Distillation column sequencing using marginal price

We introduce the concept of marginal price, the change in price of a separation task as a result of performing it in the absence of nonkey components. Marginal price can be computed using any metric that reflects process economics: vapor flow rate and total annualized cost are typical examples. We use this concept to develop some very simple evaluation functions based on Underwood's method which can then be used to explain some of the heuristics used for distillation column sequencing. As an evaluation function, marginal price is an alternate form for the predictor cost function employed in the predictor-based ordered search procedure of Gomez and Seader. Numerous test problems indicate its effectiveness in controlling the search in distillation-sequence design problems, where it outperforms the other commonly employed heuristics tested