Exchanger Train: Variable Results

[nrgeng]

This morning I experienced a problem with my main flow sheet. The Exchanger Train which has been a part of the flow sheet for a long time is now preventing the flow sheet from solving. Here is the sequence of what occurred: (1) main flow sheet solved, (2) saved main flow sheet, (3) loaded main flow sheet (note: all streams & units are green), (4) clicked [solve], main flow sheet would not solve, (5) ran main flow sheet in Debug mode, (6) located problem in main flow sheet as Exchanger Train, (7) copied and pasted Exchanger Train to a new flow sheet, and (8) Exchanger Train solved in new flow sheet. Can you explain what is occurring here? The Exchanger Train only solves out of the context of my main flow sheet. Why?

[jasper]

I will need more information to say something about this. Can you send me the flowsheet?

[nrgeng]

I cut the main recycle stream manually and the flow sheet solved immediately. Apparently COFE could not choose to cut this stream by itself. The numbers in the Exchanger Train were ridiculous--the pressure changed from unit to unit (the pressure does not change in the solved flow sheet) and the Flash Tank temperature soared to 6402 C from ~20 C. Just amazing! I have no explanation. I am providing this successful closing of this problem for future reference for others.

[jasper]

So a simple manual specification of one of the streams in the recycle may have solved the problem as well. Finding a proper initial guess is one of the hardest parts of solving a flowsheet of course. Glad to hear you solved your problem.