Introduction

Operating underground coal mines are a large source of usable methane gas emissions. Other sources of emissions include surface and abandoned mines and coal handling activities, such as storage, processing and transportation.

Methane from coal mines makes a significant contribution to global greenhouse gas emissions. It accounts for four per cent of total methane emissions and eight per cent of total global methane emissions from human activity*.

*Source: Scheehle, E. A. and Kruger, D. (2004). Global anthropogenic methane and nitrous oxide emissions (Energy Journal)

Methane in coal mines

Coal seams contain large quantities of gas which remain in place until the coal is mined or until it is drained to the surface through boreholes.

In open-pit mines there is plenty of opportunity for the gas to escape into the atmosphere as soon as mining operations release it from the coal.

In some circumstances the gas can be safely drained to the surface through boreholes drilled into the undisturbed seams from the surface. Gas drained in this way is called Coal Bed Methane (CBM).

In the majority of underground mines, however, it is not possible to drain the gas before mining takes place, and gas emission into the mine becomes a serious hazard. There are two ways to remove this Coal Mine Methane (CMM) from an active mine:

(1) Drain the gas 'at source' from mining-disturbed strata
(2) Remove diluted gas from the mine by means of the ventilation system.

Mine gas (principally Methane) is particularly hazardous when diluted by air to within its explosive range (5 per cent to 14 per cent by volume).

Gas emissions limit the rate of coal production of a mine as peaks in gas emissions necessitate temporary shutdown of the coal cutting operation. This represents a loss of revenue for the mine.

Green Gas Expertise

Good gas management reduces peaks in gas emissions thereby improving mine productivity and maintains gas levels outside the explosive range to improve safety. Our expertise will maximise the 'drained at source' proportion of the gas emitted in the mine, with the following benefits:

• Reduction in the mine-atmosphere general gas level with a corresponding increase in safety.
• Reduction in the volume of gas that must be diluted and removed by the ventilation system. This allows the existing ventilation to support an increase in coal production.
• Reduction in the severity and duration of gas 'peaks' and hence improving mine productivity and reducing lost revenue.
• Increased revenues (from green energy generation and CO₂ credits).
• Reduction in greenhouse gas emissions.

Our expertise enables the extraction of more methane of the type that can be used by the two main safe technologies:

• Combined Heat & Power plants for CMM (based on G.A.S. experience and technology) or other uses.
• Oxidizers for Ventilation Air Methane (based on MEGTEC experience and technology).

Green Gas will design the optimal utilisation model based on local requirements, which may also include other utilisation options.

With its Czech DPB drilling technology and extensive international gas-drainage experience, Green Gas offers 'Centre of Excellence' capability for mine degasification. Green Gas optimises a mine's degasification system right from the engineering parameters of individual boreholes to the whole-mine gas collection system and surface gas pumps (see below).

Coal Mine Gas Drainage

Coal mine gas drainage is an essential part of mine gas management. This is typically done through a combination of different methods as illustrated in this diagram.