Coal, a combustible black or brownish-black sedimentary rock, serves as a significant global energy source. Formed over millions of years from plant remains, it is primarily composed of carbon. Extracting this fossil fuel involves diverse mining techniques, which depend on the depth and geological characteristics of coal deposits. These methods range from surface operations to complex underground networks, each tailored to access the resource.
Surface Mining Operations
When coal deposits lie relatively close to the Earth’s surface, typically within 200 feet, surface mining techniques are used. This approach begins with clearing vegetation and topsoil, which is then stockpiled for later reclamation. Large machinery removes the “overburden,” the layers of rock and soil covering the coal seam. This material is removed to expose the coal.
One common surface method is strip mining, where long, narrow strips of overburden are removed to access the coal. After coal extraction from one strip, overburden from the next is placed into the previously mined area. Mountaintop removal is another technique, used in mountainous regions, where explosives and heavy equipment remove upper mountain sections to expose coal seams. Once overburden is removed, large excavators and loaders, such as draglines or shovels, dig out the exposed coal. Efforts to reshape and revegetate the land begin soon after coal removal.
Underground Mining Operations
When coal seams are situated hundreds or even thousands of feet beneath the surface, underground mining techniques are used. Access to these deep seams is gained via vertical shafts, inclined slopes, or horizontal drifts, depending on the topography and depth of the coal. These access points allow movement of personnel, equipment, and extracted coal.
One method is room and pillar mining, where a network of rooms is carved from the coal seam, leaving large pillars to support the mine roof. Miners use continuous mining machines to cut coal, and shuttle cars or conveyors transport the loosened coal. Longwall mining uses a shearer machine that cuts coal from a long face, often hundreds of feet wide. Hydraulic roof supports temporarily hold the roof as the shearer advances, allowing the roof behind to collapse in a controlled manner.
Maintaining a safe environment requires ventilation systems that circulate fresh air to dilute hazardous gases and control dust. Support structures, such as roof bolts and steel arches, are installed to prevent rock falls and maintain mine roadway integrity. Equipment, including continuous miners, longwall shearers, and conveyors, operates in confined, challenging underground conditions.
Coal Preparation and Transport
Once extracted, raw coal undergoes processing to prepare it for market and improve quality. This processing begins with crushing, where large lumps are broken into smaller, uniform sizes. The crushed coal proceeds to a preparation plant, sometimes called a coal wash plant. There, it undergoes washing to remove impurities such as rock, ash, and sulfur, which improves its energy content and reduces emissions when burned.
Washing involves water and gravity separation techniques to differentiate coal from denser waste materials. After washing, the coal may be screened and sorted by size and quality to meet customer requirements. The prepared coal is ready for transportation from the mine site to power plants, industrial facilities, or export terminals. Common methods include unit trains for long distances, barges for water transport, and trucks for local transport.