U.S. patent application number 14/173541 was filed with the patent office on 2014-08-14 for osmotic separation systems and methods.
The applicant listed for this patent is OASYS WATER, INC.. Invention is credited to Christopher Drover, Nathan Hancock, Marek S. Nowosielski-Slepowron.
Application Number | 20140224716 14/173541 |
Document ID | / |
Family ID | 51296749 |
Filed Date | 2014-08-14 |
United States Patent
Application |
20140224716 |
Kind Code |
A1 |
Hancock; Nathan ; et
al. |
August 14, 2014 |
OSMOTIC SEPARATION SYSTEMS AND METHODS
Abstract
Separation processes using osmotically driven membrane systems
are disclosed generally involving the extraction of solvent from a
first solution to concentrate solute by using a second concentrated
solution to draw the solvent from the first solution across a
semi-permeable membrane.
Inventors: |
Hancock; Nathan; (Cambridge,
MA) ; Nowosielski-Slepowron; Marek S.; (Boston,
MA) ; Drover; Christopher; (Somerville, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OASYS WATER, INC. |
Boston |
MA |
US |
|
|
Family ID: |
51296749 |
Appl. No.: |
14/173541 |
Filed: |
February 5, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61904882 |
Nov 15, 2013 |
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61900095 |
Nov 5, 2013 |
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61887076 |
Oct 4, 2013 |
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61762385 |
Feb 8, 2013 |
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Current U.S.
Class: |
210/143 ;
210/195.2 |
Current CPC
Class: |
C02F 1/444 20130101;
B01D 2321/12 20130101; C02F 2301/08 20130101; B01D 61/58 20130101;
B01D 2321/04 20130101; C02F 1/441 20130101; C02F 1/445 20130101;
B01D 61/002 20130101; B01D 65/02 20130101; C02F 2209/005 20130101;
B01D 2321/06 20130101; B01D 61/025 20130101; C02F 1/442
20130101 |
Class at
Publication: |
210/143 ;
210/195.2 |
International
Class: |
C02F 1/44 20060101
C02F001/44 |
Claims
1. A system for osmotic extraction of a solvent from a first
solution, comprising: a plurality of forward osmosis units, each
comprising: a first chamber having an inlet fluidly coupled to a
source of the first solution; a second chamber having an inlet
fluidly coupled to a source of a concentrated draw solution; and a
semi-permeable membrane system separating the first chamber from
the second chamber and configured for osmotically separating the
solvent from the first solution, thereby forming a second solution
in the first chamber and a dilute draw solution in the second
chamber; a separation system in fluid communication with the
plurality of forward osmosis units and configured to separate the
dilute draw solution into the concentrated draw solution and a
solvent stream, and a flushing system in fluid communication with
the plurality of forward osmosis units and the separation system,
the flushing system comprising: a source of flushing solution; a
fluid transfer device in fluid communication with the source of
flushing solution and at least one of the plurality of forward
osmosis units; a valve arrangement in fluid communication with the
source of flushing solution, the fluid transfer device, and the at
least one forward osmosis unit; and a control system in
communication with at least one of the source of flushing solution,
the fluid transfer device, or the valve arrangement, where the
control system is configured to operatively connect the source of
flushing solution with the at least one forward osmosis unit via
the fluid transfer device and the valve arrangement.
2. The system of claim 1, wherein the valve arrangement comprises:
a plurality of valves; and at least one sensor, wherein the at
least one sensor is configured to generate a signal based on at
least one operating characteristic of the system.
3. The system of claim 2, wherein the control system comprises a
set of instructions configured to control the flushing system
according to at least one of a predetermined protocol or as
triggered by one or more signals generated by the at least on
sensor.
4. The system of claim 3, wherein the control system actuates one
or more of the plurality of valves to direct a flow of flushing
solution from the source of flushing solution through the second
chamber of the at least one forward osmosis unit.
5. The system of claim 1, wherein the control system directs the
flushing solution to each of the plurality of forward osmosis units
in series.
6. A system for osmotic extraction of a solvent from a first
solution, comprising: a forward osmosis unit comprising: a first
chamber having an inlet fluidly coupled to a source of the first
solution; a second chamber having an inlet fluidly coupled to a
source of a concentrated draw solution; and a semi-permeable
membrane system separating the first chamber from the second
chamber and configured for osmotically separating the solvent from
the first solution, thereby forming a second solution in the first
chamber and a dilute draw solution in the second chamber; a
separation system in fluid communication with the forward osmosis
unit and configured to separate the dilute draw solution into the
concentrated draw solution and a solvent stream, the separation
system comprising a filtration unit, a reverse osmosis unit, and a
by-pass circuit all in fluid communication with the forward osmosis
unit, wherein: the filtration unit comprises: a first chamber
having an inlet fluidly coupled to the second chamber of the
forward osmosis unit for receiving at least a first portion of the
dilute draw solution; a second chamber having an outlet fluidly
coupled to the reverse osmosis unit for transferring a less dilute
draw solution thereto; and a filtration membrane separating the
first chamber from the second chamber and configured for partially
removing solutes from the dilute draw solution, thereby forming the
less dilute draw solution in the second chamber, wherein the
removed solutes are returned to the first chamber of the forward
osmosis unit via an outlet from the first chamber of the filtration
unit; the reverse osmosis unit comprises: a first chamber having an
inlet fluidly coupled to the second chamber of the forward osmosis
unit for receiving at least a second portion of the dilute draw
solution and an outlet fluidly coupled to the second chamber of the
forward osmosis unit for introducing the concentrated draws
solution thereto; a semi-permeable membrane coupled to the first
chamber; and a second chamber coupled to the semi-permeable
membrane and configured for receiving a solvent fluxed through the
membrane, thereby leaving the concentrated draw solution in the
first chamber for transfer to the forward osmosis unit; and the
by-pass circuit configured to selectively direct the first and
second portions of the dilute draw solution to the filtration unit
and the reverse osmosis unit.
7. The system of claim 6, wherein the forward osmosis unit
comprises a plurality of forward osmosis units, each comprising: a
first chamber having an inlet fluidly coupled to the source of the
first solution; a second chamber having an inlet fluidly coupled to
the source of a concentrated draw solution; and a semi-permeable
membrane system separating the first chamber from the second
chamber and configured for osmotically separating the solvent from
the first solution, thereby forming the second solution in the
first chambers and the dilute draw solution in the second
chambers.
8. The system of claim 6, wherein the portions of the dilute draw
solution are delivered to at least one of the filtration unit and
the reverse osmosis unit under pressure.
9. The system of claim 6, wherein the separation system further
comprises means for introducing an additive to at least one of the
first portion or the second portion of the dilute draw
solution.
10. The system of claim 6, wherein the separation system further
comprises a thermal recovery unit in fluid communication with the
outlet of the first chamber of the reverse osmosis unit for
receiving the concentrated draw solution therefrom for further
concentration and the second chamber of the forward osmosis unit
for introducing the more concentrated draw solution thereto.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to and the benefit of U.S.
Provisional Patent Application Nos. 61/762,385, filed Feb. 8, 2013;
61/887,076, filed Oct. 4, 2013; 61/900,095, filed Nov. 5, 2013; and
61/904,882, filed Nov. 15, 2013; the entire disclosures of which
are hereby incorporated by reference herein in their
entireties.
FIELD OF THE TECHNOLOGY
[0002] One or more aspects relate generally to osmotic separation.
More particularly, one or more aspects involve use of osmotically
driven membrane processes, such as forward osmosis, to separate
solutes from aqueous solutions.
BACKGROUND
[0003] Forward osmosis has been used for desalination. In general,
a forward osmosis desalination process involves a container having
two chambers separated by a semi-permeable membrane. One chamber
contains seawater. The other chamber contains a concentrated
solution that generates a concentration gradient between the
seawater and the concentrated solution. This gradient draws water
from the seawater across the membrane, which selectively permits
water to pass, but not salts, into the concentrated solution.
Gradually, the water entering the concentrated solution dilutes the
solution. The solutes are then removed from the dilute solution to
generate potable water.
[0004] There are a variety of issues that can arise with respect to
the feed solutions supplied to the forward osmosis process. For
example, the feed solution can have a sufficiently low salinity
that the concentrated draw solution on the opposite side of the
membrane becomes highly diluted by the process, thereby
complicating the recovery/regeneration of the draw solution. The
condition of the feed solution may also require the use of certain
pretreatment processes to make it usable in the forward osmosis
process. Most pretreatment processes make the overall process more
costly by, for example, requiring the use of additional energy or
chemicals (e.g., lime softening) or further steps (e.g.,
regeneration of an ion exchange resin). Additionally, there can be
disposal issues with the concentrated feed solution after forward
osmosis processing. For example, highly concentrated brine raises
environmental disposal issues, e.g., discharging concentrated brine
into a body of water negatively impacts the local ecosystem. While
there are some solutions for these problems, they tend to be
expensive and/or add undue complexity to the basic forward osmosis
process.
SUMMARY
[0005] Aspects of the invention relate generally to osmotically
driven membrane systems and methods, including forward osmosis
separation (FO), direct osmotic concentration (DOC),
pressure-assisted forward osmosis (PAFO), and pressure retarded
osmosis (PRO).
[0006] In one aspect, the invention relates to a system (and its
corresponding method steps) for the osmotic extraction of a solvent
from a first solution. The system includes a plurality of forward
osmosis units, each having a first chamber having an inlet fluidly
coupled to a source of the first solution, a second chamber having
an inlet fluidly coupled to a source of a concentrated draw
solution, and a semi-permeable membrane system separating the first
chamber from the second chamber and configured for osmotically
separating the solvent from the first solution, thereby forming a
second solution in the first chamber and a dilute draw solution in
the second chamber. The system also includes a separation system in
fluid communication with the plurality of forward osmosis units and
configured to separate the dilute draw solution into the
concentrated draw solution and a solvent stream, and a flushing
system in fluid communication with the plurality of forward osmosis
units and the separation system. The flushing system includes a
source of flushing solution (e.g., the aforementioned solvent
stream), a fluid transfer device in fluid communication with the
source of flushing solution and at least one of the plurality of
forward osmosis units, a valve arrangement in fluid communication
with the source of flushing solution, the fluid transfer device,
and the at least one forward osmosis unit, and a control system in
communication with at least one of the source of flushing solution,
the fluid transfer device, or the valve arrangement. The control
system is configured to operatively connect the source of flushing
solution with the at least one forward osmosis unit via the fluid
transfer device and the valve arrangement.
[0007] In various embodiments of the foregoing aspect, the valve
arrangement includes a plurality of valves and at least one sensor,
where the at least one sensor is configured to generate a signal
based on at least one operating characteristic of the system. The
control system includes a set of instructions configured to control
the flushing system according to at least one of a predetermined
protocol or as triggered by one or more signals generated by the at
least on sensor. The control system can actuate one or more of the
plurality of valves to direct a flow of flushing solution from the
source of flushing solution through the second chamber of the at
least one forward osmosis unit. In some embodiments, the control
system directs the flushing solution to each of the plurality of
forward osmosis units in series.
[0008] In another aspect, the invention relates to an alternative
system and method for the osmotic extraction of a solvent from a
first solution. The system includes a forward osmosis unit having a
first chamber having an inlet fluidly coupled to a source of the
first solution, a second chamber having an inlet fluidly coupled to
a source of a concentrated draw solution, and a semi-permeable
membrane system separating the first chamber from the second
chamber and configured for osmotically separating the solvent from
the first solution, thereby forming a second solution in the first
chamber and a dilute draw solution in the second chamber. The
system also includes a separation system in fluid communication
with the forward osmosis unit and configured to separate the dilute
draw solution into the concentrated draw solution and a solvent
stream. The separation system includes a filtration unit, a reverse
osmosis unit, and a by-pass circuit all in fluid communication with
the forward osmosis unit. The filtration unit includes a first
chamber having an inlet fluidly coupled to the second chamber of
the forward osmosis unit for receiving at least a first portion of
the dilute draw solution, a second chamber having an outlet fluidly
coupled to the reverse osmosis unit for transferring a less dilute
draw solution thereto, and a filtration membrane separating the
first chamber from the second chamber and configured for partially
removing solutes from the dilute draw solution, thereby forming the
less dilute draw solution in the second chamber by passing the
remaining dilute draw solution there through. The removed solutes
are returned to the first chamber of the forward osmosis unit via
an outlet from the first chamber of the filtration unit. The
reverse osmosis unit includes a first chamber having an inlet
fluidly coupled to the second chamber of the forward osmosis unit
for receiving at least a second portion of the dilute draw solution
and an outlet fluidly coupled to the second chamber of the forward
osmosis unit for introducing the concentrated draw solution
thereto, a semi-permeable membrane coupled to the first chamber,
and a second chamber coupled to the semi-permeable membrane and
configured for receiving a solvent fluxed through the membrane,
thereby leaving the concentrated draw solution in the first chamber
for transfer to the forward osmosis unit. The by-pass circuit is
configured to selectively direct the first and second portions of
the dilute draw solution to the filtration unit and the reverse
osmosis unit. Generally, the by-pass circuit includes any necessary
valves, sensors, controls, etc. for regulating (and in some
embodiments also monitoring) the portions of dilute draw solution
directed to either unit. Depending on the particular application of
the system or method (e.g., feed/draw chemistries, operating
parameters, and ambient conditions), anywhere from 0-100% of the
dilute draw solution can be directed to either the filtration unit
or the reverse osmosis unit.
[0009] In various embodiments of the foregoing aspect, the forward
osmosis unit includes a plurality of forward osmosis units, where
each includes a first chamber having an inlet fluidly coupled to
the source of the first solution, a second chamber having an inlet
fluidly coupled to the source of a concentrated draw solution, and
a semi-permeable membrane system separating the first chamber from
the second chamber and configured for osmotically separating the
solvent from the first solution, thereby forming the second
solution in the first chambers and the dilute draw solution in the
second chambers. In addition, the portions of the dilute draw
solution can be delivered to the filtration unit and/or the reverse
osmosis unit under pressure, for example, via a pump or other
pressure exchange device. In some embodiments, the separation
system further includes means for introducing an additive to the
first portion of the dilute draw solution, the second portion of
the dilute draw solution, or both. The means for introducing the
additive can include a valve and port arrangement for directly
introducing the additive to a fluid conveying line or one of the
units. Additionally, the means can include a storage and/or mixing
tank along with a metering device or the like for storing and/or
delivering the additive to the system. In one or more embodiments
of the system, the separation system can include a thermal recovery
unit in fluid communication with the outlet of the first chamber of
the reverse osmosis unit for receiving the concentrated draw
solution therefrom and the second chamber of the forward osmosis
unit for introducing a further concentrated draw solution
thereto.
[0010] In yet another aspect, the invention relates to systems and
methods for extracting a solvent from a first solution. One such
system includes a forward osmosis unit, a reverse osmosis unit, and
a separation system. The forward osmosis unit includes a first
chamber having an inlet fluidly coupled to a source of the first
solution, a second chamber having an inlet fluidly coupled to a
source of a concentrated draw solution, and a semi-permeable
membrane system separating the first chamber from the second
chamber. The semi-permeable membrane is configured for osmotically
separating the solvent from the first solution, thereby forming a
second solution in the first chamber (or on one side of the
membrane) and a dilute draw solution in the second chamber (or
opposite side of the membrane). The reverse osmosis unit is fluidly
coupled to an outlet of the second chamber of the forward osmosis
unit and includes a first chamber in fluid communication with the
second chamber of the forward osmosis unit and configured for
receiving the dilute draw solution under pressure, a semi-permeable
membrane coupled to the first chamber, and a second chamber coupled
to the semi-permeable membrane and configured for receiving a
solvent fluxed through the membrane, thereby leaving a less dilute
draw solution in the first chamber of the reverse osmosis unit. The
separation system is in fluid communication with the forward
osmosis unit and the reverse osmosis unit and is configured to
separate the dilute or less dilute draw solution into the
concentrated draw solution and a solvent stream. The separation
system includes an inlet fluidly coupled to an outlet of the first
chamber of the reverse osmosis unit for receiving the less dilute
draw solution therefrom and an outlet fluidly coupled to the second
chamber of the forward osmosis unit for introducing the
concentrated draw solution to the forward osmosis unit.
[0011] In various embodiments of the foregoing aspect, the system
includes a pressure exchanger disposed between and in fluid
communication with the second chamber of the forward osmosis unit
and the first chamber of the reverse osmosis unit. The pressure
exchanger is configured to increase the pressure of the dilute draw
solution introduced to the first chamber of the reverse osmosis
unit. The system can also include a by-pass system in fluid
communication with the first chamber of the reverse osmosis unit
and the second chamber of the forward osmosis unit for directing
the less dilute draw solution back to the forward osmosis unit. In
one or more embodiments, the system includes a porting system
(e.g., an inlet or outlet and necessary valving) for introducing
(or removing) a substance to (from) the dilute draw solution or
other associated stream. The system can also include at least one
treatment system in fluid communication with at least one of the
forward osmosis unit, the reverse osmosis unit, or the separation
system. The at least one treatment system can be configured to
remove the substance added to the dilute draw solution. In one
embodiment, the porting system is in fluid communication with the
first chamber of the reverse osmosis unit.
[0012] In additional embodiments, the system includes means for
altering, for example reducing, an osmotic pressure of the dilute
draw solution. The means for altering the osmotic pressure of the
dilute draw solution can include at least one of chemical addition,
chemical subtraction, reduction-oxidation, reactive extraction,
filtration, precipitation, or exposure to an energy signal, such
as, for example, an electromagnetic signal (photolysis), an
electrical signal (electrolysis), or a thermal signal
(thermolysis). Further, the system can also include at least one
treatment system in fluid communication with at least one of the
forward osmosis unit, the reverse osmosis unit, or the separation
system to reverse the osmotic pressure alteration of the dilute
draw solution. In one or more embodiments, the means for altering
the osmotic pressure of the dilute draw solution is in fluid
communication with the first chamber of the reverse osmosis
unit.
[0013] In yet another aspect, the invention relates to additional
systems and methods for extracting a solvent from a solution. One
example of such a system includes a first forward osmosis unit, a
second forward osmosis unit, and a separation system. The first
forward osmosis unit includes a first chamber having an inlet
fluidly coupled to a source of the first solution, a second chamber
having an inlet fluidly coupled to a source of a concentrated first
draw solution, and a semi-permeable membrane system separating the
first chamber from the second chamber. The semi-permeable membrane
is configured for osmotically separating the solvent from the first
solution, thereby forming a second solution in the first chamber
(or on a first side of the membrane) and a dilute first draw
solution in the second chamber (or opposite side of the membrane).
The second forward osmosis unit is in fluid communication with the
first forward osmosis unit and includes a first chamber having an
inlet fluidly coupled to an outlet of the second chamber of the
first forward osmosis unit and configured for receiving the dilute
first draw solution from the first forward osmosis unit, a second
chamber having an inlet fluidly coupled to a source of a
concentrated second draw solution, and a semi-permeable membrane
system separating the first chamber from the second chamber. The
semi-permeable membrane is configured for osmotically separating
the solvent from the dilute first draw solution, thereby forming
the concentrated first draw solution in the first chamber (or on
the first side of the membrane) and a dilute second draw solution
in the second chamber (or opposite side of the membrane). The
separation system is in fluid communication with the second forward
osmosis unit and configured to separate the dilute second draw
solution into the concentrated second draw solution and a solvent
stream. The separation system includes an inlet fluidly coupled to
an outlet of the second chamber of the second forward osmosis unit
for receiving the dilute second draw solution therefrom and an
outlet fluidly coupled to the second chamber of the forward osmosis
unit for introducing the concentrated second draw solution to the
second forward osmosis unit.
[0014] In various embodiments of the foregoing aspect, the system
includes a stripper in fluid communication with the second chamber
of the first forward osmosis unit and the first chamber of the
second forward osmosis unit. The stripper is configured to further
concentrate the first draw solution and/or remove draw solutes from
the second draw solution that may have reverse fluxed through the
membrane of the second forward osmosis unit. In one or more
embodiments, at least one of the first or second forward osmosis
units is submerged. Additionally, the system can include a reverse
osmosis unit in fluid communication with the second chamber of the
first forward osmosis unit and the first chamber of the second
forward osmosis unit. The reverse osmosis unit can be configured to
remove solvent from the dilute first draw solution. In addition,
this system and all systems described herein can include the
disclosed means for altering the osmotic pressure of the draw
solution to enhance the operation of their respective systems.
[0015] In another aspect, the invention relates to still further
systems and methods for extracting a solvent from a solution. In
one example of such a system, the system includes a reverse osmosis
unit, a first forward osmosis unit, a second forward osmosis unit,
and a separation system. The reverse osmosis unit includes a first
chamber in fluid communication with a source of the first solution,
a semi-permeable membrane coupled to the first chamber, and a
second chamber coupled to the semi-permeable membrane and
configured for receiving a first portion of the solvent fluxed
through the membrane, thereby leaving a concentrated first solution
in the first chamber of the reverse osmosis unit. The first forward
osmosis unit is fluidly coupled to the reverse osmosis unit and
includes a first chamber having an inlet in fluid communication
with the first chamber of the reverse osmosis unit and configured
for receiving the concentrated first solution, a second chamber
having an inlet fluidly coupled to a source of a concentrated draw
solution, and a semi-permeable membrane system separating the first
chamber from the second chamber. The semi-permeable membrane is
configured for osmotically separating a second portion of the
solvent from the concentrated first solution, thereby forming a
further concentrated first solution in the first chamber (or side
of the membrane) and a dilute draw solution in the second chamber
(or side of the membrane). The second forward osmosis unit is in
fluid communication with the first forward osmosis unit and
includes a first chamber having an inlet fluidly coupled to an
outlet of the first chamber of the first forward osmosis unit and
configured for receiving the further concentrated first solution
from the first forward osmosis unit, a second chamber having an
inlet fluidly connected to a source of a feed solution, and a
semi-permeable membrane system separating the first chamber from
the second chamber. The semi-permeable membrane is configured for
osmotically separating a solvent from the feed solution, thereby
diluting the concentrated first solution in the first chamber (or
side of the membrane) and concentrating the feed solution in the
second chamber (or side of the membrane). In various embodiments,
the further concentrated first solution is directed to the second
forward osmosis unit under pressure (e.g., via a pump). The
separation system is in fluid communication with the first forward
osmosis unit and configured to separate the dilute draw solution
into the concentrated draw solution and a solvent stream. The
separation system includes an inlet fluidly coupled to an outlet of
the second chamber of the first forward osmosis unit for receiving
the dilute draw solution therefrom and an outlet fluidly coupled to
the second chamber of the first forward osmosis unit for
introducing the concentrated draw solution to the first forward
osmosis unit.
[0016] In various embodiments of the foregoing aspect, the second
forward osmosis unit is a PRO unit and the system includes a
turbine in fluid communication with the first chamber of the second
forward osmosis unit and configured for receiving the pressurized,
diluted first solution. The system can also include a valve
arrangement (e.g., a by-pass system) in fluid communication with
the reverse osmosis unit and the second forward osmosis unit and
configured to return the diluted first solution from the outlet of
the first chamber of the second forward osmosis unit to the inlet
of the first chamber of the reverse osmosis unit. In various
embodiments, the feed solution comprises a wastewater effluent
stream. Additionally, the system can include an energy recovery
device in fluid communication with the reverse osmosis unit to
recapture energy from the reverse osmosis unit.
[0017] In another aspect, the invention relates to additional
systems and methods for extracting a solvent from a solution. One
such system includes a selective membrane unit, a forward osmosis
unit, a separation system, and at least one valve arrangement. The
selective membrane unit conditions a first solution and includes a
first chamber having an inlet fluidly coupled to a source of the
first solution, a second chamber having an inlet fluidly coupled to
a source of a second solution, and a selective membrane separating
the first chamber from the second chamber. The selective membrane
is configured to selectively allow certain ions within at least the
first solution to pass from the first solution to the second
solution, thereby conditioning the first solution (e.g., softening
the solution). The forward osmosis unit is in fluid communication
with the selective membrane unit and includes a first chamber
having an inlet fluidly coupled to at least one of the source of
the first solution or an outlet of the first chamber of the
selective membrane unit for receiving the conditioned first
solution, a second chamber having an inlet fluidly coupled to a
source of a concentrated draw solution, and a semi-permeable
membrane system separating the first chamber from the second
chamber. The semi-permeable membrane is configured for osmotically
separating the solvent from the first solution, thereby forming the
source of the second solution in the first chamber and a dilute
draw solution in the second chamber. The separation system is in
fluid communication with the forward osmosis unit and is configured
to separate the dilute draw solution into the concentrated draw
solution and a solvent stream. The separation system includes an
inlet fluidly coupled to an outlet of the second chamber of the
forward osmosis unit for receiving the dilute draw solution
therefrom and an outlet fluidly coupled to the second chamber of
the forward osmosis unit for introducing the concentrated draw
solution to the forward osmosis unit. The valve arrangement is in
fluid communication with the first chamber of the forward osmosis
unit, the second chamber of the selective membrane unit, and an
alternative source of the second solution. The valve arrangement
can be configured to direct the second solution from either the
first chamber of the forward osmosis unit or the alternative source
to the second chamber of the selective membrane unit.
[0018] In various embodiments of the foregoing aspect, the system
includes a second valve arrangement in fluid communication with the
source of the first solution, the selective membrane unit, and the
forward osmosis unit. The second valve arrangement is configured
for directing the first solution to either the selective membrane
unit or the forward osmosis unit or directing the conditioned first
solution to the forward osmosis unit. In one or more embodiments,
the various valve arrangements can include the ports (e.g., inlets)
and necessary valves for introducing a solution to the selective
membrane unit and/or the forward osmosis unit to, for example,
prime either or both units. Additionally or alternatively, the
ports can be outlets for removing a solution from either unit. In
one or more embodiments, the system includes at least one treatment
system in fluid communication with at least one of the selective
membrane unit, the forward osmosis unit, or the separation system.
The selective membrane can be a cation selective membrane or any
other type of membrane to suit a particular application.
[0019] In various embodiments of the foregoing aspects, the
concentrated draw solution includes ammonia and carbon dioxide in a
desired molar ratio of at least one to one. However, other draw
solutions are contemplated and considered within the scope of the
invention, including, for example, NaCl or any of the various
alternative draw solutions disclosed in PCT Patent Application No.
PCT/US13/69895 (the '895 application), filed Nov. 13, 2013, the
disclosure of which is hereby incorporated by reference herein in
its entirety. In addition, other systems and methods for separating
and recovering draw solutes and the solvent, such as those
disclosed in the '895 application, are contemplated and considered
within the scope of the invention. Furthermore, various
pretreatment and post-treatment systems can be incorporated in the
forgoing aspects of the invention. The pretreatment systems can
include at least one of a heat source for preheating the first
solution, means for adjusting the pH of the first solution, means
for disinfection (e.g., chemical or UV), separation and
clarification, a filter or other means for filtering the first
solution (e.g., carbon or sand filtration or reverse osmosis),
means for polymer addition, ion exchange, or means for softening
(e.g., lime softening) the first solution. The post-treatment
systems can include at least one of a reverse osmosis system, an
ion exchange system, a second forward osmosis system, a
distillation system, a pervaporator, a mechanical vapor
recompression system, a heat exchange system, or a filtration
system. In additional embodiments, the system can also include a
recycling system including an absorber configured to facilitate
reintroduction of the draw solutes to the second chamber to
maintain the desired molar ratio of the draw solution.
[0020] Still other aspects, embodiments, and advantages of these
exemplary aspects and embodiments, are discussed in detail below.
Moreover, it is to be understood that both the foregoing
information and the following detailed description are merely
illustrative examples of various aspects and embodiments, and are
intended to provide an overview or framework for understanding the
nature and character of the claimed aspects and embodiments.
Accordingly, these and other objects, along with advantages and
features of the present invention herein disclosed, will become
apparent through reference to the following description and the
accompanying drawings. Furthermore, it is to be understood that the
features of the various embodiments described herein are not
mutually exclusive and can exist in various combinations and
permutations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] In the drawings, like reference characters generally refer
to the same parts throughout the different views. Also, the
drawings are not necessarily to scale, emphasis instead generally
being placed upon illustrating the principles of the invention and
are not intended as a definition of the limits of the invention.
For purposes of clarity, not every component may be labeled in
every drawing. In the following description, various embodiments of
the present invention are described with reference to the following
drawings, in which:
[0022] FIG. 1 is a schematic representation of a system for osmotic
extraction of a solvent in accordance with one or more embodiments
of the invention;
[0023] FIG. 2 is schematic representation of one application of the
system of FIG. 1 in accordance with one or more embodiments of the
invention;
[0024] FIG. 3 is a schematic representation of an alternative
osmotic system including a forward osmosis unit and a reverse
osmosis unit in accordance with one or more embodiments of the
invention;
[0025] FIG. 3A is a schematic representation of an alternative
embodiment of the system of FIG. 3;
[0026] FIG. 4 is a schematic representation of an alternative
osmotic system including two forward osmosis units in accordance
with one or more embodiments of the invention;
[0027] FIG. 4A is a schematic representation of an alternative
embodiment of the system of FIG. 4;
[0028] FIG. 5 is a schematic representation of an alternative
osmotic system including a reverse osmosis unit, a forward osmosis
unit, and a pressure retarded osmosis unit in accordance with one
or more embodiments of the invention;
[0029] FIG. 6 is a schematic representation of an alternative
osmotic system including a forward osmosis unit and a selective
membrane unit in accordance with one or more embodiments of the
invention;
[0030] FIG. 6A is a detailed schematic representation of the
selective membrane unit of FIG. 6;
[0031] FIG. 7 is a schematic representation of an alternative
osmotic system including an osmotic back-flushing system in
accordance with one or more embodiments of the invention;
[0032] FIGS. 8A and 8B are graphical representations of the
additional solvent recovery possible with the alternative osmotic
system of FIG. 7 operated in accordance with one or more
embodiments of the invention; and
[0033] FIG. 9 is a schematic representation of an alternative
osmotic system in accordance with one or more embodiments of the
invention.
DETAILED DESCRIPTION
[0034] In accordance with one or more embodiments, an osmotic
method for extracting water from an aqueous solution may generally
involve exposing the aqueous solution to a first surface of a
forward osmosis membrane. A second solution, or draw solution, with
an increased concentration relative to that of the aqueous solution
may be exposed to a second opposed surface of the forward osmosis
membrane. Water may then be drawn from the aqueous solution through
the forward osmosis membrane and into the second solution
generating a water-enriched solution via forward osmosis, which
utilizes fluid transfer properties involving movement from a less
concentrated solution to a more concentrated solution. The
water-enriched solution, also referred to as a dilute draw
solution, may be collected at a first outlet and undergo a further
separation process to produce purified water. A second product
stream, i.e., a depleted or concentrated aqueous process solution,
may be collected at a second outlet for discharge or further
treatment. Alternatively, the various systems and methods described
herein can be carried out with non-aqueous solutions.
[0035] In accordance with one or more embodiments, a forward
osmosis membrane module may include one or more forward osmosis
membranes. The forward osmosis membranes may generally be
semi-permeable, for example, allowing the passage of water, but
excluding dissolved solutes therein, such as sodium chloride,
ammonium carbonate, ammonium bicarbonate, and ammonium carbamate.
Many types of semi-permeable membranes are suitable for this
purpose provided that they are capable of allowing the passage of
water (i.e., the solvent) while blocking the passage of the solutes
and not reacting with the solutes in the solution.
[0036] In accordance with one or more embodiments, at least one
forward osmosis membrane may be positioned within a housing or
casing. The housing may generally be sized and shaped to
accommodate the membranes positioned therein. For example, the
housing may be substantially cylindrical if housing spirally wound
forward osmosis membranes. The housing of the module may contain
inlets to provide feed and draw solutions to the module as well as
outlets for withdrawal of product streams from the module. In some
embodiments, the housing may provide at least one reservoir or
chamber for holding or storing a fluid to be introduced to or
withdrawn from the module. In at least one embodiment, the housing
may be insulated.
[0037] In accordance with one or more embodiments, a forward
osmosis membrane module may generally be constructed and arranged
so as to bring a first solution and a second solution into contact
with first and second sides of a semi-permeable membrane,
respectively. Although the first and second solutions can remain
stagnant, it is preferred that both the first and second solutions
are introduced by cross flow, i.e., flows parallel to the surface
of the semi-permeable membrane. This may generally increase
membrane surface area contact along one or more fluid flow paths,
thereby increasing the efficiency of the forward osmosis processes.
In some embodiments, the first and second solutions may flow in the
same direction. In other embodiments, the first and second
solutions may flow in opposite directions. In at least some
embodiments, similar fluid dynamics may exist on both sides of a
membrane surface. This may be achieved by strategic integration of
the one or more forward osmosis membranes in the module or
housing.
[0038] In accordance with one or more embodiments, draw solutes may
be recovered for reuse. A separation system may strip solutes from
dilute draw solution to produce product water substantially free of
the solutes. In some embodiments, the separation system may include
a distillation column or other thermal or mechanical recovery
mechanism. Draw solutes may then be returned, such as by a recycle
system, back to the concentrated draw solution. Gaseous solutes may
be condensed or absorbed to form a concentrated draw solution. An
absorber may use dilute draw solution as an absorbent. In other
embodiments, product water may be used as an absorbent for all or a
portion of the absorption of the gas streams from a solute
recycling system.
[0039] FIG. 1 presents a schematic of a system 10 for osmotic
extraction of a solvent using a forward osmosis system/process 12
including one or more pretreatment and/or post-treatment unit
operations 14, 16. Various forward osmosis systems and processes
can be used, such as those described herein and further described
in U.S. Pat. Nos. 6,391,205 and 8,002,989; and U.S. Patent
Publication Nos. 2011/0203994, 2012/0273417, 2012/0267306, and
2012/0267307; the disclosures of which are hereby incorporated by
reference herein in their entireties.
[0040] In accordance with one or more embodiments, the system 10
may include one or more pretreatment operations 14 to enhance the
forward osmosis process 12. The pretreatment operation can include
at least one of a heat source for preheating the first solution,
means for adjusting the pH of the first solution, means for
disinfection (e.g., chemical or UV), separation and clarification,
a filter or other means for filtering the first solution (e.g.,
carbon or sand filtration, nanofiltration, or reverse osmosis),
heat exchange, means for polymer addition, use of an anti-scalant,
ion exchange, or means for softening (e.g., lime softening) the
first solution.
[0041] In accordance with one or more embodiments, the system 10
may include one or more post-treatment operations 16. The
post-treatment systems/operations can include at least one of a
reverse osmosis system, an ion exchange system, additional forward
osmosis processes, a distillation system, a pervaporator, a
mechanical vapor recompression system, a heat exchange system, or a
filtration system. Post-treatment may reduce product water salinity
below that produced by a single pass forward osmosis system. In
other embodiments, post-treatment may alternatively or additionally
be used to remove draw solutes that would otherwise be present in a
product stream. In some specific non-limiting embodiments, forward
osmosis brine discharge may be post-treated using ion exchange,
distillation, pervaporation, membrane distillation, aeration,
biological treatment or other process to remove draw solutes that
reverse diffuse into brine. Additional post-treatment operations
can include zero liquid discharge (ZLD) treatment using, for
example, crystallization and evaporation. In one embodiment, the
ZLD treatment uses a forward osmosis system, for example, in place
of an evaporation system. In additional embodiments, the system can
also include a recycling system including an absorber configured to
facilitate reintroduction of the draw solutes to the second chamber
to maintain the desired molar ratio of the draw solution.
[0042] FIG. 2 represents one possible application of the system 10
for osmotic extraction of a solvent in accordance with one or more
embodiments of the invention. As discussed with respect to FIG. 1,
the system 10 includes the forward osmosis system 12 and one or
more pre- and post-treatment units 14, 16. The system 10 can
include any combination of pre- and/or post-treatment units 14, 16
in conjunction with one or more forward osmosis systems 12,
including only pretreatment or only post-treatment. The various
systems/units described herein may be interconnected via
conventional plumbing techniques and can include any number and
combination of components, such as pumps, valves, sensors, gauges,
etc., to monitor and control the operation of the various systems
and processes described herein. The various components can be used
in conjunction with a controller as described hereinbelow.
[0043] In the application shown in FIG. 2, the system 10 is used to
treat brackish water from an inland source 18; however, other feed
sources are contemplated and considered within the scope of the
invention. As shown, a feed stream 20 is directed to the
pretreatment unit 14, where the feed stream is, for example,
heated. Once the feed stream has been pretreated, the treated
stream 22 is then directed to the forward osmosis system 12, where
it provides the first solution as discussed above. Optionally, the
treated stream 22 could be directed to additional pretreatment
units for further processing (e.g., pH adjustment) before entering
the forward osmosis system 12. In some embodiments, the
pretreatment unit 14 can include a reverse osmosis module to
concentrate the feed 20 prior to introducing it to the FO module.
This arrangement can be particularly useful where the initial feed
has a low salinity, as discussed below. A draw solution is provided
to the forward osmosis system 12 via stream 24 to provide the
osmotic pressure gradient necessary to promote transport of the
solvent across the membrane, as discussed herein.
[0044] At least two streams exit the forward osmosis system 12: a
concentrated feed or treated stream 26, from which solvent has been
extracted; and a dilute draw stream 28, to which solvent has been
added. The concentrated stream 26 can then be directed to a
post-treatment unit 16 for further processing, such as a second
forward osmosis system to recover additional solvent. Additional
post-treatment processes may be utilized, for example,
crystallization and evaporation, to further provide for zero liquid
discharge. The fully processed or concentrated feed can be disposed
of, recycled, or otherwise reclaimed depending on the nature of the
concentrate (arrow 38).
[0045] The dilute draw stream 28 can be directed to a separation
system 30, where the solvent and/or draw solutes can be recovered.
Optionally, the dilute draw stream 28 can also be directed to a
post-treatment unit as desired for additional processing (stream
28a), for example, the dilute draw solution can be preheated before
being directed to the separation system 30 (stream 28b). In one or
more embodiments, the separation system 30 separates the draw
solutes from the dilute draw stream 28 to produce a substantially
purified solvent stream 32, for example, potable water, and a draw
solute stream 36. In one or more embodiments, the solvent stream 32
can also be directed to a post-treatment unit for further
processing (stream 32a) depending on the end use of the solvent.
For example, the solvent can be further treated via distillation to
remove additional draw solutes that may still be present in the
solvent. In one or more embodiments, the draw solute stream 36 can
be returned directly to the draw stream 24 (stream 36a), directed
to a recycling system 34 for reintegration into the draw stream 24
(stream 36b), or directed to a post-treatment unit (stream 36c) for
further processing depending on the intended use of the recovered
draw solutes. In one or more embodiments, the recycling system 34
can be used in conjunction with the pretreatment unit 14 to, for
example, provide heat exchange with the feed stream 20 (stream
40).
[0046] In another possible application, where the system 10 is used
to treat a low-salinity feed 20, the pretreatment system 14 can be
a reverse osmosis unit that concentrates the feed 20 before
directing it to the forward osmosis system 12. In this embodiment,
the pretreatment unit 14 provides a solvent/permeate stream 32c and
a concentrated feed stream 22 for treatment by the FO module 12.
Additionally, this pretreatment/RO unit 14 can be used in
conjunction with or in place of a post-treatment unit 16 that
treats the product solvent 32 from the separation system 30 (stream
32a). Specifically, a product solvent stream 32b is directed from
the separation system 30 to the feed stream 20, where it can be
combined therewith and introduced into the pretreatment/RO unit 14.
Alternatively or additionally, the product stream 32b can be fed
directly into the unit 14. Generally, the various streams can be
directed between the various treatment units 14, 16, modules 12,
and subsystems as necessary to optimize the operation of the
process.
[0047] FIG. 3 is a simplified schematic representation of an
alternative system 210 for the extraction of a solvent that also
uses a forward osmosis unit 212, a reverse osmosis unit 216, and a
separation/recycling system 230, all in fluid communication. The
system 210 is similar to those previously disclosed, for example,
the forward osmosis unit 212 includes a forward osmosis membrane
213, the reverse osmosis unit includes a reverse osmosis membrane
217, etc. The system 210 also includes all of the necessary valves,
pumps, piping, etc. to suit a particular application. In one
embodiment, the system 210 is configured for use with a low
salinity feed, which can result in a highly diluted draw
solution.
[0048] Specifically, and as shown in FIG. 3, a feed solution 220 is
directed to one side of the membrane 213 of the forward osmosis
unit 212, while a concentrated draw solution 224 is directed to the
other side of the membrane 213. In the case where the feed solution
220 is a low salinity feed, the draw solution becomes highly
diluted. The highly diluted draw solution 226 exits the forward
osmosis unit 212 and is directed to the reverse osmosis unit 216,
while the concentrated feed solution 222 exits the forward osmosis
unit 212, where it can be sent for further processing or otherwise
discarded. In some cases, the concentrated feed solution 222
contains one or more desirable constituents, such as a food or
pharmaceutical product.
[0049] The highly diluted draw solution 226 is pressurized in the
reverse osmosis unit 216 forcing solvent through the membrane 217.
This product solvent 232A can be removed from the reverse osmosis
unit 216 as, for example, product water that can be used as is, be
disposed of, sent for further processing, or employed as a heat
transfer fluid within an integrated system. The draw solution that
remains on the first side 216A of the reverse osmosis unit 216 is
now less diluted and can be sent for further processing to further
concentrate the draw solution and/or recycled back to the forward
osmosis unit 212 as is, as necessary to suit a particular
application. As shown in FIG. 3, the less dilute draw solution 227
is directed to the separation/recycling unit 230 for further
concentration. However, the system 210 also includes an optional
by-pass line 229 (and any necessary valving) for directing at least
a portion of the less dilute draw solution back to the forward
osmosis unit 212, either directly or in combination with the
concentrated draw solution stream 224 exiting the
separation/recycling unit 230.
[0050] Generally, the separation/recycling unit can be of any of
the types disclosed in, for example, U.S. Patent Publication No.
2012/0067819 (the '819 publication), the disclosure of which is
hereby incorporated by reference herein in its entirety, or the
'895 application. In one embodiment, the unit 230 includes a
thermal recovery process to separate the draw solutes from the
solvent. In an alternative embodiment, the unit 230 includes a
reverse osmosis module. The recovered draw solutes exit the unit
230 (in one embodiment being mixed with the by-passed dilute draw
solution stream 229) and are directed to the forward osmosis unit
212 as the concentrated draw solution 224, while the remaining
solvent 232B exits the unit 230 as, for example, product water that
can be used as is, be disposed of, or sent for further
processing.
[0051] FIG. 3A depicts an alternative to the system 210 of FIG. 3,
where the system 210 includes means for altering (e.g., reducing)
the osmotic pressure of the dilute draw solution that is directed
to the reverse osmosis unit 216. Reducing the osmotic pressure of
the dilute draw solution makes the reverse osmosis process more
efficient, as less energy is required to overcome the osmotic
pressure of the dilute draw solution, thereby resulting in greater
solvent extraction from the reverse osmosis unit 216. Generally,
the means for reducing the osmotic pressure can include a variety
of mechanisms and/or processes, such as a catalyzed phase change,
heating, cooling, addition of a reactant, or introduction of an
electrical or magnetic field. In some embodiments, a physical or
chemical agent may be introduced to the dilute draw solution 226 to
react with a draw solute therein reversibly or irreversibly to
reduce its concentration or change its rejection characteristics by
the membrane. In at least one embodiment, introduction of an
electrical or electromagnetic (e.g., UV light) signal may cause a
change in the draw solute, such as a phase change, change in degree
of ionization, or other induced changes that reduces the osmotic
pressure of the solution 226. In some embodiments, the osmotic
pressure of the dilute draw solution 226 may be reduced by
adjusting a pH level, adjusting the ionic nature of a solute, or
modifying the physical size of a solute. For example, an ionic
species may be rendered nonionic, or a large species may be made
relatively smaller. In some embodiments, techniques not using
heating, such as electrodialysis (ED), cooling, vacuum or
pressurization may be implemented. In at least one embodiment, the
solubility of an organic species of solute may be manipulated, such
as by changing temperature, pressure, pH or other characteristic of
the dilute draw solution 226. In at least some embodiments, ion
exchange may be implemented, such as sodium recharge ion exchange
techniques, or acid and base recharged ion exchange. Other means
for reducing the osmotic pressure are contemplated and considered
within the scope of the invention.
[0052] In various embodiment, the system 210 includes an inlet 225
or other point of introduction, including any necessary valving,
(i.e., a porting system) for adding a substance to the dilute draw
solution 226. In one embodiment, the substance is copper hydroxide
[Cu(OH).sub.2]; however, other metals/substances are contemplated
and considered within the scope of the invention. The additional
substance can be used to scavenge or otherwise bind to certain draw
solutes within the dilute draw solution 226. In a particular
embodiment where the draw solution is ammonia based, the copper
hydroxide will bind with the ammonia to create a larger molecule
that is more easily rejected by the membrane 217 of the reverse
osmosis unit 216, thereby altering the osmotic pressure of the
dilute draw solution.
[0053] In order to more fully recover the draw solutes for reuse
and to recover the added substance (or otherwise reverse the
results of having altered the osmotic pressure of the dilute draw
solution), the system 210 will also include one or more treatment
units 214A, 214B that can be disposed, for example, on the inlet to
the separation/recycling unit 230 and/or on the product solvent
outlet. The treatment unit(s) 214 can be of any of the types
previously described with respect to the pre- and post-treatment
units 14, 16. For example, the first treatment unit 214A can
include a phase change mechanism to separate the copper hydroxide
and ammonia, while the second treatment unit 214B can include
nanofiltration to remove the copper hydroxide from the product
solvent 232B. Additionally or alternatively, the pretreatment units
214 can be or include a heat source (e.g., heat exchanger). For
example, in one embodiment, the dilute draw solution can be
preheated before going to the separation/recycling system 230. The
various treatment units 214 can also incorporate any of the
mechanisms and/or processes described above for altering the
osmotic pressure of the dilute draw solution. In one or more
embodiments, the process can include exposing the less dilute draw
solution 227 to a thermal, electro-magnetic, or electrical signal
(e.g., an electrolytic cell). In a particular embodiment, the
dilute draw solution 226 is exposed to an ultraviolet or other
energy emission source to reduce its osmotic pressure by, for
example, overcoming the activation energy to convert ionic species
to a single neutral compound with a higher molecular weight.
Changing the chemistry of the dilute draw solution allows the
reverse osmosis process to get a higher solvent recovery with the
same pumping pressure.
[0054] FIG. 4 is a simplified schematic representation of another
alternative system 310 for the extraction of a solvent. This system
310, however, uses two forward osmosis units 312, 316 and a
separation/recycling system 330, all in fluid communication. The
system 310 is similar to those previously disclosed, for example,
the forward osmosis units 312, 316 include forward osmosis
membranes 313, 317 and the system 310 also includes all of the
necessary valves, pumps, piping, etc. to suit a particular
application. In one embodiment, the system 310 is configured for
use where the first forward osmosis unit 312 is submerged, for
example in a tank 305, and uses a different draw solution than the
second forward osmosis unit 316.
[0055] As shown in FIG. 4, a feed solution 320 is directed to one
side of the membrane 313 of the first forward osmosis unit 312,
while a concentrated first draw solution 324 is directed to the
other side of the membrane 313. In one embodiment, the first draw
solution is selected from the group consisting of MgCl.sub.2.
CaCl.sub.2, Ca(NO.sub.3).sub.2, NaCl, KCl, or similar. In one or
more embodiments, the first draw solution is selected to suit a
submerged system. The diluted first draw solution 326 exits the
forward osmosis unit 312, while the concentrated feed 322 exits the
forward osmosis unit 312. In one or more embodiments, the
concentrated feed 322 can be discharged into the tank 305 or can be
disposed of or sent for further processing. In some embodiments,
the draw solution comprises a photolytic draw solute, in which case
the diluted first draw solution 326 can be exposed to UV light or
other excitation source to lower its osmotic pressure before it is
sent to the second forward osmosis unit 316. Other means for
reducing the osmotic pressure (e.g., chemical addition) may be
incorporated as discussed hereinabove.
[0056] The dilute first draw solution 326 is directed to one side
of the membrane 317 of the second forward osmosis unit 316, while a
concentrated second draw solution 325 is directed to the other side
of the membrane 317 so as to extract solvent from the dilute first
draw solution 326, thereby reconcentrating the first draw solution
(discharge 324'). The reconcentrated first draw solution 324' is
directed to, for example, a stripper 340 or other treatment process
for further conditioning/concentrating of the first draw solution
(discharge 324) so that it may again be directed to the first
forward osmosis unit 312.
[0057] The diluted second draw solution 327 is discharged from the
second forward osmosis unit 316 and directed to the
separation/recycling system 330 for reconcentration of the second
draw solution and the recovery a product solvent 332. Generally,
the separation/recycling unit 330 can be of any of the types
disclosed herein, including in the '819 publication or '895
application and separates the draw solutes from the solvent. The
recovered draw solutes/reconcentrated draw solution 325 exit the
unit 330 and are directed back to the second forward osmosis unit
316. The remaining solvent 332 exits the unit 330 as, for example,
product water that can be used as is, sent for further processing,
or otherwise discarded.
[0058] FIG. 4A depicts an alternative to the system 310 of FIG. 4,
where the system 310 includes an additional reverse osmosis unit
346 in fluid communication with the dilute first draw solution 326
outlet of the first forward osmosis unit 312 and the feed side of
the second forward osmosis unit 316. One particular application for
this alternative system is where the first feed 320 is a low
salinity feed and the first dilute draw solution 326 may become
highly diluted. The reverse osmosis unit 346 can at least partially
concentrate the highly diluted draw solution 326 before it is fed
to the second forward osmosis unit 316. As shown in FIG. 4A, the
dilute draw solution 326 is introduced under pressure to one side
of the membrane 345 of the reverse osmosis unit 346. The
pressurization of the dilute draw solution 326 may be by virtue of
the increased volume of the solution exiting the first forward
osmosis unit 312 or with the assist of a pressure exchange device
(e.g., a pump). Product solvent 232B (e.g., potable water) is
recovered from the other side of the membrane 345 and can be used
as is, disposed of, or sent for further processing. In one or more
embodiments, the product solvent can be used as drinking water. The
less dilute first draw solution 326' exits the reverse osmosis unit
346 and is directed to the second forward osmosis unit 316 for
processing as previously described. In addition, the various means
for altering the osmotic pressure of the draw solution discussed
above may be incorporated into the system 310.
[0059] FIG. 5 is a simplified schematic representation of another
alternative system 510 for the extraction of a solvent. This system
510 uses a reverse osmosis unit 516, two forward osmosis units 512,
546, and a separation/recycling system 530, all in various states
of fluid communication. The system 510 is similar to those
previously disclosed, for example, the various osmotic units 512,
516, 546 include membranes 513, 517, 545 as previously described,
and the system 510 also includes all of the necessary valves,
pumps, piping, etc. to suit a particular application. In one
embodiment, the system 510 is configured for an application where
wastewater effluent is used to dilute the concentrated feed (e.g.,
highly concentrated brine) to make it more easily disposable.
[0060] As shown in FIG. 5, a feed stream 520 (e.g., seawater) is
introduced under pressure to one side of the membrane 517 of the
reverse osmosis unit 516. A product solvent 532A (e.g., potable
water) is recovered from the other side of the membrane 517 and can
be sent for further processing or otherwise discarded. The
concentrated feed 522 (e.g., brine) is then directed to one side of
the membrane 513 of the first forward osmosis unit 512. In one
embodiment, the reverse osmosis unit 516 can be used to concentrate
a low salinity feed before directing it to the forward osmosis unit
512. Alternatively, the reverse osmosis unit 516 can be omitted and
the feed 520 sent directly to the first forward osmosis unit
512.
[0061] A concentrated draw solution 524 is directed to the opposite
side of the membrane 513 of the first forward osmosis unit 512 to
draw solvent from the feed stream 522 (or 520 in certain
embodiments). In one embodiment, the concentrated feed stream 522'
is directed to the second forward osmosis unit 546, as described
below. The now diluted draw solution 526 exits the first forward
osmosis unit 512 and is directed to the separation/recycling system
530 for reconcentration and the recovery of product solvent 532B.
Generally, the separation/recycling unit 530 can be of any of the
types previously described. The recovered draw
solutes/reconcentrated draw solution 524 exit the unit 530 and are
directed back to the first forward osmosis unit 512. The remaining
solvent 532B exits the unit 530 as, for example, product water that
can be used as is, sent for further processing, or otherwise
discarded. Alternatively or additionally, the solvent can be
directed to the original feed 520 via solvent line 532c and
combined with the feed 520 for introduction to the RO module 516 or
fed directly to the RO module 516.
[0062] The further concentrated feed solution 522' (e.g.,
concentrated brine) is introduced to one side of the membrane 545
of the second forward osmosis unit 546. In various embodiments, the
concentrated feed solution 522' is introduced under pressure and
the second forward osmosis unit is operated as a PRO unit.
Generally, the concentrated feed 522', especially in the case of
concentrated brine, can have a negative impact on the environment
if it is discharged as is. For example, the discharge of
hyper-saline solutions into natural water sources can disrupt their
local ecosystems. The use of the second forward osmosis unit 546 to
dilute the concentrated feed 522' can make this diluted feed 522''
overall easier to dispose of and generally more acceptable to
discharge. In the present application, the concentrated feed 522'
is being used as the source of draw solution. The secondary feed
solution from which the concentrated feed 522' draws solvent (e.g.,
water) is typically a source that has limited application and/or is
generally undesirable for human use. In one embodiment, the
secondary feed 547 is wastewater effluent, which, while processed
and safe to use for many applications, is typically not desirable
for human use. Alternatively or additionally, the secondary feed
547 can be from the original feed 520, for example, a split stream
with a portion of the feed 520 replacing or supplementing the
secondary feed 547.
[0063] As shown in FIG. 5, the secondary feed 547 is directed to
the opposite side of the membrane 545 of the second forward osmosis
unit 546. The concentrated feed 522' draws solvent across the
membrane 545 creating a diluted feed 522'' that exits the forward
osmosis unit 546 and can be disposed of or sent for further
processing. In embodiments where the second forward osmosis unit
546 is a PRO unit, the system 510 can include a turbine 548 in
fluid communication with the feed/draw solution outlet 543.
Examples of PRO units are disclosed in U.S. Patent Publication Nos.
2010/0024423 and 2010/0183903, the disclosures of which are hereby
incorporated herein by reference in their entireties. Alternatively
or additionally, the system 510 can include a by-pass line 529 (and
any necessary valves) for directing at least a portion of the
diluted feed 522'' back to the feed 520 to the reverse osmosis unit
516 and/or the first forward osmosis unit 512.
[0064] The concentrated secondary feed 549 exits the second forward
osmosis unit 546 and can be disposed of or sent for further
processing. In the case of a wastewater effluent feed 547, the
concentrated effluent 549, which now has a smaller volume due to
the removal of solvent, can be directed to an incinerator or be
directed back to the wastewater processing facility for further
concentration/treatment. Additionally, the second forward osmosis
unit 546 can be submerged in one or more embodiments.
[0065] FIG. 6 is a simplified schematic representation of another
alternative system 610 for the extraction of a solvent. This system
610, however, uses one or more forward osmosis unit(s) 612 in fluid
communication with a selective membrane unit 656 and a
separation/recycling system 630. In various embodiments, the
selective membrane is a cation selective membrane 655 and the
selective membrane unit 656 is a water softening module. The system
610 is similar to those previously disclosed and can include one or
more pre- and/or post-treatment units 614, 616 as described below.
The pre- and post-treatment units 614, 616 can be of any of the
types previously described. Additionally, the system 610 also
includes all of the necessary valves, pumps, piping, etc. to suit a
particular application.
[0066] As shown in FIG. 6, the system 610 includes the selective
membrane unit 656, a by-pass circuit or valve arrangement 611
(valves 623A, 623B and line 621), the forward osmosis unit 612, the
separation/recycling system 630, a priming system or second valve
arrangement 619 (valve 623C and inlet 625), and the various pre-
and post-treatment units 614, 616. The forward osmosis unit 612 and
separation/recycling unit 630 generally operate as previously
described with respect to the other systems 10, 210, 310, 510.
Generally, the first valve arrangement 611 is configured for either
directing a feed solution stream 620 to the selective membrane unit
656 or by-passing the selective membrane unit 656 and fluidly
connecting the feed stream 620 directly to one side of the forward
osmosis membrane 613. The separation/recycling system 630 is
fluidly connected to the other side of the forward osmosis membrane
613 and supplies the concentrated draw solution 624 and processes
the dilute draw solution 626.
[0067] In various embodiments where the selective membrane unit 656
is a cation selective membrane unit, the unit 656 is used to remove
hardness ions, for example, calcium, magnesium, barium, and
strontium, from the feed solution 620. These various hardness ions
have the tendency to precipitate in desalination systems, causing
fouling and scaling, which is detrimental to the desalination
process. The softened feed solution 620' is directed to one side of
the membrane 613 of the forward osmosis unit 612. In one or more
embodiments, the initial feed solution 620 can be processed by a
first treatment unit 614A and/or the softened feed solution 620'
can be further treated in a second treatment unit 614B prior to
introduction to the forward osmosis unit 612. Typically, the cation
selective membrane unit 656 uses a concentrated feed 622 from the
forward osmosis unit 612 on the opposite side of the membrane 545
as the initial feed 620 for the exchange of hardness ions, as
discussed in more detail with respect to FIG. 6A. However, because
each unit 612, 656 relies on the other for a "feed" stream, one or
both of the units 612, 656 will typically need to be primed.
[0068] Generally, the system 610 includes the by-pass circuit 611,
including the valves 623A, 623B and line 621 necessary for
providing the feed solution, either directly as a raw feed or
indirectly after processing by one of the treatment units 614, to
the forward osmosis unit 612. The by-pass circuit 611 can include
any number and arrangement of valves and lines as necessary to suit
a particular application and may even include one or more treatment
units 614 as necessary. The by-pass circuit 611 allows the system
610 to begin producing the concentrated feed 622 needed for the
cation selective membrane unit 656 to soften the feed 620.
Alternatively, the feed 620 may be sent directly through unit 656
without processing therein to initially prime the forward osmosis
unit 612. In yet another possible embodiment, the by-pass circuit
611 can include a port or other means for introducing an
alternative feed to the forward osmosis unit 612.
[0069] Additionally or alternatively, the system 610 can include a
priming system 619 that can provide a priming solution (e.g.,
brine) to the cation selective membrane unit 656 to soften the
initial feed to the forward osmosis unit 612. The priming system
619 includes one or more valves 623C and one or more inlet(s) 625
(or other means) for introducing the priming solution to the system
610. Once the system 610 reaches a steady state, the supply of
priming solution can be turned off. The system valve(s) 623C can
also be used to redirect the concentrated feed 622 to, for example,
by-pass the cation selective membrane unit 656 or discharge the
concentrated feed 622. In one or more embodiments, the system 610
can include a post-treatment unit 616 to further process the
concentrated feed 622 before directing it to the cation selective
membrane unit 656 or discharging.
[0070] The operation of the cation selective membrane unit 656 is
shown in FIG. 6A with respect to one possible embodiment where the
feed is a source of brine. As shown in FIG. 6A, the brine feed 620
is introduced on one side of the cation selective membrane 655 of
the unit 656. The feed 620 includes sodium ions (Na+) and chloride
ions (Cl-), along with the various hardness ions, such as calcium
(Ca2+), magnesium (Mg2+), barium (Ba2+), and strontium (St2+). The
concentrated brine 622 from the forward osmosis unit 612 (or other
source) is introduced to the other side of the cation selective
membrane 655. The chemical activity difference for the positive
sodium ions (Na+) across the membrane 655 drives the sodium ions
across the membrane 655 from the brine 622 to the feed 620. The
electro-selectivity results in the passage of the positively
charged hardness ions (e.g., Ca2+, Mg2+, Ba2+, and St2+) across the
membrane 655 from the feed 620 to the brine 622. Because the
membrane 655 is cation selective, the negatively charged ions
(e.g., Cl-, SO4-, HCO3-, and CO3-) do not pass through the membrane
655, thereby resulting in a softened feed 620' for directing to the
forward osmosis unit 612. The concentrated or heavy brine 622' that
now contains the hardness ions can be sent for further processing
or discarded.
[0071] FIG. 7 depicts an alternative osmotic system 710 that
utilizes one or more forward osmosis modules 712a, 712b, 712''n''
(generally 712, where "n" represents a virtually unlimited number
of modules as may be included in any particular embodiment of the
system 710), which can be arranged in series or parallel. As shown
in FIG. 7, the forward osmosis modules 712 are arranged in series
with a separation/recycling system 730 and an osmotic back-flushing
system 750 for cleaning the membranes 713a, 713b, 713n (again,
generally 713, where n represents some corresponding number of
membranes). Generally, the forward osmosis modules 712 are
configured and work similarly to those previously described. In
addition, the separation/recycling system 730 is similar to those
previously described. Only one separation/recycling system 730 is
depicted; however, multiple systems 730 may be used to suit a
particular application (e.g., a single system 730 sized and plumbed
for each forward osmosis module 712 or for multiple systems/stages
in series or parallel). The back-flushing system 750 generally
includes a source 755 of back-flushing solution 751, a fluid
transfer device (e.g., a pump) 753, a series of valves 757, 759,
765, 767, 769, sensors 761 (with or without visual indicators, such
as gauges or status lights), and associated plumbing to carry out
the back-flushing and associated processes, as described in greater
detail below. It is noted that not all of the valves and other
components may need to be separately plumbed, as any
number/combination of valves or other components can incorporated
into one or more manifold assemblies.
[0072] The operation of the basic system 710 proceeds as follows: A
feed stream 720 is introduced into the first forward osmosis module
712a that is divided into a first chamber or side 712' and a second
chamber/side 712'' by a semi-permeable membrane 713a. The feed
stream 720 is directed to each successive forward osmosis module
712a, 712b, and 712n and exits the last module 712n as a
concentrated feed stream 722. The specific number and arrangement
of forward osmosis modules 712 will be selected to suit a
particular application (e.g., starting concentration and required
final concentration of the feed stream, flux and flow rates, etc.)
and can include any number of modules arranged in series and/or
parallel. For example, multiple parallel pairs of forward osmosis
modules may be arranged in series. In the embodiment shown in FIG.
7, a concentrated draw solution 724 is introduced to the last
module 712n in the series of forward osmosis modules 712 and to the
opposite side of the membrane 713n as the feed stream 720, thereby
providing a cross-flow between the feed stream 720 and the draw
solution 724, as the draw solution 720 is directed through the
successive modules 712. However, the concentrated draw solution 724
could be first introduced into the same module 712a as the feed
stream 720 is first introduced and/or could be introduced into
multiple stages concurrently (i.e., in parallel) to suit a
particular application. In addition, the various streams/solutions
can be adjusted/divided as necessary to achieve an optimum
differential osmotic pressure as necessary to maintain the desired
flux across the membranes 713.
[0073] The feed stream 720 becomes more concentrated as it passes
through each forward osmosis module 712, with the afore-mentioned
concentrated feed stream 722 being discharged from the final
forward osmosis module 712n. The concentrated draw solution 724
becomes diluted as it passes through each successive forward
osmosis module 712 due to the passage of solvent across the
membranes 713 from the feed stream into the draw solution;
discharging a dilute draw solution 726 from the "first" forward
osmosis module 712a. Typically, the concentrated feed stream 722 is
discarded or sent for further processing, while the dilute draw
solution 726 is directed to the separation/recycling system 730 to
recover draw solutes/reconcentrate the draw solution and recover
product solvent (e.g., water) 732. Alternatively or additionally, a
portion of the more concentrated feed stream exiting each forward
osmosis module 712 can be redirected back to and combined with the
initial feed stream 720 or directed to a subsequent forward osmosis
module 712 as necessary to maintain an optimum differential osmotic
pressure across the membranes 713. For example, if the feed stream
directed to a subsequent module 712 is too concentrated, such that
the differential osmotic pressure across the membrane 713 is so
small that an unacceptable drop in flux occurs, a portion of the
less concentrated feed exiting an earlier module 712 can be
combined with the feed entering the subsequent module via, for
example, the appropriate actuation of valves 767b-767n.
[0074] As previously described, the osmotic back-flushing system
750 will include a source 755 of flushing solution 751 that is in
fluid communication with one or more of the forward osmosis modules
712 via one or more valves 757, 759, 765, 767. In some embodiments,
the flushing solution 751 is water (e.g., the product solvent 732
or other low salinity solution); however, other fluids are
contemplated and considered within the scope of the invention, such
as, for example, a dilute version of the draw solution (e.g., a
dilute draw solution exiting one of the other modules that may be
directed to a module undergoing back-flushing) or an application
specific solution chemistry (e.g., a solution that is chemically
compatible with one or more aspects of the system and/or may have
additional beneficial effects when fluxed into the feed stream), as
long as the solution has an osmotic pressure less than the feed
stream so that flux is generated from the draw side 712' to the
feed side 712'' of the membrane 713. In some embodiments, the
flushing solution 751 includes an additive, such as an acid,
chelator, or surfactant that can reverse flux through the membrane
to reduce/eliminate fouling on the active layer of the membrane.
Examples of such additives include: citric acid, sulfuric acid,
hydrochloric acid, ethylenediaminetetraacetic acid (EDTA) and other
low molecular weight substances. In additional embodiments, the
temperature of the flushing solution 751 can be varied to suit a
particular application, for example, the temperature of the
flushing solution can be increased to assist with the reverse
fluxing of an additive through the membrane. In one or more
embodiments, the flushing solution 751 is stored within a tank 755
as part of the overall system 710; however, it may also be supplied
from an external source via, for example, a port 763b and valve
759b arrangement. The valves 757, 759, 765, 767, 769 can be
essentially any combination of shut-off and directional valves and
will typically be multi-directional valves that can control
multiple streams between the various systems 730, 750 and modules
712, as are well-known in the industry.
[0075] Generally, the back-flushing system 750 can be operated as
needed (for example, via manual initiation or as triggered by a
signal representing a change in one or more performance
characteristics of the system 710) or at specific intervals
depending, for example, on a protocol that takes into consideration
the nature/chemistry of the feed streams 720, 722 and/or draw
solutions 724, 726, the operating conditions (e.g., temperature,
flow rates, flux, pressures, etc.), presence or absence of
pretreatment, and combinations thereof. For example, the
back-flushing system 750 can programmed to flush all of the modules
712 in a single operation at, for example, three (3) hour
intervals, or other application specific interval, for example a
more frequent interval may be preferable where the feed stream 720
has a high likelihood of fouling the membranes 713. Other intervals
can include, for example, every 48 hours or every six hours during
a first period of operation and shorter or longer intervals for
subsequent periods of operations. Also, the duration of the osmotic
back-flushing procedure can be selected to suit a particular
application. Alternatively or additionally, the back-flushing
system 750 could flush individual modules 712 as necessary based on
one or more signals generated by one or more sensors 761 located
up- and/or downstream of a module 712. In some embodiments, the
system may operate an osmotic back-flushing procedure on individual
modules, each having a unique protocol. For example, each module
could be flushed every six to 24 hours on a staggered schedule,
such as the first module is flushed every 12 hours, a second module
is flushed two hours after the first module and every 12 hours, a
third module is flushed two hours later and also every 12 hours,
etc. The flush duration for the modules can be substantially the
same or can vary to suit a particular application. For example, the
last module downstream of the feed inlet may be subjected to
greater fouling since it is exposed to the most concentrated feed,
as such it may need to be flushed for a longer duration or, in some
cases, also or alternatively more frequently than the other
modules. Essentially any combination of flushing intervals and
durations are possible to suit a particular application, as may be
defined by the number of modules, the feed and draw solution
chemistries, ambient conditions, membrane materials, etc.
[0076] When it is determined that a back-flushing procedure is
necessary, either based on a predetermined protocol or the
measurement of a change in a system performance characteristic
(e.g., a drop in flux, which is typically continuously monitored),
one or more of the valves may be actuated (manually or
electronically by a control system) to redirect the flow pathways
of the various streams/solutions. Generally, in a normal operation
according to one or more embodiments of the invention, valves 757a,
757b, and 757d are positioned to allow for the direct flow of
concentrated draw solution 724 into the forward osmosis modules 712
(either from the separation/recycling system 730 or as otherwise
introduced to the system 710, for example via port 763b and valve
759b arrangement) and the discharge of dilute draw solution 726
from the forward osmosis modules 712 to the separation/recycling
system 730. Additional valves (e.g., flow control or pressure
relief type) and sensors 761 may be present to further monitor and
control the various systems and flows therebetween. For example,
the system 710 may include an additional port 763a and valve 759a
arrangement in the line that carries the dilute draw solution 726
to the separation/recycling system 730 that can be used as, for
example, a blow down to remove excess and/or undesirable solutes
(e.g., solutes that passed through the membrane 713 from the feed
stream 720) from within the dilute draw solution 726, as is
well-known in the industry. Alternatively or additionally, the port
763a and valve 759a arrangement can be used to introduce additional
chemicals and/or make-up draw solution to the system 710, for
example, disodium phosphate may be added to the dilute draw
solution 726 to adjust the pH thereof. In one or more embodiments,
the port 763b and valve 759b arrangement can be used to introduce
additional chemicals and/or prime the system 710 with an initial or
make-up source of concentrated draw solution 724.
[0077] To begin the back-flushing procedure, at least valve 757d is
actuated to stop the flow of concentrated draw solution 724 to the
forward osmosis modules 712 and introduce the flushing solution 751
from the back-flushing system 750 to the draw sides 712' of the
forward osmosis modules 712. Alternatively, valve 757d may be
actuated to significantly reduce the flow of concentrated draw
solution 724 and meter in a portion thereof into the flushing
solution 751 depending on the nature of the flushing solution to,
for example, customize the flushing solution 751 being introduced
into any given module 712. Typically, the flushing solution 751 is
introduced into the forward osmosis modules 712 in series; however,
the flushing solution 751 can be introduced into the modules 712 in
parallel or singularly via the appropriate combination and
actuation of valves 757, 759, 765, 767, 769. For example, valve
757c can be actuated to direct the flushing solution to an entire
series of modules or portion the flushing solution 751 between
multiple modules 712. In one embodiment, the osmotic back-flushing
procedure is carried out on a single module/stage at a time (the
module can be isolated from the remaining modules via actuation of
the appropriate valves), while the other modules/stages continue to
operate normally, thereby maintaining the steady state operation of
the overall system. Additional valve arrangements can be used to
blend the flushing solution 751 with other streams/solutions to
suit a particular application. In one example, the dilute draw
solution 726 can be used as the flushing solution by redirecting
the solution 724 to the modules 712 via valves 757, 759, 765.
Because the flushing solution 751 has a lower concentration of
solutes (or essentially no solutes in the case of deionized water),
i.e., a lower osmotic potential, solvent will flow from the draw
side 712' of a module 712, across the membrane 713, and into the
feed side 712'' (i.e., into the feed stream 720), thereby removing
at least a portion of any scale or other fouling matter that may
have settled on the feed side 712'' of the membrane 713. The
duration of the back-flushing procedure will vary to suit a
particular application and may last from 1 minute to 60 minutes,
preferably from 5 minutes to 45 minutes and more preferably from 10
minutes to 20 minutes. Generally, the duration of the procedure
will be selected to remove a substantial portion or all of the
scale/fouling matter that has adhered to the membrane with a
minimum amount of down time (e.g., a time when the feed stream 720
is not being concentrated). In one exemplary embodiment, the
osmotic back-flush runs for about 15 minutes every 48 hours. In yet
another embodiment, the osmotic back flush runs for about 5-10
minutes every 1-2 hours. In addition, the flow rate of the feed
stream or the draw solution through a module 712 can be varied
during a flushing procedure. For example, the flow rate of the feed
stream 720 (the draw stream during a back-flush procedure) can be
increased to, for example, increase the shear forces on any
fouling/scaling that has formed on the membrane surface. The
increased flow rate can also result in a higher flux rate during
the osmotic back-flush, further assisting in the cleaning of the
membrane. Additionally, the system 710 can include recirculation
circuits 771a, 771b, 771n on each of the forward osmosis modules
712. The circuits 771 can include a pump (or other pressure
exchange device) and any osmosis module 712. In one embodiment, the
osmotic back-flush protocol includes operating the recirculation
circuit 771 to assist with the cleaning of the membrane by, for
example, varying (e.g., increasing) the flow rate through the
module 712 and/or reversing the flow direction of at least a
portion of the feed stream. Again, the specific flushing protocol
will be selected to suit a particular application. The nature of
the feed stream's chemistry, the target flux, operating pressures,
and/or temperatures, among other operating parameters may all
factor in to determining the appropriate osmotic back-flushing
procedure (e.g., interval, duration, solution chemistry, etc.).
[0078] The "used" flushing solution 751' that exits the module(s)
712 may be directed to the separation/recycling system 730,
recirculated back through one or more modules 712, or returned to
the back-flushing system 750 via the appropriate actuation of
valves 757, 759, 765, 769, depending on the nature of the flushing
solution 751. In one or more embodiments, the flushing solution
751' is removed via the port 763a and valve 759a arrangement and
discarded, returned to the back-flushing system 750, added to the
feed stream 720, or sent elsewhere for processing. The now diluted
feed stream 722' can be recirculated back to the initial feed
stream 720 or discarded/sent for further processing with the
concentrated feed 722 via, for example, actuation of at least valve
757e.
[0079] Generally, when operating the modules 712 in a series
arrangement, it is usually desirable to operate with a cross-flow
of the feed stream 720 and the draw solution 724, as shown in FIG.
7 and described above, so that the feed stream concentration
increases as it flows through the modules 712 and the draw solution
concentration decreases as it flows through the modules 712. The
cross-flow orientation of the feed stream and draw solution can be
considered perpendicular in this embodiment; however, in other
embodiments, the cross flow of the feed stream and draw solution
may also be tangential, as opposed to just parallel or
perpendicular. This arrangement results in the least concentrated
feed stream opposing the least concentrated draw solution across
the membrane 713a in module 712a and the most concentrated feed
stream opposing the most concentrated draw solution across membrane
713n in module 712n. This results in an optimum differential
osmotic pressure across all of the modules 712. However, in some
embodiments, it may be desirable to alter the differential osmotic
pressure across one or more of the forward osmosis modules 712 to
increase flux across that or a later/subsequent (as determined by
draw solution flow direction) forward osmosis module 712 to
increase solvent recovery/removal from the feed stream 720. In one
or more embodiments, this can be achieved by using at least a
portion of the back-flushing system 750 to introduce portion(s) of
one or more other solutions to a particular module 712, thereby
altering the differential osmotic pressure across any particular
membrane 713.
[0080] In one such example, a portion of concentrated (or at least
more concentrated depending on the source) draw solution 724 may be
added to the partially diluted draw solution being introduced into
a subsequent forward osmosis module 712 during an otherwise typical
operation, which can result in additional flux across the membrane
(i.e., greater solvent recovery). This can be accomplished by
actuating valve 757b and one or more of valves 759c, 759n, 765
depending on the number of modules 712 in the system, their
arrangement, and which module's flux rate is targeted for
modification. For example, in one or more embodiments, valve 757b
can be used to meter portions of concentrated draw solution 724 to
multiple modules 712, so as not to disrupt the flow of concentrated
draw solution to any particular module 712. Alternatively,
different combinations of valves 757, 759, 765, 769 can be actuated
to introduce a portion of dilute draw solution 726, either alone or
blended with a portion of concentrated draw solution 724, to the
partially diluted draw solution directed to any particular module
712, thereby resulting in the introduction of a draw solution
having a customized concentration to any particular module 712 to
suit a particular application. One such application can include a
situation where the feed stream concentration varies, such that the
draw solution concentration needs to be varied to maintain a
relatively constant flux rate across all of the modules 712. In
such an embodiment, a variety of sensors 761 can be used to monitor
different characteristics of the feed streams 720, 722 and draw
solutions 724, 726 (e.g., concentration level via a conductivity
sensor) and trigger the actuation of the appropriate valves 757,
759, 765, 767, 769 as necessary to modify the draw solution
concentration to one or more of the modules 712.
[0081] The graphs in FIGS. 8A and 8B illustrate the potential for
increased solvent recovery from the subsequent forward osmosis
modules 712 (i.e., the earlier module relative to the feed stream
flow direction, which is also where the feed stream is less
concentrated) when operating in accordance with one or more of the
preceding examples. As shown in FIGS. 8A and 8B, lines 801/801'
represent average flux for the system 710 under normal operation,
while lines 803/803' represent the average flux for the system 710
utilizing the osmotic back-flushing system 750 as a partial by-pass
of the concentrated draw solution, with relative flux (JW) plotted
on the ordinate and the number of modules (n) plotted on the
abscissa.
[0082] In the specific example plotted in FIG. 8A, the system 710
includes 6 forward osmosis modules 712 and a portion of
concentrated draw solution 724 is by-passed to the last three
modules (i.e., 712d, 712e, 712f) ("1/2 n"); however, the system 710
may include any number of forward osmosis modules 712 and the
concentrated draw solution 724 can be by-passed to any number of
modules in any order. Generally, the introduction of additional
concentrated draw solution to the partially diluted draw solution
entering any subsequent module 712 increases the differential
osmotic pressure with respect to that module 712, which results in
an increased flux across the associated membrane 713 (i.e.,
additional solvent recovered).
[0083] As can be seen in FIG. 8A, the non-modified differential
osmotic pressure (i.e., normal operation) results in a fairly
constant flux rate through the plurality of serial forward osmosis
membranes, while with the modified differential osmotic pressure,
there is an initial increase in system flux (specifically in the
modules 712d, 712e, 712f) that eventually returns to "normal" in
the later modules 712a, 712b, 712c. As represented by FIG. 8B,
portions of the concentrated draw solution 724 are introduced to
alternate modules 712 (e.g., 712f, 712d, 712b), thereby resulting
in alternating increases in module flux for an overall increase in
the average system flux.
[0084] Furthermore, the back-flushing system 750 or portions
thereof may also be used to control other operations of the overall
system 710 and/or run alternative back-flushing protocols. For
example, in some embodiments, the differential osmotic pressure
between the draw and feed sides 712', 712'' of the membrane 713 may
be so great that the membrane may be at risk of delamination and/or
blistering. In that situation, various valves and lines of the
back-flushing system can be used to divert and/or blend different
streams/solutions. For example, during a back-flushing procedure, a
portion of dilute and/or concentrated draw solution 724, 726 may be
blended with the flushing solution 751 to achieve a suitable
osmotic potential thereof, and by extension, the optimum
differential osmotic pressure between the opposing sides of the
membrane 713. In some cases, for example where the feed stream 720
is first introduced and at its most concentrated during the
back-flushing procedure (module 712a in FIG. 7), valve 757a and/or
valve 757b, along with valve 759b and possibly valve 765 (depending
on which solution is to be introduced), may be actuated to
introduce a portion of draw solution into the flushing solution 751
introduced to forward osmosis module 712a, thereby reducing the
differential osmotic pressure across the membrane 713a. Other
portions/concentrations of draw solution can be added to the other
forward osmosis modules 712a, 712n, as necessary to obtain an
optimum differential osmotic pressure across the membranes 713 by
actuating the appropriate valves 757, 759, 765, 767, 769 depending
on the number of forward osmosis modules 712 used in any particular
embodiment of the system 710.
[0085] FIG. 9 is a simplified schematic representation of another
alternative system 910 for the extraction of a solvent. This system
910 uses one or more forward osmosis units 912 (e.g., multiple
units arranged in series and/or parallel to suit a particular
application) and a separation system 930 that incorporates one or
more of a nanofiltration/ultrafiltration unit 914, a reverse
osmosis unit 916, and a membrane distillation unit 958, all in
various states of fluid communication. The system 910 is similar to
those previously disclosed, for example, the various
osmotic/filtration units 912, 914, 916 include membranes 913, 915,
917 as previously described, and the system 910 also includes all
of the necessary valves, pumps, piping, sensors, controls, etc. to
suit a particular application. In one embodiment, the system 910 is
configured for an application where the feed stream includes
certain solutes that may be disposed to selective permeation
through the membrane 913 and/or would otherwise require
pretreatment. In some embodiments, the membrane(s) may have high
selective permeability properties, thereby allowing these solutes
to pass through the membrane(s) 913; however alternative types of
membranes may be used to maximize performance of the system 910 for
a particular application, for example, feed chemistry, draw
solution chemistry, ambient conditions, etc.
[0086] As shown in FIG. 9, a feed solution 920 is directed to one
side of the membrane 913 of the forward osmosis unit 912, while a
concentrated draw solution 924' is directed to the other side of
the membrane 913. A diluted draw solution 926 exits the forward
osmosis unit 912 and is directed to the separation system 930,
while the concentrated feed solution 922 exits the forward osmosis
unit 912, where it can be used as is, sent for further processing,
or otherwise discarded. In some cases, the concentrated feed
solution 922 contains one or more desirable constituents, such as a
food or pharmaceutical product.
[0087] Generally, the separation system 930 includes the
nanofiltration (NF) or ultrafiltration (UF) unit 914 for initially
treating at least a portion of the dilute draw solution 926 and the
reverse osmosis unit 916 for treating the dilute draw solution 926'
processed by the NF/UF unit 914, the dilute draw solution 926
directly outputted by the forward osmosis unit 912, or both. The
system 930 may optionally include a membrane distillation unit 958
or other thermal recovery system as previously described herein for
additional concentration of the draw solution and/or to recover
additional product water, as discussed in greater detail below. In
one or more embodiments, the dilute draw solution 926 may include
one or more solutes 962 that have selectively permeated across the
membrane 913, such as calcium ions (Ca2+), magnesium ions (Mg2+) or
various sulfates, sulfonates, or generally other sparingly soluble
inorganic solutes or organic constituents. At least a portion of
the dilute draw solution 926 (including the permeated solutes) can
be directed to the NF/UF unit 914. In some embodiments, all or a
portion of the dilute draw solution can by-pass the NF/UF unit 914
via by-pass line 929 and valve arrangement 959 and be sent directly
to the reverse osmosis unit 916, depending, in part, on the
condition/chemistry of the dilute draw solution 926. In some
embodiments, the by-pass valve arrangement 959 can include a
three-way valve that can meter portions of the dilute draw solution
926 to the NF/UF unit 914 and/or the reverse osmosis unit 916.
Alternatively, multiple valves can be used to selectively direct
the dilute draw solution 926, or portions thereof, to the
appropriate treatment process.
[0088] Typically, the NF/UF membrane 915 will be a "loose" NF
membrane (or possibly a "tight" UF membrane) that allows at least a
substantial portion of the draw solutes (e.g., NaCl) to pass there
through, while blocking at least a substantial portion of the
permeated solutes 962. Generally, a membrane 915 with a rejection
rate of only about 30% is acceptable (e.g., a 0%-20% rejection if
NaCl draw solutes are used is preferable), although what is
considered a desirable rejection rate will vary depending on the
various system conditions, for example, solution chemistries,
operating parameters, and ambient conditions. In one or more
embodiments, draw solutes comprising monovalent compounds, such as
NaCl, pass more readily through the NF membrane 915 where they can
be concentrated in the reverse osmosis unit 916 for use as the
concentrated draw solution 924, while the divalent or polyprotic
compounds, such as Ca2+, sulfates, or organic compounds are
rejected by the membrane 915 and returned to the feed stream 920.
These solutes 962 can be directed to the system feed 920 via line
968, which may include any necessary pumps, valves, controls, etc.
to return the solutes 962 to the feed 920. In one or more
embodiments, only about 10% of the dilute draw solution 926 is
directed to the NF/UF unit 914, which acts similar to a solute
blow-down process to remove at least a portion of undesirable
solutes that may build up in the draw solution and/or assist with
the balancing of ions between the feed and draw sides 912a, 912b of
the forward osmosis unit(s) 912, thereby eliminating the need for a
separate blow-down circuit.
[0089] Additionally, the separation system 930/by-pass circuit
(929, 959) may include means 964 (e.g., a port and valve
arrangement, with or without a tank, metering/mixing device, etc.)
for introducing one or more additives to the dilute draw solution
926 prior to processing. In some embodiments, a dispersant (e.g.,
sodium lignin sulfonate) may be added to the dilute draw solution
926 prior to the NF/UF unit 914 to facilitate the introduction of
the additive to the feed stream 920, as at least a substantial
portion of the additive will be rejected by the NF/UF membrane
allowing it to be returned to the feed with the undesirable solutes
962. In some embodiments, the additive can reduce or eliminate
fouling or scaling of the NF/UF membrane prior to be directed to
the feed stream 920. Alternatively or additionally, the
introduction means 964 can be used to introduce other additives
(e.g., anti-scalants, corrosion inhibitors, complexing agents,
dispensing agents, sequestrants, sludge conditioners, or sludge
inhibitors) to other areas of the system 910. For example, the
system 910 may include similar means 966 for introducing additional
draw solutes to the draw solution. In some embodiments, these means
966 include a brine maker (e.g., where the main draw solute is
NaCl) to replace any solutes that may have reverse fluxed through
the membrane 913 or otherwise have been lost in the draw solution
recovery process. These means 966 will typically be disposed
proximate to where the concentrated draw solution is introduced to
the forward osmosis unit(s) 912; however, other locations are
possible to suit a particular application.
[0090] The diluted draw solution 926, 926' is pressurized in the
reverse osmosis unit 916 (e.g., via pump 953 or other pressure
exchanger) forcing solvent through the membrane 917. This product
solvent 932 can be removed from the reverse osmosis unit 916 as,
for example, product water that can be used as is, be disposed of,
sent for further processing, or employed as a heat transfer fluid
within an integrated system. The draw solution that remains on the
first side 916A of the reverse osmosis unit 916 is now concentrated
draw solution 924 and can be sent back to the forward osmosis unit
912 as is, or sent for further processing to further concentrate
the draw solution and/or recover additional product solvent, as
necessary to suit a particular application. As shown in FIG. 9, the
concentrated draw solution 924 exiting the reverse osmosis unit 916
is directed to the optional membrane distillation unit 958 for
further concentration, producing additional product water 932' and
a more concentrated draw solution 926'.
[0091] In accordance with one or more embodiments, the devices,
systems and methods described herein may generally include a
controller for adjusting or regulating at least one operating
parameter of the device or a component of the systems, such as, but
not limited to, actuating valves and pumps, as well as adjusting a
property or characteristic of one or more fluid flow streams
through an osmotically driven membrane module, or other module in a
particular system. A controller may be in electronic communication
with at least one sensor configured to detect at least one
operational parameter of the system, such as a concentration, flow
rate, pH level, or temperature. The controller may be generally
configured to generate a control signal to adjust one or more
operational parameters in response to a signal generated by a
sensor. For example, the controller can be configured to receive a
representation of a condition, property, or state of any stream,
component, or subsystem of the osmotically driven membrane systems
and associated pre- and post-treatment systems. The controller
typically includes an algorithm that facilitates generation of at
least one output signal that is typically based on one or more of
any of the representation and a target or desired value such as a
set point. In accordance with one or more particular aspects, the
controller can be configured to receive a representation of any
measured property of any stream, and generate a control, drive or
output signal to any of the system components, to reduce any
deviation of the measured property from a target value.
[0092] In accordance with one or more embodiments, process control
systems and methods may monitor various concentration levels, such
as may be based on detected parameters including pH and
conductivity. Process stream flow rates and tank levels may also be
controlled. Temperature and pressure may be monitored. Membrane
leaks may be detected using ion selective probes, pH meters, tank
levels, and stream flow rates. Leaks may also be detected by
pressurizing a draw solution side of a membrane with gas and using
ultrasonic detectors and/or visual observation of leaks at a
feedwater side. Other operational parameters and maintenance issues
may be monitored. Various process efficiencies may be monitored,
such as by measuring product water flow rate and quality, heat flow
and electrical energy consumption. Cleaning protocols for
biological fouling mitigation may be controlled such as by
measuring flux decline as determined by flow rates of feed and draw
solutions at specific points in a membrane system. A sensor on a
brine stream may indicate when treatment is needed, such as with
distillation, ion exchange, breakpoint chlorination or like
protocols. This may be done with pH, ion selective probes, Fourier
Transform Infrared Spectrometry (FTIR), or other means of sensing
draw solute concentrations. A draw solution condition may be
monitored and tracked for makeup addition and/or replacement of
solutes. Likewise, product water quality may be monitored by
conventional means or with a probe such as an ammonium or ammonia
probe. FTIR may be implemented to detect species present providing
information which may be useful to, for example, ensure proper
plant operation, and for identifying behavior such as membrane ion
exchange effects.
[0093] Those skilled in the art should appreciate that the
parameters and configurations described herein are exemplary and
that actual parameters and/or configurations will depend on the
specific application in which the systems and techniques of the
invention are used. Those skilled in the art should also recognize
or be able to ascertain, using no more than routine
experimentation, equivalents to the specific embodiments of the
invention. It is, therefore, to be understood that the embodiments
described herein are presented by way of example only and that,
within the scope of the appended claims and equivalents thereto;
the invention may be practiced otherwise than as specifically
described.
[0094] Moreover, it should also be appreciated that the invention
is directed to each feature, system, subsystem, or technique
described herein and any combination of two or more features,
systems, subsystems, or techniques described herein and any
combination of two or more features, systems, subsystems, and/or
methods, if such features, systems, subsystems, and techniques are
not mutually inconsistent, is considered to be within the scope of
the invention as embodied in the claims. Further, acts, elements,
and features discussed only in connection with one embodiment are
not intended to be excluded from a similar role in other
embodiments.
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