燃煤电厂铅的迁移转化研究

采集我国6台有代表性电站锅炉的烟气以及燃煤、飞灰、底渣、脱硫石膏等样品,通过测试燃煤和燃煤副产物中铅含量以及烟气中铅的形态分布,考察了燃煤电厂铅的迁移转化规律及烟气常规污染物控制技术对大气铅排放的影响.结果表明,煤粉炉燃煤过程中,煤中铅释放强度高,平均释放率为97.11%;循环流化床锅炉铅的释放率相对较低,约为84.99%.锅炉出口烟气中铅主要为颗粒态铅(Pbp),比例高达86%~92%,并且与燃煤中氯含量具有正相关性.烟气污染物控制装置对大气铅具有协同脱除效果,尤其是除尘装置.静电除尘对铅的平均脱除效率为91.85%,布袋除尘为95.12%.石灰石-石膏湿法脱硫装置可脱除35.67%~77.81%铅,脱除效率主要与脱硫塔操作条件有关.燃煤中的铅经过燃烧和烟气污染物控制装置后,81.97%~90.18%转移到飞灰中,具有高富集性;脱硫石膏中的铅占3.94%~11.82%;只有1.75%~5.40%通过烟囱排入大气.

Lead emission and speciation of coal-fired power plants in China

A full-scale field study of lead (Pb) emission from coal combustion was conducted at six coal-fired power plants in China. Flue gas samples were taken from the inlets and outlets of the existing air pollutant control devices (APCDs) to investigate their effects on speciation and distribution of Pb in the flue gas. Concurrent with flue gas sampling, coal, bottom ash, fly ash and samples from the FGD process (desulfurization gypsum and waster water) were collected. Average release of Pb from the pulverized-coal (PC) boilers was 97.11% of Pb in feed coal. In comparison, the release of Pb from a fluidized bed furnace was lower, at 84.99%. A high proportion of Pb (86%~92%) was found as particulate-bound Pb (Pbp) in the flue gas at outlet of boiler. Further, there was a positive correlation between the proportion of particulate-bound Pb (Pbp) and the chlorine content in the coal. The existing APCDs were able to remove most of the Pb in the flue gas, dedusting devices being most effective. Around 91.85% of Pb in flue gas was removed by electrostatic precipitator (ESP), while Bag-house filters captured 95.12%. The Pb removal efficiency of wet flue gas desulfurization (FGD) varied from 35.67 to 77.81%, which depended on the process operation. The result of overall lead (Pb) balance showed that 81.97%~90.18% of Pb in feed-coals was discharged with fly ash, while 3.94%~11.82% of Pb was discharged with the desulfurization gypsum. Only 1.75%~5.40% was emitted directly into the atmosphere.