Investigation on flow pattern evolution and restraint of vibration energy to bubbles in vibrated dense medium fluidized bed

Abstract

Vibrated dense medium fluidized bed (VDMFB) provides a feasible and low-cost method for fine coal separation. In this study, empirical mode decomposition (EMD) was used to study the evolution of the dominant flow pattern and the restraint effect of vibration energy on the bubble in VDMFB. The internal pressure fluctuation signal of VDMFB was analyzed by EMD, and the intrinsic mode functions (IMFs) of the signal were extracted, and the corresponding relationship between the IMFs and dominant fluidization behavior was verified. The intermediate-frequency signal components (IMF-3 ~ IMF-4) and low-frequency signal components (IMF-5 ~ IMF-8) corresponded to the particle oscillation of emulsion phase and bubble behavior in the particle bed, respectively. Additionally, the energy variation of IMFs in different frequency bands was closely related to the evolution of dominant fluidization behavior. Further, the intermediate-frequency energy decreased and the low-frequency energy increased gradually along the bed height; additionally, the intersection point Tr existed between the two curves, indicating that the dominant energy controlling the flow pattern of the bed changed from vibration to bubbles. The constraint range of vibration energy on bubble behavior was defined, and the quasi-dispersed micro-bubble fluidization environment suitable for fine coal separation was identified in VDMFB, in which the steady vibration energy effectively controlled the unsteady bubble.