Study On Performance Enhancement Methods Of Oxidizin NO_x By Ozone Injection In Marine Exhaust Gas

Marine exhaust gas contains a lot of nitrogen oxides(NOx),which has caused serious harm to human health and ecological environment.International and domestic regulations have placed stringent requirements on NOx emissions from ships.At present,the mature ship denitrification technologies mainly include selective catalytic reduction,exhaust gas recycling,etc.,but they still have some problems to be solved.In recent years,ozone advanced oxidation denitrification technology has attracted more and more people’s attention.However,the existing ozone oxidation denitrification technology has the disadvantages of large ozone consumption and high cost.In this paper,the performance of ozone oxidation of NOx and the effects of hydrogen peroxide(H2O2)and M as synergistic additives on the performance of ozone oxidation of NOx were studied,and the related mechanism were analyzed.The specific work was summarized as follows:Firstly,the effects of flue gas temperature and ozone concentration on ozone self-decomposition and the effects of flue gas temperature,ozone concentration and gas residence time on the performance of ozone oxidation of NOx were studied by the self-built ozone oxidation denitrification experiment system.The results showed that ozone self-decomposition was greatly affected by the temperature of the flue gas,and was hardly affected by the ozone initial concentration.When the flue gas temperature was higher than 150℃,the ozone self-decomposition rate was higher than 17%,which was not conducive to ozone oxidation of NOx.At 20℃,when the molar ratio of O3/NO increased from 0 to 0.975,the performance of ozone oxidizing of NOx gradually improved,and the NO removal rate increased almost linearly to 81%.There was no significant change in the NO removal rate as the gas residence time increased from 0.3 s to 0.7 s.Secondly,based on the above research,the effects of flue gas temperature,H2O2 injection amount and solution pH value on the synergistic oxidation performance of NOx by H2O2-O3 were investigated by injecting a certain amount of H2O2 and ozone into the flue gas.The results showed that the injected H2O2 had a certain strengthening effect on ozone oxidation performance of NOx.Under the optimal experimental conditions,the NO removal rate of simultaneous injection of H2O2 and O3 increased by about 4%compared with ozone injection alone,and the Nox concentration reduced by 70 ppm.The flue gas temperature had a great influence on the synergistic oxidation performance of NOx by H2O2-O3.When the flue gas temperature was 140℃,the injected H2O2 could significantly reduce the NO2 concentration in the flue gas.With the increase of H2O2 injection amount,the concentration of NO and NO2 in the flue gas both decreased at different degrees.There was a better enhancement effect of ozone oxidation performance of NOx after injecting H2O2 solution whose pH value was 3.5.Finally,the effects of flue gas temperature,M injection amount,ozone concentration,NO concentration and gas residence time on the synergistic oxidation performance of NOx by M-ozone were studied by injecting a certain amount of M and ozone into the flue gas.The results showed that under different experimental conditions,the oxidation effect of Nox by M synergized ozone was significantly improved compared to ozone.This was because the organic radicals,which were produced by M and ozone under a certain condition,were easy to combine with NO and NO2 and promoted ozone oxidation NOx.When the flue gas flow rate was 40 m3/h,the gas temperature was 150℃,NO concentration was 400 μm,the NO removal rate reached 47%and the NOx reduction rate was 4%with only injecting 200 μm ozone.After simultaneously injecting 150 μm M and 200 μm ozone,the NO removal rate increased to 83%and the NOx reduction rate was as high as 47%.The synergistic oxidation performance of NOx by M-ozone was gradually enhanced and eventually stabilized as the injected amount of M and ozone increased.And the synergistic oxidation performance of NOx by M-ozone was promoted as the gas residence time increasing.When the temperature of flue gas was higher than 150℃,it was not conducive to M-ozone synergistic oxidation of NOx.The method of M combined with ozone oxidizing NOx has the advantages of good oxidation performence,less ozone and M consumption,lower operating costs.And this enhancement method has a better application prospect for ship gas denitrification.