Mechanism of Foaming in Amine Absorber

[consilience1]

Dear All,

I'm just wondering the mechanism of foaming generation in Amine(MEA, DEA, or MDEA) Absorber in Amine or TGTU plant, especiallly, when we fail temperature control between H2S gas and amine stream into the Absorber. It's known that the gap of temperature between the two steam is above 7'C to prevent increaing foaming tendency.

Question is why foaing happen in that case and the mechanism.

Best Regards,
Mr.Chung

 

[unclesyd]

We eliminated foaming in two different amine scrubbing systems by putting in carbon towers. My understanding was that some polymeric products caused the problem by changing the surface tension of amine streams. Don't quote me on this one.
There has been quite a lot of work done in this area, both by the amine suppliers and the liquid/liquid carbon people.

 

[25362]

I propose a visit to:

thread798-39310
thread798-62733
thread483-91444
thread469-158471
thread124-31224
thread124-122758

Some additional comments:

The [Δ]T is maintained to preclude condensation of hydrocarbons that may induce foaming. On the other hand high contactor temperatures may reduce the effectiveness of the amines to absorb acid gases. Compensating by using a higher concentration of amine reduces the capacity of the solution to absorb the heat of reaction and raises even more the contactor temperature. Dilution with water would reduce the temperature, the overall corrosivity and the foaming tendency. The last effect due to a decrease in organic content, resulting from the lower affinity to hydrocarbons.

Of course, increased amine content decreases circulation costs, but these benefits should be weighed against enhanced corrosion, foaming and amine losses.

In line with unclesyd's posting, solid fine particles are thought to stabilize foams, probably by increasing their elasticity. Iron sulfide from corrosion of upstream equipment and sulfur dust in natgas have been reported.

Foaming of the amine solutions may be caused by soap-like compounds formed by certain organic acids in the feed combining with the amines. It may be reduced by water washing the feed, or by the addition of anti-foam agents such as oleyl alcohol to the solution.

Besides, the filtering or centrifuging of a solution slip stream (10-30% of the circulating amine solution) helps.
Carbon adsorption and filtration of particulates are supposed to eliminate not only contaminants that may react with the amines, but also foam-stabilizing solids.

 

[0707]

Foaming and amine unit upsets may be caused by contamination of the amine from

Fine suspended particles (FeS) - corrosion products
Hydrocarbons
Heat stable salts
Valve greases and lube oils

Foaming is detected by

rise in pressure drop across absorbers and regenerator
loss of level in absorber or reflux drum
Reduced flow of acid gas to SRU

Foaming results in

poor treating = off spec product
reduced capacity
amine losses
sulfur plant upsets

 

[EmmanuelTop]

http://www.gastreating.com/pdf/Hc Processing April 1995.pdf

http://www.gastreating.com/pdf/Hc Processing May-June 1994.pdf