Multiple-feed, pure-product separation system synthesis

Abstract

The multiple-feed, pure-product separation system synthesis problem is identified as a distinct subproblem of process synthesis. The combinatorial structure of the problem is examined; analytic expressions are found for the resulting numbers of possible distinct intermediate streams and separators. The number of separators increases polynomially with the number of components, but exponentially with the number of feed streams. This limits exhaustive solution methods such as dynamic programming to small instances of this problem. A general approximate solution method is presented which is based on a pseudo-random search technique. The structure of the problem leads to a conceptually simple method of flowsheet selection. Very good flowsheets are found with a reasonable sample size. Due to the absence of shortcut methods for evaluating multiple-feed separators, we used a process simulator to find the cost of the candidate flowsheets.