How Do Coal-Fired Power Stations Work?
Coal is by far the number one fuel for electricity generation in the United States. In 2009, for example, coal accounted for about 45 percent of power production, according to the U.S. Energy Information Administration, compared with 23 percent for natural gas and 20 percent for nuclear, the next largest sources. Coal-fired power stations work by turning the energy locked inside coal into heat energy, then mechanical energy and finally electricity.
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Coal
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Electricity generation at a coal-fired power station starts, appropriately enough, with coal, which is usually delivered to the plant by rail or barge. The coal is first crushed into roughly 2-inch diameter chunks, then pulverized--pounded into dust. Coal dust and air are mixed together and blown into the boiler, a furnace where temperatures of up to 1,000 degrees cause the mixture to ignite immediately.
Steam
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Inside the boiler is a network of pipes carrying purified water. The heat from the burning coal boils this water, turning it to steam under extremely high pressure. The pipes carry the steam to a turbine, an enormous rotating drum covered with fan blades to catch the steam. The high-pressure steam spins the turbine at thousands of revolutions per minute.
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Generator
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The generator is where the plant produces its electricity. In the center of the generator is a shaft thickly covered with coiled wire and placed between giant magnets. The shaft is connected to the turbine, so when the turbine spins, so does the coil of wire. The generator works on the principle of electromagnetic induction. Simply put, this principle holds that moving an electrical conductor through a magnetic field will generate an electrical current. In a generator, there's a lot of conducting material moving through the magnetic field rapidly, so it produces a tremendous amount of electricity. Transformers step up the voltage of that current, and transmission wires carry the electricity off to homes and businesses.
Condenser
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After the steam has done its job--spinning the turbines--it's piped to condensers, where it is cooled down. The steam condenses back into water, which flows back to the boiler, where the process starts all over again.
Waste
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Waste products from the burning of coal include gaseous byproducts such as carbon dioxide, sulfur dioxide and nitrogen oxides, as well as fine particulates like soot and "fly ash." These are vented up the smokestack. Devices known as "scrubbers" can remove some of this pollution. Heavier ash--known as "bottom ash"--accumulates at the bottom of the boiler, where it is collected and hauled away for disposal.
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References
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- Photo Credit winter coal image by Rick Smith from Fotolia.com
