# Microwave Pyrolysis of Biomass: The Influence of Surface Area and Structure of a Layer
## 4 Results and Discussion
### Surface Structure
The H\({}_{2}\) yield was 33% higher compared to an even layer and 3% lower than with artificial channels. The CO\({}_{2}\) yield increased by 23%, and the CH\({}_{4}\) yield was 2.2 times higher compared to the even layer. An increase in the concentrations of H\({}_{2}\), CO and CO\({}_{2}\) in the presence of artificial pores on the biomass surface shows that the pyrolysis proceeded more intensively. This conclusion is confirmed by the formation of a smaller ash residue (1.6%) in comparison with an even layer (3.5%). The creation of a large number of artificial channels on the surface of the biomass facilitates the diffusion of the pyrolyzing agent into the fuel layer, which intensifies the decomposition and the release of gaseous pyrolysis products. The creation of artificial pores on the surface of the biomass increased the CO yield by 6% compared to the pyrolysis of a uniformly distributed biomass. However, with artificial channels, CO yield decreased by 6% compared with a uniformly distributed biomass because of greater compaction of the layer between the channels. The material was compacted and, as a result, heat and mass transfer became more difficult compared to the case when the layer was uniformly distributed. Figure 15 shows the concentration trends of the main combustible components of the gas mixture. Figure 13: Trends of the concentrations of gas mixture components when varying the biomass surface structure: artificial channels (**a**); artificial pores (**b**); uniform layer (**c**); comparison of gas concentrations (**d**). Figure 14: Average (**a**) and maximum (**b**) concentrations of the gas mixture components with varying surface structure of the biomass. Figure 15: Trends of the concentrations of gas mixture components when varying the biomass surface structure: CO\({}_{2}\) (**a**); CO (**b**); H\({}_{2}\) (**c**); comparison of individual concentration trends (**d**). Figure 15 shows that CO and H\({}_{2}\) emission started almost immediately for all three variants of the biomass surface structure. CO\({}_{2}\) began to be released later--after 125 s in the case of a structure with channels and pores, and after 370 s in the case of an even layer. In this case, for all three options for the structure of the biomass surface, the emission duration was the same. The maximum concentrations of CO and CO\({}_{2}\) were recorded for the structure with artificial pores (52.2% and 17.5%, respectively), and the minimum for the structure with artificial channels (35.5% and 13.5%, respectively). The values of H\({}_{2}\) concentrations changed insignificantly. Table 6 shows the gas flow rates obtained during the experiments. In modern studies, insufficient attention is paid to the structure of the biomass layer. Biomass is mainly distributed either in the form of a layer over the entire crucible bottom or in the form of granules or bars [47; 49; 55]. Analytical studies [59] of microwave heating in rectangular, cylindrical and spherical coordinate systems show that the geometry and density of an object strongly affect the distribution of temperature or humidity. [PERSON] [59] showed that the highest temperatures in rectangular blocks usually occur in the corners, directly below the surface. For small-diameter cylinders with low dielectric losses, the resulting temperature distribution resembles a \"dumbbell\" with two temperature peaks along the longitudinal axis. However, as the loss factor or cylinder diameter increases, the temperature profile becomes a high-temperature ring under the top and bottom circular surfaces. Heat in small-diameter spheres is concentrated in the center, but, as in a cylinder, it is converted to subsurface heating as the diameter or material loss factor increases. The heating time also affects the temperature distribution, with the temperature peak shifting towards the core of most objects as the heating time increases. There is a transition to subsurface heating as the diameter or material loss factor increases.