Limestone calcination-carbonation in a fluidized bed reactor/receiver for thermochemical energy storage applications

Concentrating Solar Power (CSP) systems represent a key technology to exploit solar energy thanks to the easy integration with energy storage systems. The thermochemical energy storage (TCES) relies on reversible chemical reactions to store the solar energy in the form of chemical bonds. Limestone calcination/carbonation is an appealing reaction for TCES. This cycle has been widely studied in the Calcium Looping (CaL) process for Carbon Capture and Sequestration/Use (CCS/U), within which the calcination is usually carried out in a CO2-rich environment at temperature of 940-950 °C. When the CaL cycle is considered for TCES, the energy required by the calciner is supplied by CSP and the whole system has to work in a closed loop, as the CO2 released during the calcination is required for the subsequent carbonation. Therefore, the operating conditions resemble those typical of the CCS/U CaL. The novel idea of this work is to perform a CaL-TCES cycle working in an open loop configuration, by coupling the system with a CO2 emitting industry. Calcination can then be accomplished under air atmosphere at lower temperature, thus preserving to some extent the material reactivity. In particular, the open loop CaL-TCES cycle has been experimentally investigated using a Fluidized Bed (FB) reactor directly heated by a solar simulator (3 MW m-2 peak flux, 3 kWth total power). Several looping cycles have been carried out on a commercial limestone sample to estimate the sorbent reactivity over cycling. The properties of calcined sorbents have been investigated by chemical physical analyses. A comparison with results obtained under CCS/U CaL conditions has also been performed, to scrutinize the potential advantages of working in an open loop configuration.