Comprehensive sensitivity analysis of solids mixing in a tapered fluidized bed: Experiment and CFD-MFM simulation

Abstract

Tapered fluidized beds, due to the reduction of gas velocity in the axial direction, enhance mixing and provide uniform fluidization of particles with different size distributions. This study analyses the mixing process of a binary mixture in a pseudo-two-dimensional tapered fluidized bed using computational fluid dynamics (CFD) with an Eulerian–Eulerian approach, complemented by experiments based on digital image analysis. The Lacey mixing index was used to quantify solids mixing, and the performance of various drag models, a critical parameter in CFD simulations and not yet comprehensively investigated in tapered fluidized beds, was evaluated. The Syamlal–O’Brien drag model (Syamlal, M.; O’Brien, T. J. Computer simulation of bubbles in a fluidized bed. AIChE Symp. Ser., 1989, 85, 22 −31) showed the best agreement with experimental data, calculating the Lacey mixing index with RMSE values of 0.0972 and 0.1480 at gas velocities of 0.4 and 0.6 m/s, and estimating the minimum fluidization velocity with a relative error of 5.46 %. Using this model, numerical simulations showed that increasing apex angle and gas velocity, while decreasing coarser particle fraction, particle size ratio, and initial particle height, prevents segregation. Minimum fluidization velocity was also found to affect solids mixing significantly.