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ArticleName Improved efficiency of autoclaves digesting for processing of hard bauxites
ArticleAuthor Domanskiy I. V., Davydov I. V., Borovinskiy V. P., Malofeev M. N., Morozov A. A.

OJSC RUSAL All-Russian Aluminium-Magnesium Institute (RUSAL VAMI), Saint Petersburg, Russia:

I. V. Domanskiy, Senior Researcher
I. V. Davydov, Executive Officer of Engineering Department, e-mail:
V. P. Borovinskiy, Leading Researcher
M. N. Malofeev, Researcher
A. A. Morozov, Engineer


In the stat-of-the-art process, the flows of Bayer alumina technology production of the digestion process for hardly processed diaspore and diaspore-boehmite bauxites is conducted in the multi-shell autoclave testings under the temperature of 230÷270 оС. The minimization of the energy in this power intensive process is achieved by the variation of pressure, using step by step orificing of the heated slurry and utilization of the exit-juice steam, which is formed after evaporation under reduced pressure for heating of the initial slurry at the train input. As well known, the elementary orificing appliances are the openings, made at the ends of the cross-flow pipes. These pipes connect each autoclave of the train with the corresponding flash tank, or orifices, or nozzles with appropriate diameter. The methods of the correct design for different orificing appliances allow to avoid the slurry boiling directly in the cross-flow piping and excluding the contamination of the exit -juice steam by the drops of slurry. For design of the orifices diameters it should be known the flow rate for steam-liquid mixture, the hydrodynamics of the flow, considerably different from pure liquors. At the first stage of this study there was considered the flow of the gas-liquid system (water-air) from the tube with orifice. The experiment demonstrated that the empirical values of the flow rate are located between the values, which are provided by following methods: first considers the complete phase mixing and second considers the complete phase separation in the zone of the mixture outflow. In this paper there is suggested the incomplete phase separation when only part k of liquid phase is mixed with the gas. The formula for k calculation is suggested with benchmarking of trials and theoretical values.

keywords Alumina, digestion, bauxites, slurry, autoclave train, orifice, nozzle, rate, gas-liquid system, dispersion, evaporation, Bayer method, exit-juice steam

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