A simultaneous optimization approach for heat exchanger network synthesis

Abstract: "In this paper, a mixed integer nonlinear programming (MINLP) model is presented which can generate networks where utility cost, exchanger areas and selection of matches are optimized simultaneously. The proposed model does not rely on the assumption of fixed temperature approaches (HRAT or EMAT), nor on the prediction of the pinch point for the partitioning into subnetworks. The model is based on a representation of a series of stages where, within each stage, potential exchanges between each hot and cold stream can occur. A simplifying assumption of using stage temperatures to calculate heat transfer area for stream spills allows the feasible space to be defined by a set of linear constraints.As a result, the model is robust and can be solved with relative ease. Constraints on the network design, e.g. no stream splits, forbidden matches, required and restricted matches, can be easily included in the model, as well as handling the case of multiple utilities. In addition, the model can consider matches between pairs of hot streams or pairs of cold streams, as well as variable inlet and outlet temperatures. Several examples are presented to illustrate the capabilities of the proposed simultaneous synthesis model. The results show that in many cases, heuristic rules such as subnetwork partitioning, no placement of exchangers across the pinch, number of units, fail to hold when the optimization is performed simultaneously."