3 replies to this topic

[opti]

Hi all,
Being a HYSYS newbie, I'd appreciate your advice: I'm trying to simulate a process, and for some reason the solver is holding due to consistency errors. Tightening the solver tolerances doesn't seem to work [assuming that it was done correctly], and even if I "fix" the inconsistencies, sth else comes up.
Any suggestions on how to overcome that?
Thanks!

[Koen van 't Sant]

Hi all,
Being a HYSYS newbie, I'd appreciate your advice: I'm trying to simulate a process, and for some reason the solver is holding due to consistency errors. Tightening the solver tolerances doesn't seem to work [assuming that it was done correctly], and even if I "fix" the inconsistencies, sth else comes up.
Any suggestions on how to overcome that?
Thanks!

HYSYS can be very difficult in solving consistancy errors. Sometimes it helps best to disconnect one of the offending connections, doublecheck for duplicate specifications and reconnect the streams. Before you reconnect, disable any set and adjust operations "close" to the problem location. Go step-by-step through the simulation and make absolutely sure that you don't overspecify your model (e.g. through recycles or sub-flowsheets, or by adjusts altering other variables than the one you already specified). Just keep adding manual set values one by one until the model can be solved.

[Zauberberg]

Sometimes it happens that, if material and/or energy balance within the flowsheet is violated during iteration cycles, negative values of stream flowrates are being calculated by HYSYS. This is usually the case when "Adjust" or "Databook" operations/scenarios are present in the model, handling such intervals of independent variables that are too large for the solver.

As Koen proposed, the easiest way to battle against these issues is to delete all streams/unit operations which are affected by consistency check, and to re-build them again. Also, be sure that streams are not over-specified. This is one of the most common problems for novice users.

[JoeWong]

Other way is by "trial-and-error" by creating a dummy line with Recycle operation. This pretty good in handling column operation. Once the system converged, you may starts to remove the dummy lines & operation.

Identify the operation created inconsistency error and ignore & activate the unit again. Sometime it work.