Numerical Simulation of Dense Gas-Solid Multiphase Flows Using Eulerian-Eulerian Two-Fluid Model
Numerical Simulation of Dense Gas-Solid Multiphase Flows Using Eulerian-Eulerian Two-Fluid Model
复制标题
使用欧拉-欧拉二流体模型对稠密气固多相流进行数值模拟
DOI：
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
H. Krautz
中科院分区：
文献类型：
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作者：
Teklay Weldeabzgi Asegehegn;M. Schreiber;H. Krautz
气固流化床广泛应用于干燥、燃烧、燃料合成、造粒、聚合等化工过程中，具有良好的传热传质性能，气固混合均匀，气固比表面积大，固体输送平稳，固体产物均匀，可连续大规模操作等优点。另一方面，这些反应器有几个缺点，为进一步的研究和开发提供了强大的动力。这些措施包括：难以按比例放大和设计、容器和内部构件的腐蚀、结块的形成、由于连续操作期间不均匀的固体停留时间而导致的不均匀的产物以及高颗粒夹带。这些缺点是从业者可靠地设计和放大商业流化床反应器的瓶颈。其主要原因是，气固多相流动力学耦合的热量和质量传递和化学反应，发生在这些系统是非常复杂的，尚未完全理解。在鼓泡式气固流化床中，气泡的大小、形状、速度、分布等特性对床层的流体力学特性有着重要的影响，从而影响床层作为化学反应器和/或热交换单元的性能。气固混合和分离、传热和传质以及反应转化的程度取决于通过床层的气泡的数量、大小和运动（Kunii & Levenspiel，1991）。因此，只有在对鼓泡行为有了充分的了解之后，才能对流化床的流体力学、传热传质以及化学转化有基本的了解。然而，气泡特性的预测是极其复杂的，因为当气泡从形成它们的分配器移动到它们最终爆发的床的顶部时，气泡可以生长、聚结、分裂甚至消失。此外，气泡特性随床的几何结构和操作条件而变化。在许多应用中，插入热交换器管以提高传热和传质以及化学转化的速率，控制操作温度，促进良好的混合并减少固体的海湾循环。在这些系统中，鼓泡行为还受到内部构件的几何形状和布置的强烈影响（Yates等人，1990;船体等人，1999; Asegehegn等人，2011年a）。因此，我们认为，
Gas-solid fluidized beds are widely applied in chemical processes such as drying, combustion, synthesis of fuels, granulation, polymerization etc. They have several advantageous properties including; excellent heat and mass transfer, nearly isothermal conditions due to intense gas-solid mixing, large gas-solid surface area, smooth transport of solids, uniform solid product in batch processes, and possibility of continuous and largescale operations. On the other hand, these reactors have several drawbacks that provide a strong motivation for further studies and developments. These include; difficulty in scalingup and design, erosion of vessel and internals, formation of agglomerates, non-uniform products due to non-uniform solids residence time during continuous operation, and high particle entrainment. These drawbacks are bottlenecks for practitioners to reliably design and scale-up commercial fluidized bed reactors. The main reason for this is that the gassolid multiphase flow dynamics coupled with heat and mass transfer and chemical reactions that occur in these systems are very complex and not yet fully understood. In bubbling gas-solid fluidized beds, bubble characteristics such as size, shape, velocity, distribution have a vital influence on the hydrodynamics of bed and hence on its performance as a chemical reactor and/or a heat exchange unit. The extent of gas-solid mixing and segregation, heat and mass transfer as well as reaction conversion are governed by the number, size and motion of bubbles passing through the bed (Kunii & Levenspiel, 1991). Therefore, fundamental understanding of the hydrodynamics of fluidized beds thereafter their heat and mass transfer as well as chemical conversion come only after a sound understanding of bubbling behaviour is achieved. However, prediction of bubble characteristics is extremely complex as bubbles can grow, coalesce, split or even disappear as they move from the distributor where they are formed to the top of the bed where they finally erupt. Moreover, bubble characteristics vary with geometric construction of the bed and operating conditions. In many applications, heat exchanger tubes are inserted to enhance the rate of heat and mass transfer and chemical conversion, control the operating temperature, promote good mixing and reduce gulf circulation of solids. In these systems, the bubbling behaviour is also strongly influenced by the geometry and arrangement of the internals (Yates et al., 1990; Hull et al., 1999; Asegehegn et al., 2011a). Therefore,