U.S. patent application number 10/922060 was filed with the patent office on 2005-02-17 for filtration system with anti-telescoping device.
Invention is credited to Chancellor, Dennis, Jensen, James.
Application Number | 20050035048 10/922060 |
Document ID | / |
Family ID | 34138110 |
Filed Date | 2005-02-17 |
United States Patent
Application |
20050035048 |
Kind Code |
A1 |
Chancellor, Dennis ; et
al. |
February 17, 2005 |
Filtration system with anti-telescoping device
Abstract
A filtration system includes an outer casing that houses a
plurality of elongated inner casings, which in turn house a
plurality of filters (membranes). The outer casing, inner casings,
and filters are disposed relative to one another to provide a
three-flow channel system that provides additional feed fluid at
one or more of the membrane couplings between membranes of the same
inner casing. In preferred systems and methods the feed fluid flow
path comprises an annular space between the inner casings and the
filters contained in such casings, and in more preferred
embodiments the annular space is substantially continuous past
multiple filters of the same inner casing. The inner casings may
advantageously have openings that fluidly communicate with the
lumen of the outer casing, thereby reducing the ratio of couplings
relative to the number of filters (the coupling/filter ratio). In
especially preferred embodiments the coupling/filter ratio
.ltoreq.1:2, in more preferred embodiments the coupling/filter
ratio .ltoreq.1:3, and in still more preferred embodiments the
coupling/filter ratio .ltoreq.1:4.
Inventors: |
Chancellor, Dennis; (Falls
of Rough, KY) ; Jensen, James; (San Diego,
CA) |
Correspondence
Address: |
ROBERT D. FISH
RUTAN & TUCKER LLP
611 ANTON BLVD 14TH FLOOR
COSTA MESA
CA
92626-1931
US
|
Family ID: |
34138110 |
Appl. No.: |
10/922060 |
Filed: |
August 18, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10922060 |
Aug 18, 2004 |
|
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10019066 |
Jun 24, 2002 |
|
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10019066 |
Jun 24, 2002 |
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PCT/US00/03107 |
Feb 4, 2000 |
|
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60136739 |
May 27, 1999 |
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Current U.S.
Class: |
210/321.89 ;
210/323.2; 210/340; 210/497.01 |
Current CPC
Class: |
B01D 65/00 20130101;
B01D 65/02 20130101; B01D 61/022 20130101; B01D 61/10 20130101;
B01D 65/08 20130101; B01D 61/08 20130101; B01D 63/12 20130101; B01D
2321/10 20130101; B01D 2313/105 20130101; B01D 63/043 20130101 |
Class at
Publication: |
210/321.89 ;
210/323.2; 210/340; 210/497.01 |
International
Class: |
B01D 063/00 |
Claims
What is claimed is:
1. A filtration system comprising: an elongated outer casing
defining an outer lumen; a plurality of elongated inner casings
disposed within the outer lumen, each of the inner casings having
an inner lumen in which is disposed a filter; and the outer casing,
inner casings, and filters disposed relative to one another to
define a feed fluid flow path in which a feed fluid exiting from an
upstream filter into a downstream filter is diluted by additional
feed fluid.
2. The filtration system of claim 1 wherein the additional feed
fluid passes to the downstream filter by flowing from the outer
lumen through an opening in one of the inner casings.
3. The filtration system of claim 2 wherein the opening is
dimensioned to produce a maximum operational pressure drop of about
20%.
4. The filtration system of claim 1 wherein each of the inner
casings contains a plurality of the filters.
5. The filtration system of claim 1 wherein the plurality of
filters in at least one of the inner casings is serially disposed
to provide a substantially continuous core space.
6. The filtration system of claim 6 further comprising a manifold
fluidly coupling the inner lumen of each of the inner casings, and
another manifold fluidly coupling the core space of each of the
inner casings.
7. The filtration system of claim 6 having opposite ends, and both
of the manifolds extending from the same one of the opposite
ends.
8. The filtration system of claim 1 wherein at least one of the
inner casings contains a plurality of the filters serially disposed
to provide a substantially continuous core space, and wherein a
permeate flow path extends through the substantially continuous
core space.
9. The filtration system of claim 8 wherein the serial disposition
of the filters in at least one of the inner casings defines a
substantially continuous annular space between an inner wall of
each of the inner casings and the filters disposed within the inner
CD casings.
10. The filtration system of claim 1 wherein at least one of the
filters is spiral wound.
11. The filtration system of claim 1 wherein at least one of the
filters comprises hollow fiber membranes.
12. The filtration system of claim 1 further comprising an energy
recovery device that derives energy from a waste fluid in the waste
fluid flowpath.
13. The filtration system of any one of claim 1 wherein the outer
casing is disposed substantially above ground.
14. The filtration system of claim 1 having a coupling/filter ratio
.ltoreq.1:2.
15. The filtration system of claim 1 having a coupling/filter ratio
.ltoreq.1:3.
16. The filtration system of claim 1 having a coupling/filter ratio
.ltoreq.1:4.
Description
[0001] This application claims priority to provisional patent
application No. 60/136739 filed May 27, 1999, which is incorporated
by reference herein in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to filtration of
fluids, including especially filtration of water.
BACKGROUND
[0003] There is a great worldwide demand for purified fluids, one
of the most commercially important of which is production of fresh
water. Many areas of the world have insufficient fresh water for
drinking or agricultural uses, and in other areas where plentiful
supplies of fresh water exist, the water is often polluted with
chemical or biological contaminants, metal ions and the like. There
is also a continuing need for commercial purification of other
fluids such as industrial chemicals and food juices. U.S. Pat. No.
4,759,850, for example, discusses the use of reverse osmosis for
removing alcohols from hydrocarbons in the additional presence of
ethers, and U.S. Pat. No. 4,959,237 discusses the use of reverse
osmosis for purifying orange juice.
[0004] Aside from distillation techniques, purification of water
and other fluids is commonly satisfied by filtration. There are
many types of filtration, including reverse osmosis (RO), which may
involve ultra-filtration or hyper-filtration, and all such
technologies are referred to herein using the generic term,
"filtration."
[0005] Reverse osmosis involves separation of constituents under
pressure using a semi-permeable membrane. As used herein, the tens
membrane refers to a functional filtering unit, and may include one
or more semi-permeable layers and one or more support layers.
Depending on the fineness of the membrane employed, reverse osmosis
can remove particles varying in size from the macro-molecular to
the microscopic, and modern reverse osmosis units are capable of
removing particles, bacteria, spores, viruses, and even ions such
as Cl.sup.- or Ca.sup.++.
[0006] There are several problems associated with reverse osmosis
(RO), including excessive fouling of the membranes and high energy
costs associated with producing the required pressure across the
membranes. These two problems are interrelated in that most or all
of the known RO units require flushing of the membranes during
operation with a relatively large amount of feed liquid relative to
the amount of permeate produced. The ratio of flushing liquid to
permeate recovery in sea water desalination, for example, is about
3:1. Because only a portion of the water being pumped is recovered
as purified water, energy used to pump the excess brine is wasted,
creating an inherent inefficiency.
[0007] It is known to mitigate the energy cost of filtration
pumping by employing a work exchange pump such as that described in
U.S. Pat. No. 3,489,159 to Cheng et al. (January 1970) which is
incorporated herein by reference. In such systems, pressure in the
flushing or "waste" fluid that flows past the filter elements is
used to pressurize the feed fluid. Unfortunately, known work
exchange pumps employ relatively complicated piping, and in any
event are discontinuous in their operation. These factors add
greatly to the overall cost of installation and operation.
[0008] It is also known to mitigate the energy cost of filtration
pumping by employing one or more turbines to recover energy
contained in the waste fluid. A typical example is included as FIG.
3 in PCT/ES96/00078 to Vanquez-Figueroa (publ. October 1996), which
is also incorporated herein by reference. In that example, a feed
fluid is pumped up a mountainside, allowed to flow into a
filtration unit partway down the mountain, and the waste fluid is
run through a turbine to recover some of the pumping energy.
[0009] A more generalized schematic of a prior art filtration
system employing an energy recovery turbine is shown in FIG. 1.
There a filtration system 10 generally comprises a pump 20, a
plurality of parallel permeators 30, an energy recovery turbine 40,
and a permeate or filtered fluid holding tank 50. The fluid feed
lines are straightforward, with an intake line (not shown) carrying
a feed fluid from a pretreatment device (not shown) to the pump 20,
a feed fluid line 22 conveying pressurized feed fluid from the pump
20 to the permeators 30, a permeate collection line 32 conveying
depressurized permeate from the permeators 30 to the holding tank
50, a waste fluid collection line 34 conveying pressurized waste
fluid from the permeators 30 to the energy recovery turbine 40, and
a waste fluid discharge line 42 conveying depressurized waste fluid
from the energy recovery turbine 40 away from the system 10.
[0010] A system according to FIG. 1 may be relatively energy
efficient, but is still somewhat complicated from a piping
standpoint. Among other things, each permeator 30 has at least
three pressure connections--one for the feed fluid, one for the
waste fluid, and one for the permeate. In a large system such fluid
connections may be expensive to maintain, especially where
filtration elements in the permeators need to be replaced every few
years.
[0011] U.S. Pat. No. 5,470,469 to Eckman (November 1995) describes
a pressure vessel that houses one or more hollow fiber membrane
cartridges. The outer circumference of the membranes do not extend
completely to the inner wall of the production vessel, allowing
convenient replacement of the cartridges, and also providing an
annular space between the outer portion of the filters and the
inner wall of the production vessel that is used as part of the
waste fluid flowpath. The annular space is only continuous along a
single cartridge, however, and is interrupted between adjacent
cartridges by an annular sealing ring at one end of each
cartridge.
[0012] WIPO publication 98/46338 discloses an improvement over
Eckman in which the annular spaces between the outer portion of the
membranes and the inner wall of the production vessel can be
continuous past multiple modules (cartridges). Among other things,
the improvement extends the convenient replacement benefits of the
Eckman design to spiral wound filters.
[0013] Both U.S. Pat. No. 5,470,469 and WIPO 98/46338 are also
advantageous in that they reduce the ratio of couplings relative to
the number of filters. In an ordinary reverse osmosis filtration
system, three couplings are required to provide fluid flow paths to
a single membrane, one coupling for each of the feed fluid, waste
fluid, and permeate flow paths. The ratio is thus 3:1. However, in
the U.S. Pat. No. 5,470,469 and WIPO 98/46338 designs, only three
couplings are still required to provide fluid flow paths to
multiple membranes. Thus, if the pressure vessel contains three
membranes, the ratio is 3:3, and if the pressure vessel contains
five membranes, the ratio is 3:5.
[0014] It would be advantageous to reduce the ratio of couplings
relative to the number of filters still further, but five membranes
is usually considered to be the upper limit in an Eckman type
system because pressure drops past the several membranes reduce the
feed fluid pressure to an undesirable degree. Thus, there is still
a need to provide filtration systems, and especially reverse
osmosis filtration systems, that reduce the ratio of couplings
relative to the number of filters (the coupling/filter ratio) to
less than 3:5.
SUMMARY OF THE INVENTION
[0015] The present invention is directed to modularized filtration
systems in which an elongated outer casing houses a plurality of
elongated inner casings, which in turn house a plurality of filters
(membranes). The outer casing, inner casings, and filters are
disposed relative to one another to provide a three-flow channel
system that provides additional feed fluid at one or more of the
membrane couplings between membranes of the same inner casing.
[0016] In preferred embodiments the feed fluid flow path comprises
an annular space between the inner casings and the filters
contained in such casings, and in more preferred embodiments the
annular space is substantially continuous past multiple filters of
the same inner casing. The inner casings may advantageously have
openings that fluidly communicate with the lumen of the outer
casing, thereby reducing the ratio of couplings relative to the
number of filters (the coupling/filter ratio).
[0017] In especially preferred embodiments the coupling/filter
ratio .ltoreq.1:2, in more preferred embodiments the
coupling/filter ratio .ltoreq.1:3, and in still more preferred
embodiments the coupling/filter ratio .ltoreq.1:4.
[0018] Various objects, features, aspects, and advantages of the
present invention will become more apparent from the following
detailed description of preferred embodiments of the invention,
along with the accompanying drawings in which like numerals
represent like components.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a schematic of a prior art filtration system
employing an energy recovery turbine.
[0020] FIG. 2 is a schematic of a preferred filtration system
employing an energy recovery device.
[0021] FIG. 3 is a schematic of a filtration system employing a
field of outer casings.
[0022] FIG. 4 is a schematic of a preferred end cap for an inner
casing.
[0023] FIG. 5 is a cross-section of a preferred inner casing, in
which waste fluid from an upstream filter is supplemented by fresh
feed fluid before being fed into a downstream filter, and both
waste fluid and permeate streams exit the inner casing at the same
end.
[0024] FIG. 6 is a cross-section of an alternative preferred inner
casing, in which waste fluid from an upstream filter is
supplemented by fresh feed fluid before being fed into a downstream
filter, and the waste fluid and permeate streams exit the inner
casing at the opposite ends.
[0025] FIG. 7 is a cross-section of another alternative preferred
inner casing, in which waste fluid from an upstream filter is
supplemented by fresh feed fluid before being fed into a downstream
filter, and all three of the feed fluid, waste fluid and permeate
streams enter or exit the inner casing at the same end.
DETAILED DESCRIPTION
[0026] In FIG. 2 a preferred filtration system 200 generally
comprises an outer casing 210 containing multiple internal casings
220A-220G in which filters (not shown) are disposed, and a
pump/energy recovery unit 230. Feed fluid is fed to the end plate
subassembly 211 of the outer casing 210 from feed fluid line 240,
and passes into the internal casings 220A-220G via openings 224 in
the walls of the internal casings 220A-220G. The feed fluid is
filtered by the filters, with permeate being removed from the
internal casings 220A-220G at end plate subassembly 212 via
permeate manifold 252 and permeate line 250, and waste fluid being
removed from the internal casings 220A-220G via waste fluid line
260. Arrows 241 and 242 depict fluid flow in line 240, and arrow
261 depicts fluid flow in line 260.
[0027] The outer casing 210 advantageously comprises a hollow
cylinder, although other elongated shapes including those having
triangular, rectangular, or octagonal cross sections are also
contemplated. The dimensions of the outer casing 210 depend upon
the rate of fluid being filtered, with larger dimensions
accommodating greater production flows. Outside dimensions of
commercial systems employed in purifying brine are contemplated to
fall between about 0.5 meters to several meters in diameter, and
between about three to forty or fifty meters in length. Outer
casing 210 may be fabricated from metal, plastic, composite,
concrete, reinforced concrete, or any other materials that are
strong enough to withstand pressure differentials produced by the
pump/energy recovery unit 230, and that cannot readily be
solubilized by the fluid being processed. The outer casing 210 is
preferably maintained above ground for easy access, but in
alternative embodiments may also be placed below moo ground, or
underwater. Horizontal, vertical, and all other possible
dispositions are contemplated.
[0028] Each of the internal casings 220A-220G is also contemplated
to comprise an elongated shape, such as a hollow cylinder, but with
the added limitation that multiple internal casings should fit
within the lumen of the outer casing 210. In addition, since one of
the fluid pathways extends through the openings 224 in the walls of
the internal casings 220A-220G, (the feed fluid in the embodiment
shown in FIG. 2), the shapes of the internal casings 220A-220G
should allow for fluid flow around the perimeters of the internal
casings 220A-220G. The internal casings 220A-220G are again
preferably fabricated from metal, plastic, or composite, that is
insoluble in the various fluids, but here the walls do not need to
be especially strong since the openings 224 may substantially
equalize the pressure differential across the walls. At the very
least, the openings 224 are preferably dimensioned to limit the
pressure inside the internal casings 220A-220G to no more than a
20% drop relative to the pressure outside the internal casings
220A-220G. In FIG. 2 the openings 224 are positioned towards one
end of each of the inner casings 220A-220G. Preferred shapes for
the openings 224 are slots oriented along the long axis of the
internal casings 220A-220G, although circular holes and other
shapes are also contemplated.
[0029] Contemplated filters may comprise any suitable material,
including reverse osmosis membranes. Filters are preferably spiral
wound, as for example, those discussed in WO 98/09718. In other
embodiments, however, any other types of filters can be employed.
Thus, it is expressly contemplated to employ flat membrane,
tubular, spiral, and/or hollow tube type filters. Hollow type
filters can, for example, be deployed in a manner similar to that
described in U.S. Pat. No. 5,470,469 to Eckman (November 1995). The
filters are preferably dimensioned to provide an annular space
between the filters and the inside wall(s) of the inner casings
220A-220G. The term "annular" in "annular space" should be
interpreted loosely, and is intended to include round spaces, oval
spaces, rectangular spaces, and so forth. The average thickness of
the annular spaces (i.e., the average distance between the outer
circumference of the filters and the inside wall(s) of the inner
casings 220A-220G) preferably ranges from about 1 mm to about 10
cm. Multiple filters are preferably serially disposed in each of
the inner casings 220A-220G, and the annular space within any given
inner casing is preferably continuous across (i.e. along) the long
axis of at least several consecutive filters.
[0030] The pump/energy recovery unit 230 forces the feed fluid in
feed fluid line 240 under pressure into the outer casing 210,
through the openings 224 into the lumen of the inner casings
220A-220G, and thence to the high-pressure side of the various
filters. Some of the feed fluid is forced through the filters to
become permeate, and leaves the system via permeate manifold 252
and permeate line 250. Some of the feed fluid effectively flushes
the high-pressure side of the filters as waste fluid. The waste
fluid leaves the system via waste fluid line 260, and possibly a
waste fluid manifold (not shown). In line 260 the waste fluid line
is still pressurized, and some of the energy in the pressurized
waste fluid is recovered in pump/energy recovery unit 230.
[0031] It is contemplated that any pump or pump system that
provides adequate pumping volume and pressure may be employed in
filtration system 200. This includes positive displacement pumps,
impeller pumps, head pressure devices, and many others. On the
other hand, some pumps and pumping systems will be more efficient
than others, and such pumps and systems are particularly
contemplated. An especially efficient pumping system is a two stage
turbine pump, in which feed fluid flows first to a relatively
low-pressure turbine and then on to a relatively high-pressure
turbine. It is also contemplated that the pump portion of the
pump/energy recovery unit 230 may be physically separated from the
energy recovery portion, or that a pump portion may be present
without any energy recovery portion.
[0032] Filtration systems employing one or more outer casings 210
may be deployed in any suitable manner. As such, contemplated
filtration systems may be disposed more or less horizontally on,
above or below the surface of the ground, or in some other
configuration such as a partially buried disposition. In other
contemplated embodiments, for example, filtration systems may be
set into a shallow well, perhaps less than 100 or even less than 50
feet deep. In still other embodiments, filtration systems may be
disposed within or as part of a tower, hillside, or mountain. In
yet another aspect, multiple filtration systems may be coupled
together in any combination of dispositions.
[0033] In FIG. 3, a filtration system 300 includes four outer
casings 310A-310D, each of which contains multiple inner casings
(not shown), a pump/energy recovery unit 330, a feed fluid line 340
with fluid flow depicted by arrow 341, a permeate exit line 350,
and a waste fluid line 360 with fluid flow depicted by arrow 361,
and end plate subassemblies 311, 312, the elements of which are
substantially as described above with respect to FIG. 2. A control
panel 370 is also present to control the operation, and the entire
filtration system 300 includes a base, skid, or rack 380 to
facilitate placement and access.
[0034] In FIG. 4, an end plate subassembly 400 includes an end
plate 498 coupled to a main body (not shown) of an outer casing
(not shown) using bolts 499. End plate subassembly 400 is similar
in function and appearance to endplate subassemblies 212 and 312 of
FIGS. 2 and 3, respectively, except that here there are only four
inner casings (not shown) rather than five inner casings 220A-220G
as in FIG. 2. The specific number of inner casings is generally not
critical to the operation. The end caps 414A-414D of the four inner
casings (not shown) are coupled to the permeate manifold 462
through permeate lines 460. Waste fluid exits the outer casing
though waste fluid lines 450, and waste fluid manifold 452. The
base, skid, or rack 480 used to facilitate placement and access is
also shown to establish context.
[0035] FIG. 5 depicts preferred details of the fluid flows and
structural aspects of elements employed within a preferred inner
casing, depicted here as inner casing 520, which may (for example,
be the inner casing of FIG. 4. Considering the fluid flows first, a
feed fluid enters opening 524 (similar to openings 224 of FIG. 2)
along arrow 540, and travels along arrows 541A and 541B to one end
of a first filter 551. The fluid then flows along arrows 541C
through filter 551, with permeate passing through collector pores
571 into permeate collector line 570, and waste fluid flowing along
arrows 541D to act as a feed fluid for a downstream filter 552.
[0036] The waste fluid flowing along arrow 541D enters the
inter-filter space 555 where it joins fresh feed fluid traveling
along arrows 542A, 542B to form a combined stream 542C. The
combined stream 542C then enters the downstream filter 552 in a
manner similar to feed fluid entering along arrow 541B entering the
upstream filter 551. In downstream filter 552 permeate passes along
arrows 542D through collector pores 571 into permeate collector
line 570, and then travels along arrows 572 to exit the inner
casing at arrow 550. Waste fluid flows along arrows 542E, and at
the end of a series of filters fluidly coupled as described
immediately above, accumulated waste fluid exits the inner casing
520 at arrow 560.
[0037] The waste fluid of each filter experiences a drop in
pressure relative to the feed fluid entering the filter, and has a
correspondingly higher concentration of salts or other compounds
removed by the filter. A typical pressure drop may be from about
200 psi to about 190 psi across a single filter. However, due to
the addition of fresh (i.e. "bypass" or "additional") feed fluid at
the inter-filter spaces 555, the waste fluid exiting at arrow 560
typically has a pressure of about 180 psi. Permeate exiting at
arrow 550 has an even lower pressure, which may typically be about
10 psi.
[0038] Restriction orifices 557 advantageously lower the pressure
of additional feed fluid entering inter-filter space 555 along
arrow 542B. The amount and pressure of the additional feed fluid
along arrow 542B is advantageously controlled to improve downstream
membrane performance, while avoiding excessive backpressure on
upstream membranes. Of the 100% of fluid entering the system it is
preferred that between about 50%-70% of the fluid will enter the
most upstream membrane, with about 50%-30% being used as
supplemental feed to downstream membranes. In more preferred
embodiments, the numbers are contemplated to be closer to about 50%
of the fluid entering the most upstream membrane, and about 40%
being used as supplemental feed to downstream membranes. The
preferred distribution among downstream membranes depends on the
number of membranes, and generally increases as the fluid flows
downstream. Thus, where there are four downstream membranes, the
distribution of supplemental feed relative to the original feed
entering the system may be about 7%, 8%, 11%, and 13%. Where there
are only two downstream membranes, the distribution of supplemental
feed relative to the original feed entering the system may be about
15% and 25%,
[0039] From a structural perspective, FIG. 5 also depicts
additional details that may be present in preferred embodiments
such as those of FIGS. 2 or 3. For example, on each end of the
filters it is advantageous to place an anti-telescoping device such
as ATD ribs 592. The complete ATDs are made from several
components, including the ribs 592, inner couplings 594, and outer
couplings 595, which may simply be short lengths of plastic or
other piping.
[0040] The filters 551, 552 and outer couplings 595 may
advantageously be centered in the casing by a series of tabs or
spacers (not shown) attached to the ATD ribs 592. These tabs are
intended to keep the filters from binding/sticking during insertion
or removal. Seals (not shown) can be included as needed. It should
be appreciated that because the ATD ribs 592 may be connected in
series by inner and outer couplings 594, 595 using watertight seals
597, the internal casings may be viewed as serving mainly to align
the membranes and couplings in series. Consequently, the internal
casings can have slits or other openings along their lengths, or
guide rails can be used as equivalents in place of the casings to
align the membrane/coupling components, provided that the last
inner coupling 594 would be sealed against the end plate of the
outer casing.
[0041] With respect to other structural features, it should be
appreciated that the end plate 514 (which may also be the same as
any of the end plates 414A-414D of FIG. 4) is preferably coupled to
a body of the inner casing 520 using a nut and bolt system 518.
[0042] FIG. 6 depicts an alternative preferred inner casing that is
similar to the case of FIG. 5 except that the waste fluid and
permeate streams exit the inner casing at the opposite ends rather
than at the same end. The numerals correspond with those of FIG. 5
except that they are increased in value by 100. Thus, a feed fluid
enters opening 624 (similar to openings 224 of FIG. 2 and opening
524 of FIG. 5) along arrow 640, and travels along arrows 641A and
641B to one end of a first filter 651. The fluid then flows along
arrows 641C through filter 651, with permeate passing through
collector pores 671 into permeate collector line 670 and thence
along arrows 672, with waste fluid flowing along arrows 641D to act
as a feed fluid for a downstream filter 652. The waste fluid
flowing along arrow 641D enters the inter-filter space 655 where it
joins fresh feed fluid traveling along arrows 642A and 642B to form
a combined stream 642C. The combined stream 642C then enters the
downstream filter 652 in a manner similar to feed fluid entering
along arrow 641B entering the upstream filter 651. In downstream
filter 652 permeate passes along arrows 642D through collector
pores 671 into permeate collector line 670, and waste fluid flows
along arrows 642E. At the end of a series of filters fluidly
coupled as described immediately above, accumulated permeate exits
the inner casing 620 at arrow 650. Accumulated waste fluid exits
the inner casing 620 at arrow 660. From a structural perspective,
ATDs include ribs 692, inner couplings 694, and outer couplings
695, which may simply be short lengths of plastic or other piping.
Restriction orifices 657, watertight seals 697 and a nut and bolt
system 618 are also depicted.
[0043] FIG. 7 is a cross-section of another alternative preferred
inner casing 720, in which waste fluid from an upstream filter 75 1
is supplemented by fresh feed fluid before being fed into a
downstream filter 752, and all three of the feed fluid stream 740,
permeate stream 750 and waste fluid stream 760 enter or exit the
inner casing at the same end.
[0044] In this embodiment the numerals again correspond with those
of FIG. 5, except that here they are increased in value by 200.
Thus, a feed fluid enters opening 724 (similar to openings 224 of
FIG. 2 and opening 524 of FIG. 5) along arrow 740, and travels
along arrow 741A and 741B to one end of a first filter 751. The
fluid then flows along arrows 741C through filter 751, with
permeate passing through collector pores (not shown) into permeate
collector line 770 and thence along arrows 772, with waste fluid
flowing along arrows 741D to act as a feed fluid for a downstream
filter 752. The waste fluid flowing along arrow 741D enters the
inter-filter space 755 where it joins with fresh feed fluid
traveling along arrows 742A and 742B to form a combined stream
742C. The combined stream 742C then enters the downstream filter
752 in a manner similar to feed fluid entering along arrow 741B
entering the upstream filter 751. In downstream filter 752 permeate
passes along arrows 742D through collector pores (not shown) into
permeate collector line 770, and waste fluid is carried out of the
system in channel 780 as shown by arrows 742E. At the end of a
series of filters fluidly coupled as described immediately above,
accumulated permeate exits the inner casing 720 at arrow 750.
Accumulated waste fluid exits the inner casing 720 at arrow 760.
From a structural perspective, ATDs include ribs 792, inner
couplings 794, and outer couplings 795, which may simply be short
lengths of plastic or other piping. Restriction orifices 757,
watertight seals 797 and a nut and bolt system 718 are also
depicted.
[0045] Of course, the arrangement of fluid flows described with
respect to FIGS. 5-7 are exemplary only, and many other flows are
contemplated. For example, instead of waste fluid flowing in an
annular space between the filters and the inside of the inner
casing, it is entirely possible for the feed fluid to flow in such
space. Alternatively, the permeate could accumulate in the annular
space, and feed fluid could flow through the inner core.
[0046] The presently described apparatus and methods provide
numerous benefits over the prior art. A major advantage is that by
permitting feed water to enter at the membrane couplings between
membranes of the same inner casing, the waste fluid passing from
one series filter to another is diluted, thereby reducing its
osmolarity and the pressure needed to operate the system. Lowered
pressure allows for the use of lower cost pressure vessels, and
lessens the tolerance requirements at the seals.
[0047] There are numerous other advantages as well resulting from
adding fresh feed fluid to the concentrated fluid exiting an
upstream membrane. For example, the additional feed fluid adds to
the volume of fluid passing into the downstream membrane, thus
increasing the flush rate and reducing the fouling potential. A
related benefit is that dilution of the feed fluid entering a
downstream membrane reduces the concentration of compounds that may
precipitate onto the membranes at higher concentrations. Another
benefit is that the additional feed fluid reduces the pressure drop
experienced by a downstream membrane, thereby increasing the
production of permeate. Still another benefit is that the
additional fee fluid reduces the osmotic pressure experienced by
the downstream membrane, thereby increasing the rate of
filtration.
[0048] Not only are these benefits unrecognized in the prior art,
but one of ordinary skill would be dissuaded from adding fresh feed
fluid to the concentrated fluid exiting an upstream membrane by his
knowledge of fluid dynamics. One of ordinary skill would most
likely think that adding fresh feed fluid at the membrane couplings
between membranes would merely create backpressure that would
adversely affect the functioning of the upstream membrane.
[0049] Thus, specific embodiments and applications of a filtration
system using a pressure vessel with multiple filtration channels
have been disclosed. It should be apparent to those skilled in the
art, however, that many more modifications besides those already
described are possible without departing from the inventive
concepts herein. The inventive subject matter, therefore, is not to
be restricted except in the spirit of the present disclosure.
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