Enhancement Of The S(Ⅳ) Oxidation Process In Seawater Flue Gas Desulfurization By Pulsed Water Surface Discharge

In the traditional seawater flue gas desulfurization (SWFGD) technology, the sulfite (S(IV)) containing effluent is treated by aeration. Though the operation of this technology is simple, the aeration oxidation rate of S(IV) is limited by pH and hardly proceeds when pH is about3(which is around the pH of effluent from the packed tower). So in a practical operation, the effluent is oxidized after raising the pH to about5by dilution with a huge amount of fresh seawater, which results in a large aeration basin and high power consumption. To minimize the size and power consumption of the oxidation basin, non-thermal plasma generated by pulsed water surface discharge with non-metallic electrodes is used in this paper. Based on the studies of discharge behavior and chemical behavior, several sets of novel plasma reaction systems available for treating waters with a large flux, high conductivity or high corrosivity have been constructed. In addition, some valuable results have also been obtained and are listed as following:(1) To solve the corrosion problem of metal electrodes, water surface discharge with non-metallic electrodes is introduced. Both the metal high voltage electrode and the metal ground electrode are replaced by non-metallic electrodes such as seawater electrodes, graphite electrodes and activated carbon electrodes. Comparisons of the electrical characteristic, optical spectrum characteristic and S(IV) oxidation rate between metal electrode discharge and non-metallic electrode discharge indicate that non-metallic electrode discharge influences the reactor behavior insignificantly.(2) Based on the kinetic study of S(IV) oxidation by non-metallic electrodes water surface discharge, it can be found that the discharge power density is the dominating factor of S(IV) oxidation rate. However, the selection of discharge gap distance must consider a pair of contradictory aspects. The larger discharge gap distance may leads to the higher discharge power density but the lower streamer power.(3) To improve the S(IV) oxidation rate and energy efficiency of water surface discharge, both the high voltage electrode and the ground electrode are suspended above the water surface to construct a water resistive barrier discharge reactor. This improvement raises the S(IV) oxidation rate and the energy efficiency over50%.(4) Scale-up of the non-metallic electrodes water surface discharge reactor is realized by equipping several water resistive barrier discharge units serially. The S(IV) oxidation rate in the serially setted reactors is0.02-0.03kg/kWh, which is not relate to the number of discharge units. For the S(IV) containing seawater with a concentration of2mM, the energy consumption of90%removal is1-2kWh/m3. This result provides a theoretical basis of pratical application of water surface discharge.