Rotary kiln calciner described

Refined calcined alumina is commonly used in combination with high purity limestone [1317-65-3] to produce high purity calcium aluminate cement (CAC). The manufacture, properties, and appHcations of CAC from bauxite limestone, as weU as high purity CAC, has been described (104). High purity CAC sinters readily in gas-fired rotary kiln calcinations at 1600 —1700 K. CAC reactions are considered practically complete when content of free CaO is less than 0.15% andloss on ignition is less than 0.5% at 1373 K. 

A computer model for the calculation of the temperature/tlme profile and the composition of the gas atmosphere in rotary kilns is described. The model is applied for scaling down the continuous commercial calcination of catalyst materials to batch calcination in laboratory rotary kilns as used in catalyst development work. The results of the model are compared with measurements carried out in the rotary kiln of the catalyst plant at Ghent, which produces y-alumina extrudates used as carrier for heterogeneous catalysts. The plug flow transport model assumed for the solids is confirmed by residence time distribution measurements. The measured temperature profiles are in agreement with the calculated profiles after adjustment of the kinetic rate constants. 

In dry generators, the carbide is reacted with a controlled excess of water to produce acetylene, steam and hydrated lime with 1 to 2 % of excess water. Part of the hydrated lime may be calcined to quicklime and recycled to the carbide furnace. The remainder, which acts as a purge for impurities, can be used in many of the applications described for hydrated lime (see also section 20.10). Few details of kilns used for the dehydration of carbide lime appear to have been published. Kampmann [31.4] mentions granulation and briquetting of the hydrate, presumably for feeding into a rotary kiln. Other techniques, such as fluidised bed calcining would also appear to be appropriate (see section 16.4.11). 

The scaling down of the calcination process for industrial catalyst manufacturing requires knowledge of both the processing characteristics of the commercial rotary kiln and, for each different catalyst material, the physical and chemical processes Caking place during Che calcination. In this paper the elements of the model will be described in more detail and the problems of its validation discussed. It should be realized that the model is still in the development phase. Therefore, the most important heat and mass transfer phenomena occurring in a rotary kiln must be described properly first. A description of the development of important catalytic properties such as surface chemistry, crystallinity, pore structure and metal dispersion is still beyond the scope of the present model. 

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