Optimization Of Economic And System Reliability For Heat Exchanger Networks Based On NSGA-Ⅱ Algorithm

Heat exchanger network(HEN)synthesis is an important research area in process system engineering(PSE).It is of great importance for industrial energy saving.The design of HEN has traditionally been driven by economic objective functions,such as heat exchange area,utilities and total annual cost.With the growing interest in developing sustainable design strategies,other objectives(e.g.,reliability,environmental impact,and flexibility)has been used in HEN synthesis.Though considering multiple objectives during HEN synthesis has been developed,most researchers ignore the reliability for the purpose of simple solution procedure and simplifying the model.Therefore,based on stage-wise HEN superstructure that can split,it is proposed that multi-objective MINLP model involve economy and reliability as objective functions.In order to obtain solutions that coordinate both economic and system reliability objectives,the NSGA-Ⅱ algorithm is applied to solve the multi-objective problem.The MINLP heat exchanger networks established in this work includes two objective functions: HEN economics in the form of TAC and system reliability based on the superstructure by Yee and Grossmann,which is divided into stages and any match of process streams is allowed by stream splits in each stage.Non-isothermal mixing of splits at the exit of any stage is considered and the established model doesn’t rely on pinch technology.In this work,focus is given to the system reliability of the entire network based on the matching patterns of HEN.According to the connection sequence matrix based on the HEN structure,the max irrelevant sub-networks can be identified by merging the relevant sub-networks.The max irrelevant sub-networks are the weakest part of the network,which represent the system reliability of the whole network.The program that using NSGA-Ⅱ algorithm for HEN multi-objective optimization is built.It is proposed the generation strategy that produces effective feasible initial solutions and the repair strategy that repair infeasible variables.The variables need to be optimized are heat capacity flow rate of hot and cold stream and the heat load,and the optimized HEN structure are searched by system reliability.The evolution operators(fast non-dominated sorting,elitist,crowding distance)are modified to fit better for the established multi-objective model.The evolution individuals with lower total annual cost under specific system reliability are conserved during solution procedure.Three case studies from literatures are used to assess the applicability and performance of the optimization formulation and solution algorithm.The system reliability is enhanced with the total annual cost closes to the reported minimum.Case 1 optimize both objectives by total annual cost decreased by 2.91% system reliability increased by 8.42%.For case 2,the chosen optimal solution enhances system reliability by 8.42% with TAC increased by 2.87%.For case 3,system reliability is significantly enhanced by 24.89% with a small increase in TAC(1.88%).It demonstrates that total annual cost and system reliability is not always mutually conflicting and the balance of this two objectives can be obtained.It is confirmed the benefit of solving the MINLP model with NSGA-Ⅱ algorithm.The optimal solutions can aid in the selection of the network configuration and provide multiple selections.The proposed approach can be extended to include other objectives by multi-objective optimization(e.g.,sustainability,environment influence and safety).