Removal of sulfur dioxide from flue gas

Claim 1

In a regenerative process for the removal of SO 2 from an SO 2 -containing gas which comprises the following essential operations: (a) maintaining in a scrubbing system a scrubbing zone in which said SO 2 -containing gas is continuously contacted by aqueous sodium or potassium carbonate solution under sulfite-forming conditions, to thereby remove SO 2 from said gas by conversion of SO 2 to sulfite; (b) maintaining in said scrubbing system a separate thiosulfate generation zone in which effluent sulfite solution from said scrubbing zone is continuously contacted by an aqueous solution of sulfide under thiosulfate-forming conditions to convert sulfite to thiosulfate; (c) maintaining a continuous circulation of aqueous thiosulfate solution of substantially constant thiosulfate concentration from said thiosulfate generation zone to said scrubbing zone in said scrubbing system; and (d) maintaining a regeneration system in which thiosulfate contained in a slip stream from said scrubbing system is converted to a mixture of sulfide and carbonate in the following ratio, R: ##EQU4## where the valve of R is no greater than 1; (S°)=gram atoms sulfur with valence number zero per 100 grams of solution; (S -2 )=gram atoms of M per 100 grams of solution present in said solution as MHS, M 2 S, M 2 S x , M 2 CO 3 , MHCO 3 , MOH; and M=Na or K, the improvement in said regeneration system which comprises: (1) reacting the thiosulfate in said slip stream with SO 2 gas at a tempreature greater than about 300° F. and at a pressure sufficient to maintain an aqueous solution of M 2 SO 4 in the reaction zone to produce an aqueous solution containing M 2 SO 4 and molten S, and separately recovering said molten S and said aqueous solution containing M 2 SO 4 ; (2) reducing, said M 2 SO 4 to M 2 S by reaction with coal; (3) carbonating, by reaction with CO 2 and H 2 O, the M 2 S to a mixture of sulfide and carbonate having a ratio, R, no greater than 1.