METHOD FOR PRODUCING LOW-CHLORIDE GYPSUM PRODUCTS FROM CALCIUM-CONTAINING RESIDUES OF EXHAUST GAS PURIFICATION PLANTS.

摘要

Residues comprising sulphur-containing substances are made to react in a circulating fluidised bed in the presence of water and oxygen. This oxidises the sulphite portions to sulphate and simultaneously cleaves CaCl2 to CaO and HCl by pyrohydrolysis. The gaseous HCl is immediately taken away, due to the low gas residence times. CaO reacts with the sulphur-containing substances to give CaSO4. This prevents any reverse reactions. Under these conditions, high-quality gypsum products which are low in chloride are produced at temperatures of between 500 and 650 DEG C. Moreover, the process makes it possible to use waste materials as sulphur, H2O or energy carriers. These waste materials are utilised in a manner which is harmless to the environment. In this manner, gypsum anhydrite which is low in chloride is prepared from spray absorption residues. The gypsum anhydrite produced can be rehydrated in a subsequent process step to give beta -hemihydrate gypsum.