Solid Wastes and Residues. Conversion by Advanced Thermal Processes 9780841204348, 9780841205529, 0-8412-0434-9

Table of contents :
Title Page......Page 1
Copyright......Page 2
ACS Symposium Series......Page 3
FOREWORD......Page 4
PREFACE......Page 5
CONTRIBUTORS......Page 7
PdftkEmptyString......Page 0
1 Overview of Solid Waste and Residue Generation, Disposition, and Conversion Technologies......Page 9
SOLID WASTE AND RESIDUE QUANTITIES GENERATED AND DISPOSITION......Page 10
ENERGY RECOVERY OPTIONS......Page 15
Direct Combustion......Page 17
Biochemical Conversion......Page 18
Reasons for Development......Page 20
SYMPOSIUM PAPERS......Page 21
LITERATURE CITED......Page 24
2 Economics Associated with Waste or Biomass Pyrolysis Systems......Page 27
Reasons to Consider Medium Energy Gas......Page 28
Economics of Medium Energy Gas Production......Page 29
Application 1......Page 40
Application 2......Page 42
Application 3......Page 44
Conclusions......Page 47
REFERENCES......Page 49
PROCESS DESCRIPTION......Page 50
Gasifier......Page 52
Secondary Combustion Chamber......Page 53
Air Preheating System......Page 55
DEMONSTRATION PLANT......Page 56
MARKET DEVELOPMENT......Page 57
Commercial Plants......Page 58
ECONOMICS......Page 60
CONCLUSION......Page 62
LITERATURE CITED......Page 65
4 Co-Disposal of Sludge and Refuse in a Purox Converter......Page 66
Codisposal Test Program......Page 72
Projected Economics of the Codisposal Process......Page 85
LITERATURE CITED......Page 90
5 The Caloricon Process for Gasification of Solid Wastes......Page 91
6 A Vertical-Bed Pyrolysis System......Page 97
Wood Waste System......Page 105
Municipal Refuse System......Page 113
Pyrolysis Products from Wood Waste......Page 119
Pyrolysis Products from Municipal Refuse......Page 124
Discussion......Page 126
Literature Cited......Page 128
Process Description......Page 129
Description of Testing Program......Page 131
Process Economics......Page 141
LITERATURE CITED......Page 144
8 Development of Pilot Plant Gasification Systems for the Conversion of Crop and Wood Residues to Thermal and Electrical Energy......Page 145
Gasification Reactions......Page 146
Gasifier Design, Specific Rate of Gasification and Process Variables......Page 150
Ancillary Systems......Page 153
Dual Fueling and Performance of a Standard Turbo-charged Inter-Cooled Diesel Engine......Page 155
Cost Projections......Page 161
Literature Cited......Page 165
9 Stagewise Gasification in a Multiple-Hearth Furnace......Page 166
10 Pyrolyzer Design Alternatives and Economic Factors for Pyrolyzing Sewage Sludge in Multiple-Hearth Furnaces......Page 192
Pyrolysis Process Description and Operating Modes......Page 198
Heat Balance Results......Page 205
Improved Dewatering......Page 208
Char as Supplemental Fuel.......Page 215
Conclusions......Page 216
"Literature Cited"......Page 217
GERE Process......Page 218
Experimental......Page 220
Pilot Plant Experimentation......Page 223
Commercial Biomass Processing Plant Based Upon the GERE Process......Page 231
Conclusion......Page 232
Nomenclature......Page 237
Literature Cited......Page 238
Hydraulics.......Page 239
Reactor.......Page 242
Reactor Operating Condition.......Page 243
Reactor Products.......Page 244
Energy Balance.......Page 246
Comparisions With Other Systems......Page 247
Literature Cited......Page 249
Projected Power Plants......Page 250
Power Cycle......Page 252
Experimentation-MinikiIn......Page 254
Experimentation-Biogasser......Page 260
Pilot Plant Gasifier......Page 264
Economics......Page 269
Acknowledgements......Page 271
14 Pyrolysis of Scrap Tires Using the Tosco II Process—a Progress Report......Page 272
The Key To A Successful Process Is To Maximize Capacity And Maintain Carbon Black Quality......Page 273
Literature Cited......Page 282
Experimental Apparatus......Page 283
Discussion of Experimental Results......Page 284
Literature Cited......Page 302
Synthesis Gas From Manure Process......Page 303
Internal Gas Samples......Page 305
Variable Velocity Fluidized Bed......Page 307
Results......Page 313
Conclusions & Discussion......Page 316
Literature Cited......Page 318
17 EPA's R & D Program in Pyrolytic Conversion of Wastes to Fuel Products......Page 319
Subpilot-Scale Conversion of Mixed Wastes to Fuel (ERCO)......Page 320
The Pyrolysis of Organic Wastes in Inert and Reactive Steam Atmospheres (Princeton University)......Page 335
Chemical Reclamation of Scrap Rubber (University of Tennessee)......Page 342
Conversion of Solid Waste to Polymer Gasoline (The Navy at China Lake)......Page 345
Conclusion......Page 352
Literature Cited......Page 353
Overall Material Balances......Page 355
Literature Cited......Page 365
Objectives......Page 367
Plant Commissioning......Page 369
Process Results......Page 372
Commercial Plant Concepts......Page 375
Economic Analysis......Page 379
Future Activities......Page 383
References......Page 387
Objectives......Page 388
Experimental Procedure......Page 389
Results and Discussion......Page 390
Air Classification......Page 398
Feasibility of Activated Carbon from Solid Waste......Page 402
Conclusions......Page 403
Abstract......Page 404
Literature Cited......Page 405
Β......Page 407
C......Page 408
Ε......Page 409
G......Page 410
M......Page 411
Ρ......Page 412
S......Page 414
Τ......Page 415
W......Page 416
Ζ......Page 417

Citation preview

Solid Wastes and Residues Conversion by Advanced Thermal Processes Jerry L . Jones and Shirley B. Radding, EDITORS SRI International

A symposium sponsored by the Division of Environmental Chemistry at the 175th Meeting of the American Chemical Society, Anaheim, California, March 13-17, 1978.

ACS SYMPOSIUM SERIES 76 AMERICAN

CHEMICAL

SOCIETY

WASHINGTON, D. C. 1978

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Library of Congress CIP Data Solid wastes and residues. (ACS symposium series; 76. ISSN 0097-6156. Includes bibliographical references and index. 1. Refuse and refuse disposal—Congresses. 2. Pyrolysis—Congresses. 3. Fuel—Congresses. I. Jones, Jerry L., 1946. II. Radding, Shirley B., 1922. III. American Chemical Society. Division of Environmental Chemistry. IV. Series: American Chemical Society. ACS symposium series; 76. TD796.7.S64 ISBN 0-8412-0434-9

604.6 ACSMC8

78-16293 76 1-136 1978

Copyright © 1978 American Chemical Society A l l Rights Reserved. The appearance of the code at the bottom of the first page of each article in this volume indicates the copyright owner's consent that reprographic copies of the article may be made for personal or internal use or for the personal or internal use of specific clients. This consent is given on the condition, however, that the copier pay the stated per copy fee through the Copyright Clearance Center, Inc. for copying beyond that permitted by Sections 107 or 108 of the U.S. Copyright Law. This consent does not extend to copying or transmission by any means—graphic or electronic—for any other purpose, such as for general distribution, for advertising or promotional purposes, for creating new collective works, for resale, or for information storage and retrieval systems. The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission, to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. PRINTED IN THE UNITED STATES OF AMERICA

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

ACS Symposium Series Robert F. G o u l d , Editor

Advisory Board Kenneth B. Bischoff

Nina I. McClelland

Donald G . Crosby

John B. Pfeiffer

Jeremiah P. Freeman

Joseph V . Rodricks

E. Desmond Goddard

F. Sherwood Rowland

Jack Halpern

Alan C. Sartorelli

Robert A . Hofstader

Raymond B. Seymour

James P. Lodge

Roy L. Whistler

John L. Margrave

Aaron Wold

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

FOREWORD The ACS SYMPOSIU

a medium for publishin format of the SERIES parallels that of the continuing ADVANCES IN CHEMISTRY SERIES except that in order to save time the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. As a further means of saving time, the papers are not edited or reviewed except by the symposium chairman, who becomes editor of the book. Papers published in the ACS SYMPOSIUM SERIES are original contributions not published elsewhere in whole or major part and include reports of research as well as reviews since symposia may embrace both types of presentation.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

PREFACE A lthough the word "advanced" was used in the title of the symposium, the reader should be aware that the practice of producing fuel gases from wastes and residues is not new. During the early part of the 20th century, Crossley Brothers Limited of Manchester, England, was selling gasifiers worldwide that produced a low-Btu fuel gas from agricultural or forestry residues. During World War II, many vehicles in Sweden were retrofitted with low-Btu gas producers fueled by wood or charcoal. Therefore, some individuals may consider some of the research and development work describe the gasification field. In other cases, though, the processes have been conceived only within the last decade and are concerned with concepts new to the processing of wastes and residues. (However, some of the processes may have been applied previously to the conversion of fossil fuels such as coal or oil shale. ) The first two chapters present overview discussions of the feedstocks, technologies, and economics for producing fuels from wastes and residues. Chapter One briefly describes alternative technologies, including combustion and biochemical conversion processes, and also presents waste and residue quantities and a method for categorizing pyrolysis, thermal gasification, and liquefaction processes. Chapter Two discussed the production of low-Btu and medium-Btu fuel gases and the relative advantages to the product, which has a higher heating value. The next section of the book contains six chapters that describe verticle flow packed-bed reactor (or fixed-bed reactor) processes. The feedstocks included in these chapters are municipal solid waste, municipal wastewater treatment sludge, scrap tires, agricultural residues (such as peanut shells, corn cobs, cotton gin trash, walnut shells), and wood residues. Two of the process reactors are designed to operate with oxygen, whereas the other four are air-blown. The reactor products described include low-Btu gas (which is immediately combusted in a secondary combustion chamber), a medium-Btu gas, pyrolytic oil, and char. The third section contains three papers describing processes with multiple-hearth-type staged reactors. Although this type of reactor has been used for many years for ore roasting and sludge combustion, a great deal of development work has been done recently to lower the fuel requirements for processing high-moisture feedstocks, such as sludge or

vii In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

manure. The methods developed include operating in a starved-air combustion mode and changing the conventional gas flow between stages. Processes with horizontal or inclined-flow rotary reactors are described in the fourth section. Municipal sludge and solid waste, wood, and scrap tires are the respective feedstocks for the three processes discussed. The products include char, electric power, carbon black, and a pyrolytic oil. All of the rotary reactors described use indirect heat transfer. The last section of the book describes a flash pyrolysis process based on the use of a transport reactor, a new concept in fluidized-bed design, and research work being funded by the Environmental Protection Agency on topics such as a molten salt pyrolysis reactor that will accept whole (unshredded) scrap tires and a process for producing polymer gasoline from wastes. The last chapters also discuss a multiple reactor system that can produce a high methane content gas with a heating value of 370 Btu/scf, a high-pressure catalytic liquefaction process that is currently being developed to produce oil from wood, and the processing of char (from municipal soli water treatment. Special recognition and appreciation is given to the authors whose efforts made this publication possible. We also wish to acknowledge the assistance of the officers of the Environmental Chemistry Division of the ACS, and of Linda Deans, who coordinated the Environmental Chemistry Division programs at Anaheim. SRI

International

JERRY L . JONES

Menlo Park, C A 94025

SHIRLEY B. RADDING

Received June 2, 1978

viii In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

CONTRIBUTORS Alderstein, Joseph K., Syngas Inc., Suite 1260 East, First National Center, Oklahoma City, OK 73102 Bailie, Richard, Chemical Engineering Dept., West Virginia University, Morgantown, W V 26505 Beck, Steven R., Department of Chemical Engineering, Texas Tech Uni­ versity, Lubbock, T X 79409 Bowen, M . D., Tech-Air Corp., Atlanta, GA 30341 Brunner, Paul H . , E A W A G , Swiss Federal Institutes of Technology, C H 8600, Dubendorf, Switzerlan Coffman, J. Α., Wright-Malta Corp., Malta Test Station, Plains Rd., Ballston Spa, NY 12020 Cone, Eugene J., Occidental Research Corp., 1855 Carrion Rd., La Verne, CA 91750 Davidson, Paul E., Andco-Torrax Division, Andco Inc., 25 Anderson Rd., Buffalo, NY 14225 Farrell, J. B., U.S. E.P.A., M E R L , Cincinnati, O H 45268 Feldman, Herman F., Battelle-Columbus Laboratories, 505 King Ave., Columbus, O H 43201 Funk, Harald F., 68 Elm St., Murray Hill, NJ 07974 Garrett, Donald E., Garrett Energy Research and Engineering Co., Inc., 911 Bryant Place, Ojai, C A 93023 Goss, J. R., University of California, Davis, Agricultural Engineering Dept., Davis, C A 95616 Hoang, Dinh Co, Garrett Energy Research and Engineering Co., Inc., 911 Bryant Place, Ojai, C A 93023 Hooverman, R. H., Wright-Malta Corp., Malta Test Station, Plains Rd., Ballston Spa, NY 12020 Huffman, George L., U.S. Environmental Protection Agency, Industrial Environmental Research Laboratory, Cincinnati, O H 45268 Huffman, William J., Department of Chemical Engineering, Texas Tech University, Lubbock, T X 79409 Jenkins, B., University of California, Davis, Agricultural Engineering Dept., Davis, C A 95616 Jones, Jerry L., SRI International, 333 Ravenswood Ave., Menlo Park, CA 94025 Knight, J. Α., Engineering Experiment Station, Georgia Institute of Tech­ nology, Atlanta, GA 30332

ix In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Leckie, James Ο., Department of Civil Engineering, Stanford University, Stanford, C A 94305 Liberick, Walter W., Jr., U.S. Environmental Protection Agency, Indus­ trial Environmental Research Laboratory, Cincinnati, O H 45268 Lindemuth, T. E., Research and Engineering, Bechtel National, Inc., 50 Beale St., San Francisco, C A 94119 Lucas, Theodore W., Jr., Andco-Torrax Division, Andco Inc., 25 Ander­ son Rd., Buffalo, NY 14225 Mann, Uzi, Department of Chemical Engineering, Texas Tech Univer­ sity, Lubbock, T X 79409 Mehlschau, J. J., University of California, Davis, Agricultural Engineer­ ing Dept., Davis, C A 95616 Mikesell, Ritchie D., Garrett Energy Research and Engineering Co., Inc., 911 Bryant Place, Ojai, C A 93023 Moses, C . T., Union Carbide Corp., Linde Division, Tonawanda, NY 14150 Mudge, L . K., Battelle-Northwest, P.O. Box 999, Richland, W A 99352 Negra, John S., Nichols Engineering & Research Corp., Homestead and Willow Rds., Belle Mead, NJ 08502 Purdy, K. R., Engineering Experiment Station, Georgia Institute of Tech­ nology, Atlanta, GA 30332 Ramming, J., University of California, Davis, Agricultural Engineering Dept., Davis, C A 95616 Richmond, C. Α., Wheelabrator Incineration, Inc., 600 Grant St., Pitts­ burgh, PA 15219 Roberts, Paul V., Department of Civil Engineering, Stanford University, Stanford, C A 94305 Rohrmann ,C. Α., Battelle-Northwest, P.O. Box 999, Richland, W A 99352 Schulman, B. L., Tosco Corp., 18200 West Highway 72, Golden, C O 80401 Shelton, Robert D., BSP/Envirotech, One Davis Dr., Belmont, C A 94002 Sigler, John E., 2839 Tabago Place, Costa Mesa, C A 92626 Smyly, E. D., Tech-Air Corp., Atlanta, GA 30341 Stern, G., U.S. E.P.A., M E R L , Cincinnati, O H 45268 von Dreusche, Charles, Nichols Engineering & Research Corp., Home­ stead and Willow Rds., Belle Mead, NJ 08502 White, P. Α., Tosco Corp., 10100 Santa Monica Blvd., Los Angeles, C A 90067 Williams, R. O., University of California, Davis, Agricultural Engineering Dept., Davis, C A 95616 Wong, Ho-Der, Department of Chemical Engineering, Texas Tech Uni­ versity, Lubbock, T X 79409 Young, K. W., Union Carbide Corp., Linde Division, Tonawanda, NY 14150

χ

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

1 Overview of Solid Waste and Residue Generation, Disposition, and Conversion Technologies JERRY L . JONES SRI International, 333 Ravenswood Avenue, Menlo Park, CA 94025

This discussion o to the materials that ar cluded are municipal refuse, scrap t i r e s , a g r i c u l t u r a l residues, and forestry residues as well as organic sludges (mainly from wastewater treatment). The d i s t i n c t i o n between the terms " s o l i d waste" and "residue" may be made precise by d e f i n i t i o n . Residues are defined here as s o l i d by-products that have some positive value or represent no cost for disposal. These materials that represent a disposal cost are defined as solid wastes. These definitions, however, do not allow simple c l a s s i f i c a t i o n . For many types of materials, l o c a l market conditions are quite v a r i able and the material may fall into both categories depending on the specific s i t e , the season of the year, or the state of the economy. The conversion processes to be discussed at this symposium are those that may be described as pyrolysis, thermal g a s i f i c a tion, or liquefaction processes. The products from these so-called advanced thermal processes may be gaseous or l i q u i d fuels, a synthesis gas for use as a chemical feedstock, or a carbon char. In some cases, a gaseous fuel generated from p a r t i a l combustion containing condensible tars may be immediately combusted i n a second stage. In others, a fuel product may be transported o f f s i t e for use. The process types included i n the advanced processes category are not a l l necessarily new, but their application to the conversion of s o l i d wastes and residues i s new or has been l i t t l e used i n the past. This paper provides some background on the types, quantities, and current disposition of wastes and residues as well as some information on other existing and developing processing options that are not included i n this symposium. The method used to c l a s s i f y the processes to be discussed by the symposium speakers w i l l also be described.

0-8412-0434-9/78/47-076-003$05.00/0 © 1978 A m e r i c a n C h e m i c a l Society

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

4

SOLID WASTES AND RESIDUES

SOLID WASTE AND RESIDUE QUANTITIES GENERATED AND DISPOSITION More than 500 m i l l i o n tons (dry b a s i s ) of organic s o l i d wastes and r e s i d u e s are c u r r e n t l y generated y e a r l y i n the United S t a t e s . These m a t e r i a l s represent a p o t e n t i a l energy resource equivalent to more than 5 quads.* Estimates of the q u a n t i t i e s of these m a t e r i a l s by type are summarized i n Table I . The f i g u r e s have been presented on a dry b a s i s to a l l o w comparison i n cons i s t e n t u n i t s . In f a c t , these m a t e r i a l s vary g r e a t l y i n moisture content and other p h y s i c a l and chemical p r o p e r t i e s (bulk d e n s i t y , p a r t i c l e s i z e , p a r t i c l e s i z e d i s t r i b u t i o n , i n o r g a n i c ash c o n t e n t ) . The use of a s p e c i f i c m a t e r i a l as a feedstock to an energy recovery process depends on many f a c t o r s r e l a t e d to the cost to c o l l e c t and d e l i v e r the m a t e r i a l to the s i t e of the conversion r e a c t o r , and the p h y s i c a l d chemical p r o p e r t i e f th m a t e r i a l that a f f e c t the conversio f o r i n s t a n c e , o f t e n determines the extent o preprocessing r e q u i r e d . A major cost i n c e r t a i n m u n i c i p a l r e f u s e processing systems i s the f r o n t end processing to reduce the p a r t i c l e s i z e and to separate out metals and g l a s s before the thermal conversion step. By-product wood bark, a pulp and paper m i l l s r e s i d u e , on the other hand i s o f t e n q u i t e homogeneous and r e q u i r e s minimal preprocessing. Such a d i f f e r e n c e i n preprocessing cost may be p a r t i a l l y o f f s e t , however, by the dumping fee paid to the conv e r s i o n p l a n t f o r the r e f u s e or by s a l e of the recovered m a t e r i a l s such as f e r r o u s metals and aluminum. The moisture content of m a t e r i a l s may a l s o a f f e c t the c o s t s of the preprocessing (dewatering and drying) or f u e l product s e p a r a t i o n (dehydration of a f u e l gas). Where a r e a c t o r product gas contains condensible organics and r e q u i r e s dehydration, the dehydration o p e r a t i o n can represent a major cost because of poss i b l e t a r fog removal and water p o l l u t i o n problems. The moisture contents of some common s o l i d wastes and residues are shown i n Table I I . I t may be p r e f e r a b l e to predry r a t h e r than to attempt to process a wet m a t e r i a l i n the r e a c t o r . (See reference 8 f o r a more extensive d i s c u s s i o n of t h i s t o p i c . ) The d i s p o s i t i o n of the s e v e r a l c a t e g o r i e s of m a t e r i a l s l i s t e d i n Table I has been estimated i n Tables I I I and IV. The estimates shown i n Table I are based on an exhaustive study by SRI I n t e r n a t i o n a l , whereas those shown i n Table IV are merely crude a p p r o x i mations. One t h i n g i s obvious from a l l these estimates: A l a r g e

A quad i s 1015 Btu. more than 75 quads.

Current y e a r l y U.S.

energy consumption i s

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

1.

JONES

5

Overview of Solid Waste and Residue

Table I APPROXIMATE TONNAGES OF SELECTED ORGANIC RESIDUES AND SOLID WASTES IN THE UNITED STATES IN 1975 (Dry Weight B a s i s )

Type of M a t e r i a l " Agricultural crop manures

Quantity Generated ( m i l l i o n s of dr tons)

Data Sources (references)

residues ^ 278* 2>26*

1 1

Forestry residues

2>125*

1

M u n i c i p a l refuse

-100

2

Industrial sludges

wastewater

treatment 5,6

(Food p r o c e s s i n g , pulp and paper, p l a s t i c s and s y n t h e t i c s , organic chemicals, t e x t i l e s and petroleum r e f i n i n g ) M u n i c i p a l wastewater sludges Scrap t i r e s

treatment

-5.3

3,4

3 £546

Quantity c o l l e c t e d during normal operations or r e a l i s t i c a l l y collectible.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

6

SOLID WASTES AND RESIDUES

Table I I MOISTURE CONTENT OF SELECTED SOLID WASTES AND RESIDUES Moisture Content S o l i d Wast Wood r e s i d u e s Fresh manure (with u r i n e ) Rice h u l l s

^45 85 5-10

Bagasse

~ 50

Municipal refuse

20-35

Wastewater treatment sludges G r a v i t y thickened Centrifuged Vacuum f i l t e r e d F i l t e r pressed ( p l a t e and frame f i l t e r )

95 80-85 75-80 60-70

Scrap t i r e s

Negligible

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Source:

To s o i l

Reference 1

12.3

12.2

52,389,318

52,636,074

Total

Percent of t o t a l

52,142,254 — 247,064

11,266,626 37,449,165 3,920,283

Fed

Crop Forestry Manure

Sold

4.9

21,060,223

1,741,990 19,301,797 16,436

Fuel

52.1

223,445,115

205,599,417 — 17,845,698

Returned

18.5

79,150,181

6,810,630 67,909,684 4,429,867

Wasted

T o n s — D r y Weight

100.0%

428,680,911

277,560,917 124,660,646 26,459,348

Total

CROP, FORESTRY, AND MANURE RESIDUE DISPOSITION—COTERMINOUS UNITED STATES (1975)

Table I I I

100.0%

64.7% 29.1 6.2

Percent of T o t a l

I

Co

ο

CO

Ο

M

Ο

8

SOLID WASTES AND RESIDUES

Table IV ORGANIC SLUDGE AND MUNICIPAL REFUSE DISPOSITION IN THE UNITED STATES

D i s p o s a l Technique

Municipal Sludges

Percent of T o t a l Industrial Refuse Sludges

Landfill Land a p p l i c a t i o n

25-30

Onsite lagoons

small

Thermal conversion

25-30

Ocean Dumping

15

£90

small small

4-5

Recycled

Quantity ( m i l l i o n s of d r y tons/year)

10

5-6

9

Small number of u n i t s w i t h energy recovery. Sources: References J2_, 3> 4,, _5..

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

100

1.

JONES

Overview of Solid Waste and Residue

9

amount of s o l i d waste and r e s i d u e m a t e r i a l i s s t i l l p o t e n t i a l l y a v a i l a b l e ( a t some p r i c e ) as feedstock to energy recovery processes. I n the case of sludge d i s p o s a l , a primary c o n s i d e r a t i o n i s not to recover energy, but r a t h e r , to dispose of the m a t e r i a l f o r the lowest cost p o s s i b l e w i t h minimal energy use.

ENERGY RECOVERY OPTIONS The major process o p t i o n s f o r energy recovery from s o l i d wastes and r e s i d u e s have been described p r e v i o u s l y (see F i g ure 1 ) . ^The most w i d e l y used processes f o r energy recovery from wastes and r e s i d u e s have been d i r e c t combustion i n a furnace or c o f i r i n g of the m a t e r i a l s w i t h a f o s s i l f u e l f o r steam generat i o n . A recent use of s o l i cement k i l n s . I t has bee i n the United States w i l l be a b l e to burn c o a l . v i ' I n many of these u n i t s , r e f u s e - d e r i v e d f u e l (RDF) and a g r i c u l t u r a l or f o r e s t r y r e s i d u e s can be s u b s t i t u t e d f o r the c o a l . The more advanced thermal processes of p y r o l y s i s , thermal g a s i f i c a t i o n , and l i q u e f a c t i o n (PTGL)* may produce l i q u i d , gaseous, or s o l i d char products. I n some i n s t a n c e s , the gases l e a v i n g the r e a c t o r a r e immediately combusted f o r steam generation. One advantage of t h i s approach over c o n v e n t i o n a l i n c i n e r a t i o n i s that the s o l i d waste or r e s i d u e can be burned w i t h l e s s excess a i r , which means lower gas volumes f o r c l e a n i n g (and perhaps lower p a r t i c u l a t e l o a d i n g i n the combustor f l u e gas) and a higher thermal e f f i c i e n c y ( l e s s heat l o s s out o f the s t a c k ) . Biochemical conversion processes i n c l u d e methane fermentation (anaerobic d i g e s t i o n ) f o r p r o d u c t i o n of a f u e l gas (up to 70% C H 4 and the remainder mostly C O 2 ) and fermentation of sugars to e t h y l a l c o h o l . The fermentable sugars may be produced by a c i d o r enzymatic h y d r o l y s i s of c e l l u l o s e . T h i s paper focuses on the advanced thermal processes; however, to provide a p e r s p e c t i v e on the a p p l i c a t i o n s f o r the newer processes, i t a l s o presents some i n f o r m a t i o n on the use of combustion and biochemical conversion t e c h n o l o g i e s .

For d e f i n i t i o n of terms see reference 8.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978. ' Solid Waste

Unprocessed

r - — — - · > Use as Aggregate

DISPOSAL

LAND

Steam

a

WITH S T E A M GENERATION^

BOILER

INCINERATION

INDUSTRIAL

UTILITY OR

—ι

a

Η

ι

·>

JL

Soil Conditioner

PROCESSES*

CONVERSION

BIOCHEMICAL

Fuel

Gaseous

R D F may be used as a supplemental fuel for sludge incineration

Char

Liquid Fuel

•

I I

PROCESSES*

PTGL

!

F o r district heating, industrial process heating, electric power production, water desalting

6

1 1
14) had a combined process c a p a c i t y of l e s s than 10% of the t o t a l m u n i c i p a l r e f u s e generated. By the mid-1970s, only about 160 of these r e f u s e i n c i n e r a t o r s were o p e r a t i n g i n the United States.(15) Since 1970 at l e a s t s i x w a t e r - w a l l furnaces f o r r e f u s e have been i n s t a l l e d i n the United States (16) f o r energy recovery.* The combined c a p a c i t y of these u n i t s i s approximately 1 m i l l i o n tons/year. These water w a l l u n i t s were i n i t i a l l y developed i n Europe and r e q u i r e only 50 to 100% excess a i r f o r combustion compared w i t h 150 to 200% f o r r e f r a c t o r y w a l l furnaces. This f a c t o r makes a s u b s t a n t i a l d i f f e r e n c e i n f l u e gas volume and improves thermal e f f i c i e n c y . Whereas the o l d e r i n c i n e r a t o r s r e c e i v e d a great d e a l of adverse p u b l i c i t y concerning a i r p o l l u t i o n problems, the modern u n i t s , which are equipped w i t h high energy scrubbers, e l e c t r o s t a t i c p r e c i p i t a t o r s , o r f a b r i c f i l t e r s , have been a b l e t o meet s t r i n g e n t p a r t i c u l a t e standards. (17, 18) Even though r e f u s e combustion w i l l probably continue to p l a y a r o l e i n the s o l i d waste management f i e l d , p r o d u c t i o n of RDF f o r c o f i r i n g i n b o i l e r s i s c u r r e n t l y r e c e i v i n g a great d e a l of a t t e n t i o n i n regions where c o a l i s f i r e d i n u t i l i t y b o i l e r s . Of the 47 e l e c t r i c u t i l i t y f e a s i b i l i t y s t u d i e s ( i n v o l v i n g r e f u s e use) under way i n the United States during 1976, 29 (62%) were concerned w i t h the use of shredded waste; 4 ( 8 % ) , the combustion of raw waste i n i n c i n e r a t o r s ; 3 ( 6 % ) , the use of a p e l l e t i z e d f u e l ; 6 (13%), the use of a powdered f u e l ; and 5 (11%), the use of a pyrolysis fuel,(i?) A number of p r o j e c t s based s o l e l y on m a t e r i a l s recovery (not f u e l ) from m u n i c i p a l r e f u s e are now being planned. Nevertheless, most a c t i v i t y i n the f u t u r e w i l l focus on systems that i n c l u d e energy recovery. Energy s a l e s account f o r 50% of the revenues f o r a system t h a t a l s o recovers aluminum and f e r r o u s metals. The d i s p o s a l fee may represent about 25% of the u n i t ' s revenue.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

12

SOLID WASTES AND RESIDUES

Another s o l i d waste problem f o r many c i t i e s i s the d i s p o s a l of sludges from wastewater treatment p l a n t s . Sludges from wastewater treatment p l a n t s i n the United States have been combusted i n m u l t i p l e hearth furnaces s i n c e the 1930s and i n f l u i d i z e d bed u n i t s s i n c e the 1960s. C u r r e n t l y , about 25 to 30 percent or more of the sludge generated i s i n c i n e r a t e d . ( 3 , 4) Energy recovery from the i n c i n e r a t o r f l u e gases by use of waste heat b o i l e r s has only r e c e n t l y become common p r a c t i c e , however. Co-disposal of m u n i c i p a l r e f u s e and sludge i n thermal conversion processes i s c u r r e n t l y a t o p i c of great i n t e r e s t to m u n i c i p a l i t i e s . An EPA c o n t r a c t o r r e c e n t l y reported that c o - i n c i n e r a t i o n of sludge and r e f u s e " w i l l have lower o v e r a l l cost than separate i n c i n e r a t i o n of sludge and r e f u s e " (^0); although t h i s approach has met w i t h v a r i e d degrees of t e c h n i c a l and economic success i n the p a s t , i t may represent a f u t u r e s o l u t i o n f o r c e r t a i n s i t e s where r e f u s e d i s p o s a l by thermal conversion processes can be economically j u s t i f i e d . I i n the near term, however s i d i e s a r e o f f e r e d to l o c a l government agencies. For a f u r t h e r d i s c u s s i o n of t h i s t o p i c , see reference 21. As mentioned e a r l i e r , cement k i l n s o f f e r another o p p o r t u n i t y for use of RDF because many a r e near l a r g e p o p u l a t i o n c e n t e r s . Government-supported p r o j e c t s are under way i n the United S t a t e s , Canada and the United Kingdom to determine the e f f e c t of u s i n g RDF on cement q u a l i t y . ( 2 2 . > 2 3 ) A g r i c u l t u r a l r e s i d u e s a l s o r e p r e sent a f u e l source f o r these k i l n s . At S t u t t g a r t , Arkansas, r i c e h u l l s , which have a h i g h s i l i c a content, a r e now being used as a f u e l f o r a cement k i l n . While use of organic r e s i d u e s as a f u e l by a nonproducer of the r e s i d u e s may be new, the use of r e s i d u e s as f u e l i s n o t . Combustion of wood wastes and bagasse f o r steam production c u r r e n t l y represents a major energy source f o r the pulp and paper i n d u s t r y , lumber m i l l s , and sugar cane processors.(^5) The combined consumption of these r e s i d u e s f o r f u e l s represents c l o s e to one quad of energy f o r these i n d u s t r i e s . D i r e c t combustion of whole scrap t i r e s f o r energy recovery has not been w i d e l y p r a c t i c e d i n the United States but use of a Lucas C y c l o n i c Furnace f o r t h i s purpose was reported i n 1974 f o r a Goodyear T i r e and Rubber Company P l a n t i n Jackson, M i c h i gan. (^6, 27) Use of shredded scrap t i r e s as a supplemental f u e l i n c o a l f i r e d i n d u s t r i a l b o i l e r s has been p r a c t i c e d a t s e v e r a l sites.(27) Biochemical Conversion Anaerobic d i g e s t i o n of sludges from wastewater treatment p l a n t s has been p r a c t i c e d i n the United States f o r over 50 years. According to the EPA, (?§) there are c u r r e n t l y approximately 6000 anaerobic d i g e s t i o n f a c i l i t i e s a t treatment p l a n t s i n the United S t a t e s . I n the p a s t , a p o r t i o n of the f u e l gas produced by these u n i t s has been f l a r e d and the main purpose of the process was t o s t a b i l i z e the p u t r e s c i b l e s o l i d s . Now, more and more %

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

1.

JONES

Overview of Solid Waste and Residue

13

p l a n t s are u s i n g the product gas as a f u e l f o r i n t e r n a l combust i o n engines to d r i v e pumps and compressors. Such d i g e s t e r s , however, do not produce l a r g e q u a n t i t i e s of f u e l gas. The amount of energy i n the product gas ranges from 300 to 600 Btu/day per person served by the treatment p l a n t (approximately 2000 B t u / l b of dry s o l i d s processed). Since the e a r l y 1970s, research has been under way t o develop an anaerobic d i g e s t i o n process to produce methane from a mixture of m u n i c i p a l r e f u s e and sludge.(29) The f i r s t demonstrat i o n p l a n t w i l l process about 100 tons per day of r e f u s e and sludge and i s scheduled to begin o p e r a t i o n during 1978 i n Pompano Beach, F l o r i d a , under Department of Energy sponsorship.(^0) p r o j e c t e d net gas y i e l d w i l l be about 1700 B t u / l b of dry s o l i d s processed or more than 5000 Btu/day per person served by the plant. P r o j e c t s to tap th methan produced fro th i s i t aerobic d i g e s t i o n at l a n d f i l during t h i s decade. Reserv S y n t h e t i Company Angeles County S a n i t a t i o n D i s t r i c t are r e c o v e r i n g methane a t the Palos Verdes l a n d f i l l , and the P a c i f i c Gas and E l e c t r i c Company i s r e c o v e r i n g gas from the Mountain View, C a l i f o r n i a , l a n d f i l l . ( 3 1 ) Numerous p r o j e c t s are a l s o under way to produce methane from c a t t l e manure by anaerobic d i g e s t i o n . Net gas y i e l d s are equival e n t to as high as 2000 B t u / l b of dry s o l i d s processed. A l a r g e p l a n t (processing 1000 dry tons of manure s o l i d s / d a y ) can produce approximately 4 m i l l i o n s c f of methane per day.(32) A process development program p a r t i a l l y funded by the United States Department of Energy i s c u r r e n t l y under way a t Kaplan I n d u s t r i e s , Incorporated, o f Bartow, F l o r i d a , under the d i r e c t i o n of Hamilton Standard (Windsor Locks, C o n n e c t i c u t ) . The process development u n i t w i l l a n a e r o b i c a l l y d i g e s t the manure from an environmental f e e d l o t w i t h 10,000 head of c a t t l e . Other a c t i v e Department of Energy-sponsored anaerobic d i g e s t i o n programs are under way a t C o r n e l l U n i v e r s i t y , the U n i v e r s i t y of I l l i n o i s , the U.S. Department of A g r i c u l t u r e , and Stanford U n i v e r s i t y . Carbohydrate c o n t a i n i n g m a t e r i a l s can a l s o be used as a feedstock to fermentation f o r the p r o d u c t i o n of ethanol f o r use as a t r a n s p o r t a t i o n f u e l . Ethanol production from g r a i n i s being a c t i v e l y i n v e s t i g a t e d by the S t a t e of Nebraska.(33) One of the economic problems w i t h the use of c e l l u l o s i c wastes and r e s i d u e s as a feedstock f o r ethanol production i s the cost f o r h y d r o l y s i s of the c e l l u l o s e to fermentable sugars. The conversion of carbohydrates to sugars by h y d r o l y s i s i s a very a c t i v e area of r e s e a r c h , which i n c l u d e s enzymatic h y d r o l y s i s . Enzymatic h y d r o l y s i s has been s t u d i e d a c t i v e l y by the U.S. Army Laboratory i n N a t i c k , Massachusetts, L o u i s i a n a S t a t e U n i v e r s i t y , the U n i v e r s i t y of C a l i f o r n i a a t Berkeley, Rutgers U n i v e r s i t y , the U n i v e r s i t y of Pennsylvania, the General E l e c t r i c Company, and the Massachusetts I n s t i t u t e of Technology. U n l i k e enzymatic h y d r o l y s i s technology, h y d r o l y s i s of c e l l u l o s e i n

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

14

SOLID WASTES AND RESIDUES

d i l u t e a c i d has been known f o r w e l l over a hundred years and has been p r a c t i c e d commercially. Some b e l i e v e that a c i d h y d r o l y s i s o f f e r s a more economical approach than does enzymatic h y d r o l y s i s . (_34) A c i d h y d r o l y s i s i s c u r r e n t l y under study a t Dartmouth C o l l e g e , New York U n i v e r s i t y , and Purdue U n i v e r s i t y . ADVANCED THERMAL CONVERSION PROCESSES Reasons f o r Development Based on the previous d i s c u s s i o n of a v a i l a b l e conversion t e c h n o l o g i e s , the f i r s t q u e s t i o n one might ask about the advanced thermal processes (PTGL processes) i s — w h y do we need them? Numerous answers a r e given but the most common ones a r e : (1) PTGL processes can produce gaseous or l i q u i d f u e l products that can be burned more e f f i c i e n t l y (low excess a i r ) i secondar combustio chamber used as f u e l f o designed to bur ga y minor m o d i f i c a t i o n s r e q u i r e d . ( 2 ) U n l i k e steam generated from a combustion process, l i q u i d or char f u e l products a r e s t o r a b l e — a medium Btu gas may a l s o be s t o r a b l e a t a reasonable cost. This second answer i s important because a t many s i t e s , no market e x i s t s f o r steam, and e l e c t r i c power cannot be generated economically because of the s m a l l s i z e of the e l e c t r i c a l generator. In other cases, i t i s uneconomical to s h i p the s o l i d waste or residue and the area where the m a t e r i a l i s l o c a t e d o f f e r s no market f o r the product f u e l s . Thus, the o n l y way to u t i l i z e the m a t e r i a l i s to produce a h i g h v a l u e shippable f u e l . The products a l s o may a l s o f i n d nonfuel uses. The char m a t e r i a l produced from some processes can be used as feedstock to produce a low cost adsorbent f o r wastewater treatment. This may be a t t r a c t i v e to both m u n i c i p a l i t i e s and i n d u s t r y . The r e a c t o r product gas (which i s mainly CO and H 2 from an oxygen blow r e a c t o r ) can be used as s y n t h e s i s gas to produce s t o r a b l e h i g h v a l u e products l i k e methanol or ammonia. Product o i l s may r e p r e sent a source of chemicals, but because of the h i g h l y oxygenated nature of the compounds (organic a c i d s ) , the o i l s may not be suitable f o r processing i n conventional r e f i n i n g u n i t s . Another reason o f t e n c i t e d f o r developing PTGL t e c h n o l o g i e s i s t h a t they may r e q u i r e lower investments f o r environmental cont r o l equipment. This statement may not be v a l i d i n a l l cases, as was discussed p r e v i o u s l y by t h i s author i n r e f e r e n c e 8.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

1.

JONES

Overview of Solid Waste and Residue

15

C a t e g o r i z a t i o n of Processes Numerous ways are a v a i l a b l e to c a t e g o r i z e PTGL processes, such as by: * Feedstock Type Refuse, t i r e s , sludge, a g r i c u l t u r a l and f o r e s t r y residues, etc. * Product D i s t r i b u t i o n Maximized char y i e l d Maximized f u e l gas y i e l d Maximized l i q u i d o r g a n i c s y i e l d * Product Use D i r e c t combustion of gases from r e a c t o r ( i . e . , furnaces o p e r a t i n g i n a s t a r v ed a i r o r p a r t i a l combustion mode to supply gas to a boiler) Clean f u e l gas f o r i n d u s t r i a l uses Synthesis ga Oil for offsit * S p e c i f i c Process Operating C h a r a c t e r i s t i c s Slagging versus nonslagging A i r blown versus oxygen blown * Fundamental Process Reactor C h a r a c t e r i s t i c s Solids flow d i r e c t i o n Conditions of s o l i d s i n r e a c t o r Type of r e a c t o r v e s s e l Heat t r a n s f e r method Relative gas/solid flow d i r e c t i o n The l a s t o p t i o n appears to be the most l o g i c a l approach t o analyze conversion processes and i s the approach used i n previous work.(8, 35) The b a s i c process c a t e g o r i e s are l i s t e d i n Table 5. (Reference j$ i n c l u d e s drawings showing the d i f f e r e n t types o f r e a c t o r s ). SYMPOSIUM PAPERS The other 22 speakers scheduled to p a r t i c i p a t e i n t h i s sym­ posium w i l l d e s c r i b e a wide v a r i e t y of thermal conversion process development and demonstration programs w i t h * Equipment s i z e s ranging from bench s c a l e to commercial scale. * Many types and q u a l i t i e s of f e e d s t o c k s . Numerous product types, q u a l i t i e s and uses, and * More than a dozen r e a c t o r types. Most of the papers w i l l i n c l u d e not only t e c h n i c a l d e t a i l s concerning process design and t e s t i n g , but a l s o estimates of the investment and o p e r a t i n g c o s t s . The papers have been organized f o r p r e s e n t a t i o n by process r e a c t o r type as p r e v i o u s l y d e s c r i b e d . The e x c e l l e n t response o f process developers to p a r t i c i p a t e i n t h i s symposium i s g r a t i f y i n g . β

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

16

SOLID WASTES AND RESIDUES

Table V PTGL PROCESS CATEGORIES* I

VERTICAL FLOW REACTORS D i r e c t Heat Transfer • Moving packed bed (shaft furnaces) • Moving staged s t i r r e d bed ( m u l t i p l e hearth furnaces) • Entrained bed (transport reactors)

II

III

FLUIDIZED BED REACTORS D i r e c t Heat Transfer

V VI

I n d i r e c t Heat Transfer ( r e c i r c u l a t i n g heat

HORIZONTAL OR INCLINED FLOW REACTORS D i r e c t Heat Transfer * Tumbling s o l i d s bed (rotary k i l n s ) * A g i t a t e d s o l i d s bed (on conveyer)

IV

I n d i r e c t Heat Transfer * Moving packed bed ( s h a f t furnaces) * Entrained bed ( r e c i r c u l a t i n g heat carrier)

I n d i r e c t Heat Transfer •Tumbling s o l i d s bed - Rotary c a l c i n e r s - Rotary v e s s e l s (recirculating heat c a r r i e r ) • A g i t a t e d s o l i d s bed (on conveyer) • S t a t i c s o l i d s bed (on conveyer)

MOLTEN METAL OR SALT BATH REACTORS Numerous flow and mixing options MULTIPLE REACTOR SYSTEMS Numerous flow and mixing options BACK-MIX FLOW REACTORS For s l u r r i e s and melts

Some r e a c t o r s may be designed w i t h numerous s o l i d s and gas f l o w regimes (countercurrent, cocurrent, s p l i t flow, c r o s s f l o w ) . A l s o known as f i x e d bed r e a c t o r s .

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

1.

JONES

Overview of Solid Waste and Residue

With few e x c e p t i o n s , the e n t i r e range of the technology i s represented. Every type of process r e a c t o r l i s t e d i n Table V (except the two that are checkmarked) w i l l be d i s c u s s e d . The r o t a r y k i l n r e a c t o r ( d i r e c t l y f i r e d ) i s the type being used a t the demonstration p l a n t i n B a l t i m o r e , Maryland. Information on that process may be obtained from many sources, such as r e f e r ences 36 and 37. The h o r i z o n t a l f l o w , s t a t i c s o l i d s bed r e a c t o r i s now being proposed o n l y f o r t i r e p y r o l y s i s and has not been described i n the open l i t e r a t u r e .

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

17

18

SOLID WASTES AND RESIDUES

LITERATURE CITED 1.

SRI International, Menlo Park, California, "Crop, Forestry and Manure Residue Inventory--Continental United States" (June 1976), report prepared for the U.S. Energy Research and Development Administration, Contract Ε(04-3)-115.

2.

"Fourth Report to Congress--Resource Recovery and Waste Reduction" (1977), U.S. Environmental Protection Agency, Report SW-600.

3.

Jones, J. L., Bomberger, D. C., and Lewis, F. Μ., "Energy Usage and Recovery i n Sludge Disposal," Water and Sewage Works (July 1977) 124(7), 44-47.

4.

Jones, J . L., et al., "Municipal Sludge Disposal Economics" (October 1977), Environmenta 11(10), 968-972.

5.

Jones, J . L., unpublished SRI International data (October 1977).

6.

Moore, J . G., J r . , "Wastewater Requirements Multiply Solids Problems, Hydrocarbon Processing (October 1976), 55(10), 98-101.

7.

Beckman, J. Α., et al., "Scrap Tire Disposal," Rubber Reviews--Rubber Chemistry and Technology (July 1974) 47, 597-627.

8.

Jones, J . L., "Converting s o l i d wastes and residues to fuel," Chemical Engineering (January 2, 1978), 85(1), 87-94.

9.

"Conversion to Coal F i r i n g Picks Up Steam" (February 14, 1977), Chemical Engineering, 84(4), 40, 42, 44.

10.

Venable, Ν. Μ., "Burning Refuse for Steam Production," Garbage Crematories in America, John Wiley and Sons, New York, 1906.

11.

Venable, E., "Burning Issues--Letter to the Editor," Chemical Engineering Progress (January 1977).

12.

Stephenson, J . Ν., and Cafeiro, S. Α., "Municipal Incinera­ tor Design Practices and Trends," Paper presented at the 1966 National Incinerator Conference (ASME) at New York, New York, May 1966.

13.

Combustion Engineering, Inc., Techno-Economic Study of Solid Waste Disposal Needs and Practices, U.S. Department of Health, Education and Welfare, Public Health Service (1969), SW-7c, PHS 1886.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

1.

JONES

Overview of Solid Waste and Residue

19

14.

"Nationwide Inventory of A i r Pollutant Emissions," 1968, U.S. National A i r Pollution Control Administration (1970), AP-73.

15.

"Present Status of Municipal Refuse Incinerators," American Society of Mechanical Engineers (January 1975).

16.

"Refuse to Energy Plant Uses F i r s t Von R o l l Incinerators i n United States," Environmental Science and Technology (August 1974) 8(8), 692-694.

17.

"Hard Road Ahead of City Incinerators," Environmental Science and Technology (November 1972), 6(12), 992-993.

18.

Weinstein, N. J . , and Toro, R. F., "Control Systems on Municipal Incinerators," Environmental Science and Tech­ nology (June 1976), 10(6), 545-547.

19.

" E l e c t r i c Utilities Recovery and Energ

20.

Niessen, W., et al., "A Review of Techniques for Incineration of Sewage Sludge with Solid Wastes (December 1976), EPA-600/2 EPA-600/2-76-288.

21.

Jones, J. L., "The Costs for Processing Municipal Refuse and Sludge" (1978), paper presented at the F i f t h National Conference on Acceptable Sludge Disposal Techniques, Orlando, Florida (January 31 to February 2, 1978). Pro­ ceedings to be published by Information Transfer, Inc., Rockville, Maryland, Spring 1978.

22.

"Garbage: New Fuel for Making Cement," Business Week (April 12, 1976), 720.

23.

News Release of the Ontario Ministry of the Environment, Toronto, Ontario, Canada (December 1976).

24.

"A Rice Hull Foundation for Cement," Business Week (April 12, 1976), 72Q.

25.

Tillman, D. Α., "Combustible Renewable Resources," Chemtech (1977), 7(10), 611-615.

26.

Gaunt, A. R., and Lewis, F. Μ., "Solid Waste Incineration i n a Rotary Hearth, Cyclonic Furnace," paper presented at the 67th Annual Meeting of the American Institute of Chemical Engineers, Tulsa, Oklahoma (March 1974).

27.

"Decision-Makers Guide i n Solid Waste Management" (1976), Environmental Protection Agency Report SW-500.

28.

Cost Estimates for Construction of Publicly Owned Wastewater Treatment Facilities--Summaries of Technical Data, Cate­ gories I-IV, 1976 Needs Survey(February 1977), Environmental Protection Agency Report 430/9-76-011.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

20

SOLID WASTES AND RESIDUES

29.

Pfeffer, J. T., "Reclamation of Energy from Organic Waste, U. S. Environmental Protection Agency, EPA-670/2-74-016 (1974).

30.

"Refuse Conversion to Methane-Pompano Beach, Florida"(1977), Waste Management Inc., Oak Brook, Illinois.

31.

Parkinson, G., "Short on Gas? Use L a n d f i l l " (February 13, 1978), Chemical Engineering, 85(4), 68, 70.

32.

Varani, F. T., Burford, J . , and Arber, R. P., "The Design of Large-Scale Manure/Methane Facility" (June 1977), Report from Bio Gas of Colorado, Inc., Arvada, Colorado.

33.

Scheller, W. Α., and Mohr, B. J . , "Gasoline Does, too, Mix with Alcohol" (1977), Chemtech, 7 (10), 616-623.

34.

Klee, J . , and Rogers, C. J . , "Biochemical Routes to Energy Recovery from Municipal " (1977) Proceeding f th Second P a c i f i c Chemica

35.

Jones, J . L., et al., "Worldwide Status of Pyrolysis, Thermal Gasification, and Liquefaction Processes for Solid Wastes and Residues (as of September 1977)," paper to be presented at the 1978 ASME National Solid Waste Processing Conference, Chicago, Illinois (May 1978).

36.

"Baltimore Demonstrates Gas Pyrolysis" (1974), U. S. Environ­ mental Protection Agency Report EPA/530/SW-75d.i.

37.

Weinstein, N. J . , Municipal Scale Thermal Processing of Solid Wastes, Environmental Protection Agency Report EPA/530/SW-133e (1977), available through NTIS, PB-263 396.

MARCH 3,

1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2

Economics Associated w i t h Waste or Biomass Pyrolysis Systems RICHARD BAILIE Chemical Engineering Department, West Virginia University, Morgantown, WV 26505 C. A. RICHMOND Wheelabrator Incineration, Inc., 600 Grant Street, Pittsburgh, PA 15219 In the early dats used as the primary f u e l nations wood was soon replaced by fossil fuels. Wood could not compete economically with these fossil fuels. U n t i l recent times, these fossil fuels were low in cost and available i n what seemed to be an endless supply. Recently, costs have risen and are expected to rise even further in the future. I t i s becoming more apparent that this supply of fuel is limited. Wood remains an alternative f u e l . Unlike fossil f u e l , wood i s not found i n large amounts i n concentrated areas. I t is available i n limited amounts spread over a wide area and is renewable. Consideration is being given to once again making more use of wood as a fuel source. In addition to wood, all plant life (biomass) can be used for its f u e l value. In the discussion to follow, wood represents but one type of biomass that may soon see use as a fuel. During the time that has elapsed since wood was widely used, several important changes have occurred. Two of these changes are: 7.

Energy consumption (both t o t a l and per capita) has increased dramatically.

2.

Size of energy conversion systems have increased. These large systems have achieved "economies of scale."

In terms of e l e c t r i c power generation, a 50 Mw power station i s extremely small and cannot achieve the thermal e f f i c i e n c i e s and economics that are attributed to larger systems. Even this size u t i l i t y would require 1,000 tons/day of biomass or 365,000 tons per year on a continuing basis. The Department of Energy has a study underway (1) to determine i f this amount of fuel can be obtained on a continuing basis i n a l o c a l area i n the Northeast. Wood may be burned d i r e c t l y to provide for generation of steam or e l e c t r i c i t y or i t may be converted to a more attractive fuel form such as gas or l i q u i d that may be transported to a central 0-8412-0434-9/78/47-076-021$05.75/0 © 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

22

SOLID WASTES AND RESIDUES

s i t e where generation of steam or e l e c t r i c i t y occurs. The f i n a l judgement as to what form biomass can most e f f e c t i v e l y be used as a f u e l must r e s t on economics. I t i s not l i k e l y t h a t there i s a s i n g l e conversion process that w i l l be p r e f e r r e d f o r a l l biomass f u e l s i n a l l s i t u a t i o n s . The most common process f o r conversion i s d i r e c t combustion of biomass. Burning of wood and bagasse to produce steam has been an e s t a b l i s h e d p r a c t i c e . There are many s i t u a t i o n s where d i r e c t combustion may not be the most a t t r a c t i v e a l t e r n a t i v e . This paper d e s c r i b e s one a l t e r n a t i v e to d i r e c t combustion of biomass. Biomass may be converted to a medium energy f u e l gas t h a t i s l a t e r burned. The paper makes the case f o r c o n s i d e r a t i o n of generating medium energy f u e l gas, desc r i b e s a system that can accomplish the conversion of gas at a moderate s c a l e , d i s c u s s e s the economics of t h i s system, and p r o v i d e s some examples as to how the medium energy gas compares to d i r e c t combustion. Reasons to Consider Mediu I f a power p l a n t operator were given a choice of n a t u g a l gas, petroleum, or c o a l as a f u e l ( a l l at the same cost i n $/10 Btu); n a t u r a l gas would be p r e f e r r e d . Some of the reasons f o r t h i s preference are: 1.

N a t u r a l gas can be burned i n an environmentally acceptable manner without a i r p o l l u t i o n c o n t r o l equipment.

2.

The s i z e of the furnace i s s m a l l e r . B e c h t e l i n a r e p o r t f o r the e l e c t r i c power i n d u s t r y (2) gave the r a t i o of 1.0/1.35/1.85 f o r gas, o i l and c o a l f u e l systems.

3.

There i s a lower maintenance f o r the gas systems.

fired

F i g u r e 1 i s a schematic that compares s o l i d f u e l and gas f u e l b o i l e r s . The area of the furnace b l o c k represents the s i z e . The n a t u r a l gas furnace r e q u i r e s no p o l l u t i o n c o n t r o l equipment. Both of these f a c t o r s r e l a t e d i r e c t l y to c o s t s . I t i s cheaper to conv e r t n a t u r a l gas than s o l i d f u e l to steam or e l e c t r i c i t y i n a u t i l i t y b o i l e r . In a d d i t i o n to these f a c t o r s , f a v o r i n g gas f i r e d systems, the hog f i r e d b o i l e r s and bagasse b o i l e r s have a lower t h e r mal e f f i c i e n c y . The s i z e of these biomass b o i l e r systems are much l a r g e r than these f o r f o s s i l f u e l s of the same c a p a c i t y . Based on these f a c t s , i t can be seen that n a t u r a l gas i s much more v a l u a b l e (on a Btu b a s i s ) than i s biomass f u e l . Biomass may be converted to a medium Btu f u e l gas. B e c h t e l Corporation i n t h e i r r e p o r t to the E l e c t r i c Power Industry (2) prov i d e d curves of the thermal e f f i c i e n c y , the a i r r e q u i r e d and the

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2.

BAILIE AND RICHMOND

Economics Associated with Waste

23

combustion products produced f o r gases of v a r y i n g f u e l v a l u e s . They are shown i n Figures 2 and 3. These curves show that a 300 Btu gas has a higher e f f i c i e n c y , lower a i r requirements and pro­ duce l e s s combustion product. This i n d i c a t e s that a 300 Btu gas could be burned as e f f e c t i v e l y as n a t u r a l gas. I f a 300 Btu gas can be exchanged f o r a n a t u r a l gas, then the statement regarding the d e s i r a b i l i t y of n a t u r a l gas can apply to t h i s f u e l gas. I t f o l l o w s that a 300 Btu gas would be p r e f e r r e d over biomass f u e l s i n their natural state. Figure 4 provides a r e p r e s e n t a t i o n of the f u e l costs and a l l other y e a r l y costs to o b t a i n steam or e l e c t r i c i t y from wood, c o a l , or a 300 Btu gas. The costs of o p e r a t i n g a wood f i r e d p l a n t i s higher than a c o a l f i r e d p l a n t . To produce e l e c t r i c i t y at the same c o s t , the b a s i c f u e l cost must be l e s s as shown i n Figure 4. The y e a r l y cost of o p e r a t i n g a gas p l a n t i s considerably l e s s (about 1/2) than f o r a c o a l p l a n t . I to Δ i n Figure 4 then woo e l e c t r i c i t y at the same p r i c e as c o a l . The s u b s t i t u t i o n of biomass f o r f o s s i l f u e l i n an e x i s t i n g f a c i l i t y i s seldom p o s s i b l e . The s i z e of a furnace i s l a r g e r f o r systems using a biomass f u e l than f o r f o s s i l f u e l s . Figure 5 shows a h i e r a r c h y of s u b s t i t u t i o n s that are p o s s i b l e . Gas may be s u b s t i t u t e d f o r petroleum, c o a l , and wood; p e t r o ­ leum may be s u b s t i t u t e d f o r c o a l and wood; and c o a l may be sub­ s t i t u t e d f o r wood. S u b s t i t u t i o n s cannot normally be made i n the reverse d i r e c t i o n without major r e t r o f i t and/or d e r a t i n g of the boiler. N a t u r a l gas i s p r e d i c t e d to be the f i r s t form of f o s s i l f u e l to become depleted (estimates p r e d i c t as l i t t l e as eleven years of n a t u r a l gas remain). Industry has already f e l t c u r t a i l m e n t and i t may be s a f e l y p r e d i c t e d that i t w i l l be i n d u s t r y that w i l l be f i r s t to f e e l any e f f e c t s o f dwindling s u p p l i e s . Experience over the l a s t two years shows i n d u s t r y i s the f i r s t to f e e l the e f f e c t s o f c u r t a i l m e n t . What w i l l happen to i n d u s t r i a l and u t i l i t y b o i l e r s b u i l t to f i r e gas? Many of these are r e l a t i v e l y new and many were i n s t a l l e d to meet environmental r e g u l a t i o n s . They are h i g h l y e f f i c i e n t and are i n e x c e l l e n t o p e r a t i n g c o n d i t i o n , but cannot be switched to o i l o r c o a l . In such a s i t u a t i o n a customer w i l l be w i l l i n g to pay a premium p r i c e f o r a gas that may be sub­ s t i t u t e d f o r n a t u r a l gas and use t h i s f a c i l i t y . The a l t e r n a t i v e would be to r e t i r e the present system and commit the c a p i t a l t o b u i l d a new (and expensive) furnace. In such a s i t u a t i o n , a 300 Btu gas becomes an a t t r a c t i v e f u e l . Economics of Medium Energy Gas

Production

2 Two processes are a v a i l a b l e that can produce a 300-400 Btu/ f t f u e l gas from biomass that have been demonstrated i n p i l o t plant s i z e operations.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID WASTES AND RESIDUES

Clean-Up

Solid Fuel

Furnace

Natural Gas ,

- • Steam or Electricity

Furnace

- Steam or Electricity

Figure

1,000

800

Flue Gas per 10,000 Btu of Fuel Fired

Theoretical Air Required to Burn 10,000 Btu of Fuel

ο 600h

05 400

200 J 0

2

4

J 6

I 8

I 10

I 12

L 14

16

Pounds

Figure 2.

Theoretical air and flue gas

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2.

BAILIE AND RICHMOND

25

Economics Associated with Waste

100 h

90

80

70 I

J_ 200

400

600

800

J 1000

Figure 3.

Gas Fuel Btu/Cu. Ft.

Wood-Gas

Wood

Unit efficiency

Coal

Unit Cost of Electricity (KWH)

Basic Fuel Cost I All other yearly costs.

J

Figure 4.

Cost breakdown for electricity from coal, wood, or wood^gas

Gas

i Petroleum

c

°

a l

I

Wood or Bagasse

Figure 5. Fuel substitution hierarchy

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

26

SOLID WASTES AND RESIDUES

1.

Purox - Union Carbide has operated a 200 ton/day p i l o t f a c i l i t y i n I n s t i t u t e , West V i r g i n i a ( 3 ) . The major system components are a s h a f t k i l n and an Oxygen p l a n t .

2.

Pyrox - K i k a i K u n i i has operated a 50 ton/ day p i l o t f a c i l i t y i n Japan. Some r e s u l t s have been reported by K u n i i ( 4 ) .

Both of these systems have used m u n i c i p a l waste to produce an i n t e r mediate Btu gas and the Pyrox u n i t has been operated on biomass. Since the organic p o r t i o n of m u n i c i p a l waste i s p r i m a r i l y c e l l u l o s e , comparable performance should be expected from s o l i d waste or biomass. Both processes p y r o l y z e the organic p o r t i o n present i n the s o l i d f u e l . To produce an i n t e r m e d i a t e Btu gas, i t i s necessary that the gas i s not d i l u t e t h i s i s accomplished by an a i r s e p a r a t i o n p l a n t . In the s i n g l e s h a f t k i l n r e a c t o r , both a combustion r e a c t i o n and p y r o l y s i s occur. In the Pyrox Process the combustion r e a c t i o n and the p y r o l y s i s take p l a c e i n separate f l u i d i z e d bed r e a c t o r s . S o l i d s c i r c u l a t e between the two beds to prov i d e the heat needed f o r the p y r o l y s i s r e a c t i o n . In the United States market, the p y r o l y s i s process developed by B a i l i e and a v a i l a b l e through Wheelabrator I n c i n e r a t i o n , I n c . , i s comparable to the Pyrox system. This process was the one sel e c t e d f o r t h i s paper because the authors are more f a m i l i a r w i t h the process economics and i t i s more compatible w i t h the modest s i z e d f a c i l i t y needed f o r most biomass conversion s i t e s . In a recent r e p o r t by B a t t e l l e i n a study of sugar cane as a f u e l crop (5) the f o l l o w i n g comment was made: Commercialization of r e l a t i v e l y s m a l l s y n t h e s i s gas p l a n t s needs a process such as P r o f e s s o r R. C. B a i l i e (1972) has suggested so t h a t the expense of an oxygen f a c i l i t y can be avoided. . . .The process i s admittedly s p e c u l a t i v e but i t s t r i k e s d i r e c t l y at a major drawback of the processes d i s c u s s e d a b o v e — t h e need f o r an e n e r g y - i n t e n s i v e oxygen p l a n t . F i g u r e 6 i s the b a s i c schematic of the two f l u i d i z e d bed process. The s o l i d f u e l i s fed i n t o a p y r o l y s i s r e a c t o r at about 1500 F. This r e a c t o r i s composed of hot i n e r t sand. Heat t r a n s f e r to the s o l i d feed i s r a p i d and p y r o l y s i s occurs. The r a p i d heat t r a n s f e r leads to h i g h gas y i e l d s ( 6 ) . The f u e l gas goes to a cyclone where the char i s removed. The char i s fed along w i t h a i r to a second f l u i d bed h e l d at about 1800 F. Combustion takes p l a c e and provides the energy needed f o r the p y r o l y s i s r e a c t i o n . This energy i s t r a n s f e r r e d to the p y r o l y s i s bed by a sand c i r c u l a t i o n system between the two r e a c t o r s .

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Figure 6.

CHAR

SAND

FUEL GAS + CHAR

PYROLYZER

1500°F

FUEL GAS

.

SOLID WASTE OR BIOMASS

FUEL GAS RECYCLE

Schematic flow diagram of two-reactor system: temperature—1800°F, 1500°F; feed—char —unsorted waste or biomass; products—fuel gas + char + solid waste

COMBUSTOR

1800°F

COMBUSTION GASES

- •

28

SOLID WASTES AND RESIDUES

Stanford Research I n s t i t u t e r e c e i v e d a c o n t r a c t from West V i r g i n i a U n i v e r s i t y to make an economic e v a l u a t i o n of the two f l u i d bed system to produce an intermediate Btu f u e l gas from s o l i d waste ( 7 ) . B e c h t e l Corporation working f o r the C i t y of C h a r l e s t o n , West V i r g i n i a , i n preparing a grant a p p l i c a t i o n to EPA provided a second economic e v a l u a t i o n of the two f l u i d bed system ( 8 ) . They confirmed the economics and process flow sheet given i n the SRI study. These s t u d i e s were made i n 1972 at a C. E. cost index of 135. For t h i s paper, the c o s t s are updated to a C. E. index of 210. The process flow sheet provided by Stanford Research I n s t i t u t e i s d i v i d e d i n t o three s e c t i o n s : f u e l p r e p a r a t i o n , p y r o l y s i s , and gas clean-up and a d e t a i l e d equipment l i s t . The totajL c a p i t a l i n v e s t ­ ment i n 1977 d o l l a r s i s estimated to be 18.2 χ 10 as shown i n Table 1. The annual opergting c o s t s were taken as 1.5 times the costs i n 1972 or $3.0 χ 10 /year produced from m u n i c i p a l s o l i The product gas composition developed by S.R.I, i s given i n Table 3 and the m a t e r i a l balance i n Table 4. The energy y i e l d i s defined as: Energy Value = Higher Heating Value of Gas Higher Heating Value of F u e l g y

was

77%. Chiang, Cobb and K l i n z i n g (11) have j u s t completed a study f o r Resources of the Future where they estimate the cost of f u e l gas from refuse u s i n g m u n i c i p a l waste. They based t h e i r values on the same S.R.I, study p r e v i o u s l y c i t e d ( 7 ) . These authors assumed t h a t between 1972 and 1977, the c a p i t a l costs e s c a l a t e d by a f a c t o r of 4 and the o p e r a t i n g costs doubled. Under these assump­ t i o n s and using economic c r i t e r i a s i m i l a r to "low debt economics" they c a l c u l a t e d t h a t the gas would cost $6.14/10 Btu w i t h no drop charge. The S.R.I, study cost estimate was made based upon s i z i n g and c o s t i n g a l l of the major equipment items. I t would seem t h a t the C. E. cost index between 1972 and 1977 (210/135 = 1.56) would be a more a p p r o p r i a t e procedure to update the c a p i t a l c o s t . I f a f a c t o r of 1.56^were used i n p l a c e of 4.00, the f u e l gas cost be­ comes $2.60/10 Btu which i s i n s u b s t a n t i a l agreement w i t h the cost of $2.28/10 Btu shown i n Table 2. In a more recent cost estimate by B a t t e l l e (5) the cost of gas produced i n a two f l u i d bed system i s given i n Table 5. In c o n v e r t i n g t o t a l c a p i t a l c o s t s to annualized c a p i t a l charges the r a t i o of annualized c a p i t a l costs to c a p i t a l c o s t s obtained from the c o s t s of the two bed system f o r the p y r o l y s i s of bagasse obtained by B a t t e l l e were used. The r a t i o s used were: (1) 0.167 f o r low debt economics and (2) 0.09 f o r high debt economics.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

BAILIE AND RICHMOND

Economics Associated with Waste

Table (lOOO ton/day y Municipa D o l l a r Amounts i n M i l l i o n s Feed P r e p a r a t i o n Pyrolysis Product Recovery Total Utilities General F a c i l i t i e s Total Land Start-up Working C a p i t a l Total T o t a l Working C a p i t a l

) ^-8 6.1 2· j+ 13-5 2.2 0*8 3.0 2

· .8 «8 1-8 18.2

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

30

SOLID WASTES AND RESIDUES

Table I I . Annual Operating Costs and Gas Costs Low Debt* Economics Operating Costs Annualized C a p i t a l Charge Total (

$3.0xl0 2.8 T75

6

High Debt* Economics (l.l8) (l.lO) (2.28)

3-0 1.6 Ο

(l.l8) (0*63) (1.81)

) φ per 10 B t u

* These are t h e economics developed and used by B a t t e l l e i n t h e i r r e c e n t study f o r D.O.E. and g i v e n i n Appendix A.

Table I I I .

Composition o f Product Gas from Two-Reactor System ( i n Mole P e r c e n t )

CO

co

H

2

Dry, C0 -Free

27.1# 1^.7

31.TS6 0.0

kl.J

2

c%

C2 unsaturates C H6 C3 unsaturates 3 8 Total 2

C

Dry Gas

H

7.7 7.1 0.7 0.6 0Λ 100.0$

h3.9 9.0 8.3 0.9 0.7

°Λ

100.0$ 529

Gross h e a t i n g value ( B t u / s c f ) Y i e l d o f gas, s c f / l b dry r e f u s e

2

9-3

8.0

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Depreciation Schedule

Investment Tax C r e d i t

0.0142 0.2355 Ο.Ο683

0.0261 0.2355 0.1052

3.0

0.2k

3.0

0.2k

O.3O O.7O Ο.Ο85 0.15 O.5O 20.0 11.0

Other

0.30 0.70 Ο.Ο85 0.15 O.5O 25.Ο 25.Ο

Steam P l a n t

Low Debt Economics

, t

Values f o r Economic Parameters

0.1k

0.0191 0.1645 O.067O

0.50 25.0 25.0 0.24 3.0

0.60 0.40 0.0875

Steam P l a n t

TT

0.0329 0.1645 0.1029

0.60 0.40 0.0875 0.l4 O.5O 20.0 11.0 0.24 3.0

Other

High Debt Economics

a

2k

12

1

0.05tL 0.0906 SL Ο.Ο889 0.0535 SL 0.1052 O.067O 0.1029 Ο.Ο683 SYD 12 0.0729 0.1047 0.1077 0.0715 0.0871 0.1224 Ο.Ο85Ο SYD 2k 0.1187 0.1046 0.0688 0.1046 0.0681 DDBSL 12 0.0829 0.1192 0.0823 DDBSL 2k 0.1173 A s t r a i g h t l i n e d e p r e c i a t i o n (SL) schedule was assumed f o r the values presented i n the upper p o r t i o n of Table A - I . I f a sum-of-the-year s d i g i t s (SYD) d e p r e c i a t i o n schedule and/or a 12 percent i n v e s t ­ ment t a x c r e d i t had been assumed the impact on t h e "Constant f o r ( F ) b e a r i n g the symbol L" would be t a b u l a t e d as i n the lower p o r t i o n o f Table A - I . S i m i l a r l y , values a r e shown f o r computations u s i n g a double d e c l i n i n g balance w i t h a s h i f t t o s t r a i g h t l i n e ( i n t h e n/2 year) d e p r e c i a t i o n schedule DDBSL i n the lower p o r t i o n o f Table A - I . (Constants f o r (Τ-W) and (τ) a r e n o t s u b j e c t t o change.)

A

J Κ L

Constant f o r (Τ-W) Constant f o r (τ) Constant f o r ( F )

E/T

i I R Ν η Ρ Y

D/T

Symbol

Debt f r a c t i o n Equity f r a c t i o n Interest rate Return on e q u i t y Tax r a t e P r o j e c t l i f e , years D e p r e c i a t i o n l i f e , years Investment t a x c r e d i t Years f o r t a x c r e d i t

Term

Table A - I .

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2

2

3

H

8

6

Note:

Total

C

2

2

H CJ% C2H C % C H 3 6 C H Liquids Ash Char

co

Feed CO

3.81* vt#

—

values.

22.32 -Wtfo

--

(0.12)

--

22.32 Wt/o 10.68 11.52

3.81* wt#

2.05 0.76 0.27 0.l6 0.11 (0.09) (0.O8) (O.32)

0

H

Parentheses i n d i c a t e estimated

30.85 vtjt

7.35

2.25 3.22 0.95 0.1*3 (0.52) (0.35) 3^5

—

3Ο.85 vtjt 8.01 1+.32

c

(0.1) (O.l) Wt/o

(ô~3)

( ο Λ ) vt/o

--

—

--

—

—

---

( O . l ) Vt/o

s

(0.1)

—

---

--

—

--

( 0 Λ ) wt/o

Ν

Table IV. Y i e l d s from P y r o l y s i s o f Refuse (Dry B a s i s - Weight Percent)

1+2.1*9 Μή$

--

—

1*2.1*9

--

—

--

—

1*2Λ9 wt#

ASH

100.00vt$

100.00vt$ I8.69 15.81* 2.05 3.01 3.^9 1.11 0.5^ 0.61 0.1*3 3.99 1*2.1*9 7.75

Total

to

2.

BAILIE AND RICHMOND

Table V.

Product Cost f o r a P l a n t of 1530 Tons/day

Raw M a t e r i a l Costs ( $ 1 . 0 0 / l 0 Operating Costs Annualized C a p i t a l Charge

($/l0

6

Btu)

7-9 3.9 3.6 15 Λ

Total 6

33

Economics Associated with Waste

(l.2) (0.6) (0.6) (2Λ)

7-9 ( l . 2 ) 3.9 ( 0 . 6 ) 2.0 ( 0 . 3 ) 13-8

Btu)

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

(2.l)

SOLID WASTES AND RESIDUES

34

These same r a t i o s were used throughout t h i s paper to convert t o t a l c a p i t a l cost to annualized c a p i t a l c o s t s . The b a s i s B a t t e l l e used f o r these two cases i s given i n Appendix A. The values provided by B a t t e l l e (5) were modified to r e f l e c t an energy y i e l d of 80% r a t h e r than the 62% used i n that study. Wheelabratog I n c i n e r a t i o n , Inc. (9) r e c e n t l y provided an estimate of $2.00/10 Btu f o r producing a gas from wood waste i n a p l a n t of 250 tons c a p a c i t y . In p r e p a r i n g the cost e s t i m a t e , B a t t e l l e used the gas compositions shown i n Table 6. The cost of f u e l produced i s not s e n s i t i v e to p l a n t s i z e . The cost a n a l y s i s f o r both SRI and B a t t e l l e were f o r dual t r a i n s fed 500 to 750 tons/day of s o l i d feed and there i s l i t t l e cost d i f f e r e n t i a l i n s i z e s above 500 tons/day. The cost estimates given above provide evidence that biomass can be^converted to a medium Btu gas at a cost of $2.00 to $2.50 per 10 Btu w h i l e m u n i c i p a l waste w i l l produce e g s e n t i a l l y the same q u a l i t y gas f o r abou timates assume that the cost at the s i t e was zero f o r m u n i c i p a l waste and $1.00/10 Btu f o r biomass. For m u n i c i p a l waste there would be a drop charge. This would decrease the cost of the gas produced. For biomass, there i s a cost a s s o c i a t e d w i t h t r a n s p o r t i n g the biomass from the l o c a t i o n i t was harvested to the p l a c e where i t i s to be converted to a gas. The cost a s s o c i a t e d w i t h the t r a n s p o r t a t i o n of the b i o mass and f u e l gas are not considered i n these estimates. System A p p l i c a t i o n s In t h i s s e c t i o n s e v e r a l a p p l i c a t i o n s u s i n g intermediate energy gas made from biomass are described and some economics developed. Application 1 The Department of Energy i s supporting a study on the f u e l i n g of a 50 Mw e l e c t r i c p l a n t w i t h wood. The most s t r a i g h t forward approach i s to burn the f u e l i n a power p l a n t . An a l t e r n a t i v e to t h i s approach i s to produce a gas (to be c a l l e d wood-gas) and f i r e t h i s gas i n a gas f i r e d power p l a n t . There are s e v e r a l advantages to t h i s approach. These i n c l u d e : a)

Lower power p l a n t c o s t s - A gas f i r e d power p l a n t costs about one h a l f as much as a s o l i d f u e l e d plant.

b)

Higher combustion e f f i c i e n c y - A gas f i r e d system uses l e s s excess a i r and combustion i s more complete than i n a wood f i r e d system.

c)

E n v i r o m e n t a l l y a t t r a c t i v e - A gas f i r e d p l a n t needs no s t a c k clean-up to meet environmental standards.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

BAILIE AND RICHMOND

Table V I .

Economics Associated with Waste

Estimated Composition o f Output Gas — Process fro

Bailie

Mole Percent Dry B a s i s Bagasse co co Ho C% C hydrocarbons C3 hydrocarbons H2O ( i f wet) Net Heating Value 2

2

23.29 23.01* 35.38 8.53 8.66 1.10 (25.56) lk.96 MJ per scm (1*01 B t u per s c f ) (dry)

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID WASTES AND RESIDUES

36 d)

Lower maintenance - A gas f i r e d p l a n t has much l e s s maintenance than a s o l i d f u e l e d p l a n t .

The disadvantages i n c l u d e the cost of the p l a n t needed to generate the f u e l gas and the l o s s of heating value r e s u l t i n g from the a d d i t i o n a l processing. In comparing the d i r e c t wood f i r e d system to the wood-fuel g a s - e l e c t r i c p l a n t , the f o l l o w i n g assumptions were made: 1.

C a p i t a l cost and operating cost of a wood f i r e d e l e c t r i c generating p l a n t i s twice that of a n a t u r a l gas f i r e d system.

2.

To produce 1 Kw-hr o f e l e c t r i c i t y from wood r e q u i r e s 12,750 B t u and from n a t u r a l gas i s 11,000 Btu. This i s f o r a 55 Mw system

3.

F u e l gas can

A study by M i t r e (9) estimated the c a p i t a l cost of a 55 Mw b o i l e r f i r i n g wood i s $55 χ 10^ and the operating cost i s $3.6 χ 10 /year. The previous s e c t i o n provided estimates of f u e l costs from wood t o be 2.1 χ 1 0 Btu and 2.4 χ χ 1 0 Btu f o r low debt and high debt economics. Using these values and the assumptions given above, i t i s p o s s i b l e to compare d i r e c t wood f i r e d systems to woodgas f i r e d systems. The r e s u l t s are summarized i n Table 7. The r e s u l t s shown i n Table 7 i n d i c a t e : 6

6

a)

The cost of e l e c t r i c i t y from d i r e c t wood f i r i n g are equal t o or more expensive than wood gas f i r i n g systems.

b)

The cost i s s t r o n g l y a f f e c t e d by the method of financing.

c)

For low debt f i n a n c i n g e l e c t r i c i t y from wood gas i s about 20% l e s s than d i r e c t wood f i r i n g . For high debt f i n a n c i n g the cost i s comparable.

F i g u r e 7 shows the e f f e c t of the raw m a t e r i a l costs ( b a s i c wood cost) on the cost of e l e c t r i c i t y . The d i f f e r e n t i a l between the two a l t e r n a t i v e s remains constant w h i l e the percentage d i f f e r ­ ence decreases w i t h f u e l c o s t . Application 2 I t was suggested e a r l i e r that the conversion of wood to a f u e l gas would be p a r t i c u l a r l y important i f there was an e x i s t i n g f a c i l i t y that would be shut down i f n a t u r a l gas was c u r t a i l e d . The i n d u s t r y would not only pay the cost of a new wood burning

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2.

BAILIE AND RICHMOND

Table V I I .

Economics Associated with Waste

37

Comparison o f E l e c t r i c Costs f o r Wood-Electric and Wood-Gas-Electri

6

F u e l Costs (Wood @ $ l / l 0 ) Operating Costs ($106/yr) Annualized C a p i t a l Costs Mlll/Kw-hr

Wood-- E l e c t r i c

Wood-• G a s - E l e c t r i c

High Debt

High Debt

k.l 3-6 k.Q 12.5 m

Low Debt

k.l 3-6 8.5 1ÏÏT2 (58)

8Λ 1.8 2.k 1275" (ko)

Low Debt

8.k 1.8 k.2 1O (k6)

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLED WASTES AND RESIDUES

38

f a c i l i t y , but would be f o r c e d to pay the annualized c a p i t a l cost f o r the i d l e n a t u r a l gas p l a n t . Figure 8 shows the e l e c t r i c c o s t s f o r a new wood f i r e d p l a n t and f o r wood-gas used i n an e x i s t i n g n a t u r a l gas p l a n t as a f u n c t i o n of wood f u e l c o s t . The only d i f f e r e n c e i n t h i s f i g u r e and that shown i n F i g u r e 7 i s the annuali z e d c a p i t a l cost f o r the i d l e gas p l a n t i s added to the cost of a new wood burning p l a n t . For e i t h e r f i n a n c i n g scheme, the wood gas p l a n t provides e l e c t r i c i t y a t a s i g n i f i c a n t l y lower cost than the d i r e c t f i r e d ^ s y s t e m . For the case where the b a s i c wood f u e l c o s t s are $1.00/10 B t u , the d i f f e r e n t i a l s are 15.6 and 35.7%, r e s p e c t ively. Application 3 The economies of s c a l e are s i g n i f i c a n t i n u t i l i t y power s t a t i o n s . The M i t r e report (10) provides cost estimates f o r p l a n t s using 850, 1700 and 340 converted to annualized v i o u s l y d e s c r i b e d . I n comparing c o s t s i t was assumed that the cost of the wood to gas conversion f a c i l i t y d i d not b e n e f i t from economies of s c a l e . This i s not true f o r other types of convers i o n f a c i l i t i e s . For example, the Union Carbide Process b e n e f i t s g r e a t l y from an i n c r e a s e i n s c a l e . This i s because the economies r e s u l t i n g from the l a r g e r oxygen p l a n t needed i n t h i s process. There are some s m a l l economies of s c a l e that would lower the curves f o r the wood gas systems a t l a r g e r c a p a c i t y . The curves i n F i g u r e 9 r e f l e c t the i n c r e a s e i n t r a s n p o r t a t i o n c o s t s f o r l a r g e r p l a n t s . In e v a l u a t i n g the t r a n s p o r t a t i o n costs the f o l l o w i n g assumptions were made: 1.

Cost of t r a n s p o r t a t i o n i s $0.10 per t o n m i l e .

2.

The average d i s t a n c e t r a v e l e d f o r v a r i o u s s i z e p l a n t s were: 850 tons/day 1700 tons/day 3400 tons/day

35 m i l e s 46.7 m i l e s 66 m i l e s

In F i g u r e 9 the cost of e l e c t r i c i t y i n d i r e c t f i r e d p l a n t s are seen t o cross the wood-gas f i r e d curves f o r h i g h c a p a c i t y . This i s a d i r e c t r e s u l t of not b e n e f i t i n g from economies of s c a l e for the wood-gas generators. Since there i s no cost advantage i n l a r g e r gas generating f a c i l i t i e s , i t would be more a t t r a c t i v e to l o c a t e the p l a n t s c l o s e r t o the wood source and p i p e l i n e the gas to a l a r g e c e n t r a l gas f i r e d u t i l i t y . This would reduce the d i s tance the wood i s hauled and the cost a s s o c i a t e d w i t h moving the wood t o a c e n t r a l p l a n t . This would reduce the cost below those shown i n F i g u r e 9 f o r the gas f i r e d systems. I n Figure 9 the wood-gas curves do not r e f l e c t e i t h e r the s m a l l but r e a l economies

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

BAILIE

A N D RICHMOND

Economics Associated with Waste

Figure 7. Electric cost comparison between woodfiredand wood gasfired:( ) woodfired;( ) wood/gas fired

Debt Economics

Economics

$1.00

$3.00

$2.00 6

Basic Cost of Wood $ / 1 0 Btu

Figure 8. Cost comparison of electricity betweenfiringwood gas in existing plants and building new directfiredplants: ( ) new woodfiredphnts; ( ) existing plantfiredwith wood gas

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLED

40

Figure 9.

WASTES

AND

Economies of scale

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

RESIDUES

2.

BAILIE

A N D RICHMOND

Economics Associated with Waste

41

of s c a l e o r the lower t r a n s p o r t a t i o n c o s t s . The s i t u a t i o n f o r wood gas would be b e t t e r than that shown i n F i g u r e 9. Application 4 The f i n a l h y p o t h e t i c a l s i t u a t i o n considers the use of m u n i c i p a l waste t o provide a f u e l gas t o a l a r g e m a l l , group of commerc i a l establishments o r i n d u s t r i a l park. Table 2 provided e s t i mates f o r the cost of f u e l gas from m u n i c i p a l waste. I n t h i s t a b l e no charge was made f o r the f u e l . For the case of m u n i c i p a l waste, a drop charge i s imposed i n order t o leave the waste a t the f a c i l i t y . E i g h t d o l l a r s per ton i s considered t o be a reasonable charge. I f four d o l l a r s of t h i s could be assigned t o s u b s i d i z e the wasteto-gas process, a c r e d i t of $0.79 per 10^ Btu i s r e a l i z e d . This reduces the gas cost to $1.06 t o $1.53 per m i l l i o n Btu. A t t h i s p r i c e i t becomes a h i g h l y c o m p e t i t i v e f u e l . This f u e l gas can be transported by p i p e l i n f i r e d equipment. This become c a p i t a l cost between gas f i r e d equipment t o s o l i d f i r e d equipment i s o f t e n as low as 1/6 f o r s m a l l commercial u n i t s . Conclusions 1.

Biomass and m u n i c i p a l waste can be converted t o an intermediate energy gas.

2.

The gas produced i n the twin f l u i d i z e d bed can s u b s t i t u t e f o r n a t u r a l gas i n e x i s t i n g equipment.

3.

The energy l o s t i n the biomass t o gas conversion system i s l a r g e l y made up i n higher combustion e f f i c i e n c y i n the power p l a n t .

4.

The cost of the wood-gas i s i n the p r i c e range of $2.00 t o $3.00 per 1 0 B t u . 6

5.

The economic choice between d i r e c t f i r e d o r wood gas f i r e d i s h i g h l y dependent on the method of f i n a n c i n g . I f there i s an advantage, i t would appear t o be w i t h wood-gas.

6.

Wood gas systems producing intermediate gas have not seen commercial o p e r a t i o n and has no t r a c k r e c o r d . D i r e c t f i r e d systems are o p e r a t i n g commercially but have a s p o t t y r e c o r d .

7.

When o p e r a t i n g n a t u r a l gas f i r e d u n i t must be r e p l a c e d by a wood f i r e d u n i t , i t becomes more a t t r a c t i v e t o convert wood t o gas and use the existing f a c i l i t y .

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

42

SOLID

WASTES

AND

RESIDUES

8.

For power generating systems, economies of s c a l e are s i g n i f i c a n t f o r d i r e c t f i r e d systems. The wood gas to e l e c t r i c system i s l e s s s e n s i t i v e to s c a l e because the wood gas generating system i s i n s e n s i t i v e t o s c a l e . M u l t i p l e u n i t s are b u i l t f o r l a r g e s i z e a p p l i c a t i o n s . For the Union Carbide Purox system economies of s c a l e are achieved and t h i s c o n c l u s i o n would not apply i f t h i s u n i t were s e l e c t e d to produce wood-gas.

9.

M u n i c i p a l waste can produce a f u e l gas a t a lower cost because there i s no charge f o r the feed and the system w i l l r e c e i v e a subsidy through a drop charge.

The paper has emphasized wood which was s e l e c t e d to represent biomass. Other biomas bed system w i l l more r e a d i l d i f f e r i n g p h y s i c a l c h a r a c t e r i s t i c s than the Purox system or d i r e c t f i r e d b o i l e r s . I f i t i s not p o s s i b l e to provide assurances of the economic advantages that may be obtained from wood gas there i s l i t t l e doubt that the economics of today show t h i s o p t i o n i n a more f a v o r a b l e l i g h t than the economics of a few years ago. The longest c o a l s t r i k e i n h i s t o r y i s underway. I t shows how dependent the n a t i o n i s on c o a l . The cost of c o a l w i l l without q u e s t i o n r i s e s i g n i f i c a n t l y under any new c o n t r a c t . This w i l l see a f u r t h e r s h i f t toward f a v o r a b l e economics f o r biomass u t i l i z a t i o n

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

2.

BAILIE AND RICHMOND

Economics Associated with Waste

43

REFERENCES 1Study for the United States Department of Energy, prepared by Wheelabrator Clean Fuels Corporation. 2E.P.R.I., "Fuels from Municipal Refuse for Utilities: Tech­ n i c a l Assessment." E.P.R.I. Report 261-1, March 1975 (Prepared by Bechtel Corporation). 3Fisher, T. F., Kasbohn M. L. and J . R. Riverο, "The Purox System," presented at the 80th National Meeting of the American Institute of Chemical Engineers, September 9, 1975. 4Hasegawa, Μ., Fukuda, J. and D. Kunii, "Research and Develop­ ment of Circulating System Between Fluidized Beds for Application of Gas-Solid Reactions, Congress, Denver, Augus 5

B a t t e l l e Columbus, "Fuels from Sugar Crops," BMI Report 1957A, Volume 1 through 5, March, 1977. 6Douglas, Ε., M. Webb and E. Daborn, "The Pyrolysis of Waste and Product Assessment," paper presented at Symposium on Treatment and Recycling of Solid Wastes, Manchester, England, January, ]974. (Available through Warren Spring Laboratory, Department of Industry.) 7

A l b e r t , S. B., et. al., "Pyrolysis of Solid Waste: A Techni­ c a l and Economic Assessment," P.B. 218-231, September, 1972. 8Bechtel Corporation, "West V i r g i n i a Recycle Resource Recov­ ery Center," Technical and Economic Review for City of Charleston, July 15, 1972. 9 B a i l i e , R. C. and C. A. Richmond, "New Technology and Pyroly­ s i s of Wood and Wood Waste." paper presented at the 1978 Regional Tappi Conference i n Portland, Oregon. 10Mitre Corporation, "Siloculture Biomass Farm," Mitre Techni­ c a l Report Number 7347, Volume 1 through 5, May 1977. 11Chiang, S. H., J . T. Cobb and G. E. Klinzing, "A Critical Analysis of the Technology and Economics for the Production of Liquid and Gaseous Fuels from Wastes," paper presented at the 85th National Meeting of the American Institute of Chemical Engineers, Atlanta, Georgia, February 27, through March 2, 1978. APRIL 7,

1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

3 The Andco-Torrax High-Temperature Slagging Pyrolysis System P A U L E . D A V I D S O N and T H E O D O R E W . L U C A S , JR. Andco-Torrax Division, Andco Incorporated, 25 Anderson Road, Buffalo, N Y 14225

The Andco-Torrax syste process known technically solid waste is a relatively new innovation, pyrolysis processes have been used for years by industry. Typical examples are found in the production of char and methanol from wood and coal gasification. Pyrolysis, commonly referred to as destructive distillation, is defined as an irreversible chemical change brought about by the action of heat in an oxygen deficient atmosphere. The pyrolysis of organic material causes the volatile fraction to distill, forming combustible liquids and vapors. The vapors are composed primarily of methane, hydrogen, carbon monoxide, carbon dioxide, water and the more complex hydrocarbons such as ethane, propane, oils and tars. The exact components in percent composition of these gases formed by pyrolysis of municipal waste cannot accurately be predicted in that, in a real system, the complex multi-component fractions would be converted to more stable gases such as ethylene through a continuing pyrolysis action and are a result of complex time/temperature kinetic reactions. The material remaining after pyrolysis is char, a charcoal-like substance consisting primarily of fixed carbon residue. In the Andco-Torrax system, the char remaining from the pyrolyzed material is burned to carbon monoxide and carbon dioxide using high temperature air, thus releasing sufficient heat energy to convert all non-combustibles contained in the solid waste to molten slag and to further pyrolyze incoming waste material. PROCESS DESCRIPTION The" principal components of the Andco-Torrax system are the gasifier, secondary combustion chamber, primary air preheating equipment, waste heat boiler, and gas cleaning system. These components are shown in Figures 1 and 2. These figures illustrate the primary air preheating system as a regenerative tower system, although other alternatives may be used which could include a heat recuperator or a fossil fuel fired air preheater. The gasifier and secondary combustion chamber comprise the main process 0-8412-0434-9/78/47-076-047$05.00/0 © 1978 American Chemical Society American Chemical Society Library In Solid 1155 Wastes and Jones, 1 6 tResidues; h S t . X. W . J., et al.; ACS Symposium Series; American Chemical DC, 1978. Washington, D . C . Society: 2 0 0 3 Washington, 6

SOLID

48

Figure 1.

Figure 2.

WASTES

AND

Andco-Torrax system

Andco-Torrax system schematic

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

RESIDUES

3.

DAVIDSON

A N D LUCAS

High-Temperature Slagging Pyrolysis System

49

components and are shown in Figure 3. Gasifier A crane with grapple bucket removes refuse from the refuse pit without pretreatment other than the shearing of oversize items to approximately one meter dimensions. The refuse is directed into a hopper from which it is fed into the top of the gasifier by either a reciprocating ram or a v i brating feeder. The gasifier is a vertical shaft furnace so designed that the descending refuse burden and the ascending high temperature gases become an effective countercurrent heat exchanger. The gasifier shaft is 12-15 meters (40'-50') in overall height, 1.8-2.7 meters (6'-9') in diameter, and is fabricated from mild steel with refractory lining in the lantern and hearth areas only. The main stack between the lantern and hearth is externally cooled over its length by a jacketed water cascade. The hopper has a loose sealing mechanism to decrease the infiltration of air into the top of the gasifier. As the zones are encountered - drying function of the drying zone is to evaporate the moisture in the refuse and to act as a plug to further restrict the in-flow of air during charging. Refuse entering at the top of the gasifier moves downward past the gas offtake plenum (lantern). From this point down, the refuse dries and then, in the pyrolysis zone, is heated from 260-1093°C (500-2000°F) in a reducing atmosphere where the rate of decomposition to pyrolysis products increases with temperature. Various oils formed in the low temperature region of pyrolysis continue to pass down and are cracked into gases and char at the higher temperatures. These particles of char and oil that are entrained in the hot gases are to a large extent scrubbed out by the descending refuse and are recycled down into the higher temperature zone. The heat for drying and pyrolyzing the refuse is supplied by the combustion of the carbon char with preheated air in the primary combustion zone. The preheated air at 1037°C (1900°F) is directed from the regenerative towers through a hot blast main into a circular bustle pipe. The air then passes through several downcomer-tuyere assemblies radially into the gasifier hearth where it is used to combust the char. The heat generated by this combustion process (up to 1650°C or 3000°F) also transforms the non-combustible materials to a molten slag. The temperature profile through the refractories results in the formation of a coating of solidified slag over the refractories in the hearth area. This coating assists in protecting the refractories from the high temperatures and corrosive action of the molten slag. The molten slag is drained continuously through a sealed slag tap into a water quench tank to produce a black, glassy, sterile aggregate. The sealed slag tap arrangement allows removal of the frit while maintaining pressures in the hearth slightly above atmospheric. The slag formed in the hearth of the gasifier and in the secondary combustion chamber accumulate in a common slag agitation/holding tank, and several

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

50

SOLID

WASTES

A N D RESIDUES

methods are available for transporting it from the tank. At the demonstration plant in Orchard Park, the material flowed into a slag pit and a front-end loader was used to manually carry it to a stockpile for later removal by truck. One automatic method uses drag and belt conveying equipment, with drag conveyors removing slag from the main slag pit and depositing it at a continuous rate on horizontal or inclined belt conveyors feeding a vertical bucket elevator. The bucket elevator directs the material to external storage bins or stockpiles for removal by transportation vehicles. Another method used is slurry pumping of slag from the main slag pit to dewatering tanks. The suspended solids quickly settle out in the dewatering tank for removal by grapple bucket or drag conveyor system. The conveying liquid may be pumped back through the system from the dewatering tanks for reuse in the quench tanks. Volume reduction from the raw refuse to the slag residue is approximately 95-97 percent and on the inert fraction In th present physica chemical properties of the slag residue produced at the Orchard Park demonstration plant. At least 90% of the energy content of municipal refuse is contained in the gas stream which leaves the gasifier. This energy is in the form of combustible gases, vapors, and entrained particles and as sensible and latent heat. The temperature of this gas is approximately 400°C-500°C (752°F-932°F). The complete combustion of this gas stream produces about the same volume of products of combustion per unit of heat released as would be the case with other gaseous fuels. The composition and properties of the combustible gas stream are dependent, of course, on the refuse mix. The heating value of the gas will normally be in the range of 937-1593 kcal/nm (100-170 Btu/scf). Although this combustible gas stream, with or without cleaning to remove entrained material, has potential application as an energy source where close coupling of the gasifier with the recipient combustion device (such as kilns, boilers, etc.) is possible, the present commercial AndcoTorrax plants employ a secondary combustion chamber to burn this gas to completion. Secondary Combustion Chamber The offgas exits from the gasifier via the lantern, and is drawn into the secondary combustion chamber through a refractory lined cross-over duct by the system's induced draft fan. At the inlet to the secondary combustion chamber, the offgas is mixed with air in a high energy burner and is admitted to the chamber in a tangential fashion for a high turbulence, spiral flame. A small quantity of excess air is normally used to maintain the exit temperature from the secondary combustion chamber between 1150°C and 1250°C (2100-2280°F). The secondary combustion chamber is a vertical, refractory lined vessel in which temperatures up to 1400°C 3

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

DAVIDSON

A N D LUCAS

High-Temperature Slagging Pyrolysis System

TABLE 1 -S LAG RESIDUE CHARACTERISTICS Constituent Si0 A1 0 2

2

3

T1O2 Fe 0 2

3

FeO MgO CaO MnO Na 0 2

κ ο 2

Cr 0 2

CuO ZnO Trace Oxides

3

(by weight) 45 10 0.8 10 15 2 8 0.6 6 0.7 0.5 0.2 0.1 1.1 100.0 Dry Bulk Density True Residue Density

Range % 32.00- 58.00 5.50- 11.00 0.48- 1.30 0.50 - 22.00 11.00-21.00 1.80- 3.30 4 . 8 0 - 12.10 0 . 2 0 - 1.00 4 . 0 0 - 8.60 0 . 3 6 - 1.10 0.11 - 1.70 0.11 - 0.28 0.02- 0.26

— 1.40 gm/cc 2.80 gm/cc

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

52

SOLID

WASTES

A N D RESIDUES

(2550°F) are realized, and where sufficient residence time, up to 1.7 seconds, is maintained to assure complete combustion. The particulate matter entrained in the offgas from the gasifier is burned and the inert portion is fused, melted and slagged out of the stream. This slag is also water quenched and is approximately 10% of the total residue produced in the process. Air Preheating System As discussed previously, there are a number of possible methods for the preheating of primary combustion air by utilizing the energy from the hot combustion products which exit from the secondary combustion chamber or by burning fossil fuel. One such equipment system which has been built at both the SIDOR (Luxembourg) plant and the Frankfurt plant is shown in Figures 1 and 2. This system employs two regenerative towers, a system successfully used for many years in the steel and glass industries for preheating air. Regenerative taining a high heat capacit aligned flues which readily absorbs the heat from the hot products of combustion passing through them. During the heating cycle, approximately 10% of the total products of combustion from the secondary combustion chamber are introduced into the top of the regenerative towers. The heat from these gases is transferred to the refractories, bringing them up to temperature levels of approximately 1150°C (2100°F) at the top and 260°C (500°F) at the base. The waste gas exiting the regenerative tower subsystem is returned to a duct at the inlet of the gas cleaning system. A modulating damper valve in the boiler exit duct controls the amount of gas used in heating the regenerative tower refractory. During the "blast" cycle, the combustion products from the secondary combustion chamber are diverted to the second regenerative tower to heat its refractory. Ambient process air is introduced at the base of the fully heated regenerative tower and passes up through the refractory absorbing the stored heat. The exit temperature of the air from the tower ranges from 1037°C (1900°F) to 1110°C (2030°F). A constant primary air, or blast, temperature is maintained by blending the heated air with ambient air before introduction into the gasifier. A second method for preheating the primary combustion air employs a heat recuperator as used in the Grasse and Creteil plants. The metallic recuperator recovers heat from a portion of the products of combustion from the SCC exit and produces preheated air at a temperature of 600°C. The additional 400°C temperature differential is achieved through the use of a supplementary oil or gas fired burner. A third method for preheating the primary combustion air employs a fossil fuel fired silicon carbide cross flow shell-and-tube heat exchanger similar to that used in the demonstration plant in Orchard Park, New York. While this unit proved reliable during operation, the cost and availability

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

3.

DAVIDSON

A N D LUCAS

High-Temperature Slagging Pyrolysis System

53

of liquid or gaseogs fossil fuels makes such a unit unattractive for commercial plants. Using a regenerative or recuperative type of heat exchanger results in both energy and cost savings. Waste Heat Boiler With regenerative towers as the method of air preheating, approximately 90% of the gas flow exiting the secondary combustion chamber is directed to the energy recovery system, a waste heat boiler. Typically, the waste heat boiler is of the combination radiation-convection type and is designed with certain Andco-Torrax process characteristics in mind. These characteristics are high temperature inlet gases (from 1150°C to 1250°C), constant temperature input, homogeneity of inlet gases and absence of unburned material, low volumetric gas flow, and low particulate loading. Gases leave the boiler at approximately 290°C (554°F). Gas Cleaning Equipment At the exit of the wast regenerative towers (or alternativ the exiting flow from the waste heat boiler and are ducted to the gas cleaning system. The gas cleaning system is typically a hot gas electrostatic precipitator of conventional design which can effect an outlet particulate loading of less than 100 gm/nm (.04 grains/SCF). DEMONSTRATION PLANT The development of the Andco-Torrax process began in early 1969 with the formation of a company called Torrax Systems, Inc. which was jointly owned by Andco Incorporated and the Carborundum Company. The purpose of Torrax Systems, Inc. was to acquire and develop all necessary technology for a new type of high temperature slagging pyrolysis process for disposal of municipal solid waste and then to make the necessary arrangements to build a prototype plant and to operate it successfully to prove out the technology. On July 1, 1969, Torrax Systems, Inc. entered into a contract with the County of Erie, a municipal corporation of the State of New York, to build and operate a 75-ton-per-day demonstration plant in Orchard Park, a suburb of Buffalo. This new plant program was made possible largely through the support of the U.S. Environmental Protection Agency acting under the Solid Waste Disposal Act of 1965 which provided a program of demonstration grants for the development and evaluation of new solid waste disposal technology. Other funds for the program were provided by New Ycrk State, Erie County, the American Gas Association, the Carborundum Company, and Andco Incorporated. Ground breaking ceremonies for the demonstration plant were held in July of 1970 and operation commenced in the second quarter of 1971. Between 1971 and 1973, the plant operated as an engineering development facility to evaluate and prove system design features. During that period of time, the plant operated for 2316 hours and processed 7664 tons of municipal solid waste. The longest period of continuous operations was 120 hours. Although 3

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

54

SOLID

WASTES

A N D RESIDUES

the plant design capacity was 3.1 tons per hour, the equipment operated at throughput rates as low as 1.3 tons per hour and as high as 4.7 tons per hour. In addition to normal municipal refuse, the Andco-Torrax demonstration plant handled other wastes, particularly those from industry. These wastes were mixed with municipal refuse and minor changes were made to the equipment and the operating procedures. Some of the tests at the demonstration facility included the following: Sewage Sludge. Undigested sewage sludge with 78 percent water conten t"waTcTîârgedrwith the municipal refuse in quantities averaging 28.5 percent of the total 3.8 TPH charge. Waste O i l . Waste automotive lubricating oil was charged with municipal refuse in average quantities of 6.1 percent of the 4.4 TPH charge. Combined Sludge and O i l . A test combining sewage sludge with waste oil and municipal refuse wa TPH of which 30.1 percen Tires. Unshredded automotive tires were charged by bucket with the normal refuse. The average addition was 30 tires per hour or about 10 percent of the total 3.3 TPH consumption. Polyvînylchlorîde (PVC). Bags filled with PVC plastic waste were charged with municipal refuse in quantities averaging 7 percent of the 3.2 TPH charge. In all cases no significant changes to the process operation were encountered. In these tests, changes in the process parameters (flows, temperatures, gas composition) were evident and were related to the changes in the input refuse heating value and composition. The Orchard Park plant employed equipment which for the main part was similar to that used in commercial Andco-Torrax plants. However, as discussed, the demonstration plant used a natural gas fired heat exchanger, rather than regenerative towers, to supply the high temperature primary combustion air. Other differences between the demonstration plant and commercial plants include the following: Refuse was charged into the top of the gasifier through an open cone without any type of hopper feed. The residue was removed from the slag quench area with a front end loader rather than automatically as is the case in commercial plants. A wet scrubber was used rather than an electrostatic precipitator. MARKET DEVELOPMENT It was decided by Carborundum and Andco in early 1973 that the original objectives of Torrax Systems, Inc. had been successfully concluded. Since then the demonstration plant has only operated for sales demonstration purposes. In 1973, agreements were executed between Carborundum and Andco giving Andco commercial rights to the process in Canada,

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

3.

DAVIDSON

A N D LUCAS

High-Temperature Slagging Pyrolysis System

55

Australia and Europe. A further agreement was executed in 1976 which expanded Andco's commercial rights to the process to include the United States, the USSR, Japan, New Zealand, Indonesia, and countries in Polynesia, Latin America, Africa, and the Middle East. Commercial Plants Orders for four commercial Andco-Torrax systems have been received to January 1978. One order was placed in 1975 with Antox Wurth, Andco's West German licensee, by the City of Frankfurt. The unit capacity is 200 metric tons per day (220 TPD) and the system is located within an existing conventional incineration facility. Another order was placed in 1975 with Caliqua S.A. by the municipality of Grasse, France. The construction of the new 168 metric ton-per-day (185 TPD) plant is under the authority of Caliqua for use by the "Syndicat Intercommunal pour le Traitement et l'enlèvement des Ordures Ménagères et des Déchets Urbains de la Region de Grasse." Th initial start-up phase and th in the first quarter of 1978. A third plant, with a capacity of 400 metric tons per day (440 TPD), is being built in Creteil, France, and will be completed in 1979. The first order for a commercial Andco-Torrax System was awarded to S . A . Paul Wurth, Andco's Benelux licensee, in January 1974. This system has a 192 metric-ton-per-day (211 TPD) capacity, and is owned and operated by the Syndicat Intercommunal pour la Destruction des Ordures des Cantons de Luxembourg, Esch, et Cappellen, (SIDOR), a group of 35 municipalities in Luxembourg. Process design and sizing of the hardware components for this system were based largely on prior demonstration plant experience gathered at the Orchard Park facility, correlation with specific refuse analysis data for Luxembourg, and utilization of a process simulation computer program. The design point refuse composition, expressed in weight percent, for the SIDOR Andco-Torrax System is: Refuse Composition Proximate Analysis Ultimate Analysis Combustibles 51.4 Fixed Carbon 9TÔ Carbon 29.3 Water 23.7 Volatiles 42.4 Hydrogen 3.6 Ash-lnerts 24.9 Oxygen 18.5 This refuse analysis corresponds to a lower heating value of 2500 kcal/ kg (4500 Btu/lb). Although the plant was designed for 2500 kcal/kg refuse, actual refuse quality as received is closer to 1600 kcal/kg (2880 Btu/ lb). Mass and heat balances for these two operating points are presented in Table II. The differences in system efficiencies and steam production per unit of refuse for these two points are noteworthy. The over-all SIDOR plant consists of two conventional grate-type incinerators built by CNIM (Constructions Navales et Industrielles de la Mediteranee) and one 192 ton-per-day Andco-Torrax unit built by S. A . Paul Wurth. The Andco-Torrax equipment includes the refuse feeder,

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

56

SOLID

WASTES

A N D

RESIDUES

TABLE II - HEAT AND MASS BALANCES ANDCO-TORRAX (S.I.D.O.R.) SYSTEM Refuse Qualify

1600 kcalAg Refuse (2880 Btu/lb.) Heat Mass (kcalAg) (kgAg)

2500 kcalAg Refuse (4500 Btu/lb.) Heat Mass (kcal/kg) (kgAg)

Input Refuse 1600 1.00 2500 1.00 Auxiliary Fuel 69 Combustion Air 3 3.49 4 6.26 Feedwater 244 1.74 408 2.90 Electrical — Power 69 — 69 Total 6.24 1985 10.17 3050 Output Steam 1323 1.74 2206 2.90 Slag & Flyash 92 0.29 82 0.27 Exhaust Gases 296 4.21 464 7.00 — Losses 369 — 393 Total 2080 6.24 3145 10.17 Steam Production 1.7 kg steam/kg refuse 2.9 kg steam/kg refuse System Efficiency* 62% 68% *System Efficiency = ( Steam-Feedwater ) JQQO/ (Refuse + Fuel + Electrical Power) v

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

3.

DAVIDSON

A N D LUCAS

High-Temperature Slagging Pyrolysis System

57

gasifier, secondary combustion chamber, regenerative towers, waste heat boiler, steam condensation unit, electrostatic precipitator, induced draft fan, chimney, water cooling plant, controls system, and all secondary equipment for compressed air, auxiliary fuel and waste oil subsystems. Figure 4 shows the SIDOR Andco-Torrax gasifier, Figure 5, the system. The greater portion of the hot gases exiting from the SIDOR AndcoTorrax secondary combustion chamber is fed to a waste heat boiler, where the sensible heat content is used to generate steam. The boiler has been designed for a maximum gas throughput of 36,800 rirn^/h (21,660 scf/min.), a maximum gas inlet temperature of 1370°C (2500°F) and a nominal gas in­ let temperature of 1250°C (2280°F). The boiler is a 3-pass, vertical, com­ bination radiation/convection boiler, with the first of the three passes com­ prising the radiation section. The boiler has a super heater at the end of the radiation section and an economizer in the third pass. With a feedwater temperature of 140° maximum of 60,000 Ib/hr o a temperature of 385°C (725°F). The steam produced by all three refuse conversion units is directed to a 7 MW turbine generator producing electricity at 10 kV. The turbine gen­ erator is designed for a throughput lower than the plant's corresponding re­ fuse capacity of 600 metric tons per day, in that the amount of waste cur­ rently generated and available to the plant is lower than the total design capacity. A second turbine generator will be installed as refuse production increases. Theoretically, 1 kg (2.2 lb) of 2000 kcalAg (3600 Btu/lb) refuse can be converted to 1.22 Kwh of electricity. However, due to practical tur­ bine efficiencies, line losses, and flue gas losses, the final conversion fac­ tor of refuse to electrical power is approximately 0.48 Kwh per kg of re­ fuse. Assuming the availability of the system as 85%, the total amount of electricity produced per year from the Andco-Torrax system will be approxi­ mately 28.6 χ 10° Kwh. Since the Andco-Torrax system electrical require­ ments are about 80 Kwh/ton of refuse, the total amount of electricity available to the local power distribution company is about 23.8 χ 10° Kwh per year. The waste gases from the boiler at 290°C (554°F) are combined with the exhaust gases from the regenerative towers and enter the electrostatic pre­ cipitator. The two field precipitator is designed to produce particulate emissions no greater than 100 mg/nm , corrected to 7% C 0 2 . The cleaned gases then pass through the induced draft fan to a triple flue stack, 80 meters in overall height. ECONOMICS Since 1973, Andco Incorporated and its licensees have been involved in several studies and have made qualitative and firm bids for refuse conver­ sion plants. Four such bids have resulted in the sale of Andco-Torrax 3

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID

Figure 3.

WASTES

AND

Andco-Torrax unit

Figure 4. A 192-metric TPD SIDOR gasifier

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

RESIDUES

3.

DAVIDSON

A N D LUCAS

High-Temperature Slagging Pyrolysis System

59

systems to municipalities in Europe. An estimate of 1977 capital and operating costs are presented in Table III. It may be noted that construction costs for Andco-Torrax equipment alone range from a low of $22,000 per daily ton of plant capacity for a 1500 ton-per-day plant to a high of $30,000 per daily ton of capacity for a plant with a capacity of 250 tons per day. Net disposal costs per ton for plants of 250, 500, 1000 and 1500 tons respectively are $17.51, $11.90, $3.30 and $2.20. These net disposal costs after energy credits are currently competitive with other commercially available waste-to-energy technologies. The graph in Figure 6 utilizes the cost information presented in Table III with variable tipping (disposal) fees, and variable product credits. The family of curves thus generated depict Andco-Torrax plant economics for tipping fees ranging from zero dollars per ton of refuse to $20.00 per ton of refuse. Thus for any plant capacity and for a tipping fee between zero and $20.00 per ton, breakeven estimates for plan the vertical axes. For example per ton tipping fee has breakeven plant costs of $20.00 per ton without energy credits. If plant costs are to be covered by product sales, then steam must be sold at $4.00 per thousand pounds or electricity must be sold at 48 mîlls/Kwh. CONCLUSION The Andco-Torrax System has been proven through successful development and operation of a 75-ton-per-day demonstration plant in the United States over a four-year period. The first two commercial Andco-Torrax Systems have recently commenced operation in Luxembourg and Grasse, France. The third unit, located in Frankfurt, is scheduled for start-up in the second quarter of 1978. The fourth plant, in Creteil, France, will be completed in early 1979. The Andco-Torrax high-temperature slagging pyrolysis system accomplishes the three objectives required of modern refuse conversion units: 1. Maximum Volume Reduction - Volume reduction in the AndcoTorrax System is 95-97%. Future tests at the Frankfurt plant will be made to determine what further volume reduction can be achieved with conventional incinerator residue by adding varying amounts of incinerator residue to the Andco-Torrax System. 2. Inert Residue - The fritted, glassy aggregate residue is completely sterile and inert, consisting entirely of oxidized material as a result of the high-temperature process conditions. 3. Resource Recovery - The production rate of energy in the form of steam and/or electrical power is high as a result of all of the combustible material in the refuse being totally consumed. The economics of an AndcoTorrax energy recovery plant are similar to those of other commercially available, competitive waste-to-energy technologies.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID

WASTES

A N D RESIDUES

Figure 5. SIDOR plant—Luxembourg: Andco Torrax equipment train

Figure 6. Andco-Torrax system net disposal/product costs

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

3.

DAVIDSON

A N D LUCAS

High-Temperature Shgging Pyrolysis System

61

TABLE III - ANDCO-TORRAX SYSTEM ECONOMICS (1977) 250 TPD 500 TPD 1000 TPD 1500 TPD No. of Andco-Torrax Units 2 5 1 3 Annual Refuse Throughput (TPY) 82125 164000 329000 492750 CAPITAL COSTS ($000 omitted) 33000 Andco-Torrax Equipment 14900 20000 7500 14420 Buildings & Utilities 8080 12860 5800 4030 Interest During Construction 1953 2793 1130 Start-up Expense 1730 740 850 1080 1375 Working Capital 466 672 980 Total Capital Costs 15636 54555 26455 37713 Amortization Cost/Ton 11.94 11.53 19.83 16.80 (8-1/2% interest, 20 year plant life) OPERATING COSTS ($/Ton Labor & Administration (No of Personnel) Maintenance, Power & Utilities Total Operating Costs/Ton

9.64 16.58

8.52 14.00

6.70 10.26

6.49 9.37

Total Plant Costs/Ton

36.41

30.80

22.20

2Ô.9Ô

CREDITS Steam

18.90

18.90

18.90

18.90

NET DISPOSAL Cost/Ton

17.51

n.9o

3.30

2.20

6.94(19)

5.48(30)

3.56(39)

2.88(47)

ASSUMPTIONS: 1· A 1000 TPD plant will have 3-330 TPD units. A 1500 TPD plant will have 5-300 TPD units. 2. Plant availability is 90%. 3. No escalation of capital cost to completion of project. 4. Interest during construction is estimated at 8 i % of construction costs. 5. Start-up expense is estimated at 3%-6% of construction costs. 6. Working capital is estimated at 3% of construction costs. 7. Average total wages and benefits per employee per annum is $28,000. 8. Annual maintenace costs are 4% of capital (equipment and buildings} 9. Plant electrical consumption is 80 KWH/ton of refuse. Power costs 20 Mills/KWH. 10. Auxiliary fuel usage is 2.5 nm (88.3 ft ) natural gas/ton. Natural gas costs $3.00/1000 f t . 11. Refuse is assumed to have an LHV of 2275 kcalAg (4100 Btu/lb.). Steam produced will be 2.7 kgAg refuse. Steam credits will be $3.50/1000 lb. 3

3

3

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

62

SOLID

WASTES

A N D RESIDUES

ABSTRACT In our society today, the disposal of municipal solid waste poses ever increasing social and technical problems. During recent years, widespread attention has been focused on both real and potential scarcities of conven­ tional fossil fuels. The search for economically attractive solutions to these two problems has given rise to the development of different systems to pro­ cess municipal solid waste by thermal and chemical techniques to provide alternate energy sources. This paper describes one such system called the Andco-Torrax System which is used to convert municipal solid waste into useful energy and a granulated slag byproduct by the pyrolysis and primary combustion of organic materials and by the melting of non-combustible materials at temperatures up to 1650°C (3000°F). LITERATURE CITED 1. Andco Incorporate General Informatio of Solid Refuse (1975) 2. Legille, E., Berczynski, F. Α., Heiss, Κ. G . A Slagging Pyrolysis Solid Waste Conversion System (1975). Conversion of Refuse to Energy - First International Conference and Technical Exhibition IEEE Catalog Number 75CH1008-2 CRE 3. Davidson, P. E. Andco-Torrax: A Slagging Pyrolysis Solid Waste Conversion System (1977) Canadian Mining and Metallurgy Bulletin, July 1977 MARCH

3,

1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

4 Co-Disposal of Sludge and Refuse in a Purox Converter C . T . M O S E S and K . W . Y O U N G Union Carbide Corporation, Linde Division, Tonawanda, N Y 14150 G. STERN

and J. B. F A R R E L L

U.S. E.P.A., M E R L , Cincinnati, OH

45268

The development of the PUROX System for the conversion of municipal refuse into a and an inert slag stream (1,2,3). The key element in this system is the converter which is basically an oxygen-fed shaft furnace in which solid waste is dried, pyrolyzed, combusted, and the inorganic residues slagged. The operation of the converter is supported by several subsystems: a feed material storage and preparation system, a gas cleaning system, a wastewater treatment system, and an oxygen generating system. Figure 1 presents a mass balance indicating the general process flow and typical material rates for operation with municipal refuse. One mass unit of as-received refuse undergoes shredding and magnetic separation of ferrous material. The magnetically separated, shredded material is combined with 0.22 mass units of oxygen and is converted into 0.7 mass units of product gas saturated with water at ambient condition, 0.28 mass units of wastewater, and 0.22 mass units of slag. In the S. Charleston, WV demonstration plant a small amount of natural gas is injected with the oxygen into the slagging zone to provide preheating of the entering oxygen prior to contacting the molten slag pool. In a commercial installation this heat input would be provided by recycle of a portion of the product gas stream. Figure 2 presents an energy balance for the generalized process described above. Over 70% of the entering energy is converted into product gas. The product gas is a medium-Btu fuel with its major constituents being CO, CO2 and CH4 having a heating value of 350 Btu/S f t . A natural extension of the solid waste processing capability of the PUROX System was the use of dewatered sewage sludge cake as a feed material in combination with municipal refuse. This combined processing scheme has the potential advantage of 3

0-8412-0434-9/78/47-076-063$06.25/0 This chapter not subject to U.S. copyright. Published 1978 American Chemical Society In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID

WASTES

AND

RESIDUES

6

J

ο PC

a.

> UJ ΰ Μ Ι / 1 Σ LU Ζ)

u

IL

(Λ LI U

< α α

h -

ο .

Η

·

~

«

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

Figure 2. Typical PUROX System energy balance In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

66

SOLID

WASTES

A N D RESIDUES

disposing of sludge and refuse with a net production rather than the net consumption of energy in conventional incineration techniques. Also, the positive environmental features of slagging the inorganic residues in a non-leaching, glassy matrix suggests a major environmental improvement in thermal processing techniques for sludge disposal. Following some preliminary analysis and pilot scale testing of the concept of sludge/refuse codisposal in the PUROX System, Union Carbide Corporation proposed through the Sanitary Board of the City of South Charleston, WV, to the U . S . Environmental Protection Agency that a large scale testing program be conducted utilizing the PUROX System demonstration plant in South Charleston. The EPA approved the proposed program and construction work began in the fall of 1976. Construction was completed in February of 1977 with the test program starting in mid April. The testing was conducte discussion of the test program and its results is presented below. Figure 3 presents an isometric view of the South Charleston PUROX System facility arranged for codisposal of sludge and refuse. Major pieces of processing equipment are described in the legend on the figure. The front end system consisting of the refuse storage building, the vertical-shaft, hammermill-shredder, and the drum magnetic separator was expanded to provide a dewateredsludge-cake processing capability by the following additions. Dewatered sludge cake from the wastewater treatment plant was delivered in dump trucks and stored in a sludge inventory area for subsequent use. Sludge cake was periodically loaded into a livebottom metering hopper from which it was steadily metered into the shredded refuse stream going to the converter. The mixture of sludge cake and refuse was fed into the converter where it underwent the drying, pyrolysis, combustion, and slagging steps to convert it into product gas, slag, and wastewater. The inorganic residues (slag) left the converter as a continuous molten stream which was quenched in a water tank and discharged into a storage dumpster. The products of the drying, pyrolysis and combustion reactions passed overhead through the gas cleaning system which consisted of a scrubber tower, electrostatic precipitator, and condenser. Wastewater was collected from the scrubbing and condensing operations. The product gas was continuously flared in a combustor. Figures 4 and 5 provide additional views of the actual sludge handling operation showing the sludge filter cake in the storage area being placed in the metering hopper for discharge onto the belt conveyor.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

4.

MOSES

ET

AL.

Co-Disposal of Sludge and Refuse

67

Figure 3. PUROX System facility for sludge/refuse codisposal in South Charleston, West Virginia.

PUROX System: (1) PUROX System leveling conveyor; (2) PUROX System pelletizing feeder; (3) PUROX System converter; (4) PUROX System slag quench system: (a) PUROX System slag quench tank, (b) PUROX System slag conveyor; (5) PUROX System scrubber; (6) PUROX System gas liquid separator; (7) PUROX System electrostati precipitator; (8) PUROX System condenser; (9) PUROX System combustor; (10) PUROX System solid liquid separation system: (a) PUROX Systemfiltratetank, (b) PUROX System vacuum filter, (c) PUROX System vacuum pumps, (d) PUROX System vacuum receivers; (11) PUROX System char conveyors. Front End (not PUROX System): (A) refuse storage building; (B) refuse weigh bridge and load ramp; (C) refuse feeder pit a shredder feed conveyor; (D) shredder; (E) shredder discharge conveyor; (F) magneti separator; (G) magnetic material conveyor; (H) sludge metering hopper with augers (I) sludge feed conveyors.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

SOLID

68

Figure 4.

Figure 5.

WASTES

AND

Sludge cake at dumping station

Front loader scooping sludge cake

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

RESIDUES

4.

MOSES

E T AL.

Co-Disposal of Sludge and Refuse

69

Codisposal Test Program Two types of dewatered sludge cake were selected for testing in this program. Raw primary sludge cake with a nominal moisture content of 25% solids, a volatiles content of'V 45% and a heating value of 5000 Btu per lb of dry solids, was available in sufficient quantity from the wastewater treatment plant at the City of Huntington, WV. Raw mixed sludge cake was not readily available in the South Charleston environs. It was necessary to go to the Alleghany County Sanitary Authority Waste Treatment Plant in Pittsburgh, PA to obtain a sufficient supply of dewatered, raw mixed sludge. This sludge was a mixture of 60% raw primary and 40% secondary which had been dewatered to^20% solids. The mixed sludge had a volatiles content of^60%, and a heating value of 6500 Btu per lb of dry solids. These two types of refuse from the S. Charleston area. The refuse was typical mixed municipal refuse with a moisture content of 25-35%, a dry inert content of v25%, and a heating value of 5000 Btu/lb. As noted above, the refuse was shredded and magnetic separation of the ferrous components was carried out prior to combination with the sludge. The test program consisted of a series of seven tests during which comprehensive sampling and analysis of the process streams entering and exiting the system were conducted. Test A was a baseline operating condition using refuse-only which was con­ ducted to provide a reference point for comparison of results from the codisposal tests. The converter operating rate averaged 81 tons per day for this test. Test Β was a combination of primary sludge and refuse in a sludge-dry-solids (SDS) to as-received refuse (ARR) ratio of 0.016. The plant was operated at an average rate of 61 tons per day (TPD) of refuse and 3.7 TPD of 26% solids primary sludge for a total operating rate of 64.7 TPD. Test C was conducted using primary sludge at an SDS/ARR ratio of 0.021. The plant operated at an average rate of 85 TPD of asreceived refuse and 5.6 TPD of 32.4% solids primary sludge for a total operating rate of 90.6 TPD. Test D was conducted using primary sludge at an SDS/ARR ratio of 0.027. The plant operated at an average rate of 83 TPD of refuse and 8.1 TPD of 27.5% solids sludge for a total operating rate of 91.1 TPD. Test Ε was conducted using primary sludge at an SDS/ARRratio of 0.052. The plant operated at an average rate of 95 TPD of refuse and 22.2 TPD of 22.3% solids sludge for a total operating rate of 117.2 TPD. /

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

70

SOLID

WASTES

A N D RESIDUES

Test F was a combination of mixed secondary sludge and refuse with an SDS/ARR ratio of 0.027. The plant operated at an average rate of 86 TPD of refuse and 11.6 TPD of 20.3% solids mixed sludge for a total operating rate of 97.6 TPD. Test G was conducted using raw mixed sludge at an SDS/ARR ratio of 0.031. The plant operated at an average rate of 67.3 TPD of refuse and 10 TPD of 21% solids mixed sludge for a total operating rate of 77.3 TPD. Table I presents a summary of the test conditions described above. Summary tables of the mass flows, energy flows, product gas and slag analyses for each of these tests are presented in Tables II - V. As can be noted from the tables, there was no major departure from the baseline refuse-only results in the quantities reported. The slight variations that do appear are in part the result of changes in refuse composition that occur in a ramdomly varying fashion. Mechanical problem late recycle system throughout the test program. This resulted in an inability to recycle particulate from the electrostatic precipitator and scrubber to the converter and the loss of representative wastewater samples due to the use of substantial amounts of makeup water in the scrubbing system. During subsequent plant operation with refuse-only, stable operation of the particulate recycle system was achieved. A model was developed for projecting the codisposal data to the performance obtained during particulate recycle. The projected results for refuse-only (Test A) were in good agreement with the experimental data from the particulate recycle period which gave the projection model results for the codisposal period a measure of credibility. The mass flows in Table II are presented on a per-unit-offeed basis to aid in illustrating the general similarity of the codisposal results with those obtained for refuse only. The energy flows in Table III are based on the total quantity of energy leaving the system since it was not possible to obtain reliable measurements of the energy in the input refuse stream. The mass and energy flows were also adjusted to the recycle case where particulate is returned to the converter. In examining these results, test G appears to be the only period that differs significantly from the refuse-only and other codisposal results for key parameters such as oxygen usage and conversion to product gas. These differences are the result of mechanical problems encountered using the existing feeding equipment to blend the sludge and refuse. Improper blending produced a variable porosity condition in the converter bed which permitted a high heat loss condition to develop resulting in elevated oxygen consumption and heat loss factor while

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

78.0 (86.0) 61.0 (67.3)

20.25 21.01

P/MS

P/MS

F

G

-

86.2 (95.0)

22.32

H/RP

Ε

P/MS

75.3 (83.0)

27.47

H/RP

D

-

77.1 (85.0)

32.38

H/RP

C

H/RP

55.3 (61.0)

26.23

H/RP

Β

9.1 (10.0)

10.5 (11.6)

20. 1 (22.2)

7.4 (8.1)

5.1 (5.6)

3.4 (3.7)

-

0.098

0.066

0.061

-

70. 1 (77.3)

88.5 (97.6)

0.149

0.135

106.3 (117.2) 0.234

82.7 (91.1)

82.2 (90.6)

58.7 (64.7)

73.5 (81.)

0.031

0.027

0.052

0.027

0.021

0.016

-

Sludge/Refuse Wet SDS/ARR

Secondary sludge from Pittsburgh, Pennsylvania mixed with primary sludge in approximate ratio of 60% raw primary, 40% secondary

Raw primary sludge from Huntington, West Virginia

73.5 (81.0)

-

-

A

Feed Rate Mg/d (ton/d) Refuse Sludge (Wet) Total

Sludge % Solids

Source/Type

Test #

TABLE I. SLUDGE CODISPOSAL TEST SERIES

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

1.0 0.016 0.205 1.221 0.051 0.571 0.258 0.341 1.221

1.0 0.029 0.241 1.270 0.043 0.645 0.176 0.406 1.270

1.0

0.023

0.236

1.259

0.084

0.605

0.242

0.328

1.259

Refuse-Sludge Feed

Fuel Gas

Oxygen

Total In

Metal

Product Gas

Wastewater

Total Out

Slag

Ç

Β

A

1.237

0.325

0.248

0.614

0.050

1.237

0.223

0.014

1.0

p

1.237

0.423

0.191

0.586

0.039

1.239

0.223

0.016

1.0

Ε F

1.237

0.405

0.213

0.576

0.043

1.237

0.217

0.020

1.0

TABLE II. PROJECTED MASS FLOW (PER UNIT OF TOTAL FEED)

1.295

0.450

0.193

0.616

0.036

1.295

0.277

0.018

1.0

G

C/î

Θ

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

**

*

100%

100%

100%

100%

15.0

6.5

3.7

74.8

100%

100%

18.2

6.7

6.0 15.4

3.9

71.2 4.2

74.3

Exiting streams are given as a % of total energy leaving.

Since it was not possible to obtain representative measures of the input energy streams, the output energy flows were measured.

100%

13.7%

Heat Losses

13.4

5.2

5.9

4.7%

Wastewater 14.5

5.0

5.2

3.2

4.1

Slag

16.1

4.8

75.1

74.8

76.8

D

77.0%

Product Gas

Β

(Referenced to 60 deg. F)

PROJECTED ENERGY FLOW* BASED ON TOTAL ENERGY EXITING THE PROCESS

Exiting Streams**

TABLE III.

74

SOLID

WASTES

A N D RESIDUES

TABLE IV. SUMMARY OF PRODUCT GAS ANALYSES Mole Percents Test A Test Β Test C Test D Test Ε Test F Test G Vol. % Vol. % Vol. % Vol. % Vol. % Vol. % Vol. %

Com­ ponent H

2

CO

C

° 2

CH. 4 C

2

H

2

C

2

H

4

C

2

H

6

C

3

H

6

C

3

H

8

°4* C

5

+

C

6

H

6

HHC*

H

2

S

CH^OH

°2

Ar

28.14

29.64

31.25

29.62

26.81

25.30

30.32

37.28

33.74

36.24

36.80

34.19

36.72

31.56

23.07

25.58

23.52

23.85

26.85

25.01

28.86

6.21

5.89

4.46

5.02

6.12

6.48

4.82

0.46

0.52

0.25

0.41

0.72

0.60

0.48

1.90

1.91

1.32

1.68

2.19

2.26

0.68

0.44

0.34

0.33

0.32

0.40

0.46

0.23

0.32

0.27

0.27

0.23

0.28

0.39

0.20

0.23

0.12

0.25

0.18

0.19

0.21

0.02

0.40

0.28

0.47

0.34

0.40

0.44

0.23

0.29

0.22

0.35

0.27

0.36

0.31

0.17

0.24

0.26

0.17

0.25

0.34

0.26

0.22

0.26

0.17

0.32

0.29

0.37

0.23

0.12

0.02

0.02

0.00

0.04

0.03

0.02

0.01

0.11

0.04

0.14

0.08

0.09

0.11

0.12

0.03

0.04

0.05

0.03

0.04

0.26

0.24

0.59

0.61

0.62

0.59

0.63

0.95

0.74

* C4 is a composite of butanes, butènes, butadiene, vinyl acetylene and diacetylene + C5 is a composite of pentanes, pentenes, isoprene, and cyclopenetadiene + HHC are higher hydrocarbons C6 and above excluding benzene

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

4.

MOSES

Co-Disposal of Sludge and Refuse

E T A L .

TABLE V .

75

S U M M A R Y O F S L A G ANALYSES

Major Test Components A

Test Β

Test C

Test D

Test Ε

Test F

Test G

1.8

0.8

1.0

0.8

0.4

0.9

0.2

61.5

56.1

60.0

59.8

56.8

66.5

64.0

AT 0 2 3 C Ο a FeO MgO

11.6

9.7

10.0

11.9

9.3

10.5

11.0

9.8

8.5

12.0

10.5

11.3

9.9

12.1

8.0

14.6

8.1

8.1

8.3

6.3

6.7

0.9

1.9

1.9

0.9

1.0

1.6

1.2

ΡΟ 2 5 BaO

0.6

0.

0.1

0.1

0.2

0.2

0.2

0.1

0.1

MnO

0.2

0.3

0.2

0.1

0.2

0.2

0.3

Cr O 2 3 TiO,

0.5

0.5

0.05

0.1

0.5

0.5

0.05

0.7

0.6

0.51

0.52

0.6

0.6

0.56

0.05

0.05

0.3

0.2

0.1

0.05

0.05

93.72

90.4

97.95

96.86

C (wt. %) SiO Λ

n

N i

o

95.75 93.55 95.16

Trace Components Cd (ppm)

5

5

10

10

5

5

6

Cr

342 0

342 0

891

645

3420

342 0

363

Cu

4000

3400 4300

4000

3300

2860

3800

48800

53000

0.05

0.01

Fe

61970 113100 55000

53000 64300

Hg

0.03

0.02

0.010.01

0.15

Mn

1600

1300 1200

1700

1400

1140

1400

Ni

305

959 2700

1300

1500

150

145

Pb

94

75

119

119

243

120

128

Zn

309

404

455

482

1100

350

456

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

76

SOLID

WASTES

A N D RESIDUES

depressing overall conversion to useful fuel gas. This condition was corrected as noted in the results for Test F in which similar operating rates with similar sludge were used. Careful control of the sludge-refuse blending conditions in Test F resulted in normal performance. The environmental effects of the codisposal process were the key measurements to be made during these tests. The process product streams - product gas, wastewater, and slag were carefully monitored. In addition to the overall composition of the product gas reported earlier, sampling and analysis of the particulate remaining in the product gas after cleaning were conducted. Isokinetic samples of the product gas were collected, and the particulate obtained was thoroughly analyzed for key trace metal contaminants. Since the exiting gas leaves the system at/^100 deg. F, it seemed likely that any significant amounts of trace metal vapor would be presen particulate. Table VI presents a summary of the product gas particulate levels It should be noted that these levels are for gas prior to combustion. Since the particulate regulation is based on combustion products at standard conditions with 12% CO2/ these numbers must be converted. Table VII presents the calculated particulate levels in product gas combustion products converted to 12% CO2. All the levels reported are well below the regulated value of 0.08 grains per standard cubic foot at 12% (Χ>2· Table VEII reports the average trace metal levels found in the particulate material during the codisposal test period. Levels are reported on a combustion product basis for both the refuse-only and codisposal operation. The apparent improvement in trace metal levels of the codisposal period relative to the refuse-only period is misleading. At the time the refuse-only data were collected, the electrostatic precipitator in the gas cleaning system was operating unreliably which resulted in non-optimum gas cleaning performance. In general the trace metal levels during refuse-only operation should be very comparable to those observed during codisposal tests. A comparison of these combustion product levels is also made with time-weighted-average (TWA) threshold-level-values (TLV) proposed by the American Conference of Industrial Governmental Hygienists. In the absence of more complete emission regulations, these work­ place regulations, although not specifically applicable, give an indication of regulated levels for these materials.

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

4.

MOSES

E TA L .

77

Co-Disposal of Sludge and Refuse

TABLE VI. PRODUCT GAS PARTICULATE LEVELS Test Period

Type Feed

g/Nm

3

Particulate Loading gr/Sft

A

Refuse

0.0176

0.007

Β

Refuse + Primary Sludge

0.0223

0.009

Refuse + Primary Sludge

3

No samples taken

Refuse + Primary Sludg Refuse + Primary Sludge

0.0449

0.018

Refuse + Mixed Sludge

0.0201

0.008

Refuse + Mixed Sludge

0.0188

0.008

TABLE VII. CALCULATED PARTICULATE LEVELS IN PUROX SYSTEM GAS COMBUSTION PRODUCTS AT 12 PERCENT C 0 * 2

Test Period

Particulate Level gr/Sft g/Nm

A (Refuse) Β (Primary) C (Primary) D (Primary) Ε (Primary) F (Mixed) G (Mixed)

0.0031 0.0034

3

3

0.0013 0.0014

-

-

0.0056 0.0063 0.0029 0.0031

0.0023 0.0026 0.0012 0.0013

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

78

SOLID

WASTES

A N D

RESIDUES

TABLE VIII. TRACE METAL CONCENTRATIONS IN PRODUCT GAS COMBUSTION PRODUCTS Combustion Product Concentration (mg/m , dry @ 12% CO J * Metal

Refuse + Sludge

Refuse +

Cd Cr Cu Fe Hg Mn Ni Pb Zn

+

(^L/5% sludge (ds)/refuse)+

0.0022 mg/m

3

0.0090 0.079 1.62 0.0084 0.012 0.058 0.038 0.047

3

TLV-TWA # (mg/m ) 3

0.05 mg/m

3

0.0001 mg/m 0.0007 0.0097 0.03 0.0004

0.5 0.2 5 0.05 5

0.009

5

below detection limit

* Computed from metal content in isokinetically collected particulate in the product gas. + Refuse-only with particulate recycle and non-optimum gas cleaning. Φ Based on average of measurements using primary and mixed sludges with more optimum gas cleaning performance. #(4) ACGIH, National Safety News, pp. 83-93, September 1977.

TABLE IX. PUROX SYSTEM WASTEWATER TREATABILITY DATA Wastewater Analysis

Reactor Operating Conditions

1321 ppm

BODs/da^ MLVSS t , days

1.18

Τ COD

3078 ppm

MLVSS, ppm

1684

S COD

3012 ppm

So (TBOD ), ppm

1350

2.28

Se (SBOD ), ppm

59

5

1350 ppm

5

TBOD SBOD

COD/BO D

5

'

d

5

5

In Solid Wastes and Residues; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

4.

MOSES

E T

AL.

Co-Disposal of Sludge and Refuse

79

The wastewater production is obviously strongly affected by the moisture content of the feed material. The strength of the wastewater is related to the quantity produced. In general it has been found that the wastewater can be readily treated to a level sufficient for discharge into a municipal sewer system. A 95% reduction in biological oxygen demand can be achieved by diluting at a ratio of 20 to 1 with municipal sewage to provide nutrients and control for the biological process. Table IX summarizes the wastewater treatability data. Table X presents a summary of trace metal concentrations measured in the wastewater during operation of the particulate recycle system with refuse-only. Pretreatment requirements that are also given in the table are an estimate of the current status of regulations that are now being formulated. As can be seen from the table, the raw wastewater exceeds some of the projected standards. However problem can be obtained The small amount of precipitate could then be disposed of in an environmentally acceptable fashion. TABLE X. WASTEWATER METAL CONCENTRATION FROM REFUSE ONLY OPERATION WITH PARTICULATE RECYCLE Metal Cd Cr Cu Fe Pb Mn Ni Zn Hg

Raw Wastewater 0.22 ppm