High temperature electrolysis process coupled to a very high temperature reactor is one of the most promising methods for hydrogen production using a nuclear reactor as the primary energy source. A computational fluid dynamic model for the evaluation and optimisation of the electrolyser of a high temperature electrolysis hydrogen production process flowsheet was developed using ANSYS FLUENT®. Electrolyser's operational and design parameters will be optimised in order to obtain the maximum hydrogen production and the higher efficiency in the module. A complete flowsheet is proposed for the high temperature electrolysis process coupled to an accelerator driven system, considering a Brayton cycle for the energy production and a sweep gas system for the gas separation. An acceptable value of global efficiency for the initial operating condition is obtained. Several parametric studies are conducted using the flowsheet proposed to evaluate important operating parameters in the overall process efficiency.
The objective of this work was to assess the impact of deviations from isothermality in packed bed and coated wall membrane reactors on the rates of HI decomposition. A two-dimensional modelling was done for a packed bed membrane reactor as well as a coated wall membrane reactor for HI decomposition. The smaller diameter reactor showed higher apparent catalyst activity. The reactivity results showed that the reactors suffered from significant temperature gradients. We estimated the diameter required for packed bed and coated wall membrane reactors to achieve near isothermal operation. The coated wall reactor gives lower conversion than the packed bed reactor. The model confirmed that the measured catalyst activities in different diameter reactors varied due to heat transfer and pressure drop effects.
The iodine-sulphur (IS) thermo-chemical process is being studied as a potential process for production of hydrogen by water splitting. It consists of three chemical reactions: 1) Bunsen reaction, which is the acid production step, 2) sulphuric acid decomposition to produce oxygen; 3) hydrogen iodide decomposition to produce hydrogen. In this work, a detailed parametric study of the Bunsen reaction is presented, which was carried out in agitated reactor (ABR) in counter current mode of operation. Experiments have been carried out in the reactor at different temperatures by varying the sulphur dioxide (SO2) flow rate and partial pressure of SO2. Bunsen reaction rate and SO2 conversion are calculated experimentally from feed rate and scrubbing rate of SO2. It has been observed that the reaction rate and SO2 conversion increase with increase in SO2 flow, increase in SO2 partial pressure and decrease in temperature. 'Tanks-in-series' model, one of the non-ideal reactor models, has been proposed to describe the ABR reaction system. The model has been validated with experimental results. This approach can be useful for the design and scaling up of the agitated reactor.
Agitated Bunsen reactor (ABR) is one of the reactor alternatives to carry out Bunsen reaction of iodine-sulphur thermo-chemical process for hydrogen production. It is a tubular reactor with multiple agitating blades on a common shaft to enhance the radial mixing and with an inside helical coil arrangement to remove the exothermic Bunsen reaction heat. The effective heat removal from the reactor depends on the agitation speed and velocity of fluids flowing inside the reactor and through the helical coil. Experiments are carried out in ABR, for heat transfer study with water as reactor fluid as well as helical coil fluid and also Bunsen reaction heat transfer study, by varying the operating parameters such as agitation speed, velocity of reactor fluid and velocity of helical coil fluid. It has been observed that the overall heat transfer coefficient increases with increase in agitation speed and fluid velocities. Combined effect of agitation speed and fluid velocities on heat transfer rate, in shell side/reactor side of ABR, has been presented in the form of modified correlation.
To evaluate the possibility to use molten carbonate fuel cell technology for high temperature electrolysis, the factors affecting the electrode reactions have been examined by surveying the published literature. The literature results showed that H2, CO2 and CO evolved as cathode off-gases and O2 as anode gas. At low polarisation, the discharge of oxide ions to O2 was the only anodic process; increasing polarisation and current densities, the discharge of carbonate ions contributed to the anodic reaction and CO2 was concurrently produced at the anode. Molten Li2CO3 at 850°C–900°C readily absorbed the produced CO2 (the CO2 concentration in the anode compartment was lower than 0.5%). In this condition, titanium cathode enhanced CO production. The co-production of CO represents a serious disadvantage to power a polymer electrolyte membrane fuel cell. On the other hand, the production of syngas could offer attractive applications such as synfuel production and carbon dioxide regeneration.
Global warming and climate change necessitate a serious move away from fossil-based systems toward hydrogen economy. A study has been carried out on different thermochemical cycles for hydrogen production to bring about their important aspects. The study involves process description of different routes followed by thermochemical cycles. These include metal oxide processes, sulphur family processes like iodine sulphur cycle and Westinghouse cycle, halide family processes like UT-3 and Ispra Mark cycle, copper chlorine cycle and others. This paper gives an insight into the advantages and disadvantages associated with the processes. The review is done keeping in view the relevant and useful aspects in research to present information in terms of species, operating parameters, reactors, costs involved, safety, etc. This will provide a platform for further research to save effort by referring the basic information on thermochemical cycles, so that an appropriate and satisfactory cycle may be chosen.
Nuclear hydrogen production is a technically feasible and economically viable option for addressing future energy needs. Several projects have been started on the co-generation of hydrogen and electricity from nuclear energy. In this report, the nickel sulphur iodine (NIS) cycle, a thermochemical water splitting cycle originally developed in ENEA for solar hydrogen production was studied to be coupled with a new generation nuclear reactor for massive hydrogen production.
The power increase in the nuclear power plants has been investigated for the safety aspect. Most equipment could be affected by the power uprate, which could increase the electricity power level. The quantification of the uprate reliability is performed by the system dynamics method, which is processed by the feedback and accumulation algorithms. The Vensim software package is used for the simulations, which is made by the Monte Carlo method. There are two kinds of considerations as the economic and safety properties. The result shows the stability of the operations when the power can be decided. This shows the higher efficiency of the reactor. The maximum value of risk is 157,887 in 2065 and the minimum value is 2 in 2010. Thus, the risk of the power uprate increases 78,954 times higher than the initial value in this study.
A new vision of the future human civilisation, hydrogen civilisation (HyCi) is generalised. At this rigorous, severe historical period human kind still has a real possibility to save the biosphere and make living out of humanity a possible and real process. The above objective can be achieved only by advantageous all-planetary work along the direction of the ecologically clean and economically sustainable vector ‘hydrogen energy → hydrogen economy → HyCi’. The HyCi concept includes three constituent, mutually conditioned parts: industrial-ecological, humanitarian-cultural and geopolitical-international legislative ones. This paper presents a comprehensive and analysed theoretical and humanitarian-cultural groundwork of the transition. The legislative-economic mechanism of the transition to HyCi is formulated, and the way to a hydrogen market economy – the economic basis of the HyCi – is indicated and discussed.
The European FP7 project HycycleS focuses on providing detailed solutions for the design of specific key components for sulphur-based thermochemical cycles for hydrogen production. The key components necessary for the high temperature part of those processes, the thermal decomposition of H2SO4, are a compact heat exchanger for SO3 decomposition for operation by solar and nuclear heat, a receiver-reactor for solar H2SO4 decomposition, and membranes as product separator and as promoter of the SO3 decomposition. Silicon carbide has been identified as the preferred construction material. Its stability is tested at high temperature and in a highly corrosive atmosphere. Another focus is catalyst materials for the reduction of SO3. Requirement specifications were set up as basis for design and sizing of the intended prototypes. Rigs for corrosion tests, catalyst tests and selectivity of separation membranes have been designed, built and completed. Prototypes of the mentioned components have been designed and tested.
Careful optimisation of a safe and sustainable route for hydrogen production is a pressing need.Thermochemical processes employing water as raw material and nuclear/renewable energies as energy source are believed to be the best possible option in this direction, while alarming issues such as climate change and global warming are being taken into account.Amongst the well-identified cycles, the sulphur-iodine (S-I) thermochemical route assumes the highest thermal efficiency and the best one as regards its coupling to a high temperature nuclear reactor.Material development is the key issue to be addressed to realise successfully the potential of the S-I cycle.The most important area is development of gas-permeable membranes for enhancement of the equilibrium decomposition of HI, which is the most intricate step as far as the overall process efficiency is concerned.In order to overcome the low efficiency associated with the low equilibrium decomposition of HI, the authors intend to develop a hydrogen permselective membrane reactor.As a first step towards this development, a silica membrane of asymmetric nature was developed using sol-gel processing and dip coating, and characterised using scanning electron microscopy and a BET surface area analyser.A road map
The search for a sustainable, CO 2 -free massive hydrogen production route is a strong need, if one takes into account the world-wide increasing energy demand, the deterioration of fossil fuel reserves and in particular the increasing CO 2 concentration leading to global warming.Thermo-chemical cycles for water splitting are considered as a promising alternative of emission-free routes of massive hydrogen production -with potentially higher efficiencies and lower costs compared to alkaline electrolysis of water.The hybrid-sulphur cycle was chosen as one of the most promising cycles from the 'sulphur family' of processes.Different process schemes using concentrated sunlight or nuclear generated heat or a combination of both have been elaborated and analysed by a comparative techno-economic study with regard to their potential of a large-scale hydrogen production.Options for a hybridisation of the energy supply between solar and nuclear have been also investigated, particular focused on the coupling of concentrated solar radiation into a round-the-clock operated process.Process design and simulation, industrial scale-up assessments including safety analysis and cost evaluations were performed to analyse reliability and potential of those process concepts.
The probabilistic safety assessment (PSA) is investigated in the case of the operational data shortage which is characteristic of the passive system in gas-cooled nuclear power plants (NPPs).Therefore, it is difficult to make a quantification of the PSA.One of the solutions is to compare the passive system and the active system.Using this comparison, one can find the priority of the passive system reliability.For the modelling, the anticipated transient without scram (ATWS) in the very high temperature reactor (VHTR) and the pressurised water reactor (PWR) is used.Finally, this study decides the difference in the reliability between passive and active systems.The propagation is done by the dynamically modified algorithm (DMA), which highlights the information feedback.The result is analysed by the time changes.
Interaction of hydrogen with cerium nickel and aluminium based mixed oxides (CeNi1OY and CeAl0.5Ni1OY) has been studied by catalytic hydrogenation and inelastic neutron scattering (INS). The mixed oxides are large catalytic hydrogen reservoirs and the presence of Al allows increasing hydrogen storage and giving a better stability to the system, in particular, with temperature. Neutron spectroscopy evidences in the solids studied the coexistence of different hydrogen species that can be related to hydride species, hydrogen species in interaction with metallic nickel, as well as hydrogen species from hydroxyl groups. The mobility and reactivity of these hydrogen species have been analysed and discussed.
After a brief introduction on the problems related to hydrogen storage, recent trends of the research on hydrogen storage materials are presented and discussed: metal hydrides; nanostructured magnesium-based hydrides; nanocomposites based on mixtures of amides and hydrides, amides and alanates, and borohydrides and hydrides; chemical hydrides; and nonhydride systems. The aim of the paper is to show that, even if none of these studied materials satisfies all the requirements for a very wide practical use, some niche applications are already feasible.
In the present paper, the Thermo-Catalytic Decomposition (TCD) of methane has been investigated in a laboratory-scale bubbling fluidised bed reactor using copper dispersed on γ-alumina as a catalyst. The usefulness of a fluidised bed operation instead of a fixed bed operation has been assessed in terms of methane-to-hydrogen conversion and the amount of carbon accumulated on the catalyst. The possibility of carrying out a two-stage operation for hydrogen production from methane TCD in fluidised bed reactors, which consists of operating the fluidised bed as a reactor for methane decomposition until a defined catalyst deactivation degree is achieved and then operating the fluidised bed as a combustor for catalyst regeneration by carbon oxidation, has also been investigated. The typical behaviours of fluidised bed reactors contribute to the opportunity to adopt such a regeneration strategy on the basis of the performances obtained with catalyst regeneration by means of carbon combustion in fixed and fluidised bed reactors.
The potential of amorphous/metallic glassy alloys as hydrogen-permeable membranes for hydrogen production and as bipolar plates for Polymer Electrolyte Fuel Cells (PEFCs) was investigated in this paper. Firstly, the hydrogen permeation of the melt-spun (Ni0.6Nb0.4)70Zr30-xTax (x = 5, 10, 15, 20 at%) alloys was measured. As a result, it was found that the hydrogen permeability of the alloys decreased with the Ta content. However, degradation during the permeation test of the alloy with 10 at%Ta was smaller than that with 5 at%Ta. Therefore, it can be concluded that Ta addition stabilises the permeation behaviour, preventing significant degradation over time, despite the fact that Ta addition does not affect the hydrogen permeability of the alloys. Secondly, the Ni65Cr1515P16B4 metallic glassy alloy was produced by melt-spinning in air. The bipolar plate was successfully produced by hot-pressing with dies in a supercooled liquid state. It was shown that this alloy could be a good candidate for a bipolar plate material for PEFC.
Recent progress is reviewed in the preparation of highly active magnesium-based hydrogen storage alloys by the combined process of Hydriding Combustion Synthesis (HCS) and Mechanical Milling (MM). The structural transformation of the alloys during MM determined by means of X-ray Diffraction (XRD) and the hydrogen storage properties of the alloys measured by means of Pressure-Concentration-Temperature (PCT) are reported. The HCS alloy of Mg98Ni2 after MM showed the highest hydrogen capacity of 5.60 wt.% at 373 K within 100 s and the dehydriding onset decreased from about 640 K of the HCS product to 480 K of the HCS + MM product. Besides, the absorption capacity at 373 K in 30 s increased from 3.85 wt.% for the HCS + MM product of Mg95Ni5 without Nb2O5 to 5.09 wt.% for that with 1 at.% Nb2O5. The results demonstrated that the method of HCS + MM has potential in the preparation of magnesium-based materials for vehicular application.
Density Functional Theory (DFT) is a powerful tool to predict the crystal structure of hitherto experimentally unknown phases. In this article, we demonstrate the predicting capability of DFT on the structural properties of hydrogen storage materials from different input structure models. An experimentally known structural framework is successfully reproduced for NaMgH3 and the positional and unit-cell parameters are found to be in good agreement with the experimental findings. The crystal structure of LiMgH3 has been predicted and this compound should have ferroelectric properties. The calculated phonon spectrum indicates that LiMgH3 is an energetically and thermodynamically stable phase. A pressure-induced structural transition has been identified for this phase and it transforms into CaCO3-type modification at 38 GPa.
The Hybrid Sulphur (HyS) cycle has attracted much attention as a mass production process for hydrogen. It consists of an electrolysis step and a thermal decomposition one. In order to achieve high efficiency for hydrogen production and operational cost reduction, some developments in electrode materials with high corrosion resistance, high electrical conductivity and low anodic potential is a key issue for the electrolysis in H2SO4 solution.Our research group pointed out that some electronic conductive ceramics, which are titanium (Ti)-based pyrochlores (chemical formula: A3+2Ti4+2O7) and perovskites (chemical formula: A2+Ti4+O3), might be some of the candidates for anode base materials. We developed the sintering process of electronic conductive ceramics which had high corrosion resistance and high electrical conductivity. In this paper, our research activities for the development of a new type of anode material are introduced, i.e., the material development of electronic conductive ceramics, corrosion resistance evaluation and electrical conductivity evaluation of Ti-based ceramics in a 50 weight(wt.)% H2SO4 solution at the operating temperature are summarised. Additionally, the application of a palladium (Pd)-coating technique on the titanate was evaluated using the electroless deposition technique, in order to provide some catalytic properties to the materials.
