Torrefaction of biomass
A thermo-chemical treatment
Torrefaction is a thermo-chemical treatment of biomass under the absence of oxygen. Typical process temperatures range from 250 to 300° C. During the process the remaining water in the biomass evaporates. Additionally, the hemicellulose content of the biomass is reduced. The steam together with the decomposed hemicellulose forms a gas consisting of H2O, CO, CO2, and various organic acids. The gas mass flow is typically 20% of the bone dry input material, while the energy content is only 10%. The final product is the remaining dry solid material with brown to black color. Compared to untreated biomass, torrefied material has different material properties:
- Higher energy density
- Better grindability
- Better hydrophobic properties
After torrefaction, the biomass can be densified with pelleting or briquetting equipment to increase the energy content per unit of volume.
Torrefied biomass is an excellent fuel, especially for co-firing in coal-fired power plants.
The ANDRITZ/ECN torrefaction process co-developed by ANDRITZ and the Energy Research Centre of the Netherlands (ECN) at the ANDRITZ Torrefaction Technology Demonstration Plant in Sdr. Stenderup in Denmark has been designed to scale-up to large production capacities – up to 700,000 t/a or more.
The process incorporates biomass receiving, drying, torrefaction, and pelletizing in an integrated system, utilizing key ANDRITZ technologies.