Coal mining

Coal mining is the extraction of coal from the Earth for use during combustion.

Methods of extraction

The most economical method of coal extraction from coal seams depends on the depth and quality of the seams, and also the geology and environmental factors of the area being mined.

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If the coal seams are near the surface, the coal is extracted by one of two methods. One method, strip mining, exposes the coal by the advancement of an open pit or strip. As the coal is exposed and extracted, the overburden from the still covered coal fills the former pit, and strip progresses. Most open cast mines in the USA extract bituminous coal. In South Wales opencasting for steam coal and anthracite is practised.

Related Topics:
Strip mining - USA - Bituminous coal - Wales - Steam coal - Anthracite

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However, most coal seams are too deep underground for open cast mining. In deep mining the room and pillar method progresses along the seam while pillars are left to support the roof. These pillars may be removed on retreat allowing the roof to cave in. This method of mining is used principally in the United States.

Related Topics:
Room and pillar - United States

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Another method, longwall mining, is conducted along the seam with the use of self-advancing hydraulic roof supports known as "chocks" or "shields". These supports are placed in a line (up to 400 metres long), known as a "longwall" and as coal is removed from in front of the longwall, the supports are advanced. As the longwall advances, the cavity created behind the longwall known as the "gob" caves in. Longwall mining is the principle method of underground mining in Australia.

Related Topics:
Longwall mining - Australia

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Finally, highwall mining is a form of coal mining in which a continuous miner is controlled remotely from outby, or outside the mine, and is guided along the seam straight back drilling holes in excess of 500 feet. As the coal is sheered off the face of the seam, it falls below to a conveyor belt that transports the coal to the surface. A large amount of capital is required to purchase a highwall mining unit, but the labor costs are low because an operation does not require a full crew.

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Other methods of mining include highwall auger mining. These methods are generally applied in an open cast mine, once open cut mining becomes uneconomic.

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