Effect of kaolinite additive on formation of PM2.5 under O2/CO2 atmosphere during coal combustion

The influence of kaolinite additive on the emission characteristics of PM2.5 (particulates with aerodynamic diameter less than 2.5μm) was studied with a tube furnace. The combustion tests were carried out at 1123 K under O2/CO2 atmosphere. The PM2.5 generated from coal combustion was collected and analyzed with an Electrical Low Pressure Impactor (ELPI). The results indicate that kaolinite is an important factor for the formation of PM2.5 during coal combustion under O2/CO2 atmosphere. The number and mass concentrations of PM1 diminish, but those of PM1–2.5 enhance slightly after kaolinite is added. The size distributions of PM2.5 are similar, which display two peaks around 0.2 μm and 2.0 μm, respectively. With increasing the weight ratio of kaolinite, the concentrations of S, Pb, Cu, Na and K decrease. The submicron-size ash particles smaller than 0.317 μm are formed via nucleation of vaporized ash components. The supermicron-size ash particles are formed by coagulation and coalescence of the submicron-size ash, and fragmentation and coalescence of mineral matter.