Chemical Characterization of Feed Coal, Fly Ash, and Bottom Ash from a Power Plant Utilizing Northern Appalachian Basin Coal, USA

Understanding elemental partitioning in feed coals and coal combustion products (CCPs) in coal-fired power plants is necessary for making informed decisions concerning the potential release of elements to the environment. As part of a U.S. Geological Survey study to provide comprehensive datasets on the chemical composition of feed coals and CCPs in the nation, 110 samples were collected at a plant utilizing a high-sulfur (3.7 percent) coal from the Pittsburgh coal bed, in the Northern Appalachian basin. Samples include as-received coal (washed coal from mines), feed coal (including synfuel additives), pulverized coal (excluding pyrite rejected during pulverization), pyrite rejects, and composites of economizer fly ash, fly ash, and bottom ash.

As-received and feed coal samples have a mean ash content of 10.1 percent and mean sulfur content of 3.7 percent (all values are reported on a whole-coal basis). Pulverized coal samples have a lower sulfur content (3.5 percent) than as-received and feed coal samples, as a result of pyrite removal during the pulverization process. Hg content is at or below the detection limit (0.1 ppm) for all sample types, with the exception of pyrite rejects. Pyrite rejects have the highest mean concentrations of sulfur (8.8 percent) and elements that are associated with sulfides (Hg, 1.8 ppm; As, 455 ppm; and Se, 8.7 ppm). Preliminary microprobe analysis confirms the presence of As and Se in pyrite reject samples. Fly ash samples are enriched in As (67 ppm) and Se (4 ppm) compared to bottom ash samples (As, 6 ppm; Se, 0.2 ppm); this finding is consistent with previous studies indicating that the more volatile elements are preferentially partitioned in fly ash. Cr and Ni are concentrated in bottom ash, having mean contents of 365 ppm and 211 ppm, respectively.