Study On The Removal Of Nitrogen Oxide From Diesel Engine Exhaust By Non-thermal Plasma Facilitated With Conventional Denitrification Process

Nitrogen oxides(NOx)is one of the most important air pollutants,including N2O,NO,N2O3,NO2,N2O5 and so on,almost 98%of the NOx exist in the form of NO and NO2.NOx mainly resource from coal-fired power plants,cement industry and internal combustion engine emissions,which may cause photochemical smoke,acid rain and other air pollution phenomenon,to stimulate people’s eyes,nose,throat,lung,endangering human health.As a commonly used internal combustion engine,diesel engines are widely used for generating units,industrial and agricultural machinery,transportation and other fields,and the exhaust gas is an important source of atmospheric NOx.At present,although several techniques are applied to reduce the NOx emission from combustion simultaneously,such as high pressure fuel injection,pressurized cold,exhaust gas recirculation,after treatment system is still necessary to meet the increasing emission standards.The after treatment system for diesel engines mainly includes selective catalytic reduction and NOx storage reduction technology,however,both the two process have their application limitations.Non-thermal plasma technology is a new gaseous pollutant control technology,which can simultaneously remove a variety of pollutants,attracting a great attention in the field of air pollution control.In this paper,the application and treatment of deNOx by non-thermal plasma technology were discussed.Besides,non-thermal plasma technology was combined with traditional selective catalytic reduction and activated carbon adsorption process to break through their limitations on the NOx removal and achieve higher denitrification efficiency.The results show that the direct ionization method can achieve more than 90%denitrification efficiency under anaerobic condition when the NOx is treated by non-thermal plasma technology alone,while the active component injection method can only oxidize NO into high valence nitrogen oxides,instead of reducing the NOx.When using the gas direct ionization method,all the gas components in the mixed gas are involved in the plasma reaction,O2 and H2O will inhibit the reduction of NO to N2 and promote the oxidation reaction,reduce NOx removal rate;CO2 and SO2 are electronegative gas,which will reduce the number of high-energy electrons and decrease the amount of active particles generated,inhibiting the transformation of NO and NOx removal;discharge voltage directly determines the number of high-energy electrons in the reactor,high discharge voltage is conducive to the promotion of the reactions,which have different effects on NOx conversion under different gas components.When the active component injection method is used,O3 produced by O2 is injected into the mixed gas to oxidize NO.O3 can oxidize NO into NO2 and high valence nitrogen oxides when it is excessive.The discharge voltage directly affects the amount of O3 generated,the discharge voltage increases,the reactor temperature increases,so that the O3 decomposition rate is accelerated and O3 concentration decreased,reducing the NO conversion.The amount of NO oxidation can be controled by changing the injection flow,which will help to adjust the ratio of NO and NO2 in the mixed gas.Increase the concentration of SO2 in the mixed gas will reduce the NO conversion rate,because O3 can also oxidize SO2,although the reaction rate of O3 reacting with SO2 is lower than the reaction rate with NO.Non-thermal plasma technology combined with selective catalytic reduction can significantly improve the NOx removal rate at low temperature.When using V2O5-WO3/TiO2 catalyst,the removal rate of NOx can be increased above 70%between 200℃and 250℃.With the increase of NO2 content in NOx,the removal rate of NOx is gradually increased.This promoting effect is obvious at low temperature.With the increase of temperature,the promoting effect is gradually weakened.Combining non-thermal plasma technology with activated carbon adsorption can significantly improve the NOx removal rate at high temperature.At 140℃,the addition of plasma reactor before activated carbon adsorption can increase the NOx removal rate from 3.14%to 58.30%.NO and NO2 are adsorbed on the surface of activated carbon in the form of-C(NO2)and-C(NO3).-C(NO2)is easily decomposed by heat,while-C(NO3)is relatively stable,so the adsorption capacity of NO2 is better.