| As coal is widely used in China, mercury in coal will be released into theatmosphere along with the coal processing and utilization. Along with theincreasing seriousness of mercury pollution around the world, mercury emissionand control in gas received widespread attention. Burning coal is the main formof coal utilization, mercury emissions from coal-fired power plants is the mainsource of atmospheric mercury pollution. Coal gasification as a new type ofclean coal utilization technology fast develops in the last ten years, mercuryemissions in the coal gasification also should cause enough attention. Spentdesulfurizer which contains large amounts of sulfur resources is a kind of toxicindustrial waste residue. As already know, mercury has strong sulphophileaffinity. If spent desulfurizer is used as raw material for the preparation of gasmercury sorbent, it can provide a new solution about disposal of the spentdesulfurizer and get a kind of low-cost mercury removal sorbent at the sametime. In this paper, the effects of temperature, space velocity and atmospheres of flue gas on the efficiency of Hg removal over the spent desulfurizer werestudied using a fixed bed adsorption device. The sorbents were characterized bythermal gravimetric analysis (TGA), X-ray diffraction (XRD) and X-rayabsorption spectroscopy (XAS) in order to reveal the mechanism of reaction.Moreover, ammonia washing method was adopted to deal with spentdesulfurizer and the ammonia washing solid sample was calcined. Then we gotgood performance sorbent which can remove the pollutants of Hg and H2S atthe same time. The main conclusions can be drawn as follows:(1) The spent desulfurizer TG-4can be used to remove mercury in the fluegas. It has a wide active temperature window (80~240°C) and has goodindustrial application prospect. Acid gases such as SO2, NO, HCl will reducemercury removal activity slightly.(2)After mercury removal, regeneration condition of280°C can implementthe regeneration of sorbent partly and the reclaimed sorbent remains highactivity of mercury removal. The mercury adsorption on the sorbent is relativelystable. It will not cause more secondary release of mercury when the spentdesulfurizer after mercury removal is placed under the general conditions orlandfill.(3) The sulfur forms in the spent desulfurizer are S, Fe2S3, FeS, FeS2, FeSxand sulfates. Elemental sulfur will be sublimation or oxidation at around300°C,that causes the decline of mercury removal activity. The elemental sulfur is themain active substance to remove mercury, iron sulfide may only have a little mercury removal capacity.(4) According to the differential results of used sorbent and referencesamples XANES spectra, the mercury adsorption on the sorbent is mainly in theform of HgS. The results of XAS characterization have proved that the mainmechanism for Hg removal by spent desulfurizer sorbent which can beexplained as follows: Hg+S=HgS.(5)Ammonia washing method was adopted to deal with spent desulfurizer.After solid-liquid separation, the solution can get high purity ammonium sulfateby-product using crystallization processing.(6) The solid samples were characterized by BET, SEM, XRD afterammonia washing. Its specific surface area increased and some slight changeoccured in the component of activity iron oxide. It remained high activity ofmercury removal, but poor desulfurization activity.(7) After400°C,1.5h calcination treatment, the specific surface area ofammonia washing sample would be further improved and the component ofactivity iron oxide increased. Thus, the desulfurization activity greatly beimproved. Meanwhile, it remained high activity of mercury removal. H2S isfavorable for the removal of mercury. |
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