• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.1
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• pp.14-21
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• 2008

Synthetic gas is defined as reformed gas from hydrocarbon-based fuel and the major chemical species of the synthetic gas are $H_2$, CO and $N_2$. Among them, hydrogen from synthetic gas is very useful species in chemical process such as combustion. It is a main reason that many studies have been performed to develop an effective reforming device. Furthermore, other technologies have been studied for synthetic gas application, such as the ESGI(Exhaust Synthetic Gas Injection) technology. ESGI injects and burns synthetic gas in the exhaust pipe so that heat from hydrogen combustion helps fast warmup of the close-coupled catalyst and reduction of harmful emissions. However, it is very hard to understand combustion characteristic of hydrogen under low oxygen environment and complicated variation in chemical species in exhaust gas. This study focuses on the characteristics of hydrogen combustion under ESGI operating conditions using a CVC(Constant Volume Chamber). Measurements of pressure variation and flame speed have been performed for various oxygen and hydrogen concentrations. Results have been analyzed to understand ignition and combustion characteristics of hydrogen under lower oxygen conditions. The CVC experiments showed that under lower oxygen concentration, amount of active chemicals in the combustion chamber was a crucial factor to influence hydrogen combustion as well as hydrogen/oxygen ratio. It is also found that increase in volume fraction of oxygen is effective for the fast and stable burning of hydrogen by virtue of increase in flame speed.

• Transactions of the Korean hydrogen and new energy society
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• v.32 no.6
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• pp.565-572
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• 2021

Hydrogen is currently produced from natural gas reforming or industrial process of by-product over than 90%. Additionally, there are green hydrogens based on renewable energy generation, but the import of green hydrogen from other countries is being considered due to the output variability depending on the weather and climate. Due to low density of hydrogen, it is difficult to storage and import hydrogen of large capacity. For improving low density issue of hydrogen, the gaseous hydrogen is liquefied and stored in cryogenic tank. Density of hydrogen increase from 0.081 kg/m³ to 71 kg/m3 when gaseous hydrogen transfer to liquid hydrogen. Density of liquid hydrogen is higher about 800 times than gaseous. However, since density and boiling point of liquid hydrogen is too lower than liquefied natural gas approximately 1/6 and 90 K, to store liquid hydrogen for long-term is very difficult too. To overcome this weakness, this paper introduces storage method of hydrogen based on liquid/solid (slush) and facilities for producing slush hydrogen to improve low density issue of hydrogen. Slush hydrogen is higher density and heat capacity than liquid hydrogen, can be expected to improve these issues.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.3
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• pp.343-350
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• 2012

A planar solid oxide fuel cell (PSOFC) is studied in its application in a high-temperature stationary power plant. Even though PSOFCs with external reformers are designed for application from the distributed power source to the central power plant, such PSOFCs may sacrifice more system efficiency than internally reformed SOFCs. In this study, modeling of the PSOFC with an external reformer was developed to analyze the feasibility of thermal energy utilization for the external reformer. The PSOFC system model includes the stack, reformer, burner, heat exchanger, blower, pump, PID controller, 3-way valve, reactor, mixer, and steam separator. The model was developed under the Matlab/Simulink environment with Thermolib$^{(R)}$ modules. The model was used to study the system performance according to its configuration. Three configurations of the SOFC system were selected for the comparison of the system performance. The system configuration considered the cathode recirculation, thermal sources for the external reformer, heat-up of operating gases, and condensate anode off-gas for the enhancement of the fuel concentration. The simulation results show that the magnitude of the electric efficiency of the PSOFC system for Case 2 is 12.13% higher than that for Case 1 (reference case), and the thermal efficiency of the PSOFC system for Case 3 is 76.12%, which is the highest of all the cases investigated.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.3
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• pp.285-293
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• 2016

The high velocity oxygen fuel(HVOF) thermal spray is a kind of surface modification techniques to produce the sprayed coating layer. This process is to form the coating layer after spraying the powder to molten or semi-molten state by the ultra-high speed at the high-temperature heat source and conflicting with a substrate. The efficiency of thermal spraying is dropped, however, because the semi-molten powder in a spray process become a factor that degrades the mechanical property by the formed pore within the coating layer. Therefore, it is necessary to melt completely the thermal spray powder in order to produce the coating layer with an optimal adhesive force. In this study, to improve the wear resistance, corrosion resistance and heat resistance, the plungers of high-speed and ultra-high pressure reciprocating hydraulic pumps used in ironworks are manufactured with STS $420J_2$ and are coated by the powders of WC-Co-Cr and WC-Cr-Ni including the WC of high hardness using a HVOF thermal sprayer developed in this laboratory. These are called by the surface-modified plungers. The surface roughness, hardness, and surface and cross-sectional microstructure of these two surface-modified and conventional ceramic plungers are measured and compared before operation with after operation for 100 days. It is found that the values of centerline average surface roughness and maximum height for conventional ceramic plunger are 9.5 to 10.8 and 5.2 to 5.7 times higher than those of surface-modified ones coated by WC-Co-Cr and WC-Cr-Ni because the fine tops and bottoms on surface roughness curve of conventional ceramic plunger are approximately 100 times higher than those of surface-modified ones. In addition, the pores and scratches in the surface microstructure are considerably formed in the order of conventional ceramic, WC-Cr-Ni and WC-Co-Cr surface-modified plungers. The greater the WC content of high hardness powder is less the change in the plunger surface.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.126-132
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• 2016

This study numerically investigates the characteristics of chemical reactions and thermal deformation in a steam reformer. These phenomena are significantly affected by the high-temperature burner gas and the process gas conditions. Because the high temperature of the burner gas ranges from 800 to 1000 K, the reformer tubes undergo substantial thermal deformation, eventually resulting in structural failure. Thus, it is necessary to understand the characteristics of the reaction and thermal deformation under the operating conditions to evaluate the reformer tubes for sustainable, stable operation. Extensive numerical simulations were carried out using commercial CFD code (ANSYS FLUENT/MECHANICA Ver. 13.0) while considering three-dimensional turbulent flows and combined heat transfer including conduction, convection, and radiation. Structural analysis considering conjugated heat transfer between solid tubes and fluid flows was conducted using the Fluid-Solid Interaction (FSI) method. The results show that when the injection temperature of the process gas and burner gas decreased, the hydrogen production rate decreased significantly, and thermal deformation decreased by at least 15 to 20%.

• Applied Chemistry for Engineering
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• v.27 no.5
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• pp.537-542
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• 2016

In this study, we have prepared mesophase pitch from pyrolysis fuel oil (PFO) by heterogeneous reforming process. This process was conducted by direct fluorination at various temperature and followed by the heat treatment at $390^{\circ}C$. The reformed pitch was then investigated by softening point analysis, elemental analysis, fourier-transform infrared spectroscopy, high resolution X-ray diffraction and polarization microscope analysis. Carbon contents of reformed pitch increased according to increasing the reaction temperature of fluorination, while oxygen, nitrogen and sulfur contents were completely eliminated. As the fluorination temperature increased, the creation, growth, coalescence and alignment process of mesophase spheres were observed. Also the interlayer spacing of carbon hexagonal planar structure decreased, while its crystalline size increased. In addition, aromatic ring compound contents increased by the condensation polymerization of aliphatic compound. These results can be attributed to the radical reactivity of the fluorine increased as the reaction temperature increased. It was considered that the fluorination reaction could help PFO to generate aromatic compounds, via promoting polymerization by radical reaction.

• Membrane Journal
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• v.32 no.4
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• pp.218-226
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• 2022

Hydrogen, a carrier of large-capacity chemical and clean energy, is an important industrial gas widely used in the petrochemical industry and fuel cells. In particular, hydrogen is mainly produced from fossil fuels through steam reforming and gasification, and carbon dioxide is generated as a by-product. Therefore, in order to obtain high-purity hydrogen, carbon dioxide should be removed. This review focused on free-standing polymeric membranes and mixed-matrix membranes (MMMs) that separate hydrogen from carbon dioxide reported in units of Barrer [1 Barrer = 10^-10 cm³ (STP) × cm / (cm² × s × cmHg)]. By analyzing various recently reported papers, the structure, morphology, interaction, and preparation method of the membranes are discussed, and the structure-property relationship is understood to help find better membrane materials in the future. Robeson's upper bound limits for hydrogen/carbon dioxide separation were presented through reviewing the performance and characteristics of various separation membranes, and various MMMs that improve separation properties using technologies such as crosslinking, blending and heat treatment were discussed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.4
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• pp.391-397
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• 2011

The use of Hydrogen as a fuel is receiving considerable attention and as a result, research on novel methods of hydrogen production is necessary so that the hydrogen demands in the future can be satisfied. This study presents experimental data on methanol Autothermal Reformation that quantifies the relationship between the oxygen-to-methanol ratio ($O_2/CH_3OH$) and reformer efficiency. For each catalyst configuration, the $O_2/CH_3OH$ was varied from 0.1 to 0.4, with an increment of 0.05, to investigate the effects of $O_2/CH_3OH$ on the reactor performance, including temperature profile, conversion, and efficiency. $O_2/CH_3OH$ was increased from 0.15 to 0.20, and the catalyst bed temperature increased by $235^{\circ}C$ to approximately $550^{\circ}C$. The catalyst bed temperature increased with increasing $O_2/CH_3OH$ as the reaction shifted from endothermic to exothermic reaction and as a result, excess heat, which raised the reactor temperature, was generated. The reactor performance was shown to be highly dependent on $O_2/CH_3OH$. The optimum $O_2/CH_3OH$ = 0.30 found in the experimental tests is 30% higher than the theoretical optimum of 0.23. This is attributed to a combination of factors such as the concentrations of the $O_2$ and $CH_3OH$ gas, reaction rate, catalyst effects, heat loss from the reactor, and the difference between the actual amounts of reaction products formed and the theoretical amounts of the reaction products.