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A magnetic separator for kaolin clay brightening comprising: a
ferromagnetic housing; a vertically elongated rectangular canister
enclosed within the housing, said canister being filled with a stainless
steel wool matrix and having a slurry inlet at its bottom and a slurry
outlet at its top; a pair of electromagnetic coils flanking opposed
vertical sides of the canister which generate a magnetic field
horizontally across the shortest dimension of the canister; and a
plurality of wash water inlets and outlets in said opposed vertical sides
of the canister for periodically cross flushing the matrix to regenerate
Primary Examiner: Hart; Charles N.
Assistant Examiner: Hruskoci; Peter A.
Attorney, Agent or Firm:Townsend and Townsend
1. A magnetic separator for removing magnetic particles from a fluid comprising:
a. a ferromagnetic housing;
b. a non-magnetic canister within said housing having an inlet and an outlet for said fluid;
c. a magnetic matrix within said canister for removing said particles from the fluid as it flows through the canister;
d. at least one electromagnetic coil within said housing which produces a magnetic field generally transverse to the fluid flow through said canister; and
e. a plurality of wash fluid inlets and wash fluid outlets in said canister for providing wash fluid flow through said matrix generally transverse to the flow of said fluid.
2. A magnetic separator as defined in claim 1 wherein:
f. there is a pair of electromagnetic coils which flank the canister.
3. A magnetic separator as defined in claim 1 wherein:
f. said canister has the general shape of an elongated rectangular parallelepiped with its longest dimension in the direction of flow of said fluid.
4. A magnetic separator as defined in claim 3 wherein:
g. said inlet and outlet for said fluid are in the bottom and top of the canister, respectively.
5. A magnetic separator as defined in claim 3 wherein:
g. said canister has a rectangular vertical cross section taken in a plane perpendicular to the direction of flow of said wash fluid.
6. A magnetic separator as defined in claim 3 wherein:
g. said inlet and outlet for said fluid are, respectively, at opposite ends of the canister; and including
h. a fluid distribution chamber at the fluid inlet end of said canister and a fluid discharge chamber at the fluid outlet end of canister for providing uniform fluid flow through the matrix.
7. A magnetic separator as defined in claim 6 in which:
i. said fluid distribution chamber and said fluid discharge chamber each are frustopyramidical in shape; and
j. said chambers have a multiplicity of fluid passageways extending from said inlet and outlet, respectively, to the respective inlet and outlet ends of the canister, whereby the fluid is fed uniformly across the inlet end and withdrawn uniformly
from across the outlet end.
8. A magnetic separator as defined in claim 3 in which:
g. the shortest dimension of said canister is in the direction of the wash fluid flow.
9. A magnetic separator as defined in claim 5 in which:
h. said electromagnetic coils have the shape of rectangular toroids; and
i. the housing has a central interior recess with an I-shaped cross section in a plane parallel to the fluid flow;
j. the vertical cross section area of the central air gap of each of said rectangular toroidally-shaped coils being substantially the same as said rectangular, vertical cross section area of the canister.
10. A magnetic separator as defined in claim 1 wherein:
f. said fluid is an aqueous slurry of kaolin clay;
g. said matrix is stainless steel wool.
11. A magnetic separator as defined in claim 1 including:
f. at least one partition within said canister parallel to the flows of said fluid and said wash fluid.
12. A semi-continuous process for removing magnetic particles from a fluid comprising:
a. passing the fluid through a fixed bed of a ferromagnetic matrix in a substantially rectilinear path;
b. simultaneously forming a magnetic field through said matrix substantially perpendicular to the fluid flow therethrough, the intensity of the field and residence time of the fluid in the matrix being sufficient to remove a substantial portion
of the magnetic particles from the fluid;
c. temporarily stopping the flow of fluid through said bed and terminating said field; and
d. passing a wash fluid through a plurality of inlets through the matrix in a substantially rectilinear path substantially perpendicular to the flow of said fluid and withdrawing said wash fluid through a plurality of outlets while said flow is
stopped and field terminated.
13. A semi-continuous process for removing magnetic particles from a fluid as defined in claim 12 in which:
e. the path of fluid flow through the bed is substantially longer than the path of wash fluid flow therethrough.
14. A semi-continuous process for removing magnetic particles from a fluid as defined in Claim 12 in which:
e. the fluid is an aqueous slurry of kaolin clay; and
f. the wash fluid is water.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to a novel magnetic separator for removing magnetic particles from a fluid, and specifically to a magnetic separator for removing magnetic particles from an aqueous slurry of kaolin clay.
2. Description of the Prior Art
Kaolin clay contains contaminants which may be removed by passing a slurry of the clay through a magnetic separator. Such removal is commonly called "brightening". Various magnetic separating devices and methods have been developed and used for
removing contaminants whose magnetic susceptibility ranges from very high to very low. See, for instance U.S. Pat. Nos. 3,471,011; 3,482,385; 3,567,026 and 3,627,678. In general such prior art separators consist of: a ferromagnetic housing; a
canister or enclosure within the housing which is filled with a ferromagnetic matrix, such as steel wool, and has a slurry inlet and outlet; and an electromagnetic coil which produces a magnetic field within the matrix. Their modes of operation are
basically the same: as the clay slurry passes through the matrix the particles are attracted to and retained by the magnetized elements of the matrix.
In all of these prior art clay-brightening separators the magnetic field is parallel to the slurry flow through the matrix. Many of these parallel field separators are equipped with devices at the slurry inlet and outlet which promote uniform
(called "plug") flow through the matrix. The power requirements of a parallel field, plug flow separator are greater than a parallel field, non-plug flow separator because the plug flow devices increase the gap between the magnetic poles. One older
patent, U.S. Pat. No. 2,430,157, which does not relate specifically to clay brightening and does not mention plug flow, describes a magnetic separator in which a liquid is passed horizontally through a tack-filled container with the magnetic field
perpendicular to the liquid flow.
All of the current brightening processes are either batch or semi-continuous because the matrix becomes spent, i.e., clogged with magnetic and non-magnetic particles, and must be periodically regenerated. Regeneration is accomplished by stopping
the slurry flow, shutting off the magnetic field and washing the matrix with water. The wash step is conventionally carried out by either simply disassembling the separator and hosing down the matrix or back flushing the matrix through the slurry inlet
and outlet. Naturally, it is desirable to minimize the time involved in regeneration so that the separator may be used for brightening to the greatest possible extent.
Summary of the Invention
The magnetic separator of this invention is designed to provide: a long slurry flow path, which gives improved magnetic separation; a short wash flow path, which makes regeneration faster and more effective; improved magnetic efficiency which
lessens power requirements; and plug flow of the slurry through the matrix without losing magnetic efficiency. Like the prior art, this unique separator includes a ferromagnetic housing and a canister within the housing containing a ferromagnetic matrix
and having a slurry inlet and outlet. It also includes at least one electromagnetic coil-- but unlike the prior art clay-brightening separators, its coil(s) produces a magnetic field which is generally transverse (perpendicular) to the slurry flow.
The perpendicular field is advantageous in this invention for two basic reasons. Firstly, the canister dimension in the direction of the magnetic field is kept short relative to the dimension in the slurry flow direction. This makes the gap
between the magnetic poles in the housing also short, thereby reducing the power requirement necessary to generate the magnetic field. Secondly, the plug flow devices may be located at the slurry outlet and inlet ends of the canister out of the magnetic
field path. In such locations the devices do not increase the gap between magnetic poles. In view of this the preferred canister shape for use in this invention is an elongated rectangular parallelepiped with its longest dimension in the direction of
the slurry flow and its shortest dimension in the magnetic field direction.
Unlike any of the prior art separators, the invention separator includes wash fluid inlets and wash fluid outlets in the canister for washing the matrix transversely to the slurry flow.
It is well known that as the length (in the direction of slurry flow) of a compacted stainless steel matrix is increased, the matrix becomes a more efficient and effective magnetic collecting agent. It is also well known that as the volume
density of the matrix is increased, the matrix becomes a more effective magnetic agent. However, when a more efficient matrix is made by increasing the length of the matrix in the direction of slurry flow and/or by increasing the volume density of the
compacted matrix, the cleaning of the matrix by washing with a fluid becomes increasingly difficult and ineffective.
In the present invention the wash fluid is passed through the matrix at right angles to the direction of the slurry flow and the thickness of the compacted matrix in the direction of the wash fluid flow can be selected independently to obtain
efficient and expeditious flushing of the matrix without sacrificing the efficiency of the matrix to collect contaminants. Preferably, the wash is made across the shortest dimension of the canister (in the same line as the magnetic field). By keeping
the wash path as short as possible, the matrix may be regenerated in the quickest and most efficient manner.
BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the separator of this invention is illustrated in the drawings, in which:
FIG. 1 is a perspective, partial sectional, fragmentary view of a separator according to this invention.
FIG. 2 is a sectional view taken along lines 2--2 of FIG. 1.
FIG. 3 is a sectional view taken along line 3--3 of FIG. 2.
FIG. 4 is a sectional view taken along line 4--4 of FIG. 3. and
FIG. 5 is a sectional view taken along line 5--5 of FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows the basic components of the magnetic separator of this invention: a housing 1 made of a ferromagnetic material such as soft iron; a non-magnetic canister 2 within housing 1 filled with a magnetic stainless steel wool matrix 3; a
slurry inlet pipe 4 entering the bottom of the canister and a slurry outlet pipe 5 exiting from the top of the canister; a pair of electromagnetic coils 6 flanking opposed sides of the canister and a multiplicity of wash water inlet pipes 8 and wash
water outlet pipes 9.
As seen in FIGS. 1-3 canister 2 is a rectangular parallelepiped with a rectangular cross-section in a vertical plane perpendicular to the wash water pipes 8, 9 and coils 6 are rectangular toroids whose central air gaps have slightly larger areas
than sides 10, 11 of canister 2. The canister and coils are housed within housing 1 in a horizontally elongated cavity 12 having an I-shaped cross section in a vertical plane parallel to the axes of slurry pipes 4, 5 and wash water pipes 8, 9. Canister
2 is positioned within the stem of the I and coils 6 are located in the ends of the I's cross bars. Cavity 12 includes vertical channels (not shown) which connect the ends of the cross bars of the I to accommodate the vertical sections of coils 6. The
portions of housing 1 which extend into the central air gaps of the coils and form the sides of the stem of the I facing sides 10, 11 of the canister form the poles of the magnetic field generated by the coils. The surface area of these portions of
housing 1 are approximately the same area as said sides 10, 11.
Housing 1 also has a pair of ports, 13, 14 in its bottom and top (FIG. 3) which receive the slurry inlet pipe and slurry outlet pipe, respectively.
As shown by the large vertical arrows in FIGS. 1 and 2, the slurry flow through the separator is vertical from bottom to top. The slurry is fed under a predetermined pressure and at a predetermined flow rate through inlet pipe 4 into a
frustopyramidical-shaped distribution chamber 15. Chamber 15 serves to uniformly distribute the slurry across the bottom of the canister to obtain plug flow through the stainless steel wool matrix 3. A slurry discharge chamber 16, of similar
construction to chamber 15, is located at the opposite (top) end of the canister. Discharge chamber 16 enables uniform discharge of the brightened slurry from the top of the canister. The structure of chambers 15, 16 are shown in detail in FIGS. 3, 4.
Each has a circular flat top 17, 18 respectively, (chamber 15 is inverted so that its top is located at the bottom of the separator) into which the inlet pipe 4 and outlet pipe 5 enter and exit, respectively. A series of uniformly spaced bores or
passageways 19, 20 extend in a ray-like arrangement through the respective chambers from the tops to the bottoms thereof. Thus, in the case of chamber 15, the slurry feed from pipe 4 is divided into twelve separate streams each of which is channeled
through one of the passageways 19 to the bottom of the canister. In this manner the slurry is charged uniformly across the entire horizontal cross section of the canister and matrix therein. Correlatively the brightened slurry discharged from the top
of the canister is withdrawn uniformly therefrom in twelve separate streams which flow through the passageways 20 of chamber 16 and into outlet pipe 5.
The path of the slurry flow through the stainless steel wool matrix is generally rectilinear from bottom to top-- although it will be appreciated that the actual path will involve a large number of deviations from the vertical due to the random
orientation of the individual fibers of wool which make up the matrix. This is diagrammatically illustrated in FIG. 2 by the wavy lines passing through the matrix.
An electric current is passed through the windings (not shown) of coils 6 from a source (not shown) of electricity via wires 23 (FIG. 3) to generate a magnetic field within housing 1 and the matrix 3. As shown by the dashed flux lines in FIG. 2
the field in the matrix is essentially perpendicular to the flow of slurry therethrough. As theorized by the prior art (see, for instance U.S. Pat. No. 3,627,678) the magnetic field sets up north and south poles on ends of individual matrix elements
which act as collection sites for the magnetic particles contained in the slurry. Thus, as the slurry flows up through the matrix, the particles are attracted to and held by these numerous collection sites.
As more and more particles are caught and held in the matrix, the collection sites become covered with particles and gradually lose their ability to attract and hold additional particles. Consequently, at some predetermined point, which, in the
case of kaolin clay is normally determined by the brightness of the effluent from the separator, the matrix must be regenerated by removing the held particles from it. As described above, in the prior art regeneration has been accomplished by stopping
the slurry flow, terminating the magnetic field and back-flushing the matrix.
As shown in FIGS. 2, 3 and 5 matrix regeneration in the separator of this invention is accomplished by cross-flushing the matrix. In the cross-flushing, the slurry flow is temporarily stopped and the field is temporarily terminated. The latter,
of course, abates the attraction between the matrix elements and the particles within the matrix. Valves 24 in wash water inlet pipes 8 and valves 25 in wash water outlet pipes 9 are then opened allowing wash water to flow from pipes 8 through the
matrix in a generally rectilinear path from side 10 to side 11 of the canister--which is perpendicular to the slurry flow--and out pipes 9. Since the wash is made across the shortest dimension of the canister (as opposed to the prior art in which the
wash path was the same length as the slurry path), the regeneration may be accomplished much faster and more effectively than by back-flushing. Also, although it is not critical to the invention, it is believed that the primary build up of particles in
the matrix takes place on the element surfaces which are aligned with the slurry flow and that a flush across this "grain" provides more efficient and faster regeneration than a flush with the grain.
The canister is vertically partitioned into four sections (FIGS. 3 and 5) by partitions 26. Partitions 26 do not hinder either the slurry flow or the wash water flow because they are parallel to both flows. However, they serve to divide the
canister to enable selective washing of a particular section or sections of the canister. They also help to maintain substantially rectilinear wash flow across the canister. These partitions are optional components in the separator.
After the washing is completed to the desired degree, valves 24, 25 are closed, the electrical current to the coils 6 is turned on and the slurry flow through the canister is resumed.
Although the above description has primarily concerned a magnetic separator for brightening clay, the separator of this invention may be used for removing magnetic particles from other liquids and gases. For instance it may be used as a filter
for cleaning machinery lubricants; for purifying air--such as in a mineral refining plant in which the mineral is handled as a very finely divided "dust"--or as a means to separate a magnetic substance from non-magnetic substances in a mineral refining
The wash fluid, matrix and operating parameters of this separator will vary with the fluid to be treated. For instance, for kaolin clay brightening water may be used as the wash and commercially available stainless steel wool having a volume
density of between about 5 and 20% is a suitable matrix. The operating conditions, e.g., slurry consistency and flow rate and field intensity, for clay brightening are well known. Normally the field intensity will be at least about 8,000 gauss and the
flow rate and consistency will be correlated with the canister dimensions to provide a slurry residence time in the canister of at least about 30 sec. Naturally, for other separations, other matrixes such as steel balls, tacks or iron filings might be
desirable. Likewise non-aqueous liquids might be used in place of water depending on the nature of the magnetic materials removed by the matrix or even gases in the case of, for instance, air purification.
Other variations in the structure and operation of the separator will be obvious to one of ordinary skill in this art. For instance a multiplicity of slurry inlets and outlets may be used or other known plug flow means may be employed. It is
intended that all such variations be within the scope of the following claims.