Computational model of a Calcium-looping fluidized bed calcination reactor with imposed concentrated solar irradiance

The Calcium-looping process is a promising option for thermochemical energy storage in concentrating solar power plants. A crucial element of this process is the solar calcination reactor, where the endothermic reaction of CaCO3 calcination occurs with formation of CaO and CO2. The solar energy that is chemically stored in the reaction products can be retrieved by the exothermic reaction of CaO carbonation when needed. In this article, a new computational model is developed for the solar calcination reactor in this Calcium-looping process. The calcination reaction takes place in the riser of a continuous circulating fluidized bed that corresponds to an absorber tube exposed to concentrated solar radiation, which allows the reaction chamber to be indirectly heated. A core-annulus heat transfer model and a modified version of the Kunii-Levenspiel fluid dynamics model are used. In contrast to previous models found in the literature, the change in the mass flow rate of the species and in the density of the phases due to the reaction is considered. Simulation studies are performed with a fixed and imposed concentrated solar irradiance on the reactor wall, which varies in both the axial and angular directions. Wall conduction in the angular direction is also considered. The results show that nearly complete calcination can be achieved with a reactor of 4 m of height. A sensitivity analysis with respect to the model parameters and inlet conditions shows that the calcination conversion is mostly affected by the solids mass flow rate and the bed temperature at the inlet.