Underground mining

Date: 2015-10-07; view: 440.

Most coal seams are too deep underground for open cast mining and thus this type of mining is called underground mining. In deep mining, the room and pillar or bord and pillar method progresses along the Mammoth coal vein seam, while pillars and timber are left standing to support the coal mine roof. There are four major underground mining methods:

• Longwall mining– accounts for about 50% of underground production. The longwall shearer механические ножницы has a face of 1000 feet or more. It is a sophisticated machine with a rotating drum that moves mechanically back-and-forth across a wide coal seam. The loosened coal falls onto a pan line that takes the coal to the conveyor belt for removal from the work area. Longwall systems have their own hydraulic roof supports for overlying rock that advance with the machine as mining progresses. As the longwall mining equipment moves forward, overlying rock that is no longer supported by the coal that has been removed is allowed to fall behind the operation in a controlled manner. The supports make possible high levels of production and safety. Sensors detect how much coal remains in the seam while robotic controls enhance efficiency. Longwall systems allow a 60-to-80% coal recovery rate where the surrounding geology allows their use.

• Continuous mining – Utilizes a machine with a large rotating steel drum equipped with tungsten вольфрам carbide teeth that scrape coal from the seam. Operating in a “room and pillar” system – where the mine is divided into a series of 20-to-30 foot “rooms” or work areas cut into the coalbed угольный пласт – it can mine as much as five tons of coal a minute – more than a miner of the 1920s would produce in an entire day. Continuous miners account for about 45% of underground coal production, and also utilize conveyors to transport the removed coal from the seam. Remote controlled continuous miners are used to work in a variety of difficult seams and conditions and robotic versions controlled by computers are becoming increasingly common.

• Conventional mining – An older practice that uses explosives to break up the coal seam, after which the coal is gathered and loaded onto shuttle cars or conveyors for removal to a central loading area. This process consists of a series of operations that begins with “cutting” the coalbed so it will break easily when blasted with explosives. This type of mining accounts for less than 5% of total underground production in the U.S. today.

• Shortwall mining–A method that accounts for less than 1% of deep coal production, shortwall involves the use of a continuous mining machine with moveable roof supports, similar to longwall. The continuous miner shears coal panels 150-200 feet wide and more than a half-mile long, depending on geological conditions.