Investigation of Charging and Discharging of Packed Bed Latent Heat Thermal Energy for CSP Applications

A two-dimensional numerical analysis is developed to investigate the charging and discharging characteristics of packed bed latent heat storage of a 10MWe power plant for concentrated solar thermal applications with a conversion efficiency of 0.25. The packed bed consists of a spherical shaped encapsulated phase change materials (PCM) and the bed is treated as a porous medium combined with Local Thermal Non-Equilibrium (LTNE) to carry out the analyses. Molten salt (NaNO3-KNo3) is used as HTF with a hypothetical PCM (58% Nacl-42% KCl). Parametric studies are carried out to get an insight on the effect of mass flow rate, inlet charging system and the geometry of the storage system. The maximum mass flow rate is found to be 179.57 kg/s. Energy stored in HTF is found to be 113 MJ and that stored in PCM is 307MJ. A single tank of height 8m and diameter 15 m is used for the study. The diameter of the ball is varied from 0.02m to 0.06m. The velocity of the inlet fluid is varied from 0.00135 m/sec to 0.004 m/sec. The potential of the latent heat thermal energy storage system to store and release energy is augmented by increasing mass flow rate and inlet charging temperature. The thermal performance of storing and retrieving energy increases with increasing mass flow rate and inlet charging temperature. However, storage system dimensions and porosity of the system has no significant effect on the overall effectiveness of the system with respect to the base case. The effectivedischarging efficiency can be augmented by increasing the PCT, reducing the molten-saltinlet velocity or reducing the particle diameter.