Regeneration of the Effluent from Sulphur Dioxide Absorption in Wet Desulphurization of Flue Gases

Abstract

Regeneration of sorption effluences obtained from wet desulphurization of flue gases in calcium-based solutions involves oxidation of sulfites. The efficiency of calcium sulfite oxidation is responsible for the quality of gypsum obtained via this route and for its applications. It seemed, therefore, advisable to investigate this oxidation process with the aim to assess the contribution of iron (which is present in the reaction medium) to the efficiency of calcium sulfite oxidation. The process was conducted at the following parameters: suspension concentration, 1 to 3 wt.%; temperature, 293 K; air flow rate, 8.33 x 10-6 m3/s. The efficiency of oxidation was found to depend on the pH of the solution, on the concentrate ion of the catalyst and on the duration of the process. The catalytic effect of iron and cobalt on the oxidation efficiency was compared, and its pH-dependence was quantified. Thus, in a neutral medium (pH = 7) the cobalt catalyst prevailed noticeably over the iron catalyst. In an acid medium (pH = 5.5) the efficiencies of oxidation following 1-hour aeration were identical for the two catalysts. After aeration times longer than 1 hour, the oxidation efficiency obtained in the presence of the iron catalyst was higher. The optimum oxidation parameters for a 1.0 wt.% calcium sulphite suspension over the iron catalyst were established. A maximum efficiency of oxidation (82.5%)was achieved in the presence of a 0.5 wt.% Fe catalyst at pH = 5.5 and at the adopted oxidation time of 20 minutes.