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Uses of Coal

At one time coal was predominantly used to heat homes, as well as power railroad locomotives and factories. Today, however, coal serves different purposes for society. The chief use of coal is now electricity generation. Other uses include coking coal for steel manufacturing and industrial process heating.

Electricity Generation Photo of a power plant

Eighty-two percent of Kentucky's coal is used to generate electricity. After coal is mined, it is transported to power plants by trains, barges, and trucks. A conveyor belt carries the coal to a pulverizer, where it is ground to the fineness of talcum powder. The powdered coal is then blown into a combustion chamber of a boiler, where it is burned at around 1,400ºC. Surrounding the walls of the boiler room are pipes filled with water. Because of the intense heat, the water vaporizes into superheated high-pressure steam. The steam passes through a turbine (which is similar to a large propeller) connected to a generator. The incoming steam causes the turbine to rotate at high speeds, creating a magnetic field inside wound wire coils in the generator. This pushes an electric current through the wire coils out of the power plant through transmission lines. After the steam passes through the turbine chamber, it is cooled down in cooling towers and it again becomes part of the water/steam cycle.

 

 

Graphic illustrates how electricity generated by conventional coal combusion

Electricity generation by conventional coal combustion.

 

Several by-products, including solids and gases, are created in the electricity generation process. A substance called "clinker" or bottom ash (glassy particles of melted coal ash) settles at the base of the furnace. This material is periodically removed and disposed of. Fly ash, the noncombustible minerals found in coal (including ash, dust, soot, and cinders) travels upward with gaseous by-products. Fly ash can be captured in an electrostatic precipitator and then transported by pipes to a holding pond, where it settles. Over 98 percent of all solids are captured in the plant. Gaseous by-products include carbon dioxide (CO2), sulfur oxides (SOx), and nitrogen oxides (NOx). Sulfur oxides can be controlled by the installation of scrubbers at coal-fired power plants. Scrubbers allow high-sulfur coals to be used because they remove sulfur dioxides out of the gas stream in the stacks (a process called desulfurization). Scrubbers work by spraying limestone slurry directly in the path of the materials leaving the boiler chamber. The limestone reacts with the sulfur in the gases within the stacks. The combination of carbonate (limestone) and sulfur forms the mineral gypsum. Gypsum is a solid, which falls out of the gas to the bottom of the stacks, where it can be collected. The by-product gypsum created in this process can be used to make drywall and bowling balls. Nitrogen oxides are managed by careful control of the furnace temperature. There is current technology to control carbon dioxide; however, using high-efficiency coals (such as those found in Kentucky) helps reduce the output of CO2.

Other Uses

When coal is heated in the absence of air, a porous, carbon-rich material called "coke" is formed. Bituminous coal (also called metallurgical coal or coking coal) is baked without air in an oven until most of its volatile matter is released. During this process, it softens, then liquefies and resolidifies into hard porous lumps. Coking coals are more expensive than coals used for heating or electricity. They must have a low sulfur and phosphorous content, which makes them less common than the types of coal used for heating and electricity. When iron and steel are made, coke is one of the constituents needed to properly heat the furnace (limestone and iron ore are two other constituents used). Gaseous by-products from coke ovens are also used. These include crude coal tar, light oils, and ammonia. Seventy percent of steel production comes from iron made in blast furnaces using coal and coke. In the recent past, however, the production of steel in the United States has declined because of, among other reasons, the use of plastics and imported steel. Therefore, the use of coal in the production of coke has declined over the years to 2 percent of Kentucky's annual mined coal.

In industrial process heating, coal is used to heat boilers and ovens. The cement (which represents the biggest worldwide industrial use of coal), glass, ceramic, and paper industries all use coal for this purpose. In Kentucky, industrial process heating accounts for 10 percent of Kentucky's annual mined coal.

Five percent of the coal mined in Kentucky is exported to other countries; Canada receives the most.

 

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