Clean coal technologies (CCTs) are collection of technologies being developed to mitigate the environmental impactof coal energy generation. When coal is used as a fuel source, the gaseous emissions generated by the thermal decomposition of the coal include sulphur dioxide (SO2), nitrogen oxides (NOx), carbon dioxide (CO2), mercury,and other chemical by-products that vary depending on the type of the coal being used. These emissions have been established to have a negative impact on theenvironment and human health, contributing to acid rain, lung cancer and cardiovascular disease. As a result, clean coal technologies are being developed to remove or reduce pollutant emissions to the atmosphere. Some ofthe techniques that would be used to accomplish this include chemically washing minerals and impurities from the coal,gasification (see also IGCC), improved technology for treating flue gases to remove pollutants to increasingly stringent levels and at higher efficiency, carbon capture and storage technologies to capture the carbon dioxide from the flue gas and dewatering lower rank coals (brown coals) to improve the calorific value, and thus the efficiency of the conversion into electricity. Figures from the United States Environmental Protection Agency show that these technologies have made today’scoal-based generating fleet 77 percent cleaner on the basis of regulated emissions per unit of energy produced.
Clean coal technologies usually address atmospheric problems resulting from burning coal. Historically, the primary focus was on SO2 and NOx,the most important gases in causation of acid rain, and particulates which cause visible air pollution and deleterious effects on human health. More recent focus has beenon carbon dioxide (due to its impact on global warming) and concern over toxic species such asmercury. Concerns exist regarding the economic viability of these technologies and the timeframe of delivery, potentially high hidden economic costs in termsof social and environmental damage, and the costs and viability of disposing of removed carbon and other toxic matter.

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