DK178317B1

DK178317B1 - Electrolyser Stack Divided into Sub-stacks

Info

Publication number: DK178317B1
Application number: DK201400506A
Authority: DK
Inventors: Jørgen Krogsgaard Jensen; Anders Rønne Rasmussen
Original assignee: Greenhydrogen Dk Aps
Priority date: 2014-09-05
Filing date: 2014-09-05
Publication date: 2015-11-30
Also published as: WO2016034185A1

Abstract

An electrolysis stack (2) for an electralyser (20) is disclosed. The electrolysis stack (2) comprises a plurality of electrolysis cells each comprising two electrades and a (porous) gas separating membrane and a cell frame (6, 6', 6"). 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 cells. The electrolysis stack (2) comprises electric power point members ( 46, 46', 48, 48') constituting either a cathode, an anode or a cathode and an anode. The electrolysis stack (2) is divided into a plurality of electrically separated cell frame module (M1, M2, M3).

Description

Electrolyser Stack Divided into Sub-stacks Field of invention

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

Prior art

The need for storing electric energy generated from solar panels or wind turbines is increasing due to the need of greener energy sources. Storing the electric energy in hydrogen by using electrolysers to convert water to hydrogen and oxygen has been known for decades.

An electrolyser is a device that splits water (H20) into hydrogen (H2) and oxygen (02) by means of electrical energy. An electrolyser comprises a number of modules including one or more electrolyser modules, a water supply module for supplying purified water and a power supply modules for supplying direct current to the electrolysis process.

The electrolyser modules consist of an electrolysis stack as well as a degassing system (chambers), a gas purification system and a pressure control system. The electrolysis stack comprises a series of stacked electrolysis cells comprising electrodes (e.g. bipolar electrodes) and one gas separating porous membrane. The stacked electrolysis cells are typically mounted in a ring-shaped polymer cell frame having a channel that supplies electrolyte to the cell compartment and a channel that evacuates the gas generated.

The channels may be connected to manifolds that either distribute electrolyte to all cells in a stack or collect oxygen or hydrogen from all cells in a stack.

An electrolyser generates a specific mass of hydrogen from a given amount of electrical energy. Calculation of the efficiency of an electrolyser is based on the higher heating value of hydrogen which is 141.80 MJ/kg. The electrolyser efficiency is given as the ratio of the mass of hydrogen multiplied by the higher heating value to the amount of electrical energy. Several mechanisms influence the efficiency of an electrolyser. The efficiency can never exceed 100% and for practical reasons it will always be below 100%.

The electrochemical hydrogen and oxygen generation over-potentials, the ohmic losses (IR losses) in all components carrying electrical current or ionic current, electrical energy used for the auxiliary components (e.g. electrically controlled valves, control electronics, compressor in water supply module) and loss of energy in the power supply influence the efficiency of an electrolyser.

A phenomenon called stray currents may also give rise to loss of energy in an electrolysis stack. The above mentioned supply and evacuation channels together with the manifolds form alternative current pathways for ionic currents between the cells in a stack. These currents are called stray currents.

All of the above mentioned losses of energy cause heating of the electrolyser. The generated heat has to be removed from the electrolyser in order to avoid increased temperatures, which may damage the electrolyser. Furthermore, in most cases the heat generated is purely waste, therefore in order to make the most cost-effective use of the supplied electrical energy the electrolyser must have the highest possible efficiency.

The typical way of limiting energy loss due to stray currents, is by carefully choosing the dimensions of supply and evacuation channels and manifolds. The resistance to ionic currents is inversely related to the cross-section and directly related to the length of the channel. Accordingly, channels and pipe members (e.g. of a manifold) with smaller geometrical cross-section and longer length have higher resistance to ionic currents.

The American patent application US2881123A describes a stack design having optimised channel and manifold dimensions with the purpose of reducing the energy loss due to stray currents. The problem associated with application of this strategy is that channels and manifolds having too small cross-sections may be critical to the circulation of electrolyte and gas in the stack. A reduced circulation of electrolyte and gas in the stack may cause a malfunction of the electrolysis stack and the electrolyser.

The American patent application US20100012503 A1 discloses an electrolyser module comprising a plurality of structural plates each having a sidewall extending between opposite end faces with a half cell chamber opening and at least two degassing chamber openings extending through the structural plate between the opposite end faces. The structural plates are arranged in face to face juxtaposition between opposite end plates. Each half cell chamber opening at least partially houses electrolytic half cell components comprising at least an electrode, a bipolar plate in electrical communication with the electrode and a membrane. The structural plates and half cell components define an array of series connected electrolytic cells surmounted by at least first and second degassing chambers having an upper section above a lower section. The structural plates define, at least when in face to face juxtaposition, respective gas-liquid passages extending between a top part of the half cell chambers and a bottom part of the upper section of the first and second degassing chambers to provide fluid communication between an anode part of the electrolytic cells and the first degassing chamber and between a cathode part of said electrolytic cells and said second degassing chamber. The structural plates further define, at least when in face to face juxtaposition, respective degassed liquid passages extending between a bottom part of the lower section of the first and second degassing chambers and a bottom part of the half cell chambers for degassed liquid return from the first and second degassing chambers respectively to the anode and cathode parts of the electrolytic cells. The electrolyser module further comprises respective gas discharge and feed water passages extending therethrough and fluidly communicating with the degassing chambers for gas discharge from the degassing chambers and for feed water introduction into the degassing chambers.

Thus, there is a need for an improved electrolysis stack in which the energy losses including the stray currents can be reduced.

Accordingly, it is an object of the present invention to provide an electrolysis stack that reduces the energy losses including the stray currents can be reduced.

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 9. Preferred embodiments are defined in the dependent sub claims and 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 each comprising two electrodes and a gas separating membrane and a cell frame, 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 cells, which electrolysis stack comprises electric power point members constituting either a cathode, an anode or a cathode and an anode, wherein the electrolysis stack is divided into a plurality of electrically separated cell frame modules, wherein each of the electrically separated cell 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, the electrical potential between the first and last cells in each of the cell frame module is reduced. Accordingly, it is possible to provide an electrolysis stack that reduces the energy losses including the stray currents.

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

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

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 frames has a circular outer periphery. Hereby it is possible to provide a strong and reliable electrolysis stack.

The cell frames are arranged adjacent to each other and may be an advantage that the cell frames are sealed with O-ring 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. These through-bores may, together with other structures, 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 electric power point members 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 electrolysis stack may be divided into a plurality of electrically separated cell frame module 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 an advantage that the electric power point members electrically separating the cell frame modules are basically plate-shaped and comprises an electrically insulating material.

It may be beneficial that the electrolysis stack is divided into a three or more electrically separated cell frame module.

It may be advantageous that each of the electrically separated cell frame module 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 each 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 is an advantage that each of the electrically separated cell 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 cell frames to distribute electrolyte to all the cells frames in the cell frame module. Preferably the bushings extend between two adjacent cell frame modules.

It may be an advantage that at least one support member arranged at the outside periphery of the cell frames.

Hereby it is possible to provide an electrolysis stack that is capable of being operated at elevated pressure, where thickness of the cell frame can be reduced. The support member reduces deformation in the circumferential direction of the cell frames.

It may be beneficial that the support member is cylindrical and extends along the axial length of the cell frame.

Hereby it is possible to provide a support member having the required mechanical properties.

Moreover, a cylindrical support member will be fit to enclose cell 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 that is 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 member is arranged in such a manner that it is not in mechanical contact with the flanges. Hereby it is achieved that the support member can expand in the axial direction.

It is preferred that the cell 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 extend 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, polyphenylsulfone (PPSU) or polyether ether ketone (PEEK).

It may be beneficial that the elastic modulus of the support member is significantly larger than the elastic modulus of the cell frames.

Hereby the support member is configured to keep its geometrical shape and 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 insulation 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 mutual end-to-end contact and substantially in axial extension of each other.

Hereby it is possible to provide an electrolysis stack provided with modular support members. It is thus possible to build a long electrolysis stack and apply the same support member that is 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 is configured to resist the pressure within the cell stacks.

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 cell frames are made in a material that is suitable for handling high pH values (pH values above 14)

The support member may be mechanically attached outside the cell frames.

It is possible to apply a metal (steel) support structure provided with an inner isolation structure.

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 member is made in an electrically insulation material e.g. a fibre reinforced plastic material.

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

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

The support member may be mechanically attached outside the cell frames.

Description of the Drawings

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

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 cells. 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 cell frames are sealed with O-ring gaskets of a resilient material (e.g. EPDM rubber).

Each cell frame 6 comprises four axially 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 of 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 cylindrical 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 the top of each other within the cylindrical support member 12.

The cell frames 6, 6', 6" may be manufactured in polymer material, e.g. polyphenylsulfone (PPSU) or polyether ether ketone (PEEK). Once the cell frames 6, 6', 6" are brought into mechanical contact with the support member 12, the support member 12 (a cylindrical tube) will significantly reduce further deformation in the circumferential direction of the cell 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 corresponding to 30 bar) without critical deformation of the cell frames 6, 6', 6". It can be seen that the support member 12 is slightly longer (in the axial direction) than the cell frames 6, 6', 6". Hereby it is possible to support the cell frames when the cell frames extend axially.

Fig. 2 illustrates a schematic perspective top view of an electrolyser 20 according to the invention. The electrolyser 20 comprises a frame 36 having a lower frame member 38 and an upper frame member 38' interconnected by a 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 electrolyser 20 comprises two electrolysis stacks 2, 2' mounted in the lower portion of the electrolyser 20. Each of the electrolysis stacks 2, 2' comprise 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 equally constructed and extend parallel with 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. 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 treaded 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 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-sectional 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 periphery of a plurality of cell frames 6. The electrolysis stack 2 comprises three cylindrical support members 11, 11', 12 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. Channel 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 cell 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 Mi, M2, M3. Accordingly, the total number of 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 current 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 high concentration of oxygen and hydrogen gasses). The bushings 34, 34', 34" may be made in polyphenylsulfone (PPSU) or polyether ether ketone (PEEK) by way of example.

The electrolysis stack 2 is equipped with a gas outlet channels 16 (oxygen or hydrogen gasses) and a media inlets 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 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 possibly 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 the 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 its 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 whit a modular concept in mind. The electrolysis stack 2 a number of cell frame modules Mi, M2, M3 providing a total number of cell frames of e.g. 50, 75 or 100 cells frames 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 lager configurations of e.g. 50, 75, 100 or 200 cell frames 6 by putting together a number of cell frame modules Mi, M2, M3.

When put together the cell frame modules Mi, M2, M3 are separated from one another.

The cell frame modules Mi, M2, M3 each comprise 25 cells frames. Each cell frame 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 cells frames 6 are combined into an electrolysis stack 2, three cell frame modules Mi, M2, M3 are at the end of each other. The cell frame modules Mi, M2, M3 are connected to fittings in the flanges 24, 24'.

Accordingly, a 75 cell frame electrolysis stack 2 is build 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 be the oxygen producing part of the stack and the remaining 75 chambers are connected to be the hydrogen producing part.

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 form two vessels: one carrying H2 and one carrying 02.

When direct current is applied to the first and the last cell of a cell frame module Mi, M2, M3, it causes current to flow through each cell frame 6 in the cell frame module Mi, M2, M3, dividing the potential over each cell frame in the cell frame module Mi, M2, M3. The potential of each cell frame 6 is determined by the current passing through the each cell frame 6, the temperature, the chemical composition of the (bipolar) electrode and the thickness of the electrolyte. When producing hydrogen and oxygen, there will be a gas fraction corresponding to approximately 10% of the volume in the electrolysis stack 2.

Fig. 5 a) illustrates 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 cell frames have been removed. The cell frame 6 has a circular outer periphery and is provided with a centrally and symmetrically arranged aperture 14. The aperture 14 is defined by two circular arcs connected by two parallel straight lines.

The cell frame 6 is arranged within a cylindrical support member 12 having an inner geometry that fits the outer geometry of the cell frame 6.

Fig. 5 b) illustrates a top view of an electrolysis stack 2 according to the invention. The electrolysis stack 2 comprises a plurality of cell frames 6 (only one is visible) corresponding to the one illustrated in Fig. 5 a).

The cell frame 6 is arranged within a cylindrical support member 12 having an inner geometry that fits the outer geometry of the cell frame 6. During operation gaseous 02 and H2 is generated within the central portion of the cell frame 6 by means of two electrodes (metal sheets) and a gas separating porous membrane (these are not shown). Hereby the pressure is increased significantly (up to 3 MPa). Therefore, an outwardly directed force F is created. The force F acts in all radial directions causes the need for ensuring a rather large mechanical strength of the electrolysis stack 2.

A large mechanical strength of the electrolysis stack 2 is achieved by means of the cylindrical support member 12 enclosing the cell 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 radially expansion of the cell 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 is 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 all radial directions is created.

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

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 32, 32' Plate member 34, 34', 34" 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 member 50, 50', 52, 52' Electrical connection

Mi, M2, M3 Cell frame module X Longitudinal axis F Force

Claims

1. An electrolysis cell stack (2) to an electrolysis plant (20), said electrolysis cell stack (2) comprises a plurality of electrolytic cells, each comprising two electrodes, a gassepareringsmembran and a cell frame (6, 6 ', 6 "), wherein the cell frames (6 , 6 ', 6 ") are arranged next to one another, the electrolysis cell stack (2) comprises means (18) for supplying electrolyte to the interior of the electrolytic cells and the means (16) for the disposal of oxygen gas and hydrogen gas from the electrolysis cells, said electrolyser stack ( 2) comprises electric current elements (46, 46 ', 48, 48') constituting either a cathode, an anode or a cathode and an anode, characterized in that the electrolysis stack (2) is divided into a plurality of electrically distinct cell framework modules (Mi, M2 , M3), and that each of the electrically distinct cell framework modules (Mi, M2, M3) comprises bushings (34, 34 ', 34 ") adapted to electrically isolate the electrolyte in the cell stack from the power terminals (46, 46') and / or the electric current elements (48, 48 ') disposed between adjacent cell frame modules (Mi, M2, M3) using the electrolysis stack (2).

2. An electrolysis cell stack (2) according to claim 1, characterized in that the electrolysis stack is divided into a plurality of electrically distinct cell framework modules (Mi, M2, M3) by means of electric current elements (48, 48 ') which extends along the cell frames (6, 6 ', 6 ").

3. An electrolysis cell stack (2) of claim 1 or claim 2, characterized in that the electrolysis stack is divided into three or more electrically distinct cell framework modules (Mi, M2, M3).

4. An electrolysis cell stack (2) according to one of the preceding claims, characterized in that each of the electrically distinct cell framework modules (Mi, M2, M3) comprises 10-40, preferably 15-35, such as 20-35 cell borders (6, 6 ', 6 ").

5. An electrolysis cell stack (2) according to claim 4, characterized in that each of the electrically distinct cell framework modules (Mi, M2, M3) comprises 25 cell frames (6, 6 ', 6 ").

6. An electrolysis cell stack (2) according to any one of claims 4-5, characterized in that each of the electrically distinct cell framework modules (Mi, M2, M3) comprises the same number of cell borders (6, 6 ', 6 ").

7. An electrolysis cell stack (2) according to one of the preceding claims, characterized in that each of the electrically distinct cell framework modules (Mi, M2, M3) being electrically separated from each other by power supply terminals (46, 46 ') and / or electric power elements (48, 48 ') disposed between adjacent cell frame modules (Mi, M2, M3).

8. An electrolysis cell stack (2) according to one of the preceding claims, characterized in that at least one reinforcing element (12, 12 ', 42, 42', 42 ') is arranged on the outside of the cell frames (6, 6', 6 ").

9. An electrolysis plant (20) comprising an electrolysis stack (2) according to any one of claims 1-8.