Thermochemical Cycle For Hydrogen Production Research Articles

Hydrogen production by using manganese ferrite: Evidences and benefits of a multi-step reaction mechanism

Hydrogen production by water splitting with MnFe 2 O 4 / Na 2 CO 3 system was studied at 973 K. An intermediate phase, resulting from decarbonatation of MnFe 2 O 4 / Na 2 CO 3 mixture in inert atmosphere, proved to be effective in hydrogen reduction from water with stoichiometric yield. The presence of a highly reactive intermediate phase suggests the feasibility of a high efficiency, three-step, thermochemical cycle for hydrogen production. In fact, the possibility of obtaining CO 2 separately from the gases mixture dramatically enhances process efficiency.

A pilot test plan of the thermochemical water-splitting iodine–sulfur process

Research and development (R&D) of hydrogen production systems using high-temperature gas-cooled reactors (HTGR) are being conducted by the Japan Atomic Research Institute (JAERI). To develop the systems, superior hydrogen production methods are essential. The thermochemical hydrogen production cycle, the IS (iodine–sulfur) process, is a prospective candidate, in which heat supplied by HTGR can be consumed for the thermal driving load. With this attractive feature, JAERI will conduct pilot-scale tests, aiming to establish technical bases for practical plant designs using HTGR. The hydrogen will be produced at a maximum rate of 30 m 3/h, continuously using high-temperature helium gas supplied by a helium gas loop, with an electric heater of about 400 kW. The plant will employ an advanced hydroiodic acid-processing device for efficient hydrogen production, and the usefulness of the device was confirmed from mass and heat balance analysis. Through design works and the hydrogen production tests, valuable data for construction and operation will be acquired to evaluate detailed process performance for practical systems. After completing the pilot-scale tests, JAERI will move onto the next R&D step, which will be demonstrations of the IS process to which heat is supplied from a high-temperature engineering test reactor (HTTR).

Analysis of sulfur–iodine thermochemical cycle for solar hydrogen production. Part I: decomposition of sulfuric acid

The sulfur–iodine (S–I) thermochemical water splitting cycle is one of the most studied cycles for hydrogen (H 2) production. S–I cycle consists of four sections: (I) acid production and separation and oxygen purification, (II) sulfuric acid concentration and decomposition, (III) hydroiodic acid (HI) concentration, and (IV) HI decomposition and H 2 purification. Section II of the cycle is an endothermic reaction driven by the heat input from a high temperature source. Analysis of the S–I cycle in the past thirty years have been focused mostly on the utilization of nuclear power as the high temperature heat source for the sulfuric acid decomposition step. Thermodynamic as well as kinetic considerations indicate that both the extent and rate of sulfuric acid decomposition can be improved at very high temperatures (in excess of 1000 °C) available only from solar concentrators. The beneficial effect of high temperature solar heat for decomposition of sulfuric acid in the S–I cycle is described in this paper. We used Aspen Technologies' HYSYS chemical process simulator (CPS) to develop flowsheets for sulfuric acid (H 2SO 4) decomposition that include all mass and heat balances. Based on the HYSYS analyses, two new process flowsheets were developed. These new sulfuric acid decomposition processes are simpler and more stable than previous processes and yield higher conversion efficiencies for the sulfuric acid decomposition and sulfur dioxide and oxygen formation.

高温ガス炉を利用した熱化学水素製造法ISプロセスの研究 : 連続水素製造試験(FR5 水素・燃料電池)

Thermochemical hydrogen production cycle named IS (Iodine Sulfur) process is a prospective candidate for superior hydrogen production methods so that heats supplied by High Temperature Gas-cooled Reactor (HTGR) are able to be consumed for thermal driving loads. Japan Atomic Energy Research Institute has been conducting R&D on the IS process as part of the research programs striving to utilize heat from HTGR. The R&D is currently at the laboratory stage and covers several fields including the evaluation of structural materials in corrosion environments, the improvement in thermal efficiency and the techniques for a operation in a closed-loop continuous hydrogen production. The techniques are essential for the development of such a closed-cycle chemical process. An experimental apparatus made of glass and fluorine resin for closed-loop continuous hydrogen production was operated. In the experiment, hydrogen production at the rate of 32 liters per hour for 20 hours was successfully accomplished. Feasibility of the operating stability was almost demonstrated.

Effects of Process Parameters of the IS Process on Total Thermal Efficiency to Produce Hydrogen from Water.

Thermal efficiency of the IS (sulfur-iodine) thermochemical hydrogen production cycle process was investigated. The heat and mass balance of the process were calculated with various operating conditions, and the effects of these conditions on the thermal efficiency were evaluated. The flowsheet of the H2SO4 decomposition designed by Knoche et al. (1984) was used. An electro-electrodialysis (EED) cell for the concentration of HI and a hydrogen permselective membrane reactor for decomposition of HI were applied to the process. Sensitivities of four operating conditions (the HI conversion ratio at the HI decomposition reactor, the reflux ratio at the HI distillation column, the pressure in the HI distillation column, and the concentration of HI after the EED cell) were investigated. The concentration of HI had the most significant effect on thermal efficiency. The difference of the efficiency was 13.3%. Other conditions had little effects within 2% of the efficiency. Effects of nonideality of the process (electric energy loss in the EED cell, loss at heat exchangers and loss of the waste heat recovery as electric energy) were evaluated. The difference of the efficiencies by the loss in the EED cell was 11.4%. The efficiency decreased by 5.7% by the loss at heat exchangers. The loss of the waste heat recovery lowered the efficiency by 6.3%. The result shows that the development of the EED cell, heat exchangers and electric recovery is effective in improving thermal efficiency. The operating conditions such as the HI concentration after the EED cell should be optimized to obtain the maximum thermal efficiency after the developments of the apparatuses. Change of the state of nonideality needs the optimization of the concentration. The thermal efficiency of the total process was 56.8% with ideal operating conditions of the EED cell, heat exchangers and high performance waste heat recovery.

C108 高温ガス炉を利用した熱化学法による水素製造

Research on IS process, thermochemical cycle for hydrogen production by water-splitting process, are proceeded to utilize heat from High Temperature Gas-cooled Reactor as primary heat source. So far, the continuous hydrogen production of IS process on laboratory-scale have been successfully demonstrated through stable rate (1 liter per hour) of hydrogen production for 48 hours and stoichiometric production of hydrogen and oxygen. Further studies in three fields, the evaluation of materials in corrosion environments, the modification of HI processing scheme using membrane technologies and the art to operate closed-cycle process, are conducted. Aiming to investigate operational technique on IS process, a scaled-up glass plant is under construction; the plant has ability to produce hydrogen at a rate of 50 liters per hour and higher iodine concentration to separate solutions well.

Analysis of a reaction mechanism in the UT-3 thermochemical hydrogen production cycle

The UT-3 thermochemical hydrogen production process consists of four gas-solid reactions, two Ca-compounds reactions and two Fe-compounds reactions. In this process, it is important to obtain the solid reactant with high reactivity and durability. Bromination of CaO included in the UT-3 cycle was analyzed to clarify the mechanism of this reaction, and a reaction model was proposed. Simulated results showed a good agreement with observed data.

Solar UT-3 thermochemical cycle for hydrogen production

The UT-3 thermochemical hydrogen producing cycle is a four step process developed at the University of Tokyo. In the process, only solid and gas reactants/products are used and the maximum temperature is 1033 K. The process has been developed to be coupled with gas cooled nuclear reactors (HTGR). In this article, a new UT-3 process is conceived to be coupled with a solar heat source. In the new process, all four reactions are carried out in a adiabatic equipment where steam (or steam + nitrogen) can be used as a vector. The operation of the process is done continuously. During sunshine hours, the energy to the process is supplied directly from the solar receiver. During cloudy periods and nights, it is supplied from a thermal storage system where the necessary high temperature heat is stored during sunshine hours. The solar UT-3 process has been evaluated using the ASPEN-PLUS code. It is found that the overall thermal efficiency is 49.5%, the exergetic efficiency is 52.9% and the process can be realized using conventional materials. Sizing of a solar hydrogen plant producing 2000 Nm 3 per hour hydrogen has been carried out and operation of various equipment has been discussed.

Improvement of Ca-pellet reactivity in UT-3 thermochemical hydrogen production cycle

The UT-3 thermochemical hydrogen production cycle consists of four gas-solid reactions. In these reactions, hydrolysis of CaBr 2 is the slowest reaction. Aiming at the improvement of this reaction rate, the mechanism of hydrolysis was carefully analysed, and a model for explaining the reaction progress was proposed. Then, a new Ca-pellet, which was produced by removing an obstacle out of the reaction process, was tested.

Changes in Reaction Rates and Structure of Solid Reactant Concerning the Iron Compounds in the UT-3 Thermochemical Hydrogen Production Cycle.

UT-3熱化学水素製造サイクルの鉄系反応に用いる反応固体について, 繰り返し反応による反応速度の変化を解析した.反応固体は, ZrSiO4を担体として調製した.まず, 調製直後の反応固体を用いて反応速度解析を行い, 次のように反応速度式を決定した.臭素化 : r [mol・m-3・s-1] =-dCFe3O4/dt= 1.5×10-3CHBr1.5CH2O-0.5CFe3O4加水分解 : r [mol・m-3・s-1] =-dCFeBr2/dt = 0.018 CH2OCFeBr20.5この反応固体を用いて臭素化, 加水分解反応を繰り返し行ったところ, (1) 加水分解中にFeBr2が昇華することによりペレット中の固体濃度が減少する, (2) 両反応ともに反応速度定数は20サイクル目では1サイクル目の約1.4倍に大きくなる, (3) 1サイクル目には1μm程度の細孔に存在した固体反応物が, 20サイクル後には新たに生じた10μm付近の細孔に移動したり, 反応界面の表面積が約2倍に増加するなど, 反応速度定数変化の原因となるような反応固体の構造変化が生じていることが分かった.

Reactivity improvement in the UT-3 thermochemical hydrogen production process

Abstract A modified process scheme, where all reactions are performed in a series loop flow, has been proposed for the UT-3 thermochemical hydrogen production cycle. In this scheme, appropriate gas mixtures of H2O and Br2 and HBr are introduced into each reactor. Kinetic measurements for bromination of CaO with a mixture of Br2 and steam showed that the reactivity of Ca-reactant can be maintained above 863 K. Continuous production of hydrogen was successfully achieved in the loop flow.

Kinetic study of UT-3 thermochemical hydrogen production process

Kinetic measurements have been made with thermogravimetry for UT-3 thermochemical hydrogen production cycle from water. Due to the differences of molar volume between reactant- and product-solid the structural change of pellet was found to occur in cyclic operation, leading to the influential hindrance against chemical conversion. By introducing a new pelletizing process based on alkoxide method a considerable increase in overall reaction rate was achieved.

Process simulation of “mascot” plant using the UT-3 thermochemical cycle for hydrogen production

A bench-scale plant named MASCOT for continuous hydrogen production based on the UT-3 cycle was constructed. Since then, a series of both theoretical and experimental studies aiming at industrialization of this plant have been conducted. This paper describes the modified process scheme of the plant as well as experimental results of fixed bed reactors. In addition, a two dimensional model of tubular reactor is proposed to simulate the reactor performance under the continuous operation.

Study of catalytic reduction of methanol for methane-methanol thermochemical hydrogen production cycles

Methanol was found to be reduced to methane by hydriodic acid solution containing platinum ions. The reaction was considered to proceed sequentially from methanol to methyl iodide and then to methane. Platinum ion acts as a catalyst in the methane formation. In the presence of iodine, the reaction was greatly suppressed and the reaction rate was almost independent of temperature. Methane-methanol thermochemical hydrogen production cycles utilizing the reaction are discussed.

THERMOCHEMICAL HYDROGEN PRODUCTION BY THE MAGNESIUM-SULFUR-IODINE CYCLE

Abstract A new thermochemical cycle for hydrogen production is presented. It consists of (i) redox reaction of sulfur dioxide and iodine with magnesium oxide in an aqueous solution, (ii) hydrolysis of magnesium iodide, (iii) thermal decomposition of magnesium sulfate and (iv) thermal dissociation of hydrogen iodide. Key reactions (i) and (ii) were experimentally verified.

Investigation of corrosion resistance of materials in the presence of sulphuric acid and its decomposition products applied in the thermochemical cycle of hydrogen production

The corrosion resistance of some nickel constructional steels and alloys was investigated in an atmosphere containing SO 3 + SO 2 + O 2 + H 2O, in the temperature range 600–900°C, and in boiling cone, sulphuric acid. The composition of the corrosion products is analyzed. Also the corrosion resistance of stainless nickel-chromium steel, implanted with singly charged ions, Ni +, Cr +, Al +, Pb + and He +, was investigated in boiling cone, sulphuric acid.

Reactor design for the UT-3 thermochemical hydrogen production process

The UT-3 thermochemical cycle for hydrogen production previously proposed consists of four reactions given by: (1) CaBr 2+H 2O→CaO +2HBr (2) CaO+Br 2 →CaBr 2 + 1 2 O 2 (3) Fe 3O 4+8HBr→3FeBr 2+4H 2O+Br 2 (4) 3FeBr 2+4H 2O→Fe 3O 4+6HBr+H 2 . At present, a series of both theoretical and experimental studies aiming at the industrialization of this process have been conducted. In this paper the measurements of the kinetic study for reaction (3) were first described. Based on experimental data and conceptual design of the whole process, then the simulation of the performance for the reactor using a honeycomb-shaped solid reactant was conducted. The result gives information on the reactor design.

Methods of calculating engineering parameters for gas separations

A group additivity method has been generated which makes it possible to estimate, from the structural formulas alone, the energy of vaporisation and the molar volume at 25°C of many nonpolar organic liquids. From these two parameters and appropriate thermodynamic relationships it is then possible to predict the vapour pressure of the liquid phase and the solubility of various gases in nonpolar organic liquids. The data are then used to evaluate organic and some inorganic liquids for use in gas separation stages or as heat exchange fluids in prospective thermochemical cycles for hydrogen production.

An entropy production and efficiency analysis of the Bunsen reaction in the General Atomic sulfur-iodine thermochemical hydrogen production cycle

An entropy production and efficiency analysis of the first reaction in the General Atomic sulfur-iodine thermochemical hydrogen production cycle has been carried out by simulating the reaction including the mixing of reactants and separation of the resulting phases. The reaction: ▪ was simulated at 388 K, which is slightly above the melting point of I 2. Analysis of only this reaction shows that the reaction should be run at 15–25% I 2 reacted and the greatest excess of H 2O which will produce two product phases. Actual operating conditions are however dependent on the total processing scheme. An entropy production and efficiency analysis along with economic factors for the entire process is necessary to obtain these conditions.

熱化学法による水素製造 Ｖ 臭化水素酸‐硫酸‐水系の気液平衡

Vapor-liquid equilibria for the hydrobromic acid/sulfuric acid/water system were measured in an Othmer still at low hydrobromic acid concentration, i.e., below the azeotropic composition, for use in the development of thermochemical hydrogen production cycles involving the equilibrium reaction of bromine, sulfur dioxide, and water to sulfuric acid and hydrogen bromide.