United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park NC 27711
EPA-450/3-86-002
January 1986
Air
&EPA
Emission Factors
For Equipment Leaks
Of VOC And HAP
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EPA-450/3-86-002
Emission Factors for Equipment Leaks
of VOC and HAP
Prepared by:
Radian Corporation
3200 E. Chapel Hill Road/Nelson Highway
Research Triangle Park, NC 27709
Under EPA Contract
No. 68-02-3889
*"«*
230 South Dearborn Street
Chicago, Illinois
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Radiation
Office of Air Quality Planning and Standards
Emission Standards and Engineering Division
Research Triangle Park, North Carolina 27711
January 1986
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DISCLAIMER
This report has been reviewed by the Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, and approved for publication as received from the Radian Corporation. Approval does
not signify that the content necessarily reflect the views and policies of the U.S. Environmental Protection
Agency, nor does mention of trade names or commercial products constitute endorsement or recommenda-
tion for use. Copies of this report are available from the National Technical Information Services, 5285 Port
Royal Road, Springfield, Virginia 22161.
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TABLE OF CONTENTS
Page
LIST OF TABLES y
LIST OF FIGURES v1
Section 1.0 - OVERVIEW l_l
Section 2.0 - FUGITIVE EMISSION SOURCES 2-l
2.1 VALVES 2_3
2.2 PUMPS 0 ,
£-0
2.3 COMPRESSORS 2_10
2.4 RELIEF DEVICES 2_n
2.5 OPEN-ENDED VALVES AND LINES 2-15
2.6 SAMPLING SYSTEMS 2_15
2.7 FLANGES AND OTHER CONNECTORS 2-17
Section 3.0 - EMISSION FACTORS 3.!
3.1 STUDIES CONSIDERED IN SOCMI EMISSION FACTOR DEVELOPMENT 3-1
3.1.1 Petroleum Refining Assessment Study. ? 9
3.1.2 Four Unit EPA Study ," =
3.1.3 EPA 6-Unit Study ,"?
3.1.4 DuPont Study .'.'.' 35
3.1.5 Exxon Cyclohexane Study. . *%
3.1.6 EPA 24-Unit Study ! ! ! ! 35
3.1.7 Maintenance Study ' 3 6
3.1.8 Analysis Report and Revision
of SOCMI Emission Factors 3.7
3.1.9 German Studies on Fugitive Emissions ! 37
3.1.10 Union Carbide Study 3 «
3.1.11 Analysis of Allied HOPE Unit Data.' 7 q
3.1.12 SCAQMD Study , [ ?'|
3.1.13 Coke Oven By-product Recovery and
Gas Plant Studies 3_10
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TABLE OF CONTENTS (CONTINUED)
Page
3.2 ERA'S CHOICE OF DATA FOR SOCMI EMISSION FACTORS 3-10
3.3 EMISSION FACTOR DEVELOPMENT 3.12
3.3.1 Detailed Procedural Method '.'.'.'. 3-12
3.3.2 Statistical Considerations 3-14
3.3.3 Leak/No-Leak Approach . . . 3-17
3.3.3.1 Generation of Leaking and
Nonleaking Emission Factors 3-19
3.3.3.2 Computation of Average Emission Factors. 3-20
3.4 EMISSION FACTORS PRESENTED IN THE AID 3-22
3.5 EXAMPLE HYPOTHETICAL CASE 3.27
Section 4.0 - EMISSION REDUCTION 4_!
4.1 OVERVIEW OF TECHNIQUES 4_j
4.2 LEAK DETECTION AND REPAIR (LDAR) 4.2
4.3 SUMMARY OF EMISSION REDUCTIONS 4.7
Section 5.0 - LIST OF REFERENCES 5_!
IV
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LIST OF TABLES
Table Page
3-1 FUGITIVE EMISSION STUDIES IN THE AID 3.3
3-2 LEAK FREQUENCIES AND EMISSION FACTORS:
REFINING ASSESSMENT STUDY 3.4
3-3 LEAKING AND NONLEAKING EMISSION FACTORS FOR
FUGITIVE EMISSIONS (kg/hr/source) 3-21
3-4 AVERAGE EMISSION FACTORS FOR FUGITIVE EMISSIONS
IN SOCMI 3.23
3-5 LEAK FREQUENCIES BY PROCESS FOR EQUIPMENT
IN 24 SOCMI UNITS 3.28
3-6 ESTIMATE OF "UNCONTROLLED" FUGITIVE EMISSIONS FOR
A HYPOTHETICAL CASE 3_2g
4-1 LDAR INPUTS AND COMPUTED REDUCTIONS FOR
SOCMI/MONTHLY MONITORING 4.4
4-2 LDAR MODEL RESULTS FOR SOCMI VALVES AND PUMPS 4.5
4-3 CONTROL LEVELS FOR SOCMI FUGITIVE EMISSIONS:
NSPS AND CTG 4.8
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LIST OF FIGURES
Figure Page
2-1 Estimated Emissions by Source Subcategories of SOCMI . . 2-2
2-2 Diagram of a Gate Valve 2-5
2-3 Diagrams of Valves with Diaphragm Seals 2-7
2-4 Diagram of a Double Mechanical Seal
(a) Back-to-back Arrangement 2-9
(b) Tandem Arrangement 2-9
2-5 Simple Single-stage Reciprocating Compressor 2-12
2-6 Pressure Relief Valve in a Basic RD/PRV Combination. . . 2-13
2-7 Schematics of Closed Purge Sampling Systems 2-16
3-1 Cumulative Distribution: Cumene Gas Valves 3-13
3-2 Cumulative Mass Emissions Distribution:
Cumene Gas Valves 3-15
3-3 Cumulative Distribution of Total Emissions by Screening
Values - Comparison of Confidence Intervals .... 3-18
3-4 Comparison of Emission Factors: Gas Valves 3-25
3-5 Comparison of Emission Factors: Light Liquid Valves
and Pumps 3-26
4-1 Schematic Diagram of the LDAR Model 4-3
vl
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GLOSSARY
Average emission factor - the per component mass emission rate applicable to
populations of sources, not individual component measurements.
Leak definition - the monitoring instrument reading selected as the trigger
value for initiating some action such as maintenance; e.g., 10,000 DDRIV
is the leak definition used by EPA.
Leak frequency - the percentage of sources (a particular equipment type and
service) determined to be leaking based upon a chosen leak definition.
Leak rate - see mass emissions rate.
Leaking emission factor - the per component mass emission rate associated with
the population of sources with screening values at or above the leak
definition.
Mass emissions rate - the quantity of volatile organic compound(s) released to
the atmosphere in terms of total mass per unit time.
Monitoring instrument - portable hydrocarbon analyzer meeting the performance
specifications given in Method 21.
Non-leaking emission factor - the per component mass emission rate associated
with the population of sources with screening values less than the leak
definition.
Screening value - monitoring instrument reading generally given in
concentration units; e.g., ppmv.
vn
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1.0 OVERVIEW
One of the first major efforts in the field of fugitive hydrocarbon
emissions was the Joint Refinery Study initiated by the Los Angeles County
APCD, the California State Department of Public Health, and the U. S. Public
Health Service in August 1955. Additional studies were made subsequent to
this original work. But it was not until the mid- to late-1970's that a
renewed interest was sparked by two events.
The Clean Air Act, originally passed in 1970, laid out the groundwork for
the U. S. Environmental Protection Agency (EPA) to set standards of
performance for newly constructed, modified, or reconstructed sources of air
pollution which may endanger the public health or welfare. Since these New
Source Performance Standards (NSPS) were to be promulgated for a large number
of industries or industry segments, a ranking was developed in accordance with
the 1977 amendments so that those industries with the highest potential for
impacting public health would be examined first. The Synthetic Organic
Chemical Manufacturing Industry (SOCMI) was placed first on the Priority List
of industry categories as the single most significant contributor to air
pollution.
Around this same time, an extensive study of atmospheric emissions from
petroleum refining was conducted. The study was initiated to evaluate
existing and developing refining emissions control technologies and to assess
the potential impact of atmospheric emissions from refining on the surrounding
environment. As the program began, fugitive emissions (i.e., emissions from
various types of equipment such as valves, pumps, compressors, pressure relief
devices, and connectors) were found to be a large (if not the largest) source
of hydrocarbon emissions from refining. As a result, the scope of the Refining
Study was expanded to include the quantification of fugitive emissions. This
particular objective was given added emphasis as a result of the Clean Air Act
and its emissions offsets regulations, which require emission factors for
evaluating compliance.
Subsequent to the refinery assessment, EPA's research group conducted
additional studies in chemical plants. Twenty-four separate chemical units
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were evaluated. Of these units, six were studied more closely for the effec-
tiveness of emission control techniques. These new data, coupled with a
review of data from other studies, were compiled into an Additional Informa-
tion Document (AID) on fugitive emissions of VOC in SOCMI. The AID details
EPA's conclusions about how to estimate emissions and emissions reductions for
fugitive emissions of VOC.
The concepts behind fugitive emissions and their control are relatively
simple; however, the understanding of fugitive emissions data is quite
complex. Not surprisingly, the estimates of emissions, emission reductions,
and costs still draw the bulk of comments and questions from regulatory
personnel as well as industry representatives. This document addresses the
development of emission factors for fugitive VOC emissions (or equipment leaks
of VOC). The comments and questions most often raised are given below with a
brief response. Detailed responses are contained in the substantial
literature generated by EPA to support the fugitive emission standards.
1. My emissions are already low because of OSHA regulations. Why, then, are
there also environmental emissions standards for equipment leaks?
Environmental emissions standards for equipment leaks have different
purposes from OSHA regulations. Indeed, they may even result in different
environmental benefits. Environmental standards focus on reducing the total
quantity of emissions, in this case VOC emissions, to the atmosphere. On the
other hand, OSHA regulations, unlike environmental standards, do not
necessarily limit mass emissions directly. OSHA regulations permit control of
emission sources by substitution of chemicals with less hazardous materials,
process modifications, worker rotation, process or worker isolation,
ventilation controls, or modification of work practices. Such control
measures are focused on reducing occupational exposure (as a concentration),
not necessarily reducing mass emissions of VOC to the atmosphere.
The idea of workplace concentration reduction is the key to OSHA
regulations. It is often thought that OSHA regulations result in
concentrations in the workplace well below 10,000 ppmv, the concentration
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level used to identify leaking components under the environmental regulations.
An important distinction is that environmental standards call for measurement
of VOC concentration at the leak interface, not in the surrounding area.
Field studies have shown that the concentration of VOC decreases exponentially
with increasing distance from the leak interface. Thus, a leak determined at
the interface will rarely be seen at a distance only 20 cm from the surface
and yet substantial quantities of VOC may be emitted from such a leak.
Dispersion and dilution of the VOC into the surrounding area mask the severity
of emissions from the leak. As a result, while OSHA regulations may well
reduce the concentration of VOC in the workplace, they do not guarantee that
the total mass emissions from leaks are also reduced.
I already control my emissions under the Control Techniques Guideline.
Am I subject to more environmental standards for equipment leaks?
There are several environmental regulatory programs in existence:
National Ambient Air Quality Standards (NAAQS), State Implementation Plans
(SIP's), National Emission Standards for Hazardous Air Pollutants (NESHAP's),
and New Source Performance Standards (NSPS's). All of these types of
regulations work toward meeting the goals of the Clean Air Act.
The control techniques guideline documents (CTG) are presentations of
what is considered by EPA to be "reasonably available control technology"
(RACT). RACT-based environmental regulations are established by States to
correct existing air pollution problems, focusing on existing sources in
particular. The control techniques discussed in the CTG for SOCMI fugitive
emission sources are completely consistent and compatible with standards set
under other environmental programs. The resultant control levels may vary due
to differences in the frequency of monitoring or the use of equipment control
techniques.
RACT-based standards would not be duplicative with standards set under
other environmental programs. NSPS's are applicable only to newly
constructed, modified, or reconstructed facilities. Since they apply to new
facilities, the requirements of NSPS are generally more stringent than those
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of RACT-based standards set for existing facilities. In the case of fugitive
emissions control, for example, NSPS-based standards would require monitoring
of equipment more frequently than required under RACT-based standards.
Similarly, NESHAP's are established for all facilities, new or existing.
Again, the difference between requirements of NESHAP's and RACT-based
standards is basically the degree of stringency. NESHAP's require more
frequent monitoring than RACT-based standards for fugitive emission sources.
Furthermore, NESHAP's often require the use of control equipment where
RACT-based standards may only require work practices such as leak detection
and repairs. Since NESHAP's are applicable to existing sources, as well as
new sources, their more stringent requirements would need to be met, in excess
of RACT-based standards for existing sources.
In terms of emissions estimates, process units complying with the
RACT-based standards presented in the CTG would indeed exhibit lower emissions
than would be presented by the simple use of the SOCMI emission factors. As
shown in Table 4-3 of this document varying degrees of emission reduction are
achievable under the different standards (NSPS, NESHAP, CTG). Emissions from
process units complying with the CTG can be estimated by applying the proper
efficiency to the estimated uncontrolled emissions.
2. Emissions from my process unit are lower than the SOCMI factors indicate.
I control the emissions by looking for leaks, sometimes smelling for
them. Why should my unit be covered by these standards?
The chemical industry is comprised of numerous processes producing a
large number of chemicals. Each process unit may by itself emit a relatively
small amount of VOC; however, the total amount of VOC from the industry is
significant. Therefore, individual processes or units are not exempted.
EPA recognizes the wide variability of leak percentages on a unit process
basis throughout the industry. Of the 24 units surveyed in the 24-unit study,
15 demonstrated overall leak frequencies for valves in gas/vapor and light
liquid services of less than 2 percent. Environmental standards, therefore,
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provide alternatives for units that exhibit low-leak characteristics. For
example, an owner or operator of a process unit may elect to comply with a
performance limit of 2 percent leaking valves. In such a case, the routine
leak detection and repair practices required by the basic rule would not be
followed. Instead, the process unit would be screened (using Reference Method
21) on an annual basis to demonstrate that the unit does indeed demonstrate
the low leak characteristics of less than 2 percent of valves leaking.
EPA selected this value based upon cost and emissions analyses which
showed that monthly leak detection and repair for valves is not a cost
effective control technique for process units exhibiting very low leak
characteristics. These characteristics may result from the nature of the
chemicals processed, tight plant design, or enhanced maintenance.
Fugitive emissions from my process unit are lower than estimated using
SOCMI factors. I have verified the low leak rates by measuring the
concentration and flow rate at the ventilation outlet.
It may well be true that actual fugitive emissions from any given process
unit are lower than the emissions estimated using the average SOCMI emission
factors. The SOCMI factors, however, are applicable to the industry at large,
and should be applied to any individual unit where the leak frequencies for
equipment have not been established by a rigorous application of Reference
Method 21. Concentration and ventilation flowrates give an indication of the
magnitude of fugitive emissions; they would not necessarily provide an
accurate estimate of total VOC fugitive emissions. For process units that
would have ventilation outlets, all potential sources of fugitive emissions
are not generally enclosed in the building. Also, large buildings that house
chemical process units are not generally air tight; therefore, some VOC may
not be accounted for in the ventilation air.
Furthermore, the evaluation of fugitive emissions from an enclosed
building represents a complex measurement problem. All emission points from
the building would need to be measured simultaneously for 3 hours to
constitute an emissions test. This is the only way to ensure that all
emissions from non-vented sources would be accounted for. Since fan curves
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are inaccurate for emissions measurements, EPA flow measurement methods would
need to be employed. These methods require obstruction-free ducting on either
side of the fan, a situation not always found in ventilation applications.
Finally, when applied to the estimation of hazardous air pollutants, the
analytical techniques used must be capable of speciation of organic
constituents. Common detectors are not always adequate for this task.
Concentration and ventilation flow rate could indicate that emissions are
lower than estimated by SOCMI factors. This technique, however, would not be
sufficient to prove that emissions are low. There is an acceptable
alternative to estimating emissions. Conducting a rigorous Method 21 survey
would lead to computing percent leaking values (leak frequency) for all
equipment types. These values could then be used to construct unit-specific
overall emission factors using "leaking" and "nonleaking" emission factors as
described in Section 3.3.3. Using such a procedure would develop emission
factors consistent with the vast amount of fugitive VOC emissions data
gathered to date. The unit-specific emission factors, applied to the
equipment counts for the process unit, lead to the overall estimate of VOC
emissions. As noted in this document, pre-survey maintenance would invalidate
the results of the survey and estimates.
3. It is not appropriate to use petroleum refinery test data to determine
SOCMI emission factors.
The development of VOC emission factors for equipment leaks is founded on
the concept that equipment leaks VOC at the same rate regardless of the
industry or process unit. Total emissions or average emission rates may vary,
however, based upon the relative percentage of leaks found in different
process units. In developing VOC emission factors for equipment leaks in
SOCMI, EPA examined and considered every study available. This evaluation,
explained in the AID, makes it clear that the data contained in the
Maintenance Study and 24-Unit Study are not the sole source of data on
fugitive emissions. Numerous studies have been conducted and these were
reviewed in the AID, pointing out both strengths and weaknesses associated
with each study. To gain maximum utility of the data from these studies,
interpretation of the data is required, drawing upon the strong points of a
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study while considering its weaknesses. This evaluation and interpretation of
the data was done in the context of the whole base of fugitive emissions work;
it was not done just for isolated studies. Based upon this review and
analysis, it was determined that the relevant data from different studies had
to be merged and transformed to provide a useful method for estimating
emissions. One of the most important studies was the Petroleum Refining
Assessment.
The Petroleum Refining Assessment was an enormous study of VOC emissions
from all facets of refining. A major goal of the work was the investigation
of fugitive emissions and the development of emission factors that could be
used to estimate fugitive VOC emissions. The research program, therefore, was
designed to gather data that would lend itself to generation of such factors.
As a result, the mass emissions data collected during the Petroleum Refining
Assessment represent the best available data on VOC emissions from fugitive
emission sources. Mass emissions data were gathered on sources in chemical
units to evaluate the effects of maintenance on emissions. The data were not
collected with emission factor development as the primary goal; therefore,
these mass emissions data do not represent the highest quality data on mass
emission of VOC from fugitive emission sources.
The work done in petroleum refineries and subsequent studies in chemical
process units indicated that actual mass emissions (as described by emission
factors) are related to the number of leaking components compared to the
number of non-leaking components. The mass emissions data from the Petroleum
Refining Assessment served as the basis of emission factor development for
fugitive VOC sources in SOCMI. Recognizing that leak frequencies for
equipment in SOCMI were different from those reported in the Refining
Assessment, EPA used leak frequency data for SOCMI to weight the mass
emissions data from the Petroleum Refining Assessment in generating the SOCMI
average emission factors. This procedure is detailed in the AID and in this
report. In the AID, EPA compared the emission factors generated using this
approach with the factors developed as part of the study of maintenance
effects in chemical units. The factors were found to be similar except in the
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case of gas/vapor service valves. Therefore, the chemical unit data were used
to generate the emission factor for valves in gas/vapor service.
4. Using average SOCMI emission factors overestimates emissions from my
process unit, because of the inherent nature of the chemicals I use,
their volatility, their value, etc.
In gathering data on the SOCMI, EPA sampled a number of vastly different
chemical process units. Characteristics of individual chemicals were
considered in selecting the process units sampled during the 24-Unit Study.
Hi-volume, low-priced chemicals were included, as were lower-volume,
higher-priced chemicals. Chemicals with widely divergent volatilities were
included along with chemicals that are particularly odoriferous. Not
surprisingly, the frequencies of leaks found ranged from nearly zero to thirty
percent. Leak frequencies provide an indication of the relative quantity of
mass emissions and it is apparent from this range of leak frequencies that
fugitive emissions from some units will be higher and some lower than
estimates based on the SOCMI factors. The mass emissions estimates generated
by EPA using the average SOCMI emissions factors represent an average that is
applicable to industry-wide emissions estimates. Without conducting a
rigorous Method 21 survey to determine the leak frequency (thereby generating
average emission factors based on the leak/no-leak factor components), the
average SOCMI emission factors stand as the best estimators of fugitive VOC
emissions currently available.
5. I have measured emission rates for some sources in my plant. Why aren't
these measurements better than the estimates EPA supports?
The emission factors supported by EPA are based upon a vast amount of
data gathered on fugitive VOC emission sources using rigorous sampling
protocols. The factors for each equipment type have been developed
considering two types of data: leak frequency data and mass emissions data.
The entire distribution of mass emissions from each class of sources has been
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considered. For example, 76 individual measurements of mass emission from gas
valves were taken across the distribution of screening values (i.e., analyses
measurements) to develop a mass emissions correlation to be applied to
screening data. Similar distributions of mass emissions measurements are
necessary for each equipment type to develop the correlations used in
generating average emissions factors.
Furthermore, the correlations represent only part of what goes into the
emissions factors. Screening data (i.e, screening values for all equipment
components are needed to ensure that the entire distribution of screening
values is included in emission factor development.
Limited, isolated measurements of emission rates for "some" sources,
therefore, are not representative of the entire distribution of sources in the
process unit. Only by considering the entire distribution can the emission
factor be representative.
6. How do I estimate emissions for my plant...
(A) if I have no data?
(B) if I have some measurements?
(C) if I have done a rigorous Method 21 survey?
For process units where no emissions data are available, estimates of
fugitive VOC emissions should be made using equipment counts and the typical
average emission factors developed for SOCMI. The development of these
factors given in this document, was explained in the Additional Information
Document (AID) for VOC equipment leaks.
In some cases, isolated emission rate measurements may have been made.
These measurements serve to give the owner or operator a "sense" of the
quantity of mass emissions that might be emitted from the process unit.
Again, however, the average SOCMI factors must be employed to estimate
emissions when only isolated mass emissions measurements have been made.
Isolated measurements do not represent the entire distribution of screening
values and mass emission rates present in a process unit.
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The alternative to using the average SOCMI factors is to employ complete
leak frequency data gathered using a rigorous Method 21 survey on all
equipment types. In so doing, the leak/no-leak approach described within can
be used to estimate emission factors for the specific process unit screened.
The resultant "custom" emission factors would then be applied to the equipment
counts for the specific process unit to derive the total fugitive VOC
emissions estimate for the process unit. This procedure is illustrated for an
example case in Section 3.5.
The initial step in generating surrogate emission factors is to use a
rigorous Method 21 survey on all sources in the process unit. Method 21
survey is the promulgated method developed by EPA that is used to monitor
equipment for leaks. "Rigorous" means that all sources must be screened and
that no maintenance of sources should be conducted prior to screening.
Conducting maintenance immediately prior to conducting the Method 21 survey
would bias the leak frequencies generated and thus invalidate the subsequent
emissions estimates based upon the leak frequencies.
Emissions estimated in this manner should be reviewed on a continual,
i.e., annual, basis. For example, as time passes, the leak frequencies noted
for individual equipment types in a process unit may change. An annual
testing using a rigorous Method 21 survey would ensure that emissions
estimates made using "custom" emission factors would remain representative of
the process unit.
7. I am not interested in total VOC emissions. How do I estimate emissions
of a specific pollutant?
The estimates of VOC emissions represented by the average SOCMI emission
factors are total VOC emissions. In many instances, only one component in the
VOC stream is of interest and the estimate of emissions need only reflect the
specific pollutant. In order to reflect compound-specific emissions, the
estimates, (or emission factor) should be apportioned to reflect the single
compound (or component) of interest. As illustrated in Section 3.5, a simple
mass fraction approach can be applied; that is, for equipment in VOC service
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containing X weight percent of the compound of interest, the emission factor
could be apportioned by X/100 to reflect emissions of only the single
compound.
8. The control costs associated with leak detection and repair are too high,
particularly in light of low emissions reduction.
EPA based its estimates of cost on cost data gathered from industrial
sources during standards development activities. The time estimates used for
equipment monitoring (i.e., screening) and for repair (of valves) were based
on information supplied by industry. Cost and cost effectiveness analyses
were conducted for control of individual equipment types and for complete
process units. The costs of regulatory alternatives for equipment types were
judged to be reasonable. Likewise, for process units considered on the
average, the costs were found to be reasonable.
EPA recognized, however, that not all process units could be considered
the model unit average SOCMI norm, described by model equipment counts and
average SOCMI emission factors. There are tools to examine regulatory
alternatives, as applied to an entire industry. Therefore, EPA considered
alternative control options for those situations where costs became
unreasonable with respect to the amount of emissions controlled. An example
of alternative standards allowed by EPA is the 2 percent leaking performance
limit for valves. In its analysis of regulatory alternatives, EPA determined
that the costs of control for process units with less than 1 percent leaking
valves were too high for the relatively small emissions reductions achievable
by routine leak detections and repair (monthly). To allow for variability in
measurements, EPA provided a limit of 2 percent leaking. As evidenced by data
gathered during the 24-Unit Study, there are process units which exhibit low
leak characteristics. Owners or operators of such units could opt for meeting
a 2 percent (or lower) performance limit of leaking valves, as demonstrated by
an annual Method 21 performance test.
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2.0 FUGITIVE EMISSION SOURCES
The term fugitive emissions used in the context of volatile organic
compounds (VOC) refers to leaks from equipment such as valves, pumps, com-
pressors, etc. The term fugitive emissions, also called equipment leaks,
means the loss of VOC through the sealing mechanism separating the process
fluid (contained in the equipment) from the atmosphere.
Fugitive emissions are generally more diffuse than most point sources of
emissions, especially when considering the collective emissions from widely
dispersed equipment within a processing plant. As noted by the emissions
estimates presented in Figure 2-1, fugitive emissions contribute a large
proportion of VOC emissions from the chemical industry overall (about 35 per-
cent).1
As with process-related sources, fugitive emissions sources are readily
identifiable pieces of equipment within a processing plant. But a major
difference is in the number of sources found in any given process unit. While
there may be only a few process-related sources within a process unit (e.g., a
reactor train and associated distillation columns for purification), there can
be hundreds or thousands of valves, pumps, flanges, compressors, and other
fugitive emission sources within a process unit. And while fugitive emissions
on a per component basis can be small, the collective total of emissions from
all fugitive sources within a process unit can be large.
No single control technique is applicable to the control of all types of
equipment leaks. Neither is a single emission limit universally applicable to
equipment leaks. Rather, each type of fugitive emission source must be
considered individually in establishing appropriate, applicable control
techniques. Equipment controls, operational practices, and work practices are
all valid approaches to reducing or eliminating VOC emissions from equipment
leaks, depending on the equipment type.
Chemical process plants are comprised of numerous major equipment com-
ponents such as reactors, accumulators, storage tanks, distillation columns,
condensers, and heaters. There is also a large class of ancillary equipment,
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ro
ro
Organic Chemical Hanufacturing
544 Gg/yr (100X)
Process Sources
1
1
Reactor Operations
i
i _J
Air Oxidation
Processes
110 Gg/yr
(2M)
Reactor
Processes0
32 Gg/yr
(61)
Distillation
Operations
140 Gg/yr
(261)
Non-Process Sources
Equipment
Leaks
189 Gg/yr
(351)
Storage of
Organic Liquid:
47 Gg/yr
Secondary
Sources0
26 Gg/yr
Estimates for process emissions sources estlMted using best available Information from current standards
(25 October 1982).
Figure 2-1. Estimated Emissions by Source Subcategories of SOCMI2
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most of which involves the transport of chemicals and control of chemical flow
through the process unit. These components include:
- Valves
- Pumps
- Compressors
- Pressure Relief Devices
- Open-Ended Valves or Lines
- Sampling Connections
- Flanges and Other Connectors
These ancillary items of equipment are fugitive emission sources.
2.1 VALVES
The valve is one of the most basic, common elements found in the chemical
plant. Valves are available in numerous designs for widely varying applica-
tions: gate, globe, control, plug, ball, check, and relief. Most of these
valve designs (check and relief valves excepted) have a valve stem which
operates to restrict or to open the valve for fluid flow. Typically the stem
is sealed by a packing gland or 0-ring to prevent leakage of process fluid to
the atmosphere. Packing glands are the most commonly used sealing mechanism
for valves, and a wide variety of packing materials are available to suit most
operational requirements of temperature, pressure, and compatibility. Because
of design and materials limitations, 0-rings are much less common as the
sealing mechanism for valves in chemical plants.
With time and prolonged use, the packing or sealing 0-ring in the valve
can fail. To eliminate the VOC leakage resulting from the seal failure, the
valve packing and seals must be replaced or the valve body repaired or
replaced. Leak detection and repair methods are effective means of reducing
the leakage of VOC from this class of sources in a plant. Basically, a leak
detection and repair (LDAR) program is a systematic program of routinely
monitoring individual sources (in this case, valves) to identify those sources
which are leaking. Those leaking sources would then be targeted for repair
For different source types or industries, the definition of a leak may vary
For the purpose of this document, the leak definition is a screening value
greater than or equal to 10,000 ppmv read on a portable organic compound
analyzer, in accordance with Method 21.
2-3
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(i.e., elimination of the "leak") and for subsequent follow-up monitoring to
ensure that the repair had indeed been effective in eliminating the leak.
Maintenance or repair techniques can range from simple, on-line mainten-
ance to complex techniques. Some basic types of maintenance that can be
performed on a valve while it remains in-place and in service are:
(1) tightening or replacement of bonnet bolts,
(2) tightening of packing gland nuts, and
(3) injection of lubricant into the packing or seal.
These valve components are illustrated in Figure 2-2. But simple on-line
techniques are not always applicable or effective in reducing emissions. For
example, operational or safety requirements may prohibit repair of some valves
such as control valves by simple means. Other valves simply cannot be
repaired effectively on-line and cannot be removed from service. In some
instances, repair of valves can be effected through more sophisticated repair
techniques. An example would be the injection of a sealing fluid into the
equipment. Though relatively expensive, sealant injection has been proven
effective in petroleum refining applications in California where virtually
complete elimination of leaks has been mandated.3 In cases where maintenance
or repair of valves is not possible, valve replacement may be required.
There are some valve types and designs that have little or no potential
for leakage of process fluids: valves with "leakless" or "seal!ess"
technology. Two examples are bellows sealed valves and diaphragm valves.
Bellows seals are the most effective sealing mechanism for valves. Since the
service life of the bellows can be quite variable, bellows seals are typically
backed up with conventional packing glands. Bellows seals have been used
primarily in the nuclear power industry where the relatively high cost can be
justified by stringent safety requirements. Diaphragm valves, the other major
type of "leakless11 valve, use a diaphragm of some appropriate material to seal
the process fluid from the stem of the valve. In some designs, the diaphragm
acts as the flow control element as well as the sealing mechanism. Two
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PACKING
GLAND
PACKING
VALVE
STEM
POSSIBLE
LEAK AREAS
70-1769-1
FIGURE 2-2. DIAGRAM OF A GATE VALVE
2-5
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typical designs of diaphragm valves are shown in Figure 2-3. Diaphragm
valves, however, are a source of fugitive emissions if the diaphragm fails.
2.2 PUMPS
Pumps are integral pieces of equipment in most chemical processes,
providing the motive force for transporting fluids throughout a plant. The
centrifugal pump is the chief design used in the SOCMI, but other pump types
are also used. Leakage of process fluid to the atmosphere can occur where the
moving pump shaft meets the stationary casing. To minimize such leakage, two
sealing techniques are commonly applied: packed seals and mechanical seals.
Leak detection and repair programs, described earlier for valves, are
also applicable to pumps with the potential to leak at the seal. Pumps with
maintained mechanical seals generally leak less than do pumps with packed
seals. Failure of a mechanical seal, however, can result in large emissions
from the pump. Routine monitoring can effectively identify pump seal leaks
and maintenance repair can reduce emissions.
Packed seals consist of a "stuffing box" in the pump casing. Specially
selected packing materials (chosen on the basis of the process materials and
environment) are compressed into the stuffing box with a packing gland,
resulting in a tight seal around the shaft. Since the shaft must move, either
rotationally or laterally, lubrication must be supplied to the packing and
shaft to prevent excessive heat generation from the friction between the shaft
and packing which could shorten the life of the equipment. Leaks may result
from the degradation of the packing.
Leaks from packed seals can often be reduced by tightening the packing
gland. But at some point, the packing will have deteriorated to the extent
that it must be replaced. Often, pump packing can only be replaced when the
pump is out of service.
Mechanical seals, single and dual, are used to seal pumps with rotating
shafts. Both have the common attribute of a lapped seal face between a
stationary element and a rotating seal ring. Although mechanical seals are
not leakless sealing devices, the leakage of process fluid from the seal can
be minimized by a properly installed and operating mechanical seal.
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DIAPHRAGM
DISK
STEM
DIAPHRAGM
70-1771-1
FIGURE 2-3. DIAGRAMS OF VALVES WITH DIAPHRAGM SEALS
2-7
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Since a mechanical seal will leak (unless routinely replaced), the
ultimate potential for leakage can be reduced through redundancy of sealing
mechanisms. For instance, a single seal may employ a packed seal as an
auxiliary sealing mechanism to reduce fugitive emissions. Or the same purpose
might be just as easily accomplished with some dual mechanical seal
arrangements (either back-to-back or tandem.) As shown in Figure 2-4, the
dual mechanical seals in both arrangements form a cavity.
In the back-to-back arrangement, a barrier fluid circulates between the
two seals. With the barrier fluid pressure maintained above the pump
operating pressure, any leakage is across the inboard seal face into the
process fluid and across the outboard seal face to the atmosphere. The tandem
arrangement basically has a single seal backed up by another single seal; both
seals are mounted facing the same direction. The seal fluid (also referred to
as the buffer or barrier fluid) is circulated through the space between the
seals. Any process fluids that may leak into the barrier fluid across the
inboard seal interface may be removed with the barrier fluid or degassed in a
reservoir. The degassed materials could then be treated in a control system.
In general, mechanical seals have the advantage of improved sealing
characteristics and auxiliary control for VOC that may leak into the barrier
fluid system. However, repair of mechanical seals can be both costly and time
consuming. To eliminate a leak from a pump equipped with a mechanical seal,
the pump must be taken off-line and dismantled to permit repair or replacement
of the seal. Additionally, care must be exercised to minimize emissions
resulting from dismantling the pump.
In addition to these pump types and seal designs, there are several types
of sealless technology available. Three designs have been applied in the
chemical industry where leakage cannot be tolerated. The canned-motor pump is
a shaftless design in which the pump bearings run in the process fluid. The
motor rotor housing and pump casing are interconnected. Diaphragm pumps
eliminate all seals and packing exposed to the process fluid through the use
of a flexible diaphragm (constructed of metal, rubber, or plastic material) as
the driver for moving the fluid. Magnetic-drive pumps also have no seals in
contact with the process fluid; the impeller in the pump casing is driven by
2-8
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SEAL LIQUID
POSSIBLE LEAK
INTO SEALING
FLUID
FLUID END
GLAND
PLATE
PRIMARY
SEAL
V
SECONDARY
SEAL
FIGURE 2-4a. DIAGRAM OF A DOUBLE MECHANICAL SEAL
(BACK-TO-BACK ARRANGEMENT)
FLUID
END
PRIMARY
SEAL
BUFFER LIQUID
OUT IN
(TOP) (BOTTOM)
SECONDARY
SEAL
GLAND
PLATE
70-1767-1
FIGURE 2-4b. DIAGRAM OF A DOUBLE MECHANICAL SEAL
(TANDEM ARRANGEMENT)
2-9
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an externally-mounted magnet coupled to the motor. Examples of uses of
seal less technology for pumps include the handling of organic solvents,
organic heat transfer liquids, toxic or hazardous materials, and expensive
materials.
2.3 COMPRESSORS
Compressors provide motive force for transporting gases throughout a
process unit in much the same manner that pumps are used to transport liquids.
Compressors are driven with rotating or reciprocating shafts. Thus, the
sealing mechanisms for compressors are similar to those for pumps; that is,
packed and mechanical seals are the designs primarily used. Again, it is the
sealing mechanism that is the potential source of fugitive VOC emissions.
The mechanical seals used on compressors reduce but do not eliminate
leakage of the process fluid. The types of seals commonly used on compressors
include:
- Labyrinth, comprised of interlocking teeth to restrict flow;
- Restrictive carbon rings, comprised of multiple stationary
carbon rings;
- Mechanical contact, which is similar to the mechanical seal for
pumps; and
- Liquid film, which employs an oil film between the rotating
shaft and stationary gland.
These mechanical seals can be vented in various manners to a control device
for elimination of VOC which may leak from the process. The use of packed
seals is generally restricted to reciprocating compressors where mechanical
seal designs cannot be used.
Leakage of VOC to the atmosphere from compressor seals can be detected by
instrument monitoring at the seal. Repair of mechanical seals requires
removing the compressor from service. Since compressors in the SOCMI do not
typically have spares, immediate repair may not be practical or possible
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without a process unit shutdown. There are optional control techniques that
are considered effective means of controlling emissions from mechanical seals
on compressors. One example is venting the barrier fluid system or the seal
to a control system (for example, a closed vent system connected to a control
device).
Leakage from packed seals may be reduced by tightening the packing gland.
Figure 2-5 shows a typical arrangement of a single stage reciprocating
compressor. On some reciprocating designs (particularly newer compressors),
the distance piece between the compressor cylinder and the drive crankcase can
be vented to a control device to treat any leakage through the packing. On
the older designs, however, this practice may not be possible without
replacing (or possibly recasting) the distance piece to accommodate the vent
line or completely replacing the older compressor with a newer design
incorporating a vent line connection.
2.4 RELIEF DEVICES
Relief devices are safety devices commonly used to prevent operating
pressures from exceeding the maximum allowable working pressures of process
equipment. The most common pressure relief device is a spring-loaded valve
(as shown in Figure 2-6) designed to open when the operating pressure exceeds
a set pressure. The pressure relief valve (PRV) is constructed so that it
will reseat after the operating pressure has decreased to a level below the
set pressure.
Leaks of VOC from relief devices occur through the valve seat. Basically
two mechanisms are cited for relief device leaks: (1) leakage resulting from
improper reseating of the valve after a release and (2) leakage resulting from
process operation at or near the valve set pressure. The latter condition is
often referred to as "simmering" or "popping."
Rupture disks (RDs) are pressure relief devices that allow no fugitive
emissions, if the integrity of the disk is maintained. Upon pressure relief,
however, the disk bursts and the process vents directly to the atmosphere
2-11
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Distance Piece
ro
i
Figure 2-5. Simple Single-stage Reciprocating Compressor
-------
Ttmion-idjustmtm
thimble
......Spring
CONNECTION FOR
PRESSURE GAUGE
4 8UEEO VALVE
RUPTURE DISK
FROM SYSTEM
Figure 2-6. Pressure Relief Valve in a Basic RD/PRV Combination
2-13
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until the process pressure has normalized with the atmosphere. Replacement of
the rupture disk restores the process to a condition of no fugitive emissions.
Rupture disks should be used in conjunction with relief valves to
eliminate potential fugitive emissions from relief valves. When mounted
upstream of a relief valve, fugitive emissions are blocked prior to the
potential leak source, the valve seat. (Leakage may occur if the integrity of
the disk is not maintained.) A typical arrangement of an RD/PRV combination
is shown in Figure 2-6; such systems have been specified by ASME Codes which
establish the design constraints and criteria to avoid potential safety
hazards from the practice. For instance, to meet ASME requirements, the space
between the RD and the PRV must be equipped with a bleed valve and pressure
gauge that would indicate any pressure build-up resulting from a leaking
disk.4
To ensure no fugitive emissions to the atmosphere, the rupture disk must
be replaced after an overpressure relief. One option that accommodates this
procedure consists of block valves mounted upstream of the relief devices.
This option is only possible where safety rules permit the use of a block
valve in relief line service. (Even where permitted, this practice generally
includes provisions for locking the block valve in the open position during
normal operation.) The other options are dual relief valve systems equipped
with 3-way valves. By using a 3-way valve, a relief system will always remain
in service, even when replacing a rupture disk on the other relief
combination. A number of possible configurations are possible for this
option. For instance, the "primary" side (which would be used normally) could
employ the RD/PRV combination, while the "secondary" side (which would be for
back-up service only) could consist of a rupture disk, a pressure relief
valve, or another RD/PRV combination.
Soft-seat technology for relief valves consists of using an elastomeric
0-ring to provide an improved seal when the valve reseats after an over-
pressure release. The applicability of soft-seat technology is limited by
materials compatibility and operating conditions. Furthermore, soft-seat
technology has no impact on emissions from "simmering."
Fugitive emissions from all mechanisms can be stringently controlled by
routing the discharge of the pressure relief device to an appropriate control
2-14
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device via a closed vent system. The most prevalent example of this procedure
is the use of a flare header.
2.5 OPEN-ENDED VALVES AND LINES
Open-ended valves and lines are found throughout chemical plants; they
are generally drain valves, purge valves, and vent valves. Process fluids may
be emitted to the atmosphere through the valve seat as a result of faulty
seats or incompletely closed valves. To prevent any atmospheric emissions
from valve seat leakage, a pipe plug, cap, or blind flange can be installed on
the open end. Another option is the use of a second valve, in something like
a "block-and-bleed" arrangement. Using this arrangement, after the valves have
been opened to allow flow of process fluid, it is best to close the upstream
valve first. In this manner, no process fluid can be trapped between the two
valves.
2.6 SAMPLING SYSTEMS
Routine periodic checks of process unit operation are often made by
sampling process streams to evaluate the performance of reactors, distillation
units and other operations, and to verify purity and composition of
feedstocks, intermediates, and products. Process fluids contained in sample
lines must be purged prior to sampling to obtain a representative sample for
analysis. The purged fluid is often merely drained onto the ground or into
the sewer drains, where VOC may be released to the atmosphere.
Sampling emissions can be reduced by using a closed purge sampling
system, designed to return the purged VOC to the process or to send the VOC to
a closed disposal system (e.g., a closed vent system connected to a control
device). Examples of closed purge sampling systems are shown schematically in
Figure 2-7. In one case, the sample is collected as a side-cut stream from
the purge stream, which flows around a flow-restricting device (e.g., an
orifice or valve) in the main process line. In the second example, the purge
is directed through the sample container. These two examples are not the only
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PROCESS. LI
PROCESS LI WE.
c-
ro
i
en
LJ
T
o
SAUPL.E.
COK1TA.IMER
SAMPLE.
COMTAUUE.R
Figure 2-7. Schematics of Closed Purge Sampling Systems
-------
closed purge sampling systems possible. For instance, closed purge sampling
may also be done with partially-evacuated sample containers.
2.7 FLANGES AND OTHER CONNECTORS
Flanges and other connectors comprise the single largest class of
fugitive emission sources in a process unit, in terms of total numbers.
Flanges are gasket-sealed junctions used to mate pipe and other equipment such
as valves, vessels, and pumps. Flanges may be used in pipe sizes 50 mm
(2 inches) or greater in diameter. Other connectors, such as threaded connec-
tions and nut-and-ferrule connections, perform the same function as flanges,
but they are used primarily on line sizes less than 50 mm in diameter.
Flanges and other connectors may leak VOC as a result of:
- improperly selected gaskets;
- poorly assembled flanges;
- poorly assembled nut-and-ferrule combinations; or
- cross-threaded pipe connections.
The major cause of VOC leakage from flanges and other connectors is
deformation of sealing surfaces as a result of thermal stress. VOC leaks from
flanges and other connectors can be determined using instrument monitoring
techniques; potential leaks may be evidenced through other means such as
visual, auditory, or olfactory means. Tightening bolts on flanges is one
method of effectively sealing VOC leaks from some flanges. Generally,
however, flange gasket replacement or correction of a leaking connector
requires partial or complete process unit shutdown. And emissions from the
shutdown or repair procedure could even exceed the long-term emissions from
the leak itself.
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3.0 EMISSION FACTORS
In evaluating standards of performance or even the effectiveness of
individual programs of emissions reduction, the estimation of emissions from
a given source is a key element. Source testing for process emission
sources, such as reactor vents, etc., is a relatively straightforward
procedure. Estimating emissions from widely dispersed fugitive emission
sources can be somewhat more difficult.
One of the first published studies of fugitive emissions was conducted
in several petroleum refineries in the Los Angeles County Air Pollution
Control District. The estimates of this 1950's joint study showed that
potentially a large quantity of hydrocarbons could be lost to the atmosphere
from various sources such as valves, pump and compressor seals, cooling
towers, flanges, and pressure relief valves.
It was the middle 1970's before another comprehensive assessment of
emissions from petroleum refineries was made. In this newer study,
emissions measurements were made at 13 refineries located throughout the
United States. Emission factors, screening relationships, and correlations
were generated from data collected on valves, flanges, pump seals,
compressor seals, drains, and pressure relief valves. The focus of this
study was the assessment of atmospheric emissions in petroleum refineries,
and it was surprising to many people to find that fugitive emissions were a
major contributor to the total air emissions from a refinery.
The Refining Assessment Study was subsequently used as a primary
reference in standards development activities by EPA. The Refining
Assessment Study was then augmented with other information available in the
literature and additional studies of fugitive emissions conducted in
chemical process units.
3.1 STUDIES CONSIDERED IN SOCMI EMISSION FACTOR DEVELOPMENT
Since the initial fugitive emissions work done in the 1950's LA County
studies, numerous research efforts have focused on understanding fugitive
3-1
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emissions of VOC. Studies have considered leak frequency, leak rate,
emission factors, methods of leak prevention, and the effectiveness of leak
prevention techniques on reducing the number of leaks and mass emissions
associated with them. The studies listed in Table 3-1 are briefly described
below. Each study is summarized with respect to method and results. Actual
numerical results have been summarized in the Additional Information
Document (AID) for Fugitive Emission Sources of Organic Compounds.7
3.1.1 Petroleum Refining Assessment Study
The Refining Assessment Study was designed to provide comprehensive
emissions data from a representative number of fugitive emission sources in
each refinery tested. In each of the 13 refineries tested, equipment in
several process units were sampled. A total of 500 to 600 emission sources
in each refinery were screened or sampled. To eliminate potential bias from
source selection, all individual sources were preselected from piping and
instrumentation drawings before entering the refinery.
Unlike previous studies, data were gathered on screening value (i.e.,
portable organic vapor detector instrument reading) and mass emissions.
These data permitted the development of average emission factors and the
correlation of the maximum observed screening value and the measured
non-methane leak rate of VOC. The leak frequencies determined from field
measurements and the average emission factors computed are shown in
Table 3-2. These results served as the principal data against which other
fugitive emissions work by EPA would be compared.
The Refining Assessment Study also provided some other very important
results. The only equipment or process variable found to correlate with
fugitive emission rates was the volatility of the stream components. This
result led to the separation of equipment component emissions by service:
gas/vapor, hydrogen, light liquid and heavy liquid. These classifications
have been used in most fugitive- emissions standards to direct effectively
the major effort toward equipment most likely to leak.
3-2
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Table 3-1. FUGITIVE EMISSIONS STUDIES IN THE AID
Reference
No.
6 Petroleum Refining Assessment Study
8 Four Unit EPA Study
9 EPA 6-Unit Study
10 Du Pont Study
11 Exxon Cyclohexane Study
12 EPA 24-Unit Study
13 Evaluation of Maintenance for Fugitive VOC Emissions Control
14 Analysis of Fugitive Emissions Data
15 Revision of Emission Factors/SOCMI Processes
16 German Studies
17 Union Carbide Study
18 Evaluation of Allied HOPE Study
19,20 Coke Oven By-Product Recovery and Gas Plants Studies
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TABLE 3-2. LEAK FREQUENCIES AND EMISSION FACTORS:
REFINING ASSESSMENT STUDY
Equipment
Valves
Pump Seals
Compressor Seals
Pressure Relief Valves
Flanges
Open-Ended Lines
Service
Gas
LLb
HLC
LL
HL
Gas
Gas
All
All
Emission Factor3
kg/hr/source
0.0268
0.0109
0.00023
0.114
0.021
0.636
0.16
0.00025
0.0023
Percent of
Sources
>10,000 ppma
10
11
0.2
24
2
36
7
0.5
7.7
From Appendix B of the Refining Assessment report
(EPA-600/2-80-075c). Reference 21.
LL - light liquid service; i.e., compounds with vapor pressure greater than
kerosene.
CHL - heavy liquid service; i.e., compounds with vapor pressure of kerosene
and lower.
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3.1.2 Four Unit EPA Study8
Although designed along the same lines as the Refining Assessment
Study, this study conducted by EPA-IERL (RTP) was too limited in scope to
yield results with reasonable confidence intervals for most source types.
The most important result of the Four Unit Study was that of illustrating
the need for more intensive sampling and screening.
3.1.3 EPA 6-Unit Study9
The 6-Unit Study was the next level in testing of fugitive emissions
conducted by EPA. For this study, leak frequencies (as determined using a
portable organic analyzer and considering a 10,000 ppmv leak definition)
were evaluated for all potential sources on an individual component basis.
Plant personnel identified those equipment believed to handle organics. And
no attempt was made to segregate equipment by service (e.g., in gas/vapor
service, in light liquid service, etc.). No emission rate measurements were
made, so no emission factors were determined.
3.1.4 Du Pont Study10
E. I. duPont de Nemours conducted an independent survey of two of their
process units to evaluate the leak frequencies of pumps and valves and the
leak rates of valves. A portable organic analyzer (calibrated to hexane) was
used to identify leaks of 10 ppm or greater. Du Pont evaluated actual leak
rates on only 6-8 valves. The study had a limited data base for pumps and
valves and was restricted to two older process units. Du Pont's leak
definition was inconsistent with EPA work. And finally, there was no
determination of an average emission factor.
3.1.5 -Exxon Cvclohexane Study
Exxon Chemical Company conducted a study of fugitive emissions sources
at its Baytown cyclohexane unit. Valves were screened using a soap solution
(soaping); pump seals, compressor seals and safety valves were instrument
3-5
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screened using an undefined leak definition. Valve leaks were classified as
small, medium, or large for selection for mass emissions sampling. The
percentage of leaks and emission factors determined from the study could not
be related to EPA's work due to the inconsistencies in leak definitions
between the two studies.
3.1.6 EPA 24-Unit Study12
In 1980, EPA coordinated a study of 24 individual chemical process
units. The process units were selected to represent a cross-section of the
population across SOCMI. Among the chemical compounds included in the
survey were acrylonitrile, ethylene dichloride, formaldehyde,
perch!oroethylene, and vinyl chloride. Selections of equipment to be
screened were made prior to screening activities; screening was conducted by
two-person teams using portable organic analyzers. Calibration was done
daily at a minimum. A large number of the following types of equipment were
screened in the 24 units for determination of leak frequency: flanges,
process drains, open-ended lines, agitator seals, relief valves, valves,
pump seals, and compressor seals. These sources were further grouped by the
chemical phase of the material being handled: in gas/vapor service, in light
liquid service, and in heavy liquid service.
3.1.7 Maintenance Study13
A study of the effects of maintenance on emissions was performed
concurrently at six of the units screened in the 24-Unit Study. This work
yielded quantitative estimates of leak occurrence and recurrence rates and
of the effects of maintenance on fugitive emissions. Coincident with these
estimates, correlations of screening values and leak rates were made.
The Maintenance Study focused on gas valves, light liquid valves, and
light liquid pumps in three types of process units: ethylene, cumene, and
vinyl acetate. The units selected were considered to be representative of
the level of control existing in the chemical industry.
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3.1.8 Analysis Report14 and Revision of SOCMI Emission Factors1
Data gathered during the 24-Unit Study and the Maintenance Study were
subjected to a more in-depth analysis. The data analysis tasks included in
the report were generation of average emission factors, analysis of leak
frequency as a function of process parameters and equipment design, analysis
of the impact of instrument response factors on leak frequency, and analysis
of the impact on mass emissions of leak occurrence and recurrence rates.
Leak frequencies for the various source types varied among the 15 process
units and among source types. Higher leak frequencies were found to be
associated with higher line pressures, while line temperature appeared to
have no consistent effect.
Average emission factors were developed for gas valves, light liquid
valves, and light liquid pumps in the three process unit types examined in
the Maintenance Study. In this case, emission factors were generated only
for these processes since the leak rate/screening value correlations
developed depend on process type. These emission factors were later revised
to account for data biasing due to off-scale instrument readings and
maintenance effects. The values determined were generally found to be lower
than the average emission factors determined for petroleum refineries.
3.1.9 German Studies on Fugitive Emissions
Four studies conducted by industry and government groups in West
Germany investigated fugitive emissions and methods of prevention in
chemical and petrochemical plants. The sources studied included flanges,
threaded connections, compressor seals, pump seals, agitator seals and
valves. Four different methods of leak rate determination or estimation
were employed.
The studies were inconclusive in giving the quantitative dependence of
leakages on chemical, physical, and design .parameters of sealing elements.
Insufficient data were cited as the reason. Leak rates found for the
sources investigated were in general about 1/10 of the values previously
published in the literature.5 It is important to note that the low values
represent leakage rates for well-maintained facilities. In addition,
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the studies noted that prior to any directed maintenance activity, the leak
rate for valves was 200 percent of the published value. Most of these
emissions were reduced by repair of a single large leak prior to additional
measurements.
3.1.10 Union Carbide Study17
Union Carbide conducted a study of a single process unit to 1) find all
leaking points in the unit, 2) quantify the leak rates for these points, and
3) develop a statistical fugitive emission sampling plan for future work.
Leaks were determined using a portable organic analyzer calibrated with
hexane for a 1,000 ppmv leak definition. An overall leak frequency of 6.7
percent was found for the 1,569 points screened. Pump seals and open-ended
lines demonstrated the highest leak frequencies at over 30 percent.
Point leak rates were determined by various means for all sources
determined to be leaking (i.e., screening at or above 1,000 ppmv). The
method of determining the leak rate depended upon the rate of leakage (high;
medium; low) and temperatures. The leak rates were not classified by source
type (eg., pump seal, valve, etc.). Rather, they were reported by the
degree or extent of leakage: (1) small leak (0.001 - 0.02 Ib/day); (2) wet
surface (0.1 - 0.5 Ib/day); (3) dripping or strong unbearable odor (1 - 20
Ib/day); and (4) continuous flow (50 - 150 Ib/day). No leak rates were
established for sources screening less than 1,000 ppmv. The leak rates were
not used in developing EPA's factors since they could not be compared to
data gathered by EPA.
In its recommendations, Union Carbide cited development of a leak
rate/screening value correlation as an improvement in estimating emissions.
In addition, the work done by Union Carbide recognized that, in order to
establish leak rates for 13 equipment types, some 23,000 sources would have
to be screened and 1,000 leak measurements made to obtain data within the 90
percent levels of confidence desi.red.
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3.1.11 Analysis of Allied HDPE Unit Data18
Kemron Environmental Corporation, in conjunction with Allied Chemical,
conducted a 10-month study of flanges and valves in a new high density
polyethylene (HDPE) unit. Basically focusing on maintenance effects, six
screening and emissions measurement tests were performed on valves and
flanges over the course of the study. Screening was done using a portable
organic analyzer calibrated to 1,000 ppmv hexane. (Unlike the EPA studies,
a high concentration calibration standard was not used, nor was calibration
verified at the completion of daily screening. While leak rates were
determined for sources screening at 10,000 ppmv or greater, these rates are
not comparable to average emission factors. (Average emission factors
consider emissions from all valves across an entire distribution of
screening values, not just values higher than 10,000 ppmv.) Further, some
of the valves sampled for leak rate had been subjected to a directed
maintenance program prior to sampling. This action resulted in lower
emissions than would be expected in the absence of any maintenance efforts.
3.1.12 SCAQMD Study22
To evaluate the effectiveness of fugitive emission control regulations,
EPA conducted a survey of two refineries in the South Coast Air Quality
Management District (SCAQMD) in California. Accessible valves, pumps,
agitators, open-ended lines, drains, and relief valves in 8 process units
were screened using EPA Reference Method 21. No flanges were surveyed
during this study. Since this was a maintenance-oriented study, no mass
emission rate measurements were made.
3-9
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3.1.13 Coke Oven By-Product Recovery19 and Gas Plant Studies20
Three coke oven by-product recovery plants were tested for fugitive
benzene emissions. Source screening was done with two different types of
portable organic analyzers. Emissions data gathered were categorized
according to source type and stream benzene content, but no distinction of
service was made. Non-methane hydrocarbon emission factors were generated
for valves, pump seals, and exhausters (i.e., compressors mainly in hydrogen
service).
A total of six natural gas processing plants were tested by EPA and the
American Petroleum Institute (API).23 Screening was done by both soaping
and portable organic analyzers. Leak rate data collected during the
combined study were used to estimate leak rates for emitting sources. These
results were then applied to the population to estimate the average emission
factors for connections and flanges, open-ended lines, pressure relief
devices, valves, pump seals, and compressor seals.
3.2 EPA'S CHOICE OF DATA FOR SOCMI EMISSION FACTORS
EPA used three major criteria in evaluating data to use to estimate
fugitive VOC emissions: 1) relevance to fugitive emissions, 2) validity of
the testing and analytical procedures, and 3) comparability to other studies
to allow validation of results.
The studies of fugitive emissions summarized above were evaluated in
the AID with respect to their relevance to estimating fugitive emission
factors. For example, the emission factors generated in the Maintenance
Study were not considered the highest quality, best available data on mass
emissions; estimation of emission factors was not the principal purpose of
the Maintenance Study. The factors were used, however, to evaluate the
results of the emission factor estimates made.
The second criterion was used to eliminate from consideration data that
were not collected by clear, consistent, acceptable test procedures. For
example, the result of studies under scrutiny would need to be evaluated
with respect to 1) how the samples were collected, 2) how the measurements
were made (field or laboratory), and 3) what type of equipment was
3-10
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represented by the reported data (only leaking equipment, complete distribu-
tion of equipment, etc.). This same sort of evaluation was needed to
consider differences in leak definition, method of determining leaks
(soaping, instrument screening), and monitoring instruments.
The final criterion was comparability of the studies. Data from both
the Refining Assessment Study and the combined SOCMI studies were gathered
in the same manner using comparable instrumentation and leak detection
criteria. Statistically, the data were handled in a similar manner in
studying emissions and the various effects of various parameters on
emissions. It was only because the data from the Refining Assessment Study
and the combined SOCMI studies were comparable that the two studies could be
evaluated against one another. Mass emissions data from the Refining
Assessment Study and leak frequency data from the SOCMI work were then
combined to form a single set of emission factors.
As detailed in the AID, EPA determined that the best data available for
estimating emission factors for fugitive VOC emissions from SOCMI was from
the Petroleum Refining Assessment Study and from the SOCMI 24-Unit Study.
These studies satisfied the three major criteria for emissions estimate
data. EPA compared the two data sets and acknowledged there were
differences that could not be explained conclusively. The Petroleum
Refining Assessment data were considered the best data on mass emissions
from fugitive emissions sources. The Refining Assessment Study was planned
with estimation of VOC fugitive emissions as one of its objectives. VOC
emissions data were gathered according to equipment type and service (i.e.,
gas/vapor, light liquid, heavy liquid). These data are considered
applicable to VOC fugitive emissions, regardless of industry. The 24-Unit
Study best represented the leak frequencies that might be expected across
SOCMI. Therefore, fugitive source emission factors for SOCMI were based on
the Refining Assessment and SOCMI emissions data, adjusted using the results
of the 24-Unit Study. This procedure is detailed in Section 3.4.
Several approaches to estimating the emission factors were considered.
The estimation procedure presented in the AID maintained consistency with
the mathematical procedure followed in developing the emission factors
presented in the Refining Assessment Study and SOCMI Maintenance Study.
Before detailing the estimation procedure presented in the AID, the methods
3-11
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followed in the Refining Assessment and SOCMI Maintainance Studies are
presented.
3.3 EMISSION FACTOR DEVELOPMENT
3.3.1 Detailed Procedural Method
The development of average emission factors for individual fugitive
emission sources was laid out in the Petroleum Refining Assessment Study.21
Since then, embellishments have been added to this procedure to account for
censoring of data (i.e., sources screened at the maximum instrument reading)
and other sampling effects (eg., pre-maintenance screening, post-maintenance
screening, etc.). The average emission factor is not merely the average of
the mass emissions measurements made on anv given type of equipment. The
process is somewhat more involved than a simple average.
Two types of fugitive emissions data were gathered for the development
and analysis of emission factors. First, screening data (i.e.,
concentration measurements) were collected for a set of sources. Using
these raw screening data, empirical cumulative distribution functions were
generated. The empirical distribution function would be a key element in
estimating an average emission factor. It was found that the cumulative
distribution functions were adequately described by a log-normal
distribution. This led to the generation of modeled cumulative distribution
functions for source screening. These functions relate the screening value
of a source to a leak frequency. An example of a modeled cumulative
distribution function is found in Figure 3-1. From such a figure, the
percentage of sources "leaking" (based upon a selected leak definition) can
be established.
The second type of fugitive emissions data gathered for average
emission factor development was mass emissions data. Individual sources
were "bagged" and measured for mass emission rate (leak rate) and screening
value. The mass emissions rate data pairs were regressed to yield leak
rate/screening value correlations for the various source types. As with any
experimental program, there will be some degree of variability in the data
gathered, especially as it is applied to estimate other emissions from
sources not tested. Confidence intervals give an indication of the range
3-12
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CO
I"
CO
p
R 100
c
E
N
T 80
S
C
R
E
E
N
I
N
G
G
R
E
A
T
E
R
60
40
0
Eat luted Percent of Source*
Screening Greater Then the Selected Source
9SS CooUdeoce Llalu
345
LOGI0COVA SCREENING VALUE!)
6
Figure 3-1. Cumulative Distribution: Cumene Gas Valves
-------
and the degree over which the results are applicable. The number of data
pairs necessary to develop this correlation depends upon the confidence
intervals desired in the final value. For example, for the 95 percent
confidence level currently used in fugitive emissions work, 76 data pairs
distributed over the range of screening values found are needed to generate
the screening value/mass emissions rate correlation for valves.24
By combining these two data sets, cumulative mass emissions
distributions were established. The leak rate/screening value correlation
(from mass emissions data) was applied to the cumulative distribution
function (from screening data) to result in a cumulative mass emissions
distribution function for each source type. Figure 3-2 shows an example of
this distribution for cumene gas valves. The cumulative mass emissions
distribution yields the percentage of mass emissions (of a source type)
associated with a selected leak definition. This value is important in
generating the leaking and non-leaking emission factors discussed in Section
3.3.3.
The generation of the average emission factor made use of the empirical
screening distribution data and the leak rate/screening value correlation.
Using the correlation (developed from mass emissions data), leak rates were
estimated for all sources that had been screened. The sum of the individual
leak rates represented the total mass emissions leak rate for the class of
sources being considered. The average emission factor was derived by
averaging the sum over the total number of sources that were screened. The
resultant average emission factor, therefore, considered the entire
distribution of sources (and screening values). It was not merely the
average of measured leak rates determined for some sources out of the
population. Because the result of the procedure is an average emission
factor, it should only be applied to populations of sources, and not to an
individual component.
3.3.2 Statistical Considerations
Of course, in generating emission factors and in evaluating their
quality, statistical considerations must be made. For example, there is a
3-14
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CO
I
E
R
C
E
N
T
T
0
T
A
L
E
M
I
S
S
I
0
N
20
0
0
Estimated Percent of Total
Maaa Ealaaiona Attributable
to Sources With Screening
Valuea Greater Than the
Selected Value
95Z Confidence Llalta
2345
LOG10COVA SCREENING VALUE)
Figure 3-2. Cumulative Mass Emissions Distribution: Cumene Gas Valves,
-------
minimum number of data pairs (screening value and mass emission measurement)
required to generate a statistically valid screening value/leak rate
correlation. And the number of data collected in the screening survey of
any population of sources will have a direct impact on the confidence
intervals associated with the modeled results.
From the previous discussion on the emission factor development
procedure used in the Refining Assessment and the SOCMI Maintenance Studies,
three models are necessary to generate average emission factors. The
screening value distribution is first modeled to a log-normal distribution
for sources screening at more than 10 ppmv. The confidence intervals for
the cumulative function are evaluated using the published values for the
Binominal Distribution. At the 95 percent confidence level, the estimated
cumulative percent leaking (p) is given as:
P ± 1-96 [p (1 - p)/n]1/2
where n is the number of screening values for the particular source type
under consideration. From this equation, it is evident that, since the
width of the confidence interval varies with the inverse square root of the
number of sources screened, a larger population of screened sources yields a
smaller confidence interval.
Next, the screening value/leak rate correlations should be considered,
again with respect to the confidence interval. Leak rates are modeled in a
log-log relationship assuming a binomial distribution, according to:
Log (leak rate) - a+p (log(screening value)) + Z (standard error)
where: a , p « model parameters;
Z - standard normal random number; and standard error is
associated with the individual predictor equation.
Again, published Binomial Confidence Interval tables are used to generate
the confidence intervals around the average of the log (leak rate)
estimates, (y). For example, the value at the lower confidence interval is:
3-16
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GI - y - 2.24 [s2/(n-r)]1/2
where: s2 - variance of the estimate; and
(n-r) = number of leaking sources.
The equation shows the effect of the number of data points in the survey on
the size of the confidence interval. During studies of fugitive emissions
in On-Shore Gas Production units, a minimum of 76 data pairs were necessary
to develop the screening value/leak rate correlation within the 95 percent
confidence interval required of the final emission factor.
The final confidence interval values for the emission factor are
actually the product of the value for the (bias-corrected) leak rate
estimate (shown above) and the value for the percent of sources leaking.
The confidence intervals for percent of sources leaking are obtained by
iterative solution of summation series equations. For example, the lower
confidence limit, PL, should be determined from:
" ,. ] n-i a
jfk (")>L U-\> "I
where: (1-a) represents the confidence level, n is the number of sources
screened, and k is the number of leaking sources. As the number of sources
screened increases, the confidence level increases and the confidence
interval narrows. This is vividly illustrated in Figure 3-3 which shows
95 percent confidence intervals for a cumulative distribution function,
assuming 100 and 1,000 components.
3.3.3 Leak/No-Leak Approach
The leak/no-leak approach to estimating emission factors, as presented
in the AID, is an extension of the complicated process described above. The
expanded process considers a leak rate/screening value correlation
integrated over a continuous distribution function; the leak/no-leak
approach instead assumes only two emission rates and two populations:
sources that "leak" (with screening values greater than or equal to
3-17
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CO
I1
oo
100
90
80
70
50
40
30
20
10
0
Estimated Ptrctnt of
Total Mass Emissions
-90S Confidence Interval
for Ptrctnt of Emissions
from Total Population of
Valves (n - )
90S Confidence Interval
for Percent of Emissions
In a Random Sample of
1000 Valves
90S Confidence Interval for
Percent of Emissions In a
Random Sample of 100 Valves
2345 10 50100 1000 10.000 100.000 1.000.000
Screening Value (ppmv) (Log1Q Scale)
Figure 3-3. Cumulative Distribution of Total Emissions by Screening Values
Comparison of Confidence Intervals.
-------
10,000 ppmv) and sources that do not leak (with screening values less than
10,000 ppmv).
The basis of this extension is as follows: when a group of sources
"leak" (i.e., have a screening value > 10,000 ppmv), they leak at a certain
mass emission rate on the average. Similarly, as a group, sources screened
at less than 10,000 ppmv (i.e., non-leaking sources) have on the average a
certain mass emission rate associated with them. Thus, the overall average
emission factor for a population of emission sources consists of two
components: leaking source emissions and non-leaking source emissions.
It is important to remember that fugitive emissions are found
distributed over a wide range of screening values. Mass emissions associated
with fugitive emission sources are similarly distributed. Therefore, only
emission factors generated using distribution data can be used in estimating
emissions from equipment leaks. Finally, only those emission factors
generated in such a manner can be used in the extended procedure discussed
below.
3.3.3.1 Generation of Leaking and Nonleaking Emission Factors.
Leaking and non-leaking emission factors are generated using three data:
(1) the average emission factor, (2) the leak frequency associated with the
average emission factor, and (3) the percent of mass emissions associated
with leaking sources. As an example, consider the data for light liquid
valves in the Refining Assessment Study:
Average Emission Factor 0.0109 kg/hr/source
Leak Frequency 11%
Percent of Mass Emissions, Leakers 86%
Assuming 1,000 valves, the total mass emissions would be 10.9 kg/hr; and
110 valves of the total 1,000 would account for 86 percent of the mass
emissions, or 9.37 kg/hr. Since this amount of emissions would be shared,
on the average, by all leaking valves, the individual leaking emission
factor would be (9.37 kg/hr)/(110 valves) or 0.0852 kg/hr/source. The
non-leaking emission factor is similarly computed. For this example, 890
valves that are "non-leaking" account for only 14 percent of the total
3-19
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emissions, or 1.53 kg/hr. This yields an average nonleaking emission factor
of (1.53 kg/hr)/(890 valves) or 0.00171 kg/hr/source.
Put in more general terms, the emission factors for leaking sources
(LEF) and the emission factors for nonleaking sources (NLEF) were computed
according to the following equations:
LEF . OEF * PCM and NLEF - OEF * HOO-PCMl
PCL (100 - PCL)
where: LEF - emission factor for leaking sources
NLEF - emission factor for nonleaking sources
OEF = overall average emission factor
PCM = percent of mass emissions due to leaking sources
PCL - percent of sources found leaking
The leaking and nonleaking emission factors generated by this procedure and
presented in the AID are shown in Table 3-3.
3.3.3.2 Computation of Average Emission Factors. Having computed
leaking and nonleaking emission factors in the above manner, average
emission factors can be determined by merely applying a leak frequency
determined from field studies. Continuing with the example from above, the
leak frequency for light liquid valves in SOCMI was found to be 6.5 percent
on Ihe average (based on the 24-Unit Study). For 1,000 valves in light
liquid service, an estimated 65 would leak at a rate, on the average, of
0.0852 kg/hr/valve, or 5.5 kg/hr. The 935 valves predicted to be not
leaking would account for an estimated 0.0017 kg/hr/valve, or 1.6 kg/hr. So
all 1,000 valves in light liquid service would have a predicted composite
leak rate of 7.1 kg/hr, for an average emission factor of
0.0071 kg/hr/source. This procedure, restated below in a more general form,
can be applied to a population of sources to determine the average emission
factor (AEF), provided the leak frequency of the population has been
established.
AEF - LEF * PCL -t- NLEF * HOP -
100
3-20
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TABLE 3-3. LEAKING AND NON-LEAKING EMISSION EACTORS FOR
FUGITIVE EMISSIONS (kg/hr/source)'
Equipment
Valves
Pump Seals
Compressor Seals6
Pressure Relief Valves
Flanges
Open-Ended Lines
Service
Gas
LLb
HLC
LL
HL
Gas
Gas
All
All
Leaking
(>10,000 ppm)
Emission Factor
0.26263
0.0852
0.00023d
0.437
0.3885
1.608
1.691
0.0375
0.01195
Non-leaking
(<10,000 ppm)
Emission Factor
0.0063
0.00171
0.00023
0.0120
0.0135
0.0894
0.0447
0.00006
0.00150
The leaking and non-leaking emission factors for valves in gas/vapor
service are based upon the emission factors determined for gas valves in
ethylene, cumene, and vinyl acetate units during the SOCMI Maintenance
Study. References 15 and 13.
LL - light liquid service.
HL - heavy liquid service.
Leaking emission factor assumed equal to non-leaking emission factor since
the computed leaking emission factor (0.00005 kg/hr/source) was less than
non-leaking emission factor.
eEmission factor reflects existing control level of 60 percent found in the
industry.
3-21
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3.4 EMISSION FACTORS PRESENTED IN THE AID
Table 3-4 presents the results of this estimation process for the leak
frequencies determined in the SOCMI 24-Unit Study. As the AID discussed,
these leak frequencies were considered to be representative values for a
cross-section of the large, diverse industry that is SOCMI. The average
emission factors computed based on these leak frequencies were used to
estimate emissions for the entire industry. As applied to the entire
population of sources in the industry, these "typical" average emission
factors were deemed appropriate for standards-setting activities. This was
particularly true because they were applied consistently to different
regulatory alternatives to arrive at comparisons.
EPA considered the variability of leak frequency in the industry in
developing its fugitive emission standards. The extension of the procedure
for generating emission factors considers the "typical" average emission
factor to be a function of leak frequency considered typical of the
industry. Also, in evaluating valve standards for low leak frequency plants,
the technical analysis included emission factors that varied with leak
frequency for valves. Results of this analysis provided support for the
provision in the SOCMI standards allowing annual monitoring for process
units with 2 percent or less valves leaking.
The average emission factors given in Table 3-4 were derived in a
straightforward manner using the leaking and non-leaking emission factors
from the Refining Assessment Study (derived in the manner just discussed)
and the leak frequencies from the SOCMI 24-Unit Study. There are two
instances where this approach was not used, however. These two cases
deserve specific mention.
First, the emission factor for sampling connections is based on the
amount of sample purge and not on a field-measured emission factor like
other source types. In essence, a sampling connection is considered either
"uncontrolled" (that is, the sample purge was assumed drained to the
environment) or "controlled" with the sample purge collected and returned to
the process line or disposed of properly. The actual value used for the
emission factor is based on the quantity of sampling purge reported for
3-22
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TABLE 3-4. AVERAGE EMISSION FACTORS FOR FUGITIVE EMISSIONS IN SOCMI
Equipment Component
"Average" SOCMI Factors
kg/hr/source
Pump Seals
Light Liquid
Heavy Liquid
Valves
Gas
Light Liquid
Heavy Liquid
Compressor Seals
Safety Relief Valves - Gas
Flanges
Open-Ended Lines
Sampling Connections
0.0494
0.0214
0.0056
0.0071
0.00023
0.228
0.104
0.00083
0.0017
0.0150
3-23
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25
1,000 barrels of refining throughput and the average count of sampling
connections reported for every 1,000 barrels of refining throughput
capacity. The ratio of these two values yields an emission factor of
0.0150 kg/hr/source. It is important to emphasize that emissions from
sampling connections do not include emissions through the seal or stem of
the sampling valve. These emissions are considered part of the emissions
from the valve and open-ended line categories.
The second case worthy of specific mention is the emission factor for
valves in gas service. After computing average emission factors using the
Refining Assessment leaking and non-leaking emission factors, a comparison
was made with the values determined for the three equipment types in
ethylene, cumene, and vinyl acetate process units presented in the SOCMI
Maintenance Study. From this comparison, the emission factor for gas valves
calculated from the Refining Assessment data appeared different from the
SOCMI values. The four emission factors for gas valves determined for
petroleum refining, ethylene units, cumene units, and vinyl acetate units
were then compared visually as in Figure 3-4. The confidence intervals for
the SOCMI gas valve emission factors are much narrower than those for the
refining emission factor. Furthermore, there is almost no overlap between
the SOCMI confidence intervals and those for petroleum refining. This
comparative analysis indicates that (1) the SOCMI gas valve factors are
different from the factor for petroleum refining and (2) the SOCMI gas valve
factors are better estimators of SOCMI gas valve emissions.
As a result of this comparative analysis, new leaking and non-leaking
emission factors for SOCMI gas valves were computed, based on data from the
SOCMI Maintenance Program. The final values used in forming the average
emission factor for SOCMI gas valves were:
- 0.0451 kg/hr/1eaking source and
- 0.00048 kg/hr/nonleaking source.
The factors for valves and pumps in light liquid service, shown in Figure
3-5, were not found to be different. Therefore, the emission factors
developed during the Refining Assessment Study (being based upon a more
substantial data base) were used as the basis for leaking and non-leaking
source emission factors.
3-24
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0.050
0.040
o
O
CO
0.030
O O
tO O
CO
CO
°'020
0.010
Vinyl
Acetate
Petroleum
Refining
Cumene
Ethylene
15
Leak Frequency (10,000 ppm), %
Figure 3-4. Comparison of Emission Factors: Gas Valves.
3-25
-------
Emission Factor, kg/hr/source
(95% confidence)
o
o
o
p
b
JPS
is =
sri
.0
C
O."
o
a
o
o
1
Emission Factor, kg/hr/source
(95% confidence)
p
o
o
o
~o
i
o
1
= 3
38
It
s
It
-------
These "typical" average emission factors presented in Table 3-4 would
also be appropriate for use in estimating emissions for process units where
no additional data are available. Taken on an individual basis, the factors
themselves represent a hypothetical "average", not necessarily any specific
unit or process. Given data on a specific process unit, average emission
factors could be generated using the procedure illustrated above for the
average SOCMI factors. For example, assume a process unit has been surveyed
for leaks (sources with screening values > 10,000 ppmv) and 4 percent of
light liquid valves were determined to be leaking. Then an average emission
factor for that unit could be computed as follows:
AEF = 0.0852 * (0.04) + 0.0017 * (1 - 004)
= 0.0051 kg/hr/source
The concept of an emission factor that varies with leak frequency is
also consistent with the data gathered during the SOCMI studies. Close
examination of Figure 3-14 shows some relationship of leak frequency and
average emission factor for gas valves in the three process units studied in
the Maintenance Study. Furthermore, there is wide variation in process unit
types across SOCMI, as evidenced in Table 3-5 by the variation in leak
frequencies for the process units in the 24-Unit Study. The causes of such
variation are many, but include chemicals processed, process parameters such
as operating temperatures and pressures, and the safety and maintenance
practices at a given site.
3.5 EXAMPLE HYPOTHETICAL CASE
In this section, an example of estimating emissions for a hypothetical
chemical process unit will be considered. This case assumes that the
process unit has been surveyed in accordance with Reference Method 21 and
that the leak frequencies have been established.
Table 3-6 shows this hypothetical process unit and a procedure for
estimating emissions using data in this report. The first column presents
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TABLE 3-5. LEAK FREQUENCIES BY PROCESS FOR EQUIPMENT IN 24 SOCMI UNITS12
Percent of Sources
Process
Vinyl Acetate
Ethyl ene
Cumene
Acetone/Phenol
Ethylene Dichloride
Vinyl Chloride
Formaldehyde
Methyl Ethyl Ketone
Acetaldehyde
Methyl Methacrylate
Adipic Acid
Chlorinated Ethanes
Acrylonitrile
1,1,1-Trichloro-
_ j. i
Valves,
Gas
3.7
14.8
14.1
0
1.0
7.3
2.4
9.2
4.5
0
0
0
2.3
-
Valves,
Light Liquid
0.4
23.2
10.5
0.3
1.1
1.0
0
5.1
0.5
0.1
0
0.6
0.9
1.1
Pumps,
Light Liquid
4.5
26.3
16.0
2.3
5.2
10.8
0
3.2
9.4
4.4
-
8.3
8.2
10.0
Leaking
Flanges
1.0
5.7
2.9
0
1.1
3.2
10.0
0
0
0
0
0
0.4
0
Open-Ended
Lines
3.7
12.8
9.1
1.3
2.8
5.1
0
9.9
5.7
0.3
0
1.4
2.7
1.8
3-28
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TABLE 3-6. ESTIMATE OF "UNCONTROLLED" FUGITIVE EMISSIONS
FOR A HYPOTHETICAL CASE
Source
Pump Seals
Light Liquid
Heavy Liquid
Valves
Gas/Vapor
Light Liquid
Heavy Liquid
Pressure Relief Valves
Gas/Vapor
Open-Ended Lines
Compressor Seals
Sampling Connections
Flanges
Number
Screened
47
3
625
1180
64
31
278
4
70
2880
Computed
Number Percent Emission Factor
Leaking Leaking kg/hr/source
3 6.4
1 33.3
19 3.0<:
13 1.1C
0 0
1 3.2
9 3.2
0 0
-
20 0.7
0.0256
0.1385
0.0018
0.0026
0.00023
0.0978
0.0018
0.0894
0.0150
0.00032
Annual
Emissions
Mg/yr
10.5
3.6
9.9
26.9
0.1
28.2
4.1
3.1
9.2
8.1
aBased on values from Table 3-3, using AEF - (LEF * PCL + NLEF * (100-PCL))/100.
bAssumes 8,760 hours of operation annually.
Composite percent leaking for valves is 1.8%. NOTE - In this case, valves would only
need monitoring annually to ensure less than 2 percent leaking.
3-29
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the number of sources identified in the process unit for each source type.
The second column shows the number of sources with screening values greater
than or equal to 10,000 ppmv (i.e., leaking sources). The resulting
percentage of sources leaking is shown in the third column. The average
emission factors for this hypothetical process unit can then be computed
using the leaking and non-leaking emission factors found in Table 3-3. For
example, 6.4 percent of pump seals in light liquid service were found to be
leaking. Using the leak/no-leak approach, the unit-specific emission factor
is estimated as:
(0.437 kg/hr/source)(0.064) + (0.012 kg/hr/source)(l - 0.064),
or 0.0256 kg/hr/source. The total estimated emissions for pumps in light
liquid service would then be computed by multiplying the unit-specific
emission factor by the equipment count. The last column in Table 3-6 shows
the results of this process for the hypothetical unit.
A further extension of this procedure would be to examine the procedure
to estimate the emission factor for a certain specie in the line. For
example, consider this same hypothetical case, where the light liquid pumped
contained 20 percent of compound A. The compound A emission factor for
light liquid pumps is easily computed by applying the weight percent (20
percent in this case) to the emission factor generated above:
(0.20)(0.0256 kg/hr/source) = 0.0051 kg/hr/source.
Emission factors calculated in this manner could then be applied to the
equipment counts (where the material in the process line contained 20
percent of compound A) to estimate emissions of compound A.
3-30
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4.0 EMISSION REDUCTION
No single emission reduction technique can be used for all fugitive
emission sources. The techniques applicable to fugitive emission sources
range from equipment to work practices. The various control techniques
considered were described briefly in the earlier section on fugitive
emission sources. They are covered in this section in the context of their
emissions reduction potential.
4.1 OVERVIEW OF TECHNIQUES
The techniques used to control emissions from equipment leaks can be
classified into two categories: equipment and work practices. An equipment
control technique means that some piece of equipment is used to reduce or
eliminate emissions. A common example is an add-on control device such as an
incinerator that is used to reduce organic emissions from a process vent.
For fugitive emission sources, equipment controls include: (1) leakless
technology for valves and pumps; (2) plugs, caps, blinds, etc. for
open-ended lines; (3) rupture disks and soft-seats (0-rings) for PRVs; (4)
dual mechanical seals with non-VOC barrier fluid/degassing vent systems for
rotary equipment; (5) closed loop sampling systems; and (6) enclosure of
seal area/vent to a combustion control device for dynamic seals. These
equipment control techniques can generally attain up to 100 percent
reduction of emissions, depending upon the control efficiency of the control
device. Mechanical seals and those techniques that rely upon a combustion
control technique have been assigned an overall control efficiency of 95
percent, which is consistent with the efficiency assigned to some typically
applied recovery techniques.
The control techniques used for the largest number of fugitive emission
sources are work practices. The primary work practice applied to PRVs,
valves, pumps, and other sources is leak detection and repair of sources.
4-1
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4.2 LEAK DETECTION AND REPAIR (LDAR)
The emissions reduction potential for LDAR as a control technique is
highly variable depending upon several factors. The principal element
impacting emissions reduction is the frequency of monitoring (surveying)
sources for leak detection. For example, a monthly monitoring plan would
typically be more effective in reducing emissions than a quarterly
monitoring plan since leaks would be found and corrected more quickly. Some
characteristics of individual sources also affect emissions reduction:
leaking emission factor (as compared to the nonleaking emission factor),
leak occurrence rate, leak recurrence rate, and repair effectiveness.
Gathering of these data for valves and pumps through extensive field testing
was the focus of the SOCMI Maintenance Study.
Using specific source characteristics, an evaluation of control
effectiveness can be made for different monitoring plans using the LDAR
Model. The model is a set of recursive equations that operates on an
overall population of sources that can be segregated into the following
subgroups for any given monitoring interval: (1) sources that leak due to
the leak occurrence rate; (2) sources that leak and cannot be repaired below
the 10,000 ppmv leak definition; (3) sources that leaked, were repaired
successfully, but leaked again soon after the repair (i.e., leak
recurrence); and (4) sources that do not leak (i.e., those screening below
the 10,000 ppmv leak definition). The relative numbers of sources in each
subgroup change with each monitoring interval step, based on the
characteristics for the sources. Figure 4-1 shows these subgroups and how
they may interact according to the individual source characteristics.
The LDAR Model also has the capability to examine complex monitoring
plans such as the plan permitted by EPA under its fugitive emissions
standard for valves in SOCMI. This plan allows quarterly monitoring of all
valves, supplemented with monthly monitoring of those valves that leaked and
were repaired.
4-2
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CO
< !«
«|*I«««M:« a«cc*«*f«l.
Figure 4-1. Schematic Diagram of the LDAR Model.
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Perhaps the best way to illustrate the LDAR Model is to present an
example. The particular example considered here is the "typical" SOCMI unit
presented in the AID. Table 4-1 shows the inputs used in examining a LDAR
program for valves and pumps based on monthly monitoring. The input values
were derived primarily from the SOCMI Maintenance Study. The selection of
each input value is detailed in the AID. The LDAR Model used to estimate
emissions reductions gives incremental results as well as results for a
program that has been established. For the example, once a monthly
monitoring plan is in place, emissions reductions of 73 percent and 59
percent can be expected for valves in gas and light liquid services;
likewise a 61 percent reduction in emissions can be achieved for pumps in
light liquid service under a monthly LDAR plan.
Table 4-2 presents the results of LDAR modeling published in the AID
for valves and pumps in SOCMI. The table presents results for simple
monthly, quarterly, semiannual, and annual monitoring of valves and pumps.
Additionally, the monthly/quarterly hybrid program allowed by EPA for valves
is shown. These results show that, as monitoring frequency is increased,
the anticipated emissions reduction increases. Further, the results
indicate some instances where there is no positive effect in reducing
emissions due to monitoring and repair on too infrequent a schedule. Such
results, however, are subject to interpretation for specific cases since
they are based on "average" input values for an entire industry.
The ability to model the results of LDAR programs provided the means to
examine alternative standards for valves. The LDAR Model was used to
consider monthly LDAR programs for process units exhibiting low leak
frequencies. With decreasing leak frequency, there is an associated decline
in the average emission factor and emissions reduction. Coupling this
information with the costs of the LDAR program, an analysis of the resultant
cost effectiveness values led to the selection of 2 percent leaking as the
performance limit. Thus, process units with low leak rates (and low leak
frequencies) were given a special provision in the NSPS for SOCMI fugitive
VOC emissions.
4-4
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TABLE 4-1. LDAR INPUTS AND COMPUTED REDUCTIONS FOR SOCMI/MONTHLY MONITORING
Input
Emission factor,
kg/hr/source
Occurrence rate
Initial leak
frequency
Fractional emission
Description
Initial average emission
factor for all sources
Fraction of nonleakers that
became leakers over the
interval
Fraction of sources leaking
at initiation of LDAR program
Reduction from sources not
Valves,
Gas/Vapor
0.0056
0.013
0.114
0.63
Valves,
Light
Liquid
0.0071
0.013
0.065
0.63
Pumps,
Light
Liquid
0.0494
0.034
0.088
0
reduction from
unsuccessful repair
Fractional emission
reduction from
successful repair
Fraction of un-
successful repairs
Fraction of early
failures
Turnaround frequency,
months
repaired below 10,000 ppmv
Reduction from sources 0.98
repaired below 10,000 ppmv
Sources that leaked but 0.10
attempted repair below
10,000 ppmv failed
Sources repaired below 0.14
10,000 ppmv but leaked
within the next interval
Period between plant 24
shutdowns
0.98
0.10
0.14
24
0.972
24
EMISSION REDUCTION COMPUTED:
0.73
0.59
0.608
4-5
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TABLE 4-2. LDAR MODEL RESULTS FOR SOCMI VALVES AND PUMPS
Monitoring Interval
Monthly
Monthly/Quarterly3
Quarterly
Semi-annual
Annual
Valves, Gas
0.73
0.65
0.64
0.50
0.24
Source Tvoe
Valves,
Light Liquid
0.59
0.46
0.44
0.22
(0.19)
Pumps,
Light Liquid
0.61
-
0.33
(0.076)
(0.80)
aMonthly monitoring with quarterly monitoring of "low leak" components.
NOTE: Numbers in parentheses indicate a negative control efficiency. Negative
numbers are generated when the occurrence rate for the monitoring interval
exceeds the initial leak frequency. Negative results are subject to inter-
pretation and may not be meaningful.
4-6
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4.3 -SUMMARY OF EMISSION REDUCTIONS
Emissions reductions for fugitive emissions control techniques can be
extremely variable, particularly for work practices like leak detection and
repair programs. In terms of standard-setting activities, criteria for
selection of a given control technique or a particular level of control
(eg., monitoring interval of a leak detection and repair program) can be
quite different. For example, the criterion used in establishing the best
demonstrated technology (BDT) for NSPS may not necessarily be equivalent to
the choice in setting the reasonably available control technology (RACT)
presented in control techniques guidelines (CTG) documents used by States.
These two levels of control are compared in Table 4-3 for VOC equipment
leaks (fugitive emissions) from SOCMI; the associated control effectiveness
values are also presented.
4-7
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TABLE 4-3. CONTROL LEVELS FOR SOCMI FUGITIVE EMISSIONS: NSPS AND CTG
CO
Source
Pumps* Light Liquid
Valves, Gas
Light Liquid
Pressure Relief
Valves, Gas
Open-Ended Lines
Compressors
Sampling Connections
CTG NSPS
Percent Percent
Control Technique Control Control Technique Control
Quarterly leak detection and repair 33 Monthly leak detection and repair
Dual mechanical seal/heavy liquid
barrier fluid
Quarterly leak detection and repair 64 Monthly leak detection and repair
44
Quarterly leak detection and repair 44 Rupture disk, soft seats (0-rlngs),
vent to control device
Plugs, caps, blinds, etc. 100 Plugs, caps, blinds, etc.
Quarterly leak detection and repair 33 Seal enclosed/vented to control device
Closed purge sampling
61
100
73
59
100
100
100
100
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5.0 LISTS OF REFERENCES
1. U.S. Environmental Protection Agency. VOC Emissions in Synthetic Organic
Chemicals Manufacturing Industry - Background Information for Promulgated
Standards. Research Triangle Park, N.C. Publication No.
EPA-450/3-80-033b. June 1982.
2. Memo from Stelling, J.H.E., Radian Corporation, to SOCMI Docket.
November 1, 1982. 10 p. Estimate of VOC Emissions from SOCMI.
3. Honerkamp, R. L. and M. L. Schwendemen. (Radian Corporation.)
Evaluation of Maintenance Effect on Fugitive Emissions for Refineries in
the South Coast Air Quality Management district. (Prepared for U.S.
Environmental Protection Agency.) Research Triangle Park, N.C.
Publication No. EPA-600/7-82-049. June 1982.
4. American Petroleum Institute. Guide for Pressure Relief and Depressuring
Systems. API RP 521, First Edition. September 1969.
5. Palmer, R. K. Hydrocarbon Losses from Valves and Flanges. Joint
District, Federal and State Project of the Evaluation of Refinery
Emissions. Report No. 2. March 1957.
Steigerwald, B. J. Hydrocarbon Leakage from Pressure Relief Valves.
Joint District, Federal and State Project of the Evaluation of Refinery
Emissions. Report No. 3. May 1957.
Steigerwald, B. J. Emissions of Hydrocarbons to the Atmosphere from
Seals on Pumps and Compressors. Joint District, Federal and State
Project of the Evaluation of Refinery Emissions. Report No. 6. April
1958. .
6. Wetherold, R.G., L.P. Provost, and C.D. Smith. (Radian Corporation.)
Assessment of Atmospheric Emissions from Petroleum Refining,
(Prepared for U.S. Environmental Protection Agency.) Research Triangle
Park, N.C. Publication No. EPA-600/2-80-075a-d. April 1980.
7. U.S. Environmental Protection Agency. Fugitive Emission Sources of
Organic Compounds - Additional Information on Emissions, Emission
Reductions, and Costs. Research Triangle Park, N.C. Publication No.
EPA-450/3-82-010. April 1982.
8. Memo from Hustvedt, K.C., EPArCPB, to Durham, J.F., EPA:CPB.
December 2, 1980. 170 p. MRC SOCMI Fugitive Testing.
9. U.S. Environmental Protection Agency. Air Pollution Emission Test at
Dow Chemical Company. Research Triangle Park, N. C. EMB Report
No. 78-OCM-12C.
U.S. Environmental Protection Agency. Air Pollution Emission Test at
Union Carbide Corporation. Research Triangle Park, N.C. EMB Report
No. 78-OCM-12A.
5-1
-------
U.S. Environmental Protection Agency. Air Pollution Emission Test at
Stauffer Chemical Co. Research Triangle Park, N.C. EMB Report
No. 78-OCM-12D.
U.S. Environmental Protection Agency. Air Pollution Emission Test at
Phillips Petroleum Co. Research Triangle Park, N.C. EMB Report
No. 78-OCM-12E.
U.S. Environmental Protection Agency. Air Pollution Emission Test at
Refinery E. Research Triangle Park, N.C. EMB Report No. 78-OCM-12F.
10. Meeting Report. Honerkamp. R., Radian Corporation, to Hustvedt, K.C.,
EPA:CPB, and distribution list. June 12, 1979. 14 p. Minutes of
meeting between EPA and DuPont representatives about fugitive emission
sampling.
11. Letter and attachment from Cox, J.B., Exxon Chemical Company, to
Weber, B., EPArCPB. February 21. 1978. 4 p. Copy of letter about
cyclohexane unit fugitive loss data sent to Hydroscience.
Letter and attachment from Cox, J.B., Exxon Chemical Company, to Walsh,
R.T., EPA:CPB. March 21, 1979. 4 p. Information about cyclohexane
unit.
12. Blacksmith, J. R., et al. (Radian Corporation.) Problem-Oriented
Report: Frequency of Leak Occurrence for Fittings in Synthetic Organic
Chemical Plant Process Units. (Prepared for U.S. Environmental
Protection Agency.) Research Triangle Park, N.C. Publication No.
EPA-600/2-81-003. September 1980.
13. Langley, G. J. and R. G. Wetherold. (Radian Corporation.) Evaluation of
Maintenance for Fugitive VOC Emissions Control. (Prepared for U.S.
Environmental Protection Agency.) Research Triangle Park, N.C.
Publication No. EPA-600/52-81-080. May 1981.
14. Langley, G. J. et al. (Radian Corporation.) Analysis of SOCMI VOC
Fugitive Emissions Data. (Prepared for U.S. Environmental Protection
Agency.) Research Triangle Park, N.C. Publication No. EPA-600/2-81-111
June 1981.
15. Langley, G.J., and L.P. Provost. (Radian Corporation.) Revision of
Emission Factors for Nonmethane Hydrocarbons from Valves and Pump Seals
in SOCMI Processes. Technical Note. (Prepared for U.S. Environmental
Protection Agency.) Research Triangle Park, N.C. November 1981.
16. Schwanecke, R. "Air Pollution Resulting from Leakage from Chemical
Facilities." Luftverun-reinicmna. 1970, pp. 9-15. Translated for the
U.S. Environmental Protection Agency by SCITRAN. Santa Barbara,
California.
5-2
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Kremer, H. "Leakages from Static and Dynamic Seals in Chemical and
Petrochemical Plants." 4th Meeting OG EW/DGMK. Salzburg. October 1976
Translated for the U.S. Environmental Protection Agency by SCITRAN, Santa
Barbara, California.
Bierl, Alois, et al. "Leakage Rates of Sealing Elements." Chem. Ina.
Tech. 49 (No. 2) 1977, pp. 89-85. Translated for the U.S. Environmental
Protection Agency by SCITRAN. Santa Barbara, California.
Schwanecke, R. "Air Pollution Through Small Leakages for Equipment of
the Chemical Industry and Ways for Their Prevention." Translated for the
U.S. Environmental Protection Agency by SCITRAN. Santa Barbara,
California.
17. Lee, Kun - Chich, et al. (Union Carbide Corporation. South Charleston,
West Virginia.) "A Fugitive Emission Study in a Petrochemical
Manufacturing Unit." Presented at the 73rd Annual Meeting of the Air
Pollution Control Association in Montreal, Quebec. June 22-27, 1980.
18. Harvey, Cynthia M. and A. Carl Nelson. (PEDCo Environmental Inc.) VOC
Fugitive Emission Data - High Density Polyethylene Process Unit.
(Prepared for U.S. Environmental Protection Agency.) Research Triangle
Park, N.C. Publication No. EPA-600/2-81-109. June 1981.
19. DuBose, D.A., et al. (Radian Corporation.) Emission Factors and Leak
Frequencies for Fittings in Gas Plants. (Prepared for U.S. Environmental
Protection Agency.) EMB Report No. 80-FOL-l. Research Triangle Park,
N.C. July 1982.
20. Wiesenborn, D.P., et al. (Radian Corporation.) Leak Frequency and
Emission Factors for Fittings in Coke Oven By-Product Plants. (Prepared
for U.S. Environmental Protection Agency.) EMB Report No. 81-BYC-12.
Research Triangle Park, N.C. January 1982.
21. Wetherold, R. G., L. P. Provost, and C. D. Smith. (Radian Corporation.)
Assessment of Atmospheric Emissions from Petroleum Refining, Appendix B:
Detailed Results. (Prepared for U.S. Environmental Protection Agency.)
Research Triangle Park, N.C. Publication No. EPA-600/2-80-075c. April
1980.
22. Reference 3.
23. Eaton, W.S., et al. Fugitive Hydrocarbon Emissions from Petroleum
Production Operations. American Petroleum Institute Publication
No. 4322. 1980.
24. Harris, G. E. (Radian Corporation.) Emission Test Report: Fugitive
Test Report at the Gulf Venice Gas Plant, Volume I. (Prepared for U.S.
Environmental Protection Agency.) Research Triangle Park, N.C. EMB
Report No. 81-OSP-8. July 1981.
5-3
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Harris, G. E. (Radian Corporation.) Emission Test Report: Fugitive VOC
Testing at the Texas Paradis Gas Plant, Volume I. (Prepared for U.S.
Environmental Protection Agency.) Research Triangle Park, N.C. EMB
Report No. 80-OSP-7. July 1981.
25. U.S. Environmental Protection Agency. Compilation of Air Pollutant
Emission Factors. Research Triangle Park, N.C. AP-42. February 1980.
26. Powell, D., et al. (PES, Inc.) Development of Petroleum Refinery Plot
Plans. (Prepared for U.S. Environmental Protection Agency.) Research
Triangle Park, N.C. Publication No. EPA-450/3-78-025. June 1978.
27. Williamson, H. J., et al. (Radian Corporation.) Model for Evaluating
the Effects of Leak Detection and Repair Programs on Fugitive Emissions.
Technical Note DCN 81-290-403-06-05-03. September 1981.
5-4
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-450/3-86-002
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Emission Factors for Equipment Leaks of VOC and HAP
5. REPORT DATE
February 10. IQflfi
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
John H. E. Stelling III
8. PERFORMING ORGANIZATION REPORT NO
DCN 86-203-024-63-06
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Radian Corporation
3200 E. Chapel Hill Road/Nelson Highway
Research Triangle Park, M.C. 27709
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-02-3889, WA 63
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Emission Standards and Engineering Division
Research Triangle Park, M.C. 27711
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
Project Officer is Robert E. Rosensteel, Mail Drop 13, (919) 541-5605.
16. ABSTRACT
The report summarizes the development of emission factors for volatile organic
compound (VOC) equipment leaks. The background information used in emission factor
development is reviewed. The estimation techniques for generation of VOC emission
factors are described and illustrated with an example. The application of the
estimation techniques is demonstrated for both VOC and hazardous air pollutants
(HAPs).
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Fugitive Emissions
Volatile Organic
Compounds
Hazardous Air Pollutants
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70
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