声场对导向管喷流床环隙区流化质量的影响

Effect of an Acoustic Field on Fluidization Quality in the Annulus of a Spout-fluidized Bed with a Draft Tube

以平均粒径150μm的空心微珠作为实验物料代替超细粉聚团,在以高速射流为喷动气的半圆柱形导向管喷流床中,分别利用光纤探针和压力传感器测量环隙区颗粒浓度信号、压力脉动信号,通过统计分析和功率谱分析考察了声场对环隙区流化质量的改善作用。结果表明:低频高强度的声场能有效破碎环隙区上部的气泡,减小气泡尺寸,增加气泡内颗粒浓度,使床层两相结构减弱,颗粒平均浓度增大,浓度波动减小。且声压级越大,作用效果越明显;而声波频率的影响则存在一个最佳值,本实验条件下为70 Hz,大于或小于该值,声波的作用效果都会减弱。同时声场能消除环隙区下部沟流,促进流化气均匀分布,使颗粒浓度减小,浓度波动增大,并随声压级增加而逐渐与上部接近,从而使环隙区轴向上的流化状态变得更加均匀,流化质量提高。

The signals of particle concentration and pressure fluctuation in the annulus were measured using an optical fiber probe and a pressure sensor respectively in an acoustic spout-fluidized bed with a draft tube.A half-cylinder was used as the fluidization column,instead of ultrafine powder agglomerates,hollow microbeads with an average diameter of 150μm were employed as raw materials while the high-speed atmosphere jet was utilized as the spouting gas.The effect of acoustic field on fluidization quality in the annulus was investigated by analyzing both traditional statistical analysis and power spectrum analysis.The results showed that the low-frequency and high-intensity sound wave could effectively break bubbles in the upper region of the annulus,reduce the size of bubbles,increase the concentration of particles in the bubble.The two-phase structure of the bed was weakened,the mean concentration of particles was increased,and the concentration fluctuation was reduced.The higher the sound pressure level,the more obvious the effect.However,there was an optimal value for the frequency of the sound wave,which was 70 Hz under this experimental condition.Higher or lower than this value,the effect of acoustic field was weakened.Meanwhile,the sound wave could eliminate the channeling in the bottom of the annulus,promote the uniform distribution of the fluidizing gas.The particle concentration was reduced,the concentration fluctuation was increased,and gradually approached the upper region with the increase of sound pressure level.Thus,the axial fluidization state in annular region became more uniform and the fluidization quality was improved.