The separation of multicomponent mixtures with conventional distillation sequences is energy-intensive. The use of thermal coupling sequences provides a more-efficient alternative, although their industrial usage has been quite limited, because of the complexity of design methods and potential difficulties during operation. In this work, we study a direct thermally coupled sequence for the separation of ideal ternary mixtures and perform a comparative study of two different designs, one based on the tray structure of an equivalent conventional sequence and the other specifically considering the effect of the thermal coupling on tray distribution and operational flows. Using the singular value decomposition technique on open-loop transfer function matrixes, controllability indexes were obtained. The controllability indexes of both designs are of the same order of magnitude, which means that their dynamic responses are basically the same. Although additional studies of dynamic simulation under closed-loop conditions are necessary, our results indicate that the controllability properties are similar, and that the design that provides the smallest energy consumption should be favored.
Residue curve maps are used in the preliminary stages of azeotropic distillation problems to establish feasible separation targets. Their calculations involve an iterative procedure, because of bubble point determinations. In this work, a simplified method for the generation of residue curve maps is presented. The method is based on the use of a mean relative volatility, independent of temperature, that avoids iterative calculations. Several case studies are used to show the effectiveness of the proposed method.
The use of shortcut methods for the design of complex distillation systems provides preliminary structures that need to be updated, typically by a recursive use of simulations. Although this procedure is generally effective, it can be time-consuming. In this work, collocation techniques are used as part of the design of Petlyuk distillation columns for the separation of ternary mixtures. Once a preliminary design is generated by a shortcut method, collocation techniques are applied to refine the location of the interconnecting and sidestream product stages, as well as the flowrate values of interlinking streams. The proposed method gives a proper distribution of stages for the Petlyuk system. The final designs are easily obtained with the proposed methodology, with a significant lower effort than that required when preliminary designs are corrected using recursive simulations.
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