Abstract

A liquid piston system (LP) is proposed to recover energy during the discharge of a liquid air energy storage (LAES) plant. The traditionally used air turbine is replaced with an LP system which will expand the evaporated air to generate power. Moreover, an NH3 and transcritical CO2 cycle are integrated to enhance heat and cold utilisation. The integrated LAES system was modelled using gPROMS. The numerical results have a maximum discrepancy of less than 6.4% from experimental data previously reported in the literature. The round-trip efficiency (RTE) was studied for various scenarios, including the sensitivity to thermal oil flow rate and heat exchanger efficiencies. Additionally, the study examined the influence of several LP configurations and concluded with a comparison to a conventional LAES system. With a liquefaction pressure of 40 bar, the highest RTE reached was 37%, surpassing the conventional LAES system's 25% RTE at a discharge pressure of 25 bar. The heat utilisation was 96%, which doubles that of the conventional LAES system, while the cold utilisation was enhanced by 10%. Furthermore, the LP, NH3, and CO2 cycles thermal efficiencies were 88%, 19%, and 30%, respectively. A detailed energy assessment for heat and cold utilisation is presented.