Coal seams deep under the ground contain a certain amount of methane. Methane formation may be due to the coal formation process millions of years ago, or due to microbial action in the underground seams. This methane, with high-energy content, after extraction and compression becomes a commercial energy source similar to CNG. Coal bed methane, or CBM, was an operational nuisance in the earlier coal mining days, but today is a potential energy source on the same level as the oil and gas industry.
Russia, Canada, and China are the countries that have the greatest potential resources. The United States have already started producing CBM commercially. Indonesia has recently released more than fifteen production sharing contracts for exploration and development of methane sources in its coal mines. China has pilot plants for developing CBM, and India has started demonstration plants for CBM capture.
Methane in Coal Mines - A Deadly Combination
Methane is commonly released to the atmosphere during coal mining. Methane is a greenhouse gas (GHG) 21 times more potent than carbon-dioxide. Burning this methane gives out energy and at the same time converts this into CO2 reducing the GHG potency.
During underground coal mining operations, trapped methane has causesd explosions leading to fatal accidents. China reported 898 deaths in 236 incidents in 2007. Tapping and releasing this gas avoids many deadly mine accidents.
Methane from some operating coal mines is collected, purified, and compressed. This coal mine methane reduces the explosive hazards, reduces GHG emissions, and is an energy source.
Methane in Coal Beds - Extraction and Capture
Coal bed methane, on the other hand, is methane trapped in coal seams that are deep underground. Some of these coal seams may not be commercially viable due to the depth of mining. Tapping the methane is one way to benefit from a potential energy source.
Methane is held under ground in these coal seams by water pressure. Releasing this water releases the gas. The method of capture is to drill deep wells to the top of the coal seams, pump out the water, and release the gas. The gas also is transported to the surface along with the water. This is separated, purified and compressed, and sold as compressed gas.
Environmental Issues involving Coal Bed Methane
Like any other energy source, this also results in environmental issues. Apart for the effects of GHG emissions, there are other environmental issues to be dealt with.
- Water pumped from below the ground contains chemicals or toxic materials and cannot be used for irrigation. Disposal of this water becomes a major environmental issue. In some case, this can be pumped back into the coal seams itself.
- The pumping out of the ground water can lead to lowering of the ground water level and the drying up of wells, affecting water resources of the population in the area.
- Removing water from the coals seams increases the potency for coal mine fires.
- Since the mines are deep underground, the top surface is invariably used for agriculture. Drilling operations above ground can destroy the agriculture.
As the energy crunch deepens, man’s search for alternate energy sources makes hitherto dormant energy resources viable. Coal bed methane is one such energy source.