细颗粒物污染已成为我国突出的大气环境问题，是导致大气能见度降低、雾霾天气、气候变化等重大问题的重要因素。燃煤电站是引起我国大气环境中细颗粒物含量增加的主要污染源，控制燃煤电站细颗粒物排放是迫切需要解决的关键问题。石灰石-石膏湿法烟气脱硫(WFGD)系统是燃煤烟气终端处理装置，对烟气中细颗粒物物性存在重要影响，为增强WFGD系统对细颗粒物的脱除，开展石灰石-石膏湿法烟气脱硫过程中细颗粒物转化机制研究具有重要意义。 本文首先基于实际燃煤电厂湿法脱硫系统及试验室装置，对石灰石-石膏湿法脱硫过程中细颗粒物物性变化进行了测试分析。结果表明，石灰石-石膏湿法烟气脱硫过程中，通过脱硫浆液的洗涤作用可协同脱除烟气中的部分细颗粒物，同时，脱硫过程中会形成新的细颗粒物，粒径集中在亚微米级范围。石灰石-石膏湿法烟气脱硫过程中形成的细颗粒物与脱硫浆液中固体晶粒存在一定关联，主要源于脱硫浆液中的石膏、亚硫酸钙及未反应的CaCO₃被烟气夹带出脱硫系统。随着空塔气速、液气比的提高，以及脱硫浆液浓度的增加，脱硫净烟气中细颗粒物浓度增加。 由于脱硫过程中所形成细颗粒物与脱硫浆液中固体晶粒存在一定关联，利用模拟烟气湿法脱硫试验系统，试验考察了石灰石-石膏湿法脱硫浆液结晶特性并分析探究了脱硫浆液中晶体特性与脱硫净烟气中细颗粒物物性之间的关系。结果表明，采用合适的脱硫浆液温度，较大粒度的石灰石，较低的脱硫浆液pH值及脱硫增效剂有利于抑制细小石膏晶粒的形成；脱硫浆液中Fe³⁺及F⁻有利于促进细小石膏晶粒的形成。脱硫净烟气中细颗粒物与脱硫浆液中固体晶粒形貌及主要元素相近，但颗粒物粒径明显较小，同时元素比例有所变化。随着脱硫浆液中晶体平均粒度增大，细小晶粒数量减少，脱硫净烟气中雾滴和脱硫浆液含固率比值减小，细颗粒物数量浓度降低，平均粒径有所增加。 石灰石-石膏湿法烟气脱硫过程中形成的细颗粒物主要源于脱硫浆液液滴夹带。利用模拟湿法烟气脱硫试验装置及浆液夹带试验装置，对脱硫浆液夹带及其与脱硫净烟气中细颗粒物物性关系开展了试验研究。结果表明，夹带脱硫浆液液滴特性与喷嘴雾化特性相关，随着喷淋流量、喷淋压力的增加及脱硫浆液浓度的减少，脱硫浆液液滴粒径降低。通过高温烟气蒸发作用，脱硫塔内液滴粒径有所减小。当塔进口烟气温度增加，脱硫净烟气中细颗粒物浓度有所增加。脱硫净烟气中液滴粒径分布主要集中在30μm以下，颗粒物主要集中在亚微米级。随着空塔气速、液气比、脱硫浆液浓度的提高，以及脱硫浆液中晶体粒度的降低，脱硫净烟气中微米级液滴数量百分比及亚微米级细颗粒物数量浓度增加明显。 同时，WFGD系统中存在细小SO₃酸雾，基于实际燃煤电厂湿法脱硫系统及试验室装置，试验探究了石灰石-石膏湿法脱硫系统对SO₃酸雾的脱除特性。结果表明，酸露点温度以上的燃煤烟气进入湿法脱硫系统后被急速冷却到酸露点以下，主要通过均相成核作用形成SO₃酸雾。酸露点温度以下的燃煤烟气中飞灰粒径变化与SO₃酸雾有一定关联，随着SO₃酸雾浓度的提高，脱硫塔进口飞灰粒径有所增加。石灰石-石膏湿法脱硫系统对SO₃酸雾脱除效率为30-50％。随着脱硫液气比及脱硫塔进口飞灰浓度的增加，湿法烟气脱硫系统对SO₃酸雾脱除效率均有所提高。随着塔进口烟温降低，WFGD系统对SO₃酸雾脱除效率增加，特别是当进口烟温低于酸露点时，脱除效率增加更趋明显。双塔湿法脱硫系统对SO₃酸雾脱除效率为50-65％，明显高于单塔湿法脱硫系统，随着煤中硫分与灰分的增加，SO₃酸雾脱除效率有所提高。 为控制湿法脱硫净烟气中细颗粒物排放，利用实际燃煤湿法烟气脱硫系统及实际燃煤电厂脱硫系统，试验探究了过程优化对增强石灰石-石膏湿法脱硫系统脱除细颗粒物的影响。结果表明，在保证脱硫效率的前提下，优化脱硫操作条件后，石灰石-石膏湿法脱硫系统对细颗粒物质量浓度及数量浓度脱除效率可增加15-20％。增加喷淋层数有利于细颗粒物的脱除。实际燃煤电厂单塔双循环脱硫系统可实现烟气颗粒物高效脱除，但其脱除效率存在较大波动。实际燃煤电厂双塔双循环脱硫系统可增强脱除烟气中细颗粒物，其脱除效率达50-60％。 关键词：细颗粒物；湿法烟气脱硫(WEGD)：SO₃酸雾；形成；排放

Fine particle pollution has been the most serious problem in atmospheric environment, which is the important factor resulting in significant issues such as the reduction of atmospheric visibility, haze and climate change. As the coal-fired power plant is one main source of fine particle pollution, it is urgent to control the fine particle emissions in the coal-fired power plants. Furthermore, the limestone-gypsum wet flue gas desulfurization (WFGD) system, which is the terminal processing unit of coal-fired flue gas, has important influence on the properties of emitted fine partcles. In an attempt to increase the removal efficiency of WFGD system on the fine particles, it is essential to investigate the fine particle transfer mechanism during the limestone-gypsum desulfurization. Based on the wet flue gas desulfurization systems in the coal-fired power plants and the lab, experiments on the physical property change of fine particles during the limestone-gypsum desulfurization process were carried out. The results showed that part of fine particles were removed via the desulfurization slurry scrubbing, while new fine particles with sizes mainly in the submicron range were formed during the limestone-gypsum desulfurization process. These fine particles were related to the solid crystals in the desulfurization slurry, which were mainly the initial gypsum, calcium sulfite and unreacted CaCO₃ entrained out of the WFGD system. With the increase of superficial velocity, liquid-gas ratio and slurry concentration, the fine particle concentrations after desulfurization were increased. As the generated fine particles during desulfurization were related to the solid crystals in the desulfurization slurry, the crystallization properties of the limestone-gypsum desulfurization slurry were investigated with the simulated flue gas desulfurization system. Moreover, the relationship between the crystal properties in the slurry and the fine particles emitted after desulfurization was analyzed. The results showed that proper temperature of desulfurization slurry, larger limestone, lower pH value and the addition of desulfurization synergist inhibited the formation of fine crystals in the slurry. And the additions of Fe³⁺ and F⁻ were beneficial for the formation of fine crystals in the slurry. The morphology and main elements of fine particles after desulfurization were similar to those of crystals in the slurry, while the sizes were smaller and the element percentages changed. With the increase of crystal mean sizes and the decrease of fine crystal concentrations in the slurry, the solid concentration ratio of emitted droplet and slurry was decreased and the emitted fine particle concentrations were decreased with larger mean sizes. The generated fine particles during desulfurization were mainly from the entrainment of desulfurization slurry droplets. With the simulated flue gas desulfurization system and the slurry entrainment system, the relationship between the entrained slurry droplets and emitted fine particles was investigated. The results showed that the entrained droplet properties were related to the nozzle atomization characteristics. With the increase of the spray flow, the spray pressure, and the decrease of the slurry concentration, the sizes of sprayed droplets were decreased. The droplet size was slightly decreased after the contact with high temperature flue gas. With the increase of inlet flue gas temperature, the fine particle concentrations after desulfurization were increased. The droplets entrained out of the desulfurization system were mainly smaller than 30μm and the fine particles were mainly in the submicron range. With the increase of the superficial velocity, the liquid-gas ratio, the slurry concentration, and the decrease of crystal sizes in the slurry, the count percentages of micron droplets and the number concentrations of submicron particles after desulfurization were significantly increased. Meanwhile, the fine particles of SO₃ acid mist existed in the WFGD system. With the wet flue gas desulfurization systems in the coal-fired power plants and the lab, investigations on the removal characteristics of SO₃ acid mist in the limestone-gypsum desulfurization process were carried out. The results showed that SO₃ acid mist was formed mainly via the homogeneous nucleation when the temperature of the coal-fired flue gas entering into the desulfurization system was rapidly decreased below the acid dew point. Besides, when the flue gas temperature was below the acid dew point, the sizes of fly ash paricles were related to the SO₃ acid mist and with the increase of SO₃ acid mist concentration, the fly ash particles were larger. The removal efficiency of limestone-gypsum desulfurization system on the SO₃ acid mist was from 30% to 50%. With the increase of the liquid-gas ratio and the inlet particle concentration of fly ash, the removal efficiency was increased. With the decrease of the inlet flue gas temperature, the removal efficiency was increased, especially when the inlet flue gas temperature was below the acid dew point. The removal efficiency of the desulfurization system with double towers on the SO₃ acid mist was from 50% to 65%, which was higher than that of the desulfurization system with single tower. With the increase of sulfur content and ash content in the coal, the removal efficiency was increased. For the control of fine particle emissions after desulfurization, the effect of process optimization on the fine particle removal during the limestone-gypsum desulfurization process was investigated with the coal-fired flue gas desulfurization systems in the coal-fired power plants and the lab. The results showed that the removal efficiency of limestone-gypsum desulfurization system on fine particles was increased by 15-20% on the premise that the demanded SO₃ removal efficiency was achieved. The increase of spray levels was beneficial for the fine particle removal. The desulfurization system with single tower in industry could achieve high removal efficiency of fine particles while the efficiency had great fluctuation. And the removal efficiency of the desulfurization system with double towers on fine particles was increased in industry, which was from 50% to 60%. Keywords: fine particle; wet flue gas desulfurization (WFGD); SO₃ acid mist; formation; emission