Analysis of Geometric Parameters of Cold Packed Bed Energy Storage for Liquid Air Energy Storage Systems

Among large-scale energy storage systems, liquid air energy storage systems have gained a wide interest due to their advantages such as high energy density, not being geographically restricted, and being environmentally safe. An essential component that has a large influence on the performance of the system is the cold energy storage, which stores the cold energy rejected during air evaporation in the discharging cycle and transfers this cold energy to the air liquefaction stage in the charging cycle. The aim of this paper is to identify the optimal set of geometrical parameters for cold energy storage, consisting of a packed bed, maximizing the performance of the liquid air energy storage system and minimizing the cost of the cold energy storage unit. The packed bed was modelled using a transient one-dimensional model, while the rest of the components and the overall system were modelled using a steady-state zero-dimensional thermodynamic model. We analyzed the influence of the aspect ratio and diameter of the tank on the round-trip efficiency of the liquid air energy storage system and the total cost of the cold energy storage unit, while keeping the capacity of the cold energy storage constant. The results suggest that there is an optimum aspect ratio for each diameter of the tank for reaching the minimum cost for the cold energy storage unit. On the other hand, for each diameter of the tank, the value of round-trip efficiency keeps increasing by raising the aspect ratio of the tank. Nevertheless, by selecting the optimum aspect ratio concerning the minimum cost, there is a negligible penalty on the reduction of round-trip efficiency compared to its maximum value.