Boiler emissions are the primary sources of atmospheric nitrogen oxide (NOx) emissions. Exceeding the NOx emission limit can shut down the boiler, causing financial losses. Herein, a new preheated combustion method is proposed to prevent coal-fired boilers from exceeding the NOx emission limit at low loads. This is a simulation study of internal combustion burners and a 600 MW tangentially fired boiler using a pulverized coal preheating method that explores syngas production patterns after pulverized coal is preheated, the effects of flow characteristics, and variations in NOx and unburned carbon content under different preheating ratios. Our results indicated that the internal combustion burner had a stable preheating effect. The volume fractions of CH4, CO, and H2 at the burner outlet were 0.95%, 12.7%, and 0.8%, respectively. The fuel nitrogen precipitated during the preheating process was converted into N2. High-temperature char and syngas entered the furnace chamber and were mixed with air to accelerate combustion, which enhanced the jet flow intensity and improved the combustion stability at 50% load. The top burner exhibited a more significant nitrogen reduction than the bottom burner. The NO reduction from retrofitting Layers D and E accounted for 53% after retrofitting all five layers. When the preheating ratio was increased from 0 to 100%, NOx concentration was reduced by 63.6% at 6% O2, while unburned carbon content was reduced by 41%, which improved combustion efficiency. By discussing the advantages of internal combustion burners for retrofitting a 600 MW tangentially fired boiler, this study provides theoretical guidance for the application of preheating methods in peaking conditions. Display omitted