by jasper » 21 June 2014, 16:00
The inner flowsheet and the outer flowsheet are solved separately. So the controller needs to be inside a recycle loop inside the flowsheet it is contained in. So this contraint can only be lifted in case the sub flowsheet is considered an integral part of the main flowsheet, which it is not. It is considered a unit operation in the main flowsheet. This set up has the advantage of being able to use it inside other simulators, via CAPE-OPEN.
The validation does not pick that up because the recycle analysis and tearing is done only at solution time. If tearing needs to be done at validation time it may become sluggish (well - surely not for such a small flowsheet, but it may for bigger flowsheets), as it is done at each user action.
I think it is best if the recycle analysis is done at solution time only.