• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.5
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• pp.563-569
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• 2012

The superheater and reheater tubes of a heavy-load fossil power plant boiler can be damaged by overheating, and therefore, the degree of overheating is assessed by measuring the oxide scale thickness inside the tube during outages. The tube temperature prediction from the oxide scale thickness measurement is necessarily accompanied by destructive tube sampling, and the result of tube temperature prediction cannot be expected to be accurate unless the selection of the overheated point is precise and the initial-operation tube temperature has been obtained. In contrast, if the tube temperature is to be predicted analytically, considerable effort (to carry out the analysis of combustion, radiation, convection heat transfer, and turbulence fluid dynamics of the gas outside the tube) is required. In addition, in the case of analytical tube temperature prediction, load changes, variations in the fuel composition, and operation mode changes are hardly considered, thus impeding the continuous monitoring of the tube temperature. This paper proposes a method for the short-term prediction of tube temperature; the method involves the use of boiler operation information and flow-network-analysis-based tube heat flux. This method can help in high-temperaturedamage monitoring when it is integrated with a practical tube-damage-assessment method such as the Larson-Miller Parameter.

• Journal of Radiation Protection and Research
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• v.17 no.2
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• pp.25-35
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• 1992

To evaluate tritium level in some environmental samples, tissue-free water tritium (TFWT) and tissue-bound tritium (TBT) were analyzed in rices, chinese cabbages and pine needles collected at 12 locations in Korea. The TFWT was recovered by freeze-drying of the samples and the TBT was obtained in the form of water by combustion of the dried samples. Tritium was measured by liquid scintillation counter. The concentrations of TFWT were in the range of $0.96{\sim}3.96 Bq/1,\; 0.83{\sim}3.40 Bq/1\;and\;1.02{\sim}3.01 Bq/1$ in rices, chinese cabbages and pine needles, respectively. The mean specific activity ratios (TBT/TFWT) were 0.94, 1.71 and 1.39 in rices, chinese cabbages and pine needles, respectiviely. This excess TBT in the samples may be attributed to the fact that the residence time of TBT in the plant is longer than that of TFWT. The specific activity ratio depends on the plant species, the exposed time to tritiated atmosphere, atmospheric moisture, temperature and diffusion factor.

• Clean Technology
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• v.27 no.3
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• pp.269-274
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• 2021

Bioenergy is generally considered to be one of the options for pursuing carbon neutrality. However, for a period of time, combustion of harvested plant biomass inevitably causes more carbon dioxide in the atmosphere than combustion of fossil fuels. This paper proposes a method that predicts and minimizes the total amount and payback period of this carbon debt. As a case study, a carbon cycle impact assessment was performed for immediate switching of the currently used fossil fuels to biomass. This work points out a fundamental vulnerability in the concept of carbon neutrality. As an action plan for the sustainability of bioenergy, formulas for afforestation proportional to the decrease in the forest area and surplus harvest proportional to the increase in the forest mass are proposed. The results of optimization indicate that the carbon debt payback period is about 70 years, and the carbon dioxide in the atmosphere increases by more than 50% at a maximum and 3% at a steady state. These are theoretically predicted best results, which are expected to be worse in reality. Therefore, biomass is not truly carbon neutral, and it is inappropriate as an energy source alternative to fossil fuels. The method proposed in this work is expected to be able to contribute to the approach to carbon neutrality by minimizing present and future carbon debt of the bioenergy that is already in use.

• Applied Chemistry for Engineering
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• v.33 no.4
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• pp.373-380
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• 2022

In this study, Chung's equations 1, 2, and 3 were extended to standardize smoke safety rating evaluation in case of fire, and Chung's equations-V, smoke performance index-V, and smoke growth index-V were calculated. Five types of wood were selected and their smoke indices were measured using the cone calorimeter method according to ISO 5660-1. The smoke risk was graded by the smoke risk index-VI according to Chung's equation-VI. Smoke risk index-VI increased in the order of PMMA (1) ≈ maple (1.01) < ash (1.57) < needle fir (4.98) < paulownia (46.15) < western red cedar (106.26). It was predicted that maple and ash had the lowest smoke risk, and paulownia and western red cedar had the highest. The five samples' CO mean production rate (COP_mean) was 0.0009~0.0024 g/s, indicating that these woods were incompletely burned than the polymethyl methacrylate (PMMA) reference material. Regarding the smoke properties of the chosen woods, the smoke performance index-V (SPI-V) increased as the bulk density increased, and the smoke risk index-VI (SRI-VI) decreased.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.7
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• pp.1074-1081
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• 2021

Nitrous oxide (N₂O) is one of the six major greenhouse gases and is known to produce a greenhouse ef ect by absorbing infrared radiation in the atmosphere. In particular, its global warming potential (GWP) is 310 times higher than that of CO₂, making N₂O a global concern. Accordingly, strong environmental regulations are being proposed. N₂O reduction technology can be classified into concentration recovery, catalytic decomposition, and pyrolysis according to physical methods. This study intends to provide information on temperature conditions and reaction time required to reduce nitrogen oxides with cost. The high-temperature ranges selected for pyrolysis conditions were calculated at intervals of 100 K from 1073 K to 1373 K. Under temperatures of 1073 K and 1173 K, the N₂O reduction rate and nitrogen monoxide concentration were observed to be proportional to the residence time, and for 1273 K, the N₂O reduction rate decreased due to generation of the reverse reaction as the residence time increased. Particularly for 1373 K, the positive and reverse reactions for all residence times reached chemical equilibrium, resulting in a rather reduced reaction progression to N₂O reduction.

• Korean Journal of Materials Research
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• v.5 no.7
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• pp.835-841
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• 1995

The deposition properties of Si$_3$N$_4$ deposited by low pressure chemical vapor deposition were studied to evaluate Si$_3$N$_4$as part of multi-layer coatings for anti-oxidation and anti-wear coating of graphite in the propellant-burning environment. Si$_3$N$_4$was deposited on the pack-SiC coated graphite and the tendencies of deposition rate and surface morphology changes with temperatures and reaction gas ratios were investigated. In low deposition temperatures the deposition rate increased tilth increasing temperature but in high temperatures the deposition rate decreased with increasing temperature. The grain size of Si$_3$N$_4$decreased with increasing temperature. In condition that the range of reaction gas ratios is 20$\leq$NH$_3$/SiH$_4$$\leq$40, the deposition rate and surface morphology did not change. The Si$_3$N$_4$deposited at 800~130$0^{\circ}C$ was amorphous, and by post-annealing at 130$0^{\circ}C$ in a $N_2$ambient, the Si$_3$N$_4$crystalized.

• Korean Journal of Environmental Biology
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• v.34 no.3
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• pp.216-221
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• 2016

Level and distribution of fourteen polycyclic aromatic hydrocarbons (PAHs) in the agricultural water samples collected in the waterways located in Gyeonggi and Gangwon, Korea were determined for monitoring and risk assessment. A simplified, fast but effective extraction and clean-up methods combined with gas chromatography tandem mass spectrometry (GC-MS/MS) was employed to measure the concentration of the target compounds. The extraction of the analytes of interest in water sample (10 mL) was performed with acetonitrile (10 mL) and the salt. To purify the target PAHs, the clean-up procedure was employed with 2 mL tubes of dispersive solid phase extraction. The optimized method was validated with recoveries, method detection limit (MDL), accuracy and precision. Good recoveries for each PAHs at 10 and $25{\mu}g\;L^{-1}$ were achieved (60 to 110%, with RSD <20%) with linearity (>0.99). MDL for all the analytes was achieved with $0.2{\mu}g\;L^{-1}$. GC-MS/MS results showed that concentration of phenanthrene in the water samples from Gyeonggi (20 sites) ranged from 0.82 to $2.56{\mu}g\;L^{-1}$ and from Gangwon (15 sites) ranged from 0.83 to $1.62{\mu}g\;L^{-1}$. Other PAHs were not found in the water samples but the continuous monitoring for these areas were required.

• Korean Chemical Engineering Research
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• v.43 no.6
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• pp.751-755
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• 2005

Carbon dioxide, included in the flue gas from the combustion of fossil fuel, was known as a representative green house gas and various removal and utilization technologies of it has been studied for the prevention of global warming. This study was performed as an effort to find out a method to reuse carbon dioxide separated from flue gas by magnetite powder. Magnetite powder was synthesized using various oxidizers and alkalinity controlled aqueous solutions of $FeSO_4{\cdot}7H_2O$ and NaOH at 50, 80, 90, $100^{\circ}C$ and analyzed by XRD and SEM. The analysis results showed that magnetite powder synthesized at higher alkalinity and temperature had crystalline spinel and cubic structure. The reduction by hydrogen and the oxidation by carbon dioxide of synthesized powder were studied by TGA. The results showed that magnetite powder synthesized at low alkalinity and temperature was non-cubical amorphous but crystalline and cubical at high alkalinity and temperature. Comparing magnetite powders synthesized using oxidants(air and oxygen) and nitrogen, magnetite powder using more oxygen containing oxidant synthesized more crystalline magnetite powder. The experimental results of redox reaction of the synthesized magnetite powder showed that the reduction by hydrogen and the oxidation by carbon dioxide were seldom observed below $400^{\circ}C$ and observed well at $500^{\circ}C$. Magnetite powder synthesized at $100^{\circ}C$ and alkalinity(molal concentration ratio of $FeSO_4{\cdot}7H_2O$ to NaOH) of 2.0 using $O_2$ showed the highest reduction of 27.15 wt％ and oxidation of 26.73 wt％, especially at reaction temperature of $500^{\circ}C$.

• Korean Chemical Engineering Research
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• v.50 no.2
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• pp.365-370
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• 2012

In this study, Economic analysis of supercritical coal-fired power plant with $CO_2$ capture process was performed. For this purpose, chemical absorption method using amine solvent, which is commercially available and most suitable for existing thermal power plant, was studied. For the evaluation of the economic analysis of coal-fired power plant with post-combustion $CO_2$ capture process in Korea, energy penalty after $CO_2$ capture was calculated using the power equivalent factor suggested by Bolland et al. And the overnight cost of power plant (or cost of plant construction) and the operation cost reported by the IEA (International Energy Agency) were used. Based on chemical absorption method using a amine solvent and 3.31 GJ/$tonCO_2$ as a regeneration energy in the stripper, the net power efficiency was reduced from 41.0% (without $CO_2$ capture) to 31.6% (with $CO_2$ capture) and the levelized cost of electricity was increased from 45.5 USD/MWh (Reference case, without $CO_2$ capture) to 73.9 USD/MWh (With $CO_2$ capture) and the cost of $CO_2$ avoided was estimated as 41.3 USD/$tonCO_2$.

• Korean Chemical Engineering Research
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• v.47 no.5
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• pp.572-579
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• 2009

This study is to investigate experimentally the flame structure and propagation mechanism in dust explosions and to provide the fundamental knowledge. Upward propagating laminar dust flames in a vertical duct of 1.8 m height and 0.15 m square cross-section are observed and flame front is visualized using by a high-speed video camera. Also, the thicknesses of preheated and reaction zone have been determined by a schlieren, electrostatic probe and thermocouple. The thickness of preheated zone in lycopodium dust flame is observed to be 4~13 mm, about several orders of magnitude higher than that of premixed gaseous flames. From the experimental results by a PIV(Particle Image Velocimetry) system, a certain residence time of the unburned particle in preheated zone is needed to generate combustible gas from the particle. The residence time will depend on preheated zone thickness, particle velocity and flame propagation velocity.