### Natural Gas Industry Methane Emis sion Factor Improvement Study Final Report Cooperative Agreement No. XA-83376101

Prepared by: Matthew R. Harrison Katherine E. Galloway Al Hendler Theresa M. Shires

URS Corporation 9400 Amberglen Boulevard Austin, TX 78729

Dr. David Allen Dr. Michelle Foss

James Thomas Jarett Spinhirne The University of Texas at Austin 10100 Burnet Road Austin, Texas 78758

Prepared for:

Lisa Hanle United States Environmental Protection Agency 1200 Pennsylvania Avenue

Washington D.C. 20460

December 2011

### DISCLAIMER

The scope of services performed during the Na tural Gas Industry Me thane Emission Factor Improvement Study may not be appropriate to satisfy the needs of other users, and any use or reuse of this document or of the findings, conclusion s, or recommendations presented herein is at the
sole risk of said user.

This publication was developed under Assistan ce Agreement No. XA-833 76101 awarded by the U.S. Environmental Protection Agency. It has no t been formally reviewed by EPA, and EPA does not endorse any products or commercial se rvices mentioned in this publication.Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report ES 

# Executive Summary
This report presents the work performed by the University of Texa s at Austin, and URS Corporation, with the goal of updating default methane (CH 4 

### ) emission factors for selected processes and equipment used in the natural gas i ndustry. The initial impetu s of this study was to
establish new emission factors that were both st atistically superior to the 1996 Gas Research Institute (GRI) and U.S. EPA emi ssions inventory project (GRI and EP A, 1996) emission factors, and more relevant than the GRI/EPA factors (b y including more recent samples). The default emission factors for various sources were comp iled and synthesized for a variety of source categories, and new emission rate measurements were conducted for selected sources where existing data had large uncertainties or were thought to possibly be insufficiently representative of current practices and equipment.
The study focus was high em ission rate leaks (fugitive leaks) from transmission, gathering/boosting, and gas processing recipr ocating and centrifugal compressor components, including emissions from compressor vents (i.e., blowdown lines and compressor seals). Samples were collected from 66 recipro cating compressors and 18 centrifuga l compressors, with a total of 48 reciprocating compressor s at transmission compressor stati ons. Emissions from other fugitive sources such as valves, flanges, and other components were also measured in a few locations.
As found in other similar studies, the larg est single emission sources at a compressor station are the compressor blow down (BD) vent lines and th e compressor seal vents.
The new measurements made for this project on fugitive components (i .e., valves, flanges, etc.) produced lower emission factors than the pr evious GRI/EPA study. This may be due to improved LDAR practices for accessible fugitiv e components that have been implemented by companies in the past two decades. For centrifu gal transmission compress ors this project found the average blowdown line emission factors were significantly lower than the GRI/EPA study, but found wet seal degassing vent em issions were much higher. For reciprocating transmission compressors, this project found average blowdown line emission fa ctors that were significantly higher than the GRI/EPA study, and rod packing ve nt emissions that were also much higher.Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report i 

# Table of Contents 1.0 Introduction and Background ............................................................................................... .... 1 1.1 Selection of Scope .................................................................................................... 4 1.2 Technical Background .............................................................................................. 5 1.2.1 Centrifugal Compressors .......................................................................................... 7 1.2.2 Reciprocating Compressors ...................................................................................... 8 1.2.3 Blowdown Open-Ended Lines ................................................................................ 10 1.3 Review of Existing Emission Factors .................................................................... 11 1.3.1 Transmission– Fugitive Emissions from Reciprocating and Centrifugal Compressors ........................................................................................................... 11 1.3.2 Processing– Fugitive Emissions from Reciprocating and Centrifugal Compressors ........................................................................................................... 13 1.3.3 Compressor Seals .................................................................................................... 14 2.0 Measurement Campaigns ....................................................................................... 18 2.1 Selection of Test Sites ............................................................................................ 18 2.2 Site Descriptions ..................................................................................................... 20 2.3 Field Measurement Methods .................................................................................. 20 2.3.1 Equipment Component Counts and Component Leaks .......................................... 26 2.3.2 Open-Ended Lines .................................................................................................. 27 2.3.3 VPAC Measurements.............................................................................................. 29 2.3.4 Compressor Seals .................................................................................................... 30 2.4 Quality Control ....................................................................................................... 35 3.0 Measurement Results and Analyses ....................................................................... 36 3.1 Measurement Results ............................................................................................. 36 3.3 Comparison to Existing Data ................................................................................. 38 3.4 Comparison of VPAC to Dir ect Measurement Results .......................................... 39 4.0 Conclusions and Recommendations ....................................................................... 41

Appendix A: Summary of Document Review Appendix B: Data Summary Appendix C: ReferencesNatural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report ii 

# List of Tables

Table 1-1. GRI/EPA Emi ssion Factors Summary ......................................................................... 3 Table 1-2. Operating Modes of Co mpressors in Gas Transmission ............................................ 13 Table 1-3. Operating Modes of Compre ssors in Gas Processing Service ................................... 14 Table 1-4. Comparison of Compre ssor Seal Emission Factors ................................................... 16 Table 2-1. Description of Sites Surveyed .................................................................................... 20 Table 2-2. Site-Specific Sources Sampled ................................................................................... 2 2 Table 3-1. Component Count Summary ...................................................................................... 36 Table 3-2. Fugitive Emissions from Valves a nd Flanges using Hi-Flow Sampler Compared to Previous Results .................................................................................................... 36 Table 3-3. Sampling Results for Ce ntrifugal Compressors Vents ............................................... 37 Table 3-4. Sampling Results for Reciprocati ng Compressors (Transmission Compressors) ...... 37 Table 3-5. Sampling Results for Reciproc ating Compressors (Gathering/Boosting Compressors) ............................................................................................................. 38 

# List of Figures Figure 1-1. Centrifugal Compre ssor Wet Seal Degassing Vent .....................................................6 Figure 1-2. Compresso r Blowdown Vents .....................................................................................6 Figure 1-3. Centrifugal Compressor Schematic (Rolls Royce, 2010) ............................................7 Figure 1-4. Centrifugal Comp ressors (foreground) with Trubine Driver (background) ................7 Figure 1-5. Reciprocating Comp ressor Schematic (EPA, 2006) ....................................................8 Figure 1-6. Reciproc ating Compressors .........................................................................................9 Figure 1-7. Reciprocating Compressor R od Packing Vent (Gathering Service) ..........................10 Figure 1-8. Typical Compre ssor Blowdown Arrangement ...........................................................11 Figure 2-1. Concentrations of Na tural Gas Processing Plants, 2004 ............................................18 Figure 2-2. Natural Gas Pipelin e Compressor Stations, 2008 ......................................................19 Figure 2-3. FLIR Camera and Hi-Flow Sampler ..........................................................................26 Figure 2-4. Measurement of Compressor Blowdown Vent Line Leakage with Encased Rotary Van Anemometer .......................................................................................................29 Figure 2-5. Sampling a Blowdown Vent with Hot Wire Anemometer ........................................29 Figure 2-6. Through Valve Acousti c Leak Detection (VPAC) ....................................................30 Figure 2-7. Sampling a Rod Pack ing Vent Stack with Enclosed Rotary Vane Anemometer ......31 Figure 2-8. Sampling a Rod Packing Vent with Hand-held Hot Wire Anemometer ...................31 Figure 2-9. Centrifugal Comp ressor Seal Oil Gas Measurement using Calibrated Bag Technique ...................................................................................................................3 2 Figure 2-10. Centrifugal Compressor Lube Oil System Process Flow Diagram (Picard, 2011) ..34 Figure 3-1. VPAC vs. Dire ct Flow Measurement Met hod, complete data set .............................40 Figure 3-2. Modified VPAC vs. Direct Flow Measurement Method, modified data set for lower flow .......................................................................................................................... ...41Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 1 

## 1.0 Introduction and Background This report describes work conducted under a co operative agreement sponsored by the U.S. Environmental Protection Agency (E PA). The work was performed by the University of Texas at Austin, and URS Corporation, with the goal of updating default methane (CH 4 

### ) emission factors for selected processes and equipment used in the natural gas industry. The default emission factors for various sources were compiled and synthesize d for a variety of source categories, and new
emission rate measurements were conducted for se lected sources where existing data have large uncertainties or are insufficiently representa tive of current practices and equipment.
Methane is the primary component of natura l gas and is also a potent greenhouse gas (GHG). About 32% of the U.S. anthropogenic CH 4 

### emissions have been attributed to natural gas systems, the highest emission source categor y (EPA, 2011). Published estimates of CH 4 

### emissions from the U.S. natural gas industr y are based mostly on default av erage emission factors that were developed in the early 1990s and published in 1996 by the Gas Research Institute (GRI) and EPA (GRI and EPA, 1996). 1 

### In the intervening years, economic incentives and greater awareness of
CH 4 

### as a GHG have inspired new emission reduction approaches that are not reflected in the 1996 GRI/EPA emission factors. Larg e uncertainties in some of the GR I/EPA emission factors resulted in some cases from small sample populations, vari ations in equipment design, and variations in equipment operating practices. Co nsequentially, these uncertainties may also affect the quality of
emissions estimates derived from some of the existing default factors.
EPA, in collaboration with the American Petroleum Institu te (API), the American Gas Association (AGA), and the Inters tate Natural Gas Association of America (INGAA), identified a
subset of the emission factors fr om the 1996 GRI/EPA reports belie ved to contribute the greatest uncertainty in the U.S. natural gas industry CH 4 

### emissions inventory. In 2008, EPA awarded a cooperative agreement to the University of Texa s to update emission factors for the source categories listed below:

1 The GRI/EPA study is documented in a 15 volume set. This report refers to the collective GRI/EPA study as well as specific volumes as necessary.Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 2 

###  Production: Well clean-ups, completion flari ng, well workovers, and pipelines leaks;

 Processing: Fugitive emissions from r eciprocating and centrifugal compressors;

 Transmission and Storage: Fugitive emi ssions from reciprocating and centrifugal compressors, pneumatic devices, and M&R stations; and

 Distribution: Residential customer meters, plastic mains, and services.
The objective for the project was initially to develop new emission factors for these sources that could be used to replace the existing emission factors, most of whic h were developed in the mid-1990’s under the GRI/EPA progra m. An extensive search of publicly available GHG data for the emission sources of interest to this project wa s conducted; a summary of this review is included in Appendix A. The detailed litera ture review is available as an addendum to this report and on the project web site: ( www.utexas.edu/research/ceer/GHG ).
The GRI/EPA study gathered data in the early 1990’s with th e intent of characterizing CH 4 

### emissions from the U.S. natural gas industry. The goal of the GRI/EP A report was a single,
accurate national estimate for total CH 4 

### emissions. Tight confidence bounds on the national total was important, but confidence bounds on any one of the myriad of individual sources could be wider (poorer). As a result, while the GRI/EP A study focused on understanding typical emission characteristics and extrapolating da ta gathered, for some strata of emission sources, data were gathered for a relatively few number of sample s. The GRI/EPA study gathered measurements across broad ranges of technologies and operating practices for a discreet number of emissions sources as they existed in the early 1990s. This produced nationa l average emissions factors which were applied to national level activity data. Ta ble 1-1 summarizes the emission factors for the
sources listed above and their contribution to sector and national emissions for the U.S. natural gas industry at the time of the GRI/EPA study.Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 3 

### Table 1-1. GRI/EPA Em ission Factors Summary

Source Emission Factor Contribution to Sector Emissions, % Contribution to Total National Emissions, % Well Workovers (i.e., cleanups) 0.047 ± 459% tonne CH 4 /well workover-yr 0.01% (± 1,298%) Gas Well Unloading 0.95 ± 344% tonne CH 4 /unloading gas well-yr 6.7% 1.8% (± 380%)
Well Completions 0.014 ± 200% tonne CH 4 /completion well-yr 0.027% 0.007% (± 201%)
Production Gathering Pipelines: Protected Steel 0.327± 85% tonne CH 4 /leak-yr 7.8% 2.1% (± 108%)
Production Gathering Pipelines: Unprotected Steel 0.836 ± 93% tonne CH 4 /leak-yr Production Gathering Pipelines: Plastic 1.61±166% tonne CH 4 /leak-yr Production Gathering Pipelines: Cast Iron 3.85 ± 64% tonne CH 4 /leak-yr Processing: Reciprocating compressors 78± 74% tonne CH 4 / reciprocating compressor-yr 61% 5.32% (± 95.1%)
Processing: Centrifugal compressors 148± 39% tonne CH 4 /centrifugal compressor-yr 1.79% (± 91.4%)
Transmission: Reciprocating compressors 106± 68% tonne CH 4 / reciprocating compressor-yr 39% 12.1% (± 68.1%)
Transmission: Centrifugal compressors 212 ± 44% tonne CH 4 /centrifugal compressor-yr 2.4% (± 43.7%)

Transmission: Continuous bleed pneumatics 8.915 ± 29% tonnes CH 4 /device-yr 12% 4.5% (±60%)

Transmission: Pneumatic/hydraulic devices 0.1008 ± 112% tonne CH 4 /deviceyr Transmission: Turbine pneumatic devices 1.211 ± 276 tonne CH 4 / device-yr Transmission M&R Stations: transmission-to-transmission 7.62± 80% tonne CH 4 / transmission-to-transmission station-yr 3.9% 1.43% (± 1,000%)

Transmission M&R Stations: Farm taps 0.000597± 80% tonne CH 4 /farm tap-yr Distribution: Residential meters 0.00265 ± 17% tonne CH 4 /meteryr 7.2% 1.76% (± 19.8%)

Distribution: Plastic mains 1.91± 166% tonne CH 4 /leak-yr 6.4% 1.56% (± 282%)Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 4 

### Although the GRI/EPA project was not intended to be the basis for estimating CH 4 

### emissions from any particular co mpany source, the data collected during this study provided (and continues to provide) the most co mprehensive quantification of CH 4 

### emissions data for a variety of natural gas industry sources. While the GRI/EPA st udy serves as the basis for most natural gas industry CH 4 

### emission estimates worldwide, there have been some changes in the natural gas industry since the study was performed. New and improved technologies (such as horizontal drilling of unconventional gas sources), improved operating practices, gove rnment regulation of emissions, significant participation in volunt ary programs like Natural Gas STAR, and economic conservation prompted by the ri sing price of natural gas are dr iving forces for reviewing and potentially updating specif ic emission factors. 

## 1.1 Selection of Scope

Stakeholders for this study, which included the U.S. EPA, as well as some industry participants, determined that this study should focus primar ily on the natural gas compressor station fugitive emissions from reciprocating and centr ifugal compressors. Those were among a few sources in the GRI/EPA study with high overall emission rate and relatively wide confidence bounds. For all compressors in natural gas servic e, the highest source of fugitive emissions from compressor stations occurs in transmission stations , in particular the compressor vents (continuous
leaks from blowdown lines vent stacks and from compressor seals). Therefore this study initially
focused on transmission stations.
While this study focuses on transmission, some ne arly identical compressors in gas processing were sampled as opp ortunistic surrogates, and in one regi on, some additional opportunistic data was gathered for upstream production gatheri ng/boosting station compressor emissions.
The study focus was high emissi on rate leaks (fugitive leaks) from compressor components, including emissions from compressor vents (i.e ., blowdown lines and compressor seals). Emissions from other fugitive sour ces such as valves, flanges, and other components were also
measured in a fe w locations.Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 5 

## 1.2 Technical Background Compressors are used at various points along the natural gas collection, transportation, and delivery system to move gas by means of a pressure differential. Compressors at natural gas gathering/boosting stations are used to move gas from production to either central treatment facilities, to gas processing plants , or to transmission pipelines. Within a gas processing plant, compressors are used to draw gas to the plant and/ or to move gas through various portions of the plant. In transmission, compressors are used to overcome the pressure drop that occurs in the long distances of the transmission pipeline.
Fugitive emissions include l eaks from normally sealed co mponents on th e pressurized piping and equipment systems. Th ose include flanges, screwed fittings (conne ctors), valve stem packing (valves), pressure relief valves (PRV’s), va lve seats where one side of the closed valve is open to the atmosphere (open-ended lines [OELs]), and seals, such as co mpressor rod packing or rotating seals. The most signi ficant fugitive emissions are asso ciated with three sources: 1) centrifugal compressor seal o il gas, 2) reciprocating compressor piston rod packing systems, and 3) compressor blowdown line OELs.
For this study, fugitive emi ssions from centrifugal comp ressors and reciprocating compressors were measured at gathering/boosting facilities, gas processi ng plants, and transmission compressor stations. A photo of a centrifugal compress or wet seal degassing vent is shown in Figure 1-1 and a photo of compre ssor blown vents are shown in Figure 1-2.Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 6 

### Figure 1-1. Centrifugal Compr essor Wet Seal Degassing Vent

Figure 1-2. Compressor Blowdown VentsNatural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 7 

## 1.2.1 Centrifugal Compressors Centrifugal compressors are widely used to ha ndle large volumes of gas at high pressure. A centrifugal compressor, in its simplest form, co nsists of an impeller ro tating within a casing, using centrifugal force to propel the gas to the out side of the casing at an increased pressure. A diagram of a centrifugal compressor is shown in Figure 1-3, and a photo is shown in Figure 1-4.

Figure 1-3. Centrifugal Compresso r Schematic (Rolls Royce, 2010)

Figure 1-4. Centrifugal Compresso r (foreground) with Turbine Driver (background)Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 8 

### Centrifugal compressors require seals around the rotating shaft to prevent gases from escaping where the shaft exits the compressor casi ng. These seals use oil, which is circulated under high pressure between three rings around the compressor shaft, forming a barrier against the compressed gas leakage. The cente r ring is attached to the rotating shaft, while the two rings on each side are stationary in the seal housing, presse d against a thin film of oil flowing between the rings to both lubricate and act as a leak barrier. “O-ring” rubber seals prevent leakage around the stationary rings. Very little gas escapes through th e oil barrier; considerably more gas is absorbed by the oil under the high pressures at the “inboard ” (compressor side) seal oil/gas interface, thus contaminating the seal oil. Seal oil is purged of the absorbed gas (using heaters, flash tanks, and degassing techniques) and r ecirculated. (EPA, 2006) 

## 1.2.2 Reciprocating Compressors A reciprocating compressor is a positive disp lacement device which employs pistons driven by a crank shaft to move gas. Th e pistons increase the pressure of the gas by reducing its volume.
Areas of high leak frequency from reciproca ting compressors include flanges, valves, and fittings located on compressors, due to the high vibration. Th e highest volume of gas loss, however, is associated with two sources: 1) piston rod pack ing systems, and 2) compressor
blowdown line OELs.
Packing systems are used to ma intain a tight seal around the piston rod, preventing the gas compressed to high pressure in the compressor cylinder from leak ing, while allowing the rod to move freely. A schematic of a reciproca ting compressor is shown in Figure 1-5.

Figure 1-5. Reciprocating Co mpressor Schematic (EPA, 2006)Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 9 

### Compressor rod packing consists of a series of flexible rings that fit around the shaft to create a seal against leakage. Th e packing rings are lubricated with circulating oil to reduce wear, help seal the unit, and draw off heat. Packing rings are held in place by a set of packing cups, normally one for each pair of rings, and kept tight against the shaft by a surrounding spring. A “nose gasket” on the end of the p acking case prevents leaks around the packing cups. Higher leak rates are a consequence of fit, a lignment of the packing parts, and wear. Leakage typically occurs
from four areas:

 Around the packing case through the nose gasket;

 Between the packing cups, which are typica lly mounted metal-to metal against each other;

 Around the rings from slight movement in the cup groove as the rod moves back and forth; and

 Between the rings and shaft. (EPA, 2006)
Leaking gases are vented to the atmosphere eith er directly from the en d of the packing seal, or through the compressor distance piece vent. Photos are shown in Figures 1-6 and 1-7. Sometimes, on larger compressors, these distance piece vents are piped toge ther and joined into one larger vent line.

Figure 1-6. Reciprocating Compressors (note the 2” rod packing line with orange elbows)Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 10 

### Figure 1-7. Reciprocating Compressor Rod Packing Vent (Gathering Service) (1/2” tubing) 

## 1.2.3 Blowdown Open-Ended Lines The second significant source fr om compressors is large OELs. In particular, those OELs that are connected to the compresso r blowdown vent line. The details of this source are described
below.
Compressor blowdown OELs allow a compre ssor to be depressurized when idle, and typically leak when the compressor is operating or idle.
There are two primary modes of operation leading to different emission rates for compressor blowdown OELs. For this report, compressor blowdown emissions refer to the venting of natural gas contained inside the comp ressor. The first opera ting mode is when the blowdown valve is closed and the compressor is pressurized, either during normal operation or
when idle. The second operating mode is when th e blowdown valve is ope n. This occurs when the compressor is idle, isolated from the compressor suction and discharge manifolds, and the blowdown valve is opened to depr essure the compressor. (Note: Fugitive losses do not include the vented emissions from depressu ring the compressor.) A diag ram of a typical compressor blowdown valve arrangement is presented in Figure 1-8.Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 11 

### Figure 1-8. Typical Compr essor Blowdown Arrangement (adapted from Hummel et. al, 1996)



## 1.3 Review of Existing Emission Factors 1.3.1 Transmission – Fugitive Em issions from Reciprocating and Centrifugal Compressors Most fugitive emission meas urements are conducted for a specific period of time (relatively short in comparison to annual operations), and assumed to leak continuously, at the same rate. However, compressor operations are different, in that they are often cycled for maintenance or due to changes in load requirement s. Emission factors ne ed to account for the portion of time that compressors are (1) not pr essurized, (2) pressurized and running, and (3) pressurized and idle. When co mpressors are depressurized, most components are assumed not to have fugitive emissions. The exce ption is compressor blowdown li nes, which can emit at higher rates when depressurized (note: fugitive lo sses do not include the vented emissions from depressuring the compressor).
The emission factors developed for the GR I/EPA study combined data from U.S. and
Canadian measurements. The U. S. measurements for the depr essurized blowdown fugitive emission factors were much higher than the pres surized blowdown factor, but this difference was
not observed in the Canadian measurements. The GRI/EPA study found much higher emissionNatural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 12 

### rates for depressurized reciprocating compressors than for pressurized reciprocating compressors,
as will be shown in S ection 3.0 on Measurement Results and Analyses. The difference was attributed to compressor age, wh ere compressors installed in th e 1950’s were found to have a statistically higher leak rate than other installation years. The emission factors in the GRI/EPA study are considered the primary industry refe rence for transmission compressor blowdown
emissions
Emissions from compressor-related compone nts were estimated separately due to differences in leakage characteristics for components subject to vibrational conditions. For example, compressor seal emission rates were de termined for the following modes: (1) operating and pressurized, (2) idle and fully pressurized, (3 ) idle and partially pre ssurized, and (4) idle and depressured.
Transmission compressor emission factors from the GRI/EPA study are
5.55 ± 68% MMscf CH 4 

### /reciprocating compressor-yr = 106 tonne CH 4 

### / reciprocating compressor-yr
11.1 ± 44% MMscf CH 4 

### /centrifugal compressor-yr = 212 tonne CH 4 

### /centrifugal compressor-yr
These emission factors are a summary per av erage compressor, and include individual sources such as seal leakage, starter line leak age, compressor PRV leak age, certain fugitive components on the compressors (such as cylinder valve covers and fuel valves) and blowdown open-ended-line leakage. The overall average component emission fact ors are based on the
fraction of time associated with each operating mode for reciproca ting and centrifugal compressors in gas transmission. The operating modes are shown in Table 1-2.Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 13 

### Table 1-2. Operatin g Modes of Compressor s in Gas Transmission (GRI and EPA, 1996, Table 4-20)

Operating Mode Percent of Time Associated with Operating Mode

Reciprocating Compressor Centrifugal Compressor Pressurized: In Operation 45.2% 24.2%

Pressurized: Idle 33.9% 5.8% Depressurized: Idle 20.9% 70.0%



### Of the total CH 4 

### emissions from natural gas opera tions determined from the GRI/EPA study, transmission compressor fugitive emission s contributed 12.1% (± 68.1%) for reciprocating compressors and 2.4% (± 43.7%) for centrifugal compressors (39% of CH 4 

### emissions from transmission activities). 

## 1.3.2 Processing– Fugitive Emissions from Reciprocating and Centrifugal Compressors Component emission factors for the GRI/EP A study for compressors in gas processing plants were based on the screening data noted ab ove for transmission co mpressors. Adjustments were made for the fraction of time reciprocating and centrifugal compressors are pressurized in gas processing (89.7% and 43.6% for reciprocating and centrifugal compressors, respectively). In addition, it was found th at approximately 11% of compressor s in gas processing have blowdown
valves and PRVs routed to a flare rath er than vented to the atmosphere.
Component counts for gas processing plants, including the compressors, were based on data from 21 sites compiled through the GRI/EPA study and three separate studies.
Gas Processing compressor emission factors from the GRI/EPA study are:
4.09± 74% MMscf CH 4 

### /reciprocating compressor-yr = 78 tonne CH 4 

### / reciprocating compressor-yr

7.75 ± 39% MMscf CH 4 

### /centrifugal compressor-yr = 148 tonne CH 4 

### /centrifugal compressor-yr These emission factors are a summary per av erage compressor, and include individual sources such as seal leakage, starter line le akage, compressor PRV leakage, certain fugitive components on the compressors (such as cylinder valve covers and fuel valves) and blowdown open-ended-line leakage. The overall average component emission factors are based on theNatural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 14 

### fraction of time associated with each opera ting mode for reciprocating and centrifugal compressors in gas processing service. Th e operating modes are shown in Table 1-3. Table 1-3. Operating Modes of Compressors in Gas Processing Service (GRI and EPA, 1996)

Operating Mode Percent of Time Associated with Operating Mode

Reciprocating Compressor Centrifugal Compressor

Pressurized 89.7% 43.6%

Depressurized 10.3% 56.4%



### Of the total CH 4 

### emissions from natural gas opera tions determined from the GRI/EPA study, gas processing compressor fugitive emissions contributed 5.32% (± 95.1%) for reciprocating compressors and 1.79% (± 91.4%) for centrifugal compressors (61% of CH 4 

### emissions from gas processing activities). 

## 1.3.3 Compressor Seals

This section addresses more detailed emission source information from EPA’s Natural Gas STAR program and from further studies conducte d on compressor seals since the GRI/EPA study. A 2006 California Energy Commission (CEC , 2006) document reviewed the API Compendium (American Petroleum Institute, 2004) emission factors and commented that centrifugal and reciprocating seals have different emission char acteristics and should not be combined in one emission factor. Further, th e CEC document noted that cent rifugal compressor seals can be classified as either wet or dry technologies. Th e wet seals use oil to form a barrier to prevent leakage from the compressor seal. The circulating oil is stripped ofgas that it absorbs at the highpressure seal face and vents the gas to the atmosp here. Therefore, wet seals have emissions both from fugitive leakage at th e seal face as well as the vented emissions from the circulating oil. The CEC paper indicated that the we t seals were more commonly used when the 1996 GRI/EPA study was developed, which is the basis of the Compendium emission factors.
Dry seals have much lower emissions than wet s eals since the barrier fluid is high pressure gas, which does not involve venti ng from stripping oil, and the seal design is different, resulting in much lower seal leakage. An EPA Natural Gas STAR Lessons Learned paper on replacing wetNatural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 15 

### seals with dry seals states that dry gas seals su bstantially reduce methane emissions (EPA, 2006).
The main difference in the emis sions from wet and dry seals is the vented emissions from the
recirculation oil associated with wet seals.
Based on guidance in the CEC pa per, the original emission fa ctors from the fugitives report of the 1996 GRI/EPA natural gas CH 4 

### emissions study were reviewed. The individual seal emission factors from this study were never presented in the GRI/EPA study, as compressor equipment level emission factors were presente d instead. Additionally, the Gas STAR reports were reviewed for compressor seal emissions in formation. The CEC document notes that the
authors had discussions with individuals associat ed with the original GR I/EPA measurements, who indicated that measurements were made of the seal gas leakage for the fugitives estimate, while the seal oil degassing emissions were captured in th e station venting measurements. The station venting raw data from th e 1996 GRI/EPA study were reviewed to see if they include specific seal oil vented emissions, but unfortunately the availabl e data were not disaggregated to that level of
detail.

The CEC document recommen ded reviewing the 1996 GRI/ EPA data for separate reciprocating and centrifugal emission factors, as well as the Gas ST AR reports. The CEC
document also recommended review ing a study by the Wuppertal In stitute for measurements on the Russian Gazprom transmission system for wet seal measurement data. Unfortunately, this report has not been located. Howe ver, compressor seal leak data from the 1996 GRI/EPA fugitive report and the Natural Gas STAR reports have be en reviewed and summarized in Table 1-4.
As shown in Table 1-4, there are several poten tial compressor seal emission factors. The only emission factor found that is believed to include both the wet seal vented and fugitive emissions is the last entry take n from Natural Gas STAR (the ot her entries are probably fugitive emissions from the seal face). Th e emission factors shown in Tabl e 1-4 were taken from a variety of sources and provided in different units (e.g., metric tonnes, as total gas, as CH 4 

### ); but are shown in Table 1-4 on the same basis (scf gas/seal-hou r) for comparison purposes. As observed in Table 1-4, there is a wide range of variability in the reported comp ressor seal emission factors for both hourly and annual emissions.Natural Gas Industry Methane Emission Factor Improvement StudyDecember 2011Draft Final Report16Table 1-4. Comparison of Compressor Seal Emission FactorsSeal TypeEmission FactorDefault CH4content(mole %)SourceNotes(scf CH4/seal-yr)(scf gas/seal-yr)(scf gas/seal-hr)ProductionUnspecified 2,370 3,008 0.343 78.8%Vol. 8, Table 4-8, 1996GRI/EPA CH4studyBased on western U.S. onshore; converted tohourly basis assuming 8760 hrs/yrUnspecified*42.2 Not given 1992 Picard study, inTable B-17 of the Feb. 2004 APICompendiumConverted from kg/hr-component using a naturalgas density of 1 lb/23.8 ft^3 from Table 3-5 ofthe Feb. 2004 APICompendium.ProcessingReciprocating 450,000 517,241 65.8 87.0%Vol. 8, Table 4-12, 1996GRI/EPA CH4studyConverted annual to hourly accounting for 89.7%of the year pressurizedCentrifugal 228,000 262,069 68.6 87.0%Converted annual to hourly accounting for 43.6%of the year pressurizedTransmissionReciprocating 396,000 423,983 61.2 93.4%Vol. 8, Table 4-15, 1996GRI/EPA CH4studyConverted annual to hourly accounting for 79.1%of the year pressurizedCentrifugal 165,000 176,660 83.3 93.4%Converted annual to hourly accounting for 24.2%of the year pressurizedRecip. - rodpacking - running 865,000 98.7 Not givenIndaco study, provided in GasSTAR Lessons Learned,directed inspection at comp.stns.Converted annual to hourly assuming 8760 hrs/yrRecip. - rodpacking - idle 1,266,000 144.5 Not givenCentrifugal - Dry62,700 7.16 Not givenIndaco study, provided in GasSTAR Lessons Learned,directed inspection at comp.stns.Converted annual to hourly assuming 8760 hrs/yrCentrifugal - Wet278,000 31.7 Not givenReciprocating*34.7 Not given1992 Picard study, inTable B-16 of the Feb. 2004 APICompendiumOriginal EFs were in units of kg THC/hrcomponent and converted to scf assuming anatural gas density of 1 lb/23.8 ft^3 fromTable 3-5 of the Feb. 2004 APICompendium.Centrifugal*42.7 Not givenStorageReciprocating 300,000 321,199 54.3 93.4%Vol. 8, Table 4-22, 1996GRI/EPA CH4studyConverted annual to hourly accounting for 67.5%of the year pressurizedCentrifugal 126,000 134,904 68.7 93.4%Converted annual to hourly accounting for 22.4%of the year pressurizedNatural Gas Industry Methane Emission Factor Improvement StudyDecember 2011Draft Final Report17Table 1-4. Comparison of Compressor Seal Emission Factors, continuedSeal TypeEmission FactorDefault CH4content(mole %)SourceNotes(scf CH4/seal-yr)(scf gas/seal-yr)(scf gas/seal-hr)Unspecified Gas IndustryCentrifugal -Dry**up to 3,154,000 up to3,376,000up to 385Not given;assume93.4%EPA Gas STAR LessonsLearned, replacing wet sealswith dry sealsfor centrifugalcomp.Converted scf/min to hourly and annual assumingcontinuous operation; emission factor provided interms of CH4emissions; converted to total gasemissions assuming 93.4 mole % CH4in the gas.Centrifugal -Dry**262,800 -1,576,800281,370 -1,688,20032.1 - 192.7Centrifugal - Wet(includes vented)21,024,000 -105,120,00022,510,000 -112,548,0002570 - 12,850*Emission factors already presented in the APICompendium.** The EPA Gas STAR paper presents two sets of emissionsdata for dry centrifugal seals within the same paper.Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 18 

# 2.0 Measurement Campaigns This section provides details on the test sites and measur ements collected during this study. 

## 2.1 Selection of Test Sites Figures 2-1 and 2-2 show the locations of na tural gas processing plants and interstate pipeline compressor stations ope rating in the lower 48 states, re spectively. About one-half the total number of gas plants are in Texas, Louisi ana, and Oklahoma, while a large fraction of the rest are in Wyoming, Colorado, a nd New Mexico. Interstate pi peline compressor stations are more dispersed.

Figure 2-1. Concentrations of Natural Gas Processing Plants, 2004 Voluntary partnerships with gas plant and pipeline operating companies were relied on for site access. Access to natural gas processi ng plants and transmission compressor stations was requested via emails sent on behalf of the pr oject team by the AGA, API, GPA, and INGAA to their respective members. Companies choosing to participate in the stud y were then asked to provide a list of candidate test si tes that were representative of their U.S. operations. Test sites were selected from the pool of candidates to re present a mix of comparatively older and newer facilities and different geographi c regions and pipelines. Logist ical and budgetary issues were considered by selecting sites with relatively la rge numbers of reciproca ting and/or centrifugalNatural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 19 

### compressors and comparatively easy access to emissi ons sources. Other practical issues such as distances between sites were also considered (to control travel expe nses). Incentives to participate in this study include anonymity, and site -specific emission factors. The pool of test sites ideally included:

 Reciprocating and centrifugal compressors;

 Construction dates before and afte r 1996 (the year the GRI/EPA study was published);

 Wet and dry centrifugal compressor seals;

 Compressors in operating, standby, and idle modes;

 Accessible open ended bl owdown and starter lines;

 Accessible compressor seal vents;

 A mix of compressor manufacturers, models, sizes, and ages;

 Different approaches to leak detection and repair; and

 Natural Gas STAR Partners and non-partners.

Figure 2-2. Natural Gas Pipeline Compressor Stations, 2008 (Source: Energy Information Administration, O ffice of Oil & Gas, Na tural Gas Division, Natural Gas Transportation Information System.)Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 20 

### A total of three companies granted access to their compressor sampling sites and signed access agreements with the University of Texas. Measurements were conducted during three separate campaigns during 2009 – 2011. Measuremen ts at the compressor stations included the following:

 Station fugitive screening by FLIR camera (non-quantitative);

 Fugitive measurement on identified leak ers by High Volume Sampler device; and

 Reciprocating and centrifugal compressor ve nt measurements by alternate methods (pitot tube anemometer or calibrated bag). Sampling at the first group of sites in East Texas occurred for a week in November, 2009. A second week of sampling occurred in February , 2010, at a group of sites in West Texas. A third week of sampling occurred in May, 2011, at a group of sites in New Mexico. The strategy in conducting the sampling was to collect as much data as possible at the sites, using multiple instruments.. Measurements included compressor related fugitive components (flanges, valves, OELs, PRVs), as well as blowdown vent lines and compressor seal and rod packing emissions. 

## 2.2 Site Descriptions
Measurements were made at a total of elev en sites which were constructed between the 1950s and 2000s. For comparison, the 1996 GRI/EP A compressor emission factors were based on measurements at 15 compressor stations. Sa mples were collected from 66 reciprocating compressors and 18 centrifugal compressors, with a total of 48 reciprocating compressors at transmission compressor stations. A list of the sites surveyed is provided in Table 2-1. Table 2-1. Description of Sites Surveyed

Site Survey Date Description Measured Equipment Year Built Site 1 11/2009, 5/2011 Transmission Compresso r Station 6 Reciprocating Compressors 1965 Site 2 11/2009, 5/2011 Transmission Compressor Station 3 Centrifugal Compressors 1982 Site 3 11/2009, 5/2011 Transmission Compressor Station 5 Reciprocating Compressors 1992-2009 Site 4 2/2010 Transmission Compressor Sta tion 15 Reciprocating Compressors 1948 Site 5 2/2010 Transmission Compressor St ation 5 Reciprocating Compressors 1948 Site 6 5/2011 Gathering/Boosting compre ssors 13 Reciprocating Compressors 1992 Site 7 5/2011 Gathering/Boosting compressors 6 Reciprocating Compressors 1993 Site 8 5/2011 Gathering/Boosting compre ssors 6 Reciprocating Compressors 1992 Site 9 5/2011 Gas Processing Plan t 2 Centrifugal Compressors 1993 Site 10 5/2011 Gathering/Boosting comp ressors 4 Centrifugal Compressors 1971 Site 11 5/2011 Gas Processing Plan t 6 Centrifugal Compressors 1950 

### Each of the volunteer companies that provided sites in Table 2-1 is a Participant in the EPA’s Natural Gas STAR program, however, that was not a requirement for site selection. It isNatural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 21 

### unknown whether the visited sites made any change s due to Natural Gas Star recommended best practices.



## 2.3 Field Measurement Methods Measurements of the compressor-related “vent lines” was the primary focus of the field measurement visits, since these sources were the largest single emitters in the previous studies. The “vent lines” were often elevated stacks, open to the atmosphere. The compressor-related “vent lines” that were measured were 1) the combined rod packing vent lines on reciprocating compressors, 2) the wet seal vent line on centr ifugal compressors with wet seals, and 3) the compressor open-ended line (OEL) leakage through the compressor blowdown vent line. The reciprocating compressor rod packin g vent lines were most often co mbined into a single elevated vent for each compressor (though some smaller gath ering compressors did have individual, nonelevated vents for each cylinder). The compressor Blowdown (BD) vent line was usually a direct line from each compressor, but at many sites the BD vent lines were joined into a common elevated station vent stack that also had other sources routed to the same stack. The actual blowdown events were not measured; instead the amount of continuous leakage through the blowdown line was measured. In addition to the compressor vents, fugitive screening and fugitive measurements of ordinary leaking components such as flange s, valves, OELs, PRVs were conducted throughout the site at five of the eleven sites. Not all eleven sites were measured for ordinary fugitives since the compressor vents were the main focus, and be cause the total site fugitive screening is an expensive measurement approach. Details of the sampling conducted at each host site are provided in Table 2-2. Columns in the table show which vent s and components were measured. A summary of the sampling methods are provided in the remainder of this se ction. Details of the sampling procedures are available in the project’s Quality Assurance Projec t Plans, provided in as an addendum to this report..Natural Gas Industry Methane EmissionFactor Improvement Study December 2011Draft Final Report 22Table 2-2. Site-Specific Sources SampledSiteEquipment TypeHPStatusRod PackingWetSealDegasCompressorOEL leakthrough BDLineLube OilTankSiteRodPackingCombinedVentsIndividual RodPacking SealLeaksDischargePRVIRScreeningComponentLeaksSite 1Recip 1 2,650 Idle but pressurized MN/AN/AMN/ANMM MRecip 22,650 Idle but pressurized MMNMRecip 32,650 Idle but pressurized EIMNMRecip 44,200 Idle but pressurized EIMNMRecip 58,200Idle, Depressurized,open EIM NMDebrine pipingN/A N/A N/A N/A M NMSite 2Recip 1 2,800 Idle but pressurizedN/AM,NEN/AM,NEN/ANMM MRecip 22,800 Idle but pressurized M,NE M,NE NMRecip 32,800 Idle but pressurizedMM,NENMRecip 42,800 Idle but pressurizedMM,NENMRecip 52,800 Idle but pressurizedMM,NENMRecip 62,800 Idle but pressurizedEIM,NENMStation BD Vent #1 - Yard Piping N/A--N/A N/AM NMStation BD Vent #2 - IdleLine piping N/A -- NM NMStation BD Vent #3 - Yard Piping N/A -- M NMSite 3Centrif 1 4,800 Idle, depressurizedN/A N/AM,NE MN/ANMM MCentrif 24,800 RunningM MNMCentrif 34,680 RunningM MNMM = MeasuredNM = Not MeasuredN/A = Not Applicable or Not PresentEI = InaccessibleM,NE = Measured, No EmissionsNatural Gas Industry Methane EmissionFactor Improvement Study December 2011Draft Final Report 23Table 2-2. Site-SpecificSources Sampled, continuedM = MeasuredNM = Not MeasuredN/A = Not Applicable or Not PresentEI = InaccessibleM,NE = Measured, No EmissionsSiteEquipment TypeHPStatusRod PackingWetSealDegasCompressorOEL leakthrough BD LineLube OilTankSiteRodPackingCombinedVentsIndividualRod PackingSeal LeaksDischargePRVIRScreeningComponentLeaksSite 4Recip 1 1,235 Idle, depressured NMN/A N/AMN/AMM MRecip 21,235 RunningMMMRecip 31,235 Idle, depressured NMMMRecip 41,235 RunningMMMRecip 51,235 Idle, depressured NMMMRecip 61,235 RunningMMMRecip 71,235 Idle, depressured NMMMRecip 81,235 RunningMMMRecip 91,235 Idle, depressured NMMMRecip 101,235 Idle,depressured NMMMRecip 111,800 Idle,depressured NMMMRecip 121,235 Idle,depressured NMMMRecip 133,500 Idle,depressured NMMMRecip 143,500 Idle,depressured NMMMRecip 151,800 Idle,depressured NMMMSite 5Recip 1 1,002 Running NMN/A N/ANEN/ANEM MRecip 21,002 Idle, depressured NMMMRecip 31,002 Idle, depressured NMMMRecip 41,002 RunningNMNENERecip 51,002 Idle, depressured NMMMRecip 62,278 Idle, depressured MNMNMRecip 72,278 Idle, depressured MNMNMNatural Gas Industry Methane EmissionFactor Improvement Study December 2011Draft Final Report 24Table 2-2. Site-SpecificSources Sampled, continuedSiteEquipment TypeHPStatusRod PackingWet SealDegasCompressor OELleak through BDLineLube OilTankSiteRod PackingCombinedVentsIndividual RodPacking SealLeaksDischarge PRVIR ScreeningComponentLeaksSite 6Recip 1 RunningN/AMN/AM,NE M M,NENM NMRecip 2RunningM,NE M,NE MM,NERecip 3RunningMM,NE M NMRecip 4RunningMM,NE M M,NERecip 5RunningMM,NE MMRecip 6RunningNMMNM M,NERecip 7Idle, Depressured NM M,NENMM,NERecip 8Idle, Depressured NM M,NENMMRecip 9RunningMM,NE MMRecip 10Idle, Depressured NM M,NENMNMRecip 11Idle, Depressured NM M,NENMM,NERecip 12RunningMM,NE M M,NERecip 13Idle, Depressured NM M,NENMNMSite 7Recip 1 RunningN/AMN/AM,NE M,NE MNM NMRecip 2RunningMM,NE M,NE M,NERecip 3RunningMM,NE M,NE M,NERecip 4Idle, Depressured NM M,NEM,NEM,NERecip 5Idle, Depressured NM M,NEM,NEM,NERecip 6RunningMM,NE M,NE M,NESite 8Recip 1 Idle, depressured NMN/A N/AM,NE NM M,NENM NMRecip 2RunningMM,NE M,NE NMRecip 3RunningMM,NE M,NE M,NERecip 4RunningMM,NE M,NE M,NERecip 5Idle, Depressured NMNM NM NMRecip 6Idle, Disassembled NMM,NE NM NMRecip 7RunningMM,NE M,NE M,NEM = MeasuredNM = Not MeasuredN/A = Not Applicable or Not PresentEI = InaccessibleM,NE = Measured, No EmissionsNatural Gas Industry Methane EmissionFactor Improvement Study December 2011Draft Final Report 25Table 2-2. Site-SpecificSources Sampled, continuedSiteEquipment TypeHPStatusRod PackingWetSealDegasCompressorOEL leakthrough BD LineLube OilTankSiteRodPackingCombinedVentsIndividualRod PackingSeal LeaksDischargePRVIRScreeningComponentLeaksSite 9Centrif 1 RunningN/A N/AM M,NEN/ANMNM NMCentrif 2RunningMMNMSite 10Centrif 1 RunningN/A N/AM MN/AMNM NMCentrif 2Idle, DepressuredNMMMCentrif 3RunningMMMCentrif 4RunningMMMSite 11Centrif 1 RunningN/A N/AM MN/ANMNM NMCentrif 2Idle, Depressured NMM NMCentrif 3RunningMMNMCentrif 4RunningMMNMCentrif 5RunningMMNMCentrif 6RunningMMNMM = MeasuredNM = Not MeasuredN/A = Not Applicable or Not PresentEI = InaccessibleM,NE = Measured, No EmissionsNatural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 26 

## 2.3.1 Equipment Component Counts and Component Leaks At five stations fugitive leak sources asso ciated with each compressor were classified (i.e., connector, valve, etc.) and counted. First, a FLIR infrared camera was used to locate (but not quantify) any potential leak ing components. A trained team from the company that owned the FLIR was used to make those measurements. Once the FLIR camera team located a leaking component (usually only a few sources per stat ion), then a quantifica tion was performed using the high volume (Hi-Flow) sampler. The high vo lume sampler operates by pulling in a relatively large volume of air (up to 8 cfm), and determining the CH 4 

### concentration in the air. Where possible, packing seal vents were selected ra ndomly, disconnected from the common vent, and measured with the Hi-Flow. A photograph of the FLIR camera and Hi-Flow Sampler in use is shown in Figure 2-3.

Figure 2-3. FLIR Camera (rig ht) and Hi-Flow Sampler (left) While this approach was used early in the firs t few stations, it became clear that, as in the past GRI/EPA study, onl y the few very large leaks on the compressor seals and on the compressor blowdown OELs were important c ontributors to the total emissions. 

## 2.3.1.1 High Volume Sampler The high volume (Hi-Flow) sampler is portabl e, intrinsically safe, battery-powered instrument designed to determine the rate of gas leakage around variou s pipe fittings, valve packings, and compressor seals found in natu ral gas transmission, storage, and processing
facilities. This instrument was used to measur e leak rates for fugitiv e components that were identified as leaking by an initial IR camera evaluation of the site. A component’s leak rate is measured by sampling at a high flow rate so as to capture a ll the gas leaking from the component along with a certain amount of su rrounding air. By accu rately measuring the flow rate of theNatural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 27 

### sampling stream and the natural ga s concentration within that stre am, the gas leak rate can be calculated using Equation 1. The instrument auto matically compensates for the different specific gravity values of air and natu ral gas, thus assuring accura te flow rate calculations. Leak = Flow x (Gas sample – Gas background) x 10 –2 

### Equation 1 Where, Leak = rate of gas leakage from source (cfm); Flow = sample flow rate (cfm); Gas sample = concentration of gas from leak source (%); and Gas background = background gas concentration (%). 

## 2.3.2 Open-Ended Lines
The emission rates from OELs and vents we re determined by measuring the velocity profile across the vent line and the flow area at th at point. Measurements on these lines were made using an enclosed rotary vane anemometer, or a hot-wire anemometer prob e. For measurements made at a vent tip, flow veloc ities were measured with an en cased rotary vane anemometer (Omega, model number HHF710). Rod packing tubing vents were measured using a low-flow slim probe hot wire anemometer (Omega, HHF42) . The anemometer was enclosed in a fixed plastic pipe of approximately 3” diameter. The process vent line was sealed to the anemometer pipe, using a variety of simple seals such as gask et material and duct tape. The plastic pipe of a fixed size meant that only the anem ometer readout (velocity) was need ed, rather than the exact size of the process vent pipe. With the velocity and diameter, the vo lume released per unit time was
calculated. In ideal cases, there was one blowdown line pe r vent. In a few cases, multiple compressors were routed to a single co-mingled vent line, with no access to individua l compressor vent lines upstream. These latter cases made it impossible to produce average comp ressor measurements for the site, especially where compressors in differ ent modes (idle & depressurized and operating)
were connected to one combined ve nt line. Photos of sampling a blowdown vent using a hot wire anemometer are shown in Figure 2-4 and 2-5.Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 28 

### Also, in one case the top of the combined vent was inaccessible, so a hot wire anemometer was inserted through a port (an open 1” diameter bleed valve) to make the vent velocity

measurement. When measuring flows from vent s, a distinction is made betw een continuous fugitive leak emissions and the short duration discharge of de -pressured equipment, which is often called a blowdown. Blowdown quantities fr om the equipment is not the t opic of this report, so those intermittent discharges were ignored. However, continuous leakage emissions that flow through
the blowdown vent line when it is idle were included as fugitive emissions.
Blowdown emissions from con tinuous vent systems and inte rmittent vent systems during venting events are defined as “venting” emissions. For example, blowdown valves are opened to depressurize the system when a compressor is be ing shut down. The gas that is intentionally discharged during the blowdown is considered vented – not fugitive – emissions, and was not measured as part of this study. When a blowdown valve is cl osed, any gas leakage through the
valve and out the vent stack was m easured as fugitive emissions. Additionally, some locations had lube oil tanks with separate elevated vents. If this configuration was present at a facility, the anemom eter was used to meas ure emissions from the
lube oil tank vents. Lube oil ve nts may include fuel/exhaust from the engine driver side of the compressor, unless there are separate lubrication systems for the engine side and the compression side of a compressor.Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 29 

### Figure 2-4. Measurement of Comp ressor Blowdown Vent Line Leakage with Encased Rotary Vane Anemometer

Figure 2-5. Sampling a Blowdown Vent with Hot Wire Anemometer



## 2.3.3 VPAC Me asurements In addition to the vent rate measurement equi pment listed above, a “t hrough-valve acoustic
leak detection device” was utilized at six sites (four gathering/boosting co mpressor stations and two gas processing plants). Origin ally designed as a valve loss c ontrol system for flare and steamNatural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 30 

### valves, the VPAC device uses a leak quantification algorithm to quantify a le ak rate of valves. A photo of the VPAC in use is shown in Figure 2-6. A representative of the acoustic device
manufacturer attended the site visits and conducte d the VPAC tests. Dual measurements were taken where possible with both the acoustic device and the direct flow measurements to compare readings from the two devices. The VPAC measurements were reported to this project in a singleblind fashion. That is, the VPAC results were reported without knowledge of the results of the
other direct measurements.

Figure 2-6. Through-Valve Acou stic Leak Detection (VPAC) 

## 2.3.4 Compressor Seals Measurements on compressor seals depended on th e type of compressor. For reciprocating compressors, the following techniques were employed:

 Where rod packing vent lines were piped to gether (multiple cyli nders joined into a single vent line per compressor), the enclosed rotary vane anemometer was used to
make the measurements at the top of the rod packing vent line. In those cases, one single measurement per compressor was made. An exampl e is shown in Figure 2-7.Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 31 

###  Where rod packing vent line s were individually vented to the atmosphere at the distance piece, each distance piece vent was measured with a hand-held hot wire anemometer. An exampl e of this sampling is shown in Figure 2-8.

Figure 2-7. Sampling a Rod Packing Ve nt Stack with Enclosed Rotary Vane Anemometer

Figure 2-8. Sampling a Rod Packi ng Vent with Hand-held Hot Wire Anemometer For centrifugal compressors w ith wet seals, measurements were made of wet seal degassing at the fill port to the s eal oil sump. Each su mp had a dedicated vent line, but in every case on this project, the tip of that vent line was placed above th e turbine driver exhaust stack, preventing any safe access. The dedicated vent line had no valves an d therefore could not beNatural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 32 

### blocked/closed. For these measur ements, the seal oil fill cap into the sump was opened, and it was assumed that this opening was now the path of least resistance, since the dedicated vent lines were 20-50 feet in length from the sump. Calibrated plastic bags of known internal volume were used to measure the vent rate, by timing how long each sump took to fill th e bag. A set of three repeat bag
measurements were made for each sump. In one case, there was no acces s to the fill port, and measurements were made using th e enclosed anemometer directly off the top of the sump knockout pot. This measurement tec hnique is shown in Figure 2-9.

Figure 2-9. Centrifugal Compr essor Seal Oil Gas Measurement Using Calibrated Bag Technique

On the wet seal data for centri fugal compressors, this study has found, after the fact, that there may be several technical issues surrounding a proper measurement from a wet seal system. Seal oil systems for centrifugal compressors can be complex, and may require the use of a detailed P&ID (piping and instrumentation diagram) to determine where all the flash locations in a system are. For example, as can be seen in Figure 2-10, a seal oil system may contain a flash drum/pot, where a separate vent line discharges any absorbed ga s from the oil circulating to the seal. This is
not the same line as the main vent line from th e sump, where many companie s (and this project) took samples. In addition, some seal oil systems may also have bl owers, as shown in Figure 2-10, which would affect calibrated bag measurements from the sump. Many operators are not fully aware of the detailed workings of a particular compressor’s seal oil system because it is a selfcontained, skid mounted package that is not alte red day-to-day by operations personnel. Therefore,Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 33 

### this project’s measurements of wet seal dega ssing should be used as a benchmark, but would require further analysis before th e measurements could be used to develop new emission factors.Natural Gas Industry Methane Emission Factor Improvement StudyOctober 2011Draft Final Report34Figure 2-10. Centrifugal Compressor Lube Oil System Process Flow Diagram (Picard, 2011).Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 35 

## 2.4 Quality Control Where total site fugitives were measured, CH 4 

### background concentrations were measured simultaneous with every leak test and s ubtracted from the main sample flow CH 4 

### concentration. This is necessary to prevent b ackground concentrations , which may be elevat ed by other nearby leaks, from influencing the leak rate determinations for indi vidual components. The Hi-Flow Sampler uses two detectors simultaneously to dete rmine the background and the main sample flow
concentration. One detector draws air flow from the main sample hose and the second detector draws air from a separate background probe. The background probe was held near the leak being measured while the sample hos e is held at the leak.
To check if the instrument is capturing all the gas that is escaping from the leak source, two measurements were performed at two different flow rates. The first measurement was taken at the highest possible flow rate, followed by a second measurement at a flow rate that is approximately
70–80% of the first. If the two calculated leak rates are within 10% of each other, then it was assumed that all gas has been captured during the test.

Calibration checks of both the background and leak-gas detectors were performed at the beginning and end of every day using a certified 2.5% CH 4 

### gas standard. The Hi-Flow Sampler
has a built in feature to perform these checks.
The high flow sampler was calibrated upon arriva l at each test site or whenever a single point check of the calibration is outside the ± 10% acceptability range. The calibration check was performed using the vendor-supplied calibration k it with zero air and gas standards of 2.5% and
100% CH 4 

### . The leak-gas and background gas detector s were calibrated at these concentrations using the menu-driven programmed procedure given in the Hi-Flow Sampler operation and
maintenance manual.
For the other instruments, such as the anemom eters, the instruments were calibrated before
and after the tests to assure thei r accuracy. Readings made with these instruments were corrected for the actual gas composition becaus e in most cases the instrument s were calibrated on air and had to be corrected for measuring natural gas.Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 36 

### Results of this measurement project were al so cross checked by independent technical
review of a scientist an d engineer not associated with this project. 

# 3.0 Measurement Results and Analyses This section presents the results from th e field measurement campaigns of this study. Raw measurement data is presented in Appendix B.



## 3.1 Measurement Results Component counts were collect ed for five transmission compressor stations, and are shown as an average per station in Table 3-1. Table 3-1. Compone nt Count Summary

Component Average Count per Facility Standard Deviation Valves 327 112 Flanges 415 163 Compressor Seals 22 14 PRVs 13 5 OELs 16 22 Connectors 376 209



### The overall fugitive emissions from valves, fl anges, and other sources are reported as an average over all five sites in Table 3-2 below. As the table shows, the new factors show a lower leak rate from an average component when co mpared to the GRI/EPA data from the 1990’s. While this is from a relatively small sample set compared to the GRI/EPA study, these lower emission factors may be the resu lt of better Leak Det ection and Repair (LDAR) practices that have developed since the 1990s’ for ordina ry fugitives in natural gas systems.

Table 3-2. Fugitive Emissi ons from Valves and Flanges using Hi-Flow Sampler Compared to Previous Results

Facility Component Total Number of Components

Screened Component Emission Factor (Mscfy) 1996 GRI/EPA Emission Factor (Mscfy) Valves 1,634 0.093 0.184 Flanges 1,244 0.051Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 37 

### As was found in the previous GRI/EPA st udy, the largest single emission sources at a compressor station are the compressor blowdown (BD) vent lines and the compressor seal vents. These remain the largest sources in the samp ling for this project. Sampling results for compressor vents are provided in Tables 3-3, 3-4, and 3-5. It is assumed that transmission compression, gathering/boosting, and gas proces sing centrifugal compressors emission factors can be grouped together; wher eas, transmission compression reciprocating compressors are grouped separately from othe r reciprocating compressors.
Table 3-3. Sampling Results fo r Centrifugal Compressors Vents (Includes transmission compression, gathering/boosting, and gas processing plant measurements)

Scenario Sample Size Average CH 4 Emission Factor (Mscfy) 1996 GRI/EPA Emission Factor 1 (Mscfy) Average BD vent for Run 3 83 9,352 Average BD vent for Idle + Run* 11 1,584 Wet Seal (Run) 9 8,137 165 *For some sites, the running and idle compressors were rout ed to vent with blowdown line s and PRVs, therefore individual

compressor operating mode emission f actors could not be calculated. 1 Hummel, K.E., Campbell, L.M., and M.R. Harrison ( Vol. 8), Table 4-15, 1996 GRI/EPA CH 4 study, adjusted for 24.2% time

the compressor is pressurized. 

### Table 3-4. Sampling Results fo r Reciprocating Compressors (Transmission Compressors)

Scenario Sample Size Average (Mscfy) 1996 GRI/EPA Emission Factor 1 (Mscfy) Average BD vent for Idle + pressurized 10 1,957 3,683 Average BD + PRV for Run* 6 8,512 Average BD + PRV vent for Idle + depressurized* 15 15,792 Average Rod Packing for Idle + pressurized 5 12,236 396 Average Rod Packing for Run 2 29,603 *Includes PRVs. 1 Vol. 8, Table 4-15, 1996 GRI/EPA CH4 study. 1 Hummel, K.E., Campbell, L.M., and M.R. Harrison ( Vol. 8), Table 4-15, 1996 GRI/EPA CH4 study, adjusted for 79.1% time the

compressor is pressurized.Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 38 

### Table 3-5. Sampling Results fo r Reciprocating Compressors (Gathering/Boosting Compressors)

Scenario Sample Size Average (Mscfy) 1996 GRI/EPA Emission Factor (Mscfy) Average BD vent for Run 16 28 0.215 1 Average BD vent for Idle + depressurized 8 0 Average PRV for Run 12 1,097 1.332 2 Average PRV for Idle + depressurized 6 0 N/A Average Rod Packing for Run 15 241 9.48 3

1 Hummel, K.E., Campbell, L.M., and M.R. Harri son (Vol. 8), Appendix B-4, 1996 GRI/EPA CH 4 study. (Gathering Compressors OEL).

GRI/EPA treated all OELs in production identically, an d did not separate out the compressor BD line OELs. 2 Hummel, K.E., Campbell, L.M., and M.R. Harri son (Vol. 8), Appendix B-4, 1996 GRI/EPA CH 4 study (Gathering Compressors PRV). 3 Hummel, K.E., Campbell, L.M., and M.R. Harri son (Vol. 8), Appendix B-4, 1996 GRI/EPA CH 4 study (Gathering Compressors,

Compressor Seal). Assumes four seals per compressor. 

## 3.3 Comparison to Existing Data The new measurements made for this proj ect on fugitive components produced lower emission factors than the previous GRI/EPA study, as shown in Table 3-1. This may be due to improved LDAR practices for accessible fugitive components that have been implemented by companies in the past two decades. Some of th e sites visited were for companies that have participated in Natural Gas STAR. Program s like EPA’s Natural Gas STAR and general awareness of GHG emissions may have led to an actual reduction. However, it is premature to make a definitive finding given the limited sample set for this project. For compressor vents (rod packing vent and bl owdown line vents), the results are mixed. As shown in Table 3-3, for centrifugal transmission compressors this pr oject found the average blowdown line emission factors were significantl y lower than the GRI/EPA study, but found wet seal degassing vent emissions that were much highe r. Both of the new measurements are from a very limited sample set, smaller than the prev ious sample set of the GRI/EPA study. It should also be noted that it is difficult to compare the simple emission factors from this study with the GRI/EPA emission factors for an average compresso r, which were already adjusted for operating time of the compressors. For the wet seal degassing vents, it is po ssible that this project over-measured, by capturing some exhaust gas blowthrough from the engi ne side of the shared seal oil system, or from systems with blowers if the blowers were not identified. Sin ce no gas analysis was performed on the measured volumes, we are unable to rule out that possibilit y. It is also possible that the volumes were under-measured since the ma in seal oil vent line could not be blocked during the measurement. Additional tests and in vestigations are needed to make a definitive determination; however, the expe riences from this study can help inform the design of sampling procedures under the GHG reporting rule.Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 39 

### For reciprocating transmission compressors , this project found average blowdown line emission factors that were significantly higher than the GRI/EPA study, and rod packing vent emissions that were also much higher as shown in Table 3-4. Both of the new measurements are from a very limited sample set, smaller than the previous sample set of the GRI/EPA study. While there is not enough data to draw a definitiv e conclusion, it is clear that the new data set does not indicate that reciproca ting compressor vent emission factors have been reduced since the 1990’s. This may be valid given the age of many of the reciprocating compressors, which have only aged further since the tests in the 1990 ’s. Technology for seal packing and isolation valve seats has not changed significantly since th e GRI/EPA report. Given the data from EPA’s Natural Gas STAR and the GRI/EPA study, a co mpany could monitor rod packing emissions more carefully if they so elected, and thus replace rod p acking more frequently. The measurements from this project do not seem to s how any reductions from those practices, if they exist. 

## 3.4 Comparison of VPAC to Direct Measurement Results A comparison was made between the direct measurement readings and the VPAC method measurements. A plot of the data along with a linear regression of the data are shown in Figures 3-1 and 3-2. Ideally, it would be expect ed that a one-to-one relationship would be demonstrated between two comparable measurement methods. Driven by two high values (greater than 7,000 scf/day) measured by the direct measurement approach, a slope of 0.0038 was observed for the complete set of VPAC measurements as a function of direct measurements. If the two direct measurement high flow data poi nts are removed from the data set, a negative correlation (slope) of the two measurement me thods is observed, at a slope of -0.0024.Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 40 

### Figure 3-1. VPAC vs. Dir ect Flow Measurement Meth od, complete data set (please note the axes scales) y = 0.0038x + 18.563 R2 = 0.6937

0 50 100 150 200 250

0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 45,000 50,000VPACValues(SCFD)

Direct Flow Measurement Values (SCFD) 

### VPAC (SCFD) vs Direct Flow Measurement (SCFD)Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 41 

### Figure 3-2. VPAC vs. Direct Flow Measurement Method, modified data set for lower flow (please note the axes scales) 

### There appears to be no statistically signifi cant correlation between the VPAC and the direct flow measurement methods. Therefore, it does not appear that the VPAC method should be considered as an accurate alternative to direct measurement for the few sources tested in this study at gathering/boosting compresso rs and gas processing plants. 

# 4.0 Conclusions and Recommendations The initial impetus of this study was to esta blish new emission f actors that were both statistically superior to the GRI/EPA emission factors, and more relevant than the GRI/EPA factors (by including more recent samples). Some stakeholders in the process expected that the factors might be lower, given improvements in practices. The data from this report is not as robust as the GRI/EPA data, since fewer sites were sampled. For centrifugal transmission compressors, the measurements of fugitive components and blowdown line vents produced lower emission factors than the previous GRI/EPA study; however, centrifugal wet seal degassing vent emissi ons were much higher. On the wet seal data y = ‐ 0.0024x + 20.377 R2 = 0.0015

0 10 20 30 40 50 60 70 80 90

0 200 400 600 800 1,000 1,200 1,400VPACValues(SCFD)

Direct Flow Measurement Values (SCFD) 

### VPAC (SCFD) vs Direct Flow Measurement (SCFD)Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 42 

### for centrifugal compressors, this study has found after the fact, that there may be several technical issues surrounding a proper measurement from a wet seal system; therefore, the emission factors from this report for wet seal de gassing should be used only as an evaluative measurement. A useful conclusion from this study may be that future measurement campaigns need to understand the detailed design of each unique sampled compressor seal oil system, understand all the possible degassi ng locations, and only then dete rmine where to sample the system. Since wet seal gas systems require a more detailed evaluation than was previously anticipated, installation of measurement ports may require a careful review of the P&ID drawings for the seal oil system, finding flash points such as the fl ash drum pot for measurement. If blowers are used, a sample from the seal oil su mp vent may not be representative of the total generation of all flash gas. For reciprocating transmission compressors , this project found average blowdown line and rod packing vent emission f actors that were significantly higher than the GRI/EPA study. While there is not enough data to draw a definitiv e conclusion, it is clear that the new data set does not indicate that reciproca ting compressor vent emission f actors have been reduced since the 1990’s. These higher results may be due to continued aging of the compressors since the 1996 GRI/EPA study. There appears to be no statistically si gnificant correlation between the VPAC measurements and the direct flow measurement me thods. Therefore, it doe s not appear that the VPAC method should be considered an accurate alternative to di rect measurement for the few sources tested in this stu dy at gathering/boosting compresso rs and gas processing plants. Some of the insight from this report might be useful for future measurement campaigns or compressor operators. For example:

 More explicit specifications for location of the wet seal degassing vent measurement (including possible protocols for that measurement);

 Use of calibrated bag measurements for we t seal degassing since the oil mist may adversely affect other measurement instruments;

 Reconsideration of alternate methods to th e acoustic through-valve leak device for this service, since the acous tic through-valve device appear s non-correlated to direct measurements;

 More explicit specifications for location of ports for individual compressor BD line leakage measurements; and

 Protocols for certain measurement techniques, such as use of inserted anemometers and encased anemometers.Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 43 

### Appendix A – Summary of Document Review 

### Doc. # Document or Reference Reviewed Review Comments 1 American Gas Association. Gas Fact s, 2007, A Statisti cal Record of the Gas Industry, 2006 Data. 01 March 2008. Provides activity data: miles of plastic pipeline mains 2 American Gas Association. Greenhouse Gas Emission Estimation Methodologies, Procedures, and Guidelines for the Natural Gas Distribution Sector, Draft, Prepared by innovative environmental solutions, inc., April 4, 2008. All emission factors are derived from the GRI/EPA study

3 American Petroleum Institute. Fugitive Hydrocarbon Emissions for Oil and Gas Production Operations , API Publication Number 4589, Prepared by Star Environmental. December 1993. Provides emission factors, but not for the sources of interest
4 Australian Government Department of Climate Change. Australian Methodology for the Estimation of Greenhouse Gas Emissions and Sinks 2006 Energy (Fugitive Fuel Emissions), National Greenhouse Gas Inventory Committee, Australia, December 2007. http://www.greenhouse.gov.au/inventory/methodology/index.html References E&P forum for a fugitive emission factor based on volume flared.

5 Australian Government Department of Climate Change. Australian Methodology for the Estimation of Greenhouse Gas Emissions and Sinks 2006 Energy (Stationary Sources), National Greenhouse Gas Inventory Committee, December 2007. http://www.greenhouse.gov.au/inventory/methodology/index.html Does not address emission sources of interest

6 Australian Government Department of Climate Change. National Greenhouse Accounts (NGA) Factors, Canberra ACT, January 2008. Does not address emission sources of interest 7 California Air Resources Board. Documentation of California’s Greenhouse Gas Inventory (website), April 10, 2008, http://www.arb.ca.gov/cc/inventory/doc/doc_index.php New data sources reference Gas STAR
8 California Climate Action Registry. Natural Gas Transmission and Distribution Greenhouse Gas Reporting Protocol, Draft, February 2008. Does not address emission sources of interest 9 California Energy Commission, Evaluation of Oil and Gas Sector Greenhouse Gas Emissions Estimation and Reporting, Final Draft Report FR-05-100, April 2006. Provides plastic pipeline emission factor comparison derived from GRI/EPA study data 10 California Energy Commission, Research Roadmap for Greenhouse Gas Inventory Methods , Prepared by University of California, Berkeley, Lawrence Berkeley National La boratory, California Energy Commission, Consultant Report CEC-500-2005-097, July 2005. http://www.energy.ca.gov/pier/fina l_project_reports/CEC-500-2005- 097.html Provides emission factors for production wells, compressor station, plastic pipeline, and distribution services. Cite EIIP and ICF, which are believed to be derived from GRI/EPA study 11 Canadian Association of Petroleum Producers. A National Inventory of Greenhouse Gas (GHG), Criteria Air Contaminant (CAC) and Hydrogen Sulphide (H2S) Emissions by the Upstream Oil and Gas Industry, Vols. 1-5 , Prepared by Clearstone Engineering Ltd., Calgary, Alberta, Canada, September 2004. http://www.capp.ca/default.asp? V_DOC_ID=763&SubjectID=414802 Does not address emission sources of interest

12 Delucchi, Mark A. A Lifecycl e Emissions Model (LEM): Lifecycle Emissions from Transportation Fuels, Motor Vehicles, Transportation Modes, Electricity Use, Heating an d Cooking Fuels, and Materials, Appendix E: Methane Emissions from Natural Gas Production, Oil Production, Coal Mining and Other Sources, Institute of Transportation Studies, University of California Davis, UCD-ITS-RR-03-17E, December 2003. http://pubs.its.ucdavis.edu/author_detail.php?id=5 Does not address emission sources of interest

13 Environment Canada Greenhouse Gas Division. Inventory Report: Greenhouse Gas Sources and Sinks in Canada 1990-2005, April 2007. Does not address emission sources of interestNatural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 44 

### Appendix A –Summary of Document Review, continued 

### Doc. # Document or Reference Reviewed Review Comments 14 European Environment Agency. Annual European Community Greenhouse Gas Inventory 1990-2005 and Inventory Report 2007, Technical Report No 7/2007, 27 May 2007. http://reports.eea.europa.eu/technical_report_2007_7/en Does not address emission sources of interest

15 Fernandez, Roger, Robin Petrusak, Donald Robinson, and Duane Zavadil. Cost Effective Methane Emission Reductions for Small and Midsize Natural Gas Producers, Journal of Petroleum Technology, June 2005. http://www.icfi.com/Markets/Environment/doc_files/methaneemissions.pdf Does not provide emission factors or specific data of interest to the study

16 Intergovernmental Panel on Climate Change. 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Volume 2, Chapter 4: Fugitive Emissions , Prepared by the National Greenhouse Gas Inventories Programme, Eggleston H.S., Buendia L., Miwa K., Ngara T. and Tanabe K. (eds), IGES, Japan, 2006. References the API Compendium and provides high level national emission factors. Provide combined venting and flaring emission factors associated with well testing and well servicing activities in developed and developing countries. 17 Intergovernmental Panel on Climate Change, National Greenhouse Gas Inventories Programme. IPCC Emission Factor Database (EFDB) (website), April 10, 2008. http://www.ipccnggip.iges.or.jp/EFDB/find_ef_main.php Does not address emission sources of interest

18 International Association of Oil and Gas Producers. Environmental Performance in the E& P Industry 2006 Data , Report No. 399, October 2007. http://www.ogp.org.uk/pubs/399.pdf Does not provide emission factors or specific data of interest to the study 19 International Association of Oil and Gas Producers. Flaring & Venting in the Oil & Gas Exploration & Production Industry: An Overview of Purpose, Quantities, Issues, Practices and Trends, Report No. 2.79/288, January 2000. http://www.ogp.org.uk/pubs/288.pdf Does not provide emission factors or specific data of interest to the study
20 International Petroleum Industry Environmental Conservation Association, International Associ ation of Oil and Gas Producers and American Petroleum Institute. Petroleum Industry Guidelines for Reporting Greenhouse Gas Emissions , Prepared by Battelle, December 2003. Does not provide emission factors or specific data of interest to the study

21 Interstate Natural Gas Association of America. Activities to Reduce Greenhouse Gas Emissi ons from Natural Gas , Prepared by Energy Resources International Inc., Publication F-2000-05, Washington, D.C. 20036, 2000. http://www.ingaa.org/cms/31/ 3243/3247/3229/277.aspx Does not address emission sources of interest

22 Interstate Natural Gas Association of America. Greenhouse Gas Emission Estimation Guidelines for Natural Gas Transmission and Storage, Volume 1: GHG Emission Estimation Methodologies and Procedures, Prepared by Innovativ e Environmental Solutions, Inc., Washington, D.C. 20002, Revision 2, September 28, 2005. Provides emission factors for specific types of pneumatic devices: actuators or controllers, continuous bleed pneumatics, pneumatic/ hydraulic valve operator, and turbine valve operator. Data derived from GRI/EPA study 23 Interstate Natural Gas Association of America, American Petroleum Institute, and American Gas Association. INGAA/API/AGA Natural Gas Systems GHG Emission Factor Comparison & Improvement Collaborative Project – Status Report: Task 2 - Emission Factor Comparison, Draft Technical Report, 27 November 2005. References data derived from the GRI/EPA study. Identifies emission estimate approaches that can most benefit from improved methodology and data gaps for natural gas systemsNatural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 45 

### Appendix A –Summary of Document Review, continued 

### Doc. # Document or Reference Reviewed Review Comments 24 Methane to Markets. Methane to Markets Documents, Tools and Resources, April 10, 2008. http://www.methanetomarkets.org/index.htm Does not provide emission factors or specific data of interest to the study 25 Robinson, D.R., R. Fernandez, and R.K. Kantamaneni. Methane Emissions Mitigation Options in the Global Oil and Natural Gas Industries . http://www.epa.gov/gasstar/pdf/ng020.pdf Does not provide emission factors or specific data of interest to the study 26 United Nations Economic Commission for Europe Convention on Long-range Transboundary Air Pollution Co-operative Programme for Monitoring and Evaluation of the Long-range transmission of Air Pollutants in Europe. EMEP/CORINAIR Emission Inventory Guidebook - 2007 , Technical Report No 16/2007, December 2007. http://reports.eea.europa.eu/EMEPCORINAIR5/en/page002.html Provides fugitive component emission factors for oil and gas facilities based on a 1992 Canadian study

27 U.S. Department of Energy, Energy Information Administration Office of Integrated Analysis and Forecasting. Documentation for Emissions of Greenhouse Gases in th e United States 2005 , DOE/EIA-0638 (2005), Washington, D.C. 20585, October 2007. Does not provide emission factors or specific data of interest to the study
28 U.S. Department of Energy, Energy Information Administration. Monthly Energy Review , Washington, D.C., various years. http://www.eia.doe.gov/overview_hd.html Does not provide emission factors. May provide information of interest to activity data 29 U.S. Department of Energy, Energy Information Administration. Natural Gas Annual , Washington, D.C., various years. http://tonto.eia.doe.gov/dnav/ng/ng_pub_publist.asp Does not provide emission factors. May provide information of interest to activity data 30 U.S. Department of Energy, Energy Information Administration. Natural Gas Monthly , Washington, D.C., various years. http://tonto.eia.doe.gov/dnav/ng/ng_pub_publist.asp Does not provide emission factors. May provide information of interest to activity data 31 U.S. Department of Energy, Energy Information Administration Office of Policy and International Affairs. Technical Guidelines Voluntary Reporting of Greenhouse Gases (1605(b)) Program , Office of Policy and Internal Affairs, United States Department of Energy , January 2007. References emission factors derived from the GRI/EPA study

32 U.S. Department of the Interior, Minerals Management Service Gulf of Mexico OCS Region. Year 2005 Gulfwide Emission Inventory Study , OCS Study MMS 2007-067, Prepared by Eastern Research Group, Inc., New Orleans, December 2007. http://www.gomr.mms.gov/PI/PDFImages/ESPIS/4/4276.pdf Report only provides summary data. Access to the original database could be valuable

33 U.S. Department of Transportation, Office of Pipeline Safety. Pipeline Statistics, April 15, 2008. http://ops.dot.gov/stats/stats.htm Does not provide emission factors. May provide information of interest to activity data 34 U.S. Environmental Protection Agency. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 - 2005 , Washington, D.C. 20460, April 15, 2007. http://www.epa.gov/climatechange/emissions/downloads06/07CR.pdf Does not provide emission factors or specific data of interest to the study
35 U.S. Environmental Protection Agency. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 - 2006 , Public Review Draft, Washington, D.C. 20460, February 22, 2008. http://www.epa.gov/climatechange/emissions/usinventoryreport.html Does not provide emission factors or specific data of interest to the studyNatural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 46 

### Appendix A –Summary of Document Review, continued 

### Doc. # Document or Reference Reviewed Review Comments 36 U.S. Environmental Protection Agency. Natural Gas STAR Documents, Tools and Resources . http://www.epa.gov/gasstar/ Some specific information is presented below 37 CAPP. CH4 and VOC Emission from the Canadian Upstream Oil and Gas Industry, Volume 1. Organic and Common-Pollutant Emissions by the Canadian Upstream Oil and Gas Industry. Provides Canadian emission factors for well servicing operations (by Province/Territory), counts of gas wells (high pressure sour, high pressure sweet, and low pressure sour), fugitive component counts for production wells (high pressure and shallow gas wells), and fugitive component counts and emissions for reciprocating versus centrifugal compressors. Reports are from the mid-90s. Information is used or cited in the API Compendium. 38 CAPP. A Detailed Inventory of CH4 and VOC Emission from the Canadian Upstream Oil and Gas Industry, Volume 2. Development of the Inventory. Canadian Petroleum Association (CPA). A Detailed Inventory of CH4 and VOC Emissions from Upstream Oil and Gas Operations in Alberta, Volumes I-III, March 1992.

39 CPA. A Detailed Inventory of CH4 and VOC Emissions From Upstream Oil and Gas Operations in Al berta. Volume 1. Overview of the Emission Data. Canadian Petroleum Association (CPA). A Detailed Inventory of CH4 and VOC Emissions from Upstream Oil and Gas Operations in Alberta, Volumes I-III, March 1992. In addition to information noted above for CAPP study, these reports provide fugitive compressor seal emission factors. Reports are from the mid-90s. Information is used or cited in the API Compendium. 40 CPA. A Detailed Inventory of CH4 and VOC Emissions From Upstream Oil and Gas Operations in Alberta. Volume 2. Development of the Inventory. Canadian Petroleum Association (CPA). A Detailed Inventory of CH4 and VOC Emissions from Upstream Oil and Gas Operations in Alberta, Volumes I-III, March 1992.

41 CPA. A Detailed Inventory of CH4 and VOC Emissions From Upstream Oil and Gas Operations in Alberta. Volume 3. Results of the Field Validation Program. Canadian Petroleum Association (CPA). A Detailed Inventory of CH4 and VOC Emissions from Upstream Oil and Gas Operations in Alberta, Volumes I-III, March 1992.Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 47 

### Appendix B – Data Summary (A full compilation of the data collected are ava ilable in a spreadsheet addendum to this report) 

### Table B-1. Fugitive Emissions from Va lves and Flanges using Hi-Flow Sampler Hundreds of components were screened using the FLIR camera, most components showed no leaks. The few components that did indicate a leak with the FLIR were measured using the Hi-Flow device and are presented in this table.

Site Leaking Component Mscf/yr

Site 1 Valve 1 83.52 Flange 1 77.95 Flange 2 11.14 Flange 3 53.82 Flange 4 7.42 Flange 5 22.27

Site 2 Valve 1 53.82 Valve 2 40.83 Flange 1 111.35 Flange 2 118.78 Flange 3 87.23 Flange 4 87.23

Site 3 Valve 1 1,033.73 Valve 2 11.14 Valve 3 139.19

Site 4 Valve 1 14.72 Valve 2 331.65 Valve 3 208.66 Flange 1 161.88 Flange 2 38.37 Flange 3 157.15 Flange 4 45.73 Flange 5 19.97 Flange 6 7.36

Site 5 Valve 1 62.02 Valve 2 176.60 Valve 3 259.65 Flange 1 29.43 Flange 2 129.82Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 48 

### Table B-2. Centrifugal Compressor Vents (Transmission, Gathering/Boosting , and Gas Processing Plant)

Site Equipment Name Run Mode Wet Seal Degassing Blowdown Line Leaks

SCFD VPAC Comparison SCFD SCFD VPAC Comparison SCFD

Site 3 Centrif 1 Idle, depressurized 0.00 - 129,756.40 - Centrif 2 Running 37,028.57 - 0.00 - Centrif 3 Running 51,840.00 - 0.00 -

Site 9 Centrif 1 Running 3,021.06 - 0.00 50.28 Centrif 2 Running 3,756.20 - 195.49 22.24

Site 10 Centrif 1 Running 18,103.71 - - - Centrif 2 Idle, depressured 0.00 - - - Centrif 3 Running 60,413.51 - - - Centrif 4 Running 0.00 - - -

Blow Down #1 -

Combined (4 compressors + 2

stations + 2

PRVs) n/a - - 44,745.54 193.54

Blow Down #2 - Emergency Shutoff Valve n/a - - 7,890.81 17.57

Site 11 Centrif 1 Running 12,713.28 -

747.88 5.78 Centrif 2 Idle, depressured 0.00 - 84.28 Centrif 3 Running 14,645.70 - 6.04 Centrif 4 Running 35,698.89 - 6.72 Centrif 5 Running 22,782.20 - 339.95 5.36 Centrif 6 Running 29,494.81 - 5.52Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 49 

### Table B-3. Reciprocating Compressor Vents (Transmission Compressors)

Site Equipment Name Run Mode Blowdown Line Leaks Rod Packing Vent SCFD SCFD

Site 1 Recip 1 Idle, pressurized 13,404.59 47,934.80 Recip 2 Idle, pressurized 13,404.59 57,157.16 Recip 3 Idle, pressurized 13,404.59 - Recip 4 Idle, pressurized 13,404.59 - Recip 5 Idle, depressurized, open 4,825.65 -

Site 2 Recip 1 Idle, pressurized 0.00 0.00 Recip 2 Idle, pressurized 0.00 0.00 Recip 3 Idle, pressurized 0.00 18,766.42 Recip 4 Idle, pressurized 0.00 35,709.82 Recip 5 Idle, pressurized 0.00 8,042.75 Recip 6 Idle, pressurized 0.00 - Station BD Vent #1 - Yard Piping n/a 10,187.49 -

Station BD Vent #2 - Idle Line piping n/a - -
Station BD Vent #3 - Yard Piping n/a 9,115.12 -

Site 4 Recip 1 Idle, depressured 29,021.41 - Recip 2 Running 27,984.93 - Recip 3 Idle, depressured 35,758.52 11,401.27 Recip 4 Running 26,948.45 - Recip 5 Idle, depressured 67,371.13 10,364.79 Recip 6 Running 32,130.84 - Recip 7 Idle, depressured 77,735.91 8,291.83 Recip 8 Running 52,860.42 - Recip 9 Idle, depressured 150,289.43 26,948.45 Recip 10 Idle, depressured 15,547.18 Recip 11 Idle, depressured 33,167.32 - Recip 12 Idle, depressured 18,656.62 - Recip 13 Idle, depressured 34,203.80 - Recip 14 Idle, depressured 25,911.97 - Recip 15 Idle, depressured 21,766.06 -Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 50 

### Table B-3. Reciprocating Compressor Vents (Transmission Compressors), continued

Site Equipment Name Run Mode Blowdown Line Leaks Rod Packing Vent SCFD SCFD

Site 5 Recip 1 Running 0.00 NM Recip 2 Idle, depressured 17,620.14 NM Recip 3 Idle, depressured 9,328.31 NM Recip 4 Running 0.00 NM Recip 5 Idle, depressured 107,793.80 NM Recip 6 Idle, depressured NM 55,969.86 Recip 7 Idle, depressured NM 106,239.08
NM = Not MeasuredNatural Gas Industry Methane EmissionFactor Improvement Study December 2011Draft Final Report 51Table B-4. Reciprocating Compressor Vents (Gathering/Boosting Compressors)SiteEquipment NameRun ModeRod PackingSeal LeaksBlowdown Line LeaksDischarge PRVLube Oil TankSCFDSCFDVPACMeasurementSCFDSCFDSCFDSite 6Recip 1 Running387.03 0.00 7.28 - 4,552.70Recip 2Running0.00 0.00 7.46 0.00 0.00Recip 3Running91.15 0.00 7.29 0.00 9,202.27Recip 4Running154.25 0.00 7.02 0.00 37,971.46Recip 5Running3,187.36 0.00 7.84 17,435.88 25,378.89Recip 6Running0.00 1,216.83 7.61 0.00 -Recip 7Idle, depressured0.00 0.00 40.17 0.00 -Recip 8Idle, depressured0.00 0.00 40.17 0.00 -Recip 9Running882.03 0.00 40.17 14,723.63 74,586.80Recip 10 Idle, depressured0.00 0.00 40.17 - -Recip 11 Idle, depressured0.00 0.00 40.17 0.00 -Recip 12Running112.18 0.00 7.33 0.00 5,811.96Recip 13 Idle, depressured0.00 0.00 40.17 - -Site 7Recip 1 Running15.44 0.00 9.02 3,914.03 -Recip 2Running262.40 0.00 9.10 0.00 -Recip 3Running370.45 0.00 9.27 0.00 -Recip 4Idle, depressured0.00 0.00 - 0.00 -Recip 5Idle, depressured0.00 0.00 - 0.00 -Recip 6Running308.71 0.00 9.03 0.00 -Site 8Recip 1 Idle, depressured0.00 0.00 38.02 0.00 -Recip 2Running78.33 0.00 5.29 - 0.00Recip 3Running1,345.65 0.00 8.13 0.00 0.00Recip 4Running170.65 0.00 8.18 0.00 0.00Recip 5Running2,544.43 0.00 7.99 0.00 0.00Natural Gas Industry Methane EmissionFactor Improvement Study December 2011Draft Final Report 52Natural Gas Industry Methane Emission Factor Improvement Study December 2011 Draft Final Report 53 

### Appendix C – References

American Petroleum Institute (API). Comp endium of Greenhouse Gas Emissions Estimation Methodologies for the Oil and Gas Industry, API, Washington, DC, 2004. Errata, February, 2005. http://www.api.org/ehs/clim ate/new/upload/2004_COMPENDIUM.pdf http://ghg.api.org/documents/CompendiumErrata205.pdf
California Energy Commission (CEC). Evaluation of Oil and Gas Sector Greenhouse Gas Emissions Estimation and Reporting , California Energy Commission, Consultant Report, Final Draft, April 14, 2006.
GRI and EPA. Harrison, M.R., Shires, T.M., Wessels, J.K., Cowgill, R. M. Methane Emissions from the Natural Gas Industry, Volumes 1 – 15, Final Report, GRI-94/0257 and EPA-600/R-96- 080, Gas Research Institute and US Envir onmental Protection Agency, June 1996.
Hummel, K.E., Campbell, L. M., and M.R. Harrison. Methane Emissions from the Natural Gas Industry, Volume 8: Equipment Leaks , Final Report, GRI-94/0257.25 and EPA-600/R-96-080h, Gas Research Institute and US Environmental Protection Agency, June 1996. (Part of the GRI/EPA methane emissions inventory project.) www.gastechnology.org
Picard, Dave. Centrifugal Wet Seal Schematic . Clearstone Engineerin g, LTD. E-mail to the authors. 15 August 2011.
Rolls Royce. Centrifugal compressors: Pi peline and barrel compressors fo r the energy industry. 2010. http://www.rolls-royce.com/Images/EC201(rev)_tcm92-22934.pdf
U.S. Environmental Protection Agency (EPA). Lessons Learned from Natural Gas STAR Partners. Replacing Wet Seals with Dry Se als in Centrifugal Compressors , October 2006. http://www.epa.gov/gasstar/documents/ll_wetseals.pdf
U.S. Environmental Protection Agency (EPA). Lessons Learned from Natural Gas STAR Partners. Reducing Methane Emissions from Compressor Rod Packing Systems, October 2006. http://www.epa.gov/gasstar/documents/ll_rodpack.pdf
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