Research On SCR Catalyst Preparation And Influence Factors Of De-NOx Performance

Selective catalytic reduction (SCR) gets wide applications in power plants at present and V2O5-WO3/TiO2 catalyst is the main catalyst of this technology. Research on the catalyst preparation technology has significant meanings for the localization of SCR catalyst,or the development of SCR catalysts with independent intellectual property rights in our country. This work, based on the de-NOx performance test that compared coal-fired boiler experiment with fixed-bed experiment, studied the preparation technology of V2O5-WO3/TiO2 catalyst for industrial apply with its deactivation and regeneration methods and physichemical tests and performance evaluation.The V2O5-WO3/TiO2 catalysts were made of different materials and by different methods respectively. Results of the fixed-bed performance experiment showed that, preparation methods hardly affected the catalyst de-NOx performance, but different types of titanium oxides had obvious effects on de-NOx efficiency. Staged dry and calcination procedure could better achieve the desired pore size distribution, surface area and porosity.It has been found that, when V2O5 loading content was constant, NOx conversion did not increase with WO3 addition. If the loading contents of V2O5 and WO3 went up to 2% and 10% from 1.6% and 8% respectively, there was no obvious improvement in de-NOx efficiency because of the changed morphology and surface coverage.The optimized recipe has been determined as 1.6% V2O5 with 8% WO3 dried at 80℃for 1 hour and 110℃for 1 hour, calcined at 250℃for 2 hours and at 450℃for 3 hours. Being tested under the condition of 40000 h-1 space velocity, NOx conversion approaches 100% in the temperature range of 250-450℃.Pore structure analysis showed that the appropriate pore distribution had been obtained. The observations of SEM and EDX showed that the optimized catalyst had the active components distributed in uniformed molecular conformation, which is the common characteristic shared by commercial catalysts. The existence of obvious Lewis and Bronsted acid sites on catalyst surface has been verified by DRIFT test. At actual gas condition of SV=3500h-1 and NH3/NOX=1, de-NOx efficiency of optimized catalyst module exceeded 84% between 300 and 400℃, which remained almost unchanged after 600 hours operation, indicating the module's good anti-poison capability and the mechanical strength.K2O on the surface of poisoned catalyst could be completely removed by 1% H2SO4 without changing the catalyst morphology and mechanical strength.The simulation on flue gas flow of the coal-fired boiler experiment showed that, the amendments on the geometry and arrangement of the guide vanes to improve the flow velocity distribution flue, reducing the maximum flow rate value, and make the velocity distribution in the catalyst reactor inlet homogeneous.The study on V2O5-WO3/TiO2 catalyst preparation technology showed that the optimized catalyst could satisfy the engineering application demands in power plants. This research will provide important supports to further research and improvement of SCR technology.