Flooding, holdup, and drop size measurements in a multistage column extractor

Abstract

The hydrodynamics of a pilot plant multistage mixer column extractor was studied for the tohenelwater physically equilibrated system. The effects of rotational speed, and continuous and dispersed phase flow rates were investigated under a variety of operating conditions. Dispersed phase axial holdup profiles, determined by a noninvasive ultrasonic method, showed a strong nonuniformity. Depending on the operating conditions, holdup profiles can change from a concave shape to a sigmoidal form with a maximum in the bottom of the column. Sauter mean diameter and drop size distribution profiles are strongly affected by rotational speed. Significant, but weaker, are the effects of continuous and dispersed phase flow rates. Continuous monitoring of the holdup profile in the proximity of flooding leads to the formulation of proper criteria for the prediction of flooding. These criteria are appropriate for models allowing for axial variation of the holdup along the contactor.

Prediction of mass transfer coefficients in a pulsed packed extraction column using effective diffusivity

“…This makes it difficult to determine the mass transfer coefficients in an extraction column. Moreover, very little is known about the effect of agitation, superimposed on the flow of the two phases in an extraction column, on the enhancement of mass transfer coefficients (TorabMostaedi et al, 2008;Sarker et al, 1985;Nii et al, 1997;Kirou et al, 1988). Mass transfer coefficients in extraction columns are generally obtained from the measured concentration profiles (or end concentrations) and values of operating variables by using an appropriate simulation model.…”

Mass transfer coefficients in a hanson mixer-settler extraction column

“…Mechanical agitation can promote the mass transfer rate and extractor efficiency because it increases interfacial area between the two immiscible liquids and new surfaces and high turbulence which increase mass transfer coefficients (Takahashi et al, 1993a;Horvoth and Hartland, 1985).Varieties of stirring extractors are known such as MIXCO, Kühni, RDC, ARD, QVF and mixer-settlers. As drop size decreases with agitation speed, however, the relative velocity between the dispersed phase and continuous phase decreases, which makes the throughput small (Kirou et al, 1988). Moreover, axial mixing, which lowers the stage efficiency, becomes significant at high agitation speed.…”

“…Therefore, to design an extraction column, the mass transfer characteristics should be known and it is usually not possible to design extraction equipment accurately without some experimental information about mass transfer conditions. In a usual extraction column, the diameter of dispersed drops and the dispersed phase holdup depend on vertical position of the column (Sarker and Phillips, 1985;Nii et al, 1997;Kirou et al, 1988) and accurate estimation of these variables is difficult (Tsouris et al, 1994). This makes it difficult to determine the mass transfer coefficients in an extraction column.…”

Acoustic Probe for Solid-Gas-Liquid Suspension

“…In dark field illumination, it is difficult to distinguish between solid particles and bubbles. Also, an illumination configuration such as that employed by Kirou et al (1988) is not feasible as the test cell size is too small to accommodate the fiber optic apparatus; and, according to Bongiovanni et al (1997), the relative size and close proximity of the light source to the focal distance of the particles or bubbles will introduce large errors in the size measurements. Therefore, since the experimental measurements and the optical apparati involved are similar, bubble measurements are made by the method employed by Burns et al (1997) and Shin et al (1997), and a calibration is performed using particles of known sizes to determine how much, if any, error is present in the size measurements by this method.…”