3 replies to this topic

[linkoh]

Hi I"m having a very simple problem. I've set up a short-cut distillation column in HYSYS, but it can't be solved in 20 iterations.

I want to know, where can I increase the number of iteration for the column. I've looked under optimizer and all over the program but I just can't seem to find where.

Thank you

[marchem]

which kind of short-cut method ? Typically short cuts assume constant relative volatilies and should not be used for very non ideal systems, a numerical problems may evidence a solution outside VLE limits...
In some cases you can reduce a multicomponent to a binary system (see for example Hengstebeck method) and then solve... methods as Fenske, Winn etc. can be used to estimate the number of stages in the different cases... these can be in most cases solved in Microsoft Excel and that could permit to understand why the process simulator doesn't work...
To define a short-cut in Excel you need a way to calculate Kvalues, any tool which exports fugacities in Excel can be utilized, I use Prode Properties (and run a short cut before the rigorous column model) but a process simulators should do the same...
Good luck.

[linkoh]

First of all thanks for replying. I've attached a picture of the case I'm working with, as you can see the problem seems to be that in hysys won't calculate past 20 iterations. But I simply can't find where to increase that number of iterations as I need the column solved and don't care about the number of iterations.

Attached Files

•  minrefluxiteration.png   233.95KB   36 downloads

[marchem]

please forgive my rudeness but why don't you put the data in Excel (or any other equivalent tool) and solve the short cut which possibly requires only a few formulas ?
Solving a short cut is easy and a good textbook would help.
As alternative you may get the inlet and specification data for the column (feed composition, operating conditions and flow, column operating pressure etc.) and solve separately, then you can define the column as required.
If short cut is required to estimate the number of trays, set a number and run different cases, etc.
Nowadays column's solvers are very reliable but in any case you can edit and change the specifications running different cases to find a suitable solution...
I have used this method (for example to specify different values for reflux instead to solve for purity) with Prode Properties to converge difficult solutions.