Application of closely spaced inclined channels in gravity separation of fine particles

This paper is concerned with the gravity separation of fine particles in a Reflux Classifier, a fluidized bed device with a system of parallel inclined channels located above. A significant advance is reported here over what was previously possible, through the application of a recent discovery described by Galvin et al. (2009). By using closely spaced inclined channels it is possible to achieve significant suppression of the effects of particle size, and hence produce a powerful separation on the basis of density. Experimental work was undertaken on the continuous steady state separation of coal and mineral matter, with a very narrow channel spacing of 1.77 mm used to process a feed finer than 0.5 mm in diameter, and a channel spacing of 4.2 mm used to process coarser feeds finer than 2.0 mm. These results are compared with previous findings reported in the literature for wider channels. The gravity separation performance is shown to be remarkably high, with a significant reduction in the variation of the separation density with particle size, and a significant reduction in the Ecart probable error, E_p. For example, over the particle size range 0.25–2.0 mm the composite E_p for the size range decreased from 0.14 for the wide channels used in previous studies to a typical level of 0.06 for the closely spaced inclined channels used in the present study. The separation performance was also shown to be insensitive to feed pulp density and feed solids throughput over a very broad range.