Chemical Engineering - Mass Transfer - Discussion

Total reflux in a distillation operation requires a minimum reboiler load, but it does not have any direct effect on the number of plates or the condenser load.

In a distillation column operating under total reflux conditions, all of the condensed liquid is returned to the column as reflux, and no product is withdrawn from the system. This means that the reboiler duty, which is the amount of heat required to vaporize the liquid that is fed back into the column as reflux, is at its minimum level. The reboiler duty increases as the degree of separation required in the column increases, and it is generally highest when the column is operated at its maximum product rate.

Total reflux means no over head product so number of plates minimum and condenser and reboiler load maximum.

Reboiler and condenser load increased and no of plate minimum.

As the reflux ratio is increased then; the reboiler has to evaporate more liquid and condenser has also to condense more vapour. So as reflux ratio is increased both reboiler and condenser load is increased.

Besides increasing the reflux ratio also increases the diameter of the column.

Condensed liquid send into the column is called reflux. Reflux ratio = L/D.

L= condensed liquid.
D = distillate products.
Reflux ratio is inversely proportional to the no of plate.

And by the guys its not maximum reflux ratio its only optimized or total reflux ratio.

Yes as the reflux ratio is maximum the amount of more volatile component entering the column from the top is maximum and the condenser has to do more work to condense the vapors, in reboiler the more volatile component increases and to vaporize that more amount of heat has to be supplied.

When Reflux ratio is Maximum, then load on condenser increases as condenser has to convert all vapors back into liquid phase without the extraction of overhead as product, rather it is completely sent back to the tower, thus increasing the load on condenser. Similar case is with re-boiler at this condition.

Therefore, Only thing that is to be right, the attainment of minimum no.of stages.

Minimum reflex = max.no of plates.
Max.reflex = Min. no of plates.

At R=1 you have minimum no.of plates.