Evaluation of near-field aerodynamics and gas-particle two-phase characteristics of a lab-scale CFR swirl burner derived from a 600 MWe wall-fired utility boiler under different staged-air ratios

In coal-fired boilers, maintaining stable combustion and low NO x emissions under fluctuating load conditions is a significant challenge. Air-staging technologies, which reduce secondary-air flow to control NO x emissions, can weaken the recirculation zone and compromise ignition stability. This study investigates the performance of a central fuel-rich (CFR) swirl burner under varying over-fire-air (OFA) ratios (0%, 10%, 25%) to assess its ability to balance NO x reduction with stable combustion. Through cold-flow experiments, gas-particle two-phase measurements, and full-scale industrial validation data, the study finds that the CFR burner with OFA=0-25% maintains a stable recirculation zone with a favorable size, ensuring stable ignition and efficient combustion. Key findings include: (1) The burner maintains a well-defined recirculation zone across all OFA conditions (0-25%), which is essential for ignition stability and uniform combustion; (2) Axial recirculation velocities and particle diffusion suppression effect are enhanced at OFA = 25%, leading to effective particle heating and faster burnout; (3) The optimized burner ensures ignition within 0.1-0.2 m from the burner exit, while significantly reducing NO x emissions and avoiding slagging or coking risks. These results demonstrate the burner’s potential to provide stable, low-NO x combustion, even under fluctuating load conditions, making it an ideal solution for load-following coal-fired boilers.