Refprop

[Kristian]

I have a problem with using Refprop in COFE. I have set up a water-ammonia mixture through the Refprop Cape-open ppm, which is working fine for direct calculations, but apparently not in iteration loops. I.e. for units which cannot be calculated sequentially I get the error message:

"error: calculate failed for unit HeaterCooler_8: CalcEquilibrium failed: CalcEquilibrium failed: CalcEquilibrium failed: [TPFLSH error 219] outer iteration loop for composition in 2-phase state did not converge"

According to Refprop documentation, [TPFLSH error 219] is simply a failed-to-converge error message. Could this be caused by the data (or lack of) that is sent to the refprop routine?

Kristian

[jasper]

This is a flash convergence failure and is probably due to a bad iteration guess. Can you send me the fsd file in my private mail?

[Kristian]

Sent example file to jasper@amsterchem.com. Thanks for quick reply.

I have not made any effort to provide good first guesses for the iteration. However, when using the built-in property packages(TEA) with Peng-Robinson, this and alot more complicated flowsheets easily converge with the same inputs. Unfortunately there are too large deviations between this and refprop calculations to use rely on them as is.

[jasper]

Your initial specification is fine (at least in what you sent me; there is no recycle, so no initial guesses are used).

The problem is simply that the flash at X = {water = 0.3, ammonia = 0.7}, T = 30 C, p = 2 bar does not converge. This gives the heat exchanger no starting point.

If you enter this in the NIST front-end you will find the same.

Let us forward the problem to NIST. I will get back to you on this.

[Kristian]

Thanks Jasper, you are of course right, the initial state in question here (30 C, 2 bar) is by chance the "dead" state of the process which is why I confused it for a iteration/initial guess problem.

I am impressed by the level of support you provide, and not only because this problem is caused by a 3rd part.

Kristian

[jasper]

[Kristian]

Thanks again, problem solved.