Drying kinetic and upgraded grindability of biomass with torrefaction-assisted deep drying
Geng Li, Wei Cheng, Jianfeng Chen, Hao Jiang, Shihong Zhang, Hao Song, Hanping Chen
Abstract
Deep drying can effectively improve the grindability of biomass. However, the effects of drying characteristics and pretreatment conditions on grindability during deep drying are not clear. In this study, eucalyptus wood (EW) pellets were pretreated with torrefaction assisted deep drying using a horizontal fixed-bed reactor. The drying and grindability characteristics of eucalyptus wood were studied by response surface methodology (RSM). The results showed that when the temperature increased from 200℃ to 230℃, all absorption peaks of eucalyptus wood particles increased while the internal connectivity was weakened. Large quantities of cellulose began to decompose when the temperature further increased to 260℃, which made the particles show a rich porous structure, and the grindability was improved. The energy provided by deep drying could be utilized by a large number of water molecules inside eucalyptus wood particle, and the large kinetic energy of water molecules significantly enhanced the outward migration speed of internal water molecules. As the eucalyptus wood particle size decreased, the diffusion resistance also decreased. The operating conditions were optimized by Box-Behnken design (BBD) and a pretreatment temperature of around 290℃, a particle size of 0.3–0.6 mm with a residence time of around 30 min were recommended to produce eucalyptus wood particle with good fuel and grindability properties. • The absorption peaks of torrefaction assisted deep dried biomass increased. • The energy of deep drying was utilized by water molecules inside particle. • As the fuel particle size decreased, the diffusion resistance also decreased. • 290℃, 0.3–0.6 mm of particle size with 30 min of residence time were recommended.