7 replies to this topic

[ProcessEng_12]

Hi everyone.
I am working on column model (Radfrac) in ASPEN PLUS.
There are two types of efficiencies mentioned in column setup i.e. murphee and vaporization efficiency.
Can anyone please help me explain the difference between the two?

[Bobby Strain]

Try your favorite search engine. Also, use each in your model and see how the results differ.

 

Bobby

[breizh]

http://www.separatio...on/MainSet1.htm

 

Consider the resource above and don't forget your best friend "google or others".

Good luck

Breizh 

[SilverShaded]

You most likely want to use murphree efficiency, vaporisation efficiency doesn't work well for distilation columns.  In any case, if you tuning to a real column, tray efficency is simply a tuning factor.

[ProcessEng_12]

Thank you everyone for your prompt responses.

I am able to understand the difference by reading various articles and also the ASPEN Plus help.

I would say Vaporization efficiency is pretty straight forward i.e. it is ratio actual vapor composition on a stage to the ideal vapor composition.

Whereas, Murphee efficiency is the ratio of actual change in vapor composition across a particular tray to the ideal change in vapor composition (if in equilibrium) across same tray.

Taking it further, I am still not able to find a article which states/answers "when to take which efficiency" question?

One can change and tweak efficiency just to match the ASPEN model and get the desired temperatures for plant match case.  But while column/tray designing during commissioning, which efficiency is considered, as it will affect the number of trays and ultimately the fabrication cost, operating cost (reflux, reboiler duty)?

[SilverShaded]

Thank you everyone for your prompt responses.

I am able to understand the difference by reading various articles and also the ASPEN Plus help.

I would say Vaporization efficiency is pretty straight forward i.e. it is ratio actual vapor composition on a stage to the ideal vapor composition.

Whereas, Murphee efficiency is the ratio of actual change in vapor composition across a particular tray to the ideal change in vapor composition (if in equilibrium) across same tray.

Taking it further, I am still not able to find a article which states/answers "when to take which efficiency" question?

One can change and tweak efficiency just to match the ASPEN model and get the desired temperatures for plant match case.  But while column/tray designing during commissioning, which efficiency is considered, as it will affect the number of trays and ultimately the fabrication cost, operating cost (reflux, reboiler duty)?

As allready suggested, murphree efficiency.  Partly because were are you going to get your design values from?  Most available data is in the form of Murphree efficiencies.

Edited by SilverShaded, 25 January 2021 - 05:52 AM.

[breizh]

Hi,

Consider this resource to support your work.

Breizh 

[SilverShaded]

You don't mention whether your trying to model an exisitng tower or not, however if you are do not forget that real world Tray efficiencies can be anywhere between 120% and 0%, regardless of what any theoretical correlation may suggest.