McCabe-Thiele Diagram: Murphree Efficiencies & Reboiler Stage

[jaxnnux]

Hello,

I have a question regarding Murphree efficiences and the associated McCabe-Thiele diagram.

In partial reflux distillation, should I include the reboiler stage when stepping down (i.e. determining the # of stages) from the distillate to the bottoms composition? Or should I just use the total number of trays and forget the reboiler stage?

My friend asked a professor this question last semester and he told my friend to forget the reboiler. This doesn't make sense to me because if you do not include the reboiler stage then the diagram suggests the bottoms composition (the one coming from the reboiler) is the composition coming out from the last tray.

Here's the image of my current McCabe-Thiele diagram:
http://img434.imageshack.us/my.php?image=one8xh.jpg

Thanks.

 

[thearny]

Having spent 4 years learning how to do this we have completely forgotten. It would seem to make sense to include the reboiler, but your construction just doesn't look right, if we had all the information you were given we could at least put our mind to it more completely.

 

[thearny]

In conclusio we think you are just about right.

 

[mark-ashleigh]

yer , You must include the reboiler...the first step is always the rebolier...see Coulson and Richardson or Geankopolis (mass transfer) .

 

[bajaj_383]

you shoould use a reboiler stage & counts it one extra so your total tray will become abt the trays calcualted from the graph plus the reboiler tray

 

[mbeychok]

jaxnnux:

I strongly recommend that you read the Wikipedia article at:

http://en.wikipedia.org/wiki/McCabe-Thiele_method

Milt Beychok

 

[jacone]

You have to include the reboiler.