Particle mechanics and mixture homogeneity in a demonstration reactor system for the indirect reduction of redox particles

Many studies on two-step solar-thermochemical redox cycles for fuel production consider a combined receiver–reactor to perform the concurrent sub-processes of radiation absorption and reaction, which implies process limitations and increased technical complexity. Designed to circumvent this, an indirect concept uses an inert Al 2 O 3 particle cycle absorbing heat in a receiver and transferring it to the particulate SrFeO 3 − δ redox material in a common reactor. This Particle Mix Reactor (PMR) has been experimentally demonstrated and is investigated here in terms of particle mechanics by both measurement and simulation. With a newly developed tool for experimental particle bed segmentation, the spatial distribution of mixture homogeneity could be determined. DEM simulations – beneficial for the representation of dissimilar particle types – require mechanical contact parameters, that were obtained via an adapted systematic calibration procedure. Al 2 O 3 and SrFeO 3 − δ particles clearly differ in their results for similar collisions, especially concerning the rolling friction coefficient and the coefficient of restitution. Experimental results were reproducible, and no effect of temperature on mixture homogeneity could be identified. A significant improvement potential of mixture quality was revealed, with Al 2 O 3 to SrFeO 3 − δ particle mass ratios of about 3.5 for the upmost bed layer and of about 0.5 for the lower ones. Simulation results are satisfactorily consistent with experimental results, both qualitatively for particle motion, and for mixture homogeneity at a mean deviation of 26%. This makes the simulation model valid for further design and optimization purposes and facilitates the subsequent analysis of simulated temperature results. • Redox particles were mixed with solar heat carrier particles in a reactor prototype. • Mixture homogeneity was analyzed by a novel destruction-free segmentation technique. • Experiments were conducted at ambient and at elevated temperatures (up to 1100 ° C ). • A new DEM calibration method considers collisions of different particle types. • DEM simulations of the mixing process show good agreement with the experiments.