可燃固废/煤双流化床热转化过程的LES-DCM数值模拟研究

The dual fluidized bed technology is considered as a new type of thermo-chemical conversion technology featuring high efficiency and low pollution with broad prospect. This proposal is based on the even increasing demands of developing large-scale combustible solid waste treatment method and high efficient and clean utilization of coal in China, according to the Thirteenth Five-year National Development Plan. This investigation is focusing on the mechanism of gas-solid flow, heat and mass transfer and chemical reaction during the thermal conversion processes of combustible solid waste/coal in dual fluidized beds, which has important theoretical, academic, and application reference values. Firstly, the heterogeneous drag model is coupled with MP-PIC method and a novel LES-DCM modeling method based meso-scale structure characteristics was proposed. With this method, three-dimensional simulations were carried out for gas-solid flow in a full-loop circulating fluidized bed. The macro- and meso-scale flow behaviors of particles with broad size distribution were analyzed. Furthermore, by comparing the simulation results with the experimental data, the core parameters of reaction kinetics for thermal conversion processes in dual fluidized beds were obtained. Consequently, the numerical experiment platform for gas-solid flow coupled with chemical reaction in dual fluidized beds was developed. Through the simulations, the change rule of flow and reaction characteristics with its influence factors, such as the operating conditions and particle characters were revealed. With the financial support from NSFC, there is a promising prospect of clarifying the flow, reaction, and transfer mechanism of thermal conversion processes in dual fluidized beds. In addition, the research can help to develop the novel modeling method, enriching the approach for researching the complicated gas-solid reaction system.

双流化床技术是一种具有重要前景的高效低污染热化学转化新技术。本项目针对“十三五”大力发展可燃固体废弃物规模化利用与煤炭清洁高效利用的国家重大需求，提出开展可燃固废/煤在双流化床热转化过程中的气固流动、热质传递与化学反应机制的数值模拟研究，具有重要理论、学术与应用参考价值。本项目首先将MP-PIC方法与非均匀曳力模型结合，建立基于介尺度结构特征的大涡模拟-离散颗粒团（LES-DCM）数值模拟方法，实现宽筛分颗粒在循环流化床三维全循环流场中宏观、介观尺度气固流动特性的模拟，随后通过试验反推的方法，获得适用于双流化床热转化过程反应动力学核心参数群，建立双流化床气固流动与化学反应耦合的数值模拟方法和数值实验平台。通过数值实验，阐明流动与反应特性随物性参数、操作参数等的变化规律。其研究成果有望揭示双流化床热转化过程的流动、反应与传递机制，提高认知水平；建立具有创新性的数值模拟方法，丰富研究手段。

以固体废物处理的资源化、清洁化以及煤炭清洁高效利用为背景，采用数值模拟方法，研究了煤与可燃固废在双流化床热转化过程中流动、传递与反应机制。本项目首先将不同气固曳力模型与MP-PIC方法耦合，针对Geldart A类和B类颗粒，分别构建了基于介尺度结构特征的LES-DCM三维数理模型，实现了宽筛分颗粒在循环流化床三维全场空间中的气固流动特征的模拟；随后通过试验结果反推的方法，获得了适用于煤与可燃固废共燃/共气化过程的最优反应模型、速率表达式与反应动力学核心参数群，建立了双流化床气固流动与化学反应耦合的数值模拟方法和数值实验平台；通过数值实验，研究了工业规模循环流化床煤与垃圾混烧过程以及中试规模双流化床煤与生物质共气化过程，获得了不同操作参数和物性参数下颗粒流型、气固温度、组分浓度、气态污染物排放等信息，从全回路的视角揭示了双流化床共燃/共气化过程的气固流动、热质传递与化学反应机制；最后构建了基于CFD-DEM的稠密气固流动与化学反应耦合的三维数值模拟方法，从颗粒尺度揭示了流化床热转化过程的流动与反应特性，扩充和丰富了对于本课题关键科学问题的讨论。本项目的研究结果为双流化床热转化过程的工程化应用提供理论指导和基础数据，其结果对于类似过程也具有一定的指导价值