Torrefaction is a thermal conversion method of biomass in the low temperature range of 200-300 °C. Biomass is pretreated to produce a high quality solid biofuel that can be used for combustion and gasification [16—17]. It is based on the removal of oxygen from biomass to produce a fuel with increased energy density. Different reaction conditions (temperature, in­ert gas, reaction time) and biomass resources lead to the differences in solid, liquid and gas­eous products.

Uemura et al. [16] studied the effect of torrefaction on the basic characteristics of oil palm emp­ty fruit bunches (EFB), mesocarp fibre and kernel shell as a potential source of solid fuel. It was found that mesocarp fibre and kernel shell exhibited excellent energy yield values higher than 95%, whereas OPEFB, on the other hand, exhibited a rather poor yield of 56%. Torrefaction can also be done in the presence of oxygen. Uemura and his colleagues [17] carried out OPEFB tor — refaction in a fixed-bed tubular reactor in the presence of oxygen at varied oxygen concentra­tion. The mass yield decreased with increasing temperature and oxygen concentration, but was unaffected by biomass particle size. The energy yield decreased with increasing oxygen concentrations, however, was still between 85% and 95%. It was found that the oxidative torre — faction process occurred in two successive steps or via two parallel reactions, where one reac­tion is ordinary torrefaction, and the other is oxidation.