Experimental Study On Low Temperature SCR Denitrification Of Sintering Flue Gas Based On Carbon-based Catalysts

The flue gas produced in the sintering process of iron and steel plants contains a large amount of nitrogen oxides,which will cause serious harm to the ecological environment.How to effectively control nitrogen oxides in sintering flue gas has become an important issue in environmental protection.For sintering flue gas denitrification,selective catalytic reduction(SCR)with end layout can avoid the toxicity of dust and SO2 to catalysts,which is easy to match with the existing wet FGD Systemn and has a promising application prospect.However,the flue gas after ESP and wet FGD will be cooled down to 45～100℃,which means that the flue gas needs to be heated to above 300℃ to meet the use requirements of the vanadium-based denitrification catalyst(NH3-SCR),resulting in huge energy loss.In addition,ammonia escape and other secondary pollution phenomena also exist in NH3-SCR.Urea,with its high low-temperature activity,large reduction capacity,convenient storage and transportation,and no secondary pollution,is a good low-temperature SCR reducing agent.Therefore,in this paper,carbon-based catalysts were prepared by loading active ingredients(transition metals and urea)on cheap activated carbon.The denitrification activity and modification of urea-SCR catalyst at low temperature were studied by means of denitrification experiments and characterization methods(SEM、XRD、BET、XPS、GFASS、FT-IR).Firstly,the adsorption performance of nu-AC for NO was studied at low temperature(50～100℃).The results showed that activated carbon showed only adsorption capacity for NO at low temperature,and the adsorption saturation time was inversely proportional to temperature.The maximum adsorption saturation time was 23 minutes at 50℃.Then,ureaMnOx/AC catalyst was prepared by loading transition metal Mn oxides and urea on the surface of activated carbon.The denitrification activity of urea-MnOx/AC catalyst at low temperature was investigated.The optimum preparation parameters of urea-MnOx/AC were obtained:nu-AC,particle size of 100～200 mesh,urea loading of 6%,active metal oxide loading of 12%.Secondly,the denitrification activity of 6urea-12MOx/AC catalyst at low temperature was studied.It was found that the denitrification efficiency of seven catalysts decreased with the increase of reaction temperature.The order of denitrification activity of seven metals at low temperature was:Cu>Mn>Co>Ni>Cr>Fe>Zn.Then 6urea-12(aCuOx-bMnOx)/nu-AC composite catalyst was prepared,and its low temperature activity was studied.The optimum impregnation ratio of CuOx and MnOx was 0.5:0.5,and the optimum calcination temperature was 500℃.The optimum composite catalyst can maintain 100%denitrification efficiency for 6 hours at 100℃.The surface physical structure parameters and catalytic activity of the optimum composite catalyst are better than those of CuOx and MnOx supported alone.The synergistic effect between CuOx and MnOx can improve the denitrification reaction rate.Finally,the modification of the optimum composite catalyst were studied at 100℃.The following results were obtained:Modification with K(3%KOH)can not only improve catalyst SO2 tolerance,but also greatly improve catalyst denitrification activity.The modified catalyst can maintain 100%denitrification efficiency for up to 10 hours.The negative effect of SO2 on the denitrification activity of the modified catalyst is not completely proportional to the concentration of SO2,but tends to be flat with the increase of the concentration.Compared with the non-regenerated catalyst,the catalyst with re-loaded urea has little reduction in denitrification efficiency,which indicates that the catalyst can be regenerated and recycled continuously.