Hello everyone,
I am currently working on a simulation in DWSIM involving an extraction column where I am using N-methyl-2-pyrrolidone (NMP) as a solvent to extract components from a C7+ oil bulk mixture. However, I am facing significant convergence issues, and I am looking for advice or solutions from those who might have experience with similar setups.
Despite setting reasonable initial estimates, the column simulation fails to converge.
Adjustments to flow rates and compositions do not seem to help stabilize the solution.
Tried verious thermodynamic models (Peng-Robinson,NRTL,Modified Unifac...) but still no success.
Specific Questions:
Are the chosen stage temperatures and pressure settings appropriate for ensuring vapor-liquid equilibrium with this mixture?
Are there any best practices for setting initial composition and flow estimates for complex mixtures in such columns?
Is there a recommended approach for troubleshooting convergence issues specific to solvent extraction columns in DWSIM?
Could there be any particular parameters or configurations in DWSIM that I might be overlooking?
Any insights, suggestions, or detailed guidance would be greatly appreciated.
Thank you in advance for your help
if you are unable to predict LLE for this mixture using PR or SRK EOS, the extraction column will not work. You can't use UNIFAC models because the petroleum fractions don't have unifac structure information.
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Thanks @danwbr for answering, and sorry for the long question since I'm a novice in using DWSIM!
I'm currently confused about how to set up initial estimates to solve the problem. Looking at an example of LLE that is working (one from the sample examples), I see that initial estimates are set to some values, but I don't understand how they were determined. My guess is that if I set proper estimates in my simulation, it would manage to converge.
In the default working example, the result for the vapor fraction is set to 0, but in the estimates, there are values set for vapor flow for each stage and molar fraction for each component in vapor. Also, acetone, water, and methyl isobutyl ketone have values for vapor on each stage even though temperatures are set to 23, 22, 17, and 11 degrees Celsius (which should not be enough for them to be in the vapor state).
Question 1: Is there some mechanism for determining initial estimates properly? (For a complex mixture generated by the bulk C7+ petroleum characterization utility)
Question 2: Is it even possible to do extraction with a complex mixture like the one I have in my example? (This task was given to me as part of my Faculty curriculum)
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
In order to the extraction column to work you need to make sure that the current thermo model is able to predict LLE for the current mixture. If it doesn't the column will not be able to generate initial estimates for the two liquid phases. In this case, initial estimates won't do much because subsequent iterations will not cover the LLE region.
You can try using PR or SRK and then try changing the binary interaction parameters in the property package configuration window until you're able to see two liquid phases.
Last edit: Daniel Medeiros 2024-05-27
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Hello everyone,
I am currently working on a simulation in DWSIM involving an extraction column where I am using N-methyl-2-pyrrolidone (NMP) as a solvent to extract components from a C7+ oil bulk mixture. However, I am facing significant convergence issues, and I am looking for advice or solutions from those who might have experience with similar setups.
Despite setting reasonable initial estimates, the column simulation fails to converge.
Adjustments to flow rates and compositions do not seem to help stabilize the solution.
Tried verious thermodynamic models (Peng-Robinson,NRTL,Modified Unifac...) but still no success.
Specific Questions:
Are the chosen stage temperatures and pressure settings appropriate for ensuring vapor-liquid equilibrium with this mixture?
Are there any best practices for setting initial composition and flow estimates for complex mixtures in such columns?
Is there a recommended approach for troubleshooting convergence issues specific to solvent extraction columns in DWSIM?
Could there be any particular parameters or configurations in DWSIM that I might be overlooking?
Any insights, suggestions, or detailed guidance would be greatly appreciated.
Thank you in advance for your help
if you are unable to predict LLE for this mixture using PR or SRK EOS, the extraction column will not work. You can't use UNIFAC models because the petroleum fractions don't have unifac structure information.
Thanks @danwbr for answering, and sorry for the long question since I'm a novice in using DWSIM!
I'm currently confused about how to set up initial estimates to solve the problem. Looking at an example of LLE that is working (one from the sample examples), I see that initial estimates are set to some values, but I don't understand how they were determined. My guess is that if I set proper estimates in my simulation, it would manage to converge.
In the default working example, the result for the vapor fraction is set to 0, but in the estimates, there are values set for vapor flow for each stage and molar fraction for each component in vapor. Also, acetone, water, and methyl isobutyl ketone have values for vapor on each stage even though temperatures are set to 23, 22, 17, and 11 degrees Celsius (which should not be enough for them to be in the vapor state).
Question 1: Is there some mechanism for determining initial estimates properly? (For a complex mixture generated by the bulk C7+ petroleum characterization utility)
Question 2: Is it even possible to do extraction with a complex mixture like the one I have in my example? (This task was given to me as part of my Faculty curriculum)
Hi Masa,
In order to the extraction column to work you need to make sure that the current thermo model is able to predict LLE for the current mixture. If it doesn't the column will not be able to generate initial estimates for the two liquid phases. In this case, initial estimates won't do much because subsequent iterations will not cover the LLE region.
You can try using PR or SRK and then try changing the binary interaction parameters in the property package configuration window until you're able to see two liquid phases.
Last edit: Daniel Medeiros 2024-05-27
Sir please answer my querry also
https://sourceforge.net/p/dwsim/discussion/844528/thread/e5bf25f799/#986d
Hi Daniel,
Thank you very much for your help.
I managed to change the parameters and successfully separate the components in the extraction column.
glad to know!