distillation bug

Discusses use of COCO, the process simulation and modelling software suite from AmsterCHEM, downloadable from www.cocosimulator.org

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distillation bug

Postby aken » 25 January 2019, 04:43

hi,
I expose the bottoms flowrate as an input in CAPE- OPEN and hook up a controller as shown in the attachment. But when l try to solve it, the input disappears leading to an error that the bottoms input is not found.



Kind Regards,
Attachments
BENZENE PRESSURE SWING.fsd
(35.82 KiB) Downloaded 29 times
aken
 
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Re: distillation bug

Postby jasper » 25 January 2019, 10:25

I cannot reproduce the issue - exposing the input and controlling it works (that is, a solution cannot be found, I did not check into that further, I think the specification is invalid. This can easily be checked with a parametric study).

Can you update to the latest ChemSep LITE and see whether the problem remains?
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Re: distillation bug

Postby hkooijman » 28 January 2019, 21:59

There was a bug in the most recent version of ChemSep that caused the assignment of Cape-Open parameters to fail. This is fixed. It is better to reconnect all information to ensure the parameters are passed on. I don't know whether your operation can work though, that is something you need to check out yourself.
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Re: distillation bug

Postby aken » 29 January 2019, 05:23

hi, thanks for your responses. I did install the latest chemsep and that fixed the issue of deleting the exposed bottoms flowrate. the simulation will not converge even if the specifications are valid. From the txy diagram technically we should be able to obtain pure ethanol as bottoms. l further confirmed this by doing a parametric study and at a bottoms flowrate of 29.9 kmol/h we obtain bottoms ethanol purity of 0.99. but as l try to automate the process by using the controller, the simulation does not converge, surprisingly.
Attachments
BENZENE PRESSURE SWING.fsd
(31.75 KiB) Downloaded 27 times
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Posts: 32
Joined: 18 December 2018, 06:02

Re: distillation bug

Postby jasper » 29 January 2019, 10:35

I cannot get the column to converge even without the controller. Does the column solve with you for a spec of bottom flow rate is 29.8 kmol/h?
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Re: distillation bug

Postby aken » 30 January 2019, 06:40

correction: forgot to change the column pressure to 3 bars, and the measuring unit should measure benzene instead of ethanol in the bottoms. with these corrections made, here are 2 columns one with no controller and converged to the required bottoms purity of 0.99 benzene by using a bottoms flowrate of 20 kmol/h versus with one with a controller and failed to converge.
Attachments
BENZENE PRESSURE SWING 1.fsd
(31.78 KiB) Downloaded 20 times
BENZENE PRESSURE SWING CONVERGED.fsd
(33.1 KiB) Downloaded 23 times
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Re: distillation bug

Postby jasper » 30 January 2019, 08:15

So all works as expected now, or are there still open issues?
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Re: distillation bug

Postby aken » 30 January 2019, 18:11

The only problem is that the controller does not work.
aken
 
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Re: distillation bug

Postby jasper » 01 February 2019, 12:32

Which of the above documents should I use as a starting point to check?
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Re: distillation bug

Postby aken » 02 February 2019, 07:45

the one attached below. the objective is to obtain 0.99 benzene purity by manipulating the bottoms rate using a controller. I need the controller to hold this purity constant as l will hook up a second distillation column with a recycle stream.


Regards,
Akan
Attachments
BENZENE PRESSURE SWING CONVERGED.fsd
(33.1 KiB) Downloaded 25 times
aken
 
Posts: 32
Joined: 18 December 2018, 06:02

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