Experimental Study On The Low-temperature Denitration Via Enabling Fast SCR Reaction By NO Partial Oxidation

The selective catalytic reduction denitrification technology（NH₃-SCR）using ammonia as the reducing agent is the mainstream nitrogen oxide（NO_x）removal technology in the current thermal power industry.The existing SCR denitration system requires the reaction temperature to be higher than 300°C to achieve its high denitration activity.However,when the temperature is lower than 280°C,the reaction activity of the catalyst is greatly reduced,which cannot meet the demand for high-efficiency denitration of the SCR system.In recent years,my country’s industrial fixed-source nitrogen oxide emission reduction focus has gradually shifted from coal-fired power plants to industrial boilers/kilns and other non-electric industries,and the exhaust gas temperature is generally lower than the work temperature of the existing SCR system for efficient operation.The Fast SCR reaction that occurs in the flue gas in the presence of NO₂ can improve the low-temperature denitration efficiency of the SCR system,and reaches the highest when the molar ratio of NO₂ to NO is 1:1.However,the production of NO₂ in the Fast SCR denitrification system is still a key problem to be solved urgently,which limits its realization of large-scale industrial applications.Therefore,this article focuses on the research on the source of NO₂ in the rapid SCR denitration system.First,a pre-oxidation reactor was designed at the front of the SCR denitrification system,and then the oxidation effects of two methods,homogeneous oxidation and heterogeneous catalytic oxidation,on part of NO in the flue gas were studied,and finally combined with the down-stream SCR system to obtain low-temperature flue gas conditions Under stable denitration effect.Based on the above research content,the main conclusions obtained in the full text are as follows.1.The homogeneous oxidation process of NO in the front-end pre-oxidation reactor was studied,and it was found that H₂O₂ has an excellent ability to oxidize NO,and its addition significantly improves the oxidation efficiency of NO.The experimental results show that when the molar ratio of H₂O₂ to NO is 1/1,the NO oxidation efficiency can reach 60%at 200°C,and when the molar ratio of H₂O₂ to NO is increased from 1/1 to 4/1,NO The oxidation efficiency is increased from 60%to 77%.When the molar ratio of H₂O₂ to NO is 0.5/1,the oxidation efficiency of NO can still reach about 40%at 200°C.In addition,the front-end pre-oxidation system and the back-end SCR system are combined to study the denitration performance,stability and selectivity of this composite system.It is found that the low temperature denitration performance of the composite system is significantly better than that of the independent SCR system.The activity test results show that after the establishment of the composite system,when the molar ratio of H₂O₂ to NO is 1/1,the NO_x conversion rate at 200°C is increased from 20%to 67%.And the N₂ selectivity of the catalyst remains above 99%in the temperature range of 200-350℃.2.The catalytic oxidation process of NO in the up-front pre-oxidation reactor was studied,and it was found that the method of catalytic oxidation using Co₃O₄/TiO₂catalyst can obtain higher NO oxidation efficiency.The experimental results show that when the active component Co₃O₄ loading is 3 wt.%,the oxidation rate of NO can reach34%at 280°C,and the active component Co₃O₄ loading is increased from 3 wt.%to 7wt.%,the oxidation rate of NO increases from 34%to 49%.In addition,the denitration efficiency and stability of the composite system were investigated,and it was found that the effect of the up-front Co₃O₄/TiO₂ catalyst on the catalytic oxidation of NO can significantly improve the denitrification efficiency of the back-end SCR reaction.The activity test results show that when the Co₃O₄ loading is 7 wt.%,the denitration efficiency of the composite system at 250°C increases from 40%to 82%.Finally,using XRD,SEM-EDS and other catalyst characterization methods,the Co₃O₄/TiO₂ catalyst was studied.It is found that the active component Co₃O₄ has better dispersion on the surface of the catalyst,which provides relatively more active centers for the catalytic oxidation reaction of NO,and improves the oxidation efficiency of NO.3.Based on the above research,we propose a combination of economical and high-efficiency flue gas pre-oxidation combined with SCR to synergistically remove NOx in flue gas,which can perform conventional selective catalytic reduction at high temperatures（>300℃）（SCR）reaction,the up-front pre-oxidation reactor can be used to pre-condition the flue gas below 300℃ to form a fast SCR reaction on the surface of the catalyst,and finally achieve the goal of stable denitration of flue gas in a wide temperature range with"high and low temperature mode switchable".