Structural flexibility for heat integrated distillation columns—II. Synthesis

Abstract

This paper considers the synthesis of systems of heat integrated distillation columns. The goal is to choose the configuration which has the maximum structural flexibility, a concept introduced in Part I of this series. In this work we consider only the simpler structures where columns are “stacked” one upon the other and where none of the tasks is multieffected. Two representations allow us to enumerate all the possible dominant constraint sets for such processes. Searching over dominant constraint sets is a much smaller search than searching over all alternative stackings. Under certain useful assumptions, these insights yield a particularly fast search algorithm for finding the better stackings by hand. The paper also shows how to write a more complete mixed integer linear programming model for this problem. This model includes column temperatures explicitly and thus allows constraints that limit the temperature ranges within which each of the columns must operate. It also permits the heat duty for each column to be a linear function of temperature. Examples illustrate each of the ideas.