aspen simulation of coldbox

[Jack Nicholson]

Hi. I have a question.
I am going to simulate a cryogenic plant using Aspen plus. Here is the problem:
1) In simulation of coldbox, there are lots of streams, and as you know, we encounter recycle streams and iteration calculation. How can we avoid this issue?

2) In ordinary simulation of coldboxes, we determine outlet temperature except for 1 stream. So when we change process condition of plant, how come Aspen change outlet temperature?

 

[MortenA]

You have to "clever" when setting up your recycles. Not referring to your specific issue i have attached a small sketch to illustrate a common "error". Often when you build your simulation you "go with the flow" and this will lead to more recycle loops than necessary. They must all converge and often they impact each other. Try to look at your case and see if you can reduce.

Best regards, Morten

 

[MortenA]

I should warn you, i dont work with Aspen+ but HYSYS. I just assume that the issue with recycle is more or less generic and that the solution is also...

With regards to 2) - all simulations is about reducing your number of free variable to 0 by specifying your boundary conditions - once you have achieved this all the rest are determined. So you will have to look at what you wish to specify and what you wish to get as result. Some software have limitation in what you can specify and then get results from. E.g. HYSYS if you have a pipe segment specifying both downstream pressure, temperature, composition and mass flow gives you a system that is defined but last time i checked HYSYS couldnt solve this (it requires some of the information upstream).

Best regards, Morten