Role of Intrinsic Kinetics and Catalyst Particle Size Distribution in CFD Simulations of Polymerization Reactors

Fluidized-bed reactors are widely used in the production of polyethylene. In this work, the quadrature method of moments (QMOM), a chemical reaction engineering (CRE) model, and computational fluid dynamics (CFD) are combined to investigate the role of intrinsic kinetics and the catalyst particle size distribution (PSD) in a gas phase fluidized bed reactor. The catalyst PSD is represented by a few nodes using the QMOM and an intrinsic rate model based on the age of particles is used to solve the evolution of particle temperature, particle size, and catalyst sites with age. Assuming the particle age distribution is well-mixed, the moments of the polymer PSD are calculated and compared with experimental data. It was found that the CRE model predicts slightly larger particles as compared to the experimental data. However, the general shape of the PSD is well represented. The overall predictions were quite good, indicating that combining the reaction kinetics with QMOM is a promising method for predicting the polymer PSD in a gas-phase polymerization reactor. It was also found that the initial particle temperature rise is strongly correlated to the initial catalyst PSD: the larger the catalyst particle size, the larger the polymer particle size and the higher the peak temperature in the solid phase. Hence it is very crucial to use QMOM to represent the larger particles in the upper tail of the catalyst PSD. Segregation and hot spots in the fluidized bed are investigated using CFD simulations