Thermochemical Water Decomposition Research Articles

Comparative environmental impact and efficiency assessment of selected hydrogen production methods

The environmental impacts of various hydrogen production processes are evaluated and compared, considering several energy sources and using life cycle analysis. The results indicate that hydrogen produced by thermochemical water decomposition cycles are more environmentally benign options compared to conventional steam reforming of natural gas. The nuclear based four-step Cu–Cl cycle has the lowest global warming potential (0.559kgCO2-eq per kg hydrogen production), mainly because it requires the lowest quantity of energy of the considered processes. The acidification potential results show that biomass gasification has the highest impact on environment, while wind based electrolysis has the lowest. The relation is also investigated between efficiency and environmental impacts.

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.

Investigation of an integrated hydrogen production system based on nuclear and renewable energy sources: a new approach for sustainable hydrogen production via copper-chlorine thermochemical cycles

SUMMARY Hydrogen production via thermochemical water decomposition is a potential process for direct utilization of nuclear thermal energy to increase efficiency and thereby facilitate energy savings. Thermochemical water splitting with a copper–chlorine (Cu–Cl) cycle could be linked with nuclear and renewable energy sources to decompose water into its constituents, oxygen and hydrogen, through intermediate Cu and Cl compounds. In this study, we analyze a coupling of nuclear and renewable energy sources for hydrogen production by the Cu–Cl thermochemical cycle. Nuclear and renewable energy sources are reviewed to determine the most appropriate option for the Cu–Cl cycle. An environmental impact assessment is conducted and compared with conventional methods using fossil fuels and other options. The CO2 emissions for hydrogen production are negligibly small from renewables, 38 kg/kg H2 from coal, 27 kg/kg H2 from oil, and 18 kg/kg H2 from natural gas. Cost assessment studies of hydrogen production are presented for this integrated system and suggest that the cost of hydrogen production will decrease to $2.8/kg. Copyright © 2011 John Wiley & Sons, Ltd.

Analysis of the hazards for the molten cuprous chloride pouring operation in an industrial hydrogen production facility

Hydrogen can be produced by thermochemical water decomposition from various heat sources. The copper-chlorine (Cu-Cl) cycle is a potential future cycle that could be linked with nuclear reactors to thermally decompose water into oxygen and hydrogen, through intermediate copper and chlorine compounds. Heat is transferred between various processes. Effective heat recovery from the molten CuCl within the cycle is important for achieving high efficiency. This paper described the fundamentals of a preliminary HVAC system design for the molten CuCl pouring operation in an industrial facility, and the use of air cleaning devices to remove contaminants before discharge to the outdoor air. Heat recovery from molten CuCl involves calculating duct diameters to provide the desired duct air velocity through the system. The fan size is determined by evaluating the static pressure. An adequate supply of make-up air must be provided to replace the air exhausted through the ventilation system. This paper described the economics of the ventilation system as well as ways to protect employee health and minimize the costs associated with exhaust ventilation. 20 refs., 1 tab., 5 figs.

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 SO 2-eq and from 0.63 to 0.55 kg CO 2-eq, respectively, if the lifetime of the system increases from 10 to 100 years.

Design of systems for hydrogen production based on the Cu–Cl thermochemical water decomposition cycle: Configurations and performance

In this study, we analyze several Cu-Cl cycles by examining various design schemes for an overall system and its components, in order to identify potential performance improvements. The factors that determine the number and effective grouping of steps for new design schemes are analyzed. A thermodynamic analysis and several parametric studies are presented for various configurations. The energy efficiency is found to be 44% for the five-step thermochemical process, 43% for the four-step process and 41% for the three-step process, based on the lower heating value of hydrogen. Also, conclusions regarding implementation of these new configurations are discussed and the potential benefits ascertained.

Life cycle analysis of processes for hydrogen production

Hydrogen is considered to be an ideal energy carrier in the foreseeable future and can play a very important role in the energy system. A variety of technologies can be used to produce hydrogen. One of the most remarkable methods for large-scale hydrogen production is thermo-chemical water decomposition using heat energy from nuclear, solar and other sources. Detailed simulations of the two most promising water splitting thermo-chemical cycles (the Westinghouse cycle and the Sulphur–Iodine cycle) were performed in Aspen Plus code and obtained results were used for life cycle analysis. They were compared with two different processes for hydrogen production (coal gasification and coal pyrolysis). Some of the results obtained from LCA are also reported in the paper.

Electrochemical mass transfer and entropy generation of cuprous chloride electrolysis

Diffusive mass transfer in an electrochemical cell, which produces hydrogen in a copper-chlorine cycle of thermochemical water decomposition, is investigated in this paper. A predictive model of entropy production for the electrochemical reaction of cuprous chloride and hydrochloric acid is developed. The effects of temperature and current density on entropy production are investigated with the new formulation. A comparative study is performed with respect to the relationships between current density and overpotential, using Tafel’s equation and a newly proposed method, based on the Nernst equation. The effects of ohmic and activation overpotentials on the thermodynamic irreversibilities in the electrolytic cell are also investigated. The impact of the charge transfer coefficient on the electrochemical reaction is also examined. The results of the new predictive formulation are compared successfully against Tafel’s model and past experimental data, in relation to measured electrochemistry data. The operating temperature of the electrochemical cell has a significant effect on the entropy generation. The ohmic resistance appears to have minimal effect on the electrolytic cell performance at high current densities. A significant effect of current density on overpotential was observed at low current densities (0–250 mA/cm 2). The current density has a significant effect on entropy production between 0 and 400 mA/cm 2. The activation overpotential has the most significant effect on cell performance. Although the ohmic resistance has little effect at high current densities, the effects become significant at lower current densities.

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

Abstract 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.

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.

A properties model of the HI–I 2–H 2O–H 2 system in the sulfur–iodine cycle for hydrogen manufacture

A model for the phase equilibria and energetics of the HI–I 2–H 2O–H 2 system has been developed for use in process simulations of reactive distillation to form H 2 from HI in the Sulfur–Iodine cycle for thermochemical decomposition of water. Comparisons with data and other models demonstrate that this approach is uniquely successful in describing the phase equilibria and properties of this complex system. In particular, it is able to follow the pressure minimum of the HI–H 2O binary and HI–I 2–H 2O ternary when x HI ≈ 0.15; the dramatic increase of pressure and HI vapor composition, as well as formation of two liquid phases with greater amounts of HI; and the emergence of a single liquid phase in the ternary, even though binaries of HI and of I 2 with H 2O are only partially miscible. The model incorporates two novel speciation reactions and the Electrolyte-NRTL excess Gibbs energy model with parameters that cover wide ranges of temperature, pressure and composition. The model is formulated so that process simulation, design and optimization may be done reliably to explore feasibility and innovations of the S–I process.

Efficiency analysis of a hybrid copper–chlorine (Cu–Cl) cycle for nuclear-based hydrogen production

The role of the Cu–Cl cycle for thermochemical water decomposition, potentially driven by heat from a nuclear power generation station, in producing hydrogen in a sustainable way is investigated by examining efficiencies. The energy efficiency of the cycle is found to be 45% and the exergy efficiency 10%. The energy and exergy efficiencies of the cycle are observed to vary with temperatures of the reactions and reference-environment, and cycle heat losses. A parametric study is carried out considering several heat losses, reaction and reference-environment temperatures, and component-efficiency scenarios.

Advances in hydrogen production by thermochemical water decomposition: A review

Abstract 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.

Recent Advances in Nuclear Based Hydrogen Production With the Thermochemical Copper-Chlorine Cycle

This paper presents a review of recent advances in nuclear-based hydrogen production with a thermochemical copper-chlorine cycle. Growing attention has focused on thermochemical water decomposition as a promising alternative to steam-methane reforming for a sustainable future method of large-scale hydrogen production. Recent advances in specific processes within the Cu–Cl cycle will be presented, particularly for overall heat requirements of the cycle, preferred configurations of the oxygen cell, disposal of molten salt, electrochemical process of copper electrowinning, and safety/reliability assessment of the systems. An energy balance for each individual process is formulated and results are presented for heat requirements of the processes.

Combating global warming via non-fossil fuel energy options

Non-fossil fuel energy options can help reduce or eliminate the emissions of greenhouse gases and are needed to combat climate change. Three distinct ways in which non-fossil fuel options can be used in society are examined here: the capture/production of non-fossil fuel energy sources, their conversion into appropriate energy carriers and increased efficiency throughout the life cycle. Non-fossil fuel energy sources are insufficient to avoid global warming in that they are not necessarily readily utilisable in their natural forms. Hydrogen energy systems are needed to facilitate the use of non-fossil fuels by converting them to two main classes of energy carriers: hydrogen (and hydrogen-derived fuels) and electricity. High efficiency is needed to allow the greatest benefits to be attained from energy options in terms of climate change and other factors. A case study is considered involving the production of hydrogen from non-fossil energy sources via thermochemical water decomposition. Thermochemical water decomposition provides a realistic future non-fossil fuel energy option, which can be driven by non-fossil energy sources (particularly nuclear or solar energy) and help combat global warming.

Energy and exergy analyses of the fluidized bed of a copper–chlorine cycle for nuclear-based hydrogen production via thermochemical water decomposition

Nuclear-based hydrogen production via thermochemical water decomposition using a copper–chlorine (Cu–Cl) cycle consists of a series of chemical reactions in which water is split into hydrogen and oxygen as the net result. This is accomplished through reactions involving intermediate copper and chlorine compounds, which are recycled. This cycle consists of three thermally driven reactions and one electrochemical reaction. The cycle involves five steps: (1) HCl(g) production using such equipment as a fluidized bed, (2) oxygen production, (3) copper(Cu) production, (4) drying, and (5) hydrogen production. A chemical reaction takes place in each step, except drying. In this study, the HCI(g) production step of the Cu–Cl cycle for hydrogen production as well as its operational and environmental conditions are defined, and a comprehensive thermodynamic analysis is performed, incorporating energy and exergy and considering relevant chemical reactions. The performance of the fluidized bed is evaluated through energy and exergy efficiencies, and various parametric studies on energetic and exergetic aspects with variable reaction and reference-environment temperatures are carried out.

The oxygen production step of a copper–chlorine thermochemical water decomposition cycle for hydrogen production: Energy and exergy analyses

In the copper–chlorine (Cu–Cl) thermochemical cycle water is decomposed into its constituents (oxygen and hydrogen) by a series of chemical reactions. The cycle involves five steps in which three thermally driven chemical reactions and one electrochemical reaction take place. Oxygen is produced during one of the main chemical reactions. In the present study, the O 2 production step is described with its operational and environmental conditions, and energy and exergy analyses are performed. The cycle is assumed driven using nuclear energy. Various parametric studies are carried out on energetic and exergetic aspects of the step, considering variable reaction and reference-environment temperatures. At a constant reference-environment temperature of 25 °C, the exergy destruction of the O 2 production step varies between 4500 and 23,000 kJ/kmol H 2 when the reaction temperature increases from 450 to 1000 °C. At a 500 °C reaction temperature and a 25 °C reference-environment temperature, the exergy destruction for this step is found to be 5300 kJ/kmol H 2. At a reaction temperature of 500 °C and a reference-environment temperature of 25 °C, the exergy efficiency of the step is determined to be 96% and to decrease with increasing reaction temperature and/or reference-environment temperature.

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.

Synergistic roles of off-peak electrolysis and thermochemical production of hydrogen from nuclear energy in Canada

Hydrogen as a clean energy carrier is frequently identified as a major solution to the environmental problem of greenhouse gases, resulting from worldwide dependence on fossil fuels. However, most of the world's hydrogen (about 96%) is currently produced from fossil fuels, which does not address the issue of greenhouse gases. Although there is a large motivation of the “hydrogen economy”, for improvement of urban air quality, energy security, and integration of intermittent renewable energy sources, CO 2 free energy sources are critical to hydrogen becoming a significant energy carrier. Two technologies, applied in tandem, have a promising potential to generate hydrogen without leading to greenhouse gas emissions: 1) electrolysis and 2) thermochemical decomposition of water. This paper will investigate their unique complementary roles to reduce costs of hydrogen production. Together they have a unique potential to serve both de-centralized hydrogen needs in periods of low-demand electricity, and centralized base-load production from a nuclear station. Thermochemical methods have a significantly higher thermal efficiency, but electrolysis can take advantage of low electricity prices during off-peak hours, as well as intermittent and de-centralized supplies like wind, solar or tidal power. By effectively linking these systems, water-based production of hydrogen can become more competitive against the predominant existing technology, SMR (steam-methane reforming).

Process model-free analysis for thermodynamic efficiencies of sulfur–iodine processes for thermochemical water decomposition

Material, energy, and entropy balances, which depend only on stream conditions and flows entering and leaving a system, have been used to evaluate different scenarios for thermochemical decomposition of water to manufacture hydrogen using the Sulfur–Iodine cycle. Energy efficiencies have been found for idealized systems with variable stream amounts, as well as for a common flowsheet, to locate the greatest effects on energy requirements and inefficiencies. Aspen Plus®, OLI Engine, and ProSimPlus property models have been used on the sections of a General Atomics process to reveal the effects of differences in computed energies and entropy generation. While the calculated efficiencies are generally consistent with those of the literature, differences in stream properties and phase behaviors suggest that optimal process configurations from simulations may have significant uncertainties.