What is Torrefaction?
Un-processed biomass is a difficult fuel. It has high moisture levels, and wide variations in its physical characteristics, including its heating value. Various techniques have been tried to overcome these limitations, but most still produce fuels that require special handling or major investments at the power station. Torrefaction changes the biomass to produce a fuel quality which is much closer to the properties of coal, and can be used in conventional power stations without special requirements. During the process, water in the biomass and superfluous volatiles are removed, and the biopolymers (cellulose, hemicellulose and lignin) partly decompose releasing combustable gases which are used to sustain the process. The final product is the remaining solid, dry, blackened material, referred to as “bio-coal”.
Benefits of Torrefaction
Torrefaction of biomass produces a fuel with a high energy density, typically 20-25 GJ/tonne, and physical properties that allow the fuel to be used interchangeably with high-rank coals. Torrefied biomass has the following benefits over untreated biomass:
- Significant increase of caloric value (energy density or energy per unit of weight)
- Improved grindability, allowing the fuel to be used in modern coal power stations without additional equipment.
- Improved consistency, hydrophobicity, mechanical strength and biological stability.