Hydrodynamics and mass transfer in a three-phase fixed-bed reactor with cocurrent gas—liquid downflow

Abstract

The paper presents experimental results concerning dynamic liquid holdup, wetting efficiency and local mass transfer coefficients between the liquid and solid surface in a fixed-bed three-phase reactor, in which both the gas and liquid flow cocurrently downwards. The experiments were conducted for two basic regimes of operation of trickle-bed reactors, namely the gas continuous flow regime and the pulsing flow regime under atmospheric pressure. The measurements of dynamic liquid holdup have been performed for a wide range of gas and liquid flow rates, three different packing diameters, and for two systems of working media of different physical properties. The common correlation developed determines with good accuracy the holdup values in both regimes as well as in the transition region between the two hydrodynamic modes. In experiments concerning the wetting efficiency a dynamic tracer method has been employed, for which an original mathematical model has been formulated. The results are presented in the form of diagrams and appropriate correlating formulae. The experiments concerning local solid—liquid mass transfer coefficients were carried out for two diameters of spherical particles, with the flow rates of both phases and physicochemical properties of the liquid varied over a wide range. The experimental results are correlated and compared with the appropriate literature data. A mathematical model describing the time-varying solid—liquid mass transfer process is formulated for the pulsed flow regime. The time-averaged mass transfer coefficients calculated on the basis of the model developed are compared with the experimental values. A good agreement between these two sets of values fully confirms the assumptions of the model elaborated.