Coal is a burnable carbonaceous rock, classified as sedimentary. Coal is divided into four major types, based generally on the amount of transformation undergone from the earlier plant and peat stages, heating value and other characteristics:
A brownish-black coal with generally high moisture and ash content and the lowest carbon content. Significant resources and mining operations are in Texas, North Dakota and Montana.
Coal with higher heating value than lignite. Wyoming produces the bulk of sub-bituminous coal in the Powder River Basin (PRB) area.
Soft, intermediate grade of coal that is most common and widely used in the United States. It is mined mainly in Appalachia and the Midwest regions of the US.
The hardest type of coal, consisting of nearly all carbon. Mined in the Appalachian area of Pennsylvania, it has the highest heating value and lowest moisture and ash content.
Mining methods for coal is usually accomplished by open pit (or surface) or underground (also called deep) mining techniques. Deposits of coal less than 200 feet are extracted by surface mining, which accounts for the majority (67 percent) of the annual US coal production.
Underground mining is usually accomplished by either longwall or continuous mining techniques.
- Longwall – accounts for more than 50 percent of deep mine production. The longwall miner is a huge machine with a rotating cutting drum that moves mechanically back and forth across a wide coal seam.
- Continous – accounts for most of the remaining underground production, utilizing a special cutting machine that removes the coal from a seam and automatically transports it by conveyor.
Coking coal is a bituminous coal with special characteristics that allows it to be converted into coke and used in the steel manufacturing process.
- Coal provides America’s railroads with more traffic and revenue than any other commodity.
- A typical train car holds between 115 and 117 tons of coal.
- Wyoming is the largest coal-producing state.
- Coal accounts for half of the electricity use in the U.S.
- Coal costs less than any other major fossil fuel source.
- The world’s largest producers and consumers of coal are China, Poland, Russia, India and the United States.
- Total world consumption of marketed energy is projected to increase by 57 percent from 2004 to 2030.
- Coal’s share of total world energy use climbed from 25 percent in 2003 to 26 percent in 2004 and is expected to increase to 28 percent by 2030.