Fig. 6 The separation results of -6+3 mm fine coal as a function of fluidizing time.
The cleaning of -6+3 mm fine coal was investigated by varying the size of magnetite medium in the air dense medium
fluidized bed. Magnetite medium in four different size fractions of -0.4+0.3 mm, -0.3+0.225 mm, -0.225+0.15 mm and -
0.15+0.074 mm was tested at a bed height of 120 mm and fluidizing time ranges from 15 s to 240 s. The results of Fig. 6 show
ash contents of the top layer and bottom layer as a function of fluidizing time. Overall, the difference between the top layer and
bottom layer of -0.15+0.074 mm is much greater than others. It can be explained by the smaller specific surface area and poor
adhesion force of coarse magnetite powders, which induces large bubbles and severe back-mixing inside the fluidized bed. As a
matter of fact, when the magnetite medium is -0.15+0.074 mm and fluidizing time is 45s, the ash contents of 19.55% and 60.01%
are observed in the top layer and bottom layer, respectively, showing effective separation performance.