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 and building 2 science knowledge base necessary to manage our ecological resources wisely, understand how pollutants affect our health, and prevent or reduce environmental risks in the future. 

'The National Risk Management Research Laboratory is the Agency's center for 

investigation of technological and management approaches for reducing risks 

from threats to human health and the environment. The focus of the Laboratory's 

research program is on methods for the prevention and control of pOllution to air. 

land. water. and subsurface resources; protection of water quality in public water 

systems; remediation of contaminated sites and groundwater: and prevention and 

control of indoor air pollution. The goal of this research effort is to catalyze 

development and implementation of innovative. cost-effective enVironmental 

technologies; develop scientific and engineering information needed by EPA to 

support regulatory and policy decisions; and provide technical support and infOrmation transfer to ensure effective implementation of environmental regulations 

and strategies. 

This publication has been produced as part of the Laboratory's strategic longterm research plan. It is published and made available by EPA 1 s Office of Research and Development to assist the user commnnity and to link researchers 

with their clients. 

E. Timothy Oppelt. Director 

National Risk Management Research Laboratory 

EPA REVIEW NOTICE 

This report has been peer and administratively reviewed by the U.S. Environmental 

Protection Agency, and approved for publication. Mention of trade names or 

commercial products does not constitute endorsement or recommendation for use. 

This document is available to the public through the National Jechnicallnformation 

Service, Springfield, Virginia 22161. 
(J.-;t.L - 9'!-j 112 S7. ::Z '} 

EPA -600 /R- S6-G80! 

June 1996 

METHANE EMISSIONS 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 Project Manager: Robert A. Lott 

GAS RESEARCH INSTITUTE 

Contract No. 5091-251-2171 

8600 West Bryn Mawr Ave. 

Chicago. IL 60631 

and 

EPA Project Manager: David A. Kirchgessner 

U.S. ENVIRONMENTAL PROTECTION 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 

of work sponsored by Gas Research Institute (GRI) and the U.S. Environmental Protection 

Agency (EPA). Neither EPA, GRJ, members of GRJ, nor any person acting on behalf of 

either: 

a. Makes any warranty or representation, express or implied, with respect to the 

accuracy, completeness, or usefulness of the information contained in this report, or 

that the use of any apparatus, method, or process 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, or process disclosed in this report. 

NOTE: EPA's Office of Research and Development quality assurance/quality control 

(QA/QC) requirements are applicable to some of the 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 of experts listed in Appendix D of Volume 2. 

11 
Title 

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 of methane 

emissions within the gas industry. 

The increased use of natural gas has been suggested as a strategy for 

reducing the potential for global warming. During combustion, natural 

gas generates less carbon dioxide (C02) per unit of energy produced than 

either coal or oil. On the basis of the amount of C02 emitted, the 

potential for global warming could be reduced by substituting natural gas 

for coal or oil. However, since natural gas is primarily methane, a potent 

greenhouse gas, losses of natural gas during production, processing, 

transmission, and distribution could reduce the inherent advantage of its 

lower C02 emissions. 

To investigate this, Gas Research Institute (GRI) and the U.S. 

Environmental Protection Agency's Office of Research and Development 

(EPA/ORD) cofunded a major study to quantify methane emissions from 

U.S. natural gas operations for the 1992 base year. The results of this 

study can be used to construct global methane budgets and to determine 

the relative impact on global warming of natural 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 ± I 05 Bscf for the I 992 base 

year. This is about 1.4 ± 0.5% of gross natural gas production. This 

study also showed that the percentage of methane emitted for an 

incremental increase in natural gas sales would be significantly lower 

than the baseline case. 

The program reached its accuracy goal and provides an accurate estimate 

of methane emissions that can be used to construct U.S. methane 

inventories and analyze fuel switching strategies. 

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 of the 

emission factor and activity factor. 

The natural gas industry has two primary types of pneumatic devices that 

discharge methane: I) control valves that regulate flow, and 2) gasactuated block valves. Because each segment of the industry follows its 

own specific practices regarding "typical" pneumatic device installations, 

emission factors were developed based on the types of devices 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 of each type of pneumatic 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 of devices to develop an annual emission factor for a generic 

pnewnatic device in each industry segment. 

The development of activity 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 

of devices observed during site visits. The national emissions for each 

industry segment were then based on the product of the emission factor 

for a generic pneumatic device and the activity factor. 

For the 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 

IV 
the 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 of Air 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I 0 

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 

vi 
LIST OF FIGURES 

Page 

3-1 Example of a 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-Off Snap 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 of Pneumatic 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 of Production 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 

viii 
1.0 SUMMARY 

This report is one of several volumes that provide background information 

supporting the Gas Research Institute and U.S. Environmental Protection Agency Office of 

Research and Development (GRI-EP A/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% of natural gas production starting at the wellhead and 

ending immediately downstream of the customer's meter. 

This report describes a study to quantify the annual methane emissions from 

pneumatic devices, which are a significant source of methane emissions within the gas 

industry. The gas industry has two primary types of pneumatic devices that discharge 

natural gas; control valves that regulate flow, and gas-actuated isolation (block) valves. 

Because each segment of the 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 of pneumatic devices in each industry segment was generally 

determined from counts of devices observed during site visits. The national emission factor 

for each industry segment was then based on the product of the 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, 

I 4.1 ± 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 of these 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 of gas-powered pumps and 

gas-powered compressor starters, which are characterized in other parts of the 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 not bleed gas to the atmosphere. 

The gas industry has two primary types of pneumatic devices that discharge 

natural gas: I) control valves that regulate flow, and 2) gas-actuated block valves. Section 

3 describes each type of pneumatic device and the methods of data collection used for each 

type of device. 

Section 4 discusses emission factors developed for each type of pneumatic 

device. Because each segment of the gas industry follows its own specific practices 

regarding "typical" pneumatic device installations, this section contains separate discussions 

for each segment of the 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 of the gas industry, and Section 6 provides annual national 

emissions calculated for each segment of the gas industry. 

2 
3.0 PNEUMATIC DEVICE CHARACTERISTICS 

This section describes the characteristics of the various types of pneumatic 

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 at remote production sites. Some 

pneumatic devices are powered by pressurized air from an instrument air compressor. 

However, the majority of pneumatic 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 of these 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, if powered by 

natural gas, will discharge methane to the atmosphere. In gas processing and transmission, 

isolation valves on large pipelines (also called block valves) can be actuated by natural gas, 

whereas. most of the 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 of this report. The function that a control valve affects, such as level, flow 

rate, temperature, or pressure, usually dictates the type of control 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 

lnfonnation 

Pneumatic Positioner" 

Pneumatic Controller Infonnation Information 

Type of 

Function/Service 

Controller Bleed Rate Controller Device 

Control Controller Bleed Frequency (upon valve actuation) Design Bleed Status 

Level, Flow Rate, Snap-acting 

Temperature, or 

Intennittent High rate, discharges On-off NIA 

Pressure Control 

Stationary Bleed Rate = 0 full volume of actuator (Figure 3-10) 

Throttling 

Non-zero 

Continuous Small to large volume Orifice-flapper Continuous or 

Stationary Bleed discharged (Figure 3-6) intermittent 

Rate 

Force-balance 

Throttling 

Stationary 

Intermittent Small to large volume piston Continuous or 

Bleed Rate = 0 discharged (Figure 3-3) intermittent 

Pressure Control Throttling No-bleed (discharges to No-bleed (discharges to Self-contained N/A 

downstream gas: line) downstream gas line) spring/diaphragm 

(Figure 3-2) 

Isolation NIA Imerm.ittent High rate, discharges Piston, rotary vane, N/A 

Stationary Bleed Rate = 0 full volume of actuator or turbine 

(Figures 3-4, 3-11, 

3-12, and 3-13) 

• Positioners are optional devices. 
( 

() 

I 

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

\'--==;;~~) 

000 

= 

Controller 

~ Gas Supply 

' 

v u 

n 

u..u u..u u..L 

Valve Body 

Figure 3-l. Example of a Pneumatic Controller Used for 

Level, Flow Rate, Temperature, or Pressure Control 

5 
the controller may continually bleed gas at various rates (thronling). Pressure controllers 

may bleed gas to the atmosphere, or may 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 of mechanical 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 of pipe or a piece of equipment 

rather than for process control. An example is shown in Figure 3-4. The valve is either 

open or closed. Gas is released only \Vhen the valve is moved, so the bleed frequency is 

considered intermittent. This type of operation is fairly infrequent. The bleed rate for these 

devices varies with the design of the 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 or during the actuation 

cycle. This table summarizes the bleed modes of the various devices presented in Table 3-

1. The pneumatic device bleed modes and classifications are discussed in more detail in 

the following sections. 

6 
REGULATOR 

/,- SET POINT ADJUSTMENT 

DOWNSTREAM 

PRESSURE 

REGULATED, 

LOWER 

GAS OUT OF 

REGULATOR 

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

7 
VALVE 

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 t I 

GAS t 

SUPPLY 

GAS PIPE 

0 

PISTON 

ACTUATOR 

ARM 

MOVEMENT 

Figure 3-4. Example Isolation Valve - Piston Operator 6 

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 of pneumatic 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 of gas 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. 

10 
Vlhen the pneumatic device is moving the control valve, there is an unsteady 

and different rate of bleed (actuation bleed rate). If the signal is adding pressure to the 

actuating chamber, the bleed rate drops from the stationary level. If the 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 of control, 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 of liquid in a vessel. A level float in the vessel indicates the volwne 

of liquid 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 of liquid from the tank is measured and recorded. Each of the elements ~ 

measurement, valve, and valve controller -is described 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 of level 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 of the 

restriction in the process flow are tied to a diaphragm that deflects when the pressure 

changes. The deflection of the 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 

Figure 3-5. Operating Principles 

12 
PNEUMA TIC 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 

_:========~-- PRESSURE 

OUTPUT 

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 of the valve seat inside the 

valve body can then restrict or stop process 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 of pneumatic 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 or moves because pressure is applied to 

one side of the chamber. A permanent 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 of the variable against the desired set point 

of the variable. If there is a difference, a pneumatic signal is sent to the control valve to 

open or close the valve. If the 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 in the measurement/valve/valvecontroller loop that discharges gas to the atmosphere. Contr.ollers are highly variable in 

design. Depending on the design of the controller, the stationary position may or may not 

14 
PISTON 

CYLINDER ---1 

PROCESS 

FLOW 

DIAPHRAGM 

PROCESS 

FLOW 

PISTON ACTUATOR 

PNEUMATIC 

SIGNAL FROM 

CONTROL.LER 

STEM 

VAI.VE SEAT 

DIAPHRAGM ACTUATOR 

PNEUMA TIC 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 of the valve stem from open to closed and back, always results in the 

release of gas. This cycle only occurs when the signal changes and control is needed. The 

frequency of this occurrence will be different for every application. 

Pneumatic Relay 

The key component of the 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 of mechanical amplifier that produces a 

stronger pneumatic signaL The mechanical amplifier in the controller uses the small force 

of the measurement deflection to change the supply gas flow path, which alters the resulting 

downstream supply gas pressure. The change in pressure 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 of pneumatic relays which, as the main component of 

the controller, define the type of controller. 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. 

16 
A simplified drawing of a 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 of mechanical force to alter the flow and pressure of a 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 of gas out of the orifice. If the 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 If the 

orifice is fully open, most of the supply stream bleeds to the atmosphere, and the pneumatic 

output is at its lowest value. This type of throttling device has a continuous bleed rate, 

even in the stationary position (no movement of the valve or change of signal) 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 of pneumatic relays use a chamber instead of an 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 of device only bleeds when it is out of the 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 

18 
CONSTANT 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 

Adjustment 9 
This knob contains an exhaust por: with a continuous bleed line from the actuator 

diaphragm. These additional bleed locations are typical of proportional 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 of device 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-l 0 shows two examples of on/off relay devices. As the diagram shows, when the 

device is on, the full supply-gas pressure is applied to the 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 of the 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 of the 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 of control valves in the gas industry 

have positioners since this level of fine tuning is not generally required. 

20 
ON/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-Off Snap 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 of relay. 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 of internal control adjustments, such as proportional gain 

and set point knobs); 

3. Device condition (old or worn devices may leak more); 

4. Design response time (faster response devices require higher bleed 

rates); and 

5. Supply gas pressure and supply gas type (air produces 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 

22 
throttling 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 of the 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 or throttling device are: 

l. Number of full 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 of continuous 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 of continuous 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) 3 to 15 psig; and 2) 6 to 30 psig.' These supply ranges can 

23 
be easily identified by the gauge dials on the front of the 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 of an 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 of an emergency. The valves are most 

often actuated pneumatically (by natural gas or compressed air) or by an electric motor. 

3.3.1 General Description 

Most gas operators on isolation valves discharge gas only when actuated. 

Once they reach the open or closed 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 of two basic 

types: 1) rotary vane, and 2) piston. 

The rotary vane displacement operator uses natural gas to force a fixed 

amount of oil 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 of the receiving 

pressure bottle to vent to the atmosphere. The most common manufacturer of this type of 

operator is Shafer Valve Company. 12 Figures 3-11 and 3-12 show a typical pneumatic/ 

hydraulic rotary vane operator from the Shafer catalogue. 

Similarly, Pantex Valve Actuators & Systems, Inc., manufactures a displacement operator that uses natural gas to move a piston. 6 The piston acts on an "ann" or lever 

that rotates the valve stem. Gas is supplied to one side of the piston and exhausted from the 

other to move the arm in each direction, either opening or closing the valve. An example of 

this type of operator is shown in Figure 34. 

Supply gas for these operators is usual,ly pipeline gas, so pressure varies from 

site to site. Compressed air can be used if it is available in sufficient volumes. The volume 

of gas vented depends on the vane or piston displacement size and on the supply gas 

pressure. 

Turbine operators, the second major type of isolation 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 starter turbine 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 operator on a gate valve is illustrated in Figure 3-13. 

25 
HYDRAULIC TANKS 

ROTARY VANE ACTUATOR 

HAND PUMP 

'--- VALVE BODY 

Figure 3-11. PneumaticJHydraulic Rotary Vane Operator12 

26 
SHOWN 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 of operation to 

open or close 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 or displacement); 

2. Manufacturer and model number; 

3. Supply gas pressure, supply gas type (air produces no methane 

emissions)~ and 

4. Number of full stroke cycles per year. 

The following approach was used to gather pneumatic data for this report from 

field site visits: 

1. During site visits, instrument populations and the instrument 

manufacturer and model number were gathered from several sites; and 

2. Based on observations and interviews, "the frequency of operation cycles 

per year was estimated. 

The site data were combined with manufacturers' data and measured data from 

other studies to produce an emission factor for a typical device type. 

3.4 Other Pneumatic Devices 

Numerous other devices in the field can bleed methane but do not neatly fit 

into the categories listed above. Because these devices are rare, or rarely bleed, they were 

29 
ignored for the purpose of this study. They are listed In this section only for the sa~e of 

completeness. Some key examples are: 

• Solenoid snap-acting valve controllers; 

• Self-contained pressure regulators; 

• Pneumatic transmitters; and 

• Older flow computers. 

The solenoid "snap-acting" controller acts like the pneumatic snap-acting 

controller, except that its signal is not a weak mechanical signal but an electrical one. The 

solenoid either opens a valve that puts full supply gas pressure to the top of the valve 

actuator or closes off that supply and vents the actuator to the atmosphere. Like snap-acting 

pneumatic relays, it only bleeds when the actuator is depressured. Figure 3-14 shows a 

diagram of a solenoid relay. These devices are rare since electronic signals are infrequently 

used in the gas industry. 

A corrunon example of a self-contained pressure regulator is the small "gas 

supply regulator" shown in Figure 3-2. This is a small device that lowers pneumatic gas 

supply pressure to a desired downstream pressure. These devices are commonly found 

between pneumatic supply headers and the devices that use the supply gas. Gas supply 

regulators only bleed if the downstream pressure rises above set-point. Since there are 

downstream users of the gas, the downstream pressure is almost always lower, so these 

devices rarely bleed gas. Another common, large, self-contained device is the transmission 

and distribution pressure letdown regulator (Figure 3-15). These regulators handle the entire 

gas stream but do not bleed at all. They release actuator pressure to the downstream side 

and do not bleed to the atmosphere. 

30 
FROM 

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 
Figure 3-15. Self-Contained Pressure Regulation Valve 

32 
The pneumatic transmitters and older flow computers are examples of devices 

originally installed in older facilities that are out-of-date by today 's standards of technology. 

It is difficult to list, characterize, or group all of the diverse devices in this category. Their 

total contribution to emissions is considered to be minimal. 

33 
4.0 PNEUMATIC DEVICE EMISSION FACTORS 

The various segments of the gas industry have different equipment and 

different standards for using pneumatic devices. Table 4-1 shows the general uses of devices 

in each segment. 

TABLE 4-1. STANDARD USES OF PNEUMATIC DEVICES 

Production Processing Transmission Distribution 

Control valves Yes Very Few Yes Yes 

operated by gas? 

Isolation valves No Some Yes Some 

operated by gas? 

The foiiowing subsections describe the details of pneumatic devices in each segment and the 

emission factors associated with those devices. 

4.1 Production Se~m~ent 

Valve controllers (pneumatic devices on control valves that regulate flow) are 

the most common type of pneumatic device in the production segment that discharge gas 10 

the atmosphere. As stated earlier. primary measurement devices. which detect the initial 

change in the process variable, are sealed and do not directly bleed or exhaust to the 

atmosphere. In addition, the production pipelines are small, so the isolation valves that exist 

are manually operated and do not bleed gas. 

4.1.1 General Emission Factor Characteristics 

Typical production operations include pneumatic valve controllers. 

Infrequently, production operations may contain valve positioners. There are multiple 

components (such as set-point adjustment, gain adjustment, and reset knobs) within a 

34 
controller or positioner that may bleed. These are considered part of the controller device. 

Certain valves or valve packages may have these emitting elements combined into one fieldlocated box. 

The production segment uses both basic types of pneumatic controllers: 1) . throttling, and 2) snap-acting. Throttling pneumatic relays of the "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 of zero. Throttling orifice flapper 

relays (Figure 3-6) bleed continuously, even when the valve is not moving, but their bleed 

rate varies with the strength of the signal from the process variable. Orifice flapper relays 

are considered continuous emitters since there is no position where the bleed rate is zero. 

Snap-acting controllers have a stationary bleed rate of zero and are therefore considered 

intermittent emitters. 

4.1.2 Production Emission Factors 

Five sources of information were used to determine the methane emissions 

from pneumatic devices used in the production segment: the results from a study performed 

by the Canadian Petroleum Association, 11 manufacturers' data, measured emission rates, 10 

data collected from site visits, and literature data for methane composition. Each of these 

sources is discussed in detail. 

Canadian Petroleum Association (CPA) Report 

As part of Canada's effort to 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 Table 4-2. 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 

35 
w 

"' 

TABLE 4-2. RESULTS FROM THE CANADIAN PETROLEUM ASSOCIATION PNEUMATIC 

EMISSION RATE STUDY 

Instrument Type Facility Type 

Quantity Minimum Flow, Maximum Flow, 

Equipment Type Measured scfd scfd 

Snap-Acting Oil Battery Group Treater 0.0 

Controller 

690 

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 

Controller 

0 10 

Line Heater I 55 55 

Line Heater 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 of the snap-acting and throttling 

controllers. 

It should be noted that the CPA report did not distinguish between throttling 

controllers with intermittent bleed rates and throttling controllers with continuous bleed rates. 

In addition, only one of the 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 lower than field 

measurements of similar devices in the U.S., but do agree with the manufacturer's data for 

similar devices. The CPA measurements were treated as additional data sources and 

combined with field measurements provided by another source to generate emission factors 

for intermittent and continuous bleed devices. 10 

Manufacturers' Data 

Manufacturers of pneumatic devices may report a "gas consumption" for 

specific devices based on laboratory testing of new devices. However, the manufacturers 

indicate that emissions in the field can be higher than the reported gas consumption due to 

operating conditions, age, and wear of the device. 15 •

16•

17·

18 Examples of circumstances or 

factors that can contribute to this increase include: 

• Nozzle corrosion resulting in more flow through a larger opening; 

• Broken or worn diaphragms, beiiows, fittings, and nozzles; 

• Corrosives in the gas leading to erosion or corrosion of control loop 

internals; 

• Improper installation~ 

• Lack of maintenance (maintenance includes replacement of the filter 

used to remove debris from the supply gas and replacement of o-rings 

and/or seals); 

37 
• Lack of calibration of the controller or adjustment of the distance 

between the flapper and nozzle~ 

• Foreign materia! lodged in the pilot seat; and 

• Wear in the seal seat. 

The manufacturers contacted did not have field measurements of devices in 

service and did not simulate the aging of devices with laboratory measurements, so they 

could not provided an indication of the expected increase in emissions due to the factors 

listed above. Since manufacturers' emission rates are based on new devices, actual emission 

measurements from pneumatic devices in field service, including worn or defective devices, 

were used as the basis for developing emission factors. 10·ll 

Several pneumatic device manufacturers provided information on the gas 

consumption rates for their continuous bleed devices. 9

•

16•

18•

19•

20•

21 •

22•

23·

24•

25 Table 4~3 shows the 

bleed rates for the model series observed during site visits. The manufacturers' reported gas 

consumption rates represent the gas usage at the specified supply gas pressure for the 

controller only (unless otherwise noted). Additional emissions may occur from other 

components of the control loop (i.e., set point exhaust and valve positioner). 

For the types of devices listed, gas consumption rates for the controllers can 

vary from 0 to 2,150 scfd per device. However, the manufacturers indicated that emissions 

from these devices in field operation may be higher than the reported "maximum." Some 

manufacturers provided a maximum gas flow rate or delivery capacity that the controller 

pilot could withstand (4,320 scfd for the Bristol 62411 and 8,880 for the Fisher 4100). This 

flow rate indicates the maximum amount of gas that can be supplied to the control loop. It is 

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 sanity check for the field measurements 

provided by other sources (discussed in the next section). The data reported in Table 4-3 are 

38 
TABLE 4-3. MANUFACTURER BLEED RATES FOR CONTINUOUS BLEED PNEUMATIC DEVICES 

Gas Consumption Rates, scfd 

Manufacturer/ 

Model "Minimum" "Maximum" Comments on Specified Rate 

Norriseal !000 (A) Model discontinued in the 1960s No bleed rate information available. 

Max. bleed rate is not specified by Norriseal. Estimated for 1001 model based 

Norriseal !OOI(A) 0-10 2,150 on volume of gas required for one complete actuation@ 30 psig supply 

(provided by manufacturer) and assuming one actuation/min. 

Min. based on gas consumption of the controller only. 

Bristol 624, 624 If 72-144 4,320 Bristol does not manufacture actuators, so they do not specify a gas consumption 

for the actuator. Max. bleed rate shown is based on the pilot capacity 

(maximum amount of gas that the controller pilot can accommodate). 

Fisher 2400 Model discontinued in 1957 No bleed rate information available. 

Bleed rate for 35 psig supply pressure. Min. represems the steady state pilot 

Fisher 2500 168 1,008 bleed rate (device not actuating). Max. represents gas consumption when the 

relay is completely open. 

Fisher 2900 Model discontinued in 1991 Gas consumption not listed in device brochure, hut Fisher representative 

provided a laboratory measurement of 555 scfd for 35 psig supply pressure. 

1,200 Bleed rate for 35 psig supply pressure. Min. represents the steady state pilot 

Fisher 4100 24 8,880 bleed rate of the controller. Max. represents maximum gas consumption (1200 

scfd) and delivery capacity of the controller (8800 scfd). 

lnvalco AE 155 Model discontinued - 1975 No bleed rate information available. 

Minimum bleed rate specified for supply gas pressure of 20-30 psi. Maximum 

lnvalco CT series 510 960 bleed rate shown here is reported by the manufacturer as a typical bleed rate for 

this device. A r.etrofit kit is available for this series of devices to reduce the 

typical bleed rate from 960 scfd to less than 22 scfd. 
consistent with emission measurements in the field, in that the manufacturers confirmed that 

the devices can emit at rates higher than the manufacturers' reported gas consumption rates. 

In addition, the delivery capacity reported by the manufacturers for some devices serves as 

an absolute maximum bleed rate. Any measured emission rate higher than the delivery 

capacity for a given device would indicate an error in the measurement and would justify 

discarding the measurement. 

Directly Measured Emissions for Continuous Bleed Devices 

Field measurements of throttling devices with continuous bleed rates were 

available from companies participating in a separate contractor's piogram. 10 For these 

measurements, a contractor connected a flow meter to the supply gas line between the 

pressure regulator and the controller to measure the gas consumption of the controller. A 

cumulative flow rate and the current flow (seth) were recorded and extrapolated to gas 

consumption per day. The duration of the test depended on the variability of the gas use. 

For steady operating conditions, one data point was taken for 15-20 minutes. For variable 

flow rates, several one-hour measurements were taken. 

Although the emission measurements were not perfonned under the direction 

of this study, the results are believed to be an accurate representation of pneumatic devices in 

operation in the 'U.S. natural gas industry. Through interviews with site persoiUlel and the 

contractor that performed the measurements, 10 the sampling technique, measurement 

protocol, and equipment calibration procedures were reviewed. Two measurements were 

removed from the data set because they did not follow the measurement protocol for a single 

device (in both cases a single emission measurement was reported for an unknown number of 

devices). The fmal data set was deemed acceptable by the industry review panel. 

After the QA/QC review, the data set contained a total of 41 measurements 

from a combination of continuous bleed devices from offshore platfonns, onshore production 

sites, and transmission stations. Table 4-4 summarizes the measurements. 

40 
TABLE 4-4. MEASURED EMISSION RATES FOR CONTINUOUS BLEED DEVICES 

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 of pneumatic devices in onshore versus offshore production operations 

is similar. Both use continuous bleed 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 offshore emission measurements shown in Table 4-4 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 

of this 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 continuous bleed devices in the production segment. 

Continuous bleed pneumatic 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. In the 

transmission segment, the same types of devices are used for liquid level control in filterseparators, but are also used for pressure reduction. In addition, the higher pressures and 

larger pipeline 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. For these 

reasons, separate emission factors were developed for production and transmission. 

Comparing the measured emissions for devices in production versus 

transmission indicates that there is a difference between the industry segments. The 

combined onshore and offshore production devices have a lower average emission rate of 872 

scfd, while transmission devices have an average emission rate of 1.363 scfd. When the 

Canadian data are included, the production emission factor is 654 ± 31% scfd/device. The 

transmission emission factor is unchanged because the Canadian measurements were only 

from onshore production facilities. 

The measured emission rates compare well with the gas consumption ranges 

provided by the manufacturers, although a direct comparison for ail device types can not be 

inade since manufacturer values are not available for ail of the models measured. In general, 

most of the measurements are less than 2,000 scfd (only seven out of the 41 measurements 

are greater than 2,000 scfd), and all of the measurements are below the reported controller 

delivery capacities of 4,320 and 8,880 scfd (two devices had emission measurements of 

4,215 scfd). 

As stated previously, the manufacturers' bleed rates represent laboratory 

measurements of the gas consumption for new pneumatic devices. In reality. the pneumatic 

devices in the field have various states of wear and may emit gas at rates higher than the 

manufacturers' gas consumption data suggest. The measured emissions are in the range of 

values provided by the manufacturer and are believed to reflect more typiqtl operating 

conditions for these devices and account for increased emissions due to wear. For the 

purpose of this report, the measured emissions provided by CPA are combined with the 

contractor's direct measurements to estimate the emission factor from continuous bleed 

throttling devices. The resulting natural gas emission factor .for the production segment is 

654 ± 31% scfd per continuous bleed device. 

42 
Measured Emissions for Intermittent Bleed Devices 

Field measurements for intermittent bleed devices, using the same technique 

described for the continuous bleed devices, were also available from companies participating 

in this snrdy. 10 Based on the criteria described for continuous bleed devices, measurements 

for the intermittent bleed devices were reviewed and judged to be acceptable. A total of 

seven measurements were provided from intermittent bleed devices found in onshore 

production service. No measurements were available for these types of devices in offshore 

service or the 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 of similar devices which ranged from 12 to 695 scfd/device (average of 

211 scfd from Table 4-2). Combining the 19 measurements from both sources (Canadian 

and U.S. field measurements) results in a natural gas emission factor of 323 ± 34% 

scfd/device for intermittent bleed devices in production. 

Site Data 

For this study, data were collected from a total of 22 sites to establish a count 

of pneumatic devices for production sites and to determine the fraction of intermittent versus 

continuous bleed devices at each site. The fraction of each 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. For each site, the number of snap-acting 

devices and the number of throttling devices were collected. Where possible, the 

manufacturer and model number were recorded for each device. 

As discussed in Section 3, throttling devices can be either intermittent or 

continuous bleed, while snap-acting devices are always intermittent bleed. The number of 

throttling continuous bleed devices at each site was determined based on the manufacturer 

and model type of the devices observed. Since these two deyice types have distinctly 

different emission rates, the fraction of intennittent bleed versus continuous bleed devices is 

43 
TABLE 4-5- SUMMARY OF PRODUCTION SITE DATA 

Total Number of Number of Number of 

Count of Power Snap-Acting Throttling Continuous 

Site Devices Media Devices Devices a 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 or intermittent bleed. 

b Continuous bleed devices are a sub-category of throttling devices. 

44 
required to develop an emission factor. From the site data, the fraction of continuous bleed 

devices is 0.35 ± 43%. By difference, the fraction of intermittent bleed pneumatic devices 

is 0.65 ±43%. 

Methane Composition 

The percentage by volume of methane in produced natural gas was determined 

to be 78.8% ± 5%. Details about this value are available in the report, Methane Emissions 

from the Natural Gas Industry, Volume 6: Vented and Combustion Source Summary. 26 

Emission Factor Calculation 

The weighted emission factor per device 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 of intermittent bleed versus 

continuous bleed devices: 65% ± 43% intermittent bleed and 35% ± 43% continuous bleed 

(Table 4-5). Table 4-6 summarizes· the emission factor terms, where the emission factors for 

the individual device types (intermittent versus continuous bleed) were based on the field 

measurements from the United States and Canada discussed previously. 

The final result is an average device methane emission factor of 345 

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

45 
TABLE 4-6. PRODUCTION EMISSION FACTOR CALCULATION 

Device Type 

Intermittent Bleed 

Continuous Bleed 

Fraction of Device Type 

0.65 ± 43% 

0.35 ± 43% 

Selected Natural Gas 

Emission Factor, 

scfd/device 

323 ± 34% 

654 ± 31% 

Methane Emission Factor for Average Device = 345 ± 40% scfd/device 

4.2 Transmission and Stora~e Sewnent 

The transmission segment is composed of pipelines, compressor stations, and 

storage stations. Very few pneumatic devices of any type are associated with the pipelines. 

Within the storage and mainline compressor stations, most of the pneumatic devices are gasactuated isolation valves and continuous bleed controllers. 

4.2.1 General Emission Factor Characteristics 

The type of continuous bleed devices in the transmission segment are 

essentially the same as those in the production segment. The difference is in the use of the 

devices. In the transmission segment, continuous bleed pneumatic devices are used to 

regulate pressure on compressors and are sized larger due to the higher pressures in 

transmission. In production, smaller devices are used .primarily to control the liquid level in 

separators. Since most of the same manufacturers are used, this section will not repeat the 

discussion from Section 4.1.1. 

Isolation valve actuators are predominately found in the transmission segment. 

Isolation valve actuators emit gas whenever the valve is moved to either the open or closed 

position. Most compressor stations and storage stations have many valves, since valves are 

needed to make normal changes in pipeline and equipment flow configurations, as well as to 

46 
isolate and depressure equipment for maintenance or in case of an emergency. Most sites 

use natural gas rather than 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 

Manufacturer and Site Data 

The transmission emission factors 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 on air were not included in the emission 

calculation. 

The nanrral gas emission factor for the continuous bleed devices used in 

transmission is based on measured emissions from these devices at transmission stations 

(measurement procedure and data quality checks were discussed in Section 4.1.2). 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 an average nanrral gas emission factor of 1,363 ± 29% 

scfd/device (497 ,583 scf/device annually). It should be noted that intennittent bleed devices 

were not observed at transmission stations. 

Data on the following characteristics of isolation valves were gathered at 16 

transmission sites: 

1. Basic device type (continuous bleed, turbine, or pneumatic/hydraulic)~ 

2. Manufacturer and model number; 

47 
3. Supply gas pressure, supply gas type (air produces no methane 

emissions); and 

4. Number of full stroke cycles per year (each cycle consists of two valve 

movements: open and close). 

All of the displacement isolation valves observed at the transmission sites were 

the pneumatic/hydraulic rotary vane type (Figures 3-11 and 3-12). The number of actuation 

cycles per year was based on site data. The manufacturer provided the volume of gas used 

based on the discharge pressure. These values (shown in Table 4-7) were combined to 

calculate the annual emission factor for each type of displacement-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 Shafer Valve Operating Systems show that the gas usage 

volumes vary widely •. so data on the demographics of various sizes of the rotary-vane-operated 

valves were gathered from four stations.27·

28 This information is provided in Table 4-7. The 

total emissions from displacement devices were determined for each site based on the size, 

actuation frequency, and number of each type of device. An average annual emission factor for 

this type of device was calculated to be 5,627 ± 112% scf natural gas per device based on the 

average of the site data. 

Due to the diversity of company practices for the few sites which provided data, 

no direct relationship was established between device count and station size. Therefore, for this 

emission factor, an average of the four site averages was used, as opposed to an average of all 

of the 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 of devices is not weighted higher than the other stations. 

48 
TABLE 4-7. PNEUMATIC/HYDRAULIC ROTARY VANE 

ISOLATION VALVE OPERATORS 

Supply Annual 

Gas Gas Usage Number Gas Usage, 

Pressure, Actuator per Cycle, 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 X 7 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 

49 
TABLE 4-7. (CONTINUED) 

Supply Annual 

Gas Gas Usage Number Gas Usage, 

Pressure, Actuator per Cycle, 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 of fuH stroke cycles each year (where each cycle consists of two 

valve movements), and the duration that the turbine operates to complete a valve movement, as 

follows: 

EF Turt>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 of operations per year, and the length of time required to open or close 

the valve. This information is shown in Table 4-8. Average or typical values (based on 

information provided by sites or manufacturers) were used for other sites with turbine 

operators. As with the rotary vane isolation valve emission factor, the emission factor for 

turbine operated isolation valves was also based on an average of the site data. The resulting 

annual emission factor for turbine operators is 67,599 ± 276% scf/device. 

Methane Composition 

The methane composition for 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 of each type of device found in 

the transmission segment. Data on turbine and displacement isolation valves were collected from 

16 sites. For continuous 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 number of devices for a typical transmission station and the 

51 
TABLE 4-8- MANUFACTURER DATA FOR TURBINE 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, scf natural 67,599 ± 276% 

gasfdevice 

fraction of each type of device 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 + EF turbine 

bleed opentors 

X Fraction turbine 

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 

of Devices/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 of pneumatic devices within the plant. Of the nine gas plants visited for this 

study, only one used natural gas-powered, continuous bleed devices in the plant. Approximately one-half of the 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 of the plant. All of the 

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 of I?-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 of devices 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. For the 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 of actuator, supply gas pressure, and an estimate of the number of operations. 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 

(Rotary Vane) 

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 1,704 Mscf ± 21% 

Average (for gas 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 of these devices 1s 

similar to the transmission segment, the annual emission factor of 497,584 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 of 400 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 of device 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 of natural gas 

released per actuation for the devices presented in Table 4-7. Manufacturer's 

data from Limitorque, based on a supply gas pressure of 350 psig, were used 

to estimate the emissions for the turbine operator at this site. 

Methane Composition 

The percentage of methane 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 Emissions from 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 Consumption a 

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 of 250 psig, an average of 

4. I operations per year, and two strokes (open and close) per operation. 

58 
equation: 

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 of sites that use natural gas rather than air (0.556 ± 

59%) 

number of sites operating devices with natural gas 

(5) 

Assuming that the sites surveyed are representative of the United States, the 

average emission rate for sites using natural gas was adjusted based on the ratio of sites 

using gas-operated devices to the total number of sites 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 of the 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 of pneumatic devices is used for the production and transmission segments, while the 

number of gas plants is used for the gas processing segment. 

5.1 Production Segment 

The total number of pneumatic devices in the U.S. production segment was 

determined from regionalized site data. The number of pneumatic devices at each site were 

weighted based on the number of gas wells and the marketed gas production at each site. 

The site data were extrapolated by the nwn!:ler of gas wells and the marketed gas 

production within each region. In production, the resulting count of pneumatic devices 

nationally is 249,000 ± 48%. 

5.2 Gas Processing Segment 

The activity factor for gas processing is based on the number of gas 

processing plants reported annually by the 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 engineering judgement. 

5.3 Transmission and Storage Segment 

The number of natural gas-operated pneumatic devices in the transmission 

and storage segment was calculated based on the average number of devices per station 

61 
multiplied by the total number of transmission and storage stations nationally using the 

following equation: 

AF = Average Number of Devices X Number of Stations 

Station (6) 

The average number of pneumatic devices per station is the sum of the average number of 

turbine devices per site, the average number of rotary vane displacement devices per site, 

and the average number of continuous bleed devices per site. Using the numbers shown in 

Tables 4-10 and 4-11, the average number of pneumatic 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, I 75 ± 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. 

62 
6.0 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 of the 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 on these results, pneumatic devices contribute a total of 45.6 ± 48% 

Bscf of methane for 1992. 

63 

(7) 
7.0 REFERENCES 

1. Campbell. L.M. and B.E. Stapper. Methane Emissions from the Natural Gas 

Industry, Volume 10: Metering and Pressure Regulating Stations in Natural 

Gas Transmission and Distribution. Final Report. GRI-95/0257.27 and EPA600/R-96-0SOj, Gas R~search Institute and U.S. Environmental Protection 

Agency. June 1996. 

2. Myers, D.B. and M.R. Harrison. Methane Emissions from the Natural Gas 

Industry. Volume I5: Gas-Assisted Glycol Pumps, Final Report, GRI95/0257.33 and EPA-600/R-96-0SOo, Gas Research Institute and U.S. 

Environmental Protection Agency, June 1996. 

3. Shires, T.M. Methane Emissions from the Natural Gas Industry, Volume 13: 

Chemica/Injection Pumps, Final Report, GRI-95/0257.30 and EPA-600/R-96-

0SOm, Gas Research Institute and U.S. Environmental Protection Agency, 

June 1996. 

4. Shires, T.M. and M.R. Harrison. Methane Emissions from the Natural Gas 

Industry, Volume 7: Blow and Purge Activities, Final Report, GRI-95/0257.24 

and EPA-600/R-96-0SOg, Gas Research Institute and U.S. Envirorunental 

Protection Agency, June 1996. 

5. Perry, J.H. (ed.) Chemical Engineers Handbook, 5th Edition. McGraw-Hill, 

New York, NY, 1973. 

6. Pantex Valve Actuators and Systems, Inc. Strongann Series S Actuators for 

Rotating Stem Valves, Bulletin No. SS-5-91, Stafford, TX. 

7. Hummel, K.E., L.M. Campbell, and M.R. Harrison. Methane Emissions 

from the Natural Gas Industry, Volume 8: Equipment Leaks, Final Report, 

GRI-95/0257.25 and EPA-600/R-96-0SOh, Gas Research Institute and U.S. 

Environmental Protection Agency, June 1996. 

8. Norriseai Controls. Norriseal Level Controller Series 1001-A Catalog. 

Houston, TX, 1987. 

9. Fisher Controls International, Inc. 4150K and 4160K Series Pressure 

Controllers and Transmitters, Bulletin 34:3:4150K. Marshalltown, lA, 1992. 

10. Controller survey data provided by Tenneco Gas Transportation, 1994 and 

Chevron, 1995. 

64 
11. 

12. 

13. 

14. 

15. 

16. 

17. 

18. 

19. 

20. 

21. 

22. 

23. 

24. 

Picard, D.J., B.D. Ross, and D.W.H. Koon. "A Detailed Inventory of CIL 

and VOC Emissions From Upstream Oil and Gas Operations in Alberta." 

Canadian Petroleum Association, Calgary, Alberta, 1992. 

Shafer Valve Operating Systems. Rotary Vane Valve Operators, Bulletin RV110. Houston, TX, !980. 

Personal correspondence with Belva Short of Limitorque Corporation, 

Lynchburg, VA, AprilS, !994. 

Personal correspondence with Brian Ross of Clearstone Engineering, Alberta, 

Canada, October 16, 1995. 

Personal correspondence with Bob Finley of Bristol Babcock Inc., Watertown, 

CT, October 3, 1995. 

Personal correspondence with Clark Crownover of Puffer Sweiven, Inc., 

Stafford, TX, October 6, 1995. 

Personal correspondence with Maurice Hoss of Invalco Inc., Hutchinson, KS, 

October 6, 1995. 

Personal correspondence with Quin Kroll of Norriseal, Houston, TX, October 

4, 1995. 

Dover Corporation. Norriseal Controls Series 1000 Liquid Level Control, 

Manufacturer Bulletin 1.1, Catalog Section 1, W.C. Norris Division, Houston, 

TX, July 1963. 

Bristol Babcock. 624-lllndicating Pneumatic Transmitters Specifications, 

Specification Sheet AI03-la, Watertown, CT, 1992. 

Bristol Babcock. Series 5453 Indicating Pneumatic Pressure Controllers, 

Specification Sheet All8-2c, Watertown, CT. 1992. 

Fisher Controls International, Inc. 3582 Series Pneumatic and Type 3582! 

Electro-Pneumatic Valve Positioners, Bulletin 62.1:3582. Marshalltown, IA, 

1993. 

Fisher Controls International, Inc. 36101 and 36201 Series Positioners, 

Bulletin 62.1:3610. Marshalltown, !A, !992. 

Invalco. Low Energy Pilot Retrofit Kit for CT Series Flextube, CT Series, 

Issue I, Page IVC-801-All, Tulsa, OK, December I, 1990. 

65 
25. 

26. 

27. 

28. 

29. 

30. 

Invalco. CT Series Flextube Displacer Type Level Controller, CT Series, Issue 

1, Page IVC-801-A3, Tulsa, OK, April 30, 1990. 

Shires, T .M. and M.R. Harrison. Methane Emissions from the Natural Gas 

Industry, Volume 6: Vented and Combustion Source Summary. Final Report, 

GRI-94/0257.23 and EPA-600/R-96-0SOf, Gas Research Institute and U.S. 

Environmental Protection Agency, June 1996. 

Shafer Valve Operating Systems. Gas Consumption Calculation Method for 

Rotary Vane, Gas/Hydraulic Actuators. Technical Bulletin Data, Bulletin GC00693. Mansfield, OH, June 1993. 

Shafer Valve Operating Systems. Gas Consumption Calculation Method for 

Rotary Vane, Gas/Hydraulic Actuators, Technical Bulletin Data, Bulletin GC2-00394. Mansfield, OH, March 1994. 

Stapper, B. E. Methane Emissions from the Natural Gas Industry. Volume 5: 

Activity Factors, Final Report, GRI-94/0257.22 and EPA-600/R-96-0SOe, Gas 

Research Institute and U.S. Environmental Protection Agency, June 1996. 

Bell, L. "Worldwide Gas Processing," Oil and Gas Journal, July 12, 1993, p. 

55. 

66 
APPENDIX A 

Source Sheets 

A-I 
SOURCES: 

COMPONENTS: 

OPERATING MODE: 

EMISSION TYPE: 

ANNUAL EMISSIONS: 

BACKGROUND: 

P-4 

PRODUCTION SOURCE SHEET 

Various Equipment 

(wells, heaters, separators, dehydrators, compressors) 

Pneumatic Devices 

Nanna! Operation 

Unsteady, Vented 

31.4 Bscf ± 65% 

Most of the pneumatic devices in the industry are valve actuators and controllers that use natural gas pressure as 

Gas 

the force for valve movement. There is a large population of pneumatic devices throughout the gas industry. 

from the valve actuator is vented to the atmosphere during every valve stroke, and gas may be continuously 

bled from the valve controller pilot as well. 

EMISSION FACTOR: 125,925 scf per average device ± 40% 

(This was adjusted for the production methane fraction of natural gas at 78.8 mol%.) 

Pneumatic devices (valve controllers) linked to control valves are the largest source of pneumatic emissions in 

the production segment. There are two types of devices with distinct bleed modes: intermittent and continuous. 

Intermittent bleed devices emit methane to the atmosphere only when the control valve actuates; when the device 

when 

is not moving the bleed rate is zero. Continuous bleed devices emit methane both when the valve actuates and 

the device is not moving. An emission rate for a generic pneumatic device combines the bleed rates of the 

two types of devices, weighted by the population of the device 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% 

78.8 mol % ± 5% 

Emissions for intermittent and continuous bleed devices were based on measured data provided by a Canadian 

study and U.S. field measurements from a se?arate contractor's program. The average measured emissions for 

intermittent and continuous bleed devices are 323 ± 34% and 654 ± 31% scfd/device, respectively. The 

fraction of each type of device was determined from site visits. 

Therefore the average annual emission factor for a generic pneumatic device is: 

= 125,925 ± 40% scf/device 

EF DATA SOURCES: 

l. Methane Emissions from the Natural Gas Industry, Volume 12: Pneumatic Devices (I) 

establishes the important em:ssion-affecting characteristics. 

A-2 
2. Site visit device counts establish the fraction of continuous bleed versus intenniuem bleed 

devices for multiple sites. 

3. The Canadian Producers Association (CPA) determined an average emission factor per device 

based on 19 measurements. 

4. An independent contractor provided 18 measurements of pneumatic devices in onshore and 

offshore production services. 

EF PRECISION: 

Basis: 

EF accuracy is based on error propagation from the spread of site device counts and measured 

emission rates. 

ACTIVITY FACTOR: 249,111 pneumatic controllers± 48% 

The average count of devices per equipment type was determined from multiple site visits. The ratios for the 

number of devices per gas well and the number of devices per marketed gas production were compiled by 

region. The regional values were summed to give national device counts based on well counts and marketed. gas 

production. These values were averaged to give the final national device count of 249,11 I. 

AF DATA SOURCES: 

I. Methane Emissions from the NaJural Gas Industry, Volume 5: Activity Factors (2) establishes 

the methodology for e:mapolating the site data to a national count. 

2. Site visit device counts, well counts, and production rates establish the number of devices per 

well and the number of devices per gas production. 

3. Total regional gas well counts and 1992 marketed gas production rates 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 1992 are reponed as 602,197 by the Oil & Gas Journal (5). The active oil wells that 

market gas are determined by multiplying the total national active wells by the fraction that 

market gas. The fraction is determined from a Texas Railroad Commission database (6) on oil 

leases and gas disposition from those leases; an analysis that shows the percent of oil 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 production rate are calculated from 

the spread of site data collected for each region (a total of 36 sites). 

The accuracy for wells that market gas are based on the spread of data from the Texas 

Railroad Commission database. 

ANNUAL METHANE EMISSIONS' 31.4 Bscf ± 65 % 

The national annual emissions were determined by multiplying an emission factor for an average pneumatic 

device by the population of devices in the production segment. 

125,925 scf x 249,111 devices = 31 Bscf 

A-3 
REFERENCES 

1. Shires, T.M. and M.R. Harrison. Methane Emissions from the Natural Gas Industl)', Volume 12: 

U.S. 

Pneumatic Devices. Final Report, GRI-94/0257.29 and EPA-600/R-96-0801, Gas Research Institute and 

Environmental Protection Agency, June 1996. 

2. Stapper, B. E. Methane Emissions from the Natural Gas Industry, Volume 5: Activity Factors. Final 

Report, GRI-94/0257.22 and EPA-600/R-96-0SOe, Gas Research Institute and U.S. Environmental 

Protection Agency, June 1996. 

3. American Gas Association. Gas Facts: 1993 Data, Arlington, VA, 1994. 

4. Gulf Coast Publishing Company, World Oil, Annual Forecast/Review, Vol. 214, No. 2, February !993. 

5. Oil and Gas Journal. 1992 Worldwide Gas Processing Survey Database, 1993. 

6. Texas Railroad Commission, P-1, P-2 Tapes, Radian files. Austin, TX, 1989. 

A-4 
T-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 of compressor stations, pipelines, and storage stations. There are 

essentially no pneumatic devices associated with the pipelines. Within the storage and compressor stations, 

most of the 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 of the 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 of the pneumatic devices are gas-actuated isolation 

valves. These valves block the flow to or from a pipeline and can isolate the facility for maintenance work or 

in the case of an 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 of natural gas at 93.4 mol%.) 

The average pneumatic device emission factor was determined from a compilation of information from several 

sites. Counts of devices 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 of devices for each of the 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-5 
For the isolation valves with turbine operators, the emission factor depends on the gas usage for a given 

supply 

per year. 

gas pressure, the time required to complete one movement of the valve, and the number of operations 

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. Methane Emissions from the Natural Gas Industry, Volume 12: Pneumatic Devices (I) 

establishes the important emi~sion·affecting characteristics of transmission pneumatic 

devices. 

2. Device counts from 16 compressor and storage stations establish the fraction of turbine valve 

operators, and displacement valve operators. Counts from a total of 54 stations were used to 

establish the fraction of continuous 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 of operation were estimated based on information 

from four transmission stations. 

EF ACCURACY, 

Basis: 

1. 

measured 

EF accuracy is based on error propagation from the combination of site information and 

data. 

2 It was assumed that the manufacturers' data are completely accurate. 

ACTIVITY FACTORS: 87,206 pneumatic devices ± 38% 

on 

The number of gas operated pneumatic devices in the transmission and storage segment was calculated based 

the average number of devices per station and multiplied by the total number of transmission and storage 

of 

stations nationally. The average number of devices per site was determined to be 40 ± 37%. The total count 

transmission 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 of transmission compressor stations was compiled from 1992 Fossil Energy 

Commission Fonn No. 2: Annual Report of Major Natural Gas Companies (2). 

A-6 
2. The number of underground storage facilities is taken directly from A.G.A. Gas Facts: 

"Number of Pools, Wells, Compressor Stations, and Horsepower in Underground Storage 

Fields." Data from base year 1992 were used (3). 

3. The number of liquefied natural gas storage facilities was summed from A.G.A. Gas Facts, 

"Liquified Natural Gas Storage Operations in the U.S. as of December 31, 1987 (4)." The 

table lists 54 complete plants, 32 satellite plants, and 3 import terminals for a total of 89 

facilities. 

4. The number of devices per site is based on the total number of devices 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 of compressor stations and a 5% confidence bound was assigned to 

the number of storage stations. 

The confidence bound on the number of devices per station was determined based on the 

spread of site 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 of pneumatic devices in the transmission segment. 

162,197 scf/device x 87,206 devices'=' 14.1 Bscf 

REFERENCES 

l. Shires, T.M. and M.R. Harrison. Methane Emissions from 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 of Energy. FERC Form No. 2: Annual Report of Major Natural Gas Companies. OMB 

No. 1902-0028, Department of Energy 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-7 
SOURCES' 

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% 

plant, 

The gas processing segment uses compressed air to power the majority of the pneumatic devices within the 

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 of devices 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 Mscf per average plant± 133% 

(This was adjusted for the gas processing methane fraction of natural gas at 87 mol%.) 

emission 

The average device gas emission factor was detennined from a combination of vendor information on device 

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, scf Natural Gas) 

i =I 

n 

x %Methane 

fraction of sites that use natural gas rather than air (0.56 ± 59%) 

number of sites operating with natural gas 

data 

Each 

was 

term in this equation was detennined from site specific information. The summation of the site specific 

then adjusted based on the number of sites with gas operated devices versus the total number of 

sites surveyed. The site results are shown in the following table. 

A-8 
Annual 

Number Operations/ DisplacemenU DisplacemenU 

Site Device Type of Devices 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 Emissions from the Natural Gas Industry, Volume 12: Pneumatic Devices 

establishes the important emission-affecting characteristics. 

2. Site visit device counts establish the number of continuous 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 of devices, 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 error propagation from the spread of data for the nine sites visited. 

It was 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-9 
AF DATA SOURCES: 

I. The number of gas processing plants was taken from the Oil and Gas Journal (2). 

AF PRECISION: 

Basis: 

I . AF accuracy is based on engineering judgement. 

ANNUAL METHANE EMISSIONS: 0.12 Bscf ± 133% 

methane 

The annual 

composition) 

emissions were detennined by multiplying an average site emission factor (adjusted for the 

by the total number of gas processing sites. 

165 Mscf/site x 726 sites "'" 0.12 Bscf 

REFERENCES 

I. Shires, 

Pneumatic 

T.M. 

Devices. 

and M.R. Harrison. Methane Emissions from the Natural Gas Industry. Volume !2: 

and U.S. 

Final Report, GRJ-94/0257.29 and EPA-600/R-96-0801, Gas Research Institute 

Environmental Protection Agency, June 1996. 

2. Bell, L. "Worldwide Gas Processing," Oil and Gas Journal, July 12, 1993, p. 55. 

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

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

Box 201088 

TECHNICAL fetld [R/.Jr.UCfWm Off 

Texas 78720-1088 

EPA, Office of Research and Development 

.Air Pollution Prevention and Control Division 

1-Wteseru,ch Triangle 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% of natural 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 

the lPCC and others. In addition. study results ar~ being used by the natur-al gas 

Stationary Sources 

Global Warming 

ified 
U.S. ENVIRONMENTAL PROTECTION AGENCY 

Office of Research and Development 

National Risk Management Research Laboratory 

Technology Transfer and Support Division 

Cincinnati, Ohio 45268 

OFFICIAL BUSINESS 

PENAL TV fOR PRIVATE USE. 5300 

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. 

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tear off: and return to the above llddrus. 

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reports, CHECK HER£0; tear off label, and retum it to the 

above address, 

Publication No. EPA- 600 iR-96-0801 

==t• ··- 1111 it 111111