Correlations for effective bubble rise velocity in three-phase ebullieted beds

Abstract

A knowledge of phase holdups and linear phase velocities is important for designing and predicting the performance of three-phase ebullieted bed reactors. The generalized wake model is widely used to calculate the phase holdups, in three-phase ebullieted beds. However, the value of the gas holdup, predicted by the model, is very sensitive to the value of the bubble rise velocity, relative to the liquid in the surrounding liquid-solid fluidized region, which has to be estimated independently for the model. A means of predicting the effective bubble rise velocity, in a three-phase ebullieted bed, will therefore be very useful. The equations in the generalized wake model were manipulated to give the best value of the effective bubble rise velocity, which when substituted back into the model gave values of phase holdups close to the experimentally observed values. These values of the effective bubble rise velocity were then fitted in correlations, with the liquid superficial velocity, the gas superficial velocity, the liquid viscosity, the surface tension and the solid particle size as the variables. An attempt is made, to explain the forms of the correlations through various hydrodynamic phenomena for three-phase ebullieted beds such as flow regimes and their transitions, flow transition liquid velocity, solid wettability, behavior of bubbles, apparent bed viscosity and the effect of solid particles. The three-phase systems for which the correlations were developed consist of a wide variety of materials, such as glass beads or cylindrical catalyst particles as solid phases, water or kerosene as liquid phases and air, nitrogen or helium as gas phases. The flow regimes were of industrial significance. The solid particles ranged in size from 1.0–5.0 mm.