530SW133C
r
U.S. DEPARTMENT OF COMMERCE
National Technical Information Service
PB-263 396
MUNICIPAL-SCALE THERMAL PROCESSING OF SOLID WASTES
RECON SYSTEMS, INCORPORATED
PREPARED FOR
ENVIRONMENTAL PROTECTION AGENCY
1977
UBRAftY
U. S- EKvii,v.'i.-.ic!.'iAL PRO
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PB 263 396
MUNICIPAL-SCALE THERMAL PROCESSING
OF SOLID WASTES
This final report (SW-133c) describes work performed
for the Federal solid waste management program
under contract no. 68-03-0293
and is reproduced as received from the contractor
REPRODUCED BY
NATIONAL TECHNICAL
INFORMATION SERVICE
U. S. DEPARTMENT OF COMMERCE
SPRINGFIELD, VA. 22161
U.S. ENVIRONMENTAL PROTECTION AGENCY
1977
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! BIBLIOGRAPHIC DATA j 1- Report No. 2.
; iHEET | EPA/530/SW-'133c
$4. T:tie and Subtitle
• Municipal-Scale Thermal Processing of Solid Wastes
',7. Auchor(s)
; Norman J. Weinstein
*
?9. Performing Organization Name and Address
} RECON Systems, Inc.
Cherry Valley Road
! Princeton, New Jersey 08540
12. Sponsoring Organization Name and Address
U.S. Environmental Protection Agency
» Office of Solid Waste
Washington, D. C. 20460
3. Recipient's Accession No,
5. Report Date
1977
6.
8- Performing Organization Rept,
No. ,
10. Project/Task/Work Unit No. '•
11. Contract/Grant No.
68-03-0293
13. Type of Report & Period i
Covered i
Final f
i
14. i
j
!1 5. Supplementary Notes QQUQft ILLUSTRATIONS REPRODUCED
IN BLACK AND WHITE
• 16. Abstracts
Describes the state of the art for the thermal processing of solid
waste. Subjects covered include: costs, site selection, plant design,
utilities, weighing, handling, furnace design, energy recovery, pyrolysis,
instrumentation, air pollution control, acceptance evaluation, operation
and maintenance.
17. Key Words and Document Analysis. 17a. Descriptors
waste management, combustion, incinerators
17b. Identifiers/Open-Ended Terms
17c. COSATI Field/Group
18. Availability Statement
19. Security Class (This
Report)
UNCLASSIFIED
20. Security Class (This
Page
UNCLASSIFIED
I. No. of Pages
FORM NTIS-35 (REV. 3-72)
USCOMM-DC 14952-P72
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This report had been reviewed by the U.S. Environmental Protection
Agency and approved for publication. Its publication does not signify
that the contents necessarily reflect the views and policies of the U.S.
Environmental Protection Agency, nor does mention of commercial products
constitute endorsement or recommendation for use by the U.S. Government.
An environmental protection publication (SW-133c) in the solid waste
management series.
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FOREWORD
This report has been developed to update Municipal-Scale Incinerator
Design and Operation formerly titled "Incinerator Guide!ines--1969"
(SW-13ts).Significant developments in the area of resource conservation
through the use of thermal processing have made the earlier publication
obsolete.
With the promulgation of the "Standards of Performance for New
Stationary Sources" (40 CFR 60) and the "Guidelines for the Thermal
Processing of Solid Wastes" (40 CFR 240) the technology of incinerating
solid wastes has undergone many changes. The most notable change is
a decline in the number of operating facilities due to the stringent
air pollution control methods needed to meet standards. In 1972,
there were 193 thermal processing facilities in operation; in 1976,
the number had declined to 108.
It is our intention to show the state-of-the-art of incineration
with this publication. We feel that public officials and private
groups will be able to use this information to develop environmentally
acceptable and economically sound solid waste management systems.
-SHELDON MEYERS
Deputy Assistant Administrator
Office of Solid Waste
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PREFACE
Until recent years solid waste incineration has been considered as an
expensive alternative to landfilling for disposal of municipal solid waste,
to be used only when landfill sites were not readily available. Today thermal
processes, which include incineration, pyrolysis, and combined refuse/fossil
fuel combustion, with energy and/or resource recovery can be considered as
competitors for landfilling, both because of the increased cost of landfill ing
performed in an environmentally sound manner and because of the increased
value of energy, metals, and glass which can be extracted from municipal solid
waste.
However, thermal processing of solid wastes and associated resource
recovery systems are in a state of transition from developmental to fully
operational stages. The performance of waterwall incinerators which generate
steam has been fully proven both in Europe and North America. However, no
waterwall incinerator projects in the United States are yet on sound footing
with regard to external steam sales. Three modern waterwall incinerators in
the United States are simply condensing all the steam generated, except for
the small amounts being used internally. A new waterwall incinerator recently
started up will supply steam to 27 downtown buildings for heat and air condi-
tioning. Hopefully, this project will succeed. Because of imbalance between
supply and demand for energy, only projects which have been planned with
extreme care will fully meet expectations.
On the other hand, combined refuse/fossil fuel firing in existing steam
boilers makes use of already available facilities for energy distribution and
already available markets. The uncertainties which do exist are mainly
technical. Although a large scale test has been conducted on a refuse/coal
fired boiler, each new test with varying boiler designs, other types of coal,
and oil firing raises technical questions of corrosion, erosion, fuel hand-
ling, air pollution control, and others. Careful engineering will be required
to insure broad success of this promising approach to thermal processing with
energy recovery.
Several pyrolysis processes are available for converting municipal solid
waste to fuels. One plant, recently started up, converts the fuel to steam;
another is undergoing detailed design; while a third has been undergoing tests
in a large scale prototype. While the fuels produced are not conventional in
the sense of fuels widely used today, they should find ready outlets under
contract. The importance of good project and contract planning holds as true
for pyrolysis processes as for steam generating incinerators.
IV
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Resource recovery can enhance any of the thermal processes discussed
above. Rapidly emerging technology should eventually allow recovery of not
only ferrous metals, but also color-sorted glass, aluminum, other metals, and
even paper fiber. Some resource recovery plants may separate a combustible
fraction which can be transported elsewhere for use in pyrolysis or incinera-
tion with energy recovery.
Some of the steps in resource recovery can be considered proven, for
example preparation of a combustible fraction, and ferrous metal recovery from
either mixed refuse or from incinerator residue. However, no complete system
recovering the full range of potentially valuable energy and materials is yet
fully operational and economical to the point of paying for solid waste dis-
posal. Even with technical success, many marketing and end use problems will
remain for some time to come, as industry and others become accustomed to
unfamiliar materials and energy forms available in municipal solid waste.
The terms "municipal solid waste," "solid waste," and "refuse" are used
interchangeably in this publication. No special significance should be
ascribed to the use of a specific term unless it is further modified, e.g.
"prepared refuse," "shredded solid waste," etc.
Norman J. Weinstein
Richard F. Toro
December 4, 1975
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ACKNOWLEDGEMENT
Many people have contributed to the concept and contents of this
publication. An earlier publication, MUNICIPAL-SCALE INCINERATOR DESIGN AND
OPERATION (1969), by Jack Demarco, Daniel J. Keller, Jerold Leckman, and
James L. Lewton was used extensively. Other U.S. Environmental Protection
Agency personnel who participated at various stages include William C. Achinger,
Edward L. Higgins, Harvey Rogers, and Steven Hitte, Project Officer.
The work was done by RECON SYSTEMS personnel under EPA Contract No.
68-03-0293. Major contributions were made by Richard F. Toro, Arthur T.
Coding, Jr., Charanjit Rai, and Robert Wolfertz. A special note of thanks
is due to Mrs. Gladys Freeland and Mrs. Carol Picker.
Thanks are also due to the many incinerator operators and others active
in thermal processing who gave of their time to provide RECON SYSTEMS with
maximum insight into this aspect of municipal solid waste management.
The list of operating thermal processing plants in Appendix A was con-
tributed by the American Society of Mechanical Engineers.
VI
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Contents
Page
Foreword i i -j
Preface i v
Acknowledgement vl
Chapter I Thermal Processing of Solid Wastes:
An Introduction 1
Chapter II Basic Data for Design 7
Chapter III Thermal Processing Costs 25
Cnapter IV Site Selection 48
Chapter V Plant Layout and Building Design 53
Chapter VI Utilities 74
Chapter VII Weighing 82
Chapter VIII Receiving and Handling Solid Waste 90
Chapter IX Design of Incinerator Furnace Systems 105
Chapter X Recovery and Utilization of Energy 132
Chapter XI Pyrolysis ; 155
Chapter XII Instrumentation and Controls 183
Chapter XIII Liquid and Solid Effluents and Their Control 198
Chapter XIV Air Pollution Control 217
Chapter XV Acceptance Evaluation 269
Chapter XVI Solid Wastes That Require Special Consideration 276
Chapter XVII Resource Recovery Systems 285
Chapter XVIII Operation and Maintenance 322
VII
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Appendices
A. Inventory of Municipal Solid Waste Thermal Processing Facilities .. 334
B. Summary of Resource Recovery System Implementations 342
C. Table of Abbreviations .346
D. Conversion Factors 348
vm
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FIGURE
1 Projected Per-Capita Refuse-Disposal Burden • H
2 Frequency Diagram of Cumulative Weekly Solid Waste
Quantities Delivered for Disposal During a Year. ^
3 Capital Costs for Refractory Batch Fed Incinerators 27
4 Capital Costs for Refractory Continuous Fed Incinerators 28
5 Capital Costs for Steam Generating Incinerators
(Excluding Steam Distribution) 30
6 Harrisburg, PA. Steam Producing Incinerator 59
7 Chicago Northwest Steam Producing Incinerator 60
8 Chicago Northwest Steam Producing Incinerator 61
9 A Sraph of the Reduction of Noise (dB) Over Distance (M)
for a Point Source of Noise 70
10 Sample Weight Form • 87
11 Chicago Northwest Incinerator 91
12 Plan of Tipping Area and Storage Pits With Crane 92
13 Typical Layout For Subgrade Storage Pit With Overhead
Crane» Charging Hopper and Chute 99
14 Typical Layout For Above Grade Storage With Subgrade
Charging Chute 99
15 Upright Cylindrical Furnace 110
16 Rectangular Furnace • Ill
17 Multichamber Rectangular Furnace 112
18 Rotary Kiln Furnace 113
19 Traveling Grates 116
20 Reciprocating Grates 116
21 Grates With Knife Action 117
22 Double Reciprocating Stoker -118
23 Grate Bar Action in Reverse Reciprocating Stoker (also
Shown is the Ash Discharge Roller) 11 9
24 Rocking Grates • 120
25 Vibrating Conveying Grate Stoker -12-1-
26 Three-Stoker Incinerator 123
27 Roller Grate -1 24
28 Residue Disposal From Continuous-Feed Furnace by Inclined,
Water-Sealed Conveyer -129
29 Chicago Steam-Turbine Driven Auxiliary Equipment of Four
Combinations of Incinerators and Boilers •! 38
30 Simplified Flow Diagram -141
31 Chicago Northwest Steam Generating Incinerator -145
32 Suspension Fired Boiler 1 50
33 Landgard Plant Flow Sheet -165
34 Occidental Pyrolysis Process -169
35 Glass Recovery in Occidental Pyrolysis Process -171
36 Block Diagram-Oxygen Refuse Converter -174
37 AflDCO-Torrax System -178
38 ANDCO- Torrax Unit- -180
39 Incinerator Controls -185
40 Underfire Air Flow Control Systems -186
41 Furnace Temperature Control System • •! 86
42 Furnace Pressure Control System -186
43 Spray Chamber Temperature Control System '• -186
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FIGURE
44 Diagram of the Inplant Systems Based Upon Dry Fly Ash Collection
and Conveying From Cooling and Collection Operations ] 99
45 Wastewater Treatment System for Wastewater Discharge to a
Sewage Treatment Plant 211
46 High Efficiency Wastwater Treatment System 213
47 Histogram of Particulate Furnace Emission Factors for
Municipal Incinerators .. 219
48 Incinerator Flyash Particle Size Distribution 226
49 Bulk Electrical Resistivity of Entrained Particulates
Leaving Three Large, Continuous Feed Furnaces at 6 Percent
Water Vapor 227
50 Estimated Correlation Between Opacity and Particulate
Concentration for Air Pollution Controlled Incinerators 230
51 Typical Electrostatic Precipitator 235
52 Gas Motivated Venturi Scrubber Variation 242
53 Gas Motivated Venturi Scrubber Variation 243
54 Gas Motivated Orifice Type Scrubber 244
55 Liquid Motivated Jet Ejector Scrubber 246
56 Performance Curve for Venturi Scrubbers 247
57 Filter Bag House With Mechanical Shaking 249
58 Filter Baghouse With Air Pulse Shaking 250
59 Gross Products of Compustion Per Pound of Typical Waste 258
60 Air Classification of Solid Wastes - 291
61 Cross Section of an Air Classifier 292
62 Typical Shredding Plant 299
63 City of St. Louis Solid Waste Processing Facilities 303
64 CPU-400 Material Recovery System 304
65 Occidental Research Corp. Resource Recovery and Pyrolysis
Process 305
66 Bureau of Mines Raw Solid Waste Separation System 306
67 Landgard Resource Recovery and Pyrolysis System 307
68 Hercules Resource Recovery System 308
69 Ames Resource Recovery System • 309
70 Bureau of Mines Incinerator Residue Recovery System 313
71 Elements of a Municipal Refuse Incineration System -325
TABLE
1 Calculation of Volume Reduction by Various Solid Waste
Disposal Systems 3
2 As-Received Municipal Solid Waste Composition Data 10
3 Solid Waste Collected 12
4 Range in Composition of Residential Solid Wastes in 21 U.S. cities.17
5 Analysis of Incinerator Solid Waste 18
6 Projected Average Generated Solid Waste Composition, Heating
Value, and Quantity, 1970-2000 19
7 Municipal Refuse Bulk Density 21
8 Mean 1974 Cost Per Ton of Capacity At 11.3 MT/HR (300 TPD)
Capacity 31
9 Actual Costs For Three Steam Generating Incinerators 31
10 Actual Costs of Energy Distribution and Conversion System 32
11 Capital Cost Breakdown for A Steam Generating Incinerator 32
12 Example of Operating Cost Calculation for Incinerator Operating
at Design Capacity .34
X
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TABLE
13 Major Factors Affecting Incinerator Utility Costs 36
14 Typical Ownership Cost Calculation 39
15 Economic Effect of Underutilization of Incinerator Facilities 40
16 Energy Recovery From Municipal Solid Waste Thermal Processes. 41
17 Range of Potential Values for Resource Recovery in Thermal
Processing Facilities 42
18 Front End Separation Processes Incremental Capital and
Operating Costs .. 44
19 Economic Potential for Thermal Processing Facilities with
-Resource and Energy Recovery 45
20 Projected Economics for Recent Energy Recovery Projects 46
21 Lighting Standards Applicable At Incinerators 65
22 Disposal of Refuse and Other Waste Measurements of Peak
Noise Levels In, and Near, Refuse Treatment Plants 68
23 Incinerator Water Systems ?6
24 Incinerator Fuel Requirements 79
25 Typical Municipal Solid Waste -106
26 Comparison of Adiabatic Flame Temperatures for Combustion of
a Typical Solid Waste with Varying Amounts of Excess air...].Q8
27 Comparison of Refractory Incinerators and Energy recovery
Systems .] 33
28 Examples of Reported Steam Generation Quantities -135
29 Effect of Solid Waste Heating Value on Steam Production 135
30 Example of In-Plant Usage of Steam ."137
31 Comparison of Relative Values of Refuse and Fuel Oil Based
on Heats of Combustion .] 39
32 Pertinent Data for Heating and Cooling District Supplied by
Solid Waste Generated Steam .] 42
33 Quantities and Flue Gas Analysis for Steam Generating
Incinerator .] 45
34 Boiler Losses and Efficiency for Steam Generating
Incinerator -T 47
35 Air and Gas Quantities for Steam Generating Incinerator .....143
36 Overall Energy Recovery Performance of Steam Generating
Incinerator -149
37 Simple Pyrolysis -1 57
38 The Effect of Temperature on Pyrolysis Yields .] 59
39 The Effect of Pyrolysis Temperature on Gas Composition -160
40 The Effect of Pyrolysis Temperature on Organic Product
Composition -161
41 The Effect of Pyrolysis of Temperature on Char Composition .-162
42 Municipal Solid Waste Pyrolysis Processes .] 63
43 Stack Gas Analysis -167
44 Residue Analysis .] 68
45 Typical Properties of No. 6 Fuel Oil & Pyrolytic Oil .]73
46 Fuel Gas Composition .] 75
47 Usage of Available Energy 1000 ST/D Oxygen Refuse Converter
Facility -176
48 Torrax Aggregate ."] 81
49 Monitoring Equipment .190
50 Typical Instrumentation to be considered for Thermal
Processes .1 93
XI
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TABLE
51 Comparison of Residue Composition 201
52 Typical Wastewater Analysis 206
53 Chemical Quality of Cooling-Expansion Chamber Water
Discharge at Incinerator No. 1 207
54 Scrubber Water Chemical Characteristics 208
55 Effect of pH on Cation Concentration-Flyash water,
Incinerator "A" 209
56 Typical Particulate Control Regulations for Incinerators..218
57 Particulate Emissions From the Furnace of A Modern
Waterwall Incinerator 221
58 Particulate Emissions From the Furnace of A Modern
Waterwall Incinerator , .222
59 Composition of Inorganic Components of Particulates from
Furnaces .223
60 Properties of Particulates Leaving Furnaces .225
61 National Ambient Air Quality Standards .228
62 Particulate Emission Data From Uncontrolled Waterwall
Incinerator Compared with Federal Standards .232
63 Partial Listing of Electrostatic Precipitator Installations
at Thermal Processing Facilities in The United States
and Canada, Including Design Parameters 233-
64 Typical Electrostatic Precipitator Design Parameters for
Incinerator Applications ,, .238
65 Performance Data From Electrostatic Precipitator.on.
Waterwall Furnace .239
66 Typical Venturi Scrubber Operating Parameters ,. .241
67 Operating and Design Parameters for Fabric Filter Baghouse
on Municipal Incinerators .252
68 An Illustrative Comparison of Energy Requirements for
Particulate Control Systems 254
69 Typical Gas Composition for Conventional and Steam
Generating Incinerators 259
70 Carbon Monoxide and Organic Gas Emissions from Incinerators261
71 Federal Ambient Air Quality Standards for Gaseous
Pollutants 262
72 Sulfur Oxide Ammonia Nitrogen Oxide, and Halide Gaseous
Emissions from Incinerators 264
73 Performance Requirements for Several Types of Mixed Solid
Waste -271
74 Examples of Bulky Wastes ? -276
75 Weight Distribution of Oversized Waste (New York City) ...211
76 Examples of Hazardous Wastes .278
77 Examples of Obnoxious Wastes -280
78 Comparison of Conventional Incineration and Sludge-
Municipal Solid Waste Co-Incineration Parameters .282
79 Potentially Salvageable Materials in a Mixed Municipal
Refuse -286
80 Current Size-Reduction Equipment and Potential Applications
to Municipal Solid Waste 288
81 Unit Processes for Solid Waste Separation 290
XII
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TABLE
82 Specifications for an Air Classifier 293
83 Air Classified Refuse Analyses Light Fraction 294
84 Specification for A Dry Aluminum Separation Technique 296
85 Status of Available Integrated Resource Recovery Systems ....300
86 Composition of Grate-Type Incinerator Residues 31 0
87 Composition of Rotary-Kiln Incinerator Residues 310
88 Analysis of Incinerator Residue 311
89 Expected Products from the Lowell Incinerator Residue
Resource Recovery Project (Cancelled July 1975) 314
90 Calculation of Potential Value for Fuel Prepared From
Municipal Solid Waste Based on Lower Heating Value 316
91 Estimated Manning Requirements For Municipal Incinerators....323
PHOTOGRAPH
1 Various U.S. Incinerators 55
2 Ramapo, N.Y. Incinerator 56
3 East Hamilton, Ontario Suspension-Fired Steam Producing
Incinerator 57
4 Montgomery County -..South & Montgomery County - North 58
XTM
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CHAPTER I
THERMAL PROCESSING OF SOLID WASTES: AN INTRODUCTION
A municipal solid waste management system consists of a number of steps,
starting with collection and continuing through transportation, pretreatment,
treatment, environmental controls, disposal of residues, and recycle of
byproducts. This publication deals with municipal solid wastes from the
point of delivery to a thermal processing plant to the discharge of residues
and recycle of byproducts from the process. The following introductory
discussion highlights the heart of the system, the thermal processing step.
The primary objective of any effective waste management system is
disposal, while avoiding or minimizing damage to the environment. This
objective may be met by reclaiming useful materials and/or conversion of
waste components to benign or useful materials. For example, in the
sanitary landfill of municipal solid wastes, the wastes are dumped onto
specially chosen and prepared sites, compacted, isolated into cells using
a cover such as earth, and allowed to slowly change by biochemical action to
a complex, but hopefully benign, material allowing subsequent use of the
land site.
Thermal processing of solid wastes is the elevated temperature treatment
cf those wastes in suitably designed equipment so as to convert the waste
components into benign or useful materials. In practice, thermal processing
may be accomplished in the presence of substantial quantities of added
oxygen (usually air) - in a process called incineration; or thermal processing
may be accomplished with little or no oxygen added to that already chemically
bound within the waste.
Historically, the only thermal process of importance with respect to
municipal solid waste has been incineration. In an effective incineration
process, the combustion gases are composed almost entirely of carbon dioxide,
water9 nitrogen, and oxygen, all of which are normal atmospheric constituents.
The residue should contain little or no combustible material.
In recent years other thermal processes have been developed to produce
products which are useful as fuels, and possibly as chemical raw materials.
These processes can be subdivided into three categories: simple pyrolysis,
where little or no oxygen is added to the thermal treatment zone; partial
oxidation, where appreciable amounts of oxygen or air are added, producing
substantial quantities of carbon monoxide and hydrogen in addition to carbon
dioxide and water; and reduction, where either hydrogen or carbon monoxide
is reacted with solid waste. All of these categories are usually referred
to as pyrolysis, and this practice will be followed here.
This publication will deal mainly with refractory incinerators, and
with modern evolving incineration processes and pyrolysis processes in which
resource and energy recovery is practiced.
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ihe selection of a suitable process, and some of the highlights of the
major types of thermal processes which are commercially available, are
discussed in the following paragraphs.
Selection of a Suitable Process
In the current social and regulatory environment, the choice among
alternative solid waste disposal processes will normally be made by
considering impact on local and regional environment, local and regional
optimum land use, net processing costs, and other specific local problems.
For example, one should consider the desirability of dealing with secondary
sewage sludge and special industrial and commercial wastes, and special
administrative and operating problems. The choice may also be colored by the
attitude of the local community toward environmental quality and resource
conservation.,
In the evolving technology of municipal solid waste disposal, the state
of development of new processing techniques must also be a prime consideration
in process selection. For example, in its current state of development (1975),
the choice of a pyrolysis process would necessarily entail greater risks than
the choice of a proven incineration process, though the risk might be worth
taking because of potential economies or because of questions of resource
conservation.
It is necessary to make a realistic up-to-date assessment of the status
of all the options available in order to select the best process for the
needs of a particular community. Recycling opportunities must be considered
as an integral part of such an assessment. It is a prime purpose of this
publication to acquaint those responsible for such decisions with the current
state-of-the-art, and with important factors which should be considered in
selecting a suitable municipal solid waste thermal processing system.
Incineration Processes
Incineration has been the traditional competitor to landfill in areas
where insufficient suitable landfill capacity is available within an economic
haul distance. Although most incinerators built in the past could not meet
today's performance criteria, a well-designed, carefully operated incinerator
reduces the weight and volume of municipal solid waste to produce a residue
which can be used as a fill material. Table 1 compares volume reduction
obtainable by thermal processes with that encountered in sanitary landfill.
Gases discharged to the atmosphere are treated to meet governmental standards
for emission of particulates and chemical constituents. Water used for
effluent gas scrubbing or to transport residual solids should be recycled
and/or treated to produce an essentially pollution-free effluent. New
incinerators in the United States are now normally built to recover heat in
the form of steam, instead of discharging the combustion heat to the
atmosphere as hot flue gas.
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Refractory Incinerators. Most of the incinerators which have been built in
the United States do not practice energy recovery. They utilize a refractory
furnace where the solid waste is burned with air. The furnace may be a fixed
hearth type, or an inclined rotary kiln. Excessive temperatures are avoided
by using a quantity of air in excess of that theoretically required for com-
bustion, the excess air serving as a cooling medium. Average furnace exit
temperatures are usually in the range 760 to 1010 C (1400 to 1850 F).
Grates are provided in fixed hearth furnaces as a passage for underfire
air, while supporting the solid waste being burned. The most common of the
designs available are the many types of moving grates which transport the
solid waste and residue through the furnace and, at the same time, promote
combustion by inducing agitation and passage of underfire air.
Incinerators With Heat Recovery. The simplest form of energy recovery is the
use of a waste heat boiler with a conventional refractory incinerator, that is
extracting heat from the flue gases, usually to make low pressure steam. A
more effective type of heat recovery unit utilizes furnace walls made of
closely spaced steel tubes welded together, with water or steam circulated
through the tubes to extract heat generated during combustion. This procedure
not only leads to heat recovery, but allows a major reduction in air require-
ments, thus reducing the size of air pollution control equipment and other
facilities. Where high pressure steam is made, it can be used to drive
turbines for electric power production. The decision as to energy recovery is
governed primarily by the nature of the market for steam, including demand
patterns and potential value.
Slagging Incinerators. If the combustion air flow for a given burning rate of
solid waste in a refractory incinerator is reduced, the combustion temperature
increases. At a combustion temperature of about 1600 C (2912 F), a molten
residue is obtained, which, when cooled, provides a dense inert material use-
ful as a landfill. The other advantages of this reduction in combustion air
flow are the reduced gas volume, simplifying air pollution control, and the
more effective combustion at high temperature. Slagging, high temperature,
incinerator systems are in the development stage.
Suspension-Fired Incinerators. Extensive size reduction of the solid waste
allows furnace designs analogous to pulverized coal steam boilers commonly
used by the electric utilities and large industrial plants. The pulverized
waste is suspended in an air stream and introduced into the combustion zone,
where burning is very rapid. Unlike more conventional incinerators, the major
portion of the residue or flyash is carried by the hot flue gases out of the
combustion zone directly to the air pollution control solids recovery equip-
ment. A combination refuse/coal combustion system which takes advantage of
existing coal-fired suspension type boilers has been undergoing large-scale
demonstration.
-------
Fluidized Bed Incinerators. The fluidized bed is a special form of
suspension-fired incinerator where the combustion is carried out in the
presence of a suspended bed of inert solids whose behavior is analogous to
that of a fluid. The fluidized bed aids contact between the air and the
solid waste, improving combustion. Agglomeration of the flyash may also
be promoted, improving particulate recovery. A system for extracting
electric power by expansion of flue gases from an elevated pressure
fluidized bed is under development.
Pyrolysis
As discussed earlier in this Chapter, little or no air is introduced
into the elevated temperature pyrolysis chamber. Instead of combustion, a
complex series of decomposition and other chemical reactions take place.
Pyrolysis of municipal solid waste produces low sulfur gaseous, liquid, and
solid products which are potentially useful as fuels or chemical raw
materials. The nature of these products depends primarily on the
composition of the waste, pyrolysis temperature, pressure, and residence time.
Also, unlike incineration which is highly exothermic, the addition of
heat to the pyrolysis chamber is usually necessary. The method of heat
introduction is a major distinguishing factor between various pyrolysis
processes. For example, auxiliary fuel combustion, highly preheated air,
circulating heated solids, and limited oxygen introduction to produce heat
by oxiding part of the carbon present in the waste have all been used.
The elimination of inorganic constituents of the solid waste is a
useful step in pyrolysis processes to avoid contamination of products.
Therefore, separation steps to recover glass and metal byproducts fit
naturally into pyrolysis schemes.
The control of air pollution in pyrolysis processes is eased to some
extent, as compared to incineration, because of the reduced volume of gases
to be treated. However, water pollution control problems may be more
serious than in incineration due to extensive production of water and water
soluble inorganic chemicals which must be disposed of. This is a particularly
difficult problem in low temperature pyrolysis where liquid yields are high.
-------
REFERENCES
1. DeMarco, J. et al. Municipal - Scale Incineration Design and Operation.
PHS Publication No. 2012, U.S. Government Printing Office. Washington,
D. C. 1969. (Formerly Incinerator Guidelines-1969.)
2. Franklin, W. E. et al. Resource and Environmental Profile Analysis of
Solid Waste Disposal and Resource Recovery Options. Midwest Research
Institute. Kansas City, Missouri. 1974. 28 pages.
-------
CHAPTER II
BASIC DATA FOR DESIGN
Reliable basic design data is indispensable, not only for successful
design, but also as an aid in the selection of a specific thermal processing
system. Much of the data required should be available from a previously
developed solid waste management plan.' The data to be discussed in this
Chapter is that required to provide a sound basis for design, as distinct
from engineering data used for the detailed construction drawings.
The data required encompasses both the current status of municipal solid
waste problems and projections for the future. All of the physical factors
of solid waste generation and characteristics, and of site problems, must be
considered, as well as constraints such as environmental regulations. In
addition, possible markets for solid waste byproducts should be investigated.
Regulations
Thermal process designs must meet regulations intended to preserve the
quality of the environment, and the health and safety of all those who are
associated with the operation or who live in the vicinity of the plant.
Designs should adhere to EPA's "Guidelines for Thermal Processing" which
are intended to provide for thermal processing with minimum adverse impact
on the environment.2 The guidelines apply to facilities which are designed
to process more than 50 short tons/day. Thermal processing facility
operations are expected to conform to the most stringent Federal, State,
or local standards that are legally applicable to the operation of such
facilities.
Air Pollution. Particulate matter emissions to the atmosphere from new
incinerators processing more than 50 tons/day are specifically limited by
EPA's "Standards of Performance for New Stationary Sources."3 There are
presently no specific Federal regulations for gaseous emissions from
incinerators, nor are there Federal regulations covering emissions from
pyrolysis units. There are proposed Federal standards for petroleum storage
vessels which are applicable to such vessels containing pyrolysis liquids.^
Hazardous emission standards for asbestos, beryllium, and mercury, could
possibly affect thermal process designs in the future. State or local air
pollution standards which must be met are sometimes more stringent than the
Federal standards.
Air pollution from thermal processing systems is also governed by
Federal ambient air quality standards, which establish the maximum amount
of each pollutant that will be permitted in the atmosphere consistent with
public health and welfare. National standards have been set for sulfur
oxide, particulate matter, carbon monoxide, hydrocarbons, photochemicals,
and nitrogen oxide. Other air quality standards, such as for mercury, lead,
and nitrogen dioxide, may be established in the future. The States have
-------
the broad responsibility of deciding which activities to regulate or prohibit
in order to achieve the national standards. Therefore, in planning thermal
processing systems, one should investigate State implementation plans and
existing State regulations, as well as local regulations.
Water Pollution. Under the 1972 amendments to the Federal Water Pollution
Control Act, EPA is directed to publish regulations establishing guidelines
for effluent limitations, and effluent limitations for toxic pollutants.
Permits are required for each establishment discharging effluent into water
courses, but no permit is required for discharge into a municipal waste
system, except that pretreatment standards must be complied with. Since
all State laws governing water pollution must be met, even when more
stringent than Federal standards, both State and local regulations must be
investigated.
Solid Hastes. EPA's "Guidelines for Land Disposal of Solid Wastes" provide a
design basis for this approach.2 Ocean dumping is prohibited except by Federal
permit. At this time, disposal of solid residues is governed primarily by
State and local regulations.
Noise. The Noise Control Act of 1972 authorizes EPA to establish Federal
noise emission standards for products distributed in interstate commerce.
Therefore, the operator of a thermal processing facility can look forward to
a diminishment of "unwanted sound," but he assumes no specific responsibility
under this law. State and local noise regulations will affect the design
basis.
Occupational Safety and Health. Employers excluded under provisions of the
Occupational Safety and Health Act of 1970 include the United States or any
State or political subdivision of a State.6 Municipal thermal processing
plants are thereby excluded. However, municipal plant operators should be
familiar with these standards as useful guidelines, and as a possible basis
for future Federal, State, or local regulations. OSHA standards cover noise,
ventilation, walking and working surfaces, means of egress, elevators,
hazardous materials, personnel protective equipment, sanitation, physical
hazards, medical services, fire protection, compressed gas equipment,
materials handling, machinery guards, electrical equipment, and other safety
considerations. Many of these are also regulated by State and local codes
and are the subject of insurance standards.
Other State and Local Codes. Existing State and local construction codes
governing the installation of civil, mechanical, sanitation, and electrical
facilities must be complied with. These and aesthetic regulations may
limit the options available for building and state design.
-------
In the ideal situation, a site has already been specified by an earlier
master plan^ or as a result of a solid waste planning study. If this is not
the case, zoning regulations may limit the site choice and directly or
indirectly affect building and facilities designs, for example, through
problems of space availability and transportation, or problems associated
with meteorological, geologic, or soil conditions. Incinerators have
generally been built in areas zoned for industrial use. Some future thermal
processing systems which are extremely well designed and planned may be
built in commercial or residential areas, but, in gathering basic data for
design, the planner should be aware that existing industrial zoning may
limit his options as to site and design.
Site Data
A few basic data considerations for site selection will be considered
in this Section. A most detailed discussion, including the question of
public, acceptance, will be reserved for Chapter IV, "Site Selection."
As mentioned above, the choice of site is most affected by previous
land use planning, and by solid waste transportation considerations.
Information on soil, and geological and meteorological conditions must be
gathered from local and State sources. Some information may also be
available from Federal sources, for example, the Soil Conservation Service
of the Department of Agriculture, the Geological Survey of the Department
of the Interior, or meteorological aspects of air pollution control from
the Environmental Protection Agency.
Nature of the Community
Knowledge of the community is one of the key variables in predicting
solid waste characteristics and loadings to thermal processing facilities.
For example, comparative data for three locations are shown in Table 2, all
for residential and commercial refuse.'
Seasonal variations also occur. Variations are even larger for
localities handling industrial wastes or other specialized wastes. Where
possible, existing wastes should be carefully sampled and analyzed using
available techniques. ' '
Where sampling and analysis are not possible, predictive techniques may
be used. These will be most successful when complete community data are
available. For example, conditions of climate, tourism, the presence of
industrial, commercial, governmental, and institutional facilities, the
degree of urbanization, and other special disposal problems should be Known.
Detailed information on varying land uses and proposed future uses is
important.
-------
Table 2
AS-RECEIVED MUNICIPAL SOLID WASTE COMPOSITION DATA7
Weight Percent
Weber County, Alexandria,
Utah Virginia
Food Wastes
Yard Wastes
Miscellaneous
Glass, Ceramics
Metal
Paper Products
Plastics, Leather, Rubber
Textiles
Wood
8.5
4.2
5.9
4.6
8.4
61.8
2.5
2.0
2.2
7.5
9.5
3.4
7.5
8.2
55.3
3.1
3.7
1.7
San Diego,
California
0.8
21.1
--
8.3
7.7
46.1
5.0
3.5
7.5
100.
100.
100.
10
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Population
Determining the present and future population to be served has several
important purposes. An appraisal of population density aids in locating
the incinerator at the most economic site. Another important use of
population data is to estimate the quantity of wastes to be handled and,
therefore, the thermal processing plant capacity required for the designated
area.
The population estimates should include the transient, commuter, and
permanent domestic population at the time the survey is made, when the plant
is to be opened, over the projected life of the facility, and seasonal
population variation. In determining the future population to be served,
the designer should consider the possible inclusion of adjoining developed
areas within the metropolitan complex and the possible servicing of new
areas as they develop.
Standard techniques are available for estimating current population.
Some correlate the historical census records with an historical record of
population indicators, such as number of water meters, water consumption,
or other utility or commercial consumption. Other methods relate community
growth to historical growth of nearby industries or other communities.
Statewide population projections can be obtained from the U. S. Bureau of
the Census. Regional, County and local projections often can be obtained
from local, district, County, or State planning departments and from local
utility companies.
Solid Waste Quantities
The quantity of a community's solid waste will vary markedly with the
climate, season, character of the community, the extent and type of
commercial, industrial, institutional and residential developments as well
as the extent of usage of on-site incinerators and food waste grinders.
Per Capita Quantities. The continuing increase in the quantity of solid waste
produced in the United States is attributed not only to increased population,
but also to increase in per capita generation. The wide spread in the ranges
of solid waste collected (Table 3) points out the need for local studies.
Actual weighing and analysis of waste delivered to existing disposal sites is
desirable. Projections of a per capita urban disposal burden have been made
(Figure 1), but it must be emphasized that this projection should not be
used for a specific municipality, and industrial wastes must be considered as
well.7
Weekly and Seasonal Variations. Seasonal fluctuations occur in the amount of
solid waste generated and collected within the community and must be con-
sidered. This can be done by plotting weekly waste quantities averaged over
4-week periods. The fluctuations in waste quantities occur in yearly cycles,
the maximum quantity almost always occurring during the warmer months.
11
-------
Table 3
SOLID WASTE COLLECTED*
Quantity Per Capita
Per Calendar Day
Type kilograms (pounds)
Residential (domestic) 0.7 - 2.3 (1.5 - 5.0)
Commercial (stores, restaurants,
businesses, etc.) 0.5 - 1.4 (1.0 - 3.0)
Incinerable bulky solid
wastes (furniture, fixtures,
brush demolition, and
construction wastes) 0.1 - 1.1 (0.3 - 2.5)
* From Municipal-Scale Incinerator Design and Operation (1969). See
reference 1 in Chapter 1.
12
-------
FIGURE 1
Kg/Person/Day
4.540
4.086
3.632
3.178
2.724
2.270
1.816
1.362
100
1985 1990 1995 2000
Projected Per-Copita Refuse-Disposal Burden
-------
Because of many influences, the magnitude of fluctuations is significantly
different from one community to another. Factors that influence variation are
climate, weather, geography, tourism, holidays, consumption habits, collection
procedures, and community size. Four-week averages in waste generation
within a community commonly are in the range of +10 percent of the average
weekly waste quantity; weekly variation in any year seldom exceeds 25
percent of the average weekly quantity for that year.
Sizing. Because of large daily fluctuations in solid waste quantities, a
thermal processing system should be sized on the basis of weekly quantities of
solid waste to be processed. Storage pits should be designed to handle
daily peaks.
One sizing method is based on the average weekly delivery for the
highest 4-week period projected for the design year. Another method of
sizing is based on the use of a standard frequency diagram using weekly
solid waste quantities and a time period of a year (Figure 2). With the
use of a plot of this type, the size is based on the weekly solid waste
quantity that will be exceeded a given percent of the time during a year.
If the design was to be based on a weekly quantity that was exceeded
5 percent of the time, a weekly solid waste quantity corresponding to
95 percent would be selected from the frequency diagram.
In sizing a thermal processing facility, the fact should also be
considered that it will not operate continuously over the planned period.
Past experience indicates that incinerators require about 15 percent
downtime for repairs and maintenance. Pyrolysis operating factors have
yet to be determined.
Another factor to be considered in sizing a thermal processing unit
is the possibility of selective acceptance of wastes and of resource
recovery. For example, although difficult to implement, segregated
collection with direct recycle of newspaper, cans, and other potentially
valuable materials is possible. Various types of resource recovery,
discussed in a subsequent chapter, may affect the design or design capacity
of the thermal processing facility.
Characteristics of Solid Haste
The design of a thermal processing facility will vary with varying waste
characteristics. For example, where shredders are contemplated, the maximum
size waste to be handled and the presence of hard-to-shred tramp metal is
important. The moisture content is important in pyrolysis systems where
driers are provided, and in incinerators where moisture content has a profound
effect on the available heat for combustion. Effective resource recovery
obviously depends upon knowledge of waste composition. As pointed out earlier,
significant variations in waste composition do occur and must be accounted for.
14
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FIGURE 2
32 IO
156 208 J60 312 564
NUMBER Of WEEKS VALUE IS NOT EXCEEDED
416 468 52O
JO 40 ' JO 60 7O 8O
PERCENT Of YEAR VALUE IS NOT EXCEEDED
Frequency diagram of cumulative weekly solid \va>tc quantities delivered for disposal during a year. At the
asterisk, 95 percent of the year (49 of 52 wk) the quantity of solid waste did not exceed IS percent above the average
yearly mean.
15
-------
Not only has the per capita quantity of solid waste generated across
the United States been increasing yearly, but the chemical and physical
properties have been changing as well. As examples, the moisture content
has been decreasing with a diminishing percentage of household garbage,
the ash content decreased as less coal ash entered from households and
elsewhere, and chlorine content has increased with increasing plastics
consumption. Moreover, combustible content and heat value have been
increasing, principally because of the ever larger use of both paper and
plastics. The net result has been to increase heat value of the "as
delivered" solid waste to such an extent that greater furnace volumes and
more combustion air are required to maintain the rated burning capacity of
an incinerator. This trend has positive implications with regard to heat
recovery, and to potential yields from pyrolysis.
Composition of Urban Solid Waste. The composition of solid wastes varies
widely (Tables 4 and 5), requiring estimates for the particular municipality
involved. Projections show significant trends which will affect system
designs (Table 6). Data on proximate analysis, ultimate analysis, and heats
of combustion of individual components such as newspaper, cardboard, plastics,
textiles, etc. have been published.'3''4 These can be used with component
data to project overall analyses and heats of combustion.
The chemical analysis of solid waste is important to estimate air
requirements and gas compositions for incinerators. For pyrolysis processes,
the chemical analysis must be known to predict byproduct yields and compo-
sitions. The ash or inorganic content is an indicator of residue quantities
and composition.
Sulfur, nitrogen, and chlorine analyses shown in Table 4, and other
elemental analyses are useful in air pollution control considerations. The
possible presence of toxic materials, for example, heavy metals such as
beryllium, mercury and lead, pesticides, and asbestos should be considered,
as should dangerous materials such as solvents.
The moisture content of solid waste is a particularly important variable
because of its effect on available heat for combustion. Moisture content
may also affect solid waste density and ease of handling. Good design
practice requires the availability of minimum and maximum moisture values,
as well as the average value.
Other Solid Waste Characteristics. Heats of combustion can be estimated from
solid waste elemental analyses, but are preferably measured in standard bomb
tests.17' 18 Heat of combustion or "heat value" (calories per gram or BTU/lb.)
is usually reported as the gross or higher heating value, although the net
heat released in the incineration process is more nearly related to the net
or lower value, which takes into account heat which is unavailable due to the
release of water as a vapor, rather than as a liquid. Combustion heats are
trending toward higher values (Table 5), tending to decrease the tonnage
capacity of existing incinerators. Presorting, for example metal and glass
removal, will tend to increase the heat of combustion of solid waste per unit
of weight.
16
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Table 4
RANGE IN COMPOSITION OF RESIDENTIAL
SOLID WASTES IN 21 U.S. CITIES*
Component
Food Waste
Garden Waste
Paper Products
Metals
Glass and Ceramics
Plastics, Rubber and Leather
Textiles
Wood
Rock, Dirt, Ash, etc.
Percent
Low
0.8
0.3
13.0
6.6
3.7
1.6
1.4
0.4
0.2
Composition
High
36.0
33.3
62.0
14.5
23.2
5.8
7.8
7.5
12.5
by Net Weight
Average
18.2
7.9
43.8
9.1
9.0
3.0
2.7
2.5
3.7
* Unpublished data, Division of Technical Operations, Bureau of Solid
Waste Management (currently U.S. Environmental Protection Agency, Office
of Solid Waste Management Programs). Values were determined from data
taken at 21 cities in continental United States between 1966 and 1969.
17
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Table 5
ANALYSIS OF INCINERATOR SOLID WASTE*
Percent by Weight
Constituents (as-received)
Proximate analysis
Moisture 15-35
Volatile matter 37-65
Fixed carbon 0.6-15
Noncombustibles 15-27
Ultimate analysis
Moisture 15-35
Carbon 15-30
Oxygen 15-30
Hydrogen 2-5
Nitrogen 0.02-0.3
Chlorine 0.1-0.5
Noncombustibles 15-25
Higher heating value, calories per gram (as received)
1667-3333 (3,000-6,000 BTU/lb.)
* Approximate ranges from reference 16, "Municipal-Scale Incinerator
Design and Operation" (see reference 1 in Chapter 1) and other sources.
Proximate and ultimate analyses by standard methods available from American
Society for Testing and Materials (ASTM), Philadelphia, Pennsylvania.
18
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Table 6
PROJECTED AVERAGE GENERATED SOLID WASTE COMPOSITION,
HEATING VALUE, AND QUANTITY, 1970-20008
Composition by type
(weight %, as discarded):
Paper
Yard Wastes
Food Wastes
Glass
Metal
Wood
Textiles
Leather and Rubber
Plastics
Miscellaneous
Overall Composition
(weight %, as processed):
Moisture
Volatile Carbon
Total Ash
Ash (excluding glass and metal)
Relative Heating Value and Quantity:*
Heating Value (as fired)
Heating Value (dry basis)
National Population
Per-Capita Refuse Generation
Per-Capita Refuse Heat Content
Total Generated Refuse Quantity
Total Refuse Heat Content
1970
37.
13.
20.
9.
8.
3.
2.
1.
1.
3.
100.
25.
19.
22.
6.
1.
1.
1.
1.
1.
1.
1.
4
9
0
0
4
1
2
2
4
4
1
6
7
5
00
00
00
00
00
00
00
1975
39.
13.
17.
9.
8.
2.
2.
1.
2.
3.
100.
23.
20.
23.
6.
1.
1.
1.
1.
1.
1.
1.
2
3
8
9
6
7
3
2
1
0
3
1
4
2
02
00
05
13
15
19
23
1980
40.
12.
16.
10.
8.
2.
2.
1.
3.
2.
100.
22.
20.
23.
6.
1.
1.
1.
1.
1.
1.
1.
1
9
1
2
9
4
3
2
0
7
0
6
9
1
04
00
10
26
31
38
44
1990
43.
12.
14.
9.
8.
2.
2.
1.
3.
2.
100.
20.
21.
22.
6.
1.
1.
1.
1.
1.
1.
2.
4
3
0
5
6
0
7
2
9
4
5
8
8
0
09
06
31
44
57
89
05
2000
48.
11.
12.
8.
7.
1.
3.
1.
4.
2.
100.
19.
23.
20.
6.
1.
1.
1.
1.
1.
2.
2.
0
9
1
1
1
6
1
3
7
1
9
4
1
0
17
09
51
66
94
51
93
* Ratio relative to 1970 value. Typical units for absolute values would be:
Metric (English)
Heating Value
Per-Capita Refuse Generation
Per-Capita Refuse Heat Content
Total Generated Refuse Quantity
Total Refuse Heat Content
Cal/g
Kg/person per day
Cal/person per day
Kg
Cal or Kilocalories
(BTU/lb)
(Ib/person/day)
(BTU/person/day)
Ob)
(BTU)
-------
The average heat of formation of solid waste can be predicted from
the elemental composition of heat of combustion by conventional methods.15
The heat of formation is useful in predicting heat requirements from
pyrolysis reactors.
Bulk density data are required to design materials handling equipment
and storage areas. As collected at the source in receptacles or piles,
residential solid waste generally has a bulk density between 60 and 180
kilograms per cubic meter (100 to 300 Ibs/CY). In the collection truck, solid
waste is commonly compressed to 210 to 420 kilograms per cubic meter
(354 to 707 Ibs/CY). In the storage pit, the bulk density generally ranges
from 180 to 330 kilograms per cubic meter (303 to 555 Ibs/CY). Densities
for storage in 8 to 11 meter.deep pits have been estimated as a function
of water content (Table 7). Size reduction to 3 to 15 centimeters by
shredding or pulverization may result in a waste of about 300 kilograms
per cubic meter (505 Ibs/CY), but this material is easily compacted to
double that value.'y Size reduction followed by separation of dense
components such as metals, glass, and dirt may result in relatively low
density material, well under 300 kilograms per cubic meter (505 Ibs/CY).
The presence of bulky solid waste such as furniture, fixtures,
appliances, and waste lumber present special problems in a solid waste
processing operation. This subject will be treated in Chapter XVI.
Solid Waste Forecasts
There is no effective substitute for a careful solid waste survey and
sampling to estimate current waste quantities and characteristics. However,
predictive methods to produce data such as shown in Table 6 may be useful
for estimating future wastes, including those generated by industry.8-12
Predictive methods may be based on population, land use patterns, and
industrial growth projections, all of which confirm the importance of the
community and population data cited previously.
Byproduct Markets
An awareness of possible byproduct markets, particularly local markets,
is an important element in planning and designing a thermal processing
facility. Some of those that should be considered are:
- electrical power, especially non-peaking demands
- steam for heat, power, and air conditioning, especially
non-peaking demands
- scrap iron, for example, for use as precipitant in copper
production, or in iron and steel production
- glass cullet, either sorted by color or unsorted
- aluminum and other nonferrous metal scrap
- gaseous fuels (from pyrolysis)
- liquid fuels (from pyrolysis)
- carbonaceous fuels (from pyrolysis)
- ash and slag for concrete, land reclamation, road
building, etc.
20
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Table 7
MUNICIPAL REFUSE BULK DENSITY14
Moisture, % Density, Kg/CM (Ib/CY)
10 154 (260)
20 181 (305)
30 225 (380)
40 273 (460)
50 344 (580)
21
-------
- paper and cardboard for pulp, wallboard, packing, etc.
- tires and rubber for road materials and miscellaneous uses
- plastics for fillers, remelting, etc.
- wood for building board and miscellaneous uses.
The technology is not sufficiently advanced for economical recovery of
some of these materials, but present research activity in resource and
energy recovery, coupled with changing market conditions, requires a
constant awareness of the possibilities. Further discussion of markets
for recovered energy and materials may be found in Chapters X and XVII.
22
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REFERENCES
Toftner, R. 0. Developing A State Solid Waste Management Plan.
Bureau of Solid Waste Management. 1970.
SW-42ts.
U.S. Environmental Protection Agency.
Disposal of Solid Waste. Guidelines.
29328-29338. August 14, 1974.
Thermal Processing and Land
Federal Register 39(158) Part III:
3. U.S. Environmental Protection Agency. Standards of Performance for New
Stationary Sources. Federal Register 36(247) Part II: 24876-24895.
December 23, 1971.
4. U.S. Environmental Protection Agency. Standards of Performance for
New Stationary Sources. Federal Register. Proposed Standards for Seven
Source Categories. Vol. 38 (111) Part II: 15406-15415. June 11, 1973.
Additions and Miscellaneous Amendments. Vol. 39 (47) Part II: 9308-9323.
March 8, 1974. Vol. 39 (75): 13774. April 17, 1974.
5. U.S. Environmental Protection Agency. National Emission Standards for
Hazardous Air Pollutants. Federal Register. Asbestos, Beryllium, and
Mercury. Vol. 38(66) Part II: 8820-8850. April 6, 1973. Amendments
to Standards for Asbestos and Mercury. Vol. 40(199) Part V: 48292-48311.
October 14, 1975.
6. Occupational Safety and Health Administration Publication.
U.S. Government Printing Office. Washington, D. C.
7. Niessen, W. R. and Chansky, S. H. The Nature of Refuse.
1970 National Incinerator Conference. Cincinnati, Ohio.
American Society of Mechanical Engineers, pages 1-24.
OSHA 2060.
Proceedings of
May 17-20, 1970.
8. Niessen, W. R. and Alsobrook, A. F. Municipal and Industrial Refuse:
Compositions and Rates. Proceedings of 1972 National Incinerator
Conference. New York City, June 4-7, 1972. American Society of
Mechanical Engineers, pages 319-337.
9. Kaiser, E. R., et al. Sampling and Analysis of Solid Incinerator Refuse
and Residue. Proceedings of 1970 National Incinerator Conference.
Cincinnati, Ohio. May 17-20, 1970. American Society of Mechanical
Engineers, pages 25-31. (Also see Discussions, pages 3-6.)
10. Carruth, D. E. and Klee, A. J. Analysis of Solid Waste Composition -
Statistical Technique to Determine Sample Size. SW-19ts. Bureau of
Solid Waste Management. 1969.
11. Boyd, G. B. and Hawkins, M. B. Methods of Predicting Solid Waste
Characteristics. SW-23c. U.S. Environmental Protection Agency. 1971.
23
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12. Bacher, J. H. and Ranard, E. D. Use of Mathematical Planning Models
to Predict Incinerator Requirements. Proceedings of 1969 National
Incinerator Conference. New York City. May 5-8, 1968. American
Society of Mechanical Engineers, pages 1-11.
13. Kaiser, E. R. Chemical Analyses of Refuse Components. Proceedings of
1966 National Incinerator Conference. New York City. May 1-4, 1966,
American Society of Mechanical Engineers, pages 84-88.
14. Kaiser, E. R. et al. Municipal Incinerator Refuse and Residue. Pro-
ceedings of 1968 National Incinerator Conference. New York City.
May 5-8, 1968. American Society of Mechanical Engineers, pages
142-153.
15. Dodge, B. F. Chemical Engineering Thermodynamics. McGraw-Hill. New
York. 1944. page 407.
16. Kaiser, E. R. and Carotti, A. A. Municipal Incineration of Refuse with
Two Percent and Four Percent Additions of Four Plastics: Polyethylene,
Polyurethane, Polystyrene and Polyvinyl Chloride. Proceedings of 1972
National Incinerator Conference. New York City, June 4-7, 1972.
American Society of Mechanical Engineers, pages 230-244.
17. Corey, R. C. (ed.). Principles and Practices of Incineration. Wiley-
Interscience. New York. 1969. page 20.
18. Par Instrument Company. Oxygen Bomb Calorimetry and Combustion Methods.
Technical Manual No. 130. Moline, Illinois. 1960. 56 pages.
19. Wilson, D. G. (ed.). The Treatment and Management of Urban Solid Waste.
Technomic Publishing Co. Westport, Connecticut. 1972. page 88.
24
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CHAPTER III
THERMAL PROCESSING COSTS
As for any other process plant, thermal processing costs consist of those
required to:
1. Acquire the necessary facilities (capital costs),
2. Own the plant (amortization and interest on capital costs), and
3. Operate the facilities (labor, utilities, supplies, maintenance,
overheads).
With the surgent interest in energy and resource recovery, another major cost
dimension has been added. The recovery of "byproducts" from solid waste
disposal normally increases costs for all three of the above, but sales
revenues from byproducts can also provide credits against operating costs.
Other financing arrangements which are sometimes advantageous and
feasible, such as private ownership and operation, will not be dealt with in
this publication. Provisions for working capital and depreciation may also
be considered, depending on cost management procedures used by a particular
municipality.
Accurate pre-construction and post-construction cost data are essential
for planning; for funding decisions; for municipal budgets and accountability;
to aid in decision-making for plant modifications; to set solid waste disposal
prices for private or public parties not involved in ownership; and to
negotiate byproduct prices, for example, for steam from energy recovery
incinerators, fuels from pyrolysis facilities, and for glass, metals, and
other resources recovered from a variety of thermal processing facilities.
A useful accounting procedure for incineration operations is available.'
It cannot be emphasized enough that the data presented herein are meant
for orientation and illustration only. Even for planning purposes, study
cost estimates prepared by qualifed design and construction firms for
specific facilities must be obtained. The recent very rapid rate of inflation,
changing technology, increasingly stringent environmental and worker health
and safety requirements, and other such factors, may make generalized cost
data almost immediately obsolete.
Capital Costs for Refractory Incinerators
Capital costs necessary to acquire refractory incinerator facilities
can be broken down as follows:
. pre-operating expenses such as legal, financial, and consulting fees,
and interest on construction loans
. land acquisition and site preparation, including fences, roads, and
parking lots
25
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. engineering, project management, construction expenses, and
contractors' fees
. buildings and foundations
. refuse weighing, handling, preparation, and storage systems
. furnaces and appurtenances
. fans, pumps, and motors
. residue removal systems
. air pollution control systems, including stack(s)
. water pollution control systems
. utility generation and distribution
. instrumentation, controls, and laboratory
. piping and duct work
. locker rooms, offices, and sanitary facilities
. start-up costs, including acceptance tests
Each of these cost elements is significant and requires careful consideration,
as discussed elsewhere in this publication. When budgeting capital costs, a
contingency should also be included. The contingency is a judgment factor
which may range from as little as 5 percent, based on estimates for completely
designed systems, to as much as 20 to 30 percent for systems in the planning
stage which involve incompletely developed technology.
2
A 1969 study developed capital cost ranges for batch and continuous
feed incinerators. As shown in Figures 1 and 2, these costs are grossly broken
down into furnace, building, and electrostatic precipitator costs, including
most of the above items but not pre-operating expenses, land acquisition and
site preparation, or project management.
The costs shown in Figures 3 and 4 can be corrected to the year in
question using Marshall & Swift (M&S) Indexes3 (annual average) which follow:
1968 273.1 1972 332.0
1969 285.0 1973 344.1
1970 303.3 1974 398.4
1971 321.3 1975 444.3
Capital costs for eight incinerators built before 1968, obtained from the
literature4 and other sources, corrected by use of M&S Indexes and plotted on
Figure 4, agree well with the curves for total investment. However, the wide
range of possible costs,2' 4 recent more stringent standards, as well as
previously noted uncertainties, point up the need for careful cost estimation,
and cost-benefit analyses for discretionary design factors.
Capital Costs for Steam Generating Incinerators
Steam generation, using municipal solid waste as fuel, is receiving an
unprecedented surge of interest in the U.S., with no fewer than twenty cities
planning, building, or operating facilities to produce steam in specially
designed incinerators, or to burn prepared refuse in fossil-fuel fired
boilers.
As compared to refractory furnaces, costs for the following items must
be added for steam generating incinerators:
26
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FIGURE 3. CAPITAL COSTS FOR REFRACTORY
BATCH FED INCINERATORS2
11,200
9,800
8,400
7,000
5,600
4,200
2,800
1,400
1000
I— _
Electrostatic precipitator
(minimum)
100
200 300
Fur met capacity ITPO)
400
600
*M&S factor 1969-1974 =1.40
+TPD = short tons (2000 Ibs) per day
TPD x 0.0378 = metric tons per hour
27
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FIGURE 4. CAPITAL COSTS FOR REFRACTORY
CONTINUOUS FED INCINERATORS2
Dollars/TPD+
$ 1974* $ 196
18,200 1300°
Ib i oUU 12000
~i c. A f\r\ i \ciftn
ID / 4UU IIHOO
1 A fi. n n innnn
X4 f \J\J\J iwuu
J. £. f O U U 9WW
i "j 0 n n Hnnn
Xi / £. UU OUUU
9Q A A TftftA
, OU U /uuo
84 nn 6ooo
7nn n soon
5^r n n Afwt
49 rt n innn
/ ^ U \J JUOU
2ftn(l innn
"i 4 no 1000
n o
9
eiw
\
N
V
\
N
x
\
^
v
M,n
\
VN^
X
X
V * N^^
X-^1
"^*^-*.
""*•••
!p£!..
pun,
^^
Xx^J
s
-.^
' "hi ®fai
furnac
— •— -
Cir::::
S,^V^^
N*>2>
ft^
^"^•-
"^""fiuml
lE^Tzi:
^ .
^"^
*** «-
*~ •«-»
-- ..^
7m^'..r
i
SO 100 150 200
Furnac* capacity {ton«/2*-houf day/unit)
300
*M&S factor 1969^1974 = 1.403
+TPD = short tons (2000 Ibs) per day
TPD x 0.0378 = metric tons per hour
28
-------
. waterwall furnaces (replacing refractory furnaces)
. waste heat boilers, high pressure steam piping, soot blowers, and
other appurtenances
. turbine drives for inplant steam use where feasible
boiler feedwater and condensate treatment systems
. excess steam condensers
. complete auxiliary boilers and/or burners
boiler controls and instrumentation
Although the use of waterwall steam generating boilers reduces gas flow and
therefore the cost of the gas handling equipment (e.g., fans, air pollution
control equipment, stack(s)), the above noted cost elements more than offset
these reductions, increasing overall capital cost. With present day fuel
prices, the increased capital cost can be justified by steam sales where a
market exists.
?
Referring to Figure 5, a reproduction of the 1969 study data on steam
generating incinerators, the estimated 1974 cost can be compared with a
refractory continuous fed incinerator from Figure 4, as shown in Table 8.
In Table 9, actual cost data for three steam generating incinerators
built were adjusted to 1974 and compared to the 1969 cost curves by plotting
the data in Figure 5. In this case, the capital costs for these recent
incinerators exceeded values predicted by the curves. This is most likely
due to more stringent design standards, especially with regard to air pollution
control equipment.
When tne municipality is responsible for steam distribution, an additional
major capital cost may be incurred, depending on distance and steam pressure.
If the steam is converted to another form of energy, such as chilled water or
electric power, major capital costs are also required for energy conversion
facilities and distribution. An example of such costs is provided in Table 10.
The major capital costs for a steam generating incinerator are for
furnaces, steam boiler equipment, residue handling, air handling, and air
pollution control. Together these comprised over 70 percent of the total cost
for a recent installation, as shown in Table 11.
Capital Costs for Other Types of Thermal Processing Units
Since pyrolysis facilities are only now approaching commercialization, no
historical cost data are available. It is reported that the Baltimore 37.8
metric ton per hour (1000 short tons/day) facility, using the Monsanto Landgard
process, has cost $16 million.
The prototype fossil fuel/prepared refuse combustion (co-combustion)
project was reported to have cost $3.5 million, including $2.95 million for a
12.3 metric ton per hour (325 short ton/day) refuse preparation system and
0.55 million for receiving and handling facilities at the existing power
plant.
29
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FIGURE 5. CAPITAL COSTS FOR STEAM GENERATING INCINERATORS
(EXCLUDING STEAM DISTRIBUTION)
Dollars/TPD'1'
$ 1974* $ 1969
19,600 14,000
18,200 13,000
16,800 12,000
15,400
14,000
12,600
11,200
11,000
10,000
9,000
8,000
9,800 7,000
100 200 300 400 500 600TOO
TPD/Furnace
*M&S factor 1969-»-1974 = 1.40s
+TPD = short tons (2000 Ibs.) per day
TPD x 0.0378 = metric tons per hour
30
-------
Table 8
MEAN 1974 COST PER TON OF CAPACITY AT 11.3 MT/HR
(300 TPD) CAPACITY*
Refractory incinerator $280,000 per MT/hr ($10>600/TPD)
(from Figure 2, maximum)
Steam generating $392,000 per MT/hr ($14,800/TPD)
incinerator (from
Figure 3, high end
of range)
* 1 MT/hr = 1 metric ton per hour = 2205 Ibs/hr
1 TPD = 1 short ton per day = 2000 Ibs/day
Excluding energy distribution or conversion system costs
Table 9
ACTUAL COSTS FOR THREE
STEAM GENERATING INCINERATORS*
Site
Capacity, TPD
Actual Cost, $MM
Year
M&S Cost Factor
1974 Cost, $MM
1974 Cost, $/TPD
$ per MT/hr
4 x 400
17.4
1969
1.40
24.4
15,300
403,000
4 x 250
16.8
1973
1.16
19.5
19,500
516,000
2 x 360
9.8
1973
1.16
11.4
15,800
419,000
* TPD = ST/day
31
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Table 10
ACTUAL COSTS OF ENERGY DISTRIBUTION
AND CONVERSION SYSTEMS*
Site
Year
Refuse Capacity, TPD
Distribution System
Distribution System Cost
Energy Conversion System
Energy Conversion System
Cost
Y
1973
4 x 250
steam
$2.2 MM
none
Z
1973
2 x 360
steam, chilled water
$4.0 MM
steam-n:hillecl water
$3.0 MM
TPD = ST/day
Table 11
CAPITAL COST BREAKDOWN FOR A
STEAM GENERATING INCINERATOR*
Furnaces, boilers, precipitators, ID fans,
ash conveyors, ash crane
Building, foundations and concrete works
Building, steel structure
Building, general construction
Refuse cranes
Chimney and flyash silo
Conveyor system for flyash
Pumps and steam turbine
Emergency steam condenser
Electronic weighing scales
Water treatment plant
Central control panel and instrumentation
Other plant utility equipment and systems
(fuel oil, air, steam, electrical)
Access ramps, water and sewer
Landscaping and site works
Temporary services during construction
*Derived from reference 5. Excludes land cost,
engineering, contingencies, and steam transmission.
32
-------
Recent cost projections have been made for 37.8 MT/hr (100 ST/day) co-
com bust ion arid PUROX pyrolysis systems:"
$ per MT/hr $ per ST/day
Co-combustion 251,000-291,000 9,500-11,000
PUROX 627,000-693,000 23,700-26,200
The co-combustion process produces a refuse-derived-fuel and salvage materials;
whiie the PUROX process, currently being tested in a large pilot plant,
procuces a clean fuel gas and fused frit, with the option of materials
recovery instead of frit.
Operating Costs
The operating cost for thermal processing facilities as used in this
publication, is the expense involved in keeping the facility running to dispose
of solid waste and to recover products of value, when the latter is an integral
part of the operations. Operating costs are usually broken down into direct
(or variable) costs and indirect (or fixed costs), although some costs are
semi-variable.
Direct costs, such as utilities and residue disposal, tend to be
proportional to solid waste throughput. Indirect costs, such as insurance
and facility protection, tend to be independent of throughput. When projecting
or otherwise analyzing costs, it is necessary to carefully determine which
costs for the specific facility in question are indirect or direct. For
example, although operating labor is normally considered a direct cost,
operation of a thermal processing facility with municipal employees may
require the maintenance of a fixed size labor force over a long period of
time, regardless of throughput. Thus, normal wages for such a labor force
become an indirect cost, independent of throughput.
Direct Labor and Labor Overhead Costs. As shown in Table 125 labor and labor
overheads comprise the largest single operating cost.
Labor usually represents the largest single operating cost. Unit labor
costs ($/ton) are obviously a function of wage rates and the number of
personnel required, but also depend upon actual vs design throughput where the
total number of personnel is rather inflexible. Wage rates usually are fixed
oy prevailing scales paid to comparable municipal employees. However, higher
wage scales competitive with local industry, where different than municipal
scales, may attract personnel of greater experience, training, and responsi-
bility.
Since increasing facility size does not proportionately increase personnel
requirements, large facilities show smaller unit labor costs than small ones.
For example, although three incinerator operators per shift may be required for
three 400 ton per day incinerator trains, four similar size trains may also
require only three operators, a reduction of 25 percent in unit cost for
capacity operation.
33
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Table 12
EXAMPLE OF OPERATING COST CALCULATION FOR INCINERATOR
OPERATING AT DESIGN CAPACITY
Basis: 1. 16 MT/hr average output, 24 hrs/day, 365 days/yr
2. 50 KWH/MT electric power @ 4tf/KWH
3. 5 MT/MT cooling water @ 2.5*/MT
4. Direct labor, 50 men @ $13,000/yr average wage
5. Labor overheads at 30% of direct labor
6. Contract maintenance and materials, and supplies, @
$150,000/yr
7. Indirect costs at 40% of direct labor
Operating Costs,* $/MT
Direct
Labor
Labor Overheads
Utilities
Maintenance
Indirect
$ 4.64
1.39
2.13
1.07
9.23
1.86
$ 11.09
*Excludes ownership costs
34
-------
Laoor requirements are also determined by the degree of instrumentation,
automatic control, and other labor saving devices. Similarly, added capital
investment for spares, high quality equipment components, and other methods
for improving reliability can also reduce unit labor costs, but each such
added investment should be carefully justified, using actual operating data
where possible.
Overheads which are directly related to labor requirements, for example,
payroll taxes and benefits such as retirement and health plans, vacation,
sick leave, etc., are termed labor overheads. These vary with location but
are usually identical to those used for other municipal employees, except
where special benefits such as safety shoes, safety glasses and hardhats are
supplied by the incinerator management.
When calculating labor costs, provisions must be made for overtime pay,
shift differentials, and other costs associated with continuously manning an
operating facility.
lit i 1 ity an_d Pi rect Supply Costs. Utility and supply requirements arid costs
for individual incinerators may differ markedly. Some of the factors which
affect these costs are shown in Table 13.
The major utilities normally required in incinerators are electric power
for motors and lighting, fuel for space heating and auxiliary steam production,
and water for cooling, quenching, drinking, steam generation, and sanitary
facilities. More than one type of water may be used, for example municipal
water for drinking and river water or seawater for residue quenching. Direct
supplies used in incinerators may include chemicals for water treating, charts
and other supplies for instruments, janitorial supplies, deodorants, personal
safety equipment, uniforms, and a myriad of other small items. Usually
excluded from this category are materials used in repair and maintenance.
When prices do not vary substantially with the quantity used, utility and
supply costs may be considered direct, these costs being dependent on through-
put. The estimate of utility costs for new incinerators should be based on
local projected rates and on sound engineering estimates of the quantities
required. Supply costs are normally much less significant than utility costs.
Maintenance Costs. The two major components of maintenance costs are materials
and labor used for repairs and routine maintenance, although where contract
maintenance is practiced this may be considered as a separate category. The
maintenance of instrumentation, cranes, weighing scales, and other complex
equipment by outside contractors should be considered because it is difficult
to find all necessary skills in the relatively small maintenance crews avail-
able at most incinerators. Centralized maintenance for all public works is
used in some municipalities.
Maintenance costs vary greatly with adequacy of the incinerator design,
age of the facility, quality of equipment, skill of the operators, and nature
of the solid waste. For example, replacement of refractory,-a major cost in
in most incinerators, is dependent on all these variables, with minimal costs
incurred where high quality refractory is used and where automatic tempera-
ture control is reliable.
35
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Table 13
MAJOR FACTORS AFFECTING INCINERATOR
UTILITY COSTS
Factor
Comments
Local utility
price structure
Excess air
requirements
Type of air
pollution control
Internal generation
of steam
Residue and
wastewater systems
Solid Waste
composition
Prices for purchased utilities such as
electric power and water vary greatly
between localities, due to differences
in availability of fuels for power
generation, and of natural water supplies.
Power requirements increase as excess air
increases, both for forced draft fans and
for induced draft fans. Steam generating
incinerators with waterwalls use less
excess air.
High energy scrubbers for particulate control
have high draft requirements, provided by
fans which consume much more power than is
necessary for the combined requirements of
electrostatic precipitators and fans for
that type of system.
A major portion of required power can be
supplied by internally generated steam.
Chemicals are required for boiler feedwater
treating.
Makeup-water requirements can be minimized
by reusing wastewater from scrubbers and
spray coolers to handle solid residues,
and by effective wastewater treatment systems
which allow maximum water recycle.
Increased waste moisture in refractory
incinerators can decrease excess air
required for cooling, but too high a
moisture content can necessitate auxiliary
fuel burning, especially in steam generating
incinerators. Acidic precursors in waste,
such as polyvinylchloride plastics, affect
requirements for neutralizing chemicals in
wastewaters.
36
-------
Scheduled inspection and maintenance programs help to hold down the
extraordinary cost sometimes associated with unexpected equipment breakdown
and sudden loss of incineration capability. Total maintenance costs can be
expected to lie in the range of 1 to 5 percent of the original investment per
year, although costs may be expected to increase with the age of the facility
faster than escalation, and vary greatly from year to year.
Other Overhead Costs. Overhead costs, other than labor overheads previously
discussed, are those costs that are necessary but not easily connected
directly with the operation of the facility. They are, in fact, indirect or
fixed costs incurred whether or not the incinerator is operating. These may
include management, accounting, engineering, secretarial and clerical
personnel and costs, insurance, laboratory expenses, training, travel, and
other costs. The distinction between overheads and direct costs is not
always clear, but should be made as consistently as possible. Depending on
accounting methods and the distinctions made, overhead costs may run, for
example, from 30 percent to 60 percent of direct labor.
Ownership Costs for Incinerators
Ownership costs may be described as those costs which accrue whether the
facility operates or not, temporarily or permanently. The ownership costs for
municipal thermal processing facilities are interest payments on borrowed
capital and the return of that capital. If money is actually set aside
periodically for the purpose of returning borrowed capital at a future date,
for example as prescribed in bonds issued to lenders, the process is called
amortization. If the original capital used to build a facility comes from
general tax revenues, a yearly depreciation expense should be charged, which
allows for the decrease in the value of the facility due to wear and tear and
obsolescence, recognizing the need for future capital to replace the existing
facility.
Where bond terms are such that interest is paid periodically and an actual
amortization sinking fund is established to repay the loan on a certain future
date, annual ownership costs are the annual interest cost plus the annual
amortization payment to the sinking fund, less interest earned by the sinking
fund. Even where no actual sinking fund exists, costs may be calculated in
this way. In any case, ownership costs should be calculated in such a way as
to be consistent with the terms of securities sold to raise the necessary
capital.
When depreciation expense instead of amortization is used to analyze
thermal processing ownership costs, the normal practice is to uniformly dis-
tribute the total capital cost by annual charges over a period of about 20 to
30 years, depending on the predicted life of the facility, or to depreciate
plant components over periods which range from about 4 to 30 years depending
on expected life. More complex depreciation approaches which recognize
greater depreciation in early years (accelerated depreciation) are often used
in industry, especially for tax advantages, but find little application in
thermal processing facilities.
37
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Interest charges will be determined by free market rates and the credit
rating of the municipality when bonds are sold. Since the interest on
municipal bonds is received tax-exempt by the owner of the bonds, the rates
are significantly lower than comparably rated industrial bonds. A typical
ownership cost calculation is provided in Table 14. Because of the great
significance of ownership costs, more than the usual care should be taken in
calculating these, and in being explicit about the calculation basis.
Since ownership costs are obviously directly related to the size of the
capital investment, increased investment for greater reliability of lower
labor, utility, or maintenance costs will correspondingly increase the cost
of ownership. Therefore, careful cost-benefit analysis is required to
determine the optimum investment/operating cost relationship for the specific
project being contemplated.
Underutilization dramatically increases the magnitude of indirect and
unit ownership costs ($/ton), since these costs go on even if the facility
never operates. For example, Table 15 shows the increase in total unit costs
for an existing incinerator operating on different schedules and throughputs.
Unit costs of $14.94/MT for a 7 day three-shift operation increase to $33.23/
MT for a 5 day one-shift operation, due to the effect of fixed costs. Ob-
viously, oversizing an incinerator, or underutilization, can result in an
extraordinary cost for refuse disposal.
Economics of Energy and Resource Recovery
\
Energy may be recovered from thermal processing systems in the form of
steam, fuels, or electrical power, as shown in Tables 16 and 17. Part of the
energy recovered may be used internally, but most is available for export.
Other resources, such as glass, ferrous scrap, aluminum, and other metals, can
be recovered prior to or after thermal processing. Combustible resources such
as paper fiber may also be recovered, but are not normally done so as a part
of a thermal processing system.
The value of energy and recovered resources can have a major impact on
net thermal processing costs, and can theoretically even pay for the entire
cost of thermal processing. The following discussion is designed to show the
potential promise for energy and resource recovery, but the management of
thermal processing facilities must overcome the institutional, technical, and
marketing problems inherent in realizing this promise.
Table 17 clearly shows the potential for recovery, and the effect of
price structure on this potential.
The recovery of glass and metals is of definite interest as a method of
offsetting thermal processing costs, but it is the recovery of energy in an
environment of rising energy prices that shows really major potential for
beneficial use of municipal solid waste.
However, it is insufficient simply to know the value of resource and
energy recovery, the cost of such recovery must also be thoroughly evaluated.
38
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Table 14
TYPICAL OWNERSHIP COST CALCULATION
Basis: 1. Capital Cost (per unit of capacity) = Capital
Borrowed = $397,000 per metric ton/hr
($15,000 per TPD)
2. Bond Interest Rate = 7%/yr
3. Repayment of bond after 30 years
4. 30 year life for incinerator (no salvage value)
5. Sinking fund interest = 5%/yr
6. Operation at 100% of capacity
Ownership Cost
$/metric ton
Yearly Interest & 7%/yr $ 3.17
Uniform Annual Amortization Payment* 0.68
Total Ownership Cost $ 3.85
* If this payment is made annually for 30 years to a sinking fund earning
5% interest compounded annually, the sinking fund balance at the end of the
30 years will be equal to the original capital borrowed.
39
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Table 15
ECONOMIC EFFECT OF UNDERUTILIZATION
OF INCINERATOR FACILITIES*
Operating Schedule
7 day -
3 shift
5 day -
2 shift
5 day -
1 shift
Operating Rate, % of 100 47.6 23.8
Capacity
Design Capacity,
m/iir v^'/uay;
Operating Rate, MT/yr
Operating Costs, $/MT
Direct
Indirect
Ownership
140,000
9.23
1.86
3.85
$14.94
iu \te.jj
66,640
9.23
3.91
8.09
$21.23
33,320
9.23
7.82
16.18
$33.23
* This table does not account for underutilization attributed to
maintenance or downtime, which can be as high as 20% per day.
40
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Table 16
ENERGY RECOVERY FROM MUNICIPAL
SOLID WASTE THERMAL PROCESSES
Type of Thermal Processing
Form of Energy Recovery*
(based on refuse as delivered^
Refractory Incineration
With or Without Waste Heat
Boilers
Modern Waterwall
Incinerators
Combined Fossil Fuel/Refuse
Combustion Boilers
Pyrolysis Plants
High Pressure Fluidized Bed
(Under development)
0-1.5 tons steam/ton refuse (or
electric power generated from
steam)
1.5-4 tons steam/ton refuse
(or electric power generated
from steam)
1.5-4 tons steam/ton refuse
(or electric power generated
from steam, e.g., 500-800 KWH
per metric ton of refuse)
Gaseous, liquid, or solid fuels
(or steam or power generated from
fuels)
400-500 KWH electrical power
per metric ton of refuse
* Quantitative values for recovered energy derived from reference 7
and other sources.
41
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As shown in Table 18, the cost of separation steps, required prior to thermal
processing for resource recovery, are substantial.
The overall cost of recovery must be estimated with great care for each
facility under consideration. However, for purposes of orientation only, a
hypothetical study is provided in Table 19.
It is obvious from the information in Table 19 that the critical aspect
of an economically attractive project for thermal processing with resource
recovery is locating and assuring markets for the recovered energy and
materials. The size of the project is also a critical factor.6
One recent set of cost estimates (1974) made for projects producing
refuse-derived-fuel, pyrolysis gas, pyrolysis liquid, steam from incineration,
and other forms of energy are much higher than those discussed here, but
insufficient detail is provided to evaluate this information. A more
detailed set of estimated costs for dry-shredded-fuel processing plants has
been prepared by the U.S. Environmental Protection Agency,^ showing the
effect of estimated revenue ranges, capacity utilization, and special costs
such as taxes, transportation, high residue disposal charges, unusual site
work, etc. These cost data show that such a project can range from profitable
to a high cost of solid waste disposal, depending on the specific project
conditions encountered.
Projected economics for two recent thermal processing facilities,
summarized in Table 20, show that economically attractive projects are
possible. Since both projects are still in their startup phase, these
results have yet to be verified.
43
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Table 18
FRONT END SEPARATION PROCESSES
INCREMENTAL CAPITAL AND OPERATING COSTS6
Basis: 331,000 MT/yr Plant, 365 day/yr operation
Unit Operation*
Primary
shredding
Air
Classification
Secondary
shredding
Magnetic metal
separation
Rising current/
heavy media
separation
Roll crushing
& electrostatic
separation
Color sorting
Capital Cost+ Ownership
$/MT/hr Cost*
($/ST/day) $/MT
33,070 (1250) 0.41
25,100 (950) 0.31
16,500 (625) 0.20
2,000 (75) 0.02
6,900 (260) 0.08
7,400 (280) 0.09
11,200 (425) 0.14
Operating
Cost Total
$/MT $/MT
2.78 3.19
1.50 1.81
1 . 76 1 . 96
0.43 0.45
0.45 0.53
0.49 0.58
0.44 0.58
* Those listed are not all fully proven in large scale operation
+ Does not include land or buildings
* 15 year amortization, 7%/yr interest
44
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Table 19
ECONOMIC POTENTIAL FOR THERMAL PROCESSING FACILITIES
WITH RESOURCE AND ENERGY RECOVERY
Ownership
and
Operating
Costs $/MT*
Incineration 8.47
Only
Incineration 9.88
and Residue
Recovery
Incineration 11.44
and Steam
Generation
Incineration 12.89
With Steam
Generation
and Residue
Recovery
Pyrolysis with 12.08
Resource and
Oil Recovery
Resource
Recovery*
None
Ferrous &
Nonferrous
Metals,
Glass
(1,3,4)
Steam
(5)
Ferrous &
Nonferrous
Metal,
Glass,
Steam
(1,3,4,5)
Ferrous &
Nonferrous
Metals,
Glass, Oil
(1,2,4,7)
Net
Resource Cost
Credits, (Profit),
$/MT+ $/MT
8.47
1.05-6.10 3.78-8.83
3.30-13.20 (1.76)-8.14
4.35-19.30 (6.41)-8.54
3.55-16.70 (4.62)-8.53
* For 272,000 metric ton (MT) per year facility; derived from a 1973
report to the President's Council on Environmental Quality.^ To be used
for orientation only.
+ Numbers under "Resource Recovery" heading refer to items on Table 17.
45
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Table 20
PROJECTED ECONOMICS FOR RECENT
ENERGY RECOVERY PROJECTS
Type of
Project
and Capacity
Steam Price
$/MT steam
Operating
Costs, $/MT
Ownership
Costs, $/MT
Incinerator With
Steam Generation*
4 x 227 MT/day
$2.09
$3.40
6.00
Pyrolysis
907 MT/day+
$ 1.79+ $ 4.83+
6.46 6.46
4.10 4.10
Total Costs,
$/MT
Credits from
Sale of Steam,
$/MT
Net Cost (Profit),
$/MT of Waste
Processed
$9.40
6.28
$3.12
$10.56 $10.56
4.29
11.59
$ 6.27 ($ 1.03)
* Original projected economics for 1980. Steam price to vary by formula
as Bunker C price varies.
+ Projected economics for 1975. $1.79/MT steam (81<£/1000 Ibs) based on
$3.70/barrel No. 6 fuel oil. Escalation in sales contract of $0.002189/1000
Ibs steam per U change in fuel oil price to $4.83/MT ($2.19/1000 Ibs) for
$10/barrel No. 6 fuel oil.
46
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REFERENCES
1. Zausner, E.R., An Accounting System for Incineration Operations.
Public Health Service Publication No. 2022. Bureau of Solid Waste
Management Report SW-17ts. U.S. Department of Health, Education and
Welfare. 1970. 17 pages.
2. Neissen, W. R. et al. Systems Study of Air Pollution From Municipal
Incineration. Volume I. Arthur D. Little, Incorporated, Cambridge,
Massachusetts. U.S. Department of Health, Education and Welfare.
National Air Pollution Control Administration Contract No. CPA-
22-69-23. NTIS Report PB 192 378. Springfield, Virginia, March
1970. Pages VII 89-172.
3. Ricci, L.J. CE Cost Indexes Accelerate 10-Year Climb. Chemical
Enginerring, April 28, 1975, pps 117-118.
4. Achinger, W. C. and Daniels, L.E. An Evaluation of Seven Incinerators.
U.S. Environmental Protection Agency. Publication SW-51ts.lj. May
12-20, 1970. 76 pages.
5. Aubin, H. The New Quebec Metro Incinerator. Proceedings, 1974
National Incinerator Conference. Miami, May 12-15, 1974. American
Society of Mechanical Engineers. Pages 203-212.
6. Schulz, H. W. Cost/Benefits of Solid Waste Reuse. Environmental
Science & Technology §_ (5):423-427. May 1975.
7. Resource Recovery—Catalogue of Processes. Prepared for the U.S.
Council on Environmental Quality. Midwest Research Institute.
National Technical Information Service, Springfield, Virginia
PB 214 148. February 1973. 141 pages.
8. Resource Recovery—The State of Technology. Prepared for the U.S.
Council on Environmental Quality. Midwest Research Institute.
National Technical Information Service. Springfield, Virginia.
PB 214 149. February 1973. 67 pages.
9. Fuels from Municipal Refuse for Utilities. Technology Assessment.
Prepared for Electric Power Research Institute. Bechtel Corporation.
National Technical Information Service, Springfield, Virginia.
PB 242 413. March 1975. 184 pages.
10. Third Report to Congress. Resource Recovery and Waste Reduction.
SW-161. Office of Solid Waste Management Programs. U.S.
Environmental Protection Agency. Washington, D.C. 1975. 96 pages.
47
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CHAPTER IV
SITE SELECTION
The major factors to be considered in selecting a site for an industrial
plant are:
1. raw materials sources
2. transportation facilities
3. waste disposal
4. suitable land
5. utilities
6. markets
7. environmental, zoning, and other regulations
8. public acceptance
9. labor
10. taxes
11. building costs
12. availability of repair and other labor services
13. climate
Many of these same considerations must be applied to a thermal processing
facility for municipal wastes. However, factors 9 thru 13 cannot be easily
controlled or do not apply directly to site selection for local or even
regional governmentally owned solid waste processing facilities. These will
not be considered further here.
Raw Material Sources and Alternative Disposal Plans
Obviously, the raw materials under consideration are the solid wastes,
but these may be transported from a wide area or a limited area depending upon
the nature of the community, and on the regionalization of the collection
system. A central location to minimize transport time may be an important
consideration in large regional systems, and collection economics versus site
should be studied. Transfer stations should also be considered, especially
where pre-shredding and resource recovery is to be practiced.
One major consideration for thermal processing site selection, that
usually does not exist for industrial process units, is the planning necessary
for facility downtime. For municipalities or regions with a single processing
facility, sanitary landfill sites are usually the only practical answer, with
a landfill site used for residue disposal being most convenient. If a
processing site is adjacent to or near the landfill site, normal or nearly
normal collection and traffic patterns can be maintained.
The acceptability of commercial, industrial, and bulky wastes may also be
a significant consideration. The commercial and industrial wastes can have a
major effect on traffic patterns. When bulky wastes which are to be land-
filled are collected with other wastes, the presence of a nearby landfill site
is especially advantageous.
48
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Transportati on Faci 1 j_tj es
Since solid wastes ordinarily enter the plant by truck, the surrounding
road facilities are critical. If major road changes must be made to utilize
a particular site, the cost should be considered to be a part of the cost of
that particular site. Peak rather than average traffic loads should be
considered, since most collection schemes envision a single starting time
for all crews leading to peak unloading hours.
Waste Disposal
Ordinary incinerators result in three solid waste products which may or
may not be combined before leaving the plant: grate sifting; combustion
residue; and flyash. These wastes, and bulky wastes^, are the factors which
enhance the desirability of having landfill and incinerator sites adjacent to
each other. Regardless of the location of the landfill site, it must meet
sanitary landfill criteria.1 Transport of wastes to distant sites is a
nuisance, (e.g. dry flyash recovered from electrostatic precipitator hoppers
presents dust problems; transport of wet residues may present water runoff
problems) and may be expensive, e.g. $1 to 3 ton. Recovery of ferrous metals,
and possibly other resources, from residues eases the disposal problem and
may produce some profit, as discussed in Chapter XVII.
is usually used for residue recovery and often for spray chambers
and scrubbers. Recycle and neutralization should be practiced to the greatest
extent possible, but purge water is too high in solids, BOD, and temperature
for discharge to freshwaters. Therefore, the presence of sanitary sewers can
be an important site consideration to minimize on-site water treatment, but
the availability of sufficient sewage treatment plant capacity must be assured.
In selecting a site, it is also necessary to have data on the movement of
ground waters and runoff water, and to provide design conditions which will
avoid water pollution problems.
Su i tab! e Land
Only rarely will suitable sites be found available in areas which have
not already been industrialized. The availability of already assembled land
sites in industrial areas eases the site selection problem. Existing landfill
sites are a favorite choice, but unfortunately many existing landfill sites
have been poorly chosen, e.g. in marshy areas. Existing landfill areas must
be carefully checked for foundation conditions, uncontrolled leaching, gas
generation, and possible flooding conditions.
If possible, it is desirable to avoid land areas near schools, hospitals,
and other institutions. Adjacent highways should also be avoided, especially
when scrubbers are used for air pollution control. The saturated flue gases
can be a highway hazard, especially under low temperature conditions which
result in artificial fogs or even highway surface freezing.
49
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Topography is another important land consideration. A flat site is apt
to require a ramp to the tipping floor, whereas a hillside site can provide
access at various ground levels. Topography also affects the dispersion of
flue gases and should be considered in meteorological calculations.
In many cases, a site should be chosen which is suitable for expansion.
Utilities
Electrical power, fresh water, and fuel are required for almost any
thermal processing facility. These will be discussed further in Chapter VI,
"Utilities." The availability of electrical power and fresh water facilities
may sometimes affect site selection. Natural gas or oil used as auxiliary or
startup fuel is interchangeable from a design point of view and is required
in relative small quantities, so that fuel availability will seldom signifi-
cantly affect site selection.
Markets
Markets for steam made in waterwall incinerators may have a very signifi-
cant effect on site selection. Long distance transport of steam is uneconomi-
cal because of piping costs, heat loss, and the simultaneously increasing
cost of condensate return. The costs of electrical distribution in relatively
small quantities is also expensive unless existing networks can be used.
Markets for possible resource recovery products, such as ferrous metals,
glass, aluminum, copper, and zinc have relatively little effect on thermal
processing site selection, although market availability may have a profound
effect on the economic decision of whether recovery is worthwhile.
Oil and coke made in pyrolysis processes do have significant effects on
site selection, particularly with regard to the necessity for storage tanks
and areas. Pyrolysis processes that produce primarily combustible gases for
export affect site selection much more because of the high cost of storing
and transporting combustible gases, or of the steam which can be made from
the gases.
Environmental, Zoning, and Other Regulations
Reference to local, State, and Federal regulations and master plans aid
in the early elimination of potential sites. It may be very difficult, or
almost impossible, to gain acceptance of sites which seriously conflict with
existing codes.
As discussed in Chapter II, EPA's "Guidelines for Thermal Processing" and
"Standard of Performance for New Stationary Sources" govern the construction
of new facilities. In addition, Federal, State and local air and water quality
standards must not be exceeded. For example, it may be necessary to show by
meteorological calculations for a certain site that air quality standards are
met over the entire area affected.
50
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Zoning regulations can be modified to allow thermal processing unit
construction where not already contemplated, but the inertia against such
modification is often formidable. Where plans can be formulated for regional
approaches to solid waste management, including multiple thermal processing
units, public acceptance, as discussed in the following section, may be
easier to gain.
Public Acceptance
The most important factors in gaining public acceptance for a thermal
processing facility site are:
1. The inherent logic of the site selection as compared to alternatives,
2. The proper preliminary design of the plant to fit, the site chosen,
and to overcome inasmuch as possible objectionable plant features.
3. An effective public information program which includes the prepara-
tion of attractive drawings and models; prepared plan presentations
at public meetings, with rationale for the choice as compared to
alternatives; and visits to successfully operating facilities.
Land Area Requirement
The actual area required by a thermal processing plant depends upon its
size, design, site suitability, operating mode, and auxiliary facilities to
be included. For an incinerator processing 50 to 75 metric tons per hour
(1300 to 2000 short tons/day) the minimum site required (excluding expansion
area, parking, truck storage, vehicle services areas, landfill, extensive
water treating facilities, or extensive screening areas) would be about
12,000 to 16,000 square meters (3 to 4 acres). A more suitable site in-
cluding some of the auxiliary requirements, but still excluding expansion
and landfill areas, would be two to three times the minimum.
Plants much smaller than 50 to 75 metric tons per hour obviously require
much less area, but the requirements are far from linear. It is difficult to
visualize a suitable site of less than 8000 square meters (2 acres), even for
a very small incinerator.
The area required for landfill of residue, siftings, flyash, and bulky
materials should be calculated using information such as that presented in
Table 1 of Chapter I and in Chapter II. Where possible, a landfill life of
at least twenty-five years, including growth projections, should be available.
This would provide the same order of magnitude as life expectancy for a
thermal processing facility.
A definitive calculation of land area requirements, and major participa-
tion in site selection should be assigned to the consulting engineers.
51
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REFERENCES
U.S. Environmental Protection Agency. Thermal Processing and Land Disposal
of Solid Waste. Guidelines. Federal Register 39.058) Part III; 29328-
29338. August 14, 1974.
52
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CHAPTER V
PLANT LAYOUT AND BUILDING DESIGN
Plant layout and building design must enhance the thermal processing
facility aesthetically and functionally. Successful design will achieve the
following:
2.
harmonization with the surroundings.
Utilization of the topographical features of the site to the
greatest advantage.
3. Efficient and economical traffic flow.
4. Efficient and economical process operation.
5. Ease of housekeeping and maintenance.
6. Avoidance of nuisances and hazards associated with traffic,
handling of wastes and byproducts, noise, odors, and gaseous,
liquid, and solid effluents.
Aesthetic excellence in layout and design of a thermal processing plant
is not necessarily at odds with achievement of reasonable costs. Where
conflicts exist, evaluation of alternatives and realistic compromises will
usually result in an acceptable solution. If this job is done well, the
rewards will include better public acceptance as well as ease and economy
of operation.
Plant Layout
Layout of buildings, roads, stacks, gas cleaning equipment, water treat-
ment facilities, and landfill areas (if onsite residue disposal is to be
practiced) is done with a view to both social and economic factors. The social
factors associated with plant layout have often been neglected. However, with
increasing public awareness of air and water pollution, and noise and conges-
tion related to truck traffic, site planning must take these factors into
account. For example, receiving and refuse storage are often located at the
rear of the building and out of public view. In warm climates with prevailing
wind patterns, the receiving area may be placed on the leeward side of the main
buildings to minimize wind-carried litter and odors, and to provide workers
with protection from the elements.
Hillside terrain may be used to create the impression of a low building
profile to overcome the stark visual impression of a multi-story structure.
The architectural design of the building structures should harmonize with
surrounding buildings and terrain in such a way as to maintain the visual
integrity of the neighborhood. Even tall stacks may be partially hidden from
53
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view by buildings. The materials selected for the exterior shell of the stack
should be as unobstrusive as possible. Short stacks may be used in some
instances at the expense of greater power requirements for induced draft (ID)
fans, but such stacks must be consistent with proper dispersion of gaseous
emissions.
Air cleaning equipment, such as electrostatic precipitators, cyclones, or
scrubbers, will usually be installed in such a way as to be shielded from view,
or they may be enclosed within the building to avoid excessive heat loss and
condensation of moisture. Settling ponds and lagoons used for treatment of
wastewater will normally be located at as low an elevation as possible to
facilitate incoming drainage and are, therefore, seldom detrimental to the
appearance of the plant when viewed from a distance. Through careful design,
such small bodies of water often lend almost a park-like atmosphere which,
even at close range, can enhance the appearance of the property. Retaining
walls or dikes bordering the ponds should be built to withstand erosion, and
must be properly maintained if these facilities are to remain an asset in
terms of appearance.
Layout and design of outlying structures, including weighing stations,
and maintenance buildings, garages, pumping stations, and cooling towers,
should be considered as carefully as the central buildings. Their location,
space profile and decor should be in harmony with the overall plan for the
site. Shrubs and tree plantings are often helpful devices for shielding
unsightly features of the facility. However, plantings will not take the
place of peripheral fencing which is needed to keep out intruders and to
retain windblown paper and trash.
Even at the design stage, consideration should be given to plant
obsolescence and decommissioning of the plant. Since the anticipated life
of a plant is only about 20 to 30 years, thought should be given to the
eventual uses of the site so that it will continue to meet community needs.
Possibilities for future development include revamping for continued use in
solid waste processing, recreation, an industrial park, or even housing.
Retention of as many existing natural features of the landscape as possible
will facilitate conversion to other uses. When certain areas are used for
landfill, great care should be exercised in moving the overburden of earth so
that the land is not left in unsuitable condition for future use.
Building Design
Various views of municipal incinerators are shown in Photographs 1 to 4.
Figures 6 to 8 help illustrate the relationship between buildings and equipment
which is housed. That these plants can be architecturally appealing and varied
in design treatment is apparent from the photographs.
From a functional point of view, a good building design promotes; economy
of operation and ease of maintenance. Equipment arrangement should promote
uninterrupted flow of materials through the plant. Special attention must be
paid to the movement of air which is sucked into the plant and through the
furnaces by induced and forced draft fans to avoid drafts which carry litter
and odors to working areas, and to avoid excessive space heating requirements.
54
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05
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RAMAPO, N.Y. INCINERATOR
Photograph 2
56
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"••I.^K-Xj- ;. '
57
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V
* *.
MONTGOMERY COUNTY-SOUTH
This facility, with a design capacity of 600 tons per
day provides 1/2 of a County wide system of
municipal waste disposal The North Plant, pictured
below, forms the other half.
MONTGOMERY COUNTY-NORTH
The City of Dayton, Ohio, and other communities in
me County, have used this plant and the South
Plant since 1969 to dispose of solid waste. Each
Rotary Kiln Unit is rated at 300 Tons/Day.
56
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One helpful design feature is to cause air to be drawn over storage pits
toward the fan intakes, thus drawing pit odors into the furnaces.
Adequate working space is needed for the operators and maintenance
personnel to perform their jobs efficiently. Location of work areas should
be such that the many operating tasks can be performed conveniently without
wasted time and effort. A large proportion of the maintenance required will
be performed on the operating floor, since most of the equipment is too
large to be moved to another area. Adequate space must be provided for
making repairs, with special attention to headroom, clearances for replacement
of large equipment items, and for movement of mobile equipment.
Operators are unanimous in asking that all facilities, materials, equip-
ment, tools and parts required for normal plant operation and maintenance be
included in the contract for the original design, rather than being added
piecemeal after the plant is in operation. A liberal number of electrical
outlets for power tools and welding equipment should be provided at strategic
locations throughout the building. Where compressed air and steam lines are
used, an adequate number of valved connections should be provided to eliminate
the need for long runs of hose. The same applies to service water used for
floor washing and other plant use.
The building should be constructed of durable, high quality materials and
fixtures to minimize the problems of cleaning, painting, and resurfacing.
Some of the materials which meet these requirements, include concrete, ceramic
tile, and metals which are not subject to corrosion. Surface finishes must be
dense and durable. Coving installed along the edges of floors will reduce the
accumulation of debris and allow easier cleaning. Exposed piping and ductwork
tend to collect dirt and should be enclosed but accessible wherever possible.
Because solid waste processing plants are subjected to unusually heavy wear
and considerable dirt, nothing less than the most rugged materials are accept-
able, if operating and maintenance problems are to be avoided.
Structural components of the building should have sufficient bracing to
prevent sway from crane operation. Allowance must be made for thermal expan-
sion and contraction of structures in close proximity to furnaces and other
hot areas.
Stairways should provide convenient access to each floor, and clearances,
including entrance doors, should be wide enough to accommodate supplies and
equipment to be carried up the stairs. An elevator for personnel and for
moving heavy equipment may be desirable, especially in larger plants.
An adequate number of well designed floor drains in strategic locations
are a necessity. Some plants use open sluice drains covered by subway grating
in preference to buried pipes to permit easy removal of obstructions. Plans
should show drain and floor elevations: the note "slope to drain" is seldom
sufficient.
The safety and well-being of personnel is a prime consideration. For
example, work areas should be made as pleasant as possible through the use of
attractive colors. Adequate ventilation and lighting must be provided. When
these factors are properly considered, the advantages of high morale and good
62
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performance by the plant workers are more likely to prevail. A checklist
based on the suggestions of incinerator plant operators is available for
review by designersJ
Personnel Facilities. Comfortable surroundings are important in attracting and
holding competent personnel. Considerable attention should be given to the
proper location and design of showers, lockers, toilets, wash rooms, vending
machine areas, and lunch rooms. They must be comfortable and attractive, as
well as adequately sized and well equipped. Sanitary facilities must be pro-
vided for women who may visit or be employed at the plant. All the foregoing
facilities are best located adjacent to operating areas, but in a wing or
section of the building separated from the dirt, dust and noise of plant
operations. Drinking water should be available on every floor and within 200
feet of employee stations.
Special attention directed toward the use of interesting color schemes
will alleviate monotony. Materials used should require little maintenance and
be easily cleaned. It is good practice for the original contract to provide
for all necessary fixtures including furniture, window blinds, floor cabinets,
etc.
The receiving area should be isolated from the processing section of the
plant to discourage unauthorized persons from walking through the furnace
rooms and other operating areas. Therefore, it may be necessary to provide
well marked toilets and wash rooms for use by collection crews. Snack bars
and a pay telephone to the receiving area are also desirable.
Administrative Offices. Administrative areas, including offices, conference
rooms, and supply storage should be carefully planned, adequately sized, and
properly furnished. In larger plants, the superintendent, foremen and clerical
workers may need an office which is free from the distractions of the
operators' desks and the control room, though some critical process information
may be automatically transmitted into this area.
Offices should be attractive and air conditioned to improve efficiency.
An adequate number of file cabinets and storage space for office supplies will
be required. A conference room for staff briefings, safety discussions and
training purposes may be a worthwhile investment. Smaller plants may effec-
tively combine all administrative activities in the same area.
Weighmaster's Office. The motor truck scale is an indispensable feature of all
modern solid waste processing plants. Although the weighing activities may be
conducted alongside the access road outside the incinerator plant, many
operators prefer that the control room and platform be located inside the
building at the entrance to the turning and tipping area. Provided the scale
is of electronic or semi-electronic load cell type, there is considerable
flexibility in locating the scale room with respect to the platform.
63
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The weighmaster's office should be fitted with ample glassed area to
observe the movement of weigh scale traffic. He should have adequate means
of communicating with the driver, including possible inclusion of stop and go
signal lights and/or an intercom system.
This office should be well lighted and ventilated with consideration
given to air conditioning. The equipment supplied has to be adequate to
handle all transactions and storage records, for example, credit card or even
cash transactions may be contemplated.
Maintenance and Repair Facilities. It is advisable that all facilities,
materials, equipment, tools, and parts needed to maintain the plant be sup-
plied as part of the original contract. Well equipped machine stops and
storage areas are essential, since a major portion of the repairs and major
maintenance work will normally be done on site using plant personnel. Ample
storage space is needed for electrical, mechanical, and refractory parts. At
least one spare is provided for most key equipment items including grate parts,
motors, speed reducers and drives. Floor and shelf space should be provided
for large items, and drawers and bins for smaller ones. Large municipalities
may have central maintenance and repair facilities, or contract maintenance
may be envisioned, eliminating some of the above requirements.
Laboratory. The principal purpose of the laboratory is to insure that
environmental regulations are being met. A secondary purpose of the laboratory
is to perform tests which will be indicative of facility performance, including
percent burnout of the residue from incineration and composition of incoming
waste. The laboratory should not be too elaborate, but should provide suffi-
cient space to perform the required tests. File cabinets for test records and
sample storage shelves are normal laboratory appurtenances. Some thermal
processing plants which produce fuels and other saleable materials may have
specialized quality control testing requirements. For large or complex
facilities, where full-time laboratory personnel are contemplated, an office
area must be provided.
Processing Areas. Design of the various processing areas will be extensively
treated in subsequent Chapters. Since the building is basically an enclosure
of the processing areas, process equipment is at least tentatively sized and
located prior to design of the building. However, interchange must exist
between process and building designers to insure complete compatibility.
Interior Lighting. Lighting within the plant should be adequate to insure that
tasks can be performed easily and with safety. Recommended lighting standards
are published by the Illuminating Engineering Society.^ Lighting standards for
performing certain tasks similar to those performed at incinerators are shown
in Table 21.
Consideration should be given to shielding of open lights to lessen the
hazard of breakage. Explosion-proof lighting will be necessary in sections
of pyrolysis plants which produce fuels.
64
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Table 21
LIGHTING STANDARDS APPLICABLE AT INCINERATORS3
Office and industrial tasks Foot-candles on task
Loading and trucking 20
Corridors, elevators, stairways 20
;
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Design For Fire, Explosion, and Other Hazards
Safety^ A number of safety-related design suggestions have been included in
the foregoing sections dealing with specific items of plant equipment. Safety
of operators and repair crews is promoted not only by supplying safety equip-
ment, such as hard hats and special shoes, but by thoughtful design, layout,
and specification of equipment. For example, sufficient space must be pro-
vided for walkways, and for required maintenance. As discussed in Chapter II,
Federal occupational safety and health regulations, and insurance standards
provide excellent safety guidelines.
It is essential to eliminate the hazard of objects falling onto personnel
working in areas below. Equipment which requires frequent maintenance should
not be located directly above an operating platform. Floor openings or
hatches should be provided with curbs to prevent objects from rolling or being
pushed over the edge. Guard rails, appropriately placed, are effective in
prevention of falls.
Improper specification or use of ladders frequently results in injuries.
Therefore, permanent ladders should be specified where necessary, but ladders
and steep stairs are to be avoided where materials must be carried. Hoop
cages are required on tall vertical ladders.
Electrical switch gear should be mounted in moisture and dust tight
enclosures and not be installed in locations which may be subject to wet
conditions, standing water, dust or potentially explosive vapors. Placement
of thick rubber mats on the floor in front of electrical panels is a good
precautionary measure.
Doorways used for receiving and removing bulky equipment should be of
sufficient height and width to accommodate the equipment and the truck or
fork lift used. Sheeled hoists mounted on trolleys may be required in some
areas. Doors should open either in or out, whichever is consistent with
maximum safety.
Fire Protection. Hydrants or post indicator valves (PIV) must be provided at
locations specified by local fire regulations. At least two PIV's should be
located at the tipping floor area for use in extinguishing pit fires, Others
are desirable in the area of feed chutes, and at the discharge end of the
burning stoker in an incinerator. Good practice requires standardization of
hose couplings and fittings used for in-plant fire control with those used by
the local fire department. Fire extinguishers of the dry powder or carbon
dioxide types may be installed near the entrance and exit doors, in areas of
exceptional fire hazard, and in maintenance shops. American Petroleum Insti-
tute guidelines are available to design fuel storage and handling facilities.
First Aid. Well stocked first aid cabinets should be provided at several loca-
tions throughout the plant for treatment of minor injuries. These cabinets
should never be locked. Safety fountains for the face and eyes, and safety
showers must be considered, particularly where water treatment and other
chemicals are used. Stretchers and blankets for use by injured personnel are
a necessity.
66
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Ncise__Con_siderations. A typical thermal processing plant will contain many
noise sources which may emit sound levels ranging from acceptable to annoying
ana potentially harmful. These may be within or outside the plant, including
vehicles, fans, shredders, conveyors, burners, feeders, cooling towers and so
forth. Measured noise levels of some sources at various distances from the
source are given in Table 22.
When designing buildings, two classes of noise must be dealt with:
(1; internal plant noise which is an industrial hygiene problem; (2) noise
projected beyond the plant boundaries, which becomes a public nuisance.
Methods used for noise abatement include enclosure of equipment within buiId-
ings , use of sound absorbing materials inside equipment housings and sound
barriers, use of low speed fans, selection of quiet hydraulic equipment,
vibration mounting of rotating equipment, and other measures of this nature.
If the designer is not familiar with the latest developments in noise abate-
ment, he should obtain the services of a competent consultant who specializes
in this field.
As sound waves travel through the air and over different kinds of ter-
rain, the sound energy is gradually attenuated until it is no longer a prob-
lem. Therefore, the most troublesome noise generating equipment should be
located the farthest distance from the property line which is downstream from
the prevailing wind direction. A graph showing the attenuation of noise as
it propagates from a point source and radiates to various distances is shown
in Figure 9.
fl3."t Exterior
StaCKS. Stacks are in reality part of the process equipment, but their loca-
tion, size, height, and appearance impose a burden on the building designer.
Dispersion and draft requirements determine the height and diameter. Natural
draft chimneys or stacks have an advantage over stacks with an induced draft
(ID) fans, in that they require neither a source of power nor fan maintenance.
However, present day requirements for sophisticated air pollution control
equipment with inherent pressure losses, and the usual desire to maintain
negative pressure within the thermal processing equipment to avoid odor re-
lease, dictates the use of ID fans. The stack height is then chosen primarily
by dispersion considerations, A single stack should serve no more than two
furnaces. When one stack services two furnaces, individual dampers are re-
quired for proper control of draft.
Materials used for chimney linings must be carefully selected. The most
critical service occurs during startup and shutdown operations when the com-
bustion gases are cool and moisture tends to condense in the pores of the
refractory linings. Acid gases dissolved in the condensate formed aggravates
the problem of achieving acceptable service life of stack lining materials.
More flexibility is available in the choice of external materials.
RoadwaystL_SjdewaIks_and, Parki ng Areas. Data on peak load truck arrivals are
necessary for adequate design. Road width is set to provide passage around
stalled vehicles. Entrance to the site should be carefully planned to avoid
the use of heavily traveled highways. Where feasible, an entrance lane
67
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Table 22
DISPOSAL OF REFUSE AND OTHER WASTE
MEASUREMENTS OF PEAK NOISE LEVELS IN, AND NEAR, REFUSE TREATMENT PLANTS4
PLANT NOISE LEVELS
A. External Measurements
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Plant
Refuse vehicle starting
Refuse vehicle on level
ground; steady speed
Refuse vehicle on slope,
steady speed
Forced draught fan
Induced draught fan
Cooling tower
Cooling tower
Cooling tower
General plant noise*
(mostly de-duster)
General plant noise*
General plant noise*
(mainly fan noise)
General plant noise*
Residuals (conveyor
and chute)
Several vehicles
discharging
Magnetic separators +
clinker & fly ash
conveyor
Pulveriser only
Vibratory feeder
Pulveriser with
vibratory feeder
in operation
Location
at 7.5 metres
at 7.5 metres
at 7.5 metres
at 3 metres
at 30 metres
at 30 metres
facing louvres
at 130 metres
facing louvres
at 270 metres
facing louvres
at 110 metres
from wall
at 300 metres
from plant
at 50 metres
from plant
at 100 metres
approx.
at 10 metres
at 15 metres
from entrance
(outside recep-
tion hall )
at 10 metres
at 10 metres
at 10 metres
at 10 metres
' 'J
Noise Level
84 dB(A)
80 dB(A)
83 dB(A)
76 dB(A)
71 dB(A)
69 dB(A)
60 dB(A)
54 dB(A)
52-53 dB(A)
45-46 dB(A)
(Hum of de-duster
clearly audible)
57 dB(A)
53 dB(A)
75 dB(A)
62 dB(A)
82 dB(A)
70 dB(A)
81-82 dB(A)
79-83 dB(A)
Site
C
C
C & D
C
C
M
M
M
C
C
D
P
D
C
P
F
F
F
* Variable according to plant layout and other noise sources
68
(continued)
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Table 22
DISPOSAL OF REFUSE AND OTHER WASTE
MEASUREMENTS OF PEAK NOISE LEVELS IN, AND NEAR, REFUSE TREATMENT PLANTS4 (concluded)
Internal Plant Noiset
1 Metal press
2 Cardboard press
3 Induced draught fan
In reverberant
conditions
4 Collection vehicle,
tipping
5 Water pump, rever-
berant conditions
at 3 metres
at 3 metres
at 3 metres
at 3 metres
approximately
at 3 metres
84-86 dB(A) C
(mostly clangs)
86-88 dB(A) C & D
91 dB(A) D
90-92 dB(A) D
91 dB(A) D
C. Internal Environmental Noise Levels
Predominant Noise Source
Location
Noise Level
Site
2
3
5
6
3 vehicles discharging
One conveyor plus
Conveyor
General plant noise*
General plant noise*
General plant noise*
Refuse feed chute
4 boilers in use
Turbines
Reception hall
In elevator room
on "bridge"
In elevator room
on "bridge"
Inside separation
and sorting room
Incineration room
Incineration room
(by control desk)
Inside incinera-
tion room
Inside boiler
house
Inside turbine
hall
88-91 dB(A) C
87 dB(A) C
79 dB(A) C
89-91 dB(A) C
78-82 dB(A) C
80 dB(A) D
100 dB(A) D
81 dB(A) P
88 dB(A) P
(mainly whine)
Measuring notes:
C Castle Bromwich Refuse Disposal Works
D Direct Incineration Plant, Derby
P Usine d1Issy-les-Moulineaux, Paris
M Manufacturers' Information
F Folkestone Road Refuse Pulveriser, London, E.6
tThe external noise level due to noise generated inside the plant will
depend on the insulation of the walls, and any openings in them, the in-
ternal acoustics and the distance of the measuring point. It is important
to note that there is always a considerably greater reduction in noise
transmitted from inside a building to outside, than vice-versa.
69
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0
4
,1
Ifi
74
\
I
V
y
\
\
sj
*
y,
*S
^
s.
•^
•^
%g
««
1
•*.
•^.
s*
•«•,
•u
•MM
FIGURE 9. A GRAPH OF THE REDUCTION OF NOISE (dB) OVER DISTANCE
(M) FOR A POINT SOURCE OF NOISE4
70
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parallel to the highway will permit trucks to reduce speed with minimum road-
way traffic interference.
Onsite roads will make efficient use of space not needed for other
facilities. Where possible, a separate entrance and exit will allow uni-
directional traffic flow. Roads should be hard surfaced and designed for
heavy loads. Rough surfaces provide good tire traction. Grades should not
be too steep. In general, grades for short distance truck travel will not
exceed seven percent uphill and ten percent downhill. Sharp curves and blind
spots should be avoided, and curbing, posts, or guardrails used to confine
traffic to roadways.
Parking areas are provided for trucks which are temporarily out of
service or are parked overnight. Parked trucks should not interfere with the
normal flow of traffic through the plant. In severe climates, indoor truck
parking may be advisable. Part of the tipping floor can be used for this
purpose, but a separate area should be available where extensive parking is
to be practiced. Separate parking should be provided for automobiles used by
plant personnel and visitors.
Sidewalks connecting the parking lots with the plant buildings should be
elevated sufficiently to permit water to run off. If sidewalks are used to
move heavy equipment between the main building and the maintenance shop, care
must be taken to insure that they are durable and wide enough for the load.
Fuel Tankage. Fuel tankage needed for pyrolysis products or for plant opera-
tion will be included in the design specifications. Gasoline or diesel fuel
tanks and pumps may be required for maintenance and administrative vehicles,
as well as for trucks used in hauling residue, flyash and siftings. Bull-
dozers and other earth moving equipment used on adjoining landfill sites
usually require fueling at the plant. Building space heating also requires
fuel tankage, unless natural gas or internally generated heat is used.
Auxiliary power generators, if provided, will normally be run on diesel fuel,
gasoline, or LPG.
As can be seen, fuel tankage may be practically an inconsequential site
problem, as for standard refractory furnace incinerators; or such tankage may
be an important consideration, as with pyrolysis plants, or steam producing
incinerators with standby oil burner equipment. Fuel tanks must be properly
spaced for safety reasons and can require large land areas if located above
ground. U.S. Environmental Protection Agency spill prevention control guide-
lines must be consulted.
Special Solids Handling. Some thermal processing plants employ shredders and
resource recovery systems to recover ferrous metals and other materials.
These will be described in Chapter XVII. Where salvage materials are recov-
ered, storage areas must be provided. Outside storage areas provide a real
challenge for the designer to maintain aesthetic values, since storage of
ferrous scrap and other materials can be very unsightly. Indoor storage is
expensive.
71
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Landscaping. By use of adequate plantings of trees and shrubs, unsightly
activities such as unloading or residue handling can be effectively screened
from view. A small, well-maintained garden patch strategically located near
the main plant entrance can provide a pleasant focal point for visitors and
plant personnel alike. At least one plant was surrounded with an earthworks
or berm, creating the impression of low building profile.
Additional costs incurred for landscaping are often effective in
achieving public acceptance and will help to maintain the land value of the
site itself, and of the surrounding community.
Fencing and Lighting. Durable perimeter fencing is a prerequisite for
adequate plant security in areas subject to vandalism. The usual fence is a
minimum of six feet high with three strands of barbed wire projected at a 45°
angle at the top. Commonly available cyclone fence is adequate, provided it
is fabricated from heavy gauge wire of low-maintenance, rust-proof metal. The
entrance gate should be constructed of materials which are visually compatible
with the fence. The number of additional entrances to the grounds are held to
a minimum to reduce the chance of unauthorized entrance.
Floodlighting of the immediate area surrounding the plant is important
both for the safety of the personnel working at night and for security reasons.
Floodlights may be affixed to the outside walls of the main building, unless
such location creates undesirable glare when viewed from the surrounding area.
If this is the case, lighting standards erected at a distance from the build-
ing can be used to direct the light toward the structure. Light stands should
also be provided along the on-site roadways used by collection and other
vehicles. The intensity of the outdoor lighting will vary, depending on
whether or not the area is used for the performance of required tasks.
Traffic Control. Signs used for control of traffic should be carefully
located, simply worded, and should make use of large lettering symbols. Where
one-way control of traffic is desired, the entrances and exits should be
clearly indicated. Use of directional arrows and centerline striping painted
on the roadways is helpful, lessening the need for traffic signs. A stop sign
or signal at the entrance to the scale platform is essential. Other signs for
the direction of employee and visitors' vehicles will help in avoiding un-
necessary confusion.
72
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REFERENCES
1. Stephenson, J.W. Incinerator Design with the Operator in Mind,
Proceedings, 1968 National Incinerator Conference (New York,
May 5-8, 1968). American Society of Mechanical Engineers.
pages 287-294.
2. IES Lighting Handbook: The Standard Lighting Guide, 5th Edition,
Illuminating Engineering Society, New York. 1972.
3. DeMarco, J. et al. Municipal-Scale Incineration Design and Operation.
PHS Publication No. 2012. U.S. Government Printing Office.
Washington, D. C. 1969. 98 pages.
4. Skitt, John. Disposal of Refuse and Other Waste. Hal stead
Press, New York. 1972.
5. U.S. Environmental Protection Agency. Oil Pollution Prevention-
Non-Transportation Related Onshore and Offshore Facilities.
Federal Register 38_ (237) Part II: 34164-34170. December 11, 1973.
73
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CHAPTER VI
UTILITIES
Utility system requirements for thermal processing units are not greatly
different than for any other large processing plant, except for the
possibility of energy recovery in quantities even greater than that: required
for in-plant use. Incinerators can be compared to fossil fuel combustion
boilers, requiring utilities for most of the following services: electrical
power for motors, lighting, controls, heaters, and electrostatic precipita-
tors; water for drinking, cooling, sprays, steam condensers, fire fighting,
boiler combustion, cooling, instrumentation, and plant maintenance; sewers
for the discharge of wastewaters; internal and external communications sys-
tems; and steam or fuel building and water heating, and other uses, including
incinerator auxiliary fuel. Each utility must be supplied to the plant site,
metered, and distributed safely and efficiently to all points of use at the
site. The following discussion will first deal mainly with incinerator
utility systems, and then cover utilities for pyrolysis plants.
Electric Power Systems
Electric power competes with steam as a source of energy in thermal
processing systems. In older systems, almost all of the energy requirements
were met by electric power. In newer systems, internally generated steam may
replace electric power for fan, water pump, and other drivers.
Alternating current, three phase, 460 to 480 volt electric power is
supplied to most motor drives for fans, pumps, conveyors, cranes, and other
machinery. Very large motor drives commonly used for induced draft (ID) fans
and shredders use higher voltages, such as 4,160 volt three phase service.
Several direct current motors with SCR's (silicon-controlled rectifiers)
have been installed recently to drive ID fans.
Lighting and controls are usually supplied by 120 volt, single phase
circuits, stepped down by transformers from 480 volts. Alternative systems
supply fluorescent lighting at 277 volts single phase. The power supply for
the electrostatic precipitator is a transformer-rectifier set which steps up
240 or 480 volt alternating current to high voltage direct current, in the
range of about 20,000 to 75,000 volts. The use of such high voltages demands
close attention to design details and safety procedures.
The electrical power substation required to reduce transmission voltage
to working voltages, the electrical power control center, the distribution
system, the motor starters, and other electrical equipment represent a major
capital cost. Therefore, expert engineering and cost optimization calcula-
tions should be applied to their design. The electrical system design should
take into account peak power demands, and include provision for emergency
standby power adequate for lighting, controls, and other devices necessary to
permit orderly shutdown during power failures. Gasoline or diesel-driven
generators with a suitable fuel supply can be used for emergency power.
74
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Power requirements vary greatly from plant to plant, but the following
can be used for orientation purposes:
Installed Capacity, KW for
50 Metric Ton/Hr Incinerator
Induced draft fans 800-1500 (assumes no
(when used) high energy scrubber
in system)
Forced draft and other
furnace fans 300-600
Conveyors and Cranes 100-300
Process Pumps 100-300
Hydraulic System Pumps 100-200
Shredders 300-1500
Lighting less than 50
TOTAL (all services, 1500-4000
including heating,
ventilation and air
conditioning)
As noted previously, power requirements can be reduced considerably by
substitution of steam turbine drives for electric motors. Electrical
facility design and installation may be governed by local authority or by
the National Electrical Code (NEC).* NEC has been adopted as a national
consensus standard by the Occupational Safety and Health Administration.2
Hater Systems
Water may be supplied to plant booster pumps from the city water supply,
from wells, or from bodies of water, such as rivers and lakes. Seawater or
brackish waters may also be used for cooling. Finally a major source of
water is that recycled from process or other uses. A summary of water
services is provided in Table 23. Wastewater treatment is discussed in
Chapter XIII.
The total amount of water required may vary from about 2 to 12 tons per
ton of waste incinerated (500-3,000) gallons/short ton), depending upon design
and operation.3'4 Increasingly stringent wastewater discharge regulations now
provide incentive for maximum recycle and minimum makeup of fresh water.
Where water lines may be exposed to freezing temperatures, either during
normal operation or during shutdowns, pipe tracing and/or insulation may be
necessary.
Steam Systems
Incinerator steam systems range from incinerators which have none at all
to those which produce large quantities of steam for export. In between,
75
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Table 23
INCINERATOR WATER SYSTEMS
Service
Water Quality
Disposition
Boiler feed water (for hot
water or steam production)
Drinking, sanitary, and
safety shower and eyewash
(laboratory) water
Residue quenching and
sluice water
Cooling water (where
required for chutes, com-
pressor after coolers, or
for steam condensers)
Spray or scrubber water
(where required for gas
cooling or emission control)
Fire fighting water for
hydrants, hoses, and
sprinklers (with separate
fire pump)
Requires fresh water
with extensive in-plant
pretreatment
Requires fresh water
with little or no pre-
treatment
Quality not critical--
can use water dis-
charged from other
services
Requires fresh or other
clean water; sometimes
treated to aid in
corrosion prevention
Usually requires
reasonably clean water
free from suspended
solids to prevent noz-
zle plugging and
contamination of exit
gases
Fresh water normally
stored in elevated
tanks for fire fight-
ing
Plant and vehicle wash water Normally fresh water
Surface runoff water
When used in-plant,
condensate can be re-
cycled with minor
blowdown to other water
systems.
Discharge to sanitary
sewer
Wastewater requires
treatment and sometimes
cooling
May require cooling or
treatment to prevent
pollution by additives
Part of water evapo-
rates; extensive recycle
practiced, but requires
neutralization of
dissolved acid; part of
water may be discharged
to residue water system
When used, discharge is
normally to plant
wastewater sewers
Discharge to plant
wastewater sewers
Surface waters from
areas which may be
contaminated with re-
fuse should be treated
as other wastewaters;
uncontaminated runoff
water should be handled
by storm sewers
76
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some installations have an auxiliary boiler for in-plant use, and others
produce a relatively small amount of steam with convective flue gas boilers
for export or in-plant use. There are plants in Europe and Japan which
produce electric power from the steam5'6, but electric power has rarely been
provided in the U. S.
The production of steam for export is fully discussed in Chapter X; this
discussion is limited to a brief description of in-plant uses. The most
important potential in-plant uses for steam are for fan and pump drives, which
were shown in a previous paragraph to be large consumers of electric power.
For example, the replacement of 1,500 KW (2,011 hp) induced draft fan
electric motor drives in a 50 metric ton per hour plant with steam turbines
could save 60 cents per metric ton in operating costs, assuming 2 cents per
KWH for electric power. Obviously, the cost of steam production must be con-
sidered, but as explained in Chapter IX, steam generation costs are at least
partially offset by the advantages gained in simultaneously reducing excess
air or reducing the cost of alternative methods for cooling exit flue gas.
The limitation to the use of steam for drivers is increased complexity
in startup when no steam is available. This can be solved by providing
electric motor drives to be used only during startup, by providing for at
least one furnace to be on line at all times, by providing for auxiliary
steam facilities, or by providing for "bootstrap" startup. All of these
alternatives tend to be complex and somewhat costly, but the use of internally
generated steam can be justified when electric power cost is high. The use
of steam for building heat, air conditioning, sootblowers, and electrical
power generation should also be considered.
Air and Vacuum Systems
The primary air requirement for an incinerator is, of course, for
combustion. The use of forced draft and induced draft fans for this purpose
is discussed in Chapter IX. Also discussed in that Chapter and in Chapter XIV
is the use of air for flue gas cooling. In this section, the provision of
compressed air for instrumentation, maintenance, and other plant uses will be
discussed, as will the use of vacuum systems.
Many instrumentation systems are based on the use of air, although
electronic instruments are a possible alternative. An instrument air system
consists of a compressor and facilities to clean and dry the air. The drier
usually contains a solid dessicant such as silica gel, and a means for
automatic regeneration of the spent dessicant. Normally a complete spare
system will be specified to insure reliability, although it is possible to
store cylinder nitrogen, or to draw on the plant air compressor for emergen-
cies, if provision is made for filtering and drying. The quantity of instru-
ment air required will depend on an analysis of the instrumentation specified,
but about 2 to 4 normal cubic meters per minute (71-141 SCFM) for a large
reasonably complex plant might be expected. The compressor is usually
designed for about 6.5 atmospheres absolute pressure (80 psig).
The quantity of plant air normally provided is the same order of
magnitude as the instrument air supply, unless the incinerator design calls
77 '.
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for pneumatically operated water spray nozzles. The compression pressure may
be similar to or higher than the instrument air pressure. Driers are not
provided, but some water is removed in after-coolers. This air is used for
cleaning, pneumatically operated valves, maintenance tools, other machinery,
and for sootblowers in plants where steam is generated.
Industrial vacuum cleaning systems can be a valuable addition to an
incinerator plant. This must include an exhauster, dust collectors, a means
for disposing of collected solids, ductwork, valves, and cleaning accessories,
Fuel Systems
Fuel requirements are very much dependent upon the design of the
incinerator. In each case, the services outlined in Table 24 should be
considered. Every effort should be made to minimize fuel requirements by
using energy available from refuse combustion.
Pumps are of course required to deliver liquid fuels to the necessary
services. Tanks are usually underground, but larger tanks may be above
ground.
Communication Systems
External telephone communications are provided either by a trunk line
from the main switchboard serving the municipality, with or without direct
dialing to various plant phones; or by a separate phone system with several
lines. Communications within the plant can be provided by an intercom system
with paging. Either general or selective paging through loudspeakers can be
arranged from multiple desk telephone and wall mounted intercom stations.
Intercom stations in noisy areas must be equipped with acoustic booths, and
visible signals can be used where necessary.
The use of color closed-circuit television monitoring for observing
combustion, critical operations, and stack emissions is becoming common and
should be considered for all new installations.
Utilities for Pyrolysis Processes
Since little commercial experience is yet available on pyrolysis of muni-
cipal solid waste, there is relatively little hard data on utility require-
ments. The following discussion will serve as an introduction to some of the
expected requirements for several processes discussed in Chapter XI, Pyrolysis.
Monsanto Envirochem LANDGARD Process. Power and water requirements for the
LANDGARD System, designed to produce steam, may be expected to be similar to
that required for incinerators, since complete combustion of offgases with
scrubbing and removal of solid residues are practiced. These may approach
70 to 75 KWH per metric ton of solid waste for power and about 2 to 4 tons
per ton for water. Fuel requirements are much higher than for incineration,
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Table 24
INCINERATOR FUEL REQUIREMENTS
Service
Fuels
Considered
Comments
Building heat, water
heaters, auxiliary boilers
Incinerator light off
Vehicles
Standby and supplemental
fuel for steam generation
Flue Gas Reheat
No. 2 or No. 4 fuel
oil; natural gas
Often torch used with
no fuel; kerosene, No.
2 fuel oil
Gasoline; diesel fuel
No. 2, No. 4, No. 5,
or No. 6 low sulfur
fuel oil; waste fuels
(e.g., crankcase oil);
natural gas
No. 2 fuel oil; natural
gas (or bypass hot flue
gas)
Depends on climate;
normally only offices,
labs, shops, etc.
heated
Relatively small quan-
tity required, if any
Incinerator site some-
times serves as storage
area for refuse trucks
Depends on location and
availability of fuels;
waste fuels may require
special precautions to
avoid fouling and air
pollution
Sometimes required to
minimize plumes caused
by use of scrubbers for
air pollution control
79
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about 0.03 tons of fuel oil per ton (one million BTU per short ton). However,
the high cost of utilities in the LANDGARD System is more than offset by the
sale of steam, which could also be used internally to decrease electric power
consumption. A LANDGARD plant in Baltimore should be in operation in 1976.
Occidental Process. The first Occidental plant, designed to produce gaseous
and liquid fuels, will not be in operation until late 1976. It is expected
to use about 0.0025 tons of fuel oil per ton of solid waste (106,000 BTU/ST),
and about 50 KWH/MT of electrical power. Water use will be about 0.35 tons
per ton.
Union Carbide PUROX Process. The PUROX Process, which has been operated in a
200 ton per day pilot plant, is designed to produce a fuel gas by partial
oxidation with oxygen. The electrical power requirement projected is about
130 to 140 KWH per metric ton. Most of this power is used for air separation
to produce oxygen. The oxygen may be produced on-site or purchased where
available, reducing the actual pyrolysis plant power consumption to a low
value. As pointed out in Chapter XI, the fuel gas produced in the PUROX
Process can be used to produce power greatly in excess of that required for
oxygen generation and other plant uses.
Fuel and steam requirements in the PUROX Process are equivalent to about
0.02 to 0.03 tons of fuel oil per ton (0.8 million BTU/ST), much higher than
normally required for incineration. Again, this requirement is greatly
exceeded by the amount of fuel generated. Water requirement is believed to
be similar to that required for incineration.
80
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REFERENCES
1. National Electrical Code. CI. American National Standards Institute.
New York. 1971.
2. Occupational Safety and Health Standards. Occupational Safety and Health
Administration. Federal Register 39_ (125): 23782-3. June 27, 1974.
3. Jens, W. and F. R. Rehm. Municipal Incineration and Air Pollution
Control. Proceedings, 1966 National Incinerator Conference. New York.
May 1-4, 1966. American Society of Mechanical Engineers. Pages 74-83.
4. Matuskey, F. E. and R. D. Hampton. Incinerator Waste Water. Proceedings,
1968 National Incinerator Conference. New York. May 5-8, 1968. Ameri-
can Society of Mechanical Engineers. Pages 198-203.
5. Asukata, R. and S. Kitami. Present Situation and Future Trends of
Japanese Refuse Incineration Plants with Power Generation. Proceedings,
1974 National Incinerator Conference. Miami. May 12-15, 1974. American
Society of Mechanical Engineers. Pages 127-141.
6. Astrom, L. et al. Comparative Study of European and North American Steam
Producing Incinerators. Proceedings, 1974 National Incinerator Confer-
ence. Miami. May 12-15, 1974. American Society of Mechanical Engineers.
Pages 255-266.
81
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CHAPTER VII
WEIGHING
Weighing of vehicles carrying incoming solid waste and outgoing residue,
fly ash, other waste materials, and salvage materials, if any, is an integral
part of thermal process operations. Correct weights are needed to assist to
cost control, manpower scheduling, budgeting, planning, as the basis for
billing the users of the facility, and for residue hauling charges.
Weigh scale data collected on cards, tape or in other forms are necessary
for determination of the effective capacity and efficiency of the plant. The
weight of incoming waste and outgoing residues, combined with analyses for
these materials, permits calculation of overall efficiency. If weighing
information is in haphazard form or is inaccurate, results will be unaccept-
able as a measure of plant performance. Aside from the purposes of the
guarantees on a new plant, periodic efficiency determinations are helpful in
detecting and analyzing factors which affect plant performance, e.g. to
calculate and determine the relationship of excess air on carbon burnout for
incinerators, Efftctency data may also be useful in scheduling inspections
and repairs.
The determination of optimum pickup routes and arrival times is aided by
knowledge of dates and times of arrival printed on the weigh tickets. This
is particularly important if a facility is running at or near capacity, or if
the dump pit is of inadequate size. This information also assists in making
effective use of the manpower available, and checking the efficiency of pick-
up crews.
A further benefit derived from the availability of complete and accurate
weigh scale data is the ability to do effective planning. For example,
analysis of weigh data exposes trends in the quantity of waste material re-
ceived, and aids in the prediction of life for existing landfill sites used
for disposal of residue. Decisions relating to expansion of existing facili-
ties or replacement with new facilities depend heavily on the evaluation of
weigh scale records.
Finally, the service provided to the various communities using the
facility can be most easily measured in units of weight received. Where fees
are charged to commercial and industrial waste haulers or to other communities,
they are usually assessed by weighing the incoming vehicle loads.
Scale Description
Motor truck scales normally consist of a platform suspended on a struc-
ture which transmits the weight of an impressed load to a weigh head, where
the weight is indicated and recorded. The entire weighing mechanism, with
the exception of the weigh head, is installed within a sub-surface weigh pit
which is usually constructed of poured concrete. The scale pit is designed
for adequate drainage, usually with a sump and a pump. An enclosed weigh
82
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house is provided for the weighmaster either as part of the incinerator build-
ing, or as a separate structure, depending upon traffic flow and positioning
of the scale.
Scale Types
There are three basic types of scales in general use today: (1) fully
mechanical (2) combination system of mechanical levers with a single elec-
tronic load cell and (3) fully electronic load cell types. Mechanical scales
are perhaps the most common type, but electronic scales are now in favor.
The weighing mechanism of a fully mechanical scale consists of a system
of levers, pivots (knife edges) and fulcrums (bearing blocks). The mechanical
components are installed in a reinforced concrete pit sized to accommodate
the platform. The pit is normally 4 to 6 feet in depth. A structural steel
assembly called the weighbridge is used to support the platform and to trans-
mit its weight onto the lever system beneath. The applied load is reduced by
a factor of approximately 400 to 1 by the lever mechanism before it is trans-
mitted to the weigh head. The weigh head usually consists of a dial indicator
and a printer which records on a card the date and time of the transaction,
and the weight of the vehicle. Identifying information, including the
hauler's name and address, the truck number, etc., may be transferred to the
ticket from an embossed credit card or may be written in by hand. Tare weight
and net weight are transcribed manually. One section of the ticket may be
given to the driver as a receipt, with additional copies being retained as
a permanent record. The use of a manually adjusted beam balance scale regis-
tering device in place of a direct reading dial indicator and printer is not
recommended because it is subject to operator manipulation.
A combination mechanical-electronic scale utilizes a single electronic
load cell (strain gauge transducer) which in turn transmits a mi Hi ampere
signal to the weigh head. Because this signal is carried by a cable, the
weigh head can be located at any distance up to 2000 feet from the scale
platform. Most often, however, the signal is relayed to a weigh house which
is in close proximity to the scale platform, where the weighmaster conducts
the transaction in a weather protected environment. The signal from the load
cell may also be used to operate additional indicating, printing, and total-
izing accessories which are not available with a fully mechanical scale.
The fully electronic load cell scales are available from all the major
scale manufacturers. These scales use no lever mechanisms, but utilize 4, 6
or 8 load cell measuring devices located at equally spaced weight support
points located beneath the weighbridge. Proponents of the fully electronic
scale claim that their higher cost is offset by lower maintenance costs due to
elimination of the lever system, and by cost savings associated with simpler
design of the weigh pit. Since electronic readout capability is a characteris-
tic of either the full load cell or the combination mechanical-electronic
scales, the advantages of one type over the other appear to be overstated
in some instances. A full load cell installation should never be used where
the scale pit is on low ground and is subject to flooding, since high replace-
ment costs for load cells have been experienced after prolonged periods of
submersion.
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Size and Capacity
Platform lengths may vary from 6.7 to 21.3 meters (22 to 70 feet) with
capacities of 20 to 75 tons, but typical scale platforms are 3x10.4 meters
(10x34 feet) (30 ton capacity) or 3x18.3 meters (10x60 feet) (60 ton
capacity). The platform length specified should be based on the distance
between the front and rear axles, with sufficient allowance for imprecise
positioning of the load. For example, a trailer with a between-axle length
of 49 feet can be weighed on a 50 foot platform scale, but positioning of
the truck on the platform must be nearly perfect or weighing errors will
result. An 18.3 meter (60 foot) platform is more practical when large
trailers must be weighed, as might be the case when solid waste transfer
stations are used. At the time a scale is specified, consideration should be
given to the types of equipment which may have to be weighed at some future
date.
Although highly automated weighing systems can handle well over 60
trucks per hour (600 metric tons/hr. at 10 metric tons per truck), incinera-
tors with a capacity greater than 1,000 metric tons per day may use two or
more scales to avoid traffic delays and to insure reliability.
Accuracy
The accuracy for new motor truck scales produced by the major manufac-
turers is within the National Bureau of Standards recommendation of 0.1
percent of the applied load,1 although the accuracy required is only about
±1 percent. However, the scale should meet the requirements of state and
local statutes related to weights and measures. For example, for 0.1 percent
accuracy, a full load on a 50 ton scale must be accurate to within 100 pounds
of the actual weight applied. Repeatability within 0.01 percent and linearity
within 0.05 percent are claimed by at least one scale manufacturer.
Both mechanical and electronic scales should be tested under load about
three to four times per year. The testing should include: (1) checking for a
change in indicated weight as a heavy load is moved from the front to the back
of the scale (2) observing the action of the dial during weighing or for an
irregularity or "catch" in dial motion (3) testing the scale with test
weights and (4) inspections as discussed in the paragraphs on maintenance.
Accessories
Among the large number of optional features available with either of the
electronic types of scales are:
- Electronic indicator for direct reading of weight in digital form.
- Digital tare device for automatically subtracting the tare weight of
the truck.
- Automatic zero tracking system for correction of load cell temperature
deviation, or error due to debris or ice accumulation on the scale
platform.
84
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- Vibration suppression feature.
- Pound-Kilogram selector switch (or specify provision for easy modifi-
cation at a later time).
- Automatic time and date stamp.
- Data accumulator for total!izing of all weights taken in a given
period of time.
- Combination ticket and roll tape printer (roll tape provides a
permanent record in the event that tickets are lost).
- Motion detector which will not permit weight printing until the load
is at rest (prevents printing at high or low swing points).
- Plate holder (credit card type) for printing truck identification
numbers along with the weight print. Alternatively, a keyboard for
manually punching the identifying numbers prior to weight printing
may be specified.
- Automatic-Manual switch (manual mode for use when identification plate
is not available).
Pr i ces
The 1974 price for a 10.4 meter (34 foot) mechanical motor truck scale
including platform steel and basic weigh head was $8,000. A mechanical scale
with single load cell and remote electronic printing was priced at about
$10,000, and a full electronic load cell scale at about $10,000. Approximately
$2,500 is added to the above prices when scale lengths of 15.2 or 18.3 meters
(50 or 60 feet) are specified. Prices include installation but do not include
construction of the concrete weigh pit.
The weigh pit is normally designed by the engineering contractor, using
dimensions supplied by the scale manufacturer. Actual construction of the
pit may be subcontracted using local labor. The construction cost for a
weigh pit for a 3x10.4 meter (10x34 foot) scale may range from $8,000 to
$11,000, while a 3x18.3 meter (10x60 foot) pit may range from $10,000 to more
than $20,000. The factors affecting the cost of pit construction include load
bearing properties of the soil, and especially restrictive work rules which
may be in effect at the construction site.
Load cells are very rugged and seldom fail unless subjected to misuse.
The cost of replacement is about $600 per cell, plus installation costs.
Operation
The weighing operation begins by positioning the truck on the plat-
form. The weighmaster then takes the proper card from the file (automatic
sequence) and actuates the printing mechanism. A weigh ticket showing the
85
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correct date and time is issued. This ticket serves as a receipt for the
driver, and as a permanent plant record. A typical weigh ticket is shown in
Figure 10. The transaction is simultaneously punched on a tape or data card,
depending on the type of equipment provided. Such identifying information as
truck number, route number, municipality, or billing code is also shown.
During the above procedure, the tare weight of the vehicle, obtained
during a previous weighing (and encoded on the card), is automatically
subtracted from the gross weight and the net weight is printed beneath. When
tare information is not on file, the gross weight is printed using the manual
mode. The truck then must be reweighed after unloading so that the tare
weight can be subtracted. Tare-weights should be updated by reweighing the
trucks at regular intervals. To avoid tare errors, fixed procedures should
be used; for example, always weighing with half empty fuel tanks and with
the driver in the truck and other personnel off the truck and scale.
Maintenance
Materials used for scale platforms include concrete, steel, and wood.
Concrete, which is almost maintenance-free, can be poured after scale in-
stallation is complete. One or more manholes must be provided in the platform
to provide access to the scale pit.
Regular inspection and maintenance of the mechanical portion of the scale
will result in better performance and longer equipment life. Adequate light-
ing should be provided to aid inspection and maintenance. The gap between
the platform and the pit should be cleared of debris daily to prevent undue
friction and subsequent weighing errors. The scale pit should be cleaned
frequently and kept free of standing water. If a sump pump is used,, it
should be tested during each inspection.
The pivot and levers should be inspected and cleared of obstructions at
three or four month intervals to insure that their functioning remains smooth
without undue wear. Alignment of levers and positioning of the pivots on
the bearing blocks should be checked at this time. The dial head arid other
electronic components should be inspected, cleaned, and adjusted by qualified
personnel during inspections.
Many incinerator plants maintain inspection and repair contracts with
the scale manufacturers. This procedure is not overly expensive and provides
assurance that problems will be detected before major repairs become: necessary.
The manufacturer's capability for supplying prompt service using factory-
trained repairmen is one important factor in selecting weighing equipment for
a new installation.
Pivots and bearing should be cleaned and greased annually, but not less
frequently than every three years. Weighbridge steel requires painting every
three years. If cast iron levers are used, they are not usually repainted
except during complete overhauls. Vinyl-coated steel lever systems should be
inspected for damage to the protective coating and repairs made where appro-
priate. An electrical receptacle should be installed within a short distance
of the scale platform for connection of drop lights used during inspections.
86
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Complete overhaul of the scale by the manufacturer may be required after
10 to 15 years of service. The cost of overhaul may be as little as $3,000.
This investment is usually justified, since well-maintained scales should have
a service lift of 25 to 30 years, provided that the scale pit is sound and
that the scale mechanism has not sustained basic damage.
Problems
Problems encountered in the operation of scales are often related to poor
maintenance, design deficiencies, obsolescence, or traffic control. Allowing
dirt, water, snow, and ice to accumulate on and under the platform causes wear
and rusting, hazardous driving conditions, and errors in payload.
Scales having insufficient capacity or inadequate platform length dis-
rupt the flow of vehicles and make weighing difficult or impossible. Mechani-
cal scales are not adaptable to the use of electronic data logging equipment.
Therefore, this type of equipment becomes obsolete at the time that data
handling requirements can no longer be satisfied by simple ticket printing
procedures.
Disturbance of the traffic flow through the weighing station is often
the result of both human and mechanical factors. Drivers may bypass the
scales either intentionally or by misreading their directions. Signal lights,
traffic lanes bordered by curbing, and large, plainly-lettered signs have been
used to circumvent this problem. Other causes of traffic flow problems are
lost or misplaced identification cards, stalled trucks, inadvertently dumped
refuse requiring removal, and jamming of weight printing devices.
These problems are most serious during the confusion of peak traffic
periods in the late morning and mid-afternoon. Sometimes analysis of the
weigh scale records may suggest changes in starting times, pick up routes,
dispatching of transfer trailers, or other expediencies which help to
alleviate congestion at the peak arrival times.
-------
REFERENCE
U.S. NATIONAL BUREAU OF STANDARDS, Specifications, tolerances, and other
technical requirements for commercial weighing and measuring devices
adopted by National Conference of Weights and Measures. Handbook
44, 3rd edition, Washington, U.S. Government Printing Office, 1965.
178 pp.
89
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CHAPTER VIII
RECEIVING AND HANDLING SOLID WASTE
The following discussion of solid waste receiving and handling pertains
primarily to incinerators. Practices for evolving thermal processing systems
will be similar, except for greater emphasis on resource recovery as dis-
cussed in Chapter XVII.
Solid waste is delivered, usually during the day shifts, in several types
and sizes of trucks and vehicles. The vehicles are first weighed, as dis-
cussed in Chapter VII, and then proceed to the tipping area. 'At large
installations, the trucks unload into a storage pit, whereas at some small
incinerators waste is dumped directly into the furnace charging hopper or
onto the tipping floor.
Some communities attempt to segregate solid waste during collection,
while others take anything that will go into a packer truck. Still others
bring even furniture and large metal objects such as refrigerators, stoves,
bedsprings, and bicycles to the incinerator. Sometimes commercial and
industrial wastes such as large packing crates, wooden pallets, rubber tires,
and spoiled batches of foodstuffs appear, or non-combustibles like concrete
slabs, china sinks, or rolls of fence wire. Obviously, certain of these
items should be removed by presorting, while others must be treated in some
special way, such as shredding, to get them into and through the incinerator
without causing damage.1 The handling of bulky items is discussed in Chapter
XVI, while components of the waste which may be removed for purposes of
resource recovery of salvage are discussed in Chapter XVII.
After the wastes have been unloaded into the storage pit, the material
must be transferred to the charging hopper. For incinerators with charging
hoppers located above the storage pit, the transfer is usually performed by
overhead cranes. Some incinerators have the charging floor on the same level
as the storage area, and transferring can be done with a frontend loader or
special equipment.
The solid waste is charged into the furnace by dropping it directly
through a gravity chute or pushing it into the furnace with a ram. After
deposition, the waste is mechanically moved through the furnace. Figure 11
is an isometric view of the solid waste receiving and handling facilities at
the Chicago Northwest incinerator.
Tipping Area
The tipping area is the flat area adjacent to the storage pit or charg-
ing hoppers where trucks maneuver into position for dumping (Figure 12).
Considerations in the design of the tipping area must include adequate
(1) access of trucks to the storage pit or dumping area; (2) space for
uninterrupted arrival, unloading, and departure of trucks; (3) provision for
floor cleanup without interference with the flow of traffic; (4) provision
90
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CHICAGO NORTHWEST INCINERATOR
REMJSE BURNING CAPACITY ieoo TONS/DAY
WITH FOUR 400 TONS/DAY UNITS
STEAM GENERATION 110.000 IBS /HR /UNIT AT 250 PSl
FIGURE 11.
-------
Crane
Overide
Area
Exit
I/
Trolley-
Rail
Tipping
Area
At
Ground Level
Bumper/"*"^
Stop
Entrance
•Tipping Area Width
Crane
Storage
Pit
rS
^Crane
Jridge
Rails
Loading
•Shaft
Charging
' Hopper
Charging
Floor
FIGURE 12. PLAN OF TIPPING AREA AND STORAGE PITS WITH CRANE
92
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of personnel and equipment. The area should be large enough to
a": .ow T'V ;.afe and easy maneuvering and dumping, especially during times of
pcaK traffic activity.
r,e .-fcv.ei vifi'j facilities of modern incinerators are designed primarily to
icrj,,muddle cocker trucks, but they must also be able to handle other types of
veiir.les. i'here are two principal types of receiving stations:
i. 'i,,i f\(i^r dump,, wr.ich is an open paved floor area or- which the trucks
aeposit their loads. A tractor then pusnes or lifts the refuse into
eonvtyors or feed hoppers, or piles the waste in storage heaps for
later disposition.
•: ^
i I 1
ne pit dump, used in most large incinerators, which is a concrete
n?.d s'nleft if is "later lifted by a crane.
'l'j>-_ *•' cll£ United States, practically all municipal solid waste is
delivered ti. cent, ai incinerators by motor vehicles^ usually in "packer"
trucks of '2 to ?C CUDIC meter (16 to 26 cubic yard) capacity, which results
',n loacls •>? i.h.'ct ^o tignt tons of moderately compacted refuse. The more
moaern packers ha-'e r.ieans for mechanically ejecting these loads onto a level
floor or "into ?• p,r. but many of the older types dump their loads by tilting
the truCK bod;/ s'j the refuse slides out the back. These are suitable for
dui.iping (tipping) their loads into a pit, but may not eject their entire load
onto a levd floor unless the truck is driven forward with the body tilted.
Mar.y smaller euiWi'.cities, and larger communities, in emergency situations,
srl'i ^se standard three to five cubic yard open dump trucks for solid waste
delivery. In trie dggregrate, there are many deliveries made by all sorts of
private vehicles, ranging from the family sedan with a pail of refuse in the
trucK, to lignt trucks with crates of refuse or old furniture, and large vans
loaded wich special industrial wastes.
Coll ecu on trucks tend to arrive at the incinerator in large numbers
ci.."nKj a snort time interval. To avoid a backup of trucks, the length of
c.'it- tipping area and storage pit must receive careful design consideration.
The total length of the tipping area should extend the length of the storage
pit oiid, if poss'iblt'i beyond the pit. Width of individual dumping spaces
along the pit snojld oe about three to four meters (10 to 12 feet) and
clearly n^rkeo. Support columns should not interfere with dumping spaces.
The tipping area width should be greater than the turning radii of
trucks using the tipping area. For single chassis compactor trucks, the
radius is between 7.6 and 10.7 meters (25 and 35 feet); for tractor trailers,
the rdiii'is is betveen 10.7 and 15.2 meters (35 and 50 feet). The minimum
recommended width of the tipping area is 50 to 70 feet; if space is availa-
ble, tne width should be even larger.
The entrance, exit, and ceiling of an enclosed tipping area must be high
enough to provide the necessary clearance for dump trucks. Ceiling height is
critical at the edge of the tipping area when the packer and dump bodies are
93
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raised in the unloading position. A minimum of 7.3 meters (24 feet) is
recommended, but greater vertical clearance may be necessary for some trucks,
feet)
Vehicle entrances and exits should provide a minimum of 5.5 meters (18
of vertical clearance, but greater clearance is recommended to avoid
damage by the occasional truck that leaves the area with its body raised to
the unloading position. A less desirable solution to this problem is to
provide exit warning devices, such as hanging chains, to prevent careless
drivers from attempting to exit with raised bodies. The entrance and exists
should be equipped with guards to protect the door jambs.
Tipping Floor Enclosure. Enclosing the tipping area should be considered.
Climatic conditions may make it desirable. In addition, an enclosed tipping
area is definitely recommended for good public relations. Dust control,
odor confinement, reduction of windblown refuse, noise reduction effected by
enclosure, and night and weekend storage of vehicles, will make the incinera-
tor more acceptable to the community. Even though there is much to be said
in favor of enclosed tipping areas, a significant number of incinerators, in
the interests of low first cost, make do with only a canopy over the tipping
bays, or nothing at all.
Other Aspects of Tipping Area Design.
Floor and Drainage. The floor of the tipping area should be constructed to
withstand the heavy loads placed on it, and sloped away from the storage pit
toward a drain so that the area can be regularly cleaned and flushed. The
floors are usually rough-surfaced for traction.
Because of the debris that accumulates in the tipping area, the drainage
system must accommodate large quantities of wash water. The size of the
receiving sewer is critical if the discharge is to such a system. Bar grates
or other suitable devices can be used to prevent large objects from being
discharged to the sewer and possibly obstructing flow.
Scattered dust and litter from the dumping, recasting, and charging
operations are problems common to solid waste handling. Provisions for
cleaning the tipping area should be considered during the design phase.
Vacuum cleaning facilities, a compressed air system for cleaning electrical
contacts, powered mobile sweepers, and flushers have been successful in con-
trolling the spread of dust and litter.
Curb. Most plants are constructed with a curb or backing bumper along the
entire length of the pit to prevent trucks from backing into the pit. This
barrier must be high enough to prevent trucks from overriding, yet low
er.ough to permit the chassis overhang to clear the curb. A height of about
30 centimeters (1 foot) is considered adequate. The face of the backing
bumper is usually vertical or slightly concave to conform to the shape of
the wheel. It should contain openings so that spilled waste can be shoveled
or swept from the tipping floor into the pit.
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Tr.t backing bumper must be durable enough to withstand repeated impact
fid liusc be securely anchored to prevent movement. In many plants the barrier
as Deen Inadequate., and redesign and replacement have frequently been
rec .Ired, The initial design should carefully consider the types of trucks
\,o ut used. The Dumper must not only be low enough to insure clearance of the
chassis, out the pit side slope and strength should take into account possible
impact as tne chassis opens for dumping. Breaking up of concrete is common,
6r,ci steel should be considered as a basic material of construction.
s^;-\j_. Trdfnc control ana personnel safety are important considerations
wifn neavy trucks backing into close quarters to dump their loads. Many
receiving areas attempt to provide multiple dumping areas (three to six bays
usually) to handle peak delivery loading, and separate exits so the "empties"
oorr t have to thread their way back through incoming traffic. Sometimes a
special bay is reserved for cars and light trucks to keep them out of the way
of the oig packers.
3
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for cleanout, (6) access by crane or other unloading device, (7) protection
against fire hazards, (8) suppression of dust and litter, (9) protection of
operating personnel and drivers from falls and from moving vehicles and
equipment.
Capacity of the Storage PU
When the rate of receipt of solid waste exceeds the burning rate,
material must be stored for future processing. The total space for storage
depends upon the amount of material remaining after the daily receiving
period, and the amount that is left unburned from day to day during times of
peak waste delivery. The storage pit is usually designed to contain about
1.5 times the 24-hour capacity of the incinerator.
To calculate the necessary storage volume, the bulk density of solid
waste in the storage pit must be known. The generally accepted average value
for waste in a storage pit is about 200 kilograms per cubic meter (337 pounds
per cubic yard). For example, the pit for a 19 metric ton per hour (500
ST/day) plant with provision for one full day's storage when filled up to
ground level, and one and one-half day's storage with refuse piled by the
crane, might be about 24 meters long, 8 meters wide, and 16 meters deep
(75x25x50 feet). For a larger plant, the change would probably be mostly in
increased length.
Even when travelling bridge cranes are used, the width of the storage pit
does not normally exceed 9 meters (30 feet). This avoids unnecessary use of
the crane for mixing and redistributing the waste prior to charging. For
monorail crane installations, the minimum width is usually 5 to 6 meters (16
to 20 feet), which is wide enough to allow the crane to operate without being
obstructed by the overhang of trucks in the dumping position.
If heat recovery is practiced, the pit storage capacity should receive
special study to ensure a supply of solid waste adequate to meet the heat
demand when waste is not delivered to the incinerator. Also, future changes
in waste density should be considered when designing storage pits. This may
be affected by a previous downward trend, by increased separation and recovery
of paper in the home and commercial establishments, or by other local factors.
Other Aspects of Storage Pits
Shape and Construction. Storage pits are usually rectangularly shaped because
of crane design and ease of construction. A rectangular pit allows the crane
supports to be constructed with the use of the existing pit walls and bracing.
Some pits are divided into separate rectangular units with charging hoppers
between units. With this design, a fire that may start in a pit can be
isolated, and pit cleaning is facilitated because of the ability to alter-
nately empty the pits.
To provide the required strength, storage pits are usually constructed
of reinforced concrete. Frequently, pit damage occurs during crane operations
when the crane bucket collides with the wall and crushes the concrete.
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Tr.eraiore, continuous steel plating or embedded steel "("-sections in the
corvrete are used to protect areas of the pit subject to repeated impact.
Kiros, fires occasionally develop in the pit. They can be caused by sparks
carried over by the crane during the charging operation, from live coals in
the collected waste, by fires starting in parked trucks (for example, from
truck Hydraulic oils, gasoline, or solvent wastes), or by spontaneous combus-
t~ion of stored wastes. Pit fires pose a very real danger to personnel and
pro'cecr on against injury is required. Many operators recommend a pit
ye-,;i';ation system be installed to minimize the danger of pit fires. It is
claimed that exhausting air from the pit will not only assist in controlling
du^c and odors,, but will improve safety by helping to remove smoke and heat
auririCj a pit fire.
Smoke and heat from an uncontrolled pit fire can also damage the crane,
cr-cok windows, and ruin other equipment. Crane damage can put the entire
Dlaar, out of operation for weeks, or even longer. Therefore, good design
oractsce dictates that the pit be protected by an adequate sprinkler system
10 prevent the rapid spread of fire. Also, the pit area should be equipped
with an adequate number of fire hoses of effective size and capacity.
Obviously, the walls of the pit must be built to withstand the internal
pressures or sonci waste and water in the pit, a condition which could occur
airing pit fires. The pit should be watertight arid sloped to troughs and
drains for dewate.'ing. The dewatering facilities must be adequate for the
expected quantities of water used during firefighting. Sumps equipped with
suitable pumps help to remove excess amounts of water. Screening devices to
prevent material from entering the sumps and drains are also recommended.
Groundw&ter\ In addition to withstanding the pressure of water from within,
sub-grade pits must also resist penetration by groundwater. During rainy
weather, the hydrostatic pressure exerted by the water table may cause
collapse of the pit walls unless they are properly designed. The walls should
De of waterproof construction to prevent seepage of groundwater from "water-
logging" the refuse in the pit. Unfortunately, the problem of groundwater
intrusion ^s common, since thermal processing facilities are often erected on
otherwise marginal land wnich may be poorly drained or may be the site of an
old refuse dump. Ihis can lead to expensive construction of the pits, as well
as eApensive foundations for the rest of the structure.
ClGanout. Finally, cleanout facilities are needed to empty the pit if the
furnace equipment breaks down, to remove unwanted items inadvertently unloaded
into the pit, and to remove saturated waste after a fire. A loading shaft
from a point on the charging floor which can be reached by the crane to the
ground level is useful for unloading the pit and for hoisting heavy equipment
and material from ground level to the charging floor (Figure 12).
Charging Methods
Moving the solid waste from the place it is stored to the inside of the
furnace is an unusual and exacting materials handling task. The task is
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difficult because the material to be handled presents such broad ranges of
size, shape, density, texture, hardness, slipperiness, and resilience. There
is paper in all forms, from telephone books to carton boxes to greasy garbage
wrappings. There is cloth, wood, pieces of metal machinery, all shapes of
cans and bottles, grass and brush clippings, earth, dust, and waste foodstuffs.
In good weather, the conglomerate waste (mostly paper) may be quite dry and
fluffy, but during prolonged rainy spells, or in snow storms, the waste
received at the incinerator may be soggy wet. The service imposed on the
material handling equipment can only be classified as "severe".
A popular feeding system is comprised of a below-grade storage pit and
a travelling crane with a grab bucket which lifts and carries the waste high
above the furnace, and releases it into a funnel shaped hopper which leads
to a chute that allows the waste to slide into the furnace under the action
of gravity. Other methods include the "floor dump", which utilize bulldozers
to push waste material from the charging floor into the furnace hopper, and,
in other instances, various types of conveyors are used.
Whatever charging system is used, it must supply a controlled flow of
waste to the furnaces while causing minimum interference with air supply for
combustion, and with maximum protection against flashbacks of fire or gases
through the charging opening. Besides transporting solid waste to the
charging hoppers, cranes are also used to mix and distribute the solid waste
in the pit. This action results in more uniform burning in the furnace and
better utilization of pit capacity.
Crane Types. The types most commonly used are the monorail crane and the
brid'ge crane (Figure 13). The former is a fixed unit suspended from a single
rail that crosses the pit in only one horizontal direction. The bridge crane
differs from the monorail in that it can maneuver horizontally in two direc-
tions rather than one. The capacity of the monorail crane is usually less
than that of a bridge crane; and the width of the storage pit is restricted
-co include only that lateral area within reach of the open bucket. Capital
cost of a monorail crane is less than that of a bridge crane, and at some
small incinerators, its performance may be adequate.
Tne larger incinerators have bridge cranes in which two parallel over-
nead rails mutually support a cross structure, or bridge, on wheels, so the
bridge can travel the length of the rails. The bridge, in turn, supports a
"trolley" which suspends and operates the bucket or grapple. The bucket of
the bridge crane can reach any point in the area between the support rails,
and can., therefore, handle refuse in wide pits and reach furnace charging
hoppers in more locations. Usually, the crane is operated by a man in a cab
mounted right on the bridge or trolley, although both stationary arid movable
floor level control platforms have been used.
Cat» design is very important, since it houses the operator whose judgment
and performance in sorting and mixing solid waste and controlling the rate
of feeding to the furnaces are vital to the successful operation of the
incinerator. To overcome the environment of dust, odor, heat, and noise, the
cabs are well ventilated, often air conditioned, arid are frequently provided
with communications systems.
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FiGURE 13 TYPICAL LAYOUT FOR SUBGRADE STORAGE PIT WITH
OVERHEAD CRANE, CHARGING HOPPER AND CHUTE.3
Induced-draft
Scrubber
Cpjrdtmg-floor elevation 116' 0" ,-> .—
DM a
1 v_
FiGURE 14 TYPICAL LAYOUT FOR ABOVE GRADE STORAGE WITH
SUBGRADE CHARGING CHUTE.3
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Good cranes are costly because of the sophisticated controls, the severe
duty, and the need for reliability, since a crane stoppage shuts down the
entire plant. The use of two or more cranes with a total capacity of from
50 to 100 percent in excess of that required is often used to improve
reliability. Special provisions are also required 'in the buildings which
house them; such as strong, true mountings for the rails; headroom and side
clearance for the trolleys and bridges; a heavy duty, well protected electri-
cal power source to the trolley (either the "third rail" type or festooned
retractable cables); and sometimes storage space for standby motors, bridges,
trolleys, and buckets. A typical layout for a subgrade storage pit with over-
head crane, charging hopper and chute is shown in Figure 13.
Crane Capacity and Bucket Design. Typically, the crane bucket must be large
enough to "grab" 400 to 500 kilograms (882 to 1,102 pounds), about 2 to 2.5
cubic meters (2.6 to 3.3 cubic yards) of mixed refuse from the storage pit
at each "bite," and to deliver its payload into the furnace charging hopper.
In order to withstand the jarring, abrasive service conditions, the bucket
itself may weigh five times its capacity. The crane and its drums, bearings,
cables, motors, gears, and brakes, then must all be designed to lift three
tons each time, and to do it continuously and reliably. Because of the
punishment sustained by cranes used in refuse handling, they are most often
specified as Class "E", for severe duty.2
The number of bucket loads that can be charged during a given period
depends upon the number of cycles that the crane can make during the charging
operation. A cycle is defined as the time for loading and lifting the bucket,
trolleying and bridging to the charging hopper, dumping, and returning for
another bucket load. Typical cycles vary from 1-1/2 to 3 minutes. To
determine the cycle time, the hoisting, bridging, and trolleying speeds must
be known, as well as the length, width, and depth of storage pit. Typical
hoisting and trolley speeds are between 76 and 92 meters per minute (250 and
300 ft/min), whereas bridge travel speeds may be as high as 107 meters per
minute (350 ft/min).
Incinerator cranes ordinarily use the closed scoop bucket or a grapple,
The closed scoop is a clamshell with heavy steel lips, usually equipped with
short teeth to increase penetrating ability,, The grapple type is similar
to a clamshell but has much longer teeth, called tines, and has a considerably
larger capacity than a similar closed scooped bucket. The grapple is a poor
cleanup tool because of the length and spacing of its tines. For cleaning
purposes, the grapple can be equipped with bolted-on pans.
Number of Cranes. Crane downtime will stop incinerator operation unless a
standby crane is provided. Nearly all installations with a capacity above
15 metric tons per hour have a second crane to prevent shutdown. A second
crane is recommended wherever possible, certainly for plants with capacities
exceeding 10 metric tons per hour and operating 24 hours per day. Because
of high costs, most small plants have only one crane. At larger installa-
tions, a third crane is often justified. With a second or third crane, space
in addition to the operating space required for the first crane must be pro-
vided for the storage of the units when not in service. The point of storage
for the nonoperating unit(s) must not interfere with the operating unit.
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^if'JLr.2J. ^Hi- 2bir'ft'-oTK Tne crane can be operated manually from a cab travel-
ling with che crane, or from a remote f->xed operating point. Manual opera-
tor, rrom a mob Tie cab is most common and thought to have some advantage
ever a remote fixed operating point since the operator has better visibility.
however, a remote fixed cab can be used successfully. Where the pit is long,
the oisiance judgment, error is reduced with mobile cab operation, When a
mobile rab is used, the operator should have a safe convenient boarding plat-
form. Since the charging operation may be dusty and hot, the crane cab should
be .1 r-conditioi'teu
Ac ]£«-3t one large incinerator plant utilizes a travelling bridge crane
wr;ic.'!-, employs an automatic, load cell type device for weighing the contents
of cne bucket. «:iih this device, the bucket weight can be observed by the
crane operator as required or can be automatically recorded. When automatic
wei;jiiir;g ecjjipirient is provided, weighings are made when the bucket is at rest,
usually -vhen it reaches the top of the vertical travel, and only at periodic
•intervals.
Oi5CJbsi'on of Othe? Charging Methods. Another charging method, used in some
smaller incinerators, utilizes a handling floor upon which the trucks dis-
charge me refuse. The "floor dump" consists of a concrete or bituminous
su'-faesc floor ?h£icered or enclosed by a simple structure. A bulldozer
equipped wren a lift oucket is used to move and pile the solid waste on the
floor, sori-tir.'ie^ ten feet high, until it is fed into the incinerators. The
s~:des of the enclosure are constructed to withstand the side thrusts of the
waste piles, and there are sewers for drainage and often sprinklers and
ventilation systems to cope with dust4 fire, and odor. A typical layout of
above grade storage with a subgrade cnarging chute is shown in Figure 14.
iYcjetors triih bulldozing blades and lifting buckets used with the floor
djirip charging method are simpler and less costly than travelling cranes.
s.ov,evers they can only be used to feed a furnace hopper where the waste does
not nave to be taken oat of a below-grade pit, and lifted above the furnace.
If the tipping floor is at an elevated level with respect to the furnace, as
is possible witn a hillside location or with a manmade ramp, the tractor
operator can mix, sort and feed refuse to a bank of incinerators just as
efficiently as a crane operator, and, in case of a breakdown, the machine
can be quickly replaced witn another tractor, or even, temporarily, with a
snowpluw on a trjck.
Continuous chain, bucket, or belt type conveyors are sometimes used in
feeding incinerator furnaces. However, mechanical difficulties are common
witn this type of equipment, and provision must be made to deal with the
possibility of a disabled conveyor buried under tons of solid waste.
Charging Hoppers
Charging hoppers are used to maintain a supply of solid waste to the
furnace. In batch-feed furnaces, a gate separates the charging hopper from
the furnace and supports the solid waste while the furnace is burning the
previous charge. Generally, one hopper is provided for each furnace cell.
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In a continuous-feed furnace, the waste-filled hopper and chute assist in
maintaining an air seal to the furnace as well as providing a continuous
supply of solid waste. Most charging hoppers have the shape of an inverted,
truncated pyramid. The size of the hopper opening depends somewhat upon the
size of the furnace, but it should be large enough to prevent arching of
oversized material across the hopper bottom. Common hopper openings measure
from 1x2x1.2 meters to 1x2x2.4 meters (4x4 ft to 4x8 ft). The hopper should
be deep enough to receive a bucketful! of solid waste without spilling over.
The charging hopper is generally steel and sometimes concrete lined.
Because of abrasion from solid waste, impact from the crane bucket, and heat
from the furnace, the hopper must be constructed of rugged material and built
to facilitate repair and replacement. The hopper is often equipped with a
sliding charging door at the throat, or with metal covers which can be quickly
applied to seal them off, in case of fire burning back from the furnace.
Charging Chutes
The charging chute connects the hopper to the furnace and may be nearly
as wide as the furnace so that the solid waste will pass through the chute
without clogging. The discharge of waste into the furnace is usually by
gravity, but reciprocating or vibrating feed mechanisms may also be used.
The chute is usually made of smooth temperature-resistant metal extend-
ing several feet down from the "throat" of the hopper into the furnace, and
terminating above one end of the stoker or hearth. The resultant column of
waste forms an air seal, and the lower end of the column is exposed to the
heat of the furnace for drying and ignition. The stoking action starts the
ignited material on its way through the furnace, and new waste from the
column replaces it. The "buffer" quantity of waste in the chute and hopper
permits the actual feed rate into the furnace to be controlled by the stoker
action and allows the crane to be used for stacking refuse or feeding other
furnaces for reasonable intervals of time.
The end of the chute in the furnace is usually water cooled or lined
with refractory or concrete. The welds which fasten the cooling jackets to
the chute may cause difficulties when the two metals differ in composition or
when frequent overheating occurs.
An innovation to the gravity fed chute has been the addition of an
hydraulically activated horizontal ram at the bottom of the chute to push
"slugs" of mixed waste into the furnace. This affords positive control of
the feed rate and serves as the chute seal in place of the charging gate. The
ram is arranged so as to push a load of waste onto an exposed drying and
ignition hearth, and in the next stroke, the new load tumbles the dried refuse
over a parapet onto the actual stoker.
Charging Methods for Evolving Thermal Processing Systems
The trend in newer system designs is to shred municipal solid waste
prior to thermal processing. This added step is a necessary adjunct to
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resource recovery systems, as discussed in Chapter XVII, and allows mechanical
or pneumatic conveying to be used in place of the usual cranes.
For example, suspension fired incinerators require shredding, usually to
less than 5 centimeters in size. This is true whether the refuse is to be
fired with coal in a conventional boiler, or in fluidized bed or suspension
fired boilers especially designed for municipal solid waste.
Some pyrolysis processes can handle as-received municipal solid waste,
but pyrolysis processes in which residence time is short, such as in flash
pyrolysis, must be fed solid waste reduced in size. When pyrolysis liquids
and solids for fuel use are principal products, shredding and separation of
non-combustibles prior to pyrolysis is necessary to avoid high ash contents
in the fuel. Therefore, the feed systems in such processes are based on
handling finely divided material, for example pneumatic transport of minus
24 mesh preprocessed solid waste.
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REFERENCES
1. Technical-Economic Study of Solid Waste Disposal Needs and Practices.
U.S. Department of Health, Education and Welfare, Public Health Service.
Report No. SW-7c, Vol. IX, Bureau of Solid Waste Management. Rockville,
Maryland. 1969.
2. O'Malley, W. R. Special Factors Involved in Specifying Incinerator Cranes.
Proceedings, 1968 National Incinerator Conference. (New York, May, 1968)
American Society of Mechanical Engineers, pgs. 211-215.
3. Corey, R. C. Principles and Practices of Incineration. Wiley Inter-
science, New York, 1969.
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CHAPTER IX
DESIGN OF INCINERATOR FURNACE SYSTEMS
Ihc iru-ine^Qtur furnace system serves the following functions:
1 . C::a;g ,AJ He waste to the combustion zone at a controlled rate.
i. Dryiruj tre waste sufficiently to permit ignition of combustibles.
3. bi-priri.j me waste to essentially inert solid residue and flue gases
witK a MITr.imum of polluting constituents.
4, Dissipating the heat of combustion.
b, Coliettiny, cooling, and removal of solid residues,
Receiving and Handling of the municipal solid waste, including charging
methods, pro pet dijpGi.al of effluents, process control, and recovery of energy
are covered in ~;thc-r chapters.
r'.uiuamentals of ^£lJQ_^as_i;^ Lni:l!le.i?ll0Ll
I numeration vnth air- can be thought of as occurring in three overlapping
stages which may take place in different sectors of the furnace. First, heat
from the combustion process is used to drive moisture from external and
internal surfaces.- second, the solids are further heated causing physical and
chemical changes, bonrietimes called pyrolysis; and third, oxygen in the air
reacts wit.i comb^tible materials both in the solid itself and driven from the
solid curing pyrolysis, emitting large quantities of heat. Proper incinerator
furnace design requires that adequate residence time, temperature, and turbu-
lence he provided for each stage of combustion to insure contact of oxygen with
the comcusciole mdf.enals under conditions where combustion is essentially
complete.
As siv;wn in Idble 25b the primary combustible elements in refuse are
carbon &nd hydrojen, with much lower but significant amounts of sulfur and
nitrogen Some constituents of the ash may also oxidize during incineration.
Tne net result of effective combustion is the conversion of the carbon in the
trash to carbon dioxide (CO^) and hydrogen to water (ri20). Sulfur is converted
to sulfur oxides (primarily S02), some nitrogen is converted to nitrogen
oxides, arid organic chlorides are converted to hydrogen chloride (HC1). These
latter compounds, along with particulate emissions, constitute potential air
pollutants which are discussed in Chapter XIV. Combustion at 760 to 980 C
(1400 tu 1/96 F) will normally produce a sterile residue and an effluent gas
free of odors, a^susTiing adequate furnace design, and operations which do not
exceed design feed rate.
The air supplied to the incinerator has several important functions. It
supplies the o
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Table 25
TYPICAL MUNICIPAL SOLID WASTE
CATEGORY
Metal
Paper
Plastics
Leather and Rubber
Textiles
Wood
Food Waste
Yard Waste
Glass
Miscellaneous
WEIGHT %
(as fired)*
8.7
44.2
1.2
1.7
2.3
2.5
16.6
12.6
8.5
1.7
TOO"
COMPONENT
Moisture (H20)
Carbon (C)
Oxygen (0)
Hydrogen (H)
Sulfur (S)
Nitrogen (N)
Ash
WEIGHT %
28.16
25.62
21.21
3.45
0.10
0.64
20.82
100.00
*This weight distribution shows the effects of moisture transfer between the
categories in the refuse during storage and handling. For example, the food
waste tends to lose moisture and the paper absorbs moisture. Gross; heating
value 2375 calories/gram (4275 BTU/lb).
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afio vapor i?t-d v.'jtt:.' from the incinerator; ana finally,, the air and the result-
•;ng flue gas absori heat from the combustion reactions and carry it from the
cGifu^tiun zone, /Vir may also be used to aid in establishing turbulent condi-
tions in tr;e furnace and in cooling vital furnace elements.
The quantity of air supplied to the incinerator furnace is a major
determinant as r.o me size of the equipment. In incinerators without heat
recovery in the combustion zone, the quantity of air is determined by the re-
eaif&menu fur heat, removal. For examples, as shown in Table 26., the air
required TO mai,-,ta.r; the incinerator at about 800 to 1100 C (1472 to 1990 F)
is .wo to ir.ree Lii7.es that theoretically necessary fur complete combustion,
cr 6.4 to 9,6 tons of air per ton of refuse. To reduce this air requirement,
one must either extract heat, as in the water wall steam recovery incinerator
to he aiscussed in Chapter X; or operate at a high temperature where ash tends
to f"use into a .slaij, thus the slagging type incinerator which has been under
development.
D i y i n g j n d I gjri 1 i on of Re fuse
MuJ, or the i.iujei sal in mixed solid waste has loosely bound or surface
moisture which i^ readily vaporized when heat is applied,, leaving the burnable
materiel" too ..o^.' to volatilize and ignite until most of the water has been
driven off. To ,-irfcrm the drying function and 10 prevent smothering a going
fire with L.naric:d and non-combustible material, most furnaces have some pro-
vision for exposing newly charged material to radian c heat energy and hot
gases to drive off and absorb the moisture. As previously mentioned, these
provisions take the form of exposure at the bottom of a feed chute or on a
drying stoker or hearth, or brief suspension in hot gas as the refuse falls
onto the stoker,
After the multure has been driven off, the heat radiated to the refuse
by the hot gases and hot surfaces, and conveyed to the refuse by the motion of
hot gases, increases the temperature of the refuse until combustibles pyrolyze,
vaporizt, and begin to combine with oxygen. This is the ignition process
which starts the burning. In most furnaces, the original ignition at startup
is done by a match, torch > or pilot burner., but thereafter the burning material
ignites the incoming waste Design features, like positioning of grates with
respect, to heat reflecting walls, or guiding of flame gases over the incoming
wastes i are employed to ensure ignition. In some furnaces, to ensure ignition
when there are unusually wet loads, auxiliary gas or oil burners are positioned
to direct their flames on the incoming refuse.
During the drying and ignition phases of incineration, there are large
quantities of steam and gases liberated, expanding to many times their origi-
nal volume Therefore, furnace designs provide for unrestricted flow of these
gases away from the generation zones, so that fresh air can get in to supply
oxygen and prevent smothering of the flame.
Comb us ti on F urn ace
The neart. of rlie incineration system is the combustion furnace, which
consists of a chat.iDer to contain the reaction, a stoker to transport solid
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Table 26
COMPARISON OF ADIABATIC FLAME TEMPERATURES
FOR COMBUSTION OF A TYPICAL SOLID WASTE
WITH VARYING AMOUNTS OF EXCESS AIR*
Percent excess Air 0 50 100 200 300
Air Requirement,
tons per ton
refuse 3.21 4.82 6.42 9.63 12.84
Flue Gas,
tons per ton
refuse 4.03 5.64 7.24 10.45 13.66
Adiabatic Flame
temperature, °C 1660 1343 1088 793 638
(°F) (3020) (2449) (1990) (1459) (1180)
*Based on approximately 2750 calories/gram gross heating value (4950 BTU/lb),
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waste through th^ furnace and agitate it to expose new surface to oxygen and
heat, ana air supply to furnish oxygen for combustion, and a pressure differ-
ential (draft) to cause air to enter and the gaseous products of combustion
to flow out of thfc chamber.
Configuration^ Of the many furnace shapes and sizes, common configurations
include the uprighc cylindrical (Figure 15), the rectangular (Figure 16), the
r.uVci-chamber rectangular (Figure 17), and the rotary kiln following a rectan-
gular furnace (Figure 18).
The cylindrical furnace is usually refractory lined. Solid waste is
charged through a door or lid in the upper part (usually the ceiling) and
drops onto a central cone grate and the surrounding circular grate. Underfire
forced air is the primary combustion air and also serves to cool the grates.
As tne cone and arms rotate slowly, the fuel bed is agitated and the residue
works to the- sides where it is discharged, manually or mechanically, through
a dumping grate on the periphery of the stationary circular grate. Stoking
doors are provided for manual agitation and assistance in residue dumping if
required. Overfire air is usually introduced to the upper portion of the
circular chamber, A secondary combustion chamber is adjacent to the circular
chamber. As far as is known, no cylindrical furnaces have been built in the
united States in recant years.
The murticeil rectangular type may be refractory lined or water cooled.
It contains two or more cells set side-by-side, and each cell normally has
rectangular grates. Solid waste is usually charged through a door in the
top of ectch cell. Generally the cells of the furnace have a common secondary
combustion chamber and share a residue disposal hopper.
The rectangular furnace is the most common form in recently constructed
municipal incinerators. Several grate systems are adaptable to this form.
Commonly, two or more grates are arranged in tiers so that the moving solid
waste is agitated as it drops from one level to the next level. Each furnace
has only one charging chute.
A rotary kiln furnace consists of a slowly revolving inclined kiln that
follows a rectangular furnace where drying and partial burning occurs. The
partially burned waste is fed by the grates into the kiln where cascading
action exposes unburned material for combustion. Final combustion of the
combustible gases and suspended combustible particulates occurs in the mixing
chamber beyond the kiln discharge. The residue falls from the end of the kiln
into a quenching trough.
Except for the rotary kiln, the furnaces are generally constructed on
concrete foundations with either a structural steel framework supporting inner
walls and a roof arch of refractory material (supported wall and suspended
arch construction), or typical masonry with bricks laid one atop another
(gravity walls) and self supporting arched roofs made of keystone shaped bricks
(sprung arches). The supported wall and suspended arch are almost universally
used in modern incinerators. Metal or refractory hooks secure the refractory
to the structural steel, and a layer of insulation and an outer sheet metal
109
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CtMftONG HW«I»
FIGURE 15. UPRIGHT CYLINDRICAL FURNACE1
110
-------
114
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cc
D
u.
cc
<
D
CD
O
UJ
oc
to
«—
UJ
cc
111
-------
CHARGING CHUTE
TO
SECONDARY
COMBUSTION
CHAMBER
OVERFIRE
AIR INLET
'STOKING
DOOR
RESIDUE
HOPPER
FIGURE 17. MULTICHAMBER RECTANGULAR FURNACE1
112
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Ix— Refuse charging chute
Forward-acting
reciprocating
stokers
Bypass flue
FIGURE 18. ROTARY KILN FURNACE*
113
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casing usually complete the wall structure. Water wall construction is dis-
cussed in Chapter X, "Recovery and Utilization of Energy."
Secondary combustion zones provided in incinerators are chambers con-
nected by passages from the primary combustion chamber, but seldom sharply
defined. Rather, they tend to be extensions or enlargements of the primary
chambers, sometimes set off by half walls or baffles that cause the gases to
flow in turbulent eddies for a time long enough to complete the combustion
process.
The size of the various furnace zones and openings is usually determined
by the manufacturer according to his experience for gas flow rate and residence
time; solids flow rate, depth, and residence time; avoiding obstruction due to
the inadvertent admission of oversize objects; heat release; and other mechani-
cal considerations. A few typical parameters for furnace volume and grate
area determination are provided in Table 26. These parameters may be expected
to vary by as much as 50 percent.
Refractory. Four different forms of refractory are used; fired refractory
bricks, which are laid up with a very thin layer of refractory cement between
bricks; plastic refractory which is supplied in a damp clay-like consistency
and is spread and pounded into place against lath or hooks; ramming mixes
which are usually machine rammed into place in wet form (resulting in higher
density than plastic refractory); and castable refractory which is poured into
temporary molds, like concrete.
The latter three forms are usually dried out at low furnace heat and then
assume their final vitreous strength when the furnace is brought up to its
normal operating temperature.
There are many compositions of refractory material, usually clays of
silica or alumina. These are called fire clays and are used in various grades
for varying conditions of heat, erosion, and chemical resistance. Special
high performance refractories may be used in certain areas of the furnace where
unusually severe conditions are encountered, such as high temperature and
erosion, e.g. in furnace linings at the edges of the stoker bed. For example,
silicon carbide brick is often used in side walls near the moving grate for
resistance to erosion and slag attack, and mullite or other special refrac-
tories may be selected for resistance to spelling in charging areas. Sum-
maries of refractory properties and placement are available,3 but refractory
manufacturers should be consulted prior to specification.
Grates and Stokers. In practically all municipal incinerators, except rotary
kilns, the refuse rests on grates while burning. These grates are, in general,
metal surfaces with holes or slots through which underfire combustion air
enters. Usually the grates are movable by mechanical means, so they can move
the refuse through the furnace, agitate the refuse to promote combustion, and
remove the ash and residue from the furnace. These mechanical grate systems
are called stokers, since they perform the function which used to be done by
men who tended the fire using long metal hoes and stoking bars. Many furnaces
are still equipped with doors in the sides through which manual stoking can be
done when necessary.
114
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Upright cylindrical furnaces have a floor of dimping grates above the ash
pit. These grates are pivoted on axles, so that when they are rocked large
spaces open up for residue to fall through. Above the floor of the grates,
mounted on a vertical axis, is a star shaped rabble arm which rotates slowly
and spreads and tumbles the refuse on the grate during combustion. In these
furnaces, new batches of refuse are dumped in from the top at intervals, and
they are, therefore, classed as batch type furnaces.
The flow-through furnaces are equipped with stokers which receive solid
waste at one end and continuously move it horizontally and downward through
the furnace, finally depositing the residue in a receiver at the opposite end
of the furnace. During the journey through the furnace, the refuse is supplied
with underfire air which comes up through the grates from a windbox under the
stoker. Fine particles of ash (siftings) fall through the holes in the stoker
surface and must be caught and removed to avoid eventually clogging the wind-
box and the grate openings.
There are at least six principal types of flat-bed stokers available:
1. The travelling grate stoker, which is essentially a moving chain belt
carried on sprockets and covered with separated small metal pieces
called keys. The entire top surface acts as a grate while moving
through the furnace, yet can flex over the sprocket wheels at the end
of the furnace, return under the furnace, and re-enter the furnace
over a sprocket wheel at the front. The sprockets drive this chain
conveyer, and are in turn driven by electric motors at slow speed
(Figure 19).
2. The reciprocating grate stoker, which is a bed of bars or plates
arranged so that alternate pieces, or rows of pieces, reciprocate
slowly in a horizontal sliding mode over the stationary pieces and
act to push the refuse along the stoker surface. These are driven
through links by electric motors or hydraulic cylinders (Figure 20).
An adjustable grate knife action may be added to the last portion of
grate to split refuse lumps and to knock ash from clinkers in order to
improve burnout (Figure 21). The double reciprocating stoker uses
two movable grates sandwiching a stationary grate (Figure 22).
3. The reverse reciprocating stoker is an inclined reciprocating grate
stoker in which the reciprocating action is opposite to the gravita-
tional flow of the solids. A continuously rotating motion of the
refuse bed is created, drawing burning refuse underneath, and burning
incoming refuse from the bottom up (Figure 23).
4. The rocking grate stoker is a bed of bars or plates on axles. By
rocking the axles in a coordinated manner, the refuse is lifted and
advanced along a surface of the grate. The stoker is actuated by
linkage driven by electric motors or hydraulically (Figure 24).
5. In the vibrating stoker, grates with overlapping edges are vibrated
by an electrically operated eccentric drive assembly mounted on a
shaft, resulting in a conveying action toward the discharge point
(Figure 25).
115
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FIGUFIi m TRAVEUNG GRATES1
FIGURE 20. RECIPROCATING GRATES1
116
-------
grate construction showing knives in raised position at right.
FIGURE 21. GRATES WITH KNIFE ACTION
117
-------
STATIONARY
GRATES (TYP.)
FIGURE 22. DOUBLE RECIPROCATING STOKER
118
-------
Movement
of solids
Typical
reciprocating
grates
Motion of
reciprocating
grates
Typical
stationary
grates
FIGURE 23. GRATE BAR ACTION IN REVERSE RECIPROCATING STOKER
(ALSO SHOWN IS THE ASH DISCHARGE ROLLER)
119
-------
Nunutrosmm
FIGURE 24. ROCKING GRATES1
120
-------
FIGURE 25. VIBRATING CONVEYING GRATE STOKER
121
-------
6. The inertia! grate stoker is constructed as a fixed bed of plates
with the entire bed carried on rollers. The stoker is activated by
an electrically driven mechanical drive which draws the bed slowly
back against a spring, and then releases it so that the entire bed
moves forward until stopped abruptly by another spring. The inertia
of the refuse carries it a small distance forward along the stoker
surface and then the cycle is repeated.
Flat-bed stokers may be horizontal or inclined down in the direction of
flow, and may be used as a single stoker or as a series of two or three units
arranged in stair-step array, so the refuse is tumbled and agitated as it
moves from one section to the next. Often the individual sections can be
operated so as to advance the refuse at different speeds to control drying
and burn-out (Figure 26).
In the roller grate (Figure 27), the solid waste is fed onto the first
roller, and then progresses by the action of the slowly rotating rollers to
the ash discharge point. The revolving rollers disturb, agitate, and reorient
the bed so that the new burning surfaces are constantly exposed, assisting in
complete combustion.
The grate surfaces are made of sturdy iron or steel castings, alloyed
and designed to resist distortion, growth, cracking, and oxidation. However,
in well designed furnaces, the grate surfaces do not characteristically
operate at temperatures even near that of the fire because they are protected
by unignited refuse, by ash, and by the cooling underfire air passing through
them. In the drying and ignition zones, the volatile combustible gases, water
vapor, and smoke are driven off and flow into the secondary combustion chamber
where they are mixed with air and retained long enough to complete combustion,
After the ignition zone of the stoker, the residual refuse burns off its fixed
carbon with a clean hot flame which radiates heat energy to facilitate the
proper burning of the still-combustible gases and airborne particulate matter,
Rotary Kiln. The rotary kiln (Figure 18) is really a combination fawaace and
stoker and is effective in gently tumbling the burning refuse until complete
combustion is achieved. The kiln is a large metal cylinder with its axis
horizontal or slightly inclined. It is lined with firebrick and mounted on
rollers so that electric motors can slowly rotate it about its horizontal axis.
As used in municipal incinerators, the refuse is first passed over drying and
Ignition stokers in a furnace, and then, when most moisture and volatile con-
stituents have been driven off, the burning residue is fed into the kiln for
final burnout. In such an arrangement, the volatiles driven off in the igni-
tion chamber are led through a passage above the rotating kiln and join the
hot gas effluent from the kiln in a secondary combustion chamber, where the
oxidation of the combustible gases and combustible airborne particulate matter
is completed.
Bulky Objects. A few cities have recently built a specialized type of incinera-
tor for burning logs, heavy brush, and bulky objects like discarded furniture
(Chapter XVI). This has taken the form of a large box-like furnace with typi-
cal furnace wall refractory and insulation construction, and large doors at one
end. The floor is a simple firebrick hearth and one end of the furnace is
122
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SectionaNy supported
arches and walls
FIGURE 26. THREE-STOKER INCINERATOR2
123
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constructed to collect the flue gases and treat them in a cleaning process be-
fore release to the atmosphere. The bulky refuse is pushed into the furnace
oy a bulldozer, ignited, and allowed to burn down to a residual ash, which is
-.leaned out of the incinerator by the bulldozer when the furnace has cooled.
Combustion conditions in such a furnace vary with time, complicating the
oroblem of air pollution control. Shredding is another approach to the
handling of bulky objects discussed in Chapter XVI.
^I-jJ^fL. *n constrast to the underfire air which enters the furnace through
and around the grates, air which enters the furnace above the grates through
':;•£ slues or roof of the furnace is called overfire air. Overfire air is
ised to mix with and burn the combustible gases driven off from the refuse.
Overfire air is usually introduced in high velocity jets at specific points
which vary with furnace design, and is directed so as to provide turbulence
and thorough mixing of the gases for optimum combustion. As discussed earlier,
total air flow in excess of that required for combustion is used to cool the
burning gases to temperatures which will permit reasonable furnace life.
The flow of air and other gases through a furnace is caused by forcing
air in and/or drawing gases out so that atmospheric air flows in through
openings provided. The most common arrangement in modern furnaces uses forced
draft fans for underfire air and overfire air jets, in conjunction with an
induced draft fan for flue gas removal.
rurn&ce pressures are usually held slightly below atmospheric pressure
so that if doors are opened, or if there are any leaks in the walls, atmospheric
air will be drawn into the furnace, rather than permitting the hot, odorous
and sometimes dangerous gases to flow out of the furnace to the surrounding
workspace. This "negative pressure" is maintained by drawing out slightly
more gas than the air and the gases that are positively blown in or generated
in the furnace. Natural draft, utilizing a tall stack or chimney, has been
ihe traditional way to develop a "negative pressure." The heated gases 1n
the stack are less dense than the cooler atmospheric air outside the stack and
so tend to flow upward, drawing additional gases behind them.
Stacks are popular because they are simple and can be constructed to
handle the large volumes of hot and corrosive gases (e.g. containing small
quantities of sulfur oxides and hydrogen chloride). Also, they discharge the
airborne products of combustion high into the atmosphere to aid dispersion.
After the first cost of erection, stacks require no further expense for power
and usually need only nominal maintenance. However, there are practical
limitations on height and cost, which limit the amount of suction available to
draw the flue gases through efficient dust collection devices. For these
reasons, the newer incinerators do include induced draft fans ahead of the
stack to provide the degree of suction required for efficient air pollution
control devices.
Induced draft fans, while usually much less costly initially than a
natural draft stack, do have important limitations. They have limited toler-
ance to high temperatures and to corrosive conditions such as can be caused by
condensation of acid gases, and they are susceptible to erosion by flyash.
Therefore, gases are normally cooled and cleaned, including demisting where
applicable, prior to the fan.
125
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Induced draft fans are large and require large drivers which use.con-
siderable power. These are usually electric motors, but can be steam turbines.
Depending on dispersal requirements, fans can exhaust into very tall stacks or
relatively short lightly constructed stacks. Sometimes provision is made for
varying the fan speed to control the gas flow through the furnace, but more
often dampers are used for this control.
Temperature. The temperatures in a well operated modern municipal incinerator
furnace are controlled between reasonably close limits to obtain consistently
effective combustion. Since the incoming solid waste varies in composition,
e.g. moisture content, good temperature control requires automatic control
methods, as discussed in Chapter XII. Average temperatures in the burning fuel
bed on the grates, and just above, may reach 1100 to 1400 C (2012 to 2552 F).
The temperature of the flaming gases falls from this level to about 650 to 900 C
(1202 to 1652 F) as the gases flow through the primary and secondary combustion
chambers. Generally the gas temperature is kept above 760 C (1400 F) to ensure
oxidation of all malodorous compounds, and below 980 C (1796 F) to prolong the
furnace life.
Dissipating the Heat of Combustion
Early incinerators, which had to burn solid waste of low heating value,
were designed primarily to conserve and reflect the heat of combustion so as to
dry and ignite the refuse and heat the resultant gases above the deodorizing
temperature with minimum use of supplementary fuel. Hot flue gases were dis-
charged directly through masonary stacks with refractory linings, with a
"settling chamber" at the base and a "spark screen" at the top as the air
pollution control. Early attempts to use "waste heat" from the combustion
chamber to generate steam were unsatisfactory because there was relatively
little "waste heat." Furnace walls were designed to conserve as much heat as
possible.
Modern municipal incinerators, burning refuse of much higher heating value,
and emitting their flue gases through sophisticated air pollution control de-
vices, are designed to dissipate the heat of combustion, so that after achiev-
ing the temperature necessary for complete combustion in the furnace, the flue
gases are cooled to as low as 250 C (482 F) before they enter air pollution
control systems.
With either water wall or refractory furnaces, a waste heat boiler, an
array of tubes in the path of the hot gases (convection section) in which steam
is formed by vaporizing water, can bring the flue gases down to 300 C (572 F)
and even lower. This reduces both the gas volume and temperature, making
possible the use of more economically sized exhaust fans and electrostatic pre-
cipitators, or other air pollution control devices. Heat of combustion is thus
transferred to steam, and the energy is made available to do work, as discussed
in Chapter X.
The two most common methods of reducing the flue gas temperatures are by
dilution with ambient air and by evaporation of water directly into the gas
stream. In addition, there is always some direct conduction and radiation of
heat through the walls of the furnace and ducting. Direct admission of air
126
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is a simple and easily controllable operation. A damper in the ducting allows
outside air to be drawn into the flue gases because the draft of the chimney
or of the induced draft fan causes a lower pressure inside the gas ducts than
outside. However, even though cooling the flue gases decreases their volume,
the amount of fresh air added increases the net volume so that larger and thus
more costly ducts, fans, air pollution control equipment and stacks are re-
quired.
If water is mixed with, or exposed to the hot flue gas stream, the water
tends to evaporate, and in so doing absorbs heat from the gas. In round
numbers, the evaporation of one kilogram (2.2 Ibs) of water can lower the
temperature of 10 kilograms (22 Ibs) of hot gas by 240 C (432 F). Although
increased in weight, the total volume of the cooled gas and the steam is less
than the volume of the original hot gas, so smaller fans, ducts, and pollution
control equipment can be utilized. However, if the evaporative cooling system
is not designed for complete water evaporation, the water absorbs sulfur and
chlorine compounds from the flue gases, becomes acidic, and attacks the
structure of the gas cleaning equipment unless specially designed to resist
corrosion. Often, water neutralization is practiced and water quenching is
combined with a wet scrubber for gas cleaning, since the water supply, distri-
bution, and containment systems can be used in common. This will be discussed
in Chapter XIV.
The quenching and scrubbing water may be introduced as sprays, on wet
baffles, which are obstructions placed in the gas duct with water flowing in
thin films over the structure; or as wet bottoms, which are simply shallow
water tanks which form the bottom sections of the flue gas ducting. The
effectiveness of evaporative cooling is usually dependent upon good mixing of
the gas and liquid. Complete evaporation, i.e. leaving no water residue, re-
quires sophisticated nozzle design and control systems.
Collecting, Cooling and Removal of Residual Solids
Solid residue is generated at three places in a municipal incinerator:
unburned residue conveyed through the furnace by stoker; the siftings that
fall through grate openings; and the fly ash collected from the flue gas. An
additional source of residual solids in some incinerators is material removed
from internal walls and other areas during shutdown for cleaning and mainte-
nance. Since, on average, 20 to 25 percent of the weight of municipal mixed
refuse is glass, rock, cans, and other metals and minerals, the collection,,
cooling, and removal of the non-combustible solid residue is a significant
materials handling task. Fortunately, as discussed in Chapter I, solid residue
should comprise less than 10 percent of the average volume fed into a properly
performing incinerator.2
Stoker Residue. The principal incinerator residue is that discharged from the
stoker.This consists of broken glass and ceramics, metal cans of all shapes
and sizes, stones, earth, assorted hardware, and some fused ash (clinkers)
from melted glass, metals and minerals, all surrounded by flakes and dust of
the light fluffy ash that typically results from burning paper or wood. Al-
though some incinerators do a remarkably thorough and consistent job of burning
the combustibles, insufficient residence time and varying refuse characteristics
127
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in other incinerators permit some incompletely burned material to appear in
the stoker residue.
Telephone books, catalogs, and heavy bundles of newspaper, particularly
if wet, are not readily penetrated by air for direct combustion, or by radiant
or convective heat for drying and volatilization, so 1t 1s not uncommon to
even find unbumed paper in residues. Heavy timbers or green wood may pass
through the burning cycle with a core of unburned wood still present. Certain
foodstuffs containing high water content and occurring in thick sections, like
watermelon rinds, carrots, apples or waste meats may char on the outside and
seal in liquids, thus permitting some putresdble material to appear. All this
may be aggravated by operating an incinerator at maximum feed rate to handle
a peak load, instead of slowing the stoker to permit better drying and longer
combustion time for difficult wastes. Nevertheless, a typical "good" residue
contains less than 5 percent by weight of unbumed carbon and less than 1 per-
cent of putrescible organic material. Shredding of bulky wastes aids 1n obtain-
ing good "burnout."
Large incinerators with flow-through furnaces generally use conveyer
systems to remove the stoker ash (Figure 28). The residue is usually dis-
charged from the stoker grates into a water filled trough where it Is thoroughly
quenched and cooled. It is usually conveyed from the quench system to elevated
storage hoppers, from which the residue can be discharged directly to trucks
underneath the hoppers.
Residue Conveyors. Removal of residue from the quench trough 1s commonly
accomplished By a metal drag link conveyor. This consists of a pair of end-
less metal chains with metal bars attached between the chains, Hke a rope
ladder, driven by an electric motor through sprocket wheels to drag along the
bottom of the ash trough and capture the residue, pull 1t out of the trough,
up a chute, and into a waiting bin or truck. These drag link conveyors are
heavily constructed of heat resistant cast steel drag link parts, with corro-
sion resistant metal or concrete tanks and chutes for containing and guiding
the wet, abrasive residue. They travel slowly, thus allowing water to drain
back into the tank from residue moving up an inclined chute. The unused por-
tion of the drag linked chain, which is returning from the point of discharge
of the residue back to the entrance to the quenching tank, may require as much
supporting, guiding, and protective structure as the working section of the
chain.
It is common practice to position drag link conveyor paths transversely
across the discharge ends of two or more rectangular furnaces so that the
residue of both can be carried to a common discharge point for economy of
overall structure and material of the conveyor. Because the residue removal
conveyors are such vital elements of the incineration system, and because they
are big, heavy, and somewhat difficult to service, they are often built in
parallel pairs with a diverting chute so that each of several furnaces can
direct its residue to each of two residue conveyors to ensure reliable service.
Another type of conveyor system is a metal mesh travelling belt on which
the residue falls from the stoker, and is spray quenched. Other systems, using
metal apron-type conveyors, vibrating conveyors, and rubber belts for cooled
residue are in use, but the metal drag link type is the most popular. Manual
handling of residue has practically disappeared, except for a few small older
incinerators.
128
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FIGURE 28. RESIDUE DISPOSAL FROM CONTINUOUS-FEED FURNACE
BY INCLINED, WATER-SEALED CONVEYOR2
729
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Metal Salvage. A few incinerators have equipment for separation of residue
and salvage of metal, mostly tin cans. The separation is usually done in a
metal drum or barrel with holes in its sides and mounted to rotate about its
horizontal axis. This tumbles the residue and the ash falls through into a
hopper, while the cans finally pass out the end of the drum to another hopper.
Sometimes magnetic separators are used to collect the steel from the rest of
the residue. The cans are usually pressed flat or shredded to make them into
salable scrap, either at the incinerator site or by a dealer. The non-metallic
ash is a dense, inert material, almost like a damp earth, and is sometimes
sold for road fill.
Grate Siftings. The siftings are dust-like bits of ash, often still glowing,
that drop through the grate openings and cover whatever is below. They some-
times contain an appreciable percentage of combustible and putrescible matter.
The amount varies with the type of stoker and the material being burned. Cer-
tain types of plastics that melt, or greases that can run through the grate
openings, may accumulate in the underfire air chambers and ignite and burn,
unless precautions are taken.
Some stokers rely on manual cleanout of siftings through doors provided
for the purpose. Others provide hoppers under the grates and means ranging
from mechanical and pneumatic conveyors to water sluicing to move the accumu-
lated siftings either to an outside collection point, or onto the quenching
tank with the other solid residue.
Siftings and stoker residue removal can be combined in a "wet bottom"
furnace in which the entire furnace foundation is made as a concrete basin
which is filled with water. A drag link conveyor as wide as the furnace runs
the entire length of the furnace and drags out the grate siftings which have
fallen into the water, as well as the stoker residue which falls into the
quench water at one end of the foundation.
Flyash. Flyash in a municipal incinerator is the particulate matter which is
light enough to be carried out of the furnace by the existing gas stream. Dust,
ash, fine burning particles, and even sizable pieces of burnt or burning paper
are released from the grate by underfire air and fuel bed agitation, so that
about 10 to 20 percent of the weight of the ash in the solid waste charged into
the furnace leaves as airborne flyash.^ Modern air pollution control devices,
described in Chapter XIV, are usually designed to collect 95 or more percent of
this flyash, either by dry collection in hoppers or by capturing it in water.
The flyash is conveyed by mechanical or pneumatic conveyers, or by sluicing
with intermittent floods of water through pipes, either to a storage hopper
for trunk loading, or to the quenching tank for removal with the other solid
residue.
Residue, siftings, and flyash suspended in water can be recovered in
settling tanks or lagoons. Further discussion of this topic is included in
Chapter XIII.
130
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REFERENCES
1. DeMarco, 0. et al. Municipal-Scale Incineration Design and Operation.
PHS Publication No. 2012. U.S. Government Printing Office, Washington,
D. C. 1969. (formerly Incinerator Guidelines - 1969).
2. Corey, R. C. (ed.). Principles and Practices of Incineration. New York,
Wiley Interscience, 1969. pages 163-209.
3. Paroni, J. L. et al. Handbook of Solid Waste Disposal. Van Nostrand
Reinhold Co. New York. 1975. 549 pages.
4. Niessen, W. R. and A. F. Sarofin. Incinerator Air Pollution: Facts and
Speculation. Proceedings, 1970 National Incinerator Conference (Cincinnati,
May 17-20, 1970). American Society of Mechanical Engineers, pages 167-
181.
5. Technical-Economic Study of Solid Waste Disposal Needs and Practices.
Combustion Engineering, Inc., Windsor, Connecticut. Report SW-7c. U. S.
Department of Health, Education, and Welfare, Bureau of Solid Waste
Management, 1969. Volume IV, Part 4.
6. Wilson, D. G. (ed.). The Treatment and Management of Solid Waste, Chapter
7. Municipal Incineration. Technomic Publishing Co., Westport, Connec-
ticut 1972. 210 pages.
131
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CHAPTER X
RECOVERY AND UTILIZATION OF ENERGY
While common in Europe, the conversion of solid waste to energy in the
United States was until recently only an interesting idea reduced to practice
in a very few plants,1 most using specially designed incinerators to produce
steam. However, the recent awareness of an "energy crisis" has spurred no
less than twenty cities to consider projects for steam generation by prepared
refuse combustion, many using existing fossil-fuel fired steam boilers. The
feasibility of this approach has been shown in a project partially supported
by the U.S. Environmental Protection Agency.2 Most of the following discus-
sion deals with incinerators specially designed for steam production. The
use of prepared refuse to supplement coal or other fuels i£ dealt with
specifically in a later section of this Chapter.
Energy Recovery Systems vs Refractory Incinerators
Non-energy recovery incinerators have refractory combustion chambers,
while combustion chambers in steam-producing incinerators are usually water
tube wall construction. The choice between burning refuse in refractory in-
cinerators or providing for energy recovery is generally not clear cut.
Advantages and disadvantages of both approaches are compared in Table 27.
Pyrolysis provides another alternative for energy recovery in the form
of fuels. Pyrolysis processes which produce liquid fuels are particularly
attractive, from the point of view of energy recovery, because of the ease
with which this form of energy can be stored.
Generally, energy recovery systems cost more to install and operate,
present more operating difficulties and safety considerations, and put the
municipality into a business, but do provide significant credits from the
sale of the steam. It should be noted that steam is not a storable commodity,
and major customers should be contracted before a project is justified by the
steam credits. Major investments are required for generation and distribution
systems.
To illustrate the potential for energy recovery, steam production in
several recently designed installations is shown in Table 28. For a given
incinerator, the amount of steam generated is primarily a function of the
combustible content of the refuse, as shown in Table 29.
Energy Uses
It should be noted that the primary purpose of a thermal processing
facility is to dispose of municipal solid waste. This waste never stops
coming. Therefore, any complications which tend to reduce reliability must be
carefully evaluated. Both in-plant use and export of steam should be consid-
ered, as well as the use of steam turbines to generate electric power, although
132
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Table 27
COMPARISON OF REFRACTORY INCINERATORS
AND ENERGY RECOVERY SYSTEMS
Refractory Incinerators
Energy Recovery Systems
High excess air required to con-
trol furnace temperature
Large refractory combustion
chamber to handle high gas flow
3. Costly furnace auxiliary equip-
ment due to high gas flow,
including FD and ID fans, air
pollution control equipment,
ducts, and stack.
4. No steam facilities required
Requires flue gas cooling sys-
tem such as spray chamber (waste
heat boiler sometimes used)
Relatively simple operating
procedures
Moderate potential for corro-
sion, especially in air pollu-
tion control equipment
8. Moderate operating costs
1. Moderate excess air
2. Moderate size combustion chamber,
but requires water tube wall con-
struction, and may require addi-
tional parallel lines for steam
supply reliability
3. Furnace auxiliary equipment
similar to refractory incinera-
tors, but less costly due to
lower gas flow.
Requires expensive steam facili-
ties and controls, including
water tube walls, waste heat
boiler, boiler feedwater treat-
ing, soot blowers, steam conden-
sers, and steam distribution
Waste heat boiler producing
steam used for cooling
Operations complicated by neces-
sity to meet steam supply demands,
maintenance of steam equipment,
presence of high pressure steam
systems, etc.
Possible steam tube corrosion
and erosion require monitoring
and additional maintenance cost;
air pollution control equipment
corrosion can be problem as with
refractory incinerators.
Higher operating costs because of
increased complexity.
133
-------
Table 27 (Cont'd)
Refractory Incinerators
Energy Recovery Systems
9. Only possible byproduct
credits are for pre or post
incineration salvage
9. Considerable steam
credits possible in ad-
dition to salvage, in-
cluding in-plant use of
steam for fan drives,
heating, etc.
134
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Table 28
EXAMPLES OF REPORTED STEAM GENERATION QUANTITIES3
System System System System
1234
Solid Waste Type
Steam Temperature,
°C
(°F)
Steam Pressure,
atm abs.
(psig)
Steam Production,
tons/ton refuse*
A
327
(620)
28.2
(400)
3.6
B
205
(401)
18.0
(250)
4.2
A
260
(500)
16.3
(225)
1.4-3.0
A
241
(465)
18.7
(260)
1.5-4.3+
* Tons steam per ton of refuse fed to the furnace varies with refuse
heating value, as shown in Table 29V^
+ See Table29 for variation of steam production w/t\eating value.
A Solid waste as received.
B Solid waste prepared by shredding and partial metal removal.
Table 29
EFFECT OF SOLID WASTE HEATING VALUE ON STEAM PRODUCTION
Nominal Refuse
Heating Value, cal/g.
(BTU/lb.)
Refuse, % Moisture
% Noncombustible
% Combustible
Steam Generated,
tons/ton refuse*
3611
(6500)
15
14
71
100
4.3
3333
(6000)
18
16
66
100
3.9
2778
(5000)
25
20
55
100
3.2
2222
(4000)
32
24
44
100
2.3
1667
(3000 )
39
28
33
100
1.5
* These values are calculated for a specific operating incinerator, but
they are believed to truly reflect actual results.
135
-------
the latter is not now a significant method for energy recovery in the United
States. As will be described, air conditioning can also be exported.
In-Plant Uses. The most obvious and efficient use of the energy recovered is
in the thermal processing plant itself. Power plants, oil refineries, and
chemical and other large manufacturing facilities have long practiced "energy
recycle" in order to keep the overall utility (i.e., fuel, water, electricity)
costs to a minimum.
Steam turbines to drive induced and forced draft fans, large pumps, and
other significant power requirements provide a major outlet for recovered
energy. Other uses include space heating, snow and ice melting from ramps,
and tracing to prevent freezing of water lines. One steam generating in-
cinerator estimates its steam usage as tabulated in Table 30.
All the energy requirements of the plant are not usually supplied by the
steam. Steam driven equipment has a higher capital cost; therefore the steam
is not "free." Backup electric driven equipment must be provided to startup
fans and other equipment when steam is not available. Weather protection,
heating, and other services must be provided, even when steam generating
facilities are not operating. Obviously, the necessary backup equipment adds
to capital costs. Figure 29 depicts an example of an in-plant steam distribu-
tion scheme.
In-plant usage of steam is a straightforward method of utilizing up to
about half of the energy available from combustion of the solid waste. No
capital cost is required for external steam distribution, and the complexity
of matching steam supply to export demand is avoided.
Steam Export. Because of the projected energy shortages and ever-rising fuel
costs, the economic picture has begun to favor generation and sale of energy
produced from solid waste. This is illustrated by the simple "fuel equivalent"
comparison made in Table 31.
However, it cannot be emphasized enough that these "favorable economics"
can be illusory. No credits will accrue if the energy cannot be sold. Much,
if not most of the steam produced in the U.S. solid waste incinerators is
being condensed because of the lack of customers.
Steam generated can be used directly for heating purposes. Typically, the
steam pressure as generated is in the 18 to 45 atm. (250 to 650 psig) range.
If low pressure steam, for example 11 atm. (150 psig), can be sold for space
heating, the pressure difference between the high and low pressure steam can
be Utilized to drive in-plant non-condensing turbines prior to entering the
distribution systems. The use of steam for heating may require both steam
distribution and condensate return lines. If the customer is distant, the
condensate return line may be eliminated, but this increases the cost of boiler
feedwater treating.
136
-------
Table 30
EXAMPLE OF IN-PLANT USAGE OF STEAM*
Fans 25.3 % of total steam generated
Feedwater pumps B.I
Feedwater heater 2.1
Space heating 5.3
Water heating 2.7
Condenser protection against freezing 6.1
Total in-plant usage 46.6
Maximum available for sale 53.4
* Calculated from reference 5.
137
-------
FIGURE 29B
Condensers
Steam to consumers
Feedwoter pumps
Auxiliary equipment of the four combinations of incinerators and boilers in
Chicago is steam-turbine driven, except for the electric motors needed to
start the plant when no steam is available. Note use of air-cooled condensers
T=steam turbine
M=electric motor
138
-------
Table 31
COMPARISON OF RELATIVE VALUES OF REFUSE AND FUEL OIL
BASED ON HEATS OF COMBUSTION
Crude Oil Price,
$/barrel 3.50 7.00 10.00 15.00
Equivalent "Value"
of Refuse
$/metric ton* 6.80 13.61 19.44 29.16
* Based on 42 gallons of oil per barrel, 0.9 specific gravity, 10,000
calories per gram (18,000 BTU/lb); and refuse at 2778 calories per gram
(5000 BTU/lb)
139
-------
Obviously this type of arrangement creates a responsibility for the muni-
cipality to reliably deliver the steam, the failure of which may have drastic
consequences. Therefore, the use of auxiliary burners fired by fossil fuel
and/or an auxiliary fossil fuel fired package boiler is required to meet demands
during downtime of the thermal processing facility, during pertods of wet re-
fuse, and sometimes for peak loads. An auxiliary burner can provide continu-
ity of steam supply during periods of refuse feed equipment failure or other
up-stream problems. The standby package boiler is used when the thermal pro-
cessing facility is totally inoperable. An increased number of parallel
furnace lines may also be required to improve steam supply reliability.
The use of waste lubricating oils and other waste oils have been proposed
as auxiliary fuels for steam generating incinerators. However, such use re-
quires precautions against hazardous contamination, such as flammable solvents;
consideration of the possibility of steam tube fouling due to metallic impuri-
ties, which may include lead contents on the order of 1 percent in raw waste
oils.7
Ideally, of course, the consumer has an alternative steam supply avail-
able, and therefore is not dependent on the solid waste generated steam. In
this case, the steam will usually be less valuable to the consumer and lower
prices will be obtained.
Air Conditioning. One recent project uses steam to heat downtown office
buildings in the winter and to cool them in the summer.**' 9 j^3 \
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141
-------
Table 32
PERTINENT DATA FOR HEATING AND COOLING DISTRICT
SUPPLIED BY SOLID WASTE GENERATED STEAM8.9
Total city refuse*
Number of incinera-
tors
Capacity per
incinerator
Number of buildings
served
Steam generation
capaci ty
(incinerators)
Standby steam
boiler capacity
Steam pressure as
generated
Steam temperature
as generated
Steam pressure
(saturated)
supplied for
heating and
condensing
turbines
Chilled water
capacity
Chilled water supply
temperature
Chilled water return
temperature
Length of distribution
pipeline
52.9 MT/hr.
2
13.6 MT/hr.
40
97.5 MT/hr.
56.7 MT/hr.
28.2 atm. abs.
316 C
(1400 ST/day)
11.2 atm. abs.
(360 ST/day)
(215,000 Ibs./hr.)
(125,000 Ibs./hr.)
(400 psig)
(600 F)
(150 psig)
(13,500 tons of
40.8xl06 Kcal./hr. refrigeration)
5 C
14 C
4.57 kilometers
(41 F)
(57 F)
(15,000 ft.)
* Parts of the distribution system and certain main plant components are
designed for the projected ultimate plant capacity of 56.7 MT/hr (1500 ST/
day) using five incinerators.
142
-------
Other Energy Uses. Marketing steam and chilled water to municipally owned
buildings, university complexes, and the like, for heating and cooling may be
easiest institutionally, but industrial markets for process steam where demand
is uniform, without exaggerated peaks and valleys, is much more satisfactory
from the point of view of incinerator operation. Possible industrial con-
sumers include power plants, oil refineries, chemical plants, and other plants
utilizing low level energy (i.e., steam rather than direct firing of fuel,
such as in glass or steelmaking furnaces).
Other process possibilities include municipal sewage sludge drying. Due
to increasing environmental restrictions on ocean dumping and landfill opera-
tions, sewage sludge incineration is growing in importance. Use of hot flue
gases or solid waste generated steam to predry the sludge results in economic
and energy savings. Co-incineration of the dried sludge, or even the wet
sludge, is also an interesting approach which has been used in the past to a
limited extent.
Fresh water production from seawater or brackish water by distillation or
other desalting processes requires energy which can be supplied from thermal
processing facilities. This use, which can be considered in arid areas or
other areas with special water problems, e.g., Southern California and Long
Island, may be attractive because the pure water can be stored, allowing
steady use of energy produced by the thermal processing facility.
Electricity can be produced from solid waste in four ways:
1. Generating steam to drive electrical generators.
2. Generating steam to sell to power companies.
3. Mixing prepared refuse with fossil fuel in power plant boilers.
4. High pressure, high temperature incineration using exhaust gases
to drive an expansion turbine-generator.
While several European incinerators use steam produced to generate elec-
tricity, this approach is rare in the United States. The problems of ineffi-
cient generation from the relatively low pressure steam normally produced and
the difficulties and cost in reliably producing high pressure, high tempera-
ture steam in solid waste incinerators appear to be formidable deterrent to
this approach, though future improvements may be expected. Similarly, the
sale of low pressure steam to electrical power companies is not usually at-
tractive because steam pressures near 136 atmospheres (2000 psi) are preferred
for efficient generation of electricity. Combined firing of prepared refuse
with fossil fuel, which is attractive, will be covered in a later section of
this Chapter. Direct production of electricity by incineration of prepared
solid waste in a pressurized fluidized bed, and expansion of the hot gases
through a turbine, though promising, has not yet reached commercialization JO
Energy Recovery Systems
Energy recovery may be accomplished in such diverse systems as pyrolysis
processes, high pressure fluidized beds with gas turbines, and other methods
which have not been demonstrated on a commercial scale. The systems described
here generate steam by combustion of solid waste.
143
-------
At least four general types of steam generation systems can be employed:
- Grate furnace with refractory walls and a waste heat boiler
- Grate furnace with water tube walls and a waste heat boiler
- Suspension fired steam boiler
- Combined firing of prepared refuse with fossil fuels
In the first two types, it is not necessary to shred or otherwise prepare
the solid waste. In the latter two, preparation is required.
Refractory Incinerator with Waste Heat Boiler. This is a conventional
incinerator with refractory walls followed by boiler tubes erected in the
flue gas stream leaving the furnace. While this approach obviously produces
energy credits, the full benefit of energy recovery is not achieved because
considerable excess air must be used to control temperature in the combustion
chamber. This excess air reduces the efficiency of energy recovery by carry-
ing heat from the furnace system up the stack, and also requires larger down-
stream equipment, such as fans and air pollution control equipment, based on
the high flue gas rate emitted. Careful design of boiler tubes is necessary
to control temperature and to avoid slagging and corrosion.
Incinerator With Water Tube Walls. In the water tube wall incinerator firing
unprepared waste, shown in Figure 31, heat is recovered directly from the
combustion zone, eliminating the need for large quantities of excess air used
for cooling in refractory incinerators. This is accomplished by the use of
water tube walls in place of refractory, where water is circulated to remove
energy, but reduces flue gas quantities significantly, reducing the size of
downstream equipment. For example, the use of water tube walls may be expect-
ed to reduce flue gas quantity by 30 to 40 percent over a refractory furnace
operating at the same temperature. Excess air requirements are usually on the
order of 40 to 80 percent as compared to 100 to 200 percent often encountered
in refractory furnaces.
Due to advantages of energy recovery and flue gas volume reduction, the
newest steam generating incinerators have been of the water wall type. Tables
33 to 36 provide actual operating data for such an incinerator.
Suspension Fired Steam Boiler. The suspension fired steam boiler, shown in
Figure 32, is based on the design of pulverized coal boilers commonly used
throughout the world for electric power production and industrial boilers.
Suspension firing has been used for other waste materials such as bark and
bagasse," but only recently has shredded waste been burned in suspension
boilers J4, 15, 16 jn another, the prepared waste is burned with coal J4 as
described in the next section. A third suspension fired boiler is operated
within an industrial plant.
144
-------
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145
-------
Table 33
QUANTITIES AND FLUE GAS ANALYSIS FOR
STEAM GENERATING INCINERATORl1
Heating value of refuse
Incinerator capacity
Refuse firing rate
Heat input
Gas exit temperature
Ambient air temperature
Gas Composi t ion, Vol. %
C02
02
CO
N2
Excess air
2422 Cal/g
15.2 MT/hr
15,166 kg/hr
36.7xl06 kcal/hr
211 C
22.8 C
10.49%
9.02%
0.0 %
80.49%
71.7 %
(4360 BTU/lb)
(401 ST/day)
(33,434 Ib/hr)
(145,772,000 BTU/hr)
(411 F)
(73 F)
146
-------
Table 34
BOILER LOSSES AND EFFICIENCY FOR STEAM
GENERATING INCINERATOR11
Heating value of refuse 2422 Cal/g (4360 BTU/lb)
Heat Losses
Dry flue gas 11.40%
Moisture in fuel 4.01
Moisture in air 1.22
Moisture from burning hydrogen (^ 8.83
Combustible in residue 2.83
Moisture in residue 0.30
Moisture flashed from quench 0.32
Radiation loss 0.41
Unaccounted for losses 1.50
Total losses 30.82%
Efficiency 69.18%
147
-------
Table 35
AIR AND GAS QUANTITIES FOR STEAM GENERATING INCINERATOR1
Heating Value of refuse
Refuse firing rate
Dry gas per weight of refuse
Total moisture per weight of refuse
Weight of gas per weight of refuse
Gas temperature
Density of gas
Density of water vapor
Total weight of dry gas
Total weight of water vapor
Total weight of products of combustion
Volume of Dry gas at 211 C(411 F)
Volume of water vapor at 211 C
(411 F)
Volume of products of combustion at
211 C (411 F)
Available I.D. fan capacity at 260 C
(500 F)
Weight of air for combustion
Air volume at 21.1 C (70 F)
Available FD fan capacity at 21.1 C
(70 F)
2422 Cal/g
15,166 kg/hr
6.14 kg/kg
0.516 kg/kg
6.656 kg/kg
211 C
0.734 kg/CM
0.457 kg/CM
93,117 kg/hr
7825 kg/hr
100,942 kg/hr
2116 CM/min
282 CM/min
2293 CM/min
4030 CM/min
85,192 kg/hr
1182 CM/min
2379 CM/min
(4360 BTU/lb)
(33,434 Ib /hr)
(6.14 Ib /Ib)
(0.516 Ib /Ib)
(6.656 Ib /Ib)
(411 C)
(0.0458 Ib/CF)
(0.0285 Ib/CF)
(205,285 Ib/hr)
(17,252 Ib/hr)
(222,537 Ib/hr)
(74,703 CF/min)
(9,950 CF/min)
(80,980 CF/min)
(142,300 CF/min)
(187,815 Ib/hr)
(41,750 CF/min)
(84,000 CF/min)
148
-------
Table 36
OVERALL ENERGY RECOVERY PERFORMANCE OF STEAM
GENERATING INCINERATOR11
Heating value of refuse 2422 Cal/g (4360 BTU/lb)
Steam generation per weight of refuse 2.98 kg/kg
Overall efficiency of incinerator and
boiler 69.18%
Heat loss due to combustibles in residue 2.83%
Stack gas temperature 211 C (411 F)
149
-------
1—1
V—7
Four (4) Refuse
entry ports.
FIGURE 32. SUSPENSION FIRED BOILER12
150
-------
prepared Refuse Combustion in Existing Boilers. A project which has created
rgreat interest on a prototype scale (125 megawatt boiler) is the firing of
>repared refuse in mixture with pulverized coal in an existing boiler, A
:o!T¥nercial scale facility is planned by the participants. The attractive
"eatures of this approach include:
1. The boiler units are already in place, obviating the need for new
thermal processing facilities.
2. Air pollution from sulfur oxides is reduced because the prepared
refuse is normally lower in sulfur than the coal it replaced.
Overall particulate emissions may also be reduced, compared to
separate incineration, because of the separation of inorganic
materials from the combustibles, and efficient electrostatic
precipitators on the boiler.
3, Fossil fuel consumption for power generation will be reduced.
4. Facilities and markets already exist for the electrical energy
produced.
The technique is based on the premise that if solid waste is prepared so
.hat its flow characteristics are similar to pulverized coal, and its ratio
.0 coal fired is kept low enough, the coal boiler will not be significantly
.ffected and the above advantages will accrue. Tests to date show that effi-
cient generation of electricity from prepared refuse can be accomplished by
.his approach. A single 500 megawatt boiler operated at 75 percent use
'actor could help dispose of 340,000 ST of solid waste per year, saving on the
rder of 150,000 ST of coal per year.
From the results obtained, it appears that on the order of 10 to 20
ercent of the heating value fired in a normal coal-fired boiler can be sup-
ut partially paid for by the recovered materials.
Particulate emission tests for combined firing have been inconclusive.
ne data obtained suggest possible problems with electrostatic precipitator
>erformance when burning the prepared refuse with low sulfur coal. Such
iroblems are common when burning low sulfur coal alone, but are costly to
•esolve.
The combined fossil fuel/refuse combustion approach requires additional
emonstration in various types of boilers over an extended period of time
Before it can become a fully acceptable outlet for municipal solid waste
isposal. Close observation is required to insure that no unusual corrosion
r other detrimental effects occur.
The possiblities of firing prepared refuse in oil fired boilers is now
ndergoing study. These present special problems of refuse feeding techniques,
isposal of residue, and particulate emission control, since adequate solids
andling facilities and electrostatic precipitators are available on only a
ew boilers, those that have been converted from coal to oil firing.
151
-------
Refuse-To-Energy Projects. A recent U.S. Environmental Protection report
provides a recent list of municipalities committed to or having expressed an
interest in resource recovery systems, most of which involve energy recovery.'
152
-------
REFERENCES
. Astrom, L. et al. Comparative Study of European and North American Steam
Producing Incinerators. Proceedings, 1974 National Incinerator Conference.
Miami. May 12-15, 1974. American Society of Mechanical Engineers. Pages
255-266.
L Solid Waste as Fuel for Power Plants. Horner and Shifrin, Incorporated,
St. Louis, Missouri. Report EPA-SW-36D-73. U.S. Environmental Protec-
tion Agency, Office of Solid Waste Management Programs, NTIS Report
PB 220 316. Springfield, Va. 1973. 158 p.
i. Compiled from RECON SYSTEMS, INC., Princeton, N.J. visits and communiques
with operating and planned facilities.
. Pepperman, C. M. The Harrisburg Incinerator: A Systems Approach.
Proceedings, 1974 National Incinerator Conference. Miami. May 12-15,
1974. American Society of Mechanical Engineers. Pages 247-254.
>. Bender, R. J. Steam-Generating Incinerators Show Gain. Power. McGraw
Hill. September 1970. Pages 35-37.
i. Chansky, S. et al. Study of Waste Automative Lubricating Oil as an
Auxiliary Fuel to Improve the Municipal Incinerator Combustion Process.
Contractor~GCA Corporation (Bedford, Mass.). EPA Contract No. 68-01-0186.
Office of Research and Monitoring. U.S. Environmental Protection Agency.
U.S. Government Printing Office. Washington, D.C. September 1973.
'. Weinstein, N. J. Waste Oil Recycling and Disposal. Contractor-RECON
SYSTEMS, INC. (Princeton, N. J.). EPA 670/2-74-052. U.S. Environmental
Protection Agency. Washington, D.C. August 1974. 327 p.
. Wilson, M. J. A Chronology of the Nashville, Tennessee Incinerator With
Heat Recovery and the Compatible Central Heating and Cooling Facility.
Proceedings, 1974 National Incinerator Conference. Miami. May 12-15,
1974. American Society of Mechanical Engineers. Pages 213-221.
Nashville Turns Solid Waste Into District Steam and Chilled Water. Power.
December 1974. Pages 18-19.
. Chapman, R. A. and Wocasek, F. R. CPU-400 Solid-Waste-Fired Gas Turbine
Development. Proceedings, 1974 National Incinerator Conference. Miami.
May 12-15, 1974. American Society of Mechanical Engineers. Pages 347r358.
. Stabenow, G. Performance of the New Chicago Northwest Incinerator. Pro-
ceedings, 1972 National Incinerator Conference. New York. June 4-7,
1972. American Society of Mechanical Engineers. Pages 178-194.
!. Mullen J. F. Steam Generation From Solid Wastes: The Connecticut
Rationale Related to the St. Louis Experience. Proceedings, 1974
National Incinerator Conference. Miami. May 12-15, 1974. American
Society of Mechanical Engineers. Pages 191-202.
153
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13. Regan, J. W. et al. Suspension Firing of Solid Waste Fuels. Presented
at American Power Conference, Chicago, Illinois, April 22-24, 1969. 7 p.
14. Klumb, D. L. Solid Waste Prototype For Recovery of Utility Fuel and
Other Resources. Technical Paper APCA74-94. Air Pollution Control
Association. Pittsburgh, Pa. 1974 Annual Meeting-Denver. 16 p.
15. Schwieger, R. G. Power From Waste. Power, February 1975. Pages S-l to S-24.
16. Sutin, G. L. The East Hamilton Solid Waste Reduction Unit. Engineering
Digest ]_5 (No. 7): 47-51. August 1969.
17. Third Report to Congress. Resource Recovery and Waste Reduction. SW-161.
Office of Solid Waste Management Programs. U.S. Environmental Protection
Agency. 1975. 96 p.
154
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CHAPTER XI
PYROLYSIS
Pyrolysis or "destructive distillation" is a process in which organic
material is decomposed at elevated temperature in either an oxygen-free or low-
oxygen atmosphere. Unlike incineration, which is inherently a highly exother-
mic combustion reaction with air, pyrolysis requires the application of heat,
either indirectly, or by partial oxidation or other reactions occurring in the
pyrolysis reactor. Again unlike incineration, which produces primarily carbon
dioxide and water, the products of pyrolysis are normally a complex mixture of
primarily combustible gases, liquids, and solid residues. Thus, pyrolysis
produces products which are potentially useful as fuels and chemical raw
materials.
Several pyrolysis processes have been developed for municipal solid wastes.
One full-scale plant is in its early phases of operation in the City of Balti-
more, and one is under construction in the County of San Diego. If operations
are successful, pyrolysis will be available in the near future as an alterna-
tive to incineration and other methods of solid waste disposal.
Chemistry of Pyrolysis
The organic portion of municipal solid waste is primarily composed of
the elements carbon, hydrogen, and oxygen, with minor quantities of nitrogen,
sulfur and others. Since the ratios of the major elements approximate those
in cellulose, municipal solid waste is sometimes represented chemically as
(CeH1005) , where "n" represents a variable number of the basic chemical units.
Indeed, cillulose is a major constituent of solid waste; for example, paper is
primarily cellulose, wood contains about 55 to 60 percent cellulose, and cotton
greater than 90 percent. For the purposes of this discussion, the chain or
polymeric nature of cellulose will be ignored, using the chemical representa-
tion C6H1005.
Simple Pyrolysis. A simple pyrolysis reaction may be represented by:
C6H1005 Fuel gas (including some C02 + H20)
+ Pyrolytic Oil + other condensibles (oxygenated organics in water)
+ carbonaceous solid residue
The relative quantities of gaseous, liquid, and solid products and their com-
positions depend upon the composition of the waste and the conditions of pyro-
lysis. For example, higher pyrolysis temperature increases gaseous yields.
Pyrolysis temperature for processes producing high yields of pyrolytic oil
would be about 500 C (932 F), while processes producing primarily gaseous fuels
will most likely attain 700 to 100 C (1292 to 1832 F). Solid residues are
produced in either case.
155
-------
Other Pyrolysis Reactions. Product yields can also be shifted by the appli-
cator of catalysts, high pressure, by the use of oxidizing reactants such as
air, oxygen, or water, or by the use of reducing reactants such as hydrogen
or carbon monoxide. For example, the following types of reactions are possible:
+ 1/2 02 _ 6CO + 5H2 (partial oxidation)
C6H1005 + H20 heat > 6CO + 6H2 (reforming)
C6Hio05 + H2 pressure oil + H20 (hydrogenation)
C6H1005 + 12H2 pressure 6CH/, + 5H20 (hydrogasifi cation)
C6H1005 + CO + H20 pressure> pyrolytic oil ( hydro- oxy nation)
Systems in which the partial oxidation and reforming reactions predominate
would be expected to produce primarily fuel gas, with considerable oxygenated
liquids under low temperature conditions.1 Hydrogenation reactions may lead
to oil (300 to 350 C, 200 to 300 atm)2 or to methane (650 C, 80 to ZOO^atm)3.
Hydro-oxynation, at 350 C and high pressure, yields pyrolytic oil. Carbona-
ceous residue is produced in all cases. Only simple pyrolysis and partial
oxidation are practiced in the pyrolysis systems approaching commercialization.
The composition of fuel gases produced also depends upon pyrolysis condi-
tions. Where air is introduced for partial oxidation, the fuel gas is diluted
with N2, limiting its use to industrial equipment especially designed for low
volumetric heating value gases. Hydrogenation processes producing CHtf result
in higher heating value gases which may approach natural gas, depending mainly
on the presence of unreacted H2 which has an acceptable but lower volumetric
heating value than CHit. Gases containing CO/H2 mixtures can be converted to
natural gas substitutes.
Pyrol ys is Product Compos i tions . A simple laboratory pyrolysis of dried shredded
municipal wastes, with most of the inorganics removed, at about 500 C and
atmospheric pressure resulted in the products in Table 37. 5
The advantage for removal of inorganics from solid waste before pyrolysis
can be inferred from the product compositions presented in Table 37. For
example, even with prior removal of inorganics, the char produced contained a
very high ash content, making this product only marginally useful. If inor-
ganics, such as metals and glass, are not removed prior to pyrolysis, the
higher ash content would most likely relegate the char to the status of a
waste product. Therefore, resource recovery prior to pyrolysis is doubly
advantageous.
Drying of wastes prior to pyrolysis is also advantageous. Condensation
of water formed during pyrolysis produced the water fraction indicated in
Table 37. If the waste had not been dried, this fraction would be even larger,
156
-------
Table 37
SIMPLE PYROLYSIS
Fraction
Yield, weight %
Composition, weight %
Carbon
Hydrogen
Nitrogen
Sulfur
Ash
Chlorine
Oxygen (by diff.)
Heating Value,
cal /g (BTU/lb)
Fraction
Yield, weight %
Composition
Gross Heating Value,
Kcal /NCM
(BTU/SCF)
Char
20
48.8
3.9
1.1
0.3
31.8
0.2
13.9
100.0
5000 (9000)
Gas
27
Volume %
0.1 Water
42.0 Carbon
Monoxide
27.0 Carbon
Dioxide
10.5 Hydrogen
0.1 Methyl
Chloride
5.9 Methane
4.5 Ethane
8.9 C3 to C7
hydrocarbons
SO"
5172
(550)
Pyrolytic Oil
40
57.5
7.6
0.9
0.1
0.2
0.3
33.4
100.0
5830 (10,500)
Water
13
Contains
Acetal dehyde
Acetone
Formic Acid
Furfural
Methanol
Methyl Furfural
Phenol
Etc.
-------
diluting the soluble organics produced during pyrolysis and making more dif-
ficult their recovery or disposal. Feed moisture also adds to the amount of
heat which must be added to the pyrolysis reactor.
As indicated earlier, higher pyrolysis temperature increases the amount
of gaseous product. For example, for the combustible portion of a solid waste
containing 19.77 percent free moisture, yields measured in the laboratory are
shown in Table 38.6 Gas composition also varies with pyrolysis temperature.
with Table 39 showing hydrogen content increasing as temperature increases.6
On the other hand, liquid composition does not change drastically with tempera-
ture, as shown in Table 40. An additional thirty three organic compounds
were identified, but all were present in concentrations of less than about 0.3
percent.
As could be expected, char analyses in Table 41 show decreased volatile
matter as pyrolysis temperature increases.6
Pyrolysis Processes
Early work in solid waste pyrolysis was naturally analogous to wood and
coal pyrolysis or "destructive distillation." These have usually been batch
retort or furnace processes with heat applied externally. However, recent
developments in solid waste pyrolysis are in the direction of continuous modern
engineering technology.
Many pyrolysis process developments have been undertaken in recent years.7
Those believed to be under active development and to have reached the pilot
plant stage on municipal solid waste are summarized in Table 42.
Only the Monsanto, Occidental, Union Carbide, and Carborundum processes
are considered sufficiently advanced for further discussion here.
Monsanto Envi'rochem LANDGARD Process. The Envirochem LANDGARD System encom-
passes all operations for receiving, handling, shredding and pyrolyzing waste;
for quenching and separating the residue; for generating steam from waste
heat, and for purifying the off-gases. In the basic pyrolysis process, shredded
waste is heated in an oxygen deficient atmosphere to a temperature high enough
to pyrolyze organic matter into gaseous products and a residue consisting
of ash, carbon, glass and metal. A flow chart and process description for the
LANDGARD plant follow. (Figure 33).
Waste will be received from trucks and transfer trailers at the plant six
days per week and metered from two live-bottom hoppers into their respective
shredder lines. After shredding, waste is conveyed to a shredded waste stor-
age system, from which it is continuously fed into the kiln.
Pyrolysis of shredded waste occurs in a refractory lined horizontal rotary
kiln. Shredded waste feed and direct-fire fuel (oil) enter opposite ends of
the kiln. Countercurrent flow of gases and solids exposes the feed to progres-
sively higher temperatures as it passes through the kiln so that first drying
and then pyrolysis occurs. The finished residue is exposed to the highest
temperature, 982 C (1800 F), just before it is discharged from the kiln. The
158
-------
Table 38
THE EFFECT OF TEMPERATURE ON PYROLYSIS YIELDS
Pyrolysis Temperature, °C
(°F)
Product Yields, weight %
Gases
Volatile Condensibles*
Other Condensibles
Char
482
(900)
12.33
43.37
17.71
24.71
98.12
649
(1200)
18.64
49.20
9.98
HJO
99.62
816
(1500)
23.69
47.99
11.68
12.24
100.60
927
(1700)
24.36
46.96
11.74
17.67
100.73
*Portion of Condensibles which evaporate at 103 C, including water.
159
-------
Table 39
THE EFFECT OF PYROLYSIS TEMPERATURE
ON GAS COMPOSITION
Temperature , °C
(°F)
Gas Composition, Volume %
Carbon Monoxide
Carbon Dioxide
Hydrogen
Methane
Ethane
Ethyl ene
Heating Value,* Cal /NCM
(BTU/SCF)
482
(900)
33.50
44.77
5.56
12.43
3.03
0.45
99.74
2930
(312)
649
(1200)
30.49
31.78
16.58
15.91
3.06
2.18
100.00
3780
(403)
816
(1500)
34.12
20.59
23.55
13.73
0.77
2.24
100.00
3680
(392)
927
(1700)
35.25
18.31
32.48
10.45
1.07
2.43
99.99
3610
(385)
*Gross heating value by calculation.
160
-------
Table 40
THE EFFECT OF PYROLYSIS TEMPERATURE ON
ORGANIC PRODUCT COMPOSITION
Pyrolysis Temperature, °C 649 816
(°F) (1200) (1500)
Weight % of
Condensible Orqanics
Acetaldehyde
Acetone
Methyl ethylketone
Methanol
Chloroform
Toluene
Formic Acid
Furfural
Acetic Acid
Methyl furfural
Naphthalene
Methylnaphthalene
Phenol
Cresol
100.0 100.0
161
-------
Table 41
THE EFFECT OF PYROLYSIS OF TEMPERATURE
ON CHAR COMPOSITION
Pyrolysis Temperature, °C
482
900
649
1200
816
1500
927
Char Composition, weight %
Volatile Matter 21.81 15.05 8.13 8.30
Fixed Carbon 70.48 70.67 79.05 77.23
Ash 7.71 14.28 12.82 14.47
100.00 100.00 100.00 100.00
Gross Heating Value, Cal/g 6730 6840 6400 6330
(BTU/lb) (12,120) (12,280) (11,540) (11,400)
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FIGURE 33.
LANDGARD PLANT FLOW SHEET
RECEIVING
AND
STORAGE
MAGNETIC
SEPARATOR
TO
SEPARATION
AND RECOVERY
PLUME
SUPPRESSION
165
-------
kiln is specially designed (based on successful prototype operation) to uni-
formly expose solid particles to high temperatures. This maximizes the pyroly-
sis reaction. The kiln for the Baltimore demonstration plant is designed to
handle 38 MT/hr throughput. It is 5.8 meters (19 ft) in diameter and 30.5
meters (100 ft) long, and rotates at approximately two revolutions per minute.
The hot residue is discharged from the kiln into a water-filled quench
tank where a conveyor elevates it into a flotation separator. Light material
floats off as a carbon char slurry, is thickened and filtered to remove the
water, and conveyed to a storage pile prior to truck transport from the site.
Heavy material is conveyed from the bottom of the flotation separator to a
magnetic separator for removal of iron. Iron is deposited in a storage area
or directly into a railcar or truck. The balance of the heavy material, now
called glassy aggregate, passes through screening equipment and then is stored
on-site. Plans call for eventual use of the glassy aggregate in "glasphalt"
road construction.
Pyrolysis gases are drawn from the kiln into a refractory lined gas puri-
fier where they are mixed with air and burned. The gas purifier prevents dis-
charge of combustible gases to the atmosphere and subjects the gases to tempera-
tures high enough for destruction of odors.
Hot combustion gases from the gas purifier pass through water tube boilers
where heat is exchanged to produce about 2.4 tons of steam per ton of solid
waste. Exit gases from the boilers are further cooled and cleaned of particu-
late matter as they pass through a water spray scrubbing tower.
Scrubbed gases then enter an induced draft fan which provides the motive
force for moving the gases through the entire system. Gases exiting the in-
duced draft fan are saturated with water. To suppress formation of a steam
plume, the gases are passed through a dehumidifier in which they are cooled (by
ambient air) as part of the water is removed and recycled. Cooled process gases
are then combined with heat ambient air just prior to discharge from the de-
humidifier.
Solids are removed from the scrubber by diverting part of the recirculated
water to a thickener. Underflow from the thickener is transferred to the quench
tank, while the clarified overflow stream is recycled to the scrubber. Normally
all the water leaving this system will be carried out with the residue or evapo-
rated from the scrubber.
Expected stack gas and residue analyses follow on Tables 43 arid 44.
Occidental Process. A simplified flow diagram of the Occidental Research Corp.
(formerly Garrett Research & Development Co.) recycling and pyrolysis process is
shown in Figure 34. It incorporates the following operations:
1. Primary shredding of a raw refuse to minus two inches.
2. Air classification to remove most of the inorganics such as glass,
metals, dirt, and stones from the organic feed to the pyrolysis
reactor.
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RESIDUE ANALYSIS
PROXIMATE
ANALYSIS
VOLATILES
FIXED CARBON
INERTS
(WT.X DRY BASIS)
5.5
12.5
82.0
ULTIMATE
ANALYSIS
METAL (Fe)
GLASS + ASH
CARBON
SULFUR
HYDROGEN
NITROGEN
OXYGEN
21.9
60.1
14.5
0.1
0.5
0.2
2.7
HIGHER HEATING VALUE = 2500 BTU/LB
pH = 12.0
WATER SOLUBLE SOLIDS 2%
PUTRESCIBLES <0.1% (E/C ANAL. METHOD)
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3. Drying of the air classifier overheads to about three percent
moisture.
4. Screening of the dry material to reduce the inorganic content to less
than four percent by weight.
5. Recovery of magnetic metals and glass cullett from the classifier
underflow.
6. Secondary shredding of the dry organics to about minus 14 mesh.
7. Pyrolysis of the organics.
8. Collection of the pyrolytic products.
The first six of these unit operations may be conveniently grouped to-
gether as a feed preparation subsection, the primary function of which is to
provide a dry, finely divided, and essentially inorganic-free feed to the
pyrolysis reactor. An important secondary purpose is to allow the recovery
of clean glass and magnetic metals.
The subsystem shown in Figure 35 is designed to recover over 70 percent
of the glass in the refuse. A proprietary froth flotation technique is
employed to obtain a sand-sized, mixed color product of better than 99.5 per-
cent purity. Ferrous metals are recovered magnetically.
Screening the dry, air classified wastes successively at 0.635 centimeters
(1/4 inch) and 14 mesh can reduce the inorganic content to about two weight
percent. While about 12 to 14 percent of the organics pass through the screens,
these are ultimately returned to the pyrolysis circuit by subsequent glass
recovery operations.
The heart of the pyrolysis feed preparation lies in the secondary shred-
ding operation. A finely divided organic feed to the pyrolysis reactor is
desirable if high oil yields at atmospheric pressure are to be achieved.
The Occidental flash pyrolysis process involves the rapid heating in a
transport reactor of finely shredded organic materials in the absence of air
using recycled hot char to supply heat. This technique was developed to
maximize liquid fuel yields. Typical yields were shown in Table 37. The
gaseous fuel produced and a portion of the char are used on-site for process
heat. Some No. 2 fuel oil, used with product oil to quench the process gas
stream, is vaporized with uncondensed gas and also burned for process heat.
Water formed during pyrolysis and condensed from the product gas contains
methyl chloride (from polyvinyl chloride pyrolysis) and other organic contami-
nants such as shown in Table 37. In the San Diego County demonstration project
now under construction, these will be oxidized, using fuel gas for heat, in an
afterburner (process heater). If markets were available for the energy in the
char and fuel gas produced, there would be considerable incentive to develop
biological or other treatment or recovery methods to dispose of the contami-
nated water.
170
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Air streams from the drier, air classifier, and pneumatic transport sys-
tems are used as combustion air and passed through the process heater combus-
tion chamber. About 2500 cubic meters per metric ton (80,000 cubic feet per
2000 Ibs.) of hot gas from the process heater (including one-third combustion
products) are cooled by preheating various process gas streams, including com-
bustion air for the char heater, and vented through a bag filter for particu-
late control.
The pyrolytic oil produced is the single most important product. A com-
parison between typical properties of No. 6 fuel oil and pyrolytic oil is
shown in Table 45. Pilot-scale laboratory tests have indicated that the pyro-
lytic oil can be burned successfully in utility boilers.9 The San Diego Gas
and Electric Company will test and use the pyrolytic oil produced in the San
Diego plant at one of its power generating stations. It is expected that at
least 0.195 tons of pyrolytic oil will be produced per ton of solid waste (36
gal/ST).9
Union Carbide PUROX Process. PUROX is an oxygen based system to convert
municipal refuse into a clean burning fuel gas and a compact, sterile residue.
It combines the advantages of pyrolysis to produce useful and valuable by-
products and high temperatures to melt and fuse the metal and glass. This is
made possible by the use of oxygen in the conversion step.
The key element of the system is a vertical shaft furnace (Figure 36).
As-received or preprocessed waste is fed into the top of the furnace, and
oxygen is injected into the bottom. The oxygen reacts with char formed from
the waste. This reaction generates the high temperature in the hearth needed
to melt and fuse the metal and glass. This molten mixture drains continuously
into a water quench tank where it forms a hard granular material.
The hot gases formed by reaction of the oxygen and char rise up through the
descending solid waste and pyrolyze the waste as it cools. In the upper portion
of the furnace, the gas is cooled further as it dries the incoming material.
This results in the gases exhausting from the furnace at about 93 C (200 F).
The exhaust gas contains considerable water vapor, some oil mist, and minor
amounts of other undesirable constituents. These components are removed in a
gas cleaning system.
The resultant gas is a clean burning fuel with about 2821 calories per NCM
(300 BJU/SCF) gross heating value (Table 46). It is essentially free of sulfur
compounds and nitrogen oxides. It can be effectively used as a supplementary
fuel in an existing utility boiler or other fuel consuming operation. The com-
bustion products of this fuel should easily meet air pollution codes.
The Union Carbide system is a net producer of energy. The clean burning
fuel gas represents 83 percent of the fuel value of the original solid waste
charged to the conversion system. A minor portion of this fuel gas is used to
generate process steam, for building heat, and for the heat energy needed to
maintain the auxiliary combustion chamber at operating temperatures. After
deducting the aforementioned uses for the fuel gas, approximately 75 percent
of the fuel energy in the municipal solid waste would be available in the re-
maining fuel gas for other purposes. An energy balance is shown in Table 47.
172
-------
Table 45
TYPICAL PROPERTIES OF NO. 6 FUEL OIL AND
PYROLYTIC OIL
Carbon, wt. %
Hydrogen
Sulfur
Chlorine
Ash
Nitrogen
Oxygen
Gross Heat of Combustion, cal./g.
(BTU/lb.)
Specific Gravity
Pour point F
Flash Point F
Viscosity SSU @ 190 F
Pumping temperature F
Atomization temperature F
No. 6
85.7
10.5
0.7 - 3.5
-
0.5
2.0
2.0
10,100
(18,200)
0.98
65 - 85
150
340
115
220
Pyrolytic Oil
57.5
7.6
0.7 - 0.3
0.3
0.2 - 0.4
0.9
33.4
5,800
(10,500)
1.30
90*
133*
1,150*
160*
240*
*0il containing 14 wt. % moisture
173
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£174
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•go
w
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Table 46
FUEL GAS COMPOSITION
Constituent Volume %
CO 49
H2 29
C02 15
CH^ 4
C2H2 + 1
N2 + Argon 2
Totals 100
175
-------
Table 47
USAGE OF AVAILABLE ENERGY
1000 ST/D OXYGEN REFUSE
CONVERTER FACILITY
BTll/Hour Percent
Available Energy in Refuse * 416,000,000 100
Energy Losses in Conversion Process + 70,000,000 17
Energy Available in Fuel Gas 346,000,000 83
Fuel Gas Uses
Process Steam 16,000,000 4
Building Heating 10,000,000 2
Energy to Maintain Auxiliary Combustion
Chamber at Operating Temperature 7,000,000 2
Net Energy Available in Fuel Gas 313,000,000 75
Electric Power Generation 30,000 KW ±
Electric Power Used in Plant 5,000 KW
Electric Power Available for Export 25,000 KW
*Based on a refuse heating value of 5000 BTU/lb., this is calculated as (5000)
(2000) (1000)/24.
•^Includes latent heat of moisture In refuse, sensible heat of fuel gas, heat
content of molten slag and metal, and heat leak.
±Based on combustion of the net fuel gas in a gas utility boiler with an
efficiency of 10,433 BTU/KWH (32.7% overall efficiency).
176
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If the fuel gas is used as a supplementary fuel in an existing fossil
fired steam boiler, the net energy production is shown in Table 47. For
example, the fuel gas from a 1000 ST/day disposal facility could produce
30,000 KW of electric power. Electric power required in the refuse facility
is approximately 5000 KW (including power required to separate oxygen from air),
resulting in 25,000 KW available for use elsewhere.
The residue produced from the noncombustible portion of the refuse is
sterile and compact. Because it has gone through the molten state, it is free
of any biologically active material and has been fused to a minimum volume.
There is no need to use sanitary landfill techniques for disposal, and it is
suitable as a construction fill material. The volume of the residue is two to
three percent of the volume of the incoming refuse, depending upon the amount
of noncombustible material contained in the refuse. This compares with a
residue volume of 5 to 15 percent for a conventional incinerator.
An important feature of the PUROX system is that a minimum amount of other
liiatenals are introduced and processed with the refuse. This is shown clearly
by comparing PUROX with a conventional refractory incinerator. Because a con-
ventional incinerator burns the refuse with an excess amount of air, about
seven tons of air are introduced per ton of refuse combusted. This compares
with one-fifth of a ton of oxygen introduced per ton of refuse for the PUROX
system. This is a 35 fold difference. This difference in input is reflected
by & 20 to Id difference in volume of gas to be cleaned. This advantage is, of
course, offset in part by the cost of separating oxygen from air, or for pur-
chasing oxygen,
CarborunduiTi Tor rax System. The Torrax (or Andco-Torrax) System is designed to
convert the combustibles in mixed municipal solid waste to a fuel gas by
partial uxidat on with air, while melting non-combustibles at temperatures up
to 1650 C (3000 F). The waste is processed without sorting or pre-treatment.
The combustible gas produced is of a relatively low heating value, 1130
to 1400 kccu/NCM (120 to 150 BTU/SCF). The fuel gas can be used in various
ways as a source of energy, but, because of its low heating value, it will
usually ba advantageous to burn the gas and to recover the heat in a waste heat
boiler onsite to produce steam for export, or for conversion to electrical
power,
The To^-ax System consists of the following major subsystems:
1, Gasifier for pyrolysis slagging
2. Secondary combustion chamber to complete oxidation of volatile
materials from pyrolysis
3. Regenerative towers for primary combustion air preheating
4. Waste heat boiler to burn fuel gas and convert energy to steam
5. Gas cleaning system
A diagram of the system is provided in Figure 37.
177
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ORRAX SYSTEM
LCCTftOSTATIC
PPKIPITAT0R
as
COOLCft
WASTE I4£AT
BOILEft
SCCONMftY
OMDfiUSTION
astro
FIGURE 37. ANDCO-TORRAX SYSTEM
178
-------
Grapple bucket lifts are used to charge waste into the inlet hopper of
the gasifier without sorting or pre-treatment, except that pieces of refuse
larger than one meter in any dimension are sheared before charging. An auto-
matic feeder moves the waste from the hopper into the shaft of the gasifier,
as shown in Figure 38. The waste solids then descend by gravity through the
drying, pyrolysis, the primary combustible zones of the gasifier. Primary
combustion air from the regenerative towers at 1100 C (2000 F) is introduced
with some auxiliary fuel at the tuyeres near the base of the gasifier, while
the pyrolysis vapors are drawn out of the gasifier in the drying area. The
molten slag tap into a water quench tank to produce a black, glassy aggregate
free of carbon or putrescible material. The quantity and composition of the
aggregate will vary with the waste fed, but an example is provided in Table
48. The size of a single gasifier is limited to about 11 MT/hr (300 ST/day).
The pyrolysis vapors from the gasifier at 450 to 550 C (800 to 1000 F) are
thoroughly mixed with minimum excess air (10 to 15 percent) and burned at
1200 to 1260 C (2200 to 2300 F) in the secondary combustion chamber. The high
temperature causes flyash and other inert carry-over materials to fuse and be
slagged out of the stream. This slag, which is water-quenched, is approxi-
mately 10 percent of the total aggregate produced.
Two refractory-filled steel shells, called regenerative towers, are used
to recover heat from about 15 percent of the hot combustion gas to heat the
primary combustion air. These are automatically and alternately controlled to
heat the air to 982 to 1149 C (1800 to 2100 F) and to cool that portion of the
combustion gas used in this subsystem.
The major portion (85 percent) of the combustion gas from the secondary
combustion chamber is cooled in the waste heat boiler to about 260 C (500 F),
producing as much as three tons of steam per ton of municipal solid waste.
The waste gases from the regenerative towers and the waste heat boiler are
combined, cooled to 300 C (550 F) by water spray or tempering air, and cleaned
with a conventional air pollution control system, such as a scrubber or electro-
static precipitator. The normal gaseous emission will contain 81 percent N2,
16 percent C02, and 3 percent 02 by volume.
Sewage sludge, waste oil, unshredded tires, and polyvinylchloride have been
burned with municipal waste in the Torrax pilot unit.
Summary
Each of the pyrolysis processes discussed will undergo sufficiently large-
scale demonstrations, in the period 1976-1977, so that the successful processes
can be considered as an alternative for municipal solid waste disposal. The
obvious advantages of converting solid waste to a valuable energy resource
merits a very close examination of this possibility.
179
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R£f USE PLUS
DRVING ZOM£
COMBUSTION m
PRIMARY
COMBUSTION
AND
Torrox
Unit
SLAG
MOP-OFF
AND QU£NCU
FINAL
COMBUSTION
5CCOMOAPY
(X)MBUSTIOM
CWAMBtR
FIGURE 3& ANDCO-TORRAX UNIT
180
-------
Table 48
TORRAX AGGREGATE
Constituent
Si02
Alo03
TiC2
Fe203
FeO
MgO
CaO
MnO
Na20
K20
Cr203
CuO
ZnO
Dry Bulk Density
True residue
Average %
(by weight)
45
10
0.8
10
15
2
8
0.6
6
0.7
0.5
0.2
0.1
1.40 g./cc
2.80 g./cc
Range %
32. -58.
5.5-11.
0.48-1.3
0.5-22.
11. -21.
1.8-3.3
4.8-12.1
0.2-1
4. -8. 6
0.36-1.1
0.11-1.7
0.11-0.28
0.02-0.26
Screen size
Quantity,
% of municipal
solid waste charge
4% >3 1/2 mesh (5.66 mm)
2% <30 mesh (0.59 mm)
3-5 by volume
15-20 by weight
181
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REFERENCES
1. Shuster, W. W. Partial Oxidation of Solid Organic Wastes. Final Report.
Bureau of Solid Waste Management. SW-7RG. 1970. Ill pages.
2. Groner, R. R., et al. The Chemical Transformation of Solid Wastes. AIChE
Symposium Series 68(122):28-34. 1972.
3. Feldman, H. F. Pipeline Gas From Solid Wastes. AIChE Symposium Series
68(122):125-131. 1972.
4. Appell, H. R. et al. Hydrogenation of Municipal Solid Waste with Carbon
Monoxide and Water. Proceedings of National Industrial Solid Wastes
Management Conference. Houston, Texas. March 24-26, 1970. University of
Houston and Bureau of Solid Waste Management. Pages 325-379.
5. Mallan, G. M. and Titlow, E. I. Energy and Resource Recovery from Solid
Wastes. Occidental Research Corp. (Presented to Washington Academy of
Sciences. March 13-14, 1975. College Park, Md.)
6. Pyrolysis of Solid Municipal Wastes. Prepared for National Environmental
Research Center, Cincinnati, Ohio. NTIS Report PB 222-015. Springfield,
Va. July 1973. 74 pages.
7. Levy, S. J. Pyrolysis of Municipal Solid Waste. Waste Age. October 1974.
8. Sussman, D. A. Baltimore Demonstrates Gas Pyrolysis. First Interim Report.
U.S. Environmental Protection Agency. SW-75d.l. Washington, D. C. 1975.
24 pages.
9. Levy, S. J. San Diego County Demonstrates Pyrolysis of Solid Waste. U. S.
Environmental Protection Agency. SW-80d.2. Washington, D. C. 1975. 27
pages.
182
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CHAPTER XII
INSTRUMENTATION AND CONTROLS
Modern thermal processing systems are becoming much more complex, incor-
porating energy recovery, resource recovery, air and water pollution control,
or other features which require instrumentation to a degree greater than that
previously required just for proper combustion control.
Instrumentation is needed to:
1. Control and monitor the basic incineration or pyrolysis process.
2. Control and monitor associated subsystems such as steam generation,
power generation, and resource recovery.
3. Control and monitor environmental subsystems such as flyash col-
lection, wastewater treatment, and visible plume control.
4. Protect equipment, for example, against corrosion, heat destruction,
mechanical destruction, and operator abuse.
5. Collect data for calculating disposal costs and charges, making
improvements, and designing additional facilities.
The degree of automatic versus manual control will depend not only on
technical considerations, but on capital and operating budgets, and personnel
policies regarding the experience and qualifications of plant operators. In
some cases, television monitoring, computer control, and digital data acquisi-
tion systems may be justified.
Instruments measure, indicate, transmit and record important process
conditions, including flow, temperature, pressure, weight, position, time,
speed, voltage and composition. Controls change these conditions, either
manually or automatically, in response to a signal from a measuring instru-
ment.
Control systems, either manual or automatic, ,are necessary because, as
in any process, many input factors are variable, but the end result must be
the same. That is, for example, an incinerator should process refuse to a
substantially reduced volume of inert residue containing no putrescible
materials without harming the environment, the equipment, or personnel,
regardless of the composition and wetness of the refuse, atmospheric con-
ditions, time of year, equipment condition, or other vagaries.
Incinerator Process Instrumentation
Effective combustion in incinerator furnaces requires the use of manual
and/or automatic controls. Combustion is controlled by residence time,
183
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furnace temperature, contact between combustibles and oxygen, and use of
auxiliary fuel. Residence time, in turn, is controlled by grate speed,
assuming adequate raw feed (limited by crane capacity). Furnace temperatures
are controlled by the ratio of total air flow to refuse and by overfire and
underfire air rates. The importance of excess air in determining furnace
temperatures was discussed in Chapter IX. Contact is a function of furnace
and grate design, but some control is possible by variations in underfire air
and mechanical grate action. Most of these variables are interdependent and
a change in one is likely to require a change in another.
Following is a discussion of the basic requirements for control of the
major variables of an incinerator, as illustrated in Figure 39.
Underfire Air Control. This is the primary source of oxygen for solid waste
combustion. Requirements are affected by the nature of the waste, including
percent combustibles, density, moisture content, and determined only by
measuring performance (e.g. visible appearance of burning bed, reduction of
refuse volume, burnout). Insufficient underfire air will result in incom-
plete combustion; large excesses may increase flyash generation. Since
continuous sensing and measurement of waste characteristics is impractical,
the underfire air can be controlled at a present level by sensing the flow
in a duct and adjusting flow by adjusting dampers or fan speed. A simple
control schematic is shown in Figure 40.
Overfire Air Control. This is the secondary source of oxygen for combustion,
especially for oxidizing refuse decomposition products contained in the gases,
and the primary source of dilution air for cooling. Requirements are affected
by the nature of the waste, but can be dynamically controlled by temperature
sensing. Temperatures which are too low result in unburned gases and odors;
furnaces or steam tubes can be damaged (by heat destruction and/or corrosion)
if temperatures are too high. The overfire air can be controlled at a present
level as with the underfire air, or it can be controlled by adjusting dampers
or fan speed in response to temperature measurement. A simple temperature
control schematic is shown in Figure 41. Overfire and underfire air ratio
control is sometimes used.
Draft Control. Draft refers to the pressure distribution required for main-
tenance of the proper flow in the desired direction. A prime requirement is
to keep the furnace under a slight vacuum to prevent the escape of hot gases
and odor. In a modern incinerator, draft is maintained by the use of an
induced draft fan which compensates for variations in overfire and underfire
air by drawing outside air into and through the furnace, often from the pit
area for odor and dust control. Induced draft fan operation can be preset,
or its speed can be controlled in response to a pressure measurement. A
simple control schematic is shown in Figure 42.
Auxiliary Burner Controls. These are sometimes used as a source of addi-
tional heat to sustain combustion during startup, transient, and wet feed
184
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O"
2
o
o
o
cc
O
oc
UJ
O
O)
LU
CC
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/
/
/
/
DAMPER
MOTOR
FLOW
TRANSMITTER
INDICATING
CONTROLLER
FIGURE 40. UNDERFIRE AIR FLOW
CONTROL SYSTEMS2
FIGURE 41 FURNACE TEMPERATURE
CONTROL SYSTEM2
INDICATING
CONTROL LC*
TEMPERATURE
TRANSMITTER
FIGURE 42. FURNACE PRESSURE
CONTROL SYSTEM2
FIGURE 43. SPRAY CHAMBER TEMPERATURE
CONTROL SYSTEM2
186
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periods. Generally on-off burners are sufficient, but standard burner train
controls are required for safety, e.g. flameguard and purging systems. Burners
are useful for systems generating steam to sustain output when sufficient solid
waste is not available to meet peak steam demands, and when the heating value
is low due to wetness, or for other reasons.
Grate Controls., The grates must provide solids movement, agitation, and pas-
sage for underfire air. Grate speed controls residence time, and it can also
be used to control temperature. As many as four grate sections with separate
speed controls have been used. Residence time requirements are affected by
the nature of the waste, but, as previously noted, waste characteristics can-
not be continuously measured. Therefore, sufficiency of residence time (and
temperature and turbulence) is judged by visually observing combustion and
periodically measuring burnout. Grate speed and, if possible, bed depth and
turbulence are manually adjusted accordingly.
Feed Conveyors or Crane Control. These are required to bring the waste from a
storage area to the combustion zone. Cranes are manually operated simply to
keep feed hoppers full. Feed conveyors, where used, require speed control,
obviously to coincide with grate speeds. Ram feeders are finding some favor,
and hopper gates have been used to control solid feed rate from the hoppers to
the grates.
Flue Gas Cooling Control. Cooling is practiced to reduce gas volume and to
protect downstream equipment, e.g. induced draft fans, flyash collection
equipment, and the stack from heat damage. Cooling has most often been ac-
complished with water sprays. Dilution with cold air can be used, but the
increased gas volume adds greatly to the expense of air pollution control.
The newest systems incorporate boilers for heat recovery. If water is inex-
pensive, and if the pollution control device performance is not inordinately
temperature sensitive (e.g. scrubbers), simple water flow controllers or even
manual valves to control water to the sprays may be sufficient, if accompa-
nied by temperature indicators and alarms. In many cases, as for cooling
prior to electrostatic precipitators, more sophisticated temperature control
is required, such as flow control of water rate in response to temperature
measurements. A control schematic is shown in Figure 43.
Flyash Recovery Control. Controls are essential, but vary with the type of
pollution control system(s). For example, a venturi scrubber may operate
with a fixed amount of water, and an air flow between the limits set by the
maximum induced draft fan capacity, and by the necessity for maintaining
sufficiently high flow and pressure drop to insure efficient particulate
control. One method of controlling venturi scrubber operation uses an air
bleed damper to maintain scrubber pressure drop.
In addition to gas temperature control, an electrostatic precipitator
normally requires controls for voltage, rapping, hopper temperature, and ash
discharge. The control systems are usually supplied by the manufacturer.
187
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Wastewater Control. Controls are normally required for at least pH and dis-
charge and recycle flow rates, and in some cases, temperature. These may be
necessary to meet pollution regulations, scrubber and cooling requirements,
and to minimize corrosion. Other wastewater properties are usually monitored
by laboratory tests.
Indicating and Recording Instrumentation. Indicating and recording instruments
are required for supervision of operation, troubleshooting, and record keeping.
These include, for example:
Pressures
1. Underfire air duct
2. Overfire air duct
3. Furnace combustion chamber
4. Furnace outlet
5. Flyash collector
6. Induced draft fan inlet
Temperatures
1. Water leaving feed chute
2. Furnace outlet
3. Other furnace zones
4. Spray chamber outlet
5. Flyash collector
6. Stack
Flows
1. Underfire air (to each section, if separated)
2. Overfire air
3. Water to cooling sprays
4. Water to scrubber
5. Water to flyash hoppers
6. Recycle water to quench
Alarms
Alarms which should be included are:
1. High temperature - charging hopper
2. High temperature - stoker bearings
3. Low pressure - underfire air duct
4. Low pressure - overfire air duct
5. High temperature - furnace
6. High pressure - furnace
7. High temperature - flyash collector
8. Low temperature - flyash collector
9. Low water pressure
10. High temperature - stack
188
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11. Low temperature - stack
12. Low pressure - instrument air
13. Conveyor stoppage
14. Low pressure - cooling water supply
15. High temperature - ID fan bearings
16. High reading - smoke detector
The above alarms are meant as examples. Two or more times this number may be
used in a modern incinerator, particularly when steam is produced. Alarms
should contain both a visual and a siren feature, with the latter requiring
manual shutoff. Alarms are meant to induce operator attention, and response
when necessary in accord with written instructions and his training to handle
unusual situations.
Other Instrumental on. Depending on the degree of safety, automation, and
record keeping desired, and environmental requirements, extensive additional
control and instrument systems may be incorporated:
I, Smoke density recorder
2. Measurement of ambient air temperature, barometric pressure,
wind velocity and direction
3. Emergency systems e.g. in the event of power, instrument, dust
collector, or fan failures, excessive temperatures, and fire
detection control
4. Environmental and ventilation systems e.g. for fugitive dust
control, and waste water treating
5. Cascade control systems
6. Computer control
7. Automatic weighing
8. TV monitoring of combustion flames (color), smoke stack emissions,
plant entrance grates, and critical conveyors
9. Stack gas oxygen monitor
10. Stack gas combustibles monitor
In addition, a laboratory is useful for refuse, residue, flyash, water, and
wastewater analyses, and in some cases for specification and quality control
of materials purchased.
As seen in Table 49, an example of an incinerator instrument list, a
rather extensive array of devices can be used to achieve proper control, even
without stearn generation or resource recovery.
The addition of a steam boiler to the incinerator increases the instru-
mentation requirements. Controls for feedwater treatment and flow, steam
pressure, steam temperature (if superheated), steam drum level, steam flow,
condensers, and appropriate safety devices are required. Tube metal tempera-
tures are particularly important because of potential corrosion problems.
Controls are required for soot blowers, which are usually specified for tube
cleaning, and for pump and fan drives where steam is used. A reference text
should be consulted for typical control requirements for steam boilers.'
189
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Table 49
MONITORING EQUIPMENT9
MEASUREMENTS
Flue Gas:
Flue gas flow rate
recorder
Carbon dioxide analyzer
and recorder
Oxygen analyzer and
recorder
Water vapor concentration
recorder with infrared
sampling and conditioning
equipment
Stack emission particulate
loading recorder including
continuous sampling
system
Temperature recorder,
24-point, 1-1 point with
chromel-alumel thermo-
couples
Process Water:
Water flow rate
recorder
pH analyzer and recorder-
2 points
Temperature recorder-6
point
Turbidity recorder with
flow chamber, light
source, and transmitter
Combustion Air:
Underfire air and overfire
air flow recorders with
special duct work arrange-
ments for flow measure-
ments
190
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Table 49 (Continued)
MEASUREMENTS
Temperature recorder (12,
positions) for underfire,
wall cooling, and over-
fire air
Pressure recorders for
draft and pressures in
air zones, also including
furnace, dust control
equipment, and stack
conditions
Forced draft fan motor
current recorder . . .
Furnace:
Refuse feed rate recorder .
Temperature recorder-^4
point with chrome!-
alumtl thermocouples for
refractory temperatures
to 2,000° F
Temperature recorder-24
point with platinum-rhodium
thermocouple for refractory
and face temperatures to
2,700° F
Temperature recorder-6
point with radiamatic
elements in silaramic
tubes for gas temperature
measurements
191
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Feed preparation and resource recovery, such as magnetic metal separa-
tion, shredding, air density separation, glass separation, aluminum separa-
tion and other new developments require very special operational controls as
well as conveying systems controls, fugitive particle control, and other
controls somewhat akin to the mining industry.
The use of pretreated refuse as a supplementary fuel in pulverized coal
suspension-fired boilers for power or steam generation, now under development,
will require feed preparation controls as indicated above. However, it is
expected that the boiler controls will remain essentially the same, since
refuse is expected to be limited to 10 to 20 percent of the total fuel
requirements.
Pyrolysis Process Instrumentation
Pyrolysis processes are in various stages of development, as explained in
Chapter XI. Due to the complexity of these processes, involving combustible
fuel products, the instrumentation and control requirements are likely to be
quite extensive. Since all the processes are, at this time, proprietary in
nature, little information is available on instrumentation. It is likely
that the process owners will supply a design package including necessary
instrumentation and controls.
Feed preparation and resource recovery practiced with pyrolysis will
likely be similar to that practiced with incineration. Some idea as to the
potential complexity of the pyrolysis step can be gotten by referring to
typical instrumentation for chemical reactors and pyrolysis furnaces.,
Types of Instruments and Controls. Each parameter that is measured or
detected can be indicated and/or recorded locally at the point of detection;
transmitted to a remote indicator or recorder; or the measurement can be used
to actuate local or remote control or alarm circuits. Multipoint recorders
to monitor 6 to 24 temperatures are in widespread use for cost reasons, in
spite of disadvantages in response time and opportunity for misinterpretation
as compared to separate instruments. Numerous choices are available for each
instrument function depending on the service required. For example, the
choice of a temperature sensor depends upon applicable temperature ranges,
accuracy, physical size, stability, repeatability, response time, sensitivity,
interchangeability, maximum distance to readout, and suitability for the con-
trol or alarm devices to be used. The application of various types of sens-
ing and measuring devices to thermal processing equipment is outlined in
Table 50.
Just a few of the other instrumentation choices to be made are related
to pneumatic vs. electronic controls, including consideration of the cost of
a clean dry air supply for pneumatic control; type, size, and speed of
indicating and recording instruments; modes and mechanisms for control;
remote vs. local instrumentation; control room layout; and selection of
mechanisms for the control action, including control valves, dampers, motor
speed controls, and the like. Pneumatic controls are much more widely used
than electronic controls, but the increasing availability of electronic
192
-------
Table 50
TYPICAL INSTRUMENTATION TO BE
CONSIDERED FOR THERMAL PROCESSES
APPLICATIONS
MEASURING DEVICES
Very high temperatures for combus-
tion zones (greater than 1100 C)
high temperatures for incinera-
tors and pyrolysis reactors (600-
1100 C)
Moderate temperatures for
ambient measurements, water,
driers, steam (20-600 C)
Liquid levels for quench and
wastewater tanks, feedwater and
steam drums
Solid levels for feed hoppers,
flyash hoppers
Draft pressures for furnaces, ducts,
air pollution control devices,
stacks (0.1 to 1.1 atmospheres
absolute) and differential pressures
for flow and level determination
Air, steam, water pressures (greater
than 1.1 atmospheres absolute)
Air, flue gas, fuel gas, and steam
flows
Low gas flows for special purposes
Liquid flows for fresh water, boiler
feed water, wastewater, fuel,
neutralization, water sprays
Pyrometers (infrared, radiation,
optical), platinum/rhodium thermo-
couples (sheathed)
Chrome!/alumel, chromel/constantan,
and stainless steel thermocouples,
resistance temperature detectors
(platinum)
Iron/constantan thermocouples, resist-
ance temperature detectors (platinum,
nickel, copper), filled elements,
bimetallic thermometers, liquid-in-
glass thermometers, thermistors
Floats, displacement sensors, ultra-
sonic detectors, gauge glasses, dif-
ferential pressure detectors, tape
level gauges
Capacitance probes, ultrasonic detec-
tors, radiation gages, tape level
gauges
Diaphragms, bellows, manometers,
inclined gauges, bell-type gauges
Bourden tubes, diaphragms (6-20
atmospheres maximum), bellows (6-50
atmospheres maximum)
Orifices, venturi tubes, flow nozzles,
pi tot tubes, elbow taps - with differen-
tial pressure measurement
Rotameters, laminar flowmeters, gas
displacement meters
Orifices, venturi tubes, flow nozzles,
weirs, rotameters, turbine flowmeters,
liquid displacement meters, metering
pumps, self-contained regulators
193
-------
Table 50 (Continued)
APPLICATIONS
MEASURING DEVICES
Electrical characteristics for
motors, heaters, electrostatic
precipitators, lighting
Motion for fans, stokers, conveyors
Position for dampers, valves,
controls
Visual observation of furnace and
reactor interiors, loading and
unloading operations, conveyor
belts, stack effluents, plant
entrances
Analyzers for stack and waste water
emissions, fuel products, ambient
air quality
Weight of full and empty trucks (raw
refuse, resource recovery products,
residues), crane bucket contents
Vibration of fans and other rotating
devices
Electrical measurements for power
current, voltage in fan, pump, and
other motors, electrostatic precip-
itators, control systems
Voltmeters, ammeters, watt meters,
spark meters (electrostatic precipi-
tators)
Tachometers, counters
Deflection meters
Observation ports, mirrors, closed
circuit television
Multitude of specialized instruments
available - some additional discussion
in Chapter XIV
Platform scales (discussed in Chapter
VII), load cells
Probes (transducers) to measure dis-
placement, velocity, or acceleration
with readout and preferably with warn-
ing and shutdown capabilites
Wattmeters, ammeters, voltmeters,
spark meters (precipitators)
194
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controls and their adaptability to computers without transducers to convert
pneumatic signals, may increasingly justify their use. Instrumentation de-
sign is the function of instrumentation specialists working for the design
engineering organization, guided by the needs of the client and by the recom-
mendations of the major equipment manufacturers.
Operational Problems Involving Instruments and Controls. An instrumentation
system which is carefully thought out and well designed with cost-effective-
ness choices, should result in a successful operating facility. However,
proper installation, routine calibration, and maintenance are also essential
for accurate, safe, and reliable operation. Contract maintenance service
should be considered if staff personnel are not appropriately qualified,
but operators should be trained for every day problems such as chart changing,
inking, and simple part replacement.
Enclosed or protected instruments will have less problems from dust,
dirt, water, and abuse. Sensing devices will require protection in certain
services, such as in the combustion chamber and flue gas ducts. Considera-
tion may be given to duplication of critical sensors and/or instruments.
Pneumatic instruments require dry, clean air. Especially good drying is
essential where air lines are exposed to ambient conditions in cold climates.
Virtually all instruments and controls are directly or indirectly dependent
on electrical power. The system should be "fail-safe" in the event of a
power outage or other instrument failure.
Of course, an inventory of ink, charts, and spare parts should be main-
tained and used. From an operator standpoint, simplicity and ruggedness are
desired. Dampers, for example, should be capable of withstanding the
abusive gases, have fine adjustment, lock in place, and have remote bearings,
if possible.
TV monitoring of unmanned and critical areas can reduce manpower needs
and minimize down time, damage, and unsatisfactory performance. It has been
used to monitor conveyors for jams, fire boxes for good combustion, automatic
weigh scales, and stacks for smoke. Difficulties may be encountered in
keeping camera lenses clean in dirty services; similar problems may be
encountered with smoke meters. Air purging can help overcome this problem.
Future Needs. With the advent of complex sophisticated thermal processing
systems, including steam generation, pyrolysis, resource recovery, and
pollution controls, instrumentation and control systems needs become cor-
respondingly more extensive. As in other process systems, TV monitoring and
computer control should become useful tools.
The most important single undeveloped area appears to be the control of
parameters dependent on the nature of the solid waste. For example, feed
rate, and underfire air cannot be automatically controlled because of a lack
of a sensor for refuse moisture, heat of combustion, and burning rate.
195
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Process instrumentation hardware and design engineers should be
utilized to provide systems that adequately meet the operational and
performance requirements for the least overall initial operating costs.
196
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REFERENCES
1. Liptak, B. G. Instrumentation in the Processing Industries. New York,
Chi 1 ton Book Company, 1973. 950 pages.
2. Stickley, J. D. Instrumentation Systems for Municipal Refuse Incinerators.
Proceedings, 1968 National Incinerator Conference, New York. American
Society of Mechanical Engineers, May 5-18, 1968. Pages 303-308.
3. Garrett, C. J. Accurate Incineration Control: An Interesting and
Important Engineering Challenge. In: Proceedings, 1970 National
Incinerator Conference, Cincinnati. American Society of Mechanical
Engineers, May 17-20, 1970. Pages 128-140.
4. Stephenson, J. W. Incinerator Design with the Operator in Mind. Pro-
ceedings, 1968 National Incinerator Conference, New York. American
Society of Mechanical Engineers, May 5-8, 1968. Pages 287-294.
5. Heil, T. C. Planning, Construction, and Operation of the East New
Orleans Incinerator, Proceedings, 1970 National Incinerator Conference,
Cincinnati. American Society of Mechanical Engineers, May 17-20, 1970.
Pages 141-148.
6. Hilsheimer, H. Experience After 20,000 Operating Hours The Mannheim
Incinerator. Proceedings, 1970 National Incinerator Conference,
Cincinnati, American Society of Mechanical Engineers, May 17-20, 1970.
Pages 93-106.
7. Corey, R. C. Principles and Practices of Incineration. New York,
Wiley-Interscience, 1969. Pages 190-191.
8. Niessen, W. R., et al. Systems Study of Air Pollution from Municipal
Incineration. Volume II. A. D. Little, Inc. Cambridge. National
Technical Information Service No. PB 192-379, March 1970. Pages
H-28-30.
9. Special Studies for Incinerators for the Government of the District of
Columbia. Day & Zimmerman. Philadelphia. Public Health Service No.
1748. U.S. Department of Health, Education, and Welfare. 1968. Pages
29-37.
10. Ellison, W. Control of Air and Water Pollution from Municipal Incinera-
tors with the Wet Approach Venturi Scrubber. Proceedings, 1970 National
Incinerator Conference, Cincinnati. American Society of Mechanical
Engineers. May 17-20, 1970. Pages 157-166.
197
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CHAPTER XIII
LIQUID AND SOLID EFFLUENTS AND THEIR CONTROL
Even the most efficient thermal processing of solid wastes results in
undesirable effluents. Incineration effluents are primarily inorganic, in
the form of particulate and other chemical emissions in gaseous effluents,
dissolved and suspended materials in aqueous effluents, and solid residues.
As will be discussed in a subsequent section of this Chapter, pyrolysis
effluents may also be high in organic materials.
The unit processes which are commonly used in incinerator plant design
and the associated discharges to air, land and water are shown in Figure 44.
This Chapter describes discharges to land and water, while air emissions are
treated in Chapter XIV, "Air Pollution Control." The recovery of useful
materials from residues is covered in Chapter XVII.
Hand!i ng and Storage Effl uents
Dumping, handling, and storage of municipal solid waste produces dust
and litter, as well as odors. Therefore, the storage pits and tipping floor
are areas which deserve major attention, if problems from these sources are
to be averted.
Litter, consisting mainly of paper and other debris, results from acci-
dental spillage in and around the plant. Dumping of refuse produces air-
borne dust which may be either organic or inorganic. Obnoxious odors result
primarily from the putrefaction of food wastes and other organic materials.
Odor problems are especially troublesome when waste is held in the storage
pits for long periods. The combined effect of dust and odors, if uncon-
trolled, create a condition which is very unpleasant for employees who work
in these areas. Dust can also adversely affect instrumentation and controls,
and mechanical and electrical equipment. Litter is primarily a nuisance
which creates an untidy appearance of the plant and grounds.
Frequent sweeping of the tipping floor effectively removes litter.
Cleaning of the storage pit is facilitated if the pit is divided into sec-
tions. Each section of the pit should be emptied at frequent intervals so
that putrescibles may be removed. The tipping floor and pit floor should
be washed with cleaning-disinfecting solutions for control of odors and
insects.
Wetting the solid waste in the storage pit by use of water sprays is the
most frequently used means of dust control. Some incinerator plants control
dust and odors in the pit by locating intake ducts for the forced draft fans
within the pit area, sweeping these pollutants into the fan intake and then
into the furnace, thus preventing them from being dispersed throughout the
plant.
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199
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The future may bring greater emphasis on the design of enclosed material
handling systems to permit positive exhaust of air through purification sys-
tems. When such provisions are made, dust laden air can be processed in bag
filters or other means to prevent release to the atmosphere. Odors in ex-
haust air can sometimes be eliminated by addition of ozone2 or by passing the
air through beds of activated carbon.
Provision should be, but is not always, made for treatment of water used
for dust control, and for washdown of the tipping floor, charging floor, and
storage pit. Runoffs of this type are frequently drained directly to sanitary
sewers or surface waters. Preferably, all these wastewaters should be treated
with the process wastewater.
Incinerator Residues
Incinerator residues are defined here as the solid materials remaining
after combustion. Classifications of residue include grate residue, grate
siftings and flyash. The quantity of residue produced, when front end
resource recovery is not practiced, generally ranges from 20 to 35 percent by
weight of the original refuse, but usually only about 5 to 15 percent by
volume. The proportions of grate residue, siftings, and flyash depend to a
large extent on the design of the incinerator and of the air pollution control
equipment.
Grate Residue and Siftings. Residue discharged from burning grates consists
of ash, clinkers, cans, glass, rocks and unburned organic substances. Grate
siftings are similar materials which have become sufficiently reduced in size
to filter through the grate openings or to drop between the grate and the
furnace wall. Bulk densitites of grate residue and siftings, as measured in
one test, were 640 and 1055 kilograms per cubic meter (1040 and 1780 Ibs/
cubic yard), respectively.^
Composition of combined incinerator residues from three sources are
given in Table 51. Since seawater was used for sluicing at the Oceanside
plant, a portion of the residue measured was contained in the sluice water
runoff. The Oceanside and Stamford plants employed rocking grates with com-
paratively large grate openings. The Washington, D.C. data were obtained
from five batch fed plants.
Siftings may be recovered wet or dry depending on the incinerator design.
However, most grate residues are recovered from quench water. The wet resi-
dues are drained as they are conveyed from the furnace. The siftings and
wet residue are usually trucked to nearby landfill sites. These should be,
but are not always, water tight trucks. If resource recovery is practiced,
for example, magnetic recovery of ferrous metals, the separation equipment
is built into the incinerator plant.
Flyash. As explained previously, flyash is that portion of the solid residue
from combustion carried by the combustion gases. It arises as a solid ef-
fluent after recovery from flue gases using various air pollution control
200
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Table 51
COMPARISON OF RESIDUE COMPOSITIONS4
Metals & Mill Scale
Glass
Ceramics, Stones
C linkers
Ash
Organic*
Residue Solids in Conveyor
Runoff Water
Oceans ide,
Wt. %
19.85
9.48
1.51
24.11
16.10
1.89
27.06
100.0
Stamford,
Wt. %
23.58
36.63
4.73
17.23
14.08
3.75
0
100.0
Wash. , D.C.
Wt. %
29.5
44.1
2.0
--
15.4
9.0
100.0
* Good measure of burnout
201
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devices. The flyash consists of dust, cinders, soot, charred paper and other
partially burned materials. Most flyash particles range in size from 120 to
less than 2 microns.5 Size distribution within this range is extremely vari-
able.
Flyash from efficient incineration is predominantly inorganic and con-
sists largely of.the oxides or salts of silicon, aluminum, calcium, magnesium,
iron and sodium. Compounds of titanium, barium, zinc, potassium, phospho-
rous and sulfur4 may be present in small amounts. Trace quantities of many
other elements may also be present.
Dry flyash is difficult to handle and can be easily picked up and scat-
tered by the wind. Therefore, it should be stored in closed containers. If
open storage is necessary, barriers should be erected and the surface of the
ash pile kept moist with water sprays. Transportation to the final disposal
site in covered trucks or closed containers is recommended. Some plants
reduce dust problems by intermixing ash with wet residue, or by topping off
the truck with a layer of wet residue.
Land Disposal of Residue. Although incinerator residue is comprised mainly of
insoluble inorganic material, the small fractions of soluble inorganics and
organics require land disposal methods usually classified as sanitary land-
filling. Guidelines for sanitary landfill site selection, design, and opera-
tion are available. >'
Sanitary landfill practices are designed to avoid pollution of surface
and ground waters, odors, rodents, insects, and other vectors requires
spreading the solid wastes in thin layers, compacting to the smallest prac-
tical volume, and applying a compacting cover material at the end of each
operating day, or more often. Practices for a landfill disposing of only
incinerator residue may differ from disposing of mixed municipal solid waste
because of the lower organic content (causing less gas formation) and higher
density (requiring less compaction). However, measures designed to avoid
water pollution, for example, the use of impervious membranes as a barrier
against groundwater intrusion and leaching from rainfall, interception of
rainfall and surface waters, and/or treatment of leachate, will most likely
be similar for an incinerator residue landfill.
The amount of landfill leaching which will occur is dependent upon the
composition of the residue, its permeability, and the degree of fusion of
external and internal surfaces. Also, when water contacts the residue, it
almost invariably picks up fine solid particles which contribute to increased
levels of suspended solids, turbidity, and BOD (from organic content) in the
water. Because the presence of organics in the residue may lead to particu-
larly harmful environmental effects, the degree of burnout during incinera-
tion is an important variable.
There is a good deal of disagreement regarding the efficacy of landfill
for disposal of incinerator residues. It has been determined that the water
soluble portion of the residue amounts to approximately 4.75 to 5.75 percent
of the dry weight of material placed.9 Data are generally not available,
however, on the extent to which this material is removed by leaching or the
202
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rate at which leaching takes place. Leaching tests conducted in Germany
suggest a relatively low mineral content of water after the elutriation of
finely ground incinerator residue with distilled water. The initial eluate
contained approximately 115 mg/1 minerals, and the tenth eluate contained less
than 20 mg/1. By comparison, similar tests conducted using composted refuse
produced concentrations of calcium and magnesium (as CaO and MgO) which were
an order of magnitude higher than in the residue leachate. The explanation
proposed was that as the residue reaches a combustion temperature of 800 C,
the salts are converted to oxides which are insoluble, or only slightly
soluble. Also, it was noted that glassy insoluble substances are formed with
the silica present (e.g., calcium silicate and magnesium silicate). It ap-
pears that additional testing is needed to determine the extent of the leach-
ing problem and to develop control methods.
Incinerator Wastewater
The process wastewater from incinerator plants is contaminated by both
dissolved and suspended materials. To prevent pollution of streams and under-
ground water, some form of treatment is usually required prior to discharge.
It is important to distinguish between the treatment required prior to
discharging to a sewer system which sends its water to a municipal treatment
plant, and discharging directly to the environment, for example, a marsh,
river, or tidal basin. In the former instance, minimal treatment such as
settling and possibly pH adjustment may be adequate. In the latter, the
treatment system must be designed to remove the objectionable contaminants
±o a level consistent with Federal, state and local water quality discharge
regulations.
Process Wastewater Sources and Quantity. The sources of process water from an
incinerator plant include feed chute water jackets, furnace wall cooling,
residue quenching, residue and flyash conveying, wet scrubbers, wet baffles,
wet bottoms, and settling chambers. Intermittent uses include storage pit
sprays, and floor and pit washings.
The quantity of water used in incinerator plants varies widely, depending
upon the extent and mode of water uses in air pollution control equipment,
residue conveying, and stack gas temperature control. An individual estimate
must be made for each incinerator design, but, based on previous estimates'1*'^
the quantity of water discharged can exceed 12 tons per ton of solid waste
processed (2900 gallons per 2000 Ibs) when scrubbers are used. This quantity
may be cut by a factor of two in the absence of scrubbers, and to much smaller
values when extensive recycle is used, for example, as little as 2 to 3 tons
per ton of waste.'^
Other Incinerator Wastewaters. Other than the process wastewater, an incin-
erator plant will discharge the usual sanitary wastes, and runoff waters. The
sanitary wastes are usually discharged to a sanitary sewer for treatment in
the municipal sewage plant. The quantity can be estimated from the number of
employees.
203
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Runoff water varies with washdown procedures, precipitation, terrain, and
soil characteristics. The necessity to deal with surface and runoff waters in
residue landfills was discussed in the "Incinerator Residue" section. Although
runoff water is less of a problem where only the incinerator or other thermal
processing unit has to be considered, it is nevertheless a real one. Water can
be contaminated by the litter and dust which invariably is associated with
solid waste handling.
A preferred solution to the problem is to direct storm sewer effluents
from handling areas to the process water system, but regulations do not always
permit this approach if the process water is discharged to a municipal treat-
ment plant. In that case, onsite treatment might be required. Uncontaminated
runoff waters can be handled in storm sewers.
Wastewater Quality. The quality of water discharged from the various process
units also varies widely from one plant to another, and daily variations occur
within the same plant. Variations result from non-uniformity of solid waste
composition and changes in water usage. Some important wastewater character-
istics are:
Temperature
Dissolved oxygen (DO)
Biochemical Oxygen Demand (BOD)
Chemical Oxygen Demand (COD)
Hydrogen Ion Concentration (pH)
Alkalinity
Hardness
Total Solids
Total Dissolved Solids
Suspended Solids
Settleable Solids
Phosphates
Nitrates
Fluorides
Heavy Metals
Odor
Water analyses for several incinerator plants, including quench water,
scrubber water and final effluent water are given in Table 52. The extent
of variation in the amounts of each contaminant is apparent. Residue quench
water, which may be either basic or acidic, contains moderate concentrations
of dissolved minerals, and often high concentrations of suspended solids.
Temperatures are not exceptionally high, ranging from 20 to 54 C (68 to 130 F),
but cooling is sometimes required.
Acidic conditions usually prevail in scrubber water. Dissolved material
content is much higher than in quench water, due to combined effects of low
pH and the practice of recycling a portion of this water back to the scrubber.
Average values for suspended solids in the scrubber water are lower than those
presented for quench water. This may be related to the design of the scrub-
ber, which permits settling prior to reuse of the water. The temperature of
scrubber water is considerably higher than for quench water, and ranges from
28 to 74 C (82 to 165 F).
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Combined wastewater from all sources may be either acidic or basic in
nature, as shown in Table 52, which indicates a pH range of from 4.5 to 9.9.
Dissolved solids vary from 320 to 4,060 mg/1, presumably depending upon the
extent to which water is recycled. Suspended solids content ranges from 40
to 580 mg/1, the lower values representing water sampled after settling has
taken place. Temperatures ranged from 18 to 52 C (65 to 125 F), the higher
values being of concern from the standpoint of thermal pollution and dis-
solved oxygen depletion of the receiving water.
Data in Table 53 for cooling-expansion chamber spray water show trace
contaminants such as fluoride, iron and ABS (alkyl benzene sulfonate). It
should be noted that the fluoride value of 7.8 mg/1 is significantly higher
than the permissible level for public water supply (1.2 mg/1). Other data
for minor contaminants in scrubber water are shown in Table 54. These include
cyanide, phenols, iron, chromium, lead, copper, zinc, manganese, aluminum, and
barium. Of these, all but total chromium exceeded the Florida quality stan-
dares for incinerator effluents. Additional data in Table 55'5 show the ef-
fect of pH in flyash water on the concentration of various metal ions found
in the water sampled. In almost every instance, the water having the higher
acidity (lower pH) contained larger amounts of metals.
Data on oxygen demand characteristics of incinerator water are seldom
reported in the literature. One source'5 reports 5-day BOD determinations
(expressed in mg/1) for water from the following sources: residue conveyors
- 618, 750, 560, 605, (4 different incinerator plants); ash hopper - 700;
flyash disposal - 3.2; and lagoon - 54. BOD of the combined waste water from
the incineration of municipal solid waste would be expected to be similar to
that of domestic sewage, averaging about 200 to 300 mg/1. Although good
incinerator performance results in high burnout of organics and thus lower
BOD in quench, scrubber, and other process waters, some BOD content of un-
treated waters is to be expected. Some bacterial content can also be expected
as shown by a limited study of incinerator wastewaters from a 1.9 metric ton
per hour (50 tons/day) batch feed incinerator and from an 11.3 metric ton per
hour (300 tons/day) continuous feed municipal incinerator.
The BOD and bacterial contents of the wastewater provide a potential for
odor problems, especially where wastewaters are impounded and not sept direct-
ly to treatment plants. Although not commonly necessary, chlorine,'5 ozone,'6
quaternary ammonium phenatej5 and other chemicals can be used for odor con-
trol. The quantity of such chemicals required would be greatly reduced by
pretreatment, e.g. by biological treatment.
Wastewater Treatment. There is an increasing trend in the design of process
water systems to recycle at least a portion of the water to satisfy other
process water requirements within the plant. Minimum wastewater treatment
systems recommended for solid waste processing plants include settling basins
or lagoons and pH adjustment. Oil skimmers and retention baffles may be used
in the basin to handle leakage or spillage from machinery lubricators, the
machine shop, and hydraulic systems.
Automatic pH control systems with a measurement probe and electronic
controls which proportion the feeding of chemicals are useful. Chemicals
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Table 52
TYPICAL WASTEWATER ANALYSES11
Quench
Range
Scrubber
Range
Final
Effluent
Range Avg.
pH 3.9-11.5 1.8-9.4 4.5-9.9
Temperature, °C 20-54 28-74 18-52 32
(°F) (68-130) (82-165) (65-125) (90)
Suspended Solids, mg/L 140-1860 90-1350 *40-580 210
Dissolved Solids, mg/L 360-2660 520-8840 320-4060 1190
Total Solids, mg/L 610-3960 610-9160 610-4200 1400
Alkalinity, mg/L CaCo-, 90-720 0-80 15-310 135
Chlorides, mg/L 98-850 180-3540 95-1710 455
Hardness, mg/L 95-980 190-3430 100-480 240
Sulfates, mg/L 25-830 24-1830 33-1685 390
Phosphates, mg/L 0.5-58 3-90 1-67 14
* After settling.
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Table 53
CHEMICAL QUALITY OF COOL ING-EXPANSION CHAMBER WATER
DISCHARGE AT INCINERATOR NO. 1u
Constituent
pH
Alkalinity
Nitrate
Phosphate
Chloride
Fluoride
Calcium
Sulfate
Sodium
Potassium
Iron
ABS
(CaC03)
(N03)
(P04)
(Cl)
(F)
(Ca)
(S04)
(Na)
(K)
(Fe)
(ABS)
Test 1
7.9
35.0
1.5
0.2
582.0
4.5
330.0
338.0
85.0
27.0
1.6
1.91
Test 2
5.5
9.0
1.90
0.61
453.0
6.40
220.0
238.0
63.0
14.8
0.93
0.1
Test 3
3.5
0
2.00
0.39
567.0
4.40
255.0
188.0
73.0
16.7
5.77
0.19
Test 4
6.2
10.0
2.00
0.17
422.0
7.80
250.0
300.0
60.0
14.0
0.50
0.21
All values are expressed in mg/1 except pH.
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Table 54
SCRUBBER WATER CHEMICAL CHARACTERISTICS13
Constituent
Iron
Cyanide
Total Chromium
Lead
Phenols
Copper
Zinc
Manganese
Aluminum
Barium
(Fe)
(Cn)
(Cr)
(Pb)
(Cu)
(Zn)
(Mn)
(Al)
(Ba)
Quality
Standardt
0.3
0
1.0
0.50
0.005
0.05
1.0
—
—
—
Raw
Water
0.35
0.21
0.0
0.0
0.005
0.08
0.0
0.0
0.18
0.0
Scrubber
Effluent
1.65
5.19
0.13
1.30
1.721
0.10
2.4
0.30
20.6
5.0
t State of Florida quality standard for incinerator effluents. Data from
Broward County, Florida incinerator. All values are expressed in mg/1.
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Table 55
EFFECT OF pH ON CATION CONCENTRATION-FLYASH
WATER, INCINERATOR "A"14
Concentration (parts/mi 11 ion)
Cations pH = 3.4 pH = 6.30
Ca 913 718
Na 1621 1621
K 212 173
Mg 83 64
Zn 78 52
Pb 19 10
Al 32 14
Mn 43
Sr 1 1
209
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used to adjust acidic wastewater include lime, soda ash, and caustic soda.
Sulfuric acid is generally used to reduce pH when the wastewater is alkaline.
As noted in the section on "Wastewater Quality," scrubber water is usually
acidic, while overall wastewater may be acidic or basic.
Consideration should be given to reusing water which has been thus
treated to reduce the fresh makeup water required, and to minimize the quan-
tity of contaminated water discharged. The quality of treated water from the
settling basin will often be adequate to permit reuse in flue gas scrubbing
(after filtering to prevent nozzle plugging), residue quenching, ash convey-
ing, and for utility water used for washdown, etc. Sufficient fresh makeup
water may be needed to prevent precipitation of scale in the piping and other
water handling equipment. A schematic drawing of a simple treatment: system
is shown in Figure 45.
It is desirable to be able to discharge wastewater to existing municipal
treatment plants, but, where this is not possible, maximum recycle and a
greater degree of onsite treatment should be practiced. A wastewater treat-
ment system which goes beyond simple settling and neutralization may include
flocculation, biological treatment, and filtration. These treatment steps,
which will be outlined here, are used for many industrial plants though they
have not been required for municipal incinerators.
Chemical flocculation involves the use of coagulants and coagulant aids
to remove inorganic and organic contaminants. Alum is frequently used as a
coagulant, and lime may be added to produce dense floe, which settles readily,
and to simultaneously increase pH. Coagulant aids include polyelectrolytes
and activated alumina. Suspended solids can be reduced to 20 mg/1 in a well
designed, carefully operated chemical treatment system. Dissolved solids
concentrations will also be reduced substantially, particularly when calcium,
magnesium, manganese, and iron are initially present in high concentrations.
Chemically aided flocculation is also employed as a means of reducing the
concentration of heavy metals such as lead, chromium, copper, zinc, aluminum,
barium, lead, manganese, and mercury.
Biological treatment depends upon contacting the wastewater with bac-
teria and other biological organisms to effect a metabolic breakdown of the
organic substances present in the water. This can be achieved in various
types of equipment, with perhaps the activated sludge process and the trick-
ling filter being the most common. In activated sludge, the biological
organisms are kept in suspension throughout the wastewater by means of in-
jected air or mechanical turbulence. The trickling filter, by contrast,
contains a "fill" or solid matrix to which the organisms are attached and
over which the water flows.
The process of choice depends upon capital and operating cost, strength
of the waste to be treated, degree of purification required, availability of
space, and other factors. Toxic materials including phenols, cyanide, and
pesticides can be removed to varying degrees by biological treatment. How-
ever, the design must provide positive means of control, such as equalization
tanks, to insure that the concentration of these materials entering the unit
are kept low enough to prevent upset to the biological organisms.
21C
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O
4J
ai
w
211
-------
If biological treatment were contemplated, segregation of incinerator
wastewater according to the degree of organic contamination present could be
considered. This would permit biological treatment of residue quench water
with simpler treatment of water from scrubbers, other air pollution control
equipment, and flyash handling, where BOD contamination is low.
Filtration of water by means of granular beds of sand or anthracite is
sometimes used as the final step in the removal of suspended matter from water,
usually following a settling step. Granular bed type filters are used to
polish the effluent from physical/chemical processes and/or biological treat-
ment plants. Removal of 95 percent of the influent suspended solids and 30
percent of the BOD is possible. Addition of chemicals such as clay has been
found useful in improving the removal efficiencies of granular bed filters.
Finally, disinfection might be required to allow discharge of the treated
wastewater directly to the receiving water. Chlorine has been most commonly
used, added in sufficient quantity to leave a 1 or 2 mg/1 residual. However,
toxic chlorinated organic compounds can be a problem, casting some doubt upon
the desirability of chlorine addition. The use of ozone as a disinfectant has
been the subject of recent investigations, primarily because toxic byproducts
do not appear to be generated. Also, ozone is more effective in removing
traces of cyanides and phenol from the water.
Figure 46 is a schematic diagram showing the type of treatment system
which might be used where high contaminant removal efficiences are required.
It should be noted that this more extensive treatment results in sludges which
must be disposed of, just as is the case with sewage treatment plants. In
general, where possible, it is most desirable to maximize recycle after simple
onsite wastewater treatment, discharging effluents to the municipal sewer
system.
Discharges from Pyrolysis Processes
In recent years, thermal processing techniques have been developed which
produce fuels by the pyrolysis of solid waste in an oxygen deficient or
reducing atmosphere. In some pyrolysis processes, including the current
versions of the Monsanto Process (Baltimore, Maryland plant) and the Torrax
Process (Orchard Park, New York pilot plant) the hot fuel gases are burned
in a waste heat boiler to generate steam. After combustion, the waste gases
are scrubbed with water before being released to the atmosphere. Control of
air emissions and treatment of scrubber water pose no special problems which
are not encountered in the operation of conventional incinerator plants.
Other processes, including the Occidental Research Company Process (San
Diego County, California plant), condense the pyrolytic fuel oil produced.
The condensate contains both the liquid oil, and the water which is produced
simultaneously during pyrolysis. These separate into an oil phase and a
water phase which are physically separated. However, the water phase is
highly contaminated with a multitude of water soluble organic compounds such
as acids, aldehydes, and alcohols. This contaminated water, which may con-
tain BOD values near 100,000 mg/1, poses serious recovery or disposal
problems.
212
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In Occidental's San Diego plant, which is under construction, the aqueous
phase will be vaporized and the organic contaminants burned, with a net consump-
tion of energy. A second alternative, which has been considered, is to blend
the aqueous condensate with other wastewater and to subject the combined waste
to biological treatment. Recovery of the organic compounds from the water phase
may be possible, but considerable development work would be required to find a
practical and economical method for recovery.
214
-------
REFERENCES
1. DeMarco, J. et al. Municipal-Scale Incinerator Design and Operation.
PHS Publication No. 2012. U.S. Government Printing Office, Washington,
D.C. 1969. (formerly Incinerator Guidelines-1969)
2. Sundberg, R. and Weyermuller, G. H., Ed. Ozonator Operating Cost Only
$2,600/Yr. Chemical Processing, January 1970.
3. Roeder, W. F. Carbon Filters Control Odors at Refuse Transfer Station.
Public Works 100(4).-96-97. April 1969.
4. Kaiser, E. R., et al. Municipal Incinerator Refuse and Residue. Proceed-
ings, 1968 National Incinerator Conference (New York, May 5-8, 1968).
American Society of Mechanical Engineers, pages 147-152.
5. Fernandez, J. H. Incinerator Air Pollution Control. Proceedings, 1969
National Incinerator Conference (New York, May 5-8, 1968). American Society
of Mechanical Engineers, page 102.
6. Thermal Processing and Land Disposal of Solid Waste. U.S. Environmental
Protection Agency. Federal Register 39(158) Part 111:29328-29338. August
14, 1974.
7. Hagerty, J. S. et al. Solid Waste Management. Van Nostrand Reinhold
Company, New York. 1973. 302 pages.
8. Bowen, I. G., and L. Brealey. Incinerator Ash-Criteria of Performance.
Proceedings, 1968 National Incinerator Conference (New York, May 5-8, 1968).
American Society of Mechanical Engineers, pages 18-22.
9. Schoenberger, R. J., and P. W. Purdom. Classification of Incinerator Residue.
Proceedings, 1968 National Incinerator Conference (New York, May 5-8,
1968). American Society of Mechanical Engineers, pages 237-241.
10. Eberhardt, H. and W. Mayer. Experience with Refuse Incinerators in
Europe. Proceedings, 1968 National Incinerator Conference (New York,
May 5-8, 1968). American Society of Mechanical Engineers, pages 76-77.
11. Achinger, W. C. and L. E. Daniels. Seven Incinerators. SW-51 ts.lj. U.S.
Environmental Protection Agency. 1970. 64 pages.
12. Jens, W., and F. R. Rehm. Municipal Incineration and Air Pollution
Control. Proceedings, 1966 National Incinerator Conference (New York, May
1-4, 1966). American Society of Mechanical Engineers, pages 74-83.
13. Schoenberger, R. J. and P. W. Purdom. Characterization and Treatment of
Incinerator Process Waters. Proceedings, 1970 National Incinerator Con-
ference (New York, May 17-20, 1970). American Society of Mechanical
Engineers, page 206.
215
-------
14. Wilson, D. A. and R. E. Brown. Characterization of Several Incinerator
Process Waters. Proceedings, 1970 National Incinerator Conference (New
York, May 17-20, 1970). American Society of Mechanical Engineers, page
199.
15. Matusky, F. E. and R. K. Hampton. Incinerator Wastewater. Proceedings,
1968 National Incinerator Conference (New York, May 5-8, 1968). American
Society of Mechanical Engineers, pages 201-203.
16. Ozone Water Treatment Nears Pilot Stage. Chemical Engineering News.
September 8, 1969.
17. Tucker, M. 6. Biological Characteristics of Incinerator Wastewaters.
Unpublished graduate student research project in CE 687 course. University
of Michigan, August 1967, 15 pages.
216
-------
CHAPTER XIV
AIR POLLUTION CONTROL
Historically, the air pollution problems caused by incineration have
been so severe that, in the public eye, "smoke" represents the single most
associated i;nage of incineration. However, with current day technology and
stringent Federal, State and Local regulations, modern, well-designed in-
cinerators and other thermal processing facilities can be and are socially
and environmentally acceptable.
Planning, design, specification, purchase, installation, operation,
and maintenance of air pollution control systems require at least as much
attention as the furnaces, buildings, and other sections of the facility.
Even at this late date in the evolution of regulations and technology for
proper control, several recent projects have had major difficulties with
air pollution control systems, some requiring major modifications or complete
replacement. Particulate emissions are generally of greatest concern, but
chemical emissions will also be considered in this discussion.
Most of the information presented here pertains primarily to incinerators,
both with and without energy recovery. Special sections are devoted to
emerging thermal processing systems such as combined refuse/fossil fuel boil-
ers and pyrolysis.
Uncontrolled Particulate Matter Emissions
Any general discussion of particulate emissions may create confusion,
since there is no universally accepted definition of or measurement procedure
for "particulate." In an actual situation, careful study of applicable
regulations and stack testing are essential. Examples of definitions and
test procedures which exist for regulating particulate emissions from munici-
pal incinerators are shown in Table 56.
For purposes of simplicity, particulate emissions which are filterable
at approximately 121.1 C (250 F) will be referred to as "dry catch"; particu-
lates which pass through the filter will be referred to as "wet catch"; total
particulates equal dry catch plus wet catch. Unless otherwise noted, the
data presented in this Chapter will be presumed to be "dry catch" only.
Particulate Emission Quantities
A 1970 study4 compiled particulate emission data from various locations
downstream of the furnaces at fifty (50) different incinerators which had no
air pollution control devices. Figure 47 is a histogram of these data which
show the wide variation that exists between incinerators, and even for the
same incinerator. A median value of 12 kilograms of particulate emissions
per metric ton of refuse (24 Ibs/short ton) was determined. This compares
217
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reasonably well with median values of 8.5, 17.5, 10, and 11.3 kilograms per
metric ton reported by others.5"9 A detailed study of a modern waterwall
steam generating incinerator showed similar emissions upstream of the pollu-
tion control device (Table 57).
Often, regulations are written to limit particulate emission concentra-
tions to a specified value based on operating the incinerator with an amount
of air which will result in a carbon dioxide content of 12 percent by volume
in the flue gas (excluding the contribution of auxiliary fuel), when
measured on a moisture free basis. Therefore, the Table 57 data are repre-
sented in other forms in Table 58. Reference 4 contains factors for con-
version to additional forms. It should be noted that many regulations
define "normal" or"standard" differently from historical usages. Therefore
careful reading of definitions is essential.
Uncontrolled particulate emissions vary, depending on the construction
and operation of the equipment, as well as the nature of the waste. Some of
the major variables are:
. ash content of the solid waste
. underfire and overfire air flows
. burning rate
. furnace temperature
. grate agitation
. combustion chamber design
Three mechanisms are believed to be mainly responsible for particulate
emissions:
. mechanical entrainment of particles from the burning waste bed
. the cracking of pyrolysis gases
. the vaporization of metal salts or oxides
An extensive and detailed discussion of these variables and mechanisms are
presented in Reference 4. It should be noted that while the particulate
emissions from a waterwall furnace may be similar to that from a conventional
furnace on a per ton of refuse basis, waterwall emissions may be significantly
higher on a concentration basis, due to lower air flows (See Chapter X).
Characteristics of Particulates
The composition of particulate emissions from incinerator furnaces is
dependent on design and operation, as well as on the refuse ash composition.
A poorly designed or operated incinerator may emit carbon particles (usually
referred to as soot), and the inorganic (mineral) type ash will contain a
significant quantity of combustibles. Data from six incinerators4 showed
a range of 6 to 40 percent in the combustible content of the furnace parti-
culate emissions. Inorganic contents are shown in Table 59.
220
-------
Table 57
PARTICULATE EMISSIONS FROM THE FURNACE OF A
MODERN WATERWALL INCINERATOR™
Refuse Charging Rate, short
tons/hr
Volume percent C02 In Flue Gas (Dry
Basis)
Dry catch particulates, Ib/hr
Wet catch particulates, Ib/hr
Total particulates, Ib/hr
Dry catch particulates, Ib/short
ton
Wet catch particulates, Ib/short
ton
Total particulates, Ib/short ton
Total particulates, Ib/metric ton
16.6
10.0
388
30
418
23.4
1.8
25.2
12.6
16.6
10.0
379
18
397
22.8
1.1
23.9
12.0
16.7
10.1
427
30
457
25.6
1.8
27.4
13.7
16.7
9.5
398
13
411
23.8
0.8
24.6
12.3
221
-------
Table 58
PARTICULATE EMISSIONS FROM THE FURNACE OF A
MODERN WATERWALL INCINERATOR™
Refuse Charging Rate, short
tons/hr
Excess Air, percent
Volume percent COo, dry basis
Volume percent H20
Total Particulates
COo = carbon dioxide
H2U = water
Grains = _J Pound =
7000
1 grams
15.43
16.6
78
10.0
11.0
16.6
78
10.0
10.8
16.7
87
10.1
13.9
SCF (dry) = standard cubic feet, of dry flue gas,
& 21.1 C (70 F) one atmosphere absolute pressure
= 0.0283 standard cubic meters (SCM) dry
@ 21.1 C (70 F) one atmosphere absolute pressure
16.7
98
9.5
12.7
Grains/SCF (dry), actual
Grains/SCF (dry), corr. to
12 percent C0£
Grams/SCM (dry), corr. to
12 percent C02
1.05 1.10 1.03 0.93
1.26 1.32 1.22 1.17
2.88 3.02 2.79 2.68
222
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Table 59
COMPOSITION OF INORGANIC COMPONENTS
OF PARTICIPATES FROM FURNACES4
Component
Si02
A1203
Fe203
CaO
MgO
Na20
K20
Ti02
S03
P205
ZnO
BaO
Computed for
Typical
' Refuse
53.0%
6.2
2.6
14.8
9.3
4.3
3.5
4.2
0.1
1.5
0.4
0.1
100.0%
NYC Incinerators11
73rd St.
46.4%
28.2
7.1
10.6
2.9
3.0
2.3
3.1
2.7
-
-
-
So. Shore
55.1%
20.5
6.0
7.8
1.9
7.0
-
-
2.3
-
-
-
223
-------
Particle size distribution and specific gravity of participate matter
are properties which are essential design data for most participate removal
devices. The smaller and/or finer particles require more sophisticated (and
expensive) equipment to meet a specific emission limit. Table 60 presents
data for three conventional incinerator furnaces. Due to less efficient
particle collection testing methods used in the past, it is possible these
data are in error in that a portion of the fine particles were not included.
Figure 48 presents additional particle size distribution data. Size
distribution, like loading, varies widely. Most factors which affect
particle loading also affect the size of particles emitted. Improved
incinerator performance which reduces quantities emitted, normally decreases
the size of the individual particles. The particulate matter is always
quite heterogeneous, consisting of flyash, with properties such as shown
in Tables 59 and 60, combined with large, low density flakes. Particle
density typically ranges from 2 to 3 g/cc.
Electrical resistivity is an important property of particulates necessary
for design of electrostatic precipitators, commonly used in modern incin-
erators. High resistivity reduces collection efficiency, while low resistiv-
ity may result in re-entrainment of the particle into the gas stream after
collection. Resistivity is a function of the basic particle characteristics,
and composition and temperature of the flue gas stream. The presence of
moisture and very low concentrations of certain chemical compounds, such as
sulfur trioxide and ammonia, in the flue gas may strongly influence particle
resistivity and precipitator efficiency. Figure 49 shows the particle elec-
trical resistivity for emissions from three furnaces. The desirable range
of resistivity, 10^ to 10'^ ohm-cm, influences the choice of electrostatic
precipitator operating temperature.
Target Particulate Emission Levels
Allowable particulate emissions are determined by three standards,
usually concurrently:
. Air quality in the regions affected by the thermal processing facility
. Concentration or rate of emissions from the thermal processing
facility >
. Visual appearance of the emissions from the thermal processing
facility
These standards exist on the Federal level for new facilities (construction
commenced after 12/23/71),15 and on the State level for existing facilities
as well.
Federal (and many State) requirements for air quality are set at two
levels, as shown in Table 61, a primary standard which is designed to protect
public health, and a secondary standard which is designed to protect public
welfare (e.g., animal or plant life, or property, or enjoyment thereof).
For purposes of air quality standards, "particulate" generally means that
which is filterable from the air and which remains on the filter after
conditioning at 15 to 35 C (59 to 95 F).
224
-------
Table 60
PROPERTIES OF PARTICULATES LEAVING FURNACES12
Physical Analysis
Specific gravity,
g/cc
Bulk density g/cc
(lb/CF)
Loss on ignition at
750 C, wt. percent
Size distribution
(percent by weight)
< 2 microns
< 4 microns
< 6 microns
< 8 microns
<10 microns
<15 microns
<20 microns
<30 microns
Parti cu late emission
rate, kilograms/MT
(Ib/ST)
1
(250 TPD)
2.65
-
18.5
13.5
16.0
19.0
21.0
23.0
25.0
27.5
30.0
6.1
(12.1)
Installation
2
(250 TPD)
2.70
0.495(30.9)
8.15
14.6
19.2
22.3
24.8
26.8
31.1
34.6
40.4
12.3
(24.6)
3
(120 TPD)
3.77
0.151(9.4)
30.4
23.5
30.0
33.7
36.3
38.1
42.1
45.0
50.0
4.6
( 9.1)
iPD = short tons per day
MT = metric ton
ST = short ton
225
-------
OMOfttOS 115 « «D
KHQtMT «r wfWHT UftT fHHK
FIGURE 4a INCINERATOR FLYASH PARTICLE
SIZE DISTRIBUTION*
226
-------
o i66~ zoo »«>o
-------
Table 61
NATIONAL AMBIENT AIR QUALITY STANDARDS14
National Primary Ambient Air Quality
Standards for Particulate Matter
National Secondary Ambient Air Quality
Standards for Particulate Matter
The national primary ambient air
quality standards for particulate
matter, measured by the reference
method described in the regulation,*
or by an equivalent method, are:
(a) 75 micrograms per cubic meter--
annual geometric mean.
(b) 260 micrograms per cubic
metei—maximum 24-hour con-
centration not to be exceeded
once per year.
The national secondary ambient air
quality standards for particulate
matter, measured by the reference
method described in the regulation,*
or by an equivalent method are:
(a) 60 micrograms per cubic meter-
annual geometric mean, as a guide
to be used in assessing implemen-
tation plans to achieve the 24-
hour standard.
(b) 150 micrograms per cubic meter--
maximum 24-hour concentration
not to be exceeded more than
once per year.
* High volume sampling method described in Appendix B of reference 14.
228
-------
With the sophisticated computer modeling techniques now available, the
air quality in regions affected by a thermal processing facility can be
reasonably predicted for varying stack emission rates and meteorological
conditions (e.g., wind speed and direction, vertical temperature profiles,
humidity, etc.), taking into account stack height and exit velocities, land
topography, already existing particulate concentrations, and other sources
of particulates. While not specific to thermal processing facilities, the
air quality standards nevertheless must not be exceeded because of insuffi-
cient control in new and existing installations.
For tnermal processing facilities which commenced construction after
December 23, 1971, and which charge more than 1.89 metric tons per hour (50
short tons/day) of solid waste,* the very specific Federal Regulation for
particulate emission concentrations must be met.'b These standards prohibit
the discharge into the atmosphere of particulate matter, the concentration
of which is in excess of 0.18 grams per cubic meter (@ 21.1 C, one atmosphere)
which is equal to 0.08 grains/standard cubic foot (21.1 C, one atmosphere) of
flue gas on a dry basis corrected to 12 percent carbon dioxide by volume,
maximum 2~nour average. The particulate emissions are to be measured in
accordance with U.S. Environmental Protection Agency "Method 5, Determination
of Particulate Emissions from Stationary Sources,"'^ which measures only "dry
catch" particulates. A requirement for recording burning rates, hours of
operation, and any particulate emission measurements which are made is also
included.
It was originally proposed that the Federal emission standards for
incinerators and other sources would be for total particulates, which included
dry catch and wet catch. As can be deduced from Table 57 and 58, for incin-
erators the wet catch corresponds to a quantity on the same order of magnitude
as the emission standard. As will be seen in the control section, the wet
catch portion of the particulates are not efficiently collected by some
devices and in themselves could cause noncompliance, if this proposed standard
were ever promulgated.
On the State level, similar regulations exist for both new and existing
facilities, but the actual numerical standard, the definition of "particulate,"
and the test method may be significantly different. State regulations may
also have prohibitions against particulate emissions which are visible. These
regulations may set. a specific standard such as a limit on opacity** (typical-
ly 20 percent), or an equivalent smoke density (e.g., Ringelmann No. 1), or
simple prohibition of any visible particles.2
Actual data correlating particulate concentration with the resulting
opacity or smoke density have not been found, but a correlation is presented
in Figure 50 using a method'° which takes into account particulate concentra-
tion, refractive index, geometric mean radius (and standard deviation),
density, stack diameter, and gas temperature. The claim that 0.09 grams per
standard cubic meter (0.04 grains/standard cubic foot) results in a clear
stack'" is not inconsistent with this correlation.
* Defined as refuse, more than 50 percent of which is municipal type waste.
** The degree of obstruction to the transmission of light.
229
-------
50
•H
u
m
8-
dP
30
26
10
1. Geometric mean particle radius * 0.86 micron*
2. Geometric standard deviation for particle
distribution - 1.50
3. Paniculate is silica, with density of 2.5 9/00,
refractive index of 1.50
4. Stack diameter - 1.83 meters (6 feet)
5, Stack gas temperature = 260° C (500° F)
6. (Grams per standard cubic meter) = (grains per
standard cubic foot) x 2.29
-f^ffcf cnlat»
(wwt &»si»)
*Not corrected to 12% CO2 ./+ 21.1°C, I atmosphere
__ _ _ __ : - £-*-- — - - • - ........ "i ~ ~~ ~ '•
FIGURE 50. ESTIMATED CORRELATION BETWEEN OPACITY
AND PARTICULATE CONCENTRATION FOR AIR
POLLUTION CONTROLLED INCINERATORS
230
-------
Particulate Emissions Control
Even a modern well-designed and operated incinerator cannot meet Federal
and most, if not all, State regulations for participate emissions without an
air pollution control system. Comparing data from Table 58 with Federal
emission requirements (Table 62), it is apparent that efficiencies in excess
of 93 percent on a weight basis are required. Visual requirements, by State
or local agencies, of less than 20 percent opacity may increase this effi-
ciency requirement even further.
Mass particulate emission standards are corrected to 12 volume percent
CC>2 excluding the contribution of auxiliary fuel (or some other measure of
excess air), which effectively limits the emission to a fixed amount per ton
of solid waste fired. Thus, air dilution in a refractory incinerator, which
may use twice as much air as a waterwall incinerator, is not an aid in meet-
ing emission limits. However, because opacity is an absolute standard, the
refractory incinerator may in fact be aided by normal dilution in meeting an
opacity requirement. It may also be aided by decreasing the size of a single
stack, e.g. by using four stacks with four incineration trains instead of one
or two stacks, because of the effect of stack size on opacity measurements.
Considering the particle size data presented in Figure 48, it is apparent
that to achieve a minimum of 90 percent efficiency, all the particles larger
than 1 to 3 microns (one-millionth of a meter) must be removed. This require-
ment effectively eliminates the simple air pollution control systems tradi-
tionally used on incinerators, although it may sometimes be advantageous to
use one of these simpler devices as a first stage collector, for example, to
reduce the required efficiency of the final collector. Numerous discussions
of these systems, which include settling chambers, wetted baffle spray sys-
tems, cyclones, and low energy scrubbers are available.6,19,23 Therefore,
they will not be considered further in this publication.
Electrostatic precipitators, fabric filters, and certain types of scrub-
bers appear to be the only commercially available devices which have the
capability to meet the current emission standards for municipal incinerators.
Newer forms of these devices, including charged droplet scrubbers and high
velocity wet precipitators, may have advantages over more conventional
devices but these have not been commercially demonstrated for incinerator
applications.
Electrostatic Precipitators
Electrostatic precipitators have been used in utility and industrial
steam generating boilers and many other applications for over fifty years,
with a relatively good performance record. Not until 1969 were these devices
applied to municipal incinerators in the United States, although there are
probably more than forty installations in Europe and Japan. Almost all new
thermal processing facilities built since 1969, however, have utilized elec-
trostatic precipitators for particulate emission control (Table 63).
231
-------
Table 62
PARTICULATE EMISSION DATA FROM UNCONTROLLED WATERWALL
INCINERATOR COMPARED WITH FEDERAL STANDARDS
Particulate ~Federal "~~ ' Percent
Emission Uncontrolled Standard or Reduction
Concentration Incinerator* Equivalent Requ.i red
Grains/SCF (dry)** 1.18 0.08
93.3
Grams/SCM (dry)++ 2.70 0.18
* Derived from Tables 57, 58; Average .of four tests. Corrected to
12 percent C0£ by volume, dry basis; "dry catch" only.
** Standard (70 F, 29.92"Hg) cubic feet, dry basis
++ Standard (70 F, 29.92"Hg) cubic meters, dry basis
70 F = 21.1 C
29.92"Hg = 1 atmosphere
232
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In an electrostatic precipita tor, a high, normally negative, voltage
gradient is impressed across a pair of electrodes producin a corona discharge
(the visible sign of ionization of gas molecules) at the negative electrode.
Most of the ions produced are negatively charged. As the ions migrate toward
the grounded (relatively positive) electrode, they collide with entrained
particles, charging these particles negatively. The negatively charged
particles in turn move toward the grounded electrode where they are attached
and held by a combination of electrical, adhesive, and cohesive forces while
their negative charge is gradually conducted through the layers of previously
collected dust to the grounded electrode. The resistance to conduction is
termed "dust resistivity."
Too high a resistivity results in a high voltage drop across the dust
layer, reducing particle collection because of depressed electrical fields
in the precipitation zones and lower levels of particle charge.21 In extreme
cases, very high resistivity may result in "back corona," generating positive
ions which tend to neutralize the electrical field and upset particle collec-
tion. Resistivity, which is a complex function of both gas and particle
characteristics, is a primary parameter to be considered in precipitator
design.
The major elements of a commercial electrostatic precipitator are the
high voltage power supply and controls, discharge (corona) electrodes, collect-
ing (grounded) electrodes, rappers to dislodge agglomerated dust from elec-
trode surfaces, a gas-tight shell to contain the precipitation zone, hoppers
below the precipitation zone to receive dislodged dust, and gas inlet and
discharge zones designed to distribute the gas uniformly across the precipi-
tation zone. A typical configuration is shown in Figure 51.
High Voltage Power Supply and Controls. The high voltage system is designed
to provide high voltage direct current to the discharge electrodes. The
system consists of:
1. Typically 460 volt, 60 Hz, single phase alternating current power
supply.
2. An electrical control circuit incorporating either a saturable
reactor, or an SCR (silicon-controlled rectifier).
3. A transformer-rectifier set (encased in an oil tank) to increase
the voltage to the desired value in the range of 30,000 to 80,000
volts, and to convert alternating to direct current. Silicon diode
rectifiers have replaced earlier mechanical, vacuum tube, and
selenium types.
Automatic control systems and electrical sectioning of precipitators, although
increasing initial cost somewhat, are important in maintaining maximum precip-
itator performance. ' Proper design and placement of high voltage insulators
is necessary to overcome failures due to dirt and moisture.
234
-------
235
-------
Discharge Electrodes. The discharge electrodes, which take the form of rods
or wires with or without superimposed sharp points or edges to enhance the
corona effect, hang precisely along the center lines of the gas passages
between the collection electrodes. The discharge electrodes must be designed
with great care to maintain uniform spacing and to minimize fatigue. These may
be the suspended wire type with weights, as shown in Figure 51, or the
electrodes may be mounted in stiff frames. Each electrical section, contain-
ing a multitude of discharge electrodes, is electrically isolated from the
remainder of the precipitator.
Collection Electrodes. For incinerator applications, these are parallel steel
plates carefully spaced at a predetermined value in the range of 20 to 30
centimeters (8 to 12 inches) apart, depending on the voltage used. The plates
may be smooth, but are normally corrugated or equipped with fins or carefully
designed baffles to increase strength and to provide quiescent zones, avoiding
particle re-entrainment while maintaining smooth gas flow.
Rappers. Rappers or vibrators are used during precipitator operation to shear
the collected dust layers away from the collecting electrode. Both intensity
and time may be controlled to induce shearing off relatively large agglomer-
ates, avoiding particle re-entrainment. Such losses are also minimized by
sequential rapping of shock-isolated rapping sections in series, so that an
opportunity exists to recapture particles which are re-entrained in the inlet
sections. A variety of rapping mechanisms and locations are used, including
mechanical, electromagnetic, and pneumatic devices, top or end mounted. A
group of mechanically driven free-swinging hammers on a single shaft, each
hammer rapping the end of single plate, is one simple arrangement, but one in
which intensity is not readily controlled. Similar rapping arrangements are
adapted for use on groups of discharge (negative) electrodes because some
dust almost inevitably clings to these, due to impaction and positive ion
formation.
Flyash Removal. The hoppers may be discharged periodically through slide
valves or continuously through rotary valves or feeders to a flyash removal
system. The removal system is usually dry, using screw or drag conveyers, or
vacuum or pneumatic transport. However, slurry systems can be used.
Proper hopper design and dumping procedures are vital, since buildup of
flyash can short out electrodes causing precipitator damage. Level detectors
are useful, and automatic timing devices should be used where periodic dumping
is practiced.
Gas Inlet and Discharge Zones. Uniform flow into and through the precipitator
must be maintained to insure adequate performance. The reduction in gas
velocity from the usual practice of about 10 to 20 meters per second (33 to
66 ft/sec) in inlet ducts to about 0.9 to 1.8 meters per second (3 to 6 ft/
sec) in the precipitator, changes in gas direction, and the necessity for lim-
iting the amount of total ductwork pose difficult design problems with regard
to obtaining uniform flow. Careful design of splitters or vanes and
236
-------
incorporation of perforated plates at the precipitator inlet will improve gas
distribution. Test models scaled 1 to 16 are sometimes used to aid in
design work. Flow distribution tests should be included in performance
evaluation for new or rebuilt precipitators.
Gas distribution through the precipitator is affected too by the gas
outlet design, also deserving of careful attention. Another serious problem
can be created by gas bypassing below the collecting plates through the
hopper area. This condition can usually be improved by the use of baffles.
P reel pi t a to r Sizing. The design of electrostatic precipitators is based on
knowledge of gas and solid physical and chemical properties, particle inlet
loadings, gas rate, required efficiency, and also on familiarity with the
idiosyncracies of the particular application. For example, for incinerator
operation, the design should reflect knowledge of the expected temperature
range, the frequency of shutdown, variability in flyash composition and
properties, geographical location, and other variables. Using both theoret-
ical and empirical design consideration, and considering cost optimization,
the designer will specify major parameters, usually in the ranges shown in
Table 64.
Although the required mass particle removal efficiency, based on Federal
emission standards previously discussed, may be less than 95 percent, opacity
requirements approaching a "clear stack" may bring design efficiency to 99
percent (or even higher), depending on uncontrolled loading, particle size,
condensibles present, stack diameter, and other factors. High design effi-
ciencies require extraordinary attention to all design and construction de-
tails to insure continuing high efficiency performance. It should be empha-
sized that the mechanical and electrical designs, some important aspects of
which have been discussed here, are as important to adequate electrostatic
precipitator performance as the basic size parameters. Electrostatic precip-
itator installations both in the United States and elsewhere have shown that,
witr. careful design and operation, efficiency requirements for "dry catch"
part'.culates can be met. Actual performance data for an electrostatic pre-
cipitator operating on the effluent from a waterwall incinerator are provided
in Table 65.
Corrosion due to acidic components of the flue gas, such as hydrogen
chloride, can be a problem in precipitator operation. The gas temperature
following heat and/or quench facilities must be sufficiently high to avoid
acid condensation on cold surfaces. Hot air purging and preheat burners
can minimize acid gas contact with cold surfaces during shutdown and startup.
Sufficient insulation of all metal surface exposed to outdoor conditions is
especially important. Hopper heaters are useful, both to avoid corrosion
and to avoid bridging problems due to even minor amounts of moisture deposi-
tion on flyash.
Scrubbers
Devices that contact incinerator flue gas with water have traditionally
been used both to clean the gases and to cool them for protection of duct,
stack, and fan materials. These devices, which usually consisted of little
more than a large spray chamber with baffles, are inadequate to meet modern
237
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238
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Table 65
PERFORMANCE DATA FROM ELECTROSTATIC PRECIPITATOR
ON WATERWALL FURNACE"0
Rafuse Charcjins Rate
Short tons/hr
Dry Gas Composition (by volume)
% CO?
% 02
Excess Air, %
Inlet Measurements
Flow rate, SCFM (dry)
Temperature, F
Water Content, % by volume
Parti culates--dry catch
grains/SCF (dry) corrected*
grains/SCF (dry) actual
Particulates--wet catch
grains/SCF (dry) corrected*
grains/SCF (dry) actual
Parti culates--total
grains/SCF (dry) corrected*
grains/SCF (dry) actual
Outlet Measurements
Flow rate SCFM (dry)
Temperature, F
Water Content, % volume
Particulates--dry catch
grains/SCF (dry) corrected*
grains/SCF (dry) actual
Particulates — wet catch
grains/SCF (dry) corrected*
grains/SCF (dry) actual
Particulates--total
grains/SCF (dry) corrected*
grains/SCF (dry) actual
Efficiency
% Removal --dry catch
% Removal --wet catch
% Removal --total
16.6
10.0
9.4
78
46,500
338
11.0
1.17
.975
.090
.075
1.260
1.050
48,600
358
9.7
.0331
.0276
.0103
.0086
.0434
.0362
97.17
88.56
96.56
16.6
10.0
9.4
78
42,100
307
10.8
1.26
1.05
.060
.050
1.320
1.100
43,400
356
8.5
.0283
.0236
.0134
.0112
.0417
.0348
97.75
77.67
96.84
16.7 16.7
9.9 9.1
7.4 8.5
87 98
51,900 51,500
400 415
13.9 12.7
1.14 1.14
.941 .865
.079 .036
.065 .027
1.219 1.176
1.006 0.892
51,900 51,500
393 398
13.9 12.7
.0400 .0270
.0330 .0205
.0090 .0130
.0074 .0099
.0490 .0400
.0404 .0304
96.49 97.63
88.61 63.89
95.98 96.60
* Corrected to 12 percent C02
239
-------
emission control requirements, though similar devices can still be used where
flue gas cooling is required. As noted earlier, in order to meet most recent
particulate emission regulations, it is necessary to install devices which
efficiently remove particles in the 1 to 5 micron size range. This can be
accomplished by some forms of a more sophisticated family of gas/water con-
tacting devices known as scrubbers, or sometimes as wet or water scrubbers.
Various techniques are used in scrubbing, but all rely on "wetting" the
particle with water in order to enlarge them, allowing for easier removal from
the gas stream. The efficiency of a particular type of scrubber on a given
particle size can be related to the energy used to force the gas through the
collector and to generate the water sprays. This energy may be supplied with
fans as pressure to the gas stream (gas motivated), with pumps as pressure to
the water stream (liquid motivated), or mechanically. The latter has not
found commercial usage, but the former methods are widely used.
Gas motivated scrubbers are referred to as venturi or orifice types.
Liquid motivated scrubbers are referred to as jet venturi or ejector types,
or impact scrubbers. The energy required in either case represents a very
significant incinerator operating cost, especially when electrical power is
used to drive fan or pump motors.
Research and development work is underway to improve the performance
of scrubbers and to reduce energy requirements. Various commercial claims
are made that such energy reductions are already possible. While this may
be so, it is beyond the scope of this publication to assess such developments
which have not been demonstrated for thermal processing applications. How-
ever, any scrubber proven capable of performing equivalently to those
described herein with lower energy consumption merits special consideration,
because of the very significant contribution of scrubber energy losses to
incinerator utility costs.
In the venturi-type scrubber, the gases are passed through a restricted
"throat", where water is injected and the gas velocity accelerated, typically
to 60 to 122 meters per second (200 to 400 ft/sec), promoting intimate gas-
liquid contacting, with gas pressure drops up to 122 mm Hg (60 in. ^0) and
higher. The wetted particles are then collected in a mechanical type device,
such as cyclonic separation chamber and/or wire screen demisters. Water rates
are in the range of 0.7 to 5.3 CM/1000 CM per minute (5 to 40 GPM/1000 CFM)
of gas at the scrubber outlet (Table 66). Variations of the venturi or ori-
fice gas motivated scrubbers may be found in Figures 52, 53, and 54.
Energy for a venturi scrubber is supplied by fans upstream or downstream
of the scrubber. The power requirement is about four (4) kilowatts per 1000
cubic meters/minute per mm Hg pressure drop (about 0.25 horsepower per 1000
cubic feet per minute per inch water pressure drop). Location of the fan is
significant. A downstream fan must contend with increased mass flow due to
water evaporation into the gas stream, although the volumetric flow rate may
be lower because of the lower temperature. A downstream fan must also contend
with impingement of sometimes corrosive water droplets, carried over from the
scrubber or from condensation; while an upstream fan must contend with the
design and maintenance problems associated with operation on a dirty gas at
elevated temperatures. The downstream option is normally chosen for incin-
erator type systems.
240
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FIGURE 52. GAS MOTIVATED VENTURI SCRUBBER VARIATION
{COURTESY OF CHEMICO)
242
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FIGURE 53. GAS MOTIVATED VENTURI SCRUBBER VARIATION
(COURTESY OF CHEMICO)
243
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FIGURE 54. GAS MOTIVATED ORIFICE TYRE SCRUBBER
(COURTESY OF KOCH ENGINEERING)
244
-------
In an ejector type venturi, high pressure liquid pumps rather than
fans supply the motive power. As shown in Figure 55, water is supplied
through a high pressure spray nozzle to the venturi section of the scrubber.
The gas and particulates are drawn into the scrubber and entrained by the
liquid entering the venturi. Compression of the gas in the venturi creates
the necessary pressure differential across the scrubber unit.
The gas and liquid droplets are intimately mixed by the turbulence
created in the venturi, and the wetted particulates are separated in a sec-
tion fol lowing the venturi, using baffles or other devices.
The total water requirement is usually in the range of about 5.4 cubic
meters per 1000 cubic meters of flue gas (about 40 to 50 GPM/1000 CFM),
primarily recycled water. Makeup water requirement is determined by the
rate of solids removal from the gas. The water pressure required is typi-
cally near 5.8 atmospheres absolute (about 70 psig).
Energy requirements are similar to venturi scrubbers, but the need for
a fan can be avoided where there are no other large draft requirements in the
system. There are no known applications of ejector type venturi scrubbers to
incinerators, but the possibility is worth investigating.
Since scrubber water requirements are high, recirculation is usually
practiced, both to minimize makeup water and to minimize the amount of
wastewater to be treated. The ratio of recycle to makeup water is determined
by the quantity of particulates to be removed, by the tolerance of the scrub-
ber design to the concentration of both soluble and insoluble materials in
the water, which tend to buildup with increased recycle, and the amount of
water evaporated or otherwise lost.
Incinerator stack gases contain acidic gases which are soluble in water.
These gases dissolve during scrubbing and cause the water to become acidic.
As a result, even stainless steel scrubbers have been known to corrode away.
Therefore, pH control by alkali addition must be practiced. This has two
other important effects. First, undesirable acidic gases such as hydrogen
chloride, hydrogen fluoride, and sulfur oxides are removed to some degree;
and second, some carbon dioxide is removed, increasing alkali consumption.
The latter may also have an important regulatory effect. Since emission
standards are based on a 12 percent carbon dioxide content, the lower carbon
dioxide content exiting from a scrubber can require an even lower actual
participate emission rate. The regulations are not clear on this matter.
A prediction of efficiency versus pressure drop (energy input) for a
venturi scrubber applied to a municipal incinerator has been made.^ Figure
56 presents this data assuming an inlet particulate concentration of 1.25
grains per standard cubic foot dry, (2.87 grams per standard cubic meter
dry) corrected to 12 percent COp. This data predicts that the Federal
Standard of 0.08 grains/standard cubic foot (0.18 grams per standard cubic
meter) can be reached, if at all, only at very high pressure drop.
However, several venturi scrubbers have been applied to incinerators,
operating data for which are also shown on Figure 56. This data does not
follow the predicted performance curve, but more nearly approximates the
245
-------
TREATMENT
CHEMICALS
(IF REQUIRED)
RECYCLE
DRAIN PUMP
TO TREATMENT
1
FIGURE 55. LIQUID MOTIVATED JET EJECTOR SCRUBBER
(COURTESY OF CROLL-REYNOLDS)
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FIGURE 56. PERFORMANCE CURVE FOR VENTURI SCRUBBERS
247'
-------
efficiency curve for a one micron particle or "fine particles" (<5u).24 It
would appear that a pressure drop of at least 22 to 32 mm Hg (12 to 17 in
HoO) is required to achieve the Federal standard. A "clear stack" (e.g.,
0.07 g/SCM or 0.03 gr/SCF) may require more than 37 mm Hg (20 in H?0),
although the scrubber water vapor plume tends to reduce this requirement by
masking the particulate opacity. The cleaned gases usually leave a scrubber
at a temperature near 65.6 C (150 F), saturated with water vapor, thereby
virtually always having a visible appearance from condensation of water vapor
into fine droplets in the atmosphere. Commonly referred to as a steam'or
water vapor plume, this phenomena is exempt from opacity regulations,
but has other effects which may require control. Steam plume control is
discussed elsewhere in this Chapter.
Wastewater from scrubbers can often be used to quench the furnace
residue prior to treatment or disposal, thereby reducing both water and
treatment costs.
Fabric Filters
Fabric filters or baghouses are widely used in industrial applications,
but only a few have been built for refuse incineration in the United States
and Europe. In this device, the particulate-bearing gas stream is passed
through a fabric filter medium of wo*/en or felted cloth, which traps the
particulates and allows the gas to pass through the pores of the fabric.
These pores are as large as 100 microns, but even sub micron particles are
captured, due to a buildup on the cloth of a fragile porous layer of collected
particles which blocks the pores. For various economic and practical reasons,
fabric filters are virtually always instructed in tubular form (bags) with
numerous bags housed in a steel vessel (baghouse).
In order to operate continuously, the filter must be intermittently
cleaned. This is accomplished by various means, including manual, mechanical,
or pneumatic shaking. The dislodged particulates fall to a hopper where they
are removed by screw or other types of conveyor, as with precipitator hoppers.
Figures 57 and 58 depict various bagiouse designs.
Design parameters include:
choice of fabric (based on gas temperature, humidity, and particle
characteristics)
size-length, diameter, and number of bags based on an empirically
obtained air flow to cloth ratio, and mechanical considerations.
method of cleaning (based on particle characteristics and vendor
preferences)
method of precooling the gases to the operating temperature
248
-------
TOTALLY ENCLOSED
FAN COOLED SHAKER
MOTOR EXPLOSION
PROOF OPTIONAL
PUSHROD
BAG SUPPORT
MEMBERS
POSITIVE BAG TENSIONING
FIGURE 57. FILTER BAG HOUSE WITH MECHANICAL SHAKING
(COURTESY BUFFALO FORGE)
249
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There is no apparent reason why a fabric filter will not easily meet any
existing participate standard based on dry catch. The lack of significant
use in incinerators may be due to various factors:
dramatic sensitivity to temperature
large space requirements
difficult maintenance
significant operating costs
The sensitivity of fabric filters to temperature is due to inability to with-
stand high temperatures (up to about 260 C or 500 F for the best fabrics);
and low temperatures, where moisture adsorption and condensation will occur,
blinding the bags and restricting flow. Operation consistently at tempera-
tures near the fabric high temperature limit may result in premature failure
and frequent costly replacement, while even an occasional excursion above the
temperature limit may cause failure or burnup of bags. Obviously, a well
designed, carefully operated system to reduce and control flue gas temperature
is an important part of any baghouse design.
Due to the large number of bags, baghouses require larger space than
scrubbers (excluding the wastewater system), but perhaps comparable space
compared to precipitators. Maintenance is difficult because hundreds of
bags are tightly spaced in a single housing. Physically finding and replacing
broken bags is a dirty, difficult job. Complicated electronic and pneumatic
timing and cycling devices for cleaning need specialized service.
High operating costs for baghouses are due both to the maintenance
problem and to significant pressure drops across the bags. Operating costs
are generally lower than for high efficiency scrubbers, but greater than
for electrostatic precipitators.
A pilot plant baghouse was operated with some success around 1959. One
recent commercial installation on a municipal incinerator has apparently been
operating reasonably successfully.28 Pertinent data are presented in Table
67.
Selection of Particulate Air Pollution Control Systems
To choose between electrostatic precipitator, scrubber, or fabric filter
systems for particulate removal from incinerator gases, parameters should be
compared to each specific situation.
Initial Cost
Including cooling systems, fans, stacks, waste disposal, and
other items dependent on the method of particulate control.
Operating Costs
Including power, water, maintenance, labor, and waste disposal.
251
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Table 67
OPERATING AND DESIGN PARAMETERS FOR FABRIC FILTER BAGHOUSE
ON MUNICIPAL INCINERATORS28
Air Flow,
cubic meters/min (CFM)
Air Temperature, C ( F )
Fabric
Air/Cloth Ratio,
cubic meters/min/sq.meter (CFM/ft2)
Bag Size,
diameter, meters (inches)
length, meters (feet)
Number of bags (approx.)
Method of cleaning
Design pressure drop, mm Hg ("H20)
5090 (180,000)
260 (500)
glass fiber
0.61 (2/1)
0.14 (5.5)
4.27 (14)
4350
reverse air
3.7-5.6 (2-3)
252
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Reliability
Considering best possible estimates for downtime; the effect of
downtime on other operations, sensitivity to upsets and ranges
of operating conditions; possible degradation of performance
with age, and problems which are induced in associated equipment.
Environmental and Other Considerations
including ability to meet and exceed emission standards, removal
of non-particulate pollutants, effect on the air quality of sur-
rounding areas, the possibility of undesirable plumes, and the
availability of facilities for waste disposal.
The initial cost for participate control systems tends to be comparable when
the complete system is considered, e.g., including gas coolers, hoppers, and
conveyors for precipitators; allow metal construction, alkali addition, water
supply, wastewater disposal, water vapor plume control for scrubbers; gas
coolers, hoppers, conveyors, and pulse air supply for baghouses. However,
a definitive estimate is necessary where cost is a primary consideration.
Energy requirements probably represent the single most important dif-
ference between systems. Because of low pressure drops through an electro-
static precipitator,, the total energy requirements are low, even though power
is required for the corona discharge and the rappers and heaters. Fabric
filter pressure drops are higher, requiring more energy, but scrubber energy
requirements is by far the greatest of the three systems. Table 68 illustrates
this difference. The importance of differences in energy requirements is at
least par Li ally dependent on the degree of energy recovery practices in the
incinerator and the availability of this energy for internal use.
Since all of these systems are highly automated, operating labor require-
ments are essentially comparable and low when the systems are operating properly.
Maintenance material and labor requirements for all of these particulate con-
trol systems can be very significant when designs and preventive maintenance
are inadequate, Thus, differences between systems may be less important than
the care which is tendered toward adequate design and operation.
Acid dew point corrosion of metal surfaces can be a problem in all cases,
but is more likely to occur when gases are cooled with spray water (rather
than with steam boilers), such as is sometimes done ahead of either precipi-
tators or baghouses, and always an integral part of scrubber operation.
Serious buildup of pressure drop and plugging can be serious problems with
scrubbers or baghouses, but seldom occur with precipitators. Problems of
hopper operation, which can occur with baghouses and precipitators, are
obviously not a part of scrubber operations. Moderate excursions of tempera-
ture may have relatively minor effects on precipitator and scrubber operations,
but can have drastic short or long term effects on filter bags, necessitating
frequent changes which require significant labor and downtime.
The performance of all of the particulate control systems considered here
can, at times, deteriorate. Dust buildup on either discharge or collection
electrodes will cause diminished precipitator performance. Discharge elec-
trodes in precipitators are subject to deterioration and breakage, sometimes
shorting out a section of the precipitator and reducing its effectiveness.
253
-------
Table 68
AN ILLUSTRATIVE COMPARISON OF ENERGY-REQUIREMENTS FOR PARTICULATE CONTROL
SYSTEMS*
Gas Motivated Fabric Electrostatic
System Scrubber Filter Preci pita tor
Gas pressure drop
mmHg ("H20) 28.0 (15.0 ) 9.3 (5.0) 1.9 (1.0 )
KW per 1000 m3/min. (hp/1000 CFM)
Fan Power 103.2 ( 3.92) 34.5 (1.31) 6.8 (0.26)
Pump Power 2.1 ( 0.08)
Electrostatic Power - 15.8 (0.6 )
Total Power* 105.3 ( 4.00) 34.5 (1.31) 22.6 (0.86)
This table is based on a hypothetical calculation for approximately
equivalent particulate removal efficiency, It does not necessarily
include sufficient fan power for all furnace and duct pressure drops.
Fan efficiency is approximately 60%. Power for heating hoppers
(electrostatic precipitators, baghouses) or for tracing water lines
(scrubbers) not included. These are variable depending upon design
and location.
254
-------
Hopper bridging can cause problems in both precipitators and baghouses. The
development of breaks in filter bags can have drastic effects on baghouse
performance. Deterioration in scrubbers can be caused by failure of spray
nozzles, mist eliminators, poor pump performance, and other means.
Dry flyash disposal, as usually practiced with electrostatic precipi-
tators and baghouses, is considered advantageous, but, unless the flyash is
carefully handled, a considerable amount of fugitive emission can occur. The
removal of solids in a slurry from scrubbers is less objectionable with in-
cinerators than in other applications because this system can be integrated
with the residue system for common water recycle and residue disposal
facilities.
As noted earlier, the scrubber has at least one major advantage over dry
methods for particulate removal. This advantage is the ability to simultaneous-
ly remove a significant portion of the gaseous emissions. However, present
regulations do not require this control, and, if later necessary, it is
possible to add efficient, low energy gas scrubbers such as packed column or
other types following the particulate control device. To plan for this possi-
bility, it is important to provide sufficient extra space and some static
pressure allowance in the fans. The advantage of simultaneous gaseous emis-
sion control can also be met by using wet electrostatic precipitators as is
done in certain other applications.
The major drawback to scrubbers, in addition to the high energy require-
ment, is the formation of visible moisture plumes and the possibility of
icing and condensation problems so caused. This problem is discussed in a
subsequent section.
The foregoing discussion has been designed to show that each approach
to particulate control has certain advantages and disadvantages. However,
sufficient information is available to allow a logical selection based on
careful cost and technical feasibility studies. Electrostatic precipitators
have been chosen for most recent projects.
Combined Refuse/Fossil Fuel Firing
When firing prepared refuse with coal in an existing boiler, it will
usually be necessary to adapt the available air pollution control equipment to
the new mode of operation. In most coal-fired boilers particulate control is
accomplished by high efficiency electrostatic precipitators. It is expected
that in many cases these precipitators can be used for combined firing with
little or no modification. However, where relatively low sulfur coal is
being fired with exit flue gas temperatures greater than about 270 to 280 F,
the addition of low sulfur refuse may introduce, or make worse, resistivity
problems due to the lack of sufficient sulfur trioxide conditioning agent
naturally present from the coal sulfur. The little data which is available
on this point strongly suggests this possibility.'3,26 jn this situation,
gas conditioning with sulfur trioxide or similar additives, or extensive
precipitator modification might be necessary to meet emission regulations.
255
-------
The firing of refuse with oil, which is being considered, may require
installation of special particulate control equipment, if the boiler is not
already so equipped. Some oil fired boilers have been converted from coal and
do have bottom ash removal, mechanical separators and/or electrostatic precipi-
tators which could be useful, but careful analysis is required for each situa-
tion to assess potential air pollution control and other problems.
The preparation of refuse for firing is discussed in Chapter VII. Emis-
sions from the dust collection cyclones used with the hammermill and air
classification system in a St. Louis demonstration plant have been measured. b
These measurements indicate that careful design and operating practices will
be necessary to avoid emissions from unit operations used to convert solid
waste to fuel.
Pyrolysis
The pyrolysis plants which are being built or considered can be separated
into two classes as far as air pollution control is concerned. First, there
are those plants which produce primarily fuels for sale and use in other
locations. These plants should not be prone to very serious air pollution
control problems, except for those problems, such as odors, generally asso-
ciated with handling municipal solid waste, and for possible emissions from
miscellaneous special unit processes such as shredding, air classifying,
and drying. The second class of plants are those that internally burn the
fuel produced to make steam for sale. In these plants, particulate control
could be as difficult as in incinerators, with evaluation criteria similar
to those already discussed.
Since pyrolysis processes available are primarily proprietary, the vendors
have been specifying the entire plant, including air pollution control systems.
This situation is expected to continue for some time. The limited information
available on air pollution control for commercially available pyrolysis
processes is covered in Chapter XI.
Gaseous Emissions
The overwhelming quantity of stack emissions from incinerators consists
of relatively innocuous gaseous combustion products, namely carbon dioxide
(CCL) and water (H20), and unused oxygen (02) and inert nitrogen (N9) from
the combustion airf The relative and absolute quantities of each alre deter-
mined primarily by:
the composition of the refuse
the amount of excess air used (deliberately as well as through
leakage)
the amount of air and/or water used for flue gas cooling and
cleaning.
256
-------
Figure 59 shows typical gas emissions as a function of excess air. Extensive
data for a range of solid waste compositions, excess air, and gas cooling
possibilities have been generated and reported, but as explained in the
reference cited, calculated gas flow rates are somewhat high and temperatures
lower than would actually be expected. Table 69 shows typical gas compositions
for two types of incinerator and air pollution control combinations. These
gases are generally of little concern, except for water plume formation and
insofar as certain air pollution standards are based on a specific gas composi-
tion, e.g., 12 volume percent CO^. Emissions of various inorganic and organic
contaminating gases are of concern and are considered in subsequent sections
of this Chapter.
Water Vapor Plume Control
High water vapor concentrations, under certain weather conditions, will
produce a visible plume. Given the temperature and water concentration in the
stack gas, the ambient temperature7and humidity conditions under which the
plume will form can be predicted. Water vapor plumes are not regulated, but
practical considerations, such as icing of nearby roads or buildings, fogging
over roadways, or psychological reaction to a visible emission, may necessitate
at least some degree of plume control.
As noted earlier, visible stack exhaust plumes will be experienced when
scrubbers are used, and may be experienced under certain weather conditions
with other devices. These plumes are caused by condensation of water vapor
into fine droplets when the hot, humid stack gases contact cold ambient air.
Under some circumstances, it may be necessary or desirable to eliminate the
visible plume.
The determining factors in plume formation are
stack gas temperature
stack gas water concentration (humidity)
ambient air temperature
ambient air humidity
Since ambient air conditions obviously are not controllable, the only methods
of water vapor plume control are to increase stack gas temperature and/or to
reduce stack gas water concentration. Control methods may be designed for
continuous or intermittent use, as desired.
Stack gas temperature can be increased by a stack burner which injects
very hot combustion gases directly into the stack, by mixing with a warmer
gas from another source, or by heat exchange with a source of heat (for
example, steam or furnace flue gases). The first two approaches may also
achieve a reduction in water concentration. Although relatively simple,
these methods are undesirable because of auxiliary fuel requirements. The
increased gas flow also may require a larger diameter stack.
257
-------
160 r
140
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Tfr
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EXCESS AIR (PERCENT)
250 300
FIGURE 59.
PER POUND OF TYPICAL WASTE19
258
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Heat exchange with the hot furnace flue gases is expensive because of the
large amount of heat exchange surface required. However, if the heat exchange
surface could be placed so as to remove heat directly from the combustion zone,
it is theoretically possible to decrease excess air normally required for
temperature control in conventional incinerators, thus increasing furnace
capacity as limited by solid handling capability. At least one system has
been built for heat exchange with hot flue gas, but none are known to operate
by extraction of heat directly from the combustion zone. Unlike the systems
discussed in the previous paragraph, indirect heat exchange does not decrease
moisture content, which could even increase if excess air is reduced.
Plume control by reducing stack gas moisture content may be even less
attractive than the methods described. All things considered, plume control
should be avoided unless a very serious local environmental condition, such
as road icing, results. In this case, intermittent control with the use of
fuel for a brief duration may be the best choice. Such systems have been
used on power plants.
Carbon Monoxide and Organic Gas Emissions
Poor combustion can result in emissions of carbon monoxide, hydrocarbons,
oxygenated hydrocarbons, and other complex compounds. Some of these emissions
are the source of odors which used to be associated with incinerator operation.
While no data have appeared for modern facilities, improved combustion effi-
ciency and control probably have reduced these emissions to insignificant
proportions. Table 70 lists some measurements which have been made on older
incinerators.
Handling and storage of solid waste, as well as furnace leakage, often
can create odors which may be detected both within the working areas of the
facility and in nearby residential or commercial areas.
No specific emission regulations exist which would control these emissions
from incinerators. However, ambient air quality standards for carbon monoxide
and hydrocarbons do exist (Table 71).
Inorganic Gas Emissions
Minor quantities of sulfur oxides, ammonia, and halide gases are produced
from the sulfur, nitrogen, and halide (chlorine, bromine, fluorine) content of
the solid waste. Nitrogen oxides emitted may result from the nitrogen content
of the waste or high temperature oxidation of nitrogen in the air. All these
emissions are expected to be directionally, but not necessarily quantitatively,
related to the concentration of the source element in the waste burned.
Table 16 shows typical quantities emitted.
Hydrogen chloride (HC1) has been of particular concern because of in-
creasing emissions due to increased disposal of polyvinyl chloride (PVC) and
other halide containing plastics and aerosols, because of possible health
260
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Table 71
FEDERAL1 AMBIENT AIR QUALITY STANDARDS FOR GASEOUS POLLUTANTS
Primary Standard
Secondary Standard
Carbon
Monoxide
Hydrocarbons
Photochemical
Oxidants
Sulfur Qxides+
Nitrogen
Dioxide
10 milligrams/m3
(9 ppm) maximum
8-hour concentra-
tion*
40 mi Hi grams/m3
(35 ppm) maximum
1-hour concentra-
tion*
160 micrograms/m3
(0.24 ppm) maximum
3-hour concentra-
tion (6-9 AM)*
160 micrograms/m3
(0.08 ppm) maximum
1-hour concentra-
tion*
80 micrograms/m3
(0.03 ppm) annual
arithmetic mean
365 micrograms/m3
(0.14 ppm) maximum
24-hour concentra-
tion*
100 micrograms/m3
(0.05 ppm) annual
arithmetic mean
same as primary
same as primary
same as primary
same as primary
1300 micrograms/m3
(0.5 ppm) maximum
3-hour concentra-
tion
*
+
not to be exceeded more than once per year
measured as sulfur:dioxide
262
-------
effects, and because of the possibility of corrosion, especially of tube metal
surfaces in steam generating systems (discussed in Chapter X). Table 16 shows
an approximate correlation between the PVC content of the refuse and HC1
emissions. It is believed that almost all of the chlorine in PVC (greater
than 50 percent chlorine) is converted to HC1 but that some of the HC1 reacts
with particulate matter and is removed by particulate control equipment.
Hydrogen chloride and fluoride, sulfur oxides, nitrogen oxides, and
some oxygenated hydrocarbons are acidic with at least some solubility in
water. Therefore, when flue gas is exposed to liquid water, such as in a
quench chamber or scrubber, or even due to cold wall condensation, very cor-
rosive conditions exist which will attack even stainless steel. Neutraliza-
tion, with caustic or other alkaline materials, both enhances removal and
helps prevent acid attack in wet systems.
There are no specific Federal emission standards for gaseous emissions
from incinerators, but ambient air quality standards do exist for sulfur
oxides, and nitrogen dioxide (Table 71 ). Though nitrogen oxide and sulfur
oxide emissions from power plants are limited by some regulatory standards,
no such limitations are known to exist for incinerators.
As shown in Table 72, ammonia is sometimes reported as a constituent
of incinerator effluent gases. The ammonia may result from refuse decomposi-
tion reactions. Wet pollution control systems would be expected to remove at
least some ammonia, especially where the water is acid or near neutral. No
specific regulations exist for ammonia control. Although information is only
minimal as to the extent of ammonia emissions, it does not appear to be a
serious problem.
Control of Gaseous Emissions
Carbon monoxide and hydrocarbon emissions, including odorous compounds,
are effectively controlled by a well designed combustion chamber, and careful
control of operating conditions. Odors from waste handling and storage can
be controlled by drawing the combustion air into the plant through these
areas so that the odor-bearing gases will be burned in the incinerator.
Similarly, leakage from the furnaces can be prevented by maintaining a slight
negative pressure within.
Inorganic gaseous emissions do exist in relatively low concentrations,
but they need not be controlled in the absence of specific regulations. Where
water scrubbers are used for particulate control, significant removal of hydro-
gen chloride, sulfur dioxide, and nitrogen dioxide (but not nitric oxide) will
occur. Where only electrostatic precipitators or baghouses are used for
particulate control, only a small amount of these gases will be removed,
limited to that quantity which reacts with or adsorbs onto particulates.
Monitoring
Although there are no specific requirements for air pollution monitoring,
the following stack monitors may be useful for operational as well as environ-
mental purposes and are often used.
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opacity (smoke density)
oxygen
carbon dioxide
combustibles
television
Opacity meters measure the transmission of light through the stack gases.
They can be used as an indicator of whether particulate emission standards are
being met, as well as to detect periods of poor combustion, characterized by
"smoke-laden" flue gas.
Oxygen and/or carbon dioxide monitors measure these chemical constituents
in the flue gas. They are useful as indicators of the amount of excess air
being used, although usually only one or the other is provided. Combustible
gas monitors measure organic content, and can be also used as an indicator of
furnace combustion conditions. Television cameras are useful for monitoring
smoke, water vapor plumes, and general surveillance.
In order to insure successful operation of monitoring instruments, provi-
sion for and practice of regular care, cleaning, calibration, and other
maintenance are essential.
Stacks
Traditionally, stacks have been used to provide natural drafts for the
furnaces as well as to disperse the "noxious" gases from previously uncontrolled
incinerators. With the use of fans in modern facilities, the draft aspects of
the stacks are less important. However, even with modern air pollution control
devices, stacks are generally still required to disperse residual pollutants in
order to avoid high ground level concentrations. Sophisticated dispersion
modeling techniques, usually computerized, can predict air quality resulting
from utilizing various stack heights and diameters, and can even aid in stack
location to avoid "downdraft" effects due to buildings and hills. As discussed
earlier, the choice of the number of stacks can also be affected by opacity
considerations.
If water vapor plumes are experienced, stacks also function to disperse
them before impinging on surfaces where icing or condensation can be harmful.
Numerous stack designs and materials, ranging from ordinary steel to cor-
rosion resistant steels (e.g., Corten, stainless) to brick and mortar have been
used, all with reasonable performance and expected lives. Stacks with hermeti-
cally sealed inner liners to prevent condensation and chemical attack have been
used for those installations requiring especially long-lived stacks.
265
-------
REFERENCES
1. Technical-Economic Study of Solid Waste Disposal Needs and Practices.
Combustion Engineering, Inc. Windsor, Ct. Report SW-7c. U.S. Depart-
ment of Health, Education and Welfare. Bureau of Solid Waste Management.
1969. Volume IV.
2. New Jersey Department of Environmental Protection. Regulations on Incin-
erators; New Jersey Administrative Code, Chapter 27, Bureau of Air Pollu-
tion Control Sybchapter 11, Incinerators; NJAC 7:27-11,
3. Achinger, W. C. and Daniels, L. E. An Evaluation of Seven Incinerators.
U.S. Environmental Protection Agency. Publication SW-51/ts-lj. May 12-
20, 1970. 76 pp.
4. Niessen, W. R. et al. Systems Study of Air Pollution from Municipal
Incineration. Volume I. Arthur D. Little, Incorporated. Cambridge,
Massachusetts. U.S. Department of Health, Education and Welfare, National
Air Pollution Control Administration Contract No. CPA-22-69-23. NTIS
Report PB 192 378. Springfield, Va. March 1970.
5. Duprey, R. L. Compilation of Air Pollutant Emission Factors. Public
Health Service Publication No. 999 AP-42. 1968,
6. Fernandes, J. H. Incinerator Air Pollution Control Proceedings, 1968
National Incinerator Conference., New York. May 5-8, 1968, American
Society of Mechanical Engineers,, pp. 101-116.
7. Jens, W. and Rehm, F. R. Municipal Incineration and Air Pollution Control.
Proceedings, 1966 National Incinerator Conference. New York,. 1966.
American Society of Mechanical Engineers, pp. 74-83.
8. Chass, R. L. and Rose, A. H. Discharge from Municipal Incinerators. Air
Repair. 3^(2): 119-22. November 1953.
9. Walker, A. B. Electrostatic Fly Ash Precipitation for Municipal Inciner-
ators, A Pilot Plant Study. Proceedings, 1964 National Incinerator Con-
ference. New York. May 18-20, 1964. American Society of Mechanical
Engineers, pp. 13-19.
10. Stabenow, G. Performance of the New Chicago Northwest Incinerator. Pro-
ceedings, 1972 National Incinerator Conference. New York. June 4-7,
1972. American Society of Mechanical Engineers, pp. 178-194.
11. Kaiser, E. R. 'Refuse Compositions and Flue Gas Analyses from Municipal
Incinerators. Proceedings, 1964 National Incinerator Conference. New
York. May 18-20, 1964. American Society of Mechanical Engineers, pp.
35-51.
12. Walker, A. B. and Schmitz, F. W. Characteristics of Furnace Emissions
from Large Mechanically-Stoked Municipal Incinerators. Proceedings, 1966
National Incinerator Conference. New York. May 1-4, 1966. American
Society of Mechanical Engineers, pp. 64-73.
266
-------
13. Klumb, D. L. Solid Waste Prototype for Recovery of Utility Fuel and
Other Resources. Presented at 1974 Annual Meeting of Air Pollution Con-
trol Association. Denver. June, 1974. Preprint No. APCA 74-94.
14. Environmental Protection Agency Regulations on National Primary and
Secondary Ambient Air Quality Standards. 40 CFR 50; 36 FR 22384. Novem-
ber 25, 1971. As amended by 38 FR 25678. September 14, 1973.
15. Environmental Protection Agency Standards of Performance for New Stationary
Sources. 36 FR 24880ff. December 23, 1971.
16. Bump, R. L. The Use of Electrostatic Precipitators on Municipal Inciner-
ators. Journal of Air Pollution Control Association. 18(12):807-809.
December 1968.
17. Hall, H. J. Design and Application of High Voltage Power Supplies in Elec-
trostatic Precipitation. Journal of the Air Pollution Control Association
25_(2): 132-138. February 1975.
18. Ensor, D. S. and Pilat, M. J. Calculation of Smoke Plume Opacity from
Particulate Air Pollutant Properties. Journal of Air Pollution Control
Association. 2T_(8): 496-501. August 1971.
19. De Marco, J. et al. Municipal-Scale Incinerator Design and Operation. PHS
Publication No. 2012. U.S. Government Printing Office, Washington, D.C.
1969. (formerly Incinerator Guidelines - 1969).
20. Fife, J. W. Techniques for Air Pollution Control in Municipal Incinera-
tion. American Institute of Chemical Engineers Symposium Series
70(137):465-473. 1974.
21. White, H. J. Resistivity Problems in Electrostatic Precipitation. Journal
of Air Pollution Control Association. 2^(4):313-338. April 1974.
22. Manual of Disposal of Refinery Wastes. Chapter 12. Electrostatic Pre-
cipitators. American Petroleum Institute Publication No. 931. Washing-
ton, D.C. June 1974.
23. Ross, R. D. ed. Air Pollution and Industry. Van Nostrand Reinhold. New
York. 1972. 489 pages.
24. Hesketh, H. E. Fine Particle Collection Efficiency Related to Pressure
Drop, Scrubbant and Particle Properties, and Contact Mechanism. Journal
of Air Pollution Control Association. 24^10):939-942. October 1974.
25. Shannon, L. J. et al. St. Louis Refuse Processing Plant: Equipment,
Facility, and Environmental Evaluations. EPA-650/2-75-044. U.S. Environ-
mental Protection Agency. Washington, D.C. May 1975. 122 pages. (NTIS
No. PB-243 634).
26. St. Louis/Union Electric Refuse Firing Demonstration Air Pollution Test
Report. EPA-650/2-74-073. U.S. Environmental Protection Agency. Washing-
ton, D.C. August 1974.
267
-------
27. Rohr, F. W. Suppression of the Steam Plume from Incinerator Stacks. Pro-
ceedings, 1968 National Incinerator Conference. New York. May 5-8, 1968.
American Society of Mechanical Engineers, pp. 216-224.
28. Bergmann, L. New Fabrics and Their Potential Application. Journal of
Air Pollution Control Association. 24(12):1187-1192. December 1974.
29. Carotti, A. A. and Smith, R. A. Gaseous Emissions from Municipal Inciner-
ators. U.S. Environmental Protection Agency. Publication SW-18c. 1974.
61 pp.
30. Corey, R. C. Principals and Practices of Incineration. Wiley Interscience,
New York. 1969. p. 82.
31. Gilardi, E. F. and Schiff, H. F. Comparative Results of Sampling Procedures
Used During Testing of Prototype Air Pollution Control Devices at New York
City Municipal Incinerators. Proceedings, 1972 National Incinerator Con-
ference. New York. June 4-7, 1972. American Society of Mechanical Engi-
neers, pp. 102-110.
32. Ellison, W. Control of Air and Water Pollution from Municipal Incinerators
with the Wet-Approach Venturi Scrubber. Proceedings, 1970 National Incin-
erator Conference. Cincinnati. May 17-20, 1970. American Society of
Mechanical Engineers, pp. 157-166.
33. Kaiser, E. R. and Carotti, A. A. Municipal Incineration of Refuse with
Two Percent and Four Percent Additions of Four Plastics. A Report to the
Society of the Plastics Industry. New York. June 30, 1971. Table 12.
268
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CHAPTER XV
ACCEPTANCE EVALUATION
The fundamental purpose for acceptance evaluation is to assure the owner
that the newly built thermal processing facility will adequately dispose of
the municipal solid wastes for which it has been designed. Success in meeting
schedule, cost, safety, health, aesthetic, reliability, and environmental
criteria will depend upon the adequacy of the owners planning, the consulting
engineer's design, and the contractor's performance. Planning and design work
should be completed and evaluated prior to the signing of a construction con-
tract; changes after this point are usually costly and should be made only when
imperative.
This discussion will consider only the more pragmatic purpose of accept-
ance evaluation, which is the determination that the thermal processing system
performance meets specifications, and that all provisions of construction and
sales contracts are being met. The method or means of acceptance evaluation
are provided for in contract terms. The American Society of Mechanical Engi-
neers (ASME) has been preparing test codes for measuring the efficiency and
performance of incinerators. These codes, plus the judgment of consulting
engineers and information obtained from recent experience by others, can
provide the technical basis for contract terms.
Project Management
Acceptance evaluation procedures are influenced by the nature of the
planning/design/manufacturing/construction team. A typical team consists of
the owner (municipality), the consulting engineer, an incinerator manufacturer,
and a general construction contractor. Other arrangements might include
separate contracts for chimneys, site work, cranes, and other major pieces of
equipment. Where the team becomes complicated, the owner or the consulting
engineer must supply formal project management services to coordinate con-
struction work and to handle acceptance evaluation. On the other hand, some
facilities are designed and built on a turnkey basis by a manufacturer who is
willing to take complete project responsibility.
The most meaningful overall performance guarantees are available on a
turnkey basis, but the value of guarantees should not be overrated. Although
the punitive effect of guarantees is real enough to the supplier, liability
is usually limited, subject to costly litigation, and seldom covers the
owner's true costs. Project organization should be focused on obtaining
reliable engineers and suppliers and providing tight project management, while
at the same time obtaining the best possible guarantees. The designer, who
may be the consulting engineer or a manufacturer, carries the major responsi-
bility for overall performance.
269
-------
Contracts should incorporate detailed specifications and timetables to
avoid misunderstandings between the owner and the supplier. The specifica-
tions will normally cover critical design features, selection and quality of
components, workmanship, installation responsibility, performance guarantees,
and inspection and testing procedures. Other specifications for the protec-
tion of the supplier may also be covered, including adequate space, utilities,
maintenance, access, and safety devices. Performance guarantees should cover
ranges of possible conditions when necessary to allow for variability and
uncertainty in basic data. For example, guaranteed burning efficiency and
steam generation for a new incinerator was tied to heating value in the
performance requirement shown in Table 73. "Burnout" or percent organics
in the residue is an important measure of performance which merits a guaran-
tee requirement in contracts.
Particulate emission standards and test procedures for incinerators are
provided in EPA's "Standards of Performance for New Stationary Sources,"2 and
can be included as a contract provision. Heavy metal emissions, such as com-
pounds of lead and mercury, which may occur in vapor, liquid, or solid form,
could also be limited by guarantees, but have not been done so to date.
Gaseous emissions which could be, but are not commonly, specified include
odors, carbon monoxide, hydrocarbons, sulfur oxides, nitrogen oxides, and
hydrogen chloride. Future incinerator designs could incorporate features to
minimize some of these gaseous emissions. For example, nitrogen oxide emis-
sions might be minimized through carefully controlled combustion, or hydrogen
chloride might be removed by scrubbing. Thus, it could become necessary to
include test procedures for these gases, or others, in the contract. One
important source of data for both emission and air quality testing procedures
is the Quality Assurance and Environmental Monitoring Laboratory located at
EPA's National Environmental Research Center in Research Triangle Park, North
Carolina. Some States, for example Texas,3 have recommended methods for gas
analysis. The contract should alsio specify the organizations which will carry
out the indicated tests.
Water quality test procedures may also become contract provisions. Ac-
cepted methods of analysis have been published by the U.S. Environmental
Protection Agency (EPA),4 American Public Health Association, and American
Society for Testing and Materials (ASTM). These contract provisions may
cover temperature, pH, BOD, suspended solids, dissolved solids, and other
accepted water quality measurements.
EPA also has manuals available which cover monitoring of wastewater and
analytical quality control in laboratories.8 ASTM standards cover many other
materials important in thermal processing, including petroleum products and
fuels (for pyrolysis processes) and building materials.
Quality criteria and testing procedures for pyrolysis units have not yet
been established, but close attention will have to be given to combustible
gas, liquid, and solid product qualitites where needed to meet internal uses
or sales contracts. Procedures will also be needed for resource recovery
products, and for air, water, and noise standards to be met in shredding,
separation, and resource recovery steps.
More complex contract provisions may provide formulas for the amount of
liquidated damages as a function of the performance of thermal processing
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h- QJ 4->
CO T- ro
§ja r—
S QJ
u «2 a:
271
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unit during the acceptance test, and as a function of the days of uncompleted
contract work beyond the specified completion date. Early completion may be
rewarded by a specified bonus per calendar day. Other provisions which may
affect acceptance evaluation will cover:
- payment schedules and tax payments.
- applicable codes and standards (e.g. ANSI, NEMA, ASME, ASTM, IEEE,
etc., including any local or other special standards).
- shop tests required for certification and proof that the equipment
conforms to all applicable codes and standards, including provisions
for cost, owner representation, and certified copies of test data.
- shop inspection.
- submission of certified drawings.
- instruction books.
- startup assistance and operator training.
- spare parts and lists of recommended spare parts.
- cleanliness, painting, and corrosion protection of equipment.
- special tools.
- auxiliary equipment such as controls, protective accessories, safety
devices, and measuring instruments. (All controls should be specified
for fail safe operation.)
- quality assurance programs.
- liability.
- performance bonds.
- conformity to occupational safety and health standards.
- construction schedule.
- deviations from plans, schedule, and specifications.
- warranties and maintenance standards for equipment items.
- arbitration of disputes.
- escalation of byproduct prices, e.g., escalation of steam or fuel
prices with published fuel prices.
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A "shakedown" period between completion of the facility and final accept-
ance testing or evaluation is provided for the protection of both the owner
and the contractor. This period may range from one month to as long as one
year.
Sufficient time is allowed for evaluation during actual operation when
deficiencies may be expected to occur, for on-the-job training for the
owner's operators, and for detection of equipment items which require exces-
sive maintenance. It also allows the contractors to correct deficiencies
without further monetary penalty.
Basic contract outlines should be available prior to bidding, since its
provision will affect the bidders response. However, allowance must be made
in bidding procedures for modifications and alternative proposals. Contracts
must be reviewed by technical personnel as well as by the owner's administra-
tive and legal staff to assure that the terms are comprehensive, self-
consistent, consistent with Federal, State and local regulations, and that
they properly spell out all necessary responsibilities and liabilities.
Acceptance Tests
The procedures and sampling equipment being used by the Office of Solid
Waste Management Programs (OSWMP) of the Environmental Protection Agency can
provide a basis for final acceptance evaluation for incinerators. The OSWMP
document cited covers:
- preliminary test arrangements.
- charging and operation.
- incoming solid waste characterization.
- residue and grate siftings characterization.
- flyash arid breeching fallout characterization.
- characterization of process and wastewaters.
- stack sampling.
- incinerator efficiency.
No similar document is yet available for pyrolysis facilities, but some of
the items cited above can be useful for this purpose. As stated previously,
test codes for incinerators are under development by ASME (New York City).
In addition to the overall plant acceptance, proper evaluation procedures
will cover various components of the final plant including foundations and
concrete structures, buildings and other structures, pressure vessels and
piping, non-coded vessels and piping, rotating equipment, heat exchangers,
instrumentation, electrical equipment, mobile equipment, safety equipment,
273
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communications equipment, personnel, and sanitary facilities, maintenance
facilities, roadways, landscaping, parking facilities, conveyors, stokers,
grates, cranes and hoists, scales, refractories, chimneys, laboratory equip-
ment and facilities, drainage, wastewater treatment, and air pollution con-
trol. Shop and field inspections should confirm that materials of construc-
tion have been supplied as specified, component and code requirements have
been met, workmanship is satisfactory, and that schedules are being met.
Defective construction and equipment should be identified at the earliest
possible time to minimize startup delays and costly post-completion corrections.
Proper records must be kept by those responsible for acceptance evaluation.
Preliminary tests on components in place should precede the overall
acceptance test. However, final performance tests are best done under
conditions of full operation where maximum thermal and vibrational stresses
are normally encountered. Periodic inspections of all equipment externally
and internally should be made during the "shakedown" period.
Everything possible sould be done to schedule a fullscale acceptance
test early in the "shakedown" period, so that sufficient time is available
for corrections, if necessary. All interested parties should be invited to
observe the acceptance test, including the consulting engineer, manufacturers
of major equipment (e.g. air pollution control, furnaces, fans, resource re-
covery), and representatives of regulatory agencies. Contracting for assist-
ance of unbiased third parties for pollution control and other testing is
recommended for the final acceptance test.
274
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REFERENCES
1. Rogus, C. A. Incineration with Guaranteed Top-Level Performance. Public
Works: pages 92-97, September 1970.
2. U.S. Environmental Protection Agency. Standards of Performance for New
Stationary Sources. Washington, D.C. Federal Register 38(111). Part II.
December 23, 1971. Pages 24876-24895.
3. Compliance Sampling Manual. Texas State Department of Health. Air Pollution
Control Services. March 1, 1973.
4. U.S. Environmental Protection Agency. Methods for Chemical Analysis of
Water and Wastes. National Environmental Research Center. Cincinnati,
Ohio. 1974. 298 pages.
5. Standard Methods for the Examination of Water and Wastewater. 13th Ed.
American Public Health Association. Washington, D.C. 1971. 874 pages.
6. Annual Book of ASTM Standards. Part 31. Water. Pub!. Code No. 01-031076-16.
1976. 986 pages.
7. U.S. Environmental Protection Agency. Handbook for Analytical Quality
Control in Water and Wastewater Laboratories. National Environmental
Research Center. Cincinnati, Ohio. June 1972.
8. Achinger, W. C. and J. J. Giar. Testing Manual for Solid Waste Incinerators.
U.S. Environmental Protection Agency. SW-3ts. 1973.
275
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CHAPTER XVI
SOLID WASTES THAT REQUIRE SPECIAL CONSIDERATION
Municipal refuse often contains wastes which are unsuitable for or require
special consideration for disposal in incinerators or other thermal processing
systems. These special wastes can be minimized by collection restrictions,
thereby diverting them to landfill or other disposal methods. Included as
wastes that require special consideration are bulky items, obnoxious and
hazardous materials, high and low heating value combustibles, sewage sludges,
and various industrial wastes. They can create difficult or even catastrophic
problems. Some can be handled readily in amounts sufficiently small so as to
be diluted to a harmless level by the balance of the solid waste; others, for
example bulky steel scrap, can cause damage even as isolated items.
Bulky Wastes
Typical bulky wastes are shown in Table 74. Bulky wastes require special
consideration because they may.
1. Overload, clog, or jam conveyors, grates, and other moving equipment
(e.g. stoves, branches, mattresses).
2. Be physically too large to enter or leave the thermal processing unit
(e.g. refrigerators).
3. Contain very little combustible materials.
4. Be so dense as to smolder and prevent complete burnout of other
waste (e.g. tires and rugs).
Table 74
EXAMPLES OF BULKY WASTES
Logs, branches, stumps
Furniture (metal, wood, plastic)
Mattresses, bed springs
Crates, boxes, skids, pallets, lumber
Tires, wheels, other auto parts
Stoves, washers, dryers, refrigerators, water heaters
Lawn mowers, garden equipment
Rugs
Asphalt or concrete chunks
Mixed demolition waste
276
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Included in bulky waste is the estimated five to ten percent of municipal
bOlid waste which is combustible but measures over 1.2 meters (4 ft.) in
length and eight centimeters (3 in.) in diameter.' Quantity and types of bulky
waste will vary greatly from community to community and season to season,
depending on collection practices, industrial and commercial activities, resi-
dential makeup and age, and other factors. A distribution of bulky wastes in
a New York City sample is shown in Table 75. Some data on composition, density,
quantity, fuel value, proximate analysis, ultimate analysis, combustion air
requirements, and smoke producing propensities of oversized wastes have been
developed.^
Table 75
WEIGHT DISTRIBUTION OF OVERSIZED WASTE
(NEW YORK CITY)!
Weight,Percent of
Total Oversized Waste
Trees, slumps, brush 1.3 to 9.6
Furniture and fixtures 1.2 to 40.0
Lumber and remodeling waste 6.3 to 36.0
Cardboard and paper 1.0 to 4.1
Rubbish and other 15.8 to 40.8
Non-burnable 18.7 to 38.8
Even in modern thermal processing systems, bulky wastes are often
separated, either at the collection point, or at the plant. Although it varies
from installation to installation, separation usually is "manual," requiring a
human decision and action. Separation by laborers at the pit, hoppers, or
conveyors, or by the crane operator is not unusual. Salvage is sometimes
practiced to at least partially offset separation cost.
Disposal in landfills is acceptable where suitable sites are available.
Volume requirement is high, however, and open burning of combustibles to reduce
the volume is now permissible only under very unusual circumstances. Special
incinerators to handle bulky wastes have been used, but the costs of a
separate facility may not be justified if alternative disposal means are
available.
277
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Modern approaches to the problem of bulky wastes include shredding, either
mixed with other solid waste in a feed preparation or resource recovery system,
or separately for adding-back to unshredded waste for incineration. Obviously
the shredder should be of sufficient size and durability. Shredding is
covered more fully in Chapter XVII, Resource Recovery.
Hazardous Wastes
Highly flammable, explosive, toxic, radioactive, and environmentally
disruptive materials may be classified as hazardous. Wastes that produce such
materials even thermally processed may also be classified as hazardous. The
health and safety of operating and nearby personnel, and protection of equip-
ment and of the environment, require that hazardous wastes be given special
treatment.
Typical hazardous wastes are listed in Table 76. It is impossible to
completely prevent their entry into the main municipal solid waste stream.
However, since almost all of these materials can be handled in quantities
where their effects are diluted to a harmless level, provision should be made
to minimize their quantity. This can be most effectively done by restriction
at the collection level; preferably by special pickup with segregation and
labeling of the hazardous wastes; or by requiring special pickup and disposal
by licensed operators. This approach can be effective because the most im-
portant sources of such wastes are industrial plants.
Table 76
EXAMPLES OF HAZARDOUS WASTES
Paint, solvents, gasoline, kerosene, oils
Highly flammable plastics, dusts, shavings
Explosives and pyrophoric materials
Organic chemicals, including toxic materials such as pesticides,
phenols, and chlorinated compounds
Other toxic materials such as mercury, lead, and arsenic
compounds, and wastes which contain appreciable amounts of
toxic materials (e.g. lead-containing waste crankcase oil
and paint)
Acids, caustics, other reactive chemicals
Biologically active materials e.g. pharmaceutical wastes and
some pathological wastes from veterinarians and hospitals
Radioactive wastes
Pressurized containers
Contaminated containers
278
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Solvents, oils, organic chemicals, explosives, and other highly flammable
materials present dangers of fires or explosions in trucks, pits, shredders,
and feed systems, as well as presenting heat or explosive damage potential to
furnaces. Organic chemicals, pesticides, toxic materials, biologically active
materials, acids, caustics and other similar materials present potential health
and safety hazards to the operating personnel and possible environmental
problems. The best protection against these hazardous materials is certainly
to keep them out of the system; in actual practice that is to keep the frequency
and concentration very low.
Pressurized containers, such as aerosol cans, welding gas tanks, and
propane cylinders, when heated in a furnace, can explode and become missiles.
Protection against these occurrences lies in both good design and education of
the public and collection and operating personnel to keep these out of waste
fed to thermal processing facilities.
Radioactive wastes should not be accepted, but should be disposed of by
the user in accordance with Atomic Energy Commission standards. Communities
where this is a potential problem could use detection devices on the solid
waste feed system.
Detection of hazardous wastes after collection is very difficult, if not
impossible. Severe restrictions and enforcement at the collection site appears
to be the only practical method of control. Disposal at the incinerator site
may only be safe and practical if dilution is possible, or if the facility
has been specifically designed to handle them. Disposal at industrial waste
disposal or other specially designed facilities should be considered. For
example, some highly industrialized areas now have privately run waste disposal
plants which accept and dispose of difficult wastes, mostly from industrial
plants on a toll basis. The safety and environmental problems are then dealt
within one centralized location.
Plastics
Ordinary plastic components of municipal solid waste have received much
publicity, particularly concerning acid gases (hydrogen chloride and other
hydrogen halides) formed during the combustion of polyvinyl chloride and other
halide-containing plastics. These acid gases may contribute to equipment
corrosion, including air pollution control equipment, induced draft fans,
and heat transfer surface used to generate steam, as well as to atmospheric
pollution. Insufficient information is available to fully evaluate potential
corrosion problems, but the many satisfactory operations suggest that such
problems can be overcome by good design, and operation, for example by avoiding
condensate formation and minimizing superheater tube temperatures. Even the
potential for air pollution problems is unclear because of lack of data on
adsorption of acid gases by flyash. In any case, no restrictions presently
exist on hydrochloric acid emissions. Such emissions could be controlled by
scrubbing, if necessary, but scrubbing is expensive and introduces requirements
for water treatment, including neutralization.
In spite of the above, high concentration of polyvinyl chloride and other
plastics, which can be caused by the introduction of industrial wastes, should
279
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usually be avoided since these may contribute to making significant the
potential corrosion and air pollution problems discussed, and because the
combustion characteristics of many plastics differ sufficiently from the bulk
of the solid waste that carbonaceous and gaseous emissions may increase.
Plastics do increase refuse heating value, contributing to energy recovery.
Halogen-containing plastics also present special problems in pyrolysis,
resulting in chlorinated and halogenated organics when not separated in
resource recovery systems. Nonhalogen-containing plastics such as polyethylene,
polybutylene, and polystyrene obviously do not present problems of chlorinated
byproducts.
Obnoxious Wastes
Examples of obnoxious wastes are provided in Table 77.
Table 77
EXAMPLES OF OBNOXIOUS WASTES
Pathological wastes (anatomical, surgical dressings, other human
and animal hospital wastes)
Food and meat processing wastes
Dead animals
Odiferous chemicals
Pathological wastes from hospitals, dead animals, food and meat processing
wastes, animal droppings and similar materials present potential health hazards
as well as disagreeable working conditions to operating personnel. Unless
specific arrangements are made, these wastes should not be routinely accepted.
Satisfactory arrangements may include use of appropriate disposal packages
which contain the obnoxious effects of odors, bacteria and viruses, insects,
and visual and other unpleasantness.
Most hospitals have pathological waste incinerators, but wastes from
medical laboratories, doctors offices, veterinary hospitals, research centers,
and taxidermists may find their way into municipal solid waste, if not con-
trolled. Restrictions through licensing may be most effective, but collection
practices should also be monitored.
Most large-scale food or meat processing plants have suitable disposal
facilities. Wastes from butchershops, supermarkets, fish stores, and
restaurants may become troublesome if substantial and not properly packaged.
Generally, however, these sources generate small quantities which can be
easily handled.
230
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Dead animals are collected from highways in significant numbers. These
may be handled with care in a thermal processing unit, if not too bulky.
However, landfills are often used for disposal.
If significant quantities of obnoxious wastes are generated, the thermal
processing facility should be designed to handle them; a separate special
facility may also be considered. Use of a truly sanitary landfill for
obnoxious wastes can be satisfactory assuming proper leachate control is
provided,
Sewage Sludge
Sewage sludge is the residue from treatment of raw sewage. While very
large amounts of sludge are already generated, the quantity will increase very
dramatically as municipalities build secondary treatment plants (under Federal
grant programs). Present sludge disposal practices include:
1. Ocean dumping.
2. Landfill.
3. Incineration.
Ocean dumping presents serious problems and will most likely be eliminated as
proven alternative technology becomes available. Landfill is acceptable if
available. In locations where landfill is not available for municipal solid
waste, it is not likely to be available for sludge. Therefore, thermal
processing appears to be a possible alternative.
Many fluidized bed and multiple hearth incinerators have been used for
sludge incineration, but due to the high water content and fuel requirements,
operating costs are high. An approach of interest is combined sludge-municipal
solid waste incineration, whereby the fuel value of the waste is used to
evaporate the water from the sludge.
In a refractory incinerator, air in substantial excess over that required
for combustion is used to moderate the temperature. As seen in Table 78,
simultaneous burning of solid waste and the wet sludge reduces tempering air
requirements. In addition to the obvious advantage of this dual function,
additional benefits accrue:
1. Flue gas volume is reduced, resulting in lower air pollution control
system investment and operating costs. Fans, motors, ducts, stacks
and associated equipment can be relatively smaller and less costly.
2. Alternatively, furnace throughput may be increased since this
generally is limited by the combustion air rate.
Another approach which deserves consideration is the use of the hot flue gas
from the incinerator for pre-drying of the sludge. This obviously requires
additional equipment, but does allow handling as a solid.
281
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Table 78
COMPARISON OF CONVENTIONAL INCINERATION AND SLUDGE-MUNICIPAL
SOLID WASTE CO-INCINERATION PARAMETERS
CONVENTIONAL
PARAMETER INCINERATION
Solid Waste, kg @ 25° C 454
HHVt cal/g 2780
%u r\ oo
ri-U C.L.
% Ash 21
Sludge, kg @ 25° C 0
HHVt cal/g
% H20
% Ash
Air, kg @ 25° C 4690
normal cm/metric ton* 8950
% excess 185
Flue Gas, kg 5050
°C 870
Ash, °C 870
CO-INCINERATION
454
2780
22
21
341
222
95
1.4
3150
3460
100
3840
870
870
* of solid waste plus sludge
+ HHV = high heating value; low heating value of sludge containing 5%
solids is negative.
282
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In summary, various alternatives are worthy of consideration (though
not necessarily proven):
1. Incineration of sludge and raw refuse in a refractory incinerator.
2. Incineration of sludge in a multiple hearth employing solid waste as
an auxiliary fuel.
3. Combustion of sludge with solid waste in a fluidized bed incinerator.
4. Utilization of waste heat from the combustion of solid waste to
evaporate moisture from sludge prior to disposal of sludge, or
incineration in the same or a different combustion chamber.
5. Utilization of spray technique to inject wet sludge directly into
the combustion chamber of a solid waste incinerator.
The use of solid waste incineration to aid in sludge disposal has been
practiced in the past.2»3 At least one full scale plant (in Ansonia, Connecticut)
is currently practicing the fourth possibility above with some success.
It may or may not be possible to handle all of the solid waste and sewage
sludge in a single system, depending on the quantities to be handled and their
characteristics, especially the water content of the sewage sludge.
283
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REFERENCES
1. Kaiser, E. R., D. Kasner, and C. Zitimer. Incineration of Bulky Refuse
Without Prior Shredding. New York University. New York. EPA Report
No. 670/2-73-023. National Technical Information Service No. PB 221731.
U.S. Environmental Protection Agency. July, 1973. 91 pages.
2. Stephenson, J. W. and A. S. Cafiero. Municipal Incinerator Design Practices
and Trends. Paper prepared for 1966 National Incinerator Conference. New
York. May 1-4, 1966. American Society of Mechanical Engineers. 38 pages.
3. U.S. Environmental Protection Agency. Third Report to Congress-Resource
Recovery and Waste Reduction. SW-161. Office of Solid Waste Management
Programs. 1975. Pages 93-94.
284
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.•,-/;•--•• pro^c,!":;. Fxi"-t'f'C> 'Hf'.'i C'J'T-r.llf.fj tf*f:;-nolO'4y, C0?-ib
! '". f ';'"1 ;*"'*''* T»'- r»ufir ^ ^f*'"1!,'^ ffH/r ' i '** ' ;>5! ! f',*'I'^ ' •,.,'***(-
'.,'' ;;c'i-^ w^iTi • r;r:pnr!~>nts ^* -* >y»';o"e'*y or '. !: ',-•";.>"- ''• t--. '-V'.y i11, •*•"'* *•'•
" rK> -•;•:.' ori processes *.*{?. c;o •'•'?* sir>n »o ''c*-^- by pyr
: ,' (iir» f"-"1!-!* '* i s fts a part Of thsrwgl pyvft**; inn 5 y =
.<4>y :vtsy *''skR placa prior to iherr.--'* pf«-,r.-.e?i ..<•«.
'
"-',»:•; which, in pr'n'-'ipie, can be c3lvage*J fr'-; *-«•*
•-"•;••: 1rsc]-.<;l.':' pftper pruducts, r^'^'OHS «Pt^ls} ?«'"=-*' - f"- ".
'•'-, t I'bh^r1 , and plastics. The ex?ffir-''!e tn Tabjc5 /*? -to
'
>? V', :•',, :ME>, ';) per nettle, ten of solid waste, side f 1 •./•:*• ufit.1 *)*>;» '''
- f t •»•• ,-»«^'".-« r
'.- >-\' r?(,;Mio?: at the source f^.g,. cjrbsi^e,' ^^ K^r:.}-,^,'^:^....'
'• tf::;Ut':t(".'f rtfcyHnu ceitc*1 1s tne ^oct rec.r1'* vnp^ra-'h
.-..i vrjr ^ -! "_ v ^ g ;; n;;rf ,'5;?? t( i-r *0 SC'Cre'lu*4? f;U
.- "";dC""' ^i';S r>:»X *'•'," \'?tr, t-',0 -Of."^- fii'j'i : C • Z*~
dlspOlgC Of ffl 3 }f;fKif1l'( H3r«''
• ;• or ';.f h'gh *,;r-r>t o^ laL*or, and because uf thf :-»o-i, -, •> • .;v •;..-( n r= tf-r :s i', hut a'^'; by ^c:*•^i'^":c';fi''
-------
Plastics,
leather,
rubber, tex-
tiles, wood
Garbage and
yard wastes
Miscellaneous
(ash, dirt,
etc.)
Table 79
POTENTIALLY SALVAGEABLE MATERIALS
IN A MIXED MUNICIPAL REFUSE*
Paper and
cardboard
Glass
Ferrous metals
Nonferrous
metals
Percent
Original
Refuse
33.0
8.0
7.6
0.6
by Weight
Potentially
Salvageable
15.0
5.6
6.8
0.6
Commodity
Value,$/MT
Material
5-50
5-50
5-50
150-400
Potential
Revenue
$/MT Refuse
0.75- 7.50
0.28- 2.80
0.34- 3.40
0.90- 2.40
6.4
15.6
1.8
l.O1
Moisture
73^0"
27.0
100.0
2970
$2,27-16.10/MT7r
($2.06-14.60/ST)
* Based in part on data in reference 1.
#
Potentially recoverable rags and plastics.
Excludes possible credits for energy recovery from
unsalvaged refuse.
286
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will reduce the ash component of solid and liquid fuels produced during
pyrolysis, or improve the incineration process by minimizing furnace damage
and decreasing the quantity of solid residue. Removal of non-combustibles
is a vital step in the preparation of combustible refuse for use as a fuel
component in combination fossil fuel/prepared refuse steam boilers.
Two primary steps are required to practice the type of resource
recovery technology now becoming available. The first is size reduction to
allow physically freeing the various types of materials present from each
other. Thus, size reduction usually precedes the second step, which is
physical separation based on utilizing property differences of the materials
present. Each of these steps will be discussed in more detail, followed by
a discussion of commercially available resource recovery systems.
Size Reduction
The size reduction of municipal solid waste has been variously called
shredding, milling, pulverizing, grinding, and comminution, even though only
the last term can be considered truly generic. The other terms are more or
less related to the type of equipment used. In this publication, the term
shredder will be used as a general term for equipment designed to reduce the
size of municipal solid waste, except where wet pulpers are used.
There may be as many as 70 suppliers of equipment with the potential for
use in municipal waste size reduction.2,3,6 yne many kinds of equipment
available are summarized in Table 80. The most common types now in use are
the hammermills, and rotary ring grinders, but such classifications encom-
pass many possible variations. For example, hammermills may be vertical or
horizontal; they may use swing hammers, rigid hammers, and even shredding
members; or they may differ in the design of reject systems.
The first stage of size reduction is usually designed to produce material
nominally in the 5 to 25 centimeter (2 to 10 inch) range. Ballistic separation
of metals may be an integral part of the first stage. A second stage, where
required, reduces the size to that required for the process used, or for
separation. Classification may be practiced between size reduction stages.
A 50 ton per hour shredder will usually require a motor in the 500 to 1000
horsepower range.
Well designed primary size reduction equipment should be able to handle
most objects found in unsorted municipal waste, including, for example, home
appliances, storage drums, solid wood, and even tires on wheels; but hardened
steel objects, and flammable and explosive materials can cause severe wear
or damage. Other materials, such as rugs, mattresses, wire, or plastic
sheets and milk bottles, sometimes cause operability problems. Collection
restrictions, presorting, and prescreening can be helpful in a size reduction
system, but troublesome materials are difficult to eliminate entirely. Actual
tests should be carried out wherever possible before final equipment selection.
In addition to capital and operating costs, major considerations in the
choice of size reduction equipment are durability, reliability, composition of
feed, and suitability for the particular separation process contemplated. For
287
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Table 80
CURRENT SIZE-REDUCTION EQUIPMENT AND POTENTIAL APPLICATIONS
TO MUNICIPAL SOLID WASTE2
Basic types
Variations
Potential application to
jnunicipal solid waste
Crushers
Cage disinte-
grators
Shears
Shredders,
cutters, and
chippers.
Rasp mills and
drum pulver-
izers
Disk mills
Wet pulpers
Hammermills
Impact
Jaw, roll, and
gyrating
MuHi-cage or single-
cage
Multi-blade or
single-blade
Pierce-and-tear type
Cutting type
Single or multiple
disk
Single or multiple
disk
Direct application as a form of
hammermi11.
As a primary or parallel opera-
tion on brittle or friable
materi al.
As a parallel operation on
brittle or friable material.
As a primary operation on wood
or ductile materials.
Direct as hammermi11 with mesh-
ing shredding members, or
parallel operation on paper
and boxboard.
Parallel on yard waste, paper,
boxboard, wood, or plastics.
Direct on moistened municipal
solid waste; also as bulky
item sorter for parallel line
operations.
Parallel operation on certain
municipal solid waste fractions
for special recovery treatment.
Second operation on pulpable
material.
Direct application or in tandem
with other types.
288
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example, a wet size reduction system would not be used with a dry separator,
nor would a disintegrator producing primarily very fine particles be used
with an air classifier. Wear, maintenance, and power input are other major
considerations in the choice of size reduction equipment.
Size reduction can be practiced either on the entire waste stream
prior to resource recovery, or simply as a method for reducing the size of
bulky waste to allow handling in the thermal processing system.
Physical Separation
A thorough investigation into unit processes available for solid waste
separation is provided in a 1971 U.S. Environmental Protection Agency report.
This report and more recent literature^S discuss the techniques shown in
Table 81. However, since solid waste separation is a rapidly evolving tech-
nology, the state-of-the-art must be carefully determined at the time of process
selection. A few of the more advanced techniques will be described here.
Air Classification. Development studies in recent years have shown the
feasibility of air classifying shredded municipal refuse to remove metal,
glass, rocks, rubber, and wood. As a result, air classification has been
incorporated as a primary separation step into several municipal solid waste
thermal processing systems, including the preparation of refuse for combined
prepared refuse/fossil fuel combustion in steam boilers, for pyrolysis, and
for fluidized bed combustion.
In a vertical air classifier, air is drawn upward through a vertical
column at a predetermined velocity, while the shredded solids are fed to the
top or to an intermediate point. The solid particles are fractionated accord-
ing to density, size, and shape. The particles whose properties are such that
they cannot be transported by the airstream move countercurrently to the
stream, and are discharged at the bottom of the column. The transported
particles move with the airstream through a blower and cyclone separator
for recovery. In some cases, multiple classifiers in series can be used to
separate several different products. Figure 60 is a schematic flow diagram
showing one possible arrangement for such a system, while Figure 61 shows
a cross section of an air classifier. A supplier's specification for a
45.4 metric ton per hour classifier is provided in Table 82, and an analysis
of an air classified light fraction is provided in Table 83.
Ferromagnetic Separation. Removal of ferrous metals magnetically can be
practiced prior to air classification, after air classification, or both.
As will be discussed later, when resource recovery is not practiced prior
to incineration, ferrous metals are sometimes recovered from incinerator
residue. Removing ferrous metals from municipal solid wastes is basically
rather simple, but problems arise from contamination of the recovered metal
with refuse entrapped by the metal as it is attracted to the magnetic
separator.
289
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Table 81
UNIT PROCESSES FOR SOLID WASTE SEPARATION2'4'5
Potential Municipal Solid
Waste Appli cati on
Magnetic Separation
Inertia! Separation
Ballistic
Secator
Inclined Conveyor
Eddy-Current Separation
Electrostatic Separation
Size Classification
Vibrating Screens
Spiral Classifiers
Air Classification
Vertical Chute
Zig-Zag Flow Classifier
Horizontal Chute
Vibrating Elutriator
Gravity Separation
Dense Media
Stoners
Tabling
Zigging
Osborne Dry Separator
Fluidized Bed Separator
Rising Current Separator
Optical Sorting
Sweating
Flotation
Cryogenic Separation
Magnetic materials (iron)
Differences in size, density, elastic
properties (depending on type)
Conductive non-magnetic materials (copper,
aluminum, zinc)
Aluminum from glass; plastics, paper19
Preparation for further processing or rough
cut separations
Light material, such as paper, from heavier
materials
Glass from metals, paper from other mate-
rials, and other separations based on
density difference
Dirt from glass, separation of colored
glass
Melting to separate metals (e.g., lead and
zinc from aluminum)
Air bubbles in liquid used to separate mate-
rials with differing affinities for air and
fluids used
Difference between materials in tendency to
become brittle at low temperature (e.g.,
liquid nitrogen)
290
-------
UJ
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oc
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291
-------
AIR DENSITY
StfAHAlOH
FIGURE 61. CROSS SECTION OF AN AIR CLASSIFIER30
-------
Table 82
SPECIFICATION FOR AN AIR CLASSIFIER9
Feed: Milled residential, industrial, commercial solid waste
Particle size - 95% less than 20.23 cm. (8 in.)
- 99% less than 30.48 cm. (12 in.)
Moisture - 0-40% by weight
Density - 0.064 to 0.321 grams/cc (4-20 lbs/ft3) loose
Envelope Dimensions (includes conveyors, blower, stands, etc.): 15.24 meters
long by 15.24 meters wide x 12.19 meters high (50 x 50 x 40 ft.)
Weight Installed: 54.4 metric tons (60 short tons)
Electrical Requirements: 440 Volts -3 Phase -60 Hz
Total Installed Horsepower: 100-200
Nominal Performance:
Capacity - 41 to 54 metric tons per hr. (45-60 short tons/hr.)
Light Product (80-90 weight %) - Less than 10 weight %
inerts (fine glass, sand)
Heavy Product (10-20 weight %) - Less than 5 weight %
fibrous material
- 98% of the ferrous metals
- 80% of the aluminum
- 98% of the other metals
- 80% of the glass
293
-------
Table 83
AIR CLASSIFIED REFUSE ANALYSES LIGHT FRACTION
194 samples taken November 9, 1973 through March 28, 197425
As Received Basis, Wt. %
Average
Maximum
Minimum
Moisture
30.3
66.3
11.1
Ash
16.8
31.3
7.6
Sulfur
0.10
0.28
0.04
Chlorides
Total
0.41
0.94
0.14
NaCl
0.33
0.59
0.11
Cal/g
2768
4218
1274
(Btu/lb)*
(4983)
(7593)
(2293)
Ash Analysis, Wt. %
Average
Maximum
Minimum
P205
sfo2
A1203
Ti02
Fe203
CaO
MgO
S03
K20
N320
Sn'02
CuO
ZnO
PbO
1.43
49.90
11.38
0.87
7.89
12.21
1.29
1.48
1.57
8.87
0.05
0.32
0.41
0.19
2.04
58.10
26.90
1.52
22.19
15.80
2.32
3.75
2.91
19.20
0.10
1.74
2.25
0.73
0.99
39.90
6.10
0.07
3.03
8.51
0.22
0.54
0.92
3.11
0.02
0.08
0.09
0.04
* higher heating value
294
-------
The magnets used can be of a permanent type, or electromagnets. Direct
current for the electromagnets normally required purchase of a rectifier.
Alternating current is required for belt drives. When electromagnets are
used, designs must allow for lower magnetic strength at operating temperatures
as compared to cold startup temperature.
Rotating drum and suspended magnets have been used for primary separation.
These and pulley type magnetic separators can be used after classification. ''
Although magnetic separators have been widely used in industry, design changes
have been necessary to adapt these to processing of municipal solid waste. For
example, multiple magnets in a suspended separator with a moving belt and modi-
fied drums have been developed to separate non-magnetic entrapped materials by
successive attraction and release of the ferrous metals.
Nonferrous Metal Separation. A promising advance in this field is the develop-
ment of eddy-current techniques for the separation of conducting non-magnetic
materials from municipal solid waste which has been pre-processed by shredding,
classifying, and ferrous metal removal.7 The trash-metal mix from the pre-
processing steps is conveyed into a polyphase alternating current electromagnetic
field which induces electrical currents in conducting materials, such as aluminum,
generating in turn magnetic flux opposite in direction to the initially imposed
flux. The resulting repulsive force sweeps aluminum can stock laterally off the
belt for collection.
A single aluminum separator module is designed to handle approximately 1.3
to 2.3 metric tons per hour of trash-metal mix recovered from about 9 metric tons
per hour (10 short tons/hr) of shredded waste. Therefore, a 36 metric ton per
hour (960 short tons/day) thermal processing plant would require a splitter and
at least four modules. Other limitations of this approach include the necessity
for a relatively high speed belt to allow spreading out the feed, reducing the
probability of extraneous material being swept off the belt with the aluminum
stock; the necessity for careful shredding both tb avoid too fine shredding which
can cause aluminum flaking and loss in pre-processing steps, and too coarse
shredding which can result in poor air classification increasing the contamina-
tion and quantity of the trash-metal fraction; and the potentially increased
contamination level of recovered aluminum when the fraction of aluminum in the
shredded waste is low.
System specifications for a four module aluminum separator are shown in
Table 84. A second stage separator is under development to recover a mixed
product containing the remaining aluminum, and other metallics such as copper,
zinc, stainless steel, and brass.
The heavy fraction from air classification can also be processed with a
series of screens and sink-float (dense media) devices to separate individual
metals. This approach is under development.
Met Pulping. The organic and friable fractions of solid wastes can be con-
verted into a water slurry in equipment known as a HydrapulperJO in tnis
pulping process, after separation of non-suitable feed materials such as tires,
295
-------
Table 84
SPECIFICATION FOR A DRY ALUMINUM SEPARATION TECHNIQUE7.8
Modules: Four (for a 36 MT/hr thermal processing plant)
Feed: Dense fraction of milled classified residential, commercial solid
waste, less ferrous metals
Particle size - 95% less than 15.24 cm. (6 in.)
Aluminum size - 90% greater than 2.54 cm. (1 in.)
Moisture - No limitations
Density - Greater than 0.64 grams/cc (40 lbs/ft3)
Shape - No limitations
Envelope Dimensions (includes conveyors, screen, separators): 12.2 meters
long by 6.1 meters wide by 3.05 meters high (40 ft x 20 ft x 10 ft)
Electrical Requirements: 440 Volts - 3 Phase - 60 Hz
Total Installed Horsepower: 75 (equivalent)
Efficiency: 60-80% recovery of can stock material (based on aluminum in
dense fraction); about: 50% of total aluminum in solid waste
Aluminum Analyses (based on pilot plant samples):
Chemical Analysis, weight %
Element
Si
Fe
Cu
Mn
Mg
Cr
Ni
Zn
Ti
V
Pb
Sn
Bi
Sample
I
0.28%
0.43
0.14
0.84
0.96
0.02
0.00
0.05
0.02
0.01
0.00
0.00
0.00
Sample
II
0.28%
0.41
0.16
0.83
0.99
0.02
0.00
0.45
0.02
0.01
0.00
0.00
0.00
Alcoa Grade I
0.3%
0.5
0.25
1
2.
.25
.0
0.2
0.2
0.5
0.1
0.1
0.1
Hand Picked Analysis, weight %
Pieces of Cans or Containers
Heavy Material
Foil
Dirt
91.7%
7.5
0.1
0.7
100.0
296
-------
large appliances, and building demolition wastes, water is added to the solid
waste in a large mixing vessel containing a high speed cutting rotor, similar
to a Waring blender. Non-pulpable material, such as metal cans and stones,
are ejected through an opening in the side of the mixing vessel. The slurry,
containing about 3 to 4 weight percent solids, is removed through a perforated
plate at the bottom to a liquid cyclone and other equipment for subsequent
recovery and separation of metals, glass, and organics. Wet pulping in effect
serves both as a size reduction method and as a first step in a series of
physical separations.
Usable long paper fibers can be recovered from the slurry for sale as a
low-grade paper fiber, leaving an organic residue suitable for thermal process-
ing, or the entire organic fraction can be recovered from thermal processing
without separating the paper fibers. A 5 to 7 metric ton per hour (150 short
tons/day) demonstration has been conducted.'0 The Hydrapulper in this opera-
tion was 3.66 meters (12 feet) in diameter and equipped with a 300 horsepower
motor.
Glass Separation. The recovery of mixed glass in a resource recovery operation
will normally be from a secondary or tertiary separation step, after separation
of light materials, such as paper and metals. The methods used will vary with
the overall scheme, involving processes such as air classification, dense media
separation, froth flotation, and water e-lutriation. However, the mixed glass
product has limited value unless it is color sorted and free of contaminants J'
Since a market does exist for pure color sorted glass cullet, there is consider-
able incentive for automatic color sorting to separate flint (clear), amber, and
green fractions. This technology is under development.'2sl3
In the Sortex optical separator, a continuous stream of individual
particles are dropped through an optical box, containing three photocell assem-
blies set at 120° intervals and suitable illumination sources. Opposite each
photocell head is a background with variable shades of color. Each particle
passes through the viewing area and, if there is a change in its reflectivity
with respect to the background standard, either lighter or darker as desired,
a blast of compressed air is triggered to deflect the offcol or particle from
the main stream. Two optical separators in series will first separate flint
(clear) from colored glass, and then separate the colored glass into amber and
green.'4
Conveying Systems
Conveyor performance plays a major role in determining the reliability of
resource recovery systems. Various conveyors used are called infeed con-
veyors, for feeding shredders; transfer conveyors, for transferring shredded
material from the shredder discharge to a discharge conveyor; discharge
conveyors, for discharging to a storage area or the next processing step;
and other conveyors used for magnetic separation, changes in direction, etc.
Belt conveyors are easily maintained and are usually the least expensive
of the conveyor types available, but are subject to failure by impact of sharp
objects fed onto the belt from trucks, cranes, or other feeders. Their
minimum speed of about 24 meters per minute (80 ft./min.) for good tracking is
generally too fast for feeding a shredder. On the other hand, speeds greater
297
-------
than 24 meters per minute may cause paper and other light materials to float.
In addition, angles greater than 20° without cleating are not recommended.
Therefore, the best uses for belt conveyors in resource recovery systems are
for conveying heavy materials at high speeds over level areas, and for use
with magnetic separators where ordinary steel conveyors interfere with magnetic
operation.
Apron conveyors are preferred for infeeding and transfer conveyors even
though capital cost, horsepower, and maintenance are greater than for other
types of conveyors.'5 For infeeding, these conveyors are typically 1.2 to 1.8
meters (48 to 72 in.) wide and travel 1.5 to 7.6 meters per minute (5 to 25 ft./
min.) with a variable speed drive. They can be inclined to approximately 35°
with 10 cm. (4 in.) flights welded to the pans. Compression feeders and
leveling conveyors are often used with apron conveyors for infeeding to shred-
ders. Special attention must be paid to the details of conveyor construction to
insure proper operation, rugged construction, and ease of maintenanceJ5 A
typical shredder installation with conveyors is shown in Figure 62.
Integrated Resource Recovery Systems
Although important advances have been made in recent years, no complete
resource recovery system can be categorized as fully developed for widespread
application. A summary of available systems which can provide feed for thermal
processing is provided in Table 85. Flow diagrams for some of these systems
are provided as Figures 63 to 69.
Resource Recovery After Thermal Processing
Each available thermal process produces at least one solid residual
material with limited potential value. Typical incinerator residues, shown
in Tables 86 to 88, contain large amounts of glass and ferrous metal. Resource
recovery prior to incineration, not now practiced to any significant degree,
would obviously reduce the total amount of residue considerably and change
its nature. The exact effect would depend upon: whether only ferrous metal
was recovered; whether both ferrous metal and glass were recovered; whether
other materials such as nonferrous metals were recovered; and the efficiency
of these recoveries. The separation and firing of a combustible fraction with
coal in a conventional boiler leads to an ash, mixed with and essentially
indistinguishable from the coal ash.
The residues from pyrolysis processes were discussed in the Pyrolysis
Chapter. These may be high ash chars, with some potential value as a low
grade fuel; and slag-like materials high in glass content, with some poten-
tial value as construction materials. Of the commercially available processes,
only in the Landgard process is ferrous metal recovered after pyrolysis, and
even there, plans to magnetically separate the solid waste feed will limit such
recovery from the residue.
293
-------
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Refuse Collection Truck
Belt Scale
Conveyors
^ f
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Conveyors
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Magnetic Separator —j
zz^
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\ FIGURE 6a CITY OF ST. LOUIS SOLID WASTE
- Belt Scale PROCESSING FACILITIES
L- Stationary Packer
Self—Unloading Truck
303
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KEY ,
Air to boghouse
Water to recycle
system
c=>
Glass, heavy food,
and other organics
FIGURE 66. BUREAU OF MINES RAW SOLID WASTE SEPARATION SYSTEM
306
-------
Water
1
•
Gas
Purifier
1
n ; 1 / , \
I
Wet
Scrubber
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Aggregate
FIGURE 67. LANDGARD RESOURCE RECOVERY
AND PYROLYSIS SYSTEM
307
-------
FIGURE 6a HERCULES RESOURCE RECOVERY SYSTEM
308
-------
(SCHEMATIC DIAGRAM gig
PROCESS FLOW ||
AW XM3I1
9CM*Afa
2MO STMC
1ST STAte 1 „ ,Mk.»» f
UMNCTIC
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li |3| |3S
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XX \-S XX
PROCESS FLOW DIAGRAM
LANOFILL-
LANDFIl
1
g\ | TOTAL SOLID WASTE |
AUTOS, SELF HAULEI
T
f TIPP
75%
«. TRUCKS
SCALE
ING FLOOR '
(|00%(REFUSE PROCESSED)
•j^%- MANUAL SEPARATION
REJECTS - ,
TO RECLAIM 98%
ORLANOFLL 1
L FIRST 8TA6E SHREDOINO
-------
Table 86
COMPOSITION OF GRATE-TYPE INCINERATOR RESIDUES2
Component
Glass
Tin cans
Mill scale and small iron
Iron wire
Massive iron
Nonferrous metals
Stone and bricks
Ceramics
Unburned paper and chemical
Partially burned organics
Ash
Total
Average
percentage*
44.1
17.2
6.8
0.7
3.5
1.4
1.3
0.9
8.3
0.7
15.4
100.3
Table 87
COMPOSITION OF ROTARY-KILN INCINERATOR RESIDUES2
Component
Average
percentage*
Fines, minus 8-mesh (ash, slag, glass)
Glass and slag, plus 8-mesh#
Shredded tin cans
Mill scale and small iron
Nonmetallics from shredded tin cans
Charcoal
Massive iron
Iron wire
Ceramics
Handpicked nonferrous metals
Total
35.8
99.6
* Dry weight basis.
Of the total weight of this fraction, 1.8 percent is
recoverable nonferrous„metal.
n
ff Of the total weight of this fraction, 1.4 percent is
recoverable nonferrous metal.
310
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Table 88
ANALYSIS OF INCINERATOR RESIDUE24
Component
Dry Basis
Weight
Percent
Wire and large iron
Tin cans
Small ferrous metal
Nonferrous metal
Glass
Ash
TOTAL
3.0
13.6
13.9
2.8
49.6
17.1
100.0
311
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Current Incinerator Residue Salvage
The only significant salvage practiced on incinerator residue is ferrous
metal recovery. Even this practice is limited to not more than 10 to 20 in-
cinerators in the United States. Ferrous metal, primarily cans, is recovered
from residue either magnetically, or by the use of revolving cylindrical
screens called trommels. The cans are retained by the trommel, while most
of residue passes through for .landfill disposal. Ferrous metal recovered by
either method may be washed and shredded in the incineration plant, or by the
purchaser.
Most of the recovered ferrous metals must be shipped to the western part
of the United States for use in copper precipitation. The remaining recovered
ferrous metal is either used directly in steelmaking, or first detinried and
then used for steelmaking.
Emerging Incinerator Residue Salvage Technology
Ferrous metals are valuable and relatively easy to recover from incinerator
residues, but glass and nonferrous metals in the residue are also potentially
valuable. For this reason, the U.S. Bureau of Mines has piloted a complete
resource recovery system for incinerator residue. A full-size processing plant
designed by the Raytheon Company based on Bureau of Mines data, and capable of
handling 227 metric tons of incinerator residue per 8 hours, is beina built in
Lowell, Massachusetts with Federal assistance (cancelled July 1975).'2 The
processing scheme will be similar to that shown in Figure 70, producing the
materials shown in Table 89.
Markets for Recovered Materials
The ultimate success of any resource recovery system hinges both on
the availability of suitable markets and on the availability of technology
and operating skill to produce products meeting the specifications required
in the marketplace. The commitment of capital for resource recovery facili-
ties must be preceded by identification, understanding, and security of
markets. A few of the fundamental considerations follow.
Fuel
As previously discussed, the marketing problems which exist for 100 per-
cent solid waste firing in a steam producing municipal incinerator are those
of being reasonably close to the "demand for steam or electrical power, and of
matching supply with a varying demand. On the other hand, the preparation of
combustible refuse as a fuel, for firing with fossil fuels in existing
utility system boilers, introduces normal product marketing problems such as
quality, quantity, shipping distance, storage capacity, and competition with
conventional fuels.
312
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TROMMEL WASH
I '/4-inch op«nings
WASH
AIR BLOW
»-» Recycle wattr
VACUUM PUMP
Small I'on, I
mill >cal« j
MATRIX-TYPE MAGNETIC SEPARATOR
WASH [""I WASH
it '
i
Colored qloss, Cltor
mill lean gl»»
VIBRATING
SCREEN
35
flj
DRUM i-
MAGNETIC pK-,
SEPARATOR ^
PUMP
PERIPHERAL
DISCHARGE
ROD MILL
'EENh J- nJ
mtiti r_ IT
ow 1 I Nonftrrou:
-I-*-! I I m«toll
SAND
PUMP
FIGURE 70. BUREAU OF MINES INCINERATOR
RESIDUE RECOVERY SYSTEM31
313
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Table 89
EXPECTED PRODUCTS FROM THE LOWELL INCINERATOR RESIDUE
RESOURCE RECOVERY PROJECT"(CANCELLED.'JULY 1975)
High Value Products
Aluminum
Zinc-Copper
Ferrous Products
Colorless Glass
Medium Value Products
Mixed Color Glass
Slag
Sand
Waste Products
Unburned Organics
Filter Cake
Weight Percent
of the Residue
1.5
1.0
30.5
20.8
10.2
14.0
17.0
1.4
3.6
100.0
314
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The experience already accumulated on preparing refuse derived fuel from
solid waste and firing this fuel with coal in an existing boiler lends confi-
dence to such projects. However, as other similar projects are undertaken,
great care must be observed to avoid problems which could arise due to
difference in the physical and chemical properties of the fuel, and due to
differences in steam boiler design. For example, chemical properties of the
fuel might vary with classifier operation, raising questions about corrosion,
slagging, and air pollution control in the boiler. Besides careful choice of
processing equipment, the best means for avoiding such problems are careful
analysis of raw refuse, prepared fuel, and other materials, and co-operative
testing with potential customers.
It is anticipated that carefully prepared fuel from municipal solid waste
should eventually approach the value of coal on a net heating value basis,
though more complex evaluation procedures have been developed.26 The calcula-
tion of value per ton of fuel is illustrated in Table 90. Although all
characteristics of the fuel (such as physical form, sulfur, ash, and chlorine
contents and ash fusion point) may play a role in determining its price, the
heating value and shipping distance are overriding factors, assuming the
basic acceptability of the fuel for its intended use.
A full understanding of the intended use is vital in determining its value
to the customer. For example, the low sulfur content of prepared refuse fuel
is a credit in boilers having difficulty meeting sulfur oxide emission stan-
dards, but may be a liability in boilers already burning low sulfur coal where
low sulfur levels can lead to insufficient natural sulfur trioxide gas condi-
tioning required for adequate electrostatic precipitator performance. In
other applications the ash content may be critical, where the relatively high
ash per unit of heating value in fuels derived from solid waste may increase
particulate emissions, or overload existing ash handling systems.
Paper Fiber
In some installations the recovery of paper fiber may be justified even
at the expense of feed to the thermal processing facilities. For example,
paper fiber recovered from an existing resource recovery system was reportedly
sold in the $27 to $72/M6 ($26 to $65/ST) range,27 certainly competitive with
fuel use. Therefore, it is advisable to investigate the cost of paper fiber
recovery and possible markets to determine whether such recovery is justified.
Ferrous Metals
Ferrous metal, including cans, recovered from solid waste must compete
with other sources of iron and steel scrap. Of the three major markets which
exist, the western U.S. copper precipitation market, where recovered can metal
is preferred because of its high surface area per unit of weight, is usually
unavailable because of distance and shipping cost; the detinning market has
usually been unavailable because of marginal profit and aluminum contamination;
and the steelmaking market is undependable because the contaminants in re-
covered ferrous metal make this a material of last resort. The most favorable
315
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counteractants to this picture is the emerging resource recovery technology
for separate recovery of other metals and clean ferrous metal recovery, and
the emergence of industrial organizations specializing in the cleaning and
purification of crude recovered metals for resale to processors. In some
cases, compaction of recovered metal to improve handling may be necessary.
To assure stable markets for recovered ferrous metal, cooperative testing
and long-term contracts with purchasers are recommended, even at prices well
below those which sometimes exist during peak scrap demand. Escalation clauses
should be considered based on market conditions and contamination level. A
stable supply of reasonably priced scrap may encourage foundries and steel-
makers to devise systems with the capability of handling contaminated ferrous
scrap. Both the potential for use and the problems have been demonstrated in
extensive test work.28
Aluminum
Increasing costs for electrical power and for aluminum ores have created
considerable incentive for maximizing aluminum recycle. The high price being
offered for scrap aluminum has encouraged recovery at the source through volun-
teer organizations and others.11 Although it is expected that a considerable
amount of aluminum will still find its way into solid waste, its concentration
in the waste is very low, on the order of one weight percent or less. As
shown earlier in this Chapter, even at low concentration it is well worth
recovering because of the high price. As with ferrous metals, contamination
is a very important consideration, increasing reclaiming costs, and careful
attention must be given to this problem.
An interesting possibility exists for installing aluminum scrap electrical
melting furnaces to produce aluminum ingot for sale to fabricators. In
thermal processing facilities where electrical power is produced, this possi-
bility is even more attractive. Such an operation could handle both aluminum
recovered from solid waste and aluminum separated at the source, for example
from volunteer organizations.
Other Nonferrous Metals
As shown earlier in this Chapter, other nonferrous metals such as copper
and zinc can be recovered from solid waste as mixed metal lies, or possibly as
separate metals by further processing. Many nonferrous metals are in short
supply worldwide, providing considerable incentive for improving recycling
methods.
Glass Gullet
A good market exists for clean color-sorted glass cullet in many parts of
the United States. These materials are used in existing glass melting furnaces
along with the raw materials normally used in glass making. The development of
317
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adequate methods to recover clean glass sorted into flint (colorless), amber,
and green colors is the critical problem in this market, but present techno-
logy appears to be expensive. If good quality glass can be produced consist-
ently, it should find ready market acceptance in glass melting furnaces,
because of savings in energy consumption and advantages in air pollution
control as compared to the use of raw materials for glassmaking. The poten-
tial for unsorted glass is much less favorable.
Plastics
Although no market now exists for plastics recovered from solid wastes,
it is possible that as technology develops for recovering plastics, markets
could become available either through existing reclaiming operations, or by
the development of new products which can use the reclaimed plastics. Cer-
tainly the high price paid for clean segregated plastic scrap provides con-
siderable incentive for improved technology.'' Unfortunately, the very wide
variety of plastic materials and the low concentrations present in solid
waste preclude any simple answer to the problems of separation and salvaging.
At the moment it appears that, at least in thermal processing facilities, the
best outlet for plastics is in the thermal process itself, either recovering
heat from combustion or fuels by pyrolysis.
Flyash
The principal sources of flyash in thermal processing facilities will be
from air pollution control equipment in incinerators, and in boilers where
fossil fuels and prepared refuse are fired together. These ashes may be
available wet or dry depending upon the particular forms of air pollution con-
trol and of ash handling. Some important uses of flyash from coal fired steam
boilers have been developed, primarily in construction materials, but these
uses consume only a minor part of the total available ash.29 Flyash from
incinerators will compete in the same market, either successfully or unsuccess-
fully, depending upon the particular location and aggressiveness of the facility
management. Fortunately, sterile flyash is not an objectionable fill material
and can be disposed of where fill is desired, in special landfill sites, or in
sites where a variety of wastes are accepted.
313
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REFERENCES
1. Resource Recovery - The State of Technology. Prepared for the Council
on Environmental Quality by Midwest Research Institute. National Techni-
cal Information Service. Springfield, Va. PB-214 149. Feb 1973. 67 pp.
2. Drobny, N. L. et. al. Recovery and Utilization of Municipal Solid Waste.
Report No. SW-lOc. U.S. Environmental Protection Agency. U.S. Govern-
ment Printing Office. Washington, D.C. 1971.
3. Shredders...Processing Our Solid Waste. The NCCR Bulletin. National
Center for Resource Recovery (Washington, D.C.) 111(1) :12-18, Winter 1973.
4. Dale, J. C. Recovery of Aluminum from Solid Waste. Resource Recovery.
Jan/Feb/Mar 1974. pages 10-15.
5. Cheremisinoff, P. N. Air Classification of Solid Wastes. Pollution
Engineering. December 1974. pages 36-37.
6. Boettcher, R. A. Air Classification of Solid Wastes. U.S. Environmental
Protection Agency. SW-30c. U.S. Government Printing Office. Washington,
D.C. 1972. 73 pages.
7. Campbell, J. A. Electromagnetic Separation of Aluminum and Nonferrous
Metals. Combustion Power Company, Inc. (Presented at 103rd. American
Institute of Mechanical Engineers Meeting. Dallas, Texas. February 24-28,
1974)
8. AL MAG 40-Aluminum Magnet Separator Systems. Combustion Power Company,
Inc. Menlo Park, Calif.
9. Solid Waste Air Classifier-Model 50. Combustion Power Company, Inc. Menlo
Park, Calif.
10. Neff, N. T. Solid Waste and Fiber Recovery Demonstration Plant for the
City of Franklin, Ohio. Prepared for U.S. Environmental Protection Agency
by A. M. Kinney, Inc. PB-213 646. National Technical Information Service.
Springfield, Va. 1972. 83 pages.
11. Darnay, A. and W. E. Franklin. Salvage Markets for Materials in Solid
Wastes. Contractor-Midwest Research Institute. Kansas City, Missouri.
U.S. Environmental Protection Agency. SW-29c. U.S. Government Printing
Office. Washington, D.C. 1972. 187 pages.
12. Office of Solid Waste Management Programs. Third Report to Congress-
Resource. Recovery and Waste Reduction. U.S. Environmental Protection
Agency. SW-161. U.S. Government Printing Office. Washington, D.C. 1975.
96 pages.
13. Sullivan, P. M. et. al. Resource Recovery from Raw Urban Refuse. Bureau
of Mines. RI 7760. U.S. Government Printing Office. Washington, D.C. 1973.
28 pages.
319
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14. Herbert, W. and W. A. Flower. Glass and Aluminum Recovery in Recycle
Operations. Public Works. August 1971.
15. DiGravio, V. P. Materials Handling and Shredding Systems for Size
Reduction of Solid Waste Constituents. Metcalf & Eddy, Inc., Boston,
Mass. (Presented at American Society of Mechanical Engineers Design
Committee Meeting, January 20, 1971). 9 pages.
16. CEA's Brockton Plant Now Producing Fuel. Resource Recovery. Jan/Feb/Mar/
1974. Page 30.
17. Winners Named for Construction and Operation of $80,000,000 Resource
Recovery Plants in Connecticut. Resource Recovery. Apr/May/June/1974.
Pages 8-9.
18. Small Pellets Made from the Nation's Wastes Could Help Supplemental Fuel
Supplies. The American City. March 1974. Page 137.
19. Grubbs, M. R. and K. H. Ivey. Recovering Plastics from Urban Refuse by
Electrodynamic Techniques. Technical Progress Report 63. Bureau of
Mines. PB-214 267. National Technical Information Service. Springfield,
Va. December 1972. 6 pages.
20. Can a Smaller City Find Happiness with Resource Recovery. Resource
Recovery. Nov/Dec/1974. Pages 8-12.
21. American Can Will Take Over Disposal of Milwaukee's Solid Waste. Chemical
Week. January 22, 1975. Page 35.
22. Liabilities Into Assets. Environmental Science and Technology. 8(3):210-
211. March 1974.
23. Trash-Can Contents Turned Into Fuel. The American City. March 1974. Page
137.
24. Henn, J. J. and F. A. Peters. Ccst Evaluation of a Metal and Mineral
Recovery Process for Treating Municipal Incinerator Residues. 1C 8533,
Bureau of Mines. U.S. Government Printing Office. Washington, D.C. 1971.
41 pages.
25. Klumb, D. L. Solid Waste Prototype for Recovery of Utility Fuel and Other
Resources. Union Electric Company. Paper APCA 74-94. (Presented at Air
Pollution Control Association 67th Annual Meeting. Denver, Col. June
9-13, 1974). 16 pages.
26. Eggen, A. C. and R. Kraatz. Relative Value of Fuels Derived from Solid
Wastes. Proceedings of the 1974 National Incinerator Conference. Miami,
Fla. May 12-15, 1974.
27. Colonna, R. A. and C. McLaren. Decision-Makers Guide in Solid Waste
Management. SW-127. U.S. Environmental Protection Agency. U.S. Govern-
ment Printing Office. Washington, D.C. 1974. 157 pages.
320
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28. Ostrowski, E. J. Recycling of Ferrous Scrap from Incinerator Residue in
Iron and Steel Making. Proceeding of 1972 National Incinerator Conference.
New York, N.Y. June 4-7, 1972. Pages 87-96.
29. Capp, J. P. and J. D. Spencer. Fly Ash Utilization—A Summary of Applica-
tions and Technology. 1C 8483. Bureau of Mines. U.S. Government Printing
Office. Washington, D.C. 1970. 72 pages.
30. Sutterfie'id, G. W. et al. From Solid Waste to Energy. City of St. Louis
et al. (Presented at the U.S. Conference of Mayors. Solid Waste Seminar.
Boston, Mass. October 4, 1973), 13 pages.
31. EPA Supports Incinerator Resource Recovery. Reuse/ Recycling 2(No. 8):2.
Technomic Publishing Co. Westport, Conn. Dec. 1972.
321
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CHAPTER XVIII
OPERATION AND MAINTENANCE
Having a well designed, fully equipped thermal processing facility is
a prerequisite to achieving satisfactory plant performance with acceptable
expenditures of time and money for operation and maintenance. While the
importance of at least adequate facilities may seern obvious, it is a fact
that many plants are poorly designed, or are forced to operate at above the
capacity for which they were designed. In other instances, the charac-
teristics of the solid waste burned has changed since the plant was de-
signed and performance is adversely affected. In order to achieve the
required throughput while at the same time meeting burnout criteria and
effluent control requirements, plant management people often are forced
to increase operating and maintenance staffs, make expensive equipment
modifications, and justify frequent replacement of critical equipment or
parts.
Having acknowledged the importance of design to successful thermal
processing of solid wastes, one must guard against the tendency to over-
emphasize positive and negative roles of the design engineer, which is past
history, while overlooking the important everyday contributions of opera-
tion and maintenance. Poor design is difficult to overcome, but operating
management can make or break adequately designed facilities.
Management and Personnel
As a community plans and builds a thermal processing facility, it
should also plan for the management and personnel necessary to operate it.
The plant supervisor should be involved as early as possible during the
design and construction period, but at least several months before construc-
tion is completed so that he can become thoroughly familiar with each major
component as it is installed. Operating personnel should be obtained early
enough so that they can work closely with representatives of the manufacturers
and contractors when the facility is in the latter stages of construction and
put through the acceptance tests. In this way, personnel can be trained in
proper ooeration, maintenance, and repair.
' At t?ieo~u^^eT7~the management, including the plant superintendent,
should develop a table of organization showing the number of shifts, number
and types of personnel per shift, and standby and maintenance personnel.
Approximate manning requirements for municipal refuse incinerators are given
in Table 91. Several methods of job classification exist; whatever method
is used should have sufficient flexibility to insure accomplishment of un-
foreseen as well as defined tasks. Rigid job titles that tend to limit
operating personnel duties should be avoided.
Staffing needs vary with the size and type of facility, number of shifts,
organized labor regulations (including working hours, vacations, fringe
benefits), and the extent of plant subsidiary operations, such as heat
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Table 91
ESTIMATED MANNING REQUIREMENTS FOR
MUNICIPAL INCINERATORS
Classification of Personnel
No. Required
Administrative
Plant Superintendent
Clerical
Other Administrative Personnel
(including engineers)
Operation^
Foreman
Operators^
Stationary Engineers^
Weighmasters
Cranemen .
General Plant '"k—
Truck Drivers
Labor"
(for residue disposal)
Maintenance5
Mechanical
Piping
Electrical
Welding
Instrument
General Maintenance Labor
1 per plant
1-3 per plant
0-3 per plant
1 per shift
1-3 per shift
1-3 per shift
1-2 per shift
1-2 per shift
1-4 per shift
1-3 per shift
3-23 per plant
^Staff requirements vary with plant type as well as with capacity over the
10-80 metric ton/hour range considered. For plants operating more than five
24 hour days, four or more shifts of workers may be required.
^Furnace operators may include one or more licensed firemen per shift where
heat recovery is practiced.
3Where waste heat boilers are used, State laws usually require that
operators be licensed boiler engineers.
^Including tipping area, charging floor, conveyors, and residue handling
and yard work.
^Maintenance staff requirements vary widely depending upon the extent to
which central shop facilities and contract maintenance are used.
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recovery and salvage. A useful target for man-hours in efficient incinerator
operation would be 0.5 per metric ton of solid waste processed, or less,
excluding residue disposal and major repair work. This target may be diffi-
cult to meet in very small operations, or operations where resource recovery
is practiced. Caution should be exercised by management not to over-staff
during startup operations because it may be difficult or impossible to
reduce the size of the staff at a later time.
Management should provide sufficient employment incentives to attract
suitable personnel. An acceptable working environment, equitable pay, ad-
vancement opportunities and training, retirement and other fringe benefits,
and employment security are essential.
Operation Guides
Flow Diagram. An attractive flow diagram, pictorial drawing, or scale model
of the plant should be displayed in a convenient location, such as the main
entrance or the control room. This diagram or model should show all major
equipment components by name and function. An example flow diagram is shown
in Figure 71. The reader will note that the drawing illustrates how the solid
waste and the resulting gases and residues pass through the plant. Uses of
the drawing or model include explaining the process to visitors and training
of plant operating and maintenance personnel to help in visualizing how the
various equipment components function together.
E n g i n e e r i ng Draw ings. At least one complete set of detailed engineering
drawings has to be maintained at the plant for reference by operating and
maintenance personnel. Additional sets of drawings should be filed with
the solid waste disposal agency which has jurisdiction, and other regulatory
agencies as required.
Safety Rules and Procedures. Thermal processing facilities have a number of
built-in hazards: deep storage pits; moving parts of motors, fans, etc.;
possible smoke hazards, particularly in forced draft plants; fire hazards;
conveyors; moving vehicles; shredders; and various tanks, platforms, and
other possible sources of serious falls. Therefore, a routine, short train-
ing course for new employees should include safety related aspects of the
job as well as job duties. Also, safety procedure and practices should be
a part of refresher training.
A positive, supervised plant-safety program is essential. Fires may
occur in the storage pit and in other areas of the plant. Established
procedures will assist the plant personnel to safely control these blazes
until outside assistance is obtained, ATI possible openings and moving
parts should be as well guarded as possible, consistent with efficient
operation. First-aid equipment and respirators should be readily available
and their use insisted upon. Face masks for stokers should be a standard
requirement. Particular attention must be paid to tipping-floor operation;
324
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z
u
u_
UJ
a:
0.
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X
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u.
o
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UJ
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a fall into a 30 foot pit is not to be taken lightly. Crane operation bears
careful watching, together with c<-ane maintenance; a broken cable can cause
extremely serious injuries. Above all, the plant superintendent and shift
foremen should be constantly alert for unsafe practices or physical condi-
tions. Without their constant supervision, unnecessary accidents are going
to occur, and such accidents can be costly in both personnel injury and plant
downtime. Federal occupational safety and health (OSHA) standards provide
useful guidelines in this area.
Operation Manual
Proper operating procedures end competent operators are probably the
most important elements in successful thermal processing. In addition to
carefully selecting operators and other plant personnel, they must be properly
trained. The key document used in training these persons is the operating
manual.
The operating manual will be the basis for initial and followup training
sessions. It will also continue to serve as a valuable reference, especially
when adjustments and modifications in plant operation are made. An adequate
manual will include a presentation describing the mission of the plant, the
responsibilities and functions of plant personnel, rules and procedures for
safety and good housekeeping, record keeping procedures, a description of the
process, and diagrams showing the flow of material through the plant. A sec-
tion will be included which provides detailed operating instructions for each
major item of mechanical equipment. The manufacturers operating instructions,
drawings and spare parts lists shojld be available for quick reference by
plant operators. Special emphasis should be given to the function of the
instrumentation provided and how it should be used to promote efficient opera-
tion, avoid physical (including thermally caused) damage to the process equip-
ment and structures, and at the same time achieve the required levels of
emissions to the air, water, and land environment.
The manual should discuss frequently occurring operating problems and
describe the recommended procedures for solving them. Examples of routine
operating problems include clogging of the feed chute by oversized objects;
fire back through charging chute; jamming of moving grates, mechanical
stokers or conveyors by clinkers, tramp metal, etc.; failure to control
combustion temperature within specified limits; incomplete burnout of the
residue; clogging of storage pit and residue-conveyor drains; srnoky condi-
tions within the plant; and unacceptable stack emissions. The operating
manual and training program should include the procedures for:^
1. Plant startup from c cold start.
2. Plant startup after an emergency shutdown.
3. Routine operation.
4. Routine shutdown.
5. Emergency shutdown.
6. Lubrication and routine servicing of equipment.
3;.>6
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Also, an extensive review of the causes of operating problems in municipal
incinerators and suggested procedures to eliminate these problems has been
compiled for use in plant operations. While it will not be possible to
describe every situation which might occur, a carefully prepared operating
manual will materially aid the operators in achieving the high degree of
proficiency desired. Finally, the manual should be updated frequently,
especially during the first year of operation, to reflect procedures insti-
tuted to overcome problems, and after major equipment and control changes
have been made.
Maintenance and Repairs
Records. A records systems should be established by the plant supervisor
wherein periodic maintenance of each incinerator component is scheduled to
be done by specific personnel. In contrast, certain maintenance, such as
cleaning, lubrication, and adjustment of equipment, may be done by operating
personnel as part of their daily or weekly tasks and need not be recorded.
Certification that maintenance has been performed should also be recorded.
Card files set up with an automatic reminder procedure will provide a perma-
nent record of maintenance for each item of equipment and guard against
omission of scheduled maintenance. Properly certified maintenance records,
tabs, or seals, may also be affixed to the equipment as maintenance is
performed. Major repairs, such as the replacement of refractories, will
necessarily be recorded separately. Unscheduled repairs and breakdowns
should be handled promptly and carefully recorded so that the cause can be
determined and corrected.
Maintenance and Equipment Manuals. Data required by maintenance personnel
include that which will assist in locating causes of equipment malfunctions,
and provide the information necessary to complete repairs. A complete set of
structural, equipment layout, piping and instrument, electrical, and heating
and ventilating drawings is essential to proper plant maintenance. Mainte-
nance manuals provided by the equipment contractor should describe the serv-
icing or repair of each major item of equipment, including shop and assembly
drawings, parts lists, and trouble-shooting instructions. Special procedures
for operating maintenance machinery and welding equipment, as well as safety
rules and good housekeeping procedures, should also be available for easy
reference. Methods used for the training of maintenance employees will vary
somewhat depending upon their level of experience when hired, and the main-
tenance needs of the plant.
Routine Maintenance. The importance of routine or preventive maintenance cannot
be overly stressed. Study of maintenance records will show which equipment is
most subject to failure or malfunction. These equipment items should be main-
tained on a regular schedule and/or during normal shutdowns. This will reduce
the possibility of unexpected outages due to inadequate routine maintenance.
If frequent outages persist, consideration should be given to replacement or
redesign of the troublesome equipment.
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Inspection Procedures. Components, subject to rapid wear or damage should be
inspected weekly at a time when such components are not being operated. At
each inspection, a thorough report should be made, including condition of the
furnace, repairs performed, and expectation of future repairs or major over-
haul. Plant performance records and maintenance files can be used to deter-
mine when major repairs are necessary. All equipment subject to wear, corro-
sion, erosion, or stress failure should be thoroughly inspected at least
annually and more often if necessary. Complete inspection reports should be
maintained.
Repairs. In many larger plants, the maintenance staff will be expected to
perform all but the most major repairs. Major structural repair, refractory
replacement, and repair of large irotors is sometimes excepted. In large
municipalities, central repair facilities are sometimes available to perform
major repairs. In smaller plants, plant personnel will not normally be ex-
pected to perform major repairs on equipment, building, or facilities. Other
municipal personnel may perform some repairs, and certain repairs will require
special contract services.
When major overhauls are being made, the units remaining in service
should not be overloaded to make up for the loss of capacity. The amount
of solid waste equivalent to the "down" unit's capacity should be diverted
to approved disposal facilities. Ideally, extensive repairs should be
scheduled during the season when waste generation is lowest.
When general wear and tear accumulates to the point that continued
operation is no longer economically feasible or prudent without major recon-
struction, the abandonment or demolition of the facility must be considered.
Good management demands that such determination be made in time to arrange
for the necessary financing and construction of new facilities. Since this
process may take several years, adequate lead time is essential. A capable
plant operator will be able to aid in this decision.
Management should keep abreast of new developments and decide whether
operation can be improved. The costs of revisions, expected life of the
plant, temporary disposal alternatives, and financial considerations enter
into these decisions. Unfortunately, the updating of incinerators by re-
design and reconstruction has been the exception rather than the rule.
In many instances, facilities are built with provisions for future
enlargement or for later addition of equipment. Here again, performance
evaluation will guide the decisions of when to modify equipment or to
enlarge capacity.
Maintenance of Buildings. Although certain parts of a plant are inherently
dirty, dusty, or difficult to keep clean, devices to reduce accumulation of
dust and dirt, water, or debris should be installed, and personnel should
spend some time during the shift to maintaining a clean workspace. Specific
328
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assignments to such jobs is essential. Misuse of employee facilities, such as
accumulating salvage items should not be permitted. In some instances, poor
housekeeping creates fire or safety hazards. Lighting fixtures and bulbs should
be kept clean to provide acceptable illumination at all times. Auxiliary light-
ing equipment should be maintained for inspection purposes and for use in emer-
gencies.
Maintenance and Repair Costs. The cost of proper maintenance and repairs varies
with the size, type, and age of the plant but can be expected to run between 14
and 28 percent of the operating costs (excluding depreciation and interest),
split about equally between labor and materials.6 Good management will budget
for annual maintenance and repair work based on experience and inspection
reports, including periodic major replacements and modernization.
Performance Records
A detailed data acquisition and cost accounting system should be esta-
blished, and complete records of capital, operating and maintenance costs should
be kept. Manual recording of data or primarily automatic data acquisition may
be used. The system adopted should be detailed enough to permit identification
of those portions of the operation which are contributing to unnecessarily high
costs. These data also make it possible to monitor the efficiency of the opera-
tion in terms of the weight and volume reduction of the solid wastes processed;
ability to operate at acceptably high and sustained rates of throughput; com-
pliance with air, water and solid residue discharge requirements as they affect
the environment; and performance of salvage and heat recovery operations. Often
overlooked is the value of reliable operating data in designing new or expanded
thermal processing plants. In addition to data sheets, permanent operating logs
kept by the operators and/or the foremen provide a daily record of problems, solutions
to problems, explanations for excursions of temperature and other important variables,
routine and non-routine maintenace, etc.
Criteria Used in Data Collection. Maintaining adequate records of day-to-day
operations is necessary in order to monitor the process efficiency and plant
costs. These data should be recorded in convenient form for review, and should
include sufficient information to permit appropriate decisions to be made which
will improve the operations. Since the successful operation of the plant is
dependent on the adequate recording and use of records, administration of
record keeping practices should originate at the highest level of plant manage-
ment, usually the plant superintendent.
Records will normally be reviewed by the supervisor of the person or
persons responsible for their preparation. The frequency of review should be
consistent with the purposes for which the records are kept. For example,
critical air flows, temperatures, emission data, and the like should be under
constant surveillance by the plant operators of the foremen, since prolonged
upsets could cause serious complications or plant shutdown. Data relating
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to storage pit contents, daily throughput, residue quality, and the like may
require less frequent monitoring, such as for example, once each shift, or
each day. The costs associated with keeping good records and insisting on
timely review for corrective purposes can produce handsome dividends in terms
of better plant operation and lower overall costs.
Use of Operating Data in Cost Accounting. Many of the same data used for
process monitoring will be used in implementing the cost accounting system.
One system of cost accounting is provided in Zausner's "An Accounting System
for Incinerator Operations.'
The following will illustrate how plant records might be used to improve
plant operations. It is recognized that the numbers of man-hours required for
maintenance in each particular area of the plant will be one of the signifi-
cant factors in the cost of operation. The particular cost items can be
reviewed in terms of their contribution to the overall operating cost or cost
per unit of throughput. When periodically reviewed, along with other cost
data, significant changes in these maintenance costs will be detected. Timely
detection allows corrective action to be taken before extraordinary sums are
expended. The corrective action may include, for example, increased, emphasis
on preventive maintenance, replacement of obsolete equipment, or whatever
other action is indicated.
From the foregoing, it is apparent that a well conceived cost accounting
system can be a useful means of attaining an effective plant operation at
minimum cost. The success of any cost control system depends to a great
extent upon the quality of the data provided to it.
Use of Operating Data in Process Operation. Aside from cost control and other
record keeping purposes, recording process data alerts operators to deteriora-
tion in automatic control systems and to changes in operations requiring con-
trol adjustment. This is useful in all operations, but is especially important
in plants equipped with a minimum of automatic controls. For example, changes
in incinerator temperature may require adjustments to maintain performance and
to prevent damage to equipment. Where heat recovery equipment is used, moni-
toring is required to maintain the desired performance and to detect mishaps,
such as pressure loss due to rupture of boiler tubes. Operating data is also
used to make adjustments in personnel assignments, schedule repairs, and make
periodic reports to regulatory agencies concerning environmental matters.
Thermal processing plants other than incinerators require special atten-
tion. For example, some pyrolysis processes convert solid waste to combustible
fuel gases which are burned in a waste heat boiler. Careful control of pyro-
lysis conditions are required to insure an adequate supply of fuel to the
boiler, to insure safe operation, and to protect the processing equipment.
In all pyrolysis processes monitoring is required to insure adequate perform-
ance and safety of each critical subsystem, such as the pyrolysis reactor,
condensers for liquid fuel recovery, refuse driers, etc.
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Important Operating Data
Some of the important operating data are discussed below with regard to
record keeping. A detailed analysis is required for each new plant, with
periodic updating as data needs change.
Incoming Solid Waste. Plant records should indicate the total weight of
solid waste received during each shift as well as the number of vehicles ar-
riving, identity of vehicles, and the source and nature of solid waste received.
The primary responsibility is with the weighmaster, as discussed in Chapter VII.
Rate, Temperature, and Pressure Data. Operators should record temperature at
frequent intervals, unless such data is recorded automatically. Grate speeds
(or rate of operation) should be noted throughout the shift. Air and gas
volumes and distribution should also be reported. All readings should be
made at least hourly and any major changes noted. Some instruments give
indirect readings which may require operator aids such as conversion charts
for data interpretation.
Residue. Operators should record the time or rate of residue removal. Residue
should be weighed on the scale as it leaves the plant, and the amount removed
should be recorded. Moisture correction is necessary for proper interpretation
of residue weight. The dry weight of residue can be estimated by periodically
obtaining the average moisture content. Residue quality should be visually
determined and recorded. Flyash records should be kept when this material is
handled separately.
Water Consumption. Water used for quenching and for scrubbers should be
recorded from meter readings or by other means at least at the start and end
of each shift.
Stack Discharges. Records of stack discharge characteristics commonly include
smoke indicator readings, Ringelmann readings, and analyses from stack samp-
ling. Precise stack sampling is expensive, allowing only infrequent testing
of this type.
Wastewater Discharges. Flow rates and analytical data obtained from periodic
samples taken at the inlet and outlet of the treatment facilities should be
recorded. Use of a recording instrument for effluent pH is strongly recom-
mended and daily records of the quantities of acid, caustic and other treatment
chemicals should be kept. If water recycling is practiced, the flow rate
should be recorded for comparison with the water consumption and discharge
meter readings.
Salvage and Other Resource Recovery. Data showing the amount of iron or other
salvage recovered should be recorded daily. Accurate records must be kept of
fuel produced by pyrolysis.
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Personnel Records. Accurate personnel time and cost records should be kept so
that performance can be evaluated on the basis of operating cost per ton and
on the basis of man-hours per ton. Costs of operating and maintenance labor
should be kept separately. Also, these costs should be identified by the
appropriate operation to which it applies, e.g., receiving, salvage, volume
reduction (burning), energy recovery, and effluent handling and treatment.
Direct and indirect costs should be included in the total cost of operation.
Supplies, Material, and Equipment. All supplies, material, and equipment
utilized in operation and maintenance should be recorded and charged against
thermal processing, even though provisions or purchases may be made by another
department. Major maintenance (such as rebuilding of refractories), whether
done by contract or by plant personnel, should be recorded as cost items
separate from operation. Thus, both the cost of repairs and maintenance
and the cost of plant operation can be determined.
Methods of Preparing Data Records,
Recording of plant operating data is done either manually or automatically.
As municipal thermal processing plants become more sophisticated and complex,
the trend is toward a greater reliance on automatic data collection.
Manual records are required when the information is non-routine in nature
or when automation is not justified. Prepared forms are often used to assist
in manual record keeping. Examples of manual records include time sheets,
operators' logs, laboratory reports, maintenance logs, materials requisitions,
and performance reviews.
Where manpower can be saved, or where operating efficiency can be improved,
it may be possible to justify automatic data acquisition equipment. Recorders
for various process parameters, such as temperature, air flow, stoker speed,
wastewater pH, and smoke density are familar to operators of modern plants.
Measurements made at various plant locations are often transmitted to recorders
in a central control room. Using electronic instruments and a computerized
data acquisition system, it is even possible to print out these measurements
in tabular form by use of a teleprinter. More frequently, however, tabular
summaries of chart records are compiled manually by shift personnel at hourly
intervals. Manual and automatic options for process data are similarly
available for truck weight records.
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REFERENCES
1. Technical-Economic Study of Solid Waste Disposal Needs and Practices,
U.S. Department of Health, Education and Welfare, Public Health Service.
Report No. SW-7c, Vol. IV, part 4, pg. 4. Bureau of Solid Waste
Management. Rockville, Maryland 1969.
2. Hall, P. B. Operations-Keynote to Successful Incineration. Proceedings,
1970 National Incinerator Conference, Cincinnati, May 17-20, 1970.
American Society of Mechanical Engineers, page 156.
3. Heil, T. C. Planning, Construction and Operation of the East New Orleans
Incinerator. Proceedings, 1970 National Incinerator Conference,
Cincinnati, May 17-20, 1970. American Society of Mechanical Engineers.
page 146.
4. Niessen, W. R. et al. Systems Study of Air Pollution from Municipal
Incinerators. A Report by A. D. Little, Inc. MTIS No. PB 192-379,
Washington, D.C. (Appendix K, 57 pages) March 1970.
5. Zausner, E. R. An Accounting System for Incinerator Operations.
Report No. SW-17ts. U.S. Department of Health, Education and Welfare,
Public Health Service Publication No. 2032, Environmental Health
Service, Bureau of Solid Waste Management. 1970.
6. Achinger, W. C. and L. E. Daniels. Seven Incinerators. SW-51ts.lj.
U.S. Environmental Protection Agency. 1970^ 64 pages.
7. De Marco, et al. Municipal-Scale Incineration Design and Operation,
PHS Publication No. 2012. U.S. Government Printing Office, Washington,
D.C. 1969. (formerly Incinerator Guidelines - 1969).
333
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APPENDIX A
INVENTORY OF MUNICIPAL SOLID WASTE
THERMAL PROCESSING FACILITIES
The following inventory of incinerators
the American Society of Mechanical Engineers
plants is as of December 1974.
List of Plantst
and their status was supplied by
(ASME). The status of the various
(Bostw. Ave.)
(Asylum St.)
CONNECTICUT
* Ansonia
Bridgeport
Bridgeport
Darien
East Hartford
Greenwich (#1)
Greenwich (#2)
Hartford
New Britain
New Canaan
* New Canaan
New Haven
New London
Norwalk
Stamford
* Stamford (bulky waste)
* Stamford
Stratford
Waterbury
West Hartford
West Haven
FLORIDA
Broward Co. #1
Broward Co. #2
**Broward Co. #2
Clearwater
Coral Gables
Dade Co. (N. East)
Ft. Lauderdale (#1)
Ft. Lauderdale (#2)
Hollywood
Jacksonville
Miami (Coconut Grove)
Miami (20th St.)
Orlando
* Reedy Creek (Disney U.)
St. Petersburg
Tampa
* Not on A.D. Little 1969 list
**Plant capacity currently 600 T/D
Operational as of
Dec. 74
T/D
200
300
200
130
350
150
250
600
125
720
120
360
400
100
360
264
300
300
300
300
300
300
450
250
900
150
1000
Closed since 1969
T/D
300
50
300
300
300
450
300
300
150
500
tSource: ASME, Jan. 1975
334
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Operational as of Closed since 1969
Dec. 74
T/D T/D
GEORGIA
Athens 50
Atlanta (Mayson) 350
Atlanta (Hartsfield) 750
DeKalb County 600
HAWAII
Honolulu (Kapalama) 200
Honolulu (Kewalo) 200
* Honolulu (Waipahu) 600
ILLINOIS
Aurora 40
Chicago (Medill) 720
Chicago (Calumet) 1200
*Chicago (Northwest) 1600
Chicago (Southwest) 1200
Cicero (Stickney) 500
Evanston 180
Mel rose Park 250
Schiller Park 250
Skokie 150
INDIANA
Bloomington 100
East Chicago 450
Indianapolis 450
New Albany 160
*Shelbyville 150
KANSAS
Dodge City 35
KENTUCKY
Frankfort 150
Lexington 200
Lexington 150
Louisville 1000
* Ludlow 50
Paris 100
Winchester 100
* Not on A.D. Little 1969 list
**Plant capacity currently 600T/D
335
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Operational as of Closed since 1969
Dec. 74
T/D T/D
LOUISIANA
Gretna 100
Jefferson Parish 90
Jefferson Parish 400
Morgan City 30
New Orleans (Algiers) 200
New Orleans (East) 400
New Orleans (Fla. Ave.) 400
New Orleans (7th St.) 400
* New Orleans (St. Louis St.) 450
* St. Bernard Parish
(Chalmette) 100
Shreveport (Minden) 250
* Shreveport 200
MARYLAND
Baltimore (#3) 600
Baltimore (#4) 800
* Baltimore (Monsanto) 1000 (U.C.)
Montgomery County 1400
Salisbury 125
MASSACHUSETTS
Belmont 150
Boston (South Bay) 900
Braintree 240
* Brockton (E. Bridgewater) 600
Brookline 180
Cambridge 150
Dedham 100
Fall River 600
* Framingham 500
Framingham 200
Holyoke 225
Lawrence 300
Lowell 400
Marblehead 80
New Bedford 225
Newton 240
Newton 500 ,
Pittsfield 180
* Reading 144
Salem 140
* Saugus 1200 (U.C.)
Somerville 450
Waltham 150
Watertown 320
Wellesley 150
Weymouth 300
Winchester 100
Worcester 450
* Not on A.D. Little 1969 list
U.C. - Under construction
-------
Operational as of Closed since 1969
Dec. 74
T/D T/D
MICHIGAN
Central Wayne County 800
Detroit (St. Jean) 200
Detroit (N.W.) 450
Detroit (Central) 525
Detroit (24 St.) 500
* Grosse Pt.-Clinton
(Macomb Co.) 600
River Rouge 50
S.E. Oakland County 600
Trenton 100
MINNESOTA
Minneapolis 300
MISSISSIPPI
Picayune 144
MISSOURI
St. Louis (North City) 400
St. Louis (South City) 400
NEBRASKA
Omaha 375
NEH HAMPSHIRE
Manchester 100
NEW JERSEY
Ewing 240
Hamilton Township 99
Jersey City 600
Perth Amboy 150
Princeton 120
Red Bank 120
* Red Bank 48
Spring Lake 30
* Wanaque 300
* Not on A.D. Little 1969 list
U.C. - Under construction
337
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Operational as of Closed since 1969
Dec. 74
T/D T/D
NEW YORK
Amsterdam 120
Babylon (#1) 300
Babylon (#2) 400
Beacon 100
Binghampton 300
Buffalo (East Side) 600
Buffalo (West Side) 600
Canajoharie 50
Carmel 40
Cheektowaga. 100
Corning 80
Eastchester 200
Freeport 150
Garden City 175
Hempstead (Merrick) 600
Hempstead (Oceanside) 750
Huntington (#1 & #2) 300
Huntington (#3) 150
Islip (New Sayville) 300
Lackawanna 150
* Lawrence 200
Long Beach 200
Mt. Kisco 40
Mt. Vernon 600
Newburgh 240
New Roche!le 400
NYC (Betts) 1000
NYC (Ganesvoort) 1000
NYC (Hamilton) 1000
NYC (South Shore) 1000
NYC (S.W.Bklyn) 1000
NYC (73 Street) 660
NYC (215 Street) 750
Niagara Falls 240
N. Hempstead (Denton Ave.) 200
N. Hempstead (Roslyn Harbon) 600
Oyster Bay (#1) 500
Oyster Bay (#2) 500
* Pel ham Manor 85
Port Chester 120
Poughkeepsie 200
Ramapo 200
Rochester (E. Side) 600
Rochester (W. Side) 450
Rye 150 <
* Not on A. D. Little 1969 list
338
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Operational as of Closed since 1969
Dec. 74
T/D T/D
NEW YORK (Cont'd)
Scarsdale 150
Tonawanda (City) 80
* Tonawanda (Town) 250
Tonawanda (Town) 200
Valley Stream 200
White Plains 400
Yonkers 650
OHIO
Barberton 100
Cheviot 60
Cincinnati (Center Hill) 500
Cincinnati (West Fork) 500
Cincinnati (Dunbar) 200
Cincinnati (Crookshank) 200
Cleveland 500
Cleveland Heights 150
* Dayton (S. Montgomery Cty) 600
* Dayton (N. Montgomery Cty) 600
Euclid 200
* Franklin 150
* Greenhills 50
Lakewood 300
Miami County 150
Norwood 150
Parma 225
Sharonville 500
Woodville 12
Youngstown 300
PENNSYLVANIA
Abington 200
Allentown 270
Ambridge 150
Bradford 200
Delaware County (#1) 800
Delaware County (#2) 500
Delaware County (#3) 500
Erie 100
* Harrisburg 720
Lower Merion Township 250
Meadville 80
Philadelphia (Bartram) 600
Philadelphia (E. Central) 600
Philadelphia (Harrowgate) 300
Philadelphia (N.E.) 600
* Not on A.D. Little 1969 list.
339
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Operational as of Closed since 1969
Dec. 74
T/D T/D
PENNSYLVANIA (Cont'd)
Philadelphia (N.W.) 600
Philadelphia (S.E.) 600
Red Lion Borough 60
* Shippensburg 72
West Mifflin 40
Whitemarsh Township 100
RHODE ISLAND
Newport 120
Pawtucket 400
Providence 320
Warwick TOO
Woonsocket 160
TENNESSEE
* Nashville 720
TEXAS
Amarillo 350
Houston (Holmes Rd.) 800
UTAH
Ogden 450
VIRGINIA
Alexandria (#2) 300
Alexandria (#1) 200
Arlington 750
* Newport News 400
Norfolk (Lampert's Pt. #4) 400
Norfolk (Navy Publ. Works) 360
Portsmouth 350
Roanoke 200
WASHINGTON, D.C.
Fort Totten 500
Georgetown 170
Mt. Olivet 500
0 Street 425
* Solid Waste Red. Center #1 1500
WEST VIRGINIA
Charleston 300
* Not on A.D. Little 1969 list
340
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Operational as of Closed since 1969
Dec. 74
T/D T/D
WISCONSIN
DePere 75
Fond du Lac 90
Green Bay 150
Green Bay 360
Kewaskum 24
Merrill 35
Milwaukee (Erie St.) 225
Milwaukee (Green Bay Ave.) 300
Milwaukee (Lincoln Ave.) 300
Monroe 60
Neenah-Menasha 300
Nekoosa 60
Oshkosh 100
Oshkosh 350
Port Washington 75
Racine 120
Sheboygan 240
* Sturgeon Bay 150
* Waukesha 350
Wauwatosa 165
West All is 200
Whitefish Bay 80
* Not on A. D. Little 1969 list.
Capacities listed in this Table are, to the best of our knowledge,
"nameplate" ratings confirmed by manufacturers and/or design
engineers. Actual plant operating capacities may differ from these
listed capacities.
341
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Appendix B
SUMMARY OF RESOURCE RECOVERY SYSTEM IMPLEMENTATIONS
December 1975
Location
SYSTEMS IN OPERATION (14):
Altoona, PA
Ames, IA
Blytheville, AR
Braintree, MA
N-E. Bridgewater, MA
D-Franklin, OH
Harrisburg, PA
Nashville, TN
Norfolk, VA
Palos Verdes, CA
D-St. Louis, MO
Si loam Spring, AR
Saugus, MA
N-South Charleston, WV
Type*
Compost
RDF
Small Incin.
WWI
RDF
Wet-Pulp
WWI
WWI
Landfill Wells
RDF
Small Incin.
WWI
Pyrolysis
SYSTEMS UNDER CONSTRUCTION OR SELECTED (10):
Baltimore, MD
Baltimore County, MD
Bridgeport, CT
Chicago, IL (Crawford)
Hempstead, NY
Milwaukee, WI
Monroe County, NY
N-New Orleans, LA
D-San Diego, CA
St. Louis, MO (expansion)
Pyrolysis
RDF
RDF
RDF
Wet Pulp
RDF
RDF
Shredding
&
Classification
Pyrolysis
RDF
Capacity
(TPD) Products/Markets
30 Fertilizer
400 RDF, Fe, AL
50 Steam-Industry
240 Steam-Process
160 RDF-Utility
150 Fiber, Fe
720 Steam-Heating Loop
720 Steam Heating &
Cooling
360 Steam-Navy Base
N/A Methane Gas
300 RDF-Coal-Fired
Utility
20 Steam-Industry
1600 Steam-Process
200 Gas
1000 Steam-Heating &
Cooling
550 RDF, Fe, AL, Glass
1800 RDF, Fe, AL, Glass
1000 RDF-Utility
2000 Electricity,Fe,AL,
Glass
1000 RDF, Corrugated, Fe
2000 RDF, Fe, Non-ferrous
650 Non-ferrous,
Paper, Fe, Glass
200 Liquid Fuel-Utility
8000 RDF-Utility, Fe,
Non-ferrous, Glass
Start-
Up
Date
1963
9/75
1975
11/75
1974
1971
1972
7/74
1967
6/75
4/72
9/75
1976
1974
6/75
4/76
7/77
6/76
N/A
1977
3/77
5/76
7/76
N/A
COMMUNITIES COMMITTED (29):
(RFP issued, design study underway, or construction funding made available.)
Akron, OH
WWI
Albany, NY RDF
Central Contra Costa RDF
County Sanitation District
1000 Steam-Heat, Cool,
Process
1200 RDF, Fe
1000 RDF-Sludge Inciner-
ators
7/78
N/A
1979
* See page
for code definitions.
342
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SUMMARY OF RESOURCE RECOVERY SYSTEM IMPLEMENTATIONS
December 1975
Location
COMMUNITIES COMMITTED (28):
Chemung County, NY
Cuyahuga County, OH
Dade County, FL
Detroit, Michigan
Hackensack, NJ
Honolulu, HI
G-Lane County, OR
Lawrence/Haverhill, MA
G-Lexington-Fayette Urban
County Gov't, KY
Memphis, TN
Milwaukee, WI
Minneapolis-St. Paul
G-Montgomery County, OH
Mt. Vernon, NY
New Haven, CT
Onondaga County, NY
E-Pompano Beach, FL
D-Palmer Township, PA
Portland, OR
Riverside, CA
Salem, Lynn & Beverly
Seattle, WA
Smithtown, NY
Westchester County, NY
D-Wilmington, DE
Wisconsin Recycling Auth.
Type
(continued)
RDF
RDF
WWI/Wet Pulp
RDF/WWI
RDF
N/A
RDF
WWI
WWI
WWI
RDF
Pyrolysis/
Sludge
RDF
Pyrolysis
WWI
WWI
Methane Rec.
RDF
RDF
Pyrolysis
N/A
Pyrolysis
Materials
Separation
N/A
RDF/Sludge
N/A
Capacity
(TPD)
300
1200
3000
3000
2500
2000
750
3000
750
2000
1000
360
1600
400
1800
1000
50
150
200
50
750
1500
1000
1300
300
Products/Markets
RDF, Fe
RDF-Steam- Industry
Electricity-Utility
Steam
RDF-Utility, Fe
Utility
RDF
N/A
Steam, Fe
Steam/ RDF
RDF, Fe, Paper
Corrugated
Gas, Oil
Activated Char
RDF
Gas-Electricity
Steam- Fe
Steam-Heat & Cool, Fe
Methane
Fuel -Cement Kiln
RDF-Fe
Prototype/ Demo
Methanol -Ammoni a
Hand Sort
N/A
Fe, AL, Glass
Start-
up
Date
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
1977
N/A
N/A
N/A
N/A
1978
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
11/77
N/A
N/A
RDF, Compost
1200 N/A
COMMUNITIES WHICH HAVE COMMISSIONED FEASIBILITY STUDIES (51):
Anchorage, AK
Appleton, WI
Auburn, ME
Allegheny County, PA
Babylon, Huntington & Islip, NY
Cowlitz County, WA
Columbus, OH
Dallas, TX
DeKalb County, GA
500
N/A
200
2000
3000
100
N/A
N/A
1000
343
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SUMMARY OF RESOURCE RECOVERY SYSTEM IMPLEMENTATION
December 1975
Location
Type
Capacity
(TPD) Products/Markets
Start-
up
Date
COMMUNITIES WHICH HAVE COMMISSIONED FEASIBILITY STUDIES (52): (continued)
Dubuque, IA
District of Columbia (Metro Area COG)
G-Denver, CO
Dutchess County, NY
Erie County, NY
Fairmont, MN
Ft. Lauderdale, FL
Grand Rapids, MI
Hamilton County, OH
Lawrence, NY
Lincoln, NB
Lincoln County, OR
Marquette, MI
Miami County, OH
G-Middlesex County NJ
Minneapolis (Twin Resco)
Montgomery County, MD
Madison, WI
Niagra County,
G-New York, NY
Oakland County,
Orange County,
Phoenix, AZ
Pasadena, CA
Peninsula Planning Dist.
Philadelphia, PA
G-Richmond, VA
Riverview, MI
Rochester, MN
St. Cloud, MN
Salt Lake County,
S.E. Va. Planning
Springfield, IL
Springfield, MO
Tallahassee, FL
Tampa/St. Petersburg,
Toledo, OH
Tulsa, OK
G-Tennessee Valley Authority
Western Berks Refuse Authority, PA
Western Lake Superior San. Dist.
Winnebago County, IL
Wyandotte, MI
NY
(Arthur Kill)
, MI
CA
VA
UT
District
FL
500
750
1200
700
2000
150
200
N/A
1500
500
N/A
N/A
N/A
N/A
N/A
N/A
1200
200
760
1500
N/A
1000
N/A
220
N/A
1600
N/A
N/A
N/A
N/A
750
1500
N/A
1000
N/A
N/A
1200
N/A
2000
250
400
N/A
1000
344
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SUMMARY OF RESOURCE RECOVERY SYSTEM IMPLEMENTATION
December 1975
Code
D--EPA Demonstration Grant AL—Aluminum
G--EPA Implementation Grant FE—Ferrous (magnetic metals)
N~-Non-EPA Demonstration Facility RDF--Refuse derived full
E--Energy Research & Development
Administration Grant
WWI--Waterwall Incinerator
Compiled by the Office of Solid Waste Management Programs
U.S. Environmental Protection Agency
Washington, D.C. 20460
345
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Appendix C
TABLE OF ABBREVIATIONS
ACFM = actual cubic feet per minute
B and Bbl = barrel(s) (42 U.S. gal)
Cal = calories
cc = cubic centimeter(s)
CF = cubic feet
CFH = cubic feet per hour
CFM = cubic feet per minute
cm = centimeter(s)
CM = cubic meter(s)
CY = cubic yards
$M = thousands of dollars
$MM = millions of dollars
ft = feet
ft3 = cubic foot
gal = gallon(s) (U.S.)
g = gram(s)
6PM = gallons (U.S.) per minute
gr = grains
Hg = mercury
hr = hour(s)
in = inch(es)
Kcal = kilocalories
kg = kilogram(s)
Ib = pound(s)
m3 = cubic meter
min = minute(s)
346
-------
ml = milliliter(s)
mm = millimeter(s)
MT = metric ton(s)
MT/hr = metric tons per hour
NCM = normal cubic meter(s) (0 C, 1 atm or 70 F where indicated)
SCF = standard cubic feet (60 F, 1 atm; or 70 F where indicated)
SCM = standard cubic meters (70 F, 1 atm)
ST = short tons
ST/day or ST/D = short tons per 24 hour day
tons/ton or tons per ton always refers to consistent weight units, for
example MT/MT, ST/ST, Kg/Kg, Ibs/lb
TPD = short tons/day
vol = volume
WG = water gage or water column (pressure differential)
wt = weight
yr = year(s)
347
-------
Appendix D
CONVERSION FACTORS
B x 42 = U.S. gal
BTU x 252 = calories
°C = (°F-32) * 1.8
$/MG x 0.907 = $/ST
°F = (°C x 1.8) + 32
ft x 0.3048 = meters
Cal x 3.968 x 10'3 = BTU
Cal/g x 1.80 = BTU/lb
CF x 0.02832 = CM
CM x 35.31 = CF
grains/SCF x 2.29 = grams/SCM
grams x 15.43 = grains
in x 2.54 = cm
in ^0 x 1.868 = mm Hg (pressure differential)
kcal x 3.968 = BTU
kg x 2.2046 = Ibs
Ibs x 7000 = grains
Ibs x 0.454 = kg
Ibs/CF x 0.01602 = g/cc
Ibs/CF x 27 = Ibs/CY
Ibs/CY x 1.308 = Ibs/CM
MT x 1000 = kg
MT x 2205 = Ibs
MT x 1.1025 = ST
SCF (60 F, 1 atm) x 0.0268 = NCM (0 C, 1 atm)
SCF (70 F, 1 atm) x 0.0263 = NCM (0 C, 1 atm)
348
-------
SCF (70 F, 1 atm) x 0.0283 = SCM (70 F, 1 atm)
ST x 2000 = Ibs
ST x 0.9070 = MT
(ST/24 hr) x 0.0378 = MT/hr
60 F = 15.6 C
70 F = 21.1 C
psia i- 14.7 = atmospheres absolute
PS1914.74'7 = atmosPheres absolute
349
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