Control structure selection for four-product Petlyuk column

Direct material coupling between column sections in distillation leads to energy efficient systems like the Petlyuk column but with more difficult control problems compared to conventional multicomponent distillation sequences. A control study of a four-product extended Petlyuk column operating close to minimum energy is reported here. We study the “ideal” case with all steady state degrees of freedom available for control, including the vapor split valves, which is required to achieve minimum energy under all conditions. Four decentralized control structures are proposed and tested against a wide range of disturbances. This work demonstrates also the use of the graphical Vmin tool which can be used to visualize the minimum boilup requirement for Petlyuk arrangements.