Abstract:
A backwash filter, in particular for highly viscous media, comprising a filter body ( 2 ) provided in a casing ( 1 ) and forming a cylinder jacket, wherein the casing ( 1 ) and the filter body ( 2 ) are rotatable about the axis of the filter body ( 2 ) relative to one another and wherein the filter body ( 2 ) separates a medium inflow space ( 14 ) from a medium outflow space ( 16 ), and comprising a flushing agent discharge channel ( 10 ) extending along a generatrix of the filter body ( 2 ), which flushing agent discharge channel ( 10 ) is movable relative to the filter body ( 2 ) and can be brought into flow connection with the filter body ( 2 ) across the entire length thereof and across the entire circumference thereof, with the formation of a stream of flushing agent flowing into the flushing agent discharge channel ( 10 ), is characterized, for increasing the efficiency of backwashing and of the throughput as well as for protection of the filter material, in that the flow connection always occurs only across a portion of the longitudinal extension ( 20 ) of a generatrix of the filter body ( 2 ).

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0001]    The invention relates to a backwash filter, in particular for highly viscous media, comprising a filter body provided in a casing and forming a cylinder jacket, wherein the casing and the filter body are rotatable about the axis of the filter body relative to one another and wherein the filter body separates a medium inflow space from a medium outflow space, and comprising a flushing agent discharge channel extending along a generatrix of the filter body, which flushing agent discharge channel is movable relative to the filter body and can be brought into flow connection with the filter body across the entire length thereof and across the entire circumference thereof, with the formation of a stream of flushing agent flowing into the flushing agent discharge channel. 
         [0002]    Backwash filters are known in many variants, such as, for example, from DE 198 03 083 A1, 
         [0003]    DE 195 23 462 A1 or AT 004594 U1. All these known backwash filters have a casing in which a filter body shaped like a cylinder jacket is provided, which filter body separates a medium inflow space from a medium outflow space. Due to a difference in pressure, the medium to be filtered thus flows through the filter body and thereby is cleaned from impurities. The impurities deposit on the filter body and the filter material, respectively, facing the medium inflow space and must be removed from the filter body after a certain amount of time, which is accomplished by backwashing. According to document DE 195 23 462 A1, said backwashing is effected via a flushing channel provided in the medium outflow space, which flushing channel extends along the filter body and is movable relatively around the circumference thereof, whereby the filter body rotating around its longitudinal axis is cleaned consecutively along its generatrix across the entire length thereof, by having a purified, i.e. already filtered medium flowing across the filter body into the flushing agent discharge channel in a direction opposite to the flow of the unpurified medium. 
         [0004]    According to DE 198 03 083 A1, a flushing agent feed channel is located in the medium outflow space, which flushing agent feed channel extends along a generatrix of the filter body, conveying flushing agent across the filter body to a flushing agent discharge channel arranged vis-a-vis, whereby the filter body is cleaned along a generatrix across its entire length. As a result of a relative motion between the flushing agent feed channel and the filter body or the filter body and the flushing agent discharge channel, respectively, the filter body is cleaned across its entire circumference. 
         [0005]    Backwash filters of this kind have the disadvantage that relatively large amounts of backwash liquid are required. Since the filter body is cleaned all at once across its entire length, as is shown in DE 195 23 462 A1 and DE 198 03 083 A1, the efficiency of the backwash filter decreases substantially. For this reason, the known backwash filters are suitable only for media of low viscosity. Furthermore, a relatively high pressure difference is necessary for cleaning the filter body, which pressure difference puts a lot of strain on the filter material supported by the filter body. 
         [0006]    The invention aims at avoiding the above-described disadvantages and difficulties and has as its object to provide a backwash filter of the initially described kind, which gets by with a small flushing volume. In addition, a more efficient flushing of the filter material is to be made possible with a mechanical engineering effort as small as possible so that extra fine filter materials can also be employed for backwash filters. This exceedingly good flushing should not be caused by an increased overpressure, which would be necessary for backwash filters according to the prior art, but is to be effected also in case of a small pressure difference at the filter body between the flushing agent inflow and the flushing agent outflow. In addition, it should be possible to provide, due to the small difference in pressure, larger free filter material areas not covered by supporting areas of the filter body so that the backwash filter enables a significantly larger throughput. 
       SUMMARY OF THE INVENTION 
       [0007]    According to the invention, said object is achieved in that the flow connection always occurs only across a portion of the longitudinal extension of a generatrix of the filter body. 
         [0008]    According to a preferred embodiment, the medium inflow space is formed between the casing and the filter body, and the medium outflow space is formed in the interior of the filter body, with the flushing agent discharge channel provided outside of the filter body. 
         [0009]    Preferably, the flushing agent discharge channel is formed by a pipe mounted rotatably about its longitudinal axis, which pipe is provided with a slot extending in the shape of a helix across the wall of the pipe and connecting the pipe&#39;s interior to the exterior thereof, with the outer surface of the pipe contacting the filter body across the entire longitudinal extension thereof. The purified medium can thereby be used as a backwash liquid, with only a small amount thereof being required for a high backwash effect, since said medium gets into the flushing agent discharge channel only across a very small length of a generatrix of the filter body. 
         [0010]    According to a different embodiment, the same advantage can be achieved in that the flushing agent discharge channel is formed by a pipe displaceable along its longitudinal axis, which pipe has a radially oriented flushing opening connecting its interior to its exterior, which flushing opening has an extension along the longitudinal axis of the pipe which is smaller than the longitudinal extension of the filter body, with the outer surface of the pipe preferably contacting the filter body across the entire longitudinal extension thereof and with the flushing opening being oriented toward the filter body. 
         [0011]    If it is desired, for example, to use a flushing fluid other than the purified medium for the two above-described variants, a flushing agent feed channel is advantageously provided in the interior of the filter body vis-a-vis the flushing agent discharge channel provided outside of the filter body, with the flushing agent feed channel having a longitudinal slot oriented toward the flushing agent discharge channel and extending across the entire longitudinal extension of the filter body. In this way, a flushing agent pressure can also be adjusted independently of the pressure of the purified medium. 
         [0012]    According to another advantageous embodiment, the flushing agent discharge channel has a longitudinal slot extending across the entire longitudinal extension of the filter body, and a flushing agent feed channel arranged vis-a-vis the flushing agent discharge channel is provided, which flushing agent feed channel is formed by a pipe mounted rotatably about its longitudinal axis and provided with a slot extending in the shape of a helix across the wall of the pipe and connecting the pipe&#39;s interior to the exterior thereof, with the outer surface of the pipe contacting the filter body across the entire longitudinal extension thereof. Also in this case, the flushing agent pressure is independent of the pressure of the filtered medium, and a flushing agent of a kind other than the filtered medium can also be used. 
         [0013]    Said advantages also arise in the suitable embodiment which is characterized in that the flushing agent discharge channel is provided with a slot extending across the entire longitudinal extension of the filter body and that a flushing agent feed channel is provided vis-a-vis the flushing agent discharge channel, which flushing agent feed channel is formed by a pipe mounted displaceably along its longitudinal axis, which pipe has a flushing opening radially oriented toward the slot of the flushing agent discharge channel and is displaceable with said flushing opening from one end of the filter body to the other end of the filter body and beyond, with the flushing opening having an extension in the direction of the longitudinal axis of the pipe which is shorter than the longitudinal extension of the filter body. 
         [0014]    In order to avoid losses, the flushing agent discharge channel is advantageously sealed off with gaskets against the filter body on both sides of the generatrix along which the flushing agent discharge channel contacts the filter body. 
         [0015]    Advantageously, the filter body has a pressure plate and a support plate as well as a filter material arranged therebetween. 
         [0016]    Preferably, the filter body is rotatably mounted relative to the stationary casing, wherein a feed inlet for medium to be filtered is provided in the casing in the direction of rotation of the filter body, immediately adjacent to the flushing agent discharge channel. As a result, the highest pressure prevails in the part of the filter body which is already burdened most and/or provided with most impurities, and, respectively, the contaminated medium establishes the first direct contact with the filter body, whereas the medium reaches filter areas charged with less and less impurities by flowing around the filter body at a lower pressure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    For a better understanding of the present invention, reference is made to the following examples and drawings. Referring to the drawings: 
           [0018]      FIG. 1  shows a longitudinal section through an exemplary embodiment of a backwash filter according to the invention; 
           [0019]      FIG. 2  shows a transverse section through the exemplary backwash filter shown in  FIG. 1 , 
           [0020]      FIG. 3  shows a longitudinal section through another exemplary embodiment of a backwash filter according to the invention; 
           [0021]      FIG. 4  shows a transverse section through the exemplary backwash filter shown in  FIG. 3 ; 
           [0022]      FIG. 5  shows a longitudinal section through a further exemplary embodiment of a backwash filter according to the invention; 
           [0023]      FIG. 6  shows a transverse section through the exemplary backwash filter of  FIG. 5 ; 
           [0024]      FIG. 7  shows a longitudinal section through another exemplary embodiment of a backwash filter according to the invention; 
           [0025]      FIG. 8  shows a transverse section through the exemplary backwash filter of  FIG. 7 ; 
           [0026]      FIG. 9  shows a longitudinal section through a further exemplary embodiment of a backwash filter according to the invention; 
           [0027]      FIG. 10  shows a transverse section through the exemplary backwash filter of  FIG. 9 ; 
           [0028]      FIG. 11  shows a longitudinal section through another exemplary embodiment of a backwash filter according to the invention; 
           [0029]      FIG. 12  shows a transverse section through the exemplary backwash filter of  FIG. 11 ; 
           [0030]      FIG. 13  shows an exemplary embodiment of feed channels according to the invention; 
           [0031]      FIG. 14  shows an exemplary embodiment of flushing agent discharge channels according to the invention; 
           [0032]      FIG. 15  shows a longitudinal section through discharge channels of the exemplary backwash filters of  FIGS. 9 ,  10 ,  11  and  12 ; and 
           [0033]      FIG. 16  shows a transverse section of the exemplary discharge channel of  FIG. 15 ; 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    It has turned out to be advantageous for the helical slot to be two-start. 
         [0035]    For highly viscous media, the portion of the flow connection suitably extends across at most 20%, preferably at most 5%, of the longitudinal extension of the filter body. 
         [0036]    Below, the invention is described in further detail based on several exemplary embodiments illustrated in the drawing, wherein  FIG. 1  shows a longitudinal section through a backwash filter and  FIG. 2  shows a transverse section through the same filter taken along line II-II of  FIG. 1  according to a first embodiment of a backwash filter.  FIGS. 3 and 4  and  5  and  6 , respectively, as well as  7  and  8  and also  9  and  10  and  11  and  12  each show further embodiments in illustrations which are analogous to  FIGS. 1 and 2 .  FIGS. 13 and 14  show views of flushing agent feed channels and flushing agent discharge channels, respectively, in the disassembled state.  FIGS. 15 and 16  illustrate a variant in the longitudinal section ( FIG. 15 ) and in the transverse section ( FIG. 16 ). 
         [0037]    According to the embodiment of a backwash filter illustrated in  FIG. 1 , in a casing  1  designed in the shape of a cylinder jacket, a filter body  2 , which is also shaped like a cylinder jacket, is rotatably mounted, the casing  1  being arranged in a stationary manner. The rotary drive  3  for the filter body  2  is implemented by an electric motor  4  which drives the filter body  2  via a toothed gear  5 . The backwash filter is provided with a ventilation and has a control device for the control of pressures. The casing  1  is heatable; the heating pipelines are indicated by H. 
         [0038]    The filter body  2  itself has a pressure plate  6  extending on the outside across the entire circumference, which optionally is composed of segments, and an internal support plate  7  also extending across the entire circumference, between which plates the filter material  8  is inserted. Both the pressure plate and the support plate are provided with radially oriented openings  9  so that a medium can flow through the openings  9  while passing the filter material  8 . Said openings  9  are depicted only at one end of the filter body  2 , however, they are provided across the entire longitudinal extension  20  thereof. By the longitudinal extension  20  of the filter body  2  the length is understood across which the filter material  8  extends. Thereby, various supporting areas  2 ′ for mounting the filter body remain unconsidered. 
         [0039]    A flushing agent discharge channel  10  extends along a generatrix of the filter body  2 . The flushing agent discharge channel  10  is formed by a rotatably mounted pipe  11 , which is also drivable by an electric motor  12  via a transmission  13  and tangentially contacts the filter body  2  on the outside, i.e., on the outside of the pressure plate  6 . Said pipe  11  extends across the entire longitudinal extension  20  of the filter body  2  and is rotatably mounted in the casing  1 . 
         [0040]    Between the casing  1  and the filter body  2 , a medium inflow space  14  is formed, which is supplied, via a feed inlet  15 , with fresh medium still to be purified. The interior space  16  of the filter body  2  forms the medium outflow space for the filtered medium, which filtered medium flows off through a discharge channel  17 . 
         [0041]    The pipe  11  has a slot  18  extending across its entire length, which slot connects the interior of the pipe  11 , i.e., the flushing agent discharge channel  10 , to the exterior thereof and extends in the shape of a helix across the wall of the pipe  11 . 
         [0042]    The backwash filter has the following function: 
         [0043]    The medium to be filtered gets into the medium inflow space  14  via the feed inlet  15 , namely at a point which is provided immediately adjacent to the position of the flushing agent discharge channel  10 , in the direction of rotation of the filter body  2 , which direction is indicated by the arrow  19 . The medium to be filtered now spreads evenly across the circumference of the filter body  2 , flows through the openings  9  thereof and thus reaches, in a filtered state, the central interior space of the filter body  2  forming the medium discharge space  16 . 
         [0044]    Due to the tangential contact of the pipe  11  of the flushing agent discharge channel  10  with the outer wall of the filter body  2 , the flushing agent discharge channel  10  is brought into flow connection with the filter body  2  and hence also into flow connection with the medium outflow space  16 , wherein, however—and this is essential—said flow connection extends only across a very short longitudinal extension  20  of the filter body  2 , particularly as the slot  18  helically extending around the pipe  11  is always oriented toward the filter body  2  only with a very small part  21  of its longitudinal extension. By rotating the pipe  11  continuously or also discontinuously, all openings  9  of the filter body  2  which are located on a generatrix are gradually brought into flow connection with the flushing agent discharge channel  10  so that a cleaning of all openings  9  is effected by backwashing with a medium that has already been purified. It thereby becomes possible also for highly viscous media to get by with a small pressure difference during backwashing, since said pressure difference is focused only on a small area of the filter material  8 . 
         [0045]    The filter body  2  can likewise be rotated continuously or discontinuously. The discontinuous rotation can be controlled by the pressure course so that an operation results which is as constant in pressure as possible. The rotation of the filter body  2  can occur gradually (e.g., in each case by 5°). 
         [0046]    In order to avoid losses, the flushing agent discharge channel  10 , i.e. the pipe  11 , is embedded in the casing  1 , with the casing  1  being provided, immediately adjacent to the flushing agent discharge channel  10 , with gaskets  22  oriented toward the filter body  2  and extending along the entire length of the casing  1  on both sides of the flushing agent discharge channel  10 . 
         [0047]    The flushing agent discharge channel  10 , i.e. the pipe  11 , may be provided with a slot  18  helically extending along the pipe  11  in a single-start fashion or also with a slot  18  helically extending along the pipe  11  in a two- or multi-start fashion. A two-start slot  18  is illustrated in  FIG. 14 . Analogously to the illustration of  FIG. 1 ,  FIG. 13  shows a single-start slot  18 . 
         [0048]    According to the embodiment illustrated in  FIGS. 3 and 4 , the flushing agent discharge channel  10 , i.e. the pipe  11 , is not rotatably mounted in the casing  1  but is longitudinally displaceable and has a flushing opening  23  radially oriented toward the filter body  2 . Said flushing opening  23  has a longitudinal extension  24 , i.e. an extension parallel to a generatrix of the filter body  2 , which is significantly smaller than the longitudinal extension  20  of the filter body  2 . A displacing device  25  for the flushing agent discharge channel  10  is schematically indicated in  FIG. 3 . The flushing opening  23  can be displaced continuously or discontinuously from one end of the filter body  2  to the other end of the filter body  2  across the longitudinal extension  20  thereof and beyond so that, again, all openings  9  of a generatrix of the filter body  2  are gradually cleaned. 
         [0049]    The variant of a backwash filter illustrated in  FIGS. 5 and 6  basically corresponds to the embodiment illustrated in  FIGS. 1 and 2 , except for a flushing agent feed channel  26  provided in the interior of the filter body  2 , i.e. in the medium outflow space  16 , and having a longitudinal slot  27  extending across the entire longitudinal extension  20  of the filter body  2 . The flushing agent feed channel  26  is provided in a stationary manner and thus is arranged in a stationary insert body  31  relative to which the filter body is rotatable. Because of this, it is feasible to use a flushing agent having a pressure independent of the pressure of the purified medium for cleaning the filter material  8 . A pressure booster pump  28  provided in a conduit  29  conveying the purified medium to the flushing agent feed channel  26  is schematically illustrated in  FIG. 5 . Instead of the pressure booster pump  28 , a piston pressure system can also be used. 
         [0050]      FIGS. 7 and 8  show a backwash filter variant according to which a flushing agent feed channel  26 , as illustrated in  FIGS. 5 and 6 , is provided, however, with the flushing agent discharge channel  10  being provided so as to be longitudinally displaceable, analogously to the variant shown in  FIGS. 3 and 4 . 
         [0051]      FIGS. 9 and 10  show a variant according to which the flushing agent discharge channel  10  has a straight slot  32  extending across the entire length of the filter body  2 , which slot is stationary and oriented directly toward the filter body  2 . A flushing agent feed channel  26  is, in this case, formed by a rotatable pipe  30  which is designed analogously to the flushing agent discharge channel  10  of the variant illustrated in  FIGS. 1 and 2 , i.e. the pipe  11  thereof. It has a slot  18  (single-, two- or multi-start) extending in the shape of a helix across its length, whereby the filter body  2 , i.e. the openings  9  thereof, is charged with flushing agent only across a short longitudinal extension  21 . By rotating the pipe  30  continuously or discontinuously, it is again feasible to clean the filter body  2  across the entire longitudinal extension  20  of one of its generatrices. 
         [0052]    A variant of the backwash filter comprising a pipe  30  designed analogously to the pipe  11  of the variant shown in  FIGS. 3 and 4  is illustrated in  FIGS. 11 and 12 . The flushing opening  23 , which again has only a small longitudinal extension  24  compared to the longitudinal extension  20  of the filter body  2 , is displaceable across the entire longitudinal extension  20  of the filter body  2  so that, again, the filter body  2  can be cleaned on one of its generatrices across the entire longitudinal extension  20  thereof. Also in this case, the flushing agent discharge channel  10  has a slot  32  extending across the entire longitudinal extension  20  of the filter body  2 . 
         [0053]    According to the embodiments illustrated in  FIGS. 7 to 12 , the insert bodies  31  are also supported in a stationary manner. 
         [0054]    According to the variant illustrated in  FIGS. 15 and 16 , the flushing agent discharge channel  10  is designed like in the embodiments illustrated in  FIGS. 9 to 12 , i.e. as a stationary straight slot  32 . A flow connection for the flushing agent extending only across a portion of the longitudinal extension  20  is achieved by means of a slide  33  which covers the slot  32  but exhibits a flushing opening  23  movable across the entire longitudinal extension  20 . 
         [0055]    In particular, the invention is applicable for the Lyocell technology. The backwash filter may have leakage openings analogously to EP 0 781 356 A1 in appropriate places.