INCINERATOR
DESIGN
AND OPERATION
-------
-------
-------
Reprinted by U.S. Environmental Protection Agency
1973
Public Health Service Publication No. 2012
Library of Congress Catalog Caid No. 71-607217
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402
Price $1.25 domestic postpaid or $1 GPO Bookstore
-------
FOREWORD
INCINERATION is a major method of solid
waste processing in the United States today.
Over the past several decades incinerator
technology has been developed largely
independently by industry, large institutions,
and municipal and county governments.
Independent development led to
nonstandardized incinerator design and
operation, and the diversity of regulations,
design, and management practices failed to
accomplish the major purpose of incineration:
Maximum volume and weight reduction of
solid wastes without environmental pollution.
The creation of the following Guidelines
was conceived as a method of describing the
best in incinerator technology in order to
further its development. The publication is
the result of a two-year effort. The work
included many meetings and numerous drafts
Members of the panel were:
Ralph J. Black, Chairman
Director, Office of Information
Bureau of Solid Waste
Management
Rockville, Maryland
Frank R. Bowerman
Group Vice President
Zurn Industries
Los Angeles, California
Richard B. Engdahl
Mechanical Engineering
Department
Columbus Laboratories
Battelle Memorial Institute
Columbus, Ohio
to synthesize published materials and
information newly-written by both the staff
and the panel members. The diversity of the
incinerator design and operating practices,
mentioned above, resulted in very divergent
views that had to be brought toward
concensus wherever possible. The final views
expressed in the Guidelines are the
responsibility of the Bureau of Solid Waste
Management and the authors, who worked
hard to state as fairly as possible the results of
the long study. In the absence of firm
technical data, this publication (SW—13ts)
describes desirable performance
characteristics for present-day incinerators,
the process of incineration, and the "state of
the art." The title represents this combined
approach. The Bureau intends to review and
revise the Guidelines at appropriate intervals
to reflect the latest incinerator technology.
Joseph F. Malina, Jr.
Associate Professor of Civil
Engineering
Environmental Health Engineering
University of Texas
Austin, Texas
Abraham Michaels
Consulting Engineer
Philadelphia, Pennsylvania
Melbourne Noel
Chief Engineer
Department of Streets and
Sanitation
Chicago, Illinois
in
-------
Joseph Frankel
Consulting Engineer
New York, New York
Herbert C. Johnson
Senior Air Pollution Engineer
Bay Area Air Pollution Control
District
San Francisco,-California
Elmer R. Kaiser
Project Director, Senior
Research Scientist
Department of Chemical
Engineering
School of Engineering and
Science
New York University
John Grady Phelps
Director, Department of Sanitation
Miami, Florida
Casimir A. Rogus
Consulting Engineer
Bay side, New York
Robert J. Schoenberger
Department of Environmental
Engineering and Science
Drexel Institute of Technology
Philadelphia, Pennsylvania
Morton Sterling
Director of Wayne County Air
Pollution Control Division
Detroit, Michigan
Alan B. Walker
Director of Research and Development
Research Cottrell, Inc.
Bound Brook, New Jersey
Other staff members of the Bureau of Solid
Waste Management actively contributing to
this document included M. DeVon Bogue,
Richard W. Eldredge, Charles W. Reid, Jr.,
and John B. Wheeler.
The Guidelines were reviewed by the
American Society of Mechanical Engineers,
the American Society of Civil Engineers, the
American Public Works Association, the
American Public Health Association, the
Consulting Engineers Association, the
Incinerator Institute of America, the National
Solid Wastes Management Association, the
U.S. Department of Health, Education, and
Welfare's National Air Pollution Control
Administration, the Bureau of Mines and
Federal Water Pollution Control
Administration of the U.S. Department of the
Interior, and those State agencies with
planning grants from the Bureau of Solid
Waste Management. The Bureau is grateful for
the time and effort contributed by panel
members and these groups to the
development of the Guidelines.
We hope that planners, designers, operators,
and government officials will apply these
guidelines to overcome poor performance of
existing incinerators and that they will
recognize the need for effective pollution
control equipment. This publication should
also create an awareness of the need for new
incinerators of improved design and
performance.
-RICHARD D. VAUGHAN, Director
Bureau of Solid Waste Management
IV
-------
CONTENTS
Chapter Page
I INCINERATION: A VOLUME REDUCTION
PROCESS 1
II BASIC DATA FOR DESIGN 3
Regulations
Population
Quantities of Solid Waste
Characteristics of Solid Waste
III INCINERATOR COSTS 8
Capital Costs
Operating, Owning, and Financing Costs
IV SITE SELECTION, PLANT LAYOUT, AND
BUILDING DESIGN 11
Site Selection
Plant Layout
Building Design
Plant Exterior
V UTILITIES 16
Electrical Power
Water Requirements
Sewers
Communications
Fuels
VI WEIGHING 18
Scale Description
Operation and Maintenance of Scales
VII RECEIVING AND HAND LING SOLID WASTE 21
Tipping Area
Storage Pit
Charging Methods
Charging Hoppers
Charging Chutes
-------
Chapter Pagc
VIII FURNACES AND APPURTENANCES 26
Furnace
Combustion
Combustion Temperature and Cooling
Refractories
Other Aspects
IX RECOVERY AND UTILIZATION OF HEAT 38
Heat Recovery Systems
Application for Recovered Heat
Auxiliary Fuel
Manpower Requirements
Economics
X INSTRUMENTATION AND CONTROLS 41
Uses of Instrumentation and Controls
Controlling the Incinerator Process
Types and Application of Instrumentation and
Controls
Operational Problems Involving Instruments
Future Needs
XI INCINERATOR EFFLUENTS AND THEIR CONTROL 46
Odor, Dust, and Litter
Residue from Combustion
Fly Ash
Process Water
XII AIR POLLUTION CONTROL 51
Particulate Material
Gaseous Combustion Products
Desired Emission Levels
Methods of Control
XIII ACCEPTANCE EVALUATION 62
XIV SOLID WASTES THAT REQUIRE SPECIAL
CONSIDERATION 64
Bulky Solid Waste
Special Incinerators for Bulky Wastes
Size Reduction of Bulky Solid Waste
Hazardous Wastes
Obnoxious Wastes
Combined Sewage Sludge-Solid Waste Incineration
Conclusions
VI
-------
Chapter Page
XV SALVAGE 67
XVI OPERATION AND MAINTENANCE 69
Management and Personnel
Operation Guides
Performance Records
Utilization of Recorded Data
Maintenance and Repairs
APPENDIX A AN ACCOUNTING SYSTEM FOR
INCINERATOR OPERATIONS 73
APPENDIX B EXECUTIVE ORDER 11282, MAY 26,1966
CONTROL OF AIR POLLUTION ORIGINA-
TING FROM FEDERAL INSTALLATIONS 91
Mention of commercial products in this publication does not imply endorsement by the U.S. Public Health Service
Vll
-------
CHAPTER 1
INCINERATION: A VOLUME REDUCTION PROCESS
Incineration is a controlled combustion
process for burning solid, liquid, or gaseous
combustible wastes to gases and to a residue
containing little or no combustible material.
In this regard, incineration is a disposal
process because incinerated materials are
converted to water and gases that are released
to the atmosphere. The end products of
municipal incineration, however, must be
disposed of. These end products include the
particulate matter carried by the gas stream,
incinerator residue, siftings, and process
water. Incinerator residue consists of
noncombustible materials such as metal and
glass as well as combustible materials not
completely consumed in the burning process.
The advantages of incineration are
numerous, especially where land within
economic haul distance is unavailable for
disposal of solid waste by the sanitary landfill
method. A well-designed and carefully
operated incinerator may be centrally located
and has been found acceptable in industrial
areas so that haul time and distance can be
shortened. The solid waste is reduced in
weight and volume, and the residue produced
can be nuisance-free and satisfactorily used as
fill material. In a properly designed
incinerator, the operation can be adjusted to
handle solid waste of varying quantity and
character.
An incinerator requires a large capital
investment, and operating costs are higher
than for sanitary landfill. Skilled labor is
required to operate, maintain, and repair the
facility. Thus capital and operational costs
must be compared with the costs of alternate
disposal methods, and full consideration must
be given to the effects of the methods on the
community and its neighbors.
The volume of municipal solid waste in the
storage pit can be reduced 80 to 90 percent
by incineration. In the process, usually 98 to
99 percent, by weight, of the combustible
materials can be converted to carbon dioxide
and water vapor. Total weight reduction is
commonly 75 to 80 percent based on the
weight of the as-charged solid waste, including
moisture, reduced to a dry residue.
Compaction of residue results in further
volume reduction, so that solid waste
processed in an incinerator and then
compacted in a fill may occupy only 4 to 10
percent of its volume in the storage pit. A
salvage operation can further reduce residue
volume.
Oversized or bulky burnable wastes (logs,
tree stumps, mattresses, large furniture, tires,
large signs, demolition lumber, etc.) usually
are not processed in a municipal incinerator
since they are either too large to charge, burn
too slowly, or contain frame steel of
dimension and shape that could foul grate
operation or the residue removal systems. A
few incinerators include grinding or shredding
equipment for reducing incinerable bulky
items to sizes suitable for charging. In recent
years, special incinerators have been designed
and constructed to handle portions of bulky,
combustible solid wastes without
pretreatment. '~3 Unless these materials can
be incinerated, their bulk and abundance will
1
-------
add greatly to the amount of land necessary
for final disposal. Other discarded large items,
such as washing machines, refrigerators, water
heater tanks, stoves, and large auto parts,
cannot be handled by incineration, and they,
too, add considerable volume to a fill.
The potential of incineration as a space
conserving mechanism can be demonstrated
by the following comparison: the volume
requirements for final land disposal of an
incinerator residue, with the volume
requirements for a sanitary landfill system
receiving unburned solid wastes.4 Consider
two identical samples of solid waste. Both are
free of bulky solid waste. Assume that each
sample is 2,000 Ib and 13.3 cu yd (this is a
bulk density of 5 to 6 Ib per cu ft or roughly
1 50 Ib per cu yd) and is typical of solid waste
at the generating source.
System 1: Incineration. Based on the 75 to
80 percent weight reduction mentioned
above, the residue produced from the
incinerated waste could be estimated at about
523 Ib. Studies have shown that incinerator
residue may have a landfill compacted density
of 2,700 Ib per cu yd.4 The 523-lb residue
will thus occupy about 0.194 cu yd. The
residue can be calculated as 0.194(100)/13.3
or 1.45 percent of the original volume.
System 2: Sanitary Landfill. The 2,000-lb
sample occupies 13.3 cu yd. Compaction
reduces the original volume of 13.3 cu yd to
2.2 cu yd. The reduction can be calculated as
2.22(100)/13.3 or 16.6 percent of the original
volume.
The ratio of the remaining volumes of solid
waste in the two systems is 1.45 percent to
16.6 percent, or a ratio of about 11 to 1. The
favorable volume reduction by incineration is
quite obvious for solid waste that does not
contain bulky items.
For practical purposes, however, we must
consider the disposal of bulky items and
materials that ordinarily are not processed
through conventional incinerators. Such
materials make up about 20 percent, by
volume, of community solid waste at the
collection point and under good compaction
in a landfill, can be reduced to approximately
half their volume as collected. The volume
conservation advantage of the incineration
system over the landfill system is that of 23.3
percent to 11.16 percent, or 2.1 to 1 (Table
1).
TABLE 1
COMPARISON 01- THEORETICAL INCINERATION
AND SANITARY LANDFILL VOLUME REDUCTION
RELATIONSHIPS
Original
volume
units
Reduction
factor
Final
volume
units
Incineration
0.8 X 0.0145
0.0116
Incinerable
waste
Bulky and non-
incincrablc waste* 0.2 X 0.5 = 0.1
Total 0.1116
Sanitary Landfill
Incinerable
waste
Bulky and non-
incincrablc waste
0.8 X 0.166
0.2 X 0.5
0.133
0.1
Total 0.233
*Nonincincrablc wastes are defined in this study as those
materials that ordinarily are not processed through conven-
tional incinerators.
REFERENCES
1. KAISER, E. R. The incineration of bulky refuse. In
Proceedings; 1966 National Incinerator Conference,
New York, May 1-4, 1966. American Society of
Mechanical Engineers, p. 39-48.
2. KAISER, E. R. The incineration of bulky refuse. II. In
Proceedings; 1968 National Incinerator Conference,
New York, May 5-8, 1968. American Society of
Mechanical Engineers, p. 129-135.
3. WINKLER, T. E. Discussion of "The incineration of
bulky refuse. II," by E. R. Kaiser. In Discussions;
1968 National Incinerator Conference, New York,
May 5-8, 1968. American Society of Mechanical
Engineers, p. 26.
4. KAISER, E. R. Refuse reduction processes. In
Proceedings; the Surgeon General's conference on
solid waste management for Metropolitan
Washington, July 19-20, 1967. Public Health
Service Publication No. 1729. Washington, U.S.
Government Printing Office, 1967. p. 93-104.
-------
CHAPTER II
BASIC DATA FOR DESIGN
Accurate basic data are needed to design
successfully. These data include
determination of present and future
population to be served and the quantity,
composition, and characteristics of the waste
to be incinerated. Air, land, and water
pollution control regulations and other
constraints must be considered.
Few communities have sufficient
information for designing an incinerator.
Local studies are usually needed, therefore, to
gather the data required for the community
or region that will be served by the
incinerator. Population projections and
densities and the number, type, size and
location of industries and commercial
establishments are usually available from
planning agencies, the Chamber of Commerce,
or other community organizations. Useful
records on the quantity and characteristics of
solid waste being generated may be available
from the municipal agency responsible for
solid waste control. Local stipulations as to
what wastes will be accepted for incineration,
whether householders must separate their
solid wastes, and the hours of incinerator
operation must be considered by the designer.
Some of the basic factors that influence
design are discussed in this chapter.
Regulations
Incinerator design must meet regulations
intended to preserve the quality of the
environment and the health and safety of the
operators. Local requirements include air and
water quality standards, zoning, building and
electrical code stipulations, and occupational
health, safety, and sanitary regulations.
A designer must consider existing local,
State, and Federal regulations and the
regulations of neighboring communities. He
should also recognize that more stringent
regulations on air and water pollution can
reasonably be expected in the future, and the
design should be capable of meeting these
higher future standards. To serve as a guide
where no local regulations exist, this
publication includes Executive Order 11282,
May 26, 1966, "Control of Air Pollution
Originating from Federal Installations" and
standards by the Secretary of Health,
Education, and Welfare implementing the
objectives prescribed by the Order (Appendix
B).
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 incinerated and, therefore, the
incinerator 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, and over the
projected life of the incinerator (usually 20 to
-------
40 yr). In determining the future population
to be served by the facility, 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. Updated population projections
often can be obtained from local, district,
county, or State planning departments and
from local utility companies.
Quantities of Solid Waste
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 2) points out the need for local
studies.
Weekly and Seasonal Variations. Seasonal
fluctuations occur in the amount of solid
waste generated and collected within the
community and must be considered. This can
be done by plotting weekly waste quantities
averaged over 4-wk periods.' The fluctuations
in waste quantities occur in yearly cycles, the
maximum quantity almost always peaking
during the warmer months. Because of many
influences, the magnitude of fluctuations is
TABLE 2
PER CAPITA SOLID WASTE COLLECTED
Type
Quantity
(Ibs/capita-calendar day)
Residential (domestic)
Commercial (stores, restaurants,
businesses, etc.)
Incinerable bulky solid wastes
(furniture, fixtures, brush
demolition, and construction
wastes)
1.5-5.0
1.0-3.0
0.3-2.5
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-wk
averages in waste generation within a
community commonly range from ± 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.1
Sizing. Because of large daily fluctuations
in solid waste quantities, an incinerator
should be sized on the basis of weekly
quantities of solid waste to be incinerated.
The storage pit should be designed to handle
daily peaks in quantity.
One incinerator sizing method is based on
the average weekly delivery for the highest
4-wk 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 1). With the use of a plot of this
type, the incinerator 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 an incinerator, 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.
Characteristics of Solid Waste
The design of the incinerator system,
including furnace chamber, grates, feed
mechanisms, and other parts, will vary
because of differing waste characteristics and
amounts. A plant to handle only household
waste will differ from one that handles food
waste from stores and restaurants or from one
that handles only dry, high-heat-value
industrial waste. The significant variations in
composition that will actually occur in a
particular community must be determined.
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. The moisture content has been
decreasing with diminishing household
garbage, and the ash content has been
decreasing as less coal is used for heating.
Moreover, combustible content and heat value
have been increasing, principally because of
the ever larger use of 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.
Composition of Residential Solid
Waste. Analysis of a composite of residential
solid waste shows a range of percentages for
material types (Table 3). As collected at the
source in receptacles or piles, residential solid
waste generally weighs between 100 and 300
Ib per cu yd and averages 150 Ib per cu yd. In
the collection truck, solid waste is commonly
compressed from 350 to 700 Ib per cu yd. In
the incinerator pit, the weight of the waste
generally ranges from 300 to 550 Ib per cu
yd.
Bulky Solid Waste. Unless special
provisions are made, combustible bulky items
such as furniture, fixtures, and waste lumber
present an operational problem when
delivered to an incinerator. As already noted,
exclusive of junked automobiles and
5.2 10.4 15.6 20.8 26.0 312 364 416 46.8 52.0
NUMBER OF WEEKS VALUE IS NOT EXCEEDED
20 30 40 50 60 70
PERCENT OF YEAR VALUE IS NOT EXCEEDED
80 90
Figure 1. I-requency diagram of cumulative weekly solid waste 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 15 percent above the average
yearly mean.
-------
TABLE 3
RANGE [N COMPOSITION OF RESIDENTIAL
SOLID WASTES IN 21 U.S. CITIES
Percent composition by net weight
Component
Food waste
Garden waste
Paper products
Metals
Glass and Ceramics
Plastics, rubber.
and leather
Textiles
Wood
Rock, dirt, ash, etc.
Low
0.8
0.3
13.0
6.6
3.7
1.6
1.4
0.4
0.2
High
36.0
33.3
62.0
14.5
23.2
5.8
7.8
7.5
12.5
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. Values were determined
from data taken at 21 cities in continental United States
between 1966 and 1969.
demolition waste, nonincinerable waste
amounts to about 20 percent by volume of
total community solid waste. Of this, about
50 percent is combustible material. Separate
collection service has frequently been
employed to reduce the number of such items
delivered to the incinerator. Recently the
trend has been to design incinerators capable
of processing almost everything.
Shredders and grinders are now being used
at some incinerators, and specialized
incinerators have been used for bulky waste
alone.2'3 The operational problems
encountered in handling bulky solid waste are
discussed in Chapter XIV
Other Characteristics. The heat values and
the proximate and ultimate analyses of the
solid waste as delivered to the incinerator
(Table 4) are used in calculating heat release
rates, combustion and excess air volume, grate
area, draft, and other factors. Proximate
analysis is the determination of moisture,
volatile matter, fixed carbon, and ash
expressed as percentages of total weight of
the sample. Ultimate analysis is the
determination of moisture content,
noncombustibles, and the carbon, hydrogen,
oxygen, nitrogen, and sulfur content.
Data on the proximate analysis, ultimate
analysis, and heat values of individual waste
components such as newspaper, cardboard,
grass, meat scraps, fruit peelings, etc., have
been published.4 These data can be used to
estimate proximate analysis, ultimate analysis,
and heat value once the composition (% by
weight) of a waste is determined.
The methodology for obtaining a
representative sample of solid waste and its
analysis has been described by the American
Public Works Association.5 Oxygen bomb
calorimetry for determining the amount of
heat liberated from solid materials and from
liquids has been described.6
The ultimate analysis provides a means for a
rational approach to furnace design and is
required for a complete materials balance of
incoming and outgoing material. Significant
variations in these values can occur with
seasonal and climatic change. Variation in
moisture is particularly critical; the
maximum, mean, and minimum moisture
value should, therefore, be determined to
provide a range for best, average, and worst
conditions. If these varying conditions are
TABLE 4
PHYSICAL AND CHEMICAL CHARACTERISTICS OF
INCINERATOR SOLID WASTE*
Constituents
Proximate analysis
Moisture.
Volatile matter.
Fixed carbon .
Noncombustibles
Ultimate analysis
Moisture
Carbon
Oxygen
Hydrogen .
Nitrogen
Sulfur .
Noncombustibles
Percent by weight (as received)
15-35
50-65
3- 9
15-25
15-35
15-30
12-24
2- 5
0.2-1.0
0.02-0.1
15-25
Higher heating value
Btu per Ib (as received)
3,000-6,000
*Principally residential-commercial waste excluding bulky
waste.
-------
recognized, the incinerator can be designed to
operate under them.
Heat value is one important characteristic ot
solid waste needed for incinerator design. The
term "heat value" can be used in several
different ways. One way, the "higher heat"
value or "gross heat" value, is the total
amount of heat released per unit weight of
material that is burned. The higher heat value
is determined by oxygen bomb calorimeter
measurement, although it can be estimated
from chemical composition of the sample
material if known. Another way of expressing
heat value is called "net" or "low" heat value.
To determine this value, the latent heat of
vaporization of all moisture resulting from the
combustion process is subtracted from the
high heat value.
As mentioned above, the long-term trend in
the United States has been for the
combustible fraction (principally dry paper
and plastics) of municipal solid waste to
increase and for the moisture content to
decrease (mainly because of the decrease in
wet food waste). Hence, the heat value of
waste as received at the incinerator is rising.
At present, incinerator designers are using
gross heat values ranging from 3,000 to 6,000
Btu per Ib based on waste as received. The
present trend indicates that heat values of
incinerator solid waste will increase by 500
Btu per Ib by 1980.
REFERENCES
1. Bureau of Solid Waste Management. Unpublished data
(SW-lOts).
2. KAISER, E. R. The incineration of bulky refuse. In
Proceedings; 1966 National Incineration
Conference, New York, May 1-4, 1966. American
Society of Mechanical Engineers, p. 39-48.
3. KAISER, E. R. The incineration of bulky refuse. II. In
Proceedings; 1968 National Incinerator Conference,
New York, May 5-8, 1968. American Society of
Mechanical Engineers, p. 129-135.
4. KAISER, E. R. Chemical analyses of refuse components.
In Proceedings; 1966 National Incinerator
Conference, New York. May 1-4, 1966. American
Society of Mechanical Engineers, p. 84-88.
5. American Public Works Association. Municipal refuse
disposal. 2d ed. Chicago, Public Administration
Service, 1966. 528 p.
6. Par Instrument Company. Oxygen bomb calorimetry and
combustion methods. Technical Manual No. 130.
Moline, III, 1960. 56 p.
-------
CHAPTER III
INCINERATOR COSTS
Incinerator costs are divided between those
related to ownership and those related to
operation. Ownership costs derive from the
capital costs of financing the incinerator
construction and are usually paid off through
depreciation and interest charges. Operating
costs include the direct and indirect costs of
operating and maintaining the plants. This
chapter presents costs for existing municipal
incinerators and outlines the major factors
that influence costs.
Knowledge of capital costs of existing
incinerators is of interest as the basis for
understanding, at the planning stage, how
much money is involved in constructing an
incinerator. It is also prerequisite to
determining total costs. These total costs of
ownership and operation are necessary to
compare different incinerators and to evaluate
incineration with other methods of solid
waste disposal. The data included in this
chapter present national averages of these
costs and can be used for general comparisons
or planning purposes.
Although costs are necessary in comparing
the operation of different incinerators, the
primary use of cost data is for effective
management. An example of an accounting
system that may aid in obtaining data is
included in Appendix A.
Capital Costs
Community Solid Waste Practices data. The
capital costs are reported as the 1966
estimated replacement costs and include the
costs of buildings, facilities, and engineering,
but not land.
CAPITAL COST PER TON (THOUSANDS OF DOLLARS)
The Capital COStS Ol 170 municipal Figure 2. Cumulative frequency diagram of capital costs
incinerators were obtained from the US for 170 municipal incinerators in $1,000 increments. At the
IT i i r " asterisk, 62 percent of the incinerators have capital costs
Health Service National Survey of below $6,1 so per ton (24-hr design capacity).
-------
IOO
Q
lij
Q
90
SO
70
O
o
p 6O
<
it
UJ
Q.
O
50
40
UJ
cr
Q:
^
o
o
o
tu
o
Q:
30
20
10
IO
20
30
Figure
costs for
OPERATING COST
(DOLLARS PER TON)
3. Cumulative frequency diagram of operating
78 municipal incinerators in dollar-per-ton
increments. At the asterisk, 73 percent of the incinerators
have operating costs below S5.00 per ton solid waste
received.
These data indicate an average capital cost
of municipal incinerators at about $6,150 per
ton (24-hr design capacity). (Example: capital
cost of $600,000 -H 100-ton-per-day capacity
= $6,000 per ton.) Sixty-two percent of the
incinerators studied cost less than $6,150 per
ton (Figure 2). Fifteen plants reported capital
costs above $11,000 per ton. The highest
capital cost, reported by only one plant, was
$30,000 per ton.
Some of the major equipment cost items
included in capital costs are scales, cranes,
furnaces, blowers, air pollution control
devices, process waste treatment and recycling
equipment, residue removal systems,
instrumentation, waste heat recovery
equipment, steam distribution equipment,
and flue and duct equipment. Major
construction items on the structure include
building, ramps, tipping area, storage pit,
refuse hoppers, offices, employee facilities,
piping, and chimney. Miscellaneous items
under capital cost include site preparation,
excavation, foundation preparation, roadway
and sidewalks, landscaping and seeding,
furniture and fixtures, machine shop
equipment, and tools.
Fly-ash control equipment has, in the past,
amounted to about 3 percent of the total
capital cost of municipal incinerators.1 To
achieve particulate removal as required by the
new and more stringent air pollution control
regulations, the cost of control equipment
will now range from 8 to 10 percent of the
total capital cost.
Capital cost components and their relative
importance may be grouped as follows:
furnaces and appurtenences (55% to 65%);
building (20% to 30%); air pollution control
equipment (8% to 10%); miscellaneous (7% to
13%).
Operating and Owning Costs
The 1968 National Survey data also
provided information on operating costs of
-------
municipal incinerators. Since the calculation
of the costs per ton of solid waste processed is
dependent on weighing the material, this
discussion is limited to the facilities (78) that
actually weighed their incoming solid waste.
The Survey data on operating costs gave an
average cost of operating municipal
incinerators of S5.00 per ton of refuse
processed. Seventy-three percent of the
incinerators studied had operating costs below
S5.00 per ton (Figure 3). Four of the 78
plants reported operating costs above $10 per
ton.
The wide variation in operating costs
resulted partly from differences in the
amount and types of pollution control
equipment, labor rates, cost of utilities,
residue disposal costs, and amounts of
automation. Reported operating costs are also
influenced by the fact that some cost items
are not included when calculating the total
operating cost. For example, for many
incinerators, the cost of utilities,
administration, or employee fringe benefits
are not included in operating costs.
Ownership costs include the financing costs
associated with the depreciation and interest
of the facility. The costs for depreciation and
interest have been commonly given to be
between $1.00 and $2.00 per ton. In practice
the actual costs can vary significantly
depending on factors such as utilization rate,
estimated life, and interest rates. Total costs
TABLE 5
TYPICAL INCINERATOR COST CENTERS
Operating costs
Labor (operatingand maintenance)
Salaries
Vacation and holiday pay
Sick and injury pay
Training
E-'ringe benefits
Pensions
Utilities
Water
Electricity
Gas or fuel oil
Miscellaneous charges
Materials and supplies
Contract work
Overhead
Management
Charges from other administrative departments
Ownership costs
Depreciation
Interest
of ownership and operation can be stated
either for a time period or for the quantity of
wastes incinerated, for example, annual cost
or cost per ton (Table 5).
REFERENCE
1. American Public Works Association. Municipal refuse
disposal. 2d ed. Chicago, Public Administration
Service, 1966. p. 145.
10
-------
CHAPTER IV
SITE SELECTION, PLANT LAYOUT, AND BUILDING DESIGN
Proper location of the incinerator enhances
acceptance by the public and results in
economies in waste collection. A well-planned
physical layout facilitates efficient and
economic incinerator operation. Good design
and selection of appropriate building
materials promotes a pleasing appearance and
minimizes housekeeping and maintenance.
Site Selection
Public Acceptance. Public acceptance is a
most important consideration in selecting an
incinerator site. A few suggestions for gaining
public acceptance follow.
1. Choose a site where construction can
conform with existing and planned
neighborhood character. In general, industrial
and commercial areas are more compatible
with incinerators than residential areas. An
incinerator plant is usually classed as heavy
industry, and the evaluation of its location
should reflect this. Too frequently the vacant
land surrounding an incinerator is later
developed for residential or other restricted
use, which creates conflict. To avoid potential
conflict, the undeveloped, surrounding land
should be zoned for industrial use.
2. Avoid choosing a site that may conflict
with other public buildings. The noise, lights,
and 24-hr workday of normal incinerator
operation preclude locating it near a hospital,
and heavy truck traffic makes incinerator
location near schools undesirable.
Centralized public works operations are
desirable. Often an incinerator plant can be
advantageously located near a sewage
treatment plant so that technical services may
be shared. There may be ecomomies in
locating the incinerator near a garage where
vehicle repair facilities and personnel can be
shared.
3. Where conflict with neighborhood
character is unavoidable the screening effects
of a wall or planting can reduce adverse
effects and gain public acceptance. Good
architectural design is itself a major asset in
overcoming potential neighborhood
objection.
4. Institute an effective public relations
program. Before full site and design decisions
are made, proposals and plans should be
presented through the press and for discussion
at public meetings. This would serve to
demonstrate management response to
community desires and a capability for
operating an acceptable facility. Presentation
of alternatives along with rationale for
incineration may be supported by graphic
examples and site visits to successfully
operating facilities.
Site Suitability. Factors important to
design, but generally not of concern to the
public, are foundation conditions,
topography, availability of utilities, building
restrictions, drainage, and meteorologic
conditions.
Soil and rock formations determine the
type of foundation required to support the
heavy, concentrated load of an incinerator
structure. Failure to accurately determine
foundation conditions and design to them can
11
-------
result in expensive modifications during
construction and. in certain cases,
abandonment of the site with its partially
completed structure. Groundwater conditions
also affect design and cost.
Topography and meteorological conditions
must be considered in the location and the
design of the incinerator. A flat site is apt to
require a ramp for access to the tipping floor,
whereas a hillside site can provide access at
various ground levels. Topography can also
ease or hinder the dispersion of gases and
particulates by the local atmosphere. This
aspect of plant location is complex and
requires the assistance of a meteorologist or
air pollution control specialist, who can
determine the best stack height for the
dispersion of gases. Stack height
determination requires consideration of
topography and legal restrictions, such as
those from Federal Aeronautics Agency
regulations, local building regulations, and
zoning.
Availability of public utilities may be a
governing factor in site selection, since
electricity, gas, water supply, sewage disposal,
and process water disposal are essential to the
incinerator process. Fuel such as gas or oil
may be required at some installations as an
auxiliary heat source for the furnaces or as
building heat. Communication facilities must
be available for fire and safety control and for
coordinating operations.
As in the development of any industrial site,
effective drainage of surface waters must be
an integral part of design. The site should not
be selected in an area subject to flooding
unless the facility can be protected and access
remains available during high water.
Traffic Consideration. The ideal location
for an incinerator is at the center of the
traffic pattern produced by the contributing
collection vehicles. A major argument already
made for incineration in comparison with
land disposal was that incineration can reduce
the time and cost of collection haul. This
requires that the incinerator be centrally
located. This is not always feasible tor a
variety of reasons. For example, future
growth and its effects on the collection source
must be considered.
A large plant may have literally hundreds of
vehicles delivering solid waste in relatively
short time intervals. Because of heavy traffic,
the plant must have adequate access to
preclude safety hazards in the streets of the
area. Special access roads may have to be
provided so that the trucks avoid heavily
traveled highways. Special consideration also
must be given to traffic impediments such as
bridges with low weight limits, restrictive
heights of overpasses, narrow pavements, and
railroad grade crossings with high volume
traffic. A location that avoids commuter
traffic is also preferred. Thus, a plant located
near the edge of the participating community
but readily accessible by freeways or beltways
may be better than one centrally located. The
same traffic considerations apply to residue
disposal. On-site disposal is often not possible;
therefore, incinerator residue and
nonburnables must be trucked to a landfill.
Plant Layout
An incinerator plant layout should promote
ease, simplicity and economy of operation,
and maintenance. There should be adequate
room for all parts of the operation. The
structure should harmonize with the
surrounding neighborhood and should be so
oriented that unsightly parts of the building
and operation (such as receiving and storage)
are not visible to the public. In certain
climates, it is advantageous to orient the
receiving area on the leeward side of the
prevailing wind. The on-site road pattern
should allow ready access to scales and
receiving area and an easy exit; one-way
traffic is most desirable; sharp turns and blind
spots should be avoided; and a large parking
apron should be provided outside the
receiving area to avoid congestion during peak
receiving hours.
12
-------
Adequate drainage is necessary for surface
waters. Incinerator operation requires
periodic hosing of tipping floor, vehicle wash
areas, parking aprons, and ramps. The paving
should be sloped and contain adequately sized
and strategically placed drains. This is
particularly critical in cold climates where ice
formation could interfere with operations.
Maintenance and storage of trucks may be
inside the incinerator building or on the
grounds, but these areas must be located
where they will not hamper the operation of
the incinerator.
Building Design
The incinerator should be aesthetically
pleasing and should be constructed of
durable, high-quality materials and fixtures to
reduce maintenance. Materials requiring a
minimum of painting or resurfacing, such as
concrete, tile, and noncorrosive metals,
should be used. Surfaces that require painting
should have a dense, durable finish. Corners
and bases can be coved to reduce
accumulation of debris and allow easier
cleaning. Where possible, piping and duct
work should be enclosed.
Personnel Facilities. Adequate facilities for
incinerator personnel are more a matter of
convenience and may well represent the
difference between a working situation that is
conducive to efficiency and cleanliness as
opposed to one that may create an indifferent
and inefficient work crew. A clean locker
room is needed, with 'adequate toilet,
lavatory, and shower facilities. Lockers should
have space for storing hard hats, rain and
winter gear, and a full change of clothing.
Sanitary facilities should be provided for
women who may visit or be employed at the
plant.
Lunchroom facilities should also be
provided along with a sink and suitable
outlets for coffee percolators. Drinking water
should be available on every floor and within
200 ft of employee stations. The lunchroom,
locker room, shower, and toilet areas should
be well lighted and kept clean at all times to
encourage habits of cleanliness by the
workman. It is often desirable to provide
washroom facilities convenient to collection
personnel, weighmasters, and others.
Control Room. Many large incinerators are
now being built with glassed-in control rooms
so located that the incinerator superintendent
or shift foreman can readily observe various
operations. Because all areas of the plant or
operating conditions within furnaces cannot
be observed from one location, closed-circuit
television is used in some instances. The
importance of the glassed-in area (ventilated
and air conditioned) is not merely to provide
comfort to the superintendent and foreman,
but to protect delicate recording instruments
from dust and to minimize the noise level in
an area where telephones are used. Written
records are also better maintained in an
isolated control room area. The control room
should be suitably equipped with remote
reading and recording instruments that
provide supervising personnel with the
information necessary to adjust the
incinerator operation if it is not performing
suitably.
Administrative Offices and Conference
Room. In the larger incinerator plants,
sometimes the superintendent, foremen, and
clerical workers need an office to conduct
necessary administrative activities. Attractive
decor and air conditioning will improve
morale and efficiency. Smaller incinerators
may effectively combine the operating
control room with space for administrative
activities.
At larger plants, a conference room for staff
briefings, safety discussions, and training
purposes is a worthwhile investment.
Weighmaster's Office. The weighing
activities may be conducted alongside the
access road outside the incinerator plant or at
the entrance to the turning and tipping area
within the plant proper. In either instance,
the weighmaster should have a facility with
13
-------
ample glassed area to observe the movement
of weigh scale traffic. He should have ready
means of communicating with the driver,
handling credit cards, or making cash
transactions.
Maintenance and Repair
Facilities. Regardless of the size of the
incinerator, storage space for electrical,
mechanical, and refractory parts and an
enclosed area where repair and subassembly
may be performed must be provided. For very
large plants, separately maintained storerooms
for parts, electric shops, mechanical shops, and
enclosed refractory storage facilities should be
included. Where a large municipality has a
number of incinerators, central maintenance
and repair facilities for major activities may
prove economical. There should be storage
facilities for such items as lawn mowers, skip
loaders, mechanical sweepers, refractories,
pipes, insulation material, and the various
chemicals required for insect and other pest
control.
Laboratory. The incinerator must be so
operated that the environment is not
polluted. Federal, State, and local regulations
are becoming more restrictive. Surveillance of
the water quality of incinerator effluent is
needed to ensure pollution control, and a
small laboratory and testing equipment
should be provided for this purpose.
Municipalities with several incinerators should
consider a centralized laboratory facility.
Interior Lighting. At many municipal
incinerators the interior lighting is poor.
Recommended lighting standards for various
industrial operations are published by the
illuminating Engineering Society,1 and
lighting standards exist for certain tasks
similar to those performed at incinerators
(Table 6).
Plant Exterior
Roadways, Sidewalks, and Parking
Areas. In designing the roads providing
TABLE 6
LIGHTING STANDARDS APPLICABLE AT
INCINERATORS
Office and industrial tasks
Foot-candles
on task
Loading and trucking 20
Corridors, elevators, stairways . 20
Rough, easy assembly work 30
Reading high-contrast or well-printed
material, tasks and areas not involving
critical or prolonged seeing such as
conferences, interviews, inactive files,
and washroom . 30
Medium bench and machine work, rough
grinding, medium buffing and polishing,
difficult inspection 100
Regular office work, reading good reproductions,
reading or transcribing hand writing
in hard pencil or poor paper, active
filing, indexing references,
mail sorting 100
ingress to an incinerator site, consideration
must be given to peak loading periods and
types of vehicles that may utilize the
incinerator. Where possible, the roadway
system should be built so that the traffic
flows only in one direction, thus providing
only one entrance and one exit. Arrangements
must be made for obtaining truck tare weights
without interfering with one-way traffic flow.
This is possible even where scales are used,
provided the trucks being serviced all have
established tare weights. When transient
traffic is being weighed, so that a "weighout"
is necessary, a roadway may be provided
within the site that will allow the trucks to
return across the scale for the second
weighing in the same direction as the normal
flow of traffic. All roadways should be
sufficiently wide to permit the passage of one
vehicle past another in the event that a truck
is stalled. Road grades should be suited to the
traffic operating on the grades. In general, the
grades for short-distance truck travel should
14
-------
not exceed 7 percent uphill and 10 percent
downhill. Pavements should be hard surfaced,
all weather, and designed for heavy loads.
Curbing, posts, or guardrails should be used to
confine traffic to roadways.
Incinerator plants should be provided with
sufficient sidewalks to ensure that visitors and
plant personnel will be able to walk safely
about the premises without being endangered
by vehicular traffic.
Parking areas are generally divided into two
categories: (1) parking for administrative and
operating personnel, visitors, and temporary
parking for collection vehicles, (2) parking for
overnight storage of collection vehicles and
for equipment used at the incinerator site
such as mobile sweepers. In areas with severe
winters, parking facilities inside heated garage
areas are desirable to permit proper
maintenance, cleaning, and protection of the
collection vehicles.
Landscaping. Perimeter planting around an
incinerator site presents a pleasing appearance
and reduces the noise of the truck traffic
from within the property. For maximum
benefit and to further enhance the
appearance, trees and shrubbery can be placed
outside the fencing. Provisions must be made
in advance for adequate watering and for
access so that periodic trimmings may be
performed without unreasonable expense.
Built-in sprinkling systems should be
considered for lawn and shrub areas.
Fencing and Lighting. Where the
incinerator plant is located in an area subject
to vandalism, peripheral fencing is desirable
with a minimum height of 6 ft with three
strands of barbed wire on a 45° angle
projection at the top. Such fences should be
constructed of low-maintenance, rustproof
metal. Gates should be similar in design and
provided with sturdy locks. The substitution
of peripheral plants for fencing is usually not
desirable, since most hedges can be penetrated
by intruders.
External lights placed on the incinerator
building are adequate to light most
incinerator sites. If the building lights should
prove objectionable to the surrounding
neighborhood, perimeter lights on stands
directed towards the incinerator plant may be
preferable. Light stands should also be
provided along the on-site roadways used by
collection and incinerator vehicles.
Traffic Control. Signs for the control of
traffic should be simple and the lettering
should be large. Where one-way control of
traffic is desired, the entrances and exits
should be clearly indicated. Proper design of
roadways and directional markings on the
pavements, such as arrows and centerline
striping, will lessen the need for traffic signs.
A stop sign or signal placed at the entrance to
the scale is essential. At very large plants,
electrically controlled signals operated by the
weighmaster may be desirable to route traffic.
Signs should be informative and clearly visible
so that visitors to the plant, as well as routine
users, will have no difficulty entering and
leaving the plant.
REFERENCE
1. Illuminating Engineering Society. IES lighting handbook;
the standard lighting guide. New York. 1959 [1156
P-]
15
-------
CHAPTER V
UTILITIES
For efficient operation, a municipal
incinerator requires certain utility services,
which include: (1) electricity for power and
lighting; (2) potable water for plant personnel
and suitable process water for spraying,
heating, quenching, cooling, and fire fighting;
(3) telephone service; (4) sewerage systems
for handling process waste and sewage, and
storm sewers for drainage; (5) fuel for
heating, hot water, auxiliary heat for
incineration, and possible laboratory use.
Each of these utilities supplied to the
incinerator site must be metered and
distributed safely and efficiently to all points
of usage at the site.
With increasing incinerator capacities and
with increasing use of sophisticated
equipment and devices, more utility services
will be required. The cost of providing these
utilities depends on the plant design and
mode of operation and may reasonably be
expected to range from $0.10 to $1.00 per
ton of waste processed.
Electric Power
With few exceptions, utilization of
incinerator waste heat to generate electric
power is not practiced in the United States.
The incinerator's electrical power is obtained
from other sources.
Electric power requirements vary with the
degree of mechanization and the use of
equipment. Common examples of equipment
requiring electricity are induced draft fans,
forced-air fans, pumps, cranes, hoists, air
pollution control devices, and grate-driving
mechanisms. Allowance for future electrical
needs should be included in planning and
sizing the electrical distribution systems. For
some facilities, electric power can cost as
much as $0.75 per ton of waste incinerated.
The voltage for the lighting system is
usually 110 volt, although higher voltage
fluorescent and mercury-vapor lamps are
becoming widely used. The latter types have
higher first cost, but provide lower
maintenance and operational cost. Most
instrumentation operates on standard 110- to
120-volt power, but there are times when
voltage regulators and transformers are used
to maintain a constant voltage or a lower
voltage to certain circuits.
To prevent damage to the structure and
equipment from smoke and overheating due
to power failure, an emergency standby
power system is needed. Alternate safety
measures include automatic,
temperature-control devices such as a water
cooling system, using city water or stored
water, and emergency openings in the furnace
to bypass air pollution control equipment.
Peak power demands frequently are
considerably in excess of average power
consumption and may require special
provisions. The cranes and shredders could
demand extra power and cause severe current
fluctuations that result in power shortage and
equipment failures. The electrical system
should be designed to accommodate the
power demand.
16
-------
Water Requirements
The quality of the water required for
incinerator operation will depend on its use.
Sources may include: city water, on- or
off-site wells, rivers, lakes, and wastewater
treatment plant effluents. The total amount
of water required may vary from 350 to
2,000 gal per ton of waste incinerated
depending on design and operation.1'2 Cost
for this portion of the utility service is from
$0.07 to SO.40 per ton of waste incinerated,
based on a water rate of $0.20 per 1,000 gal.
Incinerator operation requires a dependable
water supply. An elevated water supply .serves
this purpose and can be used for fire fighting.
When waste heat is used to produce steam or
hot water, the boiler feedwater and makeup
water will require extensive pretreatment.
Water for air pollution control equipment, for
gas cooling, and for dust control sprays need
not be potable, but should be free from
suspended materials. Water used in the
incineration processes will increase in
temperature, change in chemical
characteristics, and will acquire solids.
Treatment may be required before these
waters are discharged.
The costs of water recycling and reuse
should be investigated. In reuse and recycling,
treatment should be effective in preventing
clogging, erosion, and corrosion of
equipment.
Sewers
Preferably, the incinerator should be
located in an area served by sanitary sewers.
Untreated waste process water should be
disposed of through the sanitary sewer if the
system is capable of handling it. Storm sewers
should be used only for discharge of surface
waters.
Communications
External telephone communications are
normally provided by a trunk line from the
switchboard serving the municipality.
Communications within the plant are best
provided by an intercom system. Public
address systems, bells, and other devices may
also be effective. Soundproof booths with a
visible signal system have been used in areas
with continuous high-noise levels.
Extensive, closed-circuit television
monitoring is being utilized in the power
generation industry for supervision and for
observing the combustion process. Although
attempts have been made to monitor large
incinerators, systems for this purpose are still
in the development stage.
Fuels
Fuel may be required for plant processes.
including building and water heating, and for
auxiliary fuel. The choice of fuel for these
purposes will depend on availability and cost.
The need is determined by local conditions
and incinerator design.
REFERENCES
1. JENS. W., and F. R. REHM. Municipal incineration and
air pollution control. In Proceedings: 1966 National
Incinerator Conference, Ne\v York. May 1-4, 1966.
American Society of Mechanical Engineers, p
74-83.
2. MATUSKY, F. E., and R. K. HAMPTON. Incinerator
waste water. In Proceedings; 1968 National
Incinerator Conference, New York, May 5-S, 1968.
American Society of Mechanical Engineers, p.
198-203.
17
-------
CHAPTER VI
WEIGHING
An incinerator scale weighs incoming solid
waste and outgoing residue, including fly ash
and sittings. It may also be used to weigh
salvaged materials. Accurate and meaningful
weight records can be used to improve
operation, to assist management control, to
facilitate planning, and to provide an
equitable means for assessing fees. Weights are
needed for cost accounting, rating the
effective capacity of the incinerator, testing
air pollution control devices, and making a
materials balance for the facility.
A management system making use of
weights can serve to regulate and control solid
waste collection and disposal. Good collection
scheduling and routing may depend on such a
system. Distribution of waste deliveries
among available plants requires prompt access
to weights of incoming material. Cost control
to increase efficiency and eliminate excessive
expenditures of time and effort is dependent
on weight units.
Observation of the trends in quantity,
sources, and types of solid waste collected
will assist in planning for future disposal
needs. Weight records of residue assist in
determining the remaining life of residue
disposal sites, and thus assist effective
planning as well as provide a means of
calculating combustion efficiency. If a
community wishes to charge other
communities, private haulers, or commercial
haulers for using the incinerator, the weight
measurements will provide a practical,
equitable means for assessing fees.
Scale Description
Scale Types. A small incinerator (50 to
100 tons per day) may satisfactorily use a
wood platform, manually operated,
mechanical scale and keep handwritten
records. At the other extreme, large
incinerators frequently use automatic systems
employing load cells, electronic relay, and
printed output. The electronic relay scales
allow for greater flexibility in locating the
scale platform in relation to the scale house.
Highly automated electronic scales and
recorders are more costly than simple beam
scale; however, they are justified in many
cases because they are faster and more
accurate.
Size and Capacity. The scale should have
sufficient capacity to weigh the largest vehicle
anticipated to use the incinerator on a routine
basis. The platform should be long enough to
accommodate simultaneous weighing of all
axles. Separate axle loading scales, although
less expensive, are inherently inaccurate and
slow in operation. For simultaneous weighing
of all axles, the majority of collection trucks
could be accommodated with a 10- by 34-ft
platform.1 A 50-ft platform will
accommodate most trailers and semitrailers.
Scales should be capable of weighing loaded
vehicles of up to 30 tons.
Accuracy. The accuracy and internal
mechanism of the scale and recording
mechanism should meet the commercial
requirements for the State or other
jurisdictions involved. This is particularly
necessary if user fees are based on weight.
18
-------
Recommended scale requirements have been
outlined by the National Bureau of
Standards.2
Since municipal records are seldom kept
closer than to the nearest tenth of a ton, and
since most applied loads are within a range of
8 to 14 tons, scale accuracy of ±1.0 percent is
reasonable. All scales should be periodically
checked and certified to 1 percent accuracy.
Both mechanical and electronic scales
should be tested under load during a quarterly
inspection. This 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; and (3) testing the
scale with test weights.
Platform. The platform or deck of a scale
may be constructed of wood, steel, or
concrete. Wood decks are least expensive, but
least durable. Many large truck scales have a
platform constructed of reinforced concrete.
Scale Pit. Scale-pit walls are usually
concrete and should be set in a suitable
foundation to control settlement. A paved
scale-pit floor facilitates cleaning and
maintenance. In all cases, scale-pit drainage is
essential. Scale-pit depth should be sufficient
to allow periodic inspection and maintenance
of the scales. Access to the pit should be
through the wall or through a hatch on the
platform. Gutters around the edge of the.
scale pit to intercept runoff from the deck
have been used effectively to ensure a dry,
clean scale pit. Lighting should be provided
to aid in inspecting and maintaining the scale
mechanism and in cleaning the scale pit.
Operation and Maintenance of Scales
Operation. The number of vehicles that
can be weighed per unit time will vary with
the weighmaster, automation, and amount of
data to be collected. Under some conditions,
an experienced weighmaster may be able to
manually record, for short periods of time,
the net weight and type of material at a rate
of 60 trucks per hr. This rate may decrease to
as few as 10 to 20 trucks per hr, however,
under other conditions. A highly automated
weighing procedure can easily maintain a rate
of over 60 trucks per hr, record more data,
require less supervision, and be more accurate.
Incinerators with a capacity of 1,000 tons or
more per day will usually require two or more
scales.
Tare Procedures. Net weights of waste
loads require subtracting vehicle tare weights
from the gross weights of the loaded vehicles.
This process can be performed in several
ways. (1) In the case of a small incinerator
with relatively few incoming loads each day,
the vehicle can be weighed when full and
when empty. (2) At other plants, particularly
where access to the scale prevents double
weighing, it would be simpler to make a list of
the vehicles regularly delivering waste to the
facility along with their tare weights. After
each transaction or at the end of the day or
week, the tares can be subtracted to provide
net weights. In this system, it would be
necessary to weigh up and record the tare
weights of the vehicles only for the purpose
of an accurate list. (3) Some automated
electronic scale systems include devices for
automatically subtracting the tares and
providing written records of net load weights.
In such systems, each vehicle must have been
weighed up empty to provide a tare value,
which is then recorded on a credit card or a
tare key carried by the vehicle operator and
inserted in the scale mechanism at the time of
the scale transaction. (4) The most accurate
and most secure system of obtaining net
weights is through a two-scale system at each
plant with fully-controlled access. One scale
would weigh in the loaded vehicles; the other
would weigh out the empty vehicles.
Except when vehicles are weighed twice,
recorded tare weights are subject to
adjustment due to several factors. Equipment
may be added or removed from a truck. Such
19
-------
a change in tare weights can only be detected
by periodically reweighing the empty truck.
Fuel errors can be reduced by checking the
tare weights when fuel tanks are half full.
Errors resulting from the weight of collection
personnel can be avoided by using a fixed
procedure whereby personnel are always on
or off the scale during weighing operation.
Maintenance. Unless misused, motor-truck
platform scales require little maintenance.
Periodic inspections will ensure the proper
functioning of the scale. To protect the scale
from rust, the pit should be kept dry and the
metal parts of the structure should be
undercoated. If competent employees are not
available for scale maintenance, a contract
repair and maintenance program should be
considered.
Good housekeeping in the pit will reduce
maintenance and repairs of the levers in a
mechanical scale. The knife edges at the
pivots of a mechanical scale should be cleaned
and greased at least annually. The pivots and
levers should be inspected at least every 3
months to ensure freedom from obstruction,
wedging, and jamming, and alignment of
levers and position of pivots; nose irons
should be checked during the inspection. The
gap around the scale platform should be
checked daily for obstruction. An
all-electronic scale requires less maintenance
in the pit, but more electronic maintenance
aboveground.
Problems. Although a seemingly simple
operation, many problems are encountered in
weighing. The first is bypassing the scale.
Loaded trucks may bypass the scale during
the confusion of peak unloading periods and
during unattended periods. To prevent this,
elaborate controls and accounting techniques
have been developed. A two-gate system (one
at the front end and one at the back of the
scale) for locking a truck on the scale until
weighed, signal lights, curbing, alarms,
automated recording devices, one-way exit
barricades, weighmaster keys or cards tor
fixing responsibility of transaction, multicopy
weight tickets, and simultaneous transmission
of weighing information to a central
computer are all being used to ensure accurate
weighing of every incoming load.
Misplacement of the truck on the platform
can cause errors when an axle is off or only
partially resting on the scale. Suitable curbing,
markings, elevated transverse bumps, or extra
long scales can reduce or prevent
unintentional misplacement of the vehicles on
the scale.
Dirt, water, snow, and ice may accumulate
on and under the deck and cause wearing and
rusting of the scale, hazardous driving
conditions, and errors in the payload.
Cleaning the truck platform and removing
accumulated material will help alleviate these
problems. The top surface of the deck may be
crowned or pitched 1/16 to 1/8 in. per ft
transversely to improve runoff. Imbedded
heating elements may be used to prevent
buildup of ice and snow.
REFERENCES
1. ROGUS, C. A. Weigh refuse electronically. American
City, 72(4):128-130, 165, 167, 169, 171. Apr.
1957.
2. U.S. NATIONAL BUREAU OF STANDARDS.
Specifications, tolerances, and other technical
requirements for commercial weighing and
measuring devices adopted by National Conference
on Weights and Measures. Handbook 44. 3d ed.
Washington, U.S. Government Printing Office, 1965.
178pp.
20
-------
CHAPTER VII
RECEIVING AND HANDLING SOLID WASTE
Solid waste is delivered, usually during the
day shifts, in several types and sizes of trucks
and vehicles. The vehicles are first weighed
and then proceed to the tipping area. At large
installations, the trucks unload into a storage
pit, whereas at small incinerators, the practice
has been to dump the waste directly into the
furnace charging hopper or onto the tipping
floor.
After the waste 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 is usually done with a
front-end 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.
Tipping Area
The tipping area is the flat area adjacent to
the storage pit or charging hoppers where
trucks maneuver into position for dumping
(Figure 4), The area should be large enough to
allow for safe and easy maneuvering and
dumping.
Dimensions. Collection trucks tend to
arrive at the incinerator in large numbers
during a short time interval. To avoid a
backup of trucks, the length of the tipping
area and storage pit should receive careful
design consideration. The total length of the
tipping area should extend the length of the
storage pit and, if possible, beyond the pit.
Width of individual dumping spaces along the
pit should be about 10 to 12 ft. These spaces
should be clearly marked. Support columns
should be placed to avoid interfering with
dumping spaces.
The tipping area width should be greater
than the turning radii of trucks using the
tipping area. For single chassis compactor
CRANE
OVERRIDE
AREA
TIPPING
AREA
AT
GROUND LEVEL
BUMPER-'"1-''
STOP
TIPPING AREA WIDTH
STORAGE
PIT
CRANE
BRIDGE
RAILS
LOADING
^SHAFT
CHARGING
v- HOPPER
CHARGING
FLOOR
Figure 4. Plan of tipping area and storage pits with
crane.
21
-------
trucks, the radius is between 25 and 35 ft; for
tractor trailers, the radius is between 35 and
50 ft. The minimum recommended width of
the tipping area is 50 to 70 ft; if the space is
available, the width should be 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 raised in the unloading position. A
minimum of 24 ft is recommended, but
greater vertical clearance may be necessary for
some trucks.
Vehicle entrances and exits should provide a
minimum of 18 ft of vertical clearance. Exits
should be provided with warning devices, such
as hanging chains, to prevent careless drivers
from attempting to exit with raised dump
bodies. The entrance and exits should be
equipped with wheel 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, and noise
reduction effected by enclosure will help
make the incinerator more acceptable to the
community.
Other Aspects of Tipping Area Design. The
floor of the tipping area should be
constructed to withstand the heavy loads
placed on it; it should slope 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 is
required to 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 controlling the spread of
dust and litter.
Because of dangers involved in the handling
and dumping of large trucks in close quarters,
safety in the tipping area should be stressed
by the incinerator supervisor. Hold-down
chains or bumper picks are sometimes
employed to prevent trucks from being tipped
into the pit; however, use of these safeguards
is time consuming, and short ramps sloping
away from the storage pit at an angle of 8° to
12° from the horizontal will prevent mishaps
efficiently.
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
enough to permit the chassis overhang to clear
the curb. A height of about 1 ft is considered
adequate. The face of the backing bumper is
usually vertical or slightly concave to conform
to the shape of the wheel. The barrier must be
durable enough to withstand repeated impact
and must be securely anchored to prevent
movement. It should contain openings so that
spilled waste can be shoveled or swept from
the tipping floor into the pit.
Other measures to be considered for the
safe operation of a tipping area are: (1)
designing tipping area, storage pit, and crane
to eliminate possibility of crane bucket
striking extended dump body; (2) using a
traffic director at larger incinerators; (3)
permitting the dump bodies of packer trucks
to be raised only when the truck is in the
unloading space.
22
-------
Storage Pit
The purpose of the storage pit is to provide
a safe and convenient holding place for solid
waste before it is charged to the incinerator.
In a properly designed storage pit, waste from
numerous sources can be mixed to provide a
more uniform feed for the furnaces.
Capacity of the Storage Pit. 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-hr capacity of the
incinerator. 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.
To calculate the necessary storage volume,
the unit weight of solid waste in the storage
pit must be known. The generally accepted
average unit weight of waste in a storage pit is
about 350 Ib per cu yd.
When designing storage pits, future changes
in waste density should be considered. As
noted, in recent years, solid waste density has
been decreasing.
Other Aspects of Storage Pits. 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
alternately empty the pits.
The width of a storage pit usually does not
exceed 30 ft. Minimum width is usually 15 to
20 ft or wide enough to allow a monorail
crane to operate without being obstructed by
the overhang of trucks in the dumping
position.
The walls of the pit must withstand the
external forces caused by water and soil and
the internal pressures of solid waste and water
in the pit, a condition that could occur during
pit fires. During crane operations, the crane
bucket may collide with the wall and crush
the concrete. Continuous steel plating or
embedded steel T-sections in the concrete can
protect areas of the pit subject to repeated
impact.
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, or spontaneous
combustion of stored waste. Smoke and heat
can damage the crane, break windows, and
ruin equipment. Crane damage can put the
entire plant out of operation for weeks or
longer. The pit area should be equipped with
an adequate number of fire hoses of effective
size. The dewatering facilities must be
adequate for the expected quantities of water
used in fire fighting. Portable pumps help to
remove excess amounts of water.
The entire pit should be watertight and
sloped to troughs and drains for dewatering.
When a pit is constructed below grade, it will
usually be necessary to have a sump.
Screening devices to prevent material from
entering the sump are also recommended.
The sources of water and the resulting
quantities vary with the installation. When
pits are not watertight, leakage can occur as a
result of the positive hydrostatic pressure of
groundwater. Waste collected in wet weather
may be saturated, and vertical drainage will
occur in the pit. Water from dust control
sprays also enters the pit.
Cleanout facilities are needed to empty the
pit if the furnace equipment breaks down or
to remove unwanted items inadvertently
unloaded into the pit and remove saturated
waste after a fire. A loading shaft from the
charging floor to the ground level is useful for
unloading the pit and for hoisting heavy
23
-------
equipment and material from ground level to
the charging door (Figure 4).
Charging Methods
Solid waste is charged into the furnace by
several methods. In small installations where
the storage area is on the same elevation as
the charging hoppers, a front-end loader,
vibrating hopper and conveyor, or other
mechanical means are used. At larger
incinerators, cranes charge the solid waste.
Besides transporting solid waste to the
charging hoppers, cranes also mix and
distribute the solid waste in the pit. This
action results in a more uniform burning
material and better utilization of pit capacity.
Crane Types. The types most commonly
used are the monorail crane and the bridge
crane (Figure 5). 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 directions
rather than one. The capacity of the monorail
crane is usually less than that of a bridge
crane; the width of the storage pit is restricted
to 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 incinerators, its performance may be
adequate.
Crane Capacity and Bucket Design. The
size of crane needed to operate an incinerator
is a function of incinerator capacity. Each
continuous-feed-type furnace requires a given
number of bucket loads at regular intervals.
The size of the bucket, therefore, is a
function of the 24-hr furnace capacity and
number of bucket loads per 24 hr. Once the
size of bucket has been fixed, the crane
capacity can be specified. For example, a
4.5-ton crane is recommended for use with a
2.5-cu-yd bucket.
The number of bucket loads that can be
charged during a given period depends upon
the number of cycles that the crane can make
SECTION
Figure 5. Plan view and section view of bridge crane.
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 min. 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 250 and 300 ft per
min, whereas bridge travel speeds may be as
high as 350 ft per min. In general, design
criteria does not require high speeds.
Incinerator cranes usually 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. This type has a considerably
larger capacity than an equally rated closed
scooped bucket. The grapple is a poor cleanup
tool because of the length and spacing of its
24
-------
tines. For cleaning purposes, the grappple can
be equipped with bolted-on pans.
Number of Cranes. Crane downtime will
stop incinerator operations unless a standby
crane is provided. Nearly all installations with
a capacity above 400 tons per day (TPD) have
a second crane to prevent shutdowns. A
second crane is recommended for plants with
over a 300-TPD capacity. Because of high
costs, most small plants have only one crane.
At larger installations, a third crane is often
justified, and nearly 50 percent of the plants
with over a 850-TPD capacity have 'three
cranes. With a second or third crane, space in
addition to the operating space required for
the first crane must be provided for the
storage of the units when not in service. The
point of storage for the nonoperating units
must not interfere with the operating unit.
Control and Operation. The crane can be
operated manually from a cab traveling with
the crane or form a remote fixed operating
point. Manual operation form a mobile cab
has some advantage over a remote fixed
operating point. The operator has better
visibility, which usually yields better and safer
operation. Where the pit is long, the distance
judgment error is reduced with mobile cab
operation.
When a mobile cab is used, the operator
should have a safe convenient boarding
platform. Since the charging operation may
be dusty and hot, the crane cab should be
air-conditioned.
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. In a
continuous-feed furnace, the waste-filled
hopper and chute assist in maintaining an air
seal to the furnace as well as to provide 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 4 X 4 ft to 4
X 8 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
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. Several
measures may be taken to prevent solid
waste's tendency to clog chutes. These are use
of: smooth inside surfaces; corrosion resistant
materials; vertical (or nearly vertical) chutes
with increasing cross section.
The charging chute, because of its
proximity to the furnace, should be protected
against extreme heat. For this reason, chute
walls are often water jacketed. A hopper
cover or other means of closure should be
provided for ending a burning cycle in
continuous-feed furnaces.
25
-------
CHAPTER VIII
FURNACES AND APPURTENANCES
Incineration is a controlled combustion
process for burning solid, liquid, or gaseous
combustible waste to gases and to a residue
containing little or no combustible material.
When solid waste is exposed to a turbulent
atmosphere for a critical time period at
an elevated temperature, combustion occurs.
During combustion, moisture is evaporated,
and the combustible portion of the solid waste
is vaporized and then oxidized. Concurrent
reactions are the oxidation of metals and the
oxidation of such elements as sulfur and
nitrogen. Carbon dioxide, water vapor, ash,
and noncombustibles are the major end
products of combustion.
The combustion processes take place in the
furnace of the incinerator, which includes the
grates and combustion chambers. There are
numerous designs or configurations of
furnaces to accomplish combustion, and, to
date, no one design can be considered the
best.
Furnaces
Furnaces commonly used for the
incineration of municipal solid waste are the
vertical circular furnace, the multicell
rectangular furnace, the rectangular furnace,
and the rotary kiln furnace.1 Although these
furnaces vary in configuration, total space
required for each is based on a heat release
rate of about 18,000 Btu per cu ft of furnace
volume per hr, although heat release rates
varying from 12,500 to 25,000 Btu per cu ft
per hr have been used.
The vertical circular 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
(Figure 6). Underfire forced air is the primary
combustion air and also serves to cool the
grates. As the 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. Many furnaces of this
design are in operation.
The multicell rectangular type, also called
the mutual assistance furnace, may be
refractory lined or water cooled; it contains
two or more cells set side-by-side, and each
cell normally has rectangular grates (Figure
7). Solid waste is usually charged through a
door in the top of each 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 (Figure 8). 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. Secondary combustion is frequently
26
-------
- CHARGING HOPPER
Figure 6. Vertical circular furnace.
A rotary kiln furnace consists of a slowly
revolving inclined kiln that follows a
rectangular furnace where drying and partial
burning occurs (Figure 9). 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.
Grates and Stoking. The grate system must
transport the solid waste and residue through
the furnace and, at the same time, promote
combustion by adequate agitation and passage
of underfire air. The degree and methods of
agitation on the grates are important. The
abrupt tumbling encountered when burning
solid waste drops from one tier to another
will promote combustion. Abrupt tumbling,
however, may contribute to entrainment of
excessive amounts of particulate matter in the
gas stream. Continuous gentle agitation
promotes combustion and limits particulate
entrainment. Combustion is largely achieved
by air passing through the waste bed from
under the grate, but excessive amounts of
underfire air contribute to particulate
entrainment.2 Some inert materials, such as
glass bottles and metal cans, aid combustion
by increasing the porosity of the fuel bed.
Conversely, inert materials inhibit combustion
if the materials clog the grate openings.
Mechanical grate systems must withstand high
temperatures, thermal shock, abrasion,
wedging, clogging, and heavy loads. Such
severe operating conditions can result in
misalignment of moving parts, bearing wear,
and warping or cracking of castings.
27
-------
CHARGING CHUTE
TO
SECONDARY
COMBUSTION
CHAMBER
OVERFIRE
AIR INLET
STOKING
DOOR
RESIDUE
HOPPER
Figure 7. Multicell rectangular furnace
For design purposes, the required grate area
is approximated by dividing Ib per hr solid
waste to be burned by the Ib per sq ft per hr
solid waste the grates are capable of burning.
Ordinarily, the design value for the grate
loading will be between 50 and 70 Ib per sq ft
per hr. This design value depends mostly on
type of solid waste and grate design, but also
depends on the other elements of the furnace.
The grate loading is often expressed in Btu's
per sq ft per hr. An average rating of 300,000
Btu per sq ft grate per hr is often used as a
design parameter.
Grate systems may be classified by
function, such as drying grate, ignition grate,
and combustion grate. Grates for solid waste
incineration may also be classified by
mechanical type. They include traveling,
reciprocating, rocking, rotary kiln, circular,
vibrating, oscillating, and reverse reciprocating
grates; multiple rotating drums; routing cones
with arms; and variations or combinations of
these types. In the United ::'ate.;, traveling,
reciprocating, rocking rotary kiln, nad-cu <-
grates are the most widely used.
Traveling grates are continuous, belt-j;J-p
28
-------
CHARGING
CHUTE
to
SUPERSTRUCTURE v
CURTAIN
WALL
CURTAIN
WALL
GAS FLUE TO
EXPANSION
COMBUSTION CHAMBER
FURNACE
ACCESS
DOOR
ASH AND CLINKER
DISCHARGE
HORIZONTAL
BURNING GRATE
Figure 8. Rectangular furnace.
-------
TO EXPANSION CHAMBER
AND GAS SCRUBBER
RESIDUE CONVEYORS
Figure 9. Rotary kiln lurnace.
conveyors (Figure 10). A single traveling grate
does not promote agitation. Two or more
grates at different elevations provide some
agitation as the material drops from one level
to the next.
In reciprocating grate systems, the grate
sections are stacked like overlapping roof
shingles (Figure 11). Alternate grate sections
slide back and forth while adjacent grate
sections remain fixed. Like traveling grates,
reciprocating grates may be arranged in
multiple-level series providing additional
agitation as the material drops from one grate
to the next.
Rocking grates are arranged in rows across'
the width of the furnace, at right angles to
solid waste flow. Alternate rows are
mechanically pivoted or rocked to produce an
upward and forward motion, thus advancing
and agitating the solid waste (Figure 12).
Rocking grates have also been arranged in
series.
The rotary kiln has a solid refractory
surface and is commonly preceded by a
reciprocating grate. The slow rotation of the
kiln, which is inclined, causes the solid waste
to move in a slowly cascading and forward
motion.
Figure 10. Traveling grates.
30
-------
GRATES
MOVING
SRATES
Figure 11. Reciprocating grates.
RAISED POSITION
NORMAL POSITION
The circular grate, in the vertical circular
furnace, is commonly used in combination
with a central rotating cone grate with
extended rabble arms that agitate the fuel bed
(Figure 13).
Charging Solid Waste. Solid waste is
charged either continuously or in batches. In
the continuous process, solid waste is fed to
the furnace directly through a rectangular
chute that is kept filled at all times to
maintain an air seal. In the batch process,
solid waste is fed to the furnace
intermittently through a charging gate or
hatch, which is closed except when waste is
being charged. The waste may be stored in a
hopper and fed intermittently through a
chute, or the furnace may be fed directly by
opening the charging gate and dropping the
waste directly from a crane bucket, front-end
loader, or bulldozer. A ram can also be used
Figure 12. Rocking grates.
to feed a batch of material directly to the gate
through an opening in the furnace wall.
Continuous feed minimizes irregularities in
the combustion system. Batch feeding causes
fluctuations in the thermal process because of
the nonuniform rate of feeding and
intermittent introduction of large quantities
of cool air.
Siftings Removal. Siftings are the fine
materials that fall from the fuel bed through
the grate openings during the drying, ignition,
and burning processes. Siftings consist of ash,
small fragments of metal, glass and ceramics,
and unburned or partially burned organic
substances. In some designs, siftings are
collected in troughs and conveyed
continuously by sluicing or mechanical means
to a residue collection area. In other designs,
siftings are collected and returned
continuously by a conveyor to the furnace.
31
-------
A Rotating Cone
B Extended Stoking
Arm (Rabble Arm)
C Stationary Circular
Grate
D Peripheral Dumping
Grate
Figure 13. Circular grates.
Sittings may also be removed by the batch
method. If siftings containing highly
combustible materials such as oil, plastics, and
grease, accumulate, unquenched, beneath the
grate, they can burn and cause heat damage to
the grates above.
Residue Removal. Residue-all solid
materials remaining after burning—includes
ash, clinkers, tin cans, glass, rock, and
un burned organic substances. Residue
removal can either be a continuous operation
or an intermittent batch process. In a
continuous feed furnace, the greatest volume
of residue comes off the end of the burning
grate; the remainder comes from siftings and
from fly ash (Chapter XII). The residue from
the grate must be quenched and removed
from the plant.
Batch operated furnaces usually have ash
collection and storage hoppers beneath the
grates. Periodically, residue is removed,
quenched, accumulated in a residue hopper,
and discharged from the bottom by opening a
watertight gate. Discharge may be placed into
trucks or other containers for transport to a
disposal area. Access to the residue hoppers is
usually by a tunnel beneath the furnace floor.
Ash tunnels should be wide enough to allow
an employee to safely walk past a vehicle. The
tunnel should be paved, well drained, and well
lighted. Provisions should be made for
adequate ventilation and dust removal. Excess
quench water should be drained before trucks
are loaded, and the residue trucks or
containers should be watertight. Residue
trucks dripping quench water to the disposal
site are unsightly, insanitary, and they invite
complaints from the community.
In many continuous feed operations,
residue is discharged continuously into a
trough or troughs connected to all furnaces. A
slow-moving drag conveyor, submerged in the
water-filled trough, continuously removes the
residue. Usually the discharge end of the
conveyor is inclined to allow drainage of
excess quench water from the residue before
loading into a holding hopper or directly into
trucks. The residue conveyor system must be
ruggedly constructed to withstand heavy
loads and continuous use. The residue is
highly abrasive, and the quench water is
highly corrosive. Since the residue is
discharged to the conveyor below water, this
system has the advantage of maintaining an
air seal to the furnace. For continuous,
dependable operation, a dual conveyor system
is justified in plants above 250-TPD capacity.
Combustion
Time, temperature, and turbulence are
commonly called the three T's of combustion.
When solid waste is exposed for a sufficient
time to a turbulent, hot atmosphere, the
waste will be satisfactorily incinerated.
For a substance to burn, both surface and
internal moisture must be driven from the
32
-------
material. The vaporization of moisture
present in waste material will keep the
temperature of the material below 212 F
Once moisture is removed, the temperature of
the substance can be raised to the ignition
point, although the outer surface of a solid
may be dried and ignited before the inner
material is dried. This drying process
continues throughout the entire length of the
furnace, but proceeds at the greatest rate
immediately following charging of the solid
waste.
To facilitate drying, some furnace designs
use preheated air or incorporate reflecting
arches to radiate heat stored from the burning
of previously charged material. The first part
of the grate system is also frequently referred
to as the drying grate. Ignition takes place as
the solid waste is dried and continues through
the furnace. The portion of the grates where
ignition first occurs is often called the ignition
grate.
The combustion process in incineration is
thought of as occurring in two overlapping
stages, primary combustion and secondary
combustion. Primary combustion generally
refers to the physical-chemical changes
occurring in proximity to the fuel bed and
consists of drying, volatilization, and ignition
of the solid waste. Secondary combustion
refers to the oxidation of gases and
particulate matter released by primary
combustion. Secondary combustion achieves
combustion of unburned furnace gases,
elimination of odors, and combustion of
carbon suspended in the gases. To promote
secondary combustion, a sufficiently high
temperature must be maintained, sufficient
air must be supplied, and turbulence or
mixing should be imparted to the gas stream.
The function of turbulence is to ensure
mixing of each volume of gas with sufficient
air for complete burning of volatile
combustible matter and suspended
particulates. The turbulence must be intense
and must persist long enough for mixing to be
completed while the temperature is still high
enough to ensure complete burning.
Introduction of Air to the Furnaces. In the
combustion process, oxygen is needed to
complete the chemical reaction involved in
burning. The air necessary to supply the exact
quantity of oxygen required for the chemical
reactions is termed stoichiometric or
theoretical air. Any additional air supplied to
the furnace is termed excess air and is
expressed as a percentage of the theoretical
air.
Air that is purposely supplied to the furnace
from beneath the grates is termed underfire
air. Overfire air is that air introduced above
the fuel bed; its primary purpose, in addition
to supplying oxygen, is to provide turbulence.
Infiltration air is the air that enters the gas
passages through cracks and openings and is
frequently included in the figure for overfire
air.
The proportioning of underfire air and
overfire air depends on incinerator design.
Very often, the best proportions are
determined by trial and error. For most
municipal incinerator designs, underfire air is
from 40 to 60 percent of the total air. (Total
air is the total of all underfire, overfire, and
infiltration air.) This amount of underfire air
air provides acceptable combustion in the fuel
bed and adequate grate cooling. In general, as
the underfire air is decreased, the burning rate
is inhibited.
To supply adequate air for complete
combustion and to promote turbulence, a
minimum of 50 percent excess air should be
provided. Too much excess air, however, can
be detrimental because it lowers furnace
temperatures. In general, refractory furnaces
require 150 to 200 percent excess air, whereas
water tube wall furnaces require only 50 to
100 percent excess air.
Gas Flow from Furnace. The burning of
solid waste generates heat that expands the
volume of gas. The gas passages, air pollution
control devices, and stack must satisfactorily
accommodate this gas. An estimate of the
quantities of gaseous products of combustion
can be calculated from the ultimate analyses
of solid waste. Gas velocities must be
33
-------
determined so that gas passages can be sized
to prevent excessive settlement of entrained
particles.
Incinerator stacks provide natural draft and
dispersion for gases and participate matter.
Accordingly, the height and diameter of the
stack depend upon the amount of draft
required and the topographic and climatic
conditions. If necessary, induced draft fans
should be used to supplement the natural
draft in moving gases through the incinerator.
The decision to use a tall stack with natural
draft only, a short stack that relies principally
upon induced draft, or a combination of these
should be made by the designer after careful
consideration of ambient air quality, health
effects, Federal Aviation Agency regulations,
architecture, and other constraints.
To adequately control the combustion
process, the draft must be regulated. Dampers
are generally used in both natural draft stacks
and in stacks employing induced draft fans of
constant speed. Adjustable speed, induced
draft fans are also used to control draft.
Under most conditions, an induced draft fan
is preferred over natural draft stack. Control
over the burning solid waste can be better
maintained and air pollution collection
devices better operated with the constant air
volume and uniform pressure drop that the
induced draft fan creates.
Combustion Temperature and Cooling
Adequate temperature, time, and
turbulence are necessary to completely burn
the gases and carbon suspended in the gases
and to destroy the odors. If temperatures are
too low, the oxidation reactions are
incomplete; if too high, the temperatures can
cause equipment and structural damage
throughout the incinerator. Excessively high
temperatures can cause refractories to fail
through excessive expansion, can cause slag
buildup on the furnace linings, or may
produce oxides of nitrogen. When the air
stream is suddenly cooled, these nitrogen
oxides do not have time to decompose to
nitrogen and oxygen. Because of variations in
composition and density of the solid waste,
careful operation is required to maintain
furnace temperatures within the desirable
range.
Temperature. At the air intake, combustion
air is at ambient temperature. Combustion air
may be preheated to 200 to 300 F. Once in
the furnace, the temperature rapidly rises.
Immediately above the burning waste, the
temperature of the burning gases generally
ranges from 2,100 to 2,500 F, and for short
periods of time, it may reach 2,800 F in
localized areas. When the gas leaves the
combustion chamber, the temperature should
be between 1,400 and 1,800 F. The gas
temperature entering the stack can be
expected to be 1,000 F or less. Where induced
draft fans, electrostatic precipitators, and
other devices requiring lower gas temperatures
are used, the gases will have to be cooled
further. Before they enter the air pollution
control devices, the gases should be cooled to
500 to 700 F 3
In a batch feed incinerator, opening the
charging door lowers the temperature of gases
in the combustion chamber by as much as
500 F. Introducing extremely high or low Btu
wastes can also cause abrupt and extreme
temperature change.
Furnace temperature varies considerably,
depending on where it is measured. The most
widely accepted location for measuring and
reporting furnace temperature is near the roof
at the exit of the combustion chamber. At
this location, the temperature should be
maintained between 1,400 and 1,800 F to
ensure that proper combustion has occurred.
Most incinerator designs are based on
temperatures within the 1,400 to 1,800 F
range. In practice, operating temperatures
frequently fluctuate by 200 F or more from
this design range sometimes in a matter of
minutes. The furnace temperature should be
34
-------
maintained at fairly constant levels,
preferably in midrange. Such operation will
accommodate sudden temperature changes
within the 1,400 to 1,800 F range. In some
cases, auxiliary fuel will be needed to
maintain satisfactory temperature.
Methods of Cooling the Furnaces and Flue
Gas. Regulation of the combustion process
through control of furnace and flue gas
temperatures is achieved principally through
the use of excess air, water evaporation, and
heat exchange. Of these, the use of excess air
is the most common and, in refractory
furnaces, is often the only method of control.
Even when another cooling method is
available, some excess air is still used but
primarily for ensuring turbulence and
complete combustion.
In all incinerators, some heat is lost through
the furnace walls. The amount of heat
dissipated in this manner is small compared
with the total heat release; however, these
heat losses must be considered when designing
the furnace.
The purpose of excess air is to cool and mix
the hot gases through a dilution process,
which lowers gas temperatures. The cooler
ambient air is mixed with the hot combustion
gases, and an equilibrium temperature is
reached.
Water injected into the hot gas stream cools
the flue gas through evaporation of the water
and absorption of heat during superheating of
the water vapor. Although the water vapor
adds to the total gas volume in a manner
similar to the addition of excess air, the total
of water vapor and cooled gases is smaller
than the original volume of gases. Some
economy may result from reducing this
volume of gas to be treated; however, the cost
of water should also be considered. Water
cooling is used on flue gases but is not
generally employed in cooling the furnace.
Although heat exchange through the use of
water tube walls and boilers is not in
widespread use in the United States, it is
attracting greater attention and is employed
in Europe. A distinct advantage of heat
exchangers in cooling gases is that additional
gases or vapors are not added to the gas flow
to reduce temperature and significantly
smaller gas volume results. Because gas
volume is greatly reduced, the size of
collection devices, fans and gas passages can
be reduced. Heat recovery and utilization can
bring further economies.
Refractories
Refractories, materials employed to resist
heat, are commonly used in incinerators to
line furnaces, subsidence chambers,
breechings, and stacks. Most refractories are
composed wholly or in part of alumina,
magnesia, and silica although chromite and
zircon are common synthetic or artificial
refractories. Many of these materials are
interground with kaolin, the oldest and most
widely used natural refractory.
Refractories are classified according to their
physical and chemical properties which vary
considerably.4 Their thermal expansion
characteristics, heat conductivity, hardness,
strength, and chemical resistivity also vary.
Refractories are commonly precast as
bricks, which are laid with mortar. They can
also be used in the form of dry powder, which
is mixed like cement with water and cast in
forms. Plastic refractories are pre-mixed by
the manufacturer with just enough water to
be plastic or moldable on the job; they are
used mainly as a patching material and in
confined area, but have been used for
complete furnace linings.
The mortars used to lay and bond
refractory brick are either air setting or
thermal setting. Air-setting mortars harden
more or less uniformly at outside air
temperature through normal hydration
processes, whereas thermal-set mortars
depends on the degree of heat penetration.
Refractories expand in all directions when
heated; therefore, expansion joints must be
provided. Failure to do so can cause a buildup
of stresses that could produce cracks and in
35
-------
some cases even structural failure.
Furnace Walls. In the past, furnace walls
were designed to conserve as much heat as
possible from the combustion process. With
today's higher heat value waste, the previous
emphasis on conserving heat throughout the
furnace has decreased. In the last 15 yr, the
trend has been toward thinner (9-in.)
refractory walls and away from massive
fire-brick refractories. Indeed the emphasis
now is on withstanding temperatures in excess
of 2,000 F and on preventing refractory
softening, erosion, slagging, and spalling. In
areas such as the drying and ignition zone,
however, where a high temperature is desired,
the heat storage capacity of the walls and heat
reflection continues to be important.
Furnace walls constructed with refractory
linings are the most common and probably
will continue to remain popular. The thinner
walls of modern design are supported at
frequent intervals by anchors attached to a
steel superstructure that bears the majority of
the refractory weight. They are therefore
suspended walls rather than of conventional
bearing or arch construction. The large flat
roofs of most rectangular furnaces are
constructed in a similar manner. Suspended
furnace walls are usually a combination of
insulated and air-cooled construction.
Insulation reduces heat loss, maintains heat
storage in low temperature zones, and
protects the external parts of the incinerator
from excessive heat. In high-temperature
zones, insulation may be reduced or omitted
with reliance on air-cooling. Suspended wall
and roofs, usually with a refractory depth of
9 in., have the added advantage of permitting
localized repair of damaged areas. In
conventional bearing wall or arch
construction, complete reconstruction is
often required in making repairs.
The primary combustion zone is the section
of highest refractory maintenance. The
destructive influences on refractories are
excessively high temperatures, flame
impingement, thermal shock, slagging,
spalling, abrasion from stoking tools and
sliding or tumbling solid waste, and erosion
from high velocity gases with entrained
particles. Refractories of super duty or
equivalent quality best meet the physical and
thermal requirements as listed above.
The high abrasive areas immediately above
the grate line (where slagging is also likely to
occur) and the charging area frequently
require a dense refractory such as silicon
carbide or high alumina brick. Where lower
temperatures and less wear occur as in
subsidence chambers and stack, a lower
quality refractory may be used. Acid-resistant
refractories and mortar should be used in
areas subject to corrosion.
Spalling and slagging are common forms of
refractory destruction. Spalling is the
breaking away of the refractory, usually of
the outer surface, because of internal thermal
stresses developed through differential
expansion. Slagging is a form of destruction
that occurs from the buildup of a layer or
deposit of flux on the refractory surface. This
flux is composed of oxides of sodium,
potassium, iron, calcium, and other elements
from the burning waste. The increased weight
of this bonded and fused layer of buildup
causes the refractories to fail. Failure may
also be caused by differential expansion and
contraction between the bonded slag layer
and the refractory. Slag formation can also
cause damage by interfering with grate
movement. Mineralogically stable, high
melting point refractories that are dense, of
low porosity and high strength, are most
resistant to slagging and spalling.
Water tube wall furnaces are made of
closely spaced steel tubes welded together to
form a continuous wall with water or steam
circulating through the tubes. The water tube
wall furnace offers greater control over
temperatures and provides an air-tight
enclosure. These furnaces have been used
successfully in the power industry and in
some European incinerators for many years;
however, their installation in municipal
incinerators in the United States has been
limited.
36
-------
Other Aspects
Auxiliary Fuels. It is desirable to have
auxiliary fuels available for (1) furnace warm
up; (2) promotion of primary combustion
when the solid waste is wet or does not
contain an adequate Btu content for good
combustion; (3) completion of secondary
combustion to ensure odor and smoke
control; (4) supplementation of heat for heat
recovery units when the supply or heat value
of the solid waste is not sufficient.
Auxiliary fuel is usually gas or oil. Burner
location depends on the purpose of the
auxiliary fuel. The use of auxiliary fuel has
not been common practice in the United
States, and consequently, further
investigations are needed to determine the
best locations for auxiliary fuel burners.
Starting the Furnace. When an incinerator
is started, the operating temperature of 1,400
to 1,800 F should be reached as quickly as
consistent with good practice, which varies
with the incinerator design and the
refractories. Incinerators with induced draft
fans usually reach operating temperature in
less than 1 hr. Natural draft plants may
require more than 4 hr. Plants with suspended
wall construction require as little as half an
hour for heating refractories.
If new refractories are installed, the
manufacturer should be consulted for his
recommendations on refractory curing and
furnace preheating. To prevent damage to
new refractory linings, drying or curing is
usually necessary. This preheating period is
long and gradual, often requiring several days.
REFERENCES
1. HEANEY, F. L. Furnace configuration. In Proceedings;
1964 National Incinerator Conference, New York,
May 18-20, 1964. American Society of Mechanical
Engineers, p. 52-57.
2. STENBURG, R. L., R. P. HANGEBRAUCK, D. J. VON
LEHMDEN, and A. H. ROSE, JR. Field evaluation
of combustion air effects on atmospheric emissions
from municipal incinerators. Journal of the Air
Pollution Control Association, 12(2):83-89, Feb.
1962.
3. PEARL, D. R. A review of the state of the art of
modern municipal incineration system equipment.
Pt. 4, v. 4. In Combustion Engineering, Inc.
Technical-economic study of solid waste disposal
needs and practices. Public Health Service
Publication No. 1886. Washington, U.S.
Government Printing Office, 1969. p. 17. (In press.)
4. AMERICAN PUBLIC WORKS ASSOCIATION.
Municipal refuse disposal. 2d ed. Chicago, Public
Administration Service, 1966. p. 168.
37
-------
CHAPTER IX
RECOVERY AND UTILIZATION OF HEAT
The concept of the recovery and use of heat
produced during incineration has always
intrigued engineers and municipal officials.
Unless the heat is used, it is wasted—either to
the atmosphere or to a heat exchange system.
In Huropean municipal incinerators, the use
of heat recovery equipment is now common
practice. In contrast, relatively few U.S.
municipal incinerators practiced heat recovery
for other than in-plant use.
Because heat recovery and water cooling of
incinerator furnaces reduce the volume of gas
to be cleaned and hence the size of air
pollution control equipment needed, they
have been advocated as a means to effect
possible savings in the cost of air and water
pollution control equipment. The trend
toward more effective and costly pollution
control equipment increases the economic
feasibility of heat recovery. The increased
heat content of municipal solid waste also
enhances the economic feasibility of heat
recovery. The justification for installing heat
recovery equipment in most incinerators is
based on obtaining sufficient income from the
sale of steam or power to offset the additional
cost that results from utilizing excess heat.
Heat Recovery Systems
Heat is recovered by heat transfer from hot
gases or flames to steam or hot-water systems.
Four basic designs have been used: (1) waste
heat boiler systems with tubes located beyond
conventionally built refractory combustion
chambers; (2) water tube wall combustion
chambers; (3) combination water tube wall
and refractory combustion chambers; (4)
integrally constructed boiler and water tube
wall combination.
The amount of excess air required differs
significantly in the operation of these four
types. Refractory-lined chambers usually
require 1 50 to 200 percent excess air whether
waste heat recovery is practiced or not. Water
tube wall chambers usually need 50 to 100
percent excess air. Low excess air reduces the
volume of flue gas to 50 or 60 percent of that
from refractory-lined furnaces, increases
recoverable heat, and reduces the size of
necessary air pollution control equipment.
Any of these four systems of waste heat
recovery eliminates the need for evaporating
large quantities of spray water or adding large
quantities of cooling air to reduce the exhaust
temperature to the 600-F range needed by
most air pollution equipment.
Theoretical efficiency of the recovery
process may be as great as 70 percent,
depending on the type of heat recovery
equipment utilized. Steam production ranges
from 1 to as much as 3.5 Ib per Ib of solid
waste burned because of variations in excess
heat available from the solid waste.1'2
Another method of heat recovery is a
flue-gas-to-air heat exchange located at the
exit of the incinerator chamber. This method
is inefficient because the temperature of the
gas-to-air exchange metal must be held at
moderate levels to prolong its life. The
38
-------
metallic alloys necessary for a gas-to-air type
of exchange are expensive and require
excessive maintenance.
In heat recovery operations provisions must
be made for cleaning the boiler tubes and
blowing out the soot to correct the problem
of tube fouling caused by fly ash deposits
and, under some conditions, slagging.
Increasing the space between the water tubes
can reduce fly ash clogging of gas passages.
External corrosion of boiler tubes caused by
chlorides and other chemicals on the fire side
of the tubes will increase with the rising
volume of plastics in municipal solid waste,
resulting in greater maintenance costs.
Application for Recovered Heat
In the United States, most engineers
hesitate to design systems to reclaim waste
heat from incinerators because of the added
costs of heat recovery equipment, the
variability of the heat value of solid wastes,
and the difficulty of matching the supply of
waste heat to the demand for heat. Matching
the heat output of the incinerator to the
demand presents a serious problem. In most
cases, other sources of steam, hot water, or
electricity must be available to supply any
deficiency because of either increased demand
or a drop in output from the incinerator.
When the demand for reclaimed heat cannot
be met by the incineration of solid waste,
large capacity auxiliary fuel burners located
near the boiler can provide the heat recovery
system with additional heat as needed. Since
an incinerator must burn a daily quota of
solid waste of varied heat content, the output
is usually more or less than the demand.
Provisions must be made, therefore, to
dissipate excess heat.
Excess steam can be dissipated by heat
exchange through water-cooled or air-cooled
condensers. Condensers increase initial and
operating costs, and exhausted steam must be
replaced by treated feedwater, which
increases the cost of feedwater treatment and
storage facilities.
Many U.S. incinerators with heat recovery
equipment use recovered heat for in-plant use
only. These plants use recovered heat to
generate electricity, supply hot water, and
heat the incinerator plant during cold
weather. Recovered heat has also been used at
one plant for desalting sea water for in-plant
use and for supplying steam power within the
incinerator plant and to nearby sewage
treatment plants.
Several U.S. incinerators supply steam to
heating systems and to institutions such as
hospitals. The sale of steam to power
generation plants is also possible. The most
practical means of using waste heat is to
supply steam to a large power system with a
minimum demand greater than the incinerator
can produce. Under these conditions, steam
does not have to be wasted when the demand
is at a minimum, and fluctuations in
incinerator steam production are
accommodated by other sources, such as
steam plants.
Manpower Requirements
Manpower requirements for an incinerator
system with waste heat recovery are usually
greater than for a conventional incinerator.
Additional personnel are required to operate
and maintain boiler water treating equipment,
steam condensing equipment, boiler auxiliary
fuel pumps, condensate pumps, etc. The
personnel operating the heat recovery
equipment must be skilled and, in some
instances, licensed.
Economics
The decision to practice heat recovery at a
municipal incinerator should be based on a
careful study of additional costs incurred and
of the monetary return resulting from the sale
or use of the recovered heat. The study
should also carefully consider whether there
39
-------
is, in fact, a buyer for the waste heat
recovered.
The sale of steam requires
an incinerator site close to the buyer because
of the high cost of distribution and loss of
pressure. Steam prices of SO.25 to $0.50 per
1,000 Ib, which can be expected, would bring
returns of SO.50 to S3.50 per ton of solid
waste burned, assuming steam production
from 1 to 3.5 Ib per Ib of solid waste
burned.3
The generation of electricity from solid
waste for sale to power utilities has not often
been practiced in the United States mainly
because power of the dependability required
by the utility companies cannot be produced
economically by solid waste incineration.
The price realized from the generated
electricity may range up to 10 mills per
kilowatt hr (kwhr). Considering variations in
available heat and heat recovery process
efficiency, the income derived from the sale
of electrical power may range from $1.50 to
$5.00 per ton of solid waste. These values
were calculated using a steam power cycle
efficiency of 25 percent that would yield
7,300 kwhr per 100,000 Ib of steam, a steam
generation rate of 1 to 3.5 Ib per Ib of solid
waste burned, and an electricity value of 10
mills per kwhr.3
REFERENCES
1. STABENOW, G. Performance and design data for large
European refuse incinerators with heat recovery. In
Proceedings; 1968 National Incinerator Conference,
New York, May 5-8, 1968. American Society of
Mechanical Engineers, p. 278-286.
2. SHEQUINE, E. R. Steam generation from incineration.
In Proceedings; 1964 National Incinerator
Conference, New York, May 18-20, 1964.
American Society of Mechanical Engineers, p.
90-94.
3. COHAN, L. J., and J. H. FERNANDES. Potential
energy conversion aspects of refuse. Presented at
American Society of Mechanical Engineers Winter
Annual Meeting, Pittsburgh, Nov. 12-17, 1967.
ASME Paper No. 67WA/PID-6. 7 p.
40
-------
CHAPTER X
INSTRUMENTATION AND CONTROLS
Instrumentation is the equipment used to
indicate and record physical conditions, such
as weight, temperature, position, flow, time,
speed, and voltage. Instruments monitor but
do not change the conditions of operation.
Controls are mechanisms that change
conditions of operation, such as a valve that
can change flow direction or a switch that can
turn on a motor.1
Uses of Instrumentation and Controls
Process Controls. Before process
conditions can be controlled, manually or
automatically, they must be measured with
precision and reliability. Through intelligent
application of instruments, these process
conditions may be measured in a manner that
will effectively aid in the control of the
incineration process.
Instrumentation for an incineration process
is essential because of the variability of the
many factors involved in attaining good
combustion. As the heat content of the solid
waste varies, changes in the combustion
process are necessary. Instrumentation
indicates these variations so that automatic or
manual control adjustments can be made.
Protection of the Environment. Sensing
environmental pollutants and adjusting
operating conditions to reduce the pollutants
to acceptable levels are important applications
of instrumentation and controls. Although
with present, pollution control technology not
all environmental pollutants are fully
controllable by operational changes, several
applications hold promise or have proven
their success. For example, the proper use of
instruments and controls that maintain a
steady, high temperature in the secondary
combustion zone ensures that odor-producing
organic matter in the gas stream is completely
oxidized to innocuous compounds. In
addition to air pollution control applications,
instruments can serve to sense the pollution
loading of waste waters.
Protection of Equipment. Most safety
instruments are employed to detect and
sound an alarm or to activate a control when
equipment is in danger of damage. This is
particularly true for detecting undergrate fire,
overheating of the furnace, or backfires in the
charging chutes.
Overheating of the furnace chambers or hot
gas ducting can cause serious damage in a
short time. Temperature sensors with audible
and visual alarm systems should be employed
to signal these dangers. Increasing overfire air,
reducing underfire air, and reducing feed rate
are control methods used to reduce furnace
temperature. Adjustments can be manual, or
the heat sensing instruments can activate an
automatic control.
Failure of the cooling water supply,
resulting from clogged nozzles, pump failure,
electrical power failure, or lack of water, can
quickly damage the flue gas cleaning system
and fans. Automatically activated auxiliary
water supply and bypass ducting are desirable
control provisions for such emergencies.
Loss of electrical power can cause extensive
damage to the plant. Several incinerators have
41
-------
standby auxiliary power supplies with
gasoline, diesel. or turbine engines. When
power failure occurs, instrumentation
activates an automatic cut-in of an auxiliary
power system to prevent damage.
Data Collection. Data provided by
instrumentation can be used for evaluating
incinerator operation and for designing future
incinerators. This information frequently aids
design engineers in evaluating the effects of
design changes and in trying to identify the
causes of a malfunctioning incinerator. Data
on plant performance should also
demonstrate compliance with air pollution
control requirements.
Controlling the Incinerator Process
Types of Control Systems. A control
"system" must have four basic elements: (1)
the standard of desired performance; (2) the
sensor (instrument) to determine actual
performance; (3) the capability to compare
actual versus desired performance (error); and
(4) the control device to effect a corrective
change. If these elements are integrated into
an automatic system that controls the process
to a set standard (such as a household
thermostat that holds 70 F temperature), a
closed loop or automatic feedback control
system is formed. If, on the other hand,
control is effected by making a change and
then observing the result (such as steering a
car), the system is an open loop, or manual
system.
Present municipal incinerators generally
utilize their instrumentation in conjunction
with open loop control systems, although
there is increasing use of automatic
closed-loop control systems for controlling
furnace temperatures and furnace draft.1
In an open loop control system, the signal
from the instrument may be presented to the
operator in one of several forms. Perhaps the
most informative is a continuously recorded
graphic display, which permits the operator to
observe the most recent reading as well as the
previous reading to determine whether
process conditions must be changed. Graphic
displays also establish accurate, permanent
record for future analysis. Where the operator
does not have to draw conclusions or
interpret trends in data, a simple indicating
meter is sufficient. Alarms or other similar
on-off displays are especially useful where the
operator is not required to maintain
continuous watch over readings or where a
certain value must not be exceeded.
A fully instrumented control room or at
least a central instrument panel should be
provided so that the plant supervisor has, at a
glance, an understanding of the facility
performance. If the central instrument panel
is not near the furnace operating floor, a
separate, auxiliary instrument control panel
may be needed at each furnace. The readout
on instruments should be easy to understand.
For instance, to the furnace operator, the
volume of overfire and underfire air expressed
as a percentage of maximum amount of air
that can be supplied is more comprehensible
than the volume expressed in cubic feet. For
the operator's convenience, the instruments
should be grouped on the panel according to
function and use. Also, related measurements
could be recorded on a single chart, i.e.,
furnace temperatures, excess air, and possibly
smoke density. The degree and sophistication
of instrumentation depends upon plant size
and economics.
Usually the indicating and recording
instrument readouts are grouped on a control
panel centrally mounted on the operating
floor, with a system of warning lights or bells
to summon the operator when corrective
action must be taken. A duplicate panel of
critical instruments may be placed in the
plant superintendent's office for additional
surveillance.
Very often recording instruments indicate
the conditions that exist over a 24-hr period
on a removable paper chart. These records can
be very useful in making statistical summaries
42
-------
of operating conditions and in reviewing
operating conditions that may correlate with
a malfunction.
Types and Application of Instrumentation
and Controls
Types of Instruments. The physical
parameters and instruments that can be used
to assist in the operation of an incinerator
include the following.:
1. Temperatures
—Optical pyrometers for flame and wall
temperatures in the range of 2,200 to 2,500 F
^Shielded thermocouples (Chrome-Alumel)
for furnace temperatures in the 1,400 to
1,800 F range, and iron-constantan in duct
temperatures down to 100 F Gas- or liquid-
filled bulb thermometers for duct
temperatures below 1,000 F and for ambient
temperatures and water temperatures
2. Draft Pressures
—Manometers and inclined water gauges for
accurate readout close to the point of
measurement
—Diaphragm-actuated sensors where remote
readouts are desired
3. Gas or Liquid Pressures from I to
lOOpsi
—Bourdon-tube pressure gauges for direct
readout
—Diaphragm-actuated sensors for remote
readout
4. Gas Flows
—Orifice or venturi meters with differential
pressures measured by draft gauges
—Pitot tubes and draft gauges
5. Liquid Flows
—Orifices with differential pressure
measurement
—Propeller-type dynamic flowmeters
—Weirs
6. Electrical Characteristics
—Voltmeters, ammeters, and wattmeters.
7. Smoke Density
—Photoelectric pickup of a light beam across
the gas duct
8. Motion
—Tachometers for speeds of fan, stoker, or
conveyor drives
—Counters for reciprocating stokers and
conveyors
9. Visual Observation
-Vidicon closed-circuit television cameras for
viewing furnace interiors, furnace loading
operations, or stack effluents
—Peep holes in furnace doors
—Mirror systems
10. Weight
—Motor truck platform scales for measuring
the quantity of incoming solid waste and
outgoing residue, fly ash, and siftings
—Load cells for automatically weighing crane
bucket contents
Application of Instruments and
Controls. Temperature measurement is one of
the major uses of instrumentation at an
incinerator. Temperature should be measured
at various locations throughout the furnace
and gas passages. These include (1)
temperature of incoming air; (2) temperature
of gases leaving combustion chamber; (3)
temperatures at settling chamber outlet; (4)
temperature at cooling chamber outlet; (5)
temperature at dust collector inlet and outlet;
and (6) stack temperature.
Gas temperature in the furnace are often
controlled by increasing or decreasing the
amount of underfire and overfire air. The
control system can be either manual or
automatic. Some automatic control systems
not only adjust the amount of overfire air,
but also adjust the amount of underfire air
needed to maintain a specific ratio with the
overfire air.
Underfire air can be controlled so that the
flow of air remains constant even though the
underfire air pressure varies with the
characteristics- of the solid waste on the grate.
The proper flow and placement of underfire
air promotes combustion of solid waste on
the grate and reduces the amount of fly ash
particulates carried into the gas stream. Total
underfire and overfire air flow should be
43
-------
measured and recorded; and the percentage of
each to the total flow should also be
indicated.
Changes in the amount of overfire and
underfire air cause the furnace pressure to
vary. To maintain the negative pressure
necessary for proper operation, the furnace
draft must be controlled. The control can be
done manually or automatically by adjusting
the speed of the induced draft fan and the
chimney draft. Draft pressures should be
measured at the following locations: (1)
underfire air duct; (2) overfire air duct; (3)
stoker compartments; (4) sidewall air duct;
(5) sidewall low furnace outlet; (6) dust
collector inlet and outlet (pressure
differential); and (7) induced draft fan inlet.2
The hot exhaust gases leaving the furnace
must be cooled to 500 to 700 F to avoid
damage to many types of collectors and to
the induced draft fan. The gases can be cooled
by spraying with water or by dilution with
cool outside air. The proper amount of
cooling fluids needed can be regulated by a
temperature activated control system. A
control system should be installed to open an
emergency bypass in case the exit gas
temperature exceeds a safe limit. This system
should also activate an alarm.
Multiple unit cyclone collectors operate
best at certain gas velocities. Because of this
characteristic, the number of units should
vary with the velocity of the gas passing
through the furnace. Since the gas velocity is
in proportion to the speed of the induced
draft fan, fan speed can regulate the number
of units needed.
Smoke density can be monitored
continuously to check compliance with air
pollution requirements. The photoelectric
pickup of a light beam across a gas duct can
be used to measure participate density in the
exhaust gas. The monitoring device can be
ideally located between the particulate
collectors and the induced draft fan. The
fouling of lenses with smoke is reduced
because the negative pressure existing in this
area provides good operating conditions for
the device.
An incinerator should include the
instrumentation necessary for determining the
weight of incoming and outgoing material;
overfire and underfire air flow rates; selected
temperatures and pressures in the furnace,
along gas passages, in the particulate
collectors, and in the stack; electrical power
and water consumption of critical units; and
grate speed.
Operational Problems Involving Instruments
Carefully written specifications for
instrument type, quality, and location,
followed by proper installation and routine
testing and preventive maintenance are keys
to successful instrument operation. Many
instruments need frequent calibration to
ensure accurate and reliable readings. Dust
can also interfere with the working of the
instruments, and the hot and sometimes
corrosive flue gas stream can deteriorate the
sensing elements inside the gas passage.
Although the instrument responds, a testing
program is necessary to verify and maintain
the accuracy of the readings.
Repair and maintenance of instrumentation
often require qualified personnel. Contract
services should be used if qualified instrument
repair personnel are not available at the
incinerator. Incinerator personnel, however,
should be trained to identify and correct
everyday problems such as clogging of
transmission lines, fouling and damaging of
sensing devices, and improper charting and
inking. A maintenance and repair service
contract to correct daily problems is not
warranted when the expense and the time lag
from reporting the malfunction to its
correction are considered.
The incinerator personnel should be trained
in the use and interpretation of data received
from the instruments. Even if the operators
do not use the data directly, knowing its
intended use may motivate the operators to
obtain an accurate reading.
44
-------
Future Needs
Improvements in and wider application of
instrumentation and controls hold promise
for upgrading routine operations and for
lowering the operating cost of incinerators.
Although the application of present-day
instrumentation and control technology can
improve the state of the art, new concepts as
well as designs and applications in controlling
the combustion process are needed. Certainly
the need for improvements in measuring and
controlling the weight input into the furnace
is recognized. An improved device for
monitoring smoke and particulate emissions is
also needed. Further research is also needed
to understand the limitations of instruments,
to ascertain the best instrument locations, and
to better correlate the instrument readings
with incinerator performance.
REFERENCES
1. PEARL, D. R. A review of the state of the art of
modern municipal incineration system equipment.
Pt. 4, v. 4. In Combustion Engineering, Inc.
Technical-economic study of solid waste disposal
needs and practices. Public Health Service
Publication No. 1886. Washington, U.S.
Government Printing Office, 1969. p. 25-27. (In
press.)
2. STICKLEY, J. D. Instrumentation systems for
municipal refuse incinerators. In Proceedings; 1968
National Incinerator Conference, New York, May
5-8, 1968. American Society of Mechanical
Engineers, p. 303-308.
45
-------
CHAPTER XI
INCINERATOR EFFLUENTS AND THEIR CONTROL
Improper design and operation of an
incinerator can pollute air, water, and land.
Strict air and water pollution legislation at all
levels of government, coupled with the trend
to locate incinerators close to the sources of
solid waste (to reduce hauling cost), requires
an overall upgrading of the incinerator process
to ensure that it does not adversely affect the
environment.
The unit processes associated with
incineration (Figure 14) that can cause
environmental pollution, except air pollution
from stack emissions, are discussed in this
chapter. Air pollution control is discussed in
Chapter XII.
Odor, Dust, and Litter
Operation of the tipping and storage area
can cause dust, litter, and noxious odors.
Odor problems from putrefaction of organic
materials are especially severe if waste is held
in the storage pit for long periods, and several
days is not unusual, even in the best managed
plants. The dust and odors generated can
cause extremely unpleasant working
conditions.
Frequent sweeping of the tipping floor
effectively controls litter. Washing the floor
with cleaning-disinfecting solutions and
frequently removing putrescibles from the pit
floor aid in the control of odors and insects.
Pine oil may also be added to the washing
solution as an odor masking agent.
Fenthion, diazinon, naled, dimethoate,
ronnel, and malathion are among the effective
insecticides for control of flies and other
insects. These residual toxicants may be
applied directly to the floor and lower
portion of the walls of the tipping area and
the charging area with a simple, inexpensive
garden sprayer. Most of these insecticides are
available as bait in granular form that may be
sprinkled on the floors. An extensive list of
pesticides and instructions for their
application has been compiled.1
Odor and fly control are facilitated if the
storage pit is divided; the separate sections
can be alternately emptied and cleaned. Dust
and litter can be partially controlled with
water sprays that are intermittently used
when the dust level is high.
Water used for dust control and for periodic
washdown to control insects and rodents is a
potential pollutant. Current practice makes
no attempt to integrate these waters into
in-plant water treatment facilities, but allows
drainage to surface waters or sanitary sewers.
The pollution is considered minimal
compared with that of other process waters.
Even so, these waters should be conveyed to
an onsite or offsite treatment process.
Many dusty, odorous operations in industry
are fully enclosed and internal air is processed
through air purification systems. One fully
enclosed transfer station is utilizing activated
charcoal filters to purify the air.2 Such
innovations may have application to odor and
dust control of solid waste tipping, storage,
and charging in incineration. In Europe,
strategically placing combustion air intakes
within an enclosed tipping area has met with
some success in controlling dust and odor.
46
-------
ODOR DUST
LITTER
(AUXILIARY
AIR FUEL)
PLANTS WITHOUT
AIR POLLUTION CONTROL
AIR AND/OR WATER
GASES
AND
ENTRAINED
SOLIDS
DRYING
AND COMBUSTION
IGNITION
GASES
AND
ENTRAINED
SOLIDS
RESIDUE
TREATED
GASES
GASES
AND
ENTRAINED
SOLIDS
FLY ASH
(WATER)
WATER
( FLY ASH
+
WATER)
FLY ASH
< WATER)
RESIDUE (WATER)
EFFLUENT SLUDGE
WATER (FLY ASH)
FLY ASH
t
LAND SEWER
DISPOSAL
Figure 14. Diagram of the inplant systems based upon dry fly ash collection and conveying from cooling and collection operations. Alternatives for
wet collection and conveying shown in parentheses.
-------
Residue from Combustion
Fly Ash
Residue consists of all solid materials
remaining after burning. It includes ash,
clinker, tin cans, glass, rocks, and unburned
organic substances. Residue from incineration
of municipal solid waste commonly is 20 to
25 percent of the original solid waste.
Uncompacted residue occupies 10 to 20
percent of the original volume of solid waste
in the pit.
Incinerator residue is permeable and may
contain water soluble inorganic and organic
compounds. If water moves through the
deposit of residue, leaching can occur.
Pollution can occur if the leachate water
moves through the underlying soil and enters
the groundwater. Surface water can also
become contaminated where the leachate
moves laterally through the surrounding soil
and seeps out at ground surface. In many
cases, therefore, only sanitary landfill
methods can be employed to dispose of
incinerator residue.
Where there is no danger of water pollution,
residue may be used as a fill material if the
residue does not attract insects or rodents.
At the present time, there are no specific
and universally accepted quality standards for
residue from municipal incineration. Residue
containing less than 5 percent combustibles,
measured in terms of total dry weight of
residue, and having a total volume of less than
10 percent of the original solid waste charged
may, however, be acceptable from the
standpoint of volume reduction in most
locations. The degree of burnout will also
affect the degree of protection afforded
environmental quality.
The combustible content of residue is not
the only true measure of protection of
environmental quality. Other tests, still in the
developmental stage, must be used to measure
the potential of residue to cause odors, attract
insects and rodents, and pollute water.3'4
One of the products of incineration is fly
ash. This portion of the residue consists of the
solid participate matter carried by the
combustion gases. Fly ash includes ash,
cinder, mineral dust, and soot, plus charred
paper and other partially burned materials.
The size of most fly ash particles ranges from
120 to less than 5 microns. Distribution
within this range is extremely variable. The
inorganic fraction of fly ash is usually the
major constituent and consists mostly of
oxides of silicon, aluminum, calcium, and
iron.
The collected fly ash may be transported in
a water slurry or handled in a dry state. Fly
ash process water has large amounts of solids
and a low pH (Table 7). Because of these
characteristics, sluicing water should be
treated before final disposal. Usually it can be
treated with the residue process water. Dry
fly ash, which is difficult to handle, can be
easily picked up and scattered by the wind.
At the incinerator plant, dry fly ash should be
stored in suitable closed containers. If stored
in the open, the surface of the ash pile should
be kept moist. When transported to the final
disposal site, fly ash should be in closed
containers unless intermixed at the
incinerator with the moist residue.
Fly ash that is open-dumped is a potential
source of pollution. Left uncovered, dry ash
can create a dust problem and can also be a
source of water pollution because the ash
contains water soluble compounds. Sanitary
landfill methods are often necessary,
therefore, to dispose of fly ash.
Process Water
Almost without exception, all incinerator
plants utilize water for residue quenching. In
addition, many plants use water for wet
bottom expansion chambers, for cooling
charging chutes, for fly ash sluicing, for
48
-------
TABLE 7
CHARACTERISTICS OF' INCINERATOR WASTE WATER*
Characteristic
pll
Dissolved solids, mg/1
Suspended solids, mg/1
Total solids (% volatile)
Hardness (CaCO3) mg/1
Sulfatc (SO4) mg/1
Phosphate (PO4) mg/1
Chloride (Cl) mg/1
Alkalinity (CaCO3) mg/1
Five-day BOD at 20 C
Plant It
Residue quench
Max
11.6
9.005
2,680
53.6
1,574
430
55.0
3,650
1,250
-
Min
8.5
597
40
18.5
216
110
0.0
50
215
-
AVK
10.4
3,116
671
36.3
752
242
23.3
627
516
-
Plant 2f
Residue quench
Max
11.7
7,897
1,274
51.6
1,370
780
212.5
2,420
1,180
-
Min
6.0
1,341
7
10.5
112
115
1.0
76
292
-
AVK
10.5
4,283
372
31.2
889
371
23.5
763
641
-
Plant 3f
Residue Quench
Max
11.8
7,929
1,888
47.4
1,438
565
225
1,940
1,290
-
Min
9.4
901
72
17.8
574
115
2.5
128
337
-
AVK
11.0
3,894
653
26.6
904
300
33.8
868
682
-
Plant 4-|-
Residue quench
Max
11.8
5,993
5,476
57.6
1,462
830
127.5
944
749
-
Min
6.0
1,214
14
11.3
282
125
0.5
172
192
-
Avg
10.1
2,551
879
34.6
739
242
23.9
393
465
-
Fly
Max
6.5
9,364
398
_
2,780
1,350
15.0
3,821
28
13.5
Plant Sl-
ash effluent
Min
4.8
7,818
208
-
2,440
1,125
11.5
3,077
16
6.2
Avg
5.8
8,838
325
-
2,632
1,250
13.0
3,543
23
8.8
Fly
Max
4.7
6,089
2,010
24.69
3,780
862
76.2
2,404
4
-
Plant 6t
ash affluent
Min
4.5
5,660
848
23.26
3,100
625
32.2
2,155
0
-
AvK
4.6
5,822
1,351
23.75
3,437
725
51.5
2,297
1.33
-
*Data Sources:
Plants 1 through 4: SOLID WASTES PROGRAM. Report on the municipal solid wastes incinerator system of the District of Columbia. Cincinnati, U.S. Public Health
Service, June 1967. 77p.
Plants 5 and 6: Bureau of Solid Waste Management. Unpublished data (SW-llts) (SW-12ts). Values were determined from data taken at Ogden, Utah; and Alexandria,
Virginia.
|Plant 1, 110 TPD, batch, residue quench only;
Plant 2, 425 TPD, batch, residue quench only;
Plant 3, 500 TPD, batch, residue quench only;
Plant 4, 500 TPD, batch, residue quench only;
Plant 5, 300 TPD, continuous feed -Fly ash effluent only;
Rant 6, 300 TPD, continuous feed- Fly ash effluent only.
-------
residue conveying, and for air pollution
control. The quantity of water required
depends on plant design, on how well the
system is operated, and whether water is
recirculated. Jens and Rehm5 reported total
water requirements without recirculation tor
a 300-ton-per-day plant with two 150-ton
continuous feed furnaces to be about 2,000
gal of water per ton of solid waste charged.
Quenching and conveying used 1,800 gal and
the wetted baffle dust collection system used
200 gal. The study indicated that use of a
recirculation, clarification, and neutralizing
system reduced the total water needed from
2,020 to 575 gal per ton of solid waste.5
Because of extreme variation in incinerator
design, generalizing on water requirements is
of only limited value. A rule of thumb,
however, is that residue quenching and ash
conveying at most plants requires 1,000 to
2,000 gal of water per ton of solid waste
processed. With water treatment and
recirculation, total water consumption can
often be reduced 50 to 80 percent.
Studies have shown that incineration
process water contains suspended solids,
inorganic materials in solution, and organic
materials that contribute to biochemical and
chemical oxygen demand (Table 7).6'7 A
limited study of incinerator waste waters
from a 50-ton-per-day, batch feed incinerator
and from a 300-ton-per-day, continuous feed
municipal incinerator showed the presence of
bacteria in the waste water from both
operations.8
The studies indicated that incinerator
process waters can be contaminated and,
therefore, should not be discharged
indiscriminately to streams or other open
bodies of water.3"5 The most straighforward
control is the discharge of these waters to a
sanitary sewer for subsequent handling in a
central treatment plant. If the waste process
waters cannot be ultimately discharged to a
sanitary sewer, the incinerator plant should be
equipped with suitable means for primary
clarification, pH adjustment, and, if
necessary, biological treatment to meet local
standards.
REFERENCES
1. NATIONAL COMMUNICABLE DISEASE CENTER.
1967 National Communicable Disease Center report
on public health pesticides. Pest Control,
35(3)13-14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34,
36, 38,40, Mar. 1967.
2. ROEDER, W. F. Carbon filters control odors at refuse
transfer station. Public Works, 100(4):96-97, Apr.
1969.
3. BOWEN, I. G., and L. BREALEY. Incinerator
ash-criteria of performance. In Proceedings; 1968
National Incinerator Conference, New York, May
5-8, 1968. American Society of Mechanical
Engineers, p. 18-22.
4. SCHOENBERGER, R. J., and P. W. PURDOM.
Classification of incinerator residue. In Proceedings;
1966 National Incinerator Conference, New York,
May 1-4, 1968. American Society of Mechanical
Engineers, p. 237-241.
5. JENS, W., and F. R. REHM. Municipal incineration and
air pollution control. In Proceedings; 1966 National
Incinerator Conference, New York, May 14, 1966.
American Society of Mechanical Engineers, p.
74-83.
6. MATUSKY, F E., and R. K. HAMPTON. Incinerator
waste water. In Proceedings; 1968 National
Incinerator Conference, New York, May 5-8, 1968.
American Society of Mechanical Engineers, p.
198-203.
7. SOLID WASTES PROGRAM. Report on the municipal
solid wastes incinerator system of the District of
Columbia. Cincinnati, U.S. Public Health Service,
June 1967. 77 p.
8. TUCKER, M. G. Biological characteristics of incinerator
waste waters. Unpublished graduate student
research project in CE 687 course. University of
Michigan, Aug. 1967. 15 p.
50
-------
CHAPTER XII
AIR POLLUTION CONTROL
Entrained particulates and some gaseous
products are the major air pollutants from the
incineration of solid waste. Although not
extensive, a number of investigators have
identified the quantities and nature of these
effluents.1"4
Participate Material
The important properties of the entrained
particulars matter, from the standpoint of its
collection. are quantities, particle-size
distribution, specific gravity, electricity
resistivity, and chemical composition.
Quantities. Stenburg and Walker and
Schmitz ha\ e quantified entrained
particulates emitted from refractory furnaces
(Figure 15). The data were based upon studies
of furnaces ranging in size from 50 to 250
tons per day employing a variety of grate
configurations.1'3 An important parameter
that appears to affect furnace particulate
emission is the quantity of underfire un-
utilized in effecting acceptable combustion of
solid waste charged. Values from about lOlb
fly ash per ton of solid waste burned to over
60 Ib per ton have been reported from
combustion of typical municipal solid waste.
Adjustment of underfire air may partially
control emissions of entrained particulate
matter. The data on operating plants indicate,
however, that adequate combustion of the
solid waste requires substantial quantities of
underfire air, so that this technique for
reduction of furnace particulate emission
cannot be utilized without substantially
affecting the capacity of the furnace to burn
solid waste.
Particle-Size Distribution and Specific
Gravity. These two properties of particulate
matter are critical to the performance of most
particulate collectors and essentially
determine the level of sophistication of air
pollution control equipment required to meet
a given stack emission objective. Generally,
the larger the size and the higher the specific
gravity, the easier the particles can be
collected. Coarse, high-density materials can
be collected in simple inertial devices such as
settling chambers and cyclones. Fine, light
materials require more sophisticated
techniques such as high-energy wet. scrubbing.
j:
K-
FURNACE
PD ROCKING GRATE
PD TRAVELING GRATE
PD RECIPROCATING GRATE
PD BATCH FEED
PD TRAVELING GRATE
I III |
1,000
UNCERFIRE AIR (SCFM SO FT GR4TEI
Figure 15. Entrained particulate emissions.
51
-------
fabric filtration, or electrostatic precipitation.
Generally, the percentage, by weight, of fly
ash less than 10 microns in diameter
determines whether simple or more
sophisticated collection techniques are
required.
Data on typical particle size distribution,
specific gravity, and combustible content of
entrained particulates leaving the furnaces of
large (125- to 250-TPD) continuous-feed
refractory furnace incinerators are shown
(Table 8).3 The values were typical of
entrained particulates from three different
refractory furnaces with capacities ranging in
size from 120 to 250 tons per day and
burning typical municipal solid waste.
Because the nature of the waste charged and
the furnace conditions materially affect
particle size distribution, caution must be
exercised in generalizing from this
information. Nevertheless, if high collection
efficiencies are to be obtained, substantial
quantities of material in the size range below
10 microns must be collected.
Electrical Resistivity. Electrical resistivity
of the fly ash is the property of prime interest
when electrostatic precipitators are
considered for participate collection. High
resistivity particulates cause disturbances in
electrical operation that reduce collection
rates. In general collection of particulates
with higher resistivities requires larger and
more expensive precipitators. Wet scrubbers
or fabric filters may be preferred if resistivity
is very high. Very low resistivities are also
troublesome, but can be handled in properly
designed precipitators. When the resistivity is
low, the dust readily loses its charge to the
collecting electrode and takes on a positive
charge. The particle is then repelled by the
positively charged collecting electrode; this
can cause the particle, particularly if it is
large, to reenter the gas stream.
The optimum range for efficient operation
of an electrostatic precipitator lies between
104 and 1010 ohm-cm. Thus, to select the
most suitable air pollution equipment, the
resistivity of the fly ash must be known.
Typical resistivity-temperature curves of
entrained particulates leaving large,
continuous feed refractory furnace
incinerators were charted by Walker (Figure
16).3
TABLE 8
PROPERTIES OF PARTICULATES LEAVING FURNACE
Physical analysis
Specific gravity
(gm/cc)
Bulk density (Ib/cf)
Loss of ignition at
750 C (%)
Size distribution
(% by weight)
< 2M
< 4 M
< 6n
< 8n
-------
pollutants by incineration of solid waste
appears to be low. The sum of the emission of
nitrogen oxides and sulfur oxides from large
steam-electric generating stations, for
example, may be 10 to 100 times higher per
ton of fuel than municipal solid waste
incineration. The principal exceptions are
those trace constituents that can cause odor
in incinerator stack effluents. The specific
composition and odor threshold concentration
of these constituents have not yet been
identified.
Water Vapor Plumes. The undesirability of
water vapor depends on the importance
attributed to the psychological effect of
dense, visible water vapor plumes. In rural or
industrial locations, the psychological impact
of water vapor plumes may be small. In
residential locations, the effect may be
significant and a critical factor in the overall
plant design.
O 100 ZOO 3OO 400 5OO SOO 700
TEMPERATURE (F)
Figure 16. Bulk electrical resistivity of entrained
particulates leaving three large, continuous feed furnaces at 6
percent water vapor.
100 percent excess air. The reduced volume
of combustion products per ton of solid waste
burned that results from lower excess air
operation in water-cooled furnaces is an
advantage when high efficiency air pollution
control equipment is used.
In addition to the major gaseous products
of combustion, trace gases present in the
effluent can cause air pollution either because
of their odor; their direct effect on plants,
animals, and property; or their interaction
with components of the ambient air to form
undesirable secondary compounds. A number
of these have been identified (Table 9).1'4
Compared with other major combustion
processes that contribute gaseous pollutants
to the atmosphere, such as combustion of
fossil fuel, the contribution of gaseous
100 150 200
EXCESS AIR (PERCENT)
Figure 17. Gross products of combustion per pound of
solid waste. 20 percent carbon remaining in total residue.
Solid waste composition based on Kaiser's analysis. Standard
conditions for measuring gases are 29.92 inches Hg and 70 F
at 60 percent relative humidity.
53
-------
Three general situations are encountered in
the treatment of exhaust gas stream: (1) gas
cooling to temperatures acceptable to
partieulate emission control equipment is
achieved without vaporization of water, i.e.,
radiation, dilution, or indirect heat
exchange-either gas-to-gas or gas-to-liquid;
(2) gas cooling to acceptable temperatures is
achieved either partially or totally by
vaporization of water, and partieulate
collection is dry; (3) gas cooling and
participates collection is achieved by wet
methods.
TABLE 9
TRACE GAS CONSTITUENTS IN INCINERATOR
EFFLUENT1'4
Gaseous emissions
(Ib/ton)
Aldehydes
Sulfur oxides
Hydrocaibonsf
Organic acidsj
Carbon monoxide
Nitrogen oxides
Ammonia
Typical municipal
solid waste*
23.6 X 1CT4
—
0.8
—
0.51
2.7
—
Mostly branches and
twigs (no garbage)
1.1
1.9
1.4
0.6
-_
2.1
0.3
*Typical municipal solid waste: Converted from reported
units in pounds per 1,000 Ib flue gas at 50 percent excess air
to pounds per ton solid waste based on "typical refuse," as
established by Kaiser.
fHydrocarbon expressed as methane.
^Organic acids expressed as acetic acid.
In situation 1, absolute humidity is low
(approximately 0.07 Ib water vapor/lb dry
gas) since no water vapor is added in cooling.
Temperatures of the gases are high (450 to
600 F) so that dispersion capability is good.
Because of the low humidity and high
temperature, water vapor plume occurrence
will probably be restricted to very low
ambient temperatures. In situation 2, absolute
humidities may be several times higher
(approximately 0.25 to 0.30 Ib water vapor/lb
dry gas) since a substantial amount of water is
evaporated in cooling the gases from stack
temperatures of 1,200 to 1,800 F down to
450 to 600 F; however, stack temperatures
are still high, dispersion capability is good,
and condensate plumes will probably be
limited to situations of low ambient
temperature and intermediate ambient
temperatures associated with high relative
humidity. In situation 3, partieulate scrubbers
saturate the gas with moisture, absolute
humidities are high (under adiabatic
saturation conditions approximately 0.6 Ib
water/lb dry gas), and effluent temperatures
are low (in the range of 175 to 180 F under
adiabatic saturation conditions) so that
dispersion capability is poor and condensate
plumes will occur under almost all
atmospheric conditions.
Condensate plumes are usually not harmful,
and local complaints may possibly be reduced
by proper preeducation and public relations
regarding water vapor plumes. On the other
hand, there have been complaints of corrosion
on automobiles resulting from condensate
fallout and of a decrease in visibility at
ground level on roadways, etc., that have been
connected with water vapor plumes from
incineration. Thus, these potential problems
must be given serious consideration in the
design of the plant.
Desired Emission Levels
Gaseous Emissions. The principal gaseous
emissions from incineration are common to
all combustion processes: carbon dioxide,
water vapor, nitrogen, and oxygen. These are
all normal atmospheric constituents, and no
control is necessary. In recent years, attention
has been directed toward the control of
emission of sulfur oxides, nitrogen oxides,
carbon monoxide, hydrogen chloride, and
total hydrocarbons. With the possible
exception of sulfur oxides, no maximum
permissible emission levels have been
developed, although criteria do exist in
certain critical areas on nitrogen oxides and
total hydrocarbons. In the specific case of
solid waste incineration (excluding open
burning), emission of all these gaseous
contaminants apparently is well below present
54
-------
or contemplated criteria. Thus, at the present
time, and with the exception of the control of
those trace emissions that cause odors, the
control of other trace gaseous emissions from
incineration appears of minor concern.
Gas-Suspended Particulate
Emissions. Specific quantitative emission
limits on gas-suspended particulates are
becoming increasingly prevalent in the air
pollution codes of many municipalities and
States as well as in the operation of Federal
facilities. These codes may be expressed in a
variety of ways, such as: (1) total weight of
suspended particulate per unit volume of
exhaust gases; (2) total weight of suspended
particulate per unit weight of exhaust gases;
(3) total weight of suspended particulate
emitted per unit weight of solid waste
charged. Further, to prevent compliance with
emission codes by simple dilution of stack
gases with air or water vapor, almost all codes
require correction of these emission limits to
a specific reference condition.
At the present time, the most commonly
used units for emission values in incinerator
practice are pounds suspended solids per
thousand pounds of dry flue gas corrected to
50 percent excess air and grains per standard
cubic foot (29.92 in. Hg and 70 F) of dry flue
gas corrected to 12 percent carbon dioxide.
The reference conditions of 12 percent
carbon dioxide and 50 percent excess air are
approximately equivalent for municipal solid
waste. Figure 18 gives approximate
equivalents of the most common units, to 1 gr
per standard cu ft of dry gas as sampled, for
typical municipal solid waste under various
combustion conditions.
Some representative gas suspended
particulate emission limits (as they existed in
early 1968) have been summarized (Table
10).2 In the absence of local regulations, the
code established by U.S. Department of
Health, Education, and Welfare should apply
(Appendix B).
Visual Emission Levels. In addition to
provisions limiting the quantities of
particulate emission, many codes at the
municipal and State level also have opacity
restrictions —usually based upon the
Ringelmann chart.6 The Ringelmann number
is determined by a comparative visual
observation of the stack plume and a series of
reference grids of black lines on white that,
when properly positioned, appear as shades of
gray to the observer. Although the quality of
a plume in equivalent Ringelmann numbers is
not easy to determine, trained observers,
properly positioned in relation to stack, sun,
and wind direction, can provide satisfactorily
consistent evaluations.7'8 Water vapor plumes
complicate observations of stack gases, but
again, trained observers can distinguish
between water vapor and residual plumes
under selected weather conditions.
The trend in most codes on incinerator
emissions based on Ringelmann is to require
that: (1) normal, continuous plume quality
not to exceed Ringelmann No. 1; (2) for short
periods not exceeding 3 to 5 min in any one
PERCENT EXCESS AIR IN FLUE GAS
AS SAMPLED
Figure 18. Dust concentration equivalents for 1 gr/SCF
(29.92 inches Hg and 70 F) dry gas as sampled, as a function
of percent excess air in sampled gas. Conditions are based on
Kaiser's typical refuse with 20 percent carbon remaining in
the residue. Example: correct 1.5 gr/SCF as sampled at 200
percent excess air to gr/SCF at 12 percent carbon dioxide.
From graph: 1 gr/SCF as sampled at 200 percent excess air =
2.1 gr/SCF when corrected to 12 percent carbon dioxide;
therefore, 1.5 gr/SCF at 200 percent excess air when
corrected to 12 percent carbon dioxide = (1.5)(2.1) = 3.15
gr/SCF.
55
-------
hour, plume quality not exceed Ringelmann
No. 2. and (3) plume quality clearly resulting
from water vapor only be excluded from
regulation.
Plume opacity refers to the inability of light
to pass through the gas plume and is usually
applied in cases where the plume is some
color other than gray or black. Opacity
readings are expressed in terms of percent
visibility through the gas plume.
From the standpoint of plant design, a basic
problem arises from the fact that the entire
technology of particulate collection has been
based upon quantitative reduction in the
weight of total suspended materials. Thus, to
establish the level of control required to meet
a given visual code, this code must be
expressed in some quantitative gravimetric
units. Consistent and general criteria for
correlating gas quality measurements, such as
Ringelmann number, with quantitative
emission in the case of incinerators are not
yet available. Therefore, the collection
efficiency required to meet a particular
Ringelmann number is virtually impossible to
predict. Experience with large, coal-fired
steam generators indicates that loadings in the
range of 0.01 to 0.02 gr per cu ft of exit gas
result in stacks optically clear of suspended
participates (i.e., less than Ringelmann No. 1).
Achievement of these stack concentrations in
coal firing requires collector efficiency in
excess of 99 percent by weight. Similarities in
particle size distribution from coal-fired steam
generators and from incinerators indicate that
efficiencies of this order will be required on
incinerators if completely clear stack
emissions are to be achieved.
Methods of Control
Control of Odors. The best approach to
the control of odors generated in the drying
and combustion process is maintenance of
adequate retention time and sufficient
temperature to ensure complete combustion
of hydrocarbon vapors to carbon dioxide and
TABLE 10
TYPICAL PARTICULATE EMISSION CODES FOR
COMBUSTION OF SOLID WASTE IN A 250-TON-PER-DAY
INCINERATOR BURNING TYPICAL SOLID WASTE
Agency
U.S.Deptof
Health,
Education,
and Welfare,
regulations,
for Federal
Installations
Bay Area APCB
San Francisco,
California
Reg. 2,
Chapter 1
State of
New Jersey
(proposed
Chapter XI)
Emission
limit
(as written)
0.2 gr/std
dry cu ft
corrected
to 12%
C02
0.2 gr/std
dry cu ft
corrected
to 6% O2
0.1 gr/std
dry cu ft
corrected
to 12% CO 2
Approximate
lb/1,000 Ib
dry flue
gas corrected
to 50%
excess air
0.36
0.36
0.36
equivalent value
gr/std
dry cu ft
corrected
to 12%
C02
0.2
0.2
0.1
water. Elimination of odors from stack gases
demands that mixing of any volume of gas
containing odors must be completed so that
the required excess air and temperature
conditions are reached in every stream of gas.
A 0.5 sec residence time before the
temperature of the mixed gas falls below
1,500 F is generally sufficient. If the
temperature at the exit of the furnace is kept
above 1,400 F, temperatures within the
combustion chamber will be sufficient to
eliminate odors.
Another odor control technique is to dilute
the odorous gas in the atmosphere to a value
below its threshold odor so it is unapparent to
a receiver. This is achieved through the use of
stacks of sufficient effective height. Effective
stack height is a function of both the actual
stack height and plume rise as the gases leave
the stack. The height a plume will rise above
the stack is a function of the ambient
temperature and the gas temperature, exit
velocities of the stack gases, and the stability
of the atmosphere. If the threshold value of
56
-------
any identifiable odorous gas is known,
methodology is available for estimating the
maximum quantitative emission that will keep
odorous gas below the threshold value at the
nearest receiver. Presently, however, this
technique for controlling odors is not being
used for two reasons: (1) the ability to
eliminate odors by proper process operation;
and (2) the absence of identifiable odorous
contaminants and their threshold values.
Data on 107 existing batch feed plants
indicate a maximum stack height, above
grade, of 250 ft, a minimum of 39 ft, and an
average of 133 ft.5 On 44 continuous feed
plants, the values were: maximum 250 ft,
minimum 25 ft, and an average of 145 ft. The
advances that have been made in the use of
meteorological methods and data in the
design of stacks as pollutant dispersion
devices appear applicable to the design of
stacks for incinerator plants. This suggests the
desirability of competent meteorological
consultation to determine stack heights.
Control of Gaseous Emissions from
Combustion. Both nitrogen oxide and sulfur
oxide emissions occur in solid waste
incineration, but the amounts per ton of fuel
burned are several orders of magnitude below
those involved in the combustion of fossil
fuel. Solid waste is inherently a "clean fuel"
from the standpoint of sulfur content, with a
value of about 0.16 percent by weight2 as
compared to most coals and residual oils used
today, which range from about 1 to 3 percent
sulfur. Further, there is evidence to suggest
that for incineration, most of the sulfur is
retained in the ash rather than as oxides in the
stack. Thus, sulfur oxide emissions from solid
waste incineration generally are well below
even the most stringent restrictions present or
anticipated.
Restrictions on nitrogen oxide emissions
from fossil fuel combustion have not yet been
formulated. Nitrogen oxide emissions per ton
of fossil fuel are over 10 times greater than
those in an incinerator. Therefore, it appears
unlikely that this contaminant will be
regulated in incinerator plants in the near
future.
Some concern has been expressed about
emissions of hydrogen chloride (HC1) that
might occur as a result of incineration of
certain plastics. Hydrogen chloride is toxic to
the eyes and respiratory system, and if the
amounts released during incineration were
great enough, a health problem would exist.
The plastic polyvinyl chloride is found in
increasing amounts in municipal solid waste.
When it is burned, hydrogen chloride is
released, and emissions of 2.7, 2.2, 1.4, and
6.8 Ib per ton of solid waste incinerated were
measured at four New York incinerators.9 If
hydrogen chloride emissions become a
problem, control will be necessary, but since
this gas is highly soluble in water, it can
probably be effectively removed by water
scrubbers.
Control of Suspended Particulate Emission
from Combustion. The following is a brief
discussion of the various types of participate
collection systems, their performance
capabilities based upon objective test data,
the state of the art of their development with
respect to application to incinerators, and
some general indication of their capital cost.
Cost data are based upon plants in the range
of 150- to 200-ton-per-day rated capacity.
The particular type of control system used
will depend primarily on the desired level of
control, taking into account both quantitative
and optical emission criteria, and on the
overall cost to own and operate the system.
Types of Collectors. Settling Chambers.
The simplest and oldest form of particulate
particulate collector is the settling chamber
with either a dry or wet bottom. With the
exception of a very few plants equipped with
some form of sprays or baffle system within
the settling chambers, this was the only type
of collector used in incineration plants in this
country before about 1953 or 1954. Available
test data on the settling chamber indicate
efficiencies in the range of 10 to 34 percent
by weight.3'10'11 Since 1961 and 1962, the
57
-------
use of settling chambers in their simplest form
as the only participate collection device has
become essentially obsolete since they are
unacceptable as the principal means of air
pollution control.
Wetted Baffle-Spray System. Another
form of participate collection device is the
wetted baffle or baffle spray system. These
systems usually consist of vertical
impingement baffle screens that are wetted
with water by flushing sprays or overflow
weirs. There may be one or more screens in
the collection system. Participate removal
efficiency has been measured over a range of
10 to 53 percent by weight at several
different installations.3'10 Pressure drop is in
the range of 0.3 to 0.6 in. of water gauge.
Water consumption is in the range of 0.5 to
2.0 gal per min per ton of rated capacity. One
installation, which uses a spraying section and
secondary baffle section, claims an efficiency
of 69.4 percent; pressure drop and other
operating data are unavailable.1 :
These wet spray or wet baffle systems have
been used on over half of the incinerators
installed since 1957. Their installed cost is
approximately $0.02 to $0.04 per actual cu ft
per min of gas at the collector inlet
temperature (1.800F).
Cyclones and Multiple-Cyclones. Batteries
of relatively large diameter (24 to 40 in.)
parallel cyclones, with involute or scroll type
entry connections, as well as small diameter
(9 to 12 in.) multiple tube vane type cyclone
collectors have been used in about 20 percent
of the incinerator installations built or under
construction since 1957. Although there is a
substantial amount of test data available on
the performance of this type of collector,
little has been published. Unpublished data
confirm published data that indicate
efficiencies in the range of 60 to 65
percent.11 There is little information on the
performance characteristics of the small
diameter vane type collectors. Experience in a
few installations seems to indicate that
plugging of this type collector can be a
problem when used downstream ot gas
cooling systems involving the use of water.
Experience with cyclones seems to favor the
use of the involute type in tube size above 24
in. Maximum reliable efficiency appears to be
in the range of 70 to 80 percent.12 Pressure
drop is in the range of 2.5 to 4.0 in. water
gauge.
Installation cost for cyclone collectors, not
including such auxiliaries as foundations,
supporting steel, flues, and ash removal, is in
the range of $0.12 to $0.25 per actual cu ft
per min of gas treated.
Wet Scrubbers. Approximately 20 percent
of the incinerator plants built or under
construction since 1957 have been equipped
with wet scrubbers. Wet scrubbers differ in
their design and operation from wetted baffle
collectors principally in that capture of the
entrained participates is accomplished by
direct intimate contact of the participates
with the water itself rather than on
water-flushed impaction surfaces. The
particulates collide with water droplets to
effect capture. The water droplets and
impacted particles coalesce into larger
droplets (greater than 1,000 microns) that are
easily collected in an inertial collector. The
water droplets are generally formed by either
atomizing the liquid into the gas stream or by
allowing the gas stream to tear coarse water
droplets into the smaller droplets needed for
high efficiencies. With atomizing units, most
of the operating energy is expended in
pumping the water through the spray nozzles;
gas pressure drops are generally low. In units
where the gas stream tears the water apart,
most of the operating energy is expended in
moving the gases through the unit;
comparatively little energy is consumed in
pumping water. In scrubbers, collection
efficiency is primarily related to total energy
consumption whether it is energy used to
pump liquid or energy used to move gas.
Again, published test data are unavailable on
this type collector, but analysis of their
operating principles and comparison of their
58
-------
known performance on suspended
participates with characteristics similar to
those from incineration indicate an efficiency
capability in the range of 94 to 96 percent at
pressure drops in the range of 5 to 7 in. water
gauge.
Water requirements range from about 5 to
15 gal per 1,000 actual cu ft per min of gas
treated. Pumping power is based on these
figures, although actual makeup water
requirements can be much lower where
recirculating and clarification systems are
utilized. Another characteristic of wet
scrubbers is that the gases at the collector
outlet will be saturated with water vapor, an
important consideration in relation to water
vapor plumes from the stack.
Because they operate below the dewpointof
many trace corrosive constituents in
incinerator flue gases, wet scrubber systems
require corrosion-proof construction. The
installed cost for the base collector without
auxiliaries such as foundations, water
treatment systems, pumps, and piping
ductwork is in the range of $0.25 to $1.25
per actual cu ft per min of gas treated.
Electrostatic Precipitators. Electrostatic
precipitators operate on the principle of
electrically charging the suspended
particulates and depositing the charged
particles on the surface of a collecting
electrode. To remove the particles from the
collecting electrode, the collecting surface is
vibrated, although water sluicing can be used
in certain applications.
The electrical properties of the suspended
particles, the moisture content of the gas
stream, and the temperature of the gas stream
affect precipitation operation. Adding
moisture can lower the high resistance of
inorganic particles. The tendency of carbon to
lose its charge before collection can cause
some problems, but these can be overcome.
Proper insulation of the precipitator, which
eliminates the internal dewpoint
condensation, can control corrosion caused
by moisture in the gas stream. Temperature of
the gases is very important to precipitator
operation because the resistivity of entrained
particles is extremely temperature dependent.
Precipitator operation is best at temperatures
between 470 and 520 F.13
Electrostatic precipitators have no ability to
collect gaseous contaminants except as these
gaseous contaminants may be absorbed on the
particulates removed.
Electrostatic precipitators have been used in
Europe for a number of years in incinerator
plants that recover heat. Auxiliary fuels such
as coal or oil are used under most operating
conditions.14 Efficiencies in the range of 96
to 99.6 percent have been achieved at
pressure drops below 0.5 in. water gauge.
Electrical power requirements are in the range
of 200 to 400 watts per 1,000 actual cu ft per
min of gas treated. Inlet temperatures are
usually in the range of350to700F.
During pilot plant feasibility tests,
efficiencies of 89 to 94.4 percent were
obtained on suspended particulate removal
from a 220-ton-per-day continuous feed
furnace.] 5 Electrostatic precipitators have
not yet been operated on a full scale basis in
the United States, but several new plants
under construction will utilize electrostatic
precipitators with design efficiencies in the 90
to 98.5 percent range. The basic advantage of
the electrostatic precipitator over other
particulate collectors is its high efficiency at
low operation cost (pressure drop and
electrical power input) and its ability to
achieve these efficiencies in a dry system
without creating potential water pollution
problems. Typical installed cost for
electrostatic precipitators, not including
auxiliaries such as foundations, supporting
steel, flues, and fly ash removal, is in the
range of $0.85 to $1.45 per actual cu ft per
min of gas treated.
Fabric Filters. Except for a single pilot
installation on one municipal incinerator,
fabric filters have not yet been applied to
incinerators. Although they are used by many
industries, their use at incinerators must be
considered experimental.
59
-------
Fabric filters literally filter the suspended
particulatcs from gases in a manner similar to
the operation of a vacuum cleaner. The
predominant filtering media is the dust eake
itself, which accounts for the high efficiencies
obtainable (usually in the 99.9'x? + range).12
The dust cake, once it has been formed,
essentially filters all particles as the gases pass
through the pore openings in the cake; these
openings are no bigger than the smallest
particle in the gas stream.
Their utilization for a given application is
almost always based on consideration of
temperature, moisture content of the gas
stream, pressure drop characteristics of
available filtration media, and the service life
of these filter media. Fabrics, such as
fiberglass and high-temperature synthetics, are
available with continuous operating
temperature capability up to about 550 F
Many varieties exist, and their costs differ
principally in relation to their temperature
capability and resistance to chemical attack.
Another consideration in the selection of
fabric filters is the porosity of the filter cake
that is built up on the fabric surface during
normal operation. Cake porosity depends on
moisture, particle size distribution, and
physical and chemical characteristics of the
entrained participates. The typical operating
pressure drop for fabric filters would be in the
range of 4 to 7 in. water gauge. Initial cost of
fabric filters that might be applied to
incinerator operations, based upon the use of
treated fiberglass bags, would be in the range
of $0.75 to $1.50 per actual cu ft per min of
gas treated.
Factors in the Selection of Particulate
Collectors. Matching the type of collection
equipment needed to meet a particular air
pollution control objective is illustrated
(Tables 11 and 12).
Unless furnace operation is to be
significantly restricted, particularly with
respect to underfire air, even the most lenient
quantitative emission code cannot be met
with settling chambers or wetted baffles,
TABLE 1 1
COLLECTION EFFICIENCY REQUIRED TO MEET
VARIOUS EMISSION LIMITATIONS*
Code requirement Approximate % efficiency*
(Ib particulate/1,000 Ib flue gas) to meet code
0.85#/l ,000* («' 50% excess air
0.65#/1,000# r«' 50% excess air
0.20#/1,000# (<" 50% excess air
74
80
94
*Based on 32 Ib of fly ash per ton of solid waste charged
entering the collector.
TABLE 12
MAXIMUM DEMONSTRATED CAPABILITY OF
VARIOUS COLLECTORS
Type of Collector
Maximum demonstrated
efficiency (%)
Settling chambers
Wetted baffles
Cyclone collectors
Direct impaction scrubbers
(wet scrubbers)
Electrostatic prccipitators
Bag filters
34
53
70-80
94-96
99
99+
either alone or in combination. Cyclone
collectors can meet 0.85 Ib per 1,000 Ib at 50
percent excess air and probably can meet
intermediate codes. When codes require
emissions below 0.65 Ib per 1,000 Ib at 50
percent excess air; the only demonstrated
alternatives are direct impaction scrubbers,
electrostatic precipitators, or bag filters.
Control of Water Vapor Plumes. Water
vapor plumes may not be directly harmful
and are, in most cases, excluded from opacity
regulations. Droplet fallout or visible vapor
plumes, however, may constitute an
important nuisance factor. Usually the plume
problem is associated with high efficiency wet
scrubbers, so the first method of controlling
condensate plume is to use dry gas cooling
and collecting techniques. If other factors
dictate the use of high-efficiency scrubbers,
two alternatives are possible: (1) extract heat
from the hot furnace gases before collection
and reintroduce the extracted heat after
collection as stack gas reheat. Such a scheme,
60
-------
which involves the use of gas-to-gas heat
exchangers, reduces both absolute and relative
humidity of the stack gases and improves
their dispersion capability at the same time
(such systems have been used on
incinerators); (2) dehumidify the saturated
flue gases by subcooling below the normal
scrubber outlet temperatures. Cooling
requires the use of a packed cooling tower
and a source of cooling water below the wet
scrubber exhaust gas temperature.
Dehumidification of the stack gases can be
achieved by this method, water can be
recovered and recycled, and the operating
horsepower of high pressure drop fans can be
reduced. Dehumidification systems have been
used with success in other applications, but
have not, as yet, been utilized on incinerators.
REFERENCES
1. STENBURG, R. L., R. P. HANGEBRAUCK, D. J. VON
LEHMDEN, and A. H. ROSE, JR. Field evaluation
of combustion ail effects on atmospheric emissions
from municipal incinerators. Journal of the Air
Pollution Control Association, 12(2):83-89, Feb.
1962.
2. KAISER, E. R. Refuse composition and flue-gas
analyses from municipal incinerators. In
Proceedings; 1964 National Incinerator Conference,
New York, May 18-20, 1964. American Society of
Mechanical Engineers, p. 35-51.
3. WALKER, A. B., and F. W. SCHMITZ. Characteristics
of furnace emissions from large,
mechanically-stoked municipal incinerators. In
Proceedings; 1966 National Incinerator Conference,
New York, May 1-4, 1966. American Society of
Mechanical Engineers, p. 64-73.
4. STANFORD RESEARCH INSTITUTE. The smog
problem in Los Angeles County. Los Angeles,
Western Oil and Gas Association, 1954. 134 p.
5. STEPHENSON, J. W., and A. S. CAFIERO. Municipal
incinerator design practices and trends. In
Proceedings; 1966 National Incinerator Converence,
New York, May 1-4, 1966. American Society of
Mechanical Engineers, p. 1-38.
6. KUDLICH, R. Ringelmann smoke chart. Rev. by L. R.
Burdick. U.S. Bureau of Mines Information Circular
7718 (Rev. of 1C 6888). [Washington], U.S.
Department of the Interior, Mar. 1955. 4 p.
7. CONNER, W. D., and J. R. HODKINSON. Optical
properties and visual effects of smoke-stack plumes.
Public Health Service Publication No. 999-AP-30.
Cincinnati, U.S. Department of Health, Education,
and Welfare, 1967. 89 p.
8. U.S. DEPARTMENT OF HEALTH, EDUCATION,
AND WELFARE, PUBLIC HEALTH SERVICE,
DIVISION OF AIR POLLUTION. Equivalent
opacity—a useful and effective concept for
regulating visible air pollutant emissions. Presented
at East-West Gateway Coordinating Council
Hearings on the Proposed Interstate Air Pollution
Study Recommendations, St. Louis, Sept. 27,
1966. 13 p.
9. CAROTTI.A. Unpublished data, 1968.
10. JENS, W., and F. R. REHM. Municipal incineration
and air pollution control. In Proceedings; 1966
National Incinerator Conference, New York, May
1-4, 1966. American Society of Mechanical
Engineers, p. 74-83.
11. MANDELBAUM, H. Incinerators can meet tougher
standards. American City, 82(8):97-98, Aug. 1967.
12. FERNANDES, J. H. Incinerator air pollution control
equipment. Pt. 5, v. 4. In Combustion Engineering,
Inc. Technical-economic study of solid waste
disposal needs and practices. Public Health Service
Publication No. 1886. Washington, U.S.
Government Printing Office, 1969. 705 p.
13. BUMP, R. L. Conditioning refractory furnace gases for
electrostatic precipitator application. In
Proceedings; 1968 National Incinerator Conference,
New York, May 5-8, 1968. American Society of
Mechanical Engineers, p. 23-33.
14. BUMP, R. L. The use of electrostatic precipitators for
incinerator gas cleaning in Europe. In Proceedings;
1966 National Incinerator Conference, New York,
May 1-4, 1966. American Society of Mechanical
Engineers, p. 161-166.
15. WALKER, A. B. Electrostatic fly ash precipitation for
municipal incinerators—a pilot plant study. In
Proceedings; 1964 National Incinerator Conference.
New York, May 18-20, 1964. American Society of
Mechanical Engineers, p. 13-19.
61
-------
CHAPTER XIII
ACCEPTANCE EVALUATION
Acceptance evaluation is an appraisal ol an
incinerator (that can be formed) based on
inspection and tests during construction and
again at the completion of the project. The
primary purpose of this evaluation is the
determination that all provisions of the
contract are being met and that the
incinerator performance meets the
specifications. The method or means of
making the acceptance evaluation are
provided for in the terms of the contract.
Construction materials and workmanship
are inspected and evaluated from beginning of
construction through completion. Individual
mechanical components of the system such as
fans, grates, valves, etc., are certified by the
manufacturer but should also be inspected
and checked on the job. The performance of
the incinerator, however, cannot be evaluated
until all components of the system are
assembled within the completed structure, at
which time a performance or operational test
is conducted. Tests are commonly run
simultaneously on all components of the
incinerator system.
Many municipal incinerators now in
operation were built as a "package deal." The
incinerator contractor supplied design,
equipment, and facility construction, to
produce an end result of "system
performance" specifically detailed by the
owner. The contractor was responsible for all
phases of design, component selection,
assembly, construction, and final performance.
Because incinerators are now more
complex, the current trend is to employ
services of a consulting engineer to design the
incinerator system to meet the owner's
requirements. In this case, the consultant
specifies each component and how each is
related to the other. The contractor, then, is
responsible for construction and assembly of
equipment and components in accord with
the details of the designer's plans and
specifications and may not be required or
expected to ensure that the incinerator will
meet performance type requirements; this is
the responsibility of the design consultant. In
the absence of an expressed guarantee by the
contractor that the finished job will perform
as specified, all the contractor is responsible
for is that he has complied with the plans and
specifications prepared by the consultant. If
unsatisfactory performance is a matter of
negligent design, the consultant can be held
responsible.
Whether the incinerator is built by
"consulting design" or as a "package deal,"
evaluation must be conducted throughout
construction. Defective construction materials
and faulty construction methods must be
uncovered and corrected at this stage because
often corrections cannot be made later. Even
where corrections are possible after
construction is completed, they are always
expensive. Therefore, the owner should
obtain the services of a contractor who has
demonstrated his capabilities. Both the
contractor and the design consultant are
responsible for acts of negligence.
Equipment selection is often determined by
the manufacturer's willingness to guarantee
and accept responsibility for equipment
performance. Manufacturers, however, seldom
62
-------
make blanket guarantees. In air pollution
control, for example, a manufacturer will not
state that his equipment will produce a
visually clear stack effluent. He will, however,
usually be willing to guarantee that his
equipment will remove a fixed percentage of
particulates based on standard tests. This
distinction should be considered in writing
specifications.
Before performance specifications become
part of the bid proposal, they should be
reviewed by the community's engineering
staff to determine that the specified
performance will meet the antipollution and
other requirements of the community. Legal
aspects of the contract should be reviewed
with particular emphasis on the
responsibilities and liabilities of all parties
involved.
A "shakedown period" between completion
of the incinerator and final acceptance testing
or evaluation is usually required. This period
commonly ranges from 30 to 90 days. Since
there may be a lag period between completion
and acceptance, the effective date of
mechanical equipment warrantees should be
agreed upon and included in the contract.
The incinerator designer and plant
personnel commonly participate in the
acceptance evaluation test. The acceptance
test should be conducted under the range of
conditions expected to occur during normal
operation. In the acceptance evaluation of a
"package deal," it is advisable to bring in an
unbiased third party to determine contract
compliance.
The acceptance procedure varies with the
community. Usually a community does not
take over operation until the plant is
accepted; however, the community should
have personnel present for training. If the
acceptance test fails, a specified time should
be given to rectify the situation before
penalities or liquidation damages are applied.
Today, there are no consistent performance
tests to be used for municipal incinerator
acceptance procedure. The methodology for
performing various tests, such as stack
sampling for particulates and determining
residue and effluent water characteristics,
have not been standardized. To meet this
need, the American Society of Mechanical
Engineers and the Bureau of Solid Waste
Management are currently developing tests
and procedures for evaluating incinerators.
63
-------
CHAPTER XIV
SOLID WASTES THAT REQUIRE SPECIAL CONSIDERATION
Solid waste may contain combustible items
such as discarded furniture, mattresses,
automobile and truck tires, tree stumps, logs
and large branches, demolition lumber, and
industrial boxes, crates, and skids. Solid waste
may also contain a variety of noncombustible
items such as stoves, refrigerators, water
heater tanks, and metal furniture. These items
are classified as "bulky solid waste." Because
they are too large, would not burn
sufficiently in the normal process time, or
might damage or interfere with the
incinerator mechanism, it is impractical and
often impossible to process bulky
combustible wastes at conventional municipal
incinerators. Municipal solid waste also
contains materials that in their collection and
disposal may be potentially injurious and
therefore deserve special consideration. These
are classified as "hazardous wastes" and
include radioactive materials, toxic chemicals,
and highly flammable or explosive materials.
Other municipal wastes that require special
consideration include obnoxious substances,
such as pathological wastes, and various
sludges.
Bulky Solid Waste
Some municipalities dispose of their bulky
waste by sanitary land-filling; some practice
open burning of the combustible bulky items.
Where long haul distance is involved or where
land is scarce, land disposal of bulky waste
can be quite expensive. Because it is
potentially dangerous and causes air
pollution, open burning is a poor solution.
Some communities have evaded the problem
by refusing to collect bulky items. This
approach results in illicit dumping or open
burning.
Special Incinerators for Bulky Waste
Several cities are now using special
incinerators for oversized burnable waste.1
The incinerators are refractory lined and have
a refractory hearth. Charging is by the batch
method and burning time is varied to suit the
materials. Auxiliary fuel has been used to
ignite the solid waste, and in some cases, to
ensure complete combustion; however, the
bulky waste usually burns readily without the
assistance of auxiliary fuel. Charge size is
•limited by furnace dimension and maximum
size of any object is controlled by the
dimensions of the door opening.
Size Reduction of Bulky Solid Waste
Preparation of combustible bulky items for
burning in a conventional incinerator requires
reduction to fragments that can be easily
handled mechanically and that will be burned
in the normal process time. Equipment used
for size reduction has included shears, impact
mills, hammermills, flailmills, and chipping
devices such as the "wood hog."
Because of the wide variety of items that
constitute bulky solid waste and the
heterogeneity of materials making up
individual items, size reduction has been of
only limited success. Some impact mills,
64
-------
hammermills, and chippers are capable of
processing presplit logs and presplit stumps,
wood pallets and crates, demolition lumber,
and large wood furniture to suitable size for
burning. Generally, this equipment has not
been satisfactory in reducing heavy
metal-framed burnable furniture and
mattresses containing heavy steel framing and
springs. Some shearing equipment can reduce
bulky waste containing steel, such as
innerspring mattresses, to fragments of size
suitable for acceptable burnout when these
fragments are intermixed with other solid
waste. The noncombustible portion of the
processed material does not interfere with
incinerator mechanism.
Although the capability of size reduction
equipment for bulky solid waste has been
demonstrated, the practicality of some of
these methods has not been established. An
exception is shredding equipment for tree
branches; this equipment has been
successfully used for years.
The operation of most heavy equipment
used for size reduction is extremely noisy and
dusty. Heavy, fast-moving parts are inherent
to most of the processes. Where such
equipment is used, extreme care must be
taken to provide for the worker's safety. Most
operations require dust control and noise
insulation.
Hazardous Wastes
Hazardous wastes are those that are
potentially injurious such as highly flammable
or explosive materials, toxic chemicals, and
radioactive materials. Many hazardous wastes
can be routinely handled in small quantities at
the incinerator without creating problems.
For example, when a half-full gallon-can of
volatile paint is heated in an incinerator, the
only result would probably be the lid blowing
off. The burning of the small quantity of
released paint would create no problems.
However, a 5-gal drum of volatile paint or
other flammable liquid could cause
considerable damage to the furnace and could
injure the workers. Pressurized cans, so
common today, generally cause no damage to
the furnace when they "pop." They can,
however, be dangerous to workmen when
metal fragments are blown through furnace
openings. Other hazardous wastes include
gasoline, kerosene, oil, and other flammable
liquids; sawdust and wood shavings;
flammable plastics, especially when finely
divided; rubber dust; and flour and
magnesium shavings.
Because it would be practically impossible
to prevent all hazardous materials from
entering the incinerator, precaution must be
taken to minimize danger. Large quantities of
hazardous wastes can be avoided by
prohibiting those generated by industry or by
making special provisions for them if they are
accepted. A safer, and often more
economical, method is to establish a
partnership between industry and local
government for central disposal of industrial
wastes.
Even where hazardous industrial wastes are
prohibited, municipal incinerators will
occasionally receive dangerous materials from
the residential community. The waste
collectors will often be in the best position to
detect possible hazardous wastes and alert the
incinerator personnel. If suspected hazardous
wastes are inadvertently dumped into the pit,
they must be removed or mixed with the
contents of the storage pit until they are at a
safe concentration.
A municipal incinerator should not accept
radioactive wastes. The handling and disposal
of all radioactive wastes must be carried out
in accordance with recognized standards and
procedures outlined by the Atomic Energy
Commission or other responsible agency.
Obnoxious Wastes
Obnoxious wastes are those that are so
highly objectionable and unpleasant from the
standpoint of appearance, health effects, or
65
-------
odor that they should not be handled in the
conventional municipal incinerator without
special provisions. Certain wastes generated
by hospitals and medical laboratories can be
obnoxious and dangerous (disease bearing).
These include anatomical wastes, surgical
dressings, sputum cups, stool specimens, and
other test specimens. Most hospitals dispose
of these wastes in pathological incinerators.
Slaughterhouses, butcher shops, and other
food processing plants generate quantities of
obnoxious wastes that have a high moisture
content, are highly putrescible, and may
contain pathogens. Most slaughterhouses
dispose of their wastes by special drying
equipment and incineration. In many large
cities, wastes from slaughterhouses and
butcher shops are collected by private
agencies for rendering and reduction for the
production of fats, glycerine, detergents, etc.
Dead farm animals and domestic animals may
also be collected for this purpose.
With the exception of small birds and mice,
dead animals are too large and dense to be
consumed in the conventional municipal
incinerator process. Some cities have special
batch-fed incinerators for burning dead
animals and obnoxious substances, including
hospital wastes. At some incinerators,
refrigerators are provided for storing dead
animals for periodic cremation. Some
incinerators have access to a hearth in the
secondary combustion zone where the
animals can be placed until cremated by the
hot gases and flame.
Combined Sewage Sludge—Solid
Waste Incineration
Like municipal solid waste, the amount of
sewage in this country is increasing each year.
The cost of ultimate disposal of sewage sludge
and associated wastes is increasing as land
becomes less available. Sludge incineration has
been practiced for many years for volume
reduction.
A method of disposal still under
investigation is the combined incineration of
intermixed sewage sludge, screenings, greases,
and scums with municipal solid waste. Some
cities in the United States have used
combined solid waste-sewage sludge
incineration methods.2 The potential cost
savings is based primarily on using the excess
heat generated from burning the solid waste
to dry the partially dewatered sludge and thus
allow it to burn readily. Other potential
savings result from the use of a single facility
instead of separate incinerators. Although the
combined incineration process appears
economical, three factors must be considered:
(1) hauling costs; (2) sewage sludge moisture;
(3) waste production rates that affect uniform
blending of the two materials, each of which
is variable in itself.
Conclusions
There are obviously many more wastes that
require special considerations by the
incinerator designer and operators. The
engineer must vary his design according to the
wastes that may be handled over the life of
the plant. To do this, he must have accurate
information on the quantity and composition
of the wastes. Incinerator design and
operation will become increasingly more
complex and challenging as communities
strive for the single method or single system
capable of handling all wastes.
REFERENCES
1. KAISER, E. R. The incineration of bulky refuse. In
Proceedings; 1966 National Incinerator Conference,
New York, May 1-4, 1966. American Society of
Mechanical Engineers, p. 39-48.
2. BURD, R. S. A study of sludge handling and disposal.
Publication WP-20-4. [Washington], U.S.
Department of the Interior, Federal Water Pollution
Control Administration, May 1968. p. 289-293.
66
-------
CHAPTER XV
SALVAGE
Salvage is the recovery of waste goods.
Since most of our solid waste contain
materials of value, waste disposal officials
should consider salvage of waste materials.
Many municipalities have practiced salvage.
Some of these operations have been
profitable; others have become inefficient and
a nuisance. Thus, the decision to use salvage
and reclamation should be based on a
thorough engineering cost and marketing
study. In no case should such an operation
seriously interfere with the major objective of
solid waste disposal.
The major materials occurring in municipal
solid waste that may be of value in a salvage
operation include ferrous and nonferrous
metals, paper, rags, glass, rubber, plastics, and
food waste. If all of the materials of value
were recovered, the process or operation
would be classified as "total salvage." Total
salvage has been practiced in the United
States, but generally, it has not been
successful. In many cases, "partial salvage"
has met with variable degrees of success and is
currently being practiced. Partial salvage is the
selective recovery from solid waste of one or
more constituents that have economic value.
In connection with incineration, the most
commonly salvaged material is ferrous metal.
Total salvage in the United States has failed
because it has been uneconomical. The
market value of salvage materials has
fluctuated severely and some fractions have
lost their value completely. The makeup of
incoming solid waste is also subject to
extreme variation. Materials of value tend to
disappear from refuse when the market is
attractive. Schools and charitable
organizations conduct drives to collect
newspapers and magazines or scrap metal.
Where permitted, private collectors and
scavengers collect metal, rags, and paper for
resale. Conversely, when the market price is
low, the municipality will be responsible for
collection and disposal of larger amounts of
paper.
Total salvage is a costly operation. Because
of the heterogeneity of solid waste, the
process requires a great amount of hand labor.
Labor costs have continuously increased
whereas, generally, the overall market value of
salvaged material has declined. Mechanization
and semiautomation techniques in total
salvage have not reduced labor cost
sufficiently to justify the process.
Municipal officials are hesitant about
investing tax monies in projects as uncertain
as total salvage. Also, because many salvage
operations have been unsightly and have
resulted in public health problems, the public
is also apprehensive of proposed salvage
operations. In spite of these uncertainties and
the poor record of past performances, salvage
deserves further attention. Theoretically, it is
an ideal solution to the solid waste problem
and allows conservation of natural resources.
Partial salvage has been conducted either
before or after incineration. Rising labor
costs, declining salvage market, and variation
in solid waste composition have affected
partial salvage in much the same way as total
salvage.
Removal of some constituents before
incineration may affect the combustion
process. An increasingly large portion of
municipal solid waste is paper, which provides
67
-------
most of the combustibles at an incinerator.
Thus, removing paper would lower the heat
value of solid waste and the furnace would
have to be designed accordingly. An
incinerator designed to handle only
nonsalvageable materials would be inadequate
to handle all solid waste when the salvage
market fell too low to justify salvage
operations. Similarly, an incinerator capable
of handling all solid waste would be
inefficiently utilized when a high proportion
of the constituents are removed.
Noncombustibles such as cans and bottles are
believed to aid the incinerator combustion
process by creating voids in the fuel bed, thus
providing for more uniform burning.
Removing these items before incineration
might decrease the burning rate.
Salvage of metal after incineration has been
successfully conducted at some incinerators.
A major advantage of this method is that the
volume of material to be processed has been
reduced considerably. Other advantages are
that the after-incineration process is
esthetically more acceptable; the burning
process removes much of the undesirable
combustible material from the salvage; the
primary disposal process, incineration, is not
dependent on salvage; and failure of salvage
equipment or failure of the salvage market
will not directly affect the incineration
process for the salvage operation could be
bypassed and all residue could be disposed of
without making major changes in the
operation.
Including a salvage operation with
incineration can reduce residue volume and
salvage may provide an economic return. The
success of salvage depends on the size of the
operation, the type of incineration, salvage
plant design and operation, the market for
salvaged materials, and the shipping cost to
the point of usage.
-------
CHAPTER XVI
OPERATION AND MAINTENANCE
Management and Personnel
As a community plans and builds an
incinerator, it should also plan for the
management and personnel necessary to
operate it. The plant supervisor should be
employed several months before construction
is completed so that he can become
thoroughly familiar with each major
incinerator 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 incinerator is in the
latter stages of construction and put through
the acceptance tests. In this way, the
incinerator personnel can be trained in proper
operation, maintenance, and repair.
At the outset the management, and this
includes 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. Several methods of
job classification exist; whatever method is
used should have sufficient flexibility so that
incinerator personnel can be used for various
jobs. Rigid job titles that tend to limit
operating personnel duties should be avoided.
Staffing needs vary with the size and type
of incinerator, number of shifts, organized
labor regulations (including working hours,
vacations, fringe benefits), and the extent of
plant subsidiary operations, such as heat
recovery and salvage. The total man-hours
required in efficient operation range from 0.5
to 0.75 per ton of solid waste processed. This
does not include man-hours for residue
disposal and major repair work.
Management needs to provide sufficient
employment incentives. An acceptable
working environment, equitable pay,
advancement, opportunities and training,
retirement and other fringe benefits, and
employment security are essential.
Operation Guides
Flow Diagram. Every plant should post a
scaled engineering drawing, pictorial drawing,
or scale model of the plant, showing all major
components by name and function. This
diagram or scale model should illustrate how
the solid waste and its resulting gases and
residues pass through the plant, so that plant
personnel and visitors may readily understand
the various components and how they
function together.
Drawings. The local solid waste disposal
operating agency should have copies of all
engineering drawings, showing the plant and
all its components. At least one set of formal
drawings should be maintained at the plant
for reference by operational and maintenance
personnel.
Operation and Maintenance Manuals;
Equipment Manuals. Equipment manuals,
catalogs, and spare parts lists should be kept
at the incinerator for quick reference by
employees. A manual describing the various
tasks that must be performed during a typical
shift and the safety precautions and
procedures for working in various areas of the
plant should also be kept on hand.
69
-------
Performance Records
Criteria that may be used for evaluating
incinerator operation are residue
characteristics (physical and chemical),
volume and weight reduction of original solid
waste, amount of pollutants released to the
environment, various operating costs per ton
of solid waste processed, and efficiency of
heat recovery equipment or other subsidiary
operations. The use of these criteria require
that the following data be recorded.
Incoming Solid Waste. Plant records
should indicate the total weight of solid waste
received during each shift as well as the
number of vehicles arriving, identity of
vehicles, and the source and nature of solid
waste received.
Furnace-Burning Rate, Temperature, and
Air Flow Rates. Furnace operators should
record furnace temperature at frequent
intervals unless such data is recorded
automatically. Explanations should be
provided for prolonged temperatures above
1,800 F or below 1,200 F Grate speeds (or
rate of operation) should be noted
throughout the shift. Air 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 (draft in inches of
water, grate function in amperes, etc.), and so
such data must be interpreted in terms of
settings required for good furnace operation.
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.
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.
Power Consumption and
Generation. Flectncity may be metcrcd at
major units to pinpoint those equipment
malfunctions that are manifested by changes
in power consumption. Power for
electrostatic preeipitators and large electrical
motors should be separately mete red. If
power is generated, generator records should
be kept.
Steam Generation. If steam is generated,
flow meters should be installed to record
production. Hours of operation at specified
rates may be used, as well.
Stack Discharges. Records of stack
discharge characteristics commonly include
smoke indicator readings, Ringelmann
readings, and analyses from stack samplings
for participate emission.
Personnel Records. Accurate personnel
time and cost records should be kept so that
incinerator performance can be evaluated on
the basis of operating cost per ton and on the
basis of man-hours per ton. The direct and
indirect costs should be added to the total
cost of incinerator operation.
Supplies, Material, and Equipment. All
supplies, material, and equipment utilized in
incinerator operation and maintenance should
be recorded and charged against the
incinerator, even though provisions or
purchases may be made by another
department. Major incinerator maintenance
(such as rebuilding of refractories), whether
done by contract or by plant personnel,
should be recorded as cost items separate
from incinerator operation. Thus, both the
cost of repairs and maintenance and the cost
of plant operation can be determined.
Utilization of Recorded Data
Recorded data provide a permanent means
of evaluating incinerator performance. This
evaluation is needed to guide the day-to-day
operation and can also be used for making
70
-------
important adjustments in equipment,
operating procedures, and personnel
assignments, and periodic reports to the local
government.
Maintenance and Repairs
Records. A records system 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 permanent 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.
Inspection and Repairs. 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 furnace, repairs
performed, and expectation of future repairs
or major overhaul. Plant performance records
and maintenance files can be used to
determine when major repairs are necessary.
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 an approved disposal
site or to other incinerators. Ideally, extensive
repairs should be scheduled during the season
when waste generation is lowest.
Plant personnel will not normally be
expected 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 general wear and tear accumulates to
the point that continued operation is no
longer economically feasible or prudent
without major reconstruction, 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 with new
development and decide whether the
incinerator 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 redesign and reconstruction has been the
exception rather than the rule.
In many instances, incinerators 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. 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
71
-------
bulbs should be kept clean to provide
acceptable illumination at all times. Auxiliary
lighting equipment should be maintained for
inspection purposes and for use in
emergencies.
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 5 and 10 percent of
the total cost of operation, split about equally
between labor and materials. Good
management will budget for annual
maintenance and repair work, including
periodic major
modernization.2
replacements and
REFERENCES
i.
European developments in refuse
Public Works, 97(5):113-117, May
ROGUS, C. A.
incineration.
1966.
2. ROGUS, C. A. Incinerator design. Municipal solid waste
disposal. Part 3. American City, 77(4): 104-106,
Apr. 1962. Part 4. American City, 77(5):106-108'
May 1962.
72
-------
APPENDIX A
for
in.oin.era,tor
Eric R. Zausner*
Effective solid waste management requires an adequate
information system including data on activity and the costs
of operation and ownership. Although a cost accounting
system represents only one part of the total system, it does
facilitate the collection and later utilization of the data
obtained.
Present information on incineration and its associated costs
is both inadequate and nonslandardized. The proposed
system provides a guide to the type and quantity of informa-
tion to be collected, its classification, and the method of col-
lection. Incinerator supervisors and heads of agencies re-
sponsible for their operations will find the system useful.
A cost accounting system can aid a community in con-
trolling the costs and performance of its incinerator opera-
tions, as well as aid in formulating future plans.
Chief, Management Sciences Section, Operational Analysis Branch, Division of Tech-
nical Operations, Bureau of Solid Waste Management.
73
-------
System Benefits
Some of ihe more important advantages are:
1. The system facilitates orderly and efficient collection and
transmission of all relevant data. In fact, most of the data
recorded is probably being collected already, although per-
haps only sporadically and inefficiently. Hence, the added
cost of installing the proposed system is minimal.
2. Reports are clear and concise and present only that
amount of data required for effective control and analysis.
They can easily be completed and understood by incinerator
personnel.
3. Interpretation of results and comparison with data from
previous years or from other communities is simplified. This
allows analysis of relative performance and indicates areas
where corrective action is needed.
4. The system accounts for all relevant costs of operation.
5. Because the system indicates high costs and their under-
lying causes, the supervisor can control costs more effec-
tively. Similarly, performance and efficiency may be moni-
tored and controlled.
6. Accountability is superimposed on the system to indicate
who is responsible for the increased costs.
7. The data provided are in a form that aids in short- and
long-range forecasting of operating and capital budgets.
Future requirements of equipment, manpower, cash, etc., can
be estimated to aid budgeting and planning at all levels of
municipal goverment.
8. The system, with only minor modifications, is flexible
enough to meet the varying requirements of incinerators of
different sizes.
Cost Centers and Cost Allocations
The complexity of incinerator operations requires a break-
down and description of operations to facilitate analysis. In
this report, the incinerator is assumed to consist of several
interrelated suboperalions, each of which is analyzed sep-
arately. These suboperations are called cost centers because
costs are accumulated separately for each of the major func-
tional activities. Analysis and control are simplified if ex-
cessive costs or inefficiencies can be traced to a functional
activity or area of the facility.
74
-------
The number of cost centers increases as the size and com-
plexity of operations increase. More cost centers, however,
require the collection of more data and, therefore, increase
costs. For most facilities, four cost centers appear to collect
adequate data without incurring excessive collection costs.
Three of the four cost centers (Receiving and Storage,
Volume Reduction, and Effluent Handling and Treatment)
are termed the direct cost centers because they can be di-
rectly associated with certain incinerator operations and unit
processes. The operations included in each follow the process
flow from input of raw wastes to output of effluents (Diagram
I). The fourth, the Repairs and Maintenance cost center, can-
not be directly associated with waste processing. Therefore,
it is separated from other operations and not shown in the
diagram. Because it incurs a large percentage of operating
costs, a separate analysis is needed.
Although fewer cost centers would never be required,
larger operations may require more cost centers. For instance,
the Effluent Handling and Treatment cost center could be
divided into Air Pollution, Water Treatment, and Residue
Handling cost centers. Similarly, salvage or heal utilization
operations should be put in separate cost centers.
These cost centers classify the operations by function. The
costs incurred are for labor, parts and supplies, utilities, and
overhead, and they must be allocated to the cost centers in
an accurate and representative manner (Diagram II). Note
that costs are first allocated to all four cost centers/ the Repairs
and Maintenance cost center is then allocated to the three
direct cost centers. The result is the total operating cost for
each direct cost center.
There are many alternatives for actually allocating the
operating costs. A straight-forward method for each type
of expense will be outlined. Labor costs may be allocated to
the four cost centers based on the relative number of hours
employees worked in each area and their respective wage
rales. Utilities may be allocated based on an engineering
estimate of the relative usage rales of ihe equipmenl in each
cost center. Bolh water and electricity should be allocated.
Parts and supplies will be allocated to each direct cost center
75
-------
DIAGRAM I
INCINERATOR COST CENTERS
Incomin
Solid waste
Stora
ge pit
GASES
WATER
RESIDU'
T
f
RECEIVING AND
STORAGE
COST CENTER
VOLUME
REDUCTION
COST CENTER
EFFLUENT HANDLING
AND TREATMENT
COST CENTER
-------
DIAGKAM II
ALLOCATION OF COSTS
Building and
improvement
cost
Equipment
cost
BSWM (10/69)
-------
after first being recorded in ihe Repairs and Maintenance cost
center. General overhead, which includes supervision, in-
surance, etc., can be allocated equally lo each cost center
or on the basis of the relative number of employees in each
cost center. The latter technique is recommended. Finally,
the Repairs and Maintenance cost center is allocated to the
three direct cost centers based on the actual expenses in-
curred in each one.
The sum of the costs of these three direct cost centers is the
total operating cost. The total annual cost of operations rep-
resents these operating costs plus the costs of financing and
ownership.
The actual forms are designed lo facilitate the collection
and later allocation of costs to these cost centers.
Forms and Reports
The reports are most easily grouped into those that are used
lo collect the data on operations and those used lo reduce
and present the data for the purposes of analysis, decision
making, and control.
This data reduction and presentation cannot be accom-
plished without the daily recording of all pertinent activity
and cost information. Data not recorded daily are not re-
trievable at some later dale. Incinerator personnel, super-
visors, and others involved in operations primarily use the
following forms (1 through 4) lo record the data required.
Weekly Labor Report (Form 1). Daily entries of labor ac-
tivity are recorded in duplicate at the site. One copy is for-
warded lo ihe payroll deparlmenl for determining weekly
wages. The incinerator supervisor and ihe accounling de-
partment use the other copy for compuling lolal labor hours
and assigning ihese hours and associated cosls lo ihe four
cost centers.
Daily Truck Record (Form 2). The wasle received and resi-
due removed, as well as ihe types and sources of waste re-
ceived, are recorded manually on this form for ihe entire
day. (If ihe incineralor has a scale thai automatically records
the weight informalion, thai part of ihe form would be re-
placed by ihe weight lickel or record of the scale.) Each
delivery is recorded separately by ihe weighmaster. A
78
-------
FORM 1
WEEKLY LABOR REPORT
INCINERATOR:
SIGNATURE: _
DATE:
SHIFT: .
Employee
ident
-0
vo
Tot
Day 1
Cost
center
X
Hours
Day 2
Cost
center
X
Hours
Day 3
Cost
center
X
Hours
Day 4
Cost
center
X
Hours
DayS
Cost
center
X
Hours
Day 6
Cost
center
X
Hours
Day?
Cost
center
X
Hours
Individual
totals
Comments (Note causes
and hours of absence, etc.)
xxxxxxxxxxxxxxx
Instructions: Incinerator supervisor to complete this form daily. List all em-
ployees separately including temporary help. "Hours" refers to hours worked
daily. At the end of each week forward one copy to the payroll department and
retain the original for further use.
Abbreviations of cost centers and workers to be assigned to each: R&S =
receiving and storage: crane operator, weightmaster, tipping floor, and charging
attendants. VR = volume reduction: stokers, control monitors, etc. EHT =
effluent handling: residue haulers, disposal site operators, etc. R& M = repairs and
maintenance: include all general maintenance workers and part time repairmen.
BSWM (10/69)
-------
DAILY TRUCK RECORD
FORM 2
INCINERATOR: .
DATE:
SIGNATURE: .
SHIFT:
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
12
15
16
17
18
19
20
Truck *
identification
Totals
Time
X
Wastes
Source
X
Type*
X
Weight
in
X
Weight out
(or tare weight)
X
Net amount
Wastes
Residue
Instruction: To be completed by weighmaster for each delivery of waste or
removal of residue.
'Truck identification is number of the public truck; if private vehicle, the name
of company for billing purposes.
t Source: R - residential; C - commerical; I industrial.
t Type: R rubbish; G garbage (also unusual items).
80
BSWM (10/69)
-------
second weighing of the empty truck may be taken or the
vehicle's tare weight (as officially determined by a licensing
agency, etc.) may be substituted. The form is forwarded to
the accounting department at the end of each month. In
addition to utilizing recorded weight data to bill private users
later, the sources and types of waste data are useful in special
analyses of trends, compositions, and distributions of solid
wastes in the community.
Daily Report on Incinerator Operations (Form 3). When
there is actual downtime and repairs are required, the ex-
penses that will be allocated to the three direct cost centers
are recorded on the lower half of the two-purpose report.
These data are particularly useful in analyzing equipment
performance and cost. In addition, data on utility usage are
recorded on the form at the end of each month.
The lop of the report is used to summarize the daily oper-
ations. The employee and activity data give management
personnel who are not at the site daily, but who still require
daily feedback on operations, a quick and accurate summary
of the day's activities. The performance data are also useful
in assessing daily efficiency. The report is completed daily,
sent to the main office, and filed for later use.
Incinerator Capital Investment Report (Form 4). This form
is completed when construction is finished or when the cost
system is first implemented. Only when improvements or
new equipment are either constructed or purchased is it
updated. In addition to collecting the data required to cal-
culate depreciation for the period and allocating it to cost
centers, the form also summarizes the bond and interest in-
formation required to compute the total costs of financing
and ownership.
For the most part, Forms 1 through 4 are utilized to collect
the data associated with the construction and operation of an
incinerator. The cost of accumulating these data can only
be justified by its intensive and effective utilization. This is
accomplished by meaningful data reduction and presenta-
tion. The data must be presented clearly and quickly to the
personnel who can use it most effectively for analyses and
81
-------
FORM 3
DAILY REPORT ON INCINERATOR OPERATIONS
SITE:
DATE:
PERFORMANCE DATA
% Weight reduction ( ^''burned ):
Man hours per ton:
Tons of residue per trip:
Number of injuries:
EMPLOYEE HOURS
Cost center
Receiving
Volume
reduction
Effluent
Repairs
Totals
Shift
1
2
3
4
ACTIVITY DATA
Wastes received
Wastes burned
Left in pit
Residue
Loads
Tons
REPAIRS AND MAINTENANCE DATA
Equipment
description
Cost
center
Cause
Hours
down
Labor
hours
Labor
cost
Parts
cost
External
costs
Total
cost
UTILITY DATA
(Only complete this section at the end of the month)
Electric
Gas
Water
Meter reading
82
BSWM (10/69)
-------
FORM 4
INCINERATOR CAPITAL INVESTMENT REPORT
INCINERATOR;
DATE:.
Description
Site:
Land
Surveys
Preparation
Roads
Other
Buildings:
Scale house
Pit
Offices
Main building
Stacks
Other
Equipment:
Scales
Crane(s)
Furnace(s)
Air pollution
Water treatment
Residue removal (including vehicles)
Instrumentation and control
Other
Totals
Size, capacity,
amount, etc.
X
Date put
in use
X
Estimated
total life
X
New cost
Other
comments
X
Yearly
depreciation
X
^^^mmz
Monthly
depreciation
X
FINANCING DATA
Bond type
Face value
Premium
or discount
Interest rate
Yearly interest*
Monthly interest
Instructions: To be completed by supervisor or accounting department. Depreci-
ation may be straight-line or on an accelerated basis.
* Interest must account for net effect of premium or discount on bond sale.
83
BSWM (10/69)
-------
control. The following forms (as well as Form 3) are designed
lo fulfill these objectives.
Incinerator Operations Summary (Form 5). This form sum-
marizes six distinct groups of information about incinerator
operations for a specific period. For control purposes, monthly
reports would be desirable, although less frequent prepara-
tion would be possible. The first two segments present
activity and operating cost data for the total operation. Costs
are broken down by lype lo aid the cost analysis, and the
activity and performance factors are designed to help
analyze inefficiencies and performance. The remaining four
sections break the costs into the four cost centers. Total oper-
ating costs are presented for each area as are other factors
that may be useful lo analyze the functional activities. Obvi-
ously, there are many other factors and costs that could be
presented. The ones illustrated, however, are adequate for
mosl analyses. Nonetheless, modifications or additions should
be made for facilities with different operations and data
requirements.
This form, designed for control purposes, contains only
controllable expenses for which the supervisor can be held
accountable/ capital or financing costs are not included. The
form is prepared by the accounting department from the data
in Forms 1, 2, and 3 and additional data on file concerning
labor rales, insurance, fringe benefits and charges from other
departments, external expense billings, elc. Copies of the
form are forwarded to both the facility supervisor and lo his
superior. Analysis of the form indicates excessive expenses
and aids ihe supervisor in taking corrective aclion.
Incinerator Total Cost Report (Form 6). All the activities
and costs incurred by the incinerator during the period are
summarized from data in present and pasl Incinerator Opera-
lions Summaries (Form 5) and from the deprecialion and
interest data available in the Incinerator Capital Investment
Report (Form 4). Semiannual and annual preparation would
be sufficient. Form 6 — Alternate can be used if disposal
charges or other lypes of revenues are associated with incin-
erator operations.
84
-------
FORM 5
INCINERATOR:
INCINERATOR OPERATIONS SUMMARY
REPORT PERIOD: from
to
ACTIVITY AND PERFORMANCE
Tons incinerated
% Weight reduction
Total labor hours
% Capacity utilized
% Capacity available
% Utilized/% available
Actual amount
-i- % Budget variance
OPERATING COST TOTALS
Total operating cost
Total labor cost
Utilities cost
Parts and supplies
Outside charges
Overhead
Actual amount
± % Budget variance
RECEIVING COSTS
Total operating cost per ton
Labor hours
Actual amount
± % Budget variance
VOLUME REDUCTION COSTS
Total operating cost per ton
Labor hours
Average operating temperature
Actual amount
± % Budget variance
EFFLUENT HANDLING COSTS
Total operating cost per ton
Gallons of water per ton
Tons of residue per load
Actual amount
± % Budget variance
REPAIRS AND MAINTENACE COSTS
Total operating cost
Receiving repair costs
Volume reduction repair costs
Effluent handling repair costs
Actual amounts
± % Budget variance
BSWM (10/69)
85
-------
FORM 6
INCINERATOR TOTAL COST REPORT
SITE:
REPORT PERIOD:
from .
to
Data
Tons incinerated
Weight reduction
Total operating cost
Total financing
and ownership cost
Total cost
Operating cost per ton
Financing and ownership,
cost per ton
Total cost per ton
For this period
±% Variance from budget
for this period
Year to date
±% Variance from budget
for year to date
Instructions: To be completed by accounting department from data available
in "Incinerator Operations Summary" and "Incinerator Capital Investment Report"
when requested or periodically. Copy sent to city manager, head of department
of public works, or their equivalent.
BSWM (10/69)
-------
SITE:
INCINERATOR TOTAL COST SUMMARY
REPORT PERIOD: from.
FORM 6 — Alternate
to
Data
Tons of waste incinerated
Percent weight reduction
Total operating cost
Total financing and ownership cost
Total cost
Operating cost per ton
Financing and ownership cost per ton
Total cost per ton
Revenues — other communities
Revenues — private collectors
Revenues — miscellaneous
Total revenues
Total revenues per ton
Net cost (profit)
Net cost (profit) per ton
For this period
Budget — this period
Year to date
Budget — year to date
BSWM 10/69
-------
Summary of Information Flow
Operating dala are accumulated daily al the incinerator
site and transmitted periodically to the accounting depart-
ment. The accounting department combines these reports
with additional information it accumulates to get total oper-
ating costs. This summary is then returned to the supervisor
for his own use. Next, the accounting department combines
the operating cost dala with the depreciation and interest
cost data (from the Incinerator Capital Investment Reports)
to compute total costs for the period. This total cost informa-
tion is then given to the heads of departments of sanitation
and public works, or their equivalents.
System Utilization
Only with efficient and intensive utilization of the informa-
tion generated from the accounting system and forms can
the additional lime, effort, and money required to implemenl
and maintained the system be justified. The system's inten-
sive use promotes two major objectives: quality control and
cost control. Reduced costs must be accomplished without
deteriorating and operating quality. Similarly, quality is
interrelated with the costs of obtaining it.
All the factors thai affect the quality and effectiveness of
incinerator operations can be translated into costs. Amount
of volume reduction, residue characteristics, and the levels
of stack emissions and water pollution determine the quality
of operations. Cost control does not call for economizing at
the expense of quality. On the contrary, once a level of
acceptable operation has been determined along with the
attendant costs, the cost control system can help the super-
visor maintain that level of operation.
Effective cost control requires timely recognition of exces-
sive costs and identification of responsibility for the increased
costs. Comparing units costs (cost per ton of waste inciner-
ated) with both the current budget and the corresponding
period last year helps indicate excessive costs. The use of
unit cost facilitates the analysis of costs, independent of
changes in the level of activity. The cost-center breakdowns
help single out the responsible factor or person. This system
-------
allows both of ihese critical faclors to be determined; correc-
tive action may then be effectively initialed.
The Incinerator Total Cost Report (Form 6) can indicate to
the highest level of municipal management, i.e., the city
manager or the head of the sanitation department, if costs are
excessive. If so, the supervisor of the particular facility can
be held responsible to the extent that his operating costs
have increased. The supervisor, in turn, can analyze the
cause of this cost rise. He may trace the increased cost to
the type of cost, as well as the cost center, and possibly to
the employee or piece of equipment responsible. All of the
needed data are in Form 5 (the Incinerator Operations
Summary).
89
-------
APPENDIX B
Control of Air Pollution Originating
From Federal Installations
Announcement of Signing of Executive Order
11282,
May 26, 1966
President Johnson today signed an
Executive order requiring all Federal agencies
to take steps to prevent and control air
pollution from Federal installations.
The order directs the heads of all Federal
agencies to lead in the administration's efforts
to improve the quality of the Nation's air.
Today's order is similar to one the President
issued last November directing the Federal
Government to provide effective leadership in
the battle against water pollution.
The air pollution Executive order is the
result of extensive consultation with Federal
agencies and with industries affected by the
order. The Department of Health, Education,
and Welfare is issuing standards to supplement
the order, by setting precise limitations on
emissions which will be allowed from Federal
buildings and facilities.
Today's order requires that plans for new
Federal facilities and buildings in the United
States include provisions for air pollution
control measures necessary to comply with
the standards issued by the Department of
Health, Education, and Welfare. In addition,
the order directs the head of each agency to
examine existing installations and to present
to the Bureau of the Budget, by July 1, 1967,
an orderly schedule for bringing all such
installations up to the required standards.
In signing the order, the President stated
that the most difficult problem encountered
in writing the order was the lack of an
economically feasible technology for
controlling emissions of sulfur. The Federal
Government has proposed spending more
than $3 million in 1967 on research to
control sulfur emissions. This includes $1
million for designing four sulfur-removal pilot
plants, the construction of which plants
would cost a total of $8 million. The
President has directed the Secretaries of the
Interior and Health, Education, and Welfare
to explore with the Bureau of the Budget the
feasibility of increasing the Federal effort to
find a solution to the sulfur emission
problem.
The President said that a major part of the
responsibility for sulfur research rests with
the utilities, the coal and oil industries, and
other groups which will feel the economic
efforts of more stringent air pollution
regulations. He pointed out that these
industries had increased their expenditures for
air pollution research in the past few years,
but stated that much greater efforts are
needed.
The President emphasized that, although
there were great technological and economic
problems in the abatement of air pollution,
the battle for cleaner air remained a major
objective of his administration, and an
essential element in a better environment for
America.
NOTE: For the text of Executive Order 11282, see the
following item.
Control of Air Pollution Originating
From Federal Installations
Executive Order 11282. May 26, 1966
Prevention, Control, and Abatement of Air
Pollution by Federal Activities
By virtue of the authority vested in me as
President of the United States and in
furtherance of the purpose and policy of the
Clean Air Act, as amended (42 U.S.C. 1857),
it is ordered as follows:
Section 1. Policy. The heads of the
departments, agencies, and establishments of
the Executive Branch of the Government shall
provide leadership in the nationwide effort to
improve the quality of our air through the
91
-------
prevention, control, and abatement of air
pollution from Federal Government activities
in the United States. In order to achieve these
objectives—
( 1) Emissions to the atmosphere from
Federal facilities and buildings shall not be
permitted if such emissions endanger health
or welfare, and emissions which are likely to
be injurious or hazardous to people, animals,
vegetation, or property shall be minimized.
The procedures established in section 3 of this
Order shall be followed in minimizing
pollution from existing facilities and
buildings.
(2) New Federal facilities and buildings
shall be constructed so as to meet the
objectives prescribed by this Order and the
standards established pursuant to section 5 of
this Order.
(3) The Secretary of Health, Education,
and Welfare shall, in administering the Clean
Air Act, as amended, provide technical advice
and assistance to the heads of other
departments, agencies, and establishments in
connection with their duties and
responsibilities under this Order. The head of
each department, agency, and establishment
shall establish appropriate procedures for
securing advice from, and consulting with, the
Secretary of Health, Education, and Welfare.
(4) The head of each department, agency,
and establishment shall ensure compliance
with section 107(a) of the Clean Air Act, as
amended (42 U.S.C. 1857f(a)), which declares
it to be the intent of Congress that Federal
departments and agencies shall, to the extent
practicable and consistent with the interests
of the United States and within available
appropriations, cooperate with the
Department of Health, Education, and
Welfare and with any air pollution control
agency in preventing and controlling pollution
of the air.
Sec. 2. Procedures for new Federal facilities
and buildings. A request for funds to defray
the cost of designing and constructing new
facilities and buildings in the United States
shall be included in the annual budget
estimates of a department, agency, or
establishment only if such request includes
funds to defray the costs of such measures as
may be necessary to assure that the new
facility or building will meet the objectives
prescribed by this Order and the standards
established pursuant to section 5 of this
Order. Air pollution control needs shall be
considered in the initial stages of planning for
each new installation.
Sec. 3. Procedures for existing Federal
facilities and buildings, (a) In order to
facilitate budgeting for corrective and
preventive measures, the head of each
department, agency, and establishment shall
provide for an examination of all existing
facilities and buildings under his jurisdiction
in the United States and shall develop and
present to the Director of the Bureau of the
Budget, by July 1, 1967, a phased and orderly
plan for installing such improvements as may
be needed to prevent air pollution, or abate
such air pollution as may exist, with respect
to such buildings and facilities. Subsequent
revisions needed to keep any such plan up to
date shall be submitted to the Director of the
Bureau of the Budget with the annual report
required by paragraph (b) of this section.
Future construction work at each such
facility and the expected future use of the
facility shall be considered in developing such
a plan. Each such plan, and any revision
therein, shall be developed in consultation
with the Secretary of Health, Education, and
Welfare in order to ensure that adoption of
the measures proposed thereby will result in
the prevention or abatement of air pollution
in conformity with the objectives prescribed
by this Order and the standards prescribed
pursuant to section 5 of this Order.
(b) The head of each department, agency,
and establishment who has existing facilities
and buildings under his jurisdiction in the
United States shall present to the Director of
the Bureau of the Budget, by July 1, 1968,
and by the first of each fiscal year thereafter,
92
-------
an annual report describing progress of his
department, agency, or establishment in
accomplishing the objectives of its air
pollution abatement plan.
Sec. 4. Objectives for Federal facilities and
buildings, (a) Except for discharges of
radioactive emissions which are regulated by
the Atomic Energy Commission, Federal
facilities and buildings shall conform to the
air pollution standards prescribed by the State
or community in which they are located. If
State or local standards are not prescribed for
a particular location, or if the State or local
standards are less stringent than the standards
established pursuant to this Order, the
standards prescribed pursuant to section 5 of
this Order shall be followed.
(b) The emission of flyash and other
particulate matter shall be kept to a
minimum.
(c) Emission of sulfur oxides shall be
minimized to the extent practicable.
(d) Wherever appropriate, tall chimneys
shall be installed in order to reduce the
adverse effects of pollution. The
determination of chimney height shall be
based on air quality criteria, land use, and
meteorological, topographical, aesthetic, and
operating factors.
(e) Solid fuels and ash shall be stored and
handled so as not to release to the atmosphere
dust in significant quantities. Gasoline or any
volatile petroleum distillate or organic liquid
shall be stored and handled so as not to
release to the atmosphere vapor emissions in
significant quantities.
(f) In urban areas refuse shall not be
burned in open fires and in rural areas it shall
be disposed of in such a manner as to
reasonably minimize pollution. Refuse shall
not be left in dumps without being covered
with inert matter within a reasonably short
time. Whenever incinerators are used they
shall be of such design as will minimize
emission of pollutant dusts, fumes, or gases.
(g) Pollutant dusts, fumes, or gases (other
than those for which provision is made above)
shall not be discharged to the atmosphere in
quantities which will endanger health or
welfare.
(h) The head of each department, agency,
and establishment shall, with respect to each
installation in the United States under his
jurisdiction, take, or cause to be taken, such
action as may be necessary to ensure that
discharges of radioactive emissions to the
atmosphere are in accord with the rules,
regulations, or requirements of the Atomic
Energy Commission and the policies and
guidance of the Federal Radiation Council as
published in the Federal Register..
(i) In extraordinary cases where it may be
required in the public interest, the Secretary
of Health, Education, and Welfare may
exempt any Federal facility or building from
the objectives of paragraphs (a) through (g) of
this section.
Sec. 5. Standards, (a) The Secretary of
Health, Education, and Welfare shall prescribe
standards to implement the objectives
prescribed by paragraphs (a) through (g) of
section 4 of this Order. Such standards may
modify these objectives whenever the
Secretary of Health, Education, and Welfare
shall determine that such modifications are
necessary in the public interest and will not
significantly conflict with the intent of this
Order. Prior to issuing any changes in such
standards, the Secretary of Health, Education,
and Welfare shall consult with appropriate
Federal agencies and shall publish the
proposed changes in the Federal Register
thirty days prior to their issuance. All such
standards prescribed by the Secretary shall be
published in the Federal Register.
(b) The permits authorized by section
107(b) of the Clean Air Act, as amended (42
U.S.C. 1857f(b)), may be used to carry out
the purposes of this Order as the Secretary of
Health, Education, and Welfare may deem
appropriate.
93
-------
Sec. 6. Prior Executive Order
superseded. Executive Order No. 10779 of
August 20, 1958, is hereby superseded.
Lyndon B. Johnson
The White House
May 26, 1966
[Filed with the Office of the Federal Register, 8:49 a.m.,
May 27. 1966]
Title 42—PUBLIC HEALTH
Chapter I—Public Health Service, Department
of Health, Education, and Welfare
SUBCHAPTER F - Q U ARANTINE,
INSPECTION, AND LICENSING
PART 76-PREVENTION, CONTROL, AND
ABATEMENT OF AIR POLLUTION
FROM FEDERAL GOVERNMENT
ACTIVITIES: PERFORMANCE
STANDARDS AND TECHNIQUES OF
MEASUREMENT
Pursuant to section 5 of Executive Order
No. 11282, the Secretary of Health,
Education, and Welfare hereby amends
Subchapter F of Title 42, Code of Federal
Regulations, by adding a new Part 76, as
follows:
Sec.
76.1 Definitions.
76.2 Intent.
76.3 Applicability.
76.4 Combustion of fuel.
76.5 Sulfur oxides.
76.6 Stacks.
76.7 Storage and handling of fuels and ash.
76.8 Disposal of refuse.
76.9 Other pollution producing processes.
Authority: The provisions of this Part 76
issued under section 5 of Executive Order
11282.
§ 76.1 Definitions.
As used in this part:
(a) "Executive Order" means Executive
Order No. 11282.
(b) "Nonurban areas" means all areas other
than urban areas.
(c) "Ringelmann Scale" means the
Ringelmann Scale as published in the U.S.
Bureau of Mines Information Circular 7715,
(d) "Secretary" means the Secretary of
Health, Education, and Welfare.
(e) "Smoke Inspection Guide" means the
U.S. Public Health Service Smoke Inspection
Guide described in Part 75 of this title.
(0 "Urban areas" means those areas
classified as urban in the latest available
Federal census, or as Standard Metropolitan
Statistical Areas by the Bureau of the Budget.
§ 76.2 Intent.
It is the intent of these standards that
emissions to the atmosphere from Federal
facilities and buildings shall not be permitted
if such emissions endanger health or welfare
and that emissions which are likely to be
injurious or hazardous to people, animals,
vegetation, or property shall be minimized.
§ 76.3 Applicability.
(a) Unless otherwise indicated, the
standards in this part apply to both new and
existing Federal facilities and buildings. These
standards are effective upon publication in
the Federal Register, except for those
facilities and buildings which are likely to
require installation of improvements under
the plan to be submitted in accordance with
section 3 of the Executive Order.
(b) Except for discharges of radioactive
effluents which are regulated by the Atomic
Energy Commission, Federal facilities and
buildings shall conform to the air pollution
standards prescribed by the State or
community in which they are located. If State
94
-------
or local standards are not prescribed for a
particular location, or if the State or local
standards are less stringent than the standards
prescribed herein, the standards in this part
shall be applicable to discharges from such
Federal facilities and buildings except as
otherwise indicated.
(c) Temporary operations that may result
in potential air pollution problems, such as
those associated with research, development,
test, evaluation, space, and military activities,
shall be conducted with such precautions and
safeguards as are needed to achieve the intent
of these standards,
(d) The Secretary may, upon application of
the relevant department, agency or
establishment, exempt any Federal facility or
building from the objectives contained in
section 4 of the Executive order and from any
or all of these standards whenever he
determines that the activities of such building
or facility will not significantly conflict with
the intent of the Executive order and that
such an exemption is in the public interest.
§ 76.4 Combustion of fuel.
(a) The following standards apply to the
combustion units of facilities and buildings
having a heat input of less than 1,000 million
B,tu,/hour, other than fireplaces, stoves, or
grills burning wood or charcoal:
(1) Manually fired equipment shall not be
installed as new or replacement equipment,
except for the burning of anthracite, coke, or
smokeless fuel.
(2) (i) For new units, except during
startup, cleaning of fires, or soot blowing, the
density of any emission to the atmosphere
shall not exceed No. 1 on the Ringelmann
Scale or the Smoke Inspection Guide.
(ii) For existing units, except during
startup, cleaning of fires, or soot blowing, the
density of any ernission to the atmosphere
shall not exceed No. 2 on the Ringelmann
Scale or the Smoke Inspection Guide.
(3) A photoelectric or other type smoke
detector, recorder, or alarm shall be installed
on units larger than ten million BTU per hour
input, except where gas or light oil (No. 2 or
lighter), is burned.
(4) During routine operation, the emission
of particles larger than 60 microns shall not
normally occur.
(5) Means shall be provided in all newly
constructed units and wherever practicable in
existing units to allow the periodic
measurement of flyash and other partlculate
matter.
(6) All new or replacement spreader stoker
installations shall be of a type that
automatically discharges ashes to the ash pit
either continuously or in very frequent small
increments, and flyash shall be reinjected only
from boiler passes.
(7) For units of less than 10 million
BTU/hour heat input, the emission of flyash
and other particulate matter shall not exceed
0.6 pounds of particulate matter per million
BTU heat input, as measured by the American
Society of Mechanical Engineers Power Test
Code No. 27 for "Determining Dust
Concentrations in a Gas Stream," or
equivalent test method.
(8) For units between 10 million and 1,000
million BTU/hour heat input, the emission of
flyash and other particulate matter shall not
exceed that specified in figure 1, as measured
by the test method specified in subparagraph
(7) of this paragraph. Existing units shall meet
this standard within the time designated by
the plan submitted in accordance with section
3 of the Executive order except that with
respect to existing spreader stoker units the
plan may specify certain units which may
emit particulate matter at an interim rate not
exceeding 0.6 Ibs/million BTU heat input.
(b) For units having a heat input of more
than 1,000 BTU/hour, the appropriate
department, agency, or establishment shall
seek special advice from the Secretary with
regard to smoke, flyash, and other particulate
emissions.
95
-------
FIGURE I
MAXIMUM EMISSION OF PARTiCULATE MATTER
FROM FUEL BURNING INSTALLATIONS
o.io
100
TOTAL INPUT—MILLIONS OF BTU PER HOUR
ipco
§ 76.5 Sulfur oxides.
(a) Combustion units of facilities or
buildings not located in areas specified by the
Secretary under paragraph (c) of this section
and whose heat input is less than 1,000
million BTU/hour shall burn the lowest sulfur
content fuel that is reasonably available. In
determining reasonable availability, the
factors to be considered include, among
others, price, firmness of supply, extent of
existing pollution, and assurance of supply
under adverse weather and natural disaster
conditions.
(b) For combustion units of Federal
facilities or buildings not located in areas
specified by the Secretary under paragraph (c)
of this section and whose heat input is more
than 1,000 million BTU/hour, the appropriate
department, agency, or establishment shall
seek special advice from the Secretary with
regard to sulfur-oxide emissions.
(c) (1) For Standard Metropolitan
Statistical Areas or Standard Consolidated
Areas whose central city has a population
greater than 2 million and a population
density greater than 15,000 persons per
square mile, the Secretary will, within 6
months after the effective date of the
regulations in this part, establish by regulation
limits on the emission of sulfur oxides to the
atmosphere or prescribe such control steps or
measures as may be necessary over time to
abate or control sulfurous pollution from
96
-------
Federal installations. The limits or measures
so established shall be no less stringent than
the relevant State or local requirements.
(2) Such limits or measures shall be
established only after consultation with
appropriate Federal, State and local officials
and affected parties. Not less than 30 days
prior to prescribing such limits or measures,
the Secretary will publish in the Federal
Register notice of his intention to adopt such
limits or measures, and will thereafter publish
in the Federal Register the limits or measures
established. The Secretary may at any time
designate other urban areas which suffer from
extremely high air pollution levels, and after
similar consultation, and publication in the
Federal Register, prescribe such limits or
measures as he determines are necessary to
carry out the intent of this order.
(d) The emission of the oxides of sulfur
the atmosphere shall be monitored at regular
intervals by determining the sulfur content of
the fuel used or by determining the sulfur
content of flue gases.
§ 76.6 Stacks.
For buildings or facilities in nonurbanized
areas, the particle emission standards of
§ 76.4(a) (7) and (8) may be revised for an
individual installation by an amount to be
determined by the Secretary, when:
(a) The stack height exceeds by 2/4 times
the height of the highest building in that area,
and
(b) The pollution level in any area will not
be significantly increased thereby.
For large plants the determination of chimney
height shall be based on air quality criteria,
land use, and meteorological, topographical,
aesthetic, and operating factors.
§ 76.7 Storage and handling of fuels and ash.
(a) Solid fuels and ash shall be stored and
handled so as not to release to the atmosphere
dust in significant quantities.
(b) In quantities of 40,000 gallons or more,
gasoline or any volatile petroleum distillate or
organic liquid having a vapor pressure of 1.5
p.s.i.a. or greater under actual storage
conditions shall be stored in pressure tanks or
reservoirs or shall be stored in containers
equipped with a floating roof or vapor
recovery system or other vapor emission
control device.
(c) Stationary gasoline storage tanks with a
capacity of 250 gallons or more shall be
equipped with either submerged filling inlets
or with vapor recovery or emission control
systems such that loss of vapor to the
atmosphere during filling operations shall be
minimized.
(d) Gasoline or petroleum distillate tank
car or tank truck loading facilities handling
20,000 gallons per day or more shall be
equipped with submersible filling arms or
other vapor emission control systems.
§ 76.8 Disposal of refuse.
(a) Refuse shall not be burned in open fires
in urban areas. In nonurban areas there shall
not be burned in open fires, within a 24-hour
period, more than 25 pounds of material at a
single site nor more than 500 pounds of
material at any number of sites within a
1-mile radius, except that these quantities
may be exceeded when the open burning
occurs at diverse sites such as are associated
with railroad rights-of-way, interurban
highways, irrigation canals, forests,
agricultural operations, etc. Deteriorated or
unused explosives, munitions, and certain
hazardous materials may be burned in open
fires, in accordance with recognized
procedures. Refuse shall not be left in dumps
without being covered with inert matter
within a reasonably short time.
(b) Refuse shall be incinerated only in
facilities specially designed for that purpose.
Incinerators shall meet the emission visibility
standards of § 76.4 (a) (2) and (a) (3). In
addition, for installations burning 200 pounds
97
-------
of refuse or more per hour, emissions shall
not exceed 0.2 grain of particulate matter per
standard cubic foot of dry flue gas corrected
to 12 percent carbon dioxide (without the
contribution of auxiliary fuel), and shall not
normally include particles larger than 60
microns. For installations burning fewer than
200 pounds of refuse per hour, emissions shall
not exceed 0.3 grain of particulate matter per
standard cubic foot of dry flue gas corrected
to 12 percent carbon dioxide (without the
contribution of auxiliary fuel).
§ 76.9 Other pollution producing processes.
For dusts, fumes, or gases from any process
not heretofore described, except for
discharges of radioactive effluents regulated
by the Atomic Energy Commission, whatever
measures may be necessary to comply with
the intent of these regulations shall be Dated: June 2, 1966.
applied. This will generally require the
installation of equipment or devices to
minimize such emissions to the point where
they will meet the standards contained in
these regulations. For processes which emit
toxic substances in quantities which might
endanger health or welfare and for fires which
emit smoke or fumes at official fire fighting
schools, the appropriate department, agency,
or establishment shall seek special advice from
the Secretary.
(Note: Tile Department of Health, Education, and Welfare
will, from time to time, and after consultation with industries
concerned, issue "Guides of Good Practice" for specific
operations to aid Federal departments, agencies, and
establishments in the selection of equipment and methods for
meeting the performance standards. For emissions not
covered herein, or for Which there have been issued no
applicable "Guides of Good Practice," the Department of
Health, Education, and Welfare will provide technical
material and consultation to departments, agencies, and
establishments requesting such assistance. Requests for
"Guides of Good Practice," technical material, or
consultation should be directed either to the Federal
Facilities Section, Abatement Branch, Division of Air
Pollution, Public Health Service, Department of Health,
Education, and Welfare, Washington, D.C., 20201, or to the
appropriate Regional Air Pollution Program Director of the
Public Health Service located in the Department of Health,
Education, and Welfare Regional Offices.)
John W. Gardner,
Secretary of Health, Education,
and Welfare.
[F.R. Doc. 66-6201; Filed, June 2, 1966; 12:24 p.m.]
»US GOVERNMENT PRINTING OFFICE: 1973 514-151/1611-3
98
------- |