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NOx formation in ultra-low-NOx gas burners Zoran M. Djurisic, Eric G. Eddings University of Utah Slide 2 Controlling mechanisms Thermal NOx (Zeldovich) Direct N 2 oxidation High temperature required (> 1800 K) Prompt NOx (Fenimore) NN bond scission by flame radicals Occurs only in flame fronts N 2 O Pathway Through N 2 + O + M N 2 O + M Relevant under elevated pressures Fuel NOx NO formation from N-containing fuel fragments (CN, NH) Relevant if fuel contains chemically-bound nitrogen Slide 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 Slide 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 Slide 5 Ultra-low NOx burners (contd.) Commercial ultra-low NOx burner (9 vppm) Forced Internal Recirculation Flame temperature 1200 - 1400 K. Forced Internal Recirculation (FIR) burner Slide 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 N 2 O path Slide 7 Resulting NOx emissions variability Predicted NO emissions for stoichiometric oxidation in plug-flow reactor at 1200 K and 1 atm COGBFG Slide 8 NOx formation pathway analysis NO 2 HNO NH N2ON2O NO NNH N2N2 O2O2 H O O O O H H OH OH H O OH HCO O2O2 H O, HO 2 Slide 9 Prompt NOx controlling reactions - summary Methylidene is not to blame CH+N 2 has 10000 times lower rate coefficient than H + N 2 Typical HC flame contains 10 5 times more H than CH Initial step: N 2 + H NNH NNH oxidation to NO is relatively fast and easy Competing process: any H scavenging process CH 4 + H CH 3 + H 2 C 2 H 6 + H C 2 H 5 + H 2 C 2 H 5 + H C 2 H 4 + H 2 Slide 10 U-NOx datacenter Slide 11 Slide 12 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. Slide 13 Minimizing NOx emissions from hydrogen-containing fuels