Impact of the upper/lower furnace depth ratio on the strengthened low‐NOx combustion performance in a two‐stage W‐shaped flame furnace

Abstract

AbstractFor achieving the strengthened low‐NOx combustion plus high burnout in W‐shaped flame furnaces, a cascade‐arch low‐NOx and high‐burnout configuration (CLHC) is realized by positioning two burner layers in a 600 MWe furnace. The gas/particle flow, combustion, and NOx emission characteristics in the furnace are numerically evaluated at four upper/lower furnace depth ratios of CW = 0.458, 0.500, 0.529, and 0.558 (CW signifying the furnace throat shrinkage level) so as to disclose the impact of the furnace throat shrinkage level on the overall furnace performance and meanwhile establish an available CW setup. Increasing CW initially updates but then deteriorates the low‐NOx combustion performance. At the narrowest CW = 0.485 setup, the gained slightly asymmetric combustion shows relatively lower burnout loss but higher NOx emissions, while the widest CW = 0.558 setup forms severely asymmetric combustion with apparently raised carbon in fly ash but relatively lower NOx emissions. At moderate setups of CW = 0.500 and 0.529, a symmetrical combustion pattern develops, showing the low‐NOx and high‐burnout performance characterized as NOx emissions of 700–707 mg/m3 (6% O2) and carbon content in fly ash of 5.4–5.5%. In comparison to CW = 0.500, the larger downward flame penetration, higher flame fullness, and lower CO emission at CW = 0.529 suggest that a reasonable upper/lower furnace depth ratio prefers CW = 0.529. Compared with a currently advanced low‐NOx combustion technology, the CLHC lowers again NOx emissions by about 200 mg/m3 (6% O2) while maintaining high burnout, which confirms the CLHC's availability.