Simultaneous reductive and oxidative decomposition of calcium sulfate in the same fluidized bed

The continuous process of converting CaSO.sub.4 to a solid CaO product and a gaseous SO.sub.2 product by high temperature treatment of finely-divided CaSO.sub.4 in a circulating fluidized bed of solid particles into which is introduced a hydrogen-containing carbonaceous fuel and air for combustion thereof to form in said bed a reducing gas containing CO and H.sub.2, wherein the improvement comprises:

• maintaining a reducing zone in a lower portion of said fluidized bed by introducing a feed to said reducing zone portion consisting essentially of gaseous or liquid hydrocarbon fuel and primary air, controlling the quantity of said primary air so that the reducing conditions in said lower reducing zone portion are effective to convert said CaSO.sub.4 therein to a mixture of CaO and CaS, concurrently introducing secondary air into an upper portion of said bed above the level at which said fuel is introduced to provide an oxidizing zone within said bed capable of converting CaS to CaO, the solid particles of said bed during treatment continuously circulating between and through said reducing and oxidizing zones, the total amount of O.sub.2 supplied in said primary and secondary air plus the O.sub.2 produced by calcium sulfate decomposition being at least equal to the stoichiometric quantity of O.sub.2 required for complete combustion of the said fuel to CO.sub.2 and H.sub.2 O, removing the CaO product from the upper portion of said bed, and removing the gaseous SO.sub.2 product from above the bed substantially free of CO, H.sub.2 and said fuel.

The continuous process of producing a solid CaO product and a gaseous SO.sub.2 product by high temperature treatment of finely-divided CaSO.sub.4 in a circulating fluidized bed of solid particles into which is introduced a gaseous or liquid hydrocarbon fuel and air for combustion thereof to form in said bed a reducing gas containing CO and H.sub.2, wherein the improvement comprises:

• maintaining a strongly reducing zone in the lower portion of said fluidized bed by introducing a feed to said reducing zone portion consisting of said fuel and primary air, said primary air providing from 40 to 65% of the stoichiometric quantity of O.sub.2 required for complete combustion of said fuel to CO.sub.2 and H.sub.2 O and said primary air being distributed across the bottom of said bed for effective fluidization thereof, a mixture of CaO and CaS being produced in said reducing zone portion, and concurrently introducing secondary air into an upper portion of said bed above the level at which said fuel is introduced to provide an oxidizing zone within said bed above said reducing zone capable of converting CaS to CaO, said secondary air providing from 15 to 40% of the total air introduced into the fluidized bed, the solid particles of said bed during said treatment continuously circulating between and through said reducing and oxidizing zones, the total amount of O.sub.2 being supplied in said primary and secondary air plus the O.sub.2 produced by the calcium sulfate decomposition being at least equal to the stoichiometric quantity of O.sub.2 required for complete combustion of said fuel to CO.sub.2 and H.sub.2 O removing a CaO product from the uppermost portion of said bed beneath which said secondary air is fed to said oxidizing zone, and removing the gaseous SO.sub.2 product from above the bed substantially free of CO, H.sub.2, and said fuel.

The continuous process of producing a solid CaO product and a gaseous SO.sub.2 product by high temperature treatment of finely-divided CaSO.sub.4 in a circulating fluidized bed of solid particles into which is introduced a gaseous or liquid hydrocarbon fuel and air for combustion thereof to form in said bed a reducing gas containing CO and H.sub.2, wherein the improvement comprises maintaining a strongly reducing zone in the lower portion consisting essentially of a gaseous or liquid hydrocarbon fuel and primary air providing from 30 to 70% of the stoichiometric quantity of O.sub.2 required for complete combustion of said fuel to CO.sub.2 and H.sub.2 O, a mixture of CaO and CaS being produced in said reducing zone portion, the upper portion of said fluidized bed having a greater cross-sectional area than said lower portion thereof, concurrently introducing secondary air into the upper portion of said bed above the level at which said fuel is introduced to provide an oxidizing zone within said bed capable of converting CaS to CaO, the solid particles of said bed during said treatment continuously circulating between and through said reducing and oxidizing zones, said secondary air comprising from 15 to 40% of the total air introduced into said fluidized bed, the total amount of O.sub.2 supplied in said primary and secondary air plus the O.sub.2 produced by calcium sulfate decomposition being at least equal to the stoichiometric quantity of O.sub.2 required for complete combustion of said fuel to CO.sub.2 and H.sub.2 O, removing a CaO product substantially free of CaS from the upper portion of said bed at a level above the level at which said secondary air is fed to said oxidizing zone, and removing the gaseous SO.sub.2 product from above said bed substantially free of CO, H.sub.2, and said fuel.