I am looking at the hydrate study f 1

[ixchawla]

I am looking at the hydrate study for hydrocarbon gas with little hc liquid and water. I would like to know the following:
1. Is hysis good at predicting hydrates? Suggest other softwares giving better results than hysys.
2. Sometimes hysis predicts 'icing takes place first' and says no hydrate. Is icing equally bad to choke the system, say choke valve?
3. Any source of information on type of hydrates and their behavior.
Your response is highly appreciated.
Thanks in advance

 

[MortenA]

I think that hysys only do hydrate calculations "on the side" - so that the pipe calculation actually dont check for hydrate formation¨

Best regards

Morten

 

[joerd]

1. If the gas composition you have is adequate, HYSYS should give you a pretty good answer.
2. You don't want ice in your system either (although it is probably easier to melt)
3. There is a reasonably good chapter on hydrates in the GPSA engineering databook, and in the JM Campbell books (if you can get your hands on a copy)

Cheers,
Joerd

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[chriswolff]

Hysis is reasonable at predicting when Hydrates will form, but some interpretation is still required.

It will predict the T/P at which hydrates will form irrespective of whether water is present or not, hence the need for interpretation.
You can also model the addition of methanol or other supressants to shift the hydrate formation curve which will assist in design.

 

[ixchawla]

Thanks everyone for the responses. I am briefly attaching the response from Hysis:
"Because hydrate formation is such a complex phenomenon, we recommend that engineering judgment always be used in interpreting simulation results, and that if experimental data is available it also be used to evaluate simulation results."

Regards,
Inder

 

[dhamo]

PRO-II also has a module for hydrate prediction. You need the gas composition for this. If you have more than one composition (Rich and lean gas) you have to do the calculation for all the cases and take the worst case for your design.

It is advisable to take a margin of 2 to 3 degreeC with the PRO-II calculated values.

 

[Hookem]

Hysis, Hysim, Pro-II, etc. are like trying to use a sledge hammer to kill a fly. Wake up Process Engineers!!!! Entire Gas Plants, Refineries, Petrochemical have been built without computers - at least through the 1970'. Anyway, look at NGPSA Manuals, or any good natural gas process engineering handbook for hydrate predicition.

 

[reiszal]

Hi ixchawla!
This subject really interests me. In fact I am doing a process simulation for one of our new gas platform design job at this very moment of time. I just wanna share the idea and knowledge that I had gathered. Feel free for you guys to criticise and comment.


Yes, HYSYS so far so good. The Hydrate Formation Utility simulate to you the incipient of the solid formation point for hydrates. The model for the prediction of the formation are based on the fundamental thermodynamic principles and it also use the stream properties that has been generated by your selected EOS. This model can be applied to various compositions and extreme operating condition with a greater degree of reliability than any one could expect with empirical expressions or charts.

But the most important thing is I hope you know that Hydrate Formation prediction is restricted to only Peng-robinson and Soave-Redlich-Kwong EOS.

As far as I am concerns, the only requirement for hydrate formation is that some water must be present (be it in HC vapor phase or HC condensed phase) with hydrate forming components. As we all know the simplest definition for hydrates is a clathrate compound which has an ice-like structure that mixes HC gases and free water, in which the HC gas molecules are trapped inside the framewrok of cages of water molecules. Therefore, the hydrate forming components are those molecules that small enough to fit in the cavities formed by the lattice structure of the host molecules which in this case is WATER. These molecules are like low MW paraffinic HC up to n-butane, some olefins and some smaller non-HC molecules such as CO2, N2 and H2S.

If you are using HYSYS ver 3.0 (the latest so far.. might be),the Hydrate Formation Utility has been improved to give user more control over their hydrate calculation model. If your stream do not have any water, the Assume Free Water model is automatically used in the simulation even you have set to other model in the Hydrate formation utility box.

Just check

http://www.gashydat.org,

it might helpful but its only gives you the very basic idea of what hydrate is.

Stay cool!

 

[MortenA]

Hookem

Well why not stop using computers and calculators alltogether? Plant were build before these were invented. We could all start using slide rulers (again?). That would really improve things. All all this CAD and 3D - what good is it anyway. Lots a stuff was build with folio drawings - or no drawings at all!

Hookem: This may work for you (and make your clients/customers/superiors happy) but a lot of us have happy clients/customers/superiors using the other approach. In my humble opinion I can do a hydrate calculation quicker using HYSYS (allways easy at hand) than by finding some reference book, make some assumptions re. the general nature of the gas and then find the answer in a table/graph - and then later on have to justify my assumption to the client.

Best regards

Morten

 

[olef]

PVTSIM from Calsep (

http://www.calsep.com/)

is an exellent tool for hydrate prediction for single streams. In addition it does the same for wax and other things.

Regards
OleF

 

[Hookem]

MortonA: Yes, but most staffers/companies do not have the luxury of investing time and money to learn/buy/lease a software package like Hyssis, Hysim, Aspen, etc. I once audited a major company deyhydration design in which the rookie engineer used computer default values. Trouble was, the program assumed 40% tray efficiency! And, could not be convinced that there was anything wrong with that default value - until I forwarded a copy of a very long report generated by that very same major oil company - made 10 years prior! Yes, computers are wonderful (witness emails and this forum); but, garbage in, garbage out.

 

[Alph]

Reference Book
Natural Gas Hydrates - A guide for Engineers
by John Carroll
Gulf Publishing
ISBN 0-7506-7569-1

Software
Multiflash from Infochem

http://www.infochemuk.com