The Research And Development Of Low Temperature SCR Catalyst After Sintering Flue Gas Semi-dry Desulphurization

Selective catalytic reduction (SCR) is one of the most effective ways to remove NOx in gaseous emissions, but the expensive heat exchanger obviously does not apply to the characteristics of sintering flue gas nor the development situation of iron and steel industry at the present stage in China. Therefore, more and more researchers tend to focus on the development of low temperature SCR process, which hasn’t yet reach the levels of industrial application. It’s a better choice to locate the SCR reactors upstream the semi-dry desulfurizer, which aims at preventing reheating of the flue gas. However, this set-up renders the catalyst susceptible to be deactivated from high concentrations of SO2and dust. As a result, acquisition of higher SCR activity and good resistance to H2O and SO2becomes the key factor to break through the barriers of industrial application at low temperatures(less than200℃). To solve the problems above, a series of Mn/TiO2, Mn/TiO2-ZrO2, Mn/TiO2-GO (GE) catalysts with addition of Ce, Fe were prepared in this work. The SCR activity and the effects of H2O and SO2in flue gases on the activity of the catalysts for low temperature SCR of NOx with NH3were systematically investigated at a high space velocity in laboratory.Firstly, two kinds of preparation methods of TiO2, TiO2-ZrO2supports and two loading methods of active components were conducted and compared, which brought the result that the sol-gel and ultrasonic impregnation methods were more adaptive in this experiment respectively. Then the low temperature SCR activities were analyzed through related characterizations, and the TiO2-ZrO2(3:l)(molar ratio) and TiO2-GO (GE)(125:1)(mass ratio) were determined to be the best proportions of the supports. With the help of activity test and related characterizations, SCR activity and selectivities of Mn-added catalysts with different ratios were detected and compared, and the results showed that the best SCR activities of9%Mn/TiO2-GO(125:1) and7%Mn/TiO2-GE(125:1)(new types of SCR catalysts) reached94.89%and92.79%respectively, with the N2selectivities over95%. It could be deduced that the presence of stoichiometric MnOx/Mn was also the reason of the elevation of low temperature activities.In the next studies, influences of cocatalysts (Ce and Fe) on low temperature activity and N2selectivities were researched. And the results indicated that doping of the cocatalysts led to the enhancement of SCR activity and maintenance of high N2selectivity. Analysis suggested that the addition of Ce could improve the oxygen storage capacity of the catalyst, which brought about the existance of metal oxides on the surface of the catalyst with various valences, and promote the redox reaction, then improve the low temperature activity of the catalyst ultimately; while introduction of Fe could also enrich the phase types of active components, and promote the catalytic activity slightly. In this study, Fe-Ce-Mn/TiO2-GO (GE)(125:1) turned to perform high N2selectivity and the best catalytic activity at low temperatures.In addition, in view of the high humidity and high oxygen concentrations in sintering flue gas, and the residual SO2concentration after semi-desulphurization, the effects of operating parameters such as NH3/NO molar ratio, O2, H2O and SO2concentrations exerted on SCR activity of Mn-Ce/TiO2catalyst was investigated, with the purpose of providing detailed guidance for industrial application. In this step of research, catalyst resistance to H2O and SO2were studied detailedly and earnestly, and the results suggested that doping of GO (GE) played an important role in the processes of presulfurization and surface hydrophobization, and then enhanced the resistance to H2O and SO2of the catalyst greatly (for example Fe-Ce-Mn/TiO2-GO (GE)(125:1)), with the assistance of the sulfuric acid salinization of Fe.According to the achievements above, by doping of small amount GO (GE), the catalysts could achieve higher SCR activities with smaller loading of active components and then leads to lower prices of the SCR catalysts. So to speak, this work has provided reliable theoretical guidance for further research, improvement and industrial application of SCR catalysts.