Hydrodynamic behaviour of a gas—solid counter-current packed column at trickle flow
Trickle flow of a more or less fluidized catalyst through a packed column is a promising new gas—solid counter-current operation. The hydrodynamic, behaviour of such a column, filled with dumped PALL rings, has been investigated, while some results have been obtained with RASCHIG rings and cylindrical screens as packing. The solid used was a microspherical catalyst carrier. Pressure drop, hold-up, loading and flooding were evaluated and compared with literature data for gas—liquid systems. The behaviour is analogous although the absolute magnitude is different. 
 
Pressure drop is low, up to 50% of the solid being carried by the packing. A correlation for the pressure drop, which is mainly caused by suspended particles, has been derived. At low gas velocities particle velocity is constant, whilst near flooding the slip velocity between gas and solid reaches a constant value. Using empirical values for particle velocity and slip velocity, hold-up, loading and flooding can be predicted. Scaling-up problems still need to be investigated. Results on mass transfer, axial dispersion of both phases and solid spread factors will be published later.
Mass transfer in a gas—solid packed column at trickle flow
The height of an overall transfer unit has been evaluated in a gas—solid packed column at trickle flow by measuring column performance during steady state adsorption experiments. Results have been interpreted with an extraction model: mass transfer and axial dispersion in both phases. Using Bodenstein numbers for the gas and solid phases from a previous investigation the height of a true transfer unit has been calculated. 
 
The column was filled with dumped Pall rings, the solid phase was a freely flowing catalyst carrier, and the gas phase was air at ambient conditions containing freon-12 as adsorbing component. 
 
At low gas velocities column performance is entirely determined by axial dispersion but at higher gas velocities mass transfer limitations become important. For conditions of practical importance the height of a true transfer unit corresponds to 4 – 9 Pall ring layers.
Gas mixing in fluidized beds containing screen packings
Gas mixing was studied in a fluidized bed containing hollow, open-wall packings using a continuous injection of oxygen as a tracer. 
 
 
 
During bed expansion, the reciprocal of mixing length, u/E1, for a gas-fiuidized bed containing packings of dimension less than 3-in. was found to decrease and then increase with the expansion ratio, Δ, passing through a minimum, in contrast to an unpacked fluidized bed for which no minimum u/E1, was reported. 
 
 
 
The minimum u/E1, occurred always at Δ = 0.30, independent of column diameter, of the shape or of the size of the packing, and of the size of the fluidizing particle. Values of the minimum u/E1's for a fluidized bed packed with various screen cylinders depended upon the size of the packing, dn, and of the fluidized particle, d1,. An empirical correlation of (u/E1)mn, with d1, and dn is presented. 
 
 
 
On a etudie le melange de gaz dans un lit fluidise contenant des garnitures creuses et a parois ouvertes, en utilisant une injection continue d'oxygene comme indicateur. 
 
 
 
Durant l'expansion du lit, on a trouve que l'inverse de la longueur de celui-ci, (u/E1) decroissait, puis augmentait avec le coefficient d'expansion Δ, lorsqu'il s'agissait d'un lit fluidise contenant des garnitures de moins de 3 pouces; ce changement de dimension atteignait un minimum, contrairement a ce qui se passe dans le cas d'un lit fluidise sans garniture, au sujet duquel on ne fait mention d'aucun minimum pour u/E1. 
 
 
 
Le minimum d'u/E1 est toujours survenu lorsque la valeur de Δ etait 0.30, independamment du diametre de la colonne ou de la forme et des dimensions de la garniture de la particule fluidisee. Leg valeurs du minimum d'u/E1. pour un lit fluidise garni de divers cylindres-cribles, dependaient des dimensions de la garniture dn et de la particule fluidisee d1. On presente une correlation empirique entre le minimum 'u/E1 d'une part et d, et dn d'autre part.