Cryogenic energy storage characteristics in cascaded packed beds

Energy storage is a key technology required to utilize intermittent or variable renewable energy sources such as wind or solar energy. Liquid air energy storage (LAES) technology has important research value because of its advantages of high energy density and free construction from regional restrictions, and the high efficiency and stable operation of the cold thermal storage subsystem is of great significance for LAES application. Therefore, this paper experimentally studies the operating characteristics of the cryogenic energy storage device in the LAES system. By using a cascaded packed bed to store cryogenic energy in different temperature ranges, different flow rates of fluids with different specific heat capacities can be distributed. Hence, the temperature difference between the heat transfer fluids can be reduced, thereby improving the energy and exergy efficiencies. In this study, the experimental system and operating procedures are detailed herein. The pressure drop correlation of the packed beds under the combined influence of density gradient and frictional losses is obtained. The variations in the temperature fields in the charging and discharging processes are revealed, and the energy and exergy efficiencies are calculated to be 93.13 % and 85.62 % with 0.25-h preservation, and 90.46 % and 76.98 % with 4-h preservation, respectively. The exergy loss mechanism of the packed beds during the holding process is revealed. It is found that axial thermal conduction exergy loss accounts for 21.65 % and 7.04 % of the total loss in the packed beds in the full- and low-temperature regions, respectively.