Improvement of dry float–sink separation of smaller sized spheres by reducing the fluidized bed height

In this study, the influence of the fluidized bed height on the float–sink of different sized spheres in a gas–solid fluidized bed was investigated. Fluidized beds with heights h = 200, 150, 100 and 50 mm were prepared using a cylindrical column of inner diameter = 290 mm and a mixture of zircon sand and iron powder as the fluidized medium. Float–sink experiments were carried out using density adjusted spheres of diameter Dsp = 40, 30, 20 and 10 mm. It was found that the float–sink performance at Dsp ⩾20 mm is not affected by the height of the bed, and the sharpness of separation (the density range where spheres neither float nor sink completely) is less than or equal to 200 kg/m3. In the case of Dsp = 10 mm, the sharpness of separation is a larger value (1100 kg/m3 at h = 200 mm), whereas it decreases with decreasing h and is 400 kg/m3 at h = 50 mm. The fluctuation of the surface height of the fluidized bed was visually recorded. The fluctuation is reduced by reducing h. The fluctuation vs. h correlates with the sharpness of separation at Dsp = 10 mm vs. h. These results indicate that the dry float–sink separation of smaller sized spheres is improved as the fluctuation of fluidized bed surface is decreased by reducing the fluidized bed height.