# Feasibility Analysis of Brewers' Spent Grain for Energy Use: Waste and Experimental Pellets
## 3 Results and Discussion
### Characterization of Pellets from Brewers' Spent Grain  
Table 5 shows the results obtained for BSG pellets and their comparison with UNE-EN ISO 17225-6 standards. The pellets obtained showed a lower moisture content than the waste. This was due to the increase in temperature in the waste due to the friction generated between the rollers and the flat die, which caused an evaporation of water. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Atmosphere** & **Property** & **10 °C\_min\({}^{-1}\)** & **40 °C\_min\({}^{-1}\)** \\ \hline \multirow{4}{*}{Oxidative} & Ignition temperature (°C) & 150 & 171 \\  & Burnout temperature (°C) & 602 & 656 \\  & Maximum speed of combustion (\%-min\({}^{-1}\)) & 6.16 & 27.80 \\  & Peak temperature (°C) & 276 & 299 \\  & Secondary peak temperature (°C) & 311 & 332 \\  & Tertiary peak temperature (°C) & 482 & 508 \\ \hline \multirow{4}{*}{Inert} & Initial temperature (°C) & 154 & 173 \\  & Residual mass at 700°C (\%) & 21.80 & 22.97 \\ \cline{1-1}  & \(DTG_{\text{max}}\) (\%-min\({}^{-1}\)) & 5.38 & 23.56 \\ \cline{1-1}  & \(DTG_{\text{max}}\) temperature (°C) & 284 & 302 \\ \cline{1-1}  & Secondary peak temperature (°C) & 343 & 353 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: TG analysis (TGA) parameters. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Property** & **Value** & **Quality A** & **Quality B** \\ \hline Moisture (\% wb) & 9.63 \(\pm\) 0.60 & \(\surd\) & \(\surd\) \\ Bulk density (kg\_m\({}^{-3}\) wb) & 662.96 \(\pm\) 15.14 & \(\surd\) & \(\surd\) \\ Length (mm) & 20.79 \(\pm\) 3.90 & \(\surd\) & \(\surd\) \\ Diameter (mm) & 6.07 \(\pm\) 0.04 & \(\surd\) & \(\surd\) \\ Durability (\%) & 94.56 \(\pm\) 0.50 & X & X \\ \(N\) (% db) & 3.76 \(\pm\) 0.01 & X & X \\ \(S\) (% db) & 0.03 \(\pm\) 0.002 & \(\surd\) & \(\surd\) \\ Ash (\% db) & 3.37 \(\pm\) 0.10 & \(\surd\) & \(\surd\) \\ \cline{1-1} \cline{2-4} \(LHV\) (MJ\_kg\({}^{-1}\) wb) & 17.65 \(\pm\) 0.02 & \(\surd\) & \(\surd\) \\ Energy density (MJ\_m\({}^{-3}\) wb) & 11,700 & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Characterization of pellets from brewers’ spent grain. Moisture in pellets should be as low as possible. The moisture content was lower than the requirements for pellets from herbaceous biomass (12% and 15% wb, according to the standard UNE-EN ISO 17225-6) and woody pellets (10% wb, according to UNE-EN ISO 17225-2). The pellets from BSG showed bulk densities higher than those required by the standard UNE-EN ISO 17225-6. Specifically, these pellets showed a value of bulk density of around 663 kg\(\cdot\)m\({}^{-3}\) (wb), similar to that obtained for other herbaceous wastes, such as wheat straw pellets [62]. This fact implies a densification ratio of 3.14. In dimensional terms, pellets from BSG fulfilled the requirements of the standard UNE-EN ISO 17725-6 (length and diameter). Other standards, such as the Austrian ONORM M 7135 norm, introduce the extrusion ratio (L/D), which must be less than 5. Pellets from BSG also met this requirement, with average values around 3.4. Concerning mechanical durability, the results obtained by the durability tester (\(94.56\pm 0.50\)) were slightly lower than those required by the UNE-EN ISO 17225-6 standard. In turn, the results obtained by using the Lignotester were lower than those obtained through the abovementioned procedure, with a higher deviation (93.02 \(\pm\) 1.75), which was a circumstance also observed by other authors [63; 64]. However, we think that this circumstance can be easily remedied, either by increasing the extrusion rate or via the addition of other woody residues. Thus, [PERSON] et al. [28] obtained higher bulk density and durability values when the pressing intensity and extrusion ratios were increased in corn stover pellets. [PERSON] et al. [56] increased the mechanical durability of pellets from industrial cork residue with the addition of milled vine shoots. [PERSON] et al. [65] used wood residues as binders to improve the quality of wheat straw pellets (higher bulk density and heating value; lower ash content).