Highlights

Particulate Studies on the Fine Fragmentation of Coal Ash

Scientific Achievement

Recent findings on coal ash have revealed a middle fine-fragment mode centered around 2 microns.  This research desired to test whether the primary formation mechanisms of fine fragmentation mode particles was due to effects related to oxygen-to-fuel stoichiometry and/or peak combustion temperature.

Illinois #6 coal was combusted under different stoichiometry and temperature conditions to generate the ash which was collected in a Dekati Low Pressure Impactor.  Extensive scanning electron microscope (SEM) image and elemental analysis was performed, primarily at the Argonne National Laboratory EMC, and used to evaluate the significant fine-fragment ash formation mechanisms and determine any possible link between elemental composition and formation mechanism.

There appears to be some effect on the fine-fragment ash from changing oxygen-to-fuel stoichiometry, but no significant changes caused by peak combustion temperature.  SEM imaging analysis suggests that both factors may contribute to changing formation mechanisms.  Imaging also suggests that the major particle types found in fine-fragment ash are, in decreasing order, coarse-type, multi-sphere, bursted or fragments, and agglomeration of multiple particles.  SEM elemental comparisons also showed that all fine-fragment ash types appear to have lower amounts of silicon relative to iron compared to larger coarse mode ash, with fragment-type particles tending to have greater amounts of iron, calcium, and aluminum relative to the other formation mechanisms.

Significance

This project provides greater insight into the complex formation mechanisms associated with fine fragmentation particles generated during coal combustion.  While this ash has harmful effects to human health it has the least understood formation mechanism compared to larger coarse and smaller ultrafine ash.  Knowing the factors behind how this size range of particulates forms is essential in either mitigating its hazardous effects or using particle surface area for possible flue-gas reactions.  A methodology was established for categorizing particles based on morphology that can be applied universally to fine fragment particles  Two peer review papers are currently under preparation with submission expected in fall 2008.  These results, coupled with other recent work, suggest that the fine fragment region may have multiple formation modes.  Future work should focus on examining this possibility in more detail as well as extending the work to other coals to insure universality of conclusions.

Performers

G. Fix, W. Seames (U. North Dakota; funding provided under DOE EPSCoR Infrastructure Improvement Grant, no. DE-FG02-06ER46292); D. J. Miller (Argonne-MSD)