Controllability analysis of thermally coupled distillation systems: Five-component mixtures

The theoretical control properties and dynamic responses under closed-loop operation of thermally coupled distillation sequences for the separation of five-component mixtures of hydrocarbons were compared to those of conventional distillation sequences. Seven thermally coupled arrangements were investigated: five thermally coupled distillation sequences with three recycles and two thermally coupled distillation schemes with two recycles. The preliminary steady-state design of complex schemes was obtained by starting from a conventional distillation sequences and then optimizing for minimum energy consumption [Calzon-McConville, C. J.; Rosales-Zamora, M. B.; Segovia-Hernández, J. G.; Hernández, S.; Rico-Ramírez, V. Design and Optimization of Thermally Coupled Distillation Schemes for the Separation of Multicomponent Mixtures. Ind. Eng. Chem. Res. 2006, 45, 724]. The control properties of the sequences considered were obtained by using the singular value decomposition technique at zero frequency. It was found that, in general, the coupled schemes present theoretical control properties similar to or better than those of conventional distillation sequences. This result was corroborated by using rigorous closed-loop dynamic simulations. As a result, one can conclude that the energy savings predicted for thermally coupled distillation sequences are achieved without introducing additional control problems if we assume constant pressure drops in columns.