GB2228431A - Electromagnetic filter with a high field gradient - Google Patents

Abstract

An electromagnetic filter for the extraction of particles of low susceptibility suspended in a fluid, comprises an enclosure (2) with an inlet (4) and an outlet (6), an electromagnet (18) to create transversely oriented magnetic field gradients and able to entrain the particles towards the inner wall of said enclosure where they form a sludge, a partition (12) set in the plane of symmetry of the enclosure so as to obtain two chambers (E1, E2) and a plurality of pipes able to link the inlet (4) and the outlet (6) by a system of inlets and outlets (22, 25), so as to lengthen the path of the fluid in enclosure (2). The electromagnet may be a quadripolar superconductive magnet (Fig 4). The sludge may be removed through tubes 14, 15. Sludge may also be removed by rinsing through pipes 16, 17. Sludge can be scraped off after removing the bottom of the enclosure (2). Filtration may be enhanced by adding ferromagnetic material. The pipes connecting the chambers (E1, E2) are arranged so that the fluid flows in the same direction in each chamber; this enhances extraction. <IMAGE>

Description

ELEcTRoMAGNETIc FILTER WITH A HIGH FIELD GRADIENT FOR THE EXTRACTION OF PARTICLE SUSPENDED IN A FLUID The invention relates to an electromagnetic filter with a strong field gradient for the extraction of particles suspended in a fluid, in which filtering can be continuous or involve cleaning sequences and more particularly applicable to chemically aggressive or radioactive fluids.

Consideration has been given to the use of such electromagnetic filters for a large number of installations containing a fluid polluted by insoluble impurities, which remain suspended in the form of solid particles. An example is the nuclear power station, where such particles can be present either in the primary circuits, or in the secondary circuits.

Such a use is described in German patent application 2 136 352 filed on 21.7.1971 with the title steam power plant for nuclear power stations with boiling water reactors and in the report of the 30th annual meeting, 1969 of the wInternational Water Conference of the Engineer Society of Western Pennsylvania", (article by H.G. HErTMANN, p 69). Other applications more particularly relating to the elimination of heavy metal elements suspended in a liquid are described in French patent 2 4'66 282.

There are at least two filter types of different designs and whose characteristics and operation will be described hereinafter.

Firstly and in general terms, it is pointed that an electromagnetic filter for particles suspended in a fluid is constituted by an enclosure in which flows the fluid to be filtered and in which there is a magnetic field gradient for exerting forces on the particles in order to attract them in preferred directions favouring their extraction.

In a first known filter type, field gradients are created fran a magnetizable lining placed in an enclosure in which flows the fluid to be filtered. The enclosure is placed in an electrical winding arranged in the form of one or more coaxial coils or between the pole pieces of one or more independent electromagnets. The passage of an electric current in the coil leads to the appearance of a magnetic field1 whose effect is to magnetize the lining, which is itself formed in such a way that it has a large number of small cavities becoming the seat of strong magnetic field gradients.

The lining can be fixed and is generally in the form of a packing, steel wire fabric or a stack of gratings or grids. However, it can also be produced in the form of a bed of steel balls, which can be fluidized in a rinsing water flow and thus permit a regeneration by extraction of the sludge in a particularly fast and complete manner.

The application of a magnetic field to the lining material brings about its magnetization and correlatively the appearance of high magnetic field gradients in the spaces between the solid edges, which make it possible to displace the magnetizable solid particles transported by a fluid passing through this lining.

When a fluid containing solid impurities having an adequate magnetic susceptibility traverses the lining of an electromagnetic filter magnetized in this way, the impurities in question are transported fran the zones having a weak magnetic field to the zones with a strong magnetic field, i.e. towards the elementary magnetic poles in said lining.

Due to the action of the magnetic forces, these impurities becane caught in the cavities of the lining, which thus serve as a filter.

This catching more particularly takes place at the locations where the highest magnetic field exists and is naturally aided if, at this location, the linear velocity of the fluid is reduced.

In a non-banogeneous magnetic field, a magnetized particle is subject to a force measured by the product of its magnetization and the field gradient. Except in the case of saturation, the magnetization of the particle is proportional to the magnetic field and consequently the force which it undergoes in a cavity of the lining of an electromagnetic filter is proportional to the product of the field applied by the field gradient created in said cavity It is clear that particles formed by a ferranagnetic material are easily retained in an electranagnetic filter, but that particles with a moderate magnetic susceptibility are only retained with an efficiency highly dependent on the power of the electrical winding of the filter and the capacity of the lining to create strong field gradients in its cavities.

In such filters, there is always a nonqmagnetizable material envelope within a lining which catches the solid particles up to the exhaustion of its capacity, which is a function of the flow rate of the liquid to be filtered, the magnetic field applied and the field gradients obtained according to the geanetrical characteristics of this lining.

When the filter becomes inoperative, it is necessary to regenerate the lining by extracting the sludge. This extraction generally involves rinsing the lining after demagnetization.

For this reason, the filter is provided with valves making it possible to stop the flow of liquid to be filtered, as well as tubes, which also have valves and used for the circulation of a rinsing water flow.

The regeneration operation is very fast, only lasting a few minutes and can take place automatically. Nevertheless it interrupts the operation of the filter and involves an extraction of sludge and a putting back into operation by manipulating the valves. When the liquid to be filtered has a high chemical aggressiveness or corrosiveness, or gives rise to particular precautions when it has radioactive contamination risks, the manipulations of the valves and the dilution of the sludge in a rinsing water flow can be disadvantageous in several respects.

In a second known filter type, no valve or rinsing water flow are necessary, which makes a cantinuous operation possible. Thus, this filter is designed to randanly permit the continuous extraction of fluid sludge by continuous or sequential drawing off whilst the liquid to be filtered continues to circulate.

Such a filter is shown in figs. 1 and 2 and is described in greater detail in French patent application 84 11311. It comprises a pipe 100 having an inlet tube 101, an outlet tube 102 and a drawing off tube 103. Pipe 100 has a flared shape with a base 100, from which emanates the drawing off tube 103. The field gradient is obtained by means of a series of electromagnets 105 arranged laterally on either side of pipe 100.

For this purpose each electromagnet has at least two pole pieces 106, 107 cut so as to be applied to the pipe 100 in a plane perpendicular to the flow direction. The pole pieces are provided with teeth 108 located in a plane parallel to the direction of the fluid and whose width decreases in the fluid flow direction. Such a filter permits continuous or sequential drawing off, but suffers from the disadvantage of only allowing relatively modest flows in the case of fluids containing a large amount of particles with a very low magnetic susceptibility.

Moreover, with both these filter types and in the case where the fluid transports particles with a low magnetic susceptibility, it would be necessary to use large units for treating very large flow rates, so that their installation would cause problems in conjunction with existing electromagnet means.

The present invention makes it possible to obviate these disadvantages.

This, it relates to an electranagnetic particle filter able an the one hand to carry out continuous filtering without it being necessary to stop the fluid flow, but also a sequential filtering with the provisional stoppage of the fluid flow, whilst on the other hand filtering equally effectively fluids containing few or large quantities of particles, as well as fluids containing particles with a high or low magnetic susceptibility.

The present invention therefore relates to an electromagnetic filter with a strong field gradient for the extraction of particles suspended in a fluid comprising an enclosure in which flows the particlecontaining fluid, the enclosure being provided with an inlet and an outlet, characterized in that it carprises means (1) making it possible to create within the enclosure (2) magnetic field gradients oriented in a transverse manner and able to entrain the particles towards the inner wall of said enclosure, where they form a sludge, in that the enclosure has a plane of symmetry, the inlet (4) and outlet (6) of the fluid being on either side of said plane, in that the enclosure comprises, in said plane of symmetry, a partition (2) so as to obtain two chambers (EA, E2) and in that it has a plurality of pipes able to link the inlet (4) and the outlet (6) by a system of inlets and outlets (22, 25), so as to lengthen the path of the fluid in the enclosure (2).

Advantageously, the electromagnetic filter has a rrultipole electromagnet coil with at least four poles arranged around the enclosure so as to obtain a succession of alternate north and south poles.

Advantageously, the electrarnagnet is quadripolar.

Advantageously, the enclosure has an axis of symmetry passing on said plane of symnetry and the plurality of pipes is obtained on the basis of an axial pipe placed in the axis of symmetry, said pipe having two ooqpartments in a plane oriented in accordance with the axis.

Preferably, the coils are superconductor coils.

Advantageously, the partitioned axial pipe has openings positioned in such a way that the fluid flows in the same direction successively in both chambers of the filter located on either side of the enclosure partition.

Advantageously, the filter also has drawing off tubes projecting over the bottan of the chamber of the enclosure. Preferably, the enclosure bottom forms a peripheral channel facilitating the path of the sludge towards the tubes.

According to a constructional variant, in each chamber the filter has a rinsing liquid projecting or spraying device. The projecting or spraying device can have a system of isolating and rinsing water control valves permitting a sequential extraction of the sludge.

According to another variant, the filter has an opening sequentially enabling a scraping device to remove the sludge fan the side walls of each chamber of the enclosure. Advantageously, the enclosure has a detachable bottan.

The opening permitting the passage of the scraping device is advantageously constituted by the opening of the enclosure when the bottan is removed.

According to another variant, the filter has a detachable grid or grating placed on the inner wall of each chamber of the enclosure, sequential sludge extraction taking place by the withdrawal of the grating.

The axial pipe and partitions are made fran a nonHnagnetizable material according to an embodiment.

Advantageously, the internal space of the two ccnpartments defined by the inner wall of the enclosure and the partition within the enclosure is at least partly filled with a magnetizable lining.

The invention is described in greater detail hereinafter relative to non-limitative embodiments and the attached drawings, wherein show: Figs. 1 and 2 Longitudinal and cross-sectional diagrams of a prior art electranagnetic filter.

Fig. 3 The diagram of a perspective view of an electro magnetic filter according to the invention.

Fig. 4 The diagran of a cross-section of the filter according to the invention.

Fig. 5 The diagram of a section of the enclosure of the filter in a plane of symnetry of the latter in which is located the partition subdividing the enclosure into two chambers.

Fig. 6 The diagram of a section of the enclosure of the filter in a second plane of symmetry thereof in which is located the partition of the axial pipe.

Fig. 3 is the part sectional perspective view making it possible to see the internal and external structure of the filter.

According to a preferred embodiment the filter is cylindrical.

However, any other shape allowing at least one plane and an axis of symnetry passing through said plane would be suitable and in particular a parallelepipedic or truncated cone shape.

Thus, the filter has an enclosure 2 which, is cylindrical in this exemplified embodiment and about which are placed the means 1 making it possible to create a magnetic induction field with a strong gradient, the magnetid field gradients being oriented transversely so as to entrain the particles towards the inner wall of the enclosure, where they form a sludge. These means are constituted by a coil 18 placed on a soft iron support 1, the coil preferably being constituted by superductor wires. At one of its ends, enclosure 2 has two tubes 4 and 6, nanely an inlet tube 4 and an outlet tube 6. These constitute the inlet and outlet for the fluid to be filtered.

The enclosure is subdivided into two chambers El, E2 by a partition 12 placed in a longitudinal plane of symnetry for the enclosure passing through two magnetic poles with the sane sign. This partition 12 is in the form of two portions between which has been slid a pipe 8 coaxial to enclosure 2. Pipe 8 is e.g. cylindrical and is positioned along the longitudinal axis of symnetry XX' of the enclosure. The two half-partitions 12 and the envelope of pipe 8 consequently form within said enclosure 2 the two chambers El, E2 within which flows the fluid to be filtered.

Pipe 8 admits a plane of symmetry and also has a partition 10 along said longitudinal plane of symmetry. Partition 10 is positioned in such a way as to be in a plane located between the inlet tube and the outlet tube.

The thus compertmentalized pipe 8 permits a circulation of the particlecontaining fluid in an independent manner and in the sane direction in both ccmpertments C1 and C2. This flow also takes place independently and in the sane direction within the enclosure chambers El, E2.

The enclosure also has two drawing off tubes 14, 15, each located in the bottom F of the enclosure 2, i.e. at the opposite end of the inlet-outlet tubes of the filter, thus making it possible to draw off the sludge constituted by accumulations of particles attracted towards the inner walls of the enclosure and dropping under the action of gravity when the electranagnetic device is not excited.

The drawing also shows that pipe 8 is provided with inlet-outlet ports 22, 23, 24, 25 permitting the particle-cantaining fluid to flow fran inlet 4 to outlet 6 within the enclosure. Thus, the fluid arriving by inlet 4 firstly passes into ccmpartment C1 of pipe 8, passes towards the bottan F and passes out of said compartment C1 through an cpening 22 and enters chamber El, rising towards the opposite end to bottom F within said chamber El.

At said end the pipe 8 has another opening 23 located in its delimitation wall of chamber El. The fluid rises towards said end within chamber El and passes through the opening 23 so as to be located in catparbnent C2 and drops again within the latter to the bottan, where it passes out through another opening 24 made in the zone defining chamber E2 with respect to the pipe.

Thus, the liquid passes out of opening 24 and is redirected within chamber E2 towards the upper part of the chamber (as oppose to the lower part constituted by the bottom)1 so as to pass in a high zone H of ccnpeetment C2 defined by a separator 20 separating it frcm the zone below it. When the liquid penetrates said zone H through opening 25, it passes out the campartment C2 through the outlet tube 6.

Fig. 4 is a section AA along a transverse plane of the filter.

Fig. 5 is a sectional view BB along a longitudinal plane of the filter enclosure. This plane is a plane of asymmetry for the enclosure and passes through its axis of symnetry XX'.

Fig. 6 is a section CC of the filter along the longitudinal plane of symnetry for positioning partition 10. This plane passes through the axis of symmetry XX' and is a plane of symmetry for the axial pipe 8.

All these drawings provide a better understanding of the structural details of the filter according to the invention.

Fig. 4 shows the arrangement of the means 1 making it possible to create a strong field gradient within the enclosure. The magnetic induction field, whose field lines are shown in dotted line form, is able to magnetize the solid particles suspended in the fluid flowing within chambers E1 and E2.

The field gradient created makes it possible to displace these particles in order to separate them fran the fluid and is obtained by a multipole electromagnet coil 18 having a succession of alternate north N and south S poles. In exemplified manner is shown a quadri- polar electroagnet, whose poles are positioned symnetrically with respect to the partition 12 of enclosure 2 as can be seen in fig. 4.

Figs. 5 and 6 illustrate the path of the fluid symbolized by the arzows within the ccnpertments C1, C2 and the chambers El, E2.

According to the preferred embodiment, the partitions 10 and 12 are located on planes perpendicular to one another.

The axial pipe 8 also has a partition 20, like that described relative to fig. 3, as well as inlets-outlets 22-28 for carpartments Cl and C2 towards chambers El, E2.

These inlets-outlets make it possible to direct two independent fluid flows of the sane value in the sane direction fran the single inlet tube 4 to the single outlet tube 6, so as to obtain within the two filter ccTpertments fluid flows directed in the sane direction.

This arrangement makes it possible to double the path of the fluid in the useful part of the filter, i.e. in chambers El, E2, where there is the field gradient and thereby increase the effectiveness by passing said fluid successively into the first chamber El and then into the second chamber E2, the fluid entering the latter having been filtered in chamber El and therefore containing less sludge than the fluid entering the first chamber El.

Thus, a fluid containing a very large quantity of particles will be effectively filtered, because its filtering takes place in two stages within the sane enclosure without any increase in the filter volume.

As has been stated relative to fig. 3, the filter bottom F is provided with two tubes 14 and 15 permitting the continuous drawing off of the accumulaticns of particles constituting a sludge. The shape of the bottom F of enclosure 2 is adapted so as to permit this drawing off.

Thus, a channel 26 is formed in the enclosure bottan F, so as to aid the deposition of sludge and the outflow through drawing off tubes 14 and 15.

According to the embodiment shown, this drawing off of the sludge can be assisted by a powerful sprinkling or spraying of the inner wall of each chamber El, E2 of the enclosure in order to accelerate the dropping into the filter bottan of the particles accumulated on the inner walls of the enclosure.

This sprinkling takes place by means of two small dianeter pipes 16, 17 (figs. 3, 4 and 6) on either side of the edges of the separating partition 10 of pipe 8. Over their entire length, pipes 16 and 17 are provided with orifices permitting the spraying of a rinsing liquid towards the inner walls of chambers El and E2.

According to a not shown constructional variant, the sludge drawing off procedure can be based on the use of a scraping device, such as those used in the prior art. Scraping can take place fran the bottom of the filter, said bottom being detachable. For example, in this case is provided a bottom F, which is screwed onto the filter body in order to form a tight enclosure in the manner shown in figs. 5 and 6, the screw threads being shown.

According to a constructional variant, the wall of each of the chambers is provided with a detachable, replaceable grating G. Sludge extraction still takes place by means of the drawing off tubes 14, 15.

However, the filter makes it possible to carry cut sequential drawing off with a stoppage of its operation by simply withdrawing the sludgecarrying gratings, or by scraping after removing the bottom F.

Either of these variants may be preferred when it is a question of drawing off sludge concentrated until dense accumulations are formed and whose movement; under the action of gravity alone along the inner wall of the two chambers would be too slow.

Thus, preferably the sludge is drawn off by gravity by simply emptying the particles which have dipped into the bottom of the filter and discharged by tubes 14, 15. This emptying can be sequentially controlled by means of mechanically or electromagnetically controlled valves able to open or close tubes 14, 15.

The means for spraying water onto the inner walls of chambers El, E2 can also be controlled by a system of valves 30 for isolating and controlling the rinsing water with a conventional system for the control of the opening and closing of the inlets, which can be the sane as that for the valves for controlling the opening and closing of tubes 14, 15.

The filter functions as follows. The superconductor coil of electromagnet 18 is excited with a current, whose optimum value has been experimentally determined beforehand and the fluid to be filtered is made to flow in the two chambers defined by enclosure 2, the outer wall of the axial pipe 8 and the partition 12 with an optirmm flow rate, which is also experimentally determined beforehand.

More specifically, as these two variables are not independent, but are a function of the filter charge and the magnetic susceptibility of the particles to be filtered, they are chosen by means of a semi empirical operating equation. The latter is established by parametric efficiency measurements making it possible to adjust the numerical coefficients of the fundamental equation expressing the balance of the magnetic forces and the viscosity acting on the particles.

The magnetanotive force resulting fran the intensity of the current in the coil creates in the volume defined by the walls of enclosure 2, the magnetic induction field whose intensity must reach several Teslas, when it is a question of filtering a liquid transporting highly divided solids with a low magnetic susceptibility.

Simultaneously by the distribution of the force lines between the alternating N and S poles, in said volume is created a magnetic field gradient proportional to the intensity of the induction field.

Under the effect of the induction field, the solid particles acquire a magnetization proportional to their magnetic susceptibility and thus becane minute dipoles oriented in the direction of the field when they are paramagnetic. Under the effect of the field gradient, they then undergo a magnetic force proportional at all points to the volune of the filter to the product of their magnetization and the field gradient and thus travel in the direction of the rising fields until they meet a solid wall which imnobilizes them.

It is clear that the magnetic force displacing and imnobilizing the solid particles is in competition with the viscosity forces entraining them in the direction of the fluid flow and the semi-empirical operating equation makes it possible to correctly choose the good flow and magnetic induction field conditions as a function of the efficiency of the thus obtained filtration.

As the efficiency of such a filter is dependent on its charge, due to the action of these antagonizing forces, it is clear that the existence of two chambers forming the seats for identical magnetic fields in the enclosure in which the fluid circulates in a consecutive manner leads to an iprcvement in the efficiency, because in the second chamber the sludge charge is always reduced.

When the sludge charge is adequate to reduce the efficiency of the electromagnetic filter under the optimized operating conditions, it is stcpped and the regeneration of its capacity takes place by performing one of the proposed sludge drawing off processes. The frequency of drawing off the sludge is a function of the concentration of the particles transported by the fluid to be filtered.

Naturally, the operation of the electrcmagnetic filter according to the invention can also involve the use of a fermnagnetic filtration adjuvant, which is constituted by precipitated magnetite or an equivalent material.

Claims (17)

ClAIMS

1. Electranagnetic filter with a strong field gradient for the extraction of particles suspended in a fluid comprising an enclosure (2) in which flows the particle-containing fluid, the enclosure being provided with an inlet (4) and an outlet (6), characterized in that it ccmprises means (1) making it possible to create within the enclosure (2) magnetic field gradients oriented in a transverse manner and able to entrain the particles towards the inner wall of said enclosure, where they form a sludge, in that the enclosure has a plane of symnetry, the inlet (4) and outlet (6) of the fluid being on either side of said plane, in that the enclosure comprises, in said plane of symmetry, a partition (2) so as to obtain two chambers (E, E2) and in that it has a plurality of pipes able to link the inlet (4) and the outlet (6) by a system of inlets and outlets (22, 25), so as to lengthen the path of the fluid in the enclosure (2).

2. Electromagnetic filter according to claim 1, characterized in that the means making it possible to create the magnetic field with a strong gradient involve a multipolar electnmagnet coil (18) having at least four poles arranged around the enclosure (2) so as to obtain a succession of alternate north and south poles.

3. Electmmagnetit filter according to claim 2, characterized in that the electromagnet is quadripolar.

4. Electmmagnetic filter according to at least one of the claims 1 to 3, characterized in that the enclosure has an axis of symmetry passing on said plane of symmetry and in that said plurality of pipes is produced on the basis of an axial pipe (8) positioned along the axis of symmetry, said pipe (8) having two ccmpertments (C1, C2) in a plane oriented along the axis.

5. Filter according to claim 2, characterized in that the coil is constituted by superconductor wires.

6. Filter according to claim 4, characterized in that the partitioned axial pipe (8) has openings (22, 25) located in such a way that the fluid circulates in the sane direction successively in both chambers (El, E2) of the filter located on either side of the partition (12) of enclosure (2).

7. Filter according to any one of the claims 1 to 6, characterized in that it also has drawing off tubes (14, 15) projecting over the enclosure bottom (F).

8. Filter according to claim 7, characterized in that the bottan (F) of enclosure (2) forms a peripheral channel (26) facilitating the mcuement of the sludge towards the drawing off tubes.

9. Filter according to any one of the claims 1 to 8, characterized in that within each chamber (El, E2) it has a device (16, 17) for spraying rinsing liquid.

10. Filter according to claim 9, characterized in that the spraying device (16, 17) has a system of rinsing water control and isolating valves (30) permitting a sequential sludge extraction.

11. Filter according to any one of the claims 1 to 10, characterized in that it has an opening (F) sequentially enabling a scraping device to remove the sludge fron the inner side walls of each chamber of enclosure (2).

12. Filter according to any one of the claims 1 to 11, characterized in that the bottan (F) of enclosure (2) is removable.

13. Filter according to claims 11 or 12, characterized in that the opening permitting the passage of the scraping device is constituted by the opening of the enclosure when the bottan (F) is removed.

14. Filter according to any me e of the claims 1 to 14, characterized in that it has a detachable grating (G) placed on the inner side wall of each chamber (El, E2) of the enclosure, the sequential extraction of the sludge taking place by withdrawing the grating.

15. Filter according to any one of the claims 1 to 14, characterized in that the axialtpipe (8) and the partitions (10, 12) are made fran a non-magnetizable material.

16. Filter according to any one of the claims 1 to 15, characterized in that the internal space of the two chambers (El, E2) delimited by the inner wall of the enclosure and the partition (12) within the enclosure is filled at least partly with a magnetizable lining.

17. An electromagnetic filter substantially as described with reference to Figures 3-6 of the accompanying drawings.