Design and energy evaluation of a stand-alone copper-chlorine (Cu-Cl) thermochemical cycle system for trigeneration of electricity, hydrogen, and oxygen

In this article, a new stand-alone Cu-Cl cycle system (SACuCl) for trigeneration of electricity, hydrogen, and oxygen using a combination of a specific combined heat and power (CHP) unit and a 2-step Cu-Cl cycle using a CuCl/HCl electrolyzer is presented. Based on the self-heat recuperation technology for the CHP unit and the heat integration of the Cu-Cl cycle unit, the power efficiency of the SACuCl for 5 prescribed scenarios (case studies) is predicted to achieve about 48% at least. The SACuCl uses the technologies of the dry reforming of methane and the oxy-fuel combustion to achieve a relatively high CO₂ concentration in the flue gas, and CO₂ emissions for power generation could be almost restricted by 0.418 kg/kWh. From the aspect of the electricity required for hydrogen production, it is verified that the 2-step Cu-Cl cycle system is superior to the conventional water electrolyzer because the CHP process supplies the heat/electricity for Cu-Cl thermochemical reactions and a thermoelectric generator is connected to the exhaust gas for recovering the power consumption from the compressor and the CuCl/HCl electrolyzer. Finally, the heat exchanger network and the pinch technology are employed to determine the optimum heat recovery of the Cu-Cl cycle. In case 5 analyzed for the SACuCl, the electricity required for the heat-integrated 2-step Cu-Cl cycle is predicted to dramatically decrease from 4.39 to 0.452 kWh/m³ H₂ and the cycle energy efficiency could be obviously increased from 23.77 to 31.97%.