Fig. 2 shows the visual and SEM images of the surface of untreated
wood biomass and after torrefaction process. The raw wood
biomass has a coherent structure. The torrefaction process causes
damage to the wood surface and structure. The torrefied biomass
samples at 230 C temperature is characterised by a tubular-shape
structure with a partly cellular surface and elongated openings.
Torrefaction at higher temperatures (260 C and 290 C) leads to a
gradual degradation of the tubular-shape structures (Fig. 2.II.c,d).
As the torrefaction temperature increases, an increasing number of
characteristic openings in the surface are observed. The openings
are associated with the formation of pathways for gas products,
which are released during torrefaction from the solid bulk of
biomass. Most of the openings in the wood surface are visible after
torrefaction at a temperature of 290 C. It was confirmed that
temperature has significant effect in the decomposition of biomass
structure. Increasing torrefaction temperature intensifies the reaction
of cellulose, hence using the torrefied biomass as a lignin
fuel.