Noob Question - why condense vapor ?

[stevea]

I've been studying various plate column designs, and I am puzzled on an issue. Many/most designs take vapor off above the top plate and send it to a condenser. But the vapor has dramatically higher enthalpy (heat energy) than the liquid phase. We would leave a lot more heat in the still vs down the drain by taking liquid (not vapor) from a plate or thumper and reducing power to the bottom of column ? I suppose this implies an LM reflux arrangement generally.

If I'm calculating correctly the power saving for a vodka/gin operation is modest (~25-35%), but it's more like 60-80% in a whiskey column were we are cooling a lot more water. Am I missing something ?
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The fractronic control scheme seems kinda brilliant (tho' also complex). In this method, the heat added at the base of column, is controlled inversely to the pressure at the top of column. As pressure builds up this has an immediate impact throughout the column of decreasing vaporization due to increased pressure. For example at 2 bars (15psig) water boils at ~121C, and ethanol at 97.9C (so roughly a ~20C bump in BPs). The pressure/vaporization change happens at the speed of sound. Then a pressure sensor has to feed-forward to a steam/power control.

Of course pressure creates extra hazards.

Free download text with fractronic control described pg 234 fig 5.13
https://www.academia.edu/37954209/DISTILLATION_CONTROL

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