GB1360097A - Regeneration of absorbent for sulphur oxides - Google Patents

Abstract

1360097 Hydrogen sulphide; regeneration of absorbent NORTH AMERICAN ROCKWELL CORP 28 Sept 1971 [1 Oct 1970] 45193/71 Heading C1A Sulphur oxides are removed from flue gas by being contacted at a temperature of at least 350‹ C. with a molten salt mixture containing alkali metal carbonate to form alkali metal sulphite and/or sulphate, the alkali metal sulphite and/or sulphate is reduced to alkali metal sulphide by means of a carbonaceous reducing agent, and the so formed sulphide is converted back into carbonate and H 2 S by means of CO 2 and steam, the reduction step being carried out at at least 600‹ C. and the reduction temperature being maintained by addition of a supply of oxygen gas. Preferably the alkali metal carbonate melt is a mixture of lithium, sodium and potassium. As shown, the flue gas travels upwardly through the absorber 2 and contacts countercurrently a spray of molten carbonate discharged through a discharger 3. The desulphurized gas flows into a wire mist eliminator 7 to remove entrained droplets, then through a plurality of heat exchangers 9 and is discharged into the atmosphere. The sulphite/ sulphate containing melt collects in a heated sump 11 at the base of absorber 2. Part is recycled to the absorber via line 38, the remainder passing through an ash filter 40 to reducer vessel 17, where it is contacted with a stream of carbonaceous reductant 15. Suitable reducing materials include coke, charcoal and coal, fluidized coke in excess being preferred. Gaseous oxygen or air is also passed via line 16 into the reducer. A catalyst such as elemental iron, iron sulphide or iron sulphate may also be used in the reducing stage. The reduced material is transferred via heat exchanger 21 and line 22 to distributers 23 in a reformation vessel 24. CO 2 from reducer 14 is passed via cooler 26 and line 27 into vessel 24 together with steam from boiler 29. Excess CO 2 from 14 may be fed via line 28 to heat exchanger 9. H 2 S formed in vessel 24 passes through a mist eliminator and thence to a conventional plant 33 for conversion into sulphur or sulphuric acid. The carbonate melt in 24 is withdrawn via pump 36 and fed into the storage vessel 4 for use in the absorption stage.