Research On Effects Of Selenium In Coal-fired Flue Gas On SCR Denitrification Catalyst

As the focus of denitrification works shift from coal-fired power plant to other non-power industries in China,a large number of denitrification equipments will be installed to meet the requirement of ultra-low emission in future.Selective Catalytic Reduction(SCR)technology is the maturest denitrification technology in China,which is widely used in coal-fired power plants.However,the flue gas conditions in other industries are more complicated and variable.Thus it is significant to study the influence of different components in flue gas on the SCR catalyst under different working conditions.Various elements in coal-fired flue gas can lead to the deactivation of SCR catalyst,but rarely reaserches have been reported on selenium species.In this thesis,the effects of selenium species(Se,SeO2 and CaSeO3)on V2O5-WO3/TiO2 and V2O5-MoO3/TiO2 SCR denitration catalysts were investigated by catalytic activity test and a series of characterization methods.Results showed that selenium species could inhibit the activity of the catalyst,while the effects of Se and SeO2 to SCR catalyst were greater than that of CaSeO3.CaSeO3 mainly deactive the catalyst by physical poisoning,while Se and SeO2 could react with the active component to cause chemical poisoning.When tested above 250℃,the activity of the Se(SeO2)-doped catalysts was significantly inhibited.As for the V-W system catalyst,characterization results showed that Se could be oxidized by V2O5 to Se4+(Se02 and V,SeyO2)during the NH3-SCR reaction,while SeO2 could be reduced to Se by NH3.Se and SeO2 could deactivate the catalyst by reducing high-valent vanadium to affect the redox performance of the catalyst,and forming VxSeyO2 to destroy the active vanadium site.For the V-Mo system catalyst,since the MoO3 also responsed to the oxidation of Se,which would certainly protect the active component V2O5.With the sublimation of SeO2 during high temperature SCR reaction,the activity of catalyst would be partially recovered.However,since the residual Se4+ destroyed part of the active V2O5 sites,the poisoned catalyst could not be completely recovered.