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 a form of heterogeneous composite particles consisting of nano-order fine particle made mainly of soot and micron-order particle of carbon and ash components. The radiation properties were discussed by a term 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 gave unacceptably great magnitude. However, if the original char was classified into a narrow particle size distribution by a pretreatment with a wet method, extinction efficiency of each particle showed a reasonable magnitude and deduced successfully extinction coefficient of the original char dispersion with a certain content from combining that of each particle with accounting for the fraction. The effect of carbon content in char particle excluding soot on extinction efficiency could be also 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 close to rather absorption efficiency than extinction efficiecny 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 the past work was acceptable 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.