Thermochemical Hydrogen Production Process Research Articles

Investigation of a solar-assisted methanol steam reforming system: Operational factor screening and computational fluid dynamics data-driven prediction

The development of solar-to-fuel technologies has received significant attention while facing the growing interest in clean energy production. To accurately evaluate and optimize the solar-assisted thermochemical hydrogen production process, a reliable prediction method that ensures stable accuracy is essential. We utilized a gray correlation analysis (GRA) and a multi-objective genetic algorithm (GA) model to optimize the operating parameters of a methanol steam reforming system. Computational fluid dynamics simulations provided the response values for key parameters, including reactant conversion rate, syngas product yield, and CO selectivity. Additionally, the Taguchi’s method and analysis of variance (ANOVA) were employed to assess the impact of operating parameters on these target outputs. The results demonstrate that the proposed GA-Back propagation neural networks (GA-BPNN) model significantly outperforms traditional prediction models in accuracy, exhibiting robustness and generalization. The mean absolute percentage error (MAPE) of methanol conversion, hydrogen yield, and CO selectivity is 3.20 %, 4.69 % and 3.53 %. The GRA-GA-BPNN model shows a slight decline, while still maintains reliable prediction accuracy, with the MAPE value of 5.76 %, 5.11 %, and 10.4 %. This operational factor screening-based prediction model proves useful for large-scale data-driven predictions of solar thermochemical systems, especially under complex and variable external conditions and internal human interventions.

A review of methane-driven two-step thermochemical cycle hydrogen production

Solar thermochemical cycling is a promising approach to utilizing solar energy to produce H2 and CO, which can be further synthesized into liquid fuels via Fischer-Tropsch reactions, making storage and transportation easier. Despite the potential high theoretical efficiency, factors such as the high temperature and low oxygen partial pressure required for the reduction restrict the large-scale application of this technology. In the near-to-medium term, in order to accelerate the popularization and application of this technology, according to Le Chatelier's principle, the assisted reduction of methane can greatly reduce the demand for high-temperature materials and ultra-low oxygen partial pressure. However, the addition of methane will also bring additional challenges, such as carbon emissions and carbon deposition. Reducing the influence of factors such as material sintering and irreversible loss on system efficiency in the experiment will be essential for the development of this technology. This paper focuses on the methane-driven two-step thermochemical cycle hydrogen production process, summarizes its reaction mechanism, thermodynamic analysis, kinetic analysis, oxygen carrier material doping, and experimental research in detail, and comprehensively analyzes the effect of material properties and irreversible loss on the system. According to thermodynamic and kinetic analysis, rational selection and doping of metal oxygen carrier materials can effectively reduce the reaction temperature, improve gas production rates, and enhance structural stability. Analyzing and trying to reduce various irreversible losses of the system, such as reradiation energy loss, conduction energy loss, etc., and taking appropriate heat recovery measures will help to improve the system efficiency of the actual cycle. This paper would be valuable for the development of this technology and for achieving the goal of carbon neutrality.

A comparative exergoenvironmental evaluation of chlorine-based thermochemical processes for hydrogen production

Environmental impact assessment of energy generation processes is essential to evaluate their contributions toward the global carbon footprint. Even though hydrogen is a non-carbonaceous energy source, the pathways undertaken for its production can have harmful environmental implications. Thus, this study focuses on investigating the exergoenvironmental performances of the copper-chlorine, iron-chlorine, and magnesium-chlorine thermochemical hydrogen generation processes. This study also performs a comparative exergoenvironmental analysis of the three processes. The performances of the various processes are examined based on of the environmental impact rates of exergy destruction, component-related environmental impact rates, cumulative environmental impact rates, and exergoenvironmental factors. The global warming potentials of the thermochemical cycles are also evaluated and compared for various electricity sources to obtain hydrogen. The modeling and simulation of each process are performed using Aspen-plus by considering various heat recovery approaches for thermal management. The results suggest that the environmental impact rates of exergy destruction are relatively much higher compared to the environmental impact rates associated with the components for all processes. Furthermore, the hydrolysis step yields the highest component-associated environment impact rate for all thermochemical cycles considered (Fe–Cl: 3497 mPts/h, Cu–Cl: 1997 mPt/h, and Mg–Cl: 910 mPts/h). Moreover, the magnesium-chlorine cycle results in the highest environmental impact rate of exergy destruction (650,328 mPts/h) while the iron-chlorine cycle has the highest component-related environmental impact rate (5219 mPts/h) among the three cycles. In addition, the global warming potential of the magnesium-chlorine cycle is relatively higher compared to the copper-chlorine cycle for several electricity sources.

Performance evaluation of oscillatory baffle Bunsen reactor in iodine sulfur thermochemical process for hydrogen production

<abstract> <p>Hydrogen is an environmentally attractive transportation fuel that can replace fossil fuels. The iodine-sulfur (I-S) thermo-chemical process involves three reaction steps. The Bunsen reaction is one of the main reaction steps of I-S process and plays an important role in defining overall process efficiency. Different types of reactors are being studied, including the oscillatory baffle Bunsen reactor. The reactor selection is based on process intensification and process integration, i.e., reaction and separation in the single equipment. Simulations are performed for two-dimensional cases by solving incompressible Navier-Stokes equations along with continuity equation, the geometry chosen is of single section in the column and diameter of 50 mm and baffle spacing of 50, 75,100 mm i.e. 1, 1.5 and 2 times the diameter of column and baffle free area 22%. The residence time distribution experiments are carried out in a metallic reactor with NaCl as a tracer operated at different frequencies, amplitudes and flow rates. D/uL is evaluated from experimental curves. The power per unit mass is compared for oscillatory baffled column and stirred tank for a semi-batch process. From the numerical simulations, good eddy interactions are present at higher frequencies and amplitudes and at a baffle spacing of 1.5 times the diameter of the column. Residence time distribution analysis gives a lower dispersion number at medium frequencies and higher amplitudes with constant flow rate. If the flow rates are high, then it is better to operate at higher frequencies and amplitudes to achieve plug flow behavior. Power per unit mass is less for oscillatory baffle column compared to the stirred tank of given configuration. With better mixing performance and less power per unit volume, the oscillatory baffle column is a good alternative to other columns.</p> </abstract>

Assessment of the market opportunities for hydrogen derived from high temperature reactor driven processes

In the UK, a target date of 2050 for achieving net zero carbon emissions for the whole country has been set in law. It is widely recognized that achieving this will require deep decarbonization along many energy vectors and that hydrogen has a lot of potential to contribute to this effort. A review of markets where hydrogen can contribute to decarbonization has been completed alongside a qualitative analysis of how nuclear driven hydrogen production can provide benefits over other proposed solutions in the UK. Results demonstrated a significant potential for hydrogen generated using High Temperature Gas Reactor (HTGR) technology with both steam electrolysis and thermochemical processes for hydrogen production, particularly for mobility and space heating applications.

A Comprehensive Review on Recent Advancements in Thermochemical Processes for Clean Hydrogen Production to Decarbonize the Energy Sector

Hydrogen is a source of clean energy as it can produce electricity and heat with water as a by-product and no carbon content is emitted when hydrogen is used as burning fuel in a fuel cell. Hydrogen is a potential energy carrier and powerful fuel as it has high flammability, fast flame speed, no carbon content, and no emission of pollutants. Hydrogen production is possible through different technologies by utilizing several feedstock materials, but the main concern in recent years is to reduce the emission of carbon dioxide and other greenhouse gases from energy sectors. Hydrogen production by thermochemical conversion of biomass and greenhouse gases has achieved much attention as researchers have developed several novel thermochemical methods which can be operated with low cost and high efficiency in an environmentally friendly way. This review explained the novel technologies which are being developed for thermochemical hydrogen production with minimum or zero carbon emission. The main concern of this paper was to review the advancements in hydrogen production technologies and to discuss different novel catalysts and novel CO2-absorbent materials which can enhance the hydrogen production rate with zero carbon emission. Recent developments in thermochemical hydrogen production technologies were discussed in this paper. Biomass gasification and pyrolysis, steam methane reforming, and thermal plasma are promising thermochemical processes which can be further enhanced by using catalysts and sorbents. This paper also reviewed the developments and influences of different catalysts and sorbents to understand their suitability for continuous clean industrial hydrogen production.

Assessment study of a four-step copper-chlorine cycle modified with flash vaporization process for hydrogen production

This paper develops a four-step copper-chlorine cycle for hydrogen production with conceptual modification through flash vaporization and evaluates its economic and environmental performances through exergy approach. The flash vaporization method is employed as a new approach for realizing the anolyte separation under vacuum conditions for reducing the thermal requirement of the anolyte separation step and consequently of the overall cycle. A flash vaporization is usually employed commercially for seawater desalination purposes. However, its utilization in a thermochemical hydrogen production process has not been considered previously which is really one of primary novelties of this investigation. The obtained results for the exergoeconomic and exergoenvironmental analyses of the conceptually modified cycle are also compared with those of the existing integrated cycle at the Ontario Tech University. The exergoeconomic analysis of the cycle has also been carried out for the cycle operating with and without waste heat recovery. In this regard, waste heat recovery from a steel furnace has been considered for supplying the required thermal energy for the hydrolysis step. The cost assessment of the cycle is carried out in the Aspen-plus. Compared with the existing cycle, the cycle with the proposed modification results in a lower unit cost of hydrogen. Moreover, a significant reduction in the unit cost of hydrogen is observed when waste heat recovery is considered for the modified cycle. The average unit hydrogen cost for the modified version of the cycle is evaluated to be 4.7 $/kg which reduces to 2 $/kg with incorporation of waste heat recovery. Furthermore, the overall environmental impact of the existing cycle can be potentially minimized by considering the proposed modification through flash vaporization.

Techno-economic analysis of a solar thermochemical cycle-based direct coal liquefaction system for low-carbon oil production

Direct coal liquefaction turns solid coal into transportable liquid fuel with a high energy conversion efficiency of nearly 60%. However, the hydrogen used in the direct coal liquefaction process mainly comes from coal gasification units, and gasification coal consumption accounts for about 30% of the total coal consumption. The authors of this article have proposed a solar thermochemical cycle-based direct coal liquefaction system and conducted a corresponding thermodynamic analysis. In this work, the economic feasibility, environmental impact, and the influence of key factors (coal price, oil price, carbon tax) for the industrial-scale low-carbon oil production system are analyzed. Compared with the traditional direct coal liquefaction system, the total coal consumption of the new system is reduced by ∼40%. Under low carbon constraints, the economics of the new system is comparable to that of the traditional one with a lower solar thermochemical hydrogen production cost (<13–16 yuan/kg H2). With the help of the solar thermochemical hydrogen production process, CO2 emissions of the new system can be reduced by 63%. Moreover, the solar thermochemical cycle could generate additional pure oxygen and profits. The methodology and results can provide important references for coal-to-liquid technology with high efficiency and low carbon emissions.

Thermaly integrated five-step ZnSI thermochemical cycle hydrogen production process using solar energy

The main target of this study is to apply thermal integration on a five-steps ZnSI thermochemical hydrogen production cycle in order to improving the process efficiency. In this process water enters the Bunsen system at a 298 K, 1 bar with flow rate of 0.5 mol/s, and CO2 is the input stream into the zinc system at 298 K and 1 bar. Oxygen and CO are output streams of Bunsen and zinc systems, respectively. Hydrogen is output of the HI system, which is obtained as a final product at 313 K, 1 bar with the flow rate of 0.5 mol/s. A solar thermal system which uses solar dish collector is applied in order to provide a portion of the required thermal load in the process. Modeling of the solar system is done through Matlab software. By using ZnSI instead of SI process, temperature of reaction decreases. Also hydrogen and carbon monoxide are produced. The results demonstrate that by this modification number of units of the Zn system reduces and the chemical process is simplified. By performing thermal integration, heat duty of the system decreases and accordingly thermal efficiency increase by 61.06%. As well as, the minimum required hot and cold utilities decrease by 51.94% and 65.52%, respectively. Solar fraction and collector thermal efficiency were obtained 42.57% and the 82% respectively. Finnaly a parametric assessment is done on the key parameters which influence performance of the process.

Kinetic modeling and simulation of catalyst pellet in the high temperature sulfuric acid decomposition section of Iodine-Sulfur process

In the iodine-sulfur (I-S) thermochemical process for hydrogen production, the most endothermic high temperature step is the sulfuric acid decomposition which is catalytic process. Here, we introduce a model-based framework to address the effect of model uncertainty on catalyst identification, designing and optimization. To investigate the kinetic parameters, the experiments are performed in the packed bed reactor under the conditions of diffusion free regime. Further, the kinetic model is implemented in a two-dimensional heterogeneous model of the catalytic packed bed reactor developed in Multiphysics software in order to investigate the effects of catalyst composition, support material, catalyst pellet shapes, sizes (i.e., diffusional length), pellet intrinsic properties (i.e., porosity and thermal conductivity) and temperature on the catalyst effectiveness factor. The 7-hole cylindrical shapes with 0.75 and 1.5 mm principle dimension at 1073 K has been found to have negligible diffusional limitation and temperature gradients across their cross sections.

Evaluation of materials of construction for the sulfuric acid decomposition section in the sulfur–iodine (S–I) cycle for hydrogen production: Some preliminary studies on selected materials

Water splitting by Sulfur–Iodine (S–I) cycle is one of the promising thermochemical processes for hydrogen production due to its high efficiency. The decomposition of H2SO4 to produce SO2 is the reaction with the highest energy demand in the S–I cycle and it shows a large kinetic barrier. Sulfuric acid is highly corrosive and its endothermic decomposition needs elevated temperatures (>800 °C). Henceforth, before the scale-up of the process plant there is a need to explore various materials of construction under very harsh acidic environments and phase changing conditions. Corrosion studies on some of the possible materials of construction (SS-304, SS-310, SS-316, Inconel-800, Alloy-20, Inconel-600, Incoloy-800H, Hastelloy C-276) were performed in detail and the most corrosion resistant material is suggested for the construction of sulfuric acid decomposition unit. The studies were performed at low temperatures (60 °C and 120 °C) as well as at high temperatures (700 °C, 800 °C and 900 °C). The corrosion rates were determined using weight loss method at low as well as high temperature and by using electrochemical method at low temperature (80 °C). The phase changing condition was more severe and resulted in higher corrosion rate. Hastelloy C-276 showed the least corrosion rate. SYNOPSIS In order to identify the suitable materials of construction for sulfuric acid decomposition in the S–I cycle, corrosion rates of different materials were determined. Materials were exposed to the various phases of sulfuric acid. The phase changing conditions had the most adverse effect on the materials.

Kinetic and electrochemical analyses of a CuCI/HCl electrolyzer

An electrochemical analysis is carried out from a kinetic electrochemistry perspective of a CuCl/HCl electrolysis cell, within the CuCl thermochemical water splitting process for hydrogen production. The anolyte is a solution of 2 mol L−1 CuCl(aq) and 10 mol L−1 HCl(aq) while the catholyte solution is 11 mol L−1 HCl(aq). The cell current density of 0.5 A cm−2 and voltage of 0.7 V are the desired working conditions for a CuCl/HCl electrolyzer. The current density of 0.5 A cm−2 is assumed to occur at a 5% anolyte conversion degree. At 25°C, the activation overpotential of the anode half-reaction is found to be 53 mV for a current density of 0.5 A cm−2 while the activation overpotential of the cathode half-reaction for the same condition is 87 mV. An increase in working temperature decreases the overpotential of the anode half-reaction and increases the cathode half-reaction activation overpotential. The ohmic overpotential of the cell membrane is almost 1000 times smaller than that of the activation overpotentials of the electrode half-reactions for the same temperature and current density. A higher working temperature results in a lower membrane ohmic overpotential. The required voltage to trigger electrolysis for a current density of 0.5 A cm−2 is found to be 0.53 V at 25°C and 0.59 V at 80°C and a higher temperature results in a higher electrochemical efficiency. The cell electrochemical efficiency increases linearly with working temperature while the voltage efficiency peaks at 75% at 60°C.

Development of New Corrosion Test Equipment Simulating Sulfuric Acid Decomposition Gas Environment in a Thermochemical Hydrogen Production Process

Development of New Corrosion Test Equipment Simulating Sulfuric Acid Decomposition Gas Environment in a Thermochemical Hydrogen Production Process

Effect of HIx solution concentration on ion-exchange membrane performance in electro-electrodialysis

Electro-electrodialysis (EED) has been applied to the thermochemical water-splitting iodine-sulfur process for hydrogen production to enhance the hydrogen iodide (HI) component in the HI–I2–H2O mixture (HIx solution). In this work, the HIx solution concentration dependence of conductivity and transport number as the membrane-performance indexes of Nafion 212 and a styrene-grafted poly(ethylene-co-tetrafluoroethylene) (ETFE) membrane was investigated experimentally. From a theoretical analysis of measurements based on the new EED model, the effects of the H+ and I− contents and the diffusion coefficients of H+ and I− in the evaluated membranes on conductivity and transport number were as follows: HIx solution concentration dependence of the H+ and I− contents exhibited a significantly small or different variation in comparison with that of conductivity and transport number, indicating that the dominant factors for conductivity and transport number would not be the H+ and I− contents; thereby, the effect of the diffusion coefficients of H+ and I− should not be ruled out. In terms of the conductivity of Nafion 212, the diffusion coefficient of H+ is the dominant factor because the existence of I− was negligible, whereas in the case of the ETFE-St membrane, the effect of the diffusion coefficient of I− should be considered. The diffusion coefficient of I− could more strongly affect transport number for the evaluated membranes rather than the diffusion coefficient of H+, indicating that the H+ selectivity of the membranes could be determined relatively based on variations of I− behavior in the membranes.

Experimental Study for HIx Concentration by Electro-Electrodialysis (EED) Cells in the Water Splitting Sulfur-Iodine Thermochemical Cycle

The efficiency of HI concentration/separation from a HIx solution, (mixture of HI/H2O/I2) represents a crucial factor in the sulfur-iodine thermochemical water splitting process for hydrogen production. In this paper, an experimental study on HI cathodic concentration in HIx solution using stacked electro-electrodialysis (EED) cells was carried out under the conditions of 1 atm and at three different temperature (25, 55 and 85 °C) and using a current density of 0.10 A/cm2. Results showed that an increase in HI concentration can be obtained under certain conditions. The apparent transport number (t+) in all the experiments was very close to 1, and the electro-osmosis coefficient (β) changed in a range of 1.08–1.16. The tests showed a detectable, though slow, increase in both the anodic iodine and cathodic hydriodic acid concentrations.

Experimental investigation of reaction kinetics of gas–liquid–solid Bunsen reaction in iodine–sulfur process

Iodine–sulfur (IS) cycle is the most promising thermochemical water-splitting process for nuclear hydrogen production. The Bunsen reaction, which produces sulfuric and hydriodic acid for the two decomposition reactions, plays a crucial role for the continuous stable operation of the IS cycle. Insufficient kinetics studies on Bunsen reaction, particularly under the gas–liquid–solid heterogeneous conditions, have caused difficulties for the design of Bunsen reactor, as well as the optimization and improvement of the efficiency of the process. In this work, the reaction kinetics of gas–liquid–solid Bunsen reaction denoted in the pressure drop of SO2 was experimentally investigated, and the effluences of the main factors, including the initial SO2 pressure, molar ratio of I2 to H2O, temperature, and stirring rate, were studied. In addition, a kinetics model for simulating the heterogeneous reaction was proposed and verified by the experimental data obtained under the three-phase Bunsen reaction conditions.

Corrosion behavior analyses of metallic membranes in hydrogen iodide environment for iodine-sulfur thermochemical cycle of hydrogen production

HI decomposition in Iodine-Sulfur (IS) thermochemical process for hydrogen production is one of the critical steps, which suffers from low equilibrium conversion as well as highly corrosive environment. Corrosion-resistant metal membrane reactor is proposed to be a process intensification tool, which can enable efficient HI decomposition by enhancing the equilibrium conversion value. Here we report corrosion resistance studies on tantalum, niobium and palladium membranes, along with their comparative evaluation. Thin layer each of tantalum, palladium and niobium was coated on tubular alumina support of length 250 mm and 10 mm OD using DC sputter deposition technique. Small pieces of the coated tubes were subject to immersion coupon tests in HI-water environment (57 wt% HI in water) at a temperature of 125–130 °C under reflux environment, and simulated HI decomposition environment at 450 °C. The unexposed and exposed cut pieces were analyzed using scanning electron microscope (SEM), energy dispersive X-ray (EDX) and secondary ion mass spectrometer (SIMS). The extent of leaching of metal into liquid HI was quantified using inductively coupled plasma-mass spectrometer (ICP-MS). Findings confirmed that tantalum is the most resistant membrane material in HI environment (liquid and gas) followed by niobium and palladium.

Building and Verifying a Model for Mass Transfer and Reaction Kinetics of the Bunsen Reaction in the Iodine–Sulfur Process

The iodine–sulfur (IS) process is one of the most promising thermochemical water-splitting processes for nuclear hydrogen production. The Bunsen reaction, which produces sulfuric and hydriodic acids for two decomposition reactions, plays a crucial role in the IS process. Insufficient kinetics data and models of the Bunsen reaction have caused difficulties for designing a Bunsen reactor and optimizing and improving the efficiency of the process. The mass transfer and kinetics mechanism of the Bunsen reaction, which is a complicated gas–liquid slurry process, were first analyzed and proposed on the basis of double-film theory and thermodynamics calculation, and intrinsic reaction rate equation models were deduced with different hypothesized reaction mechanisms. Then, the models were further improved, and the experimental kinetics data were used to verify the models. Finally, a set of reaction rate equations was developed, thereby confirming its reliability for calculating the reaction kinetics data. The bui...

Absorption behaviors of SO2 in HI acid for the iodine-sulfur thermochemical cycle

Bunsen reaction, which produces H2SO4 and HI acids from the reaction of I2, SO2 and H2O, is a crucial reaction for the iodine–sulfur thermochemical hydrogen production process. To study the reaction kinetics of Bunsen reaction by correlating SO2 pressure drop with reaction time, the physical absorption of SO2 in HI acid should be investigated. The absorption behaviors of SO2 in HI acid were firstly studied under various conditions, including different HI concentration, absorption temperature, and SO2 partial pressures. The results show that the absorption amount of SO2 in HI solution increases with both the pressure of the SO2 and HI acid concentration, while the effect of temperature on SO2 absorption in HI solution is complex. S and SO42− were detected in HI solutions after SO2 absorption, and iodine was found in some cases, especially under the conditions of high pressure or high temperature, indicating chemical absorption occurred, which leads to the disobeying of the physical absorption rules. It is thought that the redox reaction between HI and SO2 and the formed products are the main reasons of chemical absorption.

Role of operating conditions on cross contamination of products of the Bunsen reaction in iodine-sulfur process for production of hydrogen

In iodine-sulfur (I-S) thermo-chemical process for hydrogen production, Bunsen reaction is studied to identify the role of different operating conditions on purity of Bunsen reaction product phases. The focus of this work is to find out the level of contamination in each of the Bunsen reaction product phases. Hydroiodic acid and iodine are contaminants in sulfuric acid phase and sulfuric acid is contaminant in hydroiodic acid phase. Enhancing the level of purity in two product phases will reduce the burden on purification steps in downstream of I-S process. Bunsen reaction has been studied in continuous co-current reactor made of tantalum in the range of 50–75 °C, 2–6 bar (g) with HIx (mixture of hydroiodic acid, water and iodine) flow rate of 0.8 l/h - 3.3 l/h, sulfur dioxide 0.06 g/s – 0.24 g/s & oxygen 0.008 g/s −0.016 g/s. At 4 bar (g), 70 °C with HIx and SO2 flow rates of 1.8 l/h and 0.24 g/s respectively, purity of sulfuric acid phase is maximum i.e. 99.85 mol percent. At 4 bar (g), 60 °C with HIx and SO2 flow rates of 1.5 l/h and 0.12 g/s respectively, purity in HIx phase is maximum i.e. 99.66 mol percent.