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NOx formation in ultra-low-NOx gas burners

NOx formation in ultra-low-NOx gas burners. Zoran M. Djurisic, Eric G. Eddings University of Utah. Controlling mechanisms. Thermal NOx (Zeldovich) Direct N 2 oxidation High temperature required (> 1800 K) Prompt NOx (Fenimore) N  N bond scission by flame radicals

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NOx formation in ultra-low-NOx gas burners

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  1. NOx formationin ultra-low-NOx gas burners Zoran M. Djurisic, Eric G. Eddings University of Utah

  2. Controlling mechanisms • Thermal NOx (Zeldovich) • Direct N2 oxidation • High temperature required (> 1800 K) • Prompt NOx (Fenimore) • NN bond scission by flame radicals • Occurs only in flame fronts • N2O Pathway • Through N2+ O + M N2O + M • Relevant under elevated pressures • Fuel NOx • NO formation from N-containing fuel fragments (CN, NH) • Relevant if fuel contains chemically-bound nitrogen

  3. NOx control strategies • Flame control • Temperature • Stoichiometry • Species – dilution and scavenging • Post-flame control • Post-flame NOx reduction by • Reburning • Non-catalytic selective reduction • Catalytic selective reduction

  4. Low-NOx burners • NOx-control strategies by burner design • Staging • Swirling • Recirculation These techniques effectively control: • Flame core stoichiometry • Peak flame temperature • Ultra-low NOx target: sub-10 ppm • NOx emission levels comparable to selective catalytic reduction technology (SCR) at significantly lower cost

  5. Ultra-low NOx burners (contd.) Forced Internal Recirculation (FIR) burner • Commercial ultra-low NOx burner (9 vppm) • Forced Internal Recirculation • Flame temperature 1200 - 1400 K.

  6. Case study:NOx from steel-making by-product fuels By-product fuels composition variability Potential NOx formation mechanisms: • Thermal NOx • Prompt NOx • Fuel NOx • N2O path

  7. Resulting NOx emissions variability COG BFG Predicted NO emissions for stoichiometric oxidationin plug-flow reactor at 1200 K and 1 atm

  8. N2 H O2 O NNH HNO N2O O H O2 HCO H OH NH O OH H O O OH H NO2 NO O, HO2 NOx formation pathway analysis

  9. Prompt NOx controlling reactions - summary • Methylidene is not to blame • CH+N2 has 10000 times lower rate coefficientthan H + N2 • Typical HC flame contains 105 times more H than CH • Initial step: N2 + H  NNH NNH oxidation to NO is relatively fast and easy • Competing process: any H scavenging process • CH4 + H  CH3 + H2 • C2H6 + H  C2H5 + H2 • C2H5 + H  C2H4 + H2

  10. U-NOx datacenter

  11. Acknowledgements • We gratefully acknowledge funding for this work provided by the Gas Technology Institute through a grant with the U.S. Department of Energy. • Additional funding was provided by Reaction Engineering International and the University of Utah Research Fund.

  12. Minimizing NOx emissionsfrom hydrogen-containing fuels

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