Energy consumption distillation - rule of thumb?

[dramarc]

Is there a simplifyed formula that can be used to esitmate the energy consumption of distillation of a binary mixture?
Maybe a factor times the heat of vaporization?

Looking forward to your answers

Merry X-mas

 

[mbeychok]

dramarc:

The energy consumption is a function of how difficult the distillation is and therefore of the amount of reflux and theoretical plates required. It depends upon the difference between the boiling points or relative volatilities of the two feed components. In my opinion, the possible variations are too large for any "rule of thumb" to be valid.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[6748]

A back of the envelope calculation:
Energy required at the bottom = Top product drawal multiplird by ( 1 + reflux ratio ) and further muliplied with the latent heat of evaporation of the top product.

Units:
Top product in weight unit.
Reflux Ratio in numeral.
Latent Heat in Heat units per weight unit used for the product.

Add the heat required for heating the bottom component in the feed - from its temp to the bottom temp. For that you will need the specific heat and latent heats of all components at the entry and exit conditions.

Add the heat rquired to heat the reflux from its temp to the top tray temp, if the reflux gets sub-cooled.

Add the heat required to compensate the heat loss from the column shell and the associated pipings.

OR IN OTHER WORDS Do a total thermal balance around the column.

 

[25362]

As a short example:

http://www.hyper-tvt.ethz.ch/tvt_exercises/ms_exercise05.pdf

 

[mbeychok]

.
The original poster(dramarc) asked if there was a "rule of thumb" for the energy consumption of a binary distillation. He also asked for a "simplified formula" for that energy distillation.

With all due respect, making a complete material and heat balance around the distillation is neither a "rule of thumb" nor is it a "simplified formula".

With all due respect again, the example at

http://www.hyper-tvt.ethz.ch/tvt_exercises/ms_exercise05.pdf

is neither "short" nor "simplified" nor a "rule of thumb".

The best response to the original poster is that "there is no such rule of thumb" ... which is what I tried to convey in my original response here.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[siretb]

I definitely agree with Milton: No rule of thumb or easy formula.
Best is to run a shortcut distillation program, knowing the VLE curve or, at the very least a meaningfull "relative volatility"