FLAT FILTER ELEMENT AND FILTER MODULE COMPOSED OF FILTER ELEMENTS

The invention relates to a flat filter element and a filter module composed of said filter elements, which are easy to handle and enable easy disposal when dealing with large filtering surfaces. The filter element consists of at least one inner structure ( 17 ) formed by openings ( 20 a - f, 21 a, b, 30 a - g, 31 a, b ), wherein the defining surface of the openings ( 20, 21 a, b, 30 a, b, 31 a, b ) formed by the depth filter material ( 12 ) constitutes a through-flow surface ( 11 a, b ) which is substantially perpendicular to the filter element plane.

FIG. 1 a shows a flat filter element 10 which has a meander-shaped structure. After producing a conventional filter element, for example with a quadratic shape, an opening 20 is made in the filter element 10 , by which the inner structure 17 is established. The surface of the opening 20 which is bordered by the deep-bed filter material 12 forms a flow surface 11 a or 11 b for the filtered material and unfiltered material which is roughly twice as large as the corresponding surface in a ring with the same area. In the embodiment shown here it is a finger-like opening 20 to which the outside contour 18 is likewise adapted for example by punching out. The remaining deep-bed filter material 12 thus has a meander-like structure, the width of the effective filtration areas being the same everywhere. If this filter element 10 is exposed to flow radially for example from the outside via the peripheral surface 19 , loops on the outside form unfiltered material spaces 25 . Within the filter element 10 the filtered material collects and is removed through a core hole 34 which is shown by the broken line in an end plate which is not shown. This filter element 10 can also be exposed to flow in the reverse direction by delivering the unfiltered material via the core hole 34 and thus via the opening 20 . In both cases the filter element 10 is exposed to flow parallel to the plane of the filter element, therefore essentially radially. FIG. 1 b shows in perspective the filter element 10 which is shown in FIG. 1 a to illustrate the convex bodies 60 , 62 . The filter element 10 is jacketed by the smallest possible convex body (outside body) which in the embodiment shown is a polyhedron with an octagonal base surface, the edges being rounded. The pertinent outside peripheral surface 61 can be imagined as a band placed around the filter element 10 . Similarly, a convex body as large as possible (inside body) 62 is inserted into the opening 20 and has a peripheral surface 63 . This convex inner body has a rectangular base surface. As a result of the polygonal configuration of the filter element 10 the sum of the flow surfaces 11 a , 19 is larger than the sum of the surfaces 61 and 63 . FIG. 2 shows another embodiment of a filter element in the form of a disk 10 ′ in which two concentric annular openings 20 and 30 are made in the filter disk 10 ′. Neither opening 20 , 30 is connected to one another and they form one opening of the first type and one opening of the second type. The outside peripheral surface 61 of the convex outside body 60 is identical to the outside peripheral surface 19 of the filter disk 10 ′. The openings 20 and 30 are not completely closed into a ring here because in addition there are connection openings 21 and 31 which intersect the respective circles of the openings 20 and 30 . The connection opening 21 establishes the connection from the inner opening 20 to the peripheral surface 19 . The connection opening 31 extends likewise in the radial direction and joins the outer annular opening 30 to a round hole in the middle which represents a so-called collection opening 33 . All openings together form the inner structure 17 . The collection opening 33 in the embodiment shown here represents the largest opening within the filter disk 10 ′ so that the largest possible convex inside body 62 (shown by cross hatching) which is identical to the collection opening 33 can be inserted. If the sum of all flow surfaces is compared to the sum of surface 61 and surface 63 , this sum of all flow surfaces is larger. The width of the effective filtration areas between the peripheral surface 19 and the outer opening 30 or the outer opening 30 and the inner opening 20 and between this opening 20 and the collection opening 33 is the same everywhere so that the same filtration action is achieved everywhere in the filter disk 10 ′. The disk can be operated such that the unfiltered material is supplied to the inner opening 20 via the input of the connection opening 21 labelled 24 . The filter element is thus exposed to flow not only via the peripheral surface 19 , but also in the interior via the flow surfaces which are formed by the inner opening 20 . As can be seen in FIG. 3 which shows a section along the line III-III through the filter element as shown in FIG. 2 , in the direction of the arrow 13 the unfiltered material penetrates the effective filtration areas from the outside, i.e. via the peripheral surface 19 which thus forms a flow surface. The filtered material flows on the flow surfaces 11 b into the corresponding opening 30 where the filtered material is collected and reaches the collection opening 33 via the connection opening 31 . At the same time via the connection opening 21 which is shown only in FIG. 2 unfiltered material is supplied to the opening 20 , where the unfiltered material penetrates through the flow surfaces 11 a into the deep bed filter material. As the filtered material it then passes through the flow surfaces 11 b into the opening 30 and into the collection opening 33 . In the reverse mode of operation the unfiltered material would be delivered via the collection openings 33 from where is would reach the openings 30 via the connection opening 31 where it is distributed and would emerge through the effective filtration areas as filtered material in the inner opening 20 . The filtered material would be discharged then in this case via the connection opening 21 . FIG. 4 shows another embodiment which corresponds essentially to the one shown in FIG. 2 . The entire filter disk 10 ′ under certain circumstances can become too unstable due to the annular openings 20 and 30 , especially when the diameter is very large and the thickness of the filter elements is very low. To increase stability, in the opening 20 there are two stiffening bridges 41 which divide the opening 20 into three roughly equal-sized, arc-shaped sections. Accordingly the outside opening 30 has two stiffening bridges 42 . When the filter disks 10 ′ are stacked on top of one another to form a filter module 1 , as is shown in FIG. 11 , in the embodiment shown in FIG. 4 it must be watched that the disks are exactly aligned to one another so that the connection openings 21 and 31 do not accidently cross one of the openings 20 or 30 ; this would lead to mixing of the filtered material and unfiltered material. Therefore it must be watched during assembly that the openings of the first type, here the opening 20 , 21 , cannot connect to the openings of the second type (openings 30 , 31 , 33 ). To fix the alignment of the filter disk 10 ′ on the peripheral surface 19 there are fixing structures 44 into which the rods 71 shown in FIG. 11 fit. In FIG. 11 the filter disks 10 ′ shown in FIG. 4 are combined with filter elements as shown in another embodiment, with openings which are not connected to the outer edge. When identical filter disks 10 ′ as shown in the embodiment in FIG. 4 are stacked on top of one another, the connection openings 21 all lying on top of one another, it is necessary to provide a corresponding end plate so that the individual sections of the openings 20 and 30 can communicate with one another. So that a complex end plate is not necessary, the filter disks 10 ′ can also be stacked on top of one another twisted somewhat to one another. The angle of twist must be chosen according to the width of the stiffening bridges 41 and 42 such that the openings 20 and 30 of the adjacent filter disk 10 ′ cover these stiffening bridges. On the other hand, the twist should not be chosen to be so great that the connection openings 21 and 31 cross the openings 20 and 30 . FIG. 5 shows another embodiment in which there are a total of six concentric annular openings. The openings 20 a to c form the openings of the first type, while openings 30 a to c form the openings of the second type which are connected via the common connection opening 31 to the collection opening 33 . Accordingly the openings 20 a to c are connected via the connection opening 21 to the peripheral surface 19 . This embodiment also has stiffening bridges 41 and 42 . The following table lists the flow surface in square meters for a filter module consisting of 250 filter elements with a thickness of 0.4 cm. As the number N of annular openings increases, with a correspondingly larger outside diameter d max of the filter elements at N&equals;15 openings almost 70 m 2 are reached, the width of the openings is 5 mm and the width of the effective filtration areas is 20 mm. 1 N d max &lsqb;mm&rsqb; A Filtered material &lsqb;m 2 &rsqb; 0 60 0.17 1 160 0.82 2 260 2.04 3 360 3.82 4 460 6.16 5 560 9.08 6 660 12.55 7 760 16.60 8 860 21.21 9 960 26.38 10 1060 32.12 11 1160 38.43 12 1260 45.30 13 1360 52.73 14 1460 60.73 15 1560 69.30 The quotient of the filter surface multiplied by the filter thickness and the space occupied by the filter module is of interest since this value reproduces the holding capacity of the filter module relative to the space. Considering that in conventional bed filtration there are filter frames 1 mm thick between the beds, this quotient is 29%. Conversely, in the module as claimed in the invention (for example for N&equals;12) this quotient is 73%. Thus the modules as claimed in the invention have much better space use. FIG. 6 shows another embodiment in which there a two openings 20 and 30 in the form of intertwined spirals. These openings 20 and 30 have stiffening bridges 41 and 42 . FIGS. 7 to 9 show filter disks 10 ′ which are provided with straight openings 20 a to f , 30 a to g . All openings of the first type 20 a to 20 f discharge on the peripheral surface 19 . All openings of the second type 30 a to 30 g are connected via two radial connection openings 31 a and 31 b to the collection opening 33 . FIG. 8 shows a similar embodiment, but with a quadratic outside contour. The openings 20 , 30 run parallel to the side edge 16 of the filter element 10 . In addition, there are two collection openings 33 a and b . Within the openings of the second type 30 a to c and 30 d to f thus two groups are formed again. In this embodient there are stiffening bridges 41 and 42 which divide the respective openings 20 a to 20 f and 30 a to f into sections of differing length. FIG. 9 shows an octagonal filter disk 10 ′ in which both the openings 20 a - f a, 30 a - g and also the connection openings 21 a, b , and 31 a, b are provided with stiffening bridges 41 , 42 and 43 . To form a filter module identical filter disks 10 ′ can be stacked on top of one another. There are various possibilities for this. Thus adjacent disks can be arranged turned 180° each. This is ensured by the respective connection bridges 41 , 42 and 43 coming to rest over a corresponding opening so that only the openings of the same type are connected to one another and no mixing of the filtered material and unfiltered material can occur. Turning only each n-th element by 180° is also conceivable. FIG. 10 shows another embodiment of a filter element 10 in which wide openings 20 , 30 are combined with slots 27 , 37 which are connected to the respective slots. It is also possible to provide exclusively slots 27 and 37 . FIG. 11 shows a filter module 1 which for example has nine filter disks, of which the filter disk 10 ′ corresponds to the embodiment shown in FIG. 4 . The filter elements are placed on an end plate 70 on which two rods 71 are attached which fit into the corresponding fixing recesses 44 on the disk edge and in this way guarantee the alignment of the filter disks 10 ′. On the rods 71 the entire module can be grasped and removed from the filtration device. Complicated installation and removal are eliminated. Furthermore the entire module except for rods 71 and the end plate 70 can be disposed of as a whole without the individual disks having to be separated from one another. FIG. 12 shows a stack of filter disks in an exploded view, two embodiments of filter disks 10 a ′ and 10 b ′ being placed on top of one another in alternation. The filter disks 10 a ′ have a radial connection opening 21 with one entry 24 on the edge, while filter disks 10 b ′ have exclusively concentric openings 20 , 30 . A corresponding arrangement of stiffening bridges within the openings ensures that the openings of the first type do not cross the openings of the second type. The collection openings 33 on top of one another form a channel 35 for the filtered material which is shown by the broken line, while the space 36 for the unfiltered material forms the space which surrounds the filter elements 10 a′, b′. FIG. 13 shows an enlarged extract of two disks placed on top of one another. The unfiltered material is supplied through the connection opening 21 b and is distributed into the openings 20 b . It can be clearly seen that the stiffening bridges 41 a , 42 a of the top disk 10 a ′ are above the corresponding openings of the lower disk 10 b ′. Accordingly the stiffening bridges 41 b and 42 b are located in the area of the corresponding openings 20 a and 30 of the upper disk 10 a ′. The flows 13 of unfiltered material 13 and flows 14 of filtered material are routed in the manner of waves by overflows and underflows of the stiffening bridges 41 b and 42 b into the respective holes. The collected filtered material is removed via the connection opening 31 b. Not all the stiffening bridges 41 a , 42 a , 41 b , 42 b need have the same thickness as the filter disk 10 a ′, 10 b ′. For purposes of illustration therefore the stiffening bridge 41 a ′ is shown with a reduced thickness. FIG. 14 illustrates a filtration means 51 into which a filter module 1 composed of a plurality of filter disks 10 ′ is installed. The filter module stands on a bottom solid end plate 53 . To compensate for changes in the location of the module for operation, the upper end plate 52 is movably supported. In the case shown the space 25 for the unfiltered material is located outside of and above the module 1 . The filtered material space here is located within and underneath the module 1 . The unfiltered material passes through the connection 54 in the side wall of the container jacket 56 into the filtration means 51 and the filtered material leaves it through a central connection 55 on the bottom thereof.