A FILTRATION APPARATUS AND METHOD FOR TREATING GRANULAR
FILTRATION MEDIUM
Field of the Invention
The present invention relates to a filtration apparatus and to
a method and means for treating/refreshing granular filtration
medium. More particularly, the invention relates to a method
and apparatus for filtering raw liquid through filtering
grains and effectively and rapidly treating clogged filtering
grains and removing filtration residues therefrom.
Background of the Invention
Granular filtration medium is occasionally used in the
treatment of raw water (e.g., sewage, industrial effluents)
for removing oily matter and insoluble solids suspended in the
raw water. During the filtration process residual suspended
material is filtered out and retained in the filter bed, and
after a period of use the granulated medium becomes clogged
due to formation of mud balls and solidif ications caused by
the filtration residuals.
For example in the sand and rubble stone depth filtration
apparatus of AMIAD Filtration SYSTEMS
(http: //www. ami ad. co. il/filters/ sandMedia Filters _3 .asp) the
filtrate is passed from the filtration medium via an array of
nozzles provided in the base of the vessel comprising the
filtration medium. In this apparatus the filtration medium is
typically comprised of two layers; a first layer of rubble
stone which covers the array of nozzles, and a second layer of
sand which covers the rubble stone layer, wherein the main
purpose of the rubble stone layer is to prevent the fouling of
the nozzles by sand particles. This array of nozzles is
susceptible to fouling and thus requires frequent treatment or
replacement .
Typically, a backwash or pressure wash process is applied in
order to recover the clogged filtration medium and release the
fouling of the nozzles. In order to effectively clean the
granular filtration medium from the retained filtration
residuals continuous backwash treatments are required, which
consumes great amounts of fresh water. Furthermore, due to the
frequent backwashes typically needed to open the clogged
nozzles channels are formed over time in the filtration medium
which significantly reduce the efficiency of the filtration
apparatus due to the tendency of the raw water introduced into
the device to pass through the formed chanrels directly to the
nozzles i.e., without passing through the sand grains of the
filtration medium.
A washer apparatus is described in JP 8215509 for washing and
regenerating a clogged filter medium in a moving filter bed
type filter using a granular filter medium such as sand,
wherein contaminated filter medium is washed while rising in a
screw conveyor vertically installed in the filter medium bed,
in which the filter medium is crushed and then washed by an
agitator .
JP 8266815 describes a device in which a filter medium is
washed and circulated by means of a lift pipe vertically
installed in the central part of the filter tank for conveying
the filter medium.
In the device described in US 4,102,786 clogged filter medium
is treated by introducing upward current of water from the
lower side of the filter bed and circulating filtering grains
via a circulation line back into the device via the lower side
of the filter bed, thereafter a current of rinsing water is
introduced from the lower side of the bed to wash out
filtration residuals.
International patent application No. PCT/IL2010/C00160,
(publication number WO2010/097795) of the same applicants
hereof, describes a filtration apparatus capable of refreshing
(regenerating) clogged filtering grains maintained i n its
filtration column. The present invention provides new
configurations of such filtration apparatuses capable of
rapidly and efficiently refreshing and restoring a clogged
granular filtration medium with a relatively small amount of
water .
It is therefore an object of the present invention to provide
a filtration apparatus and method and apparatus for
efficiently operating a granular medium filtration apparatus
and for refreshing and regenerating clogged filter medium.
It is another object of the present invention to provide a
method and apparatus for granulating a clogged filter medium,
separating mud balls and other solidif ications , and for
washing out filtration residuals therefrom.
It is a further object of the present invention to provide a
filtration apparatus employing a granular filtration medium
which is less susceptible to blockage and which is easy and
simple for maintenance.
Other objects and advantages of the invention will become
apparent as the description proceeds.
Summary of the Invention
The inventor of the present invention developed a filtration
apparatus and a device for refreshing (regenerating) clogged
filtering grains maintained in a filtering column (also
referred to herein as a filtration column) by means of a
suction chamber capable of pumping portions of the filtering
medium into said suction chamber, and causing and separates
formations of filtering granules and filtration residues. A
preferred approach for implementing the suction chamber is by
generating reduced pressure conditions in the suction chamber
connected to the filtering column by a first inlet, such that
portions of the filtering medium are discharged into the
suction chamber. A second inlet opening of the suction chamber
is connected to a source of a pressurized stream causing
friction and high speed turbulences of the filtration medium
which separates formations of filtering granules and
filtration residues.
The reduced pressure conditions may be achieved by any
suitable configuration (also referred to herein as a pressure
reducing device) capable of receiving the pressurized stream
(e.g. stream of water) and substantially increasing its
velocity in the portion of the suction chamber such that
portions of the filtering medium are sucked into it and
streamed therefrom and discharged into a circulation line
which is in fluid communication with the upper portion of the
filtration column. The stream having increased fluid velocity
preferably causes the low pressure conditions required for
sucking portions of the filtering medium granules, applies a
momentum over the sucked filtering medium granules for
separating the filtration residues therefrom, and streams the
same back into the filtering column.
The terms filtering granules and granular filtration medium
used herein refer to any filtration medium comprised of
particles having any geometrical shape in three dimensional
space and made from any material suitable for filtration
purposes. The terms refreshing and regenerating are used
herein interchangeably to relate to the treatment process
carried out for separating and removing filtration residues
from the filtering medium granules.
Preferably, the suction chamber is adapted to produce reduced
pressure conditions by means of a Venturi effect obtained in
the suction chamber. For example, a type of Venturi device may
be used, said Venturi device is adapted to receive a stream of
water (e.g., city tap water) and produce a pressurized stream
having an increased fluid velocity thereby producing a Venturi
effect thereinside capable of streaming portions of clogged
filtering grains from a filtration apparatus, separating
filtration residues therefrom, and directing a stream
comprising the stream of water and the separated filtering
grains and filtration residues back into the filtration
apparatus .
The term Venturi effect used herein refers to the pressure
reduction occurring when streaming a fluid through a slender
passage (constriction) thereby causing increased fluid
velocity therethrough.
In one aspect the present invention is directed to a
filtration apparatus comprising: a filtering column which
interior is divided by a perforated partition into a filtrate
zone and a filtering zone, wherein said filtering zone is
adapted to receive a stream of raw-water and a lower portion
of its volume is filled with filtering grains, and wherein
said filtrate zone is adapted to receive a filtrate obtained
from passage of said stream of raw-water via said filtering
grains and said perforated partition; and a suction chamber in
fluid communication with said lower portion of said filtering
zone and with an upper portion thereof, wherein said suction
chamber is adapted to continuously remove filtering grains
from said filtering zone, separate filtration residues from
said filtering grains, and to direct a stream comprising said
separated filtering grains and filtration residues to said
upper portion of said filtering zone.
Most preferably, the suction chamber is adapted to receive a
stream of water and responsively to continuously remove
filtering grains from said filtering zone, separate filtration
residues from said filtering grains by the reduction of
pressure conditions evolving thereinside, and to direct a
stream comprising said stream of water and said separated
filtering grains and filtration residues to said upper portion
of said filtering zone.
Advantageously, the suction chamber is adapted to increase the
momentum of the stream of water such that separation of
filtering grains and filtration residues is caused. The
pressure reducing device preferably also generates a high
speed turbulent flow in the stream comprising the filtering
grains .
Advantageously, the suction chamber may be implemented by a
type of Venturi device adapted to receive a stream of water
and continuously remove filtering grains from the filtering
zone and separate filtration residues therefrom by means of a
Venturi effect. The suction chamber may comprise a pressure
chamber having an inlet adapted to receive the stream of water
and a tapering outlet adapted to produce a pressurized stream
having an increased fluid velocity, thereby causing a Venturi
effect. The suction chamber may further comprise a
constriction placed upstream near the tapering outlet for
increasing turbulence flow and thus promoting separation of
filtration residues. Alternatively, the suction chamber may
comprise a tongue element fixedly attached thereinside
configured to produce the pressurized stream having an
increased fluid velocity for pumping portions of the filtering
grains from the filtering zone into the suction chamber and
separate filtration residues therefrom.
The stream comprising the stream of water and the separated
filtering grains and filtration residues is introduced into
the upper portion of the filtering zone, preferably through a
nozzle, in a direction substantially tangential to the wall of
the filtering column, such that the motion of the filtration
residues having smaller masses progressively converge towards
the center of the column. In this way a stream comprising
filtration residues can be flown from said filtering zone to
drainage via a drain port centrally located in the upper
portion of the filtering zone.
One specific preferred embodiment of the invention is directed
to a filtration apparatus comprising a filtering column which
interior is divided by a perforated partition into a filtrate
zone and a filtering zone, wherein said filtering zone is
adapted to receive a stream of raw-water and a lower portion
of its volume is filled with filtering grains, and wherein
said filtrate zone is adapted to receive a filtrate obtained
from passage of said stream of raw-water via said filtering
grains and said perforated partition, wherein said perforated
partition has a tapering shape (e.g., conical, funnel-shape)
which tapers downwardly towards the base of said filtering
column.
Advantageously, the perforated partition may comprise one or
more nets placed thereon. Preferably said one or more nets
comprises a fine net placed on said perforated partition and
having holes of about half the size of the granules of the
filtration medium, and a spatially curvatured net placed on
said fine net and having holes size slightly smaller than the
size of the granules.
Optionally, the stream of raw water may be introduced into the
filtering column via the circulation line used in the process
of treatment of the filtration medium. A valve may be mounted
in the line through which the filtration medium is introduced
into the suction chamber, and by setting this valve into a
closed state in the filtration process the stream of raw water
may be passed through the pressure reducing device into the
circulation line connected to it, and therethrough into the
upper portion of the filtration column.
According to another aspect the present invention is directed
to a suction chamber for regenerating (refreshing) clogged
filtering grains comprising a pressure chamber and a suction
zone in fluid communication with a vessel comprising the
filtering grains and in fluid communication with a fluid pipe,
wherein the pressure chamber is adapted to receive a stream of
water and produce a pressurized stream having an increased
fluid velocity into the suction zone thereby causing a reduced
pressure conditions in the pressure chamber capable of
discharging portions of the filtering grains from the vessel
into the suction zone, separate filtration residues therefrom,
and direct a stream comprising the stream of water and
separated filtrating grains and the filtration residues into
the fluid pipe.
According to another aspect the present invention is directed
to a filtration apparatus comprising: a filtering column
having a perforated hollow member mounted thereinside, thereby
defining a filtrate zone inside the hollow perforated member
and a filtering zone in the volume of the filtrating column
external to the hollow perforated member (in which the
filtration medium is maintained) , wherein a portion of the
filtering zone is filled with filtering grains up to a level
sufficient for entirely covering the hollow perforated member,
and wherein said filtrate zone is adapted to receive a
filtrate obtained from passage of a stream of raw-water into
the filtration column and passed through the filtering grains
and the pores of the hollow perforated member.
The perforated hollow member preferably comprises at least one
outlet suitable for streaming filtrate obtained in the
filtrate zone to a filtrate reservoir. Optionally, the
perforated hollow member may further comprise an inlet
suitable for streaming fresh water into the filtrate zone for
carrying out backwash operations.
Advantageously, the filtration apparatus may further comprise
a suction chamber in fluid communication with the lower
portion of the filtering zone and with an upper portion
thereof, wherein the suction chamber is adapted to receive a
stream of water and responsively to continuously remove
filtering grains from said filtering zone, separate filtration
residues from said filtering grains by the reduction of
pressure conditions evolving thereinside, and to direct a
stream comprising said stream of water and said separated
filtering grains and filtration residues to said upper portion
of said filtering zone. Alternatively, the suction chamber may
comprise a tongue element fixedly attached thereinside
configured to produce the pressurized stream having an
increased fluid velocity for pumping portions of the filtering
grains from the filtering zone into the suction device and
separate filtration residues therefrom.
Advantageously, the perforated hollow member is a cylindrical
hollow perforated element which external surface may be
covered by one or more nets. The perforated hollow member is
preferably adapted to prevent passage of filtration grains
from the filtering zone into the filtrate zone. Preferably,
the external surface of the perforated hollow member is
covered by one or more fine net(s) and/or one or more
spatially curvatured net(s). Most preferably, at least one
fine net is attached over the external surface of the hollow
perforated member and at least one spatially curvatured net is
attached over the fine net. For example, the spatially
curvatured net may be a type of interwoven net which is
significantly less susceptible to fouling by filtration grains
due to its interwoven structure.
Optionally, the lower portion of the filtration column may
taper downwardly to define a tapering passage leading towards
an opening provided in the base of the filtration column
through which portions of filtration medium may be passed to
the pressure reducing device. Alternatively, slanted surfaces
may be mounted in the lower portion of the filtration column
to form a tapering passage for the filtration medium to the
opening in the base of the filtration column. Advantageously,
- li ¬
the perforated hollow member is mounted above, or within the
tapering passage.
Advantageously, the filtration apparatus may be operated
carrying out filtration and filtration medium treatment
operations concurrently.
According to still yet another aspect the p resent invention is
directed to a method for regenerating a clogged filtering
medium maintained in a filtering column which interior is
divided by a perforated partition into a filtrate zone and a
filtering zone, wherein said filtering zone is adapted to
receive a stream of raw-water and a lower portion of its
volume is filled with filtering grains, the method comprising:
providing a suction chamber in fluid communication with
the lower portion of the filtering zone and in fluid
communication with an upper portion of the filtering zone,
said suction chamber is adapted to received a stream of water
and produce a low pressure conditions thereinside;
directing a stream of water into said suction chamber
thereby removing portions of the filtering grains and
separating filtration residues therefrom by means of the
reduced pressure conditions and increased fluid velocity
obtained therein;
directing a stream comprising the stream of water and the
separated filtering grains and filtration residues and
introducing it into the upper portion of the filtering zone in
a direction substantially tangential to the wall of the
filtering column thereby causing a circular centrally
converging flow of said filtration residues inside said
column; and
directing a stream comprising filtration residues from the
filtering zone to drainage via a drain port centrally located
in the upper portion of the filtering zone.
According to one specific preferred embodiment of the
invention the interior of the filtering column is divided by a
perforated hollow member into a filtering zone external to the
perforated hollow member, in which filtering granules are
placed to at least cover said perforated hollow member, and a
filtrate zone residing inside the perforated hollow member.
According t o a preferred embodiment of the invention, the
invention relates to a filtration apparatus comprising: a
filtration column having a perforated hollow member mounted
inside it to define a filtrate zone therein and a filtering
zone in the volume of said filtration column external to said
hollow perforated member, wherein a portion of said filtering
zone is filled with filtering grains up to a level sufficient
for entirely covering said hollow perforated member, and
wherein said filtrate zone is adapted to receive a filtrate
obtained from passage of a stream of raw-water introduced via
the upper portion of the filtration column and passed through
the filtering grains and the perforations of the hollow
perforated member.
Preferably, the perforated hollow member comprises at least
one outlet for streaming filtrate obtained in the filtrate
zone to a filtrate reservoir.
Preferably, the perforated hollow member comprises an inlet
suitable for streaming fresh water into the filtrate zone for
carrying out backwash.
According to a very preferred embodiment of the invention, the
apparatus further comprises a suction chamber having a first
inlet opening connected to the lower section of the filtration
column; a second inlet opening connected to a source of a
pressurized stream; and an outlet opening connected to a
circulation line which is in fluid communication with the
upper portion of the filtration column.
Preferably, the apparatus further comprises a constriction
situated near to the suction chamber outlet.
Preferably, the circulation line enters the upper portion of
the filtering zone in an orientation substantially tangential
to the wall of the filtering column.
Preferably, the apparatus further comprises a drain port
centrally located in the upper portion of the filtering zone.
Preferably, the perforated hollow member is a cylindrical
hollow perforated element which is situated in the filtration
column such that the longitudinal axes of said column and said
cylindrical element are substantially perpendicular.
The present invention preferably relates to a method for
cleaning a clogged filtering medium held in a filtering
column, the interior of which is divided by a hollow
perforated member into a filtrate zone and a filtering zone,
said method comprising the steps of:
discharging at least a portion of said clogged filtering
medium into a chamber;
directing a pressurized stream of water into said
chamber thereby removing filtration residues from said
filtration medium by means of turbulent flow inside said
chamber to form a high velocity stream comprising water,
filtration medium and the removed filtration residues;
directing said stream from an outlet of chamber through
a circulation line into the upper portion of said filtering
zone in a direction substantially tangential to the wall of
said filtering column thereby causing a circular centrally
converging flow of filtration residues inside said column;
and
removing said filtration residues from said filtering
zone via a drain port located in the center of the upper
section of said filtration column.
Preferably, the method is carried out concurrently with a
filtration of raw water.
Brief Description of the Drawings
The present invention is illustrated by way of example in the
accompanying drawings, in which similar references
consistently indicate similar elements and in which:
Figs. 1A and IB schematically illustrate the apparatus of
the invention operated during the filtering of raw water,
wherein Fig. 1A shows a sectional view of the apparatus
and Fig. IB shows a cross-sectional view of the upper
portion of the filtering column;
Figs. 2A to 2E schematically illustrate the apparatus of
the invention during restoration of the granular
filtration medium and removal of the filtration
residuals, wherein Fig. 2A shows a sectional view of the
apparatus, Fig. 2B shows a cross-sectional view of the
upper portion of the filtering column, Fig. 2C is an
enlarged view of bottom part of the filtration column
designated in Fig. 2A by reference Vv comprising a
suction chamber, Fig. 2D schematically illustrates one
preferred muitilayered implementation of the perforated
funnel, and Fig. 2E illustrates a preferred embodiment of
a suction port comprising lateral and bottom apertures;
Fig. 3 schematically illustrates the apparatus of the
invention during backwash phase;
Figs. 4A and 4B schematically illustrate the apparatus of
the invention during raw water filtration after
regenerating/refreshing the filtration medium, wherein
Fig. 4A shows a sectional view of the apparatus and Fig.
4B shows a cross-sectional view of the upper portion of
the filtering column;
Fig. 5 schematically illustrate another preferred
embodiment of the filtration apparatus of the invention
wherein the filtrate zone is defined by a hollow
perforated member located inside the filtration zone;
Fig. 6 schematically illustrate a filtration system based
on the embodiment of the filtration apparatus illustrated
in Fig. 5 further comprising a pressure reducing device
and circulation line for treating the filtration medium;
Figs. 7A to 7D schematically illustrate few sectional
views of the filtration column shown in Figs. 5 and 6 ,
wherein Fig. 7A illustrates a sectional side-view of the
apparatus, Fig. 7B illustrates a sectional side view of
the filtration column (90° rotated side view) of the
filtration apparatus, Fig. 7C illustrates a crosssectional
view of the upper portion of the filtering
column; and Fig 7D shows a perspective and sectional
views of the bottom part of the filtration column; and
Fig. 8 schematically illustrates an embodiment of the
suction chamber comprising a tongue element.
It is noted that the embodiments exemplified in the Figs, are
not intended to be in scale and are in diagram form to
facilitate ease of understanding and description.
Detailed Description of Preferred Embodiments
Treatment of clogged granular filtration medium in prior art
systems is typically carried out by means of a circulation
process used for separating the filtration residues from the
filtering medium by friction or other mechanical means and
then washing out the filtration residues by a stream of water.
The present invention provides a new filtration apparatus and
anew technique employed therein for refreshing and restoring a
clogged filtration medium by streaming clogged filtration
medium from a filtration column through a suction chamber used
for breaking solidif ications of filtration residues and
filtering grains, and thereafter separating the filtration
residues from the filtering grains by introducing the stream
received from the suction chamber back into the filtering
column in a circular motion such that centripetal forces cause
a circular centrally converging flow of said filtration
residues inside said column which draw the filtration
residuals towards the column center wherefrom said residues
are drained out.
Fig. 1A schematically illustrates a preferred embodiment of
the present invention for a water filtration apparatus 10
employing a granular filtration medium lis (e.g., sand).
Filtration apparatus 10 comprises a filtration column 11
connected by pipes to raw-water tank 7c and filtered-water
tank 6c. As will be described hereinafter, during filtration
raw water 7r from raw-water tank 7c is passed through the
granular filtration medium lis in filtration column 11, and
the filtrate 6 is then streamed into filtered-water tank 6c.
During the filtration process schematically illustrated in
Fig. 1A suspended matter 7q (also referred to herein as
filtration residues) e.g., oily matter, organic materials,
and/or insoluble solids, contained in raw water 7r is captured
in filtration medium lis, which during continuous use cause
formations with filtration medium grains lis and eventually
clogs the filtration medium grains.
Filtration column 11 is generally a cylindrical vessel having
a closed bottom and upper opening sealably closed by lid 11c.
The upper portion of column 11 comprises two inlets: ) rawwater
inlet accessed via valve 14v; and ii) circulation inlet
(18 , Fig. IB) through which circulation line 18 is introduced
into column 11, and one outlet connected to drain line 19
passing through lid 11c.
A t the bottom portion of column 11 there is mounted a
perforated funnel 11a, which tapers towards the bottom of
column 11, and which tapering end is connected to conduit lid
passing through the bottom wall of column 11. Perforated
funnel 11a separates column 11 into two zones: filtration zone
llu, which is partially filled with filtration grains lis; and
filtrate zone lib having an outlet that can be accessed via
valve 15v, and an inlet that can be accessed via valve 16v.
Conduit lid sealably passes through the base of column 11 and
connects to suction chamber 5b (thus communicating between it
and filtration zone llu) , comprising a tapered nozzle 5 and a
slender passage 4 in a section of circulation pipe 18.
It is noted that perforated funnel 11a may be implemented by
employing perforated means having other geometrical shapes and
capable of partitioning the interior o f column 11 as described
above. For example, a perforated partition 11a may be
implemented b y means o f a flar. circular perforated piece o f
material (not shown) having a central opening to which conduit
lid may be connected. O f course, in such exemplary embodiment
conduit lid passing inside filtrate zone lib should be
lengthened in order to reach the perforated partition.
With reference to Fig. IB, showing a cross-sectional view of
column 11, circulation line 18 comprises a tapered nozzle 18p
adapted to tangentially direct a stream into the upper portion
of column 11.
When filtration is performed in apparatus 10, raw-water 7r is
streamed from raw-water tank 7c through pipes 7n and 14 and
pressurized into filtration column 11, by operating pump 12
and setting valves 7v and 14v into an open state and valve 2v
in tap-water line 2 into a closed state. Since valve 19v in
drain line 19 is in a closed state the pressurized raw-water
7r is forced to pass through the grains of filtration medium
lis and through the pores of perforated funnel 11a into
filtrate zone lib. The filtrate is then streamed into
filtered-water tank 6c through filtrate line 15. Since valves
13v and 16v are in a closed state, water passing through the
filtering grains lis will pass into filtrate zone lib, through
the pores of perforated funnel 11a, and then into filtrate
line 15.
A s explained hereinabove, along continued use the amount of
residual suspended material 7q retained in filtering grains
lis is increased which thus becomes clogged, resulting in
increased pressure losses in the filtering bed and reduction
in the filtering efficiency of apparatus 10, which requires
refreshing and restoring filtering bed lis.
Fig. 2A schematically illustrates apparatus 10 when
regenerating filtration medium grains lis. In this state
filtrate outlet valve 15v and inlet valve 16v communicating
with filtrate zone lib, raw-water inlet valve 14v
communicating with filtration zone llu, and valve 7v
communicating with raw-water tank 7c, are all in a closed
state. Tap-water valve 2v and suction chamber valve 13v are in
an opened stated for streaming tap water into suction chamber
5b by means of pump 12. Valve 19v in drain line IS is also
opened. In this preferred embodiment of the invention suction
chamber 5b is implemented in an inverted "T" shape style
formed by connection of conduit lid at the center of suction
chamber 5b, having pressure vessel 3 at one side of the "T"
junction and constriction 4 at its other side.
With reference to Fig. 2C, showing an enlarged view of the
bottom section of column 11 comprising suction chamber 5b,
wherein tap water stream is pressurized by pump 12 through
pipe 13 into pressure chamber 3 in suction chamber 5b from
which it is discharged via tapered nozzle 5 . As shown in Fig.
2C, the opening of nozzle 5 is placed more or less at the "T"
shape junction, preferably towards the end of the junction.
The velocity of the stream of tap water discharged via tapered
nozzle 5 is substantially increased and thus causing reduced
pressure condition (as obtained by a Venturi effect) which
applies suction forces through conduit lid. Due to the suction
applied by suction chamber 5b filtering medium lis is streamed
through conduit lid into suction chamber 5b. The substantially
high velocity stream discharged via tapered nozzle 5 generates
a high speed turbulent flow in the section between nozzle 5
and constriction 4 . The high speed turbulence and frictional
forces applied in said section of suction chamber 5b due to
the momentum of the streamed water, breaks formations of
filtering grains and filtration residuals, such that in the
stream of tap water and filter bed lis passing through
constriction 4 the binds between filtering grains (7s) and
sustained residuals (7q) are broken.
Reverting to Fig. 2A, the stream discharged from suction
chamber 5b is circulated through circulation line 18 back into
column 11. With reference to Fig. 2B, the circulated stream is
discharged from line 18 via tapered nozzle 18p in a tangential
direction such that a circular motion of the discharged stream
is obtained in the upper portion of column 11. Since the
specific weight of the filtering grains 7s is greater (e.g.,
-1.5-2.5 g/cm) than the specific weight of the sustained
residuals 7q (-03.-1 g/cm) their motion is more or less
adjacent to the wall of column 11, while the motion of
sustained residuals 7q is progressively converging towards the
center of column 11. Due to the positive pressure inside
column 11 material from the central area of column 11 adjacent
suction port 19k is sucked to drain lOd via drain line 19,
thereby discarding sustained residuals 7q.
In one specific preferred embodiment of the invention a valve
in provided in conduit lid (not shown) , said valve is used for
closing the passage of filtering grains through conduit lid
once the regeneration (grains refreshing) stage is finished
and during the filtration stage. Such valve in conduit lid may
be further utilized for streaming the raw water into the
filtering column via the circulation line 18. More
particularly, by closing the valve in conduit lid raw water 7r
may be streamed via suction chamber 5b into circulation line
18, and through it into the upper portion llu of the filtering
column 11. Accordingly, raw water 7r may be streamed into the
filtration zone llu via circulation line 18 and/or via pipe
14.
Fig. 2D schematically illustrates a possible multilayered
embodiment of perforated funnel 11a. In this preferred
embodiment perforated funnel 11a comprises a pierced layer 25
made from a suitable metallic (e.g., tin) or plastic material
and having apertures of about 6mm in diameter, a fine net 24
placed on pierced layer 25 and having thickness of about 0.2
to 0.5 mm and holes size about half the size of the granules
of filtration medium lis, and a spatially curvatured net 22
placed on fine net 24 and having thickness of about 2 to 3 mm.
and holes size slightly smaller than the size of the granules
of the used filtration medium lis. For example, if the size of
the filtering granules is of about 1mm, then the hole size of
fine net 24 may be of about 0.4 mm, and the hole size of
spatially curved net 24 may be of about 0.75 mm. Spatially
curved net 22 may be implemented by means of an interwoven net
having a wavy configuration in three-dimensional space, such
that it enables fluid flow through it even if it becomes
partially blocked by the filtration granules llq contacting
it, as demonstrated in Fig. 2D.
This multilayered construction of perforated funnel 11a
advantageously permits passage of the liquid obtained from the
passage of raw water 7r through the filtration medium lis
through the fine net 24, substantially without meeting
obstructions caused along its path by granules of the
filtration medium lis. In particular, the three-dimensional
curving of spatially curvatured net 22 provides that there
will always be an open passage through it for the liquid
passing through the filtering grains lis, even if portions of
it holes become covered by filtration granules over time.
Several trials showed that this multilayered structure
substantially reduced fouling of perforated funnel 11a.
Fig. 2E illustrates a preferred embodiment of suction port 19k
having a cup shape comprising a plurality of holes, and which
is sealably closed by a cover 9c having an opening suitable
for fitting it over the inlet of drain line 19. A s seen, in
this embodiment suction port 19k comprises a plurality of
bottom holes 9b and lateral holes 9r having a diameter of
about 20 to 30 mm. Suction port may be made from plastic or
metal (e.g., tin) .
Fig. 3 schematically illustrates a backwash step which may be
carried out periodically to removes blockages from the
perforated funnel 11a, after numerous regeneration steps are
performed (e.g., five). In this backwash step water is
streamed into filtrate zone lib through pipeline 16 and
drained via drain line 19, such that tap-water valve 2v, inlet
valve 16v and drain valve 19v, are in an open state, and all
other valves (13v, 15v, 7v and 14v) are in a closed state in
this step. In this optional backwash step the water stream
introduced into filtrate zone lib passes via the pores of
perforated funnel 11a and wash out residuals therefrom.
Figs. 4A and 4B schematically illustrate apparatus 10 operated
again in a filtration mode after the filtration medium lis is
refreshed and after optional backwash step(s) employed for
removing blockages from perforated funnel 11a (shown in Figs.
2 and 3 ) . As explained hereinabove, in this mode of operation
the valves 2v, 16v, 13v, and 19v, are in a closed state, and
valves 7v, 14v and 15v, are in an opened state such that a
stream of raw water produced by pump 12 is continuously
introduced into the filtration zone llu of column 11, and
filtrate is steamed out from the filtrate zone lib into
filtrate tank 6c.
Filtration column 11 may be made from any material suitable
for holding pressures of up to 10 atmospheres, or .in some
specific embodiments up to 20 atmospheres, if so required,
such as for example plastic material and steel, preferably
from epoxy coated steel. In a specific preferred embodiment of
the invention filtration column is made from a cylindrical
container having a diameter of about 0.5 to 3 meters and
height of about 1 to 3 meters. The pores in perforated funnel
are generally about 200 micron. Filtering grains are
preferably sand grains having a diameter of about 0.5 to 5 mm.
The suction chamber 5b may be made from stainless steel. The
inner diameter of pressure chamber 3 may be of about 50 mm.
The diameter of the opening of tapered nozzle 5 is generally
about 10 mm, and the fluid velocity discharged through it
during the treatment of the filtering grains in the
regeneration stage is generally about 30 m/sec. The diameter
of slender passage 4 is generally about 10 mm.
The diameter of the opening of tapered nozzle 18p is generally
about 15 mm, and the fluid velocity discharged from it during
the regeneration stage is generally about 20 m/sec.
EXAMPLE
The filtering apparatus of the invention depicted in Figs. 1
to 4 was tested in a laboratory setup utilizing a filtering
column (0.5 m in diameter and 1.5 in height) as described
hereinabove filled with about 100 liter of sand used as a
filtering medium. Raw water continuously streamed through sand
eventually clogged the filtering medium such that a pressure
gradient of about 0.5 bar evolved in the filtering column. The
filtering medium was then refreshed by means of a suction
chamber as described hereinabove fed by a stream of water
having flow velocity of about 10 m/sec, which provided flow
velocity of a bout 30 m/sec through the tapered nozzle of the
suction chamber. The filtering medium was satisfactorily
cleaned within a single cycle of the filtering medium through
the circulation line by streaming 700 liters of water which is
almost 10% of the quantity of water required for regenerating
such filtering medium in conventional washing methods.
Fig. 5 schematically illustrate a filtration apparatus 20
according to another preferred embodiment of the present
invention, wherein the filtrate zone 28z is defined by a
perforated hollow member 28 mounted inside filtration column
21' and designed to prevent passage of filtration grains 21s
from the filtering zone 21 into the filtrate zone 28z.
Perforated hollow member 28 is preferably fixated inside
filtration column 21' by means of lateral mounting ports 21y
provided over two lateral openings 21n formed in opposing
sides of filtration column 21', and configured to allow easy
and fast removal and replacement of hollow perforated member
28 therethrough, and for monitoring replacing the filtration
medium, whenever required. Filtering media grains 21s should
fill a substantial portion of the volume of the filtering zone
21u, at least sufficient for covering perforated hollow member
28, preferably filling about 2/3 of the volume of the
filtering zone 21u.
Mounting port 21y at one side of filtration column 21
comprises a fluid outlet 15t employed for streaming the
filtrate to fi tered-water tank 6c through pipeline 15
attached to it. The mounting port 21y at the other side o f
filtration column 21 comprises a fluid inlet 26t configured
for carrying out backwashes, if needed, by streaming fresh
water through backwash pipe 26 into filtrate zone 28z, by
opening backwash valve 26v provided thereon and closing valve
15v provided on pipeline 15. This specific preferred
embodiment of the invention does not include means for
treating clogged filtering grain media, and accordingly the
base of filtration volume 21' is sealed.
Fig. 6 schematically illustrates a filtration apparatus 29
utilizing a filtration column 21 in which the filtrate zone
28z is defined by a hollow perforated member 28 mounted inside
filtration column 21, and further comprising a suction chamber
5b for treating the filtration medium 21s. In this example
filtration column 21 is also filled with filtration medium 21s
up to about 2/3 of its height in order to substantially cover
hollow perforated member 28.
Perforated hollow member 28 is preferably located in a
tapering portion 21t located at the bottom section of
filtration column 21 inside the filtering zone 21u. In this
example the tapering is constructed by means of slanted
surfaces 21r (and 21q in Figs. 7A, 7B and 7D) , thereby
defining an empty space 21e i.e., not participating in the
operation of the apparatus. It is however understood that
filtration column may be constructed to include such tapering
portion integrally (i.e., without the empty space 21e) .
Tapering portion 21t is designed to direct filtration medium
21s towards the base of filtration column 21 and into the
opening of conduit 21d sealably attached to the base of
filtration column 21. As will be now explained, while the
structure of filtration column 21 is different than that of
filtration column 11 discussed hereinabove with reference to
Figs. 1 to 4 , other elements of apparatus 29 referenced by the
same numerals are of the same structure and functionality as
those of apparatus 10 and thus they will not be discussed in
details hereinbelow for the sake of brevity.
In this preferred embodiment the passage of filtration medium
21s into suction chamber 5b is further controlled by means of
valve 21v provided in conduit 21d. Accordingly, when treatment
of the filtration medium 21s is performed, tap-water valve 2v,
suction chamber valve 13v and valve 21v are in an opened
stated for streaming tap water into suction chamber 5b by
means of pump 12, and the filtration process of raw water 7r
in this preferred embodiment is carried out in a substantially
similar fashion to that described hereinabove with reference
to Fig. 1 to 4. The main differences are that the raw water 7r
may be introduced through pipeline 14', and that the filtrate
is streamed from perforated hollow member 28 into filteredwater
tank 6c through pipeline 15.
Figs. 7A to 7D provide further views of the filtration column
21 shown in Figs. 5 and 6 . Fig. 7A shows a sectional side view
of the filtration column 21 without the filtration medium.
Fig. 7B shows another sectional side view of filtration column
21 of the apparatus 20 rotated by 90°, showing filtration zone
28z implemented by means of a perforated hollow member 28
fixedly attached in opposing sides of tapering portion 21t
substantially in perpendicular to the longitudinal axis of
filtration column 21. The external surface of perforated
hollow member 28 may be covered by one or more spatially
curvatured net(s) (22 in Fig. 2D, e.g., using an interwoven
net) and/or one or more fine net(s) 24, designed to allow
fluid flow through it, and through perforated hollow member 28
into filtrate zone 28z, even if the spatially curvatured
net(s) becomes covered by the filtration granules, as
discussed hereinabove with reference to Fig. 2D. .
Fig. 7C illustrates a cross-sectional view of the upper
section of filtering column 21 comprising drain line 19,
suction port 19k, circulation inlet 18 , and inlet pipe 14',
as in apparatus 10 described with reference to Figs. 1 to 4 .
As shown in Fig. , pipe line 14' is not connected by means of
pump 12 to the raw water tank 7c, pipe line 14' preferably
supplies a stream of raw water 7r provided by other means (not
shown) .
Fig. 7D shows perspective and sectional views of the bottom
part 21 of the filtration column 21. A s seen, in this
preferred embodiment tapering portion 21t is constructed from
two pairs of slanted surfaces; slanted surfaces 21q mounted in
opposing relationship in bottom part 21w beneath and along the
length of perforated hollow member 28, and slanted surfaces
21r mounted in opposing relationship in bottom part 21w in
parallel to the longitudinal axis of perforated hollow member
28. In this configuration the upper portions of slanted
surfaces 21r extend above hollow member 28 such that the
tapering portion 21t defined accommodates perforated hollow
member 28 while maximizing the contact of its external surface
with the filtration medium.
The dimensions of filtration column 21 may be more or less the
same as those of filtration column 11 discussed hereinabove
with reference to Figs. 1 to . In a preferred embodiment of
the invention perforated hollow member 28 is made of a
perforated cylindrical element made from a plastic or metallic
material, preferably from stainless steel 316, or specific
materials suitable for treating certain types of fluids to be
filtered. The length of perforated hollow member 28 is
adjusted according to the diameter of filtration column 21,
its diameter may generally be in the range of 100 to 300 mm,
and pores provides in its walls may generally be in the range
of 3 to 6 mm.
The operation of filtration apparatus 29 is substantially
similar to the operation of filtration apparatus 10 described
hereinabove, which will be only briefly explained now. Raw
water 7r from raw-water tank 7c streamed into filtration
column 21 through pipeline 14' (or through circulation line
18) pass through filtration medium 21s and the pores of
perforated hollow member 28 into the filtrate zone 28z inside
perforated hollow member 28. Since valve 26v is in a closed
state during the filtration process the filtrate obtained in
the filtrate zone 28z is streamed through pipe 15 into
iltered-water tank 6c by having valve 15v in an open state.
It was found that this configuration of the filtrate zone is
more reliable and easier to maintain due to the firmness
obtained when employing the hollow perforated body 28, in
particular when it is embodied in a form of a cylindrical
hollow perforated element, which showed improved tolerance and
longevity of the hollow perforated element in moderate to high
operational pressure differences (e.g., pressure drops of
about 0.5 to 3 Bar) .
It is noted that carrying out backwash operations with the
apparatus of the present invention via perforated funnel 11a,
or via the pores of perforated hollow member 28 is
substantially beneficial in comparison to the backwashes
performed in the prior art apparatuses via nozzles, since the
use of perforated elements (e.g., 11a or 28) prevents
formation of channels in the filtration medium, and thus
maintain efficient filtration conditions and prolonged
filtration cycles.
The flow rate of raw water stream introduced into filtration
apparatus 21 may generally be in the range of 3 to 50 m3/Hr.
One of the major advantages of the filtration apparatus 2 9 of
the invention is in its ability to carry out filtration during
the filtration medium treatment. More particularly, the water
filtration and filtration medium treatment operations may be
carried out concurrently, for example, by streaming raw water
7r into filtration column 21 through pipeline 14' and
concurrently streaming tap city water into suction chamber 5b
through pipeline 13 i.e., having valves 2v, 13v, 14v, 15v, 21v
and 19v in an opened state, and valve 7v in a closed state.
Optionally, in certain applications raw water 7r may be used
for refreshing the filtration medium, instead of using fresh
city tap water. Advantageously, in such applications
filtration apparatus 2 9 may be also operated concurrently in
the filtering mode and in the filtration medium treatment mode
i.e., by setting valves 7v, 13v, 14v, 15v, 21v and 19v in an
opened state, and valve 2v in a closed state. It is noted that
the use of valve 13v in filtration apparatus 29 is optional,
or alternatively, valve 13v may be a one way valve configured
to prevent back flows in pipeline 13 in the direction of pump
12, or yet alternatively, valve 13v may entirely removed.
Furthermore, it was noticed that only the upper layer of the
filtration medium containing about 20% of filtration medium
actively participate in the filtration process. Accordingly, a
typical filtration medium treatment cycle in accordance with
the present invention may be operated for treating only about
20% of the filtration medium. In this way only 20% of the
filtering granules in the lower portion of the filtration
medium are treated in each cycle thereby providing a refreshed
upper layer of filtering granules, while substantially saving
in the amounts of tap water required in each the filtration
medium treatments. Accordingly, while a filtration medium
treatment cycle in the filtration apparatus of the present
invention in which the entire amount of filtration medium is
treated requires about 5% of the tap water required in
conventional sand filtration apparatuses, when operating the
filtration apparatus in a filtration medium treatment: mode in
which about 20% of the filtration medium is treated requires
about 1% of the amount of water required in conventional sand
filtration apparatuses.
Fig. 8 schematically illustrates an embodiment of a suction
chamber 5q comprising a tongue element 9 . In this preferred
embodiment of the invention reduced pressure conditions are
produced in pressure chamber 3q by the slender passage 9p
obtained by means of tongue element 9 . The slender passage 9p
increases the velocity of the water streamed into pressure
chamber 3q, which cause suction of filtration granules from
via conduit 21d. The increased velocity and turbulent flow
produced in the pressure chamber 3q causes separation of
filtration residuals in a similar way, as discussed i details
hereinabove .
Pressure chamber 3q may further comprise a construction 1
placed upstream thereinside and adapted to increase the
velocity of the fluid and filtration media and residues
streamed out of pressure chamber 3q into circulation line 18,
for further separating the filtration residues from the
filtration media. In this example, constriction 1 is provided
on one side only of the pressure chamber, which may have a
circular or rectangular cross-sectional shape.
All of the abovementioned parameters are given by way of
example only, and may be changed in accordance with the
differing requirements of the various embodiments of the
present invention. Thus, the abovementioned parameters should
not be construed as limiting the scope of the present
invention in any way. In addition, it is to be appreciated
that the different tanks, columns, pipes, and other members,
described hereinabove may be constructed in different shapes
(e.g. having oval, square etc. form in plan view) and sizes
differing from those exemplified in the preceding description.
The above examples and description have of course been
provided only for the purpose of illustration, and are not
intended to limit the invention in any way. A s will be
appreciated by the skilled person, the invention can be
carried out in a great variety of ways, employing more than
one technique from those described above, all without
exceeding the scope of the invention.
CLAIMS
1 . A filtration apparatus comprising: a filtration column
having a perforated hollow member mounted inside it to define
a filtrate zone therein and a filtering zone in the volume of
said filtration column external to said hollow perforated
member, wherein a portion of said filtering zone is filled
with filtering grains up to a level sufficient for entirely
covering said hollow perforated member, and wherein said
filtrate zone is adapted to receive a filtrate obtained from
passage of a stream of raw-water introduced via the upper
portion o the filtration column and passed through the
filtering grains and the perforations of the hollow perforated
member .
2 . The apparatus according to claim 1 wherein the perforated
hollow member comprises at least one outlet for streaming
filtrate obtained in the filtrate zone to a filtrate
reservoir .
3 . The apparatus according to claim 1 wherein the perforated
hollow member comprises an inlet suitable for streaming fresh
water into the filtrate zone for carrying out backwash.
4 . The apparatus according to claim 1 further comprising a
suction chamber having a first inlet opening connected to the
lower section of the filtration column; a second inlet opening
connected to a .source of a pressurized stream; and an outlet
opening connected to a circulation line which is in fluid
communication with the upper portion of the filtration column.
5 . The apparatus according to claim 4 further comprising a
constriction situated near to the suction chamber outlet.
6 . The apparatus according to claim A wherein the circulation
line enters the upper portion of the filtering zone n an
orientation substantially tangential to the wall of the
filtering column.
7 . The apparatus according to claim 4 further comprising a
drain port centrally located in the upper portion of the
filtering zone.
8 . The apparatus according to claim 1 wherein the perforated
hollow member is a cylindrical hollow perforated element which
is situated in the filtration column such that the
longitudinal axes of said column and said cylindrical element
are substantially perpendicular.
9 . The apparatus according to claim 1 wherein the external
surface of the perforated hollow member is covered by one or
more nets.
10. The apparatus according to claim 9 wherein the external
surface of the perforated hollow member is covered by at least
one fine net and at least one spatially curvatured net.
11. The apparatus according to claim 10 wherein the fine net
having holes of about half the size of the granules of the
filtration medium, and the spatially curvatured net having
holes size slightly smaller than the size of the granules of
the filtering granules.
12. The apparatus according to claim 1 wherein the lower
portion of the filtration column tapers downwardly to define a
tapering passage towards an opening provided in the base of
the filtration column.
13. The apparatus according to claim 1 comprising slanted
surfaces mounted in the lower portion of the filtration column
to define a tapering passage for the filtration medium to an
opening in the base of the filtration column.
14. The apparatus according to claim 12 or 13 wherein the
perforated hollow member is mounted above, or within the
tapering passage.
15. A method for cleaning a clogged filtering medium held in a
filtering column, the interior of which is divided by a hollow
perforated member into a filtrate zone and a filtering zone,
said method comprising the steps of:
discharging at least a portion of said clogged filtering
medium into a chamber;
directing a pressurized stream of water into said
chamber thereby removing filtration residues from said
filtration medium by means of turbulent flow inside said
chamber to form a high velocity stream comprising water,
filtration medium and the removed filtration residues;
directing said stream from an outlet of chamber through
a circulation line into the upper portion of said filtering
zone in a direction substantially tangential to the wall of
said filtering column thereby causing a circular centrally
converging flow of filtration residues inside said column;
and
removing s a id filtration residues from said filtering
zone via a drain port located in the center of the upper
section of said filtration column.
16. A method according to claim 9 , which is carried out
concurrently with a filtration of raw water.