Effect of Molar Holdup on the Dynamic Response of a Binary Distillation Column

Consider a distillation column with stages, a partial reboiler, and a total condenser. The column is used to separate an equimolar nonideal mixture of ethanol and water. The feed, a biphasic stream with a quality equal to , enters at stage 8 at a rate equal to . The reboil ratio is constant, equal to . Suppose that the column is subject to a step in the reflux ratio.
This Demonstration performs a rigorous dynamic simulation of the column and plots the behavior of both the distillate and bottom compositions versus time. You can change the value of the molar holdups of the stages, the condenser, and the reboiler. As expected, changing the molar holdups does not affect the final value of the steady state. This is the typical result for nonreactive distillation columns. On the other hand, for reactive distillation columns, both the transient behavior and the final value of the steady state would depend on the selected values of the molar holdups. It is observed that if the molar holdups of the reboiler or the stages increase, it takes longer for the column to reach the new steady state. The effect of the condenser molar holdup is less pronounced for this case. The steady-state mole fractions are indicated by the colored dashed lines.


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[1] Z. Nasri and H. Binous, "Rigorous Distillation Dynamics Simulations Using a Computer Algebra," Computer Applications in Engineering Education, 2009. doi:10.1002/cae.20385.
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