Desulfurization And Denitrification Of The Marine Diesel Exhaust By Non-Thermal Plasma Method

Marine transportation is a vital part of the world economy.It has many advantages such as large carrying capacity,low risk and low cost.At the same time,the exhaust gas of marine diesel engines contains a large amount of pollutants such as CO₂,SO₂,NOx and PM which caused a huge impact on our environment.So the controlment of ship exhaust has received more and more attention.In this research,an experimental study on marine diesel exhaust separate desulfurization and denitrification and simultaneous desulfurization and denitrification was carried out by coupling dielectric barrier discharge（DBD）with corona discharge pulse（CDP）to generate non-thermal plasma（NTP）.The effects of Sulfur dioxide,nitrogen oxides,oxygen,carbon dioxide and water steam in exhaust gas and the amount of discharge current,gas flow rate and other factors on the desulfurization and denitrification were first investigated and the reaction mechanism of various marine diesel engine exhust components in the removal of nitrogen oxides and sulfur dioxide in NTP is also analyzed.Further more,the effects of various gas components in exhaust gas and the amount of monoethanolamine,discharge current,gas flow rate and other factors on the desulfurization and denitrification were investigated and the mechanism of denitrification by NTP was discussed.The results show that in the N₂/NOx/SO₂ system,the discharge effects can be stabilized within 5 minutes.The NOx removal rate is about 60%.And the sulfur dioxide removal rate is only about 18%.During simultaneous desulfurization and denitrification,the conversion of sulfur dioxide will consume high-energy electrons and inhibit the denitrification.Meanwhile nitrogen oxides can promote the desulfurization by increasing conversion path of sulfur dioxide.Because of the dissociation energy of carbon dioxide and water molecules is low,these two types of molecules have priority to consume high-energy electrons which produced by the discharge.Then the discharge pulse current was weaken and denitrification effects were compromise.In the N₂/NOx/SO₂/O₂ system,a negative nitrogen oxides conversion appeared.In addition,oxygen,carbon dioxide and water can promote the oxidation or reduction of sulfur dioxide and significantly increase the removal rate.when the total gas flow rate is 645 m L/min,applying 1.67 A current discharge and adding0.48%monoethanolamine to the simulated marine diesel exhaust（N₂/O₂/SO₂/NOx/CO₂/H₂O）can weaken the negative effects of oxygen and water vapor on the denitrification.Besides,monoethanolamine can also weaken the negative effects of carbon dioxide by absorbing carbon dioxide from the exhaust.And the final denitrification rate reaches 94%.Meanwhile,a high desulfurization rate（97%）is also achieved,as monoethanolamine can absorb sulfur dioxide rapidly,which is almost unaffected by any exhaust gas components.