COFE Flowsheet Unit Operation

[jasper]

Not sure which problem you observe. I replied to your e-mail with the set up. If you need the actual flow rate in the outer flow sheet, you can calculated it in the inner flowsheet from the difference between surplus and purged feed 2 using an information calculator and export the result.

[nrgeng]

My apology for being indefinite about the problem to consider. The problem that I was referring to was that upon loading the MAIN Flowsheet and selecting [Validate] the Flowsheet is ready to solve, but clicking [Solve] results in an error message. Try it yourself. I configured my Flowsheet with a Flow Constraint outside the SUB Flowsheet and with a Controller inside the SUB Flowsheet. This combination produced an error message:

message: Unit "COFE Flowsheet Unit Operation SUB": Solve failed
error: calculate failed for unit COFE Flowsheet Unit Operation SUB: Cannot solve controller "FC": it needs to take part in a recycle

I inferred from your previous post that a controller could be used within a SUB Flowsheet, yet my MAIN Flowsheet proved otherwise having received an error message. I observed a Controller within the SUB Flowsheet that you sent to me.

Technically the Controller is in a recycle through Information Stream 21 to Steam 18 connected to the Flow Constraint and Material Stream 15 outside the SUB Flowsheet connected to Stream 12 inside the SUB Flowsheet, so is this an artificial error message that can be lifted? I am sending another copy of the original fsd file that I sent to you in case you modified the original to send to me.

[jasper]

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.