Flash distillation is not effective in separating
components of comparable volatility, or in obtaining
nearly pure components.
Schematics of the column operating at a finite reflux ratio R is shown in Figure 3.
This figure also contains summary of notation for flow rates and compositions of
various streams in the system.
If we want to obtain both near pure top and bottom
products, the feed plate has to be in the central portion of
the column. The bottom is called the reboiler.
Rectification in the section below the feed plate is called
stripping, the bottom product can be nearly pure B.