CFD based investigations on hydrodynamics and energy dissipation due to solid motion in liquid fluidised bed

Abstract

Abstract CFD simulations are carried out for the prediction of flow patterns in a liquid–solid fluidised bed using Eulerian–Eulerian framework. The CFD model predictions are compared with the experimental findings reported by Limtrakul et al. [S. Limtrakul, J. Chen, P.A. Ramachandran, M.P. Dudukovic, Solids motion and holdup profiles in liquid fluidised beds, Chem. Eng. Sci. 60 (2005) 1909–1920] and the comparison shows good agreement. The CFD model has been further extended to compute solid mass balance in the core and annular regions for verifying conservation of mass and energy flows due to various dissipation mechanisms. Energy required for solid expansion in liquid fluidised bed is also compared with energy required for solid suspension in an equivalent stirred tank contactor at similar operating conditions. The influence of various interphase drag models proposed by Gidaspow [D. Gidaspow, Multiphase Flow and Fluidisation, 1st ed., Academic Press, San Diego, 1994], Di Felice et al. [R. Di Felice, The voidage functions for fluid–particle interaction system, Int. J. Multiphase Flow 20 (1994) 153–159] and Syamlal and O’Brien [M. Syamlal, T.J. O’Brien, Simulation of granular layer inversion in liquid fluidised beds, Int. J. Multiphase Flow 14 (1988) 473–481] on solid motion in liquid fluidised bed have been investigated. Even though these models predict the flow pattern of solid motion inside the fluidised bed with reasonable accuracy, the model proposed by Gidaspow showed the better quantitative agreement with experimental data. For ensuring accuracy of numerical simulation prediction, comparisons between 2D and 3D simulation, the effect of grid sensitivity, time step sensitivity and effect of inlet feed conditions have been carried out and a comprehensive CFD methodology is proposed to model the hydrodynamics of liquid–solid fluidised bed.