This work investigates thermal radiation in oxy-fired conditions. Both gas and particle radiation is modelled in an axi-symmetric cross section of a cylindrical furnace and differences in the radiative transfer between air- and oxy-firing are investigated. The particle radiative properties are calculated according to the Mie-theory, accounting for the spectral properties. The scattering by the particles is assumed to be isotropic. For the gas radiation, a Statistical-Narrow-Band (SNB) model is applied as reference. The properties of the combustion gas and the particle load are derived from measurements in a lignite flame in Chalmers University's 100 kW test rig. The wall flux and the radiative source term along the cylinder's diameter are compared to evaluate the difference in radiation between air- and oxy-fuel combustion. Special emphasis is put on the influence of load and distribution of particles, both in the flame and at the furnace exit. The results show that the presence of particles suppresses the influence of gas composition and small differences are seen between the different gas mixtures. It is also concluded that variation of temperature and particle load can have a significant impact on the radiative heat transfer. (C) 2013 Elsevier Ltd. All rights reserved.