Modeling Wood Degradation by the Unreacted-Core-Shrinking Approximation

Abstract

The unreacted-core-shrinking approximation is used to model one-dimensional transport phenomena and finite-rate kinetics of thick wood pyrolysis. A quasi-steady-state formulation of the equations is suggested because the effects of process transients along the charred region are shown to be negligible. Temperature dynamics of the unreacted core are described with either a concentrated-parameter model or a distributed-parameter model combined with an integral solution method. Though both treatments produce qualitatively similar predictions, only in the latter case is good quantitative agreement obtained with measurements of volatile release characteristics (external radiative heat fluxes in the range 40−80 kW/m2). Depending on material properties and reaction kinetics, convective heat transfer may play an important role in the particle heating rate and conversion time. The model shows significant sensitivity to the activation energy of the pyrolysis reaction, the effective thermal conductivities of wood and char, and the wood thermal capacity.