• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.14 no.2
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• pp.89-95
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• 1978

A SCR static breaker was studied on the Resistive and inductive load, then on the overload break circuit using operational Amplifier. In this paper, the principal circuit required for forced commutation was voltage commutation by the introduction of a parallel Capacitor. The results obtained are follows; 1. In thecondition that the tima constant of R-C circuit is larger than the turn off time of SCR, the breaker has low transient phenomena and no recovery vol age. 2. By using OP Amplifier on the load circuit, overcurrent trip point will be able to adjust to the wide range of over current. 3. In the over current qrcuit, the power loss was reduced remarkably.

• Journal of Environmental Science International
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• v.22 no.11
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• pp.1481-1498
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• 2013

The SCR (selective catalytic reduction) system is highly-effective technique for NOx reduction from exhaust gases. In this study, the effects of the direction and size of nozzle and the ammonia injection concentration on the performance of SCR system are analyzed by using the computational fluid dynamics method. When the nozzle is arranged in zigzaged direction which is normal to exhausted gas flow, it is shown that the uniformity of gas flow and the NH3/NO molar ratio is improved remarkably. With the change of the ammonia injection concentration from 0.2 vol%(wet) to 1.0 vol%(wet), the uniformity of gas flow shows a good results. As the size of nozzle diameter changes from 6 mm to 12 mm, the uniformity of gas flow is maintained well. It is shown that the uniformity of the $NH_3/NO$ molar ratio becomes better with decreasing the ammonia injection concentration and the size of nozzle diameter.

• Environmental Engineering Research
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• v.20 no.4
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• pp.397-402
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• 2015

SCR has been popularly approved as one of the most effective means for NOx emission control in heavy-duty and medium-duty vehicles currently. However, high urea dosing would lead to ammonia slip. And $NH_3$ sensor for vehicle emission applications has not been popularly used in real applications. This paper presents experimental studies on the diesel engine urea-SCR system by using a double NOx sensor system that is arranged in the downstream of the SCR catalyst based on ammonia cross-sensitivity. It was shown that the NOx conversion efficiency rised as $NH_3/NOx$ increases and the ammonia slip started from the $NH_3/NOx$ equal to 1.4. The increase of temperature caused high improvement of the SCR reaction rate while the space velocity had no obvious change. The ammonia slip was in advance as catalyst temperature or space velocity increase and the ammonia storage reduced as catalyst temperature or space velocity increase. The NOx real-time conversion efficiency rised as the ammonia accumulative storage increase and reached the maximum value gradually.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.2
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• pp.70-77
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• 2012

The selective catalytic reduction(SCR) system used to reduce NOx in diesel engines requires an NO/$NO_2$ ratio of about 1 in exhaust emissions to realize the fast SCR mode at temperatures lower than $300^{\circ}C$. This study investigated the characteristics of a plasma system as a pre-active apparatus for the fast SCR reaction mode of an SCR system. Plasma was generated by the pulse corona discharge(PCD) method with a four-channel wire-cylinder reactor. This study showed that plasma was easily generated in the exhaust gas by the PCD system, and the peak voltage of the normal state condition for plasma generation was generally 12 kV. The PCD system easily converted NO into $NO_2$ at lower temperatures and the NO/$NO_2$ conversion ratio increased with the discharge current for plasma generation. But the PCD system could not convert NO into $NO_2$ at higher engine speeds and higher engine loads due to the lack of oxygen in exhaust gas. The PCD system also activated the diesel oxidation catalysts(DOC) system to reduce CO emissions.

• Journal of ILASS-Korea
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• v.23 no.2
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• pp.74-80
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• 2018

Emission characteristics of regulated pollutants (CO, NOx, HC and PM) and hazardous air pollutants (HAPs) from diesel heavy duty trucks equipped with EGR+pDPF and SCR for Euro 5 emission standards were investigated using a chassis dynamometer. In the case of regulated pollutants, diesel heavy duty trucks with EGR+pDPF emitted 79% less CO than those with SCR. Also, those with the SCR emitted 36% less NOx than those with the EGR+pDPF. The results of VOCs have show that alkanes emissions for heavy duty trucks with the EGR+pDPF and the SCR have been higher than alkenes, cycloalkanes and aromatics. In the case of individual VOCs, the highest of propene emissions for 11.3~16.1% occupied. For aromatics group, benzene emissions are the highest percentage for 4.4~15.5%. In the future, the results of present study will provide basic data to set up HAPs emissions inventory for mobile source.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.97.1-97.1
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• 2011

Dimethyl ether (DME) is an attractive fuel as a hydrogen carrier for mobile PEMFC applications. However, its reforming technologies are rarely studied especially by using autothermal reforming (ATR) method. This work explored the impact of operating conditions to the performance of DME ATR. Temperature, Steam to carbon ratio(SCR), Oxygen to carbon ratio(OCR) and Gas hourly space velocity(GHSV) were considered as the operating conditions. As results, conversion efficiency was increased as the temperature increased, but saturated around $700^{\circ}C$. There was no significant effect of SCR on conversion efficiency, but high SCR led reactions in endothermic manner. High OCR substantially suppressed conversion efficiency, but it helped to sustain the temperature by stimulating exothermic reactions. Conversion efficiency was decreased as GHSV increased. The optimized operating conditions was suggested: $700^{\circ}C$, SCR of 1.5, OCR of 0.45 and GHSV below 15000/h and conversion efficiency was ~85% at the conditions.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2874-2879
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• 2008

The Selective catalytic reduction(SCR) system is a highly-effective device of $NO_x$ reduction for diesel engines. Generally, the ammonia($NH_3$) generated from a liquid urea-water solution is used for the reductant. The ideal ratio of $NH_3$ molecules to $NO_x$ molecules is 1:1 based on $NH_3$ consumption and having $NH_3$ available for reaction of all of the exhaust $NO_x$. However, under the too low and too high temperature condition, the $NO_x$ reduction efficiency becomes lower, due to temperature window. And space velocity also affects to $NO_x$ conversion efficiency. This paper reviews a laboratory study to evaluate the effects of $NO_x$ and $NH_3$ concentrations, gas temperature and space velocity on the $NO_x$ conversion efficiency of the SCR system. The maximum conversion efficiency of $NO_x$ was indicated when the $NH_3$ to $NO_x$ ratio was 1.2 and the space velocity was $60,000\;h^{-1}$. The results of this paper contribute to improve overall $NO_x$ reduction efficiency and $NH_3$ slip.

• Korean Chemical Engineering Research
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• v.47 no.1
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• pp.111-118
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• 2009

A hybrid SNCR/SCR plant was designed and manufactured, and experimented on the SNCR process in the first step to investigate the optimum operation conditions of SNCR, with the equivalence ratio of the reducing agent(NSR, 0.5~5.0), reaction temperature($850{\sim}1,100^{\circ}C$), nozzle type(wall nozzle, pipe nozzle), and nozzle position as variables. In the case of wall nozzles, the NOx reduction efficiency rapidly increased to 87% at 2.5 NSR and slowed down after this. Compared to the upward spray from the pipe nozzle, wall nozzles have narrower range of applicable reaction temperature. In the case of pipe nozzles, it rapidly increased to 77% at 1.5 NSR. But the pipe nozzle downward had no NOx reduction efficiency; on the contrary, NOx increased. When the reducing agent was sprayed upward from a pipe nozzle, the NOx reduction efficiency was 50~75% in the range of 0.5~1.5 NSR, and the NOx reduction efficiency was constant without fluctuations even in the change of reaction temperature from 890 to $1,000^{\circ}C$. When 5% urea solution was sprayed upward from the pipe nozzle, 200 ppm NOx decreased to approximately 60 ppm at 1.2 NSR, and the non-reacted $NH_3$ was 50~100 ppm. In this condition, we expect over 90% NOx reduction efficiency without additional supply of $NH_3$ to SCR at the back of SNCR.

• Journal of the Korean Society of Food Science and Nutrition
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• v.35 no.1
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• pp.115-120
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• 2006

To convert the soybean curd residue (SCR) to functional food ingredient, alkaline fermentation of SCR was performed by Bacillus firmus NA-1 and Bacillus subtilis GT-D for 22 hr at $42^{\circ}C$. The micronized full-fat soy flour (MFS) was fortified to reduce the moisture content as well as to supply protein source. The mucilage and flavor productions in the fermented SCR were enhanced by the fortification of $20\%$ MFS. The peptide production from the SCR fermented with B. subtilis GT-D substantially increased when judged by the detectable amount of tyrosine $(480\;mg\%)$. The production of fibrinolytic enzyme was increased by the fermentation for 22 hr, indicating the relative activity of $62\%$ (B. firmus NA-1) and $47\%$ (B. subtilis GT-D), respectively. The SCR fermented by B. firmus NA-1 and B. subtilis GT-D indicated the consistency of $1.95\;Pa{\cdot}s^n\;and\;0.21\;Pa{\cdot}s^n$, respectively. After freeze-drying, the protease activity (615 unit/g) and a-amylase activity (180 unit/g) were obtained from SCR fermented by Bacillus firmus NA-1 and Bacillus subtilis GT-D, respectively.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.9
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• pp.862-869
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• 2010

Numerical analysis was done to evaluate the gas flow distribution in small scale SCR system which has $2.4{\times}2.4{\times}3.1\;m^3$ in volume and 25,300 Sm3/hr in flue gas flow capacity. Various types of baffles proposed for controlling the flow uniformity were evaluated by the CFD analysis to find the optimal geometry of the baffle in the SCR system. By installing baffles in the SCR system, the RMS (%) value was raised up to 6.2% compared with the baffle-uninstalled state. The effect of baffle thicknesses on the RMS (%) value was not shown within 0 and 8 mm in thickness, but the RMS (%) value was raised by 2.5% in 10 mm of baffles thickness, which causes the unstability in flow. By comparison between the shape of baffles, it is known that the lattice type baffle has better performance in controlling the flow uniformity than the circular truncated cone type baffle or mixer type baffle. RMS (%) values have more that 10% difference according to the shape of baffle type.