# Feasibility Analysis of Brewers' Spent Grain for Energy Use: Waste and Experimental Pellets
## 3 Results and Discussion  
### Characterization of Brewers' Spent Grain Samples  
#### 3.1.1 Physical and Energy Characterization of Dried Waste  
The original waste had a moisture value of 70.46% \(\pm\) 0.88% (wb), necessitating a previous drying stage to reduce the moisture level. Although this implies an increase in the cost of production of the densified product, there were many studies on pellets produced from wet products such as grinding powder from cork industries (40%wb), olive pomace from two and three phases (57% and 73%wb) [45], tomato waste (60%wb) [46], and _Scenedesmus_ microalgae (80%wb) [47].  
After drying, a characterization of the waste was carried out before pelletizing, the results of which are shown in Table 2.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Property** & **Quality A** & **Quality B** \\ \hline Moisture (\%wb) & 12.00 & 15.00 \\ Bulk density (kg\(\cdot\)m\({}^{-3}\)wb) & 600.00 & 600.00 \\ Length (mm) & 3.15–40 & 3.15–40 \\ Diameter (mm) & \(6\pm 1\) & \(6\pm 1\) \\ Durability (\%) & 97.50 & 96.00 \\ \(N\) (\% db) & 1.50 & 2.00 \\ \(S\) (\% db) & 0.20 & 0.30 \\ Ash (\% db) & 6.00 & 10.00 \\ \(LHV\) (MJ\(\cdot\)kg\({}^{-1}\)wb) & 14.50 & 14.50 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Principal specifications of quality from nonwoody pellets. \(LHV\), low heating value.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Property** & **Value** \\ \hline Moisture (\%wb) & 12.51 \(\pm\) 1.21 \\ Bulk density (kg m\({}^{-3}\)wb) & 211.00 \(\pm\) 0.28 \\ C (\% db) & 49.44 \(\pm\) 0.21 \\ \(H\) (\% db) & 6.69 \(\pm\) 0.07 \\ \(N\) (\% db) & 3.76 \(\pm\) 0.01 \\ \(S\) (\% db) & 0.03 \(\pm\) 0.002 \\ \(Nu\) (\% db) & 0.15 \\ \(K\) (\% db) & 0.02 \\ \(Cl\) (\% db) & 0.03 \\ Volatile matter (\% db) & 72.38 \(\pm\) 0.50 \\ Ash (\% db) & 3.37 \(\pm\) 0.10 \\ Fixed carbon (\% db) & 24.25 \\ \(HHV\) (MJ\(\cdot\)kg\({}^{-1}\) db) & 21.00 \(\pm\) 0.02 \\ Energy density (MJ\(\cdot\)m\({}^{-3}\)wb) & 3605 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Characterization of brewers’ spent grain samples before pelletizing. \(HHV\), high heating value.  
Concerning the physical properties, the dry waste had a moisture value of 12.51% (wb), close to the recommended value for the subsequent pelletizing according to the literature consulted [32; 33].  
Furthermore, the bulk density value was 211 kg\(\cdot\)m\({}^{-3}\) (wb), slightly lower compared to other biomass wastes with similar moisture values, such as granulometric separation powder (379 kg\(\cdot\)m\({}^{-3}\) wb) [48]. Low values of this parameter allow its considerable increase after pelletizing. The densification ratio shows the increase in bulk density due to pelletization. Figure 5 shows the granulometric analysis. It can be observed that the median of the particle size distribution was 2.03 mm. Only 20% of the sample showed a particle size higher than 3.15 mm (recommended maximum size for densification processes) [49]. Therefore, granulometry of this waste is suitable for the pelletizing process, and pretreatments such as grinding or sieving are not necessary.  
On the other hand, the BSG samples showed high values of \(N\) (higher than 0.6% db), forecasting high \(NO_{x}\) emissions during combustion, with corresponding environmental implications (contribution to the greenhouse effect and acid-rain production). Instead, \(S\) and \(Cl\) values were acceptable (lower than 0.1% db) [50; 51; 52].  
The proximate analysis showed a high level of ash (3.37% db), lower than that of wheat straw, vine shoots, barley straw, and rice husk (5.02%, 7.10%, 9.87%, and 16.3% db, respectively) [53; 54; 55; 56]. This factor may condition its use only in industrial environments [57].  
BSG samples showed a very high \(HHV\) (21.00 MJ\(\cdot\)kg\({}^{-1}\) db), slightly higher than the values observed by other authors for the same waste (19.6 MJ\(\cdot\)kg\({}^{-1}\) db) [24].