Patent Publication Number: US-8968169-B2

Title: Decanter centrifuge having an outlet opening with an inclined edge

Description:
The present invention relates to a decanter centrifuge for separating a first substance and a second substance with different densities. The decanter centrifuge comprising includes a bowl rotatable around a horizontal axis of rotation in a direction of rotation. The axis of rotation extending extends in a longitudinal direction of the bowl. A radial direction extends perpendicular to the longitudinal direction. A base plate is provided at one longitudinal end of the bowl. The base plate has an internal side and an external side, and an outlet opening is provided in the base plate for discharge of one of the substances. The outlet opening extends through a first angular interval relative to the axis of rotation. The decanter centrifuge includes a slide valve body adapted for covering an adjustable part of the outlet opening to delimit an effective area of the outlet opening. The outlet opening includes an edge that is inclined. 
     BACKGROUND 
     A decanter centrifuge generally has fixed weir edges and thus a fixed level of the one substance to be discharged (in the following liquid, which is normally the case) in the bowl of the decanter centrifuge. The position of the weir edge is generally determined either by the radial position of the outlet opening in the base plate of the decanter centrifuge, or by the position in which an external weir edge is mounted fixedly on the base plate of the decanter centrifuge, generally such that it covers a part of the outlet opening. Such a decanter centrifuge is e.g. known from JP 11-179236. 
     Thus the liquid level in the bowl of a known decanter centrifuge is normally determined by the position of the weir edge and cannot be changed, except by unduly complex procedures. 
     It is one object of the present invention to provide a decanter centrifuge that eliminates or reduces the problem mentioned above. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention this object is achieved by providing a decanter centrifuge of the art mentioned in the first paragraph where the slide valve body includes a first edge extending in the radial direction. The edge delimits the effective area of the outlet opening when the slide valve body is in a position covering an adjustable part of said outlet opening. The outlet opening is radially away from the axis of rotation and is delimited by a second edge. The second edge has in at least a major part of the first angular interval in a radial plane perpendicular to the axis of rotation an inclination relative to the radial direction of at least 60°, preferably at least 70°, more preferably at least 75°, said second edge constituting a weir edge. 
     Thereby it becomes possible to adjust the effective area of the outlet opening that is covered and thereby to adjust the liquid level in the bowl of the decanter centrifuge, and a simple but effectively working slide valve body for adjusting the liquid level in the bowl of the decanter centrifuge is provided for. 
     According to a preferred embodiment of the invention said slide valve body is provided for rotation around the axis of rotation, thereby providing for a decanter centrifuge with a slide valve body being particularly simple to adjust. 
     According to a preferred embodiment of the invention the decanter centrifuge comprises a level sensor in the bowl, thereby providing for the possibility of measuring the liquid level within the bowl at any time before, during or after operation and regardless of the construction of weir edges and/or devices provided for energy recovery purposes. 
     According to a preferred embodiment of the invention the slide valve body is provided adjacent the plate at the internal side of the base plate, thereby providing for a particularly well functioning and easy to operate slide valve body and thus the decanter centrifuge. 
     According to an embodiment of the invention the slide valve body comprises an edge extending in a direction, which with respect to a circumferential direction comprises an inclination of less than 30°, said edge constituting an adjustable weir edge when said slide valve body is in a position covering an adjustable part of said outlet opening. 
     According to a preferred embodiment of the invention the decanter centrifuge comprises a wall projecting from said external side of said base plate for guiding the substance discharged from said outlet opening in a direction opposite the direction of rotation of the bowl to recover kinetic energy from the substance, thereby combining the above advantages with the benefits of energy recovery. 
     According to a further embodiment of the invention the decanter centrifuge, the wall is extending from the vicinity of the outlet opening towards a rim of the base plate, said wall extending through a second angular interval adjacent the first angular interval, said second angular interval being at least 30°, preferably at least 45°, more preferably at least 60°, and said wall having in a radial plane perpendicular to the axis of rotation an inclination relative to the radial direction of at least 60°, preferably at least 70°, more preferably at least 75°, and the outlet opening is radially away from the axis of rotation delimited by a second edge, the wall and the second edge having in at least a major part of the first angular interval in a radial plane perpendicular to the axis of rotation an inclination relative to the radial direction of at least 60°, preferably at least 70°, more preferably at least 75°, said second edge constituting a weir edge when said outlet opening is uncovered. In this way a decanter centrifuge combining the above advantages with a particularly advantageous energy recovering structure is provided. 
     According to a preferred embodiment of the invention the outlet opening is delimited by a circumferential edge comprising three parts, a first part constituting the second edge and having relative to the axis of rotation a proximal end and a distal end, a second part extending from the distal end of the first part towards the axis of rotation and a third part connecting the first part and the second part, the slide valve body comprises an opening delimited by a circumferential edge comprising three sections, a first section extending in a direction, which with respect to a circumferential direction comprises an inclination of less than 30°, preferably less than 20°, more preferably less than 15°, said first section having relative to the axis of rotation a proximal end and a distal end, a second section extending from the distal end of the first edge towards the axis of rotation and a third section connecting the first section and the second section, and the slide valve body is provided for rotation around the axis of rotation. Thereby is provided for a decanter centrifuge by which the abovementioned advantages are obtained in a particularly simple way. 
     According to a preferred embodiment of the invention the decanter centrifuge comprises a stop means adapted for delimiting the rotation around the axis of rotation of said slide valve body. 
     Such a stop means provides for a slide valve body that may be limited in rotation to cover a desired range of positions and that may provide for a marking of extreme positions of the slide valve body, e.g. fully closed and fully opened opening. Also, such a stop may provide for elimination of any possible disadvantages connected with positions outside the chosen range. For instance a stop may provide for avoiding rotating the slide valve body to far. For instance when desiring fully open outlet openings rotating the slide valve body too far may result in inadvertently still covering part of the outlet opening. 
     According to a preferred embodiment of the invention the base plate comprises a plurality of, preferably three, outlet openings, and said slide valve body comprises a plurality of, preferably three, corresponding openings, thereby providing for the possibility of adjusting the liquid level at more than one outlet opening simultaneously. 
     According to a preferred embodiment of the invention the decanter centrifuge comprises a drive for sliding, especially rotating, the slide valve body, thereby providing for automatic and continuous adjustment of the liquid level in the bowl and/or of the weir edge, even during operation of the decanter centrifuge. 
     According to a preferred embodiment of the invention the slide valve body is a one piece body, thereby providing for simultaneous adjustment of the liquid level in the bowl and/or of the weir edge with respect to several outlet openings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The invention will now be described in further detail based on a non-limiting exemplary embodiment, and with reference to the drawings. In the drawings, 
         FIG. 1  shows a schematic view of an embodiment of a decanter centrifuge of prior art; 
         FIG. 2  shows a bottom view of a base plate of a decanter centrifuge according to a first embodiment of the invention featuring a slide valve body; 
         FIG. 3  shows a sectional end view of the base plate of a decanter centrifuge according to  FIG. 2  showing one discharge opening with the slide valve body in a partially closed position; 
         FIG. 4  shows a bottom view of a base plate of a decanter centrifuge according to a second embodiment of the invention featuring a slide valve body; 
         FIG. 5  shows an end view of the base plate of a decanter centrifuge according to the second embodiment of the invention, the base plate being provided with two walls; 
         FIG. 6  shows a perspective view of the base plate of a decanter centrifuge according to a third embodiment of the invention, the base plate being provided with three walls; and 
         FIG. 7  shows a side view of the base plate of the decanter centrifuge according to  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a prior art decanter centrifuge  1  comprising a bowl  2  and a screw conveyor  3  which are mounted on a shaft  4  such that they in use can be brought to rotate around an axis  5  of rotation, the axis  5  of rotation extending in a longitudinal direction of the bowl  2 . Further, the decanter centrifuge  1  has a radial direction  5   a  extending perpendicular to the longitudinal direction. 
     For the sake of simplicity directions “up” and “down” are used herein as referring to a radial direction towards the axis  5  of rotation and away from the axis  5  of rotation, respectively. 
     The bowl  2  comprises a base plate  6  provided at one longitudinal end of the bowl  2 , which base plate  6  has an internal side  7  and an external side  8 . The base plate  6  is provided with a number of liquid phase outlet openings  9 . Furthermore the bowl  2  is at an end opposite to the base plate  6  provided with solid phase discharge openings  10 . 
     Further the screw conveyor  3  comprises inlet openings  11  for feeding e.g. a slurry to the decanter centrifuge  1 , the slurry comprising a light or liquid phase  12  and a heavy or solid phase  13 . During rotation of the decanter centrifuge  1  as previously described, separation of the liquid  12  and solid  13  phases is obtained. The liquid phase  12  is discharged through the outlet openings  9  in the base plate  6 , while the screw conveyor  3  transports the solid phase  13  towards the solid phase discharge openings  10  through which the solid phase  13  is eventually discharged. 
       FIG. 2  shows a base plate  6  of a decanter centrifuge  1  according to a first embodiment of the invention seen from its internal side, i.e. from the side facing the internal of the decanter centrifuge  1  when the base plate  6  is mounted. The base plate  6  of  FIG. 2  has three outlet openings  9 . However, the exact number of outlet openings may be fewer or more than the three shown. Each outlet opening  9  is delimited by a circumferential edge comprising three parts  22 ,  23 ,  24  (cf.  FIG. 3 ). A first part constitutes a weir edge  22 , a second part  23  extends between a first angular interval  25  (cf.  FIG. 5 ) and a second angular interval  26  from the weir edge  22  towards the axis of rotation  5  at one end of the weir edge  22  and a third part  24  connects the first part  22  and the second part  23 . The second part  23  is generally L-shaped comprising a small leg  46 . 
     The weir edge  22  is radially away from the axis of rotation  5  forming a delimitation of the outlet opening  9 , the weir edge  22  extending through the first angular interval  25  and having in the first angular interval  25  in a radial plane perpendicular to the axis of rotation  5  an inclination relative to the radial direction of about 82°. However, the said inclination of the weir edge  22  may in other embodiments take other smaller or larger values. 
     On the base plate  6  is provided a slide valve body  40  in one piece comprising three openings  45  corresponding in shape and orientation to the outlet openings  9 . Alternatively there may be provided a separate slide valve body for each outlet opening in the base plate  6 . 
     The slide valve body is in  FIG. 2  shown in its open position, the outlet openings  9  being completely free. The slide valve body  40  is mounted such as to be able to rotate around the axis of rotation. Furthermore the slide valve body  40  may comprise adjustment means (not shown) for sliding or rotating the slide valve body  40 . Such adjustment means is preferably a suitable drive means, but a manual adjustment means is also foreseen. 
     Furthermore, the slide valve body  40  comprises a level sensor comprising two sensor elements  42   a ,  42   b . In this embodiment the sensor elements  42   a ,  42   b  are RFID sensor elements, and are adapted for monitoring (i.e. measuring and communicating to an external device or the above mentioned adjustment means) the liquid level in the bowl  2  of the decanter centrifuge  1 . Such sensor elements are in principle capacitive elements sensing a change of the liquid level by a change in the dielectric value between the capacitor plates. The sensor elements  42   a ,  42   b  are connected to a coil  43  that is concentric with the axis of rotation  5  ( FIG. 3 ) providing a resonance circuit. The change in dielectric value between the capacitor plates of the sensor elements  42   a ,  42   b  causes a change in resonance frequency. The resonance frequency can be picked up by an external sensor, which also regularly will excite the resonance circuit. In this way the liquid level in the bowl  2  may be monitored during operation of the decanter centrifuge  1 , and the slide valve body  40 , if comprising a drive means as described above, may instantly be rotated in response to the liquid level measurement. 
     In the embodiment shown, the slide valve body  40  is provided on the internal side of the base plate  6 . However, the slide valve body  40  may in principle also be mounted on the external side, i.e. opposite the internal side, of the base plate, e.g. between the base plate and an external liquid phase discharge member mounted on the base plate  6  for the purpose of energy recovery. In case the slide valve body  40  is mounted on the external side of the base plate  6  it is, however, preferable if the sensor elements  42   a ,  42   b  are still mounted internally in the bowl  2  of the decanter centrifuge  1  to ensure correct measurement of the liquid level. 
       FIG. 3  shows a close up of a section of a base plate  6  seen from the end in the longitudinal direction. As can be seen the slide valve body  40  has been rotated counter clockwise from a neutral position shown in  FIG. 2 , such that it partially covers the outlet opening  9 . The liquid discharged through the outlet opening is thus forced out where the radius of the outlet opening is smaller, the edge  44 , which extends radially, of the slide valve body  40  thus determining the liquid level in the bowl. The outlet opening  9  may even be closed by means of the slide valve body  40 . 
     Since the size and shape of the openings  45  of the slide valve body  40  are substantially identical to the size and shape of the outlet openings  9 , the openings  45  of the slide valve body  40  comprise edges parallel to the weir edges  22  of the outlet openings  9 . Rotating the slide valve body  40  from the neutral position in the opposite direction compared to the situation in  FIG. 3 , i.e. rotating the slide valve body  40  clockwise as seen from the external side as in  FIG. 3 , the edges parallel to the weir edges  22  will emerge from behind the weir edges and delimit the open areas of the outlet openings  9 , thus effectively raising the weir edge to a smaller radial position thereby raising the level of liquid inside the bowl  2 . 
       FIG. 4  shows the internal side of a second embodiment of a base plate  6  comprising a slide valve body  40  according to the invention. In this embodiment, the slide valve body comprises two openings corresponding in shape to the two outlet openings  9  of the base plate  6 . Furthermore, the slide valve body  40  is provided with a stop mechanism  41  for limiting the angular interval through which the slide valve body  40  may be rotated. In the embodiment shown the stop mechanism  41  comprises an incision  41   a  extending along the periphery of the slide valve body  40  and determining the angular interval of the rotation and a pin  41   b  or the like blocking the rotation of the slide valve body  40  when it abuts the incision  41   a  as shown on  FIG. 4 . 
       FIG. 5  shows the external side of the second embodiment of the base plate  6 . The base plate  6  is equipped with a decanter centrifuge discharge member  20  in a first embodiment mounted on the base plate such that the axis of rotation  5  extends through a central opening  31 . The decanter centrifuge discharge member  20  may be mounted using screws or the like inserted through first holes  28 . Alternatively, the decanter centrifuge discharge member  20  may be mounted on a decanter centrifuge discharge member base plate (not shown) similar to the base plate  6  shown in  FIG. 5  that may then be mounted on the base plate  6  of the decanter centrifuge  1 . For mounting the decanter centrifuge discharge member base plate there may be provided holes such as second holes  36 . However, in the embodiment shown the second holes  36  are used to mount the base plate  6  on the decanter centrifuge  1 . As another alternative the decanter centrifuge discharge member may simply be cast or moulded in one piece with the base plate  6  of the decanter centrifuge. 
     The decanter centrifuge discharge member  20  and the base plate  6  comprise a plurality of outlet openings  9 . In the embodiment shown in  FIG. 2  there is two such outlet openings  9 . Normally such a plurality of outlet openings are provided in the base plate placed equidistantly on a common radius. 
     As previously mentioned, each outlet opening  9  is delimited by a circumferential edge comprising three parts  22 ,  23 ,  24 . The third part  24  extends in the embodiment shown along a drawing of a circle on the base plate  6 . 
     The weir edge  22  is radially away from the axis of rotation  5  forming a delimitation of the outlet opening  9 , the weir edge  22  extending through the first angular interval  25  and having in the first angular interval  25  in a radial plane perpendicular to the axis of rotation  5  an inclination relative to the radial direction of about 82°, the first angular interval  25  having an extension of about 60 to 65°. It is noted that in this embodiment the general shape of the outlet opening  9  remains uncritical as long as the weir edge  22  is provided in the first angular interval  25  in a radial plane perpendicular to the axis of rotation  5  with an inclination relative to the radial direction preferably being at least 60°. 
     Furthermore the decanter centrifuge discharge member  20  comprises adjacent each outlet opening  9  a wall  21  extending in a direction opposite to the direction of rotation denoted by an arrow  27  through the first angular interval  25  along the weir edge  22  with substantially the same inclination relative to the radial direction as the weir edge  22 . The transition from weir edge  22  to wall  21  is preferably substantially smooth. 
     The wall  21  further extends through the second angular interval  26  towards the rim  29  of the base plate  6  with an inclination relative to the radial direction increasing towards the rim  29 . In the embodiments shown the wall  21  has a total angular extension of approximately 180°, thus ending adjacent the rim  29  at the far end  39  of the wall  21  opposite the outlet opening  9 . At the rim  29 , the inclination of the wall  21  relative to the radial direction has increased from the initial about 82° to about 88° to 90°. Both the angular extension and inclination relative to the radial direction of the wall  21  and the weir edge  22  of the outlet opening  9  may take other values than stated above. However, as a rule of thumb the longer the angular extension of the wall  21  the more efficient the energy recovery obtained. Preferably the angular extension of the wall  21  through the second angular interval  26  is at least 30°. 
     The wall  21  further comprises a raised part  30 , whereby the wall  21  is provided with the shape of an open channel, as will be described in detail below. 
     At the far end  39  of the wall  21  the decanter centrifuge discharge member  20  comprises a discharge area  38 , the liquid phase leaving the wall over the discharge area  38  in a direction substantially opposite the direction of rotation denoted by arrow  27 . 
       FIG. 6  shows an end view of a base plate  6  according to the first embodiment as shown in  FIG. 2  equipped with a decanter centrifuge discharge member  20  in a second embodiment mounted on the base plate. In this embodiment the decanter centrifuge discharge member  20  comprises three outlet openings  9  each with an adjacent wall  21 . Both outlet openings  9  and walls  21  are substantially of the type described above in connection with  FIG. 5 . In this embodiment the decanter centrifuge discharge member  20  is mounted on the base plate  6  by inserting screws or the like through bushings  33  provided in extensions  32  of each wall  21 . 
     The perspective view of  FIG. 6  reveals in more detail that the raised part  30  of the wall  21  provided opposite the base plate  6  serves to provide an open channel  34  for guiding the substance discharged. 
     Furthermore, it can be seen that the second part  23  of the circumferential edge of the outlet opening  9  may be provided with an inclination with respect to a direction parallel with the axis of rotation  5  and pointing in a direction opposite the direction of rotation (arrow  27 ). A transition  37  from the outlet opening  9  to the wall  21  is preferably flush to provide a smooth, lossless flow from the outlet  9  onto the wall  21 , but a small step to a larger radial distance from the axis of rotation may be present in the transition  37  from the outlet  9  to the wall  21 . 
     Turning to  FIG. 7 , a side view of the base plate  6  according to  FIG. 5  with decanter centrifuge discharge member  20  is shown. From  FIG. 7  the course of the wall  21 , and in particular of the raised part  30  of the wall  21 , becomes clearer. As mentioned, the raised part  30  provides an open channel  34 , the curvature of which is marked with a dashed line on  FIG. 7 . As can be seen the width of the channel decreases through the second angular interval  26  in a direction opposite the direction of rotation (arrow  27 ) such that it has its largest width  35   a  between the first angular interval  25  and the second angular interval  26  and its smallest width  35   b  at its far end  39 . 
     It should be noted that the above description of preferred embodiments is merely an example, and that the skilled person would know that numerous variations are possible without departing from the scope of the claims.