Mitigating NOx production and furnace-throat slagging in a 600 MW sidewall-dominated W-flame furnace through the downward redirection of vent air for reburning: Effect of an elevated staged-air location

The sidewall-dominated W-flame furnace, with its W-shaped flame relocated from the conventional front/rear-wall arrangement to a sidewall-arranged configuration, has proven highly effective in mitigating combustion deflection, poor burnout, and excessively high NO x emissions. However, the suboptimal positioning of vent air on the arch results in high temperatures, elevated NO levels, and severe slagging in the near-throat area. To address this issue, a new combustion configuration was proposed for a 600 MW sidewall-dominated W-flame furnace. The configuration involves (i) moving the vent air downward to the lower part of the sidewalls for reburning and (ii) elevating the staged air to enhance primary combustion. To validate this strategy and evaluate the impact of an elevated staged-air location, computational studies were conducted for the original arch-mounted vent-air case and various staged-air position cases (i.e., C h = 0.35, 0.40, 0.45, and 0.50) after relocating the vent air. Simulation validation relied on the measured and calculated data comparison for a predecessor furnace (i.e., a 600 MW front/rear wall-dominated furnace sharing the same air/fuel parameters and furnace dimensions), due to the sidewall-dominated furnace still at its R&D stage. As C h increased, downward flame penetration increased, and the overall combustion first intensified and then weakened, whereas NO x production and the carbon-in-fly-ash level both decreased initially before increasing again. When balancing the combustion intensity, NO x emissions, and burnout, among the four position cases the optimal comprehensive performance was achieved at C h = 0.45, yielding an NO x production of 508 mg/m 3 (6% O 2 ) and a carbon-in-fly-ash level of 5.07%. In the sidewall-arranged furnace, compared with the original arch-mounted vent-air case (NO x emissions of 745 mg/m 3 ), relocating the vent air downward for reburning not only eliminated the high-temperature, high-NO, and severe-slagging conditions in the throat region but also achieved a 31.8% reduction in NO x while slightly improving burnout. This confirms the effectiveness of this strategy in comprehensively addressing the aforementioned issues.