含氯可燃固废典型组分中低温调质过程中二噁英前驱体生成与迁移机理研究

Municipal solid wastes(MSW) in China have high moisture content and low energy density, which leads to low efficiency in the process of incineration and secondary pollution such as dioxin, so it is necessary to improve the "quality" of combustible components before incineration. Pyrolysis is a common method to improve the "quality" of combustible MSW, and medium-low temperature conditioning become a research hotspot due to produce solid fuel with high calorific value and low pollution. The key problem to be settled urgently is to elucidate generation and transfer mechanism of dioxin precursor during medium-low temperature conditioning process, to design a conditioning method scientifically, and accordingly, to inhibit the dioxin emissions during energy-oriented use process. In this project, we will choose polyvinyl chloride, food waste and printed paper as research subjects, research of the interaction in the process of medium-low temperature conditioning, elucidate transfer and speciation of chlorine in conditioning process, explore the generation mechanism of dioxins in combustion process, obtain the correspondences between conditioning process, characteristics and formation of dioxin precursor, in order to provide theoretical basis for establish clean combustion mechanism which the dioxin is controllable.

我国城市固体废弃物含水量高，能量密度低，从而导致在焚烧过程中效率低下，易生成二噁英等二次污染。因此在焚烧前提高其中可燃组分的“品质”很有必要。热解技术是提高可燃固废“品质”的常用方法，而中低温调质由于能产生高热值低污染的固体燃料而成为研究热点。目前亟须解决的关键问题是揭示可燃固废中低温调质过程中二噁英前驱体生成与迁移机理，科学设计中低温调质方法，以进一步抑制能源化利用中的二噁英排放。 本项目选取PVC，厨余，印刷纸张三类可燃固废中含氯典型组分作为研究对象，系统研究其在中低温调质过程中的交互影响规律，揭示调质过程中氯元素迁移与赋存形态，探究其在燃烧过程中二噁英的生成机理，获得含氯可燃固废典型组分调质过程、产物特性与二噁英前驱体形成的对应关系，为建立二噁英可控的清洁燃烧机制提供理论依据。

本项目针对可燃固废典型组分氯含量高、燃料品质低等问题，主要研究了含氯可燃固废中低温调质过程中氯元素含量、赋存形态和迁移转化路径，建立中低温调质提升燃料品质的调控机制。通过找寻含氯组分调质过程中间产物，获得可燃固废典型组分源头调质过程最优方法，完善可燃固废典型组分源头调质工艺路线，形成含氯可燃固废典型组分调质工艺参数、产物理化特性与二噁英产生机理的对应关系；本项目研究发现单一组分中氯含量采用XRF法测量更为准确，但对于复杂组分的可燃固废，采用水萃取法联合艾士卡法更适合且更准确；在烘焙过程中部分无机氯转化成了有机氯并赋存在固体产物中，其机理为氯化钠等无机物与羧基等含氧官能团反应生成含Cl物质，而初始释放的少量氯化物被烘焙固体产物中的碳活性位点全部捕捉而形成有机氯（C-Cl）；首次发现在合适的方法下适当加入一些助脱氯剂对于中低温下脱除原料中的无机氯至关重要，而二氧化硅是中低温调质过程中促进无机氯释放的较好助脱氯剂，同时还可抑制无机氯向有机氯的转变，减少二噁英前驱体的生成。研究表明，烘焙作为一种中低温调质方法，是一种有效降低可燃固废中有害元素（氯）含量的预处理方式，还可有效提高可燃固废的燃料性能，但烘焙温度不宜高于300°C。