Industrial Energy Conservation, Volumes 1-2 9385059858, 9789385059858

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Industrial Energy Conservation Volume I-II

Contents iii

Industrial Energy Conservation Volume I-II

S C Bhatia BE (Chemical), BITS Pilani & MBA

Puneet Mangla (Co-Author) B.E. (Industrial Production), M.Tech. (Engineering Systems) Head and Associate Professor - Department of Mechanical Engineering, Hindustan College of Science and Technology, (Mathura)

Edited by

Sarvesh Devraj B.Tech (Mechanical), UPTU M.Tech (Renewable Energy Engineering and Management), TERI University, (Research Associate – TERI, New Delhi)

Published by Woodhead Publishing India Pvt. Ltd. Woodhead Publishing India Pvt. Ltd., 303, Vardaan House, 7/28, Ansari Road, Daryaganj, New Delhi - 110002, India www.woodheadpublishingindia.com First published 2018, Woodhead Publishing India Pvt. Ltd. © Woodhead Publishing India Pvt. Ltd., 2018 This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission. Reasonable efforts have been made to publish reliable data and information, but the authors and the publishers cannot assume responsibility for the validity of all materials. Neither the authors nor the publishers, nor anyone else associated with this publication, shall be liable for any loss, damage or liability directly or indirectly caused or alleged to be caused by this book. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming and recording, or by any information storage or retrieval system, without permission in writing from Woodhead Publishing India Pvt. Ltd. The consent of Woodhead Publishing India Pvt. Ltd. does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained in writing from Woodhead Publishing India Pvt. Ltd. for such copying. Trademark notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe. Woodhead Publishing India Pvt. Ltd. ISBN: 978-93-85059-25-4 Woodhead Publishing India Pvt. Ltd. e-ISBN: 978-93-85059-85-8

Contents

v

Contents

Volume I Preface Section I: General concepts and engineering considerations 1. Industrial energy conservation: A review 1.1 Introduction 1.2 Industrial sector energy efficiency 1.3 Energy consumption and energy related carbon dioxide emissions trends 1.4 Industrial energy efficiency 1.5 Causes of the energy crisis 1.6 Non-conventional renewable energy sources 1.7 Energy conservation 1.8 Need of energy conservation

xv 1 3 3 3 5 6 10 12 13 15

2. Energy efficiency technologies and benefits 2.1 Introduction 2.2 Benefits of increased energy efficiency 2.3 Importance of energy efficiency 2.4 Target sectors in energy efficiency 2.5 Energy efficiency actions 2.6 Barriers to implementation of energy efficiency measures 2.7 Combining renewables and energy efficiency to improve sustainability of energy development

21 21 23 25 28 31 34

3. Energy audit 3.1 Introduction 3.2 Types of energy audits 3.3 Steps for conducting energy audit 3.4 Data collection hints 3.5 Tips for energy audit

41 41 42 42 46 50

38

vi Industrial energy conservation

4. Efficient steam distribution system 4.1 Introduction 4.2 Energy conservation 4.3 Improving efficiency of steam systems

53 53 54 61

5. Energy efficiency in boilers 5.1 Introduction 5.2 Heating surfaces in a boiler 5.3 Classification of boilers 5.4 Performance evaluation of boilers 5.5 Boiler water treatment 5.6 Energy conservation opportunities in boilers 5.7 Improving boiler efficiency 5.8 Factors affecting boiler efficiency 5.9 Practical standard operating practices for improving boiler efficiency 5.10 Case study Atul limited—Ankleshwar (Gujrat)

67 67 67 68 70 71 78 83 88

6. Industrial waste heat recovery 6.1 Introduction 6.2 Basic heat recovery 6.3 Process heating 6.4 Industrial process heat recovery 6.5 Heat recovery methods 6.6 Cost considerations Section II: Energy conservation in electrical and telecom industries

89 90 97 97 97 99 100 102 118 123

7. Energy conservation in electrical industries 7.1 Introduction 7.2 Energy conservation in electrical systems 7.3 Energy conservation techniques 7.4 Diesel generator (DG)

125 125 125 126 132

8. Energy efficiency technologies for thermal power plants 8.1 Introduction 8.2 Combined cycle gas turbine (CCGT)

141 141 145

Contents

8.3 8.4 8.5 8.6 8.7 8.8

Mechanism of CCGT Typical size and configuration of CCGT plants Integrated gasification combined cycle (IGCC) Performance without CO2 capture Major IGCC blocks and components IGCC system issues

9. Energy efficient motors, compressors and refrigeration systems 9.1 Introduction 9.2 Salient aspects of motor performance 9.3 Energy efficiency in fans 9.4 Energy efficiency in compressed air systems 9.5 Refrigeration systems 10. Energy conservation in telecom sector 10.1 Introduction 10.2 Importance of green and energy efficient telecom equipments 10.3 Global initiatives in energy efficient technologies 10.4 Corporate social responsibility and community service 10.5 Telecom industry and green energy 10.6 Drivers for energy efficiency in telecommunications 10.7 Energy efficiency in telecom optical networks

vii

146 149 151 153 164 178 185 185 185 191 197 204 213 213 213 214 218 218 220 226

Section III: Energy conservation in mechanical industries

229

11. Energy efficiency in machining and gears 11.1 Introduction 11.2 Optimised automation in machine operations 11.3 Cutting power analysis in machining operations 11.4 Concepts of energy efficiency in utilisation of machine tools 11.5 Gear efficiency 11.6 Hydraulic presses

231 231 232 233 234 236 242

12. Energy conservation in forging industry 12.1 Introduction 12.2 Energy conservation in forging industry

245 245 245

viii Industrial energy conservation

12.3

Rational use of energy in induction heaters for forging industry

Section IV: Energy conservation in cement, ceramic and glass industries

250 259

13. Energy conservation in cement industry 13.1 Introduction 13.2 Major process equipments 13.3 Energy efficiency opportunities 13.4 Promotion of energy conservation techniques 13.5 Energy efficiency opportunities in individual sections in a cement plant 13.6 Cogeneration of power utilising waste heat in cement manufacture: technological perspectives 13.7 Technical consideration for cogeneration schemes 13.8 Availability of waste heat 13.9 Energy efficiency technologies and measures for the U.S. cement industry

261 261 261 263 266

14. Energy conservation in ceramic industry 14.1 Introduction 14.2 Ceramic manufacturing process 14.3 Energy consumption in ceramic manufacturing 14.4 Energy conservation measures in ceramic cluster 14.5 Tips for energy saving in various operation of ceramic industries

297 297 297 298 302

15. Energy conservation in glass industry 15.1 Introduction 15.2 Manufacture of glass 15.3 Energy consumption in glass industry

325 325 325 328

269 271 272 274 277

317

Section V: Energy conservation in metallurgical and mining industries

343

16. Energy conservation in iron and steel industry 16.1 Introduction 16.2 Iron and steel making processes 16.3 Energy conservation technologies

345 345 345 350

Contents ix

17. Energy saving in aluminium, copper and nickel industries 17.1 Introduction 17.2 Energy efficiency improvement 17.3 Energy efficiency in copper - nickel mining process 17.4 Energy consumption of electric smelters 17.5 Case study: HINDALCO industries ltd.

365 365 365 370 372 374

18. Energy conservation in cupola furnaces 18.1 Introduction 18.2 Structure of cupola 18.3 Energy conservation of cupola 18.4 Improving the heat efficiency of a cupola 18.5 Waste heat recovery in the cupola foundry 18.6 Induction furnaces 18.7 Electric arc furnaces

387 387 388 389 390 392 396 398

Volume II Section VI: Energy conservation in food and agriculture industries

403

19. Energy conservation in agricultural sector 19.1 Introduction 19.2 Mitigation options 19.3 Inputs for agriculture sector analysis 19.4 Energy sources for irrigation: water pumping 19.5 Saving energy in irrigation 19.6 Energy conservation tips using irrigation pump sets 19.7 Rainwater harvesting 19.8 Rainwater harvesting in dry lands

405 405 405 407 408 410 414 417 418

20. Energy conservation in dairy industry 20.1 Introduction 20.2 Key products in dairy industry 20.3 Energy used in the dairy processing industry 20.4 Energy efficiency opportunities 20.5 Energy conservation measures in dairy industries 20.6 Steam systems

423 423 427 436 436 437 441

x Industrial energy conservation

20.7 20.8

Combined heat and power (CHP) Process specific efficiency measures (PSEM)

448 451

21. Energy conservation in bakery industry 21.1 Introduction 21.2 Energy efficiency improvement opportunities 21.3 Hot water and steam systems 21.4 Energy efficiency opportunities for bakeries 21.5 Basic water efficiency measures

457 457 458 458 464 476

Section VII: Energy conservation in chemical process industries 479 22. Energy conservation in chemical process industries: A review 22.1 Introduction 22.2 Life cycle 22.3 Energy cost 22.4 Cogeneration system 22.5 Energy conservation in chemical industry–an analysis

481 481 482 483 483 485

23. Energy conservation in petroleum refineries 23.1 Introduction 23.2 Refinery energy requirements and CO2 emissions 23.3 Refinery energy efficiency opportunities 23.4 Short-medium term opportunities for energy efficiency improvement in refineries 23.5 Drivers and barriers to energy efficiency improvement

489 489 491 493

24. Energy conservation in petrochemicals industry 24.1 Introduction 24.2 Process specific energy efficiency measures 24.3 Distillation 24.4 Evaporator energy efficiency 24.5 Energy conservation using membrane separation technology

525 525 526 532 535

25. Energy conservation in fertiliser industry 25.1 Introduction 25.2 Energy conservation in corn nitrogen fertilisation

549 549 551

498 520

539

Contents xi

25.3 25.4 25.5

Energy analysis of evaporator system in fertiliser production Categories for energy efficiency improvement Case study: IFFCO plant – Paradeep (Orissa)

26. Energy conservation in chlor-alkali industries 26.1 26.2 26.3

Introduction Manufacturing process Energy consumption in chlor-alkali

552 561 566 577 577 577 583

Section VIII: Energy conservation in other important industries 593 27. Energy conservation in pulp and paper industry 27.1 27.2 27.3

Introduction Energy consumption and end uses Major factors affecting energy consumption in paper mills 27.4 Energy conservation in paper industry 27.5 Drying 27.6 Steam systems 27.7 Motor systems 27.8 Pumps 27.9 Fan systems 27.10 Compressed air systems 27.11 Energy management programmes and systems 27.12 Energy management guidelines in pulp and paper production 28. Energy conservation in sugar industry 28.1 28.2 28.3 28.4 28.5 28.6 28.7 28.8

Introduction Power saving Bagasse as a source of furfural in the sugarcane industry Steam drying of bagasse Basic system for steam drying Bioenergy role and potential of the sugar industry Barriers to good energy management practices Cogeneration of bagasse

595 595 597 598 603 606 607 608 610 613 615 618 619 629 629 632 632 634 635 649 652 655

xii Industrial energy conservation

29. Energy conservation in plastic industry 29.1 Introduction 29.2 Energy conservation in injection molding 29.3 Energy conservation in extrusion molding 29.4 Energy conservation in blow molding 29.5 Energy conservation in rotational molding 29.6 Energy conservation in thermoforming 29.7 Energy conservation in composites molding 29.8 Energy conservation in compression molding 29.9 Energy consumed in utilities and peripherals

659 659 660 663 665 669 672 674 675 677

30. Energy conservation in rubber industry 30.1 Introduction 30.2 Energy saving in rubber industry 30.3 Importance of steam in mixers and mills 30.4 High pressure hot water in tyre manufacturing 30.5 Cooling systems in mixing milling 30.6 Chilled water in rubber processing 30.7 Hydraulic systems in rubber processing 30.8 Compressed air in rubber processing 30.9 Ventilation systems in rubber processing 30.10 Role of insulation in rubber processing 30.11 Motors and drives in compounding and extrusion equipments 30.12 Lighting in rubber processing industry 30.13 Heating in curing and mixing rubber

679 679 680 682 690 690 693 694 695 698 700

31. Energy conservation in leather and tannery industry 31.1 Introduction 31.2 Leather manufacturing process 31.3 Material handling in tanneries 31.4 Energy recovery from tanneries by biogas production 31.5 Energy generated by anaerobic digestion 31.6 Energy recovery from wastes 31.7 Energy efficiency 31.8 Solar thermal energy in tanneries 31.9 Case study: Punjab tanneries

705 705 705 708 709 714 715 717 718 719

700 701 703

Contents xiii

32. Energy conservation in textile industry 32.1 Introduction 32.2 Types of textile sectors 32.3 Energy consumption in textile industry 32.4 Waste heat recovery in textile industries 32.5 Cost effectiveness in textile processing 32.6 Cogeneration process

725 725 725 726 727 735 743

33. Energy conservation in pharmaceutical industry 33.1 Introduction 33.2 Optimising the energy efficiency in manufacturing processes 33.3 Energy conservation in pharmaceutical manufacturing 33.4 Opportunities for energy efficiency 33.5 Water and energy conservation in the pharmaceutical industry 33.6 Clean steam in the pharmaceutical industry

747 747 747 749 749

34. Energy efficient cooling towers

769

34.1 34.2 34.3 34.4 34.5 34.6 34.7 34.8

Introduction Design specifications of cooling towers Types of cooling towers System calculations of water in cooling tower Controlling of cooling tower return temperature and energy saving Best management practice: Cooling tower management Energy conservation tips for cooling tower Pump energy-efficiency for industrial cooling systems

35. Energy efficient industrial pumps and V-belts 35.1 Introduction 35.2 Methodology adopted for performance evaluation of pumping system 35.3 Parametric approach to energy conservation in pumping 35.4 Tips to save energy on pumping systems 35.5 Energy conservation in V-belts and pipe belt conveyors

759 762

769 773 774 776 776 778 782 783 787 787 787 792 793 795

xiv Industrial energy conservation

36. Role of nanotechnology in energy conservation 36.1 Introduction 36.2 Energy sources 36.3 Energy conversion 36.4 Energy distribution 36.5 Energy storage 36.6 Energy usage 36.7 Nanotechnology helps solve the world’s energy problems 36.8 Application of nanotechnology to energy production

803 803 803 804 804 805 805 806 810

References

817

Index

819

Contents xv

Preface

The industrial sector is vital to world economy, but at the same time consumes the most energy to manufacture products we use every day. Among the most energy-intensive industries are aluminium, chemicals, forest product, glass, metal casting, mining, petroleum refining and steel. The energy supply chain begins with electricity, steam, natural gas, coal and other fuels supplied to a manufacturing plant from off-site power plants, gas companies and fuel distributors. Energy then flows to either a central energy generation utility system or is distributed immediately for direct use. Energy is then processed using a variety of highly energy-intensive systems, including steam, process heating and motor-driven equipment such as compressed air, pumps and fans. Throughout the manufacturing process, energy is lost due to equipment inefficiency and mechanical and thermal limitations. Optimising the efficiency of these systems can result in significant energy and cost savings and reduced carbon dioxide emissions. Understanding how energy is used and wasted—or energy use and loss footprints—can help plants pinpoint areas of energy intensity and ways to improve efficiency. Cross-cutting technologies such as combustion, distributed energy, fuel and feedstock flexibility and nano manufacturing are common to many industrial processes across multiple industries. Because of the widespread application of these cross-cutting systems, even small improvements in efficiency can yield large energy savings and reduce industry’s carbon footprint. Energy conservation is an important tool to deal with global issues such as the future exhaustion of resources and global warming. Energy security is to ensure a constant and stable supply of energy. In order to maintain the supply, it is necessary for countries to increase the domestic energy self-sufficiency ratio and to undertake diplomatic endeavours to secure stable energy suppliers. Especially, increasing the energy self-sufficiency ratio is a direct means to achieve the goal. As the food self-sufficiency ratio, the domestic energy self-sufficiency ratio is the core elements of the national security and thus is a politically prioritised issue. In order to increase the energy self-sufficiency ratio, it is necessary to develop and promote the use of domestic untapped energy such as nuclear, wind and solar energy and to enhance effective utilisation of existing energies (energy conservation). Energy conservation contributes to solution to the global issues such as energy security and possible future exhaustion of oil. Industrial energy

xvi Industrial energy conservation

efficiency is a key ingredient in any national energy efficiency programme. Through the implementation of energy conservation, we can reduce the expenses for wasteful energy consumption and income will increase equivalent to the amount of the reduction. Through energy conservation, payments for the utility of electricity and gas will decrease and these savings will be utilised for other expenditures at the household level. At the business and factory levels, the decrease of energy consumption per unit of production (cost reduction of production) will enhance their competitiveness. Increasing income and enhancing business competitiveness at the national level contribute to economic growth. In order to promote energy conservation, it is effective to establish an energy saving activities’ framework. At the same time, it is also important to ensure a change in the attitude of energy consumers and to promote voluntary activities of energy conservation through performing the activities of publicity, awareness and dissemination of energy conservation. Energy is one of the most important building block in human development, and, as such, acts as a key factor in determining the economic development of all countries. There is, therefore, an urgent need to conserve energy and reduce energy requirements by demand-side management and by adopting more efficient technologies in all sectors. The importance of energy in the day-today life of a human being is well-recognised. Practically, no work can be done without the application of a required amount of energy. No doubt, the source of energy is quite varied, such as fossil fuels (coal, petroleum, natural gas, etc.), hydel power, nuclear fuel, solar power energy sources like tidal, geothermal, wind, biomass, etc., and last but not the least, the fuel cell. In fact, energy is one of the pillars that support the entire superstructure of the modern civilisation. Sources of energy are varied but limited. It is well known that the conventional and common sources of energy are getting depleted at an accelerated rate. This has led us to look at and explore the alternative sources more seriously. But going by the current status of exploitation of alternate sources, it is not possible to force a shift of the epicenter from the conventional to the alternatives or renewables. More emphasis should simultaneously be placed on drastic reduction of energy waste and improvement of the efficiency of energy production and utilisation. This book on Industrial Energy Conservation summarises various aspects of energy consumption and conservation and is divided in two volumes. Volume I contains 1 to 18 chapters and Volume II has 19 to 35 chapters. Section I discusses general concepts and engineering considerations. Chapter 1 is devoted to industrial energy conservation: A review. The chapter briefly discusses energy efficiency and conservation aspects in various industrial sectors. Chapter 2 focuses on energy efficiency technologies and benefits. The chapter highlights various barriers and remedies for implementation

Contents Preface xvii

of energy efficiency measures. Chapter 3 concentrates on energy audit. Energy audit is the key to a systematic approach for decision making in the area of energy management. It attempts to balance the total energy inputs with its use and serves to identify all the energy streams in a facility. Chapter 4 deals with efficient steam distribution system. Well the function of the steam distribution system is to get the steam to where it is needed and return the condensate to the boiler, doing both as efficiently as possible. Chapter 5 focuses on energy efficiency in boilers. The chapter discusses various types of boilers – their performance evolution, parameters of selection of boilers and energy conservation and recovery aspects. A substantial amount of energy used by industry is wasted as heat in the form of exhaust gases, air stream and liquids leaving industrial facilities. Considering this chapter 6 is devoted to industrial waste heat recovery. Section II discusses energy conservation in electrical and telecom industries. Chapter 7 deals with energy conservation in electrical industries. Various energy efficient techniques in transformers, electronic ballast, adjustable speed drive (ASD) and DG sets are discussed. Chapter 8 concentrates on energy efficiency technologies for thermal power plants. There is tremendous scope for energy potential in various areas of thermal power plants including waste heat recovery for power. Chapter 9 focuses on energy efficient motors, compressors and refrigeration systems. When considering energy efficiency motors systems, a systems approach incorporating pumps, compressor and transmits be used in order to attain optimal savings and performance. Energy efficient motors use less electricity, run cooler and often last longer. Compressed air is one of the most expensive uses of energy in manufacturing plant. About 8 hours power of electricity is used to generate one horse power of compressed. Calculating the cost of compressed air can help justify improvements for energy efficiency. Compressed air is a versatile tool used widely throughout industry for variety of purposes. Unfortunately, running air compressor often uses more energy than any other equipment. Air compressor efficiency is the ratio of energy input to energy output. The total energy use of compressor system depends on several factors. The air compressor type, model and size are important factors in energy consumption, but the motor power rating, control mechanism, system design uses and maintenance are also fundamental in determining the energy consumption of a compressed air system. Telecommunication networks and broadband access are large consumer of energy for date delivery. In general, the telecom sector accounts for approximately 4% of the global electricity consumption. Keeping this in mind chapter 10 discusses various energy conservation techniques in telecom sector. Section III discusses energy conservation in mechanical industries. Chapter 11 deals with energy efficiency in machining and gears. The chapter discusses

xviii Industrial energy conservation

concepts of energy efficiency utilisation of machine tools, gears and hydraulic press. Chapter 12 concentrates on energy conservation in forging industry. The forging process energy conservation is a tool to improve environment, economy and productivity and at the same time cost saving. Section IV discusses energy conservation in cement, ceramic and glass industries. Chapter 13 deals with energy conservation in cement industry. In the cement industry, appreciable amounts of energy could be saved or conserved by preventing of leakage in the kilns, modifying the equipment to recover heat from the pre-heater and cooler in the process of cement-making and effective use of industrial waste materials. Chapter 14 focuses on energy conservation in ceramic industry. Heat recovery should be considered only after the kiln has been optimised. This minimises the heat available for recovery, but is the most energy efficient route. Chapter 15 is devoted to energy conservation in glass industry. In the glass industry, significant improvements in the level of energy efficiency could be achieved by combustion control, furnace wall insulation, exhaust heat recovery, heat balancing, use of electric booster and bubbling, electric heating of forehearth, using a great number of cullet and by low melting temperature batch technique. Section V discusses energy conservation in metallurgical and mining industries. Chapter 16 concentrates on energy conservation in iron and steel industry. In the steel industry, significant improvements in the level of energy efficiency could be achieved by utilising waste heat from furnaces, adjusting air/fuel ratio in furnace and boiler burners and using drain water, as well as by eliminating and linking production processes. Chapter 17 deals with energy saving in aluminium, copper and nickel industries. All aspects of copper production require energy changing from reverberatory to flash furnaces cuts total smelting and refining energy requirements by one third. Major energy consumption in aluminium industries is in the form of electricity that is generated by a less efficient coal fired captive power plants. Additional energy saving can be achieved through the introduction of new alloys and improved product design. Chapter 18 is devoted to energy conservation in cupola furnaces. There is a large potential for improving furnace efficiency; specifically to reduce coke consumption by proper design of cupola and adoption of Best Operating Practices (BOP). Additional energy saving can be achieved by implementing simple housekeeping measures and conducting energy audit. Section VI discusses energy conservation in food and agriculture industries. Chapter 19 deals with energy conservation in agricultural sector. Energy is mainly used for ground water pumping and farm machinery such as threshers and tractors. In many cases, electricity and fuel use tends to be inefficient because of price subsidies and thus mitigation options may offer a significant

Contents Preface xix

potential for improving efficiency and reducing GHG emissions from this sector. Chapter 20 concentrates in energy conservation in dairy industry. Electricity is used throughout the dairy processing industry to drive process motors, fans, pumps and compressed air systems, as well as building lighting and HVAC systems. Various opportunities exist within the diary processing industry to reduce energy consumption while maintaining or enhancing production. As part of the dairy industry’s aggressive move to reduce the carbon footprint and energy consumption of the industry as a whole, energy efficiency improvements to dairy processing facilities are key to attaining this goal. The most effective method to improving energy efficiency in a dairy processing facility is to implement energy saving techniques across various levels of production. Chapter 21 focuses on energy conservation in bakery industry. Saving energy not only reduces costs but also translates into reduce emissions. Efficient oven burners are at the crux of bakery energy efficiency. We can optimise burners by analysing the combustion stack gases and then adjusting the controls accordingly. Enhancing combustion efficiency through improved controls such as oxygen trim and burner operations is a standard practice in other sectors (e.g. boiler plant operation). Section VII discusses energy conservation in chemical process industries. Chapter 22 deals with energy conservation in chemical process industries: A review. Chapter 23 is devoted to energy conservation in petroleum refineries. Energy use in a refinery varies over time due to changes in the type of crude processed, the product mix (and complexity of refinery), as well as the sulphur content of the final products. A large variety of opportunities exist within petroleum refineries to reduce energy consumption. Chapter 24 focuses on energy conservation in petrochemicals industry. Energy is the most important cost factor in petrochemical industry, producing large volume of basic and intermediate organic chemicals as well as large volume of polymers. A large variety of opportunities exist within the petrochemical industries to reduce energy consumption while maintaining or enhancing the productivity of the plant. Improved energy efficiency may result in co-benefits that far outweigh the energy cost savings and may lead to an absolute reduction in carbon dioxide and other fuel-related emissions. Chapter 25 deals with energy conservation in fertiliser industry. One of the most obvious areas of energy consumption to address in the fertiliser industry is the production of anhydrous ammonia for nitrogenous fertilisers. Measures to increase the efficiency of ammonia production can be achieved by: (i) replacing process equipment with high-efficiency models, (ii) improving process controls to optimise chemical reactions, (iii) recovering process heat and (iv) maximise the recovery of waste materials. Chapter 26 concentrates on energy conservation in chlor-alkali industries. Most of the energy used in

xx Industrial energy conservation

the industry is electricity and steam. Energy consumption can be reduced in membrane cells by significantly lowering the voltage required to overcome electrochemical polarisation. (i) optimisation of electrolysers for current consumption by monitoring cell voltages and replacing membranes in time, (ii) optimum liquefaction of chlorine with respect to usage, (iii) optimisation of steam consumption in concentrating 32 to 48% caustic by using multiple effect evaporators and (iv) heat recovery by provision of brine and chlorine recuperator for pre-heating the feed brine towards the cell. Section VIII discusses energy conservation in other important industries. Chapter 27 is devoted to energy conservation in pulp and paper industry. In the pulp and paper industry, appreciable amounts of energy could be saved or conserved by regulating and insulating the temperature in the steam pipes, modifying the equipment to recover heat from the various units in the process of pulping and paper-making and effective use and reuse of paper machine white water. Chapter 28 deals with energy conservation in sugar industry. Energy can be saved through efficient production and used of steam and efficient use of mechanical/electrical energy. Chapter 29 focuses on energy conservation in plastic industry. Energy efficiency can be improved by good housekeeping, equipment improvement and process improvement. Chapter 30 is devoted to energy conservation in rubber industry. Rubber industry consumes a substantial amount of energy. Excessive use of energy is usually associated with many industrial plants worldwide and rubber plants are no exception. Enormous potential exists for cost-effective improvements in the existing energy-using equipment. Also, application of good housekeeping measures could result in appreciable savings in energy. Energy can be saved by minimising the demand for chilling and refrigeration system. Chapter 31 deals with energy conservation in leather and tannery industry. Energy consumption critically depends on the type of production concerned and raw processing materials utilised. Thermal solar energy can be an option to produce hot water in tanneries and reduce cost of energy. Heat recovery should be from compressors and spray plant. Chapter 32 focuses on energy conservation in textile industry. Textile industry uses large quantities of electricity and fuels. There are significant losses of energy within various operations of textile plants such as spinning, weaving and dyeing. Various energy conservation/saving aspects of textile processing are also discussed. Chapter 33 concentrates on Energy conservation in pharmaceutical industry. Variety of opportunities exist within pharmaceutical laboratories, manufacturing facilities and other buildings to reduce energy consumption while maintaining or enhancing productivity. Chapter 34 deals with energy efficient cooling towers. Energy efficiency can be obtained by using variable frequency drives. Install new nozzles to obtain a more uniform water pattern.

Contents Preface xxi

Chapter 35 concentrates on energy efficient industrial pumps and V-belts. Pumping systems account for a significant percentage of energy consumption of the total industrial energy usage. Various energy saving options in pumping systems are discussed. Chapter 36 deals with role of nanotechnology in energy conservation. Nanotechnology provide the potential to enhance energy efficiency across all branches of industry and to economically leverage renewable energy production through new technological solutions and optimised production technologies. Such wide coverage makes this book a treatise on the subject. Diagrams, figures, tables and index supplement the text. All topics have been covered in a cogent and lucid style to help the reader grasp the information quickly and easily. This book could not have been completed without the help of Mr Sarvesh Devraj (Research Associate – TERI, New Delhi), who worked hard in locating and organising the material and spent many hours checking the manuscript. Appreciations are also extended to Mr Harinder singh, senior DTP operator, who did type setting and drew labelled the flow diagrams and worked long hours to bring the book on time. I am also thankful to the editorial team of Woodhead Publishing India Pvt. for their wholehearted cooperation in bringing out the book in time. It may not be wrong to hold that this book on Industrial Energy Conservation is essential reading for professionals, students pursuing engineering courses. Besides students, this book will prove useful to industrialists and consultants in the respective fields. It has been prepared with meticulous care, aiming at making the book errorfree. Constructive suggestions are always welcome from users of this book. S C Bhatia Puneet Mangla

Section I General considerations and engineering aspects 1. Industrial energy conservation: A review

3

2. Energy efficiency technologies and benefits

21

3. Energy audit

41

4. Efficient steam distribution system

53

5. Energy efficiency in boilers

67

6. Industrial waste heat recovery

97

1 Industrial energy conservation: A review

1.1

Introduction

‘Energy conservation’ and ‘energy efficiency’ are often used interchangeably, but there are few differences. At the most basic level, energy conservation means using less energy and is usually a behavioural change, like turning lights off or setting thermostat lower. Energy efficiency, however, means using energy more effectively and is often a technological change. Energy efficiency measures the difference between how much energy is used to provide the same level of comfort, performance or convenience by the same type of product, building or vehicle. Conservation certainly reduces energy use, but it’s not always the best solution because it may impact comfort or safety as well. Efficiency, on the other hand, maintains the same level of output (e.g., light level, temperature) but uses less energy to achieve it. A combination of both energy conservation and energy efficiency measures yields an ideal solution.

1.2

Industrial sector energy efficiency

The industrial sector represents more than one third of both global primary energy use and energy-related carbon dioxide emissions. In developing countries, the portion of the energy supply consumed by the industrial sector is frequently in excess of 50% and can create tension between economic development goals and a constrained energy supply. Further, countries with an emerging and rapidly expanding industrial infrastructure have a particular opportunity to increase their competitiveness by applying energy-efficient best practices from the outset in new industrial facilities. Integrating energy efficiency into the initial design or substantial redesign is generally less expensive and allows for better overall results than retrofitting existing industrial facilities, as is typically required in more developed countries. Conversely, failure to integrate energy efficiency in new industrial facility design in developing countries represents a large and permanent loss in climate change mitigation potential that will persist for decades until these facilities are scheduled for major renovation. Despite the potential, policymakers frequently overlook the opportunities presented by industrial energy efficiency to have a significant impact on climate change mitigation, security of energy supply and sustainability. The common

4 Industrial energy conservation

perception holds that energy efficiency of the industrial sector is too complex to be addressed through public policy and, further, that industrial facilities will achieve energy efficiency through the competitive pressures of the marketplace alone. Neither premise is supported by the evidence from countries that have implemented industrial energy efficiency programmes. The opportunities for improving the efficiency of industrial facilities are substantial, on the order of 20–30% even in markets with mature industries that are relatively open to competition. The principal business of an industrial facility is production, not energy efficiency. This is the underlying reason why market forces alone will not achieve industrial energy efficiency on a global basis, ‘price signals’ notwithstanding. High energy prices or constrained energy supply will motivate industrial facilities to try to secure the amount of energy required for operations at the lowest possible price. But price alone will not build awareness within the corporate culture of the industrial firm of the potential for the energy savings, maintenance savings and production benefits that can be realised from the systematic pursuit of industrial energy efficiency. It is this lack of awareness and the corresponding failure to manage energy use with the same attention that is routinely afforded production quality, waste reduction and labour costs that is at the root of the opportunity. Industrial energy efficiency is dependent on operational practices, which change in response to variations in production volumes and product types. Due to this dependence, industrial energy efficiency cannot be fully realised through policies and programmes that focus solely on equipment components or specific technologies. Companies that actively manage their energy use seek out opportunities to upgrade the efficiency of equipment and processes because they have an organisational context that supports doing this wherever cost effective, while companies without energy management policies do not. Providing technology-based financial incentives in the absence of energy management will not result in significant market shifts because there is no organisational context to respond to and integrate the opportunity into ongoing business practice. A portfolio of industrial policies is needed that is designed to assist companies in developing this supporting context, while also providing consistency, transparency, engagement of industry in programme design and implementation, and, most importantly, allowance for flexibility of industry response. When these criteria are met, industry has shown that it can exceed expectations as a source of reductions in energy use and corresponding greenhouse gas (GHG) emissions, while continuing to prosper and grow.

1.2.1

Industrial sector trends

The industrial sector uses 160 Exajoules (EJ) of global primary energy, which is about 37% of total global energy use. Primary energy includes upstream

Industrial energy conservation: A review 5

energy losses from electricity, heat, petroleum and coal products production. The industrial sector is extremely diverse and includes a wide range of activities. This sector is particularly energy intensive, as it requires energy to extract natural resources, convert them into raw materials and manufacture finished products. The industrial sector can be broadly defined as consisting of energy-intensive industries (e.g., iron and steel, chemicals, petroleum refining, cement, aluminium, pulp and paper) and light industries (e.g., food processing, textiles, wood products, printing and publishing, metal processing). The aggregate energy use depends on technology and resource availability, but also on the structure of the industrial sector. The share of energy-intensive industry in the total output is a key determinant of the level of energy use. Economic development trends

Historical trends show that the importance of industry within an economy varies by its stage of economic development. The structure of the industrial sector varies between countries and their level of development since the materials demanded by an economy differ through successive stages of development. Industrialisation drives an increase in materials demand for construction of basic infrastructure needs such as roads, railways, buildings, power grids, etc. As countries develop the demand for energy conservation increases. Even though these general trends can be observed, economic development trends vary by country and there is no standard development path. India, for example, has a very high share of the service sector, accounting for 51% of total value added; even so, the industrial sector continues to grow, particularly in material production.

1.3

Energy consumption and energy related carbon dioxide emissions trends

Energy use in the industrial sector varies widely between countries and depends principally on the level of technology used, the maturity of plants, the sector concentration, the capacity utilisation and the structure of subsectors. A recent study compares regional levels of energy use intensities in 2011 and calculates that if all developing countries met the developed country average manufacturing energy use intensity, energy consumption could potentially be reduced by 70%. The largest emissions are from industrial energy use in the Centrally Planned Asia region, with more than a third of global CO2 emissions, due to increasing energy-intensive industrial production and the heavy use of coal in the industrial and power sectors. Developed countries account for 35% and transition countries for 11% of global CO2 emissions from the industrial sector, while the remaining countries account for 54%.

6 Industrial energy conservation

1.4

Industrial energy efficiency

Industrial energy efficiency—or conversely, energy intensity, which is defined as the amount of energy used to produce one unit of a commodity—is determined by the type of processes used to produce the commodity, the vintage of the equipment used and the efficiency of production, including operating conditions. Energy intensity varies between products, industrial facilities and countries depending upon these factors. Steel, for example, can be produced using either iron ore or scrap steel. Best practice primary energy intensity for producing thin slab cast steel from iron ore using a basic oxygen furnace is 16.3 gigajoules (GJ) per metric ton, while production of the same product using scrap steel only requires 6.0 GJ/T. The energy intensity of the Chinese steel industry dropped from 29 GJ/T steel in 2003 to 23 GJ/T steel in 2011 despite an increased share of primary steel production from 79% to 84%, indicating that the efficiency of steel production improved over this period as small, old inefficient facilities were closed or upgraded and newer facilities were constructed. Within industry, systems that support industrial processes that can be found to varying degrees in virtually all industrial sectors, regardless of their energy intensity. These industrial systems, which include compressed air, pumping and fan systems (referred to collectively as motor systems), steam systems and process heating systems are integral to the operation of industrial facilities, providing essential conversion of energy into energised fluids or heat required for production processes. Motor and steam systems account for 15% and 38%, respectively, of global final manufacturing energy use, or approximately 46 EJ/year. Because these systems typically support industrial processes, they are engineered for reliability rather than energy efficiency. Industrial systems that are oversized in an effort to create greater reliability, a common practice, can result in energy lost to excessive equipment cycling, less efficient part load operation and system throttling to manage excessive flow. Waste heat and premature equipment failure from excessive cycling and vibration are side effects of this approach that contribute to diminished, not enhanced, reliability. More sophisticated strategies, made possible through the emergence of modern controls, create reliability through flexibility of response—and redundancy in the case of equipment failure—rather than by brute force. The energy savings can be substantial, with savings of 20% or more common for motor systems and 10% or more for steam and process heating systems.

1.4.1

Opportunities for industrial energy efficiency

Opportunities to improve industrial energy efficiency are found throughout the industrial sector. Assessments of cost-effective efficiency improvement

Industrial energy conservation: A review 7

opportunities in energy-intensive industries in the United States, such as steel, cement and paper manufacturing, found cost-effective savings of 16% to 18% even greater savings can often be realised in developing countries where old, inefficient technologies have continued to be used to meet growing material demands. An estimate of the 2010 global technical potential for energy efficiency improvement in the steel industry with existing technologies identified savings of 24% in 2010 and 29% in 2020 using advanced technologies such as smelt reduction and near net shape casting. While the energy efficiency of individual system components, such as motors (85–96%) and boilers (80–85%) can be quite high, when viewed as an entire system, their overall efficiency is quite low. Motor systems lose approximately 55% of their input energy before reaching the process or end use work and steam systems lose 45%. Some of these losses are inherent in the energy conversion process; other losses are due to system inefficiencies that can be avoided through the application of commercially available technology combined with good engineering practices. At present, most markets and policymakers tend to focus on individual system components (motors and drives, compressors, pumps, boilers) with an improvement potential of 2–5%—that can be seen, touched and rated (rather than systems). While systems have impressive improvement potential—20% or more for motor systems and 10% or more for steam and process heating systems— achieving this potential requires engineering and measurement. The presence of energy-efficient components, while important, provides no assurance that an industrial system will be energy efficient. System optimisation requires taking a step back to determine what work (process temperature maintained, production task performed, etc.), needs to be performed. Improved energy system efficiency can also contribute to a company’s bottom line by increased production through better utilisation of equipment assets, greater reliability and reduced maintenance costs. Payback periods for system optimisation projects are typically short—from a few months to three years—and involve commercially available products and accepted engineering practices.

1.4.2

Barriers to industrial energy efficiency improvement

The decision-making process regarding investments in energy-efficient technologies is shaped by firm rules, corporate culture and the company’s perception of its level of energy efficiency. Researchers found that most firms view themselves as energy efficient even when profitable improvements are available. Lack of knowledge or the limited ability of industrial commodity

8 Industrial energy conservation

producers to research and evaluate information on energy-efficient technologies and practices is another barrier. Uncertainties related to energy prices or capital availability can lead to the use of stringent investment criteria and high hurdle rates for energy efficiency investments that are higher than the cost of capital to the firm. Capital rationing is often used within firms as an allocation means for investments, especially for small investments such as many energy efficiency retrofits. The relatively slow rate which industrial capital stock turns over can prove to be a barrier to adoption of energy efficiency improvements since new stock is typically more energy-efficient than existing facilities. Another barrier is the perceived risk involved with adopting new technology since reliability and maintenance of product quality are extremely important to commodity producers. Optimising industrial systems for energy efficiency is not taught to engineers and designers at university—it is learned through experience. Systems are designed to maintain reliability at the lowest first cost investment, despite the fact that operating costs are often 80% or more of the life cycle cost of the equipment. Facility plant engineers are typically evaluated on their ability to avoid disruptions and constraints in production processes, not energy-efficient operation. Equipment suppliers also have little incentive to promote more energy-efficient system operation, since commissions increase when equipment size is scaled upward and educating a customer to choose a more efficient approach requires extra time and skill. Plant engineering and operations staff frequently experience difficulty in achieving management support. Industrial managers are rarely drawn from the ranks of facilities operation—they come from production and often have little understanding of supporting industrial systems. This situation is further exacerbated by the existence of a budgetary disconnect in industrial facility management between capital projects (including equipment purchases) and operating expenses. In addition, most optimised industrial systems lose their initial efficiency gains over time due to personnel and production changes. Detailed operating instructions are not integrated with quality control and production management systems. Without well documented maintenance procedures, the energy efficiency advantages of high efficiency components can be negated by clogged filters, failed traps and malfunctioning valves.

1.4.3

Energy efficiency

Typically, the process for setting energy efficiency or GHG emission reduction targets requires a preliminary assessment of the energy efficiency or GHG mitigation potential of each industrial facility, which includes an inventory of economically viable measures that could be implemented.

Industrial energy conservation: A review 9

Identification of energy-saving technologies and measures

Countries with strong industrial energy efficiency programmes, whether or not they are associated with agreement programmes, provide information on energy efficiency opportunities through a variety of technical information sources including fact sheets, brochures, guidebooks, technical publications, energy efficiency databases, software tools and industry- or technology-specific energy efficiency reports. Benchmarking

Benchmarking provides a means to compare the energy use within one company or plant to that of other similar facilities producing similar products or to national or international best practice energy use levels. Benchmarking can compare plants, processes or systems. Energy efficiency audits or assessments

Energy efficiency audits or assessments involve collecting data on all of the major energy-consuming processes and equipment in a plant, documenting specific technologies used in the production process and identifying opportunities for energy efficiency improvement throughout the plant. An audit is an essential first step in identifying opportunities that can contribute to an organisation’s energy efficiency targets. Energy saving action plans

An energy action plan outlines a company’s plan for improving energy efficiency during the period covered by energy efficiency targets and is a required component of compliance with an energy management standard. The energy action plan provides primary guidance for the internal implementation of the activities that will be undertaken to reach the energy-saving target. It also serves as a reference to evaluate progress on an annual basis. The plan, which is typically reviewed by an independent third party and updated as needed in response to changes over time, includes a description of the facility’s energy uses, a description of the energy efficiency measures considered, a description of the planned energy efficiency measures, a time-frame for implementation of the energy efficiency measures and expected results in terms of energy efficiency. Monitoring

Monitoring guidelines for energy efficiency and GHG mitigation projects have been developed by numerous entities in order to understand the progress and results of specific energy efficiency projects.

10 Industrial energy conservation

1.5

Causes of the energy crisis

The energy crisis is the concern that the world’s demands on the limited natural resources that are used to power industrial society are diminishing as the demand rises. These natural resources are in limited supply. Governments and concerned individuals are working to make the use of renewable resources a priority and to lessen the irresponsible use of natural supplies through increased conservation. The energy crisis is a broad and complex topic. Most people don’t feel connected to its reality unless the price of gas at the pump goes up or there are lines at the gas station. The energy crisis is something that is ongoing and getting worse, despite many efforts. The reason for this is that there is not a broad understanding of the complex causes and solutions for the energy crisis that will allow for an effort to happen that will resolve it. ‘An energy crisis is any great bottleneck (or price rise) in the supply of energy resources to an economy. In popular literature though, it often refers to one of the energy sources used at a certain time and place, particularly those that supply national electricity grids or serve as fuel for vehicles.’

1.5.1

Factors related to energy crisis

Some of the factors related to energy crisis are discussed below: Over consumption: The energy crisis is a result of many different strains on our natural resources, not just one. There is a strain on fossil fuels such as oil, gas and coal due to over consumption – which then in turn can put a strain on our water and oxygen resources by causing pollution. Over population: Another cause of the crisis has been the steady increase in the world’s population and its demands for fuel and products. No matter what type of food or products you choose to use – from fair trade and organic to those made from petroleum products in a sweet shop – not one of them is made or transported without a significant drain on our energy resources. Poor infrastructure: Ageing infrastructure of power generating equipment is yet another reason for energy shortage. Most of the energy producing firms keep on using outdated equipment that restricts the production of energy. It is the responsibility of utilities to keep on upgrading the infrastructure and set a high standard of performance. Unexplored renewable energy options: Renewable energy still remains unused in most of the countries. Most of the energy comes from non-renewable sources like coal. It still remains the top choice to produce energy. Unless we give renewable energy a serious thought, the problem of energy crisis cannot be solved. Renewable energy sources can reduce our dependance on fossil fuels and also helps to reduce greenhouse gas emissions.

Industrial energy conservation: A review 11

Delay in commissioning of power plants: In few countries, there is a significant delay in commissioning of new power plants that can fill the gap between demand and supply of energy. The result is that old plants come under huge stress to meet the daily demand for power. When supply doesn’t matches demand, it results in load shedding and breakdown. Wastage of energy: In most parts of the world, people do not realise the importance of conserving energy. It is only limited to books, internet, newspaper ads, lip service and seminars. Unless we give it a serious thought, things are not going to change anytime sooner. Simple things like switching off fans and lights when not in use, using maximum daylight, walking instead of driving for short distances, using CFL instead of traditional bulbs, proper insulation for leakage of energy can go a long way in saving energy. Poor distribution system: Frequent tripping and breakdown are result of a poor distribution system. Major accidents and natural calamities: Major accidents like pipeline burst and natural calamities like eruption of volcanoes, floods, earthquakes can also cause interruptions to energy supplies. The huge gap between supply and demand of energy can raise the price of essential items which can give rise to inflation. Wars and attacks: Wars between countries can also hamper supply of energy specially if it happens in Middle East countries like Saudi Arabia, Iraq, Iran, Kuwait, U.A.E. or Qatar. That’s what happened during 1990 Gulf war when price of oil reached its peak causing global shortages and created major problem for energy consumers. Miscellaneous factors: Tax hikes, strikes, military coup, political events, severe hot summers or cold winters can cause sudden increase in demand of energy and can choke supply. A strike by unions in an oil producing firm can definitely cause an energy crisis.

1.5.2

Possible solutions of the energy crisis

Move towards renewable resources: The best possible solution is to reduce the world’s dependence on non-renewable resources and to improve overall conservation efforts. Much of the industrial age was created using fossil fuels, but there is also known technology that uses other types of renewable energies – such as steam, solar and wind. The major concern isn’t so much that we will run out of gas or oil, but that the use of coal is going to continue to pollute the atmosphere and destroy other natural resources in the process of mining the coal that it has to be replaced as an energy source. This isn’t easy as many of the leading industries use coal, not gas or oil, as their primary source of power for manufacturing.

12 Industrial energy conservation

Buy energy efficient products: Replace traditional bulbs with CFL’s and LED’s. They use less watts of electricity and last longer. If millions of people across the globe use LED’s and CFL’s for residential and commercial purposes, the demand for energy can go down and an energy crisis can be averted. Lighting controls: There are a number of new technologies out there that make lighting controls that much more interesting and they help to save a lot of energy and cash in the long run. Preset lighting controls, slide lighting, touch dimmers, integrated lighting controls are few of the lighting controls that can help to conserve energy and reduce overall lighting costs. Easier grid access: People who use different options to generate power must be given permission to plug into the grid and getting credit for power you feed into it. The hassles of getting credit of supplying surplus power back into the grid should be removed. Apart from that, subsidy on solar panels should be given to encourage more people to explore renewable options. Energy simulation: Energy simulation software can be used by big corporates and corporations to redesign building unit and reduce running business energy cost. Engineers, architects and designers could use this design to come with most energy efficient building and reduce carbon footprint. Perform energy audit: Energy audit is a process that helps you to identify the areas where your home or office is losing energy and what steps you can take to improve energy efficiency. Energy audit when done by a professional can help you to reduce your carbon footprint, save energy and money and avoid energy crisis. Common stand on climate change: Both developed and developing countries should adopt a common stand on climate change.

1.6

Non-conventional renewable energy sources

Renewable energy sources also called non-conventional energy, are sources that are continuously replenished by natural processes. For example, solar energy, wind energy, bio-energy, bio-fuels grown sustainably), hydropower, etc., are some of the examples of renewable energy sources. However, most of the world’s energy sources are derived from conventional sources-fossil fuels such as coal, oil and natural gases. These fuels are often termed non-renewable energy sources.

1.6.1

Various forms of renewable energy

1. Wind energy: Wind power is harnessed by setting up a windmill which is used for pumping water, grinding grain and generating electricity.

Industrial energy conservation: A review 13

2. Tidal energy: Sea water keeps on rising and falling alternatively twice a day under the influence of gravitational pull of moon and sun. This phenomenon is known as tides. 3. Solar energy: Sun is the source of all energy on the earth. It is most abundant, inexhaustible and universal source of energy. 4. Geo-thermal energy: Geo-thermal energy is the heat of the earth’s interior. This energy is manifested in the hot springs. 5. Energy from biomass: Biomass refers to all plant material and animal excreta when considered as an energy source.

1.7

Energy conservation

Energy conservation means energy prevention from being wasted more than its purpose of use such as turning off lights on a frequent basis and not extremely cooling rooms with air-conditioners and improvement of efficiency of energy use through technological improvement. Generally, ‘energy efficiency’ or ‘energy conservation’ is a common term and is familiar to us in daily lives. As a broader definition in development assistance, ‘energy conservation’ means enhancing efficiency of energy consumption throughout a society. In general, energy can be classified as in Fig. 1.1 and it would be easier to understand if energy conservation is classified in the same manner. Energy

Supply side

Demand side

Industry

Household

Transportation

Exhaustible sources

Non exhaustible resources

Figure 1.1: Classification of demand side and supply side of energy.

In addition, in Fig. 1.1, turning off lights on a frequent basis, which is quite familiar in daily life, is categorised as energy conservation in the household sector. 1. Industrial sector: Factories manufacturing industry (iron manufacture, nonferrous manufacture, machinery, chemical industry, ceramic industry, textile industry, paper and pulp industry, food industry, etc.), power generation industry, city gas, petroleum products and heat supply, etc. 2. Household sector: Buildings offices, shopping malls, hospitals, hotels and home, etc. 3. Transportation sector: Vehicles, boats and vessels, aircrafts, trans-portation systems and physical distribution systems, etc.

14 Industrial energy conservation

4. Non-renewable resources: Oil, coal, natural gas and nuclear power, etc. 5. Renewable resources: Hydraulic, geothermal and wind power, solar energy and biomass, etc. Energy conservation means enhancing ‘efficiency of energy consumption’ which is, thus, compatible with the enhancement in the industrial, household and transportation sectors on the ‘demand side,’ according to Fig. 1.1. In the issue of energy conservation, the energy suppliers of electric power, city gas and others are included in the demand side of factories as one of energy consumers since they use resources (primary energy) to create products (secondary energy). Enhancing efficiency of energy consumption for private power generation and of energy production process (e.g., efficiency of power generation and improvement of power transmission in power plants) is also the target of energy conservation. The term of energy conservation has various definitions. The term is often defined as ‘to reduce the consumption of non-renewable resources’. In Japan, since energy conservation has been promoted in its history based on unique background, the so-called ‘oil shock,’ it is often defined as ‘to reduce oil consumption’ among non-renewable resources in particular. In this definition, the efficient use of other energy such as coal and natural gas is not included in energy conservation. However, technologies that lead to oil-use reduction without influence upon energy use efficiency are called ‘energy conservation technologies,’ including the use of new energy, for example. On the other hand, demand in many developing countries is not only reducing the use of non-renewable resources but also enhancing efficiency of energy use in the entire society. Thus, the term of ‘energy conservation’ means enhancing efficiency of energy consumption including coal, natural gas and other energy as well as oil.

1.7.1

Electrical and heat energy

Upon actual consumption, energy is used either in the form of heat energy or electric energy. Heat energy means the energy that can be obtained through burning of resources such as oil, coal and charcoal. Heat energy becomes the motive energy in the engine of a vehicle or vessel, or steam locomotive via air or steam. Electric energy means the electricity that is produced in a power plant, transmitted by transmission lines and can be obtained by paying for utilities. Generally, electricity can be obtained through an outlet or battery and can be used as motive power for electrical products such as televisions and refrigerators. Heat energy and electric energy are used in a variety of ways, depending upon equipment or facilities in use. Normally, they cannot be used at 100% of full efficiency and some losses occur. For instance, at

Industrial energy conservation: A review 15

offices, if personal computers are operated only while users look at their screens, the best efficiency will take place. However, in fact, while users are on the telephone, or serving customers, screens are still displayed. Electric energy is wasted during such time. Although more computers have function of energy conservation automatically becoming stand by mode when untouched after a certain period of time, it is impossible to turn power on only while users look at screens. The same type of energy losses occurs to many aspects of energy consumption in larger size such as power plants in factories throughout society. Energy conservation is expected to reduce these kinds of losses of energy in the entire society as much as possible and aim to raise the efficiency of energy use as close to 100% of the full rate.

1.8

Need of energy conservation

The amount of energy consumption in the entire world has been increased, accompanied by economic development of each country. Many energy resources used throughout the world today are still fossil fuels such as oil, coal and natural gas. If energy consumption continues to increase at the same rate as today, exhaustion of resources would occur in the near future. Additionally, as a result of mass consumption of fossil fuels, global warming caused by an increasing amount of CO2 emissions in the air has been occurring at rapid speed, which is one of the most crucial global issues. As effective counter measures against global issues such as future exhaustion of resources and global warming, the necessity for the promotion of energy conservation in the international level has been increasingly emphasised. In recent years, various policies of energy conservation have been implemented in many countries. Also, the international framework based on the Kyoto Protocol was established and it has promoted activities towards tackling global warming along with the ratification by Russia. At the same time, many countries still have a strong tendency to focus on economic development rather than environmental measures. It cannot be said that energy conservation is the issue that society wants first and most. This tendency is seen in some developed countries such as the U.S., but especially in developing countries, policy priority is not given to energy conservation. Energy has an important function. It is the central force behind our productivity, our leisure and our environment. There is a strong correlation between energy use per person and standard of living in each economy. A higher per capita energy consumption means a higher per capita gross national product. Energy is an indispensable component of industrial product, employment, economic growth, environment and comfort. Low cost energy was abundant in the past. Energy cost was only a very small fraction of the cost of finished product. Use of low cost energy for home comfort became

16 Industrial energy conservation

very predominant. The subsequent increase in oil prices increased the energy cost in every sector, domestic, commercial, industrial, etc. The per capita energy consumption in India is very low as compared to that in advanced countries. However our energy resources are fast getting depleted. Thus energy saving or conservation is essential in developed as well as developing countries. Meaning and principles of energy conservation: Energy conservation means using energy more efficiently or reducing wastage of energy. It is important that any energy conservation plan should only to try to eliminate wastage of energy without in any way affecting productivity and growth rate. A small decrease in convenience or comfort can be tolerated. Energy conservation usually requires new investment in more efficient equipment to replace old inefficient ones. Thus energy conservation can result in more job opportunities, lower costs, cheaper and better products, etc. There are two principles of energy conservation planning which are discussed below: 1. Maximum energy efficient: A device, system or process is working at maximum efficiency when maximum work is done for a given magnitude of energy input. Only a part of the input energy is converted into useful work. The remainder is lost in energy conversion and transfer process and energy discharge. Work = Energy input – Energy loss in energy conversion transfer process and energy discharge. 2. Maximum cost effectiveness in energy use: Implementation of energy conservation entails additional investment. This investment increases as more and more energy conservation measures are adopted. Because of implementation of these measures the fuel costs decreases as extent of conservation is increased. The total cost per unit output is the sum of annual charges on investment per unit output and fuel costs per unit output. Evidently maximum cost effectiveness in energy use is obtained when total costs are the least.

1.8.1

Energy conservation planning

Energy conservation planning can be divided into four steps: 1. Specifying targets and preparing detailed plans: It is the first step in energy conservation planning. The targets should neither be too pessimistic nor too optimistic. The targets and plans can be divided into three categories viz., programmes which do not require any additional investment, programmes which require small additional investment and need a year or so for implementation and programmes which require major changes and large investment.

Industrial energy conservation: A review 17

2. Identifying energy inefficient facilities and equipment: In this step the facilities and equipment which are energy inefficient are identified. The indices used for this purpose are Energy Efficient Index (EEI), Energy Quantity Index (EQI) and energy effectiveness index energy quality index. EEI = Energy used/energy input EQI = Availability of energy output/availability of energy input 3. Implementation of energy conservation measures: The energy conservation measures includes method of installation (i.e. recycling, retrofitting) and method of heat use (e.g., installation of equipment for waste heat recovery and utilisation).

1.8.2

Objectives of the energy management programme

The primary objective of energy management is to maximise profits and minimise costs. The main objectives of energy management programmes include: 1. Improving energy efficiency and reducing energy use, thereby reducing costs. 2. Reduce greenhouse gas emissions and improve air quality. 3. Cultivating good communication on energy matters. 4. Developing and maintaining effective monitoring, reporting and management strategies for wise energy usage. 5. Finding new and better ways to increase returns from energy investments through research and development. 6. Reducing the impacts of curtailments or any interruption in energy supplies.

1.8.3

Benefits of energy conservation

Saving of usable energy, which is otherwise wasted, has direct impact on economy environment and long-term availability of non-renewable energy resources. Energy conservation implies reduction in energy consumption by reducing losses and wastage by employing energy efficient means of generation and utilisation of energy. Economical aspects

Reduction in cost of product: Energy conservation ultimately leads to economic benefits as the cost of production is reduced. In some energy intensive industries

18 Industrial energy conservation

like steel, aluminium, cement, fertiliser, pulp and paper. The cost of energy forms a significant part of the total cost of product. Energy cost as a per cent of total cost of product in the entire industrial sector in India varies from as low as 0.36% to as high as 65%. Using energy efficient technologies will reduce the manufacturing cost and lead to production of cheaper and better quality products. New job opportunities: Energy conservation usually requires new investments in more energy efficient equipments to replace old inefficient ones, monitoring of energy consumption, training of manpower, etc. Thus energy conservation can result in new job opportunities. Environmental aspects

Every type of energy generation/utilisation process affects the environment to some extent, either directly or indirectly. The extent of degradation of the environment depends mainly on the type of primary energy source. Also, during every energy conversion stage a part of energy escapes to the surroundings and appear in the form of heat. Thus, energy is generated and utilised at the expense of adverse environmental impacts. Adoption of energy conservation means can minimise this damage. Conservation of non-renewable energy assets

The vast bulk of energy used in the world today comes from fossil fuels, which are non-renewable. These resources were laid down many millions of years ago and are not being made any longer. This finite non-renewable asset is being used up very fast. The quantity of fossil fuels that world community uses in one minute actually took the earth a millennium to create. Therefore its prices are bound to go up relative to everything else. It is necessary to abandon waste practices in energy utilisation and conserve this resource by all means for future generations. Energy plays a key role in achieving the desired economic growth. Energy is an essential basic need for not only human beings, but also for national economic and social development. However, production of energy is found to exhibit both local and global environmental impacts, if not appropriate technology and management techniques are not apply. Meanwhile, energy conservation promises to fill the gap between supply and demand. Several measures for conservation of energy are very important for consideration. The conservation of energy, therefore, is using less more wisely than before. Efficient utilisation of energy resource is not only conservational it also saves capital investment. Thus conservation is really the cheapest of energy resources at least until its potential is exhausted.

Industrial energy conservation: A review 19

Electric energy occupies the top grade in the energy hierarchy. It finds innumerable uses in home, industry, agriculture and in transport. The facts that electricity can be transported practically instantaneously, is almost pollution free at the consumer level and its use can be controlled very easily, making it very attractive as compared to other forms of energy. The electrical losses are very high in India and are about 4–5 times as compared to other developed countries. These losses are in transmission, distribution, transformation and energy theft. There is a good scope of energy conservation in various sectors, viz., industry, agriculture, transport and domestic. The energy audit can unearth huge profits to the industry. The industrial sector has failed to take full advantage of many financial incentives provided by the government to encourage energy conservation strategies. Manufacturing managers need to understand the interrelated links between advanced manufacturing technology, primary and alternative energy choices, energy output values and costs and energy conservation over the life of a project. The climate change is one of the driving forces behind a new wave of energy management systems. Most of the currently available energy management systems in domestic environment are concerned with real-time energy consumption monitoring and display of statistical and real time data of energy consumption. Although these systems play a crucial role in providing a detailed picture of energy consumption in home environment and contribute towards influencing the energy consumption behaviour of household, they all leave it to households to take appropriate measures to reduce their energy consumption. Some energy management systems do provide general energy saving tips but they do not consider the household profiles and energy consumption profiles of home appliances.

2 Energy efficiency technologies and benefits

2.1

Introduction

Energy consumption is an essential element in development. While increased energy use clearly has many benefits, we are also becoming increasingly aware of the negative impacts of energy use. We experience these negative impacts globally and locally in the form of climate change (and the associated effects) and degradation of local environments in terms of—for example, poor air quality, degradation of soils (leading to desertification in extreme cases), resource depletion (e.g., water) and noise pollution. However, more efficient use of energy at all stages of the supply/demand chain could reduce the negative impacts of energy consumption, while still allowing the same economic development. In addition, the inefficient use of energy generally implies higher than necessary operating costs to the customer (the energy end-user). At the company or enterprise level, higher energy efficiency will thus reduce operating costs and enhance profitability. At a national level, improved energy efficiency implies reduced energy imports, thus reducing foreign exchange pressures as well as increasing the availability of scarce energy resources for others to utilise, allowing increases in energydependent activities to contribute to the economic well-being of the population as a whole. Society as a whole also benefits from increased energy efficiency, principally through reduced adverse environmental impacts of energy usage. Lastly, global primary energy resources (mainly fossil fuels) are finite and they will eventually be exhausted. They form part of the natural capital on which our lives and economies-depend. However, their accelerated use in recent years has only brought the date that they will run out closer and reduced availability and higher costs have increased the pressure on countries that rely on fossil fuel imports. Sustainable future development depends on using these resources wisely and maximising the benefit received for each unit of energy consumed. Energy efficiency definition: Energy efficiency is understood to mean the utilisation of energy in the most cost effective manner to carry out a manufacturing process or provide a service, whereby energy waste is minimised and the overall consumption of primary energy resources is reduced. In other words, energy efficient practices or systems will seek to use less energy while conducting any energy-dependent activity; at the same time, the corresponding

22 Industrial energy conservation

(negative) environmental impacts of energy consumption are minimised. It can be appreciated that energy efficiency is a broad term and there are various ways of using it in the real world. The specific definition depends on the context and in whatever way it is used—it represents a ratio of output to energy input (or of course the inverse, energy input per defined output). Thus, energy efficiency is a term that is used in different ways, depending on the context and possibly on the person using the term. The strict technological usage relates an energy output to an energy input and is used typically by engineers for machines and equipment. Thus, the energy efficiency of an electric motor is the ratio of mechanical output (that is, the work done using the motor) to the electrical input. Quantities must be expressed in the same units, e.g., kilowatt-hours per day and the result—a dimensionless number is conventionally expressed as a percentage. This approach is used extensively in industrial plants and buildings for a wide range of equipment including motors, pumps, compressors, furnaces and boilers. For boilers, for example, the efficiency might be say ‘85%’, meaning that 85% of the energy value of the fuel has been converted into useful steam (and the sum of various losses is thus 15%). For many manufacturing processes and other energy-dependent activities such as the operation of passenger and freight vehicles, comparing input and output in the same units to derive a dimensionless number is not a practical approach. The ‘technical’ definition is therefore little used for many types of energy efficiency analysis. In many real situations, energy efficiency is most often expressed as a surrogate, the ratio of energy input to the ‘output’ from a specific activity. Thus in industry, the energy efficiency of a cement kiln can be expressed as X thousand litres of oil fuel fired per ton of clinker produced and that of a rolling mill as Y tons of standard coal per ton of steel rebar manufactured. For the transport sector, the energy efficiency of a truck can be expressed as Z litres of diesel oil per ton-km of freight transported and of a city bus as W litres of gasoline per thousand passenger-km achieved. Such indicators are often called ‘specific energy consumptions’ and are widely used to compare energy efficiency across plants, buildings, transport vehicles and modes. In practical situations therefore, to monitor energy efficiency over time, we need to relate energy consumption to a specific level of activity or output. The indicators used to express energy efficiency are not percentages but will have defined units and changes observed from one time period to another will indicate if the activity is being carried out more or less efficiently—other factors remaining unchanged (e.g., no change in a manufacturing process, no fuel switching, similar weather conditions, etc.)

Energy efficiency technologies and benefits 23

At national level, the term ‘energy efficiency’ is not often used. Rather, ‘energy intensity’ is typically adopted. Energy intensity is the ratio of energy consumption to some measure of the demand for energy-related activities and it can be applied to an entire sector of the economy. An example is the energy intensity of say the industrial sector of a country, expressed as X joules per unit of GDP generated by that sector. Sometimes the energy intensity is expressed entirely in monetary terms, e.g., energy expenditure of Z dollars per dollar of GDP. Thus energy intensity—similar in many respects to the energy efficiency concept illustrated for processes or transport—will typically include structural and behavioural components. Changes in the sector—such as shifts in the types of product manufactured will impact on the energy intensity, irrespective of changes in energy efficiency of the plants, processes and machines involved. Energy conservation tends to be associated often wrongly with ‘deprivation’ of some sort, such as lower levels of comfort in buildings, lower industrial production levels. Energy saving generally means a lower consumption of energy and this may or may not be accompanied by changes in the quality or quantity of an output or activity.

2.2

Benefits of increased energy efficiency

There are many benefits of increased energy efficiency. These can broadly be categorised into financial/economic, environmental and social benefits. The relative importance of each of these benefits depends on the actual situation in a given country or area, including for example the prices of different types of energy, the cost of energy efficiency measures and equipment, the tax regime and the current levels of energy efficiency already being achieved. For private companies, the most important benefits of higher energy efficiency will be linked to the financial benefits of lower costs for running the business. This applies to typical manufacturing companies as well as to energy suppliers such as electricity generating plants and oil refineries. Examples are: 1. Energy efficient companies can gain a competitive advantage over less efficient companies, allowing them to increase their profits at current product prices, or lower their prices to gain market share, or a combination of these items. 2. Utility regulators may require utility suppliers to reduce their prices to consumers, with the benefits of higher operating efficiency shared between energy producers and consumers for mutual benefit (and for the overall benefit of society).

24 Industrial energy conservation

3. Reduced environmental impact can also serve as a significant marketing tool for efficient companies, as public perception of ‘green’ companies takes an increasing role in purchasing decisions. Environmental benefits include many elements, such as reduced local pollution through burning less fuel, lower greenhouse gas emissions, less use of firewood and hence less destruction of forests. 4. Even where company output is increased (e.g., through expanding manufacturing capacity) energy efficiency improvements can contribute significantly in most cases to reducing the negative impact of energy consumption per unit of output. Any increase in pollutant emissions will thus be minimised. At a national level, these kinds of benefits could reduce the dependence of a country on imported energy, or could extend the life of energy reserves where present. These are worthwhile contributions to the national economy, often achievable at modest cost to the companies involved and little or no cost to the government itself.

2.2.1

Business benefits of energy efficiency

In most businesses, the initial stages of raising energy efficiency can be achieved through little or no capital investment. Correct and timely maintenance can have a substantial effect on improving energy efficiency (e.g., replacing broken or inadequate insulation on hot or cold piping). Boilers and furnaces can usually be operated more efficiently by ensuring the proper combustion conditions are maintained at all times. In some factories or buildings, the boiler/furnace operators might lack the necessary skills (and proper testing instruments) to know how this may be achieved. However, training programmes and the installation of a few simple low-cost devices could typically pay for themselves in a matter of a few weeks. High efficiency light bulbs are another example of a modest investment that typically pays off in a very short time. Of course, some major investments in energy efficiency improvements, e.g., new process equipment, totally new boilers—are well justified in financial terms and can often be undertaken by a business to produce big increases in profits. Large investments in new equipment will often be accompanied by increase in manufacturing capacity and hence the benefits are not strictly limited to energy reduction. At the same time, new equipment may provide a safer and cleaner environment for the workers in addition to achieving higher energy efficiency. Overall, higher energy efficiency brings lower operating costs to almost all businesses, allowing an ‘efficient’ company to gain a competitive edge over more wasteful competitors.

Energy efficiency technologies and benefits 25

In addition a resource-efficient business demonstrates a responsibility towards the environment. This can be used to promote the environmentally friendly business and this can be a strong marketing message. Finally, we should note that businesses can be encouraged to undertake energy efficiency investments through various forms of tax incentives. Many of these are oriented to increasing the rate of depreciation for certain categories of efficient equipment or processes. In some countries, a lower consumption of energy can lead to a reduction in the company’s tax burden.

2.3

Importance of energy efficiency

2.3.1

Energy-dependent activities and the energy supply chain

All so-called end-users use energy to carry out an ‘activity’, such as manufacturing a product, transporting goods or passengers, cooking a meal or providing light. Customers are generally not particularly interested in the details of how the energy is provided to them, rather they are interested in the utilisation of energy within their own activities and how they may operate safely and efficiently to produce the required output and for a low, or at least acceptable, cost. Of course, the energy supply companies themselves have relatively broad interests covering both supply and demand aspects of energy use. It is useful to understand the overall supply/demand chain for providing the energy to an energy consumer and carrying out a specific activity (Fig. 2.1).

2.3.2

Energy losses

Inefficiencies can occur at any stage of the supply-demand chain. For example, the overall efficiency of a conventional electricity generating plant—even if well operated can often be little more than 30%, while a poorly operated coal fired boiler might struggle to reach 50% efficiency. The energy losses can thus be significant throughout the chain. Losses can be divided into two main types: 1. Intrinsic losses, i.e., unavoidable losses such as those that are a function of the activity and depend on thermodynamic and physical laws. For example, electricity distribution lines (and steam pipelines) will always have some associated losses, even if properly sized (or well insulated). 2. Avoidable losses, i.e., losses resulting from sub-optimal/poor design, maintenance and operation of systems (steam leaks, non-insulated lines, inadequately sized electricity wiring, incorrectly adjusted combustion equipment, etc.).

26 Industrial energy conservation Primary energy resource: coal, nuclear fuel, oil, hydro, biomass, etc.

Generator/converter: power station, refinery, nuclear reactor, etc. Supply Energy carrier: electricity, LPG, fuel oil, natural gas, etc.

Demand

Conversion appliance: electric motor, furnace, boiler, light fitting, stove, water heater, car, etc.

Activity: product manufacturing, cooling, water pumping, lighting, passenger travel, hot water, cooked meals, etc.

Figure 2.1: The energy supply-demand chain.

The avoidable losses in the supply-demand chain will result in missed opportunities, requiring additional primary energy resources to be consumed in achieving the required output from a given activity. In addition to added costs, there will be a corresponding increase in environmental degradation. Raising the energy efficiency of all steps in the supply-demand chain is of course the means by which we can reduce energy losses. In the short term, improving energy efficiency addresses directly the so-called avoidable losses but, in the long term, we may be able to address the ‘unavoidable’ losses to a degree. For example, we may be able to redesign a process or item of equipment to ensure the losses that are built-in for technical reasons are kept to the minimum. Practical experience suggests that the avoidable losses are typically much more significant than the ‘technical’ losses. Major losses occur in all sectors of the economy from the use of old and inefficient technologies or outdated processes. With very few exceptions, however, of even greater importance are the avoidable losses that result from poor management of plants, processes and equipment and in many cases from inappropriate behaviour of energy consumers.

Energy efficiency technologies and benefits 27

Efforts to improve energy efficiency can be undertaken in every step. For example: 1. Material handling could perhaps be improved by better management of equipment to reduce losses to 1.8% (efficiency 99.2%). 2. Power station efficiency could be raised through improved maintenance to 32% (losses down to 68%). 3. Transformer upgrading could reduce transmission/distribution losses to 10% (efficiency 90%). 4. An improved design and better insulation of the water heater, tanks and piping could reduce losses to 15% (efficiency 85%). The cost-effectiveness of energy efficiency measures needed to achieve such gains will depend on many factors, including the cost of new and improved equipment, the cost of energy and the value of the energy saved. Changes in the use patterns of energy-dependent activities will also offer another opportunity to increase the overall efficiency (e.g., lower usage of hot water by lowering the amounts needed for washing laundry items, or lowering the wash temperature by blending hot water with some cold water). Thus energy efficiency has an important role to play in reducing the need for energy throughout the economy.

2.3.3

Energy flows in national economies

The energy flows, together with energy consumption data and an understanding of the relevant supply-demand chains for different sectors, can be used to suggest where energy efficiency improvements could have a major impact and indicate the types of energy that could be saved. With this information, some initial priorities could be developed for an energy efficiency programme at the national level. An overall goal for such a national energy efficiency programme would be to reduce the energy intensity of the various sectors of the economy thereby decreasing the amount of primary energy per unit of economic activity (measured in GDP). Energy intensity

Energy intensity can be used as a rough measure of the energy efficiency of a nation’s economy. For that purpose it is usually expressed as the ratio of national energy consumption to GDP and quoted in units of energy per unit of GDP (e.g., kilojoules per dollar of GDP). While it is true that a high energy intensity could possibly reflect an inefficient use of energy in an economy, a high figure may also simply reflect that the underlying structure of the economy is oriented strongly to basic industries—with relatively low value added and using large quantities of energy. These basic industries might well be quite efficient

28 Industrial energy conservation

although this might not be appreciated at first sight from the quoted energy intensity. Many factors influence the overall energy intensity for a national economy. The figure will—for example, reflect the overall standards of living for a nation, as well as its climate. It is not untypical for particularly cold or hot climates to require greater energy consumption in homes and workplaces for heating or cooling. As suggested above, energy intensity is most often strongly affected by the relative size of the industrial sector and by the specific nature of industrial activities within that sector. Indicators of energy intensity are thus useful provided underlying components are well understood and the data interpreted accordingly. Without a structural context, energy intensity figures can be misleading. A well-defined and quantified structural context allows government policy makers to decide where policy changes might be made and what the potential impacts might be. These will include the impact of energy efficiency improvement measures throughout the economy (e.g., changes in the efficiency of industrial furnaces and boilers, electric motor efficiencies, standards of construction for domestic and commercial buildings, the fuel economy of vehicles).

2.4

Target sectors in energy efficiency

Energy efficiency interventions at a national level are generally developed and implemented in response to priorities identified within an integrated energy plan or an integrated resource plan. Sectoral interventions may also be developed and coordinated by government agencies or utility companies. Energy intensity and energy consumption indicators are used to identify target priority areas, e.g., sectors, specific industries. In many countries, the share of energy consumed by industry is often large although the share of the domestic and commercial buildings sector will often be almost as large. Transport is a growing energy consumer in most countries. Energy efficiency activities are therefore increasingly important in many sectors, depending not only on the total amount of energy consumed but also on the potential for cost effective improvements (broadly reflected in the current level of energy efficiencies of different sectors). In setting priorities, account has to be taken of the measures applicable in a given sector (including cost implications) and on the means of promoting energy efficiency action. The buildings and transport sectors may be complicated to address because the energy consumers are very widely dispersed and typically consume small amounts of energy individually. Industry—while perhaps also having many small consumers—will often include a relatively modest number of big consumers. It can therefore prove easier, at least administratively, to reach those consumers that represent a large proportion of sectoral energy use. Examples of proven measures in demandside sectors are given in Table 2.1

Energy efficiency technologies and benefits 29 Table 2.1: Examples of proven measures in demand-side sectors. Supply side segment

Examples of energy efficiency measures

Domestic and commercial buildings

• For heating and cooling services—use of efficient equipment, adjustments in use patterns (behavioural changes, temperature modifications, etc.), and good maintenance. • Lighting—using efficient light-bulbs, changing types of light sources, maximum use of natural lighting, behavioural changes (e.g., switching off when not needed, manually or automatically). • Office equipment and domestic appliances—installing energy efficient items, switching off when not used (e.g., reducing waste when on standby) and adopting good operating practices (e.g., running appliances only when full). • Construction materials—ensuring that appropriate materials and controls are utilised in new and retrofitted buildings (e.g., insulation, building orientation, double glazed windows). • Operations in general—routine data collection and regular analysis of energy performance, improved maintenance, good energy management using skilled and experienced staff. • Boilers and furnaces—proper combustion control with appropriate instrumentation, insulation and refractory brought up to good modern standards, burners well maintained. • Industrial processes—operated in accordance with design standards, heat losses minimised by good insulation, waste heat recovered for use elsewhere in the plant. • Industrial buildings—similar to the buildings sector, including attention to heating, cooling, lighting, etc. • Equipment—utilising existing equipment well (e.g., electric motor speed and load controls) and replacing obsolete items with new higher efficiency equipment (motors, fans, boilers, pumps, etc.) • Modal shifting—ensure freight and passenger transport is carried out in the most energy efficient mode (e.g., consider switching from road to rail, encouraging public transport over individual vehicles, etc. whenever possible).

Industry

Transport

(Cont’d…)

30 Industrial energy conservation Supply side segment

Resources and resources preparation

Power generation and energy conversion

Transmission

Examples of energy efficiency measures • Vehicles—encourage fleet replacement to modern higher efficiency equipment, improve maintenance, driver education. • Improved road maintenance. • Clean coal technologies—they allow improving the efficiency of the extraction, preparation and use of coal. They offer various solutions for coal cleaning as well as reducing NOx emissions and improve the efficiency of power generation. • Fuel substitutions—also referred to as fuel switching, is simply the process of substituting one fuel for another. This could be either a fossil fuel that allows for using more efficient conversion technologies (i.e., natural gas) or renewables (i.e., wind, solar, biomass, hydro, etc.). • Plant operations in general—these include routine data collection and regular analysis of energy performance, improved maintenance, improved logistics, good energy management using skilled and experienced staff. • Improved boilers and furnaces control—proper combustion control with appropriate instrumentation, insulation and refractory brought up to good modern standards, burners well maintained. • Upgrading generating units—it includes installation of new and improved burners, extra flue gas heat recovery, additional heat recovery from hot blow-down water as well as modernisation of instrumentation and combustion control systems. • Cogeneration—the combined production of electricity and heat can bring about major efficiency gains wherever a demand for heat exists next to a power plant (process heat for industrial factories, district heating, etc.). • Transmission and distribution line upgrading—this includes and distribution replacement/upgrade of equipment (transformers, switchgear, insulators, system control and data acquisition systems, etc.), as well as substations. • Improved control and operations—this includes data and system monitoring, power factor improvement, voltage regulation, phase balancing, preventive maintenance and other measures to reduce technical losses while increasing reliability.

Energy efficiency technologies and benefits 31

2.5

Energy efficiency actions

Energy efficiency improvements particularly focus on available technology to make such improvements, with some technology options being well-known and proven over many years of application and some of which may be relatively new and less well-known. Indeed, lack of information is a key barrier to energy efficiency improvements in many situations. However, experience in many countries of supply and demand-side activities shows that existing plants, buildings and equipment can often be improved substantially through simple low-cost/no-cost actions that have little bearing on technology. There are important opportunities for raising energy efficiency throughout the economy in every country, developed or developing, by adopting better ‘energy management’ practices. It is certainly not true to claim that energy efficiency cannot be raised without investment in new technology, a claim made all too often by managers of companies who have failed to grasp the opportunities offered by good management. At a national (or regional) level, energy efficiency interventions are best promoted in a strategic and integrated manner to use more efficient energy technologies and management practices within the context of an energy efficiency programme. For convenience, technologies and management programmes can be split into those applied to supply-side and those to demandside activities. There are of course many similarities amongst the measures actually adopted for such activities. Supply-side interventions are typically technical or management interventions, which are implemented by generators, grid operators and/or energy distributors, i.e., on the utility side of the meter or fuel pump. Demand-side interventions address aspects of energy efficiency, which can be implemented and achieved through changes in operating procedures and technologies by the customer/energy user, i.e., on the customer’s side of the meter.

2.5.1

Technologies and practices in energy efficiency

In all situations, energy efficiency actions must be carefully costed and undertaken only when it is profitable to do so. In brief, measures typically include. On the supply side

1. More efficient generation/conversion, including: (a) Minimising waste heat generation and recovering waste heat to an economic maximum. (b) Improving maintenance practices.

32 Industrial energy conservation

(c) Utilising equipment that has been manufactured to the best modern standards of efficiency, e.g., electric motors, steam and gas turbines, transformers, boilers. (d) Applying modern process technologies including clean coal processes. (e) Cogeneration (particularly where this can be combined with biomass fuel from a renewable source, e.g., bagasse, or with the utilisation of waste heat). (f) Better control systems and metering of key operating parameters. 2. More efficient transmission and distribution systems, including: (a) Closer and improved control of existing systems, e.g., better balancing of phases, voltage regulation, power factor improvement. (b) Increased use of distributed generation. (c) Higher transmission voltages. (d) State-of-the-art technologies such as low-loss transformers, fibre optics for data acquisition, smart metering, etc. On the demand side

1. More efficient equipment and appliances in all sectors, e.g., motors, boilers, furnaces, industrial dryers, pumps, compressors, lighting, domestic appliances, air conditioning systems. This is particularly important for equipment that is operated over long periods or continuously. 2. Improved maintenance of all equipment. 3. Improved metering of fuel, electricity and steam flows and of key operating parameters such as temperatures. Such figures feed into routine monitoring and performance analysis, activities that can be applied in all sectors. Information on energy usage and related levels of ‘activity’ such as production data allows energy consumers to appreciate better the quantities of energy consumed and the time and purpose of such consumption: this is an essential initial step to improving energy efficiency. 4. Control and energy system optimisation, often made practical by the improved metering mentioned above. This can include variable speed drives for electric motors, thermostats in buildings and industrial equipment, ripple control, smart appliances and power factor improvement. 5. Behavioural change on the part of the energy user, such as: (a) Monitoring energy efficiencies in major energy-consuming industrial processes and equipment to ensure design operating parameters and performance are respected.

Energy efficiency technologies and benefits 33

(b) Reporting leaks and equipment failures systematically, e.g., in industrial plants and checking the cost incurred through such deficiencies to ensure priority attention is given to repairs and replacement. (c) Changes in work practices such as working from home and/or flexitime. (d) Changes in equipment usage both at home and in the office, such as switching off appliances which are not needed and avoiding excessive use of ‘standby mode’ for many types of equipment. (e) Electricity load shifting by industrial or commercial energy users is a demand-side intervention but it has implications for improving energy efficiency of the grid network that supplies the electricity (supply-side). This is because peak loads can be reduced if electricity demand is spread out over a longer time period or if it is moved to another time of day. Since many electricity systems are forced to operate their least efficient generators to meet peak demand, this allows them to reduce the use of lower efficiency generating equipment in favour of greater use of their more efficient equipment over a longer period of time. (f) Choosing different modes of transport, e.g., public transport versus cars for individuals, rail versus road for freight, where such alternatives are available.

2.5.2

Energy efficiency programmes

It is not possible to list all types of energy efficiency programmes here but the section will give some examples of situations where government action can be particularly effective. 1. Development of energy efficiency policies and strategies. 2. Energy awareness—raising awareness of energy consumption and related aspects of energy efficiency among consumers/users. This can cover many topics, from training of energy professionals to appliance labelling and consumer education for the domestic sector. 3. Encouraging energy auditing and energy assessment both in the public and private sector. This is a logical next step after raising energy awareness. 4. Development of and publicity for, energy efficiency best practices and information on norms and standards applicable to different sectors, such as good modern practice for electric motor efficiencies, comparisons of industrial process energy consumption per unit of output. This activity can be applied in various ways to all sectors.

34 Industrial energy conservation

5. Development of the institutional capacity and human resources for implementation of energy efficiency interventions. This can range from teaching at schools and colleges, to requiring demonstrated competence at professional levels (e.g., air conditioning and heating engineers). 6. Support for technology R&D and especially for the demonstration of proven technologies to increase energy efficiency. 7. Introduction of incentive/penalty mechanisms to support improved energy efficiency. 8. Promotion and facilitation of international collaboration and cooperation. While the above items are written in the context of government-led programmes, many of the concepts are also valid for energy efficiency programmes organised and implemented by the private sector. For example, staff energy awareness is important for all companies, industrial and commercial. Raising staff and even customer—awareness can have valuable benefits to most firms. Manufacturing companies should be active in promoting good management and energy efficiency practices at all their sites and offices. Demand-side management and energy efficiency A distinction can be made between the terminology of demand-side management (DSM) and energy efficiency. In conventional usage, DSM is often applied to electricity load management, such as peak lopping or load shifting only and not to the more general range of interventions included under the topic of demand-side energy efficiency. This is particularly the case for DSM programmes implemented by utilities concerned with the management of load profile and peak-power demand. While it might seem desirable for a power utility to improve its load factor and postpone costly capacity expansion, in practice utilities companies tend to be unenthusiastic towards load shifting and DSM in general. This is because they foresee a reduction of electricity and power demand and consequently a reduction in sales and revenues.

2.6

Barriers to implementation of energy efficiency measures

Despite the fact that energy efficiency appears to make good sense in many situations—both in terms of cost savings and reductions in environmental damage—it is often very difficult to get managers of companies (and individuals) to take action. It is even more difficult to achieve effective implementation over a long period. All stakeholders are inclined to accept the status quo, which is usually a less efficient scenario and only respond in terms of energy efficiency once a crisis forces the issue, such as in the case of insufficient energy supplies. For private firms, other priorities are often quoted, such as

Energy efficiency technologies and benefits 35

capital investments to increase plant capacity and market share, leaving no funds for energy efficiency expenditures. This inherent inertia against acting to improve energy efficiency is reinforced by numerous institutional, financial and technical barriers to energy efficiency programmes, either real or perceived. These include: 1. Policy and regulatory barriers. 2. Lack of information and awareness of the potential for energy efficiency. 3. Lack of industry initiatives to emphasise energy management as an integral part of total management systems. 4. Lack of technical capacity to identify, appraise, develop and implement energy efficiency projects. 5. Financial and investment barriers. 6. Technology barriers. These barriers are discussed below.

2.6.1

Policy and regulatory barriers

Policy and regulatory oversight systems can influence the priorities and manner in which energy efficiency measures are implemented. In the case of policies, these include both national and local government policies. In many countries there simply is no policy or, if there is, it can be indifferent (and thus perhaps counter-productive) to energy efficiency. Regulations that support inappropriate tariffs can limit interest in energy efficiency. For example, it is common to see tariffs that provide for declining energy prices for incremental energy consumption by big consumers. This acts as a disincentive for such consumers to undertake energy efficiency actions. Supportive policy and regulatory environments for energy efficiency include setting targets mandatory or voluntary should be considered—from which strategies for encouraging increased levels of energy efficiency can be developed.

2.6.2

Lack of awareness and information

This barrier is the most common problem in almost all countries. Easy access to up-to-date and relevant information is typically lacking even in developed countries. Company managers are frequently observed stating that they have a particular problem that is adversely affecting their energy efficiency, yet the problem has already been solved—sometimes many times in other countries and indeed in other locations in the same country. In various countries there may be a lack of awareness of proven energy efficiency measures and programmes. The information about these is often

36 Industrial energy conservation

not well disseminated and the users are simply unaware of energy efficiency measures or their benefits to their company or the country. End-users need to be informed of the availability of efficient equipment and the respective energy cost savings and their positive environmental impacts from proper adoption. Sometimes the information to end-users (energy customers) is incorrectly perceived as being an attempt by government to restrict their energy use or deny them the right to energy, or manipulation on the part of utilities to make higher profits. Industry trade associations could play a positive role in encouraging the sharing of relevant information.

2.6.3

Lack of initiatives to emphasise energy management

This barrier is particularly important for the industrial and commercial sectors. Since energy management is a continuing process, it is essential that it becomes part of total management system. Most industries have management systems that address production, accounting, maintenance, environment and safety, but many do not include energy management as part of their management systems. As energy management requires a knowledge and skills base, medium and small industries often claim to have no staff resources to undertake energy management tasks. While this must be true for many firms, it may be possible to cover some aspects of energy management by using part-time staff—a fulltime person may not always be justified.

2.6.4

Lack of technical capacity to identify, evaluate and implement energy efficiency actions

There is a lack of qualified individuals and organisations to identify energy efficiency projects in many companies. Required skills include the ability to carry out energy audits, analyse performance data, from which opportunities to implement effective actions can be evaluated and properly justified in terms of the benefits achievable compared with the costs involved. In some countries, there are organisations that address this barrier by offering services to conduct energy audits or advising clients on energy efficiency measures. These service organisations need to: 1. Have a knowledge and understanding of energy efficiency systems and opportunities, especially in the local context. 2. Be aware of proper financial evaluation techniques and be experienced in analysing rates of return, life cycle costing, etc. 3. Demonstrate the quality and comprehensiveness of their work.

Energy efficiency technologies and benefits 37

4. Have a knowledge of the production and safety constraints of the client plant/company. A lack of technical capacity within such service organisations could result in an incorrect assessment and misdirected measures, which would be counter productive.

2.6.5

Financial and investment barriers

The cost of implementing energy efficiency measures in industry, commercial or residential sectors is sometimes said to be a barrier to effective energy efficiency. Often however, a manager will have little or no ability to evaluate energy efficiency measures properly and may not appreciate that no-cost/lowcost measures are available that require very little capital to implement. All too often the lack of awareness of potential benefits from EE actions prevents management from doing the no-cost measures first and using the cost savings to build up capital for reinvestment later in energy efficiency. In some cases of course, there are companies that really do not have funds to undertake even modest investments, even though the measures might have very short payback periods. For example, energy suppliers may need to invest in upgrading to more efficient electricity generators or transmission lines, while energy users may need to upgrade to more efficient appliances or install capacitors to increase power factors (and hence reduce the power needed for induction motors). Unfortunately these investments may not be made because there is a genuine lack of capital and interest rates on loans may not be favourable enough in most countries to justify borrowing.

2.6.6

Technology barriers

While great progress in achieving energy efficiency improvements is almost always made by improving energy management, there will be on occasions a real need for tackling deficiencies from a technology point of view. A barrier may be encountered because of a lack of availability of high efficiency equipment made to good modern standards in any particular country. There may also be insufficient cooperation amongst researchers or research organisations, making it difficult to build effective energy efficiency research, development and demonstration programmes. Thus even where research may have been effectively conducted there can be difficulty in transferring research prototypes into industrial scale working products. Examples of technology barriers include the continuing use of obsolete and inefficient equipment in the industrial, commercial and residential sectors. At times this is due to unavailability of more energy efficient technologies. It is perhaps more likely that weak marketing strategies exhibited by equipment

38 Industrial energy conservation

manufacturers or importers are contributing to the problem, especially where these do not address the inertia of customers who are reluctant to move away from obsolete and traditional products. Lack of confidence in local installers of new technologies can also be a barrier.

2.7

Combining renewables and energy efficiency to improve sustainability of energy development

Renewable energy technologies tend to have a higher profile than energy efficiency actions. This is mainly for the obvious reason that they are more visible as new installations and perceived as more ‘cutting-edge’ technologies. This occurs even though they often have higher initial capital costs than energy efficiency measures (and may have less favourable operating costs too). However, one of the benefits of adopting renewables is the ensuing increase in awareness of energy production and consumption in the owner of the installation and also often with the public who can see or might interact with the technology. For example, solar PV or solar water heating panels on a public building raises the awareness of renewable energy use in the building users and other members of the public. This increased awareness of energy consumption may be used to stimulate awareness of energy efficiency by introducing energy efficiency measures simultaneously with a new renewable energy installation. As the renewable energy installation has a significant capital costs people can become more sensitive to the idea of ‘wasting’ the energy from the system, especially if they feel a strong level of ownership of the renewable energy system. In addition, a renewable energy system supplier/installer could make recommendations on how to use the energy produced in the most efficient manner, so output from the system could generate the most benefit in terms of services to the end-users. This is often a good opportunity to introduce demandside energy savings measures. From the supply-side perspective, a switch to renewables supports sustainable energy generation and contributes to reducing dependency on imported energy. For large scale operations, currently available renewable technologies are biomass-based cogeneration for electricity generation, on-shore and off-shore wind, geothermal energy and large-scale hydro. For small-scale side installations, the following types of technologies can offset the need for electricity or gas taken from a national grid: 1. Solar water heaters for water heating. 2. Small-scale wind generators and mini-hydro systems for electricity. 3. Solar PV for electricity. 4. Small-scale biomass technologies for heat and electricity.

Energy efficiency technologies and benefits 39

To sum up the implementation of energy efficient measures at all stages of the supply/demand chain could reduce significantly the negative impacts of energy use on the environment and human well-being and increase the availability of primary energy reserves while achieving maximum benefits in terms of outputs from the available energy. The cost to both suppliers and consumers can be reduced, while maintaining the same level of energydependent activities. Indeed, the combined effect of supply and demand-side energy efficiency improvement means that the load on generating facilities is lowered and this can help keep older systems and equipment in good condition. This is because lower overall loads often allow the equipment to run below maximum capacity or be shut down more frequently (or for longer periods) for preventive maintenance. Older equipment will usually need more maintenance, depending on system characteristics, forced shutdowns for repair can be reduced and system operating efficiency can be raised. Overall system reliability can be improved as a result. Barriers to achieving a good level of energy efficiency improvement include the lack of policy or regulatory measures, the lack of information and awareness of potential benefits, a failure to emphasise good energy management and a lack of technical capacity to identify, evaluate and implement energy efficiency measures. Technology and financing barriers are also seen in some situations. Of these barriers, the failure to practice good energy management is typically one of the most important factors for enterprises. Improving energy management is almost always a low-cost action that achieves valuable benefits in the short term. Maintaining good management ensures these benefits are continually contributing to enterprise profits (and the national economy) in the long term.

3 Energy audit

3.1

Introduction

The ‘energy audit’ is the key to a systematic approach for decision-making in the area of energy management. It attempts to balance the total energy inputs with their use and serves to identify all the energy streams in a facility. It quantifies energy usage according to its discrete functions. An industrial energy audit is an effective tool in defining and pursuing a comprehensive energy management programme within a business. Energy audit is defined as ‘the verification, monitoring and analysis of use of energy including submission of technical reports containing recommendations for improving energy efficiency with cost benefit analysis and an action plan to reduce energy consumption.’ Need for energy audit: In any industry, the three top operating expenses are often found to be energy (both electrical and thermal), labour and materials. In most assessments of the manageability of the cost or potential cost savings in each of the above components, energy would invariably emerge as a top ranker and thus energy management function constitutes a strategic area for cost reduction. A well done energy audit will always help managers understand more about the ways energy and fuel are used in their industry and help to identify areas where waste can occur and where scope for improvement exists. The energy audit would give a positive orientation to the energy cost reduction, preventive maintenance and quality control programmes which are vital for production and utility activities. Such an audit programme will help to keep focus on variations that occur in the energy costs, availability and reliability of supply of energy, help decide on the appropriate energy mix, identify energy conservation technologies, retrofit for energy conservation equipment, etc. In general, the energy audit is the translation of conservation ideas and hopes into reality, by lending technically feasible solutions with economic and other organisational considerations within a specified time frame. Objective of energy audit: The primary objective of the energy audit is to determine ways to reduce energy consumption per unit of product output or to lower operating costs. The energy audit provides a benchmark, or reference point, for managing and assessing energy use across the organisation and provides the basis for ensuring more effective use of energy.

42 Industrial energy conservation

3.2

Types of energy audits

The type of energy audit to be performed depends on: 1. Function and type of industry. 2. Depth to which a final audit is needed. 3. Potential and magnitude of cost reduction desired. Thus energy audits can be classified into the following two types: 1. Preliminary audit. 2. Detailed audit.

3.2.1

Preliminary energy audit methodology

The preliminary energy audit uses existing or easily obtained data. It is a relatively quick exercise to: 1. Determine energy consumption in the organisation. 2. Estimate the scope for saving. 3. Identify the most likely (and easiest areas) for attention. 4. Identify immediate (especially no-cost/low-cost) improvements/ savings. 5. Set a reference point. 6. Identify areas for more detailed study/measurement.

3.2.2

Detailed energy audit methodology

A detailed energy audit provides a comprehensive energy project implementation plan for a facility, since it evaluates all major energy-using systems. This type of audit offers the most accurate estimate of energy savings and cost. It considers the interactive effects of all projects, accounts for the energy use of all major equipment and includes detailed energy cost saving calculations and project cost. In a detailed audit, one of the key elements is the energy balance. This is based on an inventory of energy-using systems, assumptions of current operating conditions and calculations of energy use. This estimated use is then compared to utility bill charges. Detailed energy auditing is carried out in three phases: Phase I – Pre-audit Phase II – Audit Phase III – Post-audit

3.3

Steps for conducting energy audit

Industry-to-industry, the methodology of energy audits needs to be flexible. A 10-step summary for conducting a detailed energy audit at the field level is

Energy audit 43

listed in Table 3.1. The energy manager or energy auditor may follow these steps to start with and add/change as per their needs and the industry type. Table 3.1: 10 Steps for a detailed energy audit. Step Action 1

2

3

4

5

Purpose

Phase I – Pre-audit • Resource planning; establish/organise • Plan and organise energy audit team • Walk-through audit • Organise instrumentation and time frame • Informal interviews with energy • Macro data collection (suitable to type manager, production/plant manager of industry) • Familiarisation of process/plant activities • First-hand observation and assessment of current level operation and practices • Conduct briefing/awareness session • Building up cooperation with all divisional heads and • Issue questionnaire for each department persons concerned (2–3 hrs) • Orientation, awareness creation Phase II – Audit Primary data gathering, process flow Historic data analysis; baseline data diagram and energy utility diagram collection Prepare process flowchart(s) All service utilities system diagram (Example: Single line power distribution diagram, water, compressed air and steam distribution.) Design, operating data and schedule of operation Annual energy bill and energy consumption pattern (refer to manuals, log sheets, equipment specification sheets, interviews) Conduct survey and monitoring Measurements: • Motor survey, insulation and lighting survey with portable instruments to collect more and accurate data. • Confirm and compare actual operating data with design data. Conduct detailed trials/experiments Trials/experiments: for biggest energy users/equipment • 24 hr power monitoring (MD, PF, kWh, etc.). • Load variation trends in pumps, fans, compressors, heaters, etc. • Boiler efficiency trials (4–8 hrs) • Furnace efficiency trials • Equipment performance experiments, etc. (Cont’d…)

44 Industrial energy conservation Step Action

Purpose

6

Analysis of energy use

7

Identification and development of energy conservation (ENCON) opportunities

8

Cost-benefit analysis

9

Reporting and presenting to top management Phase III – Post-audit Implementation and follow-up

Energy and material balance and energy loss/waste analysis Identification and consolidation of ENCON measures Conceive, develop and refine ideas Review ideas suggested by unit personnel Review ideas suggested by preliminary energy audit Use brainstorming and value analysis techniques Contact vendors for new/efficient technology Assess technical feasibility, economic viability and prioritisation of ENCON options for implementation Select the most promising projects Prioritise by low-, medium-, long-term measures Documentation, report presentation to top management Documentation, report presentation to top management

10

3.3.1

Assist and implement ENCON measures and monitor performance Action plan, schedule for implementation Follow-up and periodic review

Phase I–pre-audit activities

A structured methodology to carry out the energy audit is necessary for efficient implementation. An initial study of the site should always be carried out, as the planning of the audit procedures is of key importance. Initial site visit and preparation required for detailed auditing

An initial site visit may take one day and gives the energy auditor/manager an opportunity to meet the personnel concerned, to familiarise him or her with the site and to assess the procedures necessary to carry out the energy audit. During the initial site visit the energy auditor/manager should carry out the following actions: 1. Discuss with the site’s senior management the aims of the energy audit. 2. Discuss economic guidelines associated with the recommendations of the audit.

Energy audit 45

3. Analyse the major energy consumption data with relevant personnel. 4. Obtain site drawings where available–building layout, steam distribution, compressed air distribution, electricity distribution, etc. 5. Tour the site accompanied by engineering/production staff. Main aims of this visit are

1. To finalise energy audit team. 2. To identify the main energy-consuming areas/plant items to be surveyed during the audit. 3. To identify any existing instrumentation or additional metering that may be required. 4. To decide whether any meters will have to be installed prior to the audit, e.g., kWh, steam, oil or gas meters. 5. To identify the instrumentation required for carrying out the audit. 6. To plan the time frame. 7. To collect macro data on plant energy resources, major energy consuming centers. 8. To create awareness through meetings/programme.

3.3.2

Phase II–detailed energy audit activities

Depending on the nature and complexity of the site, a detailed energy audit can take from several weeks to several months to complete. Detailed studies to establish and investigate energy and material balances for specific plant departments or items of process equipment are carried out. Whenever possible, checks of plant operations are conducted over extended periods of time, at nights and at weekends as well as during normal daytime working hours, to ensure that nothing is overlooked. The audit report will include a description of energy inputs and product outputs by major departments or by major processing function and will evaluate the efficiency of each step of the manufacturing process. Means of improving these efficiencies will be listed and at least a preliminary assessment of the cost of the improvements will be made to indicate the expected payback on any capital investment needed. The audit report should conclude with specific recommendations for detailed engineering studies and feasibility analyses, which must then be performed to justify the implementation of those conservation measures that require additional capital investment. Information to be collected during the detailed audit includes: 1. Energy consumption by type of energy, by department, by major items of process equipment, by end-use.

46 Industrial energy conservation

2. Material balance data (raw materials, intermediate and final products, recycled materials, use of scrap or waste products, production of by-products for reuse in other industries, etc.). 3. Energy cost and tariff data. 4. Process and material flow diagrams. 5. Generation and distribution of site services (e.g., compressed air, steam). 6. Sources of energy supply (e.g., electricity off the grid or self-generation). 7. Potential for fuel substitution, process modifications and the use of cogeneration systems (combined heat and power generation). 8. Energy management procedures and energy awareness training programmes within the establishment. Existing baseline information and reports are useful to understand consumption patterns, production cost and productivity levels in terms of product per raw material inputs. For this the audit team should collect the following baseline data: 1. Technology, processes used and equipment details. 2. Capacity utilisation. 3. Amount and type of input materials used. 4. Water consumption. 5. Fuel consumption. 6. Electrical energy consumption. 7. Steam consumption. 8. Other inputs such as compressed air, cooling water, etc. 9. Quantity and type of wastes generated. 10. Percentage rejection/reprocessing. 11. Efficiencies/yield.

3.4

Data collection hints

It is important to plan additional data gathering carefully. Here are some basic tips to avoid wasting time and effort: 1. Measurement systems should be easy to use and provide information to the level of accuracy that is actually needed, not the accuracy that is technically possible. 2. Measurement equipment can be inexpensive (flow rates using a bucket and stopwatch). 3. The quality of the data must be such that correct conclusions are drawn (what the grade of product is in production, is the production normal, etc.)

Energy audit 47

4. Define how frequent data collection should be to account for process variations. 5. Measurement exercises over abnormal workload periods (i.e., startup and shutdown). 6. Design values can be taken where measurements are difficult (i.e., cooling water through a heat exchanger).

3.4.1

Process flow diagram to identify waste streams and energy wastage

An overview of unit operations, important process steps, areas of material and energy use and sources of waste generation should be gathered and should be represented in a flowchart as shown in Fig. 3.1. Existing drawings, records and a shop floor walk-through will help in making this flowchart. Penicillin-G fermentation Energy

Raw material

Steam, air, cooling water, chilled water

Germinator

Condensate Steam, air, cooling water, chilled water

Prefermentor

Condensate Steam, air, cooling water, chilled water

Seed inoculation Raw material

Raw material Steam leak

Fermentor

Raw material

Condensate Chilled brine

Compressed air, treated water, raw water

Non-filtered broth tank

Filter press

Mother liquor to extraction Steam, air, cooling water, chilled water, brine Extraction

Mycelium to ETP

Impurities with water to ETP

Waste stream

Waste stream

Condensate Penicillin-G

Figure 3.1: Process flow diagram for manufacturing penicillin-G.

Simultaneously the team should identify the various inputs and output streams at each process step. Example: A flowchart of a production line for penicillin is given in Fig. 3.1. Note that a waste stream (Mycelium) and obvious energy losses such as condensate drainage and steam leakages are identified in this flowchart. The

48 Industrial energy conservation

audit focus area depends on several issues such as consumption of input resources, energy efficiency potential, impact of specific process steps on the entire process, or intensity of waste generation/energy consumption. In the example, the process modularised operations such as germinator, prefermentor, fermentor and extraction are the major conservation potential areas identified.

3.4.2

Identification of energy conservation opportunities

Fuel substitution: Identifying alternative fuels for efficient energy conversion. Energy generation: Identifying efficiency opportunities in energy conversion equipment/utilities such as captive power generation, steam generation in boilers, thermic fluid heating, optimal loading of diesel generator sets, minimum excess air combustion with boilers/thermic fluid heating, optimising existing efficiencies, efficient energy conversion equipment, biomass gasifiers, cogeneration, high efficiency diesel generator sets, etc. Energy distribution: Identifying efficiency opportunities networks such as transformers, cables, switch gears and power factor improvement in electrical systems and chilled water, cooling water, hot water, compressed air, etc. Energy usage by processes: This is one of the major opportunities for improvement and many of them are hidden. Process analysis is a useful tool for process integration measures that can greatly improve energy efficiency.

3.4.3

Technical and economic feasibility

Technical feasibility assessment should address the following issues: 1. Technology availability, space, skilled manpower, reliability, service, etc. 2. The impact of energy efficiency measures on safety, quality, production, or process. 3. Maintenance requirements and availability of spare parts and components. Economic viability often becomes the key parameter for acceptance by top management. The economic analysis can be conducted by using a variety of methods. Examples include payback method, internal rate of return method, net present value method, etc. For low investment, short-duration measures, which have attractive economic viability, the simplest of the methods – payback is usually sufficient. A sample worksheet for assessing economic feasibility is provided below.

3.4.4

Sample worksheet for economic feasibility

Energy efficiency measure: 1. Investment equipment, civil works, instrumentation, auxiliaries. 2. Annual operating cost, cost of capital maintenance, manpower, energy, depreciation.

Energy audit 49

3. Annual savings thermal energy, electrical energy, raw material, waste disposal. Net savings/Year = (Annual savings minus annual operating costs). Payback period in months = (Investment/net savings/year)/12.

3.4.5

Classification of energy conservation measures

Based on the energy audit and analysis of the plant, a number of potential energy saving projects may be identified. These may be classified into three categories: (i) low cost-high return, (ii) medium cost-medium return and (iii) high cost-high return. Normally the low cost-high return projects receive priority. Other projects have to be analysed, engineered and budgeted for implementation in a phased manner. Projects relating to energy cascading and process changes almost always involve high costs coupled with high returns and may require careful scrutiny before funds can be committed. These projects are generally complex and may require long lead times before they can be implemented. To sum up energy auditing procedures are different for different industries. Given below are the brief outline auditing procedures adopted for the following industries. 1. Electrical system network: This would include detailed study of all the transformer operations of various ratings/capacities, their operational pattern, loading, no load losses, power factor measurement on the main power distribution boards and scope for improvement if any. The study would also cover possible improvements in energy metering systems for better control and monitoring. 2. Study of motors and pumps loading: Study of motors (above 10 kW) in terms of measurement of voltage (V), current (I), power (kW) and power factor and thereby suggesting measures for energy saving like reduction in size of motors or installation of energy saving device in the existing motors. Study of pumps and their flow, thereby suggesting measures for energy saving like reduction in size of motors and pumps or installation of energy saving device in the existing motors/optimisation of pumps. 3. Study of air conditioning plant: With respect to measurement of specific energy consumption, i.e., kW/TR of refrigeration, study of refrigerant compressors, chilling units, etc. Further, various measures would be suggested to improve its performance. 4. Cooling tower: This would include detailed study of the operational performance of the cooling towers through measurements of temperature differential, air/water flow rate, to enable evaluate specific performance parameters like approach, effectiveness, etc.

50 Industrial energy conservation

5. Performance evaluation of boilers: This includes detailed study of boiler efficiency, thermal insulation survey and flue gas analysis. 6. Performance evaluation of turbines: This includes detailed study of turbine efficiency, waste heat recovery. 7. Performance evaluation of air compressor: This includes detailed study of air compressor system for finding its performance and specific energy consumption. 8. Evaluation of condenser performance: This includes detailed study of condenser performance and opportunities for waste heat recovery. 9. Performance evaluation of burners/furnace: This includes detailed study on performance of furnace/burner, thermal insulation survey for finding its efficiency. 10. Windows/split air conditioners: Performance shall be evaluated as regards, their input power vis-a-vis TR capacity and performance will be compared to improve to the best in the category. 11. DG set: Study the operations of DG sets to evaluate their average cost of power generation, specific energy generation and subsequently identify areas wherein energy savings could be achieved after analysing the operational practices, etc., of the DG sets. The entire recommendations would be backed up with techno-economic calculations including the estimated investments required for implementation of the suggested measures and simple payback period. Measurement would be made using appropriate instrumentation support for time lapse and continuous recording of the operational parameters.

3.5 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Tips for energy audit Submit preliminary questionnaire (Ref. section 3.5.1 and 3.5.2). Process responses from questionnaire. Obtain fuel and elementary bills. Analyse fuel and electricity. Conduct boiler house survey and efficiency measurement. Investigate energy distribution system. Perform internal site survey. Construct energy input side of the audit. Obtain local climate data. Perform external site survey. Quantify sundry gains. Construct output side of the audit.

Energy audit 51

13. Construct the energy audit balance sheet. 14. Investigate any residual and iterate to balance the audit. 15. Analyse throughputs.

3.5.1

Energy audit preliminary questionnaire

1. Name of firm nature of business status (commercial, industrial or public sector). 2. Address of premises to be surveyed. 3. Telephone no. 4. Email. 5. Name of the contact person. 6. Position. 7. Location. 8. Number of employee. 9. Hours of work. 10. Details of shift working. 11. Weekdays. 12. Weekends. 13. Annual shutdown. 14. Required inside temperatures. 15. Required ventilation rates (if known). 16. Working area (if known). 17. Heated volume (if known). 18. Annual energy bill.

3.5.2 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Secondary questionnaire – the client interview

Energy management practices Summary of initial recommendations. Energy management procedures. Financial practices. Comments on energy consumption. Monitoring and recording practices. Personnel energy awareness. Current energy conservation measures. Comments on energy inefficiencies. Conditions of buildings, plant and equipment.

52 Industrial energy conservation

11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27.

Furnaces. Boilers. Boiler house auxiliaries. Heat distribution systems. Major items. Energy storage systems. Process plant. Space heating services. Lighting systems. Power and electrical services. Mechanical ventilation. Air conditioning systems. Domestic hot water systems. Compressed air services. Refrigeration plant. Chilled water distribution systems. Steam plant.

Challenges and prospects in energy management

To establish a coherent link between: 1. Energy and economy. 2. Energy and environment. 3. Energy and society. To utilise the emerging technologies

1. Super conductivity. 2. Fuel cells. 3. Renewable energy. 4. Co-generation and tri-generation. 5. Cold-fusion. To sum up, the energy audit is a balance sheet of energy inputs, throughputs and outputs. Its fundamental equation is as follows: Fuel energy input = Energy losses during combustion 1. 2. 3. 4.

Energy losses during conversion. Energy losses during distribution. Energy losses during utilisation. Energy losses from utilisation.

4 Efficient steam distribution system

4.1

Introduction

The function of the steam distribution system is to get the steam to where it is needed and return the condensate to the boiler, doing both as efficiently as possible. Distribution heat losses account for 3 to 10% of the total energy generated in a boiler system. Energy management can reduce the heat loss by improving the insulation, detecting and repairing steam and condensate leaks, maintaining the steam traps and condensate pumps and providing water treatment. A well designed steam distribution network can improve the efficiency of the steam systems. For optimum performance of the distribution and steam enduse equipment, a supply of right quantity and quality of steam is of vital importance. The losses in the steam distribution system can be in the form of: 1. Radiation and convection. 2. Pressure losses in the distribution pipe lines. 3. Steam leaks in joints, valves, gauges, etc. 4. Steam losses due to improper selection, incorrect location, wrong positioning and malfunctioning of traps. 5. Inappropriate location and capacity of air vents. 6. Poor dryness fraction of steam. Steam losses due to external leakages can easily be identified. Such leakages can be plugged using online sealing techniques. The valves in the bypass around the steam traps as well as malfunctioning steam traps are the prime sources of internal leakages. These are difficult to detect as they are hidden and invisible in the flash steam. It is, therefore essential to improve the steam distribution system. Following are some important aspects to be taken care of: 1. Properly select, size and maintain the distribution system steam traps. 2. Insulate all distribution system pipes, flanges and valves. 3. Ensure that steam mains are properly laid out, sized, adequately drained and adequately air vented. 4. Ensure that distribution system piping is correctly sized to maintain appropriate system pressure drops.

54 Industrial energy conservation

5. Ensure that distribution system piping is adequately supported, guided and anchored; and that appropriate allowances are made for pipe expansion at operating temperatures. A practical steam distribution system should necessarily compromise between the above ideal conditions and several other factors. Lack of attention to these will significantly increase operating costs, either because of reduction in overall efficiency or increase in maintenance costs or both.

4.2

Energy conservation

4.2.1

Steam piping layout

Steam piping transports steam from the boiler to the end-use services. Important characteristics of a well-designed steam system piping are that it is adequately sized, configured and supported. Installations of larger pipe diameters could be more expensive, but can reduce the pressure drop for a given flow rate and also help to reduce the noise associated with steam flow. Hence, one consideration should be given to the type of environment in which the steam piping will be located when selecting the pipe diameter. Important configuration issues are flexibility and drainage. Piping, especially at equipment connections, needs to accommodate thermal reactions during systems start-ups and shutdowns. Piping should be equipped with a sufficient number of appropriately sized drip legs to promote effective condensate drainage and should be pitched properly to promote the drainage of condensate to these drip lines. Typically, these drainage points experience two very different operating conditions, viz. normal operation and start-up. Both load conditions should be considered in the initial design. Mechanical type moisture separators with traps should be provided in piping at interval, to separate the fine moisture particles in the steam. Automatic air vents should be fixed at the dead end of steam mains to allow removal of air/ non-condensable which tends to accumulate in steam space.

4.2.2

Steam pipe sizing and redundancy

Proper sizing of the steam pipelines involves selecting a pipe diameter which gives acceptable pressure drop between the boiler and the user. Pipe sizing can be done either based on the velocity or on the desired pressure-drop. Pipe sizing can be done from the general recommendations on line velocities of different fluid based on the specific volume of steam for the chosen distribution pressure and quality of steam, whether wet or superheated. The velocities for various types of steams are: 1. Superheated 50–70 m/sec.

Efficient steam distribution system 55

2. Saturated 30–40 m/sec. 3. Wet or exhaust 20–30 m/sec. Unused steam piping experiences the same losses as the rest of the system. It is therefore imperative to isolate the unused steam lines immediately. Pipe routing is made for transmission of steam in the shortest possible way, so as to reduce the pressure drop in the system.

4.2.3

Steam pressure

The steam distribution pressure should be adjusted in accordance with the pressure generated and the pressure required at the consumer side. If steam piping already exists then the pressure should be adjusted for lower operating cost. However, at the designing stage, it is desirable to consider steam distribution at the same pressure at the source, or at a moderately high intermediate pressure; if the generation is at very high pressure. Distribution of the steam at the same pressure that of source has the following advantages: 1. The steam velocity along within the pipes will be lowered and this reduces both noise and erosion. 2. It provides stable pressure at the user end due to lower pressure drop and higher operating margins. 3. The capital cost is reduced as the pipe line is so smaller in size. Nonetheless, for long distribution systems, it is economical to super-heat the steam to minimise the steam losses. The piping needs to be properly sized and well insulated. Estimating pressure requirements for small distribution systems is relatively simple; viz., it should just meet the minimum user requirement, unless future expansion of the system or new equipment requiring higher pressures is envisaged. For systems where only a small quantity of high pressure steam is actually required, but where large quantities of low pressure steam are used, the possibility of separating the two should be considered.

4.2.4

Insulation in steam distribution

Heat losses through the surface of the steam distribution pipes can significantly increase energy use and cost. Good engineering design of insulation system will reduce undesirable heat loss and will often improve environmental condition. Poorly insulated/uninsulated steam distribution and condensate return lines are a constant source of wasted energy. A good and proper insulation can typically reduce energy losses by 90% and help to ensure proper steam quality and pressure at plant equipment. It would also reduce leakages and other issues due to erosions or water hammering due to excessive condensate in steam.

56 Industrial energy conservation

Table 4.1 illustrates steam line losses for non-insulated pipes of different diameters. Table 4.2 gives different types of material used for insulation. Table 4.1: Steam line losses for non-insulated pipes of different diameters. Pipe diameter (NB)

25 50 100 200 300

Heat loss (kCal/hr for 100 M Bare pipe) Steam pressure (kg/cm2g) 1.0

10.0

20.0

40.0

13210 22174 39158 69824 99546

26892 45291 80203 98130 207584

35384 59444 105679 191543 274576

46706 79259 141534 257121 369876

Table 4.2: Different types of material used for insulation. Material

Density (kg/m3)

Thermal conductivities (W/m°C) 0°C

Polystyrol Cork Glass wool (non fibre) Long fibre Short fibre Rockwool and glass wool Asbestos

4.2.5

100°C

20–50 100–200 40–60

0.032 0.032 0.031

0.050

80 100 40–250

0.031 0.036 0.028

0.048 0.051 0.039

80–250

0.042

200°C

300°C

Maximum temperature (°C) 70 80 200

0.073 0.051

0.110 0.102

500 700 800 600

Economical insulation thickness

As the thickness of the insulation increases, the cost of material and installation also goes up. The cost of lost energy, on the other hand, goes down upto a certain thickness. Above this thickness, the gains due to drop in the surface temperature are compensated with increase in the surface area of the insulation. In other words, the energy saving also goes up, but at a slower rate of increase than the cost of the materials and installation. At a particular point, the total cost, which is the sum of the lost energy and the material cost, reaches a minimum point; which is the economic thickness of insulation. Figure 4.1 illustrates the method of determining the insulation thickness.

Efficient steam distribution system 57

Cost/year Total cost

Minimum cost

Insulating cost

Lost heat cost Economic thickness

Figure 4.1: Method of determining insulation thickness.

The recommended insulation thickness for mineral wool which is commonly used in various industries is given in Table 4.3. Table 4.3: Recommended insulation for mineral wool. Temperature of process fluid (°C) Up to 90 91–150 151–250 251–350 351–450 451–550 551–650

Upto 40 25 40 65 75 90 90 90

Diameter of pipe (NB) 50–80 90–125 25 40 65 75 90 100 100

25 50 75 100 100 115 115

150–200

Flat surface/ above 200 NB

40 50 75 100 115 125 130

40 65 90 100 125 140 150

Major factors determining insulation selection are: 1. Operating temperature. 2. Thermal conductivity of the insulating material. 3. Resistance to heat, weather and adverse atmospheric conditions. 4. Ability to withstand vibration, noise and mechanical damage. 5. Resistance to chemicals/environment. 6. Resistance to fire. 7. Extent of shrinking or creaking during use. 8. Jacking for insulation.

58 Industrial energy conservation

4.2.6

Steam traps and strainers

As steam moves throughout the system, it looses a small part of heat through surfaces, due to condensation. The condensate, travelling at over 200 km/hr may erode the pipe lines (especially at bends/partially open valves) and even lead to water hammering and can damage equipment; if not removed effectively. Steam traps are automatic valves that separate condensate from the steam. A leaky trap wastes energy by allowing steam to enter the condensate return. A malfunctioning trap may not expel the condensate from the steam line, thus reducing efficiency of the system. Steam traps are classified into three main groups–mechanical, thermostatic and thermodynamic, with several different types of traps in each group. It is essential to understand the operations and functions of the traps and carefully read the instructions, since the traps operate in different ways and sizes, as positioning and installation procedures vary.

4.2.7

Selection of steam traps

Selection of an appropriate trap should be made based on the capacity curve of the trap, which varies with every manufacture. Due care must be taken to understand loading, normal as well start up and differential pressure across the trap, type of applications, possibility of non-condensable in condensate, of the capacity curve.

4.2.8

Steam trap leakage

Leakage in the steam traps allows the steam to blow into the condensate system which is then vented to the atmosphere. A regular inspection must be carried out for steam traps and valves and leaks should be attended to immediately. To emphasise on controlling leakages from the steams traps and orifices, the losses at different sizes and their pressure are shown in Table 4.4. Table 4.4: Losses at different sizes and their pressure. Steam pressure Kg/cm2 3.5

5.5

15

Orifice size inch

Steam losses kg/hr

1/8 1/4 1/2 1//8 1/4 1/2 1/8 1/4 1/2

18 72 290 26 100 400 60 240 960 (Cont’d…)

Efficient steam distribution system 59 Steam pressure Kg/cm2 42

4.2.9

Orifice size inch

Steam losses kg/hr

1/8 1/4 1/2

150 600 2400

Strainers

Performance of steam traps decreases due to dirt and scale accumulation. To eliminate this problem it is essential to install pipe-line strainer. Strainers are fitted before the traps, if the traps do not have built-in trap strainer. It is advisable to check the strainers at regular intervals.

4.2.10

Water hammer

One of the most common complaints is that a system sometimes develops a hammer-like noise commonly referred to as water hammer. Water hammer in steam lines is normally caused by the accumulation of condensate. It may indicate a condition which could produce serious consequences including damaged vents, traps, regulators and piping. Two types of water hammer can occur in steam systems: 1. The first type is usually caused by the accumulation of condensate (water) trapped in a portion of horizontal steam piping. The velocity of the steam flowing over the condensate causes ripples in the water. Turbulence builds up until the water forms a solid mass, or slug, filling the pipe. This slug of condensate can travel at the speed of the steam and will strike the first elbow in its path with a force comparable to a hammer blow. In fact, the force can be great enough to break the back of the elbow. 2. The second type of water hammer is actually cavitation. This is caused by a steam bubble forming or being pushed into a pipe completely filled with water. As the trapped steam bubble looses its latent heat, the bubble collapses, the wall of water comes back together and the force created can be severe. This condition can crush float balls and destroy thermostatic elements in steam traps. Cavitation is the type of water hammer that usually occurs in condensate return lines or pump discharge piping. Precautions to prevent water hammer in steam lines are: 1. Steam pipes must be pitched away from the boiler towards a drip trap station. Drip trap stations must be installed ahead of any risers, at the end of the main and every 100 to 150 m along the steam piping. 2. Drip traps must be installed ahead of all steam regulator valves to prevent the accumulation of condensate when the valve is in a closed position.

60 Industrial energy conservation

3. ‘Y’ strainers installed in steam lines should have screen and dirt pocket mounted horizontally to prevent condensate from being collected in the screen area and being carried along in slugs when steam flow occurs. 4. All equipment using a modulation regulator on the steam supply must provide gravity condensate drainage from the steam traps. Lifts in the return line must be avoided. Another type of loss observed in steam traps, occurs when hot or pressurised condensate passes through the traps and the water flashes off a certain percentage of the steam due to instant pressure change. This is called ‘Flash steam loss’. In this case it is recommended to use pressurised condensate recovery system and/or flash steam recovery system for complete recovery of thermal energy.

4.2.11

Steam quality

The quality of steam also determines the performance of steam distribution system. Good quality steam means dry moisture-free steam, free from air, carbon dioxide and other non-condensable matter.

4.2.12

Moisture in steam

Saturated steam generated in packaged boiler contains 2 to 5% moisture; while steam from coil type non-IBR boilers could have 10 to 60% moisture. Superheated steam on the other hand does not contain any moisture. However, some moisture is picked up while de-superheating the steam. The steam also gives away latent heat and becomes wet, while being transported through distribution system. The wet steam contains particles of water droplet which have not evaporated. These droplets do not contribute to heat transfer and it is essential to remove it from the steam. A moisture separator at the entrance of the equipment separates the droplets and drains them through traps. The wetness can also be reduced by resorting to pressure reduction of steam prior to its use.

4.2.13

Non-condensable in steam

Dissolve oxygen in the boiler feed water, if not removed properly, gets carried away with the steam. The bicarbonate salts in the feed water generate carbon dioxide which is also transported with the steam. The problems associated with non-condensable can be summed up as under. 1. Reduction in the heat transfer area to the extent of space occupied. 2. Drop in heat transfer rate due to reduction in effective steam temperature (based on the partial pressure of the steam in the steam air mixture). 3. Additional resistance to heat transfer due to formation of barrier layer.

Efficient steam distribution system 61

It is therefore very important to remove the non-condensables through air vents provided at proper location and also installing appropriate type of steam trap.

4.2.14

Salient points in steam generation

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

Replace damaged/wet insulation. Avoid steam leakages. Provide dry steam for process. Utilising steam at lower acceptable pressure for the process. Ensure proper utilisation of directly inject steam. Minimise heat transfer. Use condensate recovery system. Insulate all steam pipelines and hot process equipment. Recover flash steam. Maintain at least 125 mm per meter of falling slope for steam piping. Provide drain points at lower points in the main and where the steam main rises. 12. Drain points in the main lines should be through an equal tee connection only. 13. The branch lines from the mains should always be connected at the top. 14. Insure supports as well as an alternation in level can lead to formation of water pockets in steam, leading to wet steam delivery. Thus, steam is common and convenient mode to convey energy and is used in almost all major industrial processes. Steam economy greatly depends on delivering the steams through properly designed steam distribution lines. It is essential to adopt all possible measures including new technologies to optimise the steam distribution costs.

4.3

Improving efficiency of steam systems

Steam is the most popular heat transfer medium for process industry. However, the inefficiencies inbuilt in the design and operation of steam systems, offer great scope for energy saving. Fundamentally it involves reducing losses and recovering as much heat as possible. 1. Steam is generated by evaporation of water. 2. The process involves high heat absorption-hence plant sizes and costs are not impracticably large. Water itself is by far the most common liquid on earth and therefore plentiful and cheap. It is also chemically stable and non-hazardous to health.

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3. Steam supplies heat to any process by condensing at a constant temperature and with high heat transfer coefficients. This constant condensing temperature eliminates any temperature gradient over the heat transfer surfaces. 4. Steam does not need any circulating pump to carry it to the usage points. Steam pressure has a direct relation to its temperature. All of the above ensure that steam is the most popular heat transfer medium for process industry. However, the flexibility offered by the steam system often results in large inefficiencies inbuilt in the design and operation. That is why most process industries offer great scope for fuel savings in steam systems. In order to identify this scope lets take a look at the energy balance of a very simple steam system, having one boiler, a short distribution network and a single indirectly heated consuming point Fig. 4.2.

80% steam (Considering oil fired much lesser for solid fuel fired boilers)

77%

Process consumtion 57%

100% Energy fuel

(Losses stock, radiation blowdown, etc.)

15–20% Condensate and flash steam

Figure 4.2: Energy balance of simple steam system.

As seen in the diagram, only about 60% of the fuel energy burnt in the boiler is actually useful for the heat transfer in process. This is what makes a good steam and condensate system design. Following practices are mandatory for optimising fuel consumption. By designing a proper system, one can ensure: 1. Reducing the possibility of actual losses-by achieving better combustion efficiency in boiler, insulating distribution network, plugging leaks, keeping by-passes closed, etc.

Efficient steam distribution system 63

2. Recovering as much heat as possible - from boiler stack, condensate and flash steam, etc. Proper specification for quality of steam for process heating determines the actual demand and hence affects the mass balance directly. This section focuses only on steam generation which is the heart of the steam and condensate loop.

4.3.1

Optimising steam generation

This is a case study for furnace oil fired boilers based on a survey involving a sample size of 30 process plants for furnace oil fired boilers: Efficiency % Best Average Worst Direct 82 70 60 Indirect 84 80 75

4.3.2

Understanding boiler efficiency Direct efficiency = =

4.3.3

Output steam energy Input fuel energy Steam generation (kg/hr) × (Hs – Hw) Fuel consumption (kg/hr) × GCV of fuel

Boiler efficiency

Thus, direct efficiency translates into S:F ratio and determines the fuel consumption for a given loading (Fig. 4.3) on the boiler, steam pressure and feed water temperature. SF variation against load

16.00 15.00 14.00

SF ratio

13.00 12.00 11.00 10.00 9.00 8.00 7.00 100

90

80

70

60 50 % Load

40

Figure 4.3: SF ratio v/s load.

30

20

10

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Direct efficiency is averaged normally over a period of time, batch, day, month, etc. Indirect efficiency - as per BS-845, boiler efficiency is calculated by deducting losses. = 100 – (sum of all losses in %) where some of the losses are: 1. Loss due to sensible heat in dry flue gas (stack loss). 2. Loss due to enthalpy in the water vapour in the flue gases (enthalpy loss). 3. Radiator loss. 4. Unburnt fuel losses. Thus, indirect efficiency directly translates into corrective actions required to be taken. Normally, indirect efficiency is measured during a spot check and not averaged over a period of time and hence may give misleading results. Difference between direct and indirect efficiency is given Table 4.5. Table 4.5: Difference between direct and indirect efficiency. Direct efficiency

Indirect efficiency

Being a ratio, it is normally calculated over a period of time.

Can be calculated after capturing combustion parameters during a spot check. Practically computed by measuring actual Computed by measuring combustion flow of fuel to the boiler and steam generated parameters like stack temperature, excess from the boiler for a period of time. air (O2 % in stack), CO2, CO, etc., during a spot check. Takes into account issues related to Is an indication of combustion properties house-keeping, like oil spillage, handling and hence helps in better tuning of the losses, start-stop losses which spot checks burner, dampers, etc., to achieve better of indirect efficiency. performance.

Some of the reasons why direct efficiency was found to be lower than indirect in the sample survey are: 1. As mentioned above, direct efficiency establishes the performance over a period of time as against spot checks of indirect efficiency. It takes into account actual measurements of input and output to the boiler for a specified time period. Thus, partially the difference is accounted for, as indirect efficiency parameters are not maintained uniformly over a period of time. 2. The biggest contributor for loss of direct efficiency was observed to be: (a) The boiler loading and its turndown. Many of the boilers were observed to be grossly oversized and showed poor results when operated at partial or low loads.

Efficient steam distribution system 65

3. Another reason for poor direct efficiency was attributed to start/stop losses, i.e., the frequent tripping of burner due to pressure being achieved. 4. Lastly, losses due to blow down, oil leakages from burner assembly, steam leakage or venting (safety valve) from the boiler, etc., are all considered while computing direct efficiency-but not while computing indirect efficiency.

4.3.4

Corrective actions

1. The first step is proper diagnostics - online monitoring of the boiler efficiency - direct as well as indirect. 2. Proper selection and tuning of the burner. 3. Derating of the boiler, if oversized (only radiation losses cannot be prevented and will continue to be higher). 4. Proper pressure switch setting to prevent frequent on/off and safety valve venting or manually setting the burner on low fire instead of auto modulation. 5. Better housekeeping to avoid leakages and losses. Benefits and savings

If direct efficiency improves from 70% on an average to 82% which is the best, fuel consumption will reduce by 17% - other parameters like feed, water, temperature, etc., remaining same.

4.3.5

Waste heat recovery

Once all of the above factors are taken care of and operating parameters well established and under control, one should worry about: 1. Complete condensate and flash steam recovery. In a typical system this itself can reduce fuel consumption further by 10–15%. 2. Waste heat recovery from exhaust flue gases by way of economisers (water pre-heaters) or air pre-heaters which can further reduce fuel consumption by 3–5%. Apart from generation and condensate/flash steam recovery, equal opportunity exists in optimising steam consumption in process equipment and distribution network, which is more dependent on the type of industry and process. Unique packages have been designed to provide online energy/mass balance on steam and condensate loop, for various industries.

5 Energy efficiency in boilers

5.1

Introduction

A boiler is an enclosed pressure vessel that provides means for combustion heat to be transferred into water until it becomes steam. The steam under pressure is then usable for providing heat for an industrial process. When water is boiled into steam, its volume increases about 1600 times, producing a force that is almost as explosive as gunpowder. This makes a boiler an extremely dangerous piece of equipment that must be treated with utmost care. A boiler system comprises three parts: 1. A feed water system. 2. A steam system. 3. A fuel system. The feed water system provides water to the boiler and regulates it automatically to meet the steam demand. Various valves provide access for maintenance and repair. The steam system collects and controls the steam produced in the boiler. Steam is directed through a piping system to the point of use. Throughout the system, steam pressure is regulated using valves and checked with steam pressure gauges. The fuel system includes all the equipment used to provide fuel to generate the necessary heat. The equipment required in the fuel system depends on the type of fuel used by the system.

5.2

Heating surfaces in a boiler

The amount of heating surface of a boiler is expressed in square meters. Any part of the boiler metal that actually contributes to making steam is a heating surface. The larger the heating surface a boiler has, the higher will be its capacity to raise steam. Heating surfaces can be classified into several types: 1. Radiant heating surfaces (direct or primary) include all water-backed surfaces that are directly exposed to the radiant heat of the combustion flame. 2. Convection heating surfaces (indirect or secondary) include all those water-backed surfaces exposed only to hot combustion gases. 3. Extended heating surfaces include economisers and super heaters used in certain types of water tube boilers.

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5.3

Classification of boilers

Broadly, boilers can be classified into four types: fire tube boilers, water tube boilers, packaged boilers and fluidised bed combustion boilers.

5.3.1

Fire tube boilers

Fire tube boilers contain long steel tubes through which the hot gases from a furnace pass and around which the water to be converted to steam circulates. It is used for small steam capacities (up to 12000 kg/hr and 17.5 kg/cm2). The advantages of fire tube boilers include their low capital cost and fuel efficiency (over 80%). They are easy to operate, accept wide load fluctuations and because they can handle large volumes of water, produce less variation in steam pressure. Flow diagram of fire tube boiler is shown in Fig. 5.1. Steam outlet Boiler

Hot gas outlet

Fire tube

Hot gas

Brick work

Furnace

Figure 5.1: Fire tube boilers.

5.3.2

Water tube boilers

In water tube boilers, water passes through the tubes and the hot gasses pass outside the tubes. These boilers can be of single- or multiple-drum type. They can be built to handle larger steam capacities and higher pressures and have higher efficiencies than fire tube boilers. They are found in power plants whose steam capacities range from 4.5–120 T/hr and are characterised by high capital cost. These boilers are used when high pressure high-capacity steam production is demanded. They require more controls and very stringent water quality standards. Flow diagram of water tube boiler is shown in Fig. 5.2.

Energy efficiency in boilers 69

Feedwater Economiser Superheater

Superheated steam outlet Steam and water drum Evaporator Circulation pump Heat from gas turbine exhaust

Figure 5.2: Water tube boilers.

5.3.3

Packaged boilers

The packaged boiler is so called because it comes as a complete package. Once delivered to a site, it requires only steam, water pipe work, fuel supply and electrical connections in order to become operational. Package boilers are generally of shell type with fire tube design so as to achieve high heat transfer rates by both radiation and convection. These boilers are classified based on the number of passes (the number of times the hot combustion gases pass through the boiler). The combustion chamber is taken as the first pass, after which there may be one, two, or three sets of fire tubes. The most common boiler of this class is a three-pass unit with two sets of fire tubes and with the exhaust gases exiting through the rear of the boiler.

5.3.4

Fluidised bed combustion (FBC) boilers

In fluidised bed boilers, fuel burning takes place on a floating (fluidised) bed in suspension. When an evenly distributed air or gas is passed upward through a finely divided bed of solid particles such as sand supported on a fine mesh, the particles are undisturbed at low velocity. As air velocity is gradually increased, a stage is reached when the individual particles are suspended in the air stream. A further increase in velocity gives rise to bubble formation, vigorous turbulence and rapid mixing and the bed is said to be fluidised. Fluidised bed boilers offer advantages of lower emissions, good efficiency and adaptability for use of low calorific-value fuels like biomass, municipal waste, etc.

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5.4

Performance evaluation of boilers

The performance of a boiler, which include thermal efficiency and evaporation ratio (or steam to fuel ratio), deteriorates over time for reasons that include poor combustion, fouling of heat transfer area and inadequacies in operation and maintenance. Even for a new boiler, deteriorating fuel quality and water quality can result in poor boiler performance. Boiler efficiency tests help us to calculate deviations of boiler efficiency from the design value and identify areas for improvement.

5.4.1

Thermal efficiency

Thermal efficiency of a boiler is defined as the percentage of heat input that is effectively utilised to generate steam. There are two methods of assessing boiler efficiency: direct and indirect. In the direct method, the ratio of heat output (heat gain by water to become steam) to heat input (energy content of fuel) is calculated. In the indirect method, all the heat losses of a boiler are measured and its efficiency computed by subtracting the losses from the maximum of 100.

5.4.2

Evaporation ratio

Evaporation ratio, or steam to fuel ratio, is another simple, conventional parameter to track performance of boilers on-day-to-day basis. For small capacity boilers, direct method can be attempted, but it is preferable to conduct indirect efficiency evaluation, since an indirect method permits assessment of all losses and can be a tool for loss minimisation. In the direct method, steam quality measurement poses uncertainties. Standards can be referred to for computations and methodology of evaluation. Example of direct efficiency calculation: Calculate the efficiency of the boiler from the following data: Type of boiler : Coal-fired Quantity of steam (dry) generated : 8 TPH Steam pressure (gauge)/temp : 10 kg/cm2 (g)/180°C Quantity of coal consumed : 1.8 TPH Feed water temperature : 85°C GCV of coal : 3200 kcal/kg : 665 kcal/kg (saturated) Enthalpy of steam at 10 kg/cm2 (g) pressure Enthalpy of inlet fed water

:

85 kcal/kg

Energy efficiency in boilers 71

Bioler efficiency (η) =

8 TPH × 1000 kg × (665 – 85) × 100 1.8 TPH × 1000 kg × 3200

= 80.0 % Evaporation ratio

5.5

= 8 TPH of steam/1.8 TPH of coal = 4.4

Boiler water treatment

Boiler water treatment is an important area for attention since water quality has a major influence on the efficiency of a boiler as well as on its safe operation. The higher the pressure rating, the more stringent the water quality requirements become. Boiler water quality is continuously monitored for buildup of total dissolved solids (TDS) and hardness and blow down is carried out (involving heat loss) to limit the same. Boiler water treatment methods are dependent upon quality limits specified for TDS and hardness by the manufacturers, the operating pressure of the boiler, the extent of make-up water used and the quality of raw water at the site. For small-capacity and low-pressure boilers, water treatment is carried out by adding chemicals to the boiler to prevent the formation of scale and by converting the scale-forming compounds to free-flowing sludge, which can be removed by blow down. Limitations: Treatment is applicable to boilers where feed water is low in hardness salts, where low pressure–high TDS content in boiler water is tolerated and where only small quantities of water need to be treated. If these conditions are not met, then high rates of blow down are required to dispose of the sludge and treatment become uneconomical based on heat and water loss considerations. Chemicals used: Sodium carbonate, sodium aluminate, sodium phosphate, sodium sulphite and compounds of vegetable or inorganic origin are used for treatment. Internal treatment alone is not recommended.

5.5.1

Parameters for selection of boilers

Steam boiler is a very important equipment for all process industries. There are many codes in use for design of boilers internationally. All these codes mainly take care of safety aspects of boilers from angle of mechanical strength. Some codes stipulate norms for furnace sizing on thermal input basis. Many users who have limited knowledge of boilers tend to believe that any two boilers designed as per same design code are technically at par. This is far from the truth. In today’s modern world, mechanical strength is only one of the many criteria, which decides the superiority of any boiler. There are many other more important aspects like efficiency, availability round the clock, ease

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in maintenance, environmental compliance, etc. This section provides guidelines for any boiler user to evaluate various brands of boilers and quantify the strengths/weaknesses. The evaluation criteria and its importance are explained in brief as under.

5.5.2

Safety and reliability of boilers

Apart from mechanical strength, it is the control logic and instrumentation, which decides safety and reliability of any modern boiler. Some of the important aspects are discussed below. Number of boiler water level controllers

Keeping proper water level in the boiler is of paramount importance from boiler safety point of view. This instrument not only maintains necessary operating water level by controlling the water inflow, but also ensures burner stoppage in case of the level falling below safe limit. It is advisable to have two instruments considering the criticality of the function. Number of fusible plugs

Fusible plug avoids dry running of a boiler by sparging high-pressure water in the furnace when water level goes below the topmost area of radiation heat transfer zone. This is the ultimate safety device, which can save furnace from collapse and rupture due to dry running. It generally consists of three parts where the innermost and outermost parts are held together with ‘low melting point alloy metal’. In case of dry running, this part melts creating an opening through which water in the boiler can enter the furnace extinguishing flame. It is advisable to have two fusible plugs. Tube overheat controller

This works as an overriding control in case the water level controller does not function and the burner keeps operating inspite of very low water level. It senses the temperature of flue in the topmost row of tube. When the level drops down, this row gets exposed and flue gas temperature in these tubes rises much higher than the bulk temperature in such eventuality, this controller sounds an alarm and can also stop the burner depending on the logic. High stack alarm controller

The stack temperature is an indicator of fouling of heat transfer surfaces in the boiler from flue and waterside. This not only results into higher fuel consumption but also overheating of tubes and furnace (in case of waterside fouling). This instrument sounds an alarm in such conditions, cautioning the operator to clean the surfaces.

Energy efficiency in boilers 73

Sinking time calculation

Sinking time is the time required to lower the water level in the boiler from normal working level to the furnace crown when the feed water pump fails and burner keeps firing at high flame due to failure of all safety devices. The furnace is subjected to very high temperature flame and hence is the most critical component of boiler. In case of dry running the furnaces become the first failure points. Boilers with bottom furnace type design have much higher sinking time than those having furnaces on one side. This gives more time for corrective action in a crisis, thereby avoiding damage to the furnace and possibility of an accident. Fuel pressure monitoring system

Most of modern oil fired boilers use pressure jet burners. It is necessary to maintain fuel pressure above the minimum desired limit to ensure atomisation of fuel and complete combustion. Fuel pressure sensing system should be provided for tripping the burner in case the fuel pressure falls below the safe limit. Fuel temperature monitoring system

For heavy oil fired boilers, the fuel needs to be heated to reduce viscosity and improve atomisation. Low fuel temperature can result in incomplete combustion, unstable flame and backfiring. Fuel temperature monitoring system should stop the burner firing below safe temperature. Combustion air pressure monitoring system

This will ensure availability of air for combustion. Unavailability/shortage of air results in similar situations mentioned above. The burner should trip automatically in case air is not sufficiently available. Steam pressure modulation

Steam pressure tends to change due to fluctuations in demand from plant. Immediate correction in fuel firing rate is necessary to maintain steady fuel pressure. Stepless or continuous modulation adjusts the fuel input constantly by checking steam pressure feedback. High-low or step modulation adjusts the fuel in stages. Stepless modulation can maintain steam pressure on the boiler within a tolerance of 0.1–0.2 kg/cm2. With step or high-low type of modulation, you can expect variation of 1.0 to 1.5 kg/cm2. Above is subject to steam demand being lower than boiler capacity at any given time. Steam pressure limit switch

If the steam demand drops to a very low level, the steam pressure rises inspite of burner firing at minimum possible level. Steam pressure limit switch cuts

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off the burner and eliminates possibility of safety valve popping up, saving precious fuel. Safety valves Safety valves release steam without any need for electronic signal from instruments. This is a very important device and is a must as per all codes. The release capacity should be more than that of the steam generation capacity of boiler. Automatic blow down/continuous blow down

Salts in feed water does not evaporate with steam and hence the concentration in boiler keeps on increasing. It is essential to drain the highly concentrated boiler water and add some extra feed water, which has comparatively much lower total dissolved solids (TDS). Conventionally the operator used to give blow done a periodic intervals in full day. This is done 3 to 6 times a day. In this process the TDS in boiler keeps fluctuating. If the operator delays the blow-down the TDS increases beyond acceptable limits resulting in salts getting deposited on tubes and the furnace. In automatic blow-down steam, the TDS in boiler is sensed constantly and the opening of blow-down valve is adjusted to maintain the TDS of boiler water below desired limits. Anyhow proper care has to be taken while selecting the automatic blow-down system since there are very few systems which have performed in the field without problems. The automatic systems would be expensive for smaller sizes of boiler. One can always have a continuous blow down system where blow-down valve can be adjusted by calculating the per cent blow-down required based on boiler load and feed water TDS. It can be adjusted considering full capacity of boiler. A heat recovery system will save the heat going out from boiler due to blow down. Boiler water TDS meter/conductivity meter

Considering importance of the TDS level in the boiler, the boiler water needs to be checked for TDS periodically. Necessary meters should be provided to the operator for this job. Furnace water TDS meter

TDS of water in the tubes of water walled furnace (mainly for solid fuel fired boiler) is always much higher than the drum. On line separate TDS sensing arrangement can be very useful for such boilers. Furnace draft alarm for solid fuel boilers

The furnaces of solid fuel fired boilers are kept at a slight negative pressure (on flue side) to avoid flame, hot flue gas coming out from firing doors and

Energy efficiency in boilers 75

the fuel feeding system. Alarm can be provided to provide warning of higher pressure than desired. Pilot flame ignition For gaseous fuels pilot flame is essential to ensure flame stability during ignition. It is more so in case of lean gases like biogas. In case of liquid fuels, burner with rotary, steam and air atomisation are generally provided with pilot flame ignition. Electrical panel with fuses, O/L relays, ELCBs, earthings, etc.

The electricals are equally important. Panel should be equipped with Fuses and O/L relays for all motors. MCB is necessary for the safety of electrical components. ELCB provides safety to the operating staff. Instrumentation for measurement of parameters related to safety of a boiler

Some parameters are very important for safety of a boiler. Instruments need to be provided for measurement of these parameters. Online instruments are preferred since they provide continuous data. Records connected to these instruments create record of data round the clock which can be very useful in trouble shooting. Off-line instruments have to be used by operating staff for periodic monitoring of these parameters. Operator discipline is very crucial for these instruments to be effectively used. Parameters such as feed water TDS, boiler water TDS, boiler water level, steam pressure, stack temperature and tube overheat temperature are very important.

5.5.3

Environmental compliance of boilers

Environmental aspects are becoming more important day by day. Generally local pollution control boards have limits specified for polluting elements in flue gases. Constituents such as CO, NOx, particulate matters, SO2/SO3, hydrocarbons, in flue gases should be measured and must be below the limits specified by the pollution control boards. Following aspects are equally important even though many of them do not get covered under any statutory requirements: 1. Boiler water TDS and treatment before disposal. 2. No fuel oil spillage/proper spillage recovery (for oil fired boilers). 3. Noise level in boiler house. 4. Normal boiler house ambient. 5. Proper soot disposal system while tube cleaning and after tube cleaning.

76 Industrial energy conservation

6. 7. 8. 9. 10.

Ash disposal system (for solid fuel boilers). Lighting and illumination in boiler house. Fire extinguishers in boiler house. First aid kit in boiler house. Space for operator movement.

5.5.4

Availability to user for maintenance without stoppage

Companies without a standby boiler, need to look at this aspect in detail. Facilities for maintenance of components without stoppage of boiler can save the investment of a standby boiler. It is necessary to have facility to carry maintenance work on components like water pump, fuel pump, fuel oil heater, filters for fuel and water and instruments (viz., pressure gauge and temperature gauge), without stopping the boiler operation. Mechanical and manual cleaning convenience Convenience for cleaning saves time required for preventive maintenance shutdown. Convenience can be categorised in three areas, viz., time, manpower and efforts. These should be evaluated for both ‘water side’ and ‘flue gas side’ of any boiler. Chemicals cleaning convenience

On some occasions chemical cleaning is required to be done. This eliminates opening of boiler and saves time. Hence provisions for such cleaning should be provided. Repair convenience

In some designs this aspect is completely neglected. This is very important criterion. If proper care is not taken while designing, repairs can be very expensive and unaffordable. Pressure and non-pressure parts, tubes and furnace should be studied carefully from this point of view. Operating convenience

If it is inconvenient to carry out certain function for the operator, there is tendency to skip that particular operation, which can result in accidents, or inefficient operation. Visibility of instruments and ease of access for observation are the two important factors aiding operating convenience. Instrumentation reliability

Providing lot of instrumentation can be counter effective if the instruments are not reliable.

Energy efficiency in boilers 77

The following factors can ensure reliability of instruments: 1. Instrument manufacturers certified by instrument societies. 2. Calibration certificate available. 3. Repair convenience. 4. Replacement convenience. 5. Control panel reliability: (a) Margins on power ratings of instruments. (b) Dust proof enclosure. (c) Control panel architecture. (d) Maintenance convenience.

5.5.5

Trouble shooting logic diagnostics and support

Trouble shooting can be nightmare if lot of interlocks are provided without visual indications on panel. It can become very easy with: 1. Online logic analyser. 2. Data acquisition and control systems. 3. Indication for all parameter status. 4. Audio/visual alarms. Life expectancy

Every purchaser can use his own yardstick for this aspect. Depending on the industry, market conditions and many other factors this can change. But nevertheless it is a very important aspect which needs to be deliberated upon before making a final decision. Space/dimensions/weight

The cost of installation does not involve only boiler. The civil and steel structural requirements, cost of land occupied must be considered while evaluating commercially. Site start-up time

The investment in boiler can start paying only after the same is commissioned. Amount of site work decides the time required for starting after the boiler reaches site. Transportability

Transport costs can escalate appreciably if the shape and size of each individual component is such that it is difficult to transport. This is very significant if user is far away from the manufacturer.

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Aesthetics

Even though this does not help in day to day functioning directly, good aesthetics can have positive psychological effect on operating staff. External facility dependence

A system design which demands many external facilities result in high initial and running cost. Typically with proper designing of boiler system, one can work without such extra facilities like fuel ring main. Water treatment system simplicity

Different designs of boilers have varying requirements of feed water. A boiler design, which does not demand for very stringent water quality norms, saves initial and running cost. Thus, steam Boiler selection can be done after evaluating the technical merits on various aspects. Proper selection after detailed study can avoid problems during use of boiler. Boiler being a capital equipment is not procured on routine basis. Hence analysis of all minor and major aspects mentioned above can provide necessary inputs for selection.

5.6

Energy conservation opportunities in boilers

The various energy efficiency opportunities in boiler system can be related to combustion, heat transfer, avoidable losses, high auxiliary power consumption, water quality and blow down. Examining the following factors can indicate if a boiler is being run to maximise its efficiency: Stack temperature: The stack temperature should be as low as possible. However, it should not be so low that water vapour in the exhaust condenses on the stack walls. This is important in fuels containing significant sulphur as low temperature can lead to sulphur dew point corrosion. Stack temperatures greater than 200°C indicates potential for recovery of waste heat. It also indicate the scaling of heat transfer/recovery equipment and hence the urgency of taking an early shut down for water/flue side cleaning. Feed water pre-heating using economiser: Typically, the flue gases leaving a modern 3-pass shell boiler are at temperatures of 200 to 300°C. Thus, there is a potential to recover heat from these gases. The flue gas exit temperature from a boiler is usually maintained at a minimum of 200°C, so that the sulphur oxides in the flue gas do not condense and cause corrosion in heat transfer surfaces. When a clean fuel such as natural gas, LPG or gas oil is used, the economy of heat recovery must be worked out, as the flue gas temperature may be well below 200°C.

Energy efficiency in boilers 79

The potential for energy saving depends on the type of boiler installed and the fuel used. For a typically older model shell boiler, with a flue gas exit temperature of 260°C, an economiser could be used to reduce it to 200°C, increasing the feed water temperature by 15°C. Increase in overall thermal efficiency would be in the order of 3%. For a modern 3-pass shell boiler firing natural gas with a flue gas exit temperature of 140°C a condensing economiser would reduce the exit temperature to 65°C increasing thermal efficiency by 5%. Combustion air pre-heat: Combustion air pre-heating is an alternative to feed water heating. In order to improve thermal efficiency by 1%, the combustion air temperature must be raised by 20°C. Most gas and oil burners used in a boiler plant are not designed for high air pre-heat temperatures. Modern burners can withstand much higher combustion air pre-heat, so it is possible to consider such units as heat exchangers in the exit flue as an alternative to an economiser, when either space or a high feed water return temperature make it viable. Incomplete combustion: Incomplete combustion can arise from a shortage of air or surplus of fuel or poor distribution of fuel. It is usually obvious from the colour or smoke and must be corrected immediately. In the case of oil and gas fired systems, CO or smoke (for oil fired systems only) with normal or high excess air indicates burner system problems. A more frequent cause of incomplete combustion is the poor mixing of fuel and air at the burner. Poor oil fires can result from improper viscosity, worn tips, carbonisation on tips and deterioration of diffusers or spinner plates. With coal firing, unburned carbon can comprise a big loss. It occurs as grit carry-over or carbon-in-ash and may amount to more than 2% of the heat supplied to the boiler. Non uniform fuel size could be one of the reasons for incomplete combustion. In chain grate stokers, large lumps will not burn out completely, while small pieces and fines may block the air passage, thus causing poor air distribution. In sprinkler stokers, stoker grate condition, fuel distributors, wind box air regulation and over-fire systems can affect carbon loss. Increase in the fines in pulverised coal also increases carbon loss. Excess air control: Table 5.1 gives the theoretical amount of air required for combustion of various types of fuel. Excess air is required in all practical cases to ensure complete combustion, to allow for the normal variations in combustion and to ensure satisfactory stack conditions for some fuels. The optimum excess air level for maximum boiler efficiency occurs when the sum of the losses due to incomplete combustion and loss due to heat in flue gases is minimum.

80 Industrial energy conservation Table 5.1: Theoretical combustion data–common boiler fuels. Fuel

Solid fuels Bagasse Coal (bituminous) Lignite Paddy Husk Wood Liquid fuels Furnace Oil LSHS

Kg of air req./kg of fuel

Kg of flue gas/kg of fuel

m3 of flue/kg of fuel

Theoretical CO2% in dry flue gas

CO2% in flue gas achieved in practice

3.2 10.8 8.4 4.6 5.8

3.43 11.7 9.1 5.63 6.4

2.61 9.4 6.97 4.58 4.79

20.65 18.7 19.4 19.8 20.3

10–12 10–13 9–13 14–15 11.13

13.9

14.3

11.5

15

9–14

14.04

14.63

10.79

15.5

9–14

This level varies with furnace design, type of burner, fuel and process variables. It can be determined by conducting tests with different air fuel ratios. Typical values of excess air supplied for various fuels are given in Table 5.2. Controlling excess air to an optimum level always results in reduction in flue gas losses; for every 1% reduction in excess air there is approximately 0.6% rise in efficiency. Table 5.2: Excess air levels for different fuels. Fuel Pulverised coal

Type of furnace or burners

Excess air (% by wt)

Completely water-cooled furnace for slag-tap or dry-ash removal Partially water-cooled furnace for dry-ash removal Coal Spreader stoker Water-cooler vibrating-grate stokers Chain-grate and travelling-gate stokers Underfeed stoker Fuel oil Oil burners, register type Multi-fuel burners and flat-flame Natural gas High pressure burner Wood Dutch over (10–23% through grates) and Hofft type Bagasse All furnaces Black liquor Recovery furnaces for draft and soda-pulping processes

15–20 15–40 30–60 30–60 15–50 20–50 15–20 20–30 5–7 20–25 25–35 30–40

Various methods are available to control the excess air: 1. Portable oxygen analysers and draft gauges can be used to make periodic readings to guide the operator to manually adjust the flow of air for optimum operation. Excess air reduction up to 20% is feasible.

Energy efficiency in boilers 81

2. The most common method is the continuous oxygen analyser with a local readout mounted draft gauge, by which the operator can adjust air flow. A further reduction of 10–15% can be achieved over the previous system. 3. The same continuous oxygen analyser can have a remote controlled pneumatic damper positioner, by which the readouts are available in a control room. This enables an operator to remotely control a number of firing systems simultaneously. The most sophisticated system is the automatic stack damper control, whose cost is really justified only for large systems. Radiation and convection heat loss: The external surfaces of a shell boiler are hotter than the surroundings. The surfaces thus lose heat to the surroundings depending on the surface area and the difference in temperature between the surface and the surroundings. The heat loss from the boiler shell is normally a fixed energy loss, irrespective of the boiler output. With modern boiler designs, this may represent only 1.5% on the gross calorific value at full rating, but will increase to around 6%, if the boiler operates at only 25 per cent output. Repairing or augmenting insulation can reduce heat loss through boiler walls and piping. Automatic blow down control: Uncontrolled continuous blow down is very wasteful. Automatic blow down controls can be installed that sense and respond to boiler water conductivity and pH. A 10% blow down in a 15 kg/cm2 boiler results in 3% efficiency loss. Reduction of scaling and soot losses: In oil and coal-fired boilers, soot buildup on tubes acts as an insulator against heat transfer. Any such deposits should be removed on a regular basis. Elevated stack temperatures may indicate excessive soot buildup. Also same result will occur due to scaling on the water side. High exit gas temperatures at normal excess air indicate poor heat transfer performance. This condition can result from a gradual build-up of gas-side or waterside deposits. Waterside deposits require a review of water treatment procedures and tube cleaning to remove deposits. An estimated 1% efficiency loss occurs with every 22°C increase in stack temperature. Stack temperature should be checked and recorded regularly as an indicator of soot deposits. When the flue gas temperature rises about 20°C above the temperature for a newly cleaned boiler, it is time to remove the soot deposits. It is, therefore, recommended to install a dial type thermometer at the base of the stack to monitor the exhaust flue gas temperature. It is estimated that 3 mm of soot can cause an increase in fuel consumption by 2.5% due to increased flue gas temperatures. Periodic off-line cleaning of radiant furnace surfaces,

82 Industrial energy conservation

boiler tube banks, economisers and air heaters may be necessary to remove stubborn deposits. Reduction of boiler steam pressure: This is an effective means of reducing fuel consumption, if permissible, by as much as 1 to 2%. Lower steam pressure gives a lower saturated steam temperature and without stack heat recovery, a similar reduction in the temperature of the flue gas temperature results. Steam is generated at pressures normally dictated by the highest pressure/temperature requirements for a particular process. In some cases, the process does not operate all the time and there are periods when the boiler pressure could be reduced. The energy manager should consider pressure reduction carefully, before recommending it. Adverse effects, such as an increase in water carryover from the boiler owing to pressure reduction, may negate any potential saving. Pressure should be reduced in stages and no more than a 20 per cent reduction should be considered. Variable speed control for fans, blowers and pumps: Variable speed control is an important means of achieving energy savings. Generally, combustion air control is effected by throttling dampers fitted at forced and induced draft fans. Though dampers are simple means of control, they lack accuracy, giving poor control characteristics at the top and bottom of the operating range. In general, if the load characteristic of the boiler is variable, the possibility of replacing the dampers by a VSD should be evaluated. Effect of boiler loading on efficiency: The maximum efficiency of the boiler does not occur at full load, but at about two-thirds of the full load. If the load on the boiler decreases further, efficiency also tends to decrease. At zero output, the efficiency of the boiler is zero and any fuel fired is used only to supply the losses. The factors affecting boiler efficiency are: 1. As the load falls, so does the value of the mass flow rate of the flue gases through the tubes. This reduction in flow rate for the same heat transfer area, reduced the exit flue gas temperatures by a small extent, reducing the sensible heat loss. 2. Below half load, most combustion appliances need more excess air to burn the fuel completely. This increases the sensible heat loss. In general, efficiency of the boiler reduces significantly below 25% of the rated load and as far as possible, operation of boilers below this level should be avoided Proper boiler scheduling: Since, the optimum efficiency of boilers occurs at 65–85% of full load, it is usually more efficient, on the whole, to operate a fewer number of boilers at higher loads, than to operate a large number at low loads.

Energy efficiency in boilers 83

Boiler replacement: The potential savings from replacing a boiler depend on the anticipated change in overall efficiency. A change in a boiler can be financially attractive if the existing boiler is: 1. Old and inefficient. 2. Not capable of firing cheaper substitution fuel. 3. Over or undersized for present requirements. 4. Not designed for ideal loading conditions. The feasibility study should examine all implications of long-term fuel availability and company growth plans. All financial and engineering factors should be considered. Since boiler plants traditionally have a useful life of well over 25 years, replacement must be carefully studied.

5.7

Improving boiler efficiency

Boilers are an integral utility of any process industry and are known to consume large amounts of fuel and electrical energy. With fluctuating oil prices impacting production costs, there has been an increasing awareness for upgradation, automation and efficiency improvement in boilers and to maintain the boilers in good health. In most industries pricing of the end product is mainly decided by fuel cost and energy bill. Among utilities, boilers and heating systems consume large amount of fuel and electrical energy. Since boilers come under IBR rules and operate with various fuels, they are considered stationary equipment and once you install them, it is difficult to replace or modify. Although boiler technology has not seen any drastic changes in recent years, new avenues have opened up for upgradation, automation and efficiency improvement in boilers and heaters. It is a tough challenge for maintenance and engineering teams to constantly update newer methods and systems of boiler operations and in the process ensure efficient steam management. One of the reasons for improvement of boiler operations over the last decade is the growing awareness of global warming and the need to implement stringent pollution control norms to reduce industrial emissions and arrest green house effect. As a result, though useful boiler life is said to be anywhere between 10 to 20 years, it is important to maintain boiler operations as efficient and healthy as in the case of new equipment. Another factor that is forcing industry to go for cost effective solutions is the availability and environmental viability of fossil fuels. Shift to biomass fuels and use of multiple fuels are emerging as viable options. Various avenues for industries to improve boiler efficiency and reduce down time include: 1. Correct use of fuel and combustion equipment. 2. Retrofits and upgrades.

84 Industrial energy conservation

3. Energy recovery. 4. Steam distribution. 5. Minimising break down in boilers and avoiding production loss.

5.7.1

Correct use of fuel and combustion equipment

It is important to use specified fuel for which the boiler is designed. If the boiler is designed for Indian coal, it cannot burn Indonesian or South African coal effectively. This is mainly due to the different fuel characteristics they possess. Indian coal is typically burnt in fluidised over bed combustion more effectively as it has low fines percentage and, high ash content, where as the imported coal burns more effectively when it is fired in fluidised under bed option. Neglecting such critical choice of equipment to match fuel requirements can lead to huge carry over, lower combustion efficiency, high operational and maintenance cost. Similarly a boiler running on LDO/HSD, when changed to furnace oil (FO), it cannot work effectively without making necessary changes in the combustion system. Fuel characteristics differ widely for HSD, LDO and FO. It is a known fact that FO is difficult to atomise (creation of smaller particle for better mixing of fuel with combustion air), as it contains chain and ignition properties. Moreover, compared to other lighter fuels, it contains undesirable material like conradson carbon, asphaltines, sediments, silica, vanadium, etc., in excess. This is mainly due to depleting crude oil reserves pushing oil industries to extract maximum lighter hydrocarbons and FO is the final product that remains as a by-product. For optimum efficiency, it is important to choose the right combustion equipment for specific fuel. Due to scarcity of specific fuels, users are forced to use unspecified fuels in boilers to generate steam. The result can be any one of the following issues: 1. Low combustion efficiency. 2. High fuel combustion per ton of steam generated. 3. Higher fouling of heat transfer area and increased stack losses. 4. Poor steam generation. 5. High maintenance cost of boiler components like nozzles, fuel pumps, dust controllers. 6. Corrosion of chimney and ducts. 7. Corrosion/erosion of ID fans, ducts, boiler tubes. 8. Higher emission of pollutants such as CO, NOx, SOx, etc. 9. Frequent stop and start of boilers and associated components. 10. Operational safety hazards.

Energy efficiency in boilers 85

Proper planning of fuel selection while installing a new boiler can help avoid the issues mentioned above at later stages. Sufficient space around boilers helps to implement future upgrades and modifications in case of changes in fuel or norms or if efficiency improvement is planned.

5.7.2

Retrofits and upgrades of boilers

It has become a common practice to retrofit, upgrade old boilers with new combustor and burner designs. This is healthier and more profitable than continuing with inefficient and unsafe equipment. A bagasse fired stationary grate boiler can be converted to operate on both bagasse as well as coal with a separate fluidised bed combustor added for higher thermal efficiency. This will give the boiler the flexibility of using one fuel while keeping a second fuel option. Conventionally, industry uses pressure jet burners for most liquid oils. If a process demands trouble free operation of boilers with consistent efficiency and minimum possible stoppages for maintenance air/steam, atomised burners can be the best option. They also allow users to have multi-fuel options, where there is simultaneous burning of more than two fuels, something practically difficult in pressure jet burners. A well designed steam/air atomised burner can help maintain committed boiler efficiency consistently for longer durations of 3–4 months. In pressure jet burners, combustion efficiency drops over time due to nozzle clogging, fuel pressure variations, etc. If proper maintenance on a weekly basis is not followed for burner components, a drastic drop of efficiency ranging from 1–2% is observed. Today it is possible to step up the overall efficiency of boilers with new facets of combustion technology like oxygen trimming, oxygen control, variable frequency drive based air and draft control, boiler performance monitoring and measurement systems based on latest PLC/SCADA systems. A 20 degree rise in stack temperature can mean 1% efficiency loss and 1% oxygen saving in flue gas means 0.5% increase in thermal efficiency.

5.7.3

Energy recovery from boilers

In most boilers thermal efficiency is calculated as per BS 845 part 1 guidelines. It is clear from these guidelines that dry flue gas loss (stack loss) contributes 11 to 12% energy loss in conventional oil and gas boilers that don’t have heat recovery. In solid fuel boilers these losses can be as high as 15 to 25% depending on the type of fuel, combustor, etc. A properly designed heat recovery unit at the flue gas exit point of a boiler/heater can save fuel cost and improve overall equipment efficiency.

86 Industrial energy conservation

Some of the typical cost saving heat recovery options for boiler and heaters are: 1. Air pre-heater (integral/external)-saves fuel cost upto 4%. 2. Water pre-heater-saves fuel cost upto 3%. 3. IBR economiser-saves fuel cost upto 4%. 4. Condensing economiser-saves fuel cost upto 13% on natural gas fired boilers and heaters. Similarly, good amount of energy can be recovered if users implement condensate recovery systems in the process plants. A typical condensate recovery system comprising flash vessel, mechanical steam operated pump and de-aerator head can save up to Rs. 1 crore in fuel costs for a 10 TPH boiler running on FO. Condensate recovery has the following major benefits: 1. It saves precious water used to generate steam as condensate water is one of the best sources of feed water for boiler. 2. As condensate is at a higher temperature it saves fuel cost, as feed water is already pre-heated upto 90°C. 3. A well designed mechanical pump saves expensive electrical cost of condensate transfer from process to utility. 4. Elevated temperature of condensate helps to remove dissolved oxygen in the feed water. This minimises corrosion of boiler internals, improves safety and extends boiler life. 5. Lesser use of fuel helps to reduce carbon dioxide generation and global warming. 6. Reduces chemical load on effluent treatment plants, resulting in reduced overall cost of operations and water pollution. 7. Pure condensate water reduces blow down loss up to 60%, further improving overall efficiency of boiler.

5.7.4

Steam distribution from boilers

Another aspect of energy saving comes from effective distribution and utilisation of steam from boiler to process. While installing a steam distribution system, it is important to consider the following: 1. Optimum steam line sizing to avoid higher pressure drops, minimum heat loss, reduced water logging and hammering. 2. Properly sized and effective steam/condensate line insulation to minimise radiation and convection losses.

Energy efficiency in boilers 87

3. Air venting and vacuum breaker at proper locations to improve heat transfer from available steam. 4. Use of drain traps at recommended positions in steam lines (at least one trap at 30 meter straight distance) to remove condensate from steam lines to reduce water logging and hammering. 5. Correct selection of drain traps to minimise the steam loss—a thermodynamic trap for saturated steam line and thermostatic traps for steam tracing lines. 6. Use of right size and type of float traps for removal of condensate in indirect heating applications. Fuel additives/water side chemicals like anti-descalents for heat transfer and fuel combustion also helps to maintain boiler efficiencies. Minimising breakdown in boilers and avoiding production loss

There could be many reasons offered for boiler breakdowns and shutdowns. But it is better to realise the practical good sense in the observation what you can monitor you can correct and improve. In today’s demanding workplace, maintenance managers and supervisors are under pressure to perform and keep the utilities in good working condition. Not every plant has the luxury of stand by boilers and it becomes the responsibility of utility managers to ensure minimum shutdowns and breakdowns. Although standard maintenance practices are helpful to a great extent to minimise breakdowns, with increasing complexity of utilities and demanding production schedules, an effective and automated maintenance schedule can be of real help. Some of the newer concepts that can help utility managers are: 1. Install remote monitoring, where a computer system with simple instrumentation monitor the health of boilers and generate reports at pre-defined intervals by email or mobile phone messages (sms). 2. Plan a fixed preventive maintenance schedule for boiler, synchronised with production schedule. 3. Instead of hard copies maintain electronic log books that will generate analysis of various parameters. 4. Observe MTBF (mean time between failure) of various components of boiler and take correct action with OEMs and experts. 5. Prepare FTA (Fault Tree Analysis) for frequently occurring and critical problems to generate data base for everyone to follow. This can help new recruits and speed up resolution of problems. 6. Follow OEM instructions and best practices of maintenance. 7. Install boiler efficiency/performance monitoring system so that performance is system based and not person-dependent.

88 Industrial energy conservation

8. Do a Remaining Life Analysis (RLA) for pressure parts of boiler to predict effective safe life of boilers. This will also help to avoid safety related failures and hazards that can result in longer time to restore boilers. 9. Conduct energy/efficiency audits of boilers for fuel-energy savings and implement recommendations. 10. Use genuine parts and adopt good engineering practices while carrying out maintenance of boilers. 11. Train the operating teams at regular intervals by experts or OEMs to update knowledge. Reward people who imbibe and practice innovative ways of operating boilers. 12. Stock necessary critical parts to avoid production loss. 13. Do not bypass safety rules as it may lead to major safety hazards and breakdowns. The performance of boilers ultimately depends on how well they are maintained and operated by trained professionals. Boiler operations in an industrial plant will be efficient and safe with a utility team that keeps track of healthy maintenance practices and implement them year after year.

5.8

Factors affecting boiler efficiency

There are many factors that affect boiler efficiency. It is important to adjust the boiler regularly for these variations in order to ensure optimum boiler performance.

5.8.1

Shift variations in boilers

Typically, in plants, the load on the plant changes from shift to shift. If the boiler response to these load variations is not changed, the efficiency of the boiler drops. The change in settings required can be as simple as changing the firing rate or pressure limits of the boiler. These can be done easily from the boiler control panel itself. These changes are easy to do in either oil, gas or solid fuel fired boilers. A change may also be required in feed water tank level settings as the load may be lower in certain shifts. Also the blow down rate needs to be adjusted to reduce blow down based on TDS and not based on time as the load is low. The combustion system also needs some fine tuning as the day time and night time temperatures may change by 15 to 20°C. This variation would affect the excess air setting of the burner and hence dampers may need to be adjusted.

5.8.2

Daily variations in boilers

Load variations may occur from day to day too. Again, the boiler needs to be adjusted to cater to this efficiently.

Energy efficiency in boilers 89

5.8.3

Weekly variations in boilers

As the fuel quality is changing continuously, adjustments need to be made to the combustion system to take care of these variations. In oil or gas fired boilers, the quality of oil being received may vary from tanker to tanker. The moisture content in solid fuels changes with time and also the source of purchase. This change in fuel quality makes adjustments necessary.

5.8.4

Seasonal variations in boilers

Boiler loading pattern is an important factor here too. The production requirement of the plant may be affected by seasonal demands. This calls for adjustments again. In solid fuel fired boilers, the fuel available may change depending on seasons. The ambient air temperatures and humidity will also change from season to season. The combustion system needs adjustment too.

5.9

Practical standard operating practices for improving boiler efficiency

Step 1: Steam loading (setting the pressure control loop right)

1. 2. 3. 4. 5. 6.

Boiler loading plays an important role in varying boiler efficiency. The loading pattern can be well defined for most processes. Setting of boiler control loops as per requirement. Critical parameters - steam flow and pressure (temperature). There is no other way to do this. Losses - On/Off, combustion, radiation (in multiple boilers).

Step 2: Combustion losses (setting the air to fuel ratio right)

1. Having done step one, this can be done fairly easily. 2. Not only this, the first step holdown alignment support (HAS) to be done before attempting this for any meaningful output. 3. Critical parameters-stack oxygen, temperature and steam temperature. 4. Losses–combustion. Step 3: Blow down (ABCO)

1. 2. 3. 4.

Gets affected by-FW TDS, CRR, TDS set point, Boiler loading. Monitoring as a loss with others. Critical parameters - TDS, FW temperature. Losses-blow down.

90 Industrial energy conservation

5.9.1

Boiler efficiency improvement ladder-bridging the gaps

Gap 1: Direct efficiency of 72% and indirect efficiency of 78%

1. Losses like the chimney draft loss during standby, loss due to cold air purging during start up cycles and during standby and loss due to the on/ off cycles of the burner are generally not measured and are very small in magnitude if the boiler is operated continuously. These factors play an important role if the boiler load is low or varying a lot. 2. By monitoring the steam flow patterns over a period of time, the peak and low load demands can be easily mapped out. 3. All the boiler efficiency products generate data critical for reducing fuel consumption and also keep a check on the process itself. Gap 2: Average indirect efficiency of 78% and the best indirect efficiency of 84%

1. Improper tuning of burner. 2. This gap can be bridged easily by monitoring the stack oxygen and temperature on a regular basis. 3. The boiler loading and variations in fuel firing rate also play an important role in burner combustion. The burner tuning needs regular adjustments because of variation in fuel quality and burner nozzle condition too. 4. Bridging this gap does not mean investing in expensive control system but by simply monitoring and making slight adjustment to the excess air in the burner, good burner performance can be ensured. Gas 3: Minimum direct efficiency of 61% and maximum indirect efficiency of 84%

1. Bridged when all boiler operating parameters in terms of regular tuning, load management on the boiler, feed water temperature, etc., in the boiler house is done regularly. 2. Maintaining the correct level in the feed water tank for better feed water temperature.

5.10

Case study Atul limited—Ankleshwar (Gujrat)

5.10.1

Efficiency enhancement in natural gas fired boiler and recovery of water from flue gas

Atul limited (Aromatics division), a Lalbhai group company, located at Ankleshwar in Gujarat, is the largest manufacturer of p-cresol, p-anisic

Energy efficiency in boilers 91

aldehyde and p-anisyl alcohol in the world. The company is also the leading manufacturer of anisyl nitrile, p-methoxy phenyl acetic acid, feed grade manganese sulphate, sodium sulphite, sodium sulphate and perfumery grade products. The company achieved sales revenue of Rs. 805 crore in 2014–15 fiscal; 65–70% of total business revenue comes from exports. With growth of business, conserving environment, energy and natural resources has always been a prime focus of the organisation for sustainability.

5.10.2

Energy conservation by doing things differently

Atul Ltd. (Aromatics Division) has been using natural gas fired boiler for steam generation to meet process requirement for almost two and half decades. It is also the first customer of Gujarat Gas Company Ltd. (GGCL) at Ankleshwar Industrial Estate to use natural gas (NG), through direct pipeline, in boiler for steam generation. Natural gas is the most non-polluting and easy-to-operate fuel due to its low C/H ratio. That is why it has always been in great demand from industrial customers to meet increasingly stringent emission norms and as a means of reducing generation of greenhouse gases. Net Caloric Value (NCV) of NG used varies is in the range of 8500–8600 Kcal/Sm3. Boiler efficiency with flue gas temperature of 110–115°C normally varies in the range of 90–91 % as per usual boiler operation. Sizeable amount of heat is lost with the flue gas in a conventional mode of operation (Table 5.3). Table 5.3: Exit flue gas temperature in the chimney of steam boilers using different fuels. Boilers using different fuel Coil fired boiler Furance oil fired boiler Conventional natural gas fired boiler Condensing boiler, natural gas fired

Flue gas temperature °C 150–160°C 160–170°C 110–115°C 53–56°C

Beginning 2009 onwards, both supply and cost of natural gas has changed radically in India due to dramatic increase in consumption in various segments. This has widened the gap of demand and supply, leading to price increase three-fold. Therefore, there was no other option, but to think differently to increase boiler efficiency and reduce the energy cost for steam generation to retain the leadership position in the chosen business.

5.10.3

Boiler efficiency

Any petroleum fuel contains constituents like carbon (C), hydrogen (H), oxygen (O), sulphur (S), nitrogen (N) and water (HP), etc., in different proportion.

92 Industrial energy conservation

Combustion of C, H and S in presence of air releases energy due to exothermic nature of the reaction. Gross Calorific Value (GCV) of a fuel is defined as the energy released due to combustion per unit mass of fuel. It is generally expressed in Kcal/Kg or Kcal/Sm3. ‘Combustion of H present in fuel forms water, which remains in vapour form in flue gas. Let’s call this mass as X1. Moisture/water present in the fuel also evaporates and remains as water vapour in the flue gas, let’s call this mass as X2, X2 is normally very less in natural gas. Combustion also carries atmospheric moisture, which also remains in flue gas in vapour form. Let’s assume this mass as X3. Therefore, total water vapour present in the flue gas is X1 + X2 + X3. Evaporation of this total water and for it to reach the flue gas temperature requires energy, known as enthalpy, which is taken away from the gross energy released during combustion process. As a result, heat carried away by the water vapour in the flue gas is not available for useful recovery. It is directly lost in the atmosphere. The air and the combustion products other than water (CO2, CO, NOx) and nitrogen also take away a significant amount of heat. GCV minus heat lost in the water vapour + inerts and combustion products, per unit mass of the fuel, is called Net Caloric Value (NCV). Boiler efficiency is calculated based on NCV of the fuel, as heat carried or lost with water vapour is not available for heat transfer; it is NCV that is available for heat transfer in the boiler (Fig. 5.3). 106% 45,104%

104%

47,103%

Thermal efficiency (%)

102%

Fully condensing zone

49,102%

100% 57,98%

98%

Partial condensing zone 96%

120,95%

94% Non-condensing zone 92% 90% 245,89% 88% 0

50

100

150

200

250

300

Flue gas temperature (°C)

Figure 5.3: Efficiency of the natural gas fired boiler at different flue gas temperature.

Energy efficiency in boilers 93

Condensing boilers use heat from exhaust gases that would normally be released into the atmosphere through the flue gas. To use this latent heat, the water vapour from the exhaust gas is turned into liquid condensate. In order to make the most of the latent heat within the condensate, condensing boilers use a larger heat exchanger, or sometimes a secondary heat exchanger. Due to this process, a condensing boiler is able to extract more heat from the fuel it uses than a standard efficiency boiler. It also means that less heat is lost through the flue gases. Brainstorming was done with the competent and reputed boiler supplier and a new 24-tph (tonnes per hour) condensing boiler, designed for 14 bar steam generation, was installed and commissioned with three stage economisers in mid-2014. Flue gas temperature coming out from the boiler at 330–340°C is passed through the 1st stage non-condensing economiser and decreased to 170–175°C. Then it is again passed through a 2nd stage non-condensing water pre-heater, where temperature is reduced to 80–85°C. Finally, it is passed through a 3rd stage condensing economiser, where final temperature of the flue gas is further reduced down to 53–56°C by pre-heating the boiler feed make up water fed at 31°C. Reducing the flue gas temperature from 330°C to 55°C is very unique in industrial boiler operation (Fig. 5.4). Sensible heat

330°C from flue gases

1750°C

Sensible heat + latent heat of condensation of water vapours

85°C

Condensing water pre-heater

Non-condensing water pre-heater

Furnace

Economiser

Smoke tube boiler

55°C To stack

Figure 5.4: Schematic diagram showing reduction in flue gas temperature in stages.

Improving thermal efficiency: It helps in improving thermal efficiency by lowering NO consumption for unit production of steam. At 55°C flue gas temperature, boiler efficiency is ~100%, compared to 91–92% in a conventional boiler having flue gas temperature of 1l0–1l5°C. At 45°C flue gas temperature, boiler efficiency can be as high as 103% setting a new benchmark. Minimum 3-Sm3 of natural gas can be saved per tonne of steam generated, as compared to a conventional boiler. NO saving can be increased up to 4–5 Sm3 per tonne of steam generation, depending on the lower flue gas temperature

94 Industrial energy conservation

and efficient design. Installation of 24-tph condensing boiler led to saving of 550,000-Sm3 of natural gas per year @ 80% loading and value addition of more than Rs. 1.7 crore on account of energy conservation alone. Helps recovering water from flue gas: Due to low C/H ratio, burning of 1 mole of methane (molecular weight: 16) generates 2 moles of water (molecular weight: 18). In other words burning of 16-kg methane generates 36-kg water on complete combustion with sufficient air, which is carried away with the flue gas in the form of vapour. This water is generally lost in the atmosphere. Recovering this water from the flue gas directly leads to conservation of a natural resource. Latent heat of condensation of water from flue gas is indirectly used for pre-heating the boiler feed water entering @ 31°C. About 60,000,000 litres of water is generated per year by condensation from flue gas at flue gas exit temperature of 55°C. This is almost 40% water recovery from the flue gas. pH of condensed water varies in the range of 3–4. This water is used and recycled in the process. The acidity in the water is mainly due to presence of weak carbonic acid formed by scrubbing of CO2 gas with condensed water at lower temperature (Fig. 5.5). 3000 2666 2333

2500 2000

2000 1666 1333

1500 1000 1000 667 500 0 4

6

8

10

12

14

16

F&A boiler capacity TPH

Figure 5.5: Typical reduction in estimated CO2 emission in a condensing boiler (tonnes/year).

The improved efficiency of the boiler directly reduces greenhouse gas emissions into the atmosphere. The entire operation of 24-tph condensing boiler is automatically controlled and monitored from a dedicated PLC system.

Energy efficiency in boilers 95

Consumption of both natural gas and water recovered is measured real time, using a flow-meter installed online. The overall efficiency of the condensing boiler has been audited by Petroleum Conservation of Research Association (PCRA) in operating conditions. They have certified that the overall thermal efficiency is 100.62%, based on NCV @ flue gas temperature of 52°C and natural consumption is 69.6 Sm3/T of steam generation at 14 bar. Thus, installation of condensing boiler has gained momentum in all developed countries to reduce energy costs. There are a number of reputed boiler manufacturers who supply condensing boilers worldwide, like Loos in Germany, etc. In India too, all reputed boiler manufacturers are capable of supplying condensing boilers. Population of such boiler installation has been limited in India so far due to lack of information or lack of knowledge sharing/ openness. However, better late than never! Atul Ltd. (Aromatics Division) has successfully installed a 24-tph condensing boiler designed at 14-bar steam pressure for conservation of energy and natural resource, which is in operation for more than a year (Fig. 5.6).

96

100

104

88

3

NG saving, 0000 Sm /yr

120

72

80 56

60

80

64

48 32

40 25 20 0 8

10

12

14 16 18 20 22 F&A boiler capacity TPH

24

26

Figure 5.6: Estimated natural gas saving per year at different capacity condensing type steam boiler.

This has resulted in savings of 550,000-Sm3 of natural gas and conservation of 60,00,000 litres of water per year. This is another non-conventional step taken and innovation done by the team by doing things differently to make the overall business sustainable. Table 5.4 shows before and after scenario of 24-tph condensing boiler.

96 Industrial energy conservation Table 5.4: Before and after scenario of 24-tph condensing boiler. Description

Before

After

Flue gas temperature in chimney Water recovery from flue gas, per annum (L) Natural consumption per MT of steam, Sm3 Natural consumption saving per annum Sm3 Energy cost saving per annum, in crores Average reduction in carbon dioxide emission, MT/annum Boiler efficiency

115°C 0 74 0 0 0 92

55°C 60,00,000 70 5,50,000 2.0 1,600 99%

Challenges and benefits of installation of condensing boiler are shown in Table 5.5. Table 5.5: Challenges and benefits of installation of condensing boiler. Challenges

Benefits

Selection of proper metallurgy for designing the condensing economiser for long life as it leads to low-end corrosion due to acidic nature of the condensate and condensation of other acidic vapours such as NOx or SOx, if any. Chimney should be with proper material of construction (MaC), i.e., either FRP-lined or AISI SS 304.

Boiler efficiency can be increased > 100%. Ideally, 103% efficiency is achievable with proper design and installation.

Independent condensate collection system and suitable use in the process with by-pass arrangement of the condensing section to have flexibility in flue gas shift. Pressurised deaeration tank to remove dissolved oxygen from feed water by steam sparging.

Minimum 3-Sm3 of natural gas can be saved per tonne of steam generation, as compared to a conventional boiler. NG saving can be increased up to 4-Sm3 or 5-Sm3, depending on the lower flue gas temperature and efficient design. Highly energy efficient and eco-friendly.

Demineralised water recovery from flue gas, leading to conservation of natural resource. Reduction in CO2 emission in the atmosphere. Low ambient temperature due to lower flue gas temp in chimney (50–55°C).

Industrial waste heat recovery 97

6 Industrial waste heat recovery

6.1

Introduction

Heat recovery systems are designed to conserve energy by reusing available waste heat. They transfer heat from sources of waste heat to uses for the recovered heat, with various types of heat recovery equipment. The conservation of energy not only reduces our dependence on imported fuels, but produces a cost saving to pay back the system cost. The cost saving increases as fuel costs increase, creating an inflation-proof investment.

6.2

Basic heat recovery

The elements of a heat recovery system is shown in Fig. 6.1. The ‘source’ produces waste heat as a result of a process or building operation. The waste heat can be contained in a gas, liquid or vapour. Its temperature may be very high, as in the exhaust from a furnace or it may be close to ambient temperature, as in the exhaust from a building ventilator. Exhaust

supply

Heat recovery equipment

Source

Use

Figure 6.1: Elements of a heat recovery system.

The use consumes heat as part of its operation. Besides liquid, gas and vapour, the use can encompass process materials pre-heated before entering the process. The heat recovery equipment indicates a means for transferring the waste heat from the source in a form acceptable by the use. The type of device used for the heat recovery equipment depends upon the nature of the source and use and their respective temperatures. Examples of heat recovery equipment include heat exchangers, waste heat boilers and boiler economisers. Following the heat recovery equipment, the exhaust fluid is either vented or

98 Industrial energy conservation

drained. The supply is received from outside sources, return from the process or building return air. A simple example of a heat recovery system is shown in Fig. 6.2. As shown, exhaust gases from the boiler stack pass through an economiser in the stack. The economiser reduces the gas temperature. Returning boiler feedwater is heated in the economiser before entering the boiler. The cost saving produced by the stack economiser appears as reduced fuel to pre-heat the boiler feedwater. Stack

From deaerator

353°F

220°F Boiler stack economiser

600°F Flue gas Boiler stack

302°F Feedwater Boiler feed

Figure 6.2: Boiler feedwater heat recovery system.

The example of Fig. 6.2 illustrates the principles of heat recovery: 1. The exhaust temperature falls as a result of losing of losing recoverable waste heat. 2. The supply temperature rises as a result of using recovered waste heat. 3. The amount of recovered waste heat given up by the exhaust must equal the amount of recovered waste heat gained by the supply. 4. The amount of recovered waste heat is less than the total amount of exhaust heat. Since the presence of heat in a material is measured by the material’s temperature, the material’s loss or gain of heat is reflected by its change in temperature. The greater the amount of heat loss or gain, the greater the change in temperature. The heat loss from the exhaust must appear in the heat gained by the supply, based upon the basic laws of thermodynamics. There is no other place for the heat to exist. The temperatures of the exhaust and supply are not necessarily the same because they may originate under very different conditions, but the amount of heat lost and gained is always the same. Finally, the heat recovery equipment can recover only a portion of the total heat in the exhaust. It can reduce the exhaust temperature to the extent permitted by the supply and exhaust temperatures and by its design. The supply temperature is the lowest theoretical exhaust temperatures leaving the equipment, because

Industrial waste heat recovery 99

the supply cannot cool the exhaust below its own temperature. The equipment design fixes how closely the actual exhaust temperature approaches the supply temperature. Any remaining source heat after the heat recovery equipment is lost in the exhaust leaving the heat recovery equipment

6.2.1

Benefits of heat recovery

Heat recovery benefits fall into three categories: 1. Reduction of energy cost. 2. Reduction of equipment cost and size. 3. Reduction of energy use. Reduction of energy cost is the primary benefit of heat recovery. Any heat recovered from the exhaust and returned to the supply need not be supplied by purchase energy. Further, any increases in energy prices result in increase heat recovery benefits. A heat recovery system is both inflation and price increase-proof. Very few other investments are so free of economic risk. Additional cost benefits for heat recovery systems are available as equipment cost and size reduction. The use of recovered heat reduces the amount of heat furnished from purchased energy. Oil and gas supply pipes, electrical facilities, burners, boilers and support structures often can be reduced. If standby facilities are required, temporary, rather than permanent, equipment can be provided, preserving the cost reduction. The reduction of heat requirements can permit greater utilisation of existing process or ventilation equipment. Increased amounts of product or ventilation can be handled without increasing energy use and without new equipment. Where cyclical or peaking conditions are present, heat recovery allows a flexible way of accommodating periods of high heat demand without providing additional heating facilities.

6.3

Process heating

Process heating is a significant source of energy consumption in the industrial and manufacturing sectors and it often results in a large amount of waste heat that is discharged into the atmosphere. Industrial waste heat refers to energy that is generated in industrial processes without being put to practical use. Waste heat losses arise both from equipment inefficiencies and from thermodynamic limitations on equipment and processes. Industrial process heat recovery effectively recycles this waste heat, which typically contains a substantial amount of thermal energy. The benefits of heat recovery include improving system efficiency, reducing fuel consumption and reducing facility air emissions. While the type and cost-effectiveness of a heat recovery system are dependent on the process temperature and the facility’s

100 Industrial energy conservation

thermal requirements, many heat recovery techniques are available across low, medium and high temperature ranges. Process heating refers to the application of thermal energy to a product, raising it to a certain temperature to prepare it for additional processing, to change its properties, or for some other purpose. The energy required for process heating accounts for approximately 20% of total industrial energy use in the U.S., Europe and other development countries. As energy costs continue to rise, facilities are constantly in need of ways to improve the performance of their process heating systems and to reduce their energy consumption. In many fuel-fired heating systems the exhaust gas that is emitted through a flue or stack is the single greatest heat loss. Process heat recovery saves energy by reusing this otherwise lost heat for a variety of thermal loads, such as pre-heated combustion air, boiler feedwater and process loads, as well as for steam generation.

6.4

Industrial process heat recovery

Process heat recovery involves intercepting the waste streams before they leave the plant, extracting some of the heat they contain and recycling that heat.

6.4.1

Applications

Heat recovery can be applied in a wide range of industries. For example, the pulp and paper industry can utilise heat recovery through several processes, from pre-heating milling water with steam to cooling effluent wastewater before sending it to waste treatment. The chemical industry can apply heat recovery to most processes, including chemical manufacturing, as well as to emissions control devices such as recuperative and regenerative thermal oxidisers. The petroleum industry can use heat recovery from production water and glycol regenerators, as well as using heat exchangers between wet and dry crude, in the natural gas cleaning process and in waste treatment operations. The food and beverage industry can achieve savings through the installation of heat exchangers for food pasteurisers, blanch water heat recovery, boiler blow down heat recovery, heating feedstock in the distillation process and recovery of waste heat from dryers and cookers. In both the commercial and industrial sectors, Combined Heat and Power (CHP) systems can efficiently generate electrical power on-site as well as recovering waste heat to generate hot water or steam for process operations.

6.4.2

Benefits of waste heat recovery

The benefits of heat recovery are multiple: economic, resource (fuel) saving and environmental.

Industrial waste heat recovery 101

First, recovered heat can directly substitute for purchased energy, thereby reducing the facility’s energy consumption and its associated costs; further, waste heat substitution can lower capacity requirements for energy generating equipment, thus reducing capital costs for new installation projects. Second, for a specific heating process, fuel efficiency can be improved through the use of heat recovery, thus reducing the cost of operation. For example, the use of exhaust gas from a fuelfired burner to pre-heat the combustion air can reduce heating energy use by as much as 30%. Third, due to improved equipment efficiency, smaller equipment capacity requirements and reduced fuel consumption, heat recovery can produce environmental benefits through reductions in emissions of greenhouse gases and atmospheric pollutants. Sources and quality of waste heat

Waste heat sources can be classified by temperature range, as shown in Table 6.1. Table 6.1: Waste heat temperature categories. Category

Temperature (°F)

High Medium Low

1100 to 3000 400 to 1100 80 to 400

About 92% of process heat energy used by industry is directly provided by fossil fuels. The waste heat generated from direct-fired processes falls in the high and medium temperature ranges. In the high temperature range, sources of waste heat include refining furnaces, steel heating furnaces, glass melting furnaces and solid waste incinerators. In the low-temperature range, sources of waste heat include process steam condensate, cooling water from refrigeration condensers, welding machines, boilers and air compressors. In some applications low-temperature waste heat can be used for pre-heating through heat exchangers. For example, cooling water from a battery of spot welders can be used to pre-heat the ventilating air for winter space heating. In the medium temperature range, sources of waste heat include exhaust gases from steam boilers, gas turbines, reciprocating engines, water heating boiler furnaces, fuel cells and drying and baking ovens. Potential heat recovery opportunities include, among others, low pressure steam generation and incoming product pre-heating. High-temperature waste heat is the highest quality and most useful because it provides more heat recovery options and thus greater potential costeffectiveness than lower temperature waste heat. It can be made available to

102 Industrial energy conservation

do work through the utilisation of steam turbines or gas turbines to generate energy in a cogeneration plant. Table 6.2 lists examples of waste heat sources and their potential applications. Table 6.2: Various waste heat sources and applications. Sources

Temperature range

Exhaust gas from refining furnaces, steel heating furnaces, glass melting furnaces, solid waste incinerators

Exhaust from gas turbines, reciprocating engines, incinerators, furnaces Steam boiler blown down

Exhaust gas from fuel burner Reciprocating engine jacket cooling Waste stream from condensers, boilers and air compressors

6.5

High

Medium

Low

Application Hazardous gas reduction Steam generation Water heating Water pre-heating Combustion air pre-heating Power generation Pre-heating incoming product Steam generation Water heating Water pre-heating Combustion air pre-heating Absorption cooling Dehumidification Feedwater pre-heating Space heating Evaporation

Heat recovery methods

Various methods for recovering waste heat are given below: 1. High-temperature heat recovery through recuperators and regenerators. 2. Load pre-heating. 3. Combustion air pre-heating. 4. Steam generation in waste heat boilers. 5. Feedwater pre-heating. 6. Heat recovery in condensing boilers. 7. Heat recovery from boiler blow down. 8. Cascade heating. 9. Heat recovery using absorption chillers. 10. Heat recovery using desiccant dehumidifiers.

6.5.1

High temperature heat recovery through recuperators and regenerators

Recuperators and regenerators are two methods of recovering heat from hightemperature processes, such as incineration or thermal oxidation. Recuperators

Industrial waste heat recovery 103

are essentially gas-to-gas heat exchangers, where as the gas coming into the process is pre-heated by the high-temperature gas going out of the process. In regenerators, refractory materials are utilised to absorb heat from the hightemperature gas and release it back to the process, thus reducing the combustion energy. Regenerators typically operate in alternate cycles between two chambers. Recuperators

Recuperators are gas-to-gas heat exchangers that are installed in the stack of the furnace. There are numerous designs, but all rely on tubes or plates to transfer heat from the outgoing exhaust gas to the incoming combustion air, while keeping the two streams from mixing. A simple configuration and low-cost recuperator is a metallic radiation recuperator, as shown in Fig. 6.3. The inner tube carries the hot exhaust gas while the external annulus carries the combustion air from the atmosphere to the air inlets of the furnace burners. The assembly is often designed to replace the exhaust stack. Waste gas

Hot air to process

Cold air inlet

Flue gas

Figure 6.3: Metallic radiation recuperator.

104 Industrial energy conservation

In a recuperator, heat exchange takes place between the flue gases and the air through metallic or ceramic walls. Duct or tubes carry the air for combustion to be pre-heated, the other side contains the waste heat stream. The simplest configuration for a recuperator is the metallic radiation recuperator, which consists of two concentric lengths of metal tubing. The inner tube carries the hot exhaust gases while the external annulus carries the combustion air from the atmosphere to the air inlets of the furnace burners. The hot gases are cooled by the incoming combustion air which now carries additional energy into the combustion chamber. This is energy which does not have to be supplied by the fuel; consequently, less fuel is burned for a given furnace loading. The saving in fuel also means a decrease in combustion air and therefore stack losses are decreased not only by lowering the stack gas temperatures but also by discharging smaller quantities of exhaust gas. The radiation recuperator gets its name from the fact that a substantial portion of the heat transfer from the hot gases to the surface of the inner tube takes place by radiative heat transfer. The cold air in the annuals, however, is almost transparent to infrared radiation so that only convection heat transfer takes place to the incoming air. As shown in the diagram, the two gas flows are usually parallel, although the configuration would be simpler and the heat transfer more efficient if the flows were opposed in direction (or counterflow). The reason for the use of parallel flow is that recuperators frequently serve the additional function of cooling the duct carrying away the exhaust gases and consequently extending its service life. A second common configuration for recuperators is called the tube type or convective recuperator. As seen in Fig. 6.4, the hot gases are carried through a number of parallel small diameter tubes, while the incoming air to be heated enters a shell surrounding the tubes and passes over the hot tubes one or more times in a direction normal to their axes. If the tubes are baffled to allow the gas to pass over them twice, the heat exchanger is termed a two-pass recuperator; if two baffles are used, a three-pass recuperator, etc. Although baffling increases both the cost of the exchanger and the pressure drop in the combustion air path, it increases the effectiveness of heat exchange. Shell and tube type recuperators are generally more compact and have a higher effectiveness than radiation recuperators, because of the larger heat transfer area made possible through the use of multiple tubes and multiple passes of the gases. Radiation/convective hybrid recuperator: For maximum effectiveness of heat transfer, combinations of radiation and convective designs are used, with the high-temperature radiation recuperator being first followed by convection type. These are more expensive than simple metallic radiation recuperators, but are less bulky.

Industrial waste heat recovery 105 Exhaust gases

Recuperator

Preheated combustion air

Burner

Furnace

Figure 6.4: Preheating combustion air through a recuperator.

6.5.2

Ceramic recuperator

The principal limitation on the heat recovery of metal recuperators is the reduced life of the liner at inlet temperatures exceeding 1100°C. In order to overcome the temperature limitations of metal recuperators, ceramic tube recuperators have been developed whose materials allow operation on the gas side to 1550°C and on the pre-heated air side to 815°C on a more or less practical basis. Early ceramic recuperators were built of tile and joined with furnace cement and thermal cycling caused cracking of joints and rapid deterioration of the tubes. Later developments introduced various kinds of short silicon carbide tubes which can be joined by flexible seals located in the air headers. Earlier designs had experienced leakage rates from 8 to 60%. The new designs are reported to last two years with air pre-heat temperatures as high as 700°C, with much lower leakage rates. Regenerators

Regenerators are essentially rechargeable storage batteries for heat that utilise an insulated container filled with metal or ceramic shapes capable of absorbing and storing large amounts of thermal energy. The regeneration which is preferable for large capacities has been very widely used in glass and steel melting furnaces. Important relations exist between the size of the regenerator, time between reversals, thickness of brick, conductivity of brick and heat

106 Industrial energy conservation

storage ratio of the brick. In a regenerator, the time between the reversals is an important aspect. Long periods would mean higher thermal storage and hence higher cost. Also long periods of reversal result in lower average temperature of pre-heat and consequently reduce fuel economy. Accumulation of dust and slagging on the surfaces reduce efficiency of the heat transfer as the furnace becomes old. Heat losses from the walls of the regenerator and air in leaks during the gas period and out-leaks during air period also reduces the heat transfer. Figure 6.5 shows a plate-type regenerator. A plate-type regenerator is constructed of alternate channels that separate adjacent flows of heated and heating gases by a thin wall of conducting metal. Although their use eliminates cross-contamination, they are bulkier, heavier and more expensive than recuperators. Cooled waste gas

Hot air to process Cool air inlet

Hot waste gas

Figure 6.5: Plate-type passive gas-to-gas regenerator.

For the process to operate without interruption, at least two regenerators are required; one provides energy to the combustion air while the other is recharging. Regenerators can operate at temperatures beyond the range of recuperators and at higher efficiency ratings. They are resistant to corrosion and fouling, but because of their back-and-forth switching to maintain continuous operation, they require more complex, more expensive flow control systems than recuperators. These passive air pre-heaters are used in low- and medium-temperature applications.

6.5.3

Load pre-heating

In general, there are direct and indirect heat recovery methods. Direct heat recovery implies directly pre-heating incoming product using the process waste heat. If the high-temperature exhaust fluid can be brought into contact with a

Industrial waste heat recovery 107

relatively cool incoming fluid, energy will be transferred to pre-heat the lowtemperature fluid and reduce the energy that finally escapes with the exhaust. Direct heat recovery to the product has the highest potential efficiency because it does not require any ‘carrier’ to return the energy to the product. It does, however, require a furnace or oven configuration that permits routing the stream of exhaust counter-flow to incoming product or materials.

6.5.4

Combustion air pre-heating

Two methods of combustion air pre-heating use the technologies described above under high-temperature heat recovery through recuperators and regenerators. A large amount of energy is required to heat combustion air from atmospheric temperature to combustion temperature. Pre-heating results in the burners needing less fuel to heat the incoming air to combustion temperature. The most common means of transferring flue gas energy to combustion air is to use a recuperator placed in the exhaust stack or ductwork. This strategy can recover a sizable percentage of the exhaust heat that would otherwise be lost to the atmosphere. Regenerators can be used for applications where cross-contamination cannot be tolerated. During part of the operating cycle, process exhaust gas flows through the regenerator, heating the storage medium. Once the medium becomes fully charged, the exhaust flow is shut off and cold combustion air enters the unit. As it passes through, the supply air extracts heat from the storage medium and rises in temperature before entering the burners. Figure 6.6 shows a regenerator used to pre-heat combustion air. Air

Exhaust Regenerators

Air Exhaust

Figure 6.6: Regenerator system for storing energy.

108 Industrial energy conservation

The operation cycles between a charge mode (top) and a discharge mode (bottom). Whether air pre-heating will be cost-effective is usually determined by the process temperature: 1. Processes at temperatures above 1600°F are generally good candidates. 2. Processes operating in the range of 1000°F to 1600°F may still produce cost-effective savings, but must be evaluated case by case. 3. Processes operating below 1000°F are typically not worth the cost of installing and maintaining the regenerator system. However, lowtemperature processes should still be evaluated for heat recovery potential. If the exhaust gas flow rate is high enough, energy savings may still be achievable.

6.5.5

Heat wheels

A heat wheel is finding increasing applications in low to medium temperature waste heat recovery systems. It is a sizable porous disk, fabricated with material having a fairly high heat capacity, which rotates between two side-by-side ducts: one a cold gas duct, the other a hot gas duct. The axis of the disk is located parallel to and on the partition between, the two ducts. As the disk slowly rotates, sensible heat (moisture that contains latent heat) is transferred to the disk by the hot air and, as the disk rotates, from the disk to the cold air. The overall efficiency of sensible heat transfer for this kind of regenerator can be as high as 85%. Heat wheels have been built as large as 21 metres in diameter with air capacities up to 1130 m3/min. A variation of the heat wheel is the rotary regenerator where the matrix is in a cylinder rotating across the waste gas and air streams. The heat or energy recovery wheel is a rotary gas heat regenerator, which can transfer heat from exhaust to incoming gases. Its main area of application is where heat exchange between large masses of air having small temperature differences is required. Heating and ventilation systems and recovery of heat from dryer exhaust air are typical applications.

6.5.6

Heat pipe

A heat pipe can transfer up to 100 times more thermal energy than copper, the best known conductor. In other words, heat pipe is a thermal energy absorbing and transferring system and have no moving parts and hence require minimum maintenance. The heat pipe comprises of three elements–a sealed container, a capillary wick structure and a working fluid. The capillary wick structure is integrally fabricated into the interior surface of the container tube and sealed under vacuum. Thermal energy applied to the external surface of the heat pipe is in equilibrium with its own vapour as the container tube is sealed under vacuum. Thermal energy applied to the external surface of the heat pipe causes

Industrial waste heat recovery 109

the working fluid near the surface to evaporate instantaneously. Vapour thus formed absorbs the latent heat of vapourisation and this part of the heat pipe becomes an evaporator region. The vapour then travels to the other end of the pipe where the thermal energy is removed causing the vapour to condense into liquid again, thereby giving up the latent heat of the condensation. This part of the heat pipe works as the condenser region. The condensed liquid then flows back to the evaporated region. Heat pipe is shown in Fig. 6.7. Vapourised fluid condensed and gives up heat

Heat in

Vapour

Heat out

Metal mesh wick acts as return path for liquid working fluid

Heat evaporators working fluid

Figure 6.7: Heat pipe.

Performance and advantage: The heat pipe exchanger (HPHE) is a lightweight compact heat recovery system. It virtually does not need mechanical maintenance, as there are no moving parts to wear out. It does not need input power for its operation and is free from cooling water and lubrication systems. It also lowers the fan horsepower requirement and increases the overall thermal efficiency of the system. The heat pipe heat recovery systems are capable of operating at 315°C. with 60% to 80% heat recovery capability. Typical application: The heat pipes are used in following industrial applications: 1. Process to space heating: The heat pipe heat exchanger transfers the thermal energy from process exhaust for building heating. The pre-heated air can be blended if required. The requirement of additional heating equipment to deliver heated make up air is drastically reduced or eliminated. 2. Process to process: The heat pipe heat exchangers recover waste thermal energy from the process exhaust and transfer this energy to the incoming process air. The incoming air thus become warm and can be used for the same process/other processes and reduces process energy consumption. 3. HVAC applications: (a) Cooling: Heat pipe heat exchangers precools the building make up air in summer and thus reduces the total tons of refrigeration, apart

110 Industrial energy conservation

from the operational saving of the cooling system. Thermal energy supplied is recovered from the cool exhaust and transferred to the hot supply make up air. (b) Heating: The above process is reversed during winter to pre-heat the make up air. The other applications in industries are: (i) Pre-heating of boiler combustion air. (ii) Recovery of waste heat from furnaces. (iii) Reheating of fresh air for hot air driers. (iv) Recovery of waste heat from catalytic deodorising equipment. (v) Reuse of furnace waste heat as heat source for other oven. (vi) Cooling of closed rooms with outside air. (vii) Pre-heating of boiler feed water with waste heat recovery from flue gases in the heat pipe economisers. (viii) Drying, curing and baking ovens. (ix) Waste steam reclamation. (x) Brick kilns (secondary recovery). (xi) Reverberatory furnaces (secondary recovery). (xii) Heating, ventilating and air-conditioning systems.

6.5.7

Thermal oxidising/combustion emission control

Many chemical facilities need to treat hazardous waste gas from their process lines. A thermal oxidiser is used to decompose hazardous gases before releasing them to the atmosphere. In a thermal oxidiser, the hazardous gas is passed through an oxidising burner (oxidiser) at a controlled and optimal temperature, typically above 1500°F, at which the Volatile Organic Compounds (VOCs) are converted into safe gases such as water vapour and carbon dioxide. Because thermal oxidisers operate at such high temperatures, these systems have significant heat recovery savings potential. The simplest technique for meeting regulatory VOC reduction requirements would be to heat the gas in an after burner to more than 1500°F and not recover any heat. Without heat recovery, however, the operation of an afterburner is cost prohibitive unless the gas stream is very rich in VOCs and has a low flow rate. Alternatively, thermal oxidiser efficiency can be optimised by utilising recuperative or regenerative types of heat recovery methods. A recuperative thermal oxidiser uses a gas-to-gas heat exchanger to recover some of the energy from the high-temperature exhaust gas. Regenerative thermal oxidisers are more energy efficient, reaching thermal efficiencies of up to 95%, while recuperative types typically achieve efficiencies of up to 80%. However, the capital cost for regenerative types is higher than for recuperative types. When

Industrial waste heat recovery 111

examining the appropriate type of thermal oxidiser, some considerations are the gas stream volume, flow, temperature and moisture content; the VOC concentrations; and the desired VOC destruction efficiency. Processes with higher gas flow rates and lower VOC concentrations, for example, are more suitably managed with a regenerative thermal oxidiser. An alternative type of recuperative or regenerative oxidiser is a catalytic oxidiser, in which a catalyst reduces the temperature required to destroy VOCs from around 1500°F to around 800°F. Because the catalyst accelerates VOC destruction and lowers the required operating temperature, a catalytic oxidiser can have a 20% to 30% gain in efficiency over thermal oxidisers.

6.5.8

Steam generation in waste heat boilers

While conventional boilers are fired by fossil fuel, waste heat boilers utilise an exhaust gas stream from external sources to heat the water instead of burning fuel in the burners. Figure 6.8 shows a waste heat boiler for steam generation. Waste heat boilers may be horizontal or vertical shell boilers or water tube boilers, where hot exhaust gases are passed over parallel tubes containing water. Steam out Warm waste gas out

Feedwater in

Hot waste gas in

Figure 6.8: Waste heat steam boiler.

112 Industrial energy conservation

The water is vapourised and collected in a steam drum. These boilers can be designed to work with individual applications ranging from gas turbine exhaust to reciprocating engines, incinerators and furnaces. Waste heat boilers can be used with most furnace applications, as long as the exhaust gases contain sufficient usable heat to produce steam or hot water at the condition required. For steam generation, the exhaust gas should preferably be above 750°F. For water heating, the exhaust gas should be about 400°F or higher. When the heat source is in the low-temperature range, boilers become bulky. The use of finned tubes extends the heat transfer areas and allows a more compact size. Waste heat boilers may be an option for facilities looking for additional steam capacity; however, these boilers only generate steam coincident with the process furnace operation. It should be noted too that the physical size of a waste heat boiler may be larger than that of a conventional boiler because the furnace exhaust gas temperature is lower than the flame temperature used in conventional systems. This may pose a disadvantage in retrofits where space is limited. Boilers using exhaust gas from engines fired by heavy fuel oil must be carefully designed, because the exhaust gas may contain soot, which can form an insulation layer on the tubes and shells of the boiler. When this happens, heat transfer is impeded and the efficiency of the system can drop dramatically. Therefore, the gas exit temperature must be maintained at a predetermined level to prevent dew point from being reached and soot from accumulating inside the boiler. The exhaust gas capacities of waste heat boilers can range from less than a thousand to almost a million cubic feet per minute. If the waste heat in the exhaust gas is insufficient to generate the required process steam in an application, it may be necessary to add auxiliary fuel burners to the waste heat boiler, or to add an afterburner. Because waste heat boilers do not use burners, they are less expensive to install and operate than a new combustion boiler. However, for an industrial facility to benefit from a waste heat boiler, the waste heat source must coincide with the steam demand that would otherwise be met with a combustion boiler.

6.5.9

Economiser

In case of boiler system, economiser can be provided to utilise the flue gas heat for pre-heating the boiler feed water. On the other hand, in an air preheater, the waste heat is used to heat combustion air. In both the cases, there is a corresponding reduction in the fuel requirements of the boiler. A economiser is shown in Figure 6.9. For every 22°C reduction in flue gas temperature by passing through an economiser or a pre-heater, there is 1% saving of fuel in the boiler. In other

Industrial waste heat recovery 113 Flue gas outlet

Water inlet

Water inlet

Economiser coils

Flue gas inlet

Figure 6.9: Economiser.

words, for every 60°C rise in feed water temperature through an economiser, or 20°C rise in combustion air temperature through an air pre-heater, there is 1% saving of fuel in the boiler. Pre-heating boiler feedwater offers the following primary advantages: 1. Reduced fuel usage and increased boiler efficiency. 2. Reduced emissions due to less fuel use. 3. Quicker response to load changes. 4. Potentially increased steam production. 5. Potentially longer boiler life. Economisers are available in two types of designs: water-tube and firetube. In a firetube economiser, flue gas flows inside the tubes heating the surrounding water. This type of economiser has a large water reservoir, which makes it extremely resistant to steaming and eliminates the need for expensive feedwater-proportioning systems. For boilers larger than 400 boiler horsepower or 13.4 MMBtu/hr (1 Boiler HP is about 33.5 MBtu/hr), a water-tube type economiser can be used. In a water-tube economiser like that, feedwater flows through a tube bundle that is heated by the surrounding flue gas. In many cases water-tube economisers can be fit directly into the exhaust stack, allowing cost-effective installation. When implementing a feedwater economiser, special consideration must be given to ensure that flue gas is not cooled beyond the low-temperature limit. The lowest temperature to which flue gasses can be cooled depends on the type of fuel being used: 250°F for natural gas, 300°F for coal and low sulphur content fuel oils and 350°F for high sulphur fuel oils. Cooling below these limits can result in condensation and possible corrosion of the heat exchanger and the exhaust stack.

114 Industrial energy conservation

6.5.10

Waste heat boilers

Waste heat boilers are ordinarily water tube boilers in which the hot exhaust gases from gas turbines, incinerators, etc., pass over a number of parallel tubes containing water. The water is vapourised in the tubes and collected in a steam drum from which it is drawn off for use as heating or processing steam. Because the exhaust gases are usually in the medium temperature range and in order to conserve space, a more compact boiler can be produced if the water tubes are finned in order to increase the effective heat transfer area on the gas side. The pressure at which the steam is generated and the rate of steam production depends on the temperature of waste heat. The pressure of a pure vapour in the presence of its liquid is a function of the temperature of the liquid from which it is evaporated. The steam tables tabulate this relationship between saturation pressure and temperature. If the waste heat in the exhaust gases is insufficient for generating the required amount of process steam, auxiliary burners which burn fuel in the waste heat boiler or an afterburner in the exhaust gases flue are added. Waste heat boilers are built in capacities from 25 m3 almost 30,000 m3/min. of exhaust gas. A condensing boiler is designed to resist corrosion and allow the flue gas to be cooled to its condensing temperature, releasing the latent heat contained in the water vapour. Approximately 10% of the energy content of natural gas is used in the latent heat of vapourisation. This latent heat content is not released unless the combustion gas is condensed. Under proper operating conditions, condensing boilers can be approximately 10% more efficient than efficient non-condensing boilers. Inside the condensing boiler exhaust section, heat is transferred from the flue gas through an enlarged heat exchanger surface to pre-heat the boiler feedwater. In order to effectively extract the latent heat contained in the flue gas water vapour, the boiler inlet water temperature must be low enough to cool the flue gas to condensing temperature. Condensing boilers need to be operated at inlet water temperatures below 140°F.

6.5.11

Heat recovery from boiler blow down

Boiler blow down involves either periodic or continuous removal of water from a steam boiler in order to remove accumulated dissolved solids and/or sludge, which can have damaging effects on boiler efficiency and maintenance. However, boiler blow down wastes energy because the liquid blown down is at about the same temperature as the steam produced. Two methods are typically employed for recovering energy lost from boiler blow down and both are often incorporated in one system. In the first method, the saturated liquid high-pressure blow down is discharged into a relatively low-pressure receiver, or flash vessel. In the receiver, a portion of the liquid flashes to steam, which

Industrial waste heat recovery 115

can be used either in a low-pressure steam system or in the deaerator to preheat the boiler feedwater. Figure 6.10 shows a flash steam vessel recovering steam from condensate lines. By removing steam from the condensate system, flash steam vessels provide an efficient source of steam to low-pressure end uses. For example, 250°F condensate has a saturation pressure of about 15 psig. It can be used in low-pressure steam applications such as space heating and pre-heating. Saturated vapour supply

Low-pressure flash vessel

Saturated vapour Level controller

High-pressure condensate Steam trap

Saturated liquid Condensate discharge

Figure 6.10: Flash vessel steam recovery.

The second method of boiler blow down heat recovery takes advantage of the significant temperature difference that exists between the saturated liquid from the flash vessel and the makeup water. The remaining liquid blow down is piped through a heat exchanger to pre-heat the makeup water before entering the deaerator. A combined flash steam and residual blow down heat recovery system, can recover up to 90% of heat energy that would otherwise be wasted. Larger energy savings occur with high-pressure boilers.

6.5.12

Heat cascading

Heat cascading describes a broader application of recycling heat for external uses. Waste heat from a primary process may still contain enough energy to operate a secondary process, as long as its temperature is high enough to drive the energy to its intended destination. Cascading heat from preceding processes can reduce the amount of energy required in subsequent processes. Some examples include: Water heating with waste heat boilers, drying or evaporating using exhaust gas from high-temperature furnaces, using multipleeffect evaporators in food processes and using cooling tower water for space

116 Industrial energy conservation

heating. The goal of cascading heat is to use a continuous flow of waste gas through process after process, serving many heat needs in the facility, until no usable heat is left before the gas finally exits. In a heat cascading process, heat is transferred between sequentially smaller temperature differentials or steps, rather than a single large temperature differential—enabling efficient utilisation of thermal energy. In designing heat cascading, it is necessary that the heating load absorbing the waste heat be available during the periods of waste heat generation; otherwise, the waste heat may be useless, regardless of its quantity and quality. When source and load cannot be synchronised, either another heat load must be found, or an auxiliary heat source needs to be available to carry the load. Tying two processes together using cascading heat requires more than just the correct temperatures and heat flows. To make the system operate effectively, the logistics must also be set up correctly. For example, if a chemical plant needs a constant supply of heated water for a specific process and the water heater is totally dependent on the exhaust from an oven, then the oven must run continuously. If this is not feasible, an auxiliary burner can be installed on the water heater to carry the load when the primary process is not running. On the other hand, as long as the oven is operating there will be a supply of hot water, whether it is needed for the process or not. Another key consideration is the placement of equipment. The closer the proximity of primary and secondary processes, the better. Carrying exhaust gas through long runs of ductwork can create an expensive and difficult-to-maintain infrastructure and the efficiency of energy recovery will be compromised by the heat losses between the two processes. This is of less concern if the primary energy source is liquid or hot oil because these heat transfer mediums can carry energy over greater distances.

6.5.13

Heat recovery using absorption chillers

Combined heat and power (CHP) plants are being utilised in many facilities. In particular they are becoming more common for facilities with large cooling loads and those with balanced simultaneous demands for electric power and heating. A CHP plant generates electrical power using an internal combustion engine, gas turbine, microturbine, or fuel cell. The waste heat from the power generator can be used for process heating and cooling through a waste heat recovery loop. Applications include space heating, absorption chillers, dehumidifiers, heat pumps, heat wheels and other devices. Absorption chillers use heat rather than mechanical energy to provide cooling. A thermal compressor consists of an absorber, generator, pump and throttling device. In the evaporator, the refrigerant evaporates and extracts heat from the building. The refrigerant vapour then is absorbed by the absorbent.

Industrial waste heat recovery 117

The combined fluids go to the generator, where heat is provided from a waste steam heat source to separate refrigerant from the absorbent. The refrigerant then goes to the condenser to be cooled back down to a liquid, while the absorbent is pumped back to the absorber. The cooled refrigerant is released through an expansion valve into the evaporator and the cycle repeats. Low-pressure, steam-driven absorption chillers are available in capacities ranging from 100 to 1500 tons. Figure 6.11 illustrates an absorption chiller cycle. Controller no. 1

Controller no. 2

Hot water Condenser

Concentrator

Cooling lower by-pass

Chilled water

From cooling tower

Heat exchanger

To cooling tower

Evaporator

Absorber TT TT

Figure 6.11: Absorption chiller cycle.

Absorption chillers generally have lower coefficients of performance (chiller load/energy input) than traditional chillers; however, they can substantially reduce operating costs because they are powered by using waste heat. Considering the energy efficiency from the source to the point of use, a waste heat absorption chiller can be comparable to a large watercooled electric chiller plant. Single-effect absorption chillers have a coefficient of performance of 0.7; double-effect absorption chillers are about 40% more efficient. In an absorption chiller application in a CHP plant, the waste heat from the electrical generator is captured by a waste heat recovery boiler. The boiler provides steam for processes and also drives an absorption chiller that provides cooling to the facility. Considering the outputs of electricity, heating and cooling,

118 Industrial energy conservation

the fuel efficiency of CHP plants can be as high as 60% to 80%, compared with the 30% to 40% from conventional electrical generators.

6.5.14

Heat recovery using a desiccant dehumidifier

A desiccant dehumidifier uses a drying agent, or sorbent, to remove water from the air used to condition building space. Desiccants can run off the waste heat from distributed generation technologies, with system efficiency approaching 80% in CHP mode. The desiccant process involves exposing the desiccant material, such as silica gel, to a moisture-laden process air stream. Once the moisture is absorbed from this stream, another stream of regenerated air removes the moisture from the desiccant. A solid desiccant dehumidifier is most commonly placed on the surface of a corrugated matrix in a wheel that rotates between the process and regeneration air streams. On the process side, the desiccant removes moisture from the air while releasing heat during the sorption process. As the wheel rotates onto the regeneration side, natural gas, waste heat or solar energy can be used to regenerate the desiccant material. Humidification applications are found in the chemical manufacturing industry where control of ambient temperature and moisture content are critical for product quality.

6.6

Cost considerations

In general, waste heat recovery methods can improve performance—i.e., increase the overall efficiency of a process heating system by 5% to 30%. Table 6.3 provides a summary of the cost-saving potential and expected simple payback periods of waste heat recovery methods and applications described above. Table 6.3: Summary of waste heat recovery methods. Methods

Waste sources

High-temperature heat recovery through recuperators/ regenerators Load pre-heating

Exhaust gases H,M from incineration or thermal oxidation processes Exhaust gas from H,M,L fuel-fired burner, after burner Exhaust gas from H,M fuel-fired burner, after burner

Combustion air pre-heating

Temp range

Applications

Savings potential

Simple payback

Incoming product pre-heating

20–40%

24–48 months

Incoming product pre-heating Combustion air pre-heating

10–25%

6–24 months

10–30%

(Contd…)

Industrial waste heat recovery 119 Methods

Waste sources

Temp range

Waste heat boiler Exhaust gas from H,M gas turbines, reciprocating engines, incinerators, furnaces Feedwater Exhaust gas from H,M,L pre-heating fuel-fired burner Heat recovery through boiler blow down

Steam boiler blow down

H,M,L

Heat cascading Absorption chiller Desiccant Dehumidifier

Various H,M,L Waste steam from L gas turbines Waste steam from L gas turbines

Applications

Savings potential

Simple payback

Steam generation, Water heating

5–20%

6–24 months

Feedwater, make-up water pre-heating Steam generation, Feedwater pre heating Various Absorption cooling Air dehumidification and/or cooling

2–20%

6–24 months

Up to 90%

6–12 months

5–20%

Generally the payback period is a measure of the cost effectiveness of a project. The payback period is affected by the service life of the equipment installed. Heat exchangers generally have a service life of up to 20 to 25 years, although special applications or harsh environments can shorten that life. Waste heat boilers and turbines have a service life of about 30 years. A longer payback period is generally acceptable for projects having long-life equipment, but a payback period of three to five years is considered reasonable. The cost of a heat exchanger varies with the temperature range to which it would apply: the higher the temperature range, the higher the cost, due to higher material cost and additional engineering requirements. However, because a high-temperature source provides high-quality waste heat, the cost per unit of energy transferred can be less. Choosing appropriate heat exchange equipment is the key to high cost-effectiveness.

6.6.1

Heat exchangers

Shell and tube heat exchanger: When the medium containing waste heat is a liquid or a vapour which heats another liquid, then the shell and tube heat exchanger must be used since both paths must be sealed to contain the pressures of their respective fluids. The shell contains the tube bundle and usually internal baffles, to direct the fluid in the shell over the tubes in multiple passes. The

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shell is inherently weaker than the tubes so that the higher-pressure fluid is circulated in the tubes while the lower pressure fluid flows through the shell. When a vapour contains the waste heat, it usually condenses, giving up its latent heat to the liquid being heated. In this application, the vapour is almost invariably contained within the shell. If the reverse is attempted, the condensation of vapours within small diameter parallel tubes causes flow instabilities. Tube and shell heat exchangers are available in a wide range of standard sizes with many combinations of materials for the tubes and shells. A shell and tube heat exchanger is illustrated in Fig. 6.12. Rear header

Shell

Bundle

Front header

Figure 6.12: Shell and tube heat exchanger.

Typical applications of shell and tube heat exchangers include heating liquids with the heat contained by condensates from refrigeration and air-conditioning systems; condensate from process steam; coolants from furnace doors, grates and pipe supports; coolants from engines, air compressors, bearings and lubricants and the condensates from distillation processes. The cost of heat exchange surfaces is a major cost factor when the temperature differences are not large. One way of meeting this problem is the plate type heat exchanger, which consists of a series of separate parallel plates forming thin flow pass. Each plate is separated from the next by gaskets and the hot stream passes in parallel through alternative plates whilst the liquid to be heated passes in parallel between the hot plates. To improve heat transfer the plates are corrugated. Hot liquid passing through a bottom port in the head is permitted to pass upwards between every second plate while cold liquid at the top of the head is permitted to pass downwards between the odd plates. When the directions of hot and cold fluids are opposite, the arrangement is described as counter current. Typical industrial applications are: 1. Pasteurisation section in milk packaging plant. 2. Evaporation plants in food industry.

Industrial waste heat recovery 121

Run around coil exchanger: It is quite similar in principle to the heat pipe exchanger. The heat from hot fluid is transferred to the colder fluid via an intermediate fluid known as the heat transfer fluid. One coil of this closed loop is installed in the hot stream while the other is in the cold stream. Circulation of this fluid is maintained by means of a circulating pump. It is more useful when the hot land cold fluids are located far away from each other and are not easily accessible. Typical industrial applications are heat recovery from ventilation, air conditioning and low temperature heat recovery.

6.6.2

Heat pumps

In the various commercial options previously discussed, we find waste heat being transferred from a hot fluid to a fluid at a lower temperature. Heat must flow spontaneously ‘downhill’, that is from a system at high temperature to one at a lower temperature. When energy is repeatedly transferred or transformed, it becomes less and less available for use. Eventually that energy has such low intensity (resides in a medium at such low temperature) that it is no longer available at all to perform a useful function. It has been taken as a general rule of thumb in industrial operations that fluids with temperatures less than 120°C (or better, 150°C to provide a safe margin), as limit for waste heat recovery because of the risk of condensation of corrosive liquids. However, as fuel costs continue to rise, even such waste heat can be used economically for space heating and other low temperature applications. It is possible to reverse the direction of spontaneous energy flow by the use of a thermodynamic system known as a heat pump. The majority of heat pumps work on the principle of the vapour compression cycle. In this cycle, the circulating substance is physically separated from the source (waste heat, with a temperature of Tin) and user (heat to be used in the process, Tout) streams and is reused in a cyclical fashion, therefore called ‘closed cycle’. In the heat pump, the following processes take place: 1. In the evaporator the heat is extracted from the heat source to boil the circulating substance. 2. The circulating substance is compressed by the compressor, raising its pressure and temperature. The low temperature vapour is compressed by a compressor, which requires external work. The work done on the vapour raises its pressure and temperature to a level where its energy becomes available for use. 3. The heat is delivered to the condenser. 4. The pressure of the circulating substance (working fluid) is reduced back to the evaporator condition in the throttling valve, where the cycle repeats.

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The heat pump can be developed as a space heating system where low temperature energy from the ambient air, water or earth is raised to heating system temperatures by doing compression work with an electric motor-driven compressor. The heat pumps have the ability to upgrade heat to a value more than twice that of the energy consumed by the device. The potential for application of heat pump is growing and number of industries have been benefited by recovering low grade waste heat by upgrading it and using it in the main process stream. Heat pump applications are most promising when both the heating and cooling capabilities can be used in combination. One such example of this is a plastics factory where chilled water from a heat is used to cool injection-moulding machines whilst the heat output from the heat pump is used to provide factory or office heating. Other examples of heat pump installation include product drying, maintaining dry atmosphere for storage and drying compressed air.

6.6.3

Thermocompressor

In many cases, very low pressure steam are reused as water after condensation for lack of any better option of reuse. In many cases it becomes feasible to compress this low pressure steam by very high pressure steam and reuse it as a medium pressure steam. The major energy in steam, is in its latent heat value and thus thermocompressing would give a large improvement in waste heat recovery. The thermocompressor is a simple equipment with a nozzle where HP steam is accelerated into a high velocity fluid. This entrains the LP steam by momentum transfer and then recompresses in a divergent venturi. Thermocompressor is shown in Figure 6.13. Discharge steam M.P.

Motive steam H.P.

Suction steam L.P.

Figure 6.13: Thermocompressor.

It is typically used in evaporators where the boiling steam is recompressed and used as heating steam.

Section II Energy conservation in electrical and telecom industries 7. Energy conservation in electrical industries

125

8. Energy efficiency technologies for thermal power plants

141

9. Energy efficient motors, compressors and refrigeration systems

185

10. Energy conservation in telecom sector

213

Energy conservation in electrical industries 125

7 Energy conservation in electrical industries

7.1

Introduction

Electrical energy is universally accepted as an essential commodity for human beings. Energy is the prime mover of economic growth and is vital to the sustenance of a modern economy. Future economic growth crucially depends on the long-term availability of energy from sources. Areas of application of energy conservation are power generating station, transmission and distribution system, consumers premises. Steps are to be taken to enhance the performance efficiency of generating stations. Energy conservation technology adopted in transmission and distribution system may reduce energy losses, to the tune of 35% of total losses in power system. Acceptance of energy conservation technology will enhances the performance efficiency of electrical apparatus used by end users. Implementation of energy conservation technology will lead to energy saving which means increasing generation of energy with available source. Energy is the primary and the most universal measures of all kinds of work by human being and nature. Electrical energy is proved to be an ideal energy in all sorts of energy available in nature.

7.2

Energy conservation in electrical systems

Energy Conservation (EC) means reduction in growth of energy consumption and is measured in physical terms. Energy conservation is the practice of decreasing the quantity of energy used while achieving a similar outcome of end use. This practice may result in increase of financial capital, environmental value, national security, personal security and human comfort. Energy conservation also means reduction or elimination of unnecessary energy used and wasted.

7.2.1

Area of application of energy conservation

Electrical system is a net work in which power is generated using non-renewable sources by conventional method and then transmitted over longer distances at high voltage levels to load centers where it is used for various energy conversion process. End user sector are identified as three major areas–power generating station, transmission and distribution systems, and energy consumers. Consumers are further classified as domestic, commercial and industrial consumers.

126 Industrial energy conservation

EC in power generating station: Power sector is an essential service and in the basis of industrialisation and agriculture. It plays a vital role in the socioeconomic development. As the bulk of power generation, about 75%, is by thermal power stations, improvement in their performance would lead to increased availability and large scale energy conservation. Since the Plant Load Factor (PLF) has become a common yardstick for monitoring the availability of power stations, several efforts have been made to improve PLF. It has been estimated that one percentage point improvement in the overall PLF of thermal power sector will give additional generating capacity to the extent of 500 MW in a much shorter time and cost. However, the experience has shown that this alone has not been sufficient to bridge the gap between demand and supply. The PLF which over the years is being recognised as an index of plant performance, is not very appropriate as it itself depends upon the availability and besides other causes. The overall Availability Factor (OAF) will be a better index for comparing plant performance. Efforts are therefore required to secure operational efficiency of thermal power stations as well by identifying the various loss areas and taking appropriate actions, so as to maximise the power generation and loss make available the saved energy to the consumers. Therefore, improving efficiency of these thermal power stations in addition to increasing their PLF has become the need of the hour to bring the cost and maximise the generation levels. Technical losses in T&D system: Power losses occurring in T&D sector due to imperfection in technical aspect which indirectly cause loss of investment in this sector, are technical losses. These technical losses are due to inadequate system planning, improper voltage and also due to poor power factor, etc. Commercial losses: Commercial losses are those, which are directly responsible for wastage of money invested in transmission and distribution system. These losses are effects of inefficient management, improper maintenance, etc. Corruption is also the main reason contributing to the commercial losses. Metering losses include loss due to inadequate billings, faulty metering, overuse, because of meters not working properly and outright theft. Many of the domestic energy meters fail because of poor quality of the equipment.

7.3

Energy conservation techniques

7.3.1

EC techniques in transformers

1. Optimisation of loading of transformer: (a) By proper location of transformer preferably close to the load center, considering other features like centralised control, operational flexibility, etc. This will bring down the distribution loss in cables.

Energy conservation in electrical industries 127

(b) Maintaining maximum efficiency to occur at 38% loading [as recommended by Rural Electrification Corporation Limited (REC)], the overall efficiency of transformer can be increased and its losses can be reduced. (c) Under fluctuating load condition, more than one transformer is used in parallel operation of transformers to share the load and can be operated close to the maximum efficiency range. 2. By improvisation in design and material of transformer: (a) To reduce load losses in transformer, use thicker conductors so that resistance of conductor reduces and load loss also reduces. (b) To reduce core losses use superior quality or improved grades of Cold Rolled Grain Oriented (CRGO) laminations. 3. Replacing by energy efficient transformers: (a) By using energy efficient transformers, efficiency improves to 95–97%. (b) By using amorphous transformers, efficiency improves to 97–98.5%. (c) By using epoxy resin cast/encapsulated dry type transformer, efficiency improves to 93–97%. Transformer losses can be divided into two main components: No-load losses and Load losses. These types of losses are common to all types of transformers, regardless of transformer application or power rating. There are, however, two other types of losses; extra losses created by harmonics and losses which may apply particularly to larger transformers– cooling or auxiliary losses, caused by the use of cooling equipment like fans and pumps. No-load losses

These losses occur in the transformer core whenever the transformer is energised (even when the secondary circuit is open). They are also called iron losses or core losses and are constant. They are composed of: 1. Hysteresis losses, caused by the frictional movement of magnetic domains in the core laminations being magnetised and demagnetised by alternation of the magnetic field. These losses depend on the type of material used to build a core. Silicon steel has much lower hysteresis than normal steel but amorphous metal has much better performance than silicon steel. Nowadays hysteresis losses can be reduced by material processing such as cold rolling, laser treatment or grain orientation. Hysteresis losses are usually responsible for more than a half of total no-load losses (~50% to ~70%).

128 Industrial energy conservation

2. Eddy current losses, caused by varying magnetic fields inducing eddy currents in the laminations and thus generating heat. These losses can be reduced by building the core from thin laminated sheets insulated from each other by a thin varnish layer to reduce eddy currents. Eddy current losses nowadays usually account for 30–50% of total no-load losses. When assessing efforts in improving distribution transformer efficiency, the biggest progress has been achieved in reduction of these losses. 3. There are also marginal stray and dielectric losses which occur in the transformer core, accounting usually for no more than 1% of total noload losses. Load losses

These losses are commonly called copper losses or short circuit losses. Load losses vary according to the transformer loading. They are composed of: 1. Ohmic heat loss: Ohmic heat loss, sometimes referred to as copper loss, since this resistive component of load loss dominates. This loss occurs in transformer windings and is caused by the resistance of the conductor. The magnitude of these losses increases with the square of the load current and is proportional to the resistance of the winding. It can be reduced by increasing the cross sectional area of conductor or by reducing the winding length. Using copper as the conductor maintains the balance between weight, size, cost and resistance; adding an additional amount to increase conductor diameter, consistent with other design constraints, reduces losses. 2. Conductor eddy current losses: Eddy currents, due to magnetic fields caused by alternating current, also occur in the windings. Reducing the cross-section of the conductor reduces eddy currents, so stranded conductors are used to achieve the required low resistance while controlling eddy current loss. Effectively, this means that the ‘winding’ is made up of a number of parallel windings. Since each of these windings would experience a slightly different flux, the voltage developed by each would be slightly different and connecting the ends would result in circulating currents which would contribute to loss. This is avoided by the use of Continuously Transposed Conductor (CTC), in which the strands are frequently transposed to average the flux differences and equalise the voltage.

Energy conservation in electrical industries 129

Auxiliary losses

These losses are caused by using energy to run cooling fans or pumps which help to cool larger transformers. Extra losses due to harmonics and reactive power This category of losses includes those extra losses which are caused by reactive power and harmonics. The reactive component of the load current generates a real loss even though it makes no contribution to useful load power. Low power factor loads should be avoided to reduce losses related to reactive power. Power losses due to eddy currents depend on the square of frequency so the presence of harmonic frequencies which are higher than normal 50 Hz frequency cause extra losses in the core and winding. Extra losses due to harmonics

Non-linear loads, such as power electronic devices, such as variable speed drives on motor systems, computers, UPS systems, TV sets and compact fluorescent lamps, cause harmonic currents on the network. Harmonic voltages are generated in the impedance of the network by the harmonic load currents. Harmonics increase both load and no-load losses due to increased skin effect, eddy current, stray and hysteresis losses. The most important of these losses is that due to eddy current losses in the winding; it can be very large and consequently most calculation models ignore the other harmonic induced losses. The precise impact of a harmonic current on load loss depends on the harmonic frequency and the way the transformer is designed. In general, the eddy current loss increases by the square of the frequency and the square of the load current. So, if the load current contained 20% fifth harmonic, the eddy current loss due to the harmonic current component would be 5 × 5 × 0.2 × 0.2 multiplied by the eddy current loss at the fundamental frequency–meaning that the eddy current loss would have doubled. In a transformer that is heavily loaded with harmonic currents, the excess loss can cause high temperature at some locations in the windings. This can seriously reduce the life span of the transformer and even cause immediate damage and sometimes fire.

7.3.2

Energy efficient transformers

Most energy loss in dry-type transformers occurs through heat or vibration from the core. The new high-efficiency transformers minimise these losses. The conventional transformer is made up of a silicon alloyed iron (grain oriented) core. The iron loss of any transformer depends on the type of core used in the transformer. However the latest technology is to use amorphous

130 Industrial energy conservation

material - a metallic glass alloy for the core. The expected reduction in energy loss over conventional (Si Fe core) transformers is roughly around 70%, which is quite significant. By using an amorphous core- with unique physical and magnetic properties- these new type of transformers have increased efficiencies even at low loads–98.5% efficiency at 35% load. Electrical distribution transformers made with amorphous metal cores provide excellent opportunity to conserve energy right from the installation. Though these transformers are a little costlier than conventional iron core transformers, the overall benefit towards energy savings will compensate for the higher initial investment. At present amorphous metal core transformers are available up to 1600 kVA.

7.3.3

Electronic ballast

Role of ballast

In an electric circuit the ballast acts as a stabiliser. Fluorescent lamp is an electric discharge lamp. The two electrodes are separated inside a tube with no apparent connection between them. When sufficient voltage is impressed on these electrodes, electrons are driven from one electrode and attracted to the other. The current flow takes place through an atmosphere of low pressure mercury vapour. Since the fluorescent lamps cannot produce light by direct connection to the power source, they need an ancillary circuit and device to get started and remain illuminated. The auxiliary circuit housed in a casing is known as ballast. Conventional vs electronic ballasts

The conventional ballasts make use of the kick caused by sudden physical disruption of current in an inductive circuit to produce the high voltage required for starting the lamp and then rely on reactive voltage drop in the ballast to reduce the voltage applied across the lamp. On account of the mechanical switch (starter) and low resistance of filament when cold the uncontrolled filament current, generally tend to go beyond the limits specified by Indian standard specifications. With high values of current and flux densities the operational losses and temperature rise are on the higher side in conventional choke. The high frequency electronic ballast overcomes the above drawbacks. The basic functions of electronic ballast are: 1. To ignite the lamp. 2. To stabilise the gas discharge. 3. To supply the power to the lamp.

Energy conservation in electrical industries 131

The electronic ballasts make use of modern power semi-conductor devices for their operation. The circuit components form a tuned circuit to deliver power to the lamp at a high resonant frequency (in the vicinity of 25 kHz) and voltage is regulated through an inbuilt feedback mechanism. It is now well established that the fluorescent lamp efficiency in the kHz range is higher than those attainable at low frequencies. At lower frequencies (50 or 60 Hz), the electron density in the lamp is proportional to the instantaneous value of the current because the ionisation state in the tube is able to follow the instantaneous variations in the current. At higher frequencies (kHz range), the ionisation state cannot follow the instantaneous variations of the current and hence the ionisation density is approximately constant, proportional to the RMS (Root Mean Square) value of the current. Another significant benefit resulting from this phenomenon is the absence of stroboscopic effect, thereby significantly improving the quality of light output. One of largest advantages of an electronic ballast is the enormous energy savings it provides. This is achieved in two ways. The first is its amasingly low internal core loss, quite unlike old fashioned magnetic ballasts; and second is increased light output due to the excitation of the lamp phosphorus with high frequency. If the period of frequency of excitation is smaller than the light retention time constant for the gas in the lamp, the gas will stay ionised and, therefore, produce light continuously. This phenomenon along with continued persistence of the phosphorus at high frequency will improve light output from 8 to 12%. This is possible only with high frequency electronic ballast.

7.3.4

Adjustable-speed drive

Adjustable Speed Drive (ASD) or Variable Speed Drive (VSD) describes equipment used to control the speed of machinery. Many industrial processes such as assembly lines must operate at different speeds for different products. Where process conditions demand adjustment of flow from a pump or fan, varying the speed of the drive may save energy compared with other techniques for flow control. Where speeds may be selected from several different pre-set ranges, usually the drive is said to be at adjustable speed. If the output speed can be changed without steps over a range, the drive is usually referred to as variable speed. Adjustable and variable speed drives may be purely mechanical (termed variators), electromechanical, hydraulic, or electronic. Saving energy by using efficient adjustable speed drives: Some adjustable speed driven applications use less energy than fixed-speed operated loads, variable-torque centrifugal fan and pump loads are the world’s most energyintensive.

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Since most of the energy used for such fan and pump loads is currently derived by fixed-speed machines, use of efficient adjustable speed drives for these loads in retrofitted or new applications offers the most future energy savings potential. For example, when a fan is driven directly by a fixed-speed motor, the airflow is invariably higher than it needs to be. Airflow can be regulated using a damper, but it is more efficient to directly regulate fan motor speed. According to affinity laws, motor-regulated reduction of fan speed to 50% of full speed can thus result in a power consumption drop to about 12.5% of full power.

7.4

Diesel generator (DG)

DG set is a combination of a diesel engine and an alternator. Diesel engine is the prime mover which drives an alternator to produce electrical energy. In the diesel engine, air is drawn into the cylinder and is compressed to a high ratio (14:1–25:1). A metered quantity of diesel fuel is then injected into the cylinder which ignites spontaneously because of the high temperature. Hence, the diesel engine is also known as Compression Ignition (CI) engine. DG set can be classified according to cycle type as: two stroke and four stroke. However, the bulk of IC engines use the four stroke cycle. Types of fuel or energy used in DG sets are furnace oil and diesel.

7.4.1

Design and operation

A diesel generating set should be considered as a system since its successful operation depends on the well-matched performance of the components, namely: 1. The diesel engine and its accessories. 2. The AC generator. 3. The control systems and switchgear. 4. The foundation and power house civil works. 5. The connected load with its own components like heating, motor drives, lighting, etc. It is necessary to select the components with highest efficiency and operate them at their optimum efficiency levels to conserve energy in this system. Various components of DG set are shown in Fig. 7.1. To make a decision on the type of engine, which is most suitable for a specific application, several factors need to be considered. The two most important factors are power and speed of the engine. The power requirement is determined by the maximum load. The engine power rating should be 10–20% more than the power demand by the end use. This prevents overloading the machine by absorbing extra

Energy conservation in electrical industries 133 Excitation control

Diesel engine

AC generator

Controls

Load

Fuel control Accessories

Foundation

Figure 7.1: Diagram of DG set components.

load during starting of motors or switching of few types of lighting systems or when wear and tear on the equipment pushes up its power consumption. An engine will operate over a range of speeds, with diesel engines typically running at lower speeds (1300–3000 rpm). Speed is measured at the output shaft and given in revolutions per minute (rpm). There will be an optimum speed at which fuel efficiency will be greatest. To determine the speed requirement of an engine, one has to again look at the requirement of the load. For some applications, the speed of the engine is not critical; but for other applications such as a generator, it is important to get a good speed match. If a good match can be obtained, direct coupling of engine and generator is possible; if not, then some form of gearing will be necessary - a gearbox or belt system, which will add to the cost and reduce the efficiency. There are various other factors that have to be considered, when choosing a diesel engine for a given application. These include cooling system, abnormal environmental conditions (dust, dirt, etc.), fuel quality, speed governing (fixed or variable speed), poor maintenance, control system, starting equipment, drive type, ambient temperature, altitude, humidity, etc. Suppliers or manufacturers literature will specify the required information when purchasing an engine. The efficiency of an engine depends on various factors, for example, load factor (percentage of full load), engine size, and engine type. With the steady development of the diesel engine, the specific fuel consumption can come down. With the arrival of modern high efficiency turbochargers, it is possible to use an exhaust gas driven turbine generator to further increase the engine rated output. The net result would be lower fuel consumption per kWh and further increase in overall thermal efficiency. The diesel engine is able to burn the poorest quality fuel oils, unlike gas turbine, which is able to do so with only costly fuel treatment equipment.

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Diesel generator (DG) set selection and installation factors

1. If a DG set is required for 100% standby, then the entire connected load in HP/kVA should be added. After finding out the diversity factor (demand/ connected load), the correct capacity of a DG set can be found out. 2. For an existing installation, record the current, voltage and power factor reading at the main bus-bar of the system at every half-an-hour interval for a period of 2–3 days; and during this period, the factory should be conducting its normal operations. The non-essential loads should be switched off to find the realistic current taken for running essential equipment. This will give a fair idea about the current taken from which the rating of the set can be calculated. 3. For a new installation, an approximate method of estimating the capacity of a DG set is to add full load currents of all the proposed loads to be run in DG set. Then, applying a diversity factor depending on the industry, process involved and guidelines obtained from other similar units, correct capacity can be arrived at. Unbalanced load effects: It is always recommended to have the load as much balanced as possible, since unbalanced loads can cause heating of the alternator, which may result in unbalanced output voltages. The maximum unbalanced load between phases should not exceed 10% of the capacity of the DG sets. Load pattern: In many cases, the load will not be constant throughout the day. If there is substantial variation in load, then consideration should be given for parallel operation of DG sets. In such a situation, additional DG sets are to be switched on when load increases. The typical case may be an establishment demanding substantially different powers in first, second and third shifts. By parallel operation, DG sets can be run at optimum operating points or near about, for optimum fuel consumption and additionally, flexibility is built into the system. This scheme can also be applied where loads can be segregated as critical and non-critical loads to provide standby power to critical load in the captive power system. Energy performance assessment of DG sets

Routine energy efficiency assessment of DG sets involves following typical steps: 1. Ensure reliability of all instruments used for trial. 2. Collect technical literature, characteristics and specifications of the plant. 3. Conduct a 2 hour trial on the DG set, ensuring a steady load, wherein the following measurements are logged at 15 minutes intervals. (a) Fuel consumption (by dip level or by flow meter). (b) Amps, volts, PF, kW, kWh.

Energy conservation in electrical industries 135

(c) Intake air temperature, Relative Humidity (RH). (d) Intake cooling water temperature. (e) Cylinder-wise exhaust temperature (as an indication of engine loading). (f) Turbocharger rpm (as an indication of loading on engine). (g) Charge air pressure (as an indication of engine loading). (h) Cooling water temperature before and after charge air cooler (as an indication of cooler performance). (i) Stack gas temperature before and after turbocharger (as an indication of turbocharger performance). 4. The fuel oil/diesel analysis is referred to from an oil company data. Energy saving measures of DG sets

The following options will ensure that your diesel genset is operating at best efficiency and you can tap potential energy savings: 1. Ensure steady load conditions on the DG set, and provide cold, dust free air at intake (use of air washers for large sets, in case of dry, hot weather, can be considered). 2. Improve air filtration. 3. Ensure fuel oil storage, handling and preparation as per manufacturers’ guidelines/oil company data. 4. Consider fuel oil additives in case they benefit fuel oil properties for DG set usage. 5. Calibrate fuel injection pumps frequently. 6. Ensure compliance with maintenance checklist. 7. Ensure steady load conditions, avoiding fluctuations, imbalance in phases, harmonic loads. 8. In case of a base load operation, consider waste heat recovery system adoption for steam generation or refrigeration chiller unit incorporation. Even the jacket cooling water is amenable for heat recovery. 9. In terms of fuel cost economy, consider partial use of biomass gas for generation. Ensure tar removal from the gas for improving availability of the engine in the long run. 10. Consider parallel operation among the DG sets for improved loading and fuel economy thereof. 11. Carry out regular field trials to monitor DG set performance and maintenance planning as per requirements.

136 Industrial energy conservation

7.4.2

Energy conservation in transmission lines

1. To reduce line resistance ‘R’, solid conductors are replaced by stranded conductors (ACSR or AAC) and by bundled conductors in HT line. 2. High Voltage Direct Current (HVDC) is used to transmit large amount of power over long distances or for interconnections between asynchronous grids. 3. By transmitting energy at high voltage level reduces the fraction of energy lost due to Joule heating. (V α1/I so I2 R losses reduces). 4. As load on system increases terminal voltage decreases. Voltage level can be controlled by using voltage controllers and by using voltage stabiliser. 5. If required reactive power is transmitted through transmission lines, it causes more voltage drop in the line. To control receiving-end voltage, reactive power controllers or reactive power compensating equipments such as static VAR controllers are used.

7.4.3

Energy conservation in distribution line

1. Optimisation of distribution system: The optimum distribution system is the economical combination of primary line (HT), distribution transformer and secondary line (LT), to reduce this loss and improve voltage HT/LT line length ratio should be optimised. 2. Balancing of phase load: As a result of unequal loads on individual phase sequence, components causes over heating of transformers, cables, conductors, motors. Thus, increasing losses and resulting in the motor malfunctioning under unbalanced voltage conditions. 3. Harmonics: With increase in use of non-linear devices, distortion of the voltage and current waveforms occurs, known as harmonics. Due to presence of harmonic currents excessive voltage and current in transformers terminals, malfunctioning of control equipments and energy meter, over effect of power factor correction apparatus, interference with telephone circuits and broad casting occurs. Distribution Static Compensator (DASTACOM) and harmonic filters can reduce this harmonics. 4. Energy conservation by using power factor controller: Low power factor will lead to increased current and hence increase losses and will affect the voltage. We can use power factor controller or automatic power factor controller that can be located near receiving substations, load centers or near loads.

Energy conservation in electrical industries 137

5. Energy conservation by demand side management control demand-side management is used to describe the actions of a utility, beyond the customer’s meter, with the objective of altering the end-use of electricity whether it be to increase demand, decrease it, shift it between high and low peak periods, or manage it when there are intermittent load demands in the overall interests of reducing utility costs. Nearly energy of 15,000 MW can be saved through end-use energy efficiency.

7.4.4

Energy conservation in lighting system

Good lighting is required to improve the quality of work, to reduce humans/ workers fatigue, to reduce accidents, to protect his eyes and nervous system. In industry it improves production, and quality of products/work. To view economy of lighting system, cost of initial installation cost, running cost, and effect on production/work are to be considered as main parameters. The power consumption by the industrial lighting is nearly 2–10% of total power consumption, depending on type of industries. 1. Optimum use of natural light: Whenever the orientation of a building permits, day lighting has to be used in combination with electric lighting. The maxim use of sunlight can be transmitted by means of transparent roof sheets, north light roof, etc. 2. Replacing incandescent lamps by Compact Fluorescent Lamps (CFL’s): CFL’s are highly suitable for places such as living rooms, hotel lounges, bars, restaurants, pathways, building entrances, corridors, etc. 3. Replacing conventional fluorescent lamp by energy efficient fluorescent lamp: Energy efficient lamps are based on the highly sophisticated technology. They offer excellent colour rendering properties in addition to the very high luminous efficacy. 4. Replacement of mercury/sodium vapour lamp by Halides lamp: Mercury Halide Lamp (MHL) provides high colour rendering index and offer efficient white light. Hence for critical applications where higher illumination levels are required, these lamps are used. They are highly suitable for applications such as assembly line, inspection area, painting shops, etc. 5. Replacing HPMV lamps by High Pressure Sodium Vapour Lamp (HPSV): Where colour rendering is not critical for such applications, e.g., street lighting, yard lighting because CRI of HPSV is low but offer more efficiency. 6. Replacing filament lamps on panels by LED: LED lamps consumes less power (1 W lamp), withstand high voltage fluctuation in the power supply, longer operating life (>100,000 hrs). Hence nowadays they are also used

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in street lighting, signalling, advertising boards, even as replacement for tube light or CFL. 7. Replacement of conventional ballast by electronic ballast: Installation of high frequency (28–32 Mhz) electronic ballast in place of conventional ballasts helps to reduce power consumption up to 35%. 8. Installation of separate transformer for lighting: In most of the industries, the net lighting load varies between 2 and 10%. If power load and lighting load fed by same transformer, switching operation and load variation causes voltage fluctuations. This also affects the performance of neighbouring power load apparatus, lighting load equipments and also reduces lamps. Hence, the lighting equipment has to be isolated from the power feeders. This will reduce the voltage related problems, which in turn provides a better voltage regulation for the lighting, this also increases the efficiency of the lighting system. 9. Installation of servo stabiliser for lighting feeder: Wherever, installation of separate transformer for lighting is not economically attractive, then servo stabiliser can be installed for the lighting feeders. 10. Control over energy consumption pattern: Occupancy sensors, daylight linked control are commonly used in commercial buildings, malls, offices, where more number of lights are to be controlled as per operational hours microprocessor based light control circuits are used. As a single control unit it can be programmed to switch on/off as per the month wise, year wise and even season wise working schedule. 11. Periodic survey and adequate maintenance programme: Illumination level reduces due to accumulation of dirt on lamps and luminaries. By carrying periodic maintenance, i.e., cleaning, dusting of lamps and luminaries will improve the light output/luminance. As part of maintenance programme, periodic surveys of installation, lightning system with respect lamp positioning and illumination levels, proper operation of control gears should be conducted to take advantage of energy conservation opportunities as user requirements changes. Energy conservation in motors: Considering all industrial applications 70% of total electrical energy consumed by only electric motors driven equipments. 1. Improving power supply quality: Maintaining the voltage level within the BIS standards, i.e., with tolerance of +/–6% and frequency with tolerance of +/–3% motor performance improves and also life. 2. Optimum loading: Proper selection of the rating of the motor will reduce the power consumption. If the motor is operating at less than 50% of loading (η10 (1) >10 (1) N/A (1) (Cont’d…)

294 Industrial energy conservation Energy efficiency measure

Clinker making Energy management and control systems Seal replacement Combustion system improvement Indirect firing Shell heat loss reduction Optimise grate cooler Conversion to grate cooler Heat recovery for power generation Low-pressure drop suspension pre-heaters Addition of precalciner or upgrade Conversion of long dry kiln to pre-heater Conversion of long dry kiln to precalciner Efficient mill drives Use of secondary fuels Finish grinding Energy management and process control Improved grinding media in ball mills High pressure roller press High-efficiency classifiers Plant wide measures Preventative maintenance High efficiency motors Adjustable speed drives Optimisation of compressed air systems Efficient lighting Product change Blended cement Limestone Portland cement Use of steel slag in clinker Low alkali cement Reduced fineness of cement for selected uses

Specific fuel savings (MBtu/ton cement)

Specific electricity savings (kWh/ton cement)

Estimated payback period (1) (years)

0.10–0.20 0.02 0.10–0.39 0.13–0.19 0.09–0.31 0.06–0.12 0.23 – – 0.12–0.54 0.36–0.73 0.55–1.10 – > 0.5

1.2–2.6 – – – – 0–1.8 –2.4 18 0.5–3.5 – >10 (1) >10 (1) 0.8–3.2 –

1–3 10(1) 5(1)

– – – –

1.6 1.8 7–25 1.7–6.0

10 (1) >10 (1)

0.04 – – – –

0–5 0–5 5.5–7.0 0–2 0–0.5