Experimental Study On NO Removal From Marine Exhaust Gas By Ozone Oxidation

At present,exhaust gas from marine diesel engines includes a lot of pollutants such as SO_x,NO_x,PM and so on,which led to increasingly serious air pollution problems.The IMO has released MARPOL73/78 Convention Annex VI,which sets clear limit requirements about the ship fuel sulfur content and NOx concentration in exhaust gas.In order to effectively reduce NO_x emissions from marine exhaust gas,a variety of methods for NO_x removal have been proposed,such as selective catalytic reduction?SCR?,exhaust gas recirculation?EGR?,wet scrubbing oxidation,and ozone?O₃?oxidation.The O₃ oxidation method offers the advantages of high denitration efficiency and simple principle,thus has good application prospect.As such,the O₃ self-decomposition properties were studied in this paper,and the experimental study on O₃ oxidative denitrification was carried out.Finally,the effects of wet washing on the oxidative denitrification of O₃ and its mechanism were studied.Firstly,the self-decomposition properties of O₃ were studied.The mechanism of the reaction was also analyzed.The results showed that flue gas temperature was the main factor affecting O₃ self-decomposition.With the increase of flue gas temperature,O₃ self-decomposition rate increased.When the temperature was lower than 100 ?,the self-decomposition rate of O₃ increased slowly.When the temperature was higher than 200?,O₃ self-decomposition rate increased significantly.When the flue gas temperature was 100?,with the increase of the residence time of the flue gas in the furnace tube,the self-decomposition rate of O₃ gradually increased,while the trend of O₃ self-decomposition rate was basically the same at different O₃ concentrations.Secondly,the effects of molar ratio of O₃/NO,residence time,and SO₂ concentration on O₃ oxidative denitrification were studied and the related reaction mechanism was analyzed.The results showed that the NO oxidation rate increased with the increase of O₃/NO molar ratio.When O₃/NO molar ratio was more than 1,the NO oxidation rate was 100%.When O₃/NO molar ratio was 1,the residence time of flue gas had no obvious effect on the NO oxidation rate.When NO and SO₂ coexisted in the flue gas,SO₂ had a certain inhibitory effect on NO oxidation rate.When O₃/NO molar ratio was 1 and SO₂ concentration was 1000 ppm,the NO oxidation rate was only 90%,while SO₂ removal rate was 4%.Finally,the effects of wet wash on the oxidative denitrification of O₃ were studied.In this paper NaClO₂,NaCIO,H₂O₂ synergy O₃ oxidation denitration experiments were conducted.Comprehensive consideration,NaClO synergistic O₃ denitration was choosed.The effects of O₃ concentration,pH value of NaClO solution and free chlorine concentration on NO oxidation rate were investigated.When the pH value of NaClO solution is 7,the concentration of O₃ and the concentration of free chlorine of NaClO can obviously.increase the NO oxidation rate.Since the ratio of free chlorine in NaClO solution varies with the pH value of the solution,the pH value has a great influence on the wet denitrification performance of NaClO solution.When the concentration of O₃ was 300 ppm and the free chlorine concentration was 10 mmol/L,the NO oxidation rates at pH 3,7,and 11 were 100%,95.8%,and 66.5%,respectively.In order to consider the problem of acid-base corrosion and denitrification rate,it is suggested that NaClO solution of pH 7 should be used in conjunction with O₃ to conduct the follow-up studies.