Tray

A tray basically acts as a mini-column in which each of it performing a fraction of the separation task. From this we can conclude that the more trays there are, the better the level of separation and that overall separation efficiency will rely fundamentally upon the design of the tray.

Trays are designed to amplify vapour-liquid contact by considering the liquid distribution and vapour distribution on the tray. This is because better vapour-liquid contact means better separation at each tray and lead to a better column performance. Less trays will be needed to achieve the same level of separation. The benefits include less energy consumption and lower development costs.

Tray Tower

Sieve Tray

Sieve trays are simply metal plates with holes in them. Vapour passes straight upward through the liquid on the plate. The arrangement, number and size of the holes are design parameters. This tray are generally considered as low cost mass transfer solutions and used in applications where a high turndown is not necessary.

Advantages :

Liquid tight construction
Suitable for low liquid rate service
Fouling resistance
Wide operating range

Disadvantages :

Poor vapor/liquid contact efficiency
Moderate/high pressure drop
Most expensive type
More tray weights

Valve Tray

In valve trays, perforations are covered by liftable caps. The caps lifts due to the vapour flow from underneath. Vapour flows lifts the caps, thus self creating a flow area for the passage of vapour. The lifting cap directs the vapour to flow horizontally into the liquid. This maintains a near constant pressure drop with respect to variation in vapour flow rate. Due to this characteristic valve trays sustains higher tray efficiency. They are generally used in applications involving high turndown ratio.

Advantages :

Good vapor/liquid contact efficiency&ZeroWidthSpace;
Low/moderate pressure drop&ZeroWidthSpace;
Less expensive
Easy maintenance

Disadvantages :

Narrow operating range
High vapor escaping momentum that can cause liquid entrainment
No protection for liquid weeping
Possible fouling

Bubble Cap Tray

A bubble cap tray has riser or chimney fitted over each hole, and a cap that covers the riser. The cap is mounted so that there is a space between riser and cap to allow the passage of vapour. Vapour rises through the chimney and is directed downward by the cap, finally discharging through slots in the cap, and finally bubbling through the liquid on the tray.