Abstract:
A screen for separating solids and liquids is formed from parallel strips of wedge wire or similar material into a substantially cylindrical two-sided enclosure in a generally C-shaped profile. Unfiltered liquid containing solids contacts the screen surface on both the convex and concave sides of the C-shaped enclosure. The unit may be placed in a vessel adapted to accommodate two such C-shaped devices in concentric relationship. The vessel may function similar to a candle filter, or a more conventional flow may be used.

Description:
RELATED APPLICATION  
       [0001]     This application claims the full benefit of Provisional Application 60/662,065 filed Mar. 14, 2005. 
     
    
     FIELD OF THE INVENTION  
       [0002]     Filter or screen material having convex and concave filtering surfaces are formed into an enclosure that will fit into a generally cylindrical housing, preferably accommodating at least one additional such enclosure within the space defined by its concave surface. High throughputs and separation efficiency are obtained.  
       BACKGROUND OF THE INVENTION  
       [0003]     Good screening and filter throughput is desirable for many high volume fluid handling operations, such as filtering and screening of well completion and workover fluids, but has been difficult to sustain in the varied and generally hostile conditions of many well drilling and producing operations. Backwashing is also sometimes inefficient because of the design of the solids separation device.  
       SUMMARY OF THE INVENTION  
       [0004]     I have developed a new design for a filter or screen which overcomes to a large degree the difficulties recited in the background of the invention, namely the invention provides a sustainable throughput for large volumes of fluid, and the ability efficiently to backwash  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1  illustrates a prior art technique for manufacturing a cylindrical wedge wire screen.  
         [0006]      FIG. 2  is a simplified section of a cylindrical two-section concentric screen of my invention.  
         [0007]      FIG. 3  is a perspective of a construction similar to that of  FIG. 2 .  
         [0008]      FIG. 4  is an “exploded” view of my screen device, including the end units.  
         [0009]      FIG. 5  is an overhead view of the top plate of the reservoir which facilitates collection of the filtered fluid.  
         [0010]      FIG. 6  shows the C-shape screen in the configuration of a candle filter. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]     My invention is illustrated in terms of a wedge wire screen, but the C-shape enclosure to be described below is applicable to other types of screens and to filters, as will be explained.  
         [0012]      FIG. 1  is a detail of the construction of a wedge wire screen useful in my invention, which can be placed in various positions in the system. As is known in the art, a screen can be made by winding a wedge wire  40 , an extruded, triangular section wire, around a cage of parallel ribs  41 , fixing them to form a space or slot  42  of a desired opening dimension between them, usually by welding.  
         [0013]      FIG. 2  is a simplified sectional view of the construction of a substantially cylindrical filter or wedge wire screen of my invention. Here, there are two C-shaped screen units  43  and  44  set substantially concentrically in a cylindrical housing  45 . Each screen unit  43  and  44  has a convex face  43   a  and  44   a , and a concave face  43   b  and  44   b , both of which are to be contacted by unfiltered fluid, represented here by the shaded areas. Each screen unit  43  and  44  also has end caps  43   c  and  44   c , which may be impervious—that is, it need not be of wedge wire or other screen material. Together with the concave and convex faces, and, together with the fact that I seal the C-shaped units at the top and bottom, the end caps form an enclosure. Unfiltered fluid enters the cylindrical housing  45  through inlets not shown (from anywhere through the housing  45 , or its top, provided it passes into a portion of the shaded area labeled “unfiltered fluid) and passes through the separator media (such as wedge wire screens) of both the convex and concave sides of the screen units, leaving solids of the undesired size behind. Filtered or screened fluid within the screen units may then be removed through outlets  52  as illustrated in  FIGS. 4 and 5 . It should be noted that both the convex faces  43   a  and  44   a , and the concave faces  43   b  and  44   b  of the screen units are constructed so that, if they are made of wedge wire, the flat side of the wedge wire contacts the unfiltered fluid. One of the features of wedge wire screens is that a solid particle is not likely to become lodged in a slot  42  because the anterior of the slot is divergent, i.e. the slot is between two triangular shapes opening to the interior of the filter surface. Thus the construction of the concave faces  43   b  and  44   b  is opposite the convex orientation shown in  FIG. 1 , the wedge wire being laid on the inside of ribs  41  rather than the outside; nevertheless, the unfiltered fluid contacts only flat surfaces defining the slots  42  ( FIG. 1 ). A generally C-shaped face  43   a  or  43   b  can be made by making a longitudinal cut in the wedge wire screen of  FIG. 1 . A concave filter or screen surface may be made by bending a cylindrical surface such as that made in  FIG. 1  so that the flat surfaces face inwardly. Of course, “sheets” of wedge wire screen can be made by welding or otherwise fixing precut lengths of wedge wire to parallel ribs on a plane or flat surface and then bending them to the desired form.  
         [0014]      FIG. 3  is a perspective of the two-enclosure, substantially concentric, configuration, without the housing  45 . Wedge wires form the entire convex ( 43   a  and  44   a ) and concave ( 43   b  and  44   b ) faces of the C-shaped screen units. Slots  42  of the desired dimension are established between wedge wires  40 . In the configuration of  FIG. 3 , C-shaped screen unit  43  is shown with its elongated opening  46  aligned with elongated opening  47  of C-shaped screen unit  44 , but this is not essential—that is, screen unit  44  could be turned, for example, 180 degrees so that opening  46  is oriented away from opening  47  of screen unit  43 .  
         [0015]     Referring now to  FIGS. 4 and 5 , the top plate  50  of reservoir  51  is seen to have outlets  52  for filtered fluid having passed through the wedge wire screens of screen units  43  and  44 . When assembled, housing  45  and the two screen units  43  and  44  are sealed to top plate  50 . Filtered fluid collects in reservoir  51  and is removed through pipe  54 . A cylindrical screen  55  constructed as in  FIG. 1  may reside in the center of inner enclosure  44 , providing additional volume for the collection of filtered fluid.  FIG. 4  is an exploded view of the top seal  53 , screen units  43  and  44 , reservoir  51  with its top plate  50 , and pipe  54 . Housing  45  and the inlet for the dirty fluid are not shown in this view.  FIG. 5  is an overhead view of top plate  50 , showing the deployment of outlets  52  for screen units  43  and  44 .  
         [0016]      FIG. 6  shows the use of my C-shaped wedge wire screen in a candle filter construction, in a more or less diagrammatic fashion. The C-shaped wedge wire screen  60  is viewed from its opening  61 . The screen  60 , made of wedge wires  69  in a manner similar to that of  FIG. 1 , is located and fixed next to a ledge  62  near the top of vessel  63 . C-shaped wedge wire screen  60  is essentially the same shape and structure as screen unit  43  or  44  in  FIG. 2  (having spaces not shown, similar to slots  42  in  FIGS. 2 and 3 ), but here we are looking directly at the opening  61  (equivalent to openings  46  and  47  in  FIG. 3 ), although the screen  60  is entirely enclosed in vessel  63 . Vessel  63  has an entrance  64  (which may preferably be oriented toward opening  61 ) for dirty fluid, an exit  65  for clean fluid, and a drain  66  for solids and concentrated dirty fluid. The lower end  72  of the vessel  63  has a shape similar to a funnel so that solids may collect and drop by gravity to drain  66 . The wedge wire screen  60  is constructed in a sense opposite to that of  FIG. 4  in that the clear filtered fluid is taken off the top and sent through exit  65  instead of through the bottom; solids and dirty fluid exit in the bottom. For these purposes, it should be noted that the top of wedge wire screen  60  may be completely open to the clean fluid collection chamber  68 ; on the other hand, the bottom of the wedge wire screen  60  should either be sealed or closed off with a screen material, so that solids and dirty water will not enter the wedge wire screen  60  from the bottom. Valves  70  and  71  may be used to control the flow out of the vessel  63 .  
         [0017]     A screen such as depicted in  FIGS. 1-6 , or any other effective screen, may advantageously be placed immediately upstream of a viscometer to protect the viscometer from solids, or just ahead of a filter, to remove solids larger than the filter is designed for. In addition to removing potentially damaging solids, the wedge wire screen can perform the function of breaking up “fish-eyes” or other localized gel blobs, as well as shearing a viscous fluid, sometimes delaying the point at which the fluid is diverted or at which the pump is shut down.