Coal is primarily used as a solid fuel to produce heat through combustion.
World coal consumption is about 5,800 million short tons annually, of which about 75% is used for electricity production. The region including China and India uses about 1,700 million short tons annually, forecast to exceed 3,000 million short tons in 2025. The USA consumes about 1,100 million short 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.
When coal is used for electricity generation, it is usually pulverized and then burned in a furnace with a boiler. The furnace heat converts boiler water to steam, which is then used to spin turbines which turn generators and create electricity, with about 35–40% thermodynamic efficiency for the entire process. Approximately 40% of the world electricity production uses coal, and the total known deposits recoverable by current technologies are sufficient for 300 years' use at current rates.
A promising, more energy-efficient way of using coal for electricity production would be via solid-oxide fuel cells or molten-carbonate fuel cells, which would be able to get 60%–85% combined efficiency, compared to 35–40% normally obtained with steam-only turbines.Currently these fuel cell technologies can only process gaseous fuels, and they are also sensitive to sulfur poisoning, issues which would first have to be worked out before large scale commercial success is possible with coal. As far as gaseous fuels go, one idea is pulverized coal in a gas carrier, especially if the resulting carbon dioxide is sequestered, and has to be separated anyway from the carrier. A better idea is coal gasification with water,and then the water recycled.
