REMOVAL OF SULPHUR DIOXIDE FROM FLUE GAS

摘要

1505281 Removing sulphur dioxide from waste gases H HOLTER 18 Aug 1975 [19 Sept 1974 3 Oct 1974 6 March 1975 14 March 1975 2 May 1975 5 May 1975 19 July 1975] 34212/75 Heading C1A Waste gases containing SO 2 are purified by bringing the gas into contact with a circulating aqueous wash liquid, the pH of the wash liquid before contact with the gas being adjusted to the basic range but not exceeding 12 such that the pH of the wash liquid after contact attains the weakly acid range but does not drop below 4À5, the wash liquid circulating from a gas washing means 3, 4 to a vessel 6 where salts and/or acids 7 which increase the degree of dissociation of Ca2+ ions are added and intensive mixing of air 8 with the liquid is effected, then next to an oxidation vessel 9 wherein the CaSO 3 or Ca(HSO 3 ) 2 formed is oxidized to CaSO 4 , then from the oxidation vessel to a separator 14 wherein the wash liquid has a dwell time of at least 15 minutes and is then clarified, calcium carbonate and/or calcium oxide and/or calcium hydroxide being introduced 11 after the oxidation and before the solids separation to effect the required adjustment of the pH value of the wash liquid to the basic range not exceeding a pH value of 12, the clarified wash liquor then being returned 15 to the gas washing means. The additives increasing the degree of dissociation of calcium may be acids and/or salts of the halogen group, nitrates, phosphates, or organic acids and their salts, the anions of which form with calcium ions water-soluble compounds, which in the presence of sulphurous acid permit exchange in neutral or weakly acid medium with the acid residue of sulphurous acid and in an alkaline medium reform the water soluble calcium compounds. The additive may be formic acid or an ammonium salt (ammonium formate specified). An alkaline salt (FeCl 3 , Fe 2 (SO 4 ) 3 specified) may be added to the wash liquid during the oxidation step. The oxidation may be carried out in the presence of elemental iron optionally in the form of refined steel or copper alloy steel as catalyst. Reference has been directed by the Comptroller to Specification 1,445,228.