局部混合强化螺旋反应器生物质慢速热解过程基础研究

Biomass slow pyrolysis is an important thermochemical conversion technology for the production of value-added bio-char. Screw reactor is a promising reactor for biomass slow pyrolysis. The exothermic behavior of biomass slow pyrolysis tends to trigger temperature runaway in the area where particles tend to cluster together in the screw reactor. For handling such temperature runway, the project proposes a method by intensifying the local particle mixing in that area, which is expected to distribute the heat efficiently and uniformly in the reactor bed and to remove the heat out of the bed quickly. Based on the combined Computational Fluid Dynamics and Discrete Element Method (CFD-DEM), accurate flow model and comprehensive transport-reaction mathematic model will be separately developed for revealing the particle flow and mixing behavior in the reactor, and for revealing the coupled mechanism between the transport phenomena and the biomass pyrolysis reactions in the screw reactor, respectively. Based on the above information, the mechanism of triggering temperature runaway in the reactor bed is expected to be explained. Method is to be explored for intensifying the local particle mixing in the area where particles clustering tends to happen in order to achieve the efficient regulation on the temperature runaway in the screw reactor. The study in the project will provide helpful theoretical information for the engineering implement and regulating of the new technology—the technology of biomass slow pyrolysis in the screw reactor with local intensification of particle mixing.

生物质慢速热解技术是以高附加值产品——生物炭为目标产物的生物质转化利用重要工艺之一。螺旋反应器是一种进行生物质慢速热解的有广阔应用前景的反应器。针对慢速热解过程的放热效应容易在螺旋反应器局部颗粒聚集处引发反应器床层飞温的问题，本项目提出通过强化反应器内局部颗粒聚集处的颗粒运动与混合，以使热量在反应器床层内有效均匀分散并进一步使热量及时从床层移出，以应对飞温的解决思路。基于CFD-DEM方法，通过建立准确描述螺旋反应器内气相与颗粒相两相流动的流动模型，及进一步耦合传热、传质与生物质慢速热解反应的传递-反应综合数学模型，研究螺旋反应器内传递过程与反应的耦合机制，揭示飞温的产生机制，探索螺旋反应器内局部聚集颗粒混合的强化方法，以实现对飞温的有效调控，为局部混合强化螺旋反应器生物质慢速热解新技术的工程放大与调控奠定理论依据。

针对螺旋反应器生物质慢速热解过程的飞温及其调控，本项目通过建立准确描述螺旋反应器内气相与颗粒相两相流动的流动模型，及进一步耦合传热、传质与生物质慢速热解反应的传递-反应综合数学模型，分析了螺旋反应器内传递过程与生物质慢速热解反应的耦合机制，获得了生物质颗粒在螺旋反应器内的停留时间分布与颗粒混合特性，以及生物质慢速热解过程的温度分布、产物分布规律。结果表明，反应器内冷热颗粒之间的混合不充分、气体难以及时携带热量离开温升区间以及颗粒在反应器壁面附近的堆积作用是导致飞温的主要原因。通过优化调控，实现了对飞温过程的调控，并获得了能够提高生物质慢速热解过程关键产品——生物质炭的高热值的调控规律，为本项目的进一步推广应用奠定了重要的理论指导。. 本项目所揭示的螺旋反应器生物质颗粒流动与慢速热解机制能够为该类型反应器的工业应用提供关键的基础信息，具有重要的应用价值；同时，本项目的建模思路与数值模型也可以拓展应用至其他气固多相反应装置，如煤气化、生物质气化等过程，具有较广泛的应用潜力。