EPA-450/1-74-006
July 1974
MHiS
ODOKS
ODORS
CONTROL OF ODORS FROM
INEDIBLES-RENDERING PI
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
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EPA-450/1-74-006
CONTROL OF ODORS
FROM
INEDIBLES-RENDERING PLANTS
T.R. Osag and G.B. Crane
Emissions Standards and Engineering Division
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
July 1974
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This report is published by the Environmental Protection Agency to report information of
general interest in the field of air pollution . Copies are available free of charge to
Federal employees, current contractors and grantees, and nonprofit organizations - as
supplies permit - from the Air Pollution Technical Information Center, Environmental
Protection Agency, Research Triangle Park, North Carolina 27711. This document is
also available to the public for sale through the Superintendent of Documents, U.S.
Government Printing Office, Washington, D.C. 20402.
Publication No . EPA-450/1-74-006
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CONTENTS
Page
LIST OF FIGURES v
LIST OF TABLES vi
1. INTRODUCTION 1-1
2. RENDERING INDUSTRY STATISTICS • 2-1
2.1 EXISTING PLANTS 2-1
2.1.1 Introduction 2-1
2.1.2 Location and Size 2-2
2.1.3 Number of Facilities 2-2
2.1.4 Type of Process 2-2
2.2 FUTURE TRENDS 2-2
2.3 COST STATISTICS 2-4
2.3.1 Tallow and Meal Prices 2-4
2.3.2 Selected Cost Statistics 2-4
2.4 REFERENCES FOR SECTION 2 2-4
3. RENDERING PROCESSES 3-1
3.1 BATCH PROCESS RENDERING 3-1
3.2 CONTINUOUS PROCESS RENDERING 3-2
3.3 REFINING RENDERING PRODUCTS 3-4
3.4 BLOOD AND FEATHER PROCESSING 3-4
3.5 REFERENCE FOR SECTION 3 3-4
4. EMISSIONS 4-1
4.1 POINTS OF EMISSION 4-1
4.2 CHEMICAL NATURE OF EMISSIONS 4-1
4.3 EMISSIONS IN TERMS OF ODOR UNITS 4-2
4.4 STATE AND LOCAL ODOR REGULATIONS 4-4
4.5 DISPERSION OF ODORS 4-4
4.5.1 Odors from Uncontrolled Plants 4-6
4.5.2 Residual Odors from Chemical Scrubber 4-6
4.5.3 Residual Odors from Afterburner 4-6
4.5.4 Odors from Rendering Buildings 4-7
4.6 REFERENCES FOR SECTION 4 4-7
n
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Page
5. HEALTH AND WELFARE EFFECTS OF ODORS 5-1
5.1 INTRODUCTION 5-1
5.2 PHYSIOLOGICAL AND PSYCHOLOGICAL EFFECTS 5-1
5.3 ANNOYANCE 5-1
5.4 ECONOMIC EFFECTS 5-1
5.5 REFERENCES FOR SECTION 5 5-1
6. CONTROL TECHNIQUES FOR ODORS 6-1
6.1 CONDENSERS 6-1
6.1.1 Contact Condensers 6-1
6.1.2 Water-Cooled Surface Condensers 6-6
6.1.3 Air-Cooled Surface Condensers 6-9
6.2 INCINERATORS 6-11
6.2.1 Description 6-12
6.2.2 Boiler Firebox Incineration 6-13
6.2.3 Emission Reduction 6-16
6.2.4 Equipment Costs 6-16
6.2.5 Fuel Costs 6-17
6.3 CONDENSER-INCINERATOR SYSTEMS 6-18
6.3.1 Emission Reduction 6-19
6.3.2 Equipment Costs 6-20
6.4 SCRUBBING 6-22
6.4.1 Description 6-22
6.4.2 Emission Reduction 6-25
6.4.3 Sewage Treatment 6-25
6.4.4. Equipment Costs 6-25
6.5 REFERENCES FOR SECTION 6 6-26
7. METHODS OF ESTIMATING CAPITAL INVESTMENT AND TOTAL
ANNUAL COST FOR CONTROL EQUIPMENT 7-1
7.1 INTRODUCTION 7-1
7.2 CAPITAL INVESTMENT „ . 7-1
7.3 TOTAL ANNUAL COST 7-1
7.4 REFERENCES FOR SECTION 7 7-2
IV
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LIST OF FIGURES
Figure Page
2-1 Rendering and JFish-Reduction Plants, 1968 2-3
3-1 Batch Rendering Plant 3-2
3-2 Continuous Rendering Plant 3-3
6-1 Types of Condensers: (a) Spray Chamber, (b) Jet, and
(c) Barometric 6-2
6-2 She 11-and-Tube Condenser 6-7
6-3 Types of Air-Cooled Surface Condensers 6-10
6-4 Diagrammatic Representation of Rendering Plant Afterburner
with Heat Recovery 6-12
6-5 Flame Incinerator with Heat Recovery Unit 6-14
6-6a Poor Method of Introducing Odorous Air from Diffuser to Boiler
Firebox Through the Burner Air Register. Diffuser Restricts
Combustion Air to Burner; also the Louvers may Partially Close,
Restricting Flow of Odorous Air into Boiler Firebox 6-15
6-6b Good Method of Introducing Odorous Air to Boiler Firebox Through
a Custom-Made Air Register. There is Good Flame Contact . . . 6-15
6-7 Odor-Control System with Entrainment Separator, Surface
Condenser, and Incinerator 6-20
6-8 Odorous Emissions from Various Facilities 6-21
6-9 Types of Absorption Equipment: (a) Bubble-Cap Tray Tower and
(b) Packed Tower 6-23
6-10a Spray-Chamber Absorption Device 6-23
6-10b Venturi Scrubber Absorption Device 6-23
6-11 Two-Stage Chemical Scrubbing System 6-24
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LIST OF TABLES
Table Page
2-1 Utilization of Inedible Tallow and Grease, I960 to 1970 2-1
2-2 Statistics for Rendering Plants Based on Number of
Employees per Plant, 1967 2-4
2-3 Prices of Inedible Tallow and Meal 2-5
2-4 Selected Cost Statistics for Inedible Rendering Industry,
Animal and Marine Fats and Oils 2-5
2-5 Selected Statistics for the Inedible Fish Rendering Industry 2-6
3-1 Composition of Typical Inedible Raw Materials Charged
to Reduction Processes 3-1
4-1 Odor Threshold Levels for Selected Compounds 4-2
4-2 Odor Concentrations and Emission Rates from Inedible
Rendering Processes 4-3
4-3 State and Local Odor Control Regulations 4-5
6-1 Odor Removal Efficiencies 6-1
6-2 Treatment Charges for Municipal Sewering of Aqueous Wastes .... 6-4
6-3 Batch-Type Model Rendering Plants 6-5
6-4 Capital Investment, Direct Operation Cost, and Total Annual
Cost of a Direct-Contact Condenser 6-6
6-5 Capital Investment, Direct Operating Cost, and Total Annual
Cost of a Water-Cooled Shell-and-Tube Condenser 6-8
6-6 Capital Investment, Direct Operating Cost, and Total Annual
Cost of an Air-Cooled Surface Condenser 6-11
6-7 Volumes of Incinerated Streams 6-16
6-8 Capital Investment, Direct Operating Cost, and Total Annual
Cost of Incineration 6-17
6-9 Capital Investment, Direct Operating Cost, and Total Annual
Cost of a Condenser-Incinerator System 6-18
6-10 Capital Investment, Direct Operating Cost, and Total Annual
Cost of a Chemical Scrubbing System 6-26
7-1 Estimation of Capital Investment 7-2
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CONTROL OF ODORS
FROM
INEDIBLES-RENDERING PLANTS
1. INTRODUCTION
Although this document, describing the operation of rendering plants and placing
emphasis on the effectiveness and cost of odor control technology, is directed primarily
at the control of existing plants, the techniques presented are also applicable to new
installations. Costs were developed only for rendering plants handling inedible animal
matter because processing of inedible products is more prevalent and a much greater
source of malodors than the processing of edible lard and tallow . Rendering of edibles
is usually conducted as an adjunct to meat packing operations. Inedible rendering en-
tails a much wider array of feedstocks including packinghouse and butchershop scrap,
feathers, blood, and "dead stock" (whole animals that die by accident or through natural
causes).
Air pollutants from rendering plants are significant only from the standpoint of
malodors. The pollutants of concern--sulfides, mercaptans, organic nitrogen compounds,
aldehydes, and organic acids--do not constitute a significant health hazard in the concen-
trations at which they are released to the atmosphere. For this reason, abatement tech-
niques are aimed at reducing emissions to the extent that malodors are no longer noticeable
at receptor points in the vicinity of the plants.
In developing this document, interest was focused on proven systems for controlling
prominent odor sources in rendering plants. These sources include cookers, presses,
driers, and other heated equipment that generates highly odorous gases. The most
commonly applied control devices for these processes are condensers, afterburners, or
both, but scrubbers are finding some usage. Although control techniques for other ren-
dering operations such as grinding, handling, and storage are not fully developed, inves-
tigations into the most successful control systems, chemical scrubbers, were conducted
and results are reported .
Consideration has been given to those maintenance and operating practices that affect
the release of malodors. Control techniques for "housekeeping odors" are highly sub-
jective, and this document does not purport to provide a clear-cut solution.
1-1
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2. RENDERING INDUSTRY STATISTICS
2.1 EXISTING PLANTS
2.1.1 Introduction
The rendering industry has experienced a definite growth during the past two decades.
The production of inedible tallow and greases has increased from 2.3 billions pounds worth
$150 million in early 1950 to an estimated 5.4 billion pounds worth approximately $430
million for 1971.1 This trend can be traced largely to increases in livestock production
and meat consumption. Increased plant efficiency, which has resulted in the more com-
plete recovery of fats , has also been a factor . The preceding production data for inedible
tallow and grease reflect an average annual increase at the rate of 4 percent.
The United States is the world's leading producer, consumer, and exporter of tallow
and greases. Since the early 1950's, the United States has accounted for 55 to 60 percent
of the world tallow and grease output. 1 The export market has been the largest single
outlet, consuming about 50 percent of the domestic output. Table 2-1 provides some in-
formation regarding the various markets for inedible tallow and greases .
Table 2-1. UTILIZATION OF INEDIBLE TALLOW AND GREASE, 1960 TO 19701
(106 Ib/yr)
Year
beginning
October
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970a
Soap
732
702
688
660
690
649
665
631
637
601
615
Animal
feeds
443
732
774
861
714
855
972
990
1,061
1,093
1,140
Fatty
acids
351
402
433
478
530
575
547
576
585
610
568
Lubricants
and similar
oils
70
79
78
91
102
107
98
89
98
97
89
Other
151
177
151
230
203
208
283
291
289
320
214
Exports
1,769
1,710
1,738
2,338
2,155
1,962
2,214
2,212
2,009
2,051
2,591
Total
3,516
3,802
3,862
4,658
4,394
4,356
4,779
4,789
4,679
4,772
5,217b
^Preliminary data based on census reports.
b4,877 actual; Reference 2.
2-1
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2.1.2 Location and Size
Most rendering plants are located in or near cities and in proximity to poultry or
meat packing facilities. Many small Tenderers are, however, located in small towns and
rural areas. The larger concentrations of facilities are found in the midwestern parts of
the country as shown by Figure 2-1, which provides a general idea of the distribution of
rendering plants throughout the country; however , this information is only approximate
because edible rendering and fish reduction plants are included in the state totals .
Data obtained from the 1967 Census of Manufacturers and summarized in Table 2-2
provide some information on the size of existing rendering plants. The distribution of
plant sizes indicated in Table 2-2 should be considered approximate since only about
69 percent of the industry is reflected. Plants range in size from small operations with
1 to 4 employees and annual sales of about $100,000, to large operations with over 100
employees and sales of from $5 to $10 million. An average plant could be characterized
as employing 23 workers and having annual sales of approximately $1 million.
2.1.3 Number of Facilities
As of 1968, there were 770 firms operating 850 facilities engaged in the rendering of
inedible animal matter . * Of this number , about 460 were operated by independent ren~
derers, 330 were controlled by the meat packing and poultry industries, and the remain-
der were owned by companies having manufacturing interests other than meat and poul-
try processing. It is estimated that approximately 275 of the plants controlled by the meat
industry also are involved in edible rendering at separate locations of the same plant.
2.1.4 Type of Process
It is estimated that from 75 to 80 percent of the inedible rendering industry consists
of older batch-type facilities. New plants can be expected to use a continuous process,
although this decision is somewhat dependent upon the size of the operation. A small
operation might install new batch units.
2.2 FUTURE TRENDS
The growth pattern for the rendering industry has not been consistent because of the
divergent trends of major markets. The displacement of soap by detergents has resulted
in a considerable reduction in the demand for tallow by manufacturers of the former . The
soap industry, once the major market for tallow, has reduced its demand by 56 percent
since 1950. The annual demand for tallow has stabilized at about 0.6 billion pounds in
the past few years . This amount could increase if the use of phosphates declines because
of concern with water pollution problems.
During the same period, the use of inedible tallow in animal feeds has emerged as a
major outlet. The estimated consumption of tallow and greases by the animal feed industry
was 1.1 billion pounds during 1970 .
The estimated production of meat meal and tankage for 1970 was 4.0 billion pounds.
The production of these materials has shown an annual growth rate of 1.6 percent since
1963 compared to a growth of 1.9 percent for inedible tallow and greases during the same
period. The primary outlet for meat meal and tankage is as a high-quality protein pro-
duct for the animal feed industry. Increasing demand for this purpose is tending to in-
crease the value of meat meal and tankage.
The number of domestic rendering plants has decreased from about 850 plants in 1968
to 750 plants in 1972, and the slight decline is expected to continue. It is estimated that
2-2
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Table 2-2. STATISTICS FOR RENDERING PLANTS
BASED ON NUMBER OF EMPLOYEES PER PLANT, 1967E
Establishment size,
no. employees
1 to 4
5 to 9
10 to 19
20 to 49
50 to 99
100 to 249
Totals
Number of
establishments
132
103
127
157
51
18
588
Number of
employees
300
700
1,800
4,800
3,500
2,600
13,700
Value of
shipments, $10^
12.0
27.9
62.2
207.1
117.1
131.0
557. 9a
aTotal value of shipments from all sources.
new construction will add from 20 to 40 plants per year. Most of these facilities are ex-
pected to be replacement plants employing a continuous process.
2.3 COST STATISTICS
2.3.1 Tallow and Meal Prices
Table 2-3 gives historical data on prices of inedible tallow and bulk meat and bone
meal as derived from various issues of the trade journal of the meat packing industry.
Evidently, the products of inedible rendering are subject to severe price fluctuations.
Prices in early 1973—the basis of the emission control costs—were high, as were prices
for edible meats .
2.3.2 Selected Cost Statistics
Table 2-4 contains published cost data on the inedible rendering industry. The
statistics in this table include those for the fish rendering industry. Table 2-5 is there-
fore presented to put fish rendering economics in its proper perspective.
Comparison of the two tables shows that the value of shipments of fish rendering pro-
ducts has usually not exceeded 10 percent of that for both industries and suggests that
Table 2-4 approximates the performance of the animal inedible rendering industry.
In view of these facts. Table 2-4 indicates that costs of materials, measured as a per-
cent of sales, have been fairly uniform at approximately 60 cents of every sales dollar,
over the years 1960 to 1969. Also, over the entire time span, cash from operations
available for depreciation, interest charges, debt retirement, dividends, taxes, and
retained earnings has trended upward steadily. This performance was in spite of pro-
duct price fluctuations over long ranges. Lastly, the total payroll has declined with
respect to sales, over the time period tabulated.
2-4
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Table 2-3. PRICES OF INEDIBLE TALLOW AND MEAL7
Quotation date
January 18, 1969
June 14, 1969
December 27, 1969
March 7, 1970
June 27, 1970
December 26, 1970
February 6, 1971
July 10, 1971
December 11, 1971
January 22, 1972
May 5, 1973
June 23, 1973
July 14, 1973
September 22, 1973
November 24, 1973
Tallow,
$/lb
4 1/2
5 3/4
6 1/8
6 3/4
7 1/4
6 1/4
7
6 5/8
5 5/8
5 1/2
11 3/4
15 1/2 - 16 1/4
15 5/8
11
11 1/2
Meal ,
$/ton
92.50
92.50
105 - 107
115 - 120
95-100
105
95
90 - 95
90
TOO - 102
295
375 - 400
225
160 - 170
225 - 240
Table 2-4. SELECTED COST STATISTICS FOR INEDIBLE
Q i n
RENDERING INDUSTRY, ANIMAL AND MARINE FATS AND OILS3'IU
($106)
Year
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
Value of
shipments
318.0
376.3
400.6
474.0
550.4
669.2
765.3
557.9
515.1
608.7
790.1
865.9
Cost of
materials
190.3
219.0
232.0
280.4
347.3
425.8
460.0
349.1
318.0
373.8
500.7
580.4
Total
payroll
69.9
69.9
74.2
78.3
84.5
90.2
89.3
91.8
92.8
99.5
108.1
111.9
Cash from
operations
57.3
88.3
94.4
115.3
118.6
153.2
216.0
117.0
104.3
135.4
181.3
173.6
2-5
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Table 2-5. SELECTED STATISTICS
FOR THE INEDIBLE FISH RENDERING INDUSTRY8
Year
1960
1967
1971
Value of shipments, $106
Fish scrap and meal
25
40
44
Fish oil
13
6.1
20.7
Total
38
46.1
64.7
2.4 REFERENCES FOR SECTION 2
1. Kramer, G.W. U.S. Tallow and Grease Production and Marketing
Trends. Reprinted from: The Fats and Oils Situation. Department of
Agriculture, Economic Research Service. Washington, B.C. FOS - 260.
November 1971. 9 p.
2. Current Industrial Reports, Department of Commerce, Bureau of Census . Washington,
D. C. M20K Fats and Oils. September 1971.
3. Background Information for Proposed New-Source Performance Standards, Technical
Report No. 10 - Rendering Plants. Environmental Protection Agency. Research Tri-
angle Park, North Carolina. January 1973.
4. National Emission Standards Study. Department of Health, Education, and Welfare.
Washington, D.C. Document No. 91-63. March 1970. p.F-367.
5. 1967 Census of Manufacturers. Department of Commerce, Bureau of Census, Washing-
ton, D.C. December 1969. p. 20H-12.
6. Current Industrial Reports . Department of Commerce, Bureau of Census . Washington,
D.C. M20K. 1963-1970.
7. National Provisioner. National Provisioner, Inc. Chicago, 111. June 1969-November
1973 issues .
8. Statistical Abstract of the United States Department of Commerce. Social and Economic
Statistics Administration. Bureau of Census . Washington, D.C. 1972. p. 641, 642.
9. Annual Survey of Manufacturers for 1970. Industry Profiles M70(AS) . Bureau of
Census. U.S. Department of Commerce. Washington, D.C. June 1972.
10. Annual Survey of Manufacturers for 1971. General Statistics for Industry Groups and
Industries M71(AS)-1. Bureau of Census . U .S . Department of Commerce. Washing-
ton, D.C. April 1973.
2-6
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3. RENDERING PROCESSES
Animal matter not suitable as food for human consumption is converted into salable
by-products through various reduction processes. Cows, horses, sheep, poultry,
dogs, and cats that have died through natural or accidental causes, as well as the by-
products from slaughterhouses, butcher shops, and poultry dressers, are processed
into proteinaceous meal and tallow .
Many rendering operations are part of a meat packing or poultry processing plant
and are designed to process blood, meat, offal, and feathers produced on the premises.
These operations are referred to as captive plants. Off-site, or independent, rendering
plants are operated independently and normally rely on a number of local sources for
raw material. These sources may include hotels, restaurants, and miscellaneous
processors of food and meats .
Although the rendering process is involved mainly with the heated reduction of
fat-containing materials into tallow and proteinaceous solids, it can also include such oper-
ations as blood drying, feather drying, and grease reclaiming. Table 3-1 gives the
tallow and solids yield of material processed by the rendering industry.
Table 3-1. COMPOSITION OF TYPICAL INEDIBLE RAW MATERIALS
CHARGED TO REDUCTION PROCESSES1
(wt. %)
Source
Packing house offal and
bone
Steers
Cows
Calves
Sheep
Hogs
Dead stock (whole animals)
Cattle
Cows
Sheep
Hogs
Blood
Feathers (from poultry
houses)
Butcher shop scrap
Tallow or grease
15 to 20
10 to 20
8 to 12
25 to 35
15 to 20
12
8 to 10
22
30
--
--
37
Solids
30 to 35
20 to 30
20 to 25
20 to 25
18 to 25
25
23
25
25 to 30
12 to 13
20 to 30
25
Moisture
45 to 55
50 to 70
60 to 70
45 to 55
55 to 67
63
67 to 69
53
40 to 45
87 to 88
70 to 80
38
3-1
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3.1 BATCH PROCESS RENDERING
The process raw material is placed in a dump pit (Figure 3-1) and conveyed to a
hogger where the meat and bones are ground to facilitate mechanical handling and heat
transfer . The ground material is then conveyed to the cookers for processing .
CHARGING BINS
TO ODOR-CONTROL
SYSTEM
DUMP PIT
FREE-RUN TALLOW J
I
MEAL STORAGE
TALLOW STORAGE
COMPRESSED AIR FOR MOISTURE REMOVAL
t
WATER TO SEWER
Figure 3-1. Batch rendering plant.
The cooking process, where the actual rendering takes place, may be either batch
or continuous. Heat breaks down the flesh and bone structure, causing tallow to separate
from solids and water. In the batch process, cookers are charged with 3,000 to 12,000
pounds of animal matter and heated for 1 to 4 hours . ! Batch cookers may be operated
either at pressures greater than 50 psig to digest bones, hooves, hides, and hair, or under
a vacuum to produce high-quality tallow. The cookers are equipped with paddles to
mix the charge during processing.
Dry rendering is used almost exclusively for inedible rendering and is carried out
at atmospheric pressure or under partial vacuum. Operation can be either batch or
continuous. Moderate-sized agitating vessels are used for batch operation; continuous
operations are performed in agitating vessels designed for proper holdup time, or in
multistage evaporators. The material is cooked until all of the free moisture in the tissue
is driven off. Then the separated fat is screened to remove the solid proteinaceous
residue.
Wet rendering is employed primarily for edible materials and is seldom used to pro-
cess inedible material. However, it involves cooking under pressure by the direct
addition of live steam. The fat and water are separated after cooking . The solids are
screened out of the water, and the water is evaporated to a thick, protein-rich material
that can be added to animal feeds.
3-2
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3.2 CONTINUOUS PROCESS RENDERING
Continuous rendering is a highly mechanized dry rendering process. At least three
process equipment arrangements are commonly used. Continuous processes usually con-
sist of a series of grinders, steam-jacketed conveyor-cookers, and presses. In one
process arrangement, animal matter is ground before it is fed to a precooker. After the
initial cook, the material is again ground before its final processing in the second-stage
cooker. Tallow and steam vapors are-removed from solids at various points in the system.
In the continuous system shown in Figure 3-2, raw material is screw-conveyed to
the hogger where it is ground and fed into the end of a multicompartment cooker. Reduc-
tion to water, tallow, and solids takes place in the multicompartment cooker as the raw
material passes through the cooker compartments. On the other end of the cooker, pro-
cessed material is removed by the control wheel and placed in a drainer to separate tallow
and solids. The entrainment trap prevents solids from escaping the cooker and fouling
the air pollution control system.
The scrubber-condenser handles vapors and noncondensables from the cooker. Con-
densation takes place in a fully enclosed tubular condensing section that is cooled with a
ENTRAINMENT TRAP
CENTRIFUGE
HOGGER
SCRUBBER
CONDENSER
DRAINER
CRUDE TALLOW TANK
""" CONTROL WHEEL
PRESS
TO GRINDING
OR STORAGE
RAW MATERIAL
STORAGE
Figure 3-2. Continuous rendering plant. (Courtesy of The Dupps Company, Germantown, Ohio)
3-3
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water spray. Condensed vapors flow off as waste, and noncondensables go to the small
wet scrubber and incinerator. The same water spray also scrubs plant ventilating air,
which is passed axially upward outside the tubes, also coohng the condenser water spray.
The condensate and spray water are kept apart within the unit; the only mixing occurs on
sewering . Because of evaporation and to avoid scaling, some spray water is bled off and
some makeup is added .
The hours of operation for continuous and batch rendering plants vary and are not as
dependent upon the process as they are upon the availability of raw material. Generally,
plants pick up the raw material during the day and process it at night. If raw material
is plentiful, the operation may run 24 hours a day and on weekends.
3.3 REFINING RENDERING PRODUCTS
Tallow and solids separated during cooking require further processing to obtain fin-
ished products. The solids, or cracklings, are pressed to remove residual tallow (Fig-
ures 3-1 and 3-2) , and usually are ground to a meal before marketing .
Tallow is maintained at 200° F or above and is then processed in settling tanks, centri-
fuges, or filters (plate and frame presses or leaf filters) in order to remove the solids.
If finely divided protein particles remain suspended in the tallow, the usual settling pro-
cess of using cone-bottom tanks may be improved by washing the tallow with either tri-
sodium phosphate or citric acid in order to coagulate these particles to aid separation .
Moisture is removed from the tallow by flash drying, either at atmosphere or under vacuum,
and also by blowing air through the tallow.
The tallow is further refined by adding caustic soda to neutralize the free fatty acids.
The saponified free fatty acid settles out and is known as foots or soap stock. The tallow
is usually filtered to remove all traces of the foots and other solids.
Tallow is further processed into a "bleachable fancy" grade, which commands a higher
market price. Bleaching of the tallow is accomplished by the use of natural clays and also
acid-activated clays, which have great absorptive power for fat pigments. This latter
variety is replacing the use of natural clays because of its improved performance.
3.4 BLOOD AND FEATHER PROCESSING
Blood and feathers contain little fat and are processed only into meal. Blood is usually
dried in a horizontal dry cooker. Sometimes a tubular evaporator is used to remove a
portion of the water, and the blood is then transferred to a dry cooker for final evapor-
ation. Steam-tube and ring driers are also used for finish drying of feathers and blood,
respectively .
Feathers are initially pressure-cooked at about 50 psig in a dry cooker to hydrolyze
the protein keratin, their principal constituent. Final moisture removal may be carried
out in the cooker at ambient pressure or in separate air-drying equipment.
3.5 REFERENCE FOR SECTION 3
1. Air Pollution Engineering Manual. Danielson, J. A. (ed.). U. S. Department of
Health, Education, and Welfare. Cincinnati, Ohio. Publication Number AP-40.
1967. p. 770 - 775.
3-4
-------
4. EMISSIONS
Malodors are the principal air contaminants from rendering and companion processes.
Although participates are formed during the grinding and conveying of cracklings and
during the air drying and conveying of meals, they are usually coarse in size and are
not entrained in the ambient air. Small amounts of tallow and solids, however, are en-
trained in the cooker exhaust gas . Particulates and tallow emissions contribute to the
odor problem and can interfere with the operation of control equipment.
4.1 POINTS OF EMISSION
Cookers are a primary source of malodors in rendering plants. When animal matter
is heated, the cell structure breaks down, liberating gases and vapors. Further heating
causes chemical decomposition, and the resulting products are often highly odorous.
Cooker streams contain 95 percent or more moisture by volume. The remainder of
the stream, however, includes compounds that are highly malodorous. Emission rates
of odorous contaminants are a function of the rate of moisture evaporation . The maximum
emissions from atmospheric cookers occur in the initial portion of the cook, whereas
in pressure cookers the moisture evaporation rate and emissions proceed as the tempera-
ture builds up .
Processing tanks, in which tallow is dehydrated by boiling or air blowing, feather
driers, tallow presses, and blood spray driers are lesser but significant sources of
malodors. Driers can be a large source of malodors, particularly if feedstocks are putri-
fied or not completely cooked beforehand, or where meal is overheated in the drier.
Moisture content of drier streams is generally much lower than that of cooker streams.
Feather drier streams, for instance, contain about 20 percent moisture. ^
Odor concentrations from air blowing of tallow may be significant at high operating
temperatures. Only small volumes of air are blown through the tallow for short periods,
however. Percolator pans are also a source of significant odors for short periods. At
the end of a cooking cycle, when tallow and solids are discharged into percolator pans,
substantial quantities of steam and odors are released. Percolator pan emissions are
especially difficult to control because of the necessity to gather the vapors in suitable
hoods, but at least one western plant has recently demonstrated a control by this method.
Storage areas, dump pits, and hoggers are a significant source of malodors if raw
materials are not fresh. Ideally, raw materials should not be over 24 hours old when
processed.
4.2 CHEMICAL NATURE OF EMISSIONS
Rendering-plant malodors have been attributed to a variety of organic compounds
belonging to such classes as aldehydes, fatty acids, amines, mercaptans, and sulfides.->~
Aldehydes and fatty acids are the principal odorous breakdown products from fats; pu-
trescine and cadaverine are two extremely malodorous organic nitrogen compounds asso-
ciated with decaying flesh.2 Keratins, the primary constituents of horny material (skin,
hair, nails, feathers, etc.) are the principal source of sulfides and mercaptans.
Some specific compounds that have been identified in rendering-plant odors are
trimethyl amine, quinoline, dimethyl pyrozine, skatole, ammonia, and hydrogen sulfide.
Recent studies have identified such compounds as methyl and dimethyl sulfides; butyl-
amine and trimethyl amine; the methyl pyrazines; aldehydes, ketones, and alcohols; and
4-1
-------
o
organic acids including butyric acid. Odor threshold concentrations are extremely low
for some of the malodorous compounds, and they can be detected in concentrations as
low as 0.2 part per billion.''' Many odorous compounds have not been identified, nor have
their detectability limits been established.
Table 4-1 lists odor threshold concentrations for some odorous compounds. These
data are based upon laboratory panel work done by trained members having professional
scientific backgrounds, were compiled under ideal conditions with a minimum background
odor, and probably represent relative differences in odor threshold levels ancl not nec-
essarily absolute values .
Table 4-1. ODOR THRESHOLD LEVELS FOR SELECTED COMPOUNDS2'7
Compound
Dimethyl amine
Methyl amine
Tri methyl amine
Ammonia
Ethyl mercaptan
Hydrogen sulfide
Methyl mercaptan
Dimethyl sulfide
Dimethyl di sulfide
Skatole
Acrolein
Butyric acid
Chemical
formula
CH3NHCH3
CH3NH2
(CH3)3N
NH3
C2H5SH
H2S
CH3SH
CH3SCH3
CH3SSCH3
CgH8NH
CH2 = CHCHO
C3H7COOH
Molecular
weight
45.08
31.06
59.11
17.03
62.13
34.08
48.10
62.13
94.23
131.18
56.06
88.10
Odor threshold,
ppb
4.7
21.0
0.21
46,800
1.0
4.7
2.1
2.5
7.6
220
210
1.0
4.3 EMISSIONS IN TERMS OF ODOR1 UNITS
Terminology and test methods have been developed to quantify odor emissions.
most all methods utilize the human olfactory system as the sensor.
Al-
The odor unit is defined as the quantity of any single or combination of odorous sub-
stances that, when completely dispersed in 1 cubic foot of odor-free air, is detectable by a
median number of observers in a panel of at least eight persons. It is desirable to spec-
ify the odor sensory method upon which an odor unit quote is based.
Table 4-2 lists odor concentrations and emission rates from various inedible render-
ing processes. These odor concentrations •were determined by the Mills modification of
the ASTM syringe method. The wide variation in odor concentrations for blood and ren-
dering cookers reflects the different types and "ripeness" of raw materials.
Of the facilities listed in Table 4-2, the cookers are the predominant source of mal-
odor emissions. Typical batch cookers release 250 to 750 scfm of exhaust gases over a
2- to 4-hour cooking cycle, and continuous cookers release 3000 to 4000 scfm. At an
4-2
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average emission concentration of 50,000 odor units per scf, a batch cooker would release
up to 37.5 million odor units per minute, and a continuous cooker would release 150
million odor units per minute. On the other hand, a 2000-pound-per-hour feather drier
(1600 scfm exhaust volume) with an average emission concentration of 2000 odor units
per scf would release 3. 3 million odor units per minute.
The reliability of the ASTM ' and other known odor sensory methods leaves something
to be desired. Considerable effort is currently being expended to find more practical,
simple, and reproducible methods. Results have been described recently for an alternate
dynamic method for stack testing that uses a statistical approach.
4.4 STATE AND LOCAL ODOR REGULATIONS
Several state and local jurisdictions have adopted odor control regulations that apply
to rendering plants. Many are general prohibitions that apply to all odor sources; others
are more specific to rendering operations.
The most common type of statute is a general-nuisance regulation. The enforcement of
such regulations requires that a great deal of e"idence be assembled to show that a given
source causes nuisance or annoyance, endangers comfort, repose, health, or welfare of
persons, or causes injury or damage to property or to business.
Many jurisdictions use odor regulations that are in the form of stack emission limits
or fenceline allowances. These may be general or directed specifically at rendering plants,
canneries, pulp mills, etc. Emission limits are usually based on dilution measurement
procedures in which the human nose serves as the sensor. The use of dilution methods
has given rise to the term "odor unit," in which allowable emissions are usually ex-
pressed. Regulation APC~9 of the State of Minnesota, as listed in Table 4-3, limits
emissions from rendering plants to 1,000,000 o.u./minute.
Fenceline regulations stipulate maximum allowable odor limits at the rendering plant
property line. These limits are not necessarily indicative of the level of emissions from
the plant. The scentometer is normally used to enforce fenceline regulations. This in-
strument is essentially a clear plastic box containing two chambers of activated charcoal,
two nasal ports for sniffing, and a series of odorous inlets that are directly connected
with a mixing chamber and the nasal outlets. Air is drawn through the two charcoal beds
(to make it odor free) and then mixed with the contaminated air to produce a threshold
concentration. The unit of expression used for this work is the number of times that the
odor is as strong as its threshold concentration, or the number of dilutions with pure air
needed to dilute it to threshold concentration . H The allowable dilution limits for some
states and localities are listed in Tible 4-3.
The most common type of rendering plant odor regulation is an equipment standard
that directs the operator to use specific incinerator parameters. Several such parameters
are listed in Table 4-3; they usually .n.pply to discrete processes within the plant, e.g. ,
cookers, driers, and heated reduction processes, rather than to the entire facility. As
noted in Table 4-3, required temperatures and residence times vary from 1200 to 1600° F
and from 0.3 to 0.5 second. In jurisdictions where such equipment standards are in use,
the operator usually has the option of using any other control system if he can show it
provides equivalent odor abatement.
4.5 DISPERSION OF ODORS
No evidence exists that rendering-plant odors are harmful to health at dilute levels.
Therefore, a reasonable objective is ih.2 prevention of detectable odors at ground level
outside the plant. The regulations cited in Section 4.4 attempt to provide this assurance
by limiting odor emissions or concentrations at the stack or fenceline or by requiring air
pollution control equipment which wil1 achieve these levels. Some typical installations--
uncontrolled and controlled--will be examined to consider the effect of atmospheric dis-
persion .
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4.5.1 Odors from Uncontrolled Plants
Calculations have been made to estimate ground-level odor concentrations for an un-
controlled rendering plant. The plant assumed is approximately equal to Model C of
Table 6-3, with a stack-gas flow rate of 6000 cfm . This plant uses a shell-and-tube con-
denser for cooker off-gases and, for simplicity, all plant odors are assumed to exit from
the stack. Because Model C emits about 670 cfm from the condenser, there must be a
large amount of dilution air to make up 6000 cfm; also, the stack temperature is assumed
to be 90° F, along with a stack velocity of 10 ft/sec. The stack-gas odor concentration
is taken as 100,000 o.u. /ft , which is derived from the dilution and the usual range of
exit concentrations from rendering plant shell-and-tube condensers. The stack is
assumed to be 75 feet high, and the atmospheric stability is taken as D, with a wind
speed of 1 m/sec .
Under the preceding conditions , the maximum ground-level concentration was estimated
to lie 1600 feet downwind from the stack and to be about 1400 o.u./ft^.l^ There would
still be 170 o.u./ft at ground level 2.5 miles from the stack, and a distance of about 30
miles* would be required for complete dissipation of odor. Although these figures are
rough estimates , they are given here to illustrate the odor problem when rendering plants
are uncontrolled. The -following two sections, involving similar assumptions and calcu-
lations, illustrate the great improvment in the ground-level odor situation when reasonable
controls are used.
4.5.2 Residual Odors from Chemical Scrubber
The maximum ground-level odor concentration was estimated!* for a rendering plant
controlled by a hypochlorite water scrubber (Section 6.4) . The plant was assumed to be
well kept, with negligible odor sources other than the scrubber exit gas. The plant was
assumed to be approximately equal to Model C of Table 6-3. A stack gas flow rate of 6000
cfm at 90° F was assumed, along with an odor concentration of 200 o.u. /ft . The plume
rise was found to be negligible because the gas temperature was so close to ambient. With
such a small plume rise, the maximum ground-level concentration will occur at low -wind
speeds. Assuming a wind speed of 1 m/sec, it was initially determined that a stack height
of 30 feet would be required to prevent the ground-level concentration from exceeding
1.0 o.u./ft^. The actual odor source, however, will have a building under it and may
have other buildings near it. When air flows past a building at any velocity, the air
streamlines are bent. This bending is small at 1 m/sec, but increases with velocity,
finally resulting in turbulent eddies just downwind of the building. Therefore, odorous
air passing over the roof may be deflected groundward, or may be pushed downward in
turbulent eddies. This phenomenon is called downwash. With a 30-foot stack, the oc-
currence of downwash is likely and will occasionally cause ground-level concentrations
to exceed 1 o.u./ft3 up to several hundred feet downwind. A rule of thumb is that the
stack height--or stack plus building height if the stack is atop the building--should be
2.5 times the building height. Downwash effects from a building will extend 5 to 10
building heights downwind.
For the average rendering plant building 30 feet high, the stack should extend to 75
feet above ground. Under the described conditions, the maximum ground-level concen-
tration will then be 0.06 o.u./ft3 when a chemical scrubber is used. This determination
was made by calculating the critical wind speed at which ground-level odor concentration
is maximum .
4.5.3 Residual Odors from Afterburner
The maximum ground-level concentration was estimated for an afterburner based on
the same assumptions as for the chemical scrubber, except for the stack temperature of
750° F. The resulting plume rise was about 40 feet. The maximum ground-level odor
*The calculation assumes no disappearance of odor molecules and neglects the unknown
factors of photochemical reactions in the atmosphere, or other mechanisms of change.
4-6
-------
concentration from the 75-foot stack was only 0.01 o.u./ft3 because of the improvement
in plume rise .
Plume rise adds to effective stack height. The rise approaches zero as the difference
between stack and ambient temperatures approaches zero .
4.5.4 Odors from Rendering Buildings
The preceding discussion assumes that all odor in the rendering plant is directed up
the stack. If some odors escape from the building itself, ground-level concentrations will
be greater.
The odor concentration was estimated at an elevation of 2 meters (nose-level) 200
meters downwind of a rendering plant building with dimensions of 50 by 50 meters. For an
emission rate equal to that for the stack in the preceeding example (20,000 o.u./sec),
the odor concentration would be 1.8 o.u./ft3. * A wind speed of 1 m/sec with an F sta-
bility was assumed. The plant was considered an area source of uniform emission inten-
sity . The odor concentration would be greater or less than 1.8 o.u./ft3 at a point closer
or farther, respectively, than 200 meters downwind. The odor concentration would also
be much greater if the gases escaped the building without being incinerated, scrubbed,
or otherwise treated.
Ground-level concentration at a given point is a linear function of emission rate in
o.u./sec if all other assumptions remain unchanged. Although building emission rates
are not available, a typical dry-rendering cooker vented through a surface condenser
with condensate temperature of 80° F might release 12,500,000 o.u./min. ^ In the absence
of any other control or a stack, the ground-level concentration would be about 19 o.u./ft3
200 meters downwind of the rendering building .
The preceding statements about ground-level concentrations are valid for averaging
times of about 10 to 60 minutes. Odors are detectable in seconds, and for such short
averaging times, odor concentrations will reach values many times greater than for 40-
to-60-minute averaging times.
Actual emission rates--and therefore ground-level concentrations—are potentially
much greater when odors escape from the building itself than when they are directed up
a stack and then subjected to downwash. This is primarily because odor-control devices
are assumed to be operating when odors are directed up the stack, whereas escaping
odors are not subject to control.
In view of the preceding discussion, it is imperative that (1) odors should be directed
through control devices and a sufficiently tall stack, and (2) no strong odor source should
be permitted to vent directly into a building unless the building itself is vented through
an effective odor-control system .
The services of a professional meteorologist should be secured by those who plan to
construct new rendering plants, and by those who have received serious complaints at
existing establishments.
4.6 REFERENCES FOR SECTION 4
1. Rendering Plant Background Information for Establishing of Federal Standards of Per-
formance of Stationary Sources. Process Research, Inc. Cincinnati, Ohio. Task
Order No. 10. August 1971. p. 6.
2. Air Pollution Engineering Manual. Danielson, J. A. (ed.). U. S. Department of
Health, Education, and Welfare. Cincinnati, Ohio. Publication Number AP-40. 1967.
p. 776-778.
4-7
-------
3. Background Information for Proposed New Source Performance Standards, Technical
Report No. 10 - Rendering Plants-—Environmental Protection Agency. Research Tri-
angle Park, North Carolina. ' (Internal draft report dated January 1973.)
4. Walsh, R. T . The Inedible RenderingNlndustry, Informative Report Prepared for the
Tl-2, Chemical Industries Committee, Air Pollution Control Association. County
of Los Angeles. October 1965.
5. Burgwald, T. A. Identification of Chemical Constituents in Rendering Industry Odor
Emissions. ITT Research Institute. Chicago, Illinois. Project No. C8172. January
1971. p. 41.
6. Faith, W. L. Odor Sources and Control Systems in the Rendering Industry. Report
of the Fats and Proteins Research Foundation. July 1967. p. 7.
7. Air Pollution Aspects of Odors. Environmental Protection Agency . Washington, D. C.
(First Draft Copy) . February 1971. p . 6-205.
8. Doty, D. M. et al. Investigation of Odor Control in the Rendering Industry. Office
of Research and Monitoring , U. S. Environmental Protection Agency . Washington,
D. C. Contract No. 68-02-0260. October 1972.
9. Standard Method for Measurement of Odor in Atmospheres (Dilution Method) .
ASTM-D 1391-57. 1972 Annual Book of ASTM Standards. Part 23. American
Society for Testing Materials. Philadelphia, Pennsylvania.
10. Dravnieks, A. and W . H. Prokop. Source Emission Odor Measurement by a Dynamic
Forced-Choice Triangle Olfactometer. 66th Annual Meeting of the Air Pollution Con-
trol Association, Chicago. June 28, 1973.
11. Huey, N. A. etal. Objective Odor Pollution Control Investigations. J. Air Pollut.
Control Assoc. 10_:441-446, I960.
12. Rendering Plant Background Information for Establishing of Federal Standards of Per-
formance of Stationary Sources. Process Research, Inc. Cincinnati, Ohio. Task
Order No. 10. August 1971. p. 32.
13. Turner, D. B. Workbook of Atmospheric Dispersion Estimates (Revised). Environ-
mental Protection Agency, Office of Air Programs. Research Triangle Park, N. C.
Publication No . AP-26 . 1970 .
14. Private Communication, Herschel H. Slater to R. T. Walsh, EPA, Durham, N. C. ,
Dispersion of Odors at Rendering Plants. December 12, 1972.
15. Air Pollution Engineering Manual. Danielson, J. A. (ed.). U. S. DREW, PHS . The
National Center for Air Pollution Control. Cincinnati, Ohio. PHS No . 999-AP-40.
1967. p. 780.
4-8
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5. HEALTH AND WELFARE EFFECTS OF ODORS
5.1 INTRODUCTION
The influence of odors on the health and welfare of an individual is difficult to sub-
stantiate. This difficulty arises primarily from the lack of an objective measurement
technique. The results of several recent studies that attempted to evaluate the effects
of odors on the health and comfort of man are summarized in this section.
5.2 PHYSIOLOGICAL AND PSYCHOLOGICAL EFFECTS
The conclusions of two recent symposiums on odors are that (1) no data are available
to relate odors by themselves to any specific organic disease, and (2) odors bear no re-
lationship to the toxicity of a gas. Several studies have, however, linked odors to the
presence of the following symptoms: poor appetite, reduced consumption of water, im-
paired respiration, nausea, vomiting, insomnia, and mental perturbation.
Odors have also been associated with the aggravation of symptoms of chronic respir-
atory illness; •> they may cause attacks of asthma or other allergic conditions. It is diffi-
cult, however, to prove whether an allergic reaction is the result of the odor sensation
or of contact with the odorant substance itself.
5.3 ANNOYANCE
Public opinion surveys often identify malodors as the air pollutant that is most appar-
ent and of greatest personal concern to the individual. A recent national task group
evaluating air pollution research goals indicated that odors are of considerable concern
to the average person.^ This group also concluded that odors should be considered un-
desirable air pollutants, whether or not they are linked to long-term health effects, simply
because they constitute an annoyance to people.
Numerous cases of individuals obtaining legal redress because of damages suffered
from the presence of odors are cited. The injuries or inconveniences that resulted in
compensations for damages include loss of sleep, loss of appetite, nausea, vomiting, and
curtailment of the use or enjoyment of property.
5.4 ECONOMIC EFFECTS
The presence of odors can be expected to exert a negative trend on the price of
property. The extent of this trend depends upon the degree to which odors are perceived
as neighborhood characteristics and upon the extent to •which they are considered objec-
tionable by both the buyer and the seller of the property. The results of several studies
tend to support the preceding conclusions . 8- 11
5.5 REFERENCES FOR SECTION 5
1. The Third Karolinska Institute Symposium on Environmental Health. Methods for
Measuring and Evaluating Odorous Air Pollutants at the Source and in the Ambient
Air. Department of Environmental Hygiene, Karolinska Institute. Stockholm, Sweden.
June 1-5, 1970. p. 10-12 and 58-66. (See also Nordisk Hygienisk Tidskrift 5_1
(2) 1970.)
2. Kendall, D. A. and T . Lindvall (eds.). Evaluation of Community Odor Exposure.
Arthur D. Little, Inc. Cambridge, Mass. April 1971. p. 1 - 6.
5-1
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3. Sullivan, R. J. Preliminary Air Pollution Survey of Odorous Compounds. Department
of Health, Education, and Welfare. Raleigh, North Carolina. APTD 69-42. October
1969. p. 1 - 34 and 100 - 105.
4. Jonsson, E. , M. Deane, and G. Sanders. Community Reactions to the Odors from
Pulp Mills: A Pilot Study in Eureka, Calif. Department of Environmental Hygiene,
Karolinska Institute . June 1970. 29 p.
5. Sullivan, R. J. Preliminary Air Pollution Survey of Odorous Compounds. Department
of Health, Education, and Welfare. Raleigh, North Carolina. APTD 69-42. October
1969. p. 24.
6. Sullivan, R. J. Preliminary Air Pollution Survey of Odorous Compounds. Department
of Health, Education, and Welfare. Raleigh, North Carolina. APTD 69-42. October
1969. p. 192.
7. Peckham, B. W. Odors, Visibility and Art: Some Aspects of Air Pollution Damage.
(Presented at Seminar on the Economics of Air and Water Pollution. Water Resources
Research Center, Virginia Polytechnic Institute. Blacksburg, Virginia. April 1969.
29p.)
8. Ridker, R. G. and J. A. Henning. The Determinants of Residential Property Values
with Special Reference to Air Pollution. Review of Economics and Statistics. 49: 246 -
257, May 1967.
9. Ridker, R. G. Economic Costs of Air Pollution. Frederick O. Praeger, New York,
1967. p. 115 - 151.
10. Flesh, R. D. Property Value Differentials as a Measure of Economic Costs Due to
Odors. (Presented at Conference on the Dose-Response Relationships Affecting
Human Reactions to Odorous Compounds. Cambridge, Mass. April 1971.)
11. A Study of the Social and Economic Impact of Odors - Phase 11. A Report to the Envi-
ronmental Protection Agency from Copley International Corporation. La Jolla, Calif.
November 1971. p. 88.
5-2
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6. CONTROL TECHNIQUES FOR ODORS
There are several suitable control techniques that the rendering industry can employ
to comply with typical state and local regulations. These techniques involve treatment of
odorous streams by condensation, incineration, condensation-incineration combinations,
and chemical scrubbing . This chapter discusses the effectiveness and cost of these tech-
niques .
6.1 CONDENSERS
Selection of odor control equipment is influenced to a large degree by the moisture
content of the process stream . A high moisture content •would almost always necessitate
the use of a condenser as the preliminary component of any control system for reasons of
both efficiency and economy. Rendering plant gas streams can be divided into three gen-
eral types according to the percentage of condensables: (1) cooker gases consisting of
95 percent or more condensable moisture, (2) air drier exhaust gases with a maximum
moisture content of 30 percent, and (3) low-moisture plant ventilation air . ^
Although significant control of many high-moisture emissions can be accomplished by
condensation alone, this technique is not effective enough to be used independently as a
control for rendering plant malodors. Condensation is useful, however, •when applied in
conjunction with incineration or chemical scrubbing. Under these conditions, a conden-
ser reduces the load and energy requirement of secondary control equipment. For exam-
ple, condensation of steam from high-moisture gas streams (rendering cooker or blood
cooker exhaust) reduces the gas volume by a factor of 10 or more.
Most condensers are designed to provide sub-cooling of the gas stream and conden-
sate to approximately 120° to 140° F . The major purpose of a condenser is to reduce the
volume and moisture content of the gas stream prior to additional treatment; however,
some malodors condense or dissolve in the condensate. Table 6-1 presents measurements
of the odor-removal efficiency for both a direct-contact condenser and a surface condenser.
Table 6-1. ODOR REMOVAL EFFICIENCIES
1
Inlet cone. ,
o.u./min
25,000,000
25,000,000
Condenser
type
Surface
Direct
contact
Condensate
temp. , °F
80
80
Outlet cone. ,
o.u./min
12,500,000
250,000
Odor removal
efficiency, %
50
99
6.1.1 Contact Condensers
6.1.1.1 Description
Cooling of a rendering plant process stream can be accomplished through the use of
either a direct-contact condenser or a surface condenser . Either type of condenser will
result in some odor reduction because of the condensation of malodorous material. The
use of a direct-contact condenser results in more efficient odor removal because of the
scrubbing action associated with direct-contact cooling and because of greater liquid di-
dilution.
6-1
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Contact condensers are relatively uncomplicated pieces of equipment in which coolant,
vapor, and condensate are brought into intimate contact. Water is the usual coolant. The
direct-contact gas-liquid heat exchange can be accomplished in any of the following de-
vices: baffle-tray columns, spray chambers, barometric condensers, packed columns, or
high-velocity jets. The emphasis in this discussion will be placed on spray chambers and
barometric condensers because it is thought that these pieces of equipment are the most
applicable and the most commonly used.
The use of baffle-tray columns, packed columns, or high'-velocity jets would usually
result in unnecessary operating and maintenance problems as well as additional expenses.
Three variations of a contact condenser, including a spray chamber and a barometric
condenser, are presented in Figure 6-1.
PRESSURE
WATER
ENTRAINED
VAPORS
VAPOR
WATER
DISCHARGE b
SPRAY
Figure 6-1. Types of condensers (a) spray chamber, (b) jet, and (c) barometric (Courtesy
Schutte and Koertmg Co., Cornwell Heights, Pa.).
Spray chambers are one of the simplest types of direct-contact coolers. The liquid
coolant is introduced into the chamber by either spray nozzles or atomizers and brought
into contact with a countercurrent gas stream . The moisture content of the gas stream
is condensed and exits with the cooling water. In the case of rendering plants, this con-
taminated water must be sent to a sewage-treatment facility. The noncondensables exit
the spray chamber and are either sent to additional odor-control equipment or exhausted
to the atmosphere.
A second type of direct-contact condenser that has found considerable use in the
rendering industry is the barometric condenser shown in Figure 6-1. In this design,
part of the cooling water is sprayed into the vapor stream near the vapor inlet, and the
remainder is directed into the discharge throat. The condenser is usually positioned
high enough (34 feet minimum for high-vacuum processes) so that the •water can be dis-
charged by gravity from the vacuum in the condenser. Cooling water, condensate, and
noncondensables exit the condenser in a single stream and are collected in an enclosed
hot well in which the malodorous gases are separated from the liquid effluent. The liquid
effluent is drained from the hot well, passed through a grease trap, and sent to the sew-
age-treatment system. Noncondensable gases are vented and sent to additional control
equipment, e.g. , afterburner or scrubber.
6-2
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Some smaller installations utilize a sealed hot well for the actual condensation step .
This cooling technique is a low-cost, moderately efficient means of reducing the moisture
content of the cooker gases. The cooker off-gases are sent to an enclosed hot well where
they are introduced below the liquid level and brought into direct contact with a stream
of cooling water. The cooling water flow rate is usually adjusted to provide a liquid ef-
fluent exit temperature of approximately 140° F . Noncondensable gases are vented from
the hot well and sent to additional control equipment.
The major factor to be considered during the design of a contact condenser is the
volume of cooling water required. This volume can be calculated by computing the
amount of heat to be removed and determining the allowable cooling water exit temperature.
Both the latent heat of vaporization and the amount of sub-cooling of the condensate re-
quired should be considered when setting heat-removal requirements. In a contact-type
condenser, approximately 16 pounds of water at 70° F is required to condense 1 pound of
steam at 250° F and cool the condensate to 140° F .
In a typical cylindrical spray chamber condenser, a contact time of 1 second with a
cross-sectional velocity of 400 to 500 feet per minute has been used. 3 Pressure drops for
these units are small.
In comparison with surface condensers, contact condensers are more flexible, simpler
to operate, and less difficult to maintain. Although the initial equipment cost for a direct-
contact condenser is less than that for a surface condenser designed to provide an equiva-
lent amount of cooling, the operating costs for the former are higher. Because cooling
water is not recycled, contact condensers require far more water than surface condensers
and produce 10 to 20 times more waste water. This large volume of waste water can create
a disposal problem .
6.1.1.2 Emission Reduction
The use of a direct-contact condenser can reduce malodorous emissions from render-
ing plant process streams by approximately 99 percent. This emission reduction is
based on a volume reduction of 95 percent and is accompanied by a decrease in malodor
concentration from 50,000 to 2,000 odor units per standard cubic foot. The effectiveness
of contact cooling can be traced to the scrubbing action associated with this cooling tech-
nique. A reduction to 2,000 odor units can be accomplished only if clean water is used
in the contact condenser.
6.1.1.3 Condensate Treatment and Aqueous Waste Costs
The amount of treatment required by a particular sewage is usually measured on one
of two bases: (1) the amount of suspended solids or (2) the biological oxygen demand
(BOD) , which measures the amount of impurities by the amount of oxygen required to
oxidize it. Liquid effluent from rendering plants (condenser condensate, wash water,
etc.) is often high in both suspended solids content and BOD .
Grease traps are usually installed prior to any condensate or sewage treatment facility.
Where there is significant grease in the water, treatment with alum or similar chemicals
could be required.
If the rendering operation is located near an urban area, the sewage is in many in-
stances sent to a municipal sewage treatment facility. At least half of the industry disposes
of its aqueous wastes in this manner. The fee charged will vary with the locality and may
include a surcharge based on suspended solids content and BOD. A typical practice is to
base the sewage charge on the water consumption of the plant. In this case, the sewage
fee is usually similar to the water cost. The fee charged by one municipal treatment plant
contacted is composed of both a regular charge based on the volume of water used and a
surcharge for suspended solids and BOD . A surcharge of $30 per 1000 pounds of solids
and $23 per 1-000 pounds BOD is included for solids content and BOD in excess of 300 ppm.4
6-3
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Another way of estimating charges for sewering of wastes in a municipal sewer is as
follows:
Water charge 25
-------
Table 6-3. BATCH-TYPE MODEL RENDERING PLANTS
Model
A
B
C
D
Annual sales,
$
184,000
915,000
2,620,000
3,980,000
Number of
cookers
1
3
6
9
Raw material
process rate,
Ib/hr
1,560
5,200
15,000
22,500
Peak gas
volume to
condenser,
acfm (3 250 °F
700
2,300
6,700
10,000
effluent. Both of these estimates are based on no recirculation. Some recirculation could
be used if a good secondary control device, like an afterburner, were used.
6.1.1.4 Equipment Costs
This section presents estimates of the capital investment, direct operating cost, and
total annual cost (commonly called operating cost) associated with the installation and
use of a direct-contact condenser. Definitions of these cost and investment terms and
descriptions of the procedure used to arrive at these estimates are provided in Section 7.
All condenser costs are based on the use of stainless steel as the construction material
because of the corrosive nature of rendering plant off-gases .
The estimation of control costs for the rendering industry is difficult because of the
wide range of plant sizes. Costs are presented in this document for four model plants
that are assumed to provide a representative view of the industry. The model plants
are summarized in Table 6-3.
Approximately 80 percent of the existing rendering plants are thought to be batch
operations. Models A through D are representative of this portion of the industry. The
remaining 20 percent of existing plants are newer continuous operations that are often
adequately controlled.
The capital investment, direct operating cost, and total annual cost of a direct-con-
tact condenser for Model Plants A and B are listed in Table 6-4. The use of a direct-
contact condenser for plants similar to Models C and D was not considered because of
the large cooling water requirements and the high sewage treatment cost involved. Cap-
tive rendering plants and plants located near large bodies of water , however , may be
able to utilize kill-floor water or local water if they already have adequate BOD treatment
for their waste water. Operating costs for these plants might be lower than the figures
given in Table 6-4, and contact condensers might be economically attractive for most of
the model plants.
All operating costs and process rates are based upon operation for 2,140 hours per
year for Model A and 3,200 hours per year for Model B, derived from production and
plant size data in the 1967 U.S. Census of Manufacturers. The cookers were not nec-
essarily assumed to be of the same sizes among plants.
Condensers are sized to handle peak evaporation rates (Table 6-3) , which in turn
are assumed to be approximately double the average rate. Average evaporation rates
were calculated assuming a 50 percent moisture content of the raw feed and a 90 percent
moisture reduction during the cook cycle. Cooker off-gases were estimated to consist
of 95 percent moisture and 5 percent noncondensables.
6-5
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Table 6-4. CAPITAL INVESTMENT, DIRECT OPERATING COST,
AND TOTAL ANNUAL COST OF A DIRECT-CONTACT CONDENSER
Raw material process rate, Ib/hr
Capital investment, $
Operation, hr/yr
Operating costs, $/yr
Water
Sewage
Electricity
Total direct cost3, $
Depreciation (10-year straight
line), $/yr
Interest, taxes, insurance (10%), $/yr
Maintenance (3%), $/yr
Total annual cost,3 $/yr
Model A
1,560
2,900
2,140
720
2,280
20
3,000
290
290
90
3,700
Model B
5,200
5,000
3,200
3,500
11,400
70
15,000
500
500
150
16,000
aTotal has been rounded to two significant figures,
The costs of contact condensers for Model Plants A and B were obtained from direct
communication with several equipment vendors and manufacturers. Estimates include
the cost of a temperature-flow control on the cooling water stream. All equipment costs
reflect a January 1973 basis.
The cost of cooling water was based on a charge of $0.25 per 1000 gallons. It was
assumed that 16 pounds of water was required to condense and sub-cool each pound of
steam. The sewage charge was based on a fee of $0.75 per 1000 gallons of -waste water
treated. Electrical costs were for the operation of a 1-horsepower pump for Model A and
a 2-horsepower pump for Model B. A cost of $0.015 per kilowatt-hour was assumed.
6.1.2 Water-Cooled Surface Condensers
6.1.2.1 Description
Condensation of rendering plant vapors can also be accomplished through the use
of a surface condenser. In a surface condenser, a heat transfer surface separates the
coolant from the vapor stream. The advantage of this type of condenser is that it produces
a much smaller quantity of condensate, which results in reduced sewage treatment costs.
Surface condensers also have lower operating costs in comparison to contact condensers
since the coolant can be recycled.
The most commonly used surface condensers are shell-and-tube condensers using
water as the coolant, and extended surface condensers using ambient air as the cooling
medium. This section discussed the use of shell-and-tube (water-cooled) units. Section
6.1.3 evaluates the use of extended surface (air-cooled) condensers.
Most water-cooled surface condensers are of the shell-and-tube type with the coolant
on the tube side and the condensing vapors on the shell side. A diagram of a shell-and-
tube condenser is presented in Figure 6-2.
6-6
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VAPOR
INLET
TUBES
NON-CONDENSATE
OUTLET
WATER ft-/"
OUTLETS
WATER
INLET
CONDENSATE
OUTLET
Figure 6-2. Shell-and-tube condenser.
The vapor stream enters the condenser on the shell side and is condensed by contact
with the cool tube surface. The condensate is then drained from the bottom of the con-
denser and sent to a sewage treatment facility. Noncondensable gases are vented from the
unit and sent to additional control equipment. The cooling water exits the condenser and
is usually sent to a cooling tower where it is chilled and recycled to a condenser for reuse.
When condensers are used as air pollution control devices, care should be taken to
minimize the evolution of volatiles from the discharged condensate. This usually requires
sub-cooling of the condensate to approximately 140° F or less. In general, sub-cooling re-
quirements for surface condensers should be more stringent than for contact condensers
because of the more concentrated nature of the condensate. In a horizontal-tube unit of
the type shown in Figure 6-2, condensate sub-cooling can be obtained by: (1) reducing
the pressure on the shell side, (2) adding a separate sub-cooler, or (3) using the lower
tubes for sub-cooling . The use of a special arrangement to provide cooling of the conden-
sate may not be necessary with vertical-tube condensers since some degree of sub-cooling
is provided under ordinary operating conditions.
In the design of a surface condenser, the area available for heat transfer is the critical
factor. This area can be computed with the following equation:
A = UATm
where: A = Heat transfer area, ftr
Q = Heat to be removed, Btu/hr
U = Overall heat transfer coefficient, Btu/hr-ft^-T
ATm = Logarithmic mean temperature difference, °F
The solution of this equation may be difficult because the overall heat transfer coef-
ficient (U) is dependent on several parameters of the condensing and cooling streams. An
overall heat transfer coefficient of 130 Btu per hour per square foot per "F was estimated
for a water-cooled shell-and-tube condenser .
6.1.2.2 Emission Reduction
A surface condenser designed to provide sub-cooling of the condensate will reduce
odor emissions. In one case, a surface condenser that subcooled the condensate to 80° F
reduced the odor emissions by approximately 50 percent. Although the 50 percent re-
duction was based on measured odor concentrations, the flow rate from the condenser
was estimated because of its low velocity. This reduction is usually impractical because
6-7
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cooling-tower water cannot be cooled low enough to cool condensate to 80" F at usual wet-
bulb temperatures. In addition, odor concentrations increase across a surface condenser
as indicated in Table 6-1. These facts necessitate the venting of noncondensable gases to
additional control equipment.
6.1.2.3 Condensate Treatment
Surface condensers avoid the ten-fold water dilution that occurs with contact conden-
sers. This large reduction in volume of contaminated water requiring treatment is the
major advantage of a surface condenser . It is estimated that a plant similar to Model B
would produce approximately 280 gallons per hour of waste water; a plant similar to Model
C, 820 gallons per hour; and a plant similar to Model D, 1200 gallons per hour. A dis-
cussion of the sewage treatment required for condenser condensate was presented in
Section 6.1.1.3.
6.1.2.4 Equipment Costs
6.1.2.4.1 Introduction--The cost of a water-cooled shell-and-tube condenser is pre-
sented for Model plants B, C, and D. It is thought that a plant similar in size to Model A
would elect to install a direct-contact condenser under most circumstances. Table 6-5
Table 6-5. CAPITAL INVESTMENT, DIRECT OPERATING
COST, AND TOTAL ANNUAL COST OF A WATER-COOLED
SHELL-AND-TUBE CONDENSER
Raw material
Process rate, Ib/hr
Capital investment, $
Shell -and- tube
condenser
Cooling tower
Total capital
investment
Operation, hr/yr
Operating costs, $/yr
Water
Sewage
Electricity
Total direct costa,$
Depreciation (10-year
straight line), $/yr
Interest, taxes,
insurance (10%), $/yr
Maintenance (3%)b, $/yr
Total annual cost3,
$/yr
Model B
5,200
10,000
12,000
22,000
3,200
350
570
360
1,300
2,200
2,200
660
6,400
Model C
15,000
20,000
29,000
49,000
3,200
1,000
1,700
1,100
3,800
4,900
4,900
1,500
15,000
Model D
22,500
31,000
43,000
74,000
3,200
1,600
2,500
1,600
5,700
7,400
7,400
2,200
23,000
Total has been rounded to two significant figures.
Maintenance may also be estimated at 5 percent.
(See Section 7.)
6-8
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lists the capital investment, direct operating cost, and total annual cost associated with the
use of a shell-and-tube condenser.
6.1.2.4.2 Discussion--Condenser and cooling-tower costs were based on estimates
obtained from several equipment vendors and manufacturers. Condenser costs are for a
unit consisting of a carbon steel shell and stainless steel tubes in a fixed-tube sheet. The
condensers were assumed to operate at approximately atmospheric pressure and were de-
signed for peak evaporation rates. Design calculations were based on a logarithmic mean
temperature difference of 90° F, with a condensate exit temperature of 140° F and an overall
heat-transfer coefficient of 130 Btu per hour per square foot per °F. Cooling towers were
designed to provide cooling from 115° to 85° F at a wet-bulb temperature of 78° F. All
costs reflect a January 1973 basis.
Water costs were assumed to be 10 percent of the cost associated with a direct-contact
condenser. Sewage charges were based on a rate of $0.65 per 1000 gallons of condensate
(location near larger municipalities than were assumed in Table 6-4) . Electrical charges
were based on a 10-horsepower motor requirement for Model B, a 30-horsepower require-
ment for Model C, and a 45-horsepower requirement for Model D. These requirements in-
clude both cooling-tower fan and pumping motors. The cost of electricity was assumed to
be $0.015 per kilowatt-hour.
The operating costs for Models C and D are based on a 3,200-hour year. As with
Models A and B , these estimates were made from production and plant size data in the 1967
U. S. Census of Manufacturers .
6.1.3 Air-Cooled Surface Condensers
6.1.3.1 Description
Air-cooled surface condensers are used extensively in those cases wherein heat re-
jection from a process is possible by using ambient air as the coolant. Air-cooled con-
densers are usually constructed with either fin tubes or some other form of extended
surface to increase the heat transfer area. A typical fin tube design is shown in Figure
6-3. Condensing steam has a large heat-transfer coefficient, and air has a very small
one. Therefore, air is placed on the fin side to take advantage of the large heat-transfer
area. Condensation occurs inside the tubes.
Air-cooled condensers offer an advantage over water-cooled units in that they require
no water connections, cooling towers, or cooling-water treatment and are simpler to in-
stall'. Operating costs for an air-cooled condenser may be higher than for an equivalent
water-cooled condenser, however, because of the larger power consumption of the fan.
Air-cooled condensers are usually provided with multiple fan units, one of which has
a two-speed motor. As the ambient air temperature decreases, a temperature probe in the
condensate line senses the corresponding decrease in water temperature and either shuts
off fan motors or switches the two-speed fan motor to a lower speed. This conserves
power and prevents condenser freeze-up during the winter months.
6.1.3.2 Emission Reduction
The emission reduction associated with the use of a surface condenser was discussed
previously in Section 6.1.2.2. If a condenser could be designed to provide cooling of the
condensate to 80° F, the odor emissions would be decreased by about 50 percent.-'- Most
air-cooled condensers, however, are not designed to provide cooling of the condensate
below 140° F, and their main function is to condense water vapor.
6.1.3.3 Condensate Treatment
Condensate treatment is the same as that provided for the condensate from a direct-
contact condenser. Condensate volumes range from 280 gallons per hour for Model B to
6-9
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Figure 6-3. Types of air-cooled surface condensers (top) fin tube (courtesy
Calumet and Hecla, Inc., Allen Park,_Mich.) and (bottom) fin fan (courtesy
Hudson Engineering Corp., Houston, Texas).2
1200 gallons per hour for a plant comparable to Model D. A discussion of the required
sewage treatment was presented in Section 6.1.1.3.
6.1.3.4 Equipment Costs
6.1.3.4.1 Introduction--This section presents the cost of air-cooled condensers for
Model plants B, C, and D. The relatively high initial cost of this type of condenser would
6-10
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make its use impractical in a plant similar to Model A Table 6-6 presents estimates
of the capital investment, direct operating cost, and total annual cost.
Table 6-6. CAPITAL INVESTMENT, DIRECT OPERATING COST,
AND TOTAL ANNUAL COST OF AN AIR-COOLED SURFACE CONDENSER
Raw material process
rate, Ib/hr
Capital investment, $
Air-cooled surface
condenser
Operation, hr/yr
Operating costs, $/yr
Electri city
Sewage
Total direct cost3
Depreciation (10-year
straight line), $/yr
Interest, taxes, insurance
(10%), $/yr
Maintenance (3%), $/yr
Total annual cost,a $/yr
Model B
5,200
16,000
3,200
540
570
1,100
1,600
1,600
480
4,800
Model C
15,000
44,000
3,200
1,600
1,700
3,300
4,400
4,400
1 ,300
13,000
1 i
Model 0
22,500
58,000
3,200
2,200
2,500
4,700
5,800
5,800
1,700
18,000
Total has been rounded to two si am'ficant numbers.
6.1.3.4.2 Discussion - -The costs of air-cooled surface condensers were obtained
from recent contacts with several equipment vendors. Costs are based on the use
of stainless steel tubes equipped with aluminum fins. Design calculations assumed
a logarithmic mean temperature difference of 100° F and an overall heat-transfer
coefficient of 7 . 7 Btu per hour per square foot per °F. Condensers were sized to
handle peak evaporation rates. Costs are on a January 1973 basis.
Sewage costs were based on a charge of $0.25 per 1000 gallons of condensate treated.
Electrical costs were for the operation of a 15-horsepower fan for Model B, three 15-
horsepower fans for Model C, and four 15-horsepower fans for Model D. A rate of
$0.015 per kilowatt-hour was used for all calculations.
Comparison of Tables 6-6 and 6-5 indicates higher costs for shell-and-tube than for
air-cooled condensers for the model cases taken. In practice, such costs can be altered
by relative heat-transfer fouling tendencies of various odorous streams, relative main-
tenance requirements, meteorological conditions for the locality, and availability and
temperature of water.
6.2 INCINERATORS
Flame incineration is an effective control method for rendering-plant odors provided
the incineration Hme and temperature are sufficient for complete oxidation of odorous
vapors. In fact, many state and local control agencies have established odor-control reg-
ulations based on flame incineration time and temperature.
6-n
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The presence of the flame appears to have a very important effect on the efficiency of
odor removal. It has been suggested that in the absence of a flame, using electrical ther-
mal heat alone, much higher temperatures would be required to obtain the same efficiency
achieved with a direct-flame oxidation system . Data on themal destruction of odors by
electric heating, however, are very limited.
Incinerators have been used alone and in combination with other control equipment,
principally condensers. Total incineration is used to control low-volume, low-moisture
streams such as cooker noncondensables. In some instances, a dust collector (centrifug-
al collector, baghouse, or precipitator) must be used ahead of an incinerator to remove
particulate matter .
6.2.1 Description
Figure 6-4 is a diagrammatic representation of a rendering plant afterburner with heat
recovery. The burner has a mixing plate or other suitable design so that all of the air
used for full combustion comes from the odorous air stream . If the combustion air were
taken from outside, a greater amount of fuel would be required to raise to 1200° F the ad-
ditional air so introduced into the system. As shown, the total gas stream is raised to
1200° F to destroy odor, and about half of the heat is recovered by exchange against the
feed stream. From a practical standpoint, 65 percent heat recovery is about the maximum
attainable. The offerings of one afterburner manufacturer include units for 35 percent
and 42 percent heat recovery. The unit price increases •with the percentage of heat re-
covery, as does the power required to move the gas. Fuel saving greatly offsets this in-
creased power cost, however.
ODORLESS EXIT GASES
700°F ~^
ODOROUS AIR
250 °F )
HEAT EXCHANGER
750°F
1200°F
NATURAL GAS
OR FUEL OIL "
Figure 6-4. Diagrammatic representation of rendering plant afterburner
with heal recovery.
Ideally, the heat saving indicated by Figure 6-4 would approach 100 percent if the
exit odorless air could be cooled to perhaps 260° F instead of 700° F as indicated. This
is not feasible because of the greater heat exchange surface requirements and the phenome-
non of temperature crossing. Figure 6-4 shows a diagrammatic heat exchanger in which
the cold gas flows through tubes or other passages separated from the hot gas flow . It is
6-12
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obvious that the two shell-side baffles tend to prevent back-mixing and, therefore, aid
heat transfer by increasing the temperature differences in each of the three exchanger
portions. Each baffle also contributes to increased gas-pressure drop. Similarly, one
could get increased heat recovery with two or more shells, but at the expense of further
capital cost and pressure drop .
The usual construction of an incinerator employs a steel outer shell lined with a re-
fractory material. The purpose of the refractory is to protect the steel shell from direct
exposure to high temperatures and corrosive materials , and to improve thermal efficiency
by limiting heat losses. The refractory may have any one of a number of chemical com-
positions and physical forms. Most refractories used in incinerators are made up of high-
duty fire clay and are usually encountered in the form of bricks and castables . In some
instances high-temperature alloy metals are used as liners.
Figure 6-5 is a sketch of an incinerator with a heat-recovery unit. The odorous
stream enters the incinerator at the inlet elbow and is heated as it passes through the
crossover duct and enters the combustion chamber where it is incinerated. Heat is re-
covered from the incinerated stream as it passes around the tubes of the heat-recovery
unit before being discharged through the stack. Heat-recovery afterburners are usually
constructed almost entirely of metal.
This type of heat recovery unit is practical (fuel saving over the cost of the heat-re-
covery unit) for incinerators processing large-volume streams. Other heat-recovery
units use waste heat to produce steam. Incinerators are usually fired with gas, but may
use distillate fuel oil if gas is unavailable.
The fuel shortage and the rising costs of fuel should draw much attention to the im-
provement of afterburners and heat recovery, as well as furnish added incentive for the
improvement of scrubbers and of odor testing to demonstrate their performance.
6.2.2 Boiler Firebox Incineration
In order to minimize incineration costs, some rendering plants are using boiler fire-
boxes to incinerate cooker noncondensables and other low-volume, low-moisture reduc-
tion streams. Firebox incineration is attractive because it lowers initial capital invest-
ment and operating costs by eliminating the need for an incinerator and its associated
fuel, operation, and maintenance .
Water-tube, locomotive or HRT boilers, and fired heaters are the units most frequent-
ly used as afterburners. Burners used with these units are usually adaptable to incin-
eration, and the fireboxes are usually accessible. Scotch marine boilers, another type,
are sometimes adaptable.
The odorous gases may be introduced either through the burner or through the floor
or sides of the fireboxes . Figures 6-6a and 6~6b show examples of poor and good instal-
lations in which the odorous gases are introduced through the burner.
Boiler firebox conditions approximate those of a well-designed incinerator, provided
adequate temperature, retention time, turbulence, and flame are present Completely
satisfactory adaptations of boiler fireboxes for use as incinerators, however, are not
common. All aspects of operations should be thoroughly evaluated before this method of
odor control is used. Some problems that may accompany firebox incineration are dis-
cussed below .
Contaminants from cooker noncondensables and other reduction streams can foul the
burner and boiler tubes. Some plants use water scrubbers (contact condensers) to clean
the reduction streams before passing them through the controls and burners and incin-
erating them in the boiler firebox.
6-13
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6-14
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CONTAMINATED-AIR DUCT
BOILER FIREBOX
DIFFUSER
VARIABLE LOUVERS
FOR MULTI-JET BURNER
Figure 6-6a. Poor method of introducing odorous air from diffuser to boiler firebox
through the burner air register. Diffuser restricts combustion air to burner, also the
louvers may partially close, restricting flow of odorous air into boiler firebox.8
CONTAMINATED-AIR
DUCT
BOILER FIRE-
BOX
.VARIABLE
LOUVERS
CUSTOM-MADE AIR
REGISTER FOR MULTI-
JET BURNER
Figure 6-6b. Good method of introducing odorous air to boiler firebox through a
custom-made air register. There is good flame contact 8
The boiler must be fired at an adequate rate at all times when effluent is vented to
the firebox, regardless of steam requirements. High-low or modulating burner controls
are satisfactory provided that the minimum firing rate is sufficient to incinerate the max-
imum volume of effluent that can be expected in the boiler firebox. A burner equipped
with on-off controls •would not be feasible.
There is a possibility of accumulating concentrations of combustible gas with resul-
tant explosion hazards upon lightoff of the boiler. For instance, a batch of raw or par-
' tially cooked animal matter might be left overnight in a cooker ducted to a boiler firebox
incinerator. This decomposing matter might generate enough methane, hydrogen sulfide,
6-15
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and other organics to produce an explosive mixture in the ductwork leading 1o the boil-
er." If, subsequently, the burner were ignited without first purging the line, an explo-
sion could occur. Also, a fire hazard is created by the accumulation of organic material
in ductwork. The degree of organic accumulation can sometimes be reduced by frequent
steam purging or by heating the ductwork to prevent condensation.
6.2.3 Emission Reduction
The Los Angeles County Air Pollution Control District tested four rendering plants
that use incineration to control cookers, blood driers, and feather meal driers. Inciner-
ation units at these plants were operated at 1200° F with a stream retention time of 0 . 3
second. Outlet emissions ranged from 70 to 140 odor units per standard cubic foot, with
an average of 105 odor units per standard cubic foot. These results represented an odor-
removal efficiency of better than 99 percent."
6.2.4 Equipment Costs
The gas volumes to the incinerator were estimated by reducing peak cooker emissions
(700, 2,300, 6,700, and 10,000 acfm for Models A, B, C, and D, respectively) by a factor
of 10, and adding 400 acfm per cooker for accompanying presses and processing tanks.
The volumes of the incinerated streams are listed in Table 6-7.
Table 6-7. VOLUMES OF INCINERATED STREAMS
Volume of non- Volume of streams Approximate
condensables from presses and volume to
from cookers, Number of processing tanks, incinerator,3
Model acfm @ 250 °F cookers acfm @ 250 °F acfm (P 250 °F
A
B
C
D
70
230
670
1,000
1
3
6
9
400
1,200
2,400
3,600
500
1,500
3,000
5,000
aTotal has been rounded to two significant figures. These volumes are the
basis of the incinerator sizes used in the cost estimates in Table 6-8.
Incinerator costs (Table 6-8) were determined for low-moisture, low-volume streams
from cookers (noncondensables only), presses, process tanks, and driers. Condenser
costs must be added to these figures to obtain the total cost of control. Condenser costs
are listed in Tables 6-4, 6-5, and 6-6, and total costs are listed in Table 6-9.
Incinerator costs for the models were obtained by averaging quotes from several man-
ufacturers. The costs reflect a January 1973 basis.
Electrical costs were for the operation of a 0.75-horsepower fan motor for Model A, a
2. 5-horsepower fan for Model B, a 7-horsepower fan for Model C, and a 17. 5-horsepower
fan for Model D. A rate of $0.015 per kilowatt-hour was used for all calculations.
Table 6-8 indicates that the capital investment of flame incineration is proportionately
higher for smaller plants. For instance, Model D's 5,000 acfm incinerator, which handles
10 times the volume of Model A's 500 acfm incinerator, is just slightly over twice the coct.
Annual costs are more in line with incinerator sizes but are still proportionately higher
for smaller plants because of depreciation, taxes, and maintenance costs.
6-16
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Table 6-8. CAPITAL INVESTMENT, DIRECT OPERATING COST,
AND TOTAL ANNUAL COST OF INCINERATION
Capital investment, $
Incinerator
Operation, hr/yr
Operating costs, $/yr
Fuel
Electricity
Total direct cost,3 $
Depreciation (10-yr straight line), $/yr
Interest, taxes, insurance (10%), $/yr
Maintenance (62), $/yr
Total annual costs, a $/yr
Model A
9,500
2,140
1,000
20
1,000
950
950
560
3,500
Model B
13,000
3,200
4,600
90
4,700
1,300
1,300
780
8,100
Model C
18,000
3,200
9,200
250
9,500
1,800
1,800
1,080
14,000
Model D
20,000
3,200
15,000
630
16,000
2,000
2,000
1,200
21,000
Total has been rounded to two significant figures. See Table 6-3 for process
rate and Table 6-7 for gas volumes to incinerators.
6.2.5 Fuel Costs
It was assumed that the afterburner fuel was natural gas and that no heat recovery
was practiced. It was further assumed that the combustion air was the odorous gas
(Section 6.2.1) . The following data and assumptions were used:
1. Natural gas cost
2 . Net heating value of gas
3. Net heating value of gas
4. Density natural gas
5 . Incineration temperature
6 . Specific heat (average) air
7 . Specific heat (average) gas
$1/103 scf
900 Btu/scf
19,000 Btu/lb
0.046 Ib/ft3
1200° F
0.255
0.80
Then, for Model C, 3000 acfm of air to incinerator at 250° F is 10,200 Ib/hr of air,
basis 70° F standard.
10,200(1200 - 250)0,255 + X (1200 - 70) 0.80 = 19,600X
X = fuel rate =132 Ib/hr natural gas
From this, the annual fuel cost at 3200 hours operation is $9200.
For No. 2 fuel oil, we may find the fuel cost for Model C on the following assumptions:
net heating value of no. 2 oil 18,000 Btu/lb
Ib/gal
specific heat (average) oil
oil cost (6/73)
7.2
0.47
$0.17/gal
6-17
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Table 6-9. CAPITAL INVESTMENT, DIRECT OPERATING COST,
AND TOTAL ANNUAL COST OF A CONDENSER-INCINERATOR SYSTEM
Raw material
process rate, Ib/hr
Capital investment, $
Surface condenser
(water-cooled)
Cooling tower
Surface condenser
(air-cooled)
Contact condenser
Incinerator
Total capital investment, $
Operation, hr/yr
Operating costs, $/yr
Fuel
Water
Sewage
Electrical
Total direct cost9, $
Depreciation (10-year
straight line), $/yr
Interest, taxes, insurance
(10%), $/yr
Maintenance (3%)b, $/yr
Total annual cost,3 $/yr
Model A
1,560
2,900
9,500
12,000
2,140
1,000
720
2,280
40
4,000
1,200
1,200
650
7,100
Model B
5,200
10,000
12,000
13,000
35,000
3,20C
4,600
350
570
450
6,000
3,500
3,500
1,400
14,000
16,000
13,000
29,000
3,200
4,600
570
630
5,800
2,900
2,900
1,300
13,000
5,000
13,000
18,000
3,200
4,600
3,500
11,400
160
20,000
1,800
1,800
930
25,000
Total has been rounded to two significant figures .
Maintenance for incinerators is 6 percent of their investment.
In this case, the fuel rate is 141 Ib/hr, and the cost is $10,700/yr.
If all of the combustion air for Model C had been taken from the outside, 10.36 scf of
extra air per scf of natural gas would have been added to the stream being heated. This
amounts to 16.9 Ib air/lb natural gas burned.
(10,200 + 16.9X) (1200 - 250) 0.255 + X (1200 - 70) 0.80 = 19,600X
The fuel rate increases to 168 Ib/hr of natural gas, and the annual cost is $12,000.
6.3 CONDENSER-INCINERATOR SYSTEMS
Condenser-incinerator combinations are usually more practical as well as more ef-
ficient than incinerators, especially for controlling cooker streams. When a condenser is
used to remove steam from cooker streams before incineration, the volume of the stream
is reduced as much as 20 times, and a considerable portion of malodors is removed with
the condensate.9 Other reduction streams that contain from 15 to 40 percent moisture
6-18
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Table 6-9 (continued). CAPITAL INVESTMENT, DIRECT OPERATING COST,
AND TOTAL ANNUAL COST OF A CONDENSER-INCINERATOR SYSTEM
Raw material
process rate, Ib/hr
Capital investment, $
Surface condenser
(water-cooled)
Cooling tower
Surface condenser
(air-cooled)
Incinerator
Total capital investment, $
Operation, hr/yr
Operating costs, $/yr
Fuel
Water
Sewage
Electrical
Total direct cost3, $
Depreciation (10-year
straight line) , $/yr
Interest, taxes, insurance
(10<), $/yr
Maintenance (3%)b, $/yr
Total annual cost,* $/yr
Model
15,000
20,000
29,000
18,000
67,000
3,200
9,200
1,000
1,700
1,300
13,000
6,700
6,700
2,600
29,000
C
44,000
18,000
62,000
3,200
9,200
1,700
1,900
13,000
6,200
6,200
2,400
28,000
Model
22,500
31,000
43,000
20,000
94,000
3,200
15,000
1,600
2,500
2,200
21,000
9,400
9,400
3,400
43,000
D
58,000
20,000
78,000
3,200
15,000
2,500
2,800
20,000
7,800
7,800
2,900
39,000
Total has been rounded to two significant figures.
Maintenance for incinerators is 6 percent of their investment.
may also warrant the use of a condenser. ® Factors such as volumes, exit temperatures,
fuel costs, water availability, and equipment cost determine condenser feasibility for
these streams.
Figure 6-7 shows a typical condenser-incinerator system. The entrainment separa-
tor prevents animal matter that may escape the cooker from entering the condenser and
incinerator. The use of a water-cooled surface condenser indicates that the system is
probably designed to handle a large volume of cooker gases. Notice that the low-mois-
ture streams are added downstream from the condenser.
6.3.1 Emission Reduction
Tests by the Los Angeles County Air Pollution Control District showed the following
emissions for rendering plants controlled by condenser-incinerator systems: 9
6-19
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INCINERATED GASES TO ATMOSPHERE
ODOR PRODUCING
GASES FROM
FACILITIES OTHER
THAN COOKER
X
GASES FROM
COOKER
WATER COOLED
SURFACE CONDENSER
STACK
INCINERATOR
^"•=31
/
GAS OR OIL
SOLIDS RETURN
TO COOKER
Figure 6-7. Odor-control system with entrainment separator, surface condenser, and incinerator.
1. Contact condenser-incinerator systems:
a. Three plants with cookers and blood dryers - Avg . 63 o.u./scf*
b. Six plants with cookers -Avg. 27 o.u./scf
2. Surface condenser-incinerator systems:
a. Four plants with cookers and blood dryers
b. Three plants with cookers using boiler incineration
c. One plant with cooker, press, and processing tank
- Avg . 99 o.u./scf
- Avg . 27 o.u . /scf
- Avg . 85 o.u. /scf
Figure 6-8, which compares the effectiveness of several incineration and condenser-
incinerator systems, shows that the aforementioned odor reductions are slightly better
than the results obtained by incineration alone. Although both methods provide greater
than 99 percent efficiency, the combination system results in a much lower odor emis-
sions rate.
6.3.2 Equipment Costs
Table 6-9 outlines control costs for existing plants, represented by Models A, B, C,
and D. The cost data for contact and surface condensers were calculated in Sections
*The odor unit per standard cubic foot was defined in Section 4.3.
6-20
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JUU
200
~
o
EX5
O
C/O
CO
LU
CO
I 100
a
0
50
n
LEGEND
FACILITY
1- COOKER,
BLOOD DRYER
2 COOKER
3 COOKER, BLOOD DRYER
4 - COOKER, BLOOD DRYER
5 - COOKER
6 COOKER, PRESS
7 -COOKER, PRESS
CONTROL
DEVICE
a - CONTACT COND
AFTERBURNER
b - AFTERBURNER
c - SURFACE COND.
AFTERBURNER
U
PROCESS TANK d - SURFACE COND ,
PROCESS TANK, BOILER
BLOOD PRESS, BLOOD DRYER e - BOILER COND.
8 - FEATHER
MEAL
DRYER
- BOILER
9 - COOKER, BLOOD DRYER. BLOOD COAG
10 PRO
CESS TANK
11 - COOKER
la
la
la
n
2a
n
2a
-, 2a 2a
nn
4c
3b
3b
3b
2a
n
4c
^™~
4c
4c
5d
5d
6c
5d
n
—
8b
9c
nllc
n
ABCDE1E2FGH I Jj J2 K L Wi M2 N 0 P Q R S T U V
RENDERING PLANT
Figure 6-8 Odorous emissions from various facilities.
6.1.1.4, 6.1.2.4, and 6.1.3. 4. The cost data for incinerators were calculated in Section
6.2.4.
Cost figures for Model A are determined only for contact-condenser-incinerator sys-
tems because, in most cases, water- and air-cooled surface condensers are too costly for
this size plant. On the other hand, costs are shown for all three alternatives for Model
B (contact and air- and water-cooled condensers coupled with an incinerator) since
their costs are more comparable, and the least expensive control system will vary, de-
pending on individual plant circumstances. Local water, electricity , sewage treatment
costs, and the actual bids on equipment and installation costs will determine the most
economical choice for a plant of Model B's size. Although the control costs for contact
condensers are high for Model B, these costs were calculated for city water usage. As
pointed out in Section 6.1.1.4, some rendering operations have access to free water,
and contact condensers would be economical for these plants.
6-21
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The most economical controls for Models C and D are water- and air-cooled condenser-
incinerator systems. Again, the'least expensive control system will vary, depending
upon local water and electricity costs and the actual bids on equipment and installation
costs .
6.4 SCRUBBING
6.4.1 Description
A control technique that has received increasing attention in recent years is chemi-
cal scrubbing. Chemical scrubbing is essentially a gas-absorption technique Whereby
one or more constituents of a gas stream are removed by dissolving them in a selective
liquid solvent. In addition to simply being dissolved, the absorbed gases may chemi-
cally react with the scrubbing liquid. Scrubbing offers economic advantages over incin-
eration methods when treating large volumes of air containing relatively low concen-
trations of malodorous contaminants and saturated air streams.
One limitation on the use of chemical scrubbers has been the inlet concentration of
malodorous gases. Odor concentrations greater than 10,000 to 20,000 odor units per
cubic foot have complicated the problem of providing adequate gas-liquid contact time
in the scrubber . H This restriction would preclude the use of scrubbers on a basis
similar to incinerators, which are generally designed to treat low volumes of highly
concentrated odors. The usual solution to the odor inlet limitation of scrubbers has been ^
to reduce the odor concentration of highly odorous streams to 10,000 to 20,000 odor units
per cubic foot by mixing them with percolator pan ventilation air, expeller exhaust, and
general plant ventilation air. H Scrubbing systems are therefore designed to treat large
volumes of air that include most of the rendering plant air streams. One three-stage
system, however, is currently being installed to treat high-intensity odors.
Scrubbers are designed to provide thorough contact between the gas and liquid streams
to allow interphase diffusion of the gases being absorbed. The required degree of con-
tact can be provided by several types of equipment. Bubble-plate columns, jet scrubbers,
packed towers, spray chambers, and venturi scrubbers are types of equipment that have
been used for gas absorption work. Figures 6-9 and 6-10 present examples of several of
these systems .
Packed towers and spray chambers are the most commonly used equipment because of
their relatively low pressure losses. Spray chambers have the advantage of being able to
handle exhaust gases containing particulate matter without plugging. Packed towers pro-
vide the more effective gas-liquid contacting.
Acid, alkaline, and strong oxidizing solutions are scrubbing liquids that have been
employed to control rendering-plant malodors with varying degrees of success. It is con-
ceivable that alkaline or acid scrubbers could be effective control devices if all odorous
compounds reacted in the same manner, but the mixture of malodorous gases encountered
during the rendering process is not homogenous from an acid-base standpoint (Section 4.2).
Some success has been reported for a system using both acid and alkaline scrubbing so-
lutions in a two-stage, spray-chamber unitA^ This system has been installed in several
rendering plants about the country and usually employs a first-stage scrubbing solution
of soda ash. Sometimes a second-stage scrubbing solution of sodium bisulfite, calcium
hypochlorite, or chlorine water is also employed. Several of these scrubbers can accom-
modate an entire plant. Applications of this system to date have been primarily in the
treatment of general plant ventilation air, expeller exhausts, and percolator pan exhausts.
There is some doubt that this scrubber could effectively treat the more concentrated cook-
er and drier odors unless they were diluted. Dilution increases scrubber size and costs.
Strong oxidizing solutions such as chlorine dioxide, sodium hypochlorite, and po-
tassium permanganate are reported to be effective means of eliminating odors. Given suf-
ficiently vigorous reaction conditions, potassium permanganate is capable of oxidizing
6-22
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GAS OUT
.GAS OUT
SH I L L"1
TRAY
DOWNSPOUT
T RAY
SUPPOR
RING
TRAY —
S TI F F E N E R
VAPOR
RISER
F ROTH
LIQUID IN
BUBBLE CAP
SIDES! REAM
Wl THDRAWAL
(a)
INTE RMEDIATE
FEED
-LIQUID DISTRIBUTOR
LIQUID
RE-DISTRIBUTOR
-PACKING SUPPORT
GAS IN
J LIQUID OUT
Figure 6-9 Types of absorption equipment' (a) bubble-cap tray tower and (b) packed tower
13
LIQUID
SPRAY
MOISTURE
ELIMINATORS
=3 LIQUID
«- ABSORBENT
INLET
ABSORBENT-
CONTAMINANT
SOLUTION
OUTLET
CLEAN GAS
OUTLET
LIQUID
ABSORBENT INLET
ENTRAINMENT-
SEPARATOR
ABSORBENT-
CONTAMINANT
SOLUTION
OUTLET
Figure 6-10a. Spray-chamber absorption
device.13
Figure 6-10b.
, . 13
device.
Venturi scrubber absorption
6-23
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most organic compounds. Under the relatively mild conditions usually employed by
most scrubbing systems, however, not all organic compounds will readily react. Those
odorous compounds that are susceptible to oxidative degradation under relatively mild
conditions are aldehydes, reduced sulfur compounds, unsaturated ketones and hydro-
carbons, phenols, amines, hydrogen sulfide, and sulfur dioxide. ^ Among the com-
pounds that resist oxidation under these conditions are saturated organic acids and
hydrocarbons, ketones, and certain nitrogen ring compounds. Potassium permanga-
nate scrubbing solutions have the disadvantage of being more expensive and requiring
more extensive sewage treatment than sodium hypochlorite solutions. Sodium hypo-
chlorite has a faster reaction rate than potassium permanganate and is effective against
most of the same spectrum of odorants. 15
Available data on a two-stage scrubber that uses either a potassium permanganate
solution or a sodium hypochlorite solution as the scrubbing liquid indicate that this unit
should be able to successfully treat cooker exhaust gases. A diagram of this system is
presented in Figure 6-11.
CLEAN AIR OUT
I
EXHAUST BLOWER
ODOROUS
AIR IN
RECYCLE AND
SEPARATION TANK
WATER
CHEMICAL
Figure 6-11. Two-stage chemical scrubbing system (courtesy Environmental
Research Corp., St Paul, Minn.)
The malodorous gases enter the first stage of the system where they are treated in a
venturi scrubber using water as the scrubbing liquid. This step removes particulate
matter and cools and saturates the gas stream. The gases are then passed through a
6-24
-------
packed bed where they contact a countercurrent stream of scrubbing liquid. Malodor-
ous gases are absorbed and oxidized. The scrubbed gas stream exits the packed bed,
flows through a mist elimination section, and is exhausted to the atmosphere. The de-
pleted scrubbing liquid is collected and recycled to the scru'bber . A portion of the de-
pleted scrubbing solution is continuously removed from the recycle stream and replaced
with make-up water and chemicals.
The bleed stream is combined with the waste water from the venturi scrubber and
sent to a sewage treatment facility.
The decision on whether to install a full two-stage system in a specific rendering
plant would depend on the nature of the gases being scrubbed. A two-stage system would
be required to treat gas streams with a high particululate loading or a high odor concen-
tration, i.e. , the exhaust from blood driers or cooker off-gases. When treating general
ventilation air, percolator pan ventilation air, or expeller exhausts, the venturi scrubber
could be eliminated.
6.4.2 Emission Reduction
Available information indicates that scrubbing with a solution of either potassium per-
manganate or sodium hypochlorite may reduce odor concentrations from 25,000 odor units
per cubic foot to between 50 and 200 odor units per cubic foot. H'-"-" This reduction was
for a system similar to the one shown in Figure 6-11. Odor concentrations at the scrubber
inlet and outlet were measured by the recommended ASTM method using odor panels. The
11 plants that were tested had flow rates ranging from 6,000 to 55,000 cubic feet per min-
ute. An EPA observer participated in tests at one of these 11 plants, and believes that
the above performance was demonstrated in the case that he observed.
It must be pointed out that these tests were made by the equipment vendor and/or his
customers. The Environmental Protection Agency made odor panel tests involving three
such scrubbers at two rendering plants in January 1973. These tests did not confirm the
earlier claims. Because the EPA tests were not conducted under entirely representative
conditions, however, further testing is required.
6.4.3 Sewage Treatment
The amount of treatment required by the scrubbing system waste water is , in most
cases, similar to that required by condenser condensate. If a potassium permanganate
solution is used as the scrubbing liquid, however, additional sewage treatment may be
necessary.
The volume of liquid effluent requiring treatment will depend upon the specific scrub-
bing system and the individual plant. A two-stage system similar to the one presented in
Figure 6-11 will produce approximately 180 gallons of -waste water per hour for each 1000
cubic feet per minute of air treated in the venturi, and from 12 to 20 gallons per hour for
each 1000 cubic feet per minute of air treated in the packed-bed scrubber. There will be
some scrubbing chemical in the waste water from the packed bed. Concentrations can
range from 5 to 20 ppm of available chlorine when sodium hypochlorite is the scrubbing
chemical.
A more complete discussion of the amount of sewage treatment necessary for rendering
plant effluent and the associated cost was presented in Section 6.1.1.3.
6.4.4 Equipment Costs
The capital investment, direct operating cost, and total annual cost of a chemical
scrubbing system (Figure 6-11) are presented in Table 6-10 for Models B, C, and D.
Condenser costs must be added to these figures to obtain the total costs of control. Unit
sizing, equipment investment, and operating costs are based on data obtained from the
6-25
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Table 6-10. CAPITAL INVESTMENT, DIRECT OPERATING COST,
AND TOTAL ANNUAL COST OF A CHEMICAL SCRUBBING SYSTEM
Raw material
process rate, Ib/hr
Capital investment, $
Operation, hr/yr
Operating costs, $/yr
Water
Sewage
Chemicals
(sodium hypochlorite)
Electricity
Labor
Total direct cost3, $
Depreciation (10-year
straight line), $/yr
Interest, taxes, insurance
(10%), $/yr
Maintenance (3%), $/yr
Total annual cost,3 $/yr
Model B
5,200
30,000
3,200
420
1,300
540
1,400
2,000
5,700
3,000
3,000
900
13,000
Model C
15,000
42,000
3,200
660
2,000
710
2,200
2,000
7,600
4,200
4,200
1,300
17,000
Model D
22,500
42,000
3,200
660
2,000
710
2,200
2,000
7,600
4,200
4,200
1,300
17,000
Total has been rounded to two significant figures.
scrubber manufacturer. A standard 14,000 ft /min unit was quoted to handle Model B,
and the standard 21,000 ft^/min unit was offered to handle either Model C or D . The use
of a scrubbing system for Model A was not considered because of the large capital invest-
ment.
Water costs were based on a fee of $0.25 per 100 gallons. Sewage treatment costs were
based on a charge of $0.75 per 1000 gallons. Electrical costs assumed a power require-
ment of 38 horsepower for Model B and 60 horsepower for Models C and D . Costs were
based on a fee of $0.015 per kilowatt-hour. Che lical costs were based on a charge of
$0.028 per gallon of 1 percent sodium hypochlorite solution. Model B was assumed to use
6 gallons per hour, and Models C and D were assumed to use 8 gallons per hour of this
solution. Some labor has been included for handling of chemical scrubbing liquids and
for operation of the scrubber.
6.5 REFERENCES FOR SECTION 6
1. Air Pollution Engineering Manual. Danielson, J. A. (ed.). U.S. Department of
Health, Education and Welfare. Cincinnati, Ohio. Publication Number AP-40.
1967. p. 780.
2. Air Pollution Engineering Manual. Danielson, J. A. (ed.). U. S. Department of
Health, Education and Welfare. Cincinnati, Ohio. Publication Number AP-40.
1967. p. 203.
3. Control Techniques for Hydrocarbon and Organic Solvent Emissions from Stationary
Sources. U. S. Department of Health, Education and Welfare. Washington, D. C.
Publication Number AP-68. March 1970. p. 3-21.
6-26
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4. Private communication with Mr. B. Wheeler, Greensboro Water and Sewage Adminis-
tration, Greensboro, North Carolina. October 11, 1972.
5. Calculated from data furnished by J . B . Stamberg, Process Technology Branch, Mu-
nicipal Waste Water Systems Division, Environmental Protection Agency. November
28, 1973.
6. Private communication with Dr. B. Valentine, Richards of Rockford, Rockford, Illi-
nois. December 8, 1972.
7. Private communication with Dr. E. E. Erickson, North Star Research Insititute, Min-
neapolis, Minn. November 27, 1973.
8. Air Pollution Engineering Manual. Danielson, J. A. (ed.). U. S. Department of
Health, Education and Welfare. Cincinnati, Ohio. Publication Number AP-40.
1967. p. 188-190.
9. Background Information for Proposed New Source Performance Standards, Technical
Report Number 10 - Rendering Plants. Environmental Protection Agency. Research
Triangle Park, North Carolina. January 1973,
10. Air Pollution Engineering Manual. Danielson, J. A. (ed . ) . U. S. Department of
Health, Education and Welfare. Cincinnati, Ohio. Publication Number AP-40 .
1967. p. 783.
11. Private communication with Mr . L. W. Rees, Environmental Research Corporation,
St. Paul, Minnesota. March 1, 1972, and November 15 and 16, 1972.
12. Private communication with Mr. L. W. Anderson, Carolina By-Products Company,
Inc. , Greensboro, North Carolina. October 4, 1972.
13. Control Techniques for Hydrocarbon and Organic Solvent Emissions from Stationary
Sources. National Air Pollution Control Administration. Washington, D. C. March
1970. p. 3-15 and 3-16.
14. Anderson, C. E. Chemical Control of Odors . Pollution Engineering . 4(5):20~21,
August 1972. ~
15. Doty, D. M. et al. Investigation of Odor Control in the Rendering Industry. Office
of Research and Monitoring, U.S. Environmental Protection Agency, Washington,
D. C. Contract No. 68-02-0260. October 1972.
16. Rees, L. W. and J. J. Brennan. Case History Rendering Plant Odor Control. En-
vironmental Research Corporation, St. Paul, Minnesota. 3 p.
6-27
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7. METHODS OF ESTIMATING CAPITAL INVESTMENT
AND TOTAL ANNUAL COST FOR CONTROL EQUIPMENT
7.1 INTRODUCTION
The equipment costs used in this document are the free-on-board (f.o.b.) charge for
either a specific piece or system of control equipment. Estimates of equipment costs were
obtained by averaging quotes from manufacturers and vendors of control equipment.
The equipment cost estimates served as the basis for the calculation of the capital invest-
ment and the total annual costs.
7.2 CAPITAL INVESTMENT
The capital investment for a piece or system of control equipment includes the follow-
ing:
1. Purchase price (f.o.b. charge).
2. Cost of installation.
3 . Engineering and supervision .
4. Instrumentation and control.
5. Piping and ductwork,
6. Electrical equipment and materials.
In the preceding list, the cost of installation includes the cost of labor, foundations,
supports, platforms, construction expenses, and other factors directly related to the
erection of the purchased equipment. 1
Capital investment depends to a large extent on the circumstances of the plant instal-
ling the equipment. Factors such as freight charges, local labor costs, foundation re-
quirements, and location of equipment affect capital investment and are unique for each
plant.
The multipliers in Table 7-1 represent, as best as can be determined, an average or
typical cost associated with installation, engineering, electrical connections, piping, etc.
Capital investment is determined by multiplying f.o.b . cost by the multiplier. The multi-
pliers were obtained from manufacturers, vendors, and the literature.2 All estimates
were adjusted for special construction materials and required operating specifications.
An example of the former is the use of stainless steel on the tube side of shell-and-tube
condensers.
7.3 TOTAL ANNUAL COST
Total annual cost (also called operating cost) is a combination of the total direct op-
erating cost and the indirect operating costs. Indirect costs include depreciation, taxes,
insurance, interest, and maintenance. Depreciation was taken as 10-year straight-line,
which amounts to 10 percent of the total capital requirement per year, Annual interest,
taxes, and insurance costs were estimated at 10 percent of the total capital investment,
and maintenance at 3 percent, unless otherwise noted. The 3 percent maintenance esti-
mate is accurate for contact condensers, but may be low for other control equipment. The
reader may wish to recalculate operating costs, using 5 percent of the total capital invest-
ment for maintenance, to get more accurate values for the total annual costs of the other
control equipment.
7-1
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Table 7-1. ESTIMATION OF CAPITAL INVESTMENT
Type of equipment
Contact condenser
Shell -and-tube condenser
Cooling tower
Air-cooled condenser
Incinerator
Chemical scrubber
Model
A
B
B
C
D
B
C
D
B
___ (
D
A
B
c
D
B
C
D
FOB cost,
$
1,600
2,800
4,300
8,200
13,000
4,900
12,000
18,000
8,000
22,000
29,000
5,300
7,000
9,500
11,000
19,000
26,000
26,000
Multiplier
1.8
2.4
2.4
2.0
1.8
1.6
Capital
requirement,
$
2.900
5,000
10,000
20,000
31,000
12,000
29,000
43,000
16,000
44,000
58,000
9,500
13,000
17,000
20,000
30,000
42,000
42,000
The total direct operating cost is a combination of the water, chemicals, fuel, sewage
treatment, and electricity charges associated with the operation of a piece of control
equipment. Specific charges were discussed in detail in Section 6.
7.4 REFERENCES FOR SECTION 7
1. Peters, M.S. and K. D. Timmerhaus. Plant Design and Economics for Chemical
Engineers. New York, McGraw-Hill, 1968. p. 108.
2. Guthrie,K.M. Capital Cost Estimating . Chemical Engineering . 76(6): 114-142,
March 1969- ~~
7-2
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-450/1-74-006
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Control of Odors from Inedibles-Rendering Plants
5. REPORT DATE
July 1974
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
T . R. Osag and G. B . Crane
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Office of Air Quality Planning and Standards
Emissions Standards and Engineering Division
Research Triangle Park, North Carolina 27711
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Office of Air Quality Planning and Standards
Emissions Standards and Engineering Division
Research Triangle Park, North Carolina 27711
13. TYPE OF REPORT AND PERIOD COVERED
Information Document
14. SPONSORING AGENCY CODE
is. SUPPLEMENTARY NOTES This document was prepared in-house as a lll(d) document to accom-
pany new source performance standards for rendering plant odors . Because this standard
was abandoned, the report is issued as an information document.
16. ABSTRACT
This information document describes the inedible animal and poultry rendering industry
and the control of odors therefrom. Industry statistics are presented. Rendering processe
are described, along with the chemical nature and quantities of odors released. Odor
effects on health and welfare are discussed. Control techniques for the odors are describee
and include use of condensers, afterburners, and chemical scrubbers. The capital and
annual costs of control by each method are given on an early 1973 basis. Particular
emphasis was placed upon costs for good control at existing plants already having mediocre
control - such as by condenser. Costs for aqueous waste control are included where
applicable.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
60
20. SECURITY CLASS (Thispage)
Unclassifipri
22. PRICE
EPA Form 2220-1 (9-73)
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