Processes and apparatus for removing acid gases from flue gas

Abstract

Processes and apparatus for removing acid gases from hot flue gases utilizing a slurry consisting of water, calcium chloride and at least one absorbing agent selected from a group consisting of calcium oxides, magnesium oxides, calcium hydroxides, magnesium hydroxides, alkali metal oxides, alkali metal hydroxides, and alkali metal carbonates, introducing the slurry into the rising stream of hot flue gas to absorb the acid gas into the water and thereafter to react the absorbed acid gas with the absorption agent and thereafter to evaporate the water to produce dry solids comprising reaction products and unreacted absorption agents suspended in the flue gas. The calcium chloride reduces the water vapor pressure of the slurry to reduce the rate at which the water evaporates so as to increase the rate at which the acid gas is absorbed into the water before the water evaporates. The dry solids include relatively large, relatively small, and intermediate sized dry solids with the relatively large and intermediate dry solids being first removed from the flue gas, the relatively large sized dry solids being discharged as waste, and the intermediate sized dry solids being recycled for reuse in reacting with the acid gas and with the relatively small sized dry solids being removed second from the flue gas and the relatively small sized dry solids recycled for reuse in reaction with the acid gases.