Messen der lokalen Phasenanteile in dreiphasig betriebenen Blasensäulen mit Hilfe der Dual-Energie Röntgentomographie (English shop)

Preview

Table of Contents, Datei (38 KB)
Extract, Datei (170 KB)

In chemical and biotechnological processes, bubble columns are employed for a variety of tasks. They are cylindrical vessels filled with liquid, which are frequently gassed by means of a distributor plate located in the cross-section of the sump. The bubble swarm rising within them possesses a large interfacial area, so that such apparatus is used for mass transfer between the phases or as chemical reactors. In addition to two-phase flow with gases and liquids, particulate solids may be suspended in the latter as a third phase. In biotechnological processes, the solid serves as biomass. In chemical reactors, solid particles frequently participate in the reaction as reactants or serve as catalysts. The achievable material conversion depends, among other things, on the available interfacial area and the local phase distribution. In three-phase systems, the suspended solid particles cause bubble interaction during coalescence and breakup to differ from that in two-phase systems. To date, these processes have been investigated experimentally only inadequately for three-phase systems. Important information is therefore lacking when it comes to developing calculation methods for dimensioning bubble columns operated in three-phase mode. In the present experimental work, the local phase fractions of gas, liquid and solid are measured using a bubble column operated in three-phase mode. For this purpose, a third-generation X-ray tomograph is used. It irradiates the bubble column from different directions by means of a fan-shaped X-ray beam. The attenuation of the individual beams is measured. From these results, the local phase fractions in the respective measurement plane are reconstructed. The measurements are carried out by means of dual-energy X-ray tomography, in which X-radiation of two different wavelengths is employed. In contrast to monochromatic X-ray tomography, this technique makes it possible to distinguish three phases and to reconstruct their cross-sectional profiles.