Abstract:
A screw press includes a press-chamber, wherein a screw shaft supporting thus the screw shaft surrounding by a screen-jacket and may rotate about a screw shaft axis, wherein the screen-jacket is fastened to a screen-jacket retaining device within the press-chamber and screen-jacket is formed by multi-part screen-cages having screen-cage inserts. Multi-part screen-cages are formed by two half-shells and, between at least one pivoting hinge arranging, on a bar, extending through press-chamber and arranging parallel to the pivot axis, as part of the screen-jacket retaining device and firmly connected to both half-shells. Half-shells and supported thus the half-shells pivoting in relation to each other, unhindered access to the screen-cage inserts enabling swung-open state. A cage tab is arranged on each half-shell on the side facing away from the pivoting hinge, which cage tab detachably fastening to the screen-jacket retaining device by the cage closing in the closed state of the half-shells.

Description:
TECHNICAL FIELD 
       [0001]    The present invention describes a screw press, usable as a dewatering device, for compressing and dewatering a suspension, comprising a press chamber, in which a screw shaft is mounted in such a way that it is surrounded by a screen jacket and is rotatable about a screw shaft axis, wherein the screen jacket is fastened, held within the press chamber, to a screen jacket holding device and the screen jacket is formed of a plurality of multipart screen baskets with screen basket inserts insertable therein, a biogas plant comprising a screw press, and a maintenance process for the changing of screen basket inserts from screen baskets, in a press chamber of a screw press used as part of a dewatering device for the dewatering of suspensions. 
       PRIOR ART 
       [0002]    In the production of biogas in fermenters or fermentation plants is formed a suspension, more accurately a digestate suspension, which should be dewatered in order to improve the biogas yield, shorten the post-digestion process and reduce the odor emission. Due to the typical consistency of digestate suspension, which consists of around ⅔ liquid and ⅓ dry substance, dewatering devices comprising a screw press are usually used. From the fermenter, the digestate suspension is transferred into the screw press and is there mechanically digested and dewatered. 
         [0003]    As described in DE 199 44 110 A1, the screw press of a dewatering device comprises a press chamber, in which a screen jacket surrounding a screw shaft is mounted. After pouring of the digestate suspension through a press infeed into the press chamber, the principle of crossflow filtration is utilized within the screw press, wherein a screw shaft rotating within the pressuretight, liquid-permeable screen jacket transports the digestate suspension in the direction of the screw shaft axis, wherein, as a result of the built-up pressure within the screen jacket, a liquid or pasty filtrate is pressed out through the perforations of the screen jacket. As a result of the friction of the solid matter of the digestate suspension on the screen jacket and of the screw shaft, a throttling of the material discharge is achievable, so that a counterpressure which conveys the filtrate or press water through the openings in the screen jacket is built up. Solids of the thus dewatered digestate are retained by the screen jacket, which is usually formed of screen baskets, and are ultimately conveyed to a press material outfeed and there transported out of the screen jacket or screw press. 
         [0004]    Screw presses of this type are usually run at low speeds of just a few revolutions per minute, wherein, in the case of a continuous permanent operation, low operating and maintenance costs are incurred, while reusable dewatered digestate and filtrate continuously accrue from the press material outfeed or a filtrate outlet. 
         [0005]    In order that screw presses of this type function in a trouble-free manner, the structure has to be adapted to the expected digestate suspension. A suitable screen jacket must be configured with a suitable size of openings, the screw shaft must be operated at suitable rotation speed, and the clearance between the inner face of the screen baskets and the periphery of the screw shaft must be suitably chosen. 
         [0006]    In continuous operation of a screw press for dewatering digestate suspensions, it has been shown that the screen jacket or the screens are automatically exposed during running operation, in that solids are led past the screen areas. The screens wear relatively quickly, however, and have to be changed. According to the prior art, the exchange of screen inlays of the screen jacket is associated with high technical complexity. For this, the screen baskets are completely removed, new screen inlays are introduced and the screen baskets are reinstalled. 
         [0007]    While the pressing characteristics and throughput of the employed screw presses have been optimized for the dewatering of digestate suspensions, the maintenance of such screw presses is still problematical. 
         [0008]    From EP 2 561 981 A2 derives a dewatering device comprising a screw press which has a press chamber with a screen jacket, comprising a plurality of screen baskets formed as screen basket half shells. The press chamber is supported by a press chamber holding device, which stands on a supporting device on the floor. In the operating state, the screen baskets fully surround the screw shaft, whereby a filtration space is formed. The screen baskets are fastened to two horizontally lying beams as a screen jacket holding device, such that they run parallel to the screw shaft axis. At least the upper screen baskets are designed to be removable from the beams, so that, once the upper screen baskets are removed, the filtration space and the screw shaft become accessible. Following disassembly of the upper half of the screen baskets, the screen baskets are deposited on the floor and worn screen inlays can be exchanged. For this, new screen inlays are inserted into the screen basket half shells and fastened. Those halves of the screen baskets which have remained in the press chamber can be provided with new screen inlays once the screw shaft is removed from the press chamber. Only when the lower screen basket half shells are exposed can the associated screen inlays also be changed. Although, according to EP 2 561 981 A2, individual worn screen inlays can be exchanged, the maintenance is associated with high technical complexity. The disassembly of the screen jacket has hitherto been complex, since the screw shaft must be removed in order that access can be gained to all the screen baskets. 
         [0009]    In known screw presses of this kind, the serviceability or flexibility of maintenance is very limited. Since the accessibility of the screen jacket is made more difficult, a complex disassembly of many components must take place in order to change worn screen inlays. Often the manufacturer must carry out the periodic maintenance through a member of staff in order to ensure, for instance, the correct reinstallation of the screw shaft. 
         [0010]    In U.S. Pat. No. 4,397,230 and U.S. Pat. No. 4,279,197 are disclosed, by contrast, screw presses in which the screen basket half shells are mounted pivotably via a hinge. This enables a simpler and more rapid maintenance of the screw press and facilitates, in particular, the exchange of screen inlays. 
       REPRESENTATION OF THE INVENTION 
       [0011]    The present invention has set itself the object of providing a dewatering device comprising a screw press and a screw press comprising a screen jacket, which screw press allows not only a simple and rapid maintenance thereof, but at the same time also has a lowest possible wear which is as even as possible. 
         [0012]    Necessary periodic services of the screw press are facilitated, since only a small number of maneuvers are necessary, whereby the time expenditure for the maintenance is shortened enormously. The maintenance does not necessarily have to be carried out by a trained maintenance worker of the manufacturer, whereby a flexible and inexpensive maintenance is enabled. 
         [0013]    In the development process, particular value was placed upon an uncomplicated changing of wearing parts such as screen inlays, so that suitable screen inlays can be flexibly and rapidly replaced or provided according to requirement. 
         [0014]    In addition, as a result of the additional fastening of the screen basket half shells to a bracket of the screen jacket holding device, the stability of the construction is also improved and, in particular, also a very concentric running is achieved. This has the result that fewer forces act on the worm gearing and the screen basket inserts, which leads to lower wear and tear and thus a greater working life. 
         [0015]    Moreover, in the screw press according to the invention, the wear takes place concentrically and evenly, so that all parts are roughly equally heavily worn and therefore have to be replaced or serviced at approximately the same time. This leads to a less frequent maintenance requirement and thus, all in all, to a lesser complexity and shorter downtimes. The otherwise customary wearing shells also thereby become unnecessary. 
         [0016]    The above effects are of great benefit, in particular in longer screw presses, where often a plurality of a screen baskets are arranged one behind another. In shorter screw presses, such as are disclosed, for instance, in U.S. Pat. No. 4,397,230 or U.S. Pat. No. 4,279,197, this is of lesser importance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    A preferred illustrative embodiment of the subject of the invention is described below in connection with the accompanying drawings. 
           [0018]      FIG. 1 a    shows a perspective view of a dewatering device for a biogas plant comprising a screw press, while 
           [0019]      FIG. 1 b    shows a side view of the screw press from  FIG. 1 a   , wherein a cover hood is partially removed and thus a view of a screen jacket is enabled. 
           [0020]      FIG. 2  shows a sectional view along the line A-A from  FIG. 1 b    with indicated complete press chamber and drain pan with closed screen jacket, while 
           [0021]      FIG. 3  shows a screen jacket which is open on one side, with swung open first screen basket half shell, in a sectional view, and 
           [0022]      FIG. 4  shows a fully opened screen jacket, with first and second screen basket half shell swung open on both sides, in a sectional view, wherein a part of a screen jacket holding device and the screw shaft have been omitted. 
       
    
    
     DESCRIPTION 
       [0023]    A dewatering device for integration in a fermentation plant or biogas plant, or as part thereof, is represented in perspective view in  FIG. 1   a.  The dewatering device is designed as a screw press  2 . The screw press  2  corresponds to a possible structure in order to dewater a digestate suspension which accrues in a wet or dry fermentation plant. Digestate suspensions of this type consist of around ⅔ liquid and ⅓ dry substance. As a result of a dewatering, on the one hand the filtrate or press water formed from the liquid and, on the other hand, the dewatered digestate in the form of a pressed cake can be reused in an optimized manner. The dewatering device is mounted on press supports  10  such that it runs at an angle to the horizontal H. 
         [0024]    The screw press  2  has a press chamber  20 , in which a screw shaft  202  is arranged traversing the press chamber  20 . The screw shaft  202  runs along a screw shaft axis L and has a screw shaft helix  2021 . The screw shaft  202  is held by two shaft bearings (not represented here). The screw shaft  202  runs from a fill region, in which a press material infeed  24  is disposed, to an outfeed region, in which a pressing head  25  with a press material outfeed  250  is disposed. 
         [0025]    The press chamber  20  is shaped such that it can be covered by a cover hood  22 . In  FIG. 1 a    is represented a multipart removable cover hood  22 , wherein only the away-facing part of the cover hood  22  has been left partially covering the press chamber  20  in order that a view into the press chamber  20  is possible. The cover hood  22  is here of three-part construction. The floor-facing part of the press chamber  20  is designed as a continuous drain pan  21 , so that pressed-out filtrate can make its way into drain pan  21  and can flow, on the basis of gravity, to a filtrate outlet  26  indicated in  FIG. 1   a.    
         [0026]    The screw shaft  202  is driven by a motor  27 , a slip-on gear mechanism  28  and a hydraulic power unit  29 , controlled by a control system (not represented). Depending on the consistency of the digestate suspension and the dewatering to be achieved, the rotation speed of the screw shaft  202  and the acting torques are adjusted by the control system. The screw shaft  202  is here generally operated at no more than just a few revolutions per minute. 
         [0027]    In the press chamber  20 , a screen jacket  203  concentrically surrounds the screw shaft  202 . The screen jacket  203  comprises a plurality of multipart screen baskets  2030  arranged one behind another in the direction of the screw shaft axis L, which form a supporting frame for screen basket inserts  2033  insertable into the screen baskets  2030 . The screen baskets  2030  are here formed of respectively two screen basket half shells  2031 , wherein a first screen basket half shell  2031  is represented open and, correspondingly, the screen basket insert  2033  is discernible. The screen baskets  2030  or the screen basket half shells  2031  respectively have a basket length  1 , running in the direction of the screw shaft  202 . In the embodiment depicted in  FIG. 1 a   , five screen baskets  2030  are present. 
         [0028]    The screen jacket  203  fully encloses the screw shaft helix  2021  with a small clearance, so that a necessary pressure can be applied by the screw shaft  202  to the digestate suspension within the screen jacket  203  and a dewatering of the digestate suspension is possible in practice. The screen basket inserts  2033  are thin metal plates with continuous, evenly distributed screen holes having constant diameters from 2 millimeters up to about 6 millimeters. As a result of the small clearance and the thus small distance between the screen basket inserts  2033  and the screw shaft  202 , the screen basket inserts  2033  are cleansed during the operation by after-flowing digestate suspension. 
         [0029]    A multipart special screen jacket holding device  204 , to which the screen baskets  2030  or the screen jacket  203  are fastened, is provided running within the press chamber  20 . 
         [0030]    In  FIG. 1 b   , it is represented by arrows how the digestate suspension is fed through the screw press  2 . In a first step, the digestate suspension is introduced into the screw press  2  through the press material infeed  24 . The digestate suspension stems, for instance, from a fermenter of a biogas plant, and has a predominant liquid component mixed with solid digestate. 
         [0031]    Following on from the press material infeed  24  is a preliminary dewatering screen  205 , through which press water can escape directly after the feed-in. The digestate suspension is thereupon conveyed through the press chamber  20  by means of the screw shaft  202 . By the driven screw shaft  202  or the screw shaft helix  2021 , the digestate suspension is conveyed in the arrow direction parallel to the screw shaft axis L through a screen jacket interior  2034  which lies between the screw shaft helix  2021  and the inner face of the screen jacket  203 . The screen basket inserts  2033  of the screen jacket  203  allow liquid filtrate to be pressed out of the digestate suspension transversely to the screw shaft axis L, which filtrate is discharged into a filtrate space  201  situated between the screen jacket  203  and the cover hood  22  or drain pan  21 . The filtrate or press water escapes from the screen jacket  203  in the radial direction, while the dewatered digestate is transported as a pressed cake further in the direction of the continuous arrow in the direction of the pressing head  25 . 
         [0032]    Since the screw press  2  is arranged oriented at an angle α&gt;0°, preferredly around 30°, to the horizontal H, press water flows automatically in the direction of the filtrate outlet  26 , as indicated by the dashed arrow. No further technical measures have to be taken to convey the press water out of the press chamber  20 . 
         [0033]    In order to further dewater the pressed cake also at the point of ejection, the pressing head  25  is here of conical design, so that a taper must first be traversed before the pressed cake is ejected from the press material outfeed  250 . The compression, dewatering and ejection are enabled by the screw helix  202 . 
         [0034]    In the sectional view according to  FIG. 2 , the multipart screen jacket holding device  204  is discernible, which runs in the filtrate space  201  of the press chamber  20 . The multipart cover hood  22  and the drain pan  21  are shown schematically in dashed representation. The sectional view represents a cross section through the screw press  2 , wherein the direction of view runs in the direction of the screw shaft  202  or of the screw shaft axis L. During operation, press water is pressed in the direction of the dashed arrows radially away from the screw shaft  202 . 
         [0035]    The screen jacket holding device  204  comprises a beam  2040  and two basket suspension beams  2041 ,  2041 ′, which are arranged running parallel to the screw shaft axis L. These beams are all disposed outside the screen jacket. In the depicted embodiment, the beam  2014  is arranged vertically beneath the screw shaft  202 , while the two basket suspension beams  2041 ,  2041 ′ run above the screw shaft and slightly to the side. Between the two basket suspension beams  2041 ,  2041 ′, brackets  2042  are oriented transversely to the screw shaft  202 , i.e. perpendicular to the screw shaft axis L. To this screen jacket holding device  204 , the screen baskets  2030  are fastened such that they run along the screw shaft  202 . 
         [0036]    The first screen basket half shell  2031  is provided as a supporting device with a screen basket insert  2033  and surrounds the screw shaft  202  at a concentric distance apart on one side of the screw shaft  202 . A second screen basket half shell  2032  is provided with a screen basket insert  2033  and surrounds the screw shaft  202  concentrically on the opposite side of the screw shaft  202 . The two screen basket half shells  2032 ,  2033  form a cylindrical screen basket  2030  with a screen jacket interior  2034 . The screw shaft  202  traverses this screen jacket interior  2034 , wherein the screw shaft helix  2021  is fastened minimally distanced from the screen basket inserts  2033 . 
         [0037]    The first screen basket half shell  2031  and the second screen basket half shell  2032  are fastened such that they are pivotably movable relative to each other. The pivotal mobility is achieved by the arrangement of at least one pivot hinge  2043  between the first and second screen basket half shell  2031 ,  2032 . The pivot hinge  2043  is disposed on the centric beam  2040  and is respectively fixedly connected to both screen basket half shells  2031 ,  2032 . In order that the screen basket  2030  is closed, basket closing means  2044 , which hold together the first and the second screen basket half shell  2031 ,  2032  on the bracket  2042 , are provided. 
         [0038]      FIG. 3  shows a partially opened screen basket  2030 . The first screen basket half shell  2031  is swung away from the screw shaft  202  by means of the pivot hinge  2043 . In the opened state of the screen basket  2030 , the screen basket insert  2033  of the first screen basket half shell  2031  is easily accessible and can be easily exchanged. 
         [0039]    Both screen basket half shells  2031 ,  2032  are provided with flanges F, which run along the basket length  1  of the semicylindrical screen basket half shells  2031 ,  2032 . In order to optimize the seal between the screen basket half shells  2031 ,  2032 , the screen basket inserts  2033  are also respectively run around the flanges F. 
         [0040]    One flange side of each screen basket half shell  2031 ,  2032 , or the flange F itself, is connected to the at least one pivot hinge  2043 . As a result of the connection of the flanges F to the pivot hinge  2043 , the screen basket half shells  2031 ,  2032 , when pivoted, are swung remotely away from the screw shaft  202 , so that no unwanted contact with the screw shaft  202  can occur. In a preferred embodiment, two pivot hinges  2043  per screen basket  2030  are connected, and correspondingly two pivot hinges  2043  are arranged on each flange F. 
         [0041]    On that side of the screen basket half shell  2031 ,  2032  which is facing away from the pivot hinge  2043  is respectively arranged a basket lug S. The basket lug S has a through hole. In the closed state of the two screen basket half shells  2031 ,  2032 , the basket lug S of each screen basket half shell  2031 ,  2032  is fastened with the basket closing means  2044  to the bracket  2042  of the screen jacket holding device  204 . It is thereby ensured that the screen jacket  203  and the screw shaft  202  remain concentrically arranged also during operation. In the closed state of the screen basket  2030 , both semicylindrical screen basket half shells  2031 ,  2032  are fully closed along the basket length l in the region of the at least one pivot hinge  2043  and in the region of the bracket  2042 . 
         [0042]    As the basket closing means  2044 , nuts and bolts, with which the basket lug S is fastenable to the bracket  2042 , can be used. In this case, through holes are likewise arranged in the bracket  2042 . For the fastening, the nuts and bolts can be tightly screwed, traversing the basket lug S and the bracket  2042 . As the basket closing means  2044 , other means which allow a releasable connection can also be used. 
         [0043]    In  FIG. 4 , also the second screen basket half shell  2032  is pivoted by means of the arrangement on the pivot hinge  2043 , whereby a maximum opening of the screen basket  2030  is easily achievable. The screen basket inserts  2033  of both screen basket half shells  2032  can be exchanged without difficulty. This exchange can be performed past the screw shaft  202 . The screen basket inserts  2033  in the form of perforated plates are adapted by prior bending to the semicylindrical shape of the screen basket half shells  2032  and are inserted into the screen basket half shells  2031 ,  2032  and fixed there. 
         [0044]    A maintenance of the screw press  2 , in which screen basket inserts  2033  are changed, is realized according to the following maintenance process. Firstly, the screw press  2  is emptied as completely as possible, in that no further digestate suspension is fed and the digestate suspension which is present is compressed by means of the screw shaft  202 , dewatered and discharged. 
         [0045]    After this, the press chamber  20  is opened, in that the cover hood  22  is at least partially removed, whereby access to the filtrate space  201  is achieved. By release or removal of the basket closing means  2044  on the brackets  2042  between the basket suspension beams  2041 ,  2041 ′, each individual screen basket  2030  can be easily opened by pivoting of the first screen basket half shell  2031  and pivoting of the second screen basket half shell  2032 , whereby access is gained to the respective screen inserts  2033 . 
         [0046]    There follows a removal of the existing worn screen basket inserts  2033  and the insertion of new screen basket inserts  2033 . 
         [0047]    Following subsequent pivoting and bolting of the screen basket half shells  2031 ,  2032 , the screw press  2  is prepared for future press runs and, following closure of the press chamber  20  by means of the cover hood  22 , can be directly started up again. 
         [0048]    According to the maintenance process according to the invention, the screen basket half shells  2031 ,  2032  remain in the press space  20  and only the screen basket inserts  2033  have to be exchanged. Removal and fitting of the screw shaft  202  can be dispensed with. 
       REFERENCE SYMBOL LIST 
       [0049]      2  screw press
         20  press chamber
             201  filtrate space (between screen jacket and cover hood or drain pan)     202  screw shaft
                 2021  screw shaft helix   
                 203  screen jacket (closed-off housing, protection from injury)
                 2030  screen basket (multipart, forms with insert two hollow cylinders, pivotable in relation to each other)     2031  first screen basket half shell     2032  second screen basket half shell     2033  screen basket insert     2034  screen jacket interior   l basket length   
                 204  screen jacket holding device
                 2040  centric beam     2041  basket suspension beam     2042  bracket     2043  pivot hinge     2044  basket closing means   
                 205  preliminary dewatering screen   
             21  drain pan     22  cover hood (multipart/removable)     23  press supporting device     24  press material infeed     25  pressing head
             250  press material outfeed   
             26  filtrate outlet     27  motor     28  slip-on gear mechanism     29  hydraulic power unit (integrated)       
 
         [0078]      10  press support 
         [0079]    L screw shaft axes 
         [0080]    S basket lug 
         [0081]    H horizontal