Procedure and apparatus for the cleaning of flue gases containing sulfur dioxide

Process for the cleaning of flue gases containing sulfur dioxide produced by sulfur-containing coal which is burned by the addition of air at a temperature of 700 to 950° C. in the combustion chamber of a circulating fluidized-bed firing system, the process comprising the steps of:

• delivering a particulate SO2 sorbent to the combustion chamber;
• feeding a portion of the ash produced in the combustion and a portion of the reaction product produced in the reaction of the SO2 sorbent with the sulfur dioxide as well as a portion of the unreacted SO2 sorbent from the combustion chamber to a mechanical mixing unit;
• supplying water or an aqueous sodium-containing solution to the mixing unit:
• mixing the ash, the reaction product, the unreacted SO2 sorbent together with the water or aqueous sodium-containing solution, whereby the unreacted SO2 sorbent is converted into a hydration product at a reaction temperature of 60° C. to 100° and at atmospheric pressure;
• regulating the reaction temperature of the mixing unit;
• regulating the water or aqueous sodium-containing solution fed to the mixing unit as a function of the residual moisture of the hydration product to be carried off from the mixing unit;
• regulating the dwell time of the products introduced into the mixing unit as a function of the degree of hydration of the product to be carried off;
• returning the ash, the reaction product, and hydration product from the mixing unit into the combustion chamber of the fluidized-bed firing system;
• and
• reactivating the hydration product into an SO2 sorbent at a combustion-chamber temperature of 700° to 950° C.