HYSYS and CO2 Freeze 1

[AggieCHEN04]

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.

 

[Zoobie]

River City Engineering (

http://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.

 

[AggieCHEN04]

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.

 

[simdoc]

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

 

[AggieCHEN04]

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.