Abstract:
A solid-bowl screw centrifuge with a centrifuge drum that can rotate about a longitudinal axis during operation is created, at least one discharge opening being provided on the front wall thereof for clarified product to flow out of the centrifuge drum, a weir edge delimiting the discharge opening toward the outside radially and an energy recovery device for recovering energy from the clarified product being designed therewith. The energy recovery device is designed as a discharge pipe, which is located on the outside in front of the discharge opening and through which clarified product passes as it is discharged.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a solid-bowl screw centrifuge with a centrifuge drum, which can be rotated about a longitudinal axis during operation, on whose front side are embodied at least one discharge opening for allowing clarified product to flow out of the centrifuge drum, a weir gate bordering the discharge opening toward the outside radially and an energy recovery device for recovering energy from the clarified product discharged. Furthermore, the invention also relates to one such energy recovery device for mounting on a front wall of a centrifuge drum. 
         [0003]    2. Description of the Related Art 
         [0004]    It is known in general that a plurality of discharge openings may be provided on the front wall of the centrifuge drum of a generic solid-bowl screw centrifuge, so that the clarified product can flow out through the opening by way of a respective weir gate. The weir edge forms the radially inner edge of a respective weir gate, which is mounted on the front wall of the centrifuge drum so that it is radially adjustable. 
         [0005]    In order for the kinetic energy of the product discharged to be reusable for driving the rotational movement of the centrifuge drum, energy recovery devices are now provided on such weir edges. It is thus known that, among other things, deflecting devices may be provided on the front wall of a centrifuge drum, so that the flow of clarified product can be diverted in a tangential direction. The product, which is then emerging from the centrifuge drum, not axially but instead tangentially opposite the direction of rotation of the centrifuge drum, transmits a momentum to the centrifuge drum in the direction of rotation, driving the centrifuge drum in the direction of rotation accordingly. Such deflecting devices are known from WO 2012 013624 A2, for example. 
         [0006]    The invention is based on the object of creating a solid-bowl screw centrifuge which has a particularly effective energy recovery device. 
       SUMMARY 
       [0007]    This object is achieved according to the invention with a solid-bowl screw centrifuge having a centrifuge drum that can rotate about the longitudinal axis during operation, such that at least one discharge opening for discharge of clarified product out of the centrifuge drum is formed on its front edge, a weir edge bordering the discharge opening toward the outside radially and an energy recovery device for recovering energy from the clarified product discharged also being formed there. The energy recovery device is designed as a discharge pipe, which is located upstream from the discharge opening and through which the clarified product flows out. 
         [0008]    This object is also achieved with an energy recovery device that has been adapted for direct mounting axially on the outside in front of the respective discharge opening and is designed as a discharge pipe through which clarified product is discharged. 
         [0009]    In the solid-bowl screw centrifuge according to the invention, the discharge opening in the front wall of the centrifuge drum extends essentially transversely to the longitudinal axis of the centrifuge. The weir edge, which may be aligned at least slightly, advantageously obliquely to the longitudinal axis, is situated radially on the outside of the discharge opening. The energy recovery device according to the invention, which is designed as a pipe that is closed over essentially its entire circumference, is situated on the outside directly axially in front of the discharge opening, essentially at the height and/or the radius of the weir edge. Such a pipe thus forms a discharge conduit, which is closed over its entire circumference on the outside axially, in front of the discharge opening. On the outside radially with respect to the longitudinal axis, this discharge pipe acts like a discharge channel and/or a discharge trough and at the same time is closed on the inside radially with respect to the longitudinal axis. 
         [0010]    The approach according to the invention is based on the finding that the energy recovery effect of energy recovery devices of the aforementioned type is based in particular on this energy recovery device being closed on the inside radially. With this design, the product discharged through the energy recovery device is protected from external aerodynamic influences within the energy recovery device. Otherwise the air on the outside of the centrifuge drum, which is rotating at a high speed, will have a substantial influence on the product discharged, so that it loses a portion of its energy content due to friction with this air. This energy loss is prevented with the approach according to the invention, so that more energy can be recovered from the product discharged out of the device. With the approach according to the invention, the product discharged can be deflected from the axial direction essentially into the tangential direction in a particularly homogeneous and targeted manner. At the same time, energy losses occurring due to the diversion of the product discharged in the radial direction can be prevented. When using the discharge pipe according to the invention, the product discharged is held largely at the radius of the respective weir edge during the deflection, the discharge pipe being arranged on the outside axially in front of the discharge opening, so that even minor changes in the radius of the flow path may be advantageous, as will be explained below. 
         [0011]    In the case of such a solid-bowl screw centrifuge, the centrifuge drum may advantageously be equipped so that it can rotate in two opposing directions. With the discharge pipe, the clarified product discharged is preferably deflected in the direction opposite the respective direction of rotation of the centrifuge drum. The energy recovery device according to the invention may also be designed with two active surfaces as the discharge pipe, one active surface of which manifests an effect in the first direction of rotation and the second direction of rotation manifests its effect in the second direction of rotation. 
         [0012]    In the case of the solid-bowl screw centrifuge according to the invention, the discharge pipe is advantageously designed with at least one section having an essentially straight flow path, which is set at an inclination to the longitudinal axis of the centrifuge drum at an angle between 45° and 85°, preferably between 55° and 65°. The discharge pipe according to the invention also preferably has at least one section with an essentially straight flow path, which is set at an inclination radially toward the inside by an angle of 4° to 28°, preferably 8° to the tangential direction at the discharge opening. The bottom surface of such a section is especially advantageously designed to be flat for at least a portion and/or to be largely flat. Such a bottom surface can be produced especially favorably in terms of the manufacturing technology. In addition, the product discharged thereon experiences a uniform acceleration over a longer distance, so it is comparatively easy to reconstruct technically by modeling. The acceleration leads to an increased conversion of the centrifugal momentum into a kinetic momentum directed tangentially. As a particularly large component of the centrifugal energy, it is converted into a tangentially directed drive energy. The planar section of the bottom surface is especially preferably inclined radially inward by an angle of 4° to 28°, preferably 8° to the tangential direction. Such an alignment of the deflected product stream causes deceleration of the outgoing product, which is predefined in a targeted manner in comparison with a purely tangential flow and this leads to a precisely predetermined stagnation effect. This stagnation leads to an increase in the potential energy of the product discharged and thus an improved subsequent conversion into tangential kinetic energy. 
         [0013]    Furthermore, the discharge pipe according to the invention preferably has a discharge mouth with a flow path and/or a direction of flow, which is set obliquely at an angle between 70° and 90°, preferably between 77° and 83° with respect to the longitudinal axis of the centrifuge drum. With such a direction of flow, the product discharged is deflected from axially at first to essentially tangentially, i.e., transversely to the former. Deflection to less than 90° with respect to the longitudinal axis entails the advantage that the product exiting the discharge mouth is not directed as sharply against the front wall of the centrifuge drum and therefore the friction losses are lower. 
         [0014]    The approach according to the invention also advantageously provides a solid-bowl screw centrifuge in which the discharge pipe is designed with a flow cross section of a constant size in the direction of flow of the clarified product discharged. Alternatively, the discharge pipe is designed with a diminishing flow cross section, in particular tapering conically in the direction of flow of the clarified product discharged. A non-tapering flow shape reduces the risk of blockage of the discharge pipe during operation of the respective solid-bowl screw centrifuge. A tapering pipe shape creates an additional stagnation effect, which results in improved energy recovery. 
         [0015]    With the solid-bowl screw centrifuge according to the invention, the discharge pipe is also preferably designed with a round cross section, in particular a circular or elliptical cross section. Alternatively, the discharge pipe is designed with a rectangular cross section, in particular a square cross section. The two cross-sectional shapes mentioned above lead to energy recovery devices that are particularly inexpensive to manufacture. Furthermore, these cross sections are especially suitable for allowing the product discharged to flow out in a predetermined manner. A rectangular cross section also has the advantage that the product discharged emerges at the respective discharge mouth at a predefined radius on a wide plane. 
         [0016]    Finally, with the solid-bowl screw centrifuge according to the invention, the discharge pipe is preferably designed with an adapted aerodynamic exterior wall shape. The flow resistance of the energy recovery device and thus the respective energy loss can be reduced with this exterior wall shape. An aerodynamically adapted exterior wall shape is understood here to be a shape which offers the least possible flow resistance for oncoming air. Such a shape is rounded with no edges and is provided with a smooth surface with very little roughness. 
         [0017]    An exemplary embodiment of the approach according to the invention is described in greater detail below on the basis of the accompanying schematic drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  shows a longitudinal section through a centrifuge drum with a weir gate and an energy recovery device of a solid-bowl screw centrifuge according to the prior art. 
           [0019]      FIG. 2  shows the longitudinal section II-II in  FIG. 1 . 
           [0020]      FIG. 3  shows a side view of a centrifuge drum with a weir gate and an energy recovery device of a first exemplary embodiment of a solid-bowl screw centrifuge according to the invention. 
           [0021]      FIG. 4  shows the longitudinal section IV-IV according to  FIG. 3 . 
           [0022]      FIG. 5  show the view V according to  FIG. 4 . 
           [0023]      FIG. 6  shows a side view of centrifuge drum with a weir gate and an energy recovery device of a second exemplary embodiment of a solid-bowl screw centrifuge according to the invention. 
           [0024]      FIG. 7  shows the longitudinal section VII-VII according to  FIG. 6 . 
           [0025]      FIG. 8  shows the view VIII according to  FIG. 7 . 
           [0026]      FIG. 9  shows a side view of a centrifuge drum with a weir gate and an energy recovery device of a third exemplary embodiment of a solid-bowl screw centrifuge according to the invention. 
           [0027]      FIG. 10  shows the longitudinal section X-X according to  FIG. 9 . 
           [0028]      FIG. 11  shows the view XI according to  FIG. 10 . 
           [0029]      FIG. 12  shows a side view of a centrifuge drum with a weir gate and an energy recovery device of a fourth exemplary embodiment of a solid-bowl screw centrifuge according to the invention. 
           [0030]      FIG. 13  shows the longitudinal section XIII-XIII according to  FIG. 12 . 
           [0031]      FIG. 14  shows the view XIV according to  FIG. 13 . 
           [0032]      FIG. 15  shows a side view of a centrifuge drum with a weir gate and an energy recovery device of a fifth exemplary embodiment of a solid-bowl screw centrifuge according to the invention. 
           [0033]      FIG. 16  shows the longitudinal section XVI-XVI according to  FIG. 15 . 
           [0034]      FIG. 17  shows the view XVII according to  FIG. 16 . 
           [0035]      FIG. 18  shows the longitudinal section XVIII-XVIII according to  FIG. 19  of a centrifuge drum with a weir gate and an energy recovery device of a sixth exemplary embodiment of a solid-bowl screw centrifuge according to the invention. 
           [0036]      FIG. 19  shows a side view of a centrifuge drum according to  FIG. 18 . 
           [0037]      FIG. 20  shows the longitudinal section XX-XX according to  FIG. 21  of a centrifuge drum with a weir gate and an energy recovery device of a seventh exemplary embodiment of a solid-bowl screw centrifuge according to the invention. 
           [0038]      FIG. 21  shows a side view of a centrifuge drum according to  FIG. 20 . 
       
    
    
     DETAILED DESCRIPTION 
       [0039]      FIGS. 1 and 2  show the centrifuge drum  12  of a solid-bowl screw centrifuge  10  with its front end, i.e., front wall  14 . On the front wall  14  can be seen one of several discharge openings  16  passing axially through the front wall  14  in the direction of a longitudinal axis  18  of the centrifuge drum  12 . On the outside in front of the discharge opening  16 , a weir gate  20  is in a stationary mount on the front wall  14 , where it is adjustable. The weir gate  20  protrudes to just in front of the discharge opening  16 , so that it covers the latter on the outside on its radially outer region. The weir gate  20  has a weir edge  22  on its radially inward facing border. According to the prior art, such a weir edge  22  extends along the front wall  14  and thus across the longitudinal axis  18 . The weir edge  22  retains clarified product  24  in the centrifuge drum  12 , so that during operation of the solid-bowl screw centrifuge  10 , this clarified product  24  collects there with a pond depth  26  and then flows off over the weir edge  22  mostly continuously thereafter. 
         [0040]    An energy recovery device  28  according to the prior art is situated on the outside axially on the weir gate  20  behind, i.e., downstream from the weir edge  22  in the direction of flow of the clarified product  24 . This energy recovery device  28  is designed as a discharge trough, i.e., a discharge channel  30 , which has a flat bottom surface  32  extending tangentially at the height of the weir edge  22 . A deflecting surface  34 , which, as part of the discharge channel  30  perpendicular to the bottom surface  32 , extends in an arc shape in front of the region of the discharge opening  16  that is open as seen in the longitudinal direction according to the prior art. 
         [0041]    The deflecting surface  34  deflects the clarified product  24  that flows down axially through the discharge opening  16  on the inside radially below the weir edge  22  in a direction of inflow  38  is deflected in a direction tangential to a discharge direction  40 . Meanwhile the centrifugal drum  12  rotates in one direction of rotation  36 , while the clarified product  24  is deflected by the deflecting surface  34 , so that it emerges tangentially from the energy recovery device  28  in the opposite direction from this direction of rotation  36 . On its exit, the clarified product  24  “is repelled by” the centrifuge drum  12 , thereby transferring a portion of its momentum to the centrifuge drum and contributes toward energy recovery on the centrifuge drum  12 . This “repulsion” is mitigated by the internal fluid friction in the clarified product  24  and by the fact that the centrifuge drum  12  continues to rotate in the direction of rotation  36 . The centrifuge drum  12  therefore partially evades the repulsion. 
         [0042]      FIGS. 3 through 5  show a first exemplary embodiment of a solid-bowl screw centrifuge  10  with its centrifuge drum  12 , on which an energy recovery device  42  according to the invention is arranged. The energy recovery device  42  also has a weir gate  20  of the traditional type in front of the respective discharge opening  16 . On the outside axially there is a discharge pipe  44  on the weir gate  20 , through which discharge pipe flows the clarified product discharged through the discharge opening  16 . 
         [0043]    With regard to its cross section, the discharge pipe  44  is situated directly in front of the region of the otherwise open discharge opening  16 , so that the opening is completely covered by the discharge pipe  44  on the outside. Therefore, no air flow can act from the outside during the passage of the clarified product past the discharge opening  16  and therefore this yields a particularly uniform flow, in particular a strictly laminar flow, with the corresponding purity of the clarified product discharged. The discharge pipe  44  is situated at the height and/or radius of the weir edge  20 , so that the product thereby being discharged undergoes practically no change in position in the radial direction and there are no energy losses accordingly. 
         [0044]    On its circumference, the discharge pipe  44  is completely closed and forms a tubular line with an inflow mouth  46  in front of the discharge opening  16  and a discharge mouth  48  on its other exterior end. The outer part of this pipe on the outside radially with respect to the longitudinal axis acts like a discharge trough, i.e., a discharge channel, and at the same time is closed on the inside radially with respect to the longitudinal axis of the centrifuge drum  12 . Therefore, the product discharged through the energy recovery device  42  is also protected against external aerodynamic influences on the inside of the discharge pipe  44 . The product is deflected out of the axial direction homogeneously, without turbulence and in a targeted manner, i.e., the incoming flow direction  38  essentially into the tangential direction, i.e., the discharge direction  40 . 
         [0045]    With the discharge pipe  44 , the product discharged is largely held at the radius of the weir edge  22  during the deflection process, wherein the discharge pipe  44  has a straight flow path  50 , as seen in a side view ( FIG. 3 ), which is set at an inclination radially toward the inside by an angle  54  of 6° to 8° to the tangential direction  52  on the discharge opening  16 . A respective bottom surface  56  of the discharge pipe  44  is designed to be planar and/or largely planar and also set at an angle  54  of 6° to 8° at an inclination to the tangential direction  52 . At the same time, the discharge pipe  44  according to  FIGS. 3 through 5  has a rectangular flow cross section  56 , which is designed to taper starting from the inflow mouth  46  and going steadily to the discharge mouth  48 . With such a taper, the product discharged is subject to additional stagnation and is bundled into a stream. 
         [0046]    In the exemplary embodiment of an energy recovery device  42  according to  FIGS. 6 to 8 , the discharge pipe  44  there is designed with an oval flow cross section  56 . Such a flow cross section  56  also tapers over the flow path of the product discharged through the discharge pipe  44 . The discharge pipe  44  has a section with an essentially straight flow path  58 , as seen in the longitudinal section ( FIG. 7 ) downstream from the inflow mouth  46 , set at an angle  60  between 55° and 65° to the longitudinal axis  18  of the centrifugal drum. On the whole, this design yields a droplet shape (see  FIG. 6 ) for the discharge pipe  44 , which is particularly advantageous aerodynamically. 
         [0047]      FIGS. 9 through 11  show an exemplary embodiment of an energy recovery device  42 , in which the discharge pipe  44  is designed with an essentially circular flow cross section  56 . At the same time, the flow path  58 , which is essentially straight in the longitudinal section, extends over the total length of the discharge pipe  44 , so that the pipe is designed as a straight cylindrical pipe on the whole. Such a solution can be manufactured very inexpensively. 
         [0048]      FIGS. 12 through 14  show an exemplary embodiment of an energy recovery device  42 , in which the respective discharge pipe  44  is designed as a conical pipe set at an inclination upstream from the discharge opening  16 . The pipe is set at an inclination to the longitudinal axis  18  at an angle  60  of 60° and is conical over its entire length and is designed to be rectangular in the flow cross section  56 . The height of the flow cross section  56  is kept constant over the length of the discharge pipe  44 . 
         [0049]    The energy recovery device  42  shown in  FIGS. 15 through 17  is designed with a bent discharge pipe  44 , which has a first section with an angle  60  of 30° to the longitudinal axis  18  and a second section with an angle  64  of 75° to the longitudinal axis  18 . This second section forms one direction of flow  62  at the respective discharge mouth  48 , so that the flow path, i.e., the direction of flow  62  there, is also set at an inclination at an angle  64  of 75° with respect to the longitudinal axis  18  of the centrifuge drum  12 . With such a direction of flow  62 , the product discharged is deflected fundamentally across the longitudinal axis  18 , but at the same time, is not deflected toward the front wall  14  so strongly that it results in energy losses there due to fluid friction during the discharge. 
         [0050]    Finally, with the exemplary embodiments according to  FIGS. 15 to 21 , the discharge pipe  44  there is designed on its exterior wall  66  facing the direction of rotation  36  with an adapted aerodynamic exterior wall shape  68 . The exterior wall shape  68  here is such that the wall thickness, starting from the inflow mouth  46 , decreases steadily in the direction of flow of the product discharged, as far as the discharge mouth  48 . The outside of the exterior wall  66  is thus flatter with respect to the incoming air in rotation of the centrifuge drum  12  and therefore is designed to be smaller with respect to the flow resistance. At the same time, this form of the wall thickness is advantageous with respect to a great rigidity of the discharge pipe  44  in relation to its weight. 
         [0051]    In the exemplary embodiment according to  FIGS. 18 and 19 , this design of a discharge pipe  44  is combined with a continuously tapering inner flow cross section  56  and a continuous arc shape like that in  FIGS. 3 to 5 . The exemplary embodiment according to  FIGS. 20 and 21  also shows a continuous arc shape of the discharge pipe  44 , wherein its flow cross section  56  is kept the same size over the entire flow length. With such a flow cross section profile, blockage of the discharge pipe  44  with product being discharged is additionally prevented. 
         [0052]    In conclusion, it should be pointed out that all the features mentioned in the patent application documents and in particular in the dependent claims, which should have a formal reference back to one or more specific claims, even individually or in any combination, are entitled to independent protection either individually or in any combination. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           10  solid-bowl screw centrifuge 
           12  centrifuge drum 
           14  front wall 
           16  discharge opening 
           18  longitudinal axis of the centrifuge drum 
           20  weir gate 
           22  weir edge 
           24  clarified product 
           26  pond depth 
           28  energy recovery device according to the prior art 
           30  discharge channel according to the prior art 
           32  bottom surface according to the prior art 
           34  deflecting surface according to the prior art 
           36  direction of rotation 
           38  inflow direction of the clarified product (axially) 
           40  discharge direction of the clarified product (tangentially) 
           42  energy recovery device according to the invention 
           44  discharge pipe 
           46  inflow mouth 
           48  discharge mouth 
           50  straight flow path in a side view 
           52  tangential direction 
           54  angle between tangential direction and flat flow path in a side view 
           56  flow cross section 
           58  straight flow path in a longitudinal section 
           60  angle between longitudinal axis and flat flow path in the longitudinal section 
           62  direction of flow at the discharge mouth 
           64  angle between the longitudinal axis and the direction of flow at the discharge mouth 
           66  exterior wall of the discharge pipe facing in the direction of rotation 
           68  aerodynamic exterior wall shape