Modeling of a tubular solar reactor for continuous reduction of CeO2: The effect of particle size and loading on radiative heat transfer and conversion

•The continuous reduction of CeO2 particles is modeled in a solar tubular reactor.•The effect of particle size and particle loading are studied within the reactor.•The model couples the radiation, mass and heat transfer equations.•Increasing particle size changes the radiative transfer, favoring CeO2 reduction.•CeO2 particle loading at the reactor inlet should be kept close to 100 mg l−1.

A solar multi-tubular reactor for non-stoichiometric reduction of CeO2 is modeled under continuous operation. An aerosol, consisting on CeO2 particles and Argon, flows upwards through the reactor vertical tubes. Heat, mass and radiation transfer phenomena are efficiently implemented in an axisymmetric domain by using multi-mesh, multi-step, Finite-Volume and Monte Carlo methods. Reaction, particle diffusion, conduction, forced convection as well as radiation absorption, emission and anisotropic scattering are considered. The kinetic model for the non-stoichiometric reduction of CeO2 is taken from Ishida et al. (2014). Model results at steady-state focus on the effect of changing particle loading and diameter at different average residence times. For particle diameters of 1-20 μm, increasing particle size favors uniform radiation absorption, minimizing temperature gradients. Finally, for an outer tube surface temperature of 2500 K, a particle loading of 0.1 kg/m3 and average residence time of 30-60 s are recommended.