CFD modeling of the gas–solid two-fluid flow in polyethylene FBRs: From traditional operation to super-condensed mode

Abstract

A computational fluid dynamics (CFD) model based on the Eulerian–Eulerian approach, coupled with polymerization kinetics, has been implemented to describe the gas–solid flow behaviors in a gas phase polyethylene fluidized bed reactor (FBR). The model is firstly validated by the classic equations and reference data, and then extended to simulate the gas-phase polyethylene FBR under super-condensed mode for the first time. The influence of three important operating conditions (i.e., inlet gas velocity, inlet gas temperature, and condensable component isopentane concentration) on gas–solid flow hydrodynamics is investigated to give qualitative and quantitative insights on how these factors affecting FBR performances (like bed expansion, bed temperature and productivity) under super-condensed mode through CFD approach. The simulation results demonstrate that with the increase of inlet gas velocity, the bed expansion increases rapidly and the number of particles at the lower portion of the bed reduces while raises at the higher position. The rise of the bed temperature is mainly contributed by the increased exothermic reaction rate as the inlet gas temperature increasing, which is also influenced by the concentration of condensable component isopentane. The simulation results show that bed temperature decreases with the increase of condensable isopentane concentration in gas stream. It is found that the method of heat removal through the latent heat of vaporization is extremely significant and can effectively increases reactor productivity without enlarging the size of the reactor under super-condensed mode.