【作者】 陈曦；

【导师】 钟文琪；

【作者基本信息】 东南大学 ， 热能工程， 2018， 博士

【摘要】 随着固体废弃物导致的环境和社会问题日益严峻,生物质和可燃固体废弃物(以下称可燃固废)的资源化利用逐渐受到人们的重视。使用流化床对生物质和可燃固废进行热解、燃烧和气化等热化学处理可以实现废弃物减量化的同时提供热/电等能源,因此成为资源化利用的常见手段。生物质和可燃固废多以圆柱颗粒形式与流化介质在流化床中共同流化并发生化学反应,因此是一个异重/异形多组分颗粒共流化过程,具有复杂的多尺度流动结构,易发生温度和产物不均从而影响处理的连续性和可靠性。这些问题必须依靠基于多尺度流动理论的优化方法才能够解决,但是现有研究大多数关注于圆柱颗粒共流化过程的宏观设备尺度规律,研究结果泛用性和推广性不强。对于深层次的介观尺度和颗粒尺度机理认识不足,对于尺度间作用的耦合和传递机制研究也不完善,还远远不能满足工业应用的需求。另一方面,测量手段的不足也制约了对于圆柱颗粒多尺度气固流动特性的研究,特别是稠密气固流动状态下颗粒尺度运动细节的测量还缺乏较为可靠的方法。本文构建了基于X光的圆柱颗粒稠密气固流动测量系统和方法,并在此基础上探索了圆柱颗粒的多尺度气固流动规律,建立具有普适性的跨尺度关键参数机理模型。主要内容及结论如下:分别构建了单视/双视X光透视成像软硬件系统,并在这两套系统的基础之上实现了X光流化床空隙率测量方法、单视X光颗粒示踪测量方法、双视X光颗粒示踪测量方法以及双视X光气泡参数测量方法,对以上方法的关键技术和误差评估等方面进行了系统性研究。成功测量了稠密气固流动条件下圆柱颗粒的三维位置、速度和姿态角度,以及气泡尺寸和速度等以往技术难以获得的颗粒尺度与介观尺度运动参数。在颗粒尺度方面发现了颗粒的自转现象并阐述了其发生机理;发现了圆柱颗粒位置分布、速度和姿态角度等随颗粒形状、质量分数和气速等宏观操作参数的变化规律,为圆柱颗粒在共流化过程中的精准运动调控奠定基础;在介观尺度方面,探讨了圆柱颗粒性质和操作参数对于气泡形态和运动的影响规律,揭示了圆柱颗粒对于气泡的作用机理;在设备尺度方面,建立了适用于更宽工况范围的流型划分方式,发现了不同的流型转变途径及其变化规律,并绘制了圆柱颗粒在共流化过程中的流动相图。发现了两种不稳定流化模式并阐述了其发生机理。提出了理想均匀颗粒群与圆柱颗粒间的介观尺度一维相互作用机理模型,成功采用该模型解释了不稳定流化、无法流化等设备尺度流化现象的产生机制,并在该模型的基础上提出了部分流化(P)流型下圆柱颗粒起始(终止)流化速度的关联式。成功实现对气泡和圆柱颗粒间相互作用过程的直接测量以及三维重构,发现了颗粒性质和操作参数对于气泡-圆柱颗粒调控作用的影响规律;阐明了圆柱颗粒多种运动模式的产生机制,推动了对于圆柱颗粒多尺度气固流动的机理性认识。更多还原

【Abstract】 With the environmental and social problems caused by solid waste have become increasingly severe,the energy recovery of biomass and combustible solid waste(or CSW)has become a hotspot across the world.Performing thermochemical treatment,such as pyrolysis,combustion and gasification,of biomass and CSW in fluidized bed can realize waste reduction and obtain heating or electric energy at the same time,thus became a common means of biomass and CSW energy recovery.Biomass and CSW are usually in the form of cylindrical particle and experiencing co-fluidization with inert media like sand in the fluidized bed,so basically it is a non-uniform density/shape multi-component particles fluidization process with complex multi-scale flow structure causing inhomogeneous distribution of temperature,which can jeopardize the continuity and reliability of the production process.These problems can only be solved by the optimization method based on multi-scale flow theory,but most of the existing researches focus on the macro-scale fluidization characteristic of cylindrical particle,and the generalization of these characteristics are limited.The understanding of meso-scale and micro-scale mechanism,and the coupling and transfer mechanism between scales are also lacking,which cannot meet the needs of industrial applications.On the other hand,the lack of measuring methods also restricts the research of multi-scale gas-solid flow characteristics of cylindrical particles,especially the measurement of micro-scale motion under dense gas solid flow.In this paper,a dense gas solid flow measurement system based on X-ray is built,and multi-scale gas solid flow properties of cylindrical particles is investigated,and a multi-scale mechanism model of key parameter is established.The main contents and conclusions are as follows:Single/dual vision X-ray imaging software and hardware system are constructed as,based on which the X-ray fluidized bed voidage measurement method,single vision X-ray particle tracking measurement method,dual X optical particle tracking measurement method and dual vision X-ray bubble measurement method are proposed.Investigation on the key technology and the error evaluation of the system are performed.The three-dimensional location,velocity and orientation of cylindrical particles,as well as the size and velocity of bubbles,have been successfully measured under the dense gas solid flow conditions.In the aspect of the micro-scale characteristics,the phenomenon of cylindrical particle rotation is reported and its mechanism is explained;The effects of particle properties and macro operating parameters on the position distribution,velocity and orientation of cylindrical particles are investigated,which lays the foundation for the cylindrical particles precise motion regulation in the process of fluidization;In the aspect of the micro-scale characteristics,The effects of particle properties and macro operating parameters on bubble properties are discussed,revealing the mechanism of bubble formation and development in cylindrical particles fluidization;In the aspect of the macro-scale characteristics,flow regime definition method characterizing a wider range of operating conditions is established,and different flow regime transition route is discovered and its variation properties are discussed.The flow regime diagram of cylindrical particle is obtained.Two kinds of unsteady flow patterns are found and their mechanism was explained.A meso-scale mechanism model describing the one-dimensional interaction between the ideal uniform inert fluidization particle cloud and cylindrical particle is proposed.The model predicts the occurrence of unsteady flow and other macro-scale flow phenomena successfully.A correlation predicting the cylindrical particles fluidization initiation(termination)velocity under partial fluidization(P)flow regime is proposed and evaluated.The successfully carrying out the direct measurement of the interaction process between cylindrical particles and bubbles and 3D reconstruction of the process is performed as well;The influence of particle properties and operating parameters for the interaction between bubbles and cylindrical particles is investigated;The mechanism of cylindrical particles various motion patterns are clarified and the understanding of cylindrical particle multi-cale gas-solid flow mechanism is promoted.更多还原