Kinetics of Wood Devolatilization during Start-up

To design and optimize furnaces, modeling is a key tool. Modeling of solid fuel conversion requires the availability of valid kinetic data for the parametrization of combustion models. To provide kinetic data for low temperature devolatilization, 1 g of wood dust (oak and spruce) was devolatilized under isothermal conditions at 250-400 degrees C in ambient air. Between 250 and 300 degrees C, the reaction mechanism changes; thus only the data of 300-400 degrees C can be used for a kinetic analysis. For spruce, a pre-exponential factor of 237 s(-1) and an activation energy of 0.222 x 10(5) J/mol were measured, and for oak 89.6 s(-1) and 0.181 x 10(5) J/mol. As compared to literature data, the reaction is less temperature sensitive, indicating a diffusion limitation caused by the large sample size and experimental conditions. However, the results might be closer to reality as the conditions are similar to a furnace during start-up. Additionally, the release of the main elements, carbon, hydrogen, and oxygen, was measured. At low temperatures, carbon is enriched in the sample, as the sample is partially carbonized. With increasing temperature, more carbon is liberated as gases and less solid carbon remains.