Directly irradiated fluidized bed reactor for thermochemical energy storage and solar fuels production

The path toward a greener economy is leading the world energy scenario to an ever-increasing use of renewable energy sources. Concentrating Solar Thermal (CST) systems are typically based on technologies in which solar energy, concentrated by means of optical sun tracking mirrors, is exploited to drive power cycles or sustain chemical processes. Integration of CST technologies with relatively inexpensive energy storage systems decouples the collection of solar radiation from its use, and thus greatly increases the dispatchability of thermal energy production. Huge research efforts are currently devoted to the study of ThermoChemical Energy Storage (TCES) systems, in which solar energy is used to perform endothermal chemical reactions featuring large latent heat, so as to store solar energy in the noble and stable form of chemical bonds and/or produce solar fuels. Since most TCES processes involve gas/solid chemical reactions, multiphase chemical reactors own a key role for the success of the TCES technology. In this study, a novel batch lab-scale fluidized bed reactor for TCES of concentrated solar power and solar fuels production was designed. The reactor targets at maximizing the collection of solar energy, withstanding the highly-concentrated flux typical of high-temperature CST applications and ensuring uniform temperature distribution of the reactive materials. An experimental campaign consisting in hydrodynamical and thermal characterization of the system under inert conditions was performed. Moreover, reactive tests aimed at TCES of solar energy were performed using limestone calcination/carbonation as model reversible reaction. Heating of the system was performed by means of a simulator of concentrated solar energy made of a 7 kWe short-arc Xe lamp coupled with an elliptical reflector. The hydrodynamical characterization disclosed the main features of the reactor and the possibility of establishing different regimes of operation. Thermal characterization revealed that reactor can be safely operated at temperature of over 1000 °C. Reactive tests proved the feasibility and reliability of the designed reactor toward chemical reactions aimed at TCES of concentrated solar energy and encourage future studies toward solar fuels production.