CAPE-OPEN

l set up a controller to set the distillate acetone mole fraction to 0.98 by changing number of stages of the column, and it failed to do so. l did manual guessing till l found out that with 39 stages and feed on stage 31, l obtained the specified mole fraction of acetone. My question is why did the controller not converge? My assumption was that it varied the number of stages, but kept constant the feed stage hence, the non convegence. if that is true, is there anyway it can vary the number of stages and also vary the feed stage while mantaining the fraction of columns in the rectifying section to ones in the stripping section constant? attached is the simulation.

The number of stages is an integer variable. An assumption for the controller is that it is controlling continuous variables. For example, it takes derivatives by perturbation.

The controller will not be able to do this job for you. What is needed here is an optimized, or the mixed integer non-linear programming (MINLP) kind. COFE does not (yet) have one.

thank you