Conceptual process design of a CaO/Ca(OH)2 thermochemical energy storage system using fluidized bed reactors

Abstract

This paper analyses a thermochemical energy storage process using a CaO/Ca(OH)2 chemical loop. A single circulating fluidized bed reactor is proposed to carry out the hydration-dehydration alternating reactions. During the energy discharge step, steam is fed to the reactor and used as a fluidizing gas and as a reactant with the CaO coming from a silo, enabling heat to be recovered at a sufficiently high temperature (around 743 K) from the hydration reaction taking place in the fluidized bed. During the dehydration of Ca(OH)2 (energy charging step), heat (i.e. from a concentrated solar field) is stored in thermochemical form as CaO by using steam as a fluidizing gas. A basic process integration scheme for a reference case with a power output of 100 MWt is analysed in this work, by solving the mass and energy balances during charging and discharging steps and by calculating the volume of the silos and characteristic dimensions of the fluidized bed reactor. The effective energy storage densities of the CaO silo is shown to be over 260 kWh/m3 with reasonable activities of the solids when storing CaO solids in the silo at around 813 K.