What is coal mine gas (CMG)?
CMM is the term used to describe the methane that is released by mining coal and rock strata. The explosive nature of this methane poses a risk to safety in mines. Methane, a greenhouse gas, is 28 times more powerful than carbon dioxide in mass over a period of 100 years (read more about methane).
The coal formations contain methane gas, which is produced when plant debris (such as that found in swamps), after being buried for a very long time and covered with soil, slowly changes into coal through a coalification process.
CMM can be released by different types of mines:
1. Active underground mining releases methane via degasification (drainage systems methane), and ventilation systems.
2. Abandoned or closed mines release abandoned mine methane from diffuse vents or ventilation pipes.
3. Surface Mines emit lower methane levels than underground mines. However, because surface mines produce a large volume of coal, they can still emit large amounts of methane.
In the United States, and around the world, the majority of the methane released from coal mining is due to underground coal mines. The majority of methane released from coal mining comes in the form of diluted VAM. Surface mines, as well as post-mining operations such as storage and transport, are less significant sources of CMM.
CMM can be recovered and used with readily available technology.
Why is the EPA concerned about CMM?
In 2019, methane (CH4) from coal mining and abandoned mines contributed to 8% of the total U.S. emissions. According to the inventory of U.S. Greenhouse Gas Emissions and Sinks 1990-2019, coal mining was the fifth largest methane emitting sector.
Methane ranks second in greenhouse gases after carbon dioxide. Methane has a 28-36-fold greater mass-based potency than carbon dioxide over a period of 100 years. More information on methane is available >>
CMM emissions are a waste of potential energy and a safety risk (when they are not captured). Recovery and use of CMM emissions have positive effects on the local and global environment.
How is methane emitted from coal mines?
Mining activities release methane in three main ways:
1. Degasification Systems in active underground mines: These systems are also commonly known as drainage systems. They use vertical or horizontal wells to collect methane either before (premise drainage) or during (postmine drainage) mining activities. This helps the ventilation system maintain low methane levels in the mine (i.e., well below the explosive limits) for the safety of miners.
2. Ventilation system release of VAM: VAM is the extremely dilute methane released by underground mine ventilation shafts.
3. Closed or abandoned mining emits abandoned methane (AMM) through diffuse vents or ventilation pipes.
Surface mines, post-mining, and coal piles continue to emit methane during storage and transport.
Do closed coal mines emit methane?
Yes! Closed (or abandoned) mines are those that are no longer in operation to produce coal. These abandoned mines still emit significant amounts of methane from diffuse vents or fissures. Methane from these mines can be extracted to produce electricity or for other uses. In the United States, there are over a thousand abandoned coal mining sites. The EPA has identified 400 abandoned coal mines as “gassy”. It has also developed profiles for successful projects in abandoned mines, and mines that might be suitable candidates for project development. View opportunities for project development at abandoned mines (Abandoned Coal Mines Methane Opportunity Database [July 2017]).
How is CMM utilized?
CMM must first be brought to the surface by ventilation and/or drainage systems. The project developers examine the available data about coal mines, such as drainage efficiency and gas quality and volume, possible markets, and any other factors that may affect a potential project. Gas end uses are dependent on gas quality, methane concentration, and other contaminants. Most of the recovered CMM in the United States is sold to pipeline systems for natural gas. CMM is used in many countries for:
1. Power generation
2. District heating
3. Boiler fuel
4. Gas pipelines for sale
CMM is also used as a feedstock for manufacturing, vehicle fuel, a source of heat for mine ventilation, and a source of fuel for fuel cell fuels. By 2021, U.S. mines will have recovered and used more than 39 billion cubic feet of CMM. The United States has projects that use drainage system methane (VAM), AMM, and VAM.
How many CMM reduction projects exist in the United States?
CMOP knows of 25 coal-mine methane projects at 16 active mines, and 35 abandoned methane projects at 66 closed mines. The map “US Coal Mine Methane Current Projects & Potential Opportunities” provides more information on existing projects, active and abandoned sites. The data on the map comes from the annual national emissions inventory compiled by the EPA.
What is the difference between coalbed methane (CBM) and CMM?
CBM is methane found in coal seams and extracted from them. This is created during the coalification, or the transformation of organic plant matter into coal. CBM, also called virgin coal seam methane and coal seam gas, is an “unconventional source” of natural gas. CBM accounts for 5% of the total U.S. annual natural gas production.
CMM is methane that has been released by mining from coal and rock strata. Since CMM in underground mines can be explosive, it’s removed using ventilation and degasification. Methane can escape from surface and abandoned mines through diffuse sources such as natural fissures. CBM and CMM are similar in that they both refer to the subset of methane found in coal seams. However, CMM refers to the methane found in mining areas, e.g., within a mine plan, while CBM is the methane found in coal that will not be mined. CMM is released during mining, so the recovery and use are considered emission avoidance.
This post was written by Justin Tidd, Director at Becker Global America! For over 15 years, Becker Communications has been the industry’s leader in increasingly more sophisticated electrical mining communication systems. As they expanded into surface mining, railroads, and tunneling they added wireless communication systems, handheld radios, tagging, and tracking systems, as well as gas monitoring.
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