Influence of Burner Mass-Flow Rate Bias and Injection Direction Offset on High-Temperature Corrosion and Combustion in a 660-MW Opposed Swirling-Fired Boiler

Abstract

Low-NOx combustion with deep air staging technology is commonly adopted to reduce NOx emissions in coal-fired power plants. However, introducing deep air staging results in a strong-reducing atmosphere, which may cause high-temperature corrosion on the water-cooled wall. In general, alleviating the reducing atmosphere around the water-cooled wall is undoubtedly the lowest-cost and highest-efficiency technique. This study aims to investigate the influence of burner mass-flow rate bias and injection direction offset on high-temperature corrosion and combustion in a 660 MWe opposed wall-fired boiler. The results show that decreasing the load of burners close to the sidewalls can not only reduce the high-temperature zone and the CO and H2S concentrations near the sidewalls but also improve combustion characteristics by controlling NOx emissions. Taking the high-temperature corrosion, combustion, and NOx emissions into account, it is recommended to decrease the load of burners close to the sidewalls by 10%. In addition, as the burner injection direction offset increases from 0° to 7°, the high-temperature zone near the sidewalls enlarges slightly, but as the burner injection direction offset further increases from 7° to 10°, the high-temperature zone near the sidewalls increases significantly. Considering the high-temperature corrosion, combustion and NOx emissions, 7° may be the optimal value of the burner injection direction offset angle and is applied to the actual retrofit. The actual industrial application shows that compared to that before the retrofit, the temperatures near the sidewalls change slightly after the retrofit, but the CO concentrations significantly decrease and the boiler efficiency increases from approximately 93.27% to 93.46%. After a long period of operation, good performance without high-temperature corrosion of the sidewalls is achieved.