Mean residence time and mass fraction of tracer in a liquid-solid tapered inverse fluidized bed: numerical modelling with experimental validation

Abstract

BackgroundInverse fluidized beds have been designed to control the fluidization of low-density particles in high-density of continuous fluid. Fluidization of a large quantity of low-density particles can be challenging to control in a classic inverse fluidized bed. A tapered inverse fluidized bed can assist in the better fluidization of wider particles size distribution as the cross-sectional area have been enlarged along with the bed height from the top to the bottom. MethodsHere, a laboratory setup of a tapered inverse fluidized bed was used to examine the mean residence time characteristics and the dispersion coefficient. Additionally, a three-dimensional computational fluid dynamics (CFD) modelling was performed to examine the mass fraction of the tracer. The Eulerian-Eulerian approach and the kinetic theory of the granular flow model were used to analyze the liquid flow and solid materials behaviour, respectively. The dispersion coefficient obtained using CFD were compared and validated with the experimental results. Then, the CFD model was used to investigate the effect of liquid velocity, size and density of solid materials (i.e., lower density than the density of water) and two different bed angles (6.8o and 8o) on the mass fraction of tracer along the bed heights. Significant FindingsIt was found that the liquid tracer mean residence time and axial dispersion coefficient significantly depended on particle density, tapered angle of the column, and superficial liquid velocity. Based on the experimental data, an empirical correlation has been developed for the mean residence time of the tracer by using response surface methodology. The findings can assist in designing and operation a tapered inverse fluidized bed technology.