ef9b04091_si_001.pdf (255.04 kB)
Evaluation of NOx‑Reduction Measures for Iron-Ore Rotary Kilns
journal contribution
posted on 2020-03-12, 19:34 authored by Rikard Edland, Neil Smith, Thomas Allgurén, Christian Fredriksson, Fredrik Normann, Denver Haycock, Colson Johnson, Jacob Frandsen, Thomas H. Fletcher, Klas AnderssonThe grate-kiln process
is employed for sintering and oxidation
of iron-ore pellets. In this process, a fuel (typically coal) is combusted
with a large amount of excess air in a rotary kiln, and the high air-to-fuel
ratio leads to significant NOx formation.
The current Article is an assessment of NOx reduction measures that have been tested in pilot-scale and in full-scale
by the Swedish iron-ore company Luossavaara-Kiirunavaara Aktiebolag
(LKAB). The results show that the scaling between the full-scale kiln
and the pilot-scale kiln is crucial, and several primary measures
that reduce NOx significantly in pilot-scale
achieve negligible reduction in full-scale. In the investigated full-scale
kiln, thermal NOx formation is efficiently
suppressed and low compared with the NO formation from the fuel-bound
nitrogen (especially char-bound nitrogen). Suppressing the NO formation
from the char-bound nitrogen is difficult due to the high amounts
of excess air, and all measures tested to alter mixing patterns have
shown limited effect. Switching to a fuel with a lower nitrogen content
is efficient and probably necessary to achieve low NOx emissions without secondary measures. Simulations
show that replacing the reference coal with a biomass that contains
0.1% nitrogen can reduce NOx emissions
by 90%.