Solar thermochemical plant analysis for hydrogen production with the copper–chlorine cycle

In this article, a solar-based method of generating hydrogen from the copper–chlorine water-splitting cycle is developed and evaluated. An analysis is performed for solar plants with different hydrogen production capacities at three locations across Canada. Operating parameters of the solar field and the storage units are presented. The thermal efficiency and cost parameters of the hydrogen plant are also examined. A binary mixture of 60% NaNO₃ and 40% KNO₃ is used as the molten salt for solar energy storage. Different hydrogen production rates are analyzed. Since the solar irradiation in Calgary is much less than Toronto and Sarnia in the winter, it is found that a larger storage unit is required. The size of the storage unit increases for larger hydrogen production rates. The results support the feasibility of solar thermochemical Cu–Cl cycle as a promising and efficient pathway for large-scale production of hydrogen.     

Energy and exergy analyses of a new four-step copper–chlorine cycle for geothermal-based hydrogen production

In this paper, energy and exergy analyses of the geothermal-based hydrogen production via thermochemical water decomposition using a new, four-step copper–chlorine (Cu–Cl) cycle are conducted, and the respective cycle energy and exergy efficiencies are examined. Also, a parametric study is performed to investigate how each step of the cycle and its overall cycle performance are affected by reference environment temperatures, reaction temperatures, as well as energy efficiency of the geothermal power plant itself. As a result, overall energy and exergy efficiencies of the cycle are found to be 21.67% and 19.35%, respectively, for a reference case.     

Comparison of different copper–chlorine thermochemical cycles for hydrogen production

Copper–chlorine thermochemical cycles for hydrogen production are very promising water splitting cycles. In this paper, different types of copper–chlorine cycles with various numbers of steps are compared. The factors that determine the number and effective grouping of steps are analyzed. It is found that the water requirement in the hydrolysis step is affected by a combination of drying and hydrolysis steps. It is also found that hydrogen can be produced either from electrolysis of cuprous chloride, or from chlorination of copper by hydrogen chloride, which indicates a potential combination of disproportionation and chlorination steps. The major engineering advantages and disadvantages of these cycle variations with different amounts of steps will be analyzed and discussed.     

Coupling of copper–chloride hybrid thermochemical water splitting cycle with a desalination plant for hydrogen production from nuclear energy

Energy and environmental concerns have motivated research on clean energy resources. Nuclear energy has the potential to provide a significant share of energy supply without contributing to environmental emissions and climate change. Nuclear energy has been used mainly for electric power generation, but hydrogen production via thermochemical water decomposition provides another pathway for the utilization of nuclear thermal energy. One option for nuclear-based hydrogen production via thermochemical water decomposition uses a copper–chloride (Cu–Cl) cycle. Another societal concern relates to supplies of fresh water. Thus, to avoid causing one problem while solving another, hydrogen could be produced from seawater rather than limited fresh water sources. In this study we analyze a coupling of the Cu–Cl cycle with a desalination plant for hydrogen production from nuclear energy and seawater. Desalination technologies are reviewed comprehensively to determine the most appropriate option for the Cu–Cl cycle and a thermodynamic analysis and several parametric studies of this coupled system are presented for various configurations.     

Performance investigation of magnesium–chloride hybrid thermochemical cycle for hydrogen production

In this paper, we study the yields of reactants in hydrolysis and chlorination chemical processes of the low temperature Mg–Cl hybrid thermochemical cycle to investigate the requirements of temperature, pressure and product ratios for individual reactors of the cycle. A simulation of both hydrolysis and chlorination processes is conducted using the Aspen Plus software. A Mg–Cl cycle is developed by considering the results obtained from the present simulations. Both energy and exergy efficiencies of Mg–Cl cycle are comparatively evaluated under varying system and environmental parameters, and an efficiency comparison of the cycle with other promising thermochemical water splitting cycles is conducted. The results show that, compared to other cycles, lower pressure, higher temperature and higher steam to magnesium–chloride ratio are required for full conversion of reactants in the hydrolysis step; and hence, lower temperature, higher pressure and higher chlorine to magnesium oxide ratio is required for full conversion in chlorination reactor. The efficiency results show that Mg–Cl cycle can compete with other low temperature thermochemical water splitting cycles and under influence of various internal and external parameters.     

Design and reliability assessment of control systems for a nuclear-based hydrogen production plant with copper–chlorine thermochemical cycle

The thermochemical Copper–Chlorine (Cu–Cl) cycle is an emerging new method of nuclear-based hydrogen production. In the process, water is decomposed into hydrogen and oxygen through several physical and chemical processes. In this paper, a Distributed Control System (DCS) is designed for the thermochemical Cu–Cl cycle. The architecture and the communication networks of the DCS are discussed. Reliability of the DCS is assessed using fault trees. In the assessment, the impact of the malfunction of the actuators, sensors, controllers and communication networks on the overall system reliability is investigated. This provides key information for the selection of control system components, and determination of their inspection frequency and maintenance strategy. The hydrogen reactor unit, which is one of the major components in the thermochemical Cu–Cl cycle, is used to demonstrate the detailed design and analysis.     

Comparison of sulfur–iodine and copper–chlorine thermochemical hydrogen production cycles

Sulfur–iodine and copper–chlorine water splitting cycles are promising methods of thermochemical hydrogen production. In this paper, these two cycles are compared from the perspectives of heat quantity, heat grade, thermal efficiency, related engineering challenges, and hydrogen production cost. The heat quantity and grade required by each step of the cycles are evaluated and the thermal efficiencies are approximated from the heat requirements. It is found that the overall heat requirements of the two cycles do not have significant differences and the overall efficiencies of the two cycles are similar, between 37 and 54%, depending on the portion of heat recovery. The copper–chlorine cycle has the advantage of a lower maximum temperature of 803 K, which is 300 K lower than the maximum temperature of 1123 K in the sulfur–iodine cycle. This indicates that the copper–chlorine cycle can link more readily with various heat sources, such as grade Generation IV nuclear and fossil fuel power stations. It is also reported that the copper–chlorine cycle can have fewer challenges of equipment materials and product separation. A cost analysis shows that the copper–chlorine and sulfur–iodine cycles have similar hydrogen production costs, which are lower than steam-methane reforming, and conventional and high temperature electrolysis, due to less use of electricity, no carbon related charges and no methane requirement in the thermochemical cycles.     

Thermodynamic performance analysis of a copper–chlorine thermochemical cycle and biomass based combined plant for multigeneration

The primary objective of this work is to investigate a comprehensive thermodynamic assessment of the biomass-assisted multigeneration plant for electrical energy, hydrogen, heating-cooling, drying, and hot water production. The suggested multigeneration plant includes the biomass gasification process, Brayton cycle, Kalina cycle, organic Rankine cycle, and cascade refrigeration plant, which is to produce heating and cooling loads, drying system, hydrogen generation with copper–chlorine thermochemical process, and hydrogen liquefaction process. Based on the thermodynamic laws, the total irreversibility rate and performance assessment of the examined study is conducted. Moreover, the impact of various factors such as reference temperature, biomass gasifier temperature, and mass flow rate of biofuel, on the effectiveness and useful outputs of planned plant are examined. The outcomes of the proposed study show that 18 626, 3948 and 1037 kW electrical energy are generated by using the Brayton, Kalina, and organic Rankine cycle. Furthermore, the total cooling and heating capacities and hydrogen generation rates are 2392, 2864 kW and 0.068 kg s⁻¹. Finally, energetic and exergetic effectiveness of the examined model are calculated as 56.71% and 53.59%.     

Canadian advances in the copper–chlorine thermochemical cycle for clean hydrogen production: A focus on electrolysis

Hydrogen is a clean energy carrier that can help mitigate greenhouse gas (GHG) emissions if it is used to replace fossil fuels for power production. One way to produce hydrogen on a large scale is through the use of water splitting thermochemical cycles such as the hybrid copper chlorine (Cu–Cl) cycle. Canadian Nuclear Laboratories Ltd. (CNL) chose to develop the Cu–Cl cycle because the highest temperature required by this cycle is about 530 °C, compatible with the Canadian Super Critical Water Reactor (SCWR) or some small modular reactors (SMR). The on-going effort at CNL is to demonstrate a fully integrated Cu–Cl cycle at laboratory scale with a hydrogen production rate of 50 L/h. Some recent experimental results of the electrolysis step, one of the main steps of the cycle, are discussed in this paper.The anode reaction of CuCl oxidation was investigated using a three-electrode electrochemical cell. Half-cell experiments found that CuCl oxidation did not require noble metals as catalyst. The CuCl oxidation on carbon was found to be a mass-transfer controlled process. Hence the limiting current density increased with increasing turbulence on the electrode surface. Increasing the CuCl concentration and the solution temperature also resulted in higher limiting current densities. A current density of 0.53 A/cm² was achieved for a 1.0 M CuCl solution at 80 °C.Single cells with electrode areas up to 100 cm² were used to establish the operating conditions for the electrolysis step. The effects of flow rate, temperature, and current density on the cell voltage were studied. A hydrogen production rate of 50 L/h was successfully achieved at 0.4 A/cm² in a 2.0 M CuCl solution at 80 °C. The electrolysis step is fully developed for integration in a laboratory-scale demonstration of the Cu–Cl cycle.     

Energy and exergy analyses of a solar driven Mg–Cl hybrid thermochemical cycle for co-production of power and hydrogen

Analysis and performance assessment of a solar driven hydrogen production plant running on an Mg–Cl cycle, are conducted through energy and exergy methods. The proposed system consists of (a) a concentrating solar power cycle with thermal energy storage, (b) a steam power plant with reheating and regeneration, and (c) a hybrid thermochemical Mg–Cl hydrogen production cycle. The results show that higher steam to magnesium molar ratios are required for full yield of reactants at the hydrolysis step. This ratio even increases at low temperatures, although lowering the highest temperatures appears to be more favorable for linking such a cycle to lower temperature energy sources. Reducing the maximum cycle temperature decreases the plant energy and exergy efficiencies and may cause some undesirable reactions and effects. The overall system energy and exergy efficiencies are found to be 18.8% and 19.9%, respectively, by considering a solar heat input. These efficiencies are improved to 26.9% and 40.7% when the heat absorbed by the molten salt is considered and used as a main energy input to the system. The highest exergy destruction rate occurs in the solar field which accounts for 79% of total exergy destruction of the integrated system.     

Progress of international program on hydrogen production with the copper–chlorine cycle

This paper highlights and discusses the recent advances in thermochemical hydrogen production with the copper–chlorine (Cu–Cl) cycle. Extended operation of HCl/CuCl electrolysis is achieved, and its performance assessment is conducted. Advances in the development of improved electrodes are presented for various electrode materials. Experimental studies for a 300 cm² electrolytic cell show a stable current density and production at 98% of the theoretical hydrogen production rate. Long term testing of the electrolyzer for over 1600 h also shows a stable cell voltage. Different systems to address integration challenges are also examined for the integration of electrolysis/hydrolysis and thermolysis/electrolysis processes. New results from experiments for CuCl–HCl–H₂O and CuCl₂–HCl–H₂O ternary systems are presented along with solubility data for CuCl in HCl–H₂O mixtures between 298 and 363 K. A parametric study of multi-generation energy systems incorporating the Cu–Cl cycle is presented with an overall energy efficiency as high as 57% and exergy efficiency of hydrogen production up to 90%.     

Life cycle assessment of nuclear-based hydrogen production via a copper–chlorine cycle: A neural network approach

A comparative environmental study is reported of nuclear-based hydrogen production using thermochemical water decomposition cycles. The investigation uses a life cycle assessment (LCA) as is an analytical tool to evaluate and reduce the environmental impact of the system or product. The LCA results are presented in terms of acidification potential and global warming potential. Since LCA often utilizes software to model and analyse the system, an artificial neural network (ANN) method can be advantageous. Here, an ANN method is applied to a nuclear-based hydrogen production system. Using an ANN method in this study eliminates the need to use LCA software separately and facilitates the determination of the impacts of altering input parameters of a system (e.g., heat, work, production capacity and plant lifetime). The neural network approach to identify the best system option, consistent with LCA software results, is developed here using ten neurons in the hidden layers.     

Energy analysis of a class of copper–chlorine (Cu–Cl) thermochemical cycles

For separating water into hydrogen and oxygen through intermediate Cu–Cl compounds, the new system configurations for 5-step, 4-step and 3-step thermochemical cycles using electrolysis of CuCl/HCl or CuCl and Brayton cycle are addressed in Aspen Plus^® environment. To address the feasible predictions by thermodynamic systems, we found that (i) the pressure and temperature affect the product yields of CuO ¹ CuCl₂ and CuCl in the hydrolysis and oxygen production processes; (ii) the internal heat recovery ratio (IHRR) and the feed ratio of H₂O/CuCl₂ dominate the energy efficiencies and Cl₂ production, respectively. Based on the prescribed operating conditions, the comparative evaluations show that the 5-step Cu–Cl cycle using CuCl electrolyzer can ensure the highest energy efficiency while IHRR = 72%, the 3-step Cu–Cl cycle using CuCl electrolyzer can ensure the less equipment and the highest energy efficiency while IHRR = 100%. The 4-step Cu–Cl cycle using CuCl/HCl electrolyzer, where the electrolyzer prevents copper crossovers and safely produces the pure hydrogen gas at low temperature, has a high possibility of commercialization due to the lower grade heat requirement, the less number of equipment and the higher energy efficiency.     

Exergy analysis of Cobalt–Chlorine thermochemical hydrogen production cycle: A kinetic approach

Increasing energy needs and reducing greenhouse gas emissions require immediate studies on carbon-free energy solutions, namely hydrogen. There are numerous methods among the production methods of hydrogen in a green manner. Hydrogen, which is then primarily obtained as a result of the separation of water with thermochemical cycles, is an environmentally friendly and sustainable hydrogen production method. In this study, the Cobalt–Chlorine (Co–Cl) cycle, which is one of the new thermochemical cycles, is examined in detail in terms of thermodynamics. There are four reactions in the Co–Cl thermochemical cycle. These are listed as the hydrolysis reaction in which hydrogen is obtained, the thermolysis reaction in which oxygen is obtained, the reduction reaction and finally the hydrochlorination reaction. According to the results of the analysis performed kinetically with the Aspen Plus software, the exergy efficiency of the cycle is calculated as 33%. When the exergy destruction of all reactions is compared, it is seen that the greatest exergy destruction occurs in the hydrolysis reaction, and the lowest exergy destruction occurs in the hydrochlorination reaction. The fact that the exergy efficiency is high when evaluated in terms of kinetics shows that the cycle is feasible in terms of thermodynamics. In addition, the costs of the cycle are to be considered in the future studies as it is an important criterion.     

Progress of international hydrogen production network for the thermochemical Cu–Cl cycle

This paper presents recent advances by an international team which is developing the thermochemical copper–chlorine (Cu–Cl) cycle for hydrogen production. Development of the Cu–Cl cycle has been pursued by several countries within the framework of the Generation IV International Forum (GIF) for hydrogen production with the next generation of nuclear reactors. Due to its lower temperature requirements in comparison with other thermochemical cycles, the Cu–Cl cycle is particularly well matched with Canada's Generation IV reactor, SCWR (Super-Critical Water Reactor), as well as other heat sources such as solar energy or industrial waste heat. In this paper, recent developments of the Cu–Cl cycle are presented, specifically involving unit operation experiments, corrosion resistant materials and system integration.     

Preliminary process analysis for the closed cycle operation of the iodine–sulfur thermochemical hydrogen production process

In the iodine–sulfur thermochemical hydrogen production process, a separation characteristic of 2-liquid phase (H₂SO₄ phase and HI_x phase) in the separator at 0°C was measured. Two-phase separation began to occur at about 0.32 of I₂ molar fraction and over. The separation characteristic became better with the increase in iodine concentration in the solution. The effect of flow rate variations of HI solution and I₂ solution from the HI_x distillation column on the process was evaluated. The flow rate increase in HI solution from the distillation column did not have a large effect on the flow rate of HI solution fed to the distillation column from the separator. The decreasing flow rate of I₂ solution from the distillation column decreased the flow rate of I₂ solution fed to the distillation column from the separator. The variation of I₂ molar fraction in the H₂SO₄ phase in the separator was sensitive to the variation in flow rate of both solutions from the distillation column. The tolerance level of the variation was investigated by considering I₂ solubility, 2-liquid phase disappearance and SO₂ reaction amount.     

Exergoeconomic machine-learning method of integrating a thermochemical Cu–Cl cycle in a multigeneration combined cycle gas turbine for hydrogen production

Integrating new technologies into existing thermal energy systems enables multigenerational production of energy sources with high efficiency. The advantages of multigenerational energy production are reflected in the rapid responsiveness of the adaptation of energy source production to current market conditions. To further increase the useful efficiency of multigeneration energy sources production, we developed an exergoeconomic machine-learning model of the integration of the hydrogen thermochemical Cu–Cl cycle into an existing gas-steam power plant. The hydrogen produced will be stored in tanks and consumed when the market price is favourable. The results of the exergoeconomic machine-learning model show that the production and use of hydrogen, in combination with fuel cells, are expedient for the provision of tertiary services in the electricity system. In the event of a breakdown of the electricity system, hydrogen and fuel cells could be used to produce electricity for use by the thermal power plant. The advantages of own or independent production of electricity are primarily reflected in the start-up of a gas-steam power plant, as it is not possible to start a gas turbine without external electricity. The exergy analysis is also in favour of this, as the integration of the hydrogen thermochemical Cu–Cl cycle into the existing gas-steam power plant increases the exergy efficiency of the process.     

Determining parameters of heat exchangers for heat recovery in a Cu–Cl thermochemical hydrogen production cycle

A heat exchanger is a device built for efficient heat transfer from one medium to another. Shell and tube heat exchangers are separated wall heat exchangers and are commonly used in the nuclear and process industry. The CuCl cycle is used to thermally crack water in to H₂ and O₂. The present study presents the heat exchanger thermal design using analysis of variance for heat recovery from oxygen at 500 °C, coming from the molten salt reactor. Polynomial regressions in terms of the amount of chlorine in the oxygen, the mass flow rate on the tube side, and the shell's outlet temperature are estimated for various exchanger parameters and the results are compared with the bell Delaware method. Based on energy and exergy analysis, this study also discusses the best possible path for the recovered heat from oxygen. Optimal heat exchanger parameters are estimated by Design-Expert^® Stat-Ease for most effective heat recovery.     

Multigeneration system exergy analysis and thermal management of an industrial glassmaking process linked with a Cu–Cl cycle for hydrogen production

A multigeneration system for hydrogen production linked with a glassmaking process via thermal management is examined in this study. The exhaust gas is interconnected with a Rankine cycle and the copper-chlorine (Cu–Cl) cycle for hydrogen production. The present system consists of a steam Rankine cycle, Cu–Cl cycle with multistage compression, double-stage organic Rankine cycle, and multi-effect desalination system. A Cu–Cl cycle based on the four-step model is employed with the proposed system. The useful system outputs are electricity, hydrogen, and fresh water. The simulation software packages utilized in the analysis and modeling are Engineering Equation Solver and Aspen Plus. The energy efficiency of the overall system is 36.5% while 38.1% is the exergy efficiency. The parametric studies are conducted to investigate the system performance. In addition, the effects of exhaust gas variables, such as flow rate, temperature, and pressure are examined to investigate the system performance.     

A study on the Fe–Cl thermochemical water splitting cycle for hydrogen production

Thermochemical water splitting cycles are recognized as one of the promising pathways for sustainable hydrogen production. In the present study, Iron-chlorine (Fe–Cl) cycle as one of the chlorine family thermochemical cycles where iron chloride is consumed for hydrogen production from water, is considered for a study. This four-step cycle is modelled by Aspen Plus software package and analyzed for performance investigation of each reaction step and system's components. The parametric studies are also performed to assess the effect of operation conditions such as temperature, pressure and steam to feed ratio on the reaction products and conversion rates. Results indicated that although the effect of pressure is not significant on reaction's production rates, an increase in temperature favors oxygen production in reverse deacon reaction and magnetite production in hydrolysis and lowers hydrogen production in the hydrolysis step. On the other hand, steam to chlorine (Cl₂) ratio is directly correlated with hydrochloric acid (HCl) and oxygen production in reverse deacon reaction and hydrogen production in hydrolysis.