Reflux and Reflux Ratio
Reflux is the ratio between the amounts of material that returned to the distillation column to the material that result at distillation. In order to increase the degree of separation and high purity, amount of liquid is returned to the column in addition to getting rid of heat making the column in thermal equilibrium case.
The remaining part at the bottom of atmospheric distillation will be sent to the vaccum distillation tower.