Preparation Of SCR Catalyst For Flue Gas Denitrification In Thermal Power Plant And Its Catalytic Performance

A large amount of nitrogen oxides(NOx) in flue gas discharged from thermal power plants seriously polluted the environmental atmosphere, so the NOx-removing techologies have been focused on by all countries’ governments and scientific researchers. Among these, selective catalytic reduction(SCR) was considered as the best technology by using V2O5-WO3/TiO2 as catalyst, where NH3 reduced NOx to nitrogen and water, and achieved good NOx removal efficiency and stable operation conditions. However, the performance of the TiO2 support crucially influenced SCR reactivity, and simulated flue gas generally used in the literatures led to large deviations from actual NOx removal efficiency. In order to develop high efficient and cheap SCR catalyst and thereby laying the foundation for its application in domestic industries, the preparation of TiO2 aerogels by sol-gel and atmospheric drying method, and the influence rules of the preparation parameters and reaction conditions for the NOx removal efficiency were investigated on the own designed and built SCR experimental platform in this paper.Cheaper compound titanium tetrachloride as precursor, organic ligand propionic acid as hydrolysis speed-reducing agent, formamide as drying control additive, epoxy propane as coagulant, Ti O2 aerogels support was firstly prepared by sol-gel and ambient pressure drying method with orthogonal experimental design, and then characterized by XRD, TEM, SAXS and FT-IR. The results showed that: TiO2 aerogels achieved the specific surface area of 632.87m2/g, average pore size of 7.87 nm and pore volume of 1.24 cm3/g with the ratio of n(TiCl4) : n(deionized water) : n(formamide) : n(propionic acid) : n(propylene oxide) at 1:14:2:0.5:10; the crystallinity of TiO2 gradually enhanced with increasing calcination temperature, the weak characteristic peaks of rutile appeared until 900 oC, indicating good thermal stability of the prepared samples; TiO2 aerogels support should be calcinated at 700 oC based on the calculation of gyration radius and the XRD patterns of TiO2.Based on the above optimized TiO2 aerogels support, SCR catalysts were prepared by orthogonal design experiment with different key preparation parameters such as active component amount, load sequence and calcination temperature, and then characterized by XRD and TPR, finally NOx removal performance was evaluated on the own designed and built SCR experimental platform between the temperature range from 300 to 390 oC. The results showed that: most catalysts’ active components of vanadium and tungsten oxides well dispersed on the surface of the support with non-crystalline form; the more of V2O5 main active components was loaded, the higher NO removal efficiency was obtained; 400 oC of calcination temperature was advantageous both to form the proper crystal phase required by catalytic reaction, and to maintain the higher specific surface area of catalyst; the activity of the catalyst at low and high temperature related to the surface enrichment and components interaction, the interaction among the active components and the support significantly influenced the low-temperature denitration activity at 315 oC, tungsten oxide loaded after vanadium oxide was the proper load sequence, surface enrichment was the main reason for the high-temperature denitration activity at 390 oC, vanadium and tungsten oxides should be loaded at the same time or vanadium oxide loaded after tungsten oxide; with increasing WO3/V2O5 ratio, the highest denitration efficiency obtained at 7.5:1, then decreased rapidly, so that 6% loading amount of WO3 was appropriate. The optimal catalyst was prepared with the parameters of 0.8% V2O5 and 6% WO3 amount, tungsten oxide loaded after vanadium oxide and 400 oC calcination temperature, and then achieved 69.56% of verification denitriation activity at the low-temperature of 315 oC.