Source of information: http:/http://www.need.org/needpdf/infobook_activities/SecInfo/CoalS.pdf
Coal is a fossil fuel created from the remains of plants that lived and died about 100 to 400 million years ago when parts of the earth were covered with huge swampy forests. Coal is classified as a nonrenewable energy source because it takes millions of years to form. The energy we get from coal today comes from the energy that plants absorbed from the sun millions of years ago. All living plants store solar energy through a process known as photosynthesis. When plants die, this energy is usually released as the plants decay. Under conditions favorable to coal formation, however, the decay process is interrupted, preventing the release of the stored solar energy. The energy is locked into the coal. Millions of years ago, dead plant matter fell into swampy water and over the years, a thick layer of dead plants lay decaying at the bottom of the swamps. Over time, the surface and climate of the earth changed, and more water and dirt washed in, halting the decay process. The weight of the top layers of water and dirt packed down the lower layers of plant matter. Under heat and pressure, this plant matter underwent chemical and physical changes, pushing out oxygen and leaving rich hydrocarbon deposits. What once had been plants gradually turned into coal. Seams of coal—ranging in thickness from a fraction of an inch to hundreds of feet—may represent hundreds or thousands of years of plant growth. One seam, the seven-foot thick Pittsburgh seam, may represent 2,000 years of rapid plant growth. One acre of this seam contains about 14,000 tons of coal.
North American Indians used coal long before the first settlers arrived in the New World. Hopi Indians, who lived in what is now Arizona, used coal to bake the pottery they made from clay. European settlers discovered coal in North America during the first half of the 1600s. They used very little at first. Instead, they relied on water wheels and wood to power colonial industries. Coal became a powerhouse by the 1800s. People used coal to manufacture goods and to power steamships and railroad engines. By the American Civil War, people also used coal to make iron and steel. And by the end of the 1800s, people even used coal to make electricity. When America entered the 1900s, coal was the energy mainstay for the nation’s businesses and industries. Coal stayed America’s number one energy source until the demand for petroleum products pushed petroleum to the front. Automobiles needed gasoline. Trains switched from coal power to diesel fuel. Even homes that used to be heated by coal turned to oil or gas furnaces instead. Coal production reached its low point in the early 1950s. Since 1973, coal production has increased by more than 80 percent, reaching record highs in 1998. Today, coal supplies 32 percent of the nation’s total energy needs, mostly for electricity production.
There are two ways to remove coal from the ground surface and underground mining. Surface mining is used when a coal seam is relatively close to the surface, usually within 200 feet. The first step in surface mining is to remove and store the soil and rock covering the coal, called the overburden. Workers use a variety of equipment—draglines, power shovels, bulldozers, and front-end loaders—to expose the coal seam for mining.After surface mining, workers replace the overburden, grade it, cover it with topsoil, and fertilize and seed the area. This land reclamation is required by law and helps restore the biological balance of the area and prevent erosion. The land can then be used for croplands, wildlife habitats, recreation, or as sites for commercial development. Although only about a third of the nation’s coal can be extracted by surface mining, more than two-thirds of all coal in the U.S. is mined using this method today. Why? Surface mining is typically much less expensive than underground mining. With new technologies, productivity has more than tripled since 1973. feet. One method of underground mining is called room-and-pillar mining. With this method, much of the coal must be left behind to support the mine’s roofs and walls. Sometimes as much as half the coal is left behind in large column formations to keep the mine from collapsing.
After coal comes out of the ground, it typically goes on a conveyor belt to a preparation plant that is located at the mining site. The plant cleans and processes coal to remove dirt, rock, ash, sulfur, and other impurities, increasing the heating value of the coal. After the coal is mined and processed, it is ready to go to market. It is very important to consider transportation when comparing coal with other energy sources because sometimes transporting the coal can cost more than mining it.Underground pipelines can easily move petroleum and natural gas to market. But that’s not so for coal. Huge trains transport most coal (almost 60 percent) for at least part of its journey to market. It is cheaper to transport coal on river barges, but this option isn’t always available. Coal can also be moved by trucks and conveyors if the coal mine is close by. Ideally, coal-fired power plants are built near coal mines to minimize transportation costs.
When scientists estimate how much coal, petroleum, natural gas, or other energy sources there are in the United States, they use the term reserves. Reserves are deposits that can be harvested using today’s methods and technology. Experts estimate that the United States has about 262 billion tons of recoverable coal reserves. If we continue to use coal at the same rate as we do today, we will have enough coal to last about 270 years. This vast amount of coal makes the United States the world leader in known coal reserves. Where is all this coal located? Coal deposits can be found in 38 states. Montana has the most coal—about 75 billion mineable tons. Other top coal states in order of known reserves are Illinois, Wyoming, West Virginia, Kentucky, Pennsylvania, Ohio, Colorado, Texas, and New Mexico. Western coal generally contains less sulfur than eastern coal. Low sulfur coal produces fewer pollutants. The federal government is by far the largest owner of the nation’s coalbeds. In the West, the federal government owns 60 percent of the coal and indirectly controls another 20 percent. Coal companies must lease the land from the federal government in order to mine this coal.
Coal production is the amount of coal mined and taken to market. Where does mining take place in the United States? Although coal is mined in 33 states, more coal is mined in western states than in eastern states, a marked change from the past when most coal came from eastern underground mines. The West’s share was just five percent of total production in 1968. In 2008, the West provided 58 percent of total production, and states east of the Mississippi River provided 42 percent. Total U.S. production of coal was 1.15 billion tons in 2008, more than a 60 percent increase since 1973. The leading coal producing states are Wyoming, West Virginia, Kentucky, Pennsylvania, and Montana. These five states produce 71 percent of the coal in the U.S. Some coal produced in the United States is exported to other countries. In 2008, foreign countries bought almost seven percent of all the coal produced in the U.S. The biggest foreign markets for U.S. coal are Canada, Brazil, and some European countries.
The main use of coal in the United States is to generate electricity. In 2008, 92.9 percent of all the coal in the United States was used for electricity production. Coal generates almost half of the electricity used in the U.S. Other energy sources used to generate electricity include uranium (nuclear power), hydropower, natural gas, biomass, and wind. Another major use of coal is in iron and steelmaking. The iron industry uses coke ovens to melt iron ore. Coke, an almost pure carbon residue of coal, is used as a fuel in smelting metals. The United States has the finest coking coals in the world. These coals are shipped around the world for use in coke ovens. Coal is also used by other industries. The paper, brick, limestone, and cement industries all use coal to make products. Coal is no longer a major energy source for heating American homes or other buildings. Less than half of one percent of the coal produced in the U.S. today is used for heating. Coal furnaces, which were popular years ago, have largely been replaced by oil or gas furnaces or by electric heat pumps.
ventually, as the effects of pollution became more noticeable, Americans decided it was time to balance the needs of industry and the environment. Over a century ago, concern for the environment was not at the forefront of public attention. For years, smokestacks from electrical and industrial plants emitted pollutants into the air. Coal mining left some land areas barren and destroyed. Automobiles, coming on strong after World War II, contributed noxious gases to the air. The Clean Air Act and the Clean Water Act require industries to reduce pollutants released into the air and the water. Laws also require companies to reclaim the land damaged by surface mining. Progress has been made toward cleaning and preserving the environment. The coal industry’s largest environmental challenge today is removing organic sulfur, a substance that is chemically bound to coal. All fossil fuels, such as coal, petroleum, and natural gas, contain sulfur. When these fuels are burned, the organic sulfur is released and combines with oxygen to form sulfur dioxide. Sulfur dioxide is an invisible gas that has been shown to have adverse effects on air quality. The coal industry is working to solve this problem. One method uses devices called scrubbers to remove the sulfur in coal smoke. Scrubbers are installed at coal-fired electric and industrial plants where a water and limestone mixture reacts with sulfur dioxide to form sludge. Scrubbers eliminate up to 98 percent of the sulfur dioxide. Utilities that burn coal spend millions of dollars to install these scrubbers.The coal industry has made significant improvements in reducing sulfur emissions. Since 1989, coal-fired plants in the United States have lowered sulfur dioxide emissions per ton by a fourth and have increased efficiency significantly. Coal plants also recycle millions of tons of fly ash (a coal byproduct) into useful products such as road building materials, cement additives and, in some cases, pellets to be used in rebuilding oyster beds. Carbon dioxide is released when coal is burned, just as it is released from the human body during respiration. Carbon dioxide combines with other gases, such as those emitted from automobiles, to form a shield that allows the sun’s light through the atmosphere, but doesn’t let the heat that is produced out of the atmosphere. This phenomenon is called the greenhouse effect. Without this greenhouse effect, the earth would be too cold to support life. There is concern that human activities are causing major changes in greenhouse gas levels in the earth’s atmosphere that are responsible for a change in the earth’s climate. Most scientists believe the earth is already experiencing a warming trend due to the greenhouse effect. Long-term studies by scientists in many countries are being conducted to determine the effect of changing greenhouse gas levels in the atmosphere. Scientists are also researching new technologies to help mitigate changes to the global climate.
Áèáëèîòåêà