United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-95/046
May 1995
w EPA Project Summary
Glycol Dehydrator
BTEX and VOC Emission
Testing Results at Two Units in
Texas and Louisiana
C.O. Rueter, D.L Reif, D.B. Myers
Glycol dehydrators are used in the
natural gas industry to remove water
from natural gas and, in the process,
may also remove and emit significant
quantities of benzene, toluene, ethyl-
benzene, and xylenes (BTEX). The ob-
jective of this project was to collect
emissions test data at two triethylene
glycol (TEG) units to provide data for
comparison to GRI-GLYCalc™, a com-
puter program developed to estimate
emissions from glycol dehydrators.
Three analytical techniques were used
to determine emissions: total capture
condensation, pressurized glycol cyl-
inders, and atmospheric rich/lean gly-
col sampling.
Site 1 test results, using the various
techniques, yielded BTEX emission es-
timates that agreed reasonably well.
Total volatile organic compound (VOC)
emissions from the two glycol meth-
ods did not match well with the total
capture benchmark results; this is con-
sistent with previous results for sys-
tems without flash tanks. Site 2 atmo-
spheric rich/lean glycol and pressur-
ized glycol emission results agreed
closely with the total capture results
for both BTEX and total VOCs. GRI-
GLYCalc predictions using natural gas
samples taken before the glycol ab-
sorber agreed well with the total cap-
ture results for total BTEX emissions.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Tri-
angle Park, NC, to announce key find-
ings of the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Overview
The Emissions and Modeling Branch
(EMB) of EPA's Air and Energy Engineer-
ing Research Laboratory was established
to develop new and improved emissions
inventory methodologies for use by states.
New improved methods are reviewed by
the Emission Factor and Inventory Group
of EPA's Office of Air Quality Planning
and Standards (OAQPS). New methods
approved by OAQPS are incorporated into
EPA guidance documents for state use in
preparing emissions inventories required
by the Clean Air Act.
Emissions estimation procedures for gly-
col dehydrators are not available in cur-
rent EPA emissions estimation guidance.
EMB held discussions with the Gas Re-
search Institute (GRI) and the American
Petroleum Institute (API) and determined
that they were actively involved in the
development of process models for esti-
mation of emissions from glycol dehydra-
tors. An industry working group, chaired
by GRI, had begun a program to develop
field testing methods and to collect emis-
sions test data. The testing program and
associated emissions model development
were of immediate interest to EMB as a
potential tool for estimating emissions from
glycol dehydrators. EPA, GRI, and API
agreed that it would be appropriate for
EMB to supplement the industry program
with an independent EPA testing program
to assess the acceptability of the process
emissions model as an approved method
for inclusion in EPA emissions estimation
Printed on Recycled Paper
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guidance. This report describes two emis-
sions tesls conducted by EMB to assess
the current GRI glycol dehydrator emis-
sions model GRI-GLYCalc™. Additional
tesls, not discussed in this report, have
been performed by GRI and API at eight
other sites. These data will also be re-
viewed prior to making a recommendation
on Including GRI-GLYCalc in EPA emis-
sions inventory guidance documents.
Glycoi dehydrators are used to remove
water from natural gas and, in the pro-
cess of removing the water, may also
remove and emit significant quantities of
benzene, toluene, ethylbenzene, and xy-
lenes (BTEX). The most common glycol
dehydrator design employs an absorber,
with trielhylene glycol (TEG) used as the
absorbent, to remove water from natural
gas. In the absorption step, aromatic hy-
drocarbons such as BTEX are also ab-
sorbed into the glycol stream. Following
the absorption step, the glycol, rich with
water and BTEX compounds, is distilled
to strip water from the glycol. Recovered
lean (dry) glycol is recycled for use in the
absorber. Emissions of BTEX and other
volatile organic compounds (VOCs) oc-
cur from the glycol reboiler still vent. As a
result of the 1990 Clean Air Act Amend-
ments, hazardous air pollutant emissions
(primarily BTEX) from the reboiler still vent
stream of glycol dehydrators have become
a concern for the natural gas industry.
Site 1, a gas plant in west Texas, was
processing 3.6 million standard cubic feet
per day (MMSCFD)" of gas without a flash
tank and using a gas-driven pump. Site 2,
in southwest Louisiana, was processing
4.9 MMSCFD of gas with a flash tank and
using a gas-driven pump. Testing was con-
ducted over a 2-day period at each site.
Three emissions measurement techniques
were used at each site: total capture con-
densation (the most accurate method) and
two lower cost methods (pressurized gly-
col cylinders and atmospheric rich/lean
glycol). The lower cost methods were in-
cluded in the test protocol to evaluate
their applicability as emissions screening
tools where use of the total capture method
• Conversion factors (or nonmetrfc units are listed at the
end of this Summary.
may not be technically feasible or eco-
nomically justifiable.
In total capture condensation, the entire
still vent stream was passed through a
50-ft length of 1-in. diameter copper tub-
ing coiled inside a 55-gal barrel and sub-
merged in an ice/water mixture. Con-
densed hydrocarbons, condensed water,
and noncondensable gas were measured
and sampled. Results from total capture
condensation were used as the bench-
mark against which other methods were
compared.
The atmospheric rich/lean glycol method
used samples of glycol from both upstream
(rich) and downstream (lean) of the reboiler
collected at atmospheric pressure in vola-
tile organic analysis vials. Emissions were
calculated using the difference in analyte
concentrationsTih the rich and lean samples
and the glycol circulation rate. Based on
sampling experience in the GRI project,
the glycol methods may not produce a
representative sample for total VOC de-
termination, particularly on systems with-
out a flash tank.
The pressurized glycol cylinder method
used samples of glycol (rich) collected at
line pressure upstream of the reboiler in
stainless steel cylinders. Emissions were
calculated using the difference between
the analyte concentrations in the glycol
cylinder and a lean glycol sample down-
stream of the reboiler and the glycol circu-
lation rate.
GRI-GLYCalc is a computer program
developed by GRI as an alternative screen-
ing tool to estimate emissions from glycol
dehydrators using process operating data
and the composition of natural gas for the
unit of interest. To evaluate the use of
GRI-GLYCalc and alternative natural gas
sampling methods, five types of natural
gas samples were collected and analyzed:
• Sub-atmospheric pressure canisters
upstream of the absorber using, a sam-
pling manifold;
• High-pressure cylinders upstream of
the absorber with and without a sam-
pling manifold; and
• High-pressure cylinders downstream
of the absorber with and without a
sampling manifold.
Results
The results of Site 1 testing, presented
in tons per year plus or minus 1 standard
deviation, are listed in Table 1. BTEX emis-
sion estimates using the various tech-
niques agreed reasonably well. Prediction
by GRI-GLYCalc of total BTEX emissions
was close to the total capture results for
some of the gas sample types. Quality
control data, however, indicate that the
natural gas BTEX concentrations for the
cylinders may have been biased high,
which caused the high prediction by GRI-
GLYCalc. Total VOC emissions from the
two glycol methods did not match well
with the total capture benchmark results;
this is consistent with previous results for
systems without flash tanks.
BesulisjDLSite.2 sampling.,ara Hstedjn =__
Table 2. Atmospheric rich/lean glycol and
pressurized glycol emission results agreed
closely with the total capture results for
both BTEX and total VOC. Removal of
volatile components in a flash tank up-
stream of the glycol sample point elimi-
nates two-phase gas/liquid flow in glycol
lines, thus allowing a more representative
glycol sample. GRI-GLYCalc predictions
using natural gas samples taken before
the glycol absorber agreed well with the
total capture results for total BTEX emis-
sions.
For these two test sites, the GRI-
GLYCalc model, using natural gas
sampled with evacuated canisters, agreed
very well with measured emissions as
measured by the most accurate test
method (total capture condensation) for
each site. As shown in Tables 1 and 2,
the GRI-GLYCalc estimated emissions of
BTEX and total VOC are within 10% or
less of the measured emissions.
Metric Equivalents
The following conversion factors are pro-
... ,vided for use^by- readers more JamilLar_.
with the metric system.
Nonmetric Multiplied bv Yields metric
°F
ft
ft3
gal
in
psig
ton
5/9(°F - 32)
0.305
28.3
3.79
2.54
6.89
0.907
°C
m
L
L
cm
kPa
tonne
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Table 1. Summary of Site 1 Emission Results*
Emissions (tons per year)
Method
Total Capture Condensation
Pressurized Glycol Cylinders
Atmospheric Rich/Lean Glycol
GRI-GLYCalc with Canister
Gas Samples
GRI-GLYCalc with Cylinder
Gas Samples Before Absorber,
with Manifold
GRI-GLYCalc with Cylinder
Gas Samples Before Absorber,
without Manifold
GRI-GLYCalc with Cylinder
Gas Samples After Absorber,
with Manifold
GRI-GLYCalc with Cylinder
Gas Samples After Absorber,
without Manifold
Benzene
1.25 ±0.32
1.22 ±0.1 6
1.24 ± 0.20
1.31
2.50
2.25
1.68
1.68
Toluene
1.68 + 0.29
1.81+0.25
1.85 + 0.28
1.87
3.68
3.40
2.29
2.26
Ethylbenzene
0.08 + 0.02
0.08 + 0.01
0.08 ±0.01
0.06
0.24
0.18
0.06
- 0.06
Xylenes
0.56 + 0.15
0.61+0.09
0.62 ±0.10
0.64
1.44
1.36
1.68
0.80
Total BTEX
3.58 ±0.61
3.71+0.51
3.79 + 0.59
3.88
7.86
7.18
5.71
4.80
Total VOC
19.8+4.0
10.7+ 1.9
11.4 + 1.8
21.8
28.2
28.3
25.5
23.7
-»«, , wasa '^oenyarator treating 3.6 MMSCFD of gas at 86°F and 659 psig;glycol circulation rate was 48.6 gal/hr.
Table 2. Summary of Site 2 Emission Results3
Emissions (tons per year)
Method
Total Capture Condensation
Pressurized Glycol Cylinders
Atmospheric Rich/Lean Glycol
GRI-GLYCalc with Canister
-Gas Samples ., ». .„ ,
GRI-GLYCalc with Cylinder
Gas Samples Before Absorber,
with Manifold
GRI-GLYCalc with Cylinder
Gas Samples Before Absorber,
without Manifold
GRI-GLYCalc with Cylinder
Gas Samples After Absorber,
with Manifold
GRI-GLYCalc with Cylinder
Gas Samples After Absorber,
without Manifold
aSit& P W/AQ a TPS3 rlohi/rlr&tnr im~
Benzene
6.02+1.04
6.71+0.98
5.62 ±0.76
5.22
5.55
5.62
3.93
4.35
>*inn A f\ tt M\ Jt-*f~\^r-t
Toluene
9.87 ± 1.50
11.1 ±1.6
9.25 ±0.93
8.63
8.94
8.51
5.69
6.32
Ethylbenzene
0.84 ±0.16
0.98 + 0.18
0.80 + 0.12
0.89
0.89
0.82
0.41
0.49
Xylenes
6.14 ±0.74
7.05 ±0.82
5.74 ± 0.40
7.58
6.13
5.33
2.87
3.48
Total BTEX
22.9 ±3.2
25.9 ±3.2
21. 4 ±2.0
22.3
21.5
20.3
12.9
14.6
Total VOC
36.9 ±3.1
37.9 ±4.9
30.8 ±3.4
36.1
32.7
31.1
23.3
25.3
were 205°F and 46 psig.
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C Rueter, D. Reif, and D. Myers are with Radian Corp., Austin, TX 78720-1088.
Charles O. Mann is the EPA Project Officer (see below). •
necompletereportconsists of two volumes, entitled "GlycolDehydratorBTEX and
VOC Emissions Testing Results at Two Units in Texas and 'Louisiana
"Volume I - Technical Report" (Order No. PB95-194130; Cost: $27.00,
s" (Order No. PB95-194148; Cost: 36.50, subject
to change)
Both volumes of this report 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:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 2771 1
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
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