Numerical Simulation of the Combustion Characteristics in a Flue Gas Internal Recirculation Burner

The combustion characteristics and NOx emissions of a newly designed flue gas internal recirculation low-NOx burner (FIR) were studied. In the study, experimental and numerical simulations of the FIR low-NOx burner were conducted under natural inlet air conditions at three different powers. Results show that the fuel inlet strongly influences the jet effect, thus influencing the flue gas recirculation rate, flame stability, and NOx emissions. With a medium power of 20 kW, the NOx emission of a FIR low-NOx burner is lower than 30 mg/N m3. Higher or lower power will increase the NOx emissions or induce combustion instability. The swirling flow and bluff body structure can effectively improve the combustion stability. Three dominant frequencies of 54, 264, and 448 Hz can be observed from the power spectral densities of axial velocity, corresponding to the shedding vortex in the shear layer, the swirl frequency of processing vortex core (PVC), and the vortex induced by the PVC structure, respectively. The influences of vortex shedding and PVC structure are weak and inadequate to affect the overall flame stability.