## 3 Results
### Torrefaction Performance and Severity Index

Table 3: Physicochemical properties of raw biomass samples. Figure 3: Mass yield and energy yield with respect to torrefaction temperature and time for all five materials. Figure 3 shows the relationship between mass and energy yields for all studied torrefaction temperatures and times, respectively. In this work, the most severe torrefaction conditions were defined to be 350 \({}^{\circ}\)C and 60 min. The plots in Figure 3 show that mass yield decreased in all five torrefied biomass samples as torrefaction temperature increased, respectively, which is completely in agreement with other works in the literature regardless of the type of studied biomass materials [59; 84; 85]. Additionally, when torrefaction time increased, the mass yields decreased. Both torrefaction temperature and time have a big impact on the biomasses during the torrefaction process, with torrefaction temperature having a more significant one [86]. When the torrefaction temperature increased, moisture was removed from the samples, and mostly all volatiles were decomposed. Only a minor impact was observed on the biomasses when torrefaction time was increased from 10 to 30 min and then to 60 min. When increasing the torrefaction time from 10 min to 30 min and later to 60 min, the most significant impact was seen during the torrefaction of miscanthus and hops biomass samples; during the torrefaction of other biomass samples, only a minor impact was observed. For torrefaction time 10 min, the calculated mass yields were 84.92-34.41%, 72.36-48.38%, 84.4-59.28%, 83.72-54.15%, and 84.90-46.97% at 250, 300, and 350 \({}^{\circ}\)C for miscanthus, hops, SS, and mixtures, respectively. For torrefaction time 30 min, those values were 79.37-32.91%, 68.28-46.81%, 81.49-57.36%, 81.25-52.38%, and 81.47-45.42%, and for torrefaction time 60 min they were approximately 75.41-32.10%, 65.46-44.64%, 78.93-56.29%, 77.97-51.37%, and 77.89-44.54%. The lowest mass yields were obtained at the most severe torrefaction conditions. The same was observed in the work of [PERSON] et al. [47] and Nepal [19], whereas from their results, [PERSON] et al. [40] could also predict the optimal torrefaction temperature and time: approximately 260 \({}^{\circ}\)C and 30 min. The calculated mass yields were similar between lignocellulosic biomass samples; however, they were a little different from the calculated SS mass yields, which were generally slightly lower. At the beginning of the process, mass yields in the SS biomass sample decreased more notably than later during the process. This was also seen in the work of [PERSON] et al. [87], who investigated the torrefaction of SS at temperatures ranging between 150-400 \({}^{\circ}\)C and torrefaction time varying from 0 to 50 min. In their work, the obtained mass yields decreased when the torrefaction temperature was increased, as well as when the torrefaction time was raised. At the beginning of torrefaction, a significant mass loss was observed, while the change of mass yield was not significant with a longer torrefaction time. When adding lignocellulosic biomass to SS in our work, the mixtures then observed similar mass yield as lignocellulosic biomass, which potentially means that the properties of the fuel were improved. During the process, the HHV values were also determined. HHV values increased with both torrefaction temperature and time (Table 4). As already stated in this work, during the torrefaction process, the HHV was increased as a result of the decrease in oxygen content and increase in carbon and fixed carbon contents. The enhancement factor (EF) reflects the change in HHV during the torrefaction process. The results of EF calculated in this work are listed in Table 4. The results showed that EF increased as torrefaction temperature and time increased, which means that HHV values improved during the process. Furthermore, energy yield was proportional with mass yield and HHV values; therefore, energy yield was determined next.