| 题名 | 基于气泡的EMMS模型及其在煤气化炉CFD模拟中的应用 |
| 作者 | 石战胜 |
| 学位类别 | 博士 |
| 答辩日期 | 2011-05-31 |
| 授予单位 | 中国科学院研究生院 |
| 导师 | 李静海 ; 王维 |
| 关键词 | 介尺度 气泡 多尺度 EMMS 曳力 |
| 其他题名 | a bubble-based EMMS model and its application in the CFD simulation of a coal gasifier |
| 学位专业 | 化学工程 |
| 中文摘要 | 气固流化床是典型的非线性非平衡系统，呈现出复杂的时空多尺度结构。其中，气泡和团聚物是以颗粒聚集(乳化相，密相)和气体聚集(气泡相，稀相)共存为代表的两种典型多尺度结构。已有研究结果表明，耦合了基于团聚物的能量最小多尺度(EMMS)模型的双流体模拟可以准确地捕捉循环流化床内流动结构，但其中团聚物直径还存在误差，考虑到气泡关联式较成熟，能否建立基于气泡的EMMS模型呢？论文第二章首先讨论了不采用介尺度结构模型，而直接通过双流体模型(TFM)细网格模拟的情况。研究发现，对于A类颗粒，鼓泡流化床中，随着网格宽度的减小，膨胀高度降低，细网格模拟达到网格无关的值接近于实验数据；流化气速越高(如：湍动流化床和快速流化床)，达到网格无关时的网格宽度越大，但此时细网格模拟结果与实验值相差甚远，且无法捕捉S型分布。对于B、D类颗粒，结果显示，网格细化可以预测鼓泡流化床的膨胀高度，但是，当前的计算能力无法达到工业规模反应器的计算要求。为了弥补细网格模拟与实际的差距，论文第三章提出了气固鼓泡流化床中基于EMMS方法的EMMS/bubbling稳态模型，模型中以气泡代替原始EMMS模型中的团聚物作为介尺度结构，相应地，鼓泡流化床分为三个子相：乳化相、气泡相和相间相，以及相关的悬浮和耗散能量子系统，悬浮颗粒所消耗的能量趋于最小(Ns→min)的稳定性条件被用来封闭基于子相的动力学方程。初步计算结果显示，与文献中实验数据吻合。论文第四章进一步把EMMS/bubbling稳态模型扩展到非稳状态，并用来改进传统双流体模型中的曳力系数。结果发现：相比较传统的基于平均方法的曳力系数，耦合了EMMS/bubbling曳力系数的TFM模型允许用更粗网格，且准确性大大改善。 论文第五章将耦合了EMMS/bubbling模型的多流体模型(MFM)用于灰熔聚流化床气化炉模拟。连续性排料反应器模拟结果捕捉到了气化炉的主要特征，定性上预测了煤气化反应器的热态流动现象。论文最后总结了本论文获得的主要结论，展望了EMMS/bubbling模型前景以及进一步开展的 研究方向。 |
| 英文摘要 | Gas-solid fluidized bed is a typical non-equilibrium and non-linear system, displaying complex spatio-temporal multiscale structures. Therein, bubbles and clusters are two typical forms of heterogeneous structure which manifests coexistence of a particle-rich dense phase (emulsion phase) and a gas-rich dilute phase (bubble phase). The previous research results indicated that the two-fluid model (TFM) coupled with the cluster-based EMMS (energy-minimization multi-scale) model allows capturing flow structres in a circulating fluidized bed (CFB). However, the results are sensetive to the conditions of cluster diameter. Considering the better accuracy of bubble diameter, it is natural to question whether it is possible and necessary to propose a bubble-based EMMS model for bubbling fluidized beds. In chapter 2, we firstly analyzed the applicability of using fine-grid simulation of two-fluid model (TFM). The results show that, for Geldart A particles, with the decrease of grid size, the expansion height of the fluidized bed lowers and the simulation agrees well with experimental data when converging to its asymptotic solution. At higher gas velocity (eg. turbulent fluidized bed and fast fluidized bed), the grid size needed for convergence is larger but the simulation deviates from the experimental and fails to capture the typical S-shaped axial voidage profile. For Geldart B and D particles, fine-grid simulation predicts expansion height reasonably, but, current computation capability hardly meets the requirements of large scale simulation of industrial reactors. In chapter 3, to eliminate the gap between the fine-grid prediction and the reality, a steady state EMMS/bubbling model was proposed based on energy-minimization multi-scale (EMMS) method. In the new model, the meso-scale structure was characterized with bubbles in place of clusters of the original EMMS method. Accordingly, the bubbling fluidized bed was resolved into the suspending and the energy-dissipation subsystems over three sub-phases, i.e., the emulsion phase, the bubble phase and their inter-phase in-between. A stability condition of minimization of energy consumption for suspending particles (Ns→min) was proposed, to close the hydrodynamic equations on these sub-phases. This bubble-based EMMS model has been validated and found in agreement with experimental data available. In chapter 4, an unsteady-state model with the meso-scale effects of bubbles was established. It was then used to calculate the drag coefficient for two-fluid model (TFM) to simulate the hydrodynamics of bubbling fluidized beds. It was found that TFM with EMMS/bubbling drag coefficient allows using coarser grid than with homogeneous drag coefficient, and its predictions agree reasonably with experimental data. In chapter 5, the two fluid model coupled with the EMMS/bubbling model was used for hydrodynamic simulation of an ash-agglomerating fluidized bed coal gasifier. The simulation with continuous slag discharge captured some main characterisitics of flow, identified from experiments. Finally, we summarize the main achievements in this thesis, and presents future works on the EMMS/bubbling modeling. |
| 语种 | 中文 |
| 公开日期 | 2013-09-23 |
| 页码 | 105 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1690]  |
| 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 | 石战胜. 基于气泡的EMMS模型及其在煤气化炉CFD模拟中的应用[D]. 中国科学院研究生院. 2011. |
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