APPARATUS FOR AGGLOMERATING OF PARTICLES

Abstract: The invention provides agglomerating apparatus comprising a housing (20) defining a chamber, the chamber having an inlet, the chamber being provided with a rotable blade (28), the blade including a plurality of arms (30a, b, c, d) which divide the chamber into a number of chamber portions (36a, b, c, d), one or more passages being provided connecting one or more chamber portions to one or more other chamber portions. The passages connecting the chambers allow easier loading and unloading of the apparatus and facilitate more even agglomeration of the feed material.

Description: - 1 - APPARATUS FOR AGGLOMERATING OF PARTICLES This invention concerns improvements in and relating to agglomeration of particles, particularly but not exclusively for producing nuclear fuel materials. Nuclear fuel materials are generally produced in the form of powders with closely controlled properties which are formed into pellets by pressing and sintering. As a precursor to pelletising it is known to agglomerate or spheroidise the powder to an extent . It is known from EP-B-0331311 to employ a vertically mounted disc shaped chamber in which a bow-tie or axe-head shaped blade is provided. This and other prior art systems face a number of problems, however. In particular the rate at which the process can achieve the desired degree of spheroidising is limited and inconsistencies in powder distribution can occur within the spheroidiser if it is not very evenly loaded, leading to impaired product forms . The present invention aims to provide apparatus and a method in which the spheroidising process is faster, more efficient, more consistent and easier to operate. According to a first aspect of the invention we provide agglomerating apparatus comprising a housing defining a chamber, the chamber having an inlet, the chamber being provided with a rotatable blade, the blade including a plurality of arms which divide the chamber into a number of chamber portions, one or more passages being provided connecting one or more chamber portions to one or more other chamber portions . Preferably the passages are at least in part defined by and/or provided in the arms. Preferably at least three arms, and more preferably at least four arms are provided. The arms may be at least twice as long radially as their maximum width. The blade may have a volume less than 30% of the volume of the chamber. According to a second aspect of the invention we provide agglomerating apparatus comprising a housing defining a chamber, the chamber having an inlet, the chamber being provided with a rotatable blade, the blade comprising a plurality of arms which divide the chamber into a number of chamber portions, the volume of the blade being less than 30% the volume of the chamber. One or more of the arms may be provided with passages connecting one or more chamber portions to one or more other chamber portions. Preferably at least three arms, and more preferably at least four arms are provided. The arms may be at least twice as long radially as their maximum width. According to a third aspect of the invention we provide agglomerating apparatus comprising a housing defining a chamber, the chamber having an inlet, the chamber being provided with a rotatable blade, wherein the blade comprises three or more arms, the arms being at least twice as long radially as their maximum width. The blade may comprise a plurality of arms which divide the chamber into a number of chamber portions . The volume of the blade may be less than 30% the volume of the chamber. One or more of the arms may be provided with passages connecting one or more chamber portions to one or more other chamber portions. Other features, possibilities and options for the first, second and third aspect of the invention, independently of one another, include the following features. Preferably the arms are configured to occupy substantially all of the edge volume of the chamber at some stage during a revolution of the blade, the edge volume extending for the full axial width of the chamber and at least 2% of the distance from the edge wall of the chamber towards the axis. The edge volume may extend for at least 5%, at least - 3 - 10% or even at least 15% of the distance from the edge wall of the chamber towards the axis of rotation of the blade. Most preferably the arms are configured to occupy substantially all the chamber volume at some stage during a revolution of the blade. The passage (s) may be provided between a side face of an arm and the side face of the chamber. The passage (s) for one arm may be provided between a different side of the one arm and the chamber than between a different arm and the chamber. Preferably the passage (s) are provided on alternating sides for alternating arms . Preferably the separation between side face of an arm and the opposing side face of the chamber is between 5% and 75% of the separation between the two side walls of the chamber. A separation of between 5% and 50%, and more preferably of between 15% and 35% may be provided. Preferably the separation is constant throughout the length of the passage, radially and/or circumferentially . The passage (s) may extend over more than half, and preferably over at least 70% of the distance between the axis of rotation of the blade and the perimeter of the chamber. In a particular embodiment, the passage (s) may extend over 100% of the distance from the outside of the hub to the perimeter of the chamber. In an alternative embodiment of the invention, one or more of the arms may have one or more portions which extend across substantially the entire axial width of the chamber. Preferably the full width portion is provided at the radial end of one or more of the arms . The passage (s) may be provided through one or more of the arms . The volume of the blade is preferably less than 25% of the volume of the chamber, more preferably less than 20% of the volume of the chamber and still more preferably less than 18% of the volume of the chamber. A blade having a volume less than 15% of the chamber and ideally 12% or less than the volume of the chamber may be provided. The blade volume may be taken to include the hub and blade arms . The chamber volume may be taken to include the volume of the chamber within which the blade is provided, including any volume present in the inlet and outlet on the processing side of the inlet and / outlet closing means. Preferably the chamber is a right cylinder with an axis corresponding to the rotational axis of the blade. Preferably one, ideally both, of the axis are provided substantially horizontal. Substantially horizontal may be taken to be less than 20° to the horizontal, less than 10° or even less than 5°. The chamber may be provided with flat end walls and a curved edge wall . The blade arms may be wider, measured in the direction of rotation, at their ends than at an intermediate location. Preferably the minimum width of the arm is between 25% and 50% of the maximum width of the arm. The minimum width of the arm may be provided at the mid-point of the arm length. The maximum width of the arm may be provided adjacent to its end and/or adjacent to the mounting end. The arms may be provided with concave surfaces facing the chamber. The facing and / or trailing sides may be so provided. The concave surfaces may be defined by a radius, in one or more cases . Preferably the radii is the same as that defining the chamber perimeter. Preferably the blade is provided in the form of a Maltese cross . The arms may be mounted on a hub. The hub may be cylindrical . The arms may have an arcuate surface opposing the edge wall of the chamber, potentially of substantially equivalent profile. Preferably the arms have a planar surface opposing the edge wall of the chamber. Preferably the lead edge of the arm, defined by the direction of rotation, is provided with a lower separation between the end of the arm and the chamber wall than the trailing edge. The inlet for the chamber is preferably provided in the edge wall of the chamber. The inlet is preferably provided in the highest point of the chamber. The outlet for the chamber is preferably provided in the edge wall of the chamber. The outlet is preferably provided in the lowest point of the chamber. The outlet may be sealable, most preferably with a closure having an inner surface flush and continuous with the edge wall of the chamber. The inlet may be provided directly above the outlet. The chamber portions may be provided as generally triangular segments, the walls of the segments being defined by curves, most preferably of the same radii. The apparatus or methods of the invention may be used to agglomerate U0 2 and/or Pu0 2 . Fuel additives and/or processing additives, such as agglomeration aids, lubricants and the like may be provided. According to a fourth aspect of the invention we provide a method of agglomerating material, including feeding material to, and removing agglomerated material from, the apparatus according to the first and/or second and/or third aspects of the invention. Most preferably the method provides for the passage of through substantially the entire edge volume, and most preferably the entire volume, of the chamber of one or more arms during a revolution of the blade. The edge volume may be defined as extending for the full axial width of the chamber and at least 2% of the distance from the edge wall of the chamber towards the axis . The edge volume may extend for at least 5%, at least 10% or even at least 15% of the distance from the edge wall of the chamber towards the axis of rotation of the blade. This aspect may include the features, options, possibilities and structures set out elsewhere in this application, including method steps suitable for their implementation . - 6 - Various embodiments of the invention will now be described, by way of example only, and with reference to the accompanying drawings in which : - Figure 1 illustrates a prior art spheroidiser apparatus ; Figure 2 illustrate a spheroidiser according to one embodiment of the present invention; Figure 3 is an isometric view of the blade of the spheroidiser of Figure 2; Figure 4 illustrates a detail of the hub to blade junction for the spheroidiser of Figure 2; and Figure 5 details the material exit from the spheroidiser. The prior art spheroidiser of Figure 1 consists of a body 2 which defines a disc shaped internal space 4 in which the processing occurs. The space 4 is provided with a pivotally mounted blade 6 having the general configuration of a bow-tie or axe-head. The thickness of the blade 6, into the page as shown, equates to the depth of the disc space 4, with a close tolerance between the two,- the tolerance excludes material being processed. Material to be processed is introduced into the two chambers 8, 10 separately and the inlet 12 is closed. The blade 6 is then rotated for the necessary time period and the processed material is then extracted through outlet 14 for on going processing. The design of the spheroidiser, however, means that precautions and great care have to be taken to avoid any discrepancies between the load levels and/or the materials loaded into the respective chambers 8, 10. Failure to take such measures may embody itself in the material contained in one chamber having been spheroidised whereas the material in the other is still not finished. This would result in delay whilst that material is finished and impair the properties of the ready chamber material as that material is then over spheroidised . - 7 - The spheroidiser of the present invention is embodied by the structure illustrated in Figure 2. Once again the body 20 defines a disc shaped space 22 with its axis mounted at 90° to the vertical. Material is fed in through inlet 24 and is removed after processing through outlet 26. The blade 28 is very different in profile to the prior art blade, however. The blade 28 has the general profile of a Maltese cross, with four arms 30a, 30b, 30c and 30d, each of which is scooped out to define a curved surface 32 on each side of the arm. The curved surface 32 enhances the speed of spheroidising and is defined by a radius equivalent to that defining the disc chamber 22. The arms 30 end in a surface 33 presenting a planar surface to the curve of the disc wall and are provided with a tolerance to closely fit that curve. The tolerance is lower at the leading edge 35, with an increased gap at the trailing edge 37; a scrapping action is thus provided. The arms 30 are mounted on a central hub 34 which is pivotally mounted through the body 20 to drive means. The arms define four equivalent sized chambers 36a, 36b, 36c, 36d. When provided in this way the mass of the blade 28 is low, thus only a low power for the drive motor is needed. The volume of the working chambers 36 is also increased and the volume occupied by the blade 28 reduced when compared with the prior art. This enhances the rate at which spheroidising is achieved due to the increased tumbling volume. A rate four times that of the axe-head spheroidiser can be achieved. As can be seen in Figure 4 and the isometric view of Figure 3, the arms 30 on the blade 28 do not extend across the full depth of the disc space 22, comparable to the extent of the hub 34. Arm 30a is provided such that its face 38 is substantially flush with the front wall 39 of the disc space 22, but is spaced from the rear face 41 of the disc space 22 such that a significant gap 40 is present between the rear face 41 and the face 42 of the arm 30a. - 8 - The arms 30b and 30d, see Figure 3, which are next to arm 30a around the perimeter of blade 28 are similarly spaced. In this case, as illustrated in Figure 4 with reference to arm 30b, the gap 44 is presented to the front face 39 of the disc space 22 and with the rear face 46 of the arm flush with the rear face 41 of the disc space 22. Arm 30c is provided in an equivalent manner to arm 30a. In each case the gap 40, 44, is approximately a quarter of the front face 39 to rear face 41 distance of disc space 22, see Figure 4. The gaps 40, 44 offer many benefits to the process. Due to transfer of material through the gaps even distribution of the load is achieved, no matter how unevenly the material is introduced. Particularly during the early stages the transfer of material through the gaps also provides for thorough mixing of materials in each of the chambers 36 with one another. This achieves a more homogeneous product in terms of materials introduced on loading and additives introduced part way through the spheroidising process. Improved spheroidising and improved lubricant distribution also result in less material being held up within the apparatus at the end of the process. This reduction is particularly beneficial in the nuclear industry where highly stringent accounting of the locations of material must be provided and where the possibility of material from one batch entering another must be minimised. The provision of the gaps on opposing sides of the chamber has significant advantages too in terms of the effectiveness of the spheroidising. This configuration facilitates the transfer of material between chambers but also ensures that all of the chamber volume is active in terms of the processing material. Material lying on the bottom of the chamber which is passed by one arm, due to the gap in that arm, is invariably swept by the next arm around. Ensuring all the material is processed, there being no dead spaces in the chamber, again reduces hold-up as all the material is spheroidised evenly. - 9 - In processing material the blade 28 is initially rotated and the full amount of the fuel material 100, pre-homogenised U0 2 and Pu0 2 , and the lubricant to be processed is introduced into the space 22 under gravity. Once loaded the blade 28 is run at the spheroidising speed and is kept at that rotational speed until spheroidising reaches the desired extent. The same blade speed is then used at the end of the process during discharge. To facilitate discharge through outlet 26, Figure 5, the outlet 26 is sealed by a flap valve 156 which hinges down to allow material 102 to fall from the disc space 22 under the influence of gravity. The hinge is aligned perpendicular to the axis of rotation. The process can then be repeated for further batches of material . The term spheroidising should not be taken as referring to the production of only spherical granules a variety of other shapes may be sought and achieved, for instance through agglomeration of the feed material . The entire assembly is provided within a glove box environment due to the nature of the materials being handled. For maintenance purposes the front plate of the body 20 can be removed to allow access to the space 22 and the blade 28. The same removal unit can also, having stored away the front face of the body, be used to remove the blade 28 from the apparatus for repair or replacement . The invention in its various forms and embodiments offers a system which is particularly advantageous in the manufacture of nuclear fuels, but which is also applicable to other industries and processes involving the processing of powders too.

Claims: - 10 - CLAIMS : 1. Agglomerating apparatus comprising a housing defining a chamber, the chamber having an inlet, the chamber being provided with a rotatable blade, the blade including a plurality of arms which divide the chamber into a number of chamber portions, one or more passages being provided connecting one or more chamber portions to one or more other chamber portions. 2. Apparatus according to claim 1 in which the passage (s) are provided between a side face of an arm and the side face of the chamber . 3. Apparatus according to claim 2 in which the passage (s) for one arm are provided between a different side of the one arm and the chamber than between a different arm and the chamber . 4. Apparatus according to claim 3 in which the passage (s) are provided on alternating sides for alternating arms . 5. Apparatus according to any of claims 2 to 4 in which the separation between side face of an arm and the opposing side face of the chamber is between 5% and 75% of the separation between the two side walls of the chamber. 6. Apparatus according to any preceding claim in which the passage (s) extend over at least 70% of the distance between the axis of rotation of the blade and the perimeter of the chamber. 7. Agglomerating apparatus comprising a housing defining a chamber, the chamber having an inlet, the chamber being provided with a rotatable blade, the blade comprising a plurality of arms which divide the chamber into a number of chamber portions, the volume of the blade being less than 30% the volume of the chamber . - 11 - 8. Apparatus according to claim 7 in which the volume of the blade is less than 18% of the volume of the chamber. 9. Agglomerating apparatus comprising a housing defining a chamber, the chamber having an inlet, the chamber being provided with a rotatable blade, wherein the blade comprises three or more arms, the arms being at least twice as long radially as their maximum width. 10. Apparatus according to claim 9 in which the blade arms are wider at their ends than at an intermediate location. 11. Apparatus according to claim 9 or claim 10 in which the minimum width of the arm is between 25% and 50% of the maximum width of the arm. 12. Apparatus according to claim 11 in which the minimum width of the arm may be provided at the mid-point of the arm length, between its end and the hub. 13. Apparatus according to claim 11 or claim 12 in which the maximum width of the arm is provided adjacent to its end and/or adj acent to the hub . 14. Apparatus according to any preceding claim in which the blade is provided in the form of a Maltese cross. 15. A method of agglomerating material, including feeding material to, and removing agglomerated material from, the apparatus of any of claims 1 to 14. 16. The method of claim 15 in which the material agglomerated is U0 2 and/or Pu0 2 , with or without agglomeration aids and/or lubricants .

Inventors: BURNS PAULA JOANNE, RICHARDSON ALAN NORMAN, BURNS, PAULA, JOANNE, RICHARDSON, ALAN, NORMAN
Applicants: BRITISH NUCLEAR FUELS PLC, BURNS PAULA JOANNE, RICHARDSON ALAN NORMAN, BURNS, PAULA, JOANNE, RICHARDSON, ALAN, NORMAN
Application year: 1999
Main classification: B01J2
IPC codes: B01F7, B01J2, C01G43, C01G56, G21C21