RADIATION PROPERTIES OF COAL COMBUSTION PRODUCTS

An assessment is made of the experimental data and the theoretical bases for determining the absorption and scattering coefficients of the coal products of combustion. Particular attention is devoted to the complex refractive indices for char and ash. A dispersion relation is developed from sparse extinction data that can be used to estimate the optical constants of char. Considerable uncertainity and scatter are found in the literature data on ash optical constants and are attributed to variability in ash composition, lack of experimental rigor and limitations in the data reduction procedures. A correlation is presented for estimating the complex refractive indices of ash as a function of its mineral composition. A parametric study is conducted to elucidate the role of char, soot and ash particulates in determining the radiation properties of coal flames. The effects of combustion particulates are discussed in terms of the modification of the band structure of gas radiation to a luminous spectrum. introduction of scattering in radiation transport, particle size distribution. particle loading and particle composition. The results are interpreted as possible effects of coal beneficiation, micronization and flyash composition on heat transfer to the water walls of a coal furnace.