Bituminous coal is the third type of coal. Though it is harder than lignite or subbituminous coal, bituminous coal is often referred to as soft coal. This is due to the high sulfur content. Because bituminous coal has such a high amount of sulfur present, electricity generators that choose to burn this type of coal must equip their plants with sophisticated pollution-control systems. These mechanisms are called scrubbers because they scrub the pollution from the air by binding reactive toxins with inert, calcium-based substances located in the air stacks of power plants. The best available technology allows scrubbers to remove 98 percent of all sulfur emissions and 99 percent of all particulate matter from smoke stacks. Bituminous coal is dark black in color and may have dull-black bands striated throughout. This type of coal is typically found in Appalachian Mountain regions, the Great Lakes, the Mississippi Valley, and north and central Texas.
The final classification of coal is anthracitic coal. This is the hardest type of coal, thus, many people call it hard coal. This hardness is derived from the compact nature of the coal, which is a result of extremely high temperatures and pressure during coal formation. This coal is preferred because it has the highest thermal value and lowest sulfur content. This means that anthracite generates the most energy per unit of heat produced during combustion, and releases the smallest amount of sulfur pollutants per unit of heat emitted. Anthracite appears to be dark, shiny, and black. It has moisture content of 4 percent, and, in 2000, a ton of anthracite sold for about $40. This type of coal is found most frequently in Pennsylvania and other areas east of the Mississippi River.
Each of the four types if coal must be removed from the Earth's surface layer. Most coal is located in seams, ranging from .98 in. (2.5 cm.) to 98.4 ft. (30 m.)
thick. These seams are relatively easy to locate, and, thus, most of the available supply in the United States is well-known. Therefore, industry and scientists can focus less time searching for new coal deposits and more time devising methods for remedying the effects of the associated pollution.
Coal is mined in two different ways: surface mining or subsurface mining. The kind of mining chosen depends on the surface conditions and the depth of the coal seam. Usually, mining companies pursue surface mining, also called strip mining, when the coal seam is located within 98.4 ft. (30 m.) of the surface. Through this process, the Earth's surface is scraped away and the coal is then removed using machinery. Approximately 60 percent of all the United States' coal supply is acquired through strip mining.
The most destructive type of surface mining is mountaintop removal. This occurs when dynamite is detonated and removes the surface material above the coal seam. Also, a dragline may be used to remove large portions of earth. This machine acts as a gigantic shovel. Debris from this removal process is then placed in nearby valleys and streams. Presently, 15 to 25 percent of all mountaintops in West Virginia have been subjected to this type of destruction.
Subsurface mining provides the United States with the other 40 percent of its coal supply. This method is used when the coal seam is located deep within the Earth's crust. Long networks of tunnels and shafts are dug underground along the coal seam. Miners then recover coal. This type of mining produces less landscape effects, however, compared to surface mining, the subsurface mining method is more expensive, less effective at removing all coal, and more dangerous to mine workers.
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