Performance and structural evaluation of the torrefaction of bamboo under a high gravity (higee) environment using a rotating packed bed

The raw bamboo (Phyllostachys mankinoi), with a moisture content of 13.54 % and an HHV of 17.657 MJ/kg, was subjected to torrefaction under a higee environment. The performance of the higee torrefaction was explored in two parts: (1) effect of rotation and temperature and (2) effect of duration on the solid yield, HHV and energy yield. By statistical analyses, the results indicated that the rotation, temperature and their interaction has a significant effect on the three responses. Same remarks on the effect of duration where when the duration (temperature and rotation) increases, the HHV increases, while the solid yield and energy yield decreases. Graphical interpretations showed that at 300 °C, the rotating speed has no evident effect on the responses. At 30-min holding time, the highest HHV reached (28.389 MJ/kg) was obtained in the most severe torrefaction condition (rotating speed at 1800 rpm and temperature at 300 °C) with an EF of HHV corresponding to 1.61 and an energy yield of 63.51%. Upon inspection, the recommended operating condition under a 30-min holding time is at 255 °C-1800 rpm since the EF (1.53), HHV (26.988 MJ/kg), and energy yield (65.21%) values are relatively close to that of the aforementioned torrefaction condition. The Van Krevelen diagram of the torrefied biomass showed that the ratios decrease as the torrefaction intensifies, hence improving the hydrophobicity of the product. The spreads of the results of the solid yield, EF of HHV, energy yield, and H/C and O/C ratios were in accordance to the trends of the responses. Overall, from the results presented, it can be concluded that the quality of the product from the process is at par to that of coal (i.e. HHV of coal is 21-35 MJ/kg). The FTIR results indicated that cellulose and lignin may have been degraded at a lower temperature at high rotating speed. The results suggested that torrefaction under higee environment indicates promising process for the utilization of bamboo.