The P-1 approximation and the Monte Carlo method are applied in cylindrical coal-fired furnaces. The absorption and scattering efficiencies and the phase function of coal, char and fly-ash particles are obtained from Lorenz-Mie theory and wavelength dependent optical properties based on measurements available in the literature. The influence of each kind of particle on the radiative heat transfer is investigated. Comparisons between the P-1 and the Monte Carlo methods are performed for various particle size distributions and mass concentrations. Isotropic and neglecting of scattering are evaluated against anisotropic scattering as potential simplifications in engineering applications.