循环流化床燃煤电厂铅的迁移特性

Migration Characteristics of Lead in Fluidized Bed Furnace Coal-fired Power Plants

选取2家燃煤电厂3台循环流化床机组进行现场监测,在不同负荷条件下,采集并分析燃煤、烟气、飞灰、炉渣等样品的Pb含量,通过物料平衡核算,对循环流化床机组各环节Pb的迁移特性进行研究。结果表明:机组负荷变化对烟气、飞灰、炉渣的Pb含量影响不大,烟气Pb排放质量浓度均在2μg/m^3以下。电袋复合除尘处理后,烟气中颗粒态Pb的浓度总体低于气(溶胶)态Pb的浓度。Pb在炉渣和飞灰中均有富集,平均富集因子分别为2.16和3.02。飞灰较炉渣对Pb具有更强的富集能力,布袋灰中Pb含量略高于电除尘灰。循环流化床锅炉燃烧后Pb分布在飞灰、炉渣和外排烟气中的比例分别为62.49%、37.49%和0.02%,Pb释放率低于煤粉炉,在Pb污染控制方面更具优势。除尘过程对烟气中Pb的影响主要表现为飞灰对Pb的吸附和除尘器对飞灰的分离脱除,尤以后者为主。由于烟气中气(溶胶)态Pb所占的比例很低,Pb基本吸附在飞灰上,除尘效率的高低直接决定了Pb的去除效果。

Lead （Pb） is a harmful element and may cause environmental issues during coal combustion. A full-scale study of Pb migration was conducted at three fluidized bed furnace boiler units of two coal-fired power plants. Samples of coal, flue gas, fly ash, slag were collected under different load conditions of boiler units and their Pb content was also detected. Migration characteristics of Pb in all sectors of boiler units were studied by material balance accounting. The results revealed that changes of load had little effect on the Pb content of flue gas, fly ash and slag. Pb concentrations in flue gas emissions were less than 2 Ixg,/m3. In the flue gas after electrostatic bag dust collectors, Pb content of particulates was less than that of aerosol. Pb accumulated in slag and ash, with average enrichment factors of 2.16 and 3.02. Fly ash had more enrichment capability of Pb than slag. Pb content of dusts in bag collectors was slightly higher than those in electrostatic collectors. After combustion, the proportion of Pb distribution was 62.49% in fly ash, 37.49% in slag and 0.02% in flue gas. As fluidized bed furnace boiler had a lower release rate of Pb than pulverized coal-fired boiler, it had more advantages in Pb pollution control. Effect of dust removal process on Pb in flue gas mainly occurred as fly ash adsorption on Pb and dust collector separation on fly ash, the latter dominated. Because the proportion of Pb in flue gas was low and Pb was basically adsorbed on fly ash, the dust removal efficiency directly determined the removal efficiency of Pb.