Characterization and testing of solid particles to be used in CSP plants: Aging and fluidization tests

Abstract

The main limitation of Concentrated Solar Power (CSP) is its maximum operating temperature, since the main fluid used as heat transfer fluid (HTF) and thermal storage media (TES) is molten salts, which degrade around 565 ◦C. Therefore, there is great interest in developing HTFs that allow the maximum working temperature to be increased to more than 565 ◦C. This increase in the maximum operating temperature of the HTFs will, in turn, allow CSP plant efficiency to be enhanced. Different studies have proposed using particles as a medium to capture and store solar energy, but very little is known about the effect on the particles after resisting several cycles of cooling and heating and what happens to the particles' physical properties when they are fluidized. It is true that a variety of solid particles permit high performance to be achieved at high temperatures and with low material costs, but not all particles are valid for this purpose. This work focuses on different materials considered promising candidates for use as alternative HTF and storage materials in CSP plants, which were characterized and tested: sand, carbo Accucast ID50 and silicon carbide. The properties of the particles before and after being fluidized (assessing their resistance to abrasion) and before and after high temperature (900 ◦C) thermal treatments (aging treatment) are the main finding of this paper. This work highlights the considerable advantages of SiC and carbo over sand. This study also determines that the combination of high temperature and several hours of fluidization does not affect the diameter of the particles: However, the fluidized samples vary considerably in diameter. In this way, SEM and DSC techniques highlight the problem of the fine appearance associated with sand during fluidization.