In a typical torrefaction process the biomass is heated gently to the desired torrefaction temperature (6tor), held there for a specified reaction time, and then cooled down. The torrefaction temperature and the reaction time are two of the most important parameters in this process. The torrefaction temperature dtor generally reduces with reaction time theating.

The design norm for torrefaction is

200 °C < вІ0Г < 300 °C

fyor — 200 < і °c/s (3.12)

Theating

where 0tor is the torrefaction temperature in °C, and theating is the heating time above 200 °C. A typical reaction time is about 30 minutes. The properties of torrefied wood depend on (1) the type of wood, (2) the reaction temperature, and (3) the reaction time.

Torrefaction loses more oxygen and hydrogen than carbon. Hence, the H/C and O/C ratios decrease. However, it should not be confused with carboniza­tion, which takes place at a much higher temperature and produces charcoal with even lower H/C and O/C ratios.