In
this work, we study the thermochemical degradation and char
conversion of wet wood particles. The work is split in two main parts:
(1) the effect of the ash layer handling approach and (2) a parametric
study over different relevant parameters. In the study of the ash
layer handling, we investigate the effect of allowing the ash to remain
on the surface of the particle when the char is converted (Model A),
in contrast to removing the ash such that the reacting char layer
is always exposed (Model B). It was found that the two modeling concepts
yield significantly different mass losses and surface and center temperature
predictions. Model B presents a faster thermal conversion, while the
results predicted by Model A are in better agreement with what has
been observed experimentally. A parametric study was also done, where
the sensitivity to variations in thermal conductivity, specific surface
area, and gas permeability was studied. It was found that thermal
conductivity influences the time when drying and devolatilization
are accomplished. This is because these conversion stages are heat-transfer-controlled.
Char conversion is primarily affected by a shift to earlier times
for the initialization of the final char conversion when higher thermal
conductivities are used. It is found that the specific surface area
smaller than a critical value can significantly affect the final char
conversion time. Since char conversion is a key stage of wood combustion,
the full conversion time is also affected. The gas permeability primarily
affects mass diffusion into the particle. It was found that, up until
a critical effective gas permeability, the modeling results are sensitive
to assigned permeabilities.