Abstract: A method and apparatus for calcining an aluminum hydroxide source to an aluminum oxide in which the amount of the .alpha.-modification can be controlled from very low to very high values. In accordance with the present invention, the calcination of the source material takes place in two stages, in the first of which the material is preheated with air and then passed to a fluidized bed calciner after which it is delivered to a holding cyclone. In the second stage, the previously calcined material which may contain up to about 80% of the .alpha.-modification is calcined further in a rotary tubular kiln which is followed downsteam by a cooler.

Abstract: A self-adjusting powder distributor--which is particularly intended for use with alumina calcination apparatus--comprises a casing with a permeable partition, a plurality of outlets, and means for introducing preheated hydrate above the partition and fluidizing air therebelow. The fluidized hydrate withdraws through outlets of the casing for further treatment or partly as final product. The casing is provided with means by which the amounts and mutual ratios of the withdrawing material can be adjusted according to preselected values by altering the cross-sectional flow area or the level of the outlets.

Abstract: A self-adjusting powder distributor--which is particularly intended for use with alumina calcination apparatus--comprises a casing with a permeable partition, a plurality of outlets, and means for introducing preheated hydrate above the partition and fluidizing air therebelow. The fluidized hydrate withdraws through outlets of the casing for further treatment or partly as final product. The casing is provided with means by which the amounts and mutual ratios of the withdrawing material can be adjusted according to preselected values by altering the cross-sectional flow area or the level of the outlets.