Synergistic optimization of swirl burner structure and deep air-staged technology is conducted to achieve high-efficiency combustion and low-nitrogen emissions of pulverized coal in a 660 MW opposed-firing boiler. The optimization of burner structure includes optimizing the cone structure and adding a coal particle concentration separation ring, while multiple sets of air distribution ratios for the primary combustion zone and burnout zone are set under different air-staged conditions. Comprehensive numerical and experimental studies are conducted to investigate the flow, combustion, and pollutant generation characteristics in the furnace before and after the optimization measures. The results show that independently optimizing the burner structure or the deep air-staged technology has limitations in effectiveness. Only through the synergistic optimization of both can the combustion efficiency and NO emissions of pulverized coal reach optimal levels. When the cone structure between the primary and secondary air nozzles is synergistically optimized, specifically by shortening the radial mixing distance of the two airflows, which enhances the entrainment effect of the secondary air on the primary air. This remarkably affects the aerodynamic field and combustion, promoting the formation of a central recirculation zone (RZ) near the burner nozzle. The issue of reduced secondary air momentum in the primary combustion zone caused by the use of air-staged technology is therefore mitigated. The RZ facilitates the entrainment of high-temperature flue gas from the far end, improving the ignition, burnout, and stable combustion characteristics of pulverized coal. For instance, the unburned carbon in fly ash decreases significantly from 1.97% to 0.98%. Meanwhile, the rapid release of volatile matter in the RZ creates a locally low-oxygen and strong reducing atmosphere, which is highly beneficial for suppressing the generation of NO inside the flame. However, merely improving the burner structure has limited inhibitory effects on NO generation in zones farther from the burner nozzle, e.g., the furnace center and burnout zone. Only combined with deep air-staged technology, a further significant reduction in outlet NO emissions can be achieved.

Combustion,Optimization,nitric oxide,CFD simulation,coal