The efficient design, operation, and scale up of novel fluidized bed bioreactors for direct coal liquefaction require detailed knowledge of reactor axial pressure drop, dispersion of the solid and liquid phases, and the particle size distribution as a function of axial position. In this paper, a fully predictive mathematical description of the hydrodynamics of a liquid fluidized bed, containing no adjustable parameters, is developed. This model is compared with experimental data obtained from a liquid fluidized bed containing finely divided coal particles. The emphasis of this study is the development of a predictive mathematical model to appropriately describe the transient behavior of such systems subject to changes in the liquid superficial velocity. The underlying mathematical treatment of this problem is based on particle mass transport mechanisms of dispersion and convection. The particle velocity responsible for convection and the particle dispersion coefficients were evaluated using correlations developed previously. The comparison of the model predictions with the experimental data for coal fluidized beds shows excellent agreement.