Abstract

An air dense medium (magnetite) fluidized bed (ADMFB) provides an alternative method for dry coal beneficiation. The de-mixing (segregation) characteristics can significantly affect the quality of the final products. In this study, the segregation characteristics of fine coal (1–3mm) in an ADMFB were compared to those in an ordinary fluidized bed (FB). Specifically, the pressure drop, density-segregation behaviors, segregation degree, motions of the coal/magnetite mixture, and bubble size were determined with various gas velocities. Density-segregation occurred at a low gas velocity in the ADMFB. However, the particles started to mix when the gas velocity was increased. There was an optimum gas velocity to produce the maximum amount of segregation. The comparative analysis (ash segregation degree and bubble size characteristics) between ADMFB and FB suggested that the bubble-drive flotsam-jetsam mechanism can explain the particle segregation. Furthermore, adding dense medium to a fluidized bed led to a higher amount of segregation because of the reduction in bubble size.

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