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Analyzing the effects of particle density, size, size distribution and shape for minimum fluidization velocity with Eulerian-Lagrangian CFD simulation

机译：用欧拉 - 拉格朗日CFD模拟分析颗粒密度，尺寸，尺寸分布和形状对最小流化速度的影响

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Fluidized bed reactor systems are widely used due to excellent heat and mass transfer characteristics followed by uniform temperature distribution throughout the reactor volume. The importance of fluidized beds is further demonstrated in high exothermic reactions such as combustion and gasification where fluidization avoids the hot spot and cold spot generation. A bed material, such as sand or catalyst, is normally involved in fluidized bed combustion and gasification of biomass. Therefore, it is vital to analyze the hydrodynamics of bed material, especially the minimum fluidization velocity, as it governs the fluid flowrate into the reactor system. There are limitations in experimental investigations of fluidized beds such as observing the bed interior hydrodynamics, where CFD simulations has become a meaningful way with the high computer power. However, due to the large differences in scales from the particle to the reactor geometry, complex interface momentum transfer and particle collisions, CFD modeling and simulation of particle systems are rather difficult. Multiphase particle-in-cell method is an efficient version of Eulerian-Lagrangian modeling and Barracuda VR commercial package was used in this work to analyze the minimum fluidization velocity of particles depending on size, density and size distribution. Wen-YU-Ergun drag model was used to model the interface momentum transfer where default equations and constants were used for other models. The effect of the particle size was analyzed using monodispersed Silica particles with diameters from 400 to 800 microns. Minimum fluidization velocity was increased with particle diameter, where it was 0.225 m/s for the 600 microns particles. The density effect was analyzed for 600 microns particles with seven different density values and the minimum fluidization velocity again showed proportionality to the density. The effect of the particle size distribution was analyzed using Silica. Particles with different diameters were mixed together according to pre-determined proportions as the final mixture gives a mean diameter of 600 microns. The 600 microns monodispersed particle bed showed the highest minimum fluidization velocity. However, some particle mixtures were composed with larger particles up to 1000 micron, but with a fraction of smaller particles down to 200 microns at the same time. This shows the effect of strong drag from early fluidizing smaller particles. The only variability for pressure drop during packed bed is the particle size and it was clearly observed in all three cases.
机译：流化床反应器系统因其出色的传热和传质特性以及随后在整个反应器体积中均匀的温度分布而被广泛使用。流化床的重要性在诸如燃烧和气化的高放热反应中得到了进一步证明，其中流化避免了热点和冷点的产生。床料，例如沙子或催化剂，通常参与流化床燃烧和生物质的气化。因此，分析床料的流体动力学，尤其是最小流化速度至关重要，因为它决定了进入反应器系统的流体流量。在流化床的实验研究中存在局限性，例如观察床内部的流体动力学，在这种情况下，CFD模拟已成为具有强大计算机功能的一种有意义的方式。但是，由于从粒子到反应堆几何形状的尺度差异很大，复杂的界面动量传递和粒子碰撞，粒子系统的CFD建模和仿真相当困难。多相细胞内颗粒法是Eulerian-Lagrangian建模的有效版本，Barracuda VR商业软件包用于这项工作，根据尺寸，密度和尺寸分布来分析颗粒的最小流化速度。使用Wen-YU-Ergun阻力模型对界面动量传递进行建模，其中将默认方程式和常数用于其他模型。使用直径为400至800微米的单分散二氧化硅颗粒分析了粒径的影响。最小流化速度随颗粒直径而增加，其中600微米颗粒的最小流化速度为0.225 m / s。分析了具有七个不同密度值的600微米颗粒的密度效应，最小流化速度再次显示出与密度成比例。使用二氧化硅分析了粒度分布的影响。将不同直径的颗粒按照预定比例混合在一起，因为最终混合物的平均直径为600微米。 600微米单分散颗粒床显示出最高的最小流化速度。然而，一些颗粒混合物由最大至1000微米的较大颗粒组成，但同时具有一小部分至200微米的较小颗粒。这显示了早期流化较小颗粒产生的强大阻力。填充床期间压降的唯一变化是粒径，在所有三种情况下均清楚观察到。

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