# Microwave Pyrolysis of Biomass: The Influence of Surface Area and Structure of a Layer
## 4 Results and Discussion
### Distribution of Biomass on the Crucible Bottom
H2S, SO2 and NO had the same pattern of distribution of average concentrations (Figure 9a), in which the maximum values of gas concentrations were achieved when the biomass was distributed in the form of small fragments, and the minimum values were achieved when it was distributed in a uniform layer on a half of the crucible bottom. Similar conclusions are valid for the maximum values of H2S, SO2, NO (Figure 9b). The minimum values of CO and CO2 (8.72% and 5.27%, respectively) were recorded in the experiment with the distribution of fuel in the form of large fragments because when the biomass was distributed as separate large fragments, the contact area of the entire sample of fuel with the bottom of the crucible decreased. Due to the remoteness of the biomass fragments from each other, the intensity of heat transfer between the particles decreased. Fragments remote from the magnetron warmed up more slowly than those closer to the magnetron. Figure 8: _Cont._  
Figure 8: Trends of the concentrations of gas mixture components when varying the distribution of fuel fragments in the crucible: as a set of large fragments (**a**); as a set of small fragments (**b**); on a half of the crucible bottom (**c**); comparison of gas concentrations (**d**). Figure 10 shows the appearance of the solid residue of microwave pyrolysis of biomass with varying options for the distribution of fuel fragments on the crucible bottom. When the biomass was distributed into small fragments, the proportion of the solid residue relative to the initial mass was minimal. With the distribution of biomass along the crucible walls and on a half of the crucible bottom, this figure was 4.2% and 3.4%, respectively. Figure 11 shows that CO started to be released earlier when the fuel sample was distributed on half of the crucible bottom. CO\({}_{2}\) was released earlier (after about 240 s), when the biomass was distributed in the form of large and small fragments. When the biomass was distributed over a half of the crucible bottom, CO\({}_{2}\) emission began after 300 s. At the same time, for the last case of biomass distribution, the longest emission time of CO\({}_{2}\), CO and H\({}_{2}\) was observed: 1950 s, 2240 s and 1650 s, respectively. The shortest time for the emission of these gases was observed when the biomass was distributed in the form of small fragments (760 s, 750 s and 800 s, respectively). However, with the distribution of biomass in the form of small fragments, the highest concentrations of CO\({}_{2}\) and H\({}_{2}\) were recorded, equal to 18.7% and 4.2%, respectively (Figure 11b). The minimum values of CO and CO\({}_{2}\) were observed in the experiment with the distribution of biomass in the form of large fragments and amounted to 22.2% and 10.7%, respectively (Figure 11a,b). The minimum H\({}_{2}\) concentrations (2.6%) were recorded when the biomass was distributed in a  
Figure 10: Solid residue after microwave pyrolysis of biomass with different options for the initial distribution of a sample in the crucible: as a set of large fragments (**a**); as a set of small fragments (**b**); on a half of the crucible bottom (**c**). Figure 9: Average (**a**) and maximum (**b**) values of the concentrations of the gas mixture components when varying the fuel distribution in the crucible. uniform layer on a half of the crucible bottom (Figure 11c). Table 5 shows the gas flow rates obtained during the experiments. Figure 11 shows the emission trends for the main combustible components of the pyrolysis gas with varying distribution of fuel fragments on the crucible bottom. Thus, in the present study, the average concentrations of the components of the gas mixture had the following values: H\({}_{2}\)--1.1 vol.%; CO--11.7 vol.%; CH\({}_{4}\)--2.8 vol.%; CO\({}_{2}\)--6.5 vol.% (Figures 5a and 9a). [PERSON] et al.