燃煤电厂排放CPM相变机理研究及其衍生物对大气PM2.5贡献的环境风洞模拟

With the renovation of environmental protection facilities under ultra-low emission standard in China’s coal-fired power plants, the proportion of condensable particulate matter (CPM) in flue gas is becoming higher and higher. As one of PM2.5 precursors, the physical and chemical behaviour of CPM may be closely related to the explosive growth of PM2.5 in the atmosphere. Therefore, the present proposal proposes to study the phase transition mechanism of CPM under the ultra-low emission standards with the simulation experiment using the smoke box, and to clarify the nucleation mechanism. Combined with environmental wind tunnel and smoke box, simulate the phase change process of CPM at the chimney exit with a certain range, and elucidate the influence mechanism of meteorological factors on the phase transition and the formation of derivatives. With the help of the return-flow environmental wind tunnel, study migration and transformation rules of CPM derivatives in the mid-scale atmosphere boundary layer, and clarify the meteorological conditions on the inducement of PM2.5 generation. The research aim of this proposal is to establish and analyze the model of PM2.5 transition from the source emission to the atmospheric environment. The research results will be helpful to ascertain CPM’s contribution to atmospheric PM2.5, improve the formation mechanism of smog, and provide a theoretical basis for studying the composition and emission of fine particulate matter in the atmosphere.

随着我国燃煤电厂超低排放改造工作的深入，烟气中可凝结颗粒物（CPM）占比越来越高。作为PM2.5的前体物之一，CPM在大气中的物理化学行为可能与大气环境中PM2.5的爆发式增长存在着密切关系。基于此，本申请提出在超低排放条件下，利用烟雾箱模拟研究CPM在烟囱出口处的转化规律，探索其成核机理；借助环境风洞嵌套烟雾箱的“洞中箱”实验系统，研究烟囱出口一定范围内CPM的变化过程，明确气象因素对其相变及衍生物生成的影响机制；依托回流式环境风洞，研究CPM衍生物在中尺度大气边界层的迁移转化规律和气象条件对PM2.5生成的诱导作用。本研究旨在建立与分析CPM从源排放到大气环境PM2.5转变过程的模型，阐明其对大气环境PM2.5的贡献，完善雾霾形成机理，为大气环境中细颗粒物成分与排放特征的研究提供理论依据。

超低排放燃煤电厂中，可凝结颗粒物（condensable particulate matter，CPM）在快速冷凝条件下的气体-颗粒物转化过程受烟气成分（SO2，SO2，NH3，NOX等）、温度、湿度的调控，CPM的物理化学变化特征和扩散规律也会因为气象条件的差异性而有所不同。本项目从燃煤电厂全面实施超低排放的实际出发，自主搭建了动态烟气模拟系统，探索了其动态生成过程以及影响因素，运用烟雾箱+环境风洞模拟实验方案研究了CPM从烟囱排放口至大气边界层中尺度范围内的演变和扩散规律。项目研究内容主要包括CPM的气体-颗粒物转化机理研究，不同气象条件下CPM相变及其衍生物扩散过程模拟研究，大气边界层中CPM衍生物对环境PM2.5贡献研究。首先，本研究依据燃煤电厂烟气实际测量数据自主搭建了动态烟气模拟系统，并于快速冷凝条件下分析了CPM的气体-颗粒物转化机制，该实验从复杂多元烟气体系出发，研究了无机水溶性离子（SO42-，NO3-，NO2-和NH4+）的冷凝-团聚机制，完善了CPM形成和相变机理。然后，本项目结合并通过烟雾箱模拟大气环境，模拟研究了CPM考察湿度、光照、臭氧含量等气象条件变化对CPM及其CPM衍生物迁移转化规律的影响。最后，将动态烟雾模拟装置内污染物作为污染源并以环境风洞作为实验场地，进一步研究了中尺度范围内CPM及其衍生物的演变和扩散规律。本课题的研究成果，为我国超低排放设施的改造升级、燃煤电厂的CPM控制以及大气环境中细颗粒物成分与排放特征的研究提供基本理论依据。