GB745552A - Process of calcining finely divided solids - Google Patents

Abstract

<PICT:0745552/III/1> In the calcination of finely - divided solids of the type that evolve gas or vapour at a treament temperature lower than that of the final treatment, two successive beds of finely-divided solids are formed and maintained in a fluidized condition by upwardly passing gas streams successively through the beds and by maintaining the first of such beds at a temperature sufficient to evolve gas or vapour by insufficient to complete the treatment while maintaining the second bed at a higher temperature necessary for complete treatment but below the fusion point of the bed solids, transferring the partially treated solids from the first bed to which the solids for treatment are fed, to the second bed for completion of the treatment and maintaining the desired temperatures in the first and second beds by supplying regulated quantities of fuel directly into both the beds and combusting it there to liberate heat. The process is particularly applicable to calcination of hydrated aluminium oxide which gives up its water vapour at about 600 DEG C. but which requires a final calcination temperature of about 1100 DEG C. to yield anhydrous alumina. Another example is copperas, which gives up its water at low temperatures, but requires a higher temperature to decompose it into iron oxide and sulphur dioxide. As shown in the Figure, a reactor 35 is made up of four superposed fluidized beds 58, 55, 53 and 50 fluidized by gas entering through pipes 22; the upper bed 50 acts as a preheating bed and the lower bed 58 acts as a cooling zone. Solids are fed either to the preheating bed through a pipe 45 or by pipe 46 to the low temperature calcining bed 53 from which they flow through a downcomer to the lower fluidized bed where the final treatment is effected. Fuel is supplied to the low temperature and high temperature treatment beds through pipes 60, 61, and 62, 63 respectively and in addition a further fuel injection pipe 24 is provided for initial start up after which fuel pipe 24 is closed. A discharge 70 is provided from the lowermost cooling bed, for the final product and clean-out ports 71 to 74 are provided for each bed.