Comparative analysis of compressed carbon dioxide energy storage system and compressed air energy storage system under low-temperature conditions based on conventional and advanced exergy methods

Abstract

It is of great significance to determine the main source of exergy destruction for the optimal design of the high-efficiency energy storage system. In this paper, conventional exergy analysis and advanced exergy analysis methods were adopted to analyze the exergy destruction in the low-temperature Compressed Carbon dioxide Energy Storage (LT-CCES) system and low-temperature Compressed Air Energy Storage (LTA-CAES) system under the same system configuration as well as key parameters. Conventional exergy analysis is a commonly used method to show the exergy destruction in system components, while advanced exergy analysis takes into account the interactions between system components as well as the technical limitations of each component, and can get more detailed exergy destructions in system components. The results showed that, according to conventional exergy analysis, the exergy efficiency of the LT-CCES system was 56.28% and the exergy efficiency of the LTA-CAES system was 63.93%, indicating that the exergy destruction in the LT-CCES system was larger than that in the LTA-CAES system. In terms of components, the cold energy storage tank (CEST) had the largest exergy destruction, accounting for 30.97% and 32.23% of the total exergy destruction in the LT-CCES system and LTA-CAES system respectively. According to advanced exergy analysis, in both systems, the major exergy destruction in each component was the endogenous exergy destruction, implying the importance to optimize components themselves. In terms of the avoidable exergy destruction, the proportion of the CEST in the two systems were the largest (45.17% in LT-CCES and 44.51% in LTA-CAES). According to the results of conventional and advanced exergy analyses, in the LT-CCES system, CEST should be given the first priority for optimization, followed by turbine2 and compressor1, while in the LTA-CAES system, CEST should be given the first priority for optimization, followed by turbine1 and turbine2.