3 replies to this topic

[Armani_AD]

Dear Gents,

Am working in a gas plant, and one of our process units is Gas dehydration unit, my concern is the water content in the lean glycol is HIGH, the normal value is 0.15 %wet and the value which am getting is 0.25 % wet which is above the normal value !

in our glycol regeneration package we are using stripping gas which is natural gas to strip out the water content and the flow of the stripping gas is 300 kg/hr, and i know if i increase the stripping gas it will reduce the water content, but what i need to know in general why the water content increase in the lean glycol ? and how can i solve it ?

Thanks

[Art Montemayor]

Armani:

Your basic two questions are:

• What do I need to know, in general, to understand why the water content increases in the lean glycol?
• And how can I solve it?

The answers are:

• You need to understand how a Glycol dehydration unit works. The water content in the lean glycol is directly related to the efficiency of the glycol regeneration system. Depending on your unit’s designer and fabricator (you have not told us this information, so we can’t be specific), the rich glycol is usually reboiled at a temperature of approximately 400 °F (204.5 °C) and then subjected to a gas stripping operation directly downstream of the reboiler. Again, the degree and type of gas stripping required depends on your unit’s designer and fabricator and the product gas dew point specifications. In other words, how dry do you require the product gas? Normally, the amount of residual water in the glycol is measured as either weight fraction or weight percentage. You cite a percentage figure, but you fail to tell us what it represents. You should always state what you specifically mean – weight %, volume %, mole %, etc. Otherwise, we don’t know what you mean. Heating (not boiling) of TEG at 400 °F and 1 atmosphere will provide about 98.6 wt% glycol. This “purity” of lean glycol determines the maximum equilibrium drying that you can do of the product gas. The purer – or higher wt% - lean glycol produced in the regeneration section, the dryer the product gas will be. I normally design and obtain 99.5% lean glycol to ensure a good pipeline quality product gas. The way to achieve the 99+ wt% lean glycol is to employ the stripping gas to remove additional water from the 98.6 wt% reboiler lean solution. The more dry stripping gas that you employ, the leaner the resulting glycol will be. You may not be using the stripping gas correctly and this may be causing a higher water content in the lean glycol. What does your operating instructions from your designer say? Or, in some cases, I have had leaking lean glycol coolers that actually leaked water into the regenerated glycol after it has gone through the gas stripping. You could check this out. But clearly, it seems you are not successfully regenerating the rich glycol.
  
• You can solve your problem (if your lean glycol analysis is correct) by concentrating on making sure you are following the designer / fabricator’s specific operating instructions. Obviously, your unit at one time was commissioned and accepted into operation and performed adequately. Something must have happened to it or its operation since that time and the performance has suffered. As an engineer you should make it your business to find out what has happened. To do that you must have a complete understanding and domination of the process and follow all the prerequisites for regenerating the rich glycol. I’ve given you some personal clues or ideas, but the actual solution is out there in front of you. We cannot give you specifics since you have not given us specifics. You haven’t even furnished a P&ID, so we don’t have an idea of what your specific unit looks like. All TEG units are not 100% alike.

I hope this general response is of some help.

[aanita]

Regeneration of TEG mianly depends on Temperature ( limit to 204 deg C) and using stripping gas.
If your reboiler temperature is already 204 deg C , then increase stripping gas flow.
If still water content is high , may be gas throughput is high, unless you are in the design envelope.

Best of luck and inform us your progress.

[Anilnair]

3) 0.25% of volume? 2500 ppm right? If you are keeping Reboiler temp at above 202 C, you should get lean TEG with in spec. I believe 300 kg/hr stripping gas (IS THAT DRY GAS?) is quite higher rate also. How much is TEG circulation flow and Gas flow?

How much is your reflux temp? That should be about 98 C and below that temp, water vapours will condense back to reboiler and it give you rich WATER envoirnment in Lean TEG.

What is water content in your rich TEG? How is your Contactor inlet scrubber works? You gets enough water knock out there? What is the capacity of your TEG System? What is the feed gas temp? If you put more details, people will be able to get more idea of the system as well as they can give more suggestions.