Robert F. Rathbone

An examination of fly ash carbon and its interactions with air entraining agent

Four fly ash samples, which had previously been found to effect concrete air entrainment in a manner inconsistent with their respective loss on ignition, were investigated using several physico-chemical techniques. This study focused on characterization of the high-carbon fraction of each fly ash, obtained by a triboelectric separation process. While the four samples displayed varying reactivities toward AEA adsorption, the BET specific surface area of all four samples was determined to be essentially the same. Thermal analysis and petrographic examination revealed that the higher demand for air entraining agents exhibited by two of the samples could be directly related to the presence of a higher proportion of optically isotropic, amorphous carbon. Liquid and vapor phase adsorption analysis suggested that the surface chemistry characteristics of the isotropic carbon resulted in a higher adsorption capacity for polar compounds such as air entraining surfactants.

Characterization of fly ash from Kentucky power plants

Abstract Fly ashes from 21 Kentucky power plants were grouped according to the sulfur content of the feed coal. The highest-carbon fly ashes tended to be from the lowest-sulfur feed coals, partly because many of those plants were smaller and older than the higher-sulfur units. Iron oxide content increased at the expense of aluminium and silicon oxides in the higher-sulfur feed ashes. An increase in calcium and magnesium oxides towards the higher-sulfur feed ashes was due to the greater abundance of carbonate minerals in the higher-sulfur Illinois Basin coals. The highest arsenic values were among electrostatic precipitator ashes from medium-sulfur sources. The arsenic and lead contents of low- and medium-sulfur central Appalachian coals could be higher than those of high-sulfur Illinois Basin coals. Where direct comparison of fly ash and bottom ash was possible, the bottom ash was enriched in Fe 2 O 3 relative to the fly ash and most minor elements were depleted in the bottom ash relative to the fly ash. TCLP testing of selected fly ashes indicated that all of the leachates would pass the established RCRA limits. Some of the higher As and Cr levels were from fly ashes in the highest-sulfur category. For As, though, there is no significant correlation between fly ash As and leachate As.

Petrology, mineralogy, and chemistry of magnetically-separated sized fly ash

A class F fly ash from a high-sulfur coal source was wet-sieved at 100, 200, 325, and 500 mesh and each of the five size fractions was then magnetically separated. Each fraction was examined for petrography by optical microscopy, mineralogy by X-ray diffraction, and major and minor element chemistry by proton-induced X-ray emission (PIXE). Spinel (magnetite) is the major magnetic mineral, with hematite being another major iron oxide phase. As expected, the magnetite is most abundant in the magnetic fractions, but, due to mixed-phase fly ash particles, is not the only component in the magnetic fractions nor is it totally excluded from the non-magnetic fractions. Other mineral phases include quartz, mullite, and calcite, the latter being a secondary phase produced in the wet-sieving procedure from lime in the original fly ash. Chromium, likely associated with the spinels, is one minor element which is significantly higher in the magnetic versus non-magnetic fractions.

Activated extrudates by oxidation and KOH activation of bituminous coal

An investigation has been made of the synthesis of formed (extruded) activated carbons from a bituminous coal by KOH activation. The coal was first pretreated by oxidation with nitric acid, at different levels of oxidation severity, in an attempt to introduce properties similar to those possessed by lowrank coals that can be directly processed in this way. It is found that hard, high-surface-area activated extrudates can be successfully produced from pre-oxidized bituminous coal. The effects of nitric acid oxidation are to regenerate humic acids and introduce oxygen and NO2 functional groups, that are more concentrated in the humic acids. The magnitude of these changes increases with the severity of oxidation, the extent of which can be followed by optical microscopy using a dye technique. At nitric acid normalities above 0.25, the treated coals formed gel-like mixtures with KOH solution, and were easily extruded. Preoxidation was found to enhance the development of surface area in the heat-treated products, which also increased with the ratio of KOH to fixed carbon in the precursor. These parameters also strongly influenced the hardness of the extrudates. For a given oxidation severity, the hardness at first increased with the ratio of KOH to fixed carbon, then passed through a maximum. At high ratios, the extrudates were weak. The maximum hardness increased with the level of oxidation: at higher severities, extrudates were produced that were harder, and had higher surface areas, than samples of commercial carbons. The reduced hardness at high ratios is attributed to the dilution of the mixture of dispersed coal and coal particles by excess KOH, reducing the ability to form an extensive network of bridging linkages. Correspondingly, the optical texture of the harder extrudates was found to be homogeneous, whereas at high KOH ratios there was reduced fusion between coal particles and the appearance of cracks.

Case study of the conversion of tangential- and wall-fired units to low-NOx combustion: Impact on fly ash quality

Conversion of boilers to low-NOx combustion can influence fly ash quality in terms of the amount and forms of carbon, the overall fly ash fineness, and the relative amount of glass versus crystalline inorganic phases. All of these factors can influence the potential for a fly ash to be marketed for utilization. In this study, three coal-fired combustors, two tangentially fired and one wall-fired, all burning high-sulfur Illinois coal at the same power plant, were studied before and after conversion to low-NOx combustion. In all cases, the post-conversion fly ash was higher in carbon than the pre-conversion ash from the same unit. The fly ashes in at least two of the units would appear to have post-conversion ashes which still fall within the regional guidelines for the limit of carbon (or loss on ignition).

Petrology and palynology of the No. 5 block coal bed, northeastern Kentucky

Abstract The upper Middle Pennsylvanian (middle Westphalian D equivalent) No. 5 Block coal bed (Eastern Kentucky Coal Field of the Central Appalachian Basin) is a low-sulfur, compliance coal resource, dominantly comprised of dull, inertinite-rich lithotypes. Ash yields tend to be highly variable in the No. 5 Block, as does bed thickness and frequency of bed splitting. This study describes the petrographic, palynologic and geochemical characteristics of the No. 5 Block coal bed, and reports on some temporal and spatial trends among these parameters in eastern-northeastern Kentucky. Petrographically the No. 5 Block coal is predominated by dull, often high-ash lithotypes, with inertinite contents commonly exceeding 30% (mmf). The coal thins to the north-northwest where it tends to be higher in vitrinite and sulfur content. Representatives of large and small lycopsids and ferns (both tree-like and small varieties) dominate the No. 5 Block coal bed palynoflora. Calamite spores and cordaite pollen also occur but are less abundant. Small lycopsid ( Densosporites spp. and related crassicingulate genera) and tree fern (e.g. Punctatisporites minutus, Laevigatosporites globosus ) spore taxa are most abundant in dull lithotypes. Bright lithotypes contain higher percentages of arboreous lycopsid spores ( Lycospora spp.). Regionally, the No. 5 Block coal contains abundant Torispora securis , a tree fern spore specially adapted for desiccation prevention. This, along with overall high percentages of inertinite macerals, suggest that peat accumulation may have taken place in a seasonally dry (?) paleoclimate. The No. 5 Block coal bed thickens rather dramatically in a NW-SE direction, as does the frequency of coal bed splitting. This phenomenon appears to be related to increased accomodation space in the southeastern portion of the study area, perhaps via penecontemporaneous growth faulting. Maceral and palynomorph variations within the bed correspond with these changes. Thin coal along the northwestern margin tends to be vetrinite rich and contains abundant Lycospora , perhaps reflecting relatively stable peat-forming conditions. Thicker coal to the southeast contains more inertinite, high-ash coal layers, and inorganic partings. Spore floras contain more small lycopsid and tree fern components and are temporally variable, perhaps indicating a more unstable peat-forming environment.

Investigation of fly ash carbon by thermal analysis and optical microscopy

A previous study investigated various fly ashes that had comparable loss on ignition values, but significant differences with respect to air entrainment performance. Thermal analysis data suggested that a poorly performing fly ash, with respect to air entrainment, contained a higher proportion of carbon that gasifies (oxidizes) at comparatively low temperatures. A relatively high abundance of isotropic carbon was identified in the poor-performing ash using optical microscopy. The present investigation examined a larger collection of fly ash samples to determine if thermal analysis could be used as a prognostic tool for fly ash performance. An attempt was made to correlate mortar air and foam index values for each sample with differential thermal analysis (DTA) data. Optical microscopy and BET surface area analysis were used as supportive techniques. No clear relationship could be established with the thermal or optical methods, although fly ash performance did correlate well with BET surface area. A low temperature component of the DTA exotherms was considered to be a function of inorganic catalytic species that reside on the carbon surface and lower the ignition temperature.

Pervious Concrete: Compaction and Aggregate Gradation

Pervious concrete is very different from traditional portland-cement concrete (PCC). Therefore, there are open questions regarding the suitability of the current standard concrete testing protocols as they may be applied to pervious concrete. There are unique features associated with pervious concrete that may require special testing considerations. This paper examines the compaction and consolidation of pervious concrete. This study presents cylindrical specimen preparation techniques that will produce laboratory specimens that are similar to the field pervious concrete slab. Additionally, a simple correlation is provided that allows concrete designers to estimate the porosity ofpervious concrete based on its aggregate bulk density when crushed limestone is used. This practical tool saves time when designing pervious concrete mixtures.

Relationship between reflectance and structure of high surface area carbons

Abstract Reflectance measurements have been used to try to track the structural alterations during activated carbon synthesis by chemical activation. H3PO4 has been used as a chemical reagent with white oak, subbituminous coal and a bituminous coal, and KOH with a bituminous coal. The reflectance of thermally treated carbons follows a single correlation with heat treatment temperature (HTT), consistent with thermally induced increases in aromaticity and structural order. For chemically activated carbons, the relationship between reflectance and HTT depends upon the precursor-activant combination that is used. At low HTT, chemically activated carbons have higher reflectance than their thermally treated counterparts, due to accelerated chemical change. At higher HTT this situation is reversed, despite further increase in aromaticity. It is proposed that the development of significant porosity (principally in pores 2–50 nm in diameter) reduces the measured reflectance by contributing to the scattering of incident light.

Petrography of liquefaction residues: semifusinite concentrates from a Peach Orchard coal lithotype, Magoffin County, Kentucky

Abstract Liquefaction of a semifusinite-rich lithotype of the Peach Orchard coal from Magoffin County, Kentucky, indicated conversions at high temperatures and long residence times was a consequence of vitrinite, liptinite, and semifusinite reactivity. The percentage of oils and gases were similar to that produced at lower severity from a Springfield (Western Kentucky No. 9) coal. Semifusinite is converted to vitroplast and anisotropic semicoke in the liquefaction of an DGC inertinite concentrate and to anisotropic semicoke in the liquefaction of the parent coal. Granular residue increases in concentration in the higher severity residues.