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Coal Mine Methane

     
 

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

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Landfill Methane
Nat. Gas Emissions
Coal Mine Methane
Animal Waste Methane
SF6 Reduction

 

 Coal Mine Methane Recovery

 
 Background


In the geological process known as coalification, methane and coal are formed together. Depending upon the geologic conditions, the methane can be trapped within the coal seams and/or the surrounding rock strata. As the coal mining reduces the geologic pressure, the methane is released to the air.

The amount of methane formed generally correlates with the rank of the coal and the geologic pressure. Higher-ranked coals, such as low-volatile and mid-volatile bituminous coals, have had more of the original volatile matter squeezed out from the coal over time, and much of the methane formed adsorbs onto the coal or into the surrounding rock strata. Lower-ranked coals, such as subbituminous coal, still have most of the volatile matter in the solid coal structure itself, and typically have low methane contents. Geologic pressure, typically greater at greater depths, also correlates with methane concentrations. In the U.S., the gassiest mines are the very deep, low-volatile and mid-volatile bituminous coal mines, most notably in Alabama’s Warrior Basin and in the western part of Virginia. In contrast, surface subbituminous coal mines are typically very low in methane content.

Because methane is explosive in low concentrations, it is hazardous to mines and miners. A required safety practice at underground mines is to install ventilation systems to dilute the methane to a low concentration and then vent it directly to the atmosphere.

Methane is released during mining and post-mining activities. Methane emissions are typically divided into the following categories:

  Underground Mining. In underground mining, methane is released into the mine workings during mining. Mining regulations require methane to be diluted in the ventilation air, and then vented to the atmosphere. Mines can also remove methane before and during mining by using degasification systems. The gas can be vented, flared (not currently done in the U.S.), or recovered for its energy content. Emissions are reduced if recovered gas is flared or used. Up to 50 to 60 percent of methane can typically be recovered with degasification; the remainder is released in the ventilation air.
 
  Surface Mining. During surface mining, methane is released directly to the atmosphere as the overlying rock strata are removed. No emissions mitigation options are being used at this time. In theory, some pre-mining degasification and recovery could occur at gassy surface mines. However, the low gas content of surface mines relative to that of underground mines makes it unlikely that significant recovery would be technically feasible, let alone cost-effective.
 
  Post-Mining Activities. Some methane remains in the coal after mining and is released during subsequent processing and transportation of coal. No proven mitigation options exist at this time.
 
  Abandoned Mines. Methane emissions from closed or abandoned mines are not quantified and not included in U.S. inventory estimates, but may be significant. In some cases, degasification techniques can, and have been used to, remove methane from abandoned underground mines. There is uncertainty as to whether and at what rate the methane present in these mines would have been emitted.


In recent years, several of the gassiest mines have begun making beneficial use of recovered gas, primarily sales into the pipeline system. Most coal mine methane recovery in the U.S. is at active underground mines, with the remainder from inactive or abandoned underground mines. Because the distribution of gassiness among underground mines is so skewed, a small number of the very gassy mines have offered the greatest need to degasify as well as the greatest economic opportunities to use the gas.

Coal mines already employ a range of technologies for recovering methane. These methods have been developed primarily for safety reasons, as a supplement to ventilation systems. The major degasification techniques used at U.S. coal mines are vertical wells, long-hole and short-hole horizontal boreholes, and gob wells. Vertical wells and in-mine horizontal boreholes, which recover methane in advance of mining, produce nearly pure methane. In contrast, gob wells, which recover post-mining methane, may recover methane that has been mixed with mine air.

The quality of the gas determines how it may be used. Methane recovered from degasification can be used for pipeline injection, power generation, on-site use in a thermal coal drying facility, or sale to nearby commercial or industrial facilities. At present, most recovered coal mine methane is sold through natural gas pipelines.

Even where degasification systems are used, mines still emit significant quantities of methane via ventilation systems. Currently, technologies are in development that would catalytically oxidize the low concentrations of methane in ventilation air, producing usable thermal heat as a by-product.

Mines that are already recovering methane represent opportunities for utilities to work with the mine operators to develop a use strategy for the gas that is already being recovered. Utilities may also be able to participate in projects at coal mines that are not currently recovering any methane in conjunction with mining, by implementing projects that include both gas recovery and utilization.

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 Power Partners Projects

 

The Methane to Markets Partnership was established in November 2004 as a programmatic framework for cooperation to advance the recovery and use of methane as a valuable and clean energy source. Sixteen countries belong to the partnership, which is chaired by the United States. The partnership is organized around sources of methane: oil and gas, landfill, agriculture, and coal. One of the major goals of the partnership is to develop and transfer methods and technologies for methane capture. The Coal Mine Technical Subcommittee is leading the Partnership’s efforts to reduce methane emissions from coal mining. The Coal Subcommittee has completed an action work plan and has begun conducting workshops in member countries that will identify key barriers to wider capture and use of coal mine methane. An additional workshop, held in conjunction with the APP coal mining task force, convened in Australia in the fall of 2006.
     Action Plans and Events: http://www.methanetomarkets.org/m2m2009/coal-mines/index.aspx
     Committee Membership Contacts:  http://www.methanetomarkets.org/m2m2009/partners/
countryCommittee.aspx?sector=coal

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 References, Sources, and Other Useful Data


Asia-Pacific Partnership on Clean Development and Climate, "Coal Mining Task Force,"
http://asiapacificpartnership.org/english/tf_coal_mining.aspx

Asia-Pacific Partners collectively generate approximately 65 percent of world primary coal production. Coal is the dominant fuel source globally and among the Partners, and its use is expected to continue to grow over the coming decades. Improving the efficiency of the mining and processing of coal and improving the monitoring and control of coal mine methane gas can make a significant contribution to emissions reductions and workplace safety. The Task Force will address the reclamation and rehabilitation of mined lands, runoff, abandoned mines and best safety practice. The Coal Mining Task Force will work collaboratively with the Cleaner Fossil Energy Task Force to ensure that synergies are captured in improving coal processing and developing new coal-based generation technologies.
 

Environmental Protection Agency, “Coalbed Methane Outreach Program (CMOP)"
http://www.epa.gov/cmop/index.html

EPA’s Coalbed Methane Outreach Program (CMOP) has as a goal the reduction of methane emissions from coal mining activities. Its mission is to promote the profitable recovery and use of coal mine methane (CMM). By working cooperatively with coal companies and related industries, CMOP helps to identify and implement methods to use CMM instead of emitting it to the atmosphere.

Environmental Protection Agency, Coalbed Methane Outreach Program, “Enhanced CBM/CMM Recovery” (December 2002)
http://www.epa.gov/cmop/docs/cmm_recovery.pdf

This 9-page report describes enhanced CBM/CMM (ECBM) recovery techniques, either by reducing the partial pressure of methane and/or replacing the methane on the coal surface. Both reservoir simulations and early pilot projects indicate that ECBM can accelerate and increase methane production from unmineable coal seams, and also in mineable coal seams in advance of mining.

Environmental Protection Agency, Coalbed Methane Outreach Program, “Enhanced Gob Gas Recovery” (June 2000)
http://www.epa.gov/cmop/docs/ggasrecpv.pdf

Gas volumes liberated by gob areas into the mine ventilation system depend on the method of mining, the number and proximity of overlying and/or underlying gas-bearing strata, their reservoir characteristics, and other geological factors. There is potential at many mines to increase recovery and decrease dilution levels by adopting improved degasification and collection systems and by modifying operating practices.

Environmental Protection Agency, Coalbed Methane Outreach Program, “Identifying Opportunities for Methane Recovery at U.S. Coal Mines: Profiles of Selected Underground Coal Mines, 1999-2003” (EPA Publication EPA-430-K-04-003, September 2005)
http://www.epa.gov/cmop/docs/profiles_2003_final.pdf

This 202-page report provides information about specific opportunities to develop methane recovery projects at large underground coal mines in the U.S. The report contains profiles of 50 U.S. coal mines that may be potential candidates for methane recovery and use, and details on-going recovery projects at 10 of the mines. EPA designed the profiles to help project developers perform an initial screening of potential projects.

Environmental Protection Agency, Coalbed Methane Outreach Program, “Technical Option Series”
http://www.epa.gov/cmop/resources/technical_options.html

The Technical Option Series consists of short overviews of both proven and emerging options for directly using medium or high quality coal mine methane (CMM) and lower quality Ventilation Air Methane (VAM). About 20 different uses are described, each in a 4-page PDF document.

Environmental Protection Agency, Methane to Markets Partnership, "Underground Coal Mine Methane Recovery and Use Opportunities" (March 2008)
http://www.methanetomarkets.org/m2m2009/documents/coal_fs_eng.pdf

Methane is both the primary constituent of natural gas and a potent greenhouse gas when released to the atmosphere. Reducing emissions can yield substantial economic and environmental benefits. The implementation of available cost-effective methane emission reduction opportunities in the coal industry can lead to improved mine safety, greater mine productivity, and increased revenues. The Methane to Markets Partnership is building international alliances to promote methane recovery and use projects at underground coalmines throughout the world.
 

Environmental Protection Agency, Methane to Markets Partnership, "Coal Subcommittee Action Plan"
http://www.methanetomarkets.org/m2m2009/documents/coal_actionplan_0506.pdf

Removing fugitive methane gas from underground coal mines and using it in profitable and practical ways can improve worker safety, enhance mine productivity, increase revenues, and reduce greenhouse gas emissions. The Methane to Markets Partnership is fostering international collaboration to advance methane capture and use projects that bring more gas to market. The Coal Mine Technical Subcommittee  is leading the Partnership’s efforts to reduce methane emissions from coal mining. The Methane to Markets Partnership Terms of Reference (TOR) states that each Subcommittee should develop an action plan. The Charge to the Subcommittees adopted by the Partnership along with the TOR notes that “ideally, Action Plans would identify needs, opportunities, and priorities for project development in the sector and for interested Partners, and would be developed with input from members of the Project Network.” The Charge continues by outlining specific elements of an action plan, described further in this document.
 

U.S. Department of Energy, Office of Fossil Energy, NCCTI Energy Technologies Group, “CO2 Capture and Storage in Geologic Formations” (Revised Draft, 08-Jan-2002)
http://www.netl.doe.gov/technologies/carbon_seq/refshelf/CS-NCCTIwhitepaper.pdf

On June 11, 2001 President Bush directed the Secretaries of Energy and Commerce, along with the Administrator of the EPA, to develop a National Climate Change Technology Initiative (NCCTI). This report is one of eight energy-related white papers produced in response to the guidance for the NCCTI white paper. This 34-page white paper, revised as of January 2002, covers the capture of carbon dioxide (CO2) from current and planned fossil energy systems and its direct sequestration in geologic structures. Unmineable coal beds are one of the geologic formations evaluated.

U.S. Department of Energy, National Energy Technology Laboratory, “Enhanced Coal Bed Methane Production and Sequestration of CO2 in Unmineable Coal Seams” (NETL Project Facts Sheet)
http://www.netl.doe.gov/publications/factsheets/project/Proj249.pdf

CONSOL Energy, Inc. will demonstrate a novel drilling and production process that reduces potential methane emissions from coal mining, produces usable methane (natural gas), and creates a sequestration sink for carbon dioxide (CO2) in unmineable coal seams. CONSOL’s project will employ a slant-hole drilling technique to drain coalbed methane from a mineable coal seam and an underlying unmineable coal seam.

U.S. Department of Energy, National Energy Technology Laboratory, “Unminable Coalbeds & Enhancing Methane Production Sequestering Carbon Dioxide” (NETL Project Facts Sheet)
http://www.netl.doe.gov/publications/factsheets/project/Proj212.pdf

Unminable coalbeds are attractive targets for sequestration of CO2 because they have a large storage capacity and the sequestered CO2  can enhance the recovery of natural gas by displacing the methane that is present in the coalbeds. Oklahoma State University is leading an effort to investigate and test the ability of injected carbon dioxide to enhance coalbed methane production. The specific focus of this project is to investigate the competitive adsorption behavior of methane, CO2, and nitrogen on a variety of coals.

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