Optimization and Feasibility of Hydrogen Production via the Thermochemical Cu–Cl Cycle: A Heat and Mass Transfer Analysis

The escalating environmental impact of carbon dioxide emissions from the energy sector, particularly transportation, necessitates the exploration of alternative energy carriers capable of significantly reducing such emissions. Hydrogen emerges as a promising eco-friendly energy vector, especially for heavy-duty applications, due to its potential to mitigate greenhouse gas emissions. This dissertation investigates the development and optimization of hydrogen production technologies through the thermochemical copper-chlorine (Cu–Cl) cycle, focusing on heat and mass transfer processes and their implications for system efficiency. The Cu–Cl cycle stands out among thermochemical hydrogen generation methods because of its relatively lower temperature requirements which makes it a viable candidate for sustainable hydrogen production. This research begins by designing innovative thermoelectric-based heat exchangers within the Cu–Cl cycle to enhance waste energy harvesting. A novel heat exchanger incorporating a thermoelectric generator (TEG) is developed to recover heat from high-temperature molten cuprous chloride (CuCl) exiting the thermolysis reactor. Using numerical simulations with COMSOL Multiphysics, the performance of this heat exchanger is examined. Results indicate that the maximum generated power can exceed 40 W at a matching current of 4.5 A, with a maximum energy conversion efficiency of 7.1%. The TEG performance improves with increasing inlet Reynolds number (Re), particularly at the hot end, demonstrating a 36% discrepancy between the highest and lowest Re in the molten CuCl chamber. Further exploration involves another innovative TEG-based heat exchanger designed to recover heat from the molten salt leaving the oxygen reactor without phase change. Numerical evaluations reveal that, at matching resistance, the maximum produced power surpasses 32 W per TEG unit, and the maximum conversion efficiency reaches 5.02% at a load resistance of 2.65 Ω. Increasing the inlet Re of the molten CuCl enhances the maximum generated power and conversion efficiency by over 9%, underscoring the importance of operating conditions on TEG performance. To assess the potential for enhancing hydrogen generation, the feasibility of integrating electrolysis, a more mature technology for water decomposition, with renewable energy systems such as solar panels and wind turbines is explored. A sustainable framework for hydrogen refuelling stations along Highway 401 in Canada is evaluated, employing grid-connected photovoltaics, wind turbines, electrolyzers, hydrogen tanks, and converters under various truck number scenarios. A detailed greenhouse gas emission analysis is conducted, considering intensive programs and expenses from the central grid over the lifetime. Sensitivity evaluations examine the impact of grid price rates, capital cost multipliers, and photovoltaic output volatility on technical and financial parameters. The optimal system integrates 1,269 kW of photovoltaic arrays, 31 wind turbines, 58 electrolyzers, a 220 kg hydrogen tank, and a 901 kW converter under a 10-truck scenario, resulting in a NPC of $1.07 million, a levelized cost of hydrogen of $2.03 per kilogram, and a renewable fraction of 93%. A comprehensive feasibility study of the Cu–Cl cycle is conducted by identifying key economic and environmental benefits and comparing it with other hydrogen production processes. Similarly, a network of pilot refuelling stations for heavy-duty applications along the Highway 401 corridor is assessed, utilizing solar panels, the central grid, wind turbines, and industrial waste heat to produce hydrogen via the Cu–Cl cycle. Findings reveal the substantial impact of location on the optimal solution configuration, emphasizing the necessity of considering local weather data. An optimization algorithm determines that the best hybrid energy system in Windsor, Ontario, comprises 1,891 kW of photovoltaic arrays, 3,822 kW of wind turbines, 13.22 kg H₂ per hour production capacity, a 220 kg hydrogen tank, and a 1,064 kW converter, achieving a renewable fraction of 98%. The levelized cost of hydrogen varies by location, ranging from $2.78/kg H₂ in Windsor to $3.25/kg H₂ in Kingston. A comprehensive sensitivity analysis explores the effects of energy market fluctuations, fleet size variations, and greenhouse gas emissions on key economic and environmental parameters. This analysis demonstrates that the levelized cost of hydrogen decreases significantly with increasing fleet size from $12.48/kg H₂ for a 10-truck fleet to $1.56/kg H₂ for a 100-truck fleet. In addition to system-level analyses, the dissertation investigates bubble dynamics and two-phase gas-liquid mass transfer critical to the thermochemical Cu–Cl cycle. Phase transitions in water-splitting processes lead to bubble formation, vapour transfer, and gas redissolution, affecting energy requirements and reactor efficiency. Experimental studies using a sophisticated laser-based shadow vi imaging system examine bubble formation patterns, size distribution, and rise velocities across various sparger sizes and temperatures ranging from 23 °C to 60 °C. Results indicate that Re increases with temperature due to changes in fluid viscosity and surface tension, affecting mass transfer rates. Average Sherwood number values range from approximately 113 to 172, decreasing as temperature increases due to higher diffusion coefficients and reduced convective effects. Empirical correlations for the Sherwood number are developed using the Buckingham-PI theorem. Further on, employing a 1D mass transfer for single oxygen bubbles rising in a thermolysis reactor suggests that the thermolysis reactor height should be limited to approximately 30 cm to prevent more than 15% mass loss due to undesired mass transfer. By enhancing the efficiency and sustainability of hydrogen production via the Cu–Cl cycle, this dissertation contributes significantly to the advancement of clean energy technologies. The innovative heat recovery systems and optimized reactor design criteria proposed not only improve the overall efficiency of hydrogen production but also reduce operational costs and environmental impact. The integration of renewable energy sources with hydrogen production systems presents a viable pathway toward decarbonizing the transportation sector, particularly for heavy-duty applications, which are currently significant contributors to air pollution and greenhouse gas emissions. These findings support global efforts to transition to a hydrogen economy and demonstrate the potential of the Cu–Cl cycle as a cornerstone technology in achieving sustainable energy goals. By addressing critical challenges in heat and mass transfer processes, this work lays the groundwork for scaling up hydrogen production and facilitating its widespread adoption, thereby contributing to a net-zero emissions future.

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