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Background |
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The natural gas system in the U.S.
is vast, being comprised of hundreds of thousands of wells, hundreds of gas
processing facilities, over one million miles of pipeline, and millions of
consumers.
Methane is the major component of natural
gas, comprising about 95 percent of the processed gas. Methane emissions
from natural gas systems are generally process related, mostly stemming from
normal operations, routine maintenance, and system upsets. Emissions from
normal operations include exhaust from natural gas combustion engines and
turbines, bleed and discharge emissions from pneumatic devices, and fugitive
emissions from various system components. Routine maintenance emissions can
occur during repair and maintenance activities on pipeline, equipment, and
wells. Pressure surge relief systems and accidents can lead to system upset
emissions. Since natural gas is often found in conjunction with petroleum,
crude petroleum gathering and storage systems are also sources of methane
emissions.
Leaks in the natural gas system can also
be characterized by the stage of activity from initial production to
delivery to the end-user. Significant emissions occur from each of the four
components, with different factors affecting each one. Most of the leaks
occur from the production, transmission, and distribution stages, with
lesser leakage from the processing and storage stages:
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Field Production.
In this stage, wells extract the gas from underground formations. In
the U.S., there are hundreds of thousands of wells and their
associated piping and treatment and processing equipment. Some amount
of initial gas processing occurs in the field before gas is piped to
centralized processing facilities. The majority of emissions from
field production are fugitive emissions from well-associated equipment
(separators, meters and dehydrators) and gathering lines, and releases
from pneumatic (i.e., gas-powered) control devices.
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Processing.
Processing plants ensure that gas meets the quality standards for
transmission. Before gas is injected into the transmission system, it
is processed to remove condensate, particulates, and other compounds.
Fugitive emissions from compressors are the source of the majority of
processing-related methane emissions, with fugitive emissions from
piping and releases from pneumatic devices also significant.
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Transmission
and Storage. High
pressure, large diameter pipelines are used to transport gas from
production, processing and storage facilities to large gas consumers
and distribution networks. Pressure in the system is maintained by
compressor stations. These stations, along with metering and
regulating stations, account for the majority of methane emissions in
the transmission stage. Storage facilities, which are underground
formations into which gas is injected and kept during times of low
demand, produce emissions mainly from compressors and dehydrators.
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Distribution.
Lower pressure pipelines deliver gas
from the transmission network to consumers. This system is made up of
over one million miles of low-pressure iron, steel, and plastic piping
that supplies gas customers. Emissions from this system mainly occur
at metering and regulation stations and from pipeline leaks, primarily
in older iron and unprotected steel mains and service pipes. |
A number of technologies and practices have
been identified for reducing methane emissions from natural gas systems. EPA
and the natural gas industry, through the Natural Gas STAR Program, have
identified several Best Management Practices (BMPs) that are cost-effective
in reducing methane emissions. The Natural Gas STAR Program has sponsored a
series of Lessons Learned Studies of these BMPs and several other practices.
In addition, companies that are Natural Gas STAR Partners have identified
other practices that reduce methane emissions.
EPA has analyzed the cost and emissions
reduction potential of over 100 emissions reduction options. Many appear to
be economic at gas prices below current and forecasted levels. Some of the
more economic options that also represent relatively large opportunities for
incremental emissions reductions (e.g., over 0.5 MMTCE per year) include the
following:
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Practicing enhanced directed
inspection and maintenance at gate stations and surface facilities |
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Installing fuel gas retrofit systems
on compressors to capture otherwise vented fuel when compressors are
taken off-line |
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Replacing high-bleed pneumatic devices
with low-bleed pneumatic devices |
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Reducing glycol circulation rates in
dehydrators |
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Practicing enhanced directed
inspection and maintenance at gate stations and surface facilities |
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Installing dry seals on reciprocating
compressors |
Utilities can encourage their natural gas suppliers to use "Best Management
Practices" to reduce emissions associated with the production and
transmission of the natural gas they purchase. In addition, utilities that
distribute natural gas can undertake a variety of actions to reduce the
methane emissions associated with natural gas distribution systems.
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Power Partners℠
Projects |
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References, Sources,
and
Other
Useful Data |
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American Petroleum Institute,
“Answering the Challenge: A New U.S. Oil and Natural Gas Industry Initiative
on Climate Change”
http://www.climatevision.gov/sectors/oil_gas/index.html
Through the American
Petroleum Institute, the U.S. oil and natural gas industry is beginning a
new initiative to build on its previous work addressing climate change.
API's Climate Challenge Programs feature three components. The API Climate
Action Challenge focuses on strategies for reducing emissions. The API
Climate R&D Challenge involves support for enhanced research and development
leading to new and improved technologies. The API Climate Greenhouse Gas
Estimation & Reporting Challenge will implement more robust methods for
calculating, reporting, and tracking emissions industry-wide.
Environmental Protection Agency, “Natural
Gas STAR Program”
http://www.epa.gov/gasstar/index.htm
The Natural Gas STAR Program
is a flexible, voluntary partnership between EPA and the oil and natural gas
industry. Through the Program, EPA works with companies that produce,
process, and transmit and distribute natural gas to identify and promote the
implementation of cost-effective technologies and practices to reduce
emissions of methane, a potent greenhouse gas.
Environmental Protection Agency, “Natural
Gas STAR Program: Case Studies”
http://www.epa.gov/gasstar/resources/case_studies.htm
The Natural Gas STAR Program
is a flexible, voluntary partnership between EPA and the oil and natural gas
industry. Superior Implementation Case Studies focus on how companies
promote and implement the program internally, and how companies address
challenges to participating in the Gas STAR Program. Seven case studies of
Natural Gas STAR partners are now available.
Environmental Protection Agency, “Natural
Gas STAR Program: Lessons Learned”
http://www.epa.gov/gasstar/resources/lessons.htm
The Natural Gas STAR Program
has developed this series of PRO Fact Sheets to provide partners with ideas
and basic information for evaluating the economic and operational
feasibility of implementing relevant PROs in their operations. The PRO Fact
Sheets are intended as a guide to partners interested in evaluating
additional options for reducing emissions and improving operational
efficiency.
Environmental Protection Agency, “Natural
Gas STAR Program: Partner Reported Opportunities for Reducing Methane
Emissions”
http://www.epa.gov/gasstar/pro/index.htm
The Natural Gas STAR Program
has developed a series of Partner Reported Opportunities (PRO) Fact Sheets
to provide partners with ideas and basic information for evaluating the
economic and operational feasibility of implementing relevant PROs in their
operations. The PRO Fact Sheets are intended as a guide to partners
interested in evaluating additional options for reducing emissions and
improving operational efficiency.
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