Dynamic Evolution Analysis And Operation Optimization Of Exergy In Integrated Energy System Based On Energy Network Theory

With the continuous development of integrated energy services,there are a lot of researches on modeling and operation optimization of integrated energy system.However,most of the related studies only consider the first law of thermodynamics,and ignore the application of the second law of thermodynamics.In addition,the modeling method of integrated energy system does not pay enough attention to the physical mechanism of the system.This article reviews the development status of integrated energy services and integrated energy systems,the significance of exergy analysis and application in integrated energy systems,and the promotion of the Energy Network Theory to integrated energy system modeling and physical mechanism research.It also analyzes the domestic and foreign developments of "the study of the physical mechanism of energy transfer and conversion in the integrated energy systems" and "the study of integrated energy system modeling and dynamics analysis" which point out in combination with the second law of thermodynamics,the analysis and application research of the system from the perspective of energy quality(exergy)can point out the weak links in energy use,so as to truly improve energy utilization.Aiming at the analysis and application of exergy in the integrated energy system,this article starts from the following three aspects: 1)The modeling and analysis tools for follow-up research namely the Energy Network Theory are given;2)The dynamic evolution process of exergy in the integrated energy system is analyzed based on the Energy Network Theory modeling method;3)Based on the steadystate exergy loss analysis method,the steady-state operation model of the integrated energy system considering exergy is established,and a hybrid optimization algorithm combining generalized Newton-Raphson power flow solution and genetic algorithm with improved mutation probability is used for simulation solution.The specific work is as follows:Firstly,the paper introduces the Energy Network Theory in detail,including the theoretical system of energy network which includes two key points(unified modeling theory and dynamic behavior analysis of energy and exergy)and four key scientific issues,the energy network theoretical research methods which include the comprehensive analysis of multidisciplinary theories of mechanics,thermodynamics,electrical network,heat transfer,and fluid network based on axiomatic thinking,and the core concept of energy network which refines the core ideas of the two key points of the theoretical system.Then,combined with the two key points of the energy network theory system(unified modeling method and dynamic behavior analysis method of energy and exergy),the generalized expression of exergy in the energy network is given,and the dynamic evolution mechanism of the specific components of the system(including power network,thermal network,hydraulic network,induction motor and centrifugal pump)is analyzed.Taking the integrated energy system of 4-node power network coupled with 6-node thermal network as the model,the timevarying energy network equation is constructed.The state variables of the network are solved by using the fourth-order Runge Kutta method.The dynamic evolution of exergy in network and energy coupling elements and the exergy efficiency change of energy coupling elements are given.The weak links of energy consumption are analyzed,and the suggestions to improve the energy consumption of the system are given.Finally,the paper focuses on the exergy distribution with resistive elements(that is,the steady-state energy transfer process).Firstly,the categories of system exergy loss that includes internal exergy loss and external exergy loss in steady state are defined,and the universal exergy loss theorem is provided.Then,the steady-state exergy loss model of electric-heat-gas coupling system is written based on the proposed theorem,including power network,thermal network,hydraulic network,natural gas network,gas-fired CHP unit and gas-fired boiler.The dispatch model minimizing the exergy loss of the electric-heat-gas coupling system is proposed,and the model is solved by the improved mutation probability genetic algorithm with generalized Newton-Raphson power flow.The network state variables and the output of units are obtained when the system exergy loss are the smallest.The distribution of the exergy loss of the system is analyzed,and the size and proportion of the exergy loss is obtained.Besides,compared with the minimum operating cost based scheduling method,the necessity of the scheduling method considering the exergy is verified.Finally,the system component with the largest proportion of exergy loss is considered,and four kinds of evaluation indexes(total unit exergy efficiency,total unit energy efficiency,system energy loss and system exergy loss)are given.The influence of single change of different factors on the operation results of integrated energy system with exergy distribution is discussed.Through the exergy loss deduction and simulation analysis in this chapter,the degradation phenomenon of energy in the irreversible transfer process can be analyzed,which lays a solid theoretical foundation for improving the efficiency of integrated energy system.