Impact of excess air factor on performance and NOx emissions of an industrial water tube boiler with hydrogen enrichment

This study investigates the impact of excess air factor (λ) on performance and NOx emissions of a 207-MW boiler furnace, used for steam generation in an industrial water tube boiler installed at Saudi Aramco, at fixed volumetric fuel composition of hydrogen/methane of 10%/90%. The numerical approach employed for this investigation utilized ANSYS-Fluent software. The findings of the study revealed robust correlations between λ, temperature, and NO emissions. An increase in λ led to a decrease in both the average furnace temperature and average NO emissions at the boiler exit. Specifically, increasing the value of λ from 1.05–1.45 consistently reduces the average NO emissions from 1541 ppm to 653 ppm. In other words, a 27% increase in λ resulted in approximately a 55% reduction in NOx emissions. As λ increases, the volumetric absorbed of radiation decreases owing to the reduced concentrations of CO₂ and H₂O. Notably, the maximum combustion efficiency, reaching 37.88%, is achieved at a λ value of 1.35, corresponding to the lowest average flue gas temperature. The results show that to achieve the best performance with high efficiency and low NO emissions, the boiler needs to be operated at an excess air factor of about 1.35.