Abstract
By using low pressure impactor (LPI), fly ash was sampled at the inlet and outlet of dust cleaning equipments in a 50 MW and a 300 MW utility boiler. The emission characteristics, elemental size distribution, morphology and formation mechanisms of inhalerable particulate matter (PM10) were studied. The results show that PM10 of the two boilers has a similar bimodel distribution, in which the small and large mode are formed at 0.1 um and 4.0 um respectively; The efficiency of dust cleaning equipments decreases with the ash size decreasing; The elemental size distribution is also bimodal which is similar with the PM10 mass distribution. Mn, Cr, Cu and Zn obvious enrichment in submicron ash. The formation of submicron PM is suggested via vaporization and subsequent condensation of inorganic matter, while the supermicron ash is formed via char fragmentation, excluded mineral fragmentation and included mineral coalescence.