燃煤过程中Ti、Fe、Ba等重金属元素主导的PM2.5生成机理与逃逸特性研究

The coal consumption is large in China and the fine particulates generated from coal combustion could easily escape from the flue gas treatment system. These fine particles rich in heavy metals are harmful to human. The applicant sampled fine particulate matter at chimney inlet from several ultra-low emission power plants. In addition to the major elements such as Si, Al in fine particles, heavy metals in PM2.5 such as Ti, Fe, Ba which are trace elements in coal have also been found. The particles rich in heavy metals have obvious reflection characteristic under the electron microscope. There are some researches on the transformation behavior of Si, Al, Na, but few studies are concerned of fine particles formation mechanism and escape characteristic of heavy metals such as Ti, Fe, Ba. This project aims at synthesizing a kind of ‘simulated coal’. The release, nucleation, coagulation of heavy metal under high temperature will be studied through ‘simulated coal’ combustion and the transformation kinetic model of Ti, Fe, Ba into PM2.5 will be verified by real coal combustion. A flue gas treatment based on similarity simulation principle will be used to get the capture and escape mechanism of PM2.5 rich in heavy metals including Ti, Fe, Ba. This project aims at determining the amount and size distribution of PM2.5 rich in heavy metals and providing theoretical basis for particulate emission control.

我国煤炭消耗很大，燃煤排放的富含重金属的微细颗粒物对人体健康危害较大。申请人在多个超低排放电厂烟囱入口收集的PM2.5中除了发现较多的Si、Al外，还发现煤中本身含量较少的Ti、Fe、Ba等重金属元素为主体的微细颗粒占有相当比例，且在电镜下有明显的反光特征。目前对Ti、Fe、Ba等重金属元素向微细颗粒物转化机理及逃逸机制研究较少。本项目将首先探讨一种合成“成分可控模拟煤粉”的方法，再通过模拟煤粉燃烧试验得到Ti、Fe、Ba等重金属元素的高温气化释放、成核和团聚生长机制，获得Ti、Fe、Ba等元素向PM2.5转化的动力学计算模型，并通过真实煤粉燃烧试验对该模型进行验证。搭建超低排放烟气处理系统，研究Ti、Fe、Ba等元素主导的PM2.5在烟气处理设备中的捕集逃逸机制，最终为燃煤排放富含重金属PM2.5数量和粒径分布的精确确定和控制提供理论依据。

我国煤炭消耗很大，燃煤排放的微细颗粒物对人体健康危害较大。本项目针对燃煤排放的微细颗粒物，重点研究了：成分可控模拟煤粉的制备和应用、煤粉燃烧过程中无机元素的气粒转化特性、烟气处理系统中细颗粒物的逃逸特性。主要成果如下：.1.获得了一种成分可控的模拟煤粉的制备方法，并通过研究无机元素向细颗粒物的转化特性，验证了其用于煤粉燃烧细颗粒物研究的可行性。.2.在沉降炉系统中，研究了炉膛温度、燃烧气氛对准东煤细颗粒物生成特性的影响，及后燃烧区内细颗粒物的演化过程。在900℃至1300℃范围内，随着炉膛温度的升高，由于无机蒸汽的产生与去除机制之间的相互竞争，PM0.4的质量产率先降低后升高。O2浓度在30%~40%之间，富氧气氛下燃烧强度与空气气氛相当。在后燃烧区，在烟气温度从1000℃降至200℃的过程中，团聚、成核、冷凝、表面化学反应对PM0.4-10的质量浓度粒径分布和元素组成的影响较小。团聚机制主导了PM0.4的演变。.3.在超低排放燃煤工业锅炉、燃煤电厂上进行了颗粒物现场测试。获得了细颗粒物在不同烟气处理设备中的逃逸特性。对于燃煤工业锅炉：工业循环流化床（CFB）锅炉出口颗粒物浓度明显高于工业链条炉（CGB），CGB产生的颗粒物以PM2.5居多，占PM10的79.5%。布袋除尘器对CFB锅炉微细颗粒物的脱除效率可达98.12~99.56%，但是由于CGB炉膛出口微细颗粒物浓度较低，对应链条炉的脱除效率仅为90.0~93.6%。脱硫塔和湿式电除尘对微细颗粒物的联合脱除效率约为50~60%。两台锅炉PM2.5和PM1的排放因子分别为0.025~0.028kg/t和0.014~0.017kg/t。对于燃煤电站：SCR可以使PM1的质量浓度增加52.11%。低低温省煤器提高了ESP对于0.1μm~1μm粒径范围内颗粒的脱除效率。WFGD能有效脱除超微米颗粒，但会使PM1的质量浓度增加59.41%。WESP对PM1、PM2.5、PM10的脱除效率为55.77%~71.92%。在80％BMCR下，最终的PM10排放浓度为2.04mg/Nm3。.以上研究结果揭示了燃煤源微细颗粒物的生成特性及其在烟气处理设备中的逃逸特性。有助于煤炭清洁高效利用技术的进步。