水汽相变协同控制Hg和PM2.5的机理研究

Emission of mercury and particulate matters with an aerodynamic diameter less than 2.5μm has attracted more and more attentions. Coal-fired power plants are the main pollution source. Hence, control of mercury and PM2.5 emitted from coal-fired power plants is the key problem urgently to be solved. Since mercury and PM2.5 can not be removed efficiently in the existing wet flue gas desulfurization (WFGD) process, simultaneous removal of mercury and PM2.5 by combination of vapor heterogeneous condensation and WFGD system is proposed in this project. As vapor condenses, gaseous mercury can be dragged on to the surface of PM2.5 by thermophoresis and diffusiophoresis. Meanwhile, PM2.5 with mercury on it’s surface can enlarged and then removed efficiently. Condensation characteristic and accumulation regulation of gaseous mercury on the surface of PM2.5 in the stream phase transition room is the key point of this technique. Therefore, chemical speciation change of mercury, their accumulation regulation on the surface of PM2.5, influence of vapor heterogeneous condensation on the condensation and removal characteristic of gaseous mercury, and the simultaneous removal effect of mercury and PM2.5 in the stream phase transition room will be investigated in this project. The aims are to seek the technical basis of the simultaneous removal of mercury and PM2.5 by vapor heterogeneous condensation in the WFGD system. The research results will contribute to fundamentals for the simultaneous removal of mercury and PM2.5 from coal-fired flue gas with high efficiency.

汞和细颗粒物（PM2.5）污染问题日益受到重视，控制燃煤电厂烟气中汞和PM2.5排放是亟待解决的关键问题。鉴于现有湿法烟气脱硫（WFGD）装置不能有效脱除汞和PM2.5，本项目在湿法烟气脱硫系统中应用水汽相变技术，一方面水汽相变过程中通过热泳、扩散泳作用拖曳气态汞在PM2.5表面富集，另一方面促使富集汞的细颗粒凝结长大脱除，实现燃煤烟气中汞和PM2.5的协同高效脱除。湿法脱硫及水汽相变环境下烟气中气态汞在细颗粒物表面的吸附凝结特性和富集规律是本技术的关键；为此，针对湿法脱硫烟气降温过程中气态汞形态变化特性、水汽相变对气态汞的凝结脱除特性及其在PM2.5表面的富集规律的影响机制以及水汽相变促进WFGD系统协同脱除汞和PM2.5的性能进行试验和理论研究，以期揭示WFGD系统中应用水汽相变协同脱除汞和PM2.5的技术基础，从而为实现燃煤烟气中汞和PM2.5协同高效脱除提供试验和理论依据。

近年来雾霾频发，已成为我国大气污染的重大问题，控制燃煤电厂汞和PM2.5排放是亟待解决的关键问题。鉴于现有湿法烟气脱硫（WFGD）装置不能有效脱除气态汞和PM2.5，本研究在湿法烟气脱硫系统中应用水汽相变技术，一方面水汽相变过程中通过热泳、扩散泳作用拖曳气态汞在PM2.5表面富集，另一方面促使富集汞的细颗粒凝结长大脱除，实现燃煤烟气中汞和PM2.5的协同高效脱除。本研究基于自行搭建的湿法烟气脱硫模拟实验系统及改造后的湿法烟气脱硫热态试验装置，对燃煤烟气中汞和PM2.5的浓度及排放特性进行分析测试，在湿法烟气脱硫环境下探索了汞和PM2.5浓度及形态变化特性，并结合水汽相变技术考察水汽相变环境下PM2.5和汞协同脱除特性。获得技术指标如下：在保证良好湿法脱硫性能的同时，控制液气比10～15 L/Nm3，塔进口烟气温度110～120℃左右，脱硫液温度约45℃，在水汽相变室添加0.06～0.08kg∙Nm-3蒸汽可使PM2.5协同脱除效率达到60～70％以上，并且部分气态汞可转化为颗粒态汞随细颗粒物通过相变凝结长大后被有效脱除，总汞浓度明显降低。该成果可为实现工业湿法烟气脱硫装置协同脱除PM2.5和汞提供可靠的理论和实验依据。