408a New Insights In Distillation Design Via Column Profile Maps: Sharp Splits

Daniel A. Beneke, Diane Hildebrandt, and David Glasser. Centre of Materials and Process Synthesis (COMPS), University of the Witwatersrand, Private Bag 3, WITS 2050, Johannesburg, South Africa

In recent years there has been a renewed interest in the design of distillation processes. Holland et al. (2004 a, b) and Tapp et al. (2004) have recently introduced the use of Column Profile Maps (CPMs) to gain insight into complex distillation systems, and have also shown that separations that were previously thought infeasible are in fact feasible at certain operating conditions. They have also shown that CPMs are a simple topological transformation of Residue Curve Maps (RCMs).

CPMs are dependant on two main parameters: RΔ (reflux) and xΔ (a pseudo composition vector). This paper focuses on the interaction between these parameters for the special case of sharp splits. With the CPM technique it has been shown that sharp splits behave uniquely to non-sharp splits, so much so that by fixing the aforementioned parameters in a specific manner it may be possible to sample the intermediate boiler in an ideal system (i.e. constant relative volatilities) as a bottoms product. This is possible due to a “node bumping” phenomenon, which could allow for much more efficient designs in distillation. The effect of crossing the discontinuity region for ideal thermodynamics in CPMs has also been investigated. The discontinuity effectively changes the nature of stationary points, which might also be used to design more effective columns.

To summarize, this paper focuses on the use of CPMs to design distillation columns for sharp splits. The interesting behavior displayed by sharp splits can be of great use to the design engineer, in that many new, more efficient columns can be built.

References:

Holland, S.T., Tapp, M.; Hildebrandt, D. and Glasser, D., Column Profile Maps. 2. Singular Points and Phase Diagram Behavior in Ideal and Nonideal Systems, Ind. Eng. Chem. Res.,43(14), p3590-3603, (2004 b).

Holland, S.T., Tapp, M.; Hildebrandt, D., Glasser, D. and Hausberger, B., Novel Separation System Design Using “Moving Triangles”, Comp. and Chem. Eng.,29, p181-189, (2004 a).

Tapp, M., Holland, S.T.; Hildebrandt, D., and Glasser, D., Column Profile Maps. 1. Derivation and Interpretation, Ind. Eng. Chem. Res.,43(2), p364-374, (2004).