Dissertation Title:Removal Of SO₂ From Flue Gas By Electrochemical Oxidation Coupling With Chemical Catalytic Oxidation Method

Electrochemical method of flue gas desulphurization?FGD?is a kind of new technology which has many advantages in small-scale process to removal S02 from flue gas and been called clean technology.The advantages include high SO₂ removal efficiency,needless of reagents,simple for post-processing,small coverage of area and easy to realize automation.The present paper aimed at combination the electrolyzer with Bunsen reactor.The effect of various technical parameters on the removal efficiency of S02 and the cell voltage were discussed from the view of industrial applications.Fundamental research work on the new technology of combination of electrochemical oxidation and chemical catalytic oxidation had been carried out,which can not only improve the removal efficiency of S02 but also regenerate the catholyte.The direct electrochemical oxidation behavior of KI on graphite electrode in acidic electrolyte filled with SO₂ had been studied.It was found that there were three electro-oxidation peaks when the anode potential was polarized to 0.64 V.It was analyzed that the first peak was the direct oxidation of SO₂;the second peak was the oxidation of iodide ion with the formation of soluble iodine and the third peak corresponding to the oxidation of iodide informing insoluble solid iodine.It was found that the area of iodide ion oxidation peak and peak current increased with the existence of SO₂;the increased proportion of electricity consumption was found to be close to S02 concentration ratio,which indicated that the rate of the reaction would increase with the presence of S02.The behavior of electro-reduction of copper ion with the new technology of combination of electrochemical oxidation and chemical catalytic oxidation was investigated by the technique of cyclic voltammetry.It was found that there was catalytical function for the electro-reduction of copper ion with the existence of SO₂ in cathloyte.The peak current of electro-reduction had become bigger compared with the cathloyte without S02.The side reduction reaction was found happening and byproduct was found to be formed when the potential was polarized to more negative.Therefore,copper plating could be obtained if the cathode was controlled to be suitable potential.A kind of black deposit was found to form when the potential was polarized to-0.52 V?vs.SCE?and there was SO₂ dissolution in electrolyte.It was identified that the black solid deposit was composed of several tiny particles whose size were in the range of 50?300 nm by scanning electron microscope?SEM?and energy-dispersive X-ray spectroscopy?EDX?analysis,The particles were the mixture of several kinds of compounds.Bunsen reactor was designed and the packing size,total number of mass transfer units and mass transfer coefficient were calculated.The technology of removal of SO₂ in simulated flue gas was investigated by Bunsen reactor designed where iodine was used as absorptant.It was found that more than 90%of the SO₂ removal efficiency can be obtained when the mole ratio of iodine and S02 is in the range of 1.0?1.5,the superficial gas velocity is in the range of 0.7?0.9 and the liquid-gas ratio in the range of 1.5?2.0.The effects of various kinds of parameters on the voltage and S02 removal efficiency were investigated by combination of electrolyzer with Bunsen reactor.The results are as obtained as following:?1?It would be beneficial for voltage reduction with the increase of KI concentration.However too high values of KI concentration would cause side reaction and the cell voltage would become higher again.?2?Cell voltage would decrease with the increase of the concentration of H2SO4.However too high values of H2SO4 concentration would damage the ion exchange membrane.?3?Cell voltage would decrease with the increase of temperature.However cell voltage would decrease slowly when the temperature of electrolyte was more than 35 ?.The suitable temperature is 45 ?.?4?Cell voltage increased with the increase of current density in nearly linear way when the current density is within a certain range.