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HYSYS and CO2 Freeze

HYSYS and CO2 Freeze

HYSYS and CO2 Freeze

(OP)
I have recently been having issues with the CO2 freeze utility in HYSYS.  One of the more interesting things I've noticed is that the predicted CO2 freeze-out temperature for liquid hydrocarbons is extremely pressure dependent. For example:

For a liquid with the following composition.
CO2: 4.1%
C1:  87.4%
C2:  8.3%

at 365 psia
CO2 Freeze is -154.82F

at 321 psia
CO2Freeze is -138.01F

Shouldn't the liquid-solid equilibrium be fairly independent of pressure?  

There is also a big drop-off in the CO2 freeze temperature around 321 psi, but I've already complained about the discontinuity to their technical support staff several months ago.  I haven't received much feedback, so I've given up on them for now.

RE: HYSYS and CO2 Freeze

River City Engineering (www.rivercityeng.com) wrote a paper regarding the pitfalls of CO2 freezing predictions in various process simulators (including HYSYS).  Their paper is on the website (I think HYSYS is the A simulator in the paper).

I believe they market a utility with better results.  I looked into this but felt it was not worth it...after reading the paper I am more comfortable with the discrepanices in the HYSYS software.

RE: HYSYS and CO2 Freeze

(OP)
That's funny.  We came across the exact same paper.  We even used the trial version of the HYSYS extension and came up with the exact same conclusion.  I had to check some of your other posts to make sure you aren't my boss.  I think their version of the utility (the one time I played around with it) showed no change in the liquid-solid CO2 freeze out in relation to pressure.

RE: HYSYS and CO2 Freeze

If you call 800-776-5220 and ask for Mike (TAMU '83) I can give you the answer to your question.

RE: HYSYS and CO2 Freeze

(OP)

Quote:

If you call 800-776-5220 and ask for Mike (TAMU '83) I can give you the answer to your question.
  I appreciate that. I've already opened up a separate incident for this, but I still might call to pick your brain about that later.  I shouldn't have griped about HYSYS tech support.  For the most part they are excellent, and I definitely do a poor job of following up with most incidents.

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