GB1261199A - Recovery of sulphur dioxide from waste gases - Google Patents

Abstract

1,261,199. Recovering sulphur dioxide; sodium, lithium and beryllium, bisulphite and sulphite. WELLMAN POWER GAS Inc. 11 Nov., 1968 [9 Nov., 1967], No. 53218/68. Heading C1A. Sulphur dioxide is separated from a gas containing it, e.g. flue gas, by contacting the gas in a reaction zone, with an aqueous solution of sodium, lithium or beryllium sulphite at a temp., e.g. below 230‹ F., sufficient to react the SO 2 with the solution to give a bisulphite and below the temp. at which the bisulphite decomposes to the sulphite, so as to form an aqueous solution containing unreacted sulphite and the corresponding bisulphite, from which solution the sulphite content is removed by crystallization or, for example, by selective extraction, the bisulphite content of the solution being decomposed, simultaneously with or subsequent to the removal of the sulphite, under conditions of temp., pressure, and residence time such that gaseous SO 2 , water and the corresponding sulphite are produced, when the SO 2 so produced is separated and the sulphite so formed together with that initially separated is recycled to the SO 2 reaction step. Sodium sulphite is the preferred sulphite. In one embodiment, the sulphite/bisulphite solution produced in the first step is treated so that simultaneously it decomposes into SO 2 H 2 O and the corresponding sulphite, the water evaporates, and the sulphite crystallizes from the solution. The decomposition of the bisulphite is preferably performed at a temp. up to 300‹ F., e.g. at 230-300‹ F., under superatmospheric pressure. The crystallized sulphite may be separated from its mother liquor, dissolved in water and recycled to the SO 2 absorbing step. The mother liquor is decomposed to give SO 2 which is separated. The waste gas may contain 0À001 to 5 mole per cent sulphur dioxide and the absorbing liquor may contain 25 to 35% by wt. of dissolved solid, above 55% by weight of which is sulphite. The solution produced by the absorbing step may have a dissolved solids content of 25 to 35 wt. per cent and bisulphite constitutes 50-70% by wt. of its solids content. The Specification describes a particular form of gas/liquid contacting apparatus (Fig. 3, not shown).