5 replies to this topic

[aanita]

I want to know maximum allowable pressure drop of a fractionation tower per tray ( valve tray or bubble cap tray), so that I can get total pressure drop across the tower.

Thanks in advance.

[Dipankarc84]

Aanita,
Are you trying to provide an allowable pressure drop for a new unit? Or are you trying to estimate the pressure drop of an existing unit for revamp/ troubleshooting purposes?

In general, a pressure drop of 0.01 kg/cm2 per tray can be taken as an allowable pressure drop. Most of the times, the trays are designed with tray pressure drops close to 0.007 kg/cm2.
In case of an existing unit, if you are doing a revamp study, it is recommended to carry out a tray hydraulic study and estimate the existing pressure drops "at stable operating conditions"

[TS1979]

Maximum allowable pressure drop across each tray , delta P(psi) = 0.0143 * tray spacing * SG.
Tray spacing, inches
SG=specific gravity of liquid at operating temperature.

Above this value, you will have a flooding tower.

[aanita]

Thanks a lot. It is an existing column and to check the total differential pressure across the tower.

To TS1979: What is the unit of Tray spacing in the equastion you mentioned, Is it mm?

Regards.

[TS1979]

The unit for tray spacing is inch. With the above number mentioned you will experience significant liquid entrainment. For best tower efficiency,
delta P = 0.0064* Tray spacing * SG ~ 0.009* tray spacing* SG

[Dipankarc84]

aanita
If the intention is to check the total differential pressure across the "existing" column, it is advisable to do a tray hydraulic study with the existing tray geometry and the operating Vapor Liquid Traffic across the trays. Allowable pressure drop across a column is provided as a freedom to the column internals designer who has a scope to stretch his design upto the allowable limits. However, in case of an existing column, you should be concerned with the "actual" pressure drop and not the "allowable" pressure drop.
If I am not wrong, the correlation provided by TS1979 is to determine the "allowable" PD for a design case. The actual PD is a function of Vapor and Liquid flows and the tray geometries and hence they should be taken into account.

Dipankar