U.S. patent application number 12/596279 was filed with the patent office on 2010-08-26 for low scale potential water treatment.
Invention is credited to John W. Arba, Joseph D. Gifford.
Application Number | 20100213066 12/596279 |
Document ID | / |
Family ID | 39875888 |
Filed Date | 2010-08-26 |
United States Patent
Application |
20100213066 |
Kind Code |
A1 |
Gifford; Joseph D. ; et
al. |
August 26, 2010 |
LOW SCALE POTENTIAL WATER TREATMENT
Abstract
An electrochemical treating device having low scale potential is
disclosed. The device has a variety of configurations directed to
the layering of the anionic exchange and cationic exchange. The
treatment device can also comprise unevenly sized ion exchange
resin beads and/or have at least one compartment that provides a
dominating resistance that results in a uniform current
distribution throughout the apparatus.
Inventors: |
Gifford; Joseph D.;
(Marlborough, MA) ; Arba; John W.; (Bradford,
MA) |
Correspondence
Address: |
SIEMENS CORPORATION;INTELLECTUAL PROPERTY DEPARTMENT
170 WOOD AVENUE SOUTH
ISELIN
NJ
08830
US
|
Family ID: |
39875888 |
Appl. No.: |
12/596279 |
Filed: |
April 17, 2008 |
PCT Filed: |
April 17, 2008 |
PCT NO: |
PCT/US08/60605 |
371 Date: |
May 7, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11767438 |
Jun 22, 2007 |
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12596279 |
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60912548 |
Apr 18, 2007 |
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60805505 |
Jun 22, 2006 |
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60805510 |
Jun 22, 2006 |
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60912548 |
Apr 18, 2007 |
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Current U.S.
Class: |
204/521 ;
204/632 |
Current CPC
Class: |
C02F 1/4695 20130101;
C02F 2201/46115 20130101; B01D 61/48 20130101; B01D 61/485
20130101; C02F 1/4602 20130101; B01D 2313/30 20130101; C02F 2303/22
20130101; C02F 2201/46 20130101 |
Class at
Publication: |
204/521 ;
204/632 |
International
Class: |
C02F 1/469 20060101
C02F001/469; B01D 61/48 20060101 B01D061/48 |
Claims
1. An electrodeionization apparatus comprising: a depleting
compartment; and a first concentrating compartment in ionic
communication with the depleting compartment, and defined at least
partially by an anion selective membrane and a cation selective
membrane, the first concentrating compartment containing at least
partially a first zone comprising substantially of cation exchange
media that is substantially separated from the anion selective
membrane by a second zone comprising substantially of anion
exchange media, wherein the first concentrating compartment
comprises electrochemically inert media in an amount that adjusts
the effective current resistance of the first concentrating
compartment to a desired effective resistance.
2. The electrodeionization apparatus of claim 1, wherein the
effective resistance of the first concentrating compartment is
about the same as the effective current resistance of the second
concentrating compartment.
3. The electrodeionization apparatus of claim 1, further comprising
a source of an acidic solution in fluid communication with an inlet
of the first concentrating compartment.
4. The electrodeionization apparatus of claim 1, wherein the cation
exchange media comprises weak acid cation exchange resin.
5. The electrodeionization apparatus of claim 1, wherein the anion
exchange media comprises weak base anion exchange resin.
6. An electrodeionization apparatus comprising: a depleting
compartment; a first concentrating compartment in ionic
communication with the depleting compartment, the first
concentrating compartment comprising media with a first effective
current resistance; and a second concentrating compartment in ionic
communication with the depleting compartment, wherein a portion of
the second concentrating compartment comprising media with a second
effective current resistance greater than the first effective
current resistance.
7. The electrodeionization apparatus of claim 6, wherein the
effective resistance of the at least a portion of the second
concentrating compartment is at least two times greater than the
first effective resistance.
8. The electrodeionization apparatus of claim 6, wherein the second
concentrating compartment comprises inert media.
9. A method of assembling an electrodeionization apparatus
comprising: introducing electroactive media in a concentrating
compartment of the electrodeionization apparatus; and introducing
electroactive media in a depleting compartment of the
electrodeionization apparatus, wherein the electroactive media in
at least one of the concentrating compartment and the depleting
compartment comprises inert media in an amount that adjusts the
effective current resistance of at least a portion of the at least
one of the concentrating compartment and the depleting compartment.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of Invention
[0002] This invention relates to systems and methods of water
treatment having a low potential for scale formation and, in
particular, to reducing the potential for scale formation in
systems that utilize electrically-motivated separation
apparatus.
[0003] 2. Discussion of Related Art
[0004] Electrically-motivated separation apparatus including, but
not limited to, electrodialysis as well as electrodeionization
devices, have been used to treat water. For example, Liang et al.,
in U.S. Pat. No. 6,649,037, disclose an electrodeionization
apparatus and method for purifying a fluid by removing the
ionizable species.
SUMMARY OF THE INVENTION
[0005] One or more aspects of the invention can relate to an
electrodeionization apparatus having an anode compartment and a
cathode compartment. The electrodeionization apparatus can comprise
a first depleting compartment disposed between the anode
compartment and the cathode compartment, a concentrating
compartment in ionic communication with the depleting compartment,
a second depleting compartment in ionic communication with the
concentrating compartment, and a first barrier cell in ionic
communication with and disposed between the first depleting
compartment and at least one of the anode compartment and the
cathode compartment.
[0006] Other aspects of the invention can relate to an
electrodeionization apparatus comprising a depleting compartment
and a first concentrating compartment in ionic communication with
the depleting compartment, and defined at least partially by an
anion selective membrane and a cation selective membrane. The first
concentrating compartment typically contains, at least partially, a
first zone comprising substantially of cation exchange media that
is substantially separated from the anion selective membrane by a
second zone comprising substantially of anion exchange media.
[0007] Other aspects of the invention can relate to an
electrodeionization apparatus comprising a depleting compartment, a
first concentrating compartment in ionic communication with the
depleting compartment, and a second concentrating compartment in
ionic communication with the depleting compartment. The first
concentrating compartment typically comprises media with a first
effective current resistance and the second concentrating
compartment having a portion thereof comprising media with a second
effective current resistance greater than the first effective
current resistance.
[0008] Other aspects of the invention can relate to an
electrodeionization apparatus comprising a depleting compartment,
and a concentrating compartment in ionic communication with the
depleting compartment. The concentrating compartment typically
comprises a mixture of anion exchange resin and cation exchange
resin and amounts of the anion exchange resin and cation exchange
resin in the mixture varies relative to a flow path length of the
concentrating compartment.
[0009] Other aspects of the invention can relate to an
electrodeionization apparatus having at least one compartment with
at least one outlet port defined by a distributor having a
plurality of apertures. The electrodeionization apparatus can
comprise a first layer of particles in the compartment bounded by
ion selective membranes. The particles can comprise media having a
first effective diameter less than the smallest dimension of the
apertures. The electrodeionization apparatus further comprises a
second layer of particles in the compartment downstream of the
first layer. The second layer of particles typically has a second
effective diameter greater than the first effective diameter and
greater than the smallest dimension of the apertures.
[0010] Other aspects of the invention can relate to
electrodeionization system comprising a source of water to be
treated, a treating module comprising a depleting compartment and a
concentrating compartment, the treating module fluidly connected to
the source of water to be treated; an electrolytic module
comprising an acid-generating compartment, and a source of a brine
solution fluidly connected to an inlet of the acid-generating
compartment of the electrolytic module. The electrolytic module can
be fluidly connected upstream of the concentrating compartment.
[0011] Other aspects of the invention can relate to an
electrodeionization apparatus comprising a compartment containing a
mixture of anion exchange resins and cation exchange resins. The
anion exchange resins having an average diameter at least 1.3 times
greater than an average diameter of the cation exchange resins.
[0012] Other aspects of the invention can relate to an
electrodeionization apparatus comprising a compartment containing a
mixture of anion exchange resins and cation exchange resins. The
cation exchange resins having an average diameter at least 1.3
times greater than an average diameter of the anion exchange
resins.
[0013] Other aspects of the invention can relate to a water
treatment system comprising a source of water to be treated, an
electrodeionization device comprising a plurality of concentrating
and depleting compartments and fluidly connected to the source of
water to be treated, a chiller in thermal communication with the
water to be introduced into at least one concentrating compartment
of the electrodeionization device, a sensor disposed to provide a
representation of a temperature of at least one of water to be
introduced into the concentrating compartment and water exiting the
concentrating compartment, and a controller configured to receive
the temperature representation and generate a signal that promotes
cooling the water to be introduced into the concentrating
compartment.
[0014] Other aspects of the invention can relate to
electrodeionization apparatus comprising a depleting compartment at
least partially defined by a cation selective membrane and an anion
selective membrane, and a concentrating compartment at least
partially defined by the anion selective membrane and containing a
first layer of anion exchange media and a second layer of media
disposed downstream of the first layer, the second layer can
comprise anion exchange media and cation exchange media.
[0015] Other aspects of the invention can relate to a method of
treating water in an electrodeionization device having a depleting
compartment and a concentrating compartment. The method typically
comprises any one or more of measuring one of a temperature of a
stream in the concentrating compartment, a temperature of a stream
to be introduced into the concentrating compartment, and a
temperature of a stream exiting from the concentrating compartment;
reducing the temperature of the water to be introduced into the
concentrating compartment to a predetermined temperature;
introducing water to be treated into the depleting compartment; and
removing at least a portion of at least one undesirable species
from the water to be treated in the electrodeionization device.
[0016] Other aspects of the invention can relate to a method of
treating water in an electrodeionization device typically comprises
any one or more of introducing water having anionic and cationic
species into a depleting compartment of the electrodeionization
device, promoting transport of at least a portion of the cationic
species into a first barrier cell disposed between the depleting
compartment and a cathode compartment of the electrodeionization
device, and promoting transport of at least a portion of the
anionic species into a second barrier cell disposed between the
depleting compartment and an anode compartment of the
electrodeionization device.
[0017] Other aspects of the invention can relate to a method of
treating water in an electrodeionization device having a depleting
compartment and a concentrating compartment. The method typically
comprises any one or more of introducing water to be treated into
the depleting compartment of the electrodeionization device,
promoting transport of an undesirable species from the depleting
compartment into the concentrating compartment of the
electrodeionization device. The concentrating compartment can
contain a first layer of anion exchange media and a second layer of
media disposed downstream of the first layer and the second layer
can comprise a mixture of anion exchange media and cation exchange
media.
[0018] Other aspects of the invention can relate to a method of
treating water typically comprises any one or more of introducing
water to be treated into a depleting compartment of an
electrodeionization device, the depleting compartment typically
having at least one layer of ion exchange media; and promoting
transport of at least a portion of anionic species from the water
introduced into the depleting compartment from a first layer of ion
exchange media into a first concentrating compartment to produce
water having a first intermediate quality. The first concentrating
compartment can be defined, at least partially, by an anion
selective membrane and a cation selective membrane. The first
concentrating compartment can contain, at least partially, a first
zone comprising cation exchange media that is substantially
separated from the anion selective membrane by a second zone
comprising, for example, anion exchange media.
[0019] Other aspects of the invention can relate to a method of
treating water in an electrodeionization device. The method
comprises introducing water to be treated comprising undesirable
species into a depleting compartment of the electrodeionization
device, promoting transport of the undesirable species from the
depleting compartment to a concentrating compartment of the
electrodeionization device to produce the treated water;
electrolytically generating an acid solution in the ancillary
module; and introducing at least a portion of the acid solution
into the concentrating compartment.
[0020] Other aspects of the invention can relate to a water
treatment system comprising a source of a water to be treated, and
an electrodeionization device comprising a first depleting
compartment and a second depleting compartment, each of the first
and second depleting compartment fluidly connected to the source of
water to be treated in a parallel flow configuration; and a first
concentrating compartment in ionic communication with the first
depleting compartment and a second concentrating compartment
fluidly connected downstream of the first concentrating
compartment.
[0021] Other aspects of the invention can relate
electrodeionization apparatus comprising a plurality of depleting
compartments configured to have liquid flowing therein along
parallel flow paths, and a plurality of concentrating compartments
in ionic communication with at least one depleting compartment,
wherein at least portion of the concentrating compartments are
arranged serially.
[0022] Further aspects of the invention can relate to a method of
assembling an electrodeionization apparatus comprising introducing
electroactive media in a concentrating compartment of the
electrodeionization apparatus; and introducing electroactive media
in a depleting compartment of the electrodeionization apparatus.
The electroactive media in at least one of the concentrating
compartment and the depleting compartment comprises inert media in
an amount that adjusts the effective current resistance of at least
a portion of the at least one of the concentrating compartment and
the depleting compartment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The accompanying drawings are not intended to be drawn to
scale. In the drawings, each identical or nearly identical
component that is illustrated in various figures is represented by
a like numeral. For purposes of clarity, not every component may be
labeled in every drawing.
[0024] In the drawings:
[0025] FIG. 1 is a schematic illustration of a portion of an
electrodeionization apparatus comprising at least one barrier cell
in accordance with one or more embodiments of the invention;
[0026] FIG. 2 is a schematic illustration of a portion of an
electrodeionization apparatus having layered beds of media in at
least one concentrating compartment thereof in accordance with one
or more embodiments of the invention;
[0027] FIG. 3 is a schematic illustration of a portion of an
electrodeionization apparatus comprising at least one concentrating
compartment having zones of media in accordance with one or more
embodiments of the invention;
[0028] FIG. 4 is a schematic illustration of a portion of a
treatment system in accordance with one or more embodiments of the
invention;
[0029] FIG. 5 is a schematic illustration of a portion of an
electrodeionization apparatus having at least one compartment
modified to reduce the effective resistance or improve the current
distribution in other compartments in accordance with one or more
embodiments of the invention;
[0030] FIG. 6 is a schematic illustration of a portion of an
electrodeionization apparatus having a increased effective flow
velocity in at least one concentrating compartment thereof in
accordance with one or more embodiments of the invention;
[0031] FIGS. 7A and 7B is a schematic illustration of a portion of
an electrodeionization apparatus comprising a compartment
containing resin beads of differing sizes in accordance with one or
more embodiments of the invention; and
[0032] FIG. 8 is a graph showing the relationship between an
Langelier Saturation Index value of a water stream relative to the
temperature of the water stream;
[0033] FIGS. 9A and 9B are schematic illustrations of concentrating
and depleting compartment cell pairs in an electrodeionization
device wherein FIG. 9A shows compartments thereof comprising layers
of media and FIG. 9B shows compartments thereof comprising layers
and zones of media in accordance with one or more embodiments of
the invention; and
[0034] FIG. 10 is a graph showing the performance of
electrodeionization apparatus in accordance with one or more
embodiments of the invention.
DETAILED DESCRIPTION
[0035] The invention, in some aspects or embodiments, provides
electrically-driven separation apparatuses such as but not limited
to filled compartment electrodeionization (CEDI) devices such as
those disclosed in U.S. Pat. Nos. 4,632,745, 6,649,037, 6,824,662,
and 7,083,733, each of which is incorporated herein by reference in
their entirety for all purposes. In particular, the embodiments
implementing one or more aspects of the invention provide can be,
in some cases, characterized as having a lower potential or a lower
likelihood of forming scale during operation thereof. Although the
various aspects of the invention are presented through embodiments
involving electrodeionization devices, any of the various aspects
of the invention may be practiced, separately or in combination, in
other electrically-driven or motivated separation apparatus that
can facilitate treatment of a fluid having at least one undesirable
species. Particularly pertinent aspects of the invention can
involve electrodeionization apparatus utilized to treat or remove
at least one dissolved species from a water stream or a body of
water. Thus, the various aspects of the invention can
advantageously provide electrodeionization apparatuses that are
configured or operated to treat water having high scale
potential.
[0036] An aspect of the invention can be implemented in the
exemplary embodiment presented in FIG. 1 which schematically shows
a portion of an electrodeionization apparatus 100. The
electrodeionization apparatus typically comprises at least one
concentrating compartment 112 and at least one depleting
compartment 114, which constitute a cell pair 115, and disposed in
ionic communication with each other and, preferably, between and
with an anode compartment 120 and a cathode compartment 122. In an
advantageous embodiment of the invention, the electrodeionization
apparatus can further comprise at least one barrier cell 130 that
can trap migrating species from any of the compartments. For
example, electrodeionization apparatus 100 can have barrier or
neutral cells 130 and 132 respectively disposed adjacent anode
compartment 120 and cathode compartment 122. Barrier cells
typically provide a buffer for an electrode compartment and
separate, prevent, or at least inhibit species from forming
localized scale. Electrodeionization apparatus typically generate
hydroxide ions which can raise the pH at localized regions,
especially at the points or surfaces conducive to electrolytic
reactions. Such localized regions, or even at the electrode
compartments, typically have pH conditions much greater than the
bulk of the liquid. The barrier cells can serve to isolate such
high pH regions from scale-forming species transported from the one
or more depleting compartments during treatment of the water,
thereby inhibiting or at least reducing the potential for scale
formation. As exemplarily illustrated in FIG. 1,
electrodeionization apparatus 100 can comprise barrier cell 130
that ionically isolates at least one precipitatable component, such
as Ca.sup.2+, from a component, such as OH.sup.-, that contributes
to scale formation. Typically, one or more of barrier cells 130 or
132, for example, can be defined, at least partially, by an anion
selective membrane 140A that permits migration of anionic species
such as OH.sup.- while inhibiting the further migration of cationic
species into an adjacent compartment. As illustrated, a barrier
cell 130 can be disposed adjacent concentrating compartment 112.
One or more such barrier cells can also further be partially
defined by a cation selective membrane 140C. In this manner, for
example, a component of a precipitatable compound, such as
Ca.sup.2+, can be inhibited from being introduced into a
compartment having localized regions of high pH, such as electrode
compartment 120, that typically result from hydroxide species
generation during operation of apparatus 100.
[0037] Other embodiments of the invention can involve one or more
barrier cells that separate neutral or weakly ionized, or at least
ionizable, species, such as, but not limited to silica, SiO.sub.2.
Silica can precipitate from the bulk liquid if the concentration is
high enough or where a pH change occurs, such as change from a high
pH to a neutral pH. In electrodeionization apparatus, silica is
typically removed while in its ionized state, at high pH. One or
more barrier cells 132, preferably selective for particular kinds
of species, can be disposed to ionically isolate an anode
compartment 122 of electrodeionization apparatus 100, wherein
hydrogen ions are typically generated and consequently can have low
or neutral pH liquid flowing therein. If silica migrates from
depleting compartment 114 into concentrating compartment 112
through anion selective membrane 140A, it can be trapped or
inhibited from further migration by barrier cell 132 containing
high pH liquid flowing therein and inhibited from further migration
into the low or neutral pH compartment with neutral or near neutral
pH, and thereby reduce the likelihood of polymerizing into silica
scale. Cell 132, like cell 130, can be defined, at least partially,
by cation selective membrane 140C and anion selective membrane
140A. Indeed, because any of the barrier cells of the invention can
preferably also trap hydroxyl species, the resultant high pH level
of the fluid therein can advantageously maintain silica in its
ionized state. Barrier cell 132 can thus serve to trap
pH-precipitatable species and prevent or at least inhibit
precipitation of such species. Barrier cell 132 can also contain,
at least partially, anion exchange media and cation exchange media
or a mixture of both. Further, one or more of the barrier cells can
further comprise inert media or other filler material that can
facilitate assembly of the electrodeionization apparatus or provide
a desirable characteristic such as resistance or flow distribution
during, for example, operation of the apparatus. Likewise, one or
more of the concentrating compartments, the depleting compartments,
and the electrode compartments can contain, at least partially, a
mixture of anion and cation exchange media. Indeed, a mixture of
anion and cation exchange media in the concentrating compartments
and electrode compartments can further reduce scaling potential by
facilitating transport of precipitatable species away from the
selective membranes which avoids accumulation of an ionic species
that may occur in compartments or regions of compartments with a
single type of active exchange media.
[0038] In some embodiments of the invention, the anode compartment
can contain, at least partially, media that is substantially
comprised of oxidation resistant substrate. Thus, for example,
durable, highly cross linked ion exchange resin, such as
commercially available cation resins, can be used in the anode
compartment in which an oxidizing environment may be present.
Further, cation exchange resin when utilized in the anode
compartment can prevent or inhibit transport of chloride ions to
the anode surface where such species may be converted to oxidizing
chlorine.
[0039] The apparatus of the invention can treat water having
hardness of greater than 1 mg/L as CaCO.sub.3 or silica content of
greater than 1 mg/L, or both. Thus, the apparatus and techniques of
the invention are not confined to conventional operating limits
and, when used in a treatment system, can obviate at least one unit
operation intended to soften the water to be treated or remove
silica. This advantageously can reduce capital and operating costs
while improving the treatment system's reliability and availability
as well as capacity. For example, the treatment systems of the
invention, comprising one or more electrodeionization devices
described herein, can treat water without a two-pass reverse
osmosis (RO) subsystem, while providing water having the same or
comparable quality as a system that utilizes a two-pass RO device
to remove or reduce the concentration of hardness causing
components and silica before an electrodeionization device.
[0040] Further aspects of the invention can involve
electrodeionization apparatus comprising at least one depleting
compartment and/or at least one concentrating compartment having
layered media contained therein. For example, one or more depleting
compartments 112 of electrodeionization device 100 can comprise a
first layer of particles 112A, at least a portion thereof
comprising active media that facilitates transport or migration of
a first target, typically ionized, species. Depleting compartment
112 can further comprise a second layer 112B comprising, at least
partially, active media that facilitates transport of the first
target species and a second target species, or both. First layer
112A can comprise particles having a first effective diameter and
second layer 112B can have particles with a second effective
diameter. Further embodiments can involve a third layer 112C in
depleting compartment 112. Third layer 112C can have active or
inert media, or a mixture of both, with a third effective diameter.
The effective diameter can be a smallest dimension of a particle.
Alternatively, the effective diameter can be an average diameter of
the collective particles and is, for example, a calculated diameter
of an analogous sphere of comparable volume and surface area. For
example, the effective diameter of particles in a layer can be a
function of the ratio of the volume of a particle to the surface
area of a particle or an average of the smallest dimension of the
particles. In a preferred configuration, the particles in a
downstream layer have an effective diameter that is less than the
effective diameter of particles in an upstream layer. For example,
particles comprising layer 112C can be spherical particles with a
larger effective diameter than the effective diameter of particles
comprising layer 112B. Optionally, the effective diameter of the
particles comprising layer 112A can be greater than the effective
diameter of particles in layer 112B or 112C. One or more of the
concentrating compartments may be similarly layered.
[0041] In a preferred embodiment, the particles in an upstream
layer have an effective diameter that is at least the dimension of
interstices between the particles of a downstream layer. In further
embodiments, the upstream particles have an effective diameter or a
smallest dimension that is less than the smallest dimension of the
apertures of distributor 160 that defines an outlet port of
depleting compartment 112. Distributor 160 can be a screen that
serves to retain the media within the compartments. Thus, each of
the depleting compartments and concentrating compartments
containing media can have at least one distributor that permits
fluid flow therethrough while retaining the media and a layer of
media that are sized to retain particles in an upstream layer.
[0042] The apertures or openings of distributors are typically
designed to retain resins having a diameter of about 500 .mu.m to
about 700 .mu.m. In some of the configurations of the invention,
anion and cation exchange resins may be utilized having smaller
dimensions than the aperture dimensions which improves mass
transfer kinetics throughout the apparatus. Further, smaller ion
exchange resins can improve packing within the compartment and
reduces the likelihood of channeling or flow bypass along the
compartment walls. Close packed spheres or nearly spherical
particles have interstitial spaces of about 0.414 times the radius
of the spheres. Thus, the effective diameter of the upstream resin
is preferably not less than such dimension. For example, the fine
mesh resin beads having an effective diameter of about 62 .mu.m to
about 83 .mu.m may be utilized in an upstream layer with a layer of
resin beads having a diameter of about 300 .mu.m to about 400
.mu.m. Any of the layers may comprise any suitable fraction of the
compartment. The depth of the upstream layer may be dependent on
providing a desired performance. Further, advantageous
configurations contemplate the use of cation resin beads having a
smaller effective diameter or dimension with larger anion resin
beads to facilitate cation migration activity. Notable arrangements
are not limited to the use of active resin as the lower, downstream
media and the invention may be implemented utilizing inert media in
one or more of the downstream layers.
[0043] The interfaces between the layers may constitute a gradient
of small and large resin beads. Thus, the boundary between layers
need not be particularly delineated. Other configurations,
moreover, can involve a mixture of the fine mesh resin beads mixed
with larger resins.
[0044] Another aspect of the invention can involve
electrodeionization apparatus comprising at least one concentrating
compartment having layered media contained therein. As illustrated
in FIG. 2, the electrodeionization device 200 can have at least one
concentrating compartment 214 and at least one depleting
compartment 212. At least one of the concentrating compartments 214
can have a first layer 215 and a second layer 216. In
electrodeionization devices that treat relatively pure water, such
as RO permeate, the current efficiency is typically below 100%
because, it is believed, of water splitting and transport of the
generated hydrogen and hydroxyl ions. This can create local pH
fluctuations and can promote scale formation especially where the
hydroxyl species reacts with bicarbonate species or carbon dioxide
to form carbonate ions which forms calcium carbonate scale.
[0045] For example, in a typical electrodeionization apparatus,
bicarbonate ions transfer through the anion exchange membrane near
the inlet of the compartment but may be inhibited from migrating
further from the membrane. When water splitting occurs, the
hydroxyl species transported through the anion exchange membrane
can react with the bicarbonate species to form carbonate which then
reacts with calcium to form calcium carbonate scale.
[0046] By utilizing layers in one or more of the concentrating
compartments, target species can be directed to locations where
they are less likely to form scale. As shown in FIG. 2, a layer 215
of anion exchange media can be disposed around the inlet of
concentrating compartment 214 to promote migration of bicarbonate
species. After at least a portion of the bicarbonate species is
transported through the anion exchange membrane 240A, it is
promoted through the anion resin of layer 215 and moves towards the
cation selective membrane 240C. Even though there are hardness ions
passing through cation selective membrane 240C, the pH of the fluid
is relatively low around this membrane, which reduces the
likelihood of forming carbonate.
[0047] The depleting compartments 212 and the other one or more
layers 216 of the concentrating compartments 214 may contain mixed
anion exchange and cation exchange media.
[0048] To further reduce or inhibit scale formation, layers of
media can be disposed along a flow path length of the concentrating
compartment. As shown in FIG. 3, one or more concentrating cells
may comprise, at least partially, a first zone 314A of ion exchange
media and a second zone 314B of ion exchange media. The first and
second zones may be linearly distributed along the length of the
compartment as represented by boundary 350 or may be a gradient of
increasing or decreasing amounts of types of ion exchange media in
zones 315C and 315D and delineated by gradient boundary 351. The
first or second zones may comprise, consist essentially of, or
consist of anion exchange media, or cation exchange media. For
example, zone 314A can comprise cation exchange media that
substantially segregates zone 314B, which comprises anion exchange
media, from cation selective membrane 340C. Substantially
separating refers to, in some cases, being disposed between a zone
and a membrane such that a separating zone comprises or consists
essentially of a type of media, which can be anionic, cationic, or
inert.
[0049] In some cases, the first zone or second zone can be a
mixture of differing amounts of types of ion exchange media. For
example, zone 315C can comprise, consists essentially of, or
consist of cation exchange media adjacent cation selective membrane
340C and zone 315D can comprise, consist essentially of, or consist
of anion exchange media, wherein the amount of anion exchange
media, relative to the amount of cation exchange media increases,
or decreases, along the flow path length or lengthwise dimension,
such that a boundary between zones which is defined by gradient
boundary 351. In another embodiment, a third zone (not shown) of
media can be disposed between the first and second zones. The third
zone can comprise, consist essentially of, or consist of inert
media, cation exchange media, anion exchange media, mixed media, or
mixtures thereof. Further, one or more screens can be used between
zones or within the zones to facilitate filling the compartments of
the apparatus, which, during operation can also improve flow
distribution and further inhibit scale formation. Assembly and
filling can also be facilitated by utilizing a binder to secure the
media of each zone. For example, media of the first zone can be
mixed with a water soluble binder, such as starch. The mixture can
then be placed into the compartment. A second mixture of media of
the second zone can be similarly prepared and disposed in the
compartment.
[0050] Zone 314B facilitates transport of anionic species, such as
bicarbonate ions, away from anion selective membrane 340A and zone
315C facilitates transport of cationic species, such as calcium
ions, away from anion selective membrane 340C. Such segregating
zones thus reduce the likelihood of scale formation around membrane
surfaces.
[0051] As illustrated in FIG. 3, depleting compartment 312 can
comprise a first layer 312A of media, a second layer 312B of media,
and, optionally, a third layer 312C of media. The first layer can
comprise a mixture of anion exchange media, cation exchange media,
or inert media. The second layer can comprise, consist essentially
of, or consist of anion exchange media or inert media or a mixture
thereof. The third layer can comprise, consist essentially of, or
consist of anion exchange media, cation exchange media, inert
media, or a mixture thereof.
[0052] Further aspects of the invention involve systems and
techniques that modify the pH of a stream flowing in at least one
concentrating compartment of an electrodeionization apparatus. The
pH of the stream can be reduced to reduce the likelihood of scale
formation by generating and adding an acidic solution to one or
more of the concentrate and electrode compartments. The acidic
solution can be generated or prepared by utilizing an electrolytic
module. Further scale inhibition or tolerance can be effected by
degasification of the concentrate liquid. Any acid generating
module may be utilized such as those commercially available from
Dionex Corporation, Sunnyvale, Calif.
[0053] Typically, an electrodeionization device can treat liquids
having low hardness. This limitation limits the incoming feed water
into electrodeionization devices to a hardness level of 1 ppm or
less, as calcium carbonate. To treat water having a hardness value
greater than 1 ppm, pretreatment processes such as two-pass RO or a
softener RO, is typically used. The additional pretreatment unit
operations increase system complexity and cost as well as waste.
The electrodeionization devices of the present invention, however,
can reliably treat water having higher hardness levels thereby
eliminating or reducing the dependence on such pretreatment
operations.
[0054] Addition of an acidic solution into the concentrating
compartment of electrodialysis devices to reduce calcium
precipitation is known; however adding acidic solutions to
electrodeionization devices is not practiced because of low flow
velocity of the streams in the concentrate compartments, especially
in thick cell compartment. Further, a high quantity of acid is
typically required. As illustrated in FIG. 4, the treatment system
400 of the invention can comprise an electrochemical device 435 to
produce an acid solution to be introduced into a compartment,
typically concentrating compartment 414 of an electrodeionization
device 445 disposed to receive water to be treated from source 411.
A portion of treated product water from electrodeionization device
445 can be used to facilitate generating the acid solution in an
acid-generating compartment 472 of electrochemical device 435. At
least a portion of the treated water can be delivered to a point of
use 413. A source 462 of a brine solution comprising a salt from,
for example, softener brine tank may be introduced into
electrolytic module 435 to promote acid solution production.
Electrochemical device 435 may be portion of electrodeionization
device 445. The brine solution typically comprises sodium
chloride.
[0055] In some cases, the acidic solution can be introduced into
one or more of the depleting and concentrating compartments 412 and
414, as well as the electrode compartments of electrodeionization
device 445. Preferably, acidic solution is added in an amount to
provide a pH of the exiting stream solution leaving the compartment
of between about 2.5 to 4.3 units. Further embodiments may involve
neutralizing one or more streams from electrodeionization device
445. For example a basic solution produced from compartment 472 of
electrolytic module 435 may be combined to neutralize an outlet
stream, typically having a low pH, from concentrating compartment
414 before being discharged to drain 463 or the environment.
[0056] Degasification of the concentrate stream to remove carbon
dioxide may further reduce or eliminate the precipitation potential
in the concentrating compartment. Degasification can be
accomplished by the addition of a degasification device or by
membrane processes or other methods. Degasification may be relevant
when utilizing an acidic solution in the concentrating compartment
because of the potential formation of carbon dioxide gas, which can
diffuse back through the membrane and reduce product quality.
Further, the flow of the stream within the compartment may be
countercurrent to facilitate gas removal.
[0057] Recirculation of the concentrate compartment using a pump
and, optionally, a tank can further enhance the scale inhibition by
the acidification and degasification techniques described
herein.
[0058] The components, arrangements, and techniques of the
invention also provide improved current distribution in an
electrodeionization device. As schematically illustrated in FIG. 5,
the current resistance through the electrodeionization apparatus
500 between electrodes 520 and 522 can be characterized by a series
of compartment resistances 573, 575, and 577, which are
representative of the depleting and concentrating compartments 512
and 514, and by membrane resistances 584, 586, and 588, which are
representative of anion selective membranes 540A and cation
selective membranes 540B. Improved current distribution throughout
electrodeionization apparatus 500 can be effected by utilizing at
least one concentrating compartment 516 with at least a portion
thereof having an effective current resistance 580 that is greater
than the effective current resistance of the other compartments,
such as the concentrating compartments.
[0059] The effective current resistance of a compartment or portion
thereof may be modified by mixing inert resin beads, or low or
non-conducting materials, with in the concentrating compartment.
Selectively increasing the effective current resistance effects a
more uniform current distribution through the other compartments.
The reduced variations in current throughout the depleting
compartments, for example, improve overall performance.
[0060] In an electrodeionization device, the electrical resistance
may depend on the types of media in the device as well as the
active chemical form of those media, i.e., what ions are moving
through the media. In layered bed compartments, the resistance
typically varies between the layers because of the different types
of resin and the form of the resins. Typically, the strongly
charged species or ions are motivated and the water splitting
phenomena and weakly ion promotion follow. Thus, media resins near
the inlet of the compartment would exchange with the target species
in the feed water while media near the outlet would be mostly in
the hydrogen and hydroxide forms. Typically, most of the strongly
charged ions must be removed, which may not be effected if the feed
concentration and/or flow are high enough or if the current is low
enough.
[0061] If the resistance in the compartments can vary between
layers thereof or along the length of the bed, then the current
density can also vary accordingly. However, the resistance through
the entire module may not just be a function of the resistances of
the depleting compartments. The depleting compartments are
electrically in series with the membranes and the concentrating
compartments and electrode compartments, which may or may not also
vary in resistance along their length. If the resistances of the
depleting compartments are a small portion of the total resistance
through the module, then even if such resistances vary
significantly, the overall resistance will be dominated by other
factors and current distribution will be more uniform. However, if
the depleting compartment resistances are high relative to the
other resistances, the current distribution will be affected by
resistance differences within the depleting compartments.
[0062] Typical electrodeionization devices incorporate screen
filled concentrating and/or electrode compartments. In these
configurations, the resistance of the water in these compartments
is much greater than the resistance of the resin in the depleting
compartments in most cases, and therefore, current distribution is
not generally controlled by the resistances of the depleting
compartments. Filling the concentrating and electrode compartments
with resin as well as using lower resistance ion exchange membranes
reduces the overall module resistance significantly. However, in
certain circumstances this can lead to uneven current distribution
as the module resistances become dominated by the resistances of
the depleting compartments.
[0063] In some embodiments of the invention, therefore, screen
filled concentrating and electrode compartments may minimize uneven
current distribution. However, in most post RO applications, the
water has very low conductivity leading to high module resistance.
This high resistance further creates limitations if there are
electrical potential constraints. The invention, in contrast,
provides comparable performance without using brine injection into
the stream flowing into the concentrating compartment thereby
reducing operating cost and process complexity.
[0064] As noted, mixing inert resin in one or more concentrating
and/or electrode compartment as fillers can increase the resistance
in those compartments which improves current distribution through
the module. As shown in FIG. 5, one or more concentrating
compartment 516 can comprise inert resin to provide higher
effective resistance 580 therethrough which dominates the
collective resistances of other compartments and membranes. Because
the dominant resistance controls the overall resistivity, the
effective current distribution through the other compartments
becomes more uniform. The amount of inert resin can be varied to
increase the effective resistance and modify the current
distribution through the apparatus. Inert resin can also be used in
layers in one or more concentrating and electrode compartments to
locally increase the resistance in certain portions where the
dilute resistance is determined to be low. Thus, as shown in FIG.
5, current distribution through zone 512 can be matched or made
comparable to the current through zone 511 of the apparatus by
utilizing a higher resistivity layer in compartment 515 such that
the effective resistance 573 of the layer of compartment 515 is
increased. The amount of resistance can be effected by empirically
measuring the effective resistance relative to the amount of inert
resin utilized.
[0065] Other materials with low conductivity, such as polymeric
screens or fiber material can be used to increase the resistance
along with the above-noted inert resin beads.
[0066] Electrodeionization apparatus may be limited to a maximum
recovery of 90-95% to prevent scale formation of limited solubility
species in the feed water such as hardness and silica. If the feed
water contains very low amounts of these species the device should
be able to operate at higher recovery rates. Some aspects of the
invention involve electrodeionization apparatus having multiple
passes through concentrating compartments thereof thereby providing
recovery rates. The multiple pass configurations facilitate
maintaining a predetermined velocity without a recirculation pump
and loop. However, this invention is may be preferably utilized in
applications with recirculating loops wherein the feed water ion
concentration is low and a very high recovery is desired to avoid
wasting or discharging high purity water and/or increasing
operating time of the makeup system. In some embodiments of the
electrodeionization apparatus of the invention, the fluid flow rate
is sufficient to reduce the likelihood of creating dead volumes,
channeling and localized overheating within the compartments. For
example, the desired fluid flow rate in a compartment can be at
least about 2 gallons per minute per square foot in a concentrating
compartment. Other fluid flow rates may be dictated by other
factors including, but not limited to, the concentration of a
component of the precipitating compound, the temperature of the
fluid, and the pH of the fluid. Lower velocities may induce
channeling.
[0067] FIG. 6 schematically illustrates a portion of an
electrodeionization apparatus 600 comprising depleting compartments
614 and concentrating compartments 612 between electrode
compartments 630 and 632. The arrangement and configuration provide
one depleting compartment pass with an associated plurality of
concentrating compartment passes in the treatment apparatus and
systems of the invention. Such configurations allow for an
increased fluid flow velocity in the concentrating compartments,
preferably up to five times greater than the flow rate of a single
pass device. As shown in FIG. 6, water from source 615 is
sequentially introduced into concentrating compartments 612 and
directed into downstream concentrating compartments 612B and then
to compartments 612C and to drain or to downstream unit operation
625.
[0068] Water to be treated is introduced into depleting
compartments 614 and directed to point of use without following or
tracking the flow of water through compartments 612, 612A, and
612B. The invention, however, is not limited to the number of
associated concentrating compartment volumes relative to the number
of depleting compartment volumes and any ratio of concentrating
compartments to depleting compartments can be used to provide a
desired high fluid flow rate through the compartments.
[0069] Different size cation and anion exchange resin beads in the
mixed layers or compartment may be utilized to further reduce the
transport rate of the larger bead counter-ions and facilitate
transport of the smaller bead counter-ions.
[0070] Ion transport typically occurs through the ion exchange
resins. Successful transport may thus depend on a complete path of
like material between the beads and the membranes. A cationic
species typically diffuses onto a cation resin bead and will tend
to move toward the cathode following a path of cationic media until
it reaches the cation selective membrane and passes through into
the concentrating compartment. If the path is broken, the cationic
species will have to diffuse out of the last bead and into the bulk
solution, therefore reducing the chance it will be picked up later
in the bed and increasing the chance it will end up in the product
water. The path can be broken by poor packing such that the beads
don't have good contact or it can be broken by a bead of the
opposite charge.
[0071] Using a relatively thin cell or tightly packing the resins
can increase the probability of maintaining the desired pathway.
Utilizing cation and anion exchange resin of a similar and
relatively uniform size will also increase the likelihood of
maintaining the desired pathway. Using cation and anion exchange
resin of different sizes, however, can block transfer.
[0072] In some cases, it may be advantageous to inhibit transport
of either cations or anions. By selectively reducing the size of
one type of resin in a mixed bed, the transfer of the smaller bead
counter-ions will be enhanced due to more complete paths whereas
the transfer of the larger bead counter-ions will be retarded due
to fewer complete paths because as the size of the smaller beads
approaches some fraction of the size of the larger beads, smaller
resin beads tend to pack around the larger beads, which isolates
and breaks the path from one large bead to the next. This
phenomenon may also depend on the relative ratio of the large and
small ion exchange resin beads. For example a mix of 50% small
beads by volume would affect the transport of ions much differently
than a mix of 25% or 75% small beads by volume.
[0073] Once the size and mix ratios of the media are appropriately
selected to slow transport of a target or selected type of ion and
increase transport of different type, hydrogen or hydroxyl ions
must be transferred to maintain electro neutrality. For example, if
a bed consisting essentially of cation resin is used in a depleting
compartment as shown in FIG. 7A, cationic species would migrate
through the cation exchange resin beads 731 and the cation membrane
740C into an adjacent concentrating compartment. Water would split
at site 766 of the anion selective membrane 740A which creates a
hydrogen ion that replaces the migrating cation in the depleting
compartment and a hydroxyl ion which migrates into an adjacent
concentrating compartment which neutralizes the cationic species
migrating from another depleting compartment (not shown). This
phenomenon relies on the ability to split water on the surface of
the anion membrane where there is relatively little contact area
between the anion membrane and cation beads. Utilizing smaller
cationic exchange resin beads 733 with larger anionic exchange
resin beads 734, as illustrated in FIG. 7B, reduces the transport
rate of anionic species. Further, the use of differing resin bead
sizes provides additional water splitting sites 766 at the tangents
between the cation exchange resin 733 and anion exchange resins
beads 734, which in turn improves performance by reducing the
resistance across the module.
[0074] For example, an electrodeionization apparatus of the
invention can comprise a compartment containing a mixture of anion
exchange resins and cation exchange resins, the cation exchange
resins having an average diameter at least 1.3 times greater than
an average diameter of the anion exchange resins. Alternatively or
in addition, the electrodeionization apparatus can comprise a
compartment containing a mixture of anion exchange resins and
cation exchange resins, the cation exchange resins having an
average diameter at least 1.3 times greater than an average
diameter of the anion exchange resins.
[0075] Further aspects of the invention can relate to a method of
treating water in an electrodeionization device. The method, in
some embodiment thereof, can comprise introducing water having
anionic and cationic species into a depleting compartment of the
electrodeionization device, promoting transport of at least a
portion of the cationic species into a first barrier cell disposed
between the depleting compartment and a cathode compartment of the
electrodeionization device, and promoting transport of at least a
portion of the anionic species into a second barrier cell disposed
between the depleting compartment and an anode compartment of the
electrodeionization device. The method can also comprise adjusting
effective resistances of one or more compartments or portions of at
least one compartment of the device.
[0076] Further aspects of the invention can relate to a method of
treating water in an electrodeionization device having a depleting
compartment and a concentrating compartment. The method can
comprise introducing water to be treated into the depleting
compartment of the electrodeionization device; and promoting
transport of an undesirable species from the depleting compartment
into the concentrating compartment of the electrodeionization
device, the concentrating compartment containing a first layer of
anion exchange media and a second layer of media disposed
downstream of the first layer, the second layer comprising a
mixture of anion exchange media and cation exchange media, wherein
the first layer has an effective resistance that is about the same
as the second layer.
[0077] Further aspects of the invention can relate to a method of
treating water in an electrodeionization device. The method can
comprise introducing water to be treated comprising undesirable
species into a depleting compartment of the electrodeionization
device; promoting transport of the undesirable species from the
depleting compartment to a concentrating compartment of the
electrodeionization device to produce the treated water;
electrolytically generating an acid solution in the ancillary
module; and introducing at least a portion of the acid solution
into the concentrating compartment. The effective resistance of the
concentrating and/or depleting compartment is, preferably,
substantially uniform along its fluid flow path length.
Electrolytically generating the acid solution can comprise
introducing a halide salt solution into the ancillary module. The
method can further comprise generating a basic solution in the
ancillary module while generating the acid solution. The method can
further comprise neutralizing an outlet stream from the
concentrating compartment with the basic solution. The method can
further comprise mixing a portion of the treated water with the
brine solution and introducing the mixture into the ancillary
module. The method can further comprise degasifying at least a
portion of the liquid in the concentrating compartment. Introducing
the acid solution into the concentrating compartment can comprise
introducing an acidic solution having a pH of less than 4.3 into
the concentrating compartment.
[0078] Further aspects of the invention can relate to
electrodeionization apparatus comprising a plurality of depleting
compartments configured to have liquid flowing therein along
parallel flow paths; and a plurality of concentrating compartments
in ionic communication with at least one depleting compartment,
wherein at least portion of the concentrating compartments are
arranged serially, and, preferably, the concentrating compartments
have substantially the same effective current resistance
therethrough. The plurality of concentrating compartments can
define a single flow path through the electrodeionization
apparatus.
[0079] Further aspects of the invention can relate to an
electrodeionization apparatus comprising a depleting compartment;
and a first concentrating compartment in ionic communication with
the depleting compartment, and defined at least partially by an
anion selective membrane and a cation selective membrane, the first
concentrating compartment containing at least partially a first
zone comprising substantially of cation exchange media that is
substantially separated from the anion selective membrane by a
second zone comprising substantially of anion exchange media,
wherein the first concentrating compartment comprises
electrochemically inert media in an amount that adjusts the
effective current resistance of the first concentrating compartment
to a desired effective resistance. The effective resistance of the
first concentrating compartment, in some cases, is about the same
as the effective current resistance of the second concentrating
compartment.
EXAMPLES
[0080] The function and advantages of these and other embodiments
of the invention can be further understood from the examples below,
which illustrate the benefits and/or advantages of the one or more
systems and techniques of the invention but do not exemplify the
full scope of the invention.
Example 1
[0081] This example describes the effect of temperature on the
Langelier Saturation Index (LSI).
[0082] Calculating an LSI value is known in the art for a measure
of the potential for scale formation. LSI is a function of pH,
total dissolved solids (TDS), temperature, total hardness (TH), and
alkalinity. Using the following estimates for these parameters for
a concentrating compartment stream of an electrodeionization
apparatus, the temperature of the stream relative to the LSI value
can be defined and a representative relationship is shown in FIG.
8, based on a stream with a pH of 9.5 units, TDS of 30 ppm, TH of
15 ppm, as CaCO.sub.3, and an alkalinity of about 25 ppm, as
CaCO.sub.3.
[0083] When the LSI value of a stream, is positive scaling is
likely to occur. To inhibit scaling, the LSI value of the stream is
reduced to, preferably a negative quantity. FIG. 8 shows that as
the temperature is reduced the LSI value is reduced to below zero
around 12.5.degree. C. Thus, for the conditions described above,
cooling the stream into the concentrating compartment of an
electrodeionization device to below 12.5.degree. C. should reduce
the likelihood or prevent the formation of scale.
[0084] Cooling can be effected by thermally coupling a heat
exchanger, or chiller, upstream of the electrodeionization
apparatus. Other components and subsystems that facilitate removing
thermal energy from the one or more streams into the apparatus may
be utilized. For example, one or more sensors and controllers may
be utilized to define a temperature control loop and facilitate
maintaining the temperature of the stream to a target temperature
or even to reduce the effective LSI value to a desired or target
amount.
[0085] The target temperature can be determined empirically, by
defining a temperature of the stream to be introduced into a
concentrating compartment of the electrodeionization device, or be
calculated based at least partially on the calculated LSI value.
For example, an empirically established target temperature can be a
temperature at which no scaling is historically observed with or
without an additional margin to ensure that the scaling is further
inhibited. An LSI-based target temperature may be defined based on
a derived LSI-temperature relationship then calculating the target
temperature associated with a set reduction in LSI value.
Example 2
[0086] In this example, the effect of resin bead size on the
performance of an electrodeionization apparatus in accordance with
one or more aspects of the invention was studied.
[0087] In one test, an electrodeionization module was constructed
using an equal mixture of anion resin with an average bead diameter
of 575 .mu.m and a cation resin with an average bead diameter of
350 .mu.m in the depleting compartments. Both of these resins were
uniform particle size according to industry standards.
[0088] The module was fed a water that was previously treated by
reverse osmosis and contained about 0.5 ppm Mg and 1.5 ppm Ca (both
as CaCO.sub.3) with a pH of about 6.1. The module was operated at
almost 100% current efficiency and product quality was about 1-2
M.OMEGA.-cm without almost zero silica removal.
[0089] The product water hardness level was below detection as
measured by a Hach spectrophotometer (<10 ppb) and the pH was
reduced to about 5.7. This indicates that the module was
preferentially removing cations over anions.
Example 3
[0090] In this example, the effect on the performance of an
electrodeionization apparatus with several layers of different bead
sizes in compartments thereof in accordance with one or more
aspects of the invention, was studied.
[0091] A module was constructed with three layers of ion exchange
resin in the depleting compartments. The first and last layers
consisted of an even mix of cation and anion resin of uniform
particle diameters approximately 600 .mu.m. The middle layer
consisted of an even mix of cation exchange and anion exchange
resins with particle diameters of 150-300 .mu.m. The module spacer
had slots in the flow distributor, which are used to hold resins in
place, with a width of 254 .mu.m. The module was operated for
several months with no change in pressure drop, which indicates
that the resins in the middle layer, of which some were smaller
than the spacer apertures, did not pass through the bottom layer of
resin and exit the module.
[0092] In addition, the addition of the middle layer of smaller
resins improved the performance of a comparable electrodeionization
device, control module. The module was operated in parallel with
another electrodeionization module having compartments containing
an even mix of cation exchange and anion exchange resins with
particle diameters of about 600 .mu.m. With a feed water previously
treated by reverse osmosis having a conductivity of about 30
.mu.S/cm and containing 3.75 ppm of CO.sub.2, the module comprising
a layer of smaller ion exchange resins produced water having a
resistivity of 16.4 M.OMEGA.-cm whereas the other typical module,
without a layer of smaller ion exchange resins, produced water
having a resistivity of 13.5 M.OMEGA.-cm. Further, the module
comprising the layer of smaller exchange resins showed a silica
removal of 96.6% versus 93.2% for the control module.
Example 4
[0093] In this example, the effect on the performance of an
electrodeionization apparatus with several or multiple passes
through concentrating compartments thereof was studied.
[0094] An electrodeionization module was assembled with four
depleting compartments, three concentrating compartments, and two
electrode compartments. All of the depleting compartments were fed
a water to be treated in to parallel to each other. The
concentrating compartment and electrode compartments were fed in
series so that the stream introduced into the concentrating
compartments entered the cathode compartment first, then flowed
sequentially through the concentrating compartments and finally
through the anode compartment. This contrasts with the conventional
configuration in which a water stream is typically fed into the
electrode compartments in parallel with a water stream into the
concentrating compartments. The module thus had five effective
concentrating compartment passes.
[0095] Data for this module (labeled as "Series Concentrate") along
with performance data for a standard module operating with parallel
flows (labeled as "Parallel Concentrate") is listed in Table 1
below.
TABLE-US-00001 TABLE 1 Comparison of module with single pass
concentrate versus module with five passes. Module Parallel
Concentrate Series Concentrate Feed, .mu.S/cm 30.3 30.3 Electrical
resistance, Ohms 4.3 4.2 Product quality, M.OMEGA.-cm 3.1 3.6
Product flow, gpm 2.25 2.25 Concentrate flow, gph 7.2 1.2 Recovery,
% 94.9 99.1 Concentrate velocity, gpm/ft.sup.2 2.0 1.7
[0096] The data show that by serially arranging the stream to flow
through the concentrating and electrode compartments, a fluid flow
velocity similar to that when operating in parallel at a much lower
reject flow rate. Therefore very high recoveries can be obtained
while maintaining a minimum velocity in the concentrate.
Example 5
[0097] In this example, the effect on the performance of an
electrodeionization apparatus with horizontal and vertical layers
in the concentrating compartment was studied.
[0098] Two modules were assembled with different layering
configurations as shown in FIGS. 9A and 9B. Each module was
comprised of four of the respectively illustrated repeating cell
pairs. In the figures, "MB" refers to a mixture or resins; "A" and
"C" refer to zones or layers comprising anion exchange resin and
cation exchange resin, respectively; and "AEM" and "CEM" refer to
the anion selective membrane and cation selective membrane. The
modules were operated for two and three weeks respectively with
feed water having a conductivity of about 10 .mu.S/cm and
containing 2 ppm total hardness, as calcium carbonate.
[0099] After this period they were opened and no scale was
observed. In contrast, a non-layered module containing mixed bed
resin in the depleting and concentrating compartments showed scale
on the anion membranes in the concentrate after two weeks of
operation on the same feed water.
Example 6
[0100] In this example, the effect on the performance of an
electrodeionization apparatus with vertical layers in compartments
thereof along with addition of an acidic solution, was studied.
[0101] Three modules were assembled with horizontal layering in the
depleting compartment and vertically oriented zones or layers,
along the flow path length, in the concentrating compartments.
Barrier cells were also disposed adjacent both electrode
compartments. The modules were operated for ninety days with
post-RO feed water containing about 2 ppm of total hardness. An
acidic solution was injected into the concentrating compartments at
rate that provide a pH of the water stream exiting the
concentrating compartments of about 2.5-3.5.
[0102] FIG. 10 shows stable performance over the entire ninety
days. In the figure, "FCE" refers to feed conductivity equivalent,
which is calculated by adding the actual feed conductivity, in
.mu.S/cm, to the feed carbon dioxide, in ppm, times 2.67 and the
feed silica, in ppm times, 1.94; and "Feed TH" refers to feed total
hardness.
[0103] The controller of the system of the invention may be
implemented using one or more computer systems. The computer system
may be, for example, a general-purpose computer such as those based
on an Intel PENTIUM.RTM.-type processor, a Motorola PowerPC.RTM.
processor, a Sun UltraSPARC.RTM. processor, a Hewlett-Packard
PA-RISC.RTM. processor, or any other type of processor or
combinations thereof. Alternatively, the computer system may
include specially-programmed, special-purpose hardware, for
example, an application-specific integrated circuit (ASIC) or
controllers intended for analytical systems.
[0104] The computer system can include one or more processors
typically connected to one or more memory devices, which can
comprise, for example, any one or more of a disk drive memory, a
flash memory device, a RAM memory device, or other device for
storing data. The memory is typically used for storing programs and
data during operation of the treatment system and/or computer
system. Software, including programming code that implements
embodiments of the invention, can be stored on a computer readable
and/or writeable nonvolatile recording medium, and then typically
copied into memory wherein it can then be executed by the
processor. Components of the computer system may be coupled by an
interconnection mechanism, which may include one or more busses
(e.g., between components that are integrated within a same device)
and/or a network (e.g., between components that reside on separate
discrete devices). The interconnection mechanism typically enables
communications (e.g., data, instructions) to be exchanged between
components of the computer system. The computer system can also
include one or more input devices, for example, a keyboard, mouse,
trackball, microphone, touch screen, and one or more output
devices, for example, a printing device, display screen, or
speaker. In addition, the computer system may contain one or more
interfaces that can connect the computer system to a communication
network (in addition or as an alternative to the network that may
be formed by one or more of the components of the computer
system).
[0105] According to one or more embodiments of the invention, the
one or more input devices may include sensors for measuring
parameters. Alternatively, the sensors, the metering valves and/or
pumps, or all of these components may be connected to a
communication network that is operatively coupled to the computer
system. The controller can include one or more computer storage
media such as readable and/or writeable nonvolatile recording
medium in which signals can be stored that define a program to be
executed by one or more processors. Storage medium may, for
example, be a disk or flash memory. Although the computer system
may be one type of computer system upon which various aspects of
the invention may be practiced, it should be appreciated that the
invention is not limited to being implemented in software, or on
the computer system as exemplarily shown. Indeed, rather than
implemented on, for example, a general purpose computer system, the
controller, or components or subsections thereof, may alternatively
be implemented as a dedicated system or as a dedicated programmable
logic controller (PLC) or in a distributed control system. Further,
it should be appreciated that one or more features or aspects of
the invention may be implemented in software, hardware or firmware,
or any combination thereof. For example, one or more segments of an
algorithm executable by the controller can be performed in separate
computers, which in turn, can be communication through one or more
networks.
[0106] Those skilled in the art should appreciate that the
parameters and configurations described herein are exemplary and
that actual parameters and/or configurations will depend on the
specific application in which the systems and techniques of the
invention are used. Those skilled in the art should also recognize
or be able to ascertain, using no more than routine
experimentation, equivalents to the specific embodiments of the
invention. It is therefore to be understood that the embodiments
described herein are presented by way of example only and that,
within the scope of the appended claims and equivalents thereto;
the invention may be practiced otherwise than as specifically
described.
[0107] As used herein, the term "plurality" refers to two or more
items or components. The terms "comprising," "including,"
"carrying," "having," "containing," and "involving," whether in the
written description or the claims and the like, are open-ended
terms, i.e., to mean "including but not limited to." Thus, the use
of such terms is meant to encompass the items listed thereafter,
and equivalents thereof, as well as additional items. Only the
transitional phrases "consisting of" and "consisting essentially
of," are closed or semi-closed transitional phrases, respectively,
with respect to the claims. Use of ordinal terms such as "first,"
"second," "third," and the like in the claims to modify a claim
element does not by itself connote any priority, precedence, or
order of one claim element over another or the temporal order in
which acts of a method are performed, but are used merely as labels
to distinguish one claim element having a certain name from another
element having a same name (but for use of the ordinal term) to
distinguish the claim elements.
[0108] U.S. Provisional Patent Application Ser. No. 60/805,505,
filed on Jun. 22, 2006, titled ENHANCED HARDNESS TOLERANCE OF CEDI
MODULES; U.S. Provisional Patent Application Ser. No. 60/805,510,
filed on Jun. 22, 2006, titled METHODS TO REDUCE SCALING IN EDI
DEVICES; U.S. Provisional Patent Application Ser. No. 60/912,548,
filed Apr. 18, 2007, titled USE OF INERT RESIN IN THE CONCENTRATE
COMPARTMENT TO IMPROVE CURRENT DISTRIBUTION FOR EDI MODULES; and
U.S. patent application Ser. No. 11/767,438, filed on Jun. 22,
2007, titled LOW SCALE POTENTIAL WATER TREATMENT, and published as
U.S. Publication No. 2008/0067069 A1, are incorporated herein by
reference in their entirety for all purposes.
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