Study On Indirect Catalytic Oxidation Of Various Pollutants In Diesel Vehicle Exhaust By Micro-nano Bubble

In recent decades,China has paid more and more attention to the problem of heavy diesel vehicle exhaust pollution,and the regulations issued have become more and more strict.In July 2019,"Limits and Measurement Methods for Pollutant Emissions of Heavy-Duty Diesel Vehicles?China Sixth Phase?"have been published.The requirements for HC,NO_X and PM had been greatly improved.The pollutants emitted by diesel vehicles mainly include CO,particulate matter,NO_X,and SO_X.Compared with gasoline vehicles,the emissions of NO_X and particulate matter in diesel are higher.The most common diesel vehicle exhaust removal equipment is a combination of selective catalytic reduction converter?SCR?,oxidation catalytic converter?DOC?,and particulate trap?DPF?.Its shortcomings are mainly the use of heavy metals as catalysts It is expensive,and because the exhaust gas contains SO₂,the catalyst is poisoned.In actual operation,the removal efficiency of pollutants in the exhaust gas is difficult to reach the upcoming new standard.In this paper,based on the experiment of micro-nano bubbles directly removing diesel vehicle exhaust gas,the removal efficiency is high.At the same time,combined with the characteristics of large diesel exhaust gas volume and low concentration,the device for micro-nano bubble air intake is improved,that is,a distribution plate is added directly under the absorption tower,Focus on investigating and studying the effects of various factors on the indirect catalytic oxidation of air/ozone micro-nano bubbles to remove multiple pollutants in diesel vehicles,obtain the best removal conditions,explore the removal reaction mechanism,and integrate the removal of diesel vehicle exhaust The foundation of pollutant research is as follows:?1?The concentration of diesel vehicles is generally lower than 2000ppm.The actual diesel vehicle exhaust gas directly passed into the micro-nano bubble meter.When the absorption liquid is distilled water,when the NO concentration is 2000ppm,the micro-nano bubbles directly remove the actual diesel vehicle exhaust gas removal efficiency.It is 99.6%,and the SO₂ removal efficiency is always maintained at 100%.The quality of the actual diesel vehicle exhaust directly passed into the micro-nano bubble meter can be better than the national six standard emissions.?2?Research on the indirect removal of diesel vehicle exhaust system by micro-nano bubbles.Air/ozone micro-nano bubbles indirectly oxidize and absorb pollutants in diesel exhaust.By changing the pH and salinity of the absorption liquid,adding surfactants and catalysts,urea and other factors to explore the best reaction conditions.Air micro-nano bubbles indirectly remove diesel exhaust,under the best conditions,the removal efficiency of NO is 83.2%,and the removal efficiency of SO₂is 87.81%.The ozone micro-nano bubbles indirectly remove the diesel exhaust system.Under the best process conditions,the removal efficiency of NO is 86.34%,the removal efficiency of SO₂ is 92.05%,and the removal efficiency of CO is 65.37%.?3?After the micro-nano bubbles are removed from the diesel exhaust system,the concentration of particulate matter is greatly reduced,because the fine particles agglomerate on the surface of the micro-nano bubbles in the system,which is beneficial to the indirect removal of the micro-nano bubbles.If a particulate trap?DPF?is used in combination with ozone micro-nano bubble removal diesel exhaust system,under the best conditions,the NO concentration in the diesel exhaust is 650ppm,the NO removal efficiency is 78.67%,and the SO₂ removal efficiency is 92.87%,the removal efficiency of CO is 36.96%,and the removal efficiency of PM2.5 is 92.13%.?4?Research on the mechanism of indirect removal of diesel vehicle exhaust system by micro-nano bubbles.Micro-nano bubbles generate high-activity free radicals at the moment of burst,which is the main reason for oxidizing SO₂,NO and CO.The concentration of dissolved oxygen in ordinary aerated water is much lower than that of the micro-nano bubble system;the addition of tert-butanol for radical quenching experiments proves that the micro-nano bubble gas-liquid system contains a large concentration of hydroxyl radicals;hydroxyl radicals oxidize various reducing pollution Substances,making them easily soluble in water and increasing the removal efficiency.The air micro-nano bubbles add urea compared with the common aeration of urea,the removal efficiency of pollutants is improved,because the air micro-nano bubbles can first oxidize SO₂ and NO into more easily absorbed SO₃ and NO₂,which is beneficial to the removal and at the same time Reacts with urea to generate ammonia sulfate and nitrogen respectively to promote their removal.While in the experiment of adding urea to ozone micro-nano bubbles,ozone consumes each other due to the oxidation of urea,which is not conducive to the removal of pollutants.