复合型吸附剂对燃煤烟气中汞的中温脱除机制研究

Coal utilization has been considered as the largest anthropogenic source of mercury emissions into the atmosphere in many countries. Mercury has been identified as a hazardous pollutant to both human health and environment because of its extreme toxicity, persistence, and bioaccumulation. Hence, the emission and control of mercury has drawn worldwide attention recently. China released new mercury emission standard from coal-fired power plants following U.S.A. However, as a volatile element, mercury may be presented partially, or totally in the vapor phase, which was extremely hard to be removed in flue gas by current air pollution control devices. The aim of the proposal is to investigate the removal of mercury in mild-temperature gas phase during coal utilization. A new mineral, non-carbon based, dispersed sorbent was involved which was derived from waste paper recycling process. In our earlier study, the activated sorbent has been found that mercury capture was dominated by temperature and capture on sorbents over long scales (200-900 ℃). In this proposal, typical mineral samples will be collected. Complex mineral sorbent will be synthesized according the collected samples. Modified sorbent will be prepared by adding organic or inorganic promoters to the two series raw sorbents. The systematic experiments and theoretical studies will be conducted to analyze the effect of the mineral on the sorption of mercury and some other pollutants at temperature of 200-750 ℃. The adsorption mechanism of mercury on the mineral surface will be investigated to get a further understanding of the impacts of flue gas on mercury sorption process. The interaction mechanism between mercury - sorbent - gas phase components will be developed and heterogeneous mercury sorption kinetic model will be established, which will provide a reliable theoretical basis to the removal of elemental mercury via multi-mineral sorbent in gas phase during low rank coal utilization that contributing to the development of integrated solid waste pollution control and resource utilization.

煤炭综合利用释放的汞是最大的人为汞排放源。我国随美国等发达国家后也颁布了针对燃煤电厂的汞排放标准，控制煤利用过程中的汞排放已迫在眉睫。利用现有污染物控制设备实现汞及多种污染物的联合脱除是目前主要的研究和发展方向。前期研究结果表明，再生纸工业生产过程中产生的矿物废渣经过高温有氧活化后，在200-900 ℃对单质汞有一定的吸附能力，但有关矿物组成及热活化过程中的矿物演化、固体表面与气态单质汞的非均相吸附机理等问题尚待进一步研究。本项目通过直接选取再生纸矿物废渣或模拟配置类似组成的矿物吸附剂，并对上述两类吸附剂进行改性，利用得到的一系列吸附剂进行中温脱汞（200-750℃）及气态汞和多种污染物的联合脱除机理研究。本项目基于在实现低阶煤的资源化利用的同时联合脱除汞等有害污染元素的原则开展研究，通过实验和模拟计算相结合的方法，阐明矿物演化与气态汞吸附性能间的定量关系，研究汞—吸附剂—气相组分之间多相、多组分反应竞争协同机制，为低阶煤利用过程中的污染物一体化控制和固体废弃资源化利用提供科学依据。

中国的能源供给严重依赖于煤炭，燃煤排放的汞污染日益严重，已成为汞排放量最大的国家，燃煤汞排放的控制亟需解决。本研究从廉价高效的角度出发，制备了多种复合矿物吸附剂。项目前期研究了以碳酸钙、高岭土和氧化钙为载体负载锰氧化物的矿物吸附剂，在实验室固定床反应器上对吸附剂的脱汞性能进行研究。实验结果表明，锰盐前驱体类型显著影响脱汞性能，MnCl2改性吸附剂的脱汞性能优于Mn(NO3)2改性吸附剂，活性物质在吸附剂表面形貌不同是两者吸附性能差异的主要原因；吸附剂经过高温焙烧形成的MnOx和活性氯对Hg0有较强的吸附作用。通过实验确定了吸附剂的最佳制备条件和最佳脱汞温度窗口(300-400℃)，最高脱汞率达到90%以上。烟气气氛中4%的O2能有效的补充MnOx发生氧化反应过程中消耗的晶格氧，是维持高脱汞性能的关键。烟气中微量的SO2和HCl对脱汞有一定的抑制作用，而NO对汞的脱除有一定的促进作用。吸附剂进行掺杂Fe改性后，抗硫性能得到了显著的提高。在上述研究基础上，以赤泥为吸附剂载体，通过酸化处理和负载CuOx制备得到脱汞吸附剂。研究表明，最佳的制备条件为：加酸量液固比为15，铜浸渍量为12 %，吸附剂的最佳反应温度为250℃；10-20 ppm的HCl气体可生成氯自由基促进Hg0的氧化，从而促进汞的脱除，且HCl浓度越大，促进作用越显著；200-400 ppm的二氧化硫气体可能与气态汞存在竞争吸附，而抑制脱汞反应；NO的存在起到促进作用。通过对改性前后的吸附剂的XRD、TG/DTG分析确定主要活性物质是CuO。通过项目研究，阐明了汞—吸附剂—气相组分之间反应竞争协同机制，为低阶煤利用过程中的污染物一体化控制和固体废弃资源化利用提供技术和基础数据。在项目执行期间，培养硕士研究生7名。已在国外本学科主流刊物和重要国际会议发表论文12篇，国际会议分会报告5篇；申请权专利1项。