GB610439A - Improvements in and relating to the dehydration of particulate calcium sulphate - Google Patents

Abstract

<PICT:0610439/III/1> Particulate hydrated calcium sulphate is dehydrated by subjecting it to an elevated temperature while maintained as a bed in a "fluid" state by the upward passage therethrough of a stream of gas, the formation of an "entrained stream" being avoided. Air, nitrogen, flue gases or mixtures with or without steam may be used. Natural or artificial gypsum may be dehydrated to "calcined gypsum" or plaster of Paris of 4-9 per cent water content. The material may be dried, partially dehydrated or heated in a preliminary step. The process is preferably continuous and co-current though counter-current and batch processes may be used. The bed is preferably maintained in a "boiling" condition at 120-140 DEG C. Preheated gypsum introduced by a screw conveyer at 1 leaves vessel 2 by the overflow pipe 9. The vessel 2 has a jacket 3 heated by flue gas at about 600 DEG C. A flue gas/air/steam mixture at 500 DEG C. is introduced by a distributer 7 consisting of refractory brick fragments of size decreasing upwards at a rate sufficient to maintain the gypsum as a "boiling bed" at 130 DEG C. and leave by the pipe 8.