Research on nitrogen reduction performance of various modes combined air-staged with air humidification for gas boiler

NOx emissions from gas boilers pose a significant threat to air quality. To significantly decrease NOx emission level from the gas boiler exhaust, a novel nitrogen reduction combustion method is proposed that combines air-staging with humidification combustion techniques. A comprehensive study was conducted using CHEMKIN software to analyse the nitrogen reduction performance and sensitivity in various compound modes. The impact of combustion temperature, excess air coefficient, and injection position of over-fire air on the nitrogen reduction performance in the optimal compound mode was investigated. The results showed that the nitrogen reduction effect of the compound mode was better than that of the pure staged combustion mode. Compared with pure staged combustion, humidifying the main combustion zone could improve the nitrogen reduction rate by 4.9 %, which was 1.7 % higher than humidifying the burnout zone. The most significant nitrogen reduction effect was achieved when both combustion zones were humidified, leading to a 7.4 % increase in the nitrogen reduction rate. Further, by humidifying both combustion zones and reducing the combustion temperature, the emission of NO during boiler operation was found to be reduced significantly. The nitrogen reduction rate can be increased to 65.7 %, which is 22.1 % higher than that of the single air-staging.