Abstract:
A belt filter press for deliquifying a material comprises two endless filter belts disposed adjacent each other so that a portion of the belts travel together and converge towards one another in a curved wedge section through which a material is progressively compressed, wherein the concavity of the wedge section is oriented toward gravity.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/287,895, filed May 1, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to belt filter presses for removing liquid from a mixture of liquid and solid material. In one aspect, the invention relates to an improved wedge section for a belt filter press.  
           [0004]    2. Description of the Related Art  
           [0005]    Belt filter presses are utilized to remove liquid from a mixture of liquid and solid material, leaving a relatively dry, solid “cake” for disposal or further processing. The belt filter press comprises a frame and an assembly of rollers that support and drive an upper continuous belt and a lower continuous belt that are in operable communication with each other. The belts are permeable to allow the extrusion of the liquid therethrough. The mixture is first placed on the lower belt, then “sandwiched” between the upper and lower belts. The belts and the retained mixture then pass through a wedge section where the mixture is evenly distributed between the belts, and an initial volume of liquid is removed. The belts then pass through a series of progressively smaller diameter rollers where the retained mixture is compressed for further liquid removal. The belts are then separated and the dry “cake” is removed from the belts, generally by a scraping apparatus. The belts then pass through one or more belt washers, after which the process is repeated. The liquid from the extrusion and belt washing processes are collected for disposal.  
           [0006]    The wedge section is generally planar, which is suitable for even distribution of the mixture between the belts. However, material passing over a planar wedge section will not be as effectively dewatered as material passing over a curved wedge section. Furthermore, the wedge section typically comprises a flat plate in full contact with the lower belt. Consequently, liquid that is extruded from the mixture must flow laterally to the edges of the belts in order to be removed. The drainage path defined by this lateral movement is appreciably longer than a drainage path perpendicular to the plane of the belts. The longer drainage path impedes the removal of liquid from the mixture.  
         SUMMARY OF THE INVENTION  
         [0007]    The invention comprises an improved curved wedge section for a belt filter press for removing liquid from a mixture of liquid and solid material. The belt filter press comprises two endless filter belts disposed adjacent each other so that a portion of the belts travel together and converge towards one another in a curved wedge section through which a material is progressively compressed. The concavity of the wedge section is oriented toward gravity. The wedge section comprises a plurality of parallel-spaced belt supports comprising a rigid, polymeric material such as an ultra high molecular weight plastic or Nylotron. The supports are supported on parallel-spaced wedge support plates. The wedge section comprises a planar section that transitions into the curved section.  
           [0008]    Belts containing the mixture to be dewatered pass over the curved wedge section prior to entering the roller section of the belt filter press. The curvature of the wedge section enhances the extrusion of water from the mixture prior to the belts entering the roller section. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0009]    In the Drawings:  
         [0010]    [0010]FIG. 1 is a side elevation view of a schematic of a belt filter press illustrating a curved wedge section according to the invention.  
         [0011]    [0011]FIG. 2 is a perspective close-up view of the curved wedge section of the belt filter press of FIG. 1. 
     
    
     DETAILED DESCRIPTION  
       [0012]    Referring now to FIG. 1, a belt filter press  10  according to the invention comprises a frame  12 , an upper belt  14 , a lower belt  16 , a waste placement apparatus  18 , liquid catch pans  20 , belt washers  22 , a wedge section  24 , a primary roller  26 , secondary rollers  28 , upper belt guide rollers  38 , and lower belt guide rollers  32 . It will be readily understood by one skilled in the art that the belt filter press of FIG. 1 will also comprise suitable belt tensioning devices, belt drives, and controls, which for purposes of this disclosure will not be described herein. As with a conventional belt filter press, the belt filter press  10  of FIG. 1 extrudes liquid from a mixture of solid and liquid material by “sandwiching” the mixture between the two belts  14 ,  16 , passing the belts over the wedge section  24  and around the primary roller  26  and secondary rollers  28 , and discharging the dewatered solids upon separation of the belts  14 ,  16 .  
         [0013]    The wedge section of a conventional belt filter press provides an initial removal of liquid from the mixture through the action of the belts passing over the wedge section. Referring to FIG. 2, the wedge section  24  according to the invention comprises a pair of wedge support plates  46  arranged in opposed parallel alignment and a plurality of spaced belt supports  44  extending between the plates  46 . The belt supports  44  comprise elongated, slat-like members of rectangular cross-section somewhat longer than the spacing between the wedge support plates  46 . In the preferred embodiment, the belt support  44  is made of a rigid, polymeric material, such as Nylotron or ultra high molecular weight plastic (“UHMW”).  
         [0014]    Each wedge support plate  46  has an edge defining a straight section  40  transitioning to a curved section  42 . Each wedge support plate  46  is provided with a plurality of belt support cutouts  48  to receive the belt supports  44  as hereinafter described. The belt support cutouts  48  extend inwardly from the edge of and perpendicular to the straight section  40  and from the edge of and perpendicular to the tangent of the curved section  42 . It will be understood that each wedge support plate  46  is provided with suitable apertures, cutouts, and flanges (not shown) for mounting the wedge support plate  46  to the frame  12 . The wedge support plates  46  are mounted to the frame  12  parallel to and spaced from each other so that the belt support cutouts  48  on the opposing wedge support plates  46  are in registry with each other. Each belt support  44  is received into a pair of belt support cutouts  48  so that the belt support  44  extends between opposing wedge support plates  46 , preferably with a portion of the belt support lying above the plane of the wedge support plate edge. The belt supports  44  are retained within the belt support cutouts  48  through any suitable means, such as friction, adhesives, or screw-type fasteners. When the belt supports  44  are received in the belt support cutouts  48  and the wedge support plates  46  are mounted to the frame  12 , the belt supports  44  define a straight section transitioning to a curved section corresponding to the straight section  40  and the curved section  42  of the wedge support plates  46 . Thus, the wedge section  24  has a curved portion as well as a straight portion. In one embodiment, the curved section  42  defines a gradually decreasing radius in the direction of belt movement. In an alternate embodiment, the curved section  42  defines a constant radius.  
         [0015]    The belts  14 ,  16  with enveloped mixture pass over the belt supports  44 , proceeding from the straight section  40  through the curved section  42  and thence to the roller section. Each of the belt supports  44  imparts a “kneading” pressure to the belts  14 ,  16  and the mixture, enhancing the extrusion of liquid from the mixture, which in turn flows downwardly through the gaps between the belt supports  44  to be collected in the liquid catch pans  20  and removed. The improved wedge section  24  provides suitable support for the belts  14 ,  16  and extrusion of liquid from the mixture, while improving the flow of the liquid from the belts  14 ,  16 . The belts  14 ,  16  and retained material then pass through the rollers  26 ,  28  to undergo further liquids removal.  
         [0016]    While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation. Reasonable variation and modification are possible within the scope of the forgoing description and drawings without departing from the spirit of the invention.