Pages: 9 (2090 mots) Publié le: 31 janvier 2011
1. What Is Coal?
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 yearsago. All living plants store energy from the sun through a process known as photosynthesis. After the plants die, this energy is released as the plants decay. Under conditions favorable to coal formation, however, the decay process is interrupted, preventing the further release of the stored solar energy.
Millions of years ago, dead plant matter fell into the swampy water and over the years, athick 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 richhydrocarbon 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 even thousands of years of plant growth. One important coal 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, enoughto supply the electric power needs of 4,500 American homes for one year.
2. History of Coal in America
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 verylittle coal at first. Instead, they relied on water wheels and burning 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 the1900s, 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 theearly 1950s. Since then, coal production has steadily increased, reaching record highs again. Today coal supplies 22 percent of the nation's energy needs. Its major use today is for electricity production.
3. Mining, Processing, and Transporting Coal
Coal Mining
There are two ways to remove coal from the ground: surface mining and underground mining.
Surface mining is used when a coal seam isrelatively 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 heavy 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 withtopsoil, and fertilize and seed the area. These steps help 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 32 percent of the nation's coal can be extracted by surface mining, some 63 percent of all U.S. coal is mined using this method today. Why? Because...
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