COFE Flowsheet Unit Operation

[jasper]

[jasper]

The problem is actually unrelated, but now that I can reproduce it I can fix it. Update available via CUP.

As I am not sure I followed your scenario, I am not sure that I solved your problem. Please check.

[nrgeng]

The {select SUB} you are questioning is {select SUB Flowsheet.fsd} Load it from the File Menu into the SUB Unit GUI that is still open. I updated with CUP and this problem has been resolved. Thank you.

[jasper]

glad to hear it.

[nrgeng]

Next Issue from Message 2
The Flow Constraint & the Controller had to be removed from the SUB Unit to eliminate error messages. I am sending an fsd file. A very unusual activity has occurred before with another flowsheet and again with this flowsheet. Hope you can "kill" it.

Stream 19 head stuck to the mouse arrow like a spider web. Could not shake it loose. Copied it, deleted it, then pasted it. Cannot attach either end of Stream 19 to Controlled or to SUB Unit. Just prior to this COFE crashed twice. Not fun when it crashes!

[jasper]

The screen shots were not attached.

I have no problems for connecting stream 19. Can you provide a recipe (exact steps) to reproduce your issues?

Note that if stream 19 is connected, the problem cannot solve. The set point (0.4 mol/s) for streams 14 + 15 is below the flow rate of stream 14 (1 mol/s). Also, if this setup is representative of your actual problem, you probably do not need a controller; with an information calculator you can calculate the flow rate of stream 15 directly (set point minus flow rate of stream 14).

Do please let me know

- how to reproduce the problem with dragging the stream ends, if you can reproduce it
- if you can indeed not simply connect stream 19 (note that it is up-side-down in the slide you sent me, the connection is in the opposite direction)
- how to reproduce a crash, if you can reproduce it

[jasper]

Also, if you want to take your controlled stream into the SUB, this is possible, with a small trick. Similar to the make-up mixer.

You cannot predict the flow rate of a feed stream, but you can of a product stream. So you can make your feed rate be a surplus flow. You can calculate inside the SUB what amount of feed you actually need. Then you make a product flow with the surplus feed. You can simply report the actual flow rate as the difference between feed and surplus flow.

[nrgeng]

Please be aware that this is a contrived example to explore the use of the COFE Flowsheet Unit Operation Custom Unit. The Information Calculator (IC) and the Mixer are not related. The simulation is of no useful purpose to me other than to demonstrate the problems that I have encountered with the COFE Flowsheet Unit Operation Custom Unit. I will send you the original, unmodified, SUB flowsheet that solved. {Check email for COFE Flowsheet SUB wControls V1.1.fsd}

The original flowsheet does control the discharge flow rate despite your doubts. What you see is a work-in-progress. I am attempting to force a successfully solving flowsheet to fit the constraints of the COFE Flowsheet Unit Operation Custom Unit. I had to "cut it up" to [Validate] and to [Solve] it within the COFE Flowsheet Unit Operation Custom Unit. Since I encountered several problems, I stopped developing the MAIN Flowsheet in order to report the problems to the Forum. You see the result of an interim development effort.

This is the procedure that I use: I design a flowsheet, develop it into a solving flowsheet, then "cut out" the Flow Constraint(s) and Controller(s) in order to fit the constraints of the COFE Flowsheet Unit Operation Unit. The "cutting out" is required to allow [Validation] and [Solving] of the MAIN Flowsheet.

Thanks for the Stream 19 turnaround comment. The stream sticking problem caused me to spin the stream around, then I did not notice that the head position changed with respect to the controller. I connected Stream 19, set the Controller setpoint to the intended 4 kmol/h, and the MAIN Flowsheet solved. I now have documentation for the future use of this Unit Operation.

This exercise has taken a lot of effort. I do not see the value of this Unit Operation for my real-world intended use. My comment is that if your flowsheet does not use controls, this Unit can reduce the space consumed in a large flowsheet. This Unit can be used somewhat like a Fortran Subroutine is used in a Fortran Main Program.

This contrived example of the use of the COFE Flowsheet Unit Operation Custom Unit does solve, thanks to your help. I am stopping my reporting on the problems with this Unit since I cannot reproduce the latest reported problems. However, I will continue the effort with my complicated flowsheet. If the problems arise, I will try to reproduce them for reporting using the contrived example flowsheet. If other Forum members use this Unit, I expect that they will also be experiencing problems that may or my not be reported since reporting problems is a time consuming task. Thanks again for your help.

[jasper]

The flowsheet-as-unit-operation unit does get used. Not only inside COFE as 'sub routine' but also in other flowsheeters, particularly to provided a thermo 1.0/thermo 1.1 conversion service. Problems have been reported with the flowsheet-as-unit-operation unit. Not always via the forum, alas. And problems have been fixed in the past, and on this iteration (cf the change log). It is in the end user feed back, such as yours, that makes that things become more stable.

I looked at your SUB flow sheet. You could, possibly, if you would want to (which I understand is no longer the case), replace stream 12 and flow constraint FV by a feed stream, splitter, and a product stream. The controller should control the split ratio and the second product of the splitter would become stream 13. This way the entire control scheme can be embedded in a sub flowsheet, as the cost of having to specify a surplus feed stream (going into 12) and a purge that purges the unused part of that feed.

In any case, thanks for the feedback. Always helpful.

[nrgeng]