Characterization of inorganic components of size-segregated particles in the flue gas of a coal-fired power plant

Particulate matter (PM) in the range of 0.03-10 mu m were collected with a 13-stage cascade impactor sampler at the outlet of an electrostatic precipitator (ESP) of a 100 MW lignite-fired power plant and were characterized by number and mass size distributions, element, and ion measurements. The number size distribution in the whole range of 0.03-10 mu m appeared to be bimodal with peaks at 0.06 and 0.835 mu m. The mass size distribution over 13 size-segregated fractions was also bimodal with peaks at 0.06 and 1.8 mu m. Four out of 13 fractions (namely, 0.03 < D-p < 0.06 mu m, 0.06 < D-p < 0.1 mu m, 0.7 < D-p < 1.1 mu m, and 1.8 < D-p < 2.7 mu m) were selected to represent the nano, ultrafine, submicron, and fine particles in this research, respectively. In general, the highest concentrations of elements were found in the fine fraction, in which Al and Ca were the most abundant elements, followed by S, Fe, and Na. In the nano fraction, Na and S were found with the highest levels. Enrichment coefficients of pollution elements (As, Pb, S, Se, Sb, and Cd) and some trace metal elements (Zn, Cr, Ni, Cu, V, and Co) suggested that these elements were enriched in the particles with smaller size. pH measurements showed that these flue gas samples were acidic and the acidity became weaker with larger particle size. Sulfate was the most predominant anion and remained at rather high levels due to the lack of desulfurization equipment. The high sulfate/nitrate ratios could be taken as a rudimentary indicator of such coal combustion sources.