Torrefaction is a thermal pre-treatment technology, which produces a solid biofuel product that has a superior handling, milling and co-firing capabilities compared to other biomass fuels. The advantages of torrefied biomass are widely recognized: better transportation characteristics and compatible properties to coal such as heating value, grindability, bulk energy density and hydrophobicity. Torrefaction is seen as a breakthrough technology to decrease the handling and storage costs and reduce investment for co-firing application.
In the torrefaction process, biomass is heated to a temperature of approx. 250-350°C in a atmosphere with low oxygen concentrations, so that all moisture is removed as well as a fraction of the volatile matter of the dry biomass. Ideally, the energy contained in the released volatiles is equal to the heating requirements of the process, so that a thermal efficiency exceeding approx. 95% is achieved. Due to the substantial weight loss and a relatively smaller loss of calorific content, the heating value of processed biomass per mass unit increases significantly in the process.
Basic Torrefaction Principle
Torrefied biomass has seven immediate benefits over untreated biomass:
- Higher calorific value
- More homogeneous product
- Higher bulk density
- Excellent grindability
- Hydrophobic nature/water resistance
- No biological activity