Calcium-looping for thermochemical energy storage in concentrating solar power applications: Evaluation of the effect of acoustic perturbation on the fluidized bed carbonation

In the framework of thermochemical energy storage (TCES) in concentrating solar power (CSP) plants, the calcium-looping (CaL) process, carried out in fluidized bed reactors, is receiving increasing research interest due to the high energy density and the extremely low price, nontoxicity, and wide availability of natural CaO precursors. One of the main open challenges in CaL is represented by finding solutions to the progressive decline in the CaO carbonation conversion with the number of cycles, which is due to the sorbent deactivation caused by sintering and pore-plugging. In this framework, the reduction of the CaO particles size has been reported to improve the carbonation conversion and, therefore, the achievable energy density, by maximizing the availability of the sorbent surface exposed to the gaseous phase and hindering the natural loss of CaO mutlicyclic activity. However, the use of fine particles in fluidized bed reactors is challenging due to agglomeration, channeling and plugging phenomena. In this work, the possibility to use a fine natural limestone (<50 μm) for CaL at TCES-CSP conditions in a fluidized bed reactor has been investigated for the first time. In particular, sound-assisted fluidization has been proposed as technique to allow the use of such fine particles in fluidized bed reactors, thus overcoming the strict limitation posed by particle size applicable in ordinary fluidized bed reactors. Ordinary and sound-assisted cyclic CaL tests at CSP-TCES operating conditions have been performed in a lab-scale fluidized bed reactor in order to study the influence of the application of high intensity acoustic fields on the carbonation performances. The effect of sound parameters (SPL and frequency) has also been highlighted.