Biomass torrefaction is a thermal process used to produce high-grade solid biofuels from various streams of woody biomass or agro residues. The end product is a stable, homogeneous, high quality solid biofuel with far greater energy density and calorific value than the original feedstock. This provides significant benefits in logistics, handling and storage. It also opens up a wide range of potential uses for biomass.

Biomass torrefaction involves heating the biomass to temperatures between 250 and 320 degrees Celsius in a low-oxygen atmosphere. When biomass is heated at such temperatures, the moisture evaporates and various low-calorific components (volatiles) contained in the biomass are driven out. During this process mainly the hemi-cellulose in the biomass decomposes. This transforms the biomass from a fibrous low quality fuel into a product with excellent fuel characteristics.

Typically the torrefaction process results in a mass loss (dry basis) of 20-30% and an energy loss of 10-15%. To make a biomass torrefaction plant economically viable it is crucial to use the energy released in the volatiles. This can be done by burning the volatiles (torgas) in a lean gas combustor. The combustor can provide the heat for the drying and torrefaction. When the input feedstock has a moisture content of 35-45% the torrefaction process can be run auto-thermal. At higher mopisture content extra support fuel is needed to produce all the energy needed for the drying process.

State-of-the-art biomass torrefaction technologies, like Blackwood’s FlashTor® technology, are able to burn the torgas and control the torrefaction process in such a way that the energy released in the torgas does not exceed the energy needed for drying and torrefaction.

 

Torrefaction of biomass results in a high grade biofuel which can be used as a replacement of coal in electricity and heat production. Torrefied biomass can also be used as input for gasification processes in the production of high value biobased fuels and chemicals.