1 reply to this topic

[anubis]

Hello,

I am a new member in this board. I would like to learn more about Chemcad because I used it during my master studies and I will simulate a SCDS column to separate a mixture of ethyl acetat/acetic acid / water. The top product is ethyl acetat and water nearly at the azeotropic point and the bottom product is pure acetic acid. But the SCDS column did not converge. How I can best find the minimum of trays (e.g McCabe Chart) for this distillation unit and the best tray for the feed. Is it a try and error search. Can somebody help me and give me some ideas.

Thanks a lot

[Aaron Herrick]

Wow, that brings back memories. In 1993 my first CHEMCAD simulation was a distillation train separating those components...I was running it on a 386 (WITH math co-processor, thank you very much!)

For the convergence issue- what are you using for your specifications? Usually flat out non-convergence means you've specified somthing either ambiguously or incorrectly. If you are specifying the azeotrope temp for example, that is not a good spec, step off the azeotrope a little to let it converge, then try to tighten up.

If you're still having trouble with it, go to a reflux spec of 10, and a bottom mole flowrate=50% of the feedrate, then slowly walk the column towards your desired operating conditions. You'll learn alot about how the actual column will behave if you pay attention.

For the feed location-Once you have your column working you can plot the stage temperatures and compare to your feeds bubble pt, that will get you in the ballpark. the best thing to do is make a sensitivity analysis varying the feed location and measuring the reboiler duty. it should go through a minimmum
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