||Mercury and its derivatives as well as NOx are the major air pollutants emitted from coal-fired power plants, which could cause seriously adverse impact on the ecological system and human health. The simultaneous removal of Hg0 and NOx by the installed air pollution control devices (APCDs) could not only reach high removal efficiency of air pollutants but also reduce the installation and operational cost. One of the most potential technologies for multi-pollutant removal is to remove Hg0 by SCR. However, the current SCR has an optimum reaction temperature range of 300-400°C, which must place it in the front of ESP. However the masking effect of high-concentration particles in the flue gas reduces the removal efficiency of Hg0 by SCR. Accordingly, this study aims to combine thermo-catalysis and photocatalysis to prepare a new photothermal catalyst suitable for 100-200°C, for developing an innovative Hg0 removal technology in a lower temperature environment.|
This study was conducted in five phase: The first phase was literature, including reviewing the modification and preparation of TiO2, and the photothermal catalytic oxidation of Hg0. The second phase applied sol-gel method to prepare TiO2, CeO2/TiO2 and WO3/CeO2/TiO2 photothermal catalysts, and characterized surface properties by SEM, EDS, BET, XRD, XPS, PL and FTIR. The third phase established a photothermal catalytic reactor and an Hg0 online measurement system. A quality assurance and quality control (QA/QC) procedure was established to ensure the accuracy of Hg0 measurement. The fourth phase investigated the effects of operating parameters on Hg0 photothermal catalysis at lower temperature (100-200 °C). The operating parameters included reaction temperature, influent Hg0 concentration, and pollutant gas components. The fifth phas simulated the reaction rate constant of Hg0 L-H reaction kinetic model.
Experimental results indicated that the TiO2 prepared by sol-gel method was mainly anatase (>80%). XPS showed that Ce mostly existed in the form of Ce4+, while EDS Ce content on the surface of TiO2 that the increased linearly with the increase of Ce addition during the preparation procedure. Photothermal catalytic oxidation results indicated that CeO2/TiO2 has higher oxidation efficiency of Hg0 at 100-200 °C, and increased from 30-60% to >90%. With the increase of CeO2 added, the photothermal catalytic oxidation of Hg0 increased. Simulated by L-H kinetic model, the reaction equilibrium constant (KHg0) was determined, and KHg0 decreased with reaction temperature, which concurred with the trend of the Hg0 oxidation efficiency of the experimental results. Finally, the photothermal catalytic oxidation of Hg0 was carried out in the atmosphere of 300 ppm NO and 300 ppm SO2, respectively. The results showed that the photothermal catalytic oxidation efficiency of Hg0 by 7% CeO2/TiO2 was higher than that by 3% WO3/7% CeO2/TiO2 in NO atmosphere, but its oxidation efficiency decreased with temperature. The photothermal catalytic oxidation of Hg0 decreased significantly with reaction temperature in the atmosphere of 300 ppm SO2, but the decrease of 3% WO3/7% CeO2/TiO2 was less than 7% CeO2/TiO2, since WO3 has better sulfur resistance.