Liquid air energy storage with effective recovery, storage and utilization of cold energy from liquid air evaporation

Abstract

Liquid air energy storage (LAES), as a promising grid-scale energy storage technology, can smooth the intermittency of renewable generation and shift the peak load of grids. In the LAES, liquid air is employed to generate power through expansion; meanwhile cold energy released during liquid air evaporation is recovered, stored and later utilized for air liquefaction enhancement. However, it is challenging for effective cold recovery from liquid air in the evaporator and cold utilization to compressed air in the cold box. The current cold recovery fluids are exergy-inefficient, and thus the most suitable cold recovery fluids should be determined. In this paper, a practically dynamic LAES system with cold/heat storage packed beds is studied from the startup to stability. Some common cold recovery fluids, such as air, propane, and methanol/propane, are investigated and compared in terms of heat transfer characteristics in the heat exchangers (i.e., evaporator and cold box) and cold storage packed bed. Simulation results show that using pressurized air (10 MPa) as cold recovery fluid results in high heat transfer coefficients in the heat exchangers and cold storage packed bed. Compared to other fluids, the pressurized air leads to a larger exergy efficiency of 78.2% in the cold box, and a comparable exergy efficiency of 89.6% in the evaporator. It is found that pressurized air and methanol/propane are both good cold recovery fluids in view of the heat transfer performance in the cold box and evaporator, achieving similar idealistic round trip efficiency of 53%. However, the consideration of exergy destruction in packed beds will decline the round trip efficiency to 43% for pressurized air and 38% for methanol/propane. The cold storage packed beds with methanol/propane as cold recovery fluids are easier to be penetrated by thermoclines at the same size of pebbles, which causes a lower round trip efficiency. This study gives new insights into the effective cold recovery, storage and utilization process of LAES for industrial applications.