The impact of altering feed tray locations (for the purpose of saving energy) on the controllability of double feed reactive distillation (RD) columns is evaluated for two case studies: a hypothetical ideal RD column and a methyl acetate RD column. Energy savings of 18.3% and 36.4% over the conventional design (feed immediately above and below the reactive zone) is achieved for the ideal and methyl acetate systems, respectively. A steady-state bifurcation analysis shows that, for both systems, output multiplicity, with respect to reboiler duty, occurs at a fixed reflux rate for the different designs (conventional/altered feed tray location). The output multiplicity is eliminated at a fixed reflux ratio. Closed-loop dynamic simulation results show that the controllability of the internally heat integrated ideal RD column deteriorates, compared to the conventional design. Unlike the conventional design, temperature-based inferential control is infeasible and compositionbased control structures must be used. For the methyl acetate column, on the other hand, heat integration by altering the feed locations entails no loss in controllability using two-point temperature inferential control.
On a étudié la simulation en régime permanent des colonnes de distillation réactive à l'aide de la méthode de Naphtali-Sandholm (NS) classique. Les résultats pour les colonnes d'acétate de méthyle et de MTBE montrent que la méthode résout effi cacement les équations MEH hautement non linéaires. Dans le système MTBE, trois régimes permanents distincts sont obtenus alors que le facteur d'étapes de Newton diminue, passant de valeurs élevées à des valeurs faibles. On démontre également la polyvalence de cette méthode pour traiter des spécifi cations de colonnes différentes ainsi que son application pour des études de contrôle préliminaires. Une nouvelle caractéristique du présent travail réside dans l'inclusion de la conversion de la réaction comme une spécifi cation possible de colonne. La spécifi cation de la conversion de la réaction et la pureté des produits fournissent un moyen direct pour obtenir les conditions opératoires pour un fonctionnement de colonne avec une pureté et une conversion élevées.
Decentralized control system design is evaluated for a basic and an internally heat-integrated generic, ideal, double-feed, two-product reactive distillation system. The internally heat-integrated reactive distillation column (HiRDC) is obtained via catalyst redistribution into the rectifying zone and feed tray relocation. For basic regulatory control, three two-point control structures with a fixed reflux rate or a fixed reflux ratio operation policy are synthesized and evaluated for their closed-loop disturbance rejection characteristics using rigorous dynamic simulations. To eliminate the purity offsets for on-target product purities, product purity composition controllers manipulating the reflux ratio and stripping tray temperature set point are implemented. Reactive tray section composition control is necessary for on-target product purity operation of HiRDC.
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