• Journal of Korean Society for Atmospheric Environment
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• v.29 no.1
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• pp.27-37
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• 2013

CFCs (Chlorofluorocarbons) and HCFCs (Hydrochlorofluorocarbons) that are chemically stable were proven to be a greenhouse gases that can destroy ozone layer. On the other hand, HFCs (Hydrofluorocarbons) was developed as an alternative refrigerant for them, but HFCs still have a relatively higher radiative forcing, resulting in a large Global Warming Potential (GWP) of 1,300. Current regulations prohibit production and use of these chemicals. In addition, obligatory removal of existing material is in progress. Methods for the decomposition of these material can be listed as thermal cracking, catalytic decomposition and plasma process. This study reports the development of low cost and high efficiency plasma scrubber. Stability of steam plasma generation and effect of plasma parameters such as frequency of power supply and reactor geometry have been investigated in the course of the development. Method for effective removal of by-product also has been investigated. In this study, elongated rotating arc was proven to be efficient in decomposition of HFCs above 99% and to be able to generate stable steam plasma with steam contents of about 20%.

• Journal of Korean Society for Atmospheric Environment
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• v.24 no.3
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• pp.329-335
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• 2008

Volatile organic compounds emitted to the atmosphere can cause adverse effects on human health and participate in photochemical smog formation reactions. The destruction of a series of VOCs has been carried out by non-thermal plasma in other researches. And the characteristic of non-thermal plasma was operated at atmospheric pressure and low temperature. A new type non-thermal plasma reactor was investigated combined Glidarc plasma with water jet in this research. Also, it was found that the water-jet had an significant effect on the toluene removal efficiency. But too much water content does not favor toluene decomposition by decreasing of reaction temperature. The input toluene concentration, gas flow rate, water flow rate and specific energy input were used as experiment variables. The toluene removal efficiency, energy efficiency and specific energy input were 75.3%, 146.6 g/kWh and $1.12kWh/m^3$ at a water flow rate of 100 mL/min.

• Resources Recycling
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• v.15 no.5 s.73
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• pp.11-16
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• 2006

A novel microwave-induced pyrolysis was used for the recovery of valuable products from waste polystyrene in motor oil. Quartz tube was introduced as microwave reactor and silicon carbide was used as the microwave absorbent. In the experiments, different pyrolysis conditions were applied, such as time range from 30 minutes to 1 hour and microwave input power range from 180 to 250W. The distillate products from pyrolysis were analyzed with GC/MS. Styrene, 1-methyl styrene, toluene, ethyl benzene were the four main products. Styrene recovery rate from polystyrene was around 50%. Temperature for the complete pyrolysis using microwave was around $300^{\circ}C$ which is much lower than that of conventional thermal pyrolysis.

• Journal of Environmental Science International
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• v.21 no.5
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• pp.597-603
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• 2012

Non-thermal plasma processing using a dielectric barrier discharge (DBD) has been investigated as an alternative method for the degradation of non-biodegradable organic compounds in wastewater. The active species such as OH radical, produced by the electrical discharge may play an important role in degrading organic compound in water. The degradation of N, N-Dimethyl-4-nitrosoaniline (RNO) was investigated as an indicator of the generation of OH radical. The DBD plasma reactor of this study consisted of a plasma reactor, recycling pump, power supply and reservoir. The effect of diameter of external reactor (15 ~ 40 mm), width of ground electrode (2.5 ~ 30 cm), shape (pipe, spring) and material (copper, stainless steel and titanium) of ground electrode, water circulation rate (3.1 ~ 54.8 cm/s), air flow rate (0.5 ~ 3.0 L/min) and ratio of packing material (0 ~ 100 %) were evaluated. The experimental results showed that shape and materials of ground were not influenced the RNO degradation. Optimum diameter of external reactor, water circulation rate and air flow rate for RNO degradation were 30 mm, 25.4 cm/s and 4 L/min, respectively. Ground electrode length to get the maximum RNO degradation was 30 cm, which was same as reactor length. Filling up of glass beads decreased the RNO degradation. Among the experimented parameters, air flow rate was most important parameters which are influenced the decomposition of RNO.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.118-123
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• 2004

Cast austenitic stainless steel have been widely used for primary coolant piping in light water reactors. This material is subject to thermal embrittlement at reactor operating temperature. CF-8M and CF-8A cast austenitic stainless steel is used for several components, such as primary coolant piping, elbow, pump casing, and valve bodies in light water reactors. Thermal embrittlement results in spinodal decomposition of delta-ferrite leading to decreased fracture toughness. In this study, the specimens were prepared using an accelerated aging method. The measurement of ferrite content, Charpy impact test and J-R test were performed to verify the predicting equation for aged material properties. In case of above 25% ferrite content, predicted result of J-R curve might be non-conservative.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1174-1179
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• 2003

Cast austenitic stainless steel is used for several components, such as primary coolant piping, elbow, pump casing and valve bodies in light water reactors. These components are subject to thermal aging at the reactor operating temperature. Thermal aging results in spinodal decomposition of the delta-ferrite leading to increased strength and decreased toughness. This study shows that ferrite content can be predicted by use of the artificial neural network. The neural network has trained learning data of chemical components and ferrite contents using backpropagation learning process. The predicted results of the ferrite content using trained neural network are in good agreement with experimental ones.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.4
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• pp.460-466
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• 2004

Cast austenitic stainless steel is used for several components, such as primary coolant piping, elbow, pump casing and valve bodies in light water reactors. These components are subject to thermal aging at the reactor operating temperature. Thermal aging results in spinodal decomposition of the delta-ferrite leading to increased strength and decreased toughness. This study shows that ferrite content can be predicted by use of the artificial neural network. The neural network has trained teaming data of chemical components and ferrite contents using backpropagation learning process. The predicted results of the ferrite content using trained neural network are in good agreement with experimental ones.

• Applied Chemistry for Engineering
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• v.26 no.2
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• pp.154-158
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• 2015

In this study, the catalytic activity of ${\gamma}-Al_2O_3$ was investigated for the decomposition of $NF_3$. Reactions for $NF_3$ decomposition were carried out in the range of reaction temperature of $330{\sim}730^{\circ}C$ and GHSV of $3,000{\sim}15,000mL/g-cat{\cdot}h$ in a fixed-bed catalytic reactor system. Thermal decomposition of $NF_3$ was also performed in order to compare with the catalytic decomposition of $NF_3$. The conversion of $NF_3$ by the catalytic decomposition at $400^{\circ}C$ was four times higher than that of the thermal decomposition. It was confirmed that the reaction behavior of $NF_3$ over ${\gamma}-Al_2O_3$ exhibited two reaction pathways in the presence of steam. Fluorine in $NF_3$ over ${\gamma}-Al_2O_3$ was chemically absorbed to $AlF_3$ by the gas-solid reaction in the absence of steam. The catalytic decomposition of $NF_3$ occurred by hydrolysis with steam. It was also confirmed by FT-IR analysis that $NF_3$ was completely decomposed to NOx and HF above $500^{\circ}C$.

• Clean Technology
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• v.16 no.3
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• pp.198-205
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• 2010

Two sets of thermal reaction experiment for chlorinated hydrocarbons were performed using an isothermal tubular-flow reactor in order to investigate thermal decomposition, including product distribution of chlorinated hydrocarbons. The effects of $H_2$ or Ar as the reaction atmosphere on the thermal decomposition and product distribution for dichloromethane($CH_2Cl_2$) was examined. The experimental results showed that higher conversion of $CH_2Cl_2$ was obtained under $H_2$ atmosphere than under Ar atmosphere. This phenomenon indicates that reactive-gas $H_2$ reaction atmosphere was found to accelerate $CH_2Cl_2$ decomposition. The $H_2$ plays a key role in acceleration of $CH_2Cl_2$ decomposition and formation of dechlorinated light hydrocarbons, while reducing PAH and soot formation through hydrodechlorination process. It was also observed that $CH_3Cl,\;CH_4,\;C_2H_6,\;C_2H_4$ and HCl in $CH_2Cl_2/H_2$ reaction system were the major products with some minor products including chloroethylenes. The $CH_2Cl_2$/Ar reaction system gives poor carbon material balance above reaction temperature of $750^{\circ}C$. Chloroethylenes and soot were found to be the major products and small amounts of $CH_3Cl$ and $C_2H_2$ were formed above $750^{\circ}C$ in $CH_2Cl_2$/Ar. The thermal decomposition reactions of chloroform($CHCl_3$) with argon reaction atmosphere in the absence or the presence of $CH_4$ were carried out using the same tubular flow reactor. The slower $CH_3Cl$ decay occurred when $CH_4$ was added to $CH_3Cl$/Ar reaction system. This is because :$CCl_2$ diradicals that had been produced from $CHCl_3$ unimolecular dissociation reacted with $CH_4$. It appears that the added $CH_4$ worked as the :$CCl_2$ scavenger in the $CHCl_3$ decomposition process. The product distributions for $CHCl_3$ pyrolysis under argon bath gas were distinctly different for the two cases: one with $CH_4$ and the other without $CH_4$. The important pyrolytic reaction pathways to describe the important features of reagent decay and intermediate product distributions, based upon thermochemistry and kinetic principles, were proposed in this study.

• Applied Chemistry for Engineering
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• v.19 no.3
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• pp.270-276
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• 2008

$N_2$ doped $TiO_2$ nano-sized powder was prepared using a DC arc plasma jet and investigated with XRD, BET, SEM, TEM, and photo-catalytic decomposition. Recently the research interest about the nano-sized $TiO_2$ powder has been increased to improve its photo-catalytic activity for the removal of environmental pollutants. Nitrogen gas, reacting gas, and titanium tetrachloride ($TiCl_4$) were used as the raw materials and injected into the plasma reactor to synthesize the $N_2$ doped $TiO_2$ power. The particle size and XRD peaks of the synthesized powder were analyzed as a function of the flow rate of the nitrogen gas. Also, the characteristics of the photo-catalytic decomposition using the prepared powder were studied. For comparing the photo-catalytic decomposition performance of $TiO_2$ powder with that of $TiO_2$ coating, $TiO_2$ thin films were prepared by the spin coating and the pulsed laser deposition. For the results of the acetaldehyde decomposition, the photo-catalytic activity of $TiO_{2-x}N_x$ powder was higher than that of the pure $TiO_2$ powder in the visible light region. For the methylene blue decomposition, the decomposition efficiency of $TiO_2$ powder was also higher than that of $TiO_2$ film.