Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02792516 2012-10-17
APPARATUS FOR COMPRESSION OF A STACK AND FOR A WATER TREATMENT
SYSTEM
TECHNICAL FIELD
[0001] The present disclosure is directed at an apparatus including a membrane
based
stack and a compression device to minimize leaks. The present disclosure is
also directed at a
modular apparatus for a water treatment system that includes modules having
rigid end plates
including an electrode to facilitate electrochemical reactions in each module.
The present
disclosure is further directed at a compression device for a membrane based
stack.
BACKGROUND
[0002] Over one quarter of Earth's population does not have adequate access to
freshwater. Inadequate access to freshwater is detrimental, as it can lead to
disease and
malnutrition, limit agricultural development, and inhibit economic growth.
[0003] In contrast to freshwater, saltwater is readily available. Saltwater in
the form of
seawater constitutes about 97% of the water on Earth. Unless seawater is
sufficiently desalinated,
though, it is not only undrinkable but unsuitable for agriculture.
"Desalination" refers to the
process of removing anions and cations from saltwater. Seawater typically has
a salt
concentration of about 3.5% salt by mass; that is, about 35 grams of dissolved
salt per liter of
water. Another source of saltwater is salty, underground aquifer water, also
known as "brackish
water". The salt concentration of brackish water typically ranges from less
than 1% to more than
18% salt by mass. In contrast, drinkable water typically has a salt
concentration of, at most,
about 0.04%. Desalination also has industrial applications; for example, waste
saltwater can be
desalinated for re-use and to produce a low volume, concentrated brine for
disposal.
[0004] Given the need for freshwater, and given the abundance of saltwater,
including
saltwater that is industrial waste, there exists a continued need for methods
and systems for
producing freshwater by desalinating saltwater.
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SUMMARY
[0005] According to a first aspect, there is provided an apparatus including a
stack and a
compression device. The stack includes a pair of rigid end plates located at
opposing ends of the
stack; a plurality of membrane bounded compartments layered between one of the
rigid end
plates and the other of the rigid end plates; and fluid manifolds extending
through the membrane
bounded compartments. The compression device is fixedly coupled to opposing
ends of the pair
of rigid end plates and includes compression members movable to compress one
of the rigid end
plates towards the other of the rigid end plates, wherein the compression
members are positioned
to apply force to the stack in the vicinity of the fluid manifolds.
[0006] The apparatus may be used in a saltwater desalinating system or in a
water
treatment system.
[0007] The apparatus may include: a series of holes spaced around the
periphery of each
of the compression device, the pair of rigid end plates and the plurality of
membranes such that
when the compression device, the pair of rigid end plates and the plurality of
membranes are
aligned with each other, the holes align to form conduits extending
therethrough; a plurality of
tensioning rod having threaded ends and extending through the conduits; and a
pair of tensioning
rod nuts screwed on to the ends of the tensioning rod to compress the
compression device, the
pair of rigid end plates and the plurality of membranes together.
[0008] A tensioning frame may be positioned between the compression device and
the
rigid end plates. The tensioning frame includes holes aligned with the holes
in the pair of rigid
end plates and the tensioning rod also extend through the holes in the
tensioning frame and the
tensioning rod nuts compress the tensioning frame against the rigid end
plates.
[0009] An adjustable expansion device may be in communication with one or both
of the
rigid end plates and adjustable to compress the rigid end plates towards each
other.
[0010] The compression members may be bolts that can be screwed into and out
of struts
in the compression device.
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[0011] According to another aspect, there is provided an apparatus for water
treatment
system including a plurality of internal modules compressively coupled to each
other. The
internal modules includes a pair of rigid interior end plates located at
opposing ends of the
internal module; an electrolyte compartment bounding an internal surface of
each of the rigid
interior end plates; and a stack of membrane bounded compartments layered from
one of the
electrolyte compartments to the other of the electrolyte compartments. Each of
the rigid interior
end plates includes an electrode. The electrode of one of the rigid interior
end plates is
electrically connected to the electrode of the other of the rigid interior end
plates to complete an
ionic circuit through the internal module.
[0012] The internal modules may further include fluid manifolds extending from
one of
the interior end plates to the other of the interior end plates. The apparatus
may further include:
a pair of external end plates located on opposing ends of the plurality of
internal modules; and a
compression device fixedly coupled to the external end plates and including
compression
members movable to compress one of the external end plates towards the other
of the external
end plates. The compression members are positioned to apply force to the
internal modules in
the vicinity of the manifolds.
[0013] The stack of membrane bounded compartments may include alternating
membranes and gasket separators. The apparatus may further include: a series
of dowel holes
spaced around the periphery of each of the gasket separators, membranes,
electrolyte
compartments, and interior end plates of the internal modules such that when
the gasket
separators, membranes, electrolyte compartments, and interior end plates are
aligned with each
other, the dowel holes align to form dowel conduits extending between the
opposing ends of the
internal module; and dowels extending through the dowel conduits.
[0014] For an adjacent pair of the internal modules, the dowels may extend
through one
subset of the dowel conduits of one of the internal modules of the adjacent
pair, and additional
dowels extend through a complementary subset of the dowel conduits of the
other of the internal
modules of the adjacent pair such that when the internal modules are
compressed, the dowels in
one of the internal modules of the adjacent pair slide into empty dowel holes
in the other of the
internal modules of the adjacent pair.
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[0015] The dowels may be threaded. The apparatus may further include a pair of
dowel
nuts screwed on to the ends of each of the dowels to maintain compression of
the internal
modules.
[0016] The interior end plates of the internal modules may further include a
recess
shaped and positioned to receive one of the dowel nuts used to compress an
adjacent one of the
internal modules.
[0017] The dowels may be hollow, and the external end plates and compression
device
may include dowel holes aligned with the dowel holes in the internal modules.
The apparatus
may further include: a tensioning rod having threaded ends and extending
through the dowel
holes and through the dowels; and a pair of tensioning rod nuts screwed on to
the ends of the
tensioning rod to compress the internal modules.
[0018] The apparatus may further include a tensioning frame positioned between
the
compression device and the external end plates and overlapping the dowel holes
in the external
end plates. The tensioning frame may include dowel holes aligned with the
dowel holes in the
external end plates and the tensioning rod extends through the dowel holes in
the tensioning
frame and the tensioning rod nuts compress the tensioning frame against the
external end plates.
[0019] The fluid manifolds may pass through the gasket separators and may be
fluidly
coupled to the compartments by an inlet notch in one side of the gasket
separators that is shaped
to direct fluid flowing from the manifolds into the compartments towards at
least one of an
opposing side of the gasket separators. The notch in one of the compartments
may not overlap
the notch in an adjacent one of the compartments.
[0020] The apparatus may further include a mesh located within each of and
coplanar
with the gasket separators. The mesh may include a relatively thick portion
within the notch to
mitigate against leakage from an adjacent one of the gasket separators.
[0021] A portion of the gasket separator neighbouring the notch may be
relatively thick
to compress a membrane located between the notch and the gasket separator
adjacent to the
notch into the notch to mitigate against leakage from the gasket separator
adjacent to the notch.
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[0022] The apparatus may further include a modular container in which the
modules are
disposed, wherein the modular container includes support tracks lining its
interior and the
modules are mounted on the support tracks.
[0023] The apparatus may further include a blank module including an interior
end plate
fluidly coupled between interior end plates of adjacent modules.
[0024] According to a further aspect, there is provided a compression device
including: a
frame operably fixedly coupled to an end plate of the stack; and a plurality
of compression
members moveably connected to the frame and operable to be moved towards and
away from the
end plate. The compression members are positioned to apply compressive force
to the stack in
the vicinity of fluid manifolds extending through the stack when the
compression members are
moved towards the end plate.
[0025] The compression members may be bolts that can be screwed into and out
of struts
in the frame.
[0026] The compression device may be used with a membrane based stack for a
saltwater
desalination system or a water treatment system.
[0027] According to a further aspect, there is provided an apparatus for a
saltwater
desalinating system. The apparatus includes a plurality of internal modules
compressively
coupled to each other, wherein each of the internal modules comprises a pair
of rigid interior end
plates located at opposing ends of the internal module; and a stack of
membrane bounded
compartments layered from one of the interior end plates to the other of the
interior end plates.
[0028] The stack of membrane bounded compartments may include alternating
membranes and gasket separators, and the apparatus may also include a series
of dowel holes
spaced around the periphery of each of the gasket separators, membranes and
end plates of the
internal modules such that when the gasket separators, membranes, and end
plates are aligned
with each other, the dowel holes align to form dowel conduits extending
between the opposing
ends of the internal module.
CA 02792516 2012-10-17
[0029] For an adjacent pair of the internal modules, the apparatus may also
include
dowels extending through one subset of the dowel holes of one of the internal
modules of the
adjacent pair, and additional dowels extending through a complementary subset
of the dowel
holes of the other of the internal modules of the adjacent pair such that when
the internal
modules are compressed, the dowels in one of the internal modules of the
adjacent pair slide into
empty dowel holes in the other of the internal modules of the adjacent pair.
[0030] The dowels may be threaded, and the apparatus may also include a pair
of dowel
nuts screwed on to the ends of each of the dowels to maintain compression of
the internal
modules.
[0031] The interior end plates of the internal modules may also include a
recess shaped
and positioned to receive one of the dowel nuts used to compress an adjacent
one of the internal
modules.
[0032] A pair of end modules may be located on opposing ends of the plurality
of
internal modules, with each of the end modules including a rigid exterior end
plate; a rigid
interior end plate fluidly coupled to the rigid interior end plate of the
internal module that is
adjacent to the end module; a completion compartment located between the
exterior and interior
end plates; and a membrane located between and bounding both the interior end
plate and the
completion compartment.
[0033] A pair of adjustable expansion devices may be located on opposing ends
of the
end modules and adjustable to compress the exterior end plates towards each
other.
[0034] Each of the end modules may include an electrolyte inlet port fluidly
coupled to
the completion compartment; an electrolyte outlet port fluidly coupled to the
completion
compartment; and an electrode fluidly coupled to the completion compartment,
wherein the
electrodes on the pair of end modules are electrically coupled to each other.
[0035] Each of the end modules may also include a completion gasket separator
circumscribing the completion compartment. If the completion gasket separator
includes the
completion compartment, the apparatus may also have a series of dowel holes
spaced around the
periphery of each of the completion gasket separator, membrane, and end plates
of the end
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modules such that when the completion gasket separator, membrane, and end
plates are aligned
with each other, the dowel holes align to form dowel conduits extending
between opposing ends
of the end module. The dowel holes of the end modules may align with the dowel
holes of the
internal modules when the internal and end modules are aligned.
[0036] The dowels may be hollow and the apparatus may also include a
tensioning rod
having threaded ends and extending through the dowel holes and through the
dowels; and a pair
of tensioning rod nuts screwed on to the ends of the tensioning rod to
compress the internal and
end modules.
[0037] The apparatus may also include a tensioning frame positioned against
opposing
ends of the pair of end modules and overlapping the dowel holes in the
exterior end plates of the
end modules. Dowel holes in the tensioning frame may be aligned with the dowel
holes in the
exterior end plates of the end modules, the tensioning rod may extend through
the dowel holes in
the tensioning frame, the tensioning rod nuts may compress the tensioning
frame against the end
modules.
[0038] The periphery of the gasket separators may include fluid manifolds
extending
from one of the end plates to the other of the end plates in each of the
internal and end modules,
and the apparatus may also include a compression device fixedly coupled to the
tensioning frame
and having compression members movable to compress one of the end modules
towards the
other of the end modules. The compression members can be positioned to apply
force to the
modules in the vicinity of the manifolds.
[0039] The compartments circumscribed by the gasket separators may be
rectangular,
and the fluid manifolds passing through the gasket separators may be fluidly
coupled to the
compartments by an inlet notch in one of the short sides of the gasket
separators that is shaped to
direct fluid flowing from the manifolds into the compartments towards at least
one of the long
sides of the gasket separators.
[0040] The notch in one of the compartments may be positioned so as not to
overlap the
notch in an adjacent one of the compartments.
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[0041] The apparatus may also include a mesh located within each of and that
is coplanar
with the gasket separators. The mesh has a relatively thick portion within the
notch to mitigate
against leakage from an adjacent one of the gasket separators.
[0042] A portion of the gasket separator neighbouring the notch may be
relatively thick
to compress a membrane located between the notch and the gasket separator
adjacent to the
notch into the notch to mitigate against leakage from the gasket separator
adjacent to the notch.
[0043] The apparatus may be located within modular container, such as a
shipping
container. The modular container may have support tracks lining its interior
and the modules
may be mounted on the support tracks.
[0044] The apparatus may also include a blank module having an interior end
plate
fluidly coupled between interior end plates of adjacent modules.
[0045] The alternating membranes and gasket separators may include a drive
cell
configured to generate a drive voltage using concentration difference energy;
and a product cell.
The product cell can include a product feed compartment; and an anion exchange
membrane and
a cation exchange membrane located on opposing sides of the product feed
compartment such
that when a sufficient voltage that equals or exceeds a desalination voltage
and that comprises
the drive voltage is applied to the product feed compartment, anions and
cations contained within
saltwater in the product feed compartment are driven out of the product feed
compartment
through the anion and cation exchange membranes, respectively. The drive cell,
product cell,
and end plate compartments can be ionically communicatively coupled with each
other.
[0046] According to another aspect, there is provided a method for
desalinating
saltwater. The method includes generating a drive voltage using a drive cell;
and applying the
drive voltage to a product cell. The product cell includes a product feed
compartment; and an
anion exchange membrane and a cation exchange membrane located on opposing
sides of the
product feed compartment such that when a sufficient voltage that equals or
exceeds a
desalination voltage and that comprises the drive voltage is applied to the
product feed
compartment, anions and cations contained within saltwater in the product feed
compartment are
driven out of the product feed compartment through the anion and cation
exchange membranes,
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respectively. The drive and product cells are contained within a plurality of
internal modules
wherein each of the internal modules comprises a pair of rigid interior end
plates located at
opposing ends of the internal module and wherein adjacent interior end plates
are fluidly coupled
together to form end plate compartments.
[0047] A pair of end modules may be located on opposing ends of the plurality
of
internal modules, with each of the end modules having a rigid exterior end
plate; a rigid interior
end plate fluidly coupled to the rigid interior end plate of the internal
module that is adjacent to
the end module; a completion compartment located between the exterior and
interior end plates;
and a membrane located between and bounding both the interior end plate and
the completion
compartment.
[0048] The exterior end plates may be compressed towards each other.
[0049] The method may also include electrically coupling the completion
compartments
together; and pumping an electrolyte through the completion compartments.
[0050] The drive cell may also include ion exchange membranes and alternating
gasket
separators that circumscribe compartments, the product feed compartment may
also include a
gasket separator that circumscribes the product feed compartment, and each of
the internal
modules may also include a series of dowel holes spaced around the periphery
of each of the
gasket separators, membranes and end plates of the internal modules such that
when the gasket
separators, membranes, and end plates are aligned with each other, the dowel
holes align to form
dowel conduits extending between the opposing ends of the internal module.
[0051] Each of the end modules may include a completion gasket separator
circumscribing the completion compartment and an ion exchange membrane fluidly
coupled to
the completion compartment, and a series of dowel holes spaced around the
periphery of each of
the completion gasket separator, ion exchange membrane and end plates of the
external modules
such that when the completion gasket separator, membrane, and end plates are
aligned with each
other, the dowel holes align to form dowel conduits extending between opposing
ends of the
external module. The dowel holes of the external modules may align with the
dowel holes of the
internal modules when the internal and external modules are aligned.
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[0052] For an adjacent pair of the internal modules, the method may also
include
extending dowels through one subset of the dowel holes of one of the internal
modules of the
adjacent pair; and extending additional dowels through a complementary subset
of the dowel
holes of the other of the internal modules of the adjacent pair such that when
the modules are
compressed, the dowels in one of the internal modules of the adjacent pair
slide into empty
dowel holes in the other of the internal modules of the adjacent pair.
[0053] The dowels may be threaded, and the method may also include compressing
the
internal modules, and maintaining compression of the internal modules by
screwing a pair of
dowel nuts on to the ends of the dowels.
[0054] The interior end plates of the internal modules may have a recess
shaped and
positioned to receive one of the dowel nuts used to compress an adjacent one
of the internal
modules.
[0055] The dowels may be hollow, and the method may also include compressing
the
internal and end modules by extending a tensioning rod having threaded ends
through the dowel
holes and through the dowels; and screwing a pair of tensioning nuts on to the
ends of the
tensioning rod.
[0056] A tensioning frame may be positioned against opposing ends of the pair
of end
modules and may overlap the dowel holes in the exterior end plates of the end
modules. The
tensioning frame may include dowel holes aligned with the dowel holes in the
exterior end plates
of the end modules, the tensioning rod may extend through the dowel holes in
the tensioning
frame, and the tensioning rod nuts may compress the tensioning frame against
the end modules.
[0057] The periphery of the gasket separators may have fluid manifolds
extending from
one of the end plates to the other of the end plates in each of the internal
and external modules,
and the method may also include applying supplementary compression to the
tensioning frame
by pushing compression members into the end modules to apply force to the
modules in the
vicinity of the manifolds.
[0058] The compartments circumscribed by the gasket separators may be
rectangular,
and the fluid manifolds passing through the gasket separators may be fluidly
coupled to the
CA 02792516 2012-10-17
compartments by an inlet notch in one of the short sides of the gasket
separators that is shaped to
direct fluid flowing from the manifolds into the compartments towards the long
side of the
gasket separators farthest from the notch.
[0059] The mesh may located within each of and may be coplanar with the gasket
separators, and may include a relatively thick portion within the notch to
mitigate against leakage
from an adjacent one of the gasket separators.
[0060] A portion of the gasket separator neighbouring the notch may be
relatively thick
to compress a membrane located between the notch and the gasket separator
adjacent to the
notch into the notch to mitigate against leakage from the gasket separator
adjacent to the notch.
[0061] The notch in one of the compartments may be positioned so as not to
overlap the
notch in an adjacent one of the compartments.
[0062] The method may include mounting the modules on to support tracks
located
within a modular container.
[0063] The method may also include replacing one of the internal modules with
a blank
module comprising an interior end plate fluidly coupled between interior end
plates of adjacent
modules; and flowing an ionic solution through the blank module.
[0064] According to another aspect, there is provided a method for making a
gasket
separator. The method includes providing a gasket border material having a
certain thickness;
providing a mesh having a thickness that is about 2% to 5% thinner than the
gasket border
material; overlaying the mesh and the gasket border material; and bonding the
gasket border
material and the mesh together by melting one of the gasket border material or
mesh into the
other.
[0065] The gasket border material may have a durometer from about Shore A20 to
Shore
A60. The gasket separator may include ethylene-vinyl acetate. The mesh may
include
polypropylene. The gasket separator may have a lower melting temperature than
the mesh.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0066] In the accompanying drawings, which illustrate one or more exemplary
embodiments:
[0067] Figure 1 shows partial cutaway views of a stack composed of internal
and end
modules according to one embodiment, and a perspective view of one of the
internal modules
showing the manifolds used to transport fluids into and out of the module.
[0068] Figure 2 shows front elevation views of various types of gasket
separators and ion
exchange membranes that can be used in the stack of Figure 1.
[0069] Figure 3 shows perspective and exploded views of one of the internal
modules of
the stack of Figure 1.
[0070] Figure 4 shows a front elevation view of an interior end plate that is
at the ends of
the internal modules of the stack of Figure 1.
[00711 Figure 5 shows perspective and exploded views of one of the end modules
of the
stack of Figure 1.
[0072] Figure 6 shows an exploded view of one embodiment of a gasket separator
positioned between two ion exchange membranes, which can be used in the stack
of Figure 1.
[0073] Figure 7 shows an exploded view of a pair of the gasket separators
around one of
the ion exchange membranes, and arrows indicating how fluid flows
therethrough.
[0074] Figure 8 shows a perspective view of two of the gasket separators that
are being
aligned and stabilized using a combination of dowels and a lateral restraining
member, according
to one embodiment.
[0075] Figure 9 shows an exploded view of a series of the gasket separators
and ion
exchange membranes, with one of the gasket separators being made from a
relatively rigid
material to facilitate structural stability, according to one embodiment.
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[0076] Figure 10 shows a detailed view of a mesh that can be placed within the
gasket
separators, according to one embodiment.
[0077] Figures 11 and 12 show how the mesh and the gasket separator of Figure
10 can
be bonded together, and shows how the gasket separator itself can be
manufactured, according to
one embodiment.
[0078] Figure 13 shows how a portion of the mesh that has been bonded to one
of the
gasket separators can be made relatively thick in order to mitigate leakage,
according to one
embodiment.
[0079] Figures 14 and 15 show perspective and exploded views of one of the
internal
modules that can be used in the stack of Figure 1, according to additional
embodiments.
[0080] Figure 16 shows exploded, detailed, and sectional views of another
embodiment
of the stack composed of internal and end modules.
[0081] Figure 17 shows a perspective view of the stack of Figure 16.
[0082] Figures 18 show a perspective view of a compression device mounted on
to the
stack of Figure 16, according to another embodiment.
[0083] Figure 19, shows various views of the compression device of Figure 18
and a
schematic representation of the exterior end plate of the end module showing
load application
points of the compression device.
[0084] Figure 20 shows the compression device of Figures 18 and 19 mounting on
to a
non-modular stack, according to another embodiment;
[0085] Figure 21 shows an exploded view of another embodiment of a modular
stack
composed of internal modules with electrodes positions at either end of each
of the internal
modules;
[0086] Figure 22, shows an exploded view of the compression device of Figures
18 and
19 mounted on to the stack of Figure 21.
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DETAILED DESCRIPTION
[0087] Directional terms such as "top," "bottom," "upwards," "downwards,"
"vertically"
and "laterally" are used in the following description for the purpose of
providing relative
reference only, and are not intended to suggest any limitations on how any
article is to be
positioned during use, or to be mounted in an assembly or relative to an
environment.
[0088] Several types of desalination systems can utilize permeable membranes
of some
sort; these types of desalination systems are hereinafter collectively
referred to as "membrane
based desalination systems". For example, desalination systems that rely on
concentration
difference energy ("CDE") utilize ion exchange membranes in the form of anion
and cation
exchange membranes, which are respectively anion and cation permeable, but
which do not
allow water to pass through them. Descriptions of CDE systems can be found in
published
patent applications WO 2011/050473 (serial no. PCT/CA2010/001718) entitled
"Method and
System for Desalinating Saltwater While Generating Electricity", WO
2010/115287 (serial no.
PCT/CA2010/000537) entitled "Method and System for Desalinating Saltwater
Using
Concentration Difference Energy", and WO 2009/155683 (serial no.
PCT/CA2009/000080)
entitled "Method and System for Desalinating Saltwater Using Concentration
Difference
Energy".
[0089] Another type of membrane based desalination system is a system that
relies on
electrodialysis reversal ("EDR") technology. EDR systems utilize ion permeable
membranes
that are similar to those used in CDE systems. Similarly, membrane
distillation ("MD")
desalination systems utilize hydrophobic membranes that reject liquid water
but are permeable to
water vapour to effect desalination. Vapour transfer is typically driven by a
vapour pressure
gradient between a warmer saline compartment and a cooler, less saline
compartment.
[0090] These membrane based desalination systems are often assembled in
stacks. These
stacks may, for example, take the form of layers of membrane bounded
compartments. The
membrane bounded compartments are constructed from alternating layers of
gasket separators
and membranes. The gasket separators circumscribe the compartments in which
fluids,
including both liquids and gases, can flow and come into contact with the
membranes, which
sandwich the compartments, during desalination. In CDE systems, for example,
the
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compartments can include product feed compartments though which the saltwater
to be
desalinated flows, and concentrate and diluent compartments through which
flows solutions of
different ionic concentrations used to generate a drive voltage.
[0091] The rate at which such membrane based desalination systems can
desalinate is
directly proportional to the area of the membranes present in the stacks. One
way to increase
membrane area is to construct longer stacks having more membranes. However,
technical
problems are associated with constructing such stacks. Two such problems are
sealing the
compartments to prevent leakage and buckling. As a longer stack is built, any
gap through
which leakage can occur between one of the gasket separators and the membranes
that sandwich
it is effectively amplified by the number of compartments present in the
stack. Ideally, within
the stack the surfaces of any given one of the gasket separators and its
adjacent membranes are
flush with each other such that there is no gap between the surfaces through
which leakage can
occur. However, in practice, such gaps are often present. For example, if the
gasket separators
and membranes are shaped such that between the surfaces of each gasket
separator and
membrane pair there is a 0.03 mm gap prior to being integrated into the stack,
for a stack having
100 compartments constructed using such separators and membranes there could
be a 3 mm gap
at one end of the stack. Significant leakage could occur through this gap. In
order to eliminate
these gaps and seal long stacks, the amount of compression force that is
applied to the stack to
prevent leakage from occurring along the interfaces between the gasket
separators and the
membranes is accordingly increased. Eventually, the amount of force that is
applied to prevent
leakage causes the stack to substantially buckle, which can structurally
damage the stack as well
as, ironically, increase the stack's rate of leakage. Even if buckling can be
prevented, the amount
of force that is applied to the stack to prevent leakage increases as the
stack increases in length.
Eventually, the amount of force exceeds the compressive strength of the
membranes, and the
membranes can fail mechanically.
[0092] The embodiments discussed herein are directed at a modular stack that
includes
internal and end modules. The end modules are located at opposing ends of the
stack, and the
internal modules are located between the end modules. Each of the end and
internal modules
includes rigid end plates that are used to periodically zero any gaps within
the stack between the
gasket separators and membranes. The rigid end plates also facilitate
alignment of the gasket
CA 02792516 2012-10-17
separators and membranes and help to structurally stabilize the stack. In
addition to the entire
stack being compressed, each of the modules is also individually compressed
and fluidly sealed
using a lower compressive force than would be used if there were no individual
module
compression. This allows the amount of compressive force that any one of the
modules
experiences to be less than the compressive strength of the membranes, thereby
preventing the
membranes from mechanically failing. In addition, dividing the stack into
modules simplifies
stack assembly and handling. For example, instead of constructing one 300 cm
stack all at once,
ten smaller 30 cm stacks can be constructed in the form of the modules and the
300 cm stack can
be then be more easily assembled incrementally by using the modules.
[0093] The embodiments that follow are directed at a stack used in a CDE
system.
However, as mentioned above, in alternative embodiments (not depicted), the
stacks may be used
for alternative forms of membrane based desalination, such as EDR and MD
systems.
[0094] Referring now to Figure 1, there is shown a CDE dialytic stack assembly
101
according to one embodiment. The CDE dialytic stack assembly 101 is packaged
into a shipping
container 102 that provides protection from the environment and that acts as a
protective outer
shell. Exemplary shipping containers include intermodal containers conforming
to International
Organization for Standards' specifications and measuring roughly eight feet by
eight feet by
forty feet, but could also include other modules suited for low cost
production and handling by
existing transportation infrastructure. The CDE dialytic stack assembly 101 is
constructed from
two adjacent stacks 101a,b of 15 modules each; the 15 modules are manufactured
using 13
internal modules 104 compressed between two end modules 106. The modules 104,
106 are
compressed by a rigid tensioning frame 1606 and an adjustable expansion device
110. The
tensioning frame 1606 is discussed in more detail with respect to Figure 16,
below. The
adjustable expansion device 110 can include, for example, bolt jacks,
hydraulic jacks, turn
buckles, or another suitable device that can be used to apply compressive
force to the stack
assembly 101. The internal modules 104 and end modules 106 are mounted on
support tracks
111 lining the bottom interior side of the container 102; the support tracks
111 may include, for
example, bearing surfaces to enable simplified installation and removal of the
modules 104, 106
into and out of the container 102 while also maintaining longitudinal
alignment of the modules
104, 106. As depicted in Figure 1, the internal modules 104 and end modules
106 may also be
16
CA 02792516 2012-10-17
restrained from moving laterally within the container 102 by using lateral
restraints 112
extending laterally from the modules 104, 106. The lateral restraints 112 may
be, for example,
rigid members fastened to the container 102 wall and preventing lateral
movement of any single
one of the modules 104, 106.
[0095] The ionic solutions used to operate the CDE dialytic stack assembly 101
are
provided to the modules 104, 106 via a manifolds system that includes fluid
conduits extending
through the sides of the container 102 and that is fluidly coupled to the
modules 104, 106, as
summarized below:
= product feed manifold 120a: the product feed manifold 120a transports the
product feed
to the stack assembly 101 for desalination. The product feed is the saltwater
that is to be
desalinated.
= diluent _p manifold 120c: the diluent _p manifold 120c transports saltwater
("diluent p")
higher in concentration than the product feed and lower in concentration than
the
concentrate to the stack assembly 101. In one embodiment, the ions that exit
the product
feed during desalination migrate to the diluent] prior to being discharged
from the stack
assembly 101.
= diluent c manifold 120d: the diluent_c manifold 120d transports saltwater
("diluent c")
higher in concentration than the product feed and lower in concentration than
the
concentrate to the stack assembly 101. The diluent c is typically higher in
concentration
than the diluent _p and is used to generate a drive voltage that effects
desalination.
= concentrate manifold 120b: the concentrate manifold 120b transports the
saltwater
("concentrate") highest in concentration to the stack assembly 101. In
conjunction with
the diluent c, the concentrate is used to generate the drive voltage.
= module ion transfer fluid manifold 120e: the module ion transfer fluid
manifold 120e
transports the solution ("module ion transfer fluid') that is used to maintain
ionic
conductivity between adjacent modules 104, 106, as discussed in greater detail
below.
17
CA 02792516 2012-10-17
Typically, the module ion transfer fluid is identical to the concentrate and
is drawn from
the same reservoir.
= end module manifold 120f: in embodiments in which the ionic reactions in the
stack
assembly 101 are completed electrochemically, the end module manifold 120f
transports
electrolytes used for electrochemical completion to the end modules 106. In
embodiments in which electrochemical completion is not used and instead
completion is
performed ionically, the end module manifolds 120f may be used to pump the
concentrate or module ion transfer fluid from one of the end modules 106 to
the other.
(collectively, the manifolds 120a-f is hereinafter the "stack manifolds 120").
In the depicted embodiment, saltwater of varying ionic concentrations is used
as concentrate,
module ion transfer fluid, diluent_p, and diluent c.
[0096] Plumbing (not shown) transports the fluids conveyed using the stack
manifolds
120 to one of the end modules 106 where it then enters module inlet manifolds
140a - e
(collectively, "module inlet manifolds 140") as depicted in Figure 1. As
discussed in further
detail below, the module inlet manifolds 140 convey the solutions through the
stack assembly
101 by travelling first through one of the end modules 106, then through all
of the internal
modules 104, and then through the other of the end modules 106. Once the
fluids exit the other
of the end modules 106, they exit the shipping container via additional
manifolds (not shown)
analogous to that of the stack manifolds 120 shown in Figure 1.
[0097] In Figure 1, one of the internal modules 104 is shown in isolation.
Extending
through the periphery of the internal module 104 is module inlet manifolds
140a - e located at
the bottom of the internal module 104 shown in Figure 1, and module outlet
manifolds 141 a - e
(collectively, "module outlet manifolds 141") located at the top of the
internal module 104
shown in Figure 1. Both types of manifolds 140a - e, 141 a - e extend from end-
to-end within the
internal module 104; by "end-to-end", it is meant from the internal module 104
adjacent to one
of the end modules 106 to the internal module 104 adjacent to the other of the
end modules 106
in any given one of the stacks 101 a,b. As discussed in further detail below,
similar manifolds
exists in the end modules 106 as well. The product feed manifold 120a is
fluidly coupled to a
18
CA 02792516 2012-10-17
product feed module inlet manifold 140a; the diluents manifold 120c is fluidly
coupled to a
diluent _p module inlet manifold 140c; the diluent c manifold 120d is fluidly
coupled to a
diluent_c module inlet manifold 140d; the concentrate manifold 120b is fluidly
coupled to a
concentrate module inlet manifold 140b; and the module ion transfer fluid
manifold 120e is
fluidly coupled to a module ion transfer fluid inlet manifold 140e. As
discussed in further detail
below, the solutions entering the modules 104, 106 flow from the module inlet
manifolds 140
located at the bottom of the modules 104, 106, through inlet notches
(described below) into the
compartment circumscribed by the gasket, and then through outlet notches
(described below) to
the module outlet manifolds 141 located at the top of the modules 104, 106.
Product feed exits
the modules 104, 106 via a product feed module outlet manifold 141a; diluent
_p exits via a
diluent] module outlet manifold 141c; diluent c exits via a diluent -c module
outlet manifold
141d; concentrate exits via a concentrate outlet manifold 141b; and module ion
transfer fluid
exits via a module transfer fluid outlet manifold 141 e.
[0098] The CDE dialytic stack assembly 101 may be operated in forward polarity
for a
set period of time, and then reverse polarity for a set period of time, in
order to de-scale
membranes while maintaining production.
[0099] Referring now to Figure 2, there are depicted the various gasket
separators and
ion exchange membranes that are incorporated into the internal and external
modules 104, 106.
Each of gasket separators 202, 204, 206, 208 is shaped to fluidly couple one
of the module inlet
manifolds 140 with one of the module outlet manifolds 141. A concentrate
gasket separator 202
that circumscribes a concentrate compartment is fluidly coupled to the
concentrate module inlet
and outlet manifolds 140b, 141b via notches in the periphery of the gasket
separator 202.
Similarly, a diluent c gasket separator 204 circumscribes a diluent -c
compartment and is fluidly
coupled to the diluent -c module inlet and outlet manifolds 140d, 141d; a
diluent -p gasket
separator 206 circumscribes a diluent _p compartment and is fluidly coupled to
the diluent -p
module inlet and outlet manifolds 140c, 141c; and a product feed gasket
separator 208
circumscribes a product feed compartment and is fluidly coupled to the product
feed module
inlet and outlet manifolds 140a, 141 a. Also shown in Figure 2 are a cation
exchange membrane
21 Oa and an anion exchange membrane 21Ob (generically, "ion exchange membrane
210"),
which are structurally identical to each other but which may differ in terms
of membrane
19
CA 02792516 2012-10-17
electrochemical or mass transfer properties. As discussed in further detail
below with respect to
Figure 5, completion compartment gasket separators 209 shown in Figure 2
circumscribe
completion compartments into which an electrolyte is directly pumped for ionic
completion.
Although in the present embodiment electrolyte is pumped directly into the
completion
compartments, in an alternative embodiment (not shown) electrolyte can be
conveyed into the
completion compartment using manifolds in an analogous manner as for the
concentrate,
diluent c, diluent p, and product feed compartments.
[00100] The internal and external modules 104, 106 include an alternating
stack of the
gasket separators 202, 204, 206, 208 and the cation and anion exchange
membranes 21 Oa, 21 Ob.
The gasket separators 202, 204, 206, 208 enable separation and sealing against
the anion
exchange membrane 21 Ob on one side and the cation exchange membrane 21 Oa on
the other side
via a gasket edge 203 and separator mesh 205. The separator mesh 205 allows
for fluid passage
within the compartment from the inlet manifolds 140 to the outlet manifolds
141. When multiple
gasket separators and membranes are stacked, the internal module inlet
manifolds 140 and the
internal module outlet manifolds 141 are formed as described in reference to
Figure 3, below.
Additionally, as discussed in more detail with respect to Figures 12 to 16,
below, a series of
dowels can be inserted through dowel holes 250 in the periphery of the gasket
separators 202,
204, 206, 208, 209 and the ion exchange membranes 210 to align the separators
and membranes
as well as to restrain them from lateral movement. Although a pair of the
dowel holes 250 are
shown in Figure 2, in alternative embodiments depicted in Figures 12 to 16 a
series of
peripherally spaced dowel holes are present in the periphery of the separators
and membranes.
The stack assembly 101 that is formed from the internal and end modules 104,
106 can be
operated in forward or reverse polarity. The following table describes the
fluid held by some of
the gasket separators 202, 204, 206, 208 and conveyed by the module inlet and
outlet manifolds
140, 141 when the stack assembly 101 is operated in forward polarity and in
reverse polarity:
CA 02792516 2012-10-17
Table 1: Role of Gasket Separators and Module Inlet and Outlet Manifolds when
Stack is
Operating in Forward and Reverse Polarities
Fluid held by Fluid held by Gasket Module Inlet Module Outlet
compartment in compartment in Separator Manifold Manifold
forward polarity reverse polarity
product feed diluent _p 208 140a 141a
diluent_p product feed 206 140c 141d
diluent -c concentrate 204 140d 141c
concentrate diluent -c 202 140b 141b
[00101] Figure 3 depicts perspective and exploded views of one of the internal
modules
104 that includes the gasket separators 202, 204, 206, and 208 that
respectively circumscribe the
concentrate, diluent c, diluent p, and product feed compartments when the
stack assembly 101
in which the internal module 104 is integrated is operating in forward
polarity. These gasket
separators 202, 204, 206, 208 are separated from each other by one of the ion
exchange
membranes 210. Typically, the internal modules 104 include one or more drive
cells, which each
include adjacent diluent_c and concentrate compartments that are separated by
one of the ion
exchange membranes 210. lonically communicatively coupled to the drive cells
are one or more
product cells, each of which includes adjacent product feed and diluent -p
compartments that are
also separated by one of the ion exchange membranes 210. Two elements that are
"ionically
communicatively coupled" together would be fluidly coupled together but for
the presence of
one or more of the ion exchange membranes 210. Additionally, references to
elements that form
part of an "ionic circuit" are to those elements that contact cations and
anions as the cations
migrate within the stack assembly 101 towards one end of the stack and as the
anions within the
stack assembly 101 migrate towards the opposite end of the stack while
desalination is occurring.
21
CA 02792516 2012-10-17
[00102] Although the depicted embodiment is directed at a CDE desalination
system in
which ion exchange membranes are used, in an alternative embodiment, such as
one directed at
an MD desalination system, the membranes may instead be water vapour, instead
of ion,
permeable. In such an alternative embodiment, the fluids passing through the
compartments of
the stack assembly 101 may be, on one side of the water vapour permeable
membrane, a
relatively warm saline solution, and on the other side of the water vapour
permeable membrane,
a cooler and lower saline solution.
[00103] The ratio of drive cells to product cells varies based on the
concentration
difference between the saltwater solutions and on the desired ionic flux
through the membranes
210. In general, higher ratios of drive cells to product cells are used when
there is a relatively
low difference between the concentrations of the concentrate and diluent -c
and when there is a
relatively high difference between the concentrations of diluent_p and product
feed in order to
maintain a reasonable ionic flux through the membranes 210. As the saltwater
solutions pass
through their respective compartments, the product feed is desalinated as ions
migrate from the
product feed to the diluent p, which increases in concentration, under the
ionic current
established as salt ions transfer from the concentrate to the diluent_c due to
the salinity gradient.
Thus, the concentrate decreases in concentration as it passes through the
compartment and the
diluent -c increases in concentration.
[00104] The internal module 104 is bounded on either side by internal module
end plates
320 which provide a rigid surface that aids in compressing the gasket
separators and ion
exchange membranes 210 while also maintaining ionic communication between
adjacent internal
modules 104 via the module ion transfer fluid flowing through an end plate
compartment 402
formed by fixedly coupled together two of the end plates 320, as described
below. The modules
104 are assembled such that one of the cation exchange membranes 210a is
between one of the
module end plates 320 and the concentrate gasket separator 202 on one end of
the internal
module 106, and one of the anion exchange membranes 210b is between the module
end plate
320 and the diluent -C gasket separator 204 on the other end of the internal
module 106. Two
adjacent internal modules 106 are mated by connecting the module end plate 320
of one internal
module 104 with the module end plate 320 of an adjacent internal module 104
such that an end
plate compartment is formed with the cation exchange membrane 210a on one side
and the anion
22
CA 02792516 2012-10-17
exchange membrane 21 Ob on the other side. When two of the internal modules
104 are fluidly
coupled together, an o-ring or one or more of the completion compartment
gasket separators 209
is inserted between the two end plates 320 to provide fluidic sealing. If o-
rings are used, they are
inserted in the o-ring grooves 412 shown in Figure 4.
[00105] Referring now to Figure 4, there is shown one embodiment of the
internal module
end plates 320. In the embodiment depicted in Figure 4, the internal module
end plate 320 is
made from a thin, rigid, electrically insulating material such as high density
polyethylene or
polyvinyl chloride. The internal module end plate 320 includes the end plate
compartment 402
and module inlet and outlet manifolds 140, 141. To prevent mixing of various
saltwater solutions
o-rings may be installed in o-ring groves 412 that circumscribe the manifolds
140, 141 and end
plate compartment 402. During operation the module ion transfer fluid is
pumped through the
end plate compartment 402 to enable ionic communication between adjacent
modules 104. The
module ion transfer fluid enters the end plate compartment 402 via the module
inlet manifold
140e and exits through the module outlet manifold 141e. Optionally, the
diluent c may be
pumped into the end plate compartment 402 instead of the module ion transfer
fluid if the stack
assembly 101 is being operated in reverse polarity to effect de-scaling.
Alternative embodiments
of the internal module end plates 320, such as those depicted in and discussed
in respect of
Figures 15 to 19, are also possible.
[00106] Referring now to Figure 5, there is shown perspective and exploded
views of one
of the end modules 106, which is similar in construction to the internal
modules 104 with one
difference being it is bounded by one of the internal module end plates 320 on
the side that
interfaces with a neighbouring one of the internal modules 104 and a rigid and
electrically
insulative exterior end plate 540 on the opposite side. The exterior end plate
540 serves three
functions:
1. It provides rigid and electrically insulative end support for the stack
assembly 101 upon
which a compressive force can be placed by the tensioning frame 1606.
2. It distributes saltwater solutions from the stack manifolds 120 to the
module inlet and
outlet manifolds 140, 141.
23
CA 02792516 2012-10-17
3. It completes the ionic circuit, for example in one of the following
manners:
a. electrochemically, via oxidation and reduction reactions of an electrolyte
at
electrodes; or
b. using ionic fluid communication from one of the exterior end plates 540 to
the
other by either circulation of or submersion in a conductive electrolyte
fluid. The
conductive electrolyte fluid may be, for example, the diluent_p, diluent-c, or
concentrate.
[00107] The exterior end plate 540 can be outfitted with an electrolyte inlet
port 552 and
outlet port 553 as well as a sealed electrode connection hole 560 through
which an electrode (not
shown) is inserted. Connection of the electrode on one end of the stack
assembly 101 to the
electrode on the other end of the stack assembly 101 completes the ionic
circuit. Measurement of
the current in the wire via an ammeter enables performance measurement of the
stack assembly
101 as a direct correlation exists between measured current and desalination
rate. Decreased
current can indicate one or more of leakage, saltwater solution concentration
issues, and ion
exchange membrane fouling. Ion exchange membrane fouling may indicate that the
polarity of
the stack assembly 101 should be reversed to effect membrane de-scaling.
[00108] Optionally, sample ports (not shown) may be present in one or more of
the
module outlet manifolds 141 to allow for air relief and sampling; sampling can
be useful for
testing for the presence of leaks. Leaks may be detected by injecting a trace
compound such as a
die; by sampling the concentrations of the solutions exiting via the outlet
manifolds 141 to see if
they fall outside of a specified, acceptable range; or by closing the
saltwater inlet and outlet
valves on all fluid streams except one, opening all sample valves on the
streams whose inlet and
outlet valves have been closed, and checking to see if saltwater exits through
any of the opened
sample valves, which would indicate a leak.
[00109] In an alternative embodiment (not shown), the end module 106 may not
include
any drive or product cells, and may instead include only a single one of the
completion
compartment gasket separators 209 and one of the ion exchange membranes such
that the end
module 106 is smaller than that depicted in Figure 5 and contains only one
membrane. This
24
CA 02792516 2012-10-17
simplifies performing stack related repairs and troubleshooting since the vast
majority of
membranes are contained in internal modules 104, which can be more readily
removed than the
end modules 106 since the end modules 106 are directly coupled to various
valves and piping
(not shown) that fluidly couples the stack assembly 101 to the stack manifolds
120.
[00110] Although Figure 1 shows the container 102 with a certain number of the
modules
104, 106, in alternative embodiments (not shown) the container 102 may have a
different number
of the modules 104, 106. Additional modules may be installed to increase
desalination capacity.
The embodiment depicted includes space on the sides of the modules to enable
inspection as well
as removal of any one module without removing all modules. In another
embodiment (not
shown), the two rows of stacks shown in Figure 1 may be spaced apart to
facilitate physical
inspection from multiple sides. Operation of the stack assembly 101 can be
maintained with one
of the internal modules 104 removed by installing a "blank module" (not shown)
that is
constructed from one or more of the interior end plates 320 fastened together
to form one large
end plate compartment. One or more of the completion compartment gasket
separators 209 is
placed between the interior end plates 320 to create a fluid tight seal.
During operation, the
blank module is filled with the module ion transfer fluid, which enables the
ionic circuit to
continue conducting. Although the blank module would not generate a drive
voltage or directly
desalinate any of the product feed, it would enable continued operation of and
desalination by the
other modules 104, 106.
[00111] Figure 6 shows a perspective view of the diluent] gasket separator 206
sandwiched between the cation and anion exchange membranes 210a, 210b. The
diliuent p
gasket separator 206 is used for illustrative purposes only; the following
description applies
equally to other types of the gasket separators. The gasket separator 206 is
constructed using
three layers: a non-porous, rigid or semi-rigid, core layer 671, which is
bonded between non-
porous, flexible sealing layers 673, 675 using any one or more of heat,
adhesive, a chemical
reaction, ultrasound, ultraviolet light or radio frequency waves or other
radiation, or other
bonding means, and with or without mechanical compression, as is suitable.
Exemplary materials
for the rigid core layer 671 can include high density polyethylene, or the
like, with the material
having a high modulus of elasticity relative to the sealing layers 673, 675
and matched to the
mechanical requirements of the encompassing stack assembly 101 and chemical
compatibility
CA 02792516 2012-10-17
requirements of the fluid streams passing through the manifolds 140, 141.
Exemplary materials
for the sealing layers 673, 675 can include ethylene vinyl acetate, silicone
rubber, or another
non-porous material with low durometer, preferentially ranging from Shore 40 A
to Shore 80 A,
or matched to the mechanical sealing requirements of the adjacent membranes
210a, 210b,
having chemical compatibility with the material used in the core layer 671 and
the fluid streams
passing through the manifolds 140, 141. The exemplary embodiment of Figure 6
shows a single
core layer with one sealing layer attached or bonded to each face of the core
layer; however,
multiple core layers 671, sealing layers 673, 675 or both can be used in
alternative embodiments
(not depicted).
[00112] The manifolds 140, 141 transport fluid streams from one end of the
stack
assembly 101 to the other, while the diluent _p compartment allows fluid to
travel transverse to
the direction in which the manifolds 140, 141 extend. The separator mesh 205
helps to prevent
the cation and anion exchange membranes 21 Oa, 21 Ob from directly touching
each other, while
introducing turbulent flow and mixing to the fluids within the compartment to
facilitate contact
with a relatively large area of the membranes 210a, 210b. The mesh 205 may be,
for example, a
woven or non-woven mesh of polypropylene, polyethylene, nylon or another
suitable porous
material. In one embodiment, the polypropylene mesh 205 serves to keep the
membranes 210
separate and also serves to mechanically reinforce the sealing layers 673,
675. Also according to
this embodiment, the single sealing layer 673 consisting of ethylene vinyl
acetate heat is pressed
into mesh 205 at a temperature greater than the melting point of ethylene
vinyl acetate but less
than the melting point of the polypropylene mesh 205 such that the final heat
pressed thickness
of the ethylene vinyl acetate sealing layer 673 is 5 to 10% thicker than the
mesh 205, thereby
providing space for compression to occur.
[00113] Figure 7 is a perspective view showing the concentrate and diluent]
gasket
separators 202, 204 separated by one of the ion exchange membranes 210. As
mentioned above,
the gasket separators 202, 206 include notches that fluidly coupled the
compartments that are
circumscribed by the gasket separators 202, 206 to the inlet and outlet
manifolds 140, 141. The
notch that fluidly couples the inlet manifolds 140 to the compartment is
hereinafter referred to as
the "inlet notch", while the notch that fluidly couples the outlet manifolds
141 to the
compartment is hereinafter referred to as the "outlet notch". The notches have
different
26
CA 02792516 2012-10-17
geometries such that fluid distribution effectiveness within the compartments
is improved by
optimizing any one or more of: the velocity and direction of fluid entering
the compartment
through the inlet notch; the channelling of fluid to fill the entirety of the
compartments and to
prevent formation of the dead spots 715, and to exit through the outlet notch
to the outlet
manifolds 141; and the relief of trapped air or other gases from within the
compartment through
the outlet manifolds 141. The inlet notch includes a sloped surface 713 that
directs fluid towards
a dead spot 715 on the long side of the compartment to increase the
effectiveness of fluid
distribution within the compartment.
[00114] Figure 7 also illustrates how different fluid streams travel axially
between the
opposing ends of the stack assembly 101, and how the fluid streams enter the
compartments. In
Figure 7, when the stack assembly 101 is operating in forward polarity, a
diluent _p stream 761 is
shown in stippled lines being transported along the diluent_p manifolds,
entering the diluent -P
compartment through the inlet notch of the diluent _p compartment, and exiting
the diluent_p
compartment through the diluent] compartment's outlet notch. Similarly, a
concentrate stream
762 is shown in solid lines being transported along the concentrate manifolds,
entering the
concentrate compartment through the inlet notch of the concentrate
compartment, and exiting the
concentrate compartment through the concentrate compartment's outlet notch.
The exemplary
embodiment shows the gasket separators 202, 206 having reflection symmetry;
however, in
alternative embodiments (not shown) other forms of symmetry can be used for
any of the gasket
separators, such as rotational symmetry, translational symmetry, or other
patterns of repetition
that result in reduced costs for design and manufacturing.
[00115] Referring now to Figure 8, there is shown one embodiment of the
diluent p
gasket separator 204 placed adjacent to one of the ion exchange membranes,
which may be used
to construct one embodiment of the stack assembly 101. The gasket separator
206 includes a
semicircular dowel hole 250a with a dowel 823 passing through it to align the
gasket separator
206 with the membrane 210 and to stabilize the gasket separator 206 and
membrane 210 during
stack operation. The semicircular dowel hole 250a is beneficial in that
compared to the dowel
hole 250b described below, its end faces occupy less area and therefore less
area of the
membrane 210 is lost when the dowel 823 is inserted through it. The gasket
separator 206 also
includes the circular dowel hole 250b (collectively, the dowel holes 250a,b
are referred to as
27
CA 02792516 2012-10-17
"dowel holes 250") and another of the dowels 823 in an opposing edge of the
gasket separator
206. In this embodiment the gasket sealing surface width increases and
membrane active area
decreases slightly, but mechanical integrity and sealing reliability are
improved relative to the
semicircular dowel hole 250a. This is beneficial when, for example, tensioning
rods are inserted
through the dowels 823, described in reference to Figure 16 below. A lateral
restraining plate
817 contacts the long edge of the gasket separator 206 and is held in place by
an outer support
member 827. The dowels 823 positioned on the opposing edges of the gasket
separator 206, and
the outer support member 827 in conjunction with the restraining plate 817,
together or
separately constrain the movement of gasket separator 206, thereby improving
the alignment of
the gasket separator 206 relative to other layers within the stack assembly
101 while helping to
prevent relative movement between different layers in the stack assembly 101,
which could
result in leakage. The exemplary embodiment shows the dowels 823 being smooth,
solid, and
circular; however, as discussed in further detail below, the dowels 823 in an
alternative
embodiment may be hollow for use in combination with tensioning cables or rods
that run within
through them. Additionally, the dowels 823 may be placed in other locations,
such as within the
perimeter of the gasket separator 206 and not connected to other cut-outs, or
outside the
periphery of the gasket separator 206 and in contact with the restraining
plate 817 that is in
contact with the edge of said gasket. Exemplary dowel materials may include
stainless steel,
titanium, plastic, or another material produced from, or coated with, an
electrically insulating
material such as high density polyethelyne or polyvinyl chloride that is
matched to the
mechanical forces present in the stack assembly 101 and that is chemically
compatible with the
fluids and materials flowing through and used to construct the stack assembly
101. The
exemplary embodiment shows one of each dowel configuration; however, a
plurality of dowel
holes, dowels and restraining plates can instead be used around the perimeter
of the gasket
separator 206, as discussed in more detail in respect of Figures 15 to 19,
below.
[00116] Also shown in Figure 8 are a marking 831, a shaved edge 833 and a
raised profile
835 on the gasket separator 206, which, independently or in combination,
provide a visual
indicator that can be used to improve stack assembly efficiency, thereby
reducing manufacturing
costs. The raised profile 835 constrains the movement of the gasket separator
206 when the
gasket separator 206 is compressed against the ion exchange membrane 210,
which has a
similarly raised profile 837 into which the raised profile 835 on the gasket
separator 206 fits. The
28
CA 02792516 2012-10-17
complementary raised profiles 835, 837 help to align and stably maintain
together the gasket
separator 206 and the membrane 210 during stack assembly and operation,
thereby helping to
prevent relative movement of stack components that could result in leakage
Although Figure 8
shows one each of the marking 831, shaved edge 833, and raised profile 835 on
the gasket
separator 206, in an alternative embodiment (not shown) any suitable number of
these may be
used.
[00117] Referring now to Figure 9, there is shown a portion of the stack
assembly 101 that
includes an alternating series of the gasket separators 206, 202 and membranes
210a, 210b. The
centrally positioned gasket separator 206 is thicker than the other separators
of Figure 9, and is
made of a more rigid material. This thicker separator 206 accordingly provides
structural
support to the stack assembly 101, thereby helping to prevent the stack
assembly 101 from
buckling. Exemplary materials for the relatively thick gasket separator 206
include high density
polyethylene, low density polyethylene, silicone rubber, or any suitable non-
porous elastomer.
[00118] Referring now to Figure 10, there is shown an exemplary one of the
gasket
separators 206 adjacent to one of the ion exchange membranes 210. The diluents
gasket
separator 206 is shown for illustrative purposes, the gasket separator 206
accordingly
circumscribes diluent _p compartment. The mesh 205 is present within the
compartment, and is
composed from a woven structure 1013 that introduces fluid turbulence such
that the boundary
layer thickness at the interface between the gasket separator 206 and the
adjacent membrane 210
is reduced, resulting in improved dialytic performance across the membrane
210.
[00119] Figure 11 depicts how one of the gasket separators can be made,
according to one
embodiment of a method for making the gasket separator from a non-porous
border material
1103 and the mesh 205. The border material 1103 is attached or otherwise
bonded to the porous
mesh 205 using any combination of heat, adhesive, chemical reaction,
ultrasound, ultraviolet
light or radio frequency waves or other radiation, compression, hook and loop
fastening or other
attachment or bonding means, such that the mesh 205 fills the compartment
circumscribed by the
interior of the gasket separator and all the manifolds 140, 141 extending
through the gasket
separator. The mesh 205 prevents adjacent membranes from touching, introduces
turbulent flow
to the compartment, and when bonded into the border material 1103 through, for
example, heat
29
CA 02792516 2012-10-17
pressing techniques, will stiffen the border and manifolds 140, 141 area,
thereby preventing
stretching of the gasket separator. The manifolds 140, 141 may be introduced
into the border
material 1103 prior to bonding with the mesh 205 via die punching in a press,
using a patterned
roll in a roll-to-roll manufacturing process, water jet cutting, or by other
suitable means. After
bonding such that the mesh 205 is fully integrated into the border material
1103, the gasket
separator may be trimmed or otherwise cut to a specific shape or pattern by
the aforementioned
manufacturing process.
[00120] For example, in Figure 11 the border material 1103 may be made from
ethylene-
vinyl acetate having a durometer reading from about Shore A20 to Shore A60 and
a melting
point of around 130 C. The mesh 250 may be made from polypropylene and have a
melting
point of around 170 C. Because the mesh 250 is to fit within the compartment
circumscribed by
the gasket separator, the mesh 250 is also thinner than the border material
1103; typically, the
mesh 250 is about 2% to 5% thinner than the border material 1103. The mesh 250
is overlaid on
the border material 1103, and the temperature of the mesh 250 and the border
material 1103 is
then increased to between 130 C and 170 C. This melts the border material
1103 sufficiently
to allow the mesh 250 to be bonded to it, without melting the mesh 250 itself.
In an alternative
embodiment, the mesh 250 may have a lower melting temperature than the border
material 1103,
and the two may instead be bonded together by melting the mesh 250.
[00121] Figure 11 also depicts the gasket separator being made according to
one
embodiment in which a border material 1103 having short sides 1111, 1113 and
long sides 1115,
1117 are attached or bonded with each other to result to form a rectangular
separator. The mesh
205 and short and long sides 1111, 1113, 1115, 1117 are attached or bonded
using any of the
aforementioned means, beneficially resulting in less material wastage than if
the border material
1103 were punched from a single piece of material. The exemplary embodiment
shows four
individual pieces in the form of short and long sides 1111, 1113, 1115, 1117;
however, in an
alternative embodiment any suitable number of pieces may be joined to form the
border material
1103.
[00122] Referring now to Figure 12, there is shown a cross-sectional view of
one of the
gasket separators comprising the non-porous border material 1103 and the
porous mesh 205,
CA 02792516 2012-10-17
with the border material 1103 having a first melting point and the mesh 205
having a second
melting point higher than the first melting point to enable heat pressing of
the border material
1103 into the mesh 205. The thickness of the border material 1103 is selected
such that upon
application of suitable heat and compression, the border material 1103 melts
into the mesh 205
and, after cooling, the resulting thickness of the border material 1105 is
greater than that of the
mesh 205 by a calculated amount 1221, typically between 2 and 5% on each side
of the mesh
205.
[00123] Referring now to Figure 13, there are shown two exemplary embodiments
of the
gasket separators and adjacent membranes configured to mitigate against the
problem of leakage
caused by gaps between the surfaces of the membranes and the gasket
separators: a "thick notch
mesh embodiment 1301" and a "thick notch border embodiment 1310". As described
above in
respect of Figure 11, the mesh 205 is typically slightly thinner than the edge
of the gasket
separator. Leakage may accordingly occur in and around the inlet and outlet
notches 1317, 1319
as neighbouring gasket separators and membranes deflect into the notches 1317,
1319, thereby
creating a fluid path to or from the gasket separator of a neighbouring
compartment.
Deformation of neighbouring gasket separators into the notches 1317, 1319
increases as the
number of gasket separators and membranes in any single one of the modules
104, 106 increases.
For example, when the gap between the gasket edge 203 and mesh 205 thicknesses
is 0.03 mm
and there are a hundred layers in the stack assembly 101, total deflection at
the hundredth layer is
100 * 0.03 mm = 3 mm, which can result in significant leakage. Adding one or
both of a thick
mesh supporting region 1304 (in the thick notch mesh embodiment 1301) and a
thick gasket
supporting region 1314 (in the thick notch border embodiment 1310) increases
the thickness of
the notches 1317, 1319 or their neighbouring areas, and accordingly decreases
gap size in
neighbouring compartments as the increased thickness pushes against
neighbouring gaps,
helping to close them. This can help to prevent membrane and gasket separator
deflection and
stop leakage.
[00124] In the thick notch mesh embodiment 1301, the thick mesh supporting
region 1304
of each of the gasket separators 1302, 1303 is a relatively thick portion of
the mesh 250 in the
vicinity neighbouring the notches 1317, 1319; in the depicted embodiment, the
thick mesh
supporting region 1304 delineates the portion of the gasket separators 1302,
1303 that is punched
31
CA 02792516 2012-10-17
out to form the inlet and outlet notches 1317, 1319. The thick mesh supporting
region 1304 in
one of the gasket separators 1302 helps compress the inlet notch 1317 of an
adjacent gasket
separator 1303. The thick mesh supporting region 1304 pushes and seals the
membrane that is
between the two gasket separators 1302, 1303 against a portion 1305 of the
inlet notch 1317 in
the adjacent gasket separator 1303. The thick mesh supporting region 1304 is
typically
approximately 5% thicker than the rest of the mesh 205; it can be produced by
adhering another
layer of the mesh 205 on top of the portion of the mesh 205 where the thick
mesh supporting
region 1304 is to be formed. The portion 1305 of the inlet notch 1317 of the
adjacent gasket
separator 1303 is the same material and thickness as the gasket edge 203. In
alternative
embodiments (not depicted), the thick mesh supporting region 1304 may be more
or less than 5%
thicker than the remainder of the mesh 205, as is suitable.
[00125] In the thick notch border embodiment 1310, the mesh 205 is of uniform
thickness
throughout. However, each of the gasket separators includes a thick gasket
notch zone 1314 that
is typically approximately 5% thicker than the remainder of the gasket edge
203. In the depicted
embodiment, one of the thick gasket notch zones 1314 is formed on each of the
short sides of the
gasket separators 1312, 1313 that are not punched out when the inlet and
outlet notches 1317,
1319 are formed. The thick gasket notch zone 1314 can be produced by layering
a portion of
gasket material, with the same geometry as the notches 1317, 1319, over the
gasket edge 203
where the thick gasket notch zone 1314 is to be formed. This is typically done
during
manufacturing so that the thick gasket notch zone 1314 is fully integrated
into the gasket
separator through heat pressing or other means. The effect is that the
adjacent thick gasket notch
zone 1314 pushes and seals the membrane against the gasket notch zone 1315 of
an adjacent
gasket separator, thereby preventing inter-compartment leaks.
[00126] Also as shown in Figure 13, pairs of adjacent inlet notches 1317 or
outlet notches
1319 also do not overlap with each other so as to help prevent leakage. If
adjacent notches 1317,
1319 were to be aligned, the likelihood of significant gaps forming in any one
or more of a series
of the aligned notches 1317, 1319 would increase. By alternating notch
location through the
stack assembly 101, leakage is accordingly mitigated.
32
CA 02792516 2012-10-17
[00127] Referring now to Figure 14, there is shown perspective and exploded
views of one
embodiment of a gasket membrane cartridge 1401 manufactured from a series of
the gasket
separators 206 attached or bonded to adjacent ion exchange membranes 210,
resulting in an
improved seal between the gasket separator and membrane, and such that the
gasket-membrane
cartridge 1401 is a discrete unit for the purposes of more efficient assembly
of the encompassing
modules 104, 106 and stack assembly 101. A single one of the modules 104, 106
may be
constructed using, in part, several of the gasket-membrane cartridges 1401.
Means of attaching
the gasket separator 206 to the membrane 210 can include any combination of
heat, adhesive,
chemical reaction, ultrasound, ultraviolet light or radio frequency waves or
other radiation,
compression.. For example, a moisture cure adhesive, such as polyurethane
adhesive, could be
used to keep the membrane 210 wet during assembly. Any of the foregoing
embodiments of the
gasket separators may be incorporated into the gasket membrane cartridge 1401.
[00128] The membranes 210 may be shaped such that its surface takes on a
variety of two
or three dimensional features or patterns. For example, the membranes 210 may
be formed to
include any one or more of channels that act as a fluid conduit between the
inlet and outlet
manifolds 140, 141; the manifolds 140, 141 themselves; and ripples to
facilitate membrane
flexing. Any suitable combination of chemical etching; radiation grafting; a
die press; a
patterned roll in a roll-to-roll manufacturing process; and casting using a
mold, due, or similar
means may be used to suitably shape the membranes 210.
[00129] Referring now to Figure 15, there are shown a perspective view and an
exploded
view of the internal module 104, according to another embodiment. Central to
the internal
module 104 is an alternating series of gasket separators and ion exchange
membranes 210
("gasket and membrane assembly 1504") that form one or more of the drive
cells, product cells,
and completion compartments. Disposed on either end of the internal module 104
are a pair of
rigid interior end plates 320 that can be fluidly coupled to the interior end
plate 320 of an
adjacent one of the internal modules 104. In order to couple adjacent interior
end plates 320
together, the peripheries of two of the end plates 320 can be aligned and then
compressed
together using tensioning equipment, as described in further detail below.
33
CA 02792516 2012-10-17
[00130] When two of the interior end plates 320 are compressed together in
this fashion,
they collectively circumscribe the end plate compartment 402 into which the
module ion transfer
fluid may be pumped. As shown in Figure 15, each of the module ion transfer
fluid inlet and
outlet manifolds 140e, 141 e are fluidly coupled to the end plate compartment
402 by a series of
thin, flared conduits 1506 that converge on and that are each fluidly coupled
to the module ion
transfer fluid inlet and outlet manifolds 140e, 141e. Beneficially, the flared
conduits 1506
facilitate widespread distribution of the module ion transfer fluid within the
end plate
compartment 402, thereby facilitating a strong ionic current. Additionally,
the flared conduits'
1506 relatively thin profile helps to prevent deflection by the adjacent
completion compartment
gasket separators 209 into them, thereby helping to prevent internal leakage.
[00131] Because the interior end plates 320 are rigid, force can be applied
directly to them
in order to suitably compress the gasket and membrane assembly 1504. For
example, force may
be applied using a winching device, hydraulics, a jack, tensioning rods, or
any other suitable
device. As discussed above, the gasket and membrane assembly 1504 and the
interior end plates
320 have located around their periphery a series of spaced dowel holes 250
that extend from one
end of the internal module 104 to the other. While the gasket separators and
ion exchange
membranes in the gasket and membrane assembly 1504 are being assembled
together, the dowels
823 can be inserted through the spaced dowel holes 250 to ensure that each
additional gasket or
membrane that is added to the gasket and membrane assembly 1504 is aligned
with the gaskets
and membranes that have already been added to the assembly 1504. Once the
gasket and
membrane assembly 1504 has been fully assembled, an external force can be
applied to the
interior end plates 320 to compress the gasket and membrane assembly 1504. The
dowels 823
have threaded ends so that once the gasket and membrane assembly 1504 has been
sufficiently
compressed, dowel nuts 1502 may be screwed on to the dowels 823 and against
the interior end
plates 320 to maintain compression of the gasket and membrane assembly 1504
once the external
force is removed. For reasons discussed in more detail below, the dowels 823
are also hollow.
[00132] Once several of the internal modules have been assembled and
individually
compressed, they can be compressed together. One of the views shown in Figure
16 is a
sectional view of four of the internal modules 104 that are aligned back-to-
back. In the gasket
and membrane assembly 1504 shown in Figure 16, for any adjacent pair of the
internal modules
34
CA 02792516 2012-10-17
104 the interior end plates for one of the modules 104 has a first type of end
plate 320 and the
other of the modules 104 has a second type of end plate 320 that is
complementary to the first
type of end plate 320. The two types of the end plates 320 are identical
except that the first type
of end plate 320 has recesses 1610 that are positioned only over the dowel
holes 250 and that are
sized large enough to receive the dowel nuts 1502 that are attached to the
dowels 823 that are
inserted through a first subset of the dowel holes 250, while the second type
of end plate 320 has
the recesses 1610 positioned only over another subset of the dowel holes 250
that is
complementary to the first subset of the dowel holes 250.
[00133] The recesses 1610 serve two purposes. First, they can be used for
alignment: two
adjacent end plates 320 will only be mounted flush against each other when
then dowel nuts
1502 in one of the end plates 320 is inserted into the recesses 1610 in the
other of the end plates
320. The dowel nuts 1502 may be any suitable shape, such as circular, to
facilitate alignment.
The fact that the recesses 1610 are positioned over complementary sets of the
dowel holes 250 in
adjacent end plates 320 is beneficial for ensuring that the dowel nuts 1502
are screwed into
certain, pre-specified, and correct positions. Second, they are useful because
when the stack
assembly 101 is compressed using the tensioning frame 1604, which is discussed
in more detail
below, the dowel nuts 1502 will be pushed from one of the modules 104 into an
adjacent one of
the modules 104, as compression reduces the length of the gasket and membrane
assembly 1504.
The recesses 1610 in the end plate 320 of the adjacent one of the modules 104
provide space in
which the pushed dowel nuts 1502 can rest, thereby preventing the dowel nut
1502 from
detrimentally pushing the internal modules 104 apart. In an alternative
embodiment (not shown),
the dowel holes 250 may be sized large enough to accept the dowel nuts 1502,
and a separate
recess in the end plates 320 may not be present.
[00134] The cross-sectional view shown in Figure 16 illustrates the operation
of the
recesses 1610 and the dowel nuts 1502 when the stack of internal modules 104
is compressed.
The modules 104 labelled "Module A" utilize the first type of end plate 320,
while the modules
104 labelled "Module B" utilize the second type of end plate 320. The two
types of end plates
320 may be rotated 180 degrees relative to each other in order to produce the
complementary
hole sizes and patterns. The leftmost dowel hole 250 in the topmost module
labelled "Module
B" has one of the recesses 1610, and the dowel nut 1502 for "Module A"
immediately below the
CA 02792516 2012-10-17
topmost "Module B" accordingly slides completely into the end plate 320 for
"Module B" until
either "Module A" is compressed fully or the dowel nut 1502 contacts the
gasket and membrane
assembly 1504. Similarly, the "Module A" immediately below the topmost "Module
B" receives
the dowel nuts 1502 from the "Module B" immediately above and below it.
[00135] Figure 16 also shows exploded and detailed views of the stack assembly
101
being compressed using the tensioning frame 1606 and tensioning rods 1604. The
tensioning
frame 1606 is constructed using two rectangular frames that are placed over
the periphery of the
ends of the end modules 106. The tensioning frame 1604 is periodically
buttressed with
vertically spaced, horizontally extending reinforcing bars (not labelled) that
are coplanar with the
tensioning frame 1604's rectangular frames. Peripherally spaced in the
tensioning frame 1604
along the rectangular frame are a series of dowel holes 250 that align with
the dowel holes 250 in
the internal and end modules 104, 106. To compress the ends of the stack
assembly 101 together
after the internal and end modules 104, 106 are aligned, threaded tensioning
rods 1604 are
inserted through all of the dowel holes 250 in the tensioning frame 1604, from
the rectangular
frame on one of the ends of the stack assembly 101, through the dowel holes
250 and hollow
dowels 823 within the stack, and out the dowel holes 250 in the rectangular
frame on the other
end of the stack. Tensioning rod nuts 1602 are then threaded on to the
tensioning rods 1604 and
torqued to a set point in order to achieve a suitable compressive gasket
pressure, such as
approximately 1.4 MPa in one embodiment, thereby applying an additional
compressive force to
the stack assembly 101. After the tensioning rod nuts 1602 are screwed such
that the
compressive force applied to the stack assembly 101 is within appropriate
tolerances, the stack
assembly 101 shown in Figure 17 results.
[00136] In order to provide an extra safeguard against leakage, a compression
device 1802
such as the one depicted in Figures 18 and 19 can be used. While the
tensioning frame 1606 and
rods 1604 apply compressive force uniformly around the periphery of the stack
assembly 101,
the compression device 1802 applies compressive force directly to the stack
assembly 101 in the
vicinity immediately adjacent to the manifolds 140, 141 and the gasket notch
zones 1304, 1315,
where leakage is more likely to occur.
36
CA 02792516 2012-10-17
[00137] The compression device 1802 is constructed from two parallel bars that
are
mounted vertically on to the tensioning frame 1606 over the periphery of the
end module 106
("mounting bars"), and two struts that are mounted between and perpendicular
to the vertically
mounted, parallel bars. As is clear from Figure 18, four of the compression
devices 1802 are
mounted on to the tensioning frame 1606: one pair is mounted over the inlet
manifolds 140 in the
pair of end modules 106, and one pair is mounted over the outlet manifolds 141
in the pair of end
modules 106. Each of the mounting bars for each of the compression devices
1802 includes two
of the dowel holes 250 so that the tensioning rods 1604 can still be used to
compress the stack
assembly 101 even when the compression devices 1802 are mounted to the
tensioning frame
1606.
[00138] Extending in a direction parallel to the length of the stack assembly
101 are ten
different compression members 1804 that are movable into and away from the
tensioning frame
1606 of the stack assembly 101 near the four sets of manifolds 150 on the
external end plate 504.
The ten different compression members 1804 are used to discretely apply force
to ten load
application points 1806 on the external end plates 504, each of which is
marked using an "x" in
Figure 19. As Figure 19 shows, the load application points 1806 are adjacent
to the manifolds
140, 141 used in the stack assembly 101. The compression members 1804 in the
embodiment of
the compression device 1802 shown in Figure 19 are threaded bolts that can be
screwed into and
out of the struts. In alternative embodiments (not depicted), the compression
members 1804 may
take other forms. For example, they may not be threaded and may instead be
secured using a pin
and slot system. The compression members may also be hydraulic rams or any
other device
which is operable to be moved towards and away from the tensioning frame or
end plate of the
stack assembly and to apply a compressive force thereto. There may also be
more or less
compression members 1804 with different load application points than those
depicted in the
embodiment shown.
[00139] Beneficially, the compression device 1802 can be used to apply
compressive point
loads at discrete points nearer to the manifolds 140, 141 and the gasket notch
zones 1304, 1315
than the tensioning rods 1604 could. The tensioning rods 1604 cannot be used
to apply
compressive force as near to the manifolds 140, 141 because the tensioning
rods 1604 extend
37
CA 02792516 2012-10-17
through the length of the entire stack assembly 101, and would therefore
pierce the manifolds
140, 141 and result in leakage.
[00140] According to another embodiment, the compression device 1802 is used
with a
stack that is not a modular stack including internal and end modules, for
example a stack as
disclosed in US Patent 8,137,522 or a stack for a filter press or the like. As
with the modular
stack, the compression device applies compressive force directly to the non-
modular stack in the
vicinity immediately adjacent to manifolds and gasket notch zones (when
present), thereby
beneficially providing an extra safeguard against leaks. Referring to Figure
20, there is shown a
stack 2002 which is made up of a pair of rigid end plates 2004 and a plurality
of membrane
bounded compartments layered between. A tensioning frame 1606, tensioning rods
1604 and
tensioning rod nuts 1602 apply compressive force uniformly around the
periphery of the stack
2002 as described above with reference to Figure 16. Four compression devices
1802 are
mounted on to the tensioning frame 1606: one pair is mounted over the inlet
manifolds (not
shown) and one pair is mounted over the outlet manifolds (not shown) of the
stack 2002.
Compression members 1804 are moved towards the tensioning frame 1606 to apply
force at
discrete load application points in the vicinity of the manifolds and gasket
notch zones if present.
The compression members 1804 in the embodiment of the compression device 1802
shown in
Figure 20 are threaded bolts that can be screwed into and out of struts in the
compressive device
1802. In alternative embodiments (not depicted), the compression members 1804
may take other
forms. For example, they may not be threaded and may instead be secured using
a pin and slot
system. The compression members may also be hydraulic rams or any other device
which is
operable to be moved towards and away from the tensioning frame or end plate
of the stack
assembly and to apply a compressive force thereto. There may also be more or
less compression
members 1804 with different load application points than those depicted in the
embodiment
shown.
[00141] In addition to, or alternative with the tensioning frame, compression
of the stack
2002 may be provided by an adjustable expansion device (not shown) in
communication with
one or both of the rigid end plates 2004 and adjustable to compress the rigid
end plates 2004
towards each other. The adjustable expansion device can include, for example,
bolt jacks,
38
CA 02792516 2012-10-17
hydraulic jacks, turn buckles, or another suitable device that abut one or
both of the rigid end
plates to apply compressive force to the stack 2002.
[00142] Whilst the embodiment described herein are directed at a stack for a
saltwater
desalination system, the compression device may also be used in other membrane
based stacks to
minimize or prevents leaks, for example, but not limited to a filter press.
[00143] Referring to Figure 21, there is shown an exploded view of a modular
stack
assembly 2101 according to another embodiment. The modular stack assembly 2101
includes a
plurality of internal modules 2104 in stacked arrangement with a pair of
external end plates 504
at either end of the stacked internal modules 2104. A pair of tensioning
frames 1606 are
positioned on the opposite side of each external end plate 504 to the internal
modules 2104.
Dowel holes are spaced around the periphery of the internal modules 2104, the
external end
plates 504 and the tensioning frames 1606, which when aligned form a plurality
of dowel
conduits. Tensioning rods 1604 are inserted through the dowel conduits and
through hollow
dowels (not shown) within the internal modules 2104 as is described above with
reference to
Figure 16. Tensioning rod nuts 1602 are then threaded on to the tensioning
rods 1604 and
torqued to a set point in order to achieve a suitable compressive pressure.
[00144] The internal modules 2104 are bounded on either side by a pair of
rigid interior
end plate 2120. Each interior end plate 2120 includes an electrode 2130
mounted in a recess of
the interior end plate 2120. The interior end plates 2120 may be made of a
rigid plastic to
minimize corrosion, minimise leaks and provide electrical insulation to the
internal modules
2104. The electrodes 2130 of each pair of interior end plates 2120 are
electrically connected to
each other to complete an ionic circuit through the internal module 2104. The
electrical
connection may be in series of parallel as would be understood by a person of
skill in the art.
Alternatively, the electrodes of some of the internal modules may be connected
in series while
the electrodes of other internal modules may be connected in parallel or any
combination.
Electrochemical completion of the ionic circuit is achieved by electrolyte
circulating in an
electrolyte compartment (not shown) adjacent the internal surface of each
rigid interior end plate
2120, such that there is oxidation and reduction reactions of the electrolyte
at the electrode 2130.
The electrolyte may circulate through the electrolyte chambers in series or in
parallel as would
39
CA 02792516 2012-10-17
be understood by a person of skill in the art. Alternatively, the electrolyte
of some of the internal
modules may be circulate in series while the electrolyte of other internal
modules may circulate
in parallel. Provision of an ionic circuit through each internal module 2104
allows for a larger
number of internal modules 2104 to be utilized in the modular stack assembly
2101 whilst still
maintaining a strong electrochemical reaction within the internal modules
2104. The tensioning
frame and/or the external end plates 504 may be made of metal (for example,
but not limited to,
steel) to provide stiffness to the structure allowing the structure to be
compressed. The metal
tensioning frame and/or external end plates 504 are isolated from corroding
fluid in the internal
modules by the plastic interior end plates 2120.
[00145] Figure 22 shows the modular stack assembly 2101 of Figure 21 fitted
with the
compression device 1802. Four of the compression devices 1802 are mounted on
to the
tensioning frame 1606: one pair is mounted over the inlet manifolds 140 in the
pair of external
end plates 504, and one pair is mounted over the outlet manifolds 141 in the
pair of external end
plates 504. Compression members 1804 are moved towards the tensioning frame
1606 to apply
force at discrete load application points in the vicinity of the manifolds
140, 141 and gasket
notch zones. The compression members 1804 in the embodiment of the compression
device 1802
shown in Figure 21 are threaded bolts that can be screwed into and out of
struts on the
compression device 1802. In alternative embodiments (not depicted), the
compression members
1804 may take other forms. For example, they may not be threaded and may
instead be secured
using a pin and slot system. The compression members may also be hydraulic
rams or any other
device which is operable to be moved towards and away from the tensioning
frame or end plate
of the stack assembly and to apply a compressive force thereto. There may also
be more or less
compression members 1804 with different load application points than those
depicted in the
embodiment shown.
[00146] While particular embodiments have been described in the foregoing, it
is to be
understood that other embodiments are possible and are intended to be included
herein. It will
be clear to any person skilled in the art that modifications of and
adjustments to the foregoing
embodiments, not shown, are possible.
