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 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, 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 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, enough to supply the electric power needs of 4,500 American homes for one year.
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 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 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 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 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 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 with topsoil, 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 surface mining is typically much cheaper than underground mining.
Underground mining is used when the coal seam is buried several hundred feet below the surface. In underground mining, workers and machinery go down a vertical "shaft" or a slanted tunnel called a "slope" to remove the coal. Mine shafts may sink as much as 1,000 feet deep.
One underground mining method 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.
A more efficient and safer underground mining method, called longwall mining, uses a specially shielded machine which allows a mined-out area to collapse in a controlled manner. This method is called "longwall" mining because huge blocks of coal up to several hundred feet wide can be removed.
Processing and Transporting Coal
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. A "prep" plant cleans and processes coal to remove dirt, rock, ash, sulfur, and other impurities. Removing the impurities increases the heating value of coal.
After the coal is mined and processed, it is ready to go to market. Transportation is a very important consideration in coal's competitiveness with other fuels 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 electric power plants are built near coal mines to minimize transportation costs.
4. Coal Reserves, Production and Use
Coal Reserves
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 coal deposits that can be mined using today's mining methods and technology. Experts estimate that the United States has about 265 billion tons of coal reserves. If we continue to use coal at the same rate as we do today, we will have enough coal to last 285 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 120 billion menial tons. Other top coal states in order of known reserves are: Illinois, Wyoming, Kentucky, West Virginia, Pennsylvania, Ohio, Colorado, Texas, and Indiana. Western coal generally contains less sulfur than eastern coal (which is good for the air when coal is burned), but not always.
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
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 27 states, more coal is mined in eastern states, especially coal that is taken from underground mines, than in western states. However, the West's share of total coal production has increased steadily since 1968 when it provided just five percent of U.S. production. Today the West provides 45 percent of the nation's total production.
Total U.S. production of coal reached one billion tons in 1990, an historic high. The leading coal producing states are Wyoming, Kentucky, West Virginia, Pennsylvania, and Texas.
Some coal produced in the United States is exported to other countries. Last year, foreign countries imported seven percent of all the coal produced in the U.S. The five biggest foreign markets for U.S. coal are Japan, Canada, Italy, Brazil, and Belgium.
How Coal Is Used
What do we use coal for? Electricity is the main use. Last year 88 percent of all the coal used in the United States was for electricity production. (Other energy sources used to generate electricity include nuclear power, hydropower, and natural gas.)
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 their products.
Contrary to what many people think, coal is no longer a major energy source for heating American homes or other buildings. Less than 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.
When coal became an important energy source for American industry 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 pollution 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. Eventually, as the effects of pollution became more and more noticeable, Americans decided it was time to balance the needs of industry and the environment.
Federal laws passed in the 1960s and 70s, namely the Clean Air Act and the Clean Water Act, required industries to reduce pollutants released into the air and the water. Laws also were passed that required coal companies to reclaim the land destroyed by strip mining. Since the passage of these laws, much progress has been made toward cleaning up the environment.
The coal industry's most troublesome problem 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 into the air where it combines with oxygen to form sulfur dioxide. Sulfur dioxide is an invisible gas that has been shown to have adverse- effects on the quality of air we breathe. It also contributes to acid rain, an environmental problem that many scientists think adversely affects wildlife (especially fish) and forests.
However, the coal industry is doing something to solve this problem. One method uses "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 a sludge. Scrubbers eliminate up to 98 percent of the sulfur dioxide, but they are very expensive to build.
The coal industry is also concerned about the carbon dioxide that is produced when coal is burned. Carbon from burning coal reacts with air to form carbon dioxide. When carbon dioxide and other gases, such as those emitted from automobiles, accumulate in the earth's atmosphere, they form a shield that allows the sun's light and heat in, but doesn't let it out. This condition is called the greenhouse effect.
Scientists and others are concerned about the greenhouse effect because it could cause a change in the earth's climate. Some say the earth is already experiencing a warming trend due to the greenhouse effect; others are not so sure yet. While warmer weather might be appreciated by some in northern climates, it could cause drought in some areas of the world (the American grain belt, for example) and the erosion of ocean coasts due to rising sea levels in all areas.
The coal industry is currently researching ways to lower carbon dioxide emissions. But a wholesale approach will be needed to stop the greenhouse effect. This approach must look not only at the burning of fossil fuels as a problem, but also at automobile emissions, the deforestation of the world's forests, and several other possible contributors.