The Study Of Deactivation Mechanism And The Effect Of High-temperature Water Vapor On Commercial SCR Denitration Catalysts Used In Coal-fired Power Plant

Selective Catalytic Reduction(SCR)has become the most widely used flue gas denitration technology due to its high efficiency,maturity and no secondary pollution.The SCR flue gas denitration catalyst is the core of this technology,and its performance directly affects the denitration efficiency.Commercial SCR catalysts based on V2O5-WO3/TiO2 are commonly used in coal-fired power plants.The catalysts are not only costly but also have a limited lifetime.The activity of the catalyst will gradually decrease over time,and the service life is generally only 3 to 5 years.More importantly,the deactivated catalyst is a hazardous solid waste that requires strict disposal to avoid environmental pollution.Therefore,from either the economic or environmental point of view,it is necessary to conduct in-depth research on the deactivation and regeneration of SCR catalysts in coal-fired power plants,improve the economics of the technology,and reduce the generation of dangerous solid waste.This thesis mainly analyzes the reasons for the deactivation of vanadium-titanium commercial SCR flue gas denitration catalyst in coal-fired power plants and explores the effect of high-temperature steam on its performanceThis thesis focuses on the commercial and SCR flue gas denitration catalysts used in a 1000MW power generator of a coal-fired power plant in Zhejiang Province.The degree of the deactivation SCR denitration catalyst operating in the power plant for 40,000h were comprehensively analyzed.The activity of the catalyst was evaluated.SEM,Py-IR,BET,ICP-AES,XPS and TGA analysis were also performed to characterize the catalyst.This work has shown that the deactivation of the catalyst is the results of a combination of factors:(1)Poisoning due to As,K,S and Fe.The contents of these elements in the catalyst increased by 99.8%,199.3%233.3%and 318.0%,respectively;(2)Fly ash plugging of the catalyst surface pores.The sulfate deposition and the long-lasting high temperature reaction caused the sintering of the catalyst and the agglomeration of the particles,resulting in a decrease of 20.3%of the specific surface area of the deactivated SCR denitration catalyst compared with fresh catalyst;(3)The valence state changed of Vanadium element.The ratio of n(V4+)/n(V5+)decreased from 6.46 to 1.35,and the fraction of Lewis acid sites decreased by 34.2%.Through a high-temperature steam simulation experiment device made in-house,the effects of high-temperature steam on the activity of fresh and deactivated(Used for 40,000h)catalysts of the 1000MW power generator in the coal-fired power plant were investigated.Both the overall effects(0-20%)and the cumulative(0%,10%,15%and 20%)effects volume fraction of water vapor were investigated on the denitration performance of the deactivated catalyst.The SEM,BET,ICP-AES,Py-IR,XPS and other characterization methods were used to characterize the catalyst.Combined with DFT calculation,the microscopic mechanism of the influence of water vapor on the catalyst was examined as well.Furthermore,the conclusions from these analysis were further verified by evaluating the effects of water vapor on the fresh and deactivated(used for 30,000h)catalysts from a 660MW power generator in the coal-fired power plant.The results show that:(1)The high-temperature water vapor with a certain volume fraction had a significant regeneration effect on the deactivated SCR flue gas denitration catalyst.After the treatment with high-temperature water vapor(10?20%)for 15h,the denitration efficiency of the catalyst could be increased by 25?30%compared with the deactivated catalyst;(2)High-temperature water vapor could effectively remove Fe,Na,S elements and their compounds deposited on the surface of the deactivated catalyst,as well as SiO2 particles and sulfates covering or blocking the pores,reduce the agglomeration of TiO2,increase the specific surface area of the catalyst and improve its pore structure;(3)High-temperature water vapor could also improve the valence state of active component vanadium,increase the ratio of n(V4+)/n(V5+),restore the Lewis acid sites on the catalyst surface,and improve the denitrification activity of the deactivated catalyst.