# Biomass from Green Areas and Its Use for Energy Purposes
## 3 Results and Discussion  
### Measurement of Mechanical Properties  
Mechanical properties determine important quality parameters of the tested solid fuels. Taking into account the process of automating the feeding of fuel to the boiler, the mechanical parameters provide an answer as to whether a given type of fuel will be appropriate for such a method of use. This article includes the outcomes of tests of the mechanical properties of the eight pellet types, in order to define the suitability of the analyzed biomass for their production. The analyses were performed 24 h after pellet production (see Table 4). \begin{table}
\begin{tabular}{c c} \hline
**Parameter** & **Uncertainty** \\ \hline Destructive force (F\({}_{\rm max}\)) & 37.60 N \\ Energy needed to destroy pellets (W to F\({}_{\rm max}\)) & 1.33 MJ \\ Ash content & 0.00068\% \\ Volatile compounds & 0.0021\% \\ Calorific value & 0.00022 MJ\(\cdot\)kg\({}^{-1}\) \\ Nitrogen & 0.0015\% \\ Carbon & 0.0018\% \\ Hydrogen & 0.004\% \\ CO\({}_{2}\) & 0.53 mg\(\cdot\)m\({}^{3}\) \\ CO & 0.00027\% \\ SO\({}_{2}\) & 0.00034 mg\(\cdot\)m\({}^{3}\) \\ NO\({}_{\rm x}\) & 0.51 mg\(\cdot\)m\({}^{3}\) \\ \hline \end{tabular}
\end{table} 
Table 3: Uncertainty values for the main parameters. The values of mechanical parameters varied for the tested pellets. The lowest values of destructive force (F\({}_{\text{max}}\)) were found for acorn pellets (P3 and P4). With regard to the admixture of coniferous sawdust, the lowest destructive force was recorded for these pellets (P4). In the case of solid fuels produced from chestnuts (P1, P2), it was found that pellets made of this type of material are definitely more resistant to damage compared to pellets from acorns (P3 and P4). On the other hand, pellets made of fir cones with the addition of coniferous sawdust (P8) were the most resistant to damage. The damage-causing force for this type of fuel was 493 N. For solid fuels made of pine cones (P5) and pine cones with the addition of coniferous sawdust (P6), similar destructive force values were noted as in the case of pellets of fir cone (P7) and fir cones with the addition of sawdust from coniferous trees (P8). The addition of coniferous sawdust to chestnut (P2), pine (P6), and fir (P8) resulted in a somewhat higher resistance to mechanical damage in comparison with solid fuels without the addition of coniferous sawdust (P1, P5, and P7). Analyzing the results of pellet tests, it was found that the energy needed to destroy pellets (W to F\({}_{\text{max}}\)) corresponds to the values of the damage-causing force. The lowest value of energy until destruction was characteristic for acorn pellets with an admixture of sawdust (P4), and the highest for pellets made of fir cones and sawdust from coniferous trees (P8). For chestnut (P2), pine (P6), and fir (P8) pellets, a 50% addition of sawdust from coniferous trees raised the value of the parameter under testing. In the case of acorn pellets, a 50% addition of sawdust from coniferous trees (P4) decreased the quantity of energy needed to destroy this pellet compared to pellets made of 100% acorns (P3). The relative deformation values up to the moment of destruction of the tested pellets were diversified. Pellets with the addition of coniferous sawdust were characterized by an increased value of the tested parameter (P2, P6, and P8) in relation to solid fuels made of 100% homogeneous materials (P1, P5, and P7). The exception here is acorn pellets: as a result of the addition of sawdust, the relative deformation parameter (P4) decreased compared to pellets that were 100% made of acorns (P3). The mechanical properties of pellets depend in particular on the type of materials used for their production, the water content, the chemical composition of raw materials, and the addition of an adhesive [37; 38]. Pellets made of raw materials containing large amounts of starch are characterized by greater resistance to mechanical damage. Starch is an excellent binder in the pelletizing process.