Thermochemical hydrogen production has attracted considerable interest as a clean energy solution to address the challenges of climate change and environmental sustainability. The thermochemical ...water-splitting iodine-sulfur (IS) process uses heat from nuclear or solar power and thus is a promising next-generation thermochemical hydrogen production method that is independent of fossil fuels and can provide energy security. This paper presents the current state of research and development (R&D) of the IS process based on membrane techniques using solar energy at a medium temperature of 600 °C. Membrane design strategies have the most potential for making the IS process using solar energy highly efficient and economical and are illustrated here in detail. Three aspects of membrane design proposed herein for the IS process have led to a considerable improvement of the total thermal efficiency of the process: membrane reactors, membranes, and reaction catalysts. Experimental studies in the applications of these membrane design techniques to the Bunsen reaction, sulfuric acid decomposition, and hydrogen iodide decomposition are discussed.
•Current state of R&D of membrane IS process using solar energy was summarized.•Membrane techniques was proposed for the IS process.•Membrane IS process is expected to play a dominant role in the upcoming hydrogen society.
For the safe storage of zeolite wastes generated by the treatment of radioactive saline water at the Fukushima Daiichi Nuclear Power Station, this study investigated the fundamental properties of ...herschelite adsorbent and evaluated its adsorption vessel for hydrogen production and corrosion. The hydrogen produced by the herschelite sample is oxidized by radicals as it diffuses to the water surface and thus depends on the sample's water level and dissolved species. The hydrogen production rate of herschelite submerged in seawater or pure water may be evaluated by accounting for the water depth. From the obtained fundamental properties, the hydrogen concentration of a reference vessel (decay heat = 504 W) with or without residual pure water was evaluated by thermal-hydraulic analysis. The maximum hydrogen concentration was below the lower explosive limit (4%). The steady-state corrosion potential of a stainless steel 316L increased with the absorbed dose rate, but the increase was repressed in the presence of herschelite. The temperature and absorbed dose at the bottom of the 504 W vessel were determined as 60 °C and 750 Gy/h, respectively. Under these conditions, localized corrosion of a herschelite-contacted 316L vessel would not immediately occur at Cl
−
concentrations of 20,000 ppm.
A district heating system for household heating and road snow melting utilizing waste heat from Gas Turbine High-Temperature Reactors of 300 MW (GTHTR300s), a high-temperature gas-cooled reactor ...design, was analyzed. The application area was set in Sapporo and Ishikari, cities with heavy snowfall in northern Japan. The heat transport analyses were performed by modeling heat-transfer components in the system to estimate the system's overall heat supply profile. These components included the pipelines of the secondary water loops between the GTHTR300s and the heat-application area; heat exchangers to transfer the heat from the secondary loops to the tertiary water loops of the district-heating pipes; and the district-heating pipes of the tertiary loops between the heat exchangers and houses and roads. Single- and double-pipes for the secondary loops were compared. Although the double-pipes were advantageous for having less heat loss and a smaller excavation area, these advantages did not compensate for the higher construction cost of the pipes. To satisfy the heat demand of the application area in the month of maximum requirement, 520-529 MW of heat were supplied by 3 GTHTR300s and delivered by 6 secondary loops, 3,450 heat exchangers about 90 m long, and 3,450 tertiary loops. More efficient designs for the heat exchangers and improvements to the tertiary loops applying branched flow networks are desired to reduce the number of heat exchangers and tertiary loops and to make the heat exchangers smaller. Heat lost to the ground from the tertiary loops comprised 80%-90% of the heat loss. Applications of the larger pipe or loops using the branched flow network or double-pipe are required for more efficient heat utilization. More than 90% of the construction cost went into thermal insulators. The thickness and properties of the insulator must be reevaluated for economical heat delivery.
The thermochemical water-splitting iodine–sulfur (IS) process requires corrosion-resistant materials owing to usage of corrosive fluids, such as a mixture of HI–I2–H2O. Fluoropolymers, such as PTFE ...and PFA, are adaptable as lining materials for protecting plant components. However, there has been a concern: PTFE and PFA have the ability to permeate various permeants. From the viewpoint of corrosion of the base material, the permeation characteristics of HI and I2 should be evaluated to improve the integrity of the IS process. In this study, permeation tests on PTFE and PFA membranes were performed to measure the permeated fluxes of HI and I2, and the effects of the operating conditions on them were investigated. The introduction of a permeability parameter could be successful for normalizing the permeated fluxes for a specific membrane thickness and a vapor pressure. Then, the empirical formula of the permeability was given as an Arrhenius-type equation to use as a plant design. Finally, based on the results, the proper conditions for design of a lining material for the inhibition of HI and I2 permeation are summarized.
•Hydrogen production method, IS process has been developed.•Permeation of fluoropolymers as a lining material has been evaluated.•The permeated fluxes of HI and I2 were measured under operating conditions.•The empirical formula of the permeability of HI and I2 was given.
The thermochemical water-splitting iodine–sulfur process facilitates hydrogen production. This study proposes a new loop operation by subdividing the process configuration into four sections before ...transferring the continuous operation. The loop operation should define the section affecting the fluctuations to easily stabilize the system. The proposed loop operation was validated by analyzing the material and heat balances using a process simulator. The calculated results showed that the material balances of the respective loop sections were closed without component discharge to outside sections. The loop operation would transfer to the continuous operation by connecting all sections. Considering the switching of operation modes, the material and heat balance showed no or little difference, indicating that two operation modes can only be changed by switching the pipelines. Thus, the loop sections can be operated individually to stabilize the IS process system, and the loop operation can be transferred smoothly to the continuous operation.
•New loop operating procedure for iodine-sulfur process was proposed.•The loop operation mode subdivides process configuration into four sections.•It was confirmed that the material balances of each section were closed.•The loop operation mode can be transferred smoothly to the continuous operation.
A thermochemical water-splitting iodine–sulfur process offers the potential for mass-producing hydrogen at high-efficiency levels, and it uses high-temperature heat sources, including ...high-temperature gas-cooled reactors, solar heat, and waste heat of industries. The raw material (H2O) is split into H2 and O2 by combining three chemical reactions using sulfur and iodine. Currently, R&D tasks are essential to confirm the integrity of the components that are made of practical structural materials and the stability of hydrogen production in harsh working conditions. A test facility for producing hydrogen was constructed from corrosion-resistant components that are developed using industrial materials. In addition, for stable hydrogen production, technical issues for instrumental improvements (i.e., stable pumping of the hydrogen iodide (HI)–I2–H2O solution without locking the shaft seal, prevention of leakage by improving the quality control of glass-lined steel, prevention of I2 precipitation using a water removal technique in a Bunsen reactor) were solved. The entire process was successfully operated for 150 h at the rate of ca. 30 L/h. The integrity of components made of practical structural materials and the operational stability of the hydrogen production facility in harsh working conditions were demonstrated.
•A test facility was constructed by using corrosion-resistant structural materials.•Prevention of I2 precipitation (clogging), and pumping of HI–I2 mixture were devised.•The entire process was successfully operated for 150 h at rates of ca. 10–30 L-H2/h.•Operational stability of H2 production in handling of HI–I2 was demonstrated.
•Propose the method for quality management of glass lined steel components.•The qualified glass-lined protective sheaths are proved its applicability for IS process.•Quality management method of the ...glass-lined steel components for IS process was improved.
Japan Atomic Energy Agency (JAEA) has been conducting R&D on the thermochemical iodine-sulfur (IS) process for nuclear-powered hydrogen production. The IS process is one of the promising candidates of heat application of the high-temperature gas-cooled reactors. JAEA achieved continuous hydrogen production for one week with a hydrogen production rate of 30 NL/h by using a test apparatus made of glass and fluororesin material. Subsequently, JAEA fabricated main chemical reactors made of industrial structural materials and confirmed their integrity in practical corrosive environments in the IS process. Based on the results, JAEA has fabricated a 100 NL/h-H2-scale test facility made of industrial structural materials; one of the important materials is the glass-lined steel for corrosion resistant components such as vessels, pipes and protective sheaths of sensors. This report will present technical matters to improve reliability of the glass-lined protective sheaths of thermocouple. In addition, results of quality confirmation will be presented, which are stress analyses for the glass layer by FEM, tests for heat cycle, bending load and corrosion.
Hydrogen production from nuclear energy has attracted considerable interest as a clean energy solution to address the challenges of climate change and environmental sustainability. With respect to ...the large-scale and economical production of hydrogen using nuclear energy, the thermochemical water-splitting iodine-sulfur (IS) process is a promising method. The IS process uses sulfur and iodine compounds to decompose water into its elemental constituents, hydrogen and oxygen, by using three coupled chemical reactions: the Bunsen reaction; sulfuric acid decomposition; and hydrogen iodide (HI) decomposition. The decomposition of HI is the efficiency-determining step of the process. In this work, a membrane reactor with a silica membrane closed on one end was designed, and its potential for hydrogen production from HI decomposition was explored. In the reactor-module design, only one end of the membrane tube was fixed, while the closed-end of the tube was freely suspended to avoid thermal expansion effects. The closed-end silica membranes were prepared for the first time by a counter-diffusion chemical vapor deposition of hexyltrimethoxysilane. In application, HI conversion of greater than 0.60 was achieved at a decomposition temperature of 400 °C, which is three times greater than the equilibrium conversion (0.20). Thus, the membrane reactor with closed-end silica membrane was shown to produce a successful equilibrium shift in the production of hydrogen via HI decomposition in the thermochemical IS process.
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•A membrane reactor equipped with a silica membrane closed on one end was designed.•Its potential for hydrogen production from HI decomposition was explored.•A closed-end silica membrane was prepared by counter-diffusion CVD method.•In application, HI conversion of greater than 0.60 was achieved at 400 °C.•Developed membrane reactor is applicable for hydrogen production via HI decomposition.
•JAEA succeeded in hydrogen production of 20 L/h-H2 for 31 hours.•The strength estimation method has been developed for SiC components.•The proposed method is expected to become a standard method to ...obtain a license.
Japan Atomic Energy Agency (JAEA) has been conducting R&D on the thermochemical iodine–sulfur (IS) process for nuclear-powered hydrogen production. The IS process is one of the promising candidates of heat application of the high-temperature gas-cooled reactors. JAEA achieved continuous hydrogen production for one week with a hydrogen production rate of approximately 20 NL/h by using a test apparatus made of glass and fluororesin material. Subsequently, as a next step, JAEA fabricated main chemical reactors made of industrial structural materials and confirmed their integrity in practical corrosive environments in the IS process. Based on the results of these confirmation tests, JAEA has constructed a 100 NL/h-H2-scale test facility made of industrial structural materials. This paper presents an outline and results of hydrogen production tests by using the test facility and reliability improvements by developing a strength estimation method for heat-resistant and corrosion-resistant ceramics components made of silicon carbide.
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