Sieve Tray Column Extractor also known as perforated-plate columns is comprised of several perforated trays along with either downcomers or upcomers, depending on which phase, heavy or light, is chosen to be continuous.
The original dispersion is performed by a nozzle, as in spray columns. Cross flow contact occurs between each tray. Sieve tray column extractor are stage wise contactors due to coalescence of the dispersed phase between trays and its redistribution through the perforations in the tray.
It is important that the internals be coated with the continuous phase to avoid efficiency dampening coalescence of the dispersed phase. The droplets will coalesce and retain their form if the surface is coated with the continuous phase.
This lowers the mass transfer for the column. If the light phase is dispersed, the light liquid flows through the perforation of each plate and is dispersed into drops, which rise through the continuous phase.
The continuous phase flows horizontally across each plate and passes to the plate beneath through a downcomer. If the heavy phase is dispersed, the column is reversed and upcomers are used for the continuous phase.
Sieve Tray Column Extractor are operated semi-stage wise and are reasonably flexible and efficient.