Solid-liquid mixing measurement, solids distribution

Mixing and solids distribution. Dispersion coefficients of gas, liquid and solid phase have not been measured under conditions prevailing in the FTS. However, the liquid phase dispersion coefficient depends only slightly on liquid phase properties. It is therefore believed that correlations based on a lot of data for low viscous media and from coliomns of various sizes can be applied. Such a correlation was given by Deckwer et al. (68)... 

Electrical techniques primarily measure the electrical impedance of a mixed-phase medium. Because the dielectric constant or electrical conductivity of a solid phase differs from that of the fluid, one can measure electrical conductance or capacitance to determine phase distribution. To attain better sensitivity, conductance flowmeters are usually applied to conducting media, such as aqueous solutions or solids/water slurries, whereas capacitive flowmeters are applied to solid/gas flows and solid/nonconducting-liquid flows. Capacitance measurements are generally more reproducible because they are not affected by the ion concentration of the solution, which is difficult to control during processing. 

A description of the flow phenomena in this type of process is very complicated and is outside the scope of this book (see reviews by Shah 1979, and Shah and Sharma, 1987). Phenomena that have been studied include the various flow regimes, liquid and gas hold-ups, pressure drop, the distribution of liquid and gas flows, effective solids wetting, axial mixing, etc.. However, it is important to remenber that for chemical reactor development one can measure, separately, the mass transfer and the integral performance of the three-phase system on a small scale, using the same solid particles that are going to be used on the larger scale. 

Self-diffusion type measurements. A radiotracer of a specific form is chemical mixed with a solid and the diffusion into the non-labelled segment of the same material is measured. The procedure yields information on matrix restriction caused by pore stmcture and water content when a non-reactive component is introduced (Na-22, Cl-38 and H-3). For reactive species it will yield information on the distribution ratio between liquid and solid phase, which can be expressed as a retardation factor. By introducing components of interest in different chemical forms the mobilities of these different species in a given matrix can be determined. Analysis of diffusion profiles may result in identification of more then one species. 

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