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Research and
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METHANE EMISSIONS FROM THE
NATUBAL GAS INDUSTRY
"Volume 14: Glycol Dehjdrators
Prepared for
Energy Information Administration (V. S. DOE)
Prepared by
Nafionai Risk Management
Laboratory
Research Triangle Part, NC 27711
.
-------
f ICHWICAL REPORT DATA
t, *Ef> OUT NO.
EPA~iOO/R-96~080n
«. TITLE AND SUBTITLE
.
Methane Emissions from the Natural Gas Industry,
Volumes 1-15 (Volume 14: Glyeol Dehydrators)
PB37-143051
S. REPORT' OATE *"
June
S. PERFORMING ORGANIZATION CODE
, Campbell, M. Campbell, M. Cowcill. D. Ep-
person, M,Hall, M.Harrison, K. Hummel,D .Myers,
T. Shires, B. Stapper, C. Stapper, J. Wessels, and *
A. PERFORMING ORGANIZATION REPORT NO.
96-263-081-1?
I, PERFORMING ORGANIZATION NAME AND ADDRESS
Radian International LLC
P. O. Box
Austin, Texa» 18720-1088
10. PROGRAM ELEMENT NO,
11. CONTBACT/BRAHT WO.
251-1171
68-D1-0031
12. S?ONSOntN@ AGENCY NAME AND ADDRESS
EPA? Office erf Research and Development
Air PottuMon Prevention and Control Division
Park, NC 177E
<3. TYPE Of REPORT AND PERIOD COVERED
Final; 3/91-4/96
14. SPONSORING AGENCY CODE
EPA/600/13
project officer is D. A.Kirchgessner, MD-63,919/541-4021.
Cosponsor GM project officer is R. A. Lott, Gas Research Institute, 8600 West Bryn
Mawr Aye., Chicago, IL (*)H. Williamson 7).
15-volume report summarizes the results of a comprehensive program
to quantify methane (CH4) emissions from the U. S. natural gas industry for the base
fear. The objective was to determine CH4 emissions from .the wellhead and ending
downstream at the customer's meter. The accuracy goal to determine these
smlssions within-+/-0.5% of natural gas production for a 90% confidence interval. For
tihe 1S82 base year, total CH4 emissions for the "0, S. natural industry was 314
+/- 105 Bscf (6.04 -f/- 2.01 Tg). This is equivalent to 1.4 +/- 0. 5% of gross natural
gas production, and reflects neither emissions reductions (per the voluntary Ameri-
Gas Association/EPA Star Program) nor incremental increases (due to increased
gas usage) since 1991, Results from this program were used to compare greenhouse
from the fuel eyele for natural gas, oil, and coal using the global war-
ming potentials (GWPs) recently published by the Intergovernmental Panel on Climate
Change (IPCC). The analysis showed that natural gas contributes less to potential
global warming than coal or oil, which supports the fuel switching strategy suggested
the IPCC and others. In addition, study results are being used by the natural gas
Industry to reduce operating costs while reducing emissions.
KEY WORDS AND DOCUMENT ANALYSIS
OESCniPTORS
h.IDENTIFIERS/OPEN 6NOEO TERMS
c. COSATI Field/Croup
Pollution
Emission
Greenhouse Effect
Natural Gas
Gas Pipelines
Methane
Pollution Prevention
Stationary Sources
Global Warming
13 B
14G
04A
21D
15E
07C
18, DISTRIBUTION STATEMENT
Release to Public
W. SECURITY CLASS /Thir Keportf
Unclassified
21. NO. OF PAGES
4?
2O. SECURITY CLASS (Thitpagt)
Unclassified
22, PRICE
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The U. S, Environmental Protection Agency is charged by Congress with pro-
tecting the Nation's land, air, and water resources. Under a mandate of national
environmental iaws> the Agency strives to formulate and implement actions lead-
ing to a compatible balance between human activities and the ability of natural
systems to support nurture life. To meet this mandate, EPA's research
program is providing data and technical support for solving environmental pro-
blems today building a science knowledge base necessary to manage our eco-
logical resources wisely, understand how pollutants affect our health, and pre-
vent or reduce environmental risks in the future.
The National Risk Management Research Laboratory is the Agency's center for
investigation of technological and management approaches for reducing risks
from threats to human health and the environment. The focus of the Laboratory's
research program is on methods for the prevention and control of pollution to air,
land, water, and subsurface resources; protection of water quality in public water
systems; remediation of contaminated and groundwater; and prevention
control of indoor air pollution. The goal of this research effort is to catalyze
development and implementation of innovative. Cost-effective environmental
technologies; develop scientific and engineering information needed by EPA to
support regulatory and policy decisions; and provide technical support and infor-
mation transfer to ensure effective implementation of environmental regulations
and strategies.
This publication has been produced as part of the Laboratory's strategic long-
term research plan. It is published and made available by EPA's Office of Re-
search and Development to assist the user community and to link researchers
with their clients,
E. Timothy Oppelt, Director
National Risk Management Research Laboratory
EPA
This report has been peer and administratively reviewed by the U.S. Environmental
Protection Agency, and approved for publication. Mention of trade names or
commercial products does not constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Information
Service. Springfield, Virginia 22161.
PROTECTED UNDER INTERNATIONAL COPYRIGHT
ALL RIGHTS RESERVED.
NATIONAL TECHNICAL INFORMATION SERVICE
U.S. DEPARTMENT OF COMMERCE
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EPA-600 /R- 86-080n
June
THE NATURAL GAS INDUSTRY,
14; GLYCOL
fTOAL
Prepared by:
Duane Myers
Ridian International LLC
N,
P.O. Box
Austin, TX 78720-1088
DCN: 95-263-081-15
For
GRI Project Manager: Robert A. Lott
GAS
Contract No. 5091-251-2171
8600 West Bryn Mawr Ave.
Chicago, IL
and
HPA Project David A. Kirchgessner
U.S. ENVIRONMENTAL PROTECTION AGENCY
Contract No. 68-D1-0031
National Risk Management Research Laboratory
Park, NC 27711
-------
DISCLAIMER
LEGAL NOTICE: This report by Radian LLC as an account
of work sponsored by Gas Research Institute (GRI) and the U.S. Environmental Protection
Agency (EPA). Neither EPA, GRI, of GRI, nor any on behalf of
either:
a. Makes any warranty or representation, express or implied, w-th respect to the
accuracy, or of the in report, or
that the use of any apparatus, method, or process disclosed in this report may not
privately or
b. any liability with to the use of, or for from the
use of, any information, apparatus, method, or process disclosed in this report.
NOTE: EPA's Office of Research and Development quality assurance/quality control
(QA/QC) are applicable to of the by project.
Emission data and additional count data are from industry or literature sources, and are not
subject to EPA/ORD's QA/QC policies. In all and were reviewed by the
panel of experts listed in Appendix D of Volume 2.
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RESEARCH SUMMARY
Title
Contractor
Principal
Investigator
Report Period
Objective
Technical
Perspective
Results
Methane Emissions from the Natural Gas Industry,
Volume 14: Glyco! Dehydrators
Final Report
Radian International LLC
GRI Contract Number 5091-251-2171
EPA Contract Number 68-D1-0031
Duane B. Myers
March 1991 - June 1996
Final Report
This report describes a study to quantify the annual methane emissions
from glycol dehydrators and acid gas recovery units (AGRs), which are
significant sources of methane emissions within the gas industry.
The increased use of natural gas has been suggested as a strategy for
reducing the potential for global warming. During combustion, natural
gas generates less carbon dioxide (COj) per unit of energy produced man
either coal or oil. On the basis of the amount of CO3 emitted, the
potential for global warming could be reduced by substituting natural gas
for coal or oil. However, since natural gas is primarily methane, a potent
greenhouse gas, losses of natural gas during production, processing,
transmission., and distribution could reduce the inherent advantage of its
lower CO2 emissions.
To investigate mis, Gas Research Institute (GRI) and the U.S.
Environmental Protection Agency's Office of Research and Development
(EPA/ORD) cofunded a major study to quantify methane emissions from
U.S. natural gas operations for the 1992 base year. The results of this
study can be used to construct global methane budgets and to determine
the relative impact on global wanning of natural gas versus coal and oil.
The annual emissions rates for glycol dehydrators for each industry
segment are as follows: production, 3.42 ± 192% Bscf; gas processing,
1.05 ± 208% Bscf; transmission, 0.10 ± 392% Bscf, and storage, 0.23 ±
167% Bscf. AGR methane emissions are 0.82 ± 109% Bscf.
m
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Based on data from the entire program, methane emissions from natural
gas operations are estimated to be 314 ± 105 Bscf for the 1992 base
year. This is about 1.4 ± 0.5% of gross natural gas production. The
overall project also showed that the percentage of methane emitted for an
incremental increase in natural gas sales would be significantly lower
than the baseline case.
The program reached its accuracy goal and provides an accurate estimate
of methane emissions that can be used to construct U.S. methane
inventories and analyze fuel switching strategies.
Technical Glycol dehydrators are used to remove water from natural gas streams. A
Approach lean (low water content) glycol stream is contacted with the wet natural
gas and the glycol absorbs most of the water. The glycol also absorbs
small amounts of methane and other natural gas constituents which may
then be emitted to the atmosphere when the glycol is regenerated. AGRs
work in much the same way as glycol dehydrators. A Sean (low acid gas
content) amine is contacted with natural gas containing carbon dioxide
and/or hydrogen sulfide. The amine preferentially absorbs the carbon
dioxide and hydrogen sulfide but also absorbs some methane, which may
then be emitted to the atmosphere.
The techniques used to determine methane emissions were developed to
be representative of annual emissions from the natural gas industry.
However, it is impractical to measure every source continuously for a
year. Therefore, emission rates for glycol dehydrators and AGRs were
determined by developing annual emission factors for typical units in
each industry segment and extrapolating these data based on activity
factors to develop a national estimate, where the national emission rate is
the product of the emission factor and activity factor.
Emission factors were developed by using process simulation software to
model the glyco! dehydrator and AGR process operations. Information
from site visits and other research programs was used to develop the
characteristics of representative units used in the process modeling. An
emission factor was developed for glycoi dehydrators that reported the
amount of methane emitted per unit of natural gas throughput and for
AGRs that reported the amount of methane emitted annually for a typical
unit.
The development of activity factors for each industry segment are
presented in a separate report. In general, the gas throughput for each
industry segment was determined from surveys conducted across the
entire industrv.
IV
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Project For the 1992 year the for the
U.S. gas is 314 ± 105 Bscf (± This is
equivalent to 1.4% ± 0.5% of gross natural gas production. from
were used to compare greenhouse gas from the
fuel cycle for gas, oil, and coal the global warming
(G WPs) recently by the Intergovernmental Panel on
Climate Change (IPCC). The analysis showed that natural gas
contributes less to potential global warming than coal or oil, which
supports the fuel switching strategy suggested by IPCC and others.
In addition, results from this study are being used by the natural gas
industry to reduce operating costs while reducing emissions. Some
companies are also participating in the Natural Gas-Star program, &
voluntary program sponsored by EPA's Office of Air and Radiation in
cooperation with the American Gas Association to implement cost-
and to report reductions to the EPA, Since
this program was begun the 1992 year, any in
methane front this are not in this study's
Robert A. Lott
Senior Project Manager, Environment and Safety
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TABLE OF
Page
1.0 1
2,0 INTRODUCTION . , 2
3.0 DESCRIPTION OF GLYCOL DEHYDRATORS IN THE NATURAL GAS
INDUSTRY 3
3.1 Operation Overview , 3
3.2 Field Gas Production .,,..,.,, 6
3.3 Gas Processing Plants 6
3.4 Gas Transmission 7
3.5 Gas 7
4.0 ACTIVITY g
4.1 Industry Gas Gas Throughput Dehydrator Counts 8
4,1.1 Production Transmission 9
4.1.2 Gas Processing 10
4.1.3 . 10
4.2 Other Dehydrator Characteristics 10
4.2.1 10
4.2.2 Stripping Gas and Vapor Recovery 11
4.3 AGR Activity Factors 12
5.0 EMISSION FACTORS 13
5.1 Test Description 14
5.2 Results of Emission Estimates 16
5.3 Calculated Emission Factors 18
5.4 AGR Emission Factor ,23
5.5 Emission Factor Summary 23
6.0 ANNUAL , 24
7.0 ., 25
APPENDIX A - Emission Source A-l
vt
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LIST OF FIGURES
Page
3-1 Block Process Flow Diagram of r Typical Glycol Dehydrator 4
5-1 Methane - Glyool Regenerator Effect on Methane
Composition ,.,.,., 19
5-2 Methane - Glycol Effect on Glycol
.,,,,,, 20
5-3 Methane - Glycol • ,-ator Effect on Flash Tank
Pressure 21
LIST OF TA1LES
P
4-1 Estimated Annual Dehydrator Througl^ut , . , 9
4-2 Activity Factors for Flash Tank Populations . , 11
4-3 Dehydratots Using Stripping Gas or Vapor Recovery 11
5-1 Test Matrix for Studying the Effect of Process Parameters on
Methane from Glycol 15
5-2 Effects of Process Parameters on Methane Emissions from Glycol
Regenerators .,,,,,,..., , , , 17
5-3 Summarv of Glvcot Defavdtator AGR Emission Factors 23
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1.0 SUMMARY
This report is one of several volumes that provide background information
supporting the Gas Research Institute and U.S. Environmental Protection Agency Office of
Research and Development (GRI-EPA/QRD) methane emissions project The objective of
this comprehensive program is to quantity the methane emissions from the gas industry for
the 1992 base year to within ± 0.5% of natural gas production starting at the wellhead and
ending immediately downstream of the customer's meter.
This report describes the characteristics of glycol dehydrators that affect
methane emissions and summarizes the basis of the national estimate of emissions from mis
source. Also included in this category are methane emissions from acid gas removal
(AGR) units in gas processing plants, since AGRs are similar to glycol dehydrators in
design and characteristics that affect emissions.
The annual emissions for glycol dehydrators for each industry segment are as
follows: production, 3.42 ± 192% Bscf; gas processing, 1.05 ± 208% Bscf; transmission,
0.10 ± 392% Bscf; and storage, 0.23 ± 167% Bscf. AGR methane emissions are 0.82 ±
109% Bscf.
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2.0 INTRODUCTION
Dehydrator activity factor" demographics were developed on the basis of data
from several surveys. The percentage of glycol dehydrators (as opposed to molecular sieve
or other types) was established to be about 95% of the total population of 41,700, for a
count of 39,615 glycol dehydrators nationwide.1 Initially, the count of dehydrators in each
industry segment was used as the activity factor. At the suggestion of the Industry
Working Group (industry members who serve as project advisors), the activity factor basis
was changed to dehydrator gas throughput. The final activity factors used by this project
are documented in Section 4. An emission factorb was developed using information from
field measurements, as well as a computer simulation using ASPEN/SP® software. The
emission factor results are reported in Section 5. The estimated annual methane emissions
from dehydrators from each industry segment are given in Section 6.
"An activity factor is a count of the total industry population of a particular type of
source. It is the total number of sources in the entire target population or source category.
bAn emission factor for a source category is a measure of the average annual emission
per source. It is the summation of all measured or calculated emissions from sampled
sources divided by the total number of sources in the category that were sampled.
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3.0 DESCRIPTION OF GLYCOL DEHYDRATO1S IN THE NATURAL GAS
INDUSTRY
This describes the glycol found in the gas industry.
as -well as in in various of the industry.
3.1 OperatioB Overview
Dehydrators are designed to remove water from the natural gas vapor stream,
and the of hydrates, which are
that can flow and in valves and ever, pipelines.
There are several types of dehydrators. from molecular
to liquid absorption dehydrators.
Glycol dehydrators are liquid absorption units that absorb water in a liquid
glycol stream. Approximately 95% of glycol dehydrators use triethylene glycol (TEG),
with of the remainder ethylene (EG). (TEG and EG wry different
properties for water removal but are for methane The
usually of two primary the absorber and the regenerator. Figure 3-1
shows a typical block flow diagram for a glycol dehydrate* The lean liquid glycol usually
flows downward in an absorption tower, counter-current to the natural gas. The glycol
absorbs most of the water from the natural gas, but it also absorbs other materials present in
the gas stream. The dried gas the top of the tower. The water-rich glycol
the bottom of the tower and flows to the regenerator. The the
glycol to drive off water vapor, and the vapor is vented to the
atmosphere through the regenerator vent stack. The lean glycol is returned to the
absorber. Glycol has a high affinity for water and a relatively low affinity for non-aromatic
hydrocarbons, which makes it a very good absorbent fluid for drying natural gas. However,
the glycol does of and hydrocarbons from the
gas. The hydrocarbons are to the with the vapor the
vent
-------
Wet
Gas
Dry Gas to
Pipeline
Water Vapor and
Light Hydrocarbons,
Including CII4
(to Atmosphere or
to Control System)
Dry
Glyco!
Wet Glycol
%
and Gas
(High Pressure)
Absorber
(High Pressure)
Combustion
Gases
Glycol
Gas
Pump
Glycol
Reboiier/
Regenerator
Fla§h Tank
(Optional)
at Intermediate
Pressure
Firebox
Fuel
ReboMer
(Atmospheric
Pressure)
Figure 3-1, Block Process Flow Diagram of a Typical Glycol Dehydrator
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All giycol dehydrators have pumps to the glycol. pumps in the
are that greatly increase the the glycol
unit These pumps are powered by (wet) line gas, and the gas is
dumped the rich glycol and off in the regenerator. For the purposes of
study, the were considered sources, even the
methane they use is vented through the regenerator. Gas-assisted pumps are in a
separate report,2 and are not included in this analysis of dehydrator emissions.
Some glycol dehydrators have additional equipment. Two common additions
are flash tanks and regenerator vent emissions control equipment. The flash tank is placed
in the rich glycol loop between the absorber and the regenerator. The glycol line pressure
is dropped in the tank, causing most of the hydrocarbons to the vapor
phase. The flash gas is to the burner as fuel. The
from the vent can be significantly reduced by a tank.
Regenerator vent control devices been on to
of benzene, toluene, ethylbenzene, and xylenes (BTEX) and volatile organic
compounds (VOC) to the atmosphere. These are absorbed fern the gas
and driven off with the water in the regenerator vent Control devices usually condense the
water and hydrocarbon (containing BTEX and heavier VOC), then decant the hydrocarbon
for sale and the water for disposal. The methane in the vent is not condensed and is
usually vented, but it can be flared or used as fuel in the regenerator burner. Many glycol
dehydrator operators have installed some type of vapor recovery system on the regenerator
still vent, although the controls are primarily targeted for BTEX and not control.
Some dehydrators use stripping gas to the regenerator, the
outlet or from the flash is introduced into the to help the water and
otter compounds out of the glycol by the vapor flow rate to the
rebofler still. Methane in the stripping gas directly through the regenerator into the
vent
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3.2 Field Gas Production
Field production removes water in two First, a vessel
removes the liquid (free water and oil) from the IK viral This liquid phase water
is the oil to preserve the purity of the oil. The g?s the top of the
separator often remains saturated with absorbed water and is treated again by field
dehydrators to dry the gas to low parts per million (ppm) levels of water to prevent
corrosion and plugging of the gathering lines.
Many field dehydrators are small glycol units with very little instrumentation
and without flash tanks. Comparatively few production units have regenerator vent
controls, more are controls as new environmental
regulations effect. Many production glycol driven by gas-pressure
letdown. production use TEG as the absorption fluid,
33 Gas Processing Plants
Dehydration is fundamental to gas processing plants, especially those that use
refrigerated or cryogenic liquids recovery methods. However, if water is present, the cold
temperatures promote the formation of hydrates. Therefore, gas processing plants use
molecular sieve beds or glycol dehydrators upstream of the liquids recovery section.
Some plants do not use a typical dehydrator configuration with an absorber.
Rather, they inject the glycol directly into the gas stream and allow contact to occur in the
pipeline. The entire then through a separator, where the dry rich liquid
glyco!, and condensed hydrocarbon are The rich glycol to a
regenerator and is recycled to the injection point. injection-type use
ethylene glycol (EG) as the liquid.
-------
Plants that use a typical absorber tower may or may not have a flash tank or
vent recovery equipment. Some plants may route die vent gases to a plant flare system.
Most plant glycol pumps are powered by electricity instead of gas.
AGE units have the same basic equipment as a glycol dehydrator: an absorber
tower, a pump to circulate the liquid, and a reboiler to regenerate the absorber liquid.
AGRs typically use an aqueous solution of one of a variety of amine compounds (e.g.,
monoethanolamiffle, diethanolamine) to remove carbon dioxide and hydrogen sulfide from
natural gas.
3.4 Gts Transmission
Production gas is typically dry when it enters a gas transmission system, having
passed through field production and gas processing plant dehydrators. There usually is no
need to dry gas being transported through the pipeline, although some pipeline gas is
dehydrated.
3.5 Gas Storage
Oas stored ysd£raToiisd for distribution dunn° **e3k ussge KSV nick *m wnter
and need to be dehydrated. Dehydrators used to dry stored gas are typically me same
design as production field dehydrators but tend to be much larger and better maintained.
These large storage dehydrators are more likely to include flash tanks and some type of
vent recovery system than are production field dehydrators.
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4.0 ACTIVITY FACTORS
This section briefly summarizes activity factor calculations for dehydrators and
AGRs. A more detailed discussion is presented in the Volume 5 on activity factors.3 The
results account for the 90% confidence limits calculated for each activity factor.
The overall activity factor for each industry segment is the total segment gas
throughput. The overall activity factor is multiplied by the emission factor (given in
Section 4) to obtain the annual methane emissions.
Other characteristics of glycol dehydrators are used in the calculations overall
activity factor and emission factor. These include:
• Number of dehydrators;
• Dehydrator throughput;
• Fraction of dehydrators with flash tanks;
• Fraction of dehydrators with stripping gas; and
• Fraction of dehydrators with vent vapor recovery.
More specific information for each characteristic is given in the following sections.
4.1 Industry Segment Gas Throughput and Dehvdrator Counts
The overall activity factors are the amount of gas dehydrated annually in each
industry segment. The estimated annual glycol dehydrator throughputs for each industry
segment are listed in Table 4-1.
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TABLE 4-1. ESTIMATED ANNUAL PEHYPRATOR THROUGHPUT
., . ;. Gas T&rougjBgat (MMscgyear)
Production 12.4 x 10 6 ± 61.9%
Processing 8.63 x 10 6 ± 22.4%
Transmission 1.09 x 10 6 ± 144%
Storage 2.00 x 10 * ± 25.0%
Total Gas Industry 24.12 x 10 6± 33.5%
The total industry segment throughputs were calculated in several different ways be
discussed below.
4.1.1 Production and Transmission
The activity factors for production and transmission were calculated using the
equation:
AF= P x CP x CU x 365 days/year (1)
P = Population of dehydrators in each industry segment (see
Appendix A)
Production: 37,824 ±21.1%
Transmission: 201 ± 119%
CP = Average gas throughput capacity per dehydrator1
(NlMsefd)
Production: 2.00 ±28.1%
Transmission: 14.8 ± 29.5%
CU - Capacity utilization—ratio of actual gas throughput to
capacity (see Appendix A)
Production: 0.45 ± 32%
Transmission: 1.00 ± 0%
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4.1.2 Gas Processing
The gas activity from the reported gas plant
throughput and type from the Oil and Gas Journal survey of gas plants.4 It
all gas using a use glycol dehydration and gas
plants using a cryogenic process use some type of dry-bed dehydration (which has
negligible methane emissions). The fraction of gas processed by glycol dehydrators was
determined to be 0.495 (or 8.63 Tsctfyear) of a total of 17.44 Tscf/year.
413 Storage
The activity factor was from the of gas removed from
annually (2.4 Tsef) as in A.G.A. Gas Facts,5 It
most gas removed is dehydrated by glycol; 2.0 Tscf/year ±
25% was as the activity factor.
42 Other Dehydrator Characteristics
Fractions of dehydrator populations with flash tanks, stripping gas, and vapor
recovery systems were also used in the emission calculations. These characteristics and the
field data can be found in the Activity Factor report.3
4,2.1 Flash Tanks
The of glycol dehydrators with was by combining
the of site surveys with the of a survey by the Mid-
Continent Oil (TMOGA).S The fractions in the emission factor
calculations are listed in Table 3-2.
10
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TABLE 4-2. ACTIVITY FACTORS FOR FLASH TANK POPULATIONS
Ilasfe Tacks
Production 0.265 ± 8.35%
Processing 0.667 ± 10.1%
Transmission 0.669 ± 9.70%
Storage 0.520 ± 33.6%
4.2.2 Stripping Gas and Vapor Recovery
The fractions of glycol dehydrators that use stripping gas in the regenerator or
have a vapor recovery system that eliminates methane emissions were estimated from the
results of site surveys. The fractions used in me emission factor calculations are listed in
Table 4-3.
TABLE 4*3. DEHYDRATORS USING STRIPPING GAS OR VAPOR RECOVERY
Production 0.0047 ± 116% 0.012 ±73.1%
Processing 0.111 ± 186% 0.10 ± 0%*
Transmission 0.074± 118% 0.148 ± 80.3%
Transmission 0.080 ± 118% 0.160 ± 80.8%
*For the emissions calculations it was assumed that 10% of ga? processing dehydrators have
vent controls, although none were observed during the site visits.
11
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43 AGR Activity Factors
The number of amine-based AGRs in gas processing service has been reported
to be 371 in a report for GRI by Purvin & Gertz, Inc.7 Confidence limits were not given in
the report; therefore, they were assumed to be ± 20%. Assuming an average AGR gas
throughput of 36,5 MMscfd ± 20% (equal to a gas processing dehydrator throughput), the
AGR activity factor is 1.354 x 104 MMscf/year. Another survey reported that 18% of the
AGR reboilers vent directly to the atmosphere and would be a source of methane
emissions.8
12
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SJ FACTORS
Estimates of methane emissions from dehydrators were developed using
estimates from computer simulation and some field <*ata measurements, ASPEN/SP* (from
Simulation Sciences, Inc.) process simulation software was used for several case studies.9
Glyco! dehydrators have numerous affect
from the regenerator vent. Using a compiler simulation model and varying the key
dehydr&tor parameters, die following characteristics of glycol dehy dravors that affect
emissions were examined:
• Overall unit
— Size of the unit (MMscf of gas processed/day)
— Gtycol type
— Glycol circulation me
— Lean glycol percent water
- Regenerator reboiler temperature
* Inlet gas information
Methane composition
Flash tank information
- Use of t flash tank
Pressure
— Temperature
Stripping gas use
V«ot weowry/eotttroi equipment
The size of the unit affects how much methane is contacted, how much glyeol is
circulated, and therefore how much methane is absorbed. Several types of glycol can be
13
-------
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T.T lr°l.-^T} %^**% A J5_r^= ****** M-f^r «&a *^ &kAV iia^^iji, w~^i&Aa~£*Vf **• *_«*••**«* OA «Aa^'h?%' ^*J w^Ak? £«M*> ** O^AAA^B iofiii. «£sS.,&A.&u *• T
for methane. The glycol circulation rate affects the contact time, and therefore how much
methane is absorbed by the glycol. The lean glycol water concentration is a measure of
how well the regenerator has restored the glycol before it returns to the absorber. A high
concentration of water in the lean glycol reduces its ability to absorb water from the gas
stream.
The inlet methane composition, gas temperature, and gas pressure affect the
methane partial pressure in the absorber. This changes the amount of methane relative to
other materials that can be absorbed by the glycol.
Many characteristics that were judged to have a negligible effect on the amount
of methane absorbed were eliminated from consideration. Examples are the number of
trays in the reboiler still, the inlet BTEX composition, and the inlet water composition.
5.1 Test Description
A matrix approach was used to study the effect of process parameters on
methane emissions from a glycol regenerator. The process parameters include:
• Methane composition;
• Glycol circulation rate;
• Lean glycol water content;
• Flash tank temperature and pressure;
• Gas flow rate; and
• Gas temperature and pressure.
The test matrix is shown in Table 5-1.
14
-------
TABLE 5-1. TEST MATRIX FOR STUDYING THE OF ON METHANE
GLYCOL
•. - '-,^m ';*i^vfam^Mm
Methane Composition (wt%)
Glycoi Circulation Rite (gph)
Leal Olyeol (% water)
Tank (pM§)
Flash Tank Temperature fF)
Oas Flow Rate (MMscfd)
Gas Temperature (°F)
Gas Pressure (psig)
'"'" " '*Y;tf i' :'.;*V::: : :" '": ::!:^i;':
:%-iwii|i|P
iiiiiiii
15
Sliiil*^
S5
4.75
0.5
30
70
0.9
90
600
^;':^:^::S-'r''':':^::r-:::^':i::
^I^J^lWv:-;-^
87.5
7.14
45
iisii
iHiliii
90
9.48
1
60
110
1
95
800
giiii^
92.5
1L88
75
'-Ipi
,:;:;;;: ^f.WfllP^^:;.
95
14.28
1.5
90
150
I.I
100
1000
rS^ii^l
lipi
V«itie
l'''lim'i*'r''':';''' "'"'" "'
120
f3S!pRii
iiMliiiir
No tan c
10«
1 Glycoi circulation rate is also mcrestsed by a factor of ten.
-------
input information lor a base case denyorator was chosen to represent Radian s oest estimate
of average dehydrator parameters based on the company's experience with permitting
dehydrators and performing dehydrator studies for GRI and other private clients.
Initially, the base case was run to determine the emissions and to establish the
number of theoretical stages for the glycol dehydrator. (The number of theoretical stages
for a dehydrator is the number of absorber trays, with the gas and glycol at equilibrium,
required to dry the gas to pipeline specification.) Then, low and high values were studied
for each parameter. During the evaluation of one parameter, the other process parameters
were kept at the base case values. A few supplemental cases were also studied.
After running the initial tests, the matrix was expanded for the parameters that
showed the most variability. More tests were performed on the methane composition,
glycol recirculation rate, and flash tank pressure. A run was also performed at a gas flow
rate ten times the base case value. The glycol recirculation rate was correspondingly
increased by a factor of ten. The emission rate for this case was found to be exactly one
order of magnitude larger than the base case (0.0837 to 0.837 tons/yr), which indicates that
the emission rate is linear with the flow rate, assuming that the glycol-to-gas ratio remains
constant.
5.2 Results of Emission Estimates
Table 5-2 presents the results of the emission estimates generated from the
ASPEN/SP* model runs.9 The glycol circulation rate remained proportional to the gas flow
rate to maintain a constant glycol-to-gas ratio. Emission rate was found to be directly,
linearly proportional to the gas flow rate if the glycol-to-gas ratio was held constant. The
other variables also produced nearly linear relations.
16
-------
TABLE S-2. EFFECTS OF PROCESS PARAMETERS ON METHANE EMISSIONS FROM GLYCOL
REGENERATORS
v; - ^ ;...;;;;;;J||i^
Methane Composition (voi%)
Methane Emissions (tons/yr)
Qlycol Circulation Rate (gph)
Methane Emissions (tons/yr)
Lean Olycol (% water)
Methane Emissions (tons/yr)
Wash Tank Pressure (psig)
Methane Emissions (tons/yr)
Flash Tank Temperature (°F)
(tons/yr)
(las Flow Rate (MMscfd)
(tons/yr)
Gas Temperature (°F)
Emissions (tons/yr)
Gas Pressure (pstg)
Methane Emissions (tons/yr)
liiiiP
iliiili
IS
0,0261
'^•'•:-;";'/''-'^???r?rv £ ; v"' :-::
S5
0.0701
4.75
O.Q4191
OJ
0.0841
30
0.0442
70
0.092
0.9
O.OS37
90
0,0832
600
0.0837
•^JM^itiiffif" '
K\^^it&^
S7.5
0.0767
7.14
0.0626
45
0.0635
•Bill
90
0.0837
9.48
0.0837
1
0.0837
60
0.0837
no
0.0837
1
0.0837
95
0.0837
800
0.0837
Medium
liiii
92.5
0.0911
11.88
0.104
75
0.104
95
0.0999
14.28
0.125
1.5
0.0832
90
0.125
150
0.0753
1.1
0.0837
100
0.0841
1000
0.0837
iipi
MMi
120
0.168
;::>gx.:-:;:-:;:;-^-i:; .- ..'-vj.;. .,/:',;£,.•,. :
No tank
1.12
10b
0.837
1 Results not valid since the dry gas water content is greater than 7 Ib H2O/MMscf.
b Olycoi circulation rate is also increased by a factor of ten.
Number of absorber trays is fixed at 1.41,
-------
Figures 5-1, 5-2, and 5-3 show the relation of methane composition, glycol
circulation rate, and flash tank pressure on methane emissions. The single largest effect on
the total emission rate was the presence or absence of a flash tank. A flash tank can reduce
methane emissions by a factor of ten. One parameter not modeled was the addition of
stripping gas. When stripping gas is added to the regenerator, all of it should exit as
exhaust through the regenerator vent. This parameter has a major effect on dehydrator
methane emissions.
53 Calculated Emission Factors
The variables accounted for in the emission factor calculations were presence of
a flash tank, use of stripping gas, presence of a vapor recovery device on the still vent, and
dehydrator gas throughput. Based on field observations from other GRI programs and on
input from industry advisors, a dehydrator capacity utilization factor and glycol
overcirculation factor were included.
These data were used to produce a national emission factor estimate for the
average dehydrator in each industry segment using the average dehydrator capacity for each
segment. Emission factors were derived for dehydrators in the production, gas processing,
and transmission and transmission segments by the same basic method.
A thermodynamic computer simulation was used to determine the most
important variables affecting emissions from dehydrators. The important variables are gas
throughput, existence of a flash tank, existence of stripping gas, existence of a gas-driven
glycol pump, and existence of vent controls routed to a burner. Other variables (e.g..
reboiler temperature) were determined to be relatively unimportant from an emissions
standpoint.
Throughput, since its effect is linear, is handbd by establishing an emission rate
per unit of gas throughput for all dehydrators. Emission rates per unit of throughput are
18
-------
0.12
0.10
1
0.04
0.02
0.00
84
Si
SS
m
94
Methaae Composition (mo!e%)
Figure 5-1. Metbane - Gtycol Regenerator Effect on Composition
-------
-------
0.1$
0,10
0,05
0.00
11
13
Tank Pressure
figure 5-3. - Giyeol Rsfweritor on Hash Tank Pressure
21
-------
then established for the other important emission-affecting characteristics. Gas-assisted
pumps are ignored here and handled in a separate source analysis.2 The stripping gas rate
was determined from observations at one site from the GUI Glycol Dehydrator Sampling
and Analytical Program.10 The emission factor is then:
EF = [ (Fpr x EF^) + (FOT x EF^) + (Px x EFSG) ] x Fwc x OC (2)
Fpj — Fraction of the population WITH flash tanks
Production: 0.265 ± 8.35%
Gas processing: 0.667 ± 10.1%
Transmission: 0.669 ± 9.70%
Storage: 0.520 ± 33.6%
FOT ~ Fraction of the population WITHOUT flash tanks
Production: 0.735 ± 2.99%
Gas processing: 0.333 ± 20.1%
Transmission: 0.331 ± 19.6%
Storage: 0.480 + 36.3%
FSG = Fraction of the population WITH stripping gas
Production: 0.0047 ± 1 16%
Gas processing: 0.111 ± 186%
Transmission: 0.074 ± 118%
Storage: 0.080 ±118%
FNVC = Fraction of the population WITHOUT combustion vent controls
Production: 0.988 ± 0.87%
Gas processing: 0.900 ± 10% (estimated)
Transmission: 0.852 ± 14.0%
Storage: 0.840 ± 15.2%
EFj-j- = Total methane emission rate scf per 1 MMscf throughput per
dehydrator with a flash tank
All: 3.57 + 102% /- 58%
EFN-j. = Total methane emission rate scf per 1 MMscf throughput per
dehydrator WITHOUT a flash tank
All: 175.10 + 101% /- 50%
22
-------
EFSG = rate per 1 MMscf throughput per
dehydrator that has gas
All: 670 + 40% / - 60%
OC = Glyeol factor—number of times the industry
rule-of-thumb of 3 giycol/pound water
Production: 2.1 ± 41%
Others: 1.0 ± 0%
All of the emission factors (EFs) in these equations, such as EF^, EF,^ and EF^, were
derived from the modeling described in Section 5.2.
5.4 AGR Emission Factor
The ACR factor was by for a
typical unit He were 965 sef CH4/MMscf gas throughput.
Assuming an average AGR gas throughput of 36.5 MMsefd (equal to a gas processing
dehydrator throughput1) and a fraction of AGRs venting methane to the atmosphere of
0.18,* the methane for a typed AGR be
S.S Emissioji factor tSmuBMPC
The emission fectors for each dehydrator industry segment and for AGRs are
listed in Table 5-3.
TABLE 5-3. Of GLYCQL DEHYDRATOR AND
AGR FACTORS
ftoduction 275.6 ± 154%
C^s 121.6 ±
93.72 ±
117.2 ±160%
AGRs 6083 ±
23
-------
6.0 ANNUAL METHANE EMISSIONS
Annual methane emissions from glycol dehydrators in each industry segment
and from AGRs were calculated by multiplying the activity factor by the emission factor.
The results are as follows:
• Production:
275.6 scf CH4/MMscf x 12.4x10 6 MMscf = 3.4 Bscf ± 192%
• Gas Processing:
121.6 scf CH4/MMscf x 8.63x10 6 MMscf = 1.1 Bscf ± 208%
• Transmission:
93.72 scf CH4/MMscf x 1.09x10 6 MMscf = 0.1 Bscf ± 392%
• Storage:
117.2 scf CH4/MMscf x 2.00x10 6 MMscf = 0.2 Bscf ± 167%
« AGRs (Production and Gas Processing):
6083 scfd/unit x 371 units x 365 days = 0.8 Bscf ± 109%
The estimate for annual methane emissions from glycol dehydrators is 4.8 Bscf. The
estimate of annual methane emissions from AGRs is 0.8 Bscf.
24
-------
I. Wright & Co, Natural Gas Dehydration: and Trends, GRI-
94/W99, Gas Chicago, IL, January 1994,
2. Myers, D.B. and M.R. Harrison. Methane Emissions from the Natural Gas
Industry, Volume 15: Gas-Assisted Gfycol Pumps. Final Report, GRI-
M/025733 and EPA-600/R-96-OSOQ, Gas Research and U.S.
Envtoninental Protection Agency, Jane 1996.
3. Stapper, B.E. Methane Emissions from the Natural Gas Industry, Volume 5:
Activity Factors. Final Report, GRI-94/0257.22 and EPA-600/R~96-08Qe. Gas
Research and U.S. Environmental Protection Agency, June 1996.
4. Bell, L. "Worldwide Gas Processing.'' Oil and Gas Journal. June 13, 1994,
pp. 63-91.
5. American Gas Association. Gas Facts 1994: A Statistical Record of the Gas
Industry. Arlington, VA, 1994.
6. Texas Mid-Continent Oil and Gas Association (TMOGA) and Gas Processors
(GPA), Survey, 1991.
7. Tanndull, C.C. and C. Calvin. Business Characteristics of the Natural Gas
Conditioning Industry. Topical Report, GRI-93/0342, prepared by Purvin &
Gate, Inc., Gas Institute, Why 1993.
S, Radian Corporation. Investigation of U.S. Natural Gas Reserve Demographies
anrf Gas Treatment Processes* Topical Report, Gas Research Institute, January
1991.
9. Coiporation, ASPEN/SP* project files, 1993.
10. Radian Corporation. Glycol Dehyarator Emissions: Sampling and Analytical
Methods and Estimation Techniques. GRI-94/0324, Gas Research Institute,
Chicago, IL, 1995.
25
-------
APPENDIX A
Eaussfee Sewce Sfcetfe
A-l
-------
P-6
PRODUCTION SOUR-rt
SOURCES: Glycol Dehydrators
COMPONENTS: N/A
OPERATING MODE: Normal Operation
TYPE: Vented
ANNUAL EMISSIONS: 3.42 Bscf ± 192%
BACKGROUND:
Glycol dehydrators remove water from a gas stream by contacting the gas with giycol and then driving the
water from the giycol by heating in the glycol reboiler and into the atmosphere. The giycol also absorbs a
small amount of methane, and methane can be driven off to the atmosphere through the reboiler vent,
EMISSION FACTOR: (275,57 scCMMscf gas processed ± 154.48%)
A thermodynamic computer simulation was used to the most important emission-affecting variables
far dehytfestors. Tlhc variables are; gas throughput, existence of a existence of stripping gas,
existence of a gas driven pump, and existence of vent controls routed to a burner. Throughput, since its
effect is linear, is handled by establishing an emission rate per unit of gas throughput. Emission rates per unit
of throughput are then established for tbe other important emission affecting characteristics. Gas driven
ass ignored here and in a analysis (see Methane Emissions from the Natural
Ga$ Industry, ¥olume IS: Gas-Assisted Giycol Pumps) (I). The emission factor is then:
EF - [(FrTxEFFT) + (FwxEFOT) + (FSGxEFsa)]x F^ x OC
[ x 3.57) + (0,735 x 175.10) + x 670) j x x 2.1
Fpr = Fraction of the population WITH flash tanks
± 8.35%
FOT = Fraction of the population WITHOUT flash tanks
0.735 ± 2.99%
FSG = Fraction of the population WITH stripping gas
0,00473 ± 115.78%
FNVC = Fraction of the population WITHOUT combustion vent controls
±
EFpj. = Total methane emission rate scf per i MMscf throughput with a flash tank
3.57 +102%/-58%
EFffr = Total methane emission rate scf per I MMscf throughput WITHOUT a
tank
175.10 -H01%/-5G%
EFSC = Incremental methane emission rate per 1 MMscf throughput per dehydrator
has snipping gas
670 +40%/-60%
CXI* = Overcirculation factor For giycol—number of times the industry mle-of-
thumb of 3 gallons glyeol/lb water
2.1 ±41%
A-2
-------
EF DATA SOURCES:'
1. Methane Emissions from the Natural Gas Industry, Volume 14: Gfycol Dehydrators (2)
establishes emission affecting characteristics of dehydrates,
2. GRI/EPA site visit data fl» fm and F^ for sites (19 PROD
3. An analysis of a database TMOGA's 1019 dehydrators and GRI/EPA
site 444 dehydrators Fw and F^j, for production ckbydrators.
4. ASPEN computer were used in combination with measured data to
fPn, and EFW from the dehydrator vent
5. Sampling data from die GRI Giycoi Sampling and Analytical Program for one dehydrator
was used to determine EF^ {Gfycol Dettydraiar Emissions: Sampling and Analytical
Methods and Estimation Techniques) (3), The upper bound was calculated by assuming
that a!! of the measured noncondensable vent gas was due to stripping gas that was 100%
methane. The lower bound was calculated as the rale*of-thumb stripping gas rite recom-
mended by a glycoi dehydrator manuf&eturer.
4 Overcirculation factor determined data from the GR] Giycoi Sampling aid
Analytical Program data for ten dehydrators.
EF 275J7 gts processed ± 154.4S%
Basis:
The accuracy is propagated through die EF calculation from each term's accuracy:
1, ASPEN has been demonstrated to match actual dehydrators within ±20% within the
eaknbtted confidence intervals obtained from site data,
2, Individsml EF confidence satervals were calculated irom the data in the calcalanon.
3. Data from she visits has been assigned confidence intervals based the spread of die
444 dehydrators from GRI/EPA site data,
ACTIVITY FACTOR: (1X4 Tsc^ytar f*s tkrwigbprt in the proAKtioa segmeat)
The amount of gas processed by glyco! dehydrators in die production segment was calculated from the
estimated number of giycol dehydrators in production aid the average throughput capacity for production
dehydntms (Wright Killers &. Co., 1994), A capacity utilization factor was estimated based on observations
at several m die CM Giyco! Dehydrstor Sampling and Analytical Program.
At DATA
The report: Natwal Gas Deky&wlion Status and Trends (4) by Wright Killen tor the Gas Research Institute,
provides data and describes die raethodology used to develop an estimate of the gas dehydrator count for the
U.S. The count also estimated the number in several industry segments: production, transmission, and gas
processing.
A-3
-------
Basis:
I. A GRJ by Wright Kilfcn & Co. found 41700 in the U.S. gas industry
for 1993. Wright also a TMOGA/GPA on dehydrators to split the
population into the following industry segments:
Production: 25270
Processing: 7923
Transmission: 8507
TOTAL: 4J70Q
The study also found that 95.0 % of the dehydrators were glycol for a total of 39,615
(versus molecular sieve or other types).
2. Site visit data on 24 transmission compressor stations shows: 2/17 = 0.118 per
transmission compressor station, and 17/6 = 2,83 per storage compressor station. The site
visit numbers would lead to an estimate of 1293 total transmission and storage
dehydrators. Site visit data on 11 gas plants show 1.41 dehydrators per plant, or 1,024 in
gas plants.
Subtracting processing, transmission, and storage glycol dehydrators from the total of
39,615 yields 37824 glycol dehydrators in production.
3, Average capacity of production dehydrators was reported to be 2 MMscfd by Wright
Killea,
Information on actual dehydrator throughput as compared to capacity is, in general, difficult to obtain
especially for production field units. Data from several sites in the GRI Glycol Dehydrator Sampling and
Analytical Program and other information from various site visits indicate mat capacity utilization
may be Aan 50%, so a value of 4S% was chosen for the AF calculations.
AF PRECISION: 12.4 Tscf/year ± 61.87%
Basis:
The 90% confidence limits for total glycol dehydrators were established in the Wright Killen
report. The confidence limits for the segments other than production were based on site visit
data. Confidence limits for the capacity utilization was based on engineering judgement.
ANNUAL METHANE EMISSIONS; (3.4171 Bscf/yr ± 191,90%)
The annual methane emissions were determined by multiplying the dehydrator emission factor by the activity
factor.
REFERENCES
I. Myers, D.B. and M.R. Harrison. Methane Emissions from the Natural Gas Industry, Volume
15: Gas-Assisted Glycol Pumps, Report, GRI-94/0257.33 and EPA-6Q0/M-96-QgQo. Gas
Research Institute and U.S. Environmental Protection Agency, June 1996.
2, Mjsrs, D.B. Methane Emissions from the Natural Gas Industry, Volume 14: Glycol
Dehydrators, Final Report, GRI-94/0257.31 and EPA-600/R-96-080n. Gas Research Institute
and U.S. Environmental Protection Agency, June 1996.
A-4
-------
3, Radian Corporation. Gtycol Dehydraiat- Emissions: Sampling and Analytical Methods and
Estimation Techniques GRI-94/0324, Gm Research Institute, Chicago, IL, March 1995,
4. Wright Kiien & Company. Natural Gas Dehydration: ana' Trends, FiotI Report. GRI-
94/0099, Gas Research Institute, Chicago, Chicago, IL, January 1994,
A-5
-------
T-6
TRANSMISSION SOURCE SHEET
SOURCES; Glycol Dehydrators
OPERATING MODI: Operation
TYPE: Unsteady, Vented
COMPONENTS; Vents
ANNUAL OJO Bsef ± 392%
BACKGROUND:
Glycol dehydrators remove water from a gas stream by contacting the gas with glycol and then driving the
water from the glycol and into the atmosphere. The glycol also absorbs a small amount of methane, and
some methane can be driven off to the atmosphere through the reboiler vent.
EMISSION FACTOR: (93.72 scfflMMsef gas processed ± 287.99%)
A thermodynamie computer simulation was to determine the most important emission-affecting variables
for dehydwtors. The variables are; gas throughput, existence of a flash tank, existence of stripping gas,
existence of a gas driven pump, existence of vest controls routed to a burner. Throughput, since its effect is
linear, is handled by establishing an emission rate per gas throughput. Emission rates per throughput are then
established for the other important affecting characteristics. The emission factor is then:
EF - [ ( tn x EF^ ) * { fm x EWm ) + ( F^ x EFjo ) ] x Fwc x OC
EF = [ x 3.57) + (0.331 x 175.10} + (0.0741 x 670) ] x 0.152 x 1.0
Fpj = Fraction, of die population WITH flash
±
Fw = Fraction of the population WITHOUT
0.331 ± 19.6%
Fm - Fraction of the population WHU stripping gas
0.0741 ± 118.26%
FNVC= Fraction of the population WITHOUT combusted vent controls
0.852 ± 14.0%
EFyy^ Total CH4 emission rate per 1 MMscf throughput for dehydrator that has a
flash tank
3.57 scf/MMscf (+102% / -58%)
EFfff" Total CH4 emission rate per 1 MMscf throughput for dehydrator that does
NOT have a flash tank
175.1 scf/MMscf (+10!% / -50%)
EFSG= Incremental emission rate per J MMscf throughput for dehydrator that has
stripping gas
670 (+40% / -60%)
OC = Overcirculation factor for glycol—number of times the industry rule-of-
thumb of 3 gallons glycol/lb water
1.0 ± 0%
A-6
-------
IF DATA SOURCES;
I. Methane Emissions from the Natural Gas Industry, Volume 14: Giycol Dehydrators (1)
establishes emission affecting characteristics of dehydrators.
2. Site visit data establishes the F^ and fmc for multiple sites. Wyoming ADQ data also
verifies FNVO though it implies a higher F, and thus a higher overall EF.
3. TMOGA/GPA survey of 1019 dehydrators established Fro and F^, and TP for
dehydrators.
4. ASPEN computer simulations were used to determine EF^,, and EF^ from the dehydrator
vent.
5, Sampling data from the GRI Giycol Dehydrator Sampling and Analytical Program for one
dehydrator was used to determine EF^ (1). The upper bound was calculated by assuming
that all of die measured noncondensable vent gas was due to stripping gas that was 100%
methane. The lower bound was calculated as the rale-of-thumb stripping gas rate
recommended by a glycol dehydrator manufacturer.
EF ACCURACY: 93.72 scflMMscf ± 207.99%
Basis:
The accuracy is propagated through the EF calculation from each term's accuracy:
1. ASPEN has been demonstrated to match actual dehydrators within ±20% within the
calculated confidence intervals obtained from site data.
2. Individual EF confidence intervals were calculated based upon die spread of the site
averages.
ACTIVITY FACTOR: (1.M6 Tseffyear gas thnraibpat in the transmission segment)
Toe amount of gas processed by giyeol dshydrttors in me transmission segment was calculated from the
estimated number of glycol dehydrstors in transmission service and die average throughput capacity for
transmission dehydrators [Wright Kilkn & Co., 1994 (2)]. See Source Sheet P-6 for a detailed discussion of
the breakdown of glycol dehydrators into industry segments. The capacity utilization factor for transmission
was assumed to be 1.
AF ACCURACY: 1.086 Tscfyear ± 143.85%
Basis:
1. Uncertainty based on confidence limits from the site visit data.
ANNUAL METHANE EMISSIONS: (0.1018 Bscftyr ± 391.75%)
The annual methane emissions were determined by multiplying the dehydrator emission factor by the activity
factor.
REFERENCES
1. Myers, D.B. Methane Emissions from the Natural Gas Industry, Volume 14: Gfycol
Dehydrators, Final Report, GRI-94/Q257.31 and EPA-600/R-96-080n. Gas Research Institute
and U.S. Environmental Protection Agency, June 19%.
2. Wright Kilten & Co. Natural Gas Dehydration: Status and Trends, Final Report, GR1-
94/0099, Gas Research Institute, Chicago, IL, January 1994.
A-7
-------
S-2
STORAGE SOURCE SHEET
SOURCES: Glycol Dehydrators
OPERATING MODI: Normal Operation
TYPE; Unsteady, Vented
COMPONENTS: Vents
ANNUAL 0,23 Bscf ±
BACKGROUND:
Glycol dehydrators remove water from a gas stream by contacting the gas with glycot and then driving the
water from the glycol and into the atmosphere. The glycol also absorbs a small amount of methane, and
some methane can be driven off to the atmosphere through the reboiler vent.
FACTOR; (117.18 ± 159,76%)
A thermodynantie computer simulation was used to determine the important emission-affecting variables
for dehydrators. The variables are: gas throughput, existence of a tank, existence of stripping gas,
existence of a gas-assisted pmp, of vent to a burner. Throughput, since its effect is
linear, is handled by establishing an rate per gas throughput. Emission per throughput are then
established for die other important emission affecting characteristics. The emission factor is then:
EF = [ ( ¥n x EFn ) + ( FOT x EFm ) + ( F^ x EF^ ) j x F^c x OC
EF = [ (0,520 x 3.5?) + (0.480 x 175,10) + (O.OSO x 670) J x 0.840 x 1.0
¥„ = Fraction of the population WITH
±
¥m = Fraction of the population WITHOUT
±
Fjg = Fraction of the population WITH stripping gas
O.OSO ± 118.44%
**NVC= Fraction 01 ifae population WITHOUT combusted vcni controls
0.840 ± 15.24%
EFpf™ Total CH4 emission rate per 1 MMscf throughput for dehydrator that has a
flash tank
3.57 (+102% / -58%)
E¥m" Total CH4 emission rate per 1 MMscf throughput for dehydrator does
NOT a tank
175.10 (+101% 1-50%)
EFsc= Incremental emission rate per 1 MMscfd throughput for dehydrator that has
stripping gas
670 (+40% / -60%)
OC = Overcirculation factor for glycol—number of times the industry rule-of-
thumb of 3 gallons glycol/lb water
1.0±0%
A-8
-------
EF DATA
I. Mertswe imissims from the Netmal Gas Industry, Volume 14; Glycol DetytA-atars (1)
establishes emission affecting characteristics of dehydrators.
2. Site visit data establishes the fm and Fwc for multiple Wyoming AOQ data also
verifies F^, though it a higher F, and a higher overall EF.
3. TMOGA/OPA survey of 10! 9 dehydatora established F,r and fm and TP for dehydrates.
4. ASPEN computer simulations were used to determine EF3?, and Ef^ from the dehyclrator
vent
5. Sampling data from the GRI Giycol Dehydrator Sampling and Analytical Program for one
dehydrator was used to determine EFSG (1). The upper bound was calculated by assuming
that all of the measured noDcondeiisable vent gas was due to stripping gas that was 100%
methane. Hie lower bound was calculated as the rule-of-thumb stripping gas rate
recommended by a glycol dehydrator manufacturer.
EF ACCURACY: 117.18 ± 159.76%
Basis:
He accuracy is propagated through the Ef calculation from each term's accuracy:
1, ASPEN has been demonstrated to match actual dehydrators within ±20% within the
calculated confidence intervals obtained from site data.
2. Individua! EF confidence intervals were calculated based upon die of the site
averages.
ACTIVITY FACTOR: (2.00 Tscf/year §•$ tfcnmgfcpBt is the storage MgBent)
The meant of ps processed by glycol dehydrators in the storage segment was calculated from die
amount of gas withdrawn from underground storage, A total of 2.4 Tscf was withdrawn in 1992, and it is
assumed that most stored gas is dehydrated.
AF ACCURACY; 2.00 Tse%ear ± 25%
Bask:
L Uncertainty based on estimate of confidence limits.
ANNUAL METHANE EMISSIONS: (0.2344 Bscf ± 16456%)
The annual methane emissions were determined by multiplying the dehydrator emission factor by the activity
factor,
REFERENCES
1. Myers, D.B. Meitime Emissions from tke tfatmrol Gas JraAsoy, Fo/«we 14: Gfycol
Detytfaaoiyt Final Report, GRI-94/02S7.31 and EPA-600/R-96-OSOn. Gas Research
and U.S. Environmental Protection Agency, toe 1996.
A-9
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GP-2
SOURCES: Glycol Dehydrators
COMPONENTS: Reboiler Vent
OPERATING MODE: Normal Operation
EMISSION TYPE: Unsteady, Vented
ANNUAL EMISSIONS: 1.05 Bscf ±
BACKGROUND:
Glycol dehydrators remove water from a gas stream by contacting the gas with glycol and then driving the
water from the glycol and into the atmosphere. The glycol also absorbs a small amount of methane, and
some methane can be driven off to the atmosphere through the reboiler vent.
EMISSION FACTOR: (121.55 scfMMscf ± 201.96%)
A ifaenBodynamic computer simulation was used to determine the most important emission-affecting variables
for dehydrators. The variables are: (gas throughput, existence of a tank, existence of stripping gas,
existence of a pump, existence of vent controls routed to a burner). Throughput, since its effect
is linear, is handled by establishing an emission rate per gas throughput. Emission rates per throughput are
established for tie other important affecting characteristics. Gas dri¥en pumps are ignored here
and handted in a source analysis. The emission factor is then:
EF - [ ( Fn x EF^ ) •«• ( FNT x EFn ) + ( FK x EFM ) ] x Fwc x OC
EF = [ (0.667 x 3.57) + (0.333 x 175.10) + (0.1 II x 670) J x 0.900 x 1.0
FJT = Fraction of the population WITH flash
0.667 ± 10,13%
fm = Fraction of the population WITHOUT flash tanks = l-F^
0,333 ±20.12%
Fsc " Fraction of the population WITH stripping gas
0.111 ±186%
FNVC~ Fraction of the population WITHOUT combusted vent controls
0.90 ± 10%
EFp,.3 Total CH4 emission rate per 1 MMscf throughput for dehydrator that has a
flash tank
3.5? (+102% / -58%)
Ef w= Total CH4 emission rate per 1 MMscf throughput for dehydrator that
NOT have t flash tank
175.10 (+i01%/-50%)
EFj^ Incremental emission rate per I MMscfd for dehydrator that has
stripping gas
670 (+40% / -60%)
OC = Overcirculation factor for glycol—number of the industry rule-of-
thumb of 3 gallons glycol/lb water
1.0 ± 0%
A-10
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IF DATA
1. Methane Emissions from the Natural Gas Industry, Volume 14: Gfycol Detydraters (I)
emission affecting charactcristJcs of dehydrators.
2. Site visit data establish die F£C, and f^ for multiple (? PROC with
dehydrators).
3, TMO6A/GPA survey of 20? fis plant dehydratiws established Fw and F,® and TP far
dehydrates for the processing segment
4. ASPEN computer simulations wen used to determine EF1P> and EFW tan the dehydrator
vent.
5, Sampling data from the GR1 Glycol Dehydrator Sampling and Analytical Program for one
dehydrator was used to determine EF^ {Gfycol Dehydrator Emissions: Sampling and
Analytical Methods and Estimation Techniques) (2). The upper bound was calculated by
assuming that all of the measured noncondensable vent gas was due to stripping gas that
was 100% methane. The lower bound was calculated as the rale-of-thumb stripping gas
rate recommended by a glycol dehydrator manufacturer.
IF ACCURACY 121.55 sefMMsef ±201, 96%
Basis:
The accuracy is rigorously propagated through the EF calculation ftom each term's accuracy:
1,' ASPEN h^ been ckmoD^ted to match actoal dehydi^ors within ± 20% withii) the
calculated confidence satervais obtained inn site data.
2, Individual EF confidence intervals were calculated from the other data based upon the
spread of the il site averages,
ACTIVITY FACTOR: (8.63 Tsc£^««r gas ffcttsegfepat in the gas pocessiag segweot)
glycol dehydrttor througlspot is estimated from the fraction of gas processed by refrigerated processes (as
opposed to dry bed dehydration for cryogenic processes). The estimate was obtained from the Oil & Gas
Jownal (3) annual Cits Processing Survey, Of a total of 17,44 Tscf, 8.63 Tscf were determined to be
dehydrated by glycoi,
AF ACCURACY: 8.63 Tscfyear ± 22.45%
Basis:
1. Uncertainty based on estimate of confidence limits for Oil and Gas Journal survey.
AF DATA SOURCES;
1. OU & Gas Jownoi* (3) annual Gas Processing Survey.
ANNUAL METHANE (1.0490 Bscf ± 20&20%)
The annual methane were determined by multiplying the dehydrator factor by the activity
factor.
REFERENCES
I, Myers, D.B. Metkame Emi$$ian$ Jhm the Natural Gar Iwfcaffy, Volume 14: Glycol
DOydfaton, Final Report, GRI-94/02S7.31 and EPA-600/R-M-OS§n. Gas Research Institute
and U.S. EnviiwmieBttJ Protection Afency, Jane 1996.
A-II
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2. Radian Corporation. Gfycol Defydrator Emissions: Sampling and Analytical Methods and
Estimation Techniques. GRI-94/D324, Gas Research Institute, Chicago, 1L, 1993,
3. Oil «ft Gas Journal, 1992 Worldwide Gas Processing Survey Database, 1993.
A-1
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GP-3
PROCESSING SOURCE SHEET
SOURCES: Acid Gas Removal (AGR) Units
OPERATING MODE: Norms] Operation
EMISSION TYPE: Unsteady, Vented
ANNUAL EMISSIONS; 0.82 Bscf ± 199%
BACKGROUND:
AGR units remove acid gas (H2S and CQJ from a natural gas stream by contacting the gas with material
(usnaiiy amines) and then driving the absorbed components from the solvent. The amines can also absorb a
small amount of methane, and some methane can be driven off to the atmosphere through the reboiier vent to
the atmosphere.
EMISSION FACTOR: (
-------
ACTIVITY FACTOR: (371 active AGR units in the U.S.)
The number of AGR units in the U.S. have all been assumed to be in the processing segment. The activity
factor was extracted from the Purvin & Gertz survey.
AF DATA SOURCES:
I. Purvin & Gertz, toe. Business Characteristics of the Natural Gas Conditioning Inc'ustry,
1993 (4).
AF ACCURACY: 371 ± 20%
Basis:
1. The accuracy is based upon engineering judgement. The survey should have excellent
accuracy (± 5%), but the upper bound at 90% confidence was revised upward to 20% to
be conservative.
ANNUAL METHANE EMISSIONS: (0.8237 Bscf ± 108.85%)
The annual methane emissions were determined by multiplying an emission factor for an average dehydrator
by the population of AGRs in the segment.
REFERENCES
1. Myers, D.B. Methane Emissions from the Natural Gas Industry, Volume 14: Glycol
Dehydrators, Final Report, GRI-94/0257.31 and EPA-^00/R-96-080n. Gas Research Institute
and U.S. Environmental Protection Agency, June 1996.
2. American Petroleum Institute. 1982 Survey of Gas Processing Units Database. Washington,
DC, 1982.
3. Radian Corporation, investigation of U.S. Natural Gas Reserve Demographics and Gas
Treatment Processes," Topical Report, Gas Research Institute, January 1991.
4. Tannehill, C.C. and C. Galvin. Business Characteristics of the Nahtral Gas Conditioning
Industry. Topical Report, GRI-93/0342, prepared by Purvin & Gertz, Inc., Gas Research
Institute, May 1993.
A-14
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