Low-NOx and High-Burnout Combustion Characteristics of a Cascade-Arch-Firing, W-Shaped Flame Furnace: Numerical Simulation on the Effect of Furnace Arch Configuration

A cascade-arch-firing low-NOx and high-burnout configuration (CLHC) was proposed as a solution for the W-shaped flame furnace's incompatibility problem of strengthened low-NOx combustion and high burnout. Numerical simulations verified by industrial-size measurements of a 600 MW, W-shaped flame furnace were used to confirm the CLHC's low-NOx and high-burnout characteristics and evaluate its cascade-arch configuration effect on the gas/particle flow, coal combustion, and NOx formation. The furnace with the existing low-NOx combustion art showed NOx emissions of about 900 mg/m(3) at 6% O-2 and carbon in fly ash of about 5%. In applying CLHC as a replacement for the prior art, numerical simulations at typical cascade-arch configurations of C-L = 1/5, 1/4, and 1/3 (C-L signifying the ratio of the lower arch depth to the total arch depth) showed that as C-L increased, both the flow field and combustion symmetry initially improved but then deteriorated. In conjunction with the improvement in both NOx emissions and burnout, the C-L = 1/4 setting achieved the best furnace performance with NOx emissions 707 mg/m 3 at 6% O-2 and carbon in fly ash of 5.5%. In comparison with the prior low-NOx art, CLHC reduced further NOx emissions by 22% and almost maintains the burnout rate.