Hot blast


Hot blast

Hot blast refers to the preheating of air blown into a blast furnace or other metallurgical process. This has the result of considerably reducing the fuel consumed in the process. This was invented and patented for iron furnaces by James Beaumont Neilson in 1828 at Wilsontown Ironworks in Scotland, but was later applied in other contexts, including late bloomeries.

The invention of the hot blast process was of particular importance to the iron industry in the United States. At the time the process was invented, good coking coal was not yet being mined in the U.S., and iron furnaces were compelled to use charcoal. This meant that any given iron furnace required vast tracts of forested land for charcoal production, and generally went out of blast when the nearby woods had been felled. Attempts to use anthracite as a fuel had all ended in failure, as the coal resisted ignition under cold blast conditions. In 1831, Dr. Frederick W. Gessenhainer filed for a U.S. patent on the use of hot blast and anthracite to smelt iron. He produced a small quantity of anthracite iron by this method at Valley Furnace near Pottsville in 1836, but due to breakdowns and his illness and death in 1838, he was not able to carry the process into large-scale production. Indendependently, George Crane and David Thomas, of the Yniscedwyn Works in Wales, conceived of the same idea, and Crane filed for a British patent in 1836. They began producing iron by the new process on February 5, 1837. Crane subsequently bought Gessenhainer's patent and patented additions to it, controlling the use of the process in both Britain and the U.S. While Crane remained in Wales, Thomas would move to the U.S. on behalf of the Lehigh Coal and Navigation Company and found the Lehigh Crane Iron Company to make use of the process.

For steel the hot blast temperature can be from 900 °C to 1300 °C (1600 °F to 2300 °F) depending on the stove design and condition. The temperatures they deal with may be 2000 °C to 2300 °C (3600 °F to 4200 °F). Oil, tar, natural gas, powdered coal and oxygen can also be injected into the furnace at tuyere level to combine with the coke to release additional energy which is necessary to increase productivity. [ [http://www.steel.org/AM/Template.cfm?Section=Home&template=/CM/HTMLDisplay.cfm&ContentID=5433 AISI] ]

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