# 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  
The influence of the distribution of biomass (sample mass of 15 g) on the crucible bottom on the pyrolysis gas yield characteristics was studied. Figure 3 illustrates the options for the distribution of biomass on the crucible bottom. Figure 4 shows the trends in the concentrations of the gas mixture components released during the microwave pyrolysis of sawdust for different sample distributions in the crucible. The main components of synthesis gas are H\({}_{2}\), CO, CO\({}_{2}\), CH\({}_{4}\), NO, H\({}_{2}\)S. An intensive increase in the concentrations of the pyrolysis gas components began after 400 s (on average for three options for the biomass distribution in the crucible). This time period corresponded to the heating and drying of the biomass. The time of active release of gas components with the distribution of the biomass along the walls of the crucible and uniform distribution over the entire crucible bottom was 700 s and 800 s, respectively. When the biomass was distributed on half of the crucible bottom, this time was about 1500 s. Further, the release of volatile substances was intensified. Figure 4 shows that the concentrations of CO, H  
Figure 3: The distribution of the biomass in the crucible: along the edges (**a**); uniform distribution over the entire crucible bottom (**b**); on half of the crucible bottom (**c**); magnetron (1); biomass (2). and CH\({}_{4}\) increase, and then there is a slight decrease and again an increase (two peaks are recorded). This suggests that each fragment burns out separately from the others located separately along the edges of the crucible. The maximum values of CO, H\({}_{2}\) and CH\({}_{4}\) were 28.5, 3.9 and 10.5% (the first peak), 25, 3.7 and 6% (the second peak). For CO\({}_{2}\), there was a gradual increase and then a decrease in concentrations (one peak). The maximum CO\({}_{2}\) amounted to 18.7%. When the biomass was distributed on the crucible bottom in a uniform layer (Figure 4b), one peak of CO and CO\({}_{2}\) concentrations was observed (39% and 19% at 560 s and 700 s, respectively). CH\({}_{4}\) and H\({}_{2}\) still had two concentration peaks: 9.5% and 3.8% at 470 s and 460 s, respectively (first peak), and 8.3% and 3% at 670 s and 850 s, respectively (second peak). The nature of the trends presented in Figure 4c is generally similar to a gradual increase and decrease in gas concentrations with a uniform distribution of biomass over the entire surface of the crucible bottom (Figure 4b). In both cases, the biomass is distributed uniformly over the surface of the crucible bottom; only the area occupied by the fuel sample changes. Figure 4: _Cont._  
Figure 5 shows the average and maximum values of the concentrations of the gas mixture components. Figure 5 illustrates that CO, CH\({}_{4}\) and NO trends have a similar behavior. The maximum values of average concentrations are achieved when the biomass is distributed on a half of the crucible bottom (Figure 5a). H\({}_{2}\)S and SO\({}_{2}\) concentrations are maximum when the biomass is evenly distributed over the entire crucible bottom and minimum when the sample is located on a half of the crucible bottom. The concentrations of CO\({}_{2}\) and H\({}_{2}\) changed insignificantly with varying distribution of the biomass in the crucible. The difference was no more than 1%. Similar conclusions are valid for the maximum values of the concentrations of the gas components (Figure 5b). When the biomass was distributed on half of the crucible bottom, the average CO values were almost 2 times higher compared to the distribution along the crucible edges and 1.5 times higher compared to the distribution of the sample over the entire crucible bottom (Figure 5a).