Coal Age

AUG 2012

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1990-1999 based on programmable logic controllers allowed the drives to communicate with each other. This prevented excess sag or the drives from fighting against each oth- er and tearing the belt apart. As productivity climbed the number of faces declined. The U.S. longwall pop- ulation dropped to 90 in 1992, 80 in 1994, 72 in 1995, and 65 in 1997. Even though the population drop by more than 35%, production skyrocketed. Eimco model 2810 continuous miner is designed for mid-seam mining. *COAL, January 1990 Labeled by some as the most produc- tive mine in the country, Campbells Creek Coal Co., near Bell, W.Va., a contractor for Arch Minerals' Catenary Coal, is regularly mining 3,200 tons per shift in 1991. The single section mine cuts coal with a Joy 12CM12 continuous miner and uses two Joy 10SC shuttle cars and a battery-pow- ered Simmons-Rand Unahauler. In 1990, continuous miners represent 55% of underground production and longwalls are producing about 37%. Continuous miners accounted for 60% of under- ground production in the mid-1980s while longwalls repre- sented only 31%. While the num- ber of longwalls dropped below 100 for the first time in 1990, long- wall productivity was at an all- time high of 2,372 clean tons per unit-shift. Productivity ex- pressed in tons per man-shift also increased to 174. *COAL, December 1992 166 www.coalage.com An article detailing the Twentymile Coal Co. in Colorado (December 1992) that was operating some of the longest longwall panels in the country at the time, explained how the mine was using tripper drive technology to power the conveyor belts. At the time, a 10,000-ft longwall panel was considered long. Theoretically a tripper system, one where the conveyor trips coal back onto itself, could be de-signed for any length. Installing another tripper drive anywhere along the conveyor reduced the effec- tive tension and recently devel- oped load-sharing systems 100th Anniversary Special Issue Longwall mining tonnage first over- took continuous mining tonnage marginally in 1994, and since then, has steadily moved ahead. In 1996, total U.S. longwall production reached 196 million tons and continued to pull ahead of con- tinuous mining production, which totaled 178 million tons. In 1996, total underground production of 410 million tons was made up of longwall (48%), con- tinuous miners (43%) and other (9%). Surface Mining Several advancements are made in the field of drilling and blasting during the 1990s. Drill manufacturers have automat- ed several aspects of blasthole drilling and improved the operator interface. Several models feature new automated controls integrated with diagnostics and a hydro- static propel system. Surface mines are using bulk-loaded emulsion and emulsion-Anfo blends. An emulsion explosive can be made extreme- ly fluid and pumped long distances for fill- ing large diameter blasthole. Since they have a high velocity of detonation and high density, they have high detonation pressures. A dozen manufacturers and *COAL, July 1993 August 2012

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