Radiation properties of coal char particle cloud

Abstract

This study is to evaluate the radiation properties of coal char and ash particles. Char in coal-firing and gasification processes exists in the form of heterogeneous composite particles consisting of nano-order fine particles made mainly of soot and micron-order particles of carbon and ash components. The radiation properties are discussed in terms of apparent extinction efficiency determined from spectra of transmissivity of a particle-liquid paraffin wax dispersion film as an independent parameter of particle dispersion density. Extinction efficiency measured directly from the original char gives an unacceptably great magnitude. However, if the original char was classified into a narrow particle size distribution by pretreatment with a wet method, the extinction efficiency of each particle showed a reasonable magnitude and successfully deduced an extinction coefficient of the original char dispersion with a certain content from combining that of each particle accounting for the fraction. The effect of carbon content in char particle excluding soot on extinction efficiency could also be correlated empirically by a simple function using the properties of carbon-free ash burnt out and ash-free carbon treated by hydrofluoric acid. Additionally, the value of apparent extinction efficiency measured from transmissivity of ash dispersion was compared with the properties estimated by applying the known refractive index into Mie's theory, and noted to be closer to rather absorption efficiency than the extinction efficiency analyzed theoretically, although scattering albedo was as large as over 0.9. This fact may result in that a strong forward scattering pointed out in a previous work was reasonable and the ash particle cloud can be assumed as an absorbing-emitting medium having the properties obtained here, ignoring the effect of scattering at least. © 2013 The Society of Chemical Engineers, Japan.