A novel isobaric adiabatic compressed air energy storage (IA-CAES) system on the base of volatile fluid

Adiabatic compressed air energy storage (A-CAES) is regarded as a promising and emerging storage technology with excellent power and storage capacity. Currently, efficiencies are approximately 70%, in part due to the issue of exergy losses during the throttling of compressed air. To increase the performance of the system, a novel isobaric adiabatic compressed air energy storage (IA-CAES) is proposed on the base of volatile fluid. The air storage vessel is divided into two parts by a piston, one part for air storage and the other has introduced into suitable volatile fluid. The waste heat is utilized to keep the volatile in a desirable pressure in discharging process, which impairs the effect of ambient temperature on pressure of volatile and makes the IA-CAES system stable. CO2 is selected as the pure volatile fluid own to its environmentally properties and high saturation pressure, while the IA-CAES system based on the CO2 can work in the mid and high latitudes only, due to its low critical temperature (304.13 K). 3 binary mixtures namely CO2/HC-600, CO2/HFC-32 and CO2/HFO-1234ze(E) are investigated to improve the critical temperature of CO2, trends to adapt to a wide range of ambient temperatures for IA-CAES system. The thermodynamic analysis including energy analysis, exergy analysis and the parametric analysis are evaluated by using steady-state mathematical model and thermodynamic laws. The calculations show, when CO2 is selected as the pure volatile fluid and the ambient temperature is higher than 288.15 K (15 °C), the average of total exergy efficiency (TEE) of IA-CAES improves more than 4% compared with that of A-CAES. When the waste heat is considered as free, the round trip efficiency (RTE) improved more than 6% and power capacity increased by more than 49% compared to the conventional A-CAES system. The CO2/HC-600 mixture with the compositions 0.85/0.15 has been proposed as the mixture volatile fluid. Compare with the conventional A-CAES system, the RTE and discharge time improved 6.26% and increased by 56.44%, respectively. Meanwhile, a parametric analysis is also carried out to evaluate the effects of several key parameters on the system performance of the IA-CAES systems.