3. Results and discussion
Due to evident changes in solid torrefied material comparing to
raw biomass the physical investigation has been done. The visual
effects, where the colour of the torrefied biomass appears darker
and looks like coal, with an increase in temperature and residence
time are presented in Fig. 2 I. Morphological changes in studied
samples were carried out by Scanning Electron Microscopy (SEM)
(Fig. 2 II). SEM is technique which allows to study the
structural variations of raw biomass and after torrefaction process.
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.