Formation and reduction of NO from the oxidation of NH3/CH4 with high concentration of H2O

Sun, Zhaolin; Xu, Jun; Su, Sheng; Qing, Mengxia; Wang, Lele; Cui, Xiaoning; Zhang, Chunxiu; Wang, Yi

doi:10.1016/j.fuel.2019.02.121

Cited by 23 publications

(10 citation statements)

References 39 publications

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“…So that nitrogen-based species are released rapidly from char and then oxidized rapidly to NO under oxygen-rich conditions, causing faster formation of NO. This is consistent with the results of Sun et al that NO formation was markedly enhanced at a high concentration of H 2 O. The second stage, the H 2 O–CO reaction, known as the WGS reaction, is an exothermic process.…”

Section: Resultssupporting

confidence: 93%

Formation and Reduction of NO₂ in Fixed Bed Combustion of Coal Char under Oxy–Fuel Conditions: Experimental and Density Functional Theory Analysis

Yue

Wang

et al. 2020

Energy Fuels

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Nitrogen dioxide (NO 2 ) has been attracting a lot of attention because of its toxicity and potential in contaminating land, air, and water. However, research on NO 2 release behavior under oxy−fuel conditions is still insufficient. This paper aims to explore the formation and reduction mechanisms of NO 2 during oxy−fuel combustion of char by using both experimental and density functional theory (DFT) methods. Results showed that with the increase of temperature, the energy barrier of the NO oxidation reaction increases, while that of the NO 2 reduction reaction decreases. These facts lead to a higher peak concentration of NO and lower NO 2 emissions. Because of a larger effect of temperature on the rate constant of the NO 2 reduction reaction than that of the NO oxidation reaction, the NO 2 concentration decreases dramatically and rapidly even if the temperature increases only slightly. As the temperature increases to above 1273 K, the equilibrium constant of the NO oxidation reaction falls to below 10 5 . That is, the oxidation of NO to NO 2 is incomplete and reversible over the temperature range of 1273−1673 K. By contrast, the reduction of NO 2 to NO is complete and irreversible over this temperature range. As a result, almost no NO 2 is observed at high temperatures. In the presence of H 2 O, DFT calculations show that the water-gas-shift reaction is less important in contrast to the H 2 O−carbon reaction, which is consistent with previous research. In this case, NOx emissions under an O 2 /CO 2 /H 2 O atmosphere are lower than those under an O 2 /CO 2 atmosphere. Overall, combined experiments with DFT calculations offer a new approach to study the microcosmic mechanisms of NO 2 formation and reduction under oxy−fuel conditions during isothermal combustion of char.

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Section: Resultssupporting

confidence: 93%

Formation and Reduction of NO₂ in Fixed Bed Combustion of Coal Char under Oxy–Fuel Conditions: Experimental and Density Functional Theory Analysis

Yue

Wang

et al. 2020

Energy Fuels

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“…Recycling of about 60 % of the total flue gases [4] is needed to moderate the temperature in the furnaces and get flame stability. Several issues have been researched during the last years in relation to fuel conversion, fluid dynamics, heat transfer and pollutants formation in oxy-fired systems, aiming at determining the optimal O2/CO2 composition in comparison to the well-known air-fired performance [5][6].…”

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confidence: 99%

From O2/CO2 to O2/H2O combustion: The effect of large steam addition on anthracite ignition, burnout and NOx formation

Escudero

Aznar

Díez

et al. 2020

Fuel Processing Technology

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Steam-moderated combustion has been proposed to supress flue gas recycling in oxy-fired units, but the influence of replacing CO2 by H2O has to be deeply studied. In this paper, oxy-fuel combustion of anthracite with large steam addition has been experimentally characterized, and main results are discussed as concerns the influence upon the ignition temperature, the burnout and the NOx formation. The tests have been carried out in an electrically-heated entrained flow reactor for a set of O2/CO2 and O2/H2O/CO2 atmospheres, with steam addition up to 40 % vol. The results show that ignition temperature diminishes when steam is added in low rates (maximum decrease of 16 ºC), but the trend is reversed for the higher steam concentrations (maximum increase of 18 ºC). The effect of steam addition on coal burnout rates is more significant for the 21 % vol. O2 atmosphere, with a decrease of 2.2-5.3 percentage points, and almost negligible for the 35 % vol. O2. An outstanding reduction of NO specific emissions is detected when adding H2O, with decrements ranging 28-45 % compared to the dry conditions. The transition from O2/CO2 combustion to O2/H2O combustion barely affects the anthracite conversion but significantly diminishes NOx formation rates.

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“…The activation of the C-H bond in CH 4 serves as a rate determining step for the NO removal reaction [17]. It was found that the formation of NO is significantly increased when high concentration of steam is introduced in the enriched condition, which is due to the increase of OH roots caused by the addition of high concentration of steam in the enriched condition [85]. The adsorbed nitrate species and HCOO-have been shown to be key intermediates for the CH 4 -NO reaction in the presence of O 2 .…”

Section: Reaction Mechanismmentioning

confidence: 99%

State-of-Art Review of NO Reduction Technologies by CO, CH4 and H2

et al. 2021

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Removal of nitrogen oxides during coal combustion is a subject of great concerns. The present study reviews the state-of-art catalysts for NO reduction by CO, CH4, and H2. In terms of NO reduction by CO and CH4, it focuses on the preparation methodologies and catalytic properties of noble metal catalysts and non-noble metal catalysts. In the technology of NO removal by H2, the NO removal performance of the noble metal catalyst is mainly discussed from the traditional carrier and the new carrier, such as Al2O3, ZSM-5, OMS-2, MOFs, perovskite oxide, etc. By adopting new preparation methodologies and introducing the secondary metal component, the catalysts supported by a traditional carrier could achieve a much higher activity. New carrier for catalyst design seems a promising aspect for improving the catalyst performance, i.e., catalytic activity and stability, in future. Moreover, mechanisms of catalytic NO reduction by these three agents are discussed in-depth. Through the critical review, it is found that the adsorption of NOx and the decomposition of NO are key steps in NO removal by CO, and the activation of the C-H bond in CH4 and H-H bonds in H2 serves as a rate determining step of the reaction of NO removal by CH4 and H2, respectively.

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Formation and reduction of NO from the oxidation of NH3/CH4 with high concentration of H2O

Cited by 23 publications

References 39 publications

Formation and Reduction of NO₂ in Fixed Bed Combustion of Coal Char under Oxy–Fuel Conditions: Experimental and Density Functional Theory Analysis

Formation and Reduction of NO₂ in Fixed Bed Combustion of Coal Char under Oxy–Fuel Conditions: Experimental and Density Functional Theory Analysis

From O2/CO2 to O2/H2O combustion: The effect of large steam addition on anthracite ignition, burnout and NOx formation

State-of-Art Review of NO Reduction Technologies by CO, CH4 and H2

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Formation and reduction of NO from the oxidation of NH3/CH4 with high concentration of H2O

Cited by 23 publications

References 39 publications

Formation and Reduction of NO2 in Fixed Bed Combustion of Coal Char under Oxy–Fuel Conditions: Experimental and Density Functional Theory Analysis

Formation and Reduction of NO2 in Fixed Bed Combustion of Coal Char under Oxy–Fuel Conditions: Experimental and Density Functional Theory Analysis

From O2/CO2 to O2/H2O combustion: The effect of large steam addition on anthracite ignition, burnout and NOx formation

State-of-Art Review of NO Reduction Technologies by CO, CH4 and H2

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Product

Resources

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Formation and Reduction of NO₂ in Fixed Bed Combustion of Coal Char under Oxy–Fuel Conditions: Experimental and Density Functional Theory Analysis

Formation and Reduction of NO₂ in Fixed Bed Combustion of Coal Char under Oxy–Fuel Conditions: Experimental and Density Functional Theory Analysis