Part 4 contains the surprising truth that gives pass-through distillation its real energy saving potential. In a nutshell, gas absorption changes the state of the absorbed gas into a liquid; consequently the latent heat of evaporation must be rejected (as in a condenser). But this heat may be at a higher temperature than the contents of the evaporator. An appropriate heat exchange system then can supply the evaporator’s heat needs from the absorber. If this is done, we get the first boil-up “for free”.
We learned in part 3 that the second boil-up can use multiple effects to reduce energy consumption by 50%. So the combined energy use of the first and second boil-ups is 0 + 50% = 50% of conventional distillation.
I have found no instructive videos on Youtube to aid here,