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Natural Gas STAR Methane Challenge Program
Continuous Improvement Update
Finalizing an Equipment Leaks/Fugitive Emissions Commitment Option for
Compressor Isolation and Blowdown Valve Leakage
Proposed by: Natural Gas STAR Methane Challenge Program in coordination with National Fuel
Gas
Date proposal published: February 26, 2020
Date change finalized: July 14, 2020
Category of change: Finalizing a new BMP commitment option
Summary of change: Develop a commitment option for mitigating methane emissions from
leaking isolation and blowdown valves on compressors
Overview
Through the Natural Gas STAR Methane Challenge Program ("the Program"), EPA encourages Partners
to make ambitious commitments to reduce natural gas (methane) emissions through broad scale
implementation of cost-effective technologies and practices. EPA recognizes ongoing advances in
technologies and approaches for identifying, measuring, and mitigating methane emissions and will
consider creating new commitment options, as well as revising approaches to track, implement, and
report on current commitments through the Continuous Improvement Process.1
When the program was launched in 2016, EPA identified four emission sources that were of interest to
partners, but for which commitment options were not yet ready to be finalized in the Best Management
Practice (BMP) Commitment Option. Equipment leaks/fugitive emissions was one of these four sources.
In this document, the Program establishes a best management practice to address a specific subset of
this category: isolation and blowdown valve leakage. This comprises an initial, compressor station-
related fugitive emissions commitment option. The following sections outline the emission source and
options for voluntarily mitigating methane emissions and tracking reductions from this source. This
includes specifying data elements that will be collected to track commitment progress.
1 Details available on the Program website at https://www.epa.gov/natural-gas-star-program/methane-challenge-
continuous-improvement
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While this program update focuses on a specific subset of equipment leaks, the Program could later
expand the scope of the Equipment Leaks/Fugitive Emissions source (i.e., beyond compressor valve
leakage) as well as evaluate options for upstream segments.
Notice and Disclaimer
This document provides an overview of a best practice for reducing methane emissions from leaking
isolation and blowdown valves on compressors through maintenance, monitoring, and valve
repair/replacement. Partner companies that commit to mitigate emissions from this emission source
can use this information to better understand options available for mitigating emissions from these
sources. Each facet of the best practice may not be suited for a piece of equipment and/or facility, so
application must be determined on a site-specific basis. Information in this document is not official
guidance; rather, it provides general information about addressing methane emissions from leaking
isolation and blowdown valves on compressors. Partner companies are responsible for compliance with
applicable regulations.
Emission Source
For the purposes of this document, compressor components include those physically connected to or
immediately adjacent to a compressor. Compressor blowdown valves, unit isolation valves, and seals
(i.e., reciprocating compressor rod packing and centrifugal compressor wet or dry seals) are identified as
"major" compressor components. Non-compressor components are all other components at a
compressor station. Seals are already addressed in the Methane Challenge Best Management Practice
Commitment Option and related Technical Document and will not be discussed further in this
document. This program update addresses methane emissions at compressor stations from leakage
through compressor blowdown and isolation valves.
Compressor Mode of Operation
When a compressor is in a not-operating depressurized (NOD) mode, gas may leak to atmosphere via
unit isolation valves. In this NOD configuration, the isolation valves are closed against both high-pressure
suction and discharge pipeline gas and the exterior and elevated blowdown valve(s) is open. If through-
valve leakage is present on the isolation valves, the gas is typically routed via a vent line and through an
open blowdown valve(s), which is open to atmosphere. Figure 1 is a simple schematic of such a leak.
Such leaks, which are considered "elevated vent sources," can be visualized using optical gas imaging
(i.e., an OGI camera).
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d
Blowdowu Valve
(Opeu)
I'uit Isolation Valves
(Closed-leak)
Depressiirized
Pipeliue
Figure 1. Unit Isolation Valve Schematic
Often, compressors have multiple isolation valves that exhaust through-valve leakage to atmosphere
through a common vent. With such configurations, methods are needed to identify specific valves
contributing to through-valve leakage and quantify the relative leak rates when more than one valve is
leaking. The presence of ice and condensation on or near a valve2 is a common method to identify a
leaking isolation valve; however, not all leaking valves cause ice formation or condensation. Even when
such identification is possible, it does not provide a means to quantify the through-valve gas leak rate.
Similarly, when a compressor is operating or in standby-pressurized mode, the isolation valve is open,
the blowdown valve is closed, and potential blowdown valve leakage is typically conveyed to
atmosphere through the vent (See Figure 2).
Figure 2. Unit Blowdown Valve Schematic
The operating mode highlighted in Figure 2 presents another potential leak scenario: compressor rod
packing. As previously noted, compressor rod packing is addressed in another Methane Challenge BMP
and will not be discussed further.
2 Presence of ice and condensation is caused by the Joule-Thomson effect; i.e., temperature drop across a leaking
valve.
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Best Management Practice (BMP) to Address Isolation and Blowdown Valve
Leakage
The isolation and blowdown valve performance improvement BMP is primarily designed to address: (1)
methods to identify and measure through-valve leakage; (2) maintenance and repair practices for
isolation and blowdown valves; (3) compressor station design considerations to facilitate access to
isolation and blowdown valves for maintenance, repair, and replacement; (4) isolation and blowdown
valves that are less prone to through-valve leakage; and (5) leaking isolation and blowdown valve repair
or replacement decision guidelines (e.g., estimate emission reductions for different isolation and
blowdown valve repair/replacement options and define what constitutes an actionable leak using valve
repair/replacement cost estimates).
As with all Methane Challenge commitments, it is expected that this BMP will be applied across all
assets in a partner's operations.
Within 5 years of committing to this emission source, partners will:
Implement an annual isolation and blowdown valve leak survey at all compressor stations
o The surveys can be conducted on the compressors as found (i.e., if the compressor is in
operating mode or standby-pressurized mode, the blowdown valve will be surveyed and
if the compressor is in not-operating-depressurized mode, the isolation valve will be
surveyed). However, partners are encouraged to work up to a biannual (or more
frequent) survey, timing the surveys so both the isolation and blowdown valve can be
surveyed on each unit, each year.
Develop an isolation and blowdown valve enhanced maintenance plan
o Partners may create a plan for each compressor station, or they can create a general
maintenance plan that they then tailor to each facility to account for pressure, valve
types, station operating time, facility configuration, etc.
o The "enhanced" maintenance plan should be a data-driven "living document"that is,
the plan should be periodically assessed/updated if needed after evaluating valve
performance over the course of the commitment. Maintenance activities in this plan will
likely go beyond routine/required maintenance.
Mitigate emissions, where practical, from all detected leaks by any combination of the
following:
o Implementing activities identified in the enhanced maintenance plan that lead to
emissions reductions.
o Repairing or replacing valves where practical (e.g., considering budgetary constraints,
operating requirements and maintenance schedules). Repair/replacement should be
targeted as soon as practical, but in no more than one to three years after identifying
the leaking component.3
o Routing isolation and blowdown valve leakage to a capture system for beneficial use to
achieve at least a 95% reduction in methane emissions.
3 Operational issues such as the need for system/facility blowdown, scheduled outages for maintenance, parts/
large valve availability, availability of repair personnel, etc. can be considered when determining the valve repair/
replacement schedule.
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o Routing isolation and blowdown valve leakage to flare or control device4 to achieve at
least a 95% reduction in methane emissions.
As part of the annual leak survey, the following data should be documented:
Leak rate
o Methodologies from Subpart W of the GHG Reporting Program (40 CFR, Part 98) will be
used for leak rate measurement. Note: the acoustic device cannot be used for the
purposes of measuring leak rates for this commitment option.5
o Partners will be able to report multiple measurements per year to Methane Challenge if
they survey a component more than once a year,
o If a valve is repaired or replaced, Partners should take a measurement on the unit within
90 days after the repair/replacement to calculate annual emission reductions.
All survey, maintenance, repair, and replacement data
o This should include the repair/replacement status of all leaks, as well as information on
replacement valves' performance, installation, and design considerations.
Data collected and lessons learned by partners in the first five years of this commitment will be
evaluated and used to further refine the parameters of this Methane Challenge commitment option. In
the last year of a partner's initial commitment (typically five years after making the commitment), EPA
will request a summary report including:
A discussion of "lessons learned"
An analysis of leak counts and distribution
Year-over-year leak changes, repair methods, and practices, including a discussion of the effects
of implementing the maintenance plan
Equipment / valve-specific recommendations
Maintenance plan results and costs
Reporting Approach
When a leak is identified, measurement will be completed using Subpart W approved methods.
Measurements will be completed before and after valve repair or replacement. These measurements
will allow for quantification of emission reductions. The unit should be measured within 90 days of
repair or replacement for the purposes of calculating an emission reduction.
If partners did not complete repair or replacement on a given component, but did implement enhanced
maintenance, partners may complete periodic measurements to determine if more frequent/targeted
valve maintenance reduced emissions.
Subsequent measurements will provide insight into leak recurrence, performance characteristics for
different valve types, and effectiveness of the partner's enhanced maintenance plan. Annual reports will
provide survey results from the applicable calendar year, and the report at the end of the partner's
commitment will summarize results and lessons learned over the entire course of the partner's
commitment. This "end-of-commitment report" should include discussion of program lessons learned,
emission reductions (i.e., from enhanced maintenance, valve repair, and/or valve replacement),
maintenance / repair / replacement challenges, measurement frequency, enhanced corporate
4 Control device means any equipment used for oxidizing methane vapors. Such equipment includes, but is not
limited to, enclosed combustion devices, flares, boilers, and process heaters.
5 If a partner feels it cannot measure without the acoustic device, please contact the Methane Challenge Program.
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maintenance practices, costs, etc. Partners making this commitment should ensure they are tracking the
necessary data each year so they are able to prepare this report at the end of the commitment.
Specific proposed data elements for Methane Challenge reporting on this emission source and BMP,
including details on the end-of-commitment report, are detailed in Appendix B. Annual reports will be
submitted on a facility-level basis.
Challenges
In Methane Challenge Partner National Fuel Gas's experience, valve repair/replacement can be cost-
prohibitive.6 Cost-effective and improved isolation valve technologies, selection, maintenance, repair,
and replacement options need to be evaluated. Other costs, such as station downtime (lost revenues)
from valve malfunctions or repairs, and gas losses (and emissions) from station blowdown, may be
incurred. In addition, there are cases where a new valve may show through-valve leaks when
recommissioned.
6 https://www.epa.gov/natural-gas-star-program/proposed-bmp-targeting-unit-isolation-blowdown-valves
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Appendix A. Commitment Progress Metric Calculation
To track a Partner's progress towards achieving its commitment to this emission source, EPA would
calculate the 'progress metric' as follows:
Metric Calculation
number of facilities with implemented annual inspection and maintenance program
* 100
total number of facilities
Metric Denominator - total number of facilities
Metric Numerator - number of facilities to which the inspection and maintenance program has
been rolled-out
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Appendix B. Updates to Methane Challenge BMP Technical Document
Equipment Leaks/Fugitive Emissions - Compressor Isolation and Blowdown Valves
Applicable Segments: Transmission & Storage
Source Description: This commitment option addresses methane emissions at compressor stations from
leakage through compressor blowdown and isolation valves.
Mitigation Options:
Develop a compressor valve inspection, maintenance, and repair/replacement program
o Implement an annual isolation and blowdown valve-focused leak survey at all compressor
stations. Partners can measure the compressors as-found but are encouraged to work up to
a biannual survey, timing the surveys so both the isolation and blowdown valve can be
surveyed on each unit, each year
o Develop an isolation and blowdown valve enhanced maintenance plan
o Mitigate emissions from found leaks by any combination of the following:
¦ Implementing activities identified in the enhanced maintenance plan that lead to
emissions reductions, or
¦ Repairing or replacing valves where practical (e.g., considering budgetary
constraints, operating requirements and maintenance schedules).
Repair/replacement should be targeted as soon as practical, but in no more than
three years after identifying the leaking component, or
¦ Routing isolation and blowdown valve leakage to a capture system for beneficial use
to achieve at least a 95% reduction in methane emissions, or
¦ Routing isolation and blowdown valve leakage to flare or control device7 to achieve
at least a 95% reduction in methane emissions
Commitment Timeframe: Partners commit to implement the specified mitigation options for all sources
included in their commitment by their designated commitment achievement date, not to exceed five (5)
years from the commitment start date.
7 Control device means any equipment used for oxidizing methane vapors. Such equipment includes, but is not
limited to, enclosed combustion devices, flares, boilers, and process heaters.
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Facility-level Annual Reporting:
Emission
Quantification
Data Elements Collected via Facility-Level Reporting
GHGRP
Source
Method
Unique name or ID for the compressor
X
Compressor type (Reciprocating or Centrifugal)
X
Hours in operating-mode
X
Hours in standby-pressurized-mode
X
Hours in not-operating-depressurized-mode
X
Which, if any, compressor sources are part of a manifolded
X
group of compressor sources
Indicate all of the following that apply to blowdown valve and
Individual
NA
isolation valve emissions from the compressor during the year:
compressor
Emissions are vented to the atmosphere
X
Emissions are routed to vapor recovery
X
Emissions are routed to flare
X
Emissions are captured for fuel use or routed to a thermal
X
oxidizer
Emissions are part of a manifolded group of compressor
X
sources
Compressor in not-operating-depressurized-mode all year
X
(Y/N)
Unique name or ID for the compressor
X
Unique name or ID for the individual vent to the atmosphere
X
Type of component [Isolation valve; Blowdown valve]8
X
Did you repair or replace this component during the calendar
NA
year? [Repair; Replace; N/A]
If yes, date of repair or replacement
Did you implement an enhanced9 maintenance program on the
Individual
valve this year?
components
If yes, provide pertinent details on the maintenance
on each
activity(ies)
compressor
As found
measurement
or continuous
Mode in which the compressor was operating when measured
(Operating; Standby-pressurized; Not-operating depressurized)
The measurement method used
X
measurement
of individual
compressor10,11,
12
Measurement date
X
Was this measurement taken before or after a mitigation action
was implemented during the calendar year (if applicable)
[Before; After; N/A]
8 Wet seals on centrifugal compressors and rod packing on reciprocating compressors are outside of the scope of
this commitment and will not be included in the reporting requirements for this commitment.
9 "Enhanced" maintenance refers to a data-driven approach that uses measurement to target certain valves for
maintenance and will likely go beyond "recommended" maintenance.
10 Under this Methane Challenge commitment, partners should report measurements from all surveys conducted
during the calendar year. The reporting form will be set up to accommodate this.
11 40 CFR 98.233(p)(l)(i)(A), (p)(2)(ii), (p)(6)(i), and (p)(ll)
12 40 CFR 98.233(p)(l)(ii), (p)(3), (p)(7), and (p)(ll)
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Emission
Quantification
Data Elements Collected via Facility-Level Reporting
GHGRP
Source
Method
Flow rate based on measurement type:
a. As found: Measured volumetric flow at standard conditions
X
(scfh)
b. Continuous: Measured volumetric flow at standard
X
conditions (MMscf)
Annual CH4 emissions (mt CH4)
X
Reporter EF (scfh)
X
Site-specific
Number of measured compressors (during the current year and
X
EF13
2 previous years) from which the reporter EF was developed
Annual CH4 emissions (mt CH4)
X
Number of surveys at this facility during the calendar year
How many compressors at this facility were surveyed this year?
How many vents indicated valve leakage this year?
How many leaking isolation valves were repaired or replaced this
year?
How many leaking blowdown valves were repaired or replaced
Leak inspection
and repair /
replacement
this year?
How many leaking isolation valves were routed to a capture
NA
system for beneficial use?
How many leaking blowdown valves were routed to a capture
program
details
system for beneficial use?
How many leaking isolation valves were routed to flare or
control device?
How many leaking blowdown valves were routed to flare or
control device?
If valves were repaired or replaced, use this space to provide any
pertinent details on the replacement/repaired valve's
performance, installation, and design considerations
Voluntary
action to
reduce
methane
emissions
during the
Difference in
emissions
Has the inspection and maintenance program been rolled-out to
this facility? (Y/N)
before and after
mitigation14
Annual emissions reductions from voluntary action (mt CH4)
reporting year
13 The site-specific emissions factor approach is used when an as found measurement for the compressor is
conducted in standby-pressurized-mode or in not-operating-depressurized-mode during the year (and an as found
measurement is not conducted in operating mode). The site-specific emissions factor is developed from as found
measurements of individual rod packing vent emissions from other compressors during the same year and the 2
previous years. 40 CFR 98.233(p)(l)(i)(A), (p)(2)(ii), (p)(6), and (p)(ll).
14 This should be calculated on a compressor-by-compressor basis, subtracting emissions after mitigation from
emissions before mitigation. Emissions after mitigation should be measured within 90 days of implementing the
mitigation action.
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End-of-Commitment Report:
This emission source will have a special "end-of-commitment" report in which partners will submit an
analysis of their leak detection, maintenance, and repair/replacement program to inform future
commitments. Partners making this commitment should ensure they are tracking these data each year,
so they are able to prepare this report at the end of their commitment.
Summary of "lessons learned"
Analysis of leak counts and distribution
Year-over-year leak changes, repair methods, and practices, including a discussion of the effects of
implementing the enhanced maintenance plan
Equipment / valve-specific recommendations
Maintenance plan results and costs
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