NUMERICAL INVESTIGATION OF BUBBLING FLUIDIZED BED TO BE USED AS THERMAL ENERGY STORAGE INTEGRATED TO HIGH-TEMPERATURE CONCENTRATED SOLAR POWER

Abstract

A thermal energy storage unit designed to be used in a solid particle concentrated solar energy system is analyzed with the help of ANSYS Fluent 17.0. Hydrodynamics of the bubbling fluidized sand bed of 0.28 m × 1 m × 0.025 m dimensions to be used as a direct contact heat exchanger is modeled and validated. Geldart B-type particles with diameter of 275 micrometers and density of 2500 kg/m3 are used in modeling of bubbling fluidized sand bed. A Syamlal−O'Brien drag model with restitution coefficient of 0.99 and specularity coefficient of 0.1 predicts the reported experimental data well in terms of bed expansion ratio, temporal voidage profile, and pressure drop across the bed. According to thermal model results, a linear relation between interphase heat transfer coefficient and bed temperature is observed. A number of analyzed units are proposed as a particle-based storage system for the Ivanpah Solar Power Plant. It is shown that the system using an air Brayton cycle with thermal efficiency of 0.264 can produce 178 MW electricity for 11.22 h with 26,304 metric tons of silica sand that is required for daily storage.