Abstract:
A grit removal unit for a waste water system, including a round grit removal chamber with an input for waste water and an output, a grit storage chamber beneath the grit removal chamber, and an opening between the grit storage chamber and the grit removal chamber. A vertical drive shaft extends through the grit removal chamber into the grit storage chamber, and is rotatable to facilitate waste water flow in the grit removal chamber whereby grit in the waste water is directed toward the opening. A grit size restrictor includes a shear secured to the drive shaft for rotation therewith (the shear including a plate extending radially from the drive shaft above the opening), a first set of bars extending across the opening, and a second set of bars secured to the bottom of the shear plate with the second set of bars positioned adjacent the first set of bars.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
       [0001]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       REFERENCE TO A MICROFICHE APPENDIX 
       [0003]    Not applicable. 
       TECHNICAL FIELD 
       [0004]    The present invention relates to waste systems, and more particularly to a grit trap for a waste water system. 
       BACKGROUND OF THE INVENTION AND TECHNICAL PROBLEMS POSED BY THE PRIOR ART 
       [0005]    In many industrial and municipal waste systems, waste water which is laden with grit is pumped from a primary recovery device in the waste stream to a secondary device (e.g., a cyclone separator) which further concentrates the grit. The stream may also pass through a third device (e.g., a screw conveyor) to further dry and concentrate the grit. 
         [0006]    However, the waste water stream which enters the waste system often may include long sticks, cans, large solids, and other non-soluble debris. Such debris can disrupt, plug or stop any of the recovery devices from operating. For example, the debris can get into the pumps and piping in the system. It can span openings and wedge in openings, creating an obstruction. Further, smaller materials (e.g., stringy materials such as paper, paper towels, and rags) can get caught in the larger debris and eventually build up a dam that completely plugs pipes and openings. When that occurs, the plug has to be removed, which may require rodding or physically cleaning out the opening. During the process of removing such debris, it may be necessary to shut down the system. Shutting down the system for this purpose is, obviously, undesirable and inefficient. 
         [0007]    Screens have therefore been used to block large debris from reaching the recovery devices with the entering waste stream, while still allowing flow through of the waste stream. Such screens require relatively large openings, however, to ensure sufficient waste stream flow, and thus opening sizes have varied from around ⅜″ square to 2″ wide space between parallel (vertical) bars. As a result, various items of relatively large trash or debris may still pass through the openings and into the recovery devices, including long sticks, tooth brushes and the like through even the square openings, and large objects as well as long sticks, etc. may pass through the larger long openings. Of course, large objects may also pass through to the recovery devices if the screens are not maintained properly, or if larger openings develop around the bottom of the screen. 
         [0008]    Grit removal systems such as grit extractors or grit traps have been used in many waste systems to remove grit from the waste water prior to passing the water on to a recovery device of the system. For example, one advantageous apparatus includes flumes for injecting and extracting liquid tangentially relative to a round chamber, creating a circular flow stream which causes the grit to settle near the bottom center of the round chamber. That grit in the injected liquid is thus removed from the liquid stream and collected in the storage chamber for relatively easy removal. Such an apparatus is disclosed in U.S. Pat. No. 6,811,697 B2, the full disclosure of which is hereby incorporated by reference. 
         [0009]    U.S. Pat. Nos. 3,941,698, 4,107,038 and 4,767,532 also disclose grit extractor apparatuses. The disclosures of all of these patents are also hereby fully incorporated by reference. 
         [0010]    For example, U.S. Pat. No. 4,767,532 discloses an apparatus for removing grit in which a grit storage chamber is provided beneath the center of the round chamber of the grit removal system. A removable plate substantially aligned with the floor of the round chamber generally separates the two chambers, with a central opening through the plate permitting communication between the chambers. A cylindrical shaft is rotatably supported on its upper end above the round chamber and extends down through the round chamber through the plate central opening. Liquid flow in the round chamber causes grit particles to settle toward the chamber floor, where they are urged radially inwardly so as to drop through the plate central opening into the grit storage chamber. A multi-bladed propeller is mounted on that shaft above the plate, and rotates with the shaft to assist in the liquid flow to move the grit toward the plate center opening. A pipe also extends down through the cylindrical shaft into the grit storage chamber, and a pump is provided on the upper end of the pipe to allow grit in the bottom of the storage chamber to be removed by pumping up through the pipe. 
         [0011]    In addition to the plate with a central opening as described above, grates, perforates plates, and the like have also been used to separate the chambers while still permitting grit to pass into the grit storage chamber from the round chamber. Such grates, etc. inhibit the flow of grit and debris into such chambers, and also build up a covering which closes off the opening. This not only requires manual unplugging of piping and openings from time to time, but also causes grit which is inhibited from moving into the grit storage chamber to undesirably pass through the grit removal apparatus altogether. 
         [0012]    The present invention is directed toward overcoming one or more of the problems set forth above. 
       SUMMARY OF THE INVENTION 
       [0013]    In one aspect of the present invention, a grit size restrictor is provided for a grit removal unit for a waste system having a rotatable drive shaft directing grit in a grit removal chamber toward an opening to a grit storage chamber beneath the grit removal chamber. The restrictor includes a shear secured to the drive shaft for rotation therewith, which shear includes a plate extending radially from the drive shaft above the opening. A first set of bars extends across the opening, and a second set of bars is secured to the bottom of the shear plate and positioned adjacent the first set of bars. 
         [0014]    In one form of this aspect of the present invention, a deflector is fixed relative to the opening at a position which is substantially axially aligned with and radially spaced outside of the second set of bars. 
         [0015]    In another form of this aspect of the present invention, the outer perimeter of the opening is substantially round with a first diameter and the shear plate outer edge is substantially round with a second diameter, wherein the second diameter is at least about as large as the first diameter. In one further form, the drive shaft extends through the middle of the opening and the bars of the first set of bars project outwardly from the drive shaft to the opening outer perimeter. In another further form, the drive shaft extends through the middle of the shear plate and the bars of the second set of bars project outwardly from the drive shaft beyond the shear plate outer edge, and in a still further form the drive shaft extends through the middle of the opening and the bars of the first set of bars project outwardly from the drive shaft to the opening outer perimeter. In still another further form, the grit removal chamber has a diameter greater than the first diameter, and the opening is defined by a central hole in a plate located over the grit removal chamber. 
         [0016]    In another aspect of the present invention, a grit removal unit for a waste water system is provided, including a round grit removal chamber with an input for waste water having grit and trash therein and an output, a grit storage chamber beneath the grit removal chamber, and an opening between the grit storage chamber and the grit removal chamber. A vertical drive shaft extends through the grit removal chamber into the grit storage chamber, and is rotatable to facilitate waste water flow in the grit removal chamber whereby grit in the waste water is directed toward the opening. A grit size restrictor includes a shear secured to the drive shaft for rotation therewith (the shear including a plate extending radially from the drive shaft above the opening), a first set of bars extending across the opening, and a second set of bars secured to the bottom of the shear plate with the second set of bars positioned adjacent the first set of bars. 
         [0017]    Other forms of this aspect of the invention include those forms described above in connection with the first aspect of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a perspective view of a grit removing apparatus with which the present invention may be used; 
           [0019]      FIG. 2  is an exploded view of the present invention showing the drive shaft of the grit removing apparatus with the shear and plate structure at the entrance to the grit storage chamber; and 
           [0020]      FIG. 3  is a side view of the shear and plate structure of  FIG. 2  in operational position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]      FIG. 1  discloses a centrifugal grit removal unit or apparatus  10 , which is one such apparatus with which the present invention may be advantageously used. The apparatus  10  illustrated in  FIG. 1  is like that disclosed in U.S. Pat. No. 6,811,697 B2, the full disclosure of which has been incorporated herein by reference. 
         [0022]    As described in the &#39;697 patent, the apparatus  10  separates grit from grit-laden liquid  12  conveyed into the apparatus  10  by an inlet trough  14  having an inlet conduit  18  that conveys the liquid downwardly at a slight angle. The conduit  18  turns to the horizontal adjacent to a grit removal chamber  20 . At the intersection of the chamber  20 , a trough bottom  22  is at the same elevation as the bottom or floor  24  of the grit removal chamber  20 . One vertical wall  30  of the conduit  18  is tangent to a wall  32  of the chamber  20  where the wall  30  terminates. A vertical wall  34  is parallel to the wall  30  and enters the chamber wall  32  at an inlet location, and continues as wall  36  extending across the chamber  20  to an inlet opening  38  where the grit-laden liquid enters chamber  20 , flowing circumferentially around the wall  32  of the chamber. A top  40  of the conduit  18  is parallel to the chamber floor  24  and also functions as the bottom of an effluent flume  44  that extends across the chamber  20 . An influent tunnel is formed by the top  40 , the wall  36 , the floor  24  and the wall  32 . 
         [0023]    The grit-laden liquid flows from the opening  38  around the inside perimeter of the chamber  20 , forming a lower channel of flow  46  as shown by the dashed arrows. The liquid at the wall  32 , being of slightly higher head resulting from centrifugal force, flows down the wall  32  to the bottom  24 , across the floor  24  to a center hole  50  (described in greater detail below) at the bottom of the chamber  20 . The radial velocity component along with the rotation velocity results in a spiral movement of flow  52  shown by the arrows. The grit in this liquid comes in contact with the floor as the liquid is forced into a thin film, spread across the floor  24 . The grit contacts the floor and is deposited on the floor. The spiral movement of flow  52  moves the grit across the floor  24  to the center hole  50 . 
         [0024]    A drive shaft  54  extends vertically into the center of the chamber  20 , and is rotatably driven by a gear drive  56  to turn a paddle or multi-bladed propeller  58  at a faster rotary speed than the surrounding liquid. The result is a pumping action across the floor  24 , upward from the paddle  58 , inducing additional pushing action on the grit. The grit moves across the floor  24 , drops down the center hole  50  into the grit storage chamber  60  below (shown in  FIG. 2 ). The grit storage chamber may be as disclosed in U.S. Pat. No. 4,767,532; 4,107,038 or 3,941,698. The floor  24  may be flat or sloped downwardly toward the center hole  50 . 
         [0025]    The liquid, less the grit, flows in the lower channel of flow  46  around the inside periphery of the apparatus adjacent to the wall  32 . The wall  36  and the shelf  62  operate in unison to define the lower and upper channels of flow  46 ,  64  flowing around the inside perimeter of the chamber  20 . The lower channel of flow  46  flows under a shelf  62  and is deflected by the wall  36 . Trapped between the shelf  62 , the wall  32 , the floor  24 , and a more slowly rotating inner cylinder of liquid  52 , the lower channel of flow  46  is forced upwardly. The channel of flow is now in the upper half of the liquid height, forming an upper channel of flow  64  that flows around an upper perimeter of the chamber adjacent to the wall  32 , as shown by the dotted arrows. 
         [0026]    The upper channel of flow  64  flows into an outlet opening formed by a flume  66  defined by the wall  32 , a wall  68 , and the top of the shelf  62 . The width of the opening into the flume  66  may be narrower than the entrance width of the inlet trough  40 , to create a higher liquid level in the grit removal chamber  20  to force the incoming flow through the more narrow flume opening. The liquid flows through the flume  66  to an exit flume  68 , from which it exits the apparatus to a further apparatus or other destination (not shown). 
         [0027]      FIGS. 2 and 3  illustrate the present invention as used with the above described grit removal apparatus  10 . Specifically, as illustrated in the exploded view of  FIG. 2 , a split grate or plate  70  defines the center opening  50  and is sized to fit in a recess  74  in the round chamber floor  24  which is open to the grit storage chamber  60  therebelow. A ring  76  is centered in the center opening  50  and is supported by a plurality of bars  78  projecting inwardly from the plate opening  50 . It should be appreciated that the ring  76  will therefore provide a rotation guide at the lower end of the drive shaft  54 , with the position of the ring  76  set by the recess  74  in which the plate  70  is placed. 
         [0028]    In addition to positioning the ring  76 , the bars  78  may advantageously be spaced evenly with a large forward pitch, and placed as close together as desired to define the largest size trash which may pass through the bars  78  into the grit storage chamber  60 . Such defined size may be selected in conjunction with the size of the extraction pipe  80  (see  FIGS. 2 and 3 ) which extends down through the cylindrical drive shaft  54  into the grit storage chamber  60 . A pump  82  (see  FIG. 1 ) is also provided on the upper end of the pipe  80  and serves to pump grit out of the storage chamber  60  through the pipe  80  such as described, for example, in U.S. Pat. No. 4,767,532. It should be appreciated, however, that the drive shaft  54  itself could serve as the extraction pipe, without requiring a separate pipe  80  inside the shaft  54  such as illustrated in  FIGS. 2 and 3 . 
         [0029]    Also suitably secured near the bottom of the drive shaft  54  (below the multi-bladed propeller  58 , not shown in  FIGS. 2 and 3 ) for rotation with the shaft  54  is a shear  90  which includes a radially extending plate  92  having spacer bars or blades  96  secured on the bottom of the plate  92  in an orientation which is steeply pitched forward relative to the direction of rotation. During operation as illustrated in  FIG. 3 , the shaft  54  is positioned so that the shear  90  is positioned close to the top of the grate  70 . The shear plate  92  may advantageously be about the size of the grate center hole  50  so as to overly the entire hole  50  and thereby prevent trash from falling directly down into the grit storage chamber  60  from above. 
         [0030]    It should therefore be appreciated that sticks or similar long thin objects are limited in circumference to essentially the height of the spacer bars  96 , as the gap through which trash must pass to reach the grit storage chamber  60  is restricted to that size. Moreover, any stick which passes into the center opening  50  will be broken into pieces as the shear spacer bars  96  rotate across the top of the grate bars  78 . Further, any sticks that project out of the space between the shear plate  92  and the grate  70  will be broken by a deflector  98  which extends up from the grate  70  slightly beyond the radial extension of the spacer bars  96 . Further, large objects which ride around the outside of the shear  90  are deflected away by the deflector  98  as the shear  90  rotates around. 
         [0031]    Thus, grit may follow the path  100  shown in  FIG. 2  through the center hole  50  of the grate  70  into the grit storage chamber  60 . Moreover, it should be appreciated that the spacer bars  96  will advantageously act as pump vanes and scoop grit down between the bars  78  on the grate  70 . Accordingly, the problem of grit flow stopping when hydraulic current stops at the restriction as encountered in past structures in which grit size was restricted is avoided and desired operation may be maintained for long periods of operation. 
         [0032]    Still other aspects, objects, and advantages of the present invention can be obtained from a study of the specification, the drawings, and the appended claims. It should be understood, however, that the present invention could be used in alternate forms where less than all of the objects and advantages of the present invention and preferred embodiment as described above would be obtained.