16 replies to this topic

[lm1996]

Hi everybody!

This is my first time asking a question, it is nice to meet you all!!
 

Now on to my question: For a project I  am trying to calculate the residual enthalpy (or enthalpy departure) for a mixture of CO2/H2 with the PSRK EOS. I am comparing my results with the ASPEN V10 Plus process simulator. The problem is that my implementation (in Matlab) matches the results in Aspen accurately, but after yco2=0.25  I think the mixture begins to condensate (orange graph) but my EOS is not prediciting any liquid molar volume until about yco2=0.70. After that point the results coincide again perfectly with Aspen. Does anyone have an idea where my mistake is and why my implementation of the PSRK Eos only predicts one real solution for the gas phase?

 

Attached as a graph which compares the my calculation with Matlab and the one Aspen gives!
 

Thank you all very much in advance!
 

Cheers Lukas

 

 

[PingPong]

You provide absolutely nothing and then ask us where your mistake is?

[Pilesar]

Lukas, I see that your attachment was not successfully posted. I also was unable to use the attachment feature in the forums yesterday. It is very annoying when software tools do not work as expected. As to your question, are you sure which of the two results are correct? Perhaps the Aspen results are wrong! I would look at the results from other EOS in Aspen for additional comparisons since that is easy to do.

[breizh]

Hi ,

Please upload your attachment to get support.

Breizh

[latexman]

I tested the attachment function just now, and it appears to be working at the moment.

 

If one is going to upload attachment(s), click the "More Reply Options" (to the right of the "Post" function) to get the attachment upload function under the text window.

Attached Files

•  1969 Mach 1.jpg   101.46KB   0 downloads

[PingPong]

If one of us is supposed to locate any mistake(s) in the topicstarter's work that missing attachment, which is merely a graph that compares his Matlab calculation with the one Aspen gives, won't be enough.

 

Now it is not even clear at what temperature(s) and pressure(s) the calculations were done.

 

Any mistake(s) will be in the matlab code which nobody can see.

[lm1996]

Hello guys!

 

I am sorry for my unclear problem description: the calculations were done at 233.15 K and a pressure of 50 bars!

 

@Pilesar: yeah I compared the results from Aspen with other EOS and the results were still the same, I also compared it with Refprop!
 

I am trying now to upload the graph again! 

Thank you all!
 

[lm1996]

Ok so here is the promised graph: 

 

Attached Files

•  forum.png   15.92KB   0 downloads

[breizh]

Hi ,

Consider the resource attached to calculate the properties of the stream at given (P&T):

Other Thermodynamic Properties – Quest Consultants

 

From gas to liquid @ # .55 CO2  (233.15 K , 50 bars)   using Peng Robinson EOS

 

note : I don't have access to simulator other than above!

 

Hope this is helping you

 

Breizh

[lm1996]

Thank you very much @Breizh for your response!
 

It helped a little but I am still not sure where my mistake is, should I share my code with you guys but I think that would be a little confusing...

[breizh]

Hi,

You may have an issue with your code ! you should consider to review the pseudo components and the relations used to calculate the properties Kay's mixing rules) .

Good luck anyway

 

 

Breizh 

[SilverShaded]

They both look suspect to me, there is clearly a phase change and the error may be to do with how that is handled.  Are you using the same binary interaction parameters.

Edited by SilverShaded, 20 September 2021 - 04:02 AM.

[breizh]

Hi ,

Using PR EOS you will find my results (excel calculation) :

 

note : Just adding an excel sheet to support your work . More important is to understand the principles .

 

Nice thermodynamic application . 

 

Good luck

Breizh 

[lm1996]

@SilverShaded: yeah I think I extracted the right parameters from Aspen, since I am applying PSRK I need the UNIFAC interaction parameters, which are obtainable in Aspen as the UNIFPS parameter set if I am not mistaken..

 

@breizh: thanks again, I will have a look on that excel file, thank you very much, I will send a message when I am done with it!

[lm1996]

@breizh, in your calculation with the PR-Eos you also got the big step for the residual enthalpy in the same concentration area as me, which interaction parameters did you use?

[lm1996]

Another things which seems a little weird to me, is that the compressibility factors Z for the liquid and vapor phase are constant in Aspen for a wide mole fraction range, in the attached file, the blue line is the compressibility factor for the vapor phase and the green line for the liquid phase.

Calculations were again done at 233.15 K and 50 bars with PSRK as selected method...

Attached Files

•  forum2.png   227.06KB   0 downloads

[Vegeta]

@lm1996

I can't say much about the thermodynamic as I have limited access to simulation software and Matlab.

Back in the days of my college, one common issue was the mathematics and how it is coded in Matlab. Have you validated this (at least for one data set by hand calculation)?


Regards,