Thermochemical Cycle Research Articles

Multi-objective optimization of the hydrogen fuel production of a solar-based cobalt-chlorine (Co–Cl) thermochemical cycle with grey relational analysis

In this paper, multi-objective optimization of the hydrogen production (m˙H2) of a solar-based cobalt-chlorine (Co–Cl) thermochemical cycle with grey relational analysis (GRA) has been performed. Monthly total irradiance averages (A), wind velocity (B), receiver height (C), receiver radius (D) and number of heliostats (E) are considered to achieve the highest the useful energy absorbed by the solar receiver (Q˙abs), efficiency of the receiver (ηrec), the overall efficiency of the system (ηoverall) and hydrogen production (m˙H2). Orthogonal experimental design is planned according to L18 orthogonal array created by Taguchi method. The percent contribution rates (PCR) on the Q˙abs, ηrec, ηoverall and m˙H2 are determined with the help of ANOVA analysis. The optimal parameters are identified as monthly total irradiance average of 143.8 kW h (A3), wind velocity of 5 m/s (B2), receiver height of 8 m (C1), receiver radius of 3 m (D1) and number of heliostats of 850 (E3), respectively. The highest Q˙abs, ηrec, ηoverall and m˙H2 values corresponding to A3B2C1D1E3 are obtained as 50.2 GW; 64.1%; 22.2% and 122.59 (tons/month), respectively. The PCR of the A, B, C, D and E parameters influencing the f-factor are determined to be 12.6 %, 1.92 %, 0.48 %, 15.03 %, and 53.20 %, respectively. Also, empirical equations are developed with regression analysis (RA) to estimate the Q˙abs, ηrec, ηoverall, m˙H2 values. The statistical coefficients (R2-value) for training and testing data's are determined in the range of 0.771167–0.99608 for Q˙abs, ηrec, ηoverall and m˙H2, respectively.

Enthalpy of mixing of solid solution rhomboclase – Indium-substituted rhomboclase (H3O) Fe1−xInx(SO4)2·nH2O

Solid solution of rhomboclase [nominally (H3O) Fe(SO4)2·3H2O] with Fe-In substitution was synthesized by coprecipitation and hydrothermal treatment and investigated by chemical, X-ray diffraction, and thermodynamic analysis in this study. The solid solution is continuous over the whole stoichiometric range despite significant differences in ionic radii between Fe3+ and In3+. Enthalpy of formation of rhomboclase and enthalpies of mixing of solid solution rhomboclase – indium-substituted rhomboclase were determined by acid-solution calorimetry in 5 mol·dm−1 HCl at T = 298.15 K and p = 1 bar. The actual compositions of the studied synthetic end members are (H3O)0.798Fe(SO4)1.899·3.078H2O (rhomboclase with molecular mass of 308.8719 g·mol−1) and (H3O)1.067In(SO4)2.034·3.017H2O (indium-substituted rhomboclase with molecular mass of 384.8377 g·mol−1). The enthalpies of mixing were obtained for a series of four indium-incorporating rhomboclase synthetic samples with molar In/(In + Fe) ratios of 0.115, 0.226, 0.537, and 0.733. The enthalpy of formation from elements in their standard state at T = 298.15 K and p = 1 bar obtained in this study by thermochemical cycle for (H3O)0.798Fe(SO4)1.899·3.078H2O is: ΔfH298.15°=-2815.2±2.8 kJ·mol−1. Mean measured enthalpies of dissolution for (H3O)0.798Fe(SO4)1.899·3.078H2O and (H3O)1.067In(SO4)2.034·3.017H2O are: ΔdissH°=14.47±0.42 kJ·mol−1 and -6.68±0.27 kJ · mol−1, respectively. Enthalpies of mixingΔmixH° have small positive values and can be fitted by a regular solid solution model with a mixing parameter W=4.26±0.32 kJ·mol−1.

Performance evaluation of the Fe–Cl and Mg–Cl cycle for hydrogen production of the minor actinide fuelled PACER fusion blanket

Thermochemical processes used to produce clean hydrogen (H2) on a large scale by utilizing renewable energy and nuclear power sources are considered one of the most environmentally friendly strategies. In this study, the neutronic performance and hydrogen production potential of the PACER fusion blanket have been investigated during the operation period. Firstly, neutronic calculations have been performed to produce an electrical energy of 1000 MW from fusion explosions of 8.36 TJ to be repeated every 40 min with Monte Carlo Calculation Method (MCNP). Minor actinide flouride (MA) fuel out of the nuclear waste of LWRs with volume fractions of 2% have been mixed homogenously in the Flibe coolant. Tritium breeding ratio (TBR) at startup is calculated as 1.27. TBR and energy multiplication factor (M) decrease gradually. TBR >1.05 can be kept over 7 years for a self-sustained reactor. The M due to higher fissionable fuel content in the molten salt computes as 3.3 at initial. The burn up exceeds ∼800 GWd/tM at the end of operation period. Secondly, the potential of hydrogen production for four step iron chloride (Fe–Cl) and three step magnesium chloride (Mg–Cl) thermochemical cycles of the hydrogen unit PACER fusion blanket. The ratio of thermal power (1 − ψ), total thermal power (Phpf) and rate of mass flow of hydrogen (m˙H2) depends on M for Fe–Cl, Mg–Cl (option I) and Mg–Cl (option II) thermochemical cycle have been presented. The ratio of thermal power (1 − ψ) for Fe–Cl, Mg–Cl (option I) and Mg–Cl (option II) have been obtained as 0.6494, 0.131 and 0.095 whereas, total thermal power (Phpf) have been computed as 5298.8, 3608.43 and 3488.925 MW, respectively, at start up. The produced of hydrogen amount for Fe–Cl, Mg–Cl (option I) and Mg–Cl (option II) have been calculated as ∼ 534.65; ∼1236.82 and ∼806.03 kg/year, respectively, at startup.

Thermocatalytic Hydrogen Production from Water at Boiling Condition.

Thermochemical water-splitting cycles are technically feasible for hydrogen production from water. However, the ultrahigh operation temperature and low efficiency seriously restrict their practical application. Herein, one-step and one-pot thermocatalytic water-splitting process is reported at water boiling condition catalyzed by single atomic Pt on defective In2O3. Water splitting into hydrogen is verified by D2O isotopic experiment, with an optimized hydrogen production rate of 36.4 mmol·h-1·g-1 as calculated on Pt active sites. It is revealed that three-centered Pt1In2 surrounding oxygen vacancy as catalytic ensembles promote the dissociation of the adsorbed water into H, which transfers to singlet atomic Pt sites for H2 production. Remaining OH groups on adjacent In sites from Pt1In2 ensembles undergoes O─O bonding, hyperoxide formation and diminishing via triethylamine oxidation, water re-adsorption for completing the catalytic cycle. Current work represents an isothermal and continuous thermocatalytic water splitting under mild condition, which can re-awaken the research interest to produce H2 from water using low-grade heat and competes with photocatalytic, electrolytic, and photoelectric reactions.

Electricity and hydrogen production by integrating two kinds of fuel cells with copper chlorine thermo-chemical cycle

An innovative cogeneration system based on a solid oxide fuel cell (SOFC) and copper chlorine cycle is being investigated. Instead of directly making electricity by any thermodynamic cycle or thermoelectric generator, the waste heat from SOFC should be used to make hydrogen through the copper-chlorine cycle (Cu–Cl). A portable polymer exchange membrane fuel cell (PEMFC) has been suggested due to its compatibility with portable and non-portable applications. The obtained results reveal that increasing the current density of SOFC results in higher methane consumption, output power, overpotentials, and hydrogen production. Furthermore, temperature variation does not have as much influence on power generation and efficiency as current density, where the system efficiency, when operating at 0.7 A/cm2 and SOFC operating temperature of 900–1200 K, varies between 40.4 % and 46.3 %. Regarding the methane flow rate, as it increases, the output power increases as well, but the efficiency falls. The system's greatest power output is 677.5 kW and occurs at a methane flow rate of 2.13 mol/s, although the system efficiency is just 39.7 % at that point. Most importantly, SOFC generates nearly 65 % of the total power, while PEMFC generates around 35 %. Therefore, the percentage of additional power that PEMFC can produce is around 55 %.

A study on integrated HTR-PM driven hydrogen production using thermochemical cycles

This present study aims to design a nuclear-based hydrogen production system by using the three- and four-step magnesium-chloride cycles, and compares the three-step magnesium-chloride cycle integrated nuclear-based system and the four-step magnesium-chloride cycle integrated nuclear-based system. Within the scope of this study, four units of high-temperature gas-cooled-pebble bed modular nuclear reactor are employed, where a total of 1 GW thermal energy (heat) is secured from these four reactors. All of the heat generated by the reactors is used to drive the power generation and hydrogen production cycles. The proposed system, along with its cycles and processes, are examined by using mass, energy, entropy, and exergy balance equations. The modeling and simulations for the three- and four-step magnesium-chloride cycles are carried out via the Aspen Plus software package. The results are compared for two hydrogen production methods, and sensitivity analysis is assessed for various steam/MgCl2 ratios, as well as different reactor temperatures and pressures for each reaction in the cycles. While the three-step magnesium-chloride cycle integrated nuclear-based system produces 2.43 kg/s hydrogen, 2.13 kg/s hydrogen is produced by the four-step magnesium-chloride cycle integrated nuclear-based system. As a consequence of this present study, energy and exergy efficiencies are calculated as 54.2% and 60.9% for the three-step magnesium-chloride cycle, while these values are 48.0% and 54.0% for the four-step magnesium-chloride cycle. Additionally, while the energy and exergy efficiencies of the three-step magnesium-chloride cycle integrated overall system are 29.2% and 40.3%, these values are 25.6% and 35.2% for the four-step magnesium-chloride cycle integrated system, respectively.

Carnallite double salt for thermochemical heat storage

The potential use of carnallite (KMgCl3·6H2O) for low temperature thermochemical heat storage has been evaluated. Carnallite is an incongruently soluble double salt and its possible decomposition and dehydration reactions have been carefully evaluated from available thermodynamic data and the phase diagram has been constructed. The dehydration and rehydration reactions have been experimentally studied and the reaction products have been characterized using thermogravimetric mass spectrometry, water vapor sorption, X-ray powder diffraction, scanning electron microscopy, Raman microscopy and calorimetry. The results of the experimental investigation of these reactions confirm the model predictions and clearly show that a thermochemical cycle including carnallite and its dihydrate (KMgCl3·2H2O) is very promising for low temperature domestic thermochemical storage. In comparison to both pure MgCl2·6H2O and also other salts mentioned in the literature, the double salt carnallite offers significant advantages. It has a higher deliquescence humidity and, thus, is much less sensitive to over-hydration and liquefaction. It can be easily dehydrated at only 100 °C and is much less prone to hydrolysis (HCl release). Carnallite has also a good reversibility between dehydration and hydration and the re-formation of carnallite by rehydration is easily achieved at low water vapor pressure and faster reaction rate than the hydration of MgCl2·2H2O to MgCl2·6H2O. The enthalpy of hydration is slightly higher for the hydration of KMgCl3·2H2O than for the hydration of MgCl2·2H2O. The only price to be paid is a slightly reduced storage density of the double salt due to its larger molar volume. However, the theoretical storage density of 1.52 kJcm−3 is still excellent. Also, carnallite is a low-cost material as it is available as industrial waste material or can be easily synthesized.

Multi-injection downdraft moving bed reactor for hydrolysis in thermochemical hydrogen production

This paper investigates a downdraft multi-injection moving bed reactor (MBR) for the hydrolysis reaction in the copper-chlorine (Cu–Cl) thermochemical cycle for hydrogen production. The numerical modelling is conducted for a variety of system configurations of the MBR, with a focus on reducing the energy requirement of the reactor while achieving high conversion rates. Several design variables are investigated, including reactor volume, injection point location, and quantity of steam injection. The numerical predictions show an approximate 23% increase in CuCl2 conversion for the multi-injection MBR compared to a single injection design. A maximum conversion of 66.5% is predicted through design parameter variations. Asymptotic behavior for the quantity of injection locations with respect to conversion extent is presented for several different steam to copper ratios. The results and new insights in this paper suggest opportunities for conversion improvement and steam to copper ratio reduction in the hydrolysis reactor through the MBR design.

TiO2/MnFe2O4 co-modified alkaline papermaking waste for CaO-CaCO3 thermochemical energy storage

CaO-CaCO3 thermochemical energy storage is a promising technology for solar energy utilization and storage. Alkaline papermaking waste (APW) from paper mills, which is mainly composed of CaCO3. Herein, TiO2/MnFe2O4 co-modified APW was synthesized. The energy storage capacity of TiO2/MnFe2O4 co-modified APW was studied during CaO-CaCO3 thermochemical energy storage cycles in a duel fixed bed reactor. TiO2/MnFe2O4 co-modified APW mainly consists of CaO, MgO, CaTiO3, CaMnO3, and Ca2Fe2O5. The introductions of TiO2 and MnFe2O4 significantly improve the cyclic stability and optical absorption property of APW in 30 cycles. The co-modified APW (the mass ratio for CaO:TiO2:MnFe2O4 = 100:5:5) possesses high sintering resistance, energy storage, and optical absorption capacities in 30 cycles. The energy storage conversion and capacity of the co-modified APW are 0.72 and 2288.57 kJ/kg after 30 cycles, respectively. The optical absorptance of the co-modified APW reaches 49%, which is 9.25 times as high as that of APW. CaTiO3 and CaMnO3 effectively mitigate the sintering of CaO grains. CaMnO3 and Ca2Fe2O5 significantly increase the optical absorptance of APW. The co-modified APW possesses stronger basicity and more oxygen vacancies, which is favourable for the carbonation reaction. Thus, TiO2/MnFe2O4 co-modified APW is a good energy storage material.

Assessing the Viability of GeO2/GeO Redox Thermochemical Cycle for Converting CO2 into Solar Fuels

The solar thermochemical process of splitting CO2, known as CDS, is studied here using a redox cycle involving GeO2/GeO. The required thermodynamic data for a second-law-efficiency analysis is obtained from the HSC Chemistry software. The goal of this study is to investigate how different parameters, such as the operating temperatures and molar flow rate of the inert sweep gas, as well as the inclusion of separation units, heat exchangers, heaters, and coolers, can affect the solar-to-fuel energy conversion efficiency of the GeO2/GeO cycle. All calculations assume a constant gas-to-gas heat recovery effectiveness of 0.5. The analysis shows that the solar-to-fuel energy conversion efficiency is lower at a thermal reduction temperature of 1600 K (11.9%) compared to 2000 K. This is because high energy duties are required for heater-2, heater-3, and separator-1 due to the need for a higher inert gas flow rate. After conducting a comparative analysis of the three CDS cycles, it can be inferred that the GeO2/GeO cycle exhibits a significantly higher solar-to-fuel energy conversion efficiency in comparison to the ZnO/Zn and SnO2/SnO cycles across all thermal reduction temperatures. According to the comparison, it is confirmed that the GeO2/GeO CDS cycle can achieve a reasonably high solar-to-fuel energy conversion efficiency of 10% at less than 1600 K. On the other hand, ZnO/Zn and SnO2/SnO CDS cycles require a thermal reduction temperature of more than 1850 K to achieve a solar-to-fuel energy conversion efficiency of 10%.

QM/MM Study Into the Mechanism of Oxidative C=C Double Bond Cleavage by Lignostilbene-α,β-Dioxygenase.

The enzymatic biosynthesis of fragrance molecules from lignin fragments is an important reaction in biotechnology for the sustainable production of fine chemicals. In this work we investigated the biosynthesis of vanillin from lignostilbene by a nonheme iron dioxygenase using QM/MM and tested several suggested proposals via either an epoxide or dioxetane intermediate. Binding of dioxygen to the active site of the protein results in the formation of an iron(II)-superoxo species with lignostilbene cation radical. The dioxygenase mechanism starts with electrophilic attack of the terminal oxygen atom of the superoxo group on the central C=C bond of lignostilbene, and the second-coordination sphere effects in the substrate binding pocket guide the reaction towards dioxetane formation. The computed mechanism is rationalized with thermochemical cycles and valence bond schemes that explain the electron transfer processes during the reaction mechanism. Particularly, the polarity of the protein and the local electric field and dipole moments enable a facile electron transfer and an exergonic dioxetane formation pathway.

An integrated alkali metal thermoelectric converter with sodium hydroxide thermoelectric water splitter and organic Rankine cycle for efficient power and hydrogen production

This study proposes the integration of the NaOH thermochemical water splitting cycle with both an alkali metal thermoelectric converter and an organic Rankine cycle. The objective of the proposed model is to enhance the overall efficiency by utilizing the waste heat generated by the NaOH thermochemical water splitting process and redirecting the heat from the alkali metal thermoelectric converter using bypass when hydrogen demand is low.Performance parameters such as system efficiency, system power, hydrogen production, AMTEC power production, and ORC power production were examined in the study. The results indicated an increase in power and hydrogen production with higher hot-end temperatures, along with an overall reduction in system efficiency for low values of load resistance. The system achieved a maximum efficiency of 53.37%.The system efficiency reached its peak at an AMTEC hot end temperature of 1173 °C, achieving 53.37 % efficiency at an RL value of 1.01 O. When the system operates at its maximum AMTEC power production, the AMTEC modules supply 12.81 kW, while the ORC generates 5.57 kW, and the hydrogen compressor consumes 0.13 kW. The total electrical power generation is 18.38 kW. The findings also indicate that the utilization of the bypass led to a reduction in hydrogen production while increasing the power output of the organic Rankine cycle.

Safety Analysis of the Hydrolysis Reactor in the Cu-Cl Thermochemical Hydrogen Production Cycle—Part 1: Methodology and Selected Top Events

In this paper, IEC 61511 was used to evaluate the hazards and risks associated with the continuous operation of the hydrolysis reactor system in the copper-chlorine thermochemical hydrogen production cycle, with a specific focus on the application of automated active safety systems and safety integrated systems. The analysis presented herein was performed using a speculative but representative hydrolysis piping and instrumentation diagram (P&ID) for the hydrolysis reaction, which was based on currently published systems as well as experience with experimental hydrolysis reactors. This analysis was then used to inform the design of a set of automated safety systems that provide the redundant operation of critical devices and can bring the hydrolysis to a safe shutdown state if needed.

A review of the integration of the copper-chlorine cycle with other systems for hydrogen production

There are different methods for hydrogen production, among which thermo-chemical cycles are particularly important. One of the most common thermochemical cycles is the copper-chlorine cycle. In this cycle, the water electrolysis process takes place during a thermo-chemical reaction, and copper chlorine is used as a thermochemical reaction intermediate. This cycle requires two factors to produce hydrogen: A heat source with a temperature of about 520 oC and electricity. For this reason, it is possible to use the hot waste gases of industries or parabolic through collector and heliostat field to provide its heat. To supply electricity for this cycle, various alternatives from the power grid and wind turbine to heat recovery in cycles that use low-temperature energy sources are considered. In this article, the integration of the copper-chlorine cycle with power generation systems has been discussed and investigated from the perspective of energy, exergy, and economics. This review is divided into two general parts using renewable and non-renewable resources. At the beginning of this article, various methods of hydrogen production focusing on the copper-chlorine cycle have been briefly discussed. In the following, the way this cycle works is explained along with energy, exergy, and economic equations, and the research done in this direction is explained. Finally, a strategy for how to integrate the copper-chlorine cycle with other systems is described. Studying this article, in addition to giving a better attitude in the field of integrating this cycle with other plants, is similar to a guideline for using the cycle along with other systems for better productivity. The conducted investigations showed that the recovery of hot industrial exhaust gas as a source of heat for the Cu-Cl cycle has a high potential for saving energy consumption and reducing environmental pollutants. To produce the required electricity, it is recommended to use cycles that work with a low-temperature energy source, such as the organic Rankine cycle and Kalina cycles. Also, if renewable energy sources are used, it is recommended to use parabolic through collectors and heliostats to produce the required heat. As in the case of non-renewable energy sources, cycles with low-temperature energy sources can be used.

Tri-objective optimization of electricity, fresh water, and hydrogen production in a biomass-driven trigeneration plant: Thermoeconomic and environmental evaluation

Substituting renewable energy sources for fossil fuels is a viable option for mitigating environmental damage caused by the energy sector. Another strategy for better utilization of primary resources is integrating multigeneration energy plants. To that end, this study proposes the construction of a biomass-fired power, water, and hydrogen facility. A gasifier integrated gas turbine (for electricity generation), vanadium-chlorine thermochemical cycle (for hydrogen synthesis), and MED-TVC unit (for water desalination) make up this system. Compared to previous similar researches, the waste heat-driven hydrogen and freshwater production units is the most favorable feature of the proposed tri-generation plant in this research. Exergy, economic, and ecological impacts of the engineered plant are examined. The results of a thorough parametric analysis reveal that, each design variable uniquely impacts the values of three goods and three performance indicators (exergy efficiency, emission index, and levelized cost of product). Therefore, the proposed tri-generation plant's optimal operating conditions can only be determined by the use of a triple-criteria optimization. The best operation was found to have a levelized product cost of 0.0441 $/kWh, a CO2 emission of 0.530 kg/kWh, and an exergy efficiency of 56.64%. The parametric analysis also suggested that a lower pressure ratio and gasification temperature would be optimal for increasing hydrogen production.

The study of CO2 splitting kinetics on LSM perovskite oxides in the solar-driven two-step thermochemical cycle

La0.6Sr0.4MnO3 (LSM) has seen enormous interest since they were proposed for the two-step thermochemical cycle (TSTC). However, its oxidation kinetics is notably deficient, and few studies have been documented. In this work, the reactivity activity relaxation (RAR) and electrical conductivity relaxation (ECR) methods are used to investigate the reaction kinetics of CO2 splitting by LSM oxidation. The results of RAR test show that the Sestak-Berggren model is the most precise depiction of the reaction mechanism, and the apparent kinetic parameters are obtained. In addition, the chemical bulk diffusion coefficient and the oxygen surface exchange coefficient of the reactions are obtained using the ECR method. It’s found that the surface reaction process is the rate-limiting step of the whole oxidation reaction process. In conclusion, this study examines in detail the kinetic properties of LSM oxidation reaction and provides a reference for its application in TSTC.

Chemistry of the iron-chlorine thermochemical cycle for hydrogen production utilizing industrial waste heat

This research presents an inventive thermochemical cycle that utilizes a reaction between iron and HCl acid for hydrogen production. The reaction occurs spontaneously at room temperature, yielding hydrogen and a FeCl2 solution as a by-product. Exploring the thermal decomposition of the FeCl2 by-product revealed that, at conditions suitable for utilization of low-temperature industrial waste heat (250 °C), chlorine gas formation can be circumvented. Instead, the resulting by-product is HCl, which is readily soluble in water, facilitating direct reuse in subsequent cycles. The utilization of low-temperature industrial heat not only optimizes resource utilization and reduces operational costs but also aligns with environmentally sustainable production processes. From the kinetic studies the activation energy was calculated to be 45 kJ/mol and kinetics curves were constructed. They showed significant kinetics at room temperature and above but rapid decrease towards lower temperatures. This is important to consider during real-scale technology optimization. The theoretical overall energy efficiency of the cycle, with 100% and 70% heat recuperation, was calculated at 68.8% and 44.8%, respectively. In practical implementation, considering the efficiency of DRI iron reduction technology and free waste heat utilization, the cycle achieved a 41.7% efficiency. Beyond its energy storage capabilities, the Iron-chlorine cycle addresses safety concerns associated with large-scale hydrogen storage, eliminating self-discharge, reducing land usage, and employing cost-effective storage materials. This technology not only facilitates seasonal energy storage but also establishes solid-state energy reserves, making it suitable for balancing grid demands during winter months using excess renewable energy accumulated in the summer.

Back to the future with emerging iron technologies.

Here is a comprehensive overview of iron's potential in low-carbon energy technologies, exploring applications like metal fuel combustion, iron-based batteries, and energy-carrier cycles, as well as sustainable approaches for production and recycling with a focus on reducing environmental impact. Iron, with its abundance, safety, and electrochemical characteristics, is a promising material to contribute to a decarbonized future. This paper discusses the advancements and challenges in iron-based energy storage technologies and sustainable iron production methods. Various innovative approaches are explored as energy storage solutions based on iron, like advancements in thermochemical Fe-Cl cycles highlight the potential of iron chloride electrochemical cycles for long-term high-capacity energy storage technology. Additionally, the utilization of iron as a circular fuel in industrial processes demonstrates its potential in large-scale thermal energy generation. Sustainable iron production methods, such as electrolysis of iron chloride or oxide and deep eutectic solvent extraction, are investigated to reduce the carbon footprint in the iron and steel industry. These findings also show the importance of policy and technology improvements that are vital for the widespread use and recycling of iron-based tech, stressing the need for collaboration toward a sustainable future.

Continuous multiphase Bunsen reactor of iodine-sulfur thermochemical water splitting cycles for hydrogen production: Experimental, Modelling and Design Insights

Thermochemical water splitting cycles (TWSCs) hold promise for sustainable H2 production in future energy systems, with Iodine-Sulfur (IS) and Nickel-Iodine-Sulfur (NIS) processes standing out as efficient options. The core of both these processes lies in the Bunsen reaction, underscoring the need to identify optimal operational conditions and plant solutions for this crucial reaction section. Thus, in this study, a continuous counter-current flow Bunsen reactor fed with 5 NL h−1 of SO2 was constructed and tested. An inventive aspect was the introduction of solid I2 pellets from the top to enhance saturation at the liquid-liquid interface between sulfuric and hydriodic product phases, promoting segregation. This ingenious design achieved nearly complete SO2 conversion and optimal H2SO4 and HI concentrations in the respective product phases, while avoiding undesirable byproduct formation. The study further advanced the modelling of the experimental reactor by employing innovative kinetic and liquid-liquid equilibrium description approaches, and demonstrating exceptional validation accuracy of R2 = 0.9988. Additionally, with the aim of obtaining design charts as a potential tool for Bunsen reactor design, a microscopic model describing the gas phase trend along bubble or packed Bunsen-type reactors was developed. The model’s dimensionless analysis revealed a characteristic times ratio (Bu) comprehensively describing all the phenomena occurring to the gas phase within the Bunsen reaction section, and identified an optimal Bu value of 0.4 for pure SO2 gas inlet. Overall, the study's innovative strategies and models contribute significantly to the advancement of Bunsen reactor engineering.

A review of solar thermochemical cycles for fuel production

Solar-driven CO2/H2O splitting via a two-step solar thermochemical cycle is a promising approach for fuel production and carbon neutrality to address the intermittent instability and low energy density of solar energy while taking advantage of its clean and nonpolluting nature. However, current experimental efficiencies are still below theoretical levels due to various limitations such as material properties and energy loss occurring in the reactor. The reactor, as an important component for commercialization, still faces various challenges including high reaction temperature, limited reactor material longevity, high temperature sealing of moving parts, and slow adsorption and desorption rate of porous structure lining. This paper reviews researches on solar thermochemical oxygen carriers and related reactors, with particular focus on analyzing reactor design criteria, modeling methods, energy efficiency and energy loss analysis. In addition, obtaining low partial pressure oxygen for reduction reactions, heat recovery methods, and synergies between the reactor and solar concentrating system play a significant role in further improving energy efficiency. This work demonstrates the feasibility of two-step solar thermochemical cycles in renewable energy technologies and provides guidance for future innovations in this field.