2 replies to this topic

[TeamWORC]

Hello,

I cant seem to understand why increasing the reflux ratio doesnt change the tray efficiency significantly?

 

 

Measured efficiency was obtained using McCabe Thiele diagram at Tray 2 (top of the column) only.

 

 

Lookign forward to replies. thanks

 

 

 

Background: Methanol-water mixture

  Experiment was done on a pilot size column in university lab. The objective was o determine tray efficiencies as a function of the boilup rate and reflux ratio for the column running under normal operation while keeping the feed rate constant.

 

Heres the column data

Edited by TeamWORC, 14 April 2013 - 12:11 AM.

[katmar]

How did you predict the efficiencies?  What are the parameters that are changing with RR that you would expect to influence the efficiency?

 

What you have "discovered" is the reason why bubble cap trays were so popular.  Because they naturally have good mixing, and the liquid level remains very constant as the flow rates change, they have very wide ranges of operability - and all at good efficiency levels.  It is only because they are more expensive than sieve and valve trays that they are installed only in rare cases these days.  The only times I have seen bubble cap trays work inefficiently have been when designers have used rules of thumb instead of proper design methods.  Most of these failures have involved what Kister calls "Vapor Cross-Flow Channeling", but what really just boils down to not understanding the liquid level gradient across the tray.

[TeamWORC]

Katmar:

 

I used the AICHME method to get the predicted tray efficiency.  Not sure about your second question.