Effect of CaO additive on formation of PM 2.5 under O 2 /CO 2 atmosphere during coal combustion

The influence of CaO additive on the emission characteristics of PM 2.5 (particulates with aerodynamic diameter less than 2.5µm) was studied with a tube furnace. The combustion tests were carried out at 1123K under O 2 /CO 2 atmosphere. The PM 2.5 generated from coal combustion was collected and analyzed with an Electrical Low Pressure Impactor (ELPI). The results indicate that CaO is an important factor for the formation of PM 2.5 during coal combustion under O 2 /CO 2 atmosphere. The number and mass concentrations of PM1 diminish, but the number and mass concentrations of PM 1–2.5 enhance slightly after CaO is added. The size distributions of PM 2.5 are similar, which display two peaks around 0.2µm and 2.0µm, respectively. With increasing the additive weight ratio of CaO, the concentrations of S, Pb, Cu, Na and K decrease. The submicron-size ash particles smaller than 0.317µm are formed via nucleation of vaporized ash components, and the supermicron-size ash particles are formed by coagulation and coalescence of the submicron-size ash, and fragmentation and coalescence of mineral matter.