Converting Coal into Electricity
Nine out of every 10 tons of coal mined in the United States today is used to generate electricity, and more than half of the electricity used in this country is coal-generated electricity. How is coal converted into electricity?
Electricity from Coal
Electricity from coal is the electric power made from the energy stored in coal. Carbon, made from ancient plant material, gives coal most of its energy. This energy is released when coal is burned.
We use coal-generated electricity for
- and much more!
Releasing Coal’s Energy
The process of converting coal into electricity has multiple steps and is similar to the process used to convert oil and natural gas into electricity:
- A machine called a pulverizer grinds the coal into a fine powder.
- The coal powder mixes with hot air, which helps the coal burn more efficiently, and the mixture moves to the furnace.
- The burning coal heats water in a boiler, creating steam.
- Steam released from the boiler powers an engine called a turbine, transforming heat energy from burning coal into mechanical energy that spins the turbine engine.
- The spinning turbine is used to power a generator, a machine that turns mechanical energy into electric energy. This happens when magnets inside a copper coil in the generator spin.
- A condenser cools the steam moving through the turbine. As the steam is condensed, it turns back into water.
- The water returns to the boiler, and the cycle begins again.
Other new processes of using coal to make electricity include the following:
- Fluidized bed combustion (FBC), in which coal is inserted into a bed of particles suspended in air that react with the coal to heat the boiler and make steam
- Combined-cycle systems, in which (1) gas produced by heating coal operates a combustion turbine connected to a generator and (2) the exhaust gases from this turbine heat water, which in turn operates a steam-powered generator
- The Department of Energy is working with the coal and electrical generation industries to find ways to utilize coal more cleanly and efficiently.
- For more information about Clean Coal Technologies, click here for the Clean Coal Technology Newsletter, published by the Office of Fossil Energy, U.S. Department of Energy.
Electricity-generating plants send out electricity using a transformer, which increases the voltage of the electricity based on the amount required and the distance it must travel. Voltages are often as high as 500,000 volts at this point.
Electricity flows along transmission lines to substation transformers. These transformers reduce the voltage for use in the local areas to be served.
From the substation transformers, electricity travels along distribution lines, which can be either above or below the ground, to cities and towns. Transformers once again reduce the voltage—this time to about 120 to 140 volts—for safe use inside homes and businesses. The delivery process is instantaneous. By the time you have flipped a switch to turn on a light, electricity has been delivered. FAST FACT: There are over 6 million miles (10 million kilometers) of distribution lines in the United States!
Coal’s Role in Our Electrical Supply
Natural gas and oil are also used to make electricity. How does coal compare to these other fossil fuels? In terms of supply, coal has a clear advantage. The United States has about 260 billion tons of recoverable coal. That is enough to last about 235 years if we continue to use coal at the same rate as we use it today. In addition, coal is a versatile fuel. It can be used as a solid fuel or it can be converted to a gas to replace expensive imported fuels.
But what about costs? The mining, transportation, electricity generation, and pollution-control costs associated with using coal are increasing, but both natural gas and oil are becoming more expensive to use as well. This is, in part, because the United States must import much of its oil supply from other countries. It has enough coal, however, to take care of its electricity needs, with enough left over to export some coal as well.
The cost of using coal should continue to be even more competitive, compared with the rising cost of other fuels. In fact, generating electricity from coal is cheaper than the cost of producing electricity from natural gas. In the United States, 23 of the 25 electric power plants with the lowest operating costs are using coal. Inexpensive electricity, such as that generated by coal, means lower operating costs for businesses and for homeowners. This advantage can help increase coal’s competitiveness in the marketplace.
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