As coal is a fossil fuel that is obtained from beneath the surface of the earth one can wonder how is coal mined. Coal is created when organic matter such as plants and dead bodies of animals gets buried under overlying rocks. This organic matter is transformed into black rocks with passage of time and great pressure from the weight of the rocks from above. Coal is used to make electricity through thermal power plants. It plays a crucial role in fulfilling the energy requirements for the infrastructure of a country. Mankind has known about the existence of coal since ancient times. This article, ‘How is coal mined’ or extracted from the earth, is intended for those people interested in knowing more about this important ingredient in the energy chain . This article takes a look at the coal mining processes.
How is Coal Mined – Methods
There are two methods to extract coal from under the earth’s surface
There are primarily two different methods of mining coal from underground. These are termed as opencast and underground mining depending upon the proximity of the coal seam form the surface of the earth. Opencast mining is resorted to when coal is found at relatively shallower depths while underground or deep mining becomes necessary when coal is found at depths of more than 200 meters from the surface of the earth. Underground mining is more common than opencast mining though, in many western countries, it is opencast mining that accounts for most of the coal produced.
Also referred to as surface mining, this method of mining is preferred when coal lies near the surface of the earth. It is a less expensive method of mining that involves employing giant earth removal machines that remove the overlying rocks and soil to reveal the underlying coal beds. Once the coal has been removed, the top soil is put back and the land can be used once again for various purposes. This method is also more productive than underground mining and more than 90% of the coal lying in the coal beds can be extracted using bulldozers, bucket excavators, and other giant earth moving machines. Opencast mines can be enormous, spread across many square kilometers depending upon the presence of the coal underground. Sometimes, conveyor belts are used to transport coal extracted to the trucks that carry away large chunks of coal to the power plants.
Underground mining is the better option when the underlying coal deposits are found at a depth of more than 200 meters. Shafts are dug to reach down to the coal bed where explosives are used after providing support to the tunnels to extract coal. These shafts carry not just miners but also the entire equipment down to the coal bed. In fact, a network of rooms is created with every room being supported through pillars. These pillars are coal itself that is left behind while the rest of the coal in the room is mined out. This method of extracting coal from underground mines is called Room and Pillar mining.
Another method of underground mining is referred to as Longwall Mining. In this method, the coal bed is provided support in the form of self-advancing hydraulic support. This support holds the coal face and prevents the roof from caving while coal is being mined. Once all the coal has been extracted, the roof is allowed to collapse. This method of underground mining allows for extraction of more than 75% of the coal deposit.