Coal

B

1

Conventional Mining

Conventional mining, also called cyclic mining, involves a sequence of operations that proceed in the following order: (1) supporting the roof, (2) ventilation, (3) cutting, (4) drilling, (5) blasting, (6) coal removal, and (7) loading. First, miners make the roof above the seam safe and stable by timbering or by roof bolting, processes intended to prevent the roof from collapsing. At the same time, they create ventilation openings so that dangerous gases can escape and fresh air can reach the miners. Then one or more slots—a few centimeters wide and extending for several meters into the coal—are cut along the face of the coal seam, also known as the wall face, by a large, mobile cutting machine. The cut, or slot, provides easy access to the face and facilitates the breaking up of the coal, which is usually blasted from the seam by explosives known as permissible explosives. This type of explosive produces an almost flame-free explosion and markedly reduces the amount of noxious fumes in comparison with conventional explosives. The coal may then be transported by rubber-tired electric vehicles (shuttle cars) or by chain (or belt) conveyor systems.

B

2

Continuous Mining

Continuous mining involves the use of a single machine known as a continuous miner that breaks the coal mechanically and loads it for transport. This mobile machine has a series of metal-studded rotating drums that gouge coal from the face of the coal seam. One continuous miner can mechanically break apart about 1.8 metric tons of coal per hour. Roof support is then installed, ventilation is advanced, and the coalface is ready for the next cycle. The method used to transport the coal requires the installation of mobile belt conveyors.

B

3

Longwall Mining

The longwall mining system uses a remote-controlled self-advancing roof in which large blocks of coal are completely extracted in a continuous operation. Hydraulic or self-advancing jacks, known as chocks, support the roof at the immediate face as the coal is removed. As the face advances, the roof is allowed to collapse behind the remote-controlled, roof-building machinery. Miners then remove the fallen coal. Coal recovery is comparable to that attainable with the conventional or continuous mining systems.

B

4

Room-and-Pillar Mining

Room-and-pillar mining is a means of developing a coalface and, at the same time, retaining supports for the roof. With this technique, rooms are developed from large, parallel tunnels driven into the solid coal, and the intervening pillars of coal are used to support the roof. The percentage of coal recovered from a seam depends on the number and size of protective pillars of coal thought necessary to support the roof safely. Workers may remove some coal pillars just before closing the mine.

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VII

Coal Mining Safety

Coalmines are hazardous operations. In the 20th century, more than 100,000 miners died working in coalmines. Many accidents were caused by the mine structure failing through roof collapse or rock bursts (coal pillars exploding from the weight of excessive overburden). Other dangers that miners face include toxic or explosive gases released as the coal is mined, dangerous coal dust, and fires. Fires result when flammable gases trapped in the coal, such as methane, are released during mining operations and accidentally ignited.

Provision of adequate ventilation is an essential safety feature of underground coal mining. Not all of this ventilation is required to enable miners to work in comfort. Most of it is required to dilute the harmful gases, frequently termed damps, produced during mining operations.

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