Ammonia chemistry below 1400 K under fuel-rich conditions in a flow reactor

Skreiberg, Øyvind; Kilpinen, Pia; Glarborg, Peter

doi:10.1016/j.combustflame.2003.12.008

Cited by 259 publications

(173 citation statements)

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“…The overall rate constant k 1 was determined by fitting the computed and observed NH 2 profile, using a 118 step reaction mechanism. Their reported sensitivity analysis indicates that the NH 2 profile is mostly sensitive to k 1 and to the rate constant for the thermal dissociation of C 6 Comparison of experimental data and modeling predictions for the NH 3 /NO 2 system. Experimental data from Glarborg et al 13 The modeling is conducted with the reaction mechanism of Klippenstein et al 11 Despite the absence of oxygen in the inlet gas, reaction occurs at temperatures as low as 850 K (Figure 12).…”

Section: ■ Experimental Resultsmentioning

confidence: 99%

Rate Constant and Branching Fraction for the NH₂ + NO₂ Reaction

et al. 2013

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The NH 2 + NO 2 reaction has been studied experimentally and theoretically. On the basis of laser photolysis/LIF experiments, the total rate constant was determined over the temperature range 295−625 K as k 1,exp (T) = 9.5 × 10 −7 (T/K) −2.05 exp(−404 K/T) cm 3 molecule −1 s −1 . This value is in the upper range of data reported for this temperature range. The reactions on the NH 2 + NO 2 potential energy surface were studied using high level ab initio transition state theory (TST) based master equation methods, yielding a rate constant of k 1,theory (T) = 7.5 × 10 −12 (T/K) −0.172 exp(687 K/T) cm 3 molecule −1 s −1 , in good agreement with the experimental value in the overlapping temperature range. The two entrance channel adducts H 2 NNO 2 and H 2 NONO lead to formation of N 2 O + H 2 O (R1a) and H 2 NO + NO (R1b), respectively. The pathways through H 2 NNO 2 and H 2 NONO are essentially unconnected, even though roaming may facilitate a small flux between the adducts. High-and low-pressure limit rate coefficients for the various product channels of NH 2 + NO 2 are determined from the ab initio TST-based master equation calculations for the temperature range 300−2000 K. The theoretical predictions are in good agreement with the measured overall rate constant but tend to overestimate the branching ratio defined as β = k 1a /(k 1a + k 1b ) at lower temperatures. Modest adjustments of the attractive potentials for the reaction yield values of k 1a = 4.3 × 10 −6 (T/K) −2.191 exp(−229 K/T) cm 3 molecule −1 s −1 and k 1b = 1.5 × 10 −12 (T/K) 0.032 exp(761 K/T) cm 3 molecule −1 s −1 , in good agreement with experiment, and we recommend these rate coefficients for use in modeling. ■ INTRODUCTIONThe formation and consumption of nitrogen oxides (NO x ) at high temperatures continue to be an important area of research. Of particular interest is the chemistry of amine radicals. Ammonia is formed in significant quantities in devolatilization of solid fuels 1 and the selectivity in oxidation of amine radicals to form NO or N 2 is important for the yield of NO x . 2 Reactions of amine radicals are also important for the performance of selective noncatalytic reduction (SNCR) of NO using aminebased additives such as ammonia or urea. In the past, both NH 3 oxidation 2−6 and SNCR 2,7−11 have been studied extensively within combustion.Following the detection of NO 2 as an important intermediate in SNCR, 12 the reaction of NH 2 with NO 2 was identified as a key step. 9,11 This reaction has two major product channels:(R1a)The prior analysis of Glarborg et al. 13 provides an overall picture of the kinetics for this reaction. The NH 2 radical can add to either the N atom of NO 2 to form H 2 NNO 2 or one of the O atoms to form H 2 NONO. The H 2 NNO 2 species ultimately produces N 2 O + H 2 O (R1a) after a number of isomerizations. Meanwhile, the H 2 NONO species directly dissociates to H 2 NO + NO (R1b). Both of these sets of products are exothermic relative to reactants, and the transition states on the pathway to forming N...

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Section: ■ Experimental Resultsmentioning

confidence: 99%

Rate Constant and Branching Fraction for the NH₂ + NO₂ Reaction

et al. 2013

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“…The starting mechanism was drawn from the recent study of NH 3 -doped CH 4 /O 2 /Ar flames [13]. This mechanism relied on work on the oxidation of C 1 /C 2 -hydrocarbons [55,56], NH 3 [57], and HCN [3], as well as interactions of these components [11,55,58,59]. Thermal NO and prompt NO formation mechanisms [1,60] are not important in the present flames due to the high concentrations of amines.…”

Section: Reaction Mechanismmentioning

confidence: 99%

Fuel-nitrogen conversion in the combustion of small amines using dimethylamine and ethylamine as biomass-related model fuels

Lucassen

Zhang

Warkentin

et al. 2012

Combustion and Flame

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Laminar premixed flames of the two smallest isomeric amines, dimethylamine and ethylamine, were investigated under one-dimensional low-pressure (40 mbar) conditions with the aim to elucidate pathways that may contribute to fuel-nitrogen conversion in the combustion of biomass. For this, identical flames of both fuels diluted with 25% Ar were 2 studied for three different stoichiometries (Φ=0.8, 1.0, and 1.3) using in situ molecular-beam mass spectrometry (MBMS). Quantitative mole fractions of reactants, products and numerous stable and reactive intermediates were determined by electron ionization (EI) MBMS with high mass resolution to separate overlapping features from species with different heavy elements by exact mass. Species assignment was assisted by using single-photon vacuum- We attempted to analyze the major pathways in the two flames with a detailed combustion model developed for this purpose. For this, thermochemical values for a number of intermediates had to be determined from quantum chemistry calculations. Also, specific sets of reactions were incorporated for the two fuels. While many trends seen in the experiments can be successfully reproduced by the simulations, additional efforts may be needed to reliably describe the fuel-nitrogen chemistry in the combustion of biomass-related model fuels with amine functions.

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“…The only difference may be that, from this detailed Kilpinen mechanism, urea related elementary reactions are excluded. Skreiberg et al (2004) presented a detailed reaction mechanism comprising 35 species and 200 elementary chemical reactions, including the species NH 2 OH, NH 2 NO, H 2 NN and HNN, which are not included in the other two mechanisms. The mechanism is suitable for modeling the NO reduction by primary measures in the combustion of biomass and below the temperature of 1400 K, but the performance in comparison to the other mechanisms and experimental observations has revealed some interesting results.…”

Section: Chemical Kinetic Mechanismsmentioning

confidence: 99%

“…The computer code SENKIN (Lutz et al, 1994) is used in this study using the two published chemical kinetic mechanisms, one that is used by Zanoelo (1999 a,b ) and the other that is used by Kilpinen (Kilpinen, 1997). An additional effort to assess the SKG mechanism (Skreiberg et al, 2004) for thermal DeNO x under the presented conditions was also conducted. These kinetic modeling studies were performed to provide a direct comparison of modeling predictions with the experimental measurements undertaken at the experimental setup for SNCR process at Leeds University UK (Irfan, 1995;Irfan and Gibbs, 1996).…”

Section: Introductionmentioning

confidence: 99%

A comparative kinetic study of SNCR process using ammonia

Javed

Ahmed²,

Ibrahim³

et al. 2008

Braz. J. Chem. Eng.

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-The paper presents comparative kinetic modelling of nitrogen oxides (NO x ) removal from flue gases by selective non-catalytic reduction process using ammonia as reducing agent. The computer code SENKIN is used in this study with the three published chemical kinetic mechanisms; Zanoelo, Kilpinen and Skreiberg. Kinetic modeling was performed for an isothermal plug flow reactor at atmospheric pressure so as to compare it with the experimental results. A 500 ppm NO x background in the flue gas is considered and kept constant throughout the investigation. The ammonia performance was modeled in the range of 750 to 1250 o C using the molar ratios NH 3 /NO x from 0.25 to 3.0 and residence times up to 1.5 seconds. The modeling using all the mechanisms exhibits and confirms a temperature window of NO x reduction with ammonia. It was observed that 80% of NO x reduction efficiency could be achieved if the flue gas is given 300 msec to react with ammonia, while it is passing through a section within a temperature range of 910 to 1060 o C (Kilpinen mechanism) or within a temperature range of 925 to 1030 o C (Zanoelo mechanism) or within a temperature range of 890 to 1090 o C (Skreiberg mechanism).

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Ammonia chemistry below 1400 K under fuel-rich conditions in a flow reactor

Cited by 259 publications

References 71 publications

Rate Constant and Branching Fraction for the NH₂ + NO₂ Reaction

Rate Constant and Branching Fraction for the NH₂ + NO₂ Reaction

Fuel-nitrogen conversion in the combustion of small amines using dimethylamine and ethylamine as biomass-related model fuels

A comparative kinetic study of SNCR process using ammonia

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Ammonia chemistry below 1400 K under fuel-rich conditions in a flow reactor

Cited by 259 publications

References 71 publications

Rate Constant and Branching Fraction for the NH2 + NO2 Reaction

Rate Constant and Branching Fraction for the NH2 + NO2 Reaction

Fuel-nitrogen conversion in the combustion of small amines using dimethylamine and ethylamine as biomass-related model fuels

A comparative kinetic study of SNCR process using ammonia

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Rate Constant and Branching Fraction for the NH₂ + NO₂ Reaction

Rate Constant and Branching Fraction for the NH₂ + NO₂ Reaction