Modeling and simulation of particle size distribution behavior in gas-liquid-solid polyethylene fluidized bed reactors

In this work, population balance model (PBM) that describes particle size distribution (PSD) and liquid vaporization modeling scheme (VMS) (including the heat transfer model and droplet vaporization model), which describes liquid evaporation, were incorporated into a three-fluid computational fluid dynamics (CFD) model to analyze PSD behavior in an industrial-scale gas-liquid-solid three-phase polyethylene fluidized bed reactor (FBR). The validation of this CFD-VMS-PBM coupled model was conducted through comparing results with industrial and calculated data, which then was applied to discuss the characteristics of PSD behavior in terms of the effects of particle kinetics, node number, and condensed liquid content. Unlike gas-solid polyethylene conventional FBRs, although the PSD behavior was dominated by particle agglomeration, particle breakage kinetics exerted a great impact on PSD, especially at the initial polymerization period when it competed with aggregates to decrease the defluidization risk of the reactor. Furthermore, the number of nodes strongly affected PSD simulation results, and using three nodes was the best configuration. In this three-phase system, the increase in the condensed liquid content improved the particle growth rate, which affected the reactor's productivity and product's properties, such as mean particle size and final PSD. (C) 2018 Elsevier B.V. All rights reserved.