Coal Bed Methane (CBM) or Coal Seam Methane (CSM) is primary coal seam gas collected from unmined coal beds. These coal seams are drilled down into, releasing the associated gas which is extracted and can be used to generate electricity. CBM consists of over 90% methane and can be harvested independently of coal mining in some locations. The gas composition is normally stable, meaning that the gas can be fed directly into the natural gas network or a gas engine.
Coal Mine Methane (CMM)- Coal mine methane (CMM) is a type of gas present in active, working mine sites. This gas is extracted from the air in the coal mine helping improve safety and preventing uncontrolled release of methane to atmosphere. CMM is a mixture of methane & air released during the process of coal mining and must be vented for safety reasons. Methane has significant effects as a greenhouse gas being 21 times higher than that of carbon dioxide, therefore its capture and use in gas engines has significant environmental benefits. CMM typically has an oxygen content of 5-12%. The methane content ranges from 25-60%. However, the methane/air proportion can change suddenly, thus complicating its use in gas engines
Abandoned Mine Methane (AMM)- Even after coal mines are shut down, coal mine gas continues to be released. Coal mine gas from abandoned mines typically contains no oxygen, and its composition changes slowly. The methane content ranges from 60-80%.
Underground Coal Gasification (UCG)- Underground Coal Gasification is an industrial process by which coal is gasified in situ. This process converts the physical coal to a product gas (a type of synthetic/syngas).
Correlating Gas Engines with Coal Gas- The composition of CBM and AMM presents no technical difficulties for combustion in gas engines. Although the sudden changes in the composition of coal mine gas from active mining (CMM) put greater demands on engine design. Green Power offers specially modified gas engines that make efficient use of this gas for power generation. The electrical energy generated can be used in the coal mine to meet electricity requirements or fed into the public power grid. The thermal energy can be used for heating purposes on site or fed into a district heating scheme.