Abstract
Falling particle receiver systems, which utilize solid particles as the heat transfer medium, are a rapidly developing technology for concentrating solar power applications. Particles used in FPR systems must be resistant to changes in optical properties during long term exposure to high temperatures and thermal cycling in highly concentrated solar irradiance. Seven candidate particles were tested using simulated solar flux cycling and tube furnace isothermal aging: CARBOBEAD HSP, CARBOBEAD CP, CARBOBEAD MAX HD, CARBOBEAD Solar HSP, CARBOBEAD Solar CP, CARBOBEAD Solar MAX HD, and WanLi Diamond Black, where the first two are state-of-the-art particle compositions and the latter five are novel materials. A high-flux solar simulator with attenuating shutter was used to expose each particle candidate to 10,000 irradiation cycles to simulate a 30-year concentrated solar power plant lifetime. Irradiation of the particle surface was controlled via feedback from a pyrometer to establish maximum temperatures of 775 °C and 975 °C. Particle solar-weighted absorptance and emittance were measured at 2000 cycle intervals. Particle thermal degradation was studied by heating particles to 800, 900, and 1000 °C for 300 hours in a tube furnace purged with bottled unpurified air. Particle absorptance and emittance were measured at 100-hour intervals. Measurements taken after irradiance cycling and thermal aging were compared to measurements taken from as-received particles. CARBOBEAD HSP 40/70 particles had an initial value of 95% solar absorptance with degradation up to 1% after irradiance cycling and 4% after 1000 °C thermal aging.
