Torrefaction is a process used to produce high-grade solid bio-fuels from various streams of low-grade woody biomass.
Torrefaction involves heating the biomass in a range between 250 and 350 degrees Celsius, in an inert atmosphere (i.e. free of oxygen). When biomass is heated at such temperatures, the moisture as well as various low-calorific components contained in the biomass are driven out. Then, a process known as de-polymerization takes place: the hemi-cellulose in the biomass starts to decompose and breaks down into polymers of a lesser size, which transforms the biomass into a product with coal-like characteristics.
Torrefaction of biomass has three immediate benefits over untreated biomass:
- The calorific value (energy per unit of weight) increases considerably;
- Torrefied biomass is easy to grind and can easily be compacted into a product with high volumetric energy density (energy per unit of volume); and,
- The physical properties of torrefied biomass, such as durability, homogeneity and hydrophobic behaviour are improved significantly, while the biological activity is strongly reduced.
