A CFD-PBM coupled model of hydrodynamics and mixing/segregation in an industrial gas-phase polymerization reactor

Abstract

The particle size distribution (PSD) has a significant influence on the performance of fluidized bed reactors, as uneven distribution usually results from segregation and mixing tendencies. The objective of this paper is to study the segregation of wide range of particle size distribution in an industrial gas phase polymerization reactor by means of a CFD–PBM coupled model, where the direct quadrature method of moments (DQMOM) was implemented to solve the population balance model. It was shown that the model is able to satisfactorily predict the available operational data in terms of pressure drop and bed height. Model sensitivities of discretization scheme, maximum solid packing and fluidization/de-fluidization were also studied. The transient CFD–PBM/DQMOM coupled model is then utilized extensively to analyze minimum fluidization velocity, fluidization behavior and segregation phenomena at different velocities. The results suggested that third-order MUSCL discretization scheme, maximum solid packing value which is 0.01 higher than specific solid volume fraction and also fluidization process were mathematically and physically consistent with real observation. In addition, the segregation is strongly affected at minimum fluidization velocity range of particles. The PSD becomes well-mixed at high gas velocity while the quasi-layer inversion was predicted in low gas velocity.