Inhibiting the formation of PM_0.4 by optimizing the distribution of excess air coefficient in preheating combustion of lignite

Preheating combustion can effectively reduce NOx concentration, but the formation characteristics of PM_0.4 in preheating combustion is unclear. In this study, the emission of PM_0.4 in preheating combustion was reduced by optimizing the distribution of excess air coefficient. The mass-based particle size distribution (MPSD) of PM₁₀, mass yield of PM_0.4, elemental compositions and morphologies of PM, and the number-based particle size distribution (NPSD) were analyzed to discuss the effect of α_p on PM formation. The results showed that in preheating combustion, with an increase of α_p, the mass yield of PM_0.4 first decreased and then increased. The mass yield of PM_0.4 is minimum when α_p is 0.6. Preheating combustion can simultaneously reduce PM_0.4 mass yield and NOx concentration. The relationship between NOx concentration and α_p is similar to the relationship between the mass yield of PM_0.4 and α_p. The MPSD of PM_0.4 is multimodal and unimodal when α_p is less than 1 and larger than 1, respectively. Particle volume concentration of PM_0.4 indicates that the multimodal and unimodal of PM_0.4 is a result of evolution of particles with different characteristics of gas-to-particle transformation. The effect of α_p on the transformation of inorganic element from coal particles to PM_0.4 is S > Fe ≈ Ca ≈ Mg > Na > Si. α_p affects the mass yield of PM_0.4 by affecting the combustion intensity of coal/char particles in preheating furnace and combustion furnace. When α_p is 0.6, the combustion intensity of coal particles in preheating furnace and combustion furnace minimize the vaporization of inorganic elements.