Patent Publication Number: US-2022234053-A1

Title: Solid bowl screw centrifuge

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     Exemplary embodiments of the invention relate to a solid bowl screw centrifuge. 
       FIG. 4  shows a solid bowl screw centrifuge according to the prior art. The drum of such a centrifuge is divided into a conical region and a cylindrical region, wherein the cylindrical region is generally referred to by a person skilled in the art as the separating zone and the conical region as the drying zone. 
     This design has proven itself as such. Nonetheless, there is a further demand for improving the design of solid bowl screw centrifuges in such a way that they have further functionalities and thus subsequent work steps can be saved. 
     WO 2017/182949 discloses, in particular in  FIG. 3 a   , an assembly for processing drilling sludge in a solid bowl screw centrifuge. For this purpose, a sacrificial liquid for transporting solids was introduced in addition to the solid-loaded drilling sludge into the solid bowl screw centrifuge. The sacrificial liquid then displaces the drilling sludge while a solid phase is transported further. 
     Ultimately, a solid phase is to be separated, an additional use of the drying zone for other purposes is not disclosed. 
     Exemplary embodiments of the invention are directed to expanding the functionality of the drying zone. 
     A solid bowl screw centrifuge according to the invention has a housing and a rotor rotatably mounted in the housing. The solid bowl screw centrifuge moreover at least has the following:
         a rotatable drum having a rotational axis, wherein the drum has a cylindrical section having a length L 1  and a conical section having the length L 2 ,   at least one first feed for supplying a suspension to be processed into the drum,   at least one liquid outlet, which is arranged in the cylindrical section of the drum, and at least one solid discharge, which is arranged in the conical section of the drum,   a screw, which is rotatable relative to the rotatable drum at a differential speed and is arranged in the drum, wherein the drum and the screw jointly form the rotor.       

     The solid bowl screw centrifuge according to the invention has a second feed for supplying an additive to a solid phase inside the drum. 
     Due to the additional feed into the solid phase, the advantages of a mixing device can be combined with those of a decanter. Additional downstream mixing de-vices can advantageously be omitted, and the space required for the corresponding machines in a processing plant is thus significantly reduced. 
     The second feed can be arranged at least partially concentrically to the rotational axis of the solid bowl screw centrifuge. A line for liquids or solids into a specific region of the drum is to be understood as a feed. The line can be a pipeline, for example. At least one section of the line extends concentrically to the rotational axis. 
     The second feed can advantageously have a feed pipe protruding into a hollow shaft of the screw shaft of the screw. Furthermore, the second feed can have an apparatus for the radial discharge of the additive from the screw via at least one orifice opening. The orifice opening can be introduced into the wall of the screw shaft. Multiple orifice openings are also possible, of course. 
     The first feed can moreover have a feed pipe protruding into the screw shaft of the screw, wherein the first feed has an apparatus for the radial discharge of the suspension to be processed from the screw via an orifice opening, wherein the orifice opening of the second feed is arranged between the orifice opening of the first feed and the solid discharge. 
     The orifice opening of the second feed can preferably be arranged in the conical section. 
     The feed pipe of the second feed can be arranged on a side of the solid bowl screw centrifuge opposite to the feed pipe of the first feed, so that the two feed pipes do not obstruct one another. 
     Alternatively, the feed pipe of the second feed can be arranged inside the feed pipe of the first feed and in particular concentrically thereto. This is advantageous if the supply of the suspension and the additive is to take place from one side, for example, from a metering device. 
     An immersion disk, which protrudes radially out of the surface of the screw shaft and leaves open an annular gap to the drum inner wall, can be arranged between the orifice opening of the second feed and the orifice opening of the first feed. The immersion disk makes it possible for only thickened solids (heavy phase) to pass close to the drum inner wall from the cylindrical section of the drum into the conical section. The liquid component of the suspension (light phase) remains in the cylindrical section of the drum. The immersion disk has different levels on both sides here. Since the thickened solid separated in the cylindrical section has a higher density than the supplied suspension, the suspension fill level on one side of the solid bowl screw centrifuge has to be higher than the solid fill level on the other side of the solid bowl screw centrifuge. 
     At least one mixing element can preferably be arranged in the conical section, which protrudes out of the screw shaft or the drum wall of the drum into the intermediate space between the screw shaft and the drum. Multiple mixing elements, for example, mixing paddles or mixing blades, can particularly preferably also be arranged. 
     The apparatus for the radial discharge of the additive or the dispersion to be processed can be formed in particular as a pipeline or as a distributor, wherein the distributor is formed as a chamber inside the screw shaft into which the feed pipe opens. The screw shaft, as a wall delimiting the chamber, has at least one orifice opening into the centrifuge space between the screw shaft and the drum wall. 
     The immersion disk can advantageously be arranged in a transition region in which the cylindrical section merges into the conical section. 
     The feed pipe of the second feed can be rotatably mounted. 
     A use according to the invention of the above-mentioned solid bowl screw centrifuge according to the invention is used for mixing the solid phase in the conical section of the drum with a liquid, gaseous, or solid additive, which is supplied via the second feed to the solid phase, wherein the conical section of the drum is used at least in regions as a mixing zone, in which mixing of the solid phase with the supplied additive takes place. 
     In this context, a specific use of the solid bowl screw centrifuge takes place in a method for processing a stillage to form a dry stillage, wherein the stillage is supplied via the first feed of the solid bowl screw centrifuge and wherein processing of the stillage into a thin stillage and a solid phase takes place in the solid bowl screw centrifuge, wherein a syrup obtained from the thin stillage during the processing in the solid bowl screw centrifuge is supplied to the solid phase as an additive in the drum via the second feed. 
     The syrup from the thin stillage can be obtained by at least one evaporator, preferably by an evaporator and a downstream 3-phase separator, while additionally obtaining corn oil. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       In the following, the invention is described in more detail with reference to the drawing on the basis of exemplary embodiments. In the figures: 
         FIG. 1  shows a side view of a schematically shown solid bowl screw centrifuge according to the invention; 
         FIG. 2  shows a method scheme according to the prior art; 
         FIG. 3  shows a method scheme using a solid bowl screw centrifuge according to the invention; and 
         FIG. 4  shows a side view of a schematically shown solid bowl screw centrifuge according to the prior art. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 4  shows a solid bowl screw centrifuge  1  having a rotatably mounted drum  210 , wherein a first drum shaft section  220 , which is connected in a rotationally-fixed manner to the drum  210 , axially adjoins a drum cover  213  of the drum  210  or the actual drum  210 , and a second drum shaft section  219 , which is also connected in a rotationally-fixed manner to the drum  210 , axially adjoins the conical drum section  212 . 
     Inside the drum  210 , a rotatably mounted screw  230  is arranged concentrically to the drum  210 . The screw comprises a screw shaft  241  formed as a hollow shaft and a helical winding  242   
     The drum  210  and the screw  230  each have a cylindrical section  231  and a conical section  232 . A first screw shaft section  234 , which is connected in a rotationally-fixed manner to the screw  230 , axially adjoins the cylindrical section  231  of the screw  230 , and a second screw shaft section  233 , which is also connected in a rotationally-fixed manner to the screw  230 , axially adjoins the conical drum section  232 . 
     A drive device  400  having one or two motors  401  is used to drive the rotor  200 . At least one gear  310  is connected downstream of the drive device  400 , on which two belt pulleys  320 ,  330  are schematically shown here, which indicates that the gear  310  has at least two interfaces for feeding a respective torque of the motor or the motors into the gear  310  to drive the drum and the screw. Alternatively (not shown here), the drive of the rotor can also take place via hydraulic motors so that a gear is not required. The drive can also take place by way of a combination of electric motor(s) and hydraulic motor(s), wherein other gears are used for this purpose and the belt pulleys are entirely or partially omitted. 
     The gear  300  rotates the drum  210 , on the one hand, and the screw  230 , on the other hand. For this purpose, the gear  300  has two output shafts. The first output shaft is coupled in a rotationally-fixed manner to the first drum shaft section  220  or is coupled directly to the drum  210  and the second output shaft is coupled directly or indirectly in a rotationally-fixed manner to the first screw shaft section  234  or directly to the screw  230 . 
     The drum and the shaft are each rotatably mounted using two drum bearings  221 ,  222  arranged axially in the direction of the rotational axis. The concept of the “bearing” is not to be interpreted narrowly in this regard. Each of the bearings  221 ,  222  can respectively consist of one or multiple individual bearings, which are then arranged axially directly adjacent to one another so that they can functionally each be considered to be an individual bearing. The bearings  221 ,  222  can moreover be formed as bearings of greatly varying design, thus as roller bearings—in particular as ceramic bearings, as hybrid ceramic bearings, as magnetic bearings, or as plain bearings. 
     The drum bearings  221 ,  222  are arranged between the drum  210  and the housing  100  or a part connected to the housing so that the drum  210  can be rotated relative to the housing  100 . This also applies for all variants described hereinafter and falling under the claims. The drum bearings  221 ,  222  are preferably arranged radially between the drum  210  and the housing  100  or a part connected to the housing. 
     The screw bearings  235 ,  236 , in contrast, are arranged radially between the screw  230  and the drum  210 , so that the screw  230  is rotatable relative to the drum  210 . The screw bearings  235 ,  236  are preferably arranged radially between the drum  210  and the screw  230 . 
     In one possible embodiment variant (not shown), the one of the screw bearings  235  in the region of the solid discharge  218  can be omitted. In this case, the rotating screw centers itself automatically, which is known, for example, in the case of a vertical arrangement of the decanter. 
     According to the prior art, as shown in  FIG. 4 , the cylindrical region  231  of the solid bowl screw centrifuge is used as a separating zone for a supplied suspension SU to be divided into a liquid phase FIP and a solid phase SP. The conical region  232  is used as a drying zone, in which the solid phase is dried further. The invention begins at this point and follows a different path. 
       FIG. 1  shows a solid bowl screw centrifuge  1  having a frame, which is not rotatable or does not rotate in operation, and preferably a housing  100  and a rotor  200 , which is rotatable or rotates in operation. The solid bowl screw centrifuge shown has numerous similar components in relation to the prior art in  FIG. 4 . These are identified by the same reference signs. 
     The rotor  200  has a rotatable drum  210  having a horizontal rotational axis D. However, the rotational axis D can also be oriented differently, in particular vertically in space. Moreover, a screw  230  arranged in the drum  210 , the rotational axis of which corresponds to that of the drum  210 , is part of the rotor  200 . The screw  230  can be rotated in operation with a differential speed to the drum  210 . 
     The drum  210  has a cylindrical section  231  having a length L 1  and a conical section  232  adjoining axially thereon having a length L 2 . The cylindrical section  231  is terminated by an essentially radially extending drum cover  213 . 
     The screw  230  also has a cylindrical section and a conical section adjoining axially thereon here. It is arranged inside the drum  210 . 
     The solid bowl screw centrifuge moreover has a feed  211  for supplying a suspension SU to be processed into the drum  210  and in particular into a centrifuge space  216  inside the drum  210 . This feed is formed in  FIGS. 1 and 4  in such a way that a feed pipe  214  extending concentrically to the rotational axis D here protrudes into the drum  210 , which pipe opens into a distributor  215 , by which the suspension SU to be processed can be conducted radially via an orifice opening  243  in the screw shaft  241  into a centrifuge space  216  of the drum  210 . The feed pipe  214  can either be guided from the side of the cylindrical drum section into the drum  210  or it can be guided from the side of the conical drum section into the drum  210 . 
     One or multiple liquid drains  217  can be formed in or on the drum cover  213 . These can be formed in various ways, thus as openings in the drum cover  213 , which have a type of overflow weir, or in another way, thus as an impeller. At least one solid discharge  218  is formed at the end of the conical section  212 . 
     In general, the drum  210  is formed as a solid bowl drum. At least one liquid phase FIP is then clarified of solids SP in the rotating drum  210 . The at least one liquid phase exits at the drum cover  213  from the liquid drain  217 . The solids, in contrast, are transported by the screw  230  in the direction of the solid discharge  218  and ejected there from the drum  210 . 
     In contrast to  FIG. 4 , a feed  701  for an additive Z is arranged between the orifice opening  243  of the distributor  215  and the solid discharge  218  in  FIG. 1 . 
     Specifically, in  FIG. 1 , a second feed pipe  704  is arranged as a feed  701  for additives Z coaxially to the rotational axis D. This protrudes opposite to the feed pipe  214  into the interior of the screw shaft  241 . From the feed pipe  704 , a line  702  extends radially in the direction of the drum casing, so that the additive to be introduced is deflected via this line  702 . The line  702  has an orifice opening  703 , which is located in the region between the screw shaft  241  and the drum casing of the drum  210 . 
     Due to the rotation of the screw  230 , intensive mixing of the additive Z and the solid phase SP takes place in the conical region  232  of the solid bowl screw centrifuge. The conical region  232  can thus be referred to as a mixing zone, while the cylindrical region  231  is still the separating zone. 
     The special advantage in the design according to the invention is that the drying zone is additionally utilized as a mixing device due to the provided windings  242  of the screw  230 . Normally, a mixing device would be connected downstream of the solid bowl screw centrifuge. However, the illustrated design advantageously enables such a mixing device to be dispensed with entirely. 
     The statements on the feed  701  according to  FIG. 1  are in no way to be understood as exhaustive. Rather, other advantageous arrangements of the feed  701  are also conceivable in the scope of the present invention. 
     In a first modification to  FIG. 1 , the feed pipe  701  can also be led from the side of the cylindrical drum section into the drum  210 . In this case, the second feed pipe  704  for additives can be arranged coaxially inside the feed pipe for the suspension to be processed. Metering of suspension and additive can thus take place from one side, for example. 
     In a second modification to  FIG. 1 , the line  702  can be replaced by a distributor, similarly to the distributor  215 . Such a distributor is preferably formed as a chamber inside the screw shaft into which the respective feed pipe opens. This arrangement has the advantage that the feed pipe does not have to be embodied as rotating. The chamber has one orifice opening or multiple orifice openings in the centrifuge space  216  between the screw shaft  241  and the drum wall. 
     In a third modification of  FIG. 1 , the feed into the centrifuge space  216  can also take place through the drum wall. 
     In the transition region between the cylindrical and the conical section of the screw  230 , an optional immersion disk  650  is arranged along the screw shaft, which extends radially in the direction of the drum wall of the drum  210 . The immersion disk  650  can extend in particular perpendicularly to the rotational axis D from the screw shaft  241  and can also be arranged, inter alia, in the conical region or in the cylindrical region. It is essential that it is arranged between the orifice opening  703  of the second feed  701  for the additive and the orifice opening  243  of the distributor. 
     The outer contour of the immersion disk  650  forms a gap in the form of a circular ring, the so-called immersion ring gap  651 , with the inner wall of the drum, through which the solid reaches the solid discharge  218  from the separating zone  231 . The liquid-side end of the separating zone  231  can be sealed off from the surroundings, which is implementable, for example, by an internal impeller or a hydrohermetic seal. A hermetic closure of the separating zone  231  can thus be achieved if needed. 
     A further addition to the concept according to the invention is the arrangement of mixing elements  601 , for example, of mixing blades or mixing paddles, in addition to the windings  242  of the screw  230  along the wall of the screw shaft  241 . These mixing elements preferably protrude into the thread or the threads  244  between the windings  242  and enable the mixing of the separated solids of the suspension SU to be made more intensive with the additive Z introduced via the feed line  701 . 
     A use according to the invention of the solid bowl screw centrifuge  1  according to the invention and its advantages is explained in more detail on the basis of  FIGS. 2 and 3 . 
     In  FIG. 2 , the treatment of stillage as a suspension SU is explained in more detail. Stillage (stillage or whole stillage) results when obtaining alcohol from plants, in particular from corn. This stillage has to be processed for waste disposal. 
     This stillage SU is treated in a conventional solid bowl screw centrifuge  1  with the supply of energy. A partially-dehydrated stillage (Wet Distillers Grains WDG) as the solid phase and a thin stillage as the liquid phase are provided in this case. 
     The thin stillage (FIP) is supplied to an evaporator  4 , which provides a syrup with removal of a large quantity of water as water steam or condensate. This syrup is further processed by means of a  3 -phase separator  5 . A useful material phase can be separated here as corn oil. The further liquid phase and the solids that arise during the 3-phase separation are then supplied to the solid phase SP of the solid bowl screw centrifuge  1 . 
     Intensive mixing of the two phases takes place in a mixer  2 . The product is further processed to form a dry stillage (dried distillers grains DDGS) in a dryer  3  with introduction of steam or hot air. Intensive mixing of the syrup with the dehydrated stillage is necessary since the dryer  3  cannot process clumps having excessive syrup. These clumps would remain adhering in the dryer and combust therein. 
     If the solid bowl screw centrifuge  1  according to the invention is used, a mixer  2  can advantageously be omitted. This is shown in  FIG. 3 . The syrup produced from the thin stillage FIP in the evaporator  4  can be returned directly back into the solid bowl screw centrifuge  1 . A separator can be interconnected similarly to  FIG. 2  to separate corn oil from the syrup, since in this way the subsequent mixing of the de-oiled syrup with the dehydrated stillage is promoted. 
     The free-flowing solid phase SP, which now contains a syrup, is then transferred into a dryer  3 , which provides the dry stillage DDGS. 
     Although the invention has been illustrated and described in detail by way of preferred embodiments, the invention is not limited by the examples disclosed, and other variations can be derived from these by the person skilled in the art without leaving the scope of the invention. It is therefore clear that there is a plurality of possible variations. It is also clear that embodiments stated by way of example are only really examples that are not to be seen as limiting the scope, application possibilities or configuration of the invention in any way. In fact, the preceding description and the description of the figures enable the person skilled in the art to implement the exemplary embodiments in concrete manner, wherein, with the knowledge of the disclosed inventive concept, the person skilled in the art is able to undertake various changes, for example, with regard to the functioning or arrangement of individual elements stated in an exemplary embodiment without leaving the scope of the invention, which is defined by the claims and their legal equivalents, such as further explanations in the description. 
     LIST OF REFERENCE SIGNS 
     
         
           1  solid bowl screw centrifuge 
           2  mixer 
           3  dryer 
           4  evaporator 
           5  3-phase separator 
           100  housing 
           200  rotor 
           210  drum 
           211  feed 
           212  conical drum section 
           213  drum cover 
           214  feed pipe 
           215  distributor 
           216  centrifuge space 
           217  liquid drain 
           218  solid discharge 
           219  drum shaft section 
           220  drum shaft section 
           221  drum bearing 
           222  drum bearing 
           230  screw 
           231  cylindrical section 
           232  conical section 
           233  screw shaft section 
           234  screw shaft section 
           235  screw bearing 
           236  screw bearing 
           241  screw shaft 
           242  windings 
           243  orifice opening 
           244  winding thread 
           310  gear 
           320  belt pulley 
           330  belt pulley 
           400  drive device 
           401  motor 
           601  mixing elements 
           650  immersion disk 
           651  immersion disk 
           701  second feed 
           702  line 
           703  orifice opening 
           704  feed pipe 
         D rotational axis 
         L 1  length 
         L 2  length 
         SU suspension 
         SP solid phase 
         FIP liquid phase 
         Z additives