Synthesis of distillation configurations: I. Characteristics of a good search space

The exhaustive enumeration of all possible distillation configurations for zeotropic n-component feed mixtures into n nearly pure product streams leads to an exponentially large number of configurations, making the search for an optimal configuration intractable for even a modest number of components. To reduce the search space to a manageable level, we divide the column configurations into two categories: (i) Basic, configurations having (n − 1) distillation columns; and (ii) Non-basic, configurations having more columns. On exhaustively simulating multiple four-component feed conditions using Underwood's method for pinched columns, we find that for none of the simulated feed conditions does a non-basic configuration have a lower heat duty than the lowest heat duty basic configuration. Based on this observation, we assert that a much smaller search space containing only basic configurations should be sufficient to find an optimal n-component configuration. We also find basic configurations allowing non-sharp splits (ABC → AB/BC) have lower heat duty more often than those with only sharp splits (ABC → A/BC or ABC → AB/C). Finally, the heat duty reduction due to thermal coupling is found to be less when compared to non-sharp basic configurations as against sharp-split basic configurations.