• Nuclear Engineering and Technology
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• v.53 no.6
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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.

• Journal of Energy Engineering
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• v.15 no.2 s.46
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• pp.127-137
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• 2006

To resolve the environmental and economics problems of fossil fuel energy, a hydrogen economy is promoted in many developed countries. Massive production of hydrogen using a nuclear power is a practical way to feed fuel required for the hydrogen economy. The author introduces a very high temperature reactor and its development status. He also reviews recent achievements and directions of research in hydrogen production process, such as sulfur-iodine thermochemical cycle, sulfur hybrid cycle, and high temperature electrolysis.

• Korean Chemical Engineering Research
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• v.46 no.3
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• pp.633-638
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• 2008

The bunsen reaction, part of IS(Iodine-sulfur) cycle that one of the hydrogen production by the thermochemical water splitting, was investigated. It was observed that $H_2SO_4$ was uniformly generated and generation of $H_2SO_4$ was independent of iodine input. However, generation of HI was decreased with increasing iodine input. It was thought that HI and unreacted iodine were formed complex compound such as $HI_3$ $HI_5$ or $HI_7$. The complex compound accelerated liquid-liquid separation properties in the product. It was also revealed that reaction kinetics was increased with increasing iodine input. Liquid-liquid separation properties were improved with increasing iodine input and reaction temperature. Moreover, no side reaction was occurred at all reaction conditions.

• Transactions of the Korean hydrogen and new energy society
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• v.17 no.4
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• pp.395-402
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• 2006

Iodine-sulfur(IS) hydrogenation production process consists of three sections, which are so called a Bunsen reaction section, a HI decomposition section and a $H_2SO_4$ decomposition section as a closed cycle. For highly efficient operation of a Bunsen reaction section, we investigated the phase separation characteristics of $H_2SO_4-HI-H_2O-I_2$ system into two liquid phases($H_2SO_4$-rich phase and $HI_x$-rich phase) in the high temperature ranges, mainly from 353 to 393 K, and in the $H_2SO_4/HI/H_2O/I_2$ molar ratio of $1/2/14{\sim}30/0.3{\sim}13.50$. The desired results for the minimization of impurities in each phase were obtained in conditions with the higher temperature and the higher $I_2$ molar composition. On the basis of the distribution of $H_2O$ to each phase, it is appeared that the affinity between $HI_x$ and $H_2O$ was more superior to that between $H_2SO_4$ and $H_2O$.

• Korean Chemical Engineering Research
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• v.58 no.2
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• pp.235-247
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• 2020

Simulation study and validation on 50 L/hr pilot-scale Bunsen process was carried out in order to investigate thermodynamics parameters, suitable reactor type, separator configuration, and the optimal conditions of reactors and separation. Sulfur-Iodine is thermochemical process using iodine and sulfur compounds for producing hydrogen from decomposition of water as net reaction. Understanding in phase separation and reaction of Bunsen Process is crucial since Bunsen Process acts as an intermediate process among three reactions. Electrolyte Non-Random Two-Liquid model is implemented in simulation as thermodynamic model. The simulation results are validated with the thermodynamic parameters and the 50 L/hr pilot-scale experimental data. The SO₂ conversions of PFR and CSTR were compared as varying the temperature and reactor volume in order to investigate suitable type of reactor. Impurities in H₂SO₄ phase and HI_X phase were investigated for 3-phase separator (vapor-liquid-liquid) and two 2-phase separators (vapor-liquid & liquid-liquid) in order to select separation configuration with better performance. The process optimization on reactor and phase separator is carried out to find the operating conditions and feed conditions that can reach the maximum SO₂ conversion and the minimum H₂SO₄ impurities in HI_X phase. For reactor optimization, the maximum 98% SO₂ conversion was obtained with fixed iodine and water inlet flow rate when the diameter and length of PFR reactor are 0.20 m and 7.6m. Inlet water and iodine flow rate is reduced by 17% and 22% to reach the maximum 10% SO₂ conversion with fixed temperature and PFR size (diameter: 3/8", length:3 m). When temperature (121℃) and PFR size (diameter: 0.2, length:7.6 m) are applied to the feed composition optimization, inlet water and iodine flow rate is reduced by 17% and 22% to reach the maximum 10% SO₂ conversion.

• Transactions of the Korean hydrogen and new energy society
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• v.1 no.1
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• pp.40-47
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• 1989

The sulfur-iodine thermochemical water splitting process of GA(General atomic) cycle was studied to produce hydrogen from water by $H_2-I_2-SO_2$ reactions. The experimental scale was 500g based on iodine. The reaction took 100 minutes, products could be separated two liquid phases due to their density difference:HI solution had a density of 2.39~2.61g/cc, and $H_2SO_4$ solution had 1.37~1.38g/cc. The condition of reaction was when weight ratio of $I_2/H_2O$ was 2/1 resulting in good phase separation and productivity.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.6
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• pp.490-497
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• 2008

For continuous operation of the sulfur-iodine(SI) thermochemical cycle, which is expected practical method for massive hydrogen production, suggesting operation conditions at steady state is very important. Especially, in the Bunsen reaction section, the Bunsen reaction as well as side reactions is occurring simultaneously. Therefore, we studied on the relation between the variation of compositions in product solution and side reactions. The experiments for Bunsen reaction were carried out in the temperature range, from 268 to 353 K, and in the $I_2/H_2O$ molar ratio of $0.094{\sim}0.297$ under a continuous flow of $SO_2$ gas. As the result, sulfur formed predominantly with increasing temperature and decreasing $I_2/H_2O$ molar ratios. The molar ratios of $H_2O/H_2SO_4$ and $HI/H_2SO_4$ in global system were decreased as the more side reaction occurred. A side reactions did not appear at $I_2/H_2O$ molar ratios, saturated with $I_2$, irrespective of the temperature change. We concluded that it caused by the increasing stability of an $I_{2x}H^+$ complex and a steric hindrance with increasing $I_2/HI$ molar ratios.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.3
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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.

• Transactions of the Korean hydrogen and new energy society
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• v.21 no.4
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• pp.278-285
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• 2010

The Sulfur-Iodine (SI) thermochemical hydrogen production process of a closed cycle consists of three sections, which are so called the Bunsen reaction section, the $H_2SO_4$ decomposition section and the HI decomposition section. To identify the role of oxygen that can be supplied to the Bunsen reaction section via the $H_2SO_4$ decomposition section, Bunsen reactions with a $SO_2,\;SO_2-O_2$ mixture and $SO_2-N_2$ mixture as feed gases were carried out using a stirred reactor in the presence of $I_2/H_2O$ mixture. As the results, the amounts of $I_2$ unreacted under the feed of mixture gases were higher than those under the feed of $SO_2$ gas only, and the amount of HI produced was relatively decreased. The results of Bunsen reaction using $SO_2-O_2$ mixture were similar to those using $SO_2-N_2$ mixture. It may be concluded that an oxygen in $SO_2-O_2$ mixture has a role as a carrier gas like a nitrogen in $SO_2-N_2$ mixture. The effects of oxygen were decreased with increasing temperature and decreasing oxygen content in $SO_2-O_2$ mixture.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.5
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• pp.386-393
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• 2008

The Sulfur-iodine(SI) thermochemical cycle is one of the most promising methods for massive hydrogen production. For the purpose of continuous operation of SI cycle, phase separation characteristics into two liquid phases ($H_2SO_4$-rich phase and $HI_x$-rich phase) were directly investigated via Bunsen reaction. The experiments for Bunsen reaction were carried out in the temperature range, from 298 to 333 K, and in the $I_2/H_2O$ molar ratio of $0.109{\sim}0.297$ under a continuous flow of $SO_2$ gas. As the results, solubility of $SO_2$, decreased with increasing the temperature, had considerable influence on the global composition in the Bunsen reaction system. The amounts of impurity in each phase(HI and $I_2$ in $H_2SO_4$-rich phase and $H_2SO_4$ in $HI_x$-rich phase) were decreased with increasing $H_2SO_4$ molar ratio and temperature. To control the amounts of impurity in $HI_x$-rich phase, temperature is a factor more important than $I_2/H2_O$ molar ratio. On the other hand, the affinity between $HI_x$ and $H_2O$ was increased with increasing $I_2/H2_O$molar ratio.