Removal of sulfur oxides from waste gases

Claim 2

The process of claim 2, in which said flue gas contains fuel ash, at least a portion of said fuel ash is entrained in said aqueous scrubbing solution, and the resulting aqueous scrubbing solution containing fuel ash and dissolved alkali sulfite is processed to remove fuel ash prior to cooling said resulting solution.

Claim 3

The process of claim 2, in which said flue gas contains sulfur dioxide and sulfur trioxide, said sulfur trioxide is absorbed in said aqueous scrubbing solution to form alkali sulfate in solution, said alkali sulfate is precipitated as a solid with said alkali sulfite by said cooling of said solution, whereby said alkali sulfate is dissolved in said aqueous anolyte solution and is subsequently electrolyzed, and the resulting aqueous anolyte solution produced by said electrolytic cell is processed to remove a portion of the contained sulfuric acid, prior to mixing with solid alkali sulfite.

Claim 4

The process of claim 1, in which said alkali is selected from the group consisting of sodium hydroxide and potassium hydroxide.

Claim 5

The process of claim 5, in which said aqueous scrubbing solution contains in the range of about 1 to 5 grams of dissolved alkali per 100 ml. of aqueous scrubbing solution.

Claim 6

The process of claim 1, in which said aqueous scrubbing solution contains an oxidation inhibitor.

Claim 7

The process of claim 1, in which said makeup alkali compound added to said residual solution comprises said aqueous alkali hydroxide solution.

Claim 8

A process for the removal of sulfur dioxide, sulfur trioxide and entrained fuel ash from a flue gas stream, and the production of product concentrated sulfur dioxide, oxygen and hydrogen gas streams and sulfuric acid which comprises scrubbing said flue gas stream with an aqueous scrubbing solution, said aqueous scrubbing solution being at a temperature in the range of about 45* C. to 65* C. and containing a dissolved alkali selected from the group consisting of sodium hydroxide and potassium hydroxide, whereby sulfur dioxide and sulfur trioxide are absorbed from said flue gas stream into said aqueous solution and the absorbed sulfur oxides react with a portion of the alkali in said solution to form alkali sulfite and alkali sulfate in solution without formation of alkali bisulfite, and at least a portion of said fuel ash is entrained in said aqueous scrubbing solution, processing the resulting solution to separate solid fuel ash from the liquid phase, cooling the resulting liquid solution containing dissolved alkali sulfite, alkali sulfate and residual dissolved alkali to a reduced temperature in the range of about 5* C. to 40* C., whereby solid alkali sulfite and solid alkali sulfate are precipitated, separating a solid mixture of alkali sulfite and sulfate from the residual solution, said residual solution containing residual dissolved alkali and being free of alkali bisulfite, adding a makeup alkali compound to said residual solution, recycling the resulting residual solution for further scrubbing of said flue gas stream, dissolving said solid mixture of alkali sulfite and sulfate in an aqueous anolyte solution containing sulfuric acid and alkali sulfate, whereby said alkali sulfite reacts with sulfuric acid to form further alkali sulfate in solution and gaseous sulfur dioxide is liberated, withdrawing a product concentrated sulfur dioxide gas stream from the resulting aqueous alkali sulfate solution, electrolyzing said aqueous alkali sulfate solution in a mercury cathode electrolytic cell, whereby a mercury-alkali metal amalgam is produced at the cathode of said cell, and product free oxygen gas and an aqueous sulfuric acid-alkali sulfate solution are produced at the anode of said cell, processing said aqueous sulfuric acid-alkali sulfate solution to remove a portion of the sulfuric acid content as product sulfuric acid, recycling the residual aqueous sulfuric acid-alkali sulfate solution as said aqueous anolyte solution containing sulfuric acid and alkali sulfate, and decomposing said and decomposing said mercury-alkali metal amalgam by reaction with a stream of water, whereby product hydrogen gas and aqueous alkali hydroxide solution are formed, and regenerated mercury is formed for the cathode of said cell.

Claim 9

The process of claim 9, in which said aqueous scrubbing solution contains in the range of about 1 to 5 grams of dissolved alkali carbonate per 100 ml. of aqueous scrubbing solution.

Claim 10

The process of claim 9, in which said aqueous scrubbing solution contains an oxidation inhibitor.

Claim 11

The process of claim 9, in which said makeup alkali compound added tO said residual solution comprises said aqueous alkali hydroxide solution.