Abstract:
A fully jacketed screw centrifuge includes a rotatable drum having a horizontally oriented rotational axis, a rotatable screw arranged in the drum, and at least one discharge opening oriented at an angle to the rotational axis of the fully jacketed screw centrifuge for discharging solid from the drum in the jacket of the drum. A collecting chamber for solid, which surrounds the drum that rotates during operation in some sections and which does not rotate during operation, is associated with the at least one discharge opening. At least one hose segment not circumferentially closed in the cross-section is arranged in the collecting chamber.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
       [0001]    Exemplary embodiments of the invention relate to a solid bowl screw centrifuge. 
         [0002]    German patent document DE 43 20 265 A1 and PCT International patent document WO 2004/058409 A1 disclose solid bowl screw centrifuges. 
         [0003]    German patent document DE 42 38 568 A1 illustrates in  FIG. 1  how dirt can accumulate in a solids capture chamber when a solid bowl screw centrifuge is in operation. This necessitates repeated cleaning of the solids capture chamber in order to avoid operating impairments caused by blockages or even damage to the rotating system. 
         [0004]    To solve this problem, U.S. Pat. No. 3,399,828 discloses forming at the solids discharge of a solid bowl screw centrifuge, at its tapering end, a solids capture chamber in which is arranged, tension-mounted, an elastic air-impermeable diaphragm covering an air duct that is closed off, air-tight, with respect to the surroundings and with respect to the actual solids capture chamber. By the action of compressed air, pressure fluctuations can be generated at the diaphragm which set the latter in oscillation, thus serving to release dirt from the walls of the capture chamber, here the diaphragm. 
         [0005]    Although the problem of dirt is reduced in this way, the problem still appears to be the relatively high outlay in terms of apparatus and structure for generating pressure fluctuations at the elastic diaphragm. Furthermore, it is relatively difficult to change the diaphragms, since the diaphragms repeatedly have to be mounted, pressure-tight, in the solids capture chamber. 
         [0006]    Exemplary embodiments of the invention are directed to eliminating this problem. 
         [0007]    According to the invention, advantageously, in spite of dispensing with a chamber that is closed by an elastomer and in which a pressure gradient can be generated by the action of compressed air, movements in the elastomeric element in the solids capture chamber are sufficiently generated, solely by the impact of the solid, in order to release dirt. The number of cleanings of the solids capture chamber can consequently be reduced, compared with solids capture chambers without an elastomeric element. Moreover, maintenance work is simplified as compared with solutions with a pressure chamber in which a pressure gradient can be generated, since the elastomer no longer has to be arranged so as to be pressure-tight. Moreover, as compared with such solutions, there is no need for the means required for generating the pressure gradient (for example, a controllable pump). 
         [0008]    A further advantage is the noise reduction achieved, since the impingement momentum of the solids is effectively decoupled vibrationally from the stand or the noise-radiating surface of the centrifuge, and since the hose segment implements a dual-shell structure which has a noise-insulating effect. This is also advantageous especially in the case of harder and coarse solids and when there is a high discharge of solids for a unit time (or high solids performance). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0009]    The invention is explained in more detail below by means of exemplary embodiments, with reference to the drawing in which: 
           [0010]      FIG. 1  shows a section through part of a solid bowl screw centrifuge with a known solids capture chamber; 
           [0011]      FIG. 2  shows a section though a solids capture chamber configured according to the invention for a solid bowl screw centrifuge particularly of the type of  FIG. 1 ; 
           [0012]      FIG. 3  shows a section through a solids capture chamber of the solid bowl screw centrifuge of  FIG. 1  in the dirty state; and 
           [0013]      FIGS. 4 and 5  show sections through further solids capture chambers configured according to the invention, in each case for a solid bowl screw centrifuge particularly of the type of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]      FIG. 1  shows a solid bowl screw centrifuge with a non-rotatable housing  1  (or a hood-like cover), in which is arranged a rotatable drum  3  which has a horizontal axis of rotation D. Furthermore, a screw  5  preferably rotatable at a differential rotational speed with respect to the drum  3  is arranged in said drum  3 . 
         [0015]    The drum  3  and the screw  5  each have an essentially cylindrical portion  3   a ,  5   a  and a tapering portion  3   b ,  5   b  adjoining the latter. The screw blade  7  surrounds both the cylindrical region and the tapering region of the screw body  9 . 
         [0016]    Furthermore, the drum  3  also has a further cylindrical portion  3   c  adjoining the conically tapering portion  3   b  and which defines a co-rotating solids discharge chamber  11 . 
         [0017]    An axially extending centric inflow pipe  13  feeds the centrifugable material via a distributor  9  into the centrifuging space  15  between the screw  5  and the drum  3 . 
         [0018]    If, for example, a sludgy pulp is conducted into the centrifuge, solid particles settle on the drum wall. A liquid phase is formed further inward. 
         [0019]    The mounted screw  5  (bearing  17   a ) rotates at a somewhat lower or higher speed than the rotatably mounted drum  3  (bearing  17   b ) and conveys the ejected solids toward the conical portion  3   b  and, furthermore, to the cylindrical solids discharge chamber  11  adjoining the screw in the axial direction and located in the second cylindrical region  3   c  of the drum  3 , the solids discharge chamber in turn being provided with at least one solids discharge port  19  leading out of the drum  3  radially outward. This outlet port may also be oriented at an angle to the radial, for example in order to achieve an energy-saving repulse effect in the circumferential direction (not illustrated here). 
         [0020]    By contrast, the liquid flows to the larger drum diameter at the rear end of the cylindrical portion of the drum  3  and is diverted there at overflow ports  21 , here with an adjustable weir  23 . 
         [0021]    The solids S emerging from the solids discharge port  19  of the rotating drum  3  collect in a solids capture chamber  25  which surrounds the solids discharge chamber annularly and of which the cross-section, here of the rectangular type, can be seen in  FIGS. 1 and 3 . This cross section is preferably provided, but is not mandatory. A diverting pipe may exit preferably vertically downward (not illustrated here) from the solids capture chamber or a capture container may be provided in order further to divert or to capture the sludgy solids which have emerged. 
         [0022]      FIG. 3  illustrates that, when the solids bowl screw centrifuge is in operation, accretions  27  may form in the solids capture chamber  25  and therefore the latter has to be cleaned repeatedly. 
         [0023]    In order to reduce the number of cleaning operations, as illustrated in  FIG. 2 , a hose segment  29  is arranged in the solids capture chamber of a solid bowl screw centrifuge (for example, but not necessarily, of the type of  FIG. 1 ). The hose segment  29  has a non-planary cross section and is preferably not circumferentially closed in cross-section on the circumference (see  FIG. 3 ). This hose segment  29  is preferably arranged virtually in the form of a ring in the solids capture chamber, so that the hose segment surrounds the drum in the region of the solids discharge port  19  virtually completely, preferably with the exception of an outlet port into a diversion or a capture container (not illustrated here). 
         [0024]    The cross-section, in the section perpendicular to the chamber, is preferably non-planar, but preferably C-shaped, U-shaped or Ω-shaped, the open side of the C, of the U or of the Ω facing the solids discharge port  19 . The non-circumferentially closed region  35  of the hose segment  29  therefore faces the discharge port  19 . The two open margins of the hose segment may be fastened to small webs  31 ,  33 . The margins are oriented parallel to one another here. 
         [0025]    During operation, solids are thrown through the discharge port or discharge ports  19  into the solids capture chamber  25  where they impinge onto the inside, facing the discharge port or discharge ports  19 , of the hose segment  29 . As a result, (essentially oscillation-like) movements M are excited in the hose segment  29  moveable elastically per se, which movements prevent the accretion of solids or contribute to releasing accreting solids from the hose segment again. 
         [0026]    The number of cleanings can be reduced in this way. Moreover, it is easy to change the hose segment  29 , since the chamber or the space  37  “behind” the hose segment  29  does not have to be or is not designed to be pressure-tight. 
         [0027]    As can be seen in  FIG. 2 , the hose segment  29  may bear directly, in a region preferably spaced apart from the fastening regions (here at the webs  30 ,  31 ) in the solids capture chamber  25 , here in a region on the outside, facing away from the discharge port  19 , of the hose segment, against an inside  38  of a wall  39  of the solids discharge chamber  11  (u-shaped in section here and formed from walls oriented at right angles to one another). As a result, during operation, pronounced movements (arrows M) occur particularly in the region of the corner zones. This is advantageous because these are also the regions where deposits are preferentially formed. 
         [0028]    As can be seen in  FIG. 4  however, the hose segment  29  may also be arranged so as to be spaced apart (gap G) from the inside  38  of the walls of the solids discharge chamber  11  completely (apart from the direct or indirect connection to the walls of the solids discharge chamber via the webs  30 ,  31 ). This is particularly advantageous in terms of the generation of noise which is reduced here once again, as compared with  FIG. 2 . Moreover, any point of the hose segment can move freely in order thereby to prevent an accretion of the solids and/or release existing accretions again. 
         [0029]    The hose segment is preferably composed entirely ( FIG. 2 ,  FIG. 4 ) of an elastomer (for example a rubber material) or is formed as a composite part that is composed partially of an elastomer (see  FIG. 5 ) and partially of a non-elastomeric material such as a metal, for example steel or the like. 
         [0030]    According to the advantageous example of  FIG. 5 , the base limb  40  of the hose-shaped segment is composed of metal (or of a coated metal or the like) and the side limbs  41 ,  42  of the u-shaped hose segment are composed of the moveable elastomer. 
         [0031]    The limbs  41 ,  42  are consequently moveable and the base limb  40  is per se immovable. This variant is especially stable and durable since the rigid portion or limb constitutes wear protection. The number of necessary cleaning operations is nevertheless markedly reduced, since, upon the impingement of solids, the base limb  40  is also co-moved via the limbs  41 ,  42 . Moreover, the material can slide off the metal limb especially effectively. 
         [0032]    The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
         Housing  1   
         Drum  3   
         Screw  5   
         Cylindrical portions  3   a ,  3   c ,  5   a    
         Tapering portions  3   b ,  5   b    
         Screw blade  7   
         Screw body  9   
         Solids discharge chamber  11   
         Inflow pipe  13   
         Centrifuging space  15   
         Bearing  17   a, b    
         Discharge port  19   
         Overflow ports  21   
         Weir  23   
         Solids capture chamber  25   
         Accretions  27   
         Hose segment  29   
         Webs  31 ,  33   
         Region  35   
         Space  37   
         Inside  38   
         Wall  39   
         Base limb  40   
         Limbs  41 ,  42   
         Axis of rotation D 
         Movements M 
         Solids S 
         Gap G