Calcium sulphate hemihydrate mfr. by heating gypsum - using heat in prod. to preheat gypsum by heat-exchange

摘要

Granular or powdered material is heat-treated at a temp. above its temp. of formation. Liq. is added to the solid to form a pulp, which is fed through a heat-exchanger for preheating by a counter current of hot pulp which has already been heat treated. After heat treatment, the solid is sepd. from the liq. Two counter current preheaters may be used, the first employing the hot, sepd. liq., and the second the hot, treated pulp before the latter is fed to a separator. Heat exchangers are pref. employed using two sets of austenitic steel tubes sepd. by an Al alloy which transfers heat from the hot pulp or liq. to the fresh, cold pulp. Pref. material being treated is CaSO4, 2H2O, mixed with water and heated to 120 degrees C., the heat then being used for preheating the fresh pulp; and the solid obtd. is CaSO4, 1/2H2O.