增压富氧气氛下Hg/NO2体系的氧化机理与动力学研究

With the proposal and development of a new pressurized oxy-combustion technology, reaction between elemental mercury and nitrogen dioxide can not be ignored because of the promoted reaction rate along with the increase in produced NO2 at elevated pressure. The homogeneous oxidation reaction of Hg0 and NO2 has been proved. When the flue gas is compressed, the reaction between Hg0 and NO2 can significantly promote the oxidation of Hg0. Study on the oxidation mechanism of Hg/NO2 system will make a progress on pushing the development of improving and innovating the mercury emission and control technologies under various combustion modes. This project will carry out research on the key scientific problems of the oxidation mechanism and reaction kinetics of Hg/NO2 system, including investigating the influence of NO2 on the oxidation behavior of Hg0 in pressurized oxy-fuel coal-fired flue gas atmosphere, revealing the mechanism of homogeneous oxidation of Hg0 and NO2 at the atomic and molecular level, researching the contribution of NO2 to mercury oxidation and the reaction kinetic behavior of mercury under the condition of pressurized oxy-combustion, and building a comprehensive kinetic model for homogeneous oxidation of mercury. This research will provide theoretical basis for the study of the migration behavior and emission control of coal-fired mercury under various combustion modes.

随着新型增压富氧燃烧技术的提出与发展，在加压条件下化学反应速率的提高以及NO2生成量的增加使烟气中Hg与NO2的直接反应不容忽视。Hg与NO2的均相氧化反应已被证明存在，烟气加压时，Hg与NO2之间的相互化学反应能够显著促进Hg氧化。开展Hg/NO2体系的氧化机制研究，对于多种燃烧方式下汞排放与控制技术的完善与创新可以起到积极的推进作用。本项目将围绕Hg/NO2体系的氧化机理与反应动力学研究的关键科学问题开展研究工作：深入探索增压富氧条件下NO2对Hg的氧化作用规律，从原子分子水平揭示Hg+NO2的均相氧化反应机理，研究增压富氧烟气中NO2对Hg氧化的贡献及汞的反应动力学特性，建立较为全面的汞均相氧化机理模型，为研究燃煤汞在多种燃烧方式下的迁徙转化行为和排放控制方法提供理论依据。

增压富氧燃烧是大规模减少CO2排放的下一代碳捕集关键技术之一。利用增压富氧燃烧技术中的高压条件联合脱除烟气中的NOx和Hg具有独特的优势，是一种极具竞争力的富氧燃烧烟气净化技术。然而，现有研究缺乏对这一过程反应机理和相互作用机制的深入了解，对于其中Hg脱除的研究更是极少涉及。本项目基于富氧燃烧技术，充分利用实验与理论计算相结合的手段，研究加压条件下Hg/NO2的相互作用机制及动力学，考察了加压条件下NO2对Hg氧化的贡献，以及CO2和SO2对Hg与NO2反应的间接影响；利用量子化学理论计算，研究了加压条件下NOx/Hg联合脱除机理，确定了Hg/NO2体系的具体反应路径与产物；利用微正则变分过渡态理论结合RRKM主方程，求解了温度和压力依赖的速率常数，获得了准确的三阶动力学反应速率参数；基于富氧压缩实验与理论计算结果，形成了富氧烟气压缩过程中S/N/Hg一体化脱除工艺方案，为具有高效、经济脱除能力的富氧燃烧烟气净化技术的应用提供理论基础。