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DESIGN AND CHARACTERIZATION OF AN ULTRAFINE COAL ASH AEROSOL GENERATOR FOR DIRECT ANIMAL EXPOSURE STUDIES
Citation:
YOO, J., W. P. LINAK, C. A. MILLER, T. SHINAGAWA, H. JANG, M. IAN I. GILMOUR, AND J. O. WENDT. DESIGN AND CHARACTERIZATION OF AN ULTRAFINE COAL ASH AEROSOL GENERATOR FOR DIRECT ANIMAL EXPOSURE STUDIES. Presented at 9th International Congress on Combustion By-Products and Their Health Effects, Tucson, AZ, June 12 - 15, 2005.
Description:
Primary ultrafine particulate matter (PM) is produced during pulverized coal combustion by the nucleation and heterogeneous condensation of vapor-phase species. This differs from the mechanisms that control the formation of the supermicron fly ash that is heavily influenced by the fragmentation and coalescence of aluminosilicate phases derived from clay minerals in the coal. Although the ultrafine fraction typically represents much less than 5% of the total fly ash mass, this fraction dominates the particle number concentrations and exhibits reduced collection efficiency through particulate control systems. Recently published results from our group indicate that the ultrafine fraction of coal fly ash (operationally defined as PM<0.2 �m diameter) exhibits enhanced pulmonary toxicity compared to both PM fractions less than and greater than 2.5 �m. However, these exposures were performed by intratracheal instillation of collected particles that does not necessarily simulate actual mechanisms of pulmonary exposure. This paper describes the design and characterization of an ultrafine coal ash generator that can be used for direct animal inhalation exposure studies. The system consists of a pulverized coal feeder, an externally heated three-zone (1350 �C) drop tube furnace, a cyclone particle separator, and an exposure chamber. System air and coal feed rates are 12 L/min and approximately 1 g/h, respectively. From the furnace, the emissions are passed through a five-stage cyclone designed to aerodynamically classify the primary fly ash particles into size fractions ranging from greater than 5 to approximately 0.5 �m (diameter) with minimal pressure drop. Particles less than approximately 0.5 �m are further diluted (23 L/min) and introduced to a 134 L exposure chamber (0.26 volume exchanges per min). To-date, Utah bituminous and Illinois bituminous coals have been characterized in preparation for animal exposure studies. In addition to temperature, pressure, humidity, noise level, and gas concentrations (O2, CO2, CO, NO, and SO2), the chamber environment has been characterized for ultrafine particle mass (TEOM, M-29), particle number, and size distribution. Extracted PM samples have been characterized by scanning electron microscopy and x-ray fluorescence spectroscopy. The system as currently configured is capable of conducting acute and chronic studies and is able to operate continuously up to 12 hours with minimal supervision.