Ki Kwang Bae

Phase Separation Characteristics of Pressurized Bunsen Reaction for Sulfur-Iodine Thermochemical Hydrogen Production Process

The Sulfur-Iodine (SI) thermochemical hydrogen production process is promising method for the massive production of hydrogen using the high temperature thermal energy of VHTR. For continuous operation of SI process, the conditions of Bunsen reaction are considered as the pressurized conditions with ca. 373~393K temperature and the composition of Bunsen products should be kept constant during the reaction. Therefore, we carried out the continuous Bunsen reaction using a counter-current flow reactor at pressurized condition to investigate the phase separation characteristics of pressurized Bunsen reaction. As the results, the composition of Bunsen product was maintained constantly as the evidence for the steady-state operation. The continuous reaction was operated without occurrence of side reactions, and a H2SO4 phase and HIx phase as the product contains a small amount of impurities (HI in a H2SO4 phase and H2SO4 in a HIx phase). We concluded that the pressurized Bunsen reaction is favorable to the continuous operation of SI process than the atmospheric reaction.

The Effect of Oxygen on Bunsen Reaction with HIX Solution in Sulfur-Iodine Hydrogen Production Process

The Sulfur-Iodine thermochemical hydrogen production process (SI process) has been focused as one of the most promising method for hydrogen production by water splitting. SI process consists of three sections as follow; (1) Bunsen reaction, (2) H2SO4 decomposition and (3) HI decomposition. The O2 produced in a H2SO4 decomposition section could be supplied directly to the Bunsen reaction section without additional separation. Meanwhile, the reactant solution supplied to a Bunsen reaction section could be supplied as the type of a HIx (I2 + HI + H2O) solution, since only the separation of I2 in a HIx solution recycled from a HI decomposition section is very difficult. Therefore, we carried out the reaction using SO2 and SO2-O2 mixture gases in presence of the HIx solution to identify the effect of O2 in the Bunsen reaction. From the results, the amount of I2 unreacted under the feed of SO2-O2 mixture gases was very small higher than those under the feed of SO2 gas only, while the amount of HI produced was relatively decreased. In addition, the amount of impurities in each phase produced from the Bunsen reaction with the HIx solution was hardly affected by the O2/SO2 molar ratios.

The Characteristics of HI Decomposition using Pt/Al2O3 Catalyst Heat Treated in Air and Hydrogen Atmosphere

Abstract >> In HI decomposition, Pt/Al 2 O 3 has been studied by several researchers. However, after HI decomposition,it could be seen that metal dispersion of Pt/Al 2 O 3 was greatly decreased. This reason was expected of platinumloss and sintering, which platinum was aggregated. Also, this decrease of metal dispersion caused catalytic deactivation.This study was conducted to find the condition to minimize platinum sintering and loss. In particular, heat treatmentatmosphere and temperature were examined to improve the activity of HI decomposition reaction. First of all,although Pt/Al 2 O 3 treated in hydrogen atmosphere had low platinum dispersion between 13 and 18%, it was shownto suitable platinum form that played an important role in improving HI decomposition reaction. Oxygen in the air atmosphere made Pt/Al 2 O 3 have high platinum dispersion even 61.52% at 500°C. Therefore, in order to get high platinum dispersion and suitable platinum form in HI decomposition reaction, air heat treatment at 500°Cwas needed to add before hydrogen heat treatment. In case of 5A3H, it had 51.13% platinum dispersion and improved HI decomposition reaction activity. Also, after HI decomposition reaction it had considerable platinumdispersion of 23.89%.

Effects of Supports and Reduction Temperature on Pt Dispersion of HI Decomposition Catalyst

Pt catalysts have been researched and used for HI decomposition. Specifically, the effects of supports and reduction temperature on metal dispersion were investigated in this paper. Metal dispersion was high measured, in the order of Pt/Al2O3, Pt/ZrO2, and Pt/SiO2. HI conversion results coincided with the metal dispersion. With effect on reduction temperature, Pt dispersion was measured as 2.9 %, 26 %, and 60 % each 1173K, 973K, and 773 K. In addition, HI conversion presented 7.8%, 16.3%, and, 19.4% respectively. Consequently, Pt dispersion, influenced by supports and reduction temperature was considered to be crucial role in HI conversion.

Hydrogen Storage and Release Properties for Compacted Ti-Mn Alloy

Received 12 January, 2017 Revised 23 February, 2017 Accepted 28 February, 2017 Abstract >> Hydrogen forms metal hydrides with some metals and alloys leading to solid-state storage under moderate temperature and pressure that gives them the safety advantage over the gas and liquid storage methods. However, it has disadvantages of slow hydrogen adsorption-desorption time and low thermal conductivity. To improve characteristics of metal hydrides, it is important that activation and thermal conductivity of metal hydrides are improved. In this study, we have been investigated hydrogen storage properties of Hydralloy C among Ti-Mn alloys. Also, the characteristics of activation and thermal conductivity of Hydralloy C were enhanced to improve kinetics of hydrogen adsorption-desorption. As physical activation method, PHEM (planetary high energy mill) was performed in Ar or H2 atmosphere. Hydralloy C was also activated by TiCl3 catalyst. To improve thermal conductivity, various types of ENG (expanded natural graphite) were used. The prepared samples were compacted at pressure of 500 bar. As a result, the activation properties of H2 PHEM treated Hydralloy C was better than the other activation methods. Also, the amounts of hydrogen storage showed up to 1.6 wt%. When flake type ENG was added to Hydralloy C, thermal conductivity and hydrogen storage properties were improved.

Effects of Solubility of SO 2 Gas on Continuous Bunsen Reaction using HI x Solution

Abstract >> The Sulfur-Iodine thermochemical hydrogen production process (SI process) consists of the Bunsenreaction section, the H 2 SO 4 decomposition section, and the HI decomposition section. The HI x solution (I 2 -HI-H 2 O)could be recycled to Bunsen reaction section from the HI decomposition section in the operation of the integratedSI process. The phase separation characteristic of the Bunsen reaction using the HI x solution was similar to that of I 2 -H 2 O-SO 2 system. On the other hands, the amount of produced H 2 SO 4 phase was small. To investigate theeffects of SO 2 solubility on Bunsen reaction, the continuous Bunsen reaction was performed at variation of the amounts of SO 2 gas. Also, it was carried out to make sure of the effects of partial pressure of SO 2 in the conditionof 3bar of SO 2 -O 2 atmosphere. As the results, the characteristic of Bunsen reaction was improved with increasingthe amounts and solubility of SO 2 gas. The concentration of Bunsen products was changed by reverse Bunsen reaction and evaporation of HI after 12 h.Key words : Hydrogen production(수소 제조), SI process(황-요오드 공정), Bunsen reaction(분젠 반응), HIx solution(HIx 용액), Continuous reaction(연속식 반응), Pressurized reaction(가압 반응)

Variation in the Volume Ratio of HIX Phase/H2SO4 Phase for Improvement of Phase Separation Efficiency in the Bunsen Reaction Section

The H2SO4 phase and HIx phase solution produced from Bunsen reaction section in SI (Sulfur-iodine) process were supplied to the phase separator for the continuous operation of SI process. However, the separation of Bunsen products in the phase separator is difficult because an excess of HIx phase solution existed in the phase separator than the H2SO4 phase solution. Therefore, the additional supply of H2SO4 to the phase separator as the phase separation method was considered for improvement of phase separation efficiency. In this work, the variations in volume ratio and composition of each phase solution were examined after the Bunsen product mixing on the HIx phase/H2SO4 phase volume ratio. As the results, the variation in composition of products increases with increase of the HIx phase/H2SO4 phase volume ratio after mixing. It was also found that the high variations in composition and volume ratio of Bunsen products by mixing in the presence of excess HIx phase. From the results, we concluded that the phase separation method, additional supply of H2SO4 phase solution to the phase separator, is effective in Bunsen product separation when the variation in composition is little.

Bunsen Reaction Using a Counter-Current Flow Reactor in Sulfur-Iodine Hydrogen Production Process: Effects of Reactor Shape and Temperature

The sulfur-iodine (SI) cycle, thermochemical water splitting using heat energy from nuclear, is one of the most promising methods for massive hydrogen production. For continuous operation of Bunsen reaction section in SI process, the reactants (SO2, I2 and H2O) were fed to the reactor and the products (a H2SO4 phase and a HIx phase) were sent to storage tanks continuously during the reaction. In this study, we investigated the phase separation characteristics of continuous Bunsen reaction on the reactor shape and temperature. It was found that the reactor shape has little affected on the composition of Bunsen products. It was also observed that the phase separation characteristics of the continuous Bunsen reaction were similar to those for the semi-batch Bunsen reaction.