Abstract:
A screening device which is particularly useful for separating solids from liquids when sewerage systems overflow. The device includes an inner apertured chamber and an internal brush arrangement for sweeping over the apertures to prevent clogging. A spray enables the apertured chamber to be washed after use.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to separation devices and is particularly concerned with an overflow screening device for the separation of liquid-borne solids from a carrier liquid.  
           [0002]    There are many situations where solids/liquid mixtures in a holding or reaction tank, or a liquid conveyancing system, can overflow due to power outages, excess input flow rates, plant breakdown, and the like. In those cases it is often desirable to separate the solids from the liquid so that the solids can be returned to the tank and the liquid discharged.  
         BRIEF DESCRIPTION OF THE PRIOR ART  
         [0003]    Recently, hydrocyclones and like devices have been used for these types of separation. One such hydrocyclone is the subject of British Patent application GB 2293993A which includes a vortex-forming chamber with tangential inlet and which is characterized by a concave foraminous screen arranged to interfere with the vortex. Removal of solids on the screen is assisted, for instance, by scraping or washing devices on the exterior of the screen. Such hydrocyclones, however, are not entirely effective for removing diverse ranges of solids which are found, for instance, on sewage, particularly the more fibrous or stringy solids materials.  
           [0004]    It is therefore an object of the invention to provide an overflow screening device which overcomes this problem or which at least provides the public with a useful alternative.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    According to the present invention there is provided an overflow screening device which includes an internal coaxially aligned cylindrical chamber having a wall section with a plurality of apertures and an internal brush arrangement for sweeping over the apertures.  
           [0006]    The construction and arrangement is such that a flow of liquid and solids directly into the internal chamber by way of an inlet tangentially located with respect to the side wall of the internal chamber, results in the separation of the liquid through the apertures into a region between the internal chamber and the wall of the device for discharge through an outlet in the side wall of the device and the containment of the solids for collection at an outlet at the bottom of the device, or retained in the device for later retrieval. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a schematic side cross-sectional view of an overflow screening device according to the present invention fitted to a sewage storage tank (shown in phantom), and  
         [0008]    [0008]FIG. 2 is a partial cross-sectional plan view of the overflow screening device described in FIG. 1.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0009]    The provision of the apertured inner chamber enables effective separation of a diverse range of solids down to a size governed by the size of the apertures, and the provision of the brush arrangement ensures that the apertures are kept free from being clogged.  
         [0010]    The overflow screening device preferably has a cylindrically shaped upper section and conically-shaped lower section which leads to the solids outlet or retention area.  
         [0011]    The internal coaxially aligned cylindrical chamber preferably extends downwardly from the top of the overflow screening device to the conically-shaped section. The upper portion of the internal chamber can have a solid wall with the lower portion being apertured. The solids/liquid inlet is suitably located in the upper portion of the wall and directs the incoming solids/liquid around the wall in a swirling action.  
         [0012]    The brush arrangement preferably comprises a number of rectangular frameworks with attached bristles on lower outer sections, which are supported for rotation on a vertically extending axle which is aligned with the axis of the device. The axle is freely rotatable on bearings located in the upper wall of the device. Vanes, preferably rectangular in shape, extend outwardly from the upper sections of the rectangular frameworks. The arrangement is such that when the swirling motion of the input stream of solids/liquid comes into contact with the vanes, the vanes rotate and cause the bristles to brush over the inner wall of the apertured chamber. Preferably, the vanes extend over the entire upper portion of the internal chamber and comprise between four and twelve individual components. A particularly preferred number of vanes is six.  
         [0013]    The bristles on the brush should preferably be flexible so as not to impede the rotation of the vanes. Suitable bristles are polyethylene strands, similar to that found in soft brushes.  
         [0014]    The size of the apertures in the internal chamber will be determined by the size of the solids which it is desired to prevent passage into the overflow stream of liquid. Generally they will be in the order of 2-10 mm, most generally about 3-5 mm in diameter.  
         [0015]    A spray system can be provided to wash the vanes and the inner walls of the internal chamber. This can comprise a plurality of nozzles associated with the upper portion of the internal chamber, which are fed through the axle when automatic control valve senses that the liquid level within the chamber has dropped below a pre-set level.  
         [0016]    The overflow screening device is particularly suitable for use in association with a sewerage scheme when connected to an existing overflow. In such a situation, the device is suitably designed to separate solids of greater than about  3 - 5  mm from a discharge liquid; the solids being returned to the sewage storage.  
         [0017]    A preferred embodiment of the invention will now be described with reference to the accompanying drawings, in each of which like reference numerals refer to like parts.  
         [0018]    Referring to both drawings simultaneously, the overflow screening device  10  is connected to a sewage storage tank  12  at a sewage overflow  13  and through a solids return inlet  14 . The screening device includes a stainless steel housing  11  having an upper substantially conical section  16  which leads to the solids return inlet  14 .  
         [0019]    An internal coaxially aligned stainless steel cylindrical chamber  17  extends downwardly from an upper region of the screening device and meets the conical wall  16 . Chamber  17  has an upper wall region  19  which is solid and a lower wall region  20  which is perforated with a plurality of apertures.  
         [0020]    An axle  21  is located on the axis of the screening device and is supported by bearings  22  in the upper wall thereof. The axle has rectangular frameworks  40  projecting therefrom with six rectangular vanes  23  fitted thereto so as to rotate in a horizontal plane. The vanes are formed of light weight material. Brushes  24  extend along the lower peripheries of the framework  40  adjacent to the lower wall region  20  of the cylindrical chamber  17 .  
         [0021]    An inlet  25  to the internal cylindrical chamber  17  extends from the sewage overflow  13  of the sewage storage tank so as to direct the raw sewage mixture of liquid and solids tangentially against the vanes  23  located in the internal cylindrical chamber  17 .  
         [0022]    The bottom of the screening device has a conduit  26  which directs separated solids to the return inlet  14  of the sewage storage tank  12 .  
         [0023]    Town water supply line  27  with a backflow prevention device admits water through a hollow section of the axle  21  to outlet nozzles  29 ,  30 . The flow of water is regulated by automatic control valves  31  which sense through a level sensor  32  when the level of liquid in the chamber falls below a pre-set level.  
         [0024]    In operation, when sewage overflows through the overflow  13  due to an electrical outage or the like, the tangential flow into the internal chamber  17  of the device causes the vanes to rotate and the liquid to pass through the apertures to the outer region  33  for discharge through an outlet  34  in the wall of the screening device. Heavy solids within the device settle to the bottom and return to the one way inlet  14  of the sewage tank  12 . Solids which are buoyant remain in the chamber  17  until the level in the sewage tank drops to such an extent that these solids are also returned to the sewage tank.  
         [0025]    As the level of liquid in the overflow screening device drops, the water supply is automatically actuated and the inner walls of the camber are sprayed through nozzles  29 ,  30 . Spray from nozzle  41  is directed against vanes on the rotating mechanism to provide rotation independent of sewage inflow.  
         [0026]    In cases where there is insufficient sewage flow to rotate the brushes, the cleaning sprays may be activated during the overflow event to assist with rotation.  
         [0027]    In this manner, an effective separation of a solids/liquid feedstuffs is achieved with the liquid stream being discharged and the solids stream being returned to storage for processing.