Study On The Oxidation Of Ammonium Sulfite By Gas-surface Discharge

Ammonia-based flue gas desulfurization (FGD) has been widely used in recent years because of its high efficiency, low cost and rare fouling. Ammonium sulfite, a byproduct of desulfurization, is easily decomposed into SO2, so ammonium sulfite may produce secondary pollution in the environment. However, ammonium sulfate is stable, and can be used as agriculture fertilizers. Thus, it is critical to effectively oxidize ammonium sulfite to ammonium sulfate.Now, aeration forced oxidation method has been used to oxidize ammonium sulfite, but there are some disadvantages for aeration forced oxidation method, for example, low efficiency, long oxidation time and high energy consumption. To solve these problems, surface discharge plasma was used to oxidize ammonium sulfite because of the production of reactive oxygen species. The effect of the electrical and gas-liquid parameters on the sulfite oxidation was investigated. The production of active species and mass transfer were also studied. Additionally, the up-scaled system for sulfite oxidation was investigated. The main results are summarized as follows:(1) Surface discharge plasma was used to oxidize ammonium sulfite oxidation. The experimental results showed that increasing the applied voltage and gas flow rate could improve the ammonium sulfite oxidation; increasing gas temperature, solution quantity, mass ratio of ammonium sulfate and ammonium sulfite decreased the ammonium sulfite oxidation, the seriflux temperature had no effect on ammonium sulfite oxidation.(2) The production of active species for surface discharge plasma was investigated. The experimental results showed that ozone concentration increased with increasing the applied voltage, discharge length, high voltage electrode wire diameter, discharge medium tube diameter and pitch ratio, and decreased with increasing the gas velocity and gas temperature.(3) Active species mass transfer was studied in seriflux. The experimental results showed that dissolved ozone concentration decreased with increasing the aering stomatal aperture and seriflux temperature. Firstly, the dissolved ozone concentration in seriflux increased with increasing initial pH, and then decreased with pH. Gas flow rate in medium tube had no effect on ozone concentration dissolved.(4) The up-scaled system for oxidation of ammonium sulfite was studied. The experimental results showed that it was feasible to oxidize ammonium sulfite by adjusting the number of surface discharge reactor in the up-scaled system. Compared with aeration forced oxidation method, surface discharge plasma can effectively oxidize ammonium sulfite. Considering the practical industrial application of the surface discharge plasma, it was recommended that too long discharge length should not be used, and combination reactors should be used in parallel applications.