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### VOLATILE ORGANIC COMPOUND EMISSION CONTROLS FOR PETROLEUM REFINERY SECONDARYWASTEWATER SEPARATORS

by 

### PEDCo Environmental, Inc. 1006 N. Bowen Road Arlington, Texas 76012

Contract No. 68-02-3512 TaskOrder No. 43

ProjectOfficer Eileen Glen

U.S. ENVIRONMENTAL PROTECTION AGENCY REGION III PHILADELPHIA, PENNSYLVANIA 19106

December 1983 ·**'.~:** 

### 903R83013

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Summary
1. Introduction
1.1 Source Description and Types ofVOC Emissions 

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4. 

### Emission Control Techniques
Cost Analysis
3.1 Model plants 3.2 Assumptions 3.3 Costs 3.4 Cost-effectiveness Regulatory Analysis
References

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# I SUMMARY

Apetroleum refinerywastewater separator removes and recovers hydrocarbons from refinerywastewater. In a primary separator, this is effected through densitydifferences. Sometimes a second stage of treatment, or secondary separator, is required to comply with air and water regulations. A separator is considered 11secondary11 when all enteringwastewater streams have receivedpriortreatment that has removed at least 90 percent of the hydrocarbons. Covering the separator is the most practical control method for both primary and secondary separators. According to AP-42, coveringprimary separators can reduce emissions by an estimated 95 percent. Estimates also indicate that covering secondary covers will reduce VOC Emissions by 90 percent. Process modifications and improved process control also can reduce VOC emissions by reducing the quantity of hydrocarbons enteringthe plantwastewater stream. The estimated control cost of retrofitting a cover onto a secondary wastewater separator is $225 per ton ofVOC controlledwith hydrocarbon recoverycredits. Because very few refineries have secondary separators there is limiteddataon control costs, emission reductions, and hydrocarbon credits. Therefore, no VOC emission controls for secondarywastewater separators at petroleum refineries are presented.

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# I 1. INTRODUCTION

Over the past several years, the Office of Air Quality Planning and Standards (OAQPS) of the Environmental ProtectionAgency (EPA), has developed

a series of Control Techniques Guidelines (CTGs) for volatile organic compounds (VOCs) to assist state and local agencies in developing regulations for VOC control. Although, the CTGs covermajor 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. Airpollution control agencies in the PhiladelphiaAir Quality Control Region (AQCR) have requested guidance in determiningwhether VOC controls are available for non-CTG sources and information for use in developing appropriate regulations. Secondarywastewater separators at petroleum refineries comprise one such VOC source category.

1.1 SOURCE DESCRIPTION AND TYPES OF VOC EMISSIONS
Apetroleum refinerywastewater separator is a device that separates organicmaterial hydrocarbons from refinerywastewater. The two kinds of wastewater separators used are corrugatedplate interceptors (CPis) and American Petroleum Institute (API) separators. The smaller CPI, which is controlledby a fixed-roof cover, is effective for initial oil-water separation. The API separator has a floating-roof cover. Contaminatedwastewater originates from several sources in petroleum refineries, including leaks, spills, the cooling and flushing ofpump 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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# I remains suspended in the water. Chemicals (e.g., ferric chloride) are frequently added towastewater streams to achieve better separation ofwater and hydrocarbons. Primarywastewater separation is oftenthe only treatment required at a refinery. Separation is effectedthrough differences in the densities of water and hydrocarbons. The oil that coalesces and floats on the surface of thewater and the sludge that settles to the bottom of the separator are removed. Because the recovered hydrocarbons are pr9cessed in the refinery, primarywastewater separation is economically advantageous. 1 Floating hydrocarbons inwastewater streams have a high surface-to-volume ratio that enhances evaporation and VOC emissions. According to AP-42, uncontrolled emission factors for primary oil/water separators are 5 lb/103 gallon (0.6 kg/103 liter) ofwastewater or 200**lb/10~** 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 primarywastewater separators, which would be 0.5 lb/103 gallon (0.06 kg/103 liter) ofwastewaterprocessed or 20 lb/103 bbl of refinery feed (0.06 kg/103 1iter).1 Because no definition currentlyexists for secondary separators, for the draft regulations separators will be defined as being 11secondary11 when all entering streams have receivedprior gravity separation orequivalenttreatment that has removed at least 90 percentof the hydrocarbons. If any stream enteringthe separator has not received this priortreatment, the separator shouldbe considered a primary separator. According toAP-42 estimates, a coveredprimary separatorgives 95 percentcontrol. 2 Arefinery having an API separatorwith 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 percentof the oil entering the separator in the first bay. Otherwise, the whole unit should be considered a primarywastewater separator. Apublished 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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# I 2. EMISSION CONTROL TECHNIQUES

Primarywastewater separators can achieve reasonable control of VOC emissions ifthe separator is covered to minimize the amount of oilywater exposed to the atmosphere. The covermay 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) ofwastewater 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 primarywastewater separators. 3 Additional control may be obtainedby reducing the quantity of hydrocarbons thatenter theplantwastewatertreatment facility. Such reductionmay be possible through improved process control ormodifications that reduce the number of leaks, spills, and other upsets. Astringent fugitive leakemission 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 controlledVOC emission rate for secondarywastewater separators

was found, it is estimated that the controlledVOC emission rate will be 10 percent of the uncontrolled rate for secondary separators, or 0.05 lb/103 gallon (0.006 kg/103 liter) ofwastewaterprocessed. Although AP-42 indicates that95 percent control is achievable for primary separators,2 only 90 percent control is achieved inmost secondary separators because the more volatile, easily separated and recoverable hydrocarbons have already been removed.

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# I I I 3. COST ANALYSIS

This section defines the model plant, explains the assumptions made, and presents a costanalysis for control ofVOC from secondary separators at refineries. Cost-effectiveness is expressed in terms of the annual control
cost in dollars divided by the annual tons ofVOC controlled.

3.1 MODEL PLANTS
Petroleum refineries vary considerably in size, design, age, feedstocks, and productmixes. This report presents an evaluation of retrofit controls to

an existing secondarywastewater separator. Because most retrofits have enough unique characteristics to make each one a special case, attempting to

coverevery situationwith a model plantwould be impractical. Therefore, this report considers a single case of retrofitting a cover onto a secondary wastewater separator at on oil refinerywith a capacity of 150,000 barrel/day (23.8million 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. A1977 EPA report discusses costs for primarywastewater separator

covers.4 Costs, which are expressed as apercentage of total capital costs,
are: Capital recovery factor (10-year life and 10% interestrate) Property taxes, insurance, and administrative costs Operating and maintenance costs 16.27

4.00
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Since the equipment for coveringprimary and secondary separators is identical, the same cost factors were used for the latter.

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# I Recovered hydrocarbon credits are based on a price of $23.70/barrel and a density of8 lb/gallon. The 1977**~PA** report used a value equivalentto that of light crude oil (about $32 perbarrel).4 Because the.lighter, more valuable, and more easily recovered hydrocarbons have already been recovered in the primary separator, however, it is assumed that the material recovered in a secondary separatorwould be heavier orwould have to be recovered from water emulsions. This would make itmore difficultto process and therefore less valuable than thematerial recovered from the primary separator. The hydrocarbons recovered from a secondary separator are assumed to have a value approximately equivalentto that ofNo. 6 fuel oil ($23.70 perbarrel). 5

3.3 COSTS
The total capital cost for covering an existing secondarywastewater 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 refineryproducing 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-specificbasis. For example, the cost for covering an API separator at a refinery producing 380,000 barrels/daywas $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 refineryproducing 380,000 barrels/daywas $36.37 per ft2 (personal communication from B. Roney, PetrexCompany, 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 aprimary separator 90 percent control in the secondary separator, 330 days of operationperyear, and a value of $23.70perbarrel for the recovered hydrocarbons. Table 1 shows capital and annual costs for retrofitting a cover on a secondarywastewater separator. These represent typical costs; actual costs will vary on a site-specificbasis. Estimated net annual costs are $50,300 with hydrocarbon recovery credits.

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# I I 3.4 COST-EFFECTIVENESS
Based on net annual costs of $50,300 to control 223 tons of VOC emissions

or$225 per ton ofVOC emissions controlled, covering a secondarywastewater separatormay be considered cost-effective from a control agency point of view, as these costs are comparable toVOC control for other source categories (e.g., pneumatic rubber tires).

TABLE 1. CONTROL SYSTEM COSTS FOR

SECONDARY WASTEWATER SEPARATORSa (September 1982 dollars)

Annual capital recovery factor**(~0** year

life, 10 percent interest rate) Taxes, insurance, andbadministrative

costs (fourpercent) Operating andbmaintenance costs

(10 percent)
Total annual cost Credit for recovered hydrocarbons
Net annual cost
Tons ofVOC controlled Cost per ton ofVOC controlled $43,900 10,800 27,000 81,700 31,400 $50,300
223 $225
aCapital costs including installation are $270,000. bReference 4.

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# I 4. REGULATORY ANALYSIS

In this report, awastewater separator is defined as "secondary" when all entering streams have received prior gravity separation or equivalent treatment that has removed at least90 percent of the VOC. If any streamentering the separator has not receivedprior treatment, the separator is considered a primary separator and subject to all applicable regulations for primary separators. Regulation of secondarywastewater separators is not feasible. Although

a costof $225 per ton ofVOC controlled is often considered acceptable, the number of refineries with covered secondary separators is not large enough to support regulation of secondarywastewater separators. Estimates ofVOC emissions from secondary separators are based on AP-42 emission factors for primary separators2 and an API estimate thatemissions from secondary separators would be about 10 percent of that from primary separatori.1 In AP-42, the reliability ofemission factors is valued on a scale ofAto Eand 1to 40 points. The emission factors for primarywastewater separators received a rating of D(below average) and a numerical rating ofbetween 6and 15 points. Aprobable 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 secondarywastewater separators are only estimates. Because the cost of covering a secondary separator is sitespecific,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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# I REFERENCES

1. American Petroleum Institute. Hydrocarbon Emissions from Refineries. Publication No. 928, July 1973.
2. U.S. Environmental ProtectionAgency. Compilation ofAir Pollution Emission Factors. 3rd Ed., including Supplements 1-12. Section 9.1. AP-42, April 1, 1981.
3. U.S. Environmental ProtectionAgency. Assessment ofAtmospheric Emissions from Petroleum Refining. Vol. I. 

### EPA-600/2-80-075A, April 1980.
4. U.S. Environmental ProtectionAgency. Control of Refinery 

### Vacuum Producing Systems, Wastewater Separators and Process UnitTurnarounds. EPA 450/2-77-025 (OAQPS No. 1.2-081), October 1977.
5. Value of Residual Oil Relative to That of Crude Oil. Hydrocarbon Processing, October 1982. p. 21.

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