Removal Mechanisms Of Mercury Species From Flue Gas By Fiber Loaded With CeO₂/TiO₂

With more and more attention given to the mercury pollution, a strict limit on mercury emissions has been put forward by the country as the coal-fired power plant is the main source of atmospheric mercury emissions. The newest air pollutant emission standard on coal-fired power plant (GB13223-2011) stipulates that the emissions of mercury and its compounds from coal-fired power plant cannot exceed0.03mg/m3. Currently an economic and competitive mercury control method is to use the existing pollutant device to remove mercury. Previous studies have shown that cerium-based SCR catalyst CeO2/TiO2is a highly efficient denitration catalyst for mercury removal. The cerium-based catalyst CeO2/TiO2being loaded on high-temperature resistant fiber was put forward in order to integrate denitration, mercury and dust removal.After the sample preparation of the fiber loaded with cerium-based catalyst CeO2and technical testing of Scanning Electron Microscopy (SEM) test, strength test for single fiber, Thermogravimetric Analysis (TGA), X-ray powder diffraction(XRD), Fourier transform infrared spectrometry-Attenuated total reflectance (FTIR-ATR), studies has shown the loaded CeO2catalyst destroyed P84fiber’s excellent mechanical properties, high temperature resistance and flame retardant properties. While the PSA fiber loaded with CeO2still has a good resistance to high temperature, though the mechanical properties declined slightly, the effect is not obvious. CeO2has a good dispersibility on the carrier of PSA fiber, but CeO2crystals in P84fiber adversely affect catalysis. CeO2is simply loaded on both fibers, but physical and chemical characteristics and fiber properties of the PSA fiber are superior to P84fiber.The removal mechanisms of mercury species from flue gas on CeO2, CeO2/TiO2were studied. Two methods of density functional theory(DFT), LDA and GGA (PBE, PW91, WC and PBESOL), are used respectively to calculate the geometric parameters of CeO2. The result is compared with the experimental statistics in order to verify the reliability of the selected method. The study has shown that the results of DFT calculation are accurate within the error range and the GGA-PBESOL calculation method is the best one to fit the research. A periodic surface model of a well-characterized CeO2and CeO2/TiO2is established and the relaxation analysis indicates the relaxation phenomenon is very obvious, so the impact of surface relaxation should be fully considered in the subsequent calculations.The adsorption mechanism of mercury (Hg0) from the flue gas was discussed, including the adsorption mechanism of Hg0on the surface of pure CeO2, HC1and Hg0on the surface of CeO2/TiO2. Results indicated that mercury oxidation followed Langmuir-Hinshelwood mechanism when HC1exsisted. Compared with surface adsorption in pure CeO2, HgO in CeO2/TiO2surface not only had a stronger physical adsorption but also brought about chemical adsorption, and mercury oxidation followed Mars-Maessen mechanism.The research on the reaction mechanism of HgCl and HgCl2on the CeO2TiO2surface found that among the15adsorption configuration of HgCl on the surface of CeO2/TiO2, only one was sure to occur. The chemical adsorption was very strong with the adsorption energy of-2.976eV. The analysis of Mulliken populations showed the bond of chlorine-cerium generated in the adsorption process. There were10adsorption configuration of HgCl2on the surface of CeO2/TiO2and three kinds of them were stable configuration. All of the three adsorptions were strong chemical adsorption and generated the bond of cerium-chloride, chlorine-oxygen and cerium-chloride in the adsorption process.