Characteristics of reducing NO using urea and alkaline additives

Lee, Seungmoon; Park, Kwinam; Park, Jin Won; Kim, Byung Hwan

doi:10.1016/j.combustflame.2005.01.004

Cited by 34 publications

(21 citation statements)

References 12 publications

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“…As the existence of N 2 O, NO x1 removal efficiencies are among 50-60% and the highest NO x2 removal efficiency is just about 30%. Compared with experimental results with flue gas mixed with some pure gases [17,19,23], the optimum temperature is lower; while compared with experimental results with flue gas generated from combustion [8,12], the reaction temperature is basically consistent. The experimental results of the process with NH 3 as reduction agent also exist the problem that the optimum temperature with flue gas achieved from combustion is lower than that with flue gas mixed by a kind of pure gas [6,25,26].…”

Section: Resultssupporting

confidence: 50%

“…So far, many researches have been done on urea as reduction agent [11][12][13], but N 2 O has not been taken into consideration or given enough attention. Using additives to improve reaction characteristics of SCNR process has been studied by many scholars; the additives are usually hydrocarbons to De NO x process [14,15] and sodium salts to NO x OUT process [16][17][18][19]. Most studies on the NO x OUT process with additives did not consider the detailed effects on N 2 O for its low concentration or explained the effect just from the aspect of active radicals' effect.…”

Section: Introductionmentioning

confidence: 99%

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Experimental study of the influence of sodium salts as additive to NO x OUT process

Liang

Zhong

Jin

et al. 2010

Korean J. Chem. Eng.

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An experimental study of the SNCR process with urea as reducing agent and sodium salts as additive has been carried out, and detailed analysis of the reaction mechanism has been given here. In the temperature range of 800-975 o C, NO concentration decreases at first and then increases while the concentration of N 2 O increases at first and then decreases with the increasing of temperature, and the turning point is 900 o C. With increasing of normalized stoichiometric ratio of reduction nitrogen to NO x (NSR), NO removal efficiency increases, while the concentration of N 2 O also increases, which decreases overall NO x removal efficiency. With sodium salts as additive, the concentration of N 2 O decreases with increasing of sodium salts addition at all temperatures, while the concentration of NO decreases at first and then increases at low-temperature side of the temperature window and increases at high-temperature side with additional increasing, whose changing extent is smaller than N 2 O. Since sodium salts as additive can remove N 2 O effectively and have no large influence on the removal of NO, the effect of sodium salts as additive is the combined effect of the production of active radicals and the removal of HNCO produced by the decomposition of urea through neutralization reactions, which is more important. To achieve the same effect under each condition, the needed addition of NaOH and CH 3 COONa is less than that of Na 2 CO 3 counting as Na atom. For the decomposition of CH 3 COONa can produce CH 3 COO, its addition can promote the reduction of NO more obviously at the lower temperature than Na 2 CO 3 or NaOH. Overall NO x removal efficiency at 900 o C with NSR=1.5 had been improved from about 30% to 70.45% through the addition of sodium salts. Sodium salts as additive caused the flue gas to become alkaline gas, but it was not serious for sodium salts existing as NaNCO.

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Section: Resultssupporting

confidence: 50%

Section: Introductionmentioning

confidence: 99%

Experimental study of the influence of sodium salts as additive to NO x OUT process

Liang

Zhong

Jin

et al. 2010

Korean J. Chem. Eng.

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“…The increased concentration of sodium salts was also found to enhance the performance of SNCR process with widened temperature range at 3.9% O 2 concentration for the performed experiments [12]. Similarly, NO reduction efficiency at 1.7% O 2 concentration was found lowered than at 3.8% O 2 concentration in a separate study [13]. Moreover, an existence of conversion temperature point (CTP) has also been discussed, on the two sides of which O 2 performs differently.…”

mentioning

confidence: 64%

NOx control in coal combustion by combining biomass co-firing, oxygen enrichment and SNCR

Daood

Javed

Gibbs

et al. 2013

Fuel

103

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Article:Daood, S.S., Javed, M.T., Gibbs, B.M. et al.(1 more author) (2013) NOx control in coal combustion by combining biomass co-firing, oxygen enrichment and SNCR. Fuel, 105. 283 -292. ISSN 0016-2361 https://doi.org/10.1016/j.fuel.2012.06.087 eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. Abstract:There has been renewed interest in evaluating the effect of biomass co-firing on the multi-pollutant control system such as Selective Non-catalytic Reduction (SNCR) and oxygen enrichment. Emissions savings have been attained by combining SNCR and biomasscoal co-combustion under various oxygen enriched staged air levels. Biomasses with higher tendency of generating CO produced better reduction in NO x emission with and without using SNCR. NO reduction of around 80% were attained using SNCR for 15% and 50% blending ratios of biomasses at 21% overall O 2 concentration for unstaged combustion.Whereas, a range of 40%-80% NO reductions were attained for RC2 (a Russian Coal) and 15% co-fired biomasses with 3.1%-5.5 % overall O 2 concentration at 22%-31% levels of flame staging. Moreover, it was found that better NO x removal efficiency was attained for higher NO x emission baselines under both oxygen enriched and normal firing conditions. However, SNCR NO x control for both coal or coal-biomass blends was observed to produce higher NO x reductions during O 2 enrichment, believed to be due to the self-sustained NO x reduction reactions. Hence, NO x control by SNCR, oxygen enriched co-firing in the furnaces would result in lower NO x emissions and higher carbon dioxide concentration for efficient scrubbing with better carbon burnouts.Key words: NOx, SNCR, biomass cofiring, coal 1.IntroductionSome conventional coal fired power stations of Europe are under threat of closure, due to enforcement in 2020 (previously 2016), of the Large Combustion Plant Directive (LCPD)[1]. This is due to the economics of implementing control technologies to reduce the emission of NO x to lower than 200mg/Nm 3 . Moreover, UK is also expected to fail in meeting the NO x emissions ceiling target set by the European National Emissions Ceiling Directive (ENECD)[2]. Hence, the ENECD is reviewing to produce new emission cei...

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“…The reaction degree varies under different conditions, so the partial urea of the total injected, which factually will be implemented to reduce NO, should be predicted to confirm quantity of urea injected. Lee et al (2005) presented the ''temperature window'' for the NO x OUT process as 1,250 to 1,300 K, where hydroxyl radical formed easily in an oxidizing environment. Accurately, within the range of 1.7 to 3.8% of O 2 volume concentration, NO x reduction efficiency was congruously increased with O 2 concentration.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study on the Effect of Urea and Additive Injection for Controlling Nitrogen Oxides Emissions

Niu

Han

2010

Environmental Engineering Science

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Selective noncatalytic reduction (SNCR) for nitrogen oxides (NO x ) abatement, using urea (the NO x OUT process) as an N-agent was conducted experimentally on a multifunctional combustion facility. Results showed that the NO x OUT process resulted in 90.1% NO reduction at 1,273 K if the N-agent-to-NO mole ratio (NSR) varied between 1.5 and 2. Also, oxygen concentration of the inlet gas clearly impacted the process. NO x reduction was reduced by 17.1% when oxygen concentration was increased from 2.7 to 3.6%. If the concentration was increased further, decline of NO x reduction would become smooth. At the same time, ample residence time must be guaranteed, and a minimum value of 1.2 s was required for a thorough NO x reduction. The temperatures where 90% of the maximum reductions are achieved in low and high temperature zones are seen as the lower and upper limit temperature, respectively. The range between the lower and upper limit temperature is defined as a ''temperature window.'' Different reagents lead to different maximum reductions and the ''temperature window'' changes accordingly. Based on these findings, synergistic effect of additives was studied to broaden the narrow ''temperature window'' of SNCR. Sodium carbonate, ethanol, glycerol, and acetic acid, with a concentration of 200 ppm, respectively, were selected as additives, and the ''temperature window'' was broadened by 40-80 K. Different additives presented different characteristics. Sodium carbonate simultaneously broadened the ''temperature window'' toward low and high temperature zones and slightly compromised the maximum NO x reduction. The organic compounds mainly showed effect in low temperature zone and reduced the maximum NO x reduction by 11-14%. This investigation is performed from operating parameters to additive injection, which makes the effect of additive obvious. It is hoped that the conclusions of this work could further ascertain the NO x OUT process and make a contribution to the industrialization of the SNCR technology.

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Characteristics of reducing NO using urea and alkaline additives

Cited by 34 publications

References 12 publications

Experimental study of the influence of sodium salts as additive to NO x OUT process

Experimental study of the influence of sodium salts as additive to NO x OUT process

NOx control in coal combustion by combining biomass co-firing, oxygen enrichment and SNCR

Experimental Study on the Effect of Urea and Additive Injection for Controlling Nitrogen Oxides Emissions

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