超细颗粒聚团流化的临界流化速度

Minimum fluidization velocity of ultrafine particle agglomerates

在内径50 mm的流化床实验台上,测量SiO_2、Al_2O_3和TiO_2 3种超细颗粒原生粒径从30 nm增加到5μm的临界流化速度(Umf),并以Geldart A类颗粒(粒径45μm)为参照。结果表明:3种超细颗粒的Umf随粒径的变化规律一致,随原生粒径从30 nm增加到5μm,Umf逐渐增大;当颗粒粒径增加到45μm,Umf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,Umf由大至小的顺序依次为TiO_2、Al_2O_3、SiO_2。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Umf和安息角的影响规律一致,即5μm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Umf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。

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