• 대한수학회보
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• 제51권1호
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• pp.67-76
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• 2014

Let X be a divergence-free vector field defined on a closed, connected Riemannian manifold. In this paper, we show the equivalence between the following conditions: ${\bullet}$ X is a divergence-free vector field satisfying the shadowing property. ${\bullet}$ X is a divergence-free vector field satisfying the Lipschitz shadowing property. ${\bullet}$ X is an expansive divergence-free vector field. ${\bullet}$ X has no singularities and is Anosov.

• 한국연소학회지
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• 제12권4호
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• pp.39-46
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• 2007

The technique of $NH_3$ SCR (selective catalytic reduction) assisted by plasma oxidation has been applied to a 2,000 cc diesel engine. The present combined $deNO_x$ process consists of two steps. The first step is that about 50% of emitted NO from the engine is oxidized to $NO_2$ in a plasma oxidation process. The second step is that NO and $NO_2$ are simultaneously reduced to $N_2$ in the $NH_3$ SCR process. The engine test results showed that the $deNO_x$ rates of the present combined process are higher than those of conventional SCR process by 20%. Such a high performance of the combined process is noticeable especially, when the exhaust temperature are relatively low, i.e., $170-220^{\circ}C$. To provide a feasibility of the present technique the effects of operating conditions, such as an electrical input energy, an exhaust gas temperature, an initial NO concentration, and the amount of hydrocarbon addition, were discussed.

• 한국자동차공학회논문집
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• 제20권1호
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• pp.20-27
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• 2012

The $NH_3$-SCR characteristics of $NO_X$ over a V-based catalyst are experimentally examined over a wide range of operating conditions, i.e., $170-590^{\circ}C$ and $30,000-50,000h^{-1}$, with a simulated diesel exhaust containing $NH_3$, NO, $NO_2$, $O_2$, $H_2O$, and $N_2$. The influences of the space velocity and oxygen concentration on the standard-SCR reaction are analyzed, and it is shown that the low space velocity and high oxygen concentration promote the SCR activity by ammonia. The best $deNO_X$ efficiency is obtained with a $NO_2/NO_X$ ratio of 0.5 because of an enhanced chemical activity induced by the fast-SCR reaction, while at the $NO_2/NO_X$ ratios above 0.5 the $deNO_x$ activity decreases due to the slow-SCR reaction. The oxidation of ammonia begins to take place at about $300^{\circ}C$ and the reaction products, such as $N_2$, NO, $NO_2$, $N_2O$, and $H_2O$, are produced by the undesirable oxidation reactions of ammonia, particularly at high temperatures above $450^{\circ}C$. Also, $NO_2$ decomposes to NO and $O_2$ at temperatures above $240^{\circ}C$. Therefore, $NO_2$ decomposition and ammonia oxidation reactions deteriorate significantly the SCR catalytic activity at high temperatures.

• 한국대기환경학회:학술대회논문집
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• 한국대기환경학회 1999년도 추계학술대회 논문집
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• pp.258-259
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• 1999

각종 산업공정에서 발생되는 SO$_2$를 처리하기 위하여 화력발전소와 같은 대형 배출업소에서는 주로 FGD 공법이 사용되고, 중소형의 배출업소에서는 건식 또는 반건식 공법 등이 많이 사용되고 있다. 또한 NO$_{x}$의 제거는 SCR 또는 SNCR 공법을 사용하고 있다.(중략)

• 한국응용과학기술학회지
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• 제34권1호
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• pp.183-188
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• 2017

본 연구는 중 소형 선박의 배가스에 포함되어 있는 황산화물 및 질소산화물을 처리하기 위한 습식 스크러버의 처리효율에 관한 내용이다. 실험은 질소산화물 기술문서($NO_X$ Technical Code)의 E3 모드에 준해서 진행하였다. 엔진에서 황산화물을 배출하기 위해서, 연료로 사용되는 경유에 ditertiarybutyldusulfide를 혼합하여 황 함유량을 높인 연료로 실험을 진행하였다. 배가스 내의 질소산화물의 대부분을 차지하는 NO가스는 $NO_2$로 산화시켜 습식 스크러버로 흡수하였으며, 황산화물인 $SO_2$는 세정액에 잘 흡수되어 100% 처리효율을 확인하였다.

• Journal of Microbiology
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• 제45권5호
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• pp.388-393
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• 2007

Citrus variegated chlorosis (CVC) is a disease of the sweet orange [Citrus sinensis (L.)], which is caused by Xylella fastidiosa subsp. pauca, a phytopathogenic bacterium that has been shown to infect all sweet orange cultivars. Sweet orange trees have been occasionally observed to be infected by Xylella fastidiosa without evidencing severe disease symptoms, whereas other trees in the same grove may exhibit severe disease symptoms. The principal endophytic bacterial species isolated from such CVC-asymptomatic citrus plants is Curtobacterium flaccumfaciens. The Madagascar periwinkle [Citrus sinensis (L.)] is a model plant which has been used to study X. fastidiosa in greenhouse environments. In order to characterize the interactions of X. fastidiosa and C. flaccumfaciens, periwinkle plants were inoculated separately with C. flaccumfaciens, X. fastidiosa, and both bacteria together. The number of flowers produced by the plants, the heights of the plants, and the exhibited disease symptoms were evaluated. PCR-primers for C. flaccumfaciens were designed in order to verify the presence of this endophytic bacterium in plant tissue, and to complement an existing assay for X. fastidiosa. These primers were capable of detecting C. flaccumfaciens in the periwinkle in the presence of X. fastidiosa. X. fastidiosa induced stunting and reduced the number of flowers produced by the periwinkle. When C. flaccumfaciens was inoculated together with X. fastidiosa, no stunting was observed. The number of flowers produced by our doubly- inoculated plants was an intermediate between the number produced by the plants inoculated with either of the bacteria separately. Our data indicate that C. flaccumfaciens interacted with X. fastidiosa in C. roseus, and reduced the severity of the disease symptoms induced by X. fastidiosa. Periwinkle is considered to be an excellent experimental system by which the interaction of C. flaccumfaciens and other endophytic bacteria with X. fastidiosa can be studied.

• 한국대기환경학회지
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• 제23권3호
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• pp.277-285
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• 2007

Porous cordierite beads, of which the average pore size was $130{\mu}m$ and porosity was about 80%, were prepared by the foaming method and then their application as support of the $Pt/{\gamma}-alumina$ catalyst for $NO_x$, reduction with propene was investigated. The pressure drop of a 2 mm porous beads filter was less than that of a 1 mm porous beads filter and the difference in pressure drop between these two increased as the flow rate increased. The catalytic activity of $Pt/{\gamma}-alumina$ washcoated on the porous bead was tested with varying Pt loading $(0.005{\sim}0.1g/cm^3),\;C_3H_6/NO$ mole ratio $(0.5{\sim}8)$, space velocity $(20,000{\sim}30,000h^{-1})$ and oxygen contents (1 and 8). Pt loading of $0.04g/cm^3$ showed the highest activity for $NO_x$ conversion. The $De-NO_x$, test was operated in the temperature range of $200{\sim}400^{\circ}C$ and the best operation temperature of the catalytic filter is about $250^{\circ}C$. As the C/N ratio increased, increase of the $NO_x$, conversion might result from the increase in exhaustion of the amount of oxygen by the reduction of hydrocarbon. $NO_x$ conversion at $20,000h^{-1}$ of space velocity shows a maximum 34% higher conversion than that at $30,000h^{-1}$. On condition that $O_2$ was 5%, space velocity was $20,000h^{-1}$ and the C/N ratio was 8, the $NO_x$ conversion exhibited a maximum of 40% at $250^{\circ}C$.

• 공업화학
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• 제24권3호
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• pp.333-336
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• 2013

산업현장에서 배출되는 저온($150{\sim}250^{\circ}C$)의 배기가스에 포함된 질소산화물($NO_x$)을 제거하기 위한 공정으로써 산화 촉매와 암모니아 SCR 공정을 복합시킨 fast SCR 탈질공정에 대한 실험적인 연구가 수행되었다. Fast SCR 탈질공정을 위해서는 산화촉매를 이용 NO를 $NO_2$로 전환하는 것이 요구된다. 산화촉매 부피(Oxidation Catalyst Volume, OCV)에 따른 NO 전환율을 실험적으로 확인하였다. OCV 563000 h, 375000 h, 281000 h 각 경우에 NO 전환율은 37% : 45% : 51%이었다. 온도에 따른 fast SCR 탈질효율은 $NO_2/NO_x$ 비율 45%일 때 가장 높았다. $NO_2/NO_x$ 비율 45%, 온도 $200{\sim}250^{\circ}C$ 및 공간속도 $10000{\sim}30000h^{-1}$에서 standard SCR과 fast SCR 탈질효율을 비교한 결과, standard SCR은 공간속도 에 따라 온도별로 차이를 보였으나 fast SCR은 차이를 보이지 않았다. Fast SCR 반응을 고려한 탈질운전에서 공간속도 $10000h^{-1}$에서의 촉매부피와 비교하여 공간속도 $30000h^{-1}$으로 운전할 경우, NH3 SCR 촉매부피를 50% 이상 줄일 수 있음을 알 수 있었다.

• 청정기술
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• 제24권3호
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• pp.212-220
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• 2018

순산소 연소기술은 화력발전에 적용 가능한 유망한 온실가스 감축 기술로 평가되고 있다. 본 연구는 환경적 관점에서 순환유동층을 활용한 순산소 연소조건에 로 내 탈황 및 탈질법을 적용하여 NO 및 $SO_2$의 거동을 살펴보는 한편, $SO_3$, $NH_3$, 그리고 $N_2O$의 발생 경향도 관측하였다. 이를 위해, 연소로 내 석회석 및 요소수를 투입하였다. 로 내 탈황법은 연소가스 내 $SO_2$ 농도를 ~403에서 ~41 ppm까지 저감하였다. 또한 $SO_3$ 형성의 주원료인 $SO_2$가 저감되면서 연소가스 내 $SO_3$ 농도도 ~3.9에서 ~1.4 ppm까지 감소되었다. 그러나 석회석 내 $CaCO_3$가 NO의 발생을 촉진하는 현상도 관측되었다. 연소가스 내 NO 농도는로 내 탈질법을 적용하여 ~26 - 34 ppm까지 저감되었다. 요소수 투입량 증가에 따라 연소가스 내 $NH_3$ 농도가 증가하여 최대 ~1.8 ppm으로 나타났으며, $N_2O$의 농도도 ~61에서 ~156 ppm까지 증가하였다. $N_2O$ 발생량 증가 현상은 요소수의 열분해 과정에서 생성된 HNCO가 $N_2O$로 전환되어 나타난다. 본 연구의 결과를 통해 로 내 연소가스 세정법을 적용할 경우 $NO_x$ 및 $SO_x$의 저감뿐만 아니라, 다른 오염물질의 발생에 대한 주의가 필요할 것으로 보인다.

• 공기청정기술
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• 제11권3호통권42호
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• pp.41-58
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• 1998