Modeling And Simulation Of Supercritical Carbon Dioxide Brayton Cycle Generator Set

Based on the requirements of energy saving and emission reduction and green development,looking for both environmental protection and energy saving power generation technology has become the research direction of many scientists.In recent years,due to the mature manufacturing technology of turbine machinery and compact heat exchanger,the research of supercritical carbon dioxide（S-CO₂）Bretton cycle has become a hot field again.S-CO₂ Brayton cycle power generation technology is considered as an alternative to Rankine cycle technology due to its advantages of high efficiency,flexibility,economy and environmental protection.The study of S-CO₂cycle in China is still in the early stage.In order to further study the S-CO₂ cycle system and to build the future test bed,it is necessary to conduct a detailed study and analysis of the S-CO₂ dynamic cycle.Firstly,this paper discusses the characteristics of six S-CO₂ dynamic cycle layout modes,and uses Ebsilon software to establish three typical S-CO₂ Brayton cycle system models,which are simple regenerative cycle,recompression cycle and partial cooling cycle.The system structure selection under different working conditions is analyzed.The S-CO₂ recompression Brayton cycle system is taken as the research object.The effects of turbine inlet temperature and pressure,main compressor inlet temperature and pressure and compressor shunting coefficient on the thermal efficiency of the cycle are studied in detail.Then,considering that the utilization of waste heat can improve the Cycle efficiency,the S-CO₂/ORC combined Cycle was formed based on the S-CO₂ Brayton Cycle coupled with the Organic Rankine Cycle（ORC）.The structure selection of the combined circulation system under different working conditions is discussed.The type of ORC cycle working medium was determined by the characteristics of waste heat and the physical properties of the working medium.Then,the influence of the maximum temperature and pressure parameters of the system cycle,the efficiency of the precooler,the split ratio and other parameters on the combined cycle efficiency was studied,and the optimization direction of the system was obtained.Finally,in terms of multi-objective optimization calculation,this article takes the S-CO₂ and compression efficiency of the power cycle system,investment return period as the objective function,with turbine inlet temperature and inlet pressure as decision variables,maximizing efficiency,minimize the investment return period,using BP and GA algorithm,the multi-objective optimization model was constructed,fast accurate prediction efficiency curve for optimization.The proportion of the objective function is changed according to the actual demand,and the optimization results are obtained by quantitative calculation.When the weights of the two objective functions are 1/2,the optimal turbine inlet temperature and the optimal turbine inlet pressure of the S-CO₂ recompression dynamic cycle system are 618.52℃and 29.77MPa.This idea provides a basis for the selection of operating parameters for the future S-CO2 Brayton cycle power plant under the best operating conditions.