Amine Treatment (aMDEA) Foaming - LNG Plant

[gasnaturel]

Hi everyone,

We have a faoming problem in our Absorber, that we lose control of all Acid Gas Removal Unit (AGRU), and we inject anti foaming solution many times a day, the design cencentration of aMDEA is 40%, actually we work only with 25% (concentration) of amine, last days we receive a new inventory, I would like to know if we should remove the existing inventory or just made make-up of aMDEA.

Than you.

 

[georgeverghese]

There can be many reasons for this foaming:

a) Poor vapor liquid separation in the feed gas to the absorber, resulting in gas condensate / dissolved salt accumulation in the MDEA.

b) Some contaminant in the feedgas which is causing the foaming ; excessive corrosion inhibitor or a new corrosion inhibitor is being used upstream.

c) Thermal degradation of the MDEA due to hot spots in the regen unit reboiler tube bundle.

d) Salt accumulation in the MDEA solution : do you have a reclaimer / ion exchange unit in the regen unit to keep the solution low in TDS?

e) Excessive vapor velocity for feedgas through the trays in the absorber; typically vapor velocity should be below 60-70% of flood for CO2 removal absorbers.

 

[georgeverghese]

Adding to (e), if you have degradation of ceramic random packing in the absorber, the resulting increased dp can also be a cause for foaming.

 

[gasnaturel]

Thank you
georgeverghese:

We use the Skim oil line for the first time, and the problem seems solved, we send all drain liquids to blowdown, now we work on (aMDEA) loop cleaning using a new cartidge filtres, to remove any solid suspensions.

We reduce also the rate of lean Amine (2%)

We observe all the process ...

Thank you

 

[georgeverghese]

Presume this skim line is at the bottom scrubber / rich amine collection compartment of the absorber. This line is not easy to operate and safety devices will be required to reduce gas blowby risk.

Another reason for liquid hydrocarbons appearing in the absorber could be that the feed gas is rich in CO2 and partway up the absorber, the heavy hydrocarbon partial pressure is increased to the extent that it begins to condense. If this is the case, then some kind of feedgas dewpoint conditioning (or preheating) upstream of the absorber may be required to reduce heavy hydrocarbon concentration in the feedgas to the absorber or raise the gas temp profile going up the absorber.

Also check that the feed lean solvent temp to the absorber is kept high enough to reduce gas condensation.

 

[georgeverghese]

Skimming HC from the flash vessel is safer, and will be much better if automated and 3phase separation internals are included.
Agreed, solids filtration in regen circuit also helps.
If you have injected a lot of antifoam, the entire inventory may need to be replaced eventually - these may cause corrosion problems in the absorber later.