Industrial experimental study on combustion characteristics and NOx emission characteristics of a 600 MWe wall-fired boiler under ultra-low excess air coefficient conditions

Abstract

This paper aims to explore the effects of ultra-low excess air coefficients on the combustion performance and NO_x emission characteristics of coal-fired boilers through industrial experiments conducted on a 600 MWe wall-fired boiler. The results indicate that the burners demonstrate good ignition performance under different ultra-low excess air coefficient conditions. As the excess air coefficient increases, the temperature in the main combustion zone rises, and the ignition distance of pulverized coal shortens. Under ultra-low excess air coefficient conditions (such as 1.04), the unburned carbon content in fly ash reaches 5.50%, which is 3.23% higher than under the condition of 1.11, indicating poor pulverized coal burnout. When the excess air coefficient is close to the theoretical design value (such as 1.11), the carbon content in slag and the unburned carbon content in fly ash is relatively low (1.40% and 2.28%, respectively), indicating more complete combustion of pulverized coal. Additionally, the flue gas temperature at the air preheater outlet under this condition is relatively low; compared to the condition of an excess air coefficient of 1.07, the flue gas temperature is reduced by 6°C, thus reducing flue gas loss. Although the NO_x concentration under the condition of an excess air coefficient of 1.11 is slightly higher, the quantity of cooling water is less. Flow field tracking of the powder verifies the flow path and characteristics of the primary air of the burners, and the results show that the primary air flow path of the burners is relatively concentrated, avoiding impingement on the water-cooled walls and effectively preventing slagging issues on the water-cooled walls. The research findings are of great significance for improving the operational performance and environmental protection level of coal-fired boilers.