8 replies to this topic

[Abhimanyu Dagla]

well,
I am here working on a offshore oil platform.
Here we are processing gas for moisture removal.
The compressed natural gas at 89 kg/cm2 is dehydrated in glycol
contactors. The Glycol is regenerated in the regeneration system.
We are facing heavy glycol loss up to 100 lt/day. The dew point is in
limits.
To me it seems carryover in reboiler.
We maintain 200 degree celcius in reboiler and stripping gas rate at 30 Nm3/hr.
Gas compressed is 2 MMSCMD and glycol flow rate is 3 m3/hr.pump leakage is
negligiable.
Can anybody suggest some remedy ?
regards.

[Zauberberg]

If I calculated correctly, you are loosing approx. 3.45lb/scf of TEG. You should be somewhere around 0.5lb/scf or at least below 0.8-1.0 lb/scf.
It's hard to believe any glycol carryover can happen in TEG regenerator reboiler: what is the basis for this conclusion? High regenerator pressure drop, flooding of structured packing, liquid carryover in the overhead stream? How did you establish your diagnose?

The biggest percentage of glycol losses occurs in the absorber - due to high gas loads, improper/inefficient inlet scrubber design (or due to absence of scrubber), or inadequate absorber design.

[Abhimanyu Dagla]

thanks zauberberg, for responding.

Well, The glycol loss could occur at contactor or at TEG regenertation skid.

If, the loss is taking place in contactor, the same should be trapped in the overhead scrubber downstream. But there is no level build up in scrubber.

After that there leaves only regeneration skid. The reboiler is where losses can take place, other then the flash drum. The glycol can escape from the reboiler if there is no approriate heating, and if the packing in the still column is fouled ( no good contact of stripping gas and outgoing vapor) or more then req'd stripping gas is fed to the reboiler.

I've analysed the liquid from the reboiler vent and found 3.5% of high boiling fraction.

That can't be anything else but glycol.

[Zauberberg]

Abhimanyu,

Few more things that are worth checking:

1. Confirm if regenerator column is flooding. This can be due to excessive heat input or too high stripping gas rate - check this one by one (don't rely solely on instrument measurements), and if situation is not improving then flooding is apparently not happening in the column.

2. The other thing which may lead to glycol carryover with the overhead stream is leakage in reflux condenser. If this is a coil-type unit, these are very prone to leakage and rich TEG is being blown off together with water vapor. Try cutting reflux rate or stoping it completely for one period of time. This can happen with vertical shell & tube condensers as well, but they are usually much more reliable than reflux coils and less prone to leakage.

Let us know the results.
Best regards,

[Megalith]

Abhimanyu,

Have you found a solution to your problem? Have you tried to conduct Root Cause Failure Analysis (RCFA) to figure out the problem?

I'm having the same problem with the Dehydration unit on our platform and we're loosing the same amount of TEG (100lt/day) as you do. I would be very gratefull if you could share your experince.

Regards.

[Zauberberg]

Megalith,

Have you checked regeneration unit operation? Getting TEG into the overhead receiver vessel probably means your tower is flooded, or there is a tube/gasket leakage in the reflux condenser.

[sri]

Megalith,

Have you checked regeneration unit operation? Getting TEG into the overhead receiver vessel probably means your tower is flooded, or there is a tube/gasket leakage in the reflux condenser.

Pl check two things first:
1. Temperature of inlet gas to contactor/absorber. High temperature gas in contact with glycol in trays would cool down and condensates may form.
2. Check packings in still/stripper sections of re-generation unit if they are intact. This may be one of the reasons for such high glycol loss. Use minimum strippings gas till packing integrity is confirmed.

[Megalith]

1. Wet gas temperature is around 45 - 50 deg C, Glycol temperature in is 100 deg C.

2. The system is fairly new and has been recently commissioned, packing problem shouldn't be an issue.

[Qalander (Chem)]

Dear Megalith Hello/Good evening,

Please confirm if the problem persisted ever since the initial start-up or developed afterwards/As if the mechanical distribution system inside for the gas stream could have orientation problem if problem was since the beginning.

As regards Abhimanyu Dagla's initial problem higher gas flow rate and temperature induce heavily the entrainment/loss possibilities; if overhead condenser have been checked and ruled out for leakage.
Check against specific design values/perform test runs after thoroughly calibrating all instruments.
Hope this to help.
Best Regards
Qalander