Patent Publication Number: US-7223345-B2

Title: High-gradient magnetic filter and method for the separation of weakly magnetisable particles from fluid media

Description:
BACKGROUND OF THE INVENTION  
     The invention relates to a high-gradient magnetic filter for separating weakly magnetizable particles from fluid media, with the operating mode derived from the physical principle of generating field strength gradients by introducing a ferromagnetic structure into a magnetic field. The invention also relates to a method for operating the high-gradient magnetic filter. 
     Such filters predominantly generate the required magnetic field using permanent magnets, so that the components can be manufactured more compact and at lower cost, as well as operated more energy-efficient than filters using electromagnets. 
     DESCRIPTION OF THE RELATED ART 
     A device of this type has been described in DE 33 12 207 A1. The device includes stationary chambers that are filled with a magnetizable ferromagnetic filling material. Fittings are provided for feeding and discharging a fluid medium. Each pair of the chambers has a common magnetization arrangement, whose magnetic conductors includes two opposing elements that are arranged on different sides of a line extending through the centers of these chambers. Each of these elements includes a magnet with pole faces which are arranged on the chambers in diametrically opposed disposition in a direction perpendicular to the line extending through the centers of the chambers, whereby these two elements together with the ferromagnetic filling material form a closed magnetic circuit. 
     Disadvantageously, the device takes up considerable space and employs a complex process for separating the ferromagnetic substances from the fluid media. 
     DE 196 26 999 also discloses a high-gradient magnetic separator with a magnetic unit having two poles that together form a gap in which a homogeneous magnetic field can be generated, with a matrix frame that can be rotated about an axis and at least partially surrounds an annular interior space that is divided by partition walls into segments, as well as at least one feed and return line. It is an object of that invention to lengthen the path of the fluid within the magnetic field. This is solved in that the width of the magnetic unit along the interior space corresponds at least to the width of two segments and that each segment of the annular interior space is connected in the gap region with its adjoining segments through a respective opening, whereby the openings are located alternatingly at a first and a second location, wherein in the second location does not face the first location. 
     The magnetic field is herein also produced by permanent magnets, enabling a more compact design of the separator while lowering its manufacturing as well as operating costs. 
     Disadvantageously, the permanent magnets of this device cannot be switched off for the required backwashing operation. The filter chambers arranged in a carousel are therefore cyclically rotated out of the region of the magnetic field following the filtering operation, which takes place inside the magnetic field, and flushed in the field-free zone. Thereafter, the filter chambers are again rotated into the magnetic field and exposed to the fluid to be cleaned, until the filter is loaded and has to be backwashed again outside the magnetic field. 
     A carousel separator of this type is necessarily constructed with a large number of movable parts and, more particularly, numerous seals. This causes wear and leaks and can hence result in significant maintenance and repair costs which cannot be justified, for example, in a communal wastewater plant. 
     At least the problem caused by seals is solved by another high-gradient magnetic separator described in DE-GM 297 23 852.3. The individual filter chambers are here not moved in and out of the magnetic field. The filter system is stationary, and a magnet is mechanically moved back and forth for initiating the filtering process and backwashing. However, a large number of movable parts is still required. 
     Finally, a recently developed high-gradient magnetic separator, as described in WO01/07167 A1, is unsuitable for the problem to be solved, since it uses a different design and a different separation principle for the separation. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a high-gradient magnetic filter for separating weakly magnetizable particles from fluid media, which—through the use of a permanent magnet for generating the magnetic field—represents a compact unit that can be easily maintained and repaired, which simplifies the process for separating the particles and renders the permanent magnet ineffective in the required backwash operation. The variety and number of components should also be reduced and the sealing problem eliminated. The method of the invention for operating the high-gradient magnetic filter should ensure an efficient use of the filter. 
     The object is solved with the invention according to claim  1  in that the high-gradient magnetic filter includes
         a housing receiving the high-gradient magnetic filter with means for directing the fluid media in a pipe system with a feed and a return,   a magnetic circuit forming the actual high-gradient magnetic filter, with a filter disposed in a filter chamber that is formed between pole faces of the magnetic circuit, with the medium to be cleaned flowing through the filter,   at least one permanent magnet arranged in the magnetic circuit for generating the magnetic field between the pole faces, whereby this section of the magnetic circuit is separated from the fluid medium and therefore sealed, and   the magnetic field between the pole faces which can be switched off and switched on again by the permanent magnet.       

     According to one alternative embodiment, the permanent magnet is formed as a rotor and rotatably arranged in the correspondingly formed section of the magnetic circuit. The rotation angle of the rotor can be adjusted so that the field strength between the pole faces can be selected between a minimum and a maximum field strength value, so as to adapt the field strength to the different materials of the particles to be separated. It is also possible to lock the angular position of the rotor, for example, in steps of 90° or in steps having other angles. 
     According to the other alternative embodiment of the invention, the permanent magnet is formed as a linearly displaceable element in the correspondingly formed section of the magnetic circuit. 
     According to the method the invention for the operating the high-gradient magnetic filter, the weakly magnetizable particles are separated from the fluid medium alternatingly in the pipe system essentially according to the following steps:
     a) applying the fluid medium to be separated to the filter via the pipe system having a feed and a return while the magnetic field in the magnetic circuit between the pole faces is switched on, with the magnetic field penetrating the filter chamber of the filter containing the flowing medium, wherein the magnetic particles settle down on the filter due to the high field gradients, with the field strength being adjustable to different values that correspond to the angular position of the permanent magnet, thereafter   b) switching off the magnetic field of the permanent magnet and removing the settled and separated particles from the filter in a flushing process implemented as a counter-flow or also a co-flow process, and   c) repeating the step sequence a) and b) until the separation of the particles from the fluid medium is concluded.   

     Moreover, the method can also be operated efficiently by using a program for controlling the cycles of the fed and returned medium and/or flushing medium in cooperation with the magnetic field, which is to be switched on and off, and the magnetic field strength to be set, whereby the program also includes the functions of the features. 
     The invention will be described with reference to exemplary embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       In the drawings, 
         FIG. 1  is a simplified diagram of the high-gradient magnetic filter in a state switched on by the rotor  10 , 
         FIG. 2  shows the high-gradient magnetic filter of  FIG. 1  in a switched-off state, 
         FIG. 3  is a schematic diagram of the alternative embodiment of the invention with the permanent magnet  9  embodied as a linearly displaceable element  11 , 
         FIG. 4  is a schematic diagram of the rotor  10  with the permanent magnet  9  composed of individual permanent magnets  12 , 
         FIG. 5  is a schematic diagram of the rotor  10  with a drive  13 , 
         FIG. 6  shows schematically the support of the rotor  10 , and 
         FIG. 7  shows schematically a dual configuration according to the invention with two filters  8  and a rotor  10 . 
     
    
    
     DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
     As shown in  FIGS. 1 and 2 , the high-gradient magnetic filter according to the invention is essentially constructed of a housing  1  with a pipe system having a feed  3  and a return  4  for directing a fluid medium  2  (arrows), from which weakly magnetizable particles are to be separated. Other means (not shown) are used for this purpose, such as, for example, conventional valve control blocks that control the corresponding feed  3  and return  4  of the medium  2  in alternating circulation directions. 
     A magnetic circuit  5  is disposed inside the housing  1 . The magnetic circuit  5  is composed of two spaced flux conducting sections  5   b ,  5   b  forming at least two pole gaps  16 ,  17  therebetween. A filter  8 , through which the medium  2  flows, is disposed in a filter chamber  7  formed between pole faces  6  of the magnetic circuit  5 . A permanent magnet  9  is arranged in the magnetic circuit, which produces in a switched-on state, shown in  FIG. 1 , between the pole faces  6  a magnetic field that extends through the filter  8 . 
     The entire section of the magnetic circuit  5  is always separated from the fluid medium  2  and therefore sealed, whereby the pipe system with the feed  3  and return  4  is surrounded by the magnetic circuit  5  in a compact manner. 
       FIGS. 1 and 2  shows the alternative embodiment of the invention with a permanent magnet  9  formed as a rotor  10 . The rotor  10  is provided with individual permanent magnets  12 , as shown in  FIG. 4 .  FIG. 5  shows schematically a drive  13  for the rotor  10 , with the drive  13  being used to switch the magnetic field off ( FIG. 2 ) and on ( FIG. 1 ). Advantageously, the rotor  10  is provided with an axle  14  which is slidably and rotatably received in bearings  15  ( FIG. 6 ). 
       FIG. 3  shows schematically the alternative embodiment of the invention with the permanent magnet  9  implemented as linearly displaceable, for example slidably supported, element  11  which switches the magnetic field on and off with the help of a drive (not shown). This high-gradient magnetic filter is constructed similarly to the filter depicted in  FIGS. 1 and 2 . 
     Advantageous embodiments of this basic construction are feasible which can be implemented depending on their intended application and desired efficiency, and which can be described as follows: 
     Depending on the characteristic properties of the weakly magnetizable particles to be separated from the fluid medium  2 , the rotation angle of the rotor  10  can be adjusted so that the effective field strength between the pole faces  6  can be selected between a minimum and a maximum field strength value. In this way, the field strength to which the different materials of the particles are subjected can be adjusted so as to affect the separation effect. Advantageously, the rotor  10  can also be rotated and locked in steps of 90° or in steps having other angles. 
     To increase the throughput and efficiency of the high-gradient magnetic filters according to the invention and to reduce their complexity, the embodiment depicted in  FIG. 7  is proposed whereby the magnetic circuit  5  is implemented using two filters  8  and whereby a magnetic field produced by a permanent magnet  9  can in a switched-on state be applied simultaneously to each of the two filters  8  or switched off.  FIG. 7  shows the permanent magnet  9  in form of a rotor  10 , whereby the throughput and efficiency can also be increased by the linearly displaceable element  11  implemented as a permanent magnet  9 , if the element  11  is compatible in a likewise configured and/or arranged magnetic circuit  5  and applies a magnetic field to at least two filters  8 . 
     The method of the invention for operating all the feasible alternative embodiments provides that separating the weakly magnetizable particles from the fluid medium  2  proceeds alternatingly in the pipe system according to the following steps:
     a) In the first step sequence, the fluid medium to be separated is applied to at least one filter  8  via the pipe system. The pipe system can be alternatingly applied to a feed  3  and a return  4 , wherein in this first step sequence, for example,  FIG. 1  depicts the feed  3  and return  4  of the fluid medium  2  to be cleaned, with the magnetic field in the magnetic circuit  5  between the pole faces  6  being switched on. The magnetic field penetrates the filter  8  through which the medium  2  flows via the pipe system. The filter  8  consists, for example, of a magnetizable wire mesh. Due to the high field gradients at the filter  8 , the magnetic particles settle down on the wire mesh. The field strength can be set to different values according to the rotation (rotor  10 ) or displacement (linearly displaceable element  11 ) of the permanent magnet  9 .   b) In the following step sequence, the magnetic field of the permanent magnet  9  (rotor  10 /linearly displaceable element  11 ) is switched off. The medium (or a medium)  2  with a feed  3  in the opposite direction and return  4  (e.g. corresponding to  FIG. 2 ) removes the separated particles that settled down on the wire mesh of the filter  8  by flushing. Flushing can be carried out in several alternative ways, in that, e.g.,
       a medium  2  to be cleaned or from which particles are to be removed is used as a flushing medium, or   a separate medium  2  is used as a flushing medium   by suitably directing the medium  2  in the pipe system through valve controls disposed in the feed  3  and return  4 .   
       c) Repeating the aforedescribed sequential steps continuously with circulation in opposite directions, whereby the filter  8  can be removed from the filter chamber  7  or exchanged depending on its condition or use, for example to replace the filter  8 .   

     Both alternatives can be implemented in a counter-flow in a co-flow configuration. 
     By using a program the cycles of the forward and backward moving medium  2  and/or the flushing medium in the alternating circulation can be controlled for all alternative embodiments of the device and method in conjunction with the magnetic field, which is to be switched on and off, and the magnetic field strength to be set. 
     INDUSTRIAL APPLICABILITY 
     The industrial applicability of the concept for the device and method is distinguished in that
         on one hand, a compact unit requiring little maintenance and few repairs can be provided that has interchangeable assemblies for easy maintenance, and   on the other hand, the process and operation of the separation of the particles from fluid medium can be performed easily and cost-effectively, whereby   finally the aforedescribed disadvantages of the state of the art are successfully overcome so that many different and significant industrial applications become possible.