Theoretical Models of Gas-Liquid-Particle Operations

The purpose of this section is to present a general theoretical model of gas-liquid-particle operations, with a number of simplifying assumptions that make possible, at least in principle, the calculation of the conversion and yield from a specified amount of information regarding transport phenomena and reaction kinetics. 

Gas-liquid-particle operations are of a comparatively complicated physical nature Three phases are present, the flow patterns are extremely complex, and the number of elementary process steps may be quite large. Exact mathematical models of the fluid flow and the mass and heat transport in these operations probably cannot be developed at the present time. Descriptions of these systems will be based upon simplified concepts. 

It seems probable that a fruitful approach to a simplified, general description of gas-liquid-particle operation can be based upon the film (or boundary-resistance) theory of transport processes in combination with theories of backmixing or axial diffusion. Most previously described models of gas-liquid-particle operation are of this type, and practically all experimental data reported in the literature are correlated in terms of such conventional chemical engineering concepts. In view of the so far rather limited success of more advanced concepts (such as those based on turbulence theory) for even the description of single-phase and two-phase chemical engineering systems, it appears unlikely that they should, in the near future, become of great practical importance in the description of the considerably more complex three-phase systems that are the subject of the present review. 

In this section, a number of important elementary process steps into which a gas-liquid-particle process can be subdivided will be mentioned. Several theoretical models proposed in the literature will be discussed, and a slightly more comprehensive model will be described. 

It is assumed in this section and the next that the solid particles are completely wetted by the liquid, and, as a consequence, that the gaseous phase is not in direct contact with the solid. Systems may conceivably exist in which the particles are not completely wetted by liquid, either because of poor liquid distribution or because of the surface properties of liquid and 

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A number of theoretical models of gas-liquid-particle operations have recently appeared in the literature. Those considered most significant will be discussed briefly in the following, as introduction to a somewhat more general model that will be proposed in this paper. 

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