Particle Size Distributions of Fly Ash Arising from Vaporized Components of Coal Combustion: A Comparison of Theory and Experiment

Abstract

A 100-kW-rated down-fired pilot-scale combustor was used to explore sub-micrometer coal ash aerosol formation for two coals under various air and oxy-combustion atmospheres. Particle size distribution (PSD) data were obtained through isokinetic sampling and then by electron mobility and light-scattering particle sizing. The sub-micrometer portion of the PSD exhibited an “accumulation” mode at ∼0.3 μm and, in some cases, an additional “nucleation” mode between 0.03 and 0.07 μm. Predictions of the temporal evolution of the sub-micrometer aerosol were made using a sectional coagulation model. A comparison to experimental measurements suggested that the “accumulation” mode was formed by coagulation of vaporized silicon-rich species, which occurred and was completed very close to the parent char particle and not in the mixed flue gas. This showed the importance of carefully characterizing microscale mixing phenomena around individual particles. For the sodium-rich species that had heretofore been thought to nu...