4 replies to this topic

[keby9vam]

Hi all,

I read previous posts regarding this matter and I would like to clear this doubt. I would like to determine the hydrate formation Temperature of a fluid (oil, gas, water) using Hysys. But i noticed members of this forum say that Hysys does not give an accurate result or its unrealible. How is this so and why?

I was preparing a simulation scheme in Hysys for oil, gas and water at about 120bar and 5C. The Hydrate Formation Temp is about 16C. Is this correct? Thank you for your time.

Regards

keby9vam

[PaoloPemi]

it is difficult to answer your question, the parameters of hydrate models are (generally) tuned for mixtures of light hydrocarbons,
last year I have had the opportunity to compare Hydrate temperatures calculated by different software tools (Hysys, Prode Properties, PVT-SIM etc.) against experimental data available in Sloan's book and other sources,
according my (limited) tests results are reasonably good (errors 1-3 K) in the temperature range 240-290K for mixtures of hydrocarbons (C1 > 60%).
I have not verified the accuracy in presence of inhibitors.

[keby9vam]

Hi Paolo,

Thank you for your comments on this matter. This brings me to ask another question though. With Hysys, I have simulated a stream that has purely water at 120 bar (at 50C), being depressurized to 65 bar using a valve. I noticed the Hydrate formation temperature is very low, about 5C. I am worried as to how low this value is. Is there a reason behind this or is this expected? Thank you for your time again.

Regards,

keby9vam

[PaoloPemi]

water is not a hydrate former, for a stream of pure water the procedure shouldn't return a hydrate temperature, it may return an error.
Of course water can form ice.
I have not access to your simulator (I use Prode Properties) so I can't verify but you may refer to the books of Sloan or Carrol for detailed discussions on this matter.
Keep in mind that different software tool include different procedures and the results may be slightly different,
I have read that Hysys includes a procedure based on the work of Ng and Robinson which is considered accurate, my software (Prode Properties) has a similar model but based on CPA (with association), CPA should offer some advantages with non ideal, polar components and inhibitors but in most cases you get quite equivalent results.

[SD0775]

I guess you should first check with some references regarding hydrate in light hydrocarbon system. This will help you interpret and use simulation software better. Hydrate will not existing if it is only pure water, ice does. It would be also helpful to provide some understanding and feeling about simulation package you are using by making reference to an established data. For example, try simulate water/hydrocarbon/acid gas system with the same composition as used in many hydrate formation charts available in GPSA databook and make comparison.

Another thing I would like to share is, hysys does not take into account salt in the model if you simulate hydrate for wells stream with brine in the system. As a result, hysys will tell more conservative temperature. For a large subsea system this will affect cost a lot since inhibitor injection will tend to be done prematurely.

SD