Can the VLE Generator accurately predict results for low reflux ratios?

  • Thread starter Thread starter maistral
  • Start date Start date
  • Tags Tags
    Generator Law
Click For Summary

Discussion Overview

The discussion revolves around the capabilities and limitations of a VLE (Vapor-Liquid Equilibrium) Generator developed in Excel, particularly focusing on its accuracy at low reflux ratios in distillation processes. Participants explore various models and methods for improving the generator's functionality and stability.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant describes their VLE Generator, which uses Dalton's Law and Raoult's Law, and mentions it is still in the BETA stage, inviting feedback and suggestions.
  • Another participant expresses interest in stabilizing the VLE generation using different equations of state (EoSs) and integrating activity models into the Excel tool.
  • A participant shares their attempt to create a PS distillation method spreadsheet that works with the VLE generator but notes issues with excessive iterations consuming computer memory.
  • One participant suggests testing the PS implementation by comparing results with the McCabe Thiele method, particularly under conditions where the latter is expected to provide a good approximation.
  • Concerns are raised about the performance of the generator at low reflux ratios, with one participant indicating that problems arise when operating near or below the minimum reflux ratio.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and approaches to testing the VLE Generator, with some agreeing on the need for further testing under specific conditions, while others highlight different methodologies and challenges. No consensus is reached on the effectiveness of the generator at low reflux ratios.

Contextual Notes

Participants mention limitations related to the generator's current BETA status, potential issues with convergence at low reflux ratios, and the need for further testing and validation of the implemented models.

Who May Find This Useful

This discussion may be useful for individuals interested in chemical engineering, particularly those working with vapor-liquid equilibrium calculations, distillation processes, and the development of computational tools for chemical processes.

maistral
Messages
235
Reaction score
17
Yes, da, yes. :biggrin:

So this is my first VLE Generator using the Dalton's Law and Raoult's Law I managed to whip up in Excel. It simultaneously calculates the VLE using the DIPPR equations for vapor pressures and heat capacities. Obviously, this is still in BETA stage; so please do not expect anything grand. The instructions for the use of this thing is really, really simple: you simply select two components and press F9. Hue. :smile:

Normally the calculations converge in five iterations. The calculated VLE and enthalpies can be found, copied and pasted somewhere else from the "DATA" tab. Constants here comes from the Perry's Handbook, 8th edition.

Special thanks to Chestermiller for helping me whip this thing up, in particular the enthalpy curves, and for everything I do not understand in the chemical engineering domain for that matter. My mind was literally in chaos when I wasn't sure with the enthalpy balances. :smile:

And yes, if you may have noticed, there's an option there which says "THERMODYNAMIC MODEL". Don't bother changing them yet, they aren't ready. And for the curious mind, I used the Newton Iteration and the Simpson's cubic integration method for the VLE and the enthalpies, respectively.

DISCLAIMER: I don't take any blame if a chemical plant blows up because of this program, or any untoward incident for that matter. :smile: This is up here also because it needs more suggestions and other stuffs.

THE DOWNLOAD LINK!
 
Last edited:
Engineering news on Phys.org
I'm sorry you are not generating any responses at the moment. Is there any additional information you can share with us? Any new findings?
 
Oh, it's fine. The amount of downloads tho. I guess they don't want to give their input <_<

In any case, I'm trying to figure out ways to stabilize the generation of VLEs using SRK and PR in Excel; or even better I would like to extend it to even quartic EoSs or the virial ones, and if possible I would like to include activity models with them as well. As of the moment I managed to integrate NRTL, Wilson, van Laar and Margules models into the Excel spreadsheet with the Dalton-Raoult's laws. I'm trying to test it more to be sure; a download link might come soon. 8D
 
Thanks for doing this. I'll be a beta tester of your program for sure!
 
So this is what I have now...

I'm trying to make a PS distillation method spreadsheet that would work with that VLE generator.

So far, this is what I have. It's working now, except it iterates until tens of thousands (good-bye computer memory e.e)
 

Attachments

  • hhh.jpg
    hhh.jpg
    44.9 KB · Views: 780
I don't quite understand the question. To test your PS implementation, you should run a case where the McCabe Thiele method give a good approximation. Then you should solve the problem both ways and compare the results. Once you are satisfied that the implementation works for such a case, you can start looking at cases where MT is not expected to do a very accurate job.

As far as your immediate problem is concerned, have you tried to run the calculation with a higher reflux ratio? Does the problem persist? Maybe you are running too close to the minimum reflux ratio, in which case you would have an excessive number of plates.

Chet
 
Chestermiller said:
I don't quite understand the question. To test your PS implementation, you should run a case where the McCabe Thiele method give a good approximation. Then you should solve the problem both ways and compare the results. Once you are satisfied that the implementation works for such a case, you can start looking at cases where MT is not expected to do a very accurate job.

As far as your immediate problem is concerned, have you tried to run the calculation with a higher reflux ratio? Does the problem persist? Maybe you are running too close to the minimum reflux ratio, in which case you would have an excessive number of plates.

Chet

Yep, it happens when I run very low reflux ratios. Maybe it passed through the minimum reflux already. :|
 

Similar threads

Enthelpy-concentration diagram - how to generate.
  • · Replies 2 ·
Replies
2
Views
8K