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铁基分子筛脱除燃煤烟气中单质汞的研究
Alternative TitleStudy on removal of Hg0 from coal-fired flue gas over iron based zeolites
亓昊
Subtype工程硕士
Thesis Advisor朱廷玉 ; 徐文青
2014-05
Degree Grantor中国科学院研究生院
Degree Discipline环境工程
Keyword汞   燃煤烟气   分子筛   铁   粉煤灰
Abstract汞是生态环境中毒性最强的重金属污染物之一,具有持久性、易迁移性和高度的生物富集性等特点,成为优先控制的全球性污染物。燃煤排放是大气汞污染最主要的人为源之一,燃煤烟气中的单质汞(Hg0)是最难控制的汞形态,是目前大气汞污染控制研究的重点。由于活性炭喷射吸附脱汞法具有较高的运行成本,难以在我国广泛应用,因此,开发经济高效的新型脱汞材料具有十分重要的意义。 本论文采用燃煤废弃物粉煤灰为原料制备分子筛,对制备过程中主要影响因素进行优化,并对得到的分子筛进行Hg0脱除性能评价;采用不同过渡金属氯化物对制得的分子筛以及几种商用分子筛进行改性和脱汞性能评价,通过X射线衍射(XRD)、N2物理吸附、透射电子显微镜(TEM)、傅里叶红外光谱(FTIR)、X射线光电子能谱(XPS)等表征手段推测其脱汞性能差异的原因;分别采用FeCl3和Fe2O3对优选的HZSM-5分子筛进行改性,并考察其在不同温度、活性组分负载量和烟气组分等条件下的脱汞性能,结合表征手段,初步推测其脱汞反应的机理。通过实验研究得出以下结果: (1)优化了碱熔融水热法由粉煤灰制备分子筛NaA、NaX分子筛的工艺条件,考察了金属氯化物改性对分子筛及粉煤灰脱汞性能的影响。分子筛本身的汞吸附性能都不高,采用金属氯化物改性后,分子筛汞吸附性能较改性前所升高,但反而低于改性粉煤灰。 (2)考察了FeCl3浸渍改性的三种商用分子筛脱汞性能,阐明了影响性能差异的因素。Fe3+与NaA和NaX型分子筛中的Na+发生了离子交换作用,将Na+交换出,与Cl-结晶生成NaCl晶体,导致脱汞效率较低;HZSM-5分子筛上的FeCl3存在于材料表面,提供活性Cl原子与Hg0发生氧化反应生成HgCl2。 (3)考察了负载量及烟气组分对FeCl3/HZSM-5脱汞性能的影响,优选3%负载量。SO2通过与Hg竞争相同的吸附活性位,抑制分子筛的脱汞性能,而NO和HCl通过在材料表面生成新的活性物种,对Hg0起到氧化作用,而促进分子筛的脱汞性能。 (4)考察了负载量及烟气组分对Fe2O3/HZSM-5脱汞性能的影响,优选3%负载量。探讨了O2、HCl、SO2、NO等不同气氛中Fe2O3/HZSM-5脱汞反应机理:O2气氛中,在较高温度下Hg0被氧化成HgO脱除;在含有HCl气氛中,材料表面吸附生成活性Cl原子,将Hg0氧化生成HgCl2;在NO + O2气氛中,NO在材料表面生成结合态Fe(Ⅲ)-NO3等活性物种,与Hg0反应生成Hg(NO3)2;在SO2 + O2气氛中,SO2与Hg0抢占活性位点,从而抑制汞的吸附;在NO + SO2 + O2共存的气氛中,由于NO对汞氧化的强烈促进作用,SO2并没有表现出抑制作用,材料在不含HCl的气氛中仍然有很高的脱汞效率。 本论文为汞污染控制技术的开发提供了理论支持和实验参考,为新型脱汞材料的开发提供了研究基础。 关键词:汞,燃煤烟气,分子筛,铁,粉煤灰
Other AbstractMercury is one of the most toxic heavy metal elements in the environment. It has become the precedent-controlled harmful pollutants because of its high volatility, long persistence, and strong bioaccumulative properties. Coal combustion is one of the major anthropogenic mercury emissions sources. Elemental mercury (Hg0), which is hard to be removed, has become the most important and difficult work in flue gas mercury control. The widely application of activated carbon (AC) injection technology is limited for its high operation cost. Thus, new materials that are efficient and cost-effective still need more exploration. In this study, fly ash was used as raw material to prepare zeolites, and the main factors during the preparation process were optimized. The mercury removal efficiencies of the derived zeolites were evaluated. The derived zeolites and several commercial zeolites were modified with different transition metal chloride, and their mercury removal efficiencies were evaluated and compared. Various characterization, such as X-ray diffraction(XRD), N2 physical adsorption, transmission electron microscope(TEM), fourier Transform infrared spectroscopy(FTIR) and X-ray Photoelectron Spectroscopy(XPS), were conducted to explain the different efficiencies. HZSM-5 was modified with FeCl3 and Fe2O3, and their Hg0 removal efficiencies with different temperature, loading values of reactive species and gas components were evaluated. The mercury removal mechanism was discussed, on the basis of characterization results. The results obtained were as followed: (1)Alkali fusion-hydrothermal method was used to prepare NaA and NaX zeolites with fly ash, and the main factors during the preparation process were optimized. The mercury removal efficiency of zeolite increased after modified by transition metal chloride, but lower than that of fly ash. (2)Three kinds of commercial zeolites were modified with FeCl3, and their mercury removal efficiencies were evaluated and compared, different characterization were conducted to explain the different efficiencies. The ion exchange effect between Fe3+ and Na+ in NaA and NaX zeolite resulted in the formation of NaCl crystal, leading to the decrease of the mercury removal efficiencies. FeCl3 on the surface of HZSM-5 zeolite could provide active Cl atom, which could oxidize Hg0 into HgCl2. (3)The mercury removal efficiencies of FeCl3/HZSM-5 with different loading values were evaluated, and 3% was chosen to be the best loading value. The influences of different gas components were studied. SO2 could inhibit the mercury removal efficiency through competing active sites against Hg. NO and HCl could promote the Hg0 oxidation and removal with the active species generated on the surface of the materials. (4)The mercury removal efficiencies of Fe2O3/HZSM-5 with different loading values were evaluated, and 3% was chosen to be the best loading value. The mercury oxidation mechanisms in different atmosphere were studied. Hg0 could be oxidized into HgO at a high temperature in O2 atmosphere. In the atmosphere of HCl, Active Cl* was generated on the surface and Hg0 oxidized into HgCl2. The HgCl2 generated was completely absorbed on the material at a low temperature, and partly desorpted into gas phase at a high temperature. In the atmosphere of NO + O2, NO could be adsorbed on the surface, then formed Fe(Ⅲ)-NO3 and other active species, which could oxidize Hg0 into Hg(NO3)2. In the atmosphere of SO2 + O2, SO2 could inhibit the mercury removal efficiency through competing active sites against Hg. In the atmosphere of NO + SO2 + O2, SO2 didn’t show inhabitation against mercury removal due to the strong promotion effect of NO. Fe2O3/HZSM-5 had high mercury removal efficiency in absence of HCl. This study provided theory supports and experimental references for the exploration of mercury control technologies, and foundation for exploration of new mercury removal materials. Key words: Mercury, Coal-fired flue gas, Zeolite, Iron, Fly ash
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/15581
Collection研究所(批量导入)
Recommended Citation
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亓昊. 铁基分子筛脱除燃煤烟气中单质汞的研究[D]. 中国科学院研究生院,2014.
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