Methane Drainage

measures for pumping, collection, and removal of firedamp or gas-air mixtures from underground mine workings and bringing it to the surface. Gas is removed from pits by pipelines laid in the workings or by boreholes joining the workings with the surface.

Methane drainage is used to reduce inflows of methane from coal beds and rock to mine workings and to aid the ventilation of mine shafts and completely prevent or considerably reduce enforced idleness in extraction (production) districts caused by the filling of workings with gas. In gaseous pits, it makes possible the use of electric power in place of less efficient compressed air power, increases the productivity of the workers and the safety of mining, and under certain conditions wholly or partly prevents (by reducing the intensity) unusual gas evolution, such as fumaroles and sudden blowouts of coal and gas.

Drainage systems consist of drainage workings or boreholes, pit gas pipelines with protective equipment, drainage installations, and regulating, recording, and protective equipment and devices; in cases where the gas that is collected is used, there is also a gas pipeline to the consumer. The pipeline equipment is installed at the surface and consists of vacuum pumps or rotary air blowers with nonsparking blades to move the gas in the system, a drive system, and devices for regulating and monitoring the operation of the machinery and driving equipment.

The use of methane drainage has led to the creation of a new technology of working gaseous coal strata, which in a number of the most gaseous deposits, are worked in an integrated manner, allowing for the production of by-product methane.

There are three main methods of methane drainage: preliminary decontamination of the coal seams being worked, decontamination of adjacent coal seams, and pumping of concentrated methane-air mixtures from worked-out areas. Preliminary drainage is conducted before the work on a coal seam begins; it consists in the drilling of parallel holes about 100-250 m deep and 80-120 mm in diameter, with an interval of 10-25 m. Each drainage hole is connected by a water separator to the pit’s gas-pipeline network. Suction removal of gas from a coal seam is carried out using a vacuum of up to 13.5-27.0 kilonewtons per sq m (100-200 mm of mercury) for a long period (100-150 days). In draining adjacent coal seams, the effect of their partial release from mine pressure is used, which promotes the passage of methane absorbed by the seams into the free state. In this method of drainage, holes are drilled from the mine workings to adjacent seams lying at various distances above and below the seam being worked, but not exceeding the radius of effective drainage. The boreholes are connected to a gasepipeline system. After the gas has been pumped out of the worked-out areas, they are carefully insulated from existing workings by bulkheads and airtight strips (for example, strips of rock with various sealants), and gas of high methane content that has accumulated in spaces formed between caved-in pieces of rock is removed by means of the pit gas lines.

Industrial methane drainage was first carried out in the Ruhr (Germany) in 1943 and in the USSR, in the Donbas, in 1952. In 1970 it was being used at 518 mines in 15 countries, and the total quantity of methane collected was about 3 billion cu m annually, with 156 mines in the USSR (more than 750 million cu m).

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