Improving the Performance of a 300 MW Down-Fired Pulverized-Coal Utility Boiler by Inclining Downward the F-Layer Secondary Air

This paper presents a systematic study on improving the performance of a 300 MW down-fired pulverized-coal utility boiler by inclining downward the F-layer secondary air (SA). A numerical method was adopted to evaluate the effects of inclined angles on the characteristics of flow, combustion, and nitrogen oxide (NO x ) emissions in the furnace. Retrofitting was conducted to incline the F-layer SA downward with an optimal inclined angle of 25°. Full-scale experimental measurements were carried out before and after retrofitting. The results indicate that inclining downward the F-layer SA can increase the flame penetration depth and lower downward the flame center. The residence time of pulverized-coal particles increases, and the SA staging level enhances in the furnace. The boiler performance is improved with absolute increases of 3.55, 3.31, and 2.20% in boiler efficiencies and relative reductions of 28.65, 19.07, and 12.53% in NO x emissions under 300, 240, and 190 MW loads, respectively.