EP0429719A1

EP0429719A1 - Magnetic separation apparatus

Info

Publication number: EP0429719A1
Application number: EP89203020A
Authority: EP
Inventors: Geert Van Der Vos; Rintje Boersma
Original assignee: ENVIMAG BV; Smit Transformatoren BV
Current assignee: ENVIMAG B.V.
Priority date: 1988-06-07
Filing date: 1989-11-27
Publication date: 1991-06-05

Abstract

A magnetic separation apparatus is described, which is primarily intended for separating magnetic particals contained in a fluid. Such apparatus is primarily used in the process of sewage purification by binding magnetic particals to the substance to be removed, and by applying a magnetic filter. The invention resides in the fact that the channel for supplying the liquid to be treated has such a shape that part of the substance to be separated already precipitates before reaching the actual magnetic filter (9). This avoid the quick filling of the magnetic filter (9) thus extending periods between rinsing the filter. By applying a relatively weak field in the area (8 and 25) in wich precipitation takes place, precipitation is enhanced.

Description

The present invention relates to a magnetic separation apparatus, comprising a supply channel, a magnetisable filter and a discharge channel.
Such a magnetic separation apparatus is known from the American patent specification 4472275.
In this known apparatus the liquid, from which magnetisable parts have to be separated, is supplied from underneath through a supply channel, and is supplied to a magnetisable filter, comprising in this case two parts, after which the cleaned liquid is discharged through a discharge channel. Thus only the magnetisable filter is working in the separation process.
Such a known apparatus suffers from the disadvantage that the filter, provided therein fills up quickly, so that this has to be rinsed frequently, which disturbs the normal process, so that the effective use of this apparatus is impaired. Of course this can be avoided by the application of a filter with bigger dimensions, but in connection with the greater required volume and the greater exitation power needed in the case of an electromagnet, this is not advantageous either.
The aim of the present invention is to provide such a magnetic separation apparatus, in which - when maintaining a magnetisable filter with limited dimensions - the intervals between rinsing actions can be extended substantially.
This aim is reached by shaping the supply channel such, that before the passing of the filter at least a part of the material to be separated precipitates.
By these features already a part of the material to be separated is separated from the liquid, so that the liquid passing the filter has a more limited content of material to be separated. This avoids that the filter fills up quickly, so that the intervals between the rinsing of the filter can be extended substantially.
Subsequently the present invention will be elucidated with the help of the accompanying drawing, showing a schematic view, partly executed as a cross-section of an apparatus according to the present invention.
The magnetic separator comprises a vessel 1, of which the outer wall is rotation-symmetric. The upper part of the wall 2 of the vessel is cilindrical, the adjacent lower part is conical, while the part underneath is again cilindrical. At the upper side the vessel 1 is closed by a circular cover 3. The cover 3 is fixed to the wall of the vessel by means of bolts 4. At the lower side the vessel 1 is closed by a substantially conical lower part 5, which is again connected with the wall 2 of the vessel by means of bolts 4. This lower part encloses a chamber 25.
Fixed relative to the middle of the cover 3 a core 6 has been provided, which again is coaxial relative to the wall of the vessel. In the middle of the core a channel 7 has been provided. The lower side of the channel 6 is widened, so that a chamber 8 is obtained.
Between the core 6 and the lower part of the wall of the vessel 2 a substantially annular filter 9 has been provided, which is composed of a magnetisable grid with small apertures. The lower half of the filter encloses an annular wall 10. At the upper side of the filter is deliniated by a fixation ring 11, whereas the filter is fixed at its lower side by a fixation ring 12 extending substantially at the inner side underneath the filter 9. This fixation ring 12 is fixed to the conical lower part 5 by means of support 13. Both fixation rings 11, 12 are drawn towards each other by means of rods 15, so that the filter 9 is enclosed.
For excitation of the magnetic circuit a coil 14 has been provided around the core and directly adjacent to it. Of course this coil 14 comprises connection leads not shown in the drawings for excitation of the coil.
The magnetic circuit comprises the core 6, the cover 3, the wall 2 of the vessel, the filter 9 and the conical lower part 5. When exitation of the coil 14 takes place a magnetic field is generated within the filter 9, with the help of which the magnetic separation is executed. The magnetic circuit is dimensioned such that within the filter 9 an effective magnetic field is established with a high gradient. This high gradient is also due to the small dimensions of the apertures of the grid. The core 6 has such a shape that the edges at the lower side thereof are rounded off, so that the required smaller gradients in the field are generated. Thus the chambers 25 and 8 act as a magnetic filter with a small gradient of the field.
A supply channel 17 for supplying liquid to be cleaned is connected with a channel 7 extending through the core 6 through a one-way valve 16. In the present embodiment the one-way valve 16 is implemented as a ball valve, but it is also possible to implement this in another way. The one-way valve 16 is again connected with the cover 3 by means of bolts 4.
Further a discharge channel 18 is connected with the substantial annular chamber 20 located between the cover 3, the wall 2 of the vessel, the closing ring 11, the filter 9, the coil 14 and the core 6 by means of a biased valve 19 and a channel 21 provided in the cover 3.
By means of a channel 22 and a controllable valve 23 the annular chamber 20 is also connected with a vessel not depicted in the drawing, in which air or another gas has been stored under a high pressure.
Finally the chamber 25 is connected with a discharge channel 24 for rinsing water by means of an aperture provided in the conical lower part 5 and a biased valve 26.
This magnetic separation apparatus according to the present invention is used according to the following description: Initially the coil 24 is switched on, so that the magnetic circuit is excited and the filter 9 with a high gradient in the chambers 8 and 25 with a low gradient are magne tised. Subsequently the liquid to be cleaned is supplied through the channel 17, the one-way valve 16 and the channel 7 to the chamber 8. To allow cleaning by means of magnetic separation the pollution has to be composed of magnetisable parts or has to be united with magnetisable material.
By the two stroke widening of the supply channel 7 until the chamber 8, the chamber 25 respectively, a speed reduction of the liquid is achieved, which will already cause to make part of the pollutions to precipitate and to end up on the sloping wall of the conical lower part 5. Also a change of direction of the liquid takes place, which will also cause precipitation.
Within the chamber 8 and 25 a magnetic field with a low gradient is present, so that also precipitation will occur as a consequence of the action of this magnetic field. Thus the filter with a low gradient is combined with the action of gravity. Subsequently the liquid is fed through the filter 9. As a consequence of the high gradients of the magnetic field present within the filter the magnetisable parts will adhere to the filter, so that the cleaned liquid enters in the chamber 20 is discharged through the channel 21, the valve 19 and the discharge channel 18. This process can be maintained until the filter 9 is completely filled up with magnetisable parts.
Subsequently the coil 14 is switched off to cancel the magnetisation of the filter 9 and of the chambers 8 and 25. It can even be required to excite the magnetic during a short period in the opposite direction to compensate remanent magnetism. Then compressed air is supplied, preferrably under a pressure, as high as possible through the controlled valve 23 and the channel 22, so that the one- way valves 16 and 19 will close. As a consequence thereof the liquid present within the chamber 20 will be pressed through the filter with a high force and speed, taking the pollutions left behind during the magnetisation of the filter with it. Experience has learned, that the amount of liquid present in the annular chamber 20 is sufficient to rinse the whole annular filter 9. The rinsing liquid, strongly polluted is carried off through the wall of the conical lower part 5, in which also the material precipitated locally is carried away through the biased one-way valve 26, which will open now, and through the discharge channel 24.
Subsequently the valve 23 is closed and is the annular chamber aired through an airing valve not depicted in the drawing, after which the coil 14 can be switched on again and the whole start can start over again.
In the dimensioning of the apparatus according to the invention account is taken with the fact, that the coil 14 has been provided such, that it is cooled through the cleaned liquid. A secundairy consequence thereof is that pollution of the coil is avoided.
Only by the combination of the functions of the pressure vessel and the magnetic circuit in the wall of the vessel, it is possible to create an annular room, which is fit to withstand pressure, such that the rinsing process can be executed with the help of the water stored in the annular chamber 20 and the gas pressure.
By easily losenable bolt connections between the wall 2 of the vessel and the conical lower part, the wall 2 of the vessel, the cover and the core 7 can be moved upwardly, so that the filter can be inspected easily. Of course, it is also possible to move the filter together with the conical part downward.
For detecting the degree of filling of the filter, it is possible to provide a detection apparatus.
Instead of the one-way valve described in the present embodiment, it is of course possible to employ controllable valves, together with a suitable controlling device.

Claims

1. Magnetic separation apparatus, comprising a supply channel, a magnetisable filter and a discharge channel, characterized in that the supply channel has such a shape, that before passing the filter at least a part of the material to be separated precipitates.

2. Magnetic separation apparatus according to claim 1, characterized in that the magnetisable filter comprises a part, in which a magnetic field with a low gradient is present and comprises a part, in which a magnetic field with a high gradient is present.

3. Magnetic separation apparatus according to claim 2, characterized in that the part of the filter, in which a lower gradient is present coincides with the chamber, in which the precipitation takes place.

4. Magnetic separation apparatus according to claim 1, 2 or 3, characterized in that the supply channel is widened upstream of the filter.

5. Magnetic separation apparatus according to claim 1, 2, 3 or 4, characterized in that the supply channel upstream of the filter is bent such, that the liquid to be separated is submitted to a change of direction of movement.

6. Magnetic separation apparatus according to one of the preceeding claims, characterized by means for rinsing the filter and of the chamber, in which at least a part of the material to be separated is precipitated in the opposite direction.

7. Magnetic separation apparatus according to claim 6, characterized in that the means for rinsing the filter in the opposite direction comprise a storage vessel located in the discharge channel downstream of the filter, a one-way valve provided in the discharge channel further downstream and an apparatus for supplying compressed air.

8. Magnetic separation apparatus according to one of the preceeding claims, characterized in that the filter is being magnetised by an electromagnet, that the electromagnet has been arranged such that it is cooled by the liquid to be processed or already processed.

9. Magnetic separation apparatus according to claim 8, characterized in that the coil of the electromagnet is cooled by the liquid being present in the vessel.

10. Magnetic separation apparatus according to one of the preceeding claims, characterized in that the apparatus is arranged circle-symmetric and that the supply channel is coaxial relative to the electromagnetic and the storage vessel, in which said part of the supply channel, in which the precipitation is developped comprises a substantial cone-shaped chamber.

11. Magnetic separation apparatus according to claim 10, characterized in that the wall of the apparatus acts at least partially as a magnetic circuit.

12. Magnetic separation apparatus according to claim 10 or 11, characterized in that the wall of the supply channel acts at least partially as a magnetic circuit.