By using low pressure impactor

fly ash was sampled at the inlet and outlet of ESP in 50 MW and 100 MW utility boilers separately.The composition

mass size distribution and microstructure of fly ash were measured by using X-ray fluorescence

0.001 mg precision microbalance and scanning electron microscope (SEM).A similar bimodal distribution of PM10 was obtained in both boilers studied

the small and large modes were formed at 0.1 μm and 4 μm

respectively.The chemical composition of the size-segregated ash showed that the ash particles smaller than 0.377 μm were formed via nucleation of vaporized ash components

and the primary chemical components were the oxides and sulfates of alkali metal and alkali earth metal in submicron-size ash.The microstructure measurements showed that the supermicron-size ash was formed by coagulation and coalescence of the submicron-size ash

and fragmentation and coalescence of mineral matter.Refractory oxides were the major composition of supermicron-size ash.