Energy & Fuels 2005, 19, 1911-1918
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Distribution of Polycyclic Aromatic Hydrocarbons in Lime Spray Dryer Ash Ping Sun, Panuwat Taerakul, Linda K. Weavers,* and Harold W. Walker Department of Civil and Environmental Engineering and Geodetic Science, The Ohio State University, 470 Hitchcock Hall, 2070 Neil Avenue, Columbus, Ohio 43210 Received January 22, 2005. Revised Manuscript Received May 17, 2005
Four lime spray dryer (LSD) ash samples were collected from a spreader stoker boiler and measured for their concentrations of 16 U.S. EPA specified polycyclic aromatic hydrocarbons (PAHs). Results showed that the total measured PAH concentration correlated with the organic carbon content of the LSD ash. Each LSD ash sample was then separated using a 140 mesh sieve into two fractions: a carbon-enriched fraction (>140 mesh) and a lime-enriched fraction (140 mesh and a 140 mesh fraction was further separated using a lithiumheteropolytungstate (LST) solution with a specific gravity of 1.84 g/mL. A total of 0.5 g of the >140 mesh sample and 10 mL of the LST solution were well-mixed in a 15 mL glass centrifuge tube and centrifuged at 8000 rpm for 30 min. Because of their low density, the unburned carbon particles floated to the top of the centrifuge tubes. These unburned carbon particles were decanted, collected on filter paper, washed with 50 mL of high purity water to remove the residual LST solution, and dried in an oven at 60 °C for 12 h. Sample Characterization. Scanning electron microscopic (SEM) images were taken by a JEOL JSM-820 SEM with (14) Khim, J. S.; Kannan, K.; Villeneuve, D. L.; Koh, C. H.; Giesy, J. P. Environ. Sci. Technol. 1999, 33, 4199. (15) Arditsoglou, A.; Petaloti, C.; Terzi, E.; Sofoniou, M.; Samara, C. Sci. Total Environ. 2004, 323, 153. (16) Ghosh, U.; Talley, J. W.; Luthy, R. G. Environ. Sci. Technol. 2001, 35, 3468. (17) Taerakul, P.; Sun, P.; Walker, H.; Weavers, L.; Golightly, D.; Butalia, T. Fuel 2005, in press. (18) Low, G. K.; Batley, G. E. J. Chromatogr. 1986, 355, 177. (19) Maroto-Valer, M. M.; Taulbee, D. N.; Hower, J. C. Fuel 2001, 80, 795.
Sun et al. Oxford eXL energy-dispersive X-ray analyzer (JEOL USA Inc., Peabody, MA). Mineralogical analysis of samples was accomplished with a Philips X-ray Diffractometer (XRD) (Philips Analytical, Natick, MA) with CuKR radiation at 35 kV and 20 mA. The specific surface area (SSA) was measured by BET surface area analysis conducted on a manually controlled Micromeritics FlowSorb 2300 volumetric system (Micromeritics, Norcross, GA). A nitrogen (30% v/v) and helium mixture was used as the adsorbate gas. All SSA data were validated by a certified standard reference material CRM 171 from Bureau of Reference, European Commission. Inorganic elemental analyses were determined by a Vista Pro simultaneous inductively coupled plasma optical emission spectrometer system (Varian, Walnut Creek, CA). Detailed elemental analysis procedures are described elsewhere.17 Organic carbon content of the LSD ash was calculated by subtracting the total inorganic carbon content (TIC) from the total carbon content (TC). Samples were combusted under pure O2 at 900 °C in a ThermoQuest carbon/nitrogen analyzer (ThermoQuest, Waltham, MA) to measure TC. TIC was determined by carbon coulometry (UIC Inc., Joliet, IL). Upon introduction of a sample into the sample flask, the system was purged with a CO2-free carrier gas to eliminate atmospheric CO2. Then, 2 N HClO4 was added and heated, and inorganic carbon was oxidized to gaseous CO2 and measured by a CO2 detector. Ultrasonic Extraction of PAHs. The ultrasonic extraction was conducted based on EPA standard method 3550B and optimized based on Sun et al.20 For LSD ash and >140 mesh and 140 mesh and 140 mesh fraction using density separation with a LST solution. Characterization of PAHs on these separated fractions was then performed. Characterization of LSD Ash Fractions. An SEM image of the >140 mesh fraction separated from 4-LSD showed partially burned carbonaceous material covered with lime particles (Figure 1c). The XRD pattern (Figure 2) of this fraction showed a pattern similar to the parent 4-LSD ash except for the obvious drifting baseline, indicating the presence of amorphous carbonaceous material and graphite. As for the 140 mesh fraction was much higher than the parent LSD ash sample. For example, the >140 mesh fraction separated from 1-LSD ash had an organic carbon content of 48.5% as compared to 7.0% in the parent ash sample, indicating an enrichment of carbonaceous materials in the >140 mesh fraction. Similar to organic carbon, the concentrations of Al, Fe, and Si were also higher in the >140 mesh fraction, indicating an accumulation of fly ash constituents. As compared to the >140 mesh fraction and parent LSD ash sample, the
