| The emission and control of nitrogen oxides and mercury from coal combustion has attracted more and more attention in recent years.The coal fired power plants have been equipped with devices for desulfurization(WFGD)and denitrification(SCR),and it has been recognized as the most economic and efficient way to remove simultaneously mercury by means of WFGD and SCR.It has been proven that SCR catalysts can promote the oxidation of mercury along with reducing NO to N2,but the results are unsatisfactory,in addition,the operating temperature range of commercial SCR catalysts is too high,it is easy to make the air preheater and catalyst bloked and corrosive.Therefore,in order to realize the simultaneous removal of NO and Hg0 in coal-fired flue gas and prolong the life span of catalysts,the research of high activity and low temperature SCR denitration catalysts must be enforced.This paper presents the research progress of SCR catalyst at home and abroad.Based on these,the metal oxide SCR catalyst was used to evaluate the effects on denitrification and mercury removal,in order to provide theoretical basis and methods for the synergistic reduction of NO and Hg0 in coal combustion flue gas.Firstly,the supported Mo-Mn/Ti catalysts were prepared by impregnation method at different calcination temperatures,the optimum calcination temperature was analyzed.And then,the Mo-Mn/Ti catalysts with different loads were prepared at the optimum calcination temperature,and combined with modern characterization methods to obtain the effects of physical and chemical properties of the catalysts on the catalytic oxidation activity;Secondly,based on the experimental study of the Mo-Mn/Ti series catalyst,the best catalyst formula was optimized.Preparation conditions,operating parameters and SO2 on NO removal efficiencies were studied,and the physicochemical properties of the catalysts were characterized before and after the reaction,to clarify the mechanism of the catalysts on NO;Finally,the effects of the optimum catalyst on NO reduction and Hg0 removal were investigated under different experiment temperature,flue gas component,and some characterization techniques were employed to research the catalysts before and after SO2 poisoning reaction,on that basis,the mechanism of catalyst poisoning and interaction between NO and Hg0 removal were revealed.The experimental results indicated:(1)The calcination temperature has a great influence on the performance of Mo-Mn/Ti catalyst.After calcinated at 300 and 450 ?,MnOx and MoOx were uniformly distributed on the catalyst surface.with increasing calcination temperatures,the content of Mn4+ and O? was decreased gradually,and the crystallinity of the active components on the catalyst surface becomes stronger,the oxidation reduction was more difficult,and the anatase TiO2 transformed to rutile TiO2.In addition,the addition ofMo to Mn/TiO2 catalysts can make MnOx more dispersed on the catalyst surface,and it can increase the content of Mn4+ and O?,the active temperature window moved to the middle temperature.(2)The optimum calcination temperature of the catalysts was 450?,the Mn/Ti catalyst showed good activity of denitrification at low temperature.After doping element Mo,the NO conversion rate was kept over 90%in the temperature range of 200?440? because of the interaction between Mo,Mn and Ti,high valence Mn4+ and chemisorption oxygen O?were important factors for catalyst activity,the existence form of Mo was Mo6+,and SO2 in the flue gas can poison the catalyst and inhibit the denitrification activity,but with the increase of reaction temperature,the inhibitory effect was weakened.The results showed that Mo(0.5)-Mn(11.5)/Ti exhibited the best performance of denitrification and sulfur resistance,and has the subsequent research value.(3)Too low or too high reaction temperature was not conducive to the performance of Mo(0.5)-Mn(11.5)/Ti catalyst for NO and Hg0 removal,but at 200?,the mercury removal efficiency can reach 88.9%and the rate of denitrification was 91.8%.O2 in flue gas was the key factor in the process of NO and Hg0 removal,the reducing gas NH3 can significantly promote the denitration reaction,but greatly inhibit the removal of Hg0,the addition of HCl was beneficial to the oxidation of Hg0,but an obstacle to the NH3-SCR reaction,and SO2 played an inhibitory role of NO and Hg0 removal,the decrease of Mn4+,Oa and the sulfate,ammonium salts were the main reasons for the decrease of catalyst activity.The catalyst Mo(0.5)-Mn(11.5)/Ti showed effective abilities to remove NO and Hg0 at low temperature. |
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