ANS:B - number of plates

Certainly! Let's delve deeper into why total reflux in a distillation operation requires minimum reboiler load, number of plates, and condenser load:

1. Minimum Reboiler Load:
   • In a distillation column, the reboiler is responsible for vaporizing the liquid feed at the bottom of the column.
   • During total reflux, all the condensed vapor from the condenser is returned to the top of the column. Since no vapor is withdrawn as product, there is no liquid feed to be vaporized in the reboiler.
   • As a result, the reboiler load is minimized because no additional heat input is required to vaporize liquid feed.
2. Minimum Number of Plates:
   • The number of plates in a distillation column determines the separation efficiency and the degree of purity of the product streams.
   • During total reflux, the rising vapor and descending liquid are in thorough contact with each other. This allows for maximum mixing and equilibrium conditions between the two phases.
   • Since all the vapor and liquid are in equilibrium, the composition of the liquid at each tray is identical to the composition of the vapor in equilibrium with it.
   • As a result, the need for additional plates to achieve separation is minimized because total reflux already ensures maximum separation efficiency.
3. Minimum Condenser Load:
   • The condenser in a distillation column is responsible for condensing the vapor exiting the top of the column into liquid form.
   • During total reflux, all the vapor from the column is condensed and returned to the column as reflux. No vapor is withdrawn as product.
   • Since there is no product withdrawal, the condenser only needs to condense the vapor without needing to provide additional cooling capacity to condense product vapor.
   • As a result, the condenser load is minimized because it only needs to condense the vapor without withdrawing any product.