Investigation of the gas-solid and Fuel-N conversion characteristics during pulverized coal preheating with an improved char model

Nitrogen oxides (NO x ) emissions will exceed the limit when a coal-fired boiler is operated at low load. Preheating is an economically viable technology for reducing NO x emissions. However, current research primarily focuses on reducing NO x through organizing combustion after pulverized coal preheated. Limited attention has been given to studying the mechanism of syngas and characteristics of fuel-nitrogen (Fuel-N) conversion during the preheating stage. Therefore, it establishes a novel char model that takes into account the characteristics of the pore structure. The effects of excess air coefficients (α) on particle flow, syngas, and Fuel-N conversion are explored. The findings demonstrate that the improved char model can forecast the syngas and Fuel-N conversion correctly during preheating. The syngas decreases with increasing α, and the pore structure and preheating temperature are important factors affecting syngas. With an increase in α, there is an elevation in char conversion, but the reduction efficiency demonstrates an opposing trend. The minimum outlet NO x concentration is 26.82 mg/Nm 3 , which meets the emission standards. It clarifies the characteristics of gas-solid and Fuel-N conversion during the preheating stage, offering valuable insights for the design of novel preheating burners.