- Email: [email protected]
R&D status in thermochemical water-splitting hydrogen production iodine-sulfur process at JAEA
Available online at www.sciencedirect.com
ScienceDirect Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Procedia 00 (2017) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia
Energy (2017) 000–000 113–118 EnergyProcedia Procedia131 00 (2017) www.elsevier.com/locate/procedia
5th International Symposium on Innovative Nuclear Energy Systems, INES-5, 31 October – 2 November, 2016, Ookayama Campus, Tokyo Institute of Technology, JAPAN
R&D statusThe in15th thermochemical water-splitting hydrogen production International Symposium on District Heating and Cooling iodine-sulfur process at JAEA Assessing the feasibility of using the heat demand-outdoor a a a Hiroki Noguchia,function Hiroaki Takegami , Seiji Kasahara , Nobuyuki Tanaka , Yuforecast Kamijia, temperature fora a long-term district heat demand a a, a,b,c
I. Andrić a
Jin Iwatsuki , Hideki Aita and Shinji Kubo * a a b c c *,HTGR A. Pina , P. , J. Fournier B. Lacarrière Hydrogen andFerrão Heat Application Center, Japan.,Atomic Energy Agency , O. Le Corre a
4002 Narita cho, Oarai machi, Higashiibaraki gun, Ibaraki 311-1393, Japan IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France
Abstract
The IS process is the most deeply investigated thermochemical water-splitting hydrogen production cycle. It is in a process engineering Abstract stage in JAEA to use industrial materials for components. Important engineering tasks are verification of integrity of the total process and stability of hydrogen production in harsh environment. A test facility using corrosion-resistant materials was constructed. The hydrogen production ability was 100 Operationastests section were conducted to confirm basic District heating networks are commonly addressed in L/h. the literature one of of each the most effective solutions for decreasing the functions of reactors and separators, etc. Then, a trial operation for integration of the sections was successfully conducted to produce greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat hydrogen of about L/h for 8climate hours. conditions and building renovation policies, heat demand in the future could decrease, sales. Due to the10changed ©prolonging 2017 The Authors. Published byperiod. Elsevier Ltd. the investment return © 2017 The Authors. Published by Elsevier Ltd. committee of the 5th International Symposium on Innovative Nuclear Energy Peer-review under responsibility of the organizing The main scope this paper is of to the assess the feasibility of using the5th heat demand – outdoor temperature function for heat demand Peer-review underofresponsibility organizing committee of the International Symposium on Innovative Nuclear Energy Systems. forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 Systems. buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district Keywords: High temperature gas-cooled reactor; Hydrogen production; Water-splitting; Thermochemical Iodine-sulfur process renovation scenarios were developed (shallow, intermediate, deep). To estimate the error,process; obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications 1.(the Introduction error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). Current in widespread around the world depend heavily fossil Thisthat hascorresponds caused an issue The value energy of slopesystems coefficient increased onuse average within the range of 3.8% up on to 8% perfuels. decade, to the in athe number heating hours of 22-139h during heatingdistributed season (depending combination weather and ofdecrease securing supply of of fossil fuels, which are finite and the unevenly around on thethe Earth. This hasofled to price renovation scenarios considered). other hand, functionhydrogen intercept increased forbeen 7.8-12.7% per attention decade (depending on the fluctuations and unstable supply. On To the solve these problems, energy has attracting as a candidate coupled The values could be used to To modify thea function parameters for supply the scenarios source ofscenarios). energy system that issuggested sustainable in resources. create society whose energy comesconsidered, and improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and * Corresponding author. Tel.:+81-29-267-1919 (Extension 3791); fax:+81-29-266-7486. Cooling. E-mail address: [email protected]
Keywords: Heat demand; Forecast; Climate change 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the organizing committee of the 5th International Symposium on Innovative Nuclear Energy Systems.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the organizing committee of the 5th International Symposium on Innovative Nuclear Energy Systems. 10.1016/j.egypro.2017.09.459
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Fig. 1. Concept of the IS process.
from hydrogen, it is essential to have primary energy and resources. Technologies are also necessary that are environmentally friendly and economical and that are suitable for producing hydrogen in considerable volumes. To meet all these requirements, the high temperature gas-cooled reactor (HTGR) and thermochemical hydrogen production process have been attracting attention in recent years. Japan Atomic Energy Agency (JAEA) has been working toward the development of a means for combining these technologies for producing hydrogen from water using nuclear energy. 2. Thermochemical water-splitting iodine-sulfur process The HTGR is a type of nuclear reactor that is under research and development. It has a graphite core internal structure and graphite moderators, and helium gas as the coolant. This type of reactor supplies heat at high temperatures close to 950°C. The HTGR is capable of supplying high-temperature thermal energy externally in the form of heated helium gas. Thermochemical hydrogen production is a method of water-splitting to produce hydrogen through a few chemical reactions. Over 100 thermochemical hydrogen production processes using various compounds have been proposed. Iodine-sulfur (IS) process is considered the most promising one and this process has been most deeply investigated. One of the expected heat source of the IS process is the high-temperature thermal energy of 950°C obtained from the HTGR. The IS process has a potential for large-volume production of hydrogen at high levels of efficiency. Fig. 1 is an outline of the IS process, in which iodine and sulfur compounds are used as processing materials. This chemical process is composed of the following chemical reactions: SO 2 (g) + I 2 (aq) + 2H 2 O (aq) → 2HI (aq) + H 2 SO 4 (aq) , 2HI (g) → H 2 (g) + I 2 (g), H 2 SO 4 (g) → H 2 O (g) + SO 2 (g) + 0.5O 2 (g).
…………… Bunsen reaction …………… Hydrogen iodide (HI) decomposition …………… Sulfuric acid (H 2 SO 4 ) decomposition
Water is decomposed in the process by combining the above three chemical reactions. In the Bunsen reaction, sulfuric acid solution and hydroiodic acid solution (aqueous solution of HI) are formed from water (H 2 O), sulfur dioxide (SO 2 ), and iodine (I 2 ). The reaction takes place at around 100°C. In the HI decomposition, gaseous HI is thermally decomposed at temperatures up to 400°C to generate hydrogen (H 2 ) and I 2 using heat supply. In the H 2 SO 4 decomposition, gaseous H 2 SO 4 is thermally decomposed to generate oxygen (O 2 ) and SO 2 at temperatures up to
Hiroki Noguchi et al. / Energy Procedia 131 (2017) 113–118 Noguchi et al. / Energy Procedia 00 (2017) 000–000
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900°C with absorption of heat. As can be seen, substances other than H 2 O, O 2 , and H 2 , which are source and products
of the IS process, are circulated and held within the process. Such closed loop of the cycle of compounds is Fig. 2. R&D of the IS process in JAEA.
a feature of the IS process. The IS process and the HTGR are regarded as the most favored options for the production of hydrogen through the water-splitting using nuclear energy. The reasons are as follows: the temperature range of helium gas (300°C to 900°C) obtained from the HTGR coincides with the temperature range where H 2 SO 4 decomposition reaction, a large-scale endothermic reaction, proceeds; the method is believed to offer advantages in large-scale operation, as it contains no solid chemicals and, the numbers of elements and reactions concerning the process are small, and the equipment and materials are feasible as the temperature stays below 1,000°C. 3. R&D status of the IS process in JAEA 3.1. R&D procedure JAEA has conducted R&D on the IS process, in particular, on long-term stable hydrogen production, high thermal efficiency for hydrogen production, stable operation of components in corrosive environments, and safety in integration of the IS process and the HTGR. Fig. 2 illustrates the R&D procedure and plan in JAEA. First, reaction condition of the Bunsen reaction was determined by uncovering factors to prevent the reactions such as by-products. A lab-scale test of the process to produce hydrogen at the rate of 1 L/h for 24 hours was carried out in 1997 using the reaction conditions to confirm the theory of the IS process [1]. Second, measurement and control methods were developed to keep stable operation. A demonstration of a continuous operation of a bench-scale glass-made IS process facility at the rate of 30 L/h for one week was succeeded [2]. Electro-electro dialysis, a method of electrochemical HI concentration in the HIx solution (mixture of HI-I 2 -H 2 O) from the Bunsen reaction section was proposed to reduce heat demand to separate HI from the HIx solution. Technical feasibility of the method was experimentally confirmed [3]. In addition, structure-materials for the process components were selected by corrosion tests in IS process environment. At present, the R&D is at the stage of industrial material components test. In the stage, membrane technologies for improvement of thermal efficiency [4] and a strength evaluation method of ceramic reactors [5] are
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under development. Corrosion-resistant components made of industrial material of 100 L/h hydrogen production scale are developed. A test facility integrating the techniques obtained from the components is constructed and demonstrated. The development of the components and construction of the facility are detailed in the following sections. In future, a HTTR-GT/H 2 test, construction of a helium gas turbine (GT) and hydrogen production and integration of them with a high temperature test reactor (HTTR), a test reactor of HTGR settled in JAEA, is planned to successfully license and operate the world’s first HTGR gas turbine power generation and hydrogen production plant and to establish safety design criteria for coupling chemical plant such as hydrogen production plant to nuclear reactor. 3.2. Development of reactors and a separator Corrosion environment in the IS process is very harsh; HI and H 2 SO 4 used in the process are highly corrosive, temperature range is very wide from room temperature to 900oC, both liquid and vapor phases exist in the process. For industrialization of the IS process, test operation of process components made of practical structural materials is necessary to verify corrosion resistance. A hydrogen production facility using practical structural materials was constructed in 2013 applying reactors and a separator developed in JAEA [4]. The developed reactors and a separator are explained in the following paragraphs. The left part of Fig. 3 shows the reactors and separator. The H 2 SO 4 decomposer operates on H 2 SO 4 liquid or vapor at up to 900oC. Silicon carbide (SiC) is used as a main material because application of metal materials for this high temperature and corrosive environment is difficult. The structure is simple. Bayonet type [6] reactor made of SiC tubes fixed on a glass-lined pipe is applied to integrate H 2 SO 4 vaporization and decomposition in one reactor. This type has advantages that risk of leak decreases due to no sealing in high temperature part and that heat recovery is possible from high temperature H 2 SO 4 decomposition product to low temperature H 2 SO 4 solution through the SiC tube. In the Bunsen reactor, HI and H 2 SO 4 are produced at around 100oC. Fluoroplastic lined steel is adapted because upper limit of applicable temperature of this material is higher than the temperature of the reactor and construction of its complicated structure can be made by this material. Solution in the storage tank is circulated in an external circuit consisting of a pump, a tubular reactor with a static mixer, a cooler; functions of the reactor, mixture of reactants, Bunsen reaction, heat removal, and separation of products, are separated to each component. The HI decomposer decomposes HI to produce H 2 at around 400oC. Nickel based alloy is used for the reactor considering its thermal and corrosion resistance. A radial flow type fixed bed reactor is used aiming stable reaction rate by prevention of ununiform flow. The over-azeotropic solution is distilled and HI vapor is obtained from the top, while HI-H 2 O mixture is distilled from the HIx solution just obtained in the Bunsen reactor. Thus, HI in the HIx solution made in Bunsen reaction is concentrated by electro-electrodialysis (EED) to over-azeotropy. The EED cell consists of two electrodes and a cation exchange membrane between them. HI in the HIx solution is concentrated by RedOx reaction of I 2 on the surface of the electrodes. An actual EED cell stack is constructed by stacking several collector plates, electrodes, and membranes in order to process much amount of the solution. Impervious graphite is used for the electrodes considering its conductivity and corrosion resistance [7]. 3.3. Continuous hydrogen production test A test facility of hydrogen production was constructed applying the technology developed in construction and test of components explained in sub-section 3.2. Right side of Fig. 3 shows the schematic of the test facility. Water from outside reacted with I 2 and SO 2 to produce HIx solution and H 2 SO 4 solution in the Bunsen reaction section. In the H 2 SO 4 decomposition section, the H 2 SO 4 solution from the Bunsen reaction section is concentrated. The concentrated H 2 SO 4 is vaporized and decomposed into H 2 O, SO 2 and O 2 . In the HI decomposition section, HI in the HIx solution is concentrated to over-azeotropy in EED stacks. The over-azeotropic solution is distilled and HI vapor is obtained from the top. The HI is decomposed into H 2 and I 2 in the HI decomposer. In the total process, H 2 O from outside is decomposed into H 2 and O 2 . Appropriate practical structure materials were selected for all the components considering operation condition and
Hiroki Noguchi et al. / Energy Procedia 131 (2017) 113–118 Noguchi et al. / Energy Procedia 00 (2017) 000–000
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environment. Fluoroplastic lined steel, glass lined steel, SiC ceramic, and impervious graphite were applied for liquid
environment. Hastelloy C276, a nickel based alloy, and SUS 316, a stainless steel, were used for vapor environment. Fig.3. Components of practical structure material (left) and hydrogen production test facility (right).
All the process components were set in a steel frame covered with plastic panels to prevent accident by leak of liquid and vapor. The components were laid out to enable operation of a single section or a single reactor/separator. This facility was designed to produce hydrogen at the rate of 100 L/h. Electric heaters were used to supply heat instead of high temperature helium from a HTGR because heat requirement of the facility was much smaller than heat from the HTGR. First, basic function of heaters, pumps, stirrers in vessels, chillers, thermostatic bathes, and instrumentation devices was confirmed. Second, sealing test, gas flow test, and heating/cooling test were carried out to verify the basic function of the system. After the function check, individual test operation of each section was demonstrated and performance of reactors and separators was confirmed. Then a trial hydrogen production operation coupling all the three sections was succeeded in February 2016. Hydrogen production rate was 10 L/h and the operation continued for 8 hours. In that operation, it was clarified that prevention of solid precipitation made from I 2 and HI in the solution was important for stable operation for long term. We consider that the trial operation is an important step toward a long-term operation to confirm process control, stable operation, and corrosion resistance of the hydrogen production system. Maintenance and improvement of the facility to enable the long-term operation is under way by development of a new shaft sealing system in pumps to prevent malfunction caused by I 2 precipitation and by clarification of phase state data of the EED stack outlet stream in electric current control operation. A preliminary operation to test the function of the improved components was carried out and data from the test is now analyzed.
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4. Conclusions JAEA has conducted R&D on the thermochemical water-splitting IS process for hydrogen production from water. At present, the R&D is in a process engineering stage to verify integrity and stability of components made of industrial materials. A test facility of 100 L/h hydrogen production scale has been constructed by practical structural materials and test operations were carried out. Corrosion and thermal resistant reactors and EED stack were developed; techniques obtained by these reactors and concentrator were integrated in the test facility. Through individual test operation of each section (Bunsen reaction section, H 2 SO 4 decomposition section, and HI decomposition section), continuous hydrogen production of 10 L/h for 8 hours was succeeded by a trial operation of the total process coupling all the three sections. At present, maintenance and improvement of the process for a long-term operation is under way. A preliminary operation to confirm the improvement was just conducted. In future, these tests are planned; confirmation of a start-up and shut-down procedure considering coupling with the High Temperature Test Reactor, a test HTGR in JAEA; a long term stability of hydrogen production. After completion of all the test operations, the facility will be dismantled and investigated. The entire R&D in this process engineering stage is scheduled to be completed in the next about 3 years. References [1] Nakajima H, Ikenoya K, Onuki K, Shimizu S. Closed-cycle continuous hydrogen production test by thermochemical IS process. Kagaku Kogaku Ronbunshu 1998;24:352-5. [2] Kubo S, Nakajima H, Kasahara S, Higashi S, Masaki T, Abe H, Onuki K. A demonstration study on a closed-cycle hydrogen production by the thermochemical water-splitting iodine-sulfur process. Nucl Eng Des 2004;233:347-54. [3] Onuki K, Hwang GJ, Arifal, Shimizu S. Electro-electrodialysis of hydriodic acid in the presence of iodine at elevated temperature. J Membr Sci 2001;192:193-9. [4] Kubo S, Iwatsuki J, Takegami H, Kasahara S, Tanaka N, Noguchi H, Kamiji Y, Onuki K. Research and development on chemical reactors made of industrial structural materials and hydriodic acid concentration technique for thermochemical hydrogen production IS process. JAEATechnology 2015-028. [5] Takegami H, Terada A, Inagaki Y. Development of strength evaluation method for high-pressure ceramic components. Nucl Eng Des 2014;271:253-6. [6] Moore RC, Vernon ME, Parma EJ, Pickard PS, Rochau GE. Sulfuric acid decomposition for the sulfur-based thermochemical cycles. Nucl Technol 2012;178:111-8. [7] Tanaka N, Takegami H, Noguchi H, Kamiji Y, Iwatsuki J, Aita H, Kasahara S, Kubo S. IS process hydrogen production test for components and system made of industrial structural material (I) – Bunsen and HI concentration section –. 2016 Int. Topical Meeting on High Temperature Reactor Technology (HTR2016), HTR2016-18628, 1022-8, November 6-10, 2016, Las Vegas, NV, U.S.
ScienceDirect Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Procedia 00 (2017) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia
Energy (2017) 000–000 113–118 EnergyProcedia Procedia131 00 (2017) www.elsevier.com/locate/procedia
5th International Symposium on Innovative Nuclear Energy Systems, INES-5, 31 October – 2 November, 2016, Ookayama Campus, Tokyo Institute of Technology, JAPAN
R&D statusThe in15th thermochemical water-splitting hydrogen production International Symposium on District Heating and Cooling iodine-sulfur process at JAEA Assessing the feasibility of using the heat demand-outdoor a a a Hiroki Noguchia,function Hiroaki Takegami , Seiji Kasahara , Nobuyuki Tanaka , Yuforecast Kamijia, temperature fora a long-term district heat demand a a, a,b,c
I. Andrić a
Jin Iwatsuki , Hideki Aita and Shinji Kubo * a a b c c *,HTGR A. Pina , P. , J. Fournier B. Lacarrière Hydrogen andFerrão Heat Application Center, Japan.,Atomic Energy Agency , O. Le Corre a
4002 Narita cho, Oarai machi, Higashiibaraki gun, Ibaraki 311-1393, Japan IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France
Abstract
The IS process is the most deeply investigated thermochemical water-splitting hydrogen production cycle. It is in a process engineering Abstract stage in JAEA to use industrial materials for components. Important engineering tasks are verification of integrity of the total process and stability of hydrogen production in harsh environment. A test facility using corrosion-resistant materials was constructed. The hydrogen production ability was 100 Operationastests section were conducted to confirm basic District heating networks are commonly addressed in L/h. the literature one of of each the most effective solutions for decreasing the functions of reactors and separators, etc. Then, a trial operation for integration of the sections was successfully conducted to produce greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat hydrogen of about L/h for 8climate hours. conditions and building renovation policies, heat demand in the future could decrease, sales. Due to the10changed ©prolonging 2017 The Authors. Published byperiod. Elsevier Ltd. the investment return © 2017 The Authors. Published by Elsevier Ltd. committee of the 5th International Symposium on Innovative Nuclear Energy Peer-review under responsibility of the organizing The main scope this paper is of to the assess the feasibility of using the5th heat demand – outdoor temperature function for heat demand Peer-review underofresponsibility organizing committee of the International Symposium on Innovative Nuclear Energy Systems. forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 Systems. buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district Keywords: High temperature gas-cooled reactor; Hydrogen production; Water-splitting; Thermochemical Iodine-sulfur process renovation scenarios were developed (shallow, intermediate, deep). To estimate the error,process; obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications 1.(the Introduction error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). Current in widespread around the world depend heavily fossil Thisthat hascorresponds caused an issue The value energy of slopesystems coefficient increased onuse average within the range of 3.8% up on to 8% perfuels. decade, to the in athe number heating hours of 22-139h during heatingdistributed season (depending combination weather and ofdecrease securing supply of of fossil fuels, which are finite and the unevenly around on thethe Earth. This hasofled to price renovation scenarios considered). other hand, functionhydrogen intercept increased forbeen 7.8-12.7% per attention decade (depending on the fluctuations and unstable supply. On To the solve these problems, energy has attracting as a candidate coupled The values could be used to To modify thea function parameters for supply the scenarios source ofscenarios). energy system that issuggested sustainable in resources. create society whose energy comesconsidered, and improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and * Corresponding author. Tel.:+81-29-267-1919 (Extension 3791); fax:+81-29-266-7486. Cooling. E-mail address: [email protected]
Keywords: Heat demand; Forecast; Climate change 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the organizing committee of the 5th International Symposium on Innovative Nuclear Energy Systems.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the organizing committee of the 5th International Symposium on Innovative Nuclear Energy Systems. 10.1016/j.egypro.2017.09.459
114 2
Hiroki Noguchi et al. / Energy Procedia 131 (2017) 113–118 Noguchi et al. / Energy Procedia 00 (2017) 000–000
Fig. 1. Concept of the IS process.
from hydrogen, it is essential to have primary energy and resources. Technologies are also necessary that are environmentally friendly and economical and that are suitable for producing hydrogen in considerable volumes. To meet all these requirements, the high temperature gas-cooled reactor (HTGR) and thermochemical hydrogen production process have been attracting attention in recent years. Japan Atomic Energy Agency (JAEA) has been working toward the development of a means for combining these technologies for producing hydrogen from water using nuclear energy. 2. Thermochemical water-splitting iodine-sulfur process The HTGR is a type of nuclear reactor that is under research and development. It has a graphite core internal structure and graphite moderators, and helium gas as the coolant. This type of reactor supplies heat at high temperatures close to 950°C. The HTGR is capable of supplying high-temperature thermal energy externally in the form of heated helium gas. Thermochemical hydrogen production is a method of water-splitting to produce hydrogen through a few chemical reactions. Over 100 thermochemical hydrogen production processes using various compounds have been proposed. Iodine-sulfur (IS) process is considered the most promising one and this process has been most deeply investigated. One of the expected heat source of the IS process is the high-temperature thermal energy of 950°C obtained from the HTGR. The IS process has a potential for large-volume production of hydrogen at high levels of efficiency. Fig. 1 is an outline of the IS process, in which iodine and sulfur compounds are used as processing materials. This chemical process is composed of the following chemical reactions: SO 2 (g) + I 2 (aq) + 2H 2 O (aq) → 2HI (aq) + H 2 SO 4 (aq) , 2HI (g) → H 2 (g) + I 2 (g), H 2 SO 4 (g) → H 2 O (g) + SO 2 (g) + 0.5O 2 (g).
…………… Bunsen reaction …………… Hydrogen iodide (HI) decomposition …………… Sulfuric acid (H 2 SO 4 ) decomposition
Water is decomposed in the process by combining the above three chemical reactions. In the Bunsen reaction, sulfuric acid solution and hydroiodic acid solution (aqueous solution of HI) are formed from water (H 2 O), sulfur dioxide (SO 2 ), and iodine (I 2 ). The reaction takes place at around 100°C. In the HI decomposition, gaseous HI is thermally decomposed at temperatures up to 400°C to generate hydrogen (H 2 ) and I 2 using heat supply. In the H 2 SO 4 decomposition, gaseous H 2 SO 4 is thermally decomposed to generate oxygen (O 2 ) and SO 2 at temperatures up to
Hiroki Noguchi et al. / Energy Procedia 131 (2017) 113–118 Noguchi et al. / Energy Procedia 00 (2017) 000–000
115 3
900°C with absorption of heat. As can be seen, substances other than H 2 O, O 2 , and H 2 , which are source and products
of the IS process, are circulated and held within the process. Such closed loop of the cycle of compounds is Fig. 2. R&D of the IS process in JAEA.
a feature of the IS process. The IS process and the HTGR are regarded as the most favored options for the production of hydrogen through the water-splitting using nuclear energy. The reasons are as follows: the temperature range of helium gas (300°C to 900°C) obtained from the HTGR coincides with the temperature range where H 2 SO 4 decomposition reaction, a large-scale endothermic reaction, proceeds; the method is believed to offer advantages in large-scale operation, as it contains no solid chemicals and, the numbers of elements and reactions concerning the process are small, and the equipment and materials are feasible as the temperature stays below 1,000°C. 3. R&D status of the IS process in JAEA 3.1. R&D procedure JAEA has conducted R&D on the IS process, in particular, on long-term stable hydrogen production, high thermal efficiency for hydrogen production, stable operation of components in corrosive environments, and safety in integration of the IS process and the HTGR. Fig. 2 illustrates the R&D procedure and plan in JAEA. First, reaction condition of the Bunsen reaction was determined by uncovering factors to prevent the reactions such as by-products. A lab-scale test of the process to produce hydrogen at the rate of 1 L/h for 24 hours was carried out in 1997 using the reaction conditions to confirm the theory of the IS process [1]. Second, measurement and control methods were developed to keep stable operation. A demonstration of a continuous operation of a bench-scale glass-made IS process facility at the rate of 30 L/h for one week was succeeded [2]. Electro-electro dialysis, a method of electrochemical HI concentration in the HIx solution (mixture of HI-I 2 -H 2 O) from the Bunsen reaction section was proposed to reduce heat demand to separate HI from the HIx solution. Technical feasibility of the method was experimentally confirmed [3]. In addition, structure-materials for the process components were selected by corrosion tests in IS process environment. At present, the R&D is at the stage of industrial material components test. In the stage, membrane technologies for improvement of thermal efficiency [4] and a strength evaluation method of ceramic reactors [5] are
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under development. Corrosion-resistant components made of industrial material of 100 L/h hydrogen production scale are developed. A test facility integrating the techniques obtained from the components is constructed and demonstrated. The development of the components and construction of the facility are detailed in the following sections. In future, a HTTR-GT/H 2 test, construction of a helium gas turbine (GT) and hydrogen production and integration of them with a high temperature test reactor (HTTR), a test reactor of HTGR settled in JAEA, is planned to successfully license and operate the world’s first HTGR gas turbine power generation and hydrogen production plant and to establish safety design criteria for coupling chemical plant such as hydrogen production plant to nuclear reactor. 3.2. Development of reactors and a separator Corrosion environment in the IS process is very harsh; HI and H 2 SO 4 used in the process are highly corrosive, temperature range is very wide from room temperature to 900oC, both liquid and vapor phases exist in the process. For industrialization of the IS process, test operation of process components made of practical structural materials is necessary to verify corrosion resistance. A hydrogen production facility using practical structural materials was constructed in 2013 applying reactors and a separator developed in JAEA [4]. The developed reactors and a separator are explained in the following paragraphs. The left part of Fig. 3 shows the reactors and separator. The H 2 SO 4 decomposer operates on H 2 SO 4 liquid or vapor at up to 900oC. Silicon carbide (SiC) is used as a main material because application of metal materials for this high temperature and corrosive environment is difficult. The structure is simple. Bayonet type [6] reactor made of SiC tubes fixed on a glass-lined pipe is applied to integrate H 2 SO 4 vaporization and decomposition in one reactor. This type has advantages that risk of leak decreases due to no sealing in high temperature part and that heat recovery is possible from high temperature H 2 SO 4 decomposition product to low temperature H 2 SO 4 solution through the SiC tube. In the Bunsen reactor, HI and H 2 SO 4 are produced at around 100oC. Fluoroplastic lined steel is adapted because upper limit of applicable temperature of this material is higher than the temperature of the reactor and construction of its complicated structure can be made by this material. Solution in the storage tank is circulated in an external circuit consisting of a pump, a tubular reactor with a static mixer, a cooler; functions of the reactor, mixture of reactants, Bunsen reaction, heat removal, and separation of products, are separated to each component. The HI decomposer decomposes HI to produce H 2 at around 400oC. Nickel based alloy is used for the reactor considering its thermal and corrosion resistance. A radial flow type fixed bed reactor is used aiming stable reaction rate by prevention of ununiform flow. The over-azeotropic solution is distilled and HI vapor is obtained from the top, while HI-H 2 O mixture is distilled from the HIx solution just obtained in the Bunsen reactor. Thus, HI in the HIx solution made in Bunsen reaction is concentrated by electro-electrodialysis (EED) to over-azeotropy. The EED cell consists of two electrodes and a cation exchange membrane between them. HI in the HIx solution is concentrated by RedOx reaction of I 2 on the surface of the electrodes. An actual EED cell stack is constructed by stacking several collector plates, electrodes, and membranes in order to process much amount of the solution. Impervious graphite is used for the electrodes considering its conductivity and corrosion resistance [7]. 3.3. Continuous hydrogen production test A test facility of hydrogen production was constructed applying the technology developed in construction and test of components explained in sub-section 3.2. Right side of Fig. 3 shows the schematic of the test facility. Water from outside reacted with I 2 and SO 2 to produce HIx solution and H 2 SO 4 solution in the Bunsen reaction section. In the H 2 SO 4 decomposition section, the H 2 SO 4 solution from the Bunsen reaction section is concentrated. The concentrated H 2 SO 4 is vaporized and decomposed into H 2 O, SO 2 and O 2 . In the HI decomposition section, HI in the HIx solution is concentrated to over-azeotropy in EED stacks. The over-azeotropic solution is distilled and HI vapor is obtained from the top. The HI is decomposed into H 2 and I 2 in the HI decomposer. In the total process, H 2 O from outside is decomposed into H 2 and O 2 . Appropriate practical structure materials were selected for all the components considering operation condition and
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environment. Fluoroplastic lined steel, glass lined steel, SiC ceramic, and impervious graphite were applied for liquid
environment. Hastelloy C276, a nickel based alloy, and SUS 316, a stainless steel, were used for vapor environment. Fig.3. Components of practical structure material (left) and hydrogen production test facility (right).
All the process components were set in a steel frame covered with plastic panels to prevent accident by leak of liquid and vapor. The components were laid out to enable operation of a single section or a single reactor/separator. This facility was designed to produce hydrogen at the rate of 100 L/h. Electric heaters were used to supply heat instead of high temperature helium from a HTGR because heat requirement of the facility was much smaller than heat from the HTGR. First, basic function of heaters, pumps, stirrers in vessels, chillers, thermostatic bathes, and instrumentation devices was confirmed. Second, sealing test, gas flow test, and heating/cooling test were carried out to verify the basic function of the system. After the function check, individual test operation of each section was demonstrated and performance of reactors and separators was confirmed. Then a trial hydrogen production operation coupling all the three sections was succeeded in February 2016. Hydrogen production rate was 10 L/h and the operation continued for 8 hours. In that operation, it was clarified that prevention of solid precipitation made from I 2 and HI in the solution was important for stable operation for long term. We consider that the trial operation is an important step toward a long-term operation to confirm process control, stable operation, and corrosion resistance of the hydrogen production system. Maintenance and improvement of the facility to enable the long-term operation is under way by development of a new shaft sealing system in pumps to prevent malfunction caused by I 2 precipitation and by clarification of phase state data of the EED stack outlet stream in electric current control operation. A preliminary operation to test the function of the improved components was carried out and data from the test is now analyzed.
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4. Conclusions JAEA has conducted R&D on the thermochemical water-splitting IS process for hydrogen production from water. At present, the R&D is in a process engineering stage to verify integrity and stability of components made of industrial materials. A test facility of 100 L/h hydrogen production scale has been constructed by practical structural materials and test operations were carried out. Corrosion and thermal resistant reactors and EED stack were developed; techniques obtained by these reactors and concentrator were integrated in the test facility. Through individual test operation of each section (Bunsen reaction section, H 2 SO 4 decomposition section, and HI decomposition section), continuous hydrogen production of 10 L/h for 8 hours was succeeded by a trial operation of the total process coupling all the three sections. At present, maintenance and improvement of the process for a long-term operation is under way. A preliminary operation to confirm the improvement was just conducted. In future, these tests are planned; confirmation of a start-up and shut-down procedure considering coupling with the High Temperature Test Reactor, a test HTGR in JAEA; a long term stability of hydrogen production. After completion of all the test operations, the facility will be dismantled and investigated. The entire R&D in this process engineering stage is scheduled to be completed in the next about 3 years. References [1] Nakajima H, Ikenoya K, Onuki K, Shimizu S. Closed-cycle continuous hydrogen production test by thermochemical IS process. Kagaku Kogaku Ronbunshu 1998;24:352-5. [2] Kubo S, Nakajima H, Kasahara S, Higashi S, Masaki T, Abe H, Onuki K. A demonstration study on a closed-cycle hydrogen production by the thermochemical water-splitting iodine-sulfur process. Nucl Eng Des 2004;233:347-54. [3] Onuki K, Hwang GJ, Arifal, Shimizu S. Electro-electrodialysis of hydriodic acid in the presence of iodine at elevated temperature. J Membr Sci 2001;192:193-9. [4] Kubo S, Iwatsuki J, Takegami H, Kasahara S, Tanaka N, Noguchi H, Kamiji Y, Onuki K. Research and development on chemical reactors made of industrial structural materials and hydriodic acid concentration technique for thermochemical hydrogen production IS process. JAEATechnology 2015-028. [5] Takegami H, Terada A, Inagaki Y. Development of strength evaluation method for high-pressure ceramic components. Nucl Eng Des 2014;271:253-6. [6] Moore RC, Vernon ME, Parma EJ, Pickard PS, Rochau GE. Sulfuric acid decomposition for the sulfur-based thermochemical cycles. Nucl Technol 2012;178:111-8. [7] Tanaka N, Takegami H, Noguchi H, Kamiji Y, Iwatsuki J, Aita H, Kasahara S, Kubo S. IS process hydrogen production test for components and system made of industrial structural material (I) – Bunsen and HI concentration section –. 2016 Int. Topical Meeting on High Temperature Reactor Technology (HTR2016), HTR2016-18628, 1022-8, November 6-10, 2016, Las Vegas, NV, U.S.