| 题名 | 出入口结构对循环流化床提升管流动和传质模拟的影响 |
| 作者 | 穆丽静 |
| 学位类别 | 工程硕士 |
| 答辩日期 | 2014-04 |
| 授予单位 | 中国科学院研究生院 |
| 导师 | 王维 |
| 关键词 | 循环流化床 出入口条件 气固流动 气固传质 臭氧分解反应 二维模拟 |
| 其他题名 | Effects of Inlet and Outlet Conditions on Simulation of Gas-Solids Flow, Mass Transfer and Reactions in a CFB Riser |
| 学位专业 | 化学工程 |
| 中文摘要 | 循环流化床是典型的多相复杂系统。由于传统实验方法的局限以及气固系统固有的复杂性，通过逐级实验实现工艺放大，往往周期长且研发成本高。而采用数值模拟的手段，则有望有效缩短研发周期并降低成本。随着近年来计算机不断升级和计算方法的进步，采用计算流体力学（Computational Fluid Dynamics，CFD）方法进行数值模拟的研究和应用得到很大发展。实验表明，出入口结构和几何因素对提升管内流动和反应影响很大，然而，目前大部分模拟研究往往忽略了出入口条件或几何结构对反应器的影响。针对此问题，本文以CFD模拟为基本手段，耦合考虑介尺度结构的能量最小多尺度（Energy-Minimization Multiscale Model，EMMS）曳力及传质模型，对二维模拟时循环流化床提升管内气固流动、传质和反应过程受出入口条件的影响进行研究。 论文第二章首先对气固循环流化床二维模拟的网格无关性进行讨论，在兼顾计算精度和计算量两方面的基础上，确定了本文进行提升管二维模拟的网格无关尺寸，为后续的流动和反应的二维模拟提供了基准参数条件。 论文的第三章和第四章将多尺度流动和传质模型逐步应用于循环流化床提升管反应器的模拟。其中，第三章专注于流动模拟，确定二维模拟时出入口结构及进气条件对流动结果的影响。研究表明，入口条件确实对提升管二维模拟时的结果影响较大，应慎重选择入口条件：对于本文研究的单侧入口的提升管装置，单侧入口模拟结果与实验值最为接近；双侧入口条件下的模拟结果与实验值差别较大；改变入口宽度对模拟结果影响较小。通过对四种不同出口结构的模拟研究表明，顶直出口与延长段出口条件下的模拟结果与实验结果一致，单、双侧侧边出口条件的模拟结果与实验值差别较大。工业设备中提升管出口若为延长段出口条件，在二维模拟计算时可简化为顶直出口。在此基础上，第四章选定较常用的臭氧分解反应过程作为模拟对象，对提升管进行传质模拟研究，讨论二维模拟时改变出入口结构及进气条件对传质过程的影响。与传统方法比较表明，考虑介尺度结构对曳力和传质模型的影响，模拟结果与实验值吻合更好。进一步研究表明，出口结构对提升管内臭氧浓度影响较大。如果实际装置为延长段出口，对其传质过程进行二维模拟时，不可将出口条件简化为单侧边出口。对入口条件的研究表明，当有二次风进气时，不宜将进气条件简化为底部均匀进气。 第五章总结了本论文获得的主要结论，并对循环流化床提升管模拟的深入研究进行了讨论。 |
| 英文摘要 | Circulating Fluidized Bed (CFB) is a typical multiphase complex system. Due to the limitation of experimental measurement and inherent gas-solids complexities, the scale-up of a CFB through step-by-step experiments is time-consuming and costly. By using numerical simulation methods, the time and costs could be reduced greatly. With the development of computer technology and computing methods in recent years, the applications of computational fluid dynamics (CFD) have increased rapidly. Experiments have shown that the inlet/outlet conditions and geometric factors could have strong influence on the flow, mass transfer and reactions. However, most of CFD simulations paid little attention to their effects. To solve this problem, in this work, we coupled CFD with the energy-minimization multi-scale (EMMS) drag and mass transfer models and applied it to simulate the gas-solids flow, mass transfer and reactions in a CFB. The effects of inlet and outlet conditions have been studied thereon. The grid independence in 2D simulation of CFB is first discussed in Chapter 2. Grid dependency was studied and thereon the appropriate grid size was determined and used in following chapters for flow and mass transfer simulations. In Chapters 3 and 4, the multi-scale flow and mass transfer models are integrated and applied to the simulation of a CFB reactor. In Chapter 3, 2D simulations with different outlet and inlet geometries and conditions were performed. Comparison between experimental data and simulation shows big difference between one-side and double-side inlets where the one-side inlet configuration gives reasonable agreement with experimental data. Changing the inlet width has little influence on the simulation results. This big impact suggests geometric configuration should be set carefully when performing 2D simulations. Further, the simulations of four different outlet conditions show that the extended outlet and straight outlet configuration agree well with experimental data. The extended outlet can be simplified to straight one in 2D simulations, and double-side inlets may weaken flow asymmetry in the riser bottom. Ozone decomposition reaction was chosen as the testing case in Chapter 4. Firstly, compared with traditional methods, our EMMS-based solution shows significant improvement by considering the influence of meso-scale structure on the drag and mass transfer models. Then the influence of different inlet and outlet geometries and conditions on mass transfer process was discussed. The results showed that the outlet conditions have big impact on the distribution of ozone concentration. If a CFB reactor has an extended outlet, it should not be simplified to a single-side configuration for 2D mass transfer simulations. The secondary gas-inlet should not be simplified to uniform bottom inlet. Chapter 5 summarizes the main conclusions in the thesis, and suggests future work on riser simulations. |
| 语种 | 中文 |
| 公开日期 | 2015-07-08 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/15577]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 穆丽静. 出入口结构对循环流化床提升管流动和传质模拟的影响[D]. 中国科学院研究生院. 2014. |
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