湿法烟气脱硫过程中PM2.5物性变化及其高效脱除的研究

The emission of particulate matters with an aerodynamic diameter less than 2.5 μm, is an important environmental issue. Coal combustion is one of the main sources of fine particles in atmosphere. Although the present conventional dust removal devices have achieved high efficiencies, they are inefficient in the separation PM2.5 from flue gas. Therefore, large amount of fine particles escape into the air, and the removal of fine particles from coal-fired flue gas have become important. Process optimization on existing pollutant control equipment and multi-field synergistic effect are the main technical development trend of PM2.5 emission control. Because that PM2.5 may be formed during the wet flue gas desulfurization process and the desulfurated scrubbed flue gas can be saturated, the technical route combining optimization of desulfurization process and heterogeneous condensation is proposed for reducing the formation and efficiental removal of PM2.5 in this project. Supersaturation is achieved by mixing the desulfurated scrubbed flue gas and humid air with a proper mixing ratio, and impinging stream technique is also introduced to lower the energy consumption for establishing the supersaturated vapor environment and improve the condensational growth and removal of PM2.5. Therefore, the formation mechanism of PM2.5, the interaction and transformation between PM2.5 and SO2 during WFGD process, and the behavior law of condensational growth, collision and coalescence behavior of PM2.5 in the impinging stream phase transition room will be investigated in this project. The aims are to disclose the relationship between the variation of PM2.5 properties and WFGD process,and seek the technical basis of inhibiting the formation and improving the removal of PM2.5. The research results will contribute to the fundamentals for PM2.5 removal by WFGD system with high efficiency.

PM2.5污染已成为我国突出的大气环境问题，结合现有污染物控制设备进行过程优化及多场协同作用是控制PM2.5的重要技术发展方向；本项目针对现有湿法烟气脱硫（WFGD）过程中可形成PM2.5及其脱硫净烟气处于饱和状态的特点，提出通过优化湿法脱硫工艺抑制PM2.5形成及增进洗涤捕集，协同利用蒸汽相变促进脱硫净烟气中PM2.5脱除的技术路线，采用引入适量湿空气使脱硫净烟气达到过饱和，并将撞击流技术应用于蒸汽相变以降低建立过饱和水汽环境的能耗及增进PM2.5凝并长大效果。为此，本项目对WFGD过程中PM2.5形成及其与SO2的相互作用和转化机制、撞击流相变环境下PM2.5核化凝结长大与碰撞聚并的行为规律加以研究，揭示PM2.5物性改变与WFGD过程间的内在关联，寻求抑制PM2.5形成及撞击流与蒸汽相变耦合促进PM2.5脱除的技术基础，从而为现有WFGD系统实现高效脱除PM2.5提供试验与理论依据。

PM2.5污染已成为我国突出的大气环境问题，结合现有污染物控制设备进行过程优化及多场协同作用是控制PM2.5的重要技术发展方向。针对现有湿法烟气脱硫（WFGD）过程中可形成PM2.5及其脱硫净烟气处于饱和状态的特点，如何通过优化湿法脱硫工艺抑制PM2.5形成及增进洗涤捕集，并协同利用蒸汽相变促进脱硫净烟气中PM2.5脱除，是迫切需要解决的关键科学问题。本项目为实现WFGD系统高效脱除PM2.5，基于实际燃煤电站现场测试及自主搭建模拟试验平台，构建了PM2.5物性改变与WFGD过程间的内在关联，获得在保证脱硫效率的前提下，对WFGD工艺的优化抑制PM2.5形成、增进PM2.5洗涤脱除开展试验研究；同时，试验研究了撞击流相变环境下湿法脱硫净烟气与蒸汽（或湿空气）混合过程中过饱和水汽环境的形成规律及PM2.5核化凝结长大、碰撞聚并的行为规律。结果表明，石灰石-石膏法脱硫系统细颗粒物主要来源于脱硫浆液蒸发夹带作用，净烟气中液滴粒径分布主要集中在20μm以下，而细颗粒物粒径分布主要集中在亚微米级。通过抑制细小石膏晶粒的形成，对减少脱硫系统出口石膏晶粒排放有所作用，与之相比，液气比、空塔气速、塔内流场结构等工艺条件的影响更为显著。WFGD系统对SO3酸雾的脱除效率在30~50%左右，脱除效率随液气比的增大及塔入口烟温的降低有所提高，双塔系统脱除效率高于单塔系统。数值计算结果表明，液滴粒径分布对于除雾效率的影响作用很大，同时液滴粒径为0.2 mm时逃逸率接近100 %。氨法脱硫过程中产生的气溶胶主要通过非均相反应形成，降低脱硫浆液pH值和脱硫塔入口烟气温度有利于抑制氨法脱硫过程中SO2-H2O-NH3非均相反应。脱硫净烟气中通过添加蒸汽、烟气降温及添加湿空气可建立过饱和水汽环境，促进脱硫过程对燃煤PM2.5及SO3酸雾的脱除，典型工况下PM2.5的脱除效率可提高30%-45%。撞击流相变室可进一步提高PM2.5的脱除效率，PM2.5排放浓度降低率可由原来的40%左右提高至60%左右。研究成果不仅可为控制湿法烟气脱硫净烟气中PM2.5排放问题提供重要参考，同时为实现湿法烟气脱硫过程中PM2.5高效脱除奠定技术基础。