煤中矿物质对重金属排放和PM2.5生成控制机理研究

Chronic exposure to airborne fine particulate matter with diameter less than 2.5 μm (PM2.5) is associated with adverse human health impacts including morbidity and mortality. Although China's authorities have not revealed measurements for PM2.5, its average concentration in some big cities measured by some research institutions and universities far exceed the health standards (20 μg/m3), proposed by WHO. One of the main source of PM2.5 is the coal combustion, especially the mineral matters in coal. In this project, the study was carried on the control mechanism of mineral matters in coal on trace elements and PM2.5 emission. Coal is a complex multi-phase material, composed of macerals and an inorganic component made up of minerals. Based on the contrast of chemical composition, micro-morphology and stucture between mineral matter and PM2.5, distrubution characteristics of mineral matters and trace elements in different sized ash samples from coal combustion in drop-tube furnace, transition and reaction characteristics of different minerals, mineral assemblages in high temperature, the dynamic reaction model (fragmentation, evaporation, reaction, condensation, and combination) of mineral in coal combustion will be created. The effect and control mechanism of mineral types, crystal structure, occurrence, and assemblages of mineral on PM2.5 formation and trace elements emission will be revealed. The coupling mechanisms between PM2.5 and trace elements will be discussed.

基于我国大气中PM2.5的浓度远远超过世界卫生组织的健康指导值，燃煤是PM2.5的重要来源，煤中无机矿物质又是生成PM2.5和重金属排放的主要物源等现状和基本事实，展开对煤中矿物质对重金属排放和PM2.5生成的控制机理研究。通过PM2.5与煤中矿物质在化学组成、微观形貌和结构特征等方面的对比与内在联系研究，结合滴管炉模拟燃烧试验中矿物质和重金属元素在不同粒度级别灰样中的分布和转化特征，煤中不同矿物种类、矿物组合与不同赋存形态矿物质在高温条件下转化与反应变化特征，试图建立和优化燃煤过程中矿物质的破碎、蒸发、反应、成核和凝并变化模型，揭示矿物种类、晶体结构、赋存形态和矿物组合对PM2.5生成的影响与控制机理和PM2.5与重金属之间的耦合规律与主控因素，为通过燃前对原煤进行有效处理控制PM2.5和重金属的排放水平提供可能的方法与思路。

近年来我国大气污染非常严重，PM2.5是大气污染组分中最值得关注的组分之一，普遍认为燃煤是大气PM2.5主要来源。项目通过分析中原经济区主要煤田二叠系山西组主采煤层中的矿物质和微量元素的含量，同时对典型中小型工业城市（焦作）大气中PM2.5进行系统采样测试，研究了PM2.5含量及季节、年度变化规律，同时对PM2.5中无机组分、水溶性离子、重金属元素、碳组分和一次颗粒物与二次颗粒物的组成与变化进行了系统测定与分析。在此基础上分析了PM2.5中各组分与燃煤的内在联系。.研究表明煤层中Hg、As、Se、Pb、Cr、V和稀土元素总体含量与全国煤中微量元素平均值相比含量相近，个别地点和煤分层中含量偏高、夹矸和顶底板中的含量一般高于煤层。煤中的矿物质主要是石英和黏土矿物，碳酸盐、黄铁矿、锐钛矿等呈非均质性分布在煤层中。采集样品中PM2.5的日平均浓度值的变化范围在43-463 μg/m3之间，均值为188±87 μg/m3，其中94%的样品含量水平超过我国二级标准浓度限值（75μg/m3），空气污染严重。PM2.5浓度总体呈现冬季>春、秋季>夏季。根据对PM2.5中无机组分、水溶性离子、重金属元素、碳组分含量测定，得出二次颗粒物和一次组分分别占PM2.5的38.67%和40.27%，一次组分中以矿物粉尘为主，占60.81%，二次组分有机组分含量增加，占25.03%。颗粒物中As、Cd、Mn的均值浓度分别为二级标准限值的15.18、1.59、1.23，污染严重。TPAHs的浓度范围为7.6~672.5ng/m3，平均为119.22 ng/m3。ICR的总平均值为264.74×10-5，说明颗粒物中PAHs致癌风险已远远超过可接受水平。根据受体模型进行源解析，扬尘、钢铁尘与扬尘混合源、机动车尾气排放和SIA混合源、燃煤源、工业污染源、垃圾焚烧和SIA混合源对PM2.5的贡献率分别为24.9%、9.0%、19.4%、18.9%、12.6%、14.2%。值得特别注意的是PM2.5中的重金属、硫酸盐、硝酸盐和多环芳烃与燃煤之间的关系尤为值得关注。