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Energy efficiency prize for alumina production

By Gerald Ondrey |

At the Hannover Messe 2010, Alumina do Norte do Brasil S.A. (Alunorte; Barcarena, Brazil; www.alunorte.net) and Outotec Oyj (Espoo, Finland; www.outotec.com) received the X Prize (special recognition) for energy efficiency in alumina production. The award, part of the German Energy Agencys (dena; Berlin, Germany; www.dena.de) Initiative EnergieEffizienz, was bestowed to Alunorte for using an energy efficient calcination process developed by Outotec. To make alumina (Al2O3), bauxite is first digested in sodium hydroxide, which recovers aluminum as aluminum hydroxide. The Al(OH)3 is then calcined to form Al2O3. In the calcination process, Al(OH)3 is first mixed in two preheating stages with the hot waste gas from the calcining stage, predried and partially calcined. The mixture between gas and solid is carried out in a venturi dryer, followed downstream by a cyclone, where gas and solids are separated. The final calcination is performed at 970°C in a circulating fluidized-bed (CFB) reactor. The hot alumina is discharged from the CFB and cooled in a two-stage, fluidized-bed cooler by preheating the combustion air. Using simulations, Outotec developed a procedure that improves the efficiency of cyclone separation, which considerably…
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