Solar absorptance of fly ashes cycled in oxidizing and non-oxidizing high temperature conditions

Abstract

Storage of energy as sensible heat in solid particles is an increasingly viable strategy for the next generation of commercial concentrating solar power installments. However, additional strategies are needed to preserve particle stability and solar absorptance capacity of particles under high temperature cyclic conditions. Furthermore, identification of a low-cost substrate is necessary for lowering both the cost and the environmental impact of the production of new TES particulates. While several parameters, including heat capacity, density, and particle size must be considered for TES media, this study addresses critical knowledge gaps related to the identification of TES particulates and the impact of thermal atmosphere on particulate solar absorptance, which is a necessary, though not sufficient parameter that must be optimized for TES media. This work demonstrates that the thermal stability and solar absorptance of revalorized coal fly ash TES particles can be enhanced at high temperatures by exposure to an argon environment. Thermal cycling of ashes in argon at temperature of 800 °C and 1000 °C results in the preservation of ash microstructure as observed using SEM, and an increase in solar absorptance of between 3 % and 12 %, and between 6 % and 21 % over atmospheric environments, respectively. These results provide evidence that considerable enhancements in certain properties salient for TES may be achieved under inert atmospheres, and that fly ash in particular may be optimizable for TES purposes. Study results also suggest that next generation CSP plants should consider operational designs which support inert atmospheres for TES and/or heat transfer media.