Study On Injection Method Of Reactive Oxygen Species Produced By Dielectric Barrier Discharge For Oxidation Of Ammonium Sulfite

At present, coal is the main energy source in China. Meanwhile, sulfur dioxide is one of the main gaseous pollutants emitted from coal burning process. Emission of large amounts of sulfur dioxide results in acid rain pollution. In recent years, wet flue gas desulphurization (FGD) technology is the primary method for purification of SO2in flue gas, in which limestone or aqueous ammonia is used to absorb sulfur dioxide from flue gas and produces lots of sulfite solution in the absorption tower. As unstable sulfite is easy to decompose and result in secondary pollution, so oxidation treatment of sulfite is required. Now, the conventional process for oxidation of sulfite is to blow a large amount of air into SO2absorption tower by high-power fans, and then sulfite is oxidized by oxygen to sulfate. The conventional SO2oxidation method holds the following drawbacks:In order to achieve complete oxidation of sulfite, large contact chamber for mixing sulfite solution and air is always required, directly causing large land occupied by the absorption tower. At the same time, air is required to be continuously blowed into absorption tower due to the lower oxygen content in air and lower oxidation potential of oxygen, which results in the huge consumption of electric power.Non-thermal plasma technology can effectively produce reactive oxygen species in oxygen-containing atomosphere. In order to solve the problems of forced oxidation method, this paper focuses on generate reactive oxygen species by dielectric barrier discharge for oxidation of ammonium sulfite. Two different oxidation ways of sulfite including external and built-in method of DBD reactor were examined, and influence factors in oxidation of ammonium sulfite were investigated as well as the oxidation efficiency of sulfite by reactive oxygen species injection method was compared with that by traditional forced oxidation method. The following conclusions can be got:(1) Both the external and the built-in DBD reactor can produce lots of reactive oxygen species and effectively oxidize ammonium sulfite in solution. The oxidation efficiency achieved nearly100%in a relatively short time. Electrical parameters and solution properties had different effect on the oxidation efficiency of sulfite.(2) The external DBD reactor and air aeration for ammonium sulfite oxidation were compared in terms of the oxidation efficiency, and the factors including ozone concentration, reaction temperature and initial concentration of ammonium sulfite solution were examined. The results showed that the oxidation efficiency of ammonium sulfite by external DBD reactor had a significant increase compared with traditional air aeration. The higher oxidation efficiency of ammonium sulfite was obtained with bigger ozone concentration, higher temperature and lower initial concentration of ammonium sulfite solution. There was no connection between initial pH value and ammonium sulfite oxidation reaction.(3) The built-in DBD reactor and traditional air aeration for ammonium sulfite oxidation were compared in terms of oxidation efficiency. The operation conditions such as applied voltage, gas flow rate and content of ammonium sulfate in solution were investigated. The results showed that the oxidation efficiency of ammonium sulfite by built-in DBD reactor had an obvious increase compared with traditional air aeration. Higher applied voltage, bigger gas flow rate and lower initial pH value would benefit the oxidation of ammonium sulfite. It was proved that built-in method could inject reactive oxygen species besides ozone into sulfite solution, and energy consumption was obviously reduced compared to external method.