The present contribution reports on comprehensive hydrodynamic investigations in two pulsed sieve-plate extraction columns (PSE) on a pilot scale. The experiments were conducted with three different sieve plate geometries employing test systems recommended by EFCE, under varying pulsation conditions and throughputs. The results of the investigation add to the existing knowledge of relationships between hydrodynamic parameters, drop size, hold-up, flooding throughput and mixing and operating parameters. They also provide useful information for scaleup, selection of sieve-plate geometry, most favourable operating range, and constructive design of equipment. On the basis of measurements, analytical methods are recommended for prediction of PSE hydrodynamics.

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The present contribution reports on a new method for the simulation of the dispersed phase behaviour in liquid-liquid extraction columns. The fluid dynamic description is based on a mathematical model which explicitly takes into account drop transport, break-up and coalescence mechanisms, via a drop population balance along the column. Application of the model requires some simple measurements on single drops in order to determine transport and break-up laws, which are required by the model, and possibly also coalescence parameters. In this study the model is applied to pulsed sieve plate columns. The specific example considered here is based on systematic studies on the determination of break-up rates from the corresponding probabilities of break-up and the generated daughter drop size distributions by means of high-speed photography. The validity of the model was subsequently tested by comparison with some experimental results from studies on two different pulsed columns 80 and 225 mm in diameter for the watedtoluene system without mass transfer. The satisfactory agreement between the results justifies the use of such a method for the description of the behaviour of liquid-liquid extraction columns in a wide range of operating conditions. Furthermore, application of the model may help to dispense with long and expensive pilot tests.

for gas flow rates below 8 cm31s. After installation of the mesh, the gas hold-up for higher gas velocities increases significantly and the bubbly flow regime is expanded from about 3 cm/s to about 7 cm/s. ConclusionsBubble formation and bubble coalescence phenomena for flow of air into water through 0.14 cm diameter orifices were observed for air flow rates between 0 cm3/s and 20 cm3/s. At low gas flow rates, uniform bubbles with an average diameter of about 0.45 cm formed and then detached in quick succession at the tip of the orifice. At high gas flow rates, the bubble volume increases rapidly with the flow rate and the growing bubbles are still in contact with previous bubbles. Separation occurs in the bulk liquid close to the orifice.Bubble coalescence occurs mainly within a few centimeters of the gas distributor. By suppressing the bubble coalescence, the bubbly flow regime can be expanded and the gas hold-up can be increased, significantly.

Die Auslegung von pulsierten Siebboden‐Extraktionskolonnen allein aufgrund von Literaturdaten ist bis heute nicht möglich. Es sind zusätzliche kostenintensive Pilotversuche mit dem Originalgemisch erforderlich. Ursache hierfür ist u.a. der noch weitgehend ungeklärte komplexe Stoffaustauschmechanismus zwischen zwei flüssigen Phasen, der z.B. von oberflächenaktiven Substanzen und dem Marangoni‐Effekt beeinflusst wird. Um den experimentellen Aufwand bei der Ermittlung der für die Auslegung einer technischen Kolonne benötigten Ausgangsdaten zu minimieren, wurden am Institut für Thermische Verfahrenstechnik Standardapparaturen entwickelt, an denen die erforderlichen fluiddynamischen Daten und Stoffübergangsparameter durch Messungen an Einzeltropfen unter Einsatz des jeweiligen technischen Gemisches ermittelt werden können. Aufbauend auf diesen Stoffaus tauschdaten und bereits früher bestimmten fluiddynamischen Parametern werden die Tropfengrößen‐, Holdup‐ und Konzentrationsprofile für die Systeme Toluol‐Aceton‐Wasser und n‐Butylacetat‐Aceton‐Wasser entlang einer PSE‐Kolonne berechnet und mit Literaturdaten sowie eigenen, in einer halbindustriellen PSE‐Kolonne gemessenen Werten verglichen.