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Teg Dehydration Operation Queries


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#1 Papps

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Posted 25 July 2015 - 06:42 PM

Within few months of Commissioning, Lean TEG color turned into yellow. 

 

1.) Checked for Iron counts and found normal.

 

2.) Initially suspected for hydrocarbon contamination and replaced Carbon filter and reduced pressure in Flash Drum to induce more flashing. 

 

3.) We could not meet the delta T of 5-7 C in Contactor between the Glycol and Wet Gas due to design constraints.

 

4.) We are maintaining still column temperature around 120 - 130 C and Reboiler temperature maintaining at 195 C.

 

5.) Reboiler performance seems to be good as concentration is always above 99%.

 

6.) Lean TEG pH is maintaining around 7.5 to 7.8

 

What could be the reason for this color change ?

 

Also I would like to know about consequences which could arise for not maintaining delta T of 5-7 C between Glycol and Wet Gas in Contactor. 

 

 



#2 Pronab

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Posted 26 July 2015 - 01:50 AM

Lean TEG color in yellow!!  I have seen grey/blackish (if not black) when the TEG regenaration unit carbon filter becomes exhaust.  Once we replace the carbon filter, it becomes normal gradually.  There might be  a guard filter after the Carbon filter, please replace or clean that one also.

 

Normally, the temperature controller should take care of 5-7 oC difference.  Reboiler temperature of 195 oC is low; try to increase it up to 204 oC ( It is recommended) also the 99% lean TEG concentration is low.  Are you able to get your desired dew point with 99% concentration?  What you mention in the still column temperature is not that much important as an operational point of view.  The Lean TEG pH is perfect.  I would like to see a sketch (Preferably a PFD) of your TEG regeneration system and the Glycol contactor.



#3 ahmed abd elmonem

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Posted 27 July 2015 - 11:52 AM

I guess there is a foaming to some extent inside TEG contactor continuing to flash separator.could you please check a sample from flash separator for any foaming occurrence.

thanks in advance



#4 RockDock

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Posted 28 July 2015 - 06:15 AM

What is your delta T in the contactor? Is it lower than 5C or higher?

 

Do you have an analysis of the BTEX content in the wet gas? TEG will pick up BTEX and other heavy hydrocarbons (to a lesser extent). Do you have stripping gas? Does that have BTEX? I can see the solution turning yellow due to a build up of BTEX. You would also likely still meet your dry gas specification because BTEX will pull water out of the wet gas, too. Carbon filtration will not remove BTEX very well.



#5 Papps

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Posted 28 July 2015 - 09:29 AM

Thanks for your response.

1.) We are meeting water dew point spec with 194 C and that too it is well within the limits. Temp is consiously limited to 195 C as TEG dehydration temp is 210 C. We are getting Conc in between 99.1 to 99.4 %. No issues with that.

2.) There is no temp controller provided to control Glycol temperature. Sometimes delta T goes down to 1C also but mostly it maintains around 2.5 to 3.5. What will be the effects of maintaining delta T in lower side? Also please share how temp of Glycol is normally controlled or delta T is controlled in other TEG dehydration units.

3.) There is foaming happening inside contactor. Differential pressure across contactor is 0.01 kg/cm2g and no level fluctuations observed in Glycol level inside contactor.

4.) There is no guard filter provided downstream of carbon filter.

5.) Regarding BTEX, normally there is only minor traces in Wet gas.Is that the reason for TEG turning into yellow.

Please share your views.

Attached single line diagram for your reference.

Attached Files


Edited by Papps, 31 July 2015 - 05:31 AM.


#6 RockDock

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Posted 28 July 2015 - 10:17 AM

The lower delta T you have, the more likely you are to pick up hydrocarbons.

 

I see you also have stripping gas. That will also lead to more hydrocarbons in the glycol.

 

BTEX would likely show up as yellow.

 

What is your stripping gas ratio? Perhaps you could reduce this ratio and increase your reboiler T to 204 C. I would only introduce stripping gas if I do not meet my dry gas specification at 204 C.

 

Is your regeneration column operating at atmospheric pressure?



#7 Papps

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Posted 29 July 2015 - 05:25 AM

Stripping gas: 6.6 Am3/hr
Lean glycol circulation rate is: 1.51 m3/hr
Still column is connected to lp flare and reboiler operating pressure is 0.1 kg/cmg.
How in other plants delta T is maintained?? I want to know the control system available . Shall we put a bypass line with a TCV around lean glycol side of lean/ rich plate exchanger??
Also why still column temp is not important from operation point of view. I think if we maintain higher still column temp.glycol loss will be there. Lower still column temp means glycol purity will affect. Please correct me if i am wrong.

#8 Pronab

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Posted 30 July 2015 - 01:26 PM

There was a previous discussion about TEG regenaration troubleshooting. Follow this link:

 

http://www.cheresour...hydration-unit/



#9 Papps

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Posted 31 July 2015 - 05:32 AM

Thanks for sharing it. It was really useful.

#10 RockDock

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Posted 28 August 2015 - 09:32 AM

I assume you have a Dry Gas/Lean Glycol Exchanger. You may operate with a bypass around that exchanger, controlled by the inlet gas temperature to maintain a 5-10 C delta T.

 

I don't think you will see significant TEG losses at a 5-10 C delta T. Your ProMax model will help you understand any TEG losses you may have.

 

From the regeneration point of view, TEG losses will be very low due to the condenser coils condensing almost all the TEG in the vapor.






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