Thermodynamic study on a combined heat and compressed air energy storage system with a dual-pressure organic Rankine cycle

Compressed air energy storage (CAES) is a promising energy storage and supply technology. It has attracted attention due to its reliability, economic feasibility, longer operating lifetime and lower environmental effects compared to available storage technologies. A novel hybrid energy storage system, termed as CH-CAES-dORC, is proposed. It includes an advanced CAES, an electrical heater (EH) and a dual-pressure organic Rankine cycle (dORC). Our analysis demonstrate that integrating an dORC bottoming cycle for improving the round trip efficiency of the CH-CAES system is superior to a system relying on single-pressure ORC (sORC) system. Parametric analysis is carried out to study the effects of several key parameters on the system performance. The results indicate that the improvement of the CH-CAES round trip efficiency by means of integrating ORC bottoming cycles decreases with a higher charging pressure, and increases with a larger charge-discharge pressure ratio and a higher electrical heating temperature. The superiority of the CH-CAES-dORC, compared to the CH-CAES-sORC, is more pronounced at higher electrical heating temperature. There is always a peak round trip efficiency for the CH-CAES-dORC system with an increase in hot end temperature of low temperature evaporator under different hot end temperatures of high temperature evaporator. In other words, the dORC is a more favorable bottoming cycle for application of the CH-CAES waste heat compared with the sORC.