燃煤电厂超低排放机组重金属铅、砷排放特性

Emission characteristics of Pb and As from an ultra-low emission coal-fired power plant

为研究超低排放改造后燃煤电厂重金属元素铅(Pb)和砷(As)的排放特性,采用美国环保部推荐的EPA Method 29方法,对机组选择性催化还原(SCR)脱硝系统前、电除尘器(ESP)前后和湿式电除尘器(WESP)前后的烟气进行平行取样分析,同时对入炉燃料、底渣、ESP灰、石灰石浆液、石膏和脱硫废水等进行了取样分析,然后通过质量平衡核算得到Pb、As在燃煤副产物中的分配比例以及迁移排放特性。结果表明:燃料中的Pb和As主要迁移到ESP灰和底渣中;ESP前颗粒态重金属是Pb和As在烟气中的主要存在形式,占比均达98%以上;污染物控制装置(APCDs)对Pb和As的协同脱除效率均达到99%以上,WESP出口Pb和As的质量浓度分别为2.71mg/m^3和0.18mg/m^3,排放因子分别为0.91×10^-12 g/J和0.06×10^-12 g/J。因此,该APCDs可以有效控制烟气中Pb和As的排放。

In order to study the emission characteristics of heavy metal elements(Pb,As)from an ultra-low emission coal-fired power plant in China,the EPA Method 29 recommended by American Environmental Protection Department was used to carry out parallel sampling analysis for the flue gas in front of the selective catalytic reduction(SCR)denitration system,in front of and behind the electrostatic precipitator(ESP)and the wet electrostatic precipitator(WESP).Moreover,the feed fuel,bottom ash,ESP ash,limestone slurry,gypsum and desulfurization wastewater were also sampled and analyzed.Then,the distribution proportions and migration/emission characteristics of Pb and As in by-products of the coal combustion were obtained based on mass balance calculation.The results indicate that,the Pb and As in the fuel mainly migrates into the ESP ash and bottom slag.The particulate-bound Pb and As are the main existing forms of heavy metals in flue gas in in front of the ESP,which account for over 98%.The synergistic removal efficiency of Pb and As by the pollutant control device(APCDs)both reaches higher than 99%.The mass concentration of Pb and As in flue gas at the WESP outlet are 2.71mg/m^3 and 0.18mg/m^3.The emission factor of Pb and As is 0.91×10^-12 g/J and 0.06×10^-12 g/J.Therefore,the APCDs equipped in the ultra-low emission coal-fired power plants can effectively control the emission of Pb and As in flue gas.