The gas flow modulation
technique (GFM) is a recently proposed
approach for measuring the axial gas dispersion coefficient in bubble
columns. It is based on a time-resolved measurement of the modulated
gas holdup at different axial positions in the column and a subsequent
calculation of the axial dispersion coefficient from amplitude damping
and the phase lag of a gas holdup wave. In recent studies holdup has
been measured with gamma-ray densitometry, which is advantageous in
terms of measurement accuracy. However, the application of radiative
measurement techniques in industrial settings poses several logistical
and safety challenges. This study investigates the potential of nonradiative
measurement techniques in the context of GFM. In particular, differential
pressure sensors, conductivity needle probes and optical probes are
considered. The results obtained using these alternative techniques
are compared with gamma-ray measurements. The comparison qualifies
differential pressure sensors as a particularly viable alternative
to gamma-ray densitometry.
A direct approach for determining the tray and point efficiencies of an industrial-scale distillation tray is proposed. The stripping of isobutyl acetate from an aqueous solution with air was used, which is a manageable and nonhazardous method applicable for performance tests in large hydraulic column mockups. This work represents the first application of this system in the case of tray columns exemplified for a sieve tray. A column of 800 mm internal diameter was used for conducting the stripping experiments. The distribution of isobutyl acetate in the liquid phase on the tray was obtained via liquid sampling at several deck positions and UVspectroscopy analysis. A definition for the liquid-side tray efficiency in weeping conditions is proposed together with an experimental approach for determining tray and point efficiencies in such conditions. The derived efficiency data show good agreement with the model predictions and correlations.
The accurate identification of the transition velocities U trans in bubble columns (BCs) is important for their effective design, operation, and scale-up. In this work, a novel parameter, namely, the new hybrid index (NHI), was developed and successfully applied to gas holdup and pressure fluctuations recorded in various BCs operated with water and aqueous solutions of alcohols (ethanol and propan-2-ol). The first U trans was identified on the basis of a well-pronounced local NHI minimum, whereas the second U trans was distinguished by the point from which the NHI profile levels off. It was concluded that the main U trans depend on the type of gas-liquid system and sparger used. A set of several U trans is reported.
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