WO2016034183A1

WO2016034183A1 - Pressurised electrolysis stack

Info

Publication number: WO2016034183A1
Application number: PCT/DK2015/050263
Authority: WO
Inventors: Jørgen KROGSGAARD JENSEN; Anders RØNNE RASMUSSEN
Original assignee: Greenhydrogen.Dk Aps
Priority date: 2014-09-05
Filing date: 2015-09-04
Publication date: 2016-03-10
Also published as: DK201400505A1; DK178796B1

Abstract

An electrolysis stack (2) for an electrolyser (20) is disclosed. The electrolysis stack (2) comprises a plurality of electrolysis cells each comprising two electrodes and a (porous) gas separating membrane and a cell frame (6, 6', 6") having a circular outer periphery. The cell frames (6, 6', 6") are arranged adjacent to each other. The electrolysis stack (2) comprises means (18) for supplying electrolyte feed to the interior of the electrolysis cells and means (16) for removing oxygen gas and hydrogen gas from the electrolysis ceils. The electrolysis stack (2) comprises electric power point members (46, 46f) constituting a cathode, an anode or a cathode and an anode. The electrolysis stack (2) comprises at least one support member (12, 12', 42, 42', 42") arranged at the outside periphery of the cell frames (6, 6', 6").

Description

Pressurised Electrolysis Stack

Field of Invention

The present invention generally relates to an eiectroiyser for pressurised electrolysis, The present invention more particularly relates to an electrolysis stack for a pressurised eiectroiyser.

Prior art

The need for storing electric energy generated from solar panels or wind turbines is increasing due to the need for greener energy sources. Storing electric energy in hydrogen by using electrolysers to convert water to hydrogen and oxygen has been known for decades. However, there is a storage problem with hydrogen because the geometric volume needed for storing a given mass of hydrogen gas is inversely related to the storage pressure, i.e. the higher the pressure, the smaller the volume. Therefore, hydrogen needs to be stored under pressure. It is therefore desirable to conduct electrolysis at elevated pressures to reduce or even eliminate the need for further compression of the hydrogen.

Several methods of manufacturing an electrolysis stack capable of generating hydrogen at elevated pressure have been described.

The American patent US 2,881,123 describes an electrolysis stack wherein the cell frames are made of steel. Steel has a high mechanical strength and is the preferred choice of material for these types of pressure vessels. However the drawback is that the cell frames need to be eiectricaiiy insulated from each other in order to prevent short circuiting of the stack.

The American patent application US 2010/0078317 describes an electrolysis stack which is able to tolerate a high operating pressure. The cell frames are manufactured from polymer material which is protected by a strong outer shell of steel. There is, however, no pressure difference between the inside and the outside of the stack. The American patent US 6,554,978 describes an electrolysis stack in which the cell frames are manufactured from polymer material. However, in order for the polymer material to tolerate elevated pressure, the thickness of the cell frame is large in order to prevent failure of the material.

For these electrolysis stacks to be able to operate at elevated pressure, they have been made of pressure resistant material which is very costly. Further, the prior art electrolysis stacks are restricted with respect to the position of the electric connections. Thus, there is a need for an improved electrolysis stack which reduces or even eliminates the above-mentioned disadvantages of the prior art. Accordingly, it is an object of the present invention to provide an electrolysis stack that is capable of being operated at elevated pressure, where thickness of the cell frame may be reduced and in which the electric connections can be arranged with fewer restrictions with respect to the position of the electric connections.

Summary of the invention

The object of the present invention can be achieved by an electrolysis stack as defined in claim 1 and by an electrolyser having the features as defined in claim 15. Preferred embodiments are defined in the dependent sub claims, explained in the following description and illustrated in the accompanying drawings.

The electrolysis stack according to the invention is an electrolysis stack method for an electrolyser, which electrolysis stack comprises a plurality of electrolysis cells. The stack comprises a plurality of bipolar electrodes, gas separating membranes and cell frames, which cell frames are arranged adjacent to each other, which electrolysis stack comprises means for supplying electrolyte feed to the interior of the electrolysis cells and means for removing oxygen gas and hydrogen gas from the electrolysis ceils, which electrolysis stack comprises electric power point members constituting a cathode, an anode or a cathode and an anode, wherein the electrolysis stack comprises a plurality of support members arranged substantially in axial extension from each other, wherein said support member are arranged at the outside periphery of the cell frames.

Hereby, it is possible to provide an electrolysis stack capable of being operated at elevated pressure, where the thickness of the ceil frame can be reduced . The support member reduces deformation in the circumferential direction of the cell frames. Furthermore, the electric connections can be arranged with fewer restrictions with respect to the position of the electric connections as the electric connections can be arranged between adjacent support member. The electrolysis stack may comprise any suitable number of electrolysis cells (e.g . 25, 50, 100 or 400) . The electrolysis cells may be arranged in the same or in several different modules.

The electrolysis stack according to the invention may be adapted to handle a strong alkali electrolyte comprising potassium hydroxide (KOH) (e.g . 30wt% KOH) .

The bipolar electrodes may comprise sheet material (e.g. a metal sheet), and the separating membrane may be a porous gas separating membrane. The membrane may comprise any suitable material e.g . two layers of a polymer comprising Zr0₂. it may be an advantage that each cell frame has a circular outer periphery. Hereby, it is possible to provide a strong and reliable electrolysis stack.

The ceil frames are arranged adjacent to each other, and it may be an advantage that the cell frames are sealed with Oring gaskets made in a resilient material (e.g. EPDM rubber) . The electrolysis stack comprises means for supplying electrolyte feed to the interior of the electrolysis cells. The means for supplying electrolyte feed to the interior of the electrolysis cells may be of any suitable type and geometry. The means for supplying electrolyte feed to the interior of the electrolysis cells may comprise a channel structure constituted by the plurality of cell frames arranged side by side along the longitudinal axis of the electrolysis stack.

The electrolysis stack comprises means for removing oxygen gas and hydrogen gas from the electrolysis cells. These means may comprise a channel structure constituted by the plurality of cell frames arranged side by side along the longitudinal axis of the electrolysis stack.

It may be an advantage that each cell frame is provided with a plurality of through-bores extending through the axial length of the cell frame. Together with other structures, these through-bores may constitute a channel structure constituted by the plurality of cell frames arranged side by side along the longitudinal axis of the electrolysis stack, The electrolysis stack comprises current terminals constituting a cathode, an anode or a cathode and an anode. These electric power point members may have any suitable geometry. The electric power point members may e.g. be plate-shaped. The at least one support member arranged at the outside periphery of the cell frames may have any suitable geometry and be made in any suitable material.

It may be an advantage that the inner portion of the support member is made in an electrically insulating material, such as a plastic material.

It may be beneficial that the support members are cylindrical and extend along the axial length of the ceil frames. Hereby, it is possible to provide a support member with the required mechanical properties.

Moreover, a cylindrical support member can enclose ceil frames having a circular outer periphery.

It may be beneficial that the cell frames are arranged between two flanges, and that the flanges are mechanically attached to each other by means of a plurality of threaded rods and nuts, Hereby, it is possible to provide an electrolysis stack configured to resist large forces acting in the axial direction (causing expansion of the electrolysis stack along its longitudinal axis).

It may be an advantage that the cell frames are arranged between two flanges, and that the flanges are mechanically attached to each other by means of a plurality of threaded rods, nuts and washers,

It may be advantageous that the support members are arranged in such a manner that they are not in mechanical contact with the flanges.

Hereby, it is achieved that the cell frames can be compressed in axial direction (e.g. during tensioning of the nuts). Further, the support member can expand in the axial direction. It may be an advantage that a gap is provided between a flange and the adjacent support member.

This allows for compressing the cell frames in axial direction (e.g. during tensioning of the nuts) without damaging the support members. Further, the support members can expand in the axial direction without pressing against the flanges.

It may be advantageous that a gap is provided between at least some of the adjacent support members. Hereby, the cell frames can be compressed in axial direction (e.g. during tensioning of the nuts). Further, the support member can expand in the axial direction. It may be beneficial that a metal structure is provided under the gap.

This facilitates that the cell frames can be compressed in axial direction (e.g. during tensioning of the nuts) without damaging the support members. Further, the support members can expand in the axial direction.

The metal structure may be a current terminal made of a metal plate. The metal structure may be an electrical power member shaped as a plate.

It is preferred that the ceil frames are mounted in an outer support member made in a high-strength composite material . It may be an advantage that the outer support member extends longer in the axial direction than the cell frames contained within the outer support member. Hereby, it is possible to support the cell frames when the cell frames extend axially.

It may be beneficial that the support member is constructed in such a way that the gap between the outer diameter of the cell frames and the inner diameter of the support member is as small as possible.

In one embodiment according to the invention, the support member is a cylindrical tube made in a composite material (fibre-reinforced polymer) made of a polymer matrix reinforced with fibres (e.g. glass, carbon or aramid). The polymer may be any suitable polymer material, e.g. epoxy, polyphenyisulfone (PPSU) or polyether ether ketone (PEEK). It may be beneficial that the elastic modulus of the support member is larger than the elastic modulus of the cell frames.

Hereby, the support member is configured to keep its geometrica shape and to prevent radially expansion of the cell frames. it may be advantageous that the coefficient of thermal expansion of the support member is smaller than the coefficient of thermal expansion of the cell frames.

Hereby, the support member is configured to maintain its geometrical shape and prevent radially expansion of the cell frames during operation of the electrolysis stack.

It may be beneficial that the support member is made in an electrically insulating material e.g. a fibre reinforced plastic material.

The fibres may be glass fibre, armid fibre or carbon fibre by way of example.

It may be an advantage that the electrolysis stack comprises a plurality of support members arranged with essentially mutual end-to-end contact and substantially in axial extension of each other. However, it is preferred that a small gap is provided between adjacent support members. Hereby, it is possible to achieve an electrolysis stack provided with modular support members. It is thus possible to build a long electrolysis stack and apply the same support member as used for shorter electrolysis stacks.

It may be an advantage that the electrolysis stack comprises a first support member and at least one additional support member arranged at the outside of the first support member. Hereby, it is possible to provide additional strength to the electrolysis stack so that it is configured to resist the pressure within the cell stacks.

It may be beneficial that an electric connection is provided between adjacent support members, wherein at least the distal portion of the electric connections protrudes from the support members.

Hereby, it is possible to arrange the electric connections in more positions providing greater design freedom with respect to the electrical system of the electrolysis stack.

The electric connections may preferably extend radially - perpendicular to the support member. Hereby, easy access can be provided. It may be beneficial that an electric connection is provided at the outermost axial end of each of the outermost support members.

Hereby, the electrical system can be simplified. It may be an advantage that the electric connections extend as an extension of the electric power point members.

Hereby, the electric power point members are easily accessible electrically.

The object of the invention may be achieved by an electrolyser comprising an electrolysis stack according to the invention.

The electrolysis stack can be a single electrolysis stack or split in sections.

It is preferred that the ceil frames are made in a material suitable for handling high pH values (pH values above 14) The support member(s) may be mechanically attached on the outside of the cell frames.

It is preferred that the support member(s) are displaceable arranged on the outside of the cell frames It is possible to apply a metal (steel) support structure provided with an inner insulation structure,

It may be an advantage that the electrolysis stack is divided into a plurality of electrically separated cell frame modules.

Hereby, the electrical potential between the first and last cells in each of the cell frame modules is reduced. Accordingly, it is possible to provide an electrolysis stack that reduces stray currents and hereby energy losses.

The amount of energy loss due to stray current increases with the number of cells in the ceil frame module because the electrical potential between the first ceil frame and the last cell frame in a ceil frame module depends on the number of ceil frames in the ceil frame module.

The present invention suggests a construction in which the electrolysis stack is divided into a plurality of electrically separated cell frame modules. In this manner, the electrical potential difference between the first cell and the last ceil in a cell frame module can be significantly reduced.

The electrolysis stack may be divided into a plurality of electrically separated cell frame modules by several means. However, it may be an advantage that the electrolysis stack is divided into a plurality of electrically separated cell frame modules by means of electric power point members extending along the length of the cell frames.

It may be beneficial that the electrolysis stack is divided into three or more electrically separated ceil frame modules.

It may be advantageous that each of the electrically separated ceil frame modules comprises 10-40, preferably 15-35, such as 20-35 cell frames. Hereby, it is possible to apply standard power supplies. It may be an advantage that each of the electrically separated cell frame modules comprises 25 cell frames. Hereby, it is possible to apply a standard power supply. It may be advantageous that each of the electrically separated cell frame modules comprises the same number of cell frames. Hereby, it is possible to build an electrolysis stack by using a plurality of identical cell frame modules. It may be beneficial that all of the electrically separated cell frame modules are electrically separated from each other by means of current terminals and/or electric power point members arranged between adjacent cell frame modules. Hereby, it is possible to supply electrical current to the cell frame modules through these current terminals and/or electric power point members.

It may be an advantage that each of the electrically separated ceil frame modules comprises insulation bushings configured to electrically insulate the electrolyte within the electrolysis stack from the current terminals and/or electric power point members arranged between adjacent cell frame modules during use of the electrolysis stack.

Hereby, it is possible to reduce the stray currents giving rise to loss of energy in the electrolysis stack.

The bushings may preferably have a cylindrical shape.

It may be an advantage that the bushings are arranged in the channels that are provided in the ceil frames to distribute electrolyte to all the cells frames in the cell frame module. Preferably, the bushings extend between two adjacent ceil frame modules.

Description of the Drawings

The invention wil l become more fully understood from the detailed description given herein below. The accompanying drawings are given by way of illustration only, and thus, they are not limitative of the present invention. In the accompanying drawings:

Fig. 1 shows two schematic views of an electrolysis stack according to the invention;

Fig. 2 shows a schematic perspective top view of an electrolyser according to the invention;

Fig. 3 illustrates schematic perspective top views of an electrolysis stack according to the invention;

Fig, 4 shows schematic cross-sectional views of an electrolysis stack according to the invention;

Fig. 5 shows two schematic perspective top views of an electrolysis stack according to the invention;

Fig. 6 shows a schematic perspective top view of an electrolysis stack according to the invention

Fig. 7 a shows an end view of an electrolysis stack according to an embodiment of the invention;

Fig. 7 b shows a close-up cross-sectional view of the bushing electrically insulating the electric power point member from the electrolyte within the electrolysis stack;

Fig. 7 c shows a close-up cross-sectional view of a bushing electrically insulating a current terminal from the electrolyte;

Fig. 7 d) shows a cross-sectional view of the electrolysis stack shown in Fig. 7 a);

Fig, 7 e) shows a perspective view of the bushing shown in Fig. 7 c); Fig. 7 f) shows a perspective view of the bushing shown in Fig, 7 b);

Fig. 8 a) shows a top view of an electrolysis stack according to an embodiment of the invention;

Fig. 8 b) shows a close-up cross-sectional view of the electrical connection shown in Fig. 8 a) and

Fig. 8 c) shows a close-up cross-sectional view of the joint structure of the adjacent support members. Detailed description of the invention

Referring now in detail to the drawings for the purpose of illustrating preferred embodiments of the present invention, an electrolysis stack 2 of the present invention is illustrated in Fig, 1.

Fig, 1 illustrates two different schematic views of an electrolysis stack 2 according to the invention. Fig. 1 a) illustrates a schematic top view of an electrolysis stack 2 comprising a cylindrical support member 12 enclosing a plurality of disk-shaped cell frames 6 stacked within the support member 12.

The electrolysis stack 2 comprises a series of stacked electrolysis ceils. Each of these electrolysis cells contains two bipolar electrodes (metal sheets). A gas separating porous membrane is provided between every bipolar electrode. Each electrolysis cell comprises a disk-shaped polymer cell frame 6.

In Fig. 1, however, the membrane and bipolar electrodes of the cell frames 6 have been removed for illustration purposes. It may be an advantage that the ceil frames are sealed with O-ring gaskets of a resilient material (e.g. EPDM rubber).

Each cell frame 6 comprises four axialiy extending through bores 8, 8', 10, 10'. Each cell frame 6 comprises a centrally arranged aperture 14.

Each cell frame 6 comprises a membrane (not shown). The membrane is exposed to high temperatures (up to 100° Celsius) and pH values above 14 during operation of the electrolysis stack 2. Accordingly, the membrane must be capable of being exposed to a demanding chemical environment. The membrane may comprise any suitable material e.g. two layers of a polymer comprising Zr0₂. The electrolysis stack 2 according to the invention may be adapted to handle a strong alkali electrolyte comprising potassium hydroxide (KOH) (e.g. 30 wt% KOH). Some of the through bores 8, 8', 10, 10' may be used to transport oxygen (0₂) and hydrogen (H₂) generated by means of the electrolysis stack 2. Some of the through bores 8, 8', 10, 10' may be used to transport the electrolyte (e.g. demineralised water with 30 wt% KOH). Fig. 1 b) illustrates a schematic perspective top view of the electrolysis stack 2 shown in Fig. 1 a). The electrolysis stack 2 comprises a cylindricai support member 12 arranged at the outside of a stack of cell frames 6, 6', 6" stacked within the support member 12. Even though the cell frames 6, 6', 6" comprise membranes and bipolar electrodes, these have been removed for illustrating that the cell frames 6, 6', 6" are stacked on top of each other within the cylindrical support member 12.

The cell frames 6, 6', 6" may be manufactured in a polymer material, e.g. polyphenylsulfone (PPSU) or polyether ether ketone (PEEK). When the stack is pressurised and the cell frames 6, 6', 6" are brought into mechanical contact with the support member 12, the support member 12 (a cylindricai tube) will significantly reduce further deformation in the circumferential direction of the ceil frames 6, 6', 6". Accordingly, the use of the support member 12 makes it possible to operate the electrolysis stack 2 at high pressures (e.g. up to 3 MPa) without critical deformation of the cell frames 6, 6', 6".

Fig. 2 illustrates a schematic perspective top view of an eiectrolyser 20 according to the invention. The eiectrolyser 20 comprises a frame 36 having a lower frame member 38 and an upper frame member 38' interconnected by four (only three are visible in Fig. 2) connection members 40, 40', 40" shaped as angle bars 40, 40', 40". Each angle bars 40, 40', 40" is mechanically attached to both the lower frame member 38 and an upper frame member 38'.

The eiectrolyser 20 comprises two electrolysis stacks 2, 2' mounted in the lower portion of the eiectrolyser 20. Each of the electrolysis stacks 2, 2' comprises a cylindrical support member 12 like the one shown in Fig, 1. Each of the two electrolysis stacks 2, 2' is arranged between two flanges 24, 24'. These flanges 24, 24' are mechanically attached to each other by means of a plurality of threaded rods 26, nuts 22 and washers 44. The two electrolysis stacks 2, 2' are identically constructed and extend parallel to each other.

The electrolyser 20 comprises degassing chambers, a gas purification system and a pressure control system. The two electrolysis stacks 2, 2' are electrically connected to separate power supplies. Fig. 3 a) and Fig. 3 b) illustrate two different schematic perspective top views of an electrolysis stack 2 according to the invention. The electrolysis stack 2 is arranged between two parallel, plate-shaped flanges 24, 24'. The flanges 24, 24' are mechanically attached to each other by means of a plurality of threaded rods 26 and corresponding nuts 22 and disks 44, The disks 44 are compressible disks allowing the ceil frames to expand along the longitudinal axis X of the electrolysis stack 2. The stack may for example comprise 18 disks 44. This assembly prevents the flanges from being displaced from each other along the longitudinal axis X of the electrolysis stack 2.

It can be seen that the threaded rods 26 extend parallel to each other and to the longitudinal axis X of the electrolysis stack 2.

The electrolysis stack 2 comprises three cylindrical support members 11, 11', 12 arranged end to end at the periphery of a plurality of cell frames (not shown) within the interior of the electrolysis stack 2.

Four electrical connections 50, 50', 52, 52' are provided along the periphery of the support members 11, 11', 12. The electrical connections 50, 50', 52, 52' protrude radially from the periphery of the support members 11, 11', 12.

Fig. 4 illustrates two schematic cross-sectionai views of an electrolysis stack 2 according to the invention. Fig. 4 a) shows a side view, while Fig, 4 b) illustrates a perspective view. The electrolysis stack 2 is arranged between two flanges 24, 24' mechanically attached to each other by means of a plurality of threaded rods 26, 26' and corresponding nuts 22, 22' and washers 44. The threaded rods 26, 26' extend along the longitudinal axis X of the electrolysis stack 2.

The electrolysis stack 2 comprises a cylindrical support member 12 arranged at the periphery of a plurality of cell frames 6. The electrolysis stack 2 comprises three cylindrical support members 11, 11', 12 arranged end to end at the periphery of a plurality of cell frames 6 of the electrolysis stack 2.

Fig. 4 b) shows that a gas outlet pipe 16 and a KOH inlet pipe 18 are provided in the flange 24. Channels extending parallel to the longitudinal axis X of the electrolysis stack 2 are provided in continuation of the gas outlet pipe 16 and of the KOH inlet pipe 18. The channels extend through the plurality of cell frames 6.

The electrolysis stack 2 comprises three ceil frame modules Mi, M₂, M₃ arranged end to end along the longitudinal axis X of the electrolysis stack 2. Fifty cell frames 6 are arranged in each of the three cell frame modules M_lf M₂, M₃. Accordingly, the total number of cell frames 6 in the electrolysis stack 2 is 150.

An insulating plate member 32, 32' is arranged in each end of the electrolysis stack 2. Two electric power point members (current terminals) 46, 46' are arranged next to each of the insulating plate members 32, 32'. The electric power point member 46 is a cathode, while the electric power point member 46' is an anode. Furthermore, two electric power point members formed as bipolar electrodes 48, 48' are arranged between the first cell frame module Mi and the second cell frame module M₂ as well as between the second cell frame module M₂ and the third cell frame module M₃, respectively.

A first bushing 34, a second bushing 34' and a third bushing 34" are arranged to electrically insulate the electrolyte from the electric power point members 48, 48', 46, 46' in order to prevent unwanted currents from running through the electrolysis stack 2,

The bushings 34, 34', 34" may be made in any suitable insulating material capable of resisting the demanding working conditions (temperatures up to 100° Celsius and pH values above 14 as well as a high concentration of oxygen and hydrogen gasses), The bushings 34, 34', 34" may be made in poiyphenyisulfone (PPSU) or polyether ether ketone (PEEK) by way of example.

The electrolysis stack 2 is equipped with a gas outlet channel 16 (oxygen or hydrogen gasses) and a media inlet 18 (for demineralised water with KOH, e.g. demineralised water with 30wt% KOH). The electrolysis stack 2 is enclosed by three support members 11, 11', 12 shaped like cylindrical tubes, The support members 11, 11', 12 are constructed in such a way that they are configured to support the cell frames 6 in radial direction. It is possible to apply one large support member instead of three support members 11, 11', 12,

Along the longitudinal axis X of the electrolysis stack 2, the total length of the stack of cell frames 6 will change with temperature and over time due to thermal expansion, change of elastic modulus with temperature and compressive stress, and creep due to compressive stress,

The support members 11, 11', 12 are not subjected to any significant stress in the axial direction. Accordingly, only thermal expansion will cause changes in the length of the support members 11, 11', 12 in the direction of their longitudinal axis X,

By using support members 11, 11', 12 like the ones illustrated in Fig. 3- 4, it is possible to reduce the dimensions of the cell frames 6, 6', 6".

The electrolysis stack 2 is designed with a modular concept in mind. The electrolysis stack 2 contains??? a number of cell frame modules M_lf M₂, M₃ providing a total number of cell frames 6 of e.g. 100, 150 or 200 with a volume ranging from e.g. 4 L to 10 L or more of electrolyte inside. Depending on the customer's needs, it is possible to provide large configurations of e.g. 50, 75, 100 or 200 cell frames 6 by combining a number of cell frame modules Mi, M₂, M₃.

When assembled, the cell frame modules Mi, M₂, M₃ are separated from one.

The cell frame modules Mi, M₂, M₃ each comprises 50 cell frames 6. Each cell frame module comprises electrical power point members constituting either a cathode, an anode or a cathode and an anode. A diaphragm or membrane is provided to separate the gasses generated.

When the cell frames 6 are combined into an electrolysis stack 2, three cell frame modules Mi, M_2/ M₃ are positioned end to end. The cell frame modules i, M₂, M₃ are connected to fittings in the flanges 24, 24'.

Accordingly, a 150 cell frame electrolysis stack 2 is built up by the three cell frame modules Mi, M₂, M₃ with a total of 150 small chambers (anode, cathode, anode, cathode and so on) where 75 of the chambers are connected by channels to the oxygen producing part of the stack, and the remaining 75 chambers are connected to the hydrogen producing past.

The oxygen and the hydrogen sides are completely separated from each other by membranes/diaphragms and (bipolar) electrodes. Accordingly, the electrolysis stack 2 may be considered to take the form of two vessels: one carrying H₂ and one carrying 0₂.

When direct current is applied to the first and the last ceil of a ceil frame module Mi, M₂, M₃, it causes current to flow through each ceil (each cell comprises two cell frames 6) in the cell frame module Mi, M₂, M_3/ dividing the potentia l between each eel! frame in the cel l frame module _if M₂, M₃. The potential of each cei l frame 6 is determ ined by the current passing through each ceil frame 6, the tem perature, the chemical com position of the (bipolar) electrode and the thickness of the electrolyte.

Fig . 5 a) i ll ustrates a schematic perspective top view of an electrolysis stack 2 according to the invention . The electrolysis stack 2 comprises only one cell frame 6 since the remaining ceil frames have been removed . The ceil frame 6 has a circu lar outer periphery and is provided with a central ly and sym metrical ly arranged aperture 14. The aperture 14 is defined by two circular arcs connected by two paral lel straight lines. The cell frame 6 is arranged within a cyl indrical support mem ber 12 having an inner geometry that fits the outer geometry of the cell frame 6.

Fig . 5 b) i llustrates a top view of an electrolysis stack 2 according to the invention . The electrolysis stack 2 comprises a plural ity of cel l frames 6 (only one is visible) corresponding to the one il lustrated in Fig . 5 a) .

The cell frame 6 is arranged within a cyl indrical support mem ber 12 having an inner geometry that fits the outer geometry of the ceil frame 6. During operation, gaseous 0₂ and H₂ are generated with in the central portion of the cell frame 6 by means of two electrodes (metal sheets) and a gas separating porous mem brane (these are not shown) . Hereby, the pressure is increased sign ificantly (up to 3 M Pa) . Therefore, an outwardly directed force F is created . The force F acts in all radial directions causing a need to ensure a rather large mechanical strength of the electrolysis stack 2.

A large mechan ical strength of the electrolysis stack 2 is achieved by means of the cyl indrical support member 12 enclosing the cel l frames 6 of the electrolysis stack 2. The cell frame 6 bears against the inside portion of the support member 12, and hereby the mechanical strength of the support member 12 can directly be used to prevent radial expansion of the ceil frames 6. Thus, the mechanical strength of the cell frames 6 may be reduced provided that the mechanical strength of the support member 12 is sufficiently large.

Fig. 6 a) illustrates a schematic perspective top view of an electrolysis stack 2 according to the invention. The electrolysis stack 2 comprises a plurality of cell frames 6, 6', 6" arranged within a cylindrical support member 12. Additional support members 42, 42', 42" are provided at the outside of the cylindrical support member 12.

Hereby, it is possible to enlarge the mechanical strength of the electrolysis stack 2. The additional support members 42, 42', 42" are made as separate bands configured to fit the outer periphery of the cylindrical support member 12. However, it would be possible to apply one large additional support member 42 having the same axial extension as the cylindrical support member 12. Alternatively, it is possible to apply a larger number (e.g. four or more) of additional support members 42, 42', 42".

Fig. 6 b) illustrates a schematic top view of an electrolysis stack 2 according to the invention. The electrolysis stack 2 comprises a plurality of cell frames 6 arranged within a first cylindrical support member 12 having an inner geometry that fits the outer geometry of the cell frame 6. A second and additional support member 12' is arranged at the outside of the first cylindrical support member 12. Hereby, the mechanical strength of the construction can be increased further. During operation of the electrolysis stack 2, gaseous 0₂ and H₂ are generated within the central portion of the cell frames 6. The gaseous 0₂ and H₂ can be generated through use of two electrodes (not shown) and a gas separating porous membrane (not shown). The pressure within the central portion of the cell frames 6 is increased significantly (up to 3 MPa) due to the generated gasses, and an outwardly directed force F acting in ail radial directions is created.

The first cylindrical support member 12 as well as the second additional support member 12' provide the required mechanical strength of the electrolysis stack 2. Thus, radial expansion of the cell frames 6 can be prevented.

Fig. 7 A) illustrates an end view of an electrolysis stack 2 according to an embodiment of the invention, in which the threaded rods, washers and nuts have been removed for better illustrating the remaining structures. The electrolysis stack 2 comprises an outlet 16 and an inlet 18 protruding from the flange 24 of the electrolysis stack 2. A line A going through the outlet 16 and the inlet 18 is indicated.

Fig. 7 d) illustrates a cross-sectional view of the electrolysis stack 2 shown in Fig. 7 a), wherein the cross is made along the line A shown in Fig. 7 a). The electrolysis stack 2 comprises a first flange 24 and a second flange 24^f arranged in the opposite end of the first flange 24. The electrolysis stack 2 comprises a plurality of ceil frames 6 arranged in a first cell frame module i and in a second cell frame module M₂. The electrolysis stack 2 comprises a first support member 11 and a second support member 11' arranged in axial extension of each other. The support members 11, 11' are arranged at the outside periphery of the cell frames 6.

The first support member 11 is arranged between a first plate-shaped current terminal 46 and a plate-shaped electrical power point member 48 positioned centrally in the electrolysis stack 2. Likewise, the second support member 11' is arranged between a second plate-shaped current terminal 46 and the plate-shaped electrical power point member 48. A gap 54 is provided between the second support member 11' and the second flange 24'. The gap 54 allows for compressing the cell frames 6 in axial direction e.g. during tensioning of the nuts (not shown) without damaging the support members 11, 11'. Further, the support members 11, 11' can expand in the axial direction without pressing against the flanges.

An outlet 16 and an inlet 18 are provided in the first flange 24. The electrolysis stack 2 comprises a first insulation bushing 34 arranged and configured to electrically insulate the electrolyte within the electrolysis stack 2 from the current terminal 46'.

The electrolysis stack 2 comprises a second insulation bushing 34' and a third insulation bushing 35 arranged and configured to electrically insulate the electrolyte within the electrolysis stack 2 from the electrical power point member 48.

By electrically insulating the electrolyte within the electrolysis stack 2 from the current terminals 46, 46' and the electric power point member 48, the bushings 34, 34', 35 reduce the stray currents giving rise to loss of energy in the electrolysis stack 2.

Fig. 7 b) illustrates a close-up cross-sectional view of the bushing 34' electrically insulating the electric power point member 48 from the electrolyte within the electrolysis stack 2. A perspective close-up view of the bushing 34' is shown in Fig. 7 f). In Fig. 7 f), it can be seen that the bushing 34' comprises an inner cylindrical portion 33 surrounded by an outer cylindrical portion 33' which is an integrated part of the bushing 34'. Moreover, it can be seen that the bushings 34', 35 extend between the two adjacent cell frame modules Mi, M_2, and that the bushings 34', 35 are arranged in the channels provided in the ceil frames 6 to distribute electrolyte to all the ceil frames 6 in the ceil frame modules Mi, M₂. Further, in Fig. 7 f) it can be seen that the bushing 34 is provided with an outlet 30 for gas. The outlet 30 is provided in the inner cylindrical portion 33.

Fig. 7 c) illustrates a close-up, cross-sectional view of the bushing 34 electrically insulating the current terminal 46' from the electrolyte that flows through the through-going hole 56 during use of the electrolysis stack 2. It can be seen that the bushing 34 is arranged in the channel provided in the cel l frames 6 to distribute electrolyte to all the cell frames 6 in the cei l frame module i , A perspective close-up view of the bushing 34 is shown in Fig . 7 e) in which it can be seen that the bushing 34 comprises a centrally arranged inner cyl indrical portion 33 surrounded by an outer cylindrical portion 33' which is an integrated part of the bushing 34'. Besides, the bushing 34 is provided with an outlet 30 for gas. The outlet 30 is provided in the inner cylindrical portion 33.

Fig . 8 a) i ll ustrates a top view of an electrolysis stack 2 according to an embodiment of the i nvention . The threaded rods, washers and nuts have been removed for better illustrating the remain ing structures of the electrolysis stack 2. Part of the support mem bers 11, 11 ' has been removed in order to see the structures u nderneath the support mem bers 11, 11 '.

It can be seen that the electrolysis stack 2 com prises a first flange 24 and a second flange 24' arranged in the opposite end of the first flange 24. The electrolysis stack 2 com prises a plurality of cell frames 6 arranged between the flanges 24, 24'. The electrolysis stack 2 com prises a first support mem ber 11 and a second support member 11 ' arranged in axial extension of each other. The support mem bers 11, 11 ' are arranged at the outside periphery of the cei l frames 6.

A plate-shaped electrical connection 52 protrudes from the outside surface of the support members 1 1, 11 '. The electrical connection 52 is an integrated portion of the electrical power point member 48 arranged centrally in the electrolysis stack 2.

Fig . 8 b) i llustrates a close-up, cross-sectional view of the electrical connection 52 shown in Fig . 8 a) . It can be seen that the electrical connection 52 extends through a gap provided between the support mem bers 11, 11 '. The electrical connection 52 is provided with a through-going hole 60. Further, it can be seen that the electrical connection 52 is an integrated part (the peripheral portion) of the electrical power point member 48. The electrical connection 52 can easily be accessed from outside of the electrolysis stack 2.

Fig . 8 c) illustrates a close-up, cross-sectional view of the joint structure 58 of the adjacent support members 11, 11'. It can be seen that a gap 62 is provided between at least some of the adjacent support members 11, 11'. Hereby, the cell frames can be compressed in axial direction (e.g . during tensioning of the nuts) . Further, the support member can expand in the axial direction .

List of reference numerals

2 Electrolysis stack

6, 6', 6" Cell frame

8, 8' Bore

10, 10' Bore

11, 11' Support member

12, 12' Support member

14 Aperture

16 Pipe (gas outlet)

18 Pipe (KOH inlet)

20 Electrolyser

22, 22' Nut

24, 24' Flange

26 Threaded rod

30 Outlet

32, 32' Plate member

33 Inner portion

33' Outer portion

34, 34', 34", 35 Bushing (insulation)

36 Frame

38, 38' Frame member

40, 40', 40" Connection member

42, 42', 42" Additional support member

44 Disk

46, 46' Current terminal

48, 48' Electric power point membei

50, 50', 52, 52' Electrical connection

54, 62 Gap

56 Through-going hoie

58 Joint structure

60 Hole

M_lf M₂, M₃ Cell frame module

X Longitudinal axis

F Force

Claims

1. An electrolysis stack (2) for an electrolyser (20), which electrolysis stack (2) comprises a plurality of electrolysis cells each comprising two electrodes and a gas separating membrane and a cell frame (6, 6', 6"), which cell frames (6, 6', 6") are arranged adjacent to each other, which electrolysis stack (2) comprises means (18) for supplying electrolyte feed to the interior of the electrolysis ceils and means (16) for removing oxygen gas and hydrogen gas from the electrolysis ceils, which electrolysis stack (2) comprises electric power point members (46, 46', 48, 48') constituting either a cathode, an anode or a cathode and an anode, characterised In that the electrolysis stack (2) comprises a plurality of support members (12, 12', 42, 42', 42") arranged substantially in axial extension of each other, wherein said support members (12, 12', 42, 42', 42") are arranged at the outside periphery of the cell frames (6, 6', 6"),

2. An electrolysis stack (2) according to claim 1, characterised in that the support members (12, 12', 42, 42', 42") are cylindrical and extend along the axial length of the cell frames (6, 6', 6").

3. An electrolysis stack (2) according to claim 1 or claim 2, characterised in that the cell frames (6, 6', 6") are arranged between two flanges (24, 24'), and that the flanges (24, 24') are mechanically attached to each other by means of a plurality of threaded rods (26) and nuts (22).

4. An electrolysis stack (2) according to claim 3, characterised in that the support members (12, 12', 42, 42', 42") are arranged in such a manner that they are not in mechanical contact with at least one of the flanges (24, 24').

5. An electrolysis stack (2) according to claim 4, characterised in that a gap (54) is provided between a flange (24') and the adjacent support member (11').

6. An electrolysis stack (2) according to one of the preceding claims, characterised in that a gap (62) is provided between at least some of the adjacent support members (11, 11', 12).

7. An electrolysis stack (2) according to claim 5 or claim 6, characterised in that a metal structure (46, 46', 48) is provided under the gap (54, 62).

8. An electrolysis stack (2) according to one of the preceding claims, characterised in that the elastic modulus of the support member (12, 12', 42, 42', 42") is larger than the elastic modulus of the ceil frames (6, 6', 6").

9. An electrolysis stack (2) according to one of the preceding claims, characterised in that the coefficient of thermal expansion of the support member (12, 12', 42, 42', 42") is smaller than the coefficient of thermal expansion of the cell frames (6, 6', 6").

10. An electrolysis stack (2) according to one of the preceding claims, characterised in that the support member (12, 12', 42, 42', 42") is made in an electrically insulating material e.g. a fibre reinforced plastic material . 11. An electrolysis stack (2) according to one of the preceding claims, characterised in that the electrolysis stack (2) comprises a first support member (12) and at least one additional support member (12', 42, 42', 42") arranged at the outside of the first support member (12). 12. An electrolysis stack (2) according to one of the preceding claims, characterised in that an electric connection (52, 52') is provided between adjacent support members (11, 11', 12), wherein at least the distal portion of the electric connections (52, 52') protrudes from the support members (11,

11',

12).

13. An electrolysis stack (2) according to one of the preceding claims, characterised in that an electric connection (50, 50^f, 52, 52') is provided at the outermost axial end of each of the outermost support members (11, 11', 12).

14. An electrolysis stack (2) according to one of the preceding claims, characterised in that the electric connections (50, 50', 52, 52') extend as an extension of the electric power point members (46, 46', 48, 48').

15. An electrolyser (20) comprising an electrolysis stack (2) according to one of the preceding claims.