A Short Note About Energy-Efficiency Performance of Thermally Coupled Distillation Sequences

Abstract

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING 139R&D NOTE D istillation is a widely used separation method in the process industries and it is the largest energy consumer among individual process units. Improvement of energy efficiency in distillation systems is still an active research field. Among the issues concerned with the improvement of energy efficiency of distillation systems, the optimal design and synthesis of multicomponent distillation schemes is still one of the most challenging problems. For optimal design of distillation systems of multicomponent separations, thermally coupled distillationIn this work, we present a comparative study of the energy-efficiency performance between conventional distillation sequences and thermally coupled distillation arrangements (TCDS) for the separation of ternary mixtures of hydrocarbons under the action of feedback control loops. The influence of the relative ease of separation of the feed mixture and its composition was analyzed. The feedback analysis was conducted through servo tests with individual changes in the set points for each of the three product streams. Standard PI controllers were used for each loop. The results show an apparent trend regarding the sequence with a better dynamic performance. Generally, TCDS options performed better for the control of the extreme components of the ternary mixture (A and C), while the conventional sequences offered a better dynamic behaviour for the control of the intermediate component (B). The only case in which there was a dominant structure for all control loops was when the feed contained low amounts of the intermediate component and the mixture had similar relative volatilities. The Petlyuk column provided the optimal choice in such case, which contradicts the general expectations regarding its control behaviour. In addition, the energy demands during the dynamic responses were significantly lower than those observed for the other distillation sequences. TCDS options, therefore, are not only more energy efficient than the conventional sequences, but there are cases in which they also offer better feedback control properties.On présente dans ce travail une étude comparative de la performance d'efficacité d'énergétique entre les séquences de distillation conventionnelles et les configurations de distillation couplées thermiquement (TCDS) pour la séparation de mélanges ternaires d'hydrocarbures sous l'action de boucles de contrôle d'asservissement. L'influence de la facilité relative de séparation du mélange d'alimentation et de sa composition est analysée. L'analyse de rétroalimentation est réalisée grâce à des tests d'asservissement avec des changements individuels dans les points de consigne pour chacun des trois courants de produits. Des contrôleurs PI standards ont été utilisés pour chaque boucle. Les résultats montrent une tendance apparente pour la séquence ayant une meilleure performance dynamique. Généralement, les options TCDS sont meilleures pour le contrôle des composantes extrêmes du mélange ternaire (A ...

Dynamic Behaviour of Thermally Coupled Distillation Arrangements: Effect of the Interconnection Flowrate

“…Recent research efforts have been conducted to understand the operational properties of thermally coupled configurations. The works of Wolff and Skogestad, 1995;Abdul-Mutalib and Smith, 1998;Hernández and Jiménez, 1999b;Serra et al, 1999;Serra et al, 2001;Jiménez et al, 2001;Segovia -Hernández et al, 2002a;Segovia -Hernández et al, 2002b;Serra et al, 2003;Segovia -Hernández et al, 2004;SegoviaHernández et al, 2005a;Segovia -Hernández et al, 2005b;Segovia -Hernández et al, 2005c;Alcántara -Ávila et al, 2006;Segovia -Hernández et al, 2006a;Segovia -Hernández et al, 2006b;Segovia -Hernández et al, 2007a;SegoviaHernández et al, 2007b, among others, have shown that some of these integrated options are controllable, so that the predicted savings in both energy and capital would probably not be obtained at the expense of operational and control problems.…”

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