Abstract:
The invention relates to a backflush device ( 6 ) for a filter system ( 1 ) for removing impurities from a fluid, the backflush device ( 6 ) serving to backflush a filter body ( 3 ) in the filter system separating the clean side ( 5 ) from the inlet side ( 4 ), and comprising at least one backflush nozzle ( 7 ) for applying a rinse medium to the filter body ( 3 ), said nozzle comprising at least one opening ( 8 ) through which the rinse medium flows in a flow direction ( 9 ) during backflushing and exits the backflush nozzle ( 7 ). In order to improve the effectiveness of the backflushing, the at least one opening is designed as a slit opening ( 8 ) extending transverse to the flow direction ( 9 ) in a straight line having a constant cross-sectional profile ( 16 ) comprising a nozzle segment ( 17 ) expanding the flow direction ( 9 ).

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a National Stage application which claims the benefit of International Application No. PCT/EP2008/059561 filed Jul. 22, 2008, which claims priority based on German Application No. 10 2007 035 967.7, filed Jul. 30, 2007, both of which are hereby incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to a backflush device for a filter system for removing impurities from a fluid, the backflush device in the filter system serving to backflush a filter body in the filter system which separates a clean side from an inlet side. 
     BACKGROUND 
     Filter systems in industrial or stationary applications are used in a multiplicity of processes, for example for filtering out liquid or solid particles from a gas flow or solid particles from a liquid flow. To this end, the respective filter system uses at least one filter body which separates an inlet space from a clean space inside the system. To this end the filter body has a filter material through which the respective fluid can flow and which is impermeable for the particles which are to be filtered out. In the course of the cleaning operation or filtering operation the filtered out particles can accumulate or deposit on the filter material, that is, on the inlet side of the filter body. This increases the flow resistance of the filter body. In order that the filtering operation does not have to be interrupted, or only has to be interrupted for a short time, modern filter systems can be equipped with a backflush device, with the aid of which the filter body can be backflushed with a suitable rinse medium. The backflushing then takes place counter to the filtering direction, that is, from the clean side to the inlet side. This means that the impurities which have deposited on the inlet side of the filter body can be removed. Such a backflush device can operate with at least one backflush nozzle, with the aid of which the respective rinse medium is applied to the clean side of the filter body. To this end, such a backflush nozzle can have a multiplicity of openings through which the rinse medium flows in a flow direction, which is defined by the longitudinal axis of the opening, and exits from the backflush nozzle during backflushing. The rinse medium passes through such point-like openings at a corresponding backflush pressure with a straight jet or with a jet which fans out in a cone-shaped manner out of the respective opening and impinges on the filter body over a corresponding circular impact area. 
     SUMMARY 
     The present invention is concerned with the problem of specifying an improved embodiment for a backflush device and for a filter system equipped therewith and for a backflush nozzle of such a backflush device, which is characterised in particular in that it impinges on the filter body in a more uniform manner and thus has a more uniform backflushing effect. 
     This problem is solved according to the invention by the subject matter of the independent claims. Advantageous embodiments form the subject matter of the dependent claims. 
     The invention is based on the general idea of equipping the backflush nozzle with a slit opening, that is, with a slit-shaped opening, which extends in a straight line transversely with respect to the flow direction with a constant cross-sectional profile, with the cross sectional profile having in particular a nozzle segment which expands in the flow direction. The slit shape of the opening means that the impact area for the backflush medium against the clean side of the filter body is rectangular. This means in particular that the backflush medium is applied uniformly to the filter body over the entire length of the slit opening. Correspondingly a relatively uniform backflush effect is also produced, which leads overall to an improved performance of the backflush device and thus of the filter system equipped with it. 
     Also particularly advantageous is the nozzle profile of the slit opening, which is characterised by the nozzle segment which expands in the flow direction. The backflush medium can be accelerated in the flow direction in the slit opening through the nozzle profile, as a result of which the backflush medium obtains a relatively high momentum which can be used to increase the backflush effect on the filter body. 
     In an advantageous embodiment, the backflush nozzle can have a nozzle body which contains at least one slit opening, with the backflush nozzle also having at least one nozzle support into which the nozzle body is inserted. In this embodiment the nozzle body and the nozzle support can be produced separately, as a result of which for example different materials can be used which are optimised for the respective function of the respective component. 
     In a particularly advantageous embodiment of a filter system equipped with the backflush device, the backflush nozzle can be arranged in the filter body in such a manner that it is at a distance from the filter body in the flow direction. This means that there is no direct physical contact between the backflush nozzle and the filter body. Furthermore, the backflush jet can flow openly through the cleaned fluid which is present on the clean side of the filter body, as long as the backflushing is carried out when the filter body is full, in particular during the filtering operation. Although this is associated with increased friction, it can be compensated by the high flow speed of the backflush medium. The contactless arrangement of the backflush nozzle and the filter body means that for example wear of the backflush nozzle can be considerably reduced if a relative rotation between the backflush nozzle and the filter body is used to clean off the filter body by backflushing gradually, virtually segment by segment, in the circumferential direction. 
     Further important features and advantages of the invention can be found in the subclaims, the drawings and the associated description of the figures using the drawings. 
     It is self-evident that the features which are mentioned above and those which are still to be explained below can be used not only in the combination specified in each case, but also in other combinations or alone without departing from the framework of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Preferred exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description, with the same reference symbols referring to the same or similar or functionally identical components. 
       In the figures, 
         FIG. 1  schematically shows a cross section through a filter system, 
         FIG. 2  schematically shows a view of a backflush nozzle, 
         FIG. 3  schematically shows a view as in  FIG. 2 , but in a different embodiment of the backflush nozzle, 
         FIG. 4  schematically shows a longitudinal section through the backflush nozzle according to section lines IV in  FIG. 2 , 
         FIG. 5  schematically shows a cross section of the backflush nozzle corresponding to section lines V in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     According to  FIG. 1  a filter system  1  has a housing  2  in which a filter body  3  is arranged. The filter body  3  separates an inlet space  4  or inlet side  4  from a clean space  5  or clean side  5  in the housing  2 . The filter body  3  has a cylindrical configuration and is preferably constructed in such a manner that it is flowed through radially from outside inwards during filtering operation. Accordingly, the inlet space  4  is situated radially outside the filter body  3 , whereas the clean space  5  is surrounded by the filter body  3 . The filter body  3  can for example be what is known as an edge-split filter. In principle any other desired designs for the filter body  3  are likewise conceivable, such as a filter body consisting of micromesh material or of a pleated filter material. The filter system  1  is used to remove impurities from a fluid. In particular solid particles can be filtered out of a liquid. In principle it is also possible to filter out solid or liquid particles from a gas. The contaminated fluid is supplied via a corresponding feed (not shown) to the interior of the housing  2 , that is, the inlet space  4 , while the cleaned fluid is conducted away via a corresponding outlet (not shown) from the interior of the filter body  3 , that is, out of the clean space  5 . 
     During filtering operation the impurities which cannot flow through the filter body  3  accumulate, concentrate and in particular form what is known as a filter cake on the inlet-side outer side of the filter body  3 . Although such a layer of impurities increases the filtration effect of the filter body  3 , the flow resistance of the filter body  3  also increases. Accordingly it is necessary to remove the deposited impurities regularly. To this end the filter system  1  is equipped with a backflush device  6 , with the aid of which the filter body  3  can be backflushed. This means that a suitable rinse medium flows through the filter body  3  counter to the cleaning direction. This means in the present case that the backflush device  6  drives a backflush medium in a suitable manner through the filter body  3  from the clean space  5  in the direction of the inlet space  4 . To this end the backflush device  6  has at least one backflush nozzle  7 . The backflush device  6  can apply the respective rinse medium to the filter body  3  with the aid of this backflush nozzle  7 . The backflush nozzle  7  has at least one opening  8  through which the rinse medium flows in a flow direction  9 , which is indicated here by an arrow, and exits from the backflush nozzle  7  during backflushing. The opening  8  is open towards the filter body  3  at its exit end  10  and communicates at its entry end  11  with a feed duct  12 . The backflush device  6  supplies the respective backflush nozzle  7  with the aid of the feed duct  12  with the rinse medium, which can be applied in particular with a corresponding comparatively high rinse pressure. In principle the backflush device  6  can have more than one such backflush nozzle  7 , which can be arranged one after the other in the axial direction of the filter body  3 , that is, parallel to the longitudinal centre axis  13  of the filter body  3 . 
     In the example shown, the backflush device  6  also comprises an outlet duct  14  which is arranged in the inlet space  4  and has at least one intake opening  15  which faces the filter body  3 . The backflush medium together with the removed deposits can pass through the respective intake opening  15  into the outlet duct  14 , from where it is transported away. To this end, a correspondingly low pressure prevails in the outlet duct  14 . The intake opening  15  is expediently arranged in alignment with the opening  8  of the backflush nozzle  7 . 
     In order to be able to clean off the entire filter body  3  gradually along its entire surface, the filter system  1  can also be equipped with a drive (not shown here), which allows a relative movement between the filter body  3  on the one hand and the backflush nozzle  7  and where present the outlet duct  14  on the other. In the preferred example the components of the backflush device  6 , that is in particular the backflush nozzle  7  and the outlet duct  14 , are arranged in a stationary manner while the filter body  3  is driven such that it rotates about its longitudinal centre axis  13 . 
     According to  FIGS. 1 to 5 , the opening  8  of the backflush nozzle  7  is according to the invention configured as a slit opening which is referred to below with  8 . This slit opening  8  extends in a straight line transversely with respect to the flow direction  9 . Furthermore, the slit opening  8  has an essentially constant cross-sectional profile  16  transversely to the flow direction  9 . This cross-sectional profile  16  has according to  FIG. 5  a nozzle segment  17  which expands in the flow direction  9 . The expanding cross section which can be flowed through in the cross-sectional profile  16  leads in the nozzle segment  17  to a drop in pressure and thus to an acceleration of the rinse medium. 
     The slit opening  8  is preferably also equipped in its cross-sectional profile  16  with an entry segment  18 . This entry segment  18  is adjacent directly upstream of the nozzle segment  17  and has a cross section which can be flowed through which decreases in the flow direction  9 . This means that a concentration of pressure can be realised as far as a transitional cross section  19  in which the entry segment  18  ends and the nozzle segment  17  begins. 
     According to  FIG. 5  the cross-sectional profile  16  in the nozzle segment  17  can preferably be equipped with an acute angle. This can in particular be less than 10°. In contrast to this, the cross-sectional profile  16  in the entry segment  18  can have an obtuse angle. This obtuse angle can in particular be greater than 100°. 
     The cross-sectional profile  16  in the nozzle segment  17  and in the entry segment  18  is preferably bounded in each case by straight wall contours. According to a particularly advantageous embodiment, the slit opening  8  in the cross-sectional profile  16  can form a de Laval nozzle. Such a de Laval nozzle is especially suitable for accelerating the rinse medium. 
     In the embodiment shown in  FIG. 2  the nozzle body  7  is produced from one piece and can in this manner be inserted into a feed duct support  20  which contains the feed duct  12  and has a corresponding nozzle body holder  21  for this purpose. 
     In contrast to this,  FIG. 3  shows an embodiment in which the backflush nozzle  7  is formed in two pieces. In  FIG. 3  the backflush nozzle  7  therefore comprises a nozzle body  22  which contains the at least one slit opening  8  and a nozzle support  23  into which the nozzle body  22  is inserted. The nozzle body  22  and the nozzle support  23  expediently form components which are produced separately from each other and can be produced in particular from different materials. In the assembled state the nozzle body  22  can be fixed in a suitable manner to the nozzle support  23 . For example, the nozzle body  22  can be welded to the nozzle support  23 . The nozzle body  22  can be configured as an injection moulded part, for example of plastic. It is likewise possible in principle to configure the nozzle support  23  as an injection moulded part, for example of plastic. 
     According to  FIGS. 2 and 4 , the slit opening  8  can be broken up in its longitudinal direction by one or a plurality of webs  24 . The respective web  24  is situated in the slit opening  8  and extends parallel to the flow direction  9 . The respective web  24  is used to brace the nozzle body  22  or to brace the backflush nozzle  7 . To this end the respective web  24  connects the mutually opposite wall segments  25  which bound the slit opening  8  transversely to the flow direction  9 . The respective web  24  is preferably configured in such a manner that it is only situated in the nozzle segment  17 . An outflow edge  26  of the respective web  24  can be at a distance from the exit end  10  of the slit opening  8 . In contrast to this, an inflow edge  27  can be arranged exactly at the entry end of the nozzle segment  17 , that is, essentially in the plane of the transitional cross section  19 . In the longitudinal section of the backflush nozzle  7  the respective web  24  can have a profile which tapers in the flow direction  9  according to  FIG. 4 . 
     According to a particularly advantageous embodiment, the backflush nozzle  7  can be mounted in such a manner relative to the filter body  3  that it is at a distance from the filter body  3  in the flow direction, that is, has no direct contact with the filter body  3 . To this end, the backflush nozzle  7  is at a distance in the radial direction from the filter body  3 . Correspondingly, the feed duct support  20  can also be arranged at a distance from the filter body  3 , so that there is no contact either between the feed duct support  20  and the filter body  3  on both sides of the backflush nozzle  7  in the circumferential direction of the filter body  3 . This means that a particularly low-friction and low-wear interaction can be realised between the backflush device  6  and the filter body  3  at least on the clean side  5 . The said distance between the backflush nozzle  7  and the filter body  3  is referred to in  FIG. 1  with  28 . It corresponds to a gap which is formed radially between the filter body  3  and the backflush nozzle  7 . 
     An outlet duct support  29  can in principle likewise be positioned in the inlet space  4  opposite the filter body  3  in such a manner that a radial gap  30  is likewise formed here between the filter body  3  and the outlet duct support  29 . A relatively large overlap in the circumferential direction means that a sufficient sealing effect can be achieved. Reduced friction and reduced wear can thus also be realised on the inlet side  4  between the filter body  3  and the outlet duct support  29 . 
     The fluid which has already been cleaned can for example be used as the rinse medium. If cleaning a liquid, a gas, for example compressed air, can also be used as the rinse medium. Accordingly, compressible and incompressible media can be used as the rinse medium. Depending on the application and the rinse medium used, differently designed backflush nozzles  7  can be used. In this case the two-part design of the backflush nozzle  7  with a nozzle body  22  and nozzle support  23  makes it possible to replace each nozzle body  22  in a simple manner.