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Nat. Gas Emissions

     
 

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Major Topic Sections

Fossil-fueled Power
Non-Fossil Generation
End-Use Efficiency
Electricity T&D
Carbon Sequestration
Non-CO2 Reductions
Other GHG Reductions

Related topics in this section

Up to Section Head
Landfill Methane
Nat. Gas Emissions
Coal Mine Methane
Animal Waste Methane
SF6 Reduction

 

 Reducing Emissions of Natural Gas

 
 Background


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:

  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.
 
  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.
 
 

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.
 

  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:

  Practicing enhanced directed inspection and maintenance at gate stations and surface facilities
  Installing fuel gas retrofit systems on compressors to capture otherwise vented fuel when compressors are taken off-line
  Replacing high-bleed pneumatic devices with low-bleed pneumatic devices
  Reducing glycol circulation rates in dehydrators
  Practicing enhanced directed inspection and maintenance at gate stations and surface facilities
  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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 References, Sources, and Other Useful Data


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 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, Methane to Markets Program, “Natural Gas STAR International: Reducing Emissions, Increasing Efficiency, Maximizing Profits"
http://www.epa.gov/gasstar/documents/international_presentation.pdf

This 16-page presentation describes the Natural Gas STAR International Program.  Under the Methane to Markets framework, EPA launched Natural Gas STAR International in 2006. The program builds on the success of the domestic Natural Gas STAR Program, creates a framework for global application of the Program’s principles, and increases opportunities to reduce methane emissions from oil and gas operations worldwide.

Environmental Protection Agency, Methane to Markets Program, "Oil and Gas Systems"
http://www.methanetomarkets.org/m2m2009/oil-gas/index.aspx

Methane emissions from oil and natural gas systems are primarily the result of normal operations and system disruptions. These emissions can be cost-effectively reduced by upgrading technologies or equipment, and by improving operations. The Methane to Markets Partnership facilitates cooperative mitigation activities that result in bringing more gas to markets.

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Last revised: Dec. 11, 2009.