A mathematical moder of transport phenomena and chemical processes of the thermal degradation of cellulose is presented. The kinetic model developed by Bradbury et al. (J. Appl. Polym. Sci. 23, 3271, 1979) for primary pyrolysis is extended to include secondary reactions of volatiles: [GRAPHICS] From the physical point of view, the model describes convective, conductive and radiative heat transfer, mass convection and diffusion and velocity and pressure variations interior to the porous solid (Darcy law). Furthermore, porosity, mass diffusivity, permeability and thermal conductivity vary with the composition of the reacting medium. Time and space evolution of the main variables, and reaction product distribution, are simulated by varying the reactor temperature and the reactor healing rate.