What is Torrefaction
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.
Benefits of torrefied pellets over regular wood pellets
- Higher calorific value
- More homogeneous product
- Higher bulk density
- Excellent grindability
- Higher durability
- Hydrophobic nature/water resistance
- No biological activity
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.
Torrefied pellets are the ideal coal replacement
- Grinds & burns like coal – existing coal infrastructure can be used
- Lower feedstock costs
- Lower shipping and transport costs
- Minimal de-rating of the power plant
- Provides non-intermittent renewable energy
- Lower sulfur and ash content (compared with coal)