Investigation of tank stratification in liquid air energy storage integrated to operating nuclear plants

Abstract

Due to the increase in renewable energy, the load-following capability of existing large nuclear power plants is required. To this end, recently, an alternative of operating a large-capacity energy storage system in connection with the power generation system of a nuclear power plant has been proposed. Among various energy storage technologies, liquid air energy storage systems are attracting attention because they can store large capacity energy and can be mechanically linked to the power generation system of nuclear power plants. Liquid air energy storage technology is a technology that stores liquid air in case of excess power supply and evaporates the stored liquid air to start a power generation cycle when there is an electric power demand. In this paper, a process that can be combined with a liquid air energy storage system in a nuclear power plant was proposed, and it was evaluated that a round-trip efficiency of 52% could be achieved through thermodynamic calculations. Furthermore, when liquid air is stored for a long time during operation in connection with a nuclear power plant, the problem of safety and performance degradation that can be caused or mitigated due to tank stratification was experimentally investigated. To investigate the tank stratification, first, the heat ingress was theoretically quantified with respect to changing vacuum level when the cryogenic tank was equipped with multi-layer insulation. Furthermore, the conditions under which stratification occurs were defined in terms of temperature and concentration, and based on this, the stratification stability ratio and the stability map were defined and evaluated experimentally. Through the above study, it was theoretically shown that the operation possibility is high and technically sufficient by connecting the liquid air energy storage system to the nuclear power plant. In addition, by utilizing stratification inside the liquid air storage tank, an operation strategy that can adjust the storage time of liquid air was newly suggested.