Quality effects caused by torrefaction of pellets made from Scots pine

Abstract: The purpose of the study was to investigate the influence of torrefaction on the quality of Scots pine pellets. Pellet samples were torrefied at 230, 250 and 270°C for 1h in nitrogen atmosphere. Higher heating value (HHV) was increased from 18.37MJkg−1 to 24.34MJkg−1. The energy to crush a pellet by mechanical compression was determined using a material tester and results showed a rapid decrease before torrefaction temperature reached 250°C. Slightly further decrease was observed when increasing the temperature up to 270°C. The strength loss was confirmed by determining the energy required for grinding the pellet samples in a bench scale disc mill. Particle size distribution measurements after grinding indicated a significant increase of small particles (diameter<ca. 1mm) for torrefied pellets at a torrefaction temperature of 230°C and further increase of temperature resulted in steep decrease of large particles (diameter>ca. 2mm). To further analyze the effect on strength, the mechanical durability of pellets was tested according to wood pellet standards, EN 15210-1. The results have shown a good correlation between pellet durability and compression strength, and indicated that the pellet durability can be estimated based on compression strength data of about 25 pellets. [Copyright &y& Elsevier]