Classifying – separating – and assorting solids – Magnetic – Paramagnetic
Patent
1996-04-01
1998-04-28
Bollinger, David H.
Classifying, separating, and assorting solids
Magnetic
Paramagnetic
209215, 2092231, 209636, B03C 100
Patent
active
057434107
DESCRIPTION:
BRIEF SUMMARY
This invention relates to magnetic separation devices, in particular to the type of device in which magnetic particles are removed from a stream of material by feeding the stream on or through stationary magnetic material, the magnetic particles being held or "trapped" by the magnetic material and therefore extracted from the stream.
One form of magnetic separation device which functions by magnetic particle entrapment is generally referred to as a High Gradient Magnetic Separator or HGMS. An HGMS comprises a canister containing a liquid-permeable packing of magnetizable material between the canister inlet and outlet. The packing material may be paramagnetic or ferromagnetic and may be in particulate or filamentary form, for example, it may comprise wire wool, wire mesh, knitted mesh or steel balls. The packing may be in the form of a single block which essentially fills the canister or it may be in other forms, for example, concentric cylinders or rectangular plates. The term "matrix" is generally employed to refer to the packing and this is used, in the case where the packing is divided into a number or elements, by some in the industry to refer to the individual elements and by others to refer to the totality of the packing. The term will be employed herein in the latter way.
The canister is surrounded by a magnet which serves to magnetize the matrix contained therein, the magnet generally being arranged to provide a magnetic field in the direction of the cylindrical canister axis. With the matrix magnetized, a slurry of fine mineral ore, for example clay dispersed in water, is fed into the inlet of the canister. As the slurry passes through the canister, the magnetizable particles in the slurry are magnetized and captured on the matrix. Eventually, the matrix becomes substantially filled with magnetizable particles and the rate of capture deceases so that the quantity of magnetizable particles in the treated slurry leaving the outlet of the canister reaches an unacceptably high level. The slurry feed is then stopped and the canister rinsed with water to remove all non-magnetic material from the matrix. The magnetic field acting on the matrix is reduced to a sufficiently low value to enable the magnetic material to be washed off the matrix elements with a high speed stream of water.
The magnetic field may be reduced by de-energizing the magnet. HGMS systems operated in this way are referred to as switched HGMS systems.
De-energization, washing and subsequent re-energization is however inefficient as regards cycle time and power consumption. Accordingly, an arrangement has been developed in which the magnet does not have to be de-energized to enable regeneration of the matrix to be carried out. Instead, two matrix canisters are provided, moved alternately into the separation zone. Thus, as one matrix canister is engaged in separation, the second can be flushed and the matrix regenerated. HGMS systems operated in this way are referred to as reciprocating canister HGMS systems or RCHGMS systems.
The magnetic field required for a switched HGMS or an RCHGMS can be provided by an electromagnet operating at ambient temperatures, a permanent magnet or a super-conducting magnet operating at cryogenic temperatures. Cryogenic magnets for use with a switched HGMS or a RCHGMS in industrial applications include a close coupled helium liquefaction system which has sufficient cooling power to maintain the magnet coil below the critical super-conducting temperature. The coil is held in a reservoir of liquid helium which is surrounded by one or more radiation shields, the whole being contained in a cryostat vessel. The shields are maintained at low temperatures by refrigeration means which may include cooling pipes for circulating liquid nitrogen and/or cryocoolers.
As there is a large temperature difference T between the helium in the reservoir and the exterior of the cryostat vessel, which is at room temperature, about 300.degree. K., even with the shielding the energy losses E are high since E .alpha. T.sup.4. For thi
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Bollinger David H.
Carpco, Inc.
Yeager Arthur G.
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