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| India Infoline Sector Reports | Thu, 20-Apr-2006 16:26:17 IST (GMT+5:30) | |
| Aluminium | ||
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Technology and manufacturing process There are six aluminum manufacturing processes. These are the Hall-Herault Process, the Alcoa Smelting Process, Toth Process, Direct Reduction Process, Carbo-Thermic Process and Sub Halide Process. In the Hall-Herault process aluminum is manufactured in three stages involving bauxite mining, alumina refining, aluminum smelting. Bauxite mining is the first stage in the manufacturing process. This is conducted in benches through a share and dumper combination, which feeds the material to the crusher, where bauxite is crushed for conversion into alumina. Approximately 25 ton of bauxite yields 1 ton of alumina. Plant design is influenced by bauxite composition. The key variables are alumina silica content and mineralogical form of occurrence. Alumina refining is the second stage in a vertically integrated aluminum plant. Bauxite is converted into alumina through Bayer Process, the most economical and popular process used in alumina refining. Under the Bayer Process mineral impurities such as iron oxide and silica are removed from bauxite to ensure higher yield of alumina. Smelting, the final stage in the manufacture of aluminum metal, is an energy intensive process, the energy consumption varying from about 16,000KWH to 18,000 KWH per ton. Aluminum is conventionally produced by electrolysis using the Herault Process where calcined alumina is dissolved in molten cryolite at a temperature of 900 degree C. The process also requires an uninterrupted supply of power. Aluminum production is directly proportional to the current flowing through the electrolysis cells. The electrolytic cells have cathodes and anodes while the electrolytic bath consists of aluminum fluoride and cryolite. The anode is made of calcined petroleum coke. Alcoa Smelting Process consists of chlorinating of alumina or bauxite in the presence of carbon to produce aluminum chloride and then electrolysis of molten aluminum chloride with the recovery of chlorine. With this process power consumption can be reduced by 30 %. The Toth Process consists of exchange relation between aluminum chloride and manganese. Bauxite mixed with carbon is chlorinated through fractional condensation and purification to form aluminum chloride. The aluminum chloride reacts with manganese to produce aluminum. Direct Reduction Process adopts the blast furnace route to reduce clay/bauxite with coke and produce 70 % aluminum and 30 % silicon alloy-Alusil. The main advantage of the process is the substitution of expensive electricity by cheaper thermal energy. Carbo-Thermic Process for the production of aluminum may either use bauxite or alumina. In the case of bauxite the material is reduced in an electrical arc furnace whereby fused alumina is produced and impurities are removed. The fused alumina is then reduced in another furnace in the presence of pure carbon where aluminum is produced. The process consumes lower energy as compared to the Hall and Herault Process. Sub Halide Process developed by Alcan consists of making the aluminum alloy by smelting a mixture of bauxite and carbon in an electric arc furnace and then treating the alloy with aluminum chloride vapor at high temperature. |
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