基于Cl自由基注入的煤富氧燃烧烟气Hg高效脱除实验研究

Coal combustion is the main anthropogenic mercury emission source in China. Oxy-coal combustion technology is undergoing rapid development as a potential multipollutant control technology for simultaneously controlling of CO2, NOx and SOx from fossil fuel-fired power plants. However, mercury may cause liquid metal embrittlement and material failure of aluminum (Al) heat exchangers during CO2 compression process. Therefore, it must be high-efficiently removed before CO2 compression. However, mercury removal was determined by the Hg0 oxidation. Based on the fact that Hg0 can be effectively oxidized by Cl free radicals, this project is to conduct a systematic research on fundamental understanding about the generation and transportation of high concentration Cl free radicals. The influences of flue gas components, as well as the interaction mechanism between NO and SO2 removal by O3 and OH radicals versus Hg0(g) oxidation by Cl radicals will be investigated in detail. Hg compounds in products will be analyzed and tested in order to reveal the oxidation path and fate of Hg.

燃煤是我国最大的人为汞排放源。煤富氧燃烧技术因具有同时脱除CO2、NOx、SO2 等多种燃煤污染物的潜力而成为研究热点。富氧燃烧CO2压缩过程中，Hg由于其对铝合金换热器的低温脆化和腐蚀作用，需在CO2压缩前高效率脱除。Hg脱除的核心是Hg0的高效氧化。本项目提出一种基于Cl自由基注入的Hg0高效氧化脱除思路，拟通过实验和模拟研究，揭示高浓度Cl自由基的产生及输运机理，分析煤富氧燃烧烟气组分对Cl自由基定向氧化Hg0的影响，探讨NO及SO2脱除过程对Hg0氧化脱除过程的影响规律，揭示Hg、NO和SO2污染物间的协同脱除及相互影响机制，耦合Hg、NO、SO2的脱除过程，实现Hg的高效氧化与NO/SO2一体化脱除，以期为煤富氧燃烧烟气净化奠定理论基础；同时深入分析脱除产物中Hg的分布及形态，为Hg的最终脱除确定合理归宿。

煤的富氧燃烧因烟气压缩回收CO2过程中，Hg对其铝合金换热器的低温脆化和腐蚀作用，面临着Hg0的高效脱除需求。Hg0脱除的核心是Hg0的高效氧化。本项目基于Cl自由基注入的Hg0高效氧化脱除思路，通过实验和模拟手段，对Cl自由基的产生及输运、Cl自由基注入定向Hg0氧化及典型煤富氧燃烧烟气组分的影响、Hg的高效氧化与NO/SO2一体化脱除进行了研究。结果显示，降低注入烟气温度、增加Cl注入量以及烟气中的NO均有利于Hg0氧化，最佳放电电压的选取则与自由基源气体组成密切相关，一定条件下，注入极少量Cl2（6 ppm）即可获得97.9%的Hg0氧化率；SO2无论是单独存在，还是与NO共存，均显示了对Hg0氧化的抑制作用；在Hg/NO/SO2的协同脱除过程中，Hg更易富集至CaSO3颗粒及浆液中，而高浓度CO2气氛会降低Hg在WFGD浆液中的富集，加剧Hg0的再释放；阴离子NO3-和SO32-会导致大量的Hg从CaSO4颗粒和浆液中迁徙至气相释放出来，而Cl-离子则可使得更多的Hg残留在液相中，尤其是在NO3-和SO32-存在的情况下，但是该作用对浆液的pH值很敏感。