Cycle behaviour of iron ores in the steam-iron process

The use of several commercial iron ores usually employed as pigments, to store and supply pure hydrogen by means of the steam-iron process has been proposed and analyzed. The process roughly consists in repeated series of alternate reduction and oxidation steps in which a reducing stream (H₂ + CO, or in general H₂ enriched fuels) reacts with the iron oxide rendering the metal or a partially reduced oxide. Pure hydrogen is released during the re-oxidation with steam. The studied iron ores contain some impurities that accounting minor percentages (<10 wt%) enhance the behaviour of the solid. This improvement regards not only to the reduction and oxidation rate, but especially to the ability of the solid to maintain a given redox capacity along cycles. Also concerning this topic, the effect of the presence of these natural additives has been investigated in order to determine the inert behaviour of methane as a potential reducing agent. This study allowed the determination of the maximum temperature at which carbon formation is inhibited so that the subsequent released hydrogen will not be contaminated by carbon compounds.     

Oxidation reaction kinetics for the steam-iron process in support of hydrogen production

A hydrogen generation research program is focused on solar-driven hydrogen production by means of reactive metal water splitting. In order to dissociate water molecules at significantly reduced thermal energies as well as providing a practical means for efficient hydrogen and oxygen separation, an intermediary reactive material is introduced to realize water splitting in the form of an oxidation reaction. Elemental iron is used as the reactive material in the process commonly referred to as the steam-iron process. In order to exploit the unique characteristics of highly reactive materials and ultimately achieve the potential efficiency gains at the solar reactor scale, a monolithic laboratory-scale reactor has been designed to explore the fundamental kinetic rates during the iron oxidation reaction at temperatures ranging from about 650 to 900 K. Results show hydrogen production rates on the order of 1E-8 g/cm² s. Micro-Raman spectroscopy is used to access information on the exact iron oxide phase produced, and high resolution SEM and electron dispersion spectroscopy (EDS) are used to assess the oxide morphology and further quantify the oxide state, including spatial distributions.     

Separation and storage of hydrogen by steam-iron process: Effect of added metals upon hydrogen release and solid stability

During the last decade, the steam-iron process has re-emerged as a possible way to separate and/or storage pure hydrogen through the use of metallic oxides subjected to redox cycles. The most renamed candidate to achieve this goal has traditionally been iron oxide. Nevertheless, the study of its behaviour along repetitive reduction/oxidation stages has shown that the hydrogen storage density diminishes abruptly from the first cycle on.To cope with this problem, the inclusion of a second metal oxide in the solid structure has been tried. Isothermal experiments of reduction with hydrogen rich flows and oxidation with steam have been carried out with Al, Cr and Ce as second metals, in nominal amounts from 1% to 10 mol% added to the hematite structure, which has been synthesized in laboratory by coprecipitation. Series of up to seven cycles (reductions followed by oxidations in a thermogravimetric system acting as differential reactor for the gas) have shown that to that point, an almost repetitive behaviour can be obtained, recovering the magnetite (Fe₃O₄) structure after each oxidation step.Since the second metal oxide does not intervene in the reduction/oxidation process, the optimum content of second metal for each species has been determined with the aim to keep the highest hydrogen storage density along cycles.     

Thermodynamic possibilities and constraints for pure hydrogen production by iron based chemical looping process at lower temperatures

Iron offers the possibility of transformation of a syngas or gaseous hydrocarbons into hydrogen by a cycling process of iron oxide reduction (e.g. by hydrocarbons) and release of hydrogen by steam oxidation. From the thermodynamic and chemical equilibrium point of view, the reduction of magnetite by hydrogen, CO, CH₄ and a model syngas (mixtures CO + H₂ or H₂ + CO + CO₂) and oxidation of iron by steam has been studied. Attention was concentrated not only on convenient conditions for reduction of Fe₃O₄ to iron at temperatures 400–800 K but also on the possible formation of undesired soot, Fe₃C and iron carbonate as precursors for carbon monoxide and carbon dioxide formation in the steam oxidation step. Reduction of magnetite at low temperatures requires a relatively high H₂/H₂O ratio, increasing with decreasing temperature. Reduction of iron oxide by CO is complicated by soot and Fe₃C formation. At lower temperatures and higher CO₂ concentrations in the reducing gas, the possibility of FeCO₃ formation must be taken into account. The purity of the hydrogen produced depends on the amount of soot, Fe₃C and FeCO₃ in the iron after the reduction step. Magnetite reduction is the more difficult stage in the looping process. Pressurized conditions during the reduction step will enhance formation of soot and carbon containing iron compounds.     

Revealing market adaptation to a low carbon transport economy: Tales of hydrogen futures as perceived by fuzzy cognitive mapping

In-depth understanding of target user groups' preferences can inform the design of effective public policies for hydrogen in a competitive mobility market. Our paper attempts a re-examination of the issue based on two novelties: First, fuzzy cognitive mapping, a soft computing technique for analysing complex decision making problems, is for the first time applied in this field to elicit human cognitive structures. Secondly, hydrogen market segmentation is studied by clustering involved agents in: lay people (‘demand’), automobile salesmen (‘supply’) and experts.     

Production and purification of hydrogen by biogas combined reforming and steam-iron process

Cobalt ferrite and hematite with minor additives have been tested for production and purification of high purity hydrogen from a synthetic biogas by steam-iron process (SIP) in a fixed bed reactor. A catalyst based in nickel aluminate has been included in the bed of solids to enhance the rate of the reaction of methane dry reforming (MDR). The reductants resulting from MDR are responsible for reducing the oxides based on iron that will, in the following stage, be oxidized by steam to release hydrogen with less than 50 ppm of CO. Coke minimization along reduction stages forces to operate such reactors above 700 °C for reductions, and as low as 500 °C for oxidations to avoid coke gasification. To avoid problems such as reactor clogging by coke in reductions and/or contamination of hydrogen by gasification of coke along oxidations, steam in small proportions has been included in the feed with the aim of minimizing or even avoiding formation of carbonaceous depositions along the reduction stage of SIP. Since steam is an oxidant, it exerts an inhibiting effect upon reduction of the oxide, that slows down the efficiency of the process. It has been proved that co-feeding low proportions of steam with an equimolar mixture of CH₄ and CO₂ (simulating a poor heating value desulphurized biogas) is able to avoid coke deposition, allowing the operation of both, reductions and oxidations, in isothermal regime (700 °C). Empirical results have been contrasted with data found in literature for similar processes based in MDR and combined (or mixed) reforming process (CMR), concluding that the combination of MDR + SIP proposed in this work, taking apart economic aspects and complex engineering, shows similar yields towards hydrogen, but with the advantage of not requiring a subsequent purification process.     

Evaluation of a new Cr-free alloy as interconnect material for hydrogen production by high temperature water vapour electrolysis: Study in cathode atmosphere

For economic and ecological reasons, hydrogen is considered as a major energetic vector for the future. Hydrogen production via high temperature water vapour electrolysis (HTE) is a promising technology. A major technical difficulty related to high temperature water vapour electrolysis is the development of interconnects working efficiently for a long period. Working temperature of 800 °C enables the use of metallic materials as interconnects. High temperature corrosion behaviour and electrical conductivity of a new Cr-free Fe–Ni–Co alloy were tested in cathode atmosphere (H₂/H₂O) at 800 °C. The alloy exhibits a poor oxidation resistance but an excellent ASR parameter, as a result of the formation of a highly-conductive Cr-free surface spinel layer. Moreover, the role of water vapour and hydrogen was discussed and a diffusion mechanism in cathode atmosphere could be suggested.     

Thermochemical hydrogen production by a redox system of ZrO2-supported Co(II)-ferrite

The thermochemical two-step water splitting was examined on ZrO₂-supported Co(II)-ferrites below 1400 °C, for purpose of converting solar high-temperature heat to clean hydrogen energy as storage and transport of solar energy. The ferrite on the ZrO₂-support was thermally decomposed to the reduced phase of wustite at 1400 °C under an inert atmosphere. The reduced phase was reoxidized with steam on the ZrO₂-support to generate hydrogen below 1000 °C in a separate step. The ZrO₂-supporting alleviated the high-temperature sintering of iron oxide. As the results, the ZrO₂-supported ferrite realized a greater reactivity and a better repeatability of the cyclic water splitting than the conventional unsupported ferrites. The Co_xFe_3−xO₄/ZrO₂ with the x value of around 0.4–0.7 was found to be the promising working material for the two-step water splitting when thermally reduced at 1400 °C under an inert atmosphere.     

What governs the transition to a sustainable hydrogen economy? Articulating the relationship between technologies and political institutions

There is a lack of integrated knowledge on the transition to a sustainable energy system. The paper focuses on the relationship between technologies and institutions in the field of hydrogen from the perspective of political theory. The paper unfolds four paradigms of governance: ‘Governance by policy networking’, Governance by government’, ‘Governance by corporate business’, and ‘Governance by challenge’, and looks into the major line of argument in support of these paradigms and into their possible bias with respect to hydrogen options. Each of these paradigms reveals an institutional bias in that it articulates specific opportunities for collaboration and competition in order to stimulate the transition to a sustainable hydrogen economy. The paper makes the observation that there is a compelling need to reframe fashionable discourse such as the necessary shift from government to governance or from government to market. Instead, specific questions with respect to the impact of guiding policy frameworks on innovation will highlight that neither ‘neutral’ nor ‘optimal’ frameworks for policy making exist, where competing hydrogen options are at stake. The identification of paradigms of governance maybe considered a methodological device for (participator) policy analysis.     

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.     

Steam-iron process kinetic model using integral data regression

A kinetic model describing the gas–solid non-catalytic reaction between iron oxides and hydrogen/methane gas mixtures has been proposed. This steam-iron process constitutes an interesting alternative in order to produce hydrogen without CO₂ generation, purifying streams of thermocatalytically decomposed natural gas. The study departed from a kinetic model obtained from differential regression of data acquired by thermogravimetry. This differential model (Avrami type) did not take into account some effects regarding the chemical equilibrium between reactants and products, neither those provided by the solid bed. To cope with this problem, some parameters were introduced in the kinetic model and experiments were performed in order to test the validity of the changes. These consisted of reduction steps with hydrogen and oxidations with steam along five alternated cycles in a fixed bed reactor. The refurbished reactor model (including kinetic model) consisted of a mono-dimensional fixed bed reactor working in non-stationary state. Initial parameter values were taken from the former kinetic model and later optimized with the aid of a Levenberg–Marquardt algorithm. The new model is able to predict with great accuracy the behaviour of the fixed bed reactor and represents an interesting tool for scale-up and process design.     

Natural Fe-based catalysts for the production of hydrogen and carbon nanomaterials via methane decomposition

Tierga and Ilmenite Fe-based ores are studied for the first time in the catalytic decomposition of methane (CDM) for the production of carbon dioxide-free hydrogen and carbon nanomaterials. Tierga exhibits superior catalytic performance at 800 °C. The effect of the reaction temperature, space velocity and reducing atmosphere in the catalytic decomposition of methane is evaluated using Tierga. The highest stability and activity (70 vol% hydrogen concentration) is obtained at 850 °C using methane as a reducing agent. Reduction with methane causes the fragmentation of the iron active phase and inhibits the formation of iron carbide, improving its activity and stability in the CDM. Hybrid nanomaterials composed of graphite sheets and carbon nanotubes with a high degree of graphitization are obtained. Considering its catalytic activity, the carbon quality, and the low cost of the material, Tierga has a competitive performance against synthetic iron-catalysts for carbon dioxide-free hydrogen and solid carbon generation.     

Numerical simulation of effect of operating conditions on flash reduction behaviour of magnetite under H2 atmosphere

The flash reduction behaviour of in-flight magnetite particles under hydrogen atmosphere is investigated by an Eulerian-Lagrangian model to explore the effect of operating conditions. In addition to quantitatively analysing the variations of the reduction degree and residence time of particles at the reactor exit, the reduction state of particles moving in the reactor is depicted by time evolutions of particle temperature, reduction rate, and reduction degree. Results show that the heating time of particles is too short to affect the reduction process. Higher temperature, H₂ partial pressure, and operating pressure are conducive to the flash reduction because of a higher reaction rate. Although water vapour promotes the heat transfer inside the reactor, it weakens the reduction rate. Increasing particle feeding rate has a negative effect, with the effect becoming more significant as total gas flow declines. This study can provide a theoretical basis for flash ironmaking technology in hydrogen atmosphere.     

Hydrogen production from catalytic reforming of the aqueous fraction of pyrolysis bio-oil with modified Ni–Al catalysts

Hydrogen production from renewable resources has received extensive attention recently for a sustainable and renewable future. In this study, hydrogen was produced from catalytic steam reforming of the aqueous fraction of crude bio-oil, which was obtained from pyrolysis of biomass. Five Ni–Al catalysts modified with Ca, Ce, Mg, Mn and Zn were investigated using a fixed-bed reactor. Optimized process conditions were obtained with a steam reforming temperature of 800 °C and a steam to carbon ratio of 3.54. The life time of the catalysts in terms of stability of hydrogen production and prohibition of coke formation on the surface of the catalyst were carried out with continuous feeding of raw materials for 4 h. The results showed that the Ni–Mg–Al catalyst exhibited the highest stability of hydrogen production (56.46%) among the studied catalysts. In addition, the life-time test of catalytic experiments showed that all the catalysts suffered deactivation at the beginning of the experiment (reduction of hydrogen production), except for the Ni–Mg–Al catalyst; it is suggested that the observation of abundant amorphous carbon formed on the surface of reacted catalysts (temperature programmed oxidation results) may be responsible for the initial reduction of hydrogen production. In addition, the Ni–Ca–Al catalyst showed the lowest hydrogen production (46.58%) at both the early and stabilized stage of catalytic steam reforming of bio-oil.     

Hydrogen production from water hyacinth through dark- and photo- fermentation

This article discusses the method of producing hydrogen from water hyacinth. Water hyacinth was pretreated with microwave heating and alkali to enhance the enzymatic hydrolysis and hydrogen production in a two-step process of dark- and photo- fermentation. Water hyacinth with various concentrations of 10–40 g/l was pretreated with four methods: (1) steam heating; (2) steam heating and microwave heating/alkali pretreatment; (3) steam heating and enzymatic hydrolysis; (4) steam heating, microwave heating/alkali pretreatment and enzymatic hydrolysis. Water hyacinth (20 g/l) pretreated with method 4 gave the maximum reducing sugar yield of 30.57 g/100 g TVS, which was 45.6% of the theoretical reducing sugar yield (67.0 g/100 g TVS). The pretreated water hyacinth was used to produce hydrogen by mixed H₂-producing bacteria in dark fermentation. The maximum hydrogen yield of 76.7 ml H₂/g TVS was obtained at 20 g/l of water hyacinth. The residual solutions from dark fermentation (mainly acetate and butyrate) were used to further produce hydrogen by immobilized Rhodopseudomonas palustris in photo fermentation. The maximum hydrogen yield of 522.6 ml H₂/g TVS was obtained at 10 g/l of water hyacinth. Through a combined process of dark- and photo- fermentation, the maximum hydrogen yield from water hyacinth was dramatically enhanced from 76.7 to 596.1 ml H₂/g TVS, which was 59.6% of the theoretical hydrogen yield.     

Experimental results of the study of underburned hydrogen during burning in oxygen medium

The area of research is the experimental study of the composition of steam as a result of the combustion of hydrogen in an oxygen atmosphere in order to assess the underburning of hydrogen. The existing experience of experimental research on the combustion of hydrogen in an oxygen atmosphere is analyzed. Among the known works, the underburning of hydrogen was determined after mixing the dissociated vapor with a cooling component, which contributes to its sharp decrease in temperature. As a result, this leads to a decrease in the number of recombinations of unreacted hydrogen towards the formation of steam, which leads to an increased content of hydrogen in the steam. A large number of works are devoted to the combustion of various types of fuel with hydrogen additives in internal combustion engines in a number of European and Asian countries.The purpose of the article is to supplement and summarize a series of experiments on the study of hydrogen underburning when burning in an oxygen atmosphere without using a cooling component for mixing with combustion products (water vapor). Only external cooling of the flame tube of the experimental setup was used. This experiment was performed for the first time. For the conditions of experiments carried out by the authors of the article, a diagram, components and measuring instruments of the experimental setup are presented. The initial data on the pressure and temperature of hydrogen, oxygen, cooling water are given. The main expressions of the procedure for determining the underburning of hydrogen are given. The main results of experimental measurements are presented. The graphical results of measuring the steam temperature along the length of the flame tube of the experimental setup, the flow rates of hydrogen and oxygen, the temperature and flow rate of cooling water, the pressure inside the flame tube and in the steam extraction pipeline for chemical analysis are shown. On the basis of generalization of a series of experiments, an exponential character of the decrease in the underburning of hydrogen along the length of the flame tube of the experimental setup was obtained, which indicates the intense processes of hydrogen recombination towards the formation of steam. It was found that during the time of 0.069 s with the movement of dissociated steam inside a flame tube 980 mm long, the underburning of hydrogen decreases from 5.85 to 0.016% of the mass during stoichiometric combustion and to 0.0138% of the mass with an excess of the oxidant equal to 1.4.     

Learning curves for hydrogen production technology: An assessment of observed cost reductions

At present three key energy carriers have the potential to allow a transition towards a sustainable energy system: electricity, biofuels and hydrogen. All three offer great opportunity, but equally true is that each is limited in different ways. In this article we focus on the latter and develop learning curves using cost data observed during the period 1940–2007 for two essential constituents of a possible ‘hydrogen economy’: the construction of hydrogen production facilities and the production process of hydrogen with these facilities. Three hydrogen production methods are examined, in decreasing order of importance with regards to their current market share: steam methane reforming, coal gasification and electrolysis of water. The fact that we have to include data in our analysis that go far back in time, as well as the uncertainties that especially the older data are characterized by, render the development of reliable learning curves challenging. We find only limited learning at best in a couple of cases, and no cost reductions can be detected for the overall hydrogen production process. Of the six activities investigated, statistically meaningful learning curves can only be determined for the investment costs required for the construction of steam methane reforming facilities, with a learning rate of 11±6%$11\pm 6\%$, and water electrolysis equipment, with a learning rate of 18±13%$18\pm 13\%$. For past coal gasification facility construction costs no learning rate can be discerned. The learning rates calculated for steam methane reforming and water electrolysis equipment construction costs have large error margins, but lie well in the range of the learning reported in the literature for other technologies in the energy sector.     

Experimental investigation of hydrogen production integrated methanol steam reforming with middle-temperature solar thermal energy

Developing a hydrogen production method that utilizes solar thermal energy in an effective manner is a great challenge. In this paper we propose a new approach to solar hydrogen production with the integration of methanol steam reforming and middle-temperature solar thermal energy. An experiment on hydrogen production is conducted using a 5-kW solar reactor at 150−300 °C under atmosphere pressure. The 5-kW solar receiver/reactor is fabricated and positioned along the focal line of one-tracking parabolic trough concentrator. As a result, the chemical conversion of methanol can reach levels higher than 90%, and the volumetric concentration of hydrogen in the gas products can account for 66−74% above the solar flux of 580 W/m². The obtained maximum hydrogen yield per mole of methanol is 2.65−2.90 mol, approaching the theoretical maximum value, and the experimentally obtained thermochemical efficiency of solar thermal energy converted into chemical energy is in the range of 30−50%, which is competitive with other high-temperature solar thermochemical processes. A kinetic model of solar-driven methanol steam reforming related to solar flux is also derived based on the experimental data. The promising results demonstrate that this solar-driven hydrogen production method can be feasible in practical applications.     

Water splitting for hydrogen generation over lanthanum-calcium-iron perovskite-type membrane driven by reducing atmosphere

Here, we systematically investigated the behavior of water splitting in a La_0.9Ca_0.1FeO_3?δ (LCF-91) perovskite-type oxygen-transport membrane (OTM) reactor driven by different reducing atmospheres (i.e., CO, H₂/CO and CH₄). The LCF-91 membrane showed favorable oxygen permeability and hydrogen production rates toward different reducing atmospheres (0.0617, 0.0523 and 0.0390 μmol s^?1 cm^?2 for CO, H₂/CO and CH₄ reducing gases, respectively). The activation of CO is easier than that of CH₄ over the surface of LCF-91, which promotes the surface oxygen diffusion and following oxygen permeation rate. Further crystallization of the membrane materials is observed during the water splitting test, which is much more serious for the side exposing in the oxidation atmosphere (steam side) compared with the reducing atmospheres. Grain growth of materials in both reduction and oxidation sides of membrane is associated with the reducing atmospheres, and the growth rate follows a rank order of CH₄ > H₂/CO > CO. This crystallization of LCF-9 membrane materials is beneficial for improving the stability of the reactor for successive generation of hydrogen. The LCF-91 membrane reveals a favorable stability during the CH₄-driven water splitting test.