Browsing by Author "Metcalfe, R"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    The influence of fly ash morphology and phase distribution on collection in an electrostatic precipitator
    (Australian Institute of Physics, 2006-12-08) Metcalfe, R; Connor, J; Druskovich, D; Blackford, MG; Short, KT
    Fly Ash is the unburned portion of fuels which is carried away as solid particles in the hot gas stream of a furnace. It is of concern as a medium for the transport of heavy metal and other pollutants into the atmosphere, but has found application in cement manufacture and elsewhere. About 99% of the fly ash produced in a typical power station is removed by electrostatic precipitators or baghouse filters at the base of the emission stack. Precipitator efficiency is dependent on the charging properties of the fly ash particles and the adhesive forces between them. These forces in turn depend on the size, morphology, chemical constitution and phase distribution of the fly ash. X-ray diffraction (XRD) results indicate that about two thirds of the material from a typical Central Queensland power station is non-crystalline, mostly alumino-silicate glassy spheres; the remainder crystalline, mostly mullite, quartz, and iron oxides. Electron Microscopy shows fewer crystalline particles than expected from XRD and it is hypothesized that the crystalline material is largely embedded in the larger particles. Larger particles are usually found as aggregates held together by bridging material which may be small glassy particles, graphite sheets, or a mixture of amorphous material and small crystallites. Scanning probe microscopy gives indication of the nature and magnitude of the forces between particles, which is critical in forming the aggregates mentioned above, and in adhesion of the fly ash particles to the collector plates of the precipitator, and to one-another, and essential to the collection process.