Exergy destruction analysis of a low-temperature Compressed Carbon dioxide Energy Storage system based on conventional and advanced exergy methods

Abstract

Compressed Carbon dioxide Energy Storage (CCES) system is a novel energy storage technology, which provides a new method to solve the unstable problem of renewable energy. Since the CCES system using low-temperature thermal energy storage can avoid the technical difficulties from high-temperature thermal energy storage, the low-temperature Compressed Carbon dioxide Energy Storage (LT-CCES) system has more obvious application feasibility compared with the high-temperature energy storage system. As the research on energy conversion, transfer, and loss in CCES system under low-temperature heat storage is still missing, while it is important to understand the energy losses for the further optimization of this kind of system, in this paper, the conventional exergy analysis and advanced exergy analysis were utilized to analyze the thermodynamic characteristics of a LT-CCES system consisting of CO2 Brayton cycle, low-temperature thermal energy storage and cold energy storage, whose thermal energy storage temperature is below 200 °C. As the advanced exergy analysis takes into account the correlation between system components as well as the technical limitations of each component, exergy destruction can be split into more detailed parts (i.e., avoidable exergy destruction, unavoidable exergy destruction, endogenous exergy destruction, and exogenous exergy destruction), which makes the results of the advanced exergy analysis different from those of conventional exergy analysis. The results showed that, advanced exergy analysis pointed out that HEX3 should be given priority as endogenous avoidable exergy destruction in HEX3 was the largest, while the results from the conventional exergy analysis showed that HEX1 should be given priority. For all the components, the two methods indicated that the compressor should be given the highest priority for improvement, followed by the turbine. Besides, as the total exergy efficiency of the system was 55.3% under the real condition and the total exergy efficiency was 76.7% under the unavoidable condition, there was still room for improvement of the system. In brief, based on the advanced exergy analysis method, the real component that should be paid attention can be determined, which gives the designers a more profound understanding of exergy destruction in the LT-CCES system.