COCO, CHEMSEP AND ASPEN DIFFERENCE

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

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COCO, CHEMSEP AND ASPEN DIFFERENCE

Postby aken » 07 January 2019, 01:46

hi. i am facing a challenge with chemsep, it gives a liquid temperature different from the vapour temperature, but we know at equilibrium the temperature and pressure of the vapour and liquid is the same. further more the equilibrium compositions are different, the ones for COCO and CHEMSEP. The temperatures from COCO and ASPEN are diffrerent too. also, is there a way to plot PT plot in COCO?



Regards,
Aken
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Re: COCO, CHEMSEP AND ASPEN DIFFERENCE

Postby jasper » 07 January 2019, 09:42

If I rerun this case I find the expected (and consistent) answers on the ChemSep flash as well. Which version of ChemSep are you using?
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Re: COCO, CHEMSEP AND ASPEN DIFFERENCE

Postby jasper » 07 January 2019, 09:43

(what do you mean by TP plot? a phase envelope plot? There is no automated way to currently do that, but you could plot dew- and bubble point T as function of P at fixed Z, or vice versa).
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Re: COCO, CHEMSEP AND ASPEN DIFFERENCE

Postby aken » 07 January 2019, 22:20

yes l meant phase envelope. awesome l did that a obtained a phase envelope quite similar to one from aspen besides that after some point the graph drastically drops, without detecting the retrogate behavior. Is there anyway l can clean the graph and remain with only points consistent to the phase envelope plot, and get rid of the inconsistent parts. also is there any way l can expose vapour fraction of the outlet stream, as l want to do a parametric study of pressure (input) versus vapour fraction of the outlet stream to study retrogate behaviour near critical region of the mixture. thank you.
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Re: COCO, CHEMSEP AND ASPEN DIFFERENCE

Postby hkooijman » 08 January 2019, 08:41

when I recalculated the ChemSep unit operation it gave the exact same results as the flash implemented in COCO, namely a temperature of 80.3535 deg C, and Y of 0.614701.
If you encounter strange behaviour like this it might be wise to perform a reset and then solve again.
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Re: COCO, CHEMSEP AND ASPEN DIFFERENCE

Postby jasper » 09 January 2019, 08:39

COFE does not currently have a method to trace the phase boundary.
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Re: COCO, CHEMSEP AND ASPEN DIFFERENCE

Postby hkooijman » 10 January 2019, 01:32

to answer the original question: the temperatures differ in COCO from ASPEN because in Aspen you defined the mixture as Ethanol/Benzene whereas in the uploaded COCO flowsheet your mixture is Ethanol/Water ...
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