On Control of Distillation Columns with Input Multiplicity

In this paper, we report an input multiplicity behavior observed in the simulation of a practical extractive distillation column (tray) involving three components. Some tray temperatures, including the one selected for control, are nonmonotonic with respect to input variables such as reboiler duty and entrainer flow. Thus, for a fixed tray temperature, several input values are possible. Its implication for temperature control is discussed. It should be noted that the column temperature profile is monotonic.