Coal-fired power station. Steam rising from the cooling towers of a coal-fired power station. This station burns coal to heat water to steam, which drives a turbine, which generates electricity. The water is eventually cooled by spraying it into the cooling towers. In the foreground is a plant which processes gypsum (calcium sulphate, Ca. S. O4) produced by the power station. Flue gas, which is rich in poisonous sulphur dioxide (S. O2), is treated with a calcium based mineral such as limestone. This removes the sulphur dioxide and leaves gypsum as a by product. Gypsum produced in this way can be used in fertilisers, ceramics and cements.