Study On NO Removal From Marine Diesel Engine Exhaust Gas By Using The Combined Oxidants Of O₃ And NaClO

Shipping transportation has played an important role in development of the world economy,but it also brings some emission issues that can not be ignored.In recent years,IMO has formulated and implemented strict regulations to limit the emissions of SOx,NOx,and other pollutants from marine diesel engine exhaust gas.In order to reduce NOx emissions,people continue to explore economical diesel engine exhaust gas denitration technologies.In addition to SCR,EGR,and other mature technologies,O3 dry denitration and wet scrubbing denitration are also hotspot technologies that scholars study.O3 has strong oxidizing capacity for denitration,but O3 will decompose fleetly under the condition of high temperature(>150?).O3 also needs to consume a large amount of electric energy.Wet scrubbing denitration technology requires to store large quantities of oxidants and waste on-board.The application of O3 dry denitration and wet scrubbing denitration in ship is restricted largely.The denitration method of the combination of O3 with NaClO wet scrubbing is proposed in this paper for the first time,O3 is injected into the wet scrbbing reactor,NO is oxided by the combination of O3 with NaClO wet scrubbing.The purpose is to reduce the temperure of O3 reacting with NO by wet scrbbing process for reducing the self-decomposition of O3,so O3 denitration utilization is improved.As the same time,the dosage of O3 decreases by using NaClO to replace segmental O3,so the demand of electricity decreases.The method combines the advantages of O3 dry denitration and wet scrubbing denitration,and it has practicability and economical efficiency.Firstly,the influences of the main factors such as flus gas temperature,residence time and O3 concentration on the self-decomposition rate of O3 were experimentally studied based on the system of ozone denitration.The results showed that the self-decomposition rate of O3 was mainly related to the flus gas temperature,When the temperature rose above 200 ?,the self-decomposition rate of O3 increased significantly.Based on the O3 self-decomposition experiment,the effect of O3 concentration on the O3 dry denitration performance was experimentally studied.The results showed that NO concentration decreased linearly with the increase of O3 concentration,O3 can efficiently oxidize NO in flue gas to NOx that has high solubility in water.Secondly,the effects of NaClO concentration,pH value,NO concentration,flue gas flow,temperature of washing liquid and CO2 concentration on the denitration performance of NaClO wet scrbbing were experimentally studied.The results showed that when the initial pH value of NaClO solution changed from 4 to 12,the removal rate of NO significantly changed with the pH value.When the initial pH value was 7,the removal rate of NO was the highest.The denitration rate of NaClO wet scrbbing increased with the increase of NaClO concentration and NO concentration,but decreased with the increase of flue gas flow rate and temperature.CO2 concentration had little effect on the denitration rate.Finally,the organic combination of O3 injection and NaClO wet scrubbing was achieved on the sprinkler reactor,the effects of different kinds of liquid phase oxidant,O3 concentration and NaClO solution concentration on the denitration performance were studied.The results showed that,compared with the combination of O3 injection and other oxidant wet scrubbing,the combination of O3 injection and NaClO wet scrubbing denitration had obvious advantages.With the increase of O3 concentration and NaClO solution concentration,denitration rate increased.According to the characteristics of the shipping operation,a scheme of marine exhaust gas treatment system based on the combined oxidation of O3 with NaClO was proposed.Taking marine engine MAN B&W 5S35ME-B9 of Dalian Maritime University land-based ship training engine room as an example,the energy consumption of O3 in scheme was calculated and analyzed.