4 replies to this topic

[cheerpolo]

Dear all
I have a problem about extraction. I had already understand HETS information. But I do not how how to decide Number of Equilibrium Stages. Should I use the which method to decide it ?
Another question for stage efficiency. Shall I consider it ?

[Anthony87]

Dear all
I have a problem about extraction. I had already understand HETS information. But I do not how how to decide Number of Equilibrium Stages. Should I use the which method to decide it ?
Another question for stage efficiency. Shall I consider it ?

A common way I use is the Mccabe and Thiele method. I'm not going to explain it here but wikipedia or google should clarify it for you.

[cheerpolo]

Thanks for quick reply
I know the McCabe - Thiele method. But the method generally would be used on the university or college. On the actual condition, the designer almost does not use it. Besides the McCabe - Thiele method, Could anyone offer some equations or figures to estimate the stage number ?

[Anthony87]

Try and grab yourself "Unit Operations of Chemical Engineering" by w. mccabe, its got quite alot of info in there, most likely more than anyone will put across to you over an engineering forum.

[djack77494]

You are contacting two immisible liquid streams, one having a solute which you want to extract into the other (the solvent). If you mixed a given quantity of the two liquids together, the solute would distribute itself between the two phases. The end result of this process would be two liquid phases that were in equilibrium with each other. This is one equilibrium stage. If you are satisfied with the two product streams, than you are done; if not, an effective way of getting more of the solute out of the raffinate and in to the solvent is to add another stage. You can do this until you reach the point where you are satisfied with the results.

For the second part of your inquiry, when you design an Extractor, you must figure out how it will be constructed. Knowing the number of ideal or equilibrium stages you desire, you must translate that into the number of actual stages you will build into your extractor. Since no contacting device is perfect, the number of actual stages must equal or exceed the number of equilibrium stages.

HTH,
Doug