SYNTHESIS OF FLEXIBLE HEAT-EXCHANGER NETWORKS .1. CONVEX NETWORKS

A new methodology for the optimal synthesis of structurally flexible heat exchanger networks is presented. Since the stream supply temperatures are specified by ranges rather than fixed values, the sought network design must be able to reach the target temperatures for any realization of the uncertain parameters. Moreover, it should always require a minimum utility consumption. To this end, an optimal heat recovery strategy is derived by using the notion of transient and permanent process streams. Based on it, a novel version of the heat cascade which assumes a continuous pinch behavior is developed to determine: (i) the heat recovery targets to be achieved by the network; and (ii) the dominant pinch temperatures constraining the heat exchanges and defining the problem subnetworks. They constitute the building blocks of an MILP mathematical formulation through which a structurally flexible network featuring the least number of units is found. Unlike prior attempts, a feasibility condition handled as a model restriction eliminates the need for flexibility tests. A couple of examples involving convex pinch domains have been successfully solved in a short computer time. This shows a slight increase with the number of uncertainties. The method has been extended to the synthesis of nonconvex networks in Part II. © 1990.