Experimental Study On The Synergistic Removal Of NO And VOCs From Coal-fired Flue Gas With Modified SCR Catalyst

In recent decades,with the rapid development of China's social and economic construction,energy demand and consumption are also growing rapidly.China's energy is characterized by"rich coal,poor oil and poor gas".Coal has long been in the dominant position in China's energy structure.With the development of economy and the increase of coal consumption,China's air pollution presents an increasingly severe trend.In the process of coal-fired power generation,conventional pollutants such as nitrogen oxide(NOx),sulfur dioxide(SO₂)prevention and control have clear governance policies and regulations,which have been the power plant must-control pollutants.However,there are no clear laws or regulations on the emission of volatile organic compounds(VOCs)in the process of coal combustion.VOCs have strong irritation and toxicity,and can cause significant harm to human health and ecological environment even at small doses.Under the trend of more and more stringent environmental protection requirements,the emission requirements of VOCs in the process of coal combustion will be put on the agenda in the future.At the same time,with the improvement of air pollution control policy,multi pollutant collaborative control technology may replace the status quo of single pollutant control in the future,and become an important means of industrial pollutant emission.In this paper,the traditional V-W/Ti type catalysts was modified and prepared to achieve the synergistic removal of NOx and VOCs in the SCR denitration area(temperature range 260?420?).Emission of VOCs from coal combustion process is characterized by large quantity and variety.In this study,representative benzene and toluene were selected as the typical VOCs research objects,and an experimental platform was built to simulate the denitration area of coal-fired flue gas.In the process of multi-faceted elaboration of catalyst modification and collaborative experiment,the final obtained optimal modified catalyst can achieve 80%NOx removal rate and 90%VOCs removal rate.(1)Based on the traditional V-W/Ti SCR catalysts,by wet impregnation method,different loading amount of Ce O₂(0–17.5 wt%)or Mo O₃(3–7.5 wt%)and different calcination temperature(400–600°C)during catalyst preparation were investigated.Results showed that 10.75 wt%Ce O₂ loading as well as 4.5 wt%Mo O₃ loading on V-W/Ti catalyst calcinated at 500°C represented the best simultaneous removal effect of NO,benzene and toluene.(2)On the basis of research stage(1),the best calcination temperature and the better cerium supported SCR catalyst were selected to modify Ce O₂-V₂O₅-WO₃/Ti O₂ based SCR catalyst by using transition metals(Cr,Mn,Fe,Co,Ni or Cu)respectively,which were used to remove NOx and VOCs in the process of coal-fired power generation.Through the self-built experimental system,the factors affecting the removal of NOx and VOCs in the modified catalyst were studied.The results show that the synergistic removal rate of the catalyst is obviously improved after the transition metal was introduced.The reasons for the improvement of the performance of transition metal modified catalysts were discussed by XRD,SEM-EDS,TGA,XPS,NH₃-TPD and in-situ DRIFTs analyses.Among all prepared catalysts,Ce O₂-V₂O₅-WO₃/Ti O₂ catalyst modified by Cu performed the best NO removal efficiency,which could reach 89.9%of NO removal efficiencies when reacted at 380°C and average 87.6%of NO removal efficiencies during SCR temperature window(260-420°C).Cu or Fe modified Ce-V-W/Ti type catalyst obtained the optimal VOCs removal efficiencies.Over average 97.1%of benzene and 92.7%of toluene could be removed.From the results of comprehensive evaluations,Fe and Cu were more suitable for V-W-Ce/Ti-based SCR catalysts modification than Cr,Mn,Co and Ni.In-situ DRIFT analysis found that intermediate products of N=O group and benzaldehyde were generated during the reaction.(3)Transition metal modification of cerium-molybdenum modified SCR catalyst was studied to explore the synergistic removal of NOx and VOCs performance of V-W/Ti type SCR catalyst modified.The experimental results showed that the performance of NO and VOCs removal of V-W/Ti SCR catalyst modified by Ce,Mo and transition metals(Cr,Mn,Fe,Co,Ni or Cu)is not as good as that of single metal modified or bimetallic catalysts modified catalyst.The results show that excessive metal loading was not conducive to the performance of V₂O₅-WO₃/Ti O₂ catalyst.(4)In addition,Ce modified SCR catalysts with different Ce loading and calcination temperature were prepared by sol-gel method.The properties of Ce modified SCR catalysts for synergistic removal of NO and VOCs were studied.The effects of cerium loading and calcination temperature on the surface properties,adsorption performance,physical structure,valence and acid sites of the catalysts were investigated by nitrogen adsorption and desorption,SEM-EDS,XRD,XPS and NH₃-TPD characterization analyses.In addition,the structure optimization of V-W/Ti SCR catalyst modified with Ce was studied by software simulation.Among catalysts of Ce?-V-W/Ti-?(?=0,0.025,0.05 and 0.1 in molar ratio;?=calcination temperature of 400,500 and 600°C),Ce0.05-V-W/Ti-500 presented optimal physicochemical properties which had more pore structure,larger specific surface area,higher components dispersion and better redox ability.Ce0.05-V-W/Ti-500 could reach 92.5%NO removal efficiency,97.3%benzene and 99.4%toluene removal efficiency when at 380°C reaction temperature.This study provides a preliminary research basis for the development of SCR catalysts with high efficiency and synergistic removal of NO and VOCs in the field of clean coal combustion.