基于实测的京津冀地区燃煤工业锅炉有害重金属大气排放特征及迁移机制研究

Coal combustion from industry is one of the main contributors to the emission of toxic heavy metals. Toxic heavy metals could be emitted from coal combustion process of industrial boilers. After a series of physical and chemical reactions, toxic heavy metals could be migrated and transformed in different environment mediator, which can directly affect urban air quality and public health. Nowadays, the prevention of toxic heavy metals pollution has aroused much more concern. Therefore, study on emission characteristics and migration mechanism of atmospheric toxic heavy metals from coal-fired industrial boilers based on experimental measurements is really imminent. Firstly, based on stratified sampling and statistical analysis method, a screening method is established. Then, the database of atmospheric emission factors of atmospheric toxic heavy metals (Hg, Pb, Cd, Cr and As) from coal-fired industrial boilers in Beijing-Tianjin-Hebei (BTH) Region will be established based on experimental measurements, so as to master the atmospheric emission characteristics of five toxic heavy metals. Further, based on the principle of material balance and mass conservation, through the collection and analysis of fuel and combustion products, the chemical speciation and migration mechanism of toxic heavy metals in different combustion products will be revealed. Consequently, the main propose of this study is to provide scientific basis and fundamental data for the competent department of environmental protection to develop atmospheric heavy metal pollution control standards and countermeasures of coal-fired industrial boilers. It is very meaningful to improve the air quality and protect the health of public.

工业燃煤是我国大气有害重金属排放的主要贡献源之一。燃煤工业锅炉生产过程会释放多种重金属元素，经过一系列物理化学作用，可在不同环境介质中发生迁移转化，直接影响城市空气质量及公众健康。在重金属污染防治备受关注的今天，开展基于实测的燃煤工业锅炉有害重金属大气排放特征及迁移机制研究迫在眉睫。本研究首先利用分层抽样和统计分析等方法，建立燃煤工业锅炉代表性实测排放源筛选方法；之后基于现场实测，系统构建反映京津冀地区燃煤工业锅炉大气有害重金属（Hg、Pb、Cd、Cr和As）实际排放水平的本地化排放因子集，掌握有害重金属的大气排放特征；依据物料衡算和质量守恒原理，通过对燃料及不同燃烧产物采集与分析，探索有害重金属在不同输入和输出物料中的赋存形态及迁移规律。从而为环境保护主管部门制定相应的燃煤工业锅炉行业大气有害重金属污染防治标准及对策提供科学依据和基础数据支持，对改善空气质量、保障居民身体健康意义重大。

燃煤工业锅炉生产过程会释放多种重金属元素，经过一系列物理化学作用，可在不同环境介质中发生迁移转化，直接影响城市空气质量及公众健康。本项目立足于此研究背景，基于对代表性燃煤工业锅炉排放源的现场测试，系统开展京津冀地区燃煤工业锅炉有害重金属排放特征及迁移机制研究。本项目利用改进后的重金属烟气采样系统，选择16台代表性燃煤工业锅炉开展现场测试，对燃煤、烟气和燃烧副产物（飞灰、底灰、脱硫石膏和脱硫废水）中的五种重金属（Hg、Pb、Cd、Cr和As）进行采样，分析不同输入输出物料中重金属排放特征、富集特性及化学赋存形态，建立京津冀地区燃煤工业锅炉五种重金属高时大气空分辨率排放清单，探究有害重金属在不同输入和输出物料中的迁移规律。结果显示，燃煤工业锅炉烟气中Cd浓度均低于检出限，Hg、Cr、As和Pb四种重金属的平均排放浓度分别为0.27μg/m3、11.16μg/m3、1.64μg/m3和2.10μg/m3，其中Hg排放浓度远低于GB13271-2014中汞及其化合物的排放限值（50μg/m3）。飞灰中四种重金属的浓度普遍高于在底灰中的浓度，飞灰中重金属的相对富集因子普遍高于底灰，飞灰中重金属的富集能力更强。Hg、Cr、As和Pb四种重金属平均排放因子分别为0.005g/t，0.23g/t，0.04g/t和0.04g/t，对比两种锅炉类型来看，层燃炉Cr、As和Pb平均排放因子高于循环流化床炉，而层燃炉Hg排放因子低于循环流化床炉。利用“自下而上”的排放因子法，建立了2017年京津冀地区燃煤工业锅炉四种重金属的大气高时空分辨率排放清单，估算结果显示，2017年京津冀地区燃煤工业锅炉四种重金属的大气排放量分别为2.69吨（Hg）、57.22吨（Cr）、7.17吨（As）和69.33吨（Pb）。通过物质流分析发现，四种重金属的主要排放去向为飞灰，占比为41.7%-91.7%，且飞灰中四种重金属的主要化学赋存形态为残渣态，较为稳定，可以在环境中长久的存在，不易释放造成环境风险。研究结论可为国家相关部门制定相应的燃煤工业锅炉大气有害重金属污染防治标准及对策提供基础数据支持，对改善空气质量、保障居民身体健康意义重大。