NOx formation in ultra-low-NOx gas burners
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Transcript of NOx formation in ultra-low-NOx gas burners
NOx formationin ultra-low-NOx gas burners
Zoran M. Djurisic, Eric G. EddingsUniversity of Utah
Controlling mechanisms Thermal NOx (Zeldovich)
Direct N2 oxidation High temperature required (> 1800 K)
Prompt NOx (Fenimore) NN 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
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
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
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
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
Resulting NOx emissions variability
Predicted NO emissions for stoichiometric oxidationin plug-flow reactor at 1200 K and 1 atm
COG BFG
NOx formation pathway analysis
NO2
HNO
NH
N2O
NO
NNH
N2
O2H
O
O
O
O
H
H OH
OH H OOH
HCO
O2
H
O, HO2
Prompt NOx controlling reactions - summary
Methylidene is not to blame CH+N2 has 10000 times lower rate coefficient
than H + N2
Typical HC flame contains 105 times more H than CH
Initial step: N2 + H NNHNNH 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
U-NOx datacenter
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.
Minimizing NOx emissionsfrom hydrogen-containing fuels