Powder Technology, Vol.322, 497-509, 2017
Collaborative optimization of vibration and gas flow on fluidization quality and fine coal segregation in a vibrated dense medium fluidized bed
In a vibrated dense medium fluidized bed (VDMFB), the uniform and stable gas-solid fluidized bed where medium particles belong to the Geldart B, was formed and considered suitable for 1-6 mm fine coal separation under the combined effects of both vibration energy and air flow. Driven by the excitation force, the particles in the VDMFB had a higher kinetic activity and lower minimum fluidization gas velocity. Prior to the bed fluidizing initiation (fluidization number, N < 1), the solid particles absorbed energy during inelastic collisions with the gas distributor. Subsequently to the bed uniform fluidization, the vibration energy was continuously transferred to the quasi-elastic bed in the form of waves. The vibration amplitude and frequency played a different role in the gas-solid contact. When the operating gas velocity, U-i, was 6.26 cm/s and the vibration acceleration level, K, was lower than 7.1, it could have been quite effective for the vibration energy transfer in the bed to be enhanced by the vibration frequency increase. As the frequency increased, the transmission efficiency of vibration energy decreased. When K > 7.1, the vibration amplitude effect on the vibration energy transmission in the bed was quite significant. In the study of the vibration energy effective range, it was discovered that the bed could be utilized for the fine coal effective separation in the area below 60 mm for the VDMFB with 80 mm of static bed height, where the vibration energy was continuously and steadily transmitted and attenuated along the bed height. Regarding the raw coal with a washability variety, the separation density could be flexibly regulated in the VDMFB. The separation results demonstrated that the ash content of three clean coal products was decreased exceeding 50%, compared to the ash content of the raw coal when the separation density was set at 1.49 g/cm(3), 1.67 g/cm(3) and 1.78 g/cm(3) respectively, indicating that the VDMFB could effectively separate fine coal by a dry method. (C) 2017 Elsevier B.V. All rights reserved.