This paper describes a model for the fluidized bed combustion of volatile matter froth waste. This waste is assumed to be composed of wood, cardboard and PVC. The model assumes that a fraction of the volatile content is released within the freeboard, as a result of both pyrolysis and transport of the devolatilizing particles. The model describes precisely the diffusion-controlled combustion of the volatile matter within the bed, on the basis of a hydrodynamic model of the bed, combined with energy and mass balance equations. The results of the model show that the release of volatiles in the freeboard may increase the freeboard temperature by 200 K and may multiply the emissions of NO 25 times.