The Physics
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Temperature of a Blast Furnace

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Dorin, Henry. Chemistry: The Study of Matter. Needham, Massachusetts: Prentice Hall, 1992: 674. "The heat evolved in this exothermic reaction raises the temperature at the bottom of the furnace to about 1900 °C…. The heat absorbed in this endothermic reaction lowers the temperature in the upper part of the furnace to about 1300 °C." 1900 °C
1300 °C
Kerrod, Robin. Macmillin Revised Encyclopedia of Science. New York: Macmillin Reference USA, 1997: 29. "At furnace temperatures of about 1800 °C (3300°F), iron is molten and trickles down to collect in the base of the furnace, or hearth." 1800 °C
Walsh, Gregory C. Cost Effective Blast Furnace Stove Control. Maryland: University of Maryland, 1996: 2. "The coke burns in this hot air blast, generating temperatures exceeding 2000 °C." > 2000 °C
Helmut Föll. History of Steel. University of Kiel, 2002. "The melting point of Iron is T (Fe) = 1535 °C." > 1535 °C
Blast Furnace. The Chemistry of Steelmaking., 2002. "Because the furnace temperature is in the region of 1500 °C, the metal is produced in a molten state and this runs down to the base of the furnace." 1500 °C

The purpose of a blast furnace is to chemically reduce and physically convert iron oxides into liquid iron called "hot metal". The blast furnace is a huge, steel stack lined with refractory brick, where iron ore, coke and limestone are dumped into the top, and preheated air is blown into the bottom. The raw materials require 6 to 8 hours to descend to the bottom of the furnace where they become the final product of liquid slag and liquid iron. At furnace temperatures of about 1800 °C, give or take 200 degrees, these liquid products are molten and trickle down to collect in the base of the furnace, or hearth, where they are extracted at regular intervals. The hot air that was blown into the bottom of the furnace ascends to the top in 6 to 8 seconds after going through numerous chemical reactions. Once a blast furnace is started it will runcontinuously for four to ten years with only short, periodic stops to perform planned maintenance.

Blast furnaces were first invented in the late 14th century and were improved most significantly by Henry Bessemer during the Industrial Revolution. Blast furnaces will continue to be a useful tool for smelting in the future because of the large quantities of metals it is able to extract over a long period of time.

John Chu -- 2002

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