3 replies to this topic

[Allwyn]

How to depressurise a fluid when it is near its critical state.Hysys depressurization utility suggest to change temperature and also gives two more options.
Even if tried in Hysys dynamics the results seems not correct.
Can any one give some advise based on their experience.

[djack77494]

I don't understand what your problem is Allwyn. I'd suggest that you state your Hysys results along with your reasoning behind doubting their accuracy. I would think an isenthalpic pressure reduction would work fine except that fluid properties near their critical points are notoriously difficult. If you're pretty sure the results are nonsense, then I'd start by looking into the thermo. Garbage in = garbage out.
Doug

Edited by djack77494, 21 May 2010 - 12:18 PM.

[Himanshu Sharma]

Huuh... if any one could devise a method it would be simply great !!!

I have gone through two relevant papers (only two have been published so far as per my knowledge )published in this field.There was a calculation not justified for all cases in one and the other one had a thermodyanmic model that can not handle V-L equilibrium.(apologies i dont rememeber name of the articles and not taking the pain to google)

Isenthalpic pressure reduction is the key idea behind this Supercritical Fluid depressurization .The foremost burden that's blocking the path is that there is no thermodynamic model to handle supercritical Fluids.

Simulators try to simulate properties by either converting to Vapor or liquid during their recursions,both invalid as per my vantage point.

Then there are emergency depressurization system for high pressure units such as hydrocrackers (operating in supercritical region),those calculation are performed based on certain assumptions and you can start with Grotche Equation and validate with plant data.

The assumptions involved may be compensated one by one till your mathematical acumnen (involves a good amount of differential and integral calculus )fails to go further.

Anyone here from Hydrocracker technology background will be able to throw more light about their calculations.

[Zauberberg]

Look at the topic: http://www.cheresour...rcritical-fluid

and you'll find two PDF attachments dealing with the supercritical fluid blowdown.