&ER&
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S2-81 -111 Sept. 1381
Project Summary
Analysis of SOCMI VOC
Fugitive Emissions Data
G. J. Langley, S. M. Dennis, J. F. Ward, and L. P. Provost
The report gives results of an exami-
nation of fugitive emissions data from
Synthetic Organic Chemical Manufac-
turing Industry (SOCMI) processing
units (collected under earlier EPA
studies) for correlations between
process variables and leak frequency.
Although line temperature did not
have a consistent relationship with
leak frequency, the data showed that
leak frequency increased with increas-
ing line pressure. Also, emissions
factors for three process types (vinyl
acetate, cumene, and ethylene) were
developed and presented. Increases in
mass emissions due to occurrence and
recurrence of leaks for these three
process types are also estimated.
Finally, the effect of adjusting portable
hydrocarbon readings by chemical
response factor curves on leakage
frequency estimates is investigated.
Despite the wide range of response
factors encountered, the adjusted leak
frequencies were essentially the same
as the unadjusted frequencies.
This Project Summary was devel-
oped by EPA's Industrial Environmen-
tal Research Laboratory. Research
Triangle Park, NC. to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
The contribution of fugitive leaks from
process unit components are being
investigated as a potential source of
Volatile Organic Compound (VOC) emis-
sions in the Synthetic Organic Chemical
Manufacturing Industry (SOCMI). The
purpose of this study was to provide an
in-depth analysis of data on emissions
collected under EPA contracts 68-02-
3171-1,68-02-3173-2 and -11, 68-02-
3174-5, and 68-02-3176-1 and -6, and
68-03-2776-4. These data were col-
lected by Radian, PEDCo, TRW, and
Acurex and are summarized in EPA
reports EPA-600/2-81-003 (NTIS PB
81-141566) and 600/2-81-080 (NTIS
PB 81 -206005). The results of this study
will be available for use in evaluating
VOC fugitive emissions.
The study design and test procedures
for the data analyzed in this report are
described in the above-mentioned EPA
reports. The 24 process units studied in
the data collection programs were
selected to represent a cross-section of
the population of the SOCMI. Several
factors were considered during process
unit selection, including total annual
production in volume, number of
producers, process conditions, cor-
rosivity, volatility, toxicity, and value of
the final chemical product. Factors
varied widely from unit type to unit type,
so that the selected process unit types
represented a reasonable sample of the.
variety of chemical process .units en-
countered in SOCMI.
The leak frequency in SOCMI was
evaluated by the collection of screening
data from 24 process units, where a
screening value is the maximum re-
peatable concentration of total hydro-
carbons detected at a source with a
portable hydrocarbon detector. Main-
tenance was evaluated by measurement
of fugitive emission leak rates (Ip/hr) at
-------
selected sources before and after
maintenance at six process units
representing three chemical processes.
The results of these two programs
provide the background necessary for
the current study:
• Source population data.
• Screening value profiles for each
source type.
• Screening-to-emission rate rela-
tionships.
The screening procedures began with
the definition of the process unit
boundaries. All feed streams, reaction/
separation facilities, and product and
by-product delivery lines were identified
on process flow diagrams and in the
process unit. Process data, including
stream compositions, line temperatures,
and line pressures, were obtained for all
flow streams.
The Century Systems Models OVA-
108 and OVA-128 hydrocarbon detectors
were used for screening. The detector
probe of the instrument was placed
directly on those areas of the sources
where leakage would typically occur.
For example, gate valves were screened
along the circumference of the annular
area around the valve stem where the
stem exits the packing gland and at the
packing-gland/valve-bonnet interface.
The actual leak rates were measured
using a flow-through method described
in report EPA-600/2-80-075a (NTIS PB
80-225253), and were analyzed on
Byron Total Hydrocarbon Analyzer.
All accessible sources of the follow-
ing source types were screened:
• Process valves.
• Pump seals.
• Compressor seals.
• Agitator seals.
• Relief valves.
• Process drains.
• Open-ended lines.
Also, a randomly selected subset of
flanges were screened. Originally, only
5 percent of all flanges were screened.
The subset was increased to 20 percent
of all flanges when initial results indi-
cated a higher frequency of emitting
flanges than had been encountered in
previous programs. The important var-
iables available from this study are:
screening value, source category, stream
service, source type, chemical produced,
ambient temperature elevation, line
temperature, and line pressure. For the
purposes of this report, a source is
defined as "leaking" if its screening
value is greater than or equal to 10,000
ppmv.
This summary presents conclusions
based on four distinct data analysis
tasks: 1) an analysis of important corre-
lating process parameters (line pres-
sure, etc.); 2) emission factor develop-
ment for three specific chemical
processes (seven units); 3) an evalua-
tion of the increase in mass emissions
due to occurrence and recurrence of
leaks; and 4) an analysis of the impact
on leak frequency from adjusting
screening values by VOC detector
response factors.
Conclusions
1) Relationship of Leak Frequency to
Process Parameters
The process parameters that were
examined for their effect on leak
frequency were: process, service,
material in the line, line pressure, line
temperature, ambient temperature, and
source elevation. Data on four source
types (valves, pump seals, flanges, and
open-ended lines) were used to exam-
ine the effects of these parameters. The
sources were grouped into 32 categories
based on source type, process type,
stream service, and primary chemical in
the line. These groupings were for
statistical reasons and were not based
on engineering reasoning.
Stream service was defined as gas,
light liquid, or heavy liquid. Heavy
liquids were not included in any
analyses, since they leaked so rarely
regardless of the other conditions. Gas
stream service generally had a higher
leak frequency than light liquid service.
Proceeding with four source types and
two stream service types, the data were
then categorized by process unit as
ethylene processes, high leaking proc-
esses, or low leaking processes. The
ethylene units were analyzed separately
because of the large number of sources
in ethylene processes and their high
leak frequency. The high leaking group
consisted of all other units with greater
than 1 percent of all source types
leaking. The low leaking group consisted
of all units with less than 1 percent of all
source- types leaking. Since very few
sources leaked, the low leaking process
units were not considered in further
analyses. Within these process unit
groups, the data were further subdivided
by primary materials in the line. Caution
should be used in these evaluations,
however, since other chemicals in the
line may also have an effect on leak
frequency.
Examination of the data within these
categories resulted in the following
conclusions for this data set:
• Leak frequency was affected not
only by the type of chemical
process but also by the type of
primary material in the line.
• Control valves had a higher leak
frequency than block valves.
• For block valves, gate valves had a
higher leak frequency than most of
the other types, and plug and ball
valves had lower leak frequencies.
• On-line pump seals had an overall
leak frequency of 13.1 percent
versus 4.9 percent for off-line
pump seals.
• These data did not show a differ-
ence in leak frequency between
double and single mechanical
pump seals, although the type of
barrier fluid was unknown and
therefore unaccounted for in this
analysis.
• Line pressure was seen to have a
statistically significant effect in
almost every case, with higher
levels of pressure associated with
higher leak frequencies.
• Line temperature had no consistent I
effect on leak frequency. The
combined effect of line pressure
and temperature was important in
some cases.
• Ambient temperature had a con-
sistent effect on leak frequency;
however, the effect was not statis-
tically significant for a majority of
the cases. Higher leak frequencies
tended to be associated with the
higher ambient temperature cate-
gory.
• Elevation had no consistent effect
on leak frequencies. In the four
cases where a statistically signifi-
cant effect was observed, sources
at ground level had a higher leak
frequency than sources at higher
elevations.
2) Emission Factor Development
The sources included in the develop-
ment of the emissions factors are all
valves and pump seals screened in the
seven ethylene, cumene, and vinyl
acetate process units, or 51.2 percent
(16,575) of all valves and pump seals
screened in the screening program.
Since leak rate screening value models
were only developed for these three
process types, emissions factor estima-
tion was limited to these three processes..
The emissions factors developed inJ
this study are reported in Table 1. The"
-------
Table 1 Estimated Emission Factors for Nonmethane Hydrocarbons from Valves and Pump Seals
Emissions Factor (95% Confidence Interval)
Source Type
(Ib/hr)
(kg/hr)
Valves
— Gas Service
Ethylene processes
Cumene processes
Vinyl acetate processes
— Light Liquid
Ethylene processes
Cumene processes
Vinyl acetate processes
Pump Seals
— Light Liquid
Ethylene processes
Cumene processes
Vinyl acetate processes
0.024(0.008, 0.07)
0.011(0.003, 0.05)
0.0046(0.001, 0.03)
0.020(0.007, 0.06)
0.0056(0.002, 0.02)
0.0003(0.0001, 0.002)
0.069(0.006, 0.8)
0.052(0.001, 2.7)
0.0043(0.0001, 0.1)
0.011(0.004, 0.03)
0.0052(0.001, 0.02)
0.0021(0.0004, 0.01)
0.010(0.003, 0.03)
0.0025(0.001, 0.01)
0.0001(0.00003, 0.001)
0.031(0.003, 0.4)
0.023(0.0004, 1.2)
0.0020(0.00006, 0.06)
emissions factors for the ethylene
process are consistently higher than the
factors for the cumene and vinyl acetate
processes. The vinyl acetate process
tends to have the lowest emissions
factors of the three process types.
Cumulative distributions of screening
values and mass emissions as a
function of screening values were also
I developed for each of the three proc-
esses. Table 2 gives the estimates and
confidence intervals from these curves
for a 10,000 ppmv screening value.
3) Increase in Mass Emissions Due to
Occurrence and Recurrence
Data collected during the EPA SOCMI
maintenance program were further
analyzed to estimate the effects of leak
occurrence and recurrence on mass
emissions. The following conclusions
are based on these analyses:
• The increase in emissions for
valves for which a leak occurred
over a 1 to 6 month period was
estimated to be 530 percent (95
percent confidence interval of 200
to 900 percent).
• Not enough data was available to
accurately quantify the effect on
emissions from leak occurrence
from pump seals. However, the
percent increase estimate was 75
percent with a 95 percent confi-
dence interval of -100 to 6000
percent.
• The percent increase in emissions
for valves with a leak recurrence
within the 6 month period was
estimated to be 510 percent (95
percent confidence interval of
-100 to 1700 percent).
• Further analysis of the effect of
valve maintenance on emissions
showed a 98 percent reduction in
emissions for valves which were
"repaired" (screening value <10,000
ppmv after maintenance) and a 63
percent reduction for sources
which were "not repaired"(screen-
ing value remained >10,000 ppmv
after simple, on-line maintenance).
4) Impact of Response Adjustments on
Leak Frequency Estimation
Three different techniques were used
to adjust the original screening value for
each source:
Table 2.
Summary of Percent of Sources Distribution Curves and Percent of Mass Emissions Curves at Screening Value
of 10,000 PPMV
Percent of Sources
Screening >10,000 ppmv
Percent of Mass Emissions
Attributable to Sources
Screening > 7 0,000 ppmv
Source Type
Valves
Gas
Ethylene
Cumene
Vinyl acetate
Light Liquid
Ethylene
Cumene
Vinyl acetate
Pump Seals
Light Liquid
Ethylene
Cumene
Vinyl acetate
Estimate
15
16
3.7
26
12
0.2
30
14
1.7
95% Confidence
Interval .
(14, 16)
(13, 19)
(2,5)
(24, 27)
(10, 13)
(0, 0.4)
(20, 39)
(1. 27)
(0,4)
Estimate
94
94
90
89
80
25
96
89
67
95% Confidence
Interval
(93, 95)
(90, 96)
(85. 94)
(87, 90)
(72, 86)
( 9. 47)
(90, 98)
(50, 98)
( 5, 92)
-------
• The original OVA reading adjusted
for the associated OVA response
relationship of the primary chemi-
cal compound in the line.
• Weighted logarithmic average of
response of primary and secondary
chemicals.
'• Weighted arithmetic average of
response of primary and secondary
chemicals.
The percent of leaking valves was
calculated for each of the three esti-
mates for both gas and light liquid
services. The three estimates were
found to be similar in most cases to the
leak frequency based on the original
screening values. Table 3 presents the
overall results.
4
Table 3. Comparable Estimates for Percent Leaking (Valves/
(24 SOCMI Process Units)
Process
Stream
Gas
Light
Liquid
Number
Screened3
9,374
18,133
Percent
Leaking
Based on
OVA
Readings
11.3
6.1
Percent
Leaking
Based on
Method 1
Adjustments*
10.1
5-3
Percent
Leaking
Based on
Method 2
Adjustments0
10.2
5.6
Percent
Leaking
Based on
Method 3
Adjustments*
10.3
5.5
*119 sources with soreening values = 1O.OO1 ppmv were excluded.
^Method 1 is the adjustment to the OVA reading based on the response of the primary
chemical in the line.
"Method 2 is the mixed chemical weighted logarithmic average technique.
aMethod 3 is the mixed chemical weighted average technique.
G. J. Langley, S. M. Dennis, J. F. Ward, and L. P. Provost are with Radian Corp.,
P.O. Box 9948, Austin, TX 78766.
Bruce A. Tichenor is the EPA Project Officer (see below).
The complete report, -entitled "Analysis of SOCMI VOC Fugitive Emissions
Data," (Order No. PB 81-234 270; Cost: $18.50, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
------- |