Note: Descriptions are shown in the official language in which they were submitted.
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FILTRATION MEDIA RETENTION DEVICE
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 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 generallydisclosed 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. 4,096,911 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 a 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
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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
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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 filtration 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. Ifmaterial 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 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.
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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 materialbetween 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
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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 thebridge, 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
,,~
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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.
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 a view in cross section of the grid of the present invention shown in FIG.
3;
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FIG. 7 is a 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 toFIG. l which shows a typical filtration media retention grid of the prior art. The screen
10 shown by FIG. l 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. l, 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. l, 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
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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.
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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. l. 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 thematerial of the plate 44 may be distorted or deformed in any suitable manner, to
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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 away, 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 asingle 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
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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 singleslit 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 resultingupwardly facing angle 90 and the resulting downwardly facing angle 92 may be less
than 90 angles. The resulting angles may be approxima1ely 80 and, therefore,
sufficiently angled to prevent wedging of debris, to deflect fluid-borne debris, and to
faciiitate self-cleaning in both filtration and backwashing modes.
The present invention is directed to providing a filtration media retention gridwhich 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 theparticular application. Hence, reference herein to specific details of the illustrated
embodiments is by way of example and not by way of limitation. It will be apparent to
those skilled in the art that many additions, deletions and modifications to theillustrated embodiments of the invention may be made without departing from the
spirit and scope of the invention as defined by the following claims.
