• Journal of the Korean Applied Science and Technology
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• v.36 no.1
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• pp.153-164
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• 2019

To develop a high performance SCR catalyst which has better specific surface area, lightness of weight and fast temperature response than those of existing commercial SCR catalyst, metal foam type SCR catalysts were prepared by washcoating with vanadium, tungsten and binder. The de-NOx performance test of the prepared catalysts was carried out on atmospheric micro-test unit at lab. scale according to space velocity variation and temperature change, and the characteristics of them were analyzed by Porosimeter, SEM(scanning electron microscope), EDX(energy dispersive x-ray spectrometer), ICP(inductively coupled plasma) and Stereomicroscope. The NOx reduction performance decreased as the space velocity increased and was found to be the best at 3.5 wt.% contents of the vanadium and tungsten. It was found that the larger amount of binder was added, the worse the NOx reduction performance was, which was considered to be that the number of active sites of the prepared catalyst surface was occupied by the binder. We found that the amount of binder to be added to prepare the catalyst should be properly controlled by the condition of coated catalyt surface.

• Applied Chemistry for Engineering
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• v.22 no.6
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• pp.658-663
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• 2011

The SNCR-SCR (selective non-catalytic reduction-selective catalytic reduction) hybrid system is an economical NOx removal system. In this study, the effect of the operating parameters of the SNCR-SCR hybrid system on NOx removal efficiency was investigated. When the SNCR reactor was operated at a temperature lower than the optimum temperature ($900{\sim}950^{\circ}C$), an additional NO removal is obtained basesd on the utilization of $NH_3$ slip. On the other hand, the SNCR reactor operated above the temperature resulted in no additional NO removal of SCR due to decomposition of $NH_3$. Therefore, the SNCR process should be operated at optimum temperature to obtain high NO removal efficiency and low $NH_3$ slip. Thus, it is important to adjust NSR (normalized stoichiometric ratio) so that $SR_{RES}$ can be maintained at an appropriate level.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.1
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• pp.1-9
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• 2015

To satisfy stricter $NO_X$ emission regulations for light- and heavy-duty diesel vehicles, a control algorithm needs to be developed based on a selective catalytic reaction (SCR) dynamics model for chemical reactions. This paper presents the development and validation of a SCR dynamics model through test rig experiments and MATLAB simulations. A nonlinear state space model is proposed based on the mass conservation law of chemical reactions in the SCR dynamics model. Experiments were performed on a test rig to evaluate the effects of the $NO_X$ and $NH_3$ concentrations, gas temperature, and space velocity on the $NO_X$ conversion efficiency for the urea-SCR system. The parameter values of the proposed SCR model were identified using the experimental datasets. Finally, a control-oriented model for an SCR system was developed and validated from the experimental data in a MATLAB simulation. The results of this study should contribute toward developing a closed-loop control strategy for $NO_X$ and $NH_3$ slip reduction in the urea-SCR system for an actual engine test bench.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.9
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• pp.474-481
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• 2018

The policy-making and technological development of eco-friendly automobiles designed to increase their supply is ongoing, but the internal combustion engine still accounts for approximately 95% of automobiles in use. To meet the stricter emission regulations of internal combustion engines based on fossil fuels, the proportion of after-treatments for vehicles and (ocean going) vessels is increasing continuously. As diesel engines have high power and good fuel economy in addition to less CO2 emissions, their market share is increasing not only in commercial vehicles, but also in passenger cars. Because of the characteristics of the diesel combustion, however, NOx is generated in localized high-temperature combustion regions, and particulates are formed in the zones of diffusion combustion. LNT and urea-SCR catalysts have been developed for the after-treatment of exhaust gas to reduce NOx in diesel vehicles. This study examined the effect of a containing promoter on SCR catalysts to cope with the severe exhaust gas regulation. The de-NOx performance of the Mn-SCR catalyst was the best, and the de-NOx performance was improved as the ion exchange rate between Mn ion and Zeolyst was good and the activation energy was low. The de-NOx performance of the 7Cu-15Ba/78Zeoyst catalyst was 32% at $200^{\circ}C$ and 30% at $500^{\circ}C$, and showed the highest performance. The NOx storage material of BaO loaded as a promoter was well dispersed in the Cu-SCR catalyst and the additional de-NOx performance of BaO was affected by the reduction reaction of the Cu-SCR catalyst. Among the three catalysts, the 7Cu-15Ba/Zeolyst SCR catalyst was resistant to thermal degradation. The same type of CuO due to thermal degradation migrates and agglomerates because BaO reduces the agglomeration of the main catalyst CuO particles.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.8
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• pp.96-101
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• 2012

A surge protection device of the metal oxide varistor(MOV) has been commonly used for preventing electrical damage in many electronic equipments. The MOV has a property that leakage current is increased and might be permanently damaged when it is exposed continuously to the electrical stresses such as lightening surges. In this paper, we propose a novel surge protection circuit adopting a silicon controlled rectifier(SCR) in the traditional protection circuits using the MOV device simultaneously. When lightning surges are injected to the proposed circuit, the MOV lets the surge pulses bypassing through the ground at first up to the level that SCR begins to operate. Above the threshold level of turning on the SCR, the SCR operates bypasses large surge currents to the ground. Proposed circuit was verified with a leakage current experiment and PSpice circuit simulations under the repeated surge injection environment.

• Journal of Power System Engineering
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• v.19 no.4
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• pp.30-35
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• 2015

The purpose of this study is to identify the low temperature performance and strength characteristics of V-based extruded homogeneous SCR. The extruded catalyst and the coated catalyst showed 50% and 27% of NOx conversion performance respectively at about $210^{\circ}C$ of catalyst temperature, so the extruded SCR was higher in de-NOx performance than the coated SCR especially at a low temperature zone. The compressive strength of the Enhanced Extrusion #1, in which the content of promoters such as silica, clay, glass fiber and binder was optimized, was a 120% improvement compared to the Extrusion#1 catalyst, higher than the coated SCR.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.5
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• pp.57-63
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• 2005

The effects of an urea injection at the exhaust pipe for a 4-cylinder DI(Direct Injection) diesel engine were investigated with the parameters such as urea-SCR(Selective Catalytic Reduction) and EGR system. The urea quantity was controlled by NOx quantity and MAF(Manifold Air Flow). The urea injection quantity can be controlled with the urea syringe pump, precisely. The effects of NOx reduction for the urea-SCR system were investigated with and without ECR engine, respectively. It was concluded that the SUF(Stoichiometric Urea Flow) is calculated and the NOx results are visualized with engine speed and load. Furthermore, the NOx map is made from this experimental results. It was suggested, therefore, that NOx reduction effects of the urea-SCR system without the EGR engine were better than that with the EGR engine except of low load and low speed.

• Journal of KIISE:Software and Applications
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• v.26 no.2
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• pp.251-262
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• 1999

SCR 방법론은 고 신뢰도를 요구하는 시스템 개발을 위해 사용되는 요구사항의 정형적 명세의 하나로 , 오랜 역사와 많은 응용 사례를 가지고 있다. 이 방법론에 따라 사용자가 요구사항을 명세했을 때 그것을 어떻게 정확하게 구현할 수 있는지가 중요한 문제가 된다. 본 논문에서는 SCR로 작성된 명제를 그 의미를 보전하는 구현언어로 자동으로 변환시키는 방법을 제시한다. SCR 명제가 가지는 자료흐름언어와의 유사성을 이용하기 위해, 구현언어로, 동기적 자료흐름 언어인 LUSTRE를 선택했고, 그 변환 과정을 제시했다. 제안한 방법의 유용성을 살피기 위해, SCR과 유사한 방법으로 작성된 월성 원자력 발전소의 제 2 정지 시스템의 일부분을 변환하는 실험을 수행, 그 결과를 비교하였다. 정형명제가 도입되어서 사용될 경우 본 연구는 개발의 전체 소요시간을 줄여줄 수 있고 좀 더 신뢰성 있는 결과물을 내는데 도움을 줄 수있다.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.1
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• pp.95-105
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• 2012

The selective catalytic reduction (SCR) system is a highly-effective aftertreatment device for NOx reduction of diesel engines. Generally, the ammonia ($NH_3$) was generated from reaction mechanism of SCR in the SCR system using the liquid urea as the reluctant. Therefore, the precise urea dosing control is a very important key for NOx and $NH_3$ slip reduction in the SCR system. This paper investigated NOx and $NH_3$ emission characteristics of urea-SCR dosing system based on model-based control algorithm in order to reduce NOx. In the map-based control algorithm, target amount of urea solution was determined by mass flow rate of exhaust gas obtained from engine rpm, torque and $O_2$ for feed-back control NOx concentration should be measured by NOx sensor. Moreover, this algorithm can not estimate $NH_3$ absorbed on the catalyst. Hence, the urea injection can be too rich or too lean. In this study, the model-based control algorithm was developed and evaluated on the numerical model describing physical and chemical phenomena in SCR system. One channel thermo-fluid model coupled with finely tuned chemical reaction model was applied to this control algorithm. The vehicle test was carried out by using map-based and model-based control algorithms in the NEDC mode in order to evaluate the performance of the model based control algorithm.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.6
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• pp.73-82
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• 2012

The main and side reactions of the three selective catalytic reduction (SCR) reactions with ammonia over a vanadium-based catalyst have been investigated using synthetic gas mixtures in the temperature range of $170{\sim}590^{\circ}C$. The three SCR reactions are standard SCR with pure NO, fast SCR with an equimolar mixture of NO and $NO_2$, and $NO_2$ SCR with pure $NO_2$. Vanadium based catalyst has no significant activity in NO oxidation to $NO_2$, while it has high activity for $NO_2$ decomposition at high temperatures. The selective catalytic oxidation of ammonia and the formation of nitrous oxide compete with the SCR reactions at the high temperatures. Water strongly inhibits the selective catalytic oxidation of ammonia and the formation of nitrous oxide, thus increasing the selectivity of the SCR reactions. However, the presence of water inhibits the SCR activity, most pronounced at low temperatures. In this study, the experimental results are analyzed by means of a dynamic one-dimensional isothermal heterogeneous plug-flow reactor (PFR) model according to the Eley-Rideal mechanism.