Evaluation of the solar thermal storage of fluidized bed materials for hybrid solar thermo-chemical processes

The use of solid particles as a solar energy transport and storage medium overcomes the intermittency issues for solar energy and is advantageous for the development of a hybrid process that integrates biomass and solar thermal energy. In this study, lab-scale experimental equipment consisted of a bubbling fluidized bed (55 mm I.D. and 200 mm height) with direct irradiated solar thermal storage was designed and constructed. Sand, alumina (Al), and silica carbide (SiC) particles with 3 different particle sizes (130 µm, 250 µm, and 370 µm) were used as a solar thermal storage medium in the fluidized bed. Due to higher absorption and emissivity properties, the solar thermal efficiency of SiC was higher than those of sand and Al. As the gas velocities in the bubbling fluidized bed increased from the initial minimum fluidization velocity (Umf) to 2 Umf, the temperature differences between the upper bed and lower bed decreased from 470 to 35 °C because of vigorous solid mixing and heat transfer. Also, the increase of average particle size resulted in the decrease of solid heat storage and the increase of gas heat storage due to the differences of specific surface area and gas velocity. Therefore, the energy transported and stored according to the size of silicon carbide was the highest at 370 µm, and the receiver efficiency was 21.38%.