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 MW t 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 2 be over 260 kWh/m 3 with reasonable activities of the solids when storing CaO solids in the silo at around 813 K.

Experimental investigation and model validation of a CaO/Ca(OH)2 fluidized bed reactor for thermochemical energy storage applications

“…Recent research has been focused on the use of thermochemical energy storage (TCS) systems due to their theoretically larger energy storage densities and efficiencies compared to sensible or latent storage [4,8,9]. Basic reaction schemes for TCS systems, including the CaO/Ca(OH) 2 reaction couple, were already proposed in 1976 [10] but they are still at a very early R&D stage from the point of view of their practical development and experimental study at pilot plant scale [10][11][12][13][14][15][16][17]:…”

Gas–solid thermochemical heat storage reactors for high-temperature applications

“…Criado et al [84] predicted that a maximum net efficiency of 63% can be obtained for a proposed 100 MW th circulating CaO/Ca(OH) 2 system without utilizing the thermal energy from the condensation of water vapor.…”

Heat lost or stored: Experimental analysis of adsorption thermal energy storage

“…Heat loss is often neglected, especially in preliminary design studies. However, an in-depth evaluation requires consideration of heat losses during storage operation [5].…”