Simultaneous Optimization Method for Directly Integrating ORC with HEN to Achieve Exergy-Economy Multiobjective

Heat exchange networks (HENs) account for a large proportion of initial investment in process engineering. It is of great significance for energy recovery and cost saving to integrate organic Rankine cycles (ORCs) with HENs. However, the difficulty lies in how to get the optimum integration scheme. In the optimization, the organic working fluid and its operating parameters determine the performance of the ORC, and the system configuration scheme affects the heat transfer matching degree and economic performance. Therefore, they are all important variables that affect the energy utilization, irreversibility, and economy of the integrated system. It is necessary to optimize them simultaneously. In this paper, we take them as variables and propose a simultaneous optimization method for directly integrating an ORC with a HEN. The total exergy destruction (TED) and the total annual cost (TAC) are adopted as two objectives. To solve this complex multiobjective mixed integer nonlinear programming problem, a solving strategy based on e constraint method is adopted. We first determine two anchor points for obtaining Pareto Frontier. Then, the TED of integrated systems is equally divided into several intervals between the anchor points. Finally, a set of Pareto optimality is obtained by solving a series of optimization problems with TAC as a single objective until the end conditions are met. Two case studies are analyzed, and the results show that the proposed optimization method can effectively reduce the TED and TAC.