High Glycol Losses in TEG Dehy Unit

[RRE]

In two field natural gas dehydration units, TEG (Tri Ethylene Glycol) losses are almost 10X those accepted by the industry (0.93 gals per mmscfd VS ~0.1 gal per mmscfd of gas treated). The fabricator has come back to us and said that his design results in high glycol losses very close to these numbers from the reboiler (still column). These losses are outrageous causing us very high opex. Has anyone seen these high glycol losses from a system that is free of foaming issues and is dehydrating a very lean gas at 300 psig??

Appreciate your feedback.

 

[pronab]

RRE
In our TEG system loss of glycol is 0.12Kg/mmscfd(actual),with the design figure of 0.514Kg/mmscfd.Sytem pressure ( TEG contractor) is ~65.0 Barg. Do you have KOD outlet of cotractor. Otherwise loss will be more.

Regards. Pronab.

 

[209larry]

TEG dehydration is really a problematic process and requires close monitoring. Some already have shutdown facilities especially offshore. Pressure swing adsoption(PSA) is becoming popular as an option to TEG. Aside from moisture, PSA can remove Nitrogen and CO2 in an unmanned stations.

209larry

 

[Chemeng1122]

The first question is how sure are you that you have no foaming. Most field dehy units I have seen are relatively simple units with not much in terms of instrumentation on the towers. Assuming that you are seeing no obvious symptoms of foaming (fluctuating levels, reboiler temps, etc), the next question is how long has the plant been in service, and how long since the last turnaround where you have inspected the tower.

If it is an old plant, or you have not looked inside in a few years, it is possible that there is tray/packing damage that is messing with the hydraulics in the system. Internal damage can increase gas velocity through thr tower, causing the gas to "lift" the glycol out the top of the tower. A gamma scan is the best way to look for tray damage/foaming/channelling/ or any other phenomenon going on during plant operation. I suggest a gamma scan on both the contactor and regen.

Another possibility is a high hydrocarbon content in the inlet gas. C4/C5+ liquids (and BTEX) will be picked up by the TEG and introduced to the regen loop. If there is no flash tank especially, the TEG losses through the regen are potentially very high. The HC's will flash off in the high temp regen, resulting in a very high vapour rate out of the regen, again, lifting TEG out the top.

This is all I can provide with what I know of your system. Other questions I would have are:
- Are the losses continuous or do they occur at certain times (corresponding to ambient temps, inlet conditions, etc.)
- What are the operating conditions of the plant (T's & P's, circ rate etc)
- Filtation on the plant? Carbon? Lean or rich filtration?