Q1: In a distillation operation, what is the effect of the temperature of the reflux stream (given below) on the condenser and reboiler loads ?
Reflux conditions:
(i) Reflux stream is completely liquid and is at its bubble point.
(ii) Reflux stream is below its bubble point.

ANS:D - Both condensor and reboiler loads are higher in case (ii) as compared to case (i).

The reflux stream in a distillation operation plays a critical role in maintaining separation efficiency by providing a return flow of condensed vapor to the column. The temperature of the reflux stream affects the condenser and reboiler loads differently:

• When the reflux stream is completely liquid and at its bubble point (case i), it implies that the reflux stream is at its saturation temperature. This condition minimizes the energy required to condense the vapor back into liquid form, reducing the condenser load. However, since the reflux stream is completely liquid, it requires additional energy to vaporize it in the reboiler. Therefore, the reboiler load is higher in case (i) compared to case (ii).
• When the reflux stream is below its bubble point (case ii), it means that the temperature of the reflux stream is below its saturation temperature. In this case, more energy is required to condense the vapor back into liquid form, increasing the condenser load. However, since the reflux stream is partially vaporized, it requires less energy to be vaporized in the reboiler compared to case (i). Therefore, the reboiler load is lower in case (ii) compared to case (i).