The Optimization Of Molded Low- Temperature SCR Catalysts NO_x Removal In Cement Kiln Flue Gas

NOx, as one of the main air pollutants, has seriously affected the environment in many respects. The selective catalytic reduction (SCR) process, which is an effective way to remove NOx from stationary sources, is of great significance for NOx emission control. China is the world’s largest producer of cement, and NOx emission from cement industry has been increasingly severe in recent years. As the emission standard becomes more and more strict, NOx control of cement industry would be imperative in the near future. However, the commercial high-temperature SCR technology is not very applicable to the flue gas from cement industry. Therefore, it is of great importance to develop low-temperature SCR de-NOx technique which can be adapted to the flue gas from cement kiln. At present, there are still a lot of problems to be solved before its real application, such as poisoning of H2O and SO2, deliquescence and poor mechanical strength. Based on this, the effects of supporter, active components and doping elements were investigated in this thesis and a pilot-scale testing system had also been conducted.Firstly, the effects of the supporter on H2O resistance and mechanical strength of catalysts were studied. The results showed that molecular sieve and TiO2 had the same effect on H2O resistance, while TiO2 was better for the enhancement of mechanical strength. And the catalyst with optimum dose of TiO2 showed good mechanical strength and the best activity in the humid flue gas at low-temperature. And then, the active components’ effects on H2O resistance and deliquescence of the catalysts were investigated via orthogonal experiments and the optimal components were obtained accordingly. Mna1Ceb1Fec2Zrd3 with 5×5 holes was chosen as the best catalyst after comparison of extreme difference of the orthogonal experiments. The NO removal rate of this catalyst could be kept stably at 82% after 27h running in the flue gas cantaining 8% H2O at 120℃.Furthermore, the effects of doping elements on the activitivities of catalysts in the humid flue gas which contained SO2 were investigated. A serious deactivation was detected on undoped catalysts in the flue gas containing both SO2 and H2O. It was proved that the deactivation was caused by the sulfation of both the supporter and the active phase and the deposition of the ammonium sulfate species which plugged the reaction channels and covered the active sites. Co doping could effectively inhibit the deposition of ammonium sulfate species and the sulfation of catalysts, resulting in the enhancement of SO2 tolerance.Finally, on the basis of laboratory study, a set of 10000m3/h pilot-scale SCR de-NOx sysrem was designed, including SCR reactor, flue gas system, ammonia supplier, ammonium preparation and injection system. The economic evaluation of this system was also evaluated, basing on the running cost.