Research On The Characteristics Of Combined Cycle In Distributed Energy Supply Systems

China has become the largest energy producer and consumer in the world.In order to ensure sustainable energy supply and energy security,the National Development and Reform Commission and the National Energy Administration have formulated the action plan for energy technology revolution and innovation(2016-2030)focusing on the development of "distributed energy,energy storage,industrial energy conservation,building energy conservation,transportation energy conservation,smart grid,energy internet and other technologies".Also,the distributed energy supply system is one of the four cutting-edge technologies in the energy field in the national medium and long-term scientific and technological development plan.It integrates the advantages of energy conservation,environmental protection,economy,reliability and so on,and gets more and more attention.This paper uses the methods of theoretical research,simulation,experiment and the integration technology to study the large-scale distributed energy supply system,marine(medium-scale)distributed energy supply system and small-scale distributed energy supply system based on dimethyl ether engine based on the projects of Beijing Natural Foundation,Central University Foundation,China-Denmark international cooperation and CSC Foundation.The coupling characteristics of the combined cycles and the cascade utilization of energy are studied.The main research results are as follows:Firstly,the working principle of the main components and the main cycle units in the distributed energy supply system arc studied.The integration principle of the distributed energy supply system is analyzed,that is,cascade utilization of energy and cascade utilization of physical energy and chemical energy.The coupling mechanism of high grade,medium grade and low-grade heat sources in the system is described.Secondly,the method of exergy analysis is considered to analyze the exergy destruction of main components in the large-scale distributed energy supply system with the gas turbine as prime mover.The irreversibility of energy destruction of the main components of the system is revealed.The results show that the exergy destruction is the combustion chamber(58.8%),followed by the solar collector(14.3%).By using the advanced exergy analysis method,the exergy destruction of the main components of the system can be divided into exogenous/endogenous,unavoidable/avoidable parts.It reveals the reason for the destruction from two aspects:the self-structure and the topological structure of the system components.Additionally,the concept of "instantaneous exergy destruction" is put forward,and the exergy destruction of the main components of the large-scale distributed energy supply system is hourly analyzed.Thirdly,the importance of DME in the future energy field is discussed and the reason for using DME as fuel of proposed systems is introduced.Moreover,the original DME production process is optimized.A novel green DME production system based on biomass gasification technology is proposed to increase the DME production.The conversion rate of carbon in biomass was increased to 90%.The characteristic of the marine distributed system based on green DME are analyzed.The system performance under different working conditions,different organic refrigerants and different fuels were compared and analyzed.The most suitable organic working fluids for the marine distributed system are selected.Besides,the capability of the Stirling engine and organic Rankine cycle for recovering waste heat of flue gas was compared.The results show that the recovery performance of the Stirling engine is better than that of the organic Rankine cycle at higher engine load and exhaust temperature.Then,the energy supply mode of cooling,heating and power in the small-scale distributed energy supply system based on the DME engine is introduced.The main thermodynamic parameters of the internal combustion engine in the system under part-load conditions are obtained by the experimental method.Also,the mathematical model of other main components in the system is established.Moreover,a hotel in Shanghai is taken as the research object to analyze the operating characteristics of the proposed small-scale distributed energy supply system in a typical summer day and typical winter day.Finally,the annual operating income and the annual net present value of the proposed system are taken as the evaluation indexes,the applicability and respective economy of the internal combustion engine and gas turbine used in the small-scale distributed energy supply system are compared.It shows that when the power output of prime mover is less than 2.8MW,it is better to choose an internal combustion engine as the prime mover.The area of the collector in the small distributed energy supply system is optimized using the method of multi-objective optimizalion considering the objective functions of annual average investment,primary energy saving rate and carbon dioxide emission reduction rate.The optimal collector area in this case study is obtained,which provides a theoretical basis for the design of similar systems.Besides,the price ratio coefficient of substitution of DME for diesel and natural gas is given:rD=1.47,rN=1.69.The price advantage of DME as fuel of distributed energy supply system is analyzed.