Method of removing sulfur dioxide from combustion exhaust gas

Abstract

A method of removing sulfur dioxide from combustion exhaust gas containing sulfur dioxide by contacting the exhaust gas with an aqueous solution containing at least one organic acid salt expressed by the formula RCOOM (wherein R represents H, CH 3 , C 2 H 5 or C 3 H 7 , and M represents an alkali metal or NH 4 ) to efficiently dissolve sulfur dioxide contained in the gas in the form of a sulfite in the aqueous solution by reacting the sulfur dioxide with the salt. The resultant solution which dissolves the sulfite may be contacted with a calcium compound for producing calcium sulfite by reaction of the sulfite with the calcium compound thereby effectively removing the sulfur dioxide in the form of calcium sulfite from the combustion exhaust gas. Alternatively, the sulfite-dissolving aqueous solution may be contacted with oxygen or air for oxidizing the sulfite contained in the solution into a sulfate, followed by contacting the sulfate, which is now dissolved in the aqueous solution, with a calcium compound. The sulfate is satisfactorily reacted with the calcium compound to produce calcium sulfate and thus sulfur dioxide may be effectively ultimately removed in the form of calcium sulfate from the combustion exhaust gas.

What is claimed is: 
     
       1. A method of removing sulfur dioxide from combustion exhaust gas containing said sulfur dioxide, comprising contacting said combustion exhaust gas with an aqueous solution containing at least one organic acid salt selected from the group consisting of alkali metal salts or ammonium salts of acetic acid, propionic acid and butyric acid to dissolve the sulfur dioxide contained in the combustion exhaust gas in the form of alkali sulfite and alkali sulfate in said aqueous solution and to generate organic acid in said aqueous solution, adding into the resultant solution which contains alkali sulfite, alkali sulfate and organic acid dissolved therein a calcium compound selected from the group consisting of calcium carbonate, calcium oxide, calcium hydroxide and calcium salt of an organic acid for reaction of said alkali sulfite and said alkali sulfate contained in said solution with said calcium compound to produce calcium sulfite and calcium sulfate which precipitate in said solution resulting in formation of said organic acid salt in said solution, and recycling the organic acid saltcontaining solution obtained after separation of said calcium sulfite and said calcium sulfate for contact with said combustion exhaust gas. 
     
     
       2. The method of claim 1 in which said calcium salt of an organic acid is calcium salt of acetic acid, propionic acid, or butyric acid. 
     
     
       3. A method of removing sulfur dioxide from combustion exhaust gas containing said sulfur dioxide, comprising contacting said combustion exhaust gas with an aqueous solution containing at least one organic acid salt selected from the group consisting of alkali metal salts or ammonium salts of acetic acid, propionic acid and butyric acid to dissolve the sulfur dioxide contained in the combustion exhaust gas in the form of alkali sulfite and alkali sulfate in said aqueous solution and to generate organic acid in said aqueous solution, contacting the resultant solution which contains alkali sulfite, alkali sulfate and organic acid dissolved therein with oxygen or oxygen-containing gas to oxidize said alkali sulfite contained in said solution into alkali sulfate, adding a calcium compound selected from the group consisting of calcium carbonate, calcium oxide, calcium hydroxide and calcium salt of an organic acid into said solution for reaction of said alkali sulfate contained in said solution with said calcium compound to produce calcium sulfate which precipitates in said solution resulting in formation of said organic acid salt in said solution, and recycling the organic acid salt-containing solution obtained after separation of said calcium sulfate for contact with said combustion exhaust gas. 
     
     
       4. The method of claim 3 in which said calcium salt of an organic acid is calcium salt of acetic acid, propionic acid, or butyric acid. .Iadd. 
     
     
       5.  A method of claim 1 wherein said calcium compound is calcium hydroxide. .Iaddend. .Iadd.6. A method of claim 1 wherein said calcium compound is calcium carbonate. .Iaddend. .Iadd.7. A method of claim 3 wherein said calcium compound is calcium hydroxide. .Iaddend. .Iadd.8. A method of claim 3 wherein said calcium compound is calcium carbonate. .Iaddend.