A CFD Study of Existing Drag Models for Geldart A Particles in Bubbling Fluidized Beds

Abstract

In this study, seven drag models are examined to determine how they affect fluidization behavior of Geldart A particles of biomass and coal. Notwithstanding the notable number of numerical studies to find the best drag model for larger particles, there is a dearth of information related to drag models for finer Geldart A particles. Additionally, to our knowledge, these drag models have not been tested with a binary mixture of Geldart A particles. Computational fluid dynamics was used to model the gas and solid phases in an Eulerian-Eulerain approach to simulate the particle-particle interactions of coal-biomass mixtures and compare the predictions with experimental data. In spite of the previous findings that bode badly for using predominately Geldart B drag models for fine particles, the results of our study reveal that if static regions of mass in the fluidized beds are considered, these drag models work well with Geldart A particles. It was found that the seven drag models could be divided into two categories based on their performance. One category included the Gidaspow family of drag models (Gidaspow, Gidaspow-Blend, and Wen-Yu) and the Syamlal-O’Brien drag model; these models closely predicted the experiments for single solids phase fluidization. For binary mixtures, however, the other drag model group (BVK, HYS, Koch and Hill) yielded better predictions.