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Increases in labor and energy efficiencies from the 1st Cement Industry Technical Conference to the 50th Cement Industry Technical Conference are impressive. Production has expanded from 577 less efficient kilns producing 56 million metric tons of cement to 178 kilns producing 91 million metric tons of cement. The average energy used has declined from 9.70 MBTU (million British Thermal Units) per ton of clinker to 4.375 MBTU per equivalent [metric] ton with the lowest reported energy values dropping from 3.5 MBTU per ton of clinker to 2.74 MBTU per equivalent [metric] ton. Productivity has increased from 0.714 metric tons per employee hour to 2.97 metric tons per employee hour. The factors behind this change, and prospects for further efficiencies, are examined in this paper. IntroductionThe North American cement industry has experienced tremendous growth since the first cement industry technical conference in 1959. Fifty years of growth were accompanied by fifty years of advancement in every facet of plant technology. The chemistry behind cement manufacture remains unchanged but the energy efficiency and labor productivity of the plants of 2008 are dramatically different than those earlier facilities.Since its inception in 1916, the Portland Cement Association has surveyed its member companies for labor and energy inputs into the cement manufacturing process. These surveys, in conjunction with information from the U.S. Geological Survey and its predecessor, the U.S. Bureau of Mines, provide an historic overview of increases in labor and energy efficiencies. Issues impacting the accuracy of reporting are addressed in van Oss . Cement ManufacturingThis description is taken from the section on portland cement in the Air Pollution Engineering Manual (Greer, Dougherty, and Sweeney 2000).Portland Cement is a fine, gray powder that consists of a mixture of the hydraulic cement minerals, tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite, to which one or more forms of calcium sulfate have been added. Portland cement accounts for about 93 percent of the cement production in the United States. Blended cements are about 2 percent and masonry cement about 5 percent of domestic cement production. These cementitious materials also are produced in portland cement plants and contain portland cement as an ingredient. Raw materials are selected, crushed, ground, and proportioned so that the resulting mixture has the desired fineness and chemical composition for delivery to the pyroprocessing system. The major chemical constituents of portland cement are calcium, silicon, aluminum, iron, and oxygen. Minor constituents, generally in a total amount of less than 5 percent by weight of the mixture, include magnesium, sulfur, sodium, and potassium. And since the raw materials for portland cement come from the earth's crust, a wide variety of trace elements can be found in the cement, although these generally total less than 1 percent by weight of the mixture.There are wet-process and dry-proc...
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