6 replies to this topic

[ikeikeike]

Greetings, I want to request for help from anyone who knows how to simulate air separation plant in Aspen HYSYS. Currently, in my college we are working on a air separation plant design. I tried to simulate the air separation plant in HYSYS unfortunately the issue comes in the crude argon column. It does not converge somehow, which in turn cause the pure argon column to not converge as well. However, the LPC and HPC columns are successfully converged.

 

Hopefully, someone can help with this matter. Thankyou very much. your help is appreciated. 

[ikeikeike]

Tried to apply many literature survey into application, but it still would not work. Hence, if anyone has ever experienced simulating air separation plant unit or has any aspen file to share with for reference, it is highly appreciated. thank you 

[Pilesar]

You should use an equation of state thermo method. The boiling temperatures of nitrogen and argon are very close. The default binary interaction parameters of your thermo method may not be good enough at the pressures and temperatures of your process. At high pressures the interactions can be considered ideal, but you may need to find values in literature for low pressures. In a typical flowsheet, the Argon column is fed by a fixed-rate vapor side draw (about 20% of the air feed rate) of the LP column. This draw stream will be mostly oxygen with only very little nitrogen. The Argon column has no reboiler. The argon product purity is controlled by the LP column. The Argon column condenser duty is varied to meet an overhead recovery spec. Most of the feed to the Argon column returns in the bottoms from the Argon column back to the LP column. Because of this recycle stream, the LP column and the Argon column are generally solved together.

Edited by Pilesar, 15 October 2021 - 09:51 AM.

[ikeikeike]

Thank you for the suggestion and comment. Will work on that 

[processjit007]

Please share PFD & P&ID of air separation unit. 

Thanks in advance 

[ikeikeike]

@processjit007 

 

Unfortunately sir, we are still working on the PFD, because P&ID is still not in our scope as of now. Let me know if you want the HYSYS file. Thank you. 

[Pilesar]

Here are additional hints for the original poster once the thermo method is addressed.

 

One hint is to get the simulation to converge first. This may mean backing way off of your desired specs. Once you have a converged model, then gradually change the specs toward what you really want. I call this 'homotopy' but the technique may have a different name. When the model breaks, examine the trend of the converged solutions right before the break to see where the solution is heading and think of what you might do to keep it from falling off the cliff. In general, converged solutions give much more useful information than unconverged solutions.  Spec'ing flow rates is often more reliable than spec'ing stream purities to get initial convergence.

 

Some additional suggestions for your student project: Air Sep plants are probably common simulation projects and a thorough web search might discover someone's master thesis with lots of details about how their model was specified. Another shortcut might be to contact the technical support group for Hysys and nicely ask for a working example of an Air Sep plant. Although tech support may be limited in how they are supposed to support student licenses, they are human and might show mercy to a student with a sob story.