Enhanced Photo-catalytic Oxidation Of Elemental Mercury Using Fiber-illuminated Honeycomb Photoreactor

Mercury emission resulting from coal combustion is increasingly more serious in China due to the huge coal consumption and higher average concentration of mercury in Chinese coals.Mercury in the flue gas after coal combustion can be generally divided into three forms: elemental mercury（Hg⁰）,oxidized mercury（Hg2+）and particle bound mercury（HgP）.Most of the Hg2+ and HgP can be easily removed by the conventional air pollution control devices（APCDs）,which are installed in most of the coal-fired power plants in China.However,Hg⁰ is a relatively stable form in atmosphere and hardly removed by the conventional APCDs due to its low melting point,high equilibrium vapor pressure,water insolubility and volatility.Thus,Hg⁰ removal is difficulty and hot spot of current studies.With the characteristics of high catalytic efficiency,no secondary pollution,and multi-pollutants simultaneous removal,the photo-catalytic oxidation technologies have recently received more attention by researchers.The fiber-illuminated honeycomb reactor has the advantages of high light utilization,low gas pressure loss,and easy industrial experimentation.The fiber-illuminated honeycomb reactor has showed good performance in the field of photo-catalytic pollutants removal.The photo-catalytic removal of elemental mercury of TiO₂ and Ce-TiO₂ catalysts by using the fiber-illuminated honeycomb reactor were investigated systematically in this paper.We hope that this paper can provide new ideas for the emission control of elemental mercury resulting from coal combustion.Firstly,the TiO₂ coated ceramic honeycombs were prepared and the effects of reactor parameters on the photo-catalytic mercury remove efficiency were investigated systematically in the second chapter.The experimental results showed that TiO₂ calcined at 400℃ showed the best removal performance of elemental mercury;higher reaction temperature restrained Hg⁰ removal;the fiber-illuminated honeycomb reactor showed better Hg⁰ removal performance than the fixed-bed reactor when using more catalyst;the spent catalyst can be regenerated effectively via thermally treated at 400℃ for 1h.The Hg⁰ removal performance of TiO₂ coated ceramic honeycombs under complicated atmosphere was studied and the effect of flue gas components（O2,SO2,NO,HCl,and H2O）on the photo-catalytic mercury remove efficiency were investigated in the third chapter.The experimental results showed that the O2 was favorable for Hg⁰ removal;in the absence of O2,SO2,NO,and HCl inhibited the Hg⁰ removal;in the presence of O2,SO2 and HCl promoted the Hg⁰ removal due to the synergistic effect of SO2,HCl,and O2;H2O in the gas composition had obviously inhibitory effect on Hg⁰ removal resulting from its competitive adsorption and photo-catalytic reduction.The Ce-TiO₂ coated ceramic honeycombs were prepared to enhance the Hg⁰ removal performance under simulated flue gas.The physicochemical properties of Ce-TiO₂ catalysts were characterized and the effects of doping value and flue gas components on the photo-catalytic Hg⁰ remove efficiency were investigated in the fourth chapter.The experimental results showed that Cerium is found to be present as Ce3+/4+ oxidation states in Ce-TiO₂ catalysts;the doping of Cerium inhibited the TiO₂ grain growth,enhanced the BET surface area,reduced the band gap of catalysts;0.6wt%Ce-TiO₂ showed the best Hg⁰ removal performance,whose Hg⁰ removal efficiency is 69.3% under simulated flue gas;for Ce-TiO₂ catalysts,O2,SO2 and HCl promoted the Hg⁰ removal while NO inhibited the Hg⁰ removal.