US3380589A

US3380589A - Magnetic separation

Info

Publication number: US3380589A
Application number: US503106A
Authority: US
Inventors: C F Gray
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1965-10-23
Filing date: 1965-10-23
Publication date: 1968-04-30
Anticipated expiration: 1985-04-30

Description

April 30, 1968 c F GRAY 3,380,589

MAGNETIC SEPARATION Filed Oct. 23, 1965 FIGURE 2 I 6-6145 //vz7 FlGURE I INVENTOR C F GRAY ATTORNEY KQLMLQQJLWW l S /Lute:

United States Patent 3,380,589 MAGNETIC SEPARATION C F Gray, Baton Rouge, La., assignor to Esso Research and Engineering Company, a corporation of Delaware Filed Oct. 23, 1965, Ser. No. 503,106 4 Claims. (Cl. 209-221) ABSTRACT OF THE DISCLOSURE A vertical tubular member with spaced vanes on its inner wall, containing a bed of fluidized material in its bottom is provided adjacent its upper end with a concentric, external rotatable ring containing opposed pole pieces to separate magnetic solids from an ascending fluid stream suspension.

This invention relates to the art of separating magnetic particles from streams or fluid efiiuents containing magnetic solids particles. In particular, it relates to magnetic separators, especially devices used for the separation of magnetic and non-magnetic solids particles. More particularly, it relates to an apparatus combination comprising a vertically disposed tubular member formed by an enclosing wall, a plurality of spaced vertically aligned vanes attached upon the inside wall, a large diameter ring provided with a plurality of inwardly projecting diametrically opposed pole pieces, mounted concentric, external to and rotatable about the tubular member so that the pole pieces remain adjacent the external wall of the tubular member whereby magnetic forces can be intermittently applied to the spaces between the vanes upon rotation of the tubular member. This causes agglomeration of the magnetic particles upon application of the magnetic force, and release of the agglomerates upon discontinuance of the application of the magnetic force to cause descent of the agglomerates, the net effect of which is the stream is denuded of magnetic solids particles. In a preferred embodiment, the tubular member comprises a reactor which contains a bed fluidized by gases capable of entraining solids, some portion of which can be removed from the gas by rotation of the ring.

Devices are known which are useful for separating solids particles from fluids. One Such device, e.g., is the Cottrell precipitator for separation of fine particles from gaseous streams. In this device, a smoke or flue gas containing solid particles is brought into proximity with high voltage wires or conduits at different potentials so that the solids particles become charged and are precipitated out of the gaseous streams.

Other devices are also known, these including, e.g., those useful for the separation of magnetic particles from streams containing both magnetic and nonmagnetic solids particles. In such devices, strong electromagnetic fields are produced adjacent to mixtures containing quantities of magnetic ore particles to attract the latter while leaving the nonmetallic particles in place. These devices have been employed to separate magnetic particles from streams of particles in either wet or dry state.

While such devices have proven quite adaptable for a variety of purposes, there is need for method and apparatus which will provide separation of magnetic particles from streams or fluid efiiuents, particularly from streams or efliuents which carry both magnetic and nonmagnetic 3,380,589 Patented Apr. 30, 1968 particles. Thus, in certain processes gaseous streams are often used to convey mixtures of magnetic and nonmagnetic particles, and therein it is desired to separate and remove the magnetic particles from the streams.

In fluidized iron ore reduction processes, e. g., it is often desired to separate finely divided magnetite (magnetic oxide or iron) or metallic iron particles from effluents leaving the reduction stages of the process via the cyclone separators. In such processes, considerable portions of the fines, i.e., particles of about 325 mesh and finer (Taylor screen), are often carried from the process through the cyclone. This represents loss and inefliciency and is a debit to the process.

It is accordingly the object of the present invention to provide method and apparatus for extracting magnetic solids particles from streams or fluid effiuents, and in particular to extract such particles from process streams, and return these to the process. More particularly, it is an object to provide a magnetic separator device for removal of magnetic particles from mixtures of magnetic and nonmagnetic particles carried or suspended in liquid or gaseous efliuent.

These objects and others are achieved in accordance with the present invention which contemplates the steps comprising passing upwardly through a zone a fluid stream within which is suspended magnetic solids particles, intermittently applying a magnetic force adjacent the zone to retard, hold back, and interrupt the ascent of the magnetic particles during application of the magnetic force, and releasing the said magnetic particles during null periods or intervals of nonapplication of the magnetic force so that the magnetic particles are transported in a direction opposite to that of the moving stream.

In a preferred embodiment the applications of magnetic force are applied continuously, but at different locations around the circumference of the zone so that the net eflect at any given location is that intermittent applications of magnetic force are simulated.

The invention will be more fully understood by reference to the following detailed description of a specific and preferred embodiment, and to the drawings to which reference is made in the description.

In the drawings:

FIGURE 1 depicts the cross section of a conduit or reactor, or stage of a reactor, partitioned in part by vertically aligned vanes and within the lower portion of which is contained a fluidized bed comprising a mixture of magnetic and nonmagnetic solids particles, and through which bed is passed a fluidizing gas which entrains fines which tend to exit with the eflluent gas, and in the same figure, in section, and again in FIGURE 2, which is a section AA of FIGURE 1, is shown a cross-section of a magnetic separator device which is annular to and rotatable about a portion of the reactor.

Referring to the figures is shown a reactor or conduit 10 consisting of a tubular member 11, the inner circumference or wall 11 of which is aligned with a plurality of vertically aligned vanes or baffles 12 through 12 The vertically aligned vanes 12 are perpendicular to their points of contact or connection with the inner wall 11 and are projected or aligned upon a common center lying at the center or axis of tubular member 11. The tubular member 11 is constructed of a nonmagnetic material.

At the bottom of the tubular member 11 is provided a fluidized bed of solids particles of various sizes, some of which are magnetic and some nonmagnetic, and some of which are very finely divided, i.e., 325 mesh and finer. The particles are fluidized by gases which enter tubular member 11 via line 16 and exit via line 17 carrying entrained particles. An overflow line 18 maintains the liquid level of the bed.

A circular holder or ring member 13 is mounted upon the tubular member 11 which acts as a hub about which the ring member 13 can be rotated. The annular ring member 13 carries pairs of magnets diametrically oriented one with respect to another. Thus, upon the interior portion of annular ring member 13 is mounted a plurality of pole pieces 14, 15. Each member 14, 15 of the pair is located on the opposite sides of tubular member 11, and each member of the pair lies contiguous to the external wall surface 11 of tubular member 11. Pole pieces 14, 150ne a north pole and one a south pole are means for producing a magnetic force upon the inner wall 11 in the proximity or location of a respective polar piece.

The annular ring 13, rotatably mounted via means not shown, provides for movement of pole pieces 14, 15 around tubular member 11 so that the magnetic force therefrom is imparted through the Wall. In removing or extracting metallic particles from an ascending effluent, the magnetic field is constantly moved about tubular member 11 from one contiguous location to another so that the effect is to produce an intermittent magnetic force upon a given sector of inner wall 11 at any particular moment of time.

In operation, for illustration, it is supposed that annular ring 13 is rotated clockwise as shown in FIG- URE 2. Pole piece 14 thus moves from a space between

vertical vanes

12 and 12 to the space between

vertical vanes

12 and 12 moves from the space between vanes 12;; and 12 to the space between 12 and 12 and from the space between

vanes

12 and 12 to the space between vanes 12.; and 12 Simultaneously pole piece 15 moves from the space :between vanes 12.; and 12 to the space between

vanes

12 and 12 from the space between

vanes

12 and 12 to the space between

vanes

12 and 12 and thence to the space between

vanes

12 and 12 The movement continues ad infinitum while the device is in operation. Simultaneously with this rotational movement, a stream of gas is injected into the interior of tubular member 11 via line 16. The gas ascends through the bed and entrains solids. The solids-laden gas, or efiiuent, which contains both magnetic and nonmagnetic particles, ascends through the tubular member 11 and exits there from via line 17. The ascending gas thus entrains both magnetic and nonmagnetic particles on ascent through the bed, and the magnetic particles within the gas stream are attracted to the inner wall 11 at location near adjacent pole pieces 14, 15, respectively. The magnetic particles stick to the inner surfaces of the wall 11 at locations between the vanes 12, and their upward movement is restrained or halted with respect to the gas-solids laden stream. Thus, e.g., magnetic particles stick to the inner wall 11 at locations between vanes 12; and 12 and between

vanes

12 and 12 As the annular ring 13 is rotated to the next position, however, i.e., as. pole pieces 14, 15 move to adjacent positions between

vanes

12 and 12 and between

vanes

12 and 12 the pull upon the magnetic particles in the sectors between

vanes

12 and 12 and vanes 12.; and 12 is released. The fine particles tend to form a very loose agglomerate near the respective sectors of wall 11 and fall back to the bed.

As the magnetic field is moved to any given sector of wall 11 the metallic particles accumulate or loosely agglomerate upon the wall. As the magnetic particles tend to follow, e.g., pole piece 14 they are restrained due to the interference by vanes 12 upon which they impinge. Upon release of the magnetic force, the magnetic particles, now of higher effective particle size due to the formation of loose aggregates, fall downwardly and are returned to the bed.

By rotation of the annular ring 13 at suflicient annular velocities, and by use of sufiicient field strengths, the sum total effect is that very high quantities of the magnetic solids particles can be readily extracted from gas-solids systems and returned to the process.

It is apparent that the effectiveness of the apparatus is dependent to some extent upon the magnetic field generated by pole pieces 14, 15, by the number of pole pieces employed in a given device, by the annular velocity of the pole pieces about tubular member 11, and by the nature of the magnetic material being extracted.

It is obvious, therefore, that the illustrated device is subject to numerous modifications and changes readily apparent to those skilled in the art, and therefore the invention should not be limited to the exact construction and operation shown and described.

The instant application is found particularly applicable to the extraction, denuding or separation of fines magnetic particles from the process streams, i.e, the gaseous effluents of iron ore reduction processes. Thus, the invention is specially adaptable to fluidized iron ore reduction processes wherein particulate iron oxides are reduced through magnetite, or through magnetite and finally to substantially metallic iron. This oxide, as well as the metallic iron product, is, of course, magnetic.

The use of the instant device for separating magnetic particles from such process efiluent which contain mixtures of magnetic and nonmagnetic particles is found to be quite practical when the magnetic strength of the pole pieces is from about 20 to about 500 gauss, and preferably from about 50 to about 200 gauss while providing annular rates ranging from about 5 to about 50 revolutions per minute, and preferably from about 10 to about 20 revolutions per minute.

The magnetic force is generally intermittently applied upon any given sector at frequencies ranging from about 10 to about cycles, and preferably from about 20 to about 40 cycles per minute. The rate or frequency must be adjusted to allow the agglomerated fines to completely drop out of the magnetic zone. This rate will depend upon the length of magnetic zone and the diameter of reactor. Larger diameter reactors will require a greater number of vertical vanes.

A rotating or nonrotating member can be employed to provide the magnetic field. Thus, elcctromagnets could as well be distributed around an area and the individual electromagnets sequentially activated. This would provide the same effect as provided by a rotating member upon which is attached permanent or electromagnets.

Having described the invention, what is claimed is:

1. In apparatus for magnetically separating magnetic solid particles from a fluid stream containing solid particles, the combination comprising a vertically disposed tubular member formed by an enclosing wall having an inlet at its bottom end and an outlet at its top end, a plurality of spaced vertically aligned vanes attached parallel to the inside walls at the location of contact and aligned upon a common center lying at the axis of said tubular member, a large diameter ring provided with a plurality of inwardly projecting diametrically opposed pole pieces, means to move said stream upwardly in the tubular member from the bottom of said member to a region adjacent said ring, said pole pieces being mounted concentric, external to and rotatable about the tubular member so that the pole pieces remain adjacent the external wall of the tubular member whereby magnetic force can be intermittently applied to the spaces between the vanes upon rotation of the tubular member to cause agglomeration of the magnetic particles upon application of the magnetic force, and release of the agglomerates upon discontinuance of the application of the magnetic force to cause their descent, the net eifect of which is that said stream is denuded of magnetic solid particles.

2. The apparatus of claim 1 wherein the wall of the tubular member is constructed of nonmagnetic material.

3. The apparatus of claim 1 wherein the tubular member constitutes a reactor Within which can be contained a bed fluidized by gases capable of entraining solids.

4. The apparatus of claim 1 wherein two pole pieces are mounted on the inside of the ring.

References Cited UNITED STATES PATENTS Wedge 209-232 Fernow 209-215 Latz 2092l5 Clute 209-214 HARRY B. THORNTON, Primary Examiner. 10 R. HALPER, Assistant Examiner.