The Investigation On The Self-condensing CO₂ Transcritical Power Cycle

Under the background of fossil energy shortage and a series of environmental problems that fossil energy caused,the transcritical power cycle with CO₂ as working fluid has widely attracted the attention of scholars from various countries due to its high thermal efficiency and great development potential in the field of power generation.In the view of the disadvantage that it is difficult for CO₂ in the cooler to be condensed by conventional cooling water at30.0°C in CO₂ transcritical power cycle,it is of great significance to carry out the research on CO₂ transcritical power cycle.The self-condensing CO₂ transcritical power cycle avoids the research and development of compression component in the supercritical CO₂ Brayton cycle.Focusing on the self-condensing CO₂ transcritical power cycle,the study selects the solar thermal energy as the heat source and the LNK carbonate molten salt as the intermediate heat transfer medium.One of the most powerful mathematical calculation software---Matlab is used,and the theoretical research is carried out with the method of numerical calculation and theoretical analysis.?1?Based on the thermophysical properties of CO₂---low critical temperature,the problem that the working fluid in traditional transcritical power cycle is difficult to be condensed by conventional cooling water at 30.0°C is analyzed.Based on this problem,the self-condensing CO₂ transcritical power cycle is improved---adopting a way of embedding a refrigeration cycle in the simple transcritical cycle to achieve the operation of the cycle using conventional cooling water.Finally,the cycle is analyzed by theoretical method.?2?Focusing on the self-condensing CO₂ transcritical power cycle,the influence of cooled pressure on the cooling source,heat source and cycle parameters is studied under different final cooled temperatures.The range of the final cooled temperature,cooled pressure and condensing temperature are 31.0⁴0.0°C,7.5¹8.0 MPa,and 16.0³0.0°C,respectively.Then,aimed at the characteristics of low critical temperature of CO₂ and the problem that it is difficult for CO₂ in the supercritical cooler to be condensed to an excessively low temperature,the optimal working condition is obtained in the condition of 35.0°C of final cooled temperature,and the high thermal efficiency for solar thermal power generation is obtained.?3?The cycle is further optimized from the point of condensing temperature.At the same time,the corresponding optimal conditions at different condensing temperatures are given in the condition of 35.0°C of final cooled temperature.Finally,it is concluded that the thermal efficiency is the highest,and the corresponding cooling pressure is 8.8 MPa when the condensing temperature is 29.5°C.And the net power is the highest,the corresponding cooling pressure is 8.4 MPa when the condensing temperature is 30.0°C.?4?Based on the research and analysis,the thermal efficiency and the net power out of supercritical CO₂ Brayton cycle under the same conditions are given,and the reasons that the optimal thermal efficiency and the net power out of self-condensing CO₂ transcritical power cycle are lower than those of supercritical CO₂ Brayton cycle are analyzed.Lastly,considering various factors,the optimal working condition is obtained when the final cooled temperature is 35.0°C,the cooled pressure is 9.5 MPa,and the condensing temperature is25.0°C,the optimal condition for solar thermal power generation system is obtained.