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.     

Energy and exergy analyses of magnesium-chlorine (Mg-Cl) thermochemical cycle

In this paper, we conduct energy and exergy analyses of the magnesium-chlorine (Mg-Cl) thermochemical cycle for hydrogen production and examine the respective cycle energy and exergy efficiencies. We also undertake a parametric study to investigate how the overall cycle performance is affected by changing the reference environment temperature and operating conditions. The results show that Mg-Cl cycle offers a good potential due to its high energy and exergy efficiencies as 63.63% and 34.86%, respectively, based upon the conditions and parameters considered. In this regard, Mg-Cl cycle appears to be a promising low temperature thermochemical cycle. It may, therefore, compete with other low temperature thermochemical and hybrid cycles such as the copper–chlorine cycle.     

Potential methods for geothermal-based hydrogen production

In this study, four potential methods are identified for geothermal-based hydrogen production, namely, (i) directly from the geothermal steam, (ii) through conventional water electrolysis using the electricity generated from geothermal power plant, (iii) using both geothermal heat and electricity for high temperature steam electrolysis and/or hybrid processes, (iv) using the heat available from geothermal resource in thermochemical processes to disassociate water into hydrogen and oxygen. Here we focus on relatively low-temperature thermochemical and hybrid cycles, due to their greater application possibility, and examine them as a potential option for hydrogen production using geothermal heat. We also present a brief thermodynamic analysis to assess their performance through energy and exergy efficiencies for comparison purposes. The results show that these cycles have good potential and become attractive due to the overall system efficiencies over 50%. The copper–chlorine cycle is identified as a highly promising cycle for geothermal hydrogen production. Furthermore, three types of industrial electrolysis methods, which are generally considered for hydrogen production currently, are also discussed and compared with the above mentioned cycles.     

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.     

An exergy–cost–energy–mass analysis of a hybrid copper–chlorine thermochemical cycle for hydrogen production

An exergoeconomic assessment using exergy–cost–energy–mass (EXCEM) analysis is reported of a copper–chlorine (Cu–Cl) thermochemical water splitting cycle for hydrogen production. The quantitative relation is identified between capital costs and thermodynamic losses for devices in the cycle. A correlation detected in previous assessments, suggesting that devices in energy systems are configured so as to achieve an overall optimal design by appropriately balancing thermodynamic (exergy-based) and economic characteristics of the overall system and its components, is observed to apply for the Cu–Cl cycle. Exergetic cost allocations and various exergoeconomic performance parameters are determined for the overall cycle and its components. The results are expected to assist ongoing efforts to increase the economic viability and to reduce product costs of potential commercial versions of this process. The impacts of these results are anticipated to be significant since thermochemical water splitting with a copper–chlorine cycle is a promising process that could be linked with nuclear reactors to produce hydrogen with no greenhouse gases emissions, and thereby help mitigate numerous energy and environment concerns.     

Comparative assessment of hydrogen production methods from renewable and non-renewable sources

In this study, we present a comparative environmental impact assessment of possible hydrogen production methods from renewable and non-renewable sources with a special emphasis on their application in Turkey. It is aimed to study and compare the performances of hydrogen production methods and assess their economic, social and environmental impacts, The methods considered in this study are natural gas steam reforming, coal gasification, water electrolysis via wind and solar energies, biomass gasification, thermochemical water splitting with a Cu–Cl and S–I cycles, and high temperature electrolysis. Environmental impacts (global warming potential, GWP and acidification potential, AP), production costs, energy and exergy efficiencies of these eight methods are compared. Furthermore, the relationship between plant capacity and hydrogen production capital cost is studied. The social cost of carbon concept is used to present the relations between environmental impacts and economic factors. The results indicate that thermochemical water splitting with the Cu–Cl and S–I cycles become more environmentally benign than the other traditional methods in terms of emissions. The options with wind, solar and high temperature electrolysis also provide environmentally attractive results. Electrolysis methods are found to be least attractive when production costs are considered. Therefore, increasing the efficiencies and hence decreasing the costs of hydrogen production from solar and wind electrolysis bring them forefront as potential options. The energy and exergy efficiency comparison study indicates the advantages of biomass gasification over other methods. Overall rankings show that thermochemical Cu–Cl and S–I cycles are primarily promising candidates to produce hydrogen in an environmentally benign and cost-effective way.     

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.     

Multiphase reactor scale-up for Cu–Cl thermochemical hydrogen production

This paper examines selected design issues associated with reactor scale-up in the thermochemical copper–chlorine (Cu–Cl) cycle of hydrogen production. The thermochemical cycle decomposes water into oxygen and hydrogen, through intermediate copper and chlorine compounds. In this paper, emphasis is focused on the hydrogen, oxygen and hydrolysis reactors. A sedimentation cell for copper separation and HCl gas absorption tower are discussed for the thermochemical hydrogen reactor. A molten salt reactor is investigated for decomposition of an intermediate compound, copper oxychloride (CuO·Cl₂), into oxygen gas and molten cuprous chloride. Scale-up design issues are examined for handling three phases within the molten salt reactor, i.e., solid copper oxychloride particles, liquid (melting salt) and exiting gas (oxygen). Also, different variations of hydrolysis reactions are compared, including 5, 3 and 2-step Cu–Cl cycles that utilize reactive spray drying, instead of separate drying and hydrolysis processes. The spray drying involves evaporation of aqueous feed by mixing the spray and drying streams. Results are presented for the required capacities of feed materials for the multiphase reactors, steam and heat requirements, and other key design parameters for reactor scale-up to a pilot-scale capacity.     

Sustainable hydrogen production options and the role of IAHE

In this paper, some potential sustainable hydrogen production options are identified and discussed. There are natural resources from which hydrogen can be extracted such as water, fossil hydrocarbons, biomass and hydrogen sulphide. In addition, hydrogen can be extracted from a large palette of anthropogenic wastes starting with biomass residuals, municipal wastes, plastics, sewage waters etc. In order to extract hydrogen from these resources one needs to use sustainable energy sources like renewables and nuclear. A total of 24 options for sustainable hydrogen production are then identified. Sustainable water splitting is the most important method of hydrogen production. Five sustainable options are discussed to split water, which include electrolysis, high temperature electrolysis, pure and hybrid thermochemical cycles, and photochemical/radiochemical methods. Other 19 methods refer to extraction of hydrogen from other materials than water or in conjunction with water (e.g., coal gasification with CO₂ capture and sequestration). For each case the achievable energy and exergy efficiency of the method were estimated based on state of the art literature screening for each involved process. In addition, a range of hydrogen production capacity is determined for each of the option. For a transition period to hydrogen economy nuclear or solar assisted coal gasification and fossil fuel reforming technologies – with efficiencies of 10–55% including CO₂ sequestration – should be considered as a viable option. Other “ready to be implemented” technology is hydro-power coupled to alkaline electrolysers which shows the highest hydrogen generation efficiency amongst all electrical driven options with 60–65%. Next generation nuclear reactors as to be coupled with thermochemical cycles have the potential to generate hydrogen with 40–43% energy efficiency (based on LHV of hydrogen) and 35–37% exergy efficiency (based on chemical exergy of hydrogen). Furthermore, recycling anthropogenic waste, including waste heat, waste plastic materials, waste biomass and sewage waters, shows also good potential as a sustainable option for hydrogen production. Biomass conversion to hydrogen is found as potentially the most efficient amongst all studied options in this paper with up to 70% energy efficiency and 65% exergy efficiency.     

Comparative assessment of greenhouse gas mitigation of hydrogen passenger trains

This paper examines a comparative assessment in terms of CO₂ emissions from a hydrogen passenger train in Ontario, Canada, particularly comparing four specific propulsion technologies: (1) conventional diesel internal combustion engine (ICE), (2) electrified train, (3) hydrogen ICE, and (4) hydrogen PEM fuel cell (PEMFC) train. For the electrified train, greenhouse gases from electricity generation by natural gas and coal-burning power plants are taken into consideration. Several hydrogen production methods are also considered in this analysis, i.e., (1) steam methane reforming (SMR), (2) thermochemical copper–chlorine (Cu–Cl) cycle supplied partly by waste heat from a nuclear plant, (3) renewable energies (solar and wind power) and (4) a combined renewable energy and copper–chlorine cycle. The results show that a PEMFC powertrain fueled by hydrogen produced from combined wind energy and a copper–chlorine plant is the most environmentally friendly method, with CO₂ emissions of about 9% of a conventional diesel train or electrified train that uses a coal-burning power plant to generate electricity. Hydrogen produced with a thermochemical cycle is a promising alternative to further reduce the greenhouse gas emissions. By replacing a conventional diesel train with hydrogen ICE or PEMFC trains fueled by Cu-Cl based-hydrogen, the annual CO₂ emissions are reduced by 2260 and 3318 tonnes, respectively. A comparison with different types of automobile commuting scenarios to carry an equivalent number of people as a train is also conducted. On an average basis, only an electric car using renewable energy-based electricity that carries more than three people may be competitive with hydrogen trains.     

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.     

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.     

Geothermal‐based hydrogen production using thermochemical and hybrid cycles: A review and analysis

Geothermal‐based hydrogen production, which basically uses geothermal energy for hydrogen production, appears to be an environmentally conscious and sustainable option for the countries with abundant geothermal energy resources. In this study, four potential methods are identified and proposed for geothermal‐based hydrogen production, namely: (i) direct production of hydrogen from the geothermal steam, (ii) through conventional water electrolysis using the electricity generated through geothermal power plant, (iii) by using both geothermal heat and electricity for high temperature steam electrolysis and/or hybrid processes, and (iv) by using the heat available from geothermal resource in thermochemical processes. Nowadays, most researches are focused on high‐temperature electrolysis and thermochemical processes. Here we essentially discuss some potential low‐temperature thermochemical and hybrid cycles for geothermal‐based hydrogen production, due to their wider practicality, and examine them as a sustainable option for hydrogen production using geothermal heat. We also assess their thermodynamic performance through energy and exergy efficiencies. The results show that these cycles have good potential and attractive overall system efficiencies over 50% based on a complete reaction approach. The copper‐chlorine cycle is identified as a highly promising cycle for geothermal‐hydrogen production. Copyright © 2009 John Wiley & Sons, Ltd.     

Exergetic life cycle assessment of a hydrogen production process

Exergetic life cycle assessment (ExLCA) is applied with life cycle assessment (LCA) to a hydrogen production process. This comparative environmental study examines a nuclear-based hydrogen production via thermochemical water splitting using a copper–chlorine cycle. LCA, which is an analytical tool to identify, quantify and decrease the overall environmental impact of a system or a product, is extended to ExLCA. Exergy efficiencies and air pollution emissions are evaluated for all process steps, including the uranium processing, nuclear and hydrogen production plants. LCA results are presented in four categories: acidification potential, eutrophication potential, global warming potential and ozone depletion potential. A parametric study is performed for various plant lifetimes. The ExLCA results indicate that the greatest irreversibility is caused by uranium processing. The primary contributor of the life cycle irreversibility of the nuclear-based hydrogen production process is fuel (uranium) processing, for which the exergy efficiency is 26.7% and the exergy destruction is 2916.3 MJ. The lowest global warming potential per megajoule exergy of hydrogen is 5.65 g CO₂-eq achieved a plant capacity of 125,000 kg H₂/day. The corresponding value for a plant capacity of 62,500 kg H₂/day is 5.75 g CO₂-eq.     

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.     

Natural gas usage as a heat source for integrated SMR and thermochemical hydrogen production technologies

This paper investigates various usages of natural gas (NG) as an energy source for different hydrogen production technologies. A comparison is made between the different methods of hydrogen production, based on the total amount of natural gas needed to produce a specific quantity of hydrogen, carbon dioxide emissions per mole of hydrogen produced, water requirements per mole of hydrogen produced, and a cost sensitivity analysis that takes into account the fuel cost, carbon dioxide capture cost and a carbon tax. The methods examined are the copper–chlorine (Cu–Cl) thermochemical cycle, steam methane reforming (SMR) and a modified sulfur–iodine (S–I) thermochemical cycle. Also, an integrated Cu–Cl/SMR plant is examined to show the unique advantages of modifying existing SMR plants with new hydrogen production technology. The analysis shows that the thermochemical Cu–Cl cycle out-performs the other conventional methods with respect to fuel requirements, carbon dioxide emissions and total cost of production.     

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.     

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.     

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%.     

Economic comparison of solar hydrogen generation by means of thermochemical cycles and electrolysis

Hydrogen is acclaimed to be an energy carrier of the future. Currently, it is mainly produced by fossil fuels, which release climate-changing emissions. Thermochemical cycles, represented here by the hybrid-sulfur cycle and a metal oxide based cycle, along with electrolysis of water are the most promising processes for ‘clean’ hydrogen mass production for the future. For this comparison study, both thermochemical cycles are operated by concentrated solar thermal power for multistage water splitting. The electricity required for the electrolysis is produced by a parabolic trough power plant. For each process investment, operating and hydrogen production costs were calculated on a 50 MW_th scale. The goal is to point out the potential of sustainable hydrogen production using solar energy and thermochemical cycles compared to commercial electrolysis. A sensitivity analysis was carried out for three different cost scenarios. As a result, hydrogen production costs ranging from 3.9–5.6 €/kg for the hybrid-sulfur cycle, 3.5–12.8 €/kg for the metal oxide based cycle and 2.1–6.8 €/kg for electrolysis were obtained.