• Journal of Energy Engineering
• /
• v.23 no.4
• /
• pp.130-140
• /
• 2014

Rotary kiln burner has been developed continuously to improve process efficiency and exhaust emission. In this study, the characteristics of the flame and exhaust emission were numerically analyzed according to the diameter of primary air nozzle, equivalent ratio of burner, and equivalent ratio at center and side nozzle for development of multi-nozzle burner in the COG(Coke Oven Gas) rotary kiln for sintering iron ore. The results indicated that the flame length and $NO_x$ emission increase, as the diameter of primary air nozzle and equivalent ratio of burner increase. And according to the change of equivalent ratio at the center and the side of the nozzle, the flame length and average temperature in the kiln show very little change but the $NO_x$ emission shows obvious difference. In conclusion, the best design conditions which have satisfying flame length, average temperature and $NO_x$ emission are as follows: $D_2/D_1$ is 1.33, equivalent ratio of burner is 1.25 and center nozzle conditions are Rich.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.16 no.5
• /
• pp.68-76
• /
• 2008

Diesel $NO_x$ reduction by $NH_3$-SCR in conjunction with the effective oxidation precatalyst was analytically investigated. Physicochemical processes in regard to $NH_3$-SCR $NO_x$ reduction and catalytic NO-$NO_2$ conversion are formulated with detailed descriptions on the commanding reactions. A unified model is correctly validated with experimental data in terms of extents of $NO_x$ reduction by SCR and NO-$NO_2$ conversion by DOC. The present deterministic model based on the rate expressions of Langmuir-Hinshelwood reaction scheme finds a conversion extent directly. A series of numerical experiments concomitant with parametric analysis of the $NO_x$ reduction was conducted. $NO_x$ reduction is promoted in proportion to DOC volume ar lower temperatures and an opposite holds at lower space velocity and intermediate temperatures. $NO_x$ conversion is weakly correlated to the space velocity and the DOC volume at higher exhaust temperature. In DOC-SCR system, the $NO_x$ reduction efficiency depends on the $NH_3/NO_x$ ratio.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.20 no.1
• /
• pp.20-27
• /
• 2012

The $NH_3$-SCR characteristics of $NO_X$ over a V-based catalyst are experimentally examined over a wide range of operating conditions, i.e., $170-590^{\circ}C$ and $30,000-50,000h^{-1}$, with a simulated diesel exhaust containing $NH_3$, NO, $NO_2$, $O_2$, $H_2O$, and $N_2$. The influences of the space velocity and oxygen concentration on the standard-SCR reaction are analyzed, and it is shown that the low space velocity and high oxygen concentration promote the SCR activity by ammonia. The best $deNO_X$ efficiency is obtained with a $NO_2/NO_X$ ratio of 0.5 because of an enhanced chemical activity induced by the fast-SCR reaction, while at the $NO_2/NO_X$ ratios above 0.5 the $deNO_x$ activity decreases due to the slow-SCR reaction. The oxidation of ammonia begins to take place at about $300^{\circ}C$ and the reaction products, such as $N_2$, NO, $NO_2$, $N_2O$, and $H_2O$, are produced by the undesirable oxidation reactions of ammonia, particularly at high temperatures above $450^{\circ}C$. Also, $NO_2$ decomposes to NO and $O_2$ at temperatures above $240^{\circ}C$. Therefore, $NO_2$ decomposition and ammonia oxidation reactions deteriorate significantly the SCR catalytic activity at high temperatures.

• Journal of Korean Society for Atmospheric Environment
• /
• v.31 no.4
• /
• pp.378-384
• /
• 2015

The long-term variations of ozone and nitrogen oxides in Suwon city, the capital of Gyeong-gi province, were examined from 1991 to 2012. In this period, the annual average $O_3$ concentration increased from 13.8 ppbv to 22.7 ppbv and that of $99^{th}$ percentile increased from 58.0 ppbv to 80.0 ppbv. The monthly average and $99^{th}$ percentile of $O_3$ concentrations were the highest in June. The increase in $O_3$ concentration was the greatest in early summer (May and June) before monsoon season began. While the concentrations of NO and NOx have gradually decreased since 2000, $NO_2$ remained unchanged. As a result, $NO_2/NO_x$ ratio increased from 0.5 to 0.73 in 2012. The monthly $NO_2/NO_x$ ratio was the highest in early summer, when monthly average $O_3$ concentration was the highest. It suggests that the enhanced $NO_2/NO_x$ ratio is intimately coupled with increase in $O_3$ for the last two decades in Suwon.

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

• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• pp.1499-1504
• /
• 2004

Flue gas recirculation (FGR) is a method used to control oxides of nitrogen ($NO_x$) in combustion system. The recirculated flue gases resulted in slow reaction and low flame temperatures, which in turn resulted in decreased thermal NO production. Recently, it has been demonstrated that introducing the recirculated flue gas in the fuel stream, that is, the fuel induced recirculation (FIR), resulted in a much greater reduction in $NO_x$ per unit mass of recirculated gas, as compared to introducing the flue gases in air. In the present study, the effect on $NO_x$ reduction in turbulent swirl flame in laboratory scale using FGR/FIR methods through the dilution using $N_2$ and $CO_2$. Results. show the $CO_2$ dilution is more effective $NO_x$ reduction methods because of large temperature drop due to the larger specific heat $CO_2$ compared to $N_2$. FIR is more effective to reduce $NO_x$ emission than FGR when the same recirculation ratio of dilution gas.

• Transactions of the Korean hydrogen and new energy society
• /
• v.17 no.1
• /
• pp.75-81
• /
• 2006

Lean premixed combustion is a well known method for low $NO_x$ gas turbine combustor. But lean combustion is usually accompanied by flame instability. To overcome this problem, the hydrogen ($H_2$) was added to main fuel methane to increase flammable limit. In this paper, the effects of hydrogen addition on lean premixed combustion of methane ($CH_4$) were investigated numerically. Results showed that the extinction stretch rate increases and the extinction temperature constant with relatively small amount of $H_2$ addition. The flame temperature and NO emission increase with $H_2$ addition at the same stretch rate and equivalence ratio but it could increase the range of lean extinction and extinction equivalence ratio limit. Eventually, the $H_2$ addition case showed almost same or lower NO emission than no addictive $CH_4$ case in the extinction condition.

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

• Applied Chemistry for Engineering
• /
• v.24 no.3
• /
• pp.333-336
• /
• 2013

Experimental investigation to estimate the feasibility of fast selective catalytic reduction (SCR) or oxidation catalyst combined ammonia SCR system to abate NOx in low temperature condition ($150{\sim}250^{\circ}C$) is reported. Because the conversion of NO to $NO_2$ is pre-requisite of the fast SCR process, the effect of the amount of oxidation catalyst to NO conversion to $NO_2$ was tested. 37, 45 and 51% of conversion rates were obtained for the OCV of 563000, 375000 and 281000 h, respectively. $De-NO_x$ performance in the case of $NO_2/NO_x$ ratio of 45% showed the best result in all tested temperature conditions. Comparison of the fast SCR and standard SCR with the condition of $NO_2/NO_x$ ratio of 45%, $200{\sim}250^{\circ}C$ and space velocity of 10000~30000 h showed that the fast SCR does not show much difference according to the variance of space velocity. Also it was shown that using the fast SCR, the volume of SCR catalyst can be reduced less than half of the standard SCR condition by increasing space velocity without the loss of $De-NO_x$ performance.

• Journal of Korean Society for Atmospheric Environment
• /
• v.33 no.6
• /
• pp.605-615
• /
• 2017

Efficient simultaneous reduction conditions for $NO_x$ and $NH_3$-slip was investigated in SCR (Selective Catalytic Reduction) process with load variation by applying dual catalysts (SCR catalyst, $NH_3$ decomposition catalyst) system. $N_2O$ formation characteristics were analyzed to look into possible undesirable reaction pathways. In the experiments of catalyst characteristics, various operational variables were tested for the combined catalytic system, such as $NH_3/NO_x$ ratio, temperature, oxygen concentration and $H_2O$. The reaction characteristics of $NO_x$, $NH_3$ and $N_2O$ were analyzed and optimal conditions could be evaluated for the combustion facility with varied load. In terms of $NO_x/NH_3$ simultaneous reduction and $N_2O$ formation suppression, optimal condition was considered NSR 1.2 and temperature $300^{\circ}C$. At this operational condition, $NO_x$ conversion was 98%, $NH_3$ reduction efficiency was 95%, generated $N_2O$ concentration 9.5 ppm with inlet $NO_x$ concentration of 100 ppm. In $NH_3-SCR$ process with $NH_3$ decomposition catalyst, $NO_x$ and $NH_3$ can be considered to be reduced simultaneously at limited conditions. The results of this study may be utilized as basic data at facilities requiring simultaneous $NO_x$ and $NH_3$ reduction for facilities with load variation.