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[en] With an objective to develop a better understanding of the origin of high voltage (>4.5 V) capacities, the electrochemical behaviors of a number of spinel lithium manganese oxides with and without other transition metal ions have been studied and compared. The oxides investigated are LiMn2-yMyO4 (M=Co, Ni, and Cu), LiMn2-y-zMyLizO4, LiMn2-yLiyO4, Li2Mn4O9-δ, and Li4Mn5O12. The LiMn2-yLiyO4 (0.05≤y≤0.12) oxides are found to exhibit capacity above 4.5 V although they do not contain other transition metal ions. In the case of Li2Mn4O9-δ and Li4Mn5O12, charging above 4.5 V is found to increase the discharge capacity below 4.5 V. While both LiMn2-yCoyO4 and LiMn2-y-zCoyLizO4 show a similar behavior at >4.5 V, LiMn2-yNiyO4 and LiMn2-y-zNiyLizO4 differ significantly. Also, while LiMn1.9Li0.1O4 and LiMn1.8Co0.2O4 show a rapid decrease in their discharge capacity above 4.5 V with rest time allowed in the fully charged state (self-discharge), LiMn2-yNiyO4 does not suffer from such a difficulty. Additionally, long-range periodicity with good crystallinity is found to be essential to observe discharge capacity above 4.5 V. The results are explained on the basis of the participation of the O2-:2p band in the redox process and the relative positions of the other transition metal ion redox energies with respect to the top of the O2-:2p band
[en] Highlights: • Design specification of H_2SO_4 and HI_x decomposers for a SI process is proposed. • Start-up behaviors of H_2SO_4 and HI_x thermal decomposers are shown. • Parametric study to satisfy the H_2 production rate of 50 NL/h is carried out. • Finding a method to build the steady closed-loop operation of the SI process. - Abstract: A 50 NL-H_2/h hydrogen production scale sulfur-iodine (SI) thermochemical process test facility to be operated under a pressurized environment has been constructed in Korea. This study focused on the catalyst-packed type HI thermal decomposer and bayonet type H_2SO_4 thermal decomposer, which are the key components for the 50 NL-H_2/h SI test facility. To sustain a closed loop operation of the SI process, the catalyst particles packed in the top of the H_2SO_4 thermal decomposer are protected from coming into contact with the inlet sulfuric acid aqueous solution, and the production molar ratio of oxygen discharged from the H_2SO_4 thermal decomposer to hydrogen discharged from the HI thermal decomposer always satisfies 0.5/1. Based on the design specifications and mass balance of the SI integrated process of 50 NL-H_2/h, numerical calculations for the two decomposers were done to evaluate their start-up and static behaviors. Based on the results of these calculations, it is predicted that the boiling interface of the sulfuric acid solution is located around 280 mm from the bottom of the electric furnace to heat the bayonet type H_2SO_4 thermal decomposer, which is far from the catalyst-packed region. It is also proposed that the proper operating temperature of the HI thermal decomposer to satisfy the hydrogen production rate of 50 NL-H_2/h and sustain the closed loop operation of the SI process is 587 °C.
[en] □ Research Objective and Contents - Pilot Scale (1-5m3/h) SI Hydrogen Production Process Start-up and Operational safety analysis - Economic Analysis for Nuclear Hydrogen System - Integration of Nuclear Hydrogen Production Interface Research □ Research Result - SI Hydrogen Production Process Start-up Dynamic and Operational Safety Analysis Pilot Scale SA/HI Thermal-Decomposer Start-up Dynamic and Operational Safety Analysis Pilot Scale SA/HI multi-stage Distillation Column Start-up Dynamic and Operational Safety Analysis Pilot Scale SI test facility Normal/Abnormal Operation Behavior Analysis - Pilot Scale (1-5m3/h) SI test facility DB establishment using KAERI-DySCo Pilot Scale SI Process and Coupling System Requirement Analysis/Test Facility Database Establishment Pilot Scale Test Facility Helium Loop Sizing and Helium Thermal Disturbance Absorbing System Concept Design Pilot Scale SI Integration Process Material and Energy Balance Countermeasures - Nuclear Hydrogen Production System Economic Analysis and Evaluation Construction Cost, Operation Cost, Nuclear Fuel DB establishment for VHTR and Hydrogen Production System Economic analysis for Nuclear Hydrogen Production System using G4-ECONS and HEEP - Nuclear Hydrogen Production Interface Research.
[en] In this paper, analyses of material and heat balances on the SI, HyS, and HTSE processes coupled to a Very High Temperature gas-cooled Reactor (VHTR) were performed. The hydrogen production efficiency including the thermal to electric energy ratio demanded from each process is found and the normalized evaluation results obtained from three processes are compared to each other. The currently technological issues to maintain the long term continuous operation of each process will be discussed at the conference site. VHTR-based nuclear hydrogen plant analysis for hydrogen production with SI, HyS, and HTSE facilities has been carried out to determine the thermal efficiency. It is evident that the thermal to electrical energy ratio demanded from each hydrogen production process is an important parameter to select the adequate process for hydrogen production. To improve the hydrogen production efficiency in the SI process coupled to the VHTR without electrical power generation, the demand of electrical energy in the SI process should be minimized by eliminating an electrodialysis step to break through the azeotrope of the HI/I_2/H_2O ternary aqueous solution
[en] KAERI has developed the dynamic code (KAERI-DySCo) to analyze the start-up behaviors of the SI process components. This study focuses on the verification of a simulation module for the sulfuric acid multi-stage distillation column in the KAERI-DySCo. In agreement with the steady state values measured experimentally by KIST, it has been finally confirmed that the SAMDC, which is one of the simulation modules in KAERI-DySCo for the dynamic simulation code of VHTR-based SI hydrogen production facilities, is a feasible simulation module for calculating the start-up dynamic behavior of a sulfuric acid multistage distillation column
[en] Hydrogen produced from water using nuclear energy will avoid both the use of fossil fuel and CO_2 emission presumed to be the dominant reason for global warming. A thermo-chemical sulfur-iodine (SI) process coupled to a Very High Temperature Gas-Cooled Reactor(VHTR) is one of the most prospective hydrogen production methods that split water using nuclear energy because the SI process is suitable for large-scale hydrogen production without CO_2 emission. The dynamic simulation code to evaluate the start-up behavior of the chemical reactors placed on the secondary helium loop of the SI process has been developed and partially verified using the steady state values obtained from the Aspen Plus"T"M Code simulation. As the start-up dynamic simulation results of the SI process coupled to the IHX, which is one of components in the VHTR system, it is expected that the integrated secondary helium loop of the SI process can be successfully and safely approach the steady state condition
[en] This study focuses on the verification of a simulation module for the hydriodic acid multi-stage distillation column(HI_xMDC) in KAERI-DySCo. To verify the HI_xMDC, a comparison of the results calculated by the HI_xMDC with experimental data obtained from the operation of the 50 NL-H_2/h scale SI test facility be KIER has been carried out in this work. The VHTR-based sulfur-iodine(SI) process used to produce hydrogen from water requires a multistage distillation column to concentrate a hydriodic acid solution that can be applied to the process, its static and dynamic simulation is essentially demanded. According to this necessity, KAERI has developed a dynamic simulation code(KAERI-DySCo) to analyze the start-up behaviors of the SI process components. On the other hand, a 50 NL-H_2/h scale SI test facility to be operated under a pressurized environment has been constructed by the scientific research partners of KIER, KIST, and POSCO. In agreement with the steady state clues measured experimentally by KIER, it has been finally confirmed that the HI_xMDC, which is one of the simulation modules in KAERI-DySCo for the dynamic simulation code of VHTR-based SI hydrogen production facilities, is a feasible simulation module able to calculate the start-up dynamic behavior of the multistage hydriodic acid distillation column
[en] Nuclear hydrogen production facilities consist of a very high temperature gas-cooled nuclear reactor (VHTR) system, intermediate heat exchanger (IHX) system, and a sulfur-iodine (SI) thermochemical process. This study focuses on the coupling system between the IHX system and SI thermochemical process. To prevent the propagation of the thermal disturbance owing to the abnormal operation of the SI process components from the IHX system to the VHTR system, a helium cooling system for the secondary helium of the IHX is required. In this paper, the helium cooling system has been studied. The temperature fluctuation of the secondary helium owing to the abnormal operation of the SI process was then calculated based on the proposed coupling system model. Finally, the preliminary conceptual design of the helium cooling system with a steam generator and forced-draft air-cooled heat exchanger to mitigate the thermal disturbance has been carried out. A conceptual flow diagram of a helium cooling system between the IHX and SI thermochemical processes in VHTR-based SI hydrogen production facilities has been proposed. A helium cooling system for the secondary helium of the IHX in this flow diagram prevents the propagation of the thermal disturbance from the IHX system to the VHTR system, owing to the abnormal operation of the SI process components. As a result of a dynamic simulation to anticipate the fluctuations of the secondary helium temperature owing to the abnormal operation of the SI process components with a hydrogen production rate of 60 mol·H2/s, it is recommended that the maximum helium cooling capacity to recover the normal operation temperature of 450 .deg. C is 31,933.4 kJ/s. To satisfy this helium cooling capacity, a U-type steam generator, which has a heat transfer area of 12 m2, and a forced-draft air-cooled condenser, which has a heat transfer area of 12,388.67 m2, are required for the secondary helium cooling system
[en] Hydrogen can be an attractive energy if it can be produced cleanly and in a cost effective manner. Nuclear energy can be used as a source of a high temperature process up to 1000 .deg. C for a hydrogen production. The sulfur-iodine (SI) cycle is a baseline candidate thermo-chemical process. It consists of the following three chemical reactions which yield a dissociation of water. The decomposition at a high temperature of the sulfuric acid is the most energy-demanding reaction both from fundamental and applied points of views which represents the key reaction of the whole SI cycle. In this paper, shell-and-tube type is selected and its fluidic characteristics are applied to an overall heat transfer coefficient calculation. As a result of the study, the sulfuric acid decomposers for 300mole/s (200MWth VHTR 40% thermal efficiency) and 60mole/s (40MWth VHTR 40% thermal efficiency) hydrogen production rates are presented and discussed
[en] The steam reforming of methane is one of hydrogen production processes that rely on cheap fossil feedstocks. An overview of the VHTR-based nuclear hydrogen production process with the modified SI cycle has been carried out to establish whether it can be adopted as a feasible technology to produce nuclear hydrogen