United States Air and Energy Engineering

Environmental Protection Research Laboratory

Agency Research Triangle Park, NC 27711

E AP Project Summary

Research and Development EPA/600/SR-95/046 May 1995

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, ethylbenzene, and xylenes (BTEX). The objective of this project was to collect

emissions test data at two triethylene

glycol (TEG) units to provide data for

comparison to GRI-GLYCalcTM, a computer program developed to estimate

emissions from glycol dehydrators.

Three analytical techniques were used

to determine emissions: total capture

condensation, pressurized glycol cylinders, and atmospheric rich/lean glycol sampling.

Site 1 test results, using the various

techniques, yielded BTEX emission estimates that agreed reasonably well.

Total volatile organic compound (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. Site 2 atmospheric rich/lean glycol and pressurized glycol emission results agreed

closely with the total capture results

for both BTEX and total VOCs. GRIGLYCalc predictions using natural gas

samples taken before the glycol absorber agreed well with the total capture results for total BTEX emissions.

This Project Summary was developed

by EPA’s Air and Energy Engineering

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).

Overview

The Emissions and Modeling Branch

(EMB) of EPA’s Air and Energy Engineering 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 glycol dehydrators are not available in current EPA emissions estimation guidance.

EMB held discussions with the Gas Research Institute (GRI) and the American

Petroleum Institute (API) and determined

that they were actively involved in the

development of process models for estimation of emissions from glycol dehydrators. An industry working group, chaired

by GRI, had begun a program to develop

field testing methods and to collect emissions 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

Glycol Dehydrator

BTEX and VOC Emission

Testing Results at Two Units in

Texas and Louisiana

C.O. Rueter, D.L. Reif, D.B. Myers
2

may not be technically feasible or economically justifiable.

In total capture condensation, the entire

still vent stream was passed through a

50-ft length of 1-in. diameter copper tubing coiled inside a 55-gal barrel and submerged in an ice/water mixture. Condensed hydrocarbons, condensed water,

and noncondensable gas were measured

and sampled. Results from total capture

condensation were used as the benchmark 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 volatile organic analysis vials. Emissions were

calculated using the difference in analyte

concentrations in 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 determination, particularly on systems without 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 downstream of the reboiler and the glycol circulation rate.

GRI-GLYCalc is a computer program

developed by GRI as an alternative screening 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 sampling manifold;

• High-pressure cylinders upstream of

the absorber with and without a sampling 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 emission estimates using the various techniques 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 GRIGLYCalc. 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.

Results of Site 2 sampling are listed in

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 upstream of the glycol sample point eliminates 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 emissions.

For these two test sites, the GRIGLYCalc 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 provided for use by readers more familiar

with the metric system.

Nonmetric Multiplied by Yields metric

°F 5/9(°F - 32) °C

ft 0.305 m

ft3 28.3 L

gal 3.79 L

in 2.54 cm

psig 6.89 kPa

ton 0.907 tonne

guidance. This report describes two emissions tests conducted by EMB to assess

the current GRI glycol dehydrator emissions model GRI-GLYCalcTM. Additional

tests, not discussed in this report, have

been performed by GRI and API at eight

other sites. These data will also be reviewed prior to making a recommendation

on including GRI-GLYCalc in EPA emissions inventory guidance documents.

Glycol dehydrators are used to remove

water from natural gas and, in the process of removing the water, may also

remove and emit significant quantities of

benzene, toluene, ethylbenzene, and xylenes (BTEX). The most common glycol

dehydrator design employs an absorber,

with triethylene glycol (TEG) used as the

absorbent, to remove water from natural

gas. In the absorption step, aromatic hydrocarbons such as BTEX are also absorbed 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) occur from the glycol reboiler still vent. As a

result of the 1990 Clean Air Act Amendments, 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 conducted over a 2-day period at each site.

Three emissions measurement techniques

were used at each site: total capture condensation (the most accurate method) and

two lower cost methods (pressurized glycol cylinders and atmospheric rich/lean

glycol). The lower cost methods were included in the test protocol to evaluate

their applicability as emissions screening

tools where use of the total capture method

* Conversion factors for nonmetric units are listed at the

end of this Summary.
3

Table 1. Summary of Site 1 Emission Resultsa

Emissions (tons per year)

Method Benzene Toluene Ethylbenzene Xylenes Total BTEX Total VOC

Total Capture Condensation 1.25 ± 0.32 1.68 ± 0.29 0.08 ± 0.02 0.56 ± 0.15 3.58 ± 0.61 19.8 ± 4.0

Pressurized Glycol Cylinders 1.22 ± 0.16 1.81 ± 0.25 0.08 ± 0.01 0.61 ± 0.09 3.71 ± 0.51 10.7 ± 1.9

Atmospheric Rich/Lean Glycol 1.24 ± 0.20 1.85 ± 0.28 0.08 ± 0.01 0.62 ± 0.10 3.79 ± 0.59 11.4 ± 1.8

GRI-GLYCalc with Canister 1.31 1.87 0.06 0.64 3.88 21.8

Gas Samples

GRI-GLYCalc with Cylinder 2.50 3.68 0.24 1.44 7.86 28.2

Gas Samples Before Absorber,

with Manifold

GRI-GLYCalc with Cylinder 2.25 3.40 0.18 1.36 7.18 28.3

Gas Samples Before Absorber,

without Manifold

GRI-GLYCalc with Cylinder 1.68 2.29 0.06 1.68 5.71 25.5

Gas Samples After Absorber,

with Manifold

GRI-GLYCalc with Cylinder 1.68 2.26 0.06 0.80 4.80 23.7

Gas Samples After Absorber,

without Manifold

aSite 1 was a TEG dehydrator 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 Resultsa

Emissions (tons per year)

Method Benzene Toluene Ethylbenzene Xylenes Total BTEX Total VOC

Total Capture Condensation 6.02 ± 1.04 9.87 ± 1.50 0.84 ± 0.16 6.14 ± 0.74 22.9 ± 3.2 36.9 ± 3.1

Pressurized Glycol Cylinders 6.71 ± 0.98 11.1 ± 1.6 0.98 ± 0.18 7.05 ± 0.82 25.9 ± 3.2 37.9 ± 4.9

Atmospheric Rich/Lean Glycol 5.62 ± 0.76 9.25 ± 0.93 0.80 ± 0.12 5.74 ± 0.40 21.4 ± 2.0 30.8 ± 3.4

GRI-GLYCalc with Canister 5.22 8.63 0.89 7.58 22.3 36.1

Gas Samples

GRI-GLYCalc with Cylinder 5.55 8.94 0.89 6.13 21.5 32.7

Gas Samples Before Absorber,

with Manifold

GRI-GLYCalc with Cylinder 5.62 8.51 0.82 5.33 20.3 31.1

Gas Samples Before Absorber,

without Manifold

GRI-GLYCalc with Cylinder 3.93 5.69 0.41 2.87 12.9 23.3

Gas Samples After Absorber,

with Manifold

GRI-GLYCalc with Cylinder 4.35 6.32 0.49 3.48 14.6 25.3

Gas Samples After Absorber,

without Manifold

aSite 2 was a TEG dehydrator treating 4.9 MMSCFD of gas at 111°F and 1063 psig; glycol circulation rate was 204 gal/hr, and flash tank conditions

were 205°F and 46 psig.
4

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).

The complete report consists of two volumes, entitled “Glycol Dehydrator BTEX and

VOC Emissions Testing Results at Two Units in Texas and Louisiana”

“Volume I - Technical Report” (Order No. PB95-194130; Cost: $27.00,

subject to change)

“Volume II - Appendices” (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 27711

• •

United States

Environmental Protection Agency

Center for Environmental Research Information

Cincinnati, OH 45268

EPA/600/SR-95/046

Official Business

Penalty for Private Use $300

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