Carbonation Kinetics of Fine CaO Particles in a Sound-Assisted Fluidized Bed for Thermochemical Energy Storage

Abstract

The calcium-looping process, relying on the reversible calcination/carbonation of CaCO 3 , is one of the most promising solution to perform thermochemical energy storage (TCES) for concentrating solar power (CSP) plants. Indeed, CaO precursors such as limestone can rely on the high energy density, low cost, large availability and nontoxicity. In this work, the study of the sound-assisted carbonation of fine CaO particles (< 50 μm) for TCES-CSP has been furthered. In particular, a kinetic study has been performed to analyse the effect of the particular carbonation conditions to be used in TCES-CSP applications, i.e. involving carbonation under high CO 2 partial pressure and at high temperature. All the experimental tests have been performed in a lab-scale sound-assisted fluidized bed reactor applying high intensity acoustic field with proper frequency (150 dB–120 Hz). The carbonation kinetics has been analysed by applying a simple kinetic model, able to properly describe the fast (under kinetic control) and slow (under diffusion control) stage of the of the reaction. In particular, the reaction rate, the intrinsic carbonation kinetic constant and the characteristic product layer thickness have been evaluated, also highlighting their dependence on the temperature between 800 and 845 °C; a value of 49 kJ mol –1 has been obtained for the activation energy. Finally, a good agreement between the conversion-time profiles, evaluated from the applied kinetic models, and the experimental data has been obtained.