Application of a Novel Strong Flame-Stabilizing Swirl Technology in a 350 MW Supercritical Boiler: Gas–Solid Flow, Combustion Characteristics, and NO_x 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 NO_x emissions. At 20% and 30% load, operating only the new burners maintained the main combustion zone temperature above 1000°C.