Patent GB-1170308-A (GB)
Title: Particle Separator
Inventor: PURCELL EDWARD MILLS
IPC: B03B5/40
Filed: 1967-11-24
Abstract: 1,170,308. Classifying solids; centrifugal separators. E. M. PURCELL and H. C. BERG. 24 Nov., 1967 [1 Dec., 1966], No. 53615/67. Headings B2H and B2P. Particles are classified according to their masses by causing a fluid medium containing the particles to flow linearly along a surface while subjecting the medium to an accelerating force directed perpendicularly to the surface whereby particles having the same effective mass within the liquid travel at substantially the same average velocity in the direction of flow, the particles thus separating out into groups of particles of different masses along that direction, which groups are separately removed from one another. In Fig. 1, the flow surface is formed by the upper surface of the bottom 12 of a trough 11 in which baffles 15, 16 are mounted between the side walls 17 and spaced equally above the bottom 12. A liquid, e.g. water, is first introduced between the baffle 15 and an end wall 13 of the trough until the latter is filled to a level ho. A mixture of particles is then fed at A and allowed to settle according to their density. Further liquid is then supplied causing the liquid in the trough to flow at a very low linear velocity from left to right, the flow being greater at the surface of the liquid than adjacent the bottom 12 where it is nil. The accelerating force is due to gravity acting perpendicularly to the horizontal inner surface of the trough bottom. The light particles which are concentrated in the upper regions of the liquid reach the opposite end wall 14 of the trough before the heavy particles concentrated in the lower region of the trough, different liquid fractions containing groups of particles of different masses being drawn off in succession by means not shown. In Fig. 5, the flow surface is constituted by the inner surface 34 of an aluminium or stainless steel cylindrical centrifuge rotor 24 which is rotatably mounted in a temperature-controlled helium atmosphere 31 within a housing 32. Particle-free liquid is first introduced through a tube 30 to form a thin film 33 on the rotor surface 34. Next a sample of liquid containing particles to be separated is added and then further particle-free liquid is supplied. The liquid flows down the rotor wall at a very low rate and bands of particles separate out in accordance with their effective masses. The liquid escapes via orifices 35 at the bottom of the rotor entraining first the bands of lighter particles and then bands of progressively heavier particles, the liquid and the particles discharging into a dish 36 the walls of which are periodically washed with particle-free liquid. Liquid and particles are transferred from the dish 36 by a pump 38 to a fraction collector in which the lighter particles are collected before the heavier ones. In a modification, Fig. 6, a cylinder 40 is mounted within the centrifuge rotor 39. The cylinder-rotor assembly is rotated about a vertical or a horizontal axis and the liquid and particles are supplied to the annular space 41. The end walls of the rotor may be provided with flow channels 46 as shown in Fig. 7. In both latter embodiments, the accelerating force is the resultant force which is due to centrifugal gravitational forces and which is perpendicular to the surface of a paraboloid the shape of which depends on the rate of rotation of the rotor. The inner surface of the rotor may thus be shaped in the form of a paraboloid by machining. Alternatively, a liquid resin may be first introduced into the empty rotating rotor and allowed to set to form a hard paraboloidal surface. In another method a highly viscous liquid immiscible with, and of higher specific gravity than, the separating liquid medium is first introduced in the rotor to provide a paraboloidal surface for the flow of the liquid medium.