Performance mapping of an open absorption thermal battery with crystallization and sorbent circulation

Sorption thermal battery is promising for long-term heat storage of renewable energy. Recent advances in three-phase sorption thermal battery using fixed sorbent pursue remarkable improvement in energy storage density. However, the synergistic change in storage capacity and discharge rate has posed a challenge for capacity regulation and large-scale application. To address this issue, a three-phase sorption thermal battery accompanied with sorbent circulation is proposed, which completes crystallization while performing falling film heat transfer. Ambient humidity is utilized as working fluid to simplify the operation. A comprehensive analysis is conducted for LiBr-H2O and CaCl2-H2O working pairs in terms of energy density, coefficient of performance, temperature lift, and charge/discharge rates. Simulation results reveal that both the two working pairs exhibit high energy storage density (470.8 kWh/m3 and 525.6 kWh/m3) in the fully crystallized cycle, which is around 2.9–5 times compared to the conventional two-phase cycle. Stable and controllable discharge rate could be achieved via solution circulating and re-concentrating. The stable discharge of CaCl2-H2O could be much longer, owing to larger sorption capacity difference between hydrate and saturated solution (2.2 times of LiBr-H2O). With collaborative promotion in storage density and discharge stability, the proposed system shows great potential for real applications.