UnitedStates EnvironmentalProtection Agency 

# Research and Development

METHANE EMISSIONS FROM THE NATURAL GAS INDUSTRY Volume 11: Compressor Driver Exhaust


# Preparedfor
EnergyInformation Administration (U.S. DOE)


# Prepared 

# by National RiskManagement Research Laboratory ResearchTriangle Park, NC27711 GRI-94/0257.28 EPA

-600/R-96-080k June 1996

### FOREWORD
The U.S. Environmental Protection Agencyis charged by Congress with pro

### tecting the Nation's land. air. ami water resources. Under a mandate ofnational 

### environmental laws. the Agency strives to formulate and implement actions leading to a compatible balance between human activities and the ability of natural 

### systems to support and nurture life. To meet this mandate, EPA's research program is providing data and technical supportfor solving environmental pro

### blems today andbuilding a science knowledge base necessary to manage our ecological resources wisely, understand how pollutants affect ourhealth. and prevent or reduce environmentalrisks in 

### the future. 

### The NationalRisk ManagementResearch Laboratoryis the Agency's center for investigation oftechnological andmanagement approachesfor reducinr{ risks from threats tohumanhealth and the environment. Thefocus ofthe Laboratory's research programisonmethods for the prevention and controlofpollution to air,

**land~** 

### water, and subsurface resources; protectionofwaterqualityinpublic water systems; remediation of contaminated sites and groundwater: andprevention and controlofindoor air pollution. The goal ofthis research effortis to 

### catalyze development and implementationof

### innovative. cost-effective environmental technologies; develop scientific and 

### engineeringinformationneededbyEPA to supportregulatory and policydecisions; andprovide technical support and infOrmation transfer to ensure effective implementationofenvironmentalregulations and strategies. This publicationhas beenproduced as partoftheLaboratory's strategiclongterm research plan. It

### ispublished and made aVailableby 

### EPA1

### s Office ofResearch and Developmentto assist the user communityand to link researchers with their clients. E. Timothy Oppelt, Director NationalRisk ManagementResearch Laboratory


### EPAREVIEW NOTICE This reporthas been peerand administrativelyreviewed bythe U.S. Environmental Protection Agency, and approved for publication. Mention of trade names or commercial productsdoes notconstitute endorsementorrecommendationforuse. Thisdocument is availabletothepublicthroughthe NationalTechnica! lnfonnation Service, Springfield,Virginia22161.

### METHANEEMISSIONS FROM 

## C!{'T- 

# '!'I/o:zs7.2.8 EPA-600iR-S6-080k June 

### 1896

THENATURALGAS INDUSTRY, VOLUME 11: COMPRESSORDRIVEREXHAUST FINAL REPORT

Prepared by: 

### Carole

### J. Stapper Radian International LLC

8501 N. Mopac Blvd. P.O. Box 201088 Austin, TX 78720-1088

DCN: 95-263-081-07
For GRI ProjectManager: Robert A. Lott 

### GAS RESEARCH INSTITUTE

Contract No. 5091-251-2171 8600 WestBryn Mawr Ave. Chicago, IL 60631 and EPA ProjectManager: David A. Kirchgessner U.S. ENVIRONMENTAL PROTECTIONAGENCY Contract No. 68-Dl-0031 

### National Risk Management Research Laboratory Research Triangle Park, NC 277!1

## DISCLAIMER LEGAL NOTICE: This report was prepared by Radian International LLC as an account ofwork sponsored by 

### Gas Research Institute (GRI) and the U.S. Environmental Protection Agency (EPA). Neither EPA, GRI, members ofGRI, nor any person acting on behalfof 

### either:

a.



### b. Makes any warranty orrepresentation, express or implied, with respect to the 

### accuracy, completeness, orusefulness ofthe infonnation contained in this report, orthat the use ofany apparatus, method, orprocess disclosed in this report may not infringe privately owned

**rights~** 

### or 

### Assumes any liability with 

### respect to the 

### use of, or for damages resulting from the use of, any information, apparatus, method, or process disclosed in this report. NOTE: EPA's Office ofResearch and Development quality assurance/quality control (QA/QC)

**~equirements** 

### are applicable to some ofthe cowtt data generated by 

### this project. 

### Emission data and additional count data are from industry or literature sources, and are not subject to EPA/ORD's QAIQC 

### policies. In all cases, data and results were reviewed by the panel ofexperts listed in Appendix DofVolume 2.

IITitle

Contractor

Principal Investigator Report Period Objective

Technical Perspective

Results 

## RESEARCH SUMMARY
Methane Emissions from the Natural Gas Industry, Volume 11: Compressor Driver Exhaust Final Report 

### Radian International LLC GRI Contract Number 5091-251-2171 EPA Contract Number 68-DI-0031 Carole 

### J. Stapper
March 1991 -June 1996 Final Report This report describes a study to quantify the annual methane emissions from compressor driver exhaust, which is a significant source ofmethane 

### emissions within the gas industry. The increased use ofnatural gas has been suggested as a strategy for reducing the potential for global wanning. During combustion, natural gas generates less carbon dioxide (C02) per

### llllit ofenergy produced than 

### either coal or oil. On the basis ofthe amount ofC02

### ernined, the potential for global wanning could be reduced by substituting natural gas for coal or oil. However, since natural gas is primarily methane, a potent greenhouse gas, losses ofnatural gas during production, processing, transmission, and distribution could reduce the inherent advantage ofits lower C02emissions. To investigate this, Gas Research Institute (GRI) and the U.S. Environmental Protection Agency'sOffice ofResearch and Development (EPA/ORD) cofimded a major study to quantify methane emissions from U.S. natural gas operations for the 1992 base year. The results ofthis study can be used to construct global methane budgets .and to determine the relative impact on global warming ofnatural gas versus coal and oil. The national annual emissions for compressor drivers in each industry segment are as follows: t)roduction, 6.58 

### ± 200% Bscf; gas processing, 6.84 

### ± 130% Bscf; transmission, 10.2 

### ± 17.1% Bscf; and storage, 1.19 

### ± 27.2% Bscf.

lliTechnical Approach

Project Implications Based on data from the entire program, methane emissions from natural gas operations are estimated to be 314 

### ± 105 Bscffor the 1992 base year. This is about I.4 

### ±0.5% ofgross natural gas production. The overall program also showed that the percentage ofmethane emitted for an incremental increase in natural gas sales would be significantly lower than the baseline case. The program reached its accuracy goal and provides an accurate estimate ofmethane emissions that can be used to construct U.S. methane inventories and analyze fuel switching strategies. The industry has two primary types ofcompressor drivers that fire natural gas: 1) reciprocating engines and 2) turbines. Methane emissions result from the incomplete combustion ofnatural gas in the driver, which allows methane to exit the driver in the exhaust stream. The techniques used to determine methane emissions were developed to be representative o·fannual emissions from the natural gas industry. However, it is impractical to measure every source continuously for a year. Therefore, annual emissions for compressor drivers were determined by extrapolating measured emissions using activity factors where the national emissions estimate is the product ofthe emission factor and the activity factor. Emissions test data for each driver type were collected by Southwest Research Institute (SwRI) for compressors in natural gas industry service. SwRI datafor emissions, fuel use rates, and compressor model numbers were used with data in GRI's TRANSDAT compressor database to develop the emission factors. Equations relating the SwRI data and the distribution ofcompressor models and operating hours found in TRANSDAT were developed to calculate emission factors for each type ofcompressor driver. Activity factors for each industry segment were developed using site visit data, company surveys and databases, and datapublished in the American Gas Association's 

### Gas Facts and the 

### Oil & 

### Gas Journal. The national annual emissions for each industry segment were then calculated as the product ofthe emission factor and activity factor for each compressor driver. Forthe 1992 baseyear the annual methane emissions estimate for the U.S. natural gas industry is 314 Bscf

### ± 105 Bscf(±33%). This is equivalent to 1.4% 

### ±0.5% ofgross natural gas production. Results from this program were used to compare greenhouse gas emissions from the fuel cycle for natural gas, oil, and coal using the global warming 

### iv

### potentials (GWPs) recently published by the Intergovernmental Panel on Climate Change (IPCC). The analysis showed that natural gas contributes less to potential global warming than coal oroil, which supports the fuel switching strategy suggested by IPCC and others. In addition, results frorr. this study are being used by the natural gas industry to reduce operating costs while reducing emissions. Some companies are also participating in the Natural Gas-Star program, a voluntary program sponsored by EPA's Office ofAir and Radiation m cooperation with the American Gas Association to implement costeffective emission reductions and to report reductions to the EPA. Since this program was begun after the 1992 baseline year, any reductions in methane emissions from this program are not reflected in this study's total emissions.

Robert A. Lott Senior Project Manager, Environment and Safety



### v

### TABLE OFCONTENTS Page 

### 1.0 SUMMARY ................................................. I 2.0 INTRODUCTION ............................................. 2 3.0 DATA SOURCES 3 3.1 Previous Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

### 3 

### 3.2 TRANSDAT Database ..................................... 4 3.3 Current Study ........................................... 5 4.0 COMPRESSOR DRJVER EXHAUST EMISSION FACTORS .............. 7 5.0 COMPRESSOR DRIVER ACTIVITY FACTORS
. . . . . . . . . . . . . . . . . . . . . II 5.1 Production Industry Segment ............................... 12 5.2 Processing Industry Segment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5.3 Transmission Industry Segment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 

### 5.3.1 Compressor Station Horsepower and Hours . . . . . . . . . . . . . . . . . 19 

### 5.3.2 Underground Storage Horsepower and Hours ................ 22 5.3.3 Generator Driver Horsepower and Hours ................... 22 5.4 Industry Activity Factors .................................. 27 

### 6.0 NATIONAL COMPRESSOR DRIVER EMISSION ESTIMATES .......... 29 7.0 CONCLUSIONS ............................................. 30 8.0 REFERENCES

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 APPENDIX A - National Estimate ofMethane Emissions from Compressors 

### in the U.S. Natural Gas Industry . . . . . . . . . . . . . . . . . . . . . A-I APPENDIX B

- Source Sheet P-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1 APPENDIX C

- Production Segment Site Visit Results
. . . . . . . . . . . . . . . . . C-1 APPENDIX D - Transmission Compressor Station Site Visit Results . . . . . . . . D·l 

### APPENDIX E- Conversion Table ................................ E-1

VI

### LIST OF FIGURES Page A-1 Effect ofHorsepower and Speed on Total Hydrocarbon Emissions for a Cooper Bessemer 2 Cycle Engine ............................... A-5 

### A-2 Relative Horsepower Contribution ofEach Engine Model in the Emissions and Industry Databases ................................ A-14 A-3 Relative Horsepower Contribution ofEach Turbine Model in the Emissions and Industry Databases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-15

VII

### LIST OF TABLES Page 4-1 

### SwRI Field Test Emission Factor Statistics 9 5-1 Compressor Driver Data for Production Segment
. . . . . . . . . . . . . . . . . . . . . 12 5-2 Regional Data for Production Segment Extrapolation

. . . . . . . . . . . . . . . . . . . 13 5-3 5-4 

### 5-5 5-6 

### 5-7 

### 5-8 6-1 7-1 A-1 C-1 

### C-2 Compressor Driver Data from Processing Segment Site Visits
. . . . . . . . . . . . . 15 Annual Operating Hours for Processing Segment
. . . . . . . . . . . . . . . . . . . . . . 18 Annual Operating Hours for Storage Segment
. . . . . . . . . . . . . . . . . . . . . . . . . 23 

### Generator Driver Data from Transmission Compressor Stations
. . . . . . . . . . . . 24 Generator Driver Data from Storage Fields
. . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

### Compressor Driver Activity Factors for Each Industry Segment
. . . . . . . . . . . . 28 Compressor Driver Emissions for the Natural Gas Industry 

### by.Segment
. . . . . . . 29 Ranking ofCompressor Driver Exhaust Emissions by Industry Segment
. . . . . . 

### 30 Description ofthe Databases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-8 

### Gathering Compressor Data from Production Segment Site Visits C-4 

### Regional 

### Data for Production Segment Horsepower Extrapolation C-5 

### C-3 Annual Operating Hours for Production Segment
. . . . . . . . . . . . . . . . . . . . . C-6 D-1 

### Compressor Driver Data from Transmission Segment Site Visits
. . . . . . . . . . . DA 

### D-2 Annual Operating Hours for Transmission Segment
. . . . . . . . . . . . . . . . . . . . D-6

vm1.0 

### SUMMARY
This report is one ofseveral volumes that provide background information supporting the Gas Research Institute and U.S. Environmental Protection Agency Office of Research and Development (GRJ-EPA/ORD) methane emissions project. The objective of this comprehensive program is to quantify the methane emissions from the gas industry for the 1992 base year to within 

### ± 0.5% ofnatural gas production starting at the wellhead and ending immediately downstream ofthe customer's meter. This report quantifies the amount ofunburned methane released in compressor driver exhaust in natural gas production, gas processing, and transmission. Emissions from generator driver exhaust, while minor, are also included in this report. Emission estimates for each industry segment were based on data from one ormore ofthe following sources: l) 

### site visits, 2) company databases; and 3) published data. The factors that affect the quantity ofmethane emissions from compressor drivers are: type ofdriver, horsepower. and operating hours. Compressor driver exhaust is a significant source ofmethane emissions. It accounts for24.8 Bscfofmethane emissions, which is about 7.9% ofmethane emissions from the natural gas industry.

### 2.0 INTRODUCTION
In the natural gas industry there are two primary types ofcompressor drivers that fire natural gas: 1) reciprocating engines, and 2) gas-fired turbines. Methane emissions result from the incomplete combustion ofthe natural gas, which allows some of the methane ln the fuel to exit in the exhaust stream. Compressor driver exhaust emissions represent a significant source ofmethane emissions in all ofthe industry segments where these sources are present. Emissions from generator driver exhaust, while minor, are also included in this report. Annual emissions were calculated as the product ofthe emission factor and the activity factor. To develop the compressor driveremission factors, test data 

### from Southwest Research Institute (SwRl) and GRI's TRANSDAT compressor database 1

### were used. The activity factors were developed to characterize the compressor drivers in each industry segment. Data were gathered from site visits, company databases, and published data from the American Gas Association (A.G.A.) and the 

### OilandGasJournal. This report describes howthe emissions from compressor driver exhaust were determined. Section 3 discusses the dataused to make the emission estimates. Section 4 presents the development ofthe emission factors for engines and turbines. Section 5 describes the development ofthe activity factors for each industry segment (production, processing, and transmission, including storage and generators). The annual emissions for each segment and the overall national emissions estimate are provided in Section 6. Conclusions are given in Section 7. This report is one ofseveral documents prepared for the GRJ/EPA methane emissions project.



### 2

### 3.0 DATA SOURCES Compressor driver exhaust emissions had been identified in earlier studies as a significant source ofmethane emissions. However, these studies were based on limited data and did not calculate error bounds for the estimated emissions. This study co!Iected and.evaluated a large number ofdata for compressor drivers and performed an error analysis ofthe emissions estimate. This section provides background information on previous studies and an introduction to the data and the approach used for the current study. 3.1 Previous Studies


### Previous estimates ofmethane emissions from compressor driver exhaust have ranged from about 114 Bscf(2.2 Tg/yr) to 11.5 Bscf(0.22 Tg/yr).2•3 

### The 114 Bscf estimate, from Pipeline Systems, Inc. in 1990, was based on an estimated emission factor established by the South Coast Air Quality Management District (1120 lb/MMscffuel)-' This estimate used a "model" installation to describe typical 

### compressor facilities for field production, transmission, storage, and gas processing; then used these "model" installations to extrapolate to a national estimate. The "model" installations were based on site visits to three production facilities, three pipeline systems, five injection/withdrawal plants, and two gas plants. Eight ofthe site visits were in California, two were in Texas, and the 

### remaining site visits were in the Central Plains Region. The estimate from Pipeline Systems, Inc. was based on a limited nwnber ofdata 

### and areprobably biased due to the disproportionate use ofCalifornia sites.
The 11.5 Bscfestimate was apreliminary estimate developed in I992 as part ofthe GRIIEPA 

### methane emissions project.3 

### (The preliminary emissions estimate is described in detail in the paper titled "National Estimate ofMethane Emissions from Compressors in the U.S. Natural Gas Industry," which can be found in Appendix A.) This estimate was based on data published by A.G.A. and data contained in the GRI TRANSDAT compressor database. The GRI TRANSDAT database includes data from 3

### A.G.A. and SwRl. 

### AG.A. data are gathered from government agencies, such as U.S. Department ofEnergy (DOE) and Federal Energy Regulatory Commission (FERC), and from surveys ofits member companies in transmission and distribution. SwRl data were generated during a field testing program on natural gas compressor driver emissions and operating characteristics.
This preliminary study assumed that the GRJ TRANSDAT database included information on all compressors used in the natural gas industry when it only contained data collected from transmission companies. Therefore, this study underestimated methane emissions from compressor driver exhaust for the natural 

### gas industry. 3,2 

### TRANSDAT Database
The GRJ TRANSDAT database is actually composed ofthree data subsets: Industry Database, Operating Database, and Test Database. The Industry Database lists 8282 compressor drivers (engines and turbines) used in the gas industry in 1989. Horsepower in this database is given bycompressor model number for each gas company and accounts for a total of !6.2 million horsepower (MMhp), installed. TRANSDAT data were collected from transmission companies, and it may include a limited amount ofdata on compressors used for production and processing. The Operating Database contains annual operating hours and operating horsepower for 1515 compressors (3.2 MMhp, total). The Test Database contains emissions data from field tests collected by SwRI and includes data on methane emissions, fuel use, fuel use rate, and horsepower for 24I compressors. The Operating and Test Databases were combined to generate a fourth database, the Emissions Database, that was then used to develop weighted emission factors. This database combines compressor model number, methane emissions, fuel use rate, and annual operating hours for 775 reciprocating engines and 86 gas-fired turbines. Therefore, the emissions can be calculated for each ofthe 775 engines and 86 turbines as they were operated during the year using SwRl emissions data.
4

### 3.3 Current Study
Data were gathered during this study to supplement the GRI TRANSDAT database to account for emissions from all industry segments. Data were collected during site visits and company surveys to determine the number ofcompressors and their 

### horsepower and operating hours. Because 

### it is not practical to visit every site or test every compressor driver, a method was developed using emission factors and activity factors to calculate total emissions from compressor drivers based on a limited data set. The emission and activity factors were defined such that their product would equal the total emiSSIOns 

### from compressor driver exhaust for each segment ofthe industry. Emissions from reciprocating engines and turbines were evaluated separately.
For most source categories in the gas industry, the emission factor is defined as the average emission rate determined from alarge number ofrandomly selected sources. The activity factor is then the total number ofsources within the source category, such as the total count ofcompressor drivers. However, for compressor driver exhaust. the emission factor was evaluated in terms ofemissions perhorsepower·hour (scf/hp·hr) 

### since this has less variability than an emission factor per compressor unit. 

### By calculating emissions on a per horsepower basis the variability in emissions due to compressor size can be eliminated. As a result, the activity factor is horsepower·hours peryear. This means that:
Total Emissions (set)= EF (scf/hp·hr) x 

### AF (hp·hr) (1) 

### The site visit and company survey dataprovided information on activity factors for the various segments ofthe industry, and SwRJ test data were used to develop the emission factors. However, the emission factor was not based on a simple average of the SwRI test data because the emission factor needed to be weighted to reflect the compressor population ofthe industry and because some compressor models are used as baseloaded compressors and operate a higher percentage ofthe time. For these reasons, 

### 5

### A.G.A's Operating Database, which contains horsepower, operating hours, and model numbers for over 1500 compressors, 

### was used to develop weighted industry emission factors for reciprocating engines and turbines. The emission factors for engines and turbines are 0.240 scf!hp·hr

## ±5% and 0.0057 scf/hp·hr

## ±30"/o, respectively. The method for calculating these weighted emission factors is described in the foiiowing section.

6

### 4.0 COMPRESSOR DRIVER EXHAUST EMISSION FACTORS The emission factors for reciprocating engines and gas-fired turbines were determined from compressor test data collected by 

### SwRI and weighted to reflect both the population ofcompressor models and their operating hours in the natural gas industry. The information needed to develop the weighting procedure was available in GRI's TRANSDAT database.


### SwRI followed several procedures to ensure the quality oftheir compressor data. First, the emissions analyzers were calibrated

**us~ng** 

### gases certified by 

### the National Institute ofStandards and Testing. Second, an oxygen molar balance was performed between the reactants and the products ofcombustion to verify the results. Third, each of 

### the data trends was inspected graphically in an effort to identify potential outliers. There were generally five data points for eac}:l test. and any ofthe points that did not foilow the trend were marked as outliers. Data that were collected by outside sources and provided to SwRI for inclusion in their study were also scrutinized graphically to validate the results. Where technica11y justified, statistical outliers were discarded in the development ofthe emission factors for the GRI/EPA methane emissions project.
An 

### average emission rate was calculated for each model ofcompressor engine and turbine driver in the Emissions Database using the test data collected by SwRI for that model. Using the fuel use rate and average emission parameter for each compressor model, the emission rate was calculated as follows:
ER (m) = 

### EP (m) X 

### FUR (m) 

### (2) 

### where: 

### ER<mJ = average emission rate for model, m (scflhr) EP <ml 

### =average emission.parameter for model, m (scfCH/scffuel) FUR (m) 

### = average fuel use rate for model, m (scffuel/hr)

7

### The methane emissions for each compressor driver in the Emissions Database were calculated by multiplying the emission rate (Equation 2) by the annual operating hours for each engine or turbine. The total emissions for each model ofcompressor driver in the database were calculated as follows:

where: 

## E(m) HR, M M E(m)

**~** 

### L (ER (m) X HR ,)

**i~**

### I

= 

### total emissions for model, m(scf) = 

### annual operating hours for compressor i, 

### (hr/yr) = 

### number ofcompressors ofmodel, m The total emissions for all compressor drivers in the database were the sum ofthe total emissions calculated for each model. (3)



### (4) where: TE 

### K = 

### total emissions for database, (scf) = 

### number ofunique compressor models These emissions were calculated based on data from 775 

### engines and 86 

### turbines and weighted to reflect the distribution ofcompressor models found in the gas industry as well as the percentage oftime these models are operated. Emissions can also be affected by the compressor load. However, the emissions are generally linear over a fairly large range ofoperating horsepower. To ensure that significant differences did not exist between the horsepower at which the compressor drivers are typically operated and 

### the horsepower at which they were tested, the following comparison was made: N 

### ? 

### I hp (test); :::::: 

### i=l 

### N 

### I hp {operating) i 

### i=l
8

### The two values agreed to within 2%.3


### The 

### emission factors, for engines and 

### turbines, were then calculated using the following equation.

where: N N 

### Emission Factor

**~** 

### TE I 

### [IHP ;x 

### (IHR ,IN)]



### HP HR i=l i=l

= 

### average operating horsepower during HR, (hp)

**~** 

### annual operating hours, (hrlyr) N = 

### number ofcompressors The values obtained are: Engines: 1.165 x 

## !o' scf = 

### 0.240 scf/hp·hr (1.3 X 

## Hf hp) X 

### (3742 hr/yr)
Turbines: 

# o.oo5 x 

# 1 o• scf = 

### 0.0057 scf/hr·hr (0.4 X 

### Jo' hp) X 

### (2326 hr/yr) (5)



### Confidence limits were calculated for the emission factors based onthe variation in SwRI's field test data. Table 4-1 shows the statistics used to determine the 90% confidence limits for each ofthe emission factors. The resulting uncertainty is 

### ±5% for reciprocating engines and 

### ±30% for gas-fired turbines (using a 90% confidence limit). 

### TABLE 4-1. SwRI FIELD TEST EMISSION FACTOR STATISTICS AverageEmission Standard Factor Deviation DriverType No. Tests No. Models (lb Methanellbfuel) (lbMethaneJibfuel)

Engines 902 229 0.0307 0.0279 Turbines 105 12 0.000107 0.000187



### 9

### Appendix Bcontains the source sheetfor compressor driver exhaust emissions, which summarizes the approach taken to calculate the emission factors. The source sheet also summarizes the activity factors used to determine the overall national emissions estimate from compressor drivers. The next section describes the development ofthese activity factors.

10

### 5.0 COMPRESSORDRIVERACTIVITY FACTORS Information from site visits, company surveys, A.G.A.'s 

### Gas Facts, and the Oil 

### & GasJournal

### was used to develop the activity factors. Data on horsepower and operating hours were obtained from site visits and company databases for compressordrivers 

### located at 297 field gathering stations, 18 gas processing plants, 51 transmission compressor stations, and 11 underground storage stations. Data for electric generatordrivers at41 transmission compressor stations and 3 underground storage fields were also obtained from 

### the site visits and company databases. Compressors 

### used for gas lift (oil production) were excluded from the following analysis, since this gas is not marketed and is not considered partofthe natural gas industry. Some sites used electricaiiy driven compressors. These electrically driven compressors were also excluded in the development ofthe activity factors, sincethey have no exhaust and therefore have no methane emissions.
For the production industry segment, horsepower·hourdata were provided by one company for 516engines located at 244 gathering stations. Productiondata for 53 gathering stations (from site visits and company surveys) were analyzed separately and are presented in Appendix C forcomparison. Foreachofthe remaining industry segments, separate horsepower and operatinghour estimates were made, which were multiplied together to get the 

### horsepower·hour activity factors.
Data were gathered for engines and turbines, allowing separate activity factors tobe developed for the two drivertypes. Data were also gathered for installed versus active horsepower in each industry segment (based onoperatinghours). Finally, data were gathered that could be 

### used to estimatenational emissions from each ofthe natural gas industry segments (e.g.• site data for gas throughput).

II

### The national estimates were extrapolated using 1992 data as the base year, except for the transmission segmentestimate ofcompressor station horsepower that uses 1989data as the base year. A more detailed explanationofthis variation appears in Section 5.3.1. The following sections describe the development ofthe horsepower·hourestimate for nrntfu,..tinn !>""' th
.. hA
..<-........,,...._ **~-..t** ---··-'

**-----~'-** '-



### Confidence limits were assigned to be 

### ± 200% based upon an engineering analysis. Rigorouspropagationofthe errorusing the ratio method produced an estimate for the upperbound of

### ± 576% (185,630MMhp·hr). The ratio method assumes that sites are randomly sampled, so that a large site is proportionatelyrepresentative ofalarge section of the population (see Volume 4on statistical methodology).6 

### However, an analysis ofthis bound showed it to be unreasonably high. A.G.A.'s

### Gas Facts reports that lease and plant fuel usage for 1992 was 1.2trillion scf.7 

### Assuming all ofthis fuel was fired in

### compressor drivers, this would produce 150,080MMhp-hr. In reality, much ofthis fuel is actually used in heaterburners; therefore, the actual upperbound must be well below 150,080MMhp·hr 

### ( ± 447%). A separate analysis ofthe company database produced anupperbound ofonly 66,490MMhp·hr (± 

### 119%). Thisestimate was based on average horsepower·hours by business unit and applied a confidence limitanalysis to the average ofthese data. Each alternative approach resulted in 

### lower confidence limits than

### the calculated 

### ± 576%; therefore, the confidence limits were setat 

## ± 200%. 

### 5.2 Processin2 Industry Se2"'ent Horsepower Horsepower 

### ingas processing could be extrapolated to estimate anational total by using eitherplant throughput orplantcount. Horsepower is technically related to plant pressure 

### (aP)and throughput. However, there are no national figures foraverage plant

### ilP. Withoutthe 

### ilPfactor, planthorsepower is not related to throughput alone. Therefore, national gas plant horsepower was determinedby averaging the values obtained when extrapolating by throughput and by plantcount.

### 1992 to calculate the processing segment horsepower.8 

### This gives atotal compressor driver horsepower ofabout 2.2 MMhp forengines and 2.8 MMhp for turbines in the processing segment.

Site GPI GP2' GP3 GP4 GP5 GP6 GP7 GP8 GP9 GPIO TOTAL' AVERAGE 

### TABLE 5-3. COMPRESSORDRIVERDATA FROM PROCESSING SEGMENTSITEVISITS llmalledEngine Itmalled Turbine hp. hp. 8300 35000

0 27000 0 20000 3700 0 1!000 0 6740 (20000) 0 5925 (17490) 0 6267 (18500) 0 6267 (18500) 0 36600 23000 84799 105000 8480 10500 Total site horsepower (including gas lift for oil recovery) is shown in parentheses. b Estimated.

Excludes gas lift. 

### THROUGHPUTMETHOD: Engine 

### hp·hp = 

### Total Site hp x U.S. Throughput Total Site MMcfd

= 

### 84799 

### hp 1775 MMcfd

= 

### 2.22 MMhp 

### x 46510.7 MMcfd

15 MMcfd 350 750 140 60 49 56 40 130 130 70 1775 177.5

(7)

### Turbine hp " 105000 

### hp 1775 MMcfd "2.75 

### MMhp X 

### 46510.7 MMcfd



### The secondextrapolationmethod uses the average installed horsepowerper site and the total number ofgas plants in the United States in 1992 tocalculatetheprocessing segment horsepower.7 

### This gives atotal compressor driverhorsepower ofabout 6.2MMhp for engines and 7.6 MMhp forturbines in the processing segment. SITE METHOD 

### Total Site hp Engine hp·hp " **:=-7:':='7=~::--** x U.S. 

### Gas Plants Total Nwnber of Sites
" 84799 

### hp 10 

### Plants x 

### 726 

### Plants
"6.16 

### MMhp Turbine hp 

## = 105000 

### hp 10 

### Plants "7.62 

### MMhp x 726 

### Plants (8)



### An average ofthe results ofthe two extrapolationmethods is used to determine the national estimate forcompressordriverhorsepower in the processing segment. Theaverage engine horsepoweris 4.19MMhp, 

### and the average turbinehorsepower is 5.19 MMhp. Bothestimates are based onthe total installedhorsepowerfrom the sites visited, 

### excluding horsepowerused for gas 

### lift. Confidence limits were calculated forthe average site visithp/MMcfd and average site visithp/plantusing the ratiomethod. Confidencelimitsfor the U.S.gasplant 

### 16

### throughput and the total U.S. numberofgas plants were estimated to be± 5% and± 2%, respectively' The uncertainty for the first extrapolationmethod (based on throughput) is 

### ± 114% for engines and 

### ± 120% for turbines. The uncertainty for the second extrapolation method (based on numberofplants) is 

### ± 71.4% for engines and 

### ± 7.6% for turbines. For the average ofthe two methods, the uncertainty is 

## ± 132% for engines and 

### ± 99.4% for turbines (90% confidence limits). 

### OperatingHours
Table 5-4shows the "operating hours" forthe compressordrivers atthe 10 

### sites visited plus operating hourdata from two company databases for anadditional 18 gas plants. Forthe site visit data, actual operatinghours were only

### available for two ofthe sites. For the 

### remainingeight sites, compressors lhat were running during the site visit were assigned annual operating hours of8760. Compressors 

### that were idle were assigned annual operating hours of0. Onecompanydatabase (17plants) included operating hours of8760 for some units. Thesedata may 

### be maximumhours, not actual hours: However, no other data were availablefortheseunits, so the data 

### wereused as provided. Theoperating hours listed for each site inTable 5-4are the average hours for all ofthe drivers atthe site. Confidence limits were calculated forthe operating hours estimatefrom the variation ofthe 

### sitedata. The resulting uncertainty is 

### ± 11.5% forengines and 

## ± 48.4% forturbines (90% confidence limits). 

### 5.3 Transmission lndustnrSea:rnent Theactivity factorestimates for the transmission segment includehorsepower and operating hours forcompressor stations and storage fields. These estimateshave been calculated for compressordrivers and generatordrivers at bothtypes offacilities. Section 

### 5.3.1 discusses the compressordriveractivity factorestimates forcompressor stations. (Site visit data for transmission compressor stations are included 

### inAppendix D forcomparison.)



### 17

### TABLE 5-4. ANNUAL OPERATING HOURSFORPROCESSING SEGMENT Average No. of Average Site No. ofEngines• OperatingHours Turbines • Operating Hours GPlb 7 6257 2 4380 GP2 0 8423 GP3b 0 8760 GP4b 4 4380 0 GP5b 7 5006 0 GP6' 6 16 2920 0 GP7" 4 12 6570 0 GP8b 4 8760 0 GP9b 4 8760 0 GP10 15 5724 5 3816 GPll 2 0 0 GP12 5 7376 0 GP!3 4 4617 0 GP!4 5 8570 0 GP15 9 7949 0 GP16 8760 0 GPI7 14 8760 0 GP!8 !0 4043 0 GP19 3 5840 0 GP20 II 8760 0 GP21 7 5325 0 GP22 46 8760 0 GP23 8 8760 0 GP24 10 5011 0 GP25 8 6487 0 GP26 5 8176 0 GP27 8760 0 GP28 9 7949 0 TOTAL 203 9

**AVERAGE~** 6626 6345 90%LIMIT' 

### + 11.5% 

### + 48.4% •Total numberofdrivers (including

# sas liftfor oil recovery) are shown inparentheses. h Based on active (8760 hrs) versus i Je (0hrs). c Based on site averages.



### 18

### Section 5.3.2 discusses the compressordriver activity factor estimates for underground storage fields. Activityfactor estimates for generator drivers are discussed in Section5.3.3. 

### 5.3.1 Compressor StationHorsepowerandHours Horsepower
The transmission compressorstation horsepower estimate is based on the GRI TRANSDATdatabase, which includes transmission, storage, and associated field compression for 1989. TRANSDAThas not been revised since the 1989 data were collected; therefore, for these activity factors, 1989 was used as the base year. It is not possible to separate the compressordata in GRI TRANSDATby the specific

**application~** 

### however, an adjustmentfor storage compressorhorsepower can be made based on data from A.G.A. for !989. While the GRI TRANSDAT data could 

### be adjusted to a 1992 basis using A.G.A.'stransmissionhorsepower data, this approach was rejected because £he annual data showed no trend and differences were attributed to changes in

### reporting protocols by A.G.A.'smembercompanies.
GRI TRANSDAT'sIndustry Database contains informationon 7489 reciprocating engines and 793 gas turbines. .The total installed horsepower for these compressors is 11.2MMhp forengines and 

### 5.0MMhp for turbines, which accounts for about 97% ofthe gas utility industry installed horsepowerreported by A.G.A. for !989 (16.7MMhp).7 

### A.G.A.'sdata were gathered through a survey oftheir membercompanies and includes approximately96% oftotal gas industry sales. The GRI TRANSDAT horsepowercan be adjusted for the 1989 storagehorsepower reported by A.G.A. (!,462,971 hp) to give !0.2MMhp forengines and 4.5 MMhpforturbines. GRI TRANSDAT'S engine/turbine horsepower split of69.1% engines and 30.9%turbines was applied to 

### the storage horsepower before adjusting the totals.

19

### A.G.A. also separately reports that 13.9MMhp is for transmission in 1992.7 

### This is based upon the annual A.G.A. survey issued to membercompanies. GRI TRANSDAThorsepower, less the storage segment, is about 6% higherthan the A.G.A. number. This discrepancy probablyresults from differences in the field gathering horsepower reported by GRJ TRANSDAT and A.G.A
.. Currently, there is no way to separate this type ofhorsepower from that

### used fOrmainline transmission. No other adjustments to the GRI TRANSDAThorsepowerdata

### were made during this study. Horsepower in the GRJ TRANSDAT Industry Database is reported as site totals. The national estimate for transmission compressqr stations is simply a sum ofall of these site totals. As aresult. the uncertainty cou1d notbe calculated from the data as was done for the other industry segments. Therefore. confidence limits forcompressor station horsepower were conservatively estimated by engineeringjudgementto be 

### ± 10% foreach type ofcompressordriver. OperatingHours The average annual compressoroperatinghours for the transmission segment wasdetermined from informationreported on FERC Form No. 2 for theyear 1992. In the FERC database, transmissioncompaniesreport the total numberofoperating hours per stage ofcompression for each compressor station. The total number ofstages ofcompression operating on the date ofpeakdemand is also reported 

### by station. The value foroperating hours was divided 

### by the total number ofstages to give the average annual operating hours for the station. The average annual operatinghours at every stationfor all the companies in the FERC database were then summed and divided by 

### the total numberofstationsto produce the nationwide activity factor. Transmission compressor station annual operating hours were 3787 hours per year. Fora few stations the information in the FERC database was not considered to

### be accurate (lessthan 1

### %ofthe total), so the average operating hours for the rest ofthe company'sstations was applied to the station with questionable data. Confidence limits for the FERC operating hours were calculatedto be 

## ± 4.0%. 

### 20

### Because the FERCdatabase does not identify the type ofdriver, reciprocating engine or turbine, aprocedure was developed to 

### split the total average operating hours (3787 hrlyr) between the two types. The FERCdata were weighted by the total number ofeach type ofdriverusing data from 

### GRl TRANSDAT as shown in the following equation.

where: 

### 793rumm~ (T,) + 7489...,, (R,) = 3787 

### hr/yr (FERC) (793rumm + 7489...,
.. )

= 

### Turbine operatinghours, hr/yr = 

### Reciprocating engine operating hours, hr/yr (9)



### The following relationship between Thr

### and

## Rm was based on data provided by acompany for 107 transmission compressorstations, which included 89 turbines and 524 reciprocating engines. T,. = 2718 

### hr/yr = 

### 053 R,. 5086 hr/yr (10) 

### Using

### these two equations to solve for T11r 

### and

## Rm resulted in annual operatinghours of2118 hrlyrfor turbines and 3964hrlyrforreciprocating engines. Confidence limits for the transmission compressor stationoperating hours were calculated to be 

## ± 31.3% forturbines and 

## ± 13.9% forreciprocating engines. The confidence limits were based on assumed uncertainties of

### ± 10% for the GRI TRANSDAT data and calculatedconfidence limits forboth the FERC and company data.

21

### 5.3.2 UndergroundStorageHorsepowerandHours Horsepower Horsepower data from A.G.A.'s Gas Facts 

### were used for this industry segment. 

### A.G.A. reports that for 

### 1992 the total installed compressorhorsepower associated 

### with

### underground storage was 1,920,441 horsepower (entire United States).7 

### The horsepower data were gathered by 

### A.G.A. through a survey oftheir membercompanies, which includes approximately 96% oftotal gas industry sales. Since GRI TRANSDAT includes storage compressorhorsepower, the horsepower splitbetween engines and turbines was assumed to be the same as the split found in this database (69.1%, 

### engines and 30.9%, 

### turbines). As a result, the horsepower_attributed to engines is 1.33 MMhp and to turbines is 0.59MMhp. Confidence limitsfor storage horsepower (engines and turbines) were calculated based on an assumed 

### ± 5% uncertainty for the A.G.A. horsepower and an assumed 

### ± 10% uncertainty for the GRI TRANSDAThorsepower splits. OperatingHours Table 

### 5-5 shows the operating hours ofcompressors at four sites surveyed and the operating hours providedby one company fortheir seven storage fields. The operating hours listed are the average hours for all ofthedrivers at the site. Confidence limits were calculated for the operating hourestimatefrom the variation ofthe site data. The resulting uncertainty is 

## ± 23.1% for engines and 

## ± 620% for turbines (90% confidence limits). 

### 5.3.3 GeneratorDriverHorsepower and Hours The generatordriverestimates are based on site visit data and dataprovided by one company for34transmission compressor stations and three storage fields. Site visit data were co11ected for generator drivers (forelectricity generators) at seven ofthe transmissioncompressor stations surveyed. Forcompressor stations, an average generator 22

### TABLE 5-S. ANNUALOPERATING HOURS FORSTORAGESEGMENT Average Average No. of Operating No. of Operating Site Engines Hours Turbines Hours US! 9 2400 0 US2 !4 5122 4 52.5 US3 2 5607 0 US4 3 l!56 0 US5·1 5 2700 0 US5-2 3 38!3 0 US5-3 3 5832 0 USS-4 4 3727 0 USS-5 3 3390 0 US5-6 4 3327 0 US5-7 0 2 5781 TOTAL 50 6 AVERAGE' 3707 2917 90% LIMIT• 

### ± 23.1% 

### ± 620% •Based on site averages. 

### horsepowerper stationwas establishedto determine total generatorhorsepower. Similarly, for storage fields, an average generatorhorsepowerperfield was established to determine total generator horsepower.


### Data for generatorsused 

### in transmission compressor stations are shown in Table 5-6. Only

### one turbinedriverwas instaiied at the 

### 41 facilities surveyed; therefore, the 

### data shown in Table5-6 represent anengine/turbine horsepower split of97%/3%. Using the average installed horsepowerperstation, thetotal number oftransmission compressor stations in the United States for 1992 was used to extrapolate to a national estimateof 1.45 MMhp for reciprocating engine generatordrivers and 0.045 MMhp for turbine generator drivers.9 

### The number ofcompressor stationsis anestimate based ondata from FERCFonn No. 2 for46 transmissioncompanies and is described 

### inVolume 

### 5onactivity factors.4



### 23

### TABLE 5-6. GENERATOR DRIVER DATA FROMTRANSMISSION COMPRESSORSTATIONS Installed A.nrage Installed Average Site No. Engine Operating No. Turbine Operating 

# .

**.,..,~** bp Ho= Turbines hp Ho= GSI 3 1542 3232 0 0 GS2 I 514 0 0 0 GS3 2 1028 1095 0 0 GS4 0 0 0 0 GS5 2 3SOO 88 0 0 GS6 

### sao 88 0 0 GS7 I 

### sao 88 0 0 GSS-1 3 I IJCo 9 0 0 GSS-2 

### s ISO! 1688 0 0 GSS-3 30 0 0 0 0584 I 43S 2 0 0 "GSS-5 4 2190 44SS 1080 474 GSS-6 2 S90 4379 0 0 GSS-7 43S 0 0 0 GSS-8 4 1786 2279 0 0 GSS-9 I l9S 89S 0 0 GSS-10 22S 0 0 0 GSS-1! 60 0 0 0 GSS-12 227 12 0 0 GSS-13 64(1 5217 0 0 GSS-14 3 ll48 4756 0 0 GSS-15 

### s 1974 S290 0 0 GSS-16 43S 0 0 0 058-17 2 940 4392 0 0 GSS-18 3 1177 2060 0 0 GSS-19 7 2135 3660 0 0 GSS-20 2 816 33 0 0 GSS-21 2 816 0 0 0 GSS-22 2 290 0 0 0 GSS-23 4 1556 27 0 0 GSS-24 

# '" 0 0 0 GSS-25 2 370 129 0 0 GSS-26 

# '" 0 0 GSS-27 

### lao 0 0 0 GSS-28 I 19S 398 0 0 GSS-29 2 784 4902 0 0 GSS-30 436 6 0 0 GSS-3! 7 2365 4370 0 0 GSS-32 62S 2S4 0 0 GSS-33 2 816 269 0 0 GSS-34 I ISO 0 0 0 TOTAL 87 3S006 1080 AVERAGE' 

# "' 1352 26 474 90% LIMIT' ± 38.0% ± 620%" •Basedon site averages. ' Assumedequal ro compressorrurbinedriversa! storage fields.



### 24Engine 

### hp·hr = 

### Total hp No. Stations x No. U.S. Stations
35006 hp x 1700 Stations 41 Stations

= 1.45 MMhp
Turbine 

### hp = 

### 1080 hp x 1700 Stations 4!Stations

= 

### 0.045 MMhp Conf1dence limits were.calculated for the horsepower estimates from the 

### variation ofthe data. Theuncertainty calculated forthe compressor stationestimate is (11)



### ± 10%. The resulting uncertainties ofthe national

**e~timates** ofgeneratordriver horsepower 

### are 

### ± 23.3% for reciprocating engines and 

### ± 166% for turbines (90% confidence limits). Table 5-6also shows the annual operating hours for the generators at compressor stations. Theoperatinghours listed are the average hours for all ofthe drivers at the station. The wide variation reflects the sites that use generators for continuous electricity generation versus the sites thatuse generators only for emergency backup. Since 

### there was only 

### one data pointfor turbine drivers, the uncenainty was assumed to be the same as that for turbine compressor drivers in underground storage at 

### ± 620%. Confidence limits were calculated for the reciprocating engineoperating hours estimate from the variation of the data. The resulting uncertainty is 

## ± 38.0% (90% confidence limits). Data for generators used in storage fields are shown in Table 4-7. The data were provided by one company for 9 storage fields, but only 3fields had generators. The data shown represent an engine/turbine horsepower split of60%140%. 

### Using the average installed horsepower per field, the total numberofstorage fields in the United States for 1992 was used to extrapolateto a national estimate of0.085 MMhpfor reciprocating engine
25

### generator drivers and 0.057 MMhp for turbine generatordrivers. The number ofstorage fields is from A.G.A.'s

### Gas Facts (475 storage fields).' Confidence limits were calculated for the horsepowerestimates from the variation ofthe data. The resulting uncertainties of the national estimates ofgeneratorhorsepower are 

### ± 126% for reciprocating engines and 

### ± 184% for turbines (90% confidence limits). 

### En . h

**~-** 

### _T:..:oc::tal:::-='hp"- gme pw = ,., 

### No. Fields x No. U.S. Fields

Turbine hp = 

### 1611 hp x 475 Fields 9Fields

= 

### 0.085 MMhp

= 

### 1080 hpx 475Fields 9 Fields

= 

### 0.057 MMhp (12)



### Table 5-7also shows the annual operating hours forthe generators at storage fields. The operating hours listed are the average hours for all ofthe drivers at the field. Since there was only one datapointforturbine drivers, the uncertainty was assumed to be 

### the same as that forturbine compressordrivers in

### underground storage at 

## ± 620%. Confidence limits werecalculated from the variation in the operating hours data. The resulting uncertainty is 

## ± 377% (90% confidence limits). TABLE 5-7. GENERATORDRIVERDATAFROMSTORAGEFIELDS 

# """""" Anrage 

# ......

# .. Anrage No. 

# - Ope!rating No. Turbine Openting Site 

# ........ hp u- 

# Tw-- hp Houn GFJ I 1000 

### n 0 0 GF2 0 0 0 0 GF3 0 0 0 0 GF4 0 0 0 0 GF5 0 0 0 0 GF6 0 0 1080 36 GF7 0 0 0 0 GF8 2 611 306 0 0 GF9 0 0 0 0 TOTAL 3 1611 1080 AVERAGE• 179 191 120 36 90% LIMIT" ± 377% ± 620%. • ase onSlte averages. • Assumedequal to compressorrurbinedriversa1 storage fields. 

### 26

### Generator drivers in production and processing were not included in this analysis since these sources are negligible. Productiongenerators are rare. Processing generators are more commonbut rarely operate. The generator data reported by one production and processing company accounted for less than 3% oftheir total drivers and corresponded to less than 

### 0.01 Bscfmethane emissions. 

## 5.4 IndustryActivity Factors
The two main types ofcompressor and generatordrivers in the natural gas industry are reciprocating gas engines and gas-fired turbines. Horsepower·hour data were available for the production industry segment activity factor calculation. Twopieces of information were needed to calculate the activity factors (hp·hr)foreachtype ofdriver in each ofthe remaining industry segments. These were the installed horsepower and the average annual operating hours. The final hp·hractivity factors were calculated using the ·national estimates forcompressor horsepower and average operating hours for these industry segments, as described in thepreceding sections. Table 5-8 summarizeseach ofthese estimates and shows the resulting activity factors for both engines and turbines by industry segment. The table also includes the 90% confidence limits calculated for each factor. Activity factor confidence limits were propagated from the confidence limits for the individual terms using a standard statistical approach.

27

### TABLE 5-8. COMPRESSORDRIVER ACTIVITY FACTORS FOREACH INDUSTRY SEGMENT Installed Installed Annual Annual Engine Turbine Hours Hours Engine Turbine IndustrySegment MMhp" MMhp' Engine Turbine MMHp ·hr J\.1MHp ·hr Production NA NA NA NA 27,460 

### ± 200% 0 Processing 4.19

### ±

**132%~** 5.19 

### ± 99.4%b 6626 

### ± 11.5% 6345 

### ±48.4% 27,760 ± 133% 32,910 

### ± 121% Transmission

Compressor Drivers 10.2 

### ± 10.0% 4.55 

### ± 10.0% 3964 

### ± 13.8% 2118 

### ± 31.3% 40,380 

### ± 17.1% %35 

### ± 33.0% Generator Drivers 1.45 

### ± 23.3% 0.045 

### ± 166% 1352 

### ± 38.0% 474 

### ± 620% 1962 

### ±45.4% 2l.2 

### ± 1215% Storage

Compressor Drivers 1.33 

### ± 13.5% 0.59 

### ± 13.5% 3707 

### ± 23.1% 2917 

### ± 620% 4922 ± 26.9% 1729 

### ± 626% N 00 Generator Drivers 0.085 

### ± 126% 0.057 

### ± 184% 191 

### ± 377% 36 

### ± 620% 16.3 

### ± 621% 2.05 ± 1312% • Does not includehorsepower associated withgas lift foroil recovery orwithelectric drivers
. b Average oftwoestimationmethods.

### 6.0 NATIONAL COMPRESSORDRIVEREMISSIONESTIMATES The annual emissions forcompressor drivers were determined by multiplying 

### the emission factors (Section4) by 

### the horsepower·hour activity factors (Section 5) for reciprocating engines and gas-fired turbines and adding these values for each industry segment. Table 6-1 shows the resulting emissions for each industry segment and the overall national emissions estimate for each type ofcompressordriver. Using the same approach for errorpropagation, the total annual emissions from compressordrivers and generator drivers for the entire industry are estimated to 

### be 24.8Bscf

## ± 64%. TABLE 6-1. COMPRESSORDRIVEREMISSIONS FORTHE NATURAL GAS INDUSTRYBY SEGMENT Driver Engines, Bscf Turbines, Bscf Production 6.58 

### ± 200% 0.00 Processing 6.65 

### ± 133% 0.186 

### ± 129% Transmission 9.68 

### ± 17.9% 0.0546 

### ± 45.7% Storage l.l8 

### ± 26.9% 0.00979 ± 654% Generators 0.474 

### ± 45.6% 0.000132 

### ± 1163% 

### TOTAL 24.57 

### ± 65.1% 0.256 

### ± 97.8% 

### Approximately 92% ofthe emissions from compressordriverexhaust are estimated to be from reciprocating enginesused in the production, processing, and transmission segments; another5% ofthe emissions are from engines in the storage segment. If

### generator drivers are included, the percentages for all drivers are 94% and 5%, respectively. All othercategories are negligible in comparison; therefore, it 

### is more important to accurately detennine the activity factors for reciprocating engines in production, processing, and transmission.



### 29

### 7.0 CONCLUSIONS
As a result ofthe data generated in this study, the natural gas industry emissions from compressordriverexhaust were estimated to be 24.8 Bscf

### ± 64%. Nearly 99% of

### the methane emissions are from reciprocating engines, and approximately 40% ofthe methane emissions are from engines in the transmission industry segment. The methane emissions from compressordriverexhaust represent about 7.9% ofthe methane emissions from the entire natural gas industry. 10 

### Table 7-1 showshow these emissions rank with 

### respect to the other sources identified in each industry segment. 

### TABLE 7-1. RANKING OFCOMPRESSORDRIVER EXHAUSTEMISSIONS BY INDUSTRY SEGMENT CompressorDriver 

### Segment SegmentEmissions from Industry 

### Emissionsb 

### Emissions' CompressorDrivers 

### Segment Bscf Bscf % 

### Production 

### 6.58 84.4 7.8 

### Processing 6.84 36.4 18.9 Storage 1.19 18.2 6.5 

### Transmission 10.2 98.3 10.4 Distribution 

### 0 77.0 0 

### TOTAL' 24.8 314.3 7.9 Compressordrivertotals arefor reciprocatingengines and gas-firedturbinescombined. b 

### Includesgeneratordrivers. Compressordriverexhaust emissions represent a significant source ofmethane emissions in all ofthe industry segments where these sources are present. Since almost all ofthe emissions are due to reciprocating engines, any further work should focus onthese types ofdrivers. The confidence limits on the engineemission factor were 

### ± 5% 

### while the errorbound onthe activity factor ranged from 

### ± 17.1% to 

## ± 621%. Therefore, improving theengine activity factors would havethe greatest impact ontheprecision ofthe emissions estimate.
30

### As part ofthe requirements for Title Voperating permits, many facilities will implement recordkeeping practices that may benefit this type ofdata collection. Ifcompanies were to 

### collect horsepower·hourdata for each compressor driver, the emission factors developed as part ofthis project would allow a direct way to determine their methane emissions. Access to these databases would also provide the resource to improve the natural gas_ industry activity factors for compressordrivers. Using this kind ofdata would further improve the precision ofthe overall compressor driverexhaust emissions estimate.

31

### 8.0 REFERENCES
L 

### Biedennan, N. GRI TRANSDATDatabase: Compressor Module. (prepared 

### for Gas Research Institute). npb Associates 

### with TomJoyce and Associates, Chicago, IL, August 1991. 

### 2. Pipeline Systems, Incorporated.

### AnnualMethane Emission Estimateofthe Natural Gas 

### Systems in the UnitedStates, Phase 2. 

### Prepared for Radian Corporation, September !990. 3. Jones, D.L., L.M. Campbell, C.E. Burldin, M. Gundappa. and R.A. Lon, 

### "National Estimate ofMethane Emissions from Compressors in the U.S. Natural Gas Industry." Radian Corporationand Gas Research Institute, Air & 

### Waste Management Association Conference Proceedings, Paper# 92-142.02, Kansas City, MO, 1992. 4. Stapper, B.E. Methane Emissionsfrom theNatural GasIndustry, Volume 5: 

### ActivityFactors, 

### FinalReport, GRI-94/0257.22 and EPA-600/R-96-0BOe. Gas Research Instituteand U.S. Environmental Protection Agency, June !996. 5. U.S. DepartmentofEnergy/Energy !nfonnationAdministration. Natural Gas Annual, 

### 1992. DOE/EIA-0131 (92), Washington, DC, September 1992. 6. Williamson, H.J., M.B. Hall, and M.R. Harrison. Methane Emissionsfrom theNatural Gas Industry, Volume 4: StatisticalMethodology. 

### Final Report, GRI-9410257.21 and EPA-600/R-96-0BOd. Gas Research lnstirute and U.S. Environmental ProtectionAgency, June 1996. 

### 7. 

### Gas Facts: 1992 Data, American Gas Association, Arlington, VA, 1993. 8. Oil & 

### GasJournal. 

### 1992 Worldwide Gas Processing Survey Database, 1993. 9.
10. Federal Energy Regulatory Commission (FERC)FonnNo.2: Annual Report ofMajor Narural Gas Companies, 1992 database. Harrison, M.R., L.M. Campbell,T.M. Shires, and R.M. Cowgill. Methane Emissionsfrom the Natural Gas Industry, Volume 2: Technical

### Repon, 

### Final Report, GRI-94/0257.1 and EPA-600/R-96-0SOb. Gas Research Instirute and 

### U.S. Environmental Protection Agency, June 1996.

32

### APPENDIX A 

### NationalEstimateofMethaneEmissions from Compressors intheU.S. NaturalGas Industry

A-1

### 92-142.05 National Estimate of Methane Emissions from Compressors in the U.S. Natural Gas Industry Donna Lee Jones, Lisa M. Campbell, Clint E. Burklin, and Mahesh Gundappa Radian Corporation, Research Triangle Park, North Carolina 27709 Robert A. Lott Gas Research Institute, Chicago, Illinois 60631 

### INTRODUCTION The combustion of natural gas emits much less carbon dioxide per unit of energy generated than other fossil fuels. For this reason, one strategy that 

### has been suggested for reducing global warming is to encourage switching from other fossil fuels to natural gas. However, methane is currently thought to be a more potent greenhouse gas than carbon dioxide; if so, leakage of natural gas (which is approximately 90 percent methane) could reduce or eliminate the advantage of using natural gas because of its lower carbon dioxide emissions. Two major issues must be addressed before the consequences of the fuel switching strategy can be evaluated. First, there is a need to better define the impact of methane relative

**t~** carbon dioxide on global warming. Second, it is important to better define methane emissions from the gas industry. Because of the latter issue, the Gas Research Institute (GRI) and the U.S. Environmental Protection Agency (EPA) have developed a cooperative program to quantify methane emissions from U.S. gas operations. Currently, estimates of methane emissions from the gas industry range from 0.5 to 4.0 percent of production. The GRI/EPA program is a CQmprehensive program to determine methane emissions from the wellhead to the customer's meter. The goal is to determine emissions to within approximately 3 billion cubic meters (m3), or 100 billion standard cubic feet (scf), which is approximately 0.5 percent of U.S. production, To achieve this overall accuracy, an accuracy target has been established for each source category in the natural gas industry. One source category is the exhaust from compressor engines that are used to move the gas through the system. Compressors are located in production fields, processing plants, gas storage facilities, and along transmission lines. A preliminary study indicated that the exhaust from compressor engines might account for more than 50 percent of the industry's methane emissions. 1 Because the uncertainty in this early estimate was quite large, Radian Corporation conducted a study to determine methane emissions from both reciprocating and turbine compressor engines. The accuracy target established by the GRI/EPA program was to determine the emissions for this source category within 30 billion scf. In this study, methane emissions were estimated by multiplying the methane emission rate of the unit by the activity of the unit. The emission rate expresses the amount of emissions per operating characteristic, independent of the other features of the unit. The activity expresses the 

### A-292-142.05 operating characteristic of the unit which was, in this case, either a reciprocating engine or gas turbine. For example, when the operating characteristic is fuel usage, the activity is annual fuel used by compressors. When the operating characteristic is operating time, the activity is hours of operation (per year). The emission rates used in this study were in the form of methane emissions per hour. The activity of each unit was the annual operating hours for that unit. A national estimate of annual methane emissions was determined from emissions estimates using available data for compressors in the natural gas industry. APPROACHES The Ideal Emission Estimate Ideally, the annual methane emissions from compressors ih the natural gas industry would be determined from the sum of the annual emissions from each unit in the industry, where the emission rate may vary over time and from unit to unit, This relationship is expressed by the following equation: N Emissions

- L

# J [ ER1 (t) x A 1 (t)

### J dt i-1 (1) where ER1(t) is the instantaneous emission rate at time (t) for compressor1 , A

1(t) is the instantaneous activity at time (t) for compressor1 , and N is the total number of compressor units in the industry. To reflect annual emissions, the integral in Equation (l).is evaluated over the time interval t 1 to tz, where tz · t 1 is equal to one year. This approach produces no uncertainty in annual emissions. Emission _Estimate Using Test Data The ideal approach was considered impractical because it would require a massive data-gathering effort by the industry. Fortunately, a substantial amount of data was available for both the emission rates and activity factors of compressor engines. For the emission rates, data for reciprocating engines and gas turbines were available for a number of models that were tested during relatively short time periods. Values for the annual activity of compressors, in terms of operating hours, were also available for some models. If data for all compressors in the industry were available, the following equation could be used to estimate methane emissions: N Emissions- L (ER1 !At-test X

**~(t)** /At•ly•ul i-1



### A-3 (2)92-142.05 where ER1 is the emission rate of compressor1 (in grams of methane per hour) evaluated over the time period of the test; where the activity, Ai, of compressor1 corresponds to the annual operating hours of compressor1 ; and where N is the total number of compressor units in the industry. This equation assumes that the emission rate of the compressors during the test period represents the emission rate of the compressors during the year, on the average. Methane emissions from compressors will vary from manufacturer to manufacturer and model to model. Assuming that the compressors are properly maintained, differences in methane emissions, even for the same model, also will be caused by operating the compressors at different horsepower levels or speeds, or for longer or shorter periods of time in order to satisfy the operational needs of the system. Figure 1 illustrates the relationship between operating load and emissions for a Cooper Bessemer two-cycle engine. 2 The figure shows the total hydrocarbon emission rate at varying loads, where speed is used to lower horsepower. Total hydrocarbon emissions can be considered a surrogate for methane emissions, since metharie is expected to comprise a large portion (over 90 percent) of total hydrocarbon emissions from compressors. The data show that the emission rate for a Cooper Bessemer engine increased at lower loads, with a 40 percent increase in emissions at SO percent of rated horsepower (full load), and a possible 100 percent increase if loads close to 30 percent of full load are used. A similar increase in methane emissions can be expected for other engine and turbine models, although the magnitude of the increase for other models is not known at this time. The emission rate of any compressor, then, is a function of the rated horsepower and operating horsepower. The equation below summarizes this relationship: (3) where ER1 is the operating emission rate of compressor1 ; ER1

### ° is the emission rate of compressor1 at the rated horsepower, Hp1°; and Hp1 is the operating horsepower. The data from the Cooper Bessemer illustrate that a linear relationship can be used to represent emissions for this engine as a function of horsepower, within 3 percent accuracy, over the range of horsepower from SO to 100 percent of rated horsepower. In this situation, the average horsepower at which the engine operates over the year (as in Equation (2)) could be used to evaluate the integral in Equation (1) without any loss of accuracy. If the information needed to develop Equation (3) was known for all engines and the relationship between horsepower and emissions for each engine was linear, the following equation could be used to more accurately estimate annual methane emissions from compressor engines from test data:

A-4

## • 

# h 

# l 12 11

1 

# • 

# • 4 3 2 20 

# "'

**~**

**-~-1!] ~~**  ·-.

**··~**

30 40 50 60 70 80 fWcent Raled1-torMpowet ·H· 231 RPM ·D· 264RPM 

# . .

00 100 110 120 130 -f- 196RPM -Q 297 RPM 

## -o JJO RPM 

## L---~----------------------------------- Figure 1. Effectofhorsepowerandspeedontotal hydrocarbonemissionsfora Cooper Bessemer2cycleengine• **~** N

# . '' u•92-142.05 Annual Emissions 

### (grams) N L [ ER (Hp)1 x Annual Hours (Hp)1 ] i-1 (4) where ER (Hp) 1 is the emission rate of compressor1 as a function of horsepower (in grams of methane per hour); Annual Hours (Hp) 1 are the annual operating hours of compressori at a specified horsepower, and N is the total number of compressor units in the industry. Scaled-up Emission Estimate Using Test Data Although emission and activity data for all compressors in the industry were not known, an estimate of methane emissions for the industry was made by proportioning the emissions for a subset of the industry (with known emission and ac-tivity data) according to the proportion of horsepower contributed by this subset. This approach assumes that the emission rates for the test engines during the test period and the operating hours estimated for the subset represent the average operation of compressors in the industry. A more detailed description of this approach is found in the Method section of this paper.It was found that for the emission test data, on the average, the compressor emission rates were measured at virtually the same horsepower as the operating horsepower that was recorded for the compressors with the activity data (where the average horsepower of the compressors for the test data was equal to 0.985 times the average of the horsepower for the activity data). Therefore, knowledge of the relationship between horsepower and emissions was not needed for the analysis presented here. An estimate of methane emissions using test data for a subset of the industry may underestimate actual industry emissions if many compressors are operated at lower loads for a significant period of time, since methane emissions are likely to increase when compressors are operated at less than full load. Future work in this area should include an analysis of the relationship between horsepower and methane emissions, so that individual compressor emission rates can be estimated with more accuracy. 

### DATABASES Description of the Databases A number of databases were obtained for this study, that provided information on compressor emissions and operations. The databases were part of GRI's TRANSDAT compressor module. 3 Two databases in the compressor module contain information about the distribution of compressors in the natural gas industry. One of _the databases is an almost complete listing of engines and turbines in the gas industry, accounting for 16.2 million out of the 16.7 million total horsepower that was reported by the American Gas Association (AGA) for this industry in 1989.4 This nindustry Databaseft 

### A-692-142.05 contains information concerning 8,282 compressors in the natural gas industry. However, individual compressor horsepower is not reported in the database; only the total horsepower for all compressors of a specific type is reported for each gas company. A second smaller database in the compressor module (the "Operating Databasen) is a subset of the Industry Database (with 1,515 units) corresponding to 3.2 million total horsepower. The Operating Database is the only database in TRANSDAT that contains information on annual operating hours for each unit. The operating horsepower of each compressor is also recorded in the database. The data in the Operating Database were obtained from an AGA survey of 

### 112 companies in ozone nonattainment areas, where 

### NOx emissions were minimized. Because emissions of 

### NOx and hydrocarbons are inversely related, the operation of compressors to minimize 

### NOx will likely increase emissions of hydrocarbons and, hence, of methane. Consequently, the data in the Operating Database, such as the operating horsepower, may represent maximum methane emission conditions. The use of these data, then, presents a conservative estimate of industry emissions, if the data is representative of the industry as a whole. Data from emissions tests performed by Southwest Research Institute are contained in a third database in TRANSDAT (the "Test Database"). During the emission tests, the compressors were operated at close to full load (rated horsepower). Methane emissions, fuel use, fuel use rate, and horsepower were recorded for each emissions test for 

### 241 models of engines and turbines. Since there was some variation in horsepower in the multiple emissions tests for the same compressor, it may be possible to define the relationship between horsepower and methane emission rate for the 

### 241 models of compressors in this database. With this information, it would be possible to extrapolate from the test conditions to actual operating conditions at lower horsepower levels. Because of the limitations of this study, an analysis of this type was not performed. Because the Test Database contains only emission data and the other databases contain only operating data, a fourth database was developed that contains data for compressors for which information was found in both the Operating Database and Test Database. This fourth database was called the "Emissions Database." A total of 775 reciprocating engines and 86 gas turbines (out of 1,515 units in the Operating Database) fit the criteria and were included. Table 1 describes the contents of each of the four databases. Model-Matching Hierarchy A model-matching schema was designed to

**max~m1ze** the amount of correlation between the Test Database data and the Industry and Operations Databases. Originally, when the compressors were matched according to exact model names, the Test Database accounted for only 38 percent of the units A-7**T~BLE** I, DESCRIPTION OF THE

**O~TAB~SES** Industry Database Operating Database Test Database Ealsslons Database Data Engines Turbines Total Engines Turbines Total Engines Turbines Total Engines Turbines Total Total Units 7,489 19] 8 ,282 l'38') lJO 1,515 219 

# " 241 II> 

# " 861 Hanuf/Hodet• 922 144 1,0&6 Jta 31 )49 219 

# " 241 120 7 127 Total Hp (106) 11.2 '.0 16.2 2.4 0.8 3.2 NA NA NA I ) 0.4 I .7 Total Hours (106) NA' NA NA 4.6 0.) 4.9 NA NA NA 2.9 0 2 ) I •Nuaber of unique
**co~ressor** models in the database. bNot applicable.92-142.05 in the Operating Database and only 7 percent of the Industry Database. Through consultations with experts in the field of compressor emissions, a three-step hierarchy was designed to match more data in the Industry and Operating Databases to the Test Database. The first step, therefore, in the hierarchy was based on an exact match. For instance, an Ajax DPC-360 engine in the Industry or Operating Database was identified with Test Database data for an Ajax DPC-360 in Step (1) of the hierarchy. The second step in the matching procedure matched compressors by substring name, where the horsepower of both compressors was within ± 20 percent. An example of Step (2) in the hierarchy was a match of a Clark BA8T engine with a Clark HBAST engine (common substring of BAST), where the horsepower for the Clark HBA8T engine in the Emissions Database was 1,911, and was 2,050 for the Clark BAST engine in the Industry Database. The third step in the hierarchy consisted of matching the rated horsepower per cylinder (± 20 percent) in compressors with similar initial names (manufacturer) but with varying substrings. An example of Step (3) is a match of a Clark BAS engine, with 248 horsepower per cylinder (total horsepower- 1,242) and a Clark BAS engine, with 211 horsepower per cylinder {total horsepower- 1,000). Following the execution of the three steps in the model-matching hierarchy, 37 percent of the models and 57 percent of the units in the Operating Database (and 23 and 55 percent, respectively, in the Industry Database) were matched to emissions data. The execution of the three-step hierarchy also increased the amount of data in the Emissions Database to a total of 

### 1.7 million horsepower, from the previous total of 

### 1.3 million horsepower after Step (1) only, and accounting for over one-half of the horsepower in the Operating Database and Industry Database. 

### METHOD TO ESTIMATE METHANE EMISSIONS The Emissions Database was used to compressors in the natural gas industry. emissions is described below. Equations estimate.methane emissions from The method used to calculate

An average emission rate was obtained for each model of compressor engine and turbine in the Emissions Database from the average of all methane emission tests in the Test Database for that model. Since the time period in which each test was conducted was not given, the emission rates, in units of grams of methane per hour, were calculated from the reported methane emissions per unit of fuel (in grams per m 3) and the reported fuel use rate (in m 3 per hour) for each compressor, as in the equation below:

f\-9

### 92-142.05 Emission Rate Average Emission Rate1 '- X (g/hr) (g/m') where FUR1 was the average fuel use rate for compressor1 . The methane emissions for each compressor were then calculated as in Equation (6) below: Emissions1 l

- ER1 x Annua Operating Hours1 

### (grams) where ER1 was the methane emission rate of compressor1 calculated with 

### Equation (5), and Annual Operating Hours1 

### were obtained from the data for compressor1 in the Emissions Database. To determine the total methane emissions for the compressors in the Emissions Database, the following equation was used: Annual Emissions (grams) N L [ ER1 x Annual Operating Hours1

### J i-l (5)

(6)

(7) where the emissions from each unit are calculated as in Equation (6), and N was the total number of compressors in the database. Estimate of National Emissions If data for all compressors in the industry were available, a national estimate could be calculated using Equation (7). Since the compressors in the Emissions Database were only a subset of the compressors in the natural gas industry, a procedure was necessary to relate the methane emissions calculated with Equation (7) to a national estimate. The ratio of the total horsepower from compressors in the industry (16.7 million horsepower) to the total horsepower of the compressors in the Emissions Database (1.7 million horsepower) was used to seale up the methane emissions calculated in Equation (7) by a factor of (16.7/1.7), or 9.8, to estimate national emissions. This relationship is shown in the equation below: National Methane Emissions Methane Emissions for Emissions Database X Scaling Factor Hp, HpED (8)
where Hp1 is the total horsepower in the industry4 and Hpm is the total horsepower in the Emissions Database, which produce a scaling factor of 9.8. 

### A-10

### 92-142.05 RESULTS National Emission Estimate An estimate of national methane emissions from compressors using the approach discussed above was 0.22 teragrams (Tg) of methane. Over 99 percent of the emissions were estimated to be from reciprocating engines and less than 1 percent from gas turbines. This estimate was based on the assumption that the compressors in the Emission Database represent compressors used in the natural gas industry, on the average. If the industry compressors are operated at horsepower levels much less than the rated horsepower, the methane emissions estimated here could underestimate the industry emissions, since methane emissions are thought to vary inversely with horsepower. Field, Plant, and Pipeline Compressor Emissions Compressors are used in field and plant operations as well as in transmission activities. The emission estimate above does not apportion methane emissions among the segments of the natural gas industry that use compressors. The U.S. Department of Energy (DOE) provides estimates of the amount of fuel used in field (lease), plant, and pipeline applications, and these estimates were used to apportion methane emission estimates among the sources. 5 The methane emission estimates were based on the assumption that all the fuel reported for field and plant purposes was used by compressors. This assumption is likely to be an overestimate, because fuel is known to be used for field and plant purposes by equipment other than compressors. Although the portion of lease and plant fuel used for other purposes was not known, estimates of the fuel used by these sources served as rough estimates of fuel used by compressors in field,

**p~ant,** and pipeline operations. The result of using DOE estimates of fuel use was that 39 percent of total compressor fuel was attributed to field compressors, 26 percent to plant compressors, and 35 percent to pipeline. It is likely, however, that a higher percentage of total compressor fuel is used for pipeline, ano that lower portions are used for field and plant. The AGA estimated that 84 percent of total compressor horsepower was used for the pipeline4 ; if fuel use can be assumed to be proportional to horsepower, the percent of fuel used by pipeline compressors could be over- twice as high as the estimate based on the DOE information. Since methane emissions were assumed to be proportional to fuel use, the DOE breakdown in fuel among the three sources of compressor emissions in the natural gas industry was used to apportion the national estimate of 0.22 Tg of methane emissions between the three sources. The results were that, of the total 220 megagrams (Mg) of annual methane emissions estimated for compressors in the industry, 86 Mg of methane was estimated to be emitted from field compressors, 57 Mg from plant compressors, and 77 Mg from pipeline compressors. As discussed above for apportioning fuel use between these three sources, the emissions from pipeline compressors were probably underestimated, and the portions for the other two sources were overestimated. Another 

### A-ll92-142.05 possible error in the breakdown of emissions was the assumption that the emission rate and operating characteristics of compressors in field, plant, and pipeline applications were similar. UNCERTAINTY IN EMISSION ESTIMATES Since the true value of methane emissions from compressors in the natural gas industry is not known, the accuracy of the estimate of 0.22 Tg of methane emissions cannot be assessed. However, the data can be used to produce an approximation of the uncertainty in the emission estimate. Like confidence intervals, the uncertainty estimated for a value can describe, with a high degree of confidence, the range in which the true value lies, The target uncertainty for the total estimate of methane emissions from all sources in the natural gas industry was close to 3 billion m 3 (100 billion scf). Because there are many segments in the natural gas industry that emit methane that are part of the overall methane emission estimate in the GRI/EPA project, the goal for each segment was to produce a methane estimate with as little uncertainty as possible. The target uncertainty for compressors was approximately 800 million m 3 (30 billion scf). The following explains the procedure used to estimate the uncertainty in the annual methane emission estimate from compressors and the results of this estimate. Basis of Uncertainty in the Compressor Emission Estimate The only sources of uncertainty in the approach described above that could be estimated were the analytical error associated with the test data used to calculate the methane emission rates and the scale-up to national emissions based on the ratio of the horsepower in the Emissions Database to the estimate of compressor horsepower in the industry. The uncertainty in the hydrocarbon analysis was estimated to be 

### ± 10 percent, based on the expected gas chromatograph (with a flame ionization detector) capabilities. Likewise, the uncertainty associated with fuel flow measurements was estimated to be 

### ± 2.5 percent. The uncertainty associated with the scale-up between the Emissions Database and total industry horsepower was more difficult to quantify. Two indirect assessments of this uncertainty are discussed below, using comparisons between the Emissions Database and the Industry Database, which was taken to be a fairly good representation of the industry as a whole. The uncertainty for the scale-up to nationwide emissions was estimated to be approximately 1 percent, based on estimated significant figures in total horsepower. For an estimated industry horsepower of 16.7 million, the uncertainty was estimated to be 0.17 million horsepower; for the Emissions Database, with 1.7 million horsepower, the uncertainty was estimated to be 0.017 million horsepower.

**~12**92-142.05 Procedure to Calculate Uncertainty The software "@Risk" 6 was used to estimate the uncertainty in the estimate of methane emissions from compressors. The variables of uncertainty were entered into the program along with the values discussed above. The "@Risk" uncertainty estimating procedure recalculated the total methane emission estimate using Latin Hypercube sampling from normally distributed intervals along the range of each variable, defined by the expected value and the (estimated) standard deviation of that value. In the case where the standard deviation was estimated from significant figures, a uniform interval (as opposed to a normally distributed interval) was used for the Latin Hypercube sampling. In the "@Risk" program, the recalculation was performed 500 times, each time using a different value in the interval of each variable in the emission equations. The results of the 500 calculations, excluding values below zero, were analyzed for variation about the mean. The uncertainty was reported as the coefficient of variation, or the standard deviation divided by the mean, as a percent. Estimates of Uncertainty The uncertainty for the estimate of methane emissions from compressor engines and turbines, at 0.22 Tg (11.5 billion scf), was estimated to be approximately 1 percent, or 4.3 million m 3 (0.15 billion scf). This value is well below the 800 million m 3 target for compressor engines and turbines. Comparison of the Database One component of uncertainty in the methane emission estimate that could not be quantified for the uncertainty analysis was the degree to which the compressors in the Emissions Database represented the compressors in the industry. The Emissions Database was compared with the Industry Database in two procedures that were designed to assess the representativeness of the Emissions Database for compressors in the industry and, indirectly, the uncertainty associated with the scaling factor. Figures 2 and 3 are plots for engines and turbines, respectively, showing the total horsepower for each model in the Industry Database versus the total horsepower of that model in the Emissions Database. The line formed from the relationship between the total horsepower for each database was plotted on each graph. For engines, a line through 11.2 million and 1.3 million, the total horsepower for engines in the Industry and Emissions Databases, respectively, constituted the ideal relationship between the total horsepower for each type of engine in the two databases. Similarly, for turbines, a line through S million and 0.4 million produced the ideal relationship for the total horsepower for each type of turbine in the two databases. The figures show that the horsepower contribution of the compressors in the Emissions Database was higher than the horsepower 

### A-13

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### Figure3. Relative horsepowercontributionofeach turbinemodel inthe Emissionsand Industry Databases92-142.05 contribution in the Industry Database. However, the trend in general is in a positive direction for both databases, showing that compressors that contribute a large amount of horsepower to the total in one database also contribute significantly to the other. Conversely, compressors that are small contributors in one database are of similar ranking in the other. This comparison presents a qualitative assessment of the representativeness of the Emissions Database for the industry's compressors, A more quantitative assessment of how well the Emissions Database represents industry compressors was performed using a comparison between the emission factors derived from the Emissions Database and the Industry Database, with the Industry Database used as a close approximation of compressors in the natural gas industry. To determine the emission factors for the Emissions Database, an overall average emission factor was calculated for engines and turbines, separately, after Step 1 in the hierarchy, where only the data that were exact matches with

**th~** compressors in the Test Database were included. Overall average emission factors were calculated for engines and turbines, weighting the model-specific emission factors for each engine and turbine, respectively, by the horsepower contribution of that model in the Emissions Database. To determine the emission factors for the Industry Database, modelspecific emission factors were d_eveloped after Step III in the hierarchy, and overall average emission factors were calculated for engines and turbines, weighted by the horsepower contribution of the engine and turbine models, respectively, in the Industry Database. The results were that the overall average emission factors calculated for the Emissions Database were 18 grams of methane emitted per m 3 of fuel for engines, and 0.16 grams of methane emitted per m 3 of fuel for turbines. The overall average emisSion factors calculated for the Industry Database were 20 grams of methane emitted per m 3 of fuel for engines, and 0.17 grams of methane emitted per m 3 of fuel for turbines. This analysis showed quantitatively that the Emissions Database was a fairly good representation of the Industry Database and, therefore, the industry. CONCLUSIONS AND RECOMMENDATIONS The annual methane emissions estimate of 0.22 Tg for compressors in the natural gas industry was less than the previous estimate of 2.2 Tg by a power of 10. Although compressors are still a significant source of methane emissions, this estimate reduces the importance of compressors in the assessment of the natural gas industry's contribution to global warming. The uncertainty for the estimate, at 4.3 million m 3 of methane (0.15 billion scf), was much less than the portion of total industry methane emissions contributed by compressors, and was 0.15 percent of the target uncertainty (100 billion scf) for the industry. Future work in this area should include an assessment of the effect of compressor operation, in terms of horsepower, on the methane emission rate. 

### A-1692-142.05 On the basis of the data on this subject, the annual methane emissions could be higher than the current estimate by a factor of 2, 

### if compressor operation is at horsepower levels significantly lower than compressors' rated horsepower. REFERENCES 1. Annual Methane Emission Estimates of the National Gas Systems in the United States, Phase 2 by B. Tilkicioglu, Pipeline Systems, Inc. under subcontract to Radian Corporation, Research Triangle Park, North Carolina. U.S. Environmental Protection Agency Contract No. 68-02-4288. Research Triangle Park, North Carolina. September 1990. 2. Two Cycle Clean Burn (Integral) Gas Engines. D. Blizzard, and A. D. Gillette. Presented at the

**S~all** Prime Movers NOx Control Workshop, San Diego, CA. June 1991. 3. TRANSDAT: CompreSsor Module. Tom Joyce and Associates, Washington, D.C., for the Gas Research Institute, Washington, D.C. August 1991. 4. 1990 Gas Facts. The American Gas Association, Arlington, Virginia. 1990. Page 65. 5. Natural Gas Annual 1989. Department of Energy, Energy Information Administration, Washington, D. C. Volume I. 1989. 6. @Risk, Risk Analysis and Simulation Add·in for Lotus 1-2·3. Version 1.5. Palisade Corporation, Newfield, NY. March 1989. ACKNOWLEDGMENTS This project was cofunded by Bob Lott, of the Gas Research Institute, Chicago, Illinois, and David Kirchgessner, of the Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina. Radian gratefully acknowledges the contribution made by the sponsors.



### A-17

## '

### APPENDIX B 

### SourceSheetP-1



### B-1SOURCES: OPERATING MODE: EMISSIONTYPE: ANNUAL EMISSIONS: BACKGROUND: P-1

**AL~SEGMENTSOURCESHEET** Compressors, Generators Nonnal Operation Unsteady, Combusted (Compressor DriverExhaust) 24.4 Bscf± 64% Compressors are used to move gas throughthe system. They are located inproduction fields, processing plants, gas storage fields, and alongtransmission lines. Methane emissionsare found in compressordriver exhaust (reciprocating engines and gas turbmes) because ofthe incompletecombustionofthe natural gas burned as fuel. EMISSION FACTOR: (0.240 

### ± 5% scf/hp.flr, engines and0.0057 

### ± 30% scf/hp·hr, turbines) An average emission rate was calculated for each model ofcompressorengine and rurbine in the GRI TRANSDATEmissions Database (1), which is based on compressor tests conducted by Southwest Research Institute(SwRI). Theemission rates were calculated from the reported methane emissionsperunitoffuel and the reponed fuel use rate (FUR) for each

**oo~pressor** model, 

### as follows:

where: E:Rxm) = average emission rate for model, m (scf/hr) EPcmJ = average emission parameter for model, m (scf CHJscffuel)

**~m)** = average fuel use rate for model, m (scffuel/hr)
The following equationwas used todetermine the totalemissions for the 86turbines and 775 reciprocating engines in the Emissions Database. K 

### TE• 

## L m" 

# [ 1 (ER<•> x HR, )

# l.

where: TE = total emissions for database, (scf) HR; = annual operating hours for compressor i, QJ.r/yr)

K = number ofunique compressor mcxiels M = number ofcompressors ofmodel, m



### B-2 (I)

(2)The emission factors, for engines and turbines, were thencalculated using the followingequation. Emission Factor = TE 

### I[

# E i = I

where: HP = average operating horsepower during HR., (hp) HR. = annual operating hours, {br{yr)

N = number ofcompressors 

### (3)

This equation considersthat some models could be operatedat a higher percentage ofthe time because they are base loaded compressors. Theaverage emission factors for the compressor drivers in the Emissions Database are 0.240scf/hp·hrfor reciprocating engines and 0.0057scflhp-b.r for turbines. EF DATA SOURCES: I
. ·National EstimateofMethane Emissions from Compressors in the U.S. Natural Gas Industry" (2). EF ACCURACY: ± 5%,engines and± 30%, turbines Basis: The accuracy for the EF is estimated basedonpropagationoferrorfrom thespread ofsamples inthe database. However, engineeringjudgementwasusedto assign accuracy for twoofthe individualterms in the equation,as follows: I. Hydrocarbon analysiswas estimated to be ± 10%,based on the generally accepted accuracy ofgas chromatographs (flame ionizationdetector). 2. Likewise, fuel flow measurements were estimated tobe ± 2.5%. ACTIVITI' FACTORS: (horsepower-boor) Horsepower·hourdata were available for theproductionindustrysegment activity factor calculation. Two pieces ofinfonnation are needed to calculatethe activity factor, which is expressed as horsepower·hours (hp·hr) for each type ofdriver in each ofthe remaining industry segments. These are the installedhorsepowerand the average operating hours. The following tablepresents theseparameters and the resulting activity factors for both engines and turbines in each segment ofthe industry. Thesources and methods for calculating all the values presented in the table below are given in the next section: AF Data Sources. It is estimated that about 94% ofthe emissions tn con.pressorand generatordriverexhaust are from reciprocating engines used inproduction,processing, and transmission, with about5% attributableto reciprocating engines used in storage. All other categories are negligibleincomparison. Therefore, it is more important to accurately determine the activityfactors for reciprocating engines inproduction, processing, and transmission.



### B-3COMPRESSOR DRIVER ACTIVITY FACTORS FOREACH INDUSTRYSEGMENT lmtallod 

# """""

**Ann~! Ann~!**  Industry Engino Turbine H•= Ho= 

# E- ,.,.,. Segment MMhp' MMhp' Engine TorbiDe MMHp ·hr MMHpiuProduction NA NA NA NA 27.460 ± 200% 0 Processing 4.19± 132%' 5. !9 ± 99.4%' 6626 ± 11.5% 6345 ± 48.4% 27,760 ± !33% 32.910 ± 121% Transmission

CompressorDrivers 10.2 ± 10.0% 4.55 ± 10.0% 3964 ± 13.8% 2Il8 ± 31.3% 40.380 ± 17.1% 9635 ± 33.0% GeneratorDrivers 1.45 ± 23.3% 0.045 ± !66% 1352 ± 38.0% 474 ± 620% l%2 ± 45.4% 21.2 ± 1215% Storage

CompressorDrivers 1.33 ± 13.5% 0.59± 13.5% 3707 ± 23.!% 2917 ± 620% 4922 ± 26.9% !729± 626% GeneratorDrivers 0.085 ± 126% 0.057 ± !84% 191 ± 377% 36 ± 620% 16.3 ± 621% 2_05 ± 1312% •Doesnotincludehorsepowerassociated with gas liftforoil recoveryorwith electric drivers. 'Averageoftwo esttmation methods. AF DATA SOURCESo I. Theproductionsegment horsepower is based onthe total installedhorsepower·hours for data providedby onecompany for 516compressordrivers (all reciprocatingengines). The horsepower·hours for the companywas dividedbytheirproductionbefore scaling to a national estimate. National horsepower·hourwas calculated usingthe 1992 Jrulrketed productionfor the U.S. {Natural GasAnnual1992, (3)]. 2. Theprocessing segment horsepower was determined by takingtheaverage oftwo methods. Each ofthe methods uses sitedata for the lO gasplants visited. Thefirst method scales to a national estimatebymultiplyingthe total U.S. gas plantthroughputas ofJanuary I, 1993 {46,510.7MMcfd, Oil & CasJournal (4)] bythetotal sitevisithorsepowerperthroughput (47.8hp/MMcfd, enginesand 59.2hp/MMcfd, turbines). Thesecond method scales toa national estimate by multiplyingthetotal numberofgasplants in the U.S. {726, Oil & Gas JourTUll (4)] by thetotal sitevisithorsepowerper numberofgas plantsvisited(10), which is a scale-up ratioofabout73. The annual operatinghours are basedonthe 10 sitesplusdata from twocompanies for anadditional18gas plants. An average ofthe average operating hours persite wascalculated toget theprocessing segment operating hours (203 engines and 9 turbines). 3. Thetransmissionsegment compressor stationhorsepower for each compressordrivertype is based onthe GRI TRANSDATdatabase. Installedhorsepower was taken from the Industry Database moduleofGRI TRANSDAT. The annual operatinghours are based on information reponed on FERC Form No.2. FERC datadoes notdistinguishbetween drivertype. The FERC datawere splitbetweenengines and turbinesbased ondata inGRI TRANSDATand data providedby one transmissioncompany (524engines and 89turbines). 4. The storage segmenthorsepowercame from GasFacts (5) data for 1992 (1,920,441 hp). The split between engines and turbineswas assumed tobe the same as theengine and turbine splits found in GRITRANSDAT(69.1%, engines and 30.9%,turbines). The annual operating hours are based on 11 storage stations(50engines and 6turbines). An average ofthe average operating hoursper station was calculated toget the storagesegment operatinghours. 

### B-45. The generatordriverhorsepower (compressor stations) is based on the total installed horsepower for 7ofthe transntission sites visited and company data for 34 transmission compressor stations. To scale toanational estimate, the total horsepower per stationwas multipliedby the total numberoftransmissioncompressor stations [l700, FERC Fonn No.2 (6)J in the U.S. The annual operatinghours are alsobased on data from the site visitsand company data. An average oftheaverage generator operating hours per station was calculated to get generator operating hours (87 engines and 1turbine). 6. The generator driverhorsepower (storage fields) is based on the total installed horsepower for 9 storage fields (one company). To scale to anational estimate, the total horsepower per field was multipliedby the total numberofstorage fields [475, GasFacrs (5)J in the United States. The annual operatinghours are also based on the company data. An average oftheaverage generator operatinghours per field was calculated to get generatoroperating hours (3 engines and l turbine). AF ACCURACY' Basis: Errors were propagated from each ofthe followingterms: 1. ProductionHp·hr: TheproductionHp·hraccuracy is based upon an engineeringanalysis and set at ± 200%. 2. Transmission Hp·hr: The transmissionHp·hraccuracy is based upon an assigned estimated errorof± 10% for thehorsepowerdata in the GRITRANSDATdatabase and error propagation from the FERCoperatinghours. 3. Othersegment Hp-br: The accuracy ofthe site visitdata for horsepowerand operatinghours was also propagated using the spread ofthedata, but from much smallerdata sets. The accuracy ofthehorsepower-houractivityfactors for each industrysegment are calculated statisticallyusing the individualterms for horsepowerand operatinghours. ANNUAL EMISSIONS: (24.57

### ± 65.1%Bscf,engines 

### + 0.256 

### ± 97.8%Bscf, turbines) Theannual emissions were determined by multiplyingan emlssion factorby thehorsepower·hour activityfactor for reciprocating engines and turbinesand summing these values for each segment. The following table shows the resultingemissions for each industrysegment and the overall national estimate. ANNUAL COMPRESSOR EMISSIONSFORTHENATURALGAS INDUSTRY BY SEGMENT Compnssor Production 

# """"'"" Transmission Storage Generators TOTAL Engines, Bscf 6.58±200% 6.65±133% 9.68±17.9% l.l8±26.9% 0.474±45.6% 24.57±65.1% Turbines, Bscf 0.00 0.186±129% 0.0546±45.7% 0.00979±654% 0.000132±1163% 0.256±97.8% REFERENCES J. Biederman, N. GRl TRANSDAT Database: Compressor Module. (prepared for Gas Research Institute). npb Associates with Tom Joyce and Associates, Chicago, IL, August 1991. 2. Jones, D.L., L.M. Campbell, C.E. Burklin, M. Gundappa, and R.A. Lott, "National Estimate of Methane Emissions from Compressors in the U.S. Natural Gas Industry." Radian Corporation and Gas Research Institute, Air & Waste Management Association Conference Proceedings, Paper # 92· 142.02, Kansas City, MO, 1992.



### B-53. U.S. Department ofEnergy/Energy Information Administration. Natural GasAnnual, 1992. DOE/EIA-0131 (92), Washington, DC, September 1992. 4. Oil& Gas Journal. 1992 Worldwide Gas Processing Survey Database, 1993. 5. Gas Facts: 1992 Data, American Gas Association, Arlington, VA, 1993. 5. Federal Energy Regulatory Commission (FERC) Fonn No. 2: Annual Report ofMajor Natural Gas Companies, 1992 database.



### B-6

### APPENDIX C 

### ProductionSegmentSiteVisitResults

C-1

### Table C-1 shows the production segment data collected foreach ofthe 28 sites visited and thedata provided 

### by one c9mpany for 25 gathering stations. Thedata have been grouped into four geographic areas so that a regional extrapolationcan be conducted for this industry segment. The following four regions were selected based ondifferences in production rates and equipmentpopulations; PacificMountain. GulfCoast, Central Plains, and Atlantic & 

### Great Lakes. Differences in onshore versus offshoreproductionwere not considered because ofthe lack ofavailable site data. (This approach is described further 

### in the 

### Methane Emissionsfrom theNatural GasIndustry, Volume 5: ActivityFactors). 1 

### No turbines were installed at any ofthe production facilities surveyed; therefore, the data shown in Table C-1 represent anengine/turbine horsepower split of 100%/0% for this segment. Excludingcompressors used for gas lift

### and electrically driven compressors, the average horsepowerper MMcfd was calculated foreach region. The United States marketed natural gas production, by region, for 1992 was used to extrapolate from the regional ratios (hp/MMcfd) to a 

### national estimate ofcompressor engine driverhorsepower in the production segment of3.61 MMhp (0MMhpfor turbine drivers)' The following equationdescribes the national extrapolationusing the regional approach. Engine hp = 

### region 4 ( h ) 

# L A vg P x 

### MMcfd~,ro.. , region 1 M:Mcfd

**~gion** x 

### This estimate for the production segment is based onthe total installed horsepower from the sites surveyed. Table C-2 shows the regional dataused toextrapolateto the national horsepowerestimate. The table also shows the 90% confidence intervals for·each of the 

### values used in the calculation. Confidence limits were calculated using the ratio method foreach region's average hp/MMcfdand the total horsepower from the variationofthe site data. The resulting uncertainty is ± 63.2%. Table C-3 shows the "operating hours" for the compressors at the sites surveyed. For the production segment, annual operatinghours were not available formost ofthe sites visited; therefore, the compressors that were running during the site visit were assigned annual operating hours of8760. Compressors that were idle were assigned annual operating hours of0. This approach was used for 9 ofthe sites visited. Actual operating hours were available for two ofthe 2 sites visited and for the 25 gathering stations surveyed (one company). Operating hours for the remaining sites were not included in this analysis since compressors were eitherused for gas lift, 

### had electric drivers, orwere not found at the site. The 

### operating hours listed for these sites are the average hours for all ofthe 

### drivers at the site. This table also reflects the fact that no turbines were surveyed in the

### production industry segment. Confidence limits were calculated for the operating hours estimate from the variation ofthe data. The resulting uncertainty is± 9.7% (90% confidence limits). Activity factors based onthe site data presented here are 23,820MMhp·hrfor engines and 0 MMhp·hrfor turbines. Confidence limits were calculated for the engine driver activity factor to be ± 64.3%. This activity factor is withinthe errorbounds ofthe C-2

### activity factor calculated using the company database for horsepower·hours (Section4.1). This database provided one data.Pointfor turbine drivers in the production segment, thus affirming their presence inproduction. However, the numberofthese drivers is assumed to 

### be very small and not significantfor this estimate. REFERENCE 1. 

### Stapper, B.E. MethaneEmissionsfrom theNatural GasIndustry, Volume 5: Activity Factors, 

### Final Report, GRI-94/0257.22 and EPA-600/R-96-0SOe. Gas Research Institute and U.S. EnvironmentalProtectionAgency, June 1996. 2. U.S. DepartmentofEnergy/Energy InformationAdministration. Natural Gas Annual, 

### 1992. DOE/EIA-0131 (92), Washington, DC, September 1992.

C-3

### TABLE C-1. GATHERING COMPRESSORDATA FROM PRODUCTION SEGMENTSITEVISITS Installed Avg Site hp. MMcfd hp/MMcfd Pacific Mountain PM! 37941 (112000) 104 PM2 1650 4.5 PMJ 0 (200 

### "J 12 Total ' 39591 120.5 328.6 GulfCoast GCI 0 (NA') 4.5 GC2 7467 d 23 GCJ 4950 25.5 GC4 700 d 112 GC5 0' 12 GC6 8878 54 GC7 0 18 GC8 625 250 GC9 0 (NA') 0.50 Total r 22620 499.5 45.3 Central Plains CPI 6000 180 CP2 4650 42.7 CP3 4480 24.0 CP4

**~** 72192 542 Total 1 87322 1004.7 86.9 Atlantic & Great Lakes AGI 0 24 AG2 0 0.18 AGJ 0 0.18 AG4 0 0.17 AG5 0 0.39 AG6 0 0.37 Continued 

### C-4

### TABLE C-1. (CONTINUED)
Installed Site hp. MMcfd AG7 50' 0.37 AG& 0 0.18 AG9. 0 0.23 AGIO 0 0.30 AG!l 0 0.35 AGI2 0 0.!3 AG!3 0 0.35 Total r 50 27.2 Total site horsepower (including gas lift for oil recovery) is shown in parentheses. b Horsepower associated with electric drivers. Not available. d Estimated.

Total for 25 gathering stations; peak production rate. r Excludes gas lift and electric drivers. 

### TABLE C-2. REGIONALDATA FORPRODUCTION SEGMENT HORSEPOWEREXTRAPOLATION

Site Avg National Marketed Region hp/MM<::fd 90% Limit Production MMcfd Pacific Mountain 328.6 !:48.2% 2696 GulfCoast 45.3 ± 132% 31544 Central Plains 86.9 ±94.6% 14860 Atlantic & Great Lakes !.84 ±244% 2166 Total U.S. 51265 90% Limit



### C-5 Avg hp/MMcfd

! 84

Engine MMhp 0.886

!.43 1.29 0.00398

3.61 ± 63.2%

### TABLE C-3. ANNUAL OPERATING HOURSFORPRODUCTION SEGMENT Site No. ofEngines • Average Operating Hours PMI b 19 (56) 8760 PM2 17 7884 PM3 0 (9)'·'


# -- GCI 0 (14)


# -- GC2 b 12 8030 GC3 b 4 8760 GC4 b I 8760 GCS b 0 (!)'


# -- GC6 b 37 8523 GC7 0



# -- GC8 25. 4380 GC9 0 (I)


# -- CPI b 50'

. 8760 CP2 • 31 8195 CP3 b 64 8760 CP4-I I 5924 CP4-2 I 8364 CP4-3 2 4753 CP5-4 I 0 CP4-5 I 6884 CP4-6 18 5193 CP4-7 I 7631 CP4-8 I 7309 CP4-9 3 6953 CP4-IO 2 5833 CP4-II 5 6386 CP4-12 I 5505 CP4-13 I 7235 CP4-14 I 7333 Continued 

### C-6

### TABLE C-3. (CONTINUED)
Site No. ofEngines • Average Operating Hours CP4-15 2 8031 CP4-16 1 6841 CP4-17 1 7607 CP4-18 2 6303 CP4-19 1 6946 CP4-20 2 6340 CP4-21 7 748 CP4-22 1 7384 CP4-23 2 6908 CP4-24 2 7176 CP4-25 1 579

AG1 1


# -- AG2 0


# -- AG3 0 

## -- AG4 0


# -- AG5 0


# -- AG6 0



### -- AG7 2
. NA' AG8 0


# -- AG9 0


# -- AGIO 0


# -- AGll 0



### -- AG12 0


# -- AG13 0



### -- TOTAL AVERAGE r 315 6599 90% LIMIT r ± 9.7% • Total number ofcompressors (including gas lift for oil recovery) is shown in parentheses. b Based on active (8760 hrs) versus idle (0 hrs). cElectric drivers. d Estimated. •Not available. f Based on site averages. 1 Includes vapor recovery. 

### C-7

### APPENDIX D 

### Transmission CompressorStationSiteVisitResults

D-1

### Data were collectedduring site visits and company surveys for 51 transmission compressor stations. The compressor horsepower is related to the gas throughput and the pressure. Throughput is available for most ofthe sites surveyed, but a national figure is not available. Pressure data are not available for any ofthe sites surveyed or nationally. As a result, the only extrapolationmethod currently available for this industry segment is based on the number ofcompressor stations. Table

**D~1** 

### shows the numberofcompressors, installed horsepower, and gas throughput for each ofthe sites surveyed in the transmission segment. The engine/turbine horsepower split for this segment is 63.8% engines and 36.2% turbines (compared to 69.1% for engines and 30.9% for turbines in TRANSDAT). Using the average site horsepowerper station and the total number oftransmission compressor stations in the United States for 1992 from the FERC Form No. 2, the site data were scaled up to give a national estimate of compressorhorsepower in transmission compressor stations ofabout 11.1 MMhp for engines and 6.3 MMhp for turbines. Engine 

### hp = 

### Total hp 

### x No. U.S. Stations No. Stations

= 

### 334240 hp 

### x 1700 Stations 51 Stations

= 

### 11.1 

### MMhp Turbine hp = 

### 190030 hp x 

### 1700 Stations 51 Stations

= 

### 6.33 MMhp Confidence limits were calculated for the horsepower from the variation ofthe data. Theuncertainty calculated for the compressor stationestimateused to scale up the site visit horsepower is 

## ± I0%. The resultinguncertainties for the national horsepower estimates for this industry segment are 

## ± 22.0% for engines and 

## ± 44.9% for turbines. Table D-2 shows the operatinghours for the compressors at the 9 sites surveyed and forone company that provided data for 39 transmission compressor stations. Theoperating hours listed are the average hours forall ofthe drivers at each ofthe sites. Confidence limits were calculated for the operating hours estimate from the variation ofthe average site data. The resulting uncertainty is 

### ± 25.0% for engines and 

### ± 48.1% for turbines (90% confidence limits). Activity factors based on site visit data alone are 26,100MMhp·hrfor engines and 13,460MMhp·hrfor turbines. Theuncertainties for these activity factors are 

## ± 33.7% for D-2

### engines and 

## ± 69.2% for turbines. These activity factors are withinthe error bounds ofthe activity factors calculated using TRANSDAT (horsepower) and FERC (operating hours). However, the TRANSDATdatabase and the FERCdatabase are much more representative of the transmission industry segment and were used in the overall emissions estimates.

D-3Site TSI TS2 TS3 TS4 TS5 TS6 TS7 TS8 TS9 TSIO-I TS!0-2 TSI0-3 TSI0-4 TS!0-5 TSI0-6 TSI0-7 TS!0-8 TSI0-9 TSI0-10 TSIO-II TSIO-I2 TSIO-I3 TSIO-I4 TSIO-I5 TSIO-I6 TS!O-I7 TSI0-I8 TSIO-I9 TSI0-20 TSI0-2I 

### TABLE D-1. COMPRESSOR DRIVER DATA FROMTRANSMISSION SEGMENTSITE VISITS No. of Installed No. of Installed Engines Enginehp 

### Turbines Turbinehp I3 32650 0



### --- 0 0 2 6900 0 0 2 6900 2 800 0 

# --- 10 I4560 2 20090 I2 17570 I I2090 0 0 I 40000 4 I4000 2 26500 7 I4000 3 37500 4 6900 0



### -- 4 8000 0 

# -- 5 I340 0



### --- 3 8I5 0 

## -- 4 8400 0 

# --- 2 I200 0 

# -- I 2400 0


## -- 2 4000 0 

# -- 2 I320 0 

# -- 3 2475 0 

# - 3 4050 0


### --- 0 

# - I IOOO 10 13000 0



### --- 7 11200 0 

# -- 2 <800 0



### -- 8 I0600 0 

# - 2 I200 0


### --- I 2400 0


### --- I9 32800 0 

# -- 0


### --- I 9300 5 850 0


### ---


### D-4 MMcfd 843 200 37.5 50 

### NA NA NA 4.9 4.9 

### NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA ContinuedNo. of Site 

### Engines TSJ0-22 I TSI0-23 I TSI0-24 3 TSI0-25 I TSI0-26 I TSI0-27 7 TSI0-28 2 TSI0-29 0 TSI0-30 2 TSI0-31 2 TSI0-32 I TSI0-33 3 TSI0-34 7 TSI0-35 2 TSI0-36 I TSI0-37 I TSI0-38 II TSI0-39 I

TSII 6 TSI2 7 TSI3 13 

### TOTAL 208 

### AVERAGE' NA = Not Available
a Based on siteaverages. 

### TABLE D-1- (CONTINUED) Installed No. of 

### Engine hp Turbines 2400 0 2400 0 6000 0 2400 0 2400 0 7000 2 2700 0
.



# -- I 4800 0 3350 I 2400 0 6000 0 7510 0 4000 0 2400 0 270 0 12380 3 2400 0 16900 0 10400 0 24800 0 334240 22

6554



### D-5 Installed Turbinehp MMcfd



### --- 

### NA

--- 

### NA



### --- NA

--- 

### NA

--- 

### NA 8500 

### NA

--- 

### NA 4250 

### NA



### --- NA 4250 

### NA

-- 

### NA



# -- NA

- 

### NA



### --- NA

--- 

### NA



# - NA 12750 

### NA

-- 

### NA

-- 

### NA 0 140 0 

### NA 190030 1409.5

3726Site TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS8 TS9 TS10·1 TS10·2 TSl0-3 TSI04 TS10·5 TS!0-6 TS10-7 TS!0-8 TS!0-9 TSI0-10 TSI0-11 TSI0-12 TSI0-13 TSI0-14 TS!0-15 TS10·16 TS10·17 TSI0-18 TSI0-19 TS10-20 TSI0-21 TS!0-22 

### TABLE D-2. ANNUAL OPERATING HOURSFOR TRANSMISSION SEGMENT No. of Average No. of En2ines Operating-Hours Turbines 13 3303 0 0 .. 2 0 

### .. 2 2 7884 0 10 4066 2 12 2082 1 0 

### .. 1 4 6366 2 7 6813 3 4 5019 0 4 3020 0 5 2343 0 3 0 0 4 4310 0 2 0 0 1 5914 0 2 3150 0 2 35 0 3 1574 0 3 2307 0 0 

### .. 1 10 3653 0 7 52 0 2 158 0 8 2179 0 2 1351 0 I 4576 0 19 6117 0 0 

### -· 1 5 470 0 1 5695 0



### D-6 Average Operating·Hours



### .. 3066 1139

.. 3420 6314

0 4517 4698

..

..



### ..

..

..



### ..

..

..

..

..

.. 0



### ..

..

..



### ..

..

..



### -- 579



### --

-- Continued)No. of Site Engines TSJ0-23 I TSl0-24 3 TSI0-25 I TSI0-26 I TSI0-27 7 TSI0-28 2 TS!0-29 0 TSI0-30 2 TSI0-31 2 TSI0-32 I TSI0-33 3 TSI0-34 7 TS!0-35 2 TSI0-36 I TSJ0-37 I TSI0-38 !I TSI0-39 I TOTAL 182 AVERAGE" 90% LIMIT •
•Based on site averages. TABLED-2. (CONTINUED) Average O!"_ratinJiHours 2747 570.5 502.9 688.5 557 99


### -· 615 1015 497 4769 509 736 474.5

360 1240 586.9 2343 

### ± 25.0%



### D-7 No. of Average Turbines Operating Hours 0



### -- 0 

# -- 0


### -- 0


### -- 2 557 0


### -- I I823 0


### -- I 1015 0


### -- 0 

### ·- 0


### -- 0


### -- 0


### -- 0 

### -· 3 497 0 

# -- 22 2125 + 48.1%

### APPENDIX E 

### Conversion Table

E-1

### Unit Conversion Table English to Metric Conversions I scfmethane

**~** 

### 19.23 g methane I Bscfmethane

**~** 

### 0.01923 Tg methane 1Bscfmethane

**~** 19,230 metric tonnes methane I 

### Bscf

**~** 28.32 million standard cubic meters I 

### short ton (ton)

**~** 

### 907.2 kg I 

### lb

**~** 

### 0.4536 kg I 

### ft3

**~** 

### 0.02832 

### m 3 I 

### ft3

**~** 

### 28.32 liters I 

### gallon

**~** 

### 3.785 liters I 

### barrel (bbl)

**~** 

### 158.97 liters I inch

**~** 

### 2.540 

### em I 

### ft

**~** 

### 0.3048 m 1 mile

**~** 

### 1.609 

### km I 

### hp

**~** 

### 0.7457 kW I 

### hp-hr

**~** 

### 0.7457 kW-hr I 

### Btu

**~** 

### 1055joules I 

### MMBtu

**~** 

### 293 kW-hr I 

### lb/MMBtu

**~** 

### 430 g/GJ T

## CFJ

**~** 

### 1.8 T CC) 

### + 32 I 

### psi

**~** 

### 51.71 

### mm Hg



### Global Warming Conversions
Calculating carbon equivalents ofany gas:


## MMTCE • (MMT 

### ofgas) x 

## (MW, carbon) x 

### (GWP) 

### 1v!W, gas



### E-2Calculating C02 equivalents for methane:

MMT of C02 equiv. " (MMT CH4) x x (GWP) (MW,

# co,J

MW, CH4
where MW (molecular weight) ofC02

**~** 44, MW

**carbon~** 12, and MW CH,

**~** 16.

Notes scf

**~** Standard cubic feet. Standard conditions are at 14.73 psia and 60"F. Bscf

**~** Billion standard cubic feet (109 scf). MMscf

**~** Million standard cubic feet. Mscf

**~** Thousand standard cubic feet. Tg

**~** Teragram (1012 g). Giga (G)

**~** Same as billion (I09). Metric tonnes

**~** 1000 kg. pstg Gauge pressure. ps1a

**~** Absolute pressure (note psia = psig 

### + atmospheric pressure). GWP

**~** Global Warming Potential ofa particular greenhouse gas for a given time period. MMT

**~** Million metric tonnes ofa gas. MMTCE

**~** Million metric tonnes, carbon equivalent. MMT ofC02eq.

**~** Million metric tonnes, carbon dioxide equivalent.

E-3TECHNICAL REPORTOAT A

**(PI~~**Te4d

**l~W~Uctiom**ontM «rUU

**~jon compl~ting}**  1.REPORTNO. 

# I' 3.RECIPIENT'SACCESSIONNO. 

### EPA-600/R-96-080k 4.TITLEANDSUBTITLE 5.REPORTDATE Methane Emissions from the Natural Gas Industry, 

### June 1996

Volumes 

### 1-15 (Volume 

### 11: Compressor Driver Exhaust 6.PERFORMINGORGANIZATIONCODE '·AuTHOR(sl L. Caml&bell, M.Cam/belL M.

**Cow~l,** D.Ep- 8.PERFORMINGORGANIZATIONREPORTNO. rrerson, M.Hall, •Harrison, •Hummel,D. yers, 

### DCN 96-263-081-17 •Shires,B.Stapper,

### C.Stapper,

### J.Wessels, and

# *

.PERFORMINGORGANIZATIONNAMEANDADDRESS 10.PROGRAMELEMENTNO
. Radian International LLC 

### P.O. Box 201088 11. **CONTRACT~RANT**NO. Austin, Texas 

### 78720-1088 5091-251-2171 (GRl) 68-Dl-0031 (EPA) 12.SPONSORINGAGENCYNAMEANDADDRESS 13.TYPEOFiPORT/NOPERIODCOVERED 

### EPA, Office of Researchand Development Final; 

### 3 91-4 96 14.SPONSORINGAGENCYCODE .Air Pollution Prevention

### and Control Division 

### Research Triangle Park, NC 27711 

### EPA/600/!3 1s.suPPLEMENTARYNoTes

### EPA project officer is 

### D. A.Kirchgessner.

### MD-63.919/541-4021. ' Cosponsor 

### GRI project officer is 

### R.A.Lott. Gas ResearchInstitute, 

### 8600 West Bryn 

### I ' 

### Mawr Ave., Chicago, IL 

### 60631. (*)H. 

### Williamson (Block 7). 1' ABSTRACTThe 15-volume report summarizes the results of a comprehensive program o quantify methane {CH4) emissionsfrom the 

### U.S. natural gas industry for the base 

### lvear. The objective was to determine CH4 emissions from the wellhead and ending



### ~ownstream at the customer's meter; The accuracygoal was to determine these



### ~~issions within

### +/-0.5% ofnaturalgas production for a 

### 90% confidence interval. 

### Fm e 

### 1992 baseyear, total CH4 emissions for the U.S. naturalgas industrywas 

### 314 +/-105 Bscf (6.04 +/- 2.01 Tg). This is equivalent to 1.4+/- 0.5% ofgross natural gas production, and reflects neither emissions reductions {per the voluntary AmeriGas Association/EPA 

### Star Program) nor incremental increases (dUe to increased gas usage) since 

### 1992. Results from this program were used to compare greenhouse

as emissions from the fuel cyclefor natural

**ga~.** oil. and coalusing the global warming potentials (GWPs) recently published by the Intergovernmental Panel on Climate Change (IPCC). The analysis showed that natural gas contributes less to potential global warming 

### than coal or oil, which supports the fuel switching strategy suggested by theIPCC and others. In addition. study results are being used by the riatural gas industry to reduce operating costs while reducing emissions.

7. KEYWORDSANDDOCUMENTANALYSIS


# .. DESCRIPTORS b.IOENTIFIERSIOPENENDEDTERMS e. COSATI Field/Group Pollution IPollution Prevention 

### 13B Emission Stationary Sources 

### l4G Greenhouse 

### Effect Global Warming 

### 04A Natural Gas 

### 21D Gas Pipelines 

### 15E Methane 

## )o7c 18.OISTR18UTIONSTATEMENT 19.SECURITY CLASS [This RepCHJ 21.NO.OFPAGES 

### Unclassified 81 Releaseto Public 20.SECURITYCLASS (Thi:&page) 22.PRICE 

### Unclassified EPA Form 2220-1 (9·73) 

### E-4

### U.S. ENVIRONMENTALPROTECTIONAGENCY OfficeofResearchand Development NationalRiskManagementResearch Laboratory TechnologyTransferandSupportDivision 

### Cincinnati, Ohio45268 OFFICIAL BUSINESS PENALTY FOR PRIVATE USE. $300 AN EQUAL OPPORTUNITY EMPLOYER

Ifyouraddress isincorttJct. pl••s•

**chM~gtl**onthtJabove label tearoff; andrtJtum to th•above Mldress. Ifyoudo notdesire to continutlreceivingtht1S11 ttchniciJI reports, CHECKHER£0; tearofflabel. andreturn it {0 the ahoYe address, 

# Publication No. EPA- 600/R-96-0BOk