Characterization of limestone calcination-carbonation for thermochemical energy storage applications

Concentrating Solar Power (CSP) systems represent a growing market to exploit solar energy thanks to the easy integration with energy storage systems. The thermochemical storage (TCES) technology 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 meant 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 recall the ones of the CCS/U CaL. Our idea is to perform a CaL-TCES cycle working in an open loop configuration by coupling the system with a CO2 emitting industry. In this way, the calcination can be accomplished under air atmosphere at lower temperature, thus reducing the sintering phenomena and preserving the material reactivity. In this work, 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 regenerated sorbents have been investigated by chemical physical analyses. The results obtained have been eventually compared with those obtained under CCS/U CaL calcination conditions to scrutinize the potential advantages of working in an open loop configuration.