Coal is the most abundant and economical fossil fuel in the world. Coal is primarily used for the generation of electricity, with much smaller volumes used for industrial process heat and in steel production. Over 40 percent of the world’s electricity is produced from coal. As such, it is an important fuel source and will remain so for decades due to its low cost and abundance. However, like all fossil fuels, it is formed from carbon and when it burns, its carbon combines with oxygen to form carbon dioxide (CO2), a greenhouse gas.
CO2 emissions from coal power generation are considered a major contributing factor to global warming. Further, traces of sulfur and nitrogen are also trapped inside coal. If oxides of these elements are released into the air, they can combine with water vapor to form acid rain. Minerals and dirt are also contained in coal. These particles do not burn and result in coal ash.
Coal is formed from the decomposition of organic materials that have been subjected to millions of years of geologic heat and pressure. While coal is generically described as a single commodity, it in fact varies widely in important physical and chemical characteristics such as energy content, carbon content, moisture content, and presence of contaminants such as sulfur. These attributes determine both the price of coal and the applications for which it is used.