SO3和飞灰无机组分对汞多相转化反应与动力学的影响机制

The fundamental understanding of homogeneous and heterogeneous mercury transformation mechanism and reaction kinetics is crucial for mercury emission control in the coal-fired flue gas. However, to date, the exploration of reaction mechanism and kinetics is still preliminary and cannot predict mercury transformation accurately and quantitatively during coal combustion. In addition, the present studies mainly focused on Hg transformation in the air-coal combustion process, so the conclusions are not very suitable for predicting mercury transformation in the oxy-coal combustion conditions. Due to the limitations of present studies, especially in the case of oxy-coal combustion, this project intends to focus on the mechanisms of influence of SO3 and inorganic components in fly ash (mainly Fe-based species) on the mercury transformation. The homogeneous reactions (such as Hg/SO3 and Hg/Cl/SO3), the direct and indirect oxidation mechanism and reaction kinetics will be first investigated. The effects of SO3 will be considered to modify the existing mechanism and kinetics, and the improved chemical reaction systems will be provided under air and oxy-coal combustion conditions. The role of Fe-based active species in the fly ash in the Hg transformation process will be clarified. Specially, the active Fe-based species will be identified via CCSEM, Mossbauer spectrum and XPS, because the exact form of active Fe-based species for Hg transformation are still disputed in different reaction conditions. Then the heterogeneous Hg transformation mechanism over the Fe-based active species surface under different atmosphere will also be investigated. At last, the competitive and synergistic mechanisms of Hg/SO3 and Hg/Cl reactions on Fe-based active species were studied under complex conditions, and the homogeneous mechanism was coupled to provide a foundation for establishing a more accurate homogeneous and heterogeneous Hg transformation mechanism.

燃煤烟气汞排放控制的关键科学问题在于深刻认识煤燃烧过程汞形态转化的多相反应机理与动力学。但是，迄今有关汞反应机理和动力学的研究工作尚处于探索阶段。同时，现有研究主要针对空气燃烧过程，其研究结果难以准确预测不同的燃烧方式下汞的形态转化。本项目针对现有研究的局限性，尤其针对氧/燃料燃烧方式下的特殊反应环境，拟重点关注烟气中SO3、飞灰中无机组分(含铁组分)等在汞形态转化过程中的作用机制。申请人基于空气和氧/燃料燃烧方式，首先研究Hg/SO3、Hg/Cl/SO3等均相体系中Hg的氧化行为，揭示SO3及其生成消去反应对Hg直接和间接氧化的影响，完善Hg均相转化机理；探究飞灰无机组分对Hg非均相转化的作用，精准识别飞灰中活性Fe物种，阐明其表面上的多相反应机制；复杂体系下研究Fe活性相表面Hg/SO3和Hg/Cl反应的竞争与协同机制，结合均相机理，为建立完善的汞多相转化机理提供依据。

非常规污染物是近年来煤燃烧领域关注的重点问题之一，作为高挥发性和高毒性的痕量重金属污染物Hg，其排放控制日益受到重视。由于氧化态汞易溶于水，可以被燃煤电站已有的湿法脱硫装置协同脱除，将Hg转化为氧化态汞是实现其高效脱除的关键。因此，燃煤烟气汞排放控制的关键科学问题在于深刻认识煤燃烧过程汞形态转化的多相反应机理与动力学。但是，迄今有关汞反应机理和动力学的研究工作尚处于探索阶段。同时，现有研究主要针对空气燃烧过程，其研究结果难以准确预测不同的燃烧方式下汞的形态转化。本项目针对现有研究的局限性，尤其针对氧/燃料燃烧方式下的特殊反应环境，拟重点关注烟气中SO3、飞灰中无机组分(含铁组分)等在汞形态转化过程中的作用机制。申请人首先研究了SO3的生成和消去反应与汞的常见氧化剂HCl和NOx的交互作用，阐明SO3生成与消去反应发生过程中对Hg氧化所需物种的消耗或生成机理；其后研究了飞灰中具有催化作用的Fe活性相对Hg的非均相转化影响机制，通过多种表征手段，明确了飞灰中含铁矿物对Hg氧化的活性组分，以该组分作为模型化合物进行Hg的氧化机理研究，同时提出了一种模型化合物的快速合成方法；最后在复杂体系下研究了Hg的多相转化机理，提出了Hg在飞灰中Fe活性相表面发生氧化反应的机理模型。此外，本项目利用飞灰中含Fe矿物的磁性，将其作为载体，制备了具有可回收的的燃煤烟气Hg脱除催化剂或吸附剂，并研究了Hg的催化氧化、吸附机理，揭示了烟气中SO2、衍生SO3等对Hg氧化过程的影响规律。基于本项目的研究，为深刻认识燃煤过程Hg的形态转化与排放控制，提供理论支撑。