BACKGROUND Field of the Invention: This invention relates to filtration systems, or the like, which employ granular media, and specifically relates to filtration media retention or separation devices constructed to facilitate unobstructed filtration and backwashing.

Statement of the Art: Fluid filtering systems are known and used in many industries, including oil and gas drilling, hydrocarbon catalytic reaction, waste water filtration and materials de-watering (e.g., ore de- watering). Fluid filtering systems generally comprise a filtration media bed, or catalyst media bed, and have as one component a retention screen or grid which permits fluid to pass from one side of the screen to the other while the filtration media (e.g., sand) is maintained on one side of the screen, unable to move through the screen. Many filtration systems are structured to allow fluid movement in both directions relative to the retention screen or grid, such as in a system with a backwash capability.

Examples of filtration screens or grids used in various industries are generally disclosed in U.S. Patent No. 828,715 to Cook (strainer); U.S.

Patent No. 2,683,654 to Bergman (lined catalytic reactor); U.S. Patent No. 3,247,971 to Kastler (underdrain for filtration tank systems); U.S. Patent No. 4,013,556 to Evans (flow distribution and collection having lateral head screen); and U.S. Patent No. 4,096,91 1 to Geske (channel base well screen). One common retention grid disclosed in the prior art is a conventional mesh screen, similar to that used on windows.

Another prevalent screen or grid design comprises strips or bars of metal positioned at right angles to each other which provides a mesh- type design. Often, a mesh configuration of that type is provided in a circular or cylindrical retention screen by wrapping a continuous filament of wire or metal about a plurality of parallel spaced bars

positioned in α circle and oriented at a ninety degree angle to the filament. In other screen or grid designs, a plurality of metal strips or bars are positioned in parallel, spaced-apart configuration on a metal plate which has a number of apertures formed therethrough. Examples of such systems are disclosed in U.S. Patent No. 2,046,458 to Johnson, and U.S. Patent No. 4,276,265 to Gillespie. Related prior art systems are also illustrated in U.S. Patent No. 5,015,383 to Evans, et al.

A different type of screen or grid is disclosed in U.S. Patent No. 3,520,418 to Guinard and in U.S. Patent No. 3,708,848 to Guinard, in which a grid or screen is formed by press punching slots into a sheet of metal, then swaging an opening of the slots formed in the metal sheet to provide an angled spacing between the slots. Another retention device is one where slot are formed in a plate by means of a laser, the resulting slot having a slight angular opening therethrough. In prior art systems as previously described, the cross sectional profile of a typical screen or grid demonstrates that the slots or openings formed through the thickness of the grid are angled such that a smaller opening is oriented toward one surface of the grid and a somewhat larger opening is oriented toward the opposing surface of the grid. The angle of the smaller opening is typically about thirty degrees. Filtration media, such as granular media, is maintained against that surface of the screen or grid which presents the smaller opening. By such configuration, the filtration media or catalyst media is too large to move through the slit or opening, but fluid may pass through easily. Further, by virtue of the angular openings of these prior art devices, filtration fluid passing through the small opening effectively flushes most matter from the smaller opening and out the larger opening oriented on the opposing surface of the screen. Prior art devices are thereby self- cleaning in the direction of filtration fluid flow. Particularly in fluid filtration systems of the type used in waste water treatment systems, fluid passing through the filtration media leaves

behind residue entrapped in the filtration media and the filtration media must be cleansed or reconditioned from time to time. The filtration media is typically either replaced or, more commonly, cleaned by forcing water through the slots or openings of the screen from the side opposite placement of the filtration media. Fluid passes through the slots or larger openings of the screen and then passes through the filtration media in a direction opposite to normal filtration. The debris or residue flushed from the filtration media along with the washing fluid is removed from the system above the filtrdtion bed. That process is commonly referred to as backwashing.

In prior art systems as previously described where the slot or opening through the screen or grid is angled, backwashing fluid is forced through the surface of the screen having the larger opening facing outwardly therefrom. The backwash fluid then moves through the length of the opening (through the thickness of the screen) and exits through the small opening facing outwardly from the surface of the screen against which filtration media is positioned. Because the backwash fluid may not necessarily be free of minute residue or debris, backwash fluid passing through the thirty degree angle of the smaller opening often deposits material in the smaller opening and blockage occurs. Dead zones occur in the filtration media positioned at or about the obstructed openings and efficient filtration and/or backwashing is prevented. If material becomes tightly lodged in the smaller opening, even flow of filtration fluid through the small opening may not dislodge it. A further common obstruction occurs in mesh-type retention grids when used in systems to filter fluid containing fibrous material. The fibrous material may lodge in the openings and/or may wrap around the wires of the screen causing extensive blockage.

Thus, it would be advantageous in the art to provide a grid for use in a fluid filtration system which facilitates efficient filtration and

backwashing while preventing the clogging by filtration media or debris in the slots of the grid, either during backwash or filtration.

SUMMARY OF THE INVENTION

In accordance with the present invention, a filtration media retention or separation grid is provided having slots or openings formed in a sheet of suitable material, the slots or openings being formed to provide an opening angle of sufficient degree to prevent clogging of the slots by filtration media or debris contained in fluid passing through the slots, and to render the slots self-cleaning in both filtration and backwashing modes. The filtration media retention grid of the present invention is suitable for use in many industries, but is disclosed herein as part of an underdrain system in waster water filtration by way of example.

The filtration media retention grid of the present invention generally comprises at least one slot or opening formed in a sheet of suitable material, such as stainless steel, aluminum, molded plastic, or any other material which provides structural strength and durability under the conditions of the intended use. The sheet of material may generally be rectangular in shape having two opposing long sides and two opposing short sides, although any shape or geometric configuration may be suitably adapted to use of the invention in any intended application. Slots or openings in the sheet of material are formed, in accordance with the present invention, by any appropriate method which will render the slot or opening with the requisite angled opening to prevent clogging and to facilitate self-cleaning in both filtration and backwashing modes. Thus, slots or openings may be formed in the sheet by means including punch pressing, molding, and heat or chemical deformation.

In one embodiment of the invention, a punch press operation, for example, may be used to form pairs of parallel and spaced apart

elongated slits which extend through the entire thickness of the sheet and form a strap of material between the parallel slits. The strap of material is concurrently deformed relative to the sheet of material and is raised above the plane of the sheet to form a bridge of material between the ends of the elongated slits. At least one slot results between the bottom surface of the bridge portion and the top surface of the sheet as the bridge is formed. That is, in one embodiment, the bridge may be deformed to provide a single slot in a louvered-type of opening. In an alternative embodiment, the bridge portion may be deformed to provide a slot on either side of the bridge portion. Each slot opening (single or double slots) thus formed has a width defined by the distance between the bottom of the bridge portion and the surface of the sheet of material.

In an alternative embodiment of the device, a single slit may be formed through the thickness of the sheet of material, and the area on either side of the slit may be deformed in opposing directions to provide a slot with the requisite angled opening to prevent clogging and to facilitate self-cleaning in filtration and backwashing modes. The slit made through the sheet of material may be straight or curved, resulting in a linear or arcuate slot.

The width of the slot in any embodiment heretofore described may be selectively determined by the degree and manner of deformation the material is subjected to, such as to form the bridge. The slot width is selected in accordance with the type of filtration media that is used; that is, finer granular filtration media, such as fine sand or garnet sand, would dictate a slot width dimension less than the diameter of the granular filtration media to avoid loss of filtration media through the slot. Larger filtration media, such as coarse sand, catalyst material or anthracite, would dictate formation of larger slot width dimension. The slots thus formed provide an opening which is generally perpendicular to the surface of the sheet of material. The slot opening

presents an upward facing angle defined by the surface of the sheet of material and the slit side of the bridge, louvered or deformed portion. The slot opening also presents a corresponding downward facing angle defined by the bottom surface of the bridge, louvered or deformed portion and the slit side of the sheet of material. The angles of the slot opening are of a degree which prevents the lodgment of filtration media or debris therein. A suitable angle is thus about ninety degrees. But any one angle may range from about 80° to about 100° with the corresponding angle having a complementary angle degree generally commensurate with a 180° measurement. Both the upward facing and downward facing angles of the opening may be influenced or dictated by deformation of the bridge, louvered, or deformed portion in formation of the slot.

The slot opening angles of the present invention advantageously deflect filtration media and debris away from the slot opening thereby preventing clogging. Additionally, the orientation of the slot opening directs backwashing fluid at forty-five degree angle to the opening thereby encouraging the deflection of any debris or material away from the slot opening. The upward and downward angles of the slot opening facilitate self-cleaning of the slot opening in both fluid flow directions (i.e., filtration flow and backwash flow).

The present invention provides a filtration media retention grid which prevents clogging of the openings in the grid and promotes efficient self-cleaning in both fluid flow directions. As a result, the present invention provides an advantageous filtration grid which operates efficiently for longer periods of time without clogging, thereby improving operation efficiencies and costs. The manner in which the bridge portions are formed, and thus the slots are formed, allow the grid to be made more efficiently from stainless steel and other materials which increase the strength and operation life of the grid. Manufacturing and operation costs are lowered accordingly.

The filtration media retention grid of the present invention may be formed in a flat or substantially planar plate, or may be formed into other appropriate configurations, such as semi-circular or cylindrical forms. The filtration media grid may also be secured to an underdrain structure of the type forming a trough or distribution conduit as is frequently used in granular media filtration tanks.

Among the uses of the grid of this invention include not only the retention of media in filtration equipment such as underdrains for granular media filters of the type generally shown in U.S. Patent No. 5,019,259, overflow weirs for granular media filters of the type generally shown in U.S. Patent No. 5,227,077, but also as backing or support members for flexible sheet media of the type such as used for example in rotary vacuum filters, such as shown in U.S. Patent No. 4,330,405. or in pressure filters, such as shown in U.S. Patent No. 5,151 ,176. The grid may also be used to define a tortious flow path for fluid and, thus, be useful in oil/water separation equipment of the type generally shown in U.S. Patent No. 4,737,288.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which currently illustrate what is considered to be the best mode for carrying out the invention,

FIG. 1 is a partial view in cross section of a prior art filtration media retention grid illustrating the typical small angle opening of prior art systems;

FIG. 2 is a plan view of the filtration media retention grid of the present invention;

FIG. 3 is a partial perspective view of the grid illustrated in FIG. 2; FIG. 4 is a view in cross section of the grid illustrated in FIG. 2, taken at line 1 -1 ;

FIG. 5 is a perspective view in cross section of the grid illustrated in FIG. 3, taken at line 2-2;

FIG. 6 is α view in cross section of the grid of the present invention shown in FIG. 3;

FIG. 7 is α view in cross section of an alternative embodiment of the invention where a louvered portion is formed with a single slot opening; and

FIG. 8 is a view in cross section of another alternative embodiment of the invention where the plate is deformed in two directions.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

To best illustrate the advantages of the present invention, reference is made to FIG. 1 which shows a typical filtration media retention grid of the prior art. The screen 10 shown by FIG. 1 comprises a plurality of angular metal rods 12 in parallel and spaced apart orientation to each other and a plurality of cylindrical metal rods 14 oriented at a right angle to the angular metal rods 12. Only one cylindrical metal rod 14 is shown. Filtration media 16 is shown positioned against the outer surface 18 of the screen 10. The cross sectional profile of the angular metal rods 12 of typical prior art filtration media retention screen, and their parallel orientation to each other, result in an opening 20 through the screen 10 which is angled. As illustrated by FIG. 1 , a smaller angle 22 is oriented toward the outer surface 18 of the screen 10 against which the filtration media 16 is positioned with a resulting larger exit point 24 oriented toward an opposing surface to the outer surface 18.

Although the cross sectional geometry of the angular metal rods 12 may vary from the triangulate shape shown by FIG. 1 , the principle is consistent among such prior art screens 10 that fluid being filtered passes through the filtration media 16, through the small angle 22 of the opening and out the larger exit point 24. Further, despite different cross sectional geometries, the small angle 22 of the opening of most prior art screens 10 is an acute angle, usually about 30°. The filtration media 16

may require cleaning from time to time to dislodge or remove entrapped debris and a backwashing procedure is performed. Backwash fluid, represented by the heavy arrows, is forced through the grid opening 20 and out through the small angle 22 of the opening. The backwash fluid then passes through the filtration media 16 in a direction opposite to the normal flow of fluid during filtration. Notably, the angular metal rods 12 are oriented such that backwash fluid enters the opening 20 parallel to the center line 26 of the angle 22. If the backwash fluid contains debris or other sizable impurities, the flow direction of the backwash fluid and the acute angle 22 of the opening 20 result in a high probability of lodgment of debris 28 in the small angle 22 of the opening.

Recognizing the clogging problems which occur with prior art systems, the present invention, illustrated by FIGS. 2-8, provides a grid 40 having slots 42 formed therein which present clog-preventing angles of ingress and egress. In a first embodiment of the invention, shown in FIG. 2, the grid 40 may generally comprise a plate 44 of suitable material into which pairs of elongated parallel slits 46 are formed to produce a strap of material between each pair of slits 46 which is deformable into a bridge portion 48 which extends above the outer surface 50 of the plate 44, or grid 40. As illustrated most clearly by FIG. 2, a plurality of parallel, spaced apart bridge portions 48 are formed in the plate 44 of the grid 40. The plate 44 of the grid is illustrated in FIGS. 2-6 as being flat or substantially planar. However, the plate 44 may be molded, formed or deformed into any other suitable shape, dimension or geometry consistent with the application in connection with which the invention is used.

FIG. 3 more clearly illustrates the formation of pairs of elongated parallel slits 46 through the thickness 52 of the sheet of material. The parallel slits 46 may be formed by any suitable means, including punch pressing and laser cutting. In the conventional punch pressing method, the strap 54 of material formed between each pair of elongated slits 46

is simultaneously deformed to provide the bridge portion 48. Other appropriate techniques may be used for forming the slots as described herein dependent upon the material used to form the plate 44. Therefore, such techniques may include molding, stamping, shearing, or heat or chemical deformation. The deformation of each strap 54 of material takes place in an area, designated by reference numeral 56 in FIG. 3, which allows the strap 54 of material to be lifted above the surface 50 of the plate 44 to form a bridge portion 48. An elongated slot 42 is thereby formed between the bottom surface 58 of the bridge portion 48 and the outer surface 50 of the plate 44 at the point of the slit 46 formation.

The length 60 of the slot 42, as illustrated by FIG. 4, is dictated by the length of the pair of elongated parallel slits 46 formed through the plate 44. The width 62 of the slot 42 opening is determined by the degree of deformation subjected upon the strap 54 of material in the formation of the bridge portion 48. The width 62 of the slot 42 can, therefore, be selected in accordance with the type of filtration media being employed in the system, and is generally selected to allow fluid to pass through the slot 42 while preventing passage of the filtration media therethrough.

FIG. 5 illustrates the position of the slots 42 in relationship to the bridge portion 48 and the plate 44. FIG. 5 also illustrates the placement of filtration media 64 on the grid 40. Filtration fluid, represented by the heavy arrow 63, flows over the filtration media 64 and through the slots 42 formed on either side of the bridge portion 48. During backwashing, fluid is forced upwardly, as represented by the heavy arrows 65, through the slots 42 and through the filtration media 64 to dislodge particulate matter and other debris from the filtration media 64.

FIG. 6 illustrates more clearly the advantages of the present invention over prior art grid apparatus, as shown by FIG. 1. Specifically, it can be seen that the bridge portion 48 extends above the outer surface

50 of the plate 44 to provide a slot 42 on either side thereof. The width 62 of the opening is defined by the space between the bottom surface 58 of the bridge portion 48 and the outer surface 50 of the plate 44 of the grid 40. By virtue of the slit 46 formed through the thickness 52 of the plate 44 and formation of the bridge portion 48, a lateral bridge face 66 extends above the slot 42 opening and a slit face 68 extends below the slot 42 opening. Therefore, an upward facing angle 70 is created between the lateral bridge face 66 and the outer surface 50 of the sheet, and a downward facing angle 72 is created between the bottom surface 58 of the bridge portion 48 and the slit face 68 of the plate 44. The upward facing angle 70 and downward facing angle 72 are both shown as being substantially 90° angles, and a plane 73 is essentially common to the lateral bridge face 66 and the slit face 68. However, the slits 46 may be formed, or the material of the plate 44 may be distorted or deformed in any suitable manner, to provide an angle which facilitates the deflection of particulate matter or debris from the opening and which prevents clogging of material in the slot 42 opening. Thus, an appropriate angle for either the upward facing angle 70 or the downward facing angle 72 having the required characteristics may range from about 80° to about 100°, definable as a substantially right angle. Understandably, if, for example, the upward facing angle 70 is less than 90°, the downward facing angle 72 may be correspondingly greater than 90°. However, deformation of the plate 44 may effect the angles of the slots 42 to render corresponding angles other than strictly complementary.

The substantial right angle of the upward facing angle 70 and downward facing angle 72 of the slot 42 facilitate movement of filtration fluid, represented in FIG. 6 by arrow 74, through the slot 42. Because the fluid enters the slot 42 at substantially a 45° angle to the opening of the slot 42, wedging or suspension of debris is prevented and any material which may be positioned in the downward facing angle 72 is efficiently

flushed αwαy, and the grid 40 is, therefore, self-cleaning in the filtration mode. Further, when backwashing fluid, represented in FIG. 6 by arrow 76, approaches the slot 42 opening, it does so at substantially a 45° to the opening and any particulate matter or debris which may be in the backwash fluid is deflected away from the slot 42 opening. Also, the degree of the downward facing angle 72 prevents most materials from becoming lodged in the slot 42 opening. The angle at which the backwash fluid enters into the slot 42 also facilitates self-cleaning of the grid in the backwash mode by efficiently flushing any debris from the upward facing angle 70 of the slot 42. The configuration of the slots 42 in the present invention, therefore, present an improvement in filtration media retention grids over the prior art.

FIG. 7 illustrates an alternative embodiment of the present invention in which a single slit 46 is formed through the plate 44 and simultaneous deformation of the plate at 80 produces a raised louvered portion 82. A slot 42 is thus formed between the louvered portion 82 and the surface 50 of the plate 44. The width 62 of the slot 42 may be selected to suit the type of filtration media used in the filtration system. It can be observed, however, that the slot 42 thus formed presents a substantially 90° angle in the upward facing angle 70 and the downward facing angle 72 of the slot 42 opening.

In another alternative embodiment of the invention, as shown by FIG. 8, a single slit 46 may be formed through the thickness of the plate 44 with simultaneous deformation of the plate 44 in an area to a first side 86 of the slit 46 and to a second side 88 of the slit 46. A slot 42 is formed between the two deformations 86, 88, the width 62 of which is selectively determinable by the amount of deformation subjected upon the plate in the area of 86 and 88. As can be seen in FIG. 8, the resulting upwardly facing angle 90 and the resulting downwardly facing angle 92 may be less than 90° angles. The resulting angles may be approximately 80° and, therefore, sufficiently angled to prevent wedging of debris, to

deflect fluid-borne debris, and to facilitate self-cleaning in both filtration and backwashing modes.

The present invention is directed to providing a filtration media retention grid which is configured to prevent clogging, both during filtration and especially during backwashing. The present invention is also directed to providing a grid which is self-cleaning in both fluid flow directions of filtration and backwashing. The concept may be adapted to virtually any type of fluid filtration system which employs a filtration media maintained within a bed. The slot structure and configuration, as well as the plate configuration, of the invention may be modified to meet the demands of the particular application. Hence, reference herein to specific details of the illustrated embodiments is by way of example and not by way of limitation. The grid of this invention has utility in a wide range of filtration and separation equipment including, for example, as a barrier to media flow for underdrains in granular media filters of the type generally shown, for example, in U.S. Patent No. 5,019,259, overflow weirs in granular media filter of the type generally shown, for example, in U.S. Patent No. 5,277,077; as a backing or support members for flexible sheet media of the type such as used, for example, in rotary vacuum filters such as shown, for example, in U.S. Patent No. 4,330,405 and in pressure filters, such as shown, for example, in U.S. Patent No. 5,151 ,176 ; and as a mechanism to define a tortious flow path for fluid in oil/water separation equipment of the type generally shown, for example, in U.S. Patent No. 4,737,288. It will be apparent to those skilled in the art that many additions, deletions and modifications to the illustrated embodiments of the invention may be made without departing from the spirit and scope of the invention as defined by the following claims.