U.S. patent application number 14/211585 was filed with the patent office on 2014-07-17 for method, apparatus and system for desalinating saltwater.
This patent application is currently assigned to SALTWORKS TECHNOLOGIES, INC.. The applicant listed for this patent is Saltworks Technologies, Inc.. Invention is credited to MALCOLM MAN, BENJAMIN SPARROW, HENRY TSIN, JOSHUA ZOSHI.
Application Number | 20140197029 14/211585 |
Document ID | / |
Family ID | 47882487 |
Filed Date | 2014-07-17 |
United States Patent
Application |
20140197029 |
Kind Code |
A1 |
SPARROW; BENJAMIN ; et
al. |
July 17, 2014 |
METHOD, APPARATUS AND SYSTEM FOR DESALINATING SALTWATER
Abstract
An apparatus, method and plant for desalinating saltwater and
contaminated saltwater. The apparatus includes a stack and a
manifolding assembly. The stack includes a product chamber, a first
and second concentrate chamber, an anion exchange membrane forming
a boundary between the first concentrate chamber and the product
chamber and a cation exchange membrane forming a boundary between
the second concentrate chamber and the product chamber. The
manifolding assembly includes product and concentrate manifolding
fluidly coupled to the product and concentrate chambers
respectively, to convey a saltwater being desalinated to and away
from the product chamber, and a concentrate to and away from the
concentrate chambers. The stack may include a diluent chamber and
adjacent anion or cation exchange membranes between the product
chamber, diluent chamber and concentrate chamber to respectively
convey anions or cations across multiple chambers.
Inventors: |
SPARROW; BENJAMIN;
(VANCOUVER, CA) ; TSIN; HENRY; (VANCOUVER, CA)
; ZOSHI; JOSHUA; (VANCOUVER, CA) ; MAN;
MALCOLM; (VANCOUVER, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Saltworks Technologies, Inc. |
Vancouver |
|
CA |
|
|
Assignee: |
SALTWORKS TECHNOLOGIES,
INC.
VANCOUVER
CA
|
Family ID: |
47882487 |
Appl. No.: |
14/211585 |
Filed: |
March 14, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/CA2012/000843 |
Sep 14, 2012 |
|
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14211585 |
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61535259 |
Sep 15, 2011 |
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61538738 |
Sep 23, 2011 |
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61583310 |
Jan 5, 2012 |
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61616864 |
Mar 28, 2012 |
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61621737 |
Apr 9, 2012 |
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Current U.S.
Class: |
204/519 ;
204/522 |
Current CPC
Class: |
B01D 2313/48 20130101;
Y02A 20/131 20180101; C02F 2101/10 20130101; B01D 61/44 20130101;
C02F 2209/05 20130101; C02F 2209/005 20130101; C02F 2209/42
20130101; Y02A 20/134 20180101; B01D 65/02 20130101; B01D 2321/40
20130101; B01D 2321/02 20130101; Y02A 20/124 20180101; B01D 61/50
20130101; B01D 61/54 20130101; B01D 65/08 20130101; B01D 2321/22
20130101; C02F 1/4693 20130101; B01D 2321/16 20130101; B01D
2321/223 20130101; C02F 2201/46 20130101; C02F 2201/4613 20130101;
C02F 2303/22 20130101; C02F 2103/10 20130101; C02F 2103/08
20130101 |
Class at
Publication: |
204/519 ;
204/522 |
International
Class: |
C02F 1/469 20060101
C02F001/469 |
Claims
1. A method of reducing salinity of a product in a stack
comprising: (a) flowing a product feed through a first product
chamber in the stack, the first product chamber having a first
anion exchange membrane on one side of and in ionic communication
with the first product chamber and a first cation exchange membrane
on another side of and in ionic communication with the first
product chamber; (b) flowing a concentrate feed through a first
concentrate chamber in the stack in ionic communication with the
first anion exchange membrane; (c) flowing the concentrate feed
through a second concentrate chamber in the stack in ionic
communication with the first cation exchange membrane; (d) flowing
an electrolyte through a first and second electrolyte chamber in
the stack, the first electrolyte chamber bounded on one side by and
in ionic communication with a first stack end cation exchange
membrane and on another side by and in electrical communication
with a first electrode, the second electrolyte chamber bounded on
one side by and in ionic communication with a second stack end
cation exchange membrane and on another side by and in electrical
communication with a second electrode; (e) flowing a rinse solution
through a first and second rinse chamber in the stack, the first
rinse chamber bounded on one side by and in ionic communication
with a first stack end anion exchange membrane and on another side
by and in ionic communication with the first stack end cation
exchange membrane, the second rinse chamber bounded on one side by
and in ionic communication with a second stack end anion exchange
membrane and on another side by and in ionic communication with the
second stack end cation exchange membrane; and (f) applying a
voltage across the stack to force anions and cations respectively
across the first anion and exchange membrane and the first cation
exchange membrane from the product feed to the concentrate feed,
thereby producing a product output with a reduced salinity relative
to the product feed and a concentrate output with an increased
salinity relative to the concentrate feed, wherein the rinse
solution consists of a conductive non-scaling aqueous salt to
minimize transfer of scaling cations from the rinse solution to the
electrolyte.
2. The method of claim 1 further comprising flowing the product
feed through a second product chamber in the stack having a second
anion exchange membrane on one side of and in ionic communication
with the second product chamber and a second cation exchange
membrane on another side of and in ionic communication with the
second product chamber, the second anion exchange membrane being in
ionic communication with the second concentrate chamber or the
second cation exchange membrane being in ionic communication with
the first concentrate chamber, such that first or second
concentrate chamber positioned between the first and second product
chambers receives anions from one of the first or second product
chambers and cations from another of the first or second product
chambers.
3. The method of claim 2 further comprising periodically switching
the direction of migration of anions and cations from the product
feed to the concentrate feed to descale the anion and cation
exchange membranes by switching flow direction between: (a) a
forward flow direction comprising: (i) flowing the product feed
through the first and second product chambers; and (ii) flowing the
concentrate feed through the first and second concentrate chambers
(b) a reverse flow direction comprising: (i) flowing the product
feed through the first and second concentrate chambers; and (ii)
flowing the concentrate feed through the first and second product
chambers, and switching the voltage between a forward polarity
direction and a reverse polarity direction simultaneously with
switching the flow direction between the forward and reverse flow
directions respectively.
4. The method of claim 1, wherein the aqueous salt is sodium
chloride.
5. The method of claim 1 further comprising flowing a cleaning
solution through the stack during a cleaning cycle.
6. The method of claim 5, wherein the cleaning cycle is initiated
at system shut down.
7. The method of claim 5 further comprising calculating system
resistance and flowing the cleaning solution through the stack at a
threshold resistance.
8. The method of claim 7, wherein the system resistance comprises
at least one of hydraulic resistance of solutions flowing through
the stack and electrochemical resistance of the anion and cation
exchange membranes in the stack.
9. The method of claim 8, wherein the hydraulic resistance and the
electrochemical resistance are calculated from information obtained
by one or more sensors or transducers in the stack or in a
manifolding assembly conveying solutions to and away from the
stack.
10. The method of claim 7, wherein the cleaning cycle comprises a
slug wash comprising flowing a slug of the cleaning solution
through the stack at the threshold resistance.
11. The method of claim 7, wherein the cleaning cycle comprises a
stack wash comprising flowing the cleaning solution through the
stack for a set period of time at the threshold resistance.
12. The method of claim 7, wherein the cleaning cycle comprises a
stack chemical clean comprising flowing the cleaning solution
through the stack for a set period of time at the threshold
resistance, wherein the cleaning solution comprises a chemically
enriched water.
13. The method of claim 5 further comprising actuating a plurality
of valves to control flow of the cleaning solution to and away from
the stack during the cleaning cycle.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This application is a continuation of International
Application of PCT/CA2012/000843, filed on Sep. 14, 2012, which
claims priority to and the benefit of U.S. Provisional Application
No. 61/621,737, filed on Apr. 9, 2012, U.S. Provisional Application
No. 61/616,864, filed on Mar. 28, 2012, U.S. Provisional
Application No. 61/583,310, filed on Jan. 5, 2012, U.S. Provisional
Application No. 61/538,738, filed on Sep. 23, 2011 and U.S.
Provisional Application No. 61/535,259, filed on Sep. 15, 2011 each
incorporated herein in their entirety by reference.
TECHNICAL FIELD
[0002] The present disclosure is directed at a method, apparatus
and plant for desalinating saltwater. More specifically, the
disclosure is directed at a method, apparatus and plant for
desalinating saltwater using electrodyalisis.
BACKGROUND
[0003] Certain industrial processes produce a saltwater waste
(contaminated saltwater) while also requiring a lower salinity
make-up stream. Examples include, but are not limited to: [0004]
Mineral extraction: water and chemicals are mixed with mined rock
to extract a desired mineral such as copper or gold from the rock.
Saline waste water, known as "tailings", is produced as a result.
The tailings need to be discharged while make-up water of lower
salinity may be required to maintain production. In some cases, it
may not be possible to recycle tailings water due to its high
salinity. Lower salinity make-up water is required in order to
prevent corrosion in the process plant or to ensure effectiveness
of mineral extraction. It would be beneficial to desalinate
tailings water for re-use while also concentrating and reducing the
volume of the final discharge, thereby reducing discharge costs,
environmental impacts, and freshwater extraction from other
sources. [0005] Oil sands extraction: oil sands may be converted to
a vendible product by exemplar mining, separation and cracking, or
by exemplar steam assisted gravity drainage processes. Both of
these processes are commonly practiced in Canadian oil sands
operations and produce a saline waste stream while also requiring
lower salinity make-up water. It would be beneficial to desalinate
the waste saline stream for re-use. The primary requirement is to
remove scaling salts such as calcium and magnesium and corroding
salts such as chlorides whereas hydrocarbons present in the water
may remain. [0006] Enhanced oil recovery: water is injected into
hydrocarbon formations to displace and recover addition
hydrocarbons. The injected water may be mixed with caustic,
surfactants, and proprietary polymers that further enhance recovery
and prevent formation plugging. Practitioners of enhanced oil
recovery have found it preferable to inject water with a net salt
concentration between 2,000 and 8,000 parts per million (ppm). More
concentrated saline water, such as seawater with a salt
concentration of 35,000 ppm reduces oil recovery. Many in industry
believe the increased salt concentration reduces calcium ion
exchange in the formation clays and prevents release of hydrocarbon
molecules. Water with too low a salt concentration may also be
detrimental, for example reverse osmosis permeates with a
concentration of 400 ppm. Freshwater has been found to swell the
formation clays and hence impede hydrocarbon movement and reduce
recovery. Therefore, industrial experience has shown that water
with a salt concentration of 2,000 to 8,000 ppm is preferred. Said
water would preferably be rich in monovalent ions such as sodium
and chloride but weak in divalent ions such as calcium and sulfates
in order to assist in calcium ion exchange in the formation
clays.
[0007] After being injected, saltier water is often reproduced with
the oil. Salinity of the water increases due to the presence of
salts in the formation. The salinity of produced water can be
highly variable, for example from 500 to 200,000 ppm. At present,
produced water is commonly disposed and seawater desalinated for
injection. The produced water may be re-used and additional
chemicals such as surfactants and polymer added. It is known
however, that in order to be effective, more polymer needs to be
added for higher salinity waters resulting in increased operational
costs. If the produced water is desalinated before polymer is
added, then less polymer can be used. Polymers costs an average of
$20-30M per year per platform, and savings could be in the $15M per
year range by desalting the produced water first.
[0008] It would be beneficial to desalinate the produced
contaminated saltwater waste, thereby reducing polymer addition
requirements, waste water discharge, make-up water requirements,
and leaving some of the chemicals added present in the desalinated
produced water so as to reduce future input chemical input
requirements.
[0009] Desalination of seawater and brackish water is commonly
practiced. Desalination of industrial wastewater is also practiced,
yet presents unique challenges due to the presence of compounds,
such as hydrocarbons or chemicals not found in seawater or brackish
water. Pre-treatment may be employed to remove said compounds;
however, pre-treatment increases the cost of desalination. A brief
review of the most commonly practiced desalination processes are as
follows: [0010] 1. Reverse osmosis ("RO"): water is forced through
an osmotic membrane that rejects salts and allows water flux under
pressures in excess of the osmotic pressure. RO is presently the
most widely practiced seawater desalination process. RO has
challenges with industrial waste saltwater due to deleterious
compounds, such as hydrocarbons that permanently foul the membrane,
which cannot be adequately or economically removed with
pre-treatment. Reverse osmosis also reaches osmotic pressure limits
with saltwater reject waste stream ("brine") concentrations at
80,000 ppm, therefore making it unsuited for high salinity waters
and requiring additional brine treatment for inland operations.
Reverse osmosis is currently not a fit for many industrial
processes due to extensive pre-treatment requirements to reduce
hydrocarbon and organic content to below 10 ppm levels, in addition
to its product water being too pure for exemplar enhanced oil
recovery processes. [0011] 2. Thermal: water is evaporated and
condensed, at times in multiple effects in order to recycle the
latent heat of condensation. The condensed freshwater is used as a
product and the remaining brine discharged. Thermal process may
include multiple effect desalination (MED), multi-stage flash
(MSF), and vapor compression (VC). Thermal processes are more
tolerant to deleterious substances such as hydrocarbons, produce an
almost pure distillate, and can achieve very high brine
concentrations including the potential for solids formation in
exemplar VC crystallizers. However, thermal processes can be
expensive and environmentally intensive due to their high energy
requirement and costly materials of construction such as alloyed
steels and titanium. Thermal process are the most common industrial
waste saltwater desalination processes currently practiced but
there is a need for less expensive and environmentally intensive
processes. In addition, product water from thermal processes is
pure distillate requiring blending with saltwater for processes
that cannot tolerate pure water, such as enhanced oil recovery.
[0012] 3. Electrochemical: [0013] a. ion exchange ("IX") in packed
resin beds where the IX resins exchange scaling ions such as
calcium for sodium. IX requires frequent chemical inputs such as
sodium chloride and hydrochloric acid in order to regenerate the
resins--for example: remove the calcium from the resin and replace
it with sodium. IX resin regeneration often produces an acid waste
stream that must be managed, adding to complexity and cost. IX
processes have proven to be more tolerant to hydrocarbons than
reverse osmosis, and therefore have found application in oil and
gas waste water desalination and softening. That said, the
saltwater is not desalinated, it is softened with divalent ions
replaced with less problematic monovalent ions, as a result
chlorides are not removed and therefore the corrosive potential of
the water is not reduced. [0014] b. electrodialysis transfers salt
ions across ion exchange membranes under the application of a
galvanic potential. The galvanic potential is supplied as a voltage
generated at an anode and cathode. Ion exchange membranes offer the
advantage that they do not require regeneration, thereby reducing
the need for chemical inputs over IX processes. Membrane inorganic
scaling can be managed through polarity reversal (electrodialysis
reversal--EDR) and fouling managed through periodic flushes or
dilute acid washes. Unlike reverse osmosis, the output product
water concentration from electrodialysis can be adjusted by
adjusting the voltage applied to the stack.
[0015] Traditional electrodialysis stacks consist of two
chambers--a diluent and concentrate. Salt ions are transferred from
the diluent to the concentrate under the direct current electric
field applied at the electrodes. The concentration factor across
any single membrane has limits, which is expressed as the ratio of
concentrate to diluent salt mass. A practical concentration factor
of five to ten is common. For example, transferring ions from a
diluent with a concentration of 2000 ppm to a concentrate with a
concentration of 10,000 to 20,000 ppm. It is not to transfer ions
from a diluent of 2000 ppm to a concentrated of 200,000 ppm.
[0016] Concentration polarization at the membrane surface increases
with concentration factor, thereby limiting current density. In
addition, back diffusion across the membrane increases with
concentration factor, thereby reducing current efficiency. Reducing
the concentration factor across a single membrane will generally
increase the maximum allowable current density and also increase
current efficiency. Concentration factors can be limited with two
chamber stacks by use of external staging of the stacks. For
example, a first stack's diluent and concentrate concentrations
being respectively low (2,000 ppm) and moderate (20,000 ppm), and
the second stack's diluent and concentrate concentrations being
moderate (20,000 ppm) and high (200,000 ppm). By inserting the
moderate concentration circuit, the concentration factor across the
ion exchange membranes is reduced. However this requires multiple
stacks with increased footprint for their multiple frames and
process pipework.
[0017] It would be beneficial to devise a process that has the
advantages of electrodialysis in terms of increased fouling
tolerance, descaling through ionic current reversal, and ability to
tune the output product water concentration, but also enables a
high concentration difference in a single electrodialysis stack
allowing more compact desalination and production of a highly
concentrated low volume discharge saltwater. At increased
concentration, however, the potential for precipitation and
crystallization internal to the stack increases. Even with
electrodialysis reversal a stack may operate well on highly scaling
waters for 2-3 weeks but eventually precipitates form internal to
the stack, blocking flow channels. It would therefore be beneficial
to devise a control process and scheme that senses the on-set of
membrane scaling and internal stack precipitation, and takes action
to prevent its propagation.
[0018] Certain saltwater sources, such as inland brackish water,
can have increased concentrations of "hard" ions such as calcium
and magnesium relative to seawater. Said hard ions can present
inorganic scaling issues on desalination mass and heat transfer
surfaces; respective examples include RO membranes or MED heat
exchange surfaces. Scaling is mitigated by limiting recovery
thereby reducing the scaling ion concentration present at the mass
or heat transfer surface. Recovery is defined as the volumetric
flow rate of desalinated water production relative to feed water
input. Reducing recovery reduces the concentration of the ions in
the brine reject, thereby reducing scaling potential of the mass or
heat transfer surfaces exposed to the highest concentration
saltwater. However, reducing recovery detrimentally limits the
production of desalinated water.
[0019] Removing hard scaling ions from the plant feedwater enables
desalination plant operation at a higher brine reject concentration
and therefore a higher recovery, resulting in increased desalinated
water production. Hard ions such as calcium and magnesium may be
removed from the desalination plant feed water via conventional
methods known to those skilled in the art such as lime softening or
cation ion exchange (CIX). Both lime softening and cation ion
exchange systems require the input of chemicals: such as sodium
carbonate, regeneration acid or base, or sodium chloride. Chemical
consumption and waste generation can be quite high for lime
softening and cation exchange systems--in the order of many truck
loads per day for an exemplar 10,000 m.sup.3/day desalination
system. The addition of chemicals presents ongoing operational
costs along with increased safety and hazard risks. It would
therefore be beneficial to devise a system that removes scaling
ions from desalination plant feed water without the need for
chemical addition.
[0020] In EDR scaling ions, such as calcium and magnesium may pass
through the electrode membrane and into electrolyte chambers. The
scaling ions may precipitate and causes scaling in the electrode
chamber which cannot be easily remove without shutting down
operation of the EDR. It would therefore be beneficial to devise an
EDR system that prevents or reduces scaling ions from passing into
the electrolyte chamber.
[0021] Waters contaminated with relatively low levels of salt
concentration can still be unusable or hazardous to the
environment. For example, mines use freshwater and discharge
tailings into ponds. Tailings water is commonly 99.8% freshwater by
mass, but unusable due to low level salts, for example 0.1 to 0.2%
by mass. Commonly encountered salts include calcium, sulfates,
chlorides, carbonates, heavy metals, iron, selenium, and arsenic.
Run-off from exposed rock can also contain low level, but hazardous
salt concentrations. For example, in the case of one form of "acid
rock drainage," iron leaching from exposed rock can initiate a
reaction where acid is formed, with the acidity increasing the rate
of iron leach and propagating acidification, thereby causing
run-off water to become hazardous.
[0022] Acidic streams near abandoned mines are commonly treated
with lime or caustic addition to neutralize the acidity and
precipitate out metals. This process requires chemical inputs that
may be caustic, which present cost, transport, and handling
challenges. Mine operators are starting to practice reverse osmosis
to remediate a portion of their tailings. Reverse osmosis produces
an almost pure permeate freshwater by pressuring saltwater through
a semi-permeable membrane, also resulting in the production of
higher salinity brine. Recovery of the reverse osmosis system,
defined as produced freshwater relative to input saltwater volume,
is often limited by the concentration of the scaling ions in the
higher salinity brine. The recovery of the reverse osmosis system
must be limited to the 4 to 5% salt mass range, often due to the
scaling salts listed above. This leaves a large volume of
un-treated brine behind which still consists of 95% freshwater.
[0023] Un-treated reverse osmosis brine may be disposed by deep
well injection if such geology and regulatory framework exists.
Other commonly practiced brine management options include: [0024]
Return the brine to the tailings impoundment: this does not remove
salts from the water balance and leads to an eventual increase in
the salt concentration of the tailings impoundment, which is a
problem if the impoundment is also the reverse osmosis plant feed
source. With time, the concentration of the tailings will rise and
further limit the recovery of the reverse osmosis system. [0025]
Zero liquid discharge in a mechanical or thermal vapor compression
crystallizer: this removes the salt from the water balance, but is
a capital and energy intensive process. Due to the often low
recovery of reverse osmosis system a high capacity crystallizer is
required, resulting in high total costs.
[0026] When a first stage process, such as reverse osmosis, is
hybridized with a second stage zero liquid discharge process, such
as a crystallizer, it is beneficial to minimize the volume of the
saltwater sent to the more costly second stage. This will minimize
the capacity of the more costly second stage and can be achieved by
maximizing the concentration of the saltwater output from said
first stage. For example, doubling the first stage saltwater output
concentration from 4% salt to 8% salt will halve the size of the
second stage.
[0027] Electrochemical processes such as electrodialysis reversal
(EDR) move salts across ion exchange membranes into a more
concentrated saline solution. EDR is known for its ability to
operate at higher reject concentration than reverse osmosis, due to
two primary reasons: [0028] 1. Ionic de-scaling of membranes
through polarity reversal, which periodically "back-flushes" salt
flux through the membranes and de-scales them in the process. It is
not possible to back-flush reverse osmosis systems. [0029] 2.
Unlike reverse osmosis, EDR output concentration is not limited by
osmotic and hydraulic pressure barriers. Reverse osmosis systems
have a peak pressure rating (commonly 1200 psi) and freshwater will
not be produced unless the hydraulic pressure exceeds the osmotic
pressure (commonly limited to 8% salt mass so as to not exceed 1200
psi).
[0030] It would be beneficial to devise an improved two stage
process for desalinating low salinity water where the first stage
increasing the concentration of the output saltwater and as a
result beneficially reduces the capacity of the second stage
solution concentrating desalination system.
SUMMARY
[0031] According to a first aspect, there is provided an apparatus
for desalinating saltwater including a stack configured to receive
saltwater being desalinated, a diluent of a first ionic
concentration and a concentrate of a second ionic concentration
greater than the first ionic concentrate, and a manifolding
assembly. The stack includes an electrodialysis cell including a
product chamber bounded on one side by a product chamber anion
exchange membrane and bounded on another side by a product chamber
cation exchange membrane, a concentrate chamber bounded on one side
by a concentrate chamber anion exchange membrane and bounded on
another side by a concentrate chamber cation exchange membrane, a
first diluent chamber between the product chamber and the
concentrate chamber, and a second diluent chamber on an opposite
side of the product chamber to the first diluent chamber. The
electrodialysis cell being configured with either the product
chamber anion exchange membrane and the concentrate chamber anion
exchange membrane in adjacent alignment either side of the first
diluent chamber, or the product chamber cation exchange membrane
and the concentrate chamber cation exchange membrane in adjacent
alignment either side of the first diluent chamber, whereby under
application of a sufficient voltage across the electrodialysis cell
cations or anions respectively migrate across the adjacently
aligned cation exchange membranes or the adjacently aligned anion
exchange membranes from the product chamber through the first
diluent chamber to the concentrate chamber. The manifolding
assembly includes product, concentrate and diluent manifolding
fluidly coupled to the product, concentrate and diluent chambers
respectively, to convey the saltwater being desalinated to and away
from the product chamber, the concentrate to and away from the
concentrate chamber, and the diluent to and away from the diluent
chambers.
[0032] According to a second aspect, there is provided an apparatus
for desalinating saltwater capable of operating in forward polarity
and reverse polarity. The apparatus includes a stack configured to
receive saltwater being desalinated, a diluent of a first ionic
concentration and a concentrate of a second ionic concentration
greater than the first ionic concentrate, and a manifolding
assembly. The stack including an electrodialysis cell including a
first and second product/concentrate chamber, each
product/concentrate chamber bounded on one side by a
product/concentrate chamber anion exchange membrane and bounded on
another side by a product/concentrate chamber cation exchange
membrane; a first and second concentrate/product chamber, each
concentrate/product chamber bounded on one side by a
concentrate/product chamber anion exchange membrane and bounded on
another side by a concentrate/product chamber cation exchange
membrane; and a first, second and third diluent chamber. The
electrodialysis cell being configured with the product/concentrate
chamber anion exchange membrane of the first product/concentrate
chamber and the concentrate/product chamber anion exchange membrane
of the first concentrate/product chamber in adjacent alignment
either side of the first diluent chamber, the product/concentrate
chamber cation exchange membrane of the first product/concentrate
chamber and the concentrate/product chamber cation exchange
membrane of the second concentrate/product chamber in adjacent
alignment either side of the second diluent chamber, and either the
product/concentrate chamber anion exchange membrane of the second
product/concentrate chamber and the concentrate/product chamber
anion exchange membrane of the second concentrate/product chamber
in adjacent alignment either side of the third diluent chamber, or
the product/concentrate chamber cation exchange membrane of the
second product/concentrate chamber and the concentrate/product
chamber cation exchange membrane of the first concentrate/product
chamber in adjacent alignment either side of the third diluent
chamber, whereby under application of a sufficient voltage across
the electrodialysis cell cations and anions respectively migrate
across the adjacently aligned cation exchange membranes and the
adjacently aligned anion exchange membranes from the
product/concentrate chamber through the diluent chamber to the
concentrate/product chamber in forward polarity and from the
concentrate/product chamber through the diluent chamber to the
product/concentrate chamber in reverse polarity. The manifolding
assembly includes product/concentrate manifolding fluidly coupled
to the product/concentrate chambers and configured to convey the
saltwater being desalinated to and away from the
product/concentrate chambers when the apparatus is operating in
forward polarity and the concentrate to and away from the
product/concentrate chambers when the apparatus is operating in
reverse polarity, concentrate/product manifolding fluidly coupled
to the concentrate/product chambers and configured to convey the
concentrate to and away from the concentrate/product chambers when
the apparatus is operating in forward polarity and the saltwater
being desalinated to and away from the concentrate/product chambers
when the apparatus is operating in reverse polarity, and diluent
manifolding fluidly coupled to the diluent chambers to convey the
diluent to and away from the diluent chambers.
[0033] According to a another aspect, there is provided an
apparatus for desalinating saltwater including a stack and a
manifolding assembly. The stack being configured to receive the
saltwater being desalinated and a concentrate and including a
product chamber; a first and second concentrate chamber, the first
concentrate chamber on one side of and in ionic communication with
the product chamber and the second concentrate chamber on another
side of and in ionic communication with the product chamber; an
anion exchange membrane forming a boundary between the first
concentrate chamber and the product chamber; a cation exchange
membrane forming a boundary between the second concentrate chamber
and the product chamber; first and second electrolyte chambers for
containing an electrolyte; first and second stack end cation
exchange membranes and first and second stack end anion exchange
membranes; first and second electrodes, the first electrolyte
chamber bounded on one side by and in ionic communication with the
first stack end cation exchange membrane and on another side by and
in electrical communication with the first electrode, the second
electrolyte chamber bounded on one side by and in ionic
communication with the second stack end cation exchange membrane
and on another side by and in electrical communication with the
second electrode; and first and second rinse chambers for
containing rinse solution, the first rinse chamber bounded on one
side by and in ionic communication with the first stack end anion
exchange membrane and on another side by and in ionic communication
with the first stack end cation exchange membrane, the second rinse
chamber bounded on one side by and in ionic communication with the
second stack end anion exchange membrane and on another side by and
in ionic communication with the second stack end cation exchange
membrane. The manifolding assembly including product and
concentrate manifolding fluidly coupled to the product and
concentrate chambers respectively, to convey the saltwater being
desalinated to and away from the product chamber, and the
concentrate to and away from the concentrate chambers.
[0034] According to another aspect, there is provided an apparatus
for desalinating saltwater capable of operating in forward polarity
and reverse polarity. The apparatus includes a stack configured to
receive the saltwater being desalinated and a concentrate, and a
manifolding assembly. The stack includes at least two
product/concentrate chambers; at least two concentrate/product
chambers, each concentrate/product chamber in ionic communication
with one of the product/concentrate chambers; anion and cation
exchange membranes arranged such that an anion or cation exchange
membrane forms a boundary between each product/concentrate chamber
and an adjacent concentrate/product chamber, and each
product/concentrate chamber has an anion exchange membrane on one
side of the product/concentrate chamber and a cation exchange
membrane on another side of the product/concentrate chamber and
each concentrate/product chamber has an anion exchange membrane on
one side of the concentrate/product chamber and a cation exchange
membrane on another side of the concentrate/product chamber; first
and second electrolyte chambers for containing an electrolyte;
first and second stack end cation exchange membranes and first and
second stack end anion exchange membranes; first and second
electrodes, the first electrolyte chamber bounded on one side by
and in ionic communication with the first stack end cation exchange
membrane and on another side by and in electrical communication
with the first electrode, the second electrolyte chamber bounded on
one side by and in ionic communication with the second stack end
cation exchange membrane and on another side by and in electrical
communication with the second electrode; and first and second rinse
chambers for containing rinse solution, the first rinse chamber
bounded on one side by and in ionic communication with the first
stack end anion exchange membrane and on another side by and in
ionic communication with the first stack end cation exchange
membrane, the second rinse chamber bounded on one side by and in
ionic communication with the second stack end anion exchange
membrane and on another side by and in ionic communication with the
second stack end cation exchange membrane. The manifolding assembly
includes product/concentrate manifolding fluidly coupled to the
product/concentrate chambers and configured to convey the saltwater
being desalinated to and away from the product/concentrate chambers
when the apparatus is operating in forward polarity and the
concentrate to and away from the product/concentrate chambers when
the apparatus is operating in reverse polarity; and
concentrate/product manifolding fluidly coupled to the
concentrate/product chambers and configured to convey the
concentrate to and away from the concentrate/product chambers when
the apparatus is operating in forward polarity and the saltwater
being desalinated to and away from the concentrate/product chambers
when the apparatus is operating in reverse polarity.
[0035] According to another aspect, there is provided a method for
producing a desalinated product. The method includes flowing a
product feed and a concentrate feed through a stack, and applying a
voltage across the stack to force anions and cations respectively
across anion and cation exchange membranes in the stack from the
product feed to the concentrate feed, thereby producing a product
output with a reduced salinity relative to the product feed and a
concentrate output with an increased salinity relative to the
concentrate feed; and flowing the product output through a
desalination system to produce the desalinated product and a
desalination system concentrate.
[0036] According to another aspect, there is provided a plant for
producing a desalinated product including an electrodialysis (ED)
system, a desalination system, and a conduit. The ED system
includes a stack configured to receive a product feed and a
concentrate feed and a manifolding assembly. The stack includes a
product chamber; a first and second concentrate chamber, the first
concentrate chamber on one side of and in ionic communication with
the product chamber and the second concentrate chamber on another
side of and in ionic communication with the product chamber; a
first anion exchange membrane forming a boundary between the first
concentrate chamber and the product chamber; and a first cation
exchange membrane forming a boundary between the second concentrate
chamber and the product chamber. The manifolding assembly includes
product manifolding fluidly coupled to the product chamber to
convey the product feed to the product chamber and a product output
away from the product chamber, the product output having a reduced
salinity relative to the product feed; and concentrate manifolding
fluidly coupled to the concentrate chambers to convey the
concentrate feed to the concentrate chambers and a concentrate
output away from the concentrate chambers, the concentrate output
having an increased salinity relative to the concentrate feed. The
conduit fluidly coupling the product manifolding with an inlet to
the desalination system and configured to convey the product output
to the desalination system.
[0037] According to another aspect, there is provided a plant for
producing a desalinated product including an electrodialysis
reversal (EDR) system capable of operating in forward polarity and
reverse polarity, a desalination system, and a conduit. The EDR
system includes a stack configured to receive a product feed and a
concentrate feed, and a manifolding assembly. The stack includes at
least two product/concentrate chambers; at least two
concentrate/product chambers, each concentrate/product chamber in
ionic communication with one of the product/concentrate chambers;
and anion and cation exchange membranes arranged such that an anion
or cation exchange membrane forms a boundary between each
product/concentrate chamber and an adjacent concentrate/product
chamber, and each product/concentrate chamber has an anion exchange
membrane on one side of the product/concentrate chamber and a
cation exchange membrane on another side of the product/concentrate
chamber and each concentrate/product chamber has an anion exchange
membrane on one side of the concentrate/product chamber and a
cation exchange membrane on another side of the concentrate/product
chamber. The manifolding assembly including product/concentrate
manifolding fluidly coupled to the product/concentrate chambers and
configured to convey the product feed to and a product output away
from the product/concentrate chambers when the apparatus is
operating in forward polarity and the concentrate feed to and a
concentrate output away from the product/concentrate chambers when
the apparatus is operating in reverse polarity, the product output
having a reduced salinity relative to the product feed and the
concentrate output having an increased salinity relative to the
concentrate feed; and concentrate/product manifolding fluidly
coupled to the concentrate/product chambers and configured to
convey the concentrate feed to and the concentrate output away from
the concentrate/product chambers when the apparatus is operating in
forward polarity and the product feed to and the product output
away from the concentrate/product chambers when the apparatus is
operating in reverse polarity. The conduit fluidly coupling the
manifolding assembly with an inlet to the desalination system
configured to convey product output from the EDR system to the
desalination system.
[0038] According to another aspect, there is provided a method of
desalinating a contaminated saltwater. The method including flowing
the contaminated saltwater being desalinated from a contaminated
saltwater source through a first waste water chamber, the first
waste water chamber having a first anion exchange membrane on one
side of and in ionic communication with the first waste water
chamber and a first cation exchange membrane on another side of and
in ionic communication with the first waste water chamber; flowing
a saline water from a saline water source through a first saline
water chamber in ionic communication with the first anion exchange
membrane; and flowing the saline water through a second saline
water chamber in ionic communication with the first cation exchange
membrane, wherein anions migrate from the first waste water chamber
through the first anion exchange membrane to the first saline water
chamber and cations migrate from the first waste water chamber
through the first cation exchange membrane to the second saline
water chamber, the first anion and cation exchange membranes
configured to allow migration of salts and to reduce migration of
contaminants, such that the salt concentration in the saline water
increases to produce concentrated saline water and the contaminated
saltwater is desalinated.
[0039] According to another aspect, there is provided an apparatus
for desalinating a contaminated saltwater capable of operating in
forward flow direction and reverse flow direction. The apparatus
including a stack configured to receive the contaminated saltwater
being desalinated from a contaminated saltwater source and a saline
water from a saline water source, a manifolding assembly, and a
diverter. The stack including at least two waste/saline chambers;
at least two saline/waste chambers, each saline/waste chamber in
ionic communication with at least one of the waste/saline chambers;
and anion and cation exchange membranes arranged such that an anion
or cation exchange membrane forms a boundary between each
waste/saline chamber and an adjacent saline/waste chamber, and each
waste/saline chamber has an anion exchange membrane on one side of
the waste/saline chamber and a cation exchange membrane on another
side of the waste/saline chamber and each saline/waste chamber has
an anion exchange membrane on one side of the saline/waste chamber
and a cation exchange membrane on another side of the saline/waste
chamber. The manifolding assembly including waste/saline
manifolding fluidly coupled to the waste/saline chambers and
configured to convey the contaminated saltwater being desalinated
to and away from the waste/saline chambers when the apparatus is
operating in forward polarity and the saline water to and away from
the waste/saline chambers when the apparatus is operating in
reverse polarity; saline/waste manifolding fluidly coupled to
convey the saline/waste chambers and configured to convey the
saline water to and away from the saline/waste chambers when the
apparatus is operating in forward polarity and the contaminated
saltwater being desalinated to and away from the saline/waste
chambers when the apparatus is operating in reverse polarity; and a
saline water outlet conduit in fluid communication with the
waste/saline and saline/waste manifolding. The diverter configured
to divert a saline and contaminated saltwater mixture away from the
saline water outlet conduit for a set period of time following a
switch between operating in the forward and reverse flow direction,
or until a level of contaminated saltwater in the saline and
contaminated saltwater mixture is at or below a threshold
level.
[0040] According to another aspect, there is provided a method for
desalinating a saltwater including flowing the saltwater being
desalinated through an electrodialysis system including flowing a
product feed and a concentrate feed through a stack, the product
feed and concentrate feed including the saltwater being
desalinated, and applying a voltage across the stack to force
anions and cations respectively across anion and cation exchange
membranes in the stack from the product feed to the concentrate
feed, thereby producing a product output that has a reduced
salinity relative to the product feed and a concentrate output that
has an increased salinity relative to the concentrate feed; and
flowing the concentrate output through a solution concentrating
desalination system.
[0041] According to another aspect, there is provided a plant for
desalinating a saltwater including an electrodialysis system, a
solution concentrating desalination system, and a conduit. The
electrodialysis system including a stack configured to receive a
product feed and a concentrate feed, the product feed and the
concentrate feed including the saltwater being desalinated, and a
manifolding assembly. The stack including a product chamber; a
first and second concentrate chamber, the first concentrate chamber
on one side of and in ionic communication with the product chamber
and the second concentrate chamber on another side of and in ionic
communication with the product chamber; a first anion exchange
membrane forming a boundary between the first concentrate chamber
and the product chamber; and a first cation exchange membrane
forming a boundary between the second concentrate chamber and the
product chamber. The manifolding assembly including product
manifolding fluidly coupled to the product chamber to convey the
product feed to the product chamber and a product output away from
the product chamber, the product output having a reduced salinity
relative to the product feed; and concentrate manifolding fluidly
coupled to the concentrate chambers to convey the concentrate feed
to the concentrate chambers and a concentrate output away from the
concentrate chambers, the concentrate output having an increased
salinity relative to the concentrate feed. The conduit fluidly
coupling the concentrate manifolding with an inlet to the solution
concentrating desalination system configured to convey the
concentrate output to the solution concentrating desalination
system.
[0042] According to another aspect, there is provided a plant for
desalinating a saltwater including an electrodialysis system
capable of operating in forward polarity and reverse polarity, a
solution concentrating desalination system, and a conduit. The
electrodialysis system including a stack configured to receive a
product feed and a concentrate feed, the product feed and the
concentrate feed including the saltwater being desalinated, and a
manifolding assembly. The stack including at least two
product/concentrate chambers; at least two concentrate/product
chambers, each concentrate/product chamber in ionic communication
with one of the product/concentrate chambers; and anion and cation
exchange membranes arranged such that an anion or cation exchange
membrane forms a boundary between each product/concentrate chamber
and an adjacent concentrate/product chamber, and each
product/concentrate chamber has an anion exchange membrane on one
side of the product/concentrate chamber and a cation exchange
membrane on another side of the product/concentrate chamber and
each concentrate/product chamber has an anion exchange membrane on
one side of the concentrate/product chamber and a cation exchange
membrane on another side of the concentrate/product chamber. The
manifolding assembly including product/concentrate manifolding
fluidly coupled to the product/concentrate chambers and configured
to convey the product feed to and a product output away from the
product/concentrate chambers when the apparatus is operating in
forward polarity, and the concentrate feed to and a concentrate
output away from the product/concentrate chambers when the
apparatus is operating in reverse polarity, the product output
having a reduced salinity relative to the product feed and the
concentrate output having an increased salinity relative to the
concentrate feed; and concentrate/product manifolding fluidly
coupled to the concentrate/product chambers and configured to
convey the concentrate feed to and the concentrate output away from
the concentrate/product chambers when the apparatus is operating in
forward polarity, and the product feed to and the product output
away from the concentrate/product chambers when the apparatus is
operating in reverse polarity. The conduit fluidly coupling the
manifolding assembly with an inlet to the solution concentrating
desalination system configured to convey the concentrate output to
the solution concentrating desalination system.
[0043] According to another aspect, there is provided a plant for
desalinating a saltwater including the apparatus for desalinating a
saltwater according to the first aspect, a solution concentrating
desalination system, and a conduit. The stack being configured to
receive a product feed and a concentrate feed, the product feed and
the concentrate feed including the saltwater being desalinated. The
product manifolding being configured to convey the product feed to
the product chamber and a product output away from the product
chamber, and the concentrate manifolding being configured to convey
the concentrate feed to the concentrate chambers and a concentrate
output away from the concentrate chambers, the product output
having a reduced salinity relative to the product feed and the
concentrate output having an increased salinity relative to the
concentrate feed. The conduit fluidly coupling the concentrate
manifolding with an inlet to the solution concentrating
desalination system configured to convey the concentrate output to
the solution concentrating desalination system.
[0044] According to another aspect, there is provided a plant for
desalinating a saltwater including the apparatus for desalinating a
saltwater according to the second aspect, a solution concentrating
desalination system, and a conduit. The stack being configured to
receive a product feed and a concentrate feed, the product feed and
the concentrate feed including the saltwater being desalinated. The
product/concentrate manifolding being configured to convey the
product feed to and a product output away from the
product/concentrate chambers when the apparatus is operating in
forward polarity, and the concentrate feed to and a concentrate
output away from the product/concentrate chambers when the
apparatus is operating in reverse polarity, the product output
having a reduced salinity relative to the product feed and the
concentrate output having an increased salinity relative to the
concentrate feed. The concentrate/product manifolding being
configured to convey the concentrate feed to and the concentrate
output away from the concentrate/product chambers when the
apparatus is operating in forward polarity, and the product feed to
and the product output away from the concentrate/product chambers
when the apparatus is operating in reverse polarity. The conduit
fluidly coupling the manifolding assembly with an inlet to the
solution concentrating desalination system configured to convey the
concentrate output to the solution concentrating desalination
system.
[0045] According to another aspect, there is provided a method of
cleaning a stack of an electrodialysis system including flowing a
cleaning solution through the stack during a cleaning cycle.
[0046] According to another aspect, there is provided an apparatus
for desalinating saltwater including a stack configured to receive
the saltwater being desalinated and a concentrate, a manifolding
assembly, and a cleaning system. The stack including a product
chamber, a first and second concentrate chamber, the first
concentrate chamber on one side of and in ionic communication with
the product chamber and the second concentrate chamber on another
side of and in ionic communication with the product chamber, an
anion exchange membrane forming a boundary between the first
concentrate chamber and the product chamber; and a cation exchange
membrane forming a boundary between the second concentrate chamber
and the product chamber. The manifolding assembly including product
and concentrate manifolding fluidly coupled to the product and
concentrate chambers respectively, to convey the saltwater being
desalinated to and away from the product chamber, and the
concentrate to and away from the concentrate chambers. The cleaning
system including a cleaning reservoir for containing a cleaning
solution fluidly coupled with the manifolding assembly and
configured to convey the cleaning solution through the stack during
a cleaning cycle.
[0047] According to another aspect, there is provided an apparatus
for desalinating saltwater capable of operating in forward polarity
and reverse polarity. The apparatus including a stack configured to
receive the saltwater being desalinated and a concentrate, a
manifolding assembly and a cleaning system. The stack including at
least two product/concentrate chambers; at least two
concentrate/product chambers, each concentrate/product chamber in
ionic communication with one of the product/concentrate chambers;
and anion and cation exchange membranes arranged such that an anion
or cation exchange membrane forms a boundary between each
product/concentrate chamber and an adjacent concentrate/product
chamber, and each product/concentrate chamber has an anion exchange
membrane on one side of the product/concentrate chamber and a
cation exchange membrane on another side of the product/concentrate
chamber and each concentrate/product chamber has an anion exchange
membrane on one side of the concentrate/product chamber and a
cation exchange membrane on another side of the concentrate/product
chamber. The manifolding assembly including: product/concentrate
manifolding fluidly coupled to the product/concentrate chambers and
configured to convey the saltwater being desalinated to and away
from the product/concentrate chambers when the apparatus is
operating in forward polarity and the concentrate to and away from
the product/concentrate chambers when the apparatus is operating in
reverse polarity; and concentrate/product manifolding fluidly
coupled to the concentrate/product chambers and configured to
convey the concentrate to and away from the concentrate/product
chambers when the apparatus is operating in forward polarity and
the saltwater being desalinated to and away from the
concentrate/product chambers when the apparatus is operating in
reverse polarity. The cleaning system including a cleaning
reservoir for containing a cleaning solution fluidly coupled with
the manifolding assembly and configured to convey the cleaning
solution through the stack during a cleaning cycle.
BRIEF DESCRIPTION OF THE DRAWINGS
[0048] In the accompanying drawings, which illustrate one or more
exemplary embodiments:
[0049] FIG. 1 is a schematic view of a waste saltwater reclamation
plant (WSRP) according to an embodiment including an
electrodialysis reversal (EDR) stack.
[0050] FIG. 2 is a schematic view of the EDR stack of FIG. 1
operating in forward polarity.
[0051] FIG. 3 is a schematic view of the EDR stack of FIG. 1
operating in reverse polarity.
[0052] FIG. 4 is a schematic view of an internally staged multiple
chamber electrodialysis reversal (MC-EDR) plant including a MC-EDR
stack according to an embodiment.
[0053] FIG. 5 is a schematic view of the MC-EDR stack of FIG. 4
operating in forward polarity.
[0054] FIG. 6 is a schematic view of the MC-EDR stack of FIG. 4
operating in reverse polarity.
[0055] FIG. 7 is a schematic view of an internally staged multiple
chamber electrodialysis reversal (MC-EDR) plant including an MC-EDR
stack according to an alternative embodiment.
[0056] FIG. 8 is a schematic view of the MC-EDR stack of FIG. 7
operating in forward polarity.
[0057] FIG. 9 is a schematic view of the MC-EDR stack of FIG. 7
operating in reverse polarity.
[0058] FIG. 10 is a schematic view of a two stage desalination
plant according to an embodiment.
[0059] FIG. 11 is a schematic view of a two stage desalination
plant according to an alternative embodiment.
[0060] FIG. 12 is a schematic view of an electrodialysis
reversal-rinse (EDR-R) unit according to an embodiment operating in
forward polarity.
[0061] FIG. 13 is a schematic view of the EDR-R unit of FIG. 12
operating in reverse polarity.
[0062] FIG. 14 is a schematic view of the MC-EDR plant of FIG. 4
with additional cleaning system according to an embodiment.
[0063] FIG. 15 is a graph showing pressure-flow relationships
measured by sensors in the MC-EDR plant of FIG. 14.
[0064] FIG. 16 is a schematic view of a two stage salt extraction
plant including a first electrodialysis (ED) stage and second stage
solution concentrating desalination system according to an
embodiment.
[0065] FIG. 17 is the two stage salt extraction plant of FIG. 16
with thermally integrated multiple effect heat pump driven solution
concentrating desalination system.
[0066] FIG. 18 is a schematic view of an internally staged multiple
chamber electrodialysis reversal-rinse (MC-EDR-R) plant including a
MC-EDR-R stack and cleaning system according to an alternative
embodiment.
[0067] FIG. 19 is a schematic view of the MC-EDR-R stack of FIG. 18
operating in forward polarity.
[0068] FIG. 20 is a schematic view of the MC-EDR-R stack of FIG. 18
operating in reverse polarity.
DETAILED DESCRIPTION
[0069] Directional terms such as "top", "bottom", "upwards",
"downwards", "vertically" and "laterally" are used in the following
description for the purpose of providing relative reference only,
and are not intended to suggest any limitations on how any article
is to be positioned during use, or to be mounted in an assembly or
relative to an environment.
[0070] In conventional electrodialysis (ED) processes one water
source is input and split into two circuits--diluent and
concentrate. Salts are transferred from the diluent to the
concentrate. Desalinated diluent is often the product water and the
concentrate is eventually discharged. In conventional
electrodialysis, any substances present in the input water, such as
hydrocarbons, would end up in the concentrate stream and be
discharged.
[0071] Embodiments described herein are directed at an ED process
and plant to desalinate contaminated saltwater such as industrial
waste water (primary industrial water (PIW)) from a first
contaminated saltwater source using saline water from a second
saltwater source such as the ocean or a brackish aquifer. Salts are
transferred from the PIW to the saline water through ion exchange
membranes in an ED stack. With proper membrane selection, only
strongly ionized and low molecular weight species such as sodium,
chloride, calcium, magnesium, sulfates and the like are transferred
from the PIW through the ion exchange membrane to the saline water.
Non-ionic species such as hydrocarbons and larger weekly ionized
molecules such as organics present in the PIW do not cross the
membrane into the saline water. The saline water is therefore
concentrated in salts but not in other environmentally hazardous
materials that may be present in the PIW so that the concentrated
saline water output may be safely discharged to the environment.
The salinity of the PIW is beneficially reduced and the desalinated
PIW may be re-used in the industrial process.
[0072] The salts present in the PIW may contain scaling species
such as calcium carbonate and calcium sulfate. To prevent scale
build up on the ion exchange membranes of the stack, an
electrodialysis reversal (EDR) stack may be used and the polarity
of the EDR stack periodically reversed to change the direction of
ion transfer through the membranes, thereby descaling the
membranes. During reversal, the PIW and the saline water fed to the
EDR stack are swapped and, as a result, the PIW and saline water
present in the plant pipework and EDR stack when reversal is
initiated are mixed, resulting in a momentary and moderate
concentration waste stream. The embodiments described herein
include a reversal process that prevents the detrimental discharge
of this waste stream to the saline water stream.
[0073] Referring to FIG. 1, there is shown a waste saltwater
reclamation plant (WSRP) 1 consisting of EDR stack 2 for
desalinating a primary industrial water (PIW) where the total
dissolved solids concentrations may range from 500 ppm to 200,000
ppm. An exemplar PIW is produced water from oil and gas
operations.
[0074] PIW is conveyed through PIW manifolding in a PIW circuit. In
the PIW circuit pump 10 which draws PIW from a liquid conduit 90
within the process requiring desalination and into an optional
pre-treatment unit 11. Exemplar pre-treatment may include, but is
not limited to, physical filters such as microfiltration, or other
methods known to those skilled in the art. The effluent from the
pre-treatment unit 11 is stored in an optional PIW bulk tank 12,
which may include an optional heating element (not shown) to
increase the temperature of the PIW, which beneficially increases
EDR system efficiency. The PIW is pumped from bulk tank 12 to inlet
reversal valve array 14 by pump 13. In an alternative embodiment
(not shown) the PIW is pumped directly from pre-treatment 11 into
the feed reversal valve array 14, removing the need for tank 12 and
pump 13.
[0075] In parallel to the PIW circuit is a saline water circuit
with saline water manifolding. In the saline water circuit, pump 15
draws saline water from a saline water source 92 through an
optional saline water pre-treatment unit 26 and into a saline water
bulk tank 16, which may include an optional heating element (not
shown) to increase the temperature of the saline water in order to
increase system desalination efficiencies. Exemplar saline water
sources 92 may include, but are not limited to, seawater or saline
brine from an aquifer. Pump 17 pumps the saline water from saline
water bulk tank 16 into the inlet reversal valve array 14. In an
alternative embodiment (not shown) the saline water is pumped
directly from pre-treatment unit 26 into reversal valve array 14,
removing the need for tank 16 and pump 17.
[0076] P-S inlet conduit 18 and S-P inlet conduit 19 deliver PIW
and saline water to EDR stack 2. P-S outlet conduit 20 and S-P
outlet conduit 21 convey PIW and saline water away from EDR stack 2
to outlet reversal valve array 22. PIW passes from outlet reversal
valve array 22 to PIW exit conduit 28 and saline water passes from
outlet reversal valve array 22 to saline water exit conduit 27 and
can be discharged from the plat at saline water outlet 93 or
recycled to saline water tank 16 for further concentration. The
inlet reversal valve array 14 consists of four actuated valves 14a,
14b, 14c, 14d and the outlet reversal valve array 22 consists of
four actuated valves 22a, 22b, 22c, 22d.
[0077] EDR systems can develop scale on the membrane surface over
time. Membrane scale be can reduced by periodically reversing the
polarity of EDR stack 2, such that ions travel in opposite
directions through the ion exchange membranes under forward or
reverse polarity operating modes. In order to reverse polarity, the
solutions in their respective circuits need to be swapped, which is
achieved by a hydraulic reversal procedure involving reversal valve
arrays 14 and 22. The reversal valve position and solution
contained in each conduit 18, 19, 20, 21 depends on whether the
stack is operating in forward or reverse polarity. The reversal
valve positions in forward and reverse polarity mode, as well as
the fluid contained in each conduit 18, 19, 20, 21, is given in
Table 1 below.
TABLE-US-00001 TABLE 1 Hydraulic Reversal Procedure for EDR Plant 1
EDR EDR EDR EDR Forward Reverse Reverse Forward Polarity Flush
Polarity Flush Reversal 14a Closed Open Open Closed Valves 14b Open
Closed Closed Open 14c Closed Open Open Closed 14d Open Closed
Closed Open 22a Closed Open Open Open 22b Open Closed Closed Closed
22c Closed Closed Open Closed 22d Open Open Closed Open Conduit 18
PIW PIW-Saline Saline PIW-Saline water water water 19 Saline
PIW-Saline PIW PIW-Saline water water water 20 PIW PIW-Saline
Saline PIW-Saline water water water 21 Saline PIW-Saline PIW
PIW-Saline water water water
[0078] Immediately after the polarity is switched conduits 18, 19,
20, and 21 will have a mixture of both PIW and saline water. This
is because the solutions internal to the conduits are swapped--the
saline water conduit becomes a PIW conduit and vice-versa. With
time, the PIW-saline water mixture will be pushed through the
conduit until the solution is either entirely PIW or entirely
saline water. It would be detrimental to discharge PIW to the
saline water outlet 93. To prevent discharge of PIW at the saline
water outlet 93, analyzer 24 and saline water discharge three-way
valve 25 may be included upstream of the saline water outlet 93.
Analyzer 24 measures the PIW content of the PIW-saline water
mixture exiting outlet reversal valve array 22 in the saline water
exit conduit 27. If the PIW content is above a pre-set threshold
value, the PIW-saline water mixture is diverted by saline water
discharge three-way valve 25 away from the saline water outlet 93
and returned to PIW bulk tank 12. The pre-set threshold value for
allowable PIW discharge concentration to saline water outlet 93 can
be set by permitting conditions. Overtime, after the polarity
reversal sequence is initiated, the PIW content in the saline water
exit conduit 27 will decrease to below the pre-set threshold value.
Once below the pre-set threshold value, the saline water discharge
three-way valve 25 is actuated to discharge the solution in the
saline water exit conduit 27 to the saline water outlet 93 rather
than to PIW bulk tank 12.
[0079] In an alternative embodiment, to prevent discharge of the
PIW-saline water mixture at saline water outlet 93 following
reversal of polarity, the PIW-saline water mixture may be diverted
to the PIW exit conduit 28 using a reverse or forward flush. With
reference to Table 1 for both the reverse and forward flush, outlet
reversal valves 22a and 22d are open and outlet reversal valves 22b
and 22c are closed for a predetermined period of time (for example
one minute) following polarity reversal so that the PIW-saline
water mixture is directed to the PIW exit conduit 28 and not into
the saline water exit conduit 27. In an alternative embodiment, a
conductivity sensor (not shown) in P-S outlet conduit 20 and S-P
outlet conduit 21 may be used to detect the conductivity of the
solution exiting the EDR stack 2 and the reversal valves of outlet
reversal valve array 22 may be switched to operate in either EDR
forward polarity or EDR reverse polarity once a threshold PIW
concentration is detected indicating that the saline water is
sufficiently clear of PIW to be directed to saline water outlet
93.
[0080] A PIW discharge three-way valve 23 is included to enable
partial batch operation of the PIW circuit. PIW desalination
continues until the PIW has reached a desired salt concentration as
measured by a conductivity sensor (not shown) installed in PIW bulk
tank 12. Once the salt concentration of the PIW reaches the desired
level, PIW bulk tank 12 is emptied by pumping the PIW through the
EDR stack and actuating valve 23 to direct the PIW into the PIW
conduit at a downstream location 91 from the initial extraction
point 90. A low level sensor such as a pressure transducer or float
switch (not shown) in PIW bulk tank 12 senses a drop in PIW level
in PIW bulk tank 12. Pump 10 is actuated to fill PIW bulk tank 12
and valve 23 is actuated to direct the PIW in PIW exit conduit 28
back into PIW bulk tank 12 where the batch cycle desalination
starts again.
[0081] In an alternative embodiment, PIW discharge three-way valve
23 can also allow for the EDR system to be operated in continuous
mode such that the PIW in PIW exit conduit 28 is discharged
directly back into the PIW conduit at a downstream location 91
rather than being returned into PIW bulk tank 12. Immediately after
a reversal event, the PIW-saline water mixture in the saline water
exit conduit 27 would also be directed by saline water discharge
three-way valve 25 to PIW conduit downstream location 91 until
analyzer 24 determines that PIW content is below the threshold
concentration for discharge of the saline water to saline water
outlet 93.
[0082] FIG. 2 shows the EDR stack 2 operating in forward polarity,
where the PIW flows into P-S chambers 30 through P-S inlet conduit
18 and exits via P-S outlet conduit 20; and the saline water flows
into S-P chambers 40 through S-P inlet conduit 19 and exits via S-P
outlet conduit 21. Chambers 30 and 40 are separated by membranes
that are permeable to ions and less permeable to water, hereinafter
referred to as ion exchange membranes. There are two types of ion
exchange membranes in the EDR stack 2 arranged in alternating
sequence. The first ion exchange membrane is an anion exchange
membrane 8 which is permeable to ions of negative charge (anions)
and less permeable to ions of positive charge (cations). The second
ion exchange membrane is a cation exchange membrane 9 which is
permeable to cations and less permeable to anions. Exemplary anion
exchange membranes include Neosepta AM-1, AFN, AMX; Ralex AMH-PES;
Fumasep FAD; and Selemion DVS, APS membranes. Exemplary cation
exchange membranes include Neosepta CMX, CM-1; Ralex CMH-PES;
Fumasep FKE, FKD; and Selemion CMV membranes.
[0083] An electric potential 60 is applied to EDR stack 2 causing
an electric current 61 to flow between an anode and cathode at
either end of the EDR stack 2. In the forward polarity
anode/cathode electrode 7 becomes the positively charged anode
which anions flow towards and cathode/anode electrode 6 becomes the
negatively charged cathode which cations flow towards The combined
electric and ionic current respectively force anions and the
cations in the PIW through the anion exchange membrane 8 and the
cation exchange membrane 9 into the saline water. Thus the ions
decrease in concentration in the PIW while ions increase in
concentration in the saline water. In an alternative embodiment
(not shown), a drive cell, such as the drive cell disclosed in WO
2010/115287 or WO 2009/155683 may be used for application of a
voltage across the chambers.
[0084] When the PIW is highly concentrated ions will flow from the
more concentrated PIW to the less concentrated saline water without
the need for application of the electric potential 60 thus reducing
operating costs. Once the ionic concentration of the PIW has
dropped to the same concentration or below the ionic concentration
of the saline water, the electric potential 60 can be applied if
further desalination of the PIW is required. Sensors may be present
in the saline water circuit and/or the waste water circuit (not
shown) to detect the concentration of the saline water and/or the
PIW to determine when the ionic concentration of the PIW is at or
below the ionic concentration of the saline water and a signal sent
to a control system to actuate application of the electric
potential across the EDR stack 2.
[0085] On each end of the EDR stack 2 are electrolyte chambers,
where electrolyte chamber 5 is on the anode side and electrolyte
chamber 4 is on the cathode side in the forward polarity mode. An
electrolyte solution is contained in electrolyte tank 50 and pumped
by electrolyte pump 51 through electrolyte distribution conduit 52
into electrolyte chambers 4 and 5 in parallel. The electrolyte
solution flows back into electrolyte tank 50 in a closed loop
process. In an alternative embodiment (not shown) a series closed
loop circuit may be used where the electrolyte solution flows in
one direction through electrolyte chamber 5 and in the opposite
direction through electrolyte chamber 4. Exemplary electrolytes may
include, but are not limited to, sodium sulfate, potassium nitrate,
or others known to those skilled in the art.
[0086] As scaling constituents are present in the PIW, for example,
calcium carbonate and calcium sulfates, the ion exchange membranes
will accumulate scalants on their surfaces resulting in a decreased
desalination efficiency of the system. Scale build up on the ion
exchange membranes is indicated by an increase in resistance in
electric current 61. Once the resistance has reached a level
indicative of scaling on the ion exchange membranes, as determined
by those skilled in the art of EDR operation, the stack polarity is
switched to operate in reverse mode as shown in FIG. 3. The
polarity of the electric potential 60 is reversed resulting in
anode/cathode electrode 7 becoming the cathode and cathode/anode
electrode 6 becoming the anode. At the same time the hydraulic
reversal procedure described with reference to Table 1 is initiated
such that the PIW and saline water chambers are swapped. In reverse
polarity configuration the PIW flows through S-P inlet conduit 19
into S-P chambers 40 and exits via S-P conduit 21; and saline water
flows through P-S inlet conduit 18 into P-S chambers 30 and exits
via P-S outlet conduit 20. The counter-flow of ions through the ion
exchange membranes 8, 9 in the reverse mode effectively removes
scale build up from the forward operation mode. For a highly
concentrated PIW where application of the electric potential 60 is
not required, reversal mode is initiated by following the hydraulic
reversal procedure described with reference to Table 1 such that
the PIW and saline water chambers are swapped to reverse the flow
of ions through the membranes from the highly concentrated PIW to
the less concentrated saline water. The EDR stack 2 operates
cyclically between the forward and reverse mode to continuously
remove scale build up on the ion exchange membranes 8, 9.
[0087] In an alternative embodiment (not shown) the process may use
alternative means for switching the flow of solutions through S-P
chambers 40 and P-S chambers 30 to the reversal valve arrays 14, 22
as would be known to a person of skill in the art, for example the
gaskets described in WO 2010/115287 (incorporated herein by
reference). Furthermore, alternative embodiments (not shown) may
use an ED stack without reversal technology and the stack may be
cleaned on a regular basis, for example using the cleaning system
described herein, to minimize build up of scalants on the ion
exchange membranes.
[0088] In further alternative embodiments (not shown) the WSRP 1
may include multiple stacks 2 with an electrode positioned at each
end of each stack. Each stack is connected to the manifolding of
the PIW and saline water circuits, thereby beneficially reducing
manifolding requirements whilst increasing product output. The
multiple stack arrangement may comprise a modular apparatus as
disclosed in WO 2012/019282 (incorporated herein by reference).
[0089] The embodiments disclosed herein are directed at
desalinating contaminated waste water from an industrial process,
however in alternative embodiments, the WSRP may be used for
desalinating any contaminated saltwater.
[0090] Alternative embodiments described herein are directed at a
method and plant to desalinate a salt solution and produce a
concentrated discharge solution using a multi-chamber
electrodialysis stack. More specifically, the electrodialysis stack
is internally staged to reduce the concentration factor across any
single membrane and increase the maximum concentration difference
across a single stack. Reducing the concentration factor across ion
exchange membranes in the electrodialysis stack beneficially
reduces concentration gradient polarization resulting in increased
current limit density while also improving current efficiency. The
internally staged stack enables a higher concentration difference
in a more compact stack arrangement than would be possible with
external staging.
[0091] Referring to FIG. 4, there is shown an internally staged
multiple chamber electrodialysis reversal (MC-EDR) plant 101 with
four saltwater solutions P, Dp, Dc, C passing through MC-EDR stack
201 which can be run in forward or reverse polarity. The product
("P") solution 191 is the lowest concentration saltwater, or
desalination product, and P circuit includes manifolding fluidly
coupling the MC-EDR stack 201 with product tank 122; diluent_p
("Dp") solution 192 is weakly concentrated solution and Dp circuit
includes manifolding fluidly coupling the MC-EDR stack 201 with
diluent_p tank 123; diluent_c ("Dc") solution 193 is medium
concentrated solution and Dc circuit includes manifolding fluidly
coupling the MC-EDR stack 201 with diluent_c tank 124; and
concentrate ("C") solution 194 is highly concentrated solution and
C circuit includes manifolding fluidly coupling the MC-EDR stack
201 with concentrate tank 121. The MC-EDR stack 201 is configured
in such a way that product solution 191 flowing through stack 201
decreases in ion concentration by transfer of ions through ion
exchange membranes from product solution 191 through diluent_p
solution 192 and diluent_c solution 193 to the concentrate solution
194. The net result is that the product solution 191 is desalinated
and the concentrate solution 194 is concentrated.
[0092] Upstream saltwater source 195 feeds into product tank 122
through product inlet 102 and product inlet control valve 171 after
passing through an optional pre-treatment stage (not shown).
Exemplar pre-treatment may include, but is not limited to, physical
filters (such as microfiltration or ultrafiltration), dissolved air
filtration, coagulation and sedimentation, media filtration or
other methods known to those skilled in the art. Product solution
191 is stored in product tank 122, which may include an optional
heating element (not shown) to increase the temperature of the
solution and thereby beneficially increase MC-EDR system efficiency
through increased conductivity internal to the MC-EDR stack 201.
Product pump 115 pumps product solution 191 from product tank 122
to P-C inlet valve reversal array 110. The P-C inlet valve reversal
array 110 includes four reversal valves 110a, 110b, 110c, 110d
which can be opened or closed to direct flow of product solution
191 and concentrate solution 194 either to P-C inlet conduit 151 or
C-P inlet conduit 152 depending on whether the MC-EDR stack 201 is
operating in forward or reverse polarity configuration. Table 2
below provides the reversal valve positions for each polarity
configuration.
TABLE-US-00002 TABLE 2 Reversal Valve Positions for MC-EDR Plant
101 Reversal MC-EDR MC-EDR MC-EDR MC-EDR Valve Forward Reverse
Reverse Forward Number Polarity Flush Polarity Flush 110a Open
Closed Closed Open 110b Closed Open Open Closed 110c Closed Open
Open Closed 110d Open Closed Closed Open 111a Closed Open Open
Closed 111b Open Closed Closed Open 111c Open Closed Closed Open
111d Closed Open Open Closed 112a Open Closed Closed Closed 112b
Closed Open Open Open 112c Closed Closed Open Closed 112d Open Open
Closed Open 113a Closed Open Open Open 113b Open Closed Closed
Closed 113c Open Open Closed Open 113d Closed Closed Open
Closed
[0093] In the forward polarity configuration, product solution 191
passes through open reversal valve 110d and enters MC-EDR stack 201
via P-C inlet conduit 151. The product solution 191 passes through
the MC-EDR stack 201 and exits at a lower ion concentration through
P-C outlet conduit 155. Output product solution then enters P-C
outlet valve reversal array 112 and passes through open reversal
valve 112a and into product conduit 105.
[0094] Product concentration sensor 161, which may be a
conductivity sensor, detects the ion concentration level in output
product solution leaving P-C outlet reversal valve array 112.
Product exit control valve 141 and product return control valve 146
can be modulated to either return output product solution to
product tank 122 or remove output product solution from the
process. For example, if the ion concentration of output product
solution measured by product concentration sensor 161 is below a
specified value, product exit control valve 141 opens to allow
discharge of output product solution from the process. As a result,
the level in product tank 122 will drop. Product inlet control
valve 171 will modulate and open to allow addition of source
saltwater 195, which will result in more product to be desalinated,
an increase in the ion concentration of product solution 191 in
product tank 122, and an increase in output ion concentration
measured by product concentration sensor 161. If the ion
concentration of output product solution is above a specified
value, product exit control valve 141 closes while the product
return control valve 146 opens to allow return of output product
solution back to the product tank 122 for further desalination in
order to meet the desired output product ion concentration.
[0095] Upstream saltwater source 196 feeds into diluent_p tank 123
through diluent_p inlet 103 and diluent_p inlet control valve 172
after passing through an optional pre-treatment stage (not shown).
Diluent_p tank 123 may include an optional heating element (not
shown) to increase the temperature of the solution and thereby
beneficially increase MC-EDR system efficiency through increased
conductivity internal to the MC-EDR stack 201. Upstream saltwater
source 196 may be the same source as upstream saltwater source 195,
or it may be a different source. Diluent_p pump 116 pumps diluent_p
solution 192 from diluent_p tank 123 to Dp-Dc inlet reversal valve
array 111. In the forward polarity configuration, diluent_p
solution 192 passes through open reversal valve 111c and into
MC-EDR stack 201 via through Dp-Dc inlet conduit 154. Output
diluent_p solution exits MC-EDR stack 201 at an increased ion
concentration through Dp-Dc outlet conduit 158 into Dp-Dc outlet
valve reversal array 113. Output diluent_p solution passes through
open reversal valve 113b into diluent_p conduit 108 where diluent_p
concentration sensor 163 detects the ion concentration of output
diluent_p solution exiting the Dp-Dc outlet valve reversal array
113. If the measured ion concentration of output diluent_p solution
is above a specified value, diluent_p exit control valve 144 may be
opened slightly and diluent_p return control valve 147 may be
closed slightly to allow output diluent_p solution to be
transferred to the Dc circuit. As a result, the level in diluent_p
tank 123 will drop and the diluent_p inlet control valve 172 will
modulate to allow addition of source saltwater 196. If the measured
ion concentration of output diluent_p solution is below a specified
value, diluent_p exit control valve 144 is closed and diluent_p
return control valve 147 opened so that output diluent_p solution
is returned to diluent_p tank 123 until the desired ion
concentration is reached.
[0096] The diluent_c ("Dc") solution 193 is stored in diluent_c
tank 124, which may include an optional heating element (not shown)
to increase the temperature of the solution, thereby beneficially
increasing MC-EDR system efficiency through increased conductivity
internal to MC-EDR stack 201. Solution enters the Dc circuit
through diluent_p exit control valve 144 as described above.
Diluent_c pump 117 pumps diluent_c solution 193 to Dp-Dc inlet
reversal valve array 111. In the forward polarity configuration
diluent_c solution 193 passes through open reversal valve 111b and
into MC-EDR stack 201 through Dc-Dp inlet conduit 153. Output
diluent_c solution exits MC-EDR stack 201 at a higher ion
concentration and travels through Dc-Dp outlet conduit 157 to Dp-Dc
outlet reversal valve array 113. Output diluent_c solution passes
through open reversal valve 113c into diluent_c conduit 107 where
concentration sensor 164 detects the ion concentration of output
diluent_c solution exiting Dp-Dc outlet reversal valve array 113.
If the measured ion concentration of output diluent_c solution in
diluent_c conduit 107 is above a specified concentration, diluent_c
exit control valve 143 may be opened slightly and diluent_c return
control valve 148 may be opened slightly to allow output diluent_c
solution to enter the C circuit. If the measured concentration of
output diluent_c solution is below a specified concentration,
diluent_c exit control valve 143 is closed and diluent_c return
control valve 148 is opened to allow output diluent_c solution to
return to diluent_c tank 124 for further concentration.
[0097] Concentrate ("C") solution 194 is stored in concentrate tank
121, which may include an optional heating element (not shown) to
increase the temperature of the solution, thereby beneficially
increasing MC-EDR system efficiency through increased conductivity
internal to MC-EDR stack 201. Solution enters the C circuit from
the Dc circuit when diluent_c exit control valve 143 is opened.
Concentrate solution 194 is pumped from concentrate tank 121 by
concentrate pump 114 to P-C inlet valve reversal array 110. In the
forward polarity configuration concentrate solution 194 passes
through open reversal valve 110a and into MC-EDR stack 201 through
C-P inlet conduit 152. Output concentrate solution leaves MC-EDR
stack 201 at a higher ion concentration via C-P outlet conduit 156
and enters P-C outlet reversal valve array 112. Output concentrate
solution passes through open reversal valve 112d into concentrate
conduit 106 where concentration sensor 162 measures the ion
concentration of output concentrate solution exiting P-C outlet
reversal valve array 112. If the measured ion concentration of
output concentrate solution in concentrate conduit 106 is above a
specified concentration, concentrate exit control valve 142 is
opened to allow output concentrate solution to exit the system. If
the measured ion concentration of output concentrate solution in
concentrate conduit 106 is below a specified concentration, then
concentrate exit control valve 142 is closed and concentrate return
control valve 145 is opened to return output concentrate solution
to concentrate tank 121 to be further concentrated.
[0098] A level sensor in diluent_c tank 124 (not shown) measures
the level of diluent_c solution 193 in diluent_c tank 124. Exemplar
level sensors may include float switches, pressure sensors,
ultrasonic level sensors or other appropriate sensors known to
those skilled in the art. When a low level set point is reached,
diluent_p exit control valve 144 is opened slightly and diluent_p
return control valve 147 is closed slightly to allow solution
transfer from the Dp circuit to the Dc circuit. A level sensor in
concentrate tank 121 (not shown) measures the level of concentrate
solution 194 in concentrate tank 121. When a low level set point is
reached, diluent_c exit control valve 143 is opened slightly and
diluent_c return control valve 148 is closed slightly to allow
solution transfer from the Dc circuit to the C circuit.
[0099] If, in theory, saltwater make-up water is added to the C
circuit rather than the Dp circuit (not shown) steady state
operation may be achieved where no saltwater is transferred into or
out of the Dp circuit and Dc circuit as only ions are transferred
from product solution 191 through the ion exchange membranes to the
diluent_p solution 192, and then again through ion exchange
membranes to the diluent_c solution 193. In practice however, some
water is transferred through the ion exchange membranes either due
to osmotic, electro-osmotic, or leakage effects. As a result, it is
beneficial to include the diluent_p exit control valve 144 and
diluent_c exit control valve 143 to allow control of solution
levels. In addition, it is beneficial to add the saltwater source
solution to the lower concentration circuits such that a low
concentration factor across each circuit may be maintained and
concentration polarization and current efficiency losses are
minimized. The above described control system provides utility to
maintain low concentration factors across each circuit, maintain
circuit concentrations, maintain tank levels, and ultimately
operate an efficient system that can produce a high concentration
discharge in a non-attended (automated) manner.
[0100] Electrolyte 197 is stored in electrolyte tank 125 to
complete the electrical circuit within the MC-EDR stack 201. The
electrolyte 197 is circulated in a closed loop by electrolyte pump
118. A closed loop parallel circuit is illustrated in FIG. 4, where
electrolyte 197 flows along both ends of the MC-EDR stack 201 in
the same direction as all the saltwater solutions 191, 192, 193,
194; however, a person of skill in the art would understood that a
closed loop series circuit is also possible, where electrolyte 197
flows in the same direction as the saltwater solutions 191, 192,
193, 194 on one side of the MC-EDR stack 201 and in the opposite
direction to saltwater solution flow on the other side of the
MC-EDR stack 201. Exemplary electrolytes may include sodium
sulfate, potassium nitrate, or others known to those skilled in the
art.
[0101] FIG. 5 shows the MC-EDR stack 201 operating in forward
polarity. Product solution 191 flows into P/C chambers 210 through
P-C inlet conduit 151 and exits via P-C outlet conduit 155.
Diluent_p solution 192 flows into Dp/Dc chambers 211 through Dp-Dc
inlet conduit 154 and exits via Dp-Dc outlet conduit 158. Diluent_c
solution 193 flows into Dc/Dp chambers 212 through Dc-Dp inlet
conduit 153 and exits via Dc-Dp outlet conduit 157. Concentrate
solution 194 flows into C/P chambers 213 through C-P inlet conduit
152 and exits via C-P outlet conduit 156. P/C chambers 210, Dp/Dc
chamber 211, Dc/Dp chamber 212, and C/P chamber 213 are separated
by ion exchange membranes. There are two types of ion exchange
membranes in the MC-EDR stack 201 arranged in a unique sequence:
(1) anion exchange membrane 220 which transfer negative ions
(anions) and reject positive ions (cations); and (2) cation
exchange membrane 221 which transfer cations and reject anions.
Exemplar anion exchange membranes include Neosepta AM-1, AFN, AMX;
Ralex AMH-PES; Fumasep FAD; and Selemion DVS, APS membranes.
Exemplary cation exchange membranes include Neosepta CMX, CM-1;
Ralex CMH-PES; Fumasep FKE, FKD; and Selemion CMV membranes.
[0102] In known EDR stacks, such as the stack described in WO
2010/115287, anion and cation exchange membranes alternate
throughout the stack so that each chamber has a cation exchange
membrane on one side and an anion exchange membrane on the opposite
side of the chamber. In this arrangement cations and anions only
transfer from one chamber into an adjacent chamber and not across
multiple chambers. In the MC-EDR stack 201 shown in FIG. 5, one
side of P/C chamber 210 has three adjacently aligned cation
exchange membranes 221 and the other side of P/C chamber 210 has
three adjacently aligned anion exchange membranes 220. This results
in each of the Dc/Dp chambers 211 and the Dc/Dp chambers 212 having
a cation exchange membrane 221 on both sides of the chamber or an
anion exchange membrane 220 on both sides of the chamber, whereas
the P/C chambers 210 and the C/P chambers 213 each have a cation
exchange membrane 221 on one side and an anion exchange membrane
220 on the opposite side of the chamber. This allows transfer of
anions and cations across multiple chambers from the P/C chambers
210 to the C/P chambers 213 as is described in more detail
below.
[0103] On each end of the MC-EDR stack 201 are electrolyte
chambers: electrolyte chamber 214 on the cathode side; and
electrolyte chamber 215 on the anode side. Electrolyte solution 197
is stored in electrolyte tank 125 and pumped by electrolyte pump
118 through electrolyte inlet conduit 206 into electrolyte chamber
214 and exits electrolyte chamber 215 through electrolyte exit
conduit 245 in a closed loop. The closed loop electrolyte circuit
illustrated in FIG. 5 is a series arraignment; however, a parallel
closed loop circuit is also possible as shown in FIG. 4.
[0104] A direct current power source 235 is applied to the MC-EDR
stack 201 to provide a DC voltage and current at the cathode/anode
electrode 231 and anode/cathode electrode 232. Changing the
polarity of the DC power supply changes whether each electrode is
operating as a cathode or anode. Reduction and oxidation of
reactions of the electrolyte occur at the cathode and anode
respectively, converting the DC electrical current into an ionic
current. In the illustrated forward polarity configuration shown in
FIG. 5, cathode/anode electrode 231 operates as the cathode, and
anode/cathode electrode 232 acts as the anode. Exemplar applied
voltages may range from 0.5V to 2.5V per chamber pair in order to
drive ions across ion exchange membranes, while avoiding problems
associated with water splitting at higher voltages. Those skilled
in the art will be able to measure the current limit density of a
particular MC-EDR stack 201 under its operating concentrations and
temperatures, and then set the applied voltage to operate at the
most economic current limit density on a basis of combined capital
and operating costs. In an alternative embodiment (not shown), a
drive cell, such as the drive cell disclosed in WO 2010/115287 or
WO 2009/155683 may be used for application of a voltage across the
chambers.
[0105] The combined DC voltage and ionic current force ions across
the ion exchange membranes in the arrangement shown in FIG. 5 as
follows: [0106] cations and anions are transferred from the P/C
chamber 210 to the Dp/Dc chambers 211 on either side of the P/C
chamber 210 effecting desalination of product solution 191; and
[0107] cations and anions are transferred from the Dp/Dc chambers
211 to the Dc/Dp chambers 212, then from the Dc/Dp chambers 212 to
the C/P chamber 213.
[0108] The net effect is transfer of anions from the P/C chamber
210 across the Dp/Dc and Dc/Dp chambers 211, 212 to the C/P chamber
213 and transfer of cations from the P/C chamber 210 across the
Dp/Dc and Dc/Dp chambers 211, 212 to the C/P chamber 213. This
arrangement prevents a build-up of ions in the Dp circuit and Dc
circuit and beneficially enables a lower concentration factor
across each membrane than would be possible in a two chamber EDR
where ions are transferred directly from the P/C chamber 210 to the
C/P chamber 213.
[0109] FIG. 5 consists of two complete MC-EDR cells: cell 260 and
cell 261. Each cell 260 and cell 261 consists of one P/C chamber
210, two Dp/Dc chambers 211, two Dc/Dp chambers 212, and one C/P
chamber 213. Alternative embodiments (not shown) have more than two
MC-EDR cells together within a single stack in order to reduce the
overall footprint and increase production. It is desirable not to
have a P/C chamber 210 or C/P chamber 213 placed beside an
electrolyte chamber 214, 215. An extra Dp/Dc chamber 211 or Dc/Dp
chamber 212 may be placed on either side of cell 261 or cell 262 to
avoid placing a P/C chamber 210 or C/P chamber 213 next to an
electrolyte cell.
[0110] As scaling constituents are present in the feed solutions,
e.g., calcium carbonate and calcium sulfates, the MC-EDR ion
exchange membranes will accumulate scalants on their surfaces
resulting in a decreased desalination efficiency of the system.
Scale build up on the ion exchange membranes is indicated by an
increase in resistance, which can be measured as either decreased
current in constant voltage operating mode or increased voltage in
constant current operating mode. Once the resistance has reached a
level indicative of scaling on the ion exchange membranes, the
stack will be switched to operate in the reverse mode as depicted
in FIG. 6.
[0111] Referring now to FIG. 6 there is shown the MC-EDR stack 201
in reverse polarity wherein the direct current power source 235
polarity is reversed resulting in cathode/anode electrode 231
becoming the anode, and anode/cathode electrode 232 becoming the
cathode. The polarity of the voltage applied to the stack and the
direction of the ionic current are reversed, thereby resulting in a
change in ion transfer direction through each membrane, thereby
desalinating the ion exchange membranes.
[0112] In order to maintain production of desalinated water when
ion transfer has changed direction, the saltwater internal to each
chamber must also be changed for the reverse polarity
configuration. Concentrate solution 194 is pumped from concentrate
tank 121 through open reversal valve 110b and into P/C chambers 210
through P-C inlet conduit 151. Output concentrate solution exits
P/C chambers 210 via P-C outlet conduit 155 and passes through open
reversal valve 112b into concentrate conduit 106. Product solution
191 is pumped from product tank 122 through open reversal valve
110c and into C/P chambers 213 through C-P inlet conduit 152.
Output product solution exits C/P chambers 213 via C-P outlet
conduit 156 and passes through open reversal valve 112c into
product conduit 105. Diluent_p solution 192 is pumped from
diluent_p tank 123 through open reversal valve 111d and into Dc/Dp
chambers 212 through Dc-Dp inlet conduit 153. Output diluent_p
solution exits Dc/Dp chambers 212 via Dc-Dp outlet conduit 157 and
passes through open reversal valve 113d into diluent_p conduit 108.
Diluent_c solution 193 is pumped from diluent_c tank 124 through
open reversal valve 111a and into Dp/Dc chambers 211 through Dp/Dc
inlet conduit 154. Output diluent_c solution exits Dp/Dc chambers
211 via Dp/Dc outlet conduit 158 and passes through open reversal
valve 113a into diluent_c conduit 107. Flow direction is not
reversed in the disclosed embodiment; however, it is possible to
reverse flow in reverse polarity operation to back flush the MC-EDR
201 stack for enhanced scalant removal.
[0113] The combined DC voltage and ionic current force ions across
the ion exchange membranes in the arrangement shown in FIG. 6 as
follows: [0114] cations and anions are transferred from the C/P
chamber 213 to the Dc/Dp chambers 212 on either side of C/P chamber
213 effecting desalination of product solution 191; and [0115]
cations and anions are transferred from the Dc/Dp chambers 212 to
the Dp/Dc chambers 211, then from the Dp/Dc chambers 211 to the P/C
chamber 210.
[0116] The net effect is transfer of anions from the C/P chamber
213 across the Dc/Dp chambers 212 and the Dp/Dc chambers 211 to the
P/C chamber 210 and transfer of cations from the C/P chamber 213
across the Dc/Dp chambers 212 and the Dp/Dc chambers 211 to the P/C
chamber 210.
[0117] Directly after the polarity is switched to operate in the
reverse polarity configuration, there will be a short period where
concentrate solution 194 from operation in the forward polarity
configuration remains in the pipework which is now associated with
the P circuit. In order to prevent the concentrate solution 194
from entering the product tank 122, the reversal valves of P-C
outlet reversal valve array 112 operate a MC-EDR reverse flush mode
for a period of time, for example 1 minute, before switching to
MC-EDR reverse polarity mode. As shown in Table 2, in MC-EDR
reverse flush mode reversal valve 112c remains closed and reversal
valve 112d remains open to direct a slug of mixed concentrate and
product solution to the concentrate conduit 106. After a period of
time all remaining concentrate solution 194 should have been
flushed from the system and the reversal valves can now switch to
the MC-EDR reverse polarity mode. Conversely, when the polarity
switches from reverse configuration to forward configuration the
reversal valves of P-C outlet reversal valve array 112 operate in
MC-EDR forward flush mode for a period of time, for example 1
minute, before switching to MC-EDR forward polarity mode. In MC-EDR
forward flush mode reversal valve 112a remains closed and reversal
valve 112b remains open to direct a slug of mixed concentrate and
product solution to the concentrate conduit 106.
[0118] In an alternative embodiment, a conductivity sensor (not
shown) in P-C outlet conduit 155 and C-P outlet conduit 156 may be
used to detect the conductivity of the solution exiting the MC-EDR
stack 201 and the reversal valves of P-C outlet reversal valve
array 112 may be switched to operate in either MC-EDR forward
polarity or MC-EDR reverse polarity once a threshold low salinity
conductivity is detected indicating that the P circuit has been
sufficiently flushed of concentrate solution 194.
[0119] The reversal valves of Dp-Dc outlet reversal valve array 113
may also operate a MC-EDR reverse flush mode and MC-EDR forward
flush mode as indicated in Table 2, however the concentration
difference between the diluent_p solution 192 and the diluent_c
solution 193 may be low enough to negate the need to employ the
MC-EDR reverse flush mode and MC-EDR forward flush mode for the
Dp-Dc outlet reversal valve array 113.
[0120] FIGS. 7 through 9 show an alternative embodiment of an
internally staged multiple chamber electrodialysis reversal
(MC-EDR) plant 401. The primary difference with the MC-EDR plant
101 and MC-EDR plant 401 relates to the internal configuration of
the MC-EDR stack 201 and 501 respectively. Specifically, in MC-EDR
stack 201 Dp/Dc chambers 211 and Dc/Dp chambers 212 are bounded on
both sides by either an anion or cation exchange membrane. In the
MC-EDR stack 501 most of the chambers are bounded by an anion
exchange membrane on one side and a cation exchange membrane on the
other side, however some of the chambers have an anion exchange
membrane on both sides of the chamber or a cation exchange membrane
on both sides of the chamber. When MC-EDR stack 501 is operated in
reverse polarity, its efficiency is slightly diminished relative to
MC-EDR stack 201 since one of the product chambers is next to a
diluent_c chamber resulting in a higher concentration factor across
the chambers and that one product chamber does not desalinate but
instead acts as an ion transfer chamber, however the effect is
almost negligible. Further details are described below.
[0121] Referring to FIG. 7, upstream saltwater source 495 feeds
into product tank 422 through product inlet 402 and product inlet
control valve 471 after passing through an optional pre-treatment
stage (not shown). Exemplar pre-treatment may include, but is not
limited to, physical filters, such as microfiltration or
ultrafiltration, or dissolved air filtration, coagulation and
sedimentation, or media filtration or other methods known to those
skilled in the art. Product solution 491 is stored in product tank
422, which may include an optional heating element (not shown) to
increase the temperature of the solution and beneficially increase
MC-EDR system efficiency through increased conductivity internal to
MC-EDR stack 501. Product pump 415 pumps product solution 491 from
product tank 422 to P-Dp inlet valve reversal array 410. In the
forward polarity configuration product solution 491 passes through
open reversal valve 410d (see Table 3) and enters MC-EDR stack 501
via P-Dp inlet conduit 451. Output product solution exits MC-EDR
stack 501 at a lower ion concentration through P-Dp outlet conduit
455 and passes into P-Dp outlet valve reversal array 412. In the
forward polarity configuration, product solution passes through
open reversal valve 412a (see Table 3) into product conduit
405.
TABLE-US-00003 TABLE 3 Reversal Valve Positions for MC-EDR plant
401 Reversal MC-EDR MC-EDR Valve Forward Reverse Number Polarity
Polarity 410a Open Closed 410b Closed Open 410c Closed Open 410d
Open Closed 411a Closed Open 411b Open Closed 411c Open Closed 411d
Closed Open 412a Open Closed 412b Closed Open 412c Closed Open 412d
Open Closed 413a Closed Open 413b Open Closed 413c Open Closed 413d
Closed Open
[0122] Product concentration sensor 461 detects the ion
concentration level in output product solution leaving P-Dp outlet
reversal valve array 412. Exemplar concentration sensors 461-464
may include, but are not limited to, conductivity sensors. Product
exit control valve 441 and product return control valve 446 can be
modulated to either return output product solution to product tank
422 or remove output product solution from the process. If the ion
concentration of output product solution is below a specified value
measured by product concentration sensor 461, product exit control
valve 441 opens to allow discharge of output product solution. As a
result, the level in product tank 422 will drop. Product tank level
control valve 471 will modulate and open to allow addition of
source saltwater 495, which will allow for more product to be
desalinated, will increase the concentration of product solution
491 in product tank 422, and increase output concentration measured
by product concentration sensor 461. If the ion concentration of
output product solution is above a specified value, product exit
control valve 441 closes while the product return control valve 446
opens to allow return of output product solution to the product
tank 422 for further desalination in order to meet the desired
outlet specified ion concentration.
[0123] Upstream saltwater source 496 enters diluent_p tank 421 via
diluent_p inlet conduit 403 and diluent_p inlet control valve 472,
after passing through an optional pre-treatment process (not
shown). Diluent_p tank 421 may include an optional heating element
(not shown) to increase the temperature of the solution to
beneficially increase MC-EDR system efficiency through increased
conductivity internal to MC-EDR stack 501. Upstream saltwater
source 496 may be the same source as upstream saltwater source 495,
or it may be a different source. Diluent_p pump 414 pumps diluent_p
solution 492 from diluent_p tank 421 to P-Dp inlet reversal valve
array 410. In the forward polarity configuration, diluent_p
solution 492 passes through open reversal valve 410a and into
MC-EDR stack 501 via Dp-P inlet conduit 452. Output diluent_p
solution exits MC-EDR stack 501 at an increased ion concentration
through Dp-P outlet conduit 456 into P-Dp outlet valve reversal
array 412. Output diluent_p solution passes through open reversal
valve 412d into diluent_p conduit 406 where diluent_p concentration
sensor 462 detects the ion concentration of output diluent_p
solution exiting the P-Dp outlet valve reversal array 412. If the
measured ion concentration of output diluent_p solution is above a
specified value, diluent_p exit control valve 443 may be opened
slightly and diluent_p return control valve 445 may be closed
slightly to allow output diluent_p solution to be transferred to
the Dc circuit. As a result, the level in diluent_p tank 421 will
drop and the diluent_p inlet control valve 472 will modulate to
allow addition of source saltwater 496. If the measured ion
concentration of output diluent_p solution is below a specified
value, diluent_p exit control valve 443 is closed and diluent_p
return control valve 445 is opened so that output diluent_p
solution is returned to diluent_p tank 421 until the desired ion
concentration is reached.
[0124] Diluent_c solution 493 is stored in diluent_c tank 424,
which may include an optional heating element (not shown) to
increase the temperature of the solution, thereby beneficially
increasing MC-EDR system efficiency through increased conductivity
internal to MC-EDR stack 501. Solution enters the Dc circuit
through diluent_p exit control valve 443 as described above.
Diluent_c pump 417 pumps diluent_c solution 493 to Dc-C inlet
reversal valve array 411. In the forward polarity configuration
diluent_c solution 493 passes through open reversal valve 411b and
into MC-EDR stack 501 through Dc-C inlet conduit 453. Output
diluent_c solution exits MC-EDR stack 501 at a higher ion
concentration and travels through Dc-C outlet conduit 457 to Dc-C
outlet reversal valve array 413. Output diluent_c solution passes
through open reversal valve 413c into diluent_c conduit 407 where
concentration sensor 464 detects the ion concentration of output
diluent_c solution exiting Dc-C outlet reversal valve array 413. If
the measured ion concentration of output diluent_c solution in
diluent_c conduit 407 is above a specified concentration, diluent_c
exit control valve 444 may be opened slightly and diluent_c return
control valve 448 may be closed slightly to allow output diluent_c
solution to enter the C circuit. If the measured concentration of
output diluent_c solution is below a specified concentration,
diluent_c exit control valve 444 is closed and diluent_c return
control valve 448 is opened to allow output diluent_c solution to
return to diluent_c tank 424 for further concentration.
[0125] Concentrate solution 494 is stored in concentrate tank 423,
which may include an optional heating element (not shown) to
increase the temperature of the solution, thereby beneficially
increasing MC-EDR system efficiency through increased conductivity
internal to MC-EDR stack 501. Solution enters the C circuit from
the Dc circuit when diluent_c exit control valve 444 is opened.
Concentrate solution 494 is pumped from concentrate tank 423 by
concentrate pump 416 to Dc-C inlet reversal valve array 411. In the
forward polarity configuration concentrate solution 494 passes
through open reversal valve 411c and into MC-EDR stack 501 through
C-Dc inlet conduit 454. Output concentrate solution leaves MC-EDR
stack 501 at a higher ion concentration via C-Dc outlet conduit 458
and enters Dc-C outlet reversal valve array 413. Output concentrate
solution passes through open reversal valve 413b into concentrate
conduit 408 where concentration sensor 463 measures the ion
concentration of output concentrate solution exiting Dc-C outlet
reversal valve array 413. If the measured ion concentration of
output concentrate solution in concentrate conduit 408 is above a
specified concentration, concentrate exit control valve 442 is
opened to allow output concentrate solution to exit the system. If
the measured ion concentration of output concentrate solution in
concentrate conduit 408 is below a specified concentration, then
concentrate exit control valve 442 is closed and concentrate return
control valve 447 is opened to return output concentrate solution
to concentrate tank 423 to be further concentrated.
[0126] A level sensor in diluent_c tank 424 (not shown) measures
the level of diluent_c solution 493 in diluent_c tank 424. Exemplar
level sensors may include float switches, pressure sensors,
ultrasonic level sensors or other appropriate sensors known to
those skilled in the art. When a low level set point is reached,
diluent_p exit control valve 443 is opened slightly and diluent_p
return control valve 445 is closed slightly to allow solution
transfer from the Dp circuit to the Dc circuit. A level sensor in
concentrate tank 423 (not shown) measures the level of concentrate
solution 494 in concentrate tank 423. When a low level set point is
reached, diluent_c exit control valve 444 is opened slightly and
diluent_c return control valve 448 is closed slightly to allow
solution transfer from the Dc circuit to the C circuit.
[0127] Electrolyte 497 is stored in electrolyte tank 425 to
complete the electrical circuit within the MC-EDR stack 501. The
electrolyte 497 is circulated in a closed loop by electrolyte pump
418. A closed loop parallel circuit is illustrated in FIG. 7, where
electrolyte 497 flows along both ends of the MC-EDR stack 501 in
the same direction as all the saltwater solutions 491, 492, 493,
494; however, a person of skill in the art would understood that a
closed loop series circuit is also possible, where electrolyte 497
flows in the same direction as the saltwater solutions 491, 492,
493, 494 on one side of the MC-EDR stack 501 and in the opposite
direction to saltwater solution flow on the other side of the
MC-EDR stack 501. Exemplary electrolytes may include sodium
sulfate, potassium nitrate, or others known to those skilled in the
art.
[0128] FIG. 8 shows the MC-EDR stack 501 of FIG. 7 operating in
forward polarity, where the product solution 491 flows into P/Dp
chambers 510 through P-Dp inlet conduit 451 and exits via P-DP
outlet conduit 455; diluent_p solution 492 flows into Dp/P chambers
511 through Dp-P inlet conduit 452 and exits via Dp-P outlet
conduit 456; diluent_c solution 493 flows into Dc/C chambers 512
through Dc-C inlet conduit 453 and exits via Dc-C outlet conduit
457; and concentrate solution 494 flows into C/Dc chambers 513
through C-Dc inlet conduit 454 and exits via C/Dc outlet conduit
458. P/Dp chambers 510, Dp/P chamber 511, Dc/C chamber 512, and
C/Dc chamber 513 are separated by anion exchange membranes 520 and
cation exchange membrane 521 arranged in a specific sequence with
adjacently aligned anion exchange membranes and adjacently aligned
cation exchange membranes to respectively allow transfer of anions
and cations across multiple chambers as described below in more
detail. Exemplar anion exchange membranes include Neosepta AM-1,
AFN, AMX; Ralex AMH-PES; Fumasep FAD; and Selemion DVS, APS
membranes. Exemplary cation exchange membranes include Neosepta
CMX, CM-1; Ralex CMH-PES; Fumasep FKE, FKD; and Selemion CMV
membranes.
[0129] On each end of the MC-EDR stack 501 are electrolyte
chambers, where electrolyte chamber 515 is on the cathode side, and
electrolyte chamber 514 is on the anode side. Electrolyte solution
497 stored in electrolyte tank 425 is pumped by electrolyte pump
418 through electrolyte inlet conduit 506 into electrolyte chamber
514, through electrolyte chamber 515 and exits via electrolyte exit
conduit 545 in a closed loop. The closed loop electrolyte circuit
illustrated in FIG. 8 is a series arraignment; however, a person of
skill in the art would understand that a parallel closed loop
circuit is also possible as shown in FIG. 7.
[0130] A direct current power source 535 is applied to the MC-EDR
stack 501 to provide a DC voltage and current at the anode/cathode
electrode 531 and cathode/anode electrode 532. Changing the
polarity of the DC power supply changes whether each electrode is
operating as a cathode or anode. Reduction and oxidation of
reactions of the electrolyte occur at the cathode and anode
respectively, converting the DC electrical current into an ionic
current. In the illustrated forward polarity configuration of FIG.
8, anode/cathode electrode 531 operates as the anode, and
cathode/anode electrode 532 acts as the cathode. Exemplar applied
voltages may range from 0.5V to 2.5V per chamber pair in order to
drive ions across ion exchange membranes, while avoiding problems
associated with water splitting at higher voltages. Those skilled
in the art will measure the current limit density of a particular
MC-EDR stack 501 under its operating concentrations and
temperatures, and then set the applied voltage to operate at the
most economic current limit density on a basis of combined capital
and operating costs. In an alternative embodiment (not shown), a
drive cell, such as the drive cell disclosed in WO 2010/115287 or
WO 2009/155683 may be used for application of a voltage across the
chambers.
[0131] The combined DC voltage and ionic current force ions across
the ion exchange membranes in the arrangement shown in FIG. 8 as
follows: [0132] anions and cations are transferred from the P/Dp
chambers 510 to the Dp/P chambers 511, and anions are transferred
from the P/Dp chamber 510 to the Dc/C chamber 512 effecting
desalination of product solution 491; [0133] cations are
transferred from the Dp/P chambers 511 to the C/Dc chambers 513,
and cations and anions are transfers from the Dc/C chambers 512 to
the C/Dc chambers 513.
[0134] This arrangement prevents a build-up of ions in the Dp
circuit and Dc circuit and beneficially enables a lower
concentration factor across each membrane than would be possible in
a two chamber EDR where ions are transferred directly from the
product solution 491 to concentrate solution 494.
[0135] FIG. 8 shows two complete MC-EDR cells 563, each consisting
of two P/Dp cells 561 and two C/Dc cells 562. It is possible to
arrange more P/Dp cells 561 and C/Dc cells 562 within a single
MC-EDR cell 563 as well as more MC-EDR cells 563 within a single
stack.
[0136] Referring now to FIG. 9, which shows MC-EDR stack 501 in
reverse polarity wherein the ions are transferred through the ion
exchange membranes in a direction opposite to the direction in the
forward polarity configuration shown in FIG. 8 to descale the ion
exchange membranes. The direct current power source 535 polarity is
reversed resulting in anode/cathode electrode 531 becoming the
cathode, and cathode/anode electrode 532 becoming the anode.
[0137] In order to maintain production of desalinated water when
ion transfer has changed direction, the saltwater internal to each
chamber must also be changed. In the reverse polarity configuration
shown in FIG. 9, concentrate solution 494 enters Dc/C chambers 512
via Dc/C inlet conduit 453 and exits via Dc/C outlet conduit 457;
product solution 491 enters Dp/P chambers 511 via Dp/P inlet
conduit 452 and exits via Dp/P outlet conduit 456; diluent_p
solution 492 enters P/Dp chambers 510 via P/Dp inlet conduit 451
and exits via P/Dp exit conduit 455; and diluent_c solution 493
enters C/Dc chambers 513 via C/Dc inlet conduit 454 and exits via
C/Dc exit conduit 458. Flow direction is not reversed in the
disclosed embodiment; however, it is possible to reverse flow in
reverse polarity operation to back flush the MC-EDR stack 501 for
enhanced scalant removal.
[0138] The combined DC voltage and ionic current force ions across
the ion exchange membranes in the arrangement shown in FIG. 9 as
follows: [0139] anions and cations are transferred from the Dp/P
chambers 511 to the P/Dp chambers 510, effecting desalination of
product solution 491; and [0140] cations and anions are transfers
from the C/Dc chambers 513 to the Dc/C chambers 512.
[0141] In reverse polarity operation the end chambers along each
MC-EDR cell 563 may not be completely desalinated due to cation
transfer into the product solution 491 stream. Beneficially
multiple P/Dp cells 561 and C/Dc cells 562 may be combined in a
single MC-EDR cell 563 to reduce desalination potential along cell
boundaries.
[0142] The above embodiments describe four chamber MC-EDR stacks
201, 501 and plant arrangement 101, 401. In an alternative
embodiment (not shown) a four chamber MC-EDR stack could be
configured with diluent_p and diluent_c chambers fed from a common
and single diluent tank and circuit. For example, diluent_p tanks
and process pipework can be removed and diluent_c tank and process
pipework used to feed the diluent_p chambers and diluent_c chambers
in the MC-EDR stack. This will beneficially reduce balance of plant
hardware and costs. In alternative embodiments (not shown) the
MC-EDR stack and process plant may be expanded to include
additional saltwater circuits and stack chambers, for example six,
or eight, each at an increasing concentration thus reducing the
concentration factor across any single membrane.
[0143] In alternative embodiments (not shown) the MC-EDR plant 101,
401 may use alternative means as would be known to a person of
skill in the art for switching the flow of solutions through the
chambers of the MC-EDR stack 201, 501 rather than the reversal
valve arrays described herein, for example the gaskets described in
WO 2010/115287. Furthermore, alternative embodiments (not shown)
may use a multi-chamber ED (MC-ED) stack without reversal
technology and the stack may be cleaned on a regular basis, for
example using the cleaning system described herein, to minimize
build up of scalants on the ion exchange membranes.
[0144] In further alternative embodiments (not shown) the MC-EDR
plant 101, 401 may include multiple stacks 201, 501 with an
electrode positioned at either end of each stack. Each stack is
connected to the manifolding of the P, Dp, Dc and C circuits,
thereby beneficially reducing manifolding requirements whilst
increasing product output. The multiple stacks may be compressively
coupled and may comprise a modular apparatus as disclosed in WO
2012/019282 (incorporated herein by reference).
[0145] The MC-EDR system described herein may be used for processes
that benefit from EDR, for example the two stage desalination
process described below.
[0146] Alternative embodiments described herein are generally
directed at a two stage desalination plant and method of operating
the plant that achieves the benefits of increased recovery on hard
saltwater without the need for chemical input. The plant consists
of a first stage electrodialysis (ED) system followed by a second
stage desalination system. Exemplar second stage desalination
systems include, but are not limited to, reverse osmosis (RO),
multistage flash (MSF), multiple effect (MED) and membrane
distillation (MD). Recovery from these second stage desalination
systems is generally limited by scaling ions such as calcium,
magnesium, or sulfates. The first stage ED system uses ion exchange
membranes that have a high transference for divalent ions commonly
associated with inorganic scaling such as calcium, magnesium, and
sulfates. The result is that the first stage ED will preferentially
transport said scaling ions from the feed water of the second stage
desalination systems to its concentrated reject. This enables the
second stage desalination system to operate at a higher recovery
and produce more desalinated product water.
[0147] Electrolyte chambers of an ED stack can be bound with anion
exchange membranes to prevent scaling cations passing into the
electrolyte chambers when for example sodium chloride is used as an
electrolyte, however it is less practical to use sodium chloride
which is dangerous to handle since chlorine gas can be produced.
Other exemplar electrolytes include aqueous sodium sulfate or
sodium nitrate, with aqueous sodium sulfate being the most common
ED electrolyte due to its low toxicity. However, since a cation
exchange membrane is positioned next to the electrolyte chamber in
conventional ED units that use sodium sulfate, cations can enter
the electrolyte chamber. As a result, calcium and other scaling
cations can enter the electrolyte chambers. If the pH of the
electrolyte is basic, calcium sulfate can form and detrimentally
precipitate thus fouling the electrodes or adjacent membranes.
Electrolyte pH may fluctuate and become basic during operation.
Traditionally, ED operators have to acidified their electrolyte to
prevent calcium sulfate precipitation, and then eventually replace
the electrolyte to prevent calcium accumulation.
[0148] In an embodiment disclosed herein an ED stack includes an
extra set of chambers, referred to as "rinse" chambers, over and
above the two chambers of conventional EDR or ED stacks, or the
multiple chambers of the MC-EDR or MC-ED disclosed herein. These
"rinse" chambers prevent scaling cations, such as calcium and
magnesium, from passing into the electrolyte, thereby beneficially
reducing the risk of precipitation and scaling in the electrolyte
chambers.
[0149] Referring to FIG. 10 there is shown a two stage desalination
plant 70a. Feed saltwater 71 to be desalinated passes through
pre-treatment system 72, which removes exemplar suspended solids
and organics. Exemplar pre-treatment systems may include, but are
not limited to, a combination of coagulation, clarification,
flotation, media filtration, ultraviolet, electro-coagulation,
microfiltration and/or ultrafiltration. Pre-treated saltwater 73
passes to a electrodyalisis reversal-rinse (EDR-R) stack 601. The
pre-treated saltwater 73 is optionally mixed with concentrate
recirculation 80 to become EDR-R product feed 75a. EDR-R product
feed 75a is partially desalinated in EDR-R stack 601. Operation of
the EDR-R stack 601 will be described in greater detail below with
reference to FIGS. 12 and 13.
[0150] EDR-R product output 75b, which has a reduced salinity
relative to EDR-R product feed 75a, is passed to a second stage
desalination system 76. Exemplar second stage desalination system
76 could include, but are not limited to, RO, MED, MSF, and/or MD.
The second stage desalination system 76 produces desalinated
product 78 and desalination system concentrate 77. Second stage
desalination system concentrate 77 becomes EDR-R concentrate feed
79a and concentrate recirculation 80. EDR-R concentrate feed 79a
and EDR-R product feed 75a are passed through EDR-R stack 601,
where they are separated by ion exchange membranes that allow ionic
communication but not fluid communication.
[0151] The EDR-R stack 601 produces EDR-R concentrated output 79b,
which is higher in salinity and preferably higher in hard scaling
ions than the EDR-R concentrate feed 79a. The beneficial result is
that hard scaling ions are substantially removed from the EDR-R
product output 75b, which becomes the second stage desalination
system feed, enabling higher recovery operation of the second stage
desalination system 76. In essence, hard scaling ions are bypassed
around the second stage desalination system 76. The EDR-R
concentrated output 79b is discharged from the two stage
desalination plant 70a. The overall result is beneficially higher
plant recovery, lower volume waste discharge, and reduced risk of
scaling mass or heat transfer surfaces in the second stage
desalination system 76 than would otherwise be possible without the
presence of the EDR-R stack 601.
[0152] FIG. 11 shows another embodiment of the two stage
desalination plant 70b, which is similar to the plant 70a shown
FIG. 10 and has like parts designated with like reference numerals.
Plant 70b differs from plant 70a in that both the EDR-R product
feed 75a and concentrate feed 79a come from the desalination system
concentrate 77. The EDR-R product output 75b is recycled to the
front end of the second stage desalination system 76 by mixing with
the pre-treated saltwater 73 to produce second stage desalination
system feed 82. The EDR-R stack 601 reduces the salinity and
removes scaling ions from the second stage desalination system
concentrate 77, which after mixing with pre-treated saltwater 73
can result in reduced salinity and scaling potential of the second
stage desalination plant feed 82. This embodiment also enables
higher recovery on scaling saltwater sources.
[0153] Whilst the two stage desalination plant 70a, 70b has been
described utilizing an EDR-R stack 601, in alternative embodiments
a conventional ED or EDR stack or an internally staged MC-ED,
MC-EDR or MC-EDR-R stack as described herein may be employed. The
MC-ED, MC-EDR and MC-EDR-R stacks enables operation at a higher
concentration between the product feed and concentrate feed,
thereby enabling a higher plant recovery over a two chamber ED, EDR
or EDR-R system.
[0154] Referring now to FIGS. 12 and 13, there is shown an EDR-R
stack 601 operating in forward polarity and reverse polarity
respectively, which may be beneficial for operation on hard waters.
The EDR-R stack 601 may be built from gasket spacers, cation
exchange membranes 620 and anion exchange membranes 621 pressed
between end plates with electrodes at either end. Construction of
exemplar EDR stacks is described in detail in Canadian Patent
Publication 2,748,567 (which is incorporated herein by
reference).
[0155] EDR-R stack 601 transfers salt ions out of the EDR-R product
feed and into the EDR-R concentrate feed under the application of a
galvanic potential, for example a voltage or under the action of
concentration difference energy as described in Canadian Patent
2,649,873 (which is incorporated herein by reference). Ion exchange
membranes that have a high transference for scaling salt ions such
as calcium, magnesium and sulfates may be preferred on water
sources high in said constituents. The increased transference
results from a combination of the ions' stronger charge, for
example two plus rather than one plus, and still relatively small
molecular weight making them more mobile for electrochemical
movement within a membrane structure.
[0156] In the forward polarity operation shown in FIG. 12, product
feed ("P") flows into the EDR-R stack 601 through P-Dp conduit 605
and into P/Dp chambers 611. Concentrate feed ("Dp") flows into the
EDR-R stack 601 through Dp-P conduit 603 and into Dp/P chambers
610. P/Dp chambers 611, and Dp/P chamber 610 are separated by
alternating cation exchange membranes 620 and anion exchange
membranes 621, hereinafter collectively referred to as ion exchange
membranes, which respectively transfer cations and anions and are
relatively impermeable to water. Exemplar anion exchange membranes
include Neosepta AM-1, AFN, AMX; Ralex AMH-PES; Fumasep FAD; and
Selemion DVS, APS. Exemplar cation exchange membranes include
Neosepta CMX, CM-1; Ralex CMH-PES; Fumasep FKE, FKD; and Selemion
CMV.
[0157] On each end of the EDR-R stack 601 are electrolyte chambers
with electrolyte chamber 615 on the same side as anode/cathode
electrode 632, and electrolyte chamber 614 on the same side as
cathode/anode electrode 631. Electrolyte solution is pumped through
electrolyte inlet conduit 606 into electrolyte chamber 614 and
exits electrolyte chamber 615 through electrolyte exit conduit 645,
and may be recycled in a closed loop. The electrolyte circuit
illustrated in FIG. 12 is a series arrangement; however, a parallel
circuit is also possible.
[0158] A direct current power source 635 is applied to the EDR-R
stack 601 to provide a DC voltage at the electrodes 631 and 632.
Changing the polarity of the DC power supply changes whether each
electrode is operating as a cathode or anode. Reduction and
oxidation of reactions of the electrolyte occur at the cathode and
anode respectively, converting the DC electrical current into an
ionic current. In the forward polarity configuration of FIG. 12,
cathode/anode electrode 631 acts as the cathode, and anode/cathode
electrode 632 acts as the anode. Cations and anions are transferred
from the P/Dp chambers 611 to the Dp/P chambers 610 effecting
desalination of the product feed to produce reduced salinity
product output and concentration of the concentrate feed to produce
increased salinity concentrate output. In an alternative embodiment
(not shown), a drive cell, such as the drive cell disclosed in WO
2010/115287 or WO 2009/155683 may be used for application of a
voltage across the chambers.
[0159] Exemplar applied voltages may range from 0.5V to 2.5V per
chamber pair in order to drive ions across the ion exchange
membranes, while avoiding problems associated with water splitting
at higher voltages. Those skilled in the art will be able to
determine the current limit density of a particular EDR-R stack 601
under its operating concentrations and temperatures, and then set
the applied voltage to operate at the most economic current limit
density on a basis of combined capital and operating costs.
[0160] EDR-R stack 601 includes rinse solution chambers 608 which
"guard" the electrolyte chambers 214, 215 from pollution with
divalent scaling ions such as calcium or magnesium. Rinse solution
is supplied via conduit 602 and may consist of conductive but
non-scaling aqueous salts such as sodium chloride. A rinse solution
chamber 608 is positioned next to each of the electrolyte chambers
214, 215 and the two rinse solution chambers 608 are both bound by
an anion exchange membrane 621 on the side furthest from the
electrode. This arrangement prevents cations, such as calcium and
magnesium, from entering the rinse solution chamber 208 from
adjacent P/Dp chambers 611 and/or Dp/P chambers 610. The fact that
the rinse solution chambers 608 remain free of calcium and
magnesium prevents their passage from the rinse solution chambers
608 to the electrolyte chambers through the cation exchange
membranes 620 that bound the electrolyte chambers 614, 615. The
rinse solution chambers 608 beneficially remove the need for
electrolyte acidification while also increasing reliability over
conventional EDR stacks through reduced calcium sulfate
precipitation risk.
[0161] Precipitation and ion exchange membrane scaling risk is
still a concern for P/Dp chambers 611 and/or Dp/P chambers 610.
Since constituents may be present in the feed solutions (e.g.
calcium carbonate and calcium sulphate) the ion exchange membranes
accumulate scalants on their surfaces resulting in a decreased
desalination efficiency of the system. Scale buildup on the ion
exchange membranes is indicated by an increase in resistance, which
can be measured as either decreased current in constant voltage
operating mode or increased voltage in constant current operating
mode. Once the resistance has reached a level indicative of scaling
on the ion exchange membranes, the EDR-R stack 601 will be operated
in the reverse polarity mode as depicted in FIG. 13.
[0162] Referring now to FIG. 13, which show an EDR-R stack 601 in
reverse polarity mode wherein The polarity of direct current power
source 635 is reversed resulting in anode/cathode electrode 632
becoming the cathode, and cathode/anode electrode 631 becoming the
anode. The result is such that the polarity of the voltage applied
to the stack and the direction of the ionic current are reversed,
thereby resulting in a change in ion transfer direction through
each membrane, thereby descaling the ion exchange membranes.
[0163] In order to maintain production of desalinated water when
ion transfer has changed direction, the saltwater internal to the
P/Dp chambers 611 and the Dp/P chambers 610 must also be changed.
In the reverse polarity configuration shown in FIG. 13, product
feed and concentrated feed enter and exit through opposite
conduits, more specifically through Dp-P conduit 603 and P-Dp
conduit 605 respectively. Flow direction is not reversed in the
disclosed embodiment; however, it is possible to reverse flow in
reverse polarity operation to back flush the EDR-R stack 601 for
enhanced scalant removal.
[0164] In alternative embodiments the rinse chambers may be added
to an MC-EDR stack as described herein, or the rinse chambers may
be added to ED or MC-ED stacks which do not operate in reversal
mode.
[0165] In further alternative embodiments (not shown) multiple
ED-R, EDR-R, MC-ED-R, MC-EDR-R stacks may be combined with an
electrode, electrolyte chamber and rinse chamber positioned at
either end of each stack. The multiple stacks may be compressively
coupled and may comprise a modular apparatus as disclosed in WO
2012/019282 (incorporated herein by reference).
[0166] Alternative embodiments described herein are directed at a
EDR cleaning system which enables longer term reliable operation of
an EDR stack by sensing the on-set of scaling and removing deposits
before they become detrimental. The cleaning system beneficially
reduces operator intervention, saves downtime, and reduced
freshwater and chemical inputs. It is well known to reverse the
polarity of an EDR stack in order to de-scale membranes, with
reversal frequency based on timers. Chemical clean in place is also
used on a set frequency to remove and scale product build-up. The
cleaning system described herein adds sensors, algorithms and
control systems to sense when electrochemical cleaning is required
in addition to a flush sequence that removes deposits before they
irreversibly foul the stack to prevent detrimental hydraulic
resistance increase. The cleaning system senses and calculate
electrochemical and hydraulic resistance by applying algorithms,
and processes actions in order to remove scaling and fouling
products when resistance has reached a certain level. In order to
prevent detrimental accumulation of precipitation products, a "shut
down flush" may occur at every shut down to flush saline water out
of the stack and prevent precipitation during stand time.
[0167] Membrane electrochemical resistance is the difference
between stack resistance and solution resistance. An increase in
electrochemical resistance indicates the need for either: [0168] 1.
Ionic reversal to de-scale membranes; or [0169] 2. Chemical
clean-in-place--which is initiated after a number of repeated ionic
reversals without resistance improvement.
[0170] Hydraulic resistance is detected by measuring pressure and
flow rate. The control system can determine normal "unblocked"
operating regime and then sense when blockage commences requiring
the need for one of the following hydraulic cleaning regimes:
[0171] 1. Slug Wash: inject a "slug" of freshwater in an attempt to
remove fouling products [0172] 2. Stack Wash: full stack wash in
closed loop with a wash tank over an extended period of
time--initiated at increased hydraulic resistance or after repeated
slug washes without resistance improvement [0173] 3. Stack Chemical
Clean: full stack chemically enhanced clean-in-place in the event
of severe electrochemical fouling of membranes and/or repeated
stack washes proving unsuccessful at reducing hydraulic
resistance
[0174] Referring to FIG. 14 there is shown the MC-EDR plant 101 of
FIG. 4 with additional cleaning system. Like parts are referenced
with the same reference numerals and the MC-EDR plant 101 operates
as described above with reference to FIG. 4 with the addition of
the cleaning system and parts associated with the cleaning system
which are described below.
[0175] The following electrochemical resistance sensors are
included, or could be incorporated into variable DC power supply
235: [0176] Stack Operating Voltage Transducer 133 [0177] Stack
Operating Current Transducer 135
[0178] In addition, the hydraulic resistance sensors given in Table
4 may be included in the plant manifolding.
TABLE-US-00004 TABLE 4 Hydraulic Resistance Sensors for Cleaning
System of MC-EDR Plant 101 Hydraulic Circuit P--Prod- Dp--Diluent
Dc--Diluent C--Concen- Sensors uct P C trate Pressure 130 160 167
137 Transducer ("Pp") ("Pdp") ("Pdc") ("Pc") Flow 131 165 168 138
Transducer ("Fp") ("Fdp") ("Fdc") ("Fc") Conductivity 132 166 169
139 Transducer ("Cp") ("Cdp") ("Cdc") ("Cc")
[0179] The requirement for cleaning is sensed as increase in one or
both of electrochemical and hydraulic resistance.
[0180] Electrochemical resistance of membranes may be estimated as
follows: [0181] 1. Calculate stack net resistance ("Rstack") as the
ratio of stack operating voltage measured by voltage transducer 133
and stack operating current measured by current transducer 135.
[0182] 2. Estimate solution net resistance ("Rsoln") internal to
the stack chambers. Solution resistance is the inverse of
conductivity per unit thickness of the solution. The electrolyte
chamber resistance is excluded for reasons of simplicity, and
although not required can be added. Rsoln is calculated as
follows:
[0182] Rsoln=(P stack chamber thickness*number of P
chambers)/Cp
+(Dp stack chamber thickness*number of Dp chambers)/Cdp
+(Dc stack chamber thickness*number of Dc chambers)/Cdc
+(C stack chamber thickness*number of C chambers)/Cc [0183] 3.
Estimate net membrane resistance ("Rmem") using the equation:
[0183] Rmem=Rstack-Rsoln.
[0184] Electrochemical resistance of a stack can first be
characterized after construction through initial operation to
determine normal net membrane resistance ("Rmem"). The user can set
a "Ionic Current Reversal Threshold" in the control system such
that when Rmem exceeds a set value, for example 1.25*Rmem, the
control system will activate ionic current reversal in accordance
with the valve actuation scheme of Table 2 while also reversing the
polarity of variable DC power supply 235 as hereinbefore described
with reference to FIGS. 4-6. Ionic current reversal changes the
direction of salt ion transport through the ion exchange membranes
internal to the stack. This will de-scale the membranes as is known
by those skilled in the art of EDR. The operator can also establish
a "Stack Chemical Clean" set point, with trigger points, for
example, but not limited to: [0185] 1. 1.5*Rmem; and/or [0186] 2.
Two Ionic Current Reversals are completed within a specified time
"Tmin_rev" indicating that reversal frequency has increased and a
"Stack Chemical Clean" is required.
[0187] Hydraulic resistance is estimated for each circuit by
determining the pressure-flow relationship as measured by pressure
transducer sensors 130 ("Pp"), 160 ("Pdp"), 167 ("Pdc"), 137 ("Pc")
and flow transducer sensors 131 ("Fp"), 165 ("Fdp"), 168 ("Fdc"),
138 ("Fc"). FIG. 15 shows an exemplar pressure-flow relationship
with four curves as follows: [0188] H-0: baseline operation without
inhibited hydraulic resistance due to scaling and fouling products
internal to the pipework and stack. Baseline pressure and flow
curve is established at start-up and during re-commissioning after
system changes by varying the hydraulic circuit pressure and
measuring the flow rate in order to produce a flow-pressure
baseline curve. [0189] H-1: hydraulic resistance due to the on-set
of scaling and fouling products forming internal to the pipework
and stack. Flow rates are less than H-0 flow rates for the same
pressure. A typical H-1 curve "set point" might have flow
rates=0.85*H-0 curve. [0190] H-2: increased hydraulic resistance
due to the build-up of scaling and fouling products forming
internal to the pipework and stack. Flow rates are less than H-1
flow rates for the same pressure. A typical H-1 curve "set point"
might have flow rates=0.75*H-1 curve. [0191] H-3: excessive
hydraulic resistance due to the build-up of scaling and fouling
products forming internal to the pipework and stack. Flow rates are
less than H-2 flow rates for the same pressure. A typical H-1 curve
"set point" might have flow rates=0.65*H-2 curve.
[0192] The exemplar curves of FIG. 15 can be applied to any and all
of the hydraulic circuits: P, Dp, Dc, and C. Table 5 shows the
cleaning action that can be taken for the different pressure-flow
curves.
TABLE-US-00005 TABLE 5 Cleaning Action Activation Action Activate
When (0) Shut Down Plant 101 is shut down Flush (1) Slug Wash
Measured pressure-flow performance is below H-1 (2) Stack i.
Measured pressure-flow performance is below H-2; and/or Wash ii.
Two Slug Washes are completed within a specified time "Tmin_slug"
indicating that Slug Washes are losing effectiveness and a stack
wash is required (3) Stack i. Measured pressure-flow performance is
below H-3; and/or Chemical ii. Two Stack Washes are completed
within a specified time "Tmin_stack" Clean indicating that Stack
Washes are losing effectiveness and a Stack Chemical Clean is
required; and/or iii. Two Ionic Current Reversals are completed
within a specified time "Tmin_rev" indicating that reversal
frequency has increased and a "Stack Chemical Clean" is required
(as described above)
[0193] Referring to FIG. 14, cleaning water tank 189 holds
freshwater added through water inlet 104 and chemicals added
through chemical inlet 109. Freshwater may be used for: (0) Shut
Down Flush, (1) Slug Wash, and (2) Stack Wash. The operator can set
a freshwater fill level for automated fill of tank 189 based on
initial commissioning runs to ensure the tank fill level provides
sufficient volume for the actions given below in Table 6, as each
action requires a different tank fill level. For example, (0) Shut
Down Flush requires sufficient volume for all hydraulic circuits,
except electrolyte, however, (1) Slug Wash and (2) Stack Wash can
be completed on a single hydraulic circuit at a time, thereby
requiring less freshwater volume.
TABLE-US-00006 TABLE 6 Operation of Cleaning System for MC-EDR
Plant 101 Valves of Hydraulic Circuit Action P--Product Dp--Diluent
P Dc--Diluent C C--Concentrate Normal 188 - closed 188 - closed 188
- closed 188 - closed Operation 184 - open 182 - open 180 - open
186 - open 177 - closed 173 - closed 183 - closed 179 - closed 176
- open 174 - open 181 - open 178 - open (0) Shut Down 188 - open
188 - open 188 - open 188 - open Flush 184 - close 182 - close 180
- close 186 - close Pumps 114, 115, 177 - open 173 - open 183 -
open 179 - open 116, 117 running 176 - close 174 - close 181 -
close 178 - close P/S 235 OFF Delay: ~0.5 min Delay: ~0.5 min
Delay: ~0.5 min Delay: ~0.5 min (user set point) (user set point)
(user set point) (user set point) 184 - open 182 - open 180 - open
186 - open 188 - close 188 - close 188 - close 188 - close 176 -
open 174 - open 181 - open 178 - open 177 - close 173 - close 183 -
close 179 - close Shut down system Drain tank 189 via valve 134 (1)
Slug Wash 188 - open 188 - open 188 - open 188 - open Pumps 114,
115, 184 - close 182 - close 180 - close 186 - close 116, 117
running Delay: ~2 sec Delay: ~2 sec Delay: ~2 sec Delay: ~2 sec 184
- open 182 - open 180 - open 186 - open 188 - close 188 - close 188
- close 188 - close (2) Stack Wash 188 - open 188 - open 188 - open
188 - open Pumps 114, 115, 184 - close 182 - close 180 - close 186
- close 116, 117 running 177 - open 173 - open 183 - open 179 -
open P/S 235 OFF 176 - close 174 - close 181 - close 178 - close
Delay: ~10 min Delay: ~10 min Delay: ~10 min Delay: ~10 min (user
set point) (user set point) (user set point) (user set point) 184 -
open 182 - open 180 - open 186 - open 188 - close 188 - close 188 -
close 188 - close 176 - open 174 - open 181 - open 178 - open 177 -
close 173 - close 183 - close 179 - close Return to Normal
Operation Drain tank 189 via valve 134
[0194] Prior to a Stack Chemical Clean, a Shut Down Flush should be
initiated. For the Stack Chemical Clean a chemically enriched water
of exemplar 0.5 molar citric acid or 0.5 molar hydrochloric acid is
obtained through automatic chemical dispensing pumps at chemical
inlet 109, water addition at water inlet 104, and mixing (not
shown) in tank 189. The Stack Chemical Clean control sequence is
the same as the Shut Down Flush described above, with the pumps
114, 115, 116, 117 starting at the commencement of the user set
Chemical Clean Time Delay and stopping at the end of the Chemical
Clean Time Delay. After which plant 101 operation can revert to
normal. In the event that the Stack Chemical Clean does not return
performance to the base line, the operator can be notified to
investigate further.
[0195] Set points may need to be re-tuned by operators from time to
time in order to re-establish performance, and off-performance set
points that are used to initiate each of the above described
cleaning actions.
[0196] The foregoing description of a system and method for
cleaning a MC-EDR plant has been presented for purposes of
illustration and description and is not intended to be exhaustive
or limit the invention to the precise form disclosed; many
modifications and variations are possible in light of the above
teaching. For example, the cleaning system may utilize all or only
some of the cleaning actions described or may incorporate
additional cleaning actions of benefit to the plant. In alternative
embodiments (not shown) the cleaning system may be applied to a
conventional two chamber ED or EDR system or to the MC-ED, ED-R,
MC-ED-R, EDR-R or MC-EDR-R systems of the described
embodiments.
[0197] Alternative embodiments described herein are directed at a
salt extraction method and plant to remove salt from saltwater,
producing freshwater or freshwater vapor and solid salt or a highly
concentrated salt solution. As such, salts are removed from the
water balance. Saltwater is input to a first electrodyalisis stage,
where salt is transferred from the input saltwater through ion
exchange membranes under the application of galvanic potential into
a concentrated salt solution approaching but not exceeding
saturation of the lower solubility ionic constituents present. The
resulting concentrated salt solution is passed into a second stage
solution concentrating desalination system. The second stage
solution concentrating desalination system may be a zero liquid
discharge system as known in the art which concentrates the
concentrated salt solution to produce solid salt/highly
concentrated salt solution and freshwater when a dehumidifier is
present, or solid salt/highly concentrated salt solution and
freshwater vapor which is released to the atmosphere.
[0198] The first and second stage may be thermally integrated, such
that heat extracted from the second stage cooling salt
solidification process is upgraded and used to maintain optimal
solubility temperature of the first stage process. Excess heat from
the second stage desalination process, for example heat of
compression, may be employed to pre-heat input saltwater and
maximize solubility of ion constituents in the first stage.
Controls enable maximization of first stage concentrated solution
concentration coupled with de-scaling and cleaning.
[0199] Referring to FIG. 16 there is shown a two stage salt
extraction plant 701a, including a first electrodialysis (ED) stage
702 and second solution concentrating desalination stage 706. Input
saltwater 703, is optionally pre-heated, and fed into product tank
711 containing product solution 710 that is to be desalinated.
Product solution 710 is pumped from product tank 711 through ED
stack 722 by product pump 720. Concentrate pump 725 draws
concentrate solution 715 from concentrate tank 716 and circulates
the concentrate solution 715 through the ED stack 722. Product
solution 710 is desalinated in ED stack 722 by electrochemical or
concentration gradient energy means to produce reduced salinity
product output. ED stack 722 contains solution channels separated
by ion exchange membranes. Under the application of electric or
chemical energy gradient potential ions pass through the ion
exchange membranes from the product solution 710 to the concentrate
solution 715 to produce an increased salinity concentrate
output.
[0200] Conductivity of the product output exiting the ED stack is
measured with product conductivity sensor 726. If the salt
concentration of the product output is below a set threshold, often
related to permitted discharge limits, then outlet flow control
valve 728 is opened to modulate release of product output from the
system at product output discharge 714. Throttling valve 729 can be
used to ensure product output back pressure is sufficient to leave
the system. If the salt concentration of the product output is
above the set threshold, then outlet flow control valve 728 is
closed and throttling control valve 729 opened to return product
output to the product tank 711 for further desalination.
Conductivity sensor 726 may include additional sensors (not shown)
and exemplar techniques including inductively coupled plasma mass
spectrometry, to measure the concentration of specific constituents
of concern, for example heavy metals. Each water source and
discharge requirements may be unique; therefore the product
conductivity sensor 726 or its alternative sensor may be calibrated
based on site specific requirements to calibrate conductivity to a
measure related to constituents of concern.
[0201] A product to concentrate transfer valve 723 can be actuated
to fill concentrate tank 716 as its volume is depleted. Some
osmotic effect may occur as a result of suction of water from the
product solution 710 into the concentrate solution 715 through the
ion exchange membranes, due to the concentration gradient. Osmotic
effects may reduce the amount of product solution 710 that needs to
be transfer through valve 723 to the concentrate tank 716.
[0202] Construction of exemplar ED stacks is disclosed in Canadian
Patent Application 2,748,567. The stack may be operated in
electrodialysis reversal (EDR) mode on highly scaling waters, and
include self cleaning mechanisms as describe herein with reference
to FIGS. 14 and 18-20 and/or a rinse hydraulic circuit adjacent the
electrode chambers as described herein with reference to FIGS. 12,
13 and 18-20. For high concentration change operation an internally
staged MC-ED or MC-EDR and process as described herein with
reference to FIGS. 4-9, 14 and 18-20 may be employed.
[0203] It is beneficial to maximize the first ED stage 702 output
concentration of the concentrate. This minimizes the capacity of
the second solution concentrating desalination stage 706. A
crystallization sensor system 704 may be included to measure the
onset of crystallization in order to maximize concentrate output
concentration before it is transferred to the second solution
concentrating desalination stage 706. The crystallization sensor
system 704 operates under the principle of causing crystallization
in a known location and measuring its onset. This is achieved by
circulating the concentrate solution 715, through a strainer 740
under action of pump 741, and measuring differential pressure with
pressure transducer 742. Strainer 740 may be constructed of a
slightly finer media representation than flow channels of the ion
exchange membranes present in ED stack 722, such that
crystallization occurs in the strainer 740 before crystallization
in ED stack 722. As salt forms in the media of strainer 740, the
pressure drop across the strainer increases. This pressure drop is
measured by pressure transducer 742, which may be calibrated by the
operator to set the "crystallization onset differential pressure".
In the event of crystallization in strainer 740, a freshwater flush
745 may be employed, such as a flush similar to the flush described
above with reference to FIGS. 14 and 15. Check valve 743 may be
included to ensure the flush is in the correct direction.
Additionally or alternatively, conductivity sensor 727 may be
included in concentrate tank 716 to measure the conductivity of the
concentrate solution 715 and actuate movement of concentrate
solution 715 from the concentrate tank 716 to the second solution
concentrating desalination stage 706 before the concentrate
solution 715 crystallizes in the concentrate tank 716.
[0204] Once crystallization onset differential pressure is reached
and/or the conductivity sensor 727 detects a set threshold
concentration in tank 716, concentrate solution 715 is transferred
by pump 746 to the second solution concentrating desalination stage
706. The level of concentrate solution 715 in concentrate tank 716
will subsequently decrease which is detected by a level sensor (not
shown) in concentrate tank 716. This triggers a control system to
open transfer valve 723 to transfer product solution 710 to the
concentrate tank 716. As a result the level of product solution 710
in product tank 711 decreases which is detected by a level sensor
(not shown) in product tank 711. This triggers the control system
to open saltwater inlet valve 705 to re-fill product tank 711 with
input saltwater 703. The solution transfer sequence described above
is based on tank level controls, but an alternative embodiment (not
shown) can use flow meters and flow control valves or other means
in order to reduce tank volume requirements.
[0205] In an alternative embodiment, the first ED stage can be
thermally coupled to the second solution concentrating desalination
stage with the second stage optionally controlling the temperature
of the first ED stage and maximizing the solubility of the
concentrate solution. For example, the solubility of calcium
sulfate peaks at 30 deg C., and decreases with both increases and
decreases in temperature. The ED stage temperature can be
controlled to maximize solubility of the constituents of concern
without exceeding temperature limits of the ED system.
[0206] Referring to FIG. 17, there is shown a thermally coupled two
stage salt extraction plant 701b. Two stage salt extraction plant
701b is similar to plant 701a with like parts indicated with like
reference numerals, however, in plant 701b the solution
concentrating desalination stage 706 is a multiple effect heat pump
driven solution concentrating system as described in International
Patent Application PCT/CA2012/00495 (incorporated herein by
reference). In alternative embodiments (not shown) other solution
concentrating desalination systems may be employed in the two stage
plant, such as mechanical vapor compression driven crystallizers.
If a compression driven solution concentrating desalination stage
process is used, which is fully insulated, and saltwater is input
at the operating temperature, the heat of compression will
accumulate and raise the operating temperature. As a result, the
heat of compression must be released from the system. This
represents useful waste heat. The heat pump driven plant depicted
in FIG. 17 produces waste heat power equivalent to the power of
compression which is used by the heat pump compressor 744.
[0207] As shown in FIG. 17 solution concentrating desalination
stage 706 uses multiple air humidification-dehumidification (HDH)
effects which include a first HDH effect saltwater concentrating
circuit containing first effect humidifier-dehumidifier 730 and a
second HDH effect saltwater concentrating circuit containing second
effect humidifier-dehumidifier 732. A heat exchanger 780 is used to
pre-heat input saltwater 703 and remove heat from the solution
concentrating desalination stage 706. Optionally, the heat
exchanger 780 may be placed in the second HDH effect tank 792 as
shown in FIG. 17. In an alternative embodiment (not shown) second
HDH effect saltwater may be circulated through a heat exchanger in
thermal communication with the input saltwater 703 so that heat is
transferred from the second HDH effect saltwater to the input
saltwater 703. The net result is that input saltwater 703 is heated
using waste heat from the second stage solution concentrating
desalination system 706 to beneficially increase its temperature
and increase the solubility of constituents to be removed from the
input saltwater 703. The ED stack 722 also acts like a heat
exchanger with heat transfer through the membranes. Therefore,
heating the input saltwater 703 that enters product tank 711 will
also result in a temperature increase of the concentrate solution
715 with heat being transferred from the product solution 710 to
the concentrate solution 715 through the membranes.
[0208] The second solution concentrating desalination stage 706 may
optionally include a cooled salt auger 757 for salt removal as
described in International Patent Application PCT/CA2012/00495.
Salt auger 757 may employ an external auger coolant 751 to cool the
auger 757 and increase precipitation of salt in the auger 757. Heat
is removed from the resulting heated auger coolant 751 by
refrigeration circuit 761 so that cooled inlet auger coolant can be
re-circulated and re-used. Heat from auger coolant 751 is extracted
by heat exchanger 763 and transferred to a refrigerant in the
refrigeration circuit 761. The refrigerant evaporates at a
temperature lower than the temperature of the cooled inlet auger
coolant plus an additional margin to allow for heat transfer
resistance. Refrigeration compressor 765 compresses the resulting
refrigerant gas and the compressed refrigerant gas passes through a
condensing heat exchanger 767 in the concentrate tank 716 of first
ED stage 702. The refrigeration compressor 765 compresses the
refrigerant gas to a sufficient pressure that will enable
condensation of the refrigerant in condensing heat exchanger 767 at
a temperature greater than the temperature of the concentrate
solution 715 in the concentrate tank 716. This results in
condensation of the refrigerant internal to the condensing heat
exchanger 767, transferring the refrigerant's latent heat of
condensation to maintain the temperature of the concentrate
solution 715 at a set temperature, for example 30 deg C. Condensed
liquid refrigerant passes through an expansion device 769 which
lowers the pressure of the condensed liquid refrigerant allowing
low pressure refrigerant to enter the heat exchanger 763.
Refrigeration circuit 761 enables temperature control of the
concentrate solution 715 in concentrate tank 716, which
beneficially reduces the risk of precipitation in the tank 716 and
maximizes concentration of solution in the first ED stage 702,
while also cooling the auger 757 to increase precipitation of salt
in the salt removal system.
[0209] Alternative embodiments (not shown) use any combination of
heat exchangers to transfer heat from the second solution
concentrating desalination stage 706 to the input saltwater 703
and/or the concentrate solution 715 of the first ED stage 702.
[0210] An alternative embodiment is directed at an internally
staged multiple chamber electrodialysis reversal-rinse (MC-EDR-R)
plant with cleaning system. Referring to FIG. 18, there is shown
MC-EDR-R plant 801 with three saltwater solutions P, D, C and a
rinse ("R") solution passing through MC-EDR-R stack 901 which can
be run in forward or reverse polarity. The product ("P") solution
891 is the lowest concentration saltwater, or desalination product,
and P circuit includes manifolding fluidly coupling MC-EDR-R stack
901 with product tank 822; diluent ("D") solution 892 is an
intermediate concentrated solution and D circuit includes
manifolding fluidly coupling MC-EDR-R stack 901 with diluent tank
823; concentrate ("C") solution 894 is a concentrated solution and
C circuit includes manifolding fluidly coupling MC-EDR-R stack 901
with concentrate tank 821; and rinse ("R") solution 898 which may
consist of conductive but non-scaling aqueous salts such as sodium
chloride and R circuit includes manifolding fluidly coupling
MC-EDR-R stack 901 with rinse tank 824. The MC-EDR-R stack 901 is
configured in such a way that product solution 891 decreases in ion
concentration by transferring its ions across ion exchange
membranes through diluent solution 892 to the concentrate solution
894. The result is that the product solution 891 is desalinated and
the concentrate solution 894 is concentrated.
[0211] Upstream saltwater source 895 supplies product tank 822 via
product inlet 802 after passing through an optional pre-treatment
stage (not shown), and product source control valve 871. Exemplar
pre-treatment may include, but is not limited to, physical filters
(such as microfiltration or ultrafiltration), dissolved air
filtration, coagulation and sedimentation, media filtration or
other methods known to those skilled in the art. Product solution
891 is stored in product tank 822, which may include an optional
heating element (not shown) to increase the temperature of the
solution and thereby beneficially increase MC-EDR-R system
efficiency through increased conductivity internal to the MC-EDR-R
stack 901. Product pump 815 pumps product solution 891 from product
tank 822 through open product inlet valve 884 to P-C inlet valve
reversal array 810. Table 7 below provides the reversal valve
positions for forward and reverse polarity configuration.
TABLE-US-00007 TABLE 7 Reversal Valve Positions for MC-EDR-R plant
801 Reversal MC-EDR-R MC-EDR-R MC-EDR-R MC-EDR-R Valve Forward
Reverse Reverse Forward Number Polarity Flush Polarity Flush 810a
Open Closed Closed Open 810b Closed Open Open Closed 810c Closed
Open Open Closed 810d Open Closed Closed Open 812a Open Closed
Closed Closed 812b Closed Open Open Open 812c Closed Closed Open
Closed 812d Open Open Closed Open
[0212] In the forward polarity configuration, product solution 891
passes through open reversal valve 810d and enters MC-EDR-R stack
901 via P-C inlet conduit 851. The product solution 891 passes
through the MC-EDR-R stack 901 and exits at a lower ion
concentration through P-C outlet conduit 855. Output product
solution then enters P-C outlet valve reversal array 812 and passes
through open reversal valve 812a and into product conduit 805.
[0213] Product concentration sensor 861, which may be a
conductivity sensor, detects the ion concentration level in output
product solution leaving P-C outlet reversal valve array 812.
Product exit control valve 841 and product return control valve 846
can be modulated to either return output product solution to
product tank 822 or remove output product solution from the
process. For example, if the ion concentration of output product
solution measured by product concentration sensor 861 is below a
specified value, product exit control valve 841 opens to allow
discharge of output product solution from the process. As a result,
the level in product tank 822 will drop. Product tank level control
valve 871 will modulate and open to allow addition of source
saltwater 895, which will result in more product entering product
bulk tank 822 to be desalinated, an increase in the ion
concentration of product solution 891 in product tank 822, and an
increase in output product solution ion concentration measured by
product concentration sensor 861. If the ion concentration of
output product solution is above a specified value, product exit
control valve 841 closes while the product return control valves
846 and 876 open to return output product solution back to the
product tank 822 for further desalination in order to meet the
desired output specified ion concentration.
[0214] Upstream saltwater source 896 supplies diluent tank 823 via
diluent inlet conduit 803 and diluent source control valve 872,
after passing through an optional pre-treatment process (not
shown). Diluent tank 823 may include an optional heating element
(not shown) to increase the temperature of the solution and thereby
beneficially increase MC-EDR-R system efficiency through increased
conductivity internal to the MC-EDR-R stack 901. Upstream saltwater
source 896 may be the same source as upstream saltwater source 895,
or it may be a different source. Diluent pump 816 pumps diluent
solution 892 from diluent tank 823 through open diluent inlet valve
882 and diluent inlet conduit 853 into MC-EDR-R stack 901. Output
diluent solution exits MC-EDR-R stack 901 at an increased ion
concentration through diluent outlet conduit 857 where
concentration sensor 864 detects the ion concentration of output
diluent solution in diluent outlet conduit 857. If the measured ion
concentration of output diluent solution is above a specified
concentration, diluent exit control valve 843 may be opened
slightly and diluent return control valve 847 may be closed
slightly to allow output diluent solution to enter the C circuit.
If the measured concentration of output diluent solution is below a
specified concentration, diluent exit control valve 843 is closed
and diluent return control valves 847, 874 opened to allow output
diluent solution to return to diluent tank 823 for further
concentration.
[0215] Concentrate solution 894 is stored in concentrate tank 821,
which may include an optional heating element (not shown) to
increase the temperature of the solution, thereby beneficially
increasing MC-EDR-R system efficiency through increased
conductivity internal to MC-EDR-R stack 901. Solution enters the C
circuit from the D circuit when diluent exit control valve 843 is
opened. Concentrate solution 894 is pumped from concentrate tank
821 by concentrate pump 814 through open concentrate inlet valve to
P-C inlet reversal valve array 810. In the forward polarity
configuration concentrate solution 894 passes through open reversal
valve 810a and into MC-EDR-R stack 901 through C-P inlet conduit
852. Output concentrate solution leaves MC-EDR-R stack 901 at a
higher ion concentration via C-P outlet conduit 856 and enters P-C
outlet reversal valve array 812. Output concentrate solution passes
through open reversal valve 812d into concentrate conduit 806 where
concentration sensor 862 measures the ion concentration of output
concentrate solution exiting P-C outlet reversal valve array 812.
If the measured ion concentration of output concentrate solution in
concentrate conduit 806 is above a specified concentration,
concentrate exit control valve 842 is opened to allow output
concentrate solution to exit the system. If the measured ion
concentration of output concentrate solution in concentrate conduit
806 is below a specified concentration, then concentrate exit
control valve 842 is closed and concentrate return control valves
845 and 878 are opened to return output concentrate solution to
concentrate tank 821 to be further concentrated.
[0216] A level sensor in concentrate tank 821 (not shown) measures
the level of concentrate solution 894 in concentrate tank 821. When
a low level set point is reached, diluent exit control valve 843 is
opened slightly and diluent return control valve 847 is closed
slightly to allow diluent solution transfer from the D circuit to
the C circuit.
[0217] If, in theory, saltwater make-up is added to the C circuit
rather than the D circuit (not shown) steady state operation may be
achieved where no saltwater is transferred into or out of the D
circuit as only ions are transferred from product solution 891
through the ion exchange membranes internal to MC-EDR-R stack 901
to the diluent solution 892, and then again through ion exchange
membranes internal to MC-EDR-R stack 901 to the concentrate
solution 894. In practice however, some water is transferred
through the ion exchange membranes either due to osmotic,
electro-osmotic, or leakage effects. As a result, it is beneficial
to include the diluent exit control valve 843. In addition, it is
beneficial to add the saltwater source solution to the lower
concentration P and D circuits such that a low concentration factor
across each circuit may be maintained and concentration
polarization and current efficiency losses are minimized. The above
described control system provides utility to maintain low
concentration factors across each circuit, maintain circuit
concentrations, maintain tank levels, and ultimately operate an
efficient system that can produce a high concentration discharge in
a non-attended (automated) manner.
[0218] In an alternative embodiment (not shown) saltwater make-up
may be added to the C circuit from the P circuit by closing
reversal valves 812a, 812c and opening reversal valves 812b, 812d
so that output product solution exiting P-C outlet reversal valve
array 812 flows into concentrate outlet conduit 806 along with the
output concentrate solution. Check valves (not shown) may be
positioned after reversal valves 812b, 812d to prevent back flow of
product P into C circuit or vice versa. This embodiment may be
beneficial when the MC-EDR-R plant 801 is combined with a second
stage desalination system as described above with reference to
FIGS. 16 and 17.
[0219] In a further alternative embodiment saltwater make up may be
added directly to the C circuit from saltwater source 895 or 896. A
conduit (not shown) may fluidly connect the saltwater source 895 or
896 to concentrate tank 821. A saltwater inlet valve (not shown)
may be included to control input of saltwater make up into
concentrate tank 821.
[0220] Rinse tank 824 holds rinse solution 898 which may consist of
conductive but non-scaling aqueous salts such as sodium chloride.
Rinse tank 824 may include an optional heating element (not shown)
to increase the temperature of the rinse solution and thereby
beneficially increase MC-EDR-R system efficiency through increased
conductivity internal to the MC-EDR-R stack 901. Rinse pump 817
pumps rinse solution 898 from rinse tank 824 through open rinse
inlet valve 880 and rinse inlet conduit 854 into MC-EDR-R stack
901. Rinse solution 898 exits MC-EDR-R stack 901 through rinse
outlet conduit 858 and passes back to rinse tank 824 via open rinse
return control valve 881.
[0221] FIG. 19 shows the MC-EDR-R stack 901 operating in forward
polarity. Product solution 891 flows into P/C chambers 910 through
P-C inlet conduit 851 and exits via P-C outlet conduit 855. Diluent
solution 892 flows into D chambers 912 through D inlet conduit 853
and exits via D outlet conduit 857. Rinse solution 898 flows into R
chambers 908 through R inlet conduit 854 and exits via R outlet
conduit 858. Concentrate solution 894 flows into C/P chambers 913
through C-P inlet conduit 852 and exits via C-P outlet conduit
856
[0222] A direct current power source 935 is applied to the MC-EDR-R
stack 901 to provide a DC voltage and current at the cathode/anode
electrode 931 and anode/cathode electrode 932. Changing the
polarity of the DC power supply changes whether each electrode is
operating as a cathode or anode. Reduction and oxidation of
reactions of the electrolyte occur at the cathode and anode
respectively, converting the DC electrical current into an ionic
current. In the illustrated forward polarity configuration shown in
FIG. 19, cathode/anode electrode 931 operates as a cathode and
anode/cathode electrode 932 acts as the anode. Exemplar applied
voltages may range from 0.5V to 2.5V per chamber pair in order to
drive ions across ion exchange membranes, while avoiding problems
associated with water splitting at higher voltages. Those skilled
in the art will be able to measure the current limit density of a
particular MC-EDR-R stack 901 under its operating concentrations
and temperatures, and then set the applied voltage to operate at
the most economic current limit density on a basis of combined
capital and operating costs. In an alternative embodiment (not
shown), a drive cell, such as the drive cell disclosed in WO
2010/115287 or WO 2009/155683 may be used for application of a
voltage across the chambers.
[0223] The MC-EDR-R stack 901 consists of two complete MC-EDR-R
cells: cell 960 and cell 961. Each cell 960 and cell 961 consists
of one P/C chamber 910, two D chambers 912, and one C/P chamber
913. In alternative embodiments (not shown) there may be more or
less cells arranged together within a single stack, with more cells
beneficially reducing the overall footprint and increasing
production. It is desirable not to have a P/C chamber 910 or C/P
chamber 913 placed beside a rinse chamber 908. An extra D chamber
912 may be placed on either side of cell 960 or cell 961 to avoid
placing a P/C chamber 910 or C/P chamber 913 next to a rinse
chamber 908. On each end of the MC-EDR-R stack 901 are electrolyte
chambers with electrolyte chamber 914 next to cathode/anode
electrode 931 and electrolyte chamber 915 next to anode/cathode
electrode 932 Electrolyte solution 897 is stored in electrolyte
tank 825 and pumped by electrolyte pump 818 through electrolyte
inlet conduit 906 into electrolyte chambers 914, 915 and exits
electrolyte chamber 914, 915 through electrolyte exit conduit 945
in a closed loop. The closed loop electrolyte circuit illustrated
in FIG. 19 is a parallel arraignment where electrolyte solution
travels in the same direction as the saltwater solutions 891, 892,
894 and rinse solution 898; however, a series closed loop circuit
is also possible as shown in FIG. 5.
[0224] On one side of each C/P chamber 913 are two adjacently
aligned cation exchange membranes 921 and on the other side of each
C/P chamber 913 are two adjacently aligned anion exchange membranes
920. This results in each D chamber 912 positioned between a P/C
chamber 910 and a C/P chamber 913 having a cation exchange membrane
921 on both sides or an anion exchange membrane 920 on both sides
of the D chamber 912, whereas the P/C chambers 910 and the C/P
chambers 913 each have a cation exchange membrane 921 on one side
and an anion exchange membrane 920 on the opposite side of the
chamber. This arrangement of adjacently aligned anion and cation
exchange membranes allows transfer of anions and cations
respectively across multiple chambers from the P/C chamber 910 to
the D chamber 912, then to the C/P chamber 913 as is described in
more detail below.
[0225] A rinse solution chamber 908 is positioned next to each of
electrolyte chambers 914, 915 and the two rinse solution chambers
908 are both bound by an anion exchange membrane 920 on the side
furthest from the electrode. This arrangement prevents cations,
such as calcium and magnesium, from entering the rinse solution
chamber 908 from adjacent D chambers 912. The fact that the rinse
solution chambers 908 remain free of calcium and magnesium prevents
their passage from the rinse solution chambers 908 to the
electrolyte chambers 914, 915 through the cation exchange membranes
921 that bound the electrolyte chambers 914, 915. The rinse
solution chambers 908 beneficially remove the need for electrolyte
acidification while also increasing reliability over conventional
EDR stacks through reduced calcium sulfate precipitation risk.
[0226] The combined DC voltage and ionic current force ions across
the ion exchange membranes in the forward polarity configuration
shown in FIG. 19 as follows: [0227] cations and anions are
transferred from the P/C chamber 910 to the D chambers 912 on
either side of the P/C chamber 910 effecting desalination of
product solution 891; and [0228] cations and anions are transferred
from the D chambers 912 to the C/P chamber 913 concentrating
concentrate solution 894.
[0229] The net effect is transfer of anions from the P/C chambers
910 across the D chambers 912 to the C/P chambers 913 and transfer
of cations from the P/C chambers 910 across the D chambers 912 to
the C/P chambers 913. This arrangement prevents a build-up of ions
in the D circuit and beneficially enables a lower concentration
factor across each membrane than would be possible in a two chamber
EDR where ions are transferred directly from the P/C chamber 910 to
the C/P chamber 913.
[0230] As scaling constituents are present in the feed solutions,
e.g., calcium carbonate and calcium sulfates, the MC-EDR-R ion
exchange membranes will accumulate scalants on their surfaces
resulting in a decreased desalination efficiency of the system.
Scale build up on the ion exchange membranes are indicated by an
increase in resistance, which can be measured as either decreased
current in constant voltage operating mode or increased voltage in
constant current operating mode. Once the resistance has reached a
level indicative of scaling on the ion exchange membranes, the
stack will then be operated in the reverse mode as depicted in FIG.
20.
[0231] Referring now to FIG. 20 there is shown the MC-EDR-R stack
901 in reverse polarity where the ions are transferred through the
ion exchange membranes in a direction opposite to the forward
polarity direction shown in FIG. 19, thereby descaling the ion
exchange membranes. The polarity of the direct current power source
935 is reversed resulting in cathode/anode electrode 931 becoming
the anode and anode/cathode electrode 932 becoming the cathode.
[0232] In order to maintain production of desalinated water when
ion transfer has changed direction, the saltwater internal to P/C
chambers 910 and C/P chambers 913 must also be changed for the
reverse polarity configuration. Concentrate solution 894 is pumped
from concentrate tank 821 through open reversal valve 810b and into
P/C chambers 910 through P-C inlet conduit 851. Output concentrate
solution exits P/C chambers 910 via P-C outlet conduit 855 and
passes through open reversal valve 812b into concentrate conduit
806. Product solution 891 is pumped from product tank 822 through
open reversal valve 810c and into C/P chambers 913 through C-P
inlet conduit 852. Output product solution exits C/P chambers 913
via C-P outlet conduit 856 and passes through open reversal valve
812c into product conduit 805. Diluent solution 892 and rinse
solution 898 pass through diluent chambers 912 and rinse chambers
208 respectively as occurred in the forward polarity configuration
described above with reference to FIG. 19. Flow direction is not
reversed in the disclosed embodiment; however, it is possible to
reverse flow in reverse polarity operation to back flush the
MC-EDR-R 901 stack for enhanced scalant removal.
[0233] The combined DC voltage and ionic current force ions across
the ion exchange membranes in the reverse polarity configuration
shown in FIG. 20 as follows: [0234] cations and anions are
transferred from the C/P chamber 913 to the D chambers 912 on
either side of C/P chamber 913 effecting desalination of product
solution 891; and [0235] cations and anions are transferred from
the D chambers 912 to the P/C chamber 910 concentrating concentrate
solution 894.
[0236] The net effect is transfer of anions from the C/P chamber
913 across the D chambers 912 to the P/C chamber 910 and transfer
of cations from the C/P chamber 913 across the D chambers 912 to
the P/C chamber 910.
[0237] Directly after the polarity is switched to operate in the
reverse polarity configuration, there will be a short period where
concentrate solution 894 from operation in the forward polarity
configuration remains in the pipework which is now associated with
the P circuit. In order to prevent the concentrate solution 894
from entering the product tank 822, the reversal valves of P-C
outlet reversal valve array 812 operate a MC-EDR-R reverse flush
mode for a period of time, for example 1 minute, before switching
to MC-EDR-R reverse polarity mode. As shown in Table 7 in MC-EDR-R
reverse flush mode, reversal valve 812c remains closed and reversal
valve 812d remains open to direct a slug of mixed concentrate and
product solution to the concentrate conduit 806. After a period of
time all remaining concentrate solution 894 should have been
flushed from the system and the reversal valves can now switch to
the MC-EDR reverse polarity mode. Conversely, when the polarity
switches from reverse configuration to forward configuration the
reversal valves of P-C outlet reversal valve array 812 operate in
MC-EDR-R forward flush mode for a period of time, for example 1
minute, before switching to MC-EDR-R forward polarity mode. In
MC-EDR-R forward flush mode, reversal valve 812a remains closed and
reversal valve 812b remains open to direct a slug of mixed
concentrate and product solution to the concentrate conduit 806.
Alternatively, or additionally, P-C conductivity sensor 819 in P-C
outlet conduit 855 and a C-P conductivity sensor 820 in C-P outlet
conduit 856 may be used to detect the conductivity of the solution
exiting the MC-EDR-R stack 901 and the reversal valves of P-C
outlet reversal valve array 812 may be switched to operate in
either MC-EDR-R forward polarity or MC-EDR-R reverse polarity once
a threshold low salinity conductivity, for example within 25% of
normal operating conductivity, is detected indicating that the P
circuit has been sufficiently flushed of concentrate solution
894.
[0238] The MC-EDR-R plant 801 of FIG. 18 includes a cleaning system
as described above with reference to FIGS. 14 and 15. The cleaning
system utilizes stack operating voltage transducer 833 and stack
operating current transducer 835, as well as the hydraulic
resistance sensors given in Table 8 to sense and calculate
electrochemical and hydraulic resistance by applying the algorithms
and process actions described above with reference to FIGS. 14 and
15 in order to remove scaling and fouling products when resistance
has reached a certain level.
TABLE-US-00008 TABLE 8 Hydraulic Resistance Sensors for Cleaning
System of MC-EDR-R Plant 801 Hydraulic Circuit Sensors P--Product
D--Diluent R--Rinse C--Concentrate Pressure 830 860 867 837
Transducer ("Pp") ("Pd") ("Pr") ("Pc") Flow 831 865 868 838
Transducer ("Fp") ("Fd") ("Fr") ("Fc") Conductivity 832 866 869 839
Transducer ("Cp") ("Cd") ("Cr") ("Cc")
[0239] Cleaning water tank 889 holds freshwater added through water
inlet 804 and chemicals added through chemical inlet 809.
Freshwater may be used for: (0) Shut Down Flush, (1) Slug Wash, and
(2) Stack Wash. The operator can set a freshwater fill level for
automated fill of tank 889 based on initial commissioning runs to
ensure the tank fill level provides sufficient volume for the
actions given below in Table 9, as each action requires a different
tank fill level. For example, (0) Shut Down Flush requires
sufficient volume for all hydraulic circuits except electrolyte,
however, (1) Slug Wash and (2) Stack Wash can be completed on a
single hydraulic circuit at a time, thereby requiring less
freshwater volume. The cleaning system on the rinse circuit may not
be utilized during normal operation, however it may be initiated to
enable recovery of performance if the rinse circuit is
inadvertently polluted.
TABLE-US-00009 TABLE 9 Operation of Cleaning System for MC-EDR-R
Plant 801 Valves of Hydraulic Circuit Action P--Product D--Diluent
R--Rinse C--Concentrate Normal 888 - closed 888 - closed 888 -
closed 888 - closed Operation 884 - open 882 - open 880 - open 886
- open 877 - closed 873 - closed 883 - closed 879 - closed 876 -
open 874 - open 881 - open 878 - open (1) Shut Down 888 - open 888
- open 888 - open 888 - open Flush 884 - close 882 - close 880 -
close 886 - close Pumps 814, 815, 877 - open 873 - open 883 - open
879 - open 816, 817 running 876 - close 874 - close 881 - close 878
- close P/S 935 OFF Delay: ~0.5 min Delay: ~0.5 min Delay: ~0.5 min
Delay: ~0.5 min (user set point) (user set point) (user set point)
(user set point) 884 - open 882 - open 880 - open 886 - open 888 -
close 888 - close 888 - close 888 - close 876 - open 874 - open 881
- open 878 - open 877 - close 873 - close 883 - close 879 - close
Shut down system Drain tank 889 via valve 834 (3) Slug Wash 888 -
open 888 - open 888 - open 888 - open Pumps 814, 815, 884 - close
882 - close 880 - close 886 - close 816, 817 running Delay: ~2 sec
Delay: ~2 sec Delay: ~2 sec Delay: ~2 sec 884 - open 882 - open 880
- open 886 - open 888 - close 888 - close 888 - close 888 - close
(4) Stack Wash 888 - open 888 - open 888 - open 888 - open Pumps
814, 815, 884 - close 882 - close 880 - close 886 - close 816, 817
running 877 - open 873 - open 883 - open 879 - open P/S 935 OFF 876
- close 874 - close 881 - close 878 - close Delay: ~10 min Delay:
~10 min Delay: ~10 min Delay: ~10 min (user set point) (user set
point) (user set point) (user set point) 884 - open 882 - open 880
- open 886 - open 888 - close 888 - close 888 - close 888 - close
876 - open 874 - open 881 - open 878 - open 877 - close 873 - close
883 - close 879 - close Return to Normal Operation Drain tank 889
via valve 834
[0240] Prior to a Stack Chemical Clean, a Shut Down Flush should be
initiated. For the Stack Chemical Clean a chemically enriched water
of exemplar 0.5 molar citric acid or 0.5 molar hydrochloric acid is
obtained through automatic chemical dispensing pumps at chemical
inlet 809, water addition at water inlet 804, and mixing (not
shown) in tank 889. The Stack Chemical Clean control sequence is
the same as the Shut Down Flush described above, with the pumps
814, 815, 816, 817 starting at the commencement of the user set
Chemical Clean Time Delay and stopping at the end of the Chemical
Clean Time Delay. After which MC-EDR-R plant 801 operation can
revert to normal. In the event that the Stack Chemical Clean does
not return performance to the base line, the operator can be
notified to investigate further. It is emphasized that set points
will need to be re-tuned by operators from time to time in order to
re-establish performance, and off-performance set points that are
used to initiate each of the above described cleaning actions.
[0241] In alternative embodiments (not shown) the MC-EDR-R plant
801 may use alternative means as would be known to a person of
skill in the art for switching the flow of solutions through the
chambers of the MC-EDR stack rather than the reversal valve arrays
described herein, for example the gaskets described in WO
2010/115287. In alternative embodiments (not shown) the MC-EDR-R
plant 801 may include multiple stacks 901 with an electrode,
electrolyte chamber and rinse chamber positioned at either end of
each stack. Each stack may be connected to the manifolding of the
P, D, C and R circuits, thereby beneficially reducing manifolding
requirements. The multiple stacks may be compressively coupled and
may comprise a modular apparatus as disclosed in WO 2012/019282
(incorporated herein by reference).
[0242] While particular embodiments have been described in the
foregoing, it is to be understood that other embodiments are
possible and are intended to be included herein. It will be clear
to any person skilled in the art that modification of and
adjustments to the foregoing embodiments, not shown, are
possible.
* * * * *