Optimal recovery of thermal energy in liquid air energy storage
Zhongxuan Liu, Donghoi Kim, Truls Gundersen
Abstract
The increasing share of renewables in energy systems requires energy storage technologies to handle intermittent energy sources and varying energy sinks. Liquid air energy storage (LAES) is a promising technology since it has a high energy density and is not geographically constrained. A relatively high round-trip efficiency (RTE) is obtained by using hot and cold energy recovery cycles in the LAES. In this work, seven cases related to different cold energy recovery cycles are optimized and compared for a standalone LAES system. Multi-component fluid cycles (MCFCs) and Organic Rankine Cycles (ORCs) are considered for the first time to be used as cold recovery cycles in the LAES. The optimal results show that the LAES system with dual MCFC has the best performance with an RTE of 62.4%. This RTE can be further increased to 64.7% by reducing the minimum temperature difference of high-temperature heat exchangers from 10 °C to 5 °C. Optimization results also indicate that ORCs used in the cold energy recovery system are not producing any work, and only phase change of the working fluid takes place, thus they should not be used. Finally, the exergy transfer effectiveness is applied to measure thermodynamic performance of the charging and discharging processes.