equa on : Y= M1X +(-)b, where M1> M Need zero eleva on and (-ve) gain adjustment Curve (3): Calibra on shi ed: (+ve) zero shi and (-ve) Gain/span shi . Equa on : Y= M2X + c, where M2< M Need zero suppression and (+ve) gain adjustment

FIGURE I/1.2.1-3 Adjustment of instrument zero and span.

Flow Metering: General Discussions (An Overview) Chapter | I

that the conservation of momentum is maintained. It is very useful in establishing the relationship between circular and noncircular pipes. It is very useful for turbulent flow, but is not applicable for laminar flow. When A is the cross-section area and P is the wetted perimeter (see Subsection 1.0.2.5 in Chapter III), hydraulic diameter for full flow is defined as Dh ¼ 4A=P

(I/1.2.2-1)

Typical Dh for different geometry is shown in Fig. I/1.2.2-1 for a few shapes only. 2. Viscosity: The physical significance and phenomenon of viscosity have been discussed in Section 1.1.2 above. As already discussed, viscosity is the internal friction in a fluid. The viscosity of a fluid characterizes its ability to resist shape changes. So, the viscosity of a fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress. As discussed earlier, the shear resistance in a fluid is caused by intermolecular friction exerted when layers of fluid attempt to slide by one another. Viscosity arises from the intermolecular force and provides resistance to shear force, and is highly dependent on temperature. In connection with this Section 1.1.2 and Fig. I/1.1.2-2 may be referenced. It is worth noting that the discussions put forward here are mainly

based on Newtonian fluids (n ¼ 1) as shown in Fig. I/1.1.2-6. Discussions on this for nonNewtonian fluids are covered in Chapter VII. There are two related measures of fluid viscosity, these include the following. l Dynamic (or absolute) viscosity: Dynamic (absolute) viscosity is the tangential force per unit area required to move one horizontal plane with respect to another plane—at a unit velocity—whilst maintaining a unit distance apart in the fluid. From Section 1.1.2 it has been seen that shear stress ¼ m$shear rate. So, dynamic viscosity can be expressed as: s ¼ mdc=dy

l

Circular Pipe diameter D, so Dh =4*(πD2/4)/πD = D

Square duct of width a, so, Dh = 4*a2/4a = a

Dh = 4*a*b/2(a + b) = 2ab/(a +b)

FIGURE I/1.2.2-1 Hydraulic diameter for different geometry (typical shapes only).

(I/1.2.2-2)

Eq. (I/1.2.2-2) is termed as Newton’s law of friction and is applicable for Newtonian fluids (n ¼ 1) as shown in Fig. I/ 1.1.2-6, where, s ¼ shearing stress (N/m2), m ¼ dynamic viscosity (N s/m2), dc ¼ unit velocity (m/s), dy ¼ unit distance between layers (m) (to take care of dc with distance from center). In the SI system the dynamic viscosity units are N s/m2, Pa s or kg/(m s)—where 1 Pa s [ 1 N s/m2 [ 1 kg/(m s). In CGS this is g/(cm s), dyne s/cm2 or poise (p) where 1 P [ 1 dyne s/cm2 ¼ 1 g/ (cm s) ¼ 1/10 Pa s ¼ 1/10 N s/m2. Centipoise (cP) is often used where 1 cP [ 1/100 P. Typically, at w20 C, water viscosity ¼ 1 cP. Kinematic viscosity: The kinematic viscosity n (nu) is a density-related viscosity and has units of m2/s. It has the ratio of absolute (or dynamic) viscosity to density, a quantity independent of force. So, nðnuÞ ¼ m=r

Rectangular duct of width a, height b so,

23

(I/1.2.2-3)

where, n ¼ kinematic viscosity (m2/s); m ¼ absolute or dynamic viscosity (N s/m2) and r ¼ density (kg/m3). In SI, kinematic viscosity is in m2/s or Stoke (St), where 1 St (Stokes) ¼ 10L4 m2/s [ 1 cm2/s.

24

Plant Flow Measurement and Control Handbook

Another practical unit is Centistoke (cSt), where 1 cSt ¼ 1/100 St [ 1 mm2/s. The specific gravity for water at 20.2 C (68.4 F) is w1 and the kinematic viscosity of water at 20.2 C is w1.0 mm2/s (cStokes) (1.0038 mm2/s [cStokes]). Typical values of a few selected product are presented in Table I/1.2.2-1. There is another way kinematic viscosity is expressed, i.e., SUS (mainly used in petroleum industries). For this Fig. I/1.2.2-2 may be referenced. Reynolds number is an important issue in determining types of flow as discussed in Subsection 1.1.2.6. 3. Reynolds number: The most prominent nondimensional parameter which emerges from flow analyses is the Reynolds number, named after Osborne Reynolds for his immense contribution to fluid mechanics. The Reynolds number can be defined as

the ratio of the inertia force (rvL), and the viscous or friction force (m), i.e., rvL (I/1.2.2-4) Re ¼ m By multiplying both the numerator and denominator by the (average) velocity v, one gets   Re ¼ rv2 L mv (I/1.2.2-5) So, it can be interpreted as the ratio of the dynamic pressure (rv2) and the shearing stress (mv/L). Here, Re ¼ Reynolds number (nondimensional); r ¼ density (kg/m3, lbm/ft3); v ¼ velocity based on the actual cross-section area of the duct or pipe (m/s, ft/s); m ¼ dynamic viscosity (N s/m2, lbm/s ft); L ¼ characteristic length (m, ft) in the case of a closed circular pipe it is d; n(nu) ¼ m/r ¼ kinematic viscosity (m2/s, ft2/s).

TABLE I/1.2.2-1 Absolute Viscosity Value (in cP) of a Few Selected Materials: Unless Stated Otherwise All the Values are at 208C Materials

Viscosity (cP)

Materials

Viscosity (cP)

Air-gas

0.018

Hydrogen gas

0.009

Ammonia gas

0.00982

Kerosene

10

Benzene

0.604

Ketchup

(50e100)  103

Blood at 37 C

3e4

Light oil

1.1  102

Carbon dioxide gas

0.0148

Methanol

0.544

Carbon monoxide gas

0.01720

Molasses

(5e10)  103

Ethane gas

0.0095

Molten chocolate

(45e130)  103

Ethanol

1.074

Molten glass

(1e100)  104

Ethyl alcohol

0.12

Motor oil SAE40

250e500

Gasoline

0.6

Nitrogen gas

0.01781

Heavy oil

6.6  10

2

Helium gas

0.019

HFO380

>2000

Honey

(2e10)  10

Oxygen gas

0.020 

3

Steam at 100 C

0.013

Sulfur dioxide gas

0.01254

Water

0.894

Flow Metering: General Discussions (An Overview) Chapter | I

25

Saybolt universal Second (SUS) is an alternative unit for measuring Kinematic viscosity in classical mechanics. It is a measure of time required for 60 milliliter of petroleum product to flow through the calibrated orifice of a Saybolt universal viscometer, under controlled temperature and conditions prescribed by test method ASTM D 88. Relation between Kinematic viscosity in SSU and absolute viscosity can be expressed as:

νSSU = B μ / Sp gr. Or νSSU = Bνcentistokes ; where sp gr. Is the specific gravity, νSSU = kinematic viscosity (SSU); μ = dynamic or absolute viscosity (cP). B varies with temperature; B = 4.632 & 4.664 at 1 00 oF (37.8 oC) & 210oF (98.9 oC)respectively.

FIGURE I/1.2.2-2 Saybolt universal second for kinetic viscosity.

For a pipe or duct, the characteristic length is the hydraulic diameter. L ¼ dh, where, dh ¼ hydraulic diameter (m, ft) (see Subsection 1.2.2.1). The Reynolds number for a duct or pipe can be expressed as Re ¼ rvdh =m ¼ vdh =n ¼ ðfor circular pipe it is vd=nÞ (I/1.2.2-6) So, this inertial force and viscous force ratio consequently give relative importance to two types of force. When the viscous force is relatively more important, and disturbances in the flow are damped out by viscosity, there will be relatively low values of Reynolds number. Thus, it is difficult for disturbances to grow and sustain themselves. On the other hand, at relatively large values of Reynolds number, the damping of disturbances by viscosity is less effective, and inertia is more important, so that disturbances can perpetuate themselves. This is the basic reason why the Reynolds number serves as a measure for determining whether the flow is laminar or turbulent [16]. From the above discussions it is also clear that the transition from laminar to turbulent flow depends on the geometry, surface roughness,

flow velocity, surface temperature, and type of fluid, among other things. 4. Average velocity: From Fig. I/1.1.2-1, it can be seen that as one moves from the center of the pipe the velocity values change. The fluid velocity in a pipe changes from zero at the surface because of the no-slip condition to a maximum at the pipe center. In fluid flow, it is convenient to work with an average velocity, vavg, which remains constant in incompressible flow when the cross-sectional area of the pipe is constant, as shown in Fig. I/1.2.2-3. The average velocity for compressible fluid and heating and cooling applications may change somewhat on account of changes in density with

TURBULENT FLOW Re >4000 VELOCITY AVERAGE (Vavg)

LAMINAR FLOW Re < 2300

VELOCITY AVERAGE (Vavg)

FIGURE I/1.2.2-3 Flow types and average velocity.

26

Plant Flow Measurement and Control Handbook

temperature. However, for convenience, in practice, the fluid properties at some average temperature are evaluated and are considered as constants. The convenience of working with constant properties in most cases is usually more justifiable than slight loss in accuracy in measurement. There may be a slight change in temperature due to friction (some sensible heat) but it is not noticeable, and the pressure drop is prominent. By applying conservation of mass principle, it is possible to calculate the average velocity in the following manner. If “qm” is the mass flow rate, “r” is the density of the medium, “A” is the cross-section of a circular pipe, and vavg is the average velocity, then one can say: qm ¼ r$A$vavg

(I/1.2.2-7)

Now, when a small section of velocity profile variations across a radius represented by v(r) is taken and integrated over the area, then Z A vðrÞdA or; vavg qm ¼ r$A$vavg ¼ r 0

Z ¼

!,

A

r

vðrÞdA

ðrAÞ

0

(I/1.2.2-8)

Putting the parameters pertinent to the closed circular pipe one gets: 0 1, Z R   vðrÞrdrA vavg ¼ @2pr rpR2 0

 ¼

2 R2

Z

r

r$vðrÞdr 0

(I/1.2.2-9) Therefore it is possible to calculate vavg when the velocity profile/flow rate is known for noncompressible fluid. For compressible fluid density, variations need to be considered. 5. Pipe, tube, duct, and conduit: The terms pipe, tube, duct, and conduit are usually used interchangeably for flow sections (Fig. I/1.2.2-4). In general, flow sections of circular cross-section are referred to as pipes (especially for liquid), and flow sections of noncircular cross-section as ducts (especially for gas). Small-diameter pipes are usually referred to as tubes. Pipes are normally specified by nominal bore (NB) (or DN as per Din standard) and schedule. Corresponding to each nominal bore has one unique outer diameter while the thickness is governed by schedule. It is noticed that normally a circular pipe is chosen for fluid flow, especially for

Pipe Specifica on (example): NB4inch (DN 100mm) schedule 160: Nominal Bore 4 inch (DN 100 mm), So, Outside Diameter 114.3 mm Schedule 160 meaning wall thickness is specified as 13.4 mm so, ID =87.5 mm

Duct is specified by width and height along with thickness.

Tubes are smaller version of pipe. Tube is Important for instrumenta on in impulse line applica ons. It is specified by outside diameter and thickness. Corresponding to above pipe tube will be specified by outside diameter = 114.3 mm (DN100) and wall thickness 13.49 mm for (corresponding 160sch). This is as per ANSI standard.

FIGURE I/1.2.2-4 Pipe duct and tube as fluid flow sections.

Flow Metering: General Discussions (An Overview) Chapter | I

high-pressure services and when liquids and steam are used. Why? This is because pipes with a circular cross-section can withstand large pressure differences between the inside and the outside without undergoing significant distortion. On the other hand, ducts are chosen for fluid flows like gases and air on account of their low-pressure application, space requirements for corresponding volume, and costs. Tubes are chosen for certain special applications. 6. Flow separation and velocity profile disturbance: At the boundary wall of the circular pipe there exists a boundary layer in which the flow velocity increases from zero to v. So, when the obstruction is the

27

wall, the boundary layer extends to restrain the fluid flow more in the vicinity of the wall. Thus, downstream of the aforesaid restriction, there exists a dead zone and even a slight negative pressure. Again due to the restriction, there will be acceleration, so the fluid flows from the region of higher velocity into this dead zone and creates vortices. The flow separates from the surface of the wall as depicted in Fig. I/ 1.2.2-5. In Fig. I/1.2.2-5A acceleration, restraining, and vortex formation are shown, while in Fig. I/1.2.2-5B flow separations have been depicted for two different cases. These vortices consume energy and account for some loss. They also change the velocity

(A) RESTRAINING

ACCELERATION

VORTEX FORMATION

(B)

SEPARATION

REVERSE FLOW SHARP RESTRICTION

CONTINUOUS EXPANSION

FIGURE I/1.2.2-5 Flow separation phenomenon. (A) Dead zone and vortex formations. (B) Flow separation and profile. Based on an idea from F. Frenzel, H. Grothey, C. Habersetzer, M. Hiatt, W. Hogrefe, M. Kirchner, G. Lütkepohl, W. Marchewka, U. Mecke, M. Ohm, F. Otto, K.-H. Rackebrandt, D. Sievert, A. Thöne, H.-J. Wegener, F. Buhl, C. Koch, Deppe, E. Horlebein, A. Schüssler, U. Pohl, B. Jung, H. Lawrence, F. Lohrengel, G. Rasche, S. Pagano, A. Kaiser, T. Mutongo, Industrial Flow Measurement Basics and Practice, ABB Automation Products GmbH, http://nfogm.no/wp-content/uploads/2015/04/Industrial-Flow-Measurement_ Basics-and-Practice.pdf.

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Plant Flow Measurement and Control Handbook

profile and in some cases these are not desirable for measurement. Similarly obstructions in the flow conduit (closed circular pipe) like bends, elbows, reducers, expanders, strainers, and control valves—to name a few—also affect flow profile greatly and so affect the flow measurement. Finally, the flow profile can be restored by the natural mixing action of the fluid particles as the fluid moves through the pipe for a greater distance. This is the main reason that the upstream and downstream straight lengths are specified. Typical such velocity profile disturbance and restoration inside the closed circular pipe are detailed in Fig. I/1.2.2-6. Such flow disturbance should never be confused with turbulence which occurs due to the Reynolds number (Re). In fact, when bearing in mind the first part of the discussion in this subsection, one may note that such a disturbance will give rise to an asymmetrical velocity profile and the following interesting phenomena. l Vortex: Areas of swirling motion with high local velocity which are often caused by separation or a sudden enlargement in the pipe area as shown in Fig. I/1.2.2-5.

When a body is placed in the middle of a media flow with the Re above a certain value, separation occurs and vortices are formed on both sides. When a vortex is formed on one side, then a similar vortex is formed on the other side and this causes the first one to be shed [1]. For detailed discussions on the theoretical background of this phenomenon Section 3.0.0 of Chapter V may be referenced. One flowmeasuring instrument that has been developed based on this is discussed in Chapter V. l Swirl: Fluid rotation about the circular pipe axis. Swirl is the tangential flow component of the velocity vector. There are swirl type flow meters used for flow measurement. This is little different from a vortex flow meter and is discussed in Chapter V. 7. Surface tension: For the development of surface tension in a liquid there is a need for two kinds of forces as defined below [7]. l Cohesive force: This is the force of attraction between the molecules of a liquid by virtue of which they are bound to each other to remain as one assemblage of particles. It helps to resist tensile stress.

CHANGES IN SEPARATION & PROFILE

DISTURBANCE DUE TO BEND (ELBOW) FLOW IN A PIPE WITH ELBOW

FIGURE I/1.2.2-6

Flow separation and profile after a disturbance.

Flow Metering: General Discussions (An Overview) Chapter | I

l

Adhesion force: This is the force of attraction between unlike molecules, i.e., between the molecules of different liquids or between the molecules of a liquid and those of a solid body when they are in contact with each other. Adhesion enables it to adhere to another body. Therefore, liquid molecules exhibit cohesive forces that bind them to each other. The molecules below the surface are generally free to move within the liquid and they move at random and are subject to equal force in each direction. When they reach the surface they reach a dead end, on account of the absence of molecules above the surface to attract or pull them out of the surface. At this point at the surface the net downward force is at its maximum, so they stop and return back into the liquid. Work is done on each molecule arriving at the surface against the action of an inward force. Thus mechanical work is performed in creating a free surface or in increasing the area of the surface [7]. This is at the cost of potential energy. So, at the condition of stable equilibrium a thin layer of a few atomic thicknesses at the surface is formed. However, this is formed by the system with potential energy at its minimum. This cohesive bond exhibits a tensile strength for the surface layer and this is known as surface tension. The magnitude of surface tension is defined as the tensile force acting across an imaginary short and straight elemental line divided by the length of the line [7]. The dimensional formula is F/L or MT2. It is usually expressed in N/m in SI units. It shows a slight decrease with an increase in temperature. Surface tension causes an interface of two liquids/liquidesolid/liquidegas, etc. This is included here as it shows some effect in slurry flow measurement, e.g., bubble formation.

29

8. Vapor pressure: All liquids tend to evaporate or vaporize. Molecules constantly escape from a liquid surface and an equal number constantly enter the surface when there is no energy addition. The number of molecules escaping from the surface or reentering will depend upon the temperature. These escaped molecules above the free surface exert a certain pressure. This pressure is known as the vapor pressure corresponding to the temperature. At an elevated temperature, more molecules will leave than reenter the surface to increase the vapor pressure. This means that vapor pressure increases with temperature. In a confined area, vapor pressure goes on increasing until an equilibrium condition evolves, when the rate at which the number of vapor molecules striking back at the liquid surface and condensing is equal to the rate at which they leave from the surface; the space above the liquid then becomes saturated with vapor. The pressure at which it occurs is called the saturation pressure. The temperature corresponding to the pressure is known as the saturation temperature. From the above it can be seen that the vapor pressure of a given liquid is a function of temperature and hence the vapor pressure increases with the increase in temperature. Therefore, the phenomenon of boiling of a liquid is closely related to the vapor pressure. When the vapor pressure of liquid becomes equal to the total pressure impressed, then the liquid starts to boil. Therefore, boiling can be achieved by increasing the temperature or lowering the surrounding pressure to the vapor pressure. With the discussions on general terms related to flow measurement concluded we now discuss the basics of fluid mechanics essential for flow measurement. 9. Coanda effect: According to Bernoulli’s energy balance equation, a slow-moving high-pressure fluid becomes a fast-moving low-pressure fluid at the nozzle exit forming

30

Plant Flow Measurement and Control Handbook

a jet. The same theory has been utilized in designing the wings of aircraft. However, in 1930, the Romanian engineer Henri Coanda discovered another effect popularly known as the Coanda effect or wall attachment effect, which is more effective in producing lift. What is Coanda effect? “Coanda effect: A moving stream of fluid in contact with a curved surface will tend to follow the curvature of the surface rather than continue traveling in a straight line.” (Courtesy of http://www.discoverhover.org/ infoinstructors/guide8.htm). When a fluid moves across a surface a portion of the friction, known as the “skin friction” (something similar to the skin effect of the current!) occurs between the fluid and the surface, and tends to slow down the moving fluid. This resistance to the flow, pulls the fluid towards the surface. So, for the Coanda effect a jet flow attaches itself to a nearby surface and remains attached to it even when the surface curves away from the initial jet direction. This effect is utilized in air condition design also. In fluid flow measurement the same principles have been utilized in the fluidic meters that are discussed later. 10. Snell’s law for ultrasonic measurement: The reader may recall the laws of refraction in geometrical optics; in case of ultrasonic waves the same is applicable. The angle of incident of the ultrasonic wave is extremely important for better measurement accuracy. When a transducer is mounted externally it has to cross three media, e.g., the transducer, pipe, and fluid. In each case there will be refraction. Referring to Fig. I/1.2.2-7, it can Transmi er

S1

α Pipe Wall

β Fluid

S2 θ

S3

FIGURE I/1.2.2-7 Ultrasonic signal refraction.

be seen that there are three angles involved in two interface points. Naturally, to know exactly where the other transducer to be placed, it is important to know at what angle it reaches the bottom. As per Snell’s law for sound “the ratio of the angle of incident to any medium and sound velocity in that medium is constant.” In such a case the relationship between the various media can be established by Eq. I/1.2.2-10. cosa=Cs1 ¼ cosb=Cs2 ¼ cosq=Cs3 ¼ constant (I/1.2.2-10) This will be required for ultrasonic flow meter discussions. 11. Law of electromagnetic induction: From Faraday’s second law of electromagnetic induction one gets that the magnitude of induced emf (electromotive force) is equal to the rate of change of flux linkages with the coil. Faraday’s law also tells us that inducing a voltage into a conductor can be done by either passing it through a magnetic field, or by moving the magnetic field past the conductor. Faraday’s law of electromagnetic induction has been utilized in electromagnetic flow meters, where the process fluid acts as a conductor and electrodes are used to measure the induced emf. 12. Coriolis’ effect: Coriolis’ effect represents an inertial force. According to this effect, if the ordinary Newtonian laws of motion of bodies are to be used in a rotating frame of reference, an inertial force would act on the body and this needs to be taken into consideration for developing an equation of motion. This force will act on the right or left direction of body motion for counterclockwise or clockwise rotation of the reference frame, respectively. Therefore, the effect of the Coriolis force is an apparent deflection of the path of an object that moves within a rotating coordinate system. The object does not actually deviate, but it appears to

Flow Metering: General Discussions (An Overview) Chapter | I

ω d

B

A

R

FIGURE I/1.2.2-8 Coriolis’ effect.

be a deflection on account of the motion of the coordinate system. Coriolis’ effect is the inertial force necessary to be applied to move a mass from A to B when they are in a rotational frame as shown in Fig. I/ 1.2.2-8. See Section 3.1.4 for further details.

2.0.0 BASIC FLUID MECHANICS Accurate measurement of a flowing medium is always is very important in plants and industrial applications. The basic approach of the given measurement technique depends on the type of flowing medium, e.g., liquid/gas, the nature of the flow, i.e., laminar/turbulent, etc. [17]. As discussed earlier, there are a few influencing parameters like velocity, pressure, temperature, density, viscosity, turbulent intensity, etc. It is therefore recommended that this part of the discussions shall be read in conjunction with the relevant parts of the previous Section 1.0.0. One of the major application areas of fluid mechanics is determination of flow in a flow conduit especially for head type meters. This is of prime importance for flow measurement and control. In this section this will be discussed at length. While discussing these, associated requirements from influencing factors will also be discussed in the light of fluid mechanics. The discussion begins with Bernoulli’s equation. 1. Conservation of energy: From elementary physics it is known that when a ball is dropped from a height, initially it has potential energy

31

(PE) and finally when it touches the ground it has kinetic energy (KE). While traveling, at various points potential energy is transformed into kinetic energy and the height is reduced. So, if a ball with mass “m” starts with zero initial velocity from height “h” and attains velocity v at the time it strikes the ground, then, initial KE ¼ 0, PE ¼ mgh, final PE ¼ 0 KE½mv2 and at intermediate points it had both PE and KE. From conservation of energy, the initial PE ¼ final KE; mgh ¼ ½mv2, hence v2 ¼ 2gh or v ¼ ð2ghÞ1=2

(I/2.0.0-1)

2. Hydrostatic application: Another important issue is hydrostatic pressure (mainly of liquid) due to the level (datum) difference. This will also be necessary for flow determination with the help of Bernoulli’s theorem. A pipe is filled with medium with density (r), and is located in an inclined manner so that there is a height difference of points in the pipe as shown in Fig. I/2.0.0-1A, i.e., a point with pressure P1 is located at Z1 height above the datum level and a point with pressure P2 is located at Z2 height above the datum level, then P1  P2 ¼ (Z2  Z1)$ density(r)$g, i.e., from the basics of hydrostatics it will be P1  P2 ¼ ðZ2  Z1 Þrg or, P1 =r þ Z1 g ¼ P2 =r þ Z2 g

(I/2.0.0-2)

3. Derivation of the energy equation: Referring to Fig. I/2.0.0-1B, an attempt is made to derive the energy equation. Let there be one conduit with cross-section A, with flowing fluid with pressure P. Now, if a mass of “m” of flowing fluid is moved from point “a” to point “b” with velocity “v,” at point “a,” situated at distance Z above the datum level, potential energy (PE) ¼ mgZ. Hence, for unit weight, PE will be: mgZ=mg ¼ Z.

(I/2.0.0-3)

32

Plant Flow Measurement and Control Handbook

(A)

(B) P2 CROSS SECTION A

P1

a

b

mg

Z1

Z2 DATUM LEVEL

DATUM LEVEL

Z

P1-P2 =(Z2-Z1)*DENSITY*g

(C)

(D) P2

b & E a N a TS LI IN AM PO TRE S O TW BY AT ED b GY IN ERS JO N E NT I L TA PO O T O TW

P1

v2

v1

Z2 Z1

DATUM LEVEL

FIGURE I/2.0.0-1 Bernoulli’s equation application. (A) Pressure due to level difference. (B) Derivation of Bernoulli’s equation. (C) Application of Bernoulli’s theorem. (D) Application of Bernoulli’s equation for flow calculation.

Similarly kinetic energy for mass will be equal to 2

1=2mv .

(I/2.0.0-4)

So, kinetic energy for unit weight will be equal to    1=2 v2 g (I/2.0.0-5) On account of pressure P it will generate a force “PA” across the fluid block under consideration. When that fluid block of mass “m” crosses area A from a to b and if r is the density of the fluid, then the volume crossing will be m=r

(I/2.0.0-6)

From the figure the distance traversed will be m=ðrAÞ Therefore, Pm/r;

work

(I/2.0.0-7)

done ¼ P$A$m/(rA) ¼

For unit weight work done ¼ P=ðrgÞ (I/2.0.0-8) By summing all energies, pressure energy þ PE þ KE, one gets    P=ðrgÞ þ Z þ 1=2 v2 g ¼ Constant (I/2.0.0-9) Eq. (I/2.0.0-9) is the basis of Bernoulli’s equation.

Flow Metering: General Discussions (An Overview) Chapter | I

Also, here as all the parameters in Eq. (I/2.0.0-9) have unit length, they are often called heads, e.g., pressure head ¼ P/(rg); potential head ¼ Z and velocity head ¼ ½(v2/g). Fig. I/2.0.0-1C shows the movement from point a to b in a stream line which is defined as a line tangential to the instantaneous velocity vector direction. 4. Application of energy equation: To arrive at Bernoulli’s theorem let the above conditions be applied in moving from point a to b in a streamline as shown in Fig. I/2.0.0-1. So total energy per unit weight at “a” will be:    Pa =ðrgÞ þ Za þ 1=2 v2a g    ¼ Pb =ðrgÞ þ Zb þ 1=2 v2b g (I/2.0.0-10) In the above discussions, loss to friction and/or any other forms has not been considered, similarly energy gain from the pump is not considered as that is the basis for Bernoulli’s equation. Another interesting fact here is that in a similar manner pipe flow can be calculated. A typical application of Bernoulli’s equation for pipe flow calculation has been depicted in Fig. I/2.0.0-1D. Detailed discussion of this has been presented in the following section. 5. Bernoulli’s principles and equation: With Bernoulli’s equation, it is possible to establish an approximate relation between pressure, velocity, and elevation. It is primarily valid in regions of steady, incompressible flow where net frictional forces are negligible. The major approximation in Bernoulli’s equation is that viscosity effects are negligibly small compared to other effects. Naturally this cannot be applied to the entire flow field of interest. However, such an approximation is reasonable in certain regions of many practical flows. Such regions are referred to as an inviscid region for flow. In fluid dynamics, according to Bernoulli’s principle; for an inviscid flow of a nonconducting fluid, an increase in the speed of the fluid occurs simultaneously with

33

a decrease in pressure or a decrease in the fluid’s potential energy. In a generalized way, it can be stated that, when an incompressible fluid is flowing, the total of pressure energy, kinetic energy, and potential energy per unit mass should be constant. Bernoulli’s equation can be considered to be a statement of the conservation of energy principle applied to flowing fluids. Bernoulli’s equation is essentially a general and mathematical form of Bernoulli’s principle that also takes into account changes in gravitational potential energy. So, Bernoulli’s equation relates the pressure, speed, and height of any two points (“a” and “b”) in a steady streamline flowing fluid of unit volume with density r. So, Bernoulli’s equation can be written as: P þ 1=2rv2 þ Zrg ¼ constant.

(I/2.0.0-11)

where P ¼ static pressure, r ¼ density of fluid; Z ¼ elevation from datum. When P is static pressure, the term “½rv2” is known as dynamic pressure. By considering z ¼ 0, i.e., at datum level one can argue that in a closed pipe the sum of static pressure and dynamic pressure is constant. With reference to Fig. I/2.0.0-1D, it can be written as: P1 þ 1=2rv21 þ Z1 rg ¼ P2 þ 1=2rv22 þ Z2 rg (I/2.0.0-12) where the expression on the left-hand side (LHS) with suffix 1 represents the parameter at the upstream of the constriction (or restriction, e.g., as an orifice), and the same on the right-hand side (RHS) with suffix 2 representing the parameter at or after the constriction (or restriction, e.g. as an orifice) in a pipeline. 6. Applicability of Bernoulli’s equation: Bernoulli’s equation is quite powerful and with the help of this equation it is possible to calculate pipe flow, etc. However, the equation has some limitations on account of certain assumptions made at that point in time.

34

Plant Flow Measurement and Control Handbook

Major limitations of Bernoulli’s equation mainly encompass the following. l Flow considered is a steady irrotational flow. l It speaks of flow from one point to another in a streamline but not between two streamlines. l Density is constant or a function of pressure, indicating incompressible fluid. However, it is possible to apply it to compressible fluid also (with certain modifications). l External force must be conservative, i.e., derivable from potential energy [18]. l Velocity is derivable from velocity potential [18] and by using Bernoulli’s equation, only the mean velocity (of the liquid) should be taken into account because the velocity of liquid particles is not uniform. l In Bernoulli’s equation all other external forces are neglected, which is not possible in practical applications. l Any energy extracted from flow or supplied to the flow has to be taken into account. l In turbulent flow some kinetic energy is converted into heat energy and in a viscous flow some energy is lost due to shear forces. l If the liquid is flowing through a curved path, the energy due to centrifugal forces should also be taken into account. We now discuss how Bernoulli’s equation are applied for flow measurement, which of prime importance to us. 2.1.0 Bernoulli’s Equation for Pipe Flow Measurement In this section efforts will be made to derive a pipe flow equation by applying Bernoulli’s equation. The discussions start with the continuity equation. 2.1.1 CONTINUITY EQUATION When fluid is in motion, it must move in such a way that conservation of mass law is followed,

i.e., the mass of fluid in a flow tube is constant. This means that mass flowing in ¼ mass flowing out. This is the continuity equation. Mathematically it can be represented by: m1 ¼ m2 where m1 and m2 represent inflow and outflow of mass. So, rV1 ¼ rV2 where r is fluid density and V1 and V2 are volume of inflow and outflow of fluid. Or, rA1 v1 Dt ¼ rA2 v2 Dt where A1 and A2 are upstream and downstream area and v1 and v2 are velocity at upstream and downstream of restriction and Dt is a small time difference. Then A1 v1 ¼ A2 v2 ¼ q ¼ V=t ¼ constant E (I/2.1.1-1) Eq. (I/2.1.1-1) represents the continuity equation. 2.1.2 BERNOULLI’S EQUATION FOR FLOW CALCULATIONS The discussions start with the help of Fig. I/ 2.0.0-1D. In this figure it is clear that there are two sections. One is wider, where the pressure is P1 and velocity v1. The other part is slightly constricted, where pressure and velocity are represented by P2 and v2, respectively. In this section flow goes from the wide section to the constricted section. Instead of considering wider and constricted sections, the same section with a restriction, such as an orifice, could also be used to derive the calculation. As per Bernoulli’s equation or principles it is known that, in a closed pipe, the density will not change. Now if unit weight of fluid enters the pipe then by the equation of continuity discussed in Section 2.1.1 above, unity weight must also leave the closed pipe. If the flowing

Flow Metering: General Discussions (An Overview) Chapter | I

fluid has internal energy in the wider and constricted sections, these are designated I1 and I2. Then, by applying Eq. (I/2.0.0-12), one can write P1 þ 1=2rv21 þ Z1 rg þ I1 ¼ P2 þ 1=2rv22 þ Z2 rg þ I2

(I/2.1.2-1)

Here one thing to be noted is that as per Bernoulli’s principle, density remains constant (see Subsection 2.0.0.6), so in both sides the same density r is considered. Also, as long as temperature in both sections remains constant, then I1 ¼ I2 [19], so, one gets P1 þ 1=2rv21 þ Z1 rg ¼ P2 þ 1=2rv22 þ Z2 rg (I/2.1.2-2) This is basically the same as Eq. (I/2.0.0-12). Now, dividing both sides by rg, Z is freed.    ðP1 =rgÞ þ v21 2g þ Z1    ¼ ðP2 =rgÞ þ v22 2g þ Z2 (I/2.1.2-3) Considering the horizontal level as the datum level, a manometer is placed at the two tappings to measure pressure, then fluid height at the upstream tapping with respect to the datum will be (P1/rg) þ Z1 and at the downstream tapping it will be (P2/rg) þ Z2. So, if “h” is the difference in the manometer between the two tappings then h ¼ ðP1 =rgÞ þ Z1  ðP2 =rgÞ  Z2 (I/2.1.2-4) Combining Eqs. (I/2.1.2-3 and I/2.1.2-4) one gets v22  v21 ¼ 2gh;

(I/2.1.2-5)

and again from Eq. (I/2.1.1-1) one gets v21 ¼ ðA2 =A1 Þ2 v22 and so, putting the value of v1 in Eq. (I/2.1.2-5) one gets that    v22 1  A22 A21 ¼ 2ghm2 or, 1=2 

v2 ¼ ð2ghÞ

 1=2 1  A22 A21

or,

pffiffiffiffiffiffiffiffi.pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi v2 ¼ 2gh ð1  m2 Þ

35

(I/2.1.2-6)

where the area ratio is represented by “m.” Also 1/(1  m2)1/2 is referred to as velocity approach and represented by E. So pffiffiffiffiffiffiffiffi (I/2.1.2-7) v2 ¼ E$ 2gh Therefore, volume flow q ¼ A2 $v2 ¼ A2 $E

pffiffiffiffiffiffiffiffi 2gh

(I/2.1.2-8)

Now putting the value of dp/r ¼ hg and simplifying 2dpr pffiffiffiffiffiffiffiffiffiffiffiffiffi (I/2.1.2-9) q ¼ A2 $E 2dp=r pffiffiffiffiffiffiffiffiffiffi Mass flow ¼ qr ¼ A2 $E 2dpr (I/2.1.2-10) 2.1.3 FLOW EQUATION IN TERMS OF PIPE GEOMETRY In the previous section discussions were put forward with different elevations for upstream and downstream with constriction for flow measurement. In this case a flow restriction has been considered in a horizontal pipe, meaning Z1 ¼ Z2. From Eq. (I/2.1.2-3), e.g., in a horizontal pipe; meaning Z1 ¼ Z2       ðP1 =rgÞ þ v21 2g ¼ ðP2 =rgÞ þ v22 2g (I/2.1.3-1) or P1  P2 ¼ dp ¼ Dp ¼

 r 2 v2  v21 2 (I/2.1.3-2)

Again, from Eq. (I/2.1.1-1), we have A1$v1 ¼ A2$v2 or v1 ¼ (A2/A1)$v2, so for a closed pipe of inside diameter D and restriction bore d one gets v1 ¼ (d2/D2)$v2 or v1 ¼ (d/D)2$v2; putting the value of b (d/D) from Fig. I/2.1.2-1 one gets v1 ¼ ðbÞ $v2 2

(I/2.1.3-3)

36

Plant Flow Measurement and Control Handbook

Beta Rao: Velocity approach is the area rao of two secons. Now in case of a closed pipe if inside diameter of the pipe is “D” and the same for the restricon (say orifice plate) is “d” then the rao of d/D is referred to as Beta Rao. So, β = Bore/Pipe ID = d/D ; It is one of the major geometric parameter in Flow calculaon. Beta is always less than 1. Square edge orifice 0.2- 0.75 (0.7 max

Cd is more popular, it is used in the book) is defined as the ratio of actual flow by theoretical flow, so, Discharge coefficient Cd ¼ ðActual flowÞ=ðTheoretical flowÞ

design), Quadrant orifice 0.24- 0.6, Venture 0.4-0.7 [source:20].

FIGURE I/2.1.2-1 Beta ratio for flow elements. Adapted from Process Design Practices Flow Meters and Orifices; CK, December 2009, http://www.korf. co.uk/PDP%2006-FO-P5_P14.pdf.

i.e., actual flow ¼ Cd$theoretical flow (Eq. I/ 2.1.3-6) or   pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi qm ¼ Cd $p d2 4 2Dpr=ð1  b4Þ (I/2.1.4-1)

By combining Eq. (I/2.1.3-2 and I/2.1.3-3) one gets pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi (I/2.1.3-4) 2Dp=rð1  b4Þ ¼ v2   pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi q ¼ A2 v2 ¼ p d2 4 2Dp=rð1  b4Þ (I/2.1.3-5)   pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Mass flow qm [ p d2 4 2Dpr=ð1Lb4Þ (I/2.1.3-6) The flow calculations shown in Sections 2.1.2 and 2.1.3 are theoretical values because of various assumptions in Bernoulli’s equations discussed in Subsection 2.0.0.6 for streamline flow without losses. So, these calculations are far from real values, where the flow is turbulent in most cases, also viscosity effects cannot be ignored in this way. In view of the same some corrections are necessary, as discussed in the following sections. Another interesting issue is that after the restriction there will be some pressure recovery but it cannot recover full-pressure P1 but at a less value P3. P1  P3 is the permanent pressure loss in the system. 2.1.4 DISCHARGE COEFFICIENT Discharge coefficient (Cd) (as per standard ISO 5167:2003 it is designated as “C,” however since

in the case of compressible fluid another factor expansibility factor ε (discussed later), to be multiplied. So, mass flow   pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi qm ¼ Cd $ε$p d2 4 2Dpr=ð1  b4Þ (I/2.1.4-1A) In this case, temperature and density, etc. in both sections are the same, and above flows may be considered as volume flow. From Section 3.3.5 of ISO 5167-1:2003, one gets the following definition. Discharge coefficient, “defined for an incompressible fluid flow, which relates the actual flow rate to the theoretical flow rate through a device, and is given by the formula for incompressible fluids.” Using this, Cd (“C” in the standard) is defined as n pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi o. Cð ¼ Cd Þ ¼ Qm$ ð1  b4Þ n   pffiffiffiffiffiffiffiffiffiffiffi o  p d2 4 2Dpr . (I/2.1.4-1B) In Section 2.1.2 and Eq. (I/2.1.2-6) the velocity approach has already been defined. After having a close look at this for a closed circular pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi pipe it can be argued that the term 1 ð1Lb4Þ is the velocity approach.

Flow Metering: General Discussions (An Overview) Chapter | I

TABLE I/2.1.5-1 Relation of Discharge Coefficient and Diameter Ratio [21] Device

Beta (Min.)

Beta (Max.)

Thin sharp edge orifice

Cd 0.61

Machined Venturi nozzle

0.4

0.75

0.995

Rough weld Venturi nozzle

0.4

0.7

0.985

Rough cast Venturi nozzle

0.3

0.77

0.984

2.1.5 FLOW COEFFICIENT There is another important term, flow coefficient, which is defined as follows: .pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Flow coefficient ¼ C$1 ð1Lb4Þ or .pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ð1Lb4Þ Cd $1 Cd is a function of the jet size or area ratio ¼ Avc/A2 where Avc ¼ area in “vena contracta” discussed below. For a primary device, Cd is the dimensionless parameter determined using an incompressible fluid. Cd is dependent on Reynolds number (Re) for a given geometry. It relates the resistance coefficient discussed later in Subsection 2.1.6.2. Cd often is considered as calibration constant for a primary device. The typical relationship of Cd with various beta values has been elaborated in Table I/2.1.5-1. Re varies with pressure, temperature, viscosity and flow, as does Cd. 2.1.6 RELATED DISCUSSION TERMS 1. Vena contracta: The vena contracta was probably first conceived by Torricelli in 1643. It is the reduction in the area of a fluid jet after it emerges from a circular aperture. The vena contracta is the minimum jet area that appears just downstream of the restriction. The velocity of the fluid will be at its highest and the pressure at the lowest in the “vena contracta.”

37

2. Resistance coefficient (K): The resistance coefficient represents the multiple of velocity heads that will be lost by fluid passing through the fitting. The resistance coefficient (K) allows the user to characterize the pressure loss through fittings in a pipe. It is related to Cd by  (I/2.1.6-1) K ¼ 1 C2d . 3. Isentropic exponent: According to ISO 5167-1:2003, the isentropic exponent is defined as the ratio of the relative variation in pressure to the corresponding relative variation in density under elementary reversible adiabatic (isentropic) transformation conditions. Factor k is a property of the media and varies with the pressure and temperature of the medium also. The isentropic exponent “k” appears in different formulae for the expansibility (expansion) factor ε discussed below. It varies with the nature of the gas and with its temperature and pressure conditions. There are many gases and vapors for which no values for k have been published so far (ISO 5167-1:2003). In such cases, as per standard, “the ratio of the specific heat capacity at constant pressure to the specific heat capacity at constant volume of ideal gases can be used in place of the isentropic exponent,” i.e., Cp/Cv—specific heat ratio. For air and diatomic molecule gases it is 1.4. 4. Pipe Reynolds number (ReD) and orifice Reynolds number (Red): Dimensionless Reynolds number has been defined in Subsection 1.2.2.3. Since the velocity at the two sections of flow-measuring systems are not the same naturally there will be two different Reynolds numbers for the two sections of flowmeasuring systems—typically as shown in Fig. I/2.0.0-1D (or Fig. I/2.1.3-1) as velocity of two sections are different. So, Pipe Reynolds numberðReD Þ ¼ v1 D=n1 ¼ ð4Qm Þ=ðpm1 DÞ (I/2.1.6-2)

38

Plant Flow Measurement and Control Handbook

P1

A1

v1

P2

A2

P1 > P3 P3

v2

FLOW (Q)

RESTRICTION SEPARATION (Typ) P1-P2 PRESSURE DROP FOR RESTRICTION FOR FLOW MEASUREMENTLOSS P1-P3 PERMANENT PRESSURE LOSS (CANNOT RECOVER FULL PRESSURE)

FIGURE I/2.1.3-1

Calculation of flow through restriction (horizontal).

Orifice Reynolds numberðRed Þ ¼ ReD =b (I/2.1.6-3) Eqs. (I/2.1.6-2 and I/2.1.6-3) may be compared with the expressions given in Subsections 3.3.2.1 and 3.3.2.2 of ISO 51671:2003. 5. John Thomson coefficient: This deals with the temperature pressure coefficient, mJT, i.e., rate of change of temperature with respect to (WRT) pressure at constant enthalpy. So, mJT

vT at H ðenthalpyÞ constant. ¼ vP (I/2.1.6-4)

2.1.7 EXPANSIBILITY FACTOR In Eq. (I/2.1.4-1), the coefficient discharge has been defined for an incompressible fluid. For compressible fluids another factor expansibility factor is necessary to take care of the compressibility. Different fluids, i.e., gases and steam, have different compressibility. This is because each has a different molecular form. So, based on their form, fluid molecules are more or less compressed when they pass through any

restriction (orifice) [22]. Factor ε depends on the pressure relation and the isentropic exponent k (defined in Subsection 2.1.6.3). As per ISO 51671:2003, coefficient ε is used to take into account the compressibility of the fluid. As per ISO 51671:2003 and Eq. (I/2.1.4-1A), ε is given by n pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi o. ε ¼ qm $ ð1  b4Þ n (I/2.1.7-1)   pffiffiffiffiffiffiffiffiffiffiffiffiffiffi o 2 pd 4 $Cd 2Dpr1 From Eq. (I/2.1.7-1) it is clear that the ratio given above (except Cd) is dependent on the Reynolds number, pressure ratio, and isentropic exponent of gas (see Subsection 2.1.6.3). In the case of incompressible fluid ε [ 1 but for compressible fluids ε < 1. 2.1.8 MEASUREMENT AND FLOW COMPUTATION Standard ISO 5167-1:3 provide specific guidelines for this. In order to measure and compute flow one needs to install a primary flow device in the line and to measure the pressure difference between the upstream pressure at a suitable location depends on the tapping style discussed in

Flow Metering: General Discussions (An Overview) Chapter | I

Chapter II and a pressure at a suitable location (depends on tapping style discussed in Chapter II) at the downstream of the restriction. Various tapping styles and primary elements depend on many factors, such as pipe size, flow quantity, static pressure, etc. The mass flow rate can be determined from Eq. (I/2.1.3-6) (within the uncertainty limits in ISO 5167) as follows:   pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi qm ¼ Cd $ε$p d2 4 2Dpr=ð1  b4Þ (I/2.1.8-1) Volume flow qv ¼ qm =r$

  pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ¼ Cd $ε$p d2 4 2Dp=rð1  b4Þ (I/2.1.8-2)

For gas flow one needs to note that when gas passes through the restriction, the change of pressure is so abrupt that it can hardly absorb any heat from the surroundings. When it passes through the restriction it expands on account of pressure reduction and so it does some work. As it is unable to receive any external energy it has to spend its heat energy, meaning the temperature falls. Hence temperature is not constant, and Boyle’s law is not applicable. It undergoes adiabatic expansion. From elementary physics it is known that for adiabatic expansion (PV)Y ¼ constant; where Y ¼ Cp/Cv (see Eq. I/1.1.2-5). The value of Y varies, e.g., dry air: 1.4; other diatomic gas: 1.66; monatomic gas: 1.33. Short discussions are now put forward for sizing primary elements in line with ISO 5167-1:2003 (practical approach). Unless otherwise stated, the standard referred to here is ISO 5167. 1. Determination of d/D ratio and flow computation: Standard ISO 5167-1: 2003 provides guidance for determination of beta. When determining the beta ratio in almost all cases the Cd and ε values are not known. For this meters based on flow rate and corresponding selected DP range for a specific pipe are first selected. From Eq. (I/2.1.8-1) unknown quantities are segregated and put in the left side, while know parameters such as flow rate range, DP range, etc. are on the RHS. Also,

39

d is replaced by bD, where for a given pipe D is known. So, by rearranging Eq. (I/2.1.8-1) one gets: .pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi  2 ð1  b4Þ Cd $ε$b . pffiffiffiffiffiffiffiffiffiffiffi 2Dpr ¼ ð4Qm Þ pD2 (I/2.1.8-3) Now the iterative method discussed in Annex I of ISO 5167-1:2003 may be applied to determine beta. Once this is done it is a question of arithmetic computation using the numerical values. The determination of major parameters like density, static pressure, and temperature is important for accurate flow measurement. As per standard any method of determining reliable values of these parameters is acceptable as long as it does not interfere with the distribution of the flow in any way at the cross-section where the measurement is made. 2. Density: It is necessary to know the density of the fluid which can either be measured directly or be calculated from an appropriate equation, with knowledge of the absolute static pressure, absolute temperature, and the composition of the fluid at that location. 3. Static pressure: The static pressure of the fluid shall be measured by means of pipewall pressure tapping(s) discussed at length later. Tapping for static pressure measurement shall be separate for the same pertinent to DP measurement and this shall be located upstream of the restriction [22]. 4. Temperature: The temperature of the fluid shall preferably be measured downstream of the primary device and shall be located at least equal to 5D (and at most 15D when the fluid is a gas) if the pocket is located downstream (in the case of a Venturi tube this distance is measured from the throat pressure tapping plane; see ISO5167-1:2003). The thermometer well or pocket shall take up as little space as possible. Detailed guidelines for this are available in ISO 5167-2, ISO 5167-3, or ISO 5167-4, depending on the primary device

40

Plant Flow Measurement and Control Handbook

chosen. The temperature drop from the upstream tapping to the downstream temperature location, DT, can be evaluated using the Joule Thomson coefficient, mJT, which is described in Eq. (I/2.1.6-4). 5. Standard treatises: After the above steps, the following standard treatises [22] are applied. These are stated here so that the reader can have a feel for the standard procedure to be followed. However, they are discussed at length subsequently. l Allowed variations for different measures (pipe diameter, restriction diameter, upand downstream straight length requirements, etc). l Allowable tolerance of all measures. l Structural details of primary elements, including thickness, various angle tolerances allowed, etc.

l

l

Shaping, placement, and details (hole size, etc.) of various pressure tappings and style. The actual flow rate is calculated from the normal flow rate. As stated earlier, usually the full flow and full meter range is first selected. Usually 0.7 is considered the normal range and hence actual flow is computed by rffiffiffiffiffiffiffiffiffiffiffi DPact $ðq Þ (I/2.1.8-4) ðqm Þact ¼ DPnor m nor

6. Interrelation of various parameters: Various parameters necessary for flow measurements are highly connected with each other. The interrelationship between them has been shown in Fig. I/2.1.8-1, which is based on [22]. This will help the reader to get a good grasp of the issue.

EXPANSIBILITY FACTOR NOT APPLICABLE FOR ISENTROPIC EXPONENT

STATIC PRESSURE

UPSTREAM

P1

DOWNSTREAM

P2 Beta (d/D)

ORIFICE DIAMETER

d

PIPE DIAMETER

D ReD D(T)

UPSTREAM

mu

MASS FLOW (ESTIMATE)

Qm

TEMPERATURE INFLUENCE D,d,Cd, mu, Rho (DIRECTLY) & INDIRECTLY VIA Re TO ReD

epsilon

Cd Qm

Beta

COEFFICIENT OF PIPE DIAMETER DYNAMIC VISCOSITY

INCOMPRESSIBLE FLUID

k

DOWNSTREAM

Beta

MASS FLOW

d(T)

L1

dp

L2

Rho (P,T)

COEFFICIENT OF PIPE DIAMETER dP MEASURED FLUID DENSITY

GEOMETRY OF PRESSURE TAPING

FIGURE I/2.1.8-1 Parameter inter-relations for flow measurement. Based on an idea from P. Lau, Calculation of Flow Rate from Differential Devices-Orifice Plate, Ematem- Sommerschule; Kloster Seeon; SP Technical Research Institute Sweden, August 2008.

Flow Metering: General Discussions (An Overview) Chapter | I

2.1.9 PRESSURE/TEMPERATURE COMPENSATION FOR FLOW Head type flow measurements by primary flow elements require a pressure/temperature compensation formula when we use primary flow elements to measure gas/steam flow in pipes with variable operating conditions. The variations in pressure and temperature have a significant effect on gas/steam density, which is why without this pressure and temperature compensation the flow measurement can have large errors [23]. In fact, for variable temperature conditions, density compensation is also necessary for incompressible flow, e.g., temperature compensation feed flow measurements in utility boilers. For head type flow meters pressure and temperature compensations are typically performed upstream and downstream of the flow meter, respectively. Here the flow compensation formula shall be derived for compressible fluid and later it will be used for incompressible fluid (example given above). It is established from the gas law that PV ¼ nRT where, P ¼ pressure (absolute), V ¼ volume, n ¼ number of moles, R ¼ gas constant, T ¼ temperature (absolute). If Mw is molecular weight then, for mass m; n ¼ m/Mw. Again r ¼ m/V. So, P$m=r ¼ m=Mw$RT or p=r ¼ RT=Mw or r ¼ P$Mw=RT Therefore rreal ¼ Preal $Mw=RTreal ðsince R & Mw is constantÞ rdesign ¼ Pdesign $Mw=RTdesign

(I/2.1.9-1) (I/2.1.9-2)

So, by dividing Eq. (I/2.1.9-1) by Eq. (I/2.1.9-2) we obtain rreal ¼ rdesign $ðPreal =Pdesign Þ$ðTdesign =Treal Þ (I/2.1.9-3)

41

From Eq.p (I/2.1.3-5), it is found that Q is proporffiffiffiffiffiffiffiffiffiffiffi tional to Dp=r with other terms being constant for a particular primary element. Therefore pffiffiffiffiffiffiffiffiffiffiffi Q ¼ Constant$ Dp=r or Q ¼ Constant$ qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi  Dp rdesign $ðPreal =Pdesign Þ$ðTdesign =Treal Þ (I/2.1.9-4) Putting the value of rreal from Eq. (I/2.1.9-3). Similarly pffiffiffiffiffiffiffiffiffiffiffi qm ¼ Constant$ Dp$r or qm ¼ Constant$ qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Dp$rdesign $ðPreal =Pdesign Þ$ðTdesign =Treal Þ (I/2.1.9-5) If one considers design at STP, and temperature Tc ¼ Treal/Tdesign ¼ Treal/TSTP and similarly for pressure Pc ¼ Preal/Pdesign ¼ Preal/PSTP and if Dp ¼ h differential head, and rdesign is a known constant and so is put under main heading of Constant, the whole constant is K, then equation Eq. (I/2.1.9-5) changes to rffiffiffiffiffiffiffiffiffiffi Pc (I/2.1.9-6) qm ¼ K$ h$ Tc Therefore, the actual measurement is done as shown in Fig. I/2.1.9-1. Note here that the temperature sensor has been put downstream mainly to avoid an obstruction in the upstream side. Further discussions have been presented in connection with flow computers in Section 5.1.0 of Chapter XI. Fluid mechanics is a vast subject and it is practically impossible to cover all the details. It is therefore recommended that readers brush up their knowledge on this from a standard book on fluid mechanics and thermodynamics. With these details the discussions on basic fluid mechanics is

42

Plant Flow Measurement and Control Handbook

HEAD MEASUREMENT BY DPT (suitable tapping style)

PT

DPT

UPSTREAM PRESSURE

TT

TE

RESTRICTION FOR FLOW MEASUREMENT

COMPENSATION (MULTIPLY)

DPT: DIFFERENTIAL PRESSURE

DOWNSTREAM TEMPERATURE

TRANSMITTER PT: PRESSURE TRANSMITTER TE: tEMPERATURE ELEMENT TT: TEMPERATURE TRANSMITTER

COMPENSATION (DIVIDE)

SQUARE ROOTING AFTER COMPENSATION COMPENSATED FLOW

COMPENSATION MEASURING POINTS AND COMPUTATIONS HAVE BEEN DETAILED HERE FOR BETTER UNDERSTANDING

FIGURE I/2.1.9-1 Pressureetemperature compensation for flow.

concluded and we move on to explore various flow-measuring principles to proceed another step for overview of flow metering.

3.0.0 FLOW MEASUREMENT TYPES AND PRINCIPLES Normally flow measurements refers to fluid flow measurements. In reality this is not the case, there are many other types of flow, such as solid flow (in cement industries, food industries), multiphase flow (in oil exploration and chemical plants), and slurry flow (in mineral processing), which are important for many industrial

applications. Although many of the technologies used in fluid flow are also applicable to slurry/ multiphase flow measurements they are treated separately. So, flow measurements are first categorized as shown in Fig. I/3.0.0-1. Based on Fig. I/3.0.0-1, the discussions on various types of flow-measuring systems are Flow measurement

Fluid Flow measurement Solid Flow measurement Slurry Flow measurement Mul phase Flow measurement

FIGURE I/3.0.0-1 Basic flow measurement categories.

Flow Metering: General Discussions (An Overview) Chapter | I

presented. Under fluid flow measurement, flow measurements of both incompressible and compressible fluids are covered. The necessary fluid mechanics have already been covered in the previous section. 3.1.0 Fluid Flow Measurement Types and Principles In this subsection, the basic principle of operations, and pros and cons of various types of flow meters are discussed. Having gained some knowledge on various general and process-related terms of fluid mechanics, one needs to understand how these are deployed in developing various types of fluid flow meters. These are important in the sense that these ideas will be necessary in selecting a flow meter for the application of interest, i.e., for flow meter selection. Also, based on basic knowledge about

43

the metering principles of each type of meter, details will be developed in subsequent chapters. Therefore, the importance of this part cannot be overestimated. During this discussion most major types of flow-metering devices are covered. Fluid flow metering in a closed pipe can be classified into four classes: inferential, positive displacement, velocity, and mass. However this is not sacrosanct. When an open-channel flow measurement (frequently encountered in irrigation) is taken into consideration they can be categorized differently, such as differential pressure (head type), positive displacement, velocity, mass, variable area types, and open-channel flow measurement. Some even subcategorize them into mechanical and electrical types. In this connection a typical flow meter categorization has been illustrated in Fig. I/3.1.0-1.

OPEN CHANNEL/

CLOSED DUCT DU

FREE SURFACE

FLOW RATE METER

VENTURI/PARSHALL FLUME METER

RECTANGULAR/ V NOTCH WEIR

VARIABLE AREA

HEAD/DP TYPE

ULTRASONIC

VOLEUME

ELECTROMAGNETIC

THERMAL

ROTARY VANE

WOLTMAN METER

TURBINE

SPIRAL GEAR

SWIRL METER

VORTEX

INDIRECT

CORIOLIS

MASS

OVAL GEAR

DIRECT

OSCILLATING PISTON

FLOW RATE METER

LOBBED IMPELLER METER

TOTAL FLOW METER

ELECTRICAL TYPE FLOW METERS ARE IN BOX WITH SHADE.

CLOSED PIPE/

MECHANICAL TYPE FLOW METERS ARE IN BOX WITHOUT SHADE

FLUID FLOW METERING DEVICES

FIGURE I/3.1.0-1 Fluid flow meter types and categorization. Based on S. Basu, A.K. Debnath, Power Plant Instrumentation and Control Handbook, Elsevier, November 2014, http://store.elsevier.com/Power-PlantInstrumentation-and-Control-Handbook/Swapan-Basu/isbn-9780128011737/. Courtesy: Elsevier.

44

Plant Flow Measurement and Control Handbook

This figure shows that there are a number of ways that these can be categorized. However, there could be other categorization methods, as shown in Fig. I/3.0.1-2. Accordingly, the principle of operation of these is given in a similar order.

meter restriction is proportional to the square of the flow rate. The flow rate is calculated by extracting the square root of the reading (leaving aside other corrections). In the case of an elbow tap meter such differential pressure is created not due to any restriction but due to centrifugal force. In a variable area flow meter, gravitational force of float is balanced by force due to pressure and buoyancy force. At the equilibrium point flow is directly read from the float position (remote transmission is also possible). Let the discussions start with head type metere orifice plate.

3.1.1 INFERENTIAL FLOW METER TYPES AND PRINCIPLES Inferential flow meters calculate flow rate based on mainly nonflow measurement, with the help of some correlations that have been widely accepted. As discussed above and shown in Fig. I/3.1.0-2, there are two kinds: head type measurement and variable area flow meter. All DP elements are static in nature, i.e., they have no moving parts and most of them can be manufactured with a number of materials (SS 316 is a very popular material). In head type flow measurement, with the help of a restriction, a differential head is created and measured across the restriction. Principles of operations of these types of flow measurements are based on the premise that pressure drop across the

1. Orifice plate: Orifices are the most popular fluid flow elements used in process and other industries. The flow characteristics of orifices are very well documented. When an orifice is inserted in a pipeline, it causes an increase in flow velocity and a corresponding decrease in pressure at the downstream. The maximum velocity and minimum pressure are at the vena contracta. An orifice is simply a flat piece of metal with a specific-sized hole (d calculated)

Fluid Flow metering

Closed pipe Flow meter

Other Types

Open Channel Measurement

Coriolis Parshall Flume

Mass Inferen al

Velocity/Force

Thermal

Weir

Variable area Rotameter

CE & ME Ultrasonic Anemometer ofElectro 234 magne c

Nozzle

Nuta ng Disc

Venturi Oval gear Rota ng Piston Rota ng Vane Others types

Head Type

Vortex

Target

Orifice

P D Meter PD—Posi ve displacement

Turbine

Dall* Pitot Anubar Elbow Wedge V Cone

FIGURE I/3.1.0-2 Fluid flow meter divisions. *Dall tube is a category of ASME flow tube. CE, Coanda Effect; ME, Momentum Exchange.

Flow Metering: General Discussions (An Overview) Chapter | I

45

VARIOUS TYPES OF ORIFICE PLATES

ECCENTRIC ORIFICE CONCENTRIC ORIFICE

SEGMENTAL ORIFICE

FLOW

SQUARE EDGE ORIFICE PLATE INPIPE

FIGURE I/3.1.1-1 Orifice plate.

bored in the plate. It is less prone to maintenance. It is not only inexpensive but easier to manufacture. Another important issue is that with an increase in the pipe, the cost of the orifice does not increase significantly and no special piping or fittings are necessary. It has a few negative aspects also. It has a rangeability of 5:1 and accuracy is over 2%e4% full scale. It also creates a lot of permanent pressure loss. Mostly orifice plates are of the concentric type. There are other types also such as eccentric and segmental, as shown in Fig. I/3.1.1-1. Detailed discussions are available in Chapter II. 2. Flow nozzle: At high velocity a flow nozzle has the capability of handling a higher flow of fluid with the same pressure drop when compared to an orifice plate. This indicates that it has a small beta ratio to provide a higher discharge coefficient. Also, it has better pressure recovery, and hence less permanent loss than an orifice. It has an initial smooth, convergent section, and finally it discharges the flow parallel to the axis of the downstream pipe as shown in Fig. I/3.1.1-2. It has three versions, including the ISA 1932 nozzle

commonly used outside the United States [25], the long-radius nozzle, and the Venturi nozzle. It can be used for liquids with suspended solids. In steam flow measurements, especially in utility stations, it finds many applications for high-pressure steam flow. It is not suitable for liquids with high viscosity. It is costlier than an orifice and it is available for moderate pipe sizes only. Also, it is difficult to maintain and inspect as the pipe section needs dismantling. The characteristics of a flow nozzle are similar to those of a Venturi. 3. Venturi: The discussions start with Fig. I/ 3.1.1-3, where it is clear to see that it has a gradual tapered restriction at the inlet and outlet (normally a straight portion between the inlet and outlet, and referred to as the throat). It has a very high discharge coefficient and low pressure drop. It helps to eliminate boundary layer separations and hence has less drag. Performance characteristics are well documented [25]. The convergence and throat area is mainly responsible for pressure drop from where any other head type flow device flow is calculated.

46

Plant Flow Measurement and Control Handbook

UPSTREAM/DOWN STREAM MEASURED (say) D

FROM THIS UPSTREAM FACE OF NOZZLE

FLOW

FIGURE I/3.1.1-2 TYPICAL HIGH AND LOW PRESSURE TAPPING

FLOW

INLET CONE/ STRAIGHT/ CONVERGENT CYLINDRICAL INLET INLET

OUTLET CONE/ DIVERGENT OUTLET

FIGURE I/3.1.1-3 Venturi tube.

There are a few numbers of forms of Venturi available, such as the long-form or classical Venturi, short-form Venturi, eccentric form Venturi, and rectangular Venturi. In cases of large ducts, rectangular Venturi tubes are common. In the case of a large duct (air/gas), a Venturi with piezometer

Flow nozzle.

rings is also used. Venturi tubes find use in slurry flow with purging, but in such cases piezometer rings are not used. 4. Dall tube (flow tube): ASME defined a broad category of differential pressureproducing elements whose designs differ from Venturi tubes. Tee Dall tube is one of those categories. These proprietary primary head type devices have a higher ratio of pressure developed to pressure lost than a Venturi tube [12]. Another important issue here is that as there are several proprietary head type flow elements, they naturally have different differential pressures and head losses for a given flow as per the manufacturer calculations and assumptions. For this reason it is necessary that the manufacturer supply all necessary data and drawings for verification. A Dall tube normally has a flanged spool piece body with a short, straight inlet section terminating in an abrupt decrease in diameter (shoulder). This is followed by a

Flow Metering: General Discussions (An Overview) Chapter | I

BUTTRESS FLOW

REOCEVERY ANNULAR GAP

FIGURE I/3.1.1-4 Dall flow tube. Courtesy of Instrumentationtool.com.

conical restriction and diverging outlet with a narrow annular gap as depicted in Fig. I/ 3.1.1-4. The distance between the front face and the tip is nearly half the pipe diameter. As shown, the high-pressure and lowpressure tapping points are located at the inlet shoulder and the annular gap in the throat, respectively. Very small head losses and availability in various short sizes are advantages of the

47

Dall tube. It has high straight length requirements as it is highly sensitive to upstream disturbance on account of the tapping location being in the upstream side. 5. Pitot tube: This is a low-cost DP element, frequently used in low head air flow measurements such as HVAC. Basically this element works on the principle of converting kinetic energy into potential or pressure energy. When a stream of fluid approaches or strikes a centrally placed stationary solid body held in a pipeline, the fluid stream loses its velocity to zero directly in front of the body. This is the stagnation point. On losing the kinetic energy, the fluid stream gains a static head. In a Pitot tube type flow measurement two pressures, impact and static, are sensed. The impact unit consists of a tube with one end bent at right angles toward the flow direction. The static tube’s end is closed, but a small slot is located in the side of the unit [26]. The tubes can be mounted separately in a pipe or combined in a single casing as shown in Fig. I/3.1.1-5. It is easy to install the element into a pipe or duct (even in an existing plant). The DP

LOW PRESSURE

HIGH PRESSURE

NOS. OF HOLES ALONG LENGTH FOR MEASURING AVERAGE STATIC PRESSURE

(Typical)

IMPACT POINT OPENING IMPACT POINT PRESSURE

FIGURE I/3.1.1-5 Pitot tube.

48

Plant Flow Measurement and Control Handbook

between the pressure due to impact and the static pressure are used to compute the average velocity and hence the flow. The Pitot tube causes practically no pressure loss in the flow stream but certain characteristics of Pitot tube flow measurement have limited its industrial applications [27]. It has the problem of getting blocked frequently, and so is not suitable for dirty liquids/gas. The Pitot tube is frequently used to measure air (primary air) flow in a boiler. 6. Annubar: There is not much difference between a Pitot tube and Annubar. Fig. I/ 3.1.1-6 shows the basic principles of measurement. It is also known as an average Pitot, but in this book it will be dealt with separately in Chapter II. An Annubar may be conceived of as several Pitot tubes placed across a pipe to obtain an approximation to the velocity profile, and the total flow can be calculated based on the difference of average upstream pressure and downstream pressure measurements. At the leftmost part the velocity profile and associated changes in upstream pressure have been shown. Where there is TO HIGH (AVERAGE) PRESSURE SIDE

highest velocity at the center the change in pressure due to obstruction is the highest (and has a lesser impact towards the wall where the velocity is also lower). Thus there will be a high-pressure profile—produced by the impact of the flow velocity profile on the upstream side of the sensing tube. The flow that passes through the sensor creates a lowpressure profile [27]. Two-chamber flow tubes with several pressure openings distributed across the stream are shown in Fig. I/ 3.1.1-6. This annular averaging element is called an Annubar [27]. An Annubar flow sensor produces a DP signal that is the algebraic difference between the average value of the high pressure and low pressure. Averaging Pitot tube (APT) technology reduces the total cost of ownership of flow measurement by lowering the installation and energy costs. Like a Pitot tube, an Annubar also contributes very small pressure drops. It has limited accuracy and like a Pitot it is prone to blockage and hence is not suitable for measurement of liquid that contains dirt. It finds its use in air flow measurements in boiler plants. TO LOW (AVERAGE) PRESSURE SIDE

FLANGES WITH GASKET

HIGH PRESSURE PROFILE

LOW PRESSURE PROFILE DOWNSTREAM LP HOLE (Typical)

FLOW UPSTREAM HP HOLE (Typical)

AVERAGE VELOCITY

VELOCITY PROFILE

DIFFERENTIAL PRESSURE

FOR ON LINE CHECKING & CLEANING TEE WITH PLUG SHOWN

FIGURE I/3.1.1-6 Annubar.

Flow Metering: General Discussions (An Overview) Chapter | I

de gr ee

EL B OW

due to the acceleration of the fluid. From basic physics it is know that centrifugal force is given by mv2/R (m ¼ mass; v ¼ velocity; R ¼ radius). Naturally, on account of the higher “R,” there will be less velocity in the outer side and so to balance energy there will be more pressure (potential) energy than on the inner side with a smaller “R.” This will cause a differential pressure between the outside (higher pressure) and inside (lower pressure). Thus a differential pressure exists when a flowing fluid changes direction due to a pipe turn or elbow (see Fig. I/3.1.1-7). Taps are located at 45 degrees for a 90 degrees elbow (see Fig. I/3.1.1-7). As pipe elbows are common in plants there is no cost for restriction elements, and so measurement is less costly. Also, it does not cause any added pressure loss. However, the accuracy is very poor (not less than 4% FSD) and it is not suitable for low-velocity fluid flow. From this one can infer that when this elbow is used in a size smaller than the pipe size with a reducer, then the velocity will increase and it is possible to get a better DP. When applying this measurement in liquids containing dirt, then there is the possibility of a line blockage for which a purging method may be utilized. 8. Wedge meter: The discussions on wedge meters start with Fig. I/3.1.1-8, where it

LO PRESSURE

90

HI PRESSURE

FLOW

FIGURE I/3.1.1-7 Elbow tap.

7. Elbow tap: As stated earlier the DP is not generated due to restriction but due to centrifugal force. A typical 90 degrees elbow tap meter is shown in Fig. I/3.1.1-7. The meter operates within the general physics principles. When a fluid moves in a curved path there will be a centrifugal force

FLOW

49

D H WEDGE METER FINDS LOT OF APPLICATION IN SLURRY FLOW MEASUREMENT DP = f(H/D)

FIGURE I/3.1.1-8 Wedge.

50

Plant Flow Measurement and Control Handbook

can be seen that the element consists of a Vshaped wedge (restriction) on the top side of the meter. The slanted faces of the wedge meter provide a self-scouring action [25]. These meters are suitable for liquids with suspended solids and slurry flow and viscous fluids. However, accuracy, head loss, etc. are inferior to a Venturi tube [28]. Like other DPbased elements, here also a DP is generated due to restriction, but it is of a different type. Here a constriction wedge is fabricated on the top part and is behaviorally somewhat similar to a segmental orifice. However, here the fluid is guided along a sloping “wedge” shape rather than a sharp edge [29]. The differential produced is a function of the ratio of diameter “D” and wedge height “H,” as shown. The pressure taps are located upstream and downstream of the wedge. It is available from as low as 25 to 800 mm. Wedge meters are inherently robust, requiring less maintenance. 9. V-one device: The V-cone device meter is well recognized for its greater accuracy (up to 0.5% of the rate) and repeatability, and wider rangeability when compared to an orifice plate as a flow element. It also offers installation flexibility and reduced maintenance. As stated earlier, it can be used for very difficult flow conditions from very low to extremely high Reynolds numbers or measuring swirling fluids or lowpressure flows [30]. A V-cone flow device, shown in Fig. I/3.1.1-9, can be used for both dirty as well as clean fluid measurements. In comparison to an orifice it has better permanent pressure loss. This is a DP type flow element, one tapping (static pressure) is taken slightly upstream of the cone with the other tapping located in the downstream face of the cone itself. The design incorporates a contour-shaped cone at the center of

the pipe with annular passages which direct the flow without impacting it against an abrupt surface, thus avoiding wear of edges of the cone by dirty fluids. Because of this feature, recalibration of V-cones is rarely required [24]. They are available in different sizes from 15 to 3000 mm. A brief comparison with an orifice plate is presented in Fig. I/3.1.1-9. Operating principles have been elaborated in Chapter II (Section 8.1.1) for deriving the flow formula and sizing. 10. Rotameter: A rotameter and piston meter are two types of flow meters that fall under the category of variable area meters. Rotameters are the most popular and are discussed here. A rotameter is a kind of inferential flow meter, but metering is not carried out by DP measurement. This inexpensive flow meter provides practical flow measurement solutions for many applications. A rotameter basically consists of a tapered metering tube and a float that can freely move within the tube, there may be an outside casing and means for remote transmission also if applicable. This flow metering is a linear function of flow rate. In the case of no flow, the float, which usually has a diameter the same as the bore of the flowing tube, rests freely at the bottom of the tube. When fluid enters from the bottom of the tube, the float begins to rise. The float material has a higher density than the fluid and the position of the float varies directly with the flow rate. During flow, buoyancy helps the float into the upper position, but this force is insufficient due to float weight. At a particular flow rate the upward flow and float weight and buoyancy forces are balanced to give a direct reading. At higher flow, the float moves up so that there will be more force due to pressure multiplied by the increased area of the tube. The up- and downward movement of

Flow Metering: General Discussions (An Overview) Chapter | I

51

HIGHER RANGEABILITY, ACCURACY & REPEATIBILTY LESS STRAIGHT LENGTH REQUIREMENT NO ABRUPT SURFACE-NOT SUBJECT TO DIRTY WEAR HARDLY RECALIBRATION NECESSARY SHORT VERTICES FORMED DPT:Differential Transmistter VM:3/5 Valve Manifold

AFTER THE CONE, LOW AMPLITUDE

DPT

HI FREQUENCY SIGNAL

VM

FOR SIGNAL STABILITY

FLOW

A1

TURBINE

VORTEX (Best)

MASS FLOW (BEST)

05

ORIFICE PLATE

10

FLOW NOZZLE

15

V CONE

20

VENTURI (Low loss)

25

D

V CONE

30 (IN KPa)

D

A2

Permanent Pr. Loss

d

ORIFICE PLATE

00 METER TYPES

d1

LINE: 75NB; FLOW 1145 LPM MAX LOSS CURVE A2 = A 1

Beta =

2 1-(d/D)

d 1= D2-d2

COMPARISON OF BETA WITH ORIFICE

FIGURE I/3.1.1-9 V-cone device. Based on and courtesy of McCrometer Permanent Pressure Loss Comparison Among Various Flow Meter Technologies, McCrometer; White Paper; S. Basu, A.K. Debnath, Power Plant Instrumentation and Control Handbook, Elsevier, November 2014, http://store.elsevier.com/Power-PlantInstrumentation-and-Control-Handbook/Swapan-Basu/isbn-9780128011737/.

the float is proportional to the fluid flow rate and the annular area between the float and the tube. A typical rotameter has been depicted in Fig. I/3.1.1-10. Rotameters can

offer an accuracy of 2% of FSD, and are available in various sizes. Some rotameters may also have facilities for remote transmission.

52

Plant Flow Measurement and Control Handbook

FORCE OFGRAVITY AT EQUILIBRIUM FLOW READING

FORCE DUE TO PRESSURE

ALSO BUOYANCY FORCE

INSIDE VARIABLE AREA CHAMBER OUTER CASING

FLOW

FIGURE I/3.1.1-10 Variable area rotameter.

3.1.2 POSITIVE DISPLACEMENT FLOW METER TYPES AND PRINCIPLES Positive displacement (PD) flow meters are mechanical type flow meters with moving parts. They are deployed for direct measurement of volumetric steady flow of fluids. Here the volume is not calculated but measured directly. Accordingly, fluid velocity, pipe inside diameters (IDs), and flow profiles are not a concern [25]. In positive displacement flow meters, the mechanical moving parts are located in the flow stream to physically separate the fluid into separate known volumes based on the physical dimensions of the meter. These known volume increments are counted or totalized [27]. For this reason many of these meters are available with a flow totalizing counter (mechanical). Linear motion or counting the number of cycles of rotation provides the displaced fluid. These flow meters are used for volumetric flow in a wide range of nonabrasive fluids, including high-viscosity fluids. Accuracy may be up to 0.1% FSD. This type of meter also offers high rangeability of the order of 65:1 or better. Higher pressure drop and higher cost of installations and maintenance (moving parts) are

some of the demerits of this type of flow metering. These are not suitable for solid flow measurements but are very good candidates for measurement of volumetric flow of highly viscous fluids (possibly with low electrical conductivity, e.g., oil applications). PD meters are often used as domestic water meters because PD meters are integrating type meters. With reference to Fig. I/3.1.0-2, the discussions on PD meters start with discussions on the nutating disc. 1. Nutating disc: Fig. I/3.1.2-1 shows a schematic diagram of a flow meter. As shown in the figure there is one disc assembly. The movable disc assembly consists of a radial slotted disk with an integral ball and an axial pin. As shown in the figure there is one disc assembly. The position of the disc divides the working chamber into compartments, one above and one below the disc. These chambers are filled and emptied successively, each compartment holding a definite volume. Fluid (liquid) enters the meter through an inlet of the meter and passes upward into the top of the main casing. The fluid also acts as a lubricant for the internal gearing, etc. in the top casing part.

Flow Metering: General Discussions (An Overview) Chapter | I

53

MAGNNETIC PICK UP IN

GEAR TREND

CAM GUIDE

FLUID ENTRY HOLE

BALL

FLOW OUT FLOW IN

DISC

WORKING CHAMBER

SCHEMATIC DRAWING NOT TO SCALE

FIGURE I/3.1.2-1 Nutating disc.

The fluid enters the working chamber through a hole as shown. On entering the measuring chamber, it drives the single measuring disc which nutates and the fluid (liquid) goes to the other part of the chamber. The positive displacement cam compels it to make a complete nutation at each movement. So, with the help of this complete nutating motion, fluid comes in and goes out to the outlet port each time with a definite volume. The complete nutating motion is transmitted by a gear train to the totalizer or pick up for the pulse transmitter. It is very popular as a domestic water meter. It provides an accuracy of 1%e2% FSD. The maximum pressure- and temperature-withstand capability of the meter are about 10 kg/cm2 and 150 C, respectively. 2. Oval gear: In an oval gear meter, two oval gears are placed and mechanically interlocked by 90 degrees in the meter housing. These gears are rotated by the flowing fluid. When

the two oval gears are rotated by fluid (liquid) a defined volume of fluid is transported from the inlet through the meter to the outlet. These oval-geared meters are generally used on high viscous liquids. Fig. I/3.1.2-2 shows the flow of fluid (liquid) in the bottom part of the meter. Similarly there will be flow from the top part also. As shown in the schematic (Fig. I/ 3.1.2-2), there are various stages of movement of fluid. In the figure only one part of the flow has been shown to understand the principles of operation. A definite volume of liquid is captured by the gap formed between the housing and the gear. In the first position there is a force on the bottom of the upper gear which causes it to rotate clockwise (CW). This causes the bottom gear to rotate in a counterclockwise (CCW) direction to the position shown in the next figure. In this position a definite volume of fluid is trapped in the bottom part (the bottom part

54

Plant Flow Measurement and Control Handbook

FLOW IN FLOW OUT

ONE PORTION FLOW SHOWN FOR UNDERSTANDING OF PRINCIPLES OPERATION.

FIGURE I/3.1.2-2 Oval gear.

only is shown and discussed here). Now the fluid in the inlet side puts force on the top gear which causes the bottom gear also to move so that part of the entrapped fluid is discharged. At this time fluid in the inlet side puts force on the bottom gear in the lower part and the top gear in the upper part and because of the two different directions of movement (CW and CCW) the entire volume is discharged by the bottom gear in the last figure. Similarly, there will be flow from the top part also (not shown). Magnets are often fitted at the rotor, and with the help of these magnets and reed switch contacts often pulses are created and measured. At times these are converted to 4e20 mA DC by converters. This type of meter is available in various sizes

INLET PORT

MEASURING CHAMBER

from 6 to 600 mm (or even larger sizes) and offers high accuracy, in the order of 0.1% FSD or better. However this meter is only suited for clean fluids. 3. Rotating piston: The principles of operation of a rotating piston flow meter have been detailed in Fig. I/3.1.2-3. The measurement chamber is cylindrical with a partition separating its inlet port from its outlet. Liquid enters into a machined chamber containing an oscillating piston. The position of the piston divides the chamber into compartments containing an exact volume [32]. Fluid pressure then causes the oscillation of the piston about the central hub. The movements of the hub are sensed through the meter wall by a series of magnets.

CHAMBER DIVISION CONTROLLING ROLLER

OUTLET PORT

ROTOR PISTON HUB INLET FLOW

TRANSIT FLOW

OUTLET FLOW

MAGNETIC ASSEMBLY/PICK UP (not shown) ARE AT TOP.

FIGURE I/3.1.2-3 Rotating piston.

PISTON

Flow Metering: General Discussions (An Overview) Chapter | I

As shown in the figure, upon entry of fluid into the measuring cavity from the inlet, a differential pressure will be formed which causes the piston to rotate in a CCW direction. Accompanied with liquid flowing in, the piston will rotate to the location as shown, forming an enclosed volume. Under the action of differential pressure, the piston will continue rotating and as a result the enclosed volume will gradually open to the outlet and begin to discharge liquid as shown. For better understanding, three separate sets of fluid volumes are shown in color (green: inlet; maroon: outlet; cyan: transitional flow). The piston is guided by a control roller within the measuring chamber. In this way, piston rotation will continuously cause liquid to pass through the flow meter and volume flow of every cycle will equal the amount of measuring cavities. Therefore, it is seen that each revolution of the piston hub is equivalent to a fixed volume of liquid, which can be transmitted as a pulse count with the help of magnetic pick up for remote transmission and/or for totalizing. As stated earlier, the motion of the piston is transferred to a follower magnet which is external to the flow stream. The motion of the piston is oscillatory (not rotary) since it is constrained

to move in one plane [32]. Meters are available in various sizes to cater to the flow range from 0.7 to w300 L/min (LPM). It is also available for high-pressure applications. A very high turndown ratio of >300:1 is also possible. It offers accuracy better than 0.5% of the actual reading. 4. Rotating vane: A rotating vane is another type of PD meter. It basically has two options, one with a cam and the other without a cam. Both versions are depicted in Fig. I/3.1.2-4. The first set is for a meter with a cam. The other is with an eccentrically mounted rotor. However, the basic operation principle is the same. The principle of operation of the meter is similar to what has been discussed so far. The basic unit consists of rotating impellers (two or more) mounted inside the meter housing. These impellers divide the entire space into two/four equally divided compartments as shown in Fig. I/3.1.2-4. When fluid appears at the inlet it pushes vane 1 to a change position. A naturally fixed quantity of fluid in the measuring chamber shown is pushed out, and partly goes to the outlet. Next vane 2 is rotated. Here one thing to be noted is that one set of impellers (two impellers) is in DEFINED VOLUME HIGHLIGHTED

MEASURING CHAMBER A

55

C 1

2

1

4 3

2

3 4

FLOW IN (Typ)

ROTOR

1 B

2 D

2 4

1

FLOW IN (Typ)

3

3

ROTARY VANE WITHOUT CAM

4 FLOW IN

FLOW OUT

ROTARY VAIN WITH CAM

FIGURE I/3.1.2-4 Rotating vane.

FLOW OUT (Typ)

56

Plant Flow Measurement and Control Handbook

continuous contact with the casing to deliver a fixed volume of liquid from the inlet to meter’s outlet, from each compartment as the impeller rotates. From the figure it can be seen that in the first position (A) the impeller set comprising 1 and 4 is touching the casing to ascertain the volume and in positions B, C, and D the impeller sets are 1e3, 1e2, and 2e4, respectively. This is possible because of the cam shown. There are other versions without a cam, where spring-loaded vanes are used, along with the eccentrically mounted rotor to entrap liquid between the casing and vane as shown in the right hand side of Fig. I/3.1.2-4. Normally, a Hall sensor and magnets are used to sense the rotary motion of the vane for totalizing, and/or converting to mA signal. The meters are available with a high turndown ratio >50:1 in the range of 20e1900 LPM. 5. Other PD meters: There are a few other types than those already discussed.

FLOW OUT

l

l

Reciprocating piston: A reciprocating piston flow meter is quite a popular PD meter. Many put this meter and rotating piston under the common heading of a piston type flow meter. A typical reciprocating piston meter has been detailed in Fig. I/ 3.1.2-5. In this type of flow meter the flow piston movement makes the fluid pass through alternately between the two sides of the piston with the help of a sliding valve with both the inlet and outlet in open positions (shown). Helical gear type: This meter is named after the shape of the gear which is like a helix (spiral-shaped). The helix flow meter is a positive displacement device utilizing two uniquely nested, radically pitched helical rotors as the measuring elements [27]. When the fluid passes through the meter it enters the compartments containing rotors which start rotating as the flow passes by. The rotation of the gear is proportional to

SLIDING VALVE

PISTON

SLIDING VALVE FLOW IN

FIGURE I/3.1.2-5 Reciprocating piston.

Flow Metering: General Discussions (An Overview) Chapter | I

flow (as it passes through a fixed-volume chamber), so the rotation flow can be computed. These are used for paint spray and material manufacturing. They introduce less of a pressure drop. With this, discussions on PD meters come to an end to see how flow can be measured with velocity and force sensing. 3.1.3 VELOCITY AND FORCE FLOW METER TYPES AND PRINCIPLES There are a number of meters which deploy the means to measure the average velocity of the flowing fluid inside a pipe then multiply the same with the area inside the pipe to compute the volumetric flow. As in this case there is no square rooting, and normally high rangeability is possible. While specifying the average velocity of the fluid, operators should be concerned with the velocity profile of the fluid, which, as was seen earlier, is a function of pipe geometry and Reynolds number. Again the Reynolds number is dependent on viscosity, density, etc., so selection of average velocity from the velocity profile is of prime concern. For Reynolds number >10,000 the velocity meter is highly sensitive to changes in viscosity. Another important issue here is the straight pipe length requirement of the flow meter duly recommended by manufacturer, so as to achieve the required accuracy. In the majority of process and chemical plants typical velocity values for liquids lie between 0.15 and 60% of chosen DP range. Hence for higher flow capacity losses will be greater; l When compared to a V cone greater straight length requirement is necessary. 5.3.2 APPLICATION AREAS OF WEDGE ELEMENTS As stated during the initial discussions, as well as while describing its features, the wedge element is a universal flow element. It can be used for liquids, air/gas, and steam. However, it finds its usage more in handling difficult fluid slurries. The major areas of use are listed here: 1. Measurement of flow of fluid with high viscosity;

2. Measurement of flow of difficult fluid with high solid content and abrasive slurries; 3. Fluid flow with low Reynolds number; 4. Bidirectional flow measurement; 5. Major industries covered include: paper, alumina, tar production, well heads, and waste management of different industries. 5.4.0 Specification Details for Wedge Elements After gathering some knowledge on technical data on wedge elements, we now look at how this could be specified. Table VII/5.4.0-1 provides a specification for a wedge element. It is worth noting that the data given here are mainly based on data from reputed manufacturers. Effort has been made to put the best value or material for any specific thing. Naturally, data given may not match with any particular manufacturer. Based on the budget and application, readers should specify their requirements to get the optimum result.

TABLE VII/5.4.0-1 Specifications of Wedge Elements SL

Specifying Point

1

Fluid type

Liquid, gas, steam or two phased solid-laden liquid/slurries

2

Design pressure

10e100 bar typical

3

Design temperature

Normal 40 to 400 C

4

Flow range

To be specified

Flow capacity, for discussions refer to Subsection 5.2.2.1

5

Other physical parameters

a. Upstream absolute pressure, absolute maximum/minimum/normal b. Downstream absolute pressure, absolute maximum/minimum/normal c. Temperature maximum/minimum/normal d. Density e. Viscosity @ temperature f. Reynolds number: g. Gas molar weight h. Specific heat ratio i. Expansionability factor

1. To specify OP ¼ operating maximum pressure/is dictated by flange rating (pipe schedule) and maximum temperature is guided by material selection and application 2. Data as applicable to be specified

Standard/Available Data

User Spec.

Remarks

Continued

Complex and Slurry Flow Measurement Chapter | VII

TABLE VII/5.4.0-1 Specifications of Wedge Elementsdcont’d SL

Specifying Point

Standard/Available Data

6

Wedge ratio H/D

Based on pipe size, accuracy, discharge coefficient, and selected DP range to be specified

7

Pipe size schedule

Meter for pipe size between 15 and 600 mm (nominal bore) are standard sizes available. Flow ranges are as per manufacturer’s standard based on wedge ratio and DP range to be selected

8

Tapping style and numbers of pairs

Corner/flange/radius/pipe

9

Standards

Refer to details in Subsection 5.2.4.2

Environmental condition

To specify

10

Materials of construction

Refer to Subsection 5.2.4.1

11

Gasket material

Silicate-filled TFE/graphite

12

Chemical TEE/ remote seal

To specify as required

Connection and Mounting Details 13

Process connection and rating

Flange as per ANSI/BS/DIN/JIS etc. Refer to Subsection 5.2.4.3

14

Transmitter connection

Normally flange type connections are used

15

Mounting

Horizontal/vertical/special type of mounting

Performance and Other General Details 16

Accuracy

Calibrated accuracy around 0.5% AR flow but uncalibrated accuracy 5%; refer to Subsection 5.2.3.1

17

Repeatability

0.2% AR

18

Accessories

Meter support (as applicable), process and instrument connection flanges along with tapping points. If applicable transmitter (DPT/MVT), valve manifold, nuts, bolts

19

Special feature

If any to specify requirement

User Spec.

Remarks Based on available H/D to be checked for flow capacity

To select

To specify quantity

Based on fluid type

669

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Plant Flow Measurement and Control Handbook

5.5.0 Mounting and Installation Details for Wedge Elements

5.5.1 ELEMENT ORIENTATION AND ALIGNMENT

Basically, a wedge element is a flow element, and hence mounting or fixing the element in the pipeline of the same is more pertinent than installation of an impulse pipe. Installation of PT/DPTs is more important when corresponding transmitters are discussed, viz. Fig. VII/4.2.3-1. The high-pressure connection is always on the upstream side of the flow direction arrow and the low-pressure connection on the downstream side.

A wedge element can be mounted in either a horizontal or vertical pipe, i.e., both horizontal and vertical mounting is acceptable. These have been shown in Fig. VII/5.0.0-3. The important issue here is the alignment of the element with the pipe. For proper measurement the wedge flow element should be installed at a 90 degrees angle to the pipe axis. The wedge element should be properly aligned to avoid additional turbulence, which has little effect however on meter performance.

FLANGE WEDGE ELEMENT

1 WEDGE ELEMENT 1

DPT/MVT

1

2 1 DPT/MVT 3 2 WITHOUT CHEMICAL SEAL

WITH CHEMICAL SEAL

1

FLANGE CONNECTION WITH IMPULSE LINE

FLANGE CONNECTION FOR REMOTE SEAL

2

WITH IMPULSE LINE

CAPILLARY & ARMOR

3

TRANSMITTER & INTEGRAL 3/5-VALVE MANIFOLD

3

TRANSMITTER

FIGURE VII/5.0.0-3 Mounting and installation of wedge element. DPT, differential pressure transmitter; MVT, multi variavble transmitter. Note: Bidirectional flow hence arrow for flow not shown temperature element for compensation should be in downstream side after downstream pressure sensing point.

Complex and Slurry Flow Measurement Chapter | VII

5.5.2 INSTRUMENT CONNECTION AND TRANSMITTER TYPES As stated earlier, the instrument connections are through flanges of suitable rating and standard. There are two variations. One is a transmitter connection with an impulse line and valve manifold and the other is with a remote seal and capillary. Both are shown with suitable notes in Fig. VII/5.0.0-3. 1. Clean fluiddImpulse line: In the case of clean fluid, an ordinary impulse line can be laid to connect the transmitter with the element via a three-valve manifold. In the case of DPT/ MVT, three- or five-valve manifolds are used. l Three-valve manifold: In the case of a threevalve manifold, two valves are isolating valves in the two legs of the DPT/MVT and the third valve is the equalizing valve (which should be opened first and closed last to avoid pressure shock in any of pressure legs for the DPT/MVT for taking the transmitter into service or taking out of service); l Five-valve manifold: In the case of a fivevalve manifold, the other two valves are for line drains pertinent to each leg for DPT/MVT. For DPT and MVT, integral valve manifolds should be used for better installation and alignment. Based on fluid properties, the materials for the valve manifolds should be selected, normally these are CS and SS. However, it is better to choose an SS manifold so that it can be used for most of the applications. 2. Dirty/corrosive fluidsdCapillary connection: In the case that the fluid is dirty, with entrained solids, etc. and there is the probability of chocking of the impulse line, or the flow of the fluid to be measured is corrosive and could damage the transmitter, then chemical/mechanical sealing is called for. In the case of a remote seal (e.g., wafer seal), the same is mounted between the two flanges of suitable standard, materials, and rating. A remote seal is connected to the transmitter with the help of a capillary with suitable

671

armor. Naturally there will be no need for a three-/five-valve manifold. 3. Transmitter type: As stated at the beginning, the wedge element is basically a DP-producing element, so DP across the element is measured to compute flow as per the details discussed in Section 5.1.2. In order to measure the flow DPT is necessary. In many cases in order to measure mass flow and/or for temperature compensation, MVTs are used. Therefore, the measuring transmitter could be either DPT or MVT. Both DPTs and MVTs are available with remote seals, and can be used for both clean and dirty/corrosive fluids. In the case of MVT and/or when temperature compensation is necessary the tapping for the temperature elements is taken at a point downstream of LP pressure tapping. Normally, the tapping point for the temperature element should be about 6D from the wedge element, where D represents the nominal diameter of the pipe. There are some requirements of upstream and downstream straight length requirements which are discussed in the following section. 5.5.3 STRAIGHT LENGTH REQUIREMENTS FOR WEDGE ELEMENTS General straight length requirements for wedge elements are 5D and 3D upstream (UP) and downstream (DWN) respectively. However, these are basically minimum straight length requirements, in reality it is more than this. Also, it is worth noting that the straight length requirements vary with flow capacity, hence with a wedge ratio H/D. Many manufacturers, such as ABB, specify the minimum straight length requirement as well as recommending taking into account the wedge ratio, etc. On the other hand, some specify the same in terms of wedge ratio H/D. In Table VII/5.5.3-1 we specify the straight length requirements for some selected fittings and the straight length requirements for wedge elements at different commonly used wedge ratios. The length requirements are in terms of multiples of nominal pipe diameters (D).

672

Plant Flow Measurement and Control Handbook

TABLE VII/5.5.3-1 Straight Length Requirements for Wedge Elements H/D [ 0.2 Fitting Types

UP

Single elbow

7

4

Same plane, double elbow

10

Two elbows, different planes

H/D [ 0.5

UP

DWN

UP

DWN

9

4

10

4

12

4

4

12

4

14

4

16

4

20

4

22

4

24

4

30

4

Reducer

9

4

11

4

14

4

16

4

Expander

9

5

11

5

12

5

14

5

Different diameter TEE

7

4

9

4

10

4

12

4

10

4

12

4

14

4

16

4

7

4

7

4

9

4

10

4

10

5

10

5

10

5

10

5

Open slide valve Y run plugged

5.5.4 MECHANICAL STEPS FOR INSTALLATION OF WEDGE ELEMENTS The following are a few steps to be followed for mechanical installation described in brief: 1. After unpacking the element it is necessary to inspect to ensure that the supplied element is clean and free from damage and debris. 2. Also, it is necessary to ensure that the flange and gasket rating is suitable for the service and to ensure flow direction for element position and straight length requirements. 3. The next step is to position the meter between the mating flanges and fit sufficient bolts into the lower part of the flanges to retain the meter in place.

UP

H/D [ 0.4

DWN

Open shut-off valve

DWN

H/D [ 0.3

4. Correct gasket/sealing rings placement between the flanges on both sides of the meter is important. It is necessary to align the element. Next all the balance bolts are placed and tightened suitably. With this the discussions on wedge elements come to an end, and along with this the discussions on slurry and complex fluid flow are also concluded. As indicated earlier, it is worth noting that slurry flow is quite common in industries as well as in many other application areas. Slurry flow is an example of two-phase flow measurement. In connection with two-phase flow measurement in Section 1.2.0 of Chapter IX, further details are available, so, for complete details, the reader is advised to go to this section.

Complex and Slurry Flow Measurement Chapter | VII

LIST OF ABBREVIATIONS ABS Absolute/acrylonitrile butadiene styrene (material) AC Alternating current ADC Analog to digital converter AR Actual reading (in connection with accuracy) BHCT Bottom hole circulating temperature BHP British horse power/bottom hole pressure BHST Bottom hole static temperature CMRR Common mode rejection ratio CMV Common mode voltage CS Carbon steel DC Direct current DI Ductile iron DP Differential pressure DPT Differential pressure transmitter/transducer DSP Digital signal processing EIT Electrical impedance tomography EMC Electromagnetic compatibility EMFM Electromagnetic flow meter ERT Electrical resistance tomography FC Fail to close (for valve) FO Fail to open (for valve) FRP Fiber glass reinforced plastic (thermowetting) FSD Full-scale division (in connection with accuracy) GNF Generalized Newtonian fluid HVAC Heating ventilation and air conditioning IC Integrated chip/internal combustion (engine)

ID Internal diameter I/O Input/output LCD Liquid crystal display LED Light-emitting diode LHS Left-hand side MPD Managed pressure drill MUX Multiplexer MVT Multivariable transmitter NB Nominal bore OBM Oil-based mud OD Outer diameter PD Positive displacement (meter) PTFE Polytetrafluoroethylene PVC Polyvinyl chloride RF Raised face or radio frequency RHS Right-hand side RTD Resistance temperature detector SBM Synthetic-based mud SIL Safety integrity level SS Stainless steel STP Standard temperature and pressure (Fig. I/1.1.2-3) T/C.TC Thermocouple US Ultrasonic/United States VEF Viscoelastic fluid VM Valve manifold WBM Water-based mud WRT With respect to

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Plant Flow Measurement and Control Handbook

REFERENCES [1] R.P. Chhabra, Non-Newtonian Fluids: An Introduction, Department of Chemical Engineering; Indian Institute of Technology Kanpur; SERC School cum Symposium on Rheology of Complex Fluids at Indian Institute of Technology Madras, January 2010. http://ethesis.nitrkl.ac.in/ 5296/1/109CH0108.pdf. [2] T. Sochi, Non-Newtonian Flow in Porous Media, University College of London, Science Direct, Elsevier, August 2010. www.elsevier.com/locate/polymer. http://www.sciencedirect. com/science/article/pii/S0032386110006750. [3] J.G. Rosales, Complex Fluid Flow in Micro Fluidics, Springer, 2017. [4] P.E. Arratia, Viewpoint: Complex Fluids at Work, Department of Mechanical and applied mechanics, University of Pennsylvania, USA, January 2011. https://physics.aps.org/ articles/v4/9. [5] J.R. Semancik, Yield Stress Measurements Using Controlled Stress Rheometry, TA Instruments, Thermal Analysis & Rheology. http://www.tainstruments.com/pdf/literature/ RH058.pdf. [6] N. Cunningham, What is Yield Stress and Why Does it Matter?, Rheology School. https://www.pcimag.com/ext/ resources/WhitePapers/YieldStressWhitePaper.pdf. [7] Hydrocolloid Rheology; Water Structure and Science, Internet document; http://www1.lsbu.ac.uk/water/rheology. html. [8] K.E. Nahhas, M.A. Rayan, I.E. Sawaf, N.G.E. Hak, Flow behavior of coarse-grained settling slurries, in: Twelfth International Water Technology Conference, IWTC12, 2008. http://www.iwtc.info/2008_pdf/6-7.PDF. [9] E.E. Michaelides, C.T. Crowe, J.D. Schwarzkopf, Multiphase Flow Handbook, CRC press, April 2016. [10] J. Polanský, Experimental Investigation of Slurry Flow, University of Leeds, September 2014. http://home.zcu.cz/ wrcermak/opvk_htt/VY_02_05.pdf. [11] Guide Lines for Slurry Flow Measurement, Endressþ Hauser, Australia. http://www.ferret.com.au/c/endress-hauseraustralia/guidelines-for-slurry-flow-measurements-n695907. [12] A. Kala, S.K. Mittal, M.K. Choudhary, Characteristics of flow meters with sediment laden flow e a review, International Journal of Engineering Research 4 (5) (May 2015) 240e243. MANIT Bhopal. [13] TMS0600 Slurry Liquid Flow Meter, Data Sheet TMS0600, Turbines Inc. http://www.turbinesincorporated.com/images/ stories/TIdownloads/TI_datasheet_TMS0600_Slurry_Meter. pdf. [14] NUFLO 1502 WECO Union Liquid Turbine Flow Meter, Technical Specifications, Cameron. [15] R.C. Baker, Flow Measurement Handbook, second ed., Cambridge University Press.

[16] D. Hebert, Measure Slurry Flows Accurately, Control, May 2011. http://www.controlglobal.com/articles/2011/measures lurryflowsaccurately/. [17] Y. Aoyama, F. Sugawara, T. Shimura, Y. Kaneko, H. Noda, A. Yasumatsu, reportADMAG AXR Two-Wire Magnetic Flow meter; Yokogawa Technical Report English, Edition Vol. 53 No. 2; 2010; https://www.yokogawa.com/rd/pdf/TR/ rd-te-r05302-004.pdf. [18] P.K. Das, G. Das, S. Sen, K. Biswas, Impedance technique for the measurement of two phase flow parameters: possibilities and challenges, in: Workshop on Computerized Tomography for Scientists and Engineers; IIT Kanpur India, IIT Kharagpur WB India, February 2004. [19] J.Y. Xu, M. Wang1, B. Munir, H.I. Oluwadarey, H.I. Schlaberg, Y.X. Wu, R.A. Williams, Correlation of Electromagnetic Flow Meter, Electrical Resistance Tomography and Mechanistic Modelling for a New Solution of Solid Slurry Measurement, in: 5th World Congress on Industrial Process Tomography, Bergen, Norway; http://www.isipt. org/world-congress/5/642.html. [20] Handbook of multiphase flow metering, in: Norway society for Oil and Gas Measurement; The Norwegian Society of Chartered Technical and Scientific Professionals, Tekna, March 2005. Revision 2, http://nfogm.no/wp-content/ uploads/2014/02/MPFM_Handbook_Revision2_2005_ISBN82-91341-89-3.pdf. [21] P. Rothman, C.O’. Keefe, A. Thomas, Application of Unique Sonar Array Based Process Monitoring Measurement Equipment for Minerals Processing Applications, CiDRA Minerals Processing and Krohne Mining & Metals Processing, BI0407 Rev A. http://www.cidra.com/sites/default/files/ document_library/BI0407_Application_of_Unique_SONAR_ 7-15-09_Final.pdf. [22] S. Basu, A. Kumar, Debnath, Power Plant Instrumentation and Control Handbook, Elsevier, November 2014. http:// store.elsevier.com/Power-Plant-Instrumentation-and-ControlHandbook/Swapan-Basu/isbn-9780128011737/. [23] S.N. Shah, N.H. Shanker, C.C. Ogugbue, Future Challenges of Drilling Fluids and Their Rheological Measurements, Well Construction Technology Center, University of Oklahoma, American Association of Drilling engineers, AADE10-DF-HO-41. [24] J. Robbie, State of the Art for Drilling Fluid Measurements and the Industry Needs, Upstream Production Management forum, Houston, TX USA, February 2016. https://upmforum. com/lectures-presentations-forum-documents/presentations/ UPM%202016%20Drilling%20Fluid%20Measurements%20 Industry%20Needs24thFeb2016rev1.pdf. [25] D. Smart, C. Russell, M. Simons, Understanding and Selecting Coriolis Technology for Drilling Fluid Monitoring, Micro Motion- White Paper, Micro Motion, Inc. http://www2.emersonprocess.com/siteadmincenter/PM%20

Complex and Slurry Flow Measurement Chapter | VII

[26]

[27]

[28]

[29]

[30]

[31]

[32]

[33]

[34]

[35]

Micro%20Motion%20Documents/Drilling-Fluid-MonitoringWP-001243.pdf. Flow Measurement in Pulp, Paper Applications, Yokogawa electric; flow measurement and control; South African instrumentation and control, October 2016. https://www. yokogawa.com/in/library/resources/application-notes/pulppaper-instruments-and-solution-for-pulp-paper-industry/. Pulp and Paper Process Solutions Guide: Pulp and Paper Flow Meter Guide, Micro Motion, Emerson Process Management. http://www2.emersonprocess.com/siteadmincenter/PM%20 Micro%20Motion%20Documents/Pulp-Paper-PSG-Flow meter.pdf. Mineral Phase and Physical Properties of Red Mud Calcined at Different Temperatures;C.S. Wu and D.Y. Liu; Hindawi Publishing Corporation; Journal of Nanomaterials; Volume 2012 2012, Article ID 628592, 6 pages; https://www. hindawi.com/journals/jnm/2012/628592/. F. Frenzel, H. Grothey, C. Habersetzer, M. Hiatt, W. Hogrefe, M. Kirchner, G. Lütkepohl, W. Marchewka, U. Mecke, M. Ohm, F. Otto, K.-H. Rackebrandt, D. Sievert, A. Thöne, H.-J. Wegener, F. Buhl, C. Koch, Deppe, E. Horlebein, A. Schüssler, U. Pohl, B. Jung, H. Lawrence, F. Lohrengel, G. Rasche, S. Pagano, A. Kaiser, T. Mutongo, Industrial Flow Measurement Basics and Practice, ABB Automation Products GmbH. http://nfogm.no/wp-content/uploads/2015/04/ Industrial-Flow-Measurement_Basics-and-Practice.pdf. Discharge coefficient equation of a segmental wedge flow meter; J Y Yoon, N W Sung, and C H Lee; DOI: 10.1243/ 09544089JPME121; ARCHIVE Proceedings of the Institution of Mechanical Engineers Part E Journal of Process Mechanical Engineering 1989-1996 (vols. February 2008); Research gate. https://www.researchgate.net/publication/ 245389731_Discharge_coefficient_equation_of_a_segmental_ wedge_flowmeter. IntraWedge WEDGE FLOW METER, Intra automation, Technical Information; January 2011. http://www.bhb.pt/en/ images/Produtos/Instrumentacao/Caudal/Pressao_Diferencial/ Wedge/ds_wedge.pdf. V. Shesadri, S.N. Singh, S. Bhargave, Effect of Wedge shape and pressure tap locations on the characteristics of Wedge Flow meter, Indian Journal of Engineering and Material Sciences 1 (October 1994) 261e266. M.A. Crabtree, Industrial Flow Measurement, The University of Huddersfield, June 2009. http://eprints.hud.ac.uk/5098/ 1/macrabtreefinalthesis.pdf&sa¼u&ei¼v66ttp_ccojmialag 7mnbq&ved¼0cdiqfjat&usg¼afqjcngao5vc1jsrrbjucjvkxotj joah6q. WedgeMaster FPD570 Compact wedge flow meter, ABB limited, Data sheet DS/FPD570eEN Rev. C. https://library. e.abb.com/public/227ed7a4e24c4d6dc1257d23003589c9/DS_ FPD570-EN_C.pdf. MPP Wedge Meter, Catalog, WEDGE CATALOG Rev. 6 Part 1, February 2013. http://flowelements.net/MPP-WedgeMeters.pdf.

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FURTHER READING [1] Instrument Engineers’ Handbook, in: Process Measurement and Analysis, vol. 1, CRC Press (Chapter 2 Flow measurement). [2] S. Basu, Plant Hazard Analysis and Safety Instrumentation Systems, Elsevier, IChemE, 2016. http://store.elsevier.com/ Plant-Hazard-Analysis-and-Safety-Instrumentation-Systems/ Swapan-Basu/isbn-9780128037638/. [3] A. Nakahara, Y. Matsuo, K. Uchida, H. Izui, S. Kitsunezaki, F. Kun, Memory of Paste: Visualization as Crack Pattern and Non-destructive Structural Analysis. [4] D. Vader, H. Wyss, Introduction to Rheology, Weitzlab group meeting tutorial. http://weitzlab.seas.harvard.edu/files/ weitzlab/files/introductiontorheology2.pdf. [5] A. Shahriar, M.L. Nehdi, Rheological Properties of Oil Well Cement Slurries, TheUniversity of Western Ontario; Institution of Civil Engineers, February 2012. https://www. researchgate.net/publication/274766279. [6] Flownex Slurry and Non-Newtonian Flow, Flownex Simulation Environment, Write Up. http://www.flownex.com/ information/capabilities/fluid-models/slurry. [7] S.A. Miedema, R.C. Ramsdel, Slurry Transport: Fundamentals, Historical Overview & DHLLDV. https://www. dredging.org/media/ceda/org/documents/resources/othersonline/ miedema-2016-slurry-transport.pdf. [8] Slurry Handbook: A Guide to Slurry Pumping, Flygt, ITT industries. http://www.hidrotecaguas.com/catalogos/Bombas_ para_liquidos_abrasivos.pdf.   Spoljari [9] T. Kupanovac, Z. c, Z. Valter, Mass flow meter analysis for reliable measuring, International Journal of Electrical and Computer Engineering Systemsl 3 (November 2012). https://www.google.co.in/url?sa¼t&rct¼j&q¼&esrc¼ s&source¼web&cd¼8&cad¼rja&uact¼8&ved¼0ahUKE wjd1-6s4qvUAhXJOo8KHRhdB8wQFghSMAc&url¼http% 3A%2F%2Fhrcak.srce.hr%2Ffile%2F127568&usg¼AFQjCNE j2Xj94qE_A6dFappcRmRoxvBNIA&sig2¼QSyGcNktpSc Ei6uNJSfS9A. [10] M. Behling, D. Mewes, Process tomography: development and application of non-intrusive measuring techniques for multiphase flows, in: Workshop on Computerized Tomography for Scientists and Engineers; IIT Kanpur India, University of Hannover (Germany), Institute of Process Engineering, IfV, February 2004. [11] Drilling Fluids Management, Process Solutions Guide, Micro-Motion, Emerson Process Management. http:// www2.emersonprocess.com/siteadmincenter/PM%20Micro %20Motion%20Documents/Drilling-Mgmt-PSG-MC-001190. pdf. [12] H. Casellas, Step Changes in Drilling Fluid Measurement, Emerson Process Management, T.R. Tonnessen and K.K. KristaindHaliburton. [13] Flow and Concentration Measurement of Process Water and Spent Liquor, Flexim AMERICAS Corporation.

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https://www.flexim.com/us/industries/otherindustries/pulppaper/ flowandconcentrationmeasurementprocesswaterandspent liquor. [14] K. Deelwal, K. Dharavath, M. Kulshreshtha, Evaluation of characteristic properties of red mud for possible use as a

geotechnical material in civil construction, International Journal of Advances in Engineering and Technology 7 (3) (July 2014) 1053e1059. [15] B.E.A. Jacobs, Design of Slurry Transport System, Elsevier Applied Science.

CHAPTER VIII SOLID FLOW MEASUREMENT

Chapter Outline 1.0.0 1.0.1 1.0.2 1.0.3 1.0.4 1.0.5

2.0.0

3.0.0

4.0.0

5.0.0

Introduction: An Overview of Solid Flow Measurement Discrete Mass Delivery Weighing Systems Discontinuous Totalizing Weighing Systems In-Motion Weighing SystemsdDiscrete Mass Weighing SystemdWeighbridges Weighbridge Load Cell In-Motion Weighing SystemsdContinuous Solid Flow System 1.1.0 Discussions on Mechanical Equipment for Solid Flow 1.2.0 Material Characteristics for Solid Flow 1.3.0 Evaluations of Various Technologies for Solid Flow Metering 1.4.0 Solid Flow Measurement System Selection Mechanical Flow Meters 2.1.0 Centripetal Solid Flow Meter 2.2.0 Coriolis Solid Flow Meter 2.3.0 Impact Scale Solid Flow Meter Gravimetric Feeder and Loss in Weight 3.1.0 Gravimetric Feeder 3.2.0 Loss-in-Weight Measurement Belt Weighing System 4.1.0 Weigh Feeder Systems 4.2.0 Belt Scale/Belt Weigher System 4.3.0 Load Cell and Sensing Electronics 4.4.0 Speed Sensor and Sensing Electronics 4.5.0 Electronic Integration and Control Systems 4.6.0 Motor Speed Control 4.7.0 Conveyor Accessories: Safety Switches Noncontact Type Microwave Solid Flow Meters 5.1.0 Descriptive Details of Microwave Solid Flow Instruments

677 678 681 681 683 683 683 692 698 700 702 702 706 710 718 720 730 742 743 752 757 768 771 775 777 778 778

1.0.0 INTRODUCTION: AN OVERVIEW OF SOLID FLOW MEASUREMENT The size of solids varies widely, ranging from large size coal flow to a crushing mill, to very fine

5.2.0 Features and Applications of Microwave Solid Flow Instruments 5.3.0 Specification of Microwave Solid Flow Instrument 6.0.0 Noncontact Type Nucleonic Solid Flow Meters 6.1.0 Principles of Operation for Nucleonic Mass Solid Flow Meters 6.2.0 Configurations for Nucleonic Mass Solid Flow Meters 6.3.0 Descriptive Details of Nucleonic Solid Flow Measuring Systems 6.4.0 Features and Applications 6.5.0 Specification of Noncontact Type Nucleonic Solid Flow Measuring Systems 7.0.0 Miscellaneous Solid Flow Metering Systems 7.1.0 Screw Weigh Feeder 7.2.0 Apron Weigh Feeders 7.3.0 Capacitance Type Solid Flow Meters 7.4.0 Force Flow Type Solid Weigh Meters 8.0.0 Process Batch Weigher 8.1.0 Basic Principles Outline of Process Batch Weighers 8.2.0 Automated Process Batch Weighing Process 8.3.0 Controllers of Process Batch Weighers 9.0.0 Concluding Discussions on Solid Flow Measuring Systems 9.1.0 Load Cell 9.2.0 Speed Sensor 9.3.0 Motor Control 9.4.0 Conveyor Accessories List of Abbreviations References Further Reading

779 779 781 782 783 784 788 788 790 790 792 792 793 795 796 796 797 797 798 798 798 798 799 800 801

materials, such as raw meal feed to a cement kiln. In the case of solid flow normally mass flow is measured, as volume flow cannot be considered accurate enough. On account of variations in bulk density, entrapped gas/air mass flow are normally

Plant Flow Measurement and Control Handbook. https://doi.org/10.1016/B978-0-12-812437-6.00008-1 Copyright © 2019 Elsevier Inc. All rights reserved.

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measured for measurements of solid flow. The majority of the flow metering depends on some method of weighing. Other meters utilize other phenomena, e.g., centripetal force, impact force, Coriolis, or nucleonic for measuring mass. All weighing systems where the material being weighed is, or may be, in net motion relative to the weighing machine can be referred to as dynamic weighing systems. Therefore, dynamic weighing systems also include indirect weighing methods like Coriolis, impact, and/or centripetal type measurements. These types may also be considered as mechanical types. Apart from these, nucleonic methods and scanners can also be utilized for solid flow measurement. Weighing systems can be utilized in process plants as well as for discrete mass delivery (e.g. Batch control of course a part of process plant), discontinuous totalised system and in motion weighing system. Since the major thrust is on solid flow metering, therefore others systems will be discussed in brief so at first and detailed discussion of weighing systems in connection with solid flow measurement will be discussed at length later. These mechanical type solid flow measurement or dynamic weighing systems can be broadly divided into three categories based on their methods and means of operations as described here [1]: l

l

l

Discrete mass delivery weighing systems: These are applicable for various weighing machines used in batch weighers or gravity filling machines, where each batch may be put into a container or may be combined with other weighed masses to make up a mixture against a formula. Discontinuous totalizing weighing systems: These are used for shipping and receiving weighers and in-process weighers. The accumulated total weight of a larger bulk mass of material, and sometimes also the throughput, are recorded. In-motion weighing systems: In-motion weighing systems are those which determine the mass of a moving material passing over or through a device. The flow of measured mass may be continuous, as in a belt weigher, or it may comprise discrete weighing events,

as in the form of road vehicle or rolling stock axles or packages on a conveyor belt [1]. Now short discussions will be presented to give a clear idea about each of these systems.

1.0.1 DISCRETE MASS DELIVERY WEIGHING SYSTEMS Different discrete mass delivery weighing systems along with their classifications have been depicted in Fig. VIII/1.0.1-1. Brief discussions on each of these subsystems will now be taken up. The discussions start with a process batch weigher. Chapter XI also deals with dispensing, filling, and batch controls. 1. Process batch weigher: There are three types of process weigher systems: cumulative, simultaneous, and combinational batching, as depicted in Fig. VIII/1.0.1-2. Since these are used for batch processing, precise control of the operations is very pertinent and important. Modes of such controls can be manual, semiautomatic, and automatic. In the era of digital Discrete Mass delivery system Process Batch Weigher Cumula ve Batching Simultaneous Batching Combina onal Batching Gravimetric Filling Gross Weigher Net Weigher Conven onal Selec ve combina onal Weigh out

FIGURE system.

VIII/1.0.1-1 Discrete

mass

delivery

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(C) 2

1

3 INGREDIENTS

1

INGREDIENTS

(B) 3

2

INGREDIENTS

1

INGREDIENTS

INGREDIENTS

(A)

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2 FEED HOPPER

BATCH OUTPUT

WEIGHED HOPPER

WEIGHED HOPPER

WEIGHED HOPPER

WEIGHED HOPPER

BATCH CONTROLLER

WEIGHED BATCH HOPPER

WEIGHED BATCH CONTROLLER

BATCH HOPPER

BATCH OUTPUT

BATCH CONTROLLER

WEIGHED BATCH HOPPER

BATCH OUTPUT

FIGURE VIII/1.0.1-2 Process batch weigher. (A) Cumulative type. (B) Simultaneous type. (C) Combination type.

electronics the automated system is preferred, nevertheless in some cases, especially in certain food processing industries, complete automation processes still are not preferred, hence semiautomatic systems may be used. The automated process is used mainly for recipes, batch sequence, inventory, and operation and maintenance management: l Speed controls of feeding system as per material characteristics; l Total flow quantity control of ingredients; l In-line inventory control of output as well as ingredients used; l Recipe control and optimization for different products; l Diagnostics, operation, and maintenance management. Considerations here are given to ingredient addition, etc. not complete batch processes involving, e.g., heating processing, etc. For further details on batch controls, Chapter VI

of the author’s book [2] may be referenced. The following industries apply this type of weigher: l Food and beverage industry; l Pharmaceutical; l Chemical, e.g., soap and detergent; l Mineral processing; l Glass processing; l Animal feed; l Fertilizer; l Rubber and plastics. Two major issues to be noted in the figure are that there are two kinds of bins/ hoppers used, one is a weighing bin/hopper directly connected with the batch control of the recipes, and the other is a feed bin/ hopper. The feed hoppers are basically the same as the other hopper but are passive elements not connected with the control system directly (for weighing system) except its inlet/outlet valve operation.

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Weighing hopper or batch hopper measurement is static and in one sense is level sensing, unlike in motion (motion of material with respect to the bin). There are three mainly kinds of process batch weighing systems, as clearly shown in Fig. VIII/1.0.1-2. Cumulative type: In the cumulative type, as shown in Fig. VIII/1.0.1-2A, there is only a single weighing bin and ingredients (in this case three) are weighed one after the other. Therefore, there are at least three weighing set points, e.g., for the first ingredient it will be for the weight of the first ingredient, the second set point would be the first þ second quantities, etc. for all components. This continues until all ingredients have been weighed and the batch is discharged to the next stage, e.g., to a mixer. It is cheaper in the sense that there is one weighing system but it is slow and can be a less accurate system (errors in matching any set point can increase the inaccuracy). Simultaneous type: As shown in Fig. VIII/ 1.0.1-2B, there are separate weigh bins/hoppers for each component and each of the hopper outlets is controlled based on weight output. The final bin/hopper ensures the total set weight is achieved for discharging to the next stage. Here, better accuracy is expected and the process can be faster but is more costly.

Combinational type: As the name suggests this is a combination of the above two processes, and is used, e.g., if the quantity of some ingredients are too small then it is possible to measure a small amount in the final batch weight hopper separately. The scheme has been depicted in Fig. VIII/1.0.1-2C. 2. Gravimetric filling machine: This is different from the process batch weighing system and is used for filling bags, drums, and containers. These are always used with a single feeding system and weighing single material. These are two types of gross/net weighers: l Gross weigher: Gross weigher machines fill different varieties of containers, such as bags, with a predetermined weight of product. It fills product directly into the bag to a preset weight without employing a separate weigh hopper prior to filling, e.g., bottles filled with product such as yogurt. l Net weigher: A common bag filling example is that of a cement bag filling machine. In net weighers/machines bags/containers are filled with a predetermined weight of product prior to placement in transport containers such as bags and drums. As only the material is weighed in a weigh vessel(s) before discharging to a container, these are called net weighers. There are three types as shown in Fig. VIII/1.0.1-1, and described in Table VIII/1.0.1-1. l

TABLE VIII/1.0.1-1 Net Weigher Types Types

Description

Application

Influencing Factor

Conventional

Feeds material to weigh vessel. Types of feedings are: Gravity gate; screw feeding; belt feeder, vibratory feeder

Widest application; depending on feeding type application varies

Inconsistency of material; bulk density; system vibration; speed variations, delay in cut of point response

Weigh out

First fills the material in weighing vessel then weighs preset value prior to discharge. So no flight compensation necessary

Same as above but may be with better accuracy

Variation of bulk density to affect loss in weight when materials are not freeflowing

Selective combinational

Several weighers in single machine for variety of products and weighers are used in combinations

For products with product variations

Vibration; multiple dump; parentechild issue

Solid Flow Measurement Chapter | VIII

1.0.2 DISCONTINUOUS TOTALIZING WEIGHING SYSTEMS These machines with a single feeding weigher are used to totalize discrete batch weights for the purpose of recording accumulated total weight of a larger bulk mass of material, and sometimes the throughput as well [1]. There are two types of the weighers: shipping and receiving weighers and in-process weighers. 1. Shipping and receiving weighers: These weighers totalize bulk material movements to or from a silo to a vessel such as a road or rail tanker, a barge, or a ship. They are used for bulk feed into a compartmented road or rail wagon and bulk transportation and shipping. Naturally, these have large capacities and may be >10 m.ton. Emptying or filling a large vessel can take many hours, involving a substantial financial transaction. Thus suitable protections to take care of power failure and mechanical breakdowns are needed [1]. Air displacement is an important issue to maintain accuracy of measurement, especially for cases for rapid filling and emptying the vessel when error may creep in. 2. In-process weighers: These are versions for use in various processes and manufacturing units, such as grain or rice milling. The weighing capacity is much less than that for shipping and receiving weighers, typically about 50 kg. Their primary use is to determine both the shortand long-term cumulative process weights of a product stream within a milling process [1] for assessing the milling efficiency of the product streams. Like in shipping and receiving weighers, air displacement is an important issue, if the air pressure built up during the emptying operation falls then the weigh hopper may be lifted, introducing error in measurement.

1.0.3 IN-MOTION WEIGHING SYSTEMS—DISCRETE MASS WEIGHING SYSTEM— WEIGHBRIDGES In-motion weighing systems are of two distinct types: discrete mass weighing systems, such as

681

road/rail weighbridges, and continuous weighing systems (mostly found in major processes and industrial plants). Of these two systems, discussions will be presented on discrete mass weighing systems in this section. Discussions on continuous weighing systems are in Section 1.0.4. In discrete mass weighing systems platforms are used. These systems are designed to note both the weight of the discrete mass as it passes over the weighing platform and accumulate a total weight. The measurement can be triggered either from the increasing weight on the platform or from an external trigger. Weighing coal wagons would involve weighing individual axle weights that are accumulated into individual wagon weights, and then the total train weight. To get the measure of coal, tare weights are subtracted. There are two main kinds: road weighbridges and rail weighbridges. 1. Road vehicle weighing: Normally, a road weighbridge comprises one or more weigh platforms designed to measure individual wheel or single axle loads as a road vehicle traverses the weigh platform(s). These weighbridges are required to measure efficiently; wheel, axle, and total vehicle load for commercial purposes, safety checking as well as checking for overload for road safety. There are two broad categories of road weighbridge, namely, weighbridges with civil foundations and weighbridges without foundations. These may be referred to as fixed and portable weighing in-motion systems, respectively [1]. The former is a permanent installation with the purpose discussed above, while portable systems are used for weight checks in random locations, frequently to detect vehicles avoiding permanent check sites and for overloading. Another kind is used to collect the data from a speeding vehicle, where sensors are embedded inside the road. Weighbridges are generally designed to measure the individual wheel or axle weights separately and summated if required to obtain the total vehicle weight [1]. Normally it is possible to weigh for any approaching vehicle in either direction but not for a reversing vehicle. There are

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several measurement methods, the most common of which are: l Direct measurement: This is used when the vehicle fits the platform. This is an accurate method of measurement. With the help of this it is possible to measure the tare weight and gross weight. The tare weight and gross weight must be recorded within 24 h so that weighing tickets for net weight can be generated. l End-and-end measurement: This method is used for vehicle sizes not accommodated within the platform(s). As a result, two measurements have to be determined, one for the front and the other for the rear of the vehicle. l Axle load measurement: This is used for measurements of the mass supported by separate axles, or groups of axles, of a vehicle. l Factors affecting measurements: The following are the major factors affecting the performance of a weighbridge: ○ Speed of travel; ○ Mode of operation; ○ Site topography; ○ Road surface deficiencies. To end these discussions it is important to note that weighbridge weighing means (method) are guided by local government laws. 2. Rail weighbridge: To measure in-motion, the wheel, bogie, wagon, and total for commercial and safety reasons, rail weighbridges are utilized. Similar to road weighbridges, these also fall into two categories of rail weighbridge: rail weighbridges with civil foundations and those without foundations. These are often called conventional type and foundation-less type, respectively. There is also another type called the portable dynamic weighbridge. In rail weighbridges there are a number of strategically mounted detecting switches for

detection and control of weighing. The major functions of these are listed here: l Detection of locomotives wherever they are positioned in the train for weighing computation; l Detecting the start and end of vehicles for correct axle and/or bogie weights; l Detecting the direction and speed of travel and initiating the weighing process; l Detecting when a train stops and rolls back, to avoid wagons being weighed more than once; l Technical issues: A rail weighbridge is a load receptor, inclusive of rails for turning over railway vehicles. The weighing may be finished in motion or in a stationary position. When a train which consists of a number of wagons goes through or over the load receptor, the load cells transmit the load assessment details to the control unit with the help of an analog to digital converter (ADC). At the similar time, the track controls send signals as to the type of motor vehicle passing over it. As a result, the control unit decides which values are to be acknowledged and which are not. The gross weights of the suitable wagons are displayed with the help of a processing unit (PU) on the video display unit (VDU). With the help of an operator station, the operator can input the wagon number, etc. An associated printer provides the weighing sheet; l The major components are as listed below: ○ A load receptor (load cells—hermetically sealed shear beam load cells/embedded strain gage type); ○ A few aprons; ○ Track switch; ○ Weighing electronics; ○ Indicating devices; ○ A printer; ○ A control unit. l The key features include the following: ○ It is a pitless design with minimum excavation;

Solid Flow Measurement Chapter | VIII

○ ○ ○ ○ ○ ○ ○ ○ ○

It has low cost on installation; High-accuracy weighing electronics, with proximity to track switches; Overspeed signal and alarm; Rollback detection; All types of four-axle/two-axle railway wagons, etc.; All types of locomotive removal; Auto/manual operation; Report generation; Digital link/communication facilities.

1.0.4 WEIGHBRIDGE LOAD CELL The load cell is a common sensor required for all weighers, and hence short discussions on the same are presented here with special reference to weighbridges. However, further detailed discussions on load cells are also presented at later in this chapter also. Normally three kinds of load cells are deployed for weighbridges, these are described here: 1. Single-ended beam cells: These are cumbersome high-capacity single-ended bending beam load cells with four strain gages. In modern weighbridges these are not used often. 2. Double-ended beam cells: Double-ended shear beams provide a better mechanical solution than single-ended beams and the shear technology provides a product that is less susceptible to nonaxial forces. They require appreciable maintenance when used with a ball bearing. 3. Canister: Canister load cells have a long history in weighbridge applications and are considered to offer the best solution—provided they are well designed and built.

1.0.5 IN-MOTION WEIGHING SYSTEMS—CONTINUOUS SOLID FLOW SYSTEM There are several kinds of devices and systems available for in-motion continuous weighing systems. These are regularly used in process plants, and hence need special attention. They are discussed at length in subsequent sections

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covering all the types of measurements shown in Fig. I/3.2.0-1, including nucleonic measurement. Overview of these are already covered in Section 3.2.0 of Chapter I and so are not repeated here. Before moving on to actual discussions on continuous solid flow measurement, it is better to look into the mechanical equipment and material properties in subsequent discussions. 1.1.0 Discussions on Mechanical Equipment for Solid Flow There are various pieces of equipment responsible for feeding and transporting of solids. This is applicable for all types of solids; be they in bulk form, or powder or granular form. In the case of fluid transportation, conduits such as pipes or ducts are used. In the case of solids various kinds of feeders are deployed for transportation and feeding. Like tanks and reservoirs for liquids, in the case of solid materials, silo hoppers, etc. are used as storage equipment. Also, in many cases air/gas is used for transporting materials. Naturally, in all such cases there will be two phases of gas and solid flow. Again the sizes of solid materials may vary from large chunk of materials to very fine powder materials. On account of these (e.g., two phase) it is not possible to use volumetric flow measurement instead mass flow are generally computed for solid materials. There are wide variations in material properties, which compel the use different kinds of feeding and transporting equipment. Therefore, prior to moving on to detailed discussions on these measurement systems, it is better to acquire some knowledge through brief discussions on the mechanical equipment used in solid material handling. With reference to Figs. VIII/1.1.0-1, the discussion starts with typical feed arrangement for solid materials in the above cluster of figures. In this connection it is worth noting that often conveyor and feeders are loosely used to mean the same set of equipment to transfer solids from one place to other. However there are functional difference as indicated in Fig VIII/1.1.0-2.

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(A)

INLET GATE

(B)

MATERIAL INFLOW

GAS VENT

M

MATERIAL INFLOW

TIMER

LSH AL VIBRATOR* (AS APPLICABLE)

LSL M

FROM ALARM IF MANUAL OPEARTION

TO FEEDER

(C)

I

DE

TA IL ED

LOW INTERLOCK IF MOTORIZED SHUT OFF GATE

VI EW FLOW IN ROTARY FEEDER

(D)

(F)

(E)

(G)

(H)

(I)

PRODUCT LEAKGE AIR

FIGURE VIII/1.1.0-1 Mechanical equipment for solid flow. (A) Feeding arrangement. (B) Belt conveyor. (C) Rotary feeder. (D) Screw conveyor. (E) Drag conveyor. (F) Vibrating feeder. (G) Bucket conveyor. (H) Double flap valve. (I) Rotary valve.

Solid Flow Measurement Chapter | VIII

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Conveyor/Feeder: As the name implies, conveyor or conveyor system is a mechanical equipment and/or system used for material handling. The conveyor system is used to move solid materials from one loca on to another. When not covered Conveyors systems are used in applica ons involving the transporta on of heavy or bulky materials. However with suitable covering/skirt the system could be used for fine solids also. Feeder is also a mechanical system to convey material in a controlled manner. The major differences between a feeder and a conveyor could be: Conveyors are not flood loaded and the speed of conveyors are fixed and speed are not controlled In contrast to that feeders are flood loaded and the speed of feeders are variable and could be controlled to modulate discharge rate.

FIGURE VIII/1.1.0-2 Conveyor/feeder.

1.1.1 FEEDING ARRANGEMENT FOR SOLID FLOW Based on material properties there are a number of feeding arrangements for solid materials to flow. The feeding arrangement of cement from a cement silo, or raw meal feed from a raw material silo is an elaborate arrangement. On account of the material properties discussed later in this section, there will be possibility of materials becoming compacted, especially when there is a high moisture content. Also, in order to ensure flowability, it is necessary to have air blown to the systems, e.g., an air slide so that the material flowability is ensured for material extraction. Also for raw material conveying, there may be an intermediate bin/hopper from where the material is extracted and weighed before being fed to the system for example as raw meal to kiln. One of the simplest arrangements of material feeding has been taken for discussions and is shown in Fig. VIII/1.1.0-1A. We now investigate the functions of various components. 1. Inlet gate: Here, as can be seen, materials come to the hopper through an inlet section with an inlet gate which is motorized. The inlet gate is motorized because in the case of a high level being sensed by the level switch, it will close the inlet gate to stop the supply when the hopper level is high. Although not

shown, there should be one high alarm so that the operator can take action. Here it has been made automatic through a timer (time setting done based on hopper capacity and flow rate). 2. Vibrator: In the case of solids with fine sizes there is the possibility of it becoming compacted and losing flowability. This may be more so in the case that there is the possibility of high moisture content (may come from raw materials in the open yard). In order to get rid of such situations, vibrators are mounted in the hopper so that materials do not stick due to the vibration effect. The frequency and duration of vibration needed are a function of the solid material size and characteristics. When the solids aerate easily, there may not be any need for a vibrator (but if there is a chance of compacting it is better to have the provisions for the same—in a cement factory in Jordan initially there was no such provision but it later added to get better results, especially during the winter season when there may be heavy snow fall). 3. Outlet gate: In the case of a low level the flow of material due to gravity may be affected, so at a low level the outlet gate may be closed to fill the hopper. Normally alarms are sufficient for operator action, however an interlock has

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been shown to illustrate that here also automation could be implemented. Naturally, for implementing automation it is necessary that the outlet gate (which may be a pin type) be motorized, but it can be manual also. Closure of the outlet gate is necessary to prevent loss of the plug of material ahead of the succeeding feeding arrangement. Also, loss of a plug of deaerated material can cause production delays, because with new material there will be the need for fresh aeration. 4. Gas vent: Attention must be paid to the gas vent—this is necessary whenever materials are conveyed pneumatically. The vent should not be left open but may be connected to a bag dust filter and other dust-handling equipment. 5. Hopper design: Hopper design is another important aspect in solid flow measurement. A poorly designed hopper may yield improper flow, creating an arching rat hole in the hopper. This means that materials from all sides would not flow to the downstream conveying equipment, e.g., the belt feeder. The aim of the hopper design is to create “mass flow,” so as to ensure uniform discharge GOOD DESIGN

POOR DESIGN

ALL

FLOWING

STAGNANT'

FLOWING

STAGNANT'

MASS FLOW

RAT HOLE

FUNNELLING

ARCHING

FIGURE VIII/1.1.0-3 Hopper design.

from the bin so that material does not remain in the bin and bridge formation does not take place. If part of the material remains in the bin/hopper, it may become compacted and solidified. In poorly designed hoppers, such as “funnel flow” types, material will support itself and rat holes or bridging can occur [3]. A rat hole is a column of material flow inside, leaving material in the bin along the inside edges. Another issue is a bridge which is created when an opening occurs at the discharge of the bin, without an impact of the opening all the way to the top of the material pile. When material bridges take place in the bin, flow is stopped, additional material supplied to the bin can cause a breakdown or avalanche of material, creating an unstable disruption to the normal flow. A “mass flow” hopper design works in a first in, first out (FIFO) system, and so is very suitable for cases where aging or spoiling is a concern. These phenomena and designs are illustrated in Fig. VIII/1.1.0-3 and are further elaborated on in Subsection 4.1.2.2. 1.1.2 BELT CONVEYOR Normally, a belt conveyor system uses two pulleys over which the belt moves continuously due to rotation of one of the pulleys, called a drive pulley. The other pulley moves due to movement of the belt over it. The belt is supported by a series of rollers/idlers along the path to prevent sagging of the belt due to the load on the belt. In this connection Fig VIII/1.1.0-2 may be referenced to have clear idea about its difference with feeder. 1. Working principles: Basically, a conveyor belt can be conceived of as a machine with a moving belt. A belt conveyor system consists of two endpoint pulleys complete with driving motor and necessary gear arrangement, a closed conveyor belt, and a set of other pulleys referred to as an idler and a few other accessories. The pulley that drives the conveyor belt rotating is called the drive pulley (also the transmission drum); the other is called the tail pulley. The drive pulley is driven by a motor complete with chain/V belt and reducer.

Solid Flow Measurement Chapter | VIII

The operation of the conveyor belt relies on the friction drag between the drive pulley and the conveyor belt. In order to increase traction and ease out the drag, the drive pulley is generally installed at the discharge end and the tail pulley is located at the other end. The belt conveyor can be horizontal or inclined upward. Material is fed on the feed-side. The typical arrangement of a belt conveyor has been shown in Fig. VIII/1.1.0-1B. 2. Major components: Typically a belt conveyor consists of the following major components: l Belt: Made up of rubber and other materials like PVC, urethane, neoprene, nylon, nitrile, polyester, leather, etc. It has a specific defined width and length. This is sometimes referred to as a bed. l Pulley: A pulley is like an iron pipe, put on each end of the bed, and has a width the same as that of the belt or bed. A steel shaft of each pulley, passing through it, turns on a ball bearing. Thus, with the help of the drive and reducer, the shaft of the pulley turns on the ball bearing. The tail pulley is a freely moving pulley located at the tail end. One of these pulleys is shown in Fig VIII/ 1.1.0-1B. l Drive: One of the two pulleys is connected to a motor which runs at high speed of rotation. As the motor turns very fast, a speed reducer must be installed between the drive pulley and the motor. The motor is connected to the reducer with a V-belt or “C” face coupling. l Toughed idler: Between the two sets of pulleys there are idlers. The smaller roller type items shown just below the belt-carrying load are idlers. Idler rollers are either in sets of five, three, or two rolls. The belt conveyors can be flat or troughed belt conveyors in which the troughing angles can be from 15 to 45 degrees. In any case the belt should normally stretch over the idler uniformly. After discharging the load the belt returns back to the feeding end. The return belt also rolls over sets of idlers called a return idler.

l

l

l

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Take up screw: There are take up screws at both ends of the conveyor to adjust the tension or stretch out in the belt. Adjustments on both sides should be the same. Tension tower: For long and extra-long conveyors (motorized or hydraulically powered) take up pulleys are used to arrest belt sag and provide adequate tension through the length of the belt. These pulleys, along with auxiliary pulleys and accessories, are housed in a tension tower a few hundred meters away from the discharge end. They are normally hydraulically powered and controlled with take up pulleys used for cross-country conveyors for carrying limestone, coal, bauxite, or other mineral ores, etc. These conveyors may be as long as 10e15 km or even longer, normally pipe conveyors are used in such cases. In such an application multidrives (3e4) are deployed (could be with variable voltage variable frequency (VVVF) control on the discharge end). Tension control systems include the following: ○ Gravity towers; ○ Take-up winches; ○ Take-up trolleys; ○ Tension measurement devices; ○ Automatic tension control systems. Other components: Other components related to belt conveyors are skirt, feeding chute, discharge chute, protection devices such as a zero speed witch, pull chord, etc.

1.1.3 ROTARY FEEDER Rotary feeders are often referred to as an airlock device normally used in taking discharges from various silos, bins, or hoppers. In cement industries they find good applications. They can be classified either as feeders or air locks depending on the application; whether the regulated feed only is required or feed and air-tight boundary between upstream and downstream is required. In this section our point of interest is the rotary feeder. Airlock rotary valves are treated separately. To distinguish it is better to call this a rotary vane feeder. The sizing and shape of the pocket of the rotary feeder as shown in

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Fig. VIII/1.1.0-1C are dependent on the characteristics of the material to be handled and the required flow capacity of the rotary feeder. Rotary feeders are meant for handling solids with smaller sizes and are not recommended for handling solids with large particle sizes or if the solids are sensitive to abrasion by the feeding device. On account of the relatively smaller size and high conveying capacity, rotary vane feeders find their applications for metered discharging of a wide range of free-flowing bulk materials at very high volumetric rates from conveyors or from stored quantities in bins, hoppers, or silos and suffer only a small amount of wear. This is one of the main issues for which rotary feeders find good applications in industries. There are low-cost versions of rotary feeders for dust feeding applications. Such rotary feeders are designed to be used in dust collection hoppers and other low-pressure applications. In such cases feeders may be directly connected to the motor through a gear box. Normally rotary vane feeders have either a circular or rectangular inlet casing made of cast iron or stainless steel. They have a horizontally mounted rotor with a certain number of V-shaped cross-section compartments, a drive unit, and a casing cover opposite the drive end. There are some gravimetric applications where a rotary-vane feeder is used in conjunction with a belt type gravimetric metering system. In such a case, the upstream rotary vane feeder is provided with a variable-speed drive with, e.g., a digital control system (DCS) to regulate the volume flow. In this application the rotary vane feeder is used as the volumetric feed section in instances in which the material is aerated or has a low bulk density. For optimizing performance it is important to select a suitable rotor speed. 1.1.4 SCREW CONVEYOR/FEEDER The screw conveyor is one of the most versatile and cost-effective mechanical conveying systems, capable of handling not only dry solid materials but also semifluid materials. These screw conveyors are available in various configurations. The flour mill industry was probably the first to employ horizontal screw conveyors (or feeder) to convey corn and flour. It comprises of

a screw mounted in an enclosed U-shaped trough. In some designs there will be an inclined rotating casing. There is a shaft-mounted screw rotating in the trough referenced above, and a drive unit for running the shaft, and there are helical blades attached to the driving shaft. The material is moved forward along the axis of the trough by the thrust of the screw thread or flight. As shown in Fig. VIII/1.1.0-1D, a discharge opening is provided at the bottom of the trough. The loading and discharging points can be located anywhere along the trough. Through a rotating motion, it delivers a fixed volume. The screw may have a single or several sections. The screw conveyors have support bearing at tough ends, but if the length is too long there may be the necessity for more in-between supports. Drive units of screw feeder could be variable-speed drives for feed control of low density or aerated materials [4]. For uses in cases of fluidizable materials, such as alumina, cement can flow uncontrollably in the conveyor, therefore, screw conveyors/feeders should have a large diameter with short pitch, i.e., short distances between blades. For handling sticky and highly viscous fluids, such as sewerage sludge, a single flight ribbon screw is a better choice to avoid material deposition at joints. The screw conveyor can handle materials from free-flowing to sluggish and it is very cost-effective when compared with belt, pneumatic, and aeromechanical conveyors. Screw feeders can be used in weighing the materials also, i.e., a screw weigh feeder. 1.1.5 DRAG CONVEYOR AND APRON FEEDER 1. Drag conveyor: Drag conveyors can handle a wide range of bulk materials. The versatile design, coupled with energy-efficient drive, makes it possible to have a small footprint, saving space for handling a high quantity of materials. It is also possible to handle materials for long distances of up to almost 100 m. A typical drag chain conveyor has been depicted in Fig VIII/1.1.0-1E. With the use of suitable materials and their treatments, it is possible for drag conveyors to handle most abrasive materials. Also, in a drag chain it is possible to use a suitable liner to handle various

Solid Flow Measurement Chapter | VIII

kinds of applications. These are available both in flat or rounded bottom construction. It is possible to have an intermediate discharge so that multiple discharges are possible. It is supposed to be one of the best conveyors for dry free-flowing materials of different kinds. Clinker handling and chemical handling are popular applications of drag conveyors. The materials are static and only move en-mass by paddles or chains. It consumes less power and space than other choices. 2. Apron feeder: An apron feeder is another common feeder frequently used in many industrial applications. Apron feeders are used in conveying coarse bulk materials with fines, such as clinker, granulated blast furnace slag, or petroleum coke with crushers and reclaimers. They are also used for sticky materials. It is recommended that deep-drawn pan versions be used for these purposes. Other versions are also available. This can be used as solid flow also for solid flow measurements suitable load cell and speed sensor are necessary so that speed of the motor can be regulated to get controlled discharge e.g. cement side feeding or raw material feeding are examples of the same. An apron feeder consists of a stand of endless tractors made up of cast/fabricated steel pans bolted to link each stand. The chains are driven by a drive (speed control for weighing), connected to the chain through a reducer and sprocket at the discharge end. The pans travel with a chain and roll over the head sprocket to discharge materials. 1.1.6 VIBRATING FEEDER AND TABLE FEEDER Vibrating feeders and table feeders are two kinds of feeders regularly encountered in many industries, including the pharmaceutical industries. 1. Vibrating feeder: In vibrating feeders, vibration is one of the motive forces for material movement. In a vibrating feeder, vibration and gravity forces are used to move materials. In the principles of operation, the oscillating motion of the feeder/screen is imparted by the unbalance masses mounted on the extended

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shaft of the two motors rotating at the same speed but in opposite directions. These motors are placed symmetrically about a line at right angles to the motor base and pass through the center of gravity of the frame. Therefore, there will be a resultant force, on account of the unbalanced mass passes, to create displacement in either direction. The total displacement in either direction is called “stroke” [5]. Vibrating feeders are used where products are to be fed either continuously or in batches, such as despatching bulk materials from bins, feeding crushers, mixers, or conveyor belts, bucket elevators, vibratory screens, and loading and sorting plants. A trough is provided with wear-resistant liners which do not influence the quality and character of the product they handle. The slope and strokes are adjustable. The motors are an important component and should have good enclosure class, e.g., IP55, and the winding should be vibration-proof. A typical vibrating feeder is shown in Fig VIII/ 1.1.0-1F. The following issues are important for the sizing and design of the equipment: l Bulk density and particle size; l Inlet/outlet discharge conditions for the equipment, including placement of material on the feeder; l Application area and purpose, i.e., whether it is a batch process or continuous process, and also whether feeding equipment is a belt conveyor, bucket elevator; l Dimension of incoming stream of materials. The correct drive selection is very important for efficiency, long life, and low operating cost. 2. Table feeder: A table feeder is used in many industries including pharmaceutical industries, and typically consists of a power-driven circulated plate rotating directly below a hopper/ bunker. There will be a feeding collar immediately above the rotating table used in conjunction with an adjustable plough, to determine the volume of material discharged. The major components of a rotary table feeder are described here. The table will be fabricated thick SS/MS plates.

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Driving motor with reducing arrangement; Adjustable plough assembly; Guard ring assembly.

gear

3.

1.1.7 BUCKET CONVEYOR Bucket conveyors, similar to the one shown in Fig VIII/1.1.0-1G, are also known as bucket elevators. Bucket conveyors/elevators are designed for use in the transportation of powders or bulk solids of various kinds, vertically/steeply inclined plane even in a horizontal plane—but in a single plane. They use an endless belt or chain with a series of buckets attached to the belt or chain. Bulk materials are put through an inlet hopper. Buckets (or cups) dig into the material and convey it up and over the head sprocket/pulley, and then throw the material out through a discharge throat. Bucket feeding is done at a controlled rate. The buckets are returned back down to a tail pulley or sprocket at the bottom. Bucket conveyors/elevators are available in a variety of shapes, weights and sizes, and classes. Broad classification and description of bucket conveyor/elevators have been described here: 1. Centrifugal bucket elevator: Of the various bucket elevators, centrifugal bucket elevators are the most common. They are deployed to convey all free-flowing, powdered bulk solids, such as grains, animal feed, sand, minerals, sugar, aggregates, chemicals, etc. They operate at high speeds, which throw the materials from the buckets into discharge throats by centrifugal force. 2. Continuous bucket elevator: As continuous bucket elevators operate at slower speed, they can be used for handling friable, fragile materials because they minimize product damage or are used to handle light fluffy materials where aeration of the product must be avoided. On account of the continuous bucket placement, the force of gravity can be utilized for discharging load onto the inverted front of the proceeding bucket. The bucket then guides that material into the discharge throat on the descending side of the elevator. Because every

4.

5.

6.

bucket application is unique, selection of the proper type of bucket elevator depends largely on the capacity requirements and the characteristics of the material. Positive discharge elevators: Except two distinguishing features, positive discharge type bucket elevators are similar to the centrifugal discharge elevators. The buckets are spaced at a regular pitch and mounted on two strands of chains, and are provided with a snub wheel under the head sprockets to ensure inverting of the bucket for complete discharge. The speed of the bucket elevators is slow. These are quite suitable for handling light, fluffy, dusty, and sticky materials. The feeding is done by the digging of the buckets. Horizontal discharge: These are mainly used to handle granular materials such as in flour mills, animal feed, etc., for transferring the materials into silos. These are often used in mineralhandling applications in vertical/inclined and horizontal planes. Generally they are made from steel and are used for high-capacity material handling. Major parts: The major parts/components of bucket conveyors/elevators include the following: l Head; l Cover; l Belt/chain; l Bucket; l Drive unit; l Reducing unit. Major application areas: The following are the major application areas of bucket elevators: l Ammunition/explosives; l Animal feed; l Bottle caps/fasteners; l Frozen food products; l Grains; l Capsules/tablets; l Cement plants; l Carbon black; l Coal/sand/clay/lime; l Tobacco; l Dry chemicals.

Solid Flow Measurement Chapter | VIII

1.1.8 DIVERTER GATE VALVE, DOUBLE FLAP GATE, AND ROTARY AIRLOCK VALVE A few other pieces of equipment, like diverter gate valves, double flap valves, and rotary airlock valves that are used frequently in solid material-handling systems are briefly discussed below. 1. Diverter gate valve: A diverter gate valve is used for the selection of outlet ports in solid material handling by the position of the diverter flap. Diverter valves are designed to direct product flow outlets of storage bins, silo conveyors, gravity flow chutes, and other discharge points. These valves are available with three-positional control on the diverter. An intermediate position can be used for splitting the flow. Technical details and major application areas are as follows: l Technical details: Since it may have to handle falling abrasive materials, it has to be very rugged in design. Normally, they are made up of MS casing but other materials can also be used depending on the application. There can be a lining based on the application and material characteristics. CS and SS are common materials used for valves. Such diverter valves can be manual and/or be with an actuator, which can be electric or pneumatic. l Application: As the name suggests, it is used to determine the outflow of bulk, free-flowing material from a bin/hopper, bag filter, silo, etc. Cement, chemicals, mining, mineral process, textile, paper, food grains, and other industries use them. 2. Double flap valve: Double flap valves are used for achieving airlock sealing with controlled feeding. These valves consist of two independent flap valves mounted one upon the other, with their opening and closing alternated and synchronized to ensure that only one valve opens at a time, as shown in Fig VIII/1.1.0-1H. The upper valve chamber

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holding volume and the rate of operations determine the throughput of the valve. These are slow-operating valves, and thus show a batch feeding pattern. The selection of cone or flap depends on the characteristics of the material to be handled and the system requirement, such as pressure sealing. The cone valves usually have a round opening, whereas flap valves can have square openings. l Technical details: Normally MS are used for fabrication of these valves, but other materials are also possible. These valves can have liners to handle corrosive and abrasive materials. Flap valves can be of different inlet sizes from 200 to 500 mm. Double flap valves only leak due to the volume of high-pressure air trapped between the two flaps after the bottom flap has opened and closed. The gas between the two flaps can be purged if necessary before actuation. Valves are closed by a counterweight normally, so they require power only for opening. The valves are normally available with both electric and pneumatic actuators and are connected to DCS for control and operations. l Applications: Double flap/cone valves are used for extracting bulk material from bins, which are maintained at a pressure different to the external pressure. The bottoms of ESP hoppers and bag house hoppers are typical locations for these valves. As the valves can handle fine dusty or grainy materials, such as cement, crushed ore, sugar, minerals, grains, plastics, dust, fly ash, flour, gypsum, lime, coffee, cereals, pharmaceuticals, etc., they find their applications in industries including cement, steel, power, chemicals, mining, mineral process, textile, paper, food grains, etc. 3. Rotary airlock valve: Rotary airlock valves are used in bulk handling systems for freeflowing dry powder, granular, crystal or pellet forms of materials. Rotary airlocks are suitable for fitting below a chain conveyor/screw

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conveyor/hopper/silo/bag filter/ESP/bin, etc. Two major functions of rotary airlock valves are to seal and prevent the possibility of back flow of material in a pressurized system and to provide a rated drop-through discharge. The volume of the “V chamber” and the speed of operation determine the capacity of discharge of rotary airlock valves. Material density, material flowability, and desired capacity are major issues for the design of rotary airlock valves. l Technical details: Rotary airlock valves are available in different sizes from 200 to 900 mm, to accommodate material capacities of over 300 tons/h (TPH). DEMECH can supply rotary airlock feeders from 1 TPH to 300 TPH capacity and inlet sizes ranging from 200 to 800 mm in round or square shapes. Generally, rotary airlock valves are made up of MS, but other materials are also used. They are also available with a hard lining. The vane edges are provided with replaceable tips of flexible material, such as spring steel, to achieve a good sealing. These are normally available with a motorized actuator with a reducer either in direct coupling or chain arrangements. l Applications: Rotary airlock valves are used for handling various materials—typically, cement, ore, sugar, minerals, grains, plastics, dust, fly ash, flour, gypsum, lime, coffee, cereals, pharmaceuticals, etc. Thus they find their applications in industries like cement, chemicals, mining, mineral process, textile, paper, food grains, power, etc. 1.1.9 MISCELLANEOUS MECHANICAL EQUIPMENT AND DEVICES Apart from the various pieces of equipment discussed above, there are a few other equipments and devices used for solid material handling, such as shaker feeders, roller feeders, etc. There are other devices also necessary for regulating solid flow and maintain pollution. Such devices include but not limited to dampers and bag dust collectors of various kinds. At each transfer point

in solid material handling, especially for fine and powder solids, bag dust filters are used. There are various bag dust collector designs, such as regular hopper entry, tangential entry, etc. Also, they contain a bag dust collector with pulse jet online/ offline types. There are different kinds of dampers, i.e., nonreturn flap, guillotine damper, biplane damper, biplane damper, Louvre damper, butterfly damper, and coffee pot damper. These dampers can be manual or actuator-operated. Actuators may be pneumatic or motor-operated. With this the discussions on mechanical equipment come to an end, so as to look into the details about material characteristics which are very important for solid flow measurement. 1.2.0 Material Characteristics for Solid Flow The discharge flow patterns of feeders/conveyors vary with material characteristics as well as discharge type, style, and conveyor speed. In the case of solid flow, size and material characteristics are very important issues in selecting the conveying equipment and flow measurements. When the material sizes are large there may be a problem with its discharge, weight, etc., because when they are discharged from a height it may cause problem, e.g., there could be an issue with ripping of the belt due to sharp edges or an issue related to getting stuck at any transfer or discharge point. However, such issues are rather simpler to tackle. More problems may come from very fine/powder solids. Apparently they show good flowability but the material characteristics play a great role in flow and flowability. This will be clear from an example; materials like sulfur become compacted very quickly, even under normal conditions, in contrast, many other materials become compacted only under pressure due to a heavy load (weight of the material) in the storage space. When fine materials become compacted their flow from storage will not be uniform, unless some external means, such as a vibrator or fluidizing by air, is applied to them. A granular free-flowing material, e.g., wheat/sugar will flow smoothly off a conveyor even at

Solid Flow Measurement Chapter | VIII

low speeds. Meanwhile other materials, for example, sulfur, with a higher possibility of becoming compacted, or materials with a high angle of repose, may drop off in a nonuniform pattern or even in lumps, especially at low speed. From these examples it is clear that as with fluids in cases of bulk/powdery materials, there is a necessity for some shearing forces. In this section brief discussions will be presented on material characteristics and associated influencing factors. These will help in understanding the necessity for variations in equipment type and styles covered in the above section. 1. Solid flow properties: The solid flow properties depend on several parameters, including the following: l Particle shape and size: Varies from needlelike to spherical, dependent on sphericity, equivalent volume/surface diameter, etc.; l Particle size distribution is important for the strength of bulk solids; l Chemical composition of the particles; l Moisture content (liquid bridge); l Temperature. Some of these properties are discussed later. Theoretically it is not possible to determine the flow behavior of solids and their dependence on various parameters indicated above. Such dependences are determined with the help of a suitable testing arrangement. 2. Uniaxial compression test: The flow of solids in powder or fine forms is rather complex. For bulk solids “flowing” means that a bulk solid is deformed plastically due to the loads acting on it (e.g., failure of a previously consolidated bulk solid sample). The magnitude of the load necessary for flow is a measure of flowability. As discussed above, theoretically it is not possible to determine flow behavior, so these need to be demonstrated first with the uniaxial compression test. If a hollow cylinder filled with a fine-grained bulk solid is compressed vertically, one will observe that with an easy-flowing, dry bulk solid with large, hard particles, i.e., wheat grains, the bulk density will increase very little. With a fine and/or moist bulk solid (e.g., flour, moist sand), one

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will observe a clear increase in bulk density. In addition to the increase in bulk density from consolidation stress, one will also observe an increase in the strength of the bulk solid specimen. Hence the bulk solid is both consolidated and compressed through the effect of the consolidation stress. After this, if the bulk is relieved of the consolidation stress and then again the cylindrical bulk solid specimen is loaded with an increasing vertical compressive stress, the specimen will break (fail) at a certain stress. The stress causing failure is called compressive strength. In bulk solids technology one calls the failure “incipient flow,” because at failure the consolidated bulk solid specimen starts to flow. The bulk solid dilates somewhat in the region of the surface of the fracture, since the distances between individual particles increase. From here one can infer that incipient flow is a plastic deformation (refer to Chapter VII) with a decrease in bulk density. In addition to consolidation stress, consolidation time is also important. 3. Time consolidation (caking): Some bulk solids, such as sulfur or garlic powder, continue to gain strength if stored at rest under compressive stress for a longer time interval. This effect is called time consolidation. The following issues are responsible for time consolidation [6]: l Solid bridges due to solid crystallizing when drying moist bulk solids, where the moisture is a solution of a solid and a solvent (e.g., sand and salt water); l Solid bridges from the material itself; and after some material at the contact points have been dissolved by moisture, i.e., crystal sugars with slight dampness; l Bridges due to sintering during storage of the bulk solid (temperatures very near melting point), e.g., some plastic materials; l Plastic deformation at the particle contacts, hence there is an increase in adhesive force and larger contact area; l Chemical processes/reactions; l Biological processes (e.g., due to fungal growth).

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In the next section, various forces and their actions on bulk solids are discussed. 1.2.1 FORCES AND STRESSES IN BULK SOLIDS DURING FLOW In this section the changes in bulk solid characteristics with applied forces and stresses are discussed to give idea about the material characteristics of the same. 1. Stress in bulk solids: In the case of bulk solids, flow behavior may be similar to that for a fluid, but it cannot be analyzed as a Newtonian fluid. This is very clear from a simple example; if the bulk solid were to behave like a Newtonian fluid, the stresses in all directions would be equal in magnitude but in reality it is not be so for a solid material. In bulk solid materials, on account of vertical stress from the top there will be stress in the horizontal direction also and such stress will be less than the vertical stress. As vertical stresses are increased the interparticle space will tend to change and horizontal stress will develop. Also, it can be observed that in a bulk solid different stresses can be found in different cutting planes. This behavior shows that bulk materials cannot be treated as fluids and instead bulk materials are analogous to solids. Thus the behavior of a bulk solid is quite different from that of a fluid. Stress conditions in solids at different planes can be found with the help of a Mohr’s circle as explained in Fig. VIII/ 1.2.1-1. The procedure for finding the stress conditions at different planes is available in any standard book on mechanics.

2. Adhesive forces: Adhesive force is very predominant in bulk solids, so, in the case of bulk solid materials, this force plays an important role in the sense that flowability of the bulk materials will be affected on account of the adhesive forces between individual particles. For fine-grained, dry bulk solids, the flow properties are mainly influenced and guided by adhesive force due to the deforming force for fine-grained solids, popularly known as van der Waals interaction adhesive force and liquid bridges. Liquid bridges are formed by small regions of liquid in the contact area of particles, in which, due to surface tension effects, a low capillary pressure prevails to create the adhesive force. In addition to liquid bridges, van der Waals’ cohesive forces can also occur from electrostatic and magnetic forces. Both adhesive forces are dependent on particle size and on the distance between particles. Therefore, one may conclude that the reason for an increase in flowability of bulk solids with an increase in particle size is due to adhesive force. Conversely, it can be said that with a decrease in particle size the strength of bulk solids increases. The flowability of bulk solids also depends on the relationship of the adhesive forces to the other forces acting on the bulk solid. The outside compressive force acting on a bulk solid element can increase the adhesive forces. This mechanism is used, e.g., in the production of tablets or briquettes [6]. 3. Wall friction: Wall friction is the friction between a bulk solid and the surface of a solid, i.e., the wall of a silo/hopper/bin. The wall

Mohr’s circle: Mohr’s circle indicates the principal angles (orienta ons) of the principal stress in solids. It is a graphical representa on of plane stress strain condi ons. With the help of Mohr’s circle the stress components can be found, i.e., the coordinates of stress point on the circle, ac ng on the plane passing through it.

FIGURE VIII/1.2.1-1 Mohr’s circle.

Solid Flow Measurement Chapter | VIII

friction angle or coefficient of wall friction plays an important role not only for storage vessel design but also for solid flow. Based on the wall friction angle, depending on the required discharge, decisions are taken during vessel design, whether or not the polishing of the wall surface or the use of a liner has advantages in the flow of the bulk solid [6]. Even the shape of the wall of a storage vessel may be influenced by the wall friction coefficient. With this idea of the various forces acting on particles, it is time to look into the flowability of bulk solids, especially fine particle solids or powdered materials. 1.2.2 FLOWABILITY OF BULK SOLIDS From the above discussions, it is clear that the physical properties and characteristics are extremely important for flow of granular bulk solids. Also, it has been noted that not only handling equipment but also storage of materials is important for bulk solid flow. Definition of flowability: Like fluid flow, powder and fine bulk solid flow is complex and multidimensional and is highly dependent on bulk solid characteristics. On account of this it is not possible to quantify flowability by any single test nor is it possible to express the same as a single value or index. In fact, flowability is not an inherent material property at all [7]. Both physical properties of material affecting flow and the equipment used for handling, storing, or processing the material are responsible for the flowability of powder or fine-grained bulk solid materials. Thus it is needless to argue that equal consideration should be given to both the material characteristics and the equipment. Therefore, a more accurate definition of powder flowability is the ability of fine solid materials to flow in a desired manner in a specific piece of equipment. In view of this, the loosely used term free flowing becomes meaningless unless the specific equipment handling the material is specified [7]. The specific bulk characteristics and properties of a powder that affect flow and that can in principle

695

be measured are known as flow properties, e.g., cohesive force and wall friction as discussed above. From the above discussions it transpires that there are two factors, one is equipment associated with solid flow already covered in Section 1.1.0, also various forces related to flow have been covered in Section 1.2.1. Now discussions will be on various other properties related to flowability. 1.2.3 PROPERTIES FOR FLOWABILITY OF BULK SOLIDS The storage, handling, and flow of bulk solids, especially fine materials, are important in all industries, especially for agricultural, cement, ceramic, food, chemical, metallurgical, mining, pharmaceutical, and other bulk solids and powder-processing plants. Flow is defined as the relative movement of a bulk of particles among neighboring particles, or along the wall surface of a container (Peleg, 1977). Since flow properties and bulk material storage, handling, and processing equipment go hand in hand to achieve the desired flowability, it is important to gather some knowledge on the various parameters, such as angle of repose, bulk density, angle of internal friction, cohesion, and compressibility, etc. In this section these points shall be discussed. This discussion supplements the discussions presented in Section 1.2.1. 1. Angle of repose: As already indicated in Fig. I/3.2.1-4, the angle of repose (AR) is defined as the angle between the horizontal and the slope of a heap of granular material dropped from some designated elevation. The angle of repose is very much qualitatively related to the flow properties of that material, and is a direct indication of potential flowability. The angle of repose of a bulk solid can be described using the following equation: M þ csg þ d (VIII/1.2.3-1) tan[r ¼ an2 þ b$ Dav where Ør is the angle of repose (degrees); n is shape factor based on specific surface ();

696

Plant Flow Measurement and Control Handbook

M is moisture content (db %); Dav is average particle diameter (cm); sg is specific gravity (); and a, b, c, and d are empirical constants. From the above equation it is worth noting that with an increase in moisture content the angle of repose increases. The angle of repose is related to the bulk density and surface area, etc. From the study of documents in pharmaceutical industries where flowability and angle of repose for powders are tested it can be seen that an angle of repose between 25 and 30 degrees gives excellent flow behavior and between 30 and 35 degrees it is good but starts worsening above 40 degrees and above 50 degrees it is poor. 2. Bulk density: The bulk density of granular solids and powders is not only important for determining the volume of transport/storage vehicles but is also important for flowability of materials. From the discussions in Subsection 1.2.0.2 it has been noted that bulk density is a function of both particle size as well as handling and processing operations. Bulk density also depends on moisture and chemical compositions. Bulk density is defined as the mass of particles that occupies a unit volume of a container. Increases in bulk density have been observed when conditioners are added (Peleg and Mannheim, 1973; Hollenbach et al., 1983), which results in modification of density by lowering the interparticle interactions [8]. The bulk density of many materials, such as food powders, decreases with an increase in the particle size, as well as with an increase in equilibrium relative humidity. Porosity, which is related to bulk density, can be expressed as the percentage of voids in a bulk solid: Pð%Þ ¼ ðV  Vp Þ$100=V

(VIII/1.2.3-2)

where P is porosity (%); V is bulk volume of the bulk (cm3); and Vp is particle volume of the bulk (cm3). P is affected by the flow of the granular material. As porosity decreases, bulk density increases (Sjollema, 1963).

3. Frictional force: A measure of the force required to cause particles to move or slide on each other can be obtained from the internal friction, i.e., the angle of internal friction. Stable slopes in bins are highly dependent on the angle of internal friction (Johanson, 1971/72). Particle surface friction, shape, hardness, size, and size distribution are major issues and influential factors for internal friction. Angle of internal friction data are an important parameter for the design of gravity flow bins and hoppers (Mohsenin, 1986; Rao, 1992). This is already discussed in Section 1.2.1 also in connection with wall friction. 4. Compressibility: Much attention has been given to the behavior of bulk solids under compressive stress and this has already been covered in Subsection 1.2.0.2. This is a very important factor for flowability. There are a numbers of other factors which also influence the flowability of bulk solids/ fine powders and these will be covered in the following section. 1.2.4 FACTORS INFLUENCING FLOWABILITY OF FINE BULK SOLIDS Flowability is a factor for several processes in process and industrial plants. This will be clear from an example. In the pharmaceutical industry blending is tremendously important for the final blend. This blending not only depends on the type of blender used but also on the flow behavior of the powder during the blend cycle. Therefore, the importance of flowability and associated factors affecting it cannot be overestimated. From earlier discussion it has been established that flowability of powder/fine granular bulk solids is a consequence of the combination of a material’s physical properties, the equipment used for storage, handling, and processing these materials, and environmental conditions. In this section brief discussions are presented on these and other environmental factors. 1. Particle size: As indicated in the initial discussions, particle size and particle size

Solid Flow Measurement Chapter | VIII

distribution have a direct significant effect on flowability and other properties like bulk density, angle of repose, and compressibility of bulk solids (already discussed). Also, it has been discussed that a reduction in particle size often tends to decrease the flowability of a given granular material due to the increased surface area per unit mass [8]. An increase in particle size generally leads to an increase in compressibility with lesser changes in bulk density. 2. Moisture: With moisture absorption, materials often show increased cohesiveness on account of liquid bridges, as discussed earlier. According to Johanson (1978) moisture content thus affects the cohesive strength and arching ability of bulk materials. Moisture often modifies the physical properties of a material and can behave differently. This will be clear from two examples from Ref. [8]: the angle of internal friction of zinc ore was found to be 32 and 56 at 18% and 23% moisture contents, respectively [8]. Also the unconfined yield strength of sugar increased sevenfold as the moisture was increased by only 3% [8]. From the discussions one could infer that with an increase in moisture, the bulk density of granular solids generally decreases and the compressibility increases. 3. Humidity: The relative humidity of the air is an environmental factor, influencing material storage in bins/hoppers or silos, because humidity affects bulk material properties. Many bulk materials are hygroscopic and thus the exposure to higher humidity results in increased moisture content in the bulk materials. As a direct consequence of this there will be an increase in the bulk strength and angle of repose, and hence a decrease in flowability. Therefore, one can conclude that there will be a significant effect on the cohesiveness of granular powders, and so the flowability will be reduced. When the materials are stacked outside, as the author faced in Jordan (for limestone shale stacks), then during winter the materials used to absorb a lot of moisture (especially for snow/rain fall) and hence raw

4.

5.

6.

7.

697

meal feed was a serious issue from a flowability point of view. In all intermediate storage hopper vibrators were installed to extract materials which during summer days were easy flowing. Temperature: Temperature also has a substantial effect on bulk solid flowability. The most drastic temperature effect is the freezing of the moisture contained within the granular materials and on particle surfaces [8]. Therefore, whenever possible the materials should be kept at a temperature around 30 C above freezing to avoid the adverse effects of temperature on flowability. Caking effect can occur when there are changes in crystallinity or other properties due to temperature variations. Also, the temperature of the wall and bulk material may change the friction angle. Pressure: Compacting pressure is also an important factor that affects the flow properties of bulk solids. The bulk may be subjected to compaction on account of the pressure impact from a falling stream of solids during silo filling and/or external loading. The effect of pressure on flowability of powders is twofold [8]: l Higher pressure may lead to a larger number of contact points between particles, and hence more interparticle adhesion. l Increased compaction produces a significant increase in critical arching dimensions and overpressure effects are nonlinear, and hence vary significantly with the sample. Anticaking flow conditioner: According to BarbosaCanovas and Yan (2003), caking is defined as being when two or more macroparticles, each capable of independent translational movement, make contact and interact to form a congregate in which the particles are incapable of independent translations [8]. To improve flowability, at times anticaking agents are commonly used as additives to assist a powder in maintaining a steady flow and/or to increase its flow rate. Flow conditioners are chemically inert substances which are added for a similar effect. Fluidization: This is often used to increase flowability or for fluidized-bed processing

698

Plant Flow Measurement and Control Handbook

which shall also include processes such as granulation and drying. In cement plant, pharmaceutical plants such phenomenon is common. Material extraction from raw meal silo or cement silo fluidization is adapted for extraction of fine materials from tall silos. 8. Fat content: This is mainly applicable for organic food, food grains, etc. Free surface fat is expected to play a key role in granular flowability but has not quite been established. One may conclude that flowability of fine granular solid materials is extremely important for most industries. In the case of the pharmaceutical industry it is essential to ensure consistent feed at all times, i.e., separation of a small quantity of powder from the bulk for the creation of individual doses such as during tableting and vial filling, feed consistency to and through the equipment governs the uniformity of weight of the dose [7] and so is an absolute necessity. Material testing is critical for successful delivery of an engineered solution to meet the specific requirements of powder or fine granular bulk solids handling needs. As stated earlier, to obtain the correct material properties, testing is done. However, this is purely a part of the design of the material-handling system and so no further discussions are warranted from an instrumentation point of view. With this the discussions on material characteristics come to an end. The discussions in Chapter I Section 3.2.0, where principles of operation of various kinds of solid flow meter types have been described, should be recalled to see how different instrumentation technologies are deployed to measure various kinds of solid flow. With the primary knowledge on various meter types and mechanical and material details it is better to compare various technologies deployed for solid flow measurements so that the intricate details of various solid flow meters discussed in subsequent sections will be meaningful to the reader.

1.3.0 Evaluations of Various Technologies for Solid Flow Metering There are several ways and means for solid flow measurement in process and industrial plants. In the subsequent sections these will be discussed at length, i.e., discussions on in-motion weighing systems—continuous solid flow systems as mentioned in Section 1.0.4. There are many technologies involved in such measurements, such as weighing feeders, solid flow meters, and radiation type measurements. The discussion starts with weighing feeding systems and their comparative studies. 1.3.1 COMPARISON OF VARIOUS WEIGH FEEDER TYPES The option of flow measurement while feeding or conveying is always preferred. In order to address such an issue several weigh feeder types are used. These can be a belt scale/belt weigher, weigh feeder, apron weigh feeder, or screw weigh conveyor (feeder). Both the belt scale/belt weigher and weigh feeder use a belt conveyor in conveying material with the only difference between them being the control of drive speed. In the case of a belt scale/belt weigher, it is used for feeding/ conveying with a provision for measurement of solids conveyed without any control on the conveying materials, i.e., there is no control of feeder speed. In contrast, in the case of weigh feeders, they have driving motors used with a suitable and sophisticated drive speed control system to feed or convey a metered quantity of solid materials — as already indicated in Fig VIII/ 1.1.0-2. As already discussed in Section 1.1.0, screw conveyors and apron feeders have different ways and means to convey materials. In these cases it is also possible to measure and even control the quantity of materials conveyed. Therefore, these are called screw weigh feeders and apron weigh feeders, respectively. Table VIII/1.3.1-1 compares weigh feeding systems, showing the various pros and cons of different weigh feeding systems.

Solid Flow Measurement Chapter | VIII

699

TABLE VIII/1.3.1-1 Comparison of Weighing Systems Issues

Apron Weigh Feeding

Features

l

l

High temperature with-stand capability. Temperature up to nearly 700 C Used for bulk materials with fines and sticky materials

Capacity

Capacity w2500 t/h

Challenges

l

l

Belt Weigh Feeding l

l

l

Screw Weigh Feeding

Flexible design with varying width and length Capable of handling wide varieties of materials Available in open and closed versions

Capacity w850 t/h

Too many moving parts hence maintenance prone Large area required as it has larger footprint

l

l

I am very tempted to quote the famous saying of Matt Morrissey, Product Manager, Weighing Technology Siemens; “Solid flow meters are interesting solutions to indicate flow rates in pipe and chutes.” According to him these flow meters are as good as the whole process around them [9]. There are a number of solid flow meters, such as the impact flow meter, centripetal flow meter, Coriolis flow meter, capacitance flow meter, and microwave flow meter. In this section short discussions are presented on these. Impact and centrifugal flow meters are very similar. In impact scale, normally the horizontal component of the impact force is measured either by LVDT or

l

Can be totally sealed and well applied for sanitary applications Flexible in length; compact in design with short footprint

Capacity 0.35 t/h (performance unaffected by density but min. for operation)

8

Materials of construction

Aluminum (6061) or stainless steel (SS). SS liner with different coating for guide, SS measuring pan (detachable). Meter body and casing can be SS304/316

9

Sensing

Basically load cell quantity varies with models and manufacturers

10

Compensation

Automatic compensation

11

Output

4e20 mADC, cumulative pulse frequency and smart version supports: Fieldbus communication (e.g., PROFIBUS/Foundation Fieldbus) available. Capable of supporting Ethernet and other industrial networks, e.g., Devicenet

Standard/Available Data

User Spec.

Remarks

Friction

Continued

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Plant Flow Measurement and Control Handbook

TABLE VIII/2.1.4-1 Specifications for Centripetal Flow Meterdcont’d SL

Specifying Point

User Spec.

12

Output function

Rate flow, totalized flow, alarm, remote reset, zero adjustments

13

Display and operator function

Digital display, operator reset, calibration, plotting, trending, HMI support, programming

14

Detachable electronics unit

SS different grades

15

Enclosure class

IP 68

16

Power supply

Standard power supply 240 VAC/24 VDC

17

Hazardous application (refer to author’s book*)

ATEX FM load cell and suitable electronics

18

Connection and Mounting Details

19

Flow types

Standard/Available Data

For both in-line flow with transition* and reverse flow

Remarks

*[2]

*Refer to Fig. VIII/ 2.1.0-1B

Performance and Other General Details 20

Accuracy

0.25% AR to 1% AR

21

Reproducibility

0.1% AR

22

Turndown

1:20 standard

23

Field calibration

Remote

24

Certification

CE and other competent authoritiesdas per manufacturer

25

Accessories

Transition and other mounting accessories as required

26

Special feature

Adjustment of pan angle and others if any

(Fig. VIII/2.1.0-1B) for horizontal feed, the direction of flow is not reversed but is the same as at the meter outlet with respect to feed. For in-line flow, transitions are installed as shown in the figure. We now look for another kind of mechanical solid flow meter working on the Coriolis principle.

(Sensing error 0.017%)

2.2.0 Coriolis Solid Flow Meter From Chapter VI, a fairly good idea about the Coriolis force has been gathered. The same Coriolis force is not only utilized in fluid mass flow measurement but is used for measurement of solid mass flow. In this section discussions on Coriolis solid flow meters are given.

Solid Flow Measurement Chapter | VIII

2.2.1 THEORY OF OPERATION

ARM

LOAD CELL

LOAD CELL ARRANGEMENT DETAILED OUT METER INLET

SWIVELLING PART

DRIVE SHAFT

MOTOR SWIVEL PLATE

MOTOR

LOAD SENSOR

The basic theory behind the operation of this meter is that it uses the material’s flow energy through the meter to create a force popularly known as Coriolis force. This force through the transducer is converted into an electrical signal, which is proportional to the flow rate. The Coriolis force is the force that acts upon a particle accelerating radially outward in a rotating system (frame). This force acts perpendicular to the direction of motion of the particle and is directly proportional to the torque required to accelerate the particle to the circumferential velocity of the rotating system (see Eq. I/3.2.1-4). There are two other forces, frictional force and centrifugal force. These two forces are in different planes and cancel each other out, as depicted in Fig. I/3.2.1-1C. There is a motor located above and outside the flow-measuring enclosure. This motor is connected to a measuring wheel by a shaft to rotate the same at a constant angular velocity. This motor is also connected by a force transmission arm, as shown in Fig. VIII/2.2.0-1, to the loadsensing system (complete with load cell and associated electronics) for determination of instantaneous torque delivered. Material, which is fed from the top of the inlet, flows downward into the top of the measuring wheel. On account of the rotational motion of the measuring chamber by the motor, the materials are diverted outward in a radial direction. Therefore, the guided particles moving vertically are accelerated in a circumferential direction. As indicated earlier, there are three kinds of forces: centrifugal force, Coriolis force, and frictional force. As detailed in Chapter I (Subsection 3.2.1.3 and Fig. I/3.2.1-1C), frictional and centrifugal forces are along the surface of the vane and the Coriolis force is perpendicular to it. Frictional and centrifugal forces not only cancel each other out but at perpendicular, and hence have no effect. Therefore, the measuring principle ensures that frictional forces (between material and measuring wheel or between different material layers) do not affect the flow

FORCE TRANSMISSION

707

DEFLECTING CONE

MEASURING WHEEL INLET MEASURING WHEEL

COLLECTION CHUTE METER OUTLET

FIGURE VIII/2.2.0-1 Coriolis solid FM details. This detailing is based on an idea from T.D. Fahlenbock, Coriolis Mass Flow Meter: High Accuracy for High Flowrates, Brabender Technologie; Powder and Bulk Engineering, September 2005.

measurement and hence there is no question of friction force compensation (as in centripetal flow meters) for this type of flow meter. Also, the physical properties of the material, such as density, friction and impact coefficients, particle size, temperature, and moisture content, do not influence the accuracy or sensitivity of the meter [11]. The repeatability of the meter is also very good. The meter is suitable for both continuous as well as batch operations.

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Plant Flow Measurement and Control Handbook

2.2.2 DESCRIPTIVE DETAILS OF CORIOLIS SOLID MASS FLOW METERS A typical Coriolis solid mass flow meter, consists of a cylindrical housing with an inlet at the top, measuring wheel chamber (with shaft, swivel plate motor), deflecting cone, collection chute, and an outlet at the bottom, below a conical collection chute, as shown in Fig. VIII/2.2.0-1, with important components duly marked therein. At the top of the housing there is one AC motor mounted on a swivel plate through which the driving shaft of the motor extends into the housing. The swivel plate is mounted on flexures that move in one direction in response to force [12]. The drive shaft should be properly sealed to make the system dust-free. At the bottom of the driving shaft is the measuring wheel which is a vaned wheel/chamber. The vanes of the measuring wheel capture the material flow and accelerate the material particles to the rotation velocity. Because the drive motor speed is constant, the flow rate of particles exiting the wheel is constant [12]. The materials coming out of the measuring wheel impact the walls of the conical collection chute and flow downward through the outlet. When there are changes in the flow rate, there is a change in the torque of the motor to accelerate the changed quantity of materials. The changes in torque are transmitted to the load cell mounted on the housing top through a bar-like horizontal extension from the swivel plate, called a force transmission lever to restrict swivel movement. These are separately detailed in Fig VIII/2.2.0-1 (top side). The motor and load cell are controlled through remotely connected electronics. The footprint is moderate—even less than loss-in-weight feeders. When the material mass is accelerated by the measuring wheel’s vanes, there will be Coriolis force on the motor. A back torque will be generated by the motor to oppose the Coriolis force. As the motor is firmly mounted on the swivel plate and transmission lever, the motor can counter-rotate only slightly as the flexures bend slightly. Therefore, torque is measured with the help of the load cell connected via a transmission bar. Thus, measured force is directly proportional to the mass flow. At the remote electronics mass flow rate is

computed by multiplying mass (which changes motor torque; sensed by load cell) with the velocity of the drive. The uniqueness in the Coriolis flow meter is that the material flow velocity is accelerated in the measuring wheel (running at constant velocity of the motor) so that material exits the flow meter at the measuring wheel’s tangential velocity. In other words, the flow velocity is generated by the flow meter itself, making the flow velocity constant. In order to get good accuracy, feeding equipment is extremely important, because this is influenced by material characteristics. Coriolis measuring systems can be successfully applied to almost all kinds of pulverized materials, dusts, and granules such as cement, fly ash, filter dust, lime powders and hydrates, ground slag, silica, and marl, etc. 2.2.3 FEATURES AND APPLICATION DETAILS In this section, the features and application details of Coriolis flow meters are discussed. 1. Features: This is quite a versatile slide flowmeasuring instrument, widely used for the measurement of dust and granular materials. However, there are also a few limitations to this meter. For highly abrasive material the meter may not be suitable as the blades may be worn out quickly, calling for quick replacement. Also, large particles may become jammed at the discharge, so another limitation comes from the particle size. Other than these, the meter generally is very good for powdery materials with good accuracy at a high flow rate. Since it is suitable for pneumatic conveying it can withstand pressure up to 10 bar. This flow meter is especially suitable as a high-accuracy flow meter in high flow capacity. Some major features are listed here: l Reliable, highly accurate; l Insensitive to properties such as density, friction and impact coefficients, particle size, temperature, and moisture content; l Good control quality; l Economical with low capital and operational costs; l Simple for system integration;

Solid Flow Measurement Chapter | VIII

Compact construction; l Dust-proof housing; l Immune to external forces; l Ecologically beneficial; l Practically emission-free; l Low power consumption; l Supports pneumatic feeding. 2. Applications: From an application point of view, one can argue that the Coriolis solid flow meter is unique for dust and granular solid materials requiring high precision at a high flow rate. Coriolis solid mass flow meters find their applications in total material flows for batch control and load-out applications. This meter is also suitable for continuous flow measurement with a variety of valves or prefeeders with variable-speed controls. Therefore, the meter can be applied in many plants and can be utilized for the following: l Measuring throughput/consumption; l Delivery of volume feed rate; l Gravity-driven feeding systems; l Cement industry, for a variety of pulverized materials; l Coal feeding in power plants; l Plastic and chemical industries; l Pharmaceutical plants.

709

It is worth noting that at many places, especially in a cement plant, this meter is gaining popularity. There have been reports that in many places pneumatically conveyed kiln feed measurement by impact scales has been replaced by Coriolis to get rid of the pressure and ventilation differences across the meter and to reduce the sucking effect on the meter.

l

We now look into the specification of Coriolis solid flow meters. 2.2.4 SPECIFICATION OF CORIOLIS SOLID MASS FLOW METER A typical specification for a Coriolis solid mass flow meter has been given in Table VIII/2.2.4-1. It is worth noting that as the specification is a general one, all data will not necessarily match with any particular instrument that is chosen. As it has been attempted to pool the best possible data from different manufacturers naturally there will be deviations from actual instruments. The specification given is just a guide and the reader should specify the requirements for a specific instrument bearing in mind the application in hand.

TABLE VIII/2.2.4-1 Specification for Coriolis Solid Mass Flow Meter SL

Specifying Point

Standard/Available Data

1

Solid type

Dry free-flowing granular, powdery, grain bulk solids. Usually meant for sluggish but nonsticky materials

2

Feeding equipment

Star feeder, valve, and many other prefeeding systems

3

Design temperature

Up to 110 C (continuous operation),130 C; ambient temp: 20 to 60 C

4

Design pressure for pneumatic conveying

10 bar

5

Typical volume capacity

In various ranges; in terms of feed rate it could be as high as 750 t/h or volume 800 m3/h available

6

Particle size

Wide variation, some typical values: powdery to 25e50 mm

User Spec.

Remarks

Continued

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Plant Flow Measurement and Control Handbook

TABLE VIII/2.2.4-1 Specification for Coriolis Solid Mass Flow Meterdcont’d SL

Specifying Point

Standard/Available Data

7

Bulk density

Wide variation possible >3.8 kg/L (performance unaffected by density but minimum for operation)

8

Materials of construction

Stainless steel (SS) for components in contact with material. 316 SS measuring wheel meter body and casing coated MS but can be SS304/316 also

9

Wheel chamber protection

Wear protection and nonsticky coating

10

Sensing

Basically load cell configuration varies with models and manufacturers

11

Output

4e20 mADC, cumulative pulse frequency and smart version supports: Fieldbus communication (e.g., PROFIBUS/Foundation Fieldbus) available

12

Motor power

AC 240/110 VAC 50/60 Hz supply

13

Output function

Rate flow, totalized flow, alarm, remote reset, zero adjustments

14

Display and operator function

Digital display, operator reset, calibration, plotting, trending, HMI support, programming

15

Remote electronics unit

SS different grades

16

Enclosure class

IP 65

17

Power supply

Standard power supply 240 VAC/24 VDC

18

Hazardous application (refer to author’s book*)

ATEX FM load cell and suitable electronics possible

User Spec.

Remarks

*[2]

Performance and Other General Details 19

Accuracy

0.5% AR to 1% AR

20

Reproducibility

0.1% AR

21

Turndown

1:10 standard higher may be possible

22

Field calibration

Remote

23

Certification

CE and other competent authoritiesdas per manufacturer

24

Accessories

Cooling unit for very hot materials

25

Special feature

Adjustment of pan angle and others if any

We now explore another mechanical solid flow meter—the impact solid flow meter which is similar to the centripetal meter, with some differences in sensing and which is quite popular in material handling.

2.3.0 Impact Scale Solid Flow Meter In this section, the very popular and frequently used impact scale mechanical solid flow meter is discussed. In cement plants this is used in many

Solid Flow Measurement Chapter | VIII

applications. The basic principles have already been discussed in Chapter I, Subsection 3.2.1.2. Here more details, including the theory of operation, are described. Prior to beginning the discussions we will have a detailed look at the detailing and types shown in Fig. VIII/2.3.0-1. There are two types of impact scale solid flow meters. In both cases the horizontal component of the impact force is measured when the sensing is carried out, because the vertical component is influenced by gravity (g) making mg force dependent on mass (m)—hence measurement cannot be carried out. The type depends on the horizontal component of the force. In one it is sensed by a load cell, whereas in the other it is sensed by a linear variable differential transformer (LVDT). Both types are shown in Fig. VIII/2.3.0-1. 2.3.1 THEORY OF OPERATION FOR IMPACT SCALE SOLID FLOW METERS As stated at the beginning of this section, there are two types, i.e., load cell and LVDT. Prior to starting the discussions it is important to have a short overlook on the mechanics involved. 1. Basic mechanics: In order to understand the mechanics we first refer to the free body diagram shown in Fig. VIII/2.3.1-1. The material falls on the sensing plate from a vertical distance h. Immediately upon striking the materials will be slightly deflected and then slide along the plate. Naturally, as the material slides there will be friction along the length of the plate in the same direction as F2. Therefore, let us try to compute the horizontal components of various forces. We know that any force can be resolved in 90 degree components. Thus, if we resolve the impact force F0 one will get F1 force along the impact plate and another force at right angles to the plate F2. As stated earlier, there will be another force due to friction (Ff) which will be along the impact plate. As shown in

711

Fig. VIII/2.3.1-1 one can get the net horizontal force (in this case from left to right) FH ¼ F1H  ðF2H þ FfH Þ

(VIII/2.3.1-1)

Here FfH is the horizontal component of frictional force. If l is the length of slide of material and m is the coefficient of friction then FfH ¼ qm $

lm cosq v

(VIII/2.3.1-2)

when q is the angle at which the plate is inclined with respect to a horizontal line. For Eq. (VIII/2.3.1-2) it has been assumed that the mass flow rate of the number of particles is qm, and for derivation of the equation any standard book on particle mechanics can be consulted. From a basic impact formula, the right angle force component applied on the plate can be expressed as
 qm v1 q cosq ¼ m $u1 ð1 þ eÞcosq F1 ¼ $u1 1 þ g u1 g (VIII/2.3.1-3) where u1 ¼ velocity of impact, v1 ¼ resultant velocity at sensing plate, and e ¼ vu11 ; the coefficient of restitution. Now, taking air friction into account and 0 < k < 1 one can get pffiffiffiffiffiffiffiffi u1 ¼ k 2gh ðusing energy equationÞ (VIII/2.3.1-4) So, putting the value in Eq. (VIII/2.3.1-3) one gets sffiffiffiffiffi 2h cosq (VIII/2.3.1-5) F1 ¼ kð1 þ eÞ$qm $ g or F1H

sffiffiffiffiffi 2h cosq$sinq ¼ kð1 þ eÞ$qm $ g (VIII/2.3.1-6)

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Plant Flow Measurement and Control Handbook

(A)

ED LIN ET INC INL L FT LE ERIA T MA

LOAD CELL RIGHT INCLINED MATERIAL INLET

NS IN G

PL AT E

SENSING PLATE

HORIZONTAL IMPACT FORCE

HORIZONTAL

SE

IMPACT FOECE

(B)

TRAVEL

VERTICAL MATERIAL INLET

LVDT

FRAME

FLOW GUIDE

RANGE SPRING

BEAM

MATERIAL FLOW

BEARING

IMPACT FORCE

G IN NS SE

PIVOT POINT Fh IM PA C T

Fv

SENSING PLATE

S IL TA DE

SENSING PLATE

SENSING

RESULTANT DISPLACEMENT

FO RC E

FIGURE VIII/2.3.0-1 Impact scale details. (A) Load cell impact scale. (B) LVDT impact. (B) Developed based on an idea from Siemens.

Solid Flow Measurement Chapter | VIII

713

h θ Ff F1

F2 FfH

F0

F2H

F1H

Apparently the difference between F1H and F2H should give the net horizontal force, but there will be another component in the horizontal direc on i.e. fric onal force between plate and the material along the direc on of F2. So, FH = F1H –(F2H+FfH) when Ff is the fric onal force. If mass flow rate is qm, then FfH = qm.

cosθ ; where l is the

distance materials move over the plate, v is the average velocity of material and μ is the coefficient of fric on.

FIGURE VIII/2.3.1-1 Horizontal force calculation basis.

Similarly, the parallel component of the force will be  sffiffiffiffiffi
v2 2h $sinq (VIII/2.3.1-7) F2 ¼ qm $k 1  g u2 So, F2H ¼ F2 cosq sffiffiffiffiffi
v2 2h $sinq$cosq ¼ qm $ k 1  g u2 (VIII/2.3.1-8) So, putting these values into Eq. (VIII/2.3.1-1) one gets the expression of horizontal force in terms of qm and so measuring the horizontal force one can account for the mass flow. In these equations vu22 etc. ratios are replaced by A, B which are calibration constants for the meter. The advantage of this impact technology is that the drift due to the mechanical stability of the assembly is eliminated [13].

Materials flow down the intake pipe, which can be vertical or inclined to the left or right side as shown in Fig. VIII/2.3.0-1, and strike the impact plate. The horizontal component of the force is measured and integrated over a specified time to get the rate of flow over time. 2. Load cell: In the case of a load cell the horizontal component of the impact force is measured by suspended load cells. Sensing by load cells is a cost-effective solution for impact-based flow meters. The load cell arrangement is shown in Fig. VIII/2.3.0-1A. On account of the impact force on the sensing plate, the bar connected to the plate transfers the horizontal component to the load cell combination. Load cell combinations convert the impact force into an electrical signal and are integrated over time in remote electronics. 3. LVDT: An LVDT arrangement is shown in Fig. VIII/2.3.0-1B. There is one beam behind the sensing plate. This beam is also connected with the core of the LVDT and range spring

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Plant Flow Measurement and Control Handbook

for restoration, at the other end of the pivot. Here, on account of the impact force on the sensing plate, the connected beam will be displaced. As the beam is pivoted, it will cause the displacement of the core of LVDT to cause an electrical output to the LVDT which converts the impact force into an electrical signal. In a similar manner as described above, remote electronics convert this into an electrical signal proportional to the solid flow rate. 2.3.2 DESCRIPTIVE DETAILS OF IMPACT FLOW METERS Impact scale load cells may be used in triple beam parallelogram strain gage style as in Siemens SITRANS WF200 or they can be in two single-point load cells as in the Flo way solid impact flow meter. On the other hand, in the case of LVDT sensing, the horizontal impact created by the impact force of the product is sensed by the LDVT. Here the frictionless pivot plays a key role in excluding the vertical force. There is a damper with high viscous fluid to offer mechanical damping for pulsating flow, e.g., SITRANS WF300. These meters do not have moving parts and offer good accuracy. Normally these flow meters are provided with an access door. 1. Components: Impact scale solids flow meters are mainly comprised of the following: l Varied sizes and styles of inlet guide, some with a lining; l Mild/stainless steel (304/316) housing with epoxy painting in some cases; l Impact plate of stainless steel; l Load cell external/in house with aluminum/ SS housing; l Integrated electronic box. There are also options available for remote electronics mounting. Of the two options for impact scale flow meters, flow meters with LVDT normally can handle high-temperature materials, e.g., 230 C; that with a load cell is integrated with the meter rather closely and usually can withstand material temperatures around 60 C. However, externally mounted load cell designs are also available and these can withstand higher material temperatures up to 100 C.

2. Prefeeding: The impact scale is capable of handling aerated flow from an aerated gravity conveyor or air slides. Normally an impact scale can be fed from a numbers of feeding systems such as the following: l Belt conveyor; l Drag conveyor; l Screw feeder short pitched/double flight (fixed/variable speed); l Gravity feeder; l Bucket elevator; l Rotary feeder/valve (fixed/variable speed); l Air slide (adapter as applicable)/aerated gravity conveyor; l Long and short chute. For better results, the height, speed of fall, and angle of impact are important. There are some material characteristics which not only affect the measurement but also affect the life span of the meter. 3. Material characteristics: Material characteristics are important for impact scale damages and measurement errors may be caused on account of abrasion, causticity, and adhesiveness. l Abrasion: Abrasive materials reduce the life of the sensing plate. Not only material properties can cause abrasion, a change in direction can also cause abrasion. It is therefore recommended to use an antiabrasive coating in the sensing plate and inlet guide. PTFE, tungsten carbide, and alumina ceramic coatings are commonly used for highly abrasive materials such as alumina. Polyurethane as an antiabrasive material may not be suitable because it is resilient in nature to absorb some energy. Another way to arrest abrasion is to reduce the speed of material fall, e.g., by using a dead box in the inlet guide. l Causticity: The causticity of materials can damage the sensor, either directly or due to its vapor. Therefore, sensors should be encapsulated and SS should be used as material sensors like strain gages are kept in gels (e.g., Siemens impact scale). Normally material build up does not affect the results of measurement. l Adhesiveness: Adhesion of materials on the nonimpact surface of an impact scale is of

Solid Flow Measurement Chapter | VIII

some concern as it can affect the movement of the sensing plate. It is important to ensure that the meter is properly leveled to avoid zero drift. It is important to ensure that the materials do not stick on the sensing plate and give rise to build up. Any build up in the sensing plate or inlet guide may cause calibration shift in long run. As the vertical component is ignored, static build up barely affects performance. Depending on the requirements of the sensing plate, inlet guides are sometimes lined with nonsticky materials, such as PTFE. There are certain materials like salt cake and potato flakes which are not at all suitable for an impact meter. It is recommended that the manufacturer’s list of items that are not recommended for the meter should be consulted for special applications. 4. Air flow: At times it is necessary to have an air flow in the system, for example, for dust collection, in which case it should be both at the inlet and outlet. Light constant low air flow in the meter may vary and can be adjusted in the meter electronics. When it becomes unpredictable it is of great concern. It is recommended to select a suitable place prior to installation to avoid such situations. When there is the possibility of higher measurement inaccuracies due to air flow then it can be reduced by connecting the air flow line between the inlet to the outlet to form a bypass. 2.3.3 FEATURES AND APPLICATIONS OF IMPACT FLOW METERS Impact scale solid flow meters are one of the oldest solid flow meters, with a proven technology. A few features and application areas of these are enumerated in this section. 1. Features: The following are a few features of impact scale solid flow meters: l Impact scales can handle the flow of solids from puffed rice/wheat to iron ores of various sizes;

715

Impact scales are normally provided with an easy-access door for inspection; l Possibility for dust control with connection to dust filters; l Possible for air bypass as already discussed; l Impact scale solid flow meters can measure the flow of a low range up to high range of 900 tons/h; l As the vertical force component is discarded, material build up barely affects performance, i.e., accuracy; l Heavy-duty impact plate, SS external load cell/LVDT makes it suitable for hightemperature material handling; l Dust-proof enclosures make impact scales suitable for hazardous areas also; l Inlet guide and plates with a lining make it suitable for handling abrasive materials; l No moving parts and not prone to maintenance; l No frequent calibration is necessary for properly selected meters; l Impact scale can be used with a number of prefeeders, including air slides with an adapter. 2. Application: As impact scale solid flow meters are generally unaffected by abrasive, corrosive, adhesive (with proper measures), and hot materials they can cater to the measurement of practically any dry bulk solids. The impact scale has very wide applications in almost all industries. Some of the application areas are listed here: l Cement; l Coke/coal; l Wood chips; l Pulverized solids; l Cereal; l Grain; l Starch/sugar; l Rice/soybean hull; l Potato flakes; l Plastic pallets; l Some pet foods. l

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Plant Flow Measurement and Control Handbook

As far as fluidity is concerned it can take care of many materials from fly ash to slowmoving leather turnings. Also, these meters, along with the associated electronics, find usage in continuous flow rate measurement, totalizer applications, PID controls, batch controls, blending operations, etc. In the cement industry especially impact flow meters find wide applications from kiln feed to separator returns.

2.3.4 SPECIFICATIONS OF IMPACT SCALE SOLID MASS FLOW METERS Specifications for an impact scale solid mass flow meter are given in Table VIII/2.3.4-1. It is worth noting that as the specification is a general one, all the data will not necessarily match with any particular instrument chosen. Also, it has been attempted to put the best possible data from different manufacturers, and so there will

TABLE VIII/2.3.4-1 Specifications for Impact Scale Solid Mass Flow Meter SL

Specifying Point

Standard/Available Data

1

Solid type

Dry free-flowing granular, powdery, grain bulk solids. Food grains, animal feed, plastics, cement, and mineral processing solid aggregates to name a few. Generally nonsticky

2

Feeding equipment

Wide varieties of feeders, gate valves, rotary valve, gravity flow, and air slide with adapter. Refer to Subsection 2.3.2.2

3

Design pressure

Less than 1 bar normally

4

Design/ambient temperature

Design: ()20e230 C based on type of sensing type and sensor location. Ambient: 20 to e65 C

5

Typical volume capacity

In various ranges; in terms of feed rate it could be as high as 900 t/h or volume 650 m3/h available. Tonnage capacity is function of bulk density

6

Particle size

Wide variation, some typical value: powdery to maximum 15 mm (500); this is especially true for low belt speed. There are many schools of thought for placement of the speed sensor in the conveyor. Many manufacturers are of the opinion that on account of dirt it is better to avoid the tail end pulley as the mounting location for a speed sensor. The speed along the length of the belt is not same, so it is necessary to measure the speed at a suitable place. Modern speed sensors are used with encoders. Speed sensors with encoders should not be mounted on the head pulley as there is a greater chances of slippage there. Therefore even if there is dirt, it is always preferred to mount the speed sensor at the tail pulley to get the benefit of the fundamental sensing capability. This is the best location for sensing material speed because the belt makes a 180 degrees wrap around the tail pulley, ensuring maximum belt friction and minimal slippage. Therefore, the tail pulley only moves with the belt and material. Tension rolls, if used, are more susceptible to slippage for speed sensing. We

now concentrate on the descriptive details of speed sensing. 4.4.1 DESCRIPTIVE DETAILS OF SPEED SENSING 1. Measurement requirements: A simple tachometer mounted directly onto the speed source is the best choice for speed sensing in a belt scale/belt weigher or weigh feeder. Modern digital or optical encoders are the most common tachometers used to measure the travel of the belt. It goes without saying that the higher the resolution, the smaller the belt increment that can be measured and the better will be the measurement performance because speed measurement is very critical in feed rate measurement in belt scale/belt weighers or weigh feeders. Present-day encoders can produce a pulse per 1 mm belt travel. In order to cater to harsh feeding environments, modern encoder electronics are available in a suitable enclosure of required IP ratings. However there are cases where the return belt is used for measurement. A few types, including one on a return belt have been depicted in Figs. VIII/4.4.1-1 and associated encoder details are available in VIII/4.4.1-2. 2. Speed sensing: In modern speed-sensing (digital) tachometers, encoders are utilized. A high-resolution speed sensor provides signal pulses whose frequency is proportional to the shaft speed. Therefore, by pulse counting the shaft speed is determined accurately. Therefore, a (digital) speed-sensing tachometer converts the shaft rotation into a pulse train of 256, 500, 1000, or 2000 pulses per revolution using a high-precision rotary encoder. There are basically two kinds of encoders used, one is optical and the other is magnetic. The magnetic type may be of different kinds, such as proximity switch or Hall effect. 3. Optical encoder: Basically, this type rotary optical encoder uses a sensor to identify a position change when light passes through a patterned encoder (optical shift type) wheel or disk. Major parts of the rotary optical

Solid Flow Measurement Chapter | VIII

769

SHAFT DRIVEN SPEED

RETURN BELT SPEED SENSOR

FIGURE VIII/4.4.1-1 Speed sensor.

Encoder: An encoder is a kind of sensor for mechanical movement, to generate digital/pulse signals in response to mechanical mo on. The encoder provides the user with the informa on about the posi on, speed and direc on about the mechanical movement of the equipment for which the encoder has been deployed. The encoder could be linear type (responds to mo on along a path) or rotary type (responds to rota onal mo on – in our belt feeder it is rota onal mo on). Encoders are categorized as incremental type (that generates pulse train to get informa on about posi on and speed) and absolute type encoders (that generates unique bits corresponding to posi on). In prac cal use, there may be single and /or two (viz. quadrature) or more encoders in use. Encoding for rota onal speed can be done by op cal method or magne c method (proximity type or hall effect type).

FIGURE VIII/4.4.1-2 Encoder.

encoder are: LED light source, photo-detecting receiver/sensor, and movable disk. The LED shines through one side of the optical encoder. The encoder wheel or disk has a series of tracks opening on it. As the disk moves, it breaks the encoder light. The detecting sensor on the other side detects the same and produces output pulse proportional to the speed of the shaft as the disk is mounted on it. The code disks (also called wheels) on rotary optical encoders consist of etched metal, Mylar,

emulsion on tempered glass, or chrome on glass. In the case of the optical shift type, there will be a mask and the detector changes the open/close pattern. However, this is a basic operation in its simplified version for speed measurement. 4. Magnetic encoder: In the magnetic type encoder a small gear rotates with the shaft near a proximity switch, as the gear teeth pass the proximity switch generates a pulse output proportional to the speed of the shaft.

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Plant Flow Measurement and Control Handbook

Alternatively, a rotor fixed on the shaft contains alternating evenly spaced north and south poles around its circumference and as the shaft rotates, the sensor on the other side detects these small shifts in position N [ S and S [ N. Hall effect and magnetoresistive are the two methods that can be used to detect the changes. Hall effect sensors work by detecting a change in voltage by the magnetic deflection of electrons detailed out in chapter X. Magnetoresistive sensors detect a change in resistance caused by a magnetic field. 5. Discussions: Magnetic encoders have an edge over optical encoders. This is because of the entry of contaminants through seal failures, which can deteriorate optical encoder performance. The optical disk may shatter during vibration or impact.

4.4.2 SPECIFICATION OF SPEED SENSING A brief generalized specification of a speed sensor along with an encoder has been presented in Table VIII/4.4.2-1. The data presented here are data from reputed manufacturers and as different data are available from various manufacturers, the best possible data have been selected, and so they may not match with any particular manufacturer. The reader is requested to use the data sheet as a base document and, based on the intended application, the most suitable one should be chosen in consultation with the manufacturer. With this the discussion on speed sensing comes to an end. We now investigate details about electronic integration and control systems along with their communication systems.

TABLE VIII/4.4.2-1 Specifications for Speed Sensor With Encoders Specifying Point

Standard/Available Data

1

Sensing principle

Digital tachometer with encoder to produce pulse for shaft rotation

2

Resolution

High-resolution pulses

3

Input

Shaft rotation 0.5 to >2000 RPM

4

Ambient temperature

40 to 80 C

5

Humidity

98%

6

Shock and vibration

50 g (10 ms)/20 g (5e2000 Hz)

7

Starting/running toque

Manufacturer’s standard

8

Encoder type

Incremental (2 ch)

9

Frequency response

>200 KHz

10

Quadrature

90  22 degrees, normally CCW leading

11

Enclosure

NEMA 4X/IP66

12

Material

Painted aluminum/stainless steel

SL

User Spec.

Remarks

2.5 Ncm (typical)

Continued

Solid Flow Measurement Chapter | VIII

771

TABLE VIII/4.4.2-1 Specifications for Speed Sensor With Encodersdcont’d SL

Specifying Point

User Spec.

13

Output

Open collector/10e30 VDC Pulse: 256/500/1000/2000 pulses per revolution Frequency: 2e2000 Hz or more

14

Output function

Belt speed for weigh feeder rate computation

15

Ex-proof

ATEX rating

16

Power supply

24 VDC 10e30 VDC

17

Special feature

To specify e if any

Standard/Available Data

4.5.0 Electronic Integration and Control Systems There are two sets of signals, one each from the weigh scale and speed sensors, which need to be multiplied and integrated for computation of feed rate. Also, for a weigh feeder there should be a controller to control the speed of the driving motor for the weigh feeder. In this brief discussion electronic integration and control systems shall be presented on. The discussion starts with functional details of the above system. 4.5.1 FUNCTIONAL DETAILS OF WEIGHING ELECTRONIC INTEGRATOR AND CONTROLLER When used with Belt scale/weigher of weigh feeder, the name suggests its main function is to integrate the feed rate with time. However in reality it performs two fold functions. One of the function of this unit is to compute feed rate taking signals from load cell and speed sensor as detailed out earlier (i.e. to act as multiplier/signal processing unit). The other function is to integrate the feed rate with time. Integrators are also these in designed for easy-to-read displays with straightforward operation and calibration through keyboards or touch screens and software that allows step-by-step set-up and operational procedures. All data and user instructions are displayed on a bright alphanumeric display of different kinds

Remarks

such as LED, LCD, and vacuum-fluorescent. These intelligent operator interfaces (displays, keyboard, or touch screen, etc.) are used for all interfacing and data entry. Also these integrators for belt scale/weigher and weigh feeders are designed to accept the required analog/digital I/Os as well as with external communication facilities to interface the external control and monitoring needs of the plant. Various I/Os mentioned above may be necessary for process control interfaces (i.e., a process interlock) and also for basic protection of a belt scale/belt weigher or weigh feeder (i.e., interlock from zero speed switch, sway switch). It is worth noting that many reputed manufacturers also offer similar programmable electronics not only for belt scale/belt or weigher feeder applications alone, but that may be used for their other solid-measuring systems, such as impact scale, loss-in-weight feeder, check weighers, etc., e.g., the Ramsey 2000 series electronics can be used for many solid flow-metering devices. This means that the details given here can be used for programmable electronics of other solid flowmeasuring systems as well. In the case of a weigh feeder the feed rate can be set and controlled with a variable-speed drive connected to the weigh feeder. Therefore, in the case of a weigh feeder, in addition to the electronic integrator discussed above, there should be a controller at least with PID operation to get the set flow through the weigh feeder. As a corollary to this it transpires that in the

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case of a weigh feeder there should be one controller and associated interfaces with external control systems such as PLC/DCS. At times it is possible that a number of weigh feeders or belt scale/belt weighers are integrated through a common control, which is not uncommon in steel plants where slightly bigger control systems incorporating PLC may be adapted. This is stated here to indicate that there can be wide varieties of integration and control electronics. Therefore, only the systems are discussed in general terms, which not only can vary with manufacturers but also with applications. Therefore, the following basic functions are expected of electronic integration and control systems: 1. Acceptance of weigh scale signal from load cell and speed signal from speed sensor; 2. Computation of feed rate from above signals and integrate over specified time; 3. Integration/totalizing feed rate signal to produce totalized flow; 4. Handle interlock and protection and external I/Os; 5. Generation alarms and alarms management; 6. Display of primary signals like load and speed values, feed rate signal, and totalized flow; 7. Operator interface (e.g., reset); 8. Communication and interfacing with other systems; 9. Feed rate control (for weigh feeder); 10. Speed control and control interface for drive motor (for weigh feeder). We now look into the details of various features offered by different manufacturers, so that the reader will be in a position to select the feature best suited for their intended application. 4.5.2 FEATURES AVAILABLE FOR WEIGHING ELECTRONIC INTEGRATORS AND CONTROLLERS There are wide varieties of advanced features now available from various electronic integrators and controllers for weighing systems available in the market. A few such features are listed below

to enable the reader to choose the most suitable for the intended application. It is worth noting that all these features may not be available for a single product. Also, it may be possible that selected feature combinations are not feasible for any vendor, in which case the reader needs to assign the priorities for the application and select the vendor accordingly. Some of the features include but are not limited to the following: l l l

l

l

l

l

l

l

l

l

l

l

l l

l

l

l

Multilingual system possible; Legal trade standards possible; High-precision ADC with 16 (common)/32 bit processing and controls; Performance parameters as per applicable legal trade standard; Common operation, set-up, and calibration for all weighing applications for better familiarization; Digital electronics with accurate, drift-free performance; Synchronization of prefeeding devices/ equipment; Easy autozeroing and tracking of the same for empty operation of conveyor; Autocalibration and span method for electronic calibration standard with different test load forms; Operator-selectable time for autoreminders for recalibration timing; Suitable linearization for a wide range of operations for better measurement accuracy; Number of programmable features for customization of integrator and controller; Selectable outputs from menu and output types; Selectable output display types; Different types of displays including color, high-resolution LED monitor, and optional printers; Five to six digit totalizing (resettable) in different units; Selectable delay in time or length of belt travel for better control; Wide choice of selectable and programmable outputs and output types;

Solid Flow Measurement Chapter | VIII

l

l

l

l

l

l

l l l

l l

l l

l

Selection of a wide range of communication facilities; Support for different links, interfaces, protocols, and fieldbus systems; Independent and programmable delay in output and display; Facilities for incline compensation and moisture compensation; Refill, deviation, and other alarm management (as applicable); Surge and other applicable protection and interlocks; High electromagnetic compatibility; Optical/galvanic isolations; Suitable enclosure for harsh environmental conditions with suitable materials; Integrated diagnostic and self-test functions; Possible for ATEX certification and use of IS circuit; Power fail-safe data storage possible; Event logging-span, alarm, zero, and data change events logged; Audit trail (trade certification approved);

l

l

l l l l

773

Status, event, adjustment, and quantity protocols; Simulation operation for test and learning purposes possible; Back lash controls; Remote control set point for control; Batch quantity feed controls/dosing controls; Fuzzy logic controls for dosing conveyors.

4.5.3 DESCRIPTIVE DETAILS OF WEIGHING ELECTRONIC INTEGRATORS AND CONTROLLERS Modern weighing equipment must be capable of interfacing with a variety of peripheral equipment for monitoring, supervisory control, and data acquisition purposes. To accommodate these needs, extraordinary communication capabilities are necessary for interfacing with peripheral equipment, control systems, and networking systems. Also, operational flexibility is provided by programmable features in weighing electronics. Typical Belt feeder integrator and control has been depicted in Fig. VIII/4.5.3-1.

TO DRIVE SPEED CONTROL (AS APPLICABLE) PC & OTHER INTERFACE RS232/485 CONTROL

TOTAL FLOW

SYSTEM

FUNCTION GENERATOR FIELDBUS COMMUNICATION

OTHER HARDWIRED INPUT/OUTPUT [ANALOG INPUTT/OUTPUT SPEED SIGNAL

DIGITAL INPUT/OUTPUT PULSE O/P]

LOAD CELL SIGNAL

(e.g. RATE FLOW/TOTALIZED FLOW, WEIGHT & SPEED OUTPUT)

FIGURE VIII/4.5.3-1 Belt feeder integrator and controller.

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Plant Flow Measurement and Control Handbook

1. Basic integrator and controller: The weighing electronic integrator and controls system receives a signal from the weigh scale and speed sensor(s). Using a combination of high-resolution electronics and intelligent filtering with computational techniques, it is possible for the electronic integrator to continuously calculate the feed rate and totalized feed. From this calculation, the intelligent electronic controller utilizes a sophisticated software algorithm to produce the required controlled output to regulate the speed of the weigh feeder driving motor with help of a suitable interface with a motor speed controller. The computer (which can be embedded a microcontroller) would operate as per the customer program and desired set points (especially for the weigh feeder controller) besides being connected to external control systems, such as DCS/PLC through proper RS links, field, and other communication bus or network systems. 2. Basic displays and operator interface: The displays of integrators normally include but are not limited to: l Feed rate; l Totalized weight; l Belt load; l Belt speed; l Feed rate set point (weigh feeder); l Feeder control output (weigh feeder); l Alarm relay and management; l Set point; l Manual/auto mode; l Raise/lower. These displays could be bright LEDs and or LED/TFT monitors and associated keyboards and touch screen. There are several varieties available from different manufacturers. 3. Interfaces and communications: The integration of various systems is currently popular because with this it is possible to save space and reduce the training period for operators when common types of displays and operators’ interfaces are called for. Also, with this

it is possible to take the benefit of use of common control systems, which otherwise would have been too costly. With digital communications it is possible to connect field instruments to the main control system, such as DCS/PLC. The majority of electronic integrators and control systems are available with the following additions: l Standard built-in Modbus RTU slave or ASCII slave via RS-links, namely, RS 232/485; l Miscellaneous networks, such DEVICE NET, Ethernet/IP, MODBUS/TCP, CONTROL NET; l Field bus: Profibus DP, Profinet, Foundation fieldbus; l Standard supportive I/Os and encoders (e.g., AlleneBradley Remote I/O); l Interface for PC master control for PCbased systems with necessary links and protocol; l These are a few examples of available options. 4. Other Miscellaneous controls and programs: In weigh feeding control a number of other control systems are needed, such as: l Blending of multiple materials: Material blending with multiple weigh feeders; l Preset flow control: Preset flow control for batch and dosing controls with configurable dead range and automatic zeroing; l Program setting and diagnosis: Windowsbased programs for easing out parameter setting and use of diagnostic tools, e.g., EasyServe PC program. 4.5.4 SPECIFICATION OF WEIGHING ELECTRONIC INTEGRATORS AND CONTROL SYSTEMS A brief generalized specification of a weighing electronic integrator and control system has been presented in Table VIII/4.5.4-1. The data presented here are data from reputed manufacturers and are available from various manufacturers, with the best possible data having been selected,

Solid Flow Measurement Chapter | VIII

and so it may not match with any particular manufacturer. The reader is recommended to use the data sheet as a base document and, based on the intended application, choose the most suitable in consultation with the manufacturer. After the discussion on the integrator and controller we now look into details of the motor control system.

775

4.6.0 Motor Speed Control The drive for a weigh feeder can be either a DC motor or an AC induction motor. Speed control of DC drives is a comparatively easy proposition but these are less common nowadays. In the majority of cases, an AC motor with drive controls is used for weigh feeders. Two methods, variable-voltage

TABLE VIII/4.5.4-1 Specifications for Electronic Integrator and Control System SL

Specifying Point

Standard/Available Data

1

Application

Integration and computation of feed rate, totalizing flow, control of weigh feeder batch, and other controls

2

Operating temperature

20 to 60 C

3

Storage temperature

30 to 70 C

4

Enclosure type

NEMA 4X IP66

5

Analog input type

4/0e20 mADC/0e10 VDC

6

Analog output type

4/0e20 mADC/0e10 VDC

7

Binary input/ output

Potential free contact NO/NC For interlock and alarm

8

Contact rating

Suitable rating around 3 A at 240 VAC or 0.3 A at 30 VDC

9

Alarm management

Yes

10

Impulse input

Totalizing counter

11

Isolation

Galvanic/optical isolation for I/Os

12

Power supply

110/240 VAC 50/60 Hz or 24 VDC

13

Display type

LED (LCD also), vacuum fluorescent, TFT/LED monitor

14

Display output

Rate. Totalized, belt load and speed, control set and others

15

Features

Auto zeroing, calibration, etc.; refer to Section 4.5.2

16

Serial interface

Printer, large displays, other software systems

17

Communication

Fieldbus, Ethernet/IP, RTU MODBUS

18

Communication protocol

MODBUS RTU

19

Special feature

To specify e if any

User Spec.

Remarks

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Plant Flow Measurement and Control Handbook

variable-frequency drive (VVVFD) control and variable-frequency drive (VFD) controls are commonly used methods for AC motor control. AC drive control: Assume that the voltage applied to a three-phase induction motor is sinusoidal and neglect the voltage drop across the stator impedance. Then we have at steady state V ¼ kju[

torque requirement is not mandatory, VFDs for speed controls are well suited and have become popular. Let us now concentrate on the motor speed control by variable-frequency drive (VFD). Variable-frequency drive control: Fig. VIII/ 4.6.0-1A illustrates the basic building block for a VFD. AC motor speed (S) is given by:

(VIII/4.6.0-1)

where V ¼ voltage; k ¼ proportionality constant; u ¼ angular frequency; and Ø ¼ stator flux. Thus we can see that if the stator impedance is ignored, the torque remains constant and is independent of supply frequency and voltage if V/f remains constant. In this connection, Fig. VIII/ 4.6.0-1B may be referenced. When the voltage is low, the frequency is low and stator impedance cannot be ignored. Another issue is that at low speed there will be more flux in the air gap, and so core loss will be greater in VFD. For VVVF, faster power switching through power transistors/IGBT gives better results. However, in the case of a weigh feeder, since constant (A)

di/dt CHOKE

RECTIFIERDC BUS

S ¼

120f P

(VIII/4.6.0-2)

where f stands for frequency of the supply, and P is the number of poles. Of the two parameters responsible for motor speed, P is not changed as it calls for physical change in the motor and rewinding, but it is easier to change the frequency of supply. As long as the f/P ratio is maintained, the rated torque can be developed. This indicates that whenever the speed of an induction motor is controlled, both by frequencies as well as voltage, one would have a different torque, as shown in Fig. VIII/4.6.0-1B. This ratio is varied in input, which consists of an isolation transformer, a rectifier circuit, and a DC bus section

INVERTER

FIELD

LINK

DC CAPACITOR

M

~ VOLT

3 Ph ISOLATION TRANSFORMER

(B)

FIELD INPUT SECTION

FREQUENCY

FIGURE VIII/4.6.0-1 Variable-frequency drive control. (A) Basic building block for VFD. (B) Torque development. Taken from the author’s book: S. Basu, A.K. Debnath, Power Plant Instrumentation and Control Handbook, Elsevier, November 2014. http://store.elsevier.com/Power-Plant-Instrumentation-and-ControlHandbook/Swapan-Basu/isbn-9780128011737/.

Solid Flow Measurement Chapter | VIII

comprising a suitable filter, di/dt arrestor, etc. An isolation transformer isolates the system from the input supply. It also helps in developing a multiphase rectifier circuit as shown in Fig. VIII/4.6.01A, which shows 12 diodes in a multiphase rectifier circuit to convert the AC supply (50/60 Hz) to a DC circuit. There is a filter to smooth out the DC voltage; the multiphase rectifier circuit is used to obtain better DC voltage. The smooth DC is fed to the inverter section. In the inverter the DC voltage is transformed into AC voltage (see a standard book on power electronics for inverter action), with the help of a siliconcontrolled rectifier or an insulated gate bipolar transistor (IGBT), which is an advanced threeterminal power semiconductor switching device working on a minority carrier. IGBT has highinput impedance combined with the capability to handle high bipolar current. It combines the advantages of MOSFET and BJT and it is a voltage-controlled device. IGBT is used to turn the DC voltage on and off, and the DC voltage provides bipolar pulses of equal magnitude. In the control board the set point is compared, and it regulates turning on the waveform-positive half or waveform-negative half of the power device. The longer the device is on, the higher the output voltage and the higher the frequency and vice versa. The power device is turned ON/OFF by a carrier frequency, also known as a switching frequency. The higher the switching frequency, the higher will be the resolution of the pulse width modulation (PWM), so it is the smoother waveform of the AC signal. For further details Chapter VI of the author’s book [17] may be referenced. Prior to closing the discussions on the belt scale/belt weigher or weigh feeder we look into the details of various accessories, including the sway switch, zero speed switch, etc. 4.7.0 Conveyor Accessories: Safety Switches For conveyor and human safety there are a few switches and accessories that are used for belt

777

scale/belt weighers or weigh feeders. Local start/ stop push-button stations and deinterlock switches are mounted near each piece of equipment for starting and stopping during test/maintenance of the system. A list of major items includes but is not limited to: l l l l

Local start/stop; Pull chord switch; Belt sway switch; Speed switch (zero speed switch).

All these are used in the motor circuit of the conveyor as a safety interlock. 4.7.1 LOCAL START/STOP SWITCH Normally, near the conveyors/Feeders there will be a box containing a local start and stop switch or push buttons near the conveyor. In some, along with the local start/stop push button, there are local indication running and stop lamps. For some countries, like India, these are mandatory as per electricity legislation. A local stop push button is used in the motor control circuit as a safety interlock in the sense that when this is operated the motor stops immediately. Local start push buttons may be used for local maintenance/ testing/calibration. 4.7.2 PULL CHORD SWITCH These are used to stop the conveyor in the case of an emergency. Rope-operated emergency switches can be mounted at equidistant places on either side along the conveyor. When pulled, the switch remains in a latched position unless it is manually reset, to avoid accidental restart. When the rope is pulled from any side, the switch is operated through lever. Normally, the lever is at 45 degrees on either side, so when pulled a snap action occurs so that the switch stays put and operates with moderate torque. These are available in an IP 55/65 enclosure (flameproof or commonly a suitable class II enclosure). A contact rating of 10/15 A at 500 V AC in changeover contact or 1 NO/1 NC is standard.

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4.7.3 BELT SWAY SWITCH To protect the conveyor from damage due to misalignment, these switches are used. The switches can be mounted at equidistant (normally 25 M) places on either side along the conveyor. In the case of excess sway, an edge push operating lever (45 degrees on either side when the angle changes to, e.g., 30 degrees) actuates the switch; these may be self-resettable. Normally, belt sway switches are available in IP 55/65 enclosure (flameproof or a commonly suitable class II enclosure). The contact rating is 10/15 A at 240 VAC. 4.7.4 SPEED SWITCH (ZERO SPEED) Monitoring of speed is essential in an automation system. In speed control-modulating loops, a continuous monitoring speed is required, whereas a zero-speed switch is required for general conveyor operation. Also under-/overspeed switches can be used. Noncontact-type sensors are used for speed monitoring. These are mounted near the rotating device with a metallic flag. Thus, pulses are generated as the flag passes, and the same pulse is sent to a conditioning device. When the pulse count goes beyond a set point output, the relay operates to give contact. The speed settings, generally, are adjustable from 5 to 5000 RPM and may be self-resettable. Normally, they are available in IP 55/65 enclosure (flameproof or a commonly suitable class II enclosure). A contact rating of 10/15 A at 500 V AC in changeover contact or 1 NO/1 NC is standard. The discussion on belt weighing systems comes to an end here and we now explore the possibility of solid flow measurement utilizing microwave signals.

5.0.0 NONCONTACT TYPE MICROWAVE SOLID FLOW METERS Microwave technology has been applied for solid flow measurement. These noncontact, nonintrusive solid flow meters are mainly used for measurement of powder and solid materials, which are free-falling and/or pneumatically conveyed in

a pipe. The basic idea behind this type of flow measurement has been discussed in Subsection 3.2.3.1 of Chapter I. Since these are mounted from the outside, they are easier to install. Also, maintenance requirements and costs are low. They can be used to measure powder and other solid materials with dimensions between w0.001 mm to 20 mm in diameter. 5.1.0 Descriptive Details of Microwave Solid Flow Instruments It measures moving particles only, so any deposits will not have an effect on the measurement. The discussion starts with the principles of operation. Also Section 7.0.0 of Chapter X may be referenced for further discussions on microwave solid flow monitors. 5.1.1 PRINCIPLES OF OPERATION As stated in Subsection 3.2.3.1 of Chapter I, this instrument consists of one transreceiver which creates a low-energy microwave field in the pipe flow measuring region, as shown in Fig. I/ 3.2.3.1-1. On account of moving particles, a part of the microwave signal will be reflected back by the particles to the transreceiver. The intensity of the reflected Doppler-shifted energy is measured by the receiving sensor at the transreceiver. This small signal is sent to a converter which in turn converts a small signal into a suitable signal that it sends to the computing electronics, whereby a unique algorithm for the mass flow rate is computed and proportional 4e20 mADC is given as output. Since the meter measures the Doppler shift, it is applicable to moving particles only. 5.1.2 METER DESCRIPTION The meter consists of components, such as a flow tube, a sensor as shown in Fig. VIII/5.1.0-1, a signal converter, and computing electronics. The meter gives proportional 4e20 mADC output along with alarm contacts. As stated earlier, there are two methods for solid flow measurement by a microwave flow meter. One is free falling and the other is pneumatic conveying. Therefore, the final

Solid Flow Measurement Chapter | VIII

3. 4. 5.

FIGURE VIII/5.1.0-1 Microwave solid flow meter.

accuracy of the meter depends on the material type, material conveying and installation. Compared to pneumatic flow applications, gravity flow applications are more reliable for mass flow reading compared to pneumatic flow applications, which have more variables, such as gas flow conditions and suspension of particulates in the conveying line. To mount the equipment a hole for the mounting plug is first drilled into the conduit. The sensor is installed in line with the wall and therefore is wearfree. The meters are available for a wide range of pipe sizes, from 50 to 600 mm. These are available in various enclosure classes and associated computing units with a variety of display styles. The meters are installed in the pipe by different thread styles, such as M22  1.5 mm DIN/ISO 13 or G1 ½00 mostly through the use of welding branch (SS). Normally meters are provided with local displays of rate flow and totalized flow display in the computing electronics. The output from flow meter can be used for remote transmission also. We now explore the features and applications of this meter. 5.2.0 Features and Applications of Microwave Solid Flow Instruments In this section the features and application details of microwave solid flow meters are outlined. 5.2.1 FEATURES OF MICROWAVE SOLID FLOW METERS The following are important features of microwave solid flow meters: 1. Measurement of free-falling and pneumatic conveyed solids; 2. Sturdy nonintrusive sensor measurement flush with wall and noncontact easier installation.

6. 7. 8. 9.

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Also free from risk of radiation as in case of nucleonic instruments; Suitable even for very low flow rates; Measures and detects only “moving” particles, not deposits; Faster measurement and quick sensitivity adjustment capability; High operating safety; Continuous in-line flow measurement for solids without a weighing scale; Easy and simple installation in existing pipework; Low maintenance requirement and cost.

5.2.2 APPLICATIONS OF MICROWAVE SOLID FLOW METERS The following are the major application areas for the solid flow meter: 1. Capable of monitoring variable flow quantities due to disturbances in different densities; 2. For proper mixing of additives; 3. Capable of measuring all solids and many dusts within the sizes mentioned earlier, granular materials, powder/dust such as coal dust/ saw dust, etc.; 4. Major industrial applications include the following: l Utility (power plant for pulverized coal); l Cement and mining beneficiation; l Chemical plants; l Plastic industries; l Petroleum; l Agriculture and food grains; l Building materials industry; l Recycling process industries; l Rubber and synthetic industries; l Wood dust; l Ceramics production; l Detergent industry; l Fertilizer industry; l Glass production. 5.3.0 Specification of Microwave Solid Flow Instrument A brief specification of a microwave solid flow meter has been presented in Table VIII/5.3.0-1.

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There are not many manufacturers of this flow meter. The data presented here are data from established manufacturers and as different data are available from various manufacturers, the best possible data have been selected, which may not

match with any particular manufacturer. The reader is requested to use the data sheet as a base document and based on the intended application chose the most suitable meter in consultation with the manufacturer.

TABLE VIII/5.3.0-1 Specification for Noncontact Type Microwave Solid Flow Meter SL

Specifying Point

Standard/Available Data

1

Application

Flow of different kinds of solid and powder of different sizes both in free-falling conditions or pneumatic conveying

2

Operating temperature

20 to 90 C

3

Ambient temperature

10 to 60 C

4

Operating pressure

Up to 60 bar

5

Humidity

Product dependent

6

Particle size

0.01 mm to 20 mm

7

Pipe sizes

Up to 600 mm diameter

8

Enclosure type

NEMA 4X IP66

9

Material in touch with process

304S S (1.4307) or 316 SS (1.4571) and polyamide 6.6 welding branch AISI316Ti

10

Measuring frequency

K band (24, 125 GHz)

11

Sensor power

Through controller

12

Power supply

115 VAC/24 V AC/DC or 230 VAC/24 VDC

13

Transmitter

Mostly, Din Rail mounted

14

Controller and remote unit

Remote mounted with display of suitable IP rating

15

Controller enclosure

Desktop, 1900 rack mounted or field enclosure

16

Output

4e20 mADC, alarm contact, RS232/RS485 link for external interface, CAN network support

17

Display

Backlit LCD, LED with necessary dedicated keys, and/or TFT/LED monitor SVGA display with keyboard

18

Software

To support flow computation and programming

19

Accuracy

0.5%e2.5%

20

Response time

1s

21

Hazardous application

Yes, ATEX certification possible

22

Accessories

Welding branch as required

23

Special feature

Special cable for interconnection and others to specify

User Spec.

Remarks

Solid Flow Measurement Chapter | VIII

Like with the microwave flow meter, there is another noncontact type solid flow-sensing instrument that uses nuclear technology, which is explored in the next section.

Normally all these instruments bear a caution note, with the following being typical: All Nucleonic/Radiometric/Gamma measuring systems utilize radioactive substances which are manufactured in compliance with official regulations and are protected by suitable shields. Any hazards to personnel due to built-in radioactive substances can be ruled out, provided they are handled properly, as prescribed by laws and regulations. These instruments/measuring facilities may be operated only by specifically licensed persons with sufficient expertise and training.

6.0.0 NONCONTACT TYPE NUCLEONIC SOLID FLOW METERS This is another example of a noncontact type solid flow measurement system universally used in many plants for its versatility. One thing to be remembered is that it measures the density of material or weight of material in a unit area as indicated in Subsection 3.2.3.2 of Chapter I. Since nucleonic instruments are subject to human hazards it is an absolute necessity that these are handled only by licensed personnel with sufficient experience and training and the manufacturer’s instructions should be followed. Normally the symbol that is shown in Fig. VIII/ 6.0.0-1 is marked on nucleonic instruments. For other similar symbols and symbols for ex-proof IS instruments, the author’s book [2] may be referenced.

Therefore, suitable necessary precautions should be followed. Nucleonic or radiometric solid flow meters can be used to determine the load/solid flow in the following: l l l

l

CAUTION

l l

RADIATION

FIGURE VIII/6.0.0-1 Caution symbol. For other symbols see the author’s book S. Basu, Plant Hazard Analysis and Safety Instrumentation Systems, Elsevier; IChemE, 2016, http://store.elsevier.com/Plant-HazardAnalysis-and-Safety-Instrumentation-Systems/SwapanBasu/isbn-9780128037638/ may be referenced.

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On conveyor belts; On screw/chain/apron conveyors; For free-falling materials (nonbinding materials); For materials in pneumatic conveying. In the case of free-fall measurement, the measurements should be carried out at a place very close to the discharge station. In that case, it would reduce the theoretical rate of fall at the measuring point, otherwise as per the law of gravity the rate of fall would rise with increasing distance. So, with a rising rate of fall the weight per area, and hence the accuracy of the measurement, would decrease. There are two kinds of each of source and detector: Source: Point source or rod source; Detector: Point detection or rod type detector. Rod type sources are used in the case of free-falling material solid flow measurements. On many solid conveying systems, a nucleonic/radiometric weighing system is the only suitable method for determining mass flow. This type of measurement is very suitable for hot clinker conveying in a chain/apron conveyor. During the discussions in Subsection

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3.2.3.2 of Chapter I, illustrations such as in Fig. I/3.2.3.2-1 have been shown with rod sources, whereas here both types are illustrated. The basic theory of measurement has already been discussed in Subsection 3.2.3.2 of Chapter I, and so further discussions give functional details of nucleonic/radiometric instruments for solid flow measurement. 6.1.0 Principles of Operation for Nucleonic Mass Solid Flow Meters From the discussions in Chapter I it is clear that for nucleonic/radiometric solid flow measurement, a radiation source and a detection unit are necessary. The energy absorption of radioactive material is dependent on the load on the conveyor. Any material between the source and detector reduces the intensity of radiation to be measured at the detector. The radiation is absorbed by the product on the belt and the attenuated radiation is picked up by a detector. The output of the detector is evaluated by intelligent microcontrollers/ embedded systems. Therefore, nucleonic/ radiometric instruments illustrate the physical law of attenuation of radiation as explained in Subsection 3.2.3.2 of Chapter I from where we get that the attenuation of the radiation is dependent upon the height and bulk density of the material. The product of height and bulk density is the weight per area! When the mass per unit of area is multiplied by the material width, the result is the mass over unit length of the conveyor. When this product is again multiplied by the speed, this results in the desired mass per time unit. At this point it is worth noting that the contamination of the product being measured or the pipeline wall by gamma radiation is not possible. In radiation type solid flow meters, Caesium-137 or Cobalt-60 isotopes are normally used as radiation sources. The radiation source emits focused gamma rays, which are attenuated when penetrating the bulk material and the conveyor belt/pipe. The detector

on the other side of the conveyor belt/pipe receives the radiation, the strength of which is proportional to the bulk density of the material. As stated earlier, this type of measurement can be utilized for conveyors and in pipelines. 1. Solid flow in a conveyor: In the case of conveyor it is necessary to measure the speed of the conveyor. Conveyor speed can be inputted as a constant value manual input. Alternatively, it can be used with a constant speed conveyor giving constant speed input. In most cases these are used in conjunction with a tachometer to measure the speed of the conveyor. Therefore, for a conveyor, the following measurements are carried out: l Measurement at constant belt speed; l Measurement with a tachometer; l Measurement with moisture compensation. The attenuation occurring during maximum conveyor throughput determines the choice of source [34]. It is worth noting that radiation type solid flow measurement in a conveyor is not suitable if the conveyor loading is low, i.e., below 10% of full scale, and if the conveyors run for a short period of time, e.g., 10%, the load cell capacity is suitable; 98% 0.1% AR by vol. GVF230 C

8

Material

Stainless steel/copper-free aluminum

9

Connection

Flange of rating suitable for application

10

Sizes

Possible up to nearly 900 mm

11

Output

4e20 mADC, alarm and other digital I/O, RS 232/485 link, HART protocol. AI/AO optional

12

Local display

Digital LED/back-lit LCD display

13

Power supply

Normally 24 VDC but AC supply possible

14

Enclosure class

IP66 possible

15

Accuracy

Wide variation from þ0.05% to 5% AR based on type and range selected. Hi/low-cut inline meters offer better accuracy

16

Repeatability

0.01%e0.1%

17

Optional item

Densitometer

18

Special feature

2.3.4 WATER CUT METER DISCUSSIONS There are a few important issues associated with water cut meters in this section, which will be briefly discussed to complete the discussions on water cut meters. 1. Auto zero: It is a patented feature with a particular meter type but is very useful. It can accept density input from a densitometer to compensate for changes in fluid density in real time, meaning it uses live density for testing [26].

User Spec.

Remarks *Low/high cut types: Inline/top cut

Ref: Subsection 2.3.4.5

If any

2. Low/high and top cut: Low cut (LC) and high cut (HC) in water cut meters refer to an upper limit (span) for the water cut meter, normally these are 0%e15% and 50%, respectively. The top cut function enables measurement, using a density calculation for the cases when the meter is out of range. 3. Salinity compensation (for FC): Salinity is a function of the full cut (FC) meter, and hence is not really applicable for RF-based capacitance meters, which do not operate

Multiphase Flow Measurement Chapter | IX

in full cut range. In full cut of microwave resonant type meters this feature is retained to compensate for the salt content in the water fraction. The meter interprets the microwave signal to find the salinity of the water, and then makes use of this to produce accurate measurements [26]. In the case of NIR, this is not really applicable. In NIR, water absorption is based on the water molecule itself, not the dissolved salts. 4. Emulsion handling: As discussed at the beginning, there can be W/O emulsion which would try to scatter light in addition to light absorption, so, in NIR suitable measures are taken to nullify this scattering effect. 5. GVF effect: At up to 5% there is no effect, and up to 20% there is a minimum effect from GVF [27]. Beyond that there can be some effect for which multiple wavelength measurements are carried out. Normally GVF are 1 m) is typically several orders of magnitude larger than the length scale of any bubbles or flow nonuniformities. The long wavelength acoustics propagate through multiphase mixtures unimpeded, providing a robust and representative measure of the volumetrically averaged properties of the flow. Accurate measurement of the net oil rate from individual wells is a crucial issue which must be addressed properly for effective oil field management, production optimization, and financial allocation issues. The contribution of sonar in correct net oil measurement is immense. Normally net oil measurements are carried out by a Coriolis density meter (not very stable in the presence of gas as already discussed), microwave resonance, and microwave absorption. In all such measurements of oil cut, there will be overreading if there is the presence of gas. Sonar can be used in these cases to take care of overreadings. Use of sonar in wet gas measurement has already been discussed in Section 2.2.3. Therefore, the discussions can be concluded with the note that sonar technology helps in many ways the measurement of multiphase flow. 3.2.0 Microwave Measurements in Multiphase Microwave measurement technique and its difference with capacitive measurement as already discussed in Section 2.3.0. In the case of capacitance measurements RF signals are used whose

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frequencies are lower than microwave signals. Also, in the case of the microwave measurement technique either a change of frequencies of resonance due to permittivity is measured or absorption of microwave energy by the medium is measured. Different materials have different permittivities, and the permittivity of a mixture depends on the permittivity of the components and the composition. By measuring the permittivity of the mixture, one therefore gets information about the composition. This is especially so in the case of a mixture of gas/oil and water, because there are vast differences in the permittivity of water with respect to that of oil, and this is a major reason why microwave technology finds major applications in water cut meters. In general, permittivity is influenced by factors like temperature, density, and structure (e.g., the shape of the inclusions in a host material). When there are more than two components in the mixture (e.g., oil, water, and gas), the number of unknown parameters increases. In such cases multiparameter microwave measurements (e.g., resonant frequency and quality factor or, insertion loss and phase) [30] or other types of sensors in conjunction with this must be used. Prior to proceeding further, we look into the features, i.e., pros and cons, of measurement by microwave technology. 3.2.1 ADVANTAGES AND DISADVANTAGES OF MICROWAVE MEASUREMENT TECHNOLOGY Microwave technology enjoys some distinct advantages over other technologies involved in multiphase flow measurement, however it has some limitations also. In this section these are highlighted. 1. Advantages: Listed below are a few advantages of microwave technology: l Nonintrusive and noninvasive: Microwave sensors are nonintrusive and noninvasive sensors, so they can usually perform measurements from a distance, without interfering with the process; l Stability: On account of dependence of resonant frequency on physical dimensions

of the sensor it is stable in almost all conditions; l Penetration and volume measurement: Except metals, microwaves can penetrate all materials, making it possible to carry out measurements on the volume of the material, not the surface alone; l Permittivity difference of water: In multiphase flow measurement, microwave sensors find great contrast between water and other materials, hence they are well suited for measurement of water content; l Safety: When compared with gamma/ radioactive sensors, microwave measurements are much safer. This type of sensing is faster than its counterpart with radioactive sensing; l Material degradation: Measurement utilizing microwave technology, never affects the material under test; l Environmental effect: Microwave sensors are relatively insensitive to environmental conditions, such as humidity and dust. Also, sensors are less sensitive to material build up and hence are usable in slurries; l DC resistance: At microwave frequency of measurements DC conductivity almost disappears, hence measurement is relatively insensitive to temperature and ion concentration; 2. Disadvantages: Listed below are a few disadvantages of this measurement type: l Cost: The cost of measurement which goes up with higher frequency (for better results) is quite high; l Spatial resolution: On account of long wavelength, spatial resolution achievable is less; l Separate calibration: For each material separate calibration is essential for better results; l Compensation: On account of its sensitivity to more than a single parameter often it is necessary to compensate the same with the help of other sensor type(s); l Universality: Measurement type is application-specific, hence there is less universality [30].

Multiphase Flow Measurement Chapter | IX

3.2.2 THEORETICAL BACKGROUND FOR MEASUREMENT Microwave technology deployed in multiphase flow metering is mainly to determine void fraction and water cut. Of these two it is found more often in water cut measurements. Three physical properties are mainly exploited in microwave technology for multiphase flow metering systems. These properties are frequency (of resonance), change in wave length, and attenuation. Water content measurement by the microwave attenuation method is not only used in multiphase flow in oil and gas but is also used to measure water content in amorphous mixtures like margarine. So, in microwave measurement, there a generation source, detector, and computing system which analyzes the signal from detector(s) are required to give the results in a desired format. Therefore, the interaction between microwaves and the medium of propagation is completely determined by the relative permittivity and permeability. ε is the electric permittivity of the material, being ε ¼ ε0εr where ε0 is the permittivity of free space, and εr is the relative permittivity. If we take εr and mr as the relative permittivity and permeability of the medium, then it can be represented by εr ¼ ε0r ejε00r

(IX/3.2.2-1)

mr ¼ m0r ejm00r

(IX/3.2.2-2)

The real portion of permittivity is responsible for energy storage (or dielectric constant) and the imaginary portion stands to represent the energy loss portion which can come from dielectric rotational loss, interface polarization loss, and resistive loss. There are various kinds of sensors used in microwave measurement. These are described here. 1. Free-space transmission sensors: This is a very simple configuration. There are two dielectric windows on opposite sides of the pipe on the transmitting and receiving antennae. Here the major problematic issue is reflections from various surfaces and the measurement is highly dependent on the flow regime.

877

2. Special transmission sensing: In this type there are a set of transmitting antenna and two receiving antennas at different distances apart. In this configuration it cancels out normal error from the frequency response. For better results varying frequencies are often used. 3. Guided wave transmission sensors: Here microwave signals can be guided by coaxial cable or dielectric waveguide. The material/ medium is brought into contact with the electric field affecting the propagation factors like phase and attenuation. In this method there will be better control over impedance matching. The sensitivity is smaller and actually measures only a small fraction of the total flow in the pipe. 4. Reflection sensor: The reflection sensor measures the reflection coefficient of the wave as reflected from the end of a transmission line. It can cover a wide range of frequencies and is mainly used for measurements in laboratories. 5. Tomographic sensors: Tomography is a technique used to study (in general the crosssection of a solid object) the structure of flow in a pipe. Different kinds of tomography help to study in detail mixtures of liquid and gas, the phases separately producing various flow regimes, like annular flow, bubble flow, mist flow, churn flow, and slug flow. Microwave tomography is an advanced system. Like other tomography, for example, ultrasonic tomography, which has already been discussed in Subsection 1.2.4.2, in microwave tomography a transmitter is transmitting a wave that penetrates the medium to reach an array of receivers measuring the phase and amplitude of the wave front at different locations on the other side of the medium. 6. Resonator sensors: Microwave resonators can be implemented in many different ways for measuring in pipes. This is typically as shown in Fig. IX/3.2.0-1A. There can be two classes of resonator sensors: one type which is filled with the medium and other with a considerable part of the field outside the medium,

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(A)

(B)

MICROWAVE TRANSMITTER

COMPUTING UNIT PVC PIPE

USB CONNECTION

USB CONNECTION

COAXIAL

COAXIAL

CABLE

CABLE

MICROWAVE RECEIVER

RECEIVER

METALLIC RESONANT CAVITY TRANSMITTER BNC SYNCHRONIZING CABLE &CONNECTOT

(C) ELECTRONIC UNIT TEMPERATURE PROBE MICROWAVE OSCILLATOR

PIPE SECTION MEASURING UNIT SYSTEM

MORE WATER

CABLE

LESS WATER

STANDING WAVE POSITION

(D) ANTENNA & INSULATION

TRANSMITTER

RECEIVER 1

RECEIVER 2

FIGURE IX/3.2.0-1 Microwave sensing. (A) Sensor configuration. (B) Microwave sensing schematic. (C) Change of frequency sensing. (D) Absorption type microwave sensing.

Multiphase Flow Measurement Chapter | IX

typically as shown in Fig. IX/3.2.0-1A. The former type is limited to measuring materials with low losses. If the losses become too high, the resonance disappears. In the petroleum industry this typically means oil-continuous fluids (water drops in oil) [30]. Now let us look into different types of measurements by microwaves. 3.2.3 RESONATOR TYPE SENSING Microwave technology is based on resonant cavities that are often employed in water-cut meters. For measurement, it depends on the permittivity/dielectric properties of the multiphase medium. This technique is used in mixtures containing water, to take advantage of the large difference between the electric permittivity of water (εrw z 81 for frequencies < 1 GHz) and those of other flows such as oil (εro z 2). This is a good method of measurement as long as there is a good amount of water. The signal starts attenuating as the water content decreases. 1. Resonator basics: A resonator has a natural frequency of oscillation, a resonant frequency. During resonance energy is converted from one kind to another and back, e.g., energy transfer between electric magnetic energy in an LC oscillator. Based on the condition, the resonator can store energy so that it can continuously flip between two kinds of energies at a specific speed. In a microwave resonator electromagnetic waves travel back and forth between reflecting points resulting in a standing wave pattern, where the energy pulsates between electric and magnetic energy. Naturally, such periodic conversion of energy from one type to another normally involves losses. The quality factor in a resonator accounts for such losses. The quality factor represents the speed at which the stored energy is dissipated. Therefore, the quality factor, Q, is defined as: Q ¼ ð2p energy stored in resonatorÞ= energy lost in one cycle

879

2. Resonant frequency computation: Resonant cavities are closed metallic devices (rectangular or cylindrical shape), in which the energy is stored in the electromagnetic fields at a high frequency. The resonance occurs at distinct frequencies corresponding to different propagation modes, denoted by: transversal electric, TEnml, and transversal magnetic, Tnml, where n, m, and l, refer to a maximum electric field at a wave pattern in the cavity directions. The resonance frequency of a cylindrical cavity can be determined by: "  2 #1=2 2 c Pnm lp þ f nml ¼ pffiffiffiffiffiffiffiffi 2p mr εr d b (IX/3.2.3-1) where pnm are m-th-order Bessel functions of the first 100 kind, that vary according to the propagation mode; a is the cavity radius and d is the cavity length; m is the permeability of the material; εr is the electric permittivity of the material as already explained in Section 3.2.2. A typical sensor and sensing system has been depicted in Fig. IX/3.2.0-1A and B. By replacing the sensor parameter value one would get Kc Resonant frequency is given by: fr ¼ pffiffiffiffiffi εm (IX/3.2.3-2) where K is a constant for the sensor, c is the velocity of sound, and εm is the permittivity of mixture. Here it is noted that the resonant frequency of the cavity sensor is inversely proportional to the square root of the material’s permittivity and that the permittivity varies with the fraction of water inside. This equation may be compared with Eq. IX/2.1.0-4. For the cases ε0r [ε00r it is possible to get the relation as given in Eq. IX/2.1.0-4. This type is used by ROXAR meters. 3. Operation: With a microwave resonator it is found that when electromagnetic waves are transmitted into a particular flowing mixture there is only one peak for each percentage of

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water (except for 0% of water which has two peaks). So, in a resonant type meter, when the electromagnetic waves transmit into a particular flowing mixture there will be a peak amplitude at a characteristic frequency (wavelength) which corresponds directly to the water content of the mixture. This characteristic resonant frequency is inversely proportional to the square root of the mixture dielectric constants (In this connection Fig. IX/2.3.0-1B may be referenced). The difficulty arises when the energy loss portion of the permittivity becomes significant then the measurement technique becomes inaccurate. It is very difficult to predict when the imaginary part of the permittivity becomes dominant. Microwave resonators generally have many resonant frequencies. The frequency of the excitation (source of energy to be stored) determines the frequency of oscillation, but considerable build up of energy in the resonator takes place only when the frequency of excitation is close to a resonant frequency. Normally these types of meters include one microwave device which measures the electrical properties of the flowing mixture, and a temperature sensor to measure the temperature of the mixture. The computed device connected to the measuring system provides signals corresponding to the measured dielectric constant and temperature values and utilizes the signal in computation. Emulsion is another issue. There are two kinds of emulsions: oil-inwater and water-in-oil. Even with the same water content, the electrical properties of these two types are quite different. Therefore, instruments based on these principles have their own tables, to make the necessary corrections for better accuracy and to nullify the emulsion effect. 4. Constructional details: In typical resonant type metering, there will be a PVC type pipe through which the mixture flows. This pipe has one outer metallic (conductor) coaxial transmission line, and there will be one metal rod inside. A similar type has been shown in Fig. IX/3.2.0-1A only, instead of the inner rod, two sensors are shown schematically for better understanding. However, the basic idea is the same to complete the flow path of an

electromagnetic wave through the mixture. A basic measurement scheme has been depicted in Fig. IX/3.2.0-1B. 3.2.4 CHANGE OF FREQUENCY TYPE MEASUREMENT As the name suggests in this method, a change in the operating frequency of the system is used to detect changes to the fluid permittivity. It is reported that the measurement offers a few-fold higher sensitivity than other types. However, in this method the accuracy very much depends on salinity, density, and temperature of the fluids. Therefore, prior knowledge (and field calibration) of the fluid properties is important to maintain the required accuracy. Also, knowledge about the velocity and viscosity are important to assure the homogeneous stream necessary for measurement. A phase dynamics analyzer falls under this category of measurement. 1. Theoretical background: In this method there will be a change in the operating frequency with the change output load of the oscillator. Such a phenomenon is often referred to as load pull. Here there are complimentary loads in the entire system, i.e., permittivity of the medium in the measurement section determines the output load. The circuit components in conjunction with the external load impedance determine the oscillator frequency based on the standing wave position. As already discussed, εrm (relative permittivity of mixture) has two parts: the real part (corresponding to the dielectric constant) and the imaginary part (the loss). The temperature and loss part also affects the frequency (usually necessary compensations are provided). During measurement the permittivity of the mixture provides a complex load which causes the oscillator to precisely change in frequency, proportional to the water content of the mixture but how? It does so by sensing the standing wave position. The electronics at the end send an electrical signal down through the fluids, which due to reflection causes the generation of a standing wave. The microwave

Multiphase Flow Measurement Chapter | IX

oscillator sends out the signal automatically, detects the change in position, and adjusts its basic frequency based on the water content in the mixture. 2. Implementation: There are two sets of oscillators: the oil oscillator and the water oscillator: l Oil-continuous water-cuts: frequency: 100 MHz with 200 KHz frequency change per %WC; l Water-continuous condition: 130 MHz of frequency with 50e150 KHz frequency change per %WC (depending upon water salinity) [30]. Based on the reflected power level, the oscillator selection is carried out, i.e., due to less loss, higher reflected power levels indicate the mixture is an emulsion is and oilcontinuous and due to more loss, lower reflected power levels indicates the mixture is, an emulsion and is water-continuous. The reflected power levels of the oscillator are measured by the system, and compared with a predetermined threshold. Hence, depending on whether it is above or below the threshold, such oscillator switching is done. 3. Instrument parts: The system typically consists of three components as shown in Fig. IX/3.2.0-1C: l A measurement section; l An electronic unit; l System cable. The measurement section comprises the following parts: l Pipe section; l Temperature probe; l Microwave oscillator; l RF connector connects the measurement section and the microwave oscillator.

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velocity of the components being analyzed. These meters are available in 150 mm and above, and water cut ranges of 0%e100%. With the help of microwave absorption technology, this type of meter measures liquid-in-liquid concentrations. The major negative point in this type of measurement is a drop in accuracy if the mixture is not homogeneous, i.e., the droplet size or coating thickness can greatly affecting measurement. The fluid at the surface of the insulator dominates the effect, in particular when the fluid consists of two immiscible fluids [30].

3.2.5 ABSORPTION TYPE MEASUREMENT

1. Theoretical background: As stated above, this type of water-cut meter measures the energy absorption properties of the oil/water mixture to provide output for 0%e100% water cut. With the help of a comparator and two theoretically fed curves (one each for the oil-continuous and water-continuous phases) determines the medium category as oil-continuous phase or water-continuous phase to select the proper energy absorption data curve. The instrument consists of one transmitter and two receivers. Both the transmitter and receivers are provided with an antenna exposed to the medium. The transmitter transmits signals of specific frequency (AGAR use this type of measurement and transmit 2.45 GHz) signal. The phase difference (and/or the ratio) between the signals from two receivers are used to measure the concentration of the two measured substances. As both receiver antennae are exposed to the same fluid in exactly the same way, by taking the phase difference of these signals, the output becomes independent of the surface coating [30]. 2. Instrument parts: As shown in Fig. IX/ 3.2.0-1D the meter consists of the following: l A transmitter to transmit a high-frequency signal through duly insulated antenna; l Two receivers spaced at distance (along the length) and connected through the antenna describe above.

In this type of meter, accuracies of oil/water meters in this category are not affected by changes in salinity, density, viscosity, temperature, or

The impedance of the fluid acting on the antenna varies with the electrical properties of the fluid and can affect the amount of transmitted energy.

Let us now take a look at absorption type sensing.

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A divider divides the outputs of the receivers and supplies a linearized output. We now conclude the discussions on microwave technology in multiphase flow measurement and look at various other technologies.

components in layer form. These can be in dispersed form also. Therefore, it is better to replace xs with the pipe internal diameter d and to rewrite those equations as:

3.3.0 Gamma Ray and Neutron Integration Technology

IB ¼ I0B $eðm1 Bagdþm2 Baodþm3 BawdÞ (IX/3.3.1-2)

In this section the application of gamma ray/ X-ray and neutron technology in the measurement of multiphase flow are covered. Basic details about gamma ray measurement in multiphase flow applications have already been discussed in detail in Subsections 1.2.3.4 and 2.1.2.2. Therefore, in this section some design aspects are discussed. On the other hand, there is another new technique is Neutron activation analysis (NAA). We start the discussion with balance details of gamma ray measurement.

And use

3.3.1 GAMMA RAY ABSORPTION METERING

IA ¼ I0A $eðm1 Aagdþm2 Aaodþm3 AawdÞ (IX/3.3.1-1)

ag þ ao þ aw ¼ 1

(IX/3.3.1-3)

Rg, Ro, Rw, and Rm represent the natural logarithm of the count rates for gas, oil, water, and the mixture, respectively, at energies eA and eB. One could get the phase fraction from the solution of the following matrix. 3 2 3 2 3 2 Rg eA Ro eA Rw eA ag Rm eA 7 6 7 6 7 6 4 Rg eB Ro eB Rw eB 5$4 ao 5 ¼ 4 Rm eB 5 1 1 1 1 aw (IX/3.3.1-4)

It will not be out of place to recap what we have learnt so far on gamma ray measurements pertinent to multiphase flow metering. In this subsection we have established the relationship of gamma ray absorption and void fractions. Also, in Fig. IX/1.2.3-4 various possible configurations for source and detector(s) as well as applications of gamma ray in various flow regimes are illustrated. The basic relation formula for void fraction and absorption energy has been established. Let us refer to Subsection 2.1.2.2 along with Fig. IX/ 2.1.0-1 and associated equations (Eq. IX/2.1.0-1 through IX/2.1.0-3). In that subsection it has been found that there is established generalized way to find out phase fractions in Gas/oil/water. Here same will be used.

The elements in the matrix are calibration constants, i.e., determined during the calibration process by calibrating the instrument with 100% of each of the components (air for gas). From this we get phase fractions. This measurement in conjunction with Venturi can provide individual component flow, as explained in Fig. IX/3.3.1-1. We now examine the various design details for the measurement. 2. Energy source selection: For the study of emission and absorption of gamma rays (also X-rays), statistical methods are deployed and normally they follow a Poisson distribution. For gamma rays the following relation holds good [31]:

m $r$d ¼ 2 (IX/3.3.1-5) m$d ¼ d

1. Phase fraction determination: In Eq. IX/ 2.1.0-1 through Eq. IX/2.1.0-3, we considered gas, oil, and water to be x1, x2, x3 distance from the source. However, in a practical case it is not likely that there will be three

As indicated during the initial discussion in Section 1.2.3 of this chapter, m represents the linear absorption coefficient which is dependent on the process condition, i.e., pressure

883

DPT

GAMMA SOURCE

FLOW

Multiphase Flow Measurement Chapter | IX

d

DETECTOR

COMPUTING UNIT PF g PF o

VENTURI

PF

w

q

qg

VMIX

=C*K d

DP DENSITYMIX

=q * PFg VMIX

* PFo qo =q VMIX qw =q * PF VMIX

w

SHIELD IN BOTH SOURCE & DETECTOR

FIGURE IX/3.3.1-1 Gamma ray and Venturi. Cd, discharge coefficient; g, gas; K, constant; MIX, mixture; o, oil; PF, phase fraction legend for suffix; q, flow (volumetric); w, water.

and temperature. Here (m/r) represents the mass absorption coefficient, which is independent of the process condition. As a consequence, the uncertainty of measurement is dependent on the process condition and of course pipe internal diameter (distance between the source and detector). In dual-energy design

it is important to select the low and high energy level sources. Listed in Table IX/3.3.1-1 are some commonly used materials. Normally, a low energy source in the range of 10e30 keV is chosen. Am-241 is also an alpha emitter. The high energy level should be higher than 40e50 keV [31].

TABLE IX/3.3.1-1 Commonly Used Gamma Sources (Not All Peaks are Given) Isotope

Half Life

Approximate Photon Energy (KeV)

Armericium 241

433 years

12e22

Barium 133

10.8 years

30e36 to 384 long possibilities

Cesium 137

453 days

22e26

Cobalt 57

270 days

6.5e7; 14.4 even 136.5 various peaks

Cobalt 60

5.27 years

1300

Lead 210

22.3 years

94e16.4

Plutonium 238

128 days

60 Variations

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3. Detector: For detector selection two important issues are efficiency and resolution. Sodium iodide (Nal) scintillation crystals and Si solid-state detectors are normally used for gamma ray detection. At a lower energy level efficiency the former one is much better than a solid-state detector. For a high energy level for functioning of Si solid-state detectors, a larger area may be necessary. From a resolution point of view semiconductor detectors are far ahead of other commonly used types, i.e., Nal scintillation detectors. The smaller the area detector, the better will be the resolution. Also, resolution is more critical for a low energy level. Therefore, during selection due consideration should be taken. From the discussions it is clear that there are some contradictions in the requirements for which there have been developments of dual-area solid-state detectors in practical applications. 4. Window materials: Low-energy gamma rays demand strong, radiation-transparent wall material. Carbon fibers are transparent as well as extremely strong and it is held by an epoxy matrix, hence Carbon fiber reinforced epoxy (CFRE) is chosen as the window material. 5. Measurement uncertainty and allied issues: As stated earlier, studies of the emission and absorption of gamma rays are based on statistical methods, so the uncertainties of measurement in phase fraction calculations are due to the statistical behavior of gamma rays. It has been found that absolute uncertainty in the oil fraction is the highest. In small fluid path length since there could be insufficient contrast in the absorption between the oil and the water phases uncertainty is greater. Whereas with an increase in fluid path length it decreases as it can be distinguished. The fraction uncertainty is large for a small fluid path length, as there is, but decreases as the fluid path increases up to a certain length beyond which again uncertainty increases because, on account of high absorption, the count is too small. Salinity also has a direct effect on uncertainty in measurement.

With use of dual-energy gamma rays (DEGRA) it is possible to find three-phase fractions. With an increase of another energy level, i.e., with tripleenergy gamma rays (TEGRA), it is possible to detect another parameter, e.g., salinity. In this way there can be multiple-energy gamma rays (MEGRA). While discussing gamma rays, we now look into another gamma ray spectrum in measurement through neuron activation analysis techniques. 3.3.2 NEUTRON ACTIVATION ANALYSIS —BASIC DEFINITIONS OF TERMS Before we start any discussions we look at the term “neutron activation analysis.” There exist many definitions of neutron activation analysis (NAA), which are more or less similar but may not be complete in definition, especially in the context of multiphase flow metering. Also, during discussions on NAA, there will be a number of popular terms in nuclear engineering that will be referred to. So, in order to facilitate the reader to recap these terms to understand the system better, these are also defined and explained here. But first we define NAA in the perspective of multiphase flow metering. 1. Neutron activation analysis: This is an analytical method used to analyze material(s) to determine chemical elements and their quantity (concentration) for the components of the test material(s) by bombarding it with neutrons to produce radioactive forms that can be identified by their characterized radiation emissions, which are indicative of elements present and their quantity. In most of the definitions the term “quantity” may not be used because the main aim of NAA is to find the chemical composition. On the other hand, for multiphase flow, “quantity” measurement (which is, of course, available as part of the analysis) is important. Discovered in 1936 neutron activation analysis has been in use for bulk material analysis. It is a technique used to determine the average (bulk) concentrations of all elements,

Multiphase Flow Measurement Chapter | IX

2.

3.

4.

5.

including trace elements in the test material. As part of the characterization of the test material, it also helps in determining chemical similarities or differences. Types of NAA: With respect to the time of measurement, NAA can be categorized as: prompt gamma-ray neutron activation analysis (PGNAA) and delayed gamma-ray neutron activation analysis (DGNAA) Prompt gamma-ray neutron activation analysis (PGAA): The PGAA technique is generally performed with the use of beam of neutrons for the elements with extremely high neutron capture cross-sections which decay too rapidly. Therefore, measurements take place during irradiation. Delayed gamma-ray neutron activation analysis (DGNAA): This is the most common type and is often known as conventional NAA and is useful for the majority of elements. The technique is flexible with respect to time. The decay process is at a much slower rate than the initial de-excitation and is dependent on the unique half-life of the radioactive nucleus. Gamma ray and negative beta particles: Of several methods of radioactive decay, gamma ray and negative beta particles are important for NAA. l Gamma rays: Gamma rays are emitted when an excited nucleus transits from a higher excited energy state to a lower energy state, i.e., when the nucleus gets de-excited. Gamma rays have welldefined energies and such emission in most cases is accompanied by nuclear reactions or decay. l Negative beta particles: Negative beta particles (b-) are basically electrons formed when a neutron is transformed into a proton during nuclear transformation. After neutron transformation, the atomic number (Z) of the resultant nucleus is one unit greater, but the mass number remains unchanged.

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6. Neutron reactions and types: During bombardment with neutrons, the target nuclei undergo many possible nuclear reactions. There are four major reactions: l Neutron capture; l Transmutation; l Fission reaction; l Inelastic scattering. 7. Neutron capture: The target (material) nucleus captures (or absorbs) a neutron to produce product isotope. Naturally, there will be an increment in the mass number. If the product nucleus is unstable, it usually de-excites by emission of gamma rays and/ or b- to migrate into a stable state. The entire phenomenon is referred to as neutron capture. 8. Inelastic scattering: Of the four neutron reactions mentioned above, inelastic scattering is an important event in our case study. In this phenomenon the target nucleus does not absorb the incident neutron, except only part of the neutron energy is transferred to the target. 9. Neuron sources: Nuclear reactor, cyclotron, fast neutron generator, and of course, isotopic neutron sources are major sources used in NAA for getting neutrons. 10. Neutron flux: The amount of neutrons available for irradiation is referred to as the neutron flux. It is expressed as the number of neutrons incident per unit area per second. Therefore, it is expressed as n/cm2 s in CGS units. 11. Neutron capture cross-section: Neutron capture cross-section of the isotope leading to a specified nuclear reaction. Unit of area: barns (1 burn ¼ 1024 cm). 3.3.3 NEUTRON ACTIVATION ANALYSIS PROCESS 1. Preamble: NAA is quite popular for quantitative multielement analysis and measurement to detect various elements, including traces or rare elements. The basic process of NAA can be well understood when the sequence of events of the process is suitably followed.

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2. Theoretical background: The process starts by exposing the test material or sample to energized neutrons, which may be generated from any of the various sources mentioned in Subsection 3.3.2.9 or may be from a reactor. On account of the interaction between the neutrons with the test material, this causes formation of radioactive nuclei that emit characteristic gamma rays. Suitable semiconductor type radiation detectors are used for qualitative and quantitative measurement for the presence of a particular element. Detection of the specific gamma rays (of specific energy) indicates the presence of a particular element, while the area underneath the spectrum indicates the concentration of the element. For all such relevant measurements the detected data are sent to a computer for analysis and to produce the necessary result. The majority of elements can be assessed by this method. An NAA-based monitoring system requires little set-up time and space to provide data in-line. From an MPFM perspective, this monitoring system is accurate over the full range of possible oil-water-gas fractions, and is unaffected by the pressure, temperature, and flow regime into the pipe [32]. 3. Process sequence of event: In typical NAA, stable nuclide test material undergoes neutron capture reactions on account of the incident flux of neutrons from the source. As shown in Fig. IX/3.3.2-1, on account of the interaction of neutrons with the target material, radioactive nuclides (Aþ1Z), are produced. As part of the nuclear capture process, as described in Subsection 3.3.2.7, there will be a compound nucleus that forms in an excited state when a neutron interacts with the target nucleus via a nonelastic collision. The excitation energy of the compound nucleus comes from the binding energy of the neutron with the nucleus [33]. The compound nucleus is unstable, it may almost instantaneously de-excite into a more stable configuration through the emission of one or more characteristic prompt

gamma rays. Alternatively, in many cases, this new configuration produces a radioactive nucleus, which also may become de-excited (or decayed) by the emission of one or more characteristic delayed gamma rays, but at a much lower rate. Thus, in this activation process, there will normally be generation of emission of a beta particle (ß-) and gamma ray(s) with a unique half-life, as a result of the decaying process. Therefore, there are two such processes, as shown in Fig. IX/ 3.3.2-1, namely, prompt gamma-ray neutron activation analysis (PGNAA), where measurements take place during irradiation, and delayed gamma-ray neutron activation analysis (DGNAA radioactive decay). A highresolution gamma-ray spectrometer is used to detect energy-specific gamma rays in the presence of the artificially induced radioactivity in the sample for both qualitative and quantitative analysis. There is a sequence of events that happen in NAA and this has been depicted in Fig. IX/3.3.2-1. The usual procedure involves placement of test material vis-a-vis suitable standards. In a detector the gamma ray energies are converted into an electrical signal that is processed as a count in an energy spectrum. The accumulation of gamma counts at a particular energy generates a curve, the area of which is proportional to the concentration or radioactivity of the characteristic radionuclide. Comparing against standards allows the establishment of a relationship that can be used to determine the abundance of a particular element or elements. The measured count rate (R) of the gamma rays from the decay of a specific isotope in the irradiated sample can be related to the amount (n) of the original, stable isotope in the sample through the following equation [34].   R ¼ ε$Ig $A ¼ ε$Ig $n$4$s$ 1  elti $eltd (IX/3.3.3-1) R ¼ measured gamma-ray count rate (cps); A ¼ absolute activity of isotope Aþ1Z in sample;

Multiphase Flow Measurement Chapter | IX

ATOM

-10

RADIUS OF ORDER 10

NUCLEUS

-14

RADIUS OF ORDER 10

-18

TO GET

RADIUS OF ORDER 10

NEUTRON

AN IDEA

887

M

M M

PROBABILITY OF STRIKE DEPENDS ON ENERGY OF NEUTRON & TARGET NATURE

BETAPARTICLE E NEUTRON CAPTURE

RADIOACTIVE DECAY

NEUTRON

FINAL PRODUCT NUCLEUS

PROMPT GAMMA RADIATION (PGAA)

DELAYED GAMMA RADIATION (DGNAA)

FIGURE IX/3.3.2-1 NAA details.

ε ¼ absolute detector efficiency; Ig ¼ absolute gamma-ray abundance; n ¼ number of atoms of isotope AZ in the sample; 4 ¼ neutron flux (neutrons$cm2 s1); s ¼ neutron capture crosssection (cm2) for isotope AZ; l ¼ radioactive decay constant (s1) for isotope Aþ1Z; ti ¼ irradiation time (s); td ¼ decay time (s). When 4, s, ε, and Ig are known, the number of atoms n of isotope AZ in the sample can be calculated directly. In almost all cases the count and mass element in the test material are compared with the standard, i.e., to make ðWtest =Rtest Þ ¼ ðWstd =Rstd Þ

(IX/3.3.3-2)

where W and R represent mass element and count rate, respectively. Suffices with (R and W) “test” and “std” represent “test” (for test material) and “std” for standard, respectively. The electrical

signals from the detectors are sent to the computer where these calculations are performed and after due comparison with standard data (stored in the computer) the final result is produced. 3.3.4 PROMPT GAMMA-RAY NEUTRON ACTIVATION ANALYSIS (PGNAA) The nuclei of some elements of a test material placed in a field of neutrons absorb neutrons and are transformed to an isotope of higher mass number. This is a different kind from conventional NAA using decay of the radioactive element. As mentioned in Subsection 3.3.2.3, the PGAA technique is mainly applicable for elements with extremely high neutron capture crosssections. These elements emit prompt gamma rays at the time of neutron capture and do not produce radioactive capture products. In PGAA, a beam of neutrons from a reactor beam port is

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used. Fluxes on samples irradiated in beams are in the order of one million times lower than on samples inside a reactor but detectors can be placed very close to the sample, compensating for much of the loss in sensitivity due to flux [33] and make the measurement possible. A highresolution gamma-ray spectrometer detector is used for qualitative identification and quantitative analysis of the neutron-capturing elements present in the test material. In this method measurement is carried out with the help of a semiconductor Germanium detector. Usually the beam stop is also included in the system. 3.3.5 DELAYED GAMMA-RAY NEUTRON ACTIVATION ANALYSIS (DGNAA) Delayed gamma ray neutron activation analysis is often referred to as conventional NAA as it is applicable and useful for the vast majority of elements that produce radioactive nuclides. When the test material is irradiated, interactions of fissionable nuclei may produce radioactive products with more than one neutron emission. When these radioactive components have the capability to emit neutrons they are referred to as delayed neutron precursors (DNPs). Generally these components have a few neutrons in excess of a fully occupied, closed neutron shell, so, due to low binding energy there will be a great probability of losing them [35]. These nuclides, instead of direct neutron emission, undergo b-decay. Based on the number of atoms in the target material, a proportional number of activated atoms will be there to indicate the amount of radiation. The timing of a delayed neutron reaction is governed by the rate of b-decay. DNPs emit “late” neutrons, which are referred to as delayed neutrons. In this process there are interferences of short- and long-lived radionuclides. Interference can be improved in long-lived radionuclides by waiting for the short-lived radionuclides to decay or, in contrast, the sensitivity for short-lived isotopes can be improved by reducing the time [33]. Commonly used detectors

are 3B-BF3 or 3He detectors [35]. Sampling errors, timing of irradiation, counting system, data reduction, and low efficiency of detectors are common sources of error. 3.3.6 NAA AND OIL EXPLORATION It is interesting to note that about 70% of the oil resources in the world are heavy oil. Most of the commonly used MPFMs do not work well with heavy oil. The main problems associated with heavy oil exploration include high viscosity and low reservoir pressure. On account of this, enhanced oil recovery techniques, such as cold techniques (with sand, water flooding, vapor assistance) and hot/thermal production (steamassisted), techniques are called for. The major reasons for nonsuitability of conventional multiphase flow metering include but are not limited to the following issues: 1. Gravity contrast: Since there is practically no gravity contrast between oil and water, conventional techniques are not suitable for separation, hence multiphase flow metering. 2. Enhanced recovery method requirements: On account of enhanced oil recovery techniques for heavy oil extraction, the MPFM must be able to cope up with a few criteria needed [32]: l Emulsification of fluid; l Foaming; l High temperature; l Entrapped gas/sand/water; l High water cut. 3. NAA as MPFM: Nondestructive NAA deals with neutrons with no charge to interact with charged particles. As is already clear from previous discussions, gamma spectroscopy is used to measure the gamma ray spectra from which it is possible to get the elemental composition and the relative amount of each element in test material. NAA can be used to measure the flow rate. As already discussed there will be production of radioactive isotopes,

Multiphase Flow Measurement Chapter | IX

which decay with a variety of half-lives. With the help of neutron pulses it is possible to activate species in the fluid. On account of flow, the activated species are transported and gamma rays from the activity are detected downstream from the activation point. The system calibration can be conducted away from the site with suitable samples [32]. With known salinity, it is possible by NAA to infer the relative presence of salts also. It is possible to arrive at the mixture fractions of oil, water, and gas, with the help of measurement of oxygen, carbon, and hydrogen composition as well as measurement of the chlorine and sulfur composition of fluid provided the salinity of the fluid is known. With NAA one can get the rate of an element flow, and density of certain elements in the conduit. The detection of many specific elements for fluid of the particular oil reservoir with neutron interrogation technique will give an opportunity to determine the combination of parameters and cross-checking of the results will give more accuracy for such a multiphase flow meter [32]. Since neutrons can penetrate the pipe wall, the installation of the device is easier and faster without any change in tubing system. Neutron interrogation monitoring systems will work reliably in a heavy oil environment [32]. From this discussion one can conclude that NAA is an effective measurement method in the area of MPFM, especially for oil and gas. With this we conclude the discussions on NAA to discuss another technology for MPFM. 3.4.0 Wire Mesh and Electrical Impedance Technology In this section discussions are presented on wire mesh sensors and electrical impedance sensors for measurement of multiphase flow. Brief discussions on electrical impedance measurements have already been presented in Subsection 1.2.3.3 above. Therefore, the reader already has some idea about it. However, wire mesh sensing is a completely new topic, so the discussion starts with wire mesh sensing.

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3.4.1 WIRE MESH TYPE MEASUREMENT FUNDAMENTALS With the help of wire mesh sensors flow imaging is possible, so it can be used to investigate multiphase flow. 1. Flow imaging (not tomography): Many refer to this technology as a type of tomography. However, as tomography in principle is a noninvasive type of measurement and wire mesh measurement is invasive (i.e., electrodes fall in the path of material flow line for generation of image), it cannot be considered as a tomographic measurement. However, it can be considered as an alternative technique to the tomography systems. Compared to other technologies, wire mesh is a newer one introduced in 1998. On account of its measurement technique and data presentation technique it can be considered as an “in-between technique,” lying between local phase fraction measurement and cross-sectional imaging, i.e., tomography. In any case the measurement type offers high spatial and temporal resolution [11]. 2. Requirement: As shown in Fig. IX/3.4.1-1A and B there will be two sets of wires across the pipe cross-section, with uniform axial separation between them. Each set of parallel wires is perpendicular to the other set, as shown in Fig. IX/3.4.1-1A. One parallel set is the transmitting set and the other is the receiving set. Both transmitter sets of wires, as well as receiving set of wires, are connected to an electronic unit. At the electronic unit digitized data are processed with the help of a computer and presented for visualization and recording. It is worth noting that in the figures under reference, a schematic has been shown for conductivity measurement but it can be based on permittivity measurement also (discussed next). 3. Types of measurement: An electronic unit associated with wire mesh measurement measures electrical properties of the flowing medium, i.e., conductivity or permittivity. Depending on the excitation system and

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Plant Flow Measurement and Control Handbook

(B)

ELECTRONIC UNIT

FLOW

RECEIVER

TRANSMITTER

(A)

(C)

CONTROLLING SIGNAL ELECTRONIC A/D: ANALOG TO DIGITAL

UNIT

+

-

+ +

S3

R2 +

S4

+

R3 +

A/D CONVERSION

R1 SAMPLE & HOLD CIRCUIT

+ S2

CONTROLLING SIGNAL

S1

R4 SUPPLY VOLTAGE

+

FIGURE IX/3.4.1-1 Wire mesh measurement. (A) Typical wire mesh sensors. (B) Wire mesh measurement scheme. (C) Wire mesh measuring circuit.

Multiphase Flow Measurement Chapter | IX

measurement at the electronic unit there are two types of wire mesh sensing. These are conductivity type and permittivity or capacitance type. l Conductivity type: In conductivity type measurement, the transmitting wires are excited by bipolar DC voltage pulses. Therefore, receiving circuit measurement will be DC type. The electronic unit measures the local conductivity in the gaps of all crossing points at a high repetition rate. Therefore, in this type, in order to measure conductivity, in two-phase flow, one phase has to be an electrically conducting phase (conductivity > 0.5 mS/cm) and the other a nonconducting type, e.g., water and oil. The obtained conductivity in the gap across the cross-sectional area indicates the presence of phases at crossing points. l Permittivity/capacitance type: In capacitance type wire mesh, transmitting lines are excited by sinusoidal alternating voltage and receiving circuit encompasses demodulating scheme to interpret the changes in permittivity at the junction point to infer the fluid phase condition at the junction point. Therefore, similar to the conductivity type, this type also is capable of detecting phase distribution in gaseliquid or liquide liquid fluids. Therefore, the sensors can determine instantaneous phase fraction distributions over the pipe cross-section by measuring conductivity/ permittivity in the gaps. The measurement is quite accurate and highly repeatable. 3.4.2 ELECTRICAL MEASUREMENT OF CONDUCTIVITY TYPE WIRE MESH As indicated above, the grid circuit created by the wire mesh consists of two sets of wires, one set is connected to the transmitter circuit and the other set is connected to the receiver circuit. In Fig. IX/3.4.1-1AeC vertical wire lines (shown in Fig. IX/3.4.1-1B) are connected to the receiving circuit. The horizontal wire lines

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(shown in Fig. IX/3.4.1-1B) are connected to the transmitter circuit. A typical measurement block schematic is shown in Fig. IX/3.4.1-1C. In the block schematic wire mesh of 4  4 sensor configuration has been shown for explanation purposes only. Transmitter lines are taken into operation one by one in sequence. So, in order to bring the lines into sequence, one needs to use the switching circuit shown by S1 through S4 (time multiplexing) in the transmitter circuit. These are activated in sequence duly controlled from the electronic unit. As shown, nonactivated electrodes are connected to ground potential because of the chosen configuration. The current at the receiver wire is due to the activation of a given transmitter wire, and varies according to the conductivity of the fluid in the corresponding control volume close to the crossing point of the two wires (as they get connected by fluid). The currents from all receiver wires should be sampled simultaneously to get an idea of the conductivity distribution along the transmitter wire line. After the first transmitter (e.g., by S1) line sample measurement is completed, the next line is chosen (e.g., by S2) to repeat the same sampling procedure. In this manner the procedure is repeated for all transmitter electrodes. Therefore, after the last transmitter line is activated, a complete set of measurements for the whole cross-section has been acquired. Each switch measures a horizontal strip (subdivision/ region) and through S1 to Sn such strips are integrated, meaning that an image of the entire cross-section is received. The measurements are in fact voltages which are proportional to the conductivity of the medium around each crossing point of the wire grid at the very moment of data sampling [11]. Each crossing point represents one subregion, meaning when S1 is ON, it measures conductivity at four subregions constituted by four receiver lines. Thus each crossing point acts as a local phase indicator. Therefore, the set of data obtained from the sensors actually represents the phase distribution over the cross-section. For explanation, only 4  4 mesh has been shown, it could be 128  128 or

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Plant Flow Measurement and Control Handbook

more with a wire diameter as low as 0.05 mm. Nowadays, high-pressure high-temperature versions are available. The electronic unit regulates both signal generation by controlling the switching circuits and controls data acquisition also. A maximum temporal resolution of 10,000 frames per second has been made possible [11]. The intrusive effect of wire mesh sensors is mainly observed downstream of the sensors. However, the intrusive effect of this type of measurement has been discussed briefly in Section 3.4.4 below. The disadvantage of being intrusive is in part compensated by high temporal resolution, low cost, and simplicity when compared with other imaging systems [11]. As stated earlier in Subsection 3.4.1.3, in conductivity type wire mesh sensing, bipolar voltage pulses are used for sending signals through the transmission line. Thus, supply voltage shown in Fig. IX/3.4.1-1C is supplied through a switch under the control of an electronic unit. Similarly, the measurement scheme is a DC measurement scheme. 3.4.3 ELECTRICAL MEASUREMENT OF CAPACITANCE TYPE WIRE MESH This type of measurement was introduced later to investigation the mixture containing nonconducting fluids, such as oil. Here the change in permittivity or capacitance is measured. 1. Basic circuit description: As stated earlier, in a capacitance wire mesh sensing system, sinusoidal AC excitation voltage is applied with the receiver to encompass a demodulation scheme. Like conductivity type sensing, transmitter lines/electrodes are activated one after another sequentially and unused ones are grounded. All current flowing from the transmitter to the receiving electrodes/lines in the other plane is measured in parallel. Through the virtual ground of the measuring amplifier, the receiving section amplifiers have only signals from the active transmitter line, as shown in Fig. IX/3.4.3-1A. Here AC excitation

shown in transmitter lines/electrodes are high-frequency signals generated through a digital synthesizing oscillating circuit in the range of a few (0.1e10) MHz [11]. Like conductivity wire mesh, the AC excitation signal is switched in time-multiplexer mode to each of the transmitting lines/electrodes with the help of switches S1 through S4 (similar to that for the conductivity type). The current from the transmitting lines/electrodes is converted into voltage through the balance converting amplifier shown. Log amplifier circuitry is used for demodulation purposes. Naturally, the analog signals generated are converted into a digital signal by an analogto-digital converter (ADC) before feeding to the electronic unit. These functions are performed with the help of a microcontroller and associated circuitry in the electronic unit. 2. AC excitation system: In order to get suppression of cross-talk at each crossing point to get local phase fraction in individual subregion of transmission line/electrode, it is necessary to activate each transmission electrode sequentially with the help of a switching circuit (e.g., S1 through S4) in time multiplexed mode so that only one transmitter is active at a time and others are at ground potential. As discussed earlier, all currents flowing from the transmitter to receiver electrodes at the other wire plane are measured in parallel. At the receiver measuring circuit, one end of the amplifier is at ground potential (by virtual ground), so, for each receiver measurement, it is concentrated along the active transmitter wire and the current measured at one receiver wire is only proportional to the capacitance (permittivity) of the surrounding flow phase at the crossing point. Such sequential operation of the transmitter line and ADC has been shown schematically in Fig. IX/3.4.3-1B. 3. Permittivity assessment: We earlier noted that the permittivities of different materials are different, naturally the dielectric constant

Multiphase Flow Measurement Chapter | IX

(A)

893

CONTROLLING SIGNAL ELECTRONIC A/D: ANALOG TO DIGITAL

UNIT

-

-

C1

+

R1 -

S2

-

LOG DETECTOR

-R2

+ S3

+ C3 -

S4 S4

(EACH)

+ C2

R3 -

+

+ C4

CONTROLLING SIGNAL

+

A/D CONVERSION

S1

S/H

R4 AC EXCITATION VOLTAGE

(B)

+

(C) Cx

S1

S2

CS1 Ci

S3

Ri

-

S4 CS2

Vo

LOG DETECTOR V log

ADC

+

SH

FIGURE IX/3.4.3-1 Wire mesh measurement 2 (capacitance type). (A) Wire mesh measuring circuit (capacitance type). (B) Excitation system (capacitance type). (C) Equivalent circuit (capacitance type).

and hence the capacitance offered by different materials are different. Also, it is not known what phase fraction is present at the junction. Therefore, at each junction there will be only a single unknown quantity capacitance, Cx.

For analysis let us choose one of the many parallel receiving circuits. With reference to Fig. IX/3.4.3-1C it is clear that if Vi is the sine wave excitation voltage then for feedback

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Plant Flow Measurement and Control Handbook

resistance and capacitance Ri and Ci, respectively, the amplifier gain can be derived as Vo =Vi ¼ ðjuCx Ri Þ=ð1 þ juCi Ri Þ (IX/3.4.3-1) This is possible because an ideal high amplifier circuit (e.g., op Amp) has infinite input impedance and very high gain. So, by ignoring any resistance from the switching circuit and stray capacitances, Cs1 and Cs2, amplifier gain can be derived as given in Eq. IX/3.4.3-1. With high-frequency excitation, Cx (IX/3.4.3-2) uCi Ri [1 so Vo =Vi ¼ Ci Generally, wire mesh technology suffers from an intrusive effect, which will be dealt with in the next section. This is applicable for both types. 3.4.4 INTRUSIVE EFFECT OF WIRE MESH SENSING If one recalls the initial discussions on wire mesh it was mentioned that wire mesh measurement is intrusive in nature so it has an effect on measurement and flow characteristics. Such effects come from the sensor configuration, i.e., wire diameter, material, spatial resolution, etc. The intrusive effects are mainly on bubbles. There are two types of such effects. These were studied by researchers by comparing images with high-speed video cameras, etc. Major observations revealed that the sizes of bubbles more or less agree with other images, but there is fragmentation of bubbles in stagnant liquid. The results also showed that the repeatability on void fraction measurement showed some deviations and as a consequence typical uncertainty of measurement is around 5%. Therefore, it is a good technique for comparison purpose. With this the discussions on wire mesh technology come to an end and we now investigate another important technique of EIT. Preliminary discussions on the EIT concept have already been discussed in Section 1.2.3, which may be read prior to this discussion on EIT.

3.4.5 ELECTRICAL IMPEDANCE METHOD (GENERAL: LOCAL MEASUREMENTS) 1. Basics: The electrical impedance type (EIT) basically operates on the fundamental principle that the electrical impedance of a multiphase/mixture is usually different from the impedance of each component. Some correlation between the phase/void fraction and the mixture impedance is possible if and only if the constituents have dissimilar electrical properties. It is known that gas has poor conductivity and low dielectric constant. On the other hand, liquids if not good conductors will at least assume a higher value of the dielectric constant. Oil has low conductivity while water is conductive and oil has dielectric much lower than water, so these properties can be exploited to measure the phase fraction. 2. Method features: In connection with void fraction measurements, for multiphase (especially in two-phase) flow research on the impedance technique has been studied for nearly 4 decades and good results have been found. Impedance sensors have proved to be very successful systems for measurement of time- and volume-averaged void fraction for identification of the flow pattern from its instantaneous output. Thus, in view of a few favorable features, the electrical impedance method has been widely used for voidfraction measurement in multiphase flow metering for quite some time. Instantaneous response, nonintrusive measurement, low cost, easier installation and implementation, easy mobility, and higher safety (due to no radiation) are a few features that immediately come to mind. However, it should be noted that the response characteristics of the electrical signal heavily depend upon the flow pattern and relative phase fractions. As electrical properties change with temperature, measurement is dependent on temperature. On account of noise due to the electromagnetic field around the sensor, the signal output is significantly affected by the presence of an

Multiphase Flow Measurement Chapter | IX

electromagnetic field, which can be minimized by using a suitable shield. Another issue worth mentioning is that there is no direct relation between the admittance of the mixture and the void fraction. For a single admittance value there can be different void fraction values, depending on the different flow patterns present. In view of differences in electrical conductivities and relative permittivities, between gas and liquid phases it is possible to develop the impedance method to find the void fraction in multiphase flow. Based on sensor height, the impedance sensor determines the percentage of both phases in a given volume and not strictly across a cross-sectional area. On account of the fringe field effect, the exact boundary is hardly possible to ascertain. By reducing the electrode height some nonlocal effects can be minimized but not the fringe field effect (it is better to use a large shield for stray capacitance) [36]. Depending on the operational frequency of the signal applied and the knowledge of the electrical properties of the fluids, the average dominating impedance of the two-phase mixture filling in the cross-section may be either resistive, capacitive, or both. As mentioned in Subsection 1.2.3.3, there are two other types: the resistive and the capacitive impedance probes. Configuration of each type has been covered in Subsection 1.2.3.3 which may be referenced. The elementary electrical model of the sensor and the measuring system that operates without electrolysis near the electrodes’ surfaces can be compared to a parallel RC circuit [37]. The impedance type may consist of using capacitance and resistance in parallel, but if a component like water is present then at low frequencies there will basically be a short circuit effect. So, for taking capacitance into measurement it is preferred to use a high-frequency signal of around 80 MHz. 3. Electrode type: As indicated earlier, the relationship between void fraction and impedance depends very much on the flow regime. In order to minimize and circumvent the situation, various alternative probe designs have

895

been applied and investigated. Several types are normally encountered: l Coaxial: Quasiuniform and very sensitive to void distribution and flow pattern; l Parallel flat plates; l Wire grid; l Wall flush-mounted circular arc; l Concave type; l Helical type; l Ring type. The types listed above are generalized. In fact, there is some overlap between the types described above, e.g., in plate-type sensors, pairs of concave electrodes are arranged on the inner or outer walls of the pipe and measure the electrical impedance between them. There may be some minor variations in each of the categories, depending on the application. Selection of probe type is not always an easy task. There are different types of capacitance probes shown in Fig. IX/1.2.3-3B. Of these the helical type has a nonlinear response and poorer sensitivity and shield. On the other hand, the accuracy of the concave parallel sensors can be improved by having both electrodes of equal length to decrease the nonuniformity of the electric field between the two electrodes and eliminate the nonlinear response [36]. Concave and ring types are quite popular. As shown in Fig. IX/1.2.3-3B both ring type & concave sensor electrode covers the entire circumference, with small for a small gap to facilitate the installation of the sensor. As shown in Fig. IX/1.2.3-3A, there are full and half rings for conductivity sensors. Ring-type electrodes, covering the entire circumference, are convenient for measurements in pipes and columns of circular cross-section. 3.4.6 SOME RECENT DEVELOPMENTAL WORK IN ELECTRICAL IMPEDANCE MEASUREMENTS In this section some of the developmental work towards EIT has been presented. The first is for horizontal line research, while the latter one is for vertical line research. Developments, from literature study has been presented here, for reader to

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Plant Flow Measurement and Control Handbook

understand how EIT (not tomography) can be utilized for visualization of multiphase flow. 1. New conductivity type probe: In this method in place of two probes there is a third probe, which through numerical data analysis makes it possible to get better results. Typical electrode arrangements and measuring circuits have been presented in Fig. IX/3.4.6-1. In this method there (A)

are two steps for the measurements. In the first step, the flow pattern is identified using the conductance signal measured in all electrode pairs. Then, in the second step, the void fraction is estimated through the calibration curve for the flow pattern predetermined in the first step [38]. For further details the original article [38] may be referenced.

2

2 3

3

3

ELECTRODE C

3

ELECTRODE C GAS PHASE

ELECTRODE A

GAS PHASE ELECTRODE B

ELECTRODE A

ELECTRODE B

LIQUID PHASE LIQUID PHASE

1

1

ANNULAR FLOW

STRATIFIED FLOW

(B) SWITCH

C

A

B

VOLTAGE (LCR METER)

DATA SAMPLING

FIGURE IX/3.4.6-1 Three-probe conductance sensing. (A) Electrode arrangement for different flow. (B) Sensor measuring scheme. Figures shown here are developed based on M. Seok Ko, B.A. Lee, W.Y. Won, Y.G. Lee, D.W. Jerng, S. Kim, An Improved Electrical-Conductance Sensor for Void-Fraction Measurement in a Horizontal Pipe, Science direct, Elsevier, 2015. http://www.sciencedirect.com/science/article/pii/ S1738573315001680.

Multiphase Flow Measurement Chapter | IX

2. Void fraction visualization: By now it is clear that the electrical impedance method can be used for local measurement, i.e., to find phase fractions and in conjunction with other instruments it can be used for interpreting multiphase flow. The electrical impedance method is very much in use in noninvasive, nonintrusion tomography and is popularly known as electrical impedance tomography (EIT). EIT has been discussed separately in this chapter. In this section short further discussions will be presented on quasilocal measurement by the electrical impedance method. From literature studies it has been found that such quasilocal measurement, in conjunction with various other instruments, is possible to obtain a visualization approach of multiphase flow. Electrical impedance type can detect local changes in electrical conductivity and permittivity, the technique is used to study the unsteady mixing or flow dynamics of mixtures. Using sequences of images obtained from a dual-plane EIT flow sensor, the local flow velocity of the dispersed phase(s) can be deduced based on pixel-pixel cross-correlation methods [39]. A short description is enumerated below in order to give an idea of the tomography approach. In this method a number of other instruments are used to get individual flow parameters. Here an electromagnetic flow meter is used for continuous-phase velocity with input from EIT. “EIT technique with dual-plane sensors is used for local volume fraction distribution, local flow velocity and rate of the dispersed phases. The online measurement of local volume fraction distribution and profile of the dispersed phases is based on the average of volume fractions of individual pixels, which constitute the entire image. The three-phase flow mixture density (rFDM) estimated from the gradiomanometer (FDM) is one of the three basic variables along with those

897

measured by EIT and EMFM to enable the three phase measurement ” [39]. The mean component volume fraction is determined using the correlation of EIT and FDM and applying the following mathematical formulae:   rw  rg  ðrw  rFDM Þ   (IX/3.4.6-1) ao ¼ ro  rg ag ¼ aEIT  ao

(IX/3.4.6-2)

aw ¼ 1  aEIT

(IX/3.4.6-3)

A typical schematic of the same has been presented in Fig. IX/3.4.6-2. For further reading consult the original document [39]. There are various effects such as fringe effect, stray capacitance effects double layer effects. These are discussed in Fig. IX/3.5.0-1. With this the discussions on EIT, as well as wire mesh sensing, come to an end. Further details on electrical impedance tomography shall be dealt with under tomography in Section 3.6.0 of this chapter. Now let us look for another technology with a needle probe. 3.5.0 Needle Probe (Local Void Fraction) A needle probe is one of the most useful tools in mapping the void fractions in multiphase/multi component flows. Significant differences of thermal conductivity, electrical conductivity, and optical properties are mainly exploited in needle probes to measure local void fraction and from there it is possible to map the void fraction distribution in a given area/volume in a conduit by moving the probe in different positions. Needle probes in different configurations can be used to measure the following: l l l

Local void fraction of phases; Local axial velocity in two-phase flow; Vector velocity of dispersed phase, etc.

Plant Flow Measurement and Control Handbook

DUAL PLANE

EIT FOR HIGH

EIT SENSOR

CONDUCTIVE

ELECTROMAGNETIC FLOW SENSING

ELECTROMAGNETIC FLOW SENSING FLOW DENSITY

ABSOLUTE PRESSURE SENSOR

METER ABSOLUTE PRESSURE

TEMPERATURE SENSOR

FLUID TEMPERATURE

CONDUCTIVITY

WATER

SENSOR

CONDUCTIVITY

MULTIVARIABLE DECOMPOSITION AND FUSION

898

A vg g qg

A vo o qo

A vw w qw

FIGURE IX/3.4.6-2 Multiphase flow visualization concept. Figures shown here are developed based on M. Wang, J. Jia, Y. Faraj, Q. Wang, C. Xie, G. Oddie, K. Primrose, C. Qiu, A new visualisation and measurement technology for water continuous multiphase flows, Flow Measurement and Instrumentation, 46 (2015), Elsevier. http://ac.els-cdn.com/S095559861500076X/1-s2.0-S095559861500076X-main.pdf?_tid¼ 49d52380-992f-11e6-b592-. Miscellaneous effects: A few following important effects are described here: Fringe effect: This is a three-dimensional effect on area probes to induce error. In conduc on probe suitable guard can be used and capaci ve sizing is important to minimize the effect. Stray capacitance effect: This represents the undesired capacitance that may be between cable and ground. These are unpredictable. The change of capacitance due to change in phase frac on is less the circuit design need to take care of this. Double layer effect: This is rather less known effect and can be caused due to polariza on i.e., local build up of opposite charges in excess number (capaci ve sensing) to cause error. So, a suitable design technique should be adapted to build the system.

FIGURE IX/3.5.0-1 Miscellaneous effects.

Multiphase Flow Measurement Chapter | IX

It is seen quite often that these are used for comparison of results obtained from various other means, e.g., dual-plane EIT. If one recalls the discussions in Subsection 1.2.3.5 and described in Fig. IX/1.2.3-5 one would notice that there are basically three categories of needle probes used in day-to-day industrial applications. These basically are optical, thermal, and electrical. The principles of operation of these have been discussed already in Subsection 1.2.3.5. However, it is worth noting that in many cases a number of such categories are combined to get better results. There are conductivity and capacitance needle probes available, but in many cases these two are combined to develop an electrical impedance needle probe. Similarly, new improved needle probes are available where both electrical and thermal properties have been utilized for better measurements. As there is not much of a difference in the refractive index of organic liquid and gas (e.g., Boyer et al.) their use in multiphase flow, like that in oil and gas industries, is not recommended. However, optical needle probes find their applications in multiphase reactors. In this section brief discussions shall be presented on each of these types of needle probes in multiphase flow measurements. It is not that these probes cannot be utilized in isolation, but they find good applications in conjunction with other types of measurement technologies in multiphase flow measurement (MPFM). Signal processing is an important issue associated with needle probes, hence suitable care needs to be taken of this (Fig. IX/3.5.0-1). 3.5.1 OPTICAL TYPE NEEDLE PROBE A typical working principle of an optical needle probe has been discussed in Subsection 1.2.3.5. Here a few other options have been discussed. One of the earliest and popular methods is visualization of multiphase/component flow. Identification of the flow regime by this technique is rather subjective and mainly suitable for low-velocity

899

applications. This requires transparency in one of the phases and one viewing window. There are many options for this type of measurement. 1. LDR type: Light-detecting resistance (LDR) can be utilized for detecting the void fraction. This is very suitable for flow patterns during liquid-liquid flows in vertical and horizontal conduits. The interface may be smooth or wavy for separated flow patterns. One phase may be dispersed in the other phase as drops or bubbles. The probe response should also be sensitive to the proportion of the two fluids in the flow passage [40]. l Probe assembly: A nonintrusive and noninvasive optical probe comprises a point semiconductor laser source, a light-dependent resistance (LDR) detector, and a processing circuit. The laser source and the LDR sensor are placed at diametrically opposite points to detect light transmitted by the laser source after it passes through a conduit containing multiphase fluid, as shown Fig. IX/3.5.1-1. The narrow laser beam passes through the two-phase medium before falling on the LDR. From the source to the sensor, the laser in its path passes through two different phases with interfaces formed by bubbles, drops, waves, etc. Each of these interfaces represents the characteristics of flow pattern causing different interactions like reflection, refraction, absorption, scattering, etc. Naturally, the amount of light reaching the LDR sensor is absolutely dependent on the fraction attenuated (depends on the absorption coefficient of the fluid) and scattered by the two-phase mixture. At the onset of droplets and wavy interface there will be scattering, which is dependent on the phase content and flow pattern. This is a good and simple system; only the liquids should be transparent. The optical probe system is installed on the transparent pipe by a U-shaped perspex block [40].

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Plant Flow Measurement and Control Handbook

LASER SOURCE LASER DETECTOR

COMPUTING UNIT

POWER SUPPLY

PROCESSING UNIT

DATA ACQUISITION SYSTEM

FIGURE IX/3.5.1-1 LDR type optical needle probe.

Processing circuit: Based on the amount of light falling on the LDR, a variable resistance is generated depending on the intensity of light received at the LDR after being attenuated by the flowing fluid. Through the regulated power supply unit supplies constant DC source to the variable resistance of the LDR detector. The voltage across the resistance is the required output. The output from the LDR is amplified and processed by a processing unit, as shown in Fig. IX/3.5.1-1. Output is connected to the data acquisition system and computing unit to adjust the offset and other signal processing unit and presentation in a visualized manner in the display unit. 2. Fiberoptic sensor: Of the various noninvasive techniques, fiber-optical probes are very promising, because of their inherent advantages such as the following: l Harsh environment tolerance and strong electromagnetic interference immunity; l High temperature withstanding; l Immunity to chemical corrosion; l Small size and low power consumption; l Long-distance operation; l Multiplexing and distribution. l

Also, improved optical and mechanical properties and lower cost of the components make it

versatile. These also find their usage in multiphase flow. However, it may be somewhat more costly and unfamiliar to the end user. As discussed in Subsection 1.2.3.5, basic measurement mode can be conceived as what is shown in Fig. IX/1.2.3-5A. Light sources used to support fiberoptical sensors produce light that is often dominated by either spontaneous or stimulated emissions. A combination of both types of emission is also used for certain classes of fiberoptical sensors. Fiberoptic sensors are mainly used in multiphase reactors. 3.5.2 THERMAL TYPE NEEDLE PROBE (COMBINED) Electrical conductivity and capacitance probes can be used when there is a difference in electrical conductivity and permittivity between the components of multiphase flow. Similar is the case with optical probes, with low refractive index differences. However, temperature measurements are only possible when temperature gradient are encountered in the flow. These are used as two-phase flow measurements. Basic thermal type needle probes are an anemometer type thermal switch used to detect the presence of gas and liquid phase in multiphase flow to visualize the distribution, as discussed in Subsection 1.2.3.5. There are some improved versions of

Multiphase Flow Measurement Chapter | IX

thermal type probes available. In a true sense it is not a pure thermal probe but a combinational probe where both thermal as well as electrical properties have been utilized. In addition to anemometer type, needle probes with integrated microthermocouples are also used. Among many other difficulties with these was the slow time of response for the system. Preamble: A new combined temperature and conductivity needle probe measuring system, has fast response. This is able to handle grounded or direct sheathed thermocouple wires electrically joined to the protective sheath, as well as open thermocouples [41]. This combined probe also measures local conductivity in the test volume with a high time of resolution (10,000 samples/s). It has been found that these probes can face extreme conditions, like pressure up to 160 bar and temperature up to 300 C (water/steam) [42]. The probe combination can measure the following: Averaged local gas fractions; Flow velocities; Bubble number and bubble sizes. The probe tip, thereby, consists of a miniature sheath thermocouple, which allows the synchronous measurement of temperature and conductivity at the same measuring point in the medium, i.e., thermal and conductivity probe from Helmholtz Zentrum Dresden. The probe: There are different constructive embodiments of the probe. The basic probe consists of a coaxial structure of three stainless steel electrodes which are isolated from each other by two aluminum oxide ceramic tubes. The central (probe tip) is a direct sheath thermocouple as shown in Fig. IX/3.5.2-1. Apart from the thermocouple there are three other electrodes: The reference electrode: the outer probe connected to the ground; The shield electrode: middle one, connected to the transmittance amplifier; Measuring electrode: Thermocouple sheath; also connected to the transmittance amplifier.

901

The thermocouple measures the temperature, while the measurement of the local instantaneous electrical conductivity of the surrounding fluid gives the local void fraction. Measurement scheme: The measurement scheme consists of several amplifiers and a signal processing unit as detailed in Fig. IX/3.5.2-1. A bipolar signal is applied to the central measuring electrode. Depending on the presence of fluid in contact with the electrode either current will flow to the ground or it will stop, i.e., if the fluid in contact is the fluid of certain conductivity (say water), there will be current flow, otherwise if it is covered by a gas bubble the current will be interrupted. In order to prevent a short circuit through thin liquid films still covering the isolating ceramics, a central shielding electrode is used. The system excitation signals are generated through direct a digital synthesizer (DDS 1&2— with a common reference clock to synchronize). To make the shield active, one DDS1 signal is applied to the shield as well as the positive end of the transimpedance amplifier. Conductivity is therefore measured by connecting the measuring electrode to the other end of transmittance amplifier. The output signal of the transimpedance amplifier is thereby superimposed by a permanent signal, which has to be removed [42] and for this differential amplifier, which has another input from DDS2 (same frequency by controllable phase to match the time delay), has been used in series with a transmittance amplifier. High gain instrument amplifier is used for the low-voltage signal generated by the thermocouple. For better measurement accuracies, a cold junction compensation unit and low-pass filters are used. In the digital control part for regulating DDSs, microcontrollers are often deployed. The system is normally connected with computer/computing circuits. RS 232/422 and ethernet can be used for external communication. Here embedded electronic micro-controller play very vital role in measurement control and computation.

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Plant Flow Measurement and Control Handbook

T/C-SHEATH/ MEASURING ELECTRODE SHIELD ELECTRODE

CJ COMPENSATION

TERMOCOUPLE (T/C)

INSTRUMENT AMPLIFIER

+ CERAMIC ISOLATOR (Typ)

TRANSIMPEDANCE AMPLIFIER

REFERENCE ELECTRODE

DDS 1

REFERENCE CLOCK

LP FILTER

DIFFERENCE AMPLIFIER

AMPLITUDE DTECTOR DDS 2

MICROCONTROLLER

ADC

COMPUTING UNIT

FIGURE IX/3.5.2-1 Combined thermal and electrical needle probe. ADC, analogedigital converter; CJ, cold junction; DDS, direct digital synthesizer; LP, low pass.

3.5.3 ELECTRICAL TYPE NEEDLE PROBE (COMBINED) Electrical needle probes can be conductivity type as described in Subsection 1.2.3.5, or they can be capacitance type, and/or a combination of both, i.e., complex admittance type. Electrical probes can be single-, dual-, or four-sensor arrays, etc. These probes are often used for comparing results obtained from EITs. In this section, brief discussions on each of them shall be covered. 1. Conductivity probe application: Here some typical applications of conductivity sensors have been described from study of literature (experiment at the University of Huddersfield, UK).

l

Dual sensor: Typical sensors used are depicted in Fig. IX/3.5.3-1A [43]. These are two conductivity probes with a gap (0.5 mm gap in width). The probe consists of two PTFE-coated stainless steel needles of outer diameter 0.15 mm, with the PTFE removed at each needle tip to allow electrical contact with the multiphase flow [43]. The needles are held in place by glue in a ceramic guide and are positioned such that one needle tip, known as the front sensor, is placed an axial distance s upstream of the second needle tip, known as the rear sensor (1.5 mm gap). The local void fraction is a dimensionless, time-averaged

Multiphase Flow Measurement Chapter | IX

(A)

903

(B) PTFE COATED SS NEEDLE GLUED TO SS TUBE

GAP WIRES

STEEL TUBE GAP (s)

CONDUCTANCE

CERAMIC GUIDE

1f 1r

2f 2r

EXCITATION ISOLATION ELECTRODE

(C)

DDS EXCITATION

Vex STRAY CAPACITANCE ZX TRANSIMPEDANCE

REFERENCE

AMPLIFIER

CLOCK

DDS REFERENCE

Vo

STRAY CAPACITANCE

AMPLITUDE

MEASURING ELECTRODE

STRAY CAPACITANCE

PHASE DETECTOR

COMPUTING UNIT

PHASE

AMPLITUDE ANALOG

A/D

INPUT

CONVERTER

DIGITAL PORT

FIGURE IX/3.5.3-1 Electrical needle probe types. (A) Dual conductivity probe. (B) Probe conductance. (C) Combined electrical needle probe. A/D, analog-to-digital; DDS, direct digital synthesizer. (A and B) Developed based on G.P. Lucas, X. Zhao, Large Probe Arrays for Measuring Mean and Time Dependent Local Oil Volume Fraction and Local Oil Velocity Component Distributions in Inclined Oil-in-water Flows, Elsevier, 2013. http:// www.sciencedirect.com/science/article/pii/S0955598613000393.

quantity that can be calculated statistically over a sampling time. In contact with twophase medium when the surface of an oil droplet first contacts a sensor, there will then be a sharp drop in the measured

conductance, but this is regained when the droplet has passed over the sensor. These are shown in Fig. IX/3.5.3-1B. Let this occur with a front sensor at times t1f and t2f, respectively. Let the same for the rear

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sensor be denoted by t1r and t2r, respectively. Over the sampling period T, the number of oil droplets that strike both the front and rear sensor is N. Thus, from Fig. IX/3.5.3-1B for first encounter for n-th droplet, one can define: dt1n ¼ t1r;n et1f;n and dt2n ¼ t2r;n et2f;n (IX/3.5.2-1) If s is the distance for axial difference then the average velocity could be calculated as: One can estimate the mean local axial velocity easily utilizing a statistical mean from the acquired data. uo ¼

N 2s X 1 N 1 ðdt1n þ dt2n Þ

(IX/3.5.2-2)

Since the gap t2f and t1f is the time period tip in contact with oil, so the oil volume void fraction is: a ¼

N 1X ðt2f;n  t1f;n Þ T 1

(IX/3.5.2-3)

In the same experiment, a four-sensor array was also used. l Four-sensor array: With the help of a foursensor array it is possible to get the velocity vector also. An individual four-sensor probe is used to measure the mean local oil volume fraction a and the mean local oil droplet velocity vector averaged over a sampling period T. A four-sensor probe can be used to measure the velocity vectors also [43]. 2. Capacitance needle probe: Conductivity measurement is possible if one of the components is conductive in nature, i.e., one component has minimum conductivity. A capacitance probe based on permittivity change is also used as an electrical needle probe. Normally multineedle probes are used. There could be a multiple number of needle sensors, e.g., five needles to form four local capacitances which are sampled at a very fast rate to detect the changes in permittivity. There

can be one common excitation electrode to which the AC (sinusoidal) signal is sent and measurement is carried out in the other four measuring electrodes. These are connected to a transimpedance amplifier. The output of the transimpedance amplifier is demodulated to get DC voltage proportional to the change of permittivity, i.e., instantaneous capacitance between the excitation electrode and each measuring electrode. As in previous cases, processing of these signals and data available from sampling can provide the local multiphase flow parameters like phase fractions, local axial velocity, etc. 3. Combined electrical needle probe (complex probe): Here, instead of only conductivity or capacitance sensing, complex impedance sensing is done. l Preamble: Pure conductivity- or capacitancebased needle probes have limitations regarding the range of substances they are able to measure. Electrical conductivity and capacitance probes can be used when there is a difference in electrical conductivity and permittivity between the components of multiphase flow. As indicated earlier, there will be similar difficulty with an optical probe when there is a low difference of refractive index. A thermal probe could be the solution if there is a temperature gradient but is utilized almost exclusively in two-phase flow measurements. Therefore, there is a lack of measuring techniques for three- or multiphase flows encountered in oil extraction, chemical reactors, and petrochemical industries. An electrical probe combining conductivity and capacitance measurements could provide better solutions. This means that in electrical measurement instead of measuring in one axis (conductivity—real or capacitance— imaginary) measurement could be carried out in a complex plane of admittances. A needle probe with impedance could provide a better solution. l Probe and measurement: The probe has double coaxial geometry, as shown in Fig. IX/3.5.3-1C. The probe assembly consists of one excitation electrode and one

Multiphase Flow Measurement Chapter | IX

measuring electrode in stainless steel construction. Each probe has coaxially one grounded reference probe, which is isolated from the excitation or measuring probe by a suitable isolator as shown. The objective of measurement is to determine the complex impedance based on the amplitude and phase measurement of the sine wave signal at a fixed frequency (200 KHz to 1 Mhz). The excitation voltage Vex is supplied to the excitation electrode by means of a coaxial cable. The measuring electrode is connected to a transimpedance amplifier by means of a coaxial cable. The output voltage of the transimpedance amplifier is directly proportional to the current I flowing from the excitation to the reference electrode Vo ¼ I$Zf, where Zf is the feedback impedance (refer to Fig. IX/3.5.2-1 for details of the transimpedance amplifier). Since the unknown admittance of the fluid Zx is grounded by the operational amplifier’s virtual ground, the current I is obtained by dividing voltage Vi with impedance hence for Zf feedback impedance of transmittance amplifier: Vo ¼ I$Zf and I ¼ Vi =Zx or Vo =Vi ¼ Zf =Zx ¼ Yx =Yf .

(IX/3.5.2-4)

where it is noted that the excitation voltage generated by DDS is Vex may be (slightly) different than Vi due to stray capacitance. The complex impedance Zx, measured by the probe, is inversely proportional to the relative permittivity εr as: Zx ¼ ð1=ð ju$εr $ε0 $Kg Þ.

l

(IX/3.5.2-5)

where ε0 permittivity at vacuum 8.85 pF/m; u ¼ 2pf, Kg denotes probe geometric factor. Processing unit: As shown in Fig. IX/ 3.5.3-1C, the processing unit is similar to that shown in Fig. IX/3.5.2-1. The probe is excited by direct digital synthesizer (DDS)1 and output is measured by a

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transimpedance amplifier. There is one amplitude and phase detector unit which basically acts like a demodulator. The output from the transimpedance amplifier is fed to an amplitude and phase detector and the signal is demodulated. Amplitude and phase detectors are powered through DDS2, which has the common clock with DDS1. DDSs are controlled by microcontroller of the computing unit. With this the discussions on needle probe come to an end and we start discussions on various types of tomography techniques. 3.6.0 Tomography Techniques In order to identify the internal flow characteristics of multiphase flows, one can use either invasive measurement techniques or noninvasive methods. The difficulty with invasive methods is that they can alter the internal flow of a multiphase system causing interference with realistic process measurements. Nonintrusive acquisition of local measurements of process parameters like temperature, concentration, or volume fractions in multiphase flows is often a challenge. In many cases, instead of the desired local measurements, only integral measurements, for instance along lines, can be obtained. This is the point when process tomography comes into play [44]. Tomography is an imaging technique, to produce cross-sectional details of an object from its line integrals of projections. On account of the larger variations in density and to achieve finer resolution, the design and operation of computerized tomography (CT) machines for process/industrial and scientific applications is more complex when compared with medical systems for which the techniques was initiated. In tomography, one of the issues is the reconstruction of images from the acquired data to visualize time-resolved flow structures in 2D/3D. Such reconstruction of images from acquired data is done mathematically with the help of suitable algorithms which form an integral part of the tomography system. Depending on the measurement task, a variety of optical, electrical conductance, electrical

Plant Flow Measurement and Control Handbook

l l l l l l l

Spatial resolution; Temporal resolution; Suitability for particular applications; Availability in the market; Cost factor; Familiarity/experience of personnel; A few other pertinent issues.

of development in data acquisition and computing networks with advanced reconstruction algorithms making tomography an important measuring tool. The following are general steps for tomography: l

l

The discussions start with generalized discussions on the tomography technique.

l

3.6.1 GENERAL TOMOGRAPHY PROCESS l

An image reconstruction algorithm is a real challenge in the process of interpreting tomographic data to create images of the distribution, which gives rise to the set of measurements. This involves good mathematical interpretation issues (problems) and a good amount of developmental work for algorithms. The basic steps have been depicted in Fig. IX 3.6.1-1. For improved process utilization, and process yields, process controls and cost-effective solution tomography finds more uses in petroleum industries, especially for oil and gas exploration. With more and more use these are now available with high-quality assurance, and better environmental and safety protections.

SYSTEM

DATA

ACQUISITION

SENSOR

READING

There are a number of techniques for tomography, i.e., X-ray, CT, electrical impedance (ERT, ECT) tomography, gamma ray tomography, US tomography, etc. The application of tomography in process industries is not only in oil extraction but other plants as well, including upstream and downstream of oil and gas industries such as fluidized catalytic cracking and multiphase pipe flow [3]. Tomography often decides the calibration basis for multiphase flow meters. “In addition, the notion of tomometry as a means of nondestructive measurement technique will be introduced as tomometry relies upon cross sectional metering of process parameters utilizing multiple measurements where fulltomograms are not required” [45]. With the advancement of sensor technologies, versatile signal processing and recovery electronics make it possible to measure more and more parameters with better accuracy. Added to this there have been a number

Around the test section there shall be a number of sensors which measure the required parameter through periodic scanning of the test section; The associated electronics process the signals sequentially for presentation to the data acquisition system as inputs; The processed data are acquired by a data acquisition system, which is basically a computerized system. With the help of software these process data are interpreted; Advanced software-based reconstruction algorithm.

ALGORITHM

capacitance, X-ray, gamma ray, and other tomography can be used. Each of these systems vary significantly on the following aspects:

RECONSTRUCTION

906

RECONSTRUCTED IMAGE PROCESS PARAMETER COLORS TO GIVE A FEEL OF IMAGE (ONLY EXAMPLE)

FIGURE IX/3.6.1-1 Tomography principles.

Multiphase Flow Measurement Chapter | IX

The aim of design should be to develop a system as a simple one but with higher reliability to provide the required information and data. With an advanced tomographic system industry tomographic measurement systems are often preferred with a few views for permanently installed gauges as a measurement scheme—as long as it provides sufficient information. Tomography is used for both reservoir characterization and to search for it. A variety of new technologies have made it possible to reach a 60% recovery factor [44]. Tomography can be categorized in main three categories: l

l

l

Nuclear-based imaging technique using ionizing radiations such as X-ray, gamma ray, neutron/positron radiation. These are often referred to as “hard field” as the measurement sensitivity to measurement parameters is independent of component distribution; Nuclear-based imaging: without using ionizing radiation such as nuclear magnetic resonance; Non-nuclear-based imaging techniques such as electrical impedance tomography, US tomography, optical tomography, and microwave tomography.

Various ways and means of radiation from source and detection methods, including relative movement of source/detector with respect to the process, have been depicted in Fig. I/3.4.3.2-1. As shown, there may be single or multiple source and detector combinations with and without scanning, i.e., instantaneous type. Now, it is time to look into the details of the various tomography techniques. 3.6.2 X-RAY TOMOGRAPHY: X-RAY CT Like the gamma ray radiation technique already discussed, in this technique also, the radiation beam traveling through the heterogeneous medium undergoes attenuation before being detected at the detector. The absorption gives a measure/ indication of the line integral of local density along the beam path. 1. Process: The components have different radiation absorption characteristics, therefore, the

907

image of phase is obtained by reconstruction of a set of projections at the different orientations generated. This is achieved by rotation source and detection around the pipe or by use of two (multiple) sources and detectors, as detailed in Fig. I/3.4.3.2-1. In a digital Xray system there are image intensifiers and charge-coupled device (CCD) as described in Fig. IX/3.6.2-2, cameras read the images. The movement of this may be achieved through a suitable motor, e.g., a stepper motor, duly controlled by the data acquisition system (DAS). As indicated before, detected data are processed and sent to the DAS, which is connected to a computer (computing unit). On account of the automated process, i.e., computerassisted tomographic process, it is referred to as computer-assisted tomography (CAT) or computed tomography (CT), i.e., X-ray CT. Tungsten or molybdenum are X-ray sources that generate low-energy photons. On account of mechanical movement of the source and detector (not applicable for multiple sources and detectors) the temporal resolution is not very good but the spatial resolution is excellent. The basic process of X-ray tomography has been depicted in Fig. IX/3.6.2-1, along with some typical possible images. 2. Phase distributions: These are spatial and temporal: l Cross-sectional; l Time series. 3. Mixing effects: The mixing effects are observed in the following manners: l Cross-sectional; l Time and space distribution; l Interface roughness; l Waves. 4. Results: Typical results from X-rays are as follows (a few only): l Tomographs; l Side and top projection views; l Mean holdup traces; l Sliced sectional view; l 3D view of the flow; l Y-axis phase distribution;

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Plant Flow Measurement and Control Handbook

SOURCE 1

TYPICAL IMAGES FOR UNDERSTANDING ONLY GAS

DATA AQUISITION & COMPUTING UNIT HIGH-FREQUENCY

(TYPICAL; ONLY FOR

SAMPLING

SOURCE 2

CAMERA 2

UNDERSTANDING ONLY)

LIQUID

SEQUENCE OF TOMOGRAPH

CAMERA 1

DATA ACQUISITION & COMPUTING UNIT

FIGURE IX/3.6.2-1 X-ray tomography (CT). CCD & CMOS: Charge coupled device (CCD) and Complementary metal oxide semiconductor (CMOS) are used as sensor in digital camera/imaging devices to convert opƟcal energy into electrons or electrical energy. CMOS is a semiconductor device which can perform other duƟes as well only it is explained in this perspecƟve.

FIGURE IX/3.6.2-2 CCD and CMOS for digital imaging.

Phase transport along slug or wave; Others. 5. Statistical parameters: The following are statistical parameters that are obtainable: l Wave height; l Frequency; l Slug body length and distribution; l Three phase flow extension. l l

For X-ray spectroscopy process any standard book on X-ray spectroscopy may be referenced. To limit the book size it is beyond the scope of the book only relevant could be presented.

We now concentrate on another nuclear ionizing tomography technology of gamma rays. 3.6.3 GAMMA RAY TOMOGRAPHY The basic principles of the gamma ray detection technique with single energy or multiple energy gamma rays have already been discussed at length in Sections 1.2.3, 2.1.0, and 3.3.1. Now we concentrate on gamma ray tomography. 1. Preamble: When rotating systems are used, the results will yield time-averaged, not instantaneous, phase distribution images with time

Multiphase Flow Measurement Chapter | IX

SEMICONDUCTOR DETECTOR ARRAY

GRID LEAD COLLIMATOR

PROCESS TEST SECTION

PIPE

COLLIMATED GAMMA SOURCE

FIGURE IX/3.6.3-1 Gamma ray tomography.

resolution of such systems is limited to a few images per second. Here the description has been provided with multiple sources and detector systems, which would allow the study of dynamically changing phase distributions. However, such solutions are still comparatively complex and cost-intensive [11]. 2. Description: An industrial high-speed gammaray tomography system consisting of a number of gamma sources (refer to Subsection 3.3.1.2 —Am-241 radioisotopes more common) with principal associated gamma-ray energy and equal number of detector modules placed opposite to the source. As shown in Fig. IX/3.6.3-1, the detector system consists of a grid lead collimator and an array of semiconductor detectors. Detectors are connected to suitable readout/processing electronics, which in turn is connected to the data acquisition system. A computer is associated for reconstruction of images, like X-ray tomography. The area of each detector and thickness in design are very important for the performance of the system. The area of each detector is around 10  10 mm2 which was found to provide the best compromise between spatial resolution and ray-sum measurement error. All detectors used are w2 mm thick

909

in order to provide nearly 100% stopping efficiency—quoted data from [45]. There are a number of error sources in measurements, such as photon scattering from the same source or from other sources due to Compton scattering effect. Also, there will be errors from reconstruction pixel density. In order to minimize the errors from scattering, a highly collimated source and heavily collimated gird detector as shown can be used. In order to have better temporal resolution, a set of multiple source and detectors are used in place of a single source detector set with rotation. In oil exploration applications it has been found that high-speed gamma ray tomography is extensively used as multiphase flow loop reference imaging and for down-hole measurement [44]. There is another kind of nuclear-based tomography—the neutron type. Neutrons have some advantages in terms of their attenuation in matter in comparison to photons. 3.6.4 NEUTRON/POSITRON TOMOGRAPHY Neutron imaging may not be very common with medical applications, but for engineering process testing it is often used. In principle, neutron imaging works in the same way as X-ray radiography, with a few important physical differences in the sense that the neutron imaging can provide certain information that would be impossible with X-ray radiation. The basic principle of operation of this is generally similar to that of X-ray. In the case of neutron radiation, in addition to a radiation source, neutrons need an evacuated collimator through which the neutrons are propelled before they hit the test object. The detector behind the sample provides a two-dimensional image of the radiation. It is possible to develop a tomograph/tomogram. In the case of positron emission tomography (PET) positron-emitting radionuclides are used with an external detector. Normally, PET has longer temporal resolution and may not be a good choice for fast-changing flow investigation.

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Plant Flow Measurement and Control Handbook

X-ray radiation is a form of electromagnetic radiation, while neutron radiation is neutral and has more penetrating power. Also in X-ray reaction probability is more. Lead can be used as a shield for X-rays but not for neutron radiation. However, neutron and X-ray radiography of the same object often produce complementary information. 3.6.5 ELECTRICAL IMPEDANCE TOMOGRAPHY Electrical impedance tomography (EIT) is an important type of process tomography. As the name implies electrical impedance is exploited to get the interaction of electricity with the process. Hence it is often referred to as electrical tomography. Complex electrical impedance consists of resistance, inductance, and capacitance, and varying physical parameters associated with them are conductivity, permeability, and permittivity, respectively. Depending on the modality of exploitation of the parameter, these could be any of the following: l

l

l

Electrical resistance tomography (ERT), when conductivity distribution is exploited; Electrical capacitance tomography (ECT), when permittivity distribution is exploited; Electrical magnetic tomography (EMT), when permeability distribution is exploited.

It is clear from the above that EIT should never be used as a synonym for ERT or ECT. While ECT is nonintrusive and generally noninvasive (for metal vessels or pipes, ECT may be invasive) but ERT may be invasive but nonintrusive. An image is obtained when an electric field is applied between two electrodes and measuring the resulting sensor responses. Although in basic theory of measurement of these are similar to those discussed in Subsection 1.2.3.3, yet final output types as well as measuring processes are differenteas will be clear from the subsequent discussions. A complete dataset is obtained by successively

activating each electrode and measuring the responses of all remaining electrodes. EIT normally is quite fast, and hence has good temporal resolution. It is also low-cost and safe (from radiation). EIT offers moderate spatial resolution of the resultant image and the measured electrical signals are not a linear function of phase fractions and flow configuration. Also, the electrical field cannot be confined between the source and detectors, and is referred to as soft-field tomography. Now it is time to investigate each of the available types of electrical tomography. 1. ERT: The imaging technique ERT can capture the internal structure of a two-phase flow within an opaque pipe or vessel. As already mentioned, the basic principle of measurement is the difference in the conductivity of the constituent phases within a multiphase flow domain. ERT is used for measuring the behavior of mixing, flow, and separation where the reactants or products have different conductivity, for instance crystallization. ERT is used when the materials are conductive, for instance: water, acids, bases, and ionics. Therefore, of the several ERT applications, study of multiphase flow is an important application. ERT produces cross-sectional images showing the distribution of electrical conductivity of the process pipe/vessel from the measurements taken at the boundary of the pipe/vessel. In ERT the process flow is interrogated by an array of electrodes (typically 16 electrodes) at the periphery of the pipe wall. An electrical current is injected through a pair of electrodes and the voltage is measured through the remaining electrodes in pair, according to the predefined protocol. The next injection of current is started with another pair and voltage measurement as stated above is continued. This process is repeated until all independent measurements are over. For 16 electrodes there will be 104 possible independent measurements. A typical electrode arrangement and orientation have been depicted in Fig. IX/3.6.5-1A. By placing two sets of this at distance apart, it is

Multiphase Flow Measurement Chapter | IX

VOLTAGE MEASUREMENT

(A)

911

(B)

V PIPE* 16

ELECTRODE

1

ELECTRODE 2

PIPE

1

2

3

15

8 13

3

5 7 11

7 10

9

EXCITATION MEASUREMENT REPETITION

4 EXCITATION MEASUREMENT REPETITION

5

6

I CURRENT INJECTION

DETECTION EXCITATION

(C)

COIL

PROCESSING ELECTRONICS

EXCITATION MEASUREMENT REPETITION

DETAILING

COIL2

COIL1

V

MEASUREMENT

I AC MAGNETIC FIELD

COMPUTING UNIT

INJECTION

FIGURE IX/3.6.5-1 Electrical impedance tomography. (A) ERT electrode orientation. (B) ECT electrode orientation. *Pipe: nonmetallic electrode outside (noninvasive) for metallic pipe electrode inside invasive. (C) EMT measurement scheme.

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Plant Flow Measurement and Control Handbook

possible to get velocity profile also utilizing co relation method discussed earlier. The basic design issues include but are not limited to the following: l Electrode spacing: Electrodes shall be equally spaced; l Electrode materials: Electrodes are normally made up of SS, Br, Ag, etc. with conductivity more than process fluid; l Electrode connection: Electrodes are connected to DAS via coaxial or other special cable; l In ERT, gas volume fraction profiles in an annulus flow can be measured. 2. ECT: is another tomography technique, utilizing electrical properties, for measuring and displaying the concentration distribution of a mixture of two insulating (dielectric) fluids, such as oil, gas, plastic, and some minerals, inside a vessel/pipe. l Features and types: ECTs normally are deployed when the bulk material in question does not have conductivity. For interpretation of the ECT image, colors have suitable significance, e.g., in an ECT image red stands for high dielectric value, for instance oil, and blue stands for low dielectric value, e.g., gas. Depending on pipe materials ECT can be completely noninvasive or invasive. As stated earlier, in the case of a metal pipe, the electrodes will be inside the pipe and it will be intrusive, otherwise ECT will be noninvasive, i.e., electrodes surrounding the test section will be outside the pipe/vessel. l Principles and applications: Basically, in ECT the changes in electrical capacitance between all possible combinations of electrodes are measured. This happens when the dielectric material is poured inside the pipe or vessel introduced. Interelectrode capacitance change is caused due to differences in the permittivity

of materials (gas—low permittivity; liquid— higher permittivity) in the mixture, i.e., from these measurements, the permittivity distribution of the mixture (related to the concentration of one of the fluids) can be deduced. The basic idea is to surround the vessel with a set of electrodes of metallic plates to take capacitance measurements between each unique pair of electrodes. Vessels/pipes of any cross-section can be imaged by a set of electrodes surrounding the test section, as shown in Fig. IX/3.6.5-1B. The resolution of ECT images is relatively low, but they can be captured at high speeds. As indicated in previous discussions it is possible to measure the velocity profile with the help of a crosscorrelation method by placing two sets of measurements along the pipe length. Apart from two-phase flow applications in oil and gas fields, it finds applications in fluidized beds, flow rate measurement in pneumatic conveying systems, and flame and combustion imaging. 3. EMT: The operation of EMT is very similar to the other electrical tomography methods. Here an AC magnetic field is applied to the process in question and changes in the field contour on account of the presence various materials in the mixture. l Measurement steps and objectives: In EMT, the test section is excited with an AC magnetic field. Changes in the field contours result from the presence of the mixture in the test section. l Measurement of the field values by the sensors at the boundary surrounding the test space. l Data acquisition and interpretation of sensor data. l Image reconstruction with suitable mathematical algorithms. This involves converting

Multiphase Flow Measurement Chapter | IX

l

l

the measurements back into an image of the original material distribution. Principles of operation: As shown in Fig. IX/3.6.5-1C, the measurement involves twin coils. One coil is for excitation and the other for detection. Sinusoidal current is passed through the exciting coil so that there will be a magnetic field generated in the object area. With a presumed background condition of relative permeability in the test section, due to AC magnetic field there will be induced voltage generated across the detection coil which can be measured to detect the changes in permeability condition due to the passage or flow of the mixture. The measured voltage will be interpreted, corresponding to a background or empty space measurement [46]. On account of the introduction of mixture in the test space the spatial distribution of the magnetic field, i.e., the mutual coupling between the coils, is altered. Description: As shown in Fig. IX/3.6.5-1C, the system consists of three main subsystems, i.e., sensor array, processing electronics including data acquisition system, and computer (computing unit). As shown in the blown-up part of the figure, the sensor array consists of an outer magnetic confinement shield, excitation coils, detection coils, current driver for each excitation coil, and buffers/amplifiers for detection coils (not shown). Since the measurement is based on a change in permeability, any electrically conductive or ferromagnetic objects within the test section or nearby space would disturb the measurement. Like any other tomography reconstruction, a software algorithm is very important for the system also, so that an image of the material distribution can be properly understood and interpreted.

913

With this the discussion on EIT comes to an end and we now look into magnetic resonance imaging. 3.6.6 ULTRASOUND TOMOGRAPHY Like electrical impedance tomography, in ultrasonic tomography the changes in the acoustic impedance properties due to multiphase flow are detected. Gaseliquid flow exhibits a marked acoustic impedance difference between the gas and liquid interfaces [11]. In ultrasound tomography multiple ultrasonic transducers are mounted around the pipe, as shown in Fig. IX/ 1.2.4-1. US tomography has already been discussed in Subsection 1.2.4.2 and so is not repeated here. 3.6.7 OPTICAL TOMOGRAPHY Optical tomography makes use of low-energy electromagnetic radiation in visible, infrared, or ultraviolet wavelength range in the electromagnetic wave spectrum. Like other tomographic systems, acquired data are suitably interpreted in DAS and, with the help of an image reconstruction algorithm, images are prepared in CT mode. 3.6.8 MAGNETIC RESONANCE IMAGING Magnetic resonance imaging uses nuclear magnetic resonance of hydrogen nuclei in conjunction with radio frequency and magnetic gradient pulses to map the test section (Mantle and Sederman, 2003). As stated above, it acts on hydrogen nuclei and so fundamentally, in MRI the concentration of hydrogen atoms is detected. By this method it is possible to determine the density of nuclei and also the velocity in flow. Typical petroleum multiphase flows containing gas, oil, and water have hydrogen atoms in all these components. With reference to Fig. IX/3.6.8-1, when placed in a magnetic field the nucleus of the hydrogen

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Plant Flow Measurement and Control Handbook

Precession:

Magne c Resonance (MR) happens as a result of intrinsic magneƟc

moment of nucleus (proton and Neutron). In many atoms such as O16/ C(12) magne c moment of proton and neutron offset each other. On the contrary H atom has the strongest MR response (as H is present in gas/oil /water this is u lized in MPFM). Thus when subject to sta c magne c field, later it exerts a torque on the axis of the spinning to move the axis perpendicular to the direc on of force around the axis of magne c field. This mo on is known as Larmor Precession. The Larmor frequency of this precession around the direc on of the background magne c field B 0 is determined by Gyromagne c ra o γ and is given by

FIGURE IX/3.6.8-1 Larmor precession.

atom (proton) will always align with the applied magnetic field and processes will be active. When it is irradiated with radio waves of the same frequency, the protons resonate (as a reaction to the RF signal). The protons absorb and re-emit the radio energy of the same frequency. The emitted signal (echo) is proportional to the number of protons. Therefore, it is also called echo-planar imaging. The technique is relatively costly and discussed at length further in the following section. With this the brief discussion on tomography techniques comes to an end. We now investigate available MRI-based industrial flow meters. 3.7.0 Magnetic Resonance Multiphase Flow Meter The magnetic resonance imaging principle discussed in the above subsection, has been applied to develop a complete multiphase flow meter. This newer technology has been developed by Krohne. A brief discussion has been presented on the same (based on documents from Krohne: Courtesy: Krohne).

3.7.1 BACKGROUND THEORY FOR MR RESONANCE MEASUREMENT The basic physical phenomenon behind the measurement has been briefly explained here. As stated earlier, for H (two) alignments are possible, i.e., alignment at a certain angle with (or against) applied magnetic field. There will also be precession movement because of superimposition of external field on magnetic moment of proton (around the direction of external field). This phenomenon creates a net magnetization which is timedependent. The orientation of the macroscopic magnetization, M, can be modified by applying radio-frequency pulses with the appropriate intensity, duration, and frequency. Changes in the orientation or intensity of the macroscopic magnetization can be detected as a small voltage in an appropriate RF coil as shown in Fig. IX/3.7.0-1B. An RF pulse is created with the intensity and duration such that the magnetization vector, M, is tilted along the x-axis by 90 degrees (from the z-orientation to the xey plane). This pulse is called a P90 pulse. By applying a P180 pulse at, e.g., t ¼ s, all protons are flipped along the y-axis by

Multiphase Flow Measurement Chapter | IX

915

(A) N P B

P

P

P B

P B

P B

P B

P

P

P B

P P

P

P

P

P

P B

P B

B: MAGNETIC FIELD

P: PERMEABILITY

P B

P B

S

(C)

S9t)

(B)

P B

+

90 deg. RF PULSE

1st ECHO 2nd ECHO

t S=0 t (ms)

FIGURE IX/3.7.0-1 Magnetic resonance type MPFM. (A) Alignment with magnetic field. (B) Resonance with RF pulses. (C) Velocity measurement. Developed completely from documents from Krohne. Courtesy: Krohne.

180 degrees. As a result, there will be a gap (difference in movement) between the slower-moving protons and the faster-moving protons placed behind. With the individual resonance frequency remaining unchanged, all protons start to rephase, leading to an echo at t ¼ 2s. This is referred to as Hahn echo. Hahn echoes can be created multiple

times by repeatedly applying P180 pulses. This pulse sequence is called the CPMG pulse sequence. Besides CPMG, a variety of RF pulse sequences have been developed for measuring T1 or T2. By varying the timing of these pulse sequences, the measurement can be optimized to the expected MR response of the flowing fluids [47].

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Plant Flow Measurement and Control Handbook

3.7.2 MEASUREMENT BY MAGNETIC RESONANCE PRINCIPLES

3.8.0 Sampling Type Multiphase Flow Meter

In line with multiphase flow metering principles, phase fraction (l) and velocity of travel are measured to calculate volumetric flow rates (q). In the meter there will be pre magnetization stage, where water and oil attend max. and min. of their respective magnetization. It will be noticed there will be difference in magnetization of water and oil. For this the signal for two different magnetization lengths for oil and water to evaluate the ratio and from there the fraction of oil and water can be derived. From factory calibration S100%L, liquid phase fraction lL is measured by lL$S100% L. So, phase fraction gas is inferred by lG ¼ 1  lL. Fluid velocity is determined by the convective decay method, excited protons leave the coil due to flow measure of the decrease in amplitude of the echoes v ¼ Lc$ts¼0, as shown in Fig. IX/3.7.0-1C i.e. The flow velocity is measured by analyzing the signal attenuation as function of time (referred to as convective decay method). Rf signals are applied in discrete way in gaps of milliseconds (manipulative) to measure the decay due flow. This helps in calculating the velocity discussed above. For further details Refs. [48,49] may be referenced. External and internal views of M Phase 5000 of Krohne (Courtesy: Krohne Messtechnik GmbH; permission: e-mail dated October 16, 2017) have been depicted at the end of the chapter.

During the discussions in Subsection 3.4.2.3 of Chapter I and Subsection 1.3.1.3 of this chapter, the sampling type of measurement has been discussed. A multiphase flow meter utilizing a similar method is discussed here. This is known as the VIS multiphase flow meter of ABB. Here VIS stands or “Vega Isokinetic Sampling” of TEA Sistemi’s Vega meter [50]. “The methodology used by VIS starts with an extremely sophisticated sampling system, implemented by means of specially designed and patented devices.” [51]. This is a proprietary device naturally description is based on the product literature. Now let us look into the details of this system. This meter is basically a wet gas meter as it operates mainly in GVF >80% up to nearly 100%.

3.7.3 METER PARTS The meter consists of the following measurement sections and components: l l l l

Premagnetization section; Motor to vary premagnetization length; Main magnet with RF coil; Electronics housing in flame-proof boxes.

We now look into another kind of multiphase flow meter type.

3.8.1 PRINCIPLES OF OPERATION In multiphase flow very complex fluid dynamics are involved, and proper sampling is very important to get the representative sample. The methodology used by VIS starts with an extremely sophisticated patented isokinetic sampling. Isokinetic sampling consists of the withdrawal of a sample of the three-phase flow in such a way that the sample taken is perfectly representative of the entire stream [51]. In this method “careful management of differences in pressure between the interior of the sample probe inserted into the main duct and the duct itself ensure the conditions of equivelocity that are essential to fully representative sampling” [51]. In this meter another important issue is separation. After sampling, the meter performs the separation process with the help of high-efficiency gas liquid separation. The separated liquid and gas are measured by conventional instruments, such as pressure, temperature, and DP transmitters, as shown in Fig. IX/3.8.0-1. As shown in this figure

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P

SAMPLING

T

GAS FLOW METER

GAS SEPARATOR

LIQUID FLOW METERING

BIDIRECTIONAL ORIFICE

DP

FIGURE IX/3.8.0-1 Sampling type multiphase meter. Developed based on an idea from N. Bonavita, G. Ciarlo, ABB VIS Multiphase Flow Meter Un nuovo misuratore multifase “g-free” per il monitoraggio e l’ottimizzazione della produzione nell’Oil and Gas, ABB Measurement Products, mcT Petrolchimico, November 2014, Internet document. http://www.aisisa.it/wp-content/uploads/2014/12/VIS_mcT_Petrolchimico_Rev1.pdf. Courtesy: ABB Limited.

that sample only comes to the meter through the sampler. Then at gas separator gas is separated as shown light (yellow) arrow and liquid in dark (blue) arrow. There are separate gas meter an liquid meter (DP) as shown. All such data are transmitted to a dedicated computing unit/PC station, which uses proprietary

software for presentation of data in the form of flow rates of the individual phases. It is possible to get standard hardwired output or communication through a fieldbus, such as Profibus or Canbus. The meter is suitable for GVF > 80%. By its nature, VIS provides maximum performance precisely, in extremely high GVF.

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3.8.2 ISOKINETIC SAMPLING The following are basic regulations followed for isokinetic sampling in an ABB VIS meter: 1. Sampling is done in the pipe at a place where gas and liquid are well mixed and velocity profiles are uniform. 2. The liquid volume fraction in the sample is the same as in the main stream. 3. Isokinetic sampling requires that the ratio between the sampling flow rate and the overall flow rate be the same as the ratio between the sampling probe cross-section and the pipe cross-section (at the sampling location) [50]. 4. No field calibration is necessary and there are no empirical relations. With this the discussions on the VIS meter and on multiphase flow metering technologies come to an end. In the following section discussions on miscellaneous issue for multiphase metering shall be covered, including selection criteria.

4.0.0 MULTIPHASE FLOW METERING —MISCELLANEOUS TECHNICAL ISSUES In the above discussions, various technical issues related to fluid dynamics, terms with explanations and implications, and various technologies for measurements have been discussed. In this section brief discussions on a few other issues shall be covered to make the discussions on multiphase flow measurement complete. During the above discussions it has been shown that there are many types of instruments and instrument technologies for measurement. Also, there are different measuring types and parameters. From a user’s point of view it is extremely important to know how to select the most suitable instrument for a particular application. Therefore, let the discussions start with meter selection. 4.1.0 Multiphase Flow Meter Selection Issues The wide range of instruments and measurement technologies discussed above are designed to offer optimum performance in different fluids at

different operating conditions. Naturally, when it is used in different conditions the same performance cannot be guaranteed, in fact it may not perform at all! Therefore, it is important to understand the merits and limitations inherent to each style of instrument and the operating conditions for which it is meant. The performance requirement of two-phase flow will be different from a typical three-phase metering system. Also, the operating conditions (e.g., GVF value) of wet gas measurement and the water-in-liquid ratio will be different. In the reactor studies context this measurement is complicated by the fact that during the transient period, the fluid becomes a nonhomogeneous mixture of liquid water and steam at (or very near) saturation [36]. It is needless to emphasize, that the MOC of the meter is extremely important so that it can withstand the harsh condition(s) it has to face in the field. 4.1.1 GENERAL REQUIREMENTS AND EXTERNAL CONDITIONS FOR METER SELECTION 1. Operating conditions: Ideally an instrument meant for flow measurement should be able to withstand and respond immediately but consistently to changes in fluid velocity, even if there is a fluid hammer due to a pressure surge (to suddenly stop or change the flow direction of fluid motion). Turbulent or pulsating flow may cause flow-registering errors and suitable considerations should be given for this. Apart from these operating pressure and temperature conditions, environmental conditions are also very important for meter selection. Changes in viscosity and temperature also affect meter performance. Excess temperature may be a cause of changes to the internal dimensions. Therefore, due consideration for these is warranted. 2. Flow regime: From the above discussions, it is clear that depending on pressure and temperature ranges, there will be different flow regimes. There are different flow regime demands for different responses. Unless the selected meter is capable of spanning all the pipe section of interest to detect average values of the measured quantity, the output could be misleading [36].

Multiphase Flow Measurement Chapter | IX

3. Cavitation: This phenomenon in two-phase flow is not uncommon and the meter should be sized and installed in a suitable way so that this is avoided. 4. MOC: The MOC for a flow meter, especially those in contact with the fluid, has direct bearing on meter performance, stability, and longevity. For special and corrosive applications, suitable MOC need to be arrived at. Meters are available with a wide range of materials, such as: CS, SS316, Hastelloy, tantalum, Monel, nickel, and titanium. In addition to these there are thermoplastic materials. Noninvasive flow application problems are less. 5. Mechanical issues: A number of mechanical issues listed below are also important considerations: l Pipe size; l Connection type; l Pressure (and temperature) rating of flange; l Upstream and downstream straight length (as applicable); l Requirement of any flow conditioner; l Necessary accessories; l Installation: horizontal/vertical/inclined; l Smaller footprint and weight are a requirements for offshore application on account of space restrictions and weight control. 6. Maintenance need: On account of dirt/solid particles, flow meters with moving parts obviously have more maintenance requirements than with those without moving parts. Also, meters with bearings have maintenance needs. For meters like DP meters there is an issue of the impulse line getting plugged. Meters using radioactive sources also have safety and maintenance issues to be considered. 4.1.2 SENSING SPECIFIC REQUIREMENTS 1. Performance criteria: In certain situations where flow meters are used to give an indication of the rate at which a liquid or gas is moving through a pipeline, high accuracy may not be crucial [36]. However, for custody transfer issues, i.e., where pricing/dispensing

2.

3. 4.

5.

6.

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is involved or batching, sampling, and flow meter accuracy (refer to Chapter I for types of accuracy) are definitely an important factor in meter selection. Meter repeatability and response time are also important performance criteria. Calibration: Meter calibration, as necessary, should be as simple as possible. Some meters, such as VIS, do not require field calibration. The calibrations are carried out at a temperature different from field conditions so it is better that calibration is as independent as possible from the temperature difference between the two conditions discussed. Conformance to local regulatory requirements. Data acquisition system: As seen, many of the multiphase flow meters require a huge quantum of data collection and handling so a good data acquisition system with suitable software should be chosen. Open platform software has advantages in this regard. Another important issue is system interface especially for software based systems. Fieldbus (discussed at length in Appendix VII) systems has inherent advantage. Bidirectional operation capability: Some applications, such as in batch reactors, demand bidirectional flow capability, so that should be kept in mind. Sensor issues: There are some sensing methods, such as wire mesh sensing, where the measurement type is intrusive. In such a situation care should be taken to ensure it does not cause flow disturbance. Also, while selecting a sensor it is important to note and take necessary steps so that the sensor signal processing is not too complex.

4.2.0 Multiphase Flow Meter Specification Issues As the MPFM system covers a wide range of technologies and instruments, it is not possible to create a specification sheet. However, the following points could be taken into account for specifying MPFM systems.

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4.2.1 PERFORMANCE SPECIFICATION For any measurement, especially for MPFM performance, specification is of immense importance. Based on performance requirements often selection of MPFMs, as well as appropriate technologies for specific application, is arrived at. Standardized performance specifications will help users compare MPFMs proposed from different manufacturers for specific applications [1]. Apart from measurement uncertainty actually performance should cover broadly the following: 1. Measurement accuracy in suitable scale for comparison (AR/FSD); 2. Repeatability and reproducibility; 3. Sensitivity and resolution; 4. Reliability and stability of measurement; 5. Response time; 6. Influencing factor; 7. Measuring span; 8. Limiting conditions (as applicable); 9. Operating condition and limits of operation. Such specification should include all the components and parts of the system, including primary devices such as sensors and transmitters. Since most of the measuring technologies involve intelligent measurement systems including DAS and computer performance of software and communication and control capabilities (of microcontrollers) along with updating capabilities are also important. 4.2.2 TECHNICAL DESCRIPTION As already stated it is not possible to specify the meter type on account of the vast application area and vast combination of measuring types and technologies and associated complexities. The basic functional requirements can however be specified. As part of the specification for common understanding the following are of importance: 1. Overview of measurement scheme with suitable block schematic; 2. Description of overall measurement scheme and its objective; 3. Detailed description of all subsystems/components and devices, including sensors, transmitters, software, computers, to name a few;

TABLE IX/4.2.2-1 Input and Output Data for Specification (With Suitable Applicable Units) Input to be Specified

Output Expected

Density per phase (kg/m2)

Phase volume flow rate (m3/h*)

Viscosity per phase (m.Pa)

Phase accumulated volume (m3*)

Fluid (water) conductivity (mS/cm)

Pressure (bar)

Fluid permittivity (F/m)

Temperature ( C)

Linear attenuation coefficient (L/m)

Phase density (kg/m3)

Mass attenuation coefficient (m2/kg)

WLR (%)

Ambient condition temperature ( C)

GVF (%)

*Depending on application other lower unit are also used.

4. Basic specification (with functional details) components/instruments/sensors; 5. Outlined specification (functional details) of measurements ranges/limit, etc.; 6. Description of configuration, parameters, and required input, such as fluid properties, operating conditions, site limitations, and requirements [1]. Some of the I/Os of the meter are as given in Table IX/4.2.2-1. 4.2.3 OUTPUT SPECIFICATION REQUIREMENTS The following are the general minimum expected output from a three-phase MPFM: 1. Gas, oil, and water gas volume and/or mass flow rates; 2. For wet gas, gas/liquid volume and/or mass flow rates; 3. Phase fractions and/or WLR/GVF; 4. Density measured (as applicable); 5. Operating pressure and temperature conditions. Additionally, a few other data are also provided by the metering systems.

Multiphase Flow Measurement Chapter | IX

5.0.0 MULTIPHASE FLOW METERING —INSTALLATION AND COMMISSIONING ISSUES Field installations mean physical/mechanical installation, piping, as well as electrical connection, including communication network set up along with necessary protections. With a number of types of meters for metering technology, as well as varying site conditions, it is difficult to provide a detailed installation of metering systems like conventional single-phase meters discussed in previous chapters. Post installation comes the commissioning procedure. However, some guidelines have been established. 5.1.0 Brief Multiphase Installation Discussions In this section brief discussions on installation guidelines and requirements shall be covered. 5.1.1 INSTALLATION GUIDELINES The following points need to be considered for installations: 1. Manufacturer’s recommendations: To follow the manufacturer’s installation recommendations (as far as possible), i.e., prior to starting the installation it is necessary to get the manufacturer’s installation drawing; 2. Limits: Due consideration must be given to the limits for the meter specified by the manufacturer towards temperature, pressure, and flow rates, and any other issue including straight length requirements. Locations should be selected accordingly; 3. PVT data: Pressure, volume, and temperature data as required for optimal measurements [1] at MPFM are available; 4. Accessibility: Facilities to ease the installation and removal of the meter. It is recommended to have additional space so that in future if necessary a larger system can be accommodated. Also, proper accessibility must be kept to facilitate meter data-checking operations, accommodation of test separator and headers, and any other test equipment as required. Due consideration must be given to maintenance accessibilities;

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5. Exploration: Bypass to prevent well shutdown during testing and servicing [1]. Electrical connections: Proper power and communication, network cabling, and connections for satisfactory operation must be checked in line with manufacturer’s recommendations; 6. Sampling: Facilities to collect multiphase fluid samples; 7. Fixing: Individual meter fixing and installations with requirements for straight length flow conditioners, etc.; 8. Back up and spares arrangements, as per the site conditions. 5.1.2 INSTALLATION REQUIREMENTS General mechanical installation requirements, such as piping alignments, dimensional matching, and fitting the instruments in the pipe should be met with, to assure required straight lengths and flow conditioners are done as per manufacturer’s recommendations. Also, checking of proper power supply, connections, earthing, and communication connections have been carried out as per the recommendations. All protections for the meter and/or for hazardous locations are well taken care off. 5.2.0 Brief Multiphase Commissioning Discussions After the installation is over it is necessary to check thoroughly that the installation work has been done completely. After that the precommissioning checks, loop continuity checking, etc. are carried out. Usually the vendor requires some information on process, mechanical and operational data from the client for proper set up of the MPFM [1]. These are done in suitable drawings and documentation and a punch list is prepared. So, prior to starting commissioning it is ensured that all necessary steps have been completed. With due authorization, commissioning activities such as system testing and system checks (end to end) are carried out. System configuration tests as per relevant standard(s) are undertaken. Pressure test and communications checks are performed before the final test and performance tests are undertaken. In the final test and performance tests suitable recoding as per mutually agreed protocols are recorded and signed by the owner and the vendor to complete the procedure.

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6.0.0 MULTIPHASE FLOW METERING— TESTING AND CALIBRATION There are three main places that testing, calibration, and adjustments can be performed. These are the factoryefactory acceptance test, test facility, and in situ in sequence. In cases where there is no separate test facility, the adjustments are from FAT to in situ. Various testing and adjustment facilities have been detailed in Table IX/6.0.0-1.

Static calibration represents the normal factory tests, whereas loop testing is dynamic testing. When the results from a calibration are assessed, one should bear in mind the significant difference between MPFMs and single-phase meters [1]. Some of the adjustments based on dynamic calibrations mainly include curve fit/matrix calibration and factory calibration. With this the discussions on multiphase flow metering are concluded.

TABLE IX/6.0.0-1 Testing and Calibration Action Stages and Location

Test

Calibration

Factory

Functional of system

Static and dynamic

Routine tests of instrument

Model fluid Purpose-built loop

Test facility

Instrument and communication check

Static and dynamic Nonbias Extended test matrix Reference instruments traceable to standard Represented fluid Live process fluid

In situ

Same as above with commissioning

Static and dynamic Baseline recording Phase transition issue Performance test Satellite field start up

Based on Table 10.1 of Instrument Engineers’ Handbook, vol. 1, Process Measurement and Analysis, CRC Press (Chapter 2 flow measurement).

External and internal view of M Phase 5000. Courtesy: Krohne Messtechnik GmbH (Magnetic Resonant Type MPFM from Krohne).

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LIST OF ABBREVIATIONS ABS Absolute AC Alternating current ADC Analog-to-digital converter AI Analog input AO Analog output AR Actual reading (in connection with accuracy) CCW(/CW) Counterclockwise (/clockwise) CMRR Common mode rejection ratio CMV Common mode voltage CS Carbon steel DAS Data acquisition system DC Direct current DCS Digital control system DDS Direct digital synthesizer DEGRA Dual-energy gamma ray attenuation DI Ductile iron/digital input DO Digital output DP Differential pressure DPT Differential pressure transmitter/transducer DSP Digital signal processing EIT Electrical impedance tomography/type EMC Electromagnetic compatibility FAT Factory acceptance test FC Fail to close (for valve) FO Fail to open (for valve) FSD Full-scale division (in connection with accuracy) GOR Gaseoil ratio GVF Gas volume fraction HVAC Heating, ventilation, and air conditioning IC Integrated chip/internal combustion (engine) ID Internal diameter I/O Input/output IS Intrinsic safety LCD Liquid crystal display LDA Laser Doppler anemometry LDV Laser Doppler velocimetry

LED Light-emitting diode LHS Left-hand side MFM Multiphase flow meter (see MPFM also) MP Multiphase MPFM Multiphase flow meter MS Mild steel (main steam) MUX Multiplexer MVT Multivariable transmitter NAA Neutron activation analysis NB Nominal bore NIR Near infrared NIST National Institute of Standards and Technology OD Outer diameter PIV Particle image velocimetry PLC Programmable logic controller PNA Pulsed neutron activation PTFE Polytetrafluoroethylene PTV Particle tracking velocimetry PU Processing unit PVC Polyvinyl chloride PVT Pressure, volume, temperature RF Raised face/radiofrequency RHS Right-hand side RPM Revolutions per minute RTD Resistance temperature detector SIL Safety integrity level SS Stainless steel STP Standard temperature and pressure (Fig. I/1.1.2-3) TC Thermocouple TP Two phase US Ultrasonic/United States VDU Visual display unit VFD Variable-frequency drive VM Valve manifold VMS Virtual metering system W/O Without/water in oil (emulsion) WRT With respect to

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Engineering and Technology 5 (4) (August 2015). E-ISSN 2277 e 4106, P-ISSN 2347 e 5161, http://inpressco.com/ category/ijce. E.G. Nyfors, Cylindrical Microwave Resonator Sensors for Measuring Materials Under Flow, May 2000. Report S243, http://lib.tkk.fi/Diss/2000/isbn951225168X/isbn951225168X. pdf. A.M. Scheers, An Oil/Water/Gas Composition Meter Based On Multiple Energy Gamma Ray Absorption (Megra) Measurement. http://www.iaea.org/inis/collection/NCLCollection Store/_Public/31/024/31024457.pdf. V. Kornienkoa, P. Avtonomov, Application of Neutron Activation Analysis for Heavy Oil Production Control, Ratec Lab Limited Russia; Procedia; Elsevier (Science Direct), 2015. L. Hamidatou, H. Slamene, T. Akhal, B. Zouranen, Concepts, Instrumentation and Techniques of Neutron Activation Analysis, Intech, 2013. Internet document, http://www. iaea.org/inis/collection/NCLCollectionStore/_Public/28/059/ 28059813.pdf. D.T. Win, Neutron activation analysis (NAA), AU Journal of Technology 8 (1) (July 2014) 8e14. Assumption University Bangkok, Thailand, http://www.journal.au.edu/au_ techno/2004/jul04/vol8num1_art02.pdf. W.F. Fong, I. Pillalamarri, Delayed Neutron Activation Analysis, IAP 12.092, Internet document. https://ocw.mit. edu/courses/earth-atmospheric-and-planetary-sciences/12091-trace-element-analysis-of-geological-biologicalenvironmental-materials-by-neutron-activation-analysis-anexposure-january-iap-2005/projects/delayednaa.pdf. C. Bertani, M. De Salve, M. Malandrone, G. Monni, B. Panella; Ricerca Di Sistema Elettrico, State-of-art and selection of techniques in multiphase flow measurement, CERSE-POLITO RL 1255/2010, Agenzia Nazionale per le Nuove Tecnologie, l’Energia e lo Sviluppo Economico Sostenibile. http://editors.enea.it/it/Ricerca_sviluppo/documenti/ ricerca-di-sistema-elettrico/nuovo-nucleare-fissione/lp2/lp2033-1255-cirten-polito-rl.pdf. Rocha, E.L.L. Cabral, Two-phase flow assessment and void fraction measurement of a pilot natural circulation loop using Capacitance probe, in: 2011 International Nuclear Atlantic Conference e INAC 2011, October 2011. ISBN: 978-8599141-04-, http://www.iaea.org/inis/collection/NCLCollection Store/_Public/43/048/43048807.pdf. M.S. Ko, B.A. Lee, W.Y. Won, Y.G. Lee, D.W. Jerng, S. Kim, An Improved Electrical-Conductance Sensor for Void-Fraction Measurement in a Horizontal Pipe, Science direct; Elsevier, 2015. http://www.sciencedirect.com/ science/article/pii/S1738573315001680. M. Wang, J. Jia, Y. Faraj, Q. Wang, C. Xie, G. Oddie, K. Primrose, C. Qiu, A new visualisation and measurement technology for water continuous multiphase flows, Flow Measurement and Instrumentation 46 (2015). Elsevier, http:// ac.els-cdn.com/S095559861500076X/1-s2.0-S095559861500 076X-main.pdf?_tid¼49d52380-992f-11e6-b592-.

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[40] A.K. Jana, T.K. Mandal, D.P. Chakrabarti, G. Das, P.K. Das, An optical probe for liquideliquid two phase flows, Measurement Science and Technology 18 (5) (April 2007). [41] E. Schleicher, M. Jose da Silva, U. Hampel, New Developments in Fast Needle Probe Sensors For Multiphase Flow Measurements. http://www.hzdr.de/FWS/publikat/ JB05/JB_05_R07.pdf. [42] Conductivity and Temperature Needle Probes, Catalog, HZDR: Helmholtz Zentrum Dresden. https://www.hzdr.de/ db/Cms?pOid¼11942&pNid¼0. [43] G.P. Lucas, X. Zhao, Large Probe Arrays for Measuring Mean and Time Dependent Local Oil Volume Fraction and Local Oil Velocity Component Distributions in Inclined Oilin-water Flows, Elsevier, 2013. http://www.sciencedirect. com/science/article/pii/S0955598613000393. [44] M. Behling, D. Mewes, Process Tomography: Development and Application of Non-intrusive Measuring Techniques for Multiphase Flows, University of Hannover (Germany), Institute of Process Engineering, If V; Workshop on Computerized Tomography for Scientists and Engineers; Department of Mechanical Engineering; Indian Institute of Technology, February 2004. [45] G.A. Johansen, L. Meric, R. Maad, E.M. Bruvik, B.T. Hjertaker, C. Sætre, Non-destructive monitoring of multiphase hydrocarbon flow by high speed gamma-ray tomography, in: 11th European Conference on Nondestructive Testing (ECNDT 2014) Óct’ 2014; Prague, Czech Republic, 2014. [46] A.J. Peyton, M.S. Beck, A.R. Borges, J.E. de Oliveira, G.M. Lyon, Z.Z. Yu, M.W. Brown, J. Ferrerra, Development of electromagnetic tomography (EMT) for industrial applications. Part 1: sensor design and instrumentation, in: 1st World Congress on Industrial Process Tomography, Buxton, Greater Manchester, April 1999. http://citeseerx.ist.psu.edu/viewdoc/ download?doi¼10.1.1.548.3150&rep¼rep1&type¼pdf. [47] J. Hogendoorn, A. Boer, M. Appel, H. de Jong, R. de Leeuw (Shell), Magnetic resonance technology a new concept for multiphase flow measurement, in: 31st International North Sea Flow Measurement Workshop; Norway; Oct’ 2013, 2013. http://krohne.com/fileadmin/content/files-2/PDFUpload/2013-NSFMW-Magnetic_Resonance_TechnologyA_New_Concept_for_Multiphase_Flow_Measurement.pdf. [48] J. Hogendoorn, A. Boer, M. Zoeteweij, O. Bousché, R. Tromp, R.D. Leeuw, P. Moeleker, M. Appel, H.D. Jong, Magnetic resonance multiphase flow meter: gas flow measurement principle and wide range testing results, in: 32nd International North Sea Flow Measurement Workshop; Oct’ 2014, 2014. [49] J. Hogendoorn, M. van der Zande, Multiphase flow measurements based on magnetic resonance technology, in: Flow and Analyse Event, June 2015. http://www.flowac.nl/wpcontent/uploads/sites/59/2015/02/krohne_multiphase.pdf. [50] N. Bonavita, G. Ciarlo, ABB VIS Multiphase Flow Meter Un nuovo misuratore multifase “g-free” per il monitoraggio

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e l’ottimizzazione della produzione nell’Oil and Gas, in: ABB Measurement Products, mcT Petrolchimico, November 2014. Internet document, http://www.aisisa.it/wp-content/ uploads/2014/12/VIS_mcT_Petrolchimico_Rev1.pdf. [51] Oil, Gas and Water in Real Time Flow Rate: Measurement Becomes Multiphase, Article AT/FLOW/003eEN, ABB Limited, Internet document. https://library.e.abb.com/public/ 0e0a8d895e76377dc1257ddd003d3ee1/AT_FLOW_003EN.pdf.

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FURTHER READING [1] Instrument Engineers’ Handbook, Vol. 1: Process Measurement and Analysis, CRC Press (Chapter 2 Flow measurement). [2] M.A. Crabtree, Industrial Flow Measurement, The University of Huddersfield, June 2009. http://eprints.hud.ac.uk/ 5098/1/macrabtreefinalthesis.pdf&sa¼u&ei¼v66ttp_ccojm ialag7mnbq&ved¼0cdiqfjat&usg¼afqjcngao5vc1jsrrbjucj vkxotjjoah6q. [3] F. Frenzel, H. Grothey, C. Habersetzer, M. Hiatt, W. Hogrefe, M. Kirchner, G. Lütkepohl, W. Marchewka, U. Mecke, M. Ohm, F. Otto, K.-H. Rackebrandt, D. Sievert, A. Thöne, H.-J. Wegener, F. Buhl, C. Koch, Deppe, E. Horlebein, A. Schüssler, U. Pohl, B. Jung, H. Lawrence, F. Lohrengel, G. Rasche, S. Pagano, A. Kaiser, T. Mutongo, Industrial Flow Measurement Basics and Practice, ABB Automation Products GmbH. http://nfogm.no/wp-content/uploads/2015/04/ Industrial-Flow-Measurement_Basics-and-Practice.pdf. [4] S. Basu, Plant Hazard Analysis and Safety Instrumentation Systems, Elsevier; IChemE, 2016. http://store.elsevier.com/ Plant-Hazard-Analysis-and-Safety-Instrumentation-Systems/ Swapan-Basu/isbn-9780128037638/. https://icheme.myshop ify.com/products/plant-hazard-analysis-and-safety-instrument ation-systems-1st-edition. [5] Flow Measurement Handbook; R.C. Baker; Cambridge University Press; second ed. [6] M.W. Munir, B.A. Khalil, Cross correlation velocity measurement of multiphase flow, International Journal of Science and Research (IJSR) 4 (2) (February 2015). https:// www.ijsr.net/archive/v4i2/SUB151217.pdf. [7] B.J. Azzopardi, Multiphase flow, University of Nottingham, Chemical Engineeering and Chemical Process Technology e Vol. I. http://www.eolss.net/sample-chapters/c06/e6-34-01-05. pdf. [8] J.R. Thome, Fundamentals of void fraction in two phase flow, Chapter 17 Data Book III, Swiss Federal Institute of Technology Lausanne. http://ltcm.epfl.ch/files/content/sites/ ltcm/files/shared/import/migration/COURSES/TwoPhase FlowsAndHeatTransfer/lectures/Chapter_17.pdf. [9] R. DiGiacomo, Two Phase Flow Considerations for Coriolis Meters, ABB, ABB Whitepaper, Technical description

[12]

[13] [14]

[15]

[16]

[17]

[18]

[19]

TD/CORIOLIS/101-EN; https://library.e.abb.com/public/e16 2b8b191f0b2d3c1257ce6003bd184/TD_CORIOLIS_101_ EN_1.pdf. R. Heddle, J. Foot, H. Rees, Virtual Flow Metering Improves Field Data, British Petroleum, March 2012. http:// www.offshore-mag.com/articles/print/volume-72/issue-3/ productions-operations/virtual-flowmetering-improves-fielddata.html. H.E. de Lima Avila, D.J. Paganob, F.R. de Sousa, Improving the Performance of an RF Resonant Cavity Water-Cut Meter Using an Impedance Matching Network, Federal University of Santa Catarina, December 2014. http://lrf.ufsc.br/files/ 2012/06/VersaoEnviadaPosReview-1.pdf. J. Liu, Investigation of Trace Amounts of Gas on Microwave Water-Cut Measurement, Texas A&M University, May 2005. http://oaktrust.library.tamu.edu/bitstream/handle/1969.1/3917/ etd-tamu-2005A-PETE-Liu.pdf?sequence¼1&isAllowed¼y. C.T. Crowe (Ed.), Multiphase Handbook, Taylor and Francis Group, September 2013. E.N.D. Santos, Development and Application of Wire Mesh Sensors for High Speed Multiphase Flow Imaging (Doctoral thesis); Curitiba, 2015. Internet document, http://repositorio. utfpr.edu.br/jspui/bitstream/1/1410/1/CT_CPGEI_D_%20San tos%2C%20Eduardo%20Nunes%20dos_2015.pdf. H. Lia, M. Wang, Y.X. Wu, G. Lucas, Volume flow rate measurement in vertical oil-in-water pipe flow using electrical impedance tomography and a local probe, in: 11th Int. Conf. on Multiphase Flow in Industrial Plants, 2008. Palermo, Italy, http://www-old.hud.ac.uk/media/universityofhuddersfield/ content/image/research/sce/sergsystemsengineering/modowproject/publications/O15.pdf. Neutron Imaging, Paul Scherrer Institut, Internet document. https://www.psi.ch/industry/MediaBoard/neutron_imaging_ e_07.pdf. W. Na, J. Jia, X. Yu, Y.Faraj, Q.Wang, Y.F.Meng, M. Wang, W. Sun, Imaging of gaseliquid annular flows for underbalanced drilling usingelectrical resistance tomography, Flow Measurement and Instrumentation, Elsevier. https://ac.els-cdn.com/S0955598615001089/1-s2.0-S09555 98615001089-main.pdf?_tid¼bcddcf18-a9e0-11e7-8b2200000aacb35e&acdnat¼1507217016_dc8a862170d329f6 092a200d79d57c6c. M.S. Beck; M. Byars, T. Dyakowski, R. Waterfall, R. He, S.J. Wang, W.Q. Yang, Principles and industrial applications of electrical capacitance tomography, Process Tomography Group UMIST. http://journals.sagepub.com/doi/ pdf/10.1177/002029409703000702. VIS multiphase flow meter high gas content applications solved with no radioactive source e measurement made easy, Measurements & Analytics, ABB, Catalog, Internet document. https://library.e.abb.com/public/944ef4f5866d4 cab9930532066f319f8/PB_VIS-EN_A.pdf.

CHAPTER X SPECIAL FLOW METERS, FLOW GAGES, AND SWITCHES

Chapter Outline 1.0.0 Introduction 2.0.0 Hall Effect Sensing and Flow Measurement 2.1.0 Theoretical Background of Hall Effect 2.2.0 Hall Effect Sensor Types 2.3.0 Magnetic System 2.4.0 Hall Sensor Features and Applications 2.5.0 Specification of Hall Sensors 3.0.0 Magnetic and Proximity Pickup and Flow Measurement 3.1.0 Magnetic Pickup and Flow Measurement 3.2.0 Proximity Pickup 3.3.0 Signal Conditioning Unit 4.0.0 Cryogenic Flow Measurement 4.1.0 Discussion on Cryogenic Flow Measurements 4.2.0 Differential Pressure Type Cryogenic Flow Measurement 4.3.0 Turbine Meter in Cryogenic 4.4.0 Vortex Meter in Cryogenic Applications 4.5.0 Coriolis Mass Flow Meter in Cryogenic Applications 4.6.0 Ultrasonic Flow Meter in Cryogenic Applications 4.7.0 Processing Electronics in Cryogenic Applications

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1.0.0 INTRODUCTION Starting from various principles of measurements, various kinds of flow meters have been discussed at length in previous chapters. The flow meters discussed so far are commonly found in various plants and industrial applications. Therefore, these can be considered as common flow meters. However, apart from various common flow meters there are a few flow meters which make use of some special physical phenomena for flow measurements. These are special flow meters. These are not very commonly used. However, under certain conditions and measurement constraints they are found to be extremely useful. Cryogenic condition is a special condition, and measurement of flow in that condition is not easy.

5.0.0 Flow Gages 5.1.0 Direct-Flow Gages 5.2.0 Sight Flow Indicator 5.3.0 Digital Local Flow Indicator 6.0.0 Mechanical Type Flow Meters 6.1.0 Mechanical Water Meters 6.2.0 Mechanical Oil and Other Flow Meter 7.0.0 Flow Switch 7.0.1 Definitions and Terminologies With Explanations 7.0.2 Flow Switch Types 7.1.0 General Requirements of Flow Switches With Explanations 7.2.0 Flow/No-Flow Switch: Paddle(/Vane) Type 7.3.0 In-Line and DP Type Flow Switches 7.4.0 Variable Orifice Type Flow Switches 7.5.0 Thermal Dispersion Type Flow Switch (Monitor) 7.6.0 Discussions on Miscellaneous Flow Switches 7.7.0 Discussions on Solid (Bulk) Flow Monitors List of Abbreviations References Further Reading

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Cryogenic flow meters are examples of some of the special flow meters. In some plants it is not always necessary to use flow meters for flow monitoring. Hall effect flow sensing is not a flow meter in the true sense. It represents a way to sense flow. Like magnetic pick, up this is another special way of flow sensing. Hall effect sensors are related to flow measurement in different ways. It can be used as a sensing element to compute flow in a turbine flow meter or paddle wheel flow (switch). If we look at solid flow measurement, a Hall effect sensor is utilized here also for sensing of conveyor speed measurement, which is directly related to solid flow measurement. Hall effect can be used to sense zero flow and this is also related to protection of solid flow

Plant Flow Measurement and Control Handbook. https://doi.org/10.1016/B978-0-12-812437-6.00010-X Copyright © 2019 Elsevier Inc. All rights reserved.

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measurement through a conveyor. Simple flow/ no-flow conditions would suffice, e.g., a big fan/ pump lubrication system, here there is a need to ensure that there is flow in lubrication line when the lube pump (in fact for that matter the main fan or pump) is started locally. Therefore, a simple flow/no-flow gage is sufficient. In this case, metering of flow by a flow meter would neither be cost-effective nor in many cases, on account of the short space installation of the flow meter, may it be feasible. When a big fan and/or pump is started through an auto-program or in running condition it is necessary to interlock the fan/pump with lube oil system for the safety of the fan/ pump. When the lube oil flow is less, first there may be a pretrip alarm followed by tripping of the concerned fan/pump. In all such cases switches (not the flow meter) are deployed. Some use a flow switch, some use a pressure switch. In many mixing and batch controls, the flow switch is necessary for the recipe to maintain quality of the output product. In all such cases flow switches are used. In this section these special flow instruments and flow gage flow switches have been covered to complete the discussions on flow monitoring. In many cases the operating principles of these flow gages and switches are similar to flow meters but the designs and/or installations are different, so these need separate treatment. It has been seen that Hall effect sensors are used for flow sensing in many instruments already discussed, such as turbine flow, to measure the speed of the rotating device. In the same way it can be used to detect the speed of a conveyor and/or zero speed switch for a conveyor which is used in solid flow measurement. Other than Hall effect sensors, often magnetic pickups and proximity pickups are also used. These are very useful in flow measurement. It is better to look into the details of Hall effect sensing along with other inductive pickups. The discussion starts with Hall effect sensing.

2.0.0 HALL EFFECT SENSING AND FLOW MEASUREMENT The Hall effect is a very effective sensing technology. It is named after its inventor, Edwin Herbert Hall, who invented it in 1879. When a

metal plate is connected across a power source then charges from the battery outlet go to the metal piece and pass through it in a straight path and return to the battery to complete the current path. When the same arrangement is placed in a magnetic field perpendicular to the direction of current flow it can be noticed that, on account of Lorenz force, charge careers are deflected and move towards the edges. This is the fundamental principle on which the Hall effect has been developed. The Hall element is a solid-state device developed from a thin sheet of semiconductor material. When it is supplied with a voltage source and is subjected to a magnetic field, it responds with an output voltage proportional to the magnetic field strength, with output connections perpendicular to both the direction of current flow and direction of magnetic field. The output voltage developed is very small (mV) and requires additional electronics to achieve useful voltage levels. Therefore, the Hall element combined with the associated electronics forms the popular Hall effect sensor. This magnetic field sensor has a very wide range of applications. It can be used as a sensor for speed, flow, current, temperature, pressure, position, etc. In this connection Section 9.0.0 of Chapter IV (where short discussions on this have been provided)may be referenced also. There are a few issues pertinent to the Hall effect sensor worth noting: 1. General sensor selection: For selection of the sensor there are certain fundamental principles to be followed. One important issue is to identify the input and output requirements, application requirements, and match these with the major sensing device components. Engineering judgment is the only tool, such engineering judgments come only after the strengths and weaknesses of each approach are weighed. The major issues are listed here: l Overall cost; l Device availability; l System and device complexity; l Tolerance of field conditions; l Compatibility with other system components [1]; l Reliability;

Special Flow Meters, Flow Gages, and Switches Chapter | X

System performance including repeatability; l Maintenance issues. 2. Hall effect as the preferred sensor: While selecting a sensing element, cost, performance availability, and mounting facilities are normally considered as primary issues. From all these considerations, Hall effect sensors are preferred mainly on account of the following reasons: l True solid state: Fast acting, low power; l Static, no moving parts; l Long life; l Good performance, including high repeatability; l Operates with stationary input (zero speed) [1]; l Available in analog and digital form; l Logic compatible input and output; l Wide temperature range for operation. 3. Design requirements of the Hall effect sensor with a system: As the Hall effect sensor is a magnetic sensing it requires a magnetic system capable of responding to the physical parameter to be sensed. Since silicon has a piezoresistive effect, the design should take care to minimize this effect. The physical parameter actually interfaces with the sensor. In most cases these are mechanical interfaces. The Hall effect sensor senses the changes in magnetic field to produce an electrical output. Here it is the responsibility of the output interface to match the output signal with the system requirements to fulfill the application objective. Therefore there are basically four blocks here, i.e., input interface (measuring parameter) with input interface, magnetic system, Hall element, and finally the output interface. This has been clearly depicted in Fig. X/ 2.0.0-1. Also, there should be a suitable interconnection amongst them according to the application requirements. It is worth noting that it is not mandatory that all four elements discussed above are necessary, e.g., for any measurement related to the magnetic field sensing system, does not require a magnetic system. l

MEASURING

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QUANTITY

INPUT NPU NP UT INTERFACE HALL HA A ALL ELEMENT

SENSING G M MECHANISM ECHANISM HAN M OUTPUT OUTPU OU O UT UTP TPUT INTERFACE

ELECTRICAL OUTPUT

FIGURE X/2.0.0-1 General Hall effect device.

While defining the input to the sensor it is necessary to take care of the following: l Input parameter range values with possible rate of change (maximum and minimum); l Factors which can affect the measurement (temperature/EMI); l Safety factor to be chosen; l Probable sources of error; l Allowed tolerance limits; l Ambient conditions. Similarly, output characteristics are also guided by the following manner: l Electrical characteristics, i.e., output forms in current, voltage, pulse train, logic levels, etc.; l For digital output meaning and level of signals for 0 and 1; l Output at sensor OFF condition and interpretation; l Output load value and types (e.g., resistive); l Interconnection details with allowed cable length; l Output characteristics, i.e., sourcing/sinking; l Performance requirements; l Available space and weight. There is also requirement of system definition which includes but is not limited to the following: l Gap (minimum/maximum) between Hall element and magnet; l Maximum minimum allowed magnet travel;

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Mechanical linkage if required; Sensor output type (to match source/sinking type); Allowed operating and storage temperature; Selection of the magnetic mode, magnet, Hall effect sensor, and functional interface [1]; Matching of input/output requirements. We now examine the theory of operation for Hall effect sensing.

2.1.0 Theoretical Background of Hall Effect In this section the theory of operation of Hall effect sensing is discussed. The Hall element is a thin sheet of semiconducting material which can pass current through it. So when a voltage is applied to terminals 1 and 2 in Fig. X/2.1.0-1, the current will flow undisturbed from terminal 1 to 2 and if voltage is measured across terminals A and B there will be zero potential difference, when there is no magnetic field applied. When a magnet is brought near the Hall element, a Lorentz force is exerted on the current. This force disturbs the current distribution, based on the magnetic pole present near it, the charges are deflected from each other rather being shifted towards the sides of the Hall elements, as shown in Fig. X/ 2.1.0-1. As a result there will be positive and negative charges at the two ends. Therefore,

when voltage is measured across the Hall element there will be a potential difference between terminals A and B. This is Hall voltage, VH. It is worth noting that the voltage developed will be proportional to the vector cross-product of strength of current (in ampere) passing through the semiconductor and magnetic flux density (in Tesla) applied as shown in Eq. X/2.1.0-1. I VH ¼ RH $  B T

(X/2.1.0-1)

This also indicates that the output is perpendicular to both the direction of current and the magnetic field. RH is the Hall effect coefficient and T is the thickness in mm. The strength of voltage developed is in the order of a few microvolts, typically RH is 7 mV/Vs/Gauss. Naturally, in order to make the voltage workable for all practical applications it is necessary that there will be some signal conditioning units associated with the Hall element. Common mode voltage is an important issue here. If no magnetic field is applied, but there is some voltage at a terminal with respect to the ground, then it is common mode voltage and is the same at each output terminal. In order to get rid of this, like any other analog circuit, the first stage of the amplifier is a differential amplifier. A typical Hall element with signal conditioning unit(s) is discussed in the following section. 2.2.0 Hall Effect Sensor Types Hall Effect sensors are of two types: analog and digital. In this section both types are discussed, starting with the analog type.

N

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+

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FIGURE X/2.1.0-1 Hall effect sensing principles.

2.2.1 ANALOG TYPE SENSOR The analog sensor is depicted in the first part of Fig. X/2.2.0-1 i.e., up to the first output. As shown in the figure, a regulated voltage source drives the current through the Hall element, which is subject to a magnetic field. As the voltage is regulated it is constant, thus in analog sensors the output voltage is proportional to the strength of the magnetic field to which it is

Special Flow Meters, Flow Gages, and Switches Chapter | X

REGULATED

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ANALOG OUTPUT

SCHMITT TRIGGER STAGE IS NECESSARY

BIPOLAR DIGITAL TYPE

0 MAGNETIC FIELD

DIGITAL TRANSFER FUNCTION

FIGURE X/2.2.0-1 Hall effect sensing types.

exposed. Depending on magnetic polarity there will be different ways that the charges are migrated towards the periphery of the Hall element. As a result of this the output of the amplifier will be either positive or negative. This would then necessitate both plus and minus power supplies. In order to avoid this, a fixed bias is introduced into the differential amplifier. Therefore, when a positive magnetic field is sensed, the output increases above the null voltage and when a negative magnetic field is sensed, the output decreases below the null voltage, but remains positive. Therefore, output is always positive. Naturally, when there is no magnetic field applied, the bias value would appear on the output. This is referred to as null voltage, which is the crossing point of the voltage output curve with the magnetic field axis, i.e., where the positive side increasing output curve meets with the negative side increasing curve in Fig. X/2.2.0-1. As is seen in this figure, as the magnetic strength is increased

in either side the output voltage changes proportionately across the null point—but how long can it go? Theoretically it can go up to the supply voltage level, but before that it is saturated as shown. Transfer function represents a graph or equation of output in terms of input. An analog type sensor transfer function is characterized by sensitivity, null offset, and span as shown. Sensitivity is defined as the change in output resulting from a given change in input, i.e., the slope. Span and null points are also very well shown in Fig. X/ 2.2.0-1 and can be easily arrived at. 2.2.2 DIGITAL TYPE SENSOR As the name implies, digital type sensors give digital output. It is the same as an analog type with an additional stage as shown in Fig. X/2.2.0-1, i.e., the second output after the Schmitt trigger stage. A basic analog circuit has been modified with the use of a Schmitt trigger. A Schmitt trigger

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works basically as a comparator. It compares the output of the differential amplifier with a set point/ reference. As long as the output is greater than the set point the output is logical 1 and below that it is logical 0. Therefore, the sensor has an output that is just one of two states: ON or OFF. Hysteresis is included in the Schmitt trigger circuit for jitter-free switching [1]. Like any other hysteresis loop, here also there are two distinct reference values at times referred to as set and reset depending on whether the sensor is turned ON or OFF. The transfer function for a digital output Hall effect sensor with hysteresis is shown in Fig. X/2.2.0-1. As the magnetic field is increased, no change in the sensor output will occur until the reference/set point is attended. Once the operate point is reached, the sensor will change state, e.g., from the OFF state to the ON state and any further increases in magnetic input beyond the operate point do not have an effect. The point where the changes occur is referred to as the set point. When the magnetic field is decreased it will remain in the ON state until a point is reached when the output changes state from the ON to OFF state. Other than an ideal system this point will be separate from the set point and is called the reset point. The differential between the set and reset points is the hysteresis and serves the useful function of eliminating false triggering. The input characteristics of a digital sensor are defined in terms of set and reset points, and differential. Depending on the set and reset points the sensitivity and resolution are determined. Since these characteristics change with temperature and from sensor to sensor, they are specified in terms of maximum and minimum values. Maximum operate point refers to the level of magnetic field that will insure the digital output sensor turns ON under any rated condition. Minimum release point refers to the level of magnetic field that insures the sensor is turned OFF [1]. Digital output may be unipolar or bipolar (as shown in Fig. X/2.2.0-1). When unipolar both poles of magnet output are positive but values are different. On the other hand, when bipolar it is around the zero point as shown.

2.3.0 Magnetic System In Hall effect sensors, physical parameters such as position, speed, and flow are converted into electrical output in the presence of a magnetic field. Therefore, it is needless to say that magnetic field strength has a good influence on the operation of the sensor. This concept has been depicted in Fig. X/2.3.0-1A. Naturally the configuration and orientation of the magnetic field with respect to the Hall element are extremely important. There are two types of magnetic field: unipolar and bipolar. 2.3.1 UNIPOLAR MAGNETIC SYSTEM In a unipolar magnet only one pole is towards the sensor and the other is away, as shown in Fig. X/ 2.3.0-1B. Unipolar system can be two types viz. “head on” type and “slide by” type as shown in Fig. VII/2.3.0-1B. 1. Unipolar head-on mode: In case of a head on, the magnet’s direction of movement is directly toward and away from the sensor, with the magnetic lines of flux passing through the sensor’s reference point. In Fig. X/2.3.0-1B the south pole of the magnet will approach the sensing face of the Hall effect sensor. In the unipolar head-on mode, the relation between Gauss and distance is given by the inverse square law. Distance is measured from the face of the sensor to the pole of the magnet, along the direction of motion. Magnetic filed versus distance have been shown in Fig. X/2.3.0-1B. 2. Unipolar slide-by mode: In this mode, the sensor and magnet have a vertical gap and a magnet is moved in a horizontal plane sidewise. Distance in this mode is measured relative to the center of the magnet’s pole face and the sensor’s reference point in the horizontal plane of the magnet. The magnetic field versus distance relation in this mode is a bell-shaped curve, which is also shown in Fig. X/2.3.0-1B. 2.3.2 BIPOLAR MAGNETIC SYSTEM In a bipolar system, as the name suggests, there will be two poles of the magnet approaching and

Special Flow Meters, Flow Gages, and Switches Chapter | X

933

(A)

(B)

(C)

FIGURE X/2.3.0-1 Magnetic system of Hall sensor. (A) Effect of magnet on sensor. (B) Unipolar magnetic system. (C) Bipolar magnetic system. (C) Developed based on Hall Effect Sensing and Application, Honeywell (Technical internet document). https://sensing.honeywell.com/hallbook.pdf. Courtesy: Honeywell.

going away from the sensor. In a bipolar system a slide-by mode is possible. A bipolar system with bipolar slide-by mode has been depicted in Fig. X/2.3.0-1C. Here there are basically two sets of magnets moving in the same fashion as the unipolar slide-by mode. In this mode,

distance is measured relative to the center of the magnet pair and the sensor’s reference point. The Gauss versus distance relationship for this mode is an “S”-shaped curve as shown in Fig. X/ 2.3.0-1C [1]. There is another possibility of a magnet in ring form in this manner.

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For further reading and comparison the chart in Ref. [1] may be referenced.

2.4.2 APPLICATIONS IN FLOW MEASUREMENT

2.4.0 Hall Sensor Features and Applications

It is worth noting that the Hall effect sensor is always used with any flow transducers as measurement of any desired parameter of the flow transducer, e.g., the impeller speed of a turbine flow meter is a measure of the flow rate. The Hall effect sensor can be used to measure the flow in an indirect way. Therefore, there are several different types of flow transducers that can be used in conjunction with the sensor to measure/ compute flow rate in the conduit. Fig. X/2.4.0-1 illustrates a typical flow measurement scheme. The fluid to be measured flows through the sensor and is directed past the paddle wheel. The paddle wheel rotates and one Hall effect sensor as shown is mounted at the sensor case near the vicinity of the paddle wheel. As each of the paddle wheel edges passes the sensor it interrupts the magnetic field created by the magnet with the sensor being interrupted, hence VH of the sensor results small AC pulses at the sensor output. This small AC output of the sensor through the signal conditioning unit, including the Schmitt trigger, produces a digital signal output proportional to the flow. As the flow rate through the meter increases, there will be more pulses per second. As there are multiple pulses per rotation and the sensor is linear with regard to the number of pulses per volume irrespective of flow rate it is easy to interface with the

Hall effect sensors have a number of features and applications worth noting. However, our discussions are limited to flow applications only. As speed measurements and zero speed monitoring form a part of solid flow measurements these have been included here. 2.4.1 FEATURES OF HALL EFFECT SENSORS In flow sensing the following features of Hall effect sensors are important:

5. 6. 7. 8. 9. 10. 11.

Wide working voltage (3.8e30 VDC); Low power consumption; Maximum current drawn is DUCT PRESSURE DETAIL B SEE DETAIIL B

FIGURE XII/1.1.0-1 DP measurement by purge rotameter. Fig. II/4.2.3.2 may be referred to for fitting details. Measurement scheme only, not to scale.

1.1.3 OTHER GAS FLOW METER TYPES Apart from head type flow meters, thermal flow meters and ultrasonic flow meters also find their applications in the measurement of flow for gas laden with dusts. Factors like those detailed out below should be taken into considerations while selecting the meters type for measurement of flow in gas laden with dusts: 1. 2. 3. 4. 5.

Gas temperature; Ambient temperature; Flow meter location; Available flow meter mounting facility; Straight length requirement/available;

6. Amount of particulates in the gas; 7. Chemical composition of the gas; 8. Moisture content. High levels of particulate in the gas can cause plugging of impulse lines and the meter for head type meters (as already discussed). Similarly, a high level of dust can coat thermal sensors or obstruct the beam in an ultrasonic flow meter. Added to this, if there is a high moisture content, coating formation will be aggravated. Measuring techniques based on thermal principles are widespread. In the simplest of these—the hot-wire anemometer—gas flow is determined via the rate

Flow in Plant Applications Chapter | XII

of cooling of an electrically heated wire with a temperature-dependent resistance. Advanced methods use a heating element and at least two temperature sensors, which measure the transport of heat through the gas. A bypass thermal mass flow meter can be used also, provided coating formation can be avoided. Also, a noninvasive US technique can also be used, provided the dust concentration is not too high. 1.1.4 DUST CLOUD MEASUREMENT Apart from blocking the impulse lines during flow measurements, dust in industrial plants has very dangerous effects, especially in industrial plants where there is a combustion process. For example, coal dust not only creates measurement problems but also can be dangerous when accumulated in one place and can give rise to an explosion. That is the reason that sealing of a coal mill in a power/cement plant is important. In industrial plants producing combustible dusts or dust-containing goods, which are processed or stored, there is every possibility for explosions. When there are dust/air mixtures with concentrations above the lower explosion limit (LEL) and below the upper explosion limit (UEL), various modes of ignition explosion can always happen [1,2]. For details on LEL and UEL, Ref. [1] may be referenced. Dust clouds can be described and determined by the following parameters: l

l

Velocity and local and temporal turbulence intensity; Dust distribution: local and temporal dust concentration.

Of these two, velocity measurement is of most importance for this book. We know that turbulence may be described as a state of rapid, more or less random, movement of the particles of a dust cloud (of concern in the present context) relative to each other in threedimensional planes. Of the two kinds of turbulences, the initial turbulence is generated by the industrial process in which the dust cloud is

1069

formed, whether a cyclone, a pneumatic transport pipe, or a mill. The second kind of turbulence is generated by the explosion itself by expansioninduced flow of unburned dust clouds ahead of the propagating flame front [2]. Laser Doppler anemometry (LDA), discussed in Section 7.3.0 of Chapter V and Subsection 1.2.4.4 of Chapter IX, is commonly used to measure eddy flows in various fields. With this technique and by fast data collection, it is possible to describe the turbulent structure of the flow and to measure the velocity of particles (not of the air flow). Therefore, tracer particles like TiO2 are often used to make an air flow measurable for the laser Doppler anemometry [2]. 1.2.0 Different Flow Meters and Associated Issues Each flow meter has some pros and cons associated with it. Similarly, there are certain specific problems/issues associated with the meter. In this section some selected issues have been discussed through various literature studies and our own site experiences. 1.2.1 DIAGNOSTIC FEATURES IN ULTRASONIC FLOW METERS The most prominent feature of the modern ultrasonic flow meter, especially for multipath meters, is its ability to monitor its own health, and to diagnose any problems. Various issues associated with this diagnostic feature of USFM would encompass mainly the following factors. Auto gain: All multipath USMs have automatic gain control on all receiver channels to generate the same level of ultrasonic signal time after time. Therefore, an increase in gain indicates a weaker signal, which can be caused by a variety of problems, i.e., transducer deterioration and fouling of the transducer ports. However, pressure and flow velocity also affect the signal strength. As long as the transit times are being measured correctly then there will be no impact on the accuracy due to auto gain change. On the other hand, this gain changes help, detecting some failures in advance.

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Signal quality: Ultrasonic transducers send multiple pulses across the meter to the opposing paired transducer for updating the output. Ideally all the pulses sent would be received and used. In reality, sometimes the signal is distorted, too weak, or even the received pulse does not fulfill the set criterion, hence electronics would reject the pulse. The level of acceptance (or rejection) for each path is generally considered as a measure of performance, and is often referred to as signal quality [3]. Unless there are other influencing factors as discussed in next section, the meter should operate at full transducer performance until it reaches the highest velocity set. Here the transducer signal becomes more distorted and some of the waveforms will ultimately be eliminated since they don’t fit the pulse detection criteria within the specified tolerance [3]. Signal to noise ratio (SNR): Each transducer receives noise from extraneous sources (rather than its opposite transducer). During the interval between receiving pulses, meters monitor the “background” noise, which can be in the same ultrasonic frequency spectrum. Analysis of this SNR can give an indication about the health of the meter also. 1.2.2 FOULING EFFECT ON ULTRASONIC FLOW METERS High repeatability and natural zero pressure loss combined with extensive diagnostic features (discussed above) available with USFM give it huge appreciation and applications in industries. However, in most cases, meter laboratory calibration differs highly from actual field applications. This is mainly due to the installation effect, corrosion, and fouling. This is the case with all flow meter types. On account of huge diagnostic capabilities, USFM could be treated differently [4]. It may not be possible to completely eliminate the impact of fouling and corrosion, even with many improved designs. When comparing the specifications of different ultrasonic flow meters, most of these will show similar data but in an actual case there will be some differences. Some of the issues related to fouling and corrosion are discussed here.

1. Meter calibration: During flow calibration the meter is clean, however after a long operational period the meter might be contaminated. This will definitely affect the calibration, hence the declared uncertainty will be altered. 2. Installation effect: Added to the calibration effect discussed, there will be some effect on uncertainty due to the installation effect also and it will increase the uncertainty effect. Therefore, meters with higher sensitivity to the installation effect will be affected more. In this connection Section 1.3.3 of this chapter may be referenced also. 3. Meter design: There are a few options available for meter designs as indicated in Fig. XII/1.2.0-1, which shows three design types. l Conventional parallel chord: In these designs it is possible to measure close to the pipe wall not reflected ones, hence it lacks the interrogation of the pipe wall. l Conventional reflective chord: This design can measure a built-up triangular design, as shown in Fig. XII/1.2.0-1; the triangleshaped paths cannot get very close to the wall. l V12 design: In this configurationas shown in Fig. XII/1.2.0-1 (rightmost) [4]: ○ “There are five horizontal paths and one vertical aligned path. ○ Each path consists of two chords formed into a single V-bounce (in total the meter is equipped with 12 chords, all with a single V shape). ○ The vertical reflecting path is used solely to detect the presence of contamination liquid layers on the bottom of the pipe. ○ All paths are reflecting, whereby four of them use small acoustic mirrors at the opposite side of the pipe.” 4. Fouling and effects: Fouling can cause build up on the transducer coating inside the pipe wall. The major effects of fouling consist of: l Absorption of US signal on account of the layer of fouling on the transducer;

Flow in Plant Applications Chapter | XII

PARALLEL CHORD

REFLECTIVE CHORD

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V12 DESIGN

FIGURE XII/1.2.0-1 Ultrasonic meter design variations. Developed based on J.G. Drenthen, M. Vermeulen, M. Kurth, H. den Hollander, Ultrasonic flow meter diagnostics and the impact of fouling, AGA Operations Conference, Krohne Oil & Gas, 2011. https://cdn.krohne.com/dlc/CONFPAPERS_ALTOSONICV12_impact_ of_fouling_en_120524.pdf. Courtesy: Krohne Oil & Gas.

l l l l

l

Reduction of effective cross-sectional area; Higher roughness on the wall; Uneven and shorter acoustic path length; The attenuation of the acoustic signal through the reduction of the reflection coefficient [3]; Noise and crosstalk increase in the system.

Reflective design and extensive diagnostics can provide the necessary information on meter degradation in advance through data analysis. For further details Ref. [4] may be referenced. 1.2.3 VORTEX METER AND ASSOCIATED ISSUES Vortex flow-measuring technology is rather costly technology, applied for various flow measurement applications with the expectation of very accurate measurement. However, there are a few problems associated with the meter. The common natures to the problems and issues associated with the same will be discussed here. One of the most common issues is the proper sizing issue, which the author also faced while using a vortex meter in steam flow measurement in a Rayon factory in Rishra WB India. A few commonly found issues for vortex meters are discussed in this section.

1. Sizing and selection: Vortex meter sizing is very important and, as stated in Chapter V, the normal expected flow should be near the middle of the sizing range curve provided by the manufacturer. In many cases, people try to select a meter within the selected meter sizing range curve, with normal being near the minimum detectable flow in the curve. People are happy because the flow range is very much within the range curve. However, in that case the meter may be oversized. This was found by the author in the plant referred to above. It was a retrofit project and the logic behind it was that if a lower size would have been chosen then there would be a requirement for higher straight length. In that case the meter performance was poor on account of oversizing. Therefore, it is recommended that normal flow should always be near the middle of the range curve. For a vortex meter to work, a minimum Reynolds number of 10,000 is essential. 2. Straight length requirement: When selecting a lower size meter to meet the requirement discussed above, one must take into account the additional straight length requirement also, which could be nearly 10e15ID for proper vortice formation. In some cases the straight

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length requirement may be greater, depending on the obstruction in the line (if necessary flow conditioners may have to be used). 3. Other issues: The design of the bluff body and sensor type and location besides the signal strength also play a crucial role in the proper functioning of a vortex meter. The fluid temperature and pressure condition can also be contributory factors for meter performance [5]. However, now, multivariable vortex meters are available where there are built-in RTDs and pressure sensors for calculating mass flow. In this connection Section 3.8.0 of Chapter V may be referenced. 1.2.4 SOME COMMON PHENOMENA AFFECTING FLOW METER PERFORMANCES There are a number of physical and chemical phenomena which are frequently encountered in industrial plants and cause problems for flow measurements and deteriorate the metering performance. Some of these are listed below, except dust in gas flow measurements, which has been discussed separately above. 1. Scaling and rusting: Scaling formation takes place due to the reaction of flowing fluids with metallic pipes. Scales are attached to the inner walls of the piping and attach to the inside of the flow meter to hinder the meter operation. These scales may fragment and break off, resulting in clogging. In the case of electromagnetic flow meter scale formation, this may prevent sensing voltages. Rusting is a different phenomenon but has a similar effect. 2. Sludge: Abrasive sludge may be formed in a grinding system. Sludge continuously circulates along with the fluid and causes clogging of the flow meter and/or gives rise to noise and interference; naturally performance deteriorates. 3. Slime: Microorganisms in water may form slime and disturb the measurements, especially in electromagnetic flow meters.

4. Slurry: Details on slurry have been discussed at length in Chapter VII; slurries can obstruct flow and may cause axial wear and clogging. 5. Bubbles: Bubbles may come into the flow at intake points, often highly viscous fluids are driven by inert gases. Bubbles cause instability in flow measurement. In the case of a Coriolis meter it may cause imbalance in the meter and it may happen that enough energy may not be available to drive the coil. 1.3.0 Impact of Installation Effect on Meter Performance Installation of the flow meter is very important as installation has a direct effect on the performance of flow meters in general. A few pertinent cases are discussed here. 1.3.1 PROFILE DISTORTION Flow meter installation effects in the form of profile distortion normally occur in the following stages: 1. Development of profile distortion: The creation and development of velocity profile disturbances are due to the effects of the piping configuration mainly upstream of the flow meter. Disturbed velocity profiles may be asymmetric, contain swirling motions, or have a combination of the two. 2. Stabilization: The profile disturbances occur as a result of turbulent diffusion and pipe wall friction. Flow disturbance decay rates may be different but all disturbances require relatively long lengths of straight pipe to reestablish an ideal fully developed, symmetric, swirl-free turbulent velocity profile. 3. Sensitivity: Sensitivity to profile distortion varies with flow meter type. When orifice meters are highly sensitive to distortions in velocity profile, USFM has less sensitivity and Coriolis has zero sensitivity towards this. USFMs include computational algorithms that may correct for some amount of flow distortion.

Flow in Plant Applications Chapter | XII

1.3.2 FLOW CONDITIONERS As seen in Chapter XI, flow conditioners can be used to adjust the flow disturbances with a lower requirement for straight length. Flow straighteners/conditioners field offset the effect of flow field disturbances by greatly reducing the magnitude of the flow distortions. As seen in Chapter XI, some conditioners are effective at “isolating” a fairly broad range of flow distortions. For detailed discussions on this refer to Chapter XI. 1.3.3 INSTALLATION EFFECT ON ULTRASONIC FLOW METER Multipath meters provide improved resolution of the velocity profile; manufacturers have developed some relatively crude methods to infer swirl and velocity profile asymmetry, thereby reducing (but not eliminating) the sensitivity of this type of meter to changes in the velocity profile [6]. The velocity across the pipe cross-section varies, the velocities associated with each path are taken together to compute an average velocity which is used to calculate the volumetric flow rate. Manufacturers use their standard and proprietary method for average velocity computation. 1.3.4 INSTALLATION EFFECT ON TURBINE FLOW METERS The indicated volumetric flow rate is determined by dividing the total accumulated pulses by the K-factor. Therefore, if the velocity profile differs from the velocity profile that existed during calibration, it will cause a difference in the number of pulses accumulated during calibration and that in service. Error will therefore be introduced in the volumetric flow rate calculation. Naturally, the distorted velocity profile at the meter inlet will affect the volume flow calculation even if the meter performs well. 1.3.5 INSTALLATION EFFECT ON SECONDARY MEASUREMENT Secondary measurements are also affected due to installation effects. The accuracy of secondary

1073

measurements, like pressure and temperature measurement devices, can be adversely affected by their installations. These installation effects have a direct impact on the accuracy of the temperature element in a thermowell. The temperature of the thermal well can be affected by the pipe wall temperature, when it deviates from the flowing gas temperature and when flow rates are relatively low [6]. 1.3.6 DESIGN GUIDELINE REFERENCES AGA reports provide typical guidelines for installations. Readers should refer to these guidelines from the AGA. Some typical guideline references are listed below: 1. AGA Report No. 3: The gas industry standard for orifice meter installations: The revised standard included a recommendation for the minimum length of straight pipe required upstream of an orifice meter for a no-flow conditioner as well as for flow conditioners, e.g., a 19-tube. 2. AGA Report No. 7: The gas industry recommended practice for turbine flow measurement. Revised edition 2006. This provides recommended installation practices. It also provides guidance for installing flow conditioners, strainers, filters, and secondary instrumentation. From the discussions above it transpires that obstructing device(s) upstream distorts the flow profile which will have direct impact on flow measurement accuracy. The persistence of some types of flow disturbances suggests that potential sources of velocity profile distortion further upstream than the immediate meter run should be investigated if piping installation effects are a concern [6]. The effect of velocity profile disturbances on flow measurement accuracy may be different for each meter type. In the case of noninvasive ultrasonic meters, the number of paths and the method of “integrating” the velocity profile impacts the ability of the meter to resolve and recognize distorted velocity profiles. Also, extensive diagnostics of the meter may help early detection of the issue.

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We now investigate various plant-specific issues related to flow measurements. The discussions start with the flow issue related to thermal power plants where wide varieties of flow meter types are engaged to measure solid, liquid, gas, and slurry flows.

2.0.0 THERMAL POWER PLANT ISSUES RELATED TO FLOW MEASUREMENT Of the total energy generated in the world nearly 65% comes from fossil fuel power stations. Naturally, the accuracy of various kinds of flow measurement is of immense importance. In thermal power plants there are a number of flow measurements involved, be it solid (coal), liquid (feed water/oil), or gas (air flow). Steam flow measurement is vital for thermal power plant performance monitoring. Apart from these, there are applications of slurries in ash handling plants and gypsum handling. We start the discussions with steam measurement. This is not only very important in thermal power plant, steam flow measurement is necessary in many process plants also. Since this is a book meant for flow measurement, it is not possible to detail the intricacy of power plant operations. It is recommended that interested readers refer to the author’s “Power Plant Instrumentation and Control Handbook” by Elsevier [7] for further details. 2.1.0 Steam Flow Measurement It may appear that steam is a straightforward fluid to measure flow. In reality this is not the case, as the measurement parameters vary with the type of steam, as well as with variations in temperature and pressure. Types of steam include wet steam, saturated steam, and superheated steam, when process steam is taken into account. In large utility stations steam flow may be at very high temperature and pressure. Therefore, any technology deployed for steam flow measurement must be able to cope up with condensate handling. Turbine flow meters and Coriolis

meters are not good at handling condensate. Ultrasonic meters measure the speed of ultrasonic waves in the medium. The speed with which an ultrasonic wave travels through a metal pipe may be different to the speed of the wave through steam, hence calculation of the flow rate may be affected by interference. On account of this, the head type of meters with different flow elements and vortex flow meters are mostly used. Each of these has some advantages and disadvantages. The vortex has a relatively lower pressure drop and lower straight length requirement, but it is quite costly and sizing is very critical. For large utility stations, very high pressure/temperature may also pose problems. DP meters on the other hand are inexpensive and can be verified easily. Installation of DP type meters is straight forward. Also, process pressure/temperature compensation is easier to implement. In thermal power plants the following are major steam flow measurement points: 1. 2. 3. 4. 5.

Main steam flow; Cold reheat steam flow; Auxiliary steam flow; Extraction steam; PRDS steam flow (for process cum power application).

Apart from the vortex meter, flow nozzle and orifice plates are used as DP meter flow elements and can be used for measurement of steam as listed above with the exception of main steam flow measurement, which has been treated separately in Section 2.1.1. Measurement techniques in both types (vortex meters and DP meters) have already been discussed and hence are not repeated here. In the case of low-pressure applications the orifice plate may be used, otherwise, for high-pressure applications, flow nozzles are used. We now discuss main steam (MS) flow measurement. 2.1.1 MAIN STEAM FLOW MEASUREMENT Main steam pressure can be measured by DP meters (using a flow element) or vortex meters

Flow in Plant Applications Chapter | XII

(if temperature permits). At large units, especially in supercritical/ultrasupercritical units, very high temperatures can be withstood by the vortex at that high steam pressure. Therefore, the flow nozzle is the only choice. As stated earlier, on account of higher permanent pressure loss (PPL) often in large power plants (>500 MW) direct MS steam flow measurement by nozzles is avoided. Instead, MS flow measurement is substituted by flow computations. In order to

(A)

1075

understand this it is required to understand the process. The main steam flow basically represents the load (like current in an electrical circuit) delivered by the steam generator (SG) at its operating main steam pressure. MS flow measurement alternatives are listed below. 1. MS flow by flow nozzle: Let us understand the measurement with reference to Fig. XII/ 2.1.0-1A.

STEAM FLOW

TG CONT

NOZZLE

VALVE

MAIN STEAM FLOW NOZZLE MEASURES BOILER LOAD MAIN STEAM (MS)

PI

BOILER TURBO GENERATOR (TG)

LOAD HPBP

SUPERHEATER OUTLET HEADER

VALVE

HPBP: HIGH PRESSURE BYPASS PI : 1st STAGE PRESSURE INDICATES THE TURBINE LOAD IF THERE IS NO HPBP; Pi = TURBINE LOAD.

COLD REHEAT STEAM

TG CONT

(B)

VALVE MAIN STEAM FLOW NOZZLE

SUPERHEATER OUTLET HEADER

HPBP VALVE

TURBO GENERATOR (TG)

PI

NOZZLE

MAIN STEAM (MS)

HPBP FLOW

MEASURES BOILER LOAD

HPBP: HIGH PRESSURE BYPASS COLD REHEAT STEAM

FIGURE XII/2.1.0-1 Main steam flow measurement. (A) MS flow measurement with flow nozzle. (B) MS flow measurement without flow nozzle. Boiler load ¼ first pressure (turbine load) þ HPBP load.

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MS flow nozzles measure the total steam flow (load) generated by a steam generator (SG). In the case of a boiler of smaller size (in MW), the quantity of flow output will be lower as well as the MS pressure being lower. Naturally, PPL due to the flow nozzle will be lower. PPL time flow gives the total loss due to the flow nozzle. Therefore, if in a larger unit (>500 MW), MS flow nozzles are used, then large flow times PPL (higher) due to the flow nozzle will be quite high. Hence, for larger plants (>500 MW, especially for supercritical/ultrasupercritical units) flow measurement using a flow nozzle is avoided. Fig. XII/2.1.0-1A is mainly applicable for lower MW boilers, up to size 100 mm size cost becomes too high >150 mm size limited availability Becomes too heavy and long (especially bent tube types) with increase in size (>150)

DP types

Established method for custody transfer Dual chamber possible for inspection Higher pressure loss Slowly replaced by USFM

Used for custody transfer Used for stack gas monitoring Higher pressure loss Getting replaced by USFM [22]

PD types

Sample volume to calculate total Positive volume measurement with high accuracy and reliability Wide range of types available Custody transfer application Extensively used for metering in distribution lines, truck/tanker loading/dispensing Competition from turbine meters and now from mass flow meters

Sample volume to calculate total Positive volume measurement with high accuracy and reliability Wide range of types available Well suited for low flow 250 mm Facing competition from USFM

Ultrasonic type

Nonintrusive and noninvasive Extensive diagnostic capability Multipoint transit time gives high accuracy In-line types used for crude oil also Approved for custody transfer Cost is only limitation

Nonintrusive and noninvasive Extensive diagnostic capability Multipoint transit time gives high accuracy In-line version is better choice for its accuracy than clamp-on type Insertion type in stack gas monitoring but facing completion from DP/thermal types for cost Approved for custody transfer Cost is only limitation

Vortex type

Suited for LNG measurement Got API approval for custody transfer yet to penetrate the market

Suitable for instantaneous flow measurement They may need flow straighteners Medium accuracy

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4.1.2 USE OF INSTRUMENTS AT DIFFERENT STAGES IN THE OIL AND GAS PROCESS

areas of oil and gas fields. Typical divisions of the oil and gas system have been detailed in Fig. XII/4.1.0-1. Different types of instruments in different oil and gas streams/areas have been listed in Table XII/4.1.0-2. As shown in Fig. XII/4.1.0-1, multiphase flows are used upstream before separation, and hence these are shown separately.

Oil and gas systems can be divided into three sections, i.e., upstream: exploration and production; midstream: transportation system; and downstream: refinery. There are extensive uses of flow metering and monitoring systems in these

FLOW SYSTEMS IN OIL AND GAS

UPSTREAM

MIDSTREAM

DOWNSTREAM

LOADING UNLOADING

FPSO

OFFSHORE

REFINERY

GAS TRANSMISSION

CRUDE OIL

DISTRIBUTION & MARKETING

GAS PROCESSING

WELL HEAD

UNDERGROUND STORAGE

GAS OIL SEPARATION

GAS DISTRIBUTION

PROCESS CONTROL STORAGE

BLENDING CAPABILITIES AIR CRAFT FUELING

TRANSPORT TO MARKET TERMINAL

STORAGE AND TRANSPORT

AND BATCHING FOR TRUCKS, RAILCARS AND SHIPS

BIOFUEL TERMINALS

TRUCK AND RAILCAR LOADING

GAS RECOVERY GAS TREATMENT STORAGE AND TRANSPORT

ONSHORE WELL HEAD FLOWLINE GAS OIL SEPARATION GATHERING STORAGE

CORIOLIS FLOW METER

GAS METERING & CONTROL

FLOW COMPUTER

DP FLOW METER

LIQUID METERING & CONTROL

PROVER SYSTEM

PD METER*

TERMINAL CONTROL

TURBINE FLOW METER

CONTROL VALVE

ULTRASONIC FLOW METER

*PD= POSITIVE DISPLACEMENT

MULTIPHASE FLOW METERING

FIGURE XII/4.1.0-1 Flow meters in oil and gas.

TABLE XII/4.1.0-2 Flow Metering in Oil and Gas Stages (Major Usage) Meters and Systems

Upstream Off/Onshore

Midstream Transportation

Petroleum Refining

Distribution and Marketing

Coriolis mass

X

DP type

X

PD meter

X

X

X

X

Turbine meter

X

X

X

X

USFM

X

X

X

X

Multiphase metering

X

Flow computer and calculation

X

X

X

X Continued

Flow in Plant Applications Chapter | XII

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TABLE XII/4.1.0-2 Flow Metering in Oil and Gas Stages (Major Usage)dcont’d Meters and Systems

Upstream Off/Onshore

Flow control system

Midstream Transportation

Petroleum Refining

Distribution and Marketing

X

X

X

Control valve

X

Terminal control

X

Gas metering

X

X

Liquid metering

X

X

Prover system

X

X

4.2.0 Instruments Used in Production Oil Separators During the discussions in Chapter IX, it was noted that with the help of multiphase/two-phase instruments developed recently, people are trying to get rid of the separator. During discussions it has been noted that total separation and partial separation methods are used. Therefore, it is important to gather knowledge about separator instrumentation. There are two kinds of separator: a test separator—for periodic testing purposes and a regular production separator. Similarly, there are high-pressure and low-pressure separators. In this section short discussions are presented on separator instrumentation and other equipment and devices with separators. A typical

X X

X

X

production separator with pressure release valve and regulators is depicted in Fig. XII/4.2.0-1. The separator can be for either two phase or three phase. In our discussions the three-phase separator, as shown in Fig. XII/4.2.0-1, has been considered. The main objective of separator is to separate the gas, oil, and water from the crude. With flow measurement it is possible to get much more additional information necessary for production and operation such as the following: l

l l l

Assessment of the condition and health of the well; Management of the well in declining stage; Quantification of production gas and oil; Fine tuning of the recovery operation to maximize retrieval of hydrocarbons [15].

REGULATOR GAS OUTLET PRESSURE RELEASE

MIST INSTRUMENT

CRUDE INLET

GAS SUPPLY GAS REGULATOR WATER

EMULSION

OIL

WATER OUTLET

FIGURE XII/4.2.0-1 Production separator.

OIL OUTLET

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There are a number of instruments connected with the separator. These are listed below. Pressure release: As per ASME code and API code 510 there should be means for pressure release. In view of this, separators are provided with a pressure relief valve to protect from overpressurized situations and alert you when gas volumes are vented. Rupture disc: This is another way of protecting against overpressure situation. The disc breaks to relieve an overpressurized situation. Here the valve remains open until the disc is replaced. Gas outflow: For proper functioning of the separator steady pressure needs to be maintained for gas outflow from the separator to the tank. If the pressure is too high, gas can become entrained in the oil where it will simply vent off from the tank, resulting in higher emissions and lost product [15]. In the case of low pressure, liquefied gas will be lost. Suitable regulators are installed in the gas line and gas is measured by a suitable gas meter as discussed in Table XII/ 4.1.0-1. The vortex meter is yet to receive approval for custody transfer. Oil outflow: Like gas outflow, oil outflow is also measured. This flow is basically a quality check of the entire separator as well as that of the performance of the well. This delivery is an indication of the reservoir decline rates [15]. The oil outflow is critical because it is an allocation measurement to calculate any royalties owed to the land owner. The type of meters used for this purpose, with their pros and cons, are given in Table XII/4.1.0-1 and the water cut meter is discussed in Chapter IX. Water outflow: Water production is a byproduct of the oil production process. Accounting of water also gives an indication of the well decline curve. Cumulative flow of water also alerts to emptying of the water tank. In some oilfields, how much water is produced must be reported for regulatory reasons [15]. Standard flow meters for oil and gas, along with electromagnetic flow meters, can be used for water.

Regulator: Regulators are used for pressure controls in crude inlets, as well as in the gas line to keep the pressure regulated. They are capable of handling high pressure. There are different kinds of regulators available for different sizes, styles, and types. Instrument gas supply [15]: When using natural gas from the well to operate valves within the separator, you need to properly regulate pressure to the pneumatic controllers of the valves. Sand detector: Though not directly a production parameter it is important to carry on regular operation. “Roxar sandlog” transmitter is an example of a sand detector and can be used for subsea applications also. Flow-metering stations and associated uncertainty calculations are very important. They are guided by international standards of ISO, IEC, etc. It is not possible to discuss these at length within the limited scope of this book. In the next section detailed reference to the relevant standards has been listed along with major uncertainty formulas (only formulas, no derivations). Interested readers may refer to the relevant standards for details and calculation basis, etc. 4.3.0 Flow Metering Standards In this section brief discussions and tables shall be provided for various standards and their significance in gas and oil flow, as well as major significant standards for various measurements (flow) related to petroleum oil and gas. In Table XII/ 4.3.0-1 only standards related to flow metering have been listed, for example, those for composition have not been taken into account here. [The list has been prepared after going through available standards, as the standards are undergoing revisions, so the latest version as available should be consulted even though years are given here for the latest changes in the standards]. In this connection, Norwegian Petroleum Directorate (NPD) directives and NORSOK standards I 104 and I 105 may be referenced also.

Flow in Plant Applications Chapter | XII

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TABLE XII/4.3.0-1 Major Standards for Flow Measurements in Oil and Gas Subject

Standard

Title

General

ISO/IEC guide 98-1

Uncertainty of measurementdPart 1: Introduction to the expression of uncertainty in measurement

General

ISO/IEC Guide 98-2

Uncertainty of measurementdPart 2: Concepts and basic principles

General

ISO/IEC guide 98-3

Uncertainty of measurementdPart 3: Guide to the expression of uncertainty in measurement

General

ISO/IEC Guide 98-4

Uncertainty of measurementdPart 4: Role of measurement uncertainty in conformity assessment

General

ISO/IEC Guide 98-5

Uncertainty of measurementdPart 5: Applications of the least squares method

General

NFOGM 2001

Handbook of uncertainty calculation, Ultrasonic Fiscal Gas Metering Station

General

NFOGM 2003

Handbook of uncertainty calculation, Fiscal Orifice Gas and Turbine Oil Metering Station

General

ISO 5168:2005

Measurement of fluid flowdProcedures for the evaluation of uncertainties

General

ISO 7066-2: 1988

Assessment of uncertainty in the calibration and use of flow measurement devicesdPart 2: Non-linear calibration relationships

General

ISO 21748: 2010

Guidance for the use of repeatability, reproducibility and trueness estimates in measurement uncertainty estimation

General

API MPMS 13.1: 2011

Statistical concepts and procedures in measurement

General

API MPMS 13.2: 2011

Statistical methods of evaluating meter proving data

Liquid flows

ISO 11631: 1998

Measurement of fluid flowdMethods of specifying flow meter performance

Liquid flows

API MPMS 5.1: 2008

General considerations for measurement by meters

Liquid flows

ISO 91-1: 1992 (2)

Petroleum measurement tablesdPart 1: Tables based on reference temperatures of 15 C and 60 F

Liquid flows

ISO 91-2: 1991 (2)

Petroleum measurement tablesdPart 2: Tables based on a reference temperature of 20 C

Liquid flows

ISO 2714: 1980

Liquid hydrocarbonsdVolumetric measurement by displacement meter systems other than dispensing pumps

Liquid Applications

Continued

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TABLE XII/4.3.0-1 Major Standards for Flow Measurements in Oil and Gasdcont’d Subject

Standard

Title

Liquid flows

ISO 2715: 1981

Liquid hydrocarbonsdVolumetric measurement by turbine meter systems

Liquid flows

ISO 4124: 1994

Liquid hydrocarbonsdDynamic measurementd Statistical control of volumetric metering systems

Liquid flows

ISO 9770: 1989

Crude petroleum and petroleum productsd Compressibility factors for hydrocarbons in the range 638 kg/m3 to 1074 kg/m3

Liquid flows

ISO 10790: 1999

Measurement of fluid flow in closed conduitsd Guidance to the selection, installation and use of Coriolis meters (mass flow, density and volume flow measurements)

Liquid flows

API MPMS 5.2: 2005

Measurement of liquid hydrocarbons by displacement meters

Liquid flows

API MPMS 5.3: 2009

Measurement of liquid hydrocarbons by turbine meters

Liquid flows

API MPMS 5.6: 2008

Measurement of liquid hydrocarbons by Coriolis meters

Liquid flows

API MPMS 5.8: 2005

Measurement of liquid hydrocarbons by ultrasonic flow meters using transit time technology

Turbine meter

ISO 2715: 1981

Liquid hydrocarbonsdVolumetric measurement by turbine meter systems

Turbine meter

ISO 6551: 1982

Petroleum liquids and gasesdFidelity and security of dynamic measurementdCabled transmission of electric and/or electronic pulsed data

Turbine meter

API MPMS 5.3: 2009

Measurement of liquid hydrocarbons by turbine meters

Turbine meter

API MPMS 5.4: 2005

Accessory equipment for liquid meters

Turbine meter

API MPMS 5.5: 2010

Fidelity and Security of Flow Measurement Pulsed-Data Transmission Systems

PD meters

ISO 2714: 1980

Liquid hydrocarbonsdVolumetric measurement by displacement meter systems other than dispensing pumps

PD meters

ISO 6551: 1982

Petroleum liquids and gasesdFidelity and security of dynamic measurementdCabled transmission of electric and/or electronic pulsed data

PD meters

API MPMS 5.2: 2010

Measurement of liquid hydrocarbons by displacement meters

PD meters

API MPMS 5.4: 2005

Accessory equipment for liquid meters

PD meters

API MPMS 5.5: 2010

Fidelity and Security of Flow Measurement Pulsed-Data Transmission Systems Continued

Flow in Plant Applications Chapter | XII

1089

TABLE XII/4.3.0-1 Major Standards for Flow Measurements in Oil and Gasdcont’d Subject

Standard

Title

Coriolis meter

ISO 10790: 1999

Measurement of fluid flow in closed conduitsd Guidance to the selection, installation and use of Coriolis meters (mass flow, density and volume flow measurements)

Coriolis meter

ISO 6551: 1982

Petroleum liquids and gasesdFidelity and security of dynamic measurementdCabled transmission of electric and/or electronic pulsed data

Coriolis meter

API MPMS 5.6: 2008

Measurement of liquid hydrocarbons by Coriolis meters

Coriolis meter

API MPMS 5.4: 2005

Accessory equipment for liquid meters

Coriolis meter

API MPMS 5.5: 2010

Fidelity and Security of Flow Measurement Pulsed-Data Transmission Systems

Ultrasonic flow meter (USFM)

ISO/DIS 12242

Measurement of fluid flow in closed conduits - Ultrasonic meters for liquid

USFM

ISO 6551: 1982

Petroleum liquids and gasesdFidelity and security of dynamic measurementdCabled transmission of electric and/or electronic pulsed data

USFM

API MPMS 5.8: 2005

Measurement of liquid hydrocarbons by ultrasonic flow meters using transit time technology

USFM

API MPMS 5.4: 2005

Accessory equipment for liquid meters

USFM

API MPMS 5.5: 2010

Fidelity and Security of Flow Measurement Pulsed-Data Transmission Systems

Prover

ISO 7278-1: 1987

Liquid hydrocarbonsdDynamic measurementd Proving systems for volumetric metersdPart 1: General principles

Prover

ISO 7278-2: 1988

Liquid hydrocarbonsdDynamic measurementd Proving systems for volumetric metersdPart 2: Pipe provers

Prover

ISO 7278-3: 1998

Liquid hydrocarbonsdDynamic measurementd Proving systems for volumetric metersdPart 3: Pulse interpolation techniques

Prover

ISO 7278-4: 1999

Liquid hydrocarbonsdDynamic measurementd Proving systems for volumetric metersdPart 4: Guide for operators of pipe provers

Prover

API MPMS 4.1: 2009

Proving systemdIntroduction

Prover

API MPMS 4.2: 2003

Proving systemdDisplacement provers

Prover

API MPMS 4.4: 2010

Proving systemdTank provers

Prover

API MPMS 4.5: 2005

Proving systemdMaster Meter provers Continued

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TABLE XII/4.3.0-1 Major Standards for Flow Measurements in Oil and Gasdcont’d Subject

Standard

Title

Prover

API MPMS 4.6: 2008

Proving system - Pulse interpolation

Prover

API MPMS 4.7: 2009

Proving systemdField Standard Test Measures

Prover

API MPMS 4.8: 2007

Proving systemdOperation of Proving Systems

Flow Computer and Calculation (FCC) FCC

ISO 91-1: 1992 (2)

Petroleum measurement tablesdPart 1: Tables based on reference temperatures of 15 C and 60 F

FCC

ISO 91-2: 1991 (2)

Petroleum measurement tablesdPart 2: Tables based on a reference temperature of 20 C

FCC

ISO 4267-2: 1988

Petroleum and liquid petroleum productsd Calculation of oil quantitiesdPart 2: Dynamic measurement

FCC

ISO 9770: 1989

Crude petroleum and petroleum productsd Compressibility factors for hydrocarbons in the range 638 kg/m3 to 1074 kg/m

FCC

ISO 91-1: 1992 (2)

Petroleum measurement tablesdPart 1: Tables based on reference temperatures of 15 C and 60 F

FCC

ISO 91-2: 1991 (2)

Petroleum measurement tablesdPart 2: Tables based on a reference temperature of 20 C

FCC

ISO 4267-2: 1988

Petroleum and liquid petroleum productsd Calculation of oil quantitiesdPart 2: Dynamic measurement

FCC

ISO 9770: 1989

Crude petroleum and petroleum productsd Compressibility factors for hydrocarbons in the range 638 kg/m3 to 1074 kg/m

FCC

ISO 91-1: 1992 (2)

Petroleum measurement tablesdPart 1: Tables based on reference temperatures of 15 C and 60 F

FCC

ISO 91-2: 1991 (2)

Petroleum measurement tablesdPart 2: Tables based on a reference temperature of 20 C

FCC

ISO 4267-2: 1988

Petroleum and liquid petroleum productsd Calculation of oil quantitiesdPart 2: Dynamic measurement

FCC

ISO 9770: 1989

Crude petroleum and petroleum productsd Compressibility factors for hydrocarbons in the range 638 kg/m3 to 1074 kg/m

FCC

API MPMS 21.2: 2004

Electronic liquid volume measurement using positive displacement and turbine meters Continued

Flow in Plant Applications Chapter | XII

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TABLE XII/4.3.0-1 Major Standards for Flow Measurements in Oil and Gasdcont’d Subject

Standard

Title

General

R140:2007

Measuring systems for gaseous fuel

General

R137e1:2006

Gas metersdPart 1: Requirements

DP type

ISO 5167-1: 2003

Measurement of fluid flow by means of pressure differential devices inserted in circular cross-section conduits running fulldPart 1: General principles and requirements

DP type

ISO 5167-2: 2003

Measurement of fluid flow by means of pressure differential devices inserted in circular cross-section conduits running fulldPart 2: Orifice plates

DP type

ISO 5167-3: 2003

Measurement of fluid flow by means of pressure differential devices inserted in circular cross-section conduits running fulldPart 3: Nozzles and Venturi nozzles

DP type

ISO/TR 12767: 2007

Measurement of fluid flow by means of pressure differential devicesdGuidelines on the effect of departure from the specifications and operating conditions given in ISO 5167

DP type

ISO/TR 15377: 2007

Measurement of fluid flow by means of pressure-differential devicesdGuidelines for the specification of orifice plates, nozzles and Venturi tubes beyond the scope of ISO 5167

DP type

ISO 9300: 2005

Measurement of gas flow by means of critical flow Venturi, nozzles

DP type

AGA Report Nr 3-1: 2009 API MPMS 14.3.1

Orifice metering of natural gas Part 1: General equations & uncertainty guidelines

DP type

AGA Report Nr 3-2: 2006 API MPMS 14.3.2

Orifice metering of natural gas Part 2: Specification and installation requirements

DP type

AGA Report Nr 3-3: 2009 API MPMS 14.3.3

Orifice metering of natural gas Part 3: Natural gas applications

DP type

AGA Report Nr 3e4: 2006 API MPMS 14.3.4

Orifice metering of natural gas Part 4: Background, Development implementation procedure

USFM

ISO 17089-1 and -2: 2010

Measurement of fluid flow in closed conduitsd Ultrasonic meters for gasdPart 1: Meters for custody transfer and allocation measurement; Part 2: Meter for industrial applications

USFM

AGA Report Nr 9: 2007

Measurement of gas by multipath ultrasonic meters

USFM

AGA Report Nr 10: 2003

Speed of sound in natural gas and other related hydrocarbon gases

Gas Flow

Continued

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TABLE XII/4.3.0-1 Major Standards for Flow Measurements in Oil and Gasdcont’d Subject

Standard

Title

Coriolis

ISO 10790:1999 Amendment 2003

Measurement of fluid flow in closed conduitsd Guidance to the selection, installation and use of Coriolis meters (mass flow, density and volume flow measurements):Guidelines for gas measurement

Coriolis

AGA Report Nr 11: 2003

Measurement of natural gas by Coriolis meter

Turbine

ISO 9951:1993

Measurement of gas flow in closed conduitsd Turbine meters

Turbine

AGA Report Nr 7: 2006

Measurement of natural gas by turbine meter

Multiphase flow

NFOGM: Handbook Revision 2: 2005

Handbook of multiphase flow metering

Multiphase flow

API MPMS RP 86: 2005

Recommended practice for measurement of multiphase flow

Multiphase flow

API MPMS Publ 2566: 2004

State of the art multiphase flow metering

Multiphase flow

ISO/PRF TR 11583: 2011 (1)

Measurement of wet gas flow by means of pressure differential devices inserted in circular cross-section conduits

4.4.0 Metering Stations As seen from Section 4.1.0 above, it is clear that there are pipeline metering stations in oil and gas areas at different stages. In this section, gas and liquid measuring stations are discussed. Leakage detection is an important issue in pipeline metering and has been included. 4.4.1 GAS METERING SYSTEM (STATION) Pipeline gas metering stations are meant to continuously monitor the quality and quantity of natural gas in a pipeline to cover the following: l

l l l

Calorific value or latent energy for combustion (pricing); Concentration of sulfur; Hydrocarbon and water dew point; Natural gas volume and mass flow measurement and calculations.

Of these, flow measurement is of major concern in this book. Major instrumentation systems and devices include but are not limited to multipath ultrasonic flow meters, process gas chromatographs, and computer workstation flow control valves, automatic shutdown valves, and control systems. The main equipment includes filters, heaters, pressure reducers and regulators, and flow-metering skids. In addition to these, each station is generally equipped with drains for collection and disposal, instrument gas system, and storage tanks [16]. Some of the major process and mechanical systems include the following: 1. 2. 3. 4. 5. 6.

Filter separators; Meter skid piping; Heaters; Pressure reduction and regulation; Sound pressure; Overpressure protection;

Flow in Plant Applications Chapter | XII

7. Cathodic protection; 8. Building. Apart from these the flow metering and control system include but are not limited to: 9. Metering system: Places where custody transfer takes place are the most important, so with reference to that, the flow rates of gas need to be measured at a number of locations for the purpose of monitoring the performance of the pipeline system. There will normally be two runs of pipe with a calibrated metering orifice in each run for the custody transfer metering station. When used a multipath ultrasonic meter should meet the requirements of AGA 9 and other standards mentioned earlier (including the standards for uncertainty determination). As necessary, the meter tubes will be equipped with a flow conditioner. The fully assembled meter tubes should be calibrated at line pressure and full-flow conditions prior to use. Normally, the ultrasonic meter tubes will be designed for a minimum 10D upstream length from the flow conditioner to the meter and 5D lengths downstream of the meter [16]. Suitable measures should be taken into account to eliminate pulsation and errors. 10. Flow control valve and flow controller: A control valve is installed downstream of the meter run to control flow through and the delivery pressure. This valve will primarily operate to limit the station throughput to prevent exceeding the meter capacity. The flow control valve is regulated by flow computer and calculating (FCC) methods discussed in the standards listed in Table XII/4.3.0-1. The control valves are normally open type to minimize pressure losses through the station. The flow computer is meant to monitor and control the facilities as well as perform custody transfer quality measurement, including communication with the DCS and system control and data acquisition (SCADA) system. Gas chromatograph (GC) is meant to determine the gas composition for purposes

1093

of calculating the gas gross heating value and a moisture analyzer is used to measure the water content of the gas system. GC and moisture instruments exchange data with the flow computer and calculation (FCC) unit for calculating the total gas heating value in the metered gas. A gas sample is taken from a continuously flowing location on the meter and regulator skid. The gas sample is secured at low pressure to minimize the lag time utilizing a self-regulating sample probe and routed to the gas chromatograph and moisture analyzer [16]. 11. Automatic shutdown: An automatic shutdown system with a remotely operated shutdown valve is installed at the pipeline connection. This valve is equipped with pneumatic controls, a hydraulic manual override, and open/close limit switches. Blow down of the meter station piping is accomplished by a vent stack located on the station inlet piping and vents on the meter skid located downstream of the meter and downstream of the flow control valve [16]. 4.4.2 LIQUID MEASURING SYSTEM (STATION) The liquid measuring system is part and parcel of the petroleum or hydrocarbon liquid distribution system. It uses advanced metering technologies, control system, and flow computing and calculation system. Liquid metering can be from a single line to several lines handling different kinds of liquids with dedicated provers for individual lines. The application areas of liquid measurement stations for metering of crude oil, refined products, NGL, LNG, and chemicals include but are not limited to the following: l l l l

Pump stations feeding pipelines; Terminal stations feeding several users; Metering at inlet locations on the pipeline; Products segregated for transportation to separate the liquids [17].

Depending on the application and metering requirements there can be several parallel lines

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Plant Flow Measurement and Control Handbook

being fed from a single header. Again, based on the application, meters can be grouped and may be fed through manifolds with a suitable interlock. The arrangement mainly depends on the application. Major equipment includes but is not limited to the following: 1. Mechanical piping arrangement (application specific); 2. Inlet block valve (facilitates maintenance); 3. Strainer; 4. Downstream block valve (for allowing/ disallowing flow through the meter); 5. Miscellaneous instrumentation: Pressure and temperature instruments for volume, density corrections, etc. These are connected to the flow computer for flow computations and metering calculations. There will also be status signals; 6. Flow computer: These are meant for flow computation and metering calculations. They also support the operator interface for monitoring and control. The system is complete with an operator interface including HMI; 7. Prover: There are various designs discussed later in this book; 8. Four-way switch: For flow diversion in prover; 9. Digital counter and switch: Start/stop digital counter; 10. Flow meters: Basic requirements for meter selection include: l High accuracy (w0.25% AR) l High turndown: 10:1 l Wide flow range coverage l Comparatively lower permanent pressure loss; Therefore, flow meter types used mainly include: l Turbine meter l Ultrasonic flow meter l Positive displacement l Coriolis mass flow meter; Of these the first two, on account of their higher flow capacities, lesser foot print and weight (and also not much permanent

pressure loss), are the preferred ones. However, both types require long straight length sections, so for practical use flow conditioners are used. 11. Flow control valves: These are used for equalization flow in all meters, i.e., to remove imbalance should it exist, flow meters may be run at nearly their maximum range to increase throughput. However, normal metering flow should match with the normal operating range. Flow control valves should be designed to close against the maximum upstream pressure that will occur, with no pressure downstream, in order to avoid damage when the valve operates against full differential pressure [17]. For long pipe line leak detection it is a crucial safeguard device, which is elaborated on in the next section. 4.5.0 Leak Detection in Long Pipe Line When petroleum products are transported over a very long distance it is critical and crucial to detect any leak in the pipeline. This is important for environmental and personal safety. However, even a small leak could turn out to be a catastrophe. There are three distinct types of leak detection systems possible: visual, external instrument, and instrumented internal pipeline type. A leak detection system (LDS) with nonintrusive ultrasonic flow meters is the most popular and is used mostly in pipeline applications. The detection method and locating of the leak are important considerations. 4.5.1 ADVANTAGES OF USFM FOR LEAK DETECTION On account of some distinct advantages, USFM is used most often as the leak detection system (LDS). Major advantages of using nonintrusive USFM include the following advantages: 1. No moving parts; 2. Nonintrusive, no pipe penetration is necessary;

Flow in Plant Applications Chapter | XII

3. Inherently bidirectional; 4. No additional instrument valve necessary to remove for maintenance during operation; 5. In addition to measuring fluid velocity, USFM can measure at the speed of sound and its changes hence can detect the fluid type in the pipeline, i.e., density, viscosity, etc.; 6. Ability to detect fluid identification and liquid properties; 7. Ability to detect from small to large product release in real time, i.e., high turndown ratio; 8. Extremely sensitive to no-flow condition. With these details in mind let us look into the details of the system. 4.5.2 DESCRIPTIVE DETAILS OF THE LEAK DETECTION SYSTEM Core elements of the leak detection system based on the compensated mass balance principle are dual pair clamp on US transducers mounted at the beginning and end of the measured section [18]. There can be such measurement stations, e.g., every 100e150 km. The actual distance is influenced by the environmental protection need as well as geographical topology. In order to take care of fluid temperature variation a suitable temperature element (RTD) is used downstream of the US sensors. Similarly, the ambient temperature variation is taken care of by another set of RTDs at the local station. 1. Leak detection: As stated earlier, in addition to measuring fluid velocity, USFM also measures the sonic velocity of the liquid in the pipeline. As the sonic velocity is a signature characteristic of the fluid, the master station through suitable software is able to recognize the fluid. Also, USFM measures functions as both a flow meter and density meter [19]. It is known that sonic velocity is affected by the density of the medium, so USFM infers the liquid density by measuring the sonic velocity and establishing the relationship between density and the measured sonic velocity. Therefore, a nonintrusive mass flow measurement system is based on the actual

1095

measurement of the pipeline mass input, versus the actual measured pipeline mass output. Therefore, the meter employs the mass balance of a compressible liquid (compensated volume balance is also available, e.g., from Siemens). 2. Process conditions: Temperature is measured and compensated, whereas pressure is seen through sonic velocity as it has a direct impact on density. By measuring the sonic velocity, with the help of change pressure, condition is calculated. 3. Local and master station configuration: Local information/data collection by the transducers and RTDs are sent to the local station processor for local sampling and processing. In addition to the local computing station, there will be one master station as shown in Fig. XII/4.5.0-1. This is also an intelligent flow control and computing unit. The major functioning is to run a software for leak detection. Each local station is connected to the master station through a switch circuit (basically a way of software polling of the local station by the master station). The master station collects the temperature, liquid density, liquid viscosity, etc. to recognize the liquid and associated changes therein so that along with this information and flow it can detect the leak by mass balancing (volume balancing [18]). Additionally, important diagnostic information, such as the transducer signal strength and aeration, is also sent to the master station to help in determining the health of the meter and the quality of the liquid. All these information are measured by each site station at least 10 times per second [19]. 4. Leak location: Location of a leak in a long pipeline is extremely important. There can be several products, each of which has a different speed of sound that a pressure transient will travel through between two measuring points. When the products between two site stations are known, the master station can calculate the arrival time. In LDS, leak location is determined by measuring the amount of time the

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Plant Flow Measurement and Control Handbook

MASTER STATION

SWITCHING CIRCUIT

LOCAL

LOCAL

STATION*

STATION*

STATION*

RTD NOT SEEN

RTD

RTD

DUAL PAIRS OF US SENSOR (Typ)

FIGURE XII/4.5.0-1 Leak detection system. *Each local station with ambient temperature compensation. Digmesa Technology: Digmesa technology meets the stringent hygienic requirements of the manufacturing process to simple dispensing measurement. This is a cost-effec ve solu on for measurements; be it beverage dispensing or coffee machine or controlling fluid in hospital disinfec ng ac vi es. The flow sensor monitors the whole process to ensure that a liquid has been dispensed even under the most difficult condi on. This Swiss technology of flow sensing u lizes Laser or Ultrasonic technology. It can sense very low flow as low as 0.08 L/min.

FIGURE XII/6.3.0-1 DIGMESA technology.

low-pressure (due to leak) wave takes to travel from its source to each of the segment’s local stations. The site stations can sense the lowpressure wave’s arrival by its effect on the density of the fluid, which is measured many

times each second [19]. The speed of pressure transient in the pipeline is determined by the speed of sound for the product being transported. The measurements are done by sampling the data many times and integrating the

Flow in Plant Applications Chapter | XII

same over a fixed time period and comparing this with a leak threshold over that time period. 5. Zero flow: Zero flow conditions are frequently found in pipeline transportation. There can be many lines in zero flow for a long period. Also, zero flow occurs during bidirectional flow requirements. USFM responds nicely to this condition. There are several other leak detection systems, but the USFM type provides better performance. Various flow meters discussed in the above sections are used in refinery and petrochemical plants. In the following sections these processes are discussed. 4.6.0 Petroleum Refinery Application The basic refining process includes but is not limited to the following major headings: l l l l l l l l l l l

l l l l l l l l l

l

Treatment; Conversion; Separation; Blending; Alkylation; Catalytic reformation; Hydro-cracking; Coking; Isomerization; Polymerization; Etherification. Major conversions of crude oils and other input streams in the refinery include the following refined products: Liquefied petroleum gases (LPG); Gasoline; Jet fuel; Kerosene (for lighting and heating); Diesel fuel; Petrochemical feedstocks; Lubricating oils and waxes; Home heating oil; Fuel oil (for power generation, marine fuel, industrial and district heating); Asphalt (for paving and roofing uses).

1097

Flow metering covers a wide variety of flow meters that are deployed in such applications which include but are not limited to: DP type meters, PD meters, electromagnetic, turbine, vortex meters, and mass flow meters of both types. 4.7.0 Petrochemical Application Hydrocarbon processing plants, such as petrochemical and chemical plants, always aim to optimize the production of products used in a wide variety of end usages, which include but are not limited to cosmetics, synthetic rubber, plastics, automotive lubricants, pharmaceuticals use, cleaning products, etc. It is needless to mention the importance of flow meters for such an optimization process. Such flow metering in petrochemical plants can range from upstream production to feedstock, including intermediate stage and processing, such as gas flow measurement, catalyst injection, batching and blending, custody transfer, and fugitive emissions monitoring. Many critical decisions can be taken faster by capturing, managing, and analyzing the right flow measurement data at the right time. Flow metering covers a wide variety of flow meters that are deployed in such applications including but limited to: DP type meters, PD meters, electromagnetic, turbine, vortex meters and mass flow meters of both types. Major application areas include the following: l l l l l l l l l l

Chemical batching; Dosing/blending; Steam flow; Lubricating oil; Process cooling; Pressure regulation; Leak detection; Waste treatment; Emissions monitoring; Fiscal measurement.

Apart from custody transfer and fiscal measurement, and for accounting purposes, accurate, real-time flow data are essential to reduce

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Plant Flow Measurement and Control Handbook

resource consumption and make the best use of expensive raw materials. Also, for environmental protection and monitoring of greenhouse gas emissions, it is also important for flow metering applications. With this the discussions on oil and gas come to an end and we now investigate flow measurements in pulp, paper, and chemical plants.

5.0.0 PULP, PAPER, AND CHEMICAL INDUSTRIES Pulp and paper industries involve many chemicals and corrosive materials. In this section discussions cover pulp paper and chemical industries under one heading that covers the requirements of flow instruments which need to work with very corrosive, abrasive materials simultaneously at high temperature. In all these cases, material selection is very important for the flow meters. In this section efforts are made to cover material selection at length. Chemical plants can be of widely varied types—hence the process description cannot be included. Therefore, the discussions start with an outline of the basic process of pulp and paper plants which involves the following majors steps: 1. Pulping: This process involves mechanical and chemical processing of wood chips. Mostly used chemical pulping involves high temperatures, corrosive and abrasive substances, and vibrations, hence highly reliable measurement and controls are necessary. 2. Bleaching: Depending on its density, chemical pulp is transported via pumps, flow distributors, or conveying spirals to the bleaching tower. The process is also carried out at high temperature and chemical addition. 3. Inventory preparation: Holding large quantities of prepared stock in storage towers and chests for continuous operation in a pulp and paper plant. 4. Paper machine: This is the heart of the paper plant. Paper sheet formation is done here. At the head box, pressure and speed are kept

constant to ensure a uniform paper sheet is formed. During the drying process, a condensate film forms on the inside wall of the drying cylinder, affecting the heat efficiency of the transfer to the paper. 5. Wet end: After bleaching, pulps from different sources are mixed as needed for various products and mechanically refined prior to delivery to the head box. Sizing agents, dyes, and additives are added precisely to produce the desired paper characteristics. 6. Waste treatment: Wastes which come together from different processes are suitably monitored and treated prior to disposal. The process of treatments required is very much dependent on environmental regulations at the place. 7. Utilities: There are various steam, boiler, and recovery utilities in a pulp and paper mill that need to be controlled. One of the most important is the recovery of spent cooking chemicals. 5.1.0 Major Challenges and Aims of Flow Measurement As indicated above major flow measurement issues arise out of the chemicals used in these plants. These materials at times pose serious problems towards material selection for the different kinds of flow meters to be used in these plants. 1. Major challenges: Flow measurements in pulp paper mills and chemical plants face major challenges due to various kinds of chemicals, which in some cases are very corrosive and aggressive. Major challenges in pulp paper and chemical plants include but are not limited to the following: l Extremely aggressive chemicals; l High-viscosity fluid flow; l Corrosive materials; l Abrasive materials; l High pressures and/or temperatures. Naturally, the right selection of flow meter technology in the most suitable

Flow in Plant Applications Chapter | XII

configuration is extremely critical for efficient working of the flow meter in that environment and conditions. 2. Aim of flow meter selections: The following are the aims of flow meters in general but more so in these plants where there will be a chance of instrument failure due to corrosion/ abrasion: l Reliable and stable operation under given conditions; l Ability to withstand the harsh conditions meters need to face; l Good accuracy of measurement; l Good repeatability; l Easy to install and easy calibration; l Less downtime and lower maintenance; l Low-cost ownership. The discussion starts with various kinds of flow meters normally encountered in pulp and paper plants. While on the subject other chemical plants shall be covered also. 5.2.0 Flow Meters in Paper and Chemical Plants There are many types of flow meters used in pulp and paper plants. Meter types and typical application areas have been listed in Table XII/ 5.2.0-1.

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5.2.1 USE OF DP TYPE METERS DP type meters have been in use in different plants over many decades for their reliable operation and as cost-effective solutions to measure volumetric flow, especially in applications with large line sizes—typically 8 inch diameter. When DP type meters are used in conjunction with measurement of pressure and temperature (as required) it can give mass flow also. With suitable selection of materials it can be used in many corrosive applications. DP flow measurement can be used with conductive and nonconductive fluids, allowing it to be used with a wide range of gases and liquids. Therefore, in the case of chemical plants they find direct use in utilities, such as water, steam, and in some fuel flow applications also. On account of the primary element, there will be permanent pressure losses but with suitable selection of primary element this permanent loss can be minimized. For chemical plants with heavy dust problems, Annubar/Krell’s orifices (Chapter II) can be adapted when permitted by the process. There are several challenges to DP type measurement. One is wet leg issues. “Wet leg” is the term used to describe the impulse line connection between the DP transmitter and the primary flow-sensing element [20]. Measuring gas at times can be trapped in the wet leg. Clogging of the wet leg issue has

TABLE XII/5.2.0-1 Instrument Type and Applications in Pulp & Paper Plant Meter Type

Application Areas

Electromagnetic

Stock, liquor, chemicals, coating kitchen, coating, lime mud and water in digester blow lines, additives, etc.

Coriolis

Density, volume concentration, high-value chemicals, coatings, fuel (gas/oil) and steam: stuff boxechemical feed, coating kitchen, and coating

DP type

Utilities such as steam, fuel

Vortex

Saturated and superheated steam (with pressure/temperature compensations)

USFM

Low-conductive clean liquids

SONAR

Digester blow line

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been dealt with in detail in Section 1.1.0 in this chapter and may be referenced. As in paper and chemical plants use corrosive fluids so, DP transmitters for flow measurements are often used with suitable seals such as remote seals are often used based on applications. So, while selecting DP/multivariable transmitters same should be borne in mind. 5.2.2 USE OF MAGNETIC FLOW METERS Electromagnetic flow meters are used extensively in these plants at various applications, as shown in Table XII/5.2.0-1. The only limiting criterion is low conductivity, otherwise it can be used for most fluid applications. 1. Reasons for choice: On account of the following reasons the electromagnetic flow meter is the preferred flow meter in these plant applications: l Accuracy: Good accuracy; l Noise: Good noise (of slurries) mitigation properties; l Materials: Available with a wide range of materials to match process needs for lining and an electrode for high-temperature and liquid permeation applications; l Obstruction: Obstructionless (fiber does not build up in meter); l Plugging: No chances of plugging as no ports or impulse lines involved; l Pressure drop: Full diameter with practically no pressure drop across meter; l Communication: Fieldbus communication possible; l Maintenance: Lower maintenance requirements; l Cost: Cost-effective (for size requirement). 2. Major problems and issues: There are a good numbers of issues associated with fluids in chemical plants and pulp and paper plants. A few specific issues are listed below as examples: l Slurry noise: High slurry noise; l Corrosion: Highly corrosive chemicals; l Consistency: Stock consistency variations; l Viscosity: Viscosity variation;

Permeation: Liquid permeations are seen in the form of blisters and bubbles that can cause premature failure of the liner; l Fiber: Fiber length; l Abrasive materials: Highly abrasive fluids (with solids); l Adhesives: Adhesive chemicals and adhesion of wood resin, dye. 3. Possible solutions: For stable and accurate measurement with longer life-time solutions the listed below may be applied. These are general solutions, the reader can contact the manufacturer for further details. l Dual frequency: Dual-frequency excitation (with selection options: refer to Subsection 4.4.2.2 of Chapter V). High slurry at low frequency may pose problem. Therefore, based on the application suitable high-frequency selection options are available [21]; l Lining: A wide range of lining selections is possible. These include ceramics, PFA (with metallic earthing) lining, as necessary for adhesive fluid applications; l Electrode coating: Protective electrode coatings are available; l Sensing: For adhesive fluids, as necessary, external capacitance sensing is available; l Diagnostics: Advanced diagnostics are available for the meter. It is possible to detect lower signal to noise (S/N) ratio in advance, to take corrective action for easy changing of the coil drive to the frequency that provides the strongest signal [22]; l Permeation improvement: The temperature gradient may increase permeation rates. This is common in paper machines, as increased temperature gives better production. The choice of the correct Teflon PTFE lining and their manufacturing process mostly mitigate the problem. In this connection Fig. XII/ 5.2.2-1 may be referenced for permeation and liner manufacturing issue. Liners like Sintered PTFE Teflon Liner (thicker) Sleeves and Virgin Transfer Molded PFA can be a good choice [22]. Use of insulation can be used to reduce the temperature variation between the process and the ambient temperature. l

Flow in Plant Applications Chapter | XII

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Permeation: Permeation (imbuing) is the penetration of a permeate (liquid, gas, or vapor) through a solid. Basically permeation is the molecular diffusion of a fluid or vapor through a material. It is characterized by bubbles forming underneath the liner sleeve. Permeation depends on: Concentration gradient of the permeate, material’s permeability and materials' mass diffusivity i.e. process fluid chemistry, temperature, pressure, quality of the liner, and liner thickness. In EMFM permeation can occasionally affect PTFE Teflon lined flow tubes in high temperature

applications.

PTFE

in

compression

molding

with

special

manufacturing technique can reduce permeability rate in EMFM .

FIGURE XII/5.2.2-1

5.2.3 USE OF ULTRASONIC FLOW METERS Clamp-on ultrasonic transducers inherently enjoy the advantage of installation and mounting flexibility and can be retrofitted very easily as they are simply mounted on the outside of the pipe. On account of its nonintrusive noninvasive nature, it has practical advantages of no wear and tear by the flowing medium due to abrasion/corrosion, no risk of liquid leakage or fugitive gas emissions, no pressure loss and, above all, unlimited plant availability. Another advantage of USFM, as already discussed in Chapter V and in connection with leakage detection here, is that by measuring sonic velocity, it can take care of process condition changes. Therefore, product characteristics like concentration and density can be monitored continuously online. As a result of this it is possible to determine the flow rate and mass flow rate of liquids as well as gases with the help of transit time USFMs which can measure flow in both directions. A wide range of ultrasonic transducers, mounting fixtures, and transmitters guarantee ideal adaptation to the individual measurement task, independent of pipe material, wall thickness, and measurement range—even within hazardous areas (FM Class I, Div. 1 and 2, ATEX) [23]. These meters are available for a wide range of process and ambient temperatures and independent of pipe diameter. USFMs also

Permeation.

offer diagnostic features. In view of all these characteristics, USFM can be an easy choice as flow meters in chemical plants, integrated chemical plants with highly complex networks of mass and energy flows [23], along with problems of corrosion abrasions. Added to this they have no pressure loss. However, they have limitations in fluid medium with fibers. These are available for use in hazardous area applications also, with necessary approvals/certifications from appropriate authorities (e.g., ATEX) for safe operations. In this connection, the discussions in Sections 1.2.1 and 1.2.2 in this chapter may be referenced. 5.2.4 USE OF VORTEX Sizing of the vortex is extremely important. A properly sized vortex is very good in measurement fluids, including steam (saturated and superheated). Bluff body design is part of the manufacture design, and so sizing must be done with manufacturers. Typical vortex designs have small free spaces or crevices around sensors or shedder bars to create the movement needed to create vortices. Coating or particulate matter in the fluid can clog the crevices and inhibit sensor movement, resulting in inaccurate flow measurement [20]. Minimum flow rate (“low flow cutoff”) is necessary for the vortex to operate, so often concentric reducers are recommended.

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In this connection, Section 1.2.3 of this chapter may be referenced for further details. 5.2.5 MASS FLOW METERS In chemical plants, especially in batch processes, mass balance is usually used in recipes. Therefore, the use of direct mass flow measurement is always the first preference. Direct mass flow measurement over wide turndowns with varying fluid properties is used in chemical plants. On account of the ability to measure density and concentration measurements with high-accuracy and repeatability make them suitable for chemical batch processes. Added to these, mass flow meters do not require any straight length, so mounting and installations are easier. Direct mass measurement eliminates the cost and maintenance of temperature and pressure transmitters, and flow computers. However, cost, pressure drop, and nonavailability for large diameters make their use limited at times. However, thermal mass flow meters at times are used in certain cases in place of Coriolis flow meters for mass flow measurements. The use of insertion type thermal mass flow in some chemical plants is quite popular, especially for cases when the sensor is well protected and does not come into contact with the flowing medium. The use of a thermal mass flow meter (both direct and bypass designs) in compressed air systems, raw materials, and finished products in chemical plants is quite common. 5.2.6 SONAR FLOW METERS IN PULP AND PAPER PLANTS As indicated in Table XII/5.2.0-1, there are a number of other type flow meters used. Sonar, described in Section 9.0.0 of Chapter V, can be applied. (Courtesy: CiDRA Chemical Management, Inc.) 1. Air flow in head box: One such is a noninvasive way to measure and regulate air flow in a head box. The quality of the papermaking process is improved with suitable control of air

flow at the head box. This provides a number of benefits such as the following: l Reduction in paper breakages; l Higher run-ability; l Less pinholes and dirt spots; l Reduction in defoamer (10%e40% saving) and retention of chemical consumption [24]; l Improved formation; l Stabilized paper caliper; l Good retention controls; l Better water removal; l Improved and stabilized operation of vacuum and pumping. Air and CO2 in the head box stock cause deterioration of paper quality on account of the following: l Pinhole formation; l Dirt spots; l Affecting water removal; l More breaks; l Increased bacterial activity; l Requirement for deaeration chemicals. Noninvasive sonar technology measures in real time the amount of entrained air in the head box. This helps to enable optimizing chemical dosing. It can be used to measure total air content (both entrained and dissolved gas) in the head box stock. It also enables automated head box stock air content control to reduce the consumption of deaeration chemicals [24]. 2. Digester blow down line: Electromagnetic flow meters are mostly used in this application. However, there can be measurement error or inaccuracy on account of wear, deposits, conductivity variations, and debris. Sonar type flow meters are noninvasive and are not affected on account of these issues. Therefore sonar can be used in this particular application. Also, like electromagnetic flow meters, sonar measurements can also be full bore type with no permanent pressure loss. They are also unaffected by any abrasion effects. They are better suited for process control in some cases.

Flow in Plant Applications Chapter | XII

After going through the instrument application in pulp, paper, and chemical plants, we now investigate instrumentation in the food and pharmaceutical industries.

6.0.0 PHARMACEUTICAL, FOOD, AND BEVERAGE INDUSTRIES During the discussions in Chapter XI, Section 6.1.2, on batch process operation, it was shown that food, beverage, and pharmaceutical industries operate in a batch process mode and each of them demands a special kind of measurement— be it in yeast growth or juice preparationeto name a few. Also, in these industries, the major thrust is on hygienic use and material selection for various meters. Each of these industries has separate requirements and demands flow meters need to meet. For example, a tablet manufacturing unit may use a loss-in-weight feeder for dosing and

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mixing of recipe. On the other hand, beverage industry use of turbine meters is very common. So, prior to going into further details, we now look at the various types of meters used in these industries. It must be noted that in pharmaceutical, food, and beverage industries there are huge numbers of industries with wide variations and specialties of instruments that might be used. It is practically impossible to cover them all. Here commonly used flow meter types have been covered. The discussions start with types of instruments used in pharmaceuticals, food, and beverage industries. 6.1.0 Instrument Types Used in Pharmaceutical, Food, and Beverage Industries Listed in Table XII/6.1.0-1 are the flow instruments normally encountered in pharmaceutical, food, and beverage plants.

TABLE XII/6.1.0-1 Instrument Types in Pharmaceutical Food and Beverage (F&B) Instrument

Plant Type

Typical Features

Turbine

Pharmaceutical

Axial type or Pelton wheel magnetic pickup; bearing: ceramic/sapphire. Accuracy/repeatability: 1%/0.25% AR wide ranges; TD300:1; over range: 150%. Air and liquid flow measurement for pill coating. Ultra pure water flow

Turbine

Food beverage

Axial type; magnetic pickup; bearing: ceramic/sapphire. Accuracy/repeatability: 0.5%/0.25% AR; wide ranges; TD200:1; over range

Thermal mass FM

Pharmaceutical

Capillary/immersion type; wide flow range: accuracy/ repeatability: 1e2% AR/0.25% AR. For gas flow measurements

Coriolis mass FM

Pharmaceutical

Both bent and straight tube Coriolis are popular. Water for injection, reverse osmosis and deionized water measurement. High rangeability

Electromagnetic

Pharmaceutical and food beverage

Both AC/DC type, hygienic grade with accuracy 0.25%e0.5% AR velocity of measurement between 0.3 and 10 m/s. Also used in waste water lines

USFM

Pharmaceutical and food beverage

Both transit time and Doppler type used. Preferred selected from hygienic point of view. Available in various pipe sizes. Accuracy 0.1% AR. Additional inherent advantages like clamp on design, diagnostics already discussed Continued

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TABLE XII/6.1.0-1 Instrument Types in Pharmaceutical Food and Beverage (F&B)dcont’d Instrument

Plant Type

Typical Features

PD Meters

Food beverage

Reciprocating piston type and other PD meters are used to add ingredients, chemicals, and additives in the manufacturing process. Normally these are provided with a local counter/totalizer

Digmesa*

Food beverage

Special flow sensors used for precision measurement of flow. Laser/US technology-based Digmesa type sensor technology is found in almost all dispensing machines in beverage industries *Refer to Fig. XII/6.3.0-1

Loss in weight feeder

Pharmaceutical

Dosing and mixing of recipes. Additive additions. Mostly used for tablet making. Accuracy: 0.5% AR

(For solid flow meters in food industries for granular items Chapter VIII may be referenced.) 6.2.0 Discussions on Flow Meters in Pharmaceutical Industries In this section short discussions on major instruments used in pharmaceutical industries have been covered. 6.2.1 ULTRASONIC FLOW METER APPLICATIONS In pharmaceutical industries USFMs are found both as permanent as well as battery-operated portable types, which can be run for around 12 h. 1. General features: Hygiene and cleanliness are always a top priority in the pharmaceutical industry. Naturally, clamp-on ultrasonic flow metering technology could be an ideal solution as it does not come into contact with the measuring fluid, eliminating the chances of contamination. In pharmaceutical industries there are some temporary needs for which there is practically no alternative to clamp-on ultrasonic technology. USFM in monitoring flow in feed water flow measurements is very common. Both transit time types as well as Doppler types have been found in this industry, as in certain

applications there will be solid in liquid. These are available in various sizes from as small as 25 mm to very large-sized pipe. As already discussed, the self-diagnostic features of USFM keep their choices ahead of other types. These instruments support various forms of communication, e.g., HART, Fieldbus, etc. 2. Portable type specialties: Portable USFMs are common in this industry to monitor velocity in certain flow lines, especially in ultrapure water lines. Portable clamp-on flow meters are of choice for servicing and maintenance activities and a few other activities, e.g., the control and auditing of measurement points not covered by permanent meters, etc. These portable meters are battery-operated and can be made ready very quickly. Portable clampon flow meters are also available in an “energy” and “multifunctional” version, allowing the measurement of thermal energy/BTU flows and making the flow meter the ideal companion for the analysis or auditing of heating and chiller plants [25]. 6.2.2 TURBINE FLOW METER APPLICATIONS Turbine type flow meters with high-quality materials are used in the pharmaceutical industry.

Flow in Plant Applications Chapter | XII

These obviously will be sanitary grade to maintain hygiene. Measurement and control of ultra pure water, air, and liquid flow for pill coating are quite common. The meters to be used must have a very good response time, high accuracy, and repeatability. These are available with an accuracy of around 13450 KWH

Required for 1 kg Al production

Data given here are taken from a large producer of Al: BALCO India. Courtesy: BALCO.

Flow in Plant Applications Chapter | XII

Flocculent dosing: Chemicals are dosed to increase the molecular weight of slurry particles so as to have better settling of slurry particles and enhance the quantity of sodium aluminate. l Filtration: Tiny and fine suspended crystals need to be removed. This is security filtration to remove all impurities. The material caught by the filters, known as filter cake, is washed to recover alumina and caustic soda. The filtered liquor, sodium aluminate solution, is then cooled and pumped into precipitators. l Precipitation: The clear sodium aluminate solution from the settling tank is pumped into the precipitators with the addition of fine particles of “seed crystals” (a kind of alumina) for precipitation. Alumina crystals begin to grow around the seeds and settle at the bottom of the tank for removal to thickening tanks. l Calcination: In order to get anhydrous alumina, aluminum hydrate is calcined at a temperature above 1000 C. Aluminum particles are suspended above a screen by hot air and calcined, which results in producing white powder pure alumina. The caustic soda from the aluminum hydrate produced is recycled into the system. l Evaporation and utility section: This section is meant to reuse caustic soda obtained from various sections in the process. In order to get process steam at various stages, steam generators and a turbogenerator (for power generation) are kept in the alumina plant to meet the needs of the plant. 2. Smelting and aluminum production: The HalleHeroult process of aluminum smelting is basically an electrolysis process comprising a carbon anode and carbon in the base and sides as a cathode. As hydrogen is electrochemically much nobler than aluminum, aluminum cannot be produced by an aqueous electrolytic process. For production of liquid aluminum, an electrolyte (bath) mainly containing cryolite (Na3AlF6) is used for l

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electrolytic reduction of alumina (Al2O3) to produce aluminum. The other major ingredient used in the smelting operation is carbon. Carbon electrodes transmit the electric current through the electrolyte. Aluminum fluoride is added to lower the melting point of the electrolyte solution. Aluminum is formed at about 900 C, but once formed has a melting point of only 660 C. During the smelting operation, some of the carbon is consumed as it combines with oxygen to form carbon dioxide. As indicated earlier, a huge quantity of electrical energy is required for aluminum smelting. The buildings where the electrolysis cells are located (the potrooms) are huge. In a potroom, hundreds of electrolysis cells are arranged in series to form a cell line often referred to as a potline. The production process required to produce aluminum is a continuous process. Stopping and restarting of the process is not easy and is always avoided. If production is interrupted by a power supply failure of more than 4 h, the metal in the pots will solidify, often requiring an expensive rebuilding process. For this reason aluminum smelting plants normally have a captive power generation plant to ensure no power interruption. 3. Captive power plant: Captive power plants are standard power plants and are already discussed and hence not repeated here. 7.1.3 COAL MINING AND METHANE RECOVERY PROCESS While on the subject of applications of flow metering in metallurgical and mining industries, coal mining and methane recovery are important places for applications. In this section a process outline of these two processes has been covered. 1. Coal mining: There are two basic methods for removal of coal from earth, as described here. l Surface mining: When the coal is available within around 60 m below the surface, surface mining is used. Giant machineries are used to remove the top layers of soil and rock to expose the coal. After excavation

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of coal and mining is complete the soil and rock are returned to fill the mine. After that the entire area should be revegetated. There are two type of surface mining: strip mining (area stripping and contour stripping) and auger mining. l Underground mining: Underground mining is used when the coal is buried several hundred meters below the surface or more. Some mines can extend to depths of more than 300 m. Miners use heavy machinery to cut out the coal and rely on conveyor systems to transport the coal to the surface. Some underground mines require elevator shafts to move miners and coal to and from the surface. There are two types of mining methods available here these are: longwall mining and room and pillar mining. 2. Coal mine methane (CMM): Methane recovery is another emerging application in coalmining areas. This is not only an economical proposition but is also gaining attention from environmental pollution prevention also. There are three major sources of coal mine methane (CMM): l Degasification systems (drainage) both premine and gob; l Ventilation air (VAM); l Abandoned or closed mines. 3. Coal bed methane recovery: Natural gas, or methane, can be extracted from deep underground in coal beds. CBM is a clean-burning fuel source which is ever-expanding in nowadays. This also helps in moving away from processes that produce high levels of CO2 emissions to meet environmental regulations. We now look into the applications of flow metering in metallurgical and mining plants. 7.2.0 Instrumentation Applications in Steel Plants Right from the sintering plant there are a number of flow measurements involved in the steel

making process. Raw material flows to the sinter plant, etc. are measured with the help of solid flow measurement devices such as weigh feeders. Blasts to furnace both cold and hot are important parameters are not only measured by head type flow meters. These flows are controlled also. Clean gas and coke oven gas flow measurement along with steam flow measurements are carried out in the steel making process. Major flow measuring devices and their applications in the steel making process have been described in this section. 7.2.1 DP TYPE FLOW METERING 1. Blast flow measurement: At the lower part of the blast furnace, cold or hot blast gases are introduced and these are measured with the help of DP type instruments. For hot blast gas, a flow meter should be installed before the preheaters. 2. Hot blast flow measurement and PCI (*): The measurement of flow and safety interlocks for pulverized coal injection (PCI*) is very important for blast furnace operation. The flow measurements can be taken in the blast furnace down leg pipes by installing refractory Venturi tubes. A hot blast air flow system in the straight tubes can be accomplished by DP type flow metering with suitable pressure/ temperature compensations. This can be used to accomplish the safety interlocks of the blast furnace with pulverized coal injection (PCI). PCI helps to increase hot metal production and reduce pollution. 3. Furnace body cooling: It is an important to check the circulation water flow. A DP type instrument with high reliability and stability is essential. 4. Oxygen measurement: It is needless to mention the importance of blast efficiency calculation and ways and means to improve the same. Blast furnace efficiency is greatly influenced by the airflow supplied for combustion. Optimization of combustion can be accomplished by injecting oxygen into the

Flow in Plant Applications Chapter | XII

tuyeres of the furnace. Major criteria for oxygen measurements are listed here: l Oxygen injection is critical, so metering has to be very accurate; l To avoid the chances of combustions it has to be clean, safe, and reliable; l The instrument must be reliable to avoid any downtime. An integral orifice meter with associated DP transmitter is a good solution [27]. These integral orifice meters should meet international standards like ISO5167 and AGA 3. It is also used for billing purposes by the oxygen plant supplier. DP meters are also used for oxygen flow to an electric arc furnace. Some are replacing them with vortex meter. 7.2.2 ELECTROMAGNETIC FLOW METER APPLICATIONS Electromagnetic flow meters are applied for measurement of flow in many applications. The following are only a few examples where normally electromagnetic flow meters are used: l

l

l

Tuyere water leakage detection system for a blast furnace; Secondary cooling water flow monitoring and control continuous casting machine, i.e., intermittent control and mist spray control [28]; Hot rolling process: cooling water application in descaling process.

Some distinctive characteristics expected of electromagnetic flow meters are as follows l

l

l

l

The application demands highly reliable magnetic flow meters with diagnostic functions; The instrument should be highly accurate and repeatable; The instrument must be able to cope up with noise in measurements. In some applications dual-frequency excitation could be a better choice; High speed of response is very important in some cases associated with safety.

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In order to understand the requirements of the meters mentioned above we now look into the application areas of a few measurements deploying this flow meter type. 1. Tuyere water leakage detection: Water is used to cool the tuyeres meant for injection of air into the blast furnace. The differences in flow of cooling water at the inlet and outlet of the cooling circuits is monitored to determine any leak in the cooling circuit. A leak in the cooling water circuit changes the dynamics of the cooling system. This will have an impact on the reaction in the furnace. As a result there will be a decline in furnace performance and efficiency. Also, safety is related with this detection. If the leak is not detected in a timely manner and water is injected into the furnace, hydrogen would be produced, endangering safe operation of the furnace and there will be erosion to the furnace roof and walls. Such a repair is very costly [29]. Leak detection is important for the following reasons: l Early detection of leakage, prior to hazard, is essential to improve operational safety; l Increased furnace availability by reducing nuisance shutdowns; l Reduction in maintenance costs and improved leak detection performance. Electromagnetic flow meters in cooling water lines ensure faster and more reliable leak detection, enabling them to avoid critical safety issues and unnecessary shutdowns. 2. Hot rolling process: Hot rolling processes involve rolling long heavy thick hot steel slabs into very thin sheets. Descaling the steel throughout the process is an important phenomenon to maintain the desired quality of the sheet. Improper cooling, i.e., inadequate or interruption in the flow of cooling water, can adversely affect the descaling operation. Electromagnetic flow meters are used in these applications to ensure reliable continuous flow measurement in cooling water lines.

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7.2.3 OTHER FLOW METER TYPES IN STEEL MAKING APPLICATIONS

flow meters, especially in alumina plants. These are as listed here:

There are many other types of flow meters used in steel making plants, some typical applications are as follows:

1. Red mud bauxite slurry: Accurate measurement of the flow of bauxite slurry is very important as this decides the plant output and the efficiency of the entire system. Application of an electromagnetic flow meter for measurements of bauxite slurry, mother liquor flow all these are quite common. Red mud measurement in slurry flow is critical and important, so it has been dealt with at length in Section 4.5.0 of Chapter VII and so is not repeated here. 2. Some other applications: In addition to red mud measurements, the following applications also use electromagnetic flow meters. l Digestion and dilution: Caustic, slurry, chemical dosing, lime flow measurement; l Precipitation: Prehydrate slurry, seed slurry, and water flow measurement; l Calcination: Hydrate slurry flow.

1. Turbine and thermal mass flow: These are normally used to avoid the formation of nitrates within steel manufacturing for developing oxygen-free environment. The argone oxygen decarburization (AOD) process is used to dilute injected oxygen with argon [30]. Flow meters used are turbine type and thermal mass flow type flow meters. For better accuracy turbine flow meters are preferred at times. 2. PD meters: For measurement of oil flow PD meters are used. Typical applications include but are not limited to: cold rolling oil flow, rust prevention oil, and lubrication application 3. Vortex: These are used for measurement of steam flow in the steel making process. Vortex meters are also used for oxygen flow to electric arc furnaces. We now investigate instrumentation in the aluminum manufacturing process. 7.3.0 Instrumentation Applications in the Aluminum Making Process Like any other plants there are a number of types of flow meters deployed in aluminum manufacturing plants. These are briefly discussed here. Red mud/bauxite slurry flow is very important and that is where the discussion starts. 7.3.1 APPLICATIONS OF ELECTROMAGNETIC FLOW METERS The aluminum manufacturing process finds quite good numbers of applications for electromagnetic

7.3.2 APPLICATIONS OF WEDGE FLOW METERS Wedge flow elements along with multivariable transmitters or DPTs are very suitable for measurement of red mud. A wedge flow element has been discussed at length in Section 5.0.0 (5.3.1) of Chapter VII. 7.3.3 SONAR TYPE FLOW METERING IN ALUMINUM MANUFACTURING From previous discussions it is clear that this measurement type is the clamp-on type—a nonintrusive, noninvasive instrument type. From discussions in Chapter VII it is also clear that it can measure the volumetric flow and amount of entrained air/gas present in any liquidcontinuous-phase process fluid. In aluminum

Flow in Plant Applications Chapter | XII

manufacturing units it is applied on account of the following major features [31]: l

l l

Guaranteed volumetric flow and gas volume fraction; Immune to scale build-up; Very little maintenance and no down time for installations.

The major application areas include the following: l l l l l l l l l l l

Low-temperature digestion feed; High-rate decanter feed lines; Red mud lines; Residue disposal lines; Pregnant liquor lines; Precipitation slurry lines; Seed hydrate lines; Product hydrate lines; Liquor lines; Spent caustic liquor lines; Seawater flows.

Apart from these ultrasonic flow meters, compressed air in smelting pots and optical flow meters are also deployed in flow measurements in aluminum manufacturing. 7.4.0 Instrumentation Applications in the Coal Mining Process There are various kinds of flow measurements involved in coal mining. Management of mining slurry is very important. Nowadays smart mining automations are common, as shown in Fig. XII/7.4.0-1.

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Methane gas flow measurement is vital, and the discussions start with this. 7.4.1 METHANE GAS FLOW MEASUREMENT Methane gas measurement is essential for both CBM and CMM (discussed above). Thermal mass flow meters are used for this purpose. The discussions start with thermal mass flow. As per regulations, it is necessary that coal mines monitor and report greenhouse gas (GHG) emissions. For CMM the percentage of methane in the extracted gas can be as little as 1% (in VAM processes) to more than 20% in drainage systems. Coal bed methane (CBM) is used as a clean-burning fuel source. Therefore, it is needless to repeat the importance in measuring methane, extracted from deep underground in coal beds. There are various kinds of flow meters used for methane gas flow metering. 1. Thermal mass flow meter: A thermal mass flow meter based on thermal dispersion technology, utilizes the relation between flow rate and cooling for direct measurement. This meter does not have any moving parts. Thermal mass flow meters are well suited for gas flow measurement. Available thermal mass flow meters for methane gas measurements are reliable, highly accurate, and repeatable. They are easier to install. These meters are rugged meters with multivariable local LCD readout with the capability to communicate through intelligent means. The meters should be the very fast responding type.

Smart mining Automa on: This is a complete automa on solu on meant to manage mining slurry. This is basically microcontroller (or microprocessor) based automa on system to measure and regulate parameters per nent to mining slurries. These systems use wireless technology to work as “eyes and ears” for management of slurries for allowing a ghter control strategy. Smart mining automa on offers the following advantages: • Accurate flow measurement and control accuracy •

Extended life for measuring and control devices

•

Advanced diagnos c features

FIGURE XII/7.4.0-1 Smart mining automation.

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2. Turbine flow meter: Turbine flow meters are used for measuring flow of methane gas, with a high accuracy of around 0.1% and high turndown. However, it has moving parts. 3. Vortex flow meter: Vortex meters are used for the measurement of methane gas. They are available in insertion types. These meters are available with an accuracy of around 1% AR. For further details Section 9.2.0 may be referenced. 7.4.2 MINE WATER FLOW MEASUREMENT Normal mine water flows are through an open channel. These could be in rectangular concrete channel, partially filled channel, brown coal purification water flow, and flow of water with high solid contents. Based on the open channel type, an empirical formula is utilized to measure the differential level by ultrasonic or other means of level measurement as detailed in Chapter III (for US level sensing refer to Section 4.1.5). 7.4.3 MEASUREMENT OF FEED FLOW TO HYDROCYCLONES Hydrocyclones are used for the classification of particles in slurries. The particle size of the cyclone feed slurry ranges from 250 to 1500 mm, leading to high abrasion. The particles cause a high slurry noise, so well-responsive, reliable, and highly accurate measurement is very challenging. Also, the meter has to be of low maintenance, even after withstanding so much abrasive wear. Electromagnetic flow meters with a ceramic carbide liner and tungsten carbide electrodes could meet these needs as seen previously. Electromagnetic waves with doublefrequency excitation would be better to maintain a higher signal to noise ratio. Some electromagnetic flow meters in this application are found to have a protection ring at the inlet of the flow meter to increase service life of the sensor, protecting the liner material from abrasion due to differences in the inner diameter of the flow meter and the connected pipe. It is recommended to

install the associated transmitter/electronics away from the meter, i.e., remote electronics are preferred to avoid effects due to vibration. After completing the discussions on the application of flow instruments in metallurgical and mining industries, we investigate the application of instrumentation in cement industries.

8.0.0 FLOW MEASUREMENTS IN CEMENT PLANTS Cement, the basic ingredient of construction, is critical because only it has the ability to enhance the viscosity of concrete, which in returns provides the better locking of sand and gravels together in a concrete mix. Portland cement can be manufactured in two different processes: a dry process and a wet process. The basic ingredients of both types are the same. Limestone, shells, chalk, shale, clay, slate, silica sand, and iron ore are the main ingredients for cement manufacturing. Of these, lime and silica make up nearly 85% by mass of Portland cement. Therefore, cement plants are normally located near limestone quarries. Basic raw material handling in dry and wet cement plants are similar. In the case of wet cement plants, water is added with the raw materials mentioned above. Another difference is that in the case of the wet system raw meal in the form of slurry is introduced into the kiln, whereas in the dry process dry meal is placed into the kiln system. The wet process is obsolete and dry processes are now mostly in use. In the following the dry cement making system has been discussed in brief. The process details given here are generalized in nature. There may be some variations with different designs. 8.1.0 Brief Cement Making Process The following are the basic steps for the cement manufacturing process: 1. Quarry: Basic raw materials, e.g., limestone, are mined and sent to the plant for crushing;

Flow in Plant Applications Chapter | XII

2. Crushing: Here big lumps of mined materials are crushed into smaller pieces for stacking; 3. Stacking and reclaiming: All raw materials such as limestone, shale, coal, etc. in smaller pieces are stacked (may be in an open place). During operation the materials are reclaimed by a suitable reclaimer for sending to a raw mill; 4. Raw mill: In the raw mill, which can be of different design, such as a roller press or ball tube type, for grinding the raw materials into fines suitable for pneumatic conveying; 5. Blending and storage silo: Before entry to raw mills, various ingredients in due proportions are discharged from different bins with the help of a set of conveyors with a weighing arrangement for regulated flow of raw materials. Proper blending is done at the blending silo with the help of air flow in the silo; 6. Kiln feed: Raw meal to be charged to the kiln through a preheater series are weighed properly to regulate the flow to the kiln; 7. Preheater: There is a series of preheaters (cyclone) associated with where raw meal is preheated (and may be precalcined also) prior to feeding the materials to the kiln. This is actually a heat transfer area where solid raw meal is heated by the gas coming out of kiln due to firing and reaction. In some installations there would be precalcinator also associated with preheater precalcinations of the raw meal prior to charging to the kiln. Basically the preheater is a part of the kiln; 8. Kiln with firing, secondary, and tertiary air: It is the place where the actual chemical reaction takes place for clinker formation. Details about the reaction are not yet well defined. Kiln firing is done with the help of a suitable burner design, which may vary with the supplier’s design. Oil and/or coal are used as the fuel for combustion. Air systems are: l Primary air: This is the air from the blower that goes directly to the kiln, primarily to bring the coal powder into the

9.

10. 11.

12.

13.

14.

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kiln and/or flame adjustments. Therefore, primary air is necessary for all types of burner l Secondary air: This is the air from the grate cooler that goes directly into the kiln, i.e., it flows from the kiln head to the tail. It is the main air necessary for combustion l Tertiary air: This is the air from the grate cooler, which bypasses the kiln and goes to the preheater/precalcinator to support combustion in the decomposing furnace through the tertiary pipes; Clinker cooler: Clinkers formed in the kiln are discharged to the clinker cooler, below which air is blown by a fan/blower to cool the clinkers. This is the clinker cooler. From the clinker cooler, cold (tempered) coolers are sent for the clinker silo; Clinker storage: This is the place where clinker is stored for subsequent use in the cement mill; Clinker grinding and additive: Clinker from the clinker silo is taken for grinding in the cement mill; normally ball mills are mostly used for this purpose. During the grinding process additives like gypsum, prozolona, etc. are added for cement making; Cement silo: Cement produced in the cement mill is conveyed to the cement silo after passing through separators, etc. The cement silo is the storage place for ground cement; Dispatch and packing: Cement is sold in the market in bags. Cement is also dispatched in trucks. There are many kinds of packing/bagging machine designs available; Utilities: There are many utilities normally found in cement plants. These are coal handling and storage systems, oil handling systems. Nowadays for the heat recovery process, boilers and power generation units are also incorporated within the plant as another utility.

Since there are silos in between, it is not necessary that the raw mill and/or cement mill has to run when the kiln is in operation. This indicates that this is a noncontinuous process.

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Clinker production is a very energy-intensive activity. Nearly 65%e70% of total variable costs are due to spending on energy. Therefore, it is needless to say that choosing fuels, the right blend of hot gases, and optimum burner control, along with cogeneration are of immense importance. In view of this, the following controls are very important and effective: l l l l

Kiln burner control and fuel injection; Clinker cooler package; Cyclone preheater and precalcinator control; Cogeneration (as applicable).

In all such cases flow measurements play a major role. Various kinds of solid flow measurement systems discussed in Chapter VIII are mainly deployed in this plant to account for various flows. We now look into some of these specialties. 8.2.0 Flow Measurement Specialties in Cement Plants 8.2.1 AIR FLOW MEASUREMENT BY TRIBO ELECTRIC METHOD Measurement of air flow is necessary for proper operation of the plant. However, major difficulties arise on account of heavy dust concentration in the medium. Typical such applications in air flows are for the following cases: l l l l l

Raw mill exhaust; Primary air; Secondary air (air from grate cooler); Tertiary air; Air flow from the cement mill.

Various issues related to measurement of gas flow laden with dust have been discussed in Section 1.1.0 above. Apart from these there are a few methods for air flow measurements by deploying tribo-electric principles. Each particle has a static charge associated with it. Each measurement requires two sensors located a defined distance apart. The sensors obtain a millivolt pattern from the passing particles. Each of the sensors obtains a similar pattern. With the help of a computer correlation is established between the sets of sensors. The velocity is the average

over the effective length used in the computer for flow measurement, similar to what has been discussed in Section 2.2.3 above. A similar system has been used in Shree Cement in India for plant optimization by The MECONTROL Air system. 8.2.2 ROTARY WEIGH/GRAVIMETRIC FEEDER The rotary weigh/gravimetric feeder has been discussed in Sections 3.1.1e3.1.3 in Chapter VIII. In cement plants these can be used in limestone and coal/coke flow measurements. The following are the major advantages: l l

l l l

Highly reliable system with long life; Online calibration is possible when pre bin is with load cell; Withstand heavy pressure fluctuations; Easier maintenance [32]; High accuracy in a wide flow range from 10% to 100% flow rate [32].

These are used for feeding and dosing control. They find their applications in the kiln process, grinding process, and mill residue to the cement mill. 8.2.3 MASS FLOW MEASUREMENT OF CEMENT FOR REDUCED CHROMATIC CONCRETE In order to reduce the risk of skin-related illnesses, in the case the somebody comes in contact with fresh concrete, there is an EU directive for the reduction of chromatic concrete. Mixing iron-sulfate to the cement production process limits chrome-VI to 2 ppm or less and circumvents the risk related to skin disease. Iron-sulfate is added to cement before it goes to the bag packaging area. Iron-sulfate dosing is done precisely, at around 0.5% of mass for best results [33]. It is necessary to measure the mass flow so that an accurate amount of iron-sulfate dosing can be calculated on line and can be added. Based on the Semrad document a typical such arrangement has been detailed in Fig. XII/8.2.0-1 (courtesy: Semrad).

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CEMENT SILO

M IRON

M

SULFATE CEMENT

TO BAGGING PLANT

FIGURE XII/8.2.0-1 Iron-sulfate dosing and mass flow measurement. For detailing refer to Fig. I/3.2.3-1. Developed based on an idea from Mass Flow Measurement on Cement at Lafarge Perlmooser GmbH, Application Report Mass Flow Meter MF3000 for Solids, Semrad, NSW. http://www.semrad.com.au/images/ Articles/Impact_Weigher_Alternatives/Case_Study_Flow_Meter_For_Cement_Plant.pdf. Courtesy: Semrad.

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As result of this one gets the following advantages also: l

l

l

On-line cement mass flow for bagging measurement; Optimized mixing of iron-sulfate to achieve regulated limits; Less iron-sulfate is required for the process [33].

The measurement is carried out by noncontact microwave technology discussed in Chapter VIII. On account of the following reasons microwave technology is chosen for mass flow measurement: 1. Noncontact on-line measurement of mass flow; 2. No weighing system involved; 3. Installed flush to inner wall, hence nonintrusive; 4. Simple welding to the pipe easy installation and setup; 5. Microwave is very suitable for free-fall applications with pneumatic conveying; 6. Available with various outputs (refer to Chapter VIII); 7. Simple, low-cost installation and start-up [33]. With this, the discussion on flow meter applications in cement plants comes to an end and we now investigate a few other applications in different plants.

9.0.0 FLOW MEASUREMENTS IN MISCELLANEOUS PLANTS In Section 1.0.0 flow applications and general issues common to many plants have been elaborated on. In Sections 2.0.0e8.0.0 specific issues and processes of specific plants and industries have been outlined. Apart from these, there will be many other plant types in existence. Although it is not possible to cover them all, some attempts have been made to include flow-related issues for these plants. Ethanol plants are popular and the discussions start with ethanol plant flow issues.

9.1.0 Flow Measurements in Ethanol Plants 9.1.1 ETHANOL PRODUCTION PROCESS Ethanol, which is same as ethyl alcohol, now finds industrial applications as well as a fuel. In the US it is mainly used as a fuel. The first automobile to completely use ethanol was manufactured in 1978 in Brazil. Major steps for manufacturing (dry mill) ethanol include the following: 1. 2. 3. 4. 5. 6. 7.

Milling; Liquefaction; Saccharification; Fermentation; Distillation; Dehydration; Denaturing.

There are a few byproducts available during the above process. During the process of conversion of corn into fuel ethanol, there is need for automation of production optimization. There is a need for flow controls in this process. Also, the process finds use various types of flow meters. Some of these are discussed in this section. 9.1.2 FLOW METER TYPES AND SELECTIONS A wide range of flow meters are used in this process for measurements of the speed, volume, and mass of slurries, liquids, and gases in pipelines. Major flow measuring fluids are: beer, stillage, syrup, enzymes, water, steam, CO2, and natural gas, as well as methane that is used as an alternate fuel [34]. 1. Flow meter types: There is a wide variety of flow metering devices and technology available for flow measurement purposes. These include but are not limited to the following: l Electromagnetic flow meter; l Ultrasonic flow meter; l Vortex meter; l DP type meter;

Flow in Plant Applications Chapter | XII

Variable-area flow meter; l Coriolis mass flow meter; l Thermal mass flow meter. 2. Flow meter selection: Of the various types of flow meter discussed, for different applications flow meters are selected on the basis of the following selection criteria: l Accuracy and repeatability of the measuring technology; l Requirement for temperature compensation and arrangement for compensated flow measurement with desired accuracy and repeatability; l Calibration matched to specific applications; l Wide turndown for accurate low and high flow rate measuring; l Multipoint sensing for large pipes, stacks, and ducts as required, with desired accuracy; l Ease to install the meter; l Cost-effectiveness; l Flow conditioning for limited straight-run applications. l

3.

4.

9.1.3 FLOW METER APPLICATIONS 1. Coriolis meter: During production, in order to reduce flow problems and enzyme usage and other costs, real-time measurement and control are necessary. This allows more consistency in the slurry mix solids and enables operators to push the solids percentage higher [34]. For continuous monitoring of solids concentration, Coriolis meters can be used to get high accuracy and repeatability in density measurements. The use of an on-line flow/density meter at the intermediate and final stages of the evaporator process helps in significant reductions in energy consumption for an evaporator. Coriolis mass flow meters can also be used for steam flow consumption. 2. Magnetic flow meter: Upstream of fermentation there is extensive use of in-line electromagnetic flow meters to measure flows with high solids content, e.g., corn slurry, mash, beer, as well as on whole, thick, and thin stillage [34]. As mentioned in Chapter V, electromagnetic flow meters are applied with

5.

6.

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due consideration towards performance limitations of pulsed DC type in noisy slurry applications. Therefore, meters with selfdiagnostic capabilities for detecting sensorcoating degradation and predicting electrode or liner failure will be important in making the selection. Thermal mass flow meters: Thermal mass flow meters are used to measure air flow and fuel flow for optimization of the combustion control of process heaters such as distillation tanks. Also, thermal flow meters can be used to measure the CO2 leaving the fermentation tanks and for steam consumption measurement as indicated below. Vortex mass flow and DP measurement: For measurement of steam flow used in cooking, dehydration, and evaporation, a vortex meter or DP meter can be used. However, these are volumetric measurements for mass calculations, and necessary compensation and flow computation would be essential. Saturated steam flow measurement by these could be problematic, so Coriolis and thermal mass flow meters can be used. Turbine meter: The turbine flow meter offers an accurate, compact, and economical solution for ethanol splash blending. The meter is easily incorporated into the blending stand equipment. Miscellaneous meter types: Where there is an issue with low conductivity, such as downstream of the rectification process, DP type, turbine type, vortex type, or USFM type flow meters can be applied. The turbine type, on account of moving parts, may pose problems like mechanical failure and problems due to coating.

9.2.0 Energy Consumption in Biogas In this section brief discussions are given on flow measurement of safe, clean, low biogas—greenhouse gas (GHG), landfill gas (LFG), and coal mine methane (CMM). The basic purpose of these metering systems is to account for energy

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provided by fueling with the various gases mentioned above. Energy consumption metering systems consist of a methane analyzer to measure the methane content of the gas supply by volume. Therefore, in order to accomplish this it is necessary to measure the flow of gas. A gas meter, like a swirl meter, can be installed to note the volumetric flow rate and by measuring pressure and temperature downstream of the flow meter, it is possible to get the mass flow. Associated with this a flow computer is utilized to perform the required calculations for total consumption in energy units [35]. 9.2.1 METER DETAILS As indicated in Subsection 7.4.1.3, vortex/swirl meters can measure the actual volume flow rate of LFG, CMM, and other biogases, independent of composition, with a high accuracy of 0.5% or better for a wide range of flow. There is a specialized meter using proprietary technology [35: courtesy: ABB] that can be used also. These meters meet high accuracy in wide flow range and are not influenced by external factors. They can communicate with dedicated computers for energy consumption measurement in various forms of electrical output types, e.g., analog/pulse output as mentioned in Chapter V. 9.2.2 MEASUREMENT REQUIREMENTS AND CONSTRAINTS The following are the basic measurement requirements: l

l

l

l

l

l

Low-pressure volumetric flow measurement of biogas; Very limited up- and downstream pipe diameters; Requirements of consistent accuracy and repeatability over the flow range even at the lower end; Ability for pressure and temperature compensation for mass flow computation; Suitability of meter design for hazardous applications; Availability of meters in various sizes.

9.3.0 Heat Consumption Measurements for Centralized Steam Supply There are many industrial parks, housing societies, commercial complexes, and shopping malls, etc., where there is a needs for steam and heat supplies for a number of uses from a centralized steam generator. Quite often these are either supplied from the municipality and/or from an external agency, which generates the steam from a centralized steam generator (SG) at a nearby place and it is then distributed to subscribers through insulated pipelines. This is applicable for any integrated plant where there may be different plants with separate profit centers which also receive steam from a centralized SG. In all these cases there is a need to account for the consumptions for billing purposes. Naturally the measurement of heat (from steam) accurately must be recorded by taking a variety of individual measurements. In order to measure heat it is necessary to monitor not only steam flow but also the pressure and temperature of steam supplies. With seasonal variations (winter and summer), high and low consumption patterns are noted. As a result of these there may be two sets of flow measurements with different nominal diameters often required for accurate energy flow measurement for billing purposes, as at the lower end (during summer) the required accuracy may not be achievable with a single metering system. The installation of two devices with graded nominal diameters is recommended for measuring points where fluctuations in consumption are so great that the measurement dynamics of one device are no longer sufficient [36]. In these applications vortex/swirl meters can be applied. Vortex/swirl meters can be used along with pressure/temperature measurement for heat calculations through computers. There are swirl/vortex meters which can be used in split range mode for switching (adjusting) between these flow ranges. 9.4.0 Flow Measurements in Breweries In a typical brewery, e.g., for beer manufacturing, the main issue is to extract sugar from grains

Flow in Plant Applications Chapter | XII

so that yeast can convert into alcohol with CO2 as waste byproduct. 9.4.1 BREWING PROCESS The major ingredients are barley, hops (a green cone-like fruit of a vine plant), water, and yeast. Ingredients for other spirits and alcohol manufacturing processes may be different, but a basic outline of the process has been described below. It is worth noting that in the brewing process practically everything flows. Naturally there is a wide range of applications of flow meters and flow meter types. 1. Malting: The harvested grains are processed through heating, drying out, and cracking for malting by isolating the enzymes for brewing. 2. Mashing: At this stage the grains are steeped (softening and extracting constituents) in hot, but not boiling, water for about an hour so that grains break down to release sugars. Excess water is drained to obtain a sticky, sweet liquid, which is called wort. 3. Boiling and additives: The wort is boiled for about an hour and hops and other spices are added to remove sweetness and give bitterness. These additives also act as preservatives. 4. Cooling process: After an hour-long boiling the wort is cooled, strained, and filtered. 5. Fermentation: After filtration, it is put into a fermenting vessel with yeast added to it for fermentation to begin. The beer is stored for a couple of weeks at room temperature. During fermentation, the yeast eats up all the sugar in the wort and gives out alcohol and CO2 as a waste byproduct. There are many some variations in timing and temperature for lagers, etc. 9.4.2 FLOW METERING IN THE BREWING PROCESS Flow monitoring is essential for breweries because flow monitoring can provide information on operational errors or issues such as leaks or blockages, etc. Also, such monitoring allows for quick action to be taken to resolve the issue and in turn this reduces waste. As such, energy balance and energy optimization are possible only through

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suitable monitoring of flow at different points in breweries. The benefits achieved by flow monitoring can impact on process management, the production of reports, and ultimately profits. As stated earlier, in the brewing process there is good scope of applications of flow meters. Mostly in-line type and clamp-on type meters are used in breweries. Electromagnetic, turbine, Coriolis, vortex/swirl, and USFM types are used in breweries. In this section short discussions will be given on these flow meters. 1. Turbine meters: Turbine type flow meters are quite common in flow measurements in brewery applications. Typical triclamp process connections, which allow easy installation and removal, are quite common in most breweries. In order to circumvent upstream and downstream straight length requirements, many of these meters use flow conditioners also. The stainless steel construction meets chemical compatibility of all liquids used in the brewing process, including water, and sterilization or cleaning chemicals. These are available with external power and outputs. These meters offer good accuracy in the tune of 1% AR. They are available in low-cost versions with slightly lower accuracies. These meters are available in different sizes to cater to the requirements of breweries. They also have built-in display/indication for both total volume and flow rate. 2. Electromagnetic flow meter: Breweries also use electromagnetic flow meters in those applications when conductivity of the fluids above the minimum value are required. Like turbine flow meters these are available in different sizes to meet the demands of brewing applications. In applications it has been found to be an ideal solution for supplying information on the measurement and tracking of beer through the brewing process. These meters are without any moving parts with very low pressure loss in the system. These flow meters can be used to track the entire system with good accuracies for measurements. Electromagnetic flow meters are frequently used for automatic transfer operations as well as in wine and juice flow measurements.

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3. Vortex/swirl meter: Since the process involves heating by steam, naturally vortex/swirl meters find good applications in this process. In order to increase temperature of steam heating, suitable controls are used. The steam flow from the steam header is measured and controlled with a control valve. The steam flows in these lines are typically monitored and regulated with the help of vortex/swirl flow meters. One of the most favorable characteristics for vortex meters over other types of meters is the minimal upstream and downstream straight pipe requirements. Also, with measurements of pressure and temperature downstream of the meter mass flow, energy computations are easier. 4. Ultrasonic flow meter: Globally, brewing plants use noninvasive ultrasonic flow meters. These are very suitable for retrofitting as well as greenfield projects. They are not only used for day-to-day monitoring, but are often used to demonstrate the performance of inspection parameters. As they are noninvasive, they minimize the risk of contamination, in addition to minimizing damage to the flow meter and disruption when the devices are installed and maintained. Typical and major applications include the measurement of thermal energy flow rates in mash containers, measurement of the cooling capacity of wort coolers, etc. Wherever mass flows need to be computed, they are done with the help of the temperature difference between the media intake and the discharge of the thermal energy flow. They accurately monitor the flow rate and display data on a screen. The major advantages of USFM are listed here: l Noninvasive: These are noninvasive flow and thermal measurements and it is easy to set-up measuring points very quickly. l Hygienic: As they are noninvasive, they are very hygienic, minimizing the chances of any contamination. Hence they are perfectly safe. l Totalizer: An integrated totalizer of the meter allows it to be used as an energy meter.

Flexibility: USFMs offer maximum flexibility for the measuring system and are easily adjustable. Also, a single unit can perform several tasks. l Diagnostics: USFMs normally have diagnostic features built in to make them versatile. 5. Coriolis mass flow meter: Mass flow is important for energy balance. Therefore, Coriolis mass flow meters, which are not disturbed due to profile deformations, are always preferable solutions. These meters also offer high accuracy. As noted earlier, cost and pressure loss are the only factors which limit their applications. These meters are available with various communication facilities so they can be integrated together to form a computer network for brewing process monitoring, The discussions on applications of flow meters in various processes including a few examples have been covered. There are many other applications, be they domestic, industrial, or commercial. Frankly speaking, there are hardly any plants which do not require flow measurement. We conclude the discussions with these application notes. l

With this the main discussions on plant flow measurement and control have been concluded. To supplement the discussions presented in the main chapters additional pertinent information is provided in the appendices to look into: Appendix Regime; Appendix Appendix Appendix Appendix Appendix Appendix

I: Unit Conversion and Flow II: Material Selection Guide; III: Mechanical and Piping Data; IV: Custody Transfer; V: Safety Life Cycle Discussions; VI: Enclosure Electrical Protection; VII: Device Communication.

I would be more than happy to share my experiences with the reader. This will bring fruitful results only when it could be utilized in some of the issues people are facing day to day in their plants. Any good suggestions are always welcomed.

Flow in Plant Applications Chapter | XII

LIST OF ABBREVIATIONS ABS Absolute AC Alternating current ADC Analog-to-digital converter AI Analog input AO Analog output AR Actual reading (in connection with accuracy) CCW(CW) Counterclockwise (Clockwise) CEP Condensate extraction pump CMRR Common mode rejection ratio CMV Common mode voltage COC Change over contact CPU Condensate polishing unit CS Carbon steel CV Calorific value/control valve DAS Data acquisition system DC Direct current DCS Digital control system DI Ductile iron/digital input DO Digital output DP Differential pressure DPT Differential pressure transmitter/transducer DSP Digital signal processing EMC Electromagnetic compatibility EMI Electromagnetic interference FC Fail to close (for valve) FO Fail to open (for valve) FRP Fiber glass reinforced plastic FSD Full-scale division (of calibrated span) (in connection with accuracy) HC Hydrocarbon HVAC Heating, ventilation, and air conditioning IC Integrated chip/internal combustion (engine) ID Internal diameter I/O Input/output I/P Current to pneumatic converter IS Intrinsic safety LCD Liquid crystal display

LED Light-emitting diode LHS Left-hand side LRL Lower range limit LVM Limit value monitor MS Mild steel (main steam) MUX Multiplexer MVT Multivariable transmitter NB Nominal bore NIST National Institute of Standards and Technology OD Outer diameter PLC Programmable logic controller PD Positive displacement PT Pressure transmitter or pressure temperature (P/T) PTFE Polytetrafluoroethylene PU Processing unit PVC Polyvinyl chloride PVT Pressure volume temperature RF Raised face/radio frequency RHS Right-hand side RPM Revolutions per minute RTD Resistance temperature detector SG Specific gravity/steam generator SIL Safety integrity level SPDT Single-pole double-throw SPST Single-pole single-throw SS Stainless steel STP Standard temperature and pressure (Fig. I/1.1.2-3) TD Turndown TC Thermocouple URL Upper range limit US Ultrasonic/United States USFM Ultrasonic flow meter VDU Visual display unit VFD Variable-frequency drive VM Valve manifold W/O Without/water in oil (emulsion) WRT With respect to

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Plant Flow Measurement and Control Handbook

REFERENCES [1] S. Basu, Plant Hazard Analysis and Safety Instrumentation Systems, Elsevier; IChemE, 2016. http://store.elsevier. com/Plant-Hazard-Analysis-and-Safety-InstrumentationSystems/Swapan-Basu/isbn-9780128037638/. https://icheme. myshopify.com/products/plant-hazard-analysis-and-safetyinstrumentation-systems-1st-edition. [2] F. Hauert, A. Vogl, Measurement of Dust Cloud Characteristics in Industrial Plants, Final Technical Report; Number: PL 910695, January 1995, http://www.fsa.de/fileadmin/ user_upload/pdf/forschung/exschutz_projektliste/F05-9301_ measurementDustclouds.PDF. [3] Daniel, How Today’s Ultrasonic Meter Diagnostics Solve Metering Problems Technical White Paper, Daniel Measurement and Control Application Note, Emerson Process Management. http://www2.emersonprocess.com/ siteadmincenter/PM%20Daniel%20Documents/NSFMW-2005How-Todays-USM-Diag-Solve-techWpaper.pdf. [4] J.G. Drenthen, M. Vermeulen, M. Kurth, H. den Hollander, Ultrasonic flow meter diagnostics and the impact of fouling, in: AGA Operations Conference, Krohne Oil & Gas, 2011. https://cdn.krohne.com/dlc/CONFPAPERS_ ALTOSONICV12_impact_of_fouling_en_120524.pdf. [5] Vortex Flow Meter Problems; Is There Any Reason Why Some Vendors’ Meters Would Work while Others Would Not; Control, October 2013. Internet document, http:// www.controlglobal.com/articles/2011/vortex-flowmeterproblems/. [6] E. Kelner, Flow Meter Installation Effects, Southwest Research Institute. http://asgmt.com/wp-content/uploads/ pdf-docs/2007/1/033.pdf. [7] S. Basu, A.K. Debnath, Power Plant Instrumentation and Control Handbook, Elsevier, November 2014. http:// store.elsevier.com/Power-Plant-Instrumentation-and-ControlHandbook/Swapan-Basu/isbn-9780128011737/. [8] ASME PTC 4.2 Pulverized Coal Flow Measurement System, Airflow Sciences Equipment, LLC. http://www. airflowsciences.com/sites/default/files/docs/ASME_PTC4.2_ System.pdf. [9] Pulverised Fuel Flow Meter, PfMaster, Data Sheet SS/PFMAS_2, ABB Limited. https://library.e.abb.com/ public/a2d6b9b46145085bc1257106003c5d36/SS_ PFMAS_2.pdf. [10] B.R. Singh, S.R. Valsalam, H. Pratheesh, K.T. Sujimon, C. Aditi, Real time pulverised coal flow soft sensor for thermal power plants using evolutionary computation techniques, Control and Instrumentation Group, Centre for Development of Advanced Computing, India, ICTACT Journal on Soft Computing (January 2015). Special Issue on Soft e Computing Theory, Application and Implications in Engineering and Technology, http://ictactjournals.in/paper/ IJSC_Splissue_Jan2015_Paper_5_911_to_916.pdf. [11] Measuring pulverised fuel: using electrostatic meters, Measurement Control Vol. 42/3 (April 2009). http://citeseerx.ist. psu.edu/viewdoc/download?doi¼10.1.1.955.8135&rep¼rep1 &type¼pdf.

[12] D. Miller, P. Baimbridge, D. Eyre, Technology Status Review of PF Flow Measurement and Control Methods for Utility Boilers, Report No. COAL R201 DTI/Pub URN 00/1445, PowerGen plc, 2000, http://citeseerx.ist.psu.edu/viewdoc/ download?doi¼10.1.1.557.8769&rep¼rep1&type¼pdf. [13] M.W. Motyka, Optimising Fuel Flow in Pulverised Coal and Biomass-fired Boilers, IEACCC Ref: CCC/263, IEA Clean Coal Centre, January 2016, https://www.usea.org/ sites/default/files/media/Optimising%20fuel%20flow% 20in%20pulcerised%20coal%20and%20biomass-%20fired %20boilers%20-%20ccc263.pdf. [14] Thermal Mass Flow Meter Supports Feedback Control Loop in Boiler System for Thermal Electric Power Generation, By H. Yaqi, Z.G. Zheneng Power Generation Co Ltd. and S. Craig Fluid Components International LLC, FCI. http:// www.fluidcomponents.com/assets/media/Articles/NinghaiPower-Plant-0713.pdf. [15] L. Rumbles, Importance of Flow Measurement for Separators, Emerson Process Experts Blog, Emerson Process Management. http://www.emersonprocessxperts.com/2014/ 01/importance-of-flow-measurement-for-separators/. [16] S. Mokhatab, Fundamentals of Gas Pipeline Metering Stations, January 2009. Tehran Raymand Consulting Engineers Iran; Pipeline & Gas Journal; Vol. 236 No.1, https://pgjonline.com/2009/03/10/fundamentals-of-gas-pipelinemetering-stations/. [17] M. Frey, Liquid Measurement Station Design, Class No. 2230.1, Daniel Measurement & Control, Inc. http:// metersolution.com/wp-content/uploads/2013/02/DensityMeasurement-3.pdf. [18] J. Dorothy, Real e Time Pipeline Leak Detection Using Volume Balancing, Siemens Industries Inc., Pipeline & Gas Journal. https://webservices.siemens.com/w1/efiles/automationtechnology/pi/techn_publications/Real_time_pipeline_leak.pdf. [19] D. Dunn, M. Klien, Oil pipeline leak detection & location; ultrasonic system meets critical app requirements, Flow Control (September 2010). https://www.flowcontrolnetwork. com/national-science-board-calls-fornominations/. [20] W. Baker, R. Pozarski, Overcoming Flow Measurement Challenges, Control Engineering, December 2015. http://www. controleng.com/single-article/overcoming-flow-measurementchallenges/0fe6399984c4cbbba306b13d595b7aca.html. [21] Pulp & Paper: Instruments and Solution for Pulp & Paper Industry, Yokogawa, India, Application note. https://www. yokogawa.com/in/library/resources/application-notes/pulppaper-instruments-and-solution-for-pulp-paper-industry/. [22] Pulp and Paper Flow Meter Guide, Pulp and Paper Process Solutions Guide, Emerson Process Management. http:// www2.emersonprocess.com/siteadmincenter/PM%20Micro %20Motion%20Documents/Pulp-Paper-PSG-Flowmeter.pdf. [23] Chemical Industry Solutions, Flexim Americas Corporation, USA, Product Catalog. http://www.flexim.com/sites/default/ files/public_downloas/buchemicalv1-1us_2015_rgb.pdf. [24] Controlling Air Content at Head Box Paper Plant, Cidra SONAR Track Technology. http://www.cidra.com/sites/ default/files/document_library/BI0185_AppNote_Head_Box_ Entrained_Air.pdf.

Flow in Plant Applications Chapter | XII

[25] FLUXUS F601, Technical Catalog, FLEXIM GmbH. http:// www.flexim.com/en/devices/portable-flowmeters-liquids/ fluxus-f601. [26] Beverage (Carbonated Drinks) e Utilities, Solutions Sales Training Reference; Emerson Process Management, Internet Document. http://www2.emersonprocess.com/ siteadmincenter/PM%20Micro%20Motion%20Documents/ Beverages-Utilities-PSG-MM055706.pdf. [27] Steel Manufacturer Improves Blast Furnace Efficiency with Integral Orifice Flow Meter, Metal and Mining, ROSEMOUNT 3051SFP, Emerson Process Management. http:// www.emerson.com/documents/automation/proven-result-steelmanufacturer-improves-blast-furnace-efficiency-integral-orificeflowmeter-en-73298.pdf. [28] Instruments and Solution for Iron & Steel Industry, YOKOGAWA India, Internet Document. http://www. yokogawa.com/in/technical-library/resources/application-notes/ instruments-and-solution-for-iron-steel-industry-pdf/. [29] ArcelorMittal Increases Reliability of Critical Furnace Cooling CircuitLeak Detection with High Performance Magnetic Flow Meters, Metals & Mining, ROSEMOUNT 8700 MAGMETER, Emerson Process Management. http://www2.emersonprocess.com/siteadmincenter/pm%20 rosemount%20documents/00830-1700-4727.pdf. [30] Application News, Turbine Flow meter Measures Argon Gas During Steel Manufacturing, Flow Technology, USA. http:// www.ftimeters.com/pdfs/application_notes/an100376_argon_ gas_steel_manufacturing.pdf. [31] CiDRA Minerals Processing Alumina Refining Process Solutions, CiDRA Minerals Processing, Inc., Internet Document. http://www.cidra.com/sites/default/files/document_ library/BI0349_Alumina_Brochure.pdf. [32] Solutions for the Cement, Power, Minerals & Steel Industry, Highly Accurate Feeding & Dosing Technology, FL Smidth Pfister. http://www.flsmidth.com/w/media/ Brochures/Brochures%20FLSmidth%20Pfister/Brochures/ IB00000kGBCM0715700016ENGallproductsmail.ashx. [33] Mass Flow Measurement on Cement at Lafarge Perlmooser GmbH, Application Report Mass Flow Meter MF3000 for Solids, Semrad, NSW. http://www.semrad.com.au/images/ Articles/Impact_Weigher_Alternatives/Case_Study_Flow_ Meter_For_Cement_Plant.pdf. [34] H. Narayan, Measurement Automation Strategy Key to Bio-ethanol Refinery Efficiency, Krohne Inc. https:// krohne.com/fileadmin/content/media-lounge/PDF-US/Ethanol_ 1_on_1.pdf.

1125

[35] ABB Swirl Flow Meter, Metering Gas in Biogas Plants, Application Description AG/PS110-EN, ABB Limited. https://library.e.abb.com/public/a9d27fd135c97cb8c1257a5b 00474a65/3KDE010056R3001-AG_PS110_EN.pdf. [36] ABB Swirl Flow Meter, Metering Heat From Steam, Application Description AG/PS 108-EN, ABB Limited. https://library.e.abb.com/public/a5672d92fe2b267dc12579f4 003c6dcf/3KDE010051R3001-AG_PS108_EN_05_2012.pdf.

FURTHER READING [1] Instrument Engineers’ Handbook, Process Measurement and Analysis, vol. 1, CRC Press, (Chapter 2 Flow Measurement). [2] M.A. Crabtree, Industrial Flow Measurement, The University of Huddersfield, June 2009. http://eprints.hud.ac.uk/ 5098/1/macrabtreefinalthesis.pdf&sa¼u&ei¼v66ttp_ccojmia lag7mnbq&ved¼0cdiqfjat&usg¼afqjcngao5vc1jsrrbjucjvkx otjjoah6q. [3] F. Frenzel, H. Grothey, C. Habersetzer, M. Hiatt, W. Hogrefe, M. Kirchner, G. Lütkepohl, W. Marchewka, U. Mecke, M. Ohm, F. Otto, K.-H. Rackebrandt, D. Sievert, A. Thöne, H.-J. Wegener, F. Buhl, C. Koch, L. Deppe, E. Horlebein, A. Schüssler, U. Pohl, B. Jung, H. Lawrence, F. Lohrengel, G. Rasche, S. Pagano, A. Kaiser, T. Mutongo, Industrial Flow Measurement Basics and Practice, ABB Automation Products GmbH. http://nfogm.no/wp-content/uploads/2015/04/IndustrialFlow-Measurement_Basics-and-Practice.pdf. [4] R.C. Baker, Flow Measurement Handbook, second ed., Cambridge university Press, 2016. [5] J. Khambekar, R.A. Barnum, Fly Ash Handling: Challenges and Solutions, February 2012. Power Engineering, http:// www.power-eng.com/articles/print/volume-116/issue-2/features/ fly-ash-handling-challenges-and-solutions.html&gws_rd¼cr& dcr¼0&ei¼rewPWvL8CsPPvgSv6ozwCg. [6] J. Marinelli, When Things Go Wrong: How to Address a Solids Flow Problem, July 2013. Powder and Bulk Solid, http://www.powderbulksolids.com/article/when-things-go-wronghow-address-solids-flow-problem#comments. [7] Flue Gas Desulfurization, Yokogawa Electric Corporation, 2014. https://www.yokogawa.com/library/resources/application-notes/ flue-gas-desulfurization/. [8] ABB Electromagnetic Flow Meter Process Master FEP500, Hydrocyclone Feed in Mining Industry, Application Description AG/MI101-EN, ABB Limited. https://library.e. abb.com/public/5cfa74e0b022d901c1257b040040fc2d/AG_ MI101_EN.pdf.

APPENDIX I

UNIT CONVERSIONS AND FLOW PROPERTIES

In this appendix various unit conversions for commonly used parameters pertinent to flow measurements have been covered. For important fluids density and viscosities have been indicated in tabular forms at specified temperatures. Also, this appendix includes various flow regimes and profile changes based on Reynolds number. The discussions start with unit conversions.

1.0.0 UNIT CONVERSIONS Unit conversions of pressure, temperature, density, length, viscosity, volume, mass, and flow units have been elaborated. Units are expressed with standard abbreviations. Appendix III may be referenced for unit conversions pertinent to force, torque, power, time, and energy.

3.

4.

5.

1.1.0 Pressure Conversions Prior to going for conversion it is better to get details about various explanations for pressure types normally encountered in process plants and used in various flow element sizing calculations. 1.1.1 EXPLANATION OF PRESSURE AND VARIOUS DEFINITIONS The following are detailed explanations of various pressure terms: 1. Absolute pressure: This refers to zeroreferenced against a perfect/absolute vacuum, i.e., absolute zero pressure (or no force). 2. Absolute pressure at a point: This is the actual pressure at a given point and is called

6.

7.

the absolute pressure when it is measured relative to an absolute vacuum. Gage pressure at a point: Gage pressure at a point is the pressure relative to the atmospheric pressure, i.e., it is relative to atmospheric pressure or in other words indicates how much the pressure is above or below atmospheric pressure. Vacuum pressure: Vacuum pressure represents pressures below atmospheric pressure and expressed in terms in absolute pressure. Normally it indicates the difference between the atmospheric pressure and the absolute pressure. It will be clear from an example: Condenser vacuum 0.1 kg/cm2A means that at the condenser pressure is 0.1 kg/cm2A. Draft: Basically this is the similar to a vacuum, but when it is indicated with respect to atmospheric pressure it is referred to as draft. It will be clear from an example: Furnace draft (
)300 wcl means that at the furnace, pressure is less than atmospheric pressure by a pressure equivalent to force exerted by 300 of water column at 68 F on unit area (in sq. inch). Atmospheric pressure: The atmospheric pressure is the pressure that a unit area experiences due to the force exerted by the atmosphere. Transfer equations: From these it is clear that gage pressure (Pgage) will be absolute pressure (Pabs) minus atmospheric pressure (Patm): Pgage ¼ Pabs
Patm

(AI/1.1.0-1)

1127

1128

Appendix | I

Vacuum (Pvac) will be the absolute pressure (Pabs) less than atmospheric pressure (Patm): Pvac ¼ Patm
Pabs

(AI/1.1.0-2)

Absolute pressure (Pabs) will be gage pressure (Pgage) plus atmospheric pressure (Patm): Pabs ¼ Pgage þ Patm

(AI/1.1.0-3)

These are explained in Fig. AI/1.1.0-1. Conversion factors of pressure into various units have been elaborated in Table AI/1.1.0-1.

1.2.0 Temperature Conversion Factors Temperature unit conversion factors for commonly used temperature scales have been indicated in Table AI/1.2.0-1. 1.3.0 Volume and Mass Conversion Factor 1.3.1 VOLUME CONVERSION FACTOR Volume unit conversion factors for commonly used volume-measuring scales have been indicated in Table AI/1.3.0-1.

TABLE AI/1.1.0-1 Pressure Unit Conversion Factors (mmwcl [ 0.1 mbar) atm

bar

kg/cm2

K Pascal

psi

mmwcl

Inch Hg

Torr

1

1.01325

1.033227

101.325

14.69595

10132.5

29.9216

760

0.986923

1

1.0176

100

14.50377

10000

29.5299

750.0617

0.967842

0.982704

1

98.0665

14.22334

9806.65

28.95903

735.5592

0.009869

0.01

0.010197

1

0.145034

100

0.295299

7.500617

0.068046

0.068948

0.070307

6.894949

1

689.4757

2.036021

51.7493

9.87Ee05

0.0001

0.000102

0.01

0.00145

1

0.02953

0.750062

0.033421

0.033864

0.034532

3.386398

0.491154

33.86388

1

25.4

0.001316

0.001333

0.00136

0.133322

0.019324

1.333224

0.03937

1

Pressure at a Point

Pgage

Pabs Atmospheric Pressure

Pvac Pabs

Patm

Patm Absolute Vacuum

FIGURE AI/1.1.0-1 Pressure definitions.

TABLE AI/1.2.0-1 Temperature Unit Conversion Factors Celsius

Fahrenheit

Kelvin

Rankin

1

33.8

247.15

493.47

0.0295858

1

255.9278

450.67

0.00404613

0.00390735

1

1.8

0.00202647

0.00221892

0.5555556

1

Appendix | I

1129

TABLE AI/1.3.0-1 Volume Unit Conversion Factors cc

cft

CubMt

gal

gal (UK)

Ounce

Pint

Liter

1

3.53E
05

1.00E
06

0.000264

0.00022

0.0338

0.00211

0.001

2.83Eþ04

1

0.02832

7.48051

6.2288

957.91

59.8441

28.3168

1.00Eþ06

35.3157

1

264.1721

219.9692

33,814

2113.39

1000

3786.445

0.13368

0.00379

1

0.83267

128

4546.095

0.16054

0.00455

1.200956

1

153.72

9.6076

4.556

29.57355

0.00104

2.96E
05

0.007813

0.006505

1

0.0625

0.02957

473.1936

0.01671

0.00047

0.125

0.104084

16

1

0.4731

1000

0.03531

0.001

0.264173

0.219491

33.818

2.11372

1

3.7854

Barrel Unit for oil: 1 Barrel ¼ 42 US gal; ¼158.94 L/0.159 m3.

1.3.2 MASS CONVERSION FACTOR Conversion factors for mass unit have been elaborated in Table AI/1.3.0-2. 1.4.0 Density (Specific gravity) and Viscosity Conversion Factors 1.4.1 DENSITY UNIT CONVERSION FACTORS Density unit conversion factors have been enumerated in Table AI/1.4.0-1.

1.4.2 DENSITY SPECIFIC GRAVITY OF A FEW SELECTED MATERIALS Specific gravity of a few selected liquid and gaseous materials have been enumerated. Table AI/1.4.0-2 Specific Gravity of Selected Materials. The specific gravities for liquids at 20 C have been indicated here. The density of gases is computed at  C at 1 atm pressure. The specific gravities of liquids are based on the density of

TABLE AI/1.3.0-2 Mass Unit Conversion Factors Gal H2O @328F

kg

lb

Metric ton

Ton

1

3.785

8.345

0.003786

0.003726

0.264201

1

2.205

0.001

0.000984

0.119832

0.453515

1

0.000454

0.000446

264.131

1000

2204.586

1

0.9842

268.3843

1016.26

2240.143

1.016054

1

TABLE AI/1.4.0-1 Density Unit Conversion Factors g/cm3

kg/m3

lb/ft3

lb/inch3

oz/gal

1

1000

62.43

0.03613

133.5265

0.001

1

0.06243

3.61E
05

0.133527

0.016018

16.01794

1

0.000579

2.138889

27.67783

2.77Eþ04

1728.011

1

3696

0.007489

7.48915

0.467532

0.000271

1

1130

Appendix | I

TABLE AI/1.4.0-2 Specific Gravity of Selected Materials Material

Type

Specific Gravity

Alcohol ethyl

Liquid

0.789

Alcohol methyl

Liquid

0.792

Ammonia

Gases

0.596

Benzene

Liquid

0.897

Butane

Gas

2.067

C4H10

Carbon dioxide

Gas

1.529

CO2

Carbon monoxide

Gas

0.9671

CO

Ethylene

Gas

0.9749

C2H4

Ethylene glycol

Liquid

1.0658

50%

Hydrogen

Gas

0.06952

H2

Nitric acid

Liquid

1.0554

10%

Sea water

Liquid

1.025

Sodium hydroxide

Liquid

1.109

10%

Sulfur dioxide

Gas

2.2638

SO2

Sulfuric acid

Liquid

1.066

Remarks

NH3

water at 15.6 C. The specific gravities of gases given here are based on the density of air at  C at 1 atm pressure as 1. 1.4.3 VISCOSITY UNIT CONVERSION FACTORS Viscosity unit conversion factors have been enumerated in two tables: Table AI/1.4.0-3 (absolute viscosity) and Table AI/1.4.0-4 (kinetic viscosity). Viscosities of a few important liquids have been presented in Table AI/1.4.0-5. Viscosities of a few important gases have been presented in Table AI/1.4.0-6.

TABLE AI/1.4.0-3 Absolute Viscosity Conversion Factors Centipoise

Pascal-s

lbm/ft-s

Poise

1

0.001

6.72E
04

0.01

1000

1

0.0672

1.00Eþ01

1.49Eþ03

14.8809524

1

14.87

100

1.00E
01

0.0672495

1

TABLE AI/1.4.0-4 Kinetic Viscosity Conversion Factors Stoke

Centistoke

ft2/s

cm2/s

1

100

0.001076

1

0.01

1

0.00001076

0.01

929

1000

1

929

1

1437

0.001076

1

1.5.0 Length Conversion Factors Length (distance) unit conversion factors have been enumerated in Table AI/1.5.0-1. 1.6.0 Flow Conversion Factors Flow rate can be volumetric or mass flow rate. Unit conversions for both volumetric and mass flow rates have been indicated below. 1.6.1 VOLUMETRIC CONVERSION FACTORS Volumetric flow rate unit conversion factors are given in Table AI/1.6.0-1. 1.6.2 MASS FLOW RATE CONVERSION FACTORS Mass flow rate unit conversion factors are given in Table AI/1.6.0-2.

Appendix | I

1131

TABLE AI/1.4.0-5 Viscosity Values of Selected Liquids Materials

Absolute Viscosity

Temperature (8C)

Liquid Type

Benzene

0.6

24

Newtonian

Butter fat

20

65

Newtonian

Chocolate

280

49

Thixotropic

Cod oil

32

38

Newtonian

Condensed milk

40e80

40e50

Newtonian

Cottage cheese

30,000

18

Thixotropic

Cream 50% fat

55

32

Newtonian

Ethyl alcohol

1.07

24

Newtonian

Ethylene

18

21

Newtonian

Fruit juice

55e75

18

Newtonian

Polyester

3000

30

Thixotropic

Resin solution

880 (7140)

24 (18)

Thixotropic

SaucedApple

500

80

Thixotropic

Sodium hydroxide 30% (40%*)

1.0 (*20)

18 18

Newtonian

Toothpaste

70,000e100,000

18

Thixotropic

Yoghurt

152

40

Thixotropic

TABLE AI/1.4.0-6 Viscosity Values of Selected Gases Gaseous Material

Viscosity (CP) at 208C

Viscosity (CP) at 1008C

Viscosity (CP) at 1008C

Ammonia

0.0099

1.30

1.68

Benzene

0.0075

0.0094

0.012

Carbon dioxide

0.0147

0.0185

0.0230

Carbon monoxide

0.0174

0.0210

0.0252

Chlorine

0.0132

0.0169

0.0210

Ethylene

0.0103

0.0128

0.0154

Methane

0.0110

0.0135

0.0163

Steam

0.0097

0.0124

0.0162

Sulfur dioxide

0.0126

0.0164

0.0209

1132

Appendix | I

TABLE AI/1.5.0-1 Length (Distance) Unit Conversion Inch

Foot

Centimeter

Meter

Yard

1

0.083

2.54

0.0254

0.02777778

12

1

30.48

0.3048

0.333333

0. 3937

0.0328

1

0.01

0.0109361

39.37

3.28

100

1

1.09361

36

3

91.44

0.9144

1

TABLE AI/1.6.0-1 Volumetric Flow Rate Unit Conversion Factors gal/h

Imp.gal/h

LPM

LPH

m3/h

oz/min

y3/h

1

0.83267

0.06309

0.001052

0.003785

2.133333

0.004951

1.200956

1

0.07576

0.001263

0.004546

2.562

0.005946

15.850372

13.1995776

1

0.016667

0.06

33.814

0.07847

951.02235

791.974657

60

1

0.001

0.563567

0.001308

2.64Eþ02

219.973603

16.666667

0.277778

1

563.567

1.30795

0.4687501

3.90E
01

0.0295735

0.000493

0.001774

1

0.00232

201.9794

168.180289

12.743724

0.212395

0.764555

431.0345

1

TABLE AI/1.6.0-2 Mass Flow Rate Unit Conversion Factors g/min

g/s

kg/min

kg/h

mt.ton/h

lb/min

lb/h

1

0.166667

0.001

0.06

6.00E
05

0.002205

0.132277

60

1

0.06

3.6

0.0036

0.132277

7.93662

1000

16.66667

1

60

0.06

2.2046

132.276

16.66667

0.277778

0.166667

1

1.00E
03

0.03674

2.2044

1.67Eþ04

277.7778

16.66667

1000

1

36.7437

2204.622

453.5924

7.5599

0.4535924

27.21554

0.0272155

1

60

7.55987

0.1259979

0.0075598

0.453588

4.54E
04

0.016667

1

Appendix | I

Appendix III may be referenced for unit conversions pertinent to force, torque, power, time, and energy.

with average velocity v, the pressure loss Hv can be expressed in terms of length of pipe by the Darcy-Weisbach equation: L v2 Hv ¼ l$ $ D g

2.0.0 FLOW PROPERTIES In this part a few flow properties are discussed further. We start with flow regime and Reynolds number. 2.1.0 Flow Regime and Reynolds Number From the discussions in Chapter I it has been noted that at low flow, i.e., at low velocities and high viscosities, the fluid particles move in an orderly manner in layer forms, as already discussed. The fluid flows in layers, meaning in well-ordered adjacent sliding layers. This is known as laminar flow. Before we move on it is better to recall Reynolds number as the unitless quantity. The Reynolds (Re) number is a quantity which by definition, as already explained, takes into account both velocity and viscosity, and is used to estimate the flow regime, i.e., if a fluid flow is laminar or turbulent. This is important, because increased mixing and shearing occur in turbulent flow. When the Re is between 0 and 2300 it is laminar. Reynolds number is critical at 2300, as at this point with reasonable accuracy the transition takes place. Therefore, Re values between 2300 and 4000 are the transition flow regime. Reynolds numbers above 4000 mean turbulence starts, so Re > 4000 is turbulent flow. These are shown in Fig. AI/2.1.0-1. 2.2.0 Pressure Loss and Reynolds Number Pressure loss is an important parameter in fluid flow measurement and it varies with the type of fluid, as well as the type of meter used. In a straight pipe with internal diameter D, fluid flows LAMINAR

Re 0

(AI/2.2.0-1)

where l is the resistance coefficient g is acceleration due to gravity. The resistance coefficient is dependent on Reynolds number. With laminar flow (Re < 2300) the resistance coefficient is independent of pipe roughness and is given by l ¼

64 Re

(AI/2.2.0-2)

However, from the start of any turbulence, i.e., at transition as well as in turbulent flow, it is given by the Prandtl-Colebrook equation
   1 l1=2 ¼
2 log 2:51 Rel1=2 (AI/2.2.0-3)  þ ðK=Dh Þ=3:72 Here K is pipe roughness, and Dh is hydraulic diameter, which for a full pipe is equal to D. Relative roughness D/K is normally available in tabular forms in piping handbooks.

3.0.0 SOLID FLOW PROPERTIES In this section, the properties of solid flows discussed in Chapter VIII have been consolidated to arrive at the numerical expression for flowability. 3.1.0 Solid Flow Characteristic Features and Essential Properties For flow of bulk solid material flow properties are quite important to address flow problems, i.e., flow obstructions, segregation, irregular flow, flooding, etc. When the discussions on material properties discussed in Section 1.2.0 of Chapter VIII are

TRANSITION

Re 2300

1133

TURBULENT

Re 4000

Re: Reynolds number decides flow

FIGURE AI/2.1.0-1 Flow regime and Reynolds number.

1134

Appendix | I

recalled one would find that the flow properties depend on several main parameters: l l l l l

Particle Particle Particle Particle Particle

size distribution; shape; chemical composition; moisture content; temperature.

Often it is assumed that the behavior of a bulk solid is like that of fluids. This is not correct in many cases, so such assumptions often are misleading. The major important issues already discussed have been consolidated here as these are very important. Stress: This is because of the fact that in Newtonian fluids the stresses in all directions should be of equal magnitude. However, the behavior of a bulk solid is quite different from that. Adhesive forces: As indicated in Chapter VIII, the flowability of a bulk solid depends on the adhesive forces between individual particles. For fine-grained, dry bulk solids, adhesive forces due to van der Waals interactions play an important role. Wall friction: Friction between the wall and solid surface of bulk materials. Liquid bridge: For moist bulk solids, liquid bridges between particles usually are most important. 3.2.0 Flowability for Solid Flows Flowability represents flow behavior. Good flowability means that bulk solid flows easily, i.e., it does not consolidate much and flows out of a container such as a “silo” or “hopper” by the force of gravity alone, without the aid of promoting devices such as vibrator. In contrast to this are

products that are “poorly flowing” when they experience flow obstructions or consolidation during storage or transport. These are all qualitative statements. These can be expressed in quantitative forms also. However, prior to that it is important to know what flow in bulk solids is. “Flowing” means that a bulk solid is deformed plastically due to the loads acting on it. The magnitude of the load necessary for flow is a measure of flowability. This can be demonstrated with the uniaxial compression test. There are a number of factors which influence flowability as already discussed in Sections 1.2.2 and 1.2.3 of Chapter VIII. So, major factors are listed here: l l l

Time consolidation (caking); Yield limit; Mohr stress circles.

Flowability can be characterized numerically by its unconfined yield strength (sc) in relation to consolidation stress (s1), and storage period, t. Usually the ratio ffc of consolidation stress, s1, to unconfined yield strength, sc, is used to characterize flowability numerically as: s1 (AI/3.2.0-1) ff c ¼ sc Flowability characteristics based on numerical values have been illustrated in Fig. AI/3.2.0-1 to show flowability characteristics from free flowing to not flowing. As indicated earlier, flowability-related properties are: angle of repose, bulk density, friction forces, and compressibility.

FIGURE AI/3.2.0-1 Flowability characteristics.

APPENDIX II

MATERIAL SELECTION GUIDE

In this section short discussions will be presented on how materials are selected for flow meters. This is discussed in three parts, i.e., background chemistry discussions, general material selections with pros and cons of materials normally encountered in flow metering, and specific discussions on a few flow meters, such as Coriolis mass flow meters for fluids, electromagnetic flow meters, and turbine meters to name a few. It is worth noting that standard materials charts are available with almost all meter manufacturers, as well as on the internet, so these are not repeated in this book. These charts may be consulted for any specific process material. From the chart one can get a number of materials available for particular process fluid. With these materials in mind one has to look into the material chart offered by the manufacturers (or the book) for the closest material available. If the closest material is not available for a product then it may not be selected and alternatives should be looked for. The discussions in this book are meant for the reader to develop a basic idea of why material selection is important and how to carry out the same to get better result from their selections.

1.0.0 BRIEF DISCUSSIONS ON CHEMISTRY 1.1.0 Background Chemistry for Material Selections for Flow Meters Often it is a misconception in the mind of many designers that it is enough to select the materials for meter matching with the alloys selected for

the piping system. This is not always true, because piping materials are selected on general corrosion considerations, whereas in the case of flow meters/flow elements localized corrosion or cyclic loading and abrasion considerations needs to be considered, e.g., the main steam pipes may be made up of alloy steel but flow nozzles are selected from 316 SS normally. Since flow meters and metering pumps (need to produce desired output performance and) may be subject to widely variable environments, naturally it is extremely difficult to find possible material combinations to meet process fluid compatibility. Halogen concentration, pH, chemical potential, and temperature are major factors in selecting suitable materials for the application. If these variables can be defined for a particular environment, comparisons of alloy limitations can be made and a compatible material of construction chosen [1]. 1.1.1 CHEMICAL REACTION ISSUES FOR SOME METALS In this section brief discussions are given on major causes of chemical reactions of metals (selected metals only). 1. Halogens: As we know, halogen refers to elements like chlorine, fluorine, bromine, and iodine with the Cl
ion being the most commonly available ion. Stainless steel is suitable for many applications but is not really a good solution when Cle ions are present (except very low levels). Temperature and 1135

1136

Appendix | II

moisture make things worse. Pitting and corrosion fatigue are common problems in such cases. Nickel alloy C22 could be used. In operation temperatures of about 540 C, nickel, Inconel 600, and Hastelloy B are extremely resistant alloys. Hastelloy C is suitable for service up to 480 C. 2. pH: The pH of a solution is an indication of its acidity or alkalinity and also influences the corrosion behavior. A solution with pH near 7 is neutral and naturally will be less aggressive. Strong acidity (pH < 3) and alkalinity (pH > 11) would be very corrosive. Nickel alloy C22, Tantalum, and also 316SS (to some extent) have good corrosion resistance in neutral and acidic environments. In alkaline applications, Nickel alloy C22 is recommended. 3. Chemical potential: The chemical potential or redox potential (H2 / 2Hþ þ 2e
half reaction is considered as the basis for definition) is a measure of the oxidizing or reducing power of a process fluid. Chemical potential is often defined relative to this. Chemical potentials that are equal to or less than the reference are considered reducing, while chemical potential greater than the reference is considered oxidizing. A minimum amount of oxidizing power is required to enable the formation of protective surface oxide. Excess oxidizing or reducing will prevent stable oxide formation [1]. Inconel and Monel have good corrosion resistance and are often used in offshore and power applications with sea water. 4. Charts: Based on the above discussions a chart showing some selected materials against these chemical issues discussed in Subsections 1.1.1.1 through 3 has been depicted in Fig. AII/1.1.0-1. 1.2.0 Corrosion Corrosion is an important phenomenon which can deteriorate the performance of flow meters as well as control valves or metering pumps. In this section brief discussions will be presented to give some idea of this.

1.2.1 DISCUSSIONS ON THE CORROSION PROCESS Corrosion is a very complicated mechanism that occurs due to electrochemical reactions. Corrosion is the deterioration of a metal as a result of chemical reactions between it and the surrounding environment. The presence of apparently unnecessary factors like humidity, temperature, contaminants, or metal chlorides manipulates the corrosion level. Both “type of metal (material)” and the “environmental conditions (especially gases)” in contact with the metal, determine the form and rate of deterioration due to corrosion. General corrosion occurs when the atoms on the same metal surface are oxidized and damage the entire surface. When reduction and oxidation take place on different kinds of metal in contact with one another, the process is called galvanic corrosion. This occurs mainly in electronic devices. Some metals acquire a natural passivity, or resistance to corrosion. This occurs when the metal reacts with, or corrodes in, the oxygen in air. The result is a thin oxide film that blocks the metal’s tendency to undergo further reaction. All metals corrode but some corrode faster while some corrode slower such as; when pure iron, corrode quickly but SS is slower. Noble metals, such as silver, platinum, and gold, are much less reactive than others. 1.2.2 TYPES OF CORROSION PROCESS Various metallic corrosions can be avoided by adding alloys to a pure metal. Others can be prevented by a careful combination of metals or management of the metal’s environment. There are many types of metallic corrosions and these are enumerated below: 1. General corrosion: This is the most common form of corrosion, which is a uniform attack on the entire surface of a metal structure, caused by chemical or electrochemical reactions. It is a known and predictable result on account of the uniform attack that proceeds uniformly over the entire exposed surface area to cause metal to fail finally after becoming thinner.

Appendix | II

1137

FIGURE AII/1.1.0-1 Chemical conditions and material behavior. (A) Material reaction with chloride ion concentration. (B) pH variations. (C) Chemical potential variations. Developed based on Micro MotionÒ Corrosion Guide for Coriolis Flow and Density Meters, Density meters, and Viscosity Meters, GI-00415, Rev H, Micro motion; Emerson Process Management, January 2014; http://www2.emersonprocess.com/ siteadmincenter/PM%20Micro%20Motion%20Documents/Corrosion-Guide-GI-00415.pdf. Courtesy: Emerson Process Management.

1138

Appendix | II

2. Localized corrosion: Localized corrosion attacks a very specific location of a metal structure under a specific set of conditions. This is a very important consideration for flow meters. There are several types of localized corrosion such as pitting, crevice attack, and microbially influenced corrosion (MIC), to name a few: l Pitting: Pitting is a form of very localized corrosion that creates initially small holes in the surface of a metal. These small holes can propagate very quickly, leading to material perforation and failure in a very short period of time. l Crevice corrosion: These occur in stagnant locations. such as those found under gaskets. The microenvironment within the crevice can greatly differ from the general medium. This can progress very fast. l Filiform corrosion: Corrosion that occurs when water gets under a coating such as paint and creates weakness. l Microbially influenced corrosion (MIC): MIC is a form of crevice attack caused by certain types of bacteria forming domeshaped colonies on the metal surface. The inside of the structure is sealed from the outside. The life cycle of the bacteria produces a corrosive environment within the colony which causes a crevice attack of the metal. There are a few other types of fatigues and corrosions such as the following: l Corrosion fatigue: Reduction of fatigue resistance; l Stress corrosion cracking: Presence of stress tensile stress with corrosion; l Liquid metal cracking: A special form of stress cracking; l Hydrogen embrittlement: Common in boiler tubes (i.e. molecular hydrogen coming out of metal surface); l Intergranular corrosion: Selective attack of a metallic component at the grain boundaries by fluid.

3. Environmental cracking: This attack occurs as a result of chemical conditions within the environment and the mechanical condition of the metal itself. This can cause cracking, fatigue, or embrittlement. 4. Galvanic corrosion: As explained earlier, galvanic corrosion results from the electrical coupling of two dissimilar metals in a corrosive medium resulting in the attack of the less resistant metal. The less noble material becomes anodic, while the more noble becomes cathodic. The anodic material actually protects the cathodic, leading to its own accelerated decay. The farther apart the materials are in the series, the greater is the likelihood of attack of the less noble material. 5. Erosion corrosion: Erosion corrosion is an acceleration in the rate of deterioration or attack on a metal because of relative movement between a corrosive medium and the metal surface. With rapid movements this can cause mechanical wear or abrasions. 6. Dealloying: Dealloying is the selective removal of one element of a solid alloy by a corrosion process. A common example is dezincification. For an effective prevention system, it starts at the design stage with a proper understanding of the environmental conditions and metallurgical properties. It is essential to have good knowledge of possible chemical interactions.

2.0.0 FAMILIARIZATION WITH COMMONLY USED MATERIALS This section basically give a brief account of the materials as a guide and general aid in selecting the appropriate materials to be used in flow applications. Because chemicals and their properties can vary greatly, this is to be used at your discretion. 2.1.0 Metals and Alloys In this section commonly used metals for flow metering have been discussed.

Appendix | II

1139

2.1.1 STAINLESS STEEL

2.1.2 CAST IRON AND CARBON STEEL

Discussions on some stainless steel types are discussed here.

1. Cast iron: This is an alloy of iron, carbon, and silicon. It can be easily cast. Cast iron has excellent dampening properties and is easily machined. The cost of cast iron is moderately favorable compared with stainless steel and it is often selected for industrial water treatment chemicals when acceptable [2]. 2. Carbon steel: Both carbon steels and stainless steels contain iron, which oxidizes when exposed to the environment, creating rust. It is an alloy of iron and carbon, with the carbon content up to a maximum of 1.5%e2.0%. Carbon steel does not typically have enough chromium to form this chromium oxide layer, allowing oxygen to bond with the iron which results in iron oxide, or rust. The mechanical properties in some cases are very close to SS however, it depends on many different types and grades of each. They are less ductile when compared with SS because of nickel. Its temperature-withstand capability is nearly up to 300 C.

1. 17-4 PH stainless steel: This is a hardening stainless steel with high strength and hardness. It can withstand corrosive attack. There are three main types of PH stainless steel: low-carbon martensitic, semiaustenitic, and austenitic. 2. 301 stainless steel: This exhibits corrosion resistance similar to 304SS listed below. It is a good choice as a metallic diaphragm material. 3. 303 stainless steel: This stainless steel features physical properties that make it a good choice as a metallic diaphragm material with limited compatibility with a number of process fluids. 4. 304 stainless steel: This is often used as a casing material, as it is less expensive than SS316, which can better withstand corrosion attack. 5. 316 stainless steel: This is an alloy of iron, carbon, nickel, and chromium. It is a nonmagnetic stainless steel with ductility. It belongs to the group of austenitic stainless steels. This is essentially nonmagnetic and cannot be hardened by heat treatment. The nickel content contributes to the improved corrosion resistance, and it is also responsible for the retention of the austenitic structure. 316 stainless steel has excellent corrosion resistance to a wide range of chemicals. It is not susceptible to stress corrosion cracking. It is not affected by heat treatment. 316 stainless steel is the most widely used material in instruments deployed in process plants. 6. 430 (430F) stainless steel: 430 stainless steel is a ferritic, straight chromium alloy. This alloy is nonhardenable but has excellent corrosion resistance at higher temperatures and possesses average mechanical properties. This grade is easily formable, making it excellent for large complex geometries. It finds its use in flow meters, e.g., turbine flow meters.

2.1.3 HASTELLOY TYPES Hastelloys are material in the nickel-molybdenum family of alloys. 1. Hastelloy B: This has excellent resistance to hydrochloric acid at all concentrations and temperatures. Hastelloy B exhibits high thermal stability and excellent resistance to sulfuric, acetic, formic, and phosphoric acids, and other nonoxidizing media. 2. Hastelloy C: Hastelloy C also contains chromium. It exhibits outstanding resistance to a wide variety of chemical process environments, including strong oxidizers such as sodium hypochlorite and ferric chloride. Hastelloy C is also resistant to nitric, hydrochloric, and sulfuric acids at moderate temperatures.

1140

Appendix | II

2.1.4 NICKEL, MONEL, AND INCONEL TYPES 1. Nickel: Nickel shows good mechanical properties coupled with aqueous corrosion resistance. These are good for use in caustic soda and synthetic fiber production, and for food handling, etc. There are two kinds of alloys: nickel 200 and 201. Nickel 201 has low carbon and can prevent intergranular embrittlement at above 600 F (315 C). 2. Monel: This is an NieCu alloy with high strength and excellent resistance to a range of media including seawater, dilute hydrofluoric and sulfuric acids, and alkalis. Monel 400 finds its use in marine and offshore engineering. Monel K500 is another Monel alloy. 3. Inconel: This is an NieCreFe alloy with resistance to stress-corrosion cracking and caustic corrosion, and with high-temperature strength and oxidation-resistance. There are many alloys of Inconel and they find their use in instrumentation in corrosion applications. There are several alloys of Inconel available, including Inconel C276, 622, 600, 725. At ambient temperatures Alloy-400 (67Nie33Cu) has good resistance to most of the nonoxidizing acids. It also resists nonoxidizing salts. The nickel in the alloy improves its resistance toward alkalis. It is more susceptible to hydrogen permeation. In Alloy C-276 (54Nie16Moe16Cr), chromium and molybdenum are added to nickel to improve the alloy’s resistance to oxidizing conditions. This alloy also retains a considerable degree of resistance to nonoxidizing conditions. 2.1.5 TANTALUM AND TITANIUM 1. Tantalum: Tantalum surface alloys offer a new route to corrosion resistance in severe corrosion environments. Tantalum, having wide acceptance in the chemical industry, is a very useful material in corrosive applications involving hydrochloric acid and acidic ferric chloride solutions. Tantalum has good strength even at elevated temperatures. Its high strength allows thin sections to be used. It is very expensive.

2. Titanium: Whenever titanium is exposed to the atmosphere or to any environment containing oxygen, it immediately acquires a thin tenacious film of oxide (TiO2, Ti2O3, and TiO). Titanium’s corrosion resistance comes from a protective oxide film which is strongly adherent and stable. A stable, substantially inert oxide film provides the material with outstanding resistance to corrosion in a wide range of aggressive media including and particularly to highly corrosive environments with oxidizing and chloride-containing process streams. However, strong reducing media may cause heavy corrosion. 2.2.0 Nonmetallic Commonly Used Materials There are a number of nonmetallic materials used for flow-metering purposes. These are described here. 2.2.1 NONMETALLIC NONELASTOMERIC MATERIALS Following are commonly used nonmetallic and nonelastomeric materials in flow metering. 1. Acrylic: This is a kind of plastic offering resistance to many chemicals and which is clear like glass (also referred to as acrylic glass) and is in some cases preferred to other plastics. 2. Ceramic: High alumina (96%e99.5% Al2O3) content ceramics find their applications in flow meters and bearings. Ceramic has the advantages of having a high level of hardness while being very corrosion-resistant to a wide range of chemicals even at elevated temperatures. This is, however unsuitable for hydrofluoric, hydrofluorosilicic, and hydrochloric acids. 3. Polyethylene and polypropylene: Polyethylene shows very good chemical resistance to strong acids, bases, and is also resistant to some oxidants and reducing agents. Polypropylene offers very high chemical resistance to all the above cases and organic solvents. However, it is slightly lower in physical properties compared to PVC and it is not very effective in not strong oxidizing acids, chlorinated hydrocarbons, or aromatics.

Appendix | II

4. PVC: PVC is the most common form of thermoplastic material, which is characterized by high physical properties and resistance to corrosion and chemical attack by acids, alkalis, salt solutions, and many other chemicals. It cannot withstand high temperatures, with a maximum limit of between 50 and 60 C. It is not successful in handling ketones, some chlorinated hydrocarbons, and aromatics [2]. 5. PVDF: This is a strong and abrasion-resistant fluorocarbon material [2]. It resists distortion and retains most of its strength to 135 C. PVDF is excellent with most acids, bases, and organic solvents. 2.2.2 NONMETALLIC ELASTOMERIC MATERIALS These are some materials which are used as seals, O-rings, and linings. There are many such materials and some of them are registered trademarks of some chemical/metallurgical companies. The majority of these materials are listed below: 1. Aflas: This is a type of polymer and is resistant to petroleum products and phosphate-esters. Temperature range
30 to 210 C. It is typically used for O-rings in various pump models. 2. Buna N: This is known as nitrile rubberda general purpose oil-resistant polymer. Service temperature is in the range of w
30 to 80 C. It is resistant to most solvents, oils, water, and hydraulic fluid. 3. EPDM: EPDM has good abrasion and tear resistance and offers excellent chemical resistance to a variety of acids and alkalis. It is not recommended for applications involving petroleum oils, strong acids, or strong alkalis. Service temperature is in the range of w
30 to 120 C. 4. Kalrez: This is a highly expensive material but at times is the only choice available when others are not suitable because it shows chemical resistance to most of the chemicals normally used. It can withstand temperatures up to 170 C. 5. PEEK: This is a high-performance engineered thermoplastic that can be used as a diaphragm material. It can withstand temperatures up to nearly 300 C.

1141

6. PTFE: This is very common and offers outstanding resistance to chemical attack by most chemicals and solvents. Service temperature range w
30 to 150 C. 7. Viton: This is compatible with a broad range of chemicals (not suitable with methanol) [2]. The Viton O-ring is common. Service temperature range w
30 to 150 C.

3.0.0 MATERIALS AND USES IN SELECTED FLOW METERS In this section short discussions will be presented on various materials used in different flowmeasuring instruments. This is a generalized discussion and there can be several variations also. As this is based on applicable fluids there will be variation in materials, so material specifications given here mainly pertain to wetted parts only. In main text some of these have been covered, these are given here in a consolidated manner. Only a few commonly used materials from reputed manufactures have been presented here. Readers should use their discretions in consultation with the manufacturer(s). 3.1.0 Coriolis Mass Flow Meter for Fluid Meter Tube 1. Stainless steel 1.4571, 1.4435, Tefzel-lined 316L; 2. Hastelloy C; 3. Nickel alloy C22; 4. Tantalum; 5. Titanium. 3.2.0 Differential Pressure Transmitter The following materials are used in process transmitters (DPTs) for flow elements. 1. Diaphragm: commonly used materials are listed here: l 316L SST (UNS S31603); l Alloy C-276 (UNS N10276); l Alloy 400 (UNS N04400); l Tantalum (UNS R05440); l Gold-Plated Alloy 400; l Gold-Plated 316L SST.

diaphragm

1142

Appendix | II

2. Drain vent valves: Materials for drain and vent valves include the following: l 316L SST (UNS S31603); l Alloy C-276 (UNS N10276); l Alloy 400/K-500 (Drain vent seat: Alloy 400; Drain vent stem: Alloy K-500). 3. Process flange/adapter: Process flange and adapter materials include the following: l Plated carbon steel; l CF-8M (Cast 316 SST) (UNS J92900); l Cast C-276: CW-12MW-1 (UNS N10276); l Cast Alloy 400: M-30C (UNS N04400). 4. O-ring: O-ring materials include the following: l Glass-filled PTFE; l Graphite-filled PTFE; l Graphite (available as a special option). 3.3.0 Electromagnetic Flow Meter The following materials are commonly used in electromagnetic flow meters. 1. Electrodes: Of the various electrode materials the following are commonly used: l Stainless steel 1.4571, stainless steel 1.4539; l Hastelloy B, Hastelloy C; l NieC276; l Platinume20%iridium; l Tantalum; l Titanium. 2. Liner: There is a wide choice of materials for liner including the following: l Ceramic carbide; l ETFE; l Hard rubber, Linatex rubber, soft rubber; l Neoprene; l Peek, PFA, PTFE; l Polyurethane; l PVDF; l Torlon.

2. Sensor: Sensors are made up of: l Stainless steel 1.4571; l Hastelloy; l Ceramic. 3.5.0 Turbine Flow Meter The following are typical materials for turbine meters. In this connection Section 2.4.1 of Chapter V may be referenced. Some typical materials are listed here: 1. Housing material: 316 stainless steel; 2. Rotor material: 430F stainless steel; 3. Ballbearing material: 440C stainless steel or equivalent, ceramic; 4. Journal-bearing material: Ceramic, tungsten carbide, graphite. 3.6.0 Vortex/Swirl Meters 1. Meter tube: Meter tube materials include the following: l A105/WCB forge/cast CS; l HastelloyC; l Stainless steel 1.4571/ASTMECF8, SS316, and CF3M. 2. Sensor: Sensing materials include the following: l Stainless steel 1.4571; l HastelloyC. 3. Shedder: Shedder materials include the following: l Stainless steel 1.4571, Duplex steel; l HastelloyC. 4. Gasket: Gasket materials include the following: l Graphite; l PTFE; l Kalrez; l Viton (A); l SUS316 SS with Teflon coating.

3.4.0 Thermal Mass Flow Meter

In the following section, different fluids and materials to be used have been illustrated with the help of a table.

Normally the following materials are used for thermal mass flow meters:

4.0.0 MATERIAL COMPATIBILITY

1. Meter tube: Meter tubes are made up of: l Stainless steel 1.4571; l Hastelloy.

In Table AII/4.0.0-1 the material compatibility of flowing medium and meter materials have been illustrated.

PFA
Non Metal

PTFE
Non Metal

EPDM
Non Metal

Buna N
Non Metal

Viton
Non Metal

PVDF
Non Metal

PVC
Non Metal

R

R

NR

NR

NR

NR

60

N

R

R

R

R

R

R

R

R

100

20

N

R

R

R

R

R

R

R

R

R

100

50

N

R

R

R

R

R

R

NR

R

NR

10

Y

R

R

R

R

R

R

R

R

50

N

R

R

R

R

R

R

R

R

20

Y

NR

NR

NR

NR

R

R

R

R

R

R

R

R

R

R

R

N

R

R

R

R

R

R

R

R

20

Y

R

R

R

R

R

R

R

100

50

N

R

R

R

R

R

G

100

20

N

R

R

R

NR

R

Chlorine wet

G

100

20

N

NR

R

NR

NR

R

Copper chloride sol

L

50

20

Y

NR

NR

R

NR

Copper sulfate sol

L

50

80

Y

R

R

R

Diesel fuel

L

100

50

N

R

R

Ethanol

L

96

50

N

R

Ethyl alcohol

L

100

80

N

Fatty acid

L

100

50

Ferric chloride sol

L

10

Gasoline

L

Glycol

L

Acetone

G

Acetylene

G

Ammonia

G

Beer

L

Benzene

L

Brine

L

Butane

G

100

50

Butylene

G

100

20

Calcium chloride sol

L

100

Carbon dioxide

G

Chlorine dry

100

Platinum Metal

R

Tantalum Metal

R

Titanium Metal

R

Hastelloy C Metal

R

Hastelloy B Metal

R

316L Metal

R

80

SS321 Metal

R

L

SS304 Metal

R

Fluid Type

Y

Acetic acid

NR

R

R

NR

R

R

R

R

NR

R

R

R

R

R

R

R

R

NR

NR

R

NR

NR

R

Ceramic
Non Metal

Soft Rubber
Non Metal

R

40

Fluid Types

Glass
Non Metal

Hard Rubber
Non Metal

R

Conductive

R

Approx: Temperature

Approx Concentration

TABLE AII/4.0.0-1 Material Compatibility

R R

R

NR

R

R

R

R

R

NR

R

R

NR

R

R

R

R

R

NR R

R

NR

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

NR

R

R

NR

R

R

R

R

R

NR

R

NR

NR

R

R

NR

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

NR

R

R

R

R

R

NR

R

R

R

R

R

NR

R

R

R

R

R

R

R

R

NR

NR

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

N

R

R

R

R

R

R

R

R

NR

NR

R

R

20

Y

NR

NR

NR

NR

NR

R

R

R

R

R

NR

R

R

100

20

N

R

R

R

R

R

R

R

R

R

NR

NR

R

NR

100

50

N

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

NR

NR

R R R

R NR

R

R

R

R

R

R

R

R

R

R

R

R

NR

R

R

R

R

R Continued

Buna N
Non Metal

R

R

NR

R

R

NR

NR

NR

NR

NR

R

R

R

R

R

R

R

Y

NR

NR

NR

H2 peroxide sol

L

40

20

Y

R

R

R

Kerosene

L

100

20

N

R

Methanol

L

100

50

N

R

R

R

R

Natural gas

G

100

40

N

R

R

R

R

R

R

R

R

NR

NR

R

R

NR

R

Nitric acid

L

20

40

Y

R

R

R

NR

R

R

R

R

NR

NR

R

R

NR

Olive oil

L

50

N

R

R

R

R

R

R

R

R

R

NR

R

R

Oxygen

G

100

50

N

R

R

R

R

R

R

R

R

R

R

Petroleum

L

100

20

N

R

R

R

R

R

R

R

NR

NR

R

R

NR

Phenol

L

90

50

N

NR

R

R

R

R

R

R

R

NR

NR

R

R

Phosphoric acid

L

30

50

Y

NR

R

R

R

NR

R

R

NR

NR

R

Sea water

L

50

Y

NR

NR

NR

R

R

R

R

R

R

Sodium bicarbonate

L

20

50

Y

R

R

R

R

R

R

Sulfuric acid

L

10

50

Y

NR

R

NR

R

R

R

R

R

Toluene

L

100

50

N

R

R

R

R

R

Urea

L

30

50

Y

Wort

L

5

Y

Yeast

L

20

R

R

R

R

NR

R

Platinum Metal

20

Tantalum Metal

37

Titanium Metal

L

Hastelloy C Metal

Hydrochloric acid

Hastelloy B Metal

NR

316L Metal

R

SS321 Metal

R

SS304 Metal

Y

R

R

R

R

NR

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

Ceramic
Non Metal

EPDM
Non Metal

NR

20

Glass
Non Metal

PTFE
Non Metal

R

25

PVC
Non Metal

PFA
Non Metal

R

L

PVDF
Non Metal

Soft Rubber
Non Metal

R

Hydrazine Sol

R

R

NR

NR

R

R

R

R

R

R

R

NR

R

Viton
Non Metal

Hard Rubber
Non Metal

NR

Conductive

NR

Approx: Temperature

R

Fluid Types

Fluid Type

Approx Concentration

TABLE AII/4.0.0-1 Material Compatibilitydcont’d

R

R

R

NR

R R

R

R

R

NR

NR

R

R

R

R

R

R

R

R

R

R

R

NR

NR

R

R

R

R

R

R

R

R

NR

NR

NR

R

NR

R

R

R

R

NR

R

R

NR

R

R

R

R

R

R

R

R

NR

R

R

R

R

R

R

R

R

R

R

R

R

NR

R

R

R

R

R

NR

NR

R

R

NR

NR

R

R

NR

R

R

R

R

R

R

R

R

R

R

NR

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R

R NR

R

R

The following details may be noted prior to going through the table. Fluid type: L, liquid; G, gaseous; Temperatures are expressed in degree Celsius. Symbols: R, recommended; NR, not recommended; X or blanks, not known or not applicable. For preparation of the table some data are taken from ABB Flow handbook. F. Frenzel, H. Grothey, C. Habersetzer, M. Hiatt, W. Hogrefe, M. Kirchner, G. Lu¨tkepohl, W. Marchewka, U. Mecke, M. Ohm, F. Otto, K.-H. Rackebrandt, D. Sievert, A. Tho¨ne, H.-J. Wegener, F. Buhl, C. Koch, Deppe, E. Horlebein, A. Schu¨ssler, U. Pohl, B. Jung, H. Lawrence, F. Lohrengel, G. Rasche, S. Pagano, A. Kaiser, T. Mutongo, Industrial Flow Measurement Basics and Practice, ABB Automation Products GmbH. http://nfogm.no/wp-content/uploads/2015/04/Industrial-Flow-Measurement_Basics-and-Practice.pdf. Courtesy: ABB Limited.

Appendix | II

REFERENCES [1] Micro MotionÒ Corrosion Guide for Coriolis Flow and Density Meters, Density meters, and Viscosity Meters, GI-00415, Rev H, Micro motion; Emerson Process Management, January 2014. http://www2.emersonprocess.com/siteadmincenter/ PM%20Micro%20Motion%20Documents/Corrosion-GuideGI-00415.pdf. [2] Chemical Resistance Guide, Bulletin 230, Milton Roy. http:// www.miltonroy.com/StaticFiles/MRContent/StaticFiles/Milton Roy/en/Models/Bulletin%20230%20Chemical%20Resistance %20Guide%206-2015.pdf. [3] F. Frenzel, H. Grothey, C. Habersetzer, M. Hiatt, W. Hogrefe, M. Kirchner, G. Lütkepohl, W. Marchewka, U. Mecke, M. Ohm, F. Otto, K.-H. Rackebrandt, D. Sievert, A. Thöne, H.-J. Wegener, F. Buhl, C. Koch, Deppe, E. Horlebein,

1145

A. Schüssler, U. Pohl, B. Jung, H. Lawrence, F. Lohrengel, G. Rasche, S. Pagano, A. Kaiser, T. Mutongo, Industrial Flow Measurement Basics and Practice, ABB Automation Products GmbH, 2011. http://nfogm.no/wp-content/uploads/2015/04/ Industrial-Flow-Measurement_Basics-and-Practice.pdf.

FURTHER READING [1] T. Bell, What is Corrosion? Corrosion Is a Serious Issue for Construction and Safety, The Balance, March 2017. https:// www.thebalance.com/what-is-corrosion-2339700. [2] High-Performance Alloys for Resistance to Aqueous Corrosion, The Special Metals Corporation. http://www.parrinst. com/wp-content/uploads/downloads/2011/07/Parr_InconelIncoloy-Monel-Nickel-Corrosion-Info.pdf.

APPENDIX III

MECHANICAL AND PIPING DATA (INCLUDING FLANGE DATA)

While in Appendix II short discussions were given on process parameters, compatibility, etc. Mechanical and piping data are also equally important, especially for in-line flow meters. It is also important for flow elements as well as for insertion type flow-metering devices. This appendix is dedicated to dealing with essential mechanical and piping data and standards in connection with flow metering. The discussion begins with unit conversions for force, torque, power, and energy not covered in Appendix I where unit conversions of other pertinent parameters have been dealt with.

1.0.0 UNIT CONVERSIONS FOR FORCE, TORQUE, POWER, AND ENERGY

Unit conversion of forces has been illustrated in Table AIII/1.1.0-1. In this table gm force, kilo Newtons, and ounce forces have not been considered as these can be easily calculated using the following sums: l l l

1 kgf ¼ 1000 gf {multiplying factor 1000}; 1 N ¼ 0.001 kN {multiplying factor 0.001}; 1 lbf ¼ 16 ozf {multiplying factor 16}.

1.2.0 Unit Conversion for Torque We now consider the torque unit conversion. Many instruments are based on this e.g., target flow. Even for tightening a bolt in a flange this is important. Unit conversion of torque has been illustrated in Table AIII/1.2.0-1. Basically, this is similar to force, only length is multiplied by it. The following conversions may be noted:

1.1.0 Unit Conversion for Force We first consider force based on which many flow meters function, e.g., a target flow meter.

gf$cm ¼ 1E05 kgf$m; 1 kNf$m ¼ 0.001 N$m; 1 lbf$ft ¼ 192 oz$inch (16  12).

TABLE AIII/1.1.0-1 Unit Conversion Factors for Force Dyne

Kilo Force

Newton

Pound Force

Poundal

1

1.02E06

1.00E05

2.25E06

7.23E05

9.80Eþ05

1

9.80665

2.204623

70.93164

1.00Eþ05

1.00Eþ05

1

0.224808

7.233013

4.44Eþ05

0.4535923

4.44824

1

32.17404

1.38Eþ04

0.0140981

0.138255

0.031080958

1

1147

1148

Appendix | III

TABLE AIII/1.2.0-1 Unit Conversion Factor for Torque Dyne$cm

Kgf$m

lbf$ft

N$m

1

1.00E08

7.40E08

1.00E07

1.00Eþ08

1

7.233013

9.80665

1.35Eþ07

1.38E01

1

1.355818

1.00Eþ07

0.1019716

0.737562

1

1.3.0 Unit Conversion for Power Let us now consider power unit conversion. Unit conversion factors for power have been illustrated in Table AIII/1.3.0-1. Power is defined as work done per second, so in this table all units are in terms of seconds. However, at times power is expressed in terms of work done per

minute (or per hour). This can be done by converting the time scale: Time: 1 h ¼ 60 min ¼ 3600 s ðas 1 min ¼ 60 sÞ. 1.4.0 Unit Conversion for Energy Let us now consider energy unit conversion. Unit conversion factors for energy have been illustrated in Table AIII/1.4.0-1 (1 dyne-cm ¼ 1 erg).

TABLE AIII/1.3.0-1 Unit Conversion Factor for Power BTU/s

Cal/s

HP

Kilowatt

lbft/s

1

2.52Eþ02

1.41Eþ00

1.05Eþ00

7.77Eþ02

3.97E03

1

0.00561

0.004183

3.085279

7.07E01

1.78Eþ02

1

0.7456999

550

9.48E01

239.06287

1.341022

1

737.5621

1.29E03

0.3241198

0.001818

0.001355818

1

BTU, British thermal unit (thermal energy), calorie thermal energy; HP, horse power, normally electrical/mechanical energy.

TABLE AIII/1.4.0-1 Unit Conversion Factor for Energy BTU

Calorie

Electron Volt

erg

HP hours

Kilowatt hour

1

2.52Eþ02

6.58Eþ21

1.05Eþ10

3.93E04

2.93E04

3.97E03

1

2.61Eþ19

4.19Eþ07

1.56E06

1.63E06

1.52E22

3.83E20

1

1.60E12

5.97E26

4.45E26

9.52E11

2.39E08

6.25Eþ11

1

3.72E14

2.78E14

2.54Eþ03

6.41Eþ05

1.68Eþ25

2.69Eþ13

1

7.46E01

3.41Eþ03

6.13Eþ05

2.25Eþ25

3.60Eþ13

1.34Eþ00

1

Appendix | III

2.0.0 PIPING DATA

1149

These are explained as follows:

In this section brief discussions on piping data are covered. These are necessary for flow meter designs, i.e. flow element, in-line flow meter, fixing insertion length for insertion type meters. The discussion starts with pipe specifications. 2.1.0 Pipe and Tube Specification There are some differences in specifying pipes and tubes. It is not the intent of this book to detail pipe specifications according to different standards; here only basic guidelines are provided. The discussions start with pipe specifications. 2.1.1 PIPE SPECIFICATIONS Normally pipes are specified in terms of nominal bore which is an imaginary diameter (usuallydnot always) between the outer and inner diameters. As soon as nominal bore (NB) is specified its outer diameter (OD) is fixed (i.e. fixed relation between NB and OD). Based on the schedule (e to be specified with NB for complete specification) the thickness and hence the inner diameter of the pipe are decided. Typical NB, inlet, and outlet diameters of a pipe have been shown in Fig. AIII/2.1.0-1.

1. Pipe diameter: Two commonly used size standards are: l In Imperial units: US standards: Nominal pipe size (NPS)/nominal bore (NB) (US standards: ANSI/API/ASME) l In metric units: EU-DIN standard: Pipe diameter: Nominal diameter (DN) l Once DN/NB is specified, OD is fixed. 2. Pipe schedule: This sets the pipe wall thickness. A greater wall thickness of the pipe will result in increased mechanical strength of the pipe to handle higher design pressures. The following pipe schedules are available (in order of increasing wall thickness): 5S, 10S, 10, 20, 30, 40S, STD, 40, XS (Extra Strong), 60, 80, 100, 120, 140, XXS (Double Extra Strong), and 160. 3. Pipe internal diameter (ID): For process and instrument engineers, the most important information is the pipe internal diameter (ID), as this is primarily used in specifying straight length, as well as for in line sizing calculations. As indicated before, for a given NB, the pipe OD remains constant. So, with pipe schedule changes, the internal diameter of the pipe changes.

WITH SPECIFICATION OF NB OD IS FIXED FOR THE PIPE

TABLE AIII/2.1.0-1 Diameter Nominal (DN) and Nominal Pipe Size (NPS) NO L NA MI BO RE

R NE

)

(OD) (ID ER ET M IA

IAMETER OUTER D D

IN

THICKNESS SHOWN BY HATCH VARIES WITH SCHEDULE; HENCE ID VARIES

FIGURE AIII/2.1.0-1 Pipe specification.

Diameter Normal

Nominal Pipe Size

Diameter Normal

Nominal Pipe Size

6

1/8

150

6

8

1/4

200

8

10

3/8

250

10

12

1/2

300

12

20

3/4

600

24

25

1

800

32

40

1½

1050

42

50

2

1500

60

65

2½

1800

72

80

3

2000

80

100

4

2200

88

1150

Appendix | III

TABLE AIII/2.1.0-2 Dimensional Details of Pipes Sch10 DN

OD

Thk

ID

Sch40 Thk

ID

SchXS* Thk

Sch160

ID

Thk

ID

SchXXS Thk

ID

15

21.34

2.11

17.12

2.77

15.80

3.73

13.88

4.78

11.78

7.47

6.40

20

26.67

2.11

22.45

2.87

20.93

3.91

18.85

5.56

15.55

7.82

11.03

25

33.40

2.77

27.86

3.38

26.64

4.45

24.30

6.35

20.70

9.09

15.22

40

48.30

2.80

42.70

3.70

40.90

5.10

38.10

7.10

34.10

10.2

27.90

50

60.30

2.80

54.70

3.90

52.50

5.50

49.30

8.70

42.90

11.1

38.10

80

88.90

3.00

82.90

5.50

77.90

7.60

73.70

11.1

66.70

15.2

58.50

8.60

97.10

13.4

87.50

17.1

80.10

100

114.3

3.00

108.30

6.00

102.3

150

168.3

3.40

161.50

7.10

154.1

11.0

146.3

18.3

131.7

22.0

124.3

200

219.1

3.80

211.50

8.20

202.7

12.7

193.7

23.0

173.1

22.2

174.7

250

273.0

4.20

264.60

9.30

254.4

15.1

242.8

28.6

215.8

25.4

222.3

300

323.9

4.60

314.70

303.3

17.5

228.9

33.3

257.3

25.4

273.1

600

610.0

6.35

597.30

590.94

12.70

584.60

59.40

491.20

10.3 9.53

Table AIII/2.1.0-1 provides the relation between DN (mm) and nominal pipe size (NPS in inches) in line with ASME. Pipe dimensions for various pipe sizes at different schedules have been enumerated in Table AIII/2.1.0-2.

TABLE AIII/2.1.0-3 Stainless Steel Tube Dimensional Details and Pressure Rating (Typical) Tube Inside Diameter

Outer Diameter

Thickness

2.1.2 TUBE SPECIFICATION

6

1

4

420

In contrast to pipes, tubes are specified in terms of outer diameter and thickness. The main specifications in selecting tubes are listed here:

6

1.5

3

600

10

1

8

294

10

1.5

7

398

10

2

6

498

12

1

10

245

12

1.5

9

368

12

2

8

426

15

1

13

196

15

1.5

12

294

15

2

11

392

25

2.5

20

294

25

3

19

353

l l l l

Surface finish; Material; Hardness; Wall thickness.

Typical stainless tube dimensional details and pressure ratings have been enumerated in Table AIII/2.1.0-3. These data are taken from reputed manufacturers. At elevated temperatures there will be a derating, which will be governed by a factor as indicated in Table AIII/2.1.0-4.

Working Pressure

Tube Dimensions are in mm and pressure rating is in bar.

Appendix | III

TABLE AIII/2.1.0-4 Pressure Derating Factor at Elevated Temperature Temperature (8C)

304/304L Stainless Steel

316/316L Stainless Steel

93

1.00

1.00

204

0.93

0.96

315

0.82

0.85

426

0.76

0.79

537

0.69

0.76

3.

3.0.0 FLANGE DATA There are several types of flanges and there a few international standards, such as ANSI/API/BS/ DIN/JIS etc. to specify them. We first investigate flange types. For further details any standard book on flange may be referenced.

4.

3.1.0 Flange Types Flange types can be classified as per their connection types as well as flange face types. We investigate flange classifications according to their connection types. 3.1.1 FLANGE CONNECTION TYPES According to the connection type and style the most commonly used flange types include the following: 1. Welding neck: Welding neck flanges have a long tapered hub, which goes gradually over to the wall thickness from a pipe or fitting. This long tapered hub provides an important reinforcement for use in high pressure, and subzero and/or elevated temperatures. These flanges are bored to match the inside diameter of the mating pipe or fitting so there will be no restriction of product flow. This prevents turbulence at the joint and reduces erosion. They also provide excellent stress distribution through the tapered hub and easy radiography for flaw detection is possible. 2. Slip on: The calculated strength from a slip on flange is much lower as compared to the welding

5.

6.

1151

neck type. However, from an installation point of view it is easier. The connection with the pipe is done with two fillet welds, as well as at the outside and the inside of the flange. A disadvantage of the flange is, in principle, a pipe must always firstly be welded and then adjust the fitting. Socket weld: Socket weld flanges can be used for small-size high-pressure piping, it has strength equal to the slip on type with greater fatigue strength. The connection with the pipe is done with a fillet weld, at the outside of the flange. However, before welding, a space must be created between the flange or fitting and the pipe in line with the standard (e.g., ASME B31.1 1998). In this type there will be an expansion gap inside which must be a right gapdthe concerned standard may be referenced. Lap joint: This type is very similar to a slip on flange. It does not have a raised face and can accommodate the stub end. It has pressure-handling capability near that for a slip on type flange. Lap joint flanges have certain special advantages: l Freedom to swivel around the pipe; l No contact with fluid in the pipe, hence low-cost materials can be used. The stub end type is used with a lap joint flange, as a backing flange. Stub ends are available in almost all pipe diameters. This cheap flange connection normally is applied in low-pressure and noncritical applications. Threaded: Threaded flanges are attached to the pipe without welding. Sometimes a seal weld is also used in addition to the threaded connection. Although these are available in various sizes they are mainly applied for smaller pipe sizes at lower pressure ratings. Blind flange: Blind flanges are manufactured without a bore as these are used to blank off the ends of piping, valves, and pressure vessel openings. These flanges are suitable for higherpressure and higher-temperature applications.

3.1.2 FLANGE FACE TYPES Different types of flange faces are used at the contact surfaces to seat the sealing gasket

1152

Appendix | III

material. ASME B16.5 and B16.47 define various types of flange facings: 1. Raised face (RF): Raised face type shown in Fig. AIII/3.0.0-1B, is the most common type used in process plant applications, and is easy to identify due to its raised face to accommodate the gasket surface which is raised above the bolting circle face. This face type allows the use of a wide combination of gasket designs. In the RF flange more pressure is concentrated on a smaller gasket area to increase the pressure containment capability of the joint. The height (1.6e6.4 mm) of the RF is determined by the pressure rating. 2. Flat face (FF): The flat face flange as shown in Fig. AIII/3.0.0-1A has a gasket surface in the same plane as the bolting circle face. Applications using flat face flanges are frequently those in which the mating flange or flanged fitting is made from a casting. It should never be connected to the RF flange on the other end. 3. Ring-type joint (RTJ): The ring type joint flanges are typically used for high pressure (Class 600 rating) and/or high-temperature services above 427 C. Ring-type joint flange types have been depicted in Fig. AIII/3.0.0-1C. (A)

They have grooves cut into their faces with steel ring gaskets. The flanges seal when tightened bolts compress the gasket between the flanges into the grooves, deforming (or coining) the gasket to make intimate contact inside the grooves, creating a metal-to-metal seal. An RTJ flange may have a raised face with a ring groove machined into it. This raised face does not serve as any part of the sealing means. Ring type joint gaskets are metallic sealing rings, suitable for high-pressure and high-temperature applications. 4. Tongue and groove type: The tongue and groove faces of these flanges must be matched. One flange face has a raised ring (tongue) machined onto the flange face, while the mating flange has a matching depression (groove) machined into its face. 5. Male-and-female (M&F): In this type, the flanges also must be matched. One flange face has an area that extends beyond the normal flange face (male). The other flange or mating flange has a matching depression (female) machined into its face. Various flange face types with dimensional details for FF, RF, and RTJ flanges have been depicted in Fig. AIII/3.0.0-1.

RAISED FACE

RING GASKET

(C)

RTJ FLANGE (RAISED FACE) RTJ FLANGE (FLAT FACE)

OVAL RTJ IN OVAL GROOVE

RAISED FACE

OCTAGONAL RTJ IN OCTAGONAL GROOVE RAISED FACE HEIGHT

RING GROOVE (SHOWN IN SOLID)

OVAL RTJ IN OCTAGONAL GROOVE

SIMILARLY OTHER TYPES ALSO

DIAMETER OF HOLE

OUTSIDE DIAMETER

DIAMETER OF HOLE CIRCLE PITCH CIRCLE DIAMETER (PCD)

(B)

FIGURE AIII/3.0.0-1 Flange types. (A) Flat face flange. (B) Raised face flange. (C) Ring type joint flange.

Appendix | III

3.2.0 Flange Standards and Dimensions

1153

Flanges are available in various forms with each following particular standards, of these the following are quite commonly used internationally.

4. Japanese Standard: Japanese Industrial Standards: B2220:2004; 5. US Standard: American Society of Mechanical Engineers (ASME): ANSI B16.5:2009.

3.2.1 MAJOR STANDARDS

3.2.2 RAISED FACE HEIGHT

The following are major standards are used for flanges internationally:

Table AIII/3.2.0-1 shows the typical height for raised faces (refer to Fig. AIII/3.0.0-1).

1. British Standard: BS10:1962. Withdrawn: 30th April 2009; Current status: BS EN 1092-1:2007þA1:2013; 2. EU Standard: European standard (EN): DIN EN 1092-1:2002-06 and 2007; 3. German Standard: German National Standards Institute (DIN):DIN2527;

3.3.0 Flange Dimensional Details Standard dimensional details of various flanges are easily available from the standards. We now look at comparisons of these for a few cases (Table AIII/3.3.0-1).

TABLE AIII/3.2.0-1 Raised Face Height Raised Face Height Standard

Flange Specification

In mm

In inch

ASME ANSI B16.5:2009

300 lb

1.6 (2)

0.06

ASME ANSI B16.5:2009

400, 600

6.4 (7)

0.25

DIN EN 1092-1:2007

DN 32

2

0.08

DIN EN 1092-1:2007

>DN 32 to DN 250

3

0.12

DIN EN 1092-1:2007

>DN 250  DN 500

4

0.16

DIN EN 1092-1:2007

>DN 500

5

0.19

JIS 2220: 2004

DN 20

1.5

0.06

JIS 2220: 2004

>DN 20  DN 50

2

0.08

JIS 2220: 2004

> DN50

3

0.12

TABLE AIII/3.3.0-1 Flange Standards and Dimensions Pipe

STD

Ratings

OD

PCD

25

ASME

150

108

79

25

ASME

300

124

25

DIN

10, 16, 25*

25

JIS

10, 16, 20

Bolt

RF Dia.

Thick

Remarks

4  15.7

50.8

14.2

NPS100

89

4  19.1

50.8

17.5

NPS100

115

85

4  14

68

16*

*18 for 25

125

90

4  19

67

14e16 Continued

1154

Appendix | III

TABLE AIII/3.3.0-1 Flange Standards and Dimensionsdcont’d Pipe

STD

Ratings

OD

PCD

50

ASME

150

152

121

50

ASME

300

165

50

DIN

10, 16, 25*

50

JIS

80

Bolt

RF Dia.

Thick

Remarks

4  19.1

91.9

19.1

NPS200

127

8  19.1

91.9

22.4

NPS200

165

125

4  18

102

18

*20 for 25

10, 16*, 20*

155

120

4  19*

96

14e18

*8  19

ASME

150

190.5

152.4

4  19.1

127

23.9

NPS300

80

ASME

300

209.5

168.1

4  22.4

127

28.4

NPS300

80

ASME

600

209.5

168.1

8  22.4

127

31.8

NPS300

80

DIN

10, 16, 25*

200

160

8  18

138

20*

*24 for 25

80

JIS

10

185

150

8  19

126

18

80

JIS

16, 20*

200

160

8  23

132

20*

*22 for 20

100

ASME

150

228.6

190.5

8  19.1

139.7

23.9

NPS400

100

ASME

300

254

200.2

8  22.4

157.2

31.8

NPS400

100

ASME

600

273

215.9

8  25.4

157.2

38.1

NPS400

100

DIN

10, 16

220

180

8  18

158

20

100

DIN

25

235

190

8  22

162

24

100

JIS

10

210

175

8  19

151

18

100

JIS

16, 20*

225

185

8  23

160

22*

*24 for 20

200

ASME

150

342.9

298.5

8  22.4

269.7

28.4

800

200

ASME

300

381

330.2

12  25.4

269.7

31.8

800

200

ASME

600

419.1

349.3

12  32

269.7

55.6

800

200

DIN

10, 16*

340

295

8*  22

268

24

*12 for 16

200

DIN

25

360

310

12  26

278

30

200

JIS

10

330

290

12  23

262

22

200

JIS

16, 20*

350

305

12  25

275

26*

*30 for 20

250

ASME

150

406.4

362

12  25.4

323.8

30.2

1000

250

ASME

300

444.5

387.4

16  28.4

323.8

47.8

1000

250

ASME

600

508

431.8

16  35

323.8

63.5

1000

300

DIN

10

445

400

12  22

370

26

300

DIN

16

460

410

12  26

378

28

300

DIN

25

485

430

16  30

395

34

300

JIS

10

445

400

16  25

368

24

300

JIS

16,20*

480

430

16  27

395

30*

*36 for 20

Unless otherwise stated dimensions shown here are in mm (in reality ANSI flanges are in inches). Pipe, pipe nominal size (DN mm, for equivalence for NPS refer to Table AIII/2.1.0-1); For ASME 25, 50, 80, 100, 200, and 250 represent 100 ,200 , 300 , 400 , 800 , and 1000 , respectively. OD, outside diameter; PCD, pitch circle diameter; STD, standard.

Appendix | III

4.0.0 GASKET SYSTEM Gaskets are available in various forms. There can be nonmetallic filler, such as PTFE, ceramic, or metallic winding materials, such as different grades of SS, CS, titanium, etc. They can be color coded. There are different type of gaskets, such as spiral wound gasket, metallic serrated gasket, and metal jacketed gasket. The number of bolts on the flange and their sizes are guided by the standard for the flange. Bolting method and types has direct bearing on gasket compression. The bolting should be done cyclically (clockwise) with the recommended method of bolting as listed below: l

l l l

Torque to the bolts at 30% of the final loading using the appropriate bolt pattern; 60% of final load; 100% of final load; 100% of final torque using a clockwise pattern.

Based on the applied torque there will be compression of the gasket. Since there is some recommended applied toque there will be some recommended compression of the gasket as well, e.g., for optimum performance spiral wound gaskets have required compression for a gasket of thickness 1.6 mm to 1.3/1.4 mm or a gasket of 6.4 mm could be compressed to 4.6 mm. Gasket suppliers provide such lists for particular gasket types. Torque values limit minimum and maximum gasket seating stresses based upon pressure class and operating conditions (e.g., maximum pressure ratings for given pressure class). Extreme operating conditions, such as high temperatures, may reduce the bolt yield strength. Caution should be used in these applications. As stated earlier, there will be

1155

some recommended torque value for each of the bolt types based on its yield strength. The following are the basic assumptions considered to arrive at the recommended torques. l

l

l

l

Bolts are new, standard finish, uncoated, and not lubricated (other than the normal protective oil film); The load will be 90% of the bolt yield strength; The coefficient of friction is fixed and a standard value; The final tightening sequence is achieved smoothly and slowly.

Thus from this it is clear that based on bolt size and grade there will be a recommended torque. The torque and tension are related by: M ¼

P$D K

(AIII/4.0.0-1)

where Symbol D¼ K¼ M¼ P¼

In Imperial System

In Metric System

Bolt diameter in inch Constant K ¼ 60

Bolt diameter in mm Constant K ¼ 5000 Torque in N$m (Newton meter) Bolt tension (Newton)

Torque in lb$ft (pound feet) Bolt tension (lb)

With this, the discussions on gaskets are concluded with the note that based on the application the gasket type to be chosen and applied torque on the bolt should be within the applicable limit to get better performance.

APPENDIX IV

CUSTODY TRANSFER (INCLUDING PROVER) 1.0.0 CUSTODY TRANSFER GENERAL DISCUSSIONS Custody transfer applications are mainly connected with the oil and gas industries. It is needless to explain the requirements of flow metering in the oil and gas industries in which Custody transfer (CT) is a special flow measurement. In this section a general discussion on custody transfer has been presented. The discussion starts with a definition and explanation of the custody transfer system. 1.1.0 Explanation of Custody Transfer Basically, flow measurements in oil and gas are important not only for taxation/custody transfer but also for allocation, reservoir management, well testing, environmental reporting, etc. Fluid flow measurement in custody transfer is defined as a metering point (location) where the fluid is being measured for sale (or other purposes discussed above) from one party to another. This means that it basically refers to a transaction involving transportation of fluid from one operator to another. The term “fiscal metering” is often interchangeably used with custody transfer to refer to metering at a point of a commercial transaction when a change in ownership takes place between two parties. The accuracy of measurement is of great importance to both parties, i.e., the seller and buyer. In a custody-transfer flow measurement,

there can be one or two custody-transfer flow meters, i.e., one set measures the volume or mass of fluid before the transfer is made, and another set of flow meters measures the flow after the transfer. Custody transfer is unique among flow meter applications because of two major reasons: l l

Money changes hands; Requirement for very high accuracy.

The requirement for high accuracy will be clear from a small example, e.g., 100 barrels/day, if it costs 10 billion USD then with 0.25% uncertainty the loss would be 20 million USD per day. Therefore, accuracy is extremely important for both parties, i.e., the party delivering the product as well as to the party that is the recipient of the product. This is because uncertainty could be in either direction (positive or negative) to cause a loss. For custody transfer, as any errors or uncertainty in measurement (for custody transfer) can be very expensive, custody transfer and fiscal metering in most countries are highly regulated, with the involvement of government taxation and contractual agreements between custody transfer parties. Proving must meet the following requirements: l

l

Traceable to a standard recognized by the International Bureau of Legal Metrology (BIML); Validated at operating conditions.

1157

1158

Appendix | IV

1.2.0 Some Standards and Associations for Custody Transfer In general custody transfer (CT) involves the following: 1. Industry standards; 2. National metrology standards; 3. Contractual agreements between custody transfer parties; 4. Government regulation and taxation. Custody transfers are also influenced by a number of industry standards and associations, i.e., American Gas Association (AGA), American Petroleum Institute (API), US National Institute for Standards and Technology (NIST), PhysikalischTechnische Bundesanstalt (PTB) in Germany, China Metrology Certificate (CMC), and gosudarstvennyy standart (GOST) in Russia [3]. Therefore, in custody transfer measurement,

guidelines from these bodies are followed. AGA reports and API standards are very important and mostly used standards for measurement in custody transfer. In order to keep the uncertainty of measurement within limits as per the standards, not only is a highly accurate flow meter needed but also a system as detailed below. 1.3.0 Measuring System for Custody Transfer In order to lower the uncertainty value and to get stable reliable measurements, a complete system, as shown in Fig. AIV/1.0.0-1, comprising the following will be necessary: 1. Multiple meter runs with multiple meters in parallel. Each is referred to as a stream; 2. Flow conditioning;

FIGURE AIV/1.0.0-1 Custody transfer measurement scheme.

Appendix | IV

1159

TABLE AIV/1.0.0-1 Pros and Cons of Meter Types in Custody Transfer Meter Type

Advantages

Disadvantages

DP type (orifice)

Low cost, easy installation, and comprehensive standard

High-pressure loss, edge erosion, longer upstream straight length

PD meter

Accurate, repeatable, fast response, direct measurement, insensitive installation effect

Bulky and complicated, mechanical damage, and expensive

Turbine meter

Moderate cost, easy installation, good repeatability

Mechanical damage, bearing wear, installation effect, contaminant effect

US flow meter

Nonintrusive and noninvasive, no moving parts, bidirectional, high diagnostic

High cost, installation effect, deposit on sensor

Coriolis meter

Noninvasive, independent of process parameter, high accuracy and turndown

High cost, high-pressure loss, zero stability, limited size vibration effect

3. Pressure measurement in each stream as well as the main stream; 4. Temperature measurement in each stream as well as the main stream; 5. Stream flow computers; 6. Meter prover/master meter; 7. Prover automation; 8. Density measurement [1]; 9. Sampling system [1]; 10. Flow computation; 11. Quality measurement l For gas energy content, online gas chromatography; gas composition l For liquids, sampling systems and water monitoring (BS&W). 1.4.0 Recommended Meter Types for Custody Transfer Measurements The following flow meters have been accepted for custody transfer. In parenthesis the reference of acceptance of the meter for the measurement has been indicated. 1. DP typedorifice plate (1930 AGA1 report); 2. PD meter (API MPMS 5.2); 3. Turbine flow meter (1981: AGA 2 reprint 1982) (API MPMS 5.2);

4. Ultrasonic (AGA9: 1998) (API MPMS 5.11); 5. Coriolis mass flow meter (AGA11: 2003) (API MPMS 5.6). We now look into the pros and cons of various meter types. Table AIV/1.0.0-1 shows the advantages and disadvantages of various meters used for custody transfer. 1.5.0 Role of AGA and API in Custody Transfer Metering Two international organizations, American Gas Association (AGA) and American Petroleum Institute (API), studied custody transfer measurements and have come out with procedures for measurement. The AGA is more focused on industrial and natural gas, while the API focuses more on petroleum liquids. The AGA and API studied custody transfer measurement and published a series of reports specifying how this measurement is to be done with different types of flow meters [2]. As mentioned earlier, while the AGA’s reports are mainly related to gas flow measurements, the API has issued its own reports on the use of flow meters involving custody transfer of liquids. 1. AGA: The first AGA report AGA-1 on custody transfer measurement was in 1930, a

1160

Appendix | IV

report on the use of DP flow meters with orifice plates for custody transfer of gas. Currently AGA Report No. 3 Orifice Metering of Natural gas and Other hydrocarbon related fluids. In 1981, the AGA issued a report on custody transfer measurementda report on the use of turbine flow meters for custody transfer applications. A current AGA report is a new version of AGA-7 entitled Measurement of Natural Gas by Turbine Meters in 2006. In 1998 the AGA issued AGA-9, a report detailing the use of ultrasonic flow meters for custody transfer applications. The AGA published AGA-11 in 2003, a report on the use of Coriolis flow meters for custody-transfer applications. 2. API: This deals more with liquids flow metering. Various API reports include API MPMS 5.2 (positive-displacement meters), API MPMS 5.3 (turbine meters), API MPMS 5.6 (Coriolis flow meters), and API MPMS 5.11 (ultrasonic flow meters). There are other API reports to cover vortex, magnetic, thermal dispersion, and variable area flow meters also. Now some details on meter types, meter provers, etc. will be look into. 1.6.0 Meter Selection for Custody Transfer Metering The following are the major characteristics to be considered while selecting a meter for custody transfer: 1. 2. 3. 4. 5.

System characteristics; Product characteristics; Flow and viscosity range; Accuracy (inherent accuracy as per API); Errors considerations (as applicable): l Random error l Spurious error l Fixed and variable systematic error l Repeatability and linearity.

In this connection it is worth noting some guidance provided by the API standard.

According to the API, the following should be the major considerations for meter selection: l l l

l

The advantages of metering; Design of meter installations; Meter performance: For custody-transfer applications, meters with the highest inherent accuracy should be used and should be proven on site; Meter proving: Dependent on operating conditions.

1.7.0 Custody Transfer Measurements and Legal Issues Custody transfer is fiscal measurement used to determine the quantity and associated financial value of a petroleum product transaction (delivery). The custody transfer is normally guided by two types, i.e., legal and contract. 1. Legal: Legal is defined by Weights and Measures (W&M) in the country or jurisdiction in which the sale is conducted. Naturally the W&M codes and regulations of the concerned country would control the wholesale and retail trade requirements for fair trade. Even though there may be wide variations in the requirements pertinent to the regulations and accuracy amongst various countries, there is one common characteristicdtraceability. 2. Contract: A contract is basically a written agreement between buyers and sellers. This encompasses various requirements for the measurements as well as the accuracies (may be by referring to any international standard). These are large-volume sales between companies. In these the products are transported by marine, pipeline, or rail. Even with a very small error, there could be a large financial impact, therefore the custody transfer measurement must be at the highest level of accuracy possible and follow international standards. Such detailing are normally specified in the contract.

Appendix | IV

2.0.0 DISCUSSIONS ON METER TYPES USED IN CUSTODY TRANSFER As we have seen above, there are five main meter types (basically four types and PD meter as an additional type for petroleum products) are approved for custody transfer measurement. In DP type flow metering, the orifice plate has been approved. To the best of my knowledge, V cone flow elements are also used in Canada for custody transfer measurement. All these flow-metering types have already been discussed in the main body of this book. Here a brief outline of these meters will be covered from custody transfer measurement points of view. The flow meters discussed here are arranged according to their principle of operations (also in the order they appear in the main body of the book). 2.1.0 Differential Pressure Type Flow Metering The third AGA report on orifice metering for custody transfer, called AGA-3, was published in 1955 and reissued in 1992 and is currently in use as the standard (AGA3.1). Differential pressure (DP) flow meters are used for custody transfer (of natural gas) and can be used to measure the flow of liquid, gas, and steam. 1. Principles: DP type measurement with an orifice as the flow element is the commonest of flow-metering devices deployed for custody transfer. The DP flow meter consists of a differential pressure transmitter and a primary element (orifice plate). When discussions in Chapter II are recalled it can be seen that a machined plate with central hole is placed between two pipe pieces to create a constriction in the flow stream, while the DP transmitter measures the pressure differential between upstream and downstream of the constriction created by the flow element. Some suppliers also use DPT with an integral orifice plate, as already discussed in Chapter II. 2. Approval: Standards and criteria for the use of DP flow meters for custody transfer

1161

applications are specified by the American Gas Association (AGA) and the American Petroleum Institute (API). 3. Features: As this meter type is the most studied and best understood, this is an advantage in using DP type metering. Uncertainty offered by the metering system is moderate but it has a lower turndown ratio. Pressure loss and straight length requirements are some of the limitations of this measurement system. One important development in the use of DP flow meters for custody transfer applications has been the development of single- and dualchamber orifice fittings [4]. 2.2.0 Positive Displacement (PD) Type Flow Metering Positive displacement (PD) flow meters offer high accuracy, and hence are widely used for custody transfer of commercial and industrial water, as well as for custody transfer of oil and gas applications (mainly petroleum products). 1. Principles: PD meters measure flow by momentarily isolating segments of known volume and counting them, i.e., known segments of fluid pass through the measurement chamber and these are counted. There are two factors which affect the accuracy of a PD meterdmeasuring chamber volume displacement and slippage through the capillary seals (clearances). 2. Approval: PD flow meters have been approved by a number of regulatory bodies (API). Measurement of low flow and flow of fluid with high viscosity are major advantageous points for PD meters. The speed of flow doesn’t matter when using a PD meter. 3. Features: Performance of the meters are affected by two major factors, i.e., volume displacement and slippages. Let us look into these issues separately: l Volume displacement: Temperature and coating are two major issues which influence both displaced volume as well as measurement accuracy of the meter already

1162

Appendix | IV

discussed in Chapter IV. With a change of temperature due to expansion or contraction of the materials, the volume of the measurement chamber will vary and hence the volume of the fluid is displaced. Most PD meter designs are not highly sensitive to temperature and can operate within the allowable measurement accuracy over a fairly wide temperature range [5]. Wax of crude oils can coat the inside of the measurement chamber and reduce volumetric displacement. This directly affects the meter factor and hence measurement accuracy. l Slippage: PD meters have two parts, one moving and the other stationary, with minute clearances between them. Here a capillary seal is formed. As already discussed in Chapter IV, if there is any slippage, i.e., a small part goes to this seal part it gets unaccounted for and is known as slippage. At higher viscosity the slippage will be lower. For this reason it is seen that for a given accuracy or linearity, with an increase in viscosity the turndown ratio increases as detailed out in chapter IV. l Sizes: Normally PD meters are common for smaller line sizes. On account of its bulky design meter >250 mm is not common. 4. Advantages: The meter offers a number of advantage points such as the following: l Superior accuracy and measurement stability; l Low-pressure drop; l Low operating cost; l Long service life with ease of maintenance; l Tolerance to entrained solids. On account of possible high accuracy these meters find applications as master meters also. 2.3.0 Turbine Type Flow Metering Turbine flow meters are extensively used in custody transfer applications. Short discussions on the same are presented below.

2.3.1 PRINCIPLES OF OPERATIONS AND FEATURES OF TURBINE FLOW METERS There are many types of turbine meters, but many of those used for gas flow are called axial meters. Principle of operation: Turbine meters determine the flow rate by measuring the velocity of a bladed rotor suspended in the flow stream. The volumetric flow rate is the product of the average stream velocity and the flow area at the rotor. Turbine flow meters can be used for liquid and gas flow measurement. In 1981, the AGA:7 issued its report, “Measurement of Fuel Gas by Turbine Meters.” Features: Various features of turbine flow meters have been enumerated in Chapter V. Major features concerning custody transfer could be summarized as follows: l

l

l

l

The turbine flow meters enjoy an edge over others for measuring clean, steady, highspeed flow of low-viscosity fluids; It is very cost-effective, especially in larger meter sizes when compared with USFM and Coriolis; On account of moving parts, there will be wear and tear in the meter to cause lowering of performance; Durable materials of construction are necessary to prevent wear and tear and assure better meter performance.

2.3.2 MEASUREMENT ACCURACY The accuracy of a turbine meter is based on two assumptions: Constant area and precision stream velocity measurement. 1. Constant area: The flow area remains constant: Here meter factor k can change due to: l Erosion/corrosion/deposits; l Boundary layer thicknessdViscosity, hence Reynolds number is an influencing factor; l Cavitations; l Obstructions.

Appendix | IV

2. Stream velocity: The rotor velocity accurately represents the stream velocity: This assumption is changed on account of the following: l Fluid density; l Bearing friction; l Blade angle of the rotor; l Rotor stability; l Velocity profile change (calls for flow conditioning). 2.4.0 Ultrasonic Type Flow Metering In 1998, the ultrasonic flow meter was included as a meter type in custody transfer (AGA 9). Over the past 10 years, ultrasonic flow meters, along with Coriolis flow meters, have become the flow meters of choice for custody transfer in the oil and gas industry. 2.4.1 PRINCIPLES OF OPERATIONS Ultrasonic meters provide the volumetric flow rate by measuring the velocity of the flowing stream like turbine meters. Volume throughput is calculated by multiplying the velocity by the flow area. The flow area can be accurately determined by measuring the average internal pipe diameter in the measurement area. The transit time difference is proportional to fluid velocity, as discussed at length in Chapter V. The principle of measurement is simple but determining the true average velocity is difficult, especially to obtain custody transfer measurement accuracy. Detecting and precisely measuring this small difference in time is extremely important to measurement accuracy and each manufacturer has proprietary techniques to achieve this measurement. Velocity profiles are highly complex and one set of transducers only measures the velocity along a very thin path. To determine the velocity profile more accurately, custody transfer ultrasonic meters use multiple sets of transducers. The number of paths in multiple transducer configuration, their location, and the associated algorithms used to integrate the path velocities into an average velocity all contribute to the meter’s accuracy. Therefore,

1163

an apparently easy system in reality is slightly more complex and highly dependent on all the factors discussed. Also swirletransverse velocity due to piping configurations and local velocities at the transducer ports play a role in the path velocity. Fortunately, as the local velocities are normally symmetrical, they can be canceled statistically. The transverse velocity, if not eliminated by the flow conditioner, must be accounted for by the meter. To determine the true average velocity, ultrasonic meters measure the path and transverse velocities are sampled (unique for the meter model) many times a second and sent to the microcontroller of the control unit which provides the outputs for the volume that has passed through the meter. The greater the number of samples the better will be the accuracy. USFM measures the flow stream directly, without inertia and imposing any constraints. USFMs are more sensitive to systematic error than conventional meters. However, inertia-free measurement and pulse output delay due to sampling are key reasons behind the difficulties to prove ultrasonic meters with conventional provers [5]. 2.4.2 FEATURES AND ADVANTAGES The following are the major advantages and features available from USFM: 1. Nonintrusive (Some non invasive also) measurement; 2. No moving parts; 3. Bidirectional flow measurement; 4. No/minimal pressure loss; 5. High turndown ratio; 6. Capability to handle a wide range of fluids; 7. Extensive diagnostic features; 8. Easier installation; 9. Extensive diagnostic features and information on flow distribution make calibration easier and reduce measurement uncertainty; 10. Provide information on other fluid properties; 11. Capability for remote operation; 12. Available in a wide range of sizes, from 50 mm up to w1050 mm.

1164

Appendix | IV

2.4.3 APPLICATION AREAS USFMs are most popular for the following major applications of CT: 1. High-volume natural gas transportation; 2. Crude oil production, including heavy crudes found in oil shale and oil sands, i.e., products with entrained solids or gas can attenuate; 3. Refined products and light crude oil; high volume: transportation and processing; 4. Pipeline applications; 5. Ship loading/unloading facilities especially in harsh environment; 6. Throughput applications. 2.4.4 USFM PERFORMANCE The following are typical ultrasonic meter performance parameters: 1. Range: Flow (turndown) range: Any flow range from 10% to 100% of maximum flow rate [5]; 2. Viscosity: Large range of viscosity; Reynolds number >20,000; 3. Turndown ratio: 60:1 with linearity around 0.15%; 4. Factors affecting performance: Meter performances specified above are also affected in the following ways: l Since highly viscous products may attenuate or block US signal, hence based on meter size, there is a maximum viscosity handling limitation as specified by the manufacturer l Ultrasonic meters are affected by boundary layer thickness. Multipath USFMs have methods to minimize this effect. Even with these compensation methods there is a transitional region where the velocity profile can change significantly under the same dynamic conditions [5].

2.4.5 PROVING LIQUID ULTRASONIC FLOW METERS Field proving of liquid ultrasonic flow meters is difficult for the following reasons: l

l

The output pulse of USFM there is a time delay between measured parameter and the pulse output. So these are not related in “real time” to the meter throughput. Reducing the meter’s response time and/or increasing the prove volume are recommended. As the measurement is inertia-free, it is very sensitive to systematic error.

Measurement accuracy is improved by taking more samples. In the new API Ultrasonic Flow Meter Measurement standard, prover volumes are recommended to achieve acceptable results. Also included are prover sizes for similar-size turbine meters. 2.5.0 Coriolis Type Flow Metering In 2003, the AGA approved a report AGA-11 and in 2012 standard “Measurement of Single-Phase, Intermediate, and Finished Hydrocarbon Fluids by Coriolis Meters,” on Coriolis flow meter use for natural-gas custody transfer. In 2002, the API approved the use of Coriolis flow meters in custody transfer and fiscal metering (APIe Chapter 5.6). 2.5.1 PRINCIPLES OF OPERATION Coriolis flow meters measure mass flow directly. Since in this meter, mass flow is measured utilizing Coriolis force it is called a Coriolis flow meter. Flow is measured using Coriolis meters by analyzing the changes in the Coriolis force of a flowing substance. There are two phenomena deployed to generate Coriolis force. These are: a

Appendix | IV

rotation force created through vibration of a flow conduit and a mass moving toward and away from the axis of rotation. This is achieved with the help of fluid moving through a tube that rotates about a fixed axis perpendicular to the centerline of the tube. As fluid flows through a Coriolis flow meter, the measuring tubes twist slightly due to the Coriolis force. The natural vibration frequency of the tubes changes with the mass flow of the fluid. With a fluid mass, the Coriolis force is proportional to the mass flow rate of that fluid. A Coriolis meter has two main components: an oscillating flow tube equipped with sensors and drivers, and an electronic transmitter that controls the oscillations, analyzes the results, and transmits the information.

5. There is no requirement for upstream length. 6. In some applications it is considered the best flow-measuring technology. 2.5.4 CORIOLIS METER PERFORMANCE For actual performance, the manufacturer data sheet should be consulted. However, typical performance of the meter is as follows: Over the full range of 0%e100% high accuracy and linearity is possible. Typical turndown of flow for which assured accuracy is possible is 10:1. Viscosity turndown ratio: 10:1; however, it is guided by the pressure drop. Zero stability: This is an important issue associated with the Coriolis meter. This is already discussed at length in Chapter VI, which may be referenced.

2.5.2 METER SIZE In spite of high accuracy, Coriolis meters have limitations on meter size. Coriolis meters get large and unwieldy once they reach the 6-inch size [6]. Even 3-inch and 4-inch meters are quite large. Coriolis meters are currently available from line sizes 1/1400 to 1600 (1e400 mm). Despite the challenges involved, suppliers over the past several years have manufactured larger sizes of Coriolis flow meters. Rheonik (GE Measurement) has long had large-line-size Coriolis meters. Now companies Endress þ Hauser, Krohne, and Micro Motion have also come out with larger-size meters. Endress þ Hauser and Micro Motion offer bent-tube meters, while Krohne’s large-size meters are straight tube. Most of these meters are aimed at the custody transfer market for oil and gas applications [6]. 2.5.3 CORIOLIS METER FEATURES 1. Coriolis mass flow measuring technology offers high accuracy and reliability in measuring material flow. 2. Coriolis flow meters can have high-pressure drop. 3. Available meter size is limited to 400 mm. 4. There are as such no moving parts and high accuracies outweigh the above disadvantages.

1165

2.5.5 CORIOLIS METER CT APPLICATION AREAS The following are the major application areas of Coriolis meters in custody transfer applications: l

l

l l

Crude oil measurement in leased auto custody transfer; Transportation of liquefied natural gas (LNG), liquefied petroleum gas (LPG), and natural gas liquid (NGL); Marketing of LNG, LPG, and NGL; Transport or loading of any product with entrained particulates, as indicated for USFM.

2.5.6 CORIOLIS METER DISCUSSIONS The following are a few issues which must be addressed for better performance. Proper meter installation is very important. Also, it is important to establish an initial zero point adjustment under stable process conditions. These are important for in situ calibration when the meter is rezeroed and it is to be reproven [6]. Like USFM, Coriolis meter output pulses are also not instantaneous and hence not in “real time.” There exists a time delay between the

1166

Appendix | IV

measurement and the transmitted pulse/frequency output. An API task group has been formed to investigate these details. We now investigate prover systems/master meters.

facilities. In this connection definitions of various terms as per API and International vocabulary of basic and general terms in metrology (VIM) are important. There are three types of proving:

3.0.0 DISCUSSIONS ON PROVER SYSTEMS AND MASTER METERS

l

Custody transfer fluid flow meters are calibrated against a master meter at site, or in liquid metering applications, with the help of a meter prover which can be portable or stationary. Normally, for pipe sizes below 1050 mm (42 inch) it can be done at site. Larger-size pipes are often sent for calibration to a place with such calibration

l

l

Direct proving: Best accuracy;* Transfer proving: Reduced accuracy* due to uncertainty* of master meter; Master meter offsite proven: Lowest accuracy* due to added systemic error caused by installation and operating conditions.

(* Refer to Table AIV/3.1.0-1 for the definitions.) 1. Meter prover: This is a calibration unit usually kept at site as part of a liquid metering system to

TABLE AIV/3.1.0-1 Definitions of Terms in API and VIM Term

API

VIM

Accuracy

API (1.0): It is the ability of the measuring instrument to indicate values closely approximating the true value of the quantity measured

VIM 1995 (3.5): Closeness of the agreement between the result of a measurement and a true value of the measurand

Calibration

API Chapter 4 for prover: Calibration stands to mean the procedure to determine the volume of a prover. Proving is the procedure to determine the meter factor

VIM 1995 (6.11): this is the set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring instrument or measuring system and the corresponding values realized by standards

Error

API (4.9.1): Error is caused by differences between the metered volume and the true volume

VIM 2008 (2.16): Measured quantity value minus a reference quantity value

Error Types

API (13): Spurious error, random error, and systematic error (variable and constant)

VIM (3.1.3): Random error VIM (3.14): Systematic error

Meter Factor

API (Chapter 4): According to API VIM 1995 (3.16): Correction Factor: Chapter IV meter factor is a ratio of prover’s numerical factor by which the uncorrected volume to meter indicated volume, i.e., result of a measurement is multiplied to Prover volume compensate for (systematic) error) MF ¼ meter indicated volume Influencing factors: Flow rate, pressure, temperature, viscosity, contamination, wear, etc. Condition statement: Proving condition should match the operating conditions in flow, pressure, temperature and liquid characteristics API density and viscosity

Meter Factor

Uncertainty

API (13): This is the true value of a measurement that cannot be determined, but a valid estimator can be obtained by the statistical analysis. The range or interval within which the true value can be expected to lie is the uncertainty range

VIM 2008 (2.26): Non-negative parameter characterizing the dispersion of the quantity values being attributed to a measurand, based on the information used

Appendix | IV

compare the meter’s registered throughput to a known reference volume. Prover types: There are different kinds of provers: l Pipe prover; l Tank prover; l Compact prover. A meter should be proved on consecutive runs and in repeated measures the tolerance must be below the declared repeatability. A pipe prover which is basically a long run pipe, has known internal volume for comparison. There are different types of pipe provers, including: l Unidirectional; l Bidirectional; l Piston prover; l Compact prover. According to API a liquid flow prover is an open or closed vessel of known volume utilized as a volumetric reference standard for the calibration of meters in liquid petroleum service. This means it is a calibrated volume which is traceable to an internationally recognized measuring standard. 2. Master meter: In proving by master meter applications, one flow meter is designated as the flow prover. The meter must have an accuracy that is better (some claim one order of magnitude better, while others claim that four times better is necessary) than the meter to be tested. The master meter must also have been calibrated against a primary standard within the past 12 months [6]. The flow meter to be tested should be in series with the master meter prover. Based on the error, the correction factor is generated and programmed with a computing system. 3.1.0 Commonly Used Terms and Definitions A few commonly used terms defined in API as well as in VIM, mainly in connection with meter proving have been elaborated in Table AIV/3.1.0-1. 1. Uncertainty statement: It is very important in meter proving. It is an estimate characterizing

1167

the range of values within which the true measured value of a quantity lies and how frequently the reading does lie within this rangedconfidence level. Custody measurement starts with verification or proving a meter to a repeatability of 0.05% with five runs. Statistically this is an uncertainty of: 0.027% at a 95% confidence level [7]. 2. Meter proving: As per API, when the meter is initially installed, meter proving should be frequent. When after frequent proving, it has been established that the meter factors for any given liquid are being reproduced within narrow limits,thentheprovingfrequencycanbereduced, if the factors are under control and the overall repeatability of measurement is satisfactory. 3.2.0 Prover Types As indicated earlier, there are different kinds of provers. 3.2.1 PIPE PROVERS Pipe provers provide a dynamic calibration method in a sealed system with high accuracy. These provers can be used as a part of a metering system or as the reference. It consists of a length of pipe fitted with switches along the length and the volume between the switches is known. A displacer is introduced to the flow, the time it takes to travel between the switches gives a measure of the flow rate. The switches are used to gate a pulse counter, totalizing pulses from a flow meter, a measure of the meter factor can be found. A key component of the prover is a displacer, which is a sphere made up of an elastomeric material. The sphere is filled with liquid and pressurized to inflate the sphere slightly larger than the pipe bore so that when the sphere is inserted into the pipe it takes up an elliptical shape for good seal to the pipe wall. The internal surface of a long steel pipe with a smooth bore is usually coated with epoxy resin to provide a smooth low-friction lining and to protect against corrosion. As the prover requires long length, for practical purposes, a loop is constructed in such a

1168

Appendix | IV

way that the radius of the bends allow the sphere to pass without either sticking or leakage. At each end of the calibrated length of pipe a detector switch is located through the pipe wall. This usually takes the form of a plunger triggering a switch when the sphere passes under it. In this connection Fig II/2.4.1.2-2 B & C may be referenced. There are two kinds of provers: 1. Unidirectional pipe prover: As the name implies, a unidirectional prover has a displacer which only travels in one direction along the pipe. 2. Bidirectional pipe prover: To reduce the length of the pipe bidirectional pipe, provers are used. In this method, with the help of a four-way valve, flow can travel in both directions. 3.2.2 PISTON PROVER Piston types are used for difficult fluids which may damage the lining material. These are straight and quite long. The pipe is normally a smooth-honed bore pipe of stainless or plated carbon steel. The displacer is a piston with multiple seals. Switches are either plungers or noncontacting types. These are bidirectional, with the four-way changeover valve normally located midway along the pipe length to equalize the inlet and outlet pipe work. These are also called compact provers. 3.2.3 SMALL-VOLUME PROVER This is basically a commercially available pipe prover with a volume about one-tenth of a conventional design. These are meant for PD meters, liquid USFMs, Coriolis, and turbine meters (most popular), custody transfer, production FPSO, etc. They are usually meant for flow rates up to 4000 m3/h and can be used for any flow meter with a pulse output. There are several types of smallvolume provers (SVM), such as offshore SVMs, stationary SVMs, truck/trailer-mounted SVMs, etc. 3.3.0 Proving Conditions It is important to prove at conditions that are as similar as possible to the expected operating

conditions. The major influencing factors are described here: 1. Stable flow rate, density, temperature, and pressure are important, so system design, prover settings, and maintenance are critical for proving. 2. Minimizing the pipe length between the meter and prover and avoiding dead-end branches. To ensure measurement traceability, reproducibility, and repeatability should be well maintained (refer to API MPMS Chapter 4 and Chapter 21.2). 3. Sufficient back pressure to be maintained to avoid vapor breakout and to maintain a stable flow rate during displacer launch and travel (refer to API MPMS Chapter 5.6). 4. Accurate density measurement is crucial (refer to API MPMS Chapter 14.6). 5. Enabling compensation for the effect of pressure on the meter. Custody transfer measurement with prover has been depicted in Fig AIV/1.0.0-1. In this connection relevant part of section 2.4.0 and Fig II/2.4.1.2-2 of chapter II may be referenced. With these short discussions on custody transfer including the proving system coming to an end a brief idea is gained on custody-transfer issues. Since custody transfer in oil and gas is critical and crucial there have been developments in all directions. Therefore, it is a subject by itself and it is not really feasible to completely cover the same in this book. It is therefore recommended that the reader should familiarize themselves with the governing standards and apprise themselves with newer developments. Although the safety lifecycle deals with electrical and electronic aspects of safety, it is an important aspect for engineers of all disciplines, especially for instrumentation and process engineers. There are two sides to look into the issue of safety lifecycle, one from the manufacturer’s point of view (IEC 61508) and the other from the end-user’s point of view (IEC 61511). In Appendix V both will be covered in brief.

Appendix | IV

FURTHER READING [1] A. MacGillivray, Custody Transfer Flow Metering, National Measurement System, NEL, Internet document. http://www.tuvnel.com/ assets/content_images/Custody_Transfer_Metering.pdf. [2] J. Yoder, Custody Transfer of Oil and Gas, Flow Control, November 2012. https://www.flowcontrolnetwork.com/Custody-Transfer-of-Oil-Gas/. [3] E. Dupuis, Oil and Gas Custody Transfer, Emerson Process Management, Petroleum Africa, May 2014. http://www2.emersonprocess. com/siteadmincenter/PM%20Articles/Oil-and-Gas-Custody-Transfer_ petroleum_africa_may_2014.pdf. [4] Flow Tech Industries, What Types of Meters are Used in Custody Transfer, August 2016. Internet document. http://flow-tech.com/ blog/?p¼165.

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[5] Bulletin TP0A014; Issue/Rev. 0.0, A Comparison of Liquid Petroleum Meters for Custody Transfer Measurement; General Metering e Technical Paper, March 2005. http://info.smithmeter.com/literature/ docs/tp0a014.pdf. [6] J. Yoder, Custody Transfer of Natural Gas: Cooperation Leads to Success; AGA and API Helped Make it Possible, and Suppliers Responded with Flow Meters that Conform to Standards, Flow Meter Solutions, July 2013. http://www.flowresearch.com/articles/PDF_ Files/2013/Yoder-Flowmeter%200713.pdf. [7] FMC Technologies Measurement Solutions Inc., Fundamentals e Metering Proving and Accuracy, PR0A020I Issue/Rev. 0.0 (7/07). http://energy.org.il/wp-content/uploads/2017/01/nrg420.pdf.

APPENDIX V

SAFETY LIFECYCLE

The author thanks the International Electrotechnical Commission (IEC) for permission to reproduce information from its International Standards. All such extracts are copyright of IEC, Geneva, Switzerland. All rights reserved. Further informationontheIEC isavailablefrom www.iec.ch. IEC has no responsibility for the placement and context in which the extracts and contents are reproduced by the author, nor is IEC in any way responsible for the other content or accuracy therein. In addition, the quotation from IEC Standards should include the following footnotes: IEC 61508-1 ed.2.0 “Copyright © 2010 IEC Geneva, Switzerland. www. iec.ch”; IEC 61511-1 ed.1.0 “Copyright © 2003 IEC Geneva, Switzerland. www.iec.ch.”

PREAMBLE This appendix has been intended to give an idea to the reader about safety lifecycle, which has become part and parcel of all plants and industry as a safeguard against loss of property, personnel, and environment. This appendix has mainly been developed from my book entitled “Plant Hazard Analysis and Safety Instrumentation Systems” (APdElsevier & IChemE U.K.), which deals with detailed analysis of plant hazards and suggested safety instrumentation as a safeguard against that. It is discussed at length there. In this limited space very brief discussions pertinent to safety lifecycle as per IEC 61508 and IEC 61511 only have been presented. In order to give an idea of this factor, properly relevant

issues have been touched upon. The interested reader may refer to Ref. [1].

1.0.0 GENERAL DISCUSSIONS Assets are normally acquired against a lot of effort, toil, and monetary cost; people always wish to protect their assets. Unfortunately, this is not always possible on account of hazards in various forms, however plans to take safety measures are usually made. Until recently, in the process industry, people would incorporate the necessary safety measures in the form of protections under basic process control systems (BPCSs). In the arena of industrial hazard and risk analysis, “system” is defined as a subject of risk assessment, which includes mainly process, product, facility, and environmental and logical groups. Therefore, safety associated with it needs to be treated separately from BPCSs. Sometimes people incorporate redundancy in the system design so that, in case of the failure of one, there will be others available as backups, that is, to fall back on. This is not always true, as is the case with common cause failure. After 1995, people felt the need for integration of safety systems with BPCSs, without compromising the functional independence between the two, to get the best secured industrial systems. In order to treat these independently in a standardized manner, several international standardsdIEC 61508, IEC 61511, ISA 84d evolved [1]. These standards, especially IEC 61508 and IEC 61511, are backbone standards of safety lifecycle. These standards are meant 1171

1172

Appendix | V

RISK ASSESSMENT (PHA, SIL DETERMINATION)

DESIGN ENGG (EXECUTION & EVALUATION)

MODIFICATION INSTALLATION & COMMISSIONING (FAT, SAT, PROOF TEST)

DECOMMISSIONING

OPERATION & MAINTENANCE

FIGURE AV/1.0.0-1 Safety lifecycle of SIS [1].

for electrical, electronics, and programmable electronics (E/E/PE). These standards have been developed with the aim that at process upset, or system or equipment failure, the designed system would allow the process safety to be managed in a systematic way following a risk-based management system. Safety instrumented systems (SISs) play a great role in mitigating technical risks in industrial plants. An SIS consists of a wellengineered hardware and software control system used to monitor the condition of plant within the operating limit. When any risk condition arises, it triggers an alarm and takes the entire system to a safe condition to mitigate all kinds of risks as far as possible. [The safety life cycle, according to IEC standard, can be considered as a cyclic process or closed loop comprising in cyclic fashion of identifyeanalyzeedesigneverify and is comparable with “plan, do, check, act” of ISO 31000.] In view of this, the SIS lifecycle can be conceived of as what is shown in Fig. AV/1.0.0-1. Unless protected, a system runs at a risk. This is an inherent risk prior to any action being taken to change the consequence. Designers aim to bring the system within, or in fact below, that risk limit by incorporating various protection

measures to mitigate the risk. Even after such protection, the small risk left is often referred to as the residual risk. Some protections come from other technological means, but major protections come through the interface of BPCS with a safety system to make SIS. Readers should not confuse the operational interlock and protections of BPCS, with SIS. The concept has been clarified through Fig. AV/1.0.0-2. Prior to moving on to other discussions, it is important that a few terms are defined. 1.1.0 Definitions and Explanations of a Few Related Terms A few terms normally encountered in safety lifecycle discussions are clarified here. 1. Hazard: The term hazard has been defined by many agencies in different ways, based on their terms of reference. These are detailed in Ref. [1], interested readers may refer to the same. Here only two definitions have been defined: l General definition: Hazard can be considered as a state with a set of conditions of a system, which together with other conditions in the environment, or in the

Appendix | V

1173

FIGURE AV/1.0.0-2 Risk reduction by SIS. Based on standard IEC 61508 Concept.

environment of the system, will lead to an accident. So, a hazard can be any biological, chemical, mechanical, environmental, or physical agent which has the potential to cause harm or damage to humans, other organisms, plant, machinery, assets, or the environment, in the absence of its control. l ISO/IEC Definition: As per ISO/IEC 51 or IEC 61508, a hazard is defined as, “the potential source of harm.” In IEC 61508, harm has been defined as physical injury or damage to the health of people either directly or indirectly as a result of damage to property or to the environment. 2. Hazard analysis: Hazard analysis uncovers the hazards that exist in the workplace (in this case, industrial plant) focusing on the system or project. By hazard analysis, riskbased decisions are taken to develop means to quantify, track, develop mitigation means, and control hazards, follow-up action, verify effectiveness, and communicate. 3. Risk: According to ISO/IEC guide 51/IEC 61508, risk is, “the combination of probability of occurrence of harm and the severity of that harm.” From here it transpires that risk

refers to the likelihood that a hazard can cause actual damage. 4. Basic process/plant control system (BPCS): This system handles the process controls and monitoring for the process. According to IEC 61511, “BPCS is a key layer of protection which responds to input signals from the process, its associated equipment, other programmable systems and/or operator and generates output signals causing the process and its associated equipment to operate in the desired manner but which does not perform any safety instrumented functions with a claimed SIL 1.” 5. Safety instrumented system (SIS): SIS is designed to prevent, or mitigate from happening, a hazardous event, by taking the process to a safe state whenever a predefined or predetermined condition occurs to the system. It is a combination of sensors, logic solvers, and final control elements. These are in programmable electronics (PE), consisting of both hardware and software. 6. Safety instrumented function (SIF): SIF consists of sensors, logic solvers, and final control element combinations. SIF takes the

1174

7.

8.

9.

10.

Appendix | V

system or process into the safe zone in the event of a hazardous situation/event, which is determined by predefined conditions for the process. Functional safety: According to the ISA, “the ability of SIS or other means of risk reduction to carry out the actions necessary to achieve or to maintain a safe state for the process and its associated equipment.” Also, functional safety in SIS highly depends on proper functioning of sensors, logic solvers, and Final control element (FCE), so that a reduced risk level can be achieved. Safety integrity level (SIL): This is a measure of the performance of an SIS. It is determined by Probability of failure on demand (PFD) for SIF (SIS). There are four SIL levels represented by numbers: SIL 1, 2, 3, 4. The higher the SIL number, the better will be the performance and the lower will be the PFD value. However, with an increase in SIL number, the cost and complexity of the system increases, but the risk level reduces. It is worth noting that there can be an individual component PFD but not SIL. SIL is only given to a system (SIS). SIL certification can be issued by the company (self-certification allowed), or other competent authority to indicate that appropriate the procedure, analysis, and calculation have been followed and are compatible for use in appropriate SIL level. Probability of failure on demand (PFD): This is the probability that SIF/SIS fails to perform its intended safety function during a potentially dangerous condition. PFDavg is normally used in calculations when regularly inspected and tested. Some other associated terms: The following terms are important and associated with hazard and risk analysis: l Accident: This is an undesired, unplanned (but may not always be unexpected) event, which will result in a specified level of loss (in terms of health, property, production, etc.);

l

l

l

Mishap: This is bad luck, misfortune, etc. In terms of industry, it could be an accident, which is associated with uncontrolled release of energy and toxic material exposure; Near miss/incident: This is normally used in a good sense, meaning an event occurred, but it involved very minor or no loss (in terms of health, property, production, etc.); Safety: Freedom (or nearly freedom!) from accident or loss.

1.2.0 Discussions on BPCS and SIS In this section an overview of the interrelation amongst BPCS, SIS, SIL, and functional safety will be covered. As indicated earlier, like BPCS, SIS also consists of sensors, final control elements, and logic solvers. A typical layout has been shown in Fig. AV/1.2.0-1. In this diagram, the user interface and interface with BPCS have been shown through a communication bus. It is interesting to note that there can be separate BPCS and SIS, but these two can be integrated as long as they meet the requirements of standards like IEC 61508/61511 or ANSI/ISA 84. Functional safety is very important for the safety lifecycle, as covered below. 1. Functional safety concept: Basically, functional safety stands on the following concept: l All processes or manufacturing systems have inherent hazard; l All processes or manufacturing systems have an inherent quantifiable failure rate, which cannot be brought to zero value; l All processes or manufacturing systems have a tolerable failure rate without causing any harm to the system. Also, this failure rate is specific to the system in question; l For all processes or manufacturing systems, these failure rates can be categorized in terms of SIL (from functional safety point of view).

Appendix | V

1175

FIGURE AV/1.2.0-1 SIS boundary and layout.

2. Failure category: The failure categories in a functionally safe system are described here: l Systematic failure: Systematic failure may come from a shortcoming in system design, implementation, or manufacturing defect, or for not following of any statute, standard, or good engineering practice. These can be reduced thorough analysis and remedial measures. l Random failure: These are uncontrolled, unnoticed failures, sometimes inherent with the process and they cannot be reduced in a systematic way, only proper attention given to early detection can reduce the amount of loss (e.g., unprecedented grid collapse). Safety function may come as a result of hazard analysis and it is to be implemented in SIS. We now look into risk analysis in more detail.

2.0.0 RISK DISCUSSIONS Prior to taking up the risk analysis issue it is better to address some pertinent issues associated with risks and risk analysis.

2.0.1 RISK FREQUENCY This defines the likelihood of the risk, that is, it stands for the probability of risk. These are categorized as: Very likely: at least once in 6months; Likely: at least once a year; Unlikely: maybe once in lifetime Very unlikely: May be 1%. Typical examples are shown here. Risk frequency data and release data are available in HSE (UK), OREDA, and OGP publications.

1176

Appendix | V

2.0.2 SEVERITY Severity is loosely used to indicate the impact of risk, that is, the consequence. These are slightly harmful (e.g., superficial cut, minor cut, etc.), harmful (e.g., burns, serious pains, minor fracture), and extremely harmful (e.g., major fracture, amputation/permanent damage or even death). There are some other ways to categorize severity. Typical categorizations could be as listed here: 1. Minor: Minor system damage without causing injury; 2. Major: Low-level exposure to personnel, activates public alarm; 3. Critical: Minor injury to personnel, fire, or release of chemical to environment; 4. Catastrophic: Major injury, death, big leakage (e.g., Bhopal gas leak).

2.0.3 RISK LEVEL (BASED ON ACTION AND TIME) The levels of risks are often categorized based on the potential. The categories are termed as follows: 1. Very low: These risks are acceptable and may not need any action; 2. Low: No control may be necessary unless these are available at low cost; 3. Medium: Suitable considerations shall be there to see if the risk can be lowered, wherever applicable, to a tolerable level, within a defined time limit. However, due considerations shall be given to the additional cost for risk reduction. Whenever the risk is associated with harmful consequences, it is necessary to make sure that risk reduction controls are properly maintained; 4. High: A good amount of effort is applied to reduce risk on an urgent basis within a defined time frame. It is essential to give due considerations towards the choice

amongst suspending or restricting the activity or applying an interim control measure until the main risk reduction control is implemented. Whenever the risk is associated with a harmful consequence, it is necessary to make sure that risk reduction controls are properly maintained; 5. Very high: Unacceptable. Substantial improvements in risk reduction control measures are necessary to reduce the risk to an acceptable level. Activities need to be halted until risk reduction control is implemented. Otherwise, work shall remain prohibited. It is essential maintain the control system for risk reduction extremely with care (as without such control, systems may not be permitted to function). Risk associated with very harmful consequences needs risk assessment and analysis. The above categorizations are qualitative in nature. For quantitative calculations, one may need the help of probability and associated software, which are also available from various agencies for different applications. Interrelations amongst these factors have been depicted in Fig. AV/ 2.0.0-1. 2.1.0 Risk Analysis and Assessment For plant hazard analysis there will always be a risk target, which is a measure that expresses the consequence of a risk in relevant terms of the project and organization concerned. In order to get the measure it is necessary to go for risk analysis and risk assessment. What is risk analysis? 1. Risk analysis: As per the latest version of IEC/ISO 31010 (IEC 60300-3-9), risk analysis is the “systematic use of available information to identify hazard and to estimate the risk to individuals, populations, property or

Appendix | V

1177

LIKELIHOOD FATAL HAZARD

HAZARD SEVERITY

HAZARD EXPOSURE

LIKELIHOOD HAZARD OCCURRENCE

FIGURE AV/2.0.0-1 Combinations of risk component.

the environment.” So, essentially, risk analysis finds, organizes, and categorizes sets of risks. 2. Risk assessment: Risk assessment will be clarified from the following activities: l Identification of hazard; l Analysis and evaluation of risk; l Finding an appropriate way to control and mitigate hazards; l The main aim of risk assessment is to remove hazard, or reduce the risk level by adapting necessary control measures, to move towards safety. 3. Risk assessment procedure: The following points are major issues considered as part of the risk assessment procedure: l Hazard identification; l Evaluation of risk in terms of; likelihood, severity, and level of risk;

l l

l l

l l l

Standard operating conditions; Emergency situation (nonstandard operation); Review of all associated information; Actual and potential exposure of personnel (latency, frequency, intensity); Environmental impact; Design engineering control; Documentation.

Risk register, risk matrix, etc. are tools for risk analysis and assessments. 2.1.1 RISK REGISTER A typical risk register has been depicted in Fig. AV/2.1.0-1. A risk register is basically a record of identified risks for a project. The major characteristic

1178 Appendix | V

FIGURE AV/2.1.0-1 Risk register (typical).

Appendix | V

features of a risk register have been listed below: 1. Short description of each risk along with associated consequences; 2. Factors influencing the likelihood and impact; 3. Grading of risks e.g., low, medium, high, extreme, etc.; 4. Risk acceptability; 5. Existing and proposed actions for risk mitigation; 6. Key risk indicator (KRI) and upward reporting factor. 2.1.2 RISK MATRIX The risk matrix may be considered as a quantitative or semiquantitative tool for qualitative hazard analysis. It is very important to develop a risk matrix design very precisely so that there will not be a false sense of security after the risk matrix is done. If the likelihood or impact of any risk is not properly defined, then as a result of wrong calculation any particular risk may be considered in the low-risk level, but in reality it is not so. In that case one may be happy to note that it is low level and hence securedda false sense of security. There are several standard guidelines and published risk matrices, but at the start one has to decide the purpose for which it is to be developed. Table AV/2.1.0-1 is an example of a risk matrix available from the Center for Chemical Plant Safety (CCPS). Here, risk levels are described as I, II, III, and IV. Tables AV/2.1.0-2 and AV/2.1.0-3, which are self-explanatory, show various features of risk matrices. They also TABLE AV/2.1.0-1 Risk Matrix Consequence Frequency

1

2

3

4

4

IV

II

I

I

3

IV

III

II

I

2

IV

IV

III

II

1

IV

IV

IV

III

1179

show how a risk matrix can be qualitative as well as quantitative. Consequence range has been explained in Table AV/2.1.0-5. Here it is to be noted that both frequency as well as consequences are quantified. However, frequency and consequence can be qualitative also. TABLE AV/2.1.0-2 Risk Level. Likelihood and Consequence Ranges Have Been Explained in Tables AV/2.1.0-3 and AV/2.1.0-4 Risk Level

Category

Description

I

Unacceptable

Should be mitigated engineering and/or administrative control to risk level III or less, within a specified period (say 6months)

II

Undesirable

Should be mitigated engineering and/or administrative control to risk level III or less, within a specified period (say 12months)

III

Acceptable with controls

Should be verified that procedures and controls are in place

IV

Acceptable

No mitigation required

TABLE AV/2.1.0-3 Likelihood Ranges Based on the Levels of Protection Likelihood Range

Quantitative Frequency Criteria (Typical)

Level 4

Initiating event or failure (e.g., leakage/rupture)

Level 3

One level of protection (e.g., pipe leakage, overload)

Level 2

Two levels of protection (e.g., electrical actuator uprooting)

Level 1

Three levels of protection (e.g., vessel failure)

1180

Appendix | V

TABLE AV/2.1.0-4 Consequence Range Consequence Range

Quantitative Safety Consequence Criteria

4

Onsite/offsite: potential for multiple life-threatening injuries or fatalities Environmental: uncontained release with potential for major environmental impact Property: (including plant): plant damage value in excess (e.g., $)100M unit of currency Onsite/offsite: potential for single life-threatening injury or fatality

3

Environmental: uncontained release with potential for moderate environmental impact Property: (including plant): plant damage value in the range of (e.g., $)10e100M unit of currency Onsite/offsite: potential for an injury requires medical attention

2

Environmental: uncontained release with potential for minor environmental impact Property: (including plant): plant damage value in the range of (e.g., $)1e10M unit of currency Onsite: potential for injuries requires only first aid

1

Offsite: noise or odor Environmental: contained release with local impact only Property: (including plant): plant damage value in the range of (e.g., $) 0.1e1.0M unit of currency As stated earlier, risk matrices could be qualitative, semiquantitative, or quantitative. A typical quantitative risk matrix has been shown in Table AV/2.1.0-5.

Qualitative frequency terms include the following: l l l l l l

Frequent; Probable; Occasional; Remote; Improbable; Incredible.

Similarly, qualitative consequences include the following: l l l l

Catastrophic; Critical; Marginal; Negligible.

Now look at Table AV/2.1.0-5, and note that when either frequency or consequence sets of

TABLE AV/2.1.0-5 Quantitative Risk Matrix Consequence Probability

$1000

$10,000

$100,000

$1,000,000

Every month

Medium

High

High

High

Every year

Low

Medium

High

High

Once in 10years

Negligible

Low

Medium

Medium

Once in 100years

Negligible

Negligible

Low

Low

Appendix | V

values are replaced by a qualitative set of values mentioned above then the matrix would be semiquantitative. Similarly, when both frequency and consequence sets of values are replaced by a qualitative set of values, the risk matrix would be qualitative as in Table AV/2.1.0-5. We have concluded the discussion on risk analysis and now look at what is needed by standard IEC 61508 and 61511 for safety lifecycle.

3.0.0 SAFETY LIFECYCLE The safety lifecycle for any system is based on IEC 61508, IEC 61511, and ISA 84.1. These standards are applicable for Electrical, Electronic and Programmable electronic (E/E/PE) equipment only. Since each equivalence with IEC standards so, they are not discussed separately. IEC 61508 is basically meant for manufacturers and 61511 is basically meant for end users. As a

result, they have different approaches, so we take up each of them separately. One thing common to all of these is that each of them has three stages and these are: analysis, implementation/realization, and operation. A basic idea about safety lifecycle can be gained from Fig. AV/3.0.0-1. In addition, there will be a planning and management section. Of all stages, verification is most important. For a detailed explanation and interpretation of entire process Ref. [1], may be referred to. Conceptually, a safety lifecycle can be represented as a cyclic system [2]. This has been shown in Fig. AV/3.0.0-1. With this concept in mind, safety lifecycle discussions have been presented below. With the permission of IEC, the safety lifecycles of IEC 61508 and IEC 61511 have been reproduced as Figs. AV/3.0.0-2 and AV/3.0.0-3, respectively.

RISK & SAFETY ASSESSMENT &

N IO T AT EN IC EM F I V OD RO M P IM 5

1

FUNCTIONAL 2

4 INSTALLATION & VERIFICATION

1181

3

DESIGN VALIDATION

FIGURE AV/3.0.0-1 Concept of safety lifecycle.

REQUIREMENTS

1182

Appendix | V

ONE IMPORTANT NOTE FROM FIG 2 OF THE STD: 1) FOR CLARITY VERIFICATION, OF FUNCTIONAL SAFETY

Concept

2

Overall scope definition

3

Hazard and risk analysis

4

Overall safety requirements

5

Overall safety requirements allocation

MANAGEMENT

& FUNCTIONAL

SAFETY ASSESSMENT NOT SHOWN

Overall planning Overall operation and 6 maintenance 7 planning

1

E/E/PE system safety 9 requirements specification

Overall Overall safety installation and validation 8 commissioning planning planning

*

11

Other risk reduction measure Specification and realization

10

E/E/PE safety related systems Realization (see E/E/PE system safety lifecycle)

12

Overall installation and commissioning

13

Overall safety validation

14

Overall operation, maintenance and repair

16

Decommissioning or disposal

15

Overall modification, and retrofit

FIGURE AV/3.0.0-2 Safety lifecycledIEC 61508 (Fig. 2). Refer to Fig. 2 of IEC 61508-1:2010. Courtesy: IEC (see the detailed acknowledgment at the start of this appendix).

Appendix | V

Management

Safety

of functional

life cycle

safety and

structure

functional

and

safety

1183

Verification

Hazard and risk assessment Clause 8 1

planning

assessment and auditing

Allocation of safety functions to protection layers Clause 9 2

Safety requirements specification for the safety instrumented system Clauses 10 and 12 3 Stage 1

Designed and

Design and engineering of

development of other

safety instrumented system

means of

Clauses 11 and 12 4

risk reduction Clause 9 9

Stage 2

Installation, commissioning and validation Clauses 14 and 15 5 Stage 3

Operation and maintenance 6

Clause 16

Stage 4

Modification 7

Clause 17

Stage 5 Clause 5

Clause 6.2

Clause 7 12.4and12.7 decommissioning

10

11

8

Clause 18

9

Typical direction of information flow No detailed requirements given in this standard Requirements given in this stadard NOTE 1 Stages 1 through 5 inclusive are defined in 5.2.6.1.3 NOTE 2 All references are to part 1 unless otherwise noted

FIGURE AV/3.0.0-3 Safety lifecycle phase of IEC 61511 (Fig. 8 of IEC 61511 and IS 61511). Courtesy: IEC (see the detailed acknowledgment at the beginning of this appendix).

1184

Appendix | V

3.1.0 IEC 61508 Safety Lifecycle

3.1.3 OPERATION PART OF IEC 61508

As indicated above there are three stages, we start with the analysis part.

This really starts with the design validation through operation and maintenance to check whether the system really addressed the safety issues. Necessary modifications, including overall modification and retrofitting, as applicable, to be carried out to verify proper implementation, i.e., review of safety lifecycle activities and ensures that all steps were carried out and documentation is in place [3]. The final step is decommissioning or disposal. The system has been described here very briefly. It is recommended to refer to Section 4 of Ref. [1] for detailed discussions and treaties.

3.1.1 ANALYSIS PART OF IEC 61508 The following stages are under the analysis part. Concept: Understanding of the equipment under control and its environment (physical and legal) to determine hazard sources and hazard informationdHazard interaction with other equipment. Overall scope definitions: Here the system boundary and hazard scopes are defined. Hazard and risk analysis: Here a list of hazards and events is prepared in sequence. It is followed by finding the likelihood and consequence (refer to Section 2.1.0). Safety reallocation: This includes the overall safety requirements and safety reallocation. 3.1.2 ANALYSIS PART OF IEC 61508 This section deals with technology and architecture selections. The major issues are listed here: l

l l l

Perform reliability and safety evaluation to determine if you met your target SIL requirement; Conceptual design of SIS; Detailed design of SIS; System development, includes detail design and engineering, installation planning, installation, commissioning, including acceptance tests.

It is worth noting that there are two parts associated with the Programmable electronics (PE) system for realization/implementation; these are hardware (HW) and software (SW) implementation parts, including specification of safety requirements, safety integrity for each of HW and SW. There should be proper means to validate the planning, design development, and integration of each of HW and SW and complete system/overall validation. This stage also includes installation and commissioning of the entire safety system.

3.2.0 IEC 61511 Safety Lifecycle Basically this is management of functional safety and safety assessment with safety lifecycle structure and planning. Here safety life cycle is seen from user's point of view. The system is completed with proper verification. Here also there are three stages, i.e., analysis, implementation, and operation. 3.2.1 ANALYSIS PART OF IEC 61511 The basic structure of the analysis part consists of the following: 1. Hazard and risk assessment (Clause 8); 2. Allocation of safety function protection layer (exists around BPCS in different forms as additional protection to the system) (Clause 9); 3. Specification of SIS as safety requirement. Of these, Subsections 3.2.1.1 and 3.2.1.2 are not really part of the IEC standard but external things to interface (refer to clauses 8 and 9 of the standard). 3.2.2 IMPLEMENTATION PART OF IEC 61511 The basic structure of the implementation part consists of the following: Design and engineering of SIS; Design and development of other means of risk reduction (clause 9 not part of standard); Installation, commissioning, and validation.

Appendix | V

3.2.3 OPERATION PART OF IEC 61511 This stage starts after the erection and commissioning are over. The stages include: Operation and maintenance; Modification (as required); Decommissioning. Throughout all stages there will be verification which the end user needs to verify to establish the safety system. The basic requirements for the lifecycle have been established. However, as far as flow metering is concerned the main issue is around SIS and SIL. Naturally, without discussions on SIS and SIL the discussions will be incomplete. Therefore, the discussions will be completed with the discussions on SIS and SIL in next section. 3.2.4 SUMMARY From the above discussions it is clear that in each of the stages there will be some functions to be performed and these have been summarized below. 1. Analyzing phase: The following are the major steps: l Experiment design; l Hazard identification; l Risk assessment; l Comparison to risk tolerance criteria; l Risk reduction allocation; l Safety function definition; l Safety function specification; l Reliability verification. 2. Implementation phase: The following are the major steps: l Equipment design; l Software configuration; l Equipment build (IEC 61508); l Factory acceptance testing (IEC 61508); l Construction/installation; l Site acceptance testing; l Validation; l Training; l Pre-startup safety review.

1185

3. Operation phase: The following are the major steps: l Operation; l Training; l Proof testing; l Inspection; l Maintenance; l Management of change; l Decommissioning.

4.0.0 SIF, SIL, AND SIS Flow meters also need to be safe. As has been discussed earlier, there are several safety instrumented functions (SFI) in any safety instrumented system (SIS) comprising of sensors, logic solvers, and final control elements. Basically, flow meters are sensors in the SIS family. However, metering pumps at times can be the final control element in SIS (e.g. dosing system). Since discussions on the complete safety loop are beyond the scope of this book we need to concentrate on safety functions of individual items. This is more related to the safety integrated system (SIL). So our discussions will be mainly on the same. SIS explanation and interrelation between SIS and SIF in line with IEC 61511-1:2003, have been depicted in Fig. AV/4.0.0-1 for better understanding. Terms like SIS, SIF, and SIL have been discussed in Section 1.1.0 already. Let us now look at the relevant details. 1. Safety instrumented system (SIS) explanation: SIS is meant to prevent, control, or mitigate hazardous events and take the process to a safe state when predetermined conditions are violated. An SIS can be one or more SIFs, which is composed of a combination of sensors, logic solvers, and final control elements. SIS or SIF is extremely important especially when there is no other noninstrumented way of adequately eliminating or mitigating process risks. 2. Safety integrity level (SIL) explanation: In the context of the book, SIL basically represents to what extent a device or devices in

1186

Appendix | V

According to IEC 61511 Safety instrumented control funcon stands for safety instrumented funcon with a specified SIL operang in connuous mode which is necessary to prevent a hazardous condion from arising and/or to migate its consequences. Safety instrumented control system is instrumented system used to implement one or more safety instrumented control funcons. Also Safety instrumented system (S1S) is instrumented system used to implement one or more safety instrumented funcons (SIF). An S1S is composed of any combinaon of sensor (s), logic solver (s), and final elements(s)

FIGURE AV/4.0.0-1 SIS details as per IEC 61511-1:2003.

combination in process can be expected to perform safely. And, in the event of a failure, to what extent the process be expected to go to the safe state! Therefore, SIL gives a measure of safety risk or risk reduction to a tolerable limit for a given process. The IEC 61,508 standard also specifies the measures; such as “fault avoidance” (systematic faults) and “fault control” (systematic and random faults); to be taken into consideration in the design of safety functions consisting of a sensor, logic solver, and final control element. From IEC 61,508 one knows that SIL depends highly on two major factors: hardware failure tolerance (HFT) and safe failure fraction (SFF). 3. Hardware failure tolerance (HFT): This is the ability of hardware to continue to perform a specified safety function in the presence of faults or errors. HFT of N means that Nþ1 faults will cause a loss of safety function for the unit. 4. Safe failure fraction (SFF): This is the ratio of the average failure rates, safe plus dangerous detected failure, and safe plus dangerous failure (Ref: IEC 61508). Now let us look into SIL more closely. 5. Probability of failure on demand (PFD): PFDavg: Probability of failure on demand is the probability of a functional unit or system failing to respond to a demand for action arising out of a potentially hazardous condition, i.e., a device will fail to perform its specified safety function when it is asked to do so. In other words the probability average PFDavg is used in calculations for system reliability. When there is a probability of failure, then there has to be a question about its availability.

6. Availability: Availability is defined as the probability that equipment will perform its task. Now let us look into SIL more closely. 4.1.0 Safety Integrity Level (SIL) Discussions As per IEC 61511, each SIF shall have an associated SIL, which is a measure of safety system performance and is related to the probability of failure on demand (PFD) for the associated SIF. There are four defined SILs: SIL-1, 2, 3, 4. The higher the SIL number, the lower the PFD for the safety system, indicating a better system performance. Also, it has been found that the higher the SIL number, the higher the cost and complexity of the system will be. SIL is applicable and calculated for an entire SIF system, but not on individual products or components. As described earlier, each SIF is assigned an SIL. The reliability and availability of SIF due to SIL are achieved by design, design installation, and testing. SIL is also dependent on architectural constraints. 4.1.1 SIL CATEGORIES The following points on SIL are worth noting [4]: 1. 2. 3. 4.

SIL 0/none: lowest risk; SIL 1: 95% of the SIFs; SIL 2: 5% of SIFs; SIL 3: = 2.5 mm DIA

FINGER

5

4

>= 1 mm DIA

WIRE

5

5

DUST PROTECTED

WIRE

5

6

DUST TIGHT

WIRE

5

FIGURE AVI/4.0.0-1 Ingress protection code.

Appendix | VI

IP:1st

1207

IP:1st

CHARACTER

CHARACTER

NEMA ENCLOSURE TYPES

(IEC 3, 60529)

1

3R,

3X,

12,

4, 5

2 3S,

3SX

3RX

(IEC

12K,

60529)

6P

6

4X

13

IP 0

IP 0

IP 1

IP 1

IP 2

IP 2

IP 3

IP 3

IP 4

IP 4

IP 5

IP 5

IP 6

IP 6 IP 7

IP 8

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

A

B

FIGURE AVI/4.0.0-2 Conxversion of IP to NEMA rating. A represents NEMA enclosures types exceeds the requirements for IEC 60529 IP first character shown by cyan hatch, B represents NEMA enclosures types exceeds the requirements for IEC 60529 IP second character shown by red bricks. So, NEMA 4X ¼ IP66 from above chart. Example: conversion of IP 45: first 4 met by 3,3X,3S,3SX/4,4X/5/6/6P/12,1K,13 but for second character 5 only 3,3X,3S,3SX/4,4X/6/6P. Qualify so, they are equivalent to IP45. However many like type 3 exceed IP 45 requirement on account of corrosion gasket aging testing. Developed based on NEMA 250:2003. Courtesy: NEMA 250:2003.

TABLE AVI/4.0.0-1 NEMA Enclosure Rating With Interpretation: (I, Indoor; O, OutdoordApplication) X Indicates Applicability

O

Protection Against: Personnel Access

Protection: (Ingress): Foreign Solid Object

Type

I

Protection: (Ingress) Water Harmful Effect

1

X

To hazardous part

Falling dirt

2

X

To hazardous part

Falling dirt

Dripping/light splashing

3

X

X

To hazardous part

Falling dirt, windblown dust

Rain, sleet, snow and external ice formation

3R

X

X

To hazardous part

Falling dirt

Rain, sleet, snow and external ice formation

3S

X

X

To hazardous part

Falling dirt, windblown dust

Rain, sleet, snow. Operable when ice-laden

Continued

1208

Appendix | VI

TABLE AVI/4.0.0-1 NEMA Enclosure Rating With Interpretation: (I, Indoor; O, OutdoordApplication) X Indicates Applicabilitydcont’d

a

Protection Against: Personnel Access

Protection: (Ingress): Foreign Solid Object

Protection: (Ingress) Water Harmful Effect

Type

I

O

3X

X

X

To hazardous part

Falling dirt, windblown dust

Rain, sleet, snow and external ice formation and additional corrosion protection

3RX

X

X

To hazardous part

Falling dirt

Rain, sleet, snow and external ice formation and additional corrosion protection

3SX

X

X

To hazardous part

Falling dirt, windblown dust

Rain, sleet, snow and external ice formation and additional level of protection for corrosion. Operable when ice-laden

4

X

X

To hazardous part

Falling dirt, windblown dust

Rain, sleet, snow. Splashing and hose-directed water. Undamaged due to external ice formation on enclosure

4X

X

X

To hazardous part

Windblown dust

Rain, sleet, snow. Splashing and hose-directed water. Additional level of protection for corrosion and undamaged due to external ice formation on enclosure

5

X

e

To hazardous part

Falling dirt and settling airborne dust, lint, fibers, and flying

Dripping and light splashing

6

X

X

To hazardous part

Falling dirt

Hose-directed water, entry of water due to occasional temporary submersion at a limited depth, and undamaged due to external ice formation on enclosure

6P

X

X

To hazardous part

Falling dirt

Hose-directed water, entry of water during prolonged submersion at a limited depth. Additional level of protection for corrosion and undamaged due to external ice formation on enclosure

12/ 12 Ka

X

To hazardous part

Falling dirt, circulating dust, lint, fibers, flyings

Dripping/light splashing

13

X

To hazardous part

Falling dirt, circulating dust, lint, fibers, flyings

Dripping/light splashing. Also protection against spraying, splashing and seepage of oil and noncorrosive coolants

12 K with knockout, whereas 12 without knockout.

Appendix | VI

5.0.0 ENCLOSURE MARKINGS PROTECTION STANDARDS WITH COMPARISONS

l l l

In this section marking of enclosures, various protection types, and their comparisons are presented so that the reader can get to know the pros and cons of each type. The discussions start with enclosure markings. 5.1.0 Enclosure Markings Various enclosures, especially explosion-proof enclosures, marking on the enclosure are very important. Details of enclosure markings in line with IEC and NEC have been depicted in Fig. AVI/5.0.0-1. Brief details about the same have been presented below. The typical meaning of each of the markings is indicated also in Fig. AVI/5.0.0-1. Normally, the following information is marked on the plate: l

l l l

l

Manufacturer’s name details with model and serial number; Conformity mark and ID number; Designation for identification; Application zone including: Group, vapor/ dust/mine; Categories of approval for specific zones;

l l

l

1209

Type(s) of protection the equipment fulfills; Explosion group and subgroup; Temperature class; Ambient specification; Test laboratory where the test certificate was issued; Standard with versions for certification.

There are some differences in equipment marking types between standard EU/IEC and that of NEC. Detailed equipment markings for both IEC/ATEX (EU) and NEC standards have been elaborated in. 5.2.0 Protection Standards With Comparison It is needless to say that there are different standards for enclosure protections already discussed. Table AVI/5.0.0-1 depicts various standards and their global geographical areas of use. Various international enclosure protection standards are compared in Fig. AVI/5.0.0-2. This explosion protection concept is also applicable to fieldbus systems. We conclude the discussions on enclosure electrical protection to address device communication in next appendix (Appendix VII).

TABLE AVI/5.0.0-1 Global Enclosure Protection Standards Explosive Atmosphere

Geographical Location

Standards

Code

Class I Division 1 and 2

USA

FM3600

e

Class I Division 1 and 2

Canada

CSA C22.2-0

e

Class I Division 1 and 2

USA

ISA 60079-0

AEx

Class I Division 1 and 2

Canada

CSA C22.2-60079-0

Ex

Category 1G/2G/3G

European Union

EN 60079-0

Ex

IEC 60079-0

Ex

EPL Ga/Gb/Gc a

International IEC

a

Russia and Ukraine follow: GOST Russia/GOST Ukraine Standards; Australia follows IEC but code is IEC Ex. [1].

1210

Appendix | VI

(A)

(B)

FIGURE AVI/5.0.0-1 Equipment markings (different standards). (A) Equipment markingdEU/IEC. (B) Equipment markingdNEC based.

Appendix | VI

PROTECTION TYPE

PROTECTION

EXPLOSIVE

GEOGRPHICAL

PRINCIPLE

ATMOSPHERE

LOCATION

INTRINSIC SAFETY

LIMITED ENERGY

LIMITED ENERGY OF SPARK

ENCLOSED BREAK

EXTINGUISH THE FLAME

POWDER- FILLED

USA

FM3615

CLASS I DIVISION1

CANADA

CSA C22.2-30

CATEGORY 1G/2G/3G

EUROPE UNION

EN 60079-1

EX da/

International- IEC

IEC 60079-1

db/dc

ISA 60079-1

AEx d

CLASS I ZONE 1

CANADA

CSA C22.2-60079-1

Ex d

CATEGORY 2G

EUROPE UNION

EN 60079-5

Ex q

International- IEC

IEC 60079-5

Ex q

EPL Gb CLASS I ZONE 1

USA

ISA 60079-5

AEx q

CLASS I ZONE 1

CANADA

CSA C22.2-60079-5

Ex q

EUROPE UNION

EN 60079-15

Ex nC

International- IEC

IEC 60079-15

Ex nC

CATEGORY 3G EPL Gc CLASS I ZONE 2

USA

ISA 60079-15

AEx nC

CLASS I ZONE 2

CANADA

CSAC22.2-60079-15

Ex nC

CLASS I DIVISION1

USA

FM3610

IS

CLASS I DIVISION1

CANADA

CSA C22.2-157

IS

CATEGORY 1G/2G/3G

EUROPE UNION

EN 60079-11

EX ia/

International- IEC

IEC 60079-11

EPL Ga/Gb/Gc CLASS I ZONE 1

CANADA

CLASS I ZONE 1

USA

CSA C22.2-60079-11 ISA 60079-11

AEX ia-c EX nL

CLASS I ZONE 2

USA

ISA 60079-15

AEX nC

International- IEC

CLASS I ZONE 2

CANADA

CSAC22.2-60079-15

EX nL

CLASS I DIVISION1

USA

FM 3620(NFPA496)

TYPE

CLASS I DIVISION1

CANADA

NFPA496

X/Y

CLASS I DIVISION2

USA

FM 3620(NFPA496)

CLASS I DIVISION2

CANADA

NFPA496

EUROPE UNION

EN 60079-2

International- IEC

IEC 60079-2

CLASS I ZONE 1

CANADA

CSA C22.2-60079-2

CLASS I ZONE 1

USA

ISA 60079-2

CATEGORY 3G

EUROPE UNION

EN 60079-2

EPL Gc CLASS I ZONE 2

International- IEC CANADA

TYPE Z Ex px/py AEx px/py

IEC 60079-2

Ex pz

CSA C22.2-60079-2

CLASS I ZONE 2

USA

ISA 60079-2

AEx pz

CATEGORY 3G

EUROPE UNION

EN 60079-15

Ex nR

International- IEC

IEC 60079-15

Ex nR

EPL Gc CLASS I ZONE 2

USA

ISA 60079-15

AEx nR

CLASS I ZONE 2

CANADA

CSAC22.2-60079-15

Ex nR

CATEGORY 1G/2G/3G

EUROPE UNION

EN 60079-18

International- IEC

IEC 60079-18

CLASS I ZONE 0/1/2

CANADA

CLASS I ZONE 0/1/2

USA

CATEGORY 2G/3G OIL IMMERSED

b/c -DO-

IEC 60079-15

EPL Gc

EPL Ga/Gb/Gc ENCAPSULATED

XP

USA

EPL Gb

KEEP FLAMMABLE GAS OUT

RESTRICTED BREATHING

XP

CLASS I ZONE 1

CATEGORY 2G PRESSURIZED

CODE

CLASS I DIVISION1

EPL Ga/Gb/Gc

SURFACE TEMPERAURE

FLAME PROOF

AND

CONTAINS THE EXPLOSION AND

EXPLOSION PROOF

STANDARD

EPL Gb/Gc

CSAC22.2-60079-18 ISA 60079-18

Ex ma/mb /mc AEx ma/ m or mb /mc

EUROPE UNION

EN 60079-6

Ex o

International- IEC

IEC 60079-6

ob/oc

CLASS I ZONE 1

CANADA

CLASS I ZONE 1

USA

1211

CSAC22.2-60079-6 ISA 60079-6

Ex o AEx o

FIGURE AVI/5.0.0-2 Comparison of standards and protection concept [3]. Developed based on FM approval poster.

1212

Appendix | VI

LIST OF ABBREVIATIONS BPCS Basic process/plant control system EAC Electrical area classification EPL Equipment protection level HFT Hardware failure tolerance LEL Lower explosive limit

PFD Probability of failure on demand SFF Safe failure fraction SIF Safety instrumented function SIL Safety integration level SIS Safety instrumented system UEL Upper explosive limit

Appendix | VI

REFERENCES [1] F. Frenzel, H. Grothey, C. Habersetzer, M. Hiatt, W. Hogrefe, M. Kirchner, G. Lütkepohl, W. Marchewka, U. Mecke, M. Ohm, F. Otto, K.-H. Rackebrandt, D. Sievert, A. Thöne, H.-J. Wegener, F. Buhl, C. Koch, L. Deppe, E. Horlebein, A. Schüssler, U. Pohl, B. Jung, H. Lawrence, F. Lohrengel, G. Rasche, S. Pagano, A. Kaiser, T. Mutongo, Industrial Flow Measurement Basics and Practice, ABB Automation Products GmbH. http://nfogm.no/ wp-content/uploads/2015/04/Industrial-Flow-Measurement_ Basics-and-Practice.pdf.

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[2] B.A.R.T.E.C. Brochure, Basic Concepts for Explosion Protection, 2012, 11 revision. [3] S. Basu, Plant Hazard Analysis and Safety Instrumentation Systems, Elsevier; IChemE, 2016. http://store.elsevier.com/ Plant-Hazard-Analysis-and-Safety-Instrumentation-Systems/ Swapan-Basu/isbn-9780128037638/. https://icheme.myshopify. com/products/plant-hazard-analysis-and-safety-instrumentationsystems-1st-edition. [4] Gas Detection Handbook, Fifth ed., MSA, http://www. gilsoneng.com/reference/gasdetectionhandbook.pdf.

APPENDIX VII

DEVICE COMMUNICATION 1.0.0 GENERAL DISCUSSIONS AND HARDWIRED TRANSMISSION The duties of sensors and transducers are to sense a physical parameter and convert it into an electrical signal (in the modern world only electronic instruments are in use and pneumatic signal transmission is obsolete). This signal will be useful only when it is transmitted and/or communicated to secondary instrument for subsequent action, i.e., any control and monitoring action as necessary could be taken. In the case of flow metering, unless the flow meter signal is transmitted and/communicated to secondary instruments for action, its basic action will not be served. Therefore, it is needless to argue that the role of the transmitter, i.e., device communication, cannot be overestimated. Here I use the word communication specifically because in the modern world there can be wireless communications also, so instead of transmission I preferred the word communication which could be through a wire or wireless. There are various ways in which flow meters/transmitters can communicate with the rest of world. This could be simple hardwired communication, transmission protocols, or communication through a fieldbus (may be wireless also). Since in many cases the flow instruments will be in a hazardous location, it is necessary to take necessary action so that even under hazardous conditions the device can operate unaffected. Necessary protection through enclosures has already been discussed in Appendix VI, which does not cover the safe fieldbus system.

Therefore, in this appendix the safe fieldbus system shall also be covered. We begin our discussion by addressing all these one by one. Various ways and means used for flow device communication include but are not limited to the following: l l l

Hardwired communication; Link and protocol [1]; Fieldbus communication [1].

This appendix has been developed with help of the author’s books entitled “Power Plant Instrumentation and Control Handbook” and “plant Hazard analysis and safety instrumentation systems (approved by IChemE U.K.)” published by Elsevier. Courtesy of Elsevier USA. 1.1.0 Current LoopdHardwired Transmission A 4e20 mADC signal is the most popular electronic signal transmission in hardwired form. It is not that other types cannot be used, such as 0e10 VDC 0e50 mADC signals have been found to be used. Before going into further details let us look into the details about 4e20 mADC loop and understand the transmission process. 1.1.1 CURRENT LOOP AND SELECTION FOR 4e20 MADC In this section discussion will be on why current signal is chosen in place of voltage and why 4e20 mA has been chosen.

1215

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Appendix | VII

1. Current signal: From Ohms law it is clear that when there is current flow through the resistance there will be a voltage drop across the resistance equal to the resistance times current value passing through the resistance. Naturally, instead of current if the voltage value were chosen for the transmitter for the same value of output from the transducer the receiver would receive output which would vary depending on the distance between the transmitter and receiver on account of resistance in the wire. This means keeping all conditions the same, if the transmitter sends a signal, the receiver nearer to the transmitter would receive more signal for the same physical input, than the receiver at a far away place on account of additional resistance of the connecting wire. In contrast, in the case of a current loop the receiver and transmitter would have to be in series and the same signal would pass through the receiver and would not change (only if the proper power supply is chosen, as discussed later) unless the distance is too long. Therefore it could be argued that current transmission is preferred to voltage transmission. 2. 4e20 mA: From here it is clear that this output means the lowest value of span would give 4 mA and the highest value of span would give 20 mA. This means this is a live zero signal, meaning that for a flow of e.g., 0e100 m3/h when there will be zero flow then output will be 4 mA and at 100 m3/h, 20 mA. This means this is a live zero. It has two advantages. l 4 not zero: If the signal line is snapped then current will be zero, not 4 mA. This means it is possible to distinguish between actual zero physical input (flow) and power supply failure or cable snapping. As in the case of zero flow, output would be 4 mA when there is no cable snap or power supply failure. In case of power supply failure/cable snap output will be zero. So, it is failsafe. Also, live zero gives a better signal to noise ratio [2]. l Two-wire loop power: In case of two-wire loop power, operation would not be

possible, if there is no current flowing in the loop (0 mA), that no power for the instrument to keep its circuitry active. In order to use an instrument on a loop that has 0 mA or 0 VDC as the low end, the power for the instrument would have to come from a separate source, which would require a three-wire or four-wire instrument. l Why 4e20 mA: Typical electronic signal types could be: 4e20 mA (low end ¼ 20/5 ¼ 4, span ¼ 4  4 ¼ 16); 10e50 mA (low end ¼ 50/5 ¼ 10, span 4  10 ¼ 40); 1e5 VDC (low end ¼ 5/5 ¼ 1, span ¼ 4  1 ¼ 4). Of these the third one is voltage transmission and this is not acceptable for long distance transmission, on account of the issue discussed above. Instead of 4e20 mADC it could be 10e50 mADC also. Normally at the receiver, the current is converted into 1e5 VDC. So, in the case of 4e20 mA, 250 U resistance would be necessary. On the other hand, 100 U resistance would be necessary. Naturally, in the case of 4e20 mA the energy will be lower and is preferred for intrinsic circuits. 3. DC not AC: DC signal is inactive for capacitance. On the other hand, the AC signal attenuates in the presence of capacitance so AC is vulnerable to stray capacitance and capacitance of the cable, i.e., it is less sensitive to electrical noise. 1.2.0 4e20 mADC Current Loop Discussions In its simplest form, in a 4e20 mADC current loop at least three components are essential. These are the power supply, transmitter, and receiver. Let us look into these closely. 1.2.1 POWER SUPPLY IN A CURRENT LOOP The current loop uses DC power supply. As discussed earlier, in the case that AC power would have been used in the loop, then the magnitude of the current would be continuously

Appendix | VII

changing, also there will be stray pickup, making it difficult to discern the signal level being transmitted. For 4e20 mA current loops with two-wire transmitters, the standard and most common loop power supply voltage is 24 VDC. However, there may be use of 12, 15, and 36 VDC also. The most pertinent and important issue here is that power supply must be set to a level that is greater than the sum of the minimum voltage required to operate the transmitter, plus the IR drop in the receiver. It is to be noted that although transmitters regulate the current in the loop, the voltage at its output terminals will vary according to the loop power supply voltage, the IR voltage drop in the wires, and the IR voltage drops across the receiver (at maximum current signal should be considered). Therefore, one has to ensure that the loop supply voltage level can meet the minimum requirements mentioned. The voltage drop wire is normally not a concern, as the voltage drop of a section of wire is minuscule. However, over long distances of over 300 m, it can add up to a significant amount, depending on the thickness (gage) of the wire. At times there could be a shortfall in the power supply due to a power supply voltage that can no longer drive the necessary loop voltage due to an added load in the current loop [2]. For this reason, transmitter manufacturers provide a load versus power supply curve so that based on application suitable voltage can be adjusted. However, this can happen because of any one (or combination) of the following reasons: 1. Long distance (IR voltage drop in the wires); 2. Simply failing to include the over-range current; 3. Addition of too many receivers, or loads in the loop. 1.2.2 TRANSMITTER IN CURRENT LOOP This is the device used to transmit a signal from a sensor over the current loop. There can be only one transmitter output in any current loop. It acts like a variable resistor with respect to its input. The transmitter uses 4 mA output to represent the calibrated lowest end of span and 20 mA to

1217

represent the calibrated highest end of span 4e20 mA current loop. A common misconception is that the transmitter is the source of the loop current. It is not the source of the current. Actually it is a series-connected current-sinking circuit that draws current from a power supply wired to its output terminals. The current flowing through the transmitter is proportional to the input signal being measured. The current signal on the loop is regulated by the transmitter according to the sensor’s measurement. 1.2.3 RECEIVER IN CURRENT LOOP At the receiver an analog 4e20 mADC signal current is normally converted to a voltage input with a precision resistor. By using 4e20 mA as the driver, the voltage produced across a load resistor is easily scaled by simply changing the resistance. Common resistances used are 250 U (1e5 V), 500 U (2e10 V), 50 U (0.2e1 V), and 100 U (0.4e2 V). Depending on the source of current for the loop, receiver devices may be classified as active (supplying power) or passive (relying on loop power). These receivers can be input of PLC or DCS. They can be sourcing or sinking types. 1.2.4 CURRENT LOOP TYPES As the name implies, there should be a loop, which refers to the actual wire connecting the power supply, sensor/transmitter to receiver (the device receiving the 4e20 mA signal), and then back to complete the current loop. As per ANSI/ ISA standard 50.00.01; there can be three different current loop connection types as depicted A, B, and C in Fig. AVII/1.2.4-1. These diagrams are self-explanatory. A brief description of Fig. AVII/ 1.2.4-1 has been presented. 1. Diagram A: A two-wire transmitter where the transmitter is floated with respect to the ground which is shared commonly by the receiver and power supply. Loop-powered two-wire transmitters have their power supply and signal sharing the same pair of connection wires. This simplifies installation considerably, and

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Appendix | VII

ANSI /ISA STANDARD 50.00.01 3 CURRENT LOOPS SHOWN IN FIG A, B & C HERE SYMBOLS LEGENDS I

I TX TX

RCVR TX PS

PS

POWER SUPPLY

+

+ PS

TX

RCVR

RCVR

COMMON

[24VDC Std]

COMMON

A RCVR

4 WIRE TRANSMITTER

3 WIRE TRANSMITTER

TRANSMITTER

PS

I

+

RECEIVER 2 WIRE TRANSMITTER

(e.g. PLC/DCS]

GROUND

B

TRANSMITTER FLOATS;

TRANSMITTER RECEIVER

DC POWER IN SERIES

COMMON EARTH SEPARATE POWER SUPPLY FOR TRANSMITTER

C

TRANSMITTER & RECEIVER FLOAT SEPARATE POWER SUPPLY

I

EXTERNAL SUPPLY

I TWISTED PAIR CABLE P

TWISTED PAIR CABLE P

PLC/DCS PLC/DCS TX

TX

I +

+

E

D PLC/DCS SOURCING

PS

I

PLC/DCS

I RCVR

PS

PLC/DCS SINKING

RCVR

INPUT CHANNEL

INPUT CHANNEL AS POWERING FROM PLC/DCS

AS POWERING FROM EXTERNAL

ALSO RETURN TO PLC/DCS

ONLY RETURN TO PLC/DCS INPUT CHANNEL INPUT CHANNEL

FIGURE AVII/1.2.4-1 Current loop transmission types.

the low DC transmission levels permit the use of small, inexpensive copper wiring. 2. Diagram B: Here the transmitter, receiver, and power supply share the same ground. There is a separate wire for the power supply to the transmitter and it is a three-wire type of connection. 3. Diagram C: This is a four-wire connection complete with two separate wires for the power supply and transmitter. In the signal side both the transmitter and receivers are floating type. There are other sets of connections shown in D and E in Fig. AVII/1.2.4-1. As mentioned in regard to the receiver above, for PLC/DCS that input can be sourcing or sinking type. 4. Diagram D: This is a sourcing type because the power supply is within the input of PLC/DCS. So, PLC/DCS input sends power

supply and gets back the current as the return path due to the common ground point. 5. Diagram E: This is a sinking type as there is an external power supply source and current returns to PLC/DCS input in a return path to sink the signal using common ground. The signal is sensed in the sinking path. 1.3.0 Other Hardwire Signal Types Contact output and pulse type are two other signals also available from flow meters. 1. Contact/binary output: These are normally potential contacts of suitable rating or can be open collector type output also. They are mainly used for control and status indications. They are used in the event of a dangerous condition, e.g., device failure or an alarm and are used mainly to indicate possible changes in the

Appendix | VII

course of the process. Flow switches and limit value monitors give this type of output. 2. Pulse signal: Pulse outputs are common with flow meters. Pulse output signals are proportional to the volume flow rate and can be integrated by a totalizer to arrive at the total volume over a time period. Meter K factor discussed in the main text accounts for the proportionality constant for the meter pulse rate and volume flow. In this manner a volume signal is generated from the flow rate. The totalizer indicates the total volume that has flowed through the flow meter during a specific time interval [8].

2.0.0 LINK AND PROTOCOL During the discussions on flow meters and associated converters or electronics that some of them, e.g., thermal mass flow meter provide, in addition to hardwired output, RS links for data transfer via, e.g., MODBUS. Highway Addressable Remote Transducer (HART) is quite common with standard process transmitters as well as most modern flow meters. In this section brief discussions on various links and protocols shall be discussed. The discussion starts with important links available for communication. 2.1.0 Important Links for Device Communication These links are referred to as recommended standard (RS) or (later modified by Electronic Industries alliance) (EIA), i.e., RS (EIA232). 2.1.1 LINK RS (EIA) 232 RS 232 has been defined as an electrical interface for serial transmission of data over a short distance for point-to-point communication. This link is connected in mastereslaves (multiple) mode with normal communication rate