• Journal of Industrial Technology
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• v.18
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• pp.249-258
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• 1998

In this paper, we investigated the post-combustion removal of nitrogen oxide($NO_x$) and sulfur oxide($SO_x$) which is based on the gas to particle conversion process by the pulsed corona discharge. Under normal pressure, the pulsed corona discharge produces the energetic free electrons which dissociate gas molecules to form the active radicals. These radicals cause the chemical reactions that convert $SO_x$ and $NO_x$ into acid mists and these mists react with $NH_3$ to form solid particles. Those particles can be removed from the gas stream by conventional devices such as electrostatic precipitator or bag filter. The reactor geometry was coaxial with an inner wire discharge electrode and an outer ground electrode wrapped on a glass tube. The simulated flue gas with $SO_x$ and $NO_x$ was used in the experiment. The corona discharge reactor was more efficient in removing $SO_x$ and $NO_x$ by adding $NH_3$ and $H_2O$ in the gas stream. We also measured the removal efficiency of $SO_x$ and $NO_x$ in a cylinder type corona discharge reactor and obtained more than 90 % of removal efficiency in these experimental conditions. The effects of process variables such as the inlet concentrations of $SO_x$, $NH_3$ and $H_2O$, residence time, pulse frequencies and applied voltages were investigated.

• 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 $400^{\circ}C$.

• 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.

• International Journal of Automotive Technology
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• v.2 no.2
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• pp.77-83
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• 2001

Effect of ethene on the $DeNO_X$ conversion process in a simulated diesel engine operating conditions was investigated experimentally and theoretically. With the addition of even a small amount of ethene the NO to $NO_2$ conversion enhances greatly. The energy required to convert one NO molecule is 27 eV with 250 ppm ethene added, while 137 eV without ethene at 473 K. The effect of energy density, temperature, and the initial concentrations of ethene and oxygen are also discussed and the results show that the increase of the mentioned parameters lead to the promotion of NO oxidation. A kinetic model used in this study shows good agreement with the experimental result. Byproducts like formaldehyde ($CH_2$ 0) and methyl nitrite ($CH_3$ ONO) predicted by model calculation are broken up into CO and $H_2O$ eventually when high energy is delivered to the gas mixture. Sensitivity analysis shows that the main reactions of NO oxidation when ethene is added we: $HO_2+ NO \arrow NO_2 + OH, RO_2 + NO \arrow NO_2 + RO$, where R is a hydrocarbon radical. Also the direct oxidizing reaction of NO with O cannot be neglected.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.3
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• pp.345-351
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• 2016

This study was carried out to determine an optimal lean $NO_x$ trap (LNT) regeneration condition based on a $NO_x$ storage fraction. The LNT regeneration was performed by an in-cylinder post fuel injection method. A $NO_x$ storage fraction is defined by the ratio of current cumulated $NO_x$ amount in the LNT to the $NO_x$ storage capacity: 0 means empty and 1 fully loaded. In this study five engine operating conditions were chosen to represent the New European Driving Cycle. With various $NO_x$ storage fractions each engine operating condition, the LNT regeneration was executed and then $NO_x$ conversion efficiency, additional fuel consumption, CO and THC slip, peak catalyst temperature were measured. The results showed that there exist an optimal condition to regenerate the LNT, eg. 1500 rpm 6 bar BMEP with below 0.7 $NO_x$ storage fraction in this experimental constraint.

• Analytical Science and Technology
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• v.18 no.2
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• pp.139-146
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• 2005

Removal of NO contained in automobile exhaust gas was accomplished by the non-selective catalyst reduction method. The catalysts were prepared through loading of a specific amount of Ag into ${\gamma}-Al_2O_3$. The conversion of $NO_x$ was studied by varying the temperatures, $O_2$ concentrations and $SO_2$ concentrations for the prepared catalysts. The influence of the structure of catalyst to $NO_x$ conversion was followed through the analysis of the physical properties of the prepared catalysts. Experiments were conducted on each of the catalysts by varying the reaction conditions to find an optimum condition. The catalyst $Ag/{\gamma}-Al_2O_3$ shows a highest $NO_x$ conversion when the Ag content was 2 wt% and a reaction temperature of about $450^{\circ}C$. and after conducting the experiments, samples of before and after experiments analyzed using XRD, XPS, TPR, and UV-Vis DRS experiments. The result indicated that when Ag oxide content could not be maintained well at high temperatures $NO_x$ conversion decreased.

• Journal of Powder Materials
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• v.5 no.4
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• pp.273-278
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• 1998

$De-NO_x$ transition metals(Cu, Co)/ZSM-5 catalyst was made by mechanical alloying method, and their microstructures and repeated usage-properties were investigated by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The conversions ability of NO in the catalyst was measured. A part of ZSM-5 in CO/ZSM-5 composite powders was amorphous and the amorphous phase became less stable with increasing Co content. Conversion ability of NO in 10Cu/ZSM-5 powders decreased from 89% to 12% and that in 10Co/ZSM-5 decreased from 22% to 17% by 7 times conversion tests.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.1
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• pp.169-178
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• 2000

Perovskite oxide catalysts doped on porous alumina beads are prepared in a citric acid solution. To investigate the applicability of the catalysts to the hot gas cleanup, a series of experiments on the reduction characteristics of $NO_x$ by CO as a reducing agent are carried out in a packed bed reactor containing the catalysts. Parameters tested are the operating temperature and $CO/NO_x$ molar ratio. It is found that mixed complex oxides of $La_{0.5}Sr_{0.5}CoO_3$, $SrAl_{12}O_{19}$ and $LaAl_{11}O_{18}$ are uniformly distributed on the alumina beads. The conversion efficiency of $NO_x$ by CO sharply increases with the operating temperature up to $700^{\circ}C$ and then approaches 100% when $CO/NO_x$ molar ratio is greater than 1.0. The conversion efficiency of $NO_x$ is maintained by over 98% during a continuous operation for 23 hours at $800^{\circ}C$ and space velocity of $10700hr^{-1}$.

• Clean Technology
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• v.21 no.3
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• pp.184-190
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• 2015

Most of LNT catalysts use noble metals such as Pt for low temperature NO_x oxidation but there is an economic weakness. For the purpose of overcoming this, this study is to develop DeNO_x catalyst for LNT excluding PGM (platinum group metal) such as Pt, Pd, Rh, etc. To do so, Al/Co/Ni catalyst selected as a preliminary test is used to study fundamental property and NO_x’s conversion according to calcined temperature. Ultimately, that is, Al/Co/Ni mixed metal oxide which does not use PGM is selected and physicochemical characterization is performed by way of XRD, EDS, SEM, BET and ramp test and NO_x conversion is also analyzed. This study shows that all samples consist of mixed oxides of spinel structure of Co₂AlO₄ and NiAl₂O₄ and have enough pore volume and size for redox. But as a result of NH₃-TPD test, it is desired that calcined temperature needs to be maintained at 700 ℃ or lower. Also only samples which are processed under 500 ℃ satisfied NO and NO_x conversion simultaneously through ramp test. Based on this study’s results, optimum calcined temperature for Al/Co/Ni=1.0/2.5/0.3 mixed metal oxide catalyst is 500 ℃.

• Journal of the Korean Applied Science and Technology
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• v.22 no.2
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• pp.168-174
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• 2005

Aluminum tri-butoxide was mixed with the water/ethanol solution and then chloroplatinic acid was added to the solution. The solution was dried at $100^{\circ}C$ for 15hrs to remove the solvent and water then it was calcined at $500^{\circ}C$. The catalyst was activated with a gas mixture. During the activation, the temperature was increased from $150^{\circ}C$ to $500^{\circ}C$. The necessary amount of urea was dissolved in 50mL water and injected. Aqueous urea solution was then mixed with the feed gas stream. At low temperatures, nitrogen containing compounds of urea decomposition are used as reductants in the reducton of $NO_X$. However at high temperatures the nitrogen containing compounds are oxidized to NO and $NO_2$ by oxygen instead of being used in the reduction. The activity of the catalyst was dependent on urea concentration in the feed stream when there was not adequate water vapor in the feed. The maximum conversion was shifted from $250^{\circ}C$ to $150^{\circ}C$ when water concentration was increased from 2 to 17%. It seems that the maximum temperature shifts to lower temperatures because the hydrolysis rate of HNCO increases with water, resulting in higher amounts of $NH_3$.