Design and performance evaluation of an energy storage system using CO₂-based binary mixtures for thermal power plant under dry conditions

Super-critical compressed CO₂ energy storage system (S-CCES) is a prospective approach to alleviate the imbalance between supply and demand on the grid, however, it is less attractive for application under dry conditions due to cooling problems. In this paper, a S-CCES for thermal power plants is proposed, and its inefficiency and uneconomical effects under dry conditions are overcome by CO₂-based binary mixtures. Firstly, five CO₂-based mixtures are selected; then, parametric analysis is performed to compare and evaluate pure CO₂ and CO₂-based binary mixture systems; finally, detailed thermodynamic and exergoeconomic data are presented. The results indicate that the round-trip efficiency decreases by 7.85% and the unit electrical cost increases by 7.85 $/GJ when the cycle minimum temperature increases from 305.13 K to 323.15 K for the pure CO₂ system. An appropriate molar fraction of added gas can reduce the sensitivity of CO₂-based binary mixture systems regarding cooling temperature, and the CO₂-Propane system achieves about 10% improvement in round-trip efficiency. The high-temperature heat storage heat exchanger should be considered foremost to further improve the economy and efficiency of the proposed system.