Performance of an indirect packed bed reactor for chemical energy storage

Chemical storage systems (CS TES) are promising innovative routes to overcome the issue of the solar irradiation discontinuity, in order to make the CSP technology cost effective and with high energy density. The aim of the present work concerns the simulation of a TES system based on an indirect-packed bed heat exchanger (HX). The purpose is to investigate these types of configurations as few experimental and modelling data are available about practical applications. Given the possibility to use air both as reactant and HTF, the simulation was performed taking into account a spinel-based system characterized in a previous work, presenting low cost and toxicity and prepared with a size feasible for packed bed reactors. A symmetrical configuration was selected for the modelling and the calculation was carried out considering a 125MWth and a storage period of 8 hours. Firstly, considering the mass and energy balances for the discharging step, the minimum size of the heat exchanger was calculated and then, for the charging step, the HTF inlet temperature and mass flow were determined. By solving the relative 1D Navier-Stokes equations, the performances in function of the HX length over the charging and discharging time were modelled. Despite the necessity to use relatively high temperatures in the charging phase, the results show a good storage efficiency of the system considered.