Gas Dehydration at low gas flow 1

[Monagas]

Hi my friends, I would like to know if somebody of you has experience on operate a TEG contactor tower with low gas flow (below the operating gas volume)and if it has impact on glycol losses.

Any help will be appreciated
My best regards

 

[maddocks]

The successful operation of the TEG system will be very dependant on tower internals. If you are using bubble caps, the tower will operate on almost an infinite turndown. However, if you are using sieve or valve trays or structured packing, you may start to find channelling and lack of performance. Suggest you discuss with your tower internals vendor. You really won't get any worse carryover at turndown rates due to low gas velocity.

 

[Montemayor]

Monagas:

I've operated TEG systems with gas turn-downs and all I've seen is reboiler/heat balance inefficiencies. In other words, all I experienced is that I was circulating excessive lean TEG with minor water pickup in the absorber. Now, take into consideration that I'm talking about a gas capacity turn-down at the same pressure. A pressure turn-down as well is another story.

In fact, all TEG units are started up with 100% circulation of TEG and 0.0% gas flow; the gas flow is slowly eased into the contactor as the startup progresses. So you are operating with gas turn-downs at startup - and you should not have any TEG losses over the normal ones you expect.

Lower gas flow at the same pressure means you've reduced the water pick-up in the contactor. This in turn, means you've got a lower reboiler duty. However, since you probably are not turning-down your TEG circulation rate, then your reboiler duty essentially continues the same with the excess TEG circulation. Your dewpoint depression may go down, but I doubt it. Your water content in your product gas will probably stay the same.

You should have less TEG consumption - at least as far as the entrainment and carry-over effects are concerned. If you handle less gas throughput, you should have less TEG losses per MM Scfd.

I do not believe you will experience any "channeling" in the contactor. With the same amount of TEG circulated, the gas will have more contact time and better equilibrium conditions. It's the liquid that "channels" - not the gas. The liquid channels by seeking the internal wall surfaces and avoiding the core of the packed bed. Since you are maintaining the liquid flow the same, the channeling will not get better or worse - if it existed before the gas flow was turned down.

I've had the same effects take place in Acid Gas Absorbers as well. Amine unit losses go down when the gas flowrates go down.

 

[Monagas]

Thanks for your help Mr. Maddocks, we are using bubble caps trays.
Mr. Montemayor, your posts are always helpful for us and loaded with a god knowledge & wisdom . You should write a book for the next generation of engineers.

My best regards