Characterization of fine particulate matter produced by combustion of residual fuel oil

Combustion experiments were carried out on four different residual fuel oil s in a 732-kW boiler. PM emission samples were separated aerodynamically by a cyclone into fractions that were nominally less than and greater than 2. 5 mu m in diameter. However, examination of several of the samples by compu ter-controlled scanning electron microscopy (CCSEM) revealed that part of t he PM,, fraction consists of carbonaceous cenospheres and vesicular particl es that range up to 10 mu m in diameter. X-ray absorption fine structure (X AFS) spectroscopy data were obtained at the S, V, Ni, Fe, Cu, Zn, and As K- edges and at the Pb L-edge. Deconvolution of the X-ray absorption near edge structure (XANES) region of the S spectra established that the dominant mo lecular forms of S present were sulfate (26-84% of total S) and thiophene ( 13-39% of total S). Sulfate was greater in the PM2.5 samples than in the PM 2.5+ samples. Inorganic sulfides and elemental sulfur were present in lower percentages. The Ni XANES spectra from all of the samples agreed fairly we ll with that of NiSO4, while most of the V spectra closely resembled that o f vanadyl sulfate (VO.SO4.xH(2)O). The other metals investigated (i.e., Fe, Cu, Zn, and Pb) also were present predominantly as sulfates. Arsenic was p resent as an arsenate (As+5). X-ray diffraction patterns of the PM2.5 fract ion exhibit sharp lines due to sulfate compounds (Zn, V, Ni, Ca, etc.) supe rimposed on broad peaks due to amorphous carbons. AII of the samples contai n a significant organic component, with the loss on ignition (LOI) ranging from 64 to 87% for the PM2.5 fraction and from 88 to 97% for the PM2.5+ fra ction. Based on C-13 nuclear magnetic resonance (NMR) analysis, the carbon is predominantly condensed in graphitic structures. Aliphatic structure was detected in only one Of seven samples examined.