Perforated plate/Sieve Tray Tower/Column :
These are multistage, counter current contactors wherein the axial mixing of the continuous phase is confined to the region between trays, and redispersion occurs at each tray resulting into effective mass transfer. These are very effective, especially for systems of low interfacial tension both with respect to the liquid handling capacity and extraction efficiency. The perforations in the plates are about 1.5 to 4.5 mm in diameter and the plate/tray spacings are usually 150 to 600 mm.
Fig. : Perforated plate tower for continuous counter current extraction
(light liquid dispersed)
Fig. shows a perforated plate tower wherein the light liquid is dispersed. Here the general arrangement of plates and downcomers is the same as that used for gas-liquid contact except that a weir is not needed. Light liquid (dispersed phase) is introduced at the bottom, passes through the perforations in the plate in the form of fine droplets, which rise through the heavy continuous phase, coalesce into a layer beneath the plate and again redisperses through the plate above. The heavy liquid (continuous phase) is introduced at the top, passes across each plate and flows downward from a plate above to the plate below via downcomers. The principal interface is maintained at the top, the light liquid is removed from the top and the heavy liquid from the bottom. The heavy liquid can be dispersed in which case, the tower is turned upside down so that the downcomer of each plate becomes the upcomer.