Bituminous coal is the most common classification of coal
(on the order of 52% of coal reserves in the US is bituminous). In appearance
it ranges from dark brown to black and has a rather high heat energy (21 to 30 million Btu
per ton). Due in part to its abundance it also has the widest range of commercial
use though is paticularly used in power plant
s and boilers (86% of the bituminous coal mined in Pennsylvania
is used in electric power stations.)
Bituminous coal is also used to to make 'coke' - a form of near pure carbon that is used in the smelting of iron ore and the production of steel. The coking properties also lead to bituminous coal being used in blacksmithing. Not all bituminous coal is appropriate for this use.
Coal is 'ranked' based upon the amount of change from the original organic material to carbon. Of these, anthracite is is the most transformed while sub-bituminous and lignite have less transformation. This ranking is called coalification. As the rank increases:
- hardness increases
- reactivity decreases
- carbon content increases
- hydrogen and oxygen (partially responsible for moisture) decreases
(pure carbon) could be considered the 'ultimate' form of coal.
Bituminous coal has a high sulfur content which contributes to air pollution and the production of acid rain. The burning of bituminous coal has been banned or considered banned in many counties within the United States and in some countries.