【作者】 王岳军；

【导师】 吴忠标； 刘越；

【作者基本信息】 浙江大学 ， 环境工程， 2011， 博士

【摘要】 汞因其具有持久性、生物累积性和神经毒害作用,目前已经引起了较为广泛的关注。燃煤电厂是大气中主要的汞污染源,并且主要是以零价汞的形式排放,难以被现有除尘及脱硫装置捕集。现有ACI注入法脱汞技术因其较高的操作成本以及对飞灰品质的影响,不利于大规模工业应用。而利用氧化态汞的高溶解度,将零价汞氧化为二价汞,从而提高汞液相溶解能力并与湿法吸收技术相结合,开发基于湿法脱硫工艺的气相氧化-液相吸收联合脱硫脱汞技术将提供一种经济可行的技术途径。因此,本文针对汞的气相氧化结合液相吸收的汞控制技术,进行了系统研究。首先,基于实验室现有钛基催化剂制备技术,考察了利用溶胶凝胶法制备的不同金属掺杂催化剂汞催化氧化性能。通过筛选和优化,制备了一种在150-300℃温窗下氧化效率能达到100%的钻掺杂催化剂。此外,利用XRD、XPS、TEM和TPR等表征手段对催化剂进行了表征,确定催化剂主活性相为C0304。通过研究HCl和02在催化反应中的作用,提出了修正的Mars-Maessen模型,明确了HCl和O2在反应中的历程及对汞氧化的作用。其次,在模拟烟气二价汞吸收实验装置上对钙基湿法、双碱法和氧化镁法脱硫系统的脱汞性能进行了研究,考察了主要气相、液相条件和液相离子对脱汞性能的影响。研究结果显示：三种脱硫系统均显示出了较高的二价汞吸收性能,但汞还原现象也很明显。在吸收液pH值为4.5-5.5之间时,钙基系统中有将近70%汞被还原,而双碱法和氧化镁法也有近30%的还原量。提高吸收液硫酸根离子和氯离子浓度能明显抑制汞的还原。镁离子在钙基脱硫系统和双碱法中显示了不同的汞还原影响作用。NO和02可以提高系统的脱汞效果,而二氧化硫则不利于汞的脱除。最后,我们利用紫外可见分光光谱等表征手段,对镁离子、硫酸根和氯离子的二价汞还原抑制过程进行了研究。实验结果表明：镁离子在钙基脱硫系统中对汞还原的促进是由于在镁离子的作用下CaSO3·0.5H20固体悬浮颗粒表面积增加,从而增加了二价汞还原的活性点位；而在双碱法脱硫系统中,则生成了MgSO30中性离子对,降低了液相活性亚硫酸根含量。硫酸根的加入是由于生成了HgSO3SO42-这一相对稳定的络合物。而对于氯离子,主要是生成了较为稳定的Cl2HgSO32-和ClHgSO3-络合物,并且Cl2HgSO32-的稳定性比ClHgSO3-更强。液相HgSO3的降解是汞还原的限制步骤。硫酸根、氯离子和过量亚硫酸根主要是限制了HgSO3的降解从而实现汞还原的抑制。更多还原

【Abstract】 Mercury, due to its persistence, bio-accumulation and neurological toxicity, has received tremendous attentions. The coal-fired power plant was the major source of the gas-phase mercury, which was mainly in elemental form and could not be removed by the existing dust removal and desulfurization system. The widely industry application of the active carbon injection method(ACI) for mercury capture from coal-derived flue gases was limited by its rather high operating cost and the harmful effect on the fly ash quality. A co-effective and economic alternative was to transfer the elemental mercury to more soluble bivalent form, following removed in wet absorption process. Thus, the mercury removal process of the gas-phase oxidation and aqueous absorption combined system was systematically investigated in this dissertation.Firstly, several catalysts were prepared by doping different metals into the TiO2 for mercury oxidation tests by sol-gel method, which was optimized by our group. By the activity tests and loading content optimization, a cobalt doped catalyst having an oxidation efficiency of 100% within the temperature reaction window of 150-300℃was obtained. The chosen catalyst was then characterized by XRD, XPS, TEM, HRTEM and TPR, indicating that the main active phase of the catalyst was Co3O4. Furthermore, a modified Mars-Maessen mechanism was proposed by us through the analysis of the performance of HCl and O2 during the reaction, in which the performance of HCl and O2 as well as their effects on mercury oxidation were defined.Secondly, the removal of bivalent mercury by the wet Ca-based FGD system, the Dual-Alkali FGD system and the magnesia FGD system were evaluated in a simulated flue gas absorption device, respectively. Main gas and liquid conditions as well as some aqueous ions on mercury removal were experimental studied. The results showed that three FGD systems all showed high efficiency on bivalent mercury absorption, but the reduction amount of absorbed bivalent mercury was also very large. Within the pH value of 4.5-5.5, about 70% of the absorbed mercury was reduced to elemental form in the wet Ca-based FGD system, while that were around 30% in both the Dual-Alkali and magnesia FGD systems. The increase of sulfate and chloride ions in the absorbent greatly inhibited the mercury reduction. The magnesium ion had different effects on mercury reduction in the Ca-based FGD system and Dual-Alkali system. NO and O2 in the gas were beneficial to the mercury removal, while SO2 would somewhat lower the removal efficiency.Finally, the UV-vis spectra and some other technologies were adopted to investigate the mercury reduction behaviors in the presence of magnesium, sulfate and chloride ions, respectively. The enhancement of reduction in the Ca-based FGD system was contributed to the increased surface area of CaSO3·0.5H2O suspended solid particle, thereby increasing the active sites of mercury reduction. And the reduction was inhibited by the formation of MgSO30 ion pairs in the Dual-alkali system by the addition of magnesium. The inhibitions by the addition of sulfate and chloride were attributed to the formation of HgSO3SO42-, Cl2HgSO32- and ClHgSO3-, respectively. Cl2HgSO32- was recognized as the more stable one compared to ClHgSO3- in the presence of chloride. Aqueous HgSO3 decomposition was the key step of mercury reduction, since presences of sulfate, chloride and excess sulfite ions all limited its decomposition.更多还原