3 replies to this topic

[ChemEngStudent17]

I'm working on a sensitivity analysis for a distillation column (multicomponent) using Radfrac. I'd like to compare reboiler duty to the number of stages. However, everytime I run the analysis it comes back with errors...I suspect it is because the number of stages I've used  is the number specified by previous DSTWU column results, meaning it is a fixed value but, I still want to run this comparison. Is there anyway I can still do this? Any suggestions to help me with this?

 

Thanks in advance!

Edited by ChemEngStudent17, 25 July 2017 - 09:18 AM.

[serra]

you must input which variable is to be varied (there is a dialog for that), then the solver will iterate to optimize the solution,

as alternative you can follow a different procedure, I solve these problems in Excel (with Prode Properties), I simply call Prode n times (each time with a different number of trays as input) and plot the results,
adavantage being that you can vary any specification.

[ChemEngStudent17]

Hi Serra,

 

Yes, I input number of stages in the "vary" section and reboiler duty in "define" section however, the result still comesback with errors...I'll try your suggestion though I'd still prefer to work with ASPEN

But Thanks for your reply

[Pilesar]

I don't think AspenPlus has an option to directly vary the number of stages in a Radfrac column in an automated sensitivity analysis. Whatever Block-Var variable you are manipulating is likely tied to some other parameter. You can manipulate the stage efficiencies in a sensitivity analysis, but this method has several pitfalls for the unwary and I do not recommend this as results are readily misinterpreted whenever you use stage efficiencies other than ideal. The method I have used often is to change the number of stages by hand and record the results. Yes, this can be tedious. If feed location can be a variable, consider using the Optimizer to find the best location for the feed. You will probably want to use the optimum feed location anyway when you change the total number of stages.