低温磁性铁基SCR烟气脱硝的实验研究

在流化床反应器中,以磁性铁氧化物(Fe3O4、γ-Fe2O3)颗粒为床料,氨为还原剂,进行了中低温SCR烟气脱硝实验研究,然后对反应辅加磁场,初步研究磁场对磁性γ-Fe2O3催化剂SCR脱硝的影响,并对床料进行了XRD分析.结果表明,Fe3O4的SCR活性较差,γ-Fe2O3的SCR活性较佳,在250℃其催化脱硝效率能达到90%,但在250℃以上Fe2O3会对氨的氧化起作用,因而在250℃及以下的邻近温度区间是最佳催化温度区间.此外,在150~290℃,外加磁场能促进γ-Fe2O3对NO的吸附,提高脱硝效率,使250℃时的脱硝效率达到95%左右,但在290℃以上,则会降低脱硝效率.为了抑制氨的氧化,发挥磁场对γ-Fe2O3脱硝的作用,适合在200~250℃低温区间内采用γ-Fe2O3催化剂进行SCR脱硝.

Experimental Studies on Low-temperature Selective Catalytic Reduction of NO on Magnetic Iron-based Catalysts

Low-temperature selective catalytic reduction (SCR) of NO is a new technique needing urgent development in flue gas cleaning. Elementary studies were done about selective catalytic reduction of NO from flue gas on magnetic iron oxides with ammonia at low and medium temperatures in a fluidized bed, such as Fe_3O_4 and γ-Fe_2O_3.Magnetic field effects for NO removal on γ-Fe_2O_3 were also researched with low assisted magnetic fileds. X-ray diffraction spectroscopy was used to identify and characterize the iron oxides catalysts. Results show that γ-Fe_2O_3 is active in SCR at low temperatures, and Fe_3O_4 is apparently less active in SCR than γ-Fe_2O_3,but Fe_2O_3 is also active in ammonia oxidation by O_2 above 250℃. Therefore, the optimal catalytic temperature zone in SCR on γ-Fe_2O_3 includes 250℃:and adjacent temperature zone below it. Furthermore, a better NO conversion, which is 90%,is obtained at 250℃ on the γ-Fe_2O_3 particle catalyst. In addition, chemisorption of NO on γ-Fe_2O_3 is accelerated by assisted magnetic fields at 150-290℃,thus the NO conversion is improved and higher NO removal efficiency of 95%is obtained at 250℃.But the efficiency of NO removal decreases above 290℃ with the magnetic field. It is concluded that γ-Fe_2O_3 catalyst is fit to be used in low-temperature SCR of NO with ammonia at 200-250℃,which may suppress oxidation of ammonia and take advantage of positive effects by external magnetic fields.