• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.8 s.251
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• pp.788-795
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• 2006

From the view of the environmental protection against the use of fossil fuels, the great of efforts have been exerted to find an effective method which is not only pollutant reduction but also high thermal efficiency. Reburning is a useful technology in reducing nitric oxide through injection of a secondary hydrocarbon fuel. In this paper, an experimental study has been conducted to evaluate the hybrid effects of reburning and selective non-catalytic reaction (SNCR) on $NO_x/CO$ reduction from oxygen-enriched LPG flame. Experiments were performed in flames stabilized by a co-flow swirl burner, which was mounted at the bottom of the furnace. Tests were conducted using LPG gas as main fuel and also as reburn fuel. The paper reported data on flue gas emissions, temperature distribution in furnace and various heat fluxes at the wall for a wide range of experimental conditions. Overall temperature in the furnace, heat fluxes to the wall and $NO_x$ generation were observed to increase by oxygen-enriched combustion, but due to its hybrid effects of reburning and SNCR, $NOx/CO$ concentration in the downstream has considerably decreased.

• Journal of the Korean Society of Combustion
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• v.4 no.2
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• pp.63-74
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• 1999

The effects of EGR and premixedness on NO formation have been numerically investigated. The flame structure is classified into three categories; premixed flame($=1)$, rich/lean premixed flame(${\alpha}=0.6$ and 0.8) and diffusion flame(${\alpha}=0$). NO formation/destruction mechanisms are assorted to thermal, reburn and Fenimore mechanisms. The temperature of unburned gas is arranged to 298 and 500 K to have access to the condition in a real internal combustion engine. The results show that all three NO formation/destruction reaction rates in the fuel rich flame zone could be decreased by EGR for rich/lean premixed flames, while those in the fuel lean flame zone are not significantly changed. Near the stagnation plane, however, only the thermal NO reaction rate is decreased. The contribution of reburn and Fenimore mechanisms for the net NO production becomes less significant as the premixedness of a flame increases. The larger amount of NO reduction with EGR is expected under the higher temperature and/or higher fuel/air premixedness conditions due to the increased contribution of the thermal mechanism. The role of Fenimore and reburn mechanisms could be important for rich premixed and diffusion flames; therefore, the effect of EGR on NO reduction could vary with fuel/air premixedness. The premixedness of a partially premixed flame changes the flame structure and could affect the NO production characteristics.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1901-1903
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• 1999

To investigate invar alloy as a core material for increased capacity over-head transmission line which have high strength and low thermal expansion coefficient, hardness and thermal expansion coefficient of Fe-Ni-Co alloy have been studied. It is necessary that invar alloy have low thermal expansion coefficient and high strength for increased capacity over-head transmission line. In this paper. we tried to find out the effect of Ni and Co which has ferromagnetic properties and high saturation magnetization. It was found that Ni decrease thermal expansion coefficient and hardness, Co decrease thermal expansion coefficient but increase hardness in Fe-xNi-Co system. In Fe-(29-x)Ni-Co system, the material has no low thermal expansion properties substituting Co instead of Ni in concentration range of $1\sim7$%Co.

• Journal of Korea Foundry Society
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• v.37 no.5
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• pp.139-147
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• 2017

Microstructural evolution of cast Hastelloy X during thermal exposure has been investigated. OM, SEM, and TEM microscopy were carried out on the as-cast, the standard heat treated, and the thermally exposed conditions. Tensile tests were also conducted to understand the effect of microstructural evolution on the degradation of tensile properties. Coarse $M_6C$ and fine $M_{23}C_6$ carbides were found in as-cast Hastelloy X with fine carbides on sub-boundary. Some of $M_{23}C_6$ carbide dissolved into the matrix during solution heat treatment and dislocation network formed at the interface between the carbide and the matrix due to the misfit strain. There was no significant microstructural difference between the exposed specimens at $400^{\circ}C$ and the solution heat treated specimen. A large amount of $M_{23}C_6$ carbides precipitated along and near grain boundaries and sub-boundaries after exposure at $650^{\circ}C$. Exposure at $870^{\circ}C$ of the alloy caused precipitation of $M_6C$ and ${\mu}$. The strength increased and the elongation decreased by thermal exposure at $650^{\circ}C$ and $870^{\circ}C$ because carbides interfere with the movement of the dislocation. It was found that the precipitation of carbide gave significant effects on the tensile properties of Hastelloy X.

• Journal of Mechanical Science and Technology
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• v.20 no.9
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• pp.1459-1474
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• 2006

The present study is focused on the development of the RIF (Representative Interactive Flamelet) model which can overcome the shortcomings of conventional approach based on the steady flamelet library. Due to the ability for interactively describing the transient behaviors of local flame structures with CFD solver, the RIF model can effectively account for the detailed mechanisms of $NO_x$ formation including thermal NO path, prompt and nitrous $NO_x$ formation, and reburning process by hydrocarbon radical without any ad-hoc procedure. The flamelet time of RIFs within a stationary turbulent flame may be thought to be Lagrangian flight time. In context with the RIF approach, this study adopts the Eulerian Particle Flamelet Model (EPFM) with mutiple flamelets which can realistically account for the spatial inhomogeneity of scalar dissipation rate. In order to systematically evaluate the capability of Eulerian particle flamelet model to predict the precise flame structure and NO formation in the multi-dimensional elliptic flames, two methanol bluffbody flames with two different injection velocities are chosen as the validation cases. Numerical results suggest that the present EPFM model has the predicative capability to realistically capture the essential features of flame structure and $NO_x$ formation in the bluff-body stabilized flames.

• Journal of the Korean Society of Combustion
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• v.21 no.4
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• pp.39-47
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• 2016

The aims of this research were to investigate combustion characteristics of lab-scale pressurized oxy-fuel combustion(POFC) system. In this study, the reactor, 800 mm long, was equipped with co-axial burner. Low calorific value syngas that is composed of mainly CO and $H_2$ was used as fuel whereas pure oxygen was used as an oxidant. Thermal heat input to the reactor varied from 2.6 kW to 6.1 kW. The reactor pressure also increases from atmospheric up to 15 bar. The results show that as the pressure increase, the temperature of reactor decreases on the whole in all cases. A significant temperature drop was observed especially at the bottom section of the reactor that exist flame. In addition, the flame instability increases as the pressure increases. Furthermore $NO_x$ emissions increases from atmospheric up to 2 bar. However beyond 2 bar, $NO_x$ emission reduces as pressure increases. Lastly $NO_2$ ratio in $NO_x$ also increases as pressure increases.

• Clean Technology
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• v.25 no.1
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• pp.74-80
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• 2019

Thermochemical treatment of sewage sludge is an energy-intensive process due to its high moisture content. To save the energy consumed during the process, the hydrothermal carbonization process for sewage sludge can be used to convert sewage sludge into clean solid fuel without pre-drying. This study is aimed to investigate co-firing characteristics of the hydrothermally carbonated sewage sludge (HCS) to a pulverized coal combustion system. The purpose of the measurement is to measure the pollutants produced during co-firing and combustion efficiency. The combustion system used in this study is a furnace with a down-firing swirl burner of a $80kW_{th}$ thermal input. Two sub-bituminous coals were used as a main fuel, and co-firing ratio of the sewage sludge was varied from 0% to 10% in a thermal basis. Experimental results show that $NO_x$ is 400 ~ 600 ppm, $SO_x$ is 600 ~ 700 ppm, and CO is less than 100 ppm. Experimental results show that stable combustion was achieved for high co-firing ratio of the HCS. Emission of $NO_x$ and $SO_x$ was decreased for higher co-firing ratio in spite of the higher nitrogen contents in the HCS. In addition, it was found that the pollutant emission is affected significantly by composition of the main fuel, regardless of the co-firing ratios.

• Journal of the Korean Society of Combustion
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• v.13 no.1
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• pp.10-16
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• 2008

Numerical simulations of freely propagating premixed flames burning mixtures of methane and chlorinated hydrocarbons in fuel are performed at atmospheric pressure in order to understand the effect of chlorinated hydrocarbons on the formation of nitrogen oxide. A detailed chemical reaction mechanism is used, the adopted scheme involving 89 gas-phase species and 1017 elementary forward reaction steps. Chlorine atoms available from chlorinated hydrocarbons inhibit the formation of nitrogen oxides by lowering the concentration of radical species. The reduction of NO emission index calculated with thermal or prompt NO mechanism is not linear and is probably related to the saturation effect as $CH_3Cl$ addition is increased, In the formation or consumption of nitrogen oxide, the $NO_2$ and NOCl reactions play an important role in lean flames while the HNO reactions do in rich flames. The molar ratio of Cl to H in fuel has an effect on the magnitude of NO emission index.

• ETRI Journal
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• v.26 no.3
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• pp.252-256
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• 2004

We formed silver nanocrystallites by the thermal decomposition of a $Ag^{+1}$-oleate complex, which was prepared by a reaction with $AgNO_{3}$ and sodium oleate in a water solution. The resulting monodispersed silver nanocrystallites were produced by controlling the temperature (290$^{\circ}$C). Transmission electron microscopic (TEM) images of the particles showed a 2-dimensional assembly of the particles with a diameter of $9.5{\pm}0.7nm$, demonstrating the uniformity of these nanocrystallites. An energy-dispersive X-ray (EDX) spectrum and X-ray diffraction (XRD) peaks of the nanocrystallites showed the highly crystalline nature of the silver structure. We analyzed the decomposition of the $Ag^{+1}$-oleate complex using a Thermo Gravimetric Analyzer (TGA) and observed the crystallization process using XRD.

• Transactions of the Korean hydrogen and new energy society
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• v.32 no.6
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• pp.573-584
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• 2021

Hydrogen is evaluated as one of the new energy sources that can overcome the limitations and pollution problems of conventional fossil fuels. Although hydrogen is CO₂-free, attention is required in NO_x emission and flame stability in order to use hydrogen in existing gas fuel system. However, use of electric grids is an unrealistic strategy for decarbonization for residential and commercial heating. Instead, use of H₂ that utilizes city gas grid is suggested as a reasonable alternative in terms of compatibility with existing systems, economic feasibility, and accessibility. In this study, the thermal efficiency and NO_x performance of the boiler according to the H₂ mixture ratio and vapor humidified ratio are reviewed for a humidified NG-H₂ boiler that vapor humidity to combustion air. Mixed fuel with H₂ (20%) is almost similar to NG in terms of efficiency, flame temperature, and pollution performance. Thus, it is expected to be directly compatible with the existing NG system. If the exhaust temperature of the H₂ boiler is lowered to around 60℃ at a humidified ratio of 15-20%, the NO_x emission concentration can be suppressed to about 5-10 ppm. The level of efficiency reaches 87% of the rated load efficiency, which is equivalent to the highest grade achievable.