Mechanism And Promotion Method Of Fe（Ⅱ）/Na₂SO₃ Complexation Denitration In The Presence Of O₂

It was found that the iron-based liquid phase complexation absorption of NO has the advantages of large absorption capacity,fast absorption rate and high denitration efficiency,which is a potential denitration method for flue gas.However,since the flue gas usually contains2%-8%O₂,the presence of O₂ seriously affects the presence of Fe²⁺,which in turn greatly reduces the efficiency of complexation and absorption of NO,hindering the application of complexation denitrification.Other researchers believe that the presence of O₂ in the iron-base complex system can promote the oxidation of NO,which is conducive to the improvement of denitrification efficiency.At the same time,the regeneration of Fe²⁺is another point that needs to be paid attention to in the ferrous complex system.Although there are many researches at present,appropriate methods still need to be explored.This study re-recognized the complexation and absorption of NO by O₂ in the Fe（Ⅱ）/Na₂SO₃ system,and proposed that O₂ acts on the system through three parts:direct oxidation of NO,complex consumption and advanced oxidation reaction.On this basis,the effect of O₂ on denitrification characteristics in Fe（Ⅱ）-EDTA/Na₂SO₃ system was analyzed in depth,and the complexation reaction mechanism of Fe（Ⅱ）-EDTA/Na₂SO₃ system in the presence of O₂ was revealed.On this basis,an improved system of Fe（Ⅱ）-EDTA/Na₂SO₃synergistic ascorbic acid was proposed.The effect of O₂ on the absorption of NO in the complex without chelating agent was studied from three aspects:direct oxidation of NO,consumption of complex reactants and advanced oxidation reaction.At 8%O₂,the concentration of Fe²⁺decreased by 66.99%,which had a great effect on the complex absorption of NO.Through the free radical capture experiment,it was found that in Fe（Ⅱ）/Na₂SO₃ complex system with the participation of oxygen,advanced oxidation reaction can produce SO₄^·-and·OH,and the production of free radicals can reduce the removal efficiency of NO by 10%.The quenching experiment found that·OH had a greater effect on NO removal.On the basis of obtaining the effect of O₂ in the system without chelating agent,the effect of O₂ on denitrification in the Fe（Ⅱ）-EDTA/Na₂SO₃ system was studied.By contrast,the effect of O₂ on the denitrification efficiency of NO direct oxidation,consumption of complex reactants and advanced oxidation under the two systems with or without EDTA addition was compared.Compared with the system without EDTA,the oxidation effect of O₂ on NO was weakened and the direct consumption of Fe²⁺was reduced.The addition of EDTA is beneficial for the production of SO₄^·-,and the advanced oxidation effect of Fe（Ⅱ）-EDTA/Na₂SO₃ system is significantly enhanced;At the same time,the presence of EDTA weakens the oxidation effect of O₂ on Fe²⁺,which is conducive to stable denitrification.In order to enhance the concentration of Fe²⁺in the system,a Fe（Ⅱ）-EDTA/Na₂SO₃synergistic ascorbic acid（VC）system was proposed to chelate and absorb NO.The optimal reaction conditions for Fe（Ⅱ）-EDTA/Na₂SO₃ synergistic VC system denitrification under 8%O2 were explored as follows:T=30℃,p H=8,[Na₂SO₃]₀=100 mmol·L^-1,[Fe SO₄]₀=10mmol·L^-1,[EDTA]=10 mmol·L^-1,[C₆H₈O₆]₀=1 g·L^-1,[NO]₀=300 mg·m^-3.Under these conditions,the denitrification efficiency of the system remained stable at over 50%,and compared to the system without VC,the removal efficiency increased by 20%.