## 3 Results
### Solid Products--Biochars  
The solid products of pyrolysis, biochars, were characterized using proximate and ultimate analysis, and the results are shown in Table 2. In comparison to raw biomass materials, it can be observed that, after the evolution of H- and O-bearing compounds by devolatilization, the solid materials were enriched in carbon and minerals (with the exception of RDF at higher temperatures). Although the concentration of hydrogen decreased, the oxygen concentration was also lowered, with the net result of an increase in the higher heating value, in this case with respect to raw fuels. Calorific values of biochars obtained from pyrolysis at up to 450 \({}^{\circ}\)C, ranging between 20 MJ/kg and 39 MJ/kg, were similar or even higher than those reported in the literature for other materials [8]. Moreover, the enrichment of carbon at the expense of hydrogen and oxygen during the pyrolysis process is known to enhance carbon stability and fuel hydrophobicity, which is advantageous for its transportation and storage [17; 40]. However, Table 2 shows that when the temperature was \(\geq\)450 \({}^{\circ}\)C, the carbon content of FOR and RDF chars was reduced, suggesting its bounding in volatile species. The decrease in carbon content was reflected in the increase in oxygen concentration of the biochars. Thus, the higher heating value of these biochars dropped significantly and was lower than that corresponding to raw biomass fuels (15.2 MJ/kg vs. 17.3 MJ/kg for FOR and 11.1 MJ/kg vs. 26.3 MJ/kg for RDF).  
The concentrations of the major inorganic elements in biochars produced at 450 \({}^{\circ}\)C, expressed as oxides, are shown in Figure 3, while the slagging/fouling indices calculated according to Equations (1)-(4) are compared in Table 3 (Rs has not been included because the content of S was undetectable). With reference to the B/A index, FOR and RDF biochars present a high deposition tendency due to the dominance of basic oxides in ash in relation to acidic ones. The relatively higher Si content of PCO biochar was responsible for its medium fouling propensity, as expressed by this index. The slag viscosity index Sv indicates that all biochar fuels presented a high deposition tendency; however, the opposite was true for the AI index, given the low percentages of K and Na in all biochar ashes.  
The results in Tables 2 and 3 suggest that all the biochar materials studied that were produced at temperatures of up to 450 \({}^{\circ}\)C and that had significant calorific value can be utilized for energy through combustion or gasification processes, especially those operated at temperatures below 1000 \({}^{\circ}\)C to avoid fouling/slagging phenomena.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Sample** & **Temperature (\({}^{\circ}\)C)** & **Organic Matter** & **Ash** & **C** & **H** & **N** & **O** & **HHV (MJ/kg)** \\ \hline \multirow{4}{*}{PCO} & 350 & 87.9 & 12.1 & 62.7 & 4.9 & 1.1 & 19.2 & 24.8 \\  & 450 & 84.9 & 15.1 & 62.9 & 3.2 & 1.0 & 17.8 & 22.7 \\  & 550 & 79.5 & 20.5 & 63.4 & 1.9 & 1.0 & 13.2 & 21.8 \\  & 350 & 98.6 & 1.4 & 68.4 & 4.0 & - & 26.2 & 24.2 \\  & 450 & 98.4 & 1.6 & 62.7 & 2.9 & - & 32.8 & 19.5 \\  & 550 & 97.7 & 2.3 & 56.5 & 2.1 & - & 39.1 & 15.2 \\  & 350 & 80.2 & 19.8 & 69.2 & 10.8 & 0.1 & 0.1 & 38.7 \\ RDF & 450 & 66.7 & 33.3 & 52.0 & 6.0 & 0.1 & 8.6 & 24.6 \\  & 550 & 46.1 & 53.9 & 34.2 & 1.0 & 0.2 & 10.7 & 11.1 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Proximate and ultimate analysis of biochars (% dry).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **B/A** & **Sv** & **AI** & **Deposition Tendency** \\ \hline PCO & 0.93 & 51.9 & 0.14 & medium/high/low \\ FOR & 4.3 & 18.2 & 0.02 & high/high/low \\ RDF & 1.5 & 28.8 & 0.19 & high/high/low \\ \hline \hline \end{tabular}
\end{table}
Table 3: Slagging/fouling indices of biochars.