Solar Thermal Reduction of Cobalt Oxide: Reactor Model

Solar reactors are devices that collect concentrated solar energy from systems such as the solar furnace in the James S. Markiewicz Solar Energy Research Facility for the purpose of supplying high-temperature process heat to endothermic chemical processes. In order to efficiently utilize the concentrated sunlight, solar reactors must be designed to have a high effective solar absorbtance, to evenly distribute the solar energy to the chemical reactions within the reactor, and to minimize heat losses. Radiation heat transfer plays a central role in each of these design challenges. An accurate model of the radiation heat transfer is thus desired. In this study, we develop a model of the radiation heat transfer in a solar rotary kiln reactor designed to reduce cobalt oxide particles for the ultimate purpose of producing hydrogen from water. The rotary motion of the kiln mixes the cobalt oxide particles over the reacting volume in order to more evenly distribute the solar energy to the endothermic reaction. The heat transfer model, which is based on the Monte Carlo Ray Tracing (MCRT) technique, predicts the scattering and absorption of the solar radiation over the cloud of particles and the internal kiln surfaces. By including the VU solar furnace in the model, the model resolves the unique directional and spatial distribution of the concentrated solar energy entering the reactor. The radiation heat transfer model is coupled to a transient energy balance of the solar reactor that predicts the temperatures within the reactor. We show how the size and number of cobalt oxide particles mixed in the kiln volume affects the distribution of solar energy