基于CFD的丙烯淤浆聚合反应釜流场的数值模拟

Numerical Simulations of Flow Field in Propylene Slurry Polymerization Reactors Based on CFD

基于计算流体力学(CFD)对丙烯淤浆聚合反应釜中液固两相流进行数值模拟,建立5L、无挡板、锥形釜底和四叶推进桨反应釜模型,采用多重参考系方法(MRF)、Mixture多相流模型和RNGk-?湍流模型模拟搅拌过程,通过冷模实验验证了模型的可靠性,并模拟得到了10%聚丙烯(体积分数)下釜内流体的速度场及浓度场。结果表明,釜内流体呈双循环流特征,聚丙烯浓度轴向呈中间低两头高的分布,径向随着轴向位置的上升分别呈"下凸"型、"直线"型、"W"型分布。在桨叶安装高度为0.56D(D为筒体部分直径)、桨叶直径为0.49D的情况下,搅拌转速在1200r/min左右时,混合效果最好;在转速为1000r/min时,桨叶安装高度为0.56D的情况下,桨叶直径在0.52D时,混合效果最好;适当降低釜内桨叶安装高度,可以在一定程度上改善釜底聚丙烯的堆积。

The liquid-solid two-phase flow in a propylene slurry polymerization reactor was numerically simulated based on computational fluid dynamics model(CFD).The 5 liters reactor model with no baffle,conical bottom,and four-leaf propeller was established and the multiple reference frame(MRF),mixture multiphase fluid model and RNG k-?model were used to simulate the stirring process.The reliability of the models was verified by the cold-model experiments.The velocity and the concentration fields of the fluid in the kettle were obtained by 10%polypropylene volume concentration fraction.The results showed that the fluid in the autoclave was characterized by double circulation flow,and the axial concentration of polypropylene was distributed low in the middle and high on both sides.The radial direction appeared to be in the“lower convex”,“linear”and“W”type along with the rise of the axial position.The mixing effect was found to be the best when the stirring speed was about 1 200 r/min with the blade installation height of 0.56D(D is the diameter of the cylindrical part of the kettle),and the blade diameter 0.49D.The mixing effect appeared to be the best when the rotational speed was 1 000 r/min with the blade diameter of 0.52D and the blade installation height of 0.56D.Properly reducing the installation height of the blade in the kettle can improve the accumulation of polypropylene at the bottom of kettle to some extent.