SIC 1222 Bituminous Coal Underground Mining
SIC 1222
This classification includes establishments primarily engaged in producing bituminous coal in underground mines or in developing bituminous coal underground mines. This industry includes underground mining by owners or lessees or by establishments that have complete responsibility for operating bituminous coal underground mines for others on a contract or fee basis. Bituminous coal preparation plants performing such activities as cleaning, crushing, screening, or sizing are included if operated in conjunction with a mine. Independent bituminous coal preparation plants are classified in SIC 1221: Bituminous Coal and Lignite Surface Mining.
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Bituminous Coal Underground Mining
In 2003 there were 580 underground coal mines in the United States, which produced 352.7 million metric short tons of coal. Of total U.S. coal mines—underground and surface—48 percent were underground mines, which contributed 34 percent of all coal. West Virginia leads the nation in underground coal mining with 155 underground mines that produced 86.7 million metric short tons in 2003. Other leading underground coaling states include Kentucky (155 mines, 69.2 million short tons), Pennsylvania (58 underground mines, 52.2 million short tons), and Virginia (79 mines, 21.2 million short tons).
Despite its large size and its importance to energy and industrial markets, the U.S. underground coal mining industry is in some fundamental ways a troubled one. These difficulties first manifested themselves in the late 1960s and have continued unabated into the 2000s. A primary threat to industry participants has been the rapid proliferation of relatively efficient surface mines. Other detriments include increasing environmental constraints, labor problems, stagnant growth, and foreign competition.
In 1998 there were about 860 underground coal mines in operation. By 2001 that number had declined to 719 underground mines. Underground mines were more prevalent in the East, accounting for 64 percent of production. The majority of these mines were located in the Appalachian region. Surface coal mines were located primarily in the West, with the largest surface mines in the world found in the Powder River Basin, located in Montana and Wyoming. (See SIC 1221: Bituminous Coal Surface Mining).
Steam coal, which represents the large majority of industry output, is most often used to power electric utilities. General industry, such as glass making and cement production, accounts for the next large portion of coal consumption. Metallurgical coal, or coking coal, is used for iron and steel production. Although they are classified as part of the same industry, these three segments differ in their reserve base, production facilities, distribution channels, and marketing requirements.
Besides regional distinctions and differences in mining techniques, underground mines differ in the quality and type of bituminous coal they produce. Eastern underground coal, for instance, is more likely to exhibit coking properties. Coal mined from underground operations in the Northeast typically has a high energy content and contains a widely varying amount of sulfur, a pollutant that is believed to be a major source of acid rain. Eastern Appalachian coal is most likely to have a very high sulfur content, while central Appalachian coal is comparatively low in sulfur. Much of the underground coal mined in the Midwest, such as Illinois Basin coal, is also high in sulfur.
Because it has a higher energy content and costs much more to produce, coal extracted from underground mines is more expensive than surface-mined coal. Appalachian coal, for instance, was priced at $28.24 per ton in 1995. In contrast, western surface mined coal was selling at $9.63 per ton. High transportation costs associated with western-mined coal tend to reduce this great disparity though.
Companies engaged in this industry extract coal that lies 200 to 1,000 feet below the earth's surface, though some mines are as deep as 2,000 feet. Underground mines consist of a series of parallel and interconnecting tunnels from which the coal is cut and removed with special machinery. The process is complex and sometimes dangerous. The mine must be adequately ventilated to protect miners from dust and explosive methane gas that is released by the coal. In addition, careful ground control must be practiced to prevent the roof of the mine from collapsing on workers and equipment.
Three types of underground operations are distinguished by the method used to access the coal mine. Drift mines are characterized by the use of a level tunnel leading into the mine, while slope mines have an inclined tunnel, and shaft mines utilize a vertical tunnel. The primary methods of extracting coal from all of these mines are room-and-pillar, long-wall, and shortwall.
Room-and-pillar mining is often the least efficient method. It often allows recovery of only about 50 percent of the coal, although there are occasions when this methodology can achieve a much greater recovery percentage. Long-wall and shortwall mining, in comparison, extract up to 80 percent of the usable coal. In a room-and-pillar operation, coal is mined in a series of rooms cut into the coalbed. Pillars of unmined coal are left intact and serve to support the mine roof, as miners advance through the coal seam. Sometimes the coal in the pillars can be extracted later in the "retreat" phase.
The two basic types of room-and-pillar mining are conventional and continuous. Conventional mining consists of a series of operations that involves cutting and breaking up the coalbed, blasting the bed, and then removing the shattered coal. Continuous mining, on the other hand, uses a machine that digs and loads coal in one operation, without blasting. The majority of room-and-pillar coal was extracted using continuous mining in the 1990s.
Long-wall mines use huge machines with cutting heads. The heads are pulled back and forth across a block of coal up to about 600 feet long. Coal is sheared and plowed into slices that are removed by a conveyor. Movable roof supports allow mined-out areas to cave in behind the advancing machine. In the mid-1990s, long-wall systems accounted for about half of all coal mined underground. Shortwall mining is similar to long-wall operations, but the continuous mining machine shears smaller blocks of coal, generally less than 150 feet long.
Bituminous underground coal was created during a 250- to 400-million-year process in which the ocean covered and compressed organic deposits. Low-grade coal material that eventually developed below the ocean floor was further compacted into higher grade bituminous coal. More extreme pressure, resulting from the folding of the earth's surface into great mountain ranges, such as the Appalachians, produced the highest grade coal. This high-grade coal is most likely to be found in the United States in underground mines along the eastern seaboard.
The first coal mined from the famous Appalachian bituminous coal field, which is more than 90 miles long and covers 63,000 square miles, occurred in the mid-1700s. Most of this coal, though, was simply dug from exposed coal seams on the earth's surface. During the 1800s, after the easily removable surface coal had diminished, underground mining became the industry standard. By the early 1830s in fact, underground mines were operating in many parts of Appalachia, as well as in several areas along the Mississippi River. In 1840 the U.S. coal industry mined its first 1 million tons.
As the coal industry gained strength in the 1850s and 1860s, the federal government began to play an increasingly important role in its development. Concerned about the loss of valuable federal coal reserves...
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