Experimental study of different coatings on silica sand in a directly irradiated fluidised bed: Thermal behaviour and cycling analysis

The present work shows the experimental results obtained with sand particles, which where coated to increase the thermal absorptivity for CSP applications. The particles were tested in a lab-scale fluidised bed with concentrated irradiation on the top. The experimental results indicates that two of the three coatings tested, based on graphite and carbon black, worked properly and absorbed between 30 and 40% more energy than raw sand due to the higher thermal absorptivity. Both coatings were also experimentally tested during 10 cycles of charging/discharging without apparent deterioration of their thermal properties. Sand coated with graphite exhibited colour change, from an initial dark black to a greyish tone that did not have an impact on the particles thermal response.The extrapolation of the results observed at lab-scale, to the maximum expected temperatures in new generation of CSP plants with solid particles, up to 1250 K, shows that coated particles may enhance the energy effectively stored in the bed by 60-80% compared to raw sand.