Experimental and numerical study of a cascaded thermal energy storage system for waste heat recovery in hydrogen production plants

The overheating of alkaline water electrolyzer poses a critical threat to system safety in hydrogen production plants. In order to enable intelligent temperature regulation and thermal management demands of alkaline water electrolyzer, a cascaded latent heat thermal energy storage system based on an eco-friendly biomass carbon framework derived from discarded corn stalks was developed. The design of a cascaded latent heat thermal energy storage unit of shell-and-tube was optimized with exergy and rated outlet temperature as key target parameters. Considering the impact of temperature fluctuations in alkaline water electrolyzer induced by renewable energy generation volatility on heat recovery performance, the system performances were systematically compared under various inlet temperatures of 80∼90 °C, flow rates of 60∼240 L/h, and encapsulation configurations. Experimental results demonstrate that under the increasing inlet flow rate and temperature conditions, cascaded latent heat thermal energy storage maintains its advantage of shorter melting time. Compared with conventional single-level thermal energy storage systems, it achieves the maximum improvements of 31.71%, 43.28%, and 18.77% in exergy efficiency, rated thermal efficiency, and cycle efficiency, respectively. The maximum enhancement in charging rates reaches 119.85% while that in discharging rate is 134.21%. Numerical analysis reveals that under various operational conditions, cascaded system achieves up to 26.71% higher liquid fraction than conventional thermal energy storage, with a maximum thermal grade advantage of 4.7 °C. This demonstrates that through simultaneous optimization of thermal field uniformity and energy storage density, cascaded system provides a critical technological foundation for thermoelectric coordinated control in renewable-powered hydrogen production systems.