Spectral Analysis And Mechanism Research On Decomposition Of Methyl Violet In Waste Water And Nitric Oxides In Exhaust Gas By Dbd

With the rapid development of economy and society in the world, the environmental pollution is increasingly serious and harmful to the human living environment and health, so various countries are formulating increasingly strict emission rule. Now, in our country it is commonly difficult for the decoloration of waste water and for the removal of NOx in diesel engine exhaust gases.Dielectric Barrier Discharges (DBD) plasma which includes energetic electrons and active particles is effective and environmental techniques of handling. In this paper, the author developed DBD device and matched power supply source, whereby the characteristics and emission spectrums of various gases discharge were studied, and the related investigations were taken for the decoloration of waste water and the removal of NOx in diesel engine exhaust gases. In general, the achieved achievements were mainly as follows:(1) The DBD device and its matched power supply source was developed, and by the device the research platform of DBD was build.(2) The characteristics and emission spectrums of discharge in Ar, Ar+O2, He, He+02, N2, N2+O2, O2, and air were studied. Results show discharge is similar glow in He gas and filar in the others. The intense spectral line of N atom whose lifetime is short was observed in Ar and Ar+O2 discharge, and the reactive OH radical was observed in Ar discharge but not in the others, so it might be more value in application. Additionally, the spectral line of NO(A—X) was observed in N2, N2+O2, and air discharge, and the intensity of spectral line rapidly decreased with the increasing scale of O2 gas.(3) The results of decoloration for methyl violet show that the decoloration ratio from high to low was O2, He+02 and He, and the effect was similar in He+O2 and O2 gas discharge. For He gas discharge, consumed energy density is low, but the decoloration ratio is also lower than 50%; for O2 gas discharge, the decoloration ratio of 99.5% was achieved, but the high energy density of 32.5kJ/L was required; for He+02 discharge, the decoloration ratio of 96% was achieved, but the consumed energy density was only 7.7kJ/L. So we propose that the mixed gases of He+02 are optimal for the decoloration of methyl violet, because the high decoloration ratio can be achieved and low energy density will be cost in the system.By analyzing the decoloration mechanism of methyl violet, it is considered that OH radical and O2 gas play a key role in the decoloration, and OH radical is mainly got by the reactions related with O. So we consider the reactive oxygen (such as O2-·,H2O2, OH, O) as the key particles for the decoloration of methyl violet.(4) Using the self-developed DBD device combined with selective catalytic reduction (SCR) device, we build a research platform of DBD cooperating with SCR for NOx removal. The characteristics of NOx removal and reaction mechanisms by DBD cooperated with SCR were investigated under the conditions of high NOx concentration (800 ppm) and high space velocity (50000 h-1). Meanwhile, the effect of temperature on NOx removal was also studied, especially the NOx removal at the low temperature of 150℃was investigated and the reaction products were analyzed by FTIR spectra.By DBD cooperated with SCR the high NOx removal rate was achieved at low temperature. With C2H5OH as reductant, the NOx removal rate of 80% and the NO removal rate of 90% were achieved at 150℃when 8% H2O was fed into the exhaust gases. With C3H6 as reductant, the NOx removal rate of 88% and the NO removal rate of 94% were achieved at 150℃in dry gases, but the NOx removal rate decreased to 60% when 8% H2O was fed into the exhaust gases. The FTIR spectra confirm the NOx can effectively be removed by DBD cooperated with SCR, and the reaction products are mainly N2, CO2 and H2O.By contrast research on DBD and SCR individually and together impacting on NOx removal, the reaction mechanism of NOx removal were proposed as follows:when discharge came into being, strong oxidative particles in plasma reacted with hydrocarbons to get organic reactive particles which rapidly oxidized NO to NO2 at the acceleration of catalyst; NO2 reacted with hydrocarbons to get CxHyNzO compound over catalysts, and the more NO2 the more CxHyNzO compound were produced; discharge resulted in the activation of hydrocarbons and the rise of catalyst bed temperature, so finally the NOx was removed by reaction with CxHyNzO over catalyst, and simultaneously the hydrocarbons were removed by the generation of CO2 and H2O.Experiments show the role of O3, HO2, and so on in plasma is weak in reaction with NO, and the hydrocarbons are just the key particles for the effective oxidation of NO to NO2.