(592e) Minimum Capital Cost for a Heat Exchange Network Using the Ideas Framework

We live in an era of rapidly increasing energy costs and more strict and demanding environmental policies. During the last energy crisis, the concept of heat integration and the study of heat exchange networks (HEN) (systems of interconnected fluid containing-process streams that interchange thermal energy) were put forward as means of generating more energy efficient designs for chemical, petroleum and other processing plants. The main objective of a HEN is to enhance the heat recovery. Designing a viable HEN can thus become an optimization problem with various possible objective functions such as capital cost minimization (MCC), minimum utility cost, maximum yield, maximum selectivity, minimum total annualized cost (MTAC) and so on. Typically, a HEN problem is approached as a combinatorial problem, in which the cold and hot streams are attempted to be matched, further creating a HEN with a pre-established flowsheet that must be then solved. These conventional methods cannot guarantee global optimality.

In this work we present an approach to solving the minimum capital cost of a HEN using the Infinite-Dimensional State-Space (IDEAS) framework (Wilson and Manousiouthakis, 2000) to approach the optimization problem with the a MCC objective function that is a reverse convex function of a heat exchanger's heat transfer area. The feasible region is constructed by an infinite number of linear equations resulting in an infinite-dimensional linear program (ILP) whose solution guarantees global optimality. We will study several proposed examples (4SP1, 20SP1, 22SP1) using an IDEAS-based software developed at UCLA.

Keywords: IDEAS, Heat exchange network, optimization