Promotion Of NO Oxidation Through H₂O₂ Thermal Decomposition Using A Solid Surface

NO_xhas surpassed SO₂to become the largest polluting gas in China.In NO_xflue gas,NO content reaches more than 95%,and NO is difficult to be absorbed by wet desulfurization and denitrification.Therefore,in order to achieve denitration,the economical and efficient oxidation of NO is the key.H₂O₂thermal decomposition and direct oxidation,which directly injected H₂O₂into flue gas,avoids the disadvantages of secondary pollution and high initial investment caused by SCR,and is expected to become a new denitrification technology.·OH produced by the thermal decomposition of H₂O₂has strong oxidizing ability,and the final products of H₂O₂decomposition are water and oxygen,so no new pollutants will be generated.However,the current technology still has problems such as oxidation fluctuation,narrow temperature window,high energy consumption and low efficiency of H₂O₂atomization spray.Therefore,it is key to keep the method stable and high NO oxidation ratio over a large temperature range.In this paper,H₂O₂was sprayed on the surface of metal and zeolite,the hydrophilicity and high specific surface area were used to improve the H₂O₂evaporation rate,high and stable NO oxidation ratio was obtained.The problems of oxidation fluctuation,too narrow oxidation temperature window,high energy consumption and low efficiency of H₂O₂atomization spray method were solved.The H₂O₂solution concentration,H₂O₂:NO was also reduced while maintaining the oxidation ratio,making this study economical and safe.Finally,the effect of SO₂on NO oxidation was explored,the effect of tail liquid absorption and gas phase oxidation was analyzed.It pointed out the direction,advantages and disadvantages for the future thermal decomposition of H₂O₂combined with tail liquid absorption and simultaneous desulfurization and denitrification.Firstly,the rapid evaporation and decomposition of H₂O₂were the premise to improve the NO oxidation ratio.Oxidation fluctuations disappeared after adding to the metal surface.Stable and high NO oxidation ratio can be obtained at 300～500°C.The hydrophilicity helped H₂O₂to diffuse rapidly on the metal surface,reduced the thickness of the liquid film,increased the H₂O₂evaporation rate,and then increased the NO oxidation ratio.The metal surface was beneficial to catalyze the generation of·OH from H₂O₂and improved the NO oxidation ratio.When the temperature was lower than 300°C,the NO oxidation ratio increased with the increase of H₂O₂concentration.When the temperature was higher than300°C,the NO oxidation ratio increased slowly.Under the conditions of H₂O₂:NO=10,temperature of 400℃,2.5%H₂O₂concentration,the reaction showed high NO oxidation ratio and economic feasibility.When H₂O₂:NO<10,with the increase of H₂O₂:NO,NO oxidation ratio increased obviously.When H₂O₂:NO>10,the increase of NO oxidation ratio would be reduced due to the ineffective consumption of·OH.High and stable NO oxidation ratio can be obtained by increasing the NO initial concentration.When the temperature was higher than 300°C,the type of metal surface had no significant effect on the NO oxidation rate,steel 201 was the best material among the four materials.The inclination angleθof the metal surface significantly affected the NO oxidation ratio and H₂O₂utilization.Whenθwas0°,the NO oxidation process did not fluctuate.¹O₂and O₂did not interfere with the NO oxidation ratio in the system.Secondly,the oxidation fluctuation disappeared after the addition of zeolite surface,NO oxidation ratio increased greatly.The hydrophilic structure,pore structure and large specific surface area of zeolite can promote the diffusion of H₂O₂on the surface of zeolite,the rapid spread of droplets can improve the H₂O₂evaporation rate.The highest NO oxidation ratio was81.8%after using synthetic mordenite.Synthesis of mordenite more specific surface area,was22 times of green zeolite.Due to the unique porous structure of synthetic mordenite,the reaction speed was greatly improved,the NO oxidation ratio was higher.The rationality of zeolite selection depended on the abundance of pore size.Zeolite with multiple pore sizes was more suitable.When the temperature increased,H₂O molecules and other impurities attached in the pore structure of zeolite could be effectively removed to provide more active sites,increased pore volume and specific surface area,improved the H₂O₂evaporation rate.The higher H₂O₂concentration,the higher NO oxidation ratio.The NO oxidation ratio increased with the increase of NO concentration,and the NO oxidation ratio increased with the increase of H₂O₂:NO.The main product of NO oxidation reaction was NO₂,·OH was proved to play a major role in the reaction.In the last chapter,the influence of SO₂on the system was analyzed.When the tail liquid was not added,NO oxidation ratio decreased with the increase of SO₂concentration.When the SO₂concentration was 400 mg/m³,the NO oxidation ratio decreased to 20%,the SO₂oxidation ratio increased slowly with the increase of SO₂concentration,gradually increasing from 10%to 21%.Both H₂O₂and·OH in the system can oxidize SO₂.With the increasing concentration of SO₂,SO₂and NO formed a strong competition,especially when the concentration of SO₂exceeded 100 mg/m³.·OH had a higher reaction rate with NO than that with SO₂.Compared with the NO oxidation ratio without SO₂,the NO oxidation ratio decreased seriously.When the concentration of SO₂was much lower than that of NO,the SO₂oxidation ratio changed little with the increase of H₂O₂concentration.This indicated that in the system,the oxidative competitiveness of SO₂was less than that of NO,while the NO oxidation ratio increased greatly with the increase of H₂O₂concentration.When the concentration of SO₂was much lower than that of NO,the SO₂oxidation ratio did not increase significantly with the increase of H₂O₂:NO,while the NO oxidation ratio was on the contrary.Only by increasing the initial concentration of NO and decreasing the concentration of SO₂could the interference of SO₂on the oxidation ratio of NO be reduced to the greatest extent.The absorptivity of Na OH to SO₂and NO did not change significantly whether it was absorbed simultaneously or separately.There was NO oxidation competition between SO₂and NO in Na OH solution.As long as enough Na OH was maintained,efficient desulfurization can be achieved.Compared with the experiment without Na OH tail solution absorption,most of SO₂was absorbed by Na OH after Na OH tail solution absorption.Combined with the results of single absorption,the NO oxidation in this system was almost all completed by the thermal decomposition of H₂O₂,which was exactly the opposite of the oxidation process of SO₂.