Role of acoustic fields on the fluidized bed carbonation for TCES in CSP applications

Thermochemical energy storage (TCES) is considered as a promising technology to accomplish high-energy storage efficiency in concentrating solar power (CSP) plants. The high temperatures achievable by CSP are used to drive an endothermic chemical reaction, whose products are stored separately to be employed when needed for carrying out the exothermic reverse reaction, which releases the heat previously used. Among all the alternatives, the calcium-looping (CaL) process, based on the reversible calcination-carbonation of CaCO3, is one of the most promising solution due to the high energy density achievable and the extremely low price, nontoxicity, and wide availability of natural CaO precursors such as limestone. It is typically performed in two interconnected fluidized beds, one acting as carbonator and the other as calcinator. In particular, aiming at achieving high overall efficiency for TCES and electricity generation in CSP plants, carbonation would be carried out at high CO2 partial pressure and high temperature (around or above 800 °C), whereas, calcination could be performed at relatively low temperature (~700 °C). As regards the fast phase of the carbonation reaction, the use of fine particles (<100 microns) can be beneficial in terms of reduction of the intraparticle diffusion resistance on the reaction rate. However, the use of fine particles arises agglomeration issues caused by their intrinsic cohesiveness, which in turns would remarkably hinder the reaction efficiency due to poor and heterogeneous gas/solid contact and mass/heat transfer. In this work, sound-assisted fluidization has been used to improve the carbonation of fine CaO particles (<10 microns) at CSP conditions. In particular, CaL tests have been performed under ordinary and sound-assisted fluidization conditions in order to study the influence of the application of high intensity acoustic fields on the agglomeration of fine CaO particles. The effect of sound parameters (intensity and frequency) have been also highlighted.