4 replies to this topic

[Vergis K]

hi,

I' m an undergraduate student in mechanical engineering in the Aristotle University of Thessaloniki in Greece. Right now im doing my final project in ARS and im trying to simulate ammonia-water cycles in aspen. I have problem with EOS and i really dont know which to pick. I tried peng-robinson, nrtl, Sour-RK, but not with good results. 

Thanks in advance

[serra]

which mixture properties do not seem accurate ?

For water / ammonia (with a different software, Prode Properties)

I obtained reasonable values for H / S from Extended Peng Robinson,

while for VLE CPA did seem more accrate...

But nowadays there are so many models and options that it appears difficult to suggest one....

[Vergis K]

I face problems in the VLE.

i have more 10% error using aspen.

My tools are a little bit limited.

What about Prode Properties?

[serra]

for a two components mixture you should be able to obtain a decent VLE data fitting with many models,

you may try for example a EOS with complex mixing rules (say PR+NRTL with WS or similar rules)

errors in VLE fractions should be below 10 %  once you recalculate BIPs for the speciifc operating range,

both Aspen and Prode include utilities for that,

Prode Properties is a thermo library, I utilize Prode mainly with Excel,

if you prefer a simulator go with Aspen,

if you like Excel (or similar tools) Prode Properties may be a good solution.

[Pilesar]

Sour water thermodynamic packages are not accurate at high concentration (above 30%) but of the ones you listed the Sour-RK may have a chance to come close at lower concentrations. Ammonia forms ionic components with water and you no longer have a two-component system in the liquid phase. You may need to use an electrolytes package for higher accuracy if Sour-RK is not good enough. Can you be happy with 10% error? That does not sound so bad to me for your system and may be the best you can get.

Edited by Pilesar, 10 May 2016 - 11:39 AM.