Thermal black coal

Thermal black coal is a sedimentary rock that is combustible. It is formed from vegetation that has become consolidated between other rock strata where it becomes transformed into coal via a combination of heat, pressure and microbial action over a long period of time. This transformation is known as 'coalification'.

Thermal black coal is usually found in seams, or layers, that can be only millimetres thick, or many tens of metres thick. It comprises oxygen, three to 13 percent hydrogen, between 50 and 98 percent carbon as well as small amounts of sulphur and nitrogen. It also contains inorganic matter and water.

It is when thermal black coal is burnt it becomes valuable, as it then releases much energy in the form of heat where it finds its primary use as a 'steaming coal' in generating electricity in power stations. In 2008, 77 percent of all electricity produced in Australia was produced by coal, most of it being thermal black coal.

Thermal black coal doesn't need any processing other than crushing and screening in order to reduce it to a usable size although it may sometimes be washed to remove impurities such as minerals and pieces of rock. Washing improves its quality and reduces ash content. The washing of thermal black coal is carried out by immersing the coal in a high specific gravity liquid where the heavier impurities fall to the bottom and the lighter coal floats on the surface from where it is easily recovered.

The mining of thermal black coal takes place either underground or in an open pit method on the surface. The form of mining undertaken relies on whether the coal is deep underground or near the surface. About 80 percent of Australian thermal black coal production comes from the open pit method. However, this method of mining is only economical if the coal seam is close to the surface where more coal can be recovered. Large open cut mines cover many square kilometres of land where large drag-lines are used to remove overburden before excavators are introduced to extract coal from the exposed coal seam. Either haulage trucks, or conveyor belts, are used to transport the coal to the crusher and screening plant. Many open pits mine coal to a depth of 200 metres or deeper.

In NSW thermal black coal is mined near the western and eastern edges of the Gunnedah Basin. Mines along the eastern edge of the basin spread along the Hunter Valley from Muswellbrook to Newcastle where coal seams are close to the surface and are mined by the open pit method. In the Lithgow-Mudgee and Woolongong-Appin-Bulli area most of the mines are underground.

Thermal black coal mines in Queensland are located at Newlands, Rolleston and the Bowen Basin that includes Moura, Blackwater and Collinsville. There are also thermal black coal mines in the Callide, Surat and Moreton Basins, Commodore, New Acland and Wilkie Creek. Thermal black coal mines also operate in Western Australia at Premier and Muja, Leigh Creek in South Australia and Duncan in Tasmania.