Thermal design and analysis of a fully solar-driven copper-chlorine cycle for hydrogen production

Solar copper-chlorine (Cu-Cl) thermochemical cycle is a clean, efficient and large-scale hydrogen production technology. However, when the Cu-Cl cycle is driven by solar energy, large amounts of flows with various heat-absorption and release characters at different temperatures from 25°C to 500°C, resulting in a complex internal heat exchanger network (HEN). The feasible HEN design, the heat transfer losses, and the improvement direction of the system are still unclear. Therefore, a fully solar-driven Cu-Cl cycle for hydrogen production is proposed, in which a 100 MW solar tower and an S-CO2 cycle are utilized to supply heat and electricity. A feasible HEN and possible pinch points are obtained considering energy cascade utilization. Comprehensive energy and exergy conditions are presented and the effects of direct normal irradiance (DNI), recuperative ratio (RR) and maximum temperature (Tm) are assessed. The results show that the receiver has the highest energy efficiency but the lowest exergy efficiency, and the overall system energy and exergy efficiencies are 15.93% and 16.64%. Pinch points of heating the Cu-Cl cycle and S-CO2 cycle lead to limitations of heat transfer. Furthermore, positive effects of increasing RR and Tm are significantly weakened and even turn into negative effects for increasing Tm.