Impact of press channel diameter-to-length ratio on the mechanical properties of biomass pellets during storage

This study investigates the effects of press channel length on the quality of wood pellets, focusing on key aspects such as density, radial porosity distribution, and mechanical stability, both at the time of delivery and during storage. Wood pellets were produced using press channels with diameter-to-length (D/L) ratios of 1:3, 1:4, and 1:5 to evaluate how variations in die geometry influence pellet quality. Micro-computed tomography (μCT) analysis indicates that the D/L ratio of the press channel significantly impacts the porosity within the pellets. Short press channels are associated with great variability in the radial porosity distribution of the wood pellets, while longer press channels lead to uniformly low porosity over the radius. Furthermore, pellets produced with longer press channels exhibit a smoother surface with fewer cracks and greater resistance to structural degradation under varying humidity conditions. Although high-density pellets show improved mechanical strength and recovery potential in humid environments, remaining damage in the form of cracks and alterations in radial porosity distribution lead to reduced strength compared to their initial state. • Wood pellets of differing quality are produced using press channels with various diameter-to-length ratios. • Radial porosity variations from micro computed tomography reveal key mechanisms affecting pellet quality. • Longer press channels produce wood pellets with consistently low radial porosity. • High-density pellets exhibit greater mechanical strength under humid conditions compared to low-density pellets. • High-density pellets demonstrate superior recovery potential when in a wet state.