燃煤电厂烟囱降雨机理分析

针对国内大部分燃煤电厂取消GGH后普遍出现的“烟囱雨”现象,通过对某电厂进行现场烟气采样,收集烟囱降雨、烟道和烟囱冷凝水、和脱硫浆液等样品,通过离子色谱与XPS等方法分析各样品中的元素组分变化规律;运用扫描电镜法观察固形物的表面形貌,最终量化烟囱降雨中水分、固形物的来源.研究结果显示,即使脱硫系统、除雾器正常工作,饱和湿烟气在净烟道/烟囱壁面仍可形成的冷凝液膜,当疏水不畅、烟气流速过高的条件下,导致壁面液膜卷吸回流,从而构成烟囱雨中雨的主要来源;烟道/烟囱壁面累积黏附的飞灰、石膏等杂质,随冷凝液滴二次回流进入烟气,造成烟气中自携浆液浓度沿程呈增长趋势.烟囱降雨与烟道疏水冷凝液成分特性最为接近,“烟囱雨”中固形物为粉尘颗粒-板块状结垢的团聚体,也与冷凝水中固形物同源,降雨中固形物的成分取决于电厂除尘、脱硫、除雾器运行及疏水效率等元素的综合影响,该电厂烟囱降雨固形物中飞灰贡献率为63.1%.烟道/烟囱内冷凝液在疏水不畅的情况下的二次回流卷吸是产生烟囱雨的主要原因,基于此机理分析,需对湿烟道和湿烟囱进行优化改造,合理布置疏水系统,及时排出壁面冷凝液,以解决烟囱降雨问题.

Experimental study of formation mechanism of stack rainout from coal-fired power plant

Most coal-fired power plants in China have abandoned Gas-Gas-Heater, and thereof resulting in frequent rainout around stacks. Extensive samples, including flue gas, stack rainout, discharged liquid from duct and stack, and slurry, were collected and analyzed for elemental distribution using ICP and XPS. Morphology analysis on solid samples using SEM was also performed. The goal is to perform a source apportionment analysis of stack rainout.The results indicated that, even though FGD and mist eliminator were operated properly, the wet flue gas was condensed on the duct/stack inner surface. Part of the formed liquid droplet was re-entrained into the flue gas as the condensed liquid could not be effectively discharged and the flue gas local velocity was high, which is the main source of the stack rainout. Meanwhile, fly ash and gypsum that were adherent to the inner surface of duct and stack were also re-entrained with the liquid droplet into the flue gas, causing increased slurry concentration along the flue gas flow. Elemental distributions between stack rainout and stack liquid discharge were quite similar. The morphology of the undissolved in the stack rainout showed agglomerate of fly ash and gypsum scale, which have also been observed in the liquid discharge. The elemental composition of un-dissolved solid in the stack rainout is determined by combining results of fly ash collection, wet flue gas desulphurization, mist eliminator, and liquid discharge. Fly ash accounts for 63.1% of the total undissolved in the stack rainout for the testing plant. Since the main contributor to the stack rainout is the re-entrainment of condensed liquid discharge from duct and stack, optimization on duct/stack design and liquid discharge alignment is necessary to eliminate stack rainout.