| Mercury, as one of the atmospheric pollutants, has received increasing attention. Coal-fired power plants are a major source of anthropogenic mercury emissions,the focus of the removal of mercury from flue gas mercury is the removal of zero-valent mercury. Activated carbon injection(ACI) is the closest to the actual application and mature technology for removal of mercury from flue gas, but the costs of ACI is high. In addition, for the sales of fly ash for cement production industry, the increase of carbon content(or other chemicals which are added) will produce adverse effect. To prepare magnetic adsorbent, after the adsorption process, the adsorbent can be separated through magnetic separation from fly ash, besides, fly ash will not be contaminated. Precious metals, including gold, silver, palladium and platinum can form reversible amalgam with mercury, silver, for instance, can be combined with mercury at high temperature, mercury could be released from silver amalgam under a certain temperature, but the high cost of gold, palladium, platinum, make their practicality not strong. The precious metals in the form of nanoparticles and the precious metal can be combined to increase available surface for effective mass transfer. Based on above theory and research method, to develop materials which combined baghouse filter with regenerable magnetic adsorbent, filter material as carrier. In order to protect the magnetic nanoparticles from oxidation or corrosion dissolved under acid condition, the magnetic nanoparticles should be covered by silica shell which has reliable chemical stability. To this end, the main direction of this work is to study and develop a new-type regenerable metal-loaded magnetic adsorbent which used filter materials as carrier, silver is selected for its lower cost than gold, palladium and platinum as precious loaded metal, used for removing zero-valent mercury from flue gas.In this work, five kinds of high temperature resistant inorganic filter fiber are selected, polytetrafluoroethylene(PTFE) fibers, glass fibers, polyphenylene sulfide(PPS) fiber, Polysulfonamidefibre(PSA) and polyimide(P84) fiber are used, and pretreatment progress for the five different kind of fibers through impregnated by hydrochloric acid to modify the property of each fiber in order to achieve better load effect. Before and after the pretreatment process for the five different kind of fibers, through scanning electron microscopy(SEM) characterization experiments to observe the changes of morphology on the surface of fiber. Magnetic fiber is obtained by the experiment of combination of silicon coated Fe3O4 nanoparticles and the five different kind of fibers with binder respectively, then magnetic silver-loaded fiber is obtained, process of organic modification is through adding 3-MPTS(3-mercapto-propyl-trimethoxy-silane). Finally, characterization experiments are put on as follow: specific surface area(BET) analysis, X-ray experiments(XRD) analysis and Fourier transform infrared attenuated total reflection spectroscopy(ATR-FTIR) analysis, to study the species of functional groups on the surface, and the silver content of the five different silver loaded magnetic fibers is measured, results show that, magnetic silver-loaded PTFE fiber has the highest amount of silver, the organic modifier can be well supported on the surface of the magnetic silver-loaded fiber.The removal of zero-valent mercury(Hg~0) in simulation flue gas is mainly based on the fixed bed experimental apparatus, to begin with, stability test of system is carried out. Studied Hg~0 adsorption performance of the five kinds of fiber through pretreatment progress in simulated flue gas, on this basis, studied the Hg~0 removal effect of magnetic silver-loaded fibers based on the five kinds of fiber as adsorption material respectively, the experimental results show that magnetic silver-loaded PTFE fibers has the highest Hg~0 removal effect among the five adsorption materials which is as high as 76.5%. For different operating conditions, the influence of mercury vapor inlet concentration for mercury removal is not very obvious, different adsorption reaction temperature had a great influence on mercury removal. The influence on the effect of different gas composition NO,SO2,HCl for Hg~0 adsorption progress by magnetic silver-loaded PTFE fiber is studied, The relation between content of SiO2 coated Fe3O4 and magnetic separation recovery of magnetic silver-loaded PTFE fiber is analysised, separation recovery rate of magnetic silver-loaded PTFE fiber increased with the content increase of SiO2 coated Fe3O4, when the content of SiO2 coated Fe3O4 reaches 33%, the magnetic separation recovery rate is as high as 91.62%. High magnetic separation recovery rate has important practical value for high efficiency and low cost of processing mercury pollution from coal-fired flue gas.Regeneration process for magnetic silver-loaded PTFE fiber whose Hg~0 removal efficiency is the highest is carried out by heating under N2 atmosphere, to study on influence of three different heating regeneration temperature: 150 ℃, 200 ℃, 250 ℃ on the adsorptive effect after regeneration, the Hg~0 removal efficiency of magnetic silver-loaded PTFE fiber after regeneration gradually decreased, it can be recycled for 5-6 times. At the end, through dynamic model calculation combined with the experiment for Hg~0 removal from simulated flue gas conduct a preliminary study on the dynamics, to make Langmuir adsorption isothermal model analysis and adsorption thermodynamics analysis for adsorption process of magnetic silver-loaded PTFE fiber, and to make dynamics analysis before and after regeneration, parameters shows that after five adsorption®eneration recycle process, pseudo-first-order kinetic model is more in line with the process of Hg~0 removal. |
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