Development and modeling of a lab-scale integrated copper-chlorine cycle for hydrogen production

Abstract

Hydrogen is one of the most important energy carriers, clean fuels, and storage media in the upcoming future. Hydrogen production through the thermochemical copper-chlorine (Cu-Cl) cycle is one of the most promising methods of nuclear hydrogen production on a large scale. Researchers at the University of Ontario Institute of Technology (UOIT) have designed and developed a lab-scale integrated Cu-Cl cycle for producing hydrogen. This study aims to develop the thermodynamic, hydrodynamic, electrochemical, and heat and mass transfer models for the experimental Cu-Cl cycle to evaluate the performance of the cycle and its components. Also, an exergoeonomic and optimization study is performed for a more cost-effective approach and revealing optimal design conditions. The results of this study will be useful as a benchmark for the lab-scale Cu-Cl cycle performance assessment accounting for actual large-scale implementation. In practical operation of the Cu-Cl cycle, besides the main steps of hydrolysis, thermolysis, electrolysis and drying, the depleted anolyte (consumed anolyte at the electrolyzer) needs to be recycled to be concentrated sufficiently for the electrochemical process. Recycling of the oxidized anolyte through the separation processes is achieved by distillation of anolyte, drying unit, separation cell, pressure swing distillation unit (PSDU), and CuCl2 concentrator. The overall exergy efficiency of the integrated lab-scale Cu-Cl cycle is found to be 33.4%. The estimated cost of produced hydrogen from the scaled-up facilities with a capacity of 1000 kg/day H2 is about 3.91 $/kg H2. In the hydrolysis reactor, with an increase of St/Cu ratio (from 5 to 17 and 30), the maximum exergetic efficiency of the system occurs at the lower reactor operating temperature (from 450℃ to 388℃ and 380℃, respectively). From the hydrodynamic study of CuCl/HCl(aq) electrolyzer, the cells close to the anolyte or catholyte input ports possess a higher voltage efficiency than other cells for the X-shape bipolar modules, resulting in less decomposition potential. In the PSDU, both heat and mass transfer model results predict the same values for the low and high pressure packing column height of 1.7 m and 2 m, respectively.