Combustion performance and low NO emissions of hydrogen-enriched gas industrial boilers based on flue gas recirculation technology

To reduce the NO emissions of hydrogen-enriched industrial gas boilers caused by temperature enhancement, the flue gas recirculation technology was implemented in hydrogen-enriched industrial gas boilers to achieve low-nitrogen combustion. A Diffusion Flamelet model with the reaction mechanism of GRI-Mech 3.0 and an iterative method for calculating boundary conditions was built to numerically investigate the effects of hydrogen blending ratio and flue gas recirculation ratio on the combustion performance and NO emissions. The results show that NO emissions increase significantly at a high hydrogen blending ratio, which rises by 273.7 mg/Nm 3 when the hydrogen blending ratio increases from 60% to 100%. At an FGR ratio of 10–20%, the outlet NO emissions can be maintained below 50 mg/Nm 3 for hydrogen blending ratios of up to 80%. These findings reveal the effects and control mechanisms of hydrogen blending and flue gas recirculation on NO emissions from hydrogen-blended gas-fired boilers, which provides a reference for establishing operating conditions that achieve low NO emissions in hydrogen-enriched industrial gas boilers based on flue gas recirculation technology.