Fly Ash Characteristics and Radiative Heat Transfer in Pulverized-Coal-Fired Furnaces

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Abstract
The properties of a fly ash cloud which determine its radiative influence in furnaces are its dust burden, projected surface area and its mean absorption and scattering efficiency. The first property can be estimated by stoichiometry, the second by laboratory sizing of the ash and the radiative efficiencies should be related to its chemical character. Previous measurements of the absorption and scattering coefficients of ash in several power stations are interpreted in terms of these properties. The resulting estimates of the absorption index of the fly ashes are an order of magnitude higher than the dominant oxides in the ash. Ash is shown to be significant as an emitter and scatterer of radiation, with the present uncertainty in its optical properties leading to unacceptable errors in the calculation of radiative heat transfer.