Custom Unit "Must be Part of a Recycle" Error (COCO 3)

[nrgeng]

An erroneous message {Solve failed: "must be part of a recycle" [Ok]} was obtained during an attempt to solve an inner sub-flowsheet while converting a flowsheet from COCO 2 to COCO 3. This sub flowsheet did not cause an error in COCO 2.

This module from an inner Custom Unit Flowsheet was copied and placed into a new, blank flowsheet, where it still would not run do to a non-existent recycle for which it insisted to be a part. I think a flag has been set in error and it has ruined this module which solved without error in COCO 2. What is the problem? Can it be fixed?

It seems to me that problems solved in COCO 2 or problems not found in COCO 2 are back again or here to be solved in COCO 3. Progress comes at the high price of time!

[jasper]

Can you provide me with an fsd that shows this behaviour?

[jasper]

Does your custom unit contain a flow controller on a feed?

[nrgeng]

Thanks for your question. In response to your question, the outermost flowsheet does contain a flow controller on a feed. COCO 2 had no problem with this simulation with an open recycle created by removal of the feed controller. The problem only arose upon conversion to COCO 3.

Verification of Erroneous Recycle Problem:
By saving the file then reloading it, the new flowsheet solved without the recycle error message. So saving the file then reloading it cleared the erroneous "flag" that was set to report the recycle error. This phenomenon was also observed in COCO 2 with the Information Calculator Unit problems. Apparently it continues in COCO 3.

Even though the open recycle was closed in the outermost flowsheet, the innermost sub-flowsheet continued to report the recycle error message. Since the new flowsheet solved, this is further evidence of an existing problem. No recycle error is reported except in the innermost sub-flowsheet even after the recycle was completed in the outermost flowsheet. Saving and reloading did nothing to resolve the problem. Strange behavior!

For debugging, the sub-flowsheets should not depend on recycles in other sub-flowsheets nor in the outer flowsheet. No such dependence existed in COCO 2.

The erroneous recycle problem prevents further development in COCO 3 so my development continues in COCO 2 with subsequent conversion into COCO 3. This adds substantial time overhead to process development.

[jasper]

There should be no effect at all from saving and loading: the flowsheet structure is re-analyzed each time the flowsheet is solved; no such "flag" that you are referring to exists.

What you describe sounds as a bug. Could be anything, such as an uninitialized variable. But very hard to tell for me if I cannot reproduce it.

You have now stated several times that this is time consuming. I agree. It would help if you can send me a flowsheet that demonstrates the problem so that I can fix it. For clarity: there should be no need whatsoever to do any conversion on a COCO 2 flowsheet to run in COCO 3. With one exception: COCO 3 will not save documents that have duplicate stream or unit operation names. Those require manual fixing.