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VOLATILE ORGANIC COMPOUND EMISSION
CONTROLS FOR PETROLEUM REFINERY
SECONDARY WASTEWATER SEPARATORS
by
PEDCo Environmental, Inc.
1006 N. Bowen Road
Arlington, Texas 76012
Contract No. 68-02-3512
Task Order No. 43
Project Officer
Eileen Glen
U.S. ENVIRONMENTAL PROTECTION AGENCY
REGION III
PHILADELPHIA, PENNSYLVANIA 19106
December 1983
903R83013
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CONTENTS
Page
Summary iv
1. Introduction 1
1.1 Source Description and Types of VOC Emissions 1
2. Emission Control Techniques 3
3. Cost Analysis 4
3.1 Model plants 4
3.2 Assumptions 4
3.3 Costs 5
3.4 Cost-effectiveness 6
4. Regulatory Analysis 7
References 8
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SUMMARY
A petroleum refinery wastewater separator removes and recovers hydrocar-
bons from refinery wastewater. In a primary separator, this is effected
through density differences. Sometimes a second stage of treatment, or sec-
ondary separator, is required to comply with air and water regulations. A
separator is considered "secondary" when all entering wastewater streams have
received prior treatment that has removed at least 90 percent of the hydro-
carbons.
Covering the separator is the most practical control method for both
primary and secondary separators. According to AP-42, covering primary separ-
ators can reduce emissions by an estimated 95 percent. Estimates also indi-
cate that covering secondary covers will reduce VOC Emissions by 90 percent.
Process modifications and improved process control also can reduce VOC emis-
sions by reducing the quantity of hydrocarbons entering the plant wastewater
stream.
The estimated control cost of retrofitting a cover onto a secondary
wastewater separator is $225 per ton of VOC controlled with hydrocarbon recov-
ery credits. Because very few refineries have secondary separators there is
limited data on control costs, emission reductions, and hydrocarbon credits.
Therefore, no VOC emission controls for secondary wastewater separators at
petroleum refineries are presented.
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1. INTRODUCTION
Over the past several years, the Office of Air Quality Planning and
Standards (OAQPS) of the Environmental Protection Agency (EPA), has developed
a series of Control Techniques Guidelines (CTGs) for volatile organic com-
pounds (VOCs) to assist state and local agencies in developing regulations for
VOC control. Although, the CTGs cover major VOC source categories from an
overall nationwide perspective, several source categories that are not covered
by CTG documents are major contributors to the ozone problem within given
areas.
Air pollution control agencies in the Philadelphia Air Quality Control
Region (AQCR) have requested guidance in determining whether VOC controls are
available for non-CTG sources and information for use in developing appropri-
ate regulations. Secondary wastewater separators at petroleum refineries
comprise one such VOC source category.
1.1 SOURCE DESCRIPTION AND TYPES OF VOC EMISSIONS
A petroleum refinery wastewater separator is a device that separates
organic material hydrocarbons from refinery wastewater. The two kinds of
wastewater separators used are corrugated plate interceptors (CPIs) and Ameri-
can Petroleum Institute (API) separators. The smaller CPI, which is control-
led by a fixed-roof cover, is effective for initial oil-water separation. The
API separator has a floating-roof cover.
Contaminated wastewater originates from several sources in petroleum
refineries, including leaks, spills, the cooling and flushing of pump and
compressor seals sampling, equipment cleaning, and rain runoff. Although some
organic contaminants that are immiscible with water can be separated rather
easily, other organic constituents may dissolve or form an emulsion that
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remains suspended in the water. Chemicals (e.g., ferric chloride) are fre-
quently added to wastewater streams to achieve better separation of water and
hydrocarbons.
Primary wastewater separation is often the only treatment required at a
refinery. Separation is effected through differences in the densities of
water and hydrocarbons. The oil that coalesces and floats on the surface of
the water and the sludge that settles to the bottom of the separator are
removed. Because the recovered hydrocarbons are processed in the refinery,
primary wastewater separation is economically advantageous.1
Floating hydrocarbons in wastewater streams have a high surface-to-volume
ratio that enhances evaporation and VOC emissions. According to AP-42, uncon-
trolled emission factors for primary oil/water separators are 5 lb/103 gallon
(0.6 kg/103 liter) of wastewater or 200 lb/103 bbl (0.6 kg/103 liter) of
refinery feed.2
The April 1, 1981, AP-42 does not give an emission factor for secondary
wastewater separators.2 An American Petroleum Institute publication estimates
potential uncontrolled VOC emissions to be about 10 percent of that sustained
in primary wastewater separators, which would be 0.5 lb/103 gallon (0.06
kg/103 liter) of wastewater processed or 20 lb/103 bbl of refinery feed (0.06
kg/103 liter).1
Because no definition currently exists for secondary separators, for the
draft regulations separators will be defined as being "secondary" when all
entering streams have received prior gravity separation or equivalent treat-
ment that has removed at least 90 percent of the hydrocarbons. If any stream
entering the separator has not received this prior treatment, the separator
should be considered a primary separator. According to AP-42 estimates, a
covered primary separator gives 95 percent control.2
A refinery having an API separator with multiple bays in series may
define the first bay as a primary separator, the second bay as a secondary
separator, etc. This is appropriate only if the first bay is sized to recover
at least 90 percent of the oil entering the separator in the first bay.
Otherwise, the whole unit should be considered a primary wastewater separator.
A published estimate of the oil recovery from a primary separator at a 100,000
bbl/day refinery is 4,200 to 21,000 gallons/day (15,900 to 79,500 liters per
day).1
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2. EMISSION CONTROL TECHNIQUES
Primary wastewater separators can achieve reasonable control of VOC
emissions if the separator is covered to minimize the amount of oily water ex-
posed to the atmosphere. The cover may be either a sealed solid cover or one
that floats on the liquid. According to AP-42, covered separators and/or
vapor recovery systems achieve 95 percent control and reduce VOC emission
rates to 0.2 lb/103 gallon (0.024 kg/103 liter) of wastewater or 10 lb/103 bbl
(0.03 kg/103 liter) of refinery feed.2 At least 80 percent of the petroleum
refineries currently cover their primary wastewater separators.3
Additional control may be obtained by reducing the quantity of hydrocar-
bons that enter the plant wastewater treatment facility. Such reduction may
be possible through improved process control or modifications that reduce the
number of leaks, spills, and other upsets. A stringent fugitive leak emission
control program can result in up to a 50 percent reduction of VOCs. Adding a
CPI to the wastewater system can result in reductions of up to 90 percent in
VOC emissions.
Covering the secondary separator is the most practical control method.
Although no controlled VOC emission rate for secondary wastewater separators
was found, it is estimated that the controlled VOC emission rate will be 10
percent of the uncontrolled rate for secondary separators, or 0.05 lb/103
gallon (0.006 kg/103 liter) of wastewater processed. Although AP-42 indicates
that 95 percent control is achievable for primary separators,2 only 90 percent
control is achieved in most secondary separators because the more volatile,
easily separated and recoverable hydrocarbons have already been removed.
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3. COST ANALYSIS
This section defines the model plant, explains the assumptions made, and
presents a cost analysis for control of VOC from secondary separators at
refineries. Cost-effectiveness is expressed in terms of the annual control
cost in dollars divided by the annual tons of VOC controlled.
3.1 MODEL PLANTS
Petroleum refineries vary considerably in size, design, age, feedstocks,
and product mixes. This report presents an evaluation of retrofit controls to
an existing secondary wastewater separator. Because most retrofits have
enough unique characteristics to make each one a special case, attempting to
cover every situation with a model plant would be impractical. Therefore,
this report considers a single case of retrofitting a cover onto a secondary
wastewater separator at on oil refinery with a capacity of 150,000 barrel/day
(23.8 million liters/day).
3.2 ASSUMPTIONS
The annual costs for all control options include a capital recovery
charge and an allowance for property taxes, insurance, and adminstrative
costs. A 1977 EPA report discusses costs for primary wastewater separator
covers.4 Costs, which are expressed as a percentage of total capital costs,
are:
Capital recovery factor (10-year life and 10% 16.27
interest rate)
Property taxes, insurance, and administrative costs 4.00
Operating and maintenance costs 10.00
Since the equipment for covering primary and secondary separators is identi-
cal, the same cost factors were used for the latter.
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Recovered hydrocarbon credits are based on a price of $23.70/barrel and a
density of 8 Ib/gallon. The 1977 EPA report used a value equivalent to that
of light crude oil (about $32 per barrel).4 Because the.lighter, more valu-
able, and more easily recovered hydrocarbons have already been recovered in
the primary separator, however, it is assumed that the material recovered in a
secondary separator would be heavier or would have to be recovered from water
emulsions. This would make it more difficult to process and therefore less
valuable than the material recovered from the primary separator. The hydro-
carbons recovered from a secondary separator are assumed to have a value
approximately equivalent to that of No. 6 fuel oil ($23.70 per barrel).5
3.3 COSTS
The total capital cost for covering an existing secondary wastewater
separator at a refinery producing 150,000 barrels/day is estimated to be
$270,000. This is based on the average cost for installing covers on three
API separators in 1982 at a refinery producing 430,000 barrels/day (personal
communication from C. V. Rice, Amoco Oil Company, February 15, 1983). Costs
could be higher, however, when evaluated on a site-specific basis. For exam-
ple, the cost for covering an API separator at a refinery producing 380,000
barrels/day was $2 million. Installed costs were estimated to be $75 per
square foot up to 1000 square feet of covered surface and $35 per square foot
for up to 12,000 square feet. The cost of installing a 55,000-ft2 cover at a
refinery producing 380,000 barrels/day was $36.37 per ft2 (personal communica-
tion from B. Roney, Petrex Company, February 16, 1983).
Annual credits for recovered hydrocarbons are estimated to be $31,400.
This is based on the AP-42 controlled emission factor of 10 pounds per 1000
barrels of feed for a primary separator 90 percent control in the secondary
separator, 330 days of operation per year, and a value of $23.70 per barrel
for the recovered hydrocarbons.
Table 1 shows capital and annual costs for retrofitting a cover on a
secondary wastewater separator. These represent typical costs; actual costs
will vary on a site-specific basis. Estimated net annual costs are $50,300
with hydrocarbon recovery credits.
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3.4 COST-EFFECTIVENESS
Based on net annual costs of $50,300 to control 223 tons of VOC emissions
or $225 per ton of VOC emissions controlled, covering a secondary wastewater
separator may be considered cost-effective from a control agency point of
view, as these costs are comparable to VOC control for other source categories
(e.g., pneumatic rubber tires).
TABLE 1. CONTROL SYSTEM COSTS FOR
SECONDARY WASTEWATER SEPARATORS
(September 1982 dollars)
Annual capital recovery factor (10 year
life, 10 percent interest rate)
Taxes, insurance, and, administrative
costs (four percent)
Operating and, maintenance costs
(10 percent)
Total annual cost
Credit for recovered hydrocarbons
Net annual cost
Tons of VOC controlled 223
Cost per ton of VOC controlled $225
8Capital costs including installation are $270,000.
Reference 4.
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4. REGULATORY ANALYSIS
In this report, a wastewater separator is defined as "secondary" when all
entering streams have received prior gravity separation or equivalent treat-
ment that has removed at least 90 percent of the VOC. If any stream entering
the separator has not received prior treatment, the separator is considered a
primary separator and subject to all applicable regulations for primary separ-
ators.
Regulation of secondary wastewater separators is not feasible. Although
a cost of $225 per ton of VOC controlled is often considered acceptable, the
number of refineries with covered secondary separators is not large enough to
support regulation of secondary wastewater separators.
Estimates of VOC emissions from secondary separators are based on AP-42
emission factors for primary separators2 and an API estimate that emissions
from secondary separators would be about 10 percent of that from primary
separators.1 In AP-42, the reliability of emission factors is valued on a
scale of A to E and 1 to 40 points. The emission factors for primary waste-
water separators received a rating of D (below average) and a numerical rating
of between 6 and 15 points. A probable range of these emission factors was
not estimated. Up to 20 points could have been awarded for measured emission
data, up to 10 points for process data, and up to 10 points for engineering
analyses. Hence, VOC emission rates from secondary wastewater separators are
only estimates. Because the cost of covering a secondary separator is site-
specific,1'4 both the costs and benefits of this VOC emission control are
doubtful. If field testing confirms the control costs, emission reductions,
and recovered hydrocarbon credits, a regulation might be feasible.
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REFERENCES
1. American Petroleum Institute. Hydrocarbon Emissions from Refineries.
Publication No. 928, July 1973.
2. U.S. Environmental Protection Agency. Compilation of Air Pollution
Emission Factors. 3rd Ed., including Supplements 1-12. Section 9.1.
AP-42, April 1, 1981.
3. U.S. Environmental Protection Agency. Assessment of Atmospheric Emis-
sions from Petroleum Refining. Vol. I. EPA-600/2-80-075A, April 1980.
4. U.S. Environmental Protection Agency. Control of Refinery Vacuum Produc-
ing Systems, Wastewater Separators and Process Unit Turnarounds. EPA
450/2-77-025 (OAQPS No. 1.2-081), October 1977.
5. Value of Residual Oil Relative to That of Crude Oil. Hydrocarbon Proces-
sing, October 1982. p. 21.
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