基于CFD模拟的聚丙烯环管反应器非稳态分析

Unsteady State Analysis of a Polypropylene Loop Reactor Based on CFD Simulation

聚丙烯环管反应器中颗粒的非均匀流动现象是引发轴流泵功率波动的重要原因。基于CFD非稳态模拟,研究了环管反应器管内液固两相流体在时间尺度上的非均匀流动特性,并对比了颗粒粒径对非均匀流动的影响。模拟发现,颗粒粒径越大,环管出口处颗粒浓度及非均匀度的波动幅度和波动频率越大,越不利于轴流泵的稳定操作。此外,液固两相流体在经过环管反应器的弯头后,颗粒团聚物等结构会导致固相体积分数出现新的周期行为(脉动频率约为10 Hz),这使得流场的湍动程度加剧、颗粒-颗粒及颗粒-壁面间的摩擦碰撞加剧以及能量耗散加快。

The non-uniform particle flow in the polypropylene loop reactor is the main reason for the power fluctuation of the axial flow pump. In this paper, the non-uniform flow characteristics of liquid-solid two-phase flow in a loop reactor were studied based on the unsteady computational fluid dynamics(CFD) simulation, and the influence of particle size on the non-uniform particle flow was further compared. The simulation results showed that the larger the particle size, the larger fluctuating ranges and frequencies of the particle concentration and non-uniformity at the outlet of the circular pipe are, which is unfavorable to the stable operation of the axial flow pump. Moreover, after the liquid-solid phase flowed through the elbow, the formation of particle aggregates led to a new periodic behavior of solid volume fraction (the frequency is about 10 Hz), and the intensity of flow turbulence was strengthened. As a result, the particle-particle and particle-wall friction and collision were intensified, and the energy dissipation was accelerated.