Patent GB-1021800-A (GB)
Title: Electrostatic separation
Inventor: BULLOCK HARRY LESLIE
IPC: B03C7/00
Filed: 1964-03-20
Abstract: 1,021,800. Electrostatic separation. NATIONAL ENGINEERING CO. OF CANADA. March 20, 1964, No. 11867/64. Heading B2J. [Also in Divisions B8 and Dl] A method of electrostatic separation of mixtures of seeds, ground solids, crystals and fibrous materials &c, comprises the steps of moving the mixture in contact with dielectric surfaces and with repeated contact and separation between the particles in the mixture so as to differentially charge the particles, and then moving the mixture adjacent a charged dielectric surface for effecting separation. In a roller-type apparatus, Fig. 1, the mixture from a rotary dryer 12 is fed on to a belt-type elevator which is made of dielectric material such as rubber, the effect of friction between the belt and particles causing the charging of the particles ; dust is carried off by hot air which enters through inlets 33, 33a and leaves by an outlet 34. The mixture is then fed through an adjustable outlet 38 of a hopper 30 between a feed roll 37 and electrode roll 41 which are either made of, or surfaced with, dielectric material. Preferably, the roll 41 has a high tension lead 42 and the roll 37 a grounding connection 43; alternatively both rolls may be connected to sources of D.C. high voltage of different magnitude or sign to give the required potential gradient between the rolls. Scrapers 44, 45 are provided on the rolls to remove adhering particles. A divider 47 disposed below the rolls directs the stream of particles to the left and right for further separation between two more simliar sets of dielectric rolls, the separated fractions being carried away by screw conveyers 55. The dividers are provided with blades 47c which are maintained at an adjusted potential by leads 56, the blades being preferably made of metal; in a modification, the leads 56 are omitted and the blade portions and left-hand walls 47b made of dielectric material. Both the short 18 and the hopper 30 are also made of dielectric material. In a free-fall type apparatus, Fig. 3 (not shown), the mixture from a rotary dryer 12 is fed on to a vibratory feeder 65 made of, or surfaced with, dielectric material and, if desired, provided with baffles which are disposed in staggered relation to interrupt the flow. The mixture falls between dielectric belts 72, 72a, having a surface charging electrode 74, a grounding connection 73 and scrapers 76, 76a. Adjustable dividers 80, 81 serve to direct the separated fractions on to screw-conveyers 85; in a modification, the mixture is directed, after separation between the belts 72, 72a, to a further pair of separating belts. The rotary dryer for the above apparatus may be provided with a ceramic lining and lifting members. In an apparatus suitable only for separating fibrous material, Fig. 7 (not shown), fibres separated by the carding action of a rotating brush 107 of nylon or other dielectric material and a carding element 109 are thrown between a number of spaced-apart rotating discs 112 which are made of dielectric material and provided with the electrodes 114 and scrapers 116.