关键词: 超细颗粒, 团聚, 流化床, 临界流化速度, 力平衡模型

Abstract:

Minimum fluidization velocity (U_mf) of three ultrafine particles (SiO₂, Al₂O₃ and TiO₂) was measured in a fluidized bed with inner diameter of 50 mm. The primary particle size (d_p) of these ultrafine particles was ranged from 30 nm to 5 μm and Geldart A reference particle was a size of 45 μm. Results show that all three particles have the same U_mf change pattern with increase of primary particle size. U_mf first increased gradually as d_p increased from 30 nm to 5 μm and then U_mf decreased sharply as d_p increased further to 45 μm. U_mf at d_p=45 μm was close to that of d_p=30 nm and 200 nm. U_mf of different materials decreased in the order of TiO₂, Al₂O₃, SiO₂. For particles of the same material, d_p effect on U_mf was similar to that of repose angle, which reached to a maximum at d_p=5 μm. Simulation by agglomerate force balance model shows that average size of fluidized agglomerates is changed similarly to that of U_mf with regards to different materials and primary particle sizes.

Key words: ultrafine particle, agglomeration, fluidized bed, minimum fluidization velocity, force balance model