Development, analysis and life cycle assessment of integrated systems for hydrogen production based on the copper-chlorine (Cu-Cl) cycle
Ozbilen, Ahmet Ziyaettin
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The energy carrier hydrogen is expected to help solve many energy challenges we are facing today. Thermochemical water splitting using a Cu-Cl cycle, linked with renewable energy sources and/or the Generation IV nuclear super-critical water cooled reactor (SCWR), is a promising option for hydrogen production. The University of Ontario Institute of Technology (UOIT), Clean Energy Research Lab (CERL) has a research team working on the Cu-Cl hydrogen production cycle to demonstrate the process at the lab scale. This study aims to contribute to the development of hydrogen production using the Cu-Cl cycle by developing integrated multi-generation systems. There are three key elements of the study. First, the Cu-Cl based integrated systems are developed for multi-generation. System I has a solar tower with molten salt energy storage integrated with a steam turbine, organic Rankine cycle and a LiBr-H2O absorption cooling system. System II consists of a Generation IV SCWR integrated with the Cu-Cl cycle and a LiBr-H2O absorption cooling system. System III has a solar tower with molten salt energy storage integrated with the Cu-Cl cycle, LiBr-H2O absorption cooling system and a gas steam combined cycle. All three systems discussed in this thesis produce hydrogen as the main output. All the systems also have the capability of generating electricity and providing cooling, hot water and drying air. A novel configuration of the four-step Cu-Cl cycle is modeled in order to better understand and improve system performance and efficiency. Second, in the analysis section, the Aspen Plus process simulation package is used to evaluate the characteristics of the entire cycle in terms of energy, exergy and cost effectiveness, to support the ultimate development of a pilot plant. Alternative designs for the heat exchanger network using Aspen Energy Analyzer are studied for better thermal management. The Aspen Plus simulation results for the four-step Cu-Cl cycle illustrate that the steam to copper molar ratio can be reduced to 10 from an initial value of 16 by decreasing the pressure of the hydrolysis reactor. Thermodynamic, economic and environmental analyses are then conducted for the simulated four-step Cu-Cl cycle using various engineering tools: exergy, cost analyses, life cycle assessment and exergoenvironmental and exergoeconomic analyses. Based on the conducted research for ii the studied system under the baseline conditions, the total cost rate and environmental impact rate are determined to be 165 $/s and 37.6 Pt/s, respectively. Energy and exergy efficiencies of the four-step Cu-Cl cycle are also calculated to be 55.4% and 66.0%, respectively. Five optimization scenarios with the objective functions of exergy efficiency (single-objective), total cost rate (single-objective), environmental impact rate (single-objective), along with multi-objective exergoeconomic and exergoenvironmental optimizations are performed. Based on the single objective optimizations, it is determined that the exergy efficiency could be increased by up to 3.3% using exergy-based optimization, the cost can be reduced by up to 33% using cost-based optimization, and the environmental impact rate can be reduced by up to 39% using environmental impact-based optimization, at the expense of the nonoptimized objectives. In this regard, multi-objective optimization is conducted. Based on the exergoeconomic optimization, it is concluded that 0.80% higher exergy efficiency and 4.5% lower cost can be achieved, compared to baseline parameters. Furthermore, 0.46% higher exergy efficiency and 30% lower environmental impact rate can be achieved based on the exergoenvironmental optimization. Third, the optimized four-step Cu-Cl cycle is integrated with the novel multi-generation systems. Exergy and exergoeconomic analyses and exergetic life cycle assessment are conducted for the multi-generation systems. Multi-objective optimizations of the present integrated systems are also performed. Multi-objective optimization results show that exergy efficiencies are 45.8%, 45.3% and 46.7% for the three integrated multi-generation systems for hydrogen production. Corresponding energy efficiencies are calculated to be 76.4%, 67.4% and 81.2%, respectively, considering that rejected heat from the systems are utilized as hot water and drying air.