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[jprocess]

Dear All,
In typical configuration of acid gas removal units there is a flash tank downstream of contactor.
I heard from an experienced engineer that we should consider this separator only when the rich solvent stream leaving contactor contains methane and ethane because entering these 2 components in stripper will cause foaming.He also claims that the separator dimensions and pressure should be set in such a way that not to separate h2s and co2.
I checked chapter 21 of GPSA that states:
"Rich solution leaving the contactor may pass through a flash
tank. Gases entrained in the rich solution will be separated.
In addition, the amount of absorbed gas will be decreased because
of the lower operating pressure of the flash tank. Using
a flash tank will:
· Reduce erosion in rich/lean exchangers.
· Minimize the hydrocarbon content in the acid gas.
· Reduce the vapor load on the stripper.
· Possibly allow the off-gas from the flash tank to be used
as fuel (may require sweetening).
When heavy hydrocarbons are present in the natural gas,
the flash tank can also be used to skim off the heavy hydrocarbons
that were absorbed by the solution. Residence times
for flash tanks in amine service vary from 5-30 minutes depending
on separation requirements. Inlet gas streams containing
only methane and ethane require shorter residence
times. Rich gas streams require longer time for the dissociation
of gas from solution and/or the separation of liquid phases."
As you see there is no comment about foaming in GPSA.
Your valuable comments are appreciated.
Cheers.

[joerd]

I concur with GPSA. There are a lot of reasons for foaming, for example dirty amine, solids, degradation etc., but as far as I know, methane and ethane don't play a part in that. See also http://www.google.co...ng site:bre.com
The flash tank is used for the reasons stated in GPSA, you can recover methane as fuel gas rather than sending it to your sulfur unit.