Effect of different flue gas recirculation rates on low‐ <scp>NOx</scp> combustion characteristics: A numerical simulation based on the combustion process of a gas boiler

Abstract NOx emissions from gas boilers severely impact the environment, and flue gas recirculation (FGR) technology can effectively reduce such emissions, yet the effects of different FGR rates on combustion performance and NOx formation remain unclear. This study thus used numerical simulation (via ANSYS Fluent, adopting the realizable k ‐ ε turbulence model and eddy dissipation combustion model) to investigate variations in combustion characteristics and NOx emissions under different FGR rates, aiming to optimize low‐NOx combustion strategies. Results showed that as the recirculation rate increased from 0% to 20%: the maximum velocity in the combustion zone rose from 0.88 to 4.2 m/s; the peak temperature in the high‐temperature region dropped from 2091 to 1684 K; the peak wall heat‐flux density on furnace sidewalls decreased from ~45 to 28–32 kW/m 2 , with more uniform thermal load distribution; and NOx concentration fell significantly from 110 to 38 mg/m 3 (the most notable reduction in the 5%–10% range). Additionally, simulated reactive species distributions matched measured data well in trend and magnitude (deviations ±8%), verifying the numerical model's accuracy and engineering applicability. The findings clarify the mechanisms of FGR rate impacts on low‐NOx combustion characteristics, providing theoretical support for optimizing low‐NOx combustion technologies and a reference for selecting suitable FGR rates in industrial boiler applications.