Process design of a thermochemical cycle for hydrogen production compatible with nuclear fusion heat sources

Abstract

We quantitatively design a hydrogen-producing copper–chlorine thermochemical cycle that is thermally combinable with nuclear fusion reactors. The mass and heat balances throughout the cycle, including the hydrolysis, pyrolysis, and electrolysis reaction processes, accompanied by multiple separation steps, are numerically investigated. Through the process design, the feasibility of the practical operation of the hydrogen production cycle is presented, and the thermal and electric power required for the operation is evaluated. As we first design a process with straightforward employment of the exact reaction condition from an earlier experimental study of the electrolysis process, the heat required for the condensation of CuCl₂ solution is found enormous. By modifying the process condition with an increased electrolyte concentration, to reduce the amount of H₂O to be evaporated in the CuCl₂ condensation, the total heat for the cycle significantly decreases from 1270 GJ·h⁻¹ (20.3 MJ·mol-H₂⁻¹) to 204 GJ·h⁻¹ (3.26 MJ·mol-H₂⁻¹). This value is still larger than the heat required for hydrogen production by H₂O electrolysis, 48.2 GJ·h⁻¹ (0.772 MJ·mol-H₂⁻¹), but an extrapolation towards the saturated CuCl concentration achieves 46.0 GJ·h⁻¹ (0.736 MJ·mol-H₂⁻¹). For energy-cost performance improvement of the thermochemical cycle, the development of the electrolytic cell operable with a high concentration of CuCl aqueous solution is thus found to be of primary effectiveness.