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The photoacoustic effect is investigated as a method for measuring unburned carbon in fly ash. The technique has the potential for automatic, on-line measurements without interference from fly ash constituents other than unburned carbon. Two excitation sources were investigated in this study: 0.632 μm optical radiation from an He-Ne laser and 2450 MHz microwave radiation with a free space wavelength...
The results are reported of detailed physical characterization of six ashes from coals representative of those burned in US power plants. Centrifugal separation was used to classify the ashes into six density categories in the range < 1.6 to > 3.2 g cm -3 . The size distributions of all density classes were determined in the range 1-200 μm. For most of the density classes, log-normal...
Zeolites were synthesized from fly ash by alkaline hydrothermal activation. High-Fe fly ash from the Teruel power station in NE Spain was the starting material. The activation was performed by 0.1 M NaOH and KOH solution in a closed system. Zeolite formation was studied as a function of temperature (60 and 150°C), reaction time (24, 168 and 336 h) and sample ratio (30, 60, 100 and 200 gl - ...
Results are given on the mineralogy, morphology, geochemistry and physical characteristics of fly ash from the Megalopolis lignite fields, Peloponnese (S. Greece). The main mineral species present are quartz, anhydrite, plagioclase, haematite, gehlenite and calcite. Also present, in minor and trace amounts, are lime, alkali feldspars, bassanite, gypsum, mica and unburnt lignite. Morphologically,...
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...
The photoacoustic response of unburnt carbon in fly ash to infrared radiation was investigated. The photoacoustic effect is the conversion of modulated electromagnetic radiation absorbed by gaseous, liquid or solid media into an acoustic wave, which can be detected by a sensitive microphone. The goal of this work was to develop an off-line instrument to measure unburnt carbon in fly ash. Twenty-four...
The sulfur removal potential of the water-soluble fraction of fly ash in oxydesulfurization of coal was investigated using some high-sulfur Turkish lignites. The effects of the amount of fly ash used, temperature, partial pressure of oxygen and time were studied in the ranges 5-40 g, 403-498 K, 0.0-1.5 MPa and 15-90 min respectively. The extents of pyritic and organic sulfur removal and recoveries...
A test procedure based on heat of hydration was developed to assess more accurately the reactivity and behaviour of fly ash for utilization. The technique uses a Dewar flask or a modified oxygen bomb calorimeter to determine the temperature change and rate of change after the addition of water to fly ash. X-ray diffraction is performed on the hydrated material after the hydration test to follow...
A laboratory-scale triboelectrostatic separation system in conjunction with analytical techniques was used to study fly ash beneficiation. Fly ash samples were characterized by size analysis and carbon content and then subjected to dry triboelectrostatic separation. Due to differences in the surface physical and chemical properties of the carbon and ash, particles of unburnt carbon and fly ash were...
The present study focuses on the synthesis of zeolites after fly ash activation, the major objectives being: (a) to study the activation processes; (b) to elucidate the activation conditions for maximum synthesis efficiency; (c) to optimize the conditions for the monomineral synthesis; and (d) to test synthesis efficiencies for different fly ash types. Fly ash was activated by NaOH and KOH solutions...
The ways in which air classification, electrostatic recovery and density separation can be used to obtain specific fractions of fly ash with different characteristics are described. Possible markets for these products are discussed.
The most important commercial outlet for coal ash is as a partial replacement for Portland cement in the concrete industry. High levels of unburnt carbon can render ash samples unsuitable for this high-value market by interfering with the action of air-entraining admixtures, which are specialty surfactants used to stabilize air bubbles in concrete mixtures. An initial laboratory investigation was...
Two radiation-based techniques for determining the distribution and relative abundance of radionuclides are described, and applied to a suite of fly ash and bottom ash samples from a Kentucky power plant. The technique of fission-track radiography provides new observations of the variety of uranium hosts and of uranium distribution in individual particles of fly ash, and thus aids prediction of the...
The mineralogical, morphological, physical and chemical properties of seven different fly ashes from eastern, central and western lignite and bituminous coal fields in Turkey are compared in this study. The mineral matter in the fly ashes, determined by means of X-ray diffraction, is dominated mainly by anhydrite, lime, quartz and hematite + ferrite spinel. The three low-calcium ashes--Soma, Seyitomer...
Coal-burning plants produce large amounts of fly ash as a residue. Fly ash has been used in construction, agriculture, metal recovery and water pollution control. This paper considers the efficiency of fly ash in the removal of heavy metals (Cd and Cu). The fly ash is shown to be an effective metal adsorbent for these two metals. Adsorption capacity increases as metal initial concentration decreases...
To accommodate the many new subbituminous fly ashes, the American Society for Testing and Materials (ASTM) established two classes of fly ash, Class F from bituminous coal and Class C from subbituminous and lignite coal. However, the wide variability of the Class C ashes from location to location led to extensive X-ray diffraction studies, with the conclusion that the mineralogy was more important...
Fly ash from a power plant in Gdansk, Poland is stockpiled at two dump sites and contains an average of 15wt% combustible residue, in the form of very fine coke particles. If recovered, the coke could serve as environmentally friendly fuel or as a source of carbon-derived materials, and the ash could be utilized in the production of construction materials. Since the fly ash material is already wet,...
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...
This paper describes how low-lime fly ash can be used to develop chloride-resistant concrete by improving both its physical resistance to the ingress of chlorides and binding capacity of these ions in the cover zone. This includes optimizing the fly ash content, reducing the water/binder ratio of the concrete, processing fly ash to improve its particulate characteristics and, finally, using ternary...
The chemical characteristics of fly ash samples from combustion of three fuels: coal, peat and wood chips, have been studied. The ash materials were collected in the 12MW CFB at Chalmers University of Technology during full load combustion with similar standard combustion parameters. The samples were characterized in terms of chemical composition, mineralogy and leaching behavior. The special characteristics...
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