Copper-chlorine Cycle For Hydrogen Production Research Articles

Thermal design and analysis of a fully solar-driven copper-chlorine cycle for hydrogen production

Solar copper-chlorine (Cu-Cl) thermochemical cycle is a clean, efficient and large-scale hydrogen production technology. However, when the Cu-Cl cycle is driven by solar energy, large amounts of flows with various heat-absorption and release characters at different temperatures from 25°C to 500°C, resulting in a complex internal heat exchanger network (HEN). The feasible HEN design, the heat transfer losses, and the improvement direction of the system are still unclear. Therefore, a fully solar-driven Cu-Cl cycle for hydrogen production is proposed, in which a 100 MW solar tower and an S-CO2 cycle are utilized to supply heat and electricity. A feasible HEN and possible pinch points are obtained considering energy cascade utilization. Comprehensive energy and exergy conditions are presented and the effects of direct normal irradiance (DNI), recuperative ratio (RR) and maximum temperature (Tm) are assessed. The results show that the receiver has the highest energy efficiency but the lowest exergy efficiency, and the overall system energy and exergy efficiencies are 15.93% and 16.64%. Pinch points of heating the Cu-Cl cycle and S-CO2 cycle lead to limitations of heat transfer. Furthermore, positive effects of increasing RR and Tm are significantly weakened and even turn into negative effects for increasing Tm.

Assessment study of a four-step copper-chlorine cycle modified with flash vaporization process for hydrogen production

This paper develops a four-step copper-chlorine cycle for hydrogen production with conceptual modification through flash vaporization and evaluates its economic and environmental performances through exergy approach. The flash vaporization method is employed as a new approach for realizing the anolyte separation under vacuum conditions for reducing the thermal requirement of the anolyte separation step and consequently of the overall cycle. A flash vaporization is usually employed commercially for seawater desalination purposes. However, its utilization in a thermochemical hydrogen production process has not been considered previously which is really one of primary novelties of this investigation. The obtained results for the exergoeconomic and exergoenvironmental analyses of the conceptually modified cycle are also compared with those of the existing integrated cycle at the Ontario Tech University. The exergoeconomic analysis of the cycle has also been carried out for the cycle operating with and without waste heat recovery. In this regard, waste heat recovery from a steel furnace has been considered for supplying the required thermal energy for the hydrolysis step. The cost assessment of the cycle is carried out in the Aspen-plus. Compared with the existing cycle, the cycle with the proposed modification results in a lower unit cost of hydrogen. Moreover, a significant reduction in the unit cost of hydrogen is observed when waste heat recovery is considered for the modified cycle. The average unit hydrogen cost for the modified version of the cycle is evaluated to be 4.7 $/kg which reduces to 2 $/kg with incorporation of waste heat recovery. Furthermore, the overall environmental impact of the existing cycle can be potentially minimized by considering the proposed modification through flash vaporization.

Exergoenvironmental analysis of the integrated copper-chlorine cycle for hydrogen production

Thermochemical water-splitting cycles have the potential of producing large-scale and cost-effective sustainable hydrogen in an environmentally benign manner. Limited exergoenvironmental assessments have been reported in the literature which generally considers thermochemical hydrogen production and specifically the copper-chlorine (Cu–Cl) cycle in thid regard. Thus, the present investigation aims at assessing the four-step integrated Cu–Cl thermochemical cycle set-up located at the Ontario Tech University thereby contributing to the environmental impact assessment of thermochemical hydrogen production. In this study, the exergy analysis of the cycle is first performed by thermodynamically modeling and simulating the cycle in Aspen-plus. The fundamental principles of the exergoenvironmental analysis, analogous to the specific exergy costing (SPECO) methodology of the exergoeconomic evaluation, are applied to the cycle and the balanced environmental impact equations for all cycle components are developed. Based on the balanced environmental impact equations, the environmental impact rate, and the specific environmental impact at each state point is evaluated. The environmental impact levels for all the major cycle components are also obtained. The exergoenvironmental factor, the relative difference of the specific environmental impacts, and the environmental impact rate of exergy destruction for various cycle components are in this regard evaluated. Furthermore, the influence of various parameters on the cumulative and component-related rate of environmental impact as well as the exergoenvironmental factor is analyzed by conducting a detailed sensitivity analysis. According to the obtained results, the rate of environmental impact corresponding to exergy destruction dominates the component-related rate of environmental impact and thus the potential reduction in the cumulative environmental impact for various components could be achieved by improving their exergy efficiencies. The hydrolysis step accounts for 60% of the component-related environmental impact while the thermolysis step accounts for the highest environmental impact of exergy destruction ranging between 41 and 42%. The percentage difference between fossil fuel-based and renewable electricity in terms of the global warming potential ranges between 80% and 98% with the highest difference for wind and nuclear-based electricity.

A specific exergy costing assessment of the integrated copper-chlorine cycle for hydrogen production

In this study the specific exergy costing (SPECO) approach is employed on a four-step integrated thermochemical copper-chlorine (Cu Cl) cycle for hydrogen production for a second-law based assessment purposes. The Cu–Cl cycle is considered as one of the most environmentally benign and sustainable options of producing hydrogen and is thus investigated in this study due to its potential of ensuring zero greenhouse gas (GHG) emissions. Several conceptual Cu–Cl cycles have been exergoeconomically examined previously, however this study aims at investigating the four-step integrated Cu–Cl cycle developed at the Clean Energy Research Laboratory (CERL) at the Ontario Tech University thereby contributing to the thermo/exergoeconomic assessments of the thermochemical hydrogen production. In this study, the cycle is first thermodynamically modeled and simulated in a process simulation software (Aspen Plus) through exergy and energy approaches. The basic principles of the SPECO methodology are applied to the system and exergetic cost balances are performed for each cycle component. The exergetic costing of each cycle stream is then performed based on the cost balance equations. The purchased equipment cost and the hourly levelized capital cost rates for each cycle component is also obtained. The exergoeconomic factor, relative cost difference and exergy destruction cost rate for various cycle components are also evaluated. Moreover, the effect of several parameters on the total and hourly levelized capital cost rates is analyzed by performing a comprehensive sensitivity analysis. Based on the analysis, the exergy cost, the unit or specific exergy cost, and the unit costs of hydrogen are evaluated to be 6407.55 $/h, 0.042 $/MJ, and 4.94 $/kg respectively.

Exergoeconomic analysis of a new integrated copper-chlorine cycle for hydrogen production

In this study, an exergoeconomic analysis is performed on an integrated four-step thermochemical copper-chlorine cycle developed at the Ontario Tech. University through exergy, cost, energy, and mass (EXCEM) method. A thermodynamic model is first constructed in Aspen-plus (a process simulation software) to simulate and investigate the integrated cycle through exergy and energy analyses. The capital costs, thermodynamic loss rates, and the ratio of the thermodynamic loss rate to the capital cost of various system's components are also determined. Moreover, the average unit cost of hydrogen is evaluated and the influence of several system's parameters on the unit cost of hydrogen is analyzed. The results show that the cost of hydrogen is strongly dependent on the production capacity of the plant. Based on the analysis, our system generates hydrogen at an average unit cost of 5.54 $/kg with a plant capacity of 1619.3 kg/h considering both internal (operating and maintenance costs, etc.) and external (costs of various inputs, etc.) parameters.

Energy and exergy analyses of a new integrated thermochemical copper-chlorine cycle for hydrogen production

This paper presents a thermodynamic study on a newly built lab-scale thermochemical copper-chlorine (Cu-Cl) cycle installed at the Clean Energy Research Laboratory (CERL) at the Ontario Tech University. This study analyzes every component of the system through energy and exergy analysis by considering the heat inputs, outputs and exergy destruction within the various units of the Cu–Cl cycle. The system is modeled and simulated using the Aspen-plus software. The mass, energy and exergy balance equations for each system component are written for analysis and assessment purposes. Based on the analysis, the maximum heat input is required for the hydrolysis reactor while the HCl-condenser-1 is found to reject the maximum heat. The results suggest that the thermolysis reactor experienced the highest exergy destruction. The effect of the flow rates of certain species within the cycle on the performance of various system units, such as heat transfer rates and production flow rates are also investigated. The overall energy and exergy efficiencies of the system are evaluated to be 6.8% and 10.4%, respectively.

A multi-objective optimization of the integrated copper-chlorine cycle for hydrogen production

This paper considers a multi-objective optimization study performed on an integrated copper-chlorine cycle for hydrogen production developed and built at the Ontario Tech. University using genetic algorithm. The system is thermodynamically modeled in the Aspen-plus software considering all components in the cycle. A varied range of steam-to-copper ratios is selected for this study and four different cases are considered based on various steam input temperatures. The objective of this study is to maximize the rate of hydrogen production and overall system exergy efficiency, hence minimizing overall cost of cycle operation. The results of the multi-objective optimization study are presented in the form of the Pareto frontier solutions for identification of the optimal points. A comparison of the optimization results with Aspen-plus simulations is also presented for validation purposes. For all the cases considered, the optimal trade-off point results in steam-to-copper ratios ranging from 15.7 to 16.9. The steam input temperature is found to have a significant influence on the exergy efficiency and overall operating cost. The highest exergy efficiency is reported as 17.8% at a steam input temperature of 300 °C, while the minimum exergy efficiency is obtained to be 6.5% at a steam input temperature of 25 °C.

Thermal management of a new integrated copper-chlorine cycle for hydrogen production

This paper develops a thermal management method for the integrated lab-scale copper-chlorine cycle built in the Clean Energy Research Laboratory at the Ontario Tech. University for hydrogen production and studies thermodynamically through energy and exergy approaches. The performance of the system is assessed based on the overall system energy and exergy efficiencies. The approach is further implemented to study the possible options for the highest amount of heat recovery within the cycle. Six different steam and heat recovery configurations are considered in this study based on the various streams recovered within the cycle, with each configuration having a different steam-to-copper molar ratio. The criteria for assessing the performance of each configuration are the exergy destruction of the heater-1 of the system, net thermal exergy, net heat input, and hydrolysis unit heat input, the temperature achieved after heat recovery and the overall system energy and exergy efficiencies. The temperature achieved after heat recovery and the steam-to-copper molar ratio are found to be the key aspects impacting the performance of each configuration. The overall energy and exergy efficiencies of the system without considering heat recovery are evaluated to be 6.8% and 10.4%, respectively while the highest energy and exergy efficiencies obtained after considering heat recovery are found to be 10.7% and 16.3% respectively which shows the influence of heat recovery on the performance of the system.

Exergy and cost analyses of waste heat recovery from furnace cement slag for clean hydrogen production

This paper examines the performance and viability of a cement slag waste heat recovery system combined with a thermochemical copper-chlorine cycle for hydrogen production combined with hydrogen compression and a reheat Rankine cycle. The waste heat from the cement slag is recovered as a heat source for high-temperature reactions in the copper-chlorine cycle. The clean hydrogen production from waste heat recovery is examined with respect to both energy and exergy efficiencies. The integrated system is simulated and modeled in Aspen Plus. The multigeneration system utilizes the industrial waste heat and significantly reduces operating costs from the waste heat recovery. The overall energy efficiency of the integrated system is obtained as 32.5% while the corresponding exergy efficiency becomes 31.8%.

X-ray diffraction of crystallization of copper (II) chloride for improved energy utilization in hydrogen production

Crystallization is an effective method to recover solids from solution, due to its relatively low energy utilization, low material requirements and lower cost compared to other alternatives. Hence, crystallization is of particular interest in the thermochemical copper-chlorine cycle for hydrogen production as an energy-saving means to extract solid CuCl2 from its aqueous solution. It has been determined from experiments that there is a range of concentrations that will demonstrate crystallization. If the initial concentration exceeds the upper bound of this range, the solution will be saturated and instantly become paste-like without forming crystals. Conversely, if the initial concentrations fall below the lower bound of a specified range, the solution will remain liquid upon cooling. As a result, it has been observed that crystallization does not occur for HCl concentrations below 3 M and above 9 M. Also, it has been found that anhydrous CuCl2 does not crystallize under any of the conditions tested. To analyze the composition of the recovered solids, X-ray diffraction (XRD) was employed. The samples were also analyzed using thermogravimetric analysis (TGA) in order to determine their thermochemical properties such as melting and decomposition temperatures. The stationary point on the TGA curve was found to be around 462 °C which is below the normal melting temperature of CuCl2. Also, the vaporization of the samples was found to be approximately 600 °C.

Experimental investigation of particle dissolution rates in aqueous solutions for hydrogen production

Results of reaction kinetics studies of chemical processes related to materials integration of the thermochemical copper-chlorine cycle for hydrogen production are reported. The reaction rate of solid cuprous chloride (CuCl) in liquid hydrochloric acid is investigated experimentally for various acid concentrations. A rate constant—a function of constituent concentrations—describes how quickly the reactants are converted into products in satisfying the activation energy to enable the reaction to move forward. In this paper, the change in area of a solid CuCl particle is examined, rather than concentration in previous studies. New predictive models are developed to describe the characteristics of the chemical reaction in terms of its transition states and reaction mechanisms.

Design and simulation of a UOIT copper-chlorine cycle for hydrogen production

A design and simulation study of the four-step copper–chlorine (Cu–Cl) cycle using Aspen Plus software (Aspen Technology Inc., Cambridge, MA)is reported. The simulation consists of four main sections: hydrolysis, oxy-decomposition, electrolysis, and drying. This paper explains and justifies how the actual reaction kinetics is factored into these four main sections. Also, it illustrates all the process units that are used in the simulation of four-step Cu–Cl cycle, providing their associated specifications and design parameters. It is found that hydrolysis reactors with smaller capacities and larger (≥10/1) steam to CuCl ratios were desirable to increase the reaction efficiency and prevent the formation of side products such as CuO and CuC. In contrast, larger capacity oxy-decomposition reactors with longer residence times are preferable to allow enough time for the copper oxychloride to decompose. Therefore, 10 (or more) small-scale hydrolysis reactors can feed one oxy-decomposition reactor with large capacity to keep continuity of the flow in the overall cycle. On the basis of the process flow sheet, a pinch analysis is developed for an integrated heat exchange network to enable effective heat recovery within the Cu–Cl cycle. Copyright © 2012 John Wiley & Sons, Ltd.