Dry dehydration of gypsum - using steam injection so prod. consists predominantly of alpha:calcium sulphate hemi:hydrate with very little of the beta:hemi:hydrate

摘要

Gypsum, or CaSO4.2H2O, is heated to remove water of crystallisation; and during this dehydration process, the partial steam pressure is increased. The pref. appts. consists of a reactor into which steam can be generated, esp. at the start of dehydration. The reactor has a chimney in which the continuous removal of steam is retarded by a braking device. The braking device pref. consists of a helical stirrer, the cavities of which are filled with balls 20-100 mm. in dia. and made of a synthetic material which resists a chimney temp. of max. 160 deg.C. The prod. is the hemihydrate CaSO4,1/2H2O contg. a very high proportion of alpha-CaSO4, 1/2H2O, and thus providing very high strength when the prod. is mixed with water and allowed to set.