7 replies to this topic

[andiez]

Im having this problem here with my TEG regeneration which i hope to find some solutions.

I am working in a process design consultant company and currently I am assisting in a project, which involves in designing a new glycol regeneration package together with a new contactor. This project requires me to simulate the whole regeneration packages together with the contactor using the HYSYS Simulation. The main objectives are to obtain a dry gas product of at least –10°C with glycol purity of at least 98.9%.

One of the problems faced is in the simulation of regenerator. Based on DEP, regenerator should be operating at a lower operating pressure (almost close to atmospheric pressure). With this low pressure, it is possible to obtain a high TEG purity of over 98.9%. However, based on some other sources, it was found that normal operating pressure is around 105kPag. Most probably this value is wrong (maybe its 105kPaa instead of 105kPag). However, just out of curiosity, I tried simulated the regenerator using 105 kPag operating pressure and found out that TEG purity obtained is very low (less than 98%). Also, at this high operating pressure, it seems that lots of TEG vapor is lost to the vent from the still column, which doesn’t seems feasible. So one of my main question is:- Is 105kPag the normal operating pressure? Or is it too high?

Secondly, the new contactor to be design is going to be a big one, which might service up to 30 MMSCMD of wet gas. i am trying to simulate this packed column contactor (Sulzer Mellapak 250 Y) using HYSYS. Is there a way to simulate this in using HYSYS steady state simulation? Based on the height of the packing, is there a way to calculate the number of trays and efficiency to be used in the simulation? The reason for simulating this contactor is to ensure that the height of packing selected will meet the requirement of –10°C dew point dry gas.

Thanks

[Art Montemayor]

Andiez:

First, please answer my queries:

1. You say “based on some other sources, it was found that normal operating pressure is around 105kPag. Most probably this value is wrong (maybe its 105 kPaa instead of 105 kPag)”. Please tell us what the real design pressure is going to be. Also, who are these “other sources”? Are they recognized, credible sources or just some people talking out loud in the hall way?
2. You say “at this high operating pressure, it seems that lots of TEG vapor is lost to the vent from the still column, which doesn’t seems feasible”. How do you know that there is a lot of TEG lost to the vent? Does HySys tell you in its printout or are you listening to other sources? How much, specifically are you losing in lb/hr of TEG?
3. You say “the new contactor to be design is going to be a big one, which might service up to 30 MMSCMD of wet gas”. Actually, this is a very small capacity of wet gas. Here, I’m assuming you are talking of natural gas as the feed gas since you fail to tell us the fluid, pressures, temperatures, and flow rates. Am I correct?

To answer your questions:

“Is 105 kPag the normal operating pressure? Or is it too high?”
No. 105 kPag is much too high a pressure to operate the TEG reboiler at. Why do you want to (or need to) operate at this high a pressure?

Is there a way to simulate this in using HYSYS steady state simulation?
Yes, there is. It’s all explained in the HySys instructions.

Based on the height of the packing, is there a way to calculate the number of trays and efficiency to be used in the simulation?
You got your simulation plan all backwards. First you calculate the number of theoretical stages required for the separation. Then, knowing the packing height equivalent to a theoretical stage you calculate the actual packing height required.

As I said, your natural gas capacity is a small one. I hope you have some experience with designing a TEG unit - both absorber and regen system. If not, you would be wise to leave it to a more experienced and tested individual. There is some design "know-how" involved in designing a successful unit. You seem concerned about the contacter's packed height and while this is important, there should be some criteria put on the temperature of the entering Lean TEG into the absorber in order to avoid operating problems. The proper design of a Flash vessel, carbon filters, sock filters, and the stripping gas section are important points as well. All these things are not automatically taken into consideration nor treated by HySys - or any other simulator for that matter of fact.

I hope this helps you out in resolving your problem.

[andiez]

Based on the height of the packing, is there a way to calculate the number of trays and efficiency to be used in the simulation?
You got your simulation plan all backwards. First you calculate the number of theoretical stages required for the separation. Then, knowing the packing height equivalent to a theoretical stage you calculate the actual packing height required.

thanks for the reply. however i hav got another questions. lets say the number of theoritical stages i calculated is around 5.5 but to confirm that 5.5 is the correct stages i want to check it with HYSYS. Is that possible? In the Contactor model should i round it up and put 6 number of stages with 100% or is there another way to do it? 5 number of stages with 100% efficiency and 6 number of stages with 100% efficiency gives a very big differnce in the final water dew point. HYSYS tutorial only gives example for tray column. is the same apply for packed?

[Zauberberg]

Yes, the same applies for packed towers. For a given packing type there is HETP (height equivalent to theoretical plate) data available in Hysys - which should be confirmed from the vendor, for the specific service. You always want to play it safe, so there is no reason not to take 6 theoretical stages and have sufficiently high design margin.

Don't rely solely on simulation software outputs.

[smalawi]

HI,

such units relay mostly on experiance rather than simulaiton work. a good unit configuration is set long time ago and every new unit is more or less the same confugration.

as for the pressure in the regenrator, normally the desing is at the lowest prossible pressure consdering the back pressure of the overhead gas destination and the control valve pressure drop. so the actual number vary and you have to calculate yours.

the Sulzer packing hight are best simulated with thier software its free. hysys is not the best in tray hudrulics,

the number of trays on the other hand is some what alarming. Hysys amine package should be used and it calcualtes tray eff for the sour gaese, as a result you are dealing with hysys with atual trays. i'm not sure if you should use that package here, but eff are typically low ~30 - 45 %or bit lower.

hysys is good but try tsweet site, http://www.bre.com/ it also has good info

at last i agree with the above replys, unit design is not just simulaiton, its more of expeiance and you can find alot of it on the net.


cheers,

sm

[Art Montemayor]

Smalawi:

I believe andiez is trying to dry natural gas, not treat it for acid gas removal with an amine system. The Bryan Research group is one of the favorite sources for reliable amine treatment and TEG dehydration software. Their product is called ProMax and the TEG design package can be found at:

http://www.bre.com/P...79/Default.aspx

Their Glycol dehydration design package is pretty extensive and I consider it superior to HySys. A PFD diagram of a typical, state-of-the-art TEG unit is attached for reference work and for anyone to use when posting (or referring to) a TEG dehydration operation or query.

I hope this helps out in explaining what the BRE explanation refers to.

 Natural_Gas_TEG_Dehyration.xls   51.5KB   518 downloads

[smalawi]

thanks art,

i was confused a bit. my work is mainly refinery realted and i keep mixing up dehydration and acid gas treatment.

as you indicated bre.com still has good information on dehydration and although i personally did not use promax or other products from bre. i know that hysys is lacking in this regard as its more general in nature and did not develop specific pakcages like bre as the later is more specilized in this kind of work.

thanks again,

sm

[Andrei]

the number of trays on the other hand is some what alarming. Hysys amine package should be used and it calcualtes tray eff for the sour gaese, as a result you are dealing with hysys with atual trays. i'm not sure if you should use that package here, but eff are typically low ~30 - 45 %or bit lower.

hysys is good but try tsweet site, <a href="http://www.bre.com/" target="_blank"><a href="http://www.bre.com/" target="_blank"><a href="http://www.bre.com/" target="_blank"><a href="http://www.bre.com/" target="_blank">http://www.bre.com/</a></a></a></a> it also has good info

Smalawi,

I am sure you wanted to say Glycol Package should be used. If you really insist to use Amine Package for a Glycol dehydration application you will get just a warning saying that TEGlycol component is not supported by the selected method and deleted from your components list, and an amine component is needed. But as I know you don't need amine for dehydration.