Thermal energy storage with supercritical carbon dioxide in a packed bed: Modeling charge-discharge cycles

Abstract

Thermal energy storage in concentrated solar power systems extends the duration of power production. Packed bed thermal energy storage is studied in this work with supercritical carbon dioxide as the working fluid and α-alumina as the storage material. The operating conditions are appropriate for use in a supercritical Brayton cycle. An axisymmetric model produces temperature profiles in the bed, insulation, and pressure vessel in the axial and radial directions over time. The packed bed system has a mass flow rate of 8.17 kg s−1 at 275 bar. The inlet temperature is 750 °C for storage. In discharge, gas at 500 °C enters the bed to recover the stored energy. Discharge continues until the outlet temperature drops below 700 °C, the minimum temperature required for the turbine inlet. Ten charge-discharge cycles are considered and thermal exergetic efficiency is calculated. Due to thermal dispersion and heat losses, the exergetic efficiency varies from 0.795 to 0.844.