Liquid hold-up and backmixing in cocurrent upflow three-phase fixed-bed reactors

Abstract

Liquid-phase hydrodynamics is studied in a three-phase fixed bed with cocurrent upflow of gas and liquid. Residence-time distributions are measured to determine liquid hold-up and backmixing using different liquids and glass beads of two sizes. Two types of correlations are tested for liquid saturation. Correlations based on the drift flux concept are found to account for experimental results. Liquid mixing is described in terms of the axial dispersion model. A close relation between the axial dispersion coefficient and the bubbles sizes estimated using the theory of fluid emulsions is found. Hence, a new type of correlation is proposed to estimate axial dispersion coefficients in this type of reactors. This correlation considers the influences on the Peclet number of the liquid Reynolds number and the two-phase flow dissipation power rate, which would determine bubbles sizes.