The Optimization Study On Denitration Performance Of SCR Catalyst Based On Red Mud

Nitrogen oxides(NOx)is one of the major atmospheric pollutants in China,posing a serious threat to the ecological environment and human health.The state's latest 13th "Five-Year plan" clearly sets out the binding indicators that NOx emissions reduced by 15%in 2020 compared to 2015.Confronting with huge environmental protection pressure and strict emission target,NH3-SCR technology is still the mainstream NO.,removal technology adopted by coal-fired power plants in China.Catalyst is the core of SCR technology.Currently,the widely used V2O5-WO3/TiO2 catalysts have such problems as high cost,narrow temperature window,secondary pollution caused by V2O5 and its application prospects are limited.It is pressing to develop a new kind of cheap,efficient and environmentally-friendly SCR catalysts with wide temperature windows to replace V2O5-WO3/TiO2 catalyst.Red mud is a polluting waste discharged from production of alumina,whose comprehensive utilization has become a worldwide problem that needs to be solved.It is found that Bayer red mud has great potential for application in the field of SCR.In this study,the Bayer red mud of Shandong Aluminum Industry was used as raw material.On the basis of pre-activation treatments,different kinds of metal oxides were utilized to improve the SCR performance of catalyst.The optimal modified component Ce and the best Ce loading amount were determined.The optimized modification mechanism of Ce denitrification performance of red mud catalyst was also revealed.The effects of calcination temperature and ultrasonic treatment on the denitrification characteristics of Ce-modified red mud catalyst were investigated.What's more,the influence of reaction conditions on denitration characteristics was discussed and the industrial operating parameters were recommended.In the end,an inexpensive,efficient and environmentally-friendly SCR catalyst with wide temperature window has been developed.The main conclusions are as follows:(1)The bayer red mud of Shandong Aluminum Industry selected in this study has the potential to be applied in SCR field,but the catalytic activity of original red mud is poor,and it needs to be further modified and activated.Acid pickling and calcination is the best pre-activation method for the original red mud.Acid pickling and calcination treatment significantly reduces the the content of alkali metal and enhance internal channel connectivity.Pore volume and specific surface area are also increased.All of those are benifical for NH3-SCR reaction.The denitration activity of the ARM catalyst obtained after pickling and calcination treatment was greatly improved,and the highest conversion rate of NOx was 63.38%,which was 53.23%higher than that of the original red mud.Under the experimental conditions,the nitric acid was the most suitable acid species in acid pickling.(2)Based on the above studies,the effect of Zr,Cr,Cu and Ce components on the activity of red mud were investigated respectively.It is found that Ce component has the best optimization effect.The loading of Ce reduces the crystallinity of ?-Fe2O3 and improves the pore structure on the surface.Pore volume and specific surface area are increased.Acid sites on the catalyst surface is significantly increased which can provide more active reaction sites for the SCR reaction.All above are benifical to the improvment of red mud catalyst activity.The optimal loading of Ce is 10%.The highest NOx conversion rate of 10%Ce/ARM catalyst is 100%,the activation temperature T50 is 137.8? lower than ARM,and the denitration temperature windows is 248.4?407.8?.(3)As the calcination temperature increases,the denitration temperature window of catalyst shifts toward the high temperature range.When the calcination temperature is lower than 500?,the excessive surface oxygen concentration leads to oxidation of NH3 to NO,which narrows the denitration temperature window of the catalyst.When the calcination temperature is higher than 500?,the pore structure begins to deteriorate and the mass transfer resistance increases,which is not conducive to the SCR reaction.The catalyst calcinated at 500? has the widest denitration activity range(248.4-407.8?)and thus 500? is selected as the optimal calcination temperature.(4)Ultrasonic treatment improves the medium and low temperature catalytic activity of Ce modified red mud catalys and the catalyst treated by ultrasonic for 30min has the widest temperature windows(237.4-402.8?).The research shows that the introduction of ultrasonic treatment plays a role in refining grains and increasing the specific surface area and pore volume.The research on denitration characteristics of the catalyst in different operating conditions shows that the recommended catalyst operation O2 concentration of 3%,NH3/NO ratio of 1,and the catalyst had good O2 transient response characteristics and NH3 adsorption characteristics.