• The Korean Journal of Ceramics
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• v.4 no.4
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• pp.279-285
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• 1998

The $UO_2$ pellets are usually sintered under hydrogen gas atmosphere. Hydrogen gas may cause unexpected early failure of the refractory bricks in the sintering furnace. In this work, nitrogen was mixed with hydrogen to investigate the effect of nitrogen gas on a failure machanism of the refractory bricks and on the microstructure of the $UO_2$ pellet. The hydrogen-nitrogen mixed gas experiments show that the larger nitrogen the mixed gas contains, the less the refractory materials are reduced by hydrogen. The weight loss measurements at $1400^{\circ}C$ for fire clay and chamotte refractories containing high content of $SiO_2$ indicate that the weight loss rate for the mixed gas is about half of that for the hydrogen gas. Based on the thermochemical analyses, it is proposed that the weight loss is caused by hydrogen-induced reduction of free $SiO_2$ and/or $SiO_2$ bonded to $Al_2O_3$ in the fire clay and chamotte refractories. However, the retardation of the hydrogen-induced $SiO_2$ reduction rate under the mixed gas atmosphere may be due to the reduction of the surface reaction rate between hydrogen gas and refractory materials in proportion to volume fraction of nitrogen gas in the mixed gas. On the other hand, the mixed gas experiments show that the test data for $UO_2$ pellet still meet the related specification values, even if there exists a slight difference in the pellet microstructural parameters between the cases of the mixed gas and the hydrogen gas.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.2
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• pp.26-36
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• 2007

The thermal response characteristics of nozzle liner for a solid rocket motor applying highly aluminized PCP or HTPB propellant with slotted tube grain have been investigated. The SEM photographs of aluminum oxide particles taken from nozzle liner show that the PCP propellant with the finer and less contents of oxidizer can offer greater possibility for increasing aluminum agglomeration than the HTPB propellant. The PCP propellant shows locally greater mechanical erosion at 4 circumferential areas of the nozzle entrance in line with grain slot due to the impingement of large particles, but the HTPB propellant shows greater thermochemical ablation at the nozzle blast tube, the throat insert and the exit cone because of relatively much more mole fraction of $H_2O\;and\;CO_2$ in combustion gases.

• Journal of Power System Engineering
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• v.22 no.1
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• pp.79-86
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• 2018

Many countries have conducted extensive studies for biomass co-firing to enhance the durability of reactor on high-temperature corrosion. However, due to the complicated mechanisms of biomass co-firing, there have been limitations in accurately determining the current state of corrosion and predicting the potential risk of corrosion of power plant. In order to solve this issue, this study introduced Lab-scale corrosion system to analyze the corrosion characteristics of the A213 T91 material under the biomass co-firing conditions. The corrosion status of the samples was characterized using SEM/EDS analysis and mass loss measurement according to various biomass co-firing conditions such as corrosion temperature, $SO_2$ concentration, and corrosion time. As a result, the corrosion severity of A213 T91 material was gradually increased with the increase of $SO_2$ concentration in the reactor. When $SO_2$ concentration was changed from 0 ppm to 500 ppm, both corrosion severity and oxide layer thickness were proportionally increased by 15% and 130%, respectively. The minimum corrosion was observed when the corrosion temperature was $450^{\circ}C$. As the temperature was increased up to $650^{\circ}C$, the faster corrosion behavior of A213 T91 was observed. A213 T91 was observed to be more severely corroded by the effect of chlorine, resulting in faster corrosion rate and thicker oxide layer. Interestingly, corrosion resistance of A213 T91 tended to gradually decrease rather than increases as the oxide layer was formed. The results of this study is expected to provide necessary research data on boiler corrosion in biomass co-firing power plants.

• Nuclear Engineering and Technology
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• v.40 no.7
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• pp.593-606
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• 2008

In this study, data on radionuclide migration and retardation processes in the engineered and natural barriers of High-Level Radioactive Waste (HLW) repository have been reviewed and compiled for use in the performance assessment of a HLW disposal system in Korea. The status of the database on radionuclide migration and retardation that is being developed in Korea is investigated and summarized in this study. The solubilities of major actinides such as D, Th, Am, Np, and Pu both in Korean bentonite porewater and in deep Korean groundwater are calculated by using the geochemical code PHREEQC (Ver. 2.0) based on the KAERI-TDB(Korea Atomic Energy Research Institute-Thermochemical Database), which is under development. Databases for the diffusion coefficients ($D^b_e$ values) and distribution coefficients ($K^b_d$ values) of some radionuclides in the compacted Korean Ca-bentonite are developed based upon domestic experimental results. Databases for the rock matrix diffusion coefficients ($D^r_e$ values) and distribution coefficients ($K^r_d$ values) of some radionuclides for Korean granite rock and deep groundwater are also developed based upon domestic experimental results. Finally, data related to colloids such as the characteristics of natural groundwater colloids and the pseudo-colloid formation constants ($K_{pc}$ values) are provided for the consideration of colloid effects in the performance assessment.

• Clean Technology
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• v.14 no.2
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• pp.117-122
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• 2008

Theoretical analysis was conducted on the combustion and the NOx formation characteristics of the coal-derived synthetic gases with medium-BTU heating value. The synthetic gas was assumed to contain the major species of CO, $H_2,\;CO_2$, and $N_2$ and the minor species of $CH_4$ and $NH_3$. Through thermochemical analysis on the combustion of the synthetic gas, the flame temperature, major and minor species of exhaust gas, and thermal and fuel NOx emissions were computed. In addition, the effects of the $CH_4$ and the $NH_3$ components in syngas fuel on combustion and NOx emission were investigated. Based on the computed results on the synthetic gases, basic direction and guidelines were provided fur the low NOx design of gas turbine combustor.

• Solar Energy
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• v.15 no.3
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• pp.29-38
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• 1995

The heat-storage characteristics accompanied by exothermic reaction at the regeneration of $Ca(OH)_2$ in tile heat-storage mode of a chemical heat pump system using a $Ca(OH)_2/CaO$ reversible thermochemical reaction was examined in a lab-scale unit. In this heat-storage mode, the particle bed of CaO could be regenerated by heating the $Ca(OH)_2$ packed bed to the higher temperature at which the equilibrium pressure in the reactor is greater than the water vapor pressure in the condenser. The results are i) the dehydration, thermal decomposition, rate of $Ca(OH)_2$ was higher at the lower part of particle bed than at the upper part, ii) in the reactor, the dehydration was proceeded along radial and axial direction, from inner part to the outer part, which explains heat transfers from the center to wall and from the tenter to lower or upper part of reactor.

• Journal of Microbiology and Biotechnology
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• v.25 no.4
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• pp.459-463
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• 2015

This study evaluated the microbial conversion of coconut oil waste, a major agro-residue in tropical countries, into single cell oil (SCO) feedstock for biodiesel production. Copra cake was used as a low-cost renewable substrate without any prior chemical or enzymatic pretreatment for submerged growth of an oleaginous tropical mangrove fungus, Aspergillus terreus IBB M1. The SCO extracted from fermented biomass was converted into fatty acid methyl esters (FAMEs) by transesterification and evaluated on the basis of fatty acid profiles and key fuel properties for biodiesel. The fungus produced a biomass (8.2 g/l) yielding 257 mg/g copra cake SCO with ~98% FAMEs. The FAMEs were mainly composed of saturated methyl esters (61.2%) of medium-chain fatty acids (C12-C18) with methyl oleate (C18:1; 16.57%) and methyl linoleate (C18:2; 19.97%) making up the unsaturated content. A higher content of both saturated FAMEs and methyl oleate along with the absence of polyunsaturated FAMEs with ≥4 double bonds is expected to impart good fuel quality. This was evident from the predicted and experimentally determined key fuel properties of FAMEs (density, kinematic viscosity, iodine value, acid number, cetane number), which were in accordance with the international (ASTM D6751, EN 14214) and national (IS 15607) biodiesel standards, suggesting their suitability as a biodiesel fuel. The low cost, renewable nature, and easy availability of copra cake, its conversion into SCO without any thermochemical pretreatment, and pelleted fungal growth facilitating easier downstream processing by simple filtration make this process cost effective and environmentally favorable.

• Journal of Korean Society of Environmental Engineers
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• v.36 no.10
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• pp.704-710
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• 2014

Biomass is considered an alternative energy which can solve an greenhouse gas problem like $CO_2$ which is a major contributor to global warming. The biomass can be converted to various energy sources through thermochemical conversion. In this study, a continuous gasifier was engineered for a wood biomass gasification. The biomass was used a waste wood. The experiments of $CO_2$ gasification were achieved as the gasification temperature, moisture content and input $CO_2$ concentration. The results showed that the yield of producer gas increased with an increasing the gasification temperature. The amount of the light tar increased due to the decomposition of gravimetric tar by the thermal cracking, and the char was confirmed pore development through the SEM analysis. The CO concentration was increased with an increased input $CO_2$ concentration from Boudouard reaction. Through the parametric screening studies, the hydrogen and carbon monoxide concentration were 32.91% and 48.33% at the optimal conditions of this test rig.

• Journal of the Korean Institute of Gas
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• v.9 no.2 s.27
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• pp.1-7
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• 2005

The thermochemical parameters for safe handling, storage, transport, operation and process design of flammable substances are explosive limit, flash point, autoignition temperature, minimum oxygen concentration, heat of combustion etc.. Explosive limit and autoignition temperature are the major physical properties used to determine the fire and explosion hazards of the flammable substances. Explosive limit and autoignition temperature of methane fur LNG process safety were investigated. By using the literatures data, the lower and upper explosive limits of methane recommended 4.8 vol$\%$ and 16 vol$\%$, respectively. Also autoignition temperatures of methane with ignition sources recommended $540^{\circ}C$ at the electrically heated cruicible furnace (the whole surface heating) and recommended about $1000^{\circ}C$ in the local hot surface. The new equations for predicting the temperature dependence and the pressure dependence of the lower explosive limits for methane are proposed. The values calculated by the proposed equations were a good agreement with the literature data.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.1
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• pp.12-20
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• 2002

An integrated analysis of kerosine/LOX based KSR-III rocket body/plume flowfield has been performed. The analysis has been executed employing three kind of gas thermo-chemical models including calorically perfect gas, multiple species chemically reacting gas, and chemically frozen gas models and their effect on rocket flowfield has been accessed to provide the most appropriate gas thermo-chemical model which meets a specific purpose of performing rocket body and plume analysis. The finite-rate chemically reacting flow solution exhibited higher temperature throughout the flowfield than other gas models due to the increased combustion gas temperature caused by the chemical reactions within the nozzle. All the reactions were dominated only in the shear layer and behind the barrel shock reflection region where the gas temperature is high and the effect of finite-rate chemical reactions on the flowfield was found to be minor. However, the present plume computation including finite-rate chemical reactions revealed major reactions occurring in the plume and their reaction mechanisms and as well.