• Journal of ILASS-Korea
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• v.24 no.2
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• pp.51-57
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• 2019

In this study, the spray atomization characteristics of urea injector used in SCR system for construction machinery was analyzed, and the uniformity index at the front of mixer and NOx conversion efficiency were evaluated through numerical analysis. Spray visualization and droplet size/velocity measurement were performed and the measured results were used to verify the spray analysis model to calculate the uniformity index in the exhaust gas after-treatment system. For the flow analysis, STAR-CCM, a three-dimensional CFD, was used and the uniformity index of the SCR system at the front of the mixer was calculated using the droplet dissociation model and the wall collision model. Finally, the DeNOx performance for the average condition of the NRTC driving mode was calculated to understand the NOx conversion efficiency reflecting the exhaust gas temperature. The simulation results show that the uniformity index at the front of mixer was calculated as 0.862 and DeNOx efficiency was 75.9%.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.30-34
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• 1997

This paper Describe a modelling method for SCR(selective Catalytic reduction) system in refuse incineration plant. We consider the SCR system as a single input single output system. For modelling the SCR system, an auto regressive exogeneous(ARX) modelling method is used. In this case, we should design the white noise input for modelling and put it on the system as an input (.NH/sap2/.), and taken an outlet NOx as an output. From these two relations, we design the ARX model with 45 second delay time and transform to discrete system with 0.5 sampling time. Using the obtained SCR model, we simulate the SCR system to reduce the outlet NOx content by a conventional PID control method.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.1
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• pp.41-48
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• 2014

A urea-SCR system suffers from some issues associated with the ammonia slip phenomenon, which mainly occurs because of the shortage of evaporation and thermolysis time, and this makes it difficult to achieve an uniform distribution of injected urea. A numerical study was therefore performed by changing such various parameters as installed injector angle and application and angle of mixer to enhance evaporation and the mixing of urea water solution with exhaust gases. As a result, various parameters were found to affect the evaporation and mixing characteristics between exhaust gas and urea water solution, and their optimization is required. Finally, useful guidelines were suggested to achieve the optimum design of a urea-SCR injection system for improving the DeNOx performance and reducing ammonia slip.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.5
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• pp.85-90
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• 2010

As the environmental regulation of vehicle emission is strengthened, investigations for $NO_x$ and PM reduction strategies are popularly conducted. Two current available technologies for continuous $NO_x$ reduction onboard diesel vehicles are Selective Catalytic Reduction (SCR) using aqueous urea and lean $NO_x$ trap (LNT) catalysts. The experiments were conducted to investigate the $NO_x$ reduction performance of SCR system which can control the ratio of $NO/NO_2$, temperature and SV(space velocity), and the model gas was used which is similar to a diesel exhaust gas. The maximum reduction efficiency is indicated when the $NO:NO_2$ ratio is 1:1 and the SV is 30,000 $h^{-1}$ in $300^{\circ}C$. Generally, ammonia slip from SCR reactors are rooted to incomplete conversion of $NH_3$ over the SCR. In this research, slip was occurred in 6cases (except low SV and $NO:NO_2$ ratio is 1:1) after SCR. Among 6 case of slip occurrence, the maximum conversion efficiency is observed when SV is 60,000 $h^{-1}$ in $400^{\circ}C$.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.56 no.2
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• pp.183-192
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• 2020

This study conducted the experiment for the development of the low pressure type SCR system. The experimental equipment of SCR system was installed, which was widely used as the nitrogen oxides abatement system, and the demonstration experiment was conducted to see that it met the Tier III regulation according to the IMO NOx Technical Code. The SCR system demonstration experiment was divided into three stages: SCR system component operation test, engine parameter test by engine load, and NOx abatement performance and ammonia slip verification test. The final performance of the SCR system was verified through analysis of NOx abatement performance and ammonia slip test results for each load variation.

• Journal of the Korean Institute of Gas
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• v.23 no.3
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• pp.20-26
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• 2019

Selective catalytic reduction(SCR) method is widely used among various methods for reducing nitrogen oxides in combustion devices of coal power plant. In the present study, the computational fluid dynamic analysis was accomplished to derive the optimal shape of ammonia-dilution air mixing device in a ammonia injection grid. The distribution characteristics of flow and $NH_3$ concentration had been elucidated for the reference shape of ammonia mixing device(Case 1). In the mixing device of Case 1, it could be seen that $NH_3$ distribution was shifted to the wall opposite to the inlet of the ammonia injection pipe. For the improvement of $NH_3$ distribution, the case(Case 2) with closing one upper injection hole and 4 side injection holes, the case(Case 3) with installing horizontal plate at the upper of ammonia injection pipe, the case(Case 4) with installing horizontal plate and horizontal arc plate at he upper of ammonia injection pipe were investigated by analyzing flow and $NH_3$ concentration distributions. From the present study, it was found that the % RMS of $NH_3$ for Case 4 was 4.92%, which was the smallest value among four cases, and the range of $R_{NH3}$ also has the optimally uniform distribution, -10.82~8.34%.

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.11
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• pp.843-851
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• 2015

Among various ammonium salts and metal ammine chlorides used as solid materials for the sources of ammonia with solid SCR for lean NOx reduction, magnesium ammine chloride was taken up for study in this paper because of its ease of handling and safety. Lab-scale synthetic method of magnesium ammine chloride were studied for different durations, temperatures, and pressures with proper ammonia gas charged, as a respect of ammonia gas adsorption rate(%). To understand material characteristics for lab-made magnesium ammine chloride, DA, IC, FT-IR, XRD and SDT analyses were performed using the published data available in literature. From the analytical results, the water content in the lab-made magnesium ammine chloride can be determined. A new test procedure for water removal was proposed, by which the adsorption rate of lab-made sample was found to be approximately 100%.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.3
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• pp.1-11
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• 2014

The aim of this study is to investigate the effect of SCR reactor on the exhaust emissions characteristics in order to develop a urea-SCR aftertreatment system for reducing $NO_x$ emissions. The experiments are conducted by using a flue tube LPG steam boiler with the urea-SCR aftertreatment system. The urea-SCR aftertreatment system utilizes the ammonia converted from 17% aqueous urea solution injected in front of SCR catalyst as a reducing agent for reducing $NO_x$ emissions. The equivalence ratio, urea injection amount, ammonia slip and $NO_x$ conversion efficiency relative to boiler load are applied to discuss the experimental results. In this experiment, the average equivalence ratio is calculated by changing only the fuel consumption rate while the intake air amount is constantly fixed at $25,957.11cm^3/sec$. The average equivalence ratios are 1.38, 1.11, 0.81 and 0.57 when boiler loads are 100, 80, 60 and 40%. The $NO_x$ conversion efficiency is raised with increasing urea injection amount, and $NH_3$ slip is also boosted at the same time. Consequently, the $NO_x$ conversion efficiency relative to boiler load should be examined in combination with urea injection amount and $NH_3$ slip. The results are calculated by 89, 85, 77 and 79% for the boiler loads of 100, 80, 60 and 40%. The appropriate amount of urea injection for the respective boiler load can be not discussed by only $NO_x$ emissions, and should be determined by considering the $NO_x$ conversion efficiency, $NH_3$ slip and reactive activation temperature simultaneously. In this study, the urea amounts of 230, 235, 233 and 231 mg/min are injected at the boiler loads of 100, 80, 60 and 40%, and the final $NH_3$ slips are measured by 8.48, 5.58, 11.97 and 11.34 ppm at the same conditions. THC emission is affected by the SCR reactor under other experimental conditions except 100% engine load, and CO emission at only 40% engine load. The rest of exhaust emissions are not affected by the SCR reactor under all experimental conditions.

• Korean Chemical Engineering Research
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• v.49 no.1
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• pp.89-94
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• 2011

DeNOx characteristics of hybrid SNCR-SCR process have been investigated in a pilot scale flow reactor. DeNOx efficiency of SNCR reaction was about 80% at $970^{\circ}C$ and hybrid SNCR-SCR process showed 92% at $940^{\circ}C$ with NSR = 2.0. Compared to SNCR process alone, hybrid SNCR-SCR process was more effective at cool side, which is lower than $940{^{\circ}C}$. It should be also noted that ammonia slip from hybrid SNCR-SCR process was below 1ppm at the condition of higher space velocity and the required catalyst volume can be decreased to 2/3 of SCR process. Key factors for DeNOx efficiency of hybrid SNCR-SCR process were found to be $NH_3$ concentration and NOx selectivity of urea injected in SNCR process.