Introduction:Coal Gas

Methane is often found in association with coal deposits. These deposits might be virgin coal seams (coal seam methane/coal bed methane), be in the process of being mined or may be abandoned.

Gas from each of these may be suitable for the production of power. Using coal gas for power in the form of electricity and heat (via cogeneration) helps prevent emissions to atmosphere and provides a useful form of on-site power.

It is also possible to gasify coal deposits in situ to provide synthetic gases for use in power generation.

Coal mine degasification was originally developed to improve worker safety in mines. If not captured the methane-laden mine air is vented to atmosphere by exhaust fans.

In recent years, international studies have determined that 30-40% of all coal mines produce gas that can be effectively used for power generation with gas engines Coal mine gas (firedamp) is a problematic phenomenon associated with pit coal mining, as the gas can form explosive mixtures together with air.

The main component of the primary coal seam gas is methane in a concentration of 90-95 % the gas develops during the geochemical conversion of organic substances to coal (carbonisation).

Coal seam gas is present both as liberated gas in fissures, faults and as adsorbed gas on the inner surface of the coal and neighbouring rock.

Types of Coal Gas:

Gases derived from coal come in four key forms:

•Coal Seam Methane (CSM), or Coal Bed Methane (CBM)

•Coal Mine Methane (CMM), or Working Mine Methane (WMM)

•Abandoned Mine Methane (AMM)

•Syngas from Underground Coal Gasification (UCG)

Flow Sheet:

Coal Bed Methane (CBM):

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%.