湿法脱硫装置对燃煤锅炉PM2.5排放特征的影响

采用二级稀释采样方法对1台电厂煤粉炉、1台电厂CFB锅炉和2台工业层燃炉配备的WFGD前后烟气中PM_2.5进行现场采样。采用ELPI分析PM_2.5的数量及质量浓度粒径分布；通过SEM分析PM_2.5的显微结构，通过XRF、ICP-OES和离子色谱法分别对PM_2.5中次量、痕量元素及水溶性离子含量进行测定。研究结果表明，相比于WFGD前，煤粉炉和CFB锅炉WFGD后PM_2.5质量浓度减少，而层燃炉WFGD后PM_2.5质量浓度增加。WFGD后PM_2.5中存在大量块状、层状、片状、细小柱状和球形颗粒聚合体的结构，浆液成分及脱硫产物的附着会使PM_2.5的外观形貌特征发生显著变化。脱硫后由于脱硫浆液的参与，PM_2.5中Ca、S及相应Ca²⁺、SO₄^2-含量显著增加，Si和Al的含量下降；气相的As、Se和Hg也会发生不同的化学变化从而进入PM_2.5。湿法脱硫过程中浆液会捕集烟气中颗粒物，但脱硫浆液成分及脱硫产物会经由干化作用直接形成颗粒或与原有颗粒经碰撞聚合形成新颗粒。

Influence of wet flue gas desulfurization devices on PM2.5 emission characteristics of coal-fired boilers

In this paper, a two-stage dilution sampling method was applied to collect PM_2.5 in flue gas before and after the WFGDs in a utility pulverized coal boiler, a utility CFB boiler and an industrial grate-fired boiler, respectively. PSDs (particle size distributions) of PM_2.5 number and mass concentrations were analyzed by ELPI (electrical low pressure impactor), microstructures of PM_2.5 were analyzed by SEM (scanning electron microscopy), and the contents of minor and tract elements and water-soluble ions in PM_2.5 were analyzed by XRF (X-ray fluorescence), ICP-OES (inductively coupled plasma optical emission spectroscopy) and IC (ion chromatography), respectively. The results showed that the mass concentrations of PM_2.5 generated from the pulverized coal boiler and the CFB boiler after desulfurization were higher than those before desulfurization, but the mass concentrations of PM_2.5 generated from the pulverized coal boiler and the CFB boiler after desulfurization were lower than those before desulfurization. There existed blocky, layered and finely columnar microstructures on the surfaces of PM_2.5 after the WFGDs, and several particles belonging to PM_2.5 were the agglomerates consisting of fine spherical particles. The attachment of the slurry composition and the desulfurization product will cause a significant change in the appearance of the PM_2.5. After desulfurization, the contents of Ca, S and Ca²⁺ and SO₄^2- in PM_2.5 were significantly increased due to the participation of desulfurization slurry, while the contents of Si and Al decreased. The As, Se and Hg in the flue gas will also undergo different chemical changes to enter PM_2.5. During the wet desulfurization process the slurry can trap particles in the flue gas, but the desulfurization slurry composition and desulfurization products will be dried to form particles or be collocated with the original particles to form new ones.