Numerical Investigation of Combustion Characteristics in a 330 MW Coal-Fired Boiler with Preheating Combustion Devices at Half Load Operation

To reduce the impact of renewable energy generation on power grid stability, preheating combustion technology is introduced to maintain coal-fired boiler efficiency at low loads. A 330 MW coal-fired boiler is retrofitted with preheating combustion devices to improve combustion performance and lower NOx emissions. The device is installed in the reduction zone between the furnace burnout zone and the burner zone. The combustion characteristics of the boiler with and without these devices are examined at 50% rated load. Numerical simulations are conducted to analyze the effects of preheating coal input and burner arrangement on temperature and species distribution within the boiler. Results show that increasing preheating coal input from 0 to 30 t/h enhances NOx reduction due to a higher flow rate of preheated products. At a preheating coal input of 20 t/h, the combustion efficiency reaches 96.9%. The NOx concentration at the furnace exit rises from 122.4 to 171.3 mg/Nm3 as the height of the burner arrangement increases. The middle three-layer burner arrangement achieves a uniform temperature distribution and a peak combustion efficiency of 97.6%. The bottom and middle three-layer burner arrangements are recommended for efficient and clean combustion. Compared to the original boiler, the retrofitted boiler’s combustion efficiency increases from 96.3% to a maximum of 97.6%, while the NOx concentration at the furnace outlet drops from 168.1 to 93.2 mg/Nm3, showing that installing preheating combustion devices promotes efficient and clean combustion.