Page 1 of 12 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, D.C. 20460

OFFICE OF AIR AND RADIATION

Petroleum and Natural Gas Systems (Subpart W) of the Greenhouse Gas Reporting Rule Docket: EPA-HQ-OAR-2009-0923

Title: Revisions to Processing Leaker Em ission Factors in Rule Table W-2

Summary: This memo discusses the methodology used to develop the emission factors from emission surveys conducted by Clearstone Engineer ing Ltd. for the U.S. EPA, (Clearstone I and Clearstone II) and for the Canadian Energy Part nership for Environmen tal Innovation (CEPEI) Based on sample sizes of component leak data EP A has determined that combining the datasets provides more robust LEFs in today’s fina l rule than the April 2010 proposed rule.Page 2 of 12 Revisions to Processing Leaker Emis sion Factors in Rule Table W-2

In today’s final rule, EPA has provided total hydrocarbon leaker emission factor (LEF) for compressor related and non-compressor related components for onshore natural gas processing, natural gas transmission compression, and unde rground natural gas storage. This memo discusses the methodology used to develop th e emission factors from emission surveys conducted by Clearstone Engineering Lt d. for the U.S. EPA, (Clearstone I 1 and Clearstone II 2 ) and for the Canadian Energy Partners hip for Environmental Innovation (CEPEI 34 ) Based on sample sizes of component leak data EPA has de termined that combining the datasets provides more robust LEFs in today’s final rule than th e April 2010 proposed rule. These factors suitably characterized each applicable industry segment.

Background In considering the option of requiring leak det ection and leaker emissi on factors for quantifying equipment leaks in the onshore natural gas pr ocessing, onshore natura l gas transmission, and underground natural gas storage se gments, EPA originally investig ated the other available data sources for leaker emission factors. The first source was the SOCMI leaker factors used in conjunction with the VOC Leak Detection and Repair (LDAR) program under the Clean Air Act 40 CFR Part 60 subpart KKK (see Appendix A) for processing plants. These factors were developed from data in petroleum refineries and chemical plants, and are used for state criteria pollutant inventories of petroleum refinery and ch emical plants as well as the VOC sections of processing plants (fractionation section). These SOCMI factors were not developed from data sources within the non-VOC, high methane content, sections of processi ng plants (feed and residue gas compression and conditi oning) or the gas transmission and gas storage segments of the natural gas industry. Secondly, EPA considered the emissi on factors in the API Compendium 5 . These factors are population factors, and the actual leak detec tion and measurement data was not publicly available for EPA to reconstitute into leaker f actors, so it was not suitable for subpart W requirement of leak detection and leaker fact ors as an alternative to leak measurement. Clearstone Engineering Lt d. provided all of the field emissi ons data collected in 1998 and 2004 from leaking components in the processing s ector. It measured hydrocarbon emissions from components found in nine processing plants and categorized them by site, process unit, component type, and stream type. In 1998, four processing plants were surveyed for the

1 Clearstone Engineering Ltd. Identification and Evaluation of Opportunities to Reduce Methane Losses at Four Gas Plants . Calgary, Alberta: 2002.
2 Clearstone Engineering LTD. Cost-Effective Directed Inspection and Maintenance Control Opportunities at Five Gas Processing Plants and Upstream Gathering Compressor Stations and Well Sites. (Draft): 2006

3 Clearstone Engineering Ltd. Identification and Evaluation of Opportunities to Reduce Methane Losses at Four Gas Plants . Calgary, Alberta: 2002.

4 Clearstone Engineering Ltd. Measurement of Natural Gas Emissions from the Canadian Natural Gas Transmission and Distribution Industry, (for CEPEI). 2007.

5 API. (2009) Compendium of Greenhouse Gas Emission Methodologies for the Oil and Natural Gas Industry. pg. 6-5 <http://www.api.org/ehs/climate/new /upload/2009_GHG_COMPENDIUM.pdf>Page 3 of 12 Clearstone I report which was publis hed in 2002. The resulting data is referred to as Clearstone I data. In 2004 , an additional five processing plants were surveyed, including one processing plant surveyed in 1998 was resurveyed for the Clears tone II study, draft report submitted to EPA in 2005. The data from the five processing facilities surveyed for the Clearstone II study is referred to as Clearstone II data.

The CEPEI data consists of emission surveys conducted by Clearstone Engineering Ltd. in 1998 and 2007 and leak measurement surveys submitted by individual private sector companies between those years. The surveys examined numerous natural gas transmission, storage and distribution facilities in Canada. The results of these surveys were used to write two separate reports for CEPEI: Handbook for Estimating Methane Emissions from Canadian Natural Gas Systems 6 (referred to as CEPEI 1998) and Measurement of Natural Gas Emissions from the Canadian Natural Gas Transmissi on and Distribution Industry 7 (referred to as CEPEI 2007). This data will henceforth be referred to as CEPEI.

EPA investigated the raw data from these studi es to develop LEFs for 40 CFR 98, subpart W. The component definitions in the final reports we re not the same as those covered under subpart W, so EPA first filtered the raw data to only comb ine that which is consistent with subpart W’s source listing (e.g. compressor related valves, non-compressor related valves, etc). After eliminating inapplicable leak data, it investigat ed the remaining sample sizes and evaluated the potential to combine data sets to develop more robust LEFs.

Methodology for the Developing Emission Fact ors from Clearstone I and II Data (Onshore Natural Gas Processing)

The LEFs provided by Clearstone were filtered and reconstructed to investigate potential configurations of that data for subpart W. First, the Clearstone I and II data was re-categorized by converting Clearstone’s component categories to those consistent with the EPA/GRI study and the API Compendium, being considered for in clusion in the current draft proposed Subpart W. The Clearstone component categories were relabeled to fit: valv es, open-ended lines, connectors, pressure-re lief valves, and meters.

Next, the Clearstone I and II data was separated into components which occur before and after the de-methanizer (or dew point control) unit. This was done using the stream types provided by Clearstone. For example, components labeled PG (Process Gas) and SR/PG (Sour Process Gas) were considered to occur before the de-methanizer while compone nts labeled FG (Fuel Gas) and Residue Gas were considered to occur after the de-methanizer. Stream types such as AIR, C,

6 Clearstone Engineering Ltd. Handbook for Estimating Methane Emissions from Canadian Natural Gas Systems, (for CEPEI). 1998

7 Clearstone Engineering Ltd. Measurement of Natural Gas Emissions from the Canadian Natural Gas Transmission and Distribution Industry, (for CEPEI). 2007.Page 4 of 12 and HC Liq were excluded from the data set b ecause they are not methane related. Also, the bottoms streams from the de-methanizer, and al l other fractionation unit streams (such as C2, C2+, and C3) were excluded because they contai n negligible methane content and are regulated under the VOC LDAR program, 40 CFR Part 60 subpart KKK (i.e. not representative of unregulated methane emissions).

The Clearstone I and II data were further categorized into comp ressor and non-compressor related components. Several equipment leak st udies, including Clearstone studies, demonstrate that the mechanical (vibration) and thermal stre sses created by compressors put additional stress on connected components making them more susceptible to leaking. This was done by filtering those components with process unit descriptions referring to compressors. For example, if the process unit description contained “compressor” or a comparable label the data point would be categorized as compressor, otherwise it w ould be categorized as non-compressor.

Compressor components were further separated into reciprocating a nd centrifugal compressor related components. Reciprocating compresso rs cause higher amplitude, lower frequency vibrations than centrifugal compressors. This wa s done by filtering those data points categorized as compressors and searching for “turbine” in the process unit descri ption. If the process description contained “turbine”, the component was labeled centrifugal, otherwise it was labeled reciprocating.

Finally, hydrocarbon LEFs for the processing segm ent were calculated by dividing the sum of the leakage rates by the sum of the component counts in each source category. The above methodology is displayed as a flowchart in Figure 1. The same methodology described above was applied to both the Clearstone I and II data.

Methodology for Developing Emission Factors from CEPEI Data The collective data is described as representa tive samples of block valve stations, booster stations, border meter stations, compressor stations, control valv e stations, transmission farm taps, receipt meter stations, sales meter statio ns, storage stations, and storage wells for the transmission/storage sector; and commercial mete r sets, gate stations, distribution farm taps, district regulating stations, i ndustrial meter sets, residential meter sets, and miscellaneous pipeline equipment in the distribution sector. EPA isolated the data for compressor stations, storage stations, and storage we lls to develop LEFs for transm ission and storage segments, and isolated gate stations and distri ct regulating stations for the dist ribution segment in subpart W.

Components in the field data we re associated with a site id entifier, tag identity, source, component count, and leakage rate. The site identif iers designate the fac ility types and the tag identities distinguish the leak ing components from the non-leak ing components. The components were categorized as: blowdown vent, connector, controller, centrifugal compressor seal, reciprocating compressor seal, cont rol valve, open-ended line, orif ice meter, other flow meter,Page 5 of 12 pressure relief valve, regulator, and valve. The leakage rates provided in the field data indicates the total hydrocarbon leak er rates. In cases where there were more than one component associated with a leakage rate, it was assumed that the leakage rate was a total of those components.

Using the site identifiers, the components from th e compressor stations, gate stations and district regulating station were separated out from the raw data. Unlike the Clearst one I and Clearstone II studies, it was not possible to separate the co mpressor station components into centrifugal, reciprocating and non-compressor related. It was assumed that any component found at compressor stations was compressor related because the count of non-compressor related components is relatively small compared with compressor related components. In addition, the compressor unit could not be identified as centrif ugal or reciprocating given the labeling system used in the field data. Hydrocarbon LEFs for distribution were derive d from components found in gate stations and dist rict regulating stations as specified by Subpart W.

Components found at compressor stations were grouped together to formulate hydrocarbon LEFs for both centrifugal and reciprocating compresso rs in the transmission sector, where as components found at gate stations and district regulating stations were grouped together to calculate hydrocarbon LEFs for the distributi on sector. The data in cludes non-leaking and leaking components in the raw da ta requiring the isolation of l eaking components using their tag identities. The leaking components were then grouped according to source category. Finally, hydrocarbon LEFs for the transmission and distribu tion sectors were calculated by dividing the sum of the leakage rates by the sum of the leakin g component counts in each source category. To convert the hydrocarbon leaker emission factors to methane LEFs, a composition factor of 0.934, as stipulated by the GRI 8 report for transmission gas quality, wa s used. The data analysis process is summarized visually in Figure 2.

Initial Results The total hydrocarbon emission factors from the Clearstone I and II data are shown in Table 1. The associated component counts are in Table 2. The methane emission factors from the CEPEI data analysis for transmission and dist ribution are shown in Table 3 and 4.

Several emission source categories, such as open-ended line before the de-methanizer for reciprocating compressors, do not have sufficient da ta points or any data point to make a valid emission factor. To eliminate this issue, the segr egation of components into reciprocating versus centrifugal and before the de-methanizer versus after the de-methanizer was eliminated. The resulting emission factors and compon ent counts are shown in Table 5.

8 EPA/GRI. (1996) Methane Emissions from the Natural Gas Industry <http://www.epa.gov/gasstar/tools/related.html>Page 6 of 12 Concluding Remarks Even after eliminating certain groupings, the emi ssion factor for pressure relief valves for compressor related components are supported by only one data point (i.e. only one leak was found and quantified). Another emission factor with a small sample set is meter for compressor related components. It was not apparent whether these component s did not leak, or that there were only one of each type component in the f acilities studied. The CEPEI data was combined with the Clearstone I and II to develop LEF for both transmission and processing.

Compressors in processing and transmission are comparable in size and discharge pressure. Therefore, EPA sought to overcome the proble m of small sample se ts supporting certain emission factors in processing, by combining the CEPEI data with the Clearstone I and II to develop LEF for both transmission and processing. EPA also elected to use the same LEFs for compressor related components in underground natu ral gas storage because compressors in this sector have a large throughput and inject gas at high pressure into underground reservoirs or from reservoir re-production in to transmission pipelines. The emission factors for Table 6 shows the emission factors and component counts of compressor related components and noncompressor related components for transmission a nd processing. The final emission factors were corrected to 68  ̊ F and 14.7 psia per the definition of “sta ndard conditions” set forth in subpart A of the 40 CFR 98.Page 7 of 12 Emission Factor Calculation Component Grouping Source Categorization Clearstone II Raw Data

Methane Streams Non-Methane Streams

Before De-Methanizer After De-Methanizer

Compressor NonCompressor

Reciprocating Centrifugal Reciprocating Centrifugal Compressor NonCompressor Valves

Connector

Open-Ended Lines

Pressure Relief Valve

Meter

Component Counts

Hydrocarbon LEF Component Counts

Hydrocarbon LEF Component Counts

Hydrocarbon LEF Component Counts

Hydrocarbon LEF Component Counts

Hydrocarbon LEF Component Counts

Hydrocarbon LEF Figure 1 - Summary of Clearstone data analysisPage 8 of 12Emission FactorCalculationsSource CategorizationFacility TypeLeakingComponents Raw Data

Compressor

Stations

Leaking Components Non-leaking Components

Component Counts Hydrocarbon Leaker Emission Factors Connector

Block Valve

Control Valve

Compressor Blowdown Valve

Pressure Relief Valve

Orifice Meter

Regulator

Open-ended Line

Methane Leaker Emission

Factors DISTRIBUTION TRANSMISSION

Component Counts Hydrocarbon Leaker Emission Factors Connector

Block Valve

Control Valve

Compressor Blowdown Valve

Pressure Relief Valve

Orifice Meter

Regulator

Open-ended Line

Methane Leaker Emission

Factors District Regulating

Stations Gate Station

Leaking Components Non-leaking Components Figure 2 – Summary of CEPEI data analysisPage 9 of 12 Table 1 – Total hydrocarbon emission factors for processing

Processing Before De-methanizer Emission Factor (scf/hour/component) After De-methanizer Emission Factor (scf/hour/component) Leaker Emission Factors - Reciprocatin g Compressor Components, Gas Service Valve 0.7 2.5 Connector 2.3 3.1 Open-ended Line - 16.2 Pressure Relief Valve - - Meter - - Leaker Emission Factors - Centrifugal Compressor Components, Gas Service Valve 15.9 18.1 Connector 4.3 9.1 Open-ended Line 17.9 10.3 Pressure Relief Valve - - Meter - 48.3 Leaker Emission Factors – Non-Co mpressor Components, Gas Service Valve 6.4 Connector 5.7 Open-ended Line 11.3 Pressure Relief Valve 2.0 Meter 2.9

Table 2 – Component count for each emission factor for processing

Processing Before De-methanizer Emission Factor (scf/hour/component) After De-methanizer Emission Factor (scf/hour/component) Leaker Emission Factors - Reciprocatin g Compressor Components, Gas Service Valve 750 105 Connector 625 60 Open-ended Line - 7 Pressure Relief Valve - - Meter - - Leaker Emission Factors - Centrifugal Compressor Components, Gas Service Valve 231 844 Connector 151 777 Open-ended Line 26 61 Pressure Relief Valve - 1 Meter 1 3 Leaker Emission Factors - Other Components, Gas Service Valve 1364 Connector 1004 Open-ended Line 192 Pressure Relief Valve 9 Meter 18Page 10 of 12 Table 3 – Methane emission factors for transmission

Transmission Emission Factor (scf/hour/component) Component Count
Leaker Emission Factors - All Components, Gas Service
Connector 2.7 859 Block Valve 10.4 235 Control Valve 3.4 39 Compressor Blowdown Valve 543.5 58 Pressure Relief Valve 37.2 59 Orifice Meter 14.3 12 Other Meter 0.1 1 Regulator 9.8 27 Open-ended Line 21.5 72

Table 4 – Methane emission factors for distribution

Distribution Emission Factor (scf/hour/component) Component Count

Leaker Emission Factors - Above Grade M&R Stations Components, Gas Service
Connector 1.67 47 Block Valve 0.557 34 Control Valve 9.34 17 Pressure Relief Valve 0.270 11 Orifice Meter 0.212 4 Regulator 0.772 6 Open-ended Line 26.131 5

Table 5 – Total hydrocarbon emission factor for processing after combining before and after the de-methanizer

Emission Factor (scf/hour/component) Component Count
Leaker Emission Factors – Comp ressor Components, Gas Service Valve 16.0 1198 Connector 7.9 1003 Open-ended Line 12.8 94 Pressure Relief Valve 30.5 1 Meter 36.2 4 Leaker Emission Factors – Non-Co mpressor Components, Gas Service Valve 6.4 1364 Connector 5.7 1004 Open-ended Line 11.3 192 Pressure Relief Valve 2.0 9 Meter 2.9 18Page 11 of 12 Table 6 – Total hydrocarbon emission factor for processing, transmission and underground storage

Emission Factor (scf/hour/component) Component Count
Leaker Emission Factors – Comp ressor Components, Gas Service Valve 15.07 1499 Connector 5.68 1862 Open-ended Line 17.54 166 Pressure Relief Valve 40.27 60 Meter 19.63 17 Leaker Emission Factors – Non -C ompressor Components, Gas Service Valve 6.52 1364 Connector 5.80 1004 Open-ended Line 11.44 192 Pressure Relief Valve 2.04 9 Meter 2.98 18Page 12 of 12 Appendix A SOCMI Leaker Factors


### Uncontrolled SOCMI Fug itive Emission Factors
Equipment/Service SOCMI Average 1 SOCMI Without C 2 2 SOCMI With C 2 2 SOCMI NonLeaker 3

Valves Gas/Vapor 0.0132 0.0089 0.0258 0.00029 Light Liquid 0.0089 0.0035 0.0459 0.00036 Heavy Liquid 0.0005 0.0007 0.0005 0.0005 Pumps Light Liquid 0.0439 0.0386 0.144 0.0041 Heavy Liquid 0.019 0.0161 0.0046 0.0046 Flanges/Connectors Gas/Vapor 0.0039 0.0029 0.0053 0.00018 Light Liquid 0.0005 0.0005 0.0052 0.00018 Heavy Liquid 0.00007 0.00007 0.00007 0.00018 Compressors 0.5027 0.5027 0.5027 0.1971

Relief Valve (Gas/Vapor) 0.2293 0.2293 0.2293 0.0986

Open-ended Lines 4 0.0038 0.004 0.0075 0.0033 Sampling Connections 5 0.033 0.033 0.033 0.033

Notes: All factors are in units of (lb/hr)/component. 1. Factors are taken from EPA Document , EPA-453/R-95-017, November 1995, Page 2-12 2. Factors with ethylene (C 2 ) are TCEQ derived. 3. Control credit is included in th e factor; no additional control credit can be applied to these factors. AVO walk-through inspection required. 4. The 28 series quarterly LDAR programs require open-ended lines to be equipped with an appropriate sized cap, blind fla nge, plug, or a second valve. If so equipped, open-ended lines may be given a 100% control credit. 5. Use the SOCMI Sampling factor for Non-Leak ier. Emission factor is in terms of (lbs/hr)/Sample Taken.