Impact of Press Channel D/L Ratio on the Mechanical Properties of Biomass Pellets During Storage

Abstract

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. The 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. The study highlights the significant role of press channel geometry in optimizing wood pellet quality, providing valuable insights for improving pellet performance throughout production and storage.

Keywords: Biomass Pellet, Pelleting Process, Storage, Microcomputed Tomography, Porosity Distribution, Mechanical Stability