The four types of coal mined today, arranged by greatest to least energy potential are: anthracite, bituminous, subbituminous, and lignite.
At a power plant, mined coal is combusted to boil water in a boiler and produce steam to operate steam turbines. Most of the electricity in the United States is produced using steam turbines, where steam is forced against a series of blades mounted on a shaft, which convert the energy into mechanical power. This rotating shaft is connected to the generator, which converts mechanical energy into electrical energy based on the relationship between magnetism and electricity.
- The United States has more coal reserves than any other single country in the world. In fact, just over 1/4 of all the known coal in the world is in the United States.
- Coal reserves in the United States stand at 268 billion tons, of which 43 percent are in surface mines. The three major coal-producing states are Wyoming, West Virginia, and Kentucky.
- The large amount of reserves within the U.S. make coal very inexpensive compared to other sources of electricity.
- Coal gasification and coal liquefaction are also possible uses of coal for producing synthetic fuel.
- Coal is a nonrenewable energy source because it takes millions of years to create.
- Surface, or strip mines, are the source of about 70% of the coal that is mined in the U.S. These mining operations remove the soil and rock above coal deposits, or “seams,” disturbing land at its surface.
- Burning coal produces numerous emissions that adversely affect the environment and human health. When coal is burned, carbon dioxide, sulfur dioxide, nitrogen oxides, and mercury compounds are released. For that reason, coal-fired boilers are required to have control devices to reduce the amount of emissions that are released.
“Clean coal technology” describes a new generation of energy processes that sharply reduce air emissions and other pollutants from coal-burning power plants. Some of the early projects are showing ways to reduce greenhouse emissions by boosting the efficiency by which coal plants convert coal to electricity or other energy forms.