Closed-loop Implementation of Optimal Trajectories in Batch Distillation

HECTOR JOSE MARIA ESPINOSA; LUIS MARCHETTI, JACINTO

Computer-Aided Chemical Engineering, 24

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Lugar: Amsterdam; Año: 2007; p. 799 - 804

During the last decade, several authors worked in the development of methods to cope with the different steps of the design and synthesis of batch distillation systems. Among these methods, conceptual models based on pinch theory have been successfully applied to determine quasi-optimal trajectories intended to obtain products with both purities and recoveries above a certain level while operating the column near the condition of minimum energy demand [1,2]. Once the quasi-optimal operation is determined, the practical implementation requires an appropriate control system adjusted to track the desired conditions while maintaining the light-component purity free from unfavorable disturbances. This work proposes a temperature tracking control system composed by an open-loop reflux ratio control plus a closed-loop correction for disturbance rejection. To adjust the closed-loop controller we use the referential dynamic reaction of the process and tuning rules [3] that, though they were originally developed for dynamics valid in the neighborhood of stationary operating points, under this strategy they are useful in the neighborhood of a reference transient evolution like those occurring in batch distillation columns. Previous successful experiences in tracking a desired temperature evolution of a bioreactor [4] motivate the present application. Here, the separation of the light component from its ternary mixture of alcohols is selected as case study. [1] Espinosa, J.; Salomone, E.; Iribarren, O., 2004, Computer-Aided Conceptual Design of Batch Distillation Systems. Ind. Eng. Chem. Res., 43, 1723-1733. [2] Brüggemann, S.; Oldenburg, J.; Marquardt, W., 2004, Combining conceptual and detailed methods for batch distillation process design. In: FOCAPO 2004, 247-250. [3] Ziegler, J. G.; Nichols, N. B. Optimum Settings for Automatic Controllers. Trans. ASME, 1942, 64, 759. [4] Marchetti, J. L., 2004, Referential process-reaction curve for batch operations. AIChE J., 50, 3161. Keywords: Batch Distillation, Conceptual Model, Process Reaction Method.