U.S. patent application number 12/367613 was filed with the patent office on 2009-07-23 for scalable immersed-filtration method and apparatus.
Invention is credited to Sohail Zaiter.
Application Number | 20090184064 12/367613 |
Document ID | / |
Family ID | 40342869 |
Filed Date | 2009-07-23 |
United States Patent
Application |
20090184064 |
Kind Code |
A1 |
Zaiter; Sohail |
July 23, 2009 |
SCALABLE IMMERSED-FILTRATION METHOD AND APPARATUS
Abstract
A method and apparatus for filtering a large volume fluid intake
system using a modular immersed-filtration array that can be easily
scaled for use in a wide variety of immersion filtering
applications. The immersed-filtration array is composed of a
plurality of individual filtration modules. Each filtration module
has a mating end that allows the module to be coupled with a base
unit or plenum via a common interface port located on the base
unit. The array can be scaled in a plurality of ways.
Inventors: |
Zaiter; Sohail; (East
Taunton, MA) |
Correspondence
Address: |
SEYFARTH SHAW LLP
WORLD TRADE CENTER EAST, TWO SEAPORT LANE, SUITE 300
BOSTON
MA
02210-2028
US
|
Family ID: |
40342869 |
Appl. No.: |
12/367613 |
Filed: |
February 9, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12009946 |
Jan 23, 2008 |
7488426 |
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12367613 |
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Current U.S.
Class: |
210/767 ;
210/170.01 |
Current CPC
Class: |
B01D 29/114 20130101;
B01D 29/46 20130101; B01D 29/54 20130101; B01D 29/52 20130101 |
Class at
Publication: |
210/767 ;
210/170.01 |
International
Class: |
E02B 9/02 20060101
E02B009/02 |
Claims
1. A scalable filtration array for immersion in fluid containing
ichthyoplankton, comprising: a base configured to receive a
plurality of filtration modules, wherein said base has common
interface ports configured to accept a mating end of said
filtration modules, and said base has corresponding numbers of
common interface ports and filtration modules, and said mated
common interface ports and filtration modules form a corresponding
number of fluid connectors for filtrate discharge said plurality of
filtration modules being configured to reduce entrainment and
impingement of ichthyoplankton in said fluid.
2. The scalable filtration array of claim 1 wherein the shape of
said base is selected from the group consisting of circles,
rectangles, polygons, spheres, cubes, and polyhedra.
3. The scalable filtration array of claim 1 wherein said common
interface ports are threaded to allow mating of said filtration
modules containing a complementary threaded mating end.
4. The scalable filtration array of claim 1 wherein each of said
plurals of filtration modules, comprises: a plurality of filter
elements; a stacking core configured to allow assembly of said
filter elements into a filter stack, wherein said stacking core has
a first end configured for mating to a base, and a second end
configured to accept an end piece, and said filter elements form a
fluid connector for filtrate discharge when said filter stack is
assembled between said first end and said second end, and said
fluid connector discharges said filtrate from said first end of
said stacking core, and; an adjustable compression means, wherein
said compression means is located between said filter stack and
said cap attachment.
5. The scalable filtration array of claim 4 wherein said adjustable
compression means comprises: a compression plate that sits against
said stack of filter elements; a spring that sits against said
compression plate, and; an anti-torsion washer located between said
spring and said end piece.
6. The filtration module of claim 1 wherein said first end is
threaded to allow mating to said base.
7. A method of reducing entrainment and impingement of fluid-borne
ichthyoplankton, the method comprising the steps of: providing an
immersed filtration array; filtering fluid through a plurality of
filtration modules of said immersed filtration array, wherein said
filtration modules contain filter elements having a groove size of
about 10 times to about 1,000 times less than the average lower
diameter limit of ichthyoplankton, and; filtering at a V.sub.i such
that the ratio of V.sub.w to V.sub.i is between about 2 and 25.
8. The method according to claim 7 wherein said filter element pore
size is about 40 microns.
9. The method according to claim 7 wherein the ratio of V.sub.w to
V.sub.i is about 5.
10. The method according to claim 7 wherein V.sub.i is about 0.2
cubic feet per second.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to filtration systems, and
more particularly to filtration systems at a large volume of fluid
intake.
BACKGROUND OF THE INVENTION
[0002] Large volume fluid intake systems are used for generating
hydroelectric power, providing cooling water for manufacturing and
power generation plants, providing irrigation and potable water
supplies, and providing source water for desalinization plants. In
the U.S. alone, these systems take in more than 200 billion gallons
of fluid per day. Unfortunately, according to U.S. Environmental
Protection Agency (EPA) estimates, these fluid intake systems
remove billions of aquatic organisms from the water bodies in which
they are used, including fish, crustaceans, shellfish, sea turtles,
marine mammals, as well as a plethora of other aquatic life
forms.
[0003] Eggs and larvae of fish (commonly referred to as
ichthyoplankton) are particularly sensitive to large volume fluid
intake systems because they have little or no swimming ability.
Ichthyoplankton range in size from about 0.5 mm to greater than 1
mm in diameter, and normally reside in the upper 200 meters of the
water column, where they drift passively in the prevailing
currents.
[0004] Fluid intake systems negatively impact aquatic life in two
major ways: entrainment and impingement. Entrainment is the
circumstance where an aquatic organism is drawn into the intake
system and subjected to the physical, mechanical, chemical, and
thermal forces particular to the design and function of the fluid
manipulation system in question. Impingement describes the
circumstance where an aquatic organism is trapped against an
upstream physical barrier by the force of fluid flow entering the
intake system, and usually occurs in situations where the intake
system is screened. Most large volume fluid intake systems are
screened to prevent entrainment of debris.
[0005] Mortality rates of ichthyoplankton that are either entrained
or impinged is high, and may approach 100%. To minimize the impact
of large volume fluid intake systems on aquatic ecosystems, Section
316(b) of the Clean Water Act mandates that large volume fluid
intake systems, such as the water intake systems used in cooling
power plants, reduce impingement levels by 80-95% and entrainment
levels by 60-90%. EPA estimates suggest that Section 316(b)
compliance will result in benefits to recreational and commercial
fishing industries in excess of $100 million annually.
Additionally, Section 316(b) compliance is likely to have a
beneficial, although difficult to quantify, environmental effect by
creating healthier and more robust aquatic ecosystems.
[0006] Rates of entrainment and impingement are affected by many
factors. For example, both entrainment and impingement are affected
by the pore size of the apparatus used to screen the intake system.
There is a linear relationship between entrainment and pore size
(i.e. entrainment rates increase as filter pore size increases),
while there is an inverse relationship between impingement rates
and pore size (i.e. impingement rates increase as filter pore size
decreases).
[0007] Entrainment and impingement rates are also affected by
several other factors including, but not limited to, the velocity
of the fluid intake system (V.sub.i) and the velocity of the source
water body (V.sub.w) that serves the fluid intake system. Under
most circumstances, V.sub.i has a constant value within the fluid
intake system that is determined either by gravity or a pump.
However, at the point of fluid intake, V.sub.i interacts with the
source water body in a complex manner whereby the value of V.sub.i
decreases with distance (d) from the point of fluid intake. As d
increases relative to the point of fluid intake, it can be
recognized that d will eventually reach a critical distance
(d.sub.max) where V.sub.i is equal to V.sub.w. In other words, an
object in the source water body located outside of the d.sub.max
area is not influenced by the fluid intake system because it is
under the control of the velocity of the source water body flow
(V.sub.w). Generally, V.sub.w will be constant over short time
intervals, but may vary significantly over longer periods of time
as a result of a variety of environmental factors (for example,
tide, weather, rain, season, etc.).
[0008] The probability (p) of an object being entrained/impinged by
a filter associated with a fluid intake system is related in a
complex manner to the interactions between d, V.sub.i, and V.sub.w.
Generally, p is expected to be low if the ratio of V.sub.w/V.sub.i
is high. In other words, the likelihood of being entrained/impinged
is low if the velocity of the source water body is significantly
faster than the velocity of water being drawn into the fluid intake
system, because a high ratio of V.sub.w to V.sub.i has the effect
of decreasing the value of d.sub.max so there is a smaller distance
from the point of intake origin at which V.sub.i can exert an
effect that is stronger than V.sub.w. In this situation,
entrainment/impingement is likely to occur only if an object
happens to pass very close to the opening of the fluid intake
system.
[0009] There are few examples of anti-entrainment/impingement
solutions in the art. U.S. Pat. No. 6,051,131 and U.S. patent
application Ser. No. 0,227,962A1 recite the use of wire screens
wrapped around an intake source, or slots in an intake pipe, to
attempt to filter aquatic life forms from the intake fluid.
Disadvantageously, these systems are prone to clogging, and require
frequent and costly upkeep to maintain their intake function. U.S.
Pat. No. 7,118,307 recites the use of intake pipes covered in wire
screens and buried under a natural bed of sand located below the
intake fluid source to provide a two pass screening system.
Disadvantageously, this system is labor intensive and costly to
install, as well as difficult to maintain.
[0010] U.S. Pat. No. 5,580,454 (hereafter the "'454 patent",
incorporated by reference herein) discloses a filter cartridge that
is backwashable and may provide aspects of a filter element
suitable for screening large volume fluid intake systems. However,
the filter cartridge of the '454 patent was not heretofore used in
such a fluid intake filtering application. On the contrary, the
filter cartridge of the '454 patent was designed as an in-line
filter for use in high pressure applications; consequently, it has
aspects that are not suited for use in screening large volume fluid
intake systems. For example, the filter cartridge of the '454
patent was designed for use within a sealed, pressurized vessel
(FIG. 1A, 22), and has mounting flanges specific for this type of
in-line application (FIG. 1, 24). Additionally, because of the high
pressures involved in this filtering application (and
correspondingly high values of V.sub.i), the mounting flanges
contain narrow diameter fluid connectors for moving the filtrate
between the two chambers of the vessel (FIG. 1, 26), and such
connectors would not be suitable for an application using lower
values of V.sub.i (e.g. cooling water intake for a power
plant).
SUMMARY OF THE INVENTION
[0011] The present invention provides a method and apparatus for
filtering a large volume fluid intake system using a modular
immersion filtration array that can be easily scaled for use in a
wide variety of immersion filtering applications. The
immersed-filtration array is composed of a plurality of individual
filtration modules. Each filtration module has a mating end that
allows the module to be coupled with a base unit or plenum via a
common interface port located on the base unit. The array can be
scaled in a plurality of ways. For example, the number of common
interface ports on the plenum or base unit can be increased to
allow a corresponding increase in the number of filtration modules.
In another embodiment, the number and configuration of base units
can be increased to allow increases in flow-through and filtration
capacity that varies with the number of filtration modules per
plenum.
[0012] The filtration module comprises a plurality of filter
elements (such as, for example, those described in the '454 patent)
that are assembled onto a stacking core to create a filter stack.
Generally, each filter element comprises an outer filtration
portion connected, via a plurality of tabs, to a mounting portion
having an inner cavity and an outer arcuate surface, where the
plurality of tabs, the outer arcuate surface of the mounting
portion, and the inner surface of the filtration portion are
configured to form a plurality of integral fluid channels.
[0013] The filter stack is sandwiched between a first end and a
second end of the stacking core. The first end comprises an outer
circumference and bottom side which form a mating surface to couple
the filtration module to a common interface port of a plenum. An
abutment side of the first end forms a base against which the
filter stack abuts. The interior of the first end is hollow and the
top side contains a plurality of cavities. In the column of stacked
filter elements disposed on the stacking core, the plurality of
integral fluid channels accommodate the flow of filtrate from the
filter stack, through the cavities in the top side of the first end
of the stacking core, and out the bottom side of the first end of
the stacking core, thereby allowing the filtrate to traverse the
plenum to which the filtration module is attached and moving the
filtrate into the general fluid intake system. The second end of
the stacking core is affixed with an adjustable compression means
that provides counter-pressure to hold the filter stack against the
top side of the first end of the stacking core.
[0014] The adjustable compression means allows the filter stack to
be backwashed by reversing the flow of fluid through the filter
stack. The pressure generated by this counter flow reduces the
pressure applied to the filter stack by the compression means,
thereby allowing the filter elements within the stack to separate
as fluid flows from the interior to the exterior of the stack,
removing any impinged material from the outside of the stack in the
process. The stacking core is rigid enough to withstand high radial
forces and the integral passages reduce the potential for
preferential flow of backwash fluid. Avoidance of preferential flow
is a significant feature that ensures uniformity of flow of
backwash fluid throughout the filter elements in the stack, which
ensures even cleaning of the individual filter elements in the
filter stack.
[0015] An advantage of the filtration module of the present
invention is its modular design, which allows it to be incorporated
into any conceivable two or three dimensional configuration that
could be designed for a fluid intake system. Additionally, this
modular design allows the present invention to be easily scaled up
or down to suit essentially any large volume fluid processing
system. Yet another advantage of the modular, scalable nature of
the present invention is that it can be easily incorporated into a
wide variety of different filtration array architectures to
accommodate almost any imaginable physical location of a fluid
intake system.
[0016] Another advantage of the filtration module of the present
invention is a high ratio of surface area to three dimensional
volume, which allows a robust level of fluid processing capacity at
a low velocity of fluid intake (V.sub.i). This is advantageous in
the context of an immersed-filtration array incorporating the
present invention because it reduces ichthyoplankton
entrainment/impingement rates by maintaining a favorable ratio of
V.sub.w to V.sub.i, thereby reducing the probability of
ichthyoplankton proximity to the point of intake.
[0017] Advantageously, the filtration module of the present
invention virtually eliminates ichthyoplankton entrainment rates
because the filter element grooves are sized in the micron range,
while the lower limit of ichthyoplankton diameter is about 0.5
mm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The patent or application file contains at least one drawing
executed in color. Copies of this patent or patent application
publication with color drawing(s) will be provided by the Office
upon request and payment of the necessary fee.
[0019] The features and advantages of the present invention will be
better understood when reading the following detailed description,
taken together with the following drawings in which:
[0020] FIG. 1A is an elevation view of a filter vessel including a
plurality of filter cartridges according to the prior art;
[0021] FIG. 1B is a top view of a perforated filter plate
supporting filter cartridges in the prior art filter vessel of FIG.
1A;
[0022] FIG. 1C is a side section view of the perforated filter
plate of FIG. 1B showing a tube clamp fastening implementation
according to the prior art;
[0023] FIG. 2A is an exploded view of an exemplary filtration
module including a stacking core, a single filter element, and a
compression means according to the invention;
[0024] FIG. 2B is a perspective view of the mating end of the
stacking core depicting the mating surface and the conduit for
filtrate flow of the filtration module of FIG. 2A;
[0025] FIG. 3 is a side view of a filtration module depicting the
assembled filter stack affixed to the stacking core via the
compression means according to the invention;
[0026] FIG. 4A is a plan view of a filtration element according to
the prior art;
[0027] FIG. 4B is a perspective view of a partial stack of filter
elements according to the prior art; and
[0028] FIGS. 5A-5E, FIGS. 6A-6D, FIGS. 7A-7B and FIGS. 8A-8D are
views of a three dimensional immersed-filtration array according to
the invention.
DETAILED DESCRIPTION
[0029] As illustrated in FIGS. 2-5, an immersed-filtration
apparatus according to the invention is comprised of at least one
filtration module, which in turn is comprised of a plurality of
stacked filter elements. As generally illustrated in FIG. 2A, the
filtration module is comprised of a geometric stacking core (42),
which holds a plurality of filter elements (46) to form the filter
stack (FIG. 3, 62). The stacking core (FIG. 4A, 42) has a geometric
shape that corresponds to the inner cavity of the filter element
(FIG. 4B, 70), a mating end (FIG. 2A, 40) comprising a mating
surface (FIG. 2A, 47) and a conduit for filtrate outflow (FIG. 2A,
49), and a second end comprising an attachment means (44) for
affixing a compression means (48).
[0030] As depicted in FIG. 4B, the filter elements are 11/2'' wide
and generally constructed and configured as described in the '454
patent, consisting of an outer filtration portion (72) and an inner
geometrically shaped cavity (70) connected to one another via a
plurality of tabs (74). The inner geometrically shaped cavity
contains both an inner (79) and outer (80) side, and functions to
allow the filter element to fit onto the central shaft of the
stacking core in a manner that prevents rotation of the element
around the shaft (i.e. it resides in a fixed two dimensional plane
once positioned on the stacking core). The plurality of interstices
(76) that reside between the outer filtration portion (72), the
outer side of the inner geometric cavity (80), and the tabs (74)
form a plurality of integral fluid connectors (FIG. 4A, 76) once
the individual filter elements are combined to form the filter
stack (FIG. 3, 62).
[0031] As shown in FIG. 4B, the outer filtration portion (72) is
formed by twelve arcs (84) that contain a plurality of grooves (82)
that span the width of the outer filtration portion (72). The
twelve arcs (84) function to increase the surface area of the outer
filtration portion (72), which in turn increases the total number
of grooves (82) permeating the perimeter of the outer filtration
portion (72). The grooves (82) possess about the same three
dimensional characteristics as described in the '454 patent, but in
the exemplary embodiment are sized at about 40 microns.
[0032] In the exemplary embodiment, the stacking core is 73/4''
tall and consists of a single piece of injection molded
glass-filled polypropylene. However, one could easily construct the
stacking core with different dimensions, or from different
thermoplastic compositions, to suit different filtration
applications. As illustrated in FIG. 2A, the mating end (40) of the
stacking core is wider than the stacking core (42). The top side
(41) of the mating end serves as the base against which the filter
stack abuts, and also contains a plurality of cavities (FIG. 2B,
45) that align with the integral fluid connectors of the filter
stack (FIG. 4A, 76). The outer circumference of the first end
located below the top side (41) functions as a mating surface (47),
and while in this exemplary embodiment the mating surface is a
11/4'' National Pipe Thread (NPT) fitting, one skilled in the art
can appreciate the potential for any of a variety of additional or
alternative mating means. The region of the mating end interior to
the mating surface in the illustrative embodiment forms a conduit
for filtrate flow (49) through the plurality of cavities present in
the top side of the first end (FIG. 2B, 45). In combination, the
conduit (49) and the plurality of cavities (45) form a passageway
for moving filtrate from the filter stack through the first end of
the stacking core.
[0033] As generally illustrated in FIG. 2A, the second end of the
stacking core is threaded (44) to allow attachment of a compression
means (48). While the second end is threaded in this exemplary
embodiment, it should be appreciated that a plurality of additional
means for attaching the compression means could also be used.
Generally, the compression means comprises a compression plate
(50), a compression spring (52), an anti-torsion washer (54), and
an end piece (56). The compression plate (50) sits on top of the
filter stack and functions to seal the top end of the filter stack;
additionally, it also provides a contact surface for the bottom end
of the compression spring (52), which is located between the
compression plate (50) and the anti-torsion washer (54). In turn,
the anti-torsion washer is located between the compression spring
(52) and the end-piece (56). The compression means functions to
apply adjustable pressure to the compression plate, which
subsequently compresses the filter stack against the top side of
the first end. While this represents an exemplary embodiment, it
should be appreciated that various other means for providing
adjustable pressure against the filter stack could also be
implemented according to the present invention.
[0034] An embodiment of an immersion filtration array according to
the invention, is illustrated in FIGS. 5A-5E, and comprises a
plurality of filtration modules (28) affixed to a base (90) via a
corresponding plurality of common interface ports (92). In this
exemplary embodiment, the immersion filtration array is a
three-dimensional box (96) forming a plenum or base unit with a
filtration module containing base (90) affixed to at least one
surface of the box and a second filtration module containing base
affixed to the bottom surface of the box (96). The common interface
ports (92) are threaded to match the threaded mating end of the
filtration module (40). Additionally, the box (96) also contains an
attachment means (94) for connecting it to a fluid intake
system.
[0035] The immersion filtration array according to the invention by
its configuration is scalable. For example, the base plate (90) can
be enlarged to contain more common interface ports (92), thereby
resulting in a corresponding increase in the number of filtration
modules associated with the base, as well as a proportional
increase in the filtrate through-put capacity. Alternatively, the
system can be scaled by increasing the number of filtration
module/base assemblies associated with the fluid intake system,
thereby resulting in a linear doubling of the filtrate through-put
capacity. While the exemplary embodiment described herein depicts
the immersion filtration array as a three dimensional box, it
should be noted that it could also be a sphere or polyhedra. Other
geometries and configurations of the immersion filter according to
the invention can be implemented, such as those illustrated in
FIGS. 6A-6D, FIGS. 7A-7B and FIGS. 8A-8D.
[0036] The modular nature of the immersion filtration array
according to the invention provides for a high filtrate through-put
capacity at a relatively low velocity of fluid intake (V.sub.i). In
the exemplary embodiment, V.sub.i is equal to about 0.2 feet per
second and generates a filtrate through-put rate of about 9.25
gallons per minute per filtration module. Even if the
immersed-filtration array is implemented in a source water body
that has a relatively low main water velocity (V.sub.w) of 1.1 feet
per second, the array can still achieve an entrainment/impingement
reducing ratio of V.sub.w to V.sub.i that is about 5.5. Given this,
the immersed-filtration array can reduce entrainment/impingement
rates by maintaining an optimal ratio of V.sub.w to V.sub.i while
simultaneously maintaining an acceptable level of filtrate
through-put capacity for a large volume fluid intake system.
[0037] Although the invention has been shown and described with
respect to an exemplary embodiment thereof, it will be appreciated
that the foregoing and various other changes, additions, and
omissions in the form and detail thereof may be made therein
without departing from the spirit and scope of the invention.
* * * * *