United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park NC 2771 1
EPA-450/2-78-035
OAQPS No 1 2-110
June 1978
Air
v>EPA Guideline Series
Control of Volatile
Organic Emissions
from Manufacture of
Vegetable Oils
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EPA-450/2-78-035
OAQPS No. 1.2-110
Control of Volatile Organic Emissions
from Manufacture of Vegetable Oils
Emission Standards and Engineering Division
Chemical and Petroleum Branch
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air, Noise, and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
June 1978
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OAQPS GUIDELINE SERIES
The guideline series of reports is being issued by the Office of Air Quality Planning and Standards
(OAQPS) to provide information to state and local air pollution control agencies; for example, to
provide guidance on the acquisition and processing of air quality data and on the planning and
analysis requisite forthe maintenance of airquality. Reports published in this serieswillbe available -
as supplies permit - from the Library Services Office (MD-35), U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina 27711, or, for a nominal fee, from the National Technical
Information Service, 5285 Port Royal Road, Springfield, Virginia 22161.
Publication No. EPA-450/2-78-035
(CAQPS No. 1.2-110)
This report is based largely on information developed
under contract by PEDC0 Environmen at (Contract No.
68-02-2603, Task No. 10). Conclusions and recom-
mendations were prepared by EPA staff.
II
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TABLE OF CONTENTS
Page
Chapter 1.0 Introduction 1—1
1.1 Need to Regulate Vegetable Oil Plants 1—I
1.2 Sources and Control of Volatile Organic
Emissions From Vegetable Oil Plants 1—2
1.2.1 Extractor . . 1—2
1.2.2 Post Desolventizer Vents 1-3
1.2.3 Other Sources 1-4
1.3 Compliance and Monitoring 1—4
Chapter 2.0 Sources and Types of Volatile Organic Emissions . . 2-1
2.1 Seed Preparation and Conditioning 2-9
2.2 Conveying Flakes to the Extractor 2-12
2.3 Solvent Extraction of the Oil 2-13
2.4 Solvent/Oil Separation . . . 2-17
2.5 Solvent/Meal Separation 2—19
2.6 Crude Oil Processing 2—22
2.6.1 Refining 2—22
2.6.2 Bleaching of Vegetable Oils 2-23
2.6.3 Hydrogeneration of Vegetable Oils 2-24
2.6.4 Deodorization 2-24
2.7 References 2-26
111
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Page
Chapter 3.0 Applicable Systems of Solvent Emission Reduction . . 3-1
3.1 Introduction 3-1
3.2 Control of Solvent Losses From the Main Vent . . . . 3-2
3.3 Control of Post-Desolventizer Vents . 3-4
3.3.1 Replace Desolventization Equipment 3-5
3.3.2 Add-On Controls for Post-Desolventization
Vents 3—7
3.4 Control of Fugitive Emissions 3-9
3. 5 Summary 3—10
3.6 References . 3—11
Chapter 4.0 Cost Analysis 4-1
4.1 Introduction 4-1
4.1.1 Purpose 4-1
4.1.2 Scope 4-1
4.1.3 Use of Model Plants 4-2
4.1.4 Bases for Capital Cost Estimates . 4-3
4.1.5 Bases for Annualized Costs 4-3
4.2 Solvent Emission Control in Vegetable Oil
Extraction Plants 4-5
4.2.1 Model Plant Parameters ., . 4-5
4.2.2 Control Costs 4—7
4.3 Cost Effectiveness . . . 4—7
4.4 Summary 4-17
4.5 References 4-18
iv
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Page
Chapter 5.0 Adverse Effects of Applying the Technology . . . . 5-1
5.1 Mineral Oil Scrubber 5-i
5.2 Installation of New Desolventizer-Toaster 5—4
5.3 Carbon Bed Adsorber 5-4
5.4 Incineration 5—5
5.5 References 5-10
Chapter 6.0 Enforcement Aspects 6-i
6.1 Affected Facility 6-i
6.2 Monitoring and Compliance 6—3
AppendixA A-i
V
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LIST OF TABLES
Page
Table 2-1 Estimated Average Solvent Losses From Reasonably
Well Operated Cottonseed and Soybean Plants
(Clean Raw Seed Basis) 2-4
2-2 Estimated Average Solvent Losses per TFC From
Reasonably Well Operated Vegetable Oil Plants . . . . 2-5
Table 4-1 Cost Factors Used in Computing Annualized Costs . . . 4-4
4-2 Costs of Solvent Control Options Vegetable Oil
Extraction flants 4-8
4-3 Emission Reduction and Cost Effectiveness Data
for Control Facilities for a Well Operated
Soybean Plant 4-9
4-4 Emission Reduction and Cost Effectiveness Data
for Control Facilities for a Poorly Operated
Soybean Plant 4-10
4-5 Emission Reduction and Cost Effectiveness Data
for Control Facilities for a Well Operated
Corn Plant 4-11
4-6 Emission Reduction and Cost Effectiveness Data
for Control Facilities for a Poorly Operated
Corn Plant 4—12
Table 5-1 Secondary Pollutants Resulting From Use of a
Mineral Oil Scrubber on Main Vent 5-3
5-2 Secondary Pollutants Resulting From Use of a
Adsorber on Dryer and Cooler Vents 5-7
5-3 Secondary Pollutants Resulting From Use of a
Primary Recovery Type Afterburner on Dryer
and Cooler Vents .. 5-8
Table A-i Estimated Average Solvent Losses From Reasonably
Well Operated Cottonseed and Soybean Plants
Based on Clean Raw Seed Input A-2
vi
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LIST OF FIGURES
Page
Figure 2—1 Relative Uncontrolled Hexane Emissions From
Vegetable Oil Extraction and Related Processes . . . 2-3
2-2 Typical Process Flow Diagram for a Soybean Plant
Without a Control Device on the Main Vent 2-6
2—3 Enclosed Basket Extractor 2-15
Figure 3—1 Schematic Diagram of a Mineral Oil Scrubber 3-3
3-2 Estimated Solvent Losses From Meal Preparation
Facilities of a Reasonably Well-Operated
Soybean Plant 3-6
Figure 4-1 Cost Effectiveness Curves for a Well Operated
Soybean Plant 4—13
4-2 Cost Effectiveness Curves for a Poorly Operated
Soybean Plant 4-14
4-3 Cost Effectiveness Curves for a Well Operated
Corn Plant 4-15
4-4 Cost Effectiveness Curves for a Poorly Operated
Corn Plant 4—16
Figure 5—1 Annual Fuel Requirements for a Mineral Oil
Scrubber on the Main Vent of a Soybean Plant 5-2
5-2 Annual Fuel Requirements for Carbon Bed Adsorbers
Controlling Both the Dryer Vent and Cooler Vent . . . 5-6
5-3 Annual Natural Gas Requirements for a Direct-Fired
Afterburner (with primary recovery) Controlling
Both the Dryer Vent and Cooler Vent 5-9
vii
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ABBREVIATIONS AND CONVERSION FACTORS
EPA policy is to express all measurements in agency documents in
metric units. Listed below are abbreviations and conversion factors for
British equivalents of metric units.
Abbreviation
9 - gram
kg — kilogram
Mg - megagram
Gg — gigagram
MFC - Mg of extractor feed cake
TFC - Tons of extractor feed cake
acf - actual cubic feet
scf - standard cubic feet
i n 3 - cubic meter
m, cm - meter, centimeter
- degrees centigrade
J - joule
kJ — kilojoule
kJ/kw — kilojoule
kJ/kg — kilojoule
GJ - gigajoule
kw - kilowatt
nunHg - millimeters of mercury
ppm - parts per million
Conversion Factor
ig = 0.0022 ibm
1kg = 2.2 lbrn
1Mg = 1O 6 = 2.2 x lO ibm
iGg= 10 9 g=2.2x io 6 lbm
1 TFC = 0.91 MFC
acf = Pscf(Tacf x scf
Pacf(Tscf
where Pscf and Pacf are in like units,
Tacf and Tscf are absolute
1 ni = 35.314 ft 3 = 264 gal.
I m = 3.28 ft = 100 cm
. (°C) + 32 = OF
1 joule = 9.5 x 1O BTU
1 kJ = 9.5 x 10 -i BTU
10,550 kJ/kw =
2300 kJ/kg =
1 GJ = 950 BTU
1 kw = 1.34 x 1O hp
760 mHg = 1 atm = 14.7 psi
ppm x l0 = volume percent
per kilowatt
per kilogram
10,000 BTU/kw
1000 BTU/lb steam
v iii
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GLOSSARY
* Crude oil is vegetable oil remaining after solvent/oil distillation.
• Oesolventfzer means a process unit in which steam is used to strip
occluded solvent out of the extractor meal.
• Extraction means leaching of vegetable oil from the seed or bean
typically using a hexane solvent in a countercurrent contact
system. Extraction products are leached seed (meal) and miscella
(oil—solvent mixture).
• Feed cake means extractor feed composed of clean, dehulled,
conditioned and flaked beans (or seeds).
Full solvent plant is a vegetable oil plant exclusively utilizing
solvent extraction to produce vegetable oil.
• Meal means leached seed or bean flakes remaining after extraction.
Mineral Oil Scrubber CMOS) is a packed tower using mineral oil as
absorbent for solvent laden vapors.
• Miscella is the mixture of solvent and extracted oil.
• Prepress plant is a vegetable oil plant which mechanically removes
a portion of the oil prior to solvent extraction. In most cases,
continuous screw presses are used to “squeeze” the oil out.
• Vegetable oil plant is any facility engaged in the manufacture
of vegetable oil from soybeans, corn, cottonseed, or peanuts.
Volatile organic compounds (VOC) means organic compounds which
under favorable conditions may participate in photochemica]
reactions to form oxidants.
ix
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1.0 INTRODUCTION
This document is related to the control of volatile organic compounds
(VOC) from soybean, cottonseed, peanut, and corn oil manufacturing and
refining facilities (hereafter “vegetable oil plants”). The specific
sources discussed herein are the extractor, desolventizer—toaster,
dryer, cooler, and pneumatic conveyor.
Methodology described in this document represents the presumptive
norm or reasonably available control technology (RACT) •that can be applied
to existing vegetable oil plants. RACT is defined as the lowest emission
- limit that a particular source is capable of meeting by the application of
control technology that is reasonably available considering technological
and economic feasibility. It may require technology that has been applied
to similar, but not necessarily identical, source categories. It is not
intended that extensive research and development be conducted before a given
control technology can be applied to the source. This does not, however,
preclude requiring a short-term evaluation program to permit the application
of a given technology to a particular source. This latter effort is an
appropriate technology-forcing aspect of RACT.
1.1 NEED TO REGULATE VEGETABLE OIL PLANTS
Control techniques guidelines concerning RACT are being prepared for
those industries that emit significant quantities of air pollutants in
1—1
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areas of the country where National Ambient Air Quality Standards (NAAQS)
are not being attained.
Annual nationwide VOC emissions from vegetable oil plants are estimated
to be 72,000 megagrams (79,000 tons). This represents about 0.3 percent of
total VOC emissions from stationary sources. Annual uncontrolled VOC
emissions from a typical 1000 ton per day soybean oil plant range from 605
to 2420 Mg (665 to 2660 tons).
1.2 SOURCES AND CONTROL OF VOLATILE ORGANIC EMISSIONS FROM VEGETABLE
OIL PLANTS
Two major sources in vegetable oil plants are recomended for control
in this document: the extractor and the post desolventizer vents.
1.2.1 Extractor
The largest single source of VOC emissions in vegetable oil plants is
the extractor. It is estimated that 50 to 75 percent of the emissions from
vegetable oil plants are lost from the extractor if the extractor vent
(main vent) is controlled with only a chilled water co idenser. Extractor
emissions (mostly hexane) can be reduced 90 to 95 percent with a properly
designed and operated mineral oil scrubber (MOS) installed after the
condenser on the main vent. For a typical 1000 ton per day soybean plant,
uncontrolled emissions from the main vent are 5.4 Mg/day (5.9 tons/day),
but. only 0.5 Mg/day (0.6 tons/day) with a MOS. With the application of
reasonably available control technology the hexane concentration should not
exceed 9000 ppm prior to any dilution or bleed air stream. To ensure that
dilution does not occur the maximum flow rate should not exceed 200 cf/MFC
at 66° and 1 atm.
1—2
-------
The total capital investment for installing a MOS on a 640 Mg/day
(700 ton/day) plant is $70,000. Total annualized cost for controlling and
monitoring the same plant, including operation, maintenance, etp.i, is $26,600
(excluding recovered solvent credits). Credits for recovered solvent will
more than offset these costs.
1.2.2 Post-Desolventizer Vents
Another 11 to 32 percent of VOC emissions are lost from the post-
desolventizer vents. This includes emissions from the desolventizer,
dryer, cooler, and pneumatic conveyor.
If proper desolventizer operation and maintenance practices are used,
the hexane content of the meal exiting the desolventizer-toaster can be
reduced to below 1350 ppm. Since residual hexane will be lost in the
dryer, cooler, pneumatic conveyor, and final meal preparation areas,
reducing the hexane content of the meal curbs emissions from these sources.
It is believed that many plants are already achieving the 1350 ppm level.
Costs for desolventizer modifications and proper maintenance will
vary from plant to plant. In cases where the desolventizer cannot be
modified to keep hexane content below 1350 ppm in the exit stream,
replacement with a new desolventizer is a control option. The total
capital investment for replacing the desolventizer on a 640 Mg/day
(700 ton/day) soybean plant is $468,000. Total annualized costs for the
same plant are $103,100, not including solvent credits. Credits for re-
covered solvent will more than offset these costs. The resulting cost
effectiveness is a credit of $0.05 per kilogram of solvent emissions
controlled.
* MFC Megagrams of extractor féed cai e
TEC Tons of extractor feed cake
1-3
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1.2.3 Other Sources
The emission levels presented herein are based on engineering
calculations. Further verification of these emission levels will be made
upon review of EPA emission tests being performed in conjunction with
New Source Performance Standard development.
Fugitive emissions, which may be substantial, are not addressed in
this document. They can be minimized by good housekeeping and maintenance
practices.
1.3 COMPLIANCE AND MONITORING
It is reconmended that weekly checks of the main vent stack and the
meal leaving the desolventizer—toaster be made for one year. The data
should be reviewed at that time and the monitoring frequency adjusted as
necessary.
1-4
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2.0 SOURCES AND TYPES OF VOLATILE ORGANIC EMISSIONS
The manufacture of vegetable oil from seed generally involves seed
preparation, oil extraction, oil refining, and, in the case of solvent
extraction, desolventization and treatment of the desolventized flakes.
These processes account for potential emissions of several organic
compounds: hexane solvent used in the extraction process; deodorizers
used in heat exchangers; fatty acids removed from the vegetable oil;
miscella (the mixture of solvent and oil); and the vegetable oil itself.
The hexane solvent is a mixture of volatile organic compounds (VOC) which
are photochemically reactive, i.e. under favorable atmospheric conditions
they participate in photocheniical reactions to form oxidants.
In the United States, nearly all vegetable oil is extracted from
one of four seeds: soybeans, cotton, corn, or peanuts. Each type of
seed varies with regard to oil content, meal content, and the amount of the
seed actually fed to the extractor, i.e. 25 percent of a given quantity
of peanuts (the hulls) is separated from the process prior to solvent
*
extraction.
* Capacity is stated differently from operator to o erator. Some base
it on the total weight of cleaned raw seeds processed, others use
the total weight of conditioned seed or the weight of conditioned
seed actually put into the extractor. For the purposes of this
report, plant capacity is always stated in megagrams of conditioned
seed fed into the extractor. This conditioned seed is referred to
as “extractor feed cake or “seeds processed.” Thus a 182-Mg/day
(200-ton/day) plant that processes soybeans would handle 182 Mg/day
(200 tons/day) of cleaned raw seeds and would feed that amount of
soybean seed into the extractor.
2-1
-------
Thus, emissions of VOC vary according to the raw material and type
of extraction plant, as well as according to the condition and operation
of the plant equipment. As is seen from Figure 2-1, the major VOC
emission sources are the extraction and desolventization facilities. This
document concentrates on these facilities. VOC emissions based on raw seed
input are shown in Table 2-1. Since not all the raw seed is always fed
into the extractor, emissions are based on 0.91 megagrams of feedcake (MFC),
or one ton of feedcake (TFC) fed to the extractor in cottonseed, soybean,
corn, and peanut oil plants. Estimated emissions are shown in Table 2-2.
Since soybean oil represents more than 80 percent of the oil pro-
duced, this document will be directed toward soybean oil extraction.
Figure 2-2 shows a typical process flow diagram and material balance for
the hexane solvent used for processing 0.91 Mg (1 ton) of soybeans. This
may be considered a reasonably well operated plant, having overall un-
controlled solvent losses of 8 kg/MFC (16 lb/TFC). Overall losses
decrease to an average of 2.6 kg/MFC (5.3 lb/TFC) when the main vent is
ducted to an absorber. New plant contractors are currently guaranteeing
overall solvent losses under strictly controlled conditions of less than
1.5 kg/MFC (3 lb/TFC) for soybean plants, and it has been reported that
some plants have losses as low as 1 kg/MFC (2 lb/TFC). 1
The processes and equipment used to manufacture vegetable oil are
generally the same regardless of the type of seed being processed.
The major manufacturing divergencies are prepressing and miscella refining.
2—2
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Figure 2 —1. Relative uncontrolled hexane emission from vegetable
oil extraction and related processes.
RAW
SEEDS
SEED
PREPARAT ION
& CONDITIONING
EXTRACTOR
y
OIL EXTRACTION
& DESOLVENTIZATION
MEAL
PREPARATION
REFINED
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TABLE 2-1. ESTIMATED AVERAGE SOLVENT LOSSES FROM REASONABLY
WELL-OPERATED COTTONSEED AND SOYBEAN PLANTS BASED
ON CLEAN, RAW SEED INPUT *
Solvent loss kg/Mg (lb/ton) raw seed
Cottonseed -
Prepress
Full Solvent
Point of solvent loss
Plant
Plant
Soybeans
A. Operational losses
Meal drying
0.18 C 0.36)
0.18 ( 0.36)
0.32 C 0.65)
Meal cooling
Meal product
Oil
Waste water
Main vent (uncontrolled)
Solvent storage
Fugitive (leaks)
.
0.12 ( 0.24)
0.30 ( 0.60)
0.08 ( 0.16
0.02 ( 0.05)
3.13 ( 6.26)
0.04 C 0.09)
0.30( 0.5 !)
0.12 ( 0.24)
0.30 ( 0.60)
0.16 ( 0.32)
0.05 ( 0.10)
3.55 ( 7.10)
0.09 ( 0.18)
O.59_( l.18)
.
0.22 ( 0.45)
0.55 ( 1.10)
0.18 ( 0.36)
0.05 ( 0.10)
5.90 (11.80)
0.10 C 0.20)
O.33( 0.66)
Total Operational Losses
4.17 ( 8.35)
5.04 (10.10)
7.65 (15.32)
B. Non-operational losses
Start-up & Shutdown
Downtime
Total uncontrolled losses
(rounded)
0.18 ( 0.35)
0.1810.35)
4.5 ( 9.0)
0.20 ( 0.40)
0.20 (0.40)
•
016 ( 0.33)
0.16 ( 0.33)
5.4 (10.9)
8.0 (16.0)
Less solvent collected in
absorber (average)
2.7 ( 5.4)
3.2 ( 6.4)
5.4 (10.7)
Total controlled losses
1.8 ( 3.6)
2.2 (4.5)
2.6 ( 5.3)
* See Appendix A
2-4
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TABLE 2-2.
ESTIMATED AVERAGE SOLVENT LOSSES PER MEGAGRAM OF EXTRACTOR FEED CAKE FROM
REASONABLY WELL-OPERATED VEGETABLE OIL PLANTS
Source of Loss
Solvent Losses, kg/MFC (lb/TFC)
.
Cottonseed
Soybeans
Corn
-_____________________
Peanuts
Prepress
Full solvent
Prepress
Full Solvent
Prepress
Meal drying
Meal cooling
Meal product
oil
Wastewater
Main vent (uncontrolled)
Solvent storage
Fugitive
Start-up & Shutdown
Downtime
Total uncontrolled
losses (rounded)
Less solvent collected
in absorber (average)
Controlled loss MFC (TSP)
0.28 ( 0.55)
0.20 ( 0.40)
0.48 ( 0.95)
0.15 ( 0.30)
0.04 ( 0.08)
5.90 (11.80)
0.09 ( 0.18)
0.55 ( 1.10)
0.33 ( 0.66)
0.33 ‘( 0.66 )
8.4 (16.7)
5.4 (10.7 )
3.0 ( 6.0)
0.32 ( 0.65)
0.22 ( 0.45)
0.55 C 1.10)
0.27 ( 0.54)
0.08 ( 0.15)
5.90 (11.80)
0.15 ( 0.30)
0.99 ( 1.98)
0.33 ( 0.66)
0.33 ( 0.66 )
9.1 (18.3)
5.4 (10.7 )
3.7 ( 9.6)
0.32 ( 0.65)
0.22 ( 0.45)
0.55 (1.10)
0.18 ( 0.36)
0.05 ( 0.10)
5.90 (11.80)
0.10 ( 0.20)
0.33 ( 0.66)
0.16 ( 0.33)
0.16 ( 0.33 )
8.0 (16.0)
5.4 (10.7 )
2.6 ( 5.3)
0.20 ( 0.40)
— :i- [ o 5j
0.32 ( 0.65)
0.50 ( 1.00)
0.14 ( 0.28)
5.90 (11.80)
0.28 ( 0.55)
1.88 ( 3.77)
0.33 ( 0.66)
0.33 ( 0.66 )
0.32 ( 0.65)
0.20 ( 0.40)
0.52 C 1.05)
0.20 ( 0.40)
0.05 ( 0.10)
5.90 (11.80)
0.11 ( 0.22)
0.74 (1.47)
0.33 ( 0.66)
0.33 ( 0.66 )
8.7 (17.4)
5.4 (10.7 )
3.3 ( 6.7)
.28 ( 0.30)
.20 ( 0.20)
.48 ( 0.50)
.20 (1.20)
.04 ( 0.33)
5.90 (11.80)
.09 ( 0.67)
.55 ( 4.40)
.33 ( 0.66)
. 33 ( 0.66 )
8.4 (20.7)
5.4 (10.7 )
3.0 (10.0)
10.0 (20.0)
5.4 (10.7 )
4.6 ( 9.3)
-------
Figure 2-2.
Typical process flow diagram f r
soybean plant without: a control device on its main vent.
.07 • /, ( i SO t 3 I& i) All
66C (lsrr)
..0— HtIMf
2.6
.91
1APOS tO I 1-STAGt
tV*P. I(At UCH*IS&.I
77’t (17o
I ll (911.4 ib) IIftMIt
($200 scf ) I(6A
i.o . (,l10 icf) All I
sT
TO MI VtNI
i l0tNS($
ISrC ( 13rV1
60t
I; ’)
0
¶0.0? (0.46
0.30 kq (0.66 1b HUM6
0.04 . (i.4ft )
43•C (110c). 13%
M . (3000 ft 3 III
938 . (33. 00 t 3 ) 61$
i rc 190 ). 9O_100t I
90SC(tL* 10 1ST-S9.Gt tYAP .
163 q (360 ib) Oil.
490 q (1080 ib) HEIANt
60t (140° i
(1640 Ib)
•FLASHED HEXPINE INCUJOED IN
AMOUNT SHOWN AT DRYER VENT
HI LANE
q (0.66 ib)
HE IANI
(continued)
-------
I ST-STAGE
EVAPORATOR
Figure 2-2.
(continued)
EVAP.
STEAM IN
118 rn’ (4200 acf)
901.1 kg (1984.8 ib) HEXANE 417 kg (918.4 lb)
}IEXANE 10 SOLVEMT/ 3 rn 3 (>110 acf) AIR &
WATER SEPARATOR STEAM 7PC (170F)
118°C (245F)
163 kg (360 ib) 011
0.16 kg (0.36 ib) MEXANE
TO REFINING
21 O-STAGt
EVAPORATOR
(continued)
-------
21’t (1o’rJ
0.1 g (0.2 ib)
HEXANE
SOlVENT
STORA GE
TANK
((((1(1,1111 1
91
I b)
VENT TO
MAIN VENT
CONDENSER
c o
OPERATING LOSSES ONL.L DOES
NOT INCLUDE LOSSES DUE TO
START-UP. SHUTDOWN, AND
DOWNTIME (SEE TABLE 2.d
EVAPORATOR
82°C (180F)
0.08 m 3 (21 gel)
WATER TO SEWER
kg (O.llb) HEXANE
0.04
Figure 2-2. (continued)
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2.1 SEED PREPARATION AND CONDITIONING
The first step in processing oil seed is to screen out foreign
material such as sticks, stones, leaves, sand, and dirt. Tramp iron is
removed by permanent magnets or electromagnets mounted above the seed
conveyor. The seed is generally cleaned and dried before being stored,
and moisture content kept low to prevent heating and microbial spoilage.
Before oil separation, the seed must be cracked and completely
or partially hulled (decortication) using a combination of air classification
and screening, or in some cases, flotation. The hulls of most oil-
bearing seeds contain as little as one percent oil. If they are not
removed before extraction, they will reduce the total yield by both
adsorbing and by retaining oil in the press cake, reducing equipment capacity.
Two basic types of hulling machines are used: the bar and the disc
huller. Both are ideal for seeds with loose or flexible hulls, such
as cottonseed, peanuts, sunflower seed, etc. The essential component
of the bar huller is a cylinder with square-edged knives (“bars”)
arranged longitudinally. This device rotates inside a stationary
cylinder, similarly equipped with knives. Seed is fed between the
cylinders, where the hulls are split by the opposed cutting edges.
The disc huller is similar in principle, except that the cutting
edges consist of radial grooves in the surface of two opposed, vertically
mounted discs, one of which rotates. Seed is fed to the center of the
disc; the hulled products are discharged by centrifugal force at the
periphery.
2-9
-------
Cottonseed kernels or those with meats that adtiere to the hull
after separation must pass through a type of hammer mill called a hull
beater. The following separation system is commonly used after the hulling
of cottonseed.
I. Screening of large meat particles from hulls and uncut seed.
2. Separation of hulls from uncut seed by an air lift.
3. Separation of small meat particles from hulls by hull beating
and screening.
4. Separation of hull particles from meats by airlift.
5. Recycling of uncut seed to the hulling machine.
Soybeans are usually dehulled by cracking the beans on cracking
rolls, and then separating hulls and kernels. Each cracking roll has
two pairs of rolls approximately 30 cm (12 in.) in diameter and 130 cm
(50 in.) long and is capable of cracking 450 Mg/day (500 ton/day) of
soybeans. Uncracked beans are returned to the cracking rolls, while the
kernels are fed to a deck of fine-mesh screens. Hulls that contain
kernel particles undergoair separation, using a gravity table to
separate the light hulls from the heavier kernels.
Next, the seeds (or meats) are steam cooked to soften the meats so
a good quality, workable flake can be formed in subsequent operations.
2-10
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Oil seed is generally cooked on a continuous basis in “stack
cookers.” Cooking time may vary from 30 to 120 minutes, depending
on the nature and geometry of the seed. The temperature of the
seed leaving the cooker ranges from 600 to 99°C (140° to 210°F).
Horizontal-jacketed tubes, or “conditioners,” can serve the same
purpose as stack coOkers. In general, however, these units are more
commonly used in conjunction with stack cookers rather than as a sub-
stitute for them. There are no VOC emissions from this process.
In prepress plants (plants mechanically removing a portion of the
oil prior to solvent extraction), the seeds are next conveyed to con-
tinuous screw presses where a portion of the oil is removed. If screw
pressing is the only extractive process involved, then the press cake is
processed at much greater pressure, so that the emerging product has a
residual oil content of only four to six percent. These percentages
increase for certain seed types and older presses.
Continuous screw presses (IIexpellerstt) are used to the almost
complete exclusion of batch hydraulic presses for both mechanical
extraction and prepressing prior to solvent extraction. Continuous
presses used for oil seed in the United States are mostly high-pressure
machines designed to effect oil recovery in one step. The same machines
2—11
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can also be used for prepressing before solvent extraction. For this
purpose, however, machines specially designed or modified for low-pressure
operation have proved more satisfactory.
Prepressing removes much of the oil from the seeds before solvent
extraction, minimizing the size of the solvent extraction plant needed.
Prepressing produces a meal with a high-protein quality and maximizes
the overall oil yield.
In full solvent plants (plants exclusively utilizing solvent
extraction to produce oil), conditioned seeds are conveyed from the
conditioners to the flaking rolls. Flaking rolls are essential in the
preparation of oil seeds for continuous solvent extraction since the
extraction rate is strongly inversely proportional to the flake
thickness.
2.2 CONVEYING FLAKES TO THE EXTRACTOR
The flakes are conveyed from the flaking rolls or the screw
press to the extractor in a mass-flow type of enclosed conveyor. This is
the conveyor into which the solids from the flaking roll aspirator are
discharged. Figure 2-2 shows the aspiration air from the flake conveyor
discharging to the atmosphere. This aspiration serves two purposes.
It removes free moisture in the flakes and prevents any solvent vapors
that may escape through the extractor flake inlet from getting into the
2-12
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bean preparation area. The latter is a safety precaution. Solvent
emissions from this aspiration point are generally detectable only
during start-up and shutdown. 2 This aspiration exhaust vent generally has
a volume of approximately 0.07 m 3 /s (150 ft 3 /min) regardless of plant
size. 3 The VOC emissions from the aspiration vent are included in the
solvent losses due to shutdown and start-up in Table 2- i.
2.3 SOLVENT EXTRACTION OF THE OIL
Solvent extraction is the most efficient method of recovering oil
from almost any oil-bearing vegetable seed. Extraction is accomplished
in a countercurrent procedure, in which intimate contact is achieved
between the oil—bearing seed and the solvent. The two problems involved
in this process are that complete extraction can be accomplished only by
the use of a large volume of solvent relative to the volume of oil
extracted, and that the solvent must later be separated and recovered
from the oil. These problems represent a substantial portion of the overall
plant operating cost. A prime objective in modern solvent extraction is to
reduce the solvent-to-oil ratio yet still maintain a high oil yield.
In most efficient continuous extraction plants, the solvent-oil ratio
is as low as five or six to one on a weight basis. In order to
obtain this ratio, a certain amount of oil is left in the meal. The
accepted practice is to reduce the oil content of the meal to less
than one percent, preferably 0.5 percent.
2-13
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The most common solvent used in commercial continuous edible oil
extraction systems is a hexane-type naphtha boiling at 63° to 69° C.
(146° to 156° F). Other solvents that can be used include a pentane-type
with an ASTM boiling range of 310 to 36°C (88° to 97°F), and a heptane-
type with a boiling range from 900 to 100°C (194° to 212°F). Hexane
solvent is the most widely used for oil seed, although heptane is also
suitable for use in most modern plants. Pentane is used only in the
extraction of heat-sensitive oils, such as those needed for pharmaceuticals.
Extractor Types
Two types of continuous solvent extractors predominate, the vertically-
arranged basket type and the rotary cell type. A continuous shallow bed
rectangular loop extractor having no baskets or cells has also found use in
the industry. -
The basket-type extractor (Figure 2-3) resembles an enclosed bucket
elevator. With this unit, oil is extracted by percolating solvent through
seed flakes contained in a series of baskets with perfQrated bottoms.
To ensure uniform percolation and drainage, the width and depth of the
baskets are fixed, but the length is varied in order to obtain the
desired capacity. About 40 baskets are supported on an endless chain
within a gas-tight housing. Flaked oil seed is screw—conveyed into a
charging hopper at the top of the extractor housing. From the hopper,
the seed passes through a filled conveyor tube that serves as a seal
against solvent vapor inside the extractor. The baskets pass
continuously under the tube at about one revolution an hour. As
each basket passes below the tube and starts down the descending side
of the extractor, it is charged automatically from the seed hopper.
2-14
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Figure 2—3.
MISCELLA
ER
Enclosed basket extractor.
SOLVENT
HAL F
MI SCELLA
PUMPS HALF FULL
MISCELLA MISCELLA
2-15
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Extraction is accomplished by the percolation of solvent through
the seed baskets during their passage down the extractor and back up
again. Fresh solvent is sprayed into a basket near the top of the
ascending line at the rate of about 4.6 to 5.4 kg solvent per
kg oil(5 to 6 lb/lb oil) in the extractor feed cake. It percolates from
the highest to the lowest basket in counter-current flow. The miscella
(solvent and oil mixture) from this side of the extractor, usually
termed the “half miscella,” is collected in a sump in the base of the
housing. Half miscella is pumped from the sump to the top-most basket
of the descending line, so it percolates through the baskets in the
same manner as the fresh solvent on the ascending side. The full miscella
containing all the oil is collected in a separate sump.
As the baskets containing spent and drained flakes ascend to the
top of the housing on the opposite side from the charging hopper, they
are automatically inverted and the contents (spent seed or cake) dumped
into a discharge hopper. From there they are carried by screw conveyor
to the meal dryers.
Most basket-type extractors built for coninercial plants operate
at capacities ranging from 180 to 910 Mg (200 to 1000 tons) of flakes
per day.
The rotary cell extractor is similar in principle to the basket
extractor, except that the baskets move in a rotary motion through a
horizontal plane. The miscella percolating through the baskets falls
into separated compartments in the bottom of the extractor housing.
• From these compartments, or sumps, it is recycled by a series of pumps
to the top of the seed-filled baskets.
2-16
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Rectangular loop extractors vary from vertical and rotary
extractors in several ways. First, the rectangular loop extractor
processes the flakes continuously along a conveyor chain rather than
in baskets. Secondly, a stationary, linear, vee—bar screen and a
cyclone separator are used on the full miscella instead of filters
or screens. Discharge of flakes and miscella is continuous.
Extractors are vented to the main vent condenser. Negative
pressure removes air from the system, cutting solvent losses.
After extraction, the spent cake (containing approximately 35 to
40 percent solvent) is conveyed by a vapor-tight conveyor to the
desolventizer. Modern desolventizers also toast the flakes for purposes
of producing a product meal of higher quality. This piece of equipment
is known as a desolventizer-toaster. Negligible solvent emissions
are vented to the atmosphere directly from the desolventizer-toaster.
2.4 SOLVENT/OIL SEPARATION
After extraction, oil and solvent are separated by distillation.
Extracted oil is usually combined with press oil before being refined.
In order to preserve the quality of the virgin press, however, this stage
is sometimes eliminated, as is the case with olive oil.
From the extractor sump, miscella containing oil, solvent and
suspended solids is filtered on a continuous basis before
distillation. The amount of suspended solids varies depending on the oil
seed. After filtration the miscella is preheated in a heat exchanger
2—17
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(to which heat is often provided by the desolventizer-toaster and spent
steam from the steam ejector vacuum system), arid then it passes through
rising film or falling film evaporators. Approximately 90 to 95 percent
of the solvent is evaporated in the first-stage and second-stage eva-
porators, condensed and collected for reuse. Oil effluent from the
evaporator then passes to a vacuum distillation column, where most of
the remaining 5 to 10 percent of solvent is steam-stripped from the oil.
The temperatures and pressures at which the distillation system is
operated vary according to the nature of the oil and solvent. Oil from
the bottom of the distillation column is cooled and collected for refining.
Overhead vapor containing, residual solvent is condensed, collected, and
decanted along with the solvent condensate from the evaporator. This
solvent is then mixed with fresh makeup solvent and recycled to the
extraction system. Operating losses from this loop of the process
leave the system through the main vent stack. This contributes only a
small portion of the total amount of hexane in that exhaust stream, however.
Makeup solvent is also required as a result of fugitive losses due to system
leaks, retention of solvent in the crude oil, and retention of solvent in the
discharged wastewater.
Estimated fugitive losses from reasonably well-operated soybean oil
plants range from 0.33 kg/MFC (0.66 lb/TFC) for large plants to 0.85 kg/MFC
(1.7 lb/TFC) for smaller plants of less than 910 Mg/day (1000 tons/day)
capacity. Fugitive emissions from cottonseed, corn, and peanut plants range
from 0.6 to 1.8 kg/MFC (1.1 to 3.8 lb/TFC) as shown in Table 2-2. These
estimates may change as more data become available.
2-18
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Fugitive losses are not directly proportional to plant size. 4 This is
understandable since, for example, a large pump has less seal area per
gallon handled than a small pump. One source estimates fugitive losses
to be 3 to 5 times larger in small plants than in large plants. 5
Solvent content of the crude oil is governed by commercial practice.
If it is too high, storage of the crude oil presents a safety hazard. The
oil is subjected to a flash or “pop” test to determine that its solvent
content is within accepted limits. It must have a closed-cup flash point
in excess of 250°C (482°F). The volatile content of crude oil is limited
to 0.2 percent. Approximately 0.1 percent is solvent in the form of miscella.
2.5 SOLVENT/MEAL SEPARATION
Oil seed flakes leave the extractor saturated with solvent. In order to
reclaim the solvent and make the meal edible, the flakes are fed to a desol-
ventizer toaster. This device is similar to a stack cooker in which
live or indirect steam is used to vaporize and strip out occluded solvent.
In addition to vaporizing most of the solvent, the steam also adds moisture
to the meal, thus minimizing dust carryover to the solvent condenser.
Older plants use a device called a “Schneckens,” for removal of solvent.
It consists of a series of horizontal, steam—jacketed tubes, through which
the flakes are propelled by screws. Another method of desolventizing is to
pass superheated solvent vapors through the meal. Most large modern plants
desolventize with a desolventizer-toaSter. This is a critical piece
of equipment in the plant from a solvent-loss standpoint since the meal is
a major source of solvent loss. If the desolventizer—toaSter is new and operated
efficiently, meal can leave it containing as little as 500 ppm solvent. 6
2-19
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This is only 0.41 kg solvent/MFC (0.82 lb solvent/TFC) for soybeans.
Inefficient desolventizers may allow solvent retention to remain as high as
3.5 kg/MFC (7 lb/TFC). The solvent content of this meal is most important
since all the occluded solvent from this point on is lost. At an average
plant, approximately 50 percent of the residual solvent is thought to be
exhausted in the dryer and cooler.. 7 A poorly operated desolventizer, leaving
a higher amount of occluded solvent, will cause proportionately higher
emissions from the dryer and cooler. Both the dryer and cooler require air
for proper operation. Vent gas volumes are approximately 92 m 3 /MFC
(3000 ft 3 /TFC) for the dryer and 1032 m 3 /MFC (33,500 ft 3 /TFC) for the
cooler. 8 The National Soybean Processors Association estimates dryer gas
volumes to be 300-460 m 3 /MFC (10,000—15,000 ft 3 /TFC). The meal discharges
from the desolventizer- .toaster at a temperature above the boiling pointof
water. This causes the moisture in the meal (18 to 22 percent) to flash.
A hood and a natural draft stack are sometimes provided to carry the moisture
away. Assuming that as much as one—tenth of the moisture flashes off, volumes
in this vent are generally less than 0.05 rn 3 ls (100 ft 3 /min) for cottonseed,
corn, and peanut plants. Soybean plants have somewhat larger volumes, ranging
from 0.09 to 1.4 m 3 /s (200 to 3000 ft 3 /min) for a 180-Mg/day (200-ton/day) and
2730-Mg (3000—ton/day) plant respectively. The solvent content of this
exhaust is unknown; however, it is expected to be a small quantity relative
to the dryer and cooler vents.
Small plants very often dry the desolventized flakes in the desolventizer-
toaster itself and then pneumatically convey them to the feed conditioning
facility. The pneumatic conveyor cools the meal sufficiently to eliminate
• the need for a cooler. In short, some plants have no aspirator, dryer, or
cooler. These plants emit hexane from the pneumatic conveyor vent.
2-20
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Since the final meal product is tested for solvent content by means
of a “f1ash or pop” test, it is probable that the solvent content of the
final meal product is a maximum of 700 to 1200 ppm, regardless of the
desolventizer efficiency. For soybean meal product (not post-desolventizer,
post-dryer and cooler) solvent content ranges from 200 to 700 ppm or
0.17 to 0.56 kg/MFC (0.33 to 1.1 lb/TFC). The seed acts as an adsorbent;
thus reduction in solvent content below the 200 to 700 ppm level is
unlikely once it leaves the desolventizer-toaster.
In summary, the solvent remaining in the meal after the desolventizer-
toaster is ultimately lost to the atmosphere. A reasonably well-operated
desolventizer-toaster discharges meal with an average solvent content of
about 1350 ppm. 9 ’ 1 ° Solvent losses per given weight of extractor feed cake
vary according to the amount of meal produced.
About 50 percent of the meal-entrained solvent is vented to the
atmosphere through the post—desolventizing vents--the dryer and cooler
vents, or the pneumatic conveyor vent. The balance of the solvent remains
in the meal. The remaining solvent is probably lost as a fugitive emission
during the meal processing and marketing operations. Industry spokesmen
state that solvent odors are undetectable during meal processing and storage.
This is probably due to the low temperatures at which these operations are
carried out, the adsorbent quality of the seed, and the lowering of the
solvent’s vapor pressure as a result of its mixing with the retained oil
in the meal.
2-21
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2.6 CRUDE OIL PROCESSING
The crude oil is normally shipped to another establishment for further
processing. The occluded solvent (0.1 percent maximum) is in a miscella
form and has a vapor pressure of less than 1 m Hg. Subsequent processing
at elevated temperatures will drive off some of this solvent. Industry
spokesmen, however, are not aware of any detectable solvent vapors from
the crude oil. This is a concern where the oil is stored, since high
solvent content could cause storage tank top vapors and vent vapors to exceed
the lower explosive limit (LEL) for hexane.
Crude oil is refined, bleached, hydrogenated, and deodorized. None
of the exhausts or vents from these operations are controlled for solvent
emissions. Assuming all the occluded solvent is driven off in the refining
and bleaching processes, maximum emissions are approximately 1.0 kg/Mg of
oil (2.0 lb/ton of oil). For a soybean oil plant which yields 179 kg of oil
per MFC this represents 2 to 3 percent of the total solvent loss.
2.6.1 Refining
The primary object of refining vegetable oil is to neutralize and remove
free fatty acids. The most important and widely used method is to treat the
oil with an alkali, such as caustic soda. Free fatty acids, along with
other acidic substances, combine with the alkali and are converted into
oil-insoluble soaps. Alkali treatment also produces a decolorizing action,
affecting those substances that become oil insoluble on hydration. Caustic
soda has the disadvantage of saponifying a small proportion of the neutral
oil, in addition to reacting with free fatty acids. For this reason other
alkalies, such as soda ash or sodium bicarbonate, are used in some refining
operations.
2—22
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Another method of refining is steam stripping. Since fatty acids
are more volatile than glycerides, it is possible to distill them off at
reduced pressures and elevated temperatures. Liquid-liquid extraction has been
also used to some extent. The oil is intimately combined with an
immiscible solvent in a countercurrent operation, whereupon the free fatty
acid mass transfers from the oil phase to the solvent phase.
Acid refining is used for some oils, particularly those included
in paint. The oil is treated with strong sulfuric acid. This process
does not reduce free fatty acids, but it clears and precipitates phosphatides
and other similar impurities.
2.6.2 Bleaching of Vegetable Oils
The standard method of bleaching is to adsorb color bodies from the
oil onto the surface of activated carbon or clay earth.
In order to avoid the harmful effects of oxidation, the oil is
generally bleached under vacuum on a continuous basis. Several similar
bleaching processes using an adsorbant (earth) slurry with oil are available.
Most continuous bleaching processes use multiple-leaf filters so slurry
can be switched to a clean filter when the onstream filter is saturated with
clay. T e recovery process generally consists of boiling the spent earth
with a weak aklaline aqueous solution, then salting out and decanting off
the resulting oil layer.
2-23
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2.6.3 Hydrogenation of Ve getab1e Oils
In order to produce hard or plastic fats, or to enhance the
oxidation stability of the oils (by lowering the polyunsaturated acid content),
edible oils are often partially hydrogenated. This process requires hydrogen
under moderate pressure and a catalyst, usually reduced nickel. The reaction
involves breaking specific carbon-carbon double bonds on the triglyceride
molecule, and their conversion to a single bond by the addition of hydrogen.
2.6.4 Deodorization
Bleached and hydrogenated oils often give off odors, caused by
aldehydes or other slightly volatile materials. These oils are deodorized
by steam distillation (stripping) under high vacuum at temperatures between
204° and 260°C (4000 and 500°F).
2-24
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2.7 REFERENCES
1. “Maximum Solvent Recovery Creates Safety and Profit,” R. D. Good,
Dravo. Paper presented to the American Oil Chemists Society, October 16, 1967.
2. Meeting between Donald J. Henz of PEDC0 Environmental, Inc.,
and William A. Coombes and R. J. Hansatte of Dravo Corporation,
January 24, 1978.
3. Ibid.
4. Ibid.
5. Letter to EPA from George E. Anderson, Chief Mechanical
Engineer, Crown Iron Works Company, April 17, 1978.
6. R. P. Hutchins. “Continuous Solvent Extraction of Soybeans
and Cottonseed.” J. Am. Oil Chemists’ Society, June, 1976 (Volume 53).
pp. 279-282.
7. Reference 2, Op Cit.
8. Reference 6, Op Cit.
0. Reference 2, On. Cit.
10. George Anderson. Five Point Process Efficiency, Crown Iron Works
Company, Minneapolis, Minnesota, 1976.
2—25
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3.0 APPLICABLE SYSTEMS OF SOLVENT
EMISSION REDUCTION
3.1 INTRODUCTION
Estimated VOC emissions from the solvent extraction and refining
of vegetable oils during 1977 amount to 71,830 Mg (78,900 tons). Domestic
vegetable oil supplies for the year 1976/1977 approached 5.4 x i0 6 Mg
(6 x io6 tons). Nearly 75 percent of domestic production is soybean oil.
Not all the remaining oil is solvent extracted; other methods are used to
produce the oil. For example, in 1974 only 34 of the nation’s 83 cotton-
seed oil mills used solvent extraction. However, these 34 mills extracted
an estimated 60 to 70 percent of the nationally produced cottonseed oil.
Estimated nationwide solvent losses for 1977 are as follows:
Soybeans 61,000 Mg (67,000 tons)
Cottonseed 6,190 Mg (6,800 tons)
Corn 2,090 Mg (2,300 tons)
Peanuts 910 Mg (1,000 tons)
Other 1,640 Mg. ( 1,800 tons )
71,830 Mg (78,900 tons)
Uncontrolled emissions would exceed 181,800 Mg (200,000 tons) for this industry.
The only emission control methods employed by the industry are good operating
practices, including equipment replacement and maintenance and use of
absorbers or adsorbers on the main vent stack. Figure 2—1 indicates that
nearly all the potential solvent losses occur during the extraction and
3-1
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desolventization processes. Solvent emissions resulting from the meal
preparation, oil refining, bleaching, hydrogeneration, and deodorizing
facilities total only 6 to 10 percent of the total.
Economic and safety considerations dictate that hexane losses be
minimized. Hexane currently costs approximately $150.50/rn 3 ($0.60/gal).
All plants use condensers on their main vent to limit emissions. This
is a normal part of process operations and is not considered a control
device. However, hexane losses from the condensers are considerable,
resulting in high hexane replacement expenditures. Most plants have
an absorber or adsorber downstream from the main vent condenser)
In a vegetable oil plant, the major potential emission sources are
the main vent, the post—desolventizing vents, and system leaks.
3.2 CONTROL OF SOLVENT LOSSES FROM THE MAIN VENT
The main vent gases exit the condenser saturated with hexane. This
gas stream is typically on the order of 1.4 to 5.7 m 3 /s (50 to 200 acfni),
depending on plant size. Improper operation may draw air into the system,
increasing the vapor flow rate. The condenser typically lowers the gas
temperature to 38°C (100°F), or about 35 volume percent hexane. Very few
plants operate condensers with chilled water. Even if the vent gases
were lowered to 10°C (50°F), the hexane content would be about 10 volume
percent. For a typical 910 Mg (1000 ton/day) soybean plant using chilled
water condensers, losses would be of 1.1 Kg (2.5 lb) solvent per minute.
Mineral oil scrubbers (MOS) have been developed that are capable of
reducing the hexane content of the main vent gases to less than 0.9 volume
percent. 2 ’ 3 A schematic diagram of an MOS is shown in Figure 3-1. This con-
trol device can reduce, potential emissions from this source by approximately 95
3-2
-------
low concentration
1 PP 1 NG
Pigure .3—1. Schematic diagram of mineral oil scrubbef.
STEAM
SOLVENT VAPOR
TO CONDENSER
COOLED
VENT
3-3
-------
percent. Daily emissions from the main vent for varying plant sizes are
calculated as:
Plant size, Mg/day Hexane emissions Hexane emissions
(tons/day) seeds without MOS, with MOS,
processed Mg (tons) Mg (tons )
90 (100) 0.54 (0.59) 0.027 (0.030)
230 (250) 1.34 (1.48) 0.067 (0.074)
450 (500) 2.68 (2.95) 0.134 (0.148)
910 (1000) 5.36 (5.9) 0.269 (0.296)
1820 (2000) 10.7 (11.8) 0.536 (0.590)
2730 (3000) 16.1 (17.7) 0.804 (0.885)
The reduction in annual emissions will vary from plant to plant. Except
for unscheduled downtime, .these plants run continuously for 3 to 4 month periods.
Representative annual operating days for small cottonseed plants include:
small, 109 Mg/day (120 tons/day) for 172 days; medium, 196 Mg/day (216 tons!
day) for 228 days; large, 502 Mg/day (552 tons/day) for 227 days. Large
soybean plants operate more than 330 days/year.
The hexane captured by the mineral oil is stripped out with steam,
condensed, and reused. The condenser vapors are usually recycled through the
vapor recovery system. The stripped oil is pumped through a cooler and
into the absorption column to absorb more hexane. An MOS system for a
910 Mg/day (1000 tons/day) plant will contain about 0.8 m 3 (200 gallons)
of mineral oil.
3.3 CONTROL OF POST-DESOLVENTIZING VENTS
A portion of the solvent retained in the desolventized flakes is
evaporated in the dryer and cooler and vented to the atmosphere.
Some portion of the remainder is lost in the meal preparation processes.
3-4
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Because of the adsorbing nature of the seed, the latter is believed to be
a small amount and cannot be controlled easily. Figure 3—2 shows the
estimated losses from a reasonably well—operated soybean plant which
has a drying and a cooling facility. Maximum removal is dependent on
proper equipment operation, adequate stripping steam, and equipment
maintenance.
The aspiration vent on the outlet of the desolventizer is a
natural draft stack, its purpose is to catch the water vapor which
flashes off the hot meal. Solvent emissions from this stack are
estimated at 10 percent of the total entrained solvent, based on the
assumption that 10 percent of the moisture flashes to steam and the
solvent flash is proportional. Exhaust gas volume is estimated at
0.33 m 3 /s (700 ft 3 /min) for a 910 Mg/day (1000 ton/day) soybean plant.
Other than using good operating practices and good desolventizing
equipment, no attempt is presently made to control solvent emissions
from the desolventized flakes or meal.
Emissions from the meal-entrained solvent may be limited by more
efficient desolventizing or by controlling the post-desolventizing vents.
The aspirator vent is a relatively small source of VOC’s compared to the
dryer and cooler vents.
3.3.1 Replace Desolventization Equipment
A faulty or poorly operated desolventizer-toaster may result in
inadequate desolventization of the flakes or meal. This results in
3-5
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0 ZO q (0.4i 1k) WU*lt
Figure 3-2. Estimated solvent losses from meal preparatio.n facilities
of a reasonably well—operated soybean plant, based on
0.91 Mg Cl ton) o.f clean, raw soybeans.
iSO kg (1640 lb 1
SI
SHIPPING
frLl ibI
0.10 kq (0 ,65 1k) HtIANt
98 PSgFyr (108 t.’ s/yr)’
ItktS TI tIISACIO8
.SS *1*NE
o3 kq ( l.l ib)
ANNUAL EMISSIONS BAStD ON A 910-PAg/ddy (1000-toM/daY) P (ANI OPERATING 330 days/yr
-------
higher VOC emissions from the dryer and cooler. Emission reductions may
be achieved by màdifying the desolventizing equipment to effect better
operation. Replacement of desolventization equipment has the following
advantages:
- reduced hexane loss
- increased product (meal) quality
- possible reduced steam consumption
- no adverse environmental impacts
Under good conditions, a new desolventizer-toaster can reduce meal solvent
content to 500 ppm. 4 ’ 5 This concentration is considerably lower than the
1350 ppm found at a reasonably well-operated facility 6 ’ 7 Estimated dryer and
cooler solvent emissions from 910 Mg/day (1000 ton/day) soybean plant with
a new desolventizer-toaster is 64 Mg/yr (70 tons/yr).
3.3.2 Add—On Controls for Post Desolventizing Vents
Add-on controls on the post desolventizing vents (dryer, cooler,
and pneumatic conveyor vents) are another option to curb hexane emissions
resulting from inefficient desolventization. Although heretofore unapplied
to this source, carbon adsorption and incineration are considered acceptable
control technology by the principle of technology transfer. The National
Soybean Products Association has raised doubts regarding the safety of
these control options.
Carbon Adsorption - Solvent emissions can be removed from these
vents with a carbon bed adsorber for reuse in the extractor. Although no
plants are known which control these sources at present, carbon bed
3-7
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adsorbers are used on other high-volume hydrocarbon sources, including the
main vent in some soybean plants.
Dryer vent gases are saturated with water at 88°C (190°F).
Approximately 0.06 m 3 (2 ft 3 ) air is exhausted per 0.5 Kg (1 ib) of flakes.
This gas stream is dusty and must be cleaned prior to entering an adsorber.
Dilution air can be used to reduce the relative humidity sufficiently to
vent the gases to a fabric filter and then to the carbon bed adsorber.
The volume of gases from the cooler is about 0.6 ni 3 (20 ft 3 ) per
0.5 Kg (1 ib) of flakes. These gases have a relative humidity of about
65 percent at 43°C (110°F). They can be vented, without dilution, directly
to the fabric filter and the adsorber.
It is not practical to combine the cooler and dryer vents, since the
resulting relative humidity would be too high for the fabric filter.
Except for combustion products of fuel used to generate steam and
electricity for the adsorber, no secondary pollutants are produced by
this control device. The captured solvent is reused in the process.
Carbon bed life is approximately five years. 8 When replaced, the old
carbon is sent to a processor for reactivation and reuse. Thus, none
of the activated carbon enters the solid waste stream. Carbon bed adsorbers,
properly operated, can remove 95 percent of the hexane from the vent gases. 9
This reduces solvent emissions to a level well below that found in a
reasonably well -operated facility.
Considerable fire hazard would exist if a desolventizer-toaster accidently
dumped hexane-laden meal into the carbon adsorption equipped dryer. 10
3-8
-------
Incineration - Another method of reducing VOC emissions from the
post-desolventization vents is to incinerate the exhaust gases. Incineration
has been used successfully on hydrocarbon—containing exhausts in numerous
other industries. It must be pointed out, however, that the cooler’s low
exhaust temperature and high gas volume tend to discourage this emission
reduction technique. In addition to these problems, the National Fire
Prevention Association (NFPA) presently does not recommend flaring of process
vents because of the extreme flammability of hexane) 1 The NFPA Sectional
Comittee on Solvent Extractions is planning to propose a change in their
safety bulletin wherein flares will be permitted for process vents, provided
the flares are located more than 30 m (100 ft) from the extraction process
and that approved devices are installed to prevent flashback in the vent
piping. 12
Incineration of vent gases can eliminate 99 percent of the VOC
emissions from these facilities.
3.4 CONTROL OF FUGITIVE EMISSIONS
The VOC emissions resulting from liquid and gaseous leaks may be
as high as 0.85 Kg/MFC (1.7 lb/TFC) 13 for a 910 Mg/day (1000 ton/day) soybean
plant. These emissions can be reduced to 0.33 Kg/MFC (0.66 lb/TFC) in a
reasonably well-operated plant. Since these losses result mainly from leaks
and spills, control is best effected by an adequate maintenance and
housekeeping program.
3-9
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3.5 SUMMARY
Emissions of VOC from a reasonably welt-operated 910 Mg/day (1000 ton/
day) soybean plant approximate 8 Kg/MFC (16 lb/TFC) without a main vent
control and 2.7 Kg/MFC (5.3 lb/TFC) with a control system on the main vent.
Poorly operated plants may lose over 8 Kg/MFC (16 lb/TFC) even with a control
device on the main vent.
Mineral oil scrubbers on the main vents can remove 95 percent of the
solvent in that gas stream. Other emissions are limited by good operating
practices and maintenance. The industry does not currently use control
devices on the post-desolventizing vents. These gas streams could be
controlled with carbon bed adsorbers or afterburners under the principle
of technology transfer.
3-10
-------
3.6 REFERENCES
1. Telephone conversation between Donald J. Loudin of PEDCo
Environmental and Robert Reynolds of French Oil Machinery Company on
February 14, 1977.
2. Meeting with William Coombes and Roger Hansatte of Dravo,
January 24, 1978.
3. Telephone conversation with Mr. W. B. Thayer of French Oil Mill
Machinery Company, December 14, 1977.
4. Reference 2, Op Cit.
5. Hutchins, R. P., “Continuous Solvent Extraction of Soybeans
and Cottonseed.” J. Am. Oil Chemists’ Society, June, 1976 (Volume 53).
pp. 279-282.
6. Reference 2, Op. Cit.
7. George Anderson. Five Point Process Efficiency, Crown Iron Works
Company, Minneapolis, Minnesota, 1976.
8. Control of VOC From Existing Stationary Sources, Volume 1,
OAQPS No. l.2--67, p.35, November, 1976.
9. Vic Manufacturing Company quotation.
10. Meeting with NSPA, June 21, 1978, and Kern Brothers, EPA, i n Durham, N.C.
11. National Fire Protection Association. Solvent Extraction
Plants 1974 , Boston, Massachusetts, pp.29.
12. Letter to Donald J. Henz of PEDCo Environmental, Inc., from
Miles E. Woodworth of National Fire Protection Association, dated
January 12, 1978.
13. Reference 7, op. Cit.
3—11
-------
4.0 COST ANALYSIS
4.1 INTRODUCTION
4.1.1 Purpose
The purpose of this chapter is to present capital and annualized
costs for alternative ways of controlling volatile organic compound
(VOC) emissions at vegetable oil extraction plants. A cost-effective-
ness analysis is included as an extension of the cost development.
4.1.2 Scope .
Estimates of capital and annualized costs are presented for con-
trolling VOC emissions from meal drying, meal cooling, meal product, and
main vent sources in vegetable oil extraction plants. Since all
plants are concerned with hexane losses and since the mode of process
operation affects the cost effectiveness of the control options, two
types of oil extraction plants are analyzed: well-operated plants and
poorly operated plants. Cost analyses are performed for soybean plants
and corn plants. The following control alternatives are analyzed for
each type of plant:
1. Mineral oil scrubber (MOS) on the main vent associated with
effective operation of the desolventizer toaster (DT).
2. MOS on the main vent and replacement of DI.
3. MOS on the main vent and carbon adsorbers for meal dryer and
cooler emissions.
4-1
-------
4. MOS on the main vent and incinerators for meal dryer and
cooler emissions.
4.1.3 Use of Model Plants
The cost analysis is based solely on model sizes. Additional costs
resulting from retrofitting the installation are considered, but no
consideration has been given to detailed design characteristics of the
model plants in terms of process equipment requirements, control system
design, etc. It was necessary, however, to consider gas flow rates for
model plants in order to size the VOC control systems.
It must be emphasized that model plants used in these analyses are
ideal because they assume minimal space limitations for retrofitting the
VOC control systems. The level of retrofit difficulty will alter the
costs of control systems. Although control cost estimates based on
model plants may differ from actual costs incurred, they are considered
the best means of comparing relative costs and cost effectiveness of
alternative control measures.
For purposes of estimating the cost effectiveness of various
control options, the hexane recovery credit for a well-operated plant is
based on the amount of hexane recovered over and above that recovered in
a well-operated plant (i.e., one having a 90 percent efficient MOS and
an effectively operated DT). The hexane recovery credit for the control
options relative to a poorly operated plant is based on the amount of
hexane recovered over and above that recovered in a poorly operated
plant prior to upgrading.
4-2
-------
4.1.4 Bases for.Capital Cost Estimates
Capital costs represent the investment required for retrofitting a
control system, including cost of equipment, material, labor for in-
stallation, and other associated costs. The capital cost estimates were
developed by two different methods that include the same capital cost
components such as equipment control and instrumentation, piping, duct-
work, insulation, painting, etc. The methods of cost estimation were
either to “build” an investment cost based upon the free on board
(f.o.b.) equipment cost supplied by the manufacturer or to update in-
vestment costs that had been previously developed. The former method
was employed to obtain the DT, 1 MOS, 2 and carbon adsorber 3 ’ 4 ’ 5
investment cost. The latter method was used to derive costs of
afterburner systems with primary heat recovery. 6 ’ 7
4.1.5 Bases for Annualized Costs
Annualized costs represent the cost of operating and maintaining
the control system and of recovering the capital investment.
Operating costs include costs of materials, utilities, and normal main-
tenance. The annualized costs also take into consideration the credit
resulting from solvent recovery by emission control systems. All con-
trol equipment operating costs are estimated on an annual basis by the
use of data from either the manufacturer or the literature. The unit
costs and assumptions for the annualized costs are delineated in Table
4-1.
4-3
-------
Table 4-1. COST FACTORS USED IN COMPUTING ANNUALIZED COSTS
I. Annual operating time
II. Direct operating costs
1. Materials (as purchased) 8
- Carbon for adsorbers (5-yr life)
- Mineral oil for scrubbers (1-yr life)
- Recovered he ane solvent
2. Utilities
- Electricity
- Steam [ saturated, 100 kPa (15 psig)]
- Natural gas
- Cooling water
3. Direct labor (0.5 man-hour/shift)
4. Maintenance charges
III. Annualized capital charges
.1. Depreciation and interest
2. Taxes and insurance
3. Administrative overhead
6000 h for small and medium
size plants
8000 h for large size plants
$1.76/kg ($0.80/lb) 9
$530 /imS ($2/gal) 10
$0.19/kg ($0.085/lb)
$0.0126/IvlJ ($0.0455/kWh) 1 ’
$0.01/kg ($3.30/bOO ib) 12
$0.07/Nm 3 ($2.01/bOO scf)
$0.01/rn 3 ($0.04/bOO gal)’ 3
$10/man-hour 14
1% of capital investment’ 5
14.67% of capital cost
2% of capital cost
2% of capital cost
4-4
-------
The annualized cost analyses of model plants are provided as a
means of comparing the relative costs of alternative control measures.
The costs in actual practice may vary depending on factors such as mate-
rial rates, utility costs, and total capital investment.
4.2 SOLVENT EMISSION CONTROL IN VEGETABLE OIL EXTRACTION PLANTS
4.2.1 Model Plant Parameters
Cost analyses are presented for three model sizes of vegetable oil
extraction plants: small, medium, and large. These plants have a daily
extractor feed cake processing capacity of 90, 640, and 1360 Mg (100,
700, and 1500 tons), respectively. Small and medium plants are assumed
to operate 6000 h/yr, and large plants 8000 h/yr.
The exhaust volumes used for determining control costs of the main
vent are 0.023, 0.041, and 0.087 m 3 /s (48, 86, and 184 acfm) for plants
having daily extractor feed cake processing capacities of 90, 640, and
1360 Mg (100, 700, and 1500 tons), respectively. Dryer and cooler
exhausts are considered directly proportional to plant size for the
model plant. Control costs of meal dryers are based on 0.115 m 3 /s (244
acfm) per 90 Mg (100 tons) of daily extractor feed cake capacity, while
control costs of meal coolers are based on 1.?0 m 3 /s (2550 acfm) per 90
Mg (100 tons) of daily extractor feed cake capacity. Exhaust tempera-
ture are estimated at 66°C (150°F) and 44°C (110°F) for the dryer and
cooler, respectively.
The model plant cost analysis is performed for four control options
discussed in Section 4.1.2. Hexane absorption by means of MOS units is
4-5
-------
almost universally used in the industry to control emissions from the
main vapor vent. These units, which handle relatively small gas flow
rates, can achieve up to 98 percent removal of hexane from the stream
when properly operated.
Effective operation of the DI or replacement with a more efficient
DI decreases solvent emissions to the atmosphere because it decreases
the solvent carryover to the meal dryer and cooler; hence, the DI can
also be considered as an alternative for controlling solvent emissions
from the meal dryer vent and cooler vent. For some plants though, process
variables upstream may prevent a new DT from achieving full effectiveness.
The operating and maintenance costs of DT’s are considered part of.pro—
cessing cost and are not included in the costs of the control options.
Carbon-bed adsorbers may be applicable for removal and recovery of
hexane in the exhaust streams from meal dryers and meal coolers. For
both applications, however, removal of particulate matter is required
prior to entry of the stream into the adsorber. The cost of a fabric
filter is included in the adsorber system cost.
Afterburners with primary heat recovery can be employed for incin-
erating the solvent contents in the exhaust streams from meal dryers and
coolers. Primary heat recovery is employed to reduce fuel requirements.
Afterburners pose a fire risk because of high incinerating temperatures.
Therefore, an isolated location is required for afterburners. Cost of
an additional 30.5 m (100 ft) of ducting is included in the capital costs
of model plants to allow for afterburner compliance with the National
Fire Prevention Association requirement. 16
4-6
-------
4.2.2 Control Costs
Table 4-2 presents control costs of the four control options
analyzed in this report. Costs are presented for three model sizes:
small, medium, and large. The costs in Table 4-2 do not include the
credit for recovered hexane. The capital costs of the afterburner in-
clude the cost of an additional 30.5 m (100 ft) of ducting. The capital
cost of each option also includes the cost of monitoring equipment on
the exhaust stacks. Three monitoring systems are assumed for each
plant, one each for the main vent stack, dryer stack, and cooler stack.
4.3 COST EFFECTIVENESS
The emission control efficiencies and solvent emission reduction
quantities are presented in Tables 4-3 through 4-6. These tables also
indicate the solvent credit and cost effectiveness of each control op-
ti on.
Cost-effectiveness curves are presented in Figures 4-1 through
4-4. For all the vegetable extraction plants analyzed in this report,
control option No. 2 (MOS and replacement of DT) seems to be the most
cost-effective option. This option also provides the maximum control
efficiency among the options analyzed. The least cost-effective option
is apparently an MOS coupled with an afterburner on the dryer and
cooler. This is due to the high fuel requirements of the afterburner
and also partly to the loss of hexane in this unit.
4-7
-------
Table 4-2. COSTS OF SOLVENT CONTROL OPTIONS VEGETABLE OIL EXTRACTION PLANTS, $
°
Cost item, $
Capital lnvestlnentt)
Control option
No. 1
No. 2
No. 3
No. 4
HOS plus effective
operation DT
Small Medium large
MOS plus replacement
of UT
-_Small Medium Large
MOS plus carbon edsorbers
Small Medium large
MOS plus afterburners for
y r flt Q era
Small Medium large
Capital cost of control
system
34,000
58,000
84,000
390,400
468,000
734,000
212,500
573,000
843,000
298,000
377,000
471,000
Capital cost of
monitoringc
12,000
12,000
12,000
12,000
12,000
12,000
P12,000
12,000
12,000
12,000
12,000
12,000
Total capital
investment
46,000
70,000
96,000
402,400
480,000
746,000
224,500
585,000
855,000
310,000
389,000
483,000
°
Annual
Operation and
maintenance cost
7,300
13,500
31,100
7,300
13,500
31,100
22,000
61,400
147,400
34,400
145,200
403,000
Capital charges, Insur-
ance, and overheade
8,600
13,100
17,900
75,100
89,600
139,300
42,000
109,200
159,600
57,900
72,600
90,200
Total annualized cost
15,900
26,600
49,000
82,400
103,100
170,400
64,000
170,600
307,000
92,300
217,800
493,200
• Capital costs of afterburners Include the cost of en additional 30.5 m (100 ft) of ducting.
b Capital cost is in Noven er 1977 dollars.
C Monitoring system costs $4000/stack, three stacks per plant.
d Does not include monitoring costs of approximately $2000 per year.
C 14.67% amortization, 2% Insurance, and 2% aánlnlstrative overhead.
-------
Table 4-3. EMISSION REDUCTION AND COST EFFECTIVENESS DATA FOR CONTROL FACILITIES
FOR A WELL-OPERATED SOYBEAN PLANT
Cost it n
No. 1
S plus effective
noeration of D I
Small Medium Large Small
Control notion
No. 2
MOS olus replacement
of DI
Ned I tin
No. 3
MOS plus carbon adsorbers
for dr er and c oler
Large
Small
Med nun
No. 4
Solvent emissions controlled,
kg/Mg of extraction feed
cake pracessed
Solvent emission control
efficiency,
Solvent emission reduction,
kg/yr
Annualized cost of control
system, S
Annual credit for recovered
hexane, S
Net annualized cost
(credit), S
Cost effectiveness (cretht),
S/kg of solvent controlled
Large
MOS plus afterburners for
dryer and coc 1 er
Small
Medium
By definition these
plants already in
corporate control
option no. 1
Large
0.69
42
15,600
82,400
2,900
79,500
5.10
0.69
42
109,500
103,100
20,500
82,600
0.75
0.69
42
313,000
170,400
58.700
111 ,700
0.36
0.53
32
11,900
64,000
2,200
61 .800
5.29
0.53
32
83,300
170,600
15,600
155,000
1 .86
0.53
32
238,100
307,000
44,600
262,400
1.10
0.54
33
12,200
92,300
92,300
7.57
0.54
33
85 • 700
217,800
217,800
2.54
0.54
33
244,900
49 3.200
493,200
2.01
-------
-I
Table 4-4. EMISSION REDUCTION AND COST EFFECTIVENESS DATA FOR CONTROL FACILITIES
FOR A POORLY OPERATED SOYBEAN PLANT
Cost Item
,tion
Mn. 4
No. 1
No. 2
P S plus effective
operation_of DI
MOS plus replacement
of OT
MOS plus carbon adsorbers
r jru coojer
MOS plus afterburners for
driera d oo ler
Small Medium large
Small
Medium
Large
Small
W funi
Large
Small
Medium
large
Solvent emissions controlle i,
kg/Mg of extractor feed
cake processed
3.9
3.9
.
3.9
4.6
4.6
4.6
3.3
3.3
3.3
3.3
3.3
3.3
Solvent emission control
efficiency, %
70
70
70
83
83
83
‘
59
59
59
60
60
60
Solvent emissions
controlled, kg/yr
88,500
619,200
1,769,000
04,100
728:700
,082,000
74,000
518,300
1,481,000
76,000
529,500 1,512,700
Annualized cost of
control system, $
15,900
26,600
49,000
82,400
103,100
170,400
64,000
.
170.600
307,000
92,300
217,800
493,200
Annual credit for
recovered hexane, $
7,206
50,600
144,500
19,500
136,600
390,200
13,900
97,100
277,300
7,200
50,600
144,500
Net annualized cost
(credit), $
8,700
(24,000)
(95,500) 62,900
(33,500) (219,800
50,100
13,500
29,700
85,100
167.200
348,700
Cost effectiveness
(credit), S/kg of
solvent controlled
0.10
(0.04,
(0.05)
0.60
(0.05)
(0.11
0.68
0.14
0.02
1.12
0.32
0.23
-------
-J
1
Table 4-5. EMISSION REDUCTION AND COST EFFECTIVENESS DATA FOR CONTROL FACILITIES
FOR A WELL-OPERATED CORN PLANT
Cost item
Coii toj
oo ion_______________
No. 4
No. I
No. 2
No. 3
for
$0S plus effective
$05 plus replacement
MOS plus carbon adsorbers
MOS plus
and cooler
operation_of DT
Small Medlun Large
Small
of DT
Mediun
large
for
SmaiT
oo !er_ . ..
Medltr Large
y r
Small Medium large
Solvent emissions controlled,
kg/Mg of extractor feed
cake processed
0.4
0.4
0.4
0.3
0.3
0.1
0.3
0.3
0.3
Solvent emission control
efficiency, %
34
34
34
26
26
26
27
27
27
Solvent emissions
controlled. kg/yr
Annualized cost of
control system, $
By definition these
plants already in-
corporate control
option no. 1
9,300
82,400
65,100
103,100
186,000
170,400.
7,000
U,000
49,200
170,600
140,600
307,000
7,300
92,300
51,000
217,800
145,800
493,200
Annual credit for
recovered hexane, $
1,700
12,200
34,900
1,300
9,200
26,400
Net annualized cost
(credit), S
80,700
90,900
135,500
62,700
161,400
280,600
92,300
217,800
493,200
Cost effectiveness
(credit), S/kg of
solvent controlled
8.68
1.40
0.73
8.96
3.28
2.00
12.64
4.27
3.38
-------
-a
Table 4-6. EMISSION REDUCTION AND COST EFFECTIVENESS DATA FOR CONTROL FACILITIES
FOR A POORLY OPERATED CORN PLANT
Cost item
Control optlon
No. J
No.2
No.3
!Io.4
PUS plus effective
PUS plus replacement
PUS plus carbon adsorbers
P105 plus afterburners for
Small
operation_of
Medi un
DT
Large
Small
of DI
Medium
t.arge
for
Small
dryer and cooler -
Medium Large
dryer and co ’ ler
Small Medium Large
Solvent emissions controlled,
kg/Mg of extractor feed
cake processed
3.0
3.0
3.0
3.4
3.4
3.4
2.6
2.6
2.6
2.7
2.1
2.7
Solvent emission
.
.
control effIciency, S
71
71
71
81
81
81
‘63
63
63
63
63
63
Solvent emissions
controlled, kg/yr
68,000
476,300
,360 800
77,300
541,400 1,546,800
59,500
416.700
.190,700
60,400
429,100
1,208,800
Annualized cost of control
system, S
15.900
26.600
49,000
82,400
103,100
170,400
64,000
170,600
307,000
92.300
217.800
493,200
Annual credit for
.
recovered hexane, $
1,200
50,600
144,500
14,500
101.400
289,900
11,200
78,100
223,100
7,200
50,600
144,500
Net annualized cost
(credit), S
8,700
(24,000)
(95,500)
67,900
1,700 (119,500)
52,800
92,500
83.900
85,100
167,200
348,700
Cost effectiveness
(credit), S/kg of
solvent controlled
0.13
(0.05)
(0.07)
0,88
0.00
(0.08)
0.89
0.22
0.07
1.41
0.39
0.29
-------
I I
200
(220)
400 600 800 1000 1200 1400
(440) (660) (880) (1100) (1320) (1540)
PLANT CAPACITY, Mg (tons) OF EXTRACTOR FEED CAKE/DAY
WELL• OPERATED SOYBEAN PLANT
Figure 4-1
Cost-effectiveness curves for a well—operated
soybean plant
7.0
Note
Number represents
control option
5.0 -
w
-J
_-i 6.0
0
I-
0
(-)
0
L-
a
4.0
a
C ,,
LiJ
w
1-4
I—
C-)
L&J
U-
L&J
I—
C,,
a
C-)
3.0
2.0
1.0-
C
I I I I
4-13
-------
- 1.
•1
Li.J I
-J
-J
I-
0
L)0
L)
0
U-
0
(0.2
Figure 4-2. Cost-effectiveness curves for a poorly operated
soybean plant
1.2
0.
200 1000
(220) (440) (660) (880) (1100) (1320) (1540)
PLANT CAPACITY, Mg (tons) OF EXTRACTOR FEED CAKE/DAY
POORLY OPERATED SOYBEAN PLANT
4-14
-------
PLANT CAPACITY, Mg (tons) OF EXTRACTOR FEED CAKE/DAY
WELL-OPERATED CORN PLANT
Figure 4-3.. Cost-effectiveness curves for a well-operated
corn plant
4-15
-J
-j
o
C-,
o
a
CI J
(I )
w
I—
C-)
w
w
-------
1.2
LU
—I 1
I-
D V.
C,
a
LU
LU
0.4
C.)
LU
U-
U-
LU
0.2
(0.2 200 400 600 800 1000 1200 1400
(220) (440) (660) (880) (1100) (1.320) (1540)
PLANT CAPACITY, Mg (tons) OF EXTRACTOR FEED CAKE/DAY
POORLY OPERATED CORN PLANT
Figure 4-4 Cost effectiveness curves for a poorly operated
corn plant
1 .4
I U
1
.1
Note
Number represents
control option
4
I I I I
4-16
-------
4.4 SUMMARY
Cost analyses of model plants indicate that the cost of emission
control in the vegetable oil industry is sensitive to the amount of
solvent recovered. The increasing value of hexane used in
oil extraction plants causes emission control with more effective
hexane recovery to be increasingly attractive economically as well as
necessary for compliance with emission standards.
4-17
-------
REFERENCES
1. Telephone conversation between Donald J. Henz of PEOCo Environmental,
Inc., and Robert Reynolds of French Oil Machine Co., February 2, 1978.
2. Telephone conversation between Donald J. Henz of PEDC0 Environmental,
Inc., and W.B. Thayer of French Oil Machine Co., December 14, 1977.
3. Letter from 1. Cannon, vic Manufacturing Co., Minneapolis, Minnesota,
to Donald J. Henz, PEDC0 Environmental, Inc., January 6, 1978.
4. Control of Vo1atile Organic Emissions from Exisiting Stationary
Sources - Volume I. OAQPS Report No. 1.2-067. November 1976. pp.
103, 111, 129, 131.
5. M. M. Mattin. Process for Solvent Pollution Control, Chemical
Engineering Progress. December 1970. pp. 75 and 78.
6. Op. cit. Ref. 4.
7. Study of Systems for Heat Recovery from Afterburners. EPA Contract
No. 68-02-1473, Task 23, Industrial Gas Cleaning Institute. Feb-
ruary 1978. pp. 5-1, B-2.
8. Op. cit. Ref. 4.
9. Ibid.
10. Chemical Marketing Reporter. January 30, 1978.
ii. Op. cit. Ref. 7.
12. Ibid.
13. Op. cit. Ref. 4.
14. Op. cit. Ref. 7.
15. Op. cit. Ref. 3.
16. Letter from M. Woodward, National Fire Prevention Association, Boston,
Massachusetts, to Donald J. Henz, PEDCo Environmental, Inc. January 12,
1978.
4-18
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5.0 ADVERSE EFFECTS OF APPLYING THE TECHNOLOGY
This chapter addresses the fuel/energy requirements for applying
the control technology discussed in Chapter 3.0. Also discussed is the
impact of these energy expenditures with regard to air, water, and solid
waste pollution.
5.1 MINERAL OIL SCRUBBER
The mineral oil scrubber (MOS) requires steam for heating and stripping
the mineral oil and electrical energy to pump the oil. Efficient operation
of an MOS depends on the amount of air introduced into the system. For
purposes of assessing the energy impacts, it is assumed that the plant
is fairly well-operated and the main vent exhaust volume is 3 Nm 3 (100 scf)
per 0.91 MFC (1 TFC). Daily energy requirements are generally proportioned
to plant size, although smaller plants have slightly higher air requirements
due to the introduction of air into the system from miscellaneous leaks.
This infiltration rate does not decrease in proportion to plant size. Annual
energy requirements for MOS operation, by plant size, are shown in Figure 5-1.
Secondary pollutants based on the following emission factors are shown in
Table 5—1: Allowable Emissions
Pollutant Mg/KJ (lb/lO 6 Btu) Kg/Mg (lb/ton) coal
Particulate Matter 0.04 (0.1) 1.2 (2.4
Sulfur Dioxide 0.86 (2 ) 24 (48
Hydrocarbon 0.02 (0.04) 0.5 (1)
Nitrogen Oxide 026 (0.6) 7.5 (15)
Carbon Monoxide 0.03 (0.08) 1 (2)
* MFC niegagrams of extractor feed cake
TFC tons of extractor feed cake
5-1
-------
2730
(3000)
Figure 5—1. Annual fuel requirements for a mineral oil
scrubber on the main vent of a soybean plant.
4. ,
w
>
•I-
C-
w
0
9 228 455 637 1920 2280
(100)(250} (500X700) (1000) (2000) (2500)
PLANT CAPACITY, Mg/day (tons/day) OF SEEDS PROCESSED
5—2
-------
Table 5-1. ECONDARYPOLLtJTANT5 RESULTING FROM USE OF MINERAL OIL
SCRU ER ON MAIN VENT
Plant size, Mg/day
(tons/day) seeds
processed
Part
En
So 2
lssions, Mg/yr(
MC
tons/yr)
NO 2
CO
90 (lao)
230 (250)
4so (500)
910 (1000)
1820 (2000)
2130 (3000)
0.009 (0.01)
0.036 (0.04)
0.013 (0.08)
0.182 (0.2)
0.454 (0.5)
0.636 (0.1)
0.182 (0.2)
0.636 (0.7)
1.545 (1.7)
4.364 (4.8)
8..727 (9.6)
13.091 (14.4)
.0.004 (0.005)
0.018 (0.02)
0.036 (0.04)
0.091 (0.1)
0.182 (0.2)
0.273 (0.3)
0.073 (0. 18)
0.182 (0.2)
0.454 (0.5)
1.364 (1.5)
2.727 (3.0)
4.091 (4.5)
0.00° ( ).O1)
0.027 (0.03)
0. 36 (V .7)
0.182 (C.2)
0.364 (0.4)
0.545 (0.6)
-------
Very little water or solid waste pollution results from the use of
an MOS. The collected solvent is recycled and the mineral oil itself
theoretically lasts indefinitely as long as the system is properly operated.
(In actual practice the mineral oil is replaced once or twice a year.) If
the mineral oil heater fails, however, the oil will mix with condensate
from the condensing stream to form an emulsion. This emulsion must be
replaced. When the oil must be replaced, it is put into drums and hauled
away by a waste oil dealer and normally sold to asphalt plants for use as
fuel.
5.2 INSTALLATION OF A N W DESOLVENTIZER-TOASTER
The purpose of a desolventizer-toaster is to recover hexane from the
flakes and to produce a marketable meal product. New desolventizer—
toasters are generally more than twice as efficient for solvent removal
than older, reasonably well-operated ones. Incorporation of this equipment
has no adverse environmental impacts.
5.3 CARBON BED ADSORBER
Carbon bed adsorbers require stripping steam and electrical energy
to drive the gases through the carbon bed. When used to control dryer
and cooler vent emissions, typical energy requirements for a 910 Mg/day
(1000 ton/day) plant are as follows:
Steam Electrical
Kg/s (lb/hr) Power, kW
Dryer 2 0.05 (400) 25
Cooler 0.08 (600) 75
5-4
-------
Annual energy requirements are shown in Figure 5-2. Secondary
emissions are estimated using the same emission factors as the MOS
as shown in Table 5—2. The activated carbon used in the adsorbers
has a life of approximately 5 years. 5 At the end of its useful life,
the carbon is replaced with a new charge. The spent carbon is reactivated
for use elsewhere. It does not enter the solid waste stream.
5.4 INCINERATION
Exhausts from the dryer vent and cooler vent may be introduced to an
afterburner, where the hexane vapors are incinerated. This control method
requires no waste disposal or recycling of adsorbent agent. It has its
drawbacks, however, in that it destroys the hexane and requires a large
quantity of fuel even with heat recovery. Pollutants in the products of
cornbustions would be emitted as shown in Table 5-3. Annual gas consumption
is shown in Figure 5-3.
5-5
-------
—
M I
-a
LI .
0
*1
P. gure 5-2. Annual fuel requirements for carbon-bed
...adsorberscontrolling both the dryer vent and cooler vent.
91 228 455 637 910 1820
.(100)(250) (500)(700) (1000) (2000)
SLANT CAPACITY. $ g/day (toin/dsy) SEEDS PROCESSED
5-6
-------
‘table 5 -2. St CONDARY I’OLLtiTANTS RESULTING FROM tJ E OF ADSORBER ON
DRYER AND COOLER VENTS
I- -
Plan€ size, Mg/day
(tons/day) seeds
processed
--
.
trnI sions, Mg/yr (tons/yr)
Part
SO 2
AC
NO 2
Co
90 (100)
230 (250)
450 (500)
910 (1000)
1820 (2ooo
2730 (3000)
0.05 (0.055)
0.13 (0.14)
0.25 (0.28)
0.72 (0.79)
i.4s (1.6)
2.18 (2.4)
1.0 (1.1)
2.54 (2.8)
5.0 (5.5)
14.36 (15.8)
28.73 . (31.6)
43.18 (41.5)
0.021(0.023)
0.054 (0.06)
0.100 (0.11)
0.300 (fl.33)
0.600 (0.66)
0.909 (1.0)
0.032 (0.035)
0.082 (0.09)
0.164 (0.18)
0.454 (0.50)
0.909 (1.0)
1.364 (1.5)
0.042 (0.0461
0.109 (0.12)
0.209 (0.23)
fl.E00 (0.66)
1.182 (1.3)
1.818 (2.0)
-------
SECONDARY POt t tJTANTS RESULTING ROft USE OF A PRIHARY RECO.VERY TYPE
01
3
Table 5—3.
AFTERfltJRNER ON DRYER AND COOLER VENTS
Plant size, Mg/day
(tons/day) seeds
processed
tnissions, Mg/yr (tons/yr)
Part
SO 2
HC
uo 2
Co
90 (100)
230 (250)
4so (500)
910 ilooo)
1820 (2000)
2730 (i000)
0.028 (0.0.31)
0.011 (0.078)
0.141 (0.155)
0.409 (0.450)
0.818 (0.900)
1.227 (1.35)
0.0017 (0.0019)
0.0043 (0.0047)
0.0845 (0.093)
0.0245 (0.027)
0.0491 (0.054)
0.0736 (0.081)
0.023 (0:025)
0.056 (0.062)
0.113 (0.124)
0.327 (0.360)
0.654 (0.720)
0.982 (1.08)
0.28 (0.31)
0.71 (0.78)
1.41 (1.55)
4.09 (4.50)
8.18 (9.0)
L2.27 (13.5)
0.056 (0.062)
0.142 (0.156)
0.282 (0.310)
0.818 (0.90)
1.636 (1.80)
2.454 (2.70)
-------
2730
(3000)
Figure 5-3. Annual natural gas requirements for a
direct-fired afterburner (with primary recovery)
controlling both the dryer vent and cooler vent.
1.
0
1 .
B
0
U,
-J
I —
91 228 455 637 910 1820 2280
(100)(250) (500)(700) (1000) (2000) (2500)
PLAKI CAPACITY Mg/day (tons/day) SEEDS PROCESSED
5-9
-------
5.5 REFERENCES
1. R. D. Good, “Maximum Solvent Recovery Creates Safety and Profit,”
Dravo Corporation, Pittsburgh, Pennsylvania, October 16, 1967.
2. Engineering calculations based on information contained in a
January 6, 1978, letter to Mr. Don Henz, PEDCo, from VIC Manufacturing Co.
3. Engineering calculations based on information contained in
Chemical Engineering Progress Vol. 65, No. 12, December 70, p. 75.
4. Reference 2, Op. Cit.
5. Control of VOC From Existing Stationary Sources, Volume 1,
OAQPS No. 1.2-067, p. 35, November, 1976.
6. Engineering calculations based on AP-42 emission factors.
5-10
-------
6.0 ENFORCEMENT ASPECTS
The purpose of this chapter is to define facilities to which regulations
will apply, select appropriate regulatory format, and to recommend emission
limits which represent RACT. Compliance and monitoring techniques are also
recommended in this chapter.
6.1 AFFECTED FACILITY
In formulating regulations, it is recommended that the affected
facility be defined as the extraction system, from the extractor to the
cooler (or pneumatic flake conveyor). As discussed in Chapter 2, the
principal emission points include but are not limited to:
1. Extractor
2. Desolventizer or desolventizer-toaster
3. Dryer
4. Cooler
5. Pneumatic flake conveyor
RACT for the major sources is defined as follows:
A. Extractor
Major extractor losses are through the main vent. Solvent emissions
from the main vent are effectively controlled with a mineral oil scrubber (MOS).
This device can reduce main vent emissions by 90 to 95 percent. Carbon—bed
adsorbers are also effective on this vent, but have found very limited use.
6-1
-------
Limitation of this vent stream to a concentration of 9000 ppm is
currently achievable with a mineral oil scrubber. This will reduce hexane
emissions from a 910 Mg/day (1000 ton/day) plant from 5400 kg/day to
500 kg/day (11,900 to 1,100 lb/day). Emissions of VOC will be reduced
by 5.4 kg/MFC (10.7 lb/TFC) or more by application of a mineral oil
scrubber on the main vent.
B. Desolventizer, Dryer, Cooler, Pneumatic Conveyor
These sources each discharge to the atmosphere through separate
vents. No attempt is currently made to capture the hexane in these gas
streams. These losses, however, are a function of the efficiency of the
desolventizing equipment. Thus VOC discharges from these vents may be
limited by means of vent control or process control. New desolventizer-
toasters (DI) desolventize flakes to the 500 ppm level. Reasonably well-
operated plants desolventize to a level of about 1350 ppm hexane. This is
approximately 1.35 kg/Mg (2.7 lb/ton)of desolventized flakes. Smaller
plants without dryers and coolers pneumatically convey the desolventized
flakes to the meal conditioning area. Approximately half of the entrained
solvent (about 0.7 kg/Mg desolventized meal) is lost in the dryer-cooler
arrangement or, in smaller plants, along the pneumatic conveyor.
Properly operated and maintained desolventizing equipment is capable
of reducing the level of hexane in desolventized meal well below 1350 ppm.
Plants not able to achieve this concentration can control their emissions
with carbon-bed adsorbers or incinerators installed on the dryer and cooler
vents. Carbon-bed adsorbers and incinerators reduce emissions by 90 to 99 percent.
6-2
-------
6.2 MONITORING AND COMPLIANCE
The main vent stack and the meal leaving the desolventizer—toaster
should be monitored by operating personnel weekly during the first year.
After the first year, the data should be reviewed so that monitoring and
reporting requirements can be adjusted as necessary.
Analytical methods for determining the hexane concentration of meal
from the desolventizer are being investigated. Pending completion of the
evaluation, no test method is recommended at present.
6-3
-------
APPENDIX A
A-i
-------
Table A-]. ESTIMATED AVEPSAGE SOLVENT LOSSES rRo:I REASONABLY
WELL-OPERATED COTTONSEED AND SOYBEAN PLANTS BASED
ON CLEAN, RAW SEED INPUT (r•letric Units)
Solvent loss, kg/rig raw seed
Cottonseed
Prepress
Full solvent
Point of solvent loss
plant
plant
Soybeans
A. Operational losses
neai.dryingasb
rieal cooiingasb
Neal productasb
0 j 1 c,d
0.18
0.12
()3fl
0.08
0.18
0.12
0.30
0.16
0.32
0.22
0.55
.l8
Waste watere
1 ain vent (uncontro11ed)
0.02
3.13
0.05
3.55
0.05
5.90
Solvent storages
Fugitive (1eaks) ’
0.04
0.30
0.09
0.10
0.33
Total operational losses
4.17
5.04
7.65
.8. Non—operational losses
.
Start—up.& shutdown 1
Downtixne
0.18
0.18
0.20
0.20
0.16
0.16
Total uncontrolled losses
4 ,5
5.4
8.0
(rounded)
,d
Less solvent collected in
absorber (average))
2.7
3.2
5.4
Total controlled losses
1.8
2.2
2.6
-------
FOOTNOTES TO TABLE A-i
a) Based on 1 kg (2.2 lb) total loss in meal. 1 This is the amount of
solvent in the soybean meal as it exits the desolventizer-toaster (DI).
It represents a solvent content of approximately 1300 ppm. Approxi-
mately 30 percent of this is lost in the dryer and approximately
30 percent of the remainder is lost in the cooler.
b) Based on a meal content of 450 kg/Mg (900 lb/ton) of clean raw
cottonseed. Meal exiting the DT has same solvent concentrations
as soybean meal. See Footnote (a).
c) Based on 0.1 solvent content and 163 kg(360 lb) soybean oil per
0.91 Mg (1 ton) of clean, raw seed and 145 kg (320 lb) cottonseed
oil per 0.91 Mg (1 ton) of clean, raw seed.
d) See Footnote (c). Oil from a prepress plant contains an average
of only 0.05 percent solvent since only half the oil is extracted
using solvent.
e) This assumes a direct function of solvent input to extractor.
Approximately 2.7 kg (6 lb) solvent is required per kg (ib) of oil
in the extractor feed cake. Thus, soybean plants and full solvent
cottonseed plants require approximately 910 kg (200 ib) solvent
per 0.91 Mg (1 ton) of clean, raw seed, and a prepress plant
requires about half that amount.
f) This is directly proportional to the volume of air introduced into
the system which, in turn, is approximately proportional to the
weight of the feed to the extractor. It is estimated that 1.8 Nm
(65 scf) is i ntroduced per 0.91 Mg (1 ton) of soybean flakes and
another I Nm (35 scf) is introduced as a result of equipment leaks.
Using this same ratio, approximately 1.7 Nm 3 (60 scf) air per 0.91 Mg
(1 ton) of white seed is introduced into a cottonseed full-solvent
air extraction process. The gases leaving the main vent condenser
are approximately 38 C (100°F) and saturated with hexane. Thus the
stream is approximately 35 percent (volume) hexane. This is
approximately 1.5 m” (55 ft ). In summary, solvent loss is assumed
to be directly proportional to the weight of the extractor feed cake.
A- 3
-------
g) Proportional to solvent usage. Estimated loss for s ybean oil
plants is 0.1 kg/Mg (0.2 lb/ton) of beans processed.’ Solvent
usage is approximately 3 kg/Mg (6 ib/ib) of oil in the extractor
feed cake.
h) Generally not proportional to plant size. It is dependent on leaks
from valve packings, pump seals, gaskets and the like. Estimated
fugitive losses from 910 Mg/day (1000 tons/day) of soybean plants
are 0.33 kg/MFC (0.66 lb/TFC), and smaller plants have a higher loss
rate. 3 Cottonseed, corn, and peanut plants are smaller than soybean
plants, and fugitive losses are estimated at 100 percent higher
per kg (Ib) of oil which is solvent extracted.
i) Estimated at 0.16 kg/MFC (0.33 lb/TFC) for 910 Mg/day (1000 tons/day)
of soybean plants. 4 Smaller plants such as cottonseed oil mills
assumed to have a loss double that rate.
j) Based on information given in published papers 5,6, the average
efficiency of mineral oil adsorbers on the main vent is approximately
90 percent.
A-4
-------
REFERENCES
1. George Anderson. 5 Point Process Efficiency. Crown Iron
Works Company, Minneapolis, Minnesota, 1976.
2. Ibid.
3. Ibid.
4. Ibid.
5. Ibid.
6. Robert D. Good, Dravo Corporation. Maximum Solvent Recovery
Creates Safety and Profit. Presented to the American Oil Chemists Society,
Chicago, Illinois, 1967. pp. 1—17.
A-. 5
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing,)
1. REPORT NO. 2.
EPA-450/2-78—035
3. RECIPIENT’S ACCESSION NO.
4. TITLE AND SUBTITLE
Control of Volatile Organic Emissions From Manufacture
of Vegetable Oils
5. REPORT DATE
June 1978
6. PERFORMING ORGANIZATION CODE
7.AUTHOR(S) Donald Henz, Donald Louden, and Fred Hall of
PEDCo Environmental, Inc.
K rri_C._Rrntlwrc_Rnd_Frank_Bunyard_of_EPA
9. PERFORMING ORGANIZATION NAME AND ADDR SS
8.PERFORMINGORGANIZATIONREPORTNO.
OAQPS No. 1.2-110
10. PROGRAM ELEMENT NO.
PEDCo Environmental, Inc.
11499 Chester Road
Cincinnati, Ohio 45246
11.CONTRACT/GRANTNO.
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Research Triangle Park, N.C. 27711
13. TYPE OF REPORT AN’D PERIOD COVERED
14.SPONSORINGAGENCVCODE
.
15. SUPPLEMENTARY NOTES
lb. AbSTMACT
This report provides the necessary guidance for development of regulations
limiting emissions of volatile organic compounds (VOC) from the manufacture of
vegetable oil. Only soybean, cottonseed, corn, and peanut oil manufacturing
facilities are addressed in this document.
Reasonably available control technology (RACT) is defined in this document
and cost analysis for RACT is included for evaluating the cost effectiveness of
controlling vegetable oil plants.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
C. COSATI Field/Group
Air Pollution
Regulatory Guidance
Vegetable Oil Plants
Air Pollution Control
Stationary Sources
VOC Emissions
.
18. DISTRIBUTION STATEMENT
.
Unlimited
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
84
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220—1 (Rev. 4—77) PREvIOUS EDITION IS OBSOLETE
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