GB2044635A - A magnetic separator cell and a method of removing contaminants from a carrier liquid by magnetic separation in the cell - Google Patents

Abstract

A magnetic separator cell for liquid/liquid separation is a tube (10) enclosing chamber (11) with a flow passage for liquid being treated from an inlet (12) to an outlet (13). Magnetic wires (15) forming a matrix (14) in the chamber extend in the flow direction, so that magnetically responsive contaminant liquid droplets attracted to the wires tend to be drawn downstream along the wires. The contaminant liquid droplets are collected at the downstream ends (20) of the wires and flow out of the chamber through a separate outlet (25). The cell can operate for longer since contaminant liquid does not build up in the matrix. <IMAGE>

Description

SPECIFICATION A magnetic separator cell and a method of removing contaminants from a carrier liquid by magnetic separation in the cell The present invention relates to a magnetic separator cell and also to a method of removing contaminants from a carrier liquid by magnetic separation in the cell. The prime use of magnetic separation, especially high gradient magnetic separation, has been hitherto in the extraction of particulate material from a fluid, normally liquid, medium.

Normally the particulate material to be removed is already paramagnetic, or has been flocculated onto magnetic seed particles introduced into the liquid. In order to separate the magnetic or magnetised particles, the liquid containing the particles is passed through a magnetic separator cell, and a powerful magnetic field is applied across the cell eithertransversely of or anti-parallel to the direction of flow of the liquid through the cell. Most prior art cells have contained either a matrix of randomly orientated magnetic wires in the form of wire wool or an assembly of woven magnetic wire mesh. During operation of the cell magnetic particles in the liquid flowing through the matrix are attracted onto the wires of the wool or mesh.

Some work has been reported on matrixes for magnetic separator cells in which the wires are aligned parallel to one another and to the direction of flow (pages 895 to 897, IEEE Transactions of Magnetics, Vol. Mag-12, No.6, November 1976, "Performance of Parallel Stream Type Magnetic Filterfor HGMS" by S. Uchiyama and others).

There has also been a proposal for the magnetic separation of droplets of an immiscible contaminant liquid from a carrier liquid (pages 115 to 126, AIChE Symposium Series, 68, 124, (1972), "Water- 1971" - "Magnetically Induced Separation of Stable Emulsions" by Kaiser and others). In this article a method is proposed of removing oil from fine oil-in-water emulsions by adding an oil-soluble, water-insoluble ferrofluid to the oil phase in the emulsion to render it magnetically responsive. The emulsion is then passed through a form of separator cell to separate out the magnetised oil phase. The article proposes the use of a "packed bed configuration" of magnetic material in the separator cell.

In all the prior art separator cells whether for removing particulate material or separating a liquid from liquid, there is a problem with the cell becoming progressively clogged by the material separated out of the liquid flowing through the cell. Hitherto, this problem has been dealt with by periodically either interrupting the flow of liquid to be treated through the cell and then switching off the magnetic field or simply removing the matrix from the field, and then flushing the cell to remove contaminant material from the matrix.

According to the present invention, a magnetic separator cell for extracting magnetically responsive droplets of an immiscible contaminant liquid from a carrier liquid, comprises a chamber having an inlet for contaminated liquid to be treated in the cell and an outlet for treated liquid, the chamber defining a liquid flow passage between the inlet and the outlet, a plurality of lengths of wire of magnetic material, extending in the direction of flow of liquid in the passage, so that contaminant liquid attracted in dro plets to the wire, during operation of the cell, tends to be drawn by the flow of liquid in the chamber down stream along the lengths of wire, and means for collecting the contaminant liquid so drawn at the down steam ends of the lengths of wire and with drawing the collected liquid from the chamber.

The present invention also envisages a magnetic separator cell for extracting magnetically responsive droplets of an immiscible contaminant from a carrier liquid, the cell comprising a chamber having an inlet for contaminated liquid to be treated in the cell and an outlet for treated liquid, the chamber defining a liquid flow passage between the inlet and the outlet, a plurality of lengths of wire of magnetic material extending acutely relative to the direction of flow of liquid in the passage and with the downstream ends of the lengths adjacent to a side of the passage, so that contaminant liquid, attracted in droplets to the wire during operation of the cell, tends to be drawn by the flow of liquid in the chamber along the lengths of wire to the side of the passage, and means for collecting contaminant liquid so drawn to the side of the passage and withdrawing the collected liquid from the chamber.

With the separator cell of the present invention, contaminant liquid attracted to the wires in the cell can be withdrawn from the chamber of the cell while the cell is operating. This permits the cell to operate continuously with substantially no build up of con taminant liquid in the matrix of the cell since the contaminant liquid is collected at the downstream ends of the wires of the matrix and can be withdrawn from the chamber. In certain processes, the separator cell of the present invention may be used with a contaminant liquid which has been seeded with magnetic particles to make the liquid droplets magnetically responsive.Then the magnetic seed particles themselves will not normally be swept down the lengths of the wires together with the con taminant liquid and so continued operation of the cell will cause a progressive build-up of solid magne tic particles in the matrix. However, normally the volume of the magnetic seed particles is only one to two percent of the volume of the droplets of conta minant liquid extracted in the cell and therefore the volume of contaminant liquid which can be extracted by the cell before the cell becomes clogged with the magnetic particles may be fifty to a hundred times that extracted if all the extracted contaminant liquid remains static at the point of capture in the matrix.In summary, therefore, it is believed that the magnetic separator cell of the present invention may be operated continuously to remove a paramagnetic contaminant liquid without becoming blocked; and may have a duty cycle fifty to a hundred times greater than that of prior art cells when the contaminant liquid droplets have been made magnetically responsive by the introduction of magnetic seed particles.

Conveniently, the lengths of the wire in the matrix extend parallel to one another in an array of rows which extend across the flow passage. Then, the means for collecting and withdrawing the contaminant liquid may comprise a channel adjacent the downstream ends of the lengths of wire in the downstream row of the array, so that contaminant liquid collecting at said downstream row can coalesce into said channel, and a contaminant outlet pipe connecting to said channel to allow collected contaminant liquid to flow out of the chamber.

It will be appreciated that as droplets of contaminant liquid are attracted to the wires of the matrix and tend to flow down the wires towards the side of the chamber, the droplets coalesce with one another progressively becoming larger. At the downstream ends of the lengths of wire adjacent to the side of the passage still further coalescence takes place so that the contaminant liquid can coalesce and flow downstream from row to row of the wires until reaching the downstream row whereupon the contaminant liquid flows into the collection channel adjacentto this downstream row and thence into the outlet pipe.

Some of the carrier liquid may flow also into the contaminant liquid outlet pipe, and indeed the carrier liquid flowing in this pipe may be in the majority.

However, the material flowing in the pipe will include relatively large drops of the contaminant liquid which can easily be removed from the carrier liquid also flowing in the pipe by various known liquid/liquid separation techniques.

A further channel may be provided extending along the side of the passage in the flow direction between the downstream ends of the rows of the array of wires to assist the coalescence and transfer to the downstream row of collected liquid from the downstream ends of the wires of the upstream rows.

The separator cell described may be used in combination with means for establishing a magnetic field in the chamber of the cell directed transversely of the liquid flow direction and transversely of the lengths of wire.

It will be appreciated that once the droplets of contaminant liquid are captured by a wire of the matrix, the droplets are subject to three forces, the hydrodynamic drag force exerted by the carrier liquid flowing pass the wire, the resultant of gravitational and buoyancy force of the droplet and a surface tension force which tends to hold the droplets on to the wires of the matrix. Whilst the droplets are very small, the hydrodynamic drag force dominates and the droplets are pushed along the wires in the direction of flow through the passage of the cell. However, once the droplets have coalesced to produce larger drops of a contaminant liquid, the resultant gravitational force may become significant.In order to ensure that this resultant gravitational force acts also to encourage the flow of the contaminant liquid along the wires to the downstream ends and also to the downstream row of the wires, it is desirable to orientate the separator cell in operation so that there is a substantial component of the resultant gravitational force resolved parallel to the lengths of the matrix wires, in the downstream direction.

The present invention further envisages a method of removing contaminant from a carrier liquid by magnetic separation in a cell as described above, the method comprising the steps of dispersing magnetic seed particles in a scavenger liquid which is immiscible in the carrier liquid and which is capable of scavenging the contaminants from the carrier liquid, emulsifying a mixture of the scavenger liquid and a pure sample of the carrier liquid to form a suspension of fine droplets of the seeded scavenger liquid in the sample of the carrier liquid, introducing the emulsion into a stream of the contaminated carrier liquid to be treated so that the droplets of the scavenger liquid scavenge the contaminants in the stream, passing the scavenged stream with introduced emulsion through the magnetic separator cell and operating the cell to remove from the carrier liquid the suspended droplets of scavenger liquid with scavenged contaminants.

As explained above, although the scavenger liquid with scavenged contaminants can be withdrawn from the separator cell during operation, the magnetic seed particles will tend to remain at or near their points of capture on the wires of the matrix. Thus, the matrix does eventually become clogged with the seed particles and has to be flushed out with the magnetic field switched off.

Examples of the present invention are now described with reference to the accompanying drawings, in which: Figure lisa cross-sectional view of a magnetic separator cell embodying the present invention; Figure 2 is a view of one of the frames of wires forming the matrix of the cell of Figure 1; Figure 3 is a greatly enlarged view of a single wire of the matrix of a cell illustrating the coalescence of droplets of contaminants liquid on the wire and the flow of the liquid along the wire; Figure 4 is a schematic diagram of a typical process for removing contaminants from a liquid using a magnetic separator cell embodying the present invention; and Figure 5 is a cross-sectional view of an alternative form of magnetic separator cell embodying the invention.

Referring to Figure 1, there is shown in crosssection a magnetic separator cell which comprises a tube 10 defining a chamber 11 having at one end an inlet 12 for contaminated liquid to be treated in the cell and at the other end an outlet 13 for treated liquid. The chamber 11 defines a liquid flow passage between the inlet 12 and the outlet 13 with liquid flowing through the chamber in the direction of the arrow Y. The chamber 11 contains a matrix 14 of fine wire 15 of magnetic material.

When the cell is in use, a magnetic field is applied to the cell so as to be substantially perpendicular to the wires of the matrix, e.g. perpendicular to the plane of Figure 1 as shown atZ.

Magnetic particles or droplets of liquid in suspension in the liquid flowing through the chamber 11 of the cell are then attracted to the wires of the matrix 14 and are captured by the wires and thereby extracted from the liquid flowing through the cell.

In the illustrated cell, the wires 15 of the matrix 14 are arranged in a plurality of lengths, substantially parallel to one another and extending acutely relative to the flow direction Y right across the width of the flow passage formed by the chamber 11. As shown in the Figure, the lengths of wire 15 are arranged to be substantially straight at an acute angle to the direction Y. The lengths of wire 15 are arranged in an array of rows 16 which rows extend across the flow passage substantially perpendicularly to the flow direction Y. Conveniently, these rows 16 of wires are supported on frames 17. A single such frame 17 is illustrated in Figure 2 which is a view of the topmost frame of the stack in the matrix 14 viewed along an arrow X in Figure 1. The frame comprises a pair of cross members 18 interconnecting the ends of side members 19 to produce an open rectangular frame.The wire 15 is wound on the frame 17 between the cross members 18 to produce a flat open coil with adjacentwindings of the coil separated from each other to permitthe passage of the liquid to be treated through the matrix. The frame 17 is made so that the distance between the cross members 18 is rather greater than the width of the tube 10 of the cell so that the frames 17 with the wire 15 wound on them are supported in the chamber 11 of the cell at an acute angle to the flow direction Y as shown in Figure 1.

In this way, all the lengths of wire 15 extending between respective pairs of cross members 18 are aligned substantially parallel to one another and at the acute angle to the flow direction Y. The angle between the lengths of wire 15 and the direction Y is not critical provided the hydrodynamic force exerted by the liquid flowing down through the passage 11 on droplets captured by the wire 15 is sufficient to move these droplets progressively along the wires towards the downstream ends 20 adjacent the side 21 of the chamber. An angle of 45" has been found suitable.

A channel 22 is formed along the downstream end of the side 21 of the tube 10. The channel 22 is formed with an opening 23 immediately adjacent the downstream cross member 18 of the downstream frame 24 of the stack of frames 17. Thus, the opening 23 of the channel 22 is immediately adjacent the downstream ends of the downstream row of lengths of wire 15.

With this geometry for the matrix 14, droplets of contaminant liquid in the stream of carrier liquid flowing through the chamber 11 are captured on the wires 15 and flow along the wires downstream towards the ends 20. Droplets collecting at the ends 20 of the wires tend to coalesce forming larger drops which in turn tend to transfer downstream from one row 16 of wires to the next. At the downstream row, or at the cross member 18 of the downstream frame 24, the collected contaminant liquid coalesces and flows into the opening 23 of the channel 22. A contaminant liquid outlet 25 communicates with the channel 22 and allows the collected contaminant liquid to be withdrawn from the chamber 11 via the channel 22.

Normally, some carrier liquid will also flow into the channel 22 and out through the outlet 25. However, the resulting mixture emerging from channel 25 will contain relatively large drops of one liquid in the other which can be separated relatively easily using well known techniques.

Referring now to Figure 3, there is shown a greatly enlarged view of a portion of a single length of wire 15 in the matrix 14. The Figure is taken from a photograph of an operating magnetic separator cell, but in which the magnetic field is applied at an acute angle to the matrix wires rather than in direction Z as in Figure 1. In the example, the carrier liquid is low viscosity cable oil and the contaminant liquid is water present as a fine emulsion in the carrier liquid entering the cell. The water has been magnetically seeded to renderthe droplets magnetically responsive.

As can be seen in the Figure, droplets 30 of the contaminant liquid have been attracted to the wire 15. The magnetic seed particles in the contaminate liquid arrange themselves to form chains 31 ofparti- cles aligned in the direction Z of the magnetic field.

As droplets of contaminant liquid collect on the wire 15 the droplets coalesce together forming larger formations 32 of the liquid. These larger formations 32 especially are swept down the wire 15 by the flow of carrier liquid through the chamber of the separator cell. The flow direction is indicated by the arrow Y. In the Figure, the formations 32 of contaminant liquid on the upstream side of the wire 15 are migrating along the wire downstream and towards the side of the chamber. The droplets 30 underneath the wire are still stationary on the wire. The chains 31 of seed particles are found to be initially beneficial to operation of the separator cell since they provide a structure of increased surface area for droplets of the contaminate liquid to "wet".The chains 31 also provide a stable mechanical structure to assistthe passage of coalesced formations 32 of contaminant liquid along the wire.

It will be appreciated that because the collected contaminant liquid tends to migrate along the wire 15 to the side of the chamber and thence down the side 21 into the channel 22, there is no substantial build up of contaminant liquid on the matrix of wires 15 in the cell. However, with the example shown in Figure 3, the magnetic seed particles remain stationary on the wires 15 and will eventually clog the matrix. However, the volume of magnetic seed particles is only a small proportion of the total amount of contaminant material removed from the carrier liquid passing through the cell, so that the duty cycle of the cell is very much improved with the described arrangement. When the collected magnetic seed particles start to clog the matrix, the cell can be flushed out in the usual way.

If the contaminant liquid to be removed from the cell is itself paramagnetic so that magnetic seed paricles do not have to be added, then the cell can be used continuously since the collected contaminant liquid will not clog the matrix.

Referring now to Figure 4, there is shown a block diagram of a process for removing contaminants from a carrier liquid using magnetic separation in a cell embodying the present invention such as that described with reference to Figures 1 and 2. In the example of Figure 4 the magnetic separator cell 40 is used in a process for removing an undesirable contaminant from a liquid B of a process stream 41. A scavenger liquid A suitable to scavenge the undesirable contaminant from the liquid of the stream 41 is first prepared at 42 by seeding the scavenger liquid with magnetic seed particles. To disperse the magnetic seed particles in the scavenger liquid, which may be water, a suitable dispersing agent may be employed together with ultrasonics agitation.The scavenger liquid A is then fed to a container 43 together with a quantity of pure liquid B free of the contaminants present in the liquid stream 41. In the container 43, the seeded scavenger liquid A and the pure liquid B are emulsified to produce a fine suspension of droplets of the scavenger liquid A in the liquid B. The emulsion from the container 43 is then fed into the contaminated liquid stream 41 so that the droplets of scavenger liquid A are dispersed in the contaminated liquid stream. The scavenger liquid then extracts the contaminants from the liquid stream 41 at44 so that the resultant liquid leaving 44 is an emulsion of seeded scavenger liquid A with contaminants, in the now purified liquid B. This emulsion is then fed into the magnetic separator40 wherein the droplets of scavenger liquid with the scavenged contaminants are removed from the purified liquid B.The collected scavenger liquid emerges from the cell 40 via the outlet 25 and the now treated liquid B emerges from outlet 13. Some liquid B may emerge via the outlet 25 with the scavenger liquid and contaminants, but as explained previously the combination from the outlet 25 will comprise relatively large drops of one liquid in another which can be relatively easily separated by know techniques.

During the normal separator operation, the valves H and G shown in Figure 4 remain closed and the valves C, D, E and F remain open. However, when the matrix jn the cell 40 becomes clogged with the magnetic seed particles from the scavenger liquid, the cell 40 can be flushed out in the normal way by closing valves C, D, E and F, turning off the magnetic field opening the valves H and G and circulating pure liquid B through the cell 40 in the reverse direction.

Figure 5 illustrates an alternative construction of the magnetic separator cell providing most of the advantages of the arrangement of Figures 1 and 2. In the Figure 5 embodiment, wires 50 of the matrix 51 are contained in a chamber 52 and aligned substantially parallel to the flow direction P of liquid to be treated through the cell. Liquid to be treated enters the chamber via an inlet 53 and leaves the chamber by an outlet 54. The outlet 54 is slightly above the bottom ends of the wires 50 of the matrix and is in one side of the chamber 52. As with the Figure 1 embodiment, contaminant liquid attracted to the wires 50 of the matrix during operation of the cell tends to be forced down along the wires 50 by the hydrodynamic drag of the carrier liquid flowing through the cell. The resultant gravitational force on the droplets may assist this migration.Thus, the captured contaminant liquid accumulates towards the bottom ends of the wires 50. An outlet 55 for the contaminant liquid is provided at the bottom end of the chamber 52 of the cell. Contaminant liquid flowing down the wires 50 eventually reaches the level of the outlet 54 for the carrier liquid. However, the relatively fine droplets of contaminant liquid originally attracted to the wires 50 have by the time they reach the level of the outlet 54 coalesced and merged into one another to form relatively large formations of the contaminant liquid. Provided the contaminant liquid has a higher specific gravity than the carrier liquid, these large accumulations tend to continue to move down the wires 50 under the influence of gravity until they can be collected and withdrawn from the chamber 52 by the outlet 55.Once again some carrier liquid may also flow out through the outlet 55 but the combination of liquids comprises relatively large drops of one liquid in the other which can be easily separated.

In one test of the apparatus of Figures 1 and 2, a contaminant liquid comprising water was seeded with magnetic seed particles comprising magnetite (Fe3O4) of size 0.2 to 1.2 x 10-6m. A dispersing agent, Triton GR-5, was used to aid in the dispersion of the seed particles in the water. The concentration of seed particles in the water was 2% by volume. The water was then emulsified in low viscosity cable oil as carrier liquid and the concentration of the contaminant water in the oil was 1% by volume. The separator cell was constructed using a matrix comprising stainless steel wire, EN60 (AlSl 430), 50 x 10-"m diameter.The cross members 18 of each frame 17 of the stack forming the matrix was provided with a 6BA thread and the wire was wound around the frame on these threaded cross members 18 so that adjacent turns of the wire were located in adjacent threads of the members 18. A DC magnetic field of 9.6 kilo Gauss was applied to the cell and a liquid flow rate through the cell of up to 4mm per second was established.

With this arrangement, 99.4% of the contaminant liquid in the carrier liquid was found to have been removed from the treated carrier liquid emerging from the outlet 13. The contaminant liquid with some water flowed from the cell via the outlet 25 and it was found that the cell could be operated until the matrix began to be clogged by the magnetic seed particles.

In the arrangement shown in Figure 1, the flow direction of liquid through the cell is vertically downwards, so that, assuming the resultant gravitational force on captured droplets is directed down wards, there is a component of this force parallel to the matrix wires assisting migration of droplets along the wires. Improved migration may be achieved by orientating the cell so that the wires are vertical and the liquid flows obliquely downwards through the cell. Then the resultant gravitational force is parallel to the matrix wires.

Afurther improvement in the performance of the cell of Figure 1 may be achieved by arranging that the magnetic field is applied directed obliquely upstream and perpendicular to the planes of the frames 17, i.e. extending from bottom left to top right in Figure 1. There is then a component of the magnetic force acting on the droplets in the carrier liquid which is directed upstream and tends to slow down the droplets in the carrier liquid, thereby improving the capture performance of the cell. If this orientation of magnetic field is combined with the orientation of the cell described in the last paragraph then the field is arranged substantially horizontally.

Claims (13)

1. A magnetic separator cell for extracting magnetic responsive droplets of an immiscible contaminant liquid from a carrier liquid, comprising a chamber having an inlet for contaminated liquid to be treated in the cell and an outlet for treated liquid, the chamber defining a liquid flow passage between the inlet and the outlet, a plurality of lengths of wire of magentci material, extending in the direction of flow of liquid in the passage, so that contaminant liquid attracted in droplets to the wire, during operation of the cell, tends to be drawn by the flow of liquid in the chamber down stream along the lengths of wire, and means for collecting the contaminant liquid so drawn at the down stream ends of the lengths of wire and withdrawing the collected liquid from the chamber.

2. A magnetic separator cell for extracting magnetically responsive droplets of an immiscible contaminant from a carrier liquid, the cell comprising a chamber having an inlet for contaminated liquid to be treated in the cell and an outlet for treated liquid, the chamber defining a liquid flow passage between the inlet and the outlet, a plurality of lengths of wire of magnetic material extending acutely relative to the direction of flow of liquid in the passage and with the downstream ends of the lengths adjacent to a side of the passage, so that contaminant liquid, attracted in droplets to the wire during operation of the coil, tends to be drawn by the flow of liquid in the chamber along the lengths of wire to the side of the passage, and means for collecting contaminant liquid so drawn to the side of the passage and withdrawing the collected liquid from the chamber.

3. A magnetic separator cell as claimed in claim 2, wherein the lengths of the wire in the matrix extend parallel to one another in an array of rows which extend across the flow passage.

4. A magnetic separator cell as claimed in claim 3 wherein the means for collecting and withdrawing the contaminant liquid may comprise a channel adjaccent the downstream ends of the lengths of wire in the downstream row of the array, so that contaminant liquid collecting at said downstream row can coalesce into said channel, and a contaminant outlet pipe connecting to said channel to allow collected contaminant liquid to flow out of the chamber.

5. A magnetic separator cell as claimed in claim 4 wherein a further channel is provided extending along the side of the passage in the flow direction between the downstream ends of the rows of the array of wires to assist the coalescence and transfer to the downstream row of collected liquid from the downstream ends of the wires of the upstream rows.

6. A magnetic separator cell as claimed in any preceding cell, in combination with means for establishing a magnetic field in the chamber of the cell directed transversely of the lengths of wire.

7. A magnetic separator cell as claimed in claim 6, wherein the lengths of wire extend parallel to one another and the magnetic field is perpendicularto them.

8. A magnetic separator cell as claimed in claim 7 wherein the magnetic field is directed to have a component upstream of the flow passage of the cell.

9. A magnetic separator cell as claimed in any preceding claim wherein the cell is orientated, in use, so that the resultant gravitational force on the captured contaminant liquid droplets has at least a component directed downstream along the lengths of wire of the matrix.

10. A magnetic separator cell as claimed in claim 9 wherein the lengths of wire are parallel to one another and the cell is orientated, in use so that the lengths are vertical.

11. A method of removing contaminants from a carrier liquid by magnetic separation in a cell as claimed in any preceding cell, the method comprising the steps of dispersing magnetic seed particles in a scavenger liquid which is immiscible in the carrier liquid and which is capable of scavenging the contaminants from the carrier liquid, emulsifying a mixture of the scavenger liquid and a pure sample of the carrier liquid to form a suspension of fine droplets of the seeded scavenger liquid in the sample of the carrier liquid, introducing the emulsion into a stream of the contaminated carrier liquid to be treated so that the droplets of the scavenger liquid scavenge the contaminants in the stream, passing the scavenged stream with introduced emulsion through the magnetic separator cell and operating the cell to remove from the carrier liquid the suspended droplets of scavenger liquid with scavenged contaminants.

12. A magnetic separator cell substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 3 or Figure 5 of the accompanying drawings.

13. A method of removing contaminants from a carrier fluid substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.