Lean TEG pH increasing gradually to 9.8 1

[mmansar72]

In our gas dehydration unit last 4 months we faces problem with Lean glycol pH increasing gradully to 9.8 which creates foaming and loss of glycol. We dont have amine gas sweetening unit in our plant to suspect the pH increase due to amine. At this point I seek your kind help and advise....
What might be the possible cause of the increase in pH?
How to identify the root cause and solve the problem?
What is the possible way to bring down the pH time being?
Thank you.....

 

[georgeverghese]

If this is a new development that started 4months ago, then it can only be due to the plant production engineers / corrosion engineers who have either changed the chemical dosing program upstream or increased the chemical dosage of one or more chemicals around that time to counteract some problem. These chemicals may be related directly to production fluids quality or corrosion management.

A well sized gas scrubber / filter coalescer upstream of the the glycol contactor always helps to minimise liquids entrainment / dissolution of these undesirable chemicals (and heavy hydrocarbons) into lean glycol.

 

[EmmanuelTop]

1) You also need to verify pH of the TEG solvent delivered to your plant. I remember cases when contaminated glycol with pH in excess of 8.0 (sometimes above 9.0) had reached end users. This is definitely worth checking.

2) Secondly, please follow George's advice and have somebody look in the chemical dosing system. If you are using a chemical for pH adjustment and corrosion inhibition, reduce injection rate and observe the effects on glycol pH.

3) Take a sample of liquid/aqueous phase from the inlet gas knockout drum upstream of the glycol contactor and check for pH. There is no amine unit upstream, but you may be receiving some other high pH compounds/chemicals with the inlet gas stream.

4) Check if there was any change in composition of the inlet gas and the stripping gas (if your plant uses it), particularly with regards to Base components (NH3 etc.)

5) Ultimately try to submit a sample of TEG to a lab and see what are the components causing increased pH. This should give you some ideas of their origin.

Dejan IVANOVIC
Process Engineer, MSChE

 

[mmansar72]

Thank you very much George and Emmanuel for your valuable suggestions...

Plant is not new, already 9 years we never faced this problem. Once we face TEG salt contamination and we replaced the TEG and problem solved. Let me check for any changes in chemical injections.

Fresh TEG we checked pH and it is 7.2 only. No problem with fresh TEG. From chromatography gas analysis shown no any changes in the inlet gas compositions. We will check the inlet scrubber sample and TEG composition in the lab and come back to you.

Once again thank you very much for the advise.

 

[EmmanuelTop]

Alkaline components must come from somewhere. Either they come with the inlet gas and they get carried over from the inlet separator, or they come with the glycol (you have confirmed this is not the case), or they come with overdosing of the injection chemicals. If you take a detailed look at the PFD/P&ID of the unit, you can see if there are any other external streams flowing to the unit, and verify their composition/quality.

You may also try to completely switch off the chemical injection for pH control. It doesn't seem logical to maintain injection when pH is close to 10. Depending on the materials of construction, accelerated corrosion rates are possible so identifying and eliminating the causes of high alkalinity should be a priority task.


Dejan IVANOVIC
Process Engineer, MSChE

 

[MortenA]

CoUld it be mercaptans?