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Figure 19. Rotating disc contactor (RDC).

With increasing rotational speed, efficiency improves as drops become smaller, but maximum capacity is lessened. Increased rotational speed also increases continuous phase backmixing, and causes some segregation of the phases as the lighter phase accumulates around the shaft while the denser phase hugs the wall. At the same energy input, dispersing the light phase leads to smaller drops because all of the light phase must pass over the tips of the spinning discs; whereas dispersion of a denser phase is brought about primarily by fluid motion over the stationary ring baffles.

Oldshue-Rushton Column. This column is similar to the RDC, except that the flat rotor discs have been replaced with turbine type agitators (Fig. 20). As with the RDC, the diameter of the agitators can be varied along the shaft to compensate for the progressive change in the physical properties of the system as extraction occurs.

Other variations of stirred columns which are available include the asymmetric rotating disc (ARD) contactor, the Kiihni column, and two types of Scheibel columns. The rotor of the ARD is located off center, which permits more elaborate baffling for the necessary transport of flows with less backmixing.

Figure 20. Oldshue-Rushton column.

The Kiihni column employs radial flow impellers located between perforated plates for compartmentalization. The first Scheibel column used wire mesh zones to promote coalescence and limit backmixing between turbine-agitated mixing zones. A later Scheibel column used a shrouded radial impeller and multiple ring baffles to direct most of the rotor's energy towards dispersion and away from axial mixing.

Raining Bucket Contactor. This contactor consists of a series of scoops located on a slowly rotating, baffled rotor within a horizontal cylindrical vessel (Fig. 21). An interface is maintained near the middle, and the scoops capture and then allow one phase to rain through the other, and vice versa, once each revolution.

Rotating Disc Contactor Rdc Column

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