Roles of Inherent Fine Included Mineral Particles in the Emission of PM10 during Pulverized Coal Combustion

Abstract

A coal sample was prepared from a Western Australia sub-bituminous coal via density separation (1.4–1.6 g/cm3) and size separation (63–90 μm). The mineral matter in the coal is of included nature, of which ~90% are fine mineral particles <10 μm. The raw coal was then washed by dilute acid to prepare an acid-washed coal from which char sample was generated in a quartz drop-tube/fixed-bed reactor at 1000 °C under argon atmosphere. The acid-washed coal and char samples were then combusted in a drop-tube furnace at 1400 °C in air. The PM10 samples collected (mostly PM1–10) contains mainly refractory species including Si, Al, Fe, Mg, and Ca and account for ~19.4% of the total ash collected in both the low-pressure impactor and the cyclone. This suggests important roles of the abundant fine included mineral particles originally present in coal. The significant roles of fine included mineral particles in PM1–10 emission during acid-washed coal and char combustion are also clearly evidenced with the presence of abundant individual but partially molten quartz ash particles in the PM1–10 range. PM0.1 contains dominantly volatile elements (e.g., Na, K, P, S, and Cl) and refractory elements (Fe and Si), while PM0.1–1 are mainly composed of Al, Fe, and Si. The significant roles of fine included kaolinite and/or Al-silicates particles in the emission of PM0.1–1 from char combustion are also observed. The results suggest that liberation and transformation of fine included mineral particles in coal/char during combustion is a key mechanism responsible for PM10 formation and/or emission. Experimental evidence further suggests that the fine included minerals within a burning coal particle clearly experience coalescence to form large agglomerated ash particles.