Analysis of Minimum Vapor Flowrate Requirements for the Fully Thermally Coupled Distillation System with Postfractionator

In past few decades, thermally coupled distillation schemes, such as the fully thermally coupled distillation system (Petlyuk column), have been studied with particular interest because of the significant energy savings that have been reported with respect to the implementation of conventional distillation columns. A disadvantage of the Petlyuk column is that such savings decrease when a high purity of the intermediate component of a ternary mixture is required. Kim has recently proposed a Petlyuk column structure with postfractionator. This new structure has been shown to improve the thermodynamic efficiency of the separation sequence. However, because of the additional recycle streams, the design and simulation tasks of this system provide a more difficult problem than that of the original Petlyuk configuration.

This work presents an analysis on the degrees of freedom (DOF) for the Petlyuk system with postfractionator, and a set of design variables that meets such DOF is proposed. Also, Underwoodxs equation is used as a basis for the development of a shortcut design method to calculate minimum vapor flowrates.

Finally, one important problem for the solution of Underwood′s equation is the specification of values for flowrates and compositions for the postfractionator interlinking streams. We show an approach for the solution of this complex arrangement using a graphical McCabe-Thiele analysis.

References

Henley, E. J. and Seader, J. D., 2006. Separation Process Principles, Joh Wiley & Sons, Inc.

Kim, Y. H., 2006. A New Fully Thermally Coupled Distillation Column with Postfractionator, Chemical Engineering and Processing, 45, 254-263.

Underwood, A. J. V., 1948. Fractional Distillation of Multicomponent Mixtures, Chemical Engineering Progress, 44, (8), 603-614.