Heat Exchanger Network Retrofit Based On Performance Simulation

The heat exchanger network(HEN),as a sub-system for energy recovery and utilization in process industry,affects the energy efficiency and economy through the whole life cycle.Due to the unreasonable design and low energy conversion efficiency,the existing heat transfer network has great potential for energy saving and urgently needs to be optimized and upgraded.With energy and environmental issues increasing attention,the retrofit of existing heat exchanger network has become the principal solution to improve energy efficiency and reduce energy consumption in energy-intensive process industry.Reusing existing heat exchangers as much as possible to reduce the investment cost while increasing the heat recovery of HEN is the most effective method in the retrofit of existing heat exchanger network.The feasibility and rationality of the reuse of the old heat exchanger directly affect the correctness and economy of the retrofit decision.The reassignment of original heat exchangers result in an inevitable problem that the supply and demand of area is hard to be exactly equal.However,the deviations between the actual areas of existing heat exchangers and required areas by retrofitting are ignored in previous retrofit methods,which leads to errors in performance evaluation for the HEN retrofit alternatives and even gives infeasible results.Thus,a new methodology base on performance simulation for HEN retrofit is proposed in this paper,and the main research works are as follows:1.The mathematical model with performance simulation for HEN retrofit problem is established,which is based on the stage-wise superstructure with non-isothermal mixed stream splitting.By use of performance simulation,the influence caused by the deviations between the real area of the recycled heat exchanger and the heat transfer area required by retrofit is considered and evaluated.The performance of retrofitted HEN is accurately estimated.The infeasible or unreliable retrofit results are avoided.2.The objective function used in the optimization is to maximize the annualized retrofit profit.The complicated mixed integer non-linear programming(MINLP)problem is solved by genetic algorithm.A systematic solution strategy is proposed to obtain the optimal retrofitted heat exchange network.3.Based on the MATLAB and the GUI platform,software system used for HEN retrofit is developed,which can realize the functions of HEN retrofit based on performance simulation by parallel computing.The specific functions and operating procedures of the software are introduced though the case demonstration.4.For demonstration,four case studies from small-scale to large-scale HEN retrofit problems are carried out.Case studies show that the retrofit of an existing HEN can make a considerable retrofit profit and energy saving with a relatively short payback period of investment.The rationality and reliability of the data are verified by heat transfer calculation of heat exchanger.Compared with previous research results,the effectiveness and superiority of the proposed superstructure model and solving method are verified in this work.