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Useful links Powerworks http://www.powerworks.com.au World Coal Association http://www.coal.org CSIRO http://www.csiro.au EnergyAustralia Pty Ltd ABN 99 086 014 968 Locked Bag 14060 Melbourne VIC 8001 Coal Electricity Generation Coal is a fossil fuel which is a natural substance, and is one of the world’s most important sources of energy that is used to generate around 37% * of electricity worldwide. How is coal converted to electricity? Coal is burnt in power stations to generate electricity. Generally, brown coal is first ground into a powder which allows it to burn more quickly. The powdered coal is burnt at a high temperature of around 1100 degrees Celsius. The heat converts into steam. The high-pressure steam is passed into the turbine, which is connected to a generator which is in turn connected to the electricity grid. When the steam is passed into the turbine it causes the turbine shaft to rotate at high speeds (the speed is usually fixed at 3000 rotations per minute). This energy is converted into electricity by the generator and passed into the electricity grid. At our Yallourn power station in the LaTrobe Valley in Victoria, the electricity generated is passed through a transformer which converts the voltages (a unit of measure for electricity) to a level appropriate for the transmission lines. The transmission line transports the power to the networks where the voltage is lowered at a zone substation to an appropriate level for industrial and commercial use. EnergyAustralia Coal Electricity Generation Every hour at the EnergyAustralia Yallourn power station, 2,200 tonnes of brown coal are used to boil water into superheated steam to drive the four turbine generators. These turbines have a combined capacity of 1,480 megawatts of electricity and generate approximately 10,500 gigawatt hours per annum. This is enough to supply electricity to around 2 million homes. When it nears our homes, businesses and schools, the electricity is converted to safer level of 240 volts (at the distribution substation), which is used to power all our electrical appliances including televisions, game consoles, fridges, toasters and washing machines. How is coal formed? Coal is a type of rock formed millions of years ago from plant and mineral materials in swampy areas. Over time, sediments covered these materials, forming heavy rock layers. This forced the plant material to decompose into a spongy material called peat. As the water and gasses were squeezed out by the heavy rock layers, above the peat was heated at great temperatures in the earth and coal began to form, first as brown coal (lignite) and then harder black coals. The coal formed in layers called seams. Brown coal is a relatively young coal at around 30 million years old compared to black coal which is 10 to 20 times older. The brown coal seam at Yallourn is around 100m in depth and there are other seams lower down. The brown coal is characterised by being relatively high in moisture content (60 to 70%) but very low in ash and sulphur as compared to black coal. How is coal mined? At the EnergyAustralia power station, brown coal is mined in the adjacent open cut mine. Open cut simply means that coal is mined at the surface, rather than by using underground methods. In the case of Yallourn the material at the surface of the mine, known as overburden, is removed by the use of Bucket Wheel Excavators or Dredgers to reveal the coal. The coal is then dug up, using bucket wheel excavators or large dozers and loaded on to conveyer belts which transport the coal to the coal bunkers which provide around 20 hours of coal storage for the power station. As areas of the mine are depleted of coal, the land is rehabilitated so it can fulfil a new purpose. Rehabilitation typically includes reducing the slope of the steeper mine walls and capping over coal surfaces. Once this is done, indigenous vegetation can be introduced into the area which will generally include plants, trees and grasses. In some cases, rehabilitation can also involve man made lakes. The revegetation of depleted mines can provide a potential habitat for wildlife in the region. Coal to the Power Station From the mine, the coal is carried through crushers into the short-term boiler bunkers of each of the generating units. The coal is then delivered to the pulverised fuel mill to be crushed into a powdered consistency. In conjunction with the crushing, hot gases drawn from the furnance. The mill, acting as a large fan, then delivers the pulverised fuel (powdered coal) into the furnace where it ignites. The heat from the coal combustion is transferred into the boiler surfaces thereby generating steam to be delivered to the turbine. *Source: Australia Coal Association Energy Information Sheets
