Patent Publication Number: US-2006006189-A1

Title: Method and apparatus for manufacturing microfibrillated cellulose fiber

Description:
THE INVENTION relates to a method of controlling the movement of spherical elements and to apparatus for regulating the movement of spherical elements.  
      The Inventors are aware of situations where it is desirable to control the movement of elements from one location to another.  
      One such situation is in a nuclear power plant making use of a high temperature gas cooled reactor of the pebble bed type. Pebble bed reactors make use of spherical fuel elements and spherical moderator elements and it is extremely important that the movement of the spherical elements through the reactor and around the plant be carefully controlled.  
      According to one aspect of the invention there is provided a method of controlling the movement of spherical elements which includes the steps of 
          feeding the spherical elements into a downwardly directed feed path; and     rotating a feed head in the feed path to regulate the movement of the spherical elements through a feed passage which leads from the feed path.        

      The method may include feeding the spherical elements from a container in which the elements are contained into the feed path. Hence the method may be particularly well suited to the dispensing of spherical elements from a container containing the elements.  
      The method may include regulating the rate at which the spherical elements enter the feed passage.  
      Regulating the rate at which spherical elements enter the feed passage may include permitting the spherical elements to enter the feed passage only at one or more predetermined positions of the head.  
      According to another aspect of the invention there is provided regulating apparatus for regulating the movement of spherical elements from one location to another, which apparatus includes 
          a feed path defining means defining a downwardly extending feed path within which spherical elements are receivable;     at least one feed passage leading from the feed path; and     a feed head mounted for rotation in the feed path to regulate the flow of spherical elements from the feed path into the feed passage.        

      The invention may find application particularly in the dispensing of spherical elements from a container containing the elements the feed path then typically extends downwardly from an outlet of the container containing the spherical elements.  
      The feed passage may be dimensioned to permit the passage of spherical elements in single file therethrough.  
      In one embodiment of the invention the feed passage may have an upper end which opens upwardly out of the feed head.  
      The feed head may have ah upper surface which is inclined so as to feed the spherical elements in the feed path towards the upper end of the feed passage. In a preferred embodiment of the invention, the upper surface of the feed head may taper upwardly inwardly from a radially outer edge thereof, the upper end of the passage opening out of the feed head at a radially outer edge region thereof.  
      It will be appreciated that with the arrangement described above, the spherical elements can enter and pass through the feed passage one at a time providing a degree of control of the discharge of the elements from the container. However, it may be desirable to regulate the rate at which the spherical elements are discharged more closely.  
      To this end, the regulating apparatus may include regulating means for regulating the rate at which spherical elements pass through the feed passage. This may be achieved by regulating the rate at which the spherical elements enter the feed passage.  
      Hence, the method may include permitting the spherical elements to enter the feed passage only at one or more predetermined positions of the feed head. In this way the number of spheres entering the feed passage per revolution of the feed head can be closely controlled.  
      The regulating means may include a discontinuous barrier which covers the upper end of the feed passage and inhibits the entry of spheres into the feed passage for part of the rotation of the feed head.  
      The barrier may be formed by a circumferential shoulder which is positioned adjacent the upper surface of the radially outer edge region of the feed head, the shoulder having at least one radially inwardly and downwardly open recess within which recess a spherical element is receivable. Hence under the influence of gravity a spherical element will enter the recess. As the feed head rotates, each time the upper end of the feed passage comes into register with the recess a spherical element will enter the passage. Preferably, a plurality of circumferentially spaced recesses is provided in the shoulder. Hence, the number of spherical elements being discharged per revolution of the feed head will correspond to the number of recesses.  
      In another embodiment of the invention the feed passage has an upper end which opens upwardly into the feed path, a lower end which is angularly offset from the upper end and an intermediate portion extending between the upper and lower ends.  
      The intermediate portion may extend circumferentially adjacent to a radially outer surface of the feed head for at least part of its length. Hence, the lower end may be angularly offset from the upper end in the direction of rotation of the feed head.  
      A plurality of circumferentially spaced feed passages may be provided.  
      The invention extends to a nuclear power plant which includes a spherical element handling system including at least one regulating apparatus of the type described above.  
      The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings. 
    
    
      In the drawings:  
       FIG. 1  shows a schematic sectional elevation of regulating apparatus in accordance with the invention;  
       FIG. 2  shows a schematic sectional elevation, similar to  FIG. 1 , of another regulating apparatus in accordance with the invention;  
       FIG. 3  shows a side elevation taken at  111 - 111  in  FIG. 2 ;  
       FIG. 4  shows a schematic sectional elevation, similar to  FIGS. 1 and 2 , of another regulating apparatus in accordance with the invention;  
       FIG. 5  shows a sectional elevation of the apparatus of  FIG. 4  taken at 90° relative to the elevation of  FIG. 4 ;  
       FIG. 6  shows a plan view of the apparatus of  FIGS. 4 and 5 ;  
       FIG. 7  shows a three-dimensional fragmentary view of the apparatus of FIGS.  4  to  6 ; and  
       FIG. 8  shows a plan view, similar to  FIG. 6 , of yet another regulating apparatus in accordance with the invention. 
    
    
      In  FIG. 1  of the drawings, reference numeral  10  refers generally to regulating apparatus in accordance with the invention.  
      The regulating apparatus  10  is intended for dispensing spherical elements  12 , particularly fuel spheres and/or moderator spheres from a container  14  in which the spherical elements  12  are contained. The container  14  includes a downwardly directed outlet  16  which opens out of a bottom of the container  14 . The bottom of the container  14  is inclined downwardly towards the outlet  16  so as to feed the spherical elements  12  contained therein towards the outlet  16 .  
      The regulating apparatus  10  includes a cylindrical tubular member  18  extending downwardly from the outlet  16  of the container  14 . A feed head  20  is mounted in the cylindrical tubular member  18  such that it is rotatable relative thereto about an axis of rotation  22 . The feed head  20  is dimensioned such that the clearance between the feed head  20  and the inner surface of the tubular member  18  is too small to permit a spherical element  12  to enter therebetween.  
      The feed head  20  comprises a circular cylindrical centre portion  24 , a generally conical upper portion  26  and a tubular stem  28 , the upper portion  26  and stem  28  being provided on opposite sides of the centre portion  24 . The stem  28  typically functions as a drive shaft.  
      The upper portion  26  has an upper surface or crown  30  which slopes downwardly outwardly from the centre thereof towards the radially outer edge thereof.  
      A feed passage  32  extends downwardly through the feed head  20 . More particularly, the feed passage  32  has an upper end  32 . 1  which opens upwardly out of the crown  30  in a radially outer edge portion thereof. Initially, the feed passage  32  extends vertically downwardly from its upper end  32 . 1  whereafter it extends downwardly and radially inwardly towards the centre of the feed head  20  and then downwardly through the stem or drive shaft  28 . A drive mechanism (not shown) will typically be drivingly connected to the drive shaft  28  whereby the shaft and hence the feed head  20  is rotatable about the axis  22 .  
      In the embodiment described above, the tubular member  18  defines a feed path  34 .  
      In use, the spherical elements  12  are fed under the influence of gravity through the outlet  16  and down the feed path  34  where they accumulate on top of the feed head  20 . In addition, by virtue of the inclination of the crown  30 , the spherical elements  12  are urged radially outwardly and downwardly. As the feed head  20  rotates about the axis  22 , the spherical elements will be arranged in a circular row of spherical elements along the radially outer edge portion of the crown  30 . As the spherical elements  12  line up with the upper end  32 . 1  of the feed passage  32  they fall downwardly into the feed passage, under the influence of gravity. In this way, the discharge of the spherical elements can be controlled. However, the possibility does exist that strings of spherical elements may be discharged and it may be desirable to control the rate at which the spherical elements are discharged more closely.  
      Hence, in another embodiment of the invention, shown in  FIGS. 2 and 3  of the drawings, in which unless otherwise indicated, the same reference numerals are used to designate similar parts, a tubular insert  40  is positioned within the member  18 .  
      Typically, the wall thickness of the insert  40  will be slightly larger than the diameter of a spherical element  12 . A plurality of inwardly and downwardly opening recesses  42  is provided in a lower edge of the insert  40 , the recesses  42  being separated by circumferentially extending lands  44 . Each recess  42  will typically be dimensioned such that a single spherical element  12  is receivable therein.  
      Hence, in use, in this embodiment of the invention, the spherical elements  12  will be urged under the influence of gravity downwardly so that a spherical element  12  will enter each of the recesses  42 . When the upper end  32 . 1  of the feed passage  32  is in register with one of the lands  44  then the feed path  34  is essentially blocked off inhibiting the entry of a spherical element therein. However, when the upper end  32 . 1  comes into register with one of the recesses  42 , the spherical element positioned in the recess falls into the feed path  34  and can be discharged at a desired location in the usual manner. In this way, the number of spherical elements discharged per revolution of the feed head  20  can be closely controlled.  
      Naturally, dimensions of the components of the regulating apparatus could vary. However, the Inventors believe that the feed path  34  will typically have an internal diameter which is at least six times the diameter of the spherical elements with which the regulating apparatus is intended for use.  
      The Inventors believe that regulating apparatus in accordance with the invention will permit a controlled discharge of spherical elements. In addition, the Inventors believe that the apparatus will inhibit the formation of blockages as a result of bridge building. Further, the apparatus will permit the unloading of spheres to be interrupted, e.g. by stopping the feed head in a position in which the upper end  32 . 1  of the feed passage  32  is in register with one of the lands  44 . The apparatus will also permit the discharge of spherical elements in a manner which reduces the risk of damage to the spherical elements. In addition, by virtue of the relative simplicity of the apparatus, the Inventors believe that it will be reliable in operation.  
      Reference is now made to FIGS.  4  to  7  of the drawings, in which reference numeral  50  refers generally to part of another regulating apparatus in accordance with the invention and, unless otherwise indicated, the same reference numerals used above are used to designate similar parts  
      In this embodiment of the invention, the feed passage  32  does not extend through the drive shaft  28 . Accordingly, the drive shaft need not necessarily be hollow although this possibility is not excluded.  
      Further, the tubular member  18  has a portion of generally increased wall thickness, generally indicated by reference numeral  52 . The wall thickness increases downwardly such that a portion  18 . 1  of a radially inner surface of the tubular member  18  tapers inwardly downwardly.  
      The feed passage  32  has an upper end  54  which opens upwardly out of the surface  18 . 1 . The feed passage  32  further has a lower end  56  which is inclined downwardly and spaced angularly from the upper end  54  and an intermediate portion  58  extending between the upper end portion  54  and the lower end portion  56 . The upper end portion  54  and intermediate portion  58  are defined by a recess in the tubular member  18  and a surface of the feed head  20 .  
      The dimensions of the feed passage  34  are selected such that the spherical elements  12  can enter and pass along the feed passage  32  one at a time.  
      In use, the feed head  20  is rotated in the direction of arrow  60 . This serves to agitate the spherical elements  12  within the tubular member  18  so that they become aligned with and enter the upper end  54  of the feed passage  32 . The spherical elements move downwardly, under the influence of gravity, into the intermediate portion  58  of the feed passage  32  and are transported therealong as a result of the rotation of the head  20 . The spherical elements  12  then come into register with the lower end  56  of the feed passage  32  and are discharged, under the influence of gravity, therethrough.  
      Reference is now made to  FIG. 8  of the drawings, in which reference numeral  70  refers generally to part of yet another regulating apparatus in accordance with the invention and, unless otherwise indicated, the same reference numerals used above, are used to designate similar parts.  
      The main difference between the apparatus  70  and the apparatus  50  is that, whereas in the apparatus  50  a single feed passage  32  is provided, in case of the apparatus  70 , two angularly spaced feed passages  32  are provided. Naturally, any number of feed passages could be provided.  
      A cavity  80  ( FIG. 5 ) is provided below the feed head  20  within which dust and wear products are receivable without influencing the operation of the apparatus.  
      The Inventors believe that by not routing the feed passage through the drive shaft  28 , the drive arrangement can be simplified. This further leads to a reduction in the radiation hazard to maintenance and operating personnel. The Inventors further believe that the apparatus shown in FIGS.  4  to  8  of the drawings will further reduce the risk of damage to the spherical elements.