Longwall mining is a mechanized underground coal mining technique that uses machines with coal clippers mounted on hydraulic ceiling mounts. It accounts for over half of US coal production and can extract up to 30,000 tons of coal per day. The technique replaces the room and column method and is feasible for deep mining. However, it can cause environmental damage, and the machines are expensive.
Longwall mining is a highly productive underground coal mining technique. Longwall mining machines consist of multiple coal clippers mounted on a series of self-advancing hydraulic ceiling mounts. The whole process is mechanized. Longwall mining machines are approximately 800 feet (240 meters) wide and 5 to 10 feet (1.5 to 3 meters) tall. Miners mine “panels” – rectangular blocks of coal as wide as mining machinery and up to 12,000 feet (3,650 meters) long. Huge shears cut coal from a wall, which falls onto a conveyor belt for removal. As the miner progresses along a panel, the roof behind the miner’s path can collapse.
Longwall mining was first introduced in the 1950s and 1960s. Today it accounts for more than half of all coal production in the United States. On any given day, a typical longwall mining system is capable of extracting between 10,000 and 30,000 tons (9 to 27 million kilograms) of coal from one panel. The main disadvantage of this very productive technique is a prohibitive initial investment: these mining machines usually run between 5 and 15 million dollars.
Longwall mining replaces the historic “room and column method,” whereby underground “rooms” of coal are manually mined and the columns are left to support the roof so the miners can work safely. In mining regions deeper than 1,000 feet (300 meters), the room and column method becomes highly uneconomical because the dimensions of the pillars needed to support the roof are much larger, meaning that valuable coal cannot be extracted from them. Long wall systems make deep mining feasible.
Sometimes this type of mining is called destructive or environmentally hazardous because it causes the earth to sink on top of the mined panel. This can damage groundwater, surface structures and can cause soil erosion. A careful geological survey can help improve these problems. As technological advances continue to make longwall miners ever more efficient, they will become responsible for an increasing share of the world’s total coal production.
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