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

Abstract

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 Al2O3 particle cycle absorbing heat in a receiver and transferring it to the particulate SrFeO3 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. Al2O3 and SrFeO3 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 Al2O3 to SrFeO3 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.