Abstract:
The invention relates to a control head constructed for use with rotary filters for controlling separation of filtrate from the filters into adjustable filtrate zones. It is characterized by the fact that at least one filtrate separator (7) is provided, which includes a mechanism for diverting of the flow (9) from axial flow in channels that are axially arranged with respect to the axis of the filter to radial flow without causing entrainment or formation of air bubbles in the diverted flow.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a control head for rotary filters with adjustable filtrate zones. 
     Known control heads in rotary filters, for instance as described in EP 0 400 787, (U.S. Pat. No. 5,053,123) have the recurring problem of bubbles forming and air being discharged, causing the water column formed in the dropleg to break and consequently the vacuum formed to break as well. As a result, there is no more dewatering action. There have been attempts, for instance in WO 94/12261, at shaping the control head such as to collect the bubbles at one point. This did not yield the desired effect, however, because time and again, larger groups of bubbles were entrained, with the resulting above-described effect. 
     It is the objective of the invention to reduce the flow resistance in the control head. 
     This is achieved by providing at least one filtrate separator, which is furnished with means to deflect the flow. On account of the deflection of flow provided, the filtrate can advantageously be routed to the droplegs without hitting against a surface and thus causing bubbles to form by the vortex created. 
     A further development of the invention is characterized by the fact that at least one deflector is foreseen for diverting the flow, advantageously with several deflectors being foreseen in a parallel arrangement. Thus, flow deflection is achieved especially efficiently and by simple means. 
     One advantageous development of the invention is characterized by the fact that the filtrate separate runs in a deflector plate which is fixed in the casing. With such an arrangement, the flow is completely diverted whatever the position of the filtrate separator. One advantageous development of the invention is characterized by the fact that the channels formed by the means of flow deflection run into channels formed in the casing between fixed guiding plates. Thus, the filtrate flowing from the control head can be especially well deflected to the filtrate pipes, whereby flow losses are minimized. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is now explained in an exemplary manner with reference to the following the figures, where: 
     FIG. 1 is a section view through a state-of-the art control head; 
     FIG. 2 shows a control head according to the invention; 
     FIG. 3 depicts a three-dimensional representation of a development according to the invention; 
     FIG. 4 is a section view through the control head by analogy to FIG. 2; 
     FIG. 5 is a section view along line V--V in FIG. 4; 
     FIG. 6 shows a further variant of the invention; 
     FIG. 7 is a section view along line VII--VII in FIG. 6; 
     FIG. 8 shows a further variant of the invention; 
     FIG. 9 is a section view along line IX--IX in FIG. 8; 
     FIG. 10 shows another variant of the invention; and 
     FIG. 11 is a section view along line XI--XI in FIG. 10. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The control head in FIG. 1 corresponds to FIG. 6 of U.S. Pat. No. 5,053,123, the disclosure of which is hereby incorporated by reference. FIG. 1 shows the end of the filter shaft 45 with filtrate channels 47, a control disc 42, and the internals in the control head proper 36. Specially identifiable are the filtrate discharge pipes 72, 73 and the filtrate separator 53. It can also be seen from FIG. 1 that the control head is terminated by a front plate (broken-line front). 
     FIG. 2 shows a control head according to the invention, where the control head front plate is cambered and thus smoothly deflects the filtrate toward the dropleg 5 without air bubbles forming, as occurs conventionally. The filtrate coming from the filter segments is led to the control head or filtrate head 1 via the filtrate channels 2 in filter shaft 3. The curved front 4 of filtrate head 1, in its lower section, ensures advantageous deflection of the filtrate. The filtrate is then discharged through dropleg 5, with which the vacuum is created. 
     FIG. 3 shows a three-dimensional representation of a variant of deflection in accordance with the invention. Here the filter axis 6, around which the individual filtrate pipes are arranged, is represented. The essential fact is that the movable, adjustable filtrate separator 7 with the closing plate 8 has several deflectors 9&#39;, 9&#34;, 9&#39;&#34; with which the flow of the filtrate can be advantageously deflected in the filtrate zone, as received from the collection channels in the shaft from the direction of arrow 10 toward the direction of arrow 11, into the dropleg, with least possible velocity losses. Filtrate separator 7 and closing plate 8 are movable along line 12. 
     FIG. 4 shows a section through the control head according to the invention. Here, the filter shaft 3 with filter axis 6 and filtrate pipes 2 can be seen. The filtrate from filtrate pipes 2 flows in the direction of arrow 10, into control head 1, and there runs into the deflectors 9&#39;, 9&#34; and 9&#39;&#34; mounted to the filtrate separator 7 and the closing plate 8. From there, it is deflected in the direction of arrow 11, into dropleg 5. Additional deflectors 12, which are fastened to dropleg 5, can further improve deflection. The rotation of the filter shaft 3 is as represented by arrow 18. 
     The section through the control head along line V--V in FIG. 4 is represented in FIG. 5. Here the two end positions of the filtrate separator 7 and 7&#39; are to be seen. In position 7&#39;, the deflector 9&#34; is flush with the edge of dropleg 5&#39;, through which the clear filtrate is discharged. The cloudy filtrate flows through dropleg 5. In Position 7, more clear filtrate is discharged. The last of the deflectors is now in position 9&#39; and deflects the filtrate to the other, fixed deflectors 12 and into dropleg 5. (The outlets for the individual droplegs are not represented here.) 
     In the variant of the invention represented in FIGS. 6 and 7, the connections for droplegs 5 and 5&#39; are partly arranged one after the other when seen in the axial direction, which means that an even larger part of cloudy filtrate is discharged. The reference numbers are the same as those on the other figures. For better deflection of the cloudy filtrate, fixed deflectors 13 are foreseen here. (The outlets for the individual droplegs are not represented here.) 
     FIGS. 8 and 9 represent a further variant of the invention. FIG. 8 shows two positions of the filtrate separator 7 and the resulting filtrate flows 14, 14&#39; for the clear filtrate, and 15, 15&#39;, 15&#34; for the cloudy filtrate. Also to be seen are the deflectors 9 mounted to the movable filtrate separator 7 and the fixed deflectors 13 in the control head in the area of the cloudy filtrate discharge. When the filtrate separator 7 is in position 1, there will be a clear filtrate flow 14 for clear filtrate, and a large portion of cloudy filtrate (arrows 15, 15&#39; and 15&#34;). For guiding the closing plate 8 when filtrate separator 7 is moved, a deflector plate 17 is foreseen. When the filtrate separator 7 is in position 2, the clear filtration portion is increased (shown in FIG. 8 by the broken-line arrow 14&#39;). The cloudy filtrate flow now follows arrows 15 and 15&#39;. The cloudy filtrate following arrow 15&#34; is in this case routed to dropleg 5 in an overflow channel 16, which is mounted in the area of the dropleg 5&#39;. This overflow channel 16 thus reduces the cross section of dropleg 5&#39; in the upper part of the latter. 
     To avoid this reduction of the cross section, the filtrate discharges so the droplegs can be placed one after the other in accordance with FIGS. 10 and 11. Thus, for the clear filtrate, there is an even better flow deflection involving fewer losses. 
     By use of the variants with which the flow deflection in the control head toward the droplegs is improved, savings can be achieved in terms of the hydraulic head (approx. 0.5 to 1 m depending on the amount of filtrate and the variant selected) due to lower pressure losses, while maintaining the vacuum created. In existing plants it is possible to achieve a higher vacuum through the use of a control head according to the invention. At a dropleg length of 5-7 m, this results in a higher filter performance of around 7% to 20%. The invention suits all types of rotary filters, but especially disc and drum filters. So-called internal filters can also be used, or disc filters where the collecting pipes are mounted on their outer diameter and knock-off the filter cake or filter mat takes place toward the inside, from where it is discharged into a tray placed in the center of the open, horizontal pipe.