Mined coal is of variable quality and is frequently associated with mineral and chemical material including clay, sand, sulphur and trace elements. Coal cleaning by washing and beneficiation removes this associated material, prepares the coal to customer specifications and is an important step in reducing emissions from coal use.
Coal cleaning reduces the ash content of coal by over 50% resulting in less waste, lower sulphur dioxide (SO2) emissions and improved thermal efficiencies, leading to lower CO2 emissions. While coal preparation is standard practice in many countries, greater uptake in developing countries is needed as a low-cost way to improve the environmental performance of coal.
Coal is a chemically complex substance, naturally containing many trace elements including mercury, selenium and arsenic. The combustion of coal can result in trace elements being released from power stations with potentially harmful impacts to both human health and the environment. A number of technologies are used to limit the release of trace elements including coal washing, particulate control devices, fluidised bed combustion, activated carbon injection and FGDs. The choice of mitigation technology will be dependent on the trace elements present and local air quality standard objectives. Research is ongoing to develop better sorbents and reagents that will improve the performance of FGD with respect to trace element removal.
Source: worldcoal.org