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Anthracite is a type of coal that has the highest carbon content and the lowest moisture and ash content. Anthracite burns slowly and makes a good heating fuel for homes. The United States has about 7.3 billion tons of anthracite, most of which can be found in Pennsylvania.

Bituminous is a type of coal that contains very little moisture and has high heat value. It is used to generate electricity and to produce coke, a coal residue used in the steel industry. Bituminous coal is the most plentiful type in the United States.

Btu is an abbreviation for British thermal unit, the standard for measuring the energy required to raise the temperature of 1 pound of water by 1 degree Fahrenheit.

Clean Air Act
The Clean Air Act is a strict air pollution control law that was passed in 1970.

Clean Coal Technology (CCT) program
The CCT program refers to a number of technological advances that make the burning process of coal cleaner by removing pollutants such as sulfur, nitrogen, and fly ash that can contaminate the air and water.

Coal is a burnable carbonaceous rock that contains large amounts of carbon. Coal is also a fossil fuel—a substance that contains the remains of plants and animals and that can be burned to release energy. Coal contains other elements such as hydrogen, oxygen, and nitrogen; has various amounts of minerals; and is itself considered to be a mineral of organic origin.

Coal gasification
Coal gasification is the process that changes coal into a gas that has the same heating value as natural gas and that is cleaner than burning coal itself.

Coke is a substance made by heating coal to very high temperatures. Coke is used in the iron and steel industry.

Combined-cycle system
In a combined-cycle system, gas from heating coal operates a combustion turbine connected to a generator, and the exhaust gases from this turbine heat water that, in turn, operates a steam-powered generator.

Continuous miner
A continuous miner is a machine with large, rotating cutters that break into the coal and with arms that scoop the coal onto a built-in conveyor.

Deep mining
See Underground mining.

Electrostatic precipitator
An electrostatic precipitator is a device that gives coal dust particles an electric charge so they can be attracted to a collector plate. Electrostatic precipitators help prevent air pollution.

A flue is a pipe through which gases and smoke escape from burning coal.

Flue gas desulfurization system
A flue gas desulfurization system, or scrubber, is a device that removes more than 90 percent of the sulfur dioxide emissions from the burning process of coal.

Fluidized-bed combustion (FBC)
FBC is a process of burning coal in which the coal is inserted in a bed of particles that are suspended in the air and that react with the coal to heat the furnace more cleanly. In FBC, coal is burned at a slightly lower temperature, which helps prevent some nitrogen oxide gases from forming.

Fly ash
Fly ash refers to the fine particles contained in the gases that are released when coal is burned.

Fossil fuel
A fossil fuel is a fuel formed from the remains of organic materials. Fossil fuels include coal, oil, and natural gas.

A generator is a machine that turns mechanical energy into electric energy.

Igneous is one of three types of rock. Igneous rock forms when magma, molten rock material within the earth, forces its way to the surface and cools.

Land reclamation
Land reclamation is the process of protecting, restoring, and possibly even improving the land before, during, and after surface mining. As coal is removed from one section of a surface mine, the land at another part is returned, regraded, and replanted. In the end, this means that the land is preserved, nature has been protected, water and soil are conserved, and the land can be turned into productive farmland, forests, and lakes.

Lignite is a type of coal that contains a lot of moisture and ash and breaks apart easily. Of the four types, lignite has the lowest carbon content and heating value. Also called brown coal, lignite is used mainly at electricity-generating plants.

Longwall mining machine
A longwall mining machine is a cutting machine that works along walls of coal up to 1,000 feet long to cut coal and drop it onto a conveyor belt.

Magma is molten rock material within the earth. When magma forces its way to the surface and cools, it forms igneous rock.

Metamorphic is one of three types of rock. Metamorphic rock is rock whose minerals and texture have been changed by high temperatures, water, and pressure.

Nonrenewable energy
Nonrenewable energy is the energy supplied by fossil fuels—coal, oil, and natural gas. Fossil fuels are limited in supply.

Overburden is the material that is removed from the earth’s surface to uncover the coal. Overburden includes layers of earth and rock.

Peat is a soggy, spongelike material that forms from plants and trees after they die. Peat from plants and trees that died about 300 million years ago became buried and compressed under the earth’s surface over a long period of time. Over millions of years and through the forces of heat and pressure, the compressed peat became coal.

Recoverable coal
Recoverable coal refers to the amount of coal that can be removed. There are approximately 275 billion tons of recoverable coal reserves in the United States.

Sedimentary is one of three types of rock. Sedimentary rock forms from mineral fragments deposited by wind, water, or glaciers.

Sludge is the muddy waste that is produced during processes to remove sulfur from coal.

A slurry is coal that is ground to a powder and mixed with water. In this form, coal can be pumped through a pipeline.

Slurry pipeline
A slurry pipeline is a pipeline that transports coal that has been ground to a powder and mixed with water. A coal slurry pipeline connects a mine in Arizona with a power plant in Nevada.

Subbituminous is a type of coal that is dull black and has less moisture than lignite. Subbituminous is generally used to produce steam for electricity generation. Reserves of subbituminous coal are found mostly in western states and Alaska.

Surface mining
Surface mining is used when coal is found close to the surface or on hillsides. It involves removing the topsoil and subsoil and setting them aside while the coal is removed.

Surface Mining Control and Reclamation Act (SMCRA)
The SMCRA, enacted in the late 1970s, is the first comprehensive national surface-mining law. Under the law, each state that establishes federally approved enforcement programs has the primary responsibility for enforcing mining regulations in the state. If a state lacks these programs, the Office of Surface Mining Reclamation and Enforcement in the U.S. Department of Interior implements the federal law.

A turbine is an engine that spins around, causing the heat energy of burning coal to become mechanical energy.

Underground mining
Underground mining is used to extract coal that is deep beneath the surface or in seams exposed on hillsides. It involves drilling two openings called shafts into the coal bed—one to transport miners and equipment and the other to bring coal to the surface.

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