Mathematical modelling of slow pyrolysis of a particle of impregnated wood

Abstract

Low-temperature pyrolysis is a possible route for the disposal of chromated copper arsenic (CCA) impregnated wood waste. A mathematical model (heat and mass transfer) including chemical reactions of the thermal degradation of a particle of wood is presented. A spherical particle is heated by a convective nitrogen flow. The progress of the pyrolysis process is characterized by three main steps: 1) as initially it contains water, the moisture content goes down and water vapour is evacuated through the outlet surface; 2) the dried wood temperature increases, reaches a certain temperature and pyrolysis reactions start; 3) up to 270°C, pyrolysis starts and wood produces a solid called char and several volatiles. During each step, time and space evolution are observed. Our model predicts intra-particle profiles for several variables (temperature, moisture content, concentration of wood). Simulations are presented with a spherical particle of 1cm radius. The results shown are in accordance with what was expected. It clearly shows three main steps: heating + drying; only heating; and heating + thermal degradation.