声场强化微小流化床流动特性研究

Fluidization Characteristics in Micro-scale Fluidized Beds with Acoustic Intensification

在内径4.3mm微小流化床中,考察了声场对FCC及石英砂颗粒流化质量的影响。重点讨论了声压级与频率对微小流化床最小流化速度的影响。结果表明,声场能改善微小流化床流化质量。尤其对于51μm石英砂颗粒,声场可以使其消除沟流,实现稳定流化。声压越大,声场对微小流化床流化质量改善越明显。最小流化速度随声压增高呈单调下降趋势。相同声场条件下,声波对微小流化床最小流化速度数值降低幅度大于大尺度流化床。声场对微小流化床最小流化速度的影响存在最佳频率。但不同颗粒的最佳频率不同。内径4.3mm流化床,51,67,83μm石英砂颗粒与83μmFCC颗粒对应的最佳频率分别为90,90,140和140Hz。在一定的声压与频率下,声场可以降低最小流化速度约9%～21%。对于微小流化床,床径越小,则床层空隙率越大,越有利于实现外场强化,最小流化速度的降低幅度也逐渐增大。

In a micro-scale fluidized bed（MFB） with inner diameter of 4.3 mm,the effects of adding acoustic field on the minimum fluidization velocity and fluidization quality of quartz and FCC catalyst particles were investigated.The experiment results show that the sound field added can improve the fluidization quality of the MFB;especially for quartz sand particles of 51 μm,adding sound field can disrupt channeling and stabilize the fluidization.The stronger the sound pressure applied,the more evident the improvement of the fluidization quality in the MFB,and the minimum fluidization velocity decreases monotonously with the increase of the sound pressure level.Under the same applied sound field,the decrease range of the minimum fluidization velocity in MFB is bigger than that in fluidized bed with bigger size dimension.It was found that the minimum fluidization velocities of FCC（83 μm） and three kinds of quartz sand particles（51,67 and 83μm） have their minimum value when the applied sound frequencies are 140,90,90 and 140 Hz,respectively.With the assistance of acoustic wave added,the minimum fluidization velocities in micro-scale fluidized beds with inner diameters of 4.3,5.5,10.5 and 15.5 mm can be decreased by 9%～21%.For the MFBs,the smaller the inner diameter,the bigger the bed voidage,the more beneficial the realization of the intensification by externally added sound field and the bigger the decrease range of the minimum fluidization velocity.