Patent ID: 7556791

Claim:
A process for manufacturing calcium sulfate anhydrite comprising the steps of: feeding a 10-70 wt. % gypsum feed slurry to a reactor system, the feed slurry comprising particles comprising calcium sulfate dihydrate and water; calcining the feed slurry in the reactor system, while at least 95% of the water of the slurry remains liquid, at conditions sufficient to form a calcined slurry, wherein the slurry is wet ground in the reactor system at a temperature above 400° F. and a pressure above 250 psia prior to cooling the slurry from its temperature in the reactor to below 400° F., and wherein the slurry is held in the reactor system at conditions for calcining the calcium sulfate dihydrate to convert 95 to 100% of the calcium sulfate dihydrate to calcium sulfate anhydrite.