Effects of physical and chemical properties of bright and dull coal lithotypes on the formation of char particles
Date of Award
Master of Science (MS)
The Energy and Environmental Research Center is working with EPRI and a consortium of companies in partnership with DOE to determine factors causing sticky ash to blind or bridge hot-gas cleanup filters. In this study, bright and dull lithotypes were separated from bituminous, subbituminous and lignitic coals to determine physical and chemical properties that may lead to the formation of different charforms, and consequently, fine and sticky ash that is problematic in coal-fired combustion systems.
Proximate and ultimate, maceral, and energy dispersive X-ray fluorescence (EDXRF) analyses were used to characterize each lithotype. A bench-scale pressurized fluidized-bed reactor (PFBR) was used to produce ash and char from the lithotypes. The lithotypes and char were examined with transmission electron microscopy. Nanometer-scale inorganic inclusions found in the char were investigated with energy dispersive spectroscopy. Char morphology and abundance were determined by scanning electron microscopy using image point-counting techniques.
PFBR tests and electron microscopy show that lithotype reactivity controls char morphologies, does not influence ash liberation in fluidized bed combustors, but may have an effect in other types of combustion. In addition, nanometer-scale inclusions observed in the subbituminous bright lithotype may affect fine ash formation in coal-fired combustion systems. Bright and dull lithotypes are similar with respect to the results of proximate and ultimate analyses except ash. The dull lignite, subbituminous, and bituminous lithotypes contain 9.39, 10.29, and 3.74 weight percent ash. The lignite, subbituminous, and bituminous bright lithotypes contain 3.90, 4.80, and 3.33 percent ash. EDXRF analyses show that the ash obtained from dull lithotypes contains more silicon whereas the ash associated with the bright lithotypes has more calcium, magnesium, sodium, and sulfur. Maceral analyses show that the bright lithotypes separated from lignite, subbituminous, and bituminous coals contain 97%, 97%, and 89% reactive macerals. Dull lithotypes of lignite, subbituminous, and bituminous coals have 74%, 89%, and 66% reactive macerals. The principal charforms identified are cenosphere, honeycomb, and solid. Bituminous bright lithotypes produce thin-walled cenosphere and thin-walled honeycomb charforms. Dull lithotypes produce thick-walled cenospheres, honeycomb char particles, and solid fragments. Subbituminous bright lithotypes produce abundant thin-walled honeycomb charforms. Less reactive charforms are associated with dull samples. High contrast nanometer-scale inclusions found in the subbituminous bright lithotype may influence the formation of fine and sticky ash. The PFBR tests show that the effect of lithotype on the quantity of fine ash formation in the PFBR is negligible. However, the lithotypes differ in char morphology, which is related to original maceral content.
Tomforde, Chad G., "Effects of physical and chemical properties of bright and dull coal lithotypes on the formation of char particles" (1998). Theses and Dissertations. 300.