Steel is an alloy of iron, usually containing less than 1% carbon. The process of steel production occurs in several sequential steps. The basic oxygen furnace (BOF) and the electric arc furnace (EAF) are two types of technology in use today for steel making. Although these technologies use different input materials, the output from both furnace types is in the form of molten steel that is further processed into steel mill products. The BOF input materials include molten iron, scrap, and oxygen. In the EAF, the input materials are electricity and scrap. BOFs are typically used for high tonnage production of carbon steels, and EAFs are used to produce carbon steels, low-tonnage alloy, and specialty steels. During the manufacturing of steel using a BOF, coke making and iron making precede steel making; however these steps are not needed for steel making with an EAF. Coke, which acts as a fuel and carbon source, is produced by heating coal in the absence of oxygen at high temperatures in coke ovens. Pig iron is produced by heating the coke, iron ore, and limestone in a blast furnace. In the BOF, molten iron from the blast furnace is combined with flux and scrap steel, followed by the injection of high-purity oxygen. In an EAF process, the input material consist primarily of scrap steel, which is melted and refined by passing an electric current from electrodes through the scrap. The molten steel from either process is formed into ingots or slabs and rolled into finished products. Rolling operations may require reheating, rolling, cleaning, and coating the steel. The process of coke making, iron making, steel making, and subsequent forming and finishing operations is collectively referred to as fully integrated production. Figure 2.1 presents a detailed flowsheet of the iron and steel manufacturing process. This chapter describes the various processes involved in steel making, the sources and types of wastes generated from these manufacturing processes, and the technical advancement necessary for pollution prevention and economic operation of the iron and steel plant.17-20
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