Modeling And Performance Analysis Of Supercritical Carbon Dioxide Power Cycle System For Nuclear-powered Vessels

Equipment developing and technology upgrading of marine vessels is the top priority in the development of coastal defense,adopting nuclear reactor to power marine vessels is a clear direction for the future.At present,the widely used marine power plant of pressurized water reactor combined with steam cycle has relatively low thermal efficiency and limited further improvement.Developing an efficient and compact new power system is one of the most important technical approaches to improve the overall performance of mairne vessels.Supercritical carbone dioxide（S-CO₂）cycle within the temperature range of the reactor coolant outlet,has outstanding advantages of high energy conversion efficiency,compact system equipment and excellent security,and has great development prospects.In this paper,the S-CO₂power cycle is integrated with the marine nuclear reactor to establish S-CO₂cycle system for nuclear-powered vessels,and a systematic study of the comprehensive performance of the overall systems and their key components is carried out.In this study,four efficient S-CO₂power cycles（with recompression,intercooling,partial-cooling and reheating,respectively）were selected and integrated with four typical marine nuclear reactors including a lead-cooled fast reactor（LFR）,a high temperature gas-cooled reactor（HTGR）,a sodium-cooled fast reactor（SFR）and a pressurized water reactor（PWR）.16 groups of marine propulsion system consist of nuclear reactor integrates S-CO₂power cycle and their thermodynamic models were established.The influence of key parameters such as coolant outlet temperature,turbine inlet pressure,compressor inlet pressure,and cycle minimum temperature on cycle thermal efficiency of each system was analyzed.Based on the analysis results to optimize the cycle parameters,16 efficient operation schemes of S-CO₂power cycle for nuclear marine propulsion system was formed.The S-CO₂reheating cycle was selected as the optimal cycle system for each marine nuclear reactor by taking the cycle thermal efficiency as evaluation index,and the arrangement plan for marine propulsion systems of nuclear reactor integrated with optimal S-CO₂power cycle were proposed.Based on the above optimal propulsion system,the characteristics analysis of key components including turbines,compressors and heat exchangers was carried out.The effect of performance design parameters such as turbomachinery isentropic efficiency and regenerator minimum temperature difference on the cycle thermal efficiency was investigated,and the variation characteristics of the thermal power conversion process in each system under different operating conditions were analyzed.By constructing the three-dimensional numerical models of the printed circuit heat exchanger（PCHE）of straight linear and zigzag channels with a semicircular cross section,the influence of operating parameters such as the Reynolds number,inlet temperature,and outlet pressure of the working fluid,and structural parameters including channel diameter,bending angle and pitch were analyzed.The thermal-hydraulic characteristics of key heat exchange components（intermediate heat exchanger and low-temperature regenerator）of the optimal propulsion system were revealed,and the correlations of flow and heat transfer under different conditions were also proposed.The exergetic analysis model and volume calculation model were developed.Comprehensive evaluation indexes such as cycle thermal efficiency,exergetic efficiency and compactness were used to evaluate the performance of S-CO₂cycle system for nuclear-powered vessels.The exergetic efficiency of the optimal S-CO₂cycle system for LFR,SFR,HTGR and PWR was successively decreased,and the exergetic efficiency of all componets in each system is higher than 90%.The volume of the S-CO₂reheating cycle system is higher than that of the recompression cycle,and compared with HTGR,the cycle system is more compact when applied to LFR.The comprehensive evaluation results show that the system of optimal S-CO₂power cycle integrated with LFR has both high thermodynamic efficiency and compact structure,is very suitable for marine propulsion system.