This is a distillation step by step. This process don't start when the feed enter into the vessel (this is the main different with flash distillation), first the vessel is fill up to volume determinate. After that, it get heat, and the process start, until one of specific condition happen. This condition determinate the type of batch distillation
Consideration and main equation
The mixture R will be considerate in equilibrium with their vapors.
The distillation start when the temperature in R, is bit more than its boil temperature, however this temperature is considerated equal boil temperature, and change because the composition in R change.