- By controlling distillate-flow rate, the overhead composition can be generally kept constant despite of changes in feed composition.
- However, the concentration of bottom products does not change as feed composition changes.
- If feed plate is correctly located for a normal feed, a shift in feed composition means feed is now introduced too high or too low in the column, this tends to decrease the separation.
- The separation can be increased by using a higher vapor rate and higher reflux rate.
- Hence, from stedy-state point of view, both composition can be controlled by varying D/F & V/F independently.