The Effect of Biomass Pellet Length, Test Conditions and Torrefaction on Mechanical Durability Characteristics According to ISO Standard 17831-1

Mechanical Durability and Grindability of Pellets after Torrefaction Process

Renewable energy sources and their part in the global energy mix are beneficial to energy diversification and environment protection. However, raw biomass is characterized by low heating value, hydrophilic properties, various mechanical durability, and the logistic challenges related to transportation and storage. One frequently used process of combined biomass valorization is torrefaction and pelletization, which increase the heating value, homogeneity, and hydrophobicity of the fuel. However, industrial clients need fuel characterized by favorable grindability, whereas, the individual clients (householders) need fuel with high mechanical durability. Due to the different expectations of final customers regarding biomass fuel properties, it is necessary to investigate the influence of the torrefaction on the mechanical durability of the pellets. In this paper, five various types of pellets and their torreficates (obtained at a temperature of 200 and 300 °C) were examined. Then the mechanical durability index DU and the grindability of the untreated and torrefied pellets were determined. The results indicated that the mechanical durability of untorrefied pellets is significantly greater than torrefied pellets. Interestingly, no significant differences in mechanical durability between torrefied pellets at 200 and 300 °C were observed, For sunflower husk pellets, the DU index amounted to 95.28 ± 0.72 (untorrefied), 47.22% ± 0.28% (torrefied at 200 °C), and 46.34% ± 0.72% (torrefied at 300 °C). Considering the grindability, as the treatment temperature increased the energy demand for grindability decreased. For example, the grindability of pine tree pellets was 15.96 ± 3.07 Wh·kg−1 (untreated), 1.86 ± 0.31 Wh·kg−1 (torrefied at 200 °C), and 0.99 ± 0.17 Wh·kg−1 (torrefied at 300 °C). The highest difference between raw and torrefied pellets was determined for beetroot pomace pellet: 36.31 ± 2.06 Wh·kg−1 (untreated), 3.85 ± 0.47 Wh·kg−1 (torrefied at 200 °C), and 1.03 ± 0.12 Wh·kg−1 (torrefied at 300 °C).

Durability Assessment of Wooden Pellets in Relation with Vibrations Occurring in a Logistic Process of the Final Product

Vibrations occurring during road transport can vary in a wide spectrum and they can lead to losses in quality of transported materials. However, the vibrations are definitely different than the loads experienced by pellet samples in the tester used for durability tests according to the standard ISO 17831-1. pThe aim of the study was to evaluate the durability of wood biomass pellets available for sale in large-area stores, in terms of loads occurring in transport. The durability of the ellets was tested by subjecting them to vertical and horizontal vibrations similar to those occurring during local transport of this type of fuel for the needs of households. Durability tests were also carried out in accordance with ISO 17831-1. The results were analyzed statistically. Among other, it was found that the vibration time impact on the tested pellet durability was significantly lower in case of horizontal vibrations than in vertical. Moreover, pellets with a diameter of 8 mm showed lower durability than pellets with a diameter of 6 mm. Durability tests carried out in accordance with ISO 17831-1 showed lower pellet strength results compared to the test methods based on lateral and vertical vibrations.