[Laga]

Dear Eugene,

We changed our acid gas removal solvent from DIPA to MDEA. It worked fine using DIPA but it foaming badly after we changed to MDEA. The original plant design was using DIPA and has total recycle of basically everything. The feedgas contains significant heavies from C5+ and higher with small amounts of aromatics. We installed a liquid/gas coalescer upstream of the absorber but it is not collecting any liquid. In your opinion, do we need to condition the feedgas to knock off more heavies and/or redesign the back end of the system by not recovering the returning streams from the absorber and regenerator overheads any longer as we did using the DIPA.

Rgds
Laga

[eugenedakin]

Hello Laga,

It appears that you have an interesting problem. Can you confirm that MDEA is increasing the foaming tendencies? (field experience example, or prior work with the sweetening system?).

There are many aspects which can cause foaming, and C5+ contamination is definitely one of them. Another strong consideration is salt concentration (most hydrocarbon is accompanied by reservoir water containing salt) which increases foaming in the system. Another aspect is the over-addition of antifoam/defoamer. Usually ~500 parts per million is the rule-of-thumb for the maximum dose of antifoam. Higher concentrations will actually promote foaming, rather than inhibit foaming.

Generally speaking, it is always best to prevent contaminants from entering the system in the first place (knock off more heavies in the feedgas). However, this is not always possible, nor economical. If the streams are not recovered, supplementing amines can be expensive if volumes get too high. You could perform a test to determine the amine losses that occur, and determine the economics of replenishing the amine.

If there is sufficient contamination (from salts, hydrocarbons, etc), your system will continue to remain dirty. Sometimes, removing the old amine, cleaning the system, and charging the system with fresh amine is periodically needed. Again, economics (downtime, turnaround time) needs to be considered.

I hope this gave you a few ideas, and feel free to ask more great questions  .

Happy New Year!

Eugene