Basic oxygen furnace
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A basic oxygen furnace, also known as an LD converter, is the place within an integrated steel mill where molten iron from the blast furnace is changed into liquid steel. LD is short for Linz-Donawitz, the names of the two towns in Austria, near the Voest-Alpine steelworks where the process was developed.[1] The process is known as basic due to the pH of the refractories - calcium oxide and magnesium oxide - that line the vessel. The vast majority of steel manufactured in the world is produced using the basic oxygen furnace. Modern furnaces will take a charge of iron of up to 350 tons and convert it into steel in less than 40 minutes.
High purity oxygen is blown into the furnace or BOS vessel through a vertically oriented water-cooled lance.[2] This oxidizes carbon and the other unwanted elements in the hot metal. Carbon is oxidised to carbon monoxide gas, which passes from the converter to a cleaning plant. After cleaning, it can be re-used as a fuel gas. The rest of the elements in the metal are converted to acidic oxides. They combine with the lime and other fluxes that are added during the blow - mainly to neutralise the acidic oxides and prevent excessive wear of the lining. This produces a slag that floats on the surface of the metal.
The steel is tapped from the furnace when it is at the correct temperature and composition. The furnace is tilted and the molten metal is run out via the taphole into a ladle. Once the steel has been removed, the furnace is turned upside down and the slag that is left inside runs into another ladle. The solidified slag can be used in the production of cement and as an aggregate in road building.
The first company in the U.S. to use this type of furnace was the McLouth Steel (Detroit Steel Company) out of Trenton, MI.
[edit] References
McGannon, Harold E. editor (1971). The Making, Shaping and Treating of Steel: Ninth Edition. Pittsburgh, Pennsylvania: United States Steel Corporation.
