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We have an operating issue in our LPG sweetening process; the level between LPG and amine interface is highly unstable (big fluctuation). We've checked the functionality of the meter (flow; level; pressure; temperature..etc) which is fine, but observed an abnormal phenomenon - rich amine is "boiling", a certain amount of LPG is dissolved in the rich amine solvent, the pressure and flash gas rate from the RA flash drum is relative high.
Question: a couple days ago we treated with a high dose of antifoam additive to cure the foaming problem in another unit, and the LPG sweetening unit is using the same source of amine solvent (containing excess antifoam additive). Is it possible that excess antifoam led to enhanced LPG solubility?
13/05/2020 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
I would not expect antifoam to impact solubility of LPG in amine; however, antifoam is a surface active material. As such excessive antfoam could cause an emulsion to form and drag some LPG into the amine in the form of an emulsion. Operations often takes the approach with antifoam usage that if a little bit is good a lot is better. That approach can lead to problems as you appear to have experienced.
13/05/2020 A: Morgan Rodwell, Fluor Canada Limited, morgan.rodwell@fluor.com
LPG is not very soluble in amine. It is more likely entrainment of small droplets (an emulsion). Antifoam agents may contain emulsifiers (especially silicone antifoams). This emulsifying agent may have caused small droplets of LPG to stay suspended in the rich amine flowing down the contactor that would normally coalesce into larger droplets and rise against the motion of the amine. I witnessed this in the early 90s.

Another factor to look at is the design of the column and the distributor that introduces the LPG into the amine. If the exit velocity from the distributor is too high it will tend to atomize the LPG into smaller droplets, making it easier for them to be entrained in the rich amine. I would recommend that the LPG distributor exit velocity be kept below 1.25 ft/s (0.38 m/s) with a minimum hole size of 3/8" (10 mm). It is also recommended to have a superficial velocity for the rich amine less than 0.5 ft/min (15 cm/min) to allow for droplets to rise. You can use Stokes law calculations to determine what droplet size of LPG will rise against whatever rich amine downward velocity you have.