Abstract:
A separation conveyor ( 10 ) for separating a mass or slurry of different sized particles is provided. The separation conveyor includes a filter belt ( 12 ) including a feed side for receiving the mass or slurry and a filtrate side. The separation conveyor further includes a conveyor assembly ( 16 ) for conveying the filter belt, an overhead spray array ( 28 ) for spraying fluid downwards onto the slurry as it travels on the filter belt, and a lower spray array ( 30 ) for spraying fluid upwards against an underside of the belt. The upper and lower spray arrays are arranged in combination to assist in promoting separation of oversized particles on the feed side of the belt and undersized particles on the filtrate side of the belt.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to apparatus and methods of separating out from fluid slurries of differently sized particulate matter over- and under-sized particulate fractions. In one particular aspect, the invention relates to separating out fine coal particles from ultra-fine coal particles. 
       BACKGROUND OF THE INVENTION 
       [0002]    In materials processing the separation of fine particles by their size tends to be expensive and/or inaccurate in certain applications where the undersize fraction is the contaminant and the oversized fraction the desired product. This expense/inefficiency has resulted in additional inefficiencies in downstream processes. In order to reduce such inefficiencies, separation processes are often designed to separate the majority of the undersized contaminant, but in doing so also separate (and waste) part of the oversized desired product. 
         [0003]    In applications such as the briquetting of coal fines from tailings dams, ultrafines (particles having a size of around less than 40 μm) cannot effectively be used in the briquetting process (unless they are further beneficiated, which is generally too expensive a process to be viable). In separating waste material (such as clay) of size less than 40 μm from the coal particles, however, valuable coal particles of size greater than 50 μm are also often separated and lost, in particular when conventional vibrating screens are used having typical mesh sizes of 300 μm or more. 
         [0004]    Various types of filter or separator arrangements are used to separate out the coal ultrafines from the coal fines before briquetting takes place. A coal slurry is typically formed, which is then fed over a filter bed configured with a mesh size through which ultra-fines can pass. 
         [0005]    One problem which has been encountered is that of clogging, in which near-sized particles tend to clog the apertures through which the ultrafine particles are arranged to pass. A further problem which may arise is that of stratification or settling, in which larger heavier particles settle on the filter bed below the ultra-fines and affect the passage of ultra-fine particles through the filter apertures. In addition, in a high speed and high volume briquetting operation, it is desirable that throughput of particles is maximised or at least significantly increased. 
         [0006]    Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art. 
       SUMMARY OF THE INVENTION 
       [0007]    In one aspect, the invention provides a separation conveyor for separating a mass or slurry of different sized particles, the separation conveyor including: a filter belt including a feed side for receiving the mass or slurry and a filtrate side; a conveyor assembly for conveying the filter belt; an overhead spray array for spraying fluid downwards onto the slurry as it travels on the filter belt; a lower spray array for spraying fluid upwards against an underside of the filter belt, wherein the upper and lower spray arrays are arranged in combination to assist in promoting separation of oversized particles on the feed side of the belt and undersized particles on the filtrate side of the belt. 
         [0008]    The overhead spray array may include an array of overhead spray bars, and the lower spray array includes an array of lower spray bars, wherein the upper and lower spray bars are offset relative to one another. 
         [0009]    The conveyor assembly may include a plurality of rollers around which the filter belt travels, the upper and lower spray arrays being arranged between the rollers 
         [0010]    The lower spray array may include at least one sidewardly or downwardly directed spray bar directed against an undersurface of the filter belt. 
         [0011]    In another aspect the invention provides a method of separating a mass or slurry of different sized particles into undersize and oversize particles including: feeding the slurry onto a filter belt having an upper feed side and a lower filtrate side; conveying the slurry along the filter belt; directing sprays downwards onto the slurry via an overhead spray array; directing sprays upwards against an underside of the filter belt via a lower spray array to unclog the filter belt, and collecting the filtrate including the undersize particles and collecting the oversize particles at a downstream end of the filter belt. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  shows a side view of one embodiment of a separation apparatus of the invention; 
           [0013]      FIG. 2  shows a top plan view of the separation apparatus of  FIG. 1 ; 
           [0014]      FIG. 3  shows a front view of the separation apparatus; 
           [0015]      FIG. 4  is a schematic side view illustrating an alternative configuration of the separation apparatus; and 
           [0016]      FIG. 5  shows a side view of another embodiment of the separation apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0017]    Preferred embodiments of the separation or belt filter apparatus  10  are illustrated in  FIGS. 1-5 . 
         [0018]    The apparatus  10  includes a filter medium in the form of a continuous conveyer belt  12 . The conveyor belt  12  may be manufactured from a variety of materials including, for example, woven steel mesh (e.g. stainless steel) or durable synthetic fibres (such as polyester, nylon or polyamide). Composite conveyor belts may also be used, for example a fine stainless steel bonded to an open weave polyester or nylon belt. The conveyor belt will typically be formed from a material having an aperture size of between approximately 50 μm to 150 μm. It will be appreciated that different sized apertures may be used depending on the material being separated and the desired sizes of the undersized and oversized fractions. These may range for example from materials with aperture sizes of 40 μm to 250 μm or more, but are preferably in the 40-50 μm to 150 μm range. Apertures of approximately 100 μm will be appropriate for certain applications. Parts of the belt including the side margins may be impregnated with a polymer such as polyurethane to increase wearability. Typically, a narrow polyurethane strip, having in the particular embodiment a width of 25 mm, is applied to each side margin to reduce fraying and increase wearability. The belt may be made of a woven stainless steel. Alternatively, the belt may be a woven polyester. For example, the belt may be a woven polyester with an aperture size around 125 micron. This may obtained by weaving a belt from a 0.125 mm polyester fibre using a schedule 2 weave with a secondary fibre of 1 mm diameter woven through the material using a schedule 2 weave to provide additional strength. There are around 50-60 threads per cm of the 0.125 mm fibres per cm to provide the desired aperture size. The material used for the belt is preferably not hydrophobic. 
         [0019]    The conveyor belt  12  is guided on top and bottom end rollers  14 A,  14 B,  14 C and  14 D respectively. Equispaced support rollers  14 E,  14 F,  14 G,  14 H and  14 I are positioned in a uniplanar configuration to support an upper reach  12 A of the conveyer belt  12 . In this embodiment roller  14 A is also a drive roller which is coupled to a variable speed motor  16  to drive the conveyor belt  12 . Roller  14 B is mounted to the frame  20  via a tensioning arrangement  17  which maintains correct tension in the conveyor belt  12 . The tensioning arrangement  17  includes a threaded bar which passes through a complementarily threaded aperture. The bar can be screwed in/out to adjust the position of the roller  14 B and, consequently, the tension in the conveyor belt  12 . The rollers  14 A to  141  are journalled on bearings  18  which are in turn mounted on a support frame  20  having legs  22  and a lower frame portion  24 . 
         [0020]    In one embodiment the heights of the legs  22  are independently adjustable (e.g. telescopically) to allow the angle of the conveyor belt  12  to be altered. By extending the legs  22  at the discharge end of the conveyor belt  12  (i.e. the end proximate roller  14 B), the belt  22  can be inclined in the direction of travel thereby increasing the retention time of the slurry on the belt  12 . The degree of inclination of the belt can be adjusted to effectively stop (or reduce) excess water from flowing off either end of the belt  12 . This is typically achieved by providing the belt  12  with a greater inclination when it is running at a higher/faster speed. 
         [0021]    The apparatus  10  also includes a tracking assembly  50  mounted on the support frame  20 , the tracking assembly  50  assisting in keeping the conveyor belt  12  centred on the rollers. The tracking assembly  50  includes a pivotally mounted tracking roller  14 J which bears up against an undersurface of the lower reach  12 B of the conveyor belt  12 . The tracking assembly  50  further includes a tracking sensor  52  which tracks the alignment of the conveyor belt  12  and two air bellows  51 . Based on information from the tracking sensor  52 , the two air bellows are operated to move the tracking roller  14 J and vary the tension of the conveyor belt  12  from side-to-side, thereby maintaining a central alignment of the conveyor belt  12 . 
         [0022]    An upper frame portion  26  carries five overhead spray bars  28 . 1  to  28 . 5  extending transversely relative to the direction of the conveyor belt  12 . In one arrangement the spray bars are equi-spaced. The spray bars  28 . 1 - 28 . 5  are formed with a plurality of lowermost apertures configured to direct jets of water  35  vertically down onto the slurry being carried on the upper reach  12 A of the conveyer belt  12 . The lowermost apertures will generally be along the length of the relevant spray bar extending over the conveyor belt  12 . The number of lowermost apertures per spray bar will depend on the width of the belt  12 , however there will typically be up to 6 lowermost apertures per spray bar. The upper frame  26  supports the sprays such that their nozzles (apertures) are approximately 200 mm from the upper reach  12 A of the conveyor belt  12 . The spray bars  28 . 1 - 28 . 5  span the entire width of the conveyor belt  12  and the jets are configured so that they fan out to provide complete coverage across the width of the conveyor belt  12 , with the end sprays being angled inwardly to keep the material on the belt. It can clearly be seen in  FIG. 1  how the spray bars are positioned so that they are offset from the rollers  14 E- 14 I. 
         [0023]    Five lower spray bars  30 . 1 - 30 . 5  are mounted on an intermediate frame portion  32  of the frame beneath the upper reach  12  of the conveyer belt. The spray bars  30 . 1 - 30 . 5  are formed with uppermost apertures which direct a plurality of jets of water  31 , for example two to five jets of water,  31  upwardly against the under-surface of the upper reach  12 A of the conveyer belt  12  across its entire width. The intermediate frame portion  32  supports the lower sprays such that their nozzles are approximately 200 mm from the under surface of the upper reach  12 A of the conveyor belt  12 . The lower spray bars  30 . 1 - 30 . 5  are offset from both the upper spray bars and the rollers  14 E- 14 I so that there is minimal or at least reduced interference between the upper and lower sprays and the rollers in operation, with each of the upper spray bars, lower spray bars and rollers offset from one another. 
         [0024]    The upper reach  12  of the conveyor belt will typically extend (and carry the slurry being filtered) a distance beyond the last spray bar in order to allow for further draining. While this distance may be varied according to the characteristics of the slurry, extending the upper reach  12  around one to two meters beyond the last spray bar will typically be suitable. 
         [0025]    In one embodiment the upper and lower spray bars are plumbed so as to allow the bars to be operated independently of one another. Accordingly, if a filtering operation does not require use of all spray bars some spray bars can be shut off, thereby minimising or at least reducing water consumption. The characteristics of the solid matter in the various slurries being separated will vary from site to site. Shutting spray bars off may be appropriate in instances where there is less fine material to be removed and/or there is a low concentration of solids in the feed slurry. 
         [0026]    In operation, a coal slurry containing a mixture of differently sized coal particles is introduced onto the feed end  34  of the conveyer belt through a feed box or hopper  38 . In one embodiment, the feed box  38  distributes the slurry substantially over the entire width of the conveyor belt  12 , and supplies the slurry at a rate of approximately 200-300 m 3 /hour. As will be appreciated, though, the rate at which the slurry is fed will depend on a variety of factors, including the size of the belt  12 , the size of the apertures in the filter belt  12 , and the quality/characteristics of the slurry itself. For example, a slurry having a lower percentage of solids will filter more rapidly than a slurry having a high percentage of solids. Similarly, a belt having apertures of 0.1 mm will filter more rapidly (have a higher capacity than) a belt having apertures of 0.06 mm. In certain embodiments a feed rate of 100 to 150 m 3 /hour may be appropriate. 
         [0027]    As the slurry is conveyed along the conveyer belt, the jets or sprays  35  extending from the upper spray bars prevent the slurry from settling and create a turbulent flow in the slurry which ensures that there is free circulation of coal particles on the filter bed, which it maintains in a fluidized condition. In addition to promoting turbulent flow of the slurry and preventing stratification, the sprays  35  also assist in washing the ultra-fine particles from the surfaces of the larger particles and through the belt filter as filtrate. The filtrate accumulates in a sloped tray  37  which is angled to permit the free flow of filtrate to a discharge pipe  39  which discharges the filtrate to one side of the apparatus  10 . 
         [0028]    At the same time, the sprays  31  from the lower array of spray bars  30 . 1 - 30 . 5  clear the belt filter of any near-sized particles that may have become wedged or clogged in the apertures. The sprays  31  also serve to counter any stratification that may have occurred at the base of the filter bed and also assist in maintaining a slurry in a turbulent state as it travels along the belt filter. Each of the spray bars  30 . 1 - 30 . 5  and  28 . 1 - 28 . 5  is fitted with a regulating valve (not shown) to control both water flow and pressure in order to arm the belt filter. The pressure of the sprays  31  should be sufficient for the water to penetrate the filter cloth, for example by about 25 mm above the surface of the belt filter. 
         [0029]    The spray bars are also fitted with a flush valve which, in the event that the sprays become clogged, can be opened to allow water to flow straight through the spray bars and flush/dislodge any material. The spray bars are fed from a single manifold arranged so that any combination of spray bars can be used to maximise their effect at minimal water consumption. 
         [0030]    The sides of the upper reach  12 A of the conveyer belt are angled upwardly as shown at  38  by means of elongate deflectors  40  extending inwardly from side portions of the frame. This enables the conveyer belt to accommodate a greater volume of slurry. 
         [0031]    In order to promote further dislodging of near size particles from apertures in the belt filter, auxiliary spray bars  30 . 6  and  30 . 7  are configured to direct jets of water against the inner surface of a side reach of the conveyor belt  12 . These auxiliary sprays assist in cleaning the belt on its return path to the discharge box  38 . 
         [0032]    As will be appreciated, the dimensions/positioning of the various components separation or belt filter apparatus  10  can be adapted to suit the desired purpose/throughput, and in accordance with the characteristics of the feed material. 
         [0033]    By way of non-limiting example, the apparatus  10  may use a conveyor belt  12  having a width of between 1 to 3 meters, typically around 1.1 m. The belt  12  may have an upper reach  12 A of between 4 to 6 meters long. As one example, the length of the upper reach  12  may be around 4.5 m and include 1 m of drainage, 1.5 m of travel above/beneath spray bars, and a further 2 m of drainage. The speed of the belt  12  will be varied to give maximum filtering efficiency for the instant feed material conditions. For example, for a slurry containing a low percentage of solids the belt can be operated at relatively high speeds, while a slurry with a high percentage of solids and a high proportion of finer material may require the belt to be operated at relatively low speeds. Typically, the apparatus  10  will be configured to provide for belt speeds of between approximately 500 m/hour to 1300 m/hour. In some embodiments a belt speed of 1000 m/hour will be suitable. 
         [0034]    The number and spacing of the upper spray bars  28  and lower spray bars  30  will, again, depend on the application. Where fine material is being processed, a greater number of lower spray bars  30  may be warranted in order to clear the fine material from the apertures in the belt  12 . Where coarser material is being processed, a greater number of upper spray bars  28  may be desired. In order to provide a reasonable coverage of the belt  12 , a spacing of approximately 0.45 meters between spray bars may suffice, however alternate spacings could also be used. 
         [0035]    The number and spacing of the apertures/nozzles on each spray bar are selected to as to provide complete coverage across the width of the belt  12 . This number/spacing will depend on the type of aperture/nozzle, the direction of the apertures/nozzles, water pressure, and distance between the spray bar and the belt  12 . In one embodiment: the upper spray bars  28 . 1 - 28 . 5  are positioned approximately 200 mm above the upper reach  12 A of the belt; the lower spray bars  30 . 1 - 30 . 5  are positioned approximately 200 mm below the upper reach  12 A of the belt; the apertures/nozzles on the top spray bars  28 . 1 - 28 . 5  are 90 degree sprays and are arranged to have an approximate spacing of 250 mm; the apertures/nozzles on the bottom spray bars  30 . 1 - 30 . 5  are 110 degree sprays and are arranged to have an approximate spacing of 300 mm; water is supplied to the upper and lower spray bars at approximately 2 litres/minute per spray bar at approximately 2 bar pressure. 
         [0036]    The arrangement of overhead and lower sprays, in combination with the moving belt, resulted at least for the illustrated prototype an increase in throughput of coal fines by up to threefold to fivefold from 11 m 3  per hour from a Baleen™ filter having a stationary screen and moving upper and lower spray arms to above 30 m 3  per hour. 
         [0037]      FIG. 4  is a schematic illustration of another configuration of the separation apparatus. In this arrangement there are two upper spray bars  28  that spray downward onto the material  62  lying on the belt  12 . The upper spray bars are positioned towards the discharge end of the separation apparatus. The apparatus may be inclined so that the discharge end of the filter area is higher than the feed end. For example, the belt may be inclined by around 1 degree. The upper spray bars  28  may be set in order to form a ‘water dam’, for example dam  64 , to hold the slurry for longer on the upper reach  12 A of the filter belt. 
         [0038]    In the illustrated arrangement there are more bottom spray bars (eg  30 . 1 ) than upper spray bars  28 . Tests have indicated that the efficiency of the separation apparatus is dependent on the bottom spray bars. The bottom spray bars may be spaced at intervals of around 100 mm, although in some applications the spacing may be increased for the bottom spray bars closer to the discharge end. For example, the spacing may increase to 150 mm towards the discharge end. 
         [0039]    The belt length plays an important role in the overall separation efficiency, provided the belt is not blinded. Thus, the number of bottom spray bars is increased if the belt length is increased. The water from the bottom spray bars penetrates the slurry  62 , for example to around 25 mm about the surface of the belt  12 . This removes near-sized particles from the pores of the belt and also agitates the slurry  62 , thus aiding the removal of the finer material. 
         [0040]    One or more auxiliary sprays  60 . 1  to  60 . n  are provided on the belt&#39;s return path to clean the pores of the belt. As illustrated, there is spray  60 . 1  cleans a side reach of the belt  12  and a plurality of sprays  60 . 2  to  60 . n  spray downwards to clear obstructions from the pores of the belt along its lower reach. 
         [0041]      FIG. 5  shows another arrangement of the separation apparatus, which differs from the arrangement of  FIG. 1  in that there are only two upper spray bars  28 . 3  and  28 . 5 , but an increased number of bottom spray bars  30 . 1  to  30 . 10 . The first bottom spray bar  30 . 1  is positioned beneath the outlet of the feed box  38 . There are two bottom spray bars between adjacent rollers  14 E- 14 I. For example, bottom spray bars  30 . 2  and  30 . 3  are positioned between rollers  14 E and  14 F. 
         [0042]    There are two auxiliary spray bars, eg  30 . 11 , cleaning a side reach the belt on its return path, and two auxiliary spray bars  60  cleaning the lower reach  12 B of the belt, thus reducing cumulative blinding of the belt. 
         [0043]    In one arrangement the length of the apparatus is around 6 m and the length from the discharge of feed box  38  to the discharge of the apparatus is around 5.5 m. 
         [0044]    An example of source material that is suitable for processing by the separation apparatus described herein is a cyclone overflow stream from a classifying or de-sliming cyclone in a coal preparation system. The streams may, for example, have a solids content in the range of 4-10%. 
         [0045]    In a series of tests the separation apparatus has been used to process material from a primary classifying cyclone overflow stream. Table 1 shows a size analysis of the material in this stream. The table describes a 13.0 kg sample with a % solids of 4.74. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Size Analysis 
               
             
          
           
               
                   
                 Particle size 
                   
                   
                   
                   
                   
               
               
                   
                 ranges (mm) 
                   
                 Fractional 
                   
                 Cumulative 
               
             
          
           
               
                   
                 − 
                 + 
                 Mass % 
                 Ash % 
                 Mass % 
                 Ash % 
               
               
                   
                   
               
             
          
           
               
                   
                   
                 0.250 
                 0.50 
                 6.7 
                 0.50 
                 6.7 
               
               
                   
                 0.250 
                 0.125 
                 3.93 
                 5.1 
                 4.43 
                 5.3 
               
               
                   
                 0.125 
                 0.090 
                 4.25 
                 5.2 
                 8.68 
                 5.2 
               
               
                   
                 0.090 
                 0.063 
                 4.30 
                 8.3 
                 12.98 
                 6.3 
               
               
                   
                 0.063 
                 0.038 
                 7.51 
                 13.3 
                 20.50 
                 8.8 
               
               
                   
                 0.038 
                   
                 79.50 
                 65.0 
                 100.00 
                 53.5 
               
               
                   
                   
               
             
          
         
       
     
         [0046]    The left hand column lists the size ranges of the feed material in the sample. The separation apparatus described herein permits recovery of material in the size category &gt;0.090 mm. It may be seen from the cumulative figures that this category includes 8.68% of the sample and furthermore the recoverable size category has an ash content of 5.2%. The recovered material thus has a relatively high grade. 
         [0047]    An alternative technique of recovering material in this size fraction is to use froth flotation. However, it is considered that the separation apparatus described herein provides a simpler and cheaper means of recovering this useful material. 
         [0048]    Tests on the cyclone overflow feed were run on a separation apparatus similar to that of  FIG. 1 , with five bottom spray bars. The apparatus used in the test is 4 m long, and the bottom spray bars are spaced along a drainage region between 2 to 2.5 m in length. The operating speed of the belt was around 1000 m/hr. Variations in belt speed affect the capacity of the unit and it was found that a belt speed of between 1000 and 1500 m/hr gave the greatest efficiency. The discharge end of the apparatus was raised by about 50 mm. If the belt speed is increased the discharge end may be further raised to reduce the potential for the slurry  62  to flow off the discharge end. 
         [0049]    The tests showed a direct relationship between the bottom sprays and the capacity of the separation apparatus. For example, when one of the five bottom spray bars was switched off, the capacity of the unit in one trial fell from 37 m 3 /hr to 30 m 3 /hr. If the number of spray nozzles in use in the bottom spray bars was increased from 15 to 30, the capacity of the unit increased from 37 m 3 /hr to 58 m 3 /hr. 
         [0050]    The aperture of the belt filter is selected in view of the size distribution of the feed material. In the example described above, the belt aperture is around 125 micron. This is obtained by weaving a belt from a 0.125 mm polyester fibre using a schedule 2 weave with a secondary fibre of 1 mm diameter woven through the material using a schedule 2 weave to provide additional strength. There are around 50-60 threads per cm of the 0.125 mm fibres per cm to provide the desired aperture size. This aperture size enables the recovery of material in the +0.090 mm class and the rejection of material less than 90 micron, which is predominantly clay. If the aperture size is reduced to around 75 micron, for example, there would be a greater proportion of the feed material liable to cause blinding of the filter. This may be counteracted by increasing the number of bottom spray bars and nozzles and/or the pressure of the water supply. 
         [0051]    In general, the aperture size is chosen to recover desired material from the feed material. The relation of the aperture size to the size distribution of the feed material affects the likelihood of material blinding the filter. Thus, if a relatively fine mesh size is used (relative to the size distribution of the material) it may be necessary to increase the number of bottom spray bars and nozzles and/or the pressure of the water supply to avoid blinding of the filter. 
         [0052]    It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.