Functions of Tray In Distillation Column

     One of the most prominent hardware used for mass transfer is tray. Tray columns are widely used in various types of mass transfer operations. All the simulation results, which predict a certain number of theoretical stages, can be converted to actual trays depending upon tray efficiency for a particular service.

      Basic functioning of a tray/plate is mass transfer. It actually brings about vapor-liquid contact. More the vapor-liquid contact, more would be the mass transfer. This is practically achieved when a liquid is held on a perforated tray and vapors pass through this liquid layer from below the liquid depth through the perforations. It should be noted here that, flow rate should be adjusted such as the liquid "may not" come down from the tray above "through perforations". If this happens, then vapor-liquid contact would be less which will result in low vapor liquid contact and hence it lowers the efficiency of tray. This condition is said to be weeping.

     Similarly, vapor velocity must not be so high, since it may take the liquid over the tray to the tray above it, in form of droplets. This will again reduces the efficiency of the tray in the similar manner. This process is called entrainment.

     In any conventional tray vapour rises through the liquid pool on the tray deck and then disengages from the liquid in the space above the deck. Liquid enters the tray from a downcomer above and leaves via a downcomer below.

     

Conventional Tray has three functional zones:

1. Active area for mixing vapour and liquid: This is the zone where mass transfer occurs.
2. Vapour space above the active area: This is the zone in which liquid is separated from vapour.
3. Downcomer between trays. This zone has two functions, first moving liquid from one contacting tray to another and second disengaging vapour from liquid.