United Stales
environmental Prelection
Agency
GRI-94 / 0257.29
EFA-600/R-96-080I
June 1996
i on a
lit
14103C
METHANE EMISSIONS FROM THE
NATURAL GAS IMDUSTRY
Volume 12: Pneumatic Devices
d for
Energy Information Administration (11. S, DOE)
National Risk Management
Research
Research Triangle Park, NC 27711
a! ¥;a*ehaleal feiromiallan Sa
iTlrwfiald. WrgWa 22101
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TECHNICAL WEPORT DATA
e read In&mc&om
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FOREWORD
The U.S. Environmental Protection Agency is charged by Congress with pro-
tec&ig the Nation's land, air, and water resources. Under a mandate of national
environmental laws, the Agency strives to formulate and implement actions lead-
ing 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 pro-
blems today and building a science knowledge base necessary fe manage our eeo-
lefseal resources wisely, understand how pollutants affect our health, and pre-
vent 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, east-effective environmental
technologies; develop scientific sad engineering information needed by EPA to
support regulatory and policy decisions; and provide technical support and infoe-
mation transfer to ensure effective implementation of environmental regulations
and strategies.
This publication fesffl been produced as part of the Laboratory's strategic long-
term research plan. It is published and made available by EPA's Office of Re-
search and Development to assist the user comsMtmity and to link researchers
with their clients*
E. Timothy Qppelt, 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 ^indorsement or recommendation for use.
This document is available to the public through the National Technical Information
Service, Springfield, Virginia 22161.
PROTECTED UNDER INTERNATIONAL COPYRIGHT
ALL R1BHTS RESERVED.
NATIONAL TECHNICAL INFORMATION SERVICE
U,S. DEPARTMENT OF COMMERCE
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£R£~600/R-96-08t)l
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. Lett
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-D1-0031
National Risk Management Research Laboratory
Research Triangle Park, NC 27711
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DISCLAIMER
LEGAL NOTICED 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, GRI, members of GRI, 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. Assumes any liability with respect to the use of, or for damages resulting from the
use of, any information, apparatus, method, or process disclosed in this report,
NOTE: EPA's Office 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 EPA/ORD's QA/QC policies. In all cases, data and results were reviewed by the
panel of experts listed in Appendix D of Volume 2,
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RESEARCH SUMMARY
Title Methane Emissions from the Natural Gas Industry,
Volume 12: Pneumatic Devices
Final Report
Contractor Radian International LLC
QM Contract Number 5091-251-2171
EPA Contract Number 68-D1-0031
Principal
Investigators
Report Period
Objective
Technical
Perspective
Results
Theresa M, Shires
Matthew R, Harrison
March 1991 - June 1996
FinsI Report
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 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 (CO3) per unit of energy produced than
either coai or oil. On the basis of the amount of CO2 emitted, the
potential for global wanning could be reduced by substituting natural gas
for coal or oil. However, since natural gas is primarily methane, a potent
greenhouse gas, losses 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 gts 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.)
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Based on data from the entire program, methane emissions from natural
gas operations are estimated to be 314 ± 105 Bscf for the 1992 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 in natural gas would be significantly lower
than the
The program reached its accuracy goal and provides an
of methane emissions that be used to construct U.S. methane
inventories and fuel
Technical Emission rates for pneumatic devices were determined by developing
Approach 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 rational emission rate is the product of the
emission factor and activity factor.
The gas industry has two primary of
1) control flow, and 2) gas-
aotuated block valves, of the industry its
own specific practices regarding "typical" device installations,
emission factors were developed based CJL the types of devices observed
from site visits.
Emission factor data for the various device types were collected from
sources: provided from other studies,
manufacturers* and collected site visits. collected
site included: the of type of device,
manufacturer model numbers, conditions (e.g., supply gas
and supply gas type), and device frequency.
Equations relating developed for the different
types of devices to develop an annual emission factor for a gt-neric
pneumatic 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 determined from counts
of devices site visits. The for
industry on the of the emission factor
for a generic device and the activity factor,
Project For the 1992 year, the methane emissions for the
Implications U.S. natural gas industry L 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
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the fuel cycle for natural gas, oil, and coal using the global warming
potentials (GWPs) recently published by the Intergovernmental Pariei on
Climate Change (IPCC). The analysis showed that natural gas
contributes less to potential global warming than coal or oil, which
supports the fuel switching strategy suggested by 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 in
cooperation with the American Gas Association to implement cost-
effective emission reductions and to report reductions to the EPA. Since
this program was begun after the 199? baseline year, any reductions in
methane emissions from this program are not reflected in this study's
total emissions.
Robert A. Lott
Senior Project Manager, Environment and Safety
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TABLE OF CONTENTS
Pag*
l.Q SUMMARY .., 1
2X3 INTRODUCTION , 2
3.0 PNEUMATIC DEVICE CHARACTERISTICS 3
3.1 Overview , , , , , , j
3,2 Gas-Actuated Control Halves ,: , , , 10
3.2.1 Operating Principles ... .. 10
3.2.2 Data Requirements ,., 22
3.3 Gas-Actuated Isolation Valves 24
3,3.1 General Description ,,, .-. -. 2:4
3.3.2 Data Requirements -,,,.. 2f
3.4 Other Pneumatic Devices , , 29
4,0 PNEUMATIC DEVICE EMISSION FACTORS 34
4.1 Production Segment , 34
4.1.1 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 , 4T
4.3 Gas Processing Segment 55
4.4 Distribution Segment , 59
5,0 PNEUMATIC DEVICE ACTIVITY FACTORS , 61
5.1 Production Segment 63
5.2 Gas Processing Segment 61
5.3 Transmission and Storage Segment . . 61
6.Q NATIONAL EMISSION RATE , , 63
7,6 REFERENCES ,. ,,; ,.., ._, 64
APPENDIX A - Source Sheets , A-l;
VI
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LIST OF FIGURES
Page
3-1 Example of a Pneumatic Controller T'I.J for Level,
Flow Rate, Temperature, or Pressure Control . , , , 5
3-2 Self-Contf ined, Spring-Loaded Pressure Regulator . 7
3-3 Pneumatic Device with Positioner - Force Balaace 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 , , 13
3-6b Throttling Continuous Bleed Pneumatic Relay -
Orifice Flapper Design , , 13
3-7 Actuator Types 15
3-8 Force Balance P-ston Device , , , 18
Lt-9 Th-ottling Continuous Bleed Controller with Proportional Adjustment 19
3-10 On-Off Snap Devices . r , ,, 21
3-11 Pneumatic/Hydraulic Rotary Vane Operator . . , v 26
3-12 Pneumatic/Hydraulic Rotary Vane Operator - Cross Section , , 27
3-13 Turbine Operator , 28
3-14 Solenoid Reky , , , , 31
3-1S Self-Contained Pressure Regulation Valve , 32
Vll
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LIST OF TABLES
Page
3-1 Pneumatic Dsvice Classifications ..,,.,,, 4
3-2 Typical Pneumatic Device Bleed Modes , IB
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 Emissi&a 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
6-1 Emission Rate Results 63
V1I1
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1.0 SUMMARY
This report is one nf several volumes that provide background information
supporting the Gas Research Institute and U.S. Environmental Protection Agency Office of
Research and Development (GRI-EPA/ORD) methane emissions project. The objective of
this comprehensive program is to quantify the methane emissions from the gas industry for
the 1992 base year to within ±0,5% of natural gas production starting at the wellhead and
ending immediately downstream of {he 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 va'ves that regulate flow, and gas-actuated isolation (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 were collected from several sources;
measured emissions provided from other studies, manufacturers' data, and data collected
from site visits.
The population of pneumatic devices in eacL -i.iiustry 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 produet 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, Q.60 ± 64% Bscf; and transmission,
14.1 + 60% Bscf. [Distribution emissions are included in Volume 10 on metering and
pressure regulating stations.1)
PISTON ACTUATOR
PNEUMATIC
SiGNAL FROM
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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 all "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 GRI/EPA
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. Enissions from pneumatic devices in the distribution segment are characterized in
a separate report on meter and regulation station emissions.' 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.
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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
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3 !.
Valve
Information
Function/Service
Level, Flow Rate,
Temperature, or
Pressure Control
Control
Isolation
Pneumatic" Controller Information
Type of
Control
Snap-acting
Throttling
Throttling
Throttling
N/A
Controller "Bleed Frequency
Intermittent
Stationary Bleed Rate = 0
Continuous
Non-zero Stationary Bleed
late
Intermittent
Stationary Bleed Rate = 0
No-bleed (discharges to
downstream gas line)
Intermittent
Stationary Bleed Rate = 0
Controller Bleed Rate
(upon valve actuation)
High rate, discharges
Ml volume of actuator
Small to large volume
discharged
Small to large volume
discharged
No-Weed (discharges to
downstream gas tine)
High rate, discharges
full volume of actuator
Controller Device
Design
On-off
(Figure 3-10)
Orifice-flapper
(Figure 3-6)
Force-baltnee
piston
(Figure 3-3)
Self-contained
spring/dkphragm
3-2)
Piston, rotary vane,
or turbine
(Figures 3-4, 3-11,
-3-12, and 3-13)
Pneumatic Positioner3
Information
N/A
Continuous or
intermittent
Continuous or
intermittent
N/A
N/A
Positioners are optional devices.
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Actuator
TfTTfn1 IJ 1 i TTJITTTT
Valve Body
Figure 3-1. Example of" a Pneumatic Controller Used for
Level, Flow Rate, Temperature, or Pressure Control
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the controller may continually bleed gas at various rates (throttling). 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 Ptmosphere,
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 when 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 pneumatic devices commonly used in the natural gas
industry and wnether 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.
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SET POINT ADJUSTMENT
DOWNSTREAM
PRESSURE
GAS INTO
REGULATOR
DOWNSTRiAM
PRESSURE
REGULATED,
LOWER
GAS OUT OF
REGULATOR
Figure 3-2. Self-Contained, Spring-Loaded Pressure Regulator5
ON/OFF SNAP DEVICE
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VALVE
ACTUATOR
QA8
SUPPLY
C0HTH0L
VALVE
STEM
CAEI
Figure 3-3. Pneumatic Device with Positioner-Force Balance Piston Type3
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•VALVE «JOOY
SUPPLY
Q&S
EXHAUST /
©AS /
,-WPH
EXHAUI
GAS
Figure 3-4. Example Isolation Valve <• Piston Gj:
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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
Does the Device
Steady-State
Operations?
No
No
No
No
No
Yes
No
Yes
No
No
Bleed During:
Actuation Cycle
(Valve Stroke)?
Mo
No
No
Yes
Yes
Yes
Yes
Yes
No
Yes
3.2
Gas-Actuated Cestrol Valves
3.2.1
Operating Principles
Pneumatic devices (valve controllers) iinked 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
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When 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 late.
Actuating bleed rates-inust be considered over a long period to determine average
emissions. Since the rate varies with me 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 ail 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 volume
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 P 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 flovv 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.
11
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MEASUREMENT
(LEVEL)
VALVE
3-5. Operating
12
-------
PRESSURE
REGULATOR
r
PWEUMATIC
.
PRESSURE
OAUQE
!
ao FBI
AIR OBttET
VARIABLE
OBIFIGE
(MOZZli)
FIXED UftfFICE
L_ _?f-'_
SUPPORT PIVOT
TO
ERASURING MEANS
Figure 3-6a. Threttling Continuous Bleed Pneumatic Controller! Orifice
Flapper Design5
NOZZLE
SUPPLY
PRESSURE
OUTPUT
PRESSURE
TO
ACTUATOR
Figure 3-6b. Tfaroftling Continuous Bleed Pneumatic Relay: Orifice
Flapper Design*
13
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Valve
Flow is regulated by a control valve. The valve operates by moving a valve
stem and a valve seat attached to the stern. The movement of the valve seat inside the
valve body can then restrict or stop process flow through the valve. The stern 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 vaive stem in the opposite
direction when the paetimatic 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. All actuation gas discharge
is emitted back through the valve controller,
Vaive 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 serial 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/valve-
controller loop that discharges gas to the atmosphere. Controllers are highly variable in
design. Depending on me design of the controller, the stationary position may or may not
14
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PISTON ACTUATOR
POSITIONER —
PISTON
CYLINDER *-
PNEUMATIC
CONTROLLER
FEEDBACK
SPI- '!G
VALVE
ACTUATOR
DIAPHRAGM
HEIGHT
Figure 3-7, Actuator Types*
15
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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 ceatrol is needed. The
frequency of this occurrence wil! 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 ferce 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 as 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 ^ssHfe
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 molt common are throttling and snap-
acting. 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
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A simplified drawing of a throttling contioiler's pneumalie 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 higSier 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 pneumatic output is at its highest level, If the
orifice is fully opers, most of the supply stream bleeds ta 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 uce 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
gam, proportional-integral gain, or propoitional-mtegral-derivative gain), mid 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
-------
TO/FROM
ACTUATOR
WiAK
APPLIED
FORCE
Figure 3-8, Force Balance Piston Device8
18
-------
CONSTANT SUPPLY PRESSURE
INLET EMD OF
RELAY VALVE
SMALL DIAPHRAGM
URGE DIAPHRAGM
FIJtEB ORIFICE
POBPORTIOSAL BELLOWS
PIVOTING CROSS SPRINGS
SXHAUST
EXHAUST 910 OF RELAY VALVE
BOURDON
EEfiH MS
FL3PPEH
oft nesaois PNEUMATIC
16AOWQ PRESSURE
POBPOHTIOMAL VALVE
EXHAUST
SBiSED
iOAOMQ ffiESSURE
NOZZtE PRESSURE
PROPORTIONAL P8ESSUS5S
Figuf e 3-9. Throttling ComliBMoiis Bleed Controller with Proportional
-------
This knob contains an exhaust port with a continuous bleed line from the actuator
diaphragm. These additional bleed locations are typical of proportional controllers.
For throttling control leys, manufacturers car. 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 rales.
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 snap-
acting controller has no continuous bleed, it only bleeds when the actuator is depressured.
Figure 3-10 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 eff, the actuator is vented to the
atmosphere and Hie 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
WEAK
APPLIED
FORGE
WEAK
APPLIED
FORCE1
SUPPLY
GAS
TO/FROM
ACTUATOR
EXHAUST
POST
PNEUMATIC SWITCH
VEHT
TO/FROM
ACTUATOR
SUPPLY
GAS
Figure 3-10, On-Off Snap Devices'
21
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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 Meed rate and a
stationary or steady-state bleed rate. The stationary bleed rate occurs when the signal is
constant 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 controllei are;
1. Basic device type (controller, positioner, self-contained device);
2, Pneumatic relay construction (orifice-flapper versus force balance pis-
ton, number of internal control adjustments, such as proportional gain
and set point »ce
3. Device condition (old or worn devices may leak more);
4. Design response time (fa'rter response devices require higher bleed
rates); and
5, Supply gas pressure and supply gas type (air produces no methane
emissions).
All 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
inerease above the stationary level so that the actuator ean be depressured, For all
22
•a r,
i. a
5 .3
"
-------
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:
1. Number of full stroke - rtes per year (how often the valve makes a
full stroke cycle);
2. Actuating chamber size; and
3. Supply gas pressure.
Based on (he characteristics of continuous bleed and intermittent bleed
pneumatic devices, the following approach was used to gatl ".r pneumatic data from site
visits for this report:
1. 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 Heed rate will vary with the supply gas pressure. The two common
signal pressure ranges are: 1) 3 to 15-psig; and 2) 6 to 30 psig.5 These supply ranges can
23
-------
fee 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 existing sources)10'" to produce an annual estimate of
emissions for intermittent and continuous bleed actuated controllers.
3,3 Gas-Acttiated Isolation Valves
Transmission compressor stations, transmission pipelines, storage stations,
and gas plants have large-diameter pipelines, and therefore have large pipsline 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.
Qnce 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-turn plug valves or quarter-turn ball valves. These operators use gas
pressure (pneumatie force) to move an actuator element in one direction. Sometimes the
pneumatic 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 ftom its original position by tne
pneumatic or hydraulic fcrce. Displacement operators in fhe 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, T lie oil moves through she vane
operator, delivering hydraulic force to the vane, and moving it and the attached valve stem
one quarter turn. The oil moving ittto 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 Shafec Valve Company,12 Figures 3-11 and 3-12 show a typical pneumatic/
hydraulic rotary vane operator from the Shafer catalogue.
Similarly, Pantex VaTve Actuators & Systems, Inc., manufactures a displace-
ment operator that uses natural gas to move a piston,6 The piston acts en an "arm" or lever
that rotates the valve stem. Gas is supplied to one side of the piston arid exhausted from the
ether to move the arm in each direction, either opening 01 closing the valve. An example of
this type of operator is shown in Figure 3-4.
Supply gas for these operators is usually pipeline gas, so pressure varies from
site to site. Compressed air can be used if it is availabl-; 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 small 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 valv? is illustrated in Figure 3-13.
25
-------
HYDRAULIC TAMKS
ROTARY VANE ACTUATOR
VALVg
Figure 3-11. Pneumatic/Hydraulic Rotary Vane Operator12
26
-------
TO CLOSE
- TO
HAND RUMP FOR MANUAL
OPERATION
Figure 3-12. Pneumatic/Hydraulic Rotary Vane Operator - Cross Section12
-------
GATE STEW
GEAR 10X
EXHAUST
TURBINE
Figure 3-13, Turbine Operator
28
-------
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 rale for isolation valve operators are:
1, Basic device type (turbine or displacement);
2, Manufacturer rad model number;
3, Supply gas presKpre, supply gas type {air produces 110 methane
emissions); and
4. Number of Ml stroke cycles per year.
The following approach was used to gather pneumatic data fer 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
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 hi this section only for the sake of
completeness. Some key examples are:
e 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
teed in the gas industry,
A common 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 oniy bleed if the downstreaffl 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-ecotained device is the transmission
arid distribution pressure letdown regatator (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
-------
FRGm
ACTUATOR
TO
ACTUATOR
DE-ENERGIZED;
SOLENOID
TO VENT
SOLENOID
e
ELECTRONIC
SIGNAL
I
(SUPPLY ©AS
IS BLOCKED)
ELECTRONIC
SIGNAL
I
(SIGNAL IS ON)
SUPPLY GAS
(VENT IS
BLOCKED)
Figure 3-14. Solenoid Relay5
31
-------
Figure 3-15. Self-Contained Pressure Regulation Valve
-------
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
- Production Processing --Jfrausinission Distribution
Control valves Yes Very Few Yes Yes
operated by gas?
Isolation valves No Some Yes Some
operated by gas?
The following subsections describe the details of pneumatic devices in each segment and the
emission factors associated with those devices.
4.1 Production Segment
"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 to
the atmosphere. .As stated earlier, primary measurement devices, which detect the initial
change in the process variable, are seated 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 (sueh 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 field-
loeated box.
The production segment uses both basic types of pneumatic:.controllers: 1)
titfattling, and 2) soap-acting. Throttling pneumatic relays of the "force balance piston" type
(Figure 3-8) bleed only when they mov; 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. Qrifiee 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.I.? 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," 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
sefd/device ±57% (90% confidence interval), and the average emission rate for throttling
35
-------
TABLE 4-2. RESULTS FROM THE CANADIAN PETROLEUM ASSOCIATION PNEUMATIC
EMISSION RATE STUDY
Instrument Type
Snap-Acting
Controller
Facility Type Equipment Tfype
Oil Battery Group Treater
Test Treater
Group Treater
Group Treater
Group Treater
Group Treater
Group Treater
Group Treater
Group Treater
Test Treater
Test Separator
Group Separator
"Quantity
Measured
1
2
1
2
2
2
1
1
1
2
2
1
Minimum Flow,
scfd
0.0
172
0,0
0.0
0,0
0.0
0.0
0.0
0.0
Maximum Flow,
scfd
690
172
>951
>933
>9S9
S73
> 1 ,9 1!
430
1397
Average Natural
Gas Emission,
sefd
33
179
14
226
59
140
81
69S
12
210
233
677
Average Emission for Snap-Acting Controllers 213 ± f7%
Throttling
Controller
Oil Battery Dehydrator
Line Heatsr
Line Heater
Line Heater
Group Treater
Test Separator
Test Separator
3
1
i
1
6
1
3
•0
ss
11
3.1
7
529
9
to
55
11
3:1
7
!529
240
2
•60
11
34
8
529
11
Average Emission for Throttling Controllers 94 ± 152%
-------
devices was 94 scfd/device ± 152%," The 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 he higher than the reported gas consumption due to
operating conditions, age, and wear of the device,11'16-17-18 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, bellows, fittings, and nozzles;
e Corrosives in the gas leading to erosion or corrosion of control loop
internals;
8 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 distauje
between the flapper and nozzle;
• Foreign material lodged in the pilot seat; and
* Wear in the seal seat.
The manufacturers contacted did net 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.10'11
Several pneumatic device manufacturers provided information on the gas
consumpti >n rates for their continuous bleed devices.9'16-18'19'20'JU2i23'24>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 fielcloperation may be higher than the reported "maximum," Some
manufacturers provided a maximum gas flow rate or delivery capacity that the controller
pilot C€«ld withstand (4,320 scfd for the Bristol 624II and 8,880 for the Fisher .4100). This
flow Tsfs indtca.xs the maximum amount of gas that can be supplied to the control loop. It is
possible ths.' wyie pneumatic devices could continue to operate up to these flow rates, but
TT-:-I fi"b;>ve thefct 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
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TABLE 4-3. BLEED FOR CONTINUOUS BLEED PNEUMATIC DEVICES
Manufacturer/
Model
Norriseal 1000 (A)
Norriseal 1001(A)
Bristol 624, 624 II
Fisher 2400
Fisher 2500
Fisher 2900
Fisher 4100
Invako AE 155
Invalco CT series
Gas C«nsiis;!|)l!*ti[ • Rates; Scfd
"Minimum"
"IVfsidEliEn"
Mode! discontinued in the 1960s
0-10
72-144
2,150
4,320
Model discontinued in 1957
168
1,008
Model dissontinued in 1991
24
1,200
8,880
Model discontinued - 1975
510
960
Comments on Specified Rate
No bleed rate information available.
Max. bleed rate is not specified by Norriseal. Es'irrtated for iTOl model ba:,ed
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 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 piloi can accommodate).
No bleed rate information available.
Bleed rate for 35 psig supply pressure. Mm. represents the steady state pilot
bleed rate (device not actuating) . MM. represents gas consumption when the
relay is completely :open.
Gas consumption not listed in device brochure, but Fisher representative
provided a laboratory: measurement of 555 'scfd for 35 psig supply pressure.
Bleed rate for 35 psig supply pressure. Min. represents the steady state pilot
bleed rate of the controller. Max. represents maximum gas consumption (1200
scfd) and delivery capacity of the conttoUe'F (8300 .scfd).
No bleed rate information available.
Minimum bleed rate specified for supply gas pressure of 20-30 psi. Maximum
bleed rate shown bete is reported by the manufacturer as a typical bleed rate for
(his device, A rettcrfit kit is available for this series of devices ;o 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 can at the manufacturers* gas consumption rates,
In addition, the delivery capacity reported by the manufacturers for some devices serves as
an absolute maximum Meed rate. Any measured emission higher than the deliver}'
for a given device would indicate an error in the and would justify
discarding the measurement.
for Continuous Devices
Field of devices with were
available from companies participating in a contractor's program,10 For
measurements, a contractor connected a flow meter to the supply gas line between the
regulator and the controller to the gas of the controller, A
cumulative flow rate and the current flow (scfh) were recorded and extrapolated to gas
consumption per day. ""he duration of the test depended on the variability of the gas use,
For operating conditions, one for 15-20 minutes. For
flow rates, several one-hour measurements were taken.
Although the not performed under the direction
of this study, the results are believed to be an accurate representation of pneumatic devices in
operation in the U.S. gas industry. Through with site and the
contractor the measurements,10 the technique,
protocol, and equipment calibration procedures were reviewed. Two measurements were
the set hscause they did not follow the for a
device (in both a sinyle reported for an unknown number of
devices). The final data set was deemed acceptable by the industry review panel.
After the QA/QC review, the set contained a of 41 measurements
from a combination of continuous bleed devices from offshore platforms, onshore production
sites, and Table 4-4 the
40
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TABLE 4-4. MEASURED EMISSION RATES FOR CONTINUOUS BLEED DEVICES
Production Production Total
Onshore Offshore Production Transmission
Number of
Measurements
Minimum,
scfd/device
Maximum,
scfd/device
Average,
scfd/device
9 9 18 23
380 108 108 152
2,334 962 2,334 4,215
1,189 ± 39% 556 ± 33% 872 + 30% 1,363 ± 29%
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 in 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 operatiens. 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 filter-
separators, 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
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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 transrtiission.
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% sefd/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 consuiiiption ranges
provided by the manufacturers, although a direct comparison for all device types can not be
made since manufacturer values are not available for all 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 repotted 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 emissiopr are in the range of
values provided by the manufacturer ar4 are believed to reflect more typical! operating
conditions for these devices and account for increased emissions due to wear. For the
purpose of this reports 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
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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 study.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 alwa' f 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 device types have distinctly
different emission rates, the fraction of intermittent bleed versus continuous bleed devices is
43
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TABLE 4-3. SUMMARY OF PRODUCTION SITE DATA
Site
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
TOTALS
FRACTION
Total
Count Of
Devices
136
18
405
68
2!
13
3
3
6
14
76
600
107
69
13
1
2
4
46
5
11
31
4,204
BY DEVICE
Power
Media
Gas
Gas
Gas
Gas
Gas
Gas
Gas
Gas
Gas
Gas
Gas
Gas
Air
Gas
Gas
Gas
Gas
Air
Air
Gas
Gas
Gas
TYPE
Number of
Snap-Acting
Devices
114
75
405
48
26
94
999
667
3
0
0
0
71
42
8
1
3
3
6
4
5
0
2,574
Number of
Throttling
Devices "
22
95
0
20
83
534
0
0
3
14
76
600
36
27
5
0
0
!
40
1
42
31
1,630
Non Continuous Bleed
0.65 ± 43%
Number of
Continuous
Bleed Devices'1
22
29
0
20
21
534
0
0
3
0
76
600
25
20
0
0
0
0
40
0
42
31
1,463
Continuous Bleed
0,35 :± 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 factor. From the site data, the fraction of continuous
devices is 0.35 ±43%, By difference, the fraction of intermittent pneumatic devices
is 0.65 ±43%.
Methane Composition
The by volume of in product .d gas was determined
to be 78.8% ±5%, this are in th? report,
from the Natural Gas Industry, Volume 6: Vented and Combustion Source Summary, *
Emission Factor Calculation
The factor per device calculated for production
as follows:
= «™eD* X B!eed + Oontmnoas Bleed X X
f Fraction of „,
Beed Methane
Factor n Devices Factor
v Devices Factor
m
The site were used to the fraction of intermittent bleed versus
continuous bleed devices; 65% ±43% and 35% ± 43% continuous
(Table 4-5). Table 4-6 the factor terms, the emission for
the individual device continuous bleed) on the
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, CALCJHLATION
Seleitsd Natural Gas
Fraction of Devie* Type Emission Factor,
Device Type sd'd/device
n
?0
Intermittent Bleed 0.65 ± 43% 323 ± 34%
Continuous Bleed 0.35 ±43% 654 ±31%
Methane Emission Factor for Average Device = 345 ±40% sefd/device
4.2 Transmission and Storage Segment
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 gas-
actuated 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
-------
aed equipment for or in of an emergency,
use natural gas rather than compressed air to actuate 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 Factors
Manufacturer and Site
The transmission emission factors were determined from information gathered
during site visits and from manufacturers' data. The gas-operated devices used in the
transmission were classified three continuous devices,
valves with operators, and valves with displacement-type
pneumatic/hydraulic Devices on air not in the
calculation,
The natural 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 quality checks were discussed in Section 4.1.2).10 As
shown in Table 4-4, 23 devices 152 to 4,215 scfd of
gas per device, with an gas of 1,363 ±29%
scfd/device (497,383 scf/device annually). It be noted that devices
were not observed at transmission stations.
Data on the following characteristics of isolation valves were gathered at 16
transmission sites:
1. device (continuous Heed, turbine, or pneumatic/hydraulic);
2, Manufacturer and number;
47
-------
3, Supply gas pressure, gas type (air produces no
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
the type (Figures 3-11 and 3-12). The of actuation
cycles per on site data. The manufacturer the of gas
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 v Discharge Pressure v Frequency v 2 Valve Movements ,
(P"W (cycles/year) X
Data provided by Shafer Valve Operating the gas
vary widely, so on the of of the rotary-vane-operated
valves were gathered from four stations.27-18 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
of the site data.
Due to the diversity of company for the 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
number of devices is not weighted higher than the other
48
-------
TABLE 4-7. PNEUMATIC/HYDRAULIC ROTARY VANE-
ISOLATION VALVE OPERATORS
Supply
Gas GBS Usage
Pressure, Actuator per Cycle,
Site psig Size sctfpsi
1 935 6.5 x 3.5 0.0042
6.5 x 3.5 0.0042
9x7 0.0123
11x7 0.022
14,5 x 14 0,0852
16.5x16 0.1183
16.5 x 16 0.1183
18x8 0.0489
18 x 8 0.0489
18 x 12 0,0852
25x16 0,31 g
25 x 16 0.318
Total Emissions for Site 1
Site Weighted Average = 1,879
2 935 25 x 16 0.318
25 x 16 0.318
25 x 16 0.3!8
20x16 0.1981
12.5 x 12 0.0482
12 x 12 0.0482
15 x 8 0.0279
18 x 8 0.0489
18x8 0.0489
20x16 0.1981
20 x 16 0.1981
26 x 36 0.7565
25x16 0.318
9x7 0.0123
9x7 0,0123
Total Emissions for Site 2 *
Site Weighted Average = 16,680
Number
of
Devices
4
1
1
1
1
3
2
3
1
5
I
= 45,086 scf
scfMevice±
4
2
2
6
4
i
S
2
= 583,803 scf
scf/deviEe 1
Cycles/
Yenr
12
1
f
1
1
1
12
J
12
t
12
1
54%
92
64
50
5
92
5
6
6
50
2
15
36
2
5
2
37%
Annual
Gas Usage,
•8tf/
Device Type
3:83:
8
23.
42
162
674:
5,393
279
1,115
162
36,242
604
237,496
82,607
64,537
147,649
1,467
587
340
4,962
198
6,031
14,473
3,071
19,361
624
100
Continued
49
-------
TABLE 4-7. (CONTINUED)
Site
3
Supply
Gas
Pressure,
psig
1000
Actuator
Si2e
5,5 x 3.5
6.5 x 8
9x7
11 x 10
12,5 x 10
12.5 x 12
20 x 16
25 x 16
16.5 x 16
14.5 x 14
12.5 x 12
Gas Usage
per Cycle,
sef/psi
0,0035
0.008
0.0123
0.03! 8
0.0279
0.0482
0,198)
0.318
0.1183
0.0852
0.0482
Number
of
Devices
7
14
8
1
1
5
3
12
9
1
1
Cycles/
Year
15.2'
15.2
15.2
15.2
15.2
15.2
15.2
15.2
15.2
15.2
15,2
Annual
Gas Usage,
scf/
Device Type
705
3,224
2,833
915
803
6,93 S
17,108
109,853
30,650
2,453
1,388
Total Emissions for Site 3 = 176,870 scf
Site Weighted Average = 2.853 scf/device ± 27%
950
12.5 x 12
6.5 x 3.5
11 x 10
16 wkm
0.0482
0.0042
0.0318
0.072
12
12
12
12
Total Emissions for Site 4 = 7,688 scf
Site Weighted Average = 1,098 scf/device ± 39%
3,348
97
736
3,507
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 full 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:
— Device Gas Usage Operating Duration v Frequency /2 Valye Movements]
A A
/2 Valye Movements
}* I ^ J (3)
(serf/mm) (^operation) Ccycfes/year} Q^
Isolation
Valve
Information on the approximate turbine motor gas consumption for a given gas
pressure was provided by Limitorque Corporation. l3 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 emissioa 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%. m
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
Supply
Gas
Gas Time/
Pressure, Consumption, Operation,
Site
1
2
3
(Typical Values)
4
(Typical Values)
5
(Typical Values)
psig
900.970
800:
800
SOD
800
AVERAGE ANNUAL TURBINE
gas/device
scfm
500-520
470
470
470
470
DEVICE EMISSION
sec
30
120
180
90
90
90
FACTOR
Gas Usage,
scf/Qpera(ion
:-255
1020
1430
705
705
705
, scf natural
Annual
Natural
Gas
Cycles/ Emissions,
Year
11
1
75
29
29
29
scf/device
3,825
211,500
40,890
40,890
40,890
67,599 ± 276%
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 — EFeertmuons X Fraction
-------
TABLE 4-9, TRANSMISSION DEVICE COUNTS - TURBINE AND
DISPLACEMENT DEVICES
Site
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Average Number
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%
Rotary Vane
Displacement
Devices/Site
26
62
34
0
0
11
17
35
69
6
18
4
50
2
0
0
2Q.9 ± 48%
0.522 ± 48%
5,62? ± 1 12%
53
-------
TABLE 4-10, TRANSMISSION DEVICE COUNTS - CONTINUOUS BLEED
Site
t
2
3
4
5
6
7
8
9
10
11
12
13
K
15
16
17
18
19
20
21
22
23
24
25
26
27
Continuous Bleed .ftevkes/Site
39
16
4
3
4
I
1
4
6
2
2
127
IS
4
22
3
4
4
4
1
1
I
15
92
3
6
i
Site
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
:47
4S
49
50
51
52
53
54
Average Number Devices/She
Fraction of Deviee/Site
Annual Natural Gas Emission: Factor, scOTevice
Continuous Bleed
11
ii
32
9
12
4
21
12
3
15
3
11
10
44
3
3
9
12
4
26
2
7
n
11
15
6
1
Devices/Site
12,9 ± 69%
0,32 ± 69%
497,583 ± 29%
54
-------
4.3 5m Processing Segment
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. Approxi-
mately 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 natural gas powered pneumatic device throughout
the plant. Stratification by device type could not be determined, so emissions '.vere
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
Site
1
2
3
4
5
6
7
8
9
Pe^Ice Type
Continuous
Bleed
(Fisher)
Isolation
(Fisher)
Air
Isolation
(Turbine)
Isolation
Piston Type
(Rotary Vane)
Isolation
(TurbiEe &
Pneumatic/
Hydraulic-type
Rotary Vane)
Air
Air
Air
Number • • Natural
of Operations/ Displacement/ Gas
Devices Year Device, scf
2 Continuous 497,584 995,168 ± 29%
3 12 214,675 ± 29%
-
25 1 780 ± 112%
7 12 48 1,206 ± 49%
18 1
1 1 660 44,115 4- 68%
16 12 2,716
..
--
.,
Total IJMMscf + 21%
(for gas sites) 341 site ± 103%
-------
Site 1: Continuous bleed devices, such as those in the transmission
segment, were observed at this site. Since the application of these devices is
similar to the transmission segment, the annual emission factor of 497,584 scf
per device (based on 1,363 scfd/device from Tabie 4-4) was used.
Site 2: Fisher devices were used to operate isolation vahes 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).
5: Piston-type isolation valve found at only one
for the specific device were provided by Pantex, the
manufacturer.6 Table 4-12. lists the manufacturer's 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%.
6: For the pneumatic/hydrauiic-type rotary devicp" observed at
site, the emission factor was on the volume 01 natural
per for the In Table 4-7. Manufacturer's
Limitorque, on a supply gas of 350
to estimate the emissions for the turbine operator at this site.
Methane Composition
The percentage of in gas in gas
to be 87,0% ± 5%. Details about this value are available in the GRI/EPA
report, Methane Emissions from the Natural Gas Industry, Volume 6: Vented and
Combustion Source Summary?6
57
-------
TABLE 4-12. GAS USE INFORMATION FOR PANTEX DEVICES
(PISTON DISPLACEMENT ISOLATION DEVICES)
No.
Devices
6
2
1
2
5
1
1
2
Piston
Diameter
(in.)
8.0
3.0
3.5
2.0
8.0
2.5
jg.O
6.0
Stroke
Length
(in.)
20
4
4
4
16
8
16
12
Gas
Usage
(acf/stroke)
0.5818
0.0164
0.0222
0,0073
0.4654
0.0227
0.2618
0.1964
Annual Site Gas Consumption, scf
Weighted Annual
Average per Device,
scf
Annual Gas
Consumption a
(scf/device)
512
4.8
3.3
2.1
341
3.3
38.4
57.6
965
48.1
a Gas consumption calculated based on supply pressure of 250 psig, an average of
4-, 1 operations per year, and two strokes (open and close) per operation.
58
-------
equation:
Emission Factor Calculation
The gas processing emission factor was caleulated according to the following
Annual Site Emissions, scf Natural Gas
EF= K X
1=1
(I);
x % methane
where:
K = fraction of sites that use natural gas rather than air (0.556 ±
59%)
n = number of sites operating devices with natural gas
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:
EF
EF
0.556 ± 59% gas sites/total sites surveyed x 341 + 103%
Mscf/gas site x 0.87 ± 5% mpl methane/mo! gas
165 + 133% Mscf/site
4.4
Distribadon Segment
The pneumatic devices in the distribution segment primarily consist of
pressure reduction throttling valves at vaster and pressure regulation (M&R) stations. The
actuators and controllers for there 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
of!,, (v-^m A r: A
-------
measured as part ,of the tracer campaign for M&R stations and included in the M&R stalfon
emission rates.1 Distribution pneumatic emissions are therefore excluded from this report,
Isolation valve actuators at distribution M&R stations ate usually manually or
motor-operated. There were so few pneumatic operators on isolation valves that this
emission source is considered negligible.
60
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5.0 PNEUMATIC DEVICE ACTIVITY FACTORS
Pneumatic device activity factors are discussed in detail in Volume 5 on
activity factors,2* 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.
S«l 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 number 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 p".r station
61
-------
multiplied by the total number of transmission and storage stations nationally using the
following equation:
A-~ Average Number of Devices „ ,., , ,, _, ... tf^
AF = •—^ — X Number of Stations (»}
Station
The average number of pneumatic devices per station is the sum of the average number of
turbine devices pef 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 pneumalie devices per site Is 40 ± 37%.
Therefore, the pneumatic device activity factor for transmission stations is:
AF = $,.25 ± 94% turbine devices/site
•+'- 20.9 ± 48% rotary vane devices/site
+ 12.9 ± 69% continuous bleed devices/site)
x 2,175 ± 8% stations
AF = (40 ± 37% devices/sfation) 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 arid are therefore
excluded from the national activity factor.
62
-------
6,6
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
Production
Gas Processing
Transmission
. Methane Emission
Factor
125,925 ± 40%
scf/device
165 ± 133% Msc&ite
162,197 ± 44%
sef/device
Acfivity Factor
249,111 ±48%
devices
726 ± 2% sites
87,206 ± 38%
devices
Annual Eitiission
Rate
31.4± 65%Bscf
O.J2± 133% Bscf
14.1 ±60% Bscf
Based on these results, pneumatic devices contribute a total of 45.6 ±48%
Bscf of methane for 1992.
63
-------
7.0 REFERENCES
1, Campbell, L.M. and B,B, 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 EPA-
600/R-96-080J, Gas Research Institute and U.S. Environmental Protection
Agency, June 1996,
2, Myers, D.B. and M.R, Harrison. Methane Emissions front the Natural Gas
Industry, Volume 15: Gm-Assisted Glycol Pumps, Final Report, GRI-
95/0257.33 and EPA-609/R-96-Q80o, Gas Research Institute and U.S.
Environmental Protection Agency, June 1996.
3, Shires, T.M. Methane Emissions from the Natural Gas Industry, Volume 13:
Chemical Injection Pumps, Final Report, GRl-95/0257,30 and EPA-60G/R-96-
080m, 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-96-080g, Gas Research Institute and U.S. Environmental
Protection Agency, June 1996.
5, Perry, J.M. (ed.) Chemical Engineers Handbook, 5th Edition. McGraw-Hill,
New York, NY, 1973.
6. Pantex Valve Actuators and Systems, Inc. Strongarm Series S Actuators for
Rotating Stem Valves, Bulletin No. SS-5-91, Stafford, XX.
7. Hummel, K.E., L.M. Campbell, and M.R, Harrison. Methane Emissions
from "the Natural Gas Industryf Volume S: Equipment Leaks? Final Report,
GRI-9S/0257.25 and EPA-600/R-96-080h, Gas Research Institute and U.S.
Environmental Protection Agency, June 1996.
8. Norrjseal Controls. Nmriseal Level Controller Series 1001-A Catalog.
Houston, TX, 1987.
9, Fisher Controls International, Inc. 415QKmd 4160K Series Pressure
Controllers and Transmitters, Bulletin 34:3.:4150K. Marshalltown, IA, 1992,
10. Controller survey data provided by Tenneca Gas Transportation, 1994 and
Chevron, 1995.
64
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II. Picard, D.J., B.D, Ross, and D.W.H. Kaon. "A Detailed Inventory of CE,
and ¥OC Emissions From Upstream Oil and Gas Operations in Alberta."
Canadian Petroleum Association, Calgary, Alberta, 1992,
12. Shafer Valve Operating Systems. Rotary Vane Valve Operators, Bulletin RV-
110, Houston, TX, 1980.
13, Personal correspondence with Belva Short of Limitorque Corporation,
LyneMHirg, VA, April 5, 1994
14. Personal correspondence with Brian Ross of Clearstone Engineering, Alberta,
Canada, October 16, 1995.
15. Personal correspondence with Bob Finley of Bristol Babcock Inc., Watertown,
CT, October 3, 1995.
16. Personal correspondence with Clark Crownover of Puffer Sweiven, Inc.,
Stafford, TX, October 6, 1995.
17, Personal correspondence with Maurice Hoss of Invalco Inc., Hutchinson, KS,
October 6, 1995.
18, Personal correspondence with Quin Kroll of Norriseal, Houston, TX, October
4, 1995.
19. Dover Corporation, N&rriseal Controls Series 1000 Liquid Level Control,
Manufacturer Bulletin 1.1, Catalog Section 1, W.C, Norris Division, Houston,
TX, July 1963.
20, Bristol Babcock. 624-If Indicating Pneumatic Transmitters Specifications,
Specification Sheet A103-la, Watertown, CT, 1992.
21. Bristol Babcock. Series 5453 Indicating Pneumatic Pressure Controllers,
Specification Sheet A118-2c, Watertown, CT. 1992,
22. Fisher Controls International, Inc. 3582 Series Pneumatic and Type 35821
Electro-Pneumatic Valve Positioners, Bulletin 62.1:3582. Marshalltown, IA,
1993,
23. Fisher Controls International, Inc. 3610J and 36203 Series Positioners,
Bulletin 62.1:3610, Marshalltown, IA, 1992,
24. Invalco. Low Energy Pilot Retrofit Kit for CT Series Flextuke, CT Series,
Issue 1, Page IVC-8Q1-A11, Tulsa, OK, December 1, 1990.
65
-------
25. Invafco, CT Seriss Flextube Displacer Type Level Controller, CT Series,
1, Page IVC-801-A3, OK, April 30, 1990,
26, 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-6G0/R-96-08Gf, Gas Research Institute and U.S.
Environmental Protection Agency, June 1996.
27, Shafer Valve Systems, Gas Consumption Calculation Method for
Rotary Gas/Hydraulic Actuators, Technical Data, GC-
OH, lune 1993.
28. Shafer Valve Operating Systems. Gas Consumption Calculation Method for
Rotary Vane, Gas/Hydraulic Actuators, Technical Bulletin Data, Bulletin GC-
2-00394. Mansfield, OH, March 1994,
29. Stapper, B.E. Methane Emissions from the Natural Gas Industry, Volume 5:
Activity Factors, GM-94/0257.22 and EPA-600/R-96-080e, Gas
Research and U.S. Environmental Protection Agency, June 1996.
30. Bell, L. "Worldwide Gas Processing," Oil and Gas Journal, My 12, 1993, p.
55,
66
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APPENDIX A
Source Sheets
A-1
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P-4
PRODUCTION SOURCE SHEET
SOURCES: Various Equipment
(wells, healers, separators, dehydrators, compressors)
COMPONENTS; Pneumatic Devices
OPERATING MODE;: Normal Operation
EMISSION TYPE: Unsteady, Vented
ANNUAL EMISSIONS:! 31.4 Bscf ± 65 %
BACKGROUND:
Most or the pneumatic devices in the industry are valve actuators and controllers lhat use natural gas pressure as
the force for valve movement. There is a large population of pneumatic devices throughout the gas industry.
Gas from the val-ve actuator Is veated to the atmosphere during every valve stroke, and gas may be continuously:
bled from the valve controller pilot as well.
EMISSION FACTOR; 125,925 set per average device ± 40%
(This was adjusted for the production methane fraction of natural gas at 78,8 ino!%,}
Pneumatic devices (valve controllers) linked to control valves are the largest source of pneumatic emissions in
tfie production segment. There are two types of devices with distinct bleed modes: intermittent and continuous.
Iiftennitteni bleed devices emit methane to the atmosphere only when the control valve actuates; when the device
is not moving the bleed rate is zero. Continuous bleed devices emit methane both when the valve actuates and;
when 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:
EF^f™.*™,: = (Rraction ,„,„„„„, X f.W ^miva + Fraction ^^^ x EF^^^J
:X % methane
where:
Fraction lmtmi
-------
2. Site visit device counts establish the fraction of continuous Meed versus intermittent bleed
devices for multiple sites.
3. The Canadian Producers Association (CPA) deterntiiied an average emission factor per device
based oil -19 measurements.
4. An independent contractor provided IS measurements of pneumatic devkcs'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 fates.
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 weffi 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 249,111.
AF DATA SOURCES:
1. Methane Emissions from ihe Natural Gas Industry, Vglume 5: Activity Fa&on (2) establishes
the methodology for extrapolating 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 reported as 602,197 by the Oil & Gas Journal (5). The active oil wells that
market gas are determined by multiplying the total niational active wells by ihe 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 She associated gas in Texas is 34.7 55.
AF PRECISION:
Basis:
1, 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),
2. 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 Bsc? ± 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 24:9,111 devices = 31 Bscf
A-3
-------
KEFERENCES
1. Shires, T.M. and M.R, Harrison, Methane Emissions from the Natural Gas Industry, Volume 12:
Pneumatic Devices. Final Report, GRI-94/0257.29 and EPA-600/R-96-0801, Gas Research Institute and
U.S. 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-6QQ/R-96-080e, 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 0(7, Annual Forecast/Review, Vol. 214, No. 2, February 1993,
5, Oil and Gas Journal, 1992 Worldwide Gas Processing Survey Database, 1993.
6. Texas Railroad Commission, P-l, P-2 Tapes, Radian files, Austin, TX, 1989.
A-4
-------
T-4
TRANSMISSION AND STORAGE SOURCE SHEET
SOURCES: Various Equipment (vessels, compressors, piping)
OPERATING MODE; Normal Operation
EMISSION TYPE: Unsteady, Vented
COMPONENTS: Pneumatic Devices
ANNUAL EMISSIONS: 14.1 Bscf ± ;60%
BACKGROUND:
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 gar.-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 filter-
separatois and pressure reduction. The higher pressures anj large pipe diameters associated with transmission
operatif.is require larger actuators and valves than typically found in production, resulting in larger emissions
than '.milar 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 eafl isolate the facility for maintenance work or
in the case of 5,1 emergency. Therefore, the isolation vaives are actuated infrequently and their emissions are
intermittent.
EMISSION FACTOR: 162,197 scf/device ± 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 determined based on the following equation:
EF Pneurnauc devi«s = ( EF com biHd v,sv« x Fraction
ecnt.:bjfrial va!v«
turbine operators riddlOn turbine operaton
EF ^taeoMm OPHMOB x Fraction „;„„«„,„, „„,„,„„ ) x % methane
Listed below are the average fraction of devices for each of the three valve categories:
Fraction „„, ^:„„„, = 0.32 ± 69%
Fraction ^^^^ = 0,1.6 ±94%
Fraction ,,,DlraratnlMMlm = 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/deviee ± 29% (497,584
scfFdevice).
A-5
-------
Per the isolation valves with turbine operators, the emission factor depends on the gas: usage for a given
supply gas pressure, the rime required to complete one movement of the valve, and the number of operations
per year. The annual emission factor is then;
EF Mtiint optima = Gas Usage (scf/aiin) x Operating Duration (min/operation) x 1
(operations/cycle) x Frequency (cycles/year)
EF ^iaeafmlal, = 67,599 ± 276% seffdevice
The equation for isolation valves with displacement operators is similar;
EF dM>«™« op***. = Gas Usag* (scf/psia) x Supply Pressure (psia) x 2
(operations/cycle) x Frequency {eycles/yeai1)
EF „„,,««„» opK>aw = 5,627 ± J12% scf/device
EF DATA SOURCES;
1. MethatiB Emissions from the Natural Gas Industry, Volume 12: Pneumatic Devices (1)
establishes the important emission-ahecting 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 ftom a total of 54 stations were used to
establish the fraction of continuous bleed devices,
3, The emission factor for the continuous bleed vaJvss was based on 23 field measurements,
4, Gas usages for the turbine valve operators were provided by LimitorqaCi Operating duration
and frequency were estimated based on information from two transmission stations.
5. Gas usages for the dispjacunent valve operators were provided by Shafer Valve Operating
System,^ Supply pressure and frequency of operation were estimated based on information:
from fear transmission stations.
EF ACCURACY:
Basis;
1. EF accuracy is based on error propagation from the combination of site information and
measured data.
2, It was assumed that the manufacturers' data are completely accurate,
ACTIVITY FACTORS: 87,206 pneumatit devices ± 38%
The number of gas operated pneumatic devices in the transmission and storage segment was calculated based
on the average number of devices per station and multiplied by the total number of transmission and storage
stations nationally. The average number of devices per site was determined to be 40 ± 37%. The total count
of transmission compression facilities is 2,175, based on 1,700 compressor stations, 386 UG storage stations,
and 89 LNG storage stations'.
AF *ATA SOURCES;
1. The number of transmission compressor , was compiled from 1©2 Fossil Energy
Commission Form No. 2: Annual Report 01 Majw Natural Oas 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 ob.eived during site
visits.
AF ACCURACY: 38%
Basis:
1. Extremely tight confidence limits are expected due to the well documented and reviewed
numbers published in A.G.A. Oas Facts and FERC forms. A 10% confidence bound was
assigned to the number of corfipressor stations and a 5% confidence bound was assigned to
the number of storage stations,
2. The confidence bound on the number of devices per station was det-srmined based on the
spread of site data.
ANNUAL METHANE EMISSIONS: 14.1 Bscf ± 60 %
The annual emissions were determined by multiplyinfe an emission fetor 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
1. Shires, T.Tvl, 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 Na. 2: Annual Report of Major Natural Gas Companies OMB
No, 1902-0028, department of Energy Federal Energy Regulatory Commission, Washington, DC,
December 1994.
3. American Gas Association. Gas Facts:, 1993 Data, Arlington, VA, 1994.
4. American Gas Association. Gas Facts:. 1991 Data, Arlington, VA, 1992.
A-7
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GP-6
GAS PROCESSING SOURCE SHEET
SOURCES; Various Equipment (vessels, compressors, piping)
COMPONENTS: Pneumatic Devices
OPERATING MODE; Normal Operation
EMISSION TYPE; Unsteady, Vented
ANNUAL EMISSIONS: 0.1Bscf±133%
BACKGROUND:
The gas processing segment uses compressed air to power the majority of the pneumatic devices within the
plant, although some devices may be powered b;y natural gas. Many plants use gas driven pneumatic.
controllers on isolation valvs for emergency sfaiti-down or maintenance work.
The same type of devices used in the transmission segment are also commonly used in the gas process»r»g
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 moi%.)
The average device gas esnission faeiar was determined from a combination of vendor information on device
emission rates and device ewmts from several sites. The average emission factor was calculated using the
following equation:
n
]P( Annual Site Emissions, acf Natural Gas)
= * * — ~ — — x % Methane
K = fraction of sites that use natural gas rather than air (0.56 rt 59%)
n *«• number of sites operating with natural gas
Each i.Kjrm in this equation was determined from site specific information. The summation of the site specific
data was than adjusted based on the number of sites with gas operated devices versus the total number of
sites .surveyed. The site resilts are shown in the following table.
A-8
-------
"'•Site
1
2
3
4
5
§
7
8
9
TOTAL
Number Operations/
Device Type of Devices Year
Throttling (Fisher)
isolation (Fisher)
Air
Isolation (Turbine)
Isolation (Rotary Vane)
Isolation
(Turbine & Rotary Vane)
Air
Air
Air
2 Continuous
3 12
..
25 1
7 12
IS I
i 1
16 12
,.
..
_
Annual
Displacement/ Displacement/
Device, set . Site, scf
497,584 995, 168 ±29%
214,675 644,025 ± 29%
-
780 ! 9,500 ±112%
48 1,206 ± 45%
3,376 44,115 + 68:%
--
..
-
1,704 MiCf ±21%
Average (for gas sites)
341 Mscf± 103%
EF DATA SOURCES:
1, 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.
EFACCURACY;
Basis:
1. EF accuracy is based on error propagation from the spread of data for the nine sites visited.
2. It wcs assumed that the manufacturers' data are completely accurate.
ACTIVITY FACTOR; 726 gas processing ptanls ± Z%
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 OH and Gas Journal (2),
AF PRECISION:
Basis:
1. AF accuracy is based on engineering judgement.
.ANNUAL 0,12 Bscf ±
The annual emissions were by multiplying an average site emission (adjusted for the
methane composition) by the number of gas sites,
165 x 726 sites = 0.12 Bscf
REFERENCES
1. Shires, T.M. and MR. Harrison. Methane Emissions from the Natural Gas Industry, Volume 12;
Pneumatic Devices. Final Report, GRI-94/0257.29 and EPA-600/R-96-0801, Gas Research Institute
and U.S. Environmental Protection Agency, June 1996.
2.. Bell, L. "Worldwide. Gas Processing," Oil. and Gas Journal, My 12, 1993,. p. 55.
A-10
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