Solar Reduction of Cobalt Oxide Particles: Rotary Kiln Reactor Model and Experimental Results
Solar Furnace Research
A solar rotary kiln reactor was analyzed numerically to determine how efficiently it utilizes concentrated solar energy to reduce Co3O4 to CoO as a function of reactor operational parameters, including the rotation rate, the feed rate of Co3O4, and the solar power. The solar thermal efficiency, defined as the fraction of solar energy used to drive the reduction reaction, is calculated using an axisymmetric, finite-volume model of the rotary kiln reactor. The model iteratively solves the nonlinear, coupled energy and species equations accounting for conduction heat transfer, volumetric and surface radiation heat transfer, and cobalt oxide reduction kinetics within cloud of cobalt oxide particles that moves through the reactor in a plug flow. Radiation is simulated using Monte Carlo Ray Tracing, and the reduction kinetics follow the shrinking core model. For a cloud of 15 micrometer-diameter particles with a volume fraction of 10-5, we show an optimum solar thermal efficiency of 27% with a Co3O4 feed rate of 3.6 kilograms per hour and 3.5 kilowatts of solar power. At this optimum operating point, we show the temperature and conversion fields within the reactor. Furthermore, the results of a preliminary experiment are shown and provide experimental evidence of the promise of the solar rotary kiln reactor: 18% of the Co3O4 was reduced to CoO.
Greenhagen, Jesse R.; Hoeniges, Jack D.; Kopping, Samantha J.; and Venstrom, Luke J., "Solar Reduction of Cobalt Oxide Particles: Rotary Kiln Reactor Model and Experimental Results" (2016). Symposium on Undergraduate Research and Creative Expression (SOURCE). 579.