| Coal is the primary energy in China, mainly for combustion. Large emission of NOx, dust and SO2due to coal combustion damage the environment and the health of human. Technologies of the desulfurization have been widely used during "Eleventh-Five Plan" which has a great advancement. However, controlling of NOx pollutants was ignored in the past, leads to serious pollution duo to the large emission of NOx. Measures on reducing of NOx pollutants will be starting during "Twelve-Five Plan".The overseas practice proves that selective catalytic reduction (SCR) of NO by NH3which is based on V2O5/TiO2catalyst has been widely used due to high efficiency and high selectivity. However, practical operation of catalyst at thermal power plants has showed that dusts from flue gas could poison and abrade catalyst, leading to a deactivation of catalyst, so that catalyst life is always3years. Researchers have achieved certain results on the deactivation of V2O5/TiO2catalyst by alkali metal, in order to extend the life of catalyst and reduce operating costs. Predecessors always simulate the deactivation of catalyst by doping alkali metal from impregnation method and get the poisoning mechanism through short-term activity test. However, deactivation of V2O5/TiO2catalyst is a complex process; it could not be explained clearly by just only impregnation method. In view of this, this paper proposes to do a research about the effect of SO2on catalyst deactivation by alkali metal, and the effect of alkali metal poisoning degree to catalyst by impregnation method (marked Imp), alkali metal sublimation deposition method (marked Sub) and calcination of mixed catalyst with alkali metal-diffusion method (marked Dif). Deeply analyzed the change of catalyst’s pore structure and chemical forms, studied the real poisoning way and essence of deactivated catalyst. The main conclusions are as follows:(1) The poisoning degree of alkali metal on catalyst is different while the flue gas contains SO2or not. SO2will bring more obvious deactivation of catalyst and make Ti sulfide.(2) SO2will take an interaction with alkali metal on active center V during SCR activity test. It will lead to a chemical structure change of V and a formation of eutectic whose melting point is lower than SCR operating temperature. The formation of eutectic can alter the physical structure of the catalyst, reducing the specific surface area and pore volume of the catalyst, resulting in decreased activity of SCR.(3) The poisoning effects of three ways are in different degrees, there is a exponential relationship between SCR activity and specific surface area. The poisoning capacity from strong to weak is as followed:Sublimation method>> Diffusion method> Impregnation method.The poisoning degree of diffusion method on catalyst is close to industrial fact, and the poisoning degree of impregnation method on catalyst is lower.(4) The deactivation of sublimation method on catalyst is mainly because of decreased pore volume and decreased adsorption of NH3due to the formation of K-V eutectic; the deactivation of diffusion method on catalyst is mainly because of decreased surface acidity and increased surface oxidative activity; the difference between diffusion method and impregnation method on deactivation of catalyst is mainly because of different pore structure and surface oxidative activity.(5) Water-soluble of V changes little after activity test with SO2. |
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