Mechanism of improving fluidization quality and efficient dry fine coal separation in vibrated dense medium fluidized bed for separation

Clean and efficient utilization of coal is a major strategic demand in China. With the strategic transfer of China’s coal industry to the western region and the wide application of comprehensive mining technology, the raw coal, especially steam coal, is becoming increasingly “poor, fine, and miscellaneous”. There is an urgent need for an efficient dry fine coal separation technology. Fine coal has the characteristics of small windward area and weak gravity effect. Wind separation methods have large differences in medium density and separation density, as well as large bubbles and severe backmixing when using traditional air dense medium separation technology. These methods cannot achieve an effective separation of fine coal in a limited time and space. In this study, simple harmonic vibration and upward airflow were synergistically inputted into a gas-solid fluidized bed, aiming to enhance gas-solid contact, suppress bubble merging, and improve fluidization quality through vibration energy. The transfer process of vibration energy in the bed and the response law of the bed particles were studied. It was found that the disturbance degree of bed density mainly depends on the competition and coordination between the upward airflow and vibration energy. The bubbles cause random fluctuations in bed density, and the vibration energy transforms particles from irregular random motion to periodic oscillation. The bubbles are compressed and broken axially along the bed. Combining the classical two-phase theory and the escape law of bubble phase and emulsified phase during bed collapse, the distribution ratio of gas in the bubble phase and emulsion phase under vibration excitation was calculated. It was found that vibration energy can effectively drive the gas from the bubble phase to the emulsified phase, reducing the bubble volume by 19.23%, effectively weakening the bed wave caused by bubbles. The fluidization quality has been improved. A uniform and stable fluidized separation environment is formed. A quantitative evaluation model for the effect of vibration energy on fluidization quality improvement has been established. The synergistic operation ranges of amplitude, frequency, and gas velocity suitable for an efficient separation of fine coal have been clarified. A series of separation experiments were conducted, which increased the calorific value of 6-1 mm clean coal from the Heishan Coal Mine in Xinjiang by 4 571 kJ/kg compared to raw coal.