# Feasibility Analysis of Brewers' Spent Grain for Energy Use: Waste and Experimental Pellets
## 3 Results and Discussion
### Characterization of Brewers' Spent Grain Samples
#### 3.1.3 Thermogravimetric Analysis  
Figures 6 and 7 show the weight loss rate curves. TG means Thermo Gravimetry and DTG is an acronym for the first derivative of temperature for thermal phase transitions (Derivative Thermo Gravimetry).  
Figure 5: Granulometric analysis of BSG dried.  
DTG curves (Figures 6b and 7b) at two heating rates were qualitatively similar, consisting of one small shoulder peak, one pronounced double peak, and one long tailing. In an oxidative atmosphere, an additional peak was observed.  
According to each peak in the DTG curve, three stages could be considered (Figures 6b and 7b).  
The first stage corresponds to the lowest-temperature region, which includes the range between room temperature and 153-173 \({}^{\circ}\)C, depending on the heating rate. In this stage, a small weight loss took place, possibly due to the water evaporation contained in the sample and the release of volatile gas [59].  
The second stage was related to the highest weight loss, which was due to devolatilization, taking place at a temperature range between 154-173 and 378-407 \({}^{\circ}\)C. Figures 6b and 7b show, in both cases, a double peak, whereby that with a lower value was produced at higher temperatures.  
Stage 3 took place in the highest temperature range (from 378-407 \({}^{\circ}\)C). This stage was that showing the greatest difference between the test carried out in oxidative and inert  
Figure 6: TG (a) and DTG (b) curves for heating rates studied under oxidative atmosphere.  
\begin{table}
\begin{tabular}{c c} \hline
**Property** & **Value** \\ \hline \(SiO_{2}\) & 62.20\% \\ \(P_{2}O_{5}\) & 20.20\% \\ \(CaO\) & 8.06\% \\ \(K_{2}O\) & 4.43\% \\ \(MgO\) & 3.94\% \\ \(Fe_{2}O_{3}\) & 0.41\% \\ \(ZnO\) & 0.29\% \\ \(Na_{2}O\) & 0.17\% \\ \(MnO\) & 0.13\% \\ \hline \end{tabular}
\end{table}
Table 3: Ash composition (% db).  
Figure 7: TG (a) and DTG (b) curves for heating rates studied under inert atmosphere.  
atmospheres. For the former, a peak occurred corresponding to char combustion. The final waste was related to the ash amount of the sample. For inert atmosphere tests, Figure 7b shows a very slow weight loss, possibly due to the thermal decomposition of carbonaceous materials contained in the byproduct [59].  
The profile obtained in the oxidative atmosphere (Figure 6a,b) was similar to that presented in other research, such as [PERSON] et al. [60].  
TGA parameters related to oxidative and inert atmospheres are shown in Table 4.  
In all cases, a higher heating rate led to peaks being obtained at higher temperatures. Similarly, the difference between peak temperature and secondary peak temperature values increased with the heating rate. In addition, the initial temperature, as well as the peak and secondary peaks, was higher in and oxidative atmosphere compared to the tests carried out in inert atmosphere.  
\(DTG_{\text{max}}\) values were higher for high heating rates in both atmospheres, obtaining higher values for the tests carried out in an oxidative atmosphere.  
Similar profiles were found for agro-industrial wastes with comparable characteristics, such as olive pomace [61].