The effect of preheating temperature and combustion temperature on the formation characteristics of PM0.4 from preheating combustion of high-alkali lignite

•Preheating combustion can simultaneously reduce the formation of PM0.4 and NOx.•The yield of PM0.4 can be reduced by 77.9% − 82.2% in preheating combustion with optimized preheating and combustion temperature.•The vaporization of inorganic elements mainly occurs in preheating furnace when combustion temperature is lower than preheating temperature.•A higher temperature under fuel-rich condition and a lower temperature under fuel-lean condition is preferred to reduce PM0.4 formation.•The vaporization of inorganic elements in preheating combustion is controlled by particle temperature rather than reductive atmosphere. Preheating combustion is getting popular because it can reduce NOx formation, but its effect on particulate matter (PM) formation is still unclear. This study focuses on the effect of preheating temperature (Tp) and combustion temperature (Tc) on the formation characteristics of fine mode particles (PM0.4) in preheating combustion. The mass-based particle size distribution, elemental compositions and morphologies of PM and number-based particle size distribution were analyzed to reveal the mechanisms of reducing PM0.4 formation during preheating combustion. The results showed that compared with conventional combustion, preheating combustion with optimized Tp and Tc can effectively decrease the mass yield of PM0.4 and NOx concentration by 77.9% − 82.2% and 70.9% − 77.8%, respectively. In preheating combustion, the mass yield of PM0.4 basically didn’t change with Tp. When Tc was lower than Tp, the mass yield of PM0.4 was basically unchanged with Tc. The precursors of PM0.4 mainly vaporized in the preheating furnace. The vaporization of inorganic elements, gas-to-particle transformation, and coagulation occurring in the combustion furnace had a negligible effect on the mass yield of PM0.4. When Tc was higher than Tp, increasing Tc can significantly increase the vaporization of inorganic elements from unburned char/coal particles in the combustion furnace. As a result, the mass yield of PM0.4 increased. To effectively reduce the formation of PM0.4 and NOx, a higher Tp and a lower Tc is suggested. The volatility of inorganic elements in preheating combustion has an order as S > Na > Mg > Fe≈Ca > Si. Refractory elements including Fe, Mg, and Ca contributed the most to decrease of PM0.4 in preheating combustion compared with conventional combustion. Preheating combustion has a stronger reductive atmosphere and a lower particle temperature. The vapori