A model is constructed to assess the contribution of fly-ash particles to radiative heat transfer in a coal-tired combustion system. The measured fly-ash optical properties are used to prediet spectral extinction and scattering coefficients as well as the scattering phase function from the Lorenz-Mie theory. Radiative transfer calculations are then performed on the spectral basis for a one-dimensional planeparallel geometry using the Pq/approximation, which is known to be very reliable. The results show that scattering by the fly-ash particles impede the transfer of radiation from the hot flame to the walls of the combustion system and the blockage of radiation is strongly dependent on the wavelength.