Alan S. Trimble

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.

Studies of the relationship between coal petrology and grinding properties

Abstract The maceral and microlithotype composition of selected coals has been investigated with respect to the grinding properties, specifically Hardgrove grindability index (HGI), of the coals. The study expands upon previous investigations of HGI and coal petrology by adding the dimension of the amount and composition of the microlithotypes. Coal samples, both lithotypes and whole channels, were selected from restricted rank ranges based on vitrinite maximum reflectance: 0.75–0.80% R max , 0.85–0.90% R max and 0.95–1.00% R max . In this manner, the influence of petrographic composition can be isolated from the influence of rank. Previous investigations of high volatile bituminous coals demonstrated that, while rank is an important factor in coal grindability, the amount of liptinite and liptinite-rich microlithotypes is a more influential factor. In this study, we provide further quantitative evidence for the influence of microlithotypes on HGI and, ultimately, on pulverizer performance.

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).

Temporal and spatial variations in fly ash quality

Abstract Fly ash quality, both as the amount of petrographically distinguishable carbons and in chemistry, varies in both time and space. Temporal variations are a function of a number of variables. Variables can include variations in the coal blend organic petrography, mineralogy, and chemistry; variations in the pulverization of the coal, both as a function of the coals Hardgrove grindability index and as a function of the maintenance and settings of the pulverizers; and variations in the operating conditions of the boiler, including changes in the pollution control system. Spatial variation, as an instantaneous measure of fly ash characteristics, should not involve changes in the first two sets of variables listed above. Spatial variations are a function of the gas flow within the boiler and ducts, certain flow conditions leading to a tendency for segregation of the less-dense carbons in one portion of the gas stream. Caution must be applied in sampling fly ash. Samples from a single bin, or series of bins, may not be representative of the whole fly ash, providing a biased view of the nature of the material. Further, it is generally not possible to be certain about variation until the analysis of the ash is complete.

Major and Minor Element Distribution in Fly Ash from a Coal-Fired Utility Boiler in Kentucky

Study of the combustion of a multiseam blend of southeastern Kentucky high volatile A bituminous medium sulfur coal in a 220-MW wall-fired utility boiler demonstrated that there is significant asymmetry in the distribution of major elements and oxides, including sulfur and carbon, and minor elements in the ash collection system. Partitioning of volatile elements, such as Zn and As, according to flue gas temperature is a well-known phenomenon. Hg distribution is related to both the flue gas temperature and the amount of carbon in the fly ash. In addition, many elements show a distinct lateral asymmetry within individual rows of the ash-collection system. Certain aspects of the element distribution appear to be related to the carbon distribution. Hg is an example of an element with a lateral distribution tied to carbon. Other elements, such as Mo, As, Mn, and Cr, may be incidental relationships, tied to the relative increase in glassy fly ash constituents in the absence of carbon.

Further Investigation of the Impact of the Co-combustion of Tire-derived Fuel and Petroleum Coke on the Petrology and Chemistry of Coal Combustion Products

Abstract A Kentucky cyclone-fired unit burns coal and tire-derived fuel, sometimes in combination with petroleum coke. A parallel pulverized combustion (pc) unit at the same plant burns the same coal, without the added fuels. The petrology, chemistry, and sulfur isotope distribution in the fuel and resulting combustion products was investigated for several configurations of the fuel blend. Zinc and Cd in the combustion products are primarily contributed from the tire-derived fuel, the V and Ni are primarily from the petroleum coke, and the As and Hg are probably largely from the coal. The sulfur isotope distribution in the cyclone unit is complicated due to the varying fuel sources. The electrostatic precipitator (ESP) array in the pc unit shows a subtle trend towards heavier S isotopic ratios in the cooler end of the ESP.