# 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
It is believed that the thermal conductivity of biomass materials limits heat and mass transfer. Usually, to achieve a very high rate of heat transfer, the biomass particles are crushed to small sizes. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Experiment**} & \multirow{2}{*}{**Gas**} & **Average** & **Average** & **Average** & **Total Amount of** \\  & & **Concentrations** & **Concentrations** & **Concentrations** & **Pyrolysis Gas** \\  & & **(\%)** & **(ppm)** & **(mg/m\({}^{3}\))** & **(mg/m\({}^{3}\))** \\ \hline \multirow{6}{*}{Biomass is distributed along the edges of the crucible (\(\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C} \mathrm{C}\mathrm{C}\mathrm{C}\mathrm{C}\mathrmFigure 7 shows options for the distribution of the fuel sample in the crucible in the form of a combination of large and small fragments and a uniform distribution of fuel on a half of the crucible bottom. Figure 8 shows the trends in the concentrations of the components of the gas mixture during the pyrolysis of sawdust. An intensive increase in the concentration of the main components of the gas mixture began with a decrease in O\({}_{2}\) concentration after 230 s (on average for the first two options of fuel distribution) and after 315 s when the fuel was distributed on a half of the crucible bottom. The time of intense release of gas components when the biomass was located in the form of large fragments, small fragments, and on half of the crucible bottom was 1220 s, 586 s and 1575 s, respectively. This suggests that the smaller fragments took less time to heat and dry up before the devolatilization began. The nature of emission trends (Figure 8a) is in good agreement with the data of Figure 4a. Two peaks are observed for the concentrations of CO, H\({}_{2}\), CH\({}_{4}\) and CO\({}_{2}\). The maximum values for CO and CO\({}_{2}\) were 22% and 11% (the first peak), 20% and 10.5% (the second peak). Figure 7: Distribution of the fuel sample in the crucible: a set of large fragments (**a**), a set of small fragments (**b**), on a half of the crucible bottom (**c**). The peak concentrations of CH4 and H2 were 7.7% and 4% (first peak), and 8.2% and 3.8% (second peak). When the biomass was distributed on the crucible bottom in the form of small fragments (Figure 8b), one concentration peak was observed for CO, CO2 and CH4, and two concentration peaks were for H2. The nature of the trends in Figure 4c is generally similar to a gradual increase and decrease in gas concentrations when biomass was distributed in the form of small fragments (Figure 4b). The difference lies in the duration of gas yield, which was 2.5 times shorter for small fragments than when biomass was distributed in a uniform layer on a half of the crucible bottom. The maximum values of CO, CO2 and CH4 were 43%, 17% and 11%, respectively. The maximum H2 concentration was 2.7% and 2.8% in the first and second peaks, respectively. Figure 9 shows the values of the average and maximum concentrations of the components of the gas mixture for different options of the fuel distribution in the crucible. CO and CO2 have the same distribution pattern of average concentrations, in which the average maximum concentrations were achieved when the biomass was distributed on a half of the crucible bottom, and the minimum when distributed in the form of large fragments (Figure 9a). When the fuel was evenly distributed, CO concentrations were 42% higher than when the biomass was distributed as large fragments and 33% higher than when distributed as small fragments. CH4 and H2 slightly depended on the method of fuel distribution.