Dynamic Simulation of a Binary Distillation Column

Consider an ideal equimolar binary mixture of benzene and toluene at . This mixture, with a thermal quality equal to 0.5, is fed to a 10-stage column with a total condenser and partial reboiler. The feed stage is stage 7. The feed flow rate is taken equal to . Up to time , the reflux and reboil ratios are and , respectively. At times above , the column is subject to a step in the reflux ratio, , while is kept equal to .

This Demonstration computes the dynamic behavior of the distillate and bottom compositions (e.g. benzene mole fractions). It can be seen that an increase in the reflux ratio causes a simultaneous increase in distillate purity at the expense of a decrease in bottom composition purity.

Similarly, one can easily extend this study to see the effect of a step in the reboil ratio, .

For the purpose of simplicity, the molar holdups of the condenser, reboiler, and plates are assumed constant, and equal to , , and , respectively. As an alternative route, one could use the Francis weir formula in order to compute time-dependent molar holdups.