Bituminous coal—a dense coal, usually black, sometimes dark brown, often with well-defined bands of bright and dull material, used primarily as fuel in steam-electric power generation, with substantial quantities also used for heat arid power applications in manufacturing and to make coke.
Anthracite—the highest rank; a harder, glossy, black coal used primarily for residential and commercial space heating.
Graphite—technically the highest rank, but difficult to ignite and is not so commonly used for ignition.
Coal as Fuel
Coal is primarily used as a solid fuel to produce electricity and beat through combustion. World coal consumption is about 5.3 billion tonnes annually, of which about 75% is used for the production of electricity.
The region including the People’s Republic of China and India uses about 1.7 billion tonnes annually, forecast to exceed 2.7 billion tonnes in 2025.
The USA consumes about 1.0 billion tons of coal each year, using 90% of it for generation of electricity.
Coal is the fastest growing energy source in the world, with coal use increasing by 25% for the three-year period ending in December 2004.
The total known deposits recoverable by current technologies, including highly polluting, low energy content types of coal (i.e. lignite, bituminous), might be sufficient for 300 years’ use at current consumption levels, although maximal production could be reached within decades.
Coking and Use of Coke
Coke is a solid carbonaceous residue derived from low-ash, low-sulfur bituminous coal from which the volatile constituents are driven off by baking in an oven without oxygen at temperature as high as 1, 000°C (1, 832°F) so that the fixed carbon and residual ash are fused together.