FOREWORD The U.S. Environmental Protection Agency is charged by Congress with protecting the Nation's land, air, and water resources. Under a mandate of national 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 support for solving environmental problems today andbuilding 2 science knowledge base necessaryto manage our ecologicalresources wisely, understand how pollutants affect ourhealth, and prevent or reduce environmentalrisks in the future. 'The National Risk Management Research Laboratoryis the Agency's centerfor investigation of technological andmanagement approachesfor reducing risks from threats tohumanhealth and the environment. Thefocus of the Laboratory's research programis on methods for the prevention and controlof pOllution 

### to air. land. water. and subsurface resources; protectionof waterqualityin public water systems; remediation ofcontaminated sites and groundwater: and prevention and controlofindoor air pollution. The goalof this research effortis 

### to catalyze development and implementationofinnovative. cost-effective enVironmental technologies; develop scientific and engineeringinformationneededby EPA to supportregulatory andpolicydecisions; and provide technical support and infOrmation transfer to ensure effective implementation of environmental regulations and strategies. This publicationhas been produced as partofthe Laboratory's strategiclongterm research plan. Itis published and made availableby EPA1s Office of Research and Developmentto assistthe user commnnity and to link researchers with their clients. E. Timothy Oppelt. Director NationalRisk ManagementResearch Laboratory
EPA REVIEW NOTICE This reporthas been peerand administrativelyreviewedbythe U.S. Environmental Protection Agency, and approved for publication. Mention of trade names or commercial productsdoesnotconstituteendorsementorrecommendationforuse. Thisdocument is availabletothepublicthrough the NationalJechnicallnformation Service, Springfield, Virginia22161.

## (J.-;t.L - 

# 9'!-j112

# S7.::Z'} EPA-600/R-S6-G80! June 

### 1996
METHANEEMISSIONS FROM THE NATURAL GAS INDUSTRY, VOLUME 12: PNEUMATIC DEVICES FINAL REPORT
Prepared by: 

### Theresa M. Shires 

### Matthew R. Harrison Radian International LLC

8501 N. Mopac Blvd. P.O. Box 201088 Austin, 

### TX 78720-1088

DCN: 95-263-081-09
For GRI ProjectManager: Robert A. Lott GAS RESEARCH INSTITUTE

ContractNo. 5091-251-2171 8600West Bryn MawrAve. Chicago. IL 60631 and EPAProjectManager: David A. Kirchgessner U.S. ENVIRONMENTALPROTECTION AGENCY Contract No. 68-DI-0031 

### National Risk Management Research Laboratory Research Triangle Park, NC 27711

### 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, GRJ, members ofGRJ, nor any person acting on behalfof either:

a. Makes any warranty or representation, express orimplied, with respect to the accuracy, completeness, or usefulness ofthe information contained in this report, or that the use ofany apparatus, method, orprocess disclosed in this report may not infringe privately owned rights; or b. Asswnes any liability with respect to the use of, or for damages resulting from the use of, any information, apparatus, method, orprocess disclosed in this report. NOTE: EPA's Office ofResearch and Development quality assurance/quality control (QA/QC) requirements are applicable to some ofthe count data generated by this project. Emission data and additional count data are from industry or literature sources, and are not subject to EPNORD's 

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

11Title
Contractor
Principal Investigators Report Period Objective

Technical Perspective

Results 

### RESEARCH SUMMARY Methane Emissions from the Natural Gas Industry, Volume 12: Pneumatic Devices Final Report Radian International LLC GRI Contract Number 5091-251-2171 EPA Contract Number 68-Di-0031 Theresa M. Shires Matthew R. Harrison March 1991 -June 1996 Final Report This report describes a study to quantifY the armual methane emissions from pnewnatic devices, which are a significant source ofmethane emissions within the gasindustry. The increased use ofnatural gas has been suggested as a strategy for reducing the potential for global warming. During combustion, natural gas generates less carbon 

### dioxide (C02) per unit ofenergy produced than either coal oroil. On the basis ofthe amount ofC02emitted, the potential for global warming could be reduced by substituting natural gas for coal oroil. However, since natural gas isprimarily methane, a potent greenhouse gas, losses ofnatural gas during production, processing, transmission, and distribution could reduce the inherent advantage ofits lower 

### C02 emissions. To investigate this, Gas Research Institute (GRI) and the U.S. Environmental Protection Agency'sOffice ofResearch and Development (EPA/ORD) cofunded a major study to quantify methane emissions from U.S. natural gas operations for the 1992 base year. The results 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 annual national emission rates for pneumatic devices for each industry segment are as follows: production, 31.4± 65% Bscf; gas processing, 0.60

## ±64% Bscf; and transmission, 14.1 

## ±60% Bscf. (Distribution emissions 

### are presented 

### in another report.)

iii

### Technical 

### Approach

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

### be 314 

### ± I05 Bscffor the I992 base year. This is about 1.4 

### ±0.5% ofgross natural gas production. This study 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. Emission rates for pneumatic devices were determined by developing average annual emission factors for devices used in each industry segment and extrapolating these data based on activity factors to develop a national estimate, where the national emission rate is the product ofthe emission factor and activity factor. The natural gas industry has two primary types ofpneumatic devices that 

### discharge methane: I) control valves that regulate flow, and 2) gasactuated block valves. Because each segment ofthe industry follows its own specific practices regarding "typical" pneumatic device installations, emission factors were developed based on the types ofdevices observed from site visits. Emission factor data 

### for the various device types were collected from several sources: measured emissions provided from other studies, manufacturers' data, and data collected frOm site visits. Data collected during site visits included: the number ofeach type ofpneumatic device, manufacturer and model numbers, operating conditions (e.g., supply gas pressure and supply gas type), and annual device actuation frequency. Equations relating these parameters were developed for the different types ofdevices to develop an annual emission factor for a generic pnewnatic device in each industry segment. The development ofactivity factors for each industry segment are presented in a separate report. In general though, the population of pneumatic devices in each industry segment was determined from counts ofdevices observed during site visits. The national emissions for each industry segment were then based on the product ofthe emission factor for a generic pneumatic device and the activity factor. Forthe 1992 base year, 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% of 1992 gross natural gas production. Results from this program were used to compare greenhouse gas emissions from
IVthe fuel cycle for natural gas, oil, and coal using 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 wanning than coal or oil, which supports the fuel switching strategy suggested by IPCC and others. In addition, results from this study are being used by the natural gas industry to reduce operating costs while reducing emissions. Some companies are also participating in the Natural Gas-Star program, 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, Envirorunent and Safety



### v

### TABLE OF CONTENTS Page !.0 SUMMARY ................................................. I 2.0 INTRODUCTION ......................................... . 

### 2 3.0 PNEUMATIC DEVICE CHARACTERISTICS

. . . . . . . . . . . . . . . . . . . . . . 3 3.1 Overview
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.2 Gas-Actuated Control Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I0 3.2.1 Operating Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.2.2 Data Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 3.3 Gas-Actuated Isolation Valves ............................... 24 3.3.1 General Description .......... , ...................... 24 3.3.2 Data Requirements .................................. 29 3.4 Other Pneumatic Devices .................................. 29 4.0 PNEUMATIC DEVICE EMISSION FACTORS ....................... 34 4.1 Production Segment
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 

### 4.I.l 

### General Emission ·Factor Characteristics . . . . . . . . . . . . . . . . . . . 34 4.1.2 Production Emission Factors ........................... 35 

### 4.2 Transmission and Storage Segment . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 4.2.1 General Emission Factor Characteristics . . . . . . . . . . . . . . . . . . . 46 4.2.2 Transmission Emission Factors . . . . . . . . . . . . . . . . . . . . . . . . . 47 4.3 Gas Processing Segment ................................... 55 4.4 Distribution Segment
._. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 

### 5.0 PNEUMATIC DEVICE ACTIVITY FACTORS ....................... 

### 6! 5.1 Production Segment ...................................... 61 5.2 Gas Processing Segment ................................... 61 5.3 Transmission and Storage Segment . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 I 6.0 NATIONAL EMISSION RATE .................................. 63 7.0 REFERENCES .............................................. 64 APPENDIX A- Source Sheets .................................. A-I

viLIST OFFIGURES Page 3-1 Example ofa Pneumatic Controller Used for Level, Flow Rate, Temperature, or Pressure Control .......................... 5 3-2 Self-Contained, Spring-Loaded Pressure Regulator
. . . . . . . . . . . . . . . . . . . . . . 7 

### 3-3 Pneumatic Device with 

### Positioner 

### -Force Balance Piston Type ............. 8 3-4 Example Isolation Valve

- Piston Operator
. . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3-5 Operating Principles
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3-6a Throttling Continuous Bleed Pneumatic Controller

- Orifice Flapper Design
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I 3 3-6b 

### Throttling Continuous Bleed Pneumatic Relay

- Orifice Flapper Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3-7 Actuator Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3-8 Force Balance Piston Device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 3-9 Throttling Continuous Bleed Controller with Proportional Adjustment
. . . . . . . . 19 3-10 On-OffSnap Devices .......................................... 21 3-11 Pneumatic/Hydraulic Rotary Vane Operator .......................... 26 3-12 Pneumatic/Hydraulic Rotary Vane Operator- Cross Section ............... 27 3-13 Turbine Operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 3-14 Solenoid Relay .............................................. 31 3-15 Self-Contained Pressure Regulation Valve .... , .. , . . . . . . . . . . . . . . . . . . . 32



### vii

### LIST OF TABLES Page 

### 3-1 Pneumatic Device Classifications ................................... 4 3-2 Typical Pneumatic Device Bleed Modes ............................. 10 4-1 Standard Uses ofPneumatic Devices
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 4-2 Results from the Canadian Petroleum Association Pneumatic 

### Emission Rate Study
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 4-3 Manufacturer Bleed Rates for Continuous Bleed Pneumatic Devices
. . . . . . . . . 39 

### 4-4 Measured Emission Rates for Continuous Bleed Devices . . . . . . . . . . . . . . . . 41 4-5 Summary ofProduction Site Data
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 4-6 Production Emission Factor Calculation ............................. 46 

### 4-7 Pneumatic/Hydraulic Rotary Vane Isolation Valve Operators ............................................. 49 4-8 Manufacturer Data for Turbine Operated Isolation Valves ................ 52 

### 4-9 Transmission Device Counts

- Turbine and Displacement Devices
. . . . . . . . . 53 4-10 Transmission Device Counts

- Continuous Bleed . . . . . . . . . . . . . . . . . . . . . 54 4-11 Gas Processing Site Emission Estimates for Natural Gas
. . . . . . . . . . . . . . . . . 56 4-12 Gas Use Information for Pantex Devices .................. , . . . . . . . . . 58 6-l Emission Rate Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63



### viii1.0 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 (GRI-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 describes a study to quantify the annual methane emissions from pneumatic devices, which are a significant source ofmethane emissions within the gas industry. The gas industry has two primary types ofpneumatic devices that discharge natural gas; control valves that regulate flow, and gas-actuated isolation (block) valves. Because each segment ofthe industry fo11ows its ovm specific practices regarding "typical" pneumatic device insta11ations, emission factors were developed based on the types of devices observed from site visits. Emission factor data were co11ected from several sources: measured emissions provided from other studies, manufacturers' data, and data collected from site visits.
The population ofpneumatic devices in each industry segment was generally determined from counts ofdevices observed during site visits. The national emission factor for each industry segment 

### was then based on the product ofthe emission factor for a generic pneumatic device and activity factor. The annual emissions for pneumatic devices for each industry segment are as follows: production 31.4 

### ±65% Bscf; gas processing, 0.60

### ±64% Bscf; and transmission, I4.1 

### ± 60% Bscf. (Distribution emissions are included in Volume 10 on metering and pressure regulating stations.1)

### 2.0 INTRODUCTION
A pneumatic device is a mechanical device operated 

### by some type of compressed gas. In the oil and gas industry, many devices, especially instruments and valves, are powered by natural gas. Some ofthese devices discharge the power gas (also called supply gas) to the atmosphere. This report is concerned with ali "pneumatic devices," but focuses on devices that release natural gas to the atmosphere, with the exception ofgas-powered pumps and gas-powered compressor starters, which are characterized in other parts ofthe GRIIEPA study.2• 3•

4 Also, it is important to note that some pneumatic devices do not emit gas. For example, gas supply regulators and flow measurement devices such as Barton Chart recorders and strip chart recorders are sealed and do notbleed gas to the atmosphere. The gas industry has two primary types ofpneumatic devices that discharge natural gas: I) control valves that regulate flow, and 2) gas-actuated block valves. Section 3 describes each type ofpneumatic device and the methods ofdata collection used for each type ofdevice. Section 4 discusses emission factors developed for each type ofpneumatic device. Because each segment ofthe gas industry follows its own specific practices regarding "typical" pneumatic device installations, this section contains separate discussions for each segment ofthe gas industry: production, gas processing, and transmission and storage. Emissions from pneumatic devices in the distribution segment are characterized m a separate report on meter and regulation station emissions. 1 Section 5 describes activity factors for each segment ofthe gas industry, and Section 6 provides annual national emissions calculated for each segment ofthe gas industry.

2

### 3.0 PNEUMATIC DEVICE CHARACTERISTICS This section describes the characteristics ofthe various types ofpneumatic devices used in the natural gas industry, the data collected, and the methods used to extrapolate·the data. 

### 3.1 Overview Pneumatically operated equipment became the standard in the oil and gas industry since electricity was not readily available atremote production sites. Some pneumatic devices are powered by pressurized airfrom an instrument air compressor. However, the majority ofpneumatic instruments and valves in the gas industry are powered by natural gas. The pneumatic device can be used to move a valve or make a measurement. Most pneumatic measurement devices in the gas industry are sealed and do not emit natural gas unless they have a defect. However, many ofthese measurement devices send a signal to a control valve that regulates flow and thus controls process variables such as pressure, temperature, flow rate, and level. The controller for the control valve, ifpowered by natural gas, will discharge methane to the atmosphere. Ingas processing and transmission, isolation valves on large pipelines (also called block valves) can be actuated by natural gas, whereas.most ofthe isolation valves in the production and distribution industry segments are operated manually. Table 3-1 presents the pneumatic device classifications that will be used for the purpose ofthis report. The function that a control valve affects, such as level, flow rate, temperature, or pressure, usually dictates the type ofcontrol device and therefore the controller bleed rate. Pneumatic controllers linked to valves that control process temperature, flow rate, or level (Figure 3-1)bleed gas. The controller bleed rate may be intermittent

- alternating between bleeding gas to the atmosphere and not bleeding gas - or 

### 3

### TABLE 3-1. PNEUMATIC DEVICE CLASSIFICATIONS Valve Pneumatic Positioner" lnfonnation Pneumatic ControllerInfonnation Information Typeof ControllerBleed Rate Controller Device Function/Service Control ControllerBleed Frequency (upon valveactuation) Design Bleed Status Level, Flow Rate, Snap-acting Intennittent High rate, discharges On-off NIA Temperature, or Stationary Bleed Rate = 0 full volumeofactuator (Figure3-10) Pressure Control Throttling Continuous Small tolarge volume Orifice-flapper Continuousor Non-zero StationaryBleed discharged (Figure 3-6) intermittent Rate Force-balance Throttling Intermittent Small to large volume piston Continuousor Stationary Bleed Rate = 0 discharged (Figure 3-3) intermittent Pressure Control Throttling No-bleed (discharges to No-bleed (discharges to Self-contained N/A downstreamgas: line) downstream gas line) spring/diaphragm (Figure3-2) Isolation NIA Imerm.ittent Highrate, discharges Piston, rotary vane, N/A Stationary Bleed Rate = 0 full volumeofactuator orturbine (Figures 3-4, 3-11,

3-12, and 3-13) • Positionersare optionaldevices.

# ( 

# () I



## ~(_~======\:h.. Actuator



# \'--==;;~~) 000

= Controller

**~** Gas Supply ' 

# v u
n

u..u u..u u..L Valve Body Figure 3-l. Example ofa Pneumatic Controller Used for Level, Flow Rate, Temperature, orPressure Control



### 5

### the controller may continually bleed gas at various rates (thronling). Pressure controllers may bleed gas to the atmosphere, ormay be self-contained (Figure 3-2). Self-contained devices bleed gas from a high-pressure source to 

### a lower pressure source without releasing gas to the atmosphere. Throttling pneumatic control valves can be equipped with a valve positioner (shown in Figure 3-3), which is a type ofmechanical feedback device that senses the actual valve stem position, compares it to the desired position, and adjusts the gas pressure to the valve accordingly. In addition to gas bleeding through the valve controller, the positioner also bleeds gas to the atmosphere. Isolation valves are used to isolate a segment ofpipe ora piece ofequipment rather than for process control. An 

### example is shown in Figure 3-4. The valve is either open orclosed. Gas is released only \Vhen the valve is moved, so the bleed frequency is considered intermittent. This type ofoperation is fairly infrequent. The bleed rate for these devices varies with the design ofthe actuator. Table 3-2 lists 

### the pnewnatic devices commonly used in the natural gas industry and whether gas would be emitted in steady-state operation orduring the actuation cycle. This table summarizes the bleed modes ofthe various devices presented in Table 3- 1. The pneumatic device bleed modes and classifications are discussed in more detail in the following sections.

6REGULATOR /,- SET POINT ADJUSTMENT

DOWNSTREAM PRESSURE REGULATED, LOWER GAS OUT OF REGULATOR

Figure 

### 3-2. Self-Contained, Spring-Loaded Pressure Regulator'


### 7VALVE ACTUATOR SPOOL VALVE SIGNAL DIAPHRAGM 

### y


### ~~~----EXHAUST

....._-POSITIONER CAM



### Figure 3-3. Pneumatic Device with **Positioner~Force** 

### Balance Piston Type5



### 8

### SUPPLY GAS A 

### EXHAUST GAS 

# '

PISTON ACTUATOR ARM MOVEMENT **~-VALVE** 

### BODY PIPE

VALVE BODY EXHAUST 

# tI GAS 

# t SUPPLY GAS PIPE

0


### PISTON ACTUATOR ARM MOVEMENT

Figure 3-4. Example Isolation Valve

- Piston Operator6



### 9

### TABLE 3-2. TYPICAL PNEUMATIC DEVICE BLEED MODES
Pneumatic Device Type Measurement Device

- Recording

- Control Control Valve (Operator/Actuator) Valve Controller

- Snap-Acting

- Throttling

a. Force Balance b. Orifice/Flapper Valve Feedback Positioner a. Force Balance b. Orifice/Flapper Self-Contained Pressure Regulators Gas-Actuated Isolation Valves 3.2 Gas-Actuated Control Valves 3.2.1 Operating Principles Does the Device Bleed During: Steady-State Actuation Cycle Operations? (Valve Stroke)? 

### No No No No No No No Yes 

### No Yes Yes Yes 

### No Yes Yes Yes 

### No No No Yes

Pneumatic devices (valve controllers) linked to control valves are the largest source ofpneumatic emissions in the gas industry. These devices can have two distinct bleed modes: a stationary bleed rate and an actuating bleed rate. The stationary bleed is the rate ofgas released when the signal is constant, and the device is not moving. For intermittent bleed pneumatic controllers, the stationary bleed rate is zero. For continuous bleed controllers, the stationary bleed rate is non-zero; it is required to maintain a constant gas supply to the device to provide for a quick response to changes in the controlled process.

10Vlhen the pneumatic device is moving the control valve, there is an unsteady and different rate ofbleed (actuation bleed rate). Ifthe signal is adding pressure to the actuating chamber, the bleed rate drops from the stationary level. Ifthe signal is to release pressure from the actuating chamber, the bleed rate increases above the stationary rate. Actuating bleed rates must be considered over a long period to determine average emissions. Since the rate varies with the frequency ofcontrol, the actuating bleed rate is not available from the device manufacturers. Various parameters such as pressure, temperature, flow rate, and liquid levels are all controlled by opening or closing a control valve in the process line. The necessary elements for controlling a parameter are a parameter measurement device, a valve, a valve controller, and possibly a feedback positioner. For example, Figure 3-5 illustrates a device to control the volume ofliquid in a vessel. A level float in the vessel indicates the volwne ofliquid based on the level measurement. The measurement device sends a weak signal to the controller. The controller receives the weak pneumatic signal and converts it to a stronger pneumatic signal which is sent to the valve actuator to move· the valve stem. The flow rate ofliquid from the 

### tank is measured and recorded. Each ofthe elements

**~** measurement, valve, and valve controller -isdescribed in detail below. Measurement Weak signals from a measurement device are translated by sealed transmitters into a stronger signal that can physically change valve position, and thus affect flow control. For example, measurement oflevel using a level float produces a weak mechanical signal that can be used to move the flapper shown in Figure 3-6a. Other measurement media can also serve as the controlling parameter. For example, process flow is typically measured by a drop in pressure across a restriction. The pressure taps on either side ofthe restriction in the process flow are tied to a diaphragm that deflects when the pressure changes. The deflection ofthe diaphragm produces a weak mechanical signal that can be used to move the flapper (baffle) shown in Figure 3-6b. II{STRONG PNEUMATIC

SIGNAL} YAl.YE **ACTUAT'OR-~** PII'E IIEASUREWENT (LEVEL}



### ---r I I I (WEAK

PHEUUAnC I IIQNAI.) YALYE CONTROLLER I I I I

**~'----::::-..-** - - - 

# -

**~**



# U U f-o-.!.SU::P;::PL"Y::O::!A;,Sc:li"-- r - VENT TO ATM: 

### I **L__J--....!:::::~::.=:....-** 1 

### I 

### I
PIPE FLOW RECORDER

VALVE ORIFICE PLATE 

### Figure3-5. OperatingPrinciples

12PNEUMATIC RE1..J.. · 

# I 

# I PRESSURE GAUGE 

# ---,

PRESSURE REGULATOR 

# I

CONNECTION TO MEASURING MEANS CONTROL VALVE AND ACTUATOR



### Figure 3-6a. Throttling Continuous Bleed Pneumatic Controller: Orifice Flapper Design5

MEASUREMENT 

# I c_NOZZLE 

# _:========~-- OUTPUT PRESSURE TO ACTUATOR



### Figure 3-6b. Throttling Continuous Bleed Pneumatic Relay: Orifice Flapper Designs 13

### Valve Flow is regulated by a control valve. The valve operates by moving a valve stem and a valve seat attached to the stem. The movement ofthe valve seat inside the valve body can then restrict or stopprocess flow through the valve. The stem can be moved by any force method. Some valves in the field are moved by small electrical motors; however, a pneumatic device is the most common. In the case ofpneumatic actuated valves, the stem is moved by force from the actuator chamber. The actuator chamber is either a diaphragm or a piston device (see Figure 3-7), which deflects ormoves because pressure is applied to 

### one side ofthe chamber. Apermanent coiled spring pushes the valve stem in the opposite direction when the pneumatic force is reduced. The valve and valve actuator never bleed directly unless there is a defect. Emissions from such defects are considered fugitive emissions and are considered in the Equipment Leaks7 

### report. Ali actuation gas discharge is emitted back through the valve controller. Valve Controller A valve controller is the device that enables a process variable to be changed. The controller device links the valve and the measurement signal to produce a control loop. The controller checks the current measurement ofthe variable against the desired set

### point ofthe variable. Ifthere is a difference, a pneumatic signal is sent to the control valve to open or close the valve. Ifthe measurement matches the set point, equilibrium is maintained and the signal holds a constant level. The controller may bleed at the stationary rate depending on the design. In the field, the measurement device, valve, and valve controller are often integral. However, the controller is the one element inthe measurement/valve/valvecontroller loop that discharges gas to the atmosphere. Contr.ollers are highly variable in design. Depending on the design ofthe controller, the stationary position may or may not 14PISTON CYLINDER

### ---1

PROCESS

FLOW

DIAPHRAGM

PROCESS

FLOW PISTON ACTUATOR PNEUMATIC SIGNAL FROM CONTROL.LER

STEM

VAI.VE SEAT DIAPHRAGM ACTUATOR PNEUMATIC SIGNAL DIAMETER



## If--\---STEM



### Figure 3-7. Actuator Types5

15

### involve a continuous bleed rate. However, the actuation cycle, which is the actual movement or stroke ofthe valve stem from open to closed and back, always results in the release ofgas. This cycle only occurs whenthe signal changes and control is needed. The frequency ofthis occurrence will be different for every application. Pneumatic Relay The key component ofthe controller is the pneumatic relay (also called a booster, transmitter, or amplifier). In the simplest case, a controller is only a supply gas regulator and a pneumatic relay. Since the signal from the measurement device is usually weak, it can not produce enough force to open the valve. A controller device amplifies the signal using a higher-pressure supply gas. The supply gas is often taken directly from the produced gas at the field site. The pneumatic relay is a kind ofmechanical amplifier that produces a stronger pneumatic signaL The mechanical amplifier in the controller uses the small force ofthe measurement deflection to change the supply gas flow path, which alters the resulting downstream supply gas pressure. The change inpressure is a pneumatic signal that is sent to the valve actuator. Controllers may not bleed at all when there is an increasing signal. An 

### increasing signal sends higher-pressure gas into the actuator, deflecting the diaphragm and compressing the spring. When the signal decreases, the controller reduces the pressure on the actuator by releasing gas to the atmosphere. There are several types ofpneumatic relays which, as the main component of the controller, define the type ofcontroller. The most common are throttling and snapacting. Throttling implies that the valve can be moved to any position proportional to the signal. These devices are most often used for their quick response to system changes or where more precise control is needed.

16A simplified drawing ofa throttling controller's pneumatic relay shows one method that a pneumatic device may use to change a weak mechanical signal into a stronger pneumatic signal (Figure 3-6b). Basically, the pneumatic device uses a small amount ofmechanical force to alter the flow and pressure ofa supply gas at higher pressure. This higher pressure stream then becomes the amplified control signal. The higher pressure gas stream is "altered" by being partially diverted through a small orifice that bleeds to the atmosphere. The weak mechanical signal moves a "flapper" that alters the flow ofgas out ofthe orifice. Ifthe flapper is fully extended towards the orifice, the device bleeds at a very low rate, and the p:teumatic output is at its highest leveL Ifthe orifice is fully open, most ofthe supply stream bleeds to the atmosphere, and the pneumatic output is at its lowest value. This type ofthrottling device has a continuous bleed rate, even in the stationary position (no movement ofthe valve orchange ofsignal) because the orifice opening is not completely closed. Figure 3-6a shows that a small mechanical force can be used to deflect a flapper arm that covers or uncovers an orifice, changing the gas supply into an amplified measurement signal. Other types ofpneumatic relays use a chamber instead ofan orifice flapper apparatus. The most common chamber relay is called a "force balance piston device." One example was shown in Figure 3-3, and another is shown in Figure 3-8. This type ofdevice only bleeds when it is out ofthe neutral position; its continuous bleed rate is zero. In addition to the primary relay amplifier, many throttling controllers have adjustment devices that allow the operator to alter the set point and response (proportional gain, proportional-integral gain, or proportional-integral-derivative gain), and devices that allow the controller to be reset. These additional devices may also bleed gas, but their rates are steady and are included in the manufacturers' reported total gas consumption rate for the controller. Figure 3-9 shows a device with a proportional set point and reset knob.

17

# t WEAK APPLIED

FORCE 

## SUPPLY GAS

Figure



### 3~8. Force Balance Piston Devices

18CONSTANT SUPPLY PRESSURE

EXHAUST --- /----- INLET END OF RELAY VALVE SMALL DIAPHRAGM
FIXED ORIFICE 

## ~p;~~b~~~--==~-~~~ lARGE DIAPHRAGM EXHAUST END OF RELAY VALVE**-lf;;;!~{====[]** BOURDON TUIOE-, ,---- PORPORTIONAL BELLOWS

FIXED



# B SfNSED PRESSURE

**[::\~:)./]** LOADING PRESSURE VENT OR REMOTE PNEUMATIC LOADING PRESSURE ---- PORPORTIONAL VALVE EXHAUST 

# D NOZZLE PRESSURE 

# D PROPORTIONAL PRESSURE PIVOTING CROSS SPRINGS

Figure 3-9. Throttling Continuous Bleed Controller with Proportional Adjustment9This knob contains an exhaust por: with a continuous bleed line from the actuator diaphragm. These additional bleed locations are typical ofproportional controllers. For throttling controllers, manufacturers can design for any desired bleed rate by sizing the orifice flapper or the force balance piston relay. In general, devices with a lower design bleed rate are slower to respond to signal changes, and have longer response times; therefore, some applications that require fast response also require higher bleed rates. Snap-acting controllers are another type ofdevice common to the gas industry. A snap-acting or "on/off' device is either fully open or fully closed. A snapacting controller has no continuous bleed, it only bleeds when the actuator is depressured. Figure 3-l0 shows two examples ofon/offrelay devices. As the diagram shows, when the device is on, the full supply-gas pressure is applied tothe control valve actuator, and the vent/exhaust line is blocked off. When the device is off, the actuator is vented to the atmosphere and the supply gas is blocked off. Some controllers have an additional feedback device: a valve positioner that measures, amplifies, and sends a second signal about the position ofthe valve stem. These positioner devices introduce a second pneumatic relay device to the existing control loop; therefore, a second bleed rate can also be introduced. Positioners are typically used for "slow systems" such as temperature control, where more precise movement ofthe valve is needed. Figure 3-3 illustrates a force balance spool relay and the valve positioner that the relay controls. These devices can be easily identified in the field by the positioner·arm attached to the valve stem. Only a small percentage ofcontrol valves in the gas industry have positioners since this level offine tuning is not generally required.



### 20ON/OFF SNAP DEVICE 

## !- 

# 1n ' /



# I~ 

# /



# ~ I L 

## lr--1

**~**

**~**



# ' I WEAK APPLIED

FORCE

WEAK APPLIED

FORCE 

# ' t SUPPLY GAS

TO/FROM ACTUATOR

EXHAUST

PORT

PNEUMATIC SWITCH VENT GAS 

# I

-

**~**

**~** 

# - ' I 

# ,, TO/FROM ACTUATOR 

### Figure 3-10. On-OffSnap Devices5 

### 21 SUPPLY GAS

### 3.2.2 Data Requirements As mentioned in the previous section, pneumatic controllers can have two distinct bleed modes, based on the type ofrelay. There is an actuating bleed rate and a stationary or steady-state bleed rate. The stationary bleed rate occurs when the signal is

**cor~stant** 

### and the valve is not moving; the actuating rate occurs when the valve actuator is depressured. The stationary bleed rate for a device may be zero, depending on its construction. However, every pneumatic controller has a non-zero actuating bleed rate. The various characteristics that can affect the stationary bleed rate for a production controller are: 1. 

### Basic device type (controller, positioner, self-contained device); 2. Pneumatic relay construction (orifice-flapper versus force balance piston, number ofinternal control adjustments, such asproportional gain and set point knobs); 3. Device condition (old orworn devices may leak more); 4. Design response time (faster response devices require higher bleed rates); and 5. Supply gas pressure and supply gas type (airproduces no methane emissions). Ail controller types have an actuation bleed rate. The actuation bleed occurs when the controller moves the valve stem by either releasing pneumatic pressure or applying pneumatic pressure. As the pneumatic pressure is released, the actuator must be vented. The venting occurs through the controller device. For throttling controllers with continuous bleed rates, the bleed rate will increase above the stationary level so that the actuator can be depressured. For all


### 22throttling controllers, actuation bleed rates depend on how far and how often the valve is moved, and must be considered over a long period to determine average emissions. For snap·acting valves, the actuating bleed depressures the entire actuator to the atmosphere. The actuation bleed rate depends on the size ofthe device and on how often the valve is moved. The various parameters that can affect the yearly average actuating bleed rate for a snap·acting orthrottling device are: l. Number offull stroke cycles per year (how often the valve makes a 

### full stroke cycle); 2. Actuating chamber size; and 

### 3. Supply gas pressure. Based on the characteristics ofcontinuous bleed and intermittent bleed pneumatic devices, the following approach was used to gather pneumatic data from site visits for this report: I. Basic device type (intermittent versus continuous bleed), the instrument manufacturer, and model number were gathered from several sites by visual inspection; 2. Instrument populations; 

### 3. Supply gas pressure and type; and 4. Field measurements ofcontinuous bleed devices were provided from existing sources.
The bleed rate will vary with the supply gas pressure. The two common 

### signal pressure ranges are: I) 3to 15 psig; and 2) 6to 30 psig.' These supply ranges can 23be easily identified by the gauge dials on the front ofthe controller box. The 3-15 range will operate at approximately 20 psi gauge; the 6-30 range will operate at about 35 psi gauge. The site data were combined with manufacturers' data and field measurements (provided from exist:ng sources)10

·11 to produce an annual estimate of emissions for intermittent and continuous bleed actuated controllers. 3.3 Gas-Actuated Isolation Valves Transmission compressor stations, transmission pipelines, storage stations, and gas plants have large-diameter pipelines, and therefore have large pipeline Isolation valves. These valves block the flow to or from a pipeline, and can isolate the facility for maintenance work or in the case ofan emergency. The valves are usually actuated remotely by a power source. The valves are so large that manual operation would be extremely slow, and certainly unsuitable in the case ofan emergency. The valves are most often actuated pneumatically (by natural gas or compressed air) orby an electric motor. 3.3.1 General Description Most gas operators on isolation valves discharge gas only when actuated. Once they reach the open orclosed position, they do not bleed gas. These valves are actuated infrequently, so their emissions are very intermittent. The pneumatically actuated isolation valves can generally be divided into two types: 1) displacement operators, and 2) turbine operators. Displacement operators are attached to quarter-tum plug valves or quarter-turn ball valves. These operators use gas pressure (pneumatic force) to move an actuator element in one direction. Sometimes the pnewnatic force is applied directly to the actuator element, and sometimes it is applied to oil, so that hydraulic force moves the actuator; in either case, gas is discharged when the 24

### valve is actuated. The actuator element is displaced from its original position by the pneumatic or hydraulic force. Displacement operators in the gas industry are oftwo basic types: 1) rotary vane, and 2) piston. The rotary vane displacement operator uses natural gas to force a fixed amount ofoil from one pressure bottle to another. The oil moves through the vane operator, delivering hydraulic force to the vane, and moving it and the attached valve stem one quarter turn. The oil moving into the bottle forces gas in the top ofthe receiving pressure bottle to vent to the atmosphere. The most common manufacturer ofthis type of operator is Shafer Valve Company. 12 

### Figures 3-11 and 3-12 show a typical pneumatic/ hydraulic rotary vane operatorfrom the Shafercatalogue. Similarly, Pantex Valve Actuators & 

### Systems, Inc., manufactures adisplacement operatorthat uses natural gas to moveapiston.6 

### Thepiston acts onan "ann" orlever that rotates the valve stem. Gas is supplied to one side ofthe piston and exhausted from the otherto move the arm in

### each direction, eitheropening orclosing the valve. Anexample of this type ofoperator is shown in Figure 34. Supply gas forthese operators is usual,ly pipeline gas, so pressure varies from site to site. Compressed air canbe used 

### ifit is available in sufficient volumes. The volume ofgas vented depends onthe vane orpistondisplacement

### size and onthe supply gas pressure. Turbine operators, the second major type ofisolation valve operators, are usually attached to gate valves. 13 

### The turbine operators simply release gas to the atmosphere across a smal1 turbine similar to

### a gas starterturbine for a reciprocating compressor. The gas spins the turbine blades, and the turbine shaft then turns gears that move the gate valve stem. A turbine operatoron a gate valve is illustrated in Figure 3-13.

25HYDRAULIC TANKS ROTARY VANE ACTUATOR HAND PUMP

'--- VALVE BODY

Figure 

### 3-11. PneumaticJHydraulic Rotary Vane Operator12



### 26SHOWN OPEN

I I
HAND PUMP FOR MANUAL OPERATION


### Figure 3-12. Pneumatic/Hydraulic Rotary Vane Operator -Cross Section12

27

### GATE STEM----.. GEAR BOX-'-

. GAS IN.--'



### Figure 3-13. Turbine Operator



### 28 EXHAUST TURBINE

VALVE BODY

### Pipeline gas is typically used as the supply gas for the turbine devices, so the pressure varies from site to site. The volumes vented depend on the duration ofoperation to open orclose the valve and on the supply gas pressure. 

### 3.3.2 Data Requirements Based upon the operating principles discussed above, the various characteristics that affect the bleed rate for isolation valve operators are: I. Basic device type (turbine ordisplacement); 2. Manufacturer and model number; 

### 3. Supply gas pressure, supply gas type (airproduces no methane

**emissions)~** 

### and 

### 4. Number offull stroke cycles peryear. The following approach was used to gatherpneumatic data for this report from field site visits: 1. During site visits, instrumentpopulations and the instrument manufacturer and model number were gathered from several sites; and 2. Based on observations and interviews,"the frequency ofoperation cycles peryear was estimated. The site data were combined with manufacturers' data and measured data from other studies to produce an emissionfactorfor a typical device type. 

### 3.4 OtherPneumatic Devices Numerous otherdevices in the field can bleed methane but do not neatly fit into the categories listed above. Because these devices are rare, orrarely bleed, they were


### 29ignored for the purpose ofthis study. They are listed In this section only for the

**sa~e** of completeness. Some keyexamples are:

• Solenoid snap-acting valve controllers; • Self-contained pressure regulators; • Pneumatic transmitters; and • Older flow computers. The solenoid "snap-acting" controlleracts like the pneumatic snap-acting controller, except that 

### its signal is not a weak mechanical signal but anelectrical one. The solenoid eitheropens a valve thatputs full supply gaspressure to the top ofthe valve actuator orcloses offthat supply and vents the actuator to the atmosphere. Like snap-acting pneumatic relays, 

### itonly bleeds when the actuatoris depressured. Figure 3-14 shows a diagram ofa solenoid relay. Thesedevices are rare since electronic signals are infrequently used 

### inthe gas industry.
Acorrunonexample ofa self-containedpressure regulator is the small "gas supply regulator" shown 

### in Figure 3-2. This is a small device that lowerspneumatic gas supply pressure to adesired downstreampressure. These devices arecommonly found betweenpneumatic supply headers and the devices thatuse the supply gas. Gas supply regulators only bleed ifthe downstreampressure rises above set-point. Since there are downstream users ofthe gas, the downstreampressure is almostalways lower, so these devices rarely bleed gas. Anothercommon, large, self-contained device is the transmission and distribution pressure letdownregulator (Figure 3-15). These regulators handle the entire gas stream but do not bleed at all. They release actuatorpressure to the downstream side and do not bleed to the atmosphere.

30FROM ACTUATOR

TO ACTUATOR 

### DE·ENERGIZED:

SOLENOID



# ' TO VENT



### ENERGIZED:

SOLENOID

(VENT IS BLOCKED) ELECTRONIC SIGNAL

____ ...J

(SUPPLY GAS IS BLOCKED)

ELECTRONIC SIGNAL

____ ..J (SIGNAL IS ON)

SUPPLY GAS



### Figure 3-14. Solenoid Relay5

31

### Figure3-15. Self-ContainedPressure RegulationValve
32

### The pneumatic transmitters and older flow computers are examples ofdevices originally installed in olderfacilities that are out-of-date by today's standards oftechnology. It is difficult to list, characterize, orgroup all ofthe diverse devices in this category. Their total contributionto emissions is considered to be minimal.

33

### 4.0 PNEUMATICDEVICEEMISSIONFACTORS The various segmentsofthegas industry have differentequipmentand different standards for using pneumaticdevices. Table 4-1 shows the general uses ofdevices in each segment. 

### TABLE4-1. STANDARDUSES OFPNEUMATIC DEVICES Production Processing 

### Transmission Distribution Control valves Yes Very Few Yes Yes operated by 

### gas? Isolationvalves 

### No Some 

### Yes Some operated by gas?
The foiiowing subsections describe the details ofpneumatic devices in each segment and the emission factors associated with those devices. 

### 4.1 Production

**Se~m~ent** Valvecontrollers (pneumatic devices on control valves that regulate flow) are the most commontype ofpneumaticdevice in theproduction segment that discharge gas 10 the atmosphere. As stated earlier. primary measurement devices. which detect the initial change in theprocess variable, are sealed and donot directly bleed orexhaustto the atmosphere. In addition, theproductionpipelines are small, so the isolation valves that exist are manually operated and donot bleed gas. 

### 4.1.1 General EmissionFactorCharacteristics Typical productionoperations include pneumatic valve controllers. Infrequently, productionoperationsmay contain valve positioners. There are multiple components (such as set-pointadjustment, gain adjustment, and reset knobs) within a 34controller orpositionerthat may bleed. These are considered part ofthe controller device. Certain valves orvalve packages may have these emitting elements combined into one fieldlocated box. The production segment uses both basic types ofpneumatic controllers: 1)



# . throttling, and 2) snap-acting. Throttling pneumatic relays ofthe "force balance piston" type (Figure 3-8)bleed only when they move from the neutral position. They are therefore intermittent emitters and have a stationary bleed rate ofzero. Throttling orifice flapper relays (Figure 3-6)bleed continuously, even when the valve is not moving, but their bleed rate varies with the strength ofthe signal from the process variable. Orifice flapper relays are considered continuous emitters since there is no position where the bleed rate is zero. Snap-actingcontrollershave a stationarybleed rate ofzero and are therefore considered intermittent emitters. 

### 4.1.2 ProductionEmission Factors Five sources ofinformation were used to determine the methane emissions from pneumatic devices used in the production segment: the results from a study performed by the CanadianPetroleumAssociation,11 manufacturers' data, measured emission rates, 10 data collected from site visits, and literature data for methane composition. Each ofthese sources is discussed in detail. 

### CanadianPetroleum Association (CPA) Report As part ofCanada'seffortto reduce atmospheric emissions, the Canadian Petroleum Association sponsored a project to quantify methane and VOC emissions in upstream oil and gas operations. 11 Emission measurements from 19 snap-acting pneumatic devices and 16 throttling devices were collected during this study. The results are presented in Table4-2. The average natural gas emission rate for snap-acting devices was 213 scfd/device 

### ± 57% (90% confidence interval), and the average emission rate for throttling 35w 

# "' TABLE 4-2. RESULTS FROM THE CANADIAN PETROLEUM ASSOCIATION PNEUMATIC EMISSION RATE STUDY Quantity Minimum Flow, Maximum Flow, Instrument Type Facility Type Equipment Type Measured scfd scfd Snap-Acting Oil Battery Group Treater 0.0 690

Controller Test Treater 2 172 172 Group Treater I Group Treater 2 0.0 >951 Group Treater 2 0.0 >933 Group Treater 2 0.0 >959 Group Treater 2 0.0 573 Group Treater 0.0 >1,911 Group Treater

Test Treater 2 Test Separator 2 0.0 430 Group Separator 0.0 1:097 Average Emission for Snap-Acting Controllers Throttling Oil Battery Dehydrator 3 0 10 Controller Line Heater I 55 55 LineHeater I II II Line Heater 31 31 Group Treater 6 7 7 Test Separator I 529 529 Test Separator 3 9 240 Average Emission for Throttling Controllers Average Natural Gas Emission, scfd 33 179

14 226

59 140 81 695

12 210 233 677 213 ±57% 2 60 II 34

8 529

II 94 ± 152%

### devices was 94 scfd/device 

### ± 152%.n TI:e CPA report concluded that there was no statistically significant difference between the bleed rates ofthe snap-acting and throttling controllers.
It should be noted that the CPA report did not distinguish betweenthrottling controllers with intermittentbleed rates and throttling controllers with continuous bleed rates. In addition, only one ofthe throttling devices actuated while they were measuring it. The measurements recorded for the other throttling devices only represent the stationary or continuous bleed emissions. 14 

### Therefore, the Canadian measurements are lowerthan field measurements ofsimilar devices in the U.S., but do agree with the manufacturer'sdatafor similardevices. The CPA measurements were treated as additional data sources and combined with field measurements provided byanother source to generate emission factors for intermittent and continuousbleed devices. 10 Manufacturers' Data 

### Manufacturers ofpneumatic devices may report a "gas consumption" for specific devices based on laboratory testing ofnew devices. However, the manufacturers indicate that emissions in the field canbe higher than the reported gas consumptiondue to operatingconditions, age, and wear ofthe device. 15•16•17

·18 

### Examples ofcircumstances or factors that can contributeto this increase include:
• Nozzle corrosion resulting inmore flow through a largeropening; • Broken orworn diaphragms, beiiows, fittings, and nozzles; • Corrosives in the gas leading to erosion orcorrosion ofcontrol loop internals;
• Improper

**installation~** 

### • Lack ofmaintenance (maintenance includes replacement ofthe filter used to remove debris from the supplygas and replacement ofo-rings and/or seals);
37

### • Lack ofcalibrationofthe controlleroradjustment ofthe distance between the flapper and

**nozzle~** 

### • Foreignmateria! lodged in the pilot seat; and • Wear in the seal seat. The manufacturers contacted did not have field measurements ofdevices in service and did not simulate the aging ofdevices with laboratory measurements, so they could not provided an indication ofthe expected increase in emissions due to 

### the factors listed above. Since manufacturers' emissionrates are based on new devices, actual emission measurements from pneumatic devices in field service, including worn ordefective devices, were used as the basis fordeveloping emission factors. 10·ll 

### Several pneumaticdevice manufacturers provided informationonthe gas consumption rates for their continuousbleed devices.9•16•18•19• 20•

21•

22•23

·24• 25 

### Table

**4~3** 

### shows the bleed rates for the model seriesobservedduring sitevisits. Themanufacturers' reported gas consumption rates represent the gas usage at the specified supply gas pressure for the controlleronly (unless otherwise noted). Additional emissions may occur from other components of

### the control loop 

### (i.e., setpointexhaust and valve positioner). Forthe types ofdevices listed, gas consumptionrates for the controllers can vary from 0 to 

### 2,150scfd perdevice. However, the manufacturers indicated that

### emissions from these devices in field operationmay be 

### higher than 

### the reported "maximum." Some manufacturers provided a maximum gas flow rate ordeliverycapacity that the controller pilotcould withstand (4,320scfd forthe Bristol 62411 and 8,880for the Fisher4100). This 

### flow rate indicates the maximum amount ofgas that canbe supplied to the control loop. Itis possible that some pneumatic devices could continue to

### operate up to these flow rates, but not above these rates. The manufacturers' data serve as a sanitycheck for the field measurements provided by othersources (discussed in the next section). The data reported in Table 4-3 are 38

### TABLE 4-3. MANUFACTURER BLEED RATES FORCONTINUOUS BLEED PNEUMATIC DEVICES Gas Consumption Rates, scfd Manufacturer/ Model "Minimum" "Maximum" Comments onSpecified Rate Norriseal !000(A) Modeldiscontinued in the 1960s No bleed rate information available. Max. bleedrate is not specified by Norriseal. Estimated for 1001 model based Norriseal !OOI(A) 0-10 2,150 onvolume ofgasrequiredfor onecompleteactuation@ 30psig supply (providedby manufacturer)and assuming oneactuation/min. Min. basedongasconsumptionofthe controlleronly. Bristol 624, 624 If 72-144 4,320 Bristoldoes not manufactureactuators, so they donot specify a gasconsumption for the actuator. Max. bleedrate shownis basedonthepilot capacity (maximumamountofgasthatthe controllerpilotcan accommodate). Fisher2400 Modeldiscontinuedin 1957 No bleedrate informationavailable. Bleedrate for 35 psig supply pressure. Min. represemsthe steady state pilot Fisher2500 168 1,008 bleedrate (devicenot actuating). Max. representsgasconsumptionwhen the relayis completelyopen. Fisher 2900 Modeldiscontinuedin 1991 Gasconsumptionnotlisted in devicebrochure,hut Fisher representative provideda laboratorymeasurementof555 scfd for 35 psig supply pressure. 1,200 Bleedrate for 35psig supply pressure. Min. representsthe steady state pilot Fisher4100 24 8,880 bleedrate ofthe controller. Max. representsmaximumgasconsumption (1200 scfd) and deliverycapacityofthe controller(8800 scfd). lnvalcoAE 155 Model discontinued

- 1975 Nobleedrate informationavailable. Minimumbleed rate specified for supply gas pressureof20-30psi. Maximum lnvalcoCT series 510 960 bleedrate shown hereis reportedby the manufactureras a typical bleedrate for this device. A r.etrofit kit is availablefor this seriesofdevicesto reducethe typical bleedrate from 960scfd to less than 22 scfd.consistent with emissionmeasurements in the field, in that the manufacturers confirmed that the devices can emit at rates higher thanthe manufacturers' reported gas consumptionrates. In addition, the deliverycapacity reported by the manufacturers for some devices serves as an absolute maximumbleed rate. Any measured emissionrate higherthan the delivery capacity for agivendevice wouldindicate anerror in the measurement and wouldjustify discardingthe measurement. DirectlyMeasuredEmissions for ContinuousBleed Devices Fieldmeasurements ofthrottling devices 

### with continuous bleed rates were availablefrom companiesparticipating in a separate contractor's piogram. 10 Forthese measurements, acontractorconnected a flow meterto the supplygas line between the pressure regulator and the controllerto measure the gas consumptionofthe controller. A cumulative flow rate and the currentflow (seth) were recorded andextrapolated to gas consumptionperday. Theduration ofthetest depended on the variability ofthegas use. Forsteady operatingconditions, onedatapointwas taken for 15-20 minutes. Forvariable flow rates, several one-hourmeasurements were taken. Althoughthe emissionmeasurements were notperfonnedunderthe direction ofthis study, the results are believedto be anaccurate representation ofpneumaticdevices in operation in the 'U.S. natural gas industry. Through interviews with sitepersoiUlel and the contractor that performed the measurements,10the samplingtechnique, measurement protocol, and equipmentcalibrationprocedures were reviewed. Two measurements were removed from the data setbecause they did not follow the measurementprotocol for a single device (inbothcases a singleemission measurement was reported for an unknown numberof devices). The fmal data set was deemed acceptable by the industry review panel. Afterthe QA/QCreview, the data set contained a total of41 measurements from a combinationofcontinuousbleed devices from offshoreplatfonns, onshoreproduction sites, and transmission stations. Table4-4summarizes the measurements. 40TABLE4-4. MEASURED EMISSION RATES FOR CONTINUOUS BLEEDDEVICES Production Production Total

Onshore Offshore Production Transmission Number of 9 9 18 23 

### Measurements Minimum, 380 108 108 !52 scfd/device 

### Maximum, 2,334 962 2,334 4,215 scfd/device Average, 1,189 

### ± 39% 556 

### ± 33% 872 

### ± 30% 1,363 

### ± 29% scfd/device


### The use ofpneumatic devices in onshore versus offshore production operations is similar. Both use continuousbleed devices primarily for liquid level control in separators. Comparing the average measurements

## ill Table 4-4, the average emission rate for pneumatic devices in offshore operations is much smaller than the emission rate for these devices in onshore operations. However, the offshoreemission measurements shown in Table4-4 are from one company. Therefore, any difference between onshore and offshore device emissions might also be attributed to a company difference. Because most industry reviewers ofthis study believe that there is no technical reason to divide the data set between onshore and offshore, and additional data were not available to validate a distinction between onshore and offshore, the measurements for these two categories are combined into one emission factor for continuousbleed devices in the production segment. Continuousbleedpneumatic devices are used for different functions in production versus transmission operations. As mentioned previously, most continuous bleed pneumatic devices in production are used to control the liquid level in separators. Inthe transmission segment, the same types ofdevices areused for liquid level control in filterseparators, but are also used for pressure reduction. In addition, the higher pressures and largerpipeline sizes associated with transmission operations require larger actuators and
41

### larger valves than are typically found in production, and therefore pneumatic devices used in transmission operations would be expected to result in higher emission rates. Forthese reasons, separate emission factors were developed forproduction and transmission. Comparing the measured emissions for devices in production versus transmission indicates that there is adifferencebetween the industry segments. The combined onshore and offshore production devices have a lower average emissionrate of872 scfd, while transmission devices have an average emission rate of 1.363 scfd. When the Canadiandata are included, the productionemission factor is 654 

### ± 31% scfd/device. The transmission emission factor is unchanged because the Canadianmeasurements were only from onshore productionfacilities. The measured emissionrates compare well with the gas consumptionranges provided by the manufacturers, althougha directcomparisonfor ail device types can not be inade sincemanufacturervalues are not available for ail ofthe models measured. In general, most ofthe measurements are less than 2,000scfd (only seven out ofthe 41 measurements are greaterthan 2,000 scfd), and all ofthe measurements are below the reported controller deliverycapacities of4,320and 8,880 scfd (twodevices had emission measurements of 4,215 scfd). 

### As stated previously, the manufacturers' bleed rates represent laboratory measurements ofthe gas consumptionfor new pneumatic devices. Inreality. the pneumatic devices in the field have various states ofwear and may emitgas at rates higher than the manufacturers' gas consumptiondatasuggest. The measured emissions are in the range of values provided by the manufacturerand are believed to reflect more typiqtl operating conditions for these devices and account for increased emissions due to wear. For the purpose ofthis report, the measured emissionsprovided by CPA are combined with the contractor's directmeasurements to estimatethe emission factor from continuous bleed throttling devices. The resulting natural gas emissionfactor.forthe production segment is 654 

### ± 31% scfd percontinuousbleed device. 42

### MeasuredEmissions for IntermittentBleed Devices Fieldmeasurements for intermittent bleed devices, using the same technique described for the continuousbleed devices, were also available from companies participating in this snrdy. 10 

### Based onthe criteria described for continuous bleed devices, measurements for the intermittentbleed devices were reviewed andjudged to be acceptable. Atotal of seven measurements were provided from intermittentbleed devices found in onshore production service. No measurements were available for these types ofdevices in offshore service orthe transmission segment. The average emission rate for the seven devices is 511 scfd 

### ± 36%. The measurements ranged from 211 to 950 scfd/device, as compared to the CPA measurements ofsimilardevices which ranged from 12 to 695 scfd/device (average of 211 scfd from Table4-2). Combining the 19 measurements from both sources (Canadian and U.S. field measurements) results in a natural gas emission factor of323 

### ± 34% scfd/device for intermittent bleed devices in production. SiteData Forthis study, data were collected from a total of22 sites to establish acount ofpneumaticdevices for production sites and to determine the fraction ofintermittentversus continuous bleed devices at each site. The fraction ofeach device type was used to scale the emission factor to generate one emission factor for a "generic" pneumatic device. Table 4-5 summarizes the data collected at production sites. Foreach site, the number ofsnap-acting devices and the numberofthrottlingdevices were collected. Where possible, the manufacturer and model number were recorded for each device. As discussed in Section 3, throttling devices can be eitherintermittent or continuous bleed, while snap-acting devices are always intermittentbleed. The number of throttling continuous bleed devices at each site was determined based on the manufacturer and model type ofthe devices observed. Since these two deyice types have distinctly different emission rates, the fraction ofintennittentbleed versus continuous bleed devices is 43

### TABLE 4-5- SUMMARY OFPRODUCTION SITE DATA Total Number of Number of Number of Count of Power Snap-Acting Throttling Continuous Site Devices Media Devices Devicesa Bleed Devicesb 136 G" 114 22 22 2 18 Gas 75 95 29 3 405 Gas 405 0 0 4 68 Gas 48 20 20 5 21 Gas 26 83 21 6 13 Gas 94 534 534 7 3 Gas 999 0 0 8 3 Gas 667 0 0 9 6 Gas 3 3 3 10 14 G" 0 14 0 II 76 Gas 0 76 76 12 600 G" 0 600 600 13 107 Air 71 36 25 14 69 Gas 42 27 20 15 13 Gas 8 5 0 16 Gas 0 0 17 3 G" 3 0 0 18 4 Air 3 0 19 46 Air 6 40 40 20 5 Gas 4 0 21 II Gas 5 42 42 22 31 Gas 0 31 31 TOTALS 4,204 2,574 1,630 1,463 FRACTION BY DEVICE TYPE Non Continuous Bleed Continuous Bleed 0.65 ± 43% 0.35 :t 43% Throttling devices can be either continuous orintermittent bleed. b Continuous bleed devices are asub-category ofthrottling devices.



### 44

### required to develop an emission factor. From the site data, the fraction ofcontinuous bleed devices is 0.35 

### ± 43%. 

### By difference, the fraction ofintermittent bleed pneumatic devices is 0.65 ±43%. MethaneComposition The percentage by volume ofmethane in produced natural gas was determined to be 78.8% 

### ± 5%. Details about this value are available in the report,Methane Emissions from theNatural Gas Industry, Volume 6: Ventedand Combustion Source Summary.26 

### Emission FactorCalculation The weighted emissionfactorperdevice was calculated for production facilities as follows: Weighted Emission

Factor (Fraction of Intermittent 

## = Intermittent Bleed Bleed X Emission Devices Factor Fraction of Continuous Bleed) M than 

## + Continuous Bleed X Emission X C e .

**~** Devices Factor omposltmn (I) 

### The site data 

### were used to estimate the fraction ofintermittentbleed versus continuous bleed devices: 65% 

### ± 43% intermittentbleed and 35% 

### ± 43% continuous bleed (Table 4-5). Table4-6 summarizes·the emission factor terms, where the emissionfactors for the individual device types (intermittent versus continuousbleed) were based onthe field measurements from the United States and Canada discussed previously. The final result is an average device methane emission factor of345 scfd/device 

### ± 40% (90% confidence interval), or 126,000scf/device annually.

45

### TABLE 4-6. PRODUCTION EMISSIONFACTOR CALCULATION DeviceType Intermittent Bleed Continuous Bleed 

### Fraction ofDeviceType 0.65 

### ± 43% 0.35 

### ± 43% 

### SelectedNatural Gas Emission Factor, scfd/device 323 

### ± 34% 654 

### ± 31% Methane Emission Factorfor Average Device = 345 

### ± 40% scfd/device


### 4.2 Transmission and

**Stora~e**

### Sewnent The transmission segment is composed ofpipelines, compressor stations, and storage stations. Very few pneumatic devices ofany type are associated with the pipelines. Withinthe storage and mainlinecompressor stations, most ofthe pneumaticdevices aregasactuated isolation valves and continuousbleed controllers. 

### 4.2.1 GeneralEmission FactorCharacteristics The type ofcontinuous bleed devices in the transmission segment are 

### essentially the same as those in

### the production segment. The difference is in the use ofthe devices. In the transmission segment, continuousbleedpneumaticdevices are used to regulate pressure oncompressors and are sized largerdue tothe higherpressures in transmission. Inproduction, smallerdevices areused.primarily to control the liquid level in separators. Since most ofthe same manufacturers are used, this section will not repeat the discussion from Section4.1.1. Isolationvalve actuators are predominately found inthe transmission segment. Isolation valve actuators emitgas wheneverthe valve is moved to eitherthe open orclosed position. Most compressor stations and storage stationshave many valves, 

### since valves are needed to make normal changes in pipeline and equipmentflow configurations, as well as to 46isolate and depressure equipment for maintenance or in case ofanemergency. Most sites use natural gas ratherthan compressed air to acnrate these large valves. A large volume of gas is needed to move multiple valves and this requires a large investment in equipment if compressed air is used. 

### 4.2.2 Transmission Emission Factors ManufacturerandSiteData The transmission emissionfactors were determined from information gathered during site visits and from manufacturers' data. The gas-operated devices used in the transmission segment were classified into three categories: continuous bleed devices, isolation valves with turbine operators, and isolation valves with displacement-type pneumatic/hydraulic operators. Devices operating onair were not included in the emission calculation. The nanrral gas emissionfactor for the continuous bleed devices used in transmission is based onmeasured emissions from these devices at transmission stations (measurementprocedure and data quality checks were discussed in Section4.1.2).10 As shown in Table 4-4, measured emissions from 23 devices ranged from 152 to 4,215 scfd of natural gas per device, with anaverage nanrral gas emission factor of 1,363 

### ± 29% scfd/device (497,583 scf/device annually). 

### Itshould be noted that intennittentbleed devices were not observed at transmission stations. Data on the following characteristics ofisolation valves were gathered at 16 transmission sites: 1. Basic device type (continuousbleed, turbine, or **pneumatic/hydraulic)~** 2. Manufacturer and model number;

47

### 3. Supply gas pressure, supply gas type (airproduces no methane emissions); and 4. Number offull stroke cycles peryear (each cycle consists oftwo valve movements: open and close).
All ofthe displacement isolation valves observed at the transmission sites were the pneumatic/hydraulic rotary vane type (Figures 3-11 and 3-12). The number ofactuation cycles peryear was based on site data. Themanufacturerprovided the volume ofgas used based on the discharge pressure. These values (shown in Table4-7) were combined to calculate the annual emission factor for each type ofdisplacement-operated isolation valve: 

### = Device Gas Usage X Discharge Pressure X Frequency X (scf/psia) (psia) (cycles/year) 2 Valve Movements Cycle 

### (2) Data provided by ShaferValve Operating Systems show that the gas usage volumes vary widely•.so data onthedemographics ofvarious sizes ofthe rotary-vane-operated valves were gathered from four stations.27

·28 

### This information is provided in Table 4-7. The total emissions from displacementdevices were determined for each site based on the size, actuationfrequency, and number ofeach type 

### ofdevice. An average annual emission factor for this type ofdevice was calculated to be 5,627 

### ± 112% scfnatural gas per device based on the average ofthe sitedata. Due to the diversity ofcompany practices for the few sites which provideddata, no direct relationship was establishedbetweendevice count and station size. Therefore, for this emission factor, an average ofthe 

### four site averages was used, as opposed to an average ofall ofthe individual device measurements. In effect, this weights the 

### measurement by site (transmission station) rather than by device count. Thus, a site with a disproportionately high number ofdevices is not weighted higher than the other stations.



### 48

### TABLE 4-7. PNEUMATIC/HYDRAULIC ROTARY VANE ISOLATIONVALVE OPERATORS Supply Annual

Gas Gas Usage Number Gas Usage, Pressure, Actuator perCycle, of Cycles! scf/ Site psig Size sef!psi Devices Year Device Type 935 6.5 X 3.5 0.0042 4 12 383 6.5 X 3.5 0.0042 8

9 X7 O.OI23 

## ,. _, ]] X 7 0.022 42 14.5 X ]4 0.0852 I I62 16.5 X 16 0.1183 3 674 !6.5 X 16 O.I I83 2 I2 5.393

18 X 8 0.0489 3 I 279 18 X 8 0.0489 1 12 1,115 18 X 12 0.0852 1 1 !62 25 X 16 0.318 5 12 36.242 25 X ]6 0.318 1 604 Total Emissions for Site 1 = 45,086 scf Site Weighted Average = 1,879 set/device± 54% 2 935 25 X 16 0.318 4 92 237,496 25 X 16 0.318 2 64 82,607 25 X 16 0.318 2 50 64,537 20 X 16 0.1981 6 5 147,649 12.5 X 12 0.0482 4 92 1,467 12 X 12 0.0482 3 5 587 15 X 8 0.0279 1 6 340 18 X 8 0.0489 6 4,962 18 X 8 0.0489 50 I98 20 X 16 0.1981 2 6,031 20 X 16 0.1981 15 14,473 26 X 36 0.7565 36 3,071 25 X 16 0.318 2 !9,361

9x7 0.0123 5 5 624 9x7 0.0123 2 2 IOO Total Emissions for Site 2 = 583,803 scf Site Weighted Average= 16,680 scf/device ± 37% Continued



### 49TABLE4-7. (CONTINUED) Supply Annual

Gas Gas Usage Number Gas Usage, Pressure, Actuator perCycle, of Cycles/ scf/ Site psig Size scf/psi Devices Year Device Type

3 1000 5.5 X 3.5 0.0035 7 15.2 • 705 6.5 X 8 0.008 14 15.2 3,224 9d 0.0123 8 15.2 2,833 JJ X J0 0.0318 15.2 915 12.5 X JQ 0.0279 15.2 803 ]2.5 X 12 0.0482 5 15.2 6,938 20 X 16 0.1981 3 15.2 17,!08 25 X]6 0.318 12 15.2 109,853 16.5 X !6 0.1183 9 15.2 30,650 ]4.5 X J4 0.0852 I 15.2 2,453 ]2.5 X ]2 0.0482 15.2 1,388 Total Emissions for Site 3 = 176,870 scf Site Weighted Average = 2,853 scf/device ± 27% 4 950 !2.5 X J2 0.0482 3 12 3,348 6.5 X 3.5 0.0042 I 12 97 II X 10 0.0318 I 12 736 16 wkm 0.072 2 12 3,507 Total Emissions for Site 4 = 7,688 scf Site Weighted Average= 1,098 scf/device ± 39% AVERAGE DISPLACEMENT DEVICE EMISSION FACTOR = 5,627 ± 112% scf/device

50

### Discharge volumes for the turbine-operated isolation valves depend on the supply gas pressure, the number offuH stroke cycles each year (where each cycle consists oftwo valve movements), and the duration that the turbine operates to complete a valve movement, as follows:

EFTurt>illeOptn.rared Isolation V.olve 

### = Device Gas Usage (scf/min) X Operating Duration (min/operation) X Frequency (2 Valve Movements) (cycles/year)x Cycle (3) 

### Information on the approximate turbine motor gas consumption for a given gas pressure was provided by Limitorque Corporation. 13 

### The manufacturer also provided a typical value for the time required to open or close a valve. Two sites furnished the supply gas pressure, the number ofoperations peryear, and the length oftime required to 

### open orclose the valve. This information is shown in Table 4-8. Average ortypical values (based on information provided by sites or manufacturers) were used for other sites with turbine operators. As with 

### the rotary vane isolationvalve emission factor, the emission factor for turbine operated isolation valves was also based on an average ofthe site data. The resulting annual emission factor for turbine operators is 67,599 

### ± 276% scf/device. Methane Composition 

### The methane compositionfor the transmission and storage segment was estimated to be 93.4% 

### ± 1.5%.26 Emission Factor Calculation 

### Site data were used to estimate a relative fraction ofeach type ofdevice found in the transmission segment. Data on turbine and displacement isolation valves were collected from 16 sites. Forcontinuous bleed devices, data for an additional 38 sites were available from a large transmission company participating in this project. Based on the average number of devices at each site, the total numberofdevices for a typical transmission station and the 

### 51

### TABLE 4-8- MANUFACTURER DATA FORTURBINE OPERATED ISOLATION VALVES Annual Supply Natural

Ga• Ga• Time/ Ga. Pressure, Consumption, Operation, Gas Usage, Cycles/ Emissions, Site psig scfm 

### •ec scf/Operation Year scf/device 900·970 500-520 30 255 II 3,825 120 1020 2 800 470 180 1410 75 211,500 3 800 470 90 705 29 40,890 (Typical Values) 4 800 470 90 705 29 40,890 (Typical Values) 5 800 470 90 705 29 40,890 (Typical Values) AVERAGE ANNUAL TURBINE DEVICE EMISSION FACTOR, scfnatural 67,599 ± 276% gasfdevice
fraction ofeach type ofdevice were determined. Tables 4-9 and 4-10 summarize the site information for each device type. The annual transmission segment emission factor (scf/site) was determined from the following equation: 

### EF

EF

EF FractiOlloontinuous 

# + EFturbine bleed opentors X Fractionturbine operators X FractiOildispiacement) X 

### % methane operators ( 497,584 scf/device x 0.32 cont. bleed devices/total 

### + 67,599 scf/device x 0.16 turbine devices/total 

### + 5,627 scf/device x 0.52 displacement devices/total) x 0.934 mol methane/mol gas 162,197 

### ±44% scf/device 

### 52 

### (4)

### TABLE 4-9. TRANSMISSIOK DEVICE COUNTS- TURBINE AND DISPLACEMENT DEVICES
Site

2 

### 3 4 5 6 7 8 9 10 II 12 13 14 15 16 Average Nwnber

ofDevices/Site Fraction Device/Site Annual Natural Gas Emission Factor scf/device Turbine Devices/Site 3 16 12 35 44 0 0 0 0 0 0 0 0 0 0 0 6.25 

### ±94% 0.156

### ±94% 67,599 

### ±276%

53 Rotary· Vane Displacement

Devices/Site 26 62 34 0 0 II 17 35 69 6 18 4 50 2 0 0 20.9 

### ±48% 0.522 

### ±48% 5,627

### ± 112%

### TABLE 4-10. TRANSMISSION DEVICE COUNTS

- CONTINUOUS BLEED Site Continuous Bleed Devices/Site Site Continuous Bleed Devices/Site 39 28 II 2 :6 29 II 3 4 30 32 4 3 3J 9 5 4 32 12 6 33 4 7 34 21 8 4 35 12 9 6 36 3 10 2 37 15 II 2 38 3 12 127 39 II 13 18 40 10 14 4 41 44 15 22 42 3 16 3 43 3 17 4 44 9 18 4 45 12 19 4 46 4 20 47 26 21 48 2 22 49 7 23 15 50 II 24 92 51 II 25 3 52 15 26 6 53 6 27 54 Average Number Devices/Site 12.9 ± 69% Fraction of Device/Site 0.32 ± 69% Annual Natural Gas Emission Factor, scf/device 497,583 ± 29%

54

### 4.3 Gas Processing Seement 

### The gas processing segment (gas plants) uses compressed air to power the majority ofpneumatic devices within the plant. Ofthe nine gas plants visited for this study, only one used natural gas-powered, continuous bleed devices in the plant. Approximately one-halfofthe plants visited had natural gas-driven pneumatic controllers for the isolation valves on the main pipeline emergency shut-down system for the plant or for isolation valves used for maintenance work on specific sections ofthe plant. All ofthe other sites used compressed air to power their pneumatic continuous bleed devices and isolation valves. Unlike the production and transmission industry segments, a mix of pneumatic devices was not observed at each gas processing site. Instead, the gas plants visited generally used only one type ofI?-atural gas powered pneumatic device throughout the plant. Stratification by device type could not be determined, so emissions were calculated on a site basis rather than a device type basis. Manufacturers' and Site Data The same type ofdevices used in the transmission segment are also commonly used in the gas processing segment
- continuous bleed throttling devices, displacement-operated isolation valves, and turbine-operated isolation valves. Forthe sites where specific information was provided, emission calculations were based on that information. However, for some sites, the information provided included little more than the type ofactuator, supply gas pressure, and an estimate ofthe number ofoperations. In these cases, average values from the transmission segment were used to complete the calculations. The site data with the emission estimates are shown in Table 4-11. The technique used to develop emission factors for each site is discussed separately.

55

### TABLE 4-11. GAS PROCESSING SITE EMISSION ESTIMATES FOR NATURAL GAS 

### Number Annual Natural of 

### Operations/ Displacement/ 

### Gas Emissions Site Device Type 

### Devices Year Device, scf 

### scf/Site

I 

### Continuous 2 Continuous 

### 497,584 995,168 

### ± 29% Bleed (Fisher) 2 

### Isolation 3 12 214,675 644,025 

### ± 29% (Fisher) 3 

### Air 4 

### Isolation 25 I 

### 780 19,500 

### ± 112% (Turbine) 

### 5 Isolation 7 12 48 1,206 

### ± 49%

**~** Piston Type 

### 18 I 

## "' (RotaryVane) 6 

### Isolation I I 660 44,ll5 

### ± 68% (Turbine & 

### 16 12 2,716 

### Pneumatic/ Hydraulic-type Rotary Vane) 7 

### Air 8 Air 

### 9 

### Air Total 1,704Mscf

### ± 21% Average (forgas sites) 

### 341 Mscfigas site 

### ± 103%

# • Site I: Continuous bleed devices, such as those used in the transmission segment, were observed at this site. Since the application ofthese devices 1s similar to the transmission segment, the annual emission factor of497,584 scf per device (based on I,363 scfd/device from Table 4-4) was used. Site 2: Fisher devices were used to operate isolation valves at this site. Information on the bleed rate for the specific device type was provided by the site. Site 4: Manufacturer's data from Limitorque were used to estimate emissions for the turbine operators observed at this site. 13 The plant provided the supply gas pressure of400 psig, and a typical actuation time of 1.5 minutes was used (based on manufacturer data)
. Site 5: Piston-type isolation valve operators were found at only one site; information for the specific device types were provided by Pantex, the manufacturer.6 Table 4-12 lists the manufacturer's data for the model types identified at this site. The weighted average annual emission factor for this type ofdevice was determined to be 48 scf/device 

### ±49%. Site 6: For the pneumatic/hydraulic-type rotary vane devices observed at this site, the emission factor was based on the average volume ofnatural gas released per actuation for the devices presented in Table 4-7. Manufacturer's data from Limitorque, based on a supply gas pressure of350 psig, were used to estimate the emissions for the turbine operator at this site. Methane Composition The percentage ofmethane in gas 

### used in gas processing plants was determined to be 87.0% 

### ± 5%. Details about this value are available in the GRJ/EPA report, Methane Emissionsfrom the Natural Gas Industry, Volume 6: Vented and Combustion Source Summary.26 57

### TABLE 4-12. GAS USE INFORMATION FOR PANTEX DEVICES (PISTON DISPLACEMENT ISOLATION DEVICES) Piston Stroke 

### Gas Annual Gas 

### No. Diameter 

### Length Usage Consumptiona Devices 

### (in.) (in.) (acf/stroke) (scf/device) 6 8.0 20 0.5818 512 2 3.0 4 0.0164 4.8 3.5 4 0.0222 3.3 2 2.0 4 0.0073 2.1 5 8.0 16 0.4654 341 2.5 8 0.0227 3.3 6.0 16 0.2618 38.4. 2 6.0 12 0.1964 57.6 

### Annual Site Gas Conswnption, scf 965 Weighted Annual Average per Device, scf 48.1

a Gas consumption calculated based on supply pressure of250psig, an average of



### 4.Ioperations peryear, and two strokes (open and close) peroperation.

58equation:

where: Emission Factor Calculation The gas processing emission factor was calculated according to the following

EF= K X

K

n n 

# L Annual Site Emissions, scf Natural Gas i=I x % methane n

fraction ofsites that use natural gas rather than air (0.556 

### ± 59%) number ofsites operating devices with natural gas (5)

Assuming that the sites surveyed are representative ofthe United States, the average emission rate for sites using natural gas was adjusted based onthe ratio ofsites using gas-operated devices to the total number ofsites surveyed. The annual gas processing methane emission factor of 165 Mscf/site ± 133% was calculated as shown:

4.4 EF EF = 0.556 ± 59% gas sites/total sites surveyed x 341 ± 103% Mscf/gas site x 0.87 

### ±5% mol methane/mol gas 165 

### ± 133% Mscf/site Distribution Segment The pneumatic devices in the distribution segment primarily consist of pressure reduction throttling valves at meter and pressure regulation (M&R) stations. The actuators and controllers for these valves are generally gas powered, but may or may not bleed gas to the atmosphere, depending on their design. Emissions from these devices were

59

### measured as part ofthe tracer campaign for M&R stations and included in the M&R station emission rates. 1 

### Distribution pneumatic emissions are therefore excluded from this report. Isolation valve actuators at distribution M&R stations are usually manually or motor-operated. There were so few pneumatic operators on isolation valves that this emission source is considered negligible.



### 60

### 5.0 PNEUMATIC DEVICE ACTIVITY FACTORS Pneumatic device activity factors are discussed in detail in Volume 5 on activity factors.29 The techniques used to develop pneumatic device activity factors for the various industry segments are summarized in this section. For each industry segment, the activity factor corresponds to the emission factor units presented in Section 4. That is, a count ofpneumatic devices is used for the production and transmission segments, while the 

### number ofgas plants is used for the gas processing segment. 5.1 Production Segment The total number ofpneumatic devices in the U.S. production segment was determined from regionalized site data. The number ofpneumatic devices at each site were weighted based on the number ofgas wells and the marketed gas production at each site. The site data were extrapolated by the nwn!:ler ofgas wells and the marketed gas production within each region. In production, the resulting count ofpneumatic devices nationally is 249,000 

### ±48%. 5.2 Gas Processing Segment The activity factor for gas processing is based onthe number ofgas processing plants reported annually bythe 

### Oil and Gas Journal. For the base year 1992, the U.S. activity factor for gas processing is 726 gas plants.30 A confidence bound of±2% was assigned based on engineeringjudgement. 

### 5.3 Transmission and Storage Segment The number ofnatural gas-operated pneumatic devices in the transmission and storage segment was calculated based on the average number ofdevices per station

61multiplied by the total number oftransmission and storage stations nationally using the following equation: AF = Average Number ofDevices X Number of Stations Station (6) The average number of pneumatic devices per station is the sum ofthe average number of turbine devices per site, the average number ofrotary vane displacement devices per site, and the average number ofcontinuous bleed devices per site. Using the numbers shown in Tables 4-10 and 4-11, the average number ofpneumatic devices per site is 40 ± 37%. Therefore, the pneumatic device activity factor for transmission stations is: AF = (6.25 

### ± 94% turbine devices/site 

### + 20.9 

### ±48% rotary vane devices/site 

### + 12.9 

### ± 69% continuous bleed devices/site) x 2,I75 

### ± 8% stations AF = (40 

### ± 37% devices/station) x (2,175 ± 8% stations) AF = 87,206 

### ± 38% pneumatic devices The activity factor includes only pneumatic devices operated by natural gas. Mechanical, electrical, and air-operated devices were excluded from the site counts and are therefore excluded from the national activity factor.



### 626.0 NATIONAL EMISSION RATE National emission rates from pneumatic devices for each industry segment were calculated by multiplying the emission factor by the activity factor: National Emission Rate = Emission Factor x Activity Factor Table 6-1 presents the final results ofthe emission rate calculations for each industry segment. TABLE 6-1. EMISSION RATE RESULTS Methane Emission Annual Emission Factor Activity Factor Rate Production 125,925 ± 40% 249,111 ±48% 31.4 ± 65% Bscf scf/device devices Gas Processing 165 ± 133% Mscf/site 726 ± 2% sites 0.12 ± 133% Bscf Transmission 162,197 ± 44% 87,206 ±3SO/o 14.1 ± 60% Bscf scf/device devices 

### Based onthese results, pneumatic devices contribute a total of45.6 

### ± 48% Bscfofmethane for 1992.

63 (7)

### 7.0 REFERENCES 1. 

### Campbell. L.M. and B.E. Stapper. Methane Emissionsfrom theNatural Gas 

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**R~search** 

### Institute and U.S. Environmental Protection Agency.June 1996. 

### 2. Myers, D.B. and M.R. Harrison. 

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### 5thEdition. McGraw-Hill, New York, NY, 1973. 

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### Houston, TX, 1987. 9. Fisher Controls International, Inc. 4150Kand4160KSeries Pressure Controllers andTransmitters, 

### Bulletin 34:3:4150K. Marshalltown, lA, 1992. 10. Controller survey data provided by Tenneco Gas Transportation, 1994 and 

### Chevron, 1995.



### 6411.

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16. 17. 18. 19.

20. 21.
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### Personal correspondence 

### with Brian Ross ofClearstone Engineering, Alberta, Canada, October 16, 1995. 

### Personal correspondence with Bob Finley ofBristol Babcock Inc., Watertown, CT, October 3, 1995. 

### Personal correspondence with Clark Crownover ofPuffer Sweiven, Inc., Stafford, TX, October6, 1995. 

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### Dover Corporation. Norriseal Controls Series 1000LiquidLevel Control, 

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28.

29.
30. 

### Invalco. CTSeries FlextubeDisplacerTypeLevel Controller, 

### CT Series, Issue 1, Page IVC-801-A3,Tulsa, OK, April 30, 1990. 

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### July 12, 1993, p. 55.

66

### APPENDIX A SourceSheets

A-ISOURCES: COMPONENTS: OPERATINGMODE: EMISSIONTYPE: ANNUAL EMISSIONS: BACKGROUND: P-4 PRODUCTION SOURCE SHEET Various Equipment (wells, heaters, separators, dehydrators, compressors) Pneumatic Devices Nanna! Operation Unsteady, Vented 31.4Bscf± 65% Most ofthe pneumaticdevices in the industry are valve actuators and controllers that use natural gas pressure as the force for valve movement. There is a largepopulationofpneumaticdevices throughout the gas industry. Gas from the valve actuator is vented tothe atmosphere duringevery valve stroke, and gas may be continuously bled from the valve controllerpilot as well. EMISSIONFACTOR: 125,925scfperaverage device ± 40% (This wasadjustedfortheproductionmethanefraction ofnaturalgasat78.8mol%.) Pneumaticdevices (valvecontrollers) linkedtocontrol valves are the largest source ofpneumatic emissions in the productionsegment. There are twotypes ofdevices withdistinctbleed modes: intermittent and continuous. Intermittentbleed devices emit methane tothe atmosphere only when thecontrol valve actuates; when the device is not moving the bleed rate is zero. Continuousbleed devices emit methane both when the valveactuates and when thedevice is not moving. Anemission rate for a generic pneumatic devicecombines the bleed rates ofthe two types ofdevices, weightedby the populationofthedevice types as follows:

where: EF•'11· p,.um. dcYx:e

Fraction''""""'lit"' Fraction

### com•""""' % Methane =

= = = (Fraction ;,..,,,..,_ X EF ,,.,.,;,,nc 

### + Fraction""""""""' x EF""""""""") 

### x %methane

0.65 ± 43% 0.35 

### ± 43% 78.8mol % ± 5%
Emissions for intermittentand continuousbleed deviceswere based on measured dataprovided by a Canadian study and U.S. field measurements from a se?arate contractor'sprogram. Theaverage measured emissions for intermittent and continuous bleeddevices are 323 

### ± 34% and 654 

### ± 31% scfd/device, respectively. The fraction ofeach type ofdevice was determined from sitevisits. Therefore the average annual emission factor for ageneric pneumatic device is:
= 125,925 

### ±40% scf/device EF DATA SOURCES: l. Methane Emissionsfrom theNatural Gas Industry, Volume 12: PneumaticDevices (I) establishes the importantem:ssion-affectingcharacteristics.
A-22. Site visit device countsestablish the fraction ofcontinuousbleed versus intenniuembleed devices for multiple sites. 3. The Canadian Producers Association (CPA) determined an average emission factor per device based on 19 measurements. 4. An independent contractorprovided 18 measurements ofpneumatic devices in onshore and offshore productionservices.
EF PRECISION: Basis: EF accuracy is based on errorpropagation from the spread ofsite device countsand measured emission rates. ACTIVITYFACTOR: 249,111 pneumaticcontrollers± 48% The average count ofdevices per equipment type wasdetermined from multiple site visits. The ratios for the numberofdevices per gas well and the numberofdevices per marketed gas productionwere compiled by region. Theregional values were summed togivenational device countsbasedon well counts and marketed.gas production. These values were averaged to givethe final national device count of249,11I. AF DATA SOURCES: I. MethaneEmissionsfrom theNaJuralGasIndustry, Volume 5:ActivityFactors (2) establishes the methodology for e:mapolatingthe sitedata to anational count. 2. Site visitdevice counts, well counts,and productionrates establish the number ofdevices per well and the numberofdevices per gas production. 3. Total regional gas well counts and 1992 marketed gas productionrates are from A.G.A. Gas Facts (3). 4. The oil wells that market gas were calculated by this report and World Oil (4). Total oil wells for 1992are reponed as 602,197by the Oil& GasJournal (5). The activeoil wells that market gas are determined by multiplyingthetotal national active wells by the fraction that market gas. The fraction is determined from a Texas Railroad Commission database (6) onoil leases and gas dispositionfrom thoseleases; an analysis that shows the percent ofoil leases that market the associated gas in Texas is 34.7%. AF PRECISION' Basis: 1. 2. The accuracy for the devices per well and devices per gas productionrate are calculated from the spread ofsitedatacollected for each region (a total of36 sites). The accuracy for wellsthat market gas are based onthe spread ofdata from the Texas Railroad Commissiondatabase. ANNUAL METHANEEMISSIONS' 31.4Bscf± 65 % The national annual emissions were determined by multiplying an emission factor for an average pneumatic device by the populationofdevices in theproductionsegment. 125,925 scf x 249,111 devices = 31 Bscf
A-3REFERENCES 1. Shires,T.M. and M.R.Harrison. MethaneEmissionsfrom theNatural GasIndustl)', Volume 12: PneumaticDevices. Final Report, GRI-94/0257.29and EPA-600/R-96-0801, Gas Research Instituteand U.S. Environmental Protection Agency, June 1996. 2. Stapper, B.E. Methane Emissionsfrom theNatural GasIndustry, Volume 5: Activity Factors. Final Report, GRI-94/0257.22and EPA-600/R-96-0SOe, Gas Research Instituteand U.S. Environmental Protection Agency, June 1996. 3. American Gas Association. Gas Facts: 1993 Data, Arlington, VA, 1994. 4. GulfCoast PublishingCompany, World Oil, Annual Forecast/Review, Vol. 214, No. 2, February !993. 5. OilandGasJournal. 1992 WorldwideGas Processing Survey Database, 1993. 6. Texas Railroad Commission, P-1, P-2 Tapes, Radian files. Austin, TX, 1989.

A-4T-4 TRANSMISSION AND STORAGE SOURCE SHEET SOURCES' OPERATING MODE: EMISSION TYPE: COMPONENTS: ANNUAL EMISSIONS: BACKGROUND' Various Equipment (vessels, compressors, piping) Nonnal Operation Unsteady, Vented Pneumatic Devices 14.1 Bscf± 60% The transmission segment is comprised ofcompressor stations, pipelines, and storage stations. There are essentially no pneumatic devices associated with the pipelines. Within the storage and compressor stations, most ofthe pneumatics are gas-actuated isolation valves, and there are a few continuous bleed controllers. Meter-only stations do not have venting pneumatics. Meter and regulation (M&R) stations do have regulating pneumatic controllers (the pressure regulator valves), but all ofthe M&R station pneumatic emissions are counted in the fugitive calculation for M&R stations and so are not included in this sheet. The continuous bleed controllers in transmission compressor stations are used for liquid level control in filterseparators and pressure reduction. The higher pressures and large pipe diameters associated with transmission operations require larger actuators and valves "than typically found in production, resulting in larger emissions than similar devices in production. Within the storage and mainline compressor stations, most ofthe pneumatic devices are gas-actuated isolation valves. These valves block the flow to orfrom apipeline and can isolate the facility for maintenance work or in the case ofan emergency. Therefore, the isolation valves are actuated infrequently and their emissions are intermittent. EMISSION FACTOR' 162,197 scfldevice 

### ± 44% (This was adjusted for the transmission methane fraction ofnatural gas at 93.4 mol%.) The average pneumatic device emission factor was determined from a compilation ofinformation from several sites. Counts ofdevices per site were taken during Radian site visits. The devices were classified into three categories: continuous bleed valves, isolation valves with turbine operators, and isolation valves with displacement operators. The emission factor was detennined based on the following equation: EF pn..,matie devo= ( EF """' bl....d val>os X Fraction """' bi...O valv.. + EF lll.t>ono opm.to<> X Fraction IU<bon. opm.<<m + EF dospl•cern.,, open."'" x Fraction d..pl•eem.., opm.toB ) x % methane Listed below are the average fraction ofdevices for each ofthe three valve categories: Fraction """' 01.,.. valves Fraction <Urt>mo opm.ton Fraction

**d>~plocem**.. , operators 0.32 ± 69% 0.16 ± 94% 0.52 ±48% Emissions from continuous bleed pneumatics in the transmission segment were measured by an independent contractor. The average emission factor, based on 23 measurements, is 1,363 scfd/device ± 29% (497,584 scf/device).



### A-5For the isolation valves with turbine operators, the emission factor depends on the gas usage for a given supply gas pressure, the time required tocomplete one movement ofthe valve, and the number ofoperations per year. The annual emission factor is then;

E F '"tbm< opONitors = Gas Usage (scf/min) x Operating Duration (min/operation) x 2 (operations/cycle) x Frequency (cycles/year)

= 67,599 ±276% scf/device The equation for isolation valves with displacement operators is similar:

EF DATA SOURCES: = Gas Usage (scf/psia) x Supply Pressure (psia) x 2 (operations/cycle) x Frequency (cycles/year)

= 5,627 ± 1!2% scf/device

1. MethaneEmissionsfrom the Natural Gas Industry, Volume 12: Pneumatic Devices (I) establishes the important **emi~sion·affecting** characteristics oftransmission pneumatic devices. 2. Device counts from 16 compressor and storage stations establish the fraction ofturbine valve operators, and displacement valve operators. Counts from a total of54 stations were used to establish the fraction ofcontinuous bleed devices. 3. The emission factor for the continuous bleed valves was based on 23 field measurements. 4. Gas usages for the turbine valve operators were provided by Limitorque. Operating duration and frequency were estimated based on information from two transmission stations. 5. Gas usages for the displacement valve operators were provided by Shafer Valve Operating Systems. Supply pressure and frequency ofoperation were estimated based on information from four transmission stations. EF ACCURACY, Basis: 1. EF accuracy is based on error propagation from the combination ofsite information and measured data. 2 Itwas assumed that the manufacturers' data are completely accurate. ACTIVITY FACTORS: 87,206 pneumatic devices 

### ± 38% The number ofgas operated pneumatic devices in the transmission and storage segment was calculated based on the average number ofdevices per station and multiplied by the total number oftransmission and storage stations nationally. The average number ofdevices per site was determined to be 40 ± 37%. The total count oftransmission compression facilities is 2,175, based on 1,700 compressor stations, 386 UG storage stations, and 89 LNG storage stations. AF DATA SOURCES: I. The number oftransmission compressor stations was compiled from 1992 Fossil Energy Commission Fonn No. 2: Annual Report ofMajor Natural Gas Companies (2).
A-62. The number ofunderground storage facilities is taken directly from A.G.A. Gas Facts: "Number ofPools, Wells, Compressor Stations, and Horsepower in Underground Storage Fields." Data from base year 1992 were used (3). 3. The number ofliquefied natural gas storage facilities was summed from A.G.A. Gas Facts, "Liquified Natural Gas Storage Operations in the U.S. as ofDecember 31, 1987 (4)." The table lists 54 complete plants, 32 satellite plants, and 3import terminals for a total of89 facilities. 4. The number ofdevices per site is based on the total number ofdevices observed during site visits. AF ACCURACY: 38% Basis: !.

2. Extremely tight confidence limits are expected due to the well documented and reviewed numbers published in A.G.A. Gas Facts and FERC forms. A 10% confidence bound was assigned to the number ofcompressor stations and a 5% confidence bound was assigned to the number ofstorage stations. The confidence bound on the number ofdevices per station was determined based on the spread ofsite data. ANNUAL METHANE EMISSIONS: 14.1 Bscf :!: 60 % The annual emissions were determined by multiplying an emission factor per device (corrected for the methane composition) by the population ofpneumatic devices in the transmission segment. 162,197 scf/device x87,206 devices'=' 14.1 Bscf REFERENCES l. Shires, T.M. and M.R. Harrison. Methane Emissionsfrom the Natural Gas industry, Volume 12: Pneumatic Devices. Final Report, GRl-94/0257.29 and EPA-600/R-96-0801, Gas Research Institute and U.S. Environmental Protection Agency, June 1996. 2. Department ofEnergy. FERCForm No. 2: AnnualReport of Major Natural Gas Companies. OMB No. 1902-0028, Department ofEnergy Federal Energy Regulatory Commission, Washington, DC, December !994. 3. American Gas Association. Gas Facts:. 1993 Data, Arlington, VA, 1994. 4. American Gas Association. Gas Facts:. 1991 Data, Arlington, VA, 1992.

A-7SOURCES' COMPONENTS' OPERA T!NG MODE' EMISSION TYPE' ANNUAL EMISSIONS: BACKGROUND: GP-6 GAS PROCESSING SOURCE SHEET Various Equipment (vessels, compressors, piping) Pneumatic Devices Normal Operation Unsteady, Vented 0.! Bscf± 133% The gas processing segment uses compressed airto power the majority ofthe pneumatic devices within the plant, although some devices may be powered by natural gas. Many plants use gas driven pneumatic controllers on isolation valves for emergency shut·down or maintenance work. The same type ofdevices used in the transmission segment are also commonly used in the gas processing segment
- continuous bleed throttling/regulating valves, displacement operators, and turbine operators. EMISSION FACTOR: 165 Mscfper average plant± 133% (This was adjusted for thegas processing methane fraction ofnatural gas at 87 mol%.) The average device gas emission factor was detennined from a combination ofvendor information on device emission rates and device counts from several sites. The average emission factor was calculated using the following equation:

EFavg.pneum.dcv1ce = K X

K n n 

# L (Annual Site Emissions, scfNatural Gas) i

### =I n x %Methane

fraction ofsites that use natural gas rather than air(0.56 ± 59%) number ofsites operating with natural gas Each term in this equation was detennined from site specific information. The summation ofthe site specific data was then adjusted based on the number ofsites with gas operated devices versus the total number of sites surveyed. The site results are shown in the following table.

A-8Annual Number Operations/ DisplacemenU DisplacemenU Site Device Type ofDevices Year Device, scf Site, scf Throttling (Fisher) 2 Continuous 497,584 995,168 ±29% 2 Isolation (Fisher) 3 12 214,675 644,025 ±2go/n 3 Air 4 5
6 7 8 9 TOTAL Isolation (Turbine) Isolation (Rotary Vane) Isolation (Turbine & Rotary Vane) Air Air Air 25 7 18 I 16 12 I 12 780 48 3,376 19,500 ± 112% 1,206 ±49% 44,115 ± 68%

1,704 Mscf± 21% Average (for gas sites) 341 Mscf± 103% EF DATA SOURCES' I. Methane Emissionsfrom theNatural Gas Industry, Volume 12: Pneumatic Devices establishes the important emission-affecting characteristics. 2. Site visit device counts establish the number ofcontinuous bleed devices, turbine operators, and displacement operators for each site. 3. The emission factor for continuous bleed devices was estimated using data provided by one site and measurements for transmission pneumatic devices. 4. Gas usages for the displacement operators were provided by Pantex Valve Actuators and Systems and Shafer Valve Operating Systems. The number ofdevices, supply gas pressure, and operating frequency were based on site information. 5. Gas usages for the turbine operators were provided by Limitorque Corp. Operating duration, frequency, and supply gas pressure were based on site information. EF ACCURACY' Basis: I. 2. EF accuracy is based on errorpropagation from the spread ofdata for the nine sites visited. Itwas assumed that the manufacturers' data are completely accurate. ACTIVITY FACTOR: 726 gas processing plants 

### ± 2% The activity factor for the gas processing segment was taken from published information from the year 1992.

A-9AF DATA SOURCES: I. The number ofgas processing plants was taken from the OilandGas Journal (2). AF PRECISION: Basis: I. AF accuracy is based on engineeringjudgement. ANNUAL METHANE EMISSIONS: 0.12 Bscf± 133% The annual emissions were detennined by multiplying an average site emission factor (adjusted for the methane composition) bythe total number ofgas processing sites. 165 Mscf/site x 726 sites "'" 0.12 Bscf REFERENCES I. Shires, T.M. and M.R. Harrison. Methane Emissionsfrom the Natural Gas Industry. Volume !2: Pneumatic Devices. Final Report, GRJ-94/0257.29 and EPA-600/R-96-0801, Gas Research Institute and U.S. Environmental Protection Agency, June 1996. 2. Bell, L. "Worldwide Gas Processing," OilandGasJournal, July 12, 1993, p. 55.

A-10-------- --- ------ --

---- ---------- - ---

Box 201088 TECHNICAL fetld[R/.Jr.UCfWm Off

Texas 78720-1088 EPA, 

### Office of ResearchandDevelopment .Air Pollution Prevention and Control Division 

### 1-Wteseru,chTriangle Park, NC 277ll is IL 60631. 

## ' '

EPA/600/13 West Bryn report re program quantify methane (CH4) emissions from the U.S. natural gas industry for the base The objective was to determine CH4 emissions from the wellhead and ending 

### I:J•ow•m;tr·e,rm at the customer's meter. The accuracy goal was to determine these .,rni,ssi,on.s within+/-0.5% ofnatural gas production for a 90% confidence interval. F 1992 base year. total CH4 emissions for the U.S. natural gas industry was 314



### 105 Bscf 

### (6.04 

### +/- 2.01 Tg). This is equivalent to 

### !.4

### +/- 0.5% of gross natural production, and reflects neither emissions reductions (per the voluntary Amerias Association/EPA Star Program) nor incremental increases (due to increased usage) since 1992. Results from this program were used to compare greenhouse emissions from the fuel cycle for natural gas. oil, and coal using the global warfrr•ing potentials (GWPs) recently published by the Intergovernmental Panel on Climate Char.tge (IPCC). ThP. analysis showed that natural gas contributes less to potential jgJlot>al warming than coal or oil. which s:1pports the fuel switching strategy suggested thelPCC and others. In addition. study results**ar~** being used by the natur-al gas

Stationary Sources Global Warming



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. IIyour**addr~SI** is**incorr~ct,** pl,esl!changeon th• above label tearoff: andreturn to the above llddrus. IIyoudo notduire to continue recl!iving thttSII technical reports, CHECKHER£0; tear offlabel, andretum it to the above address, 

## Publication No. EPA- 600 iR-96-0801



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