Patent Publication Number: US-11027288-B2

Title: Device and method for magnetic separation

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to an apparatus for removing magnetizable particles in a substance by means of magnetic separation. The invention further relates to a device for pre-magnetizing magnetizable particles. Furthermore, the invention relates to a method of removing magnetizable particles from a substance by means of magnetic separation. 
     Description of the Related Art 
     The application of substances such as paint, primer, degreasing and rinsing fluids to surfaces is a common manufacturing step across a diverse range of industries, such as automobile manufacturing. Some techniques for applying substances to surfaces include spray painting, spray coating, airbrushing and dip coating. In implementing these techniques, it is desirable to have compositions which are substantially free from impurities. 
     However, such compositions become contaminated due to, for example, the actual manufacturing process i.e. welding, shaving, drilling, deburring etc. or from displacement along conveying equipment such as pipes or tubes which may release particles as a result of friction with the substance or by contact with the painted object. Such particles which are inherent to the manufacturing process, will have a negative impact on the quality and finish of the application, and can lead to issues such as rust formation (in the case of iron particles), and gaps in a coloring or functional coating/finish due to the interfering particles. 
     Therefore, such substances are commonly treated prior to or during application in order to remove undesirable particles. 
     Magnetic separation is one technique which is employed in the removal of metallic particles, and which involves the application of a magnetic field within a substance resulting in magnetization, the metallic particles are drawn from the substance and onto a particle collecting element. 
     However, this technique has proven less effective in the removal of particles of a smaller size and of particles of a paramagnetic material, which are more resistant to magnetization. This is the case, for example, with (sub)micron-sized particles or for mixed steel/aluminum production. Recent advances in technology have led to development of increasingly thinner coatings applied to compositions. This requires more efficient filtration methods of the substances especially in the lower micron-size range of impurities. Smaller particles are less susceptible to the regular magnetic fields in separators, such that these smaller particles remain in the substance flow and may cause damage and/or failure in the long run. 
     Therefore, there is a need for separation techniques which can achieve particle removal at a higher resolution or degree, and which provides removal that is effective throughout a broader range of particle sizes and materials. 
     It would therefore be desirable to provide an improved apparatus for separating particles from a substance that alleviated some or all of the above problems. Therefore, it is an object of the invention to provide an improved device and method by which to effectively remove metallic impurities or contaminants from a substance, and in particular particles of a relatively small size. 
     BRIEF SUMMARY OF THE INVENTION 
     This is achieved by providing an apparatus for removing magnetizable particles in a substance, the apparatus comprising: 
     a magnetic separation chamber for filtering magnetizable particles and flocs from the substance, wherein the magnetic separation chamber comprises a first housing that defines a first space through which the substance can flow, as well as at least one first magnet of which a first magnetic field reaches into the first space, and which first magnet is located within a first holder that has an interface with the first space; and 
     a flocculation chamber for inducing flocculation of the particles in a substance, the flocculation chamber being in fluid connection with the magnetic separation chamber; 
     wherein the magnetic separation chamber is located downstream of the flocculation chamber, and wherein the flocculation of the magnetizable particles results in magnetizable flocs, and the magnetic field of the first magnet causes the magnetizable flocs to be attracted towards the first magnet, thereby removing the flocs of magnetizable particles from the substance. 
     By forcing the magnetizable particles to form flocs, the magnetizable parts, i.e. particles and/or flocs, to be removed by the magnetic separator will be larger than the original magnetizable particles. In particular for (sub)micron-sized particles or paramagnetic particles, the magnetic separator can have problems removing these particles without any pre-treatment to increase the removal efficiency. By floccing these small particles together, the magnetic field of the magnet in the magnetic separator, i.e. the first magnet, is large enough to get hold of the flocs and to separate the flocs from the substance. Floccing may be achieved by the addition of inorganic electrolytes or polymers, or by magnetic flocculation. 
     In an embodiment, the flocculation chamber comprises a second housing that defines a second space through which the substance can flow, as well as at least one second magnet of which a second magnetic field reaches into the second space, and which second magnet is located within a second holder that has an interface with the second space, and wherein the magnetic field of the second magnet causes the magnetizable parts to be attracted to each other, thereby undergoing flocculation and forming flocs. 
     A preferred way to form flocs of the magnetizable particles is by means of a second magnetic field induced by a second magnet in the flocculation chamber. The second magnetic field is large enough to magnetize the particles enough to floc together and form flocs, i.e. larger magnetizable parts. Preferably, the flocculation chamber is arranged immediately adjacent to the magnetic separation chamber. This may be achieved when the flocculation chamber and the magnetic separation chamber are integrally formed, this can be by using flanges, welds, glue or any other sort of connections. They can be separate parts or a monolithic integral element. 
     In that case the flocs formed in the flocculation chamber travel only a short distance. The rate of flocculation is determined by the interplay between the dipolar magnetism induced by the magnetic field that flocs the particles, and the hydrodynamics of the substance flow that tend to disintegrate the flocs. 
     When the applied magnetic field is large enough, the attractive magnetic energy will be greater than the sum of the repulsive energy and the particle will tend to form aggregates, i.e. flocs. Another condition to be satisfied is that the time needed to floc is smaller than the residence time of the particles in the second magnetic field. The second magnetic field should not be too large in combination with a too low substance flow, as the flocculation chamber may then act as magnetic separator. 
     The adhesion strength of the aggregates or flocs must be adequately large to prevent them from breaking up by the fluid shear stress induced by the hydrodynamics of the substance flow. To efficiently counteract this disintegration, the flocculation magnetic field, i.e. the second magnetic field, in the flocculation chamber has to be designed in such a way that the flocculating magnetic field is kept at a minimum distance from the main magnetic field, i.e. the separating or first magnetic field. 
     Furthermore, in a turbulent flow the flocs will undergo more disintegration forces than in a laminar flow. Maintaining a laminar flow between the flocculation field and the main separation field is another condition to be satisfied. 
     In order to have the first and/or second magnetic fields extend into the first and/or second space, the first and/or second holders may extend into the first and/or second spaces, respectively. Preferably, each first and/or second holder comprises a tube that is closed at an end that extends into the first and/or second space, respectively. 
     In that case, the first and/or second magnets may have a rod shape, that have a releasable fit into the first and/or second holder. As the magnets extend into the space, the respective magnetic fields also extend into the space of the chambers, being the flocculation and/or magnetic separation chamber. 
     The first and/or second holder may have a top side from which each tube extends into the first and/or second space, respectively. The magnetizable particles or flocs may accumulate now on the outside of the first and/or second holders, as a result of which the magnets themselves are not exposed to the substance and/or the magnetizable particles. 
     Preferably, the first and/or second magnets are connected to a moving mechanism to move the first and/or second magnet with respect to the first and/or second space, respectively. The moving mechanism can remove the first and/or second magnet from the holder. As a result of removing the magnet from the holder, the magnetic field in the space is removed or at least decreased in strength so that the holder can be cleaned in a simple manner. 
     The housing of the magnetic separation chamber may further comprise a removable attachment, wherein the magnetic elements of the magnetic separation chamber are connected to the attachment. The housing further comprises one or more holders for respectively holding the one or more magnetic elements. 
     When the magnets are raised out of their holder, the magnetic field decreases considerably in the liquid in the magnetic space, as a result of which the particles accumulated on the outside of the holders can easily be removed. In order to ensure that the material does not enter the cleaned liquid again, a bottom wall of at least one of the chambers may be provided with a discharge for removing magnetizable parts which have accumulated on the outside of each tube. 
     According to an embodiment, the housing of the flocculation chamber is provided with an inlet part that is connectable to a conduit system through which the substance flows, and wherein the housing of the magnetic separation chamber is provided with an outlet part that is connectable to the conduit system. Preferably, the inlet part widens out to the flocculation chamber to decrease a flow rate of the substance flowing into the flocculation chamber. 
     For the particles to form aggregates or flocs in the flocculation field the magnetic field of the second magnet has to be sufficiently large and the time the particles spend in the flocculation field should be longer than the time it takes to form aggregates from the particles. The residence time of the particles in the flocculation field is increased by an enlarged diameter of the inlet with respect to that of the conduit system. This reduces the flowrate of the substance and therefore increases the residence time of the particles in the flocculation field. Preferably, the second magnetic field is low enough to prevent the particles to accumulate on the second holder, but high enough that the particles are magnetized and thereby attracted to each other to form aggregates. 
     After the magnetic separation chamber, the substance may flow into the conduit system again. Therefore, the outlet part may taper away from the magnetic separation chamber. The outlet part then again reduces the diameter of the piping to be compatible with the conduit system. 
     The first space of the magnetic separation chamber may define a spatial volume which is greater than the spatial volume defined by the second space of the flocculation chamber. The larger the spatial volume of a chamber, the more the flow rate is reduced and the longer the residence time in the chamber. As such, the residence time in the magnetic separation chamber may be longer than that in the flocculation chamber. This is to increase the separation efficiency of the magnetic separation chamber by allowing more time for accumulation of the parts on the first holder. 
     A longitudinal direction of the one or more first and/or second holders may be substantially perpendicular to a downstream direction from the flocculation chamber towards the magnetic separation chamber. Additionally or alternatively, a direction of the first and/or second magnetic fields may be substantially perpendicular to the downstream direction. 
     Alternatively, the longitudinal direction of the one or more first and/or second holders may be substantially parallel to a downstream direction from the flocculation chamber towards the magnetic separation chamber. Additionally or alternatively, a direction of the first and/or second magnetic fields may be substantially parallel to the downstream direction. 
     Alternatively, the longitudinal directions of the one or more first and/or second holders may differ, such that the holders are arranged in a combination of substantially perpendicular and substantially parallel longitudinal directions with respect to the downstream direction from the flocculation chamber towards the magnetic separation chamber. Additionally or alternatively, a direction of the first and/or second magnetic fields may comprise a combination of substantially perpendicular and substantially parallel directions with respect to the downstream direction. 
     As used herein, longitudinal direction refers to that direction along which a length of the respective element is greatest, that is, the direction along the long axis of a body. 
     To counteract the disintegration of the aggregates formed in the flocculation field the distance of this field to the main separation field is kept at a minimum and the flow pattern is kept within a regime of unseparated flow. The flocculation field is mounted as close as possible to the magnetic separation chamber with the main separation field. With an average incoming flow velocity of between 1-4 m/s, preferably about 2 m/s, the time between leaving the flocculating magnetic field and reaching the main separating magnetic field is between 0.1 and 1 second, preferably between 0.1-0.4 second. The magnitude of the magnetic field provided by each of the one or more first magnets of the magnetic separation chamber may be between 0.03 and 1 Tesla. 
     A cross section of the second holder of the second magnet has a greater dimension in the downstream direction with respect to a dimension in a direction transverse to the downstream direction. In order to keep a laminar flow between the flocculation field and the main separation field the outer tubes of the flocculation unit have a major dimension in the downstream direction. Preferably, the second holder of the second magnet has an oval cross section, wherein a major axis of the oval cross section is directed in the downstream direction. Computational Fluid Simulations on this design have proven that the use of oval shaped tubes significantly contribute to maintaining a laminar flow at Reynolds numbers smaller than 5. 
     The cross section of the first magnets may be circular. However, the cross section of the first and/or second magnets may be any kind of shape suitable for magnetic separation or flocculation. The cross section of the first and/or second holders may be similar to that of the respective magnets. Alternatively, the first and/or second holders have distinct cross section from that of the respective magnets. 
     The flocculation chamber may be configured to induce flocculation of particles in the smaller range of particles present in the substance, preferably having a size equal or smaller than 15 micrometer, more preferably of particles having a size in the order of 3 to 10 micrometers. 
     In magnetic separation of alkaline degreasing fluids, the process of magnetic flocculation plays a positive role by increasing the efficient recovery of ferritic particles from 3 to 15 micron. The effect for paramagnetic particles will be relatively lower albeit still enhances capturing these particles in the matrix of ferromagnetic particles. The process of magnetic flocculation may also play a positive role in the recovery of ferromagnetic of other sizes, as well as recovery of paramagnetic particles. 
     The invention further relates to a device for pre-magnetizing magnetizable particles, the device comprising a flocculation chamber for inducing flocculation of the particles in a substance, the flocculation chamber being fluidly connectable to a magnetic separation chamber located downstream from the flocculation chamber, wherein the flocculation chamber comprises a housing that defines a space through which the substance can flow, as well as at least one magnet of which a magnetic field reaches into the space, and which magnet is located within a holder that has an interface with the space; 
     wherein the magnetic field of the magnet causes the magnetizable particles to be attracted to each other, thereby undergoing flocculation and forming flocs. 
     By having the process medium flow through the flocculation field first, the medium and the pollution in the medium will be distributed more evenly through the magnetic separation chamber. Because of this better medium distribution the flow velocity in the magnetic separation chamber will be reduced, which leads to more efficient separation. 
     The device may further comprise an inlet part that is connectable to a conduit system through which the substance flows; and one or more flanges for connection to the magnetization chamber. Preferably, the inlet part widens out into the flocculation chamber to decrease a flow rate of the substance flowing into the flocculation chamber. The residence time of the particles in the flocculation field is increased by an enlarged diameter of the inlet with respect to that of the conduit system. This reduces the flowrate of the substance and therefore increases the residence time of the particles in the flocculation field. 
     The device may be an (integral) part of a magnetic particle separation system or the device is configured for retrofitting into a magnetic separation system, an existing magnetic separation system or any other system, method, or technology for separation, for instance by combination with a pre-installed magnetic separator chamber. 
     The invention furthermore relates to a method of removing magnetizable particles from a substance, the method comprising the steps of:
         inducing flocculation of the magnetizable particles in the substance to produce flocs in a flocculation chamber;   providing a first magnetic field in order to magnetize the flocs;   conveying the substance through a magnetic separation chamber to remove the magnetized flocs from the substance.       

     The method may further comprise the step of inducing flocculation providing a second magnetic field applied in the flocculation chamber. Forming the flocs is thus done by means of magnetic flocculation. 
     Preferably, the method comprises the step of reducing a flow rate of the substance prior to and/or during the step of forming flocs. By reducing the flow rate of the substance, the time for forming flocs, i.e. the residence time in the flocculation chamber, is increased and the flocculation efficiency is increased. 
     After the flocculation and the separation step, the method may further comprise cleaning the magnetic separation chamber and/or the flocculation chamber. During the process, some of the magnetizable particles may adhere in the respective chamber. This may impair the flocculation and/or separation process. Cleaning the respective chamber will enhance the efficiency of the further separation process. Preferably, cleaning any of the chambers comprises removing the respective magnets from the chamber. By removing the magnetic field from the respective chamber, the magnetizable particles remaining there will not be under the influence of the magnetic field anymore. Thus, the cleaning process of the respective chamber is facilitated. Further, cleaning of any of the chambers comprises using the substance flow or injecting a pressurized fluidum into any of the chambers. 
     Preferably, the method is used for an apparatus as described above for removing magnetizable particles in the substance. 
     In an embodiment, a method is provided for removing magnetizable particles from a substance, the method comprising the steps of
         inducing flocculation of the magnetizable particles in the substance to produce flocs;   providing a first magnetic field in order to magnetize the flocs and single particles;   conveying the substance through a magnetic separation chamber to remove the magnetized flocs and single particles from the substance. The term single particles as used herein refers to those particles which have not been formed or joined into a floc.       

     In an embodiment, the step of inducing flocculation comprises providing a second magnetic field applied in the flocculation chamber. 
     In an embodiment, the method further comprises the step of reducing the flow velocity of the substance prior to and/or during the step of forming flocs and during the step of separation in the magnetic separation chamber. 
     In an embodiment, the method further comprises the step of cleaning the magnetic separation chamber and/or the flocculation chamber. 
     In an embodiment, the step of cleaning any of the chambers comprises removing the respective magnets from the chamber. 
     In an embodiment, the step of cleaning of any of the chambers comprises using the substance flow or injecting a pressurized fluidum into the any of the chambers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a top view of an apparatus for magnetic separation according to the invention. 
         FIG. 2  shows a cross section along line A-A of the apparatus of  FIG. 1 . 
         FIG. 3  shows a perspective view of a device for pre-magnetizing magnetizable particles according to the invention. 
         FIG. 4  shows a top view of a magnetic separation system comprising the apparatus of  FIG. 1  including the bypass system. 
         FIGS. 5 a -5 f    show a schematic view of a magnetic separation process and a cleaning process. 
         FIG. 5 a    shows a schematic view of a magnetic separation system according to the invention during active filtration prior to a cleaning process. 
         FIG. 5 b    shows a schematic view of the magnetic separation system according to the invention during a first step of the cleaning process. 
         FIG. 5 c    shows a schematic view of the magnetic separation system according to the invention during a second step of the cleaning process. 
         FIG. 5 d    shows a schematic view of the magnetic separation system according to the invention during a spray cleaning step of the cleaning process. 
         FIGS. 6 a -6 b    shows a schematic view of a magnetic separation system according to the invention, wherein the holders, magnets, and magnetic fields are arranged substantially parallel to the flow direction, and  FIG. 6 c    shows a top view. 
         FIGS. 7 a -7 c    shows a further schematic view of a magnetic separation system according to the invention, wherein the holders, magnets, and magnetic fields are arranged substantially perpendicular to the flow direction, in which a draining outlet is visible. 
     
    
    
     DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
       FIG. 1  shows a perspective view of an apparatus  100  for removing magnetizable particles in a substance, being a part of a magnetic separation system.  FIG. 2  shows a cross section along line A-A of the apparatus of  FIG. 1 . The term ‘substance’ as used herein refers to any one of a liquid, gas, fluid, suspension, dry substance, or a mixture thereof. An exemplary embodiment is described with respect to a fluid substance, such as a liquid or gas, but it will be within the scope that a dry substance can be processed with the apparatus. 
     The apparatus  100  is a magnetic separator or filtration system comprising a magnetic separation or filter chamber  110  for filtering magnetizable particles and flocs from the substance, and a flocculation chamber  130 , possibly comprised in a pre-magnetizing device  150 , for inducing flocculation of the particles in the substance. 
     The magnetic separation chamber  110  comprises a first housing  112  that defines a first space  114  through which the substance can flow. The magnetic separation chamber further comprises a plurality of first magnets  116  of which a first magnetic field reaches into the first space  114 . The first magnets  116  are each located within first holders  118  that have an interface  120  with the first space  114 . 
     The flocculation chamber  130  comprises a second housing  134  that defines a second space  136  through which the substance can flow. In addition, the flocculation chamber  130  comprises a plurality of second magnets  138  of which second magnetic fields reach into the second space  136 . The second magnets  138  are each located within second holders  140  that each have an interface  142  with the second space  136 . The magnetic fields of the second magnets  138  causes the magnetizable parts in the substance to be attracted to each other, thereby undergoing flocculation and forming flocs. 
     The flocculation chamber  130  is in fluid connection with the magnetic separation chamber  110  through connection flanges  122  and  132 , respectively, placing the magnetic separation chamber  110  and the flocculation chamber  130  adjacent to each other. 
     The magnetic separation chamber  110  is located downstream of and adjacent to the flocculation chamber  130 . The flocculation of the magnetizable particles by means of pre-magnetization, results in magnetizable flocs. The magnetic field of the first magnets  116  causes the magnetizable flocs to be attracted towards the first magnets  116  thereby removing the flocs of magnetizable parts from the substance. The first space of the magnetic separation chamber defines a spatial volume which is greater than the spatial volume defined by the second space of the flocculation chamber, and which second space spatial volume is greater than the spatial volume of the conduit system. The spatial volume of a chamber defines the residence time of the substance in the chamber. 
     The second housing  134  of the flocculation chamber  130  is provided with an inlet part  144  that is connectable to a conduit system  106 , see  FIG. 4 , through which the substance flows. The first housing  112  of the magnetic separation chamber  110  is provided with an outlet part  124  that is connectable to the conduit system  106 . 
     The inlet part  144  widens out to the flocculation chamber  130  to decrease a flow rate of the substance flowing into the flocculation chamber. As such, a first part  146  of the inlet part  144  has a diameter similar to that of the conduit system  106 , and a second part  148  of the inlet part  144  tapers out to a larger diameter similar to the diameter of the flocculation chamber  130 . The outlet part  124  tapers away from the magnetic separation chamber  110  to a diameter similar to that of the conduit system  106 . In this embodiment the inlet part  144  and the outlet part  124  are arranged on different sides (such as opposite) of the magnetic separation chamber. 
     The first holders  118  of the magnetic separation chamber  110  extend into the first space  114 , such that a longitudinal direction of the first holders  118  is substantially perpendicular to a downstream direction Du directed from the flocculation chamber  130  towards the magnetic separation chamber  110 . Each first holder  118  comprises a tube that is closed at one end that is located in the first space  114 . The first magnets  116  have a rod-like shape. Each rod-like first magnet  116  extends into one first holder  118  with a releasable fit, i.e. an air gap between an internal wall of the first holder and the first magnet  116 . As the first magnets extend into the first space, a direction of the first magnetic fields is substantially perpendicular to the downstream direction Du. 
     The second holders  140  of the flocculation chamber  130  extend into the second space  136 , such that a longitudinal direction of the second holders  140  is substantially perpendicular to a downstream direction Du directed from the flocculation chamber  130  towards the magnetic separation chamber  110 . Each second holder  140  comprises a tube that is closed at one end that is located in the first space  136 . The tube may even extend from a first side of the flocculation chamber  130  to beyond a second opposite side of the flocculation chamber  130 , as shown in  FIG. 2 . The second magnets  138  have a rod-like shape. Each rod-like second magnet  138  extends into one second holder  140  with a releasable fit, i.e. an air gap between an internal wall of the second holder  140  and the second magnet  138 . A longitudinal direction of the second holders is substantially perpendicular to the downstream direction Du from the flocculation chamber towards the magnetic separation chamber. As the second magnets  138  extend into the second space  136 , a direction of the second magnetic fields is substantially perpendicular to the downstream direction Du. 
     The second magnets  138  have a cross section that has a greater dimension in the downstream direction Du with respect to a dimension in a direction transverse to the downstream direction, i.e. the major dimension is directed in the downstream direction.  FIG. 1  shows that the cross section of the second magnets  138  is rectangular with rounded transverse edges, looking like a flattened ellipse or circle. The major dimension of the rectangular cross section is directed in the downstream direction. The cross section of the second holder  140  is similar to that of the second magnet  138 , however with slightly larger dimensions to allow for an air gap between the second holder  140  and the second magnet  138 . 
     The first magnets  116  have a circular cross section. The cross section of the first holder is similar to that of the first magnets, however with a slightly larger diameter to allow for an air gap between the first holder  118  and the first magnet  116 . 
     The magnetic separation chamber  110  further comprises a cleaning system  126  to clean the inside of the first housing  112 . The cleaning system  126  may comprise, a sprinkling or spraying member to clean the outside of each tube by spraying a fluidum towards the first holders  118 . Said sprinkling or spraying member may comprise an annular pipe provided with a plurality of sprinkling or spraying nozzles which can be fed with a fluid, such as a liquid or gas. The nozzles can be situated in the first space  114  in various ways. According to  FIG. 1 , the nozzles are situated near the closed end of the tubes  118  in the first space  114 , near the bottom of the first housing  112 . 
       FIGS. 3 a -3 d    show several views of a device  150  for pre-magnetizing magnetizable particles according to the invention (perspective, front view, side view, and top view, respectively). The device  150  comprises the flocculation chamber  130  for inducing flocculation of the particles in the substance. The flocculation chamber comprises the housing  134  that defines the second space  136  through which the substance can flow, as well as a plurality of second magnets  138  that extend into the second space  136 , such that their magnetic fields reach into the second space  136 . The magnets are located within the second holders  140  that each have an interface  142  with the second space  136 . 
     The device  150  is connectable to the magnetic separation chamber  110  by means of connection flange  132 . Further connection flange  128  can be used to connect the inlet part  144  to the flocculation chamber  130 . The device  150  can be used for retrofitting an existing magnetic separation system or any other system, method, or technology for separation in need of a pre-magnetization treatment such as those involving hydro cyclone or multi cyclone technology. 
       FIG. 4  shows a top view of the magnetic separation system comprising the apparatus  100  of  FIG. 1 . The system further comprises a part of the conduit system  106  and a bypass system  108 . The bypass system  108  is used at least during a cleaning process of the apparatus  100 . The flow of substance through the apparatus  100  can be stopped by means of closure of a first valve  152  located before the inlet part, with respect to the flow direction of the substance. In addition, to avoid a backflow of the substance into the apparatus  100  while cleaning, a second valve  154  located downstream from the magnetic separation chamber  110  is closed as well, closing off the magnetic separation chamber  110 . A third valve  156  provided at the bypass system  108 , is opened to open the bypass system, such that the flow of substance bypasses the apparatus  100 .  FIG. 4  further shows a first movement mechanism  102  to move the first magnets  116  with respect to the first holders  118 , and a second movement mechanism  104  to move the second magnets  138  with respect to the second holders  140 . 
       FIG. 5 a    shows a schematic view of an active magnetic separation system according to the invention, while the substance flows through the apparatus  100  and the magnetizable particles are separated from the substance by the apparatus  100 . The first and second valves  152 ,  154  are open to allow the flow of the substance through the apparatus. The third valve  156  of the bypass system  108  is closed. The first magnets  116  are located in the first holders  118 , and extend into the first space  114  of the magnetic separation chamber  130 . The second magnets  138  are located in the second holders  140 , and extend into the second space  136  of the flocculation chamber  130 . 
       FIGS. 5 b -5 e    show the system at various stages of a cleaning process. In a first step  5   b  of the cleaning process the first and second valves  152 ,  154  are open and the third valve  156  is closed (thus fluid flows through the unit). Only the second magnets are raised so that any captured particles will be forced by the fluid flow into the magnetic separation chamber where they will be captured by the first magnetic field. 
       FIG. 5 c    shows a schematic view of a magnetic separation system according to the invention during a further step of the cleaning process. The first and second valves  152 ,  154  are in their closed position, stopping the flow of substance through the apparatus  100 . The third valve  156  is in its open position, allowing the substance to flow through the bypass system  108 . 
     Additionally, the second magnets  138  and the first magnets  116  have been removed from the second and first holders, respectively, by the first and second movement mechanism  102 ,  104 , respectively. The movement mechanisms  102 ,  104  can be hydraulically actuated, but other forms of actuation may be used as well. For the apparatus of  FIGS. 1-5 , the movement mechanisms  102 ,  104  raise the magnets with respect to the respective holders. This direction of movement with respect of the holders of course depends on the orientation of the holders and the apparatus and may be in any horizontal and/or vertical direction applicable. 
       FIG. 5 d    shows a schematic view of the magnetic separation system according to the invention during the cleaning process. The first and second magnets  116 ,  138  have been raised from the respective holders  118 ,  140 . When the magnets  116 ,  138  are raised out of their holder, the strengths of the magnetic fields in the first and second spaces decrease considerably, as a result of which the particles and/or flocs accumulated on the outside of the holders can easily be removed. In order to ensure that the particles or flocs do not enter the cleaned liquid again, the bottom wall of the first housing  112  is provided with a discharge  158  for removing the magnetizable parts which accumulated on the outside of each tube. 
     Despite the removal of the magnets, some particles may nevertheless remain behind on the holder wall. In order to be able to remove these particles reliably, the sprinkling or spraying member for cleaning the outside of each tube is situated near the bottom end of each tube. The spraying member is part of the cleaning system and sprays a fluid (liquid or gas) towards the tubes to remove any particles left on the holder wall. The sprayed-off particles are then removed from the magnetic separation chamber  110  through the discharge  158 . 
       FIG. 5 e    shows a schematic view of a magnetic separation system according to the invention during finishing of the cleaning process. The first and second magnets  116 ,  138  are lowered again by the respective movement mechanisms  102 ,  104  into their respective holders  118 ,  140 . While lowering the magnets, the first and second valves  152 ,  154  remain closed and the third valve  156  remains open. The discharge  158  is closed as well. Only when the magnets are fully lowered into their holders, will the first and second valves be opened and the third valve be closed again. Then the substance will flow through the apparatus  100  again and the magnetizable particles will undergo flocculation and separation, subsequently, according to  FIG. 5   a.    
       FIG. 5 f    shows a schematic view of a magnetic separation system according to the invention during active filtration, after the cleaning process is finished. 
       FIGS. 6 a -6 b    show a cross-section A-A and a top view, respectively, of an embodiment wherein the magnetic elements are arranged in substantially parallel orientation with respect to the general direction of the substance flow (downstream direction Du), while  FIG. 6 c    shows a top view of this embodiment connected to the conduit and bypass system. The flow in this embodiment enters the magnetic separation chamber via an inlet  144  and via the flocculation chamber  130 . The substance flows downward through the magnetic separation chamber and exits via the outlet  124 .  FIGS. 6 a -6 b    show the inlet part  144  and the outlet part  124  are both arranged on the same side of the magnetic separation chamber. Alternatively, the inlet part  144  and the outlet part  124  may be arranged on different (such as opposite) sides of the magnetic separation chamber. Moreover, it is noted herein that Du can alternatively flow in a different direction from the one depicted in the figure. For example, the elements can be arranged such that Du flows in a direction opposite as the depicted direction. In that case the function of the shown elements  124  and  144  would be respectively inverted, with the shown outlet  124  assuming an inlet function, and the shown inlet  144  assuming an outlet function. 
       FIGS. 7 a -7 b    show a cross-section A-A and a top view, respectively, of an embodiment of the magnetic separation system according to the invention wherein the magnets are arranged in perpendicular orientation to the general direction of the substance flow.  FIG. 7 c    shows a view of the magnetic separation system with a bypass element  108 . A draining outlet  158  is shown in  FIG. 7 a   , which functions to drain residue during the cleaning process. 
     While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims. 
     LIST OF PARTS 
     
         
           100 . Apparatus/system 
           102 . First moving mechanism 
           104 . Second moving mechanism 
           106 . Conduit system 
           108 . Bypass system 
           110 . Magnetic separation chamber 
           112 . First housing 
           114 . First space 
           116 . First magnet 
           118 . First holder 
           120 . First interface 
           122 . Connection flange 
           124 . Outlet part 
           126 . Cleaning system 
           128 . Further connection flange 
           130 . Flocculation chamber 
           132 . Connection flange 
           134 . Second housing 
           136 . Second space 
           138 . Second magnet 
           140 . Second holder 
           142 . Second interface 
           144 . Inlet part 
           146 . First part of inlet 
           148 . Second part of inlet 
           150 . Pre-magnetizing device 
           152 . First valve 
           154 . Second valve 
           156 . Third valve 
           158 . Draining outlet