(378a) Grindability of Torrefied Wood Pellets

Torrefied wood pellets can be used directly or co-fired with coal in an existing power plant, if they can be completely size reduced using the existing mill or coal pulverizes. The size reduction characteristics of torrefied pellets could be determined by grindability parameters. However, the generalized size reduction parameter or specific grinding procedure has not been developed yet for densified biomass materials. In this study, the effect of torrefaction temperature on the specific grinding energy of torrefied pellets was studied. The grinding energy followed an exponential or power trend rather linear trend over the torrefaction temperature. The applicability of three well-known grinding equations: Kick, Rittinger, and Bond was also investigated for torrefied and raw wood pellets. Rittinger’s and Bond’s equations were well matched with the experimental data (R²=0.93-1). The HGI and ISO grindability indices, that are both based on the Rittinger’s theory, were calculated for the torrefied pellets. Also, the bond work index (BWI), based on the Bond’s theory were determined for each type of the pellets, and a correlation between HGI and BWI were proposed. The BWI decreased by an increase in torrefaction temperature contrary to HGI index. It decreased from 732 kWh t^-1 for control wood pellets to 70 kWh t^-1 for torrefied wood pellets at 290°C. Further studies are recommended for grinding through different mill types and different lignocellulosic materials.