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Field measurements on the generation and emission characteristics of PM2.5 from industrial fluidized bed boilers

ABSTRACT This study presented new field measurement data on the particle size distributions, morphological characteristics, and elemental composition of particulate matter (PM)2.5 (particle diameter less than 2.5 mm) from 12 industrial boilers, including eight circulating fluidized bed boilers (CFB) and four bubbling fluidized bed boilers (BFB). Measurement in situ was taken with an electrical low-pressure impactor equipped with a two-stage dilution sampling system. Morphological characteristics were determinded by electron microscope (SEM), and elemental compositions of the samples were determinded by X-ray fluorescence (XRF) and inductively coupled plasma (ICP). The results show that before and after the dust removal, the number concentration distributions of PM2.5 display bimodal distributions, one peak is between 0.07 and 0.12 μm, and the other peak is between 0.32 and 0.48 μm. And the particle concentrations of PM2.5 depended mainly on submicron particles (less than 1 µm in diameter), formed by gasification-condensation mechanisms. The mass concentration distributions of PM2.5 showing no peak distribution and increase with the particle size. Compared to electrostatic precipitators (ESPs) and fabric filters (FFs) , the ESPs has a lower removal efficiency of PM2.5. The morphological characteristics of PM2.5 before and after dust removal contain irregular particles and spherical particles. The mass percentages of Na, K, and Fe in PM2.5 after the dust removal are nearly the same as those before the dust removal, but Si, Ca, and Al in PM2.5 decreased after dust removal and S in PM2.5 increased after dust removal. Although the hazardous elements Cr, V, Mn, and Ni in PM2.5 after dust removal did not change significantly, the Pb, Cd, As, Se, and Hg increased after dust removal. These data clearly show that the composition of PM2.5 changes as dust are removed by air pollution control devices.