The hydrodynamic behaviour of gas—solid trickle flow over a regularly stacked packing

Abstract

The hydrodynamic properties of counter-current gas—solid flow over a regularly stacked packing at trickle flow conditions have been studied. The flow properties of the solids phase were examined, using five types of solid particles with a mean particle diameter ranging from 70 to 880 μm and a particle density from 800 to 7800 kg m −3. Data on the solids hold-up and the pressure drop caused by the solids flow were obtained from experiments in a test column of 0.10 m square cross-section. A particle flow model has been developed based on the momentum equation of a single particle. In this model, particles are assumed to collide regularly with the packing and the mean particle velocity has been derived by taking account of the acceleration due to gravity and the drag forces exerted by the upward gas flow. The experimental data are described reasonably well by this model in the case of trickle flow of coarse particles. On the other hand, the flow behaviour of small particles is substantially influenced by particle shielding and solids agglomeration phenomena, resulting in slip velocities well above the single-particle terminal velocity. Generally, the drag force exerted by the particles on the gas flow is smaller than the net gravitational force for both small and large particles, although for different reasons. As a consequence, the pressure drop caused by the solids flow is generally below the value to be expected for fully suspended particles.