Comprehensive thermo-exploration of a near-isothermal compressed air energy storage system with a pre-compressing process and heat pump discharging

Compressed air energy storage (CAES), a technology that stores energy in the form of compressed air at times of excess supply and releases it to meet the higher demand in peak load periods, has been considered for numerous applications, most notably to support the electric grid for load leveling applications. Nonetheless, one of the downsides of CAES is the large energy losses incurred in the form of waste compression heat. Considering this issue, a novel CAES system integrating two separate compression process in sequence was proposed in this study. The near-isothermal compression pressurized the air from adiabatic pre-compression could enhance the thermodynamic performance of liquid piston and eliminate the generation of compression heat fundamentally. Through setting up a systematic model, the thermodynamic performance of the system was investigated in detail and the most outstanding advantage characterized with the efficient near-isothermal compressed air process within the liquid piston due to (after) the pre-compression was explored. For the comprehensive utilization of system energy, the intercooler, compressor, and expander were found to be the main contributors to exergy destruction and accounted for 25.8%, 17.3%, and 15.7% of the total exergy destruction, respectively. The significant effects of the liquid piston on thermal management led to the improvement in thermal performance. Moreover, with an optimum inlet pressure of liquid piston, the round-trip efficiency and exergy efficiency were achieved to be 62.6% and 55.4%, respectively, in actual operating conditions.