• Nuclear Engineering and Technology
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• 제51권1호
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• pp.214-220
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• 2019

Thermochemical cycles have been predominantly used for energy transformation from heat to stored chemical free energy in the form of hydrogen. The thermochemical cycle based on uranium (UTC), proposed by Oak Ridge National Laboratory, has been considered as a better alternative compared to other thermochemical cycles mainly due to its safety and high efficiency. UTC process includes three steps, in which only the first step is unique. Hydrogen production apparatus with hectogram reactants was designed in this study. The results showed that high yield hydrogen was obtained, which was determined by drainage method. The results also indicated that the chemical conversion rate of hydrogen production was in direct proportion to the mass of $Na_2CO_3$, while the solid product was $Na_2UO_4$, instead of $Na_2U_2O_7$. Nevertheless the thermochemical cycle used for hydrogen generation can be closed, and chemical compounds used in these processes can also be recycled. So the cycle with $Na_2UO_4$ as its first reaction product has an advantage over the proposed UTC process, attributed to the fast reaction rate and high hydrogen yield in the first reaction step.

• 융복합기술연구소 논문집
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• 제2권2호
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• pp.30-34
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• 2012

The SI thermochemical cycle process accomplishes water splitting through distinctive three chemical reactions. We focused on thermodynamic models applicable to the process. Recently, remarkable models based on the assumed ionic species have been developed to describe highly nonideal behavior on the liquid phase reactions. ElecNRTL models with ionic reactions were proposed in order to provide reliable process simulation results for phase equilibrium calculations in Section II and III. In this study, the current thermodynamic models of SI thermochemical cycle process were briefly described and the calculation results of the applied ElecNRTL models for phase equilibrium calculations were illustrated for binary systems.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2012년도 춘계학술발표대회 논문집
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• pp.113-119
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• 2012

The two-step water splitting thermochemical cycle is composed of the T-R (Thermal Reduction) and W-D (Water Decomposition) steps. The mechanism of this cycle is oxidation-reduction, which produces hydrogen. The reaction temperature necessary for this thermochemical cycle can be achieved by a dish-type solar thermal collector (Inha University, Korea). The purpose of this study is to validate a water splitting device in the field. The device is studied and fabricated by Kodama et al (2010, 2011). The validation results show that the foam device, when loaded with $CeO_2$ powder, was successfully achieved hydrogen production under field conditions. Through this experiment, we can analyze the characteristics of the catalyst and able to determine which is more advantageous thing to produce hydrogen compared with previous experiment that used ferrite-device.

• 한국수소및신에너지학회논문집
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• 제19권3호
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• pp.226-231
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• 2008

Cu/Fe/$Al_2O_3$ granules with various sizes have been prepared by a combination of sol-gel and oil drop method for the use in sulfur trioxide decomposition, a subcycle in thermochemical sulfur-iodine cycle to split water in the hydrogen and oxygen. The size of composite granules have been mainly changed by the flow-rate of the gel mixture before dropping in the synthesis. The structural properties of the samples were comparable with granule size. In the reaction, the catalytic activity was enhanced by decreasing size in the entire reaction temperature ranges.

• 에너지공학
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• 제15권2호
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• pp.107-117
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• 2006

물을 분해하여 수소를 만드는 방법으로서 열화학싸이클을 이용한 방법에 대하여 그동안의 연구 동향에 대하여 살펴보았다. 수소생산이란 관점에서 열화학싸이클이 갖는 장점은 일정한 고온의 열을 얻을 수 있다면, 반응속도의 향상과 아울러 대용량화가 가능하다는 점이다. 안정한 물을 분해하려면 물의 산화/환원이 용이한 매개체를 써서 수소 및 산소를 발생하게 하고 순환시키게 되는데, 매개체가 유독성 물질이라면 이 과정에서 누출이 되지 않도록 하여야 한다. 아직 상용화단계에는 미치지 못하였지만, 일본, 스위스, 이스라엘, 미국, 한국 등에서 집중적으로 연구되고 있는 내용은 IS 싸이클과 ZnO/Zn, $Fe_3O_4/FeO$등과 같은 금속산화물계를 이용한 싸이클들이며, 고온용 및 내부식성 소재와 시스템 분야에서 아직 해결해야할 점이 많다.

• 한국수소및신에너지학회논문집
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• 제22권2호
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• pp.139-151
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• 2011

The sulfur-iodine (SI) thermochemical water splitting cycle is one of promising hydrogen production methods from water using high-temperature heat generated from a high temperature gas-cooled nuclear reactor (HTGR). The SI cycle consists of three main units, such as Bunsen reaction, HI decomposition, and $H_2SO_4$ decomposition. The feasibility of continuous operation of a series of subunits for $H_2SO_4$ decomposition was investigated with a bench-scale facility working at ambient pressure. It showed stable and reproducible $H_2SO_4$ decomposition by steadily producing $SO_2$ and $O_2$ corresponding to a capacity of 1 mol/h $H_2$ for 24 hrs.

• 한국태양에너지학회 논문집
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• 제37권5호
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• pp.27-37
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• 2017

In this study, an artificial solar simulator composed of a 2.5 kW Xe-Arc lamp and mirror reflector was used to carry out the solar thermal two step thermochemical water decomposition cycle which can produce high efficiency continuous hydrogen production. Through various operating conditions, the change of hydrogen production due to the possibility of a dual-zone reactor and heat recovery were experimentally analyzed. Based on the reaction temperature of Thermal-Reduction step and Water-Decomposition step at $1,400^{\circ}C$ and $1,000^{\circ}C$ respectively, the hydrogen production decreased by 23.2% under the power off condition, and as a result of experiments using heat recovery technology, the hydrogen production increased by 33.8%. Therefore, when a thermochemical two-step water decomposition cycle is conducted using a dual-zone reactor with heat recovery, it is expected that the cycle can be operated twice over a certain period of time and the hydrogen production amount is increased by at least 53.5% compared to a single reactor.

• 한국태양에너지학회 논문집
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• 제33권3호
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• pp.42-50
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• 2013

Solar thermal reactor was studied for hydrogen production with a two step thermochemical cycle including T-R(Thermal Reduction) step and W-D(Water Decomposition) step. NiFe2O4 and Fe3O4 supported by monoclinic ZrO2 were used as a catalyst device and Ni powder was used for decreasing the T-R step reaction temperature. Maintaining a temperature level of about $1100^{\circ}C$ and $1400^{\circ}C$, for 2-step thermochemical reaction, is important for obtaining maximum performance of hydrogen production. The controller was designed for adjusting high temperature solar thermal energy heating the foam-device coated with nickel- ferrite powder. A Pill temperature control system was designed based on 2-step thermochemical reaction experiment data(measured concentrated solar radiation and the temperature of foam device during experiment). The cycle repeated 5 times, ferrite conversion rate are 4.49~29.97% and hydrogen production rate is 0.19~1.54mmol/g-ferrite. A temperature controller was designed for increasing the number of reaction cycles related with the amount of produced hydrogen.

• Nuclear Engineering and Technology
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• 제53권6호
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• pp.2066-2073
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• 2021

The use of nuclear reactors is a large studied possible solution for thermochemical water splitting cycles. Nevertheless, there are several problems that have to be solved. One of them is to increase the efficiency of the cycles. Hence, in this paper, a thermal energy optimization of a Sulfur-Iodine nuclear hydrogen production cycle was performed by means a heuristic method with the aim of minimizing the energy targets of the heat exchanger network at different minimum temperature differences. With this method, four different heat exchanger networks are proposed. A reduction of the energy requirements for cooling ranges between 58.9-59.8% and 52.6-53.3% heating, compared to the reference design with no heat exchanger network. With this reduction, the thermal efficiency of the cycle increased in about 10% in average compared to the reference efficiency. This improves the use of thermal energy of the cycle.

• 한국수소및신에너지학회논문집
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• 제13권3호
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• pp.204-213
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• 2002

In this work, hydrogen production by a 2-step water-spritting thermochemical cycle based on metal oxides redox pairs was investigated on the bases of the thermodynamics and technical feasibility. Also, a 2nd-law analysis performed on the closed cyclic process indicates a maximum exergy conversion efficiency of 7.1% when using a solar cavity-receiver operated at 2300K and air/Fe3O4 molar ratio = 10.