The torrefaction of biomass materials is considered to be a very promising technology for the promotion of the large-scale implementation of bioenergy. Torrefaction involves heating biomass in the absence of oxygen to a temperature of 250-320 °C. At these temperatures, a dry, torrefied product is obtained, which is stable, brittle and water resistant. This makes it much easier to grind than the parent biomass material and reduces biological degradation in storage. By combining torrefaction with pelletisation or briquetting, biomass materials can be converted into a high-energy-density commodity solid fuel or bioenergy carrier with improved behaviour in (long-distance) transport, handling and storage, and also with superior properties in many major end-use applications.
Provided that the torrefaction process is conducted in an energy-efficient manner, i.e. with heat recovery and integration, overall biomass-to-torrefied-pellets energy efficiencies in excess of 90% (based on lower heating value) can be reached. In this way the overall energy efficiency of torrefaction-based biomass supply chains is increased, simultaneously reducing the CO2 footprint and costs. In addition to the possible reduction of CO2 emissions, torrefaction can help to exploit the large potential of residues. An increased use of residues might be one possibility to ease challenges for a sustainable bioenergy supply such as food vs. fuel issues or direct and indirect Land Use Change effects.
Torrefaction has the potential to provide a significant contribution to an enlarged raw material portfolio for biomass fuel production inside Europe by including both agricultural and forestry biomass. The main focus will be on residual materials. It may enable the opening of new feedstock sources worldwide and allow import into Europe in an economically and environmentally sustainable manner. For example, due to the high energy density of torrefied and densified materials, typically three to five times higher than the original biomass, the energy requirements for intercontinental transport can be limited to only a few percent of the energy content of the bioenergy carrier. This is similar to the transport energy levels for coal, and due to the consistent quality of the torrefied product, it is possible that trading schemes similar to those for coal can be applied. With respect to the end-use, torrefaction-based bioenergy carriers may form a good starting point for (thermo-chemical) biorefinery routes.