Choice of Trays or Packed Tower

 The choice between a tray and backed tower for a particular application can only be made with complete assurance by costing each design.  However, this will not always be worthwhile, or necessary, and the choice can usually be made, on the basis of experience by considering main advantages and disadvantages of each type; which are listed below:

1. Plate towers can be designed to handle a wider range of liquid and gas flow-rates than packed towers.
2. Packed towers are not suitable for very low liquid rates.
3. The efficiency of a tray can be predicted with more certainty than the equivalent term for packing (HETP or HTU).
4. Plate towers can be designed with more assurance than packed towers. There is always some doubt that good liquid distribution can be maintained throughout a packed tower under all operating conditions, particularly in large towers. 
5. It is easier to make provision for the withdrawal of side-streams from tray towers; coils can be installed on the trays. 
6. It is easier to make provision for the withdrawal of side streams from tray towers.
7. If the liquid causes fouling, or contains solids, it is easier to make provision for cleaning in a tray tower; man ways can be installed on the trays. With small diameter towers it may be cheaper to use packing and replace the packing when it becomes fouled.
8. For corrosive liquids a packed tower will usually be cheaper than the equivalent plate tower.
9. The liquid hold-up is appreciably lower in a packed tower than a plate tower. This can be important when the inventory of toxic or flammable liquids needs to be kept as small as possible for safety reasons.
10. Packed towers are more suitable for handling foaming systems.
11. The pressure drop per equilibrium stage (HETP) can be lower for packing than plates; and packing should be considered for vacuum towers.
12. Packing should always be considered for small diameter towers, say less than 0.6m, where trays would be difficult to install, and expensive.