废弃物热解半焦重整同源挥发分生产高值可燃气的机理与调控基础研究

Pyrolysis is a potential clean technology for waste to energy process, however the products from a single pyrolysis step are complicated and of poor quality; they need further treatment before put into any applications except for combustion. In this research a new method is proposed: by using hot char from waste pyrolysis as catalyst, the warm volatile (syngas and oil products together, in gaseous phase at high temperatures) from the same pyrolysis process is reformed to produce higher added-value gas product. The higher added-value gas product is characterized with higher H2 content and high higher heating values (HHV). By using municipal solid wastes (MSW) with a typical fixed component as an example, the reaction mechanism between the volatile and the char will be investigated, which include the following steps: 1) To explore the reactions that preferentially take place in the reaction system with help of independent reaction analysis and thermodynamic analysis; 2) To identify the catalytic functions of the different components in the char including carbon matrix, activating components such as alkali and alkali-earth metals (AAEM) and iron oxides during the reforming process and the influence caused by other inorganic minerals with help of model compounds and simulation based on ReaxFF Molecular Dynamics; 3) To understand how the key influencing factors including reaction pyrolysis temperature and reforming temperature, reaction time, ratio of char to volatile, partial pressure of steam in the volatile affect the final products. Based on the above knowledge, the reactions between the hot char and the warm volatile will be controlled to produce the desired products such as higher added-value syngas, to eliminate liquid products and to consume steam. The purpose is to set stone for improving waste to energy technologies and to obtain more valuable products from wastes.

热解是废弃物清洁能源化的重要模式，然而废弃物单步热解产物品质低、不适合燃烧方式以外的其它途径高价值利用。本项目提出一种利用废弃物热解半焦重整同源挥发分生产高值可燃气的新方法。以生活垃圾为废弃物的代表、研究某代表性组分的生活垃圾热解产生的炽热半焦与同源高温气态的挥发分之间的反应机理，包括1)借助独立反应式和热力学分析剖析该复杂反应体系的主要反应群组；2）利用挥发分模化物解耦半焦中的碳骨架、碱金属与碱土金属等活性成分和其它矿物成分在过程中所起的作用；3)确定关键参数如热解和重整温度、半焦/挥发分的反应时间、半焦/挥发分的量比、挥发分中水蒸汽分压等对最终产物的影响规律。在上述基础上掌握催化重整过程的调控机理，以实现对最终产物的定向控制，尤其是促进H2O转化、提高可燃气的产量和H2浓度水平、促进热解油裂解的调控机制，为开发新的废弃物利用工艺、提升废弃物能源化和资源化水平奠定基础。

热解是废弃物清洁能源化的重要模式，尤其适用目前分类后的干垃圾以及分布式和县域垃圾的处置。然而废弃物单步热解产物品质低、不适合燃烧方式以外的其它途径高价值利用。本项目提出一种利用废弃物热解半焦重整同源挥发分生产高值可燃气的新方法，以生活垃圾、污泥等典型废弃物的代表、研究废弃物热解产生的炽热半焦与同源产生高温气态的挥发分之间的反应行为、产物特征和对应机理。主要研究内容包括1)析剖挥发分—炽热半焦之间发生的主要反应群组；2）探讨和解耦了半焦中的碳骨架、碱金属与碱土金属等活性成分和其它矿物成分在过程中所起的作用；3)确定了关键参数如热解和重整温度、半焦/挥发分的反应时间、半焦/挥发分的量比、挥发分中水蒸汽分压等对最终产物的影响规律。获得的重要结果包括：1）宏观上挥发分-半焦之间的反应有3个独立反应式：CO2+H2=CO+H2O，C+H2O=CO+H2 和 CH4=C+2H2；在温度为600 oC时，其正向反应Gibbs自由能均>0，逆向反应可以自发进行，因此在相对低温下大量生成CO2,H2,CH4，碳被消耗，这与实际过程一致。微观上对塑料、生物质在热解过程中挥发分析出及其二次反应的步骤进行了ReaxFF-MD 模拟，掌握了分子水平上的反应规律，有助掌握产物形成机理。2）含有丰富矿物质的垃圾热解半焦重整热解挥发分比生物质半焦更具有催化活性；酸溶性矿物阻止了半焦中碳的微晶化使得未活化的半焦具有活性，能有效促进焦油的分解；而与半焦有机结合及水溶性的AAEMs会导致碳的深度芳香化并失去活性；半焦的比表面积并非重要的影响因素；除AAEMs外，Fe和Ni是半焦中促进挥发分中焦油降解有效的催化剂，尤其是被酸活化后；温度在800℃及以下具有很好的效果。3）半焦-挥发分重整的关键参数包括热解和重整温度、半焦/挥发分的接触时间、量比、挥发分中水蒸汽分压等。其中温度最为重要，随着重整温度升高，产气中H2比例升高。上述研究成果指导挥发分-半焦催化重整过程的调控，实现了对最终产物的定向控制，获得热值可调的可燃气体和实现热解油裂解，形成了全新的废弃物能源化工艺、提升了废弃物能源化和资源化水平。