Coal is a black, rock-like fossil fuel that is used all over the world as a source of power. Coal can usually be found in coal beds or coal seams. It is mostly made of carbon as it formed from decaying organic matter that has undergone extreme pressure under the surface of the earth. There are six distinct types of coal, each with different properties. Coal is mined on almost every continent of the world. How is coal mined? Read on to find out.
Coal is mined in two separate ways, open cut mining and underground mining, depending on the depth of the coal deposit. Open cut mining, also known as strip mining, is chosen when the coal seam is close to the surface of the earth. These mines recover a higher percentage of the coal than underground methods. Open cut mining involves using explosives to blast away the unwanted material on the surface called the overburden. This overburden is cleared away using draglines, trucks and shovels. Once the overburden has been removed and the coal seam has been exposed it is drilled, fractured and mined in strips. This coal is loaded into the back of large trucks and transported to a coal preparation plant. Open cut mines can be hundreds of miles in length and over many hundreds of square miles. This can also be done in strips, thus the name strip mining, and the strips once mined of all the coal are filled back up with the overburden from the next strip to be mined.
The types of underground mining
When a coal seam in a long way underground then underground mining methods are used. Large underground tunnels are dug using heavy machinery and pillars and supports are placed along the route to ensure that the roof does not collapse. Heavy machinery is used to cut away the coal from the rock. There are five methods of underground mining that are used. The first method is longwall mining. A piece of machinery called a longwall shearer is used to strips the coal from the seam by breaking it into small pieces. These pieces fall onto a conveyor belt which takes them to the surface of the mine for processing. As the Longwall shearer moves forward loose rock is allowed to fall behind it.
The second method is known as continuous mining. Once again a specialized machine is used to extract the coal from the seam. The continuous miner is equipped with rotating drums with carbide teeth which scrape the coal from the seam. These are usually operated in a room and pillar mine. Conveyors are used to transport the coal to the surface of the mine.
Blast mining is another method used to extract coal underground. In this method explosives are placed in a very specific pattern inside the coal seam. The explosives are set off shattering the coal from the rock. The coal is them collected in carts by miners and taken up to the surface. This is one of the oldest methods of mining coal.
Shortwall mining is also used, but far less extensively than longwall mining. Shortwall mining works in the same manner as longwall mining except that only short distances of the coal seam are mined at a time, hence the name.
Retreat mining is used when the coal seam is almost exhausted. The miners work backwards through the mine towards the entrance extracting the coal from the pillars that were left to support the roof of the mine. This can be very dangerous as the collapse of the roof cannot be predicted.