VERFAHREN ZUR HERSTELLUNG VON ALPHA-CALCIUMSULFAT-HALBHYDRAT

摘要

A process for preparing alpha-calcium sulfate hemihydrate by pressureless heating of a suspension of calcium sulfate in the presence of a dehydration catalyst and subsequent filtration, washing and drying is carried out by a) the underflow of a hydrocyclone of a flue gas desulfurization plant is employed as the calcium sulfate dihydrate suspension; b) calcium chloride originating from the flue gas is employed as the dehydration catatyst; c) part of the mother filtrate rich in calcium chloride is re-circulated as dehydration catalyst and part of the mother filtrate rich in calcium chloride is dried in a spray-drier using a portion of the flue gas after the air pre-heating (LUVO); d) heating without pressure of the calcium sulfate dihydrate suspension is carried out using another portion of the flue gas after the air pre-heating (LUVO); e) the flue gas portions of the steps c) and d) are combined with the portion, if any, of the flue gas directly passed on after the air pre-heating (LUVO) and the combined flue gas portions are introduced into the flue gas desulfurization plant; and f) the hot washing water of the filtration is introduced into the flue gas desulfurization plant. The process is particularly suitable for flue gases rich in chloride contents.