Abstract:
A disc filter for separation of liquids from suspensions, in particular fiber stock suspensions, having several filter elements, in particular sector-shaped filter elements, which have a frame and filter areas mounted on both sides, over which a filter medium is mounted, with the filter areas having a lower-lying and higher-lying sections that form area filtrate channels, and having a center core which is provided with core filtrate channels. The filter elements contain collecting channels that receive and collect filtrate flow from the area filtrate channels formed by the lower-lying and higher-lying sections for delivery of the collected filtrate.

Description:
BACKGROUND OF THE INVENTION 
     The present invention concerns a disc filter for separation of liquids from suspensions, in particular fiber stock suspensions, having several filter elements, in particular sector-shaped filter elements, which have a frame and filter areas mounted on both sides, over which a filter medium is mounted, with the filter areas having lower-lying and higher-lying portions that form channels, and having a center core provided with filtrate channels. 
     The known disc filters and filter segments of the type described above have a great disadvantage in that the channels formed by the lower-lying and higher-lying sections for evacuation of the filtrate at the of the filter segment form a bottleneck. Also, holes are present at the surface of the filter element for evacuation of the filtrate, whereby the filtrate flow is caused to deflect and thus the filtrate discharge is hampered. This means that the filtrate cannot be sufficiently evacuated and sufficient dehumidification cannot be attained. 
     SUMMARY OF THE INVENTION 
     It is the purpose of the present invention to avoid the above disadvantages by a suitable design of the disc filter and the filter elements, especially for dewatering suspensions of relatively low solids content, occurring, in particular, in fiber recovery in the paper industry. 
     According to the invention, the filter elements contain collecting channels that receive flow from the channels formed by the lower-lying and higher-lying sections, and deliver flow toward the filtrate channels in the core. By arranging a collecting channel on each element, the filtrate is discharged over a larger cross-section so that no filtrate bottlenecks exist. 
     Preferably, the collecting channels are asymmetrically arranged in the filter element and are partly formed by the frame. With such an arrangement of the collecting channels, the filter element can be designed and manufactured at particularly low cost, while the entire surface of the filter element remains available for filtration. 
     A favorable design feature of the invention, is that the core has fixed holding devices or guides for the filter elements. As a result of this design feature the filter elements can be easily slid into the holding devices and mounted. 
     Another favorable design feature of the invention, is that the core has inlet fittings connected to the core filtrate channels, with the discharge fitting of each filter element being connected to an inlet fitting of the core, preferably by coaxial interference fit. This makes safe filtrate discharge in the center core and sealing possible, combined with ease of installation of the filter elements. 
     A further advantage of the invention, is that the filter areas and the frame form a hollow area, or cavity, which is open at the side of the filter element facing the center core. Through this cavity it is easy to achieve a pressure compensation between the cavity and the surrounding area both in the suspension and in the dry suction area, which means that costly support structures are no longer needed in the cavity of the filter element. 
     A particularly favorable design feature of the invention is that the cross-section of the collecting channels of the filter elements widens in the direction of the discharge into the core channels. This takes account of the filtrate quantity which increases in the direction of the center core, resulting in unimpeded discharge of the filtrate. 
     Another favorable design feature of the invention is that the channels of the filter elements formed by the lower-lying and higher-lying sections are inclined toward the center core at an angle α to the radially extending center line of the element, this angle α being between 30° and 90°, preferably about 60°. The filtrate discharge can be favorably influenced by this inclination of the channels toward the core. 
     A particularly favorable design feature of the invention is that the cross-section of the channels of the filter elements widens in the direction of the collecting channel. This results in lowest overall volumes of the filtrate channels, while the cross-section adapts to the filtrate quantity at the same time. 
     Another favorable aspect of the invention is that fixing of the filter elements is effected by connection to the neighboring filter element at the filter disc periphery, i.e., outer circumference. This method of connection stabilizes the entire disc filter, and if the filter elements are slid into holding devices it is sufficient to provide only the peripheral connection between elements. This ensures particularly favorable installation features, because fixings have only to be mounted on the filter disc circumference. This is particularly advantageous where filters with a large filter disc diameter are concerned. 
     A further advantage of the invention is that the filtrate flow cross section narrows at the filtrate discharge from the filter element into the channels of the core. The narrowing of the cross section can be provided at the outlet of the filter element if it directly engages the core filtrate channel. With this narrowing of the cross-section, the flow of the discharge from the filter element is sped up, which results in a more rapid emptying of the filter element. Alternatively, this narrowing can be provided in an inlet fitting to the filtrate channels of the filter core, which receives filtrate flow from the discharge fitting of the element. This arrangement can take into account on one hand, the flow conditions for different stocks that are to be dewatered and, on the other hand, special manufacturing facilities for replacement elements. 
     A further design feature of the invention is that the narrowing of the cross-section is achieved by means of a baffle plate at the side of the discharge opening at the core channel, for imparting a flow component in the direction of the flow of filtrate in the filter core. The narrowing of the cross-section is alternatively achievable by narrowing the wall of the fitting at the side of the discharge direction of the filtrate in the filter core. Depending on the manufacturing facilities the narrowing of the cross section can be achieved by providing a special shape for the fitting or otherwise by installing a baffle plate, which also makes revamping of the filter elements at a later date possible. If the narrowing of the cross-section is achieved by narrowing the core inlet fitting at the side in the discharge direction of the filtrate in the filter core, standard filter elements can be used. 
     Another feature of the invention is that at the side opposite to the discharge direction of the filtrate in the filter core, a baffle plate can be provided which optionally protrudes into the core filtrate channel. This helps achieve a particularly favorable deflection and speed-up of the flow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiment of the invention is described below with reference to the accompanying drawings, in which 
     FIG. 1 shows a disc filter according to the invention; 
     FIG. 2 shows a filter element according to the invention; 
     FIG. 3 is a cross-section along line III--III in FIG. 2; 
     FIG. 4 is a cross-section along line IV--IV in FIG. 2; 
     FIG. 5 is a cross-section along line V--V in FIG. 2; 
     FIG. 6 is a detail at VI from FIG. 2; 
     FIG. 7 is a cross-section along line VII--VII in FIG. 2; 
     FIG. 8 shows one design of a narrowing flow path of the element discharge fitting in accordance with the invention; 
     FIG. 9 shows a variant of a narrowing flow path, of the core inlet fitting in accordance with the invention; and 
     FIGS. 10 and 11 are analogous variants of the invention shown in FIGS. 8 and 9. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2 show the principal structure of a disc filter 1 in accordance with the invention. The filter comprises a filter vat 2 containing the suspension to be filtered, a substantially tubular filter core 3, and optionally a hood 4. Radially extending holding devices and guides 5 are fixed to the filter core 3. Sector-shaped filter elements 6 are slid radially inward into the guides 5. The filter core 3 has core inlet fittings 7, which are integral with or affixed to the core and lead radially to the core filtrate channels 8, which extend axially through the core. Discharge fittings 13 of the filter elements is slid into these inlet fitting(s) 7. The filter rotates about the axis in the direction of the arrow 9, whereby the discharge fitting 13 of the filter element 6 is the last to emerge from the suspension in vat 2, and prevents the filtrate from flowing backward, away from core 3. 
     FIGS. 2 and 3 show details of a filter element 6 according to the invention, with the adjoining filter core 3. The filter element 6 comprises a frame 10, to which spaced apart plates 16 are mounted. Each element 6 has frame portions 10 along the leading and trailing edges, and at the radially outer side. The plate areas have lower-lying sections or grooves 11, which serve as plate filtrate channels and lead to an element collecting channel 12 extending radially along the trailing edge of the filter element 6. The cross-section of the element collecting channel 12 widens in the direction of the filter core 3 and leads to element discharge fitting 13, which in turn connects to the core inlet fitting(s) 7 of the filter core. 
     At the radially inner side 14 of the filter element 6, the cavity 17 formed by the plates 16 is open toward the environs. Through this opening, the suspension in vat 2 can get into the cavity, whereby any pressure forces mutually relieve each other. The same applies by analogy to the section of humidification under hood 4. 
     The individual filter elements 6 are connected to each other at the outer circumference by holding devices 15. The filter media in the form of a porous bag or the like, is shrunk onto and defines the two outer filtration surfaces of the filter element in the customary manner. The bag is fixed at the lower end which faces the filtrate discharge, using holding plates. These holding plates serve at the same time as covers for the core filtrate channels 8 required for filtrate discharge but which do not serve as dewatering areas, in the foot of the sectors. This favors dewatering by suitable adaption of the disc filter control times. 
     FIG. 3 shows a section along line III--III in FIG. 2, along a plate filtrate channel 11. The filter element 6 consists of symmetrically arranged plates 16, which have higher and lower-lying areas (i.e., resembling corrugations), and thus form filtrate channels 11. Between plates 16 there is a cavity 17. At one end there is an element collecting channel 12, which is partly formed by the frame 10. Through the inclination of the plate filtrate channels 11 (i.e., transverse to the radial extension of element 6), there is a flow into the collecting channel 12, having a radially inward directed component, which is also in the direction of the flow in element discharge fitting 13, whereby flow diversions and hence flow impediments are prevented. 
     FIG. 4 shows the mounting of discharge fitting 13 of the filter element 6 in the inlet fitting 7 of the filter core 3. In the transitional section the discharge fitting 13 has a reduced outer diameter, which corresponds to the inner diameter of the inlet fitting 7. A sealing ring 18 is provided at the juncture of fitting 7 with the shoulder in the transition section of fitting 13. 
     FIG. 5 shows a section along line V--V in FIG. 2 and represents the mounting of the filter elements 6 in the holding devices and guides 5. The holding devices 5 are shaped such as to enclose the frames 10 of the filter elements and the filter bags mounted on top, providing safe guidance of the filter elements 6. 
     FIG. 6 shows a detail VI from FIG. 2, with the connection between two filter elements 6 in this case being effected as shown by segment connections 15 above its frame 10, and above the filter medium, e.g., the filter bag 5. These connections 15 are connected by means of screw 20 in the holding devices 5 at the radially outer side of the filter elements. 
     FIG. 8 shows the section through the direct connection of a filter element discharge fitting 13&#39; to the core filtrate channel 8, with the deflection and narrowing of the cross-section being effected by welded deflection plates 13a, 13b ending flush with the edge of the filtrate channel 8. 
     FIG. 9 shows an analogous section for the embodiment wherein the filter has an inlet fitting 7&#39; affixed to the core 3. The wall of the core inlet fitting 7&#39; is recessed at 7a, resulting in a narrowing of the flow cross section. The baffle plate 7b is identical to plate 13b of FIG. 8. The region of discharge from the elements 6 to the core channel 8, can be considered a &#34;discharge elbow&#34;, whether or not an inlet fitting 7 is present. 
     FIG. 10 shows an analogous design to FIG. 8 with the exception that the baffle plate 13c of fitting 13&#34; protrudes into the cross section of the core filtrate channel 8. 
     FIG. 11 corresponds to FIG. 9, also with the exception that the baffle plate 7c of fitting 7&#34; protrudes into the cross section of the core filtrate channel 8. 
     Thus, as shown in FIGS. 8-11, the filter elements have, or cooperate with, means for directing the collected filtrate through a flow cross-section to a discharge opening into the core filtrate channel. The flow cross-section narrows toward the discharge opening. Preferably, the narrowing is achieved by a concave flow surface 13b, 7b, 13c, 7c in opposition to a convex flow surface 13a, 7a formed at the opening of the discharge elbow. 
     This invention is not limited to the design shapes presented here. It is well possible for the filter elements to be directly fixed to the filter core. In this case, the holding devices and guides are not absolutely necessary. These holding devices and guides can take other shapes than those shown.