3.2. Solid mass yield, energy yield and energy analysis
Table 2 shows the high heating values (HHVs), solid mass and energy yields as well as energy densities of raw and torrefied biomass samples at various temperatures. Solid mass yield is defined as the mass ratio of torrefied biomass over its raw form (refer equation 1) and typical solid yield ranges from 50 to 90 wt% [4]. Mass yields decreased to about half of its original weight when torrefied temperature reached 300oC for both samples. This is due to the effect of moisture removal and volatiles released i.e. hemicellulose and some short-chain lignin compounds during thermal treatment [37]. As for energy yield, the values generally reduced from its raw form by 29 wt% and 40 wt% for torrefied OPF and LL, respectively. Energy yield can be regarded as a significant indicator to the amount of energy retained after torrefaction [17]. However, with reference to Equation 2, energy yield is largely dependent on mass yield values and it was also reported that energy yield is directly linked to biomass type [3,38].