Significant Roles of Inherent Fine Included Mineral Particles in the Emission of PM_1–10 During Pulverised Coal Combustion

This study investigates the roles of inherent fine included mineral particles in coal in the formation of inorganic particulate matter (PM) during pulverized coal combustion at 1,400°C. A Western Australia sub-bituminous coal (Collie coal) was used to prepare a raw coal sample of density-separated fraction (1.4–1.6 g/cm³) that is narrow-sized (63–90 μm). The raw coal was also washed using dilute acid to prepare an acid washed coal sample that is free of organically-bound inorganic species. Computer-controlled scanning electron microscopy (CCSEM) analysis shows that mineral matter in the raw coal is of included nature, of which ~90% are fine mineral particles <10 m. Combustion of the coal samples produces substantial PM_1–10 that accounts for 20.3–24.8% of total ash collected. The PM_1–10 samples contain abundant fine ash particles that are clearly originated from fine included mineral particles (e.g. quartz) inherent in the coal. The results suggest that liberation and transformation of fine included mineral particles in coal during combustion is a key mechanism responsible for PM_1–10 formation under the combustion conditions. Experimental evidence further suggests that significant coalescence of fine included minerals within a burning coal particle can clearly take place to form large ash particles in the form of agglomerates.