3 replies to this topic

[wojtar]

Another question regarding chemcad.

How should I add new UNIQUAC BIP's to CHEMCAD.
I recieved the following data from some institute:

1. CYCLOHEXANONE
2. CYCLOHEXANOL

Aij UNIQUAC CONSTANTS [K]
A B
1-2 -283 0,7601
2-1 567 -1,41


Aij=A+B*T

It's only an example. I know that those two components exist in chemcad database.

Thanks in advance for your reply.

[Zauberberg]

The Thermophysical menu command Edit BIPs can be used to view/edit existing BIPs for the system. Once when you select these components and choose the thermodynamic model (UNIQUAC), you can access this feature.

[wojtar]

The Thermophysical menu command Edit BIPs can be used to view/edit existing BIPs for the system. Once when you select these components and choose the thermodynamic model (UNIQUAC), you can access this feature.

Yes ...I know that ...but what should I do with it?? After ading my own constants the simulation did not converge. I have a feeling that chemcad uses different units.
Let me explain that in other words. Could I tell chamcad that azeotrope point exists for my user added components? I know mass fraction, temperature and pressure for that azeotrope point. Can Chemcad predict it for wider pressure range? If so -> how could I do that. I assume you have an experience with Chemcad (most people here uses HYSYS or ASPEN ...unfortunatelly I've got licence for Chemcad).

Edited by wojtar, 12 March 2010 - 03:56 PM.

[milenkom]

The Thermophysical menu command Edit BIPs can be used to view/edit existing BIPs for the system. Once when you select these components and choose the thermodynamic model (UNIQUAC), you can access this feature.

Yes ...I know that ...but what should I do with it?? After ading my own constants the simulation did not converge. I have a feeling that chemcad uses different units.
Let me explain that in other words. Could I tell chamcad that azeotrope point exists for my user added components? I know mass fraction, temperature and pressure for that azeotrope point. Can Chemcad predict it for wider pressure range? If so -> how could I do that. I assume you have an experience with Chemcad (most people here uses HYSYS or ASPEN ...unfortunatelly I've got licence for Chemcad).

I think I know what your problem might be simulators have equation for BIPS set up differently. I had same problem where I entered my own BIPS and simulation did not converge, until I have checked that this was because the way equation is set up. I think Apsen and Hysys use same equation while chemcad uses one with signs reverted. So I changed BIP signs, I used - where + and vice versa. And after that it worked like charm. Once I figured that out I never used to do this again. I was far more satisfied if I entered VLE and LLE data for components manually and let Chemcad to regress the BIPS. So you can always tell chemcad about your azeotrope point if you've got proper VLE data.