Study On The Deactivation Mechanism And Optimization In Operation Management Over SCR Catalysts

Along with the demolition of its bypass system and the implementation of Near-Zero Emissions in China,the effects of the SCR(selective catalytic reduction)deNOx equipment on the safety and efficiency of thermal power plants is becoming more obvious.In this context,more insistent demands are put forward on the optimum operation in order to both improve the safety and efficiency of the SCR equipment as well as generating unit.Therefore,studies on the deactivation mechanism of ternary V2O5-WO3/TiO2 SCR catalyst installed in thermal power plants and the development of relevant technologies for optimization of SCR system and catalyst management are undertaken in this dissertation.A review of studies on the SCR technology and V2O5/TiO2 based SCR catalysts were undertaken first.Then the deactivation mechanism of ternary V2O5-WO3/TiO2 catalyst and the safe and economic operation of SCR equipments were investigated intensively and comprehensively focusing on the demands of Chinese thermal power plants.For this purpose,various methods were employed,such as the performance test of SCR equipments,the activity test and characterization of SCR catalysts,studies on the deactivation mechanism and kinetics of SCR catalysts,performance simulation of SCR reactors,simulation and evaluation of catalyst renewal schemes.A method system for the operation management of SCR catalysts and equipments was proposed based on the above research work,and was developed to meet the needs of thermal power industry in China.Furthermore,two comprehensive analysis systems were developed to supply supports for the optimization operation of SCR systems and catalyst management.Besides,a Client/Server structure-based system was designed for the LAN user.And A Browser/Server structure-based system was designed for the Internet user.Some advanced functions were developed in addition to the information management functions,such as prediction in the renewal period of SCR catalysts,type selection of commercial SCR catalysts,evaluation of catalyst renewal schemes,3-D simulation of SCR reactors.The research results showed that there is a great effect of catalyst type on its deactivation behavior.It was found that the deactivation of the corrugated-plate catalyst is mainly caused by loss of active materials and specific surface area due to fly ash abrasion and deposition,as well as alkali poisoning.However,the deactivation of the honeycomb catalyst is mainly caused by the concentration and poisoning of alkali metals.The mechanism underlying the deactivation of commercial V2O5-WO3/TiO2 catalysts after exposure to the flue gas of coal-fired power plants was investigated by a transient kinetic analysis that focused on the distinction between the deactivation behaviors of adsorption sites and redox sites.The results showed that alkali dopants preferentially poison the active sites associated with vanadium(V5+-OH or/and V5+?O)rather than the adsorption sites associated with titania and tungsten.It was also found that loss of V2O5 leads to the rise of activation energies for NH3 oxidation and SCR surface reaction.Alkali poisoning can leads to the decline of activation energy for NH3 desorption.In addition,slight sintering can leads to the decline of activation energies for NH3 oxidation and SCR surface reaction.The impacts of the decline in catalystic activity caused by the most popular deactivation type in coal-fired power plants were analyzed using the comprehensive analysis system.It was found that the NH3-DeNOx temperature window shifts to a higher temperature zone and the temperature of maximum efficiency point increases when the catalystic activity is reduced.The impacts of maldistribution of NH3 and gas flow on the performance of SCR reactors were also investigated.The maldistribution of NH3 and gas flow could enlarge the impacts of catalyst decay and the local NH3 slip.Thus the operating temperature window of SCR reactor and its safe amount of NH3 injection would be greatly reduced after the catalyst is decayed.The significant increase of local NH3 slip would increase the difficulty in accurate monitoring of DeNOx efficiency and NH3 slip.In conclusion,an entire methodology and technology for the catalyst management and optimization operation of SCR equipment was developed through above experimental and theoretical researches and the development of comprehensive analysis systems.In this way,the catalystic activity test,deactivation analyses,prediction of catalyst renewal,evaluation of catalyst renewal schemes,kintic study of NH3-DeNOx reaction and performance simulation of SCR reactor were integrated together with the the performance test of SCR equipments.These works are useful for improving the safety and economy of the SCR equipment as well as the generating unit.