Process for producing calcium sulphate alpha-hemihydrate, suitable as building material, from moist, finely divided flue-gas desulphurisation gypsum

摘要

Process for producing calcium sulphate alpha-hemihydrate from finely divided flue-gas desulphurisation gypsum from brown coal (lignite) power stations by recrystallisation of the calcium sulphate dihydrate in the presence of saturated steam, with shaped bodies being formed from the calcium sulphate dihydrate, which bodies have a pore volume of from 15 to 60% and more than 5% by volume of air in the pores (all percentages based on the volume of the individual shaped bodies). The shaped bodies are introduced into an autoclave. In the presence of a sufficient amount of water in the pores, the crystal habit and the crystal growth of the calcium sulphate alpha-hemihydrate crystals, which grow from an aqueous solution phase, is controlled by a treatment temperature in the range between 110@C and 180@C and by the pressure of the treatment atmosphere in the autoclave. The shaped bodies are taken from the autoclave after the recrystallisation and are passed on for use.