© 2021The effect of soot particles and aggregates on radiative heat transfer in bubbling fluidized bed combustors is investigated. For this purpose, a soot radiative property model based on Rayleigh scattering theory is coupled with in-house developed 1-D gray and spectral radiation codes and a 3-D spectral radiation code based on method of lines solution of discrete ordinates method for the application of (i) a 1-D slab problem involving combustion gases and soot and (ii) freeboard of a 0.3 MWt atmospheric bubbling fluidized bed combustion test rig including combustion gases, fly ash particles and soot. The predictions of the 1-D radiation code reveal that (i) Planck-mean soot radiative properties provide reasonably accurate radiative heat transfer predictions (ii) soot particle diameter and number of soot particles in an aggregate do not considerably influence the net wall heat fluxes and source terms as absorption coefficient of soot is not significantly affected by those parameters and is orders of magnitude higher than scattering coefficient. Application of 3-D radiation model to the test rig shows that soot significantly contributes to radiative heat transfer in the freeboards of bubbling fluidized bed combustors. Soot has a noticeable impact on radiation even at very low volume fractions.