# Thermochemical Conversion of Olive Oil Industry Waste: Circular Economy through Energy Recovery
## 3 Results and Discussion
### Heating Value  
The results obtained for the calculation of High Heating Value (HHV) are shown in Table 4.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Elements** & **Original Dry Sample** & **T\({}_{\bf 300}\)**\(\cdot\)**C & **T\({}_{\bf 400}\)**\(\cdot\)**C & **T\({}_{\bf 500}\)**\(\cdot\)**C \\ \hline C (\%) & 56.2 & 63.9 & 77.3 & 86.7 \\ H (\%) & 6.8 & 7.2 & 3.8 & 3.4 \\ N (\%) & 1.2 & 1.6 & 2.5 & 1.2 \\ O (\%) & 35.8 & 27.3 & 16.4 & 8.7 \\ S (\%) & \textless{}0.01 & \textless{}0.01 & \textless{}0.01 & \textless{}0.01 \\ \hline \end{tabular}
\end{table}
Table 2: Ultimate analysis for the different process temperatures.  
\begin{table}
\begin{tabular}{c c c c c} \hline  & **Original Dry Sample** & **Test at 300 \({}^{\circ}\)C** & **Test at 400 \({}^{\circ}\)C** & **Test at 500 \({}^{\circ}\)C** \\ \hline Fixed Carbon (\%) & 18.84 & 26.12 & 75.49 & 82.14 \\ Volatiles (\%) & 79.85 & 75.59 & 21.08 & 14.36 \\ Ashes (\%) & 1.31 & 1.30 & 3.45 & 3.51 \\ Moisture (\%) & 3.51 & 1.52 & 0.91 & 0.57 \\ \hline \end{tabular}
\end{table}
Table 3: Proximate composition for the different process temperatures.  
The determination of HHV by the method described by [PERSON] et al. (2005) [24] allows the evaluation of the energy content of a fuel by knowing other properties, such as fixed carbon, volatile and ash content. Thus, the initial heating value of the thermally untreated sample, of 19.20 MJ.kg\({}^{-1}\), increases up to 31.26 MJ.kg\({}^{-1}\). These values are in accordance to those presented in previous studies, such as the presented by [PERSON] et al. (2016), where a two-step process based on torrefaction and combustion is proposed for olive pomace recovery and where is concluded that torrefaction improves strongly the combustion properties [20].  
The mass loss verified during the tests was, respectively, 37%, 76%, and 78%. This result can be interesting if associated with the energy recovery is also the environmental issue of reducing the volume of waste generated. Previous studies such as those from [PERSON] et al. (2008) found yields for torrefaction of _Phalaris arundinacea_, processed in a range of temperatures comprised from 230 to 290 \({}^{\circ}\)C, with mass losses of 7% to 32% [34]. [PERSON] and [PERSON] (2005) report typical values of 20% for mass loss [35]. [PERSON] et al. (2005) found mass losses from 6% to 46%, respectively for temperatures from 220 \({}^{\circ}\)C to 270 \({}^{\circ}\)C, for wooden briquettes processed for a period of 60 min [36]. Concerning higher temperature tests can be found several in the literature available [37; 38; 39]. However, once in these studies the technology used was fast high temperature pyrolysis, the main objective was to obtain a gaseous yield the highest possible, being in the majority of the cases reached 95% [37]. When comparing the results obtained in the tests conducted in the present study with those found in the referred literature, mass loss results for torrefaction temperature range can be considered similar. For the pyrolysis temperature range, above 300 \({}^{\circ}\)C, it was not possible to find comparable results, once the procedures used to the obtention of the samples were considerably different from the one used here.