Limits of variations on the structure and the fuel characteristics of sunflower seed shell through torrefaction

• This study shows how deep variations can be created on a woody biomass through torrefaction.
• H/C and O/C ratios of biomass moved from nearly a cellulosic model to a point between lignite and subbituminous coal.
• Low temperature reactivity was eliminated.

Sunflower seed shell (SSS) that is a woody waste biomass was torrefied at 300 °C which is the upper limit of torrefaction temperature to monitor the most severe variations on chemistry, morphology, functional groups, and the burning characteristics of biomass. Since, this biomass is rich in holocellulose (hemicellulosics + cellulosics) and relatively poor in lignin contents, it offers opportunity to observe the heat-induced variations on a woody biomass. Besides, the effects of torrefaction on SSS were firstly investigated in this paper. Comparison of H/C and O/C ratios before and after torrefaction revealed that the composition of SSS moved from nearly a cellulosic model to a point between lignite and subbituminous coal. It was also concluded that the torrefaction should be implemented at around the upper temperature limit to assure effective removal of volatiles and to improve the biomass. However, the residence time should be optimized to justify the effectiveness of torrefaction and to avoid the loss of carbon.