Abstract:
An apparatus for removing magnetic particles from a mud slurry is disclosed, and includes one or more endless belts or chains enclosed almost wholly within a pipe. A motor drives the chain around the pipe. When the pipe is located within a mud slurry, magnetic particles in the mud slurry are drawn to the pipe and carried along the outside and away from the slurry until a collar is reached. Once se-separated the particles can be collected for disposal. The chain comprises a series of units linked together. Each unit includes a magnet with pole pieces at either pole to direct magnetic flux. Wear discs prevent the magnets and pole pieces from abrasion as they are drawn through the pipe. Units can be included in the chain which units do not include a magnet, thereby providing a break in the field, allowing particles to fall away from the collar region.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 11/990,870, filed Mar. 20, 2009, entitled “REMOVAL OF MAGNETIC PARTICLES FROM A FLUID”, which is a National Stage Application of International Application No. PCT/GB2006/003148 filed Aug. 22, 2006, which claims the benefit of United Kingdom Patent Application No. 0517252.3, filed Aug. 24, 2005 and United Kingdom Patent Application No. 0614493.5, filed Jul. 21, 2006, all of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. The Field of the Invention 
         [0003]    The present invention relates to apparatus for removing magnetic particles from a fluid. The apparatus finds particular application in the oil and gas industry in relation to separating iron-containing swarf from free-flowing or viscous liquid mud. 
         [0004]    2. The Relevant Technology 
         [0005]    Oil and gas wells usually have their bore holes lined with steel pipes, referred to normally as casing. In mature wells, when oil or gas production drops below economic production levels, it is often useful to utilise at least part of said bore hole. In order to be able to do this one alternative is to remove the casing completely. However, it is more cost effective to simply drill the pipeline out, or at least to drill a window in the pipeline. The window can then be used to allow a drilling assembly to exit the bore hole and reach a new part of the reservoir. 
         [0006]    Such a method obviously produces large quantities of steel swarf derived primarily from the pipeline. The swarf is mixed during the drilling process with large quantities of mud either from the bore hole or from its introduction as a lubricant. Typically the mud/swarf mixture will comprise a sufficient quantity of water to enable the mixture to flow. Due to the high steel content of the mud when it exits the bore hole and its potential hazard, in part due to the sharpness of the metal slithers it contains, disposal or re-use of the mud can be problematic. One method of decontamination is simply to remove excess water from the mixture and then separate the larger swarf pieces by hand. This is obviously a time consuming and potentially dangerous mode of separation. 
         [0007]    It is an object of the present invention to provide an improved apparatus to separate the solid magnetic or magnatisable particles from a fluid system and in particular, apparatus which can be applied in the oil and gas industry. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    According to a first aspect of the invention there is provided an apparatus for removing magnetic particles from a liquid or slurry; the apparatus comprising; 
         [0009]    (a) an endless belt or chain, including along its length, a plurality of magnetic field generation units to attract magnetic particles; 
         [0010]    (b) an enclosing means preventing contact of magnetic particles with the magnetic field generators; 
         [0011]    (c) drive means to circulate the endless belt within the enclosing means; 
         [0012]    (d) collection means to collect the particles. 
         [0013]    The apparatus provides a simple and efficient method to separate the magnetic particles from the slurry allowing the magnetic particles to be disposed of more easily or to be reused. 
         [0014]    Preferably, one or more magnetic field generation units comprises one or more permanent magnets, which do not therefore require an electricity supply to function. The units further preferably comprise one or more pole pieces to direct the magnetic field of the magnets. Optionally the units include one or more wear discs to reduce wear on the magnets or pole pieces. Advantageously, the or each magnet includes a hole along its axis to enable linkage means to be attached to the unit. 
         [0015]    Preferably the endless belt or chain consists of a plurality of units linked together. Particularly preferably the chain includes one or more units not including a magnet. The gap in the magnetic field resulting in the lack of magnet allows swarf to be more easily removed from the apparatus. 
         [0016]    The apparatus preferably includes one or more enclosing means arranged in an array each enclosing means associated with an endless belt. By combining a plurality of enclosing means a larger flow of mud can be subjected to swarf removal. 
         [0017]    The relative positions of enclosing means can optionally be adjusted, thereby allowing channels of different shapes to be used to allow mud flow. Advantageously, the or each enclosing means is mounted to mounting means. Further advantageously, the enclosing means is formed of steel. 
         [0018]    According to a second aspect of the invention there is provided a device for removing magnetic particles from a liquid or slurry, the device comprising; 
         [0019]    (a) an elongate magnetic field generator; 
         [0020]    (b) a casing separating the generator from a liquid or slurry; 
         [0021]    (c) the magnetic field passing through the casing causing magnetic particles to be attracted to the device and be retained on the casing; 
         [0022]    (d) means for removing the attracted particles from the field generated by the generator, enabling the particles to be removed from the device. 
         [0023]    Preferably, the device comprises a helical cleaning means, rotatable about the axis of the magnetic field generator, the inner surface of the cleaning means engaging the casing and rotation of the cleaning means moving the attracted particles from the field generated by the generator. 
         [0024]    Alternatively, the device preferably includes a cleaning barrier, engaging the casing around the generator, the barrier being moveable between a first and second position, the motion pushing the particles out of the field generated by the generator. The particulars can thereby easily be removed from the device. 
         [0025]    Advantageously, the magnetic generator comprises a stack of magnets alternating polarity along the length of the generator. 
         [0026]    Optionally, the magnetic poles are orientated along the length of the axis of the field generator. The magnetic field generated levels to push away from the device which is of assistance when moving particles. Alternatively, the poles are orientated perpendicularly to the axis of the field generator. The magnetic field assists motion of the particles along the axis of the device. 
         [0027]    According to a third aspect of the invention there is provided an array for removing magnetic particles from a liquid or slurry, the device comprising; 
         [0028]    (a) one or more magnets, said the or each magnet being housed within a casing; 
         [0029]    (b) the housing being attached to a framework, which framework being locatable on a fluid-carrying channel, and such that the or each casing is at least partially immersed in the fluid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0030]    The invention will now be described with respect to the accompanying drawings which show by way of example only, embodiments of swarf removing apparatus. In the drawings; 
           [0031]      FIG. 1   a  is a side view of a first embodiment of swarf removing apparatus; 
           [0032]      FIG. 1   b  is an end view of the first apparatus shown in  FIG. 1   a;    
           [0033]      FIG. 2  is an illustrative side view of the embodiment of  FIGS. 1   a  and  1   b;    
           [0034]      FIGS. 3   a,    3   b  are side views illustrative of a first configuration of the embodiment of  FIG. 1 ; 
           [0035]      FIGS. 4   a,    4   b  are side views illustrative of a second configuration of the embodiment of  FIG. 1 ; 
           [0036]      FIGS. 5   a  to  5   e  are diagrams of magnetic elements and means of joining the elements together; 
           [0037]      FIGS. 6   a,    6   b  are detailed side and end views of drive means for use in the apparatus; 
           [0038]      FIG. 7  shows two configurations of the second embodiment of swarf removing apparatus; 
           [0039]      FIGS. 8   a  to  8   d  show in use configurations of the apparatus of  FIG. 7 ; 
           [0040]      FIG. 9  shows a further example of the second embodiment of swarf removing apparatus;  FIG. 10  shows an array of swarf removing apparatus according to the second embodiment; 
           [0041]      FIGS. 11A ,  11 B show two orientations for magnets within the second embodiment; and 
           [0042]      FIG. 12  shows further apparatus for use in the embodiment of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0043]    Referring initially to  FIGS. 1 and 2 , these show an overview of an apparatus combining two embodiments of the invention for use as a swarf remover, removing swarf from a mud slurry. In  FIG. 1 , swarf is to be removed from mud flowing from right to left across the figure. The apparatus shown comprises two distinct sections which act together to remove the maximum percentage of swarf. 
         [0044]    In the first section, the mud is passed around a series of steel pipes  11  of an apparatus  10  through which pipes  11  an endless chain of magnets, moving in the opposite direction to the flow of the mud, is circulated. In the second section, the mud passes a series of static magnets  13  the magnets  13  remove any swarf not caught in the first section. 
         [0045]      FIG. 2  is a schematic representation of the apparatus  10 , showing a series of magnets  21 , linked together into an endless chain drawn through a steel pipe  22   a . Motive force for the movement of the magnets  21  is provided by the rotating driver  23 . Swarf attracted towards the magnets  21  is held against the outside of the steel pipe  22   a  and drawn with the magnets  21  along the pipe  22   a.  Eventually, the swarf is prevented from moving further along the pipe  22   a  by a collar  24  located across the pipe  22   a.  As the magnets  21  continue through the pipe therefore, the magnetic force holding the swarf against the pipe  22   a  is removed and the swarf drops into a collection chute  25 . 
         [0046]    The apparatus  10  is shown in more detail in  FIG. 1  and comprises a series of magnets  21  linked together to form a chain  12 . The chain  12  is drawn through the pipe  22   a  by a drive means  26  mounted to a support frame  27 . Motive force to the drive means  26  is provided by a motor  28 , driving a shaft  29 —mounted on bearings  30 —onto which a drive gear  31  is mounted. The drive gear  31  comprises a series of paddles or projections  32  to engage the chain  12  of magnets conveying the chain  12  through the pipe  22   a.    
         [0047]    In  FIG. 1   b,  an apparatus is shown having four magnetic chains and pipes  22   a - d  mounted alongside each other to enable the width of the channel  33  carrying the mud to be subjected to the magnetic fields generated. The whole volume of the mud is therefore subject to magnetic fields to remove the metal swarf. As can be seen from  FIG. 1   b , the drive gears associated with the chains are mounted about a common shaft. Moreover, the swarf collected from each pipe is collected into the common chute  25 . 
         [0048]    The above arrangement allows the apparatus to be used in mud channels of differing cross-sectional shape. This is illustrated in  FIGS. 3 and 4 . In  FIGS. 3   a,    3   b  the channel is of rectangular cross-section and the steel pipes  34   a  to  d  are lined up with one another much that the lowest point of each pipe  34   a  to  d  is at substantially the same distance from the channel  33  as its neighbour. In  FIGS. 4   a,    4   b  the channel  43  is deeper on one side. By tilting the drive means associated with certain of the pipes  44   a  to  d , the pipes can be lowered further into the channel so that swarf does not slip underneath the pipe. The side view of the pipes in  FIG. 4   a  shows the non-overlapping configuration of the pipes. 
         [0049]    It will be obvious to the skilled man, that through this means, channels of different cross-sectional shape to the above exemplified can be dealt with by the apparatus. 
         [0050]    Turning to the magnetic chain, this is shown in more detail in  FIGS. 5   a  to  d . The basic unit for the chain is shown in  FIGS. 5   a  to  c  and comprises a magnet with means for linking this to neighbouring magnets. 
         [0051]    The basic magnetic unit comprises a substantially cylindrical magnetic element or magnet  50  formed of a transition metal magnet having a cylindrical hole along its axis. Pole pieces  51   a,    51   b  are affixed to the end of the magnet  50 . The pole pieces  51   a ,  51   b  are formed of soft iron and act to direct magnetic flux out of the pipe to facilitate attraction of swarf in the mud flow. Wear discs  52   a,    52   b  which are resistant to wear are secured to each pole piece  51   a,    51   b.  As can be seen from the Figures, the diameter of the wear discs  52   a,    52   b  greater than that of the magnet  50  and the pole pieces  51  to ensure that the wear discs  52   a,    52   b  wear away sacrificially. The elements  50 ,  51  and  52  can be quickly removed and replaced with a similar unit when necessary. 
         [0052]    In order to enable the magnets to be secured to one another, the unit is provided at a first end with a female clevis  57  and at a second end with a corresponding male clevis  58 . To ensure that the basic unit remains together, a stud  53  is fixed across the assembly passing through the holes in the magnet  50 , pole pieces  51   a,    51   b  and wear discs  52   a,    52   b.  A screw or bolt is passed through the holes  54 ,  55  in each clevis  57 ,  58  and through the stud  53 . 
         [0053]    In order to link adjacent magnets therefore, the clevis of each neighbouring magnetic unit is aligned, with opposite poles adjacent to each other, and secured to one another, allowing the units to pivot relative to one another. Sufficient units are linked together eventually to form an endless chain which passes through and is enclosed almost completely, by the steel pipe. 
         [0054]    In use it has been found that care needs to be taken to provide breaks in the magnetic field, to allow the swarf to be released from the pipe, to enable the outside of the pipe  22  around the region of the collar  24  to be kept free of swarf. One solution to this problem is to replace the magnet in alternate links with a dummy, non-magnetic element  56 . As the chain moves through the pipe therefore, the region around the collar  24  is periodically subject to magnetic fields which are not strong enough to retain the swarf, allowing the swarf to drop into the collection chute  25 . It will be apparent that the weakening of the field can be achieved in a number of ways. For example, in similar fashion to the embodiment described above, every third, fourth etc magnet can be excluded. Alternatively or additionally, the distance between magnets can be increased. 
         [0055]    Although it has been found advantageous to include gaps in the field it is not essential, and the amount of swarf in the collar region can be allowed to build up until its own weight causes a proportion of the mass built up to fall into the chute. 
         [0056]      FIG. 5   e  shows an alternative, more flexible linkage means  59  between adjacent magnets, allowing curvature of the chain in two places. 
         [0057]    A drive mechanism for the chain including the magnet units of  FIGS. 5   a  to  5   d  is shown in  FIGS. 6   a,    6   b  which illustrate a drive head assembly. A drive wheel  60  is mounted to a rotatable shaft  61 . The magnet is held between the teeth  62  of the drive wheel  60  and as the wheel  60  rotates therefore, the endless chain of magnets is drawn around the pipe  22 . Loosening of the nut  63  allows the assembly to be rotated about the shaft  61  in order to change the orientation of the steel pipe  22  in the manner described above. Once the pipe  22  is in the required orientation, the nut  63  can be tightened. Tensioning of the chain of magnets can be achieved through the use of tensioning adjuster  64 . This effectively moves the drive gear to make the overall length of the path followed by the chain longer or shorter. 
         [0058]    In use therefore, the supporting frame is located above the channel through which the mud contained in the swarf is to flow. The drive mechanism and the steel pipes through which the magnetic chains are drawn, are located on the support frame such that the base of the steel pipes guiding the chain are close to the bottom of the channel and spaced apart sufficient that the space between the pipes is small enough for the entire width of the mud in the channel to be subjected to a magnetic field. If necessary, a pipe can be tilted to enable the pipe layout to conform to the shape of the channel. Moreover, the pipes are aligned such that the movement of the chain within the pipe is opposed to the flow of the mud in the section of pipe below the mud surface. 
         [0059]    The drive meal&#39;s is then activated, circulating the magnetic chain within the pipe. The mud is allowed to flow within the channel. As the mud flows past the pipes, metal swarf is attracted to the pipe and, due to the chain circulation, is carried out of the mud along the outside of the pipe until it engages the collar  24 . As a magnetic element  50  of the chain together with the swarf particles attracted by that element  50  circulates beyond the collar  24 , the magnetic field retaining the swarf particles drops and the swarf particles fall from the pipe into a collection chute. Using the above apparatus, and a typical swarf-containing mud, approximately 800-1000 gallons of mud have been processed at a rate of yield of I ton/hour of swarf. 
         [0060]    The second section of the apparatus shown in  FIG. 1  is shown in  FIG. 7 . In  FIG. 7 , a rod  70  comprises an outer tubular steel case  71  closed at its in use lower end to prevent penetration of water into the tubular case  71 . Slideably mounted within the case  71 , a cylindrical magnet  72  is capable of moving from a lower in use position (left-hand view) to a raised cleaning position (right-hand view). The magnet  72  comprises alternatively rare-earth type magnets  77  and soft iron pole pieces  78 , again to force lines of flux outside the case  71 . In this section, the magnets  77  are orientated in N-N, S-S relationship with neighbouring magnets. As can be seen from  FIG. 7 , the height of the magnet is approximately half that of the case  71 . A shaft-rod  73  is mounted at its first end to the upper end of the magnet  72  and passes through the upper, open end of the case  71 . A seal is maintained at the open end to prevent water ingress. The second end of the shaft  73  comprises a handle  74  to operate the rod  70 . 
         [0061]    The rod  70  further includes a swarf stop  75  in the form of an annulus mounted about the outside of the case  71  and at the height of the top of the magnet  72 , when the magnet  72  is in its lower position. A support  76  enables the rod  70  to be held in position in the channel by a suitable frame. 
         [0062]    In use therefore, the rod or series of rods  70  is positioned in the channel. The magnet  72  is lowered within the case  71  by operation of the swarf-rod  73 . The flow of mud within the channel is commenced and as the mud flows around the rod  70 , swarf in the mud is attracted to the case  71  and held there by the magnet  72 . When sufficient swarf has been collected, the rod  70  is lifted out of the mud stream. The handle  74  is used to pull the magnet  72  from one end of the case  71  to the other. As this occurs, the accumulated swarf is pulled along the case until it reaches the stop  75 . Eventually, as all of the magnet  72  is withdrawn above the level of the stop  75 , the swarf drops off, preferably into a suitable collection vessel. 
         [0063]      FIGS. 8   a  to  8   d  show an alternative embodiment comprising a series of rods  80 , secured to a framework  81 . The rods  80  comprise an outer casing, formed of steel. The casing houses a series of magnets, fixed in position, and separated by pole pieces as described above. The magnets can be orientated, with respect to a neighbouring magnet in an N-S, N-N or S-S configuration. The framework  89  is designed specifically for the channel  82  in which the mud flows, and is such that the rods  80  follow the contours of the channel  82 . In use, once the rods  80  have accumulated sufficient swarf, the framework  81  is lifted out of the channel  82  and the swarf removed, usually by hand. The framework  81  can then be replaced in the channel. 
         [0064]    A further embodiment of the rods shown in  FIG. 7  is shown in  FIG. 9 . The rod  100  is designed to be self cleaning which again minimises operator time which needs to be devoted to maintenance. The rod  100  comprises a central shaft  101  which contains a series of magnets assembled together in the same fashion as those in the embodiment of  FIG. 7 . The rod  100  further comprises a helix  102  wound about the shaft  101 : the inner surface of the helix  102  being in contiguous relationship with the surface of the shaft  101 . The helix  102  is rotatably mounted and its motion about the shaft  101  is driven by the motor  103  which drives the helix  102  in the direction indicated; the helix therefore functions in the same fashion as a conventional auger. 
         [0065]    As will be envisaged therefore any swarf attracted to the magnets in the shaft  101  will be pushed by the helix  102  up the shaft  101  towards the motor  103 . Eventually as the swarf reaches the upper half of the shaft  101 , the magnetic attraction exerted by the magnets in the shaft  101  on the swarf reduces eventually until the force is insufficient to retain the swarf and it falls from the rod  100 . The rod  100  is orientated at around 45° to the horizontal to ensure that when the swarf is released from the rod it does not fall back down the rod  100 , but instead falls into a collection element (not illustrated). 
         [0066]    In  FIG. 10 , an array of rods  110  shown in  FIG. 9  is shown. The array comprises four rods  110  (which are according to the rod  100  described above) mounted together and deployed in a vertical orientation in a channel (not illustrated) through which mud from which swarf is to be removed is flowing. The array has a further rod  104  which is also of the same type as  100 , which is orientated horizontally. The rod  104  is so positioned that the magnetic elements of the rod  110  are sufficiently close to the non-magnetic regions of the vertically orientated rods  100  to remove any swarf from these regions of the vertically orientated rods  100 . 
         [0067]    In use therefore, swarf removed from the mud flow by the rods  110  is conveyed by the helices  102  up the shaft  101  of the rod  110 . The swarf is eventually conveyed into the non-magnetic region of the rods  110 . Here the swarf is attracted to the magnetic region of the rod  104 . From here, the swarf is conveyed along the rod  104  by the helix  102  in the direction of the motor  105 . Swarf is conveyed to the nonmagnetic region of the rod  104  from which it falls under gravity and can be collected in a suitable container. 
         [0068]      FIGS. 11A ,  11 B describe two orientations for magnets contained within rods. In  FIG. 11A , the magnet  120  has a north pole running along one side of the length of an Internal core  121  of the rod  122 . As can be seen from the sectional drawing of this rod, the resultant magnetic flux extends away from the rod and is symmetric across the plane running from the north pole to the south pole. In the arrangement shown in  FIG. 11B , the magnets  125  are arranged in a stacked fashion giving a series of alternate poles  126 . As can be seen from the section taken through the stack of magnets shown under the main drawing of the rod. In this particular arrangement the magnetic flux assists in movement of swarf along the rod, as flux lines connect adjacent magnets. 
         [0069]    In a further embodiment of the invention, as shown in  FIG. 1   a,  the two above embodiments can be used cooperatively with one another. In this embodiment, apparatus including an endless chain described above is used upstream of the rods, the rods being used effectively to collect the swarf missed by the chain apparatus. 
         [0070]      FIG. 12  shows a further embodiment of an apparatus including an endless chain, the apparatus being designed particularly for use where space for the chain to turn is limited and the path described by the chain includes regions of high curvature. In addition to the features described above, the apparatus includes a gearing mechanism  130  to assist the motor ( FIGS. 1 ,  28 ) to circulate the chain and to ensure that the tension within the chain remains suitable. 
         [0071]    In an alternative embodiment, not illustrated, the swarf can be removed from the steel pipe by a brush means. Such a brush means is particularly suited for use where the magnetic field generated by the magnetic chain is fairly continuous, and at least sufficient to hold the swarf against the pipe in the region of the collar. 
         [0072]    It will be appreciated that the embodiment of  FIGS. 7-11  employing the static magnets and the embodiment incorporating the moving magnets can be used independently of one another. In some situations the more portable static magnet arrangement is more easily deployed and serviced, whereas in other the moving magnet arrangement will be more suitable. 
         [0073]    It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible with the scope of the appended claims.