|Primary Particles Generated by the Combustion of Heavy Fuel Oil and Coal (56 pp, 1.3 MB) (EPA/600/R-02/093) November 2002
Researchers in EPA’s Office of Research and Development (ORD) have conducted a series of tests to characterize the size and composition of primary particulate matter (PM) generated from the combustion of heavy fuel oil and pulverized coal. These tests, conducted at ORD’s National Risk Management Research Laboratory in Research Triangle Park, North Carolina, involved burning four heavy fuel oils and seven coals in three small combustion systems and measuring size distributions and composition of the particles formed in the combustion process.
The research found that, for heavy fuel oils, particle composition and size are dependent on the combustion environment in the combustor. In the coolest test unit, unburned carbon in the fly ash was very high (70–90 percent by mass) and PM mass emissions were also high, with the majority of the mass being in the coarse (>2.5 micrometers [μm] in aerodynamic diameter) size range. In the hottest test unit, the PM mass emissions were approximately 50 percent of those from the coolest unit, unburned carbon levels were approximately zero, and the entire PM mass was in particles smaller than 1 μm in aerodynamic diameter.
For coal, the research identified a previously unreported trimodal particle size distribution with an ultrafine (~0.1 μm in aerodynamic diameter) mode, a coarse (>5 μm in aerodynamic diameter) mode, and a central mode of particles between 2 and 4 μm in aerodynamic diameter. The central mode has a composition similar to the coarse mode, but significantly different from the ultrafine mode. It is hypothesized that the composition of the ultrafine coal particle fraction is similar to the fine particle fraction in heavy fuel oil, which has been shown to generate increased toxicological responses following pulmonary exposure in laboratory animals. These findings may have implications for future PM control strategies, given the influence of operating conditions and the water-soluble composition of the smallest particle fractions of PM from metal-bearing fossil fuels.
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