【作者】 房明明；

【导师】 樊建人； 罗坤； 岑可法；

【作者基本信息】 浙江大学 ， 工程热物理， 2013， 博士

【摘要】 气固两相流动是工业生产和口常生活中常见的流动形式。本文以稠密气固两相流动为研究对象,采用欧拉-拉格朗日框架对气固流动进行描述、以离散元耦合大涡模拟方法(DEM-LES)为主要研究手段,在对数值方法进行验证、对相关参数进行敏感性分析的基础上,针对概念上极为相似的两种气固流态化装置——内循环床(ICFB)和循环流化床(CFB)内若干问题进行了较为系统的研究。研究内容主要包含四个部分。第一部分是气固物性、操作和设计参数对内循环床运行表现的影响。全面地研究了相关气固物性(颗粒的碰撞恢复系数、摩擦系数、杨氏模量、粒径、密度及流体的压力等)、操作条件(各腔室流化风速)和设计参数(隔板倾角、热交换腔侧墙倾角、隔板底部通道高度等)对表征装置运行表现的颗粒循环通量和气流短路通量的影响。指出系统的最小流化风速是确定各腔室中颗粒流化状态和预测装置运行表现最为重要的参数,并为装置的运行参数选择、结构的优化设计和相关过程的强化提供了一些重要信息。第二部分是内循环床颗粒混合机理及其影响因素分析。分析了内循环床内颗粒混合发展过程,阐述了混合发展的各个阶段及不同混合机理在时问和空间上的作用范围。此外,对相关设计、运行及颗粒物性参数对装置内颗粒混合过程的影响进行了量化分析。并在相同流化风量下对比了内循环床和对应的均匀配风鼓泡床内颗粒混合过程发展,发现内循环床在颗粒混合方而有一定优势。第三部分是内循环床腔室内置埋管的研究：对加入埋管后装置内颗粒流动、混合过程进行了定量分析。并对比了颗粒循环时间、颗粒在各腔室内的停留时间随布置埋管的数量和位置不同而产生的变化。此外,还对各腔室中埋管磨损的圆周分布规律进行了分析,为工程实践提供了一些参考。第四部分是三维循环流化床气固流动细节及提升管截面形状对装置内气固流动影响的研究。尝试用数值模拟方法揭示循环流化床内气固流动细了,对时均固含率、时均气固速度及其通量、时均压力、颗粒速度脉动强度等重要物理量在装置内的分布按照从整体到局部的规律系统地进行阐述,并重点对方形和圆形截面提升管的循环流化床内气固流动特征的异同点进行对比。此外,还计算了提升管中颗粒扩散运动及相关受力、转动信息,并分析了不同操作风速下颗粒的扩散、受力及转动等产生的变化,讨论了这些信息作为装置内流型转变判据的可能性。更多还原

【Abstract】 Gas-solid two-phase flow is commonly encountered in both industrial manufacture and daily life. This thesis mainly focuses on the dense gas-solid two-phase flow, describing the flow dynamics based on the Eulerian-Lagrange framework and using discrete element method coupled large eddy simulation (DEM-LES) as investigation tool. Based on the proper procedure of numerical validation and parameter sensitivity analysis, the DEM-LES is used to study some basic issues in the conceptually-similar gas-solid fluidization system—internally circulating fluidized bed (ICFB) and circulating fluidized bed (CFB). This thesis is mainly constituted by the following four parts.The first part is the influence of gas-solid properties on the operation of ICFB. Systematic study on the relevant gas-solid properties (particle restitution coefficient, friction coefficient, Young modulus, diameter, density and gas pressure), operational condition (aeration to the chambers) and design parameters (gap height beneth the baffle, incline angle of the baffle and HEC side wall, and so on) are conducted to investigate the solid circulating flux (SCF) and gas bypassing flux (GBF), which are the typical representative of operation state of the facility. The results obtained indicate that the minimum fluidization velocity (Umf) is a key parameter to predict the fluidization state of each chamber and the performance of the bed. Meanwhile, these numerical experiments provide some valuable information for the determination of appropriate operation condition, optimization of design and intensification of relevant process inside the rig.The second part is the mixing mechanisms and the influence of different factors on the mixing of ICFB. Progress of solid mixing inside the ICFB is analyzed. Different stages of mixing and the temporal and spatial range of each mixing mechanism are distinguished. Besides, relevant design, operation and solid parameters’influence on the mixing is quantified. Based on the same aeration, process of solid mixing in the ICFB and the corresponding evenly-aerated bubbling fluidized bed is compared, and the ICFB is found to be more advantage on the solid mixing.The third part is the study of ICFB equipped with immersed tubes. Solid flow dynamics and solid mixing process inside the ICFB with immersed tubes arc quantitatively analyzed. The solid cycle time between the chambers and solid residence time in each of the chambers are comparatively studied for the influence of different number of immersed tubes and the position where they are located. In addition, the circular distribution of tube erosion is extracted and analyzed, and the obtained rule can provide some reference for the wear-proof of such facilities.The last part is the3-D simulation of detailed gas-solid flow dynamics inside a CFB, and the influence of riser cross-section shape on the characteristics of gas-solid flow. A trial to uncover the details of gas-solid flow in the CFB is conducted using numerical method. The distribution of time-averaged solid holdup, pressure, turbulent intensity of solid velocity and gas-solid velocity and its corresponding flux is discussed from whole to local. Emphasis is focused on the comparison of the similarities and differences between the gas-solid flow dynamics of the facilities equipped with square and circular risers. Additional calculation of solid dispersion and its relevant stress and rotation is carried out, and the variation of these parameters under the influence of different fluidization gas velocities is analyzed. Finally, the possibility that whether this information can be used as judgement to the transition of flow pattern is discussed.更多还原