Hello. I am using heat integrated distillation column. However, one of the column`s exergy efficiency is greater than 100%? I have seen a lot of literature but still unable to figure out.

Formula:

Exergy Efficiency = (Wmin)/Wm+dB

Wmin = Ed + Eb - Ef

dB = Ef - Ed - Eb - Qreb (1-To/Tb)

f = Feed

d = Distillate

b = Bottom

The reboiler of this column and condenser of other column (exergy efficiency of 91%) are heat integrated.