GB698379A - Method of separating mixtures of particles into fractions according to specific gravity, and means therefor - Google Patents

Abstract

698,379. Washing granular materials. MAATSCHAPPIJ VOOR KOLENBEWERKING STAMICARBON N.V. Sept. 28, 1951 [Sept. 30, 1950], No. 22688/51. Class 82(ii) A method of separating a mixture of particles into three fractions of different specific gravities comprises feeding the mixture into a sink-and-float bath, passing the sink fraction into an upward current separator for separation into heavy and middle fractions, passing liquid separating medium continuously from the upward current separator into the sink-and-noat bath and continuously recirculating medium from the bath together with medium overflowing with the middle fraction to the separator, the medium in the sink-and-float bath and the upward current separator being held at different specific gravities by feeding correcting medium to the bath at a rate depending on the variation. of the specific gravity of the medium in the bath, and the medium recirculated to the upward current separator being thickened. In an apparatus shown for carrying out this method, raw coal is supplied at 1 to the sink-and-float bath 3, the coal being removed over the screening plate 4 and the shale and middle fraction lifted by a scraper and passed, via a trough 6 to an upward current separator 8 which is preferably of the type described in Specification 699,132. The middle fraction overflows at 9 and the suspension draws off through a screen 10 to a pump 12, any further suspension being rinsed off on a screen 14 and the diluted suspension thickened in a cyclone 28, the output of which also passes to the pump 12. The suspension rinsed from the shale on screen 16 is thickened in a cyclone 29 and that rinsed from the coal on screen 5 thickened in a cyclone 27, both the thickened suspensions passing to the pump 12. From the pump 12 the suspension is returned to the separator via the pipe 13 and to an overflow chamber 17 on the separator, via a pipe 18, from which chamber some passes into the separator and some passes through an overflow pipe 20 to the bath. The specific gravity of the suspension in the sink-and-float bath may be reduced by the addition of water or dilute suspension at 22, which additions may be automatically controlled by a device described in Specification 608,876, [Group XXIX]. Fine coal contained in the suspension rinsed from the coal is removed by a froth flotation machine 33 and suspension losses are compensated at 37 and any surplus liquid drained off at 38. The cyclones 27, 28, 29 may be replaced by a single cyclone. Specification 465,126 also is referred to.