## 3 Results and Discussion  
### Characterization of the Biomass  
For the samples of sawdust and shavings collected, the moisture content for both of the wood of the genus _Pinus_ ranged from 18.00-67.82% (Figure 5). This figure is lower than in earlier studies [51], but adequate for elaborating densified materials, since they will not require a lengthy drying process to reach a value suitable for producing solid biofuels [38; 52]. \begin{table}
\begin{tabular}{c c} \hline \hline
**Average Amount of Material Utilized.** & **Cost Per Briquette (\$USD)** \\ \hline
0.25 L & \(\$4.50\times 10^{-3}\) \\
75 g shavings & \(\$1.02\times 10^{-5}\) \\
65 g sawdust & \(\$5.40\times 10^{-2}\) \\  & Cost per briquette: \(\$0.058\) USD \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Production cost per briquette in dollar (\(\$\) USD). Figure 4: (a) Combustion test in the thermal chamber; (b) three thermally-insulated chambers; (c) three different types of fuel, including the briquettes. The granulometry results for the samples of sawdust generated an average of 78.32-79.92% in the 0.5 mm screen. These particle size percentages are similar to those reported in other studies, which range from 75.8% [38; 53], to 76.9% [51]. In our work, the particle size that resulted from using the 0.5-2.00 mm screens was 30.05-79.92%, a size range suitable for making briquettes, as reported in a previous study that determined a percentage of 73.1% for wood of the genus _Pinus_ after filtering through the same screen sizes [54]. The granulometric analysis of the sawdust showed that 54.9% by volume can be used to produce briquettes, while another 30.05% can be incorporated into the production of other types of biofuel; pellets, for example. There are two suggestions for utilizing the remaining 15.05%: first, re-milling it to obtain a new percentage; second, mixing it with another lot of biomass for re-screening. The granulometry of the sample of shavings produced an average of 64.1-86.3% through a 3.35 mm screen. These percentages are similar to those reported in earlier studies [38; 53], where values were 75.8% and 76.9% [51]. These results indicate that the material used does not require extensive milling to obtain a suitable particle size for briquette-making, as the 0.5 to 2.00 mm screens separated an average of 13.7-35.9% [55]. Those screens produced an estimated percentage of 26.9% for wood of the genus _Pinus_. The granulometric analysis of the shavings showed that 26.2% can be utilized to produce briquettes, and 13.7% to manufacture other types of biofuel, such as pellets. The remaining 60.1% can be re-processed as indicated above for the sawdust (i.e., re-milling or mixing). Both cases are illustrated in Figure 6.  
The apparent densities reported for conifer wood show values of 160-330 kgm\({}^{-3}\)[56]. The bulk density reported for our samples of sawdust and shavings had values of 160 and 170 kgm\({}^{-3}\), respectively, though other studies report figures of 160 and 235 kgm\({}^{-3}\)[54]. The apparent density determined in our study lies within the acceptable parameters published in earlier reports [52]. Figure 5: Humidity content of the samples. Figure 6: Potential percentage of material available for briquette production: (**a**) sawdust; (**b**) shavings. The results of this analysis were in a range of 0.49-1.55% for the samples of sawdust, while the value for the shavings was 0.38-1.78%. These satisfy this parameter and concur with figures reported in previous studies, which indicate a range of 0.28-1.25%. In fact, these values surpass those determined elsewhere [51; 55; 56; 57; 58]. For the case of the wood used in our work, the results for ash content satisfy the established standard. The samples of shavings had a range of 91.26-95.01% for volatility, while the figure for the sawdust was 65.3-90.29%. These values are higher than in other reports, which found a range of volatile material of 80.84-81.27% for samples of the genus _Pinus_[48].