Sponsored by: LMD Aluminum Committee
Program Organizer: C.G. Hendriks, Kaiser Aluminum and Chemical Corp.,9131 Interline Drive, Baton Rouge, LA 70809
Wednesday, PM Room: A6
February 7, 1996 Location: Anaheim Convention Center
Session Chairman: J.L. Anjier, Kaiser Aluminum and Chemical Corp., Box 337, Gramercy, LA 70052
MORE COMPLETE DESILICATION OF ALUMINATE SOLUTION IS THE KEY-FACTOR TO RADICAL IMPROVEMENT OF ALUMINA REFINING: Dr. Victor Rayzman, 7329-D Alicante Rd., Carlsbad, CA 92009
In the nepheline process for alumina production, alumina is precipitated from the liquor by carbonation. This also co-precipitates all the dissolved silica which, if allowed to remain at a high level, unacceptably contaminates the product. This is controlled by desilicating the liquor prior to precipitation to a level in which the Al2O3:SiO2 ratio is 1000-1200:1. In the Bayer process this ratio is typically 300-350:1, as most of the silica in solution passes through precipitation without co-precipitating with the alumina. This residual silica has serious effects on the process, leading to the formation of DSP which encrusts heat exchange surfaces and increases the viscosity of the liquor thus reducing settling rates. There are a serious reasons to suppose that the rise in the rate of aluminum hydroxide precipitation and, consequently, Al2O3 yield are limited due to excessive SiO2 concentration. This supposition is well-founded by thermodynamic calculations. Some processes for the more complete desilication of aluminate solution are described.
WORLDWIDE BAUXITE AND ALUMINA PRODUCTION CAPACITY-1996: Errol D. Sehnke, U.S. Bureau of Mines, 810 7th. st., NW, Washington DC 20241-0002
A comprehensive review indicates that total worldwide "in place" capacity for the production of bauxite and bauxite-alternative ores currently is approximately 133 million metric tons per year. This includes the annual capacity to produce 123 million metric tons of metallurgical grade bauxite, 7 million metric tons of bauxite used for non-metal applications, and 3 million metric tons of alumina equivalent non-bauxitic materials (alunite and nepheline syonite). Current total world alumina production capacity amounts to about 51 million metric tons per year. This includes the annual capacity to produce approximately 48 million metric tons per year of smelter-grade alumina for the production of primary aluminum metal and about 3 million metric tons for non-metal specialty applications.
OPTIMIZATION OF MULTISTAGE PLANT AT C.V.G. BAUXILUM: Karel Fort, Ph.D., KF Engineering Services, P. O. Box 2111, 8604 Volketswil, Switzerland; Saul Escalonia, Alberto Parra, Paolo Murgia, C.V.G. Bauxilum, Cuidad Guiana, Venezuela; Jose Angel Sorrentino, Universidad Central de Venezuela, Caracas, Venezuela
The three thermal areas, Digestion, HID and evaporation are at BAUXILUM designed as Multi Stage Flash Units. Whereas the digestion Flash Unit has been operating from the begining with the expected hydraulic performance and is producing process condensate of excellent quality, the HID and Evaporation Units had to be optimized since notorious high levels in the flash vessels and high entrainment of the process condensate caused operational problems. A pilot plant consisting of two typical flash modules was built and operated as a side stream to the Evaporation Area at different temperature levels. Detailed measurements of the two-phase flow in the flash device, its analysis and comparison with models provided a sound basis for later development of modifications. The capacity of the Evaporation Unit increased by 25% after the modification whereas the process condensate quality improved by a factor of 10.
ALUMINA CALCINATION WITH THE ADVANCED CIRCULATING FLUID BED TECHNOLOGY: A DESIGN WITH INCREASED EFFICIENCY COMBINED WITH OPERATING FLEXIBILITY: Dr. Hans-Werner Schmidt, Vice President, Lurgi Metallurgie GmbH, Lurgi-Allee 5, 60295 Frankfurt am Main, Germany; Alan N. Silberberg, Senior Vice President, Lurgi Corporation, West 115 Century Road, Paramus, NJ 07652; Dipl. Eng. Werner Stockhausen, Lurgi Mettalurgie GmbHLurgi-Allee 5, 60295 Frankfurt am Main, Germany
The Circulating Fluid Bed (CFB) technology has now been applied for alumina calcination for a quarter of a century. The combined capacity of the 32 units installed is greater than 10 million metric tons per year. The paper highlights the consistency of the product quality which is based upon the operating experience of the last decade and improvements to the calcination system which in addition provide lower heat consumption. The principal modifications are incorporated in the preheating and cooling sections of the plant. These design modifications have also reduced capital cost. Overall the plant retains its proven features of high flexibility, unique temperature control, high availability, reliable performance, and low maintenance cost. The design is applicable to single train units up to a capacity of 3,000 MTPD (alumina).
4:00 pm BREAK
MEASUREMENT OF MUD LEVEL INTERFACES: A TOOL FOR OPTIMIZATION OF RED MUD WASHING AT C.V.G. BAUXILUM: Amilcar Pineda, C.V.G. Bauxilum, C.A. Gerencia de Desarrollo, Zona Industrial Matanzas, Edo. Bolivar, Venezuela; Guillermo Adrian, C.V.G. Bauxilum, Ciudad Guayana, Venezuela
For the expansion to 2.0 MTPY of the alumina plant, the area of clarification and red mud washing was rearranged from four parallel trains of 5 washing stages each to two trains of 7 stages each. The tanks being of the flat bottom type. As a result of this, the specific capacity of the tanks for handling mud was tripled, increasing the necessity for an on-line system that would allow better and faster control of mud handling. With this scope, it was developed and installed a new continuous mud level detector that gives the measurement of both mud level and turbid zone in the tanks. The development of the new instrument started from commercial instruments for density measurements and was completely re-engineered in order to obtain the maximum reliability. Actually twenty eight tanks are equipped with these instruments and are working satisfactorily.
THE MULTIPLE APPLICATIONS OF HYDROCYCLONES IN ALUMINA PRODUCTION: Nils Oeberg, Gerald Kelton, 1205 Chrysler Drive, Menlo Park, CA 94025-1178
Hydrocyclones are used in many alumina refineries to enhance efficiency. A partial list of applications includes bauxite grinding, bauxite refinement, sands separations from red muds, sand washing, hydrate classification and product size control, seed size control, hydrate thickening and deliquoring, agglomeration, preferential separation/reduction of oxalates, spent liquor solids recovery, cooling tower water clean-up, and lime slurry degritting. This paper reviews these applications including viable flowsheets and operating experience; and summarizes basic hydrocyclone selection including the main factors affecting performance.
INTEGRATED TECHNOLOGY FOR COMBUSTION OF ALUMINUM-CONTAINING COAL AND THE RECOVERY OF ALUMINA AND BYPRODUCTS FROM THE FORMED ASH: Dr. Victor Rayzman, 933 Regal Road, Encinitas, CA 92024
Coal is a major contributor to power and heat generation in the U.S..
Consumption is projected to steadily increase through 2010, with consequent
waste disposal problems. The alumina contained in this waste, 2 3 million tons
annually, if recovered, would satisfy the annual U.S. need. Numerous processes
have been proposed and investigated to recover alumina and other products from
coal ash. None of them have been developed completely because in previous
processes the conditions for both coal combustion and alumina recovery are
economically unattractive. An integrated and environmentally friendly coal
combustion ash-sintering sinter-leaching process, which completely uses the
thermal and chemical potential of the boiler wastes, bottom ash, fly ash, and
flue gases, is proposed. Alumina or alumina concentrate and material suitable
for construction use is produced. Key aspects of the proposed method have been
bench-scale and pilot-plant tested in the former USSR. The next stage of the
integrated process development would be a pilot-plant test of the entire cycle,
and design of a demonstration project.
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