• 한국연소학회지
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• 제12권1호
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• pp.28-37
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• 2007

Numerical study is conducted to grasp the flame structure and NO emissions for a wide range of oxy-fuel combustion (covering from air blown combustion to pure oxygen combustion) and for various mole fractions of recirculated $CO_2$ in $CH4-O_2/N_2/CO_2$ counterflow diffusion flames. Special concern is given to the difference of the flame structure and NO emissions between air blown combustion and oxy-fuel combustion w/o recirculated $CO_2$ and is also focused on chemical effects of recirculated $CO_2$. Air blown combustion and oxy-fuel combustion w/o recirculated $CO_2$ are shown to be considerably different in the flame structure and NO emissions. Modified fuel oxidation reaction pathways in oxygen-enriched combustion are provided in detail compared to those in air blown combustion w/o recirculated $CO_2$. The formation and destruction of NO through Fenimore and thermal mechanisms are also compared for air blown combustion and oxyegn-enriched combustion w/o recirculated $CO_2$, and the role of the recirculated $CO_2$ and its chemical effects are discussed. Importantly contributing reaction steps to the formation and destruction of NO are also estimated in oxygen-enriched combustion in comparison to air blown combustion.

• Journal of Mechanical Science and Technology
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• 제18권12호
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• pp.2303-2309
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• 2004

Flue gas recirculation (FGR) is a method widely adopted to control NOx in combustion system. The recirculated flue gas decreases flame temperature and reaction rate, resulting in the decrease in thermal NO production. Recently, it has been demonstrated that the recirculated flue gas in fuel stream, that is, the fuel induced recirculation (FIR), could enhance a much improved reduction in NOx per unit mass of recirculated gas, as compared to the conventional FGR in air. In the present study, the effect of FGR/FIR methods on NOx reduction in turbulent swirl flames by using N$_2$ and CO$_2$ as diluent gases to simulate flue gases. Results show that CO$_2$ dilution is more effective in NO reduction because of large temperature drop due to the larger specific heat of CO$_2$ compared to N$_2$ and FIR is more effective to reduce NO emission than FGR when the same recirculation ratio of dilution gas is used.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1499-1504
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• 2004

Flue gas recirculation (FGR) is a method used to control oxides of nitrogen ($NO_x$) in combustion system. The recirculated flue gases resulted in slow reaction and low flame temperatures, which in turn resulted in decreased thermal NO production. Recently, it has been demonstrated that introducing the recirculated flue gas in the fuel stream, that is, the fuel induced recirculation (FIR), resulted in a much greater reduction in $NO_x$ per unit mass of recirculated gas, as compared to introducing the flue gases in air. In the present study, the effect on $NO_x$ reduction in turbulent swirl flame in laboratory scale using FGR/FIR methods through the dilution using $N_2$ and $CO_2$. Results. show the $CO_2$ dilution is more effective $NO_x$ reduction methods because of large temperature drop due to the larger specific heat $CO_2$ compared to $N_2$. FIR is more effective to reduce $NO_x$ emission than FGR when the same recirculation ratio of dilution gas.

• Journal of Mechanical Science and Technology
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• 제19권6호
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• pp.1358-1365
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• 2005

Flue gas recirculation (FGR) is widely adopted to control NO emission in combustion systems. Recirculated flue gas decreases flame temperature and reaction rate, resulting in the decrease in thermal NO production. Recently, it has been demonstrated that the recirculated flue gas in fuel stream, that is, the fuel induced recirculation (FIR), could enhance much improved reduction in NO per unit mass of recirculated gas, as compared to conventional FGR in air. In the present study, the effect of dilution methods in air and fuel sides on NO reduction has been investigated numerically by using $N_2$ and $CO_2$ as diluent gases to simulate flue gases. Counterflow diffusion flames were studied in conjunction with the laminar flamelet model of turbulent flames. Results showed that $CO_2$ dilution was more effective in NO reduction because of large temperature drop due to the larger specific heat of $CO_2$ compared to $N_2$. Fuel dilution was more effective in reducing NO emission than air dilution when the same recirculation ratio of dilution gas was used by the increase in the nozzle exit velocity, thereby the stretch rate, with dilution gas added to fuel side.

• International Journal of Fluid Machinery and Systems
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• 제2권1호
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• pp.72-79
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• 2009

The effect of symmetric and asymmetric micro regenerative pump impellers on their pressure performance was studied. The shut off head of the pump with the symmetric impeller was about 2.5 times as that with the asymmetric impeller. The computation of the internal flow was performed to clarify the cause of the increase of the head. It was found that the contribution of the angular momentum supply was larger than that of shear stress for the head development in both cases. The larger head and momentum supply in the case of the symmetric impeller were caused by larger recirculated flow rate and larger angular momentum difference between the inlet and outlet to the impeller. The larger recirculated flow rate was caused by smaller pressure gradient in the direction of recirculated flow. The decrease of the circumferential velocity in the casing was attributed to the smaller local flow rate in the casing.

• 한국생산제조학회지
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• 제23권3호
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• pp.299-309
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• 2014

When using an automotive heating, ventilation, and air conditioning (HVAC) system, we can obtain fresh outside air while maintaining the interior vehicle temperature. In this study, a correction equation considering experimental data for automotive indoor air leakage is defined to simulate the ratio of fresh air to recirculated air in the automobile cabin. With this correction equation, numerical results are compared with experimental data and validated. The $CO_2$ concentration in the automotive cabin is evaluated by considering various boarding conditions and mass flow rates of the HVAC system. The $CO_2$ concentration model derived in this study is expected to be used to control the effective air conditioning and become a basic research tool for automotive air quality control system development.

• 대한기계학회논문집B
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• 제34권1호
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• pp.35-43
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• 2010

본 연구에서는 물을 재순환하는 이상적인 순산소 발전시스템의 작동조검 변화에 따른 성능해석을 수행하였다. 순산소 발전시스템에서의 터빈은 작동유체의 연소기 출구온도에 따라 증기터빈 또는 가스터빈을 사용할 수 있다. 본 연구의 순산소 사이클에서는 터빈입구온도를 가스터빈 수준으로 가정하였으며, 터빈출구의 과열도 증대를 위해 재열시스템을 채택하였다. 또한 터빈출력 증대를 위해 터빈출구 압력을 진공상태로 가정하였으며, 이에 따라 가스터빈 출구에서 추가의 팽창과정이 요구된다. 터빈입구온도, 압력비, 응축기압력과 같은 중요 작동 조건의 변화에 따른 시스템 성능이 해석되었으며, 시스템 구성 변화에 따른 효율 변화도 검토하였다. 결론에서는 성능을 최적화시키면서 고순도의 이산화탄소 회수가 가능한 순산소 발전시스템의 최적 작동조건을 제안하였다.

• 유기물자원화
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• 제20권2호
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• pp.66-75
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• 2012

본 연구에서는 폐기물매립지에서 매립가스 및 폐기물 안정화 촉진을 위한 메탄생성균 활성 침출수 재순환 공법의 효과를 평가하였다. 기존 매립공법(Lys-A), 침출수 재순환 공법(Lys-B), ASBR 전처리 후 침출수 재순환 공법(Lys-C, Lys-D)을 묘사하기 위해 4개의 모의매립조를 만들어 4년 이상 운영하였다. Lys-D는 전처리된 침출수의 재순환 양을 Lys-C의 2배로 하였다. 침출수 재순환 공법과 ASBR 전처리 후 침출수 재순환 공법의 경우 600일까지 메탄발생량이 증가하였으나 600일 이후에는 침출수 재순환이 메탄발생량 증가에 미치는 영향은 거의 없는 것으로 나타났다. 이는 분해 가능한 유기물질이 부족할 경우 침출수의 재순환 효과가 없기 때문으로 판단된다. Lys-C와 Lys-D는 폐기물의 안정화촉진 뿐만 아니라 누적메탄수율도 가장 높은 것으로 나타났다. 누적메탄수율의 경우 Lys-C(35.51 mL $CH_4/g$ VS)와 Lys-D(36.12 mL $CH_4/g$ VS)는 Lys-A(28.37 mL $CH_4/g$ VS)와 Lys-B(30.07 mL $CH_4/g$ VS)보나 높게 나타났다. 침출수 재순환율이 동일한 Lys-B와 Lys-C의 경우 Lys-C의 COD 농도가 Lys-B보다 더욱 빠르게 감소하였다. 이는 메탄생성균 활성 침출수에 의해 저해물질의 희석뿐만 아니라 메탄생성균의 존재에 기인하는 것으로 사료된다. 따라서 ASBR 전처리 후 침출수 재순환 공법은 폐기물 안정화 및 매립가스 증대에 가장 적합한 것으로 판단된다.

• 한국연소학회지
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• 제18권4호
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• pp.1-11
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• 2013

The oxy-fuel combustion is $CO_2$ capture technology that uses mixture of pure $O_2$ and recirculated exhaust as oxidizer. Currently some Oxy-fuel power plants demonstration project is underway in worldwide. Meanwhile research project for converting 125 MWe Young-Dong power plant to 100 MWe oxy-fuel power plants is progress. In this paper, 1 D process analytical approach was applied for conducting process design and operating parameters sensitivity analysis for oxy-fuel combustion of Young-Dong power plant. As a result, appropriate gas recirculation rates was 74.3% that in order to maintain normal rating superheater, reheater steam temperature and boiler heat transfer patterns. And boiler efficiency 85.0%, CPU inlet $CO_2$ mole concentration 71.34% was predicted for retrofitted boiler. The oxygen concentration in the secondary recycle gas is predicted as 27.1%. Meanwhile the oxygen concentration 22.4% and moisture concentration 5.3% predicted for primary recycle gas. As the primary and secondary gas recirculation increases, then heat absorption of the reheater is tends to increases whereas superheater side is decreased, and also the efficiency is tends to decrease, according to results of sensitivity analysis for operating parameters. In addition, the ambient air ingression have a tendency to lead to decline of efficiency for boiler as well as decline of $CO_2$ purity of CPU inlet.

• 청정기술
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• 제27권4호
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• pp.367-371
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• 2021

순산소 석탄 화력 발전 시스템은 CO₂ 가스 회수 및 저장 기술(CCS: carbon capture & storage)의 하나로 순산소와 재순환된 연소가스를 이용하여 석탄 연소를 수행하는 기술이다. 이는 이산화탄소와 질소가 혼합된 배출 가스를 생산하는 기존의 공기 연소 시스템과 달리 공기 중의 산소를 먼저 분리하여 생산된 순산소와 재순환된 연소 가스를 이용하여 석탄을 연소하면 이산화탄소와 질소를 분리하는 후처리 공정 없이 이산화탄소만으로 이루어진 배출 가스를 생성하여 이의 저장을 용이하게 하는 기술이다. 본 연구에서는 O₂/CO₂ 혼합 모의 가스를 이용하여 순산소 연소 시 발생되는 대기오염물질인 NO, SO₂의 생성 특성을 살펴보았다. 반응 온도를 900 ℃ ~ 1200 ℃, 산소 분율을 30% ~ 50%로 변화시키면서 실험한 결과 생성 가스 내 NO 및 SO₂의 농도는 반응 온도와 산소 분율이 증가할수록 증가하는 현상을 나타내었으며 CO₂의 분율도 증가하는 현상을 나타내었다. 순산소 연소에서 30% O₂/CO₂를 이용한 연소와 air 조건인 21% O₂/N₂ 연소에서 NO 발생을 비교한 결과 양쪽 모두 반응 온도에 따라서 NO 발생이 증가하게 되며 순산소 연소 조건에서 air 연소에 비하여 약 40 ~ 80 ppm까지 NO 발생이 낮아지는 현상을 나타내었다.