Research On Conversion Reaction Mechanism Of NO_x For Ship Exhaust On The Process Of O₃ Oxidation Denitration

Nowadays,with the globalization of trade,ships play an irreplaceable role in trade and transportation with the advantage of cost.Meanwhile,the problem of pollution caused by ship exhaust has been paid more and more attention from all aspects.The technology of O₃oxidation-wet absorption denitration has a significant effect on integrative removing various pollutants,which can meet the increasingly stringent requirements of ship exhaust emissions.In the limited space and special environment of the ship,through understanding path and condition of conversion reaction of NO_x,it can promote that NO_x are converted to the target product by controlling relevant parameters,so as to achieve safe and efficient denitration for ship exhaust.The denitration effect can be predicted under different working conditions by simulating results with appropriate reaction mechanism model.The thermodynamic and kinetic data of chemical reactions are essential for the mechanism model,and their accuracy will directly affect the final simulating results.In view of the above problems,conversion reaction mechanism of NO_x for ship exhaust on the process of O₃ oxidation denitration are researched.The main work and results are as follows,In order to solve the problem that the actual effect of O₃ and other oxidants on conversion of NO_x in the process of oxidation denitration of ship exhaust is not clear,the oxidation reaction mechanisms of N₂,N·and NO are respectively researched.Firstly,by studying the oxidation reaction mechanism of N₂ and N·,the formation reaction mechanism of NO_x is clarified,and the effect of O₃ and other oxidants on the conversion of N₂ and N·to NO_x in ship exhaust is discussed.The results show that O₃ and other oxidants would not cause excess NO_x in ship exhaust.Then,by researching oxidation reaction mechanism of NO,the reaction path and degree of difficulty for the conversion of NO to other N-containing substances in ship exhaust by O₃ and other oxidants are analyzed,and the oxidation reaction mechanism of NO is elucidated.The results show that different oxidants would have different oxidation effects on NO,and their oxidation mechanism and products are different.Based on this,oxidant can be selected according to different requirements.Finally,the kinetic data are fitted to the form of Arrhenius equation（A,n,E）,and the reliability of the fitting results and method is verified.The fitting results can be directly used for related numerical simulation,meanwhile,they can provide relevant data for improving related databases as well.In order to solve the problem that the actual effect of decomposition reaction on conversion of NO_x on the process of oxidation denitration of ship exhaust is not clear.The minimum reaction path is analyzed and kinetics are calculated for the decomposition reaction of NO_x.The decomposition reaction mechanism of NO_x is elucidated,and the influence of temperature,pressure and anharmonic effects on the kinetics is analyzed.The results show that N₂O₃ and N₂O₄ should not be ignored on the process of NO_x conversion.Besides,for the reaction of asym-N₂O₃→NO+NO₂,when the temperature is 400 K,the difference of rate constant between high-pressure limiting and 0.01 atm can reach 7.22×10⁴ times.Therefore,for the low temperature technology of oxidation denitration,it is necessary to consider the influence of pressure on decomposition reaction of NO_x.In order to solve the problem that the actual effect of consumption reaction on conversion of NO_x on the process of oxidation denitration of ship exhaust is not clear,the reaction mechanisms of NO_x and H₂O molecule are researched.The consumption reaction mechanism of NO_x is elucidated,and the influence of temperature,solvation and anharmonic effects on minimum reaction path and kinetics are analyzed,respectively.The results show that N₂O₅ is the key species for the removing NO_x by H₂O molecule,and the product of N₂O₅+H₂O is the relatively stable with only HNO₃.However,the reactions of N₂O₃+H₂O and N₂O₄+H₂O should not be ignored.In addition,the aqueous solvent is more conducive to the reaction of NO_x+H₂O than gaseous phase,which contributed to improve the absorption efficiency and rate for NO_x absorbed by H₂O molecule.Especially,for the reaction of N₂O₅+H₂O,the barrier decreases by 58.27%,which is from 108.65 k J·mol^-1 to 45.34 k J·mol^-1,exotherm increases by 30.06%,which is from 21.49 k J·mol^-1 to 27.95 k J·mol^-1.Therefore,the aqueous solvent is more conducive to absorbing NO_x by H₂O molecule than gaseous phase.In order to solve the problem of selection difficulty caused by difference of existing mechanism model of O₃ oxidation denitration and referring thermodynamic data,establishing mechanism model of O₃ oxidation denitration and calculating thermodynamic data are respectively carried out.Firstly,aiming at the existing problem of thermodynamic data,the thermodynamic parameters of related species on the process of O₃ oxidation denitration are calculated and fitted by enthalpy change of atomization and ab initio method,the obtained thermodynamic data with high accuracy and strong applicability are provided for the model of O₃ oxidation denitration under a wide temperature condition.Meanwhile,the effects of temperature,isomerization and solvation on the thermodynamic parameters for different substances are researched.The results indicate that it is necessary to distinguish the spatial structure and state of matter of the relevant thermodynamic data in the O₃ oxidation denitration mechanism.Finally,aiming at the existing problem of mechanism model,based on the study of NO_x conversion reaction mechanism and calculated kinetic and thermodynamic results,the mechanism model of O₃ oxidation denitration containing 25species and 40 reactions is established by MRN method,and its accuracy is verified.