Characteristic Study On Wet Oxidation And Absorption Of NO_x Using Dual Oxidant?H₂O₂/Na₂S₂O₈?Solution

Due to its insolubility,NO,which is not like SO2,is difficult to be removed by existing wet flue gas desulfurization method,therefore,a number of chemical reagents are needed to add into the liquid phase to oxidize the insoluble NO into the soluble nitrogen-containing compound,which can be removed by using wet scrubbing.But,the traditional chemical oxidation method has the the disadvantages of high cost,regeneration problem and secondary environmental pollution,hydroxyl radical based advanced oxidation processes(HR-AOPs)and sulfate radical based advanced oxidation processes(SR-AOPs)have been widely studied.Based on these two kinds of advanced oxidation technology,in this paper,the characteristic study of wet oxidation and absorption process of NOx with dual oxidant(H2O2/S2O82-)solution was carried out in self-designed device of a bubble column reactor,including single factor experimental research,parameter optimization research,mechanism research,thermodynamics research and macrodynamics research.(1)The effects of different reaction conditions such as different reaction systems,H2O2 concentration,Na2S2O8 concentration,molar ratio of H2O2 to Na2S2O8,reaction temperature,initial pH,NO concentration,O2 concentration,on the removal efficiency of NO were investigated.The results indicated that,the combination of Na2S2O8 and H2O2 had a significant synergistic effect on NO removal.With the increase of H2O2 concentration and Na2S2O8 concentration,NO removal efficiency increased at first and then became stable gradually.The optimal molar ratio of H2O2 to Na2S2O8 was 0.3:0.1 mol/mol.The optimum temperature for the wet oxidation and absorption of NOx with dual oxidant(H2O2/S2O82-)solution was 50?.With the increase of pH,NO removal efficiency increased at first,and then decreased,and then increased again.NO removal efficiency decreased with the increase of NO concentration.NO removal efficiency increased with the increase of O2 concentration.Five groups of parallel experiments were carried out under the conditions of Na2S2O8 concentration of 0.1 mol/L.H2O2 conc,entration of 1%?reaction temperature of 50 ??solution initial pH of 11?flue gas flow rate of 1500 mL/min?O2 concentration of 0%and NO concentration of 550 ppm,the results showed that the experimental results had good reproducibility and reliability.(2)Response surface methodology(RSM)based on Box-Behnken statistical experiment design(BBD)was used for the parameter optimization study of wet oxidation and absorption process of NOx with dual oxidant(H2O2/S2O82-)solution.The second order polynomial models of NO removal efficiency and NO absorption rate were obtained to describe the relationship between the operation conditions and the responses.The effect of temperature on the NO removal efficiency and NO absorption rate was most significant,followed by pH and Na2S2Os/H2O2 molar ratio.The interaction of temperature and pH was most significant.The results of analysis of variance(ANOVA)concluded that the accurate and reliable models were obtained to analyze the varibles of wet denitration process by dual oxidant(H2O2/S2O82-)thermal excitation system.Under the obtained optimum conditions of pH(a value of 11),temperature(50 ?)and Na2S2O8/H2O2 molar ratio(a value of 0.005),NO removal efficiency of 78.68%and NO absorption rate of 7.58E-07 mol/m2·s were observed respectively.(3)The main free radicals existed in the wet oxidation and absorption process of NOx with dual oxidant(H2O2/S2O82-)solution were SO4·-and ·OH by the free radical qualitative detection method.The study of radical scavenging method further verified that the roles of free radicals in the wet oxidation and absorption process of NOx with dual oxidant(H2O2/S2O82-)solution were different with the different of pH.The final ionic products were analyzed by ion chromatography.Combined with N material balance,NO3-and SO42-were the final ionic product in spent reaction solution.A plausible reaction pathway for the wet oxidation and absorption process of NOx with dual oxidant(H2O2/S2O82-)solution was essentially the reaction process of NO oxidation and absorption with free radicals generated from the free radicals chain reactions.(4)The thermodynamic parameters of the wet oxidation and absorption process of NOx with dual oxidant(H2O2/S2O82-)solution under different reaction temperature,such as chemical reaction enthalpy change?chemical reaction gibbs function?chemical reaction equilibrium constant and NO gas partial pressure,were calculated and analyzed for the first time,the results of the thermodynamics calculation verified that wet oxidation and absorption process of NOx by using dual oxidant(H2O2/S2O82-)solution was feasible.(5)The effects of different reaction conditions such as different reaction systems,H2O2 concentration,Na2S2O8 concentration,gas flow rate,initial pH,NO concentration,and O2 concentration,on the rate of NO absorption were investigated.The results showed that,the combination of Na2S2O8 and H2O2 had a significant synergistic effect on NO absorption.With the increase of H2O2 concentration?Na2S2O8 concentration and reaction temperature,NO absorption rate increased at first and then became stable gradually.With the increase of pH,NO absorption rate increased at first,and then decreased,and then increased again.NO absorption rate increased slightly with the increase in O2 concentration.NO absorption rate increased linearly with the increase in NO concentration and gas flow rate.On basis of kinetic theory and two-film theory,the mass transfer-reaction kinetics model of NO absorption was established.The NO reaction order was measured.The mass transfer-reaction process of NO absorption was discussed.The effective reinforcement measures for NO absorption process were proposed.The results showed that,the wet oxidation and absorption process of NOx with dual oxidant(H2O2/S2O82-)solution was a fast pseudo-first order reaction.The NO absorption rate equation and pseudo-first order reaction rate constant correlation empirical equation under different reaction conditions can be used to simulation the mass transfer-reaction process of NO absorption.Improving chemical reaction conditions and NO gas partial pressure can strengthen the NO absorption rate.