• Journal of Energy Engineering
• /
• v.16 no.4
• /
• pp.170-180
• /
• 2007

This paper deals with the economy of scale for domestic on-site hydrogen stations fueled with natural gas and naptha. We evaluate the economic feasibility of on-site hydrogen stations with hydrogen production capacities of $30Nm^3/hr,\;100Nm^3/hr\;and\;300Nm^3/hr$. We build a classical economic feasibility model and we make some sensitivity analyses by changing the values of input factors such as the hydrogen sale price and the discount rate. The estimated hydrogen prices of steam methane reforming stations with production capacities of $30\;Nm^3/hr,\;100\;Nm^3/hr\;and\;300\;Nm^3/hr$ are 18,472 won/kg, 10,689 won/kg and 7,758 won/kg, respectively. Also, the hydrogen prices are about the same if we use naptha as a raw material for hydrogen energy instead of natural gas. It turns out that small and medium size domestic on-site hydrogen stations will not be economical in the near future. This indicates that we need to construct large scale on-site hydrogen fueling stations even for the initial phase of the hydrogen economy.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.13 no.1
• /
• pp.60-67
• /
• 2010

For sustainable use of the resources of uninhabited islands of Korea, their ecological economic potential needs to be fully integrated into their management policy and the carrying capacity of the islands should be evaluated before using or developing them. The emergy methodology was used to evaluate the ecological economic value and carrying capacity of Sungap-do which is an uninhabited island in Incheon, Korea. The system boundary for the emergy evaluation of the island included the sea area within 1km from the high tide level, following the management boundary for the uninhabited islands of Korea stipulated in the Law on the Conservation and Management of Uninhabited Islands. The total renewable emergy input to Sungap-do was $1.04{\times}10^{20}$ sej/yr from tidal energy. The annual ecological economic contribution of the island was evaluated high at 29.9 billion Em￦/yr. If Sungap-do were developed to the national average, its carrying capacity was 6,586 persons at the current living standard of Korea. The carrying capacity of Sungap-do for the long-term sustainability scenario was 2,337 persons at the same living standard as in the developed scenario. When only emergy contribution of the land area was considered, the carrying capacity of Sungap-do sharply decreased to 14 persons for the developed scenario and 5 persons for the long-term sustainability scenario. The carrying capacity of the uninhabited islands of Korea including Sungap-do, thus, needs to be considered from the initial stage of utilization or development projects to sustain the ecosystem benefits and their sustainable uses.

• Economic and Environmental Geology
• /
• v.42 no.5
• /
• pp.457-469
• /
• 2009

Applicability of bioleaching techniques using a sulfur-oxidizing bacteria, Acidithiobacillus thiooxidans, for remediation of shooting range soil contaminated with toxic heavy metals was investigated. The effects of sulfur concentration, the amount of bacterial inoculum and operation temperature on the efficiency of heavy metal solubilization were examined as well. As sulfur concentration and the amount of bacterial inoculum increased, the solubilization efficiency slightly increased; however, significant decrease of heavy metal extraction was observed with no addition of sulfur or bacterial inoculum. Bacteria solubilized the higher amount of heavy metals at $26^{\circ}C$ than $4^{\circ}C$. Lead showed the highest removal amount from the contaminated soil but the lowest removal efficiency when compared with Zn, Cu and Cr. It was likely due to formation of insoluble $PbSO_{4(s)}$ as precipitate or colloidal suspension. Sequential extraction of the microbially treated soil revealed that the proportion of readily extractable phases of Zn, Cu and Cr increased by bacterial leaching, and thus additional treatment or optimization of operation conditions such as leaching time were required for safe reuse of the soil. Bioleaching appeared to be a useful strategy for remediation of shooting range soil contaminated with heavy metals, and various operating conditions including concentration of sulfur input, inoculum volume of bacteria, and operation temperature exerted significant influence on bioleaching efficiency.

• Economic and Environmental Geology
• /
• v.42 no.5
• /
• pp.427-434
• /
• 2009

Indigenous bacterium which shows a tolerance to high metal toxicity was isolated from soil concomitantly contaminated with oil and heavy metals. The characteristics of the bacterium for Pb and Cd biosorption was investigated under the various experimental conditions such as bacterial growth phase, the initial metal concentration, the input biomass amount, temperature and pH. The Langmuir adsorption isotherm modeling was described to know the capacity and intensity of biosorption. The low initial concentration of heavy metals and high biomass has a maximum heavy metal removal efficiency, but biosorption capacity of Pb and Cd has different values. Biosorption efficiency was highest in the end of the microbial growth stage and under pH 5~9 condition, but was less affected by temperature variation of 25~$35^{\circ}C$. The maximum biosorption capacity for Pb and Cd was 62.11 and 192.31 mg/g, respectively and each $R^2$ was calculated as 0.71 and 0.98 by applying Langmuir isothermal adsorption equation. Biosorption for Cd was considered as monomolecular adsorption to single layer on the surface of cells, whereas biosorption for Pb was considered as accumulation process into the cell by the microbial metabolism and precipitation reaction with anion of bacteria.

• Journal of the Korean Wood Science and Technology
• /
• v.36 no.3
• /
• pp.93-100
• /
• 2008

For investigation of adsoption properties of cadmium elimination by wood charcoal, $25m{\ell}$ aqueous cadmium solutions in various concentrations were treated with 0.2 g wood charcoal of Red Oak (Quercus mongolica) for 280 minutes. Almost 100% of cadmium elimination ratio was obtained in the solutions with initial concentration of 20 and 40 ppm in the treatment, whereas they were 75 and 50% in those of 80 and 160 ppm. In the effect of treatment time, the highest amount of cadmium ions was eliminated during the first ten minutes in each solution so that the elimination ratio of each case was over 70% of the maximum elimination value. From the analysis of adsorptive cadmium adsorption mechanism using the Langmuir adsorption isotherm, it was suggested that cadmium ion molecules were adsorbed at the active sites on the charcoal particle in form of one layer. The Gibbs free energy of the adsorption process was calculated in negative value for each solution. This means the adsorption processes are spontaneous which do not require the extra input energy.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.19 no.3
• /
• pp.180-188
• /
• 1999

The dynamic elastic properties of metal matrix composites were investigated by resonant ultrasound spectroscopy(RUS). The composites used in this study consisted of 2124 aluminum alloy reinforced with different concentrations of SiC particles. RUS can determine the nine independent elastic stiffness($C_{ij}$) for the orthorhombic symmetry on a small specimen simultaneously. The elastic constants were determined as a function of the volume fraction. A concept of effective aspect ratio. which combine the aspect ratio and the orientation of reinforcement. was used to calculate the initial moduli from Mori-Tanaka theory for the input of RUS minimization code. Young's moduli can be obtained from the measured stiffnesses. The results show that the elastic stiffness increases with increment of the particle content. The behavior of elastic stiffness indicates that the particle redistribution induced by the extrusion process enlarges the transversely isotropic symmetry as the fraction of reinforced particles increase. This relationship could be used for determination of the volume fractions of reinforcement as a potential tool of nondestructive material characterization.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2014.10a
• /
• pp.565-568
• /
• 2014

This paper presents a 0.2V DC/DC boost converter with regulated output for thermoelectric energy harvesting. To use low voltages from a thermoelectric device, a start-up circuit consisting of native NMOS transistors and resistors boosts an internal VDD, and the boosted VDD is used to operate the internal control block. When the VDD reaches a predefined value, a detector circuit makes the start-up block turn off to minimize current consumption. The final boosted VSTO is achieved by alternately operating the sub-boost converter for VDD and the main boost converter for VSTO according to the comparator outputs. When the VSTO reaches 2.4V, a buck converter starts to operate to generate a stabilized output VOUT. Simulation results shows that the designed converter generates a regulated 1.8V output from an input voltage of 0.2V, and its maximum power efficiency is 60%. The chip designed using a $0.35{\mu}m$ CMOS process occupies $1.1mm{\times}1.0mm$ including pads.

• Tunnel and Underground Space
• /
• v.31 no.4
• /
• pp.221-242
• /
• 2021

A numerical study of the performance assesment of coupled thermo-hydro-mechanical (THM) processes in improved Korean reference disposal system (KRS⁺) for high-level radioactive waste is conducted using TOUGH2-MP/FLAC3D simulator. Decay heat from high-level radioactive waste increases the temperature of the repository, and it decreases as decay heat is reduced. The maximum temperature of the repository is below a maximum temperature criterion of 100℃. Saturation of bentonite buffer adjacent to the canister is initially reduced due to pore water evaporation induced by temperature increase. Bentonite buffer is saturated 250 years after the disposal of high-level radioactive waste by inflow of groundwater from the surrounding rock mass. Initial saturation of rock mass decreases as groundwater in rock mass is moved to bentnonite buffer by suction, but rock mass is saturated after inflow of groundwater from the far-field area. Stress changes at rock mass are compared to the Mohr-Coulomb failure criterion and the spalling strength in order to investigate the potential rock failure by thermal stress and swelling pressure. Additional simulations are conducted with the reduced spacing of deposition holes. The maximum temperature of bentonite buffer exceeds 100℃ as deposition hole spacing is smaller than 5.5 m. However, temperature of about 56.1% volume of bentonite buffer is below 90℃. The methodology of numerical modeling used in this study can be applied to the performance assessment of coupled THM processes for high-level radioactive waste repositories with various input parameters and geological conditions such as site-specific stress models and geothermal gradients.

• Journal of the Society of Disaster Information
• /
• v.18 no.1
• /
• pp.10-18
• /
• 2022

Purpose: For smooth performance of flood analysis due to heavy rain disasters at energy storage facilities in the Incheon area, field surveys, observational surveys, and pre-established reports and drawings were analyzed. Through the field survey, the characteristics of pipelines and rivers that have not been identified so far were investigated, and based on this, the input data of the SWMM model selected for inundation analysis was constructed. Method: In order to determine the critical duration through the probability flood analysis according to the calculation of the probability rainfall intensity by recurrence period and duration, it is necessary to calculate the probability rainfall intensity for an arbitrary duration by frequency, so the research results of the Ministry of Land, Transport and Maritime Affairs were utilized. Result: Based on this, the probability of rainfall by frequency and duration was extracted, the critical duration was determined through flood analysis, and the rainfall amount suggested in the disaster prevention performance target was applied to enable site safety review. Conclusion: The critical duration of the base was found to be a relatively short duration of 30 minutes due to the very gentle slope of the watershed. In general, if the critical duration is less than 30 minutes, even if flooding occurs, the scale of inundation is not large.

• Membrane Journal
• /
• v.33 no.4
• /
• pp.181-190
• /
• 2023

Wastewater purification is one of the most important techniques for controlling environmental pollution and fulfilling the demand for freshwater supply. Various technologies, such as different types of distillations and reverse osmosis processes, need higher energy input. Capacitive deionization (CDI) is an alternative method in which power consumption is deficient and works on the supercapacitor principle. Research is going on to improve the electrode materials to improve the efficiency of the process. A reverse electrodialysis (RED) is the most commonly used desalination technology and osmotic power generator. Among many studies conducted to enhance the efficiency of RED, MXene, as an ion exchange membrane (IEM) and 2D nanofluidic channels in IEM, is rising as a promising way to improve the physical and electrochemical properties of RED. It is used alone and other polymeric materials are mixed with MXene to enhance the performance of the membrane further. The maximum desalination performances of MXene with preconditioning, Ti₃C₂T_x, Nafion, and hetero-structures were respectively measured, proving the potential of MXene for a promising material in the desalination industry. In terms of osmotic power generating via RED, adopting MXene as asymmetric nanofluidic ion channels in IEM significantly improved the maximum osmotic output power density, most of them surpassing the commercialization benchmark, 5 Wm^-2. By connecting the number of unit cells, the output voltage reaches the point where it can directly power the electronic devices without any intermediate aid. The studies around MXene have significantly increased in recent years, yet there is more to be revealed about the application of MXene in the membrane and osmotic power-generating industry. This review discusses the electrodialysis process based on MXene composite membrane.