Study On The Enhancement Effect Of UV Online Irradiation On NO_x Removal By Wet Scrubbing Using NaClO₂ Solution

In recent years,nitrogen oxides(NOx)emission from ships has caused serious atmospheric pollution on the environment.The International Maritime Organization(IMO)has enacted a revised convention to control NOx emission from ships.In order to meet the inceasingly strict requirements,several technologies have been developed to mitigate NOx emissions from marine diesel engines.Since wet scrubbing oxidation denitrification technology can remove NOx from exhaust gas of marine diesel engine effectively,it has extracted more and more researchers' interest.NaClO2 has strong oxidation ability and can be used as oxidative additive for NOx removal from flue gas by wet scrubbing,so it has great potential for applying in NOx abatement for marine industry.Here it is proposed for the first time to combine UV online irradiation with NaClO2 solution to enhance the NOx removal efficiency during wet scrubbing using NaClO2 solution.The effects of various key parameters(NaClO2 concentrations,initial solution pH,absorbent temperature,NO concentrations,O2 concentrations,SO2 concentrations,CO2 concentrations,and gas flow)on NO removal efficiencies were investigated,and the relevant reaction mechanism was also discussed.The results showed that the introduction of UV online irradiation could obviously enhance the NO removal efficiency of wet scrubbing using NaClO2 solution.When the concentration of NaClO2 was 10 mmol/L,initial pH was 7,and inlet NO concentration was 1000 ppm,the NO removal efficiency of wet scrubbing using NaClO2 was 77%.NO removal efficiency was increased to 90%significantly by the introduction of UV online irradiation.When initial solution pH was 12,the alkaline ambient would suppress the oxidative ability of NaClO2 to a large extent,resulting in a very low NO removal efficiency of 2%.However,NO removal efficiency could be improved to 47%after combining with UV online irradiation.A certain amount of active free radicals were generated in a series of photochemical reactions between UV and NaClO2,which was considered as the main reason for the enhancement effect on NO removal.With the increase of solution temperature,the enhancement effect of UV online irradiation increased slightly.With the decrease of inlet NO concentration of reactor,the enhancement effect of UV online irradiation increased.The enhancement effect of UV online irradiation was not obvious with the gas flow rate increasing from 3 L/min to 5 L/min.This paper designs a denitrification system which combines UV online irradiation with NaClO2 solution during wet scrubbing using NaClO2 solution and the spray tower.The denitrification system and spray tower was designed based on the denitrification requirement of MAN 5S35ME-B9 marine diesel.