• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.5
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• pp.213-218
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• 2014

An investigation of the influence of $WO_3$ addition with different precursors and preparation methods on the phase formation and selective catalytic reduction (SCR) efficiency of anatase-$TiO_2$ powders has been carried out. An anatase-$TiO_2$ synthesized by precipitation process was used as a catalyst support. For $WO_3(10wt%)/TiO_2$, the W loading to the $TiO_2$ support led to the lower in anatase to rutile transition temperature to ${\sim}900^{\circ}C$ from $1200^{\circ}C$ of the $TiO_2$ support alone. In the case of $WO_3(10wt%)/TiO_2$ SCR powders obtained from a wet process with ammonium meta-tungstate (AMT) precursor, the highest $NO_X$ conversion efficiency was achieved at $450^{\circ}C$ remaining high efficiency at $500^{\circ}C$, while the same composition prepared from a dry process with $WO_3$ addition showed the lowered efficiency with temperature after reaching the efficiency maximum at $350^{\circ}C$. The same tendency has been found that the $V_2O_5(5wt%)-WO_3(10wt%)/TiO_2$ SCR powders obtained from the wet process with AMT precursor has shown the superior $NO_X$ conversion efficiency over 90 % in a wider temperature range of $300{\sim}500^{\circ}C$.

• 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.

• Journal of the Korea Society of Computer and Information
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• v.22 no.1
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• pp.63-69
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• 2017

In this paper, we propose a method to optimize the geometry and installation position of the mixer in the selective catalytic reduction (SCR) system by computational fluid dynamic(CFD). Using the commercial CFD software of CFD-ACE+, the flow dynamics of the flue gas was numerically analyzed for improving the injection uniformity of the reduction agent. Numerical analysis of the mixed gas heat flow into the upstream side of the primary SCR catalyst layer was performed when the denitrification facility was operated. The characteristics such as the flow rate, temperature, pressure loss and ammonia concentration of the mixed gas consisting of the flue gas and the ammonia reducing gas were examined at the upstream of the catalyst layer of SCR. The temperature difference on the surface of the catalyst layer is very small compared to the flow rate of the exhaust gas, and the temperature difference caused by the reducing gas hardly occurs because the flow rate of the reducing gas is very small. When the mixed gas is introduced into the SCR reactor, there is a slight tendency toward one wall. When the gas passes through the catalyst layer having a large pressure loss, the flow angle of the exhaust gas changes because the direction of the exhaust gas changes toward a smaller flow. Based on the uniformity of the flow rate of the mixed gas calculated at the SCR, it is judged that the position of the test port reflected in the design is proper.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2000.11a
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• pp.257-258
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• 2000

산업 발전에 따른 대기오염물질의 배출로 인한 대기오염은 날로 심각해지고 있다. 대기오염물질중 NO는 제어에 대한 관심이 높아지고 있는데 NOx의 배연 처리 기술중 가장 보편화되어 있는 기술은 선택적 촉매 환원법(selective catalytic reduction, SCR)이다. 그중 암모니아(NH$_3$)를 환원제로 사용한 SCR법이 가장 널리 사용되고 있는데 이러한 NH$_3$에 의한 탈질공정은 미반응 NH$_3$의 배출, 경제성 등의 문제점이 있어 다른 환원제 즉 urea나 hydrocarbon을 사용하는 탈질기술의 개발이 요구되고 있으며, 특히 hydrocarbon이나 alcohol 계열을 이용한 SCR법에 대한 연구가 활발하게 진행되고 있다. (중략)

• Journal of Korean Society for Atmospheric Environment
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• v.20 no.2
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• pp.185-193
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• 2004

A catalyst with CuO ceramic filter for simultaneous treatment of dust and HAP was prepared and characterized. Catalytic ceramic filter can not only potentially achieve the substantial savings in energy but provide with effective optimization and integration of process for simultaneous removal of SO$_2$, NO$_{x}$ and particulates from flue gases. Catalytic ceramic filters remove simultaneously particulates on exterior surface of filters and reduce NO to $N_2$ and $H_2O$ by SCR (Selective Catalytic Reduction) process. Preparation of catalyst impregnated ceramic filter with disk shape (Ψ 50) follow the processing of alumino-silicate ceramic filter, support impregnation and catalyst impregnation (copper oxide). Preparation routes of alumino-silicate catalyst carrier suitable for production of catalytic filters practically were studied and developed using the sol-gel and colloidal processing, homogeneous precipitation and impregnation method. Characterization of the catalyst, catalyst carrier catalytic filter materials have been performed the using various techniques such as BET, XRD, TGA, SEM. Combination of the sol-gel and colloidal processing and impregnation method is recommended to prepare catalyst carriers economically for catalytic filter applications.s.

• 한국연소학회:학술대회논문집
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• 2006.04a
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• pp.49-54
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• 2006

The present study conducted a numerical modeling on the diesel SCR (selective catalytic reduction) system using ammonia as a reductant over vanadium-based catalysts $(V_2O_5-WO_3/TiO_2)$. Transient modeling for ammonia adsorption/desorption on the catalyst surface was firstly carried out, and then the SCR reaction was modeled considering for it. In the current catalytic reaction model, we extended the pure chemical kinetic model based on laboratory-scale powdered-phase catalyst experiments to the chemico-physical one applicable to realistic commercial SCR reactors. To simulate multi-dimensional heat and mass transfer phenomena, the SCR reactor was modeled in two dimensional, axisymmetric domain using porous medium approach. Also, since diesel engines operate in transient mode, the present study employed an unsteady model. In addition, throughout simulations using the developed code, effects of space velocity on the DeNOx performance were investigated.

• Applied Chemistry for Engineering
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• v.16 no.3
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• pp.328-336
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• 2005

In order to remove the NO contained in exhaust gas by the non-selective catalyst reduction method, the catalysts were prepared by varing the loading amount of Ag and V into ${\gamma}-Al_2O_3$. The conversion of $NO_x$ using the prepared catalysts was studied by varying the temperatures, $O_2$ concentrations and $SO_2$ concentrations using. The influence of the catalyst structure on $NO_x$ conversion was studied through the analysis of the physical properties of the prepared catalysts. In the case of $AgV/{\gamma}-Al_2O_3$ catalyst, the $NO_x$ conversion was lower than that of $Ag/{\gamma}-Al_2O_3$ at higher temperatures but higher than that of $Ag/{\gamma}-Al_2O_3$ at lower temperatures. Even though $SO_2$ was contained in the reaction gas, the $NO_x$ conversion did not decrease. Based on the analysis including XRD, XPS, TPR, and UV-Vis DRS before and after the experiments, the experimental results were examined. The results indicated that, $NO_x$ conversion decreased at higher temperatures since Ag oxide could not be maintained well due to the addition of V, whereas it increased at temperatures lower than $300^{\circ}C$ due to the catalytic action of V.

• Environmental Engineering Research
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• v.10 no.1
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• pp.31-37
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• 2005

The selective catalytic experiments using both sulfated/sulfur-free titania and V2O5/TiO2 catalysts have been conducted for NO reduction by NH3 in a packed-bed, down-flow reactor. The sulfated and vanadia loaded titania exhibited higher activity for NO removal than the sulfur-free catalysts, where > 90% NO removal was achieved over the sulfated V2O5/TiO2 catalyst between 280∼500 C. The surface structure of vanadia species on the catalyst surface played a critical role in the high performance of catalysts in which the existence of monomeric/polymeric vanadate is revealed by Raman spectra studies. Water vapor and SO2 were added to the reacting system for the catalyst deactivation tests. At higher temperatures (T ≥ 350 C), little deactivation was observed over the sulfated V2O5/TiO2 catalysts, showing good durability against SO2 and water vapor, which is compared with deactivation at lower temperatures.

• KEPCO Journal on Electric Power and Energy
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• v.2 no.3
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• pp.437-445
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• 2016

This paper discussed the effect of ammonia concentration adsorbed on fly ash for the ammonia emission as AAFA (Ammonia Adsorbed Fly Ash) produced from coal fired plants due to operation of NOx reduction technologies was landfilled with distilled or sea water at closed and open systems, respectively. Ammonia bisulfate and sulfates adsorbed on fly ash is highly water soluble. The pH of ammonium bisulfate and sulfate solution had significant effect on ammonia odor emission. The effect of temperature on ammonia odor emission from mixture was less than pH, the rate of ammonia emission increased with increased temperature when the pH conditions were kept at constant. Since AAFA increases the pH of solution substantially, $NH_3$ in the ash can release the ammonia order unless it is present at low concentration. $NH_4{^+}$ ion is unstable in fly ash and water mixtures of high pH at open system, which is changed to nitrite or nitrate and then released as ammonia gas. The proper conditions for < 20 ppm of ammonia concentration released from the AAFAs landfilled in ash pond were explored using an open system with sea water. It was therefore proposed that optimal operation to collect AAFA of less than 168 ppm ammonia at the electrostatic precipitator were controlled to ammonia slip with less than 5 ppm at SCR/SNCR installations, and, ammonia odor released from mixture of fly ash of 168 ppm ammonia with sea water under open system has about 20 ppm.

• 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.