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

摘要：

在内径50 mm的流化床实验台上，测量SiO₂、Al₂O₃和TiO₂ 3种超细颗粒原生粒径从30 nm增加到5 μm的临界流化速度（U_mf），并以Geldart A类颗粒（粒径45 μm）为参照。结果表明：3种超细颗粒的U_mf随粒径的变化规律一致，随原生粒径从30 nm增加到5 μm，U_mf逐渐增大；当颗粒粒径增加到45 μm，U_mf大幅度减小，其与原生粒径为30和200 nm时接近。对于不同材料，U_mf由大至小的顺序依次为TiO₂、Al₂O₃、SiO₂。粉体安息角测量表明：对于同种材料颗粒，原生粒径对超细颗粒的U_mf和安息角的影响规律一致，即5 μm超细颗粒的安息角最大。聚团尺寸模型计算表明：稳定流化时，聚团尺寸随原生粒径的变化趋势以及随不同材料的变化趋势均与U_mf的变化趋势一致。研究结果为超细颗粒流化临界速度预测研究奠定了基础。

关键词: 超细颗粒, 团聚, 流化床, 临界流化速度, 力平衡模型