• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.8
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• pp.677-685
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• 2014

A direct carbon fuel cell (DCFC) generates electricity directly by converting the chemical energy in coal. In particular, a DCFC system with a solid oxide electrolyte and molten carbonate anode media has been proposed by SRI. In this system, however, there are conflicting effects of temperature, which enhances the ion conductivity of the solid electrolyte and reactivity at the electrodes while causing a stability problem for the anode media. In this study, the effect of temperature on the stability of a carbon-carbonate mixture was investigated experimentally. TGA analysis was conducted under either nitrogen or carbon dioxide ambient for $Li_2CO_3$, $K_2CO_3$, and their mixtures with carbon black. The composition of the exit gas was also monitored during temperature elevation. A simplified reaction model was suggested by considering the decomposition of carbonates and the catalyzed Boudouard reactions. The suggested model could well explain both the measured weight loss of the mixture and the gas formation from it.

• Journal of Korean Society of Forest Science
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• v.98 no.2
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• pp.183-188
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• 2009

It is necessary to determine the amount of carbon dioxide ($CO_2$) absorbed by plants and released from forest floor into atmosphere, to gain a better understanding how forests participate in the global carbon cycle. Soil $CO_2$ efflux, litter production, and decomposition were investigated in Q. variabilis and P. densiflora stands in the vicinity of Gwangju, Chonnam province. Soil $CO_2$ efflux was measured using Infrared Gas Analyzer (IRGA) at midday of the 10th day at every month over 12-month period, to quantify seasonal and annual budgets of soil $CO_2$ efflux. Soil temperature and soil moisture were measured at the same time. Seasonal soil $CO_2$ efflux in Q. variabilis and P. densiflora were the highest in summer season. In August, maximum soil $CO_2$ efflux in Q. variabilis and P. densiflora was 7.49, $4.61CO_2{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$, respectively. Annual $CO_2$ efflux in each stand was 1.77, $1.67CO_2kg{\cdot}m^{-2}$ respectively. Soil $CO_2$ efflux increased exponentially with soil temperature and related strongly in Q. variabilis ($r^2$=0.96), and in P. densiflora ($r^2$=0.91). Litter production continued throughout the year, but showed a peak on November and December. Annual litter production in the Q. variabilis and P. densiflora stands were $613.7gdw{\cdot}m^{-2}{\cdot}yr^{-1}$ and $550.5gdw{\cdot}m^{-2}{\cdot}yr^{-1}$.$yr^{-1}$, respectively. After 1 year, % remaining mass of Q. variabilis and P. densiflora litter was 48.2, 57.1%, respectively. The soil $CO_2$ efflux rates in this study showed clear seasonal variations. In addition, the temporal variation in the $CO_2$ efflux rates was closely related to the soil temperature fluctuation rather than to variations in the soil moisture content. The range of fluctuation of soil $CO_2$ efflux and litter decomposition rate showed similar seasonal changes. The range of fluctuation of soil $CO_2$ efflux and litter decomposition rate was higher during summer and autumn than spring and winter.

• Journal of Environmental Science International
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• v.14 no.6
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• pp.555-563
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• 2005

This study presents the characteristics of nocturnal inversion layer and their effect on the concentration variations of surface air pollutants using tethersonde and automatic weather station (AWS, 2 layer tower) system in Ulsan during 2003, The method for the distinction of inversion intensity was decided based on the sum of nocturnal temperature gradient. As the results, there was a close correlation (correlation coefficient of 0,76) between the maximum inversion height obtained from tethersonde and the sum of nocturnal temperature gradient. The air pollutant concentration was also directly proportional to the inversion intensity. When the inversion intensity was strong in the nighttime, ozone $(O_3)$ concentration was lower, while nitrogen dioxide $(NO_2)$ concentration was higher. The carbon monoxide (CO) concentration was gradually higher according to the nocturnal inversion intensity, whereas sulfur dioxide $(SO_2)$ concentration was relatively constant. In addition, we found that there was no correlation between the inversion intensity and TSP concentration.

• Membrane Journal
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• v.25 no.2
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• pp.99-106
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• 2015

Polysulfone (PSF) hollow fiber membrane was prepared to separate $CO_2$ from the flaring gas. Fabricated PSF membrane system was fulfilled under 1 stage, 2 stage membrane process and simulation in order to confirm the operating condition for 99% of $CH_4$ and 1% of $CO_2$ concentration. Also, $25Nm^3/h$ bench scale $CO_2$ separation membrane system was operated under 1% of $CO_2$ concentration during 100 hr, and $CH_4$ recovery ratio was 98%.

• Journal of Hydrogen and New Energy
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• v.27 no.4
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• pp.357-364
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• 2016

Recently, the world faces the environmental problem such as air pollution due to harmful gas discharged from car and abnormal climate due to the green-house gases increased by the discharge of $CO_2$. Compressed Natural Gas (CNG), one of alternative for this problem, is less harmful, compared to the existing fossil fuel, as gaseous fuel, and less carbon in fuel ingredients and carbon dioxide generation rate relatively favorable more than the existing fuel. However, CNG fuel has the weakness of slow flame propagation speed and difficult fast burn. On the other hand, hydrogen does not include carbon in fuel ingredients, and does not discharge harmful gas such as CO and HC. Moreover, it has strength of quick burning velocity and ignition is possible with small ignition energy source and it's has wide Lean Flammability Limit. If using this hydrogen with CNG fuel, the characteristics of output and discharge gas is improved by the mixer's burning velocity improved, and, at the same time, is possible to have stable lean combustion with the reduction of $CO_2$ expected. Therefore, this research tries to identify the characteristics of engine and emission gas when mixing CNG fuel and hydrogen in each portion and burning them in spark igniting engine, and grasp the combustion stability and emission gas characteristics according and use it as the basic data of hydrogen-CNG premixed engine.

• Journal of Soil and Groundwater Environment
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• v.21 no.6
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• pp.46-55
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• 2016

This experimental study was aimed to estimate interfacial tension of brine-$CO_2$ by using a pendant bubble method and image analysis. Measurements were performed for wide ranges of temperatures, pressures, and salinities covering reservoir conditions in Pohang basin, a possible candidate for $CO_2$ storage operation in Korea. The profiles of $CO_2$ bubbles in brine obtained from image analysis with the densities of brine and $CO_2$ from previous studies were applied to Laplace-Young equation for calculating interfacial twnsion in brine-$CO_2$ system. The experimental results reveals that the interfacial tension is significantly affected by reservoir conditions such as pressure, temperature and water salinity. For conditions of constant temperature and water salinity, the interfacial tension decreases as pressure increases for low pressures (P < $P_c$), and approaches to a constant value for high pressures. For conditions of constant pressure and water salinity, the interfacial tension increases as temperature increases for T < $T_c$, with an asymptotic trend towards a constant value for high temperatures. For conditions of constant pressure and temperature, the interfacial tension increases with increasing water salinity. The trends in changes of interfacial tension can be explained by the effects of the reservoir conditions on the density difference of brine and $CO_2$, and the solubility of $CO_2$ in brine. The information on interfacial tensions obtained from this research can be applied in predicting the migration and distribution of injecting and residual fluids in brine-$CO_2$-rock systems in deep geological environments during geological $CO_2$ sequestrations.

• Journal of the Korean Society for Marine Environment & Energy
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• v.12 no.3
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• pp.217-226
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• 2009

Marine geological storage of $CO_2$ is regarded as one of the most promising options to response climate change. Marine geological storage of $CO_2$ is to capture $CO_2$ from major point sources, to transport to the storage sites and to store $CO_2$ into the marine geological structure such as deep sea saline aquifer. Up to now, process design for this $CO_2$ marine geological storage has been carried out mainly on pure $CO_2$. Unfortunately the captured $CO_2$ mixture contains many impurities such as $N_2$, $O_2$, Ar, $H_2O$, $SO_x$, $H_2S$. A small amount of impurities can change the thermodynamic properties and then significantly affect the compression, purification and transport processes. In order to design a reliable $CO_2$ marine geological storage system, it is necessary to perform numerical process simulation using thermodynamic equation of state. The purpose of the present paper is to compare and analyse the relevant equations of state including PR, PRBM, RKS and SRK equation of state for $CO_2-N_2$ mixture. To evaluate the predictive accuracy of the equation of the state, we compared numerical calculation results with reference experimental data. In addition, optimum binary parameter to consider the interaction of $CO_2$ and $N_2$ molecules was suggested based on the mean absolute percent error. In conclusion, we suggest the most reliable equation of state and relevant binary parameter in designing the $CO_2-N_2$ mixture marine geological storage process.

• Journal of Korean Society on Water Environment
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• v.35 no.4
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• pp.316-331
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• 2019

Carbon dioxide($CO_2$) emission from rivers to the atmosphere is a key component in the global carbon cycle. Most of the rivers are supersaturated with $CO_2$. At a global scale, the amount of $CO_2$ emission from rivers is reported to be five-fold greater than that from lakes and reservoirs, but relevant data are rare in Korea. The objectives of this study is to estimate the $CO_2$ net atmospheric flux(NAF) from the upstream of Gangjeong-Goryeong Weir(GGW), Dalseong Weir(DSW), Hapcheon-Changnyeong Weir(HCW), and Changnyeong-Haman Weir(CHW) located in Nakdong River South Korea) using field and laboratory experiments and to apply data mining techniques to develop parsimonious prediction models that can be used to estimate $CO_2$ NAF with physical and water quality variables that can be collected easily. As a result, the study sites were all heterotrophic systems that often released $CO_2$ to the atmosphere, except when the algal photosynthesis was active.The median $CO_2$ NAF was minimum $391.5mg-CO_2/m^2$ day at GGW and maximum $1472.7mg-CO_2/m^2$ day at DSW. The $CO_2$ NAF showed a negative correlation with pH and Chl-a since the overgrowth of the algae consumed $CO_2$ in the water and increased the pH. As the parsimonious multiple regression model and random forest model developed, this study showed an excellent performance with the $Adj.R^2$ value higher than 0.77 in all weirs. Thus, these methods can be used to estimate $CO_2$ NAF in the river even if there is no $pCO_2$ measurement data.

• Clean Technology
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• v.12 no.2
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• pp.53-61
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• 2006

A PGSS (Particles from Gas Saturated Solutions) process designed to generate nano-particles using supercritical fluids has been conducted for the fabrication of Poly(lactide-co-glycolide) (PLGA) microparticles that encapsulate a protein drug. It is demonstrated that the polymer and the dry powder of a protein can be mixed under supercritical carbon dioxide conditions and that the protein component retains its biological activity. In this experiment, the mixture of polymer which is plasticized and dry powder protein was sprayed to form solid polymer that encapsulate the protein. It is found that supercritical fluid process give fine tuning of particle size and particle size distribution by simple manipulations of the process parameters. Porous particles were formed with irregular shape. Protein encapsulated in the polymer was found to have enzymatic activity without significant loss of its initial value.

• Journal of the Korean Applied Science and Technology
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• v.27 no.3
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• pp.318-324
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• 2010

In this study, commercial pellet type sorbents for the collection of $CO_2$ from a local municipal waste incinerator were prepared and characterized in terms of adsorption efficiency by varying the operating conditions of a field process. The concentration of $CO_2$ in the flue gas ranged from 8 to 10%, which entered the test packed bed. As a result of this experiment, the sorbent procured from A-company, which is mainly composed of calcium compounds, showed the highest adsorption efficiency. The regeneration efficiency was fairly low, however. It also was found that based on adsorption breakthrough time, the relatively low flow rate of 10 LPM into the bed allowed higher collection efficiency. The higher flow rate of 40 LPM, on the other hand, tended to decrease the retention of the adsorption.