Abstract:

When the gas-phase polyethylene process is operated in the condensation mode, the liquid phase evaporates in the bed and the fluid flow pattern changes to the rotary type, and the effect of lift force can't be ignored. In this paper, the CFD model of the gas-liquid-solid three-phase flow polyethylene fluidized bed reactor was established, and the effects of three different lift models of Saffman-Mei, Legendre-Magnaudet and Moraga on the multiphase fluid flow of the polyethylene fluidized bed reactor were explored. The simulation results show that the lift model has no significant effect on the average bed height and the average reactor temperature after fluidization stabilization, but there are differences in the particle phase distribution in different height regions of the bed and the temperature distribution in the low region. The different particle sizes of solid phase particles have different fluidization processes under the influence of lift, small particles tend to produce larger bubbles in the fluidization process, and the aggregation phenomenon of large particles at the wall is more obvious. The Saffman-Mei and Moraga models have similar evaporation rates of the liquid phase. The Moraga model has the most intense particle and bubble motion. The bed pressure drop predicted by the Legendre-Magnaudet model is the most accurate, and the phase distribution and temperature distribution during the fluidization process are more uniform.

Key words: computational fluid dynamics, fluidized bed, multiphase flow, fluid mechanics, lift model

摘要：

气相法聚乙烯工艺在冷凝模式操作下，液相在床层内部蒸发使流体流型转变为旋转型，升力的影响不可忽略。建立了气-液-固三相流聚乙烯流化床反应器CFD模型，并探究Saffman-Mei、Legendre-Magnaudet和Moraga三种不同升力模型对聚乙烯流化床反应器多相流体流动的影响。模拟结果表明，升力模型对于流化稳定后床层平均高度、反应器平均温度无明显影响，但在床层不同高度区域内颗粒相分布和低区域内温度分布存在差别。不同粒径固相颗粒在升力的影响下具有不同的流化过程，小粒径颗粒在流化过程中易产生较大的气泡，大粒径颗粒在壁面处的聚集现象更为明显。Saffman-Mei模型使得颗粒沿着壁面以及向较高床层运动更为明显，在低床层趋于温度较低；Saffman-Mei模型和Moraga模型具有相似的液相蒸发速率；Moraga模型的颗粒和气泡运动最为剧烈；Legendre-Magnaudet模型预测的床层压降最为准确，并且流化过程中的相分布和温度分布等更为均匀。

关键词: 计算流体力学, 流化床, 多相流, 流体力学, 升力模型