Sulphur distribution during air gasification of kraft black liquor solids in a fluidized bed of TiO2 particles

The sulphur distribution was measured during atmospheric air gasification a nd pyrolysis of kraft black liquor solids in a fluidized bed of TiO2 partic les at 700-900 degrees C. The detected gaseous sulphur species are H2S, COS , CH3SH, C3H7SH, (CH3)(2)S and (CH3)(2)S-2. H2S is the major gaseous sulphu r species: while C3H7SH is the dominant organosulphur species. The present gasification data indicate that the formation of H2S by the H2S stripping r eaction is not important. Therefore, it is suggested thar thermal cracking of CH3SH and (CH3)(2)S is the major route for H2S generation. The gaseous s ulphur yields of H2S, COS and organosulphur are found to decrease with incr easing temperature for both gasification and pyrolysis. The mechanism of C3 H7SH formation is proposed to be insertion of sulphur vapor, S-2, in the pr opyl side chain of lignin fragments. In the bed residual solids, the identi fied sulphur species are sulphide, thiosulphate, sulphite and sulphate. Sul phide is the major species. The total sulphur content of the BRS for both g asification and pyrolysis increases with increasing temperature, presumably because more H2S is recaptured by Na2CO3 via the reverse of the H2S stripp ing reaction. The total sulphur reduction efficiency, which considers both Na2S and H2S, is conservatively estimated ro be about 90% and 80% at 750 an d 820 degrees C respectively.