SIC 1221 Bituminous Coal and Lignite Surface Mining
SIC 1221
This classification covers establishments primarily engaged in producing bituminous coal or lignite at surface mines or in developing bituminous coal or lignite surface mines. This industry includes auger mining, strip mining, culm bank mining, and other surface mining, by owners or lessees or by establishments that have complete responsibility for operating bituminous coal and lignite surface mines for others on a contract or fee basis. Bituminous coal and lignite preparation plants performing such activities as cleaning, crushing, screening, or sizing are included if operated in conjunction with a mine site, or if operated independently of any type of mine.
212111
Bituminous Coal and Lignite Surface Mining
In 2003 there were 714 surface coal mines in the United States, which produced 717.8 million short tons of coal. Surface mines accounted for 62 percent of all the nation's coal mines and 66 percent of all coal produced. Wyoming, the country's dominant surface mining state, has 18 surface mines that produced 376.2 million short tons of coal in 2003. This represented 49 percent of all surface-mined coal and 33 percent of all coal mined in the United States. The 12 mines within Campbell County in Wyoming accounted for 333.8 million short tons of the state's coal production.
During 2004 U.S. coal production totaled 1.11 million short tons, up 3.7 percent from 1.07 million short tons in 2003. In 2004 coal was used to generate 51 percent of U.S. electric power.
Surface mining faces many of the same issues as underground coal mining, including regulatory restrictions, environmental concerns, and declining prices. Surface mines also must address reclamation issues pertaining to abandoned and depleted mines.
According to the Energy Information Administration, some 1,750 mines operated in 25 states in 1998. Surface mining was the exclusive mining technique used in 9 of those states. Mines range in size from small facilities that generate several thousand tons of coal per year to mammoth surface operations that extract 10 to 20 million tons per year. The surface and underground mining industry produced more than 1.1 billion tons of coal in 1998.
Surface mining usually is practiced on relatively flat ground; the coal is recovered from a depth of less than 200 feet. At mines where the coal is located on steep inclines, though, material may be excavated from open pits that can reach depths of several hundred feet.
To reach coal deposits, miners must first remove the overburden, or strata, that covers the coal bed. Between 1 and 30 cubic yards of strata must be excavated for each ton of coal recovered. Dragline excavators, power shovels, bulldozers, front-end loaders, scrapers, and other heavy pieces of equipment are used to move the strata and extract the coal.
The two common methods of surface mining are strip and auger. At strip mines, large drills bore holes in the strata. Explosives are placed in these cavities and detonated. Power shovels or draglines operating at surface level then move the broken strata, while power shovels below dig up the coal and load it into trucks. The strata and coal are removed in long strips. This is done so that the debris from the newest strip can be dumped into an adjacent strip, from which the coal already has been recovered.
Auger mining consists of boring a series of holes that are 2 to 5 feet in diameter and 300 or more feet deep. This parallel and horizontal pattern is carved into a seam of coal that already has been exposed by an outcropping or by strip mining methods. No blasting takes place, and the overburden is left intact. The coal simply is removed and loaded into waiting trucks. Auger mining frequently is used in open-pit mines, where the strata is too thick to economically remove it using strip methods.
Because surface mining is less expensive and more productive than traditional underground mining, new surface extraction technology has allowed this method to dominate U.S. coal production. Moreover, producers are able to remove an estimated 90 percent of the coal at surface mines, while underground mines permit only a 50 to 80 percent extraction rate, depending on the mining method used.
After it is processed, different types of coal are often blended to produce uniform grades of commercial material. Blending also may occur at the point of use. Coal preparation plants can produce anywhere from 200 to 20,000 tons of coal per day. From the preparation plant, 70 percent of the coal is delivered to users by rail. Barges and ships deliver an additional 20 percent of industry output. Some coal also is stored for future use.
Four grades of coal mined in the coal industry include lignite, subbituminous, bituminous, and anthracite. Each grade differs in moisture content, volatile matter, and fixed carbon content. Anthracite, the highest grade material, accounts for less than one-half of 1 percent of total output and is classified in its own industry (see SIC 1231: Anthracite Mining).
Bituminous coal, or soft coal, is the most common type of coal produced in the United States. It represents more than 70 percent of total industry output and accounts for approximately 50 percent of total U.S. reserves. The mineral is composed of 80 to 90 percent carbon and about 10 to 20 percent moisture. A ton of bituminous coal typically generates 19 to 30 million BTUs (British Thermal Units) and ignites at between 700 and 900 degrees Fahrenheit. Bituminous coal possesses a relatively low sulfur content, which causes it to burn more cleanly than some lower grades. Because of its properties, bituminous coal is the principal steam coal used for generating electricity. It also is the primary coking coal used in the steel-making process.
Bituminous coal can be further categorized as low-, medium-, and high-volatile coal, according to its moisture content and heating capacity. Low- and medium-volatility grade bituminous coal typically generates between 26 and 30 million BTUs per ton. High-volatile coal, in contrast, usually produces anywhere from 18 to 29 million BTUs per ton. For comparison, a ton of bituminous coal, assuming an average 22 million BTUs, produces about the same amount of energy as one cord of hardwood, 22,000 cubic feet of natural gas, or 160 gallons of fuel oil.
Subbituminous coal has a 75 to 85 percent carbon content. It produces 16 to 24 million BTUs per ton and is used primarily to generate electricity. In 1995 subbituminous coal represented 31.7 percent of industry output. Although its sulfur content is low relative to lignite, a high moisture content, along with other negative properties, makes it less desirable than higher coal grades for most applications.
Lignite, the lowest ranked coal, is a brownish-black mineral containing a moisture content of 30 to 40 percent. It produces about 9 to 17 million BTUs per ton and ignites at roughly 600 degrees Fahrenheit. Because it deteriorates rapidly in air, has a high sulfur content, and is liable to combust spontaneously, lignite mainly is used to generate electricity in power plants that are close to mines. In 1995 lignite accounted for 8.3 percent of industry production. Lignite also is subject to high royalties charged by the federal government.
In 1998, 83 percent of the coal produced in the United States, 912.1 million short tons, was consumed by utilities. Percentage-wise, this was down from 88 percent in 1995. Coal-fired facilities produced approximately 55 percent of the total electricity generated domestically.
The second largest coal customer was the general industry sector, which accounted for 76.5 short tons of coal in 1998. Industry uses for coal include production of materials such as calcium carbide, silicon carbide, refractory bricks, carbon and graphite electrodes, and various food and paper products. Coal also is used to produce gall and stone, primary metals, textiles, and plastics. One of the largest industrial uses of coal is cement production. In fact, 90 percent of U.S. cement plants use coal—at a rate of about 1 ton for each 3.5 tons of cement produced.
Iron and steel manufacturers are the third largest coal consumers. These industries use coal to produce coke—a primary ingredient in the smelting of iron. In 1995 approximately 27.6 million short tons of coal was used in the processing of iron and...
To continue reading
Request your trial