Application of a Novel Strong Flame-Stabilizing Swirl Technology in a 350 MW Supercritical Boiler: Gas–Solid Flow, Combustion Characteristics, and NO <i> _x </i> Emissions

Current research on faulty coal-fired swirl burners has shortcomings in secondary air distribution, limited understanding of multi-jet interactions, and a primary focus on full-load conditions, which hinders achieving stable combustion at 20%–30% boiler rated load. This work implemented a self-developed flame stabilization technology, combining gas–solid experiments using a laser particle dynamic anemometer (PDA) with full-furnace simulations. PDA results showed that at inner secondary air (ISA) ratios of 38%, 43%, and 47%, the recirculation zones formed annular structures, originating at distances of 0.3d, 0.1d, and 0.1d from the burner outlet, with maximum diameters of 0.578d, 0.448d, and 0.598d, respectively (where d represents the inner diameter of the burner outlet). A net flux ratio metric was proposed to quantitatively assess the annular recirculation zone. With an ISA ratio of 43%, the total net flux was positive, reflecting weak recirculation; at 38% and 47%, the total net flux was less than zero, indicating a strong overall recirculation tendency. The full-furnace simulation revealed a low-velocity zone under hot-state conditions that closely matched the recirculation distribution obtained from the gas–solid experiments. An increase in the ISA proportion led to a larger low-velocity zone and strengthened the flame’s radial spreading. The novel technology increased the temperature of the main combustion zone, reduced fly ash carbon content, and substantially lowered NOx emissions. At 20% and 30% load, operating only the new burners maintained the main combustion zone temperature above 1000°C.