Environmental evaluation of hydrogen production via thermochemical water splitting using the Cu-Cl Cycle: A parametric study

Variations of environmental impacts with lifetime and production capacity are reported for nuclear based hydrogen production plants using the three-, four- and five-step (copper-chlorine) Cu-CI thermochemical water decomposition cycles. Life cycle assessment is utilized which is essential to evaluate and to decrease the overall environmental impact of any system and/or product. The life cycle assessments of the hydrogen production processes indicate that the four-step Cu-Cl cycle has lower environmental impacts than the three- and five-step cycles due to its lower thermal energy requirement. Parametric studies show for the four-step Cu-Cl cycle that acidification and global warming potentials can be reduced from 0.0031 to 0.0028 kg SO₂-eq and from 0.63 to 0.55 kg CO₂-eq, respectively, if the lifetime of the system increases from 10 to 100 years.     

Thermodynamic performance assessment of boron based thermochemical water splitting cycle for renewable hydrogen production

The present study is related with the thermodynamic performance assessment of renewable hydrogen production through Boron thermochemical water splitting cycle. Therefore, all step efficiencies and overall cycle efficiency are calculated based on complete reaction. Additionally, a parametric study is conducted to determine the effect of the reference environment temperature on the overall cycle efficiency. In this regard, exergy efficiencies, exergy destruction rates and also inlet and outlet exergy rates of the cycle are calculated and presented for various reference temperatures. The exergy efficiency of the cycle is calculated as 0.4393 based on complete reaction and occurs at 298 K. This study has shown that Boron thermochemical water splitting cycle has a great potential due to cycle performance. As a result, Boron based thermochemical water splitting cycle can help achieve better environment and sustainability due to high exergetic efficiency. By the way, economic and technical issues of the storage and transportation of the hydrogen can find a proper solution if the hydrogen production reaction of the Boron thermochemical water splitting cycle takes place on-board of a vehicle.     

A comparative life cycle analysis of hydrogen production via thermochemical water splitting using a Cu-Cl cycle

In this paper, a comparative environmental study is reported of the Cu-Cl water-splitting cycle with various other hydrogen production methods: the sulphur-iodine (S-I) water-splitting cycle, high temperature water electrolysis, conventional steam reforming of natural gas and hydrogen production from renewable resources. The investigation uses life cycle assessment (LCA), which is an analytical tool to identify and quantify environmentally critical phases during the life cycle of a system or a product and/or to evaluate and decrease the overall environmental impact of the system or product. The LCA results for the hydrogen production processes indicate that the thermochemical cycles have lower environmental impacts while steam reforming of natural gas has the highest.     

Advances in hydrogen production by thermochemical water decomposition: A review

Hydrogen demand as an energy currency is anticipated to rise significantly in the future, with the emergence of a hydrogen economy. Hydrogen production is a key component of a hydrogen economy. Several production processes are commercially available, while others are under development including thermochemical water decomposition, which has numerous advantages over other hydrogen production processes. Recent advances in hydrogen production by thermochemical water decomposition are reviewed here. Hydrogen production from non-fossil energy sources such as nuclear and solar is emphasized, as are efforts to lower the temperatures required in thermochemical cycles so as to expand the range of potential heat supplies. Limiting efficiencies are explained and the need to apply exergy analysis is illustrated. The copper–chlorine thermochemical cycle is considered as a case study. It is concluded that developments of improved processes for hydrogen production via thermochemical water decomposition are likely to continue, thermochemical hydrogen production using such non-fossil energy will likely become commercial, and improved efficiencies are expected to be obtained with advanced methodologies like exergy analysis. Although numerous advances have been made on sulphur–iodine cycles, the copper–chlorine cycle has significant potential due to its requirement for process heat at lower temperatures than most other thermochemical processes.     

Experimental study of effect of anolyte concentration and electrical potential on electrolyzer performance in thermochemical hydrogen production using the Cu-Cl cycle

An important process in the copper-chlorine water splitting cycle for hydrogen production is electrolysis which occurs after a series of cycle steps that produce the constituents for the anolyte of the electrochemical cell. In this investigation, an anolyte mixture of HCl/CuCl/H₂O of varying concentrations is circulated through the electrolyzer to assist in optimizing its performance. It is observed that the concentration and temperature of the anolyte directly affect the process. The efficiency of the electrolyzer is adversely affected, after running a series of experiments, due to copper deposition on the membrane. An important implication of the results is that, to determine the optimal electrolyzer performance, one needs to vary the flow rate and the concentration of anolyte, for a given constant voltage source. In addition, this work demonstrates that aqueous CuCl₂ can be recovered from the waste solution exiting the electrolyzer and recycled to the hydrolysis reactor.     

Commercial activated carbon for the catalytic production of hydrogen via the sulfur-Iodine thermochemical water splitting cycle

Eight commercial activated carbon catalysts were examined for their catalytic activity to decompose hydroiodic acid (HI) to produce hydrogen; a key reaction in the sulfur-iodine (S-I) thermochemical water splitting cycle. Activity was examined under a temperature ramp from 473 to 773 K. No statistically significant correlation was found between the measured catalyst sample properties and catalytic activity. Four of the eight samples were examined for one week of continuous operation at 723 K. All samples appeared to be stable over the period of examination.     

Exergy analysis of hydrogen production by thermochemical water decomposition using the Ispra Mark-10 Cycle

An investigation is reported of the thermodynamic performance of the Ispra Mark-10 thermochemical water decomposition process for hydrogen production. Thermochemical water decomposition has been identified as a potentially important future process for the production of hydrogen, which is currently an important industrial commodity and has significant future potential as a fuel. Exergy analysis is used since energy analysis on its own does not pinpoint true process inefficiencies, and often does not provide rational efficiencies. The analysis indicates that the principle thermodynamic losses occur in the primary water decomposition reactors and are mainly due to internal irreversibilities associated with chemical reaction and heat transfer across large temperature differences, and that the losses associated with effluents (particularly cooling water) are not that significant. Energy and exergy efficiencies are provided and are observed to depend strongly on the main external process inputs, i.e., electricity and process heat, or heat, or the raw resource from which heat and electricity are produced.     

Two-step water splitting thermochemical cycle based on iron oxide redox pair for solar hydrogen production

This study deals with solar hydrogen production from the two-step iron oxide thermochemical cycle (Fe₃O₄/FeO). This cycle involves the endothermic solar-driven reduction of the metal oxide (magnetite) at high temperature followed by the exothermic steam hydrolysis of the reduced metal oxide (wustite) for hydrogen generation. Thermodynamic and experimental investigations have been performed to quantify the performances of this cycle for hydrogen production. High-temperature decomposition reaction (metal oxide reduction) was performed in a solar reactor set at the focus of a laboratory-scale solar furnace. The operating conditions for obtaining the complete reduction of magnetite into wustite were defined. An inert atmosphere is required to prevent re-oxidation of Fe(II) oxide during quenching. The water-splitting reaction with iron(II) oxide producing hydrogen was studied to determine the chemical kinetics, and the influence of temperature and particles size on the chemical conversion. A conversion of 83% was obtained for the hydrolysis reaction of non-stoichiometric solar wustite Fe_(1−y)O at 575 °C.     

Manganese oxide based thermochemical hydrogen production cycle

A MnO/NaOH based three-step thermochemical water splitting cycle was modified to improve the hydrolysis of α-NaMnO₂ (sodium manganate) and to recover Mn(III) oxides for the high-temperature reduction step. Sodium manganate forms in the reaction of NaOH with MnO that releases hydrogen. The hydrolysis of α-NaMnO₂ to manganese oxides and NaOH is incomplete even with a large excess of water and more than 10% sodium cannot be removed prior to the high-temperature reduction step.When mixed oxides of manganese with iron were used in the cycle, the NaOH recovery in the hydrolysis step improved from about 10% to 35% at NaOH concentrations above 1M. Only 60% sodium was removed at 0.5M from the mixed oxides whereas more than 80% can be recovered at the same NaOH concentration when only manganese oxides are used. A 10:1 Mn/Fe sample was cycled through all steps three times to confirm that multiple cycles are possible. The high-temperature reduction was carried out for 5h at 1773 K under vacuum and the conversion was about 65% after the 3rd cycle.Since sodium carryover into the high-temperature reduction cannot be avoided, even with the energy intensive hydrolysis step, a modified two-step cycle without low-temperature sodium recovery is proposed where α-NaMnO₂ is reduced directly to MnO at 1773 K under vacuum. On a laboratory scale, about 60% of the sodium that volatilized at the high temperatures was trapped with a water-cooled cold finger and conversions were stable at about 35% after three completed cycles.     

Clean hydrogen production with the Cu-Cl cycle - Progress of international consortium, II: Simulations, thermochemical data and materials

This second of two companion papers presents the latest advances of an international team on the thermochemical copper-chlorine (Cu-Cl) cycle of hydrogen production. It specifically focuses on simulations, thermochemical data, advanced materials, safety, reliability and economics of the Cu-Cl cycle. Aspen Plus simulations of various system configurations are performed to improve the cycle efficiency. In addition, simulations based on exergo-economic and exergy-cost-energy-mass (EXCEM) methods for system design are presented. Modeling of the linkage between nuclear and hydrogen plants demonstrates how the Cu-Cl cycle would be integrated with an SCWR (Super Critical Water Reactor; Canada’s Generation IV reactor). Chemical potentials, solubilities, formation of Cu(I) and Cu(II) complexes and properties of Cu₂OCl₂, Cu(I) and Cu(II) chloride species are reported. In addition, the development of new advanced materials with improved corrosion resistance is presented. In particular, the performance of new anode electrode structures and thermal spray coatings is presented. This companion set of two papers presents new advances in a range of key enabling technologies for the thermochemical copper-chlorine cycle.     

Thermodynamic viability of a new three step high temperature Cu-Cl cycle for hydrogen production

A new three step high temperature Cu-Cl thermochemical cycle for hydrogen production is presented. The performance of the proposed cycle is investigated through energy and exergy approaches. Furthermore, the effects of various parameters, such as the temperatures of the steps of the cycle and power plant efficiency, on various energy and exergy efficiencies are assessed with parametric studies. The results show that the exergy and energy efficiencies of the proposed cycle are 68.3% and 32.0%, respectively. In addition, the exergy analysis results reveal that the hydrogen production step has the maximum specific exergy destruction with a value of 150.9 kJ/mol. The results suggest that proposed cycle may provide enhanced options for high temperature thermochemical cycles by improving thermal management without causing a sudden temperature jump/fall between the hydrogen production step and other steps.     

Development and test of a solar reactor for decomposition of sulphuric acid in thermochemical hydrogen production

Decomposition of sulphuric acid is a key step of sulphur based thermochemical cycles for hydrogen production by thermal splitting of water. The Hybrid Sulphur Cycle (HyS) consisting of two reaction steps is considered as one of the most promising cycles: firstly, sulphuric acid is decomposed by high temperature heat of 800–1200 °C forming sulphur dioxide, which in a second step is used to electrochemically split water. Compared to conventional water electrolysis only about a tenth of the theoretical voltage is required making the HyS one of the most efficient processes to produce hydrogen by concentrated solar radiation. As a result, this thermochemical cycle has the potential to significantly reduce the amount of energy required for water splitting and to efficiently generate hydrogen free of carbon dioxide emissions. The European research project HycycleS aims at a technical realisation of the HyS. One objective of the project is to develop and qualify a solar interface, meaning a device to couple concentrated solar radiation into the endothermal steps of the chemical process. Therefore, a test reactor for decomposition of sulphuric acid by concentrated solar radiation was developed and tested in the solar furnace of DLR in Cologne. Tests in concentrated solar radiation were carried out for temperatures of the honeycomb up to 950 °C decomposing sulphuric acid of 50 and 96 weight-percent. Mass and energy flow of the process were calculated in order to determine energy efficiency and chemical conversion. The influence of process parameters like temperature, flow rates and space velocity on chemical conversion and reactor efficiency was analysed in detail. If catalysts like iron oxide (Fe₂O₃) and mixed oxides (i.e. CuFe₂O₄) were used a conversion of SO₃ to SO₂ of more than 80% at a thermal efficiency of over 25% could be reached.     

Pressure drop of packed bed vertical flow for multiphase hydrogen production

In this paper, fluid flow characteristics through a packed bed reactor are investigated. The packed bed is utilized in the hydrogen production step of the copper-chlorine (Cu-Cl) thermochemical cycle. The hydrogen reaction is given by 2Cu(s) + 2HCl(g) = 2CuCl(molten) + H₂(g) at 450 °C. Effectively controlling the pressure drop through the packed bed is important for increasing the system efficiency, since auxiliary pumps and other parasitic losses are affected by the pressure drop. Also, the chemical processes in the packed bed are affected by changes in pressure, temperature and heat transfer rates.Experimental results from a laboratory scale packed bed reactor, operating at ambient conditions, are presented and compared with analytical predictions, in terms of the pressure drop caused by fluid flow through the packing material. Three different packing materials, with various sphericities, are investigated with diameters of 450 μm, 4 mm, and 1 cm. The Ergun equation is shown to provide good agreement for flow conditions in the upper region of Reynolds numbers investigated (20 < Re_p < 150); however, lack of agreement is observed at lower Reynolds numbers (Re_p < 20). An analytical formulation for micro scale particles in a packed bed is developed based on the Stokes law for creeping flow. Good agreement is achieved with the corresponding experimental data. A new correction is also developed to connect the two flow regimes, as well as predict trends in the transition region. The results successfully demonstrate close agreement between the predictions and measured data.     

Experimental assessment of the cyclability of the Mn2O3/MnO thermochemical cycle for solar hydrogen production

The cyclability of Mn₂O₃/MnO thermochemical cycle for solar hydrogen production has been experimentally evaluated. The results of three consecutive cycles show a stable hydrogen production per mass of initial solid that is in agreement with the maximum expected amount according to the stoichiometry of the process. The characterization of the material recovered after each cycle shows a mixture of different manganese oxide phases that are completely converted into MnO in the subsequent thermal reduction, maintaining the productivity of the cycles. Based on that, a modification of the thermochemical cycle scheme is proposed taking into account the differences observed between the first cycle and the following ones. MnO₂/MnO thermochemical cycle appears as a promising alternative, working in the same temperature range but with a theoretical hydrogen production per unit mass of solid manganese oxide almost twice than that obtained with the conventional Mn₂O₃/MnO cycle. Finally, the results of exergy efficiency of the complete cycle give new insights into the commercial possibilities of the cycle for hydrogen production, demonstrating the sustainable cyclability of the process regarding the manganese containing materials at lower temperatures than those theoretically reported in literature and consequently with higher exergy efficiencies that the common values associated to this cycle.     

A comparative evaluation of three CuCl cycles for hydrogen production

The thermochemical CuCl cycle has received greater attention by numerous researchers during the past decade as a promising hydrogen production method because of some operational advantages. The present paper analyzes three different configurations of the CuCl thermochemical cycle, namely three, four and five step ones thermodynamically. Some comparative parametric studies are conducted in order to investigate the overall energy and exergy efficiencies of the cycles considered. The Aspen plus is the software tool employed for the modeling and simulation of the cycles. The energy and exergy efficiencies of the five-step CuCl cycle are found to be 38.8% and 70.2% while the three-step CuCl cycle has an energy efficiency of 39.6% and an exergy efficiency of 68.1%, respectively. On the other hand, the four-step CuCl cycle provides the highest energy and exergy efficiencies of 41.9% and 75.7%. A parametric study is also conducted to investigate the effect of varying ambient temperature on the exergy efficiencies of all three cycles. The present study results further reveal that the cycle performance can be enhanced by improving the thermal management and reducing the exergy destructions.     

Analysis of solar chemical processes for hydrogen production from water splitting thermochemical cycles

This paper presents a process analysis of ZnO/Zn, Fe₃O₄/FeO and Fe₂O₃/Fe₃O₄ thermochemical cycles as potential high efficiency, large scale and environmentally attractive routes to produce hydrogen by concentrated solar energy. Mass and energy balances allowed estimation of the efficiency of solar thermal energy to hydrogen conversion for current process data, accounting for chemical conversion limitations. Then, the process was optimized by taking into account possible improvements in chemical conversion and heat recoveries. Coupling of the thermochemical process with a solar tower plant providing concentrated solar energy was considered to scale up the system. An economic assessment gave a hydrogen production cost of 7.98$ kg⁻¹ and 14.75$ kg⁻¹ of H₂ for, respectively a 55 MW_th and 11 MW_th solar tower plant operating 40 years.     

Environmental impacts of a standalone solar water splitting system for sustainable hydrogen production: A life cycle assessment

Hydrogen is broadly utilized in various industries. It can also be considered as a future clean energy carrier. Currently, hydrogen is mainly produced from typical fuels such as coal; however, there exist some other clean alternatives which use water decomposition techniques. Water splitting via the copper-chlorine (Cu–Cl) thermochemical cycle is a superb option for producing clean carbon-free fuel. Here, the life cycle assessment (LCA) technique is used to investigate the environmental consequences of an integrated solar Cu–Cl fuel production facility for large-scale hydrogen production. The impact of varying important input parameters including irradiation level, plant lifetime, and solar-to-hydrogen efficiency on various environmental impacts are investigated next. For instance, an improve in the solar-to-hydrogen efficiency from 15% to 30%, results in a reduction in the GWP from 1.25 to 6.27E-01 kg CO₂ eq. An uncertainty analysis using Monte Carlo simulation is conducted to deal with the study uncertainties. The results of the LCA show that the potential of acidification and global warming potential (GWP) of the current system are 8.27E-03 kg SO₂ eq. and 0.91 kg CO₂ eq./kg H₂, respectively. According to the sensitivity analysis, the plant lifetime has the highest effect on the total GWP of the plant with a range of 0.63–1.88 kg of CO₂ eq./kg H₂. Results comparison with past thermochemical-based studies shows that the GWP of the current integrated system is 7% smaller than that of a solar sulfur-iodine thermochemical cycle.     

Clean hydrogen production with the Cu-Cl cycle - Progress of international consortium, I: Experimental unit operations

Advancement of the thermochemical copper-chlorine (Cu-Cl) cycle for hydrogen production is reviewed and discussed in this paper. Individual unit operations and their linkage into an integrated cycle are being developed by a Canadian consortium, as part of the Generation IV International Forum (GIF) for hydrogen production with the next generation of nuclear reactors. This paper focuses on the consortium’s latest advances on the Cu-Cl cycle, particularly with respect to hydrogen production with Canada’s Generation IV reactor, called SCWR (Super-Critical Water Reactor). Other heat sources may also be utilized for the Cu-Cl cycle, such as solar energy or industrial waste heat. In this first of two companion papers, recent developments in Canada’s nuclear hydrogen program are reported, specifically unit operation experiments of the Cu-Cl cycle and system integration. The following second companion paper will present system modeling with Aspen Plus, corrosion resistant materials, thermochemistry, safety, and reliability aspects of the Cu-Cl cycle.     

Study on an original cobalt-chlorine thermochemical cycle for nuclear hydrogen production

In this paper, a theoretical and experimental study on a novel cobalt-chlorine thermochemical cycle for hydrogen production is presented. The cobalt-chlorine cycle comprises a closed loop of four thermochemical reactions occurring at 700 °C that is a reaction temperature compatible with the present generation of high-temperature gas-cooled reactors. Firstly, a thermodynamic analysis was done for determining whether this cycle is attractive for hydrogen production in terms of both energy and exergy efficiencies. Following, proof-of-principle experiments were carried out at laboratory scale in a batch reactor at temperatures in the range from 550 °C to 950 °C and holding times between 1 h and 72 h. Experimental results complemented by the characterization of condensed compounds deposited on the reactor walls allowed confirm the reaction pathway of thermochemical reactions originally proposed, define the slowest step of the global process, and explain the beneficial effect of increasing the system pressure on the hydrogen yield. Even both performance assessment and proof-of-principle experimental results look like promising more research will be required in the future to confirm these preliminary findings. Finally, a modified version of the cobalt-chlorine cycle is proposed for enhancing the global kinetics, based on the experimental evidence found in the proof-of-principle tests.     

Analytical prediction of heat capacity of molten AgCl and CuCl with application to thermochemical Cu-Cl cycle for hydrogen production

To sustain our power-dependent world, there is a need for technological innovation in all aspects of science and engineering. Many times, thermophysical and material properties are not well defined for the specific application, which leads to implementing assumptions and approximations from the published data. In the thermochemical copper-chlorine (Cu-Cl) cycle for hydrogen (H₂) production, heat is recovered from cuprous chloride (CuCl) molten salt and it is then reacted with hydrochloric acid (HCl) in stoichiometric proportions to produce the anolyte for the H₂ production step of the cycle. However, the lack of precise thermophysical properties on CuCl heavily hinders the detailed investigations of heat recovery from the molten salt as it cools from 450 °C to 90 °C. In this paper a new method is developed to determine the thermophysical property of CuCl and silver chloride (AgCl) as the molten salts are changing phases to solid. This is achieved by correlating electrochemistry data with thermal data. A model that predicts the specific heat capacity during phase change process is developed based on the existing electromotive force (EMF) and thermal data from literature. Developed model shows the EMF derived specific heat capacity values of AgCl and CuCl are similar with a slight offset since they have similar EMF's at higher temperatures.