Chemical determination of oxygen transfer rates, transfer efficiencies and interphases evoked by aeration elements for liquid flows

Abstract

Aeration using bubble clusters is a central practice in biological and industrial process technology. The oxygen transfer capacity of state-of-the-art aeration elements was analysed by means of sulphite (S IV ) oxidation in liquid phase. Oxygen transfer rate, oxygen transfer efficiency and specific values for the size of the interphase were derived. Measurements were carried out in a pilot scale seawater flue gas desulphurisation plant, using an aeration basin equipped with a gas-tight cover. Aeration elements representing different types and materials were installed in the basin and fed with pressurised dried air. Liquid temperature and pH were controlled during experiments. 0.5 mol/l sulphite solution was used for the experiments, which were carried out at pH = 9 and T l = 22-25• C in presence of a cobalt catalyst. Under these conditions, the liquid phase mass transfer resistance was negligible, allowing the determination of the interphase. Elements were tested at rates of feed flowṁ air = 12, 18, 24 m 3 STP /h. The oxygen consumption due to oxidation of the sulphite, which is a direct measure of the transferred gas flux, was derived by means of two measurement methods: exhaust gas analysis and iodometry. While the results of both methods showed comparable trends, discrepancies in total mass transfer were found, which were attributed to the experimental setup. Results showed significant differences in characteristics of the tested aeration elements. Influences due to assembly regarding the orientation of an element inside an aeration basin were analysed for pipe aerators with doublesided perforation.