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# Retention Time for Two-Phase Separator

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## Retention Time for Two-Phase Separator

(OP)
We will come across retention time when we are designing the two-phase separator.

1. Could anyone here please further explain the definition of retention time?
2. How do we get the value of retention time ?
3. Can we use aspen hysys to size the two-phase separator?

### RE: Retention Time for Two-Phase Separator

you can find several threads at eng-tips discussing this topic, also consider GPSA or similar references.
To calculate (liquid) retention time for a two-phase separator divide the liquid volume inside the vessel by the liquid flow rate,
these values are normally in the range 1-3 minutes depending from application.
Yes, many simulators as Aspen include utilities to size separators,
GPSA and similar references provides detailed information about the procedures,
there are also Excel pages (see for example Prode Properties applications) and online resources, see for example

https://checalc.com/calc/vertsep.html

### RE: Retention Time for Two-Phase Separator

For a two phase separator the aim is to separate the phases. The longer the time available for the liquid to drop out of the gas the better. This is retention time in the separator.

How long?

Variable depending on how well you want to separate the phases, velocity of gas, size of droplets etc.

Then add in things like the inlet vanes/ shoepentoter, de mister pads and you have many things to determine an effective time vs cost of a larger vessel.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Retention Time for Two-Phase Separator

(OP)
Hi PaoloPemi,

I am now referring to the link below to do manual calculation of the vessel sizing, however, the final result is quite far from what I calculated..
https://petrowiki.org/Separator_sizing

However, sizing with manual calculation : Diameter - 2.1 m / Length - 6.1 m

Hi LittleInch,

Good to see you again and Thanks for the explanation!

Can i define retention time as the time required to reach equilibrium condition between liquid phase and gas phase, thus, separate the liquid and gas accordingly from mixture fluid?

### RE: Retention Time for Two-Phase Separator

Sam Low,
I would suggest to follow the procedure proposed in Separation Equipment of GPSA Engineering Data Book,
as said I have a Excel page based on GPSA procedure as well as different procedures and I do not see large differences comparing the different methods...
take care to utilize the correct units and parameters

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