双峰聚乙烯颗粒临界流化速度的研究

Minimum fluidization velocity of bimodal polyethylene particles

针对环管和流化床串联的组合工艺中双峰聚乙烯黏性颗粒流化状况不佳的现状,利用压差法系统考察了温度和粒径对临界流化速度的影响,以及温度对粒径分布的影响.结果表明,压降-气速关系不符合经典轨迹,压降曲线波动较普通树脂显著,流化过程依次表现为颗粒流化和聚团流化两个过程.由于双峰聚乙烯中低相对分子质量部分的存在,聚合物颗粒间表现出较强的黏性,引起团聚现象,粒径分布变宽.表观最小流化速度与经典公式计算数据偏离较大,其数值随温度的升高呈增大趋势,且粒径越小,温度对最小流化速度的影响就越大.通过添加黏性力项,重新建立颗粒的力平衡,获得了具有较高精度的临界流化速度模型.

The influences of temperature and particle size on the minimum fluidization velocity and the influence of temperature on the particle size distribution were observed by pressure-drop method according to the abnormal fluidization of bimodal polyethylene sticky particles in the combined process of loop reactor and fluidized bed. Results showed that the pressure curves were different from the classical ones, which had remarkable fluctuation and two fluidization processes including particle fluidization and agglomeration fluidization. The polymer particles showed strong stickiness and had wider particle size distribution by agglomeration for the relative lower molecular mass part exist in bimodal polyethylene. The minimum fluidization velocity of the sticky bimodal particles was different with that from classical formula. The minimum fluidization velocity increased with temperature. The smaller particles were, the greater effect temperature played on the minimum fluidization velocity. A model to calculate the minimum fluidization velocity of bimodal polyethylene was deduced by adding a cohesion item to the particle force balance.