Transient Modeling And Analysis Of Supercritical Carbone Dioxide Brayton Cycle

Supercritical Carbon Dioxide(sCO2)Brayton cycle has the characteristics of high energy density,compact structure,and simple layout,especially its high thermal efficiency in the range of 450-700°C(compared with the current energy conversion system).The advantages make it the recommended energy conversion system for GEN-?.However,the current sCO2 Brayton cycle is still in the research level,and the domestic cyclic transient simulation analysis program has not been developed yet.In this paper,the sCO2 recompression Brayton cycle transient simulation system was built and related research on the sCO2 recompression Brayton cycle is carried out.A 10MW sCO2 recompressed Brayton cycle was established with Modelica language,and the main components of the compressor,turbine,heat exchanger,etc.in the cycle were modeled separately.The efficiency of the turbine mechanical model was revised and optimized based on the characteristic curve of turbine machinery in the sCO2 cycle built by the Sandia National Lab.The steady-state analysis of cyclic variable conditions was carried out.The influences of cycle input power and circulation mass flowrate were introduced.Components temperature,power and cycle efficiency are affected.The results show that the fixed turbomachinery efficiency has a huge impact on the cycle results.Consideration of turbine mechanical characteristic curve modeling helps improve cycle results.The heat exchanger has a large proportion in the cycle exergy loss,and its heat transfer capacity has a significant influence on the efficiency of the cycle.Optimizing the components of the heat exchanger helps to increase the efficiency of the cycle.The changes in input power and circulating mass flowrate hace a direct impact on the cycle efficiency.When the circulating mass flowrate increases,increasing the input power can effectively increase the cycle net power and the efficiency.When the circulating mass flowrate decreases,increasing the input power has little effect on the efficiency.When the input power decreases,reducing the flow can increase the net power and efficiency of the cycle.Transient response analysis and control strategy comparisons were performed on the 10MW sCO2 recompressed Brayton cycle transient simulation system.The results show that:when the input power reduced by the same magnitude,the faster the speed of reduction the more oscillations came out in the components and greater loss to the components.When changing the cycle condition,a slower speed change helps maintain the cycle stability.The faster the mass flowrate at the inlet of the maincompressor changes,the more obvious the mass flowrate and temperature oscillations of the circulating components are.It can speed up the system reply steady rate effectively with a manner of first fast then slow down when increasing the mass flowrate.