## 3 Results and Discussion
### Proximate Analysis  
Table 4 summarizes the results of the proximate analysis of broom and gorse and their derived biochars. The VM values were higher for the broom and gorse samples, decreasing with pyrolysis temperature. No differences were found between the residence times at 600 \({}^{\circ}\)C but, for the biochars prepared at 300 \({}^{\circ}\)C, the VM contents were greater in the biochars pyrolyzed for 1 h than in those obtained after 3 h. There was a marked decrease in the VM content of the biochars pyrolyzed at 600 \({}^{\circ}\)C with respect to that of the biochars pyrolyzed at 300 \({}^{\circ}\)C. All biochars had a low ash content, which was related to the low values in the two feedstocks. The ash content of broom and gorse in another investigation was lower than 1% [54]. In the broom-derived biochars, the highest ash content was found for BB600-3H, and, in gorse-based biochars, it was in BG600-1H. In all cases, the ash content was lower than that of coal fuels [77; 78]. The FC content increased with pyrolysis temperature, and, at 600 \({}^{\circ}\)C, no statistical differences were found between the residence times for the broom- and gorse-derived biochars, but the FC contents were above 80% in these high-temperature-pyrolyzed biochars compares to those of the biochars pyrolyzed at 300 \({}^{\circ}\)C.  
The FC content increased with the increase in temperature due to the combination of processes that happen during pyrolysis: (i) polycondensation, (ii) aromatization, and (iii) defunctionalization of the matrix [84]. This occurred according to the evolution of the other properties with pyrolysis temperature (Table 2 and Figure 1). The biochars prepared at 600 \({}^{\circ}\)C had a high FC content; in all cases, it was possible to produce more heat with a longer combustion, which was proportional to the energy content [61]. The FC/VM values (Table 4), known as the fuel ratio, were greater for biochars prepared at 600 \({}^{\circ}\)C [63]. This result is consistent with the evolution of the H/C and O/C ratios as well as the FC content. The thermal stability, in accordance with the FC/(VM + FC) index, was highest for BB600 and BG600 at 1 h and 3 h and the lowest for the feedstock. The FC/VM and the FC/(VM + FC) had the same behavior. This means that biochars pyrolyzed at 600 \({}^{\circ}\)C were more stable owing to the larger number of aromatic carbon structures. The more-labile \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **VM (\%)** & **Ash (\%)** & **FC (\%)** & **FC/VM** & **FC/(VM + FC)** \\ \hline BROOM & 80.71 \(\pm\) 0.29 d & 3.16 \(\pm\) 1.03 a & 16.12 \(\pm\) 1.32 a & 0.2 \(\pm\) 0.02 a & 0.17 \(\pm\) 0.01 a \\ BB300-1H & 56.32 \(\pm\) 2.41 c & 3.91 \(\pm\) 0.73 a,b & 39.78 \(\pm\) 3.11 b & 0.71 \(\pm\) 0.09 a,b & 0.41 \(\pm\) 0.03 b \\ BB300-3H & 47.38 \(\pm\) 0.73 b & 4.33 \(\pm\) 0.8 a,b & 48.29 \(\pm\) 1.33 c & 1.02 \(\pm\) 0.04 b & 0.5 \(\pm\) 0.01 c \\ BB600-1H & 13.47 \(\pm\) 0.82 a & 5.89 \(\pm\) 1.64 b,c & 80.64 \(\pm\) 2.46 d & 6.01 \(\pm\) 0.57 c & 0.86 \(\pm\) 0.01 d \\ BB600-3H & 12.03 \(\pm\) 0.81 a & 7.58 \(\pm\) 1.73 c & 80.39 \(\pm\) 2.54 d & 6.71 \(\pm\) 0.69 c & 0.87 \(\pm\) 0.01 d \\ \hline GORSE & 82.94 \(\pm\) 0.9 D & 2.47 \(\pm\) 0.47 A & 14.6 \(\pm\) 1.16 A & 0.18 \(\pm\) 0.02 A & 0.15 \(\pm\) 0.01 A \\ BG300-1H & 60.05 \(\pm\) 1.76 C & 3.17 \(\pm\) 0.21 B & 36.77 \(\pm\) 1.97 B & 0.61 \(\pm\) 0.05 A & 0.38 \(\pm\) 0.02 B \\ BG300-3H & 48.01 \(\pm\) 2.42 B & 4.26 \(\pm\) 0.36 C & 47.73 \(\pm\) 2.78 C & 1 \(\pm\) 0.11 A & 0.5 \(\pm\) 0.03 C \\ BG600-1H & 12.82 \(\pm\) 1.84 A & 5.8 \(\pm\) 0.32 E & 81.37 \(\pm\) 1.52 D & 6.45 \(\pm\) 1.14 B & 0.86 \(\pm\) 0.02 D \\ BG600-3H & 10.3 \(\pm\) 0.51 A & 5.09 \(\pm\) 0.32 D & 84.61 \(\pm\) 0.8 D & 8.23 \(\pm\) 0.5 C & 0.89 \(\pm\) 0.01 D \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Proximate analyses (dry basis) for broom, gorse, and the respective biochars.