Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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RADIAL-FLOW FLUIDIZABLE FILTER
TECHNICAL FIELD OF THE INVENTION
The present invention relates in general to a device for coacting a porous
media
with an influent, or for removing impurities, solids or particulate matter
from an influent,
and more particularly to a radial-flow type of filter having a nonbonded
filter media, and
in which the flow of the fluids can be reversed in a backwash operation to
remove the
filtered matter and thus regenerate the filter for reuse.
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BACKGROUND OF THE INVENTION
While there exists many types of filters for removing particulate matter from
an
influent, such filters are generally classified as the type having a bonded or
nonbonded
media. A bonded media filter includes a removable cartridge element
constructed of a
fibrous woven or nonwoven material. The material can be selected with a given
porosity so that particulate matter of a given size can be removed from the
influent.
When the bonded cartridge filter element has a sufficient accumulation of
filtered matter
thereon, it is simply removed and cleaned, or replaced. The cartridge type f
lters are not
easily backwashed. However, many cartridge-type filters are of the radial-flow
type,
whereby a maximum surface area is provided for filtering, thereby allowing a
reduced
resistance to the flow of the influent.
Another family of filters contains a nonbonded media, such as sand, glass
beads,
diatomaceous earth and other granules or particles through which the influent
flows.
The nonbonded media is generally of a granular type of material, circular,
rounded or
irregular in shape so that the spacing between the particles is effective to
filter the
particulate matter. The advantage of utilizing a nonbonded media filter is
that it can be
backwashed to regenerate the media. Backwashing can include the fluidizing of
the
media which allows the fluid to dislodge the entrapped contaminants from both
the
interstices between the grains of the media, as well as from the surface of
each grain
itself The primary disadvantage of such type of filter is the size
requirements and costs,
as well as filter inefficiencies, in that they have little surface area of the
filter exposed to
the incoming flow, and thus are forced to utilize larger media grains and
higher flow
rates per unit area exposed to the incoming flow. In other words, the
development of a
radial-flow, nonbonded media filter that can be regenerated by backwashing is
not a
simple task.
In U.S. Pat. No. 3,415,382, by Martin, there is disclosed a radial-flow filter
utilizing glass beads as the nonbonded media. While such filter is effective
for its
intended purpose, it utilizes a rather large-size bead media and can not be
regenerated
without disassembly.
Radial-flow filters have a broad range of applications in the manufacturing or
process industries which require the removal of impurities or solids from an
influent. A
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generalized diagram of a basic radial-flow filter 10 is shown in Figure I .
The filter
consists of two concentric perforated pipes 12 and 14 and a porous filter
media 16 filling
the annular space 20 between the two pipes, all housed within a filter case
18. The
porous media 16 is composed of tiny glass spheres which are of uniform size
for a
particular filter but can range widely in size for different filters. The
spheres can be
submicron sized, micron sized or as large as coarse sand, and completely fill
the
compartment 20 between the perforated pipes 12 and 14. The perforations in the
pipes
are circular, of uniform size and arrayed in a uniform pattern, but it can be
of other
arrangements. The concentric-pipes-porous-medium assemblage is encased so that
fluid
completely surrounds the assemblage during filtration. Filtration takes place
along the
entire axial length of the filter 10 as the fluid flows radially into the
porous media 16
through the perforations in the outer pipe 12, and exits the porous media 16
through the
inner perforated pipe 14. The impurities are trapped as the fluid traverses
the porous
media 16.
The porous media 16 must be cleaned by backwashing after one or more
filtration cycles. Backwashing consists of surges of clean fluid that flows
radially
outwardly from the inner pipe 14, into the porous media 16 and out through the
outer
perforated pipe 12. The direction of flow is basically opposite to that which
takes place
during filtration. Figure 2 shows the filter 10 during a conventional backwash
cycle.
The relatively high fluid velocities and surges that are generated around the
glass
spheres dislodge and flush out the accumulated impurities. The impurities are
sufficiently small to pass through the spaces between the glass spheres that
comprise the
porous media 16. However, not all of the impurities are able to be dislodged
as a gum
residue and particles gradually build up in the porous media 16. Therefore,
after a
number of filtration backwashing cycles, the filter 10 must be disassembled to
replace or
recondition the porous media 16.
From the foregoing, it can be seen that a need exists for a radial-flow filter
of the
type employing a nonbonded media, and constructed so that backwashing
capabilities
are afforded. flnother need exists for a nonbonded media filter constructed
such that
during the backwashing cycle, the porous media is completely regenerated,
thereby
eliminating the need to periodically disassemble the filter and completely
clean the same
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or replace the porous media. Another need exists for a nonbonded media filter
of the
type that can be backwashed, and where the backwashing pressures need not be
excessive. Another need exists for a filter of the type where the end of a
backwash
operation results in a high restriction to the flow of the backwash liquid,
thereby
increasing the pressure of the liquid and signaling that the backwash
operation is
complete.
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SUMMARY OF THE INVENTION
In accordance with the principles and concepts of the invention, disclosed is
a
radial-flow filter utilizing a nonbonded media and which can be efficiently
backwashed
to dislodge the impurities and particulate matter to thereby regenerate the
filter media.
5 According to a preferred embodiment of the invention, the radial-flow filter
includes an
over-sized filter media chamber for the granular filter beads. During a
backwash cycle,
the reverse flow of the backwash liquid provides an upward lifting force on
the granular
beads and transfers the beads into an upper portion of the chamber, thereby
separating
the beads and allowing accumulated particulate matter to be dislodged and
carried away.
During the filtration cycle, the granular beads settle to the bottom of the
filter media
chamber so that the influent flows between the beads to filter the particulate
matter
therefrom.
In accordance with the preferred embodiment of the radial-flow filter, the
influent passes through the screen mesh covering the outer perforated cylinder
and
radially through the fclter granules. The filtered influent then passes
through an inner
screen mesh-covered perforated cylinder. The filtered influent then passes
through a
series of open check valves located within the mesh-covered inner perforated
cylinder,
and then to the outlet port of the filter.
During the backwash cycle, the backwash liquid is forced through the filter in
a
reverse direction, whereby the check valves are closed and the backwash liquid
is
directed in a reverse direction through the granular media. In the backwash
operation,
the liquid may generally through the granular filter media in a radial
direction, and in an
upward axial direction. The upward force of the backwash liquid causes the
check
valves to close; thereby forcing a majority of the liquid into the granular
filter media
rather than upwardly through the inner perforated cylinder. The upward or drag
force
of the backwash liquid causes an upper section of the granules to be lifted
into a
backwash chamber where the particulate matter is separated therefrom and
carried out
of the filter. This movement and separation of the granular media is sometimes
denoted
herein as "fluidization," and occurs when the drag force exceeds the buoyant
weight of
the upper layer or section of the granular media. Once the upper filter
section has been
fully fluidized, then the subsequent underlying section also becomes
fluidized, whereby
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the section of granular media is forced upwardly so as to be separated and the
particulate
matter released therefrom. Each underlying section of the filter is
sequentially fluidized to
thereby regenerate the filter media during the backwash cycle. Because each
filter section
is sequentially fluidized, the backwash pressure is significantly reduced,
thereby easing the
requirements of backwash pumps, equipment and the like.
In the preferred embodiment of the radial-flow filter, the backwash chamber is
constructed with a volume to hold substantially all of the fluidized granular
media. When
fully fluidized, the granular media completely covers the portion of the mesh-
covered
inner perforated pipe that extends into the backwash chamber. As such, the
pressure of the
backwash liquid increases because there is no easy or unrestricted flow path
from the
backwash chamber into the upper portion of the mesh-covered inner perforated
cylinder.
This increase in the liquid pressure can be used as a signal that the backwash
operation has
been completed. Once the flow of the backwash liquid has been stopped, the
granular
media falls back into the bottom part of the media chamber so that a
filtration operation
can commence.
In accordance with one aspect of the present invention there is provided a
device
for fluidizing spent media with a backwash fluid, comprising: a media adapted
for
coacting with an influent until the media is spent; a support structure
comprising
concentric walls for holding therebetween the media, said walls each having
perforations
therein; said support structure having a first chamber for containing said
media so that said
influent passes radially through said media and coacts therewith; an inlet
structure for
directing the influent to said media so as to flow radially through said
media; and said
support structure having a fluidizing chamber different from said first
chamber to which
substantially all said media is carried during fluidizing thereof with the
backwash fluid,
said fluidizing chamber being of a sufficient volume for allowing said media
to separate
into particles when carned from said first chamber to said fluidizing chamber,
and having
an apertured terminal end at said fluidizing chamber adapted for allowing the
backwash
fluid to pass therethrough but not said media particles.
In accordance with another aspect of the present invention there is provided a
method for coacting a nonbonded media with an influent, and for fluidizing
spent media,
comprising the steps of: supporting said media in a first volume; passing the
influent
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6a
radially through the media; coacting the media with the influent until the
media is spent;
fluidizing the spent media by using a treatment fluid to transport the spent
media to a
second volume, thereby separating the spent media into particles; and
regenerating the
spent media and preventing loss of the spent media out of said second volume
during
regeneration of the spent media.
Other embodiments of the invention include different arrangements, such as o-
rings, perforated bladders and check valves for enhancing the fluidizing of
the filter media.
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BRIEF DESCRIPTION OF THE DRAWINGS
E~urther features and advanta~__>es will become apparent from the following
and
more particular description of the preferred and other embodiments of the
invention, as
illustrated in the accompanying drawings in which like reference characters
generally
refer to the same parts, elements or components throughout the views, and in
which:
FIG. 1 is a generalized cross-sectional view of a radial-flow filter well
known in
the prior art, showing the liquid flow during a f ltration cycle;
FIG. 2 illustrates the radial-flow filter of FIG. 1, but during a backwash
cycle;
FIGS. 3 and 4 illustrate in generalized form the structural features of the
radial-
flow filter assembly constructed in accordance with the invention, during a
respective
filtration cycle and during a backwash cycle;
FIGS. Sa-Sf are generalized sectional views of a portion of a radial-flow
filter
showing the different stages of the fluidization of the granular filter media;
FIG. 6a is a partial cross-sectional view of a portion of a radial-flow filter
showing velocity vectors that act upon the granular filter media to produce an
upward
drag force to thereby cause fluidization of the granular media;
FIG. 6b is a partial cross-sectional view of a radial flow filter equipped
with o-
rings between the housing and the outer perforated cylinder, with velocity
vectors
showing the drag forces on the filter media.
FIG. 7 is a computer generated drawing of the liquid flow pattern during a
backwash operation;
FIG. 8 is a cross-sectional view of one embodiment of a radial-flow filter
provided with the backwash and fluidizing capabilities of the invention;
FIG. 9 is a cross-sectional view of a check valve of one embodiment employed
in
the inner perforated cylinder;
FIG. 10 is a top view of a check value plate constructed in accordance with a
second embodiment;
FIGS. 1 1 and 12 are cross-sectional views of a check valve in respective
closed
and open positions, as utilized in the case that houses the filter assembly;
FIG. 13 is a cross-sectional view through different portions of a radial-flow
filter
constructed in accordance with another embodiment of the invention.;
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FIGS. 14a and 14b are generalized cross-sectional views of a radial flow
filter
constmcted in accordance with another embodiment of the invention,
illustratin~~ a
perforated bladder in a filter cycle and in a backwash cycle; and
FIGS. 1 Sa and 1 Sb are generalized cross-sectional views of a radial flow
filter
constructed in accordance with yet another embodiment of the invention,
showing a
radial flow filter operating in an inverted manner.
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DETAILED DESCRIPT10N
FIG. 3 illustrates in a generalized diagrammatic form, the radial-flow filter
assembly 50 constructed in accordance with the invention. The radial-flow
filter
assembly SO employs a new backwashing technique, thereby avoiding the downtime
and
S expense of reconditioning the nonbonded porous media, as was periodically
required by
the prior art filters. While the preferred and other embodiments will be
described in
connection with a device using a granular filter media for filtering
particulate matter
from an influent, the principles and concepts of the invention can be utilized
for coacting
a media with an influent, a gas or liquid, where the media periodically
requires
backwashing to cleanse or regenerate the media.
The radial-flow filter assembly 50 is constructed with a rigid cylindrical
housing
S2 that extends the entire length of the filter assembly. An inner perforated
cylinder S4
with a screen mesh extends the entire length of the filter housing 52. While
not shown,
the inner screen mesh is formed onto the perforated cylindrical support
structure 54 for
1 S preventing collapse of the screen mesh. The volume in which the porous
media S6 is
contained includes two chambers. During the filtration cycle, the porous media
56 is
situated in a first chamber 58 situated generally in the lower or bottom part
of the filter
assembly 50. The first porous media chamber 58 comprises an annular area
bounded by
concentric screen mesh cylinders, one defining the inner screen mesh S4 and
the other
defining an outer cylindrical screen mesh 60. Much like the inner screen mesh
cylinder
S4, the outer screen mesh 60 is supported by a perforated cylindrical pipe
that extends
axially only about half way through the filter assembly S0. The size of the
pores in the
screen mesh cylinders 54 and 60 is smaller than the general diametric size of
the porous
media 56. In this manner, the screen mesh contains the porous media within the
filter
50.
As noted in FIG. 3, and in accordance with an important feature of the
invention,
the radial flow filter assembly 50 includes an upper backwash chamber 62 of a
volume
that is preferably about the same as that of the lower chamber 58. As will be
described
more fully below, the general diameter of the top backwash chamber 62 is
greater than
that of the bottom porous media chamber 58 to facilitate fluidizing,
separation and
agitation of the porous media 56 during the backwash cycle. Fixed within the
inner
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perforated cylinder S4 and screen mesh is a plug 64 that prevents the passage
of the
influent axially from the top portion of the screen mesh cylinder to the
bottom portion of
the screen mesh cylinder and vice versa. One or more orifices, one shown as
reference
numeral 66 are fixed at spaced-apart locations within the inner perforated
cylinder S4.
S The size of each spaced-apart orifice is smaller so that the backwash flow
of liquid
therethrough toward the plug 64 becomes more restricted. As will be described
below
in conjunction with the backwash cycle, the orifices 66 force the backwash
liquid
outwardly into the porous medium S6 to thereby provide a lifting function for
fluidizing
vertical sections of the porous media.
10 In the filtration cycle, a small portion of the influent with suspended
particulate
enters the top of the inner perforated cylinder S4 and flows radially through
the screen
mesh and down the top backwash chamber 62, as noted by arrows 68. This flow of
influent facilitates the downward transport of any porous media 56 that may
have hung
up in the backwash chamber 62 during a backwash cycle. However, a majority of
the
influent flows through plural ports 70 located in the housing 52 and is
directed around
the outer perforated cylinder 60. While not shown in FIGS. 3 and 4, the filter
assembly
SO is housed in yet another housing having inlet and outlet piping coupled to
other
pumping equipment. The ports 70 each include a check valve for allowing the
entry of
the influent into the filter assembly S0, but prevent an opposite flow of
backwash liquid.
The influent passes through the outer perforated cylinder 60 and radially
through the
porous media S6 where the particulate matter becomes lodged within the
interstices of
the porous media, as well as to the surface of the porous media S6 itself. The
influent is
thus filtered. The filtered liquid passes through the mesh-covered inner
perforated
cylinder S4 and flows downwardly therein through the orifices 66. The filtered
liquid
2S exits the radial flow filter assembly SO as shown by arrow 72.
The porous media may be glass or other types of beads, sand, diatomaceous
earth, activated carbon, anthracite coal or any other granular media that has
the desired
characteristics for removing particulate matter of a specified size or
impurities of
specified type. It is well known that beads of a nominal diameter of 100
microns, when
tightly settled together as shown in FIG. 3, can filter particulate matter
much smaller
than the size of the beads. Hence, the mesh screen covering the perforated
cylinders S4
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and 60 contains the beads, but allows the particulate matter to flow
therethrough and
become lodged and filtered by the media beef. Dependin<, upon the amount of
particulate matter suspended in the influent being filtered and the volume of
the porous
media 56, the interstices thereof eventually become full of the particulate
matter, thereby
S reducing the efficiency of the filter assembly 50 and increasing the load on
the pump.
In accordance with an important feature of the invention, the radial-flow
filter
assembly 50 can be efficiently backwashed by reversing the flow of liquid
therethrough.
The flow of the backwash liquid is shown in FIG. 4. The backwash liquid enters
the
radial-flow filter assembly 50 at the location shown by arrow 74. The backwash
liquid
attempts to flow through the inner perforated cylinder 54 in an axial
direction, but due
to the series of smaller orifices 66, the flow is directed outwardly into the
porous media
56. It is noted that the check valve at the port 70 is forced closed during
the backwash
operation, thereby directing all of the backwash liquid upwardly in the
filtration chamber
58.
In accordance with an important feature of the invention, an upper portion of
the
porous media 56 is first fluidized, as shown in FIG. 4, due to the uplifting
drag force
exerted thereon by the backwash liquid. In addition, the size of the different
orifices 66
allow sections or stages of the porous medium 56 to be fluidized in a
sequential manner.
It is noted that the top portion of the porous media 56 becomes fluidized
first, because
the lifting force thereon is greater than the buoyant weight of the layer of
the upper
portion of the porous media and particulate matter accumulated therein. Once
the upper
section or portion of the porous media 56 becomes fluidized, the weight
thereof is
removed from a section portion of the porous media, whereby such section is
then
fluidized. All of the porous media 56 in the filtration chamber 58 eventually
becomes
fluidized, whereby substantially all of the filtering media is carried by the
backwash
liquid into the overlying backwash chamber 62. The sectional fluidization
overcomes
the need of a large backwash pressure to lift the entire annular column of the
porous
media. The lifting of the media column is difficult to accomplish without a
substantial
amount of backwash pressure.
The backwash chamber 62 provides two important functions. First of all, the
fluidizing of the porous media 56 from the smaller-diameter filtration chamber
58 is
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propelled by a swirling action into the backwash chamber 62. This swirling
motion
tends to agitate the porous medium S6 so that it separates and thereby
releases the
particulate matter. The particulate matter is carried by the backwash liquid
through the
mesh-covered inner perforated cylinder S4 and out of the filter assembly SO in
the
direction noted by arrow 76. The upper portion of the filter housing 52 can be
perforated for allowing larger particulate and impurities to be carried out of
the filter
assembly 50. By choosing the sizes of the orifices 66 as a function of the
volume and
pressure of the backwash liquid, and as a function of the size and weight of
the porous
media 56, the backwash liquid can impart sufficient drag forces on the
sections of the
porous medium 56 to lift all of the granules and transfer the same from the
filtration
chamber 58 to the backwash chamber 62. A second feature of this technique is
that
when substantially all of the porous medium 56 has been transferred to the
backwash
chamber 62, the flow of the backwash liquid is impeded by the accumulation of
the
fluidized porous media around that part of the inner mesh-covered perforated
pipe 54
that extends into the backwash chamber 62. Thus, when fluidization of the
porous
media 56 is completed, a rise in the pressure of the backwash liquid is noted.
This can
be a signal that the backwash cycle of the filter assembly 50 is complete and
measures
can be taken to proceed with the filtration cycle.
The increased resistance to the flow of the backwash liquid can be
advantageously utilized when plural radial-flow filters are utilized in
parallel. If each of
the radial-flow filter assemblies 50 is provided with a common source of the
backwash
liquid, then when one filter becomes completely fluidized and thereby
increases the flow
of the backwash liquid therethrough, the pressure of the backwash liquid is
then
available to the other filters for facilitating fluidizing of the porous media
thereof. In
other words, once one filter becomes fluidized, it does not allow a
substantial flow of
backwash liquid therethrough, but substantially impedes the t7ow therethrough.
This can
be very helpful when one filter of a number of parallel-coupled filters has a
very clogged
porous media which requires a major amount of the backwash pressure for
fluidizing the
porous media thereof.
FIGS. 5a-Sf pictorially illustrate an example of the sequential fluidizing of
the
different stages of the porous media S6. Shown is an exemplary radial-flow
filter having
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four check valves 90-9S disposed in the inner perforated cylinder, thus
creating five
sections or stages of the porous media S6. The check valves are shown in more
detail in
FIG. 9. FIG. Sa illustrates the annular column of the filter media S6 during
the initial
backwash cycle, just before fluidization of the granular beads In FIG. Sb, the
top
S porous media section 80 begins to become fluidized and is lifted by the drag
forces into
the backwash chamber 62. As noted above, this is because the axial drag force
exerted
on the top portion 80 of the porous media S6 exceeds the buoyant weight of the
media
itself, thereby causing the porous media to be forced upwardly into the
backwash
chamber 62. As the process continues, the first section 80 of the porous media
is
completely lifted and directed into the backwash chamber 62, as noted in FIG.
Sc. In
FIG. Sc, the subsequent section 82 begins to fluidize and become transported
upwardly
to the backwash chamber 62 where it separates from itself, as well as from the
filtered
particulate matter. The second media section 82 is lifted at this time in the
backwash
cycle because the buoyant weight of the first or upper section 80 has been
removed. In
1 S FIG. Sd, a subsequent section 84 of the porous media S6 begins to fluidize
and be lifted
upwardly to the backwash chamber 62. FIG. Se shows the fluidizing of the media
section 86. In FIG. Sf, the bottom-most section 88 of the porous media is
lifted due to
the drag forces exerted thereon by the backwash liquid entering the bottom
inlet 96 of
the filter assembly.
It is important to note that the check valves 90-94 and 9S each have orifices
of a
different size. The top orifice in the check valve 90 has the smallest opening
therein, the
bottom orifice 9S has the largest opening, while the middle orifices of check
valves 92
and 94 have intermediate-size openings. The inlet 96 preferably has no actual
orifice
structure, but the opening itself functions as an orifice that is larger than
that of the
2S bottom orifice structure 95. The sizes of the orifices are important in the
staged
fluidizing of the porous media S6. The size of the top orifice in check valve
90 is
selected so that, based on the pressure of the backwash liquid flowing into
the inlet 96,
the drag forces imparted to the porous media S6 cause the upper section 80 to
be lifted.
Once the top section 80 of the porous media 56 is hydraulically transported
upwardly,
the backwash liquid continues to flow through the orifice in check valve 90,
unimpeded
by the porous media S6. However, since the orifice in check valve 90 is
somewhat
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14
small, the remaining force of the backwash liquid directed through the
intermediate
orifice in check valve 92 imparts a sufficient drag force to the second
section 82 to lift
the porous media ~6. With the different sized orifices in check valves 90-9~,
it is
assured that each section of the porous media 56 is acted upon by
substantially the same
drag force, when the section thereabove has been fluidized and moved to the
backwash
chamber 62. The appropriate size of the orifices can be selected as a function
of the
pressure of the backwash liquid, the size and weight of the porous media 56,
and other
parameters, based on trial, error and experimental techniques. As an
alternative, the
radial-flow filter section 50 constructed according to the invention can be
modeled and
analyzed by way of appropriate software programs. One such filter fluid
dynamics
program is identified as Fluent. The radial filter of the invention was
appropriately
modeled and the characteristics thereof were determined by such program. The
results
thereof are identified in a Ph.D. thesis entitled Process Characteristics of a
Radial Flow
Filter During Backwash, by Miguel Amaya, presented August 17, I 996.
As noted above, an important feature of the invention that allows sectional
fluidizing of the porous media during the backwashing operation, is the
provision of a
series of spaced-apart orifices of decreasing radii installed in the inner
perforated
cylinder 54. Shown in FIG. 6a is a drawing of the computer analysis of a
radial-flow
filter structure utilizing such type of orifices and the effect thereof on the
porous media
located in the annular area between the inner perforated cylinder 54 and the
outer
perforated cylinder 60. A first orifice structure 90 and a second orifice
structure 92 are
shown fixed within the inner perforated cylinder 54. In this embodiment, the
inner
perforated cylinder 54 has a major internal area thereof covered by a bladder
100. The
bladder 100 can be a durable sheet-like elastomeric material bonded or
otherwise
adhered to the inner surface of the perforated cylinder 54. The bladder 100
covers the
perforations and obstructs the flow of liquid therethrough. A small area 102
of
perforations 104 in the inner perforated cylinder 54 remains uncovered by the
bladder
l 00 in a location just under the perforated structures 90 and 92. As an
alternative,
rather than employing a bladder 100, the inner cylinder 54 can simply be
constructed
without being fully perforated. The flow of the backwash liquid in the inner
perforated
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cylinder 54 is shown by the arrows 106. The arrows 108 shown in the filtration
chamber 58 illustrate velocity vectors of the backwash liquid.
The orifices 90 and 92 restrict the flow of the backwash liquid in the inner
perforated cylinder 54 and give rise to drag forces on the porous media. It
can be
5 appreciated that the porous media can be displaced axially upwardly during
the
backwashing operation, only if the drag forces are greater than the buoyant
weight of
the porous media itself The magnitude of the axial components of the liquid
velocities
identify the regions where the drag forces can exceed the buoyant weight of
the porous
media. The velocity vectors 108 of FIG. 6a illustrate the dynamics of the
fluid flow and
10 drag forces at one instant of time. In the porous media generally shown in
media section
110, the velocity vectors 108 are directed generally in an upward direction.
Assuming
that the top of the porous media is as shown in FIG. 6a, then the buoyant
weight of the
porous media is the least at this location, with respect to the drab forces
produced
thereon as a result of the orifice 90. By computer analysis, it has been
determined that
15 by the appropriate selection of the size of the orifice 90, the size and
spacing of the
perforations 104 in the inner perforated cylinder 54, the size and weight of
the porous
material, the drag forces can be made to exceed the buoyant weight of the
porous
material. In this event, the porous material is lifted upwardly and removed
from the
filtration chamber 58 to the backwash chamber 62.
It is noted in the region I 12 of the filtration chamber 58 that the velocity
vectors
are substantially zero and there is no net drag forces exerted on the porous
material at
such location. The velocity vectors I 11 just above the region 1 12 are
directed
downwardly. This downward force on region 112 prevents the entire column of
the
media from being lifted as a plug. However, once the upper section of the
media above
orifice 90 has been removed, the downwardly directed vectors become
nonexistent, thus
preparing the subsequent media section for fluidizing. Sequential fluidization
from the
top to the bottom is thus enhanced. With respect to the second orifice 92,
upwardly-
directed drag forces are exerted on the porous media at section I 14. However,
due to
the accumulated weight of the porous media situated thereabove, the drag
forces do not
exceed the buoyant weight of the porous media at section 1 14. When, however,
the
upper section 110 of the porous media has been removed and fluidized, the drag
forces
CA 02256385 1998-11-23
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16
at section 1 14 then exceed the buoyant weight of the porous material, and the
granular
filter particles of such section begin to rise anti are transferred to the
backwash chamber
62 for fluidization. 'hhis same type of fluid dynamic action occurs with the
remaining
orifice sections until the entire annular filtration chamber 58 has been
emptied of the
porous media.
FIG. 6b is a partial cross-sectional view of the radial flow filter equipped
with an
annular band 116, or the like, between the outer perforated cylinder 60 and
the housing
52 of the filter assembly. As can be seen, there is one such annular band
associated with
each section of the porous media 56. The annular band or other type of
obstruction,
functions to redirect the backwash liquid from the outer annular chamber 1 I8
back into
the porous media 56. The annular band 116 can be constructed integral with the
inside
wall of the filter assembly housing 52, or integral with the outer sidewall of
the outer
perforated cylinder 60.
FIG. 7 illustrates the flow of the liquid stream during the backwash
operation.
The porous media of the top section has already been transported by
fluidizing. A
vertical cross-section of the filter is illustrated, where the inner
perforated cylinder is
equipped with five orifices with decreasing radii. The heavy and darkened
areas
illustrate the heavy flow of the backwash liquid, while the individual wavy
lines show
areas of reduced flow of the backwash liquid. It is noted that in this
illustration, the
upper section of the porous media 56 has been fluidized, while the lower
sections of the
porous media bed are exposed to drag forces that are less than the buoyant
weight of the
overlying media, whereby no fluidization is yet occurring. It can thus be seen
that a
radial-flow filter can be structured to provide fluidization of the porous
material without
requiring excessively high pressures or otherwise compromising the efficiency
of the
filtration operation.
As noted above, various structural elements of the radial-flow fitter affect
the
capability and efficiency of the fluidization process. Amongst the many
variables that
must be considered in the fluidization of the porous media, it is noted that
the magnitude
and effect of the flow rate on both the axial drag force component and the
pressure drop
is larger than the effect of many of the other variables. By computer
analysis, it was
found that a larger drag force was obtained by increasing the flow rate to the
filter, but
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l7
at the expense of a large pressure drop. The properties and characteristics of
the porous
media tend to influence the responses more than changes in the perforation
pattern of
the inner perforated cylinder 54. As an example, the decrease of the particle
size of the
porous media increased the pressure by 5955Pa on the average, which is nine
times the
magnitude of the effect of percent of the perforated open area change of the
inner
perforated cylinder 54. The drag force experienced an average increase of with
respect
to the magnitude of the effect of the percent open area increase. With regard
to the
design of a radial-flow filter, this suggests that as smaller particle sizes
are employed, the
type of perforation pattern becomes less critical. It is also noted that
changes in the
percent open area have an opposite effect on the drag force. For example, the
average
effect of increasing the percent open area was a decrease in the drag force,
while the
effect of increasing the perforation size resulted on the average, in an
increase in the
drag force. As also noted with the computer analysis, with a high percent open
area,
large perforations in the inner perforated cylinder 54 decrease the drag
force, while at
1 S low percent open areas, large perforations increase the drag force.
Increases in both the
percent open area and the perforation size produced comparable decreases in
pressure
drop across the radial-flow filter. It was also noted that the flow rate of
the backwash
liquid and the particle diameter of the porous media were found to have the
largest
influence on the drag force and pressure drop in the filter. The particular
type of
perforation pattern becomes less relevant with respect to the drag force and
pressure
drop, with higher flow rates and smaller particle diameters.
In one of the embodiments of the invention, as analyzed by way of computer
analysis on the program FLUENT (V4.31 ), Fluid Flow Modeling, 1995, Fluent,
Inc.,
Centerra Resource Park, 10 Cavendish Court, NH 03766, the filter was
structured as
follows. Five orifices were employed, with radii ranging from 0.254 inches to
I .047
inches. The general diameter of the granular particles were between 44-840
microns,
with a specific gravity of 2.5, which is very similar to that of sand. The
radius of the
inner perforated cylinder 54 was 0.75 inches, with perforations comprising an
open area
of 66 percent. The annular dimensions of the filtration chamber containing the
porous
media was 0.80 inches (radial) by 22.625 inches (axial). The flow rate or
pressure of the
liquid media was between 3 gpm to 28 gpm. The backwash pressure was in the
range of
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18
0.5 kPa to 10.0 kPa. With a filter constructed as such, it is contemplated
that the
porous media can be successfully fluidized to thereby completely remove the
impurities
therefrom and prevent down time by disassembly of the filter for replacement
of the
porous media.
FIG. 8 illustrates in cross-sectional form a radial-flow filter incorporating
many
aspects and features described above. The filter 120 includes a base 122 and a
removable housing 124 coupled thereto by way of a bolt and clamp arrangement
126.
The housing 124 is sealed to the base 122 by means of elastomeric or other
types of
seals, not shown. The base 122 includes an inlet connection 128 coupled to a
supply of
influent that is pumped in the direction of arrow 130. The influent includes
impurities
which may comprise particulate matter, liquids, etc., that are separated by
way of the
filtration bed contained within the housing 124. Once the impurities are
removed, the
effluent exits the filter by way of an outlet connection 132, in the direction
of arrow 134
In a backwash operation, the backwash liquid is directed into the filter 120
by way of
1 S connection 132, and exits the filter with the impurities suspended therein
by way of
connection 128. Different valuing arrangements and control systems are well
known to
those skilled in the art for disconnecting filters from pumping systems and
reconnecting
the same to backwash systems.
Fixed within the housing 124 is a radial-flow filter assembly 136. The filter
assembly 136 includes an enclosed case 138 for containing and supporting
therein the
filter parts and components. The case 138 includes a cylindrical sidewall 140
fixed
between a top end cap 142 and a bottom end cap 144. The internal volume of the
case
138 is sealed to the influent that is coupled to the filter 120 by way of
inlet connection
128, except for one or more ports 70 formed in the sidewall 140 thereof. Each
port 70
includes a check valve for allowing the influent to enter into the case 138,
but prevents
liquid from passing in the reverse direction. The case 138 can be constructed
of
different types of plastics or metals to suit the particular needs of the
filtration system.
For filtering impurities from water and similar liquids, under iow-pressure
conditions,
the case I38 can be constructed with a PVC or polyethylene plastic. In this
event, the
end caps 142 and 144 can be bonded, welded or otherwise secured to the
cylindrical
sidewall 140. Where higher pressures or caustic liquids are employed, such as
chemicals
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19
to be filtered, the case 138 can be constmcted of stainless steel or other
types of
materials, and welded together.
Disposed within the case 138 of the filter assembly I 36 are a pair of
perforated
cylinders. An inner perforated cylinder 54 is supported within respective
holes formed
in the top end cap 142 and the bottom end cap 144. Moreover, the inner
perforated
cylinder 54 is supported by a bottom filter chamber end cap 146. The parts can
be
bonded, threaded or otherwise fixed together for permanent or removable
attachment.
Secured around the outer circumference of the inner perforated cylinder 54 is
a screen
mesh 148. The screen mesh can be of a synthetic or metallic material having a
porosity
sufficiently small to prevent passage therethrough of the granular particles
comprising
the porous media or filter bed. Fixed within the inner perforated cylinder 54
is a plug 64
to provide an obstruction so as to prevent liquid passage axially along the
inner
perforated cylinder 54.
As an alternative to the orifice structures 66 described above in connection
with
FIGS. 3 and 4, the embodiment of FIG. 8 includes plural check valves, one
shown as
reference character 150. It is contemplated that check valves with orifices
will be the
preferable structure. The check valves 150 each include a seat, and a ball
constructed of
a synthetic material so as to be buoyant on the liquids. The check valve 150
includes
one or more orifices, and will be described in more detail below.
Nevertheless, the
check valves 150 are open during the filtration operation, but are generally
closed,
except for the orifice formed therein during the backwash operation. In this
manner, the
restriction to the fluid flow during the filtration operation is eliminated.
An outer perforated cylinder 60 is fastened at a bottom end thereof to the
filter
chamber end cap 146. At the upper end, the outer perforated cylinder 60 is
fixed to an
annular-shaped piece 152 and bonded or otherwise fastened to the internal
surface of the
filter assembly case 140. Much like the inner perforated cylinder structure
54, the outer
perforated cylinder 60 has attached to the inside surface thereof a screen
mesh 154 that
serves the same function as the screen mesh 148. The annular space between the
outer
perforated cylinder 60 and the inner perforated cylinder 54 defines a
filtration chamber
156. The filtration chamber 156 is filled with a porous media, such as
granular particles
for removing impurities from an influent. Located above the f ltration chamber
156 is
CA 02256385 2005-O1-20
the backwash chamber 62. Preferably, the backwash chamber is about the same
volume
as the filtration chamber 1 ~6, although it may be of a larger volume. As
noted in FIG. 8,
the backwash chamber 62 has a larger radial dimension than the filtration
chamber 156.
This difference in radial dimensions is believed to impart a swirling action
to the granular
5 particles 56 as they are lifted from the filtration chamber 156 to the
backwash chamber
62. The swirling action is believed to agitate and facilitate separation of
the particles to
free the impurities therefrom. Without the difference in the radial
dimensions, the
tendency is to lift the entire column of media as a plug.
During a filtration operation, the influent is directed in the following path.
From
10 the inlet connection 128, the influent is forced into the space 160 that
surrounds the
filter assembly case 138. The influent is then forced into the port 70 via the
check valve
in the sidewall of the filter assembly case 138. Once the influent is forced
through the
check valve port 70, it fills the annular chamber 162 and completely surrounds
the outer
surface of the outer perforated cylinder 60. The influent then passes radially
through the
15 porous filter media 56 where the impurities are removed. The filtered
influent then
passes through the perforations of the inner perforated cylinder 54 and into
the internal
volume I 64 of the inner perforated cylinder 54. The filtered influent then
passes
through the opened check valves 150 and exits at the bottom of the filter 120
to the
outlet connection 132. The radial flow aspect allows a large surface area of
the porous
20 media 56 to be exposed to the influent. This process continues until the
pressure rises at
the inlet of the filter 120, denoting that the porous media 56 has accumulated
a sufficient
amount of impurities that the filtration process is becoming inefficient.
Once it is determined that a backwash operation must be carried out, the
appropriate valves are activated, whereby a backwash liquid is forced into the
connection 132. The flow path of the liquid is effective to remove the
impurities from
the porous material 56 and carry the impurities with the backwash liquid out
of the filter
via the connection 128. The backwash liquid is forced into the connection 132
and up
into the central part 164 of the inner perforated cylinder 54. The check
valves I 50
close, except for the small orifices formed therein. In this manner, the flow
of the
3 0 backwash liquid encounters successively smaller orifices, thereby
facilitating the
fluidiaing of the granular particles, as described above. Each section of the
porous
CA 02256385 2005-O1-20
21
media 56 in the filtration chamber 156 becomes fluidized and carried up into
the
backwash chamber 62. In the backwash chamber 62, the swirlin; and agitation
action
imparted to the granular particles 56 frees the impurities therefrom. The
impurities flow
from the backwash chamber 62 into the central area 166 of the inner perforated
cylinder
54, and out the end 168 thereof. It is noted that during the fluidization
process, the
check valve closes the port 70 in the filter assembly case 138, thereby
preventing a
substantial flow of the backwash liquid radially outwardly through the outer
perforated
cylinder 60. In any event, the impurities carried by the backwash liquid are
directed
from the top end 168 of the inner perforated cylinder 54 into the outer
annular area 160,
and therefrom to the filter connection 128.
FIG. 9 illustrates one embodiment of the check valves 150 fixed within the
inner
perforated cylinder 54. The check valve 150 is constructed with a plate 170
having a
primary hole 172 that can be plugged with a spherical-shaped ball 174. The
ball 174 is
preferably constructed of a plastic or similar material that is buoyant. The
individual
I S check valve balls may be of different buoyant weights. While not shown,
those skilled in
the art may prefer to maintain the ball 174 within a wire cage, or the like,
to prevent the
ball from falling downwardly and inadvertently stopping the hole in the check
valve plate
located therebelow. Also formed within the plate 170 are one or more orifices
176 that
are not plugged or otherwise stopped by the check valve ball 174. The oriftces
176
function much like those noted above in connection with FIG. 3 and identified
as
reference numeral 66. Again, the cumulative open area of each of the orifices
176 of
one check valve plate 170 are preferably different from that of the other
check valve
plates fixed within the inner perforated cylinder 58.
FIG. 10 illustrates another embodiment of a check valve plate 180 that can be
fixed within the inner perforated cylinder 58. Rather than having the
apertures 176
shown in FIG. 9, the check valve plate 180 of FIG. 10 includes a roughened or
serrated
edge 182 to prevent the ball 174 from seating in a sealed manner to the plate
180. The
irregular-shaped seat 182 of the plate 180 allows liquid to pass therethrough
even when
the ball 174 is forced within the hole of the plate 180.
3 0 FIGS. 11 and 12 illustrate a check valve that can be employed within
sidewall
140 the filter assembly case 138, and particularly in connection with the port
70 of FIG.
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22
8. This check valve includes an elastomeric stopper 184 having a planar
portion I 86
and a stem portion 188. Formed at the end of the stem 188 is a conical or
enlarged end
190 that can be pressed through the anchor hole 183 in one direction during
installation,
but cannot be easily removed. As noted in FIG. 1 l, fluid flow in the
direction of arrow
S I 92 causes the port holes 70 to be closed by the stopper flap 186, thereby
preventing
liquid flow through the filter assembly case 140. In FIG. 12, the liquid flow
in the
direction of arrow 194 allows fluid to flow through the ports 70. Thus, during
the
filtration operation, influent can pass through the ports 70 into the volume
162
surrounding the outer perforated cylinder 60 (FIG. 8). While only two ports 70
are
shown, many more holes can be formed so as to be covered by the elastomeric
check
valve flapper 186. Other types of check valves, such as elastomeric flaps can
be
fastened along one edge thereof to the inside wall of the filter assembly case
140 to
thereby be forced closed or opened by the directional flow of liquid, and
thereby
function as a check valve. Those skilled in the art may prefer to employ a
host of other
types of inlet check valves and inner cylinder check valves in connection with
the filter
120, including mechanical and electrical operated devices.
FIG. I 3 illustrates another embodiment of the radial-flow filter constructed
in
accordance with the principles and concepts of the invention. The filter
assembly 200
has structural features similar to that shown in FIG. 8. With the construction
of filter
assembly 200, there are shown plural elastomeric O-rings 202 located between
the outer
perforated cylinder 60 and a cylindrical case 204. While four O-rings are
shown in the
embodiment of FIG. 13, any number of O-rings may be utilized Each O-ring 202
provides a seal between the outer perforated cylinder 60 and the inner surface
of the
case 204. The O-rings 202 function to change or modify the direction of the
liquid flow
inside the porous media 56. A substantial amount of the radial flow through
the porous
media 56 is changed to axial flow. Moreover, additional axial forces are
generated
within the porous media 56. The use of the O-rings 202 may change the number
of
check valves I 50 needed, and indeed may require a leak hole 206 in the side
wall of the
case 204. The leak holes 206 would be located between each adjacent O-ring 202
in
order to allow for liquid flow in and out of each section of the porous media.
As can be
appreciated, the selection of the number of O-rings and the orifice sizes in
the check
CA 02256385 1998-11-23
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23
valves 150 and the axial lengths of the sections can insure that adequate
axial forces on
the porous media 56 exist during the backwash operation.
The filter assembly 200 is also shown to include the bladder i 00. The bladder
100 can be used in combination, with or without the orifices in the check
valve I50, as
well as the O-rings 202. The bladder I 00 functions to concentrate
substantially all of
the backwash liquid flow in the inner perforated cylinder 54 is directed to
that area
located directly beneath each check valve I50. The bladder 100 maximizes the
amount
of axial flow that exists in each porous media section. The bladder I 00 is
shown with
the sidewall deformed inwardly in a concave shape, due to the fluid pressure
exerted on
the outer surface thereof during a filtration cycle.
Lastly, the filter assembly 200 includes a backwash outlet check valve 210.
The
outlet check valve 210 is placed in an unperforated portion of the inner
cylinder 54,
preferably near the bottom of the filter assembly 200. When forced to an open
condition
by the pressure of the backwash liquid, the outlet check valve 210 provides a
flow path
from the internal volume of the inner cylinder 54 to the annular volume 162
that exists
between the case 204 and the outer perforated cylinder 60. The outlet check
valve 210
allows for the backwash liquid to exit below the filtration chamber and be
carried
directly to the outside annular volume 162 without first having to pass
through the
porous media 56. Once entering the outside annular volume 162, the backwash
liquid
exits through either the leak holes 206 or out into the top backwash chamber
62 via the
porous media 56.
The outlet check valve 210 also functions to seal the inlet check valves 184
closed during backwashing. This is helpful in situations where very small
granular
porous media 56 becomes packed with contaminants and allows small amounts of
the
backwash liquid to reach the outside annular volume 162. In addition, the
outlet check
valve 2I0 provides backwash liquid to the outside annular volume 162 and
assists in the
fluidization of the porous media 56 by the additional liquid diverted inwardly
by the O-
rings 202 into the porous media 56. It also produces a water scour to the
outside
annular volume 162 and significantly reduces the amount of backwash liquid
required to
remove the impurities from the porous media 56. This is because the larger
impurities
lodged in the screen mesh are flushed directly out of the leak holes 206,
rather than
CA 02256385 1998-11-23
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24
being carried back into the porous media 56 and out through the backwash
chamber 62
By discharging the larger impurities directly out of the leak holes 206, the
particulate
matter that would otherwise be too large to enter through the outer screen
mesh
covering the outer perforated cylinder 60 is completely removed.
As an alternative, all leak holes but the leak hole 206 at the top can be
eliminated
if each O-ring 202 has a vertical channel cut therein to allow the backwash
liquid to flow
upwardly around each O-ring 202. Moreover, alternatives to the check valves
150 may
be devised by those skilled in the art, including forming orifices in the
bladder 100 itself,
and allowing a portion of the bladder to block the vertical passageway in the
inner
perforated cylinder 54.
As can be seen, the filter assembly 200 of FIG. 13 provides additional
features
which may be considered optional, and in some circumstances may be necessary.
Those
skilled in the art may find that in various situations, various individual
features of the
embodiments may be selected so as to produce optimum filtering and backwash
results.
Also, while the filter media 56 has been described above generally in
connection with the
removal of particulate matter or impurities, other types of media can be
selected so as to
remove dissolved solids, provide coaction between solids and fluids, provide
coalescing
capabilities and even provide a catalyst to the influent supplied to the
filter.
Nevertheless, the filter constructed according to the principles and concepts
of the
invention provides an increased surface area for the radial flow of fluids
through the
media, whether or not it is used for filtering purposes, and provides for an
efficient
backwash for fluidizing the media.
FIGS. 14a and 14b illustrate another embodiment of the radial flow filter 220,
incorporating a perforated bladder 222. The bladder is preferably made of a
flexible
eiastomeric material suitably constructed to withstand the pressures
encountered within
the filter, as well as the type of influent and backwash fluids passed through
the filter
220. The bladder 222 may be constructed as a tubular member. A rigid plate 224
functions as the blocking obstruction within the inner perforated cylinder 54.
Rather than utilizing check valves with orifices or orifice plate structures
described above, the bladder 222 includes a pattern of perforations 226
functioning as
orifices. The orifices 226 formed in the bladder 222 adjacent a top section 80
of the
CA 02256385 1998-11-23
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filter media _56 functions to enable fluidization during a backwash cycle. The
orifices
226 can be located annularly around the upper section of the bladder 222.
Associated
with a second section 82 of the porous media 56, are an additional set of
orifices 228
formed in the bladder 222. Subsequent sets 230-236 of orifices are formed in
the
5 bladder 222. The open area of each set 226-236 of orifices is larger, as a
function of
distance away from the plate 224. As such, the sets of orifices function very
much like
that described above in conjunction with the orifice structures shown in FIGS.
3 and 4.
The variation in the open area between the sets of orifices can be
accomplished in
various ways. For example, the top orifice set 226 can comprise a pre-defined
number
I O of openings having a first diameter. The second set 228 of orifices can
include the same
number of openings, but of a larger diameter. Each subsequent set 230-236 of
the
orifices can be formed with orifices of successively larger diameters. As an
alternative,
the orifices of the sets can be of the same diameter, but ranging from a small
number of
orifices associated with set 226, and with larger numbers of orifices as a
function of the
I S distance from the plate 224. Many other arrangements can be devised by
those skilled in
the art to achieve an orifice structure that facilitates the fluidizing of the
porous media
56.
It is significant to note that the orifices of the various sets 226-236 are
fabricated
so as to be aligned with respective perforations in the inner perforated
cylinder 54. In
20 this manner, the backwash fluid is allowed to flow through both the
orifices of the
bladder 222 and the perforations in the inner perforated cylinder 54, into the
porous
media 56. With regard to the bottom set 236 of orifices, they are
substantially large so
as to pass the filtered influent therethrough without creating a pressure
differential
thereacross.
25 FIG. 14a illustrates the radial flow filter assembly 220 during the filter
cycle.
During such cycle, the influent enters the assembly 220 in the direction of
arrow 240 and
enters the column of the porous media 56 at the top thereof However, a
majority of the
influent passes through the opened check valves 184 and flows radially through
the
respective sections of the porous media 56. Each section is separated by a
respective o-
ring 202 for facilitating fluidization during the backwash cycle. Because of
the pressure
of the filtered influent passing radially through the media 56, the sidewall
of the bladder
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26
222 is forced inwardly, as shown in FIG. 14a. While some of the filtered
influent passes
through the various sets of orifices during the filtration cycle, a majority
of the influent
passes through the set of large orifices 236 and out of the filter assembly,
shown by
arrow 242.
FIG. 14b illustrates the filter assembly 220 during a backwash cycle. During
the
backwash cycle, the backwash fluid enters the assembly in the direction of
arrow 244.
The backwash liquid enters the inner volume of the bladder 222, thus pressing
it against
the inside surface of the inner perforated cylinder 54. The backwash liquid is
forced
through the sets of orifices, as noted by arrows 246. The backwash fluid then
flows into
the porous media 66 for fluidization thereof in the manner noted above. The
check
valves 184 are closed during the backwash cycle for facilitating sequential
fluidization of
the various sections of the porous media 56. The backwash fluid carries the
impurities
and the released particles out of the filter assembly 220 in the direction
noted by arrow
248.
FIGS. 1 Sa and 1 Sb illustrate another embodiment of the radial-flow filter
that
operates in an inverted manner. This embodiment is particularly well suited
for use with
granular beads that are either large or generally lightweight. In the filter
cycle, as shown
in FIG. 15a, a porous media setting liquid, which is preferably not the
influent, is
pumped into the filter assembly 250 in the direction of arrow 252. The drag
forces
imparted from the setting fluid to the porous media 56 caused the beads to be
lifted
upwardly into the top portion of the filter chamber. Each check valve 150
fixed withing
the inner perforated cylinder 54 in the backwash chamber 62 is closed, while
the check
valves 150 situated in the filtration chamber are opened. Unce the porous
media 56 is
lifted into the filtration chamber by the setting liquid, a valuing
arrangement (not shown)
is actuated to thereby allow the influent to pass into the filter assembly 250
in the
direction noted by arrow 252. Moreover, the influent is allowed to pass
through the
open inlet check valves 184 in the direction of arrows 254. The influent
passes radially
through the media 56 and into the internal volume of the inner perforated
cylinder 54,
via the opened check valves 150. The filtered influent then exits the assembly
250 in the
direction noted by arrow 256.
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27
FIG. I _Sb illustrates the inverted filter assembly 250 during, a backwash
cycle. In
the backwash cycle, the porous media 56 is simply allowed to settle lw w av of
gravity
into the filter chamber located at the bottom of the assembly. Durin~_ the
movement of
the filter media 56 from the upper filtration chamber to the lower backwash
chamber,
the granular particles are separated and the impurities are removed therefrom.
The
particulate matter and impurities pass through the opened check valves within
the lower
portion of the inner perforated cylinder 54 and are carried out of the
assembly 250 by
the backwash liquid, in the direction of arrow 260. In the event that the
column of the
porous media 56 is not moved downwardly by the force of gravity, the backwash
liquid
entering the assembly 250 in the direction of arrow 262 causes sequential
fluidization of
the sections in the manner described above.
While the preferred and other embodiments of the invention have been disclosed
with reference to a specific radial-flow filter, it is to be understood that
many changes in
detail may be made as a matter of engineering choices, without departing from
the spirit
and scope of the invention, as defined by the appended claims. Indeed, those
skilled in
the art may prefer to utilize only certain features of the invention, or
utilize various
features from the different embodiments to achieve the individual or combined
advantagesthereof.
