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Longwall Mining

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Mining Processes

Longwall mining is one of two underground mining methods used to extract ore from flat coalbeds, the other is the room and pillar method. Introduced in the 1950s and 1960s, it involves using a series of specialized equipment, such as plows, coal shearers, hydraulic jacks, continuous miners, and conveyor systems to extract panels of rectangular blocks of coal by shearing it and spilling it onto a conveyor belt to be carried out of the mine.

Longwall is the most common type in the U.S. and in many parts of the world. It accounts for more than half of the coal that is produced in the U.S. and typically extracts between 10,000 and 30,000 tons of coal from a single panel (equivalent to nine to 27 million kg).

Longwall mining has many advantages: it requires fewer miners inside the actual mine, and places the miners in fewer working sections, making it easier to manage and control, reducing the chances of injury.

One of the major drawbacks is the cost of equipment, especially when it is an investment that does not immediately see results. Longwall also requires the functioning of all of the equipment in order for the process to take place. If something goes wrong with one machine, the entire process is delayed until it is remedied. Dust control is another prevalent problem in longwall mining and great lengths and special equipment is needed at all times to keep dust levels at a minimum.[1] Longwall is criticized for its harmful effects on the environment, including soil erosion and damage to underground water tables.[2]

Longwall mining is an underground alternative to the room and pillar method, which involves extracting ore from rooms within a mine, leaving behind supportive pillars that may contain valuable ores. This type is usually used in mines that are deeper than 1,000 feet (300 m) and run the risk of having the cave collapse if the pillars are not thick enough to support the hollowed rooms and rocky ceiling. It also poses a disadvantage because ultimately, miners are leaving behind valuable ore that cannot be recovered from the pillars.

[edit] Process

Longwall mining is a continuous operation that involves a lot of expensive, heavy machinery. The hydraulic jack is used to provide support for the roof, while the shearing machine makes its way by conveyor across the coal face, cutting and spilling coal on the conveyor. When it has traveled the full length of the face, it reverses direction automatically and travels back along the face for the next cut. The hydraulic jack, in the meantime, moves closer to the newly sheared face after each cut. This is carried out in a continuous manner until the entire panel of coal is removed. Continuous miners are large machines, usually 800 feet (240 m) wide and five to 10 feet (1.5 to 3 m) tall. They are also expensive, running anywhere from five to 15 million dollars.[3]

The longwall method involves selecting a block of coalbed and sectioning it into panels typically 800 feet (240 m) in width, seven feet (2.1 m) in height and 7,000 feet (2,134 m) in length. This amount has the potential to produce one million tons of coal. But not all of the coal is recovered, as some is left behind to support the mined area. The panels are sectioned into blocks by excavating a series of passages or roadways.

[edit] Equipment Used

[edit] References

  1. Longwall Mining. Energy Information Administration: U.S. Department of Energy, March, 1995. (accessed: 2008-09-29)
  2. What is Longwall Mining? Wise Geek, 2008-09-29.
  3. What is Longwall Mining? Wise Geek, 2008-09-29.