# Influences of the Pretreatments of Residual Biomass on
## 4 Discussion
### Integral-Average Quantities  
Figure 2 highlights that the devolatilization temperature is a parameter with a significant effect on devolatilization performances, whatever the considered biomass kind; for all biomasses, the gas yield (\(\eta^{av}\), Equation (1), Figure 2a) and the H\({}_{2}\)/CO molar ratio (\(\lambda^{av}\), Equation (2), Figure 2b) grew as the temperature was increased. With regard to the carbon conversion (\(\chi^{av}_{C}\), Equation (3), Figure 2c), the difference between values at 800 and 900 \({}^{\circ}\)C was not always evident (net of standard deviations), so that trends with respect to temperature were not as much clear as in the case of \(\eta^{av}\) and \(\lambda^{av}\). Anyway, one can state that the temperature increasing from 700 to 800 \({}^{\circ}\)C always improved \(\chi^{av}_{C}\). As a matter of fact, [PERSON] et al. (2019) reported how the gas yield, the carbon conversion and the H\({}_{2}\) and CO content in the syngas increased as the devolatilization temperature was increased, with experiments on sawdust pellets in a fluidized bed reactor, within the range 750-950 \({}^{\circ}\)C. Consequently, considerations about Figure 2 may suggest that one should obtain the best performance of thermochemical conversion of wheat straw biomasses by operating at the highest tested temperature (900 \({}^{\circ}\)C). In general, the increase in gas yield (\(\eta^{av}\), Equation (1), Figure 2a) is not necessarily accompanied by an improvement in syngas quality (e.g., in terms of H\({}_{2}\)/CO ratio for Fischer-Tropsch synthesis). Remarkably, in the case of study of this work, the H\({}_{2}\)/CO molar ratio (\(\lambda^{av}\), Equation (2), Figure 2b) grew together with gas yield (\(\eta^{av}\), Equation (1), Figure 2a) as the temperature was increased; in other words, there is a general improvement in the quality and quantity of the syngas due to the increase of devolatilization temperature, which in turn appeared to enhance the extent of reforming and cracking reactions. In addition to the devolatilization temperature influence, minor effects due to pretreatments were observed on devolatilization performances. A comparison between the results of torrefied pellets (WSP-T1, WSP-T2, WSP-T3) and those of WSP, suggested that:  
* the \(\eta^{av}\) of torrefied pellets was close to that of WSP (Figure 2a), with differences even less evident if standard deviations are taken into account;
* the \(\lambda^{av}\) of torrefied pellets is slightly higher than that of WSP (Figure 2b);
* with torrefied pellets, a substantial decrease of the \(\chi^{av}_{C}\) emerged in comparison to the same quantity of WSP (Figure 2c); this is in agreement with the expected effects of the torrefaction pretreatment (defined elsewhere (2018)). As highlighted by [PERSON] et al. (2019), torrefaction can lead to a reduction of carbon conversion in the thermochemical conversion of the biomass, because of devolatilization, polycondensation, and carbonization which occur during the pretreatment; as a matter of fact, [PERSON] et al. (2019) referred that torrefaction increased the elemental carbon content per unit of mass, because of the release of volatiles (such as water and CO\({}_{2}\)), which in turn made the biomass properties shift towards those of coal (2019). With regard to torrefied samples (WSP-T1, WSP-T2, WSP-T3), a further focus was performed on effects of torrefaction temperature:  
* no evident influences emerged on gas yield (\(\eta^{av}\), Equation (1), Figure 2);  
The highest H\({}_{2}\)/CO molar ratio (\(\lambda^{av}\), Equation (2), Figure 2b) resulted for WSP-T3; [PERSON] et al. (2019) found that 270 \({}^{\circ}\)C was the best torrefaction temperature for pelletized pine and spruce sawdust, among investigated values of 240, 270, 300, and 330 \({}^{\circ}\)C: they carried out devolatilizations by thermogravimetric measurements and determined, by kinetic analyses, that the activation energy of H\({}_{2}\) release was minimum when the torrefaction temperature was equal to T3 (270 \({}^{\circ}\)C).