Note: Descriptions are shown in the official language in which they were submitted.
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ELECTROLYSER
Field of the Invention
This invention relates to an assembly for securing and compressing a stack
electrolysis
cell.
Background of the Invention
Electrolysis cells have long been used to generate hydrogen from water,
generally in
the form of an electrolyte solution.
In a particular electrolysis cell, porous anode and cathode plates are
arranged in a
stack with an electrolyte permeable-gas impermeable membrane placed between
each
anode and cathode pair (for example as described in PCT Publication No.
W02004/020701 and Canadian Patent Application No. 2,400,775 ELECTROLYZER,
Helmke et al., both of which are incorporated herein by reference). By
providing
separate channels to each of the anodes and cathodes, the product gases
generated at
each of the anodes and cathodes may be separately output from the cell.
Electrolyte is
circulated through the porous anodes and cathodes. In order to circulate the
electrolyte
and provide an outlet for the product gases, the channels are created by
cutting holes
or slots in each plate that align when the plates are stacked. The aligned
holes and
slots form the channels to circulate electrolyte and provide for output of the
product
gases.
An advantageous method of manufacturing such a cell has been to stack the
anode
plates, cathode plates and membranes and encase the resulting stack in an
electrolyte
impermeable-gas impermeable membrane such as epoxy resin. The epoxy is used to
assist in sealing the edges of the plates and to secure the plates in an
aligned stack.
The resultant electrolyser may thus be comprised of multiple electrolysis
cells encased
in an epoxy resin casing. Ports may be provided through the epoxy casing to
permit
circulation of electrolyte and output of the product gases. Electricity may be
provided
to the cells via an electrical connection that extends out of the epoxy.
While this method of creating an electrolyser from a stack of anode and
cathode plates
has been successful, it does suffer from some limitations. The resulting
electrolysers
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are limited in their gas output rate as elevated internal pressures cause the
epoxy to
swell and allow the plates to separate. Once the plates separate, even by a
relatively
small amount, the channels may no longer be completely separate. Even a small
breakdown in channel integrity may result in co-mingling of product gases and
electrolyte, reducing output from the electrolyser.
It would be advantageous to provide for a stack cell and a method of
manufacturing
such a stack cell that alleviates these limitations.
Brief Description of the Drawings
In drawings which illustrate embodiments of the invention by way of example
only:
1o Figure IA is an exploded perspective view of a stack of electrolysis
plates.
Figure lB is a perspective view of the assembled stack of electrolysis plates
of Figure
I a.
Figure 2 perspective view of an assembled electrolyser according to an
embodiment of
the invention.
Figure 3 is a cross-sectional elevation of the electrolyser of Figure 2.
Detailed Description of the Invention
The invention provides an electrolyser comprising a stack of electrolysis
plates, the
plates being maintained in substantially parallel alignment, and a press for
applying a
compressive force transversely to the stack, to compress the stack between
opposed
faces of the cell, the press comprising a front face, a compression support
plate fixed
in position relative to the front face and spaced from the front face, a
moving platen,
the stack being disposed between the platen and the front face, and a
compression
member for applying a compressive force to the platen such that the platen
applies a
transverse compressive force substantially uniformly over a face of the stack,
whereby
the press maintains the electrolysis plates in substantially parallel
alignment when the
electrolyser is in operation.
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In further embodiments of the electrolyser of the invention: The compression
member
comprises a spring bearing against the platen; the spring is actuated by a
disk
threadedly secured to the compression support plate and bearing against the
spring;
the spring is disposed in a recess disposed on a face of the platen; the
spring surrounds
a hub disposed in the recess; the hub surrounds a key; the front face is
formed by a
jacket; the front face is formed integrally with side faces of the jacket;
and/or the
compression support plate is affixed to the side walls.
The invention further provides a method of stabilising an electrolyser
comprising a
stack of electrolysis plates, the electrolysis plates being in substantially
parallel
alignment, the method comprising the steps of: a. locating the stack of
electrolysis
plates in a press comprising a front face and a compression support plate
fixed in
position relative to the front face; and b. rotating a threaded compression
member to
apply a compressive force to a platen bearing against the stack, such that the
platen
applies a transverse compressive force substantially uniformly over a face of
the stack;
whereby the press maintains the electrolysis plates in substantially parallel
alignment
when the electrolyser is in operation.
Figure IA illustrates an exploded view of a stack 10 of electrolysis plates 12
comprising alternating porous anode and cathode plates with an electrolyte
permeable-
gas impermeable membrane 12a between each anode-cathode pair.
The electrolysis plates 12 maybe assembled into the stack 10 having positive
and
negative terminals 11, 13, respectively, as illustrated in figure 1B, and
encased in a
sealant such as epoxy, a silicone compound or any other suitable sealant, to
seal the
edges of the plates and, in conjunction with the compression member described
below, maintain the plates 12 in the stack 10 in precise parallel alignment
within the
electrolysis cell 20.
As more fully described in W02004/020701 and CA2,400,775, which are
incorporated herein by reference, slots in the plates align when stacked to
form
channels through the stack 10. The channels permit circulation of electrolyte
through
the stack 10 and output of the product gases from the cell 20. A first product
gas (in
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the case of the electrolysis cell shown, one of hydrogen and oxygen) is output
from
one or more first gas output ports 22, a second product gas (in the case of
the
electrolysis cell shown, the other of hydrogen and oxygen) is output from one
or more
second gas output ports 24, electrolyte is input through one or more
electrolyte input
ports 28, and electrolyte is output through a set of one or more electrolyte
output ports
26, as illustrated in Figures 1B and 2. As will be appreciated, the placement
and
number of ports may vary from the embodiment illustrated in Figures 1B and 2.
Also
shown is an output 29 for a thermocouple, for monitoring the temperature of
the
electrolysis cell 20.
During operation of the cell 20, a current supplied to electrodes 11, 13
results in
hydrogen and oxygen gas being generated in the electrolysis plates 12 of the
cell 20.
The generation of these product gases increases the internal pressure of the
cell 20,
causing the product gases to egress through the first and second product gas
ports 22,
24. In order to increase the gas output of the cell 20, a higher electrical
input may be
supplied to the electrodes 11, 13. The higher electrical input results in the
product
gases being generated more quickly, the internal pressure of the cell 20
increasing and
a higher flow rate of product gases from product gas ports 22, 24.
However, the higher electrical input increases the temperature of the stack 10
with
attendant increased thermal expansion of the stack 10. Any separation of the
plates 12
within the stack 10 (either by spreading or by loss of parallel alignment)
consequent to
thermal expansion causes loss of output gases and therefore reduces the
efficiency of
the cell 20.
It has been found that the electrolysis cell 20 may be operated at higher
levels of gas
output, and consequent higher internal operating pressures, if a substantially
even
compressive force is applied to opposite faces of the cell 20 and maintained
during
operation. In the preferred embodiment the compression member accommodates
thermal expansion of the encased stack 10 while under the compressive force.
In the embodiment illustrated, the invention provides a press for securing the
electrolyser containing the stack 10 of electrolysis plates 12, comprising a
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compression plate for compressing the encased stack 10 against the jacket 30
of the
cell 20, and a disk spring 50 which can be adjusted to set a rest compression
and
which allows the compression plate to move as the stack 10 expands while
maintaining a relatively constant pressure against the encased stack 10 as the
cell 20
heats up.
As illustrated in Figures 2 and 3, the stack 10 is contained within a jacket
30
constructed of a sturdy, rigid material such as stainless steel, carbon fibre,
plastic (for
example polyetheretherketon (PEEK), PVC, CPVC), or other suitable material. As
shown the jacket 30 is bent to form the front face 30a and sides 30b, however
these
maybe formed as separate components if desired. The electrodes 11, 13 protrude
through one end plate 30c and another end plate 30d seals the opposite end of
the cell
20. The ends 30c, 30d may be bolted or otherwise suitably affixed to the front
face
and sides 30a, 30b of the jacket 30.
A compression platen 32 is movably disposed opposite to the face 30a,
preferably
nested within the jacket 30 as shown in Figure 3. The compression platen 32 is
similarly formed from a sturdy, rigid material and spans the length and width
of the
stack 10.
A compression member comprising a disk spring 50 is disposed generally
centrally
along the platen 32, for applying a compressive force to the stack 10. The
disk spring
50 may be mounted in a recess 32a in the outer face of the platen 32, and
surrounds a
hub 52 and key 54 which interlocks with a rotatable disk 56 threadedly engaged
to an
opening 42 through a compression support plate 40, the hub 52 maintaining the
spring
50 in axial alignment beneath the disk 56.
The compression support plate 40 is in turn bolted to the jacket 30 (as seen
in Figure
2). The compression support plate 40 and jacket 30 thus form a press frame
containing
disk spring 50 in contact with moving platen 32.
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Optionally an elastomer layer 46 may be positioned between the stack 10 and
the face
30a of the electrolysis cell 20, serving as a thermal insulator and allow for
any
imperfections between face 30a and the facing side of the electrolysis cell
20. The
elastomer layer 46 may for example be composed of Ethylene Propylene Dieene
Monomer, but any suitable thermal insulating material may be used if desired.
The cell 20 is assembled by inserting the encased stack 10 into the jacket
(after
inserting a thermally insulating layer 46, if desired), and inserting the
platen 32 over
the stack 10. The disk spring 50 is mounted in the recess 32a about the hub 52
and key
54, and the support plate 40 (with disk 56 threaded into opening 42) is bolted
to the
jacket 30.
After assembly of the cell 20, the disk 56 can be tightened to a desired
torque, forcing
platen 32 toward stack 10 and thus applying a uniform compression over the
face of
the stack 10 (the opposite face of the stack 10 bearing against the interior
of face 30a
of jacket 30, applying a uniform compression over the opposite face of the
stack 10).
This manner of compression is superior to conventional compression means such
as
corner bolts, because a single member can be adjusted to apply even
compression over
the entire face of the stack. Moreover, even if corner bolts could be
tightened to
supply an initial uniform compression, through constant expansion and
contraction the
compression will eventually become non-uniform and allow the plates 12 to come
out
of parallel alignment. Even the slightest loss of parallel alignment between
the plates
12 will result in reduced efficiency of the cell 20, and substantial loss of
parallel
alignment will result in catastrophic failure of the cell 20.
In operation, as described in W02004/020701 and CA2,400,775, which are
incorporated herein by reference, slots in the plates 12 form channels (not
shown)
through the stack 10 which permit circulation of electrolyte through the stack
10 and
output of the product gases from the cell 20. A current supplied to electrodes
11, 13
results in hydrogen and oxygen gas being generated in the electrolysis plates
12 of the
cell 20 via electrolysis, as is well known. The generation of the product
gases
increases the internal pressure of the cell 20, causing the product gases to
egress
through the first and second product gas ports 22, 24. In the case of the
electrolysis
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cell shown, hydrogen is output from first gas output port 22, and oxygen is
output
from second gas output port 24. Electrolyte is circulated through input port
28 and
output port 26, ensuring a constant supply of electrolyte solution.
Increasing the electrical input results in the product gases being generated
more
quickly, the internal pressure of the cell 20 increasing and a higher flow
rate of
product gases from product gas ports 22, 24. However, it also results in
greater
thermal expansion of the stack 10. As the stack 10 expands transversely
(relative to
the plane parallel to the plates 12) the disk spring 50 yields to maintain a
substantially
constant compression against the stack 10. This not only prevents misalignment
of the
plates 12, but also reduces the risk of cracking of the epoxy encasement
material. The
compression remains uniform, because the pressure from disc spring 50 is
applied
generally centrally to the platen 32 over the area of the disk spring 50.
Various embodiments of the present invention having been thus described in
detail by
way of example, it will be apparent to those skilled in the art that
variations and
modifications may be made without departing from the invention. The invention
includes all such variations and modifications.
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