Patent Publication Number: US-11660609-B2

Title: Outlet device of a solid-bowl screw centrifuge with a diverting channel

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an outlet device of a solid-bowl screw centrifuge for separating a multi-phase material, which outlet device is arranged on an end wall of a centrifuge drum, which rotates about a longitudinal axis, at an outlet opening formed in the end wall, which outlet device comprises a diverting channel for diverting a liquid phase of the material which passes through the outlet opening and which has an aligned rectilinear weir edge for limiting the emergence of the liquid phase. 
     In general, solid-bowl screw centrifuges have a rotatable centrifuge drum, which have a drum shell, which is closed to the greatest possible extent, with a mostly horizontally extending rotational axis or longitudinal axis. The centrifuge drum is rotated by means of a drive at high rotational speed. Into the centrifuge drum, a multi-phase material to be centrifuged is introduced by means of an inlet tube that is centrally arranged in most cases. By the rotation of the centrifuge drum, the multi-phase material is then subjected to a high centrifugal force, whereby it attaches inside to the drum shell as a pool. In the material centrifuged in such a way, a phase separation occurs, wherein a comparatively light-weight material in the pool migrates radially inward as a light liquid phase, and comparatively heavy material migrates radially outward as a heavy solid phase. Radially inside, the light liquid phase can be discharged by means of an outlet device, whereas the heavy solid phase is withdrawn from the centrifuge drum by means of a screw. 
     From DE 20 2011 110 235 U1, a liquid phase outlet port component arranged at a drum of a decanter centrifuge is known, for example, which has a rectilinear channel. This channel forms a track which is arranged spaced from a longitudinal axis of the decanter centrifuge by a track radius. The channel is arranged at an acute angle relative to an end-sided base plate of the drum so as to divert a material reaching an outlet opening present in the base plate sideways of the drum. This allows the material exiting the outlet opening substantially in an axial direction to be diverted laterally outward along the track element for the purpose of energy recovery, before it is dropped at the end of the straight channel or the track at the level of the track radius from the liquid phase outlet port component. 
     Basic Task 
     The invention is based on the task of further developing generic outlet devices of a solid-bowl screw centrifuge in order to achieve an effective energy recovery. 
     Solution According to the Invention 
     The task of the invention is solved by an outlet device of a solid-bowl screw centrifuge for separating a multi-phase material, which outlet device is arranged on an end wall of a centrifuge drum, which rotates about a longitudinal axis, at an outlet opening formed in the end wall, which outlet device comprises a diverting channel for diverting a liquid phase of the material which passes through the outlet opening, wherein the diversion relative to the longitudinal axis amounts to an angle between 50° and 90° with respect to the circumferential direction, and which outlet device has an aligned rectilinear weir edge for limiting the emergence of the liquid phase, wherein the alignment of the weir edge relative to the end wall as viewed from the outlet opening amounts to between 0° relative to the end wall and minus 6° toward the end wall. 
     According to the invention, the outlet device comprises a diverting channel quite specially formed with respect to the angle of diversion with a thereto quite specially adapted configuration and alignment of the weir edge. Verifications according to the invention have shown that such a configuration altogether results in a particularly strong rebounding effect of the exiting liquid phase at the outlet device. According to the invention, the energy saving for driving the centrifuge drum achieved with the outlet device may again be improved. 
     The task of the invention is also solved by an associated method for energy recovery at a solid-bowl screw centrifuge. 
     The outlet device according to the invention is advantageously provided with a diverting channel formed as a channel that is open radially inward. This allows the diverting channel to not become plugged and to be better cleaned during maintenance. Alternatively, the diverting channel may be designed as a tube enclosing the exiting liquid phase. 
     The diverting channel is further designed to be narrowing, in particular continuously narrowing, preferably in the flow direction of the liquid phase. Such a narrowing allows a nozzle effect to be achieved for the exiting liquid phase. Alternatively, the diverting channel is designed to have substantially equally spaced sidewalls all throughout the entire flow track of the liquid phase. 
     In an optional embodiment of the invention, it is possible that the alignment of the weir edge relative to the end wall as viewed from the outlet opening amounts to less than 0° relative to the end wall. 
     In other words, the weir edge extends at an angle of between 0° relative to the end wall and minus 6° toward the end wall. 
     It is possible for the angle to be less than 0° to minus 6°. 
     Furthermore, at least one flow guiding element is preferably arranged in the diverting channel. Such a flow guiding element may be designed preferably in the form of a rib or web extending in the flow direction. 
     The flow guiding element leads to a division of the diverting channel into a plurality of narrow channels in which mostly equally high liquid levels will then develop. This will prevent the exiting liquid phase during the diversion from accumulating at the outside in the diversion curve, which would reduce the energy saving effect as verifications according to the invention have shown. 
     In the flow direction of the liquid phase, the outlet device according to the invention further advantageously has a flow guiding surface behind the weir edge, over which surface exiting liquid phase flows, and which is designed at least in sections as viewed in the axial direction to have no side wall on one side. Particularly advantageously, the flow guiding surface according to the invention has no side wall especially in the area of the axial projection of the weir edge. The side wall lacking there forms a kind of lateral air inlet area for ambient air to the upper side of the flow guiding surface. 
     The flow guiding surface preferably has a main flow direction which is oriented to be pivoted above the weir edge toward the end wall as compared to a main flow direction of the liquid phase. Such an orientation of the flow guiding surface achieves that exiting liquid phase will not flow off laterally, thus in the axial direction from the flow guiding surface, even if the side wall is lacking. 
     The flow guiding surface is in this case designed to be preferably spaced from the end wall on the side of the drum. Alternatively, the flow guiding surface is designed to be adjacent outside at the end wall in the axial direction. Both variants have particular advantages with respect to the attachment and adjustability of the outlet device according to the invention. 
     The effect of hitherto known outlet devices normally is based on the fact that the liquid phase having passed through the outlet opening is diverted in a channel with side walls and is drained in the such diverted state. Here, the flow velocity of the liquid phase, which will be guided toward the end wall circumference and withdrawn, depends to a large extent on the liquid amount flowing in the channel per unit of time. If the liquid amount is large, a high liquid level will develop in the channel. If the liquid amount is low, a small liquid level will develop. According to the height of the liquid level, however, the amount of recovered energy decreases as verifications according to the invention have shown. The solution according to the invention, however, enables the exiting liquid phase to laterally distribute on a flow guiding surface, whereby the liquid level can be kept comparatively low. 
     In the outlet device, the diverting channel is further advantageously integrated at least in part into a drum cover of the centrifuge drum. Thus, a particularly compact, space-saving solution can be created which is particularly advantageous in comparatively small machines. 
     Furthermore, the diverting channel of the outlet device according to the invention may be advantageously mounted to the end wall of the centrifuge drum so as to be adjustable. Adjusting allows the liquid level of the light phase in the centrifuge drum, the so-called pool depth, to be adjusted. The liquid level is in this case determined by the shortest radial distance of the weir edge of the outlet device from the longitudinal axis of the centrifuge drum. The outlet device according to the invention accordingly is adjustable in a particularly preferred manner in the distance from the longitudinal axis and/or in the angle of inclination to the circumferential direction. 
     The invention is finally also directed to a use of such an outlet device according to the invention on a solid-bowl screw centrifuge for separating a multi-phase material by means of a centrifuge drum. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Hereinafter, exemplary embodiments of the outlet device according to the invention on a solid-bowl screw centrifuge will be explained in more detail with reference to the attached schematic drawings. Shown is in: 
         FIG.  1    a frontal view of an end wall of a centrifuge drum of a solid-bowl screw centrifuge, with an outlet device according to the invention being arranged on the end wall, 
         FIG.  2    a section II-II of the end wall according to  FIG.  1   , 
         FIG.  3    a first variant of the embodiment according to  FIG.  2   , 
         FIG.  4    a second variant of the embodiment according to  FIG.  2   , 
         FIG.  5   ,  FIG.  5   a    the view V of the outlet device according to  FIG.  1   , 
         FIG.  6    a first variant of the embodiment according to  FIG.  5   , 
         FIG.  7    a second variant of the embodiment according to  FIG.  5   , 
         FIG.  8    a third variant of the embodiment according to  FIG.  5   , 
         FIG.  9    a fourth variant of the embodiment according to  FIG.  5   , 
         FIG.  10    a fifth variant of the embodiment according to  FIG.  5   , 
         FIG.  11    a sixth variant of the embodiment according to  FIG.  5   , and 
         FIG.  12    a longitudinal section of the end wall according to  FIG.  1    with the outlet device according to  FIG.  11   . 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     In  FIGS.  1  to  12   , diverse outlet devices  10  are depicted, which are each arranged to be radially adjustable on an end wall  12  of a not further depicted centrifuge drum of a solid-bowl screw centrifuge of the conventional type of construction. The centrifuge drum may in this case rotate at high speed about a longitudinal axis  14  in a rotational direction  16 . Inside the centrifuge drum, a material to be cleared is present, whose light liquid phase accumulates radially inside and occupies a pool radius or a liquid level  18 . The liquid level  18  is determined by an outlet opening  20  positioned in the end wall  12  and through which the material of the light phase may flow out of the centrifuge drum to the outside. 
     In  FIGS.  2  to  4   , three variants of the outlet opening  20  are illustrated, with the variant according to  FIG.  2    being designed as a cylinder passage opening oriented in the longitudinal direction, the variant according to  FIG.  3    being designed as an obliquely oriented cylinder passage opening, and the variant according to  FIG.  4    being designed as a passage opening tapering in the form of a truncated cone. 
     In the flow through direction behind the outlet opening  20  or outside in front of the outlet opening  20 , the outlet device  10  is positioned with an associated diverting channel  22 . The exiting light phase flows through the outlet opening  20  into this diverting channel  22  and is diverted on this occasion from the direction of the longitudinal axis  14  transversely to the longitudinal axis  14  into the associated circumferential direction of the centrifuge drum. In this manner, the flow pulse of the liquid phase flowing out may be utilized to impart a pulse to the centrifuge drum acting in the rotational direction. This allows driving energy for driving the centrifuge drum to be recovered. 
     The diverting channel  22  is designed as a radially inward open channel with a first side wall  24 , a bottom surface  26  and a second side wall  28 . In this case, the side walls  24  and  28  are oriented such that this channel continuously tapers in the flow direction of the exiting light phase. At the end of the gutter-like channel, an associated weir edge  30  of the outlet device  10  is positioned. This weir edge  30  forms the part of the bottom surface  26  projecting furthest radially inward, and this defines the liquid level  18 . 
     The diversion of the outflowing material of the liquid phase by means of the diverting channel  22  relative to the outside of the end wall  12  has an angle  32  of between 50° and 90° from the direction of the longitudinal axis  14  toward the circumferential direction or rotational direction  16  of the centrifuge drum. 
     The weir edge  30  at the end of the diverting channel  22  is in this case designed to be rectilinear and extends at an angle  34  of between minus 6° toward the end wall  12  and 0° away from the end wall  12 . In other words, the weir edge  30  extends at an angle  34  of between 0° relative to the end wall  12  and minus 6° toward the end wall  12 . 
     A rib-shaped flow guiding element  36  is positioned in the diverting channel  22  according to  FIG.  6    in the center of the bottom surface  26  thereof. This flow guiding element  36  projects radially inward from the bottom surface  26  as a narrow wall. The flow guiding element  36  extends from the beginning to the end of the diverting channel  22 . 
     In  FIG.  7   , one embodiment of the outlet device  10  is depicted, wherein a flow guiding surface  38  is formed at the end of the channel of the diverting channel  22 . To this end, the side wall  28  of the diverting channel  22  pointing toward the end wall  12  is shortened, and the weir edge  30  is designed to have a second weir edge portion  40  pointing toward the end wall  12 . As viewed in the top view, the weir edge  30  thus forms a tip pointing in the flow direction of the material flowing off (see  FIG.  7    at the bottom). 
       FIG.  8    shows an outlet device  10 , in which the side walls  24  and  28  are designed like in the example shown in  FIG.  6   . At the same time, a flow guiding surface  38  is positioned in the flow direction behind the weir edge  30 . This flow guiding surface  38  is designed as a mostly planar surface without side edges or side walls and so as to expand in a funnel-shape in the flow direction. 
       FIG.  9    depicts one exemplary embodiment of an outlet device  10 , in which such a flow guiding surface  38  as shown in  FIG.  8    is provided in addition, on its side facing away from the end wall  12 , with an end wall  42 . The side wall  42  extends in this case only over the rear part of the flow guiding surface  38  in the flow direction, whereas an area or portion  44  of the projection of the weir edge  30  in the axial direction  46  is designed without a side wall. This free area on the flow guiding surface allows as little air resistance as possible to develop there during the rotation of the centrifuge drum because of the minimum projection surface. 
     In  FIGS.  10  and  11   , two further embodiments of an outlet device  10  are depicted, in which the flow guiding surface  38  is provided with a second side wall  48  also on its side facing the end wall  12 . In this case, the side walls  42  and  48  according to  FIG.  10    are designed such as to form a channel tapering in the flow direction, whereas the side walls  42  and  48  according to  FIG.  11    extend in parallel to one another. 
       FIG.  12    finally depicts that the respective flow guiding surfaces  38  are always radially slightly further outside directly behind the associated weir edges  30  so that a small step  50  is developed directly behind the weir edge  30 . 
     Finally, it should be noted that all of the features mentioned in the application documents and in particular in the dependent claims should be provided, even individually or in any combination, with individual protection, despite of the formal back reference made to one or more particular claims. 
     LIST OF REFERENCE NUMERALS 
     
         
         
           
               10  outlet device 
               12  end wall of a centrifuge drum of a solid-bowl screw centrifuge 
               14  longitudinal axis 
               16  rotational direction 
               18  pool radius or liquid level 
               20  outlet opening 
               22  diverting channel 
               24  side wall of the diverting channel 
               26  bottom surface of the diverting channel 
               28  side wall of the diverting channel 
               30  weir edge 
               32  angle of the diversion of the flow of the liquid phase 
               34  angle of the orientation of the weir edge 
               36  flow guiding element 
               38  flow guiding surface 
               40  second weir edge portion 
               42  side wall of the flow guiding surface 
               44  portion without side wall 
               46  axial direction 
               48  side wall of the flow guiding surface 
               50  step