流态化下生物质颗粒流动、热解实验及多尺度模拟研究

This project was to investigate the flow and pyrolysis of biomass particles in fluidized bed through experimental research and multi-scale simulation. Nonlinear analysis method and fuzzy clustering theory were applied to classify the flow patterns of binary particles consisted of biomass particles and quartz sands in fluidized bed, and some techniques were used to measure the pressure and void fraction under different working conditions. Traditional discrete element method was improved by the combination of experimental measurements and theoretical derivation to meet demand of force calculation of binary particles, and the improved method was coupled with traditional computational fluid dynamics and immersed boundary method to simulate the gas-solid flow in fluidized bed under meso-scopic and micro-scopic condition respectively, and the simulation results were compared with the experimental results. Based on the findings by other researchers, three components model for biomass pyrolysis was improved based on advanced instrument analysis techniques and pyrolysis experiments in tubular furnace, and the improved biomass pyrolysis model was coupled with discrete element method to simulate the biomass pyrolysis in fluidized bed, and the concrete components of gas and liquid products from biomass pyrolysis were predicted and compared with the experimental results.

本项目对流态化下的生物质颗粒流动及热解过程进行实验及多尺度模拟研究。利用非线性分析及模糊聚类理论对流化床中生物质与石英砂混合而成的双组份颗粒流型进行智能分类，并对双组份流化床中不同流型下的压力及空隙率分布进行实验测量分析；通过材料物性测量实验及理论推导对传统的离散元方法进行改进，使之能够满足双组份异质颗粒之间碰撞受力的计算需要，并将改进后的离散元方法与传统的计算流体力学方法和浸没边界法分别耦合，对双组份颗粒的流动在介观尺度和微尺度上进行模拟，模拟结果与实验结果进行对比分析；借助于先进的仪器分析技术及管式炉实验，在以往研究基础上，对生物质三组分热解模型进行改进, 将改进后的热解模型与离散元方法相耦合，建立流态化下描述生物质热解过程的数学模型, 预测不同实验工况下气相和液相产物的主要成分,并与流化床热解实验结果进行对比，完善数学模型。

流化床内生物质快速热解是生物质能利用领域的研究热点。生物质流化床热解过程中气固两相流动，传热传质过程和热解反应都极其复杂，本项目建立经验模态-递归分析(EMD-RA)信号分析方法，研究生物质流动与单组份流动的中高频信号递归特征；对流态化下的生物质颗粒流动及热解过程进行实验及多尺度模拟研究；改进传统离散元方法（DEM），并分别耦合传统计算流体力学方法（CFD）和浸没边界（IB）法对流化床双组份颗粒的流动实现介观尺度和微尺度模拟；进行了生物质热解热性的研究；还进行了在流化条件下生物质快速热解CFD模拟研究。.在本项目通过EMD-RA分析法，发现代表颗粒行为的高频信号递归图呈现相似的结构。建立的多尺度异形颗粒混合流动模型中，在低床层高度时，气体受布风板射流作用影响明显；在中等床层高度垂直方向气速随着与壁面距离减小而减小；在高床层高度时，床中心区域垂直方向气速很低，垂直气速从中心到壁面呈现先增大后减小的趋势。在搭建的可视化-透红外流化床实验台中研究发现，在常温空气的冷却作用下，流化床内颗粒冷却速度随表观气速的增大而有所增加，不同表观气速下颗粒的冷却速度差异主要表现在进风后5s的时间内。在生物质热解特性研究中，发现生物质与高密度聚乙烯共催化热解时，500-600°C时可获得最高的芳香烃相对含量。在流化条件下开展生物质快速热解的CFD模拟研究，热解温度对热解产物的产率影响最为显著，随着热解温度的升高，热解油产率先增加后逐步减少并在600℃的温度工况条件下达最大值，热解气的产率则先减少后增加，而热解炭的产率则呈波动趋势，变化较小。