How is coal extracted




















With increasing time, and higher heat and pressure, the plant material first forms into peat, then is converted into brown coal, then sub-bituminous coal, bituminous coal, and lastly anthracite. Australia has the fourth-largest share of coal reserves in the world. Since the late s about million tonnes of black coal and about million tonnes of brown coal have been mined in Australia and the industry still provides significant employment, capital investment and domestic and export income to the national economy.

These two states are also the largest coal producers. Locally important black coal mining operations also include Collie in Western Australia, and Fingal and Kimbolton in Tasmania.

The Gippsland Basin in Victoria contains a substantial world-class deposit where seams can be up to m thick. Minor resources occur in Tasmania's Longford Basin. Currently, brown coal is only mined in Victoria where the open-cut mines at Loy Yang and Yallourn supply coal to nearby power stations.

Brown coal is also mined at Maddingley to produce soil conditioners and fertilisers. Other products from Victorian brown coal are briquettes for industrial and domestic use and low-ash and low-sulphide char products.

Open-cut mining is possible because coal seams are close to the surface. Many brown coal beds lie close to the surface and can be hundreds of metres thick, so can be extracted easily and cheaply. Firstly the topsoil is removed and stored for use later in restoring the disturbed land. The surface rock called overburden covering the coal is then blasted with explosives and removed by excavators.

The uncovered coal is in turn then blasted to break up the layers and loaded into large trucks which can hold up to tonnes of material. The coal is transported to the processing plant where impurities are removed.

Coal that is deeper than a few hundred metres under the surface must be extracted using two underground mining methods. Some coal is mined by the Bord and Pillar method.

This is where a machine continually cuts into the coal. It tunnels through the coal seams leaving pillars supported by roof bolts to hold up the roof. An alternative is longwall mining, which uses a large cutting blade to slice across the coal layer to remove the coal seam. The coal is then transported to the surface on a conveyor belt. After the coal is mined the machine is dismantled and relocated to another section of the mine allowing the roof to collapse behind.

Advances in technology have led to the introduction of automated longwall mining systems. In addition, some mining companies are using driverless trucks, trains and drones to improve safety and gather information. Black coal can be used without any processing, but is usually crushed, screened and sorted according to customer requirements. Sometimes it is also washed to remove any pieces of waste minerals that do not burn. This improves the quality and reduces the production of ash when the coal is burned.

To wash the coal it is placed into tanks with liquids and chemicals which assist in recovering more of the coal as it floats to the surface. The coal is then left to dry out. It is stored according to size and may be blended, again according to customer specifications. From there it is stockpiled or stored in bins ready for transport by road or rail.

Lower quality coal such as sub-bituminous or brown coal can be refined to remove moisture and other impurities. This increases the efficiency of the coal as a fuel and reduces emissions of greenhouse gases and other pollutants, when the coal is burned. In Victoria the brown coal is upgraded by the Coldry Process. A mechanical shear is used to crush the coal into small particles, releasing water that was held in the pores holes in the coal.

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