Production of alumina from aluminum hydroxide

Claim 1

A process for producing anhydrous alumina from moist aluminum hydroxide, comprising the steps of: a. heating dewatered and partially dehydrated aluminum hydroxide particles to a temperature of 600* to 1,200* C. and converting same to anhydrous alumina in a fluidized bed by introducing a fluidizing gas at a temperature of at least 300* C. into said fluidized bed above the bottom thereof and a combustionsustaining fluidizing gas into said bed through the bottom thereof; b. removing from above said fluidized bed a mixture of solids and hot exhaust gas and separating the hot exhaust gas from said solids; c. recirculating at least part of the solids separated in step (b) to the bed of step (a); d. dewatering and partially dehydrating moist aluminum hydroxide at least in part by subjecting the same to direct contact with at least part of the hot exhaust gas separated in step (b) while suspending the moist aluminum hydroxide in said hot exhaust gas, and recovering dewatered and partially dehydrated aluminum hydroxide therefrom; e. feeding the dewatered and partially dehydrated aluminum hydroxide from step (d) to the fluidized bed in step (a); f. recovering anhydrous alumina from said fluidized bed at a temperature of 600 to 1,200* C.; g. cooling the anhydrous alumina recovered in step (f) by fluidizing same with a first portion of cooling air and abstracting heat from the anhydrous alumina with a second portion of cooling air in indirect heat exchange with the hot anhydrous alumina, thereby heating said first and said second portions of said cooling air; h. feeding said first portion of the air heated in step (g) to said fluidized bed in step (a) at a location above said bottom as secondary air, and feeding said second portion of said air heated in step (g) to said bed through said bottom as a fluidizing gas, said location having a height above said bottom between 0.3 and 1.5 times the pressure drop across the fluidized bed in terms of millimeters of a water-column measure of said pressure drop, the volumetric ratio of said second portion to said first portion ranging between 1:2 to 4:1; and i. introducing a combustible fuel into said fluidized bed between said grate and said location to further heat said bed.