Thermochemical Hydrogen Production Process Research Articles

Numerical modeling of a bayonet heat exchanger-based reactor for sulfuric acid decomposition in thermochemical hydrogen production processes

Sulfur-based thermochemical hydrogen production cycles represent one of the most appealing options to produce hydrogen from water on a large scale. The Hybrid Sulfur is one of the most advanced thermochemical cycles. The high temperature section of the process, common to all sulfur-based cycles, operates the sulfuric acid thermal decomposition reaction at temperatures on the order of 800 °C. The paper shows and discusses the modeling results obtained for a bayonet heat exchanger based high temperature reactor that decomposes the sulfur compounds into sulfur dioxide and oxygen. A detailed transport phenomena model, including suitable decomposition kinetics, has been set up using a finite volume numerical approach. A preliminary configuration of the reactor, established based on process simulation results and on the initial reactor prototype developed at Sandia National Laboratory, has been examined and simulated. Results, obtained for a reactor driven by thermal power provided by helium flow, demonstrate the effective decomposition performance at maximum temperatures on the order of 800 °C and pressures of 14 bar. For a laminar flow configuration a sulfur dioxide production yield of about 28 wt% (with sulfur trioxide reduction from 69 wt% to approximately 33 wt%) has been achieved, representing decomposition rates practically equal to the corresponding equilibrium values. Limited pressure drops of approximately 2500 Pa have also been achieved in the sulfur mixture region.

Tantalum membrane reactor for enhanced HI decomposition in Iodine–Sulphur (IS) thermochemical process of hydrogen production

HI decomposition reaction in Iodine–Sulphur (IS) thermochemical process for hydrogen production is one of the critical steps, which suffers from low equilibrium conversion. Metallic membrane reactor is proposed to be a process intensification tool that can enable efficient HI decomposition by overcoming the equilibrium limitation of the reaction. In this study, we report the fabrication and characterization of clay alumina supported tantalum (Ta) membrane and its application in packed bed catalytic membrane reactor for HI decomposition section of IS process for the first time. The alumina tubes were coated with thin film of Ta metal of thickness 2.5 μm using DC sputter deposition technique under the optimum set of parameters. The membranes were found to remain stable upto 200 Hrs of exposure under HI-H2O environment at 125 °C. Modeling of a packed bed Ta membrane reactor for HI decomposition was carried out to find out the optimum operating parameters of the membrane reactor to get a conversion of at least 95%. A packed bed membrane reactor (PBMR) assembly was fabricated with integration of the in-house synthesized Ta membrane and Pt-alumina catalyst for carrying out HI decomposition studies at 450 °C. The tube side was chosen as permeation zone and the shell side as the reaction zone. A single-pass conversion of 94.7% of HI to hydrogen was obtained by employing Ta metal membrane reactor against the theoretical equilibrium conversion value of 22%. The findings showed that Ta-based PBMR shall offer a potential benefit to reach higher efficiency of IS thermochemical process.

Effects of the operation modes on the HIx phase purification in the iodine–sulfur thermochemical cycle for hydrogen production

In the iodine–sulfur thermochemical water-splitting process for hydrogen production, purification of hydriodic phase (HIx) had to be adopted to eliminate the minor components in the HIx phases (the mixture of mainly HI, H2O, I2 and small amounts of H2SO4), so as to avoid the undesirable side reactions between HI and H2SO4. In this work, experimental studies on HIx phase purification were carried out. Effects of the operation modes (such as batch operation, continuous operation and the mixed modes of the continuous and discontinuous operation), and process parameters (such as the reaction temperature, feed flowrate of the HIx solution, and the flowrate of the stripping gas N2) on the purification of HIx phase were investigated. The experimental results showed that increase of temperature and N2 flowrate, and decrease of feed flowrate of HIx solution favored the removal of H2SO4 from HIx phase. The purification efficiency would be improved by combining the continuous operation with the batch operation during the purification process. These results were favorable for achieving the closed operation of IS cycle.

Numerical simulations of HI decomposition in coated wall membrane reactor and comparison with packed bed configuration

HIx decomposition step of the Iodine-Sulphur (IS) thermochemical process for hydrogen production is the most critical step. The Coated Wall Membrane Reactor (CWMR) is an important configuration that can be used for carrying out HI decomposition. The present study uses Computational Fluid Dynamics (CFD) as a tool to assess the performance of a CWMR that ensures higher conversion for HI decomposition, which in turn positively affects the overall thermochemical efficiency of the IS process. The effects of various operating parameters, geometry and properties on conversion are studied. The results show that using a CWMR instead of a coated wall reactor (CWR) leads to significant process intensification by coupling reaction and separation in a single unit and enhancing conversion of the reaction. The operating parameters having significant impact on conversion are identified. Comparison of a CWMR with a Packed Bed Membrane Reactor (PBMR) shows that the PBMR gives higher conversion (at least 6%) than the CWMR for the entire range of parameters considered. For very low space velocity, high membrane permeability and low reactor diameters, conversions in PBMR and CWMR are almost the same.

HI<sub>x</sub> 용액을 이용한 연속식 분젠 반응에 미치는 SO<sub>2</sub>용해도의 영향

The Sulfur-Iodine thermochemical hydrogen production process (SI process) consists of the Bunsen reaction section, the <TEX>$H_2SO_4$</TEX> decomposition section, and the HI decomposition section. The <TEX>$HI_x$</TEX> solution (<TEX>$I_2-HI-H_2O$</TEX>) could be recycled to Bunsen reaction section from the HI decomposition section in the operation of the integrated SI process. The phase separation characteristic of the Bunsen reaction using the <TEX>$HI_x$</TEX> solution was similar to that of <TEX>$I_2-H_2O-SO_2$</TEX> system. On the other hands, the amount of produced <TEX>$H_2SO_4$</TEX> phase was small. To investigate the effects of <TEX>$SO_2$</TEX> solubility on Bunsen reaction, the continuous Bunsen reaction was performed at variation of the amounts of <TEX>$SO_2$</TEX> gas. Also, it was carried out to make sure of the effects of partial pressure of <TEX>$SO_2$</TEX> in the condition of 3bar of <TEX>$SO_2-O_2$</TEX> atmosphere. As the results, the characteristic of Bunsen reaction was improved with increasing the amounts and solubility of <TEX>$SO_2$</TEX> gas. The concentration of Bunsen products was changed by reverse Bunsen reaction and evaporation of HI after 12 h.

Effect of agitation speed and fluid velocity on heat transfer performance in agitated Bunsen reactor of iodine-sulphur thermo-chemical cycle

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.

Characteristic of the Pressurized Continuous Bunsen Reaction using HIxSolution

The Sulfur-Iodine thermochemical hydrogen production process (SI process) consists of the Bunsen reaction section, the H 2 SO 4 decomposition section and the HI decomposition section. The HI x solution (HI-I 2 -H 2 O) could be recycled to Bunsen reaction section from the HI decomposition section in the operation of the integrated SI process. The phase separation characteristic of the Bunsen reaction using the HI x solution was similar to that of SO 2 -I 2 -H 2 O system. However, the amount of produced H 2 SO 4 phase was too small. To solve this problem, the study was carried out by the pressurized continuous Bunsen reaction. Bunsen reactions were performed at variation of feed rate of SO 2 /O 2 gas in 3 bar of atmosphere. Also, it was performed to check the effects of the residence time in the reservoir on the characteristics of Bunsen products. As the results, the concentration of H 2 SO 4 and HI in Bunsen products was increased with increasing the amounts of SO 2 . When the residence time in the reservoir increased, the concentration of H 2 SO 4 and HI in HI x phase was decreased by reverse Bunsen reaction.

초고온가스로를 이용한 원자력수소생산 기술개발

미래에너지의 해법으로 원자력에너지를 이용한 물분해 수소생산시스템의 핵심기술을 개발하였다. 안전성을 보장할 수 있는 제4세대 원자로인 초고온가스로의 고열을 이용하여 황요오드 열화학적인 방법으로 물을 분해하여 수소를 생산하는 기술이다. 원자력수소생산 핵심기술은 초고온에서의 열을 공급하는 것을 모사하는 초고온 실험기술, 초고온가스로의 안전성을 모사하는 연구, 초고온가스로의 노심과 안전성을 해석할 수 있는 도구의 개발, 초고온가스로에 사용하는 연료제조기술, 물을 분해하여 열화학적인 방법으로 수소를 생산하는 기술로 구성된다. 원자력수소생산에 필요한 핵심기술을 개발하고 실험실 규모로 입증하였으며, 대규모 실용화를 위해서 선결되어할 미완성 기술을 제시하였다. 본 기술은 제4세대 원자로개발 국제공동연구로 수행한 기술로서 향후 미래의 원자로 기술이다.

수소 생산을 위한 SI Cycle 공정에서의 중간 열교환 공정 모사 연구

SI Cyclic process is one of the thermochemical hydrogen production processes using iodine and sulfur for producing hydrogen molecules from water. VHTR (Very High Temperature Reactor) can be used to supply heat to hydrogen production process, which is a high temperature nuclear reactor. IHX (Intermediate Heat Exchanger) is necessary to transfer heat to hydrogen production process safely without radioactivity. In this study, the strategy for the optimum design of IHX between SI hydrogen process and VHTR is proposed for various operating pressures of the reactor, and the different cooling fluids. Most economical efficiency of IHX is also proposed along with process conditions.

Hydrogen generation from biomass materials: challenges and opportunities

In this review, various processes for conversion of ligno(hemi)cellulosic biomass into hydrogen gas are comprehensively reviewed in terms of two main groups, namely (1) thermochemical processes [pyrolysis, catalytic pyrolysis, different gasification, co‐gasification, supercritical water gasification (SCWG)] and (2) biochemical‐cum‐biological conversions, along with electrolytic and photolytic processes. This review depicts much about the thermochemical processes for hydrogen production and its utilization via pyrolysis of biomass, gasification, gasification combined with pyrolysis, supercritical water (fluid‐gas) extraction, steam reforming (SR), auto thermal reforming (ATR), dry reforming (DR), liquid phase reforming (LPR), aqueous‐phase reforming (APR), and partial oxidation (POX) of renewable carboxylates such as bioethanol, acetic acid, phenol, glycerol, carbohydrates, different water‐soluble sugars, and bio‐oil, which are some of the areas to be explored for widespread awareness of hydrogen usage. Biomass‐based hydrogen production systems are emphasized and discussed in terms of their energetic and exergetic aspects with the help of reaction mechanisms. Different oxygenate compounds as derived from biomass with their potential catalyst tested by several literature studies and potential methods are then summarized. WIREs Energy Environ 2015, 4:139–155. doi: 10.1002/wene.111This article is categorized under: Bioenergy &gt; Science and Materials Fuel Cells and Hydrogen &gt; Science and Materials Fuel Cells and Hydrogen &gt; Systems and Infrastructure Energy and Development &gt; Science and Materials

Flux Measurement of a New Beam-down Solar Concentrating System in Miyazaki for Demonstration of Thermochemical Water Splitting Reactors

A two-step thermochemical water splitting cycle using nonstoichiometric cerium oxide is a promising solar thermochemical hydrogen production process. One of the present authors has developed new solar reactors using “internally circulating fluidized beds” with cerium oxide particles for the high-temperature cycle. These solar reactors need to be combined with a beam-down solar concentrating system. Niigata University, University of Miyazaki, and Mitaka Kohki Co. Ltd. recently started an R&D joint project to demonstrate the up-scaled fluidized bed reactors with solar. A new type of 100 kWth beam-down solar concentrating system was built in August, 2012 at the campus of University of Miyazaki. This paper describes the first results of solar flux measurements on the new Miyazaki beam-down system for demonstration of thermochemical water splitting reactors. The fluxes of concentrated solar radiation at the focus point were measured by moving an array of thirteen Gardon gauges. The solar power in an area of 130 × 130cm in the focal spot was larger than 90 kWth during three hours of daytime radiation, exceeding 110 kWth around noon on October 12, 2012. A new CPC specific to this new beam-down system was designed and fabricated to concentrate the solar fluxes into a 44cm diameter circle of the solar reactor aperture. The solar demonstration of the reactors will start at the Miyazaki beam-down system from October 2013.

Study on Apparent Kinetics of the Reaction between Sulfuric and Hydriodic Acids in the Iodine-Sulfur Process

The iodine–sulfur (IS) thermochemical process for hydrogen production is one of the most promising approaches in using high-temperature process heat supplied by a nuclear reactor. This process includes three reactions that form a closed cycle: the Bunsen reaction, in which iodine, water, and sulfur dioxide react to form sulfuric acid and hydriodic acid (HI); HI decomposition; and sulfuric acid decomposition. However, the side reactions between H2SO4 and HI may disturb the operation of the IS closed cycle. For optimal process conditions, the reaction kinetics between H2SO4 and HI should be examined. In this work, a preliminary kinetic study was conducted. Using the initial reaction rate method, the kinetic parameters of the reaction between sulfuric acid and HI, such as the apparent reaction orders and rate constant were determined. For I−, the apparent reaction order was approximately 1.77, whereas the orders for H+ and SO42− were 7.78 and 1.29, respectively. The apparent rate constant at 85 ± 1°C was approximately 2.949 × 10−11 min−1 (mol/L)−9.84. The H+ concentration had more significant influence on the reaction rate than those of SO42− and I−. Such basic data provide useful information for related process design and further kinetics study.

Efficiency of the sulfur–iodine thermochemical water splitting process for hydrogen production based on ADS (accelerator driven system)

The current hydrogen production is based on fossil fuels; they have a huge contribution to the atmosphere's pollution. Thermochemical water splitting cycles don't present this issue because the required process heat is obtained from nuclear energy and therefore, the environmental impact is smaller than using conventional fuels. Although, solar hydrogen production could be also used for practical applications because it's lower environmental impact. One of the promising approaches to produce large quantities of hydrogen in an efficient way using nuclear energy is the sulfur–iodine (S–I) thermochemical water splitting cycle. The nuclear source proposed in this paper is a pebble bed gas cooled transmutation facility. Pebble bed very high temperature advanced systems have great perspectives to assume the future nuclear energy. Softwares based on CPS (chemical process simulation) can be used to simulate the thermochemical water splitting sulfur-iodine cycle for hydrogen production. In this paper, a model for analyzing the sulfur-iodine process sensibility respect to the thermodynamics parameters: temperature, pressure and mass flow is developed. Efficiency is also calculated and the influence of different parameters on this value. The behavior of the proposed model for different values of initial reactant's flow, is analyzed.

Experimental study on the purification of HIx phase in the iodine–sulfur thermochemical hydrogen production process

Purification of hydriodic phase (HIx) plays an important role in avoiding the undesirable side reactions between HI and H2SO4 in the sulfur–iodine thermochemical cycle. In this paper, a series of experiments on HIx phase purification were conducted by means of a stirred reactor using N2 as stripping gas. The effects of the iodine concentration, reaction temperature, and the striping gas flow rate on HIx phase purification were investigated systematically in terms of the conversion of H2SO4 and the reaction types during purification. It was observed that the iodine concentration played a significant role in dictating the reactions during purification. The quantitative analysis of the compositions of the initial and purified HIx phases showed that not only the conversion of H2SO4 was enhanced but also the side reactions were effectively impeded by increasing the iodine concentration, temperature and the stripping gas flow rate. Based on the experimental data, the suitable operating conditions for HIx phase purification were proposed.

HIx용액을 이용한 분젠 반응에서 상 분리 조성에 미치는 SO2-O2혼합물 기체의 영향

The Sulfur-Iodine (SI) thermochemical hydrogen production process is one of the most promising thermochemical water splitting technologies. In the integrated operation of the SI process, the produced from a decomposition section could be supplied directly to the Bunsen reaction section without preliminary separation. A () solution could be also provided as the reactants in a Bunsen reaction section, since the sole separation of in a solution recycled from a HI decomposition section was very difficult. Therefore, the Bunsen reaction using mixture gases in the presence of the solution was carried out to identify the effect of . The amount of unreacted under the feed of mixture gases was little higher than that under the feed of gas only, and the amount of HI produced was relatively decreased. The in mixture gases also played a role to decrease the amount of a impurity in phase by only striping effect, while that in phase was hardly affected.

Phase Separation Characteristics of Pressurized Bunsen Reaction for Sulfur-Iodine Thermochemical Hydrogen Production Process

The Sulfur-Iodine (SI) thermochemical hydrogen production process is promising method for the massive production of hydrogen using the high temperature thermal energy of VHTR. For continuous operation of SI process, the conditions of Bunsen reaction are considered as the pressurized conditions with ca. 373~393K temperature and the composition of Bunsen products should be kept constant during the reaction. Therefore, we carried out the continuous Bunsen reaction using a counter-current flow reactor at pressurized condition to investigate the phase separation characteristics of pressurized Bunsen reaction. As the results, the composition of Bunsen product was maintained constantly as the evidence for the steady-state operation. The continuous reaction was operated without occurrence of side reactions, and a H2SO4 phase and HIx phase as the product contains a small amount of impurities (HI in a H2SO4 phase and H2SO4 in a HIx phase). We concluded that the pressurized Bunsen reaction is favorable to the continuous operation of SI process than the atmospheric reaction.

The Effect of Oxygen on Bunsen Reaction with HI&lt;sub&gt;X&lt;/sub&gt; Solution in Sulfur-Iodine Hydrogen Production Process

The Sulfur-Iodine thermochemical hydrogen production process (SI process) has been focused as one of the most promising method for hydrogen production by water splitting. SI process consists of three sections as follow; (1) Bunsen reaction, (2) H2SO4 decomposition and (3) HI decomposition. The O2 produced in a H2SO4 decomposition section could be supplied directly to the Bunsen reaction section without additional separation. Meanwhile, the reactant solution supplied to a Bunsen reaction section could be supplied as the type of a HIx (I2 + HI + H2O) solution, since only the separation of I2 in a HIx solution recycled from a HI decomposition section is very difficult. Therefore, we carried out the reaction using SO2 and SO2-O2 mixture gases in presence of the HIx solution to identify the effect of O2 in the Bunsen reaction. From the results, the amount of I2 unreacted under the feed of SO2-O2 mixture gases was very small higher than those under the feed of SO2 gas only, while the amount of HI produced was relatively decreased. In addition, the amount of impurities in each phase produced from the Bunsen reaction with the HIx solution was hardly affected by the O2/SO2 molar ratios.

THERMODYNAMIC CONSIDERATIONS ON THE PURIFICATION OF H2SO4 AND HIX PHASES IN THE IODINE-SULFUR HYDROGEN PRODUCTION PROCESS

The reaction equilibrium and phase equilibrium in H2SO4 and HIx phases produced by the Bunsen reaction of the iodine-sulfur thermochemical hydrogen production process were examined using a chemical process simulator, ESP, with a thermodynamic database based on the mixed solvent electrolyte model. At temperatures lower than ca. 110°C, the reaction of HI and H2SO4 produced elemental sulfur in both phases. At higher temperatures, the reverse Bunsen reaction occurred, and SO2 was produced in the H2SO4 phase. In the HIx phase, conversely, SO2 formation predominated in a narrow temperature range and H2S was produced with the increase in temperature. The presence of N2 gas lowered the temperature of the predominant reaction change. A feed of O2 for purification was proposed to suppress the consumption of objective components in the H2SO4 phase purification, and an O2 feed to the HIx phase for the suppression of H2S and S impurities was proposed by the simulation.

R&D Status on Thermochemical IS Process for Hydrogen Production at JAEA

Thermochemical hydrogen production process is one of the candidates of industrial fossil fuel free hydrogen production. Japan Atomic Energy Agency (JAEA) has been conducting R&D of the thermochemical water splitting iodine-sulfur (IS) process since the end of 1980s. This paper presents the recent study on the IS process in JAEA. In 2005-2009, test-fabrication of components, collection of design database, improvement of process components for higher thermal efficiency, and proposition of composition measurement method were carried out. On the basis of them, the integrity test of process components is carried out in 2010-2014 to examine their integrities in severe process environments. At present, a Bunsen reactor, which produces acids, and incidental equipments has been already manufactured using corrosion resistant materials such as glass lining steel and fluoroplastic lining steel. Flow tests to examine the functionality and integrity of the materials are planned in 2012.

CO2 Mitigation in Thermo-Chemical Hydrogen Processes: Thermo-Environomic Comparison and Optimization

A systematic comparison and optimization of thermo-chemical hydrogen production processes with CO2 capture is performed. The process options include the resource type, the syngas production method and the hydrogen purification technology, including CO2 separation by ab- or adsorption or membrane processes. With regard to climate change mitigation, the removed CO2 can be compressed for storage. To analyze the competitiveness of different CO2 capture options and H2 process alternatives a consistent multi-objective optimization methodology combining energy-flow models with process integration techniques and economic and environmental evaluation is applied. The potential of efficient decarbonization in fossil and renewable H2 processes is highlighted.