Method for removing sulfur oxide from stack gas

#1. Field of the Invention

#The present invention relates to a method for removing sulfur oxides from a stack gas.

#2. Description of the Prior Art

#FIGS. 1 and 2 are schematic flow diagrams illustrating embodiments of the present invention.

#FIG. 3 is a plot of the molar ratio of Mg/Ca versus the absorption efficiency of SO.sub.2.

#In accordance with the present invention, a magnesium compound or compounds is added to an absorbent consisting mainly of a calcium compound or compounds, the absorbent being used to absorb sulfur oxides and remove the same from a stack gas in the form of sulfite. The sulfite produced is oxidized into gypsum. The gypsum is separated and a double decomposition performed which regenerates Mg(OH).sub.2 for reuse.

#The present invention thus relates to a method for removing sulfur oxides in a stack gas with improved absorption efficiency and an increased rate of sulfite oxidation, which permits the amount of sulfuric acid needed for neutralizing the sulfite-containing absorption product to be reduced, prevents equipment scaling and provides good quality gypsum, by adding a magnesium compound or compounds such as Mg(OH).sub.2, MgSO.sub.4, MgSO.sub.3, MgCO.sub.3, etc., or a mixture thereof, to a circulating slurry of an absorbent which comprises primarily one or more calcium compounds.

#With reference to FIG. 1, Ca(OH).sub.2 9, H.sub.2 O 10 and supernatant liquid from thickener 5 (supplied by line 17, 19) are fed to a double decomposition reactor 1. The main component of the supernatant liquid from thickener 5 is an MgSO.sub.4 solution, the balance being CaSO.sub.4 in proportion to solubility.