Energy analysis of a class of copper–chlorine (Cu–Cl) thermochemical cycles

For separating water into hydrogen and oxygen through intermediate Cu–Cl compounds, the new system configurations for 5-step, 4-step and 3-step thermochemical cycles using electrolysis of CuCl/HCl or CuCl and Brayton cycle are addressed in Aspen Plus^® environment. To address the feasible predictions by thermodynamic systems, we found that (i) the pressure and temperature affect the product yields of CuO ^∗ CuCl₂ and CuCl in the hydrolysis and oxygen production processes; (ii) the internal heat recovery ratio (IHRR) and the feed ratio of H₂O/CuCl₂ dominate the energy efficiencies and Cl₂ production, respectively. Based on the prescribed operating conditions, the comparative evaluations show that the 5-step Cu–Cl cycle using CuCl electrolyzer can ensure the highest energy efficiency while IHRR = 72%, the 3-step Cu–Cl cycle using CuCl electrolyzer can ensure the less equipment and the highest energy efficiency while IHRR = 100%. The 4-step Cu–Cl cycle using CuCl/HCl electrolyzer, where the electrolyzer prevents copper crossovers and safely produces the pure hydrogen gas at low temperature, has a high possibility of commercialization due to the lower grade heat requirement, the less number of equipment and the higher energy efficiency.