*2.1. Torrefied Biomass Pellets*

Five different types of wood, one batch of straw and one batch of forest residue were torrefied at different temperatures and retention time. The raw materials were torrefied at different pilot plants (capacity <200 kg/h) with slightly different technology: willow and forest residue material was torrefied in northern Sweden (conveying screw reactor); the pine, poplar, beech and straw material in Spain (rotating shaft reactor) and the spruce material in the Netherlands (moving bed reactor). All torrefied material was compressed into pellets on site with the available pelletizing technology resulting in two different pellet diameters (6 and 8 mm).

Most relevant fuel characteristics (chemical parameters), pellet characteristics (physical-mechanical parameters) and torrefaction characteristics (temperature and time) were analysed (via one representative sample of each pellet type) according to standard methods (if available) and are presented and discussed in Section 3.1. The degree of torrefaction (TFdgr), for which no standardized method exists yet, was defined here as the reduction in volatile matter content (VM) caused by the torrefaction process, based on dry matter (DM) values, according to Equation (1):

$$\text{TF}\_{\text{dgr}} = 100 - \left(\frac{\text{VM}\_{\text{before}}\left(\% \text{DM}\right)}{\text{VM}\_{\text{after}}\left(\% \text{DM}\right)} \times 100\right) \tag{1}$$

The pellet length is an average value of 20 randomly sampled pellets from the bulk as was required for the method described in Section 2.2.
