Experimental study on packed-bed thermal energy storage using recycled ceramic as filler materials

Thermal energy storage (TES) is used in renewable energy systems such as concentrated solar power (CSP) or electric thermal energy storage (ETES) plants to provide heat for dispatchable power production. This paper presents the experimental results of a new 100% recycled ceramic material, ReThink Seramic - Flora, for used in sensible heat packed-bed thermal energy storage. Results are compared to conventional α-alumina (alumina) materials. The study focuses on a full charge-discharge cycle and multiple repeated partial charge-discharge cycles. Air was used as the heat transfer fluid (HTF) with an inlet temperature of 150 °C. Three flow rates were considered in the study, 0.0034 m³/s, 0.0048 m³/s, and 0.0061 m³/s (5–9 SCFM). The thermal performance of ReThink Seramic - Flora was analyzed and compared to alumina in terms of energy stored/recovered, temperature distribution, thermal exergy efficiency, pressure drop, and net exergy efficiency (combined thermal and pressure drop losses). The results showed that alumina beads have higher performance in terms of thermal exergy efficiency than ReThink Seramic - Flora. The exergy efficiency increased from 46.8% to 55.4% for alumina and from 44.6% to 51.6% during full charge/discharge process at three flow rates. Pressure drop results indicate exergy losses over the flow rates from 3.6% to 7.9% for alumina and 2.5% to 5.1% for ReThink Seramic - Flora. This results in net exergy efficiencies at the three flow rates of 43.2%, 47.1%, and 47.5% for alumina compared to 42.1%, 45.4%, and 46.5% for ReThink Seramic - Flora.