Study on the separation and mixing laws of wide-grained dense medium in vibration separation fluidized bed

Abstract

Vibro-fluidized dry coal beneficiation involves the unavoidable mixing of −1 mm coal dust into a fluidized bed, which compromises the stability and homogeneity of the bed density and reduces the effectiveness of fine-grained coal separation. To understand the features of coal powder separation and mixing (-1 mm) in a vibrating fluidized bed, as well as to achieve a uniform and stable bed density, a wide-grained dense medium consisting of −1 mm coal dust and 0.3–0.15 mm magnetite powder was homogeneously mixed in this work. The degree of density separation in the entire bed and the local mixing properties of the wide-grained dense medium were examined. It was discovered that when low vibrational energy was introduced at the same air velocity, particle separation was enhanced compared to the usual fluidized bed. Small bubbles were found to ensnare fine coal dust and migrate upwards, increasing the density separation. The introduction of high vibrational energy led to particle disorder within the bed and an increase in the level of particle mixing. The beneficial effects of the vibration on the bed diminished when the air velocity was gradually increased under the specified vibration conditions. This caused large bubbles to develop more frequently, which increased particle mixing. The 1–0.5 mm fine-grained coal exhibited the best mixing state; it was less affected by variations in air velocity and vibration levels, whereas the −0.5 mm coal dust was more affected by each variable. Furthermore, the particle system achieved a wide range of air velocity regulations without a significant segregation state change under the vibration conditions of f= 25 Hz and A=1 mm and f= 25 Hz and A=2 mm.