Double-alkali gypsum flue-gas desulphurisation process

The double-alkali gypsum flue-gas desulfurization process (concentrated active sodium mode) was investigated on pilot-plant scale downstream of a test boiler fired with heavy oil, in order to obtain design and operating data. A solution of sodium sulfite was used in this process as soluble absorbent for SO2. The absorbent was regenerated with lime in a separate reactor. Calcium sulfite and calcium sulfate were coprecipitated during the regeneration. The coprecipitates were removed from the regenerated absorbent by filtration. The coprecipitates of calcium sulfite and calcium sulfate were suspended in water and oxidized by air to form gypsum. The double-alkali gypsum process is much more complicated than the lime/limestone-gypsum flue-gas desulfurization process. The regeneration of the absorbent and the subsequent filtration are especially rather difficult to control.