Flüssigphase-Rückvermischung in gepackten Blasensäulen

Liquid phase backmixing in packed bubble columns . Correlations for the axial liquid phase dispersion coefficient in bubble columns packed with metal Raschig rings and Pall rings are given as Pe_g = f (Ga, Re_g, H/D). The dependencies on physical and operational properties are discussed in detail with the aid of diagrams. Pall rings are not able to completely suppress greater turbulences and backmixing in columns of diameters D > 20 cm. A rule of thumb is also given for the apparent dispersion coefficient in this range. Raschig rings, however, are well suited for suppressing backmixing. The problems of adequate fulfilling of the model and undisturbed measurement of the backmixing behaviour are dealt with in detail.     

Rückvermischung in Blasensäulen mit Einbauten

Back-mixing in Bubble Columns Fitted with Internals. Interals installed in bubble column reactors serve mainly for heat transfer and for influencing (suppressing) liquid circulation. Reinforcement of mixing is observed for experimentally for internals subjected to longitudinal flow, which is attributable in limitation of transverse exchange and the resulting increase of axial eddy dimensions. The experimental findings can be readily described by the axial dispersion model for uniform cross sections and equations are given for estimating the dispersion coefficients of the gaseous and liquid phases as a function of the central liquid circulation velocity. Internals subjected to transverse flow hinder the establishment of a large scale circulatory motion and therefore suppress mixing on the bubble column. Two calculation procedures of differing model depth are presented which permit determination of concentration and temperature profiles in bubble column reactor cascades. Moreover, equations are given for estimating reflux conditions on sieve plates and bundled tube heat exchangers in cross flow which are based on experimental investigations.     

Auslegung von Blasensäulen mithilfe von Compartmentmodellen

In bubble columns, the phenomena of mass and heat transfer as well as the reaction are closely linked to the complex fluid dynamics. Compartment modeling offers the opportunity to integrate these phenomena while enabling an axial and radial distribution with acceptable computing effort. This article includes methods for generating the compartment geometry and fluid dynamic parameters of this modeling approach, facilitating the opportunity to optimize an industrial bubble column.