Electrolyser frame concept, method and use

Abstract

The present invention comprises a module for an electrolyzer of filterpress type comprising at least one closed frame defining at least one first opening, wherein said module comprises a sealing and electric insulating material, wherein said material at least partly covers the surface of the frame. In addition the present invention comprises a method for producing a module for an electrolyzer of filterpress type and use thereof.

Claims

1. A module for an electrolyser of filterpress type comprising at least one closed frame defining at least one first opening, wherein the module comprises a sealing and electric insulating material, where said material at least partly covers a surface of the at least one closed frame, wherein at least one first element is placed around the at least one closed frame by a sealing and electric insulating material such that the at least one element is free from mechanical connection to the at least one closed frame, wherein the at least one first element is selected from at least one of the following: a diaphragm, a bi-polar plate, pressure element, and electrodes.

2. The module according to claim 1, wherein the material provides sealing against a possible adjacent module or an end section of said electrolyser.

3. The module according to claim 1, wherein the frame comprises at least one of the following: metal, structured plastic, reinforced plastic, thermoset plastic.

4. The module according claim 1, wherein the module comprises at least one positioning means.

5. The module according to claim 1, wherein the module comprises at least one supply channel.

6. The module according to claim 5, wherein the at least one supply channel is covered with a sealing and electric insulating material.

7. The module according to claim 5, wherein the at least one supply channel is connected with at least one first opening by at least one separate transfer channel.

8. The module according to claim 7, comprising at least two separate collecting channels that are connected with at least one first opening by at least two separate transfer channels and the at least two separate transfer channels are each connected to each side of said at least one first opening.

9. The module according to claim 1, wherein the module further comprises at least two separate collecting channels.

10. The module according to claim 9, wherein the at least two separate collecting channels are covered with a sealing and electric insulating material.

11. The module according to claim 9, wherein the at least two separate collecting channels are connected with at least one first opening by at least one separate transfer channel.

12. The module according to claim 1, wherein the at least one first opening is completely or partly covered by the at least one first element.

13. The module according to claim 1, wherein the module comprises a load carrying part of the electrolyser.

14. The module according to claim 1, wherein said pressure element is a fluid-permeable and resilient pressure element.

15. The module according to claim 14, wherein said pressure element possess an inherent conductivity.

16. The module according to claim 14, wherein said pressure element tolerates current density from 0 to 5 A/cm.

17. The module according to claim 14, wherein said pressure element tolerates a compression pressure in at least one of the following ranges: 0.001 to 100 bar, 0.01 to 50 bar, 0.1 to 1.0 bar.

18. The module according to claim 14, wherein said pressure element is fluid permeable in at least two dimensions.

19. The module according to claim 14, wherein said pressure element is resistant to corrosion.

20. The module according to claim 14, wherein said pressure element comprises at least one of the following components: stretched material, perforated foil, mesh or felt fibre mat.

21. A method for producing a module for an electrolyser of filterpress type comprising at least one closed frame defining at least one first opening, the method comprising: placing at least one first element around the at least one closed frame by a sealing and electric insulating material, wherein the at least one first element is selected from at least one of the following: a diaphragm, a bi-polar plate, pressure element, and electrodes; and at least partly covering the surface of said frame with the sealing and electric insulating material such that the at least one element is free from mechanical connection to the at least one closed frame.

22. The method according to claim 21, further comprising providing sealing with said material against a possible adjacent module or an end section of said electrolyser.

Description

SUMMARY OF THE DRAWINGS

(1) FIG. 1 illustrates an expanded view of electrolyser cell according to the prior art. The bolting is not shown in FIG. 1;

(2) FIG. 2 illustrates a detailed view of electrolyser cell according to prior art. The bolting is not shown in FIG. 2;

(3) FIG. 3 illustrates a frame according to the present invention. Each side of the rubber frame shown in the drawings 3a and 3b can function as a cathode or an anode space.

(4) FIG. 4 illustrates compression curves for pressure element according to example 1 of the present application

(5) FIG. 5 illustrates a test of compression and reversibility according to example 2 of the present application.

(6) FIG. 6 illustrates one embodiments of the present pressure element.

(7) FIG. 1 illustrates an expanded view of a prior art electrolyser cell. Electrolysers of filter press type are commonly used for the production of hydrogen and oxygen from brines and lyes, usually aqueous alkali hydroxide solutions. Cell stacks in such configurations are formed by cells which commonly consist of bipolar plates, electrodes (anode and cathode), a steel frame with a diaphragm placed between two bipolar plates, separating anode and cathode compartment and gasket(s) for sealing purposes.

(8) These steel frames can be covered by vulcanizable material, i.e., rubber. This rubber serves as electrical insulation and as sealing material. Patent EP0833963B1 describes a configuration whereby the rubber frames have an integrated fastening means for bolting the diaphragm to the frame. Furthermore, T-shaped elements forming lye channels are bolted to the frame and are also covered by vulcanizable material and thus form an integral part of the frame, see FIG. 2. The bolting and fastening of the mentioned components are not shown in FIG. 1 or 2.

DETAILED DESCRIPTION

(9) The present invention comprises a module consisting of a at least one frame as mentioned above which is partly covered with a sealing and electric insulating material and said frame and material constitutes the load carrying part of the electrolyser. The module of the present invention is universal in the meaning it can be used with oxygen or hydrogen producing electrodes on either of the sides. Furthermore it can be stacked manually, semi automatic or automatic.

(10) The insulation of the bipolar plates from the outside is obtained by stacking as the bipolar plate becomes completely retained within the said module and isolated from the outside.

(11) The O-ring effect is obtained by stacking said modules and operating the electrolyser at elevated pressures. O-ring effect contributes to the minimization of the risk of leakages.

(12) In one aspect of the present invention a one step process for manufacturing modules comprises at least one closed frame and at least one first element such as e.g., diaphragm, bipolar plate, pressure element and/or electrodes where the one step process should be understood as moulding the first element and the frame together utilizing a vulcanizable material thereby simultaneously placing the at least one first element around the at least one frame, insulating the frame and providing sealing. The gaskets can be regarded as built into the module according to the present invention. It should be noted that at least one first element can be fully integrated in the present module.

(13) In one aspect of the present invention a one step process for manufacturing modules comprises at least one closed frame and at least one first element such as e.g., diaphragm, bipolar plate, pressure element and/or electrodes, where the one step process should be understood as comprising a pre-moulded sealing of electric insulating material which is placed around/threaded around the first element and the frame thereby simultaneously fixing the constituents, the at least one frame and the at least one element, insulating the frame and providing sealing. The gaskets can be seen as built into the module according to the present invention. It should be noted that at least one first element can be fully integrated in the present module.

(14) Accordingly no bolting, no fastening, no gluing, no welding of the first element to the frame is required concerning the present invention.

(15) A further aspect of the invention is the compact design due to the reduced number and size of constituent parts that need to be stacked. The present design of the invention can be seen as a compact design which is well suited for zero gap design, where electrodes are in intimate contact with a diaphragm.

(16) The bipolar plates can have a smaller diameter than at least one first opening. The bipolar plates can have a smaller diameter than the outer diameter of the module.

(17) The diameter of the module is variable and can be produced in the required size: e.g., diameter from 0.10 m to 5.00 m. Some ranges of the required size given in meters of the mentioned diameter is as follows: 0.1-0.5; 0.5-1; 1-1.5; 1.5-2; 2-2.5; 2.5-3; 3-3.5; 3.5-4; 4-4.5; 4.5-5.

(18) The present invention will be described in detail with reference to the enclosed FIG. 3. The present module comprises a first opening being completely or partly covered by at least one first element e.g., a diaphragm, and at least one closed frame e.g., steel frame being at least partly covered by vulcanizable or other mouldable material characterised by its electrical insulation and mechanical sealing properties. The diaphragm is fastened by vulcanizable material being cast onto the edges of diaphragm and onto the steel frame and not by a separate mechanical device or by bolting to the frame, see FIG. 3. The supply- and collecting channels forming the lye and gas ducts are made of a vulcanizable/mouldable material. The present module including e.g., the diaphragm element is made in a one manufacturing step whereby moulding or threading the vulcanisable material around the steel frame, simultaneously fastening e.g., the diaphragm and forming the at least one supply channel, the at least two collecting channels and the transfer channels. Geometrical, the supply- and collecting channels can be either fully symmetric or alternatively asymmetric. The transfer channels connecting the first opening with the supply and the collecting channels can be made in two ways:

(19) 1) Moulded as profiles of sealing and electric insulating material such as inter alia rubber profile so that channels are formed by intimate contact of rubber with bipolar plate.

(20) 2) Transfer channels penetrating the sealing and electric insulating material such as inter alia rubber and formed either in the moulding process or by post-moulding.

(21) There is optionally a positioning means such as a groove around the inner edge of the module to accommodate the bipolar plate. The frame is completely isolated from the electrolyte and gases, thus no high quality steel is needed for pressurised components and the secondary electrolysis is suppressed. The frame which is at least partly covered by a sealing and electric insulating material e.g., rubber is the load carrying element. The diaphragm can be cast into the module. The cell stack is made of in sequence rubber frame module with diaphragm, first electrode, first pressure element, bipolar plate, second pressure element, second electrode, rubber frame module with diaphragm. The bi-polar plates can be cast into the module. The cellstack module is made of in sequence rubber frame module with bipolar plate, first pressure element, first electrode, diaphragm, second electrode, second pressure element and rubber frame module with bipolar plate. The electrode can be cast into the module. The cell stack is made of in sequence rubber frame module with first electrode, diaphragm, rubber frame module with second electrode, first pressure element, bipolar plate, second pressure element. The pressure element can be cast into the module. The cell stack is made of in sequence rubber frame module with first pressure element, first electrode, diaphragm, second electrode, rubber frame module with second pressure element, bipolar plate. The pressure bearing element with collecting channels can be the vulcanised rubber covered steel frame without diaphragm or bipolar plate: The cell is made of in sequence bipolar plate, rubber frame module, first pressure element, first electrode, diaphragm, second electrode, second pressure element and second rubber frame module.

(22) According to the present invention a cell stack module comprising a number of cell constituent parts such as electrodes, placed between endplates is possible. The end plates are fastened with tie rods. The fastening of the endplates of the electrolysers must not be mixed with the bolting mentioned in prior art. In addition, no spring system is needed in the present invention to assure tightness of the present modules constituting the electrolyzer. The system can be operated under pressure as it is a self-sealing system. When the modules are made of elastic material, the rubber frame module stacked is self-sealing under pressurized conditions (O-ring effect). The stack does not need to be tightened/compressed with a force corresponding to the force of the internal pressure. The rubber modules are provided with an area for placing batch number. From the perspective of operating an electrolyser stack made of such modules, the modules do not need to be covered completely by vulcanizable material on the outside. This allows a fixation of the frame during the high injection pressures of the moulding process. While the moulding-in of the frame, e.g., steel frame, eliminates the post-moulding shrinkage of the rubber modules, the modules can also be made by a steel frame and a separate pre-moulded rubber module which can be threaded over the steel frame after being moulded. Optionally all contacting surfaces are equipped with ridges to secure complete tightness between the components and channels.

(23) The present invention provides one embodiment comprising a fully-integrated diaphragm element based on steel frame with rubber surface and moulded-in diaphragm and lye/gas channels formed by the rubber.

(24) FIG. 3 shows a module consisting of a diaphragm and a frame covered completely by vulcanizable or other mouldable material characterised by its electrical insulation and mechanical sealing properties. The diaphragm is fastened by vulcanizable material being cast into the diaphragm and steel frame and not by a separate mechanical device or by bolting to the frame

(25) The frame may have a smooth surface or it may be provided with grooves or similar to enhance the adhesion force of the rubber to the frame.

(26) In one embodiment of the present invention the collecting channels within the circular module are functioning as gas flow ducts which do not comprise an inner metal element but are fully formed of the mouldable material.

(27) In one embodiment of the present invention a pressure element in the form of a metal mesh of well-defined geometry is described to have following functions: reducing ohmic resistance by keeping the electrode in intimate contact with the diaphragm, conducting electrical current from bipolar plate to electrode and permitting gas to escape from the electrode surface.

(28) The pressure element of the present invention is resilient, by resilient it should be understood, that the mechanical and geometrical properties of the said pressure element, e.g., a metal mesh, are balanced with regard to flexibility and stiffness in order to press the electrode to the diaphragm at all operational temperatures and not deform during cell assembly. The metal mesh has sufficient mesh opening to allow for non-hindered passing of fluid in both horizontal and vertical directions while maintaining the mechanical function.

(29) In one embodiment of the pressure element the pressure element is in the corrugated form. The wording corrugated form should be understood as any wave form such as i.a. sinus wave or square wave. FIG. 6 shows a sinus wave.

(30) In one embodiment the mesh or felt fibre mat can be described by the following properties:

(31) Wire thickness is function of mesh opening and is defined by this function:

(32) $\sqrt[3]{2*\mathrm{opening}\left(\mathrm{mm}\right)}*A=\mathrm{wire}\mathrm{thickness}\left(\mathrm{mm}\right),$
with parameter A being chosen from one of the following ranges: 0.01-10, 0.1-1, 0.1-0.3. A is a parameter which relates mesh opening to the wire thickness, without limitation to only 1 wire dimension for any given opening. The values of parameter A originate from the experimental data and allow the person skilled in the art to reproduce the results. Outside of the given ranges, the element will not have sufficient mechanical strength. Height of the meshheight is a function of maximum production capacity of the electrolyser. Angle of the wave walls (limited by desired mechanical strength: sharp=stiff+deforming, dull=too weak+flattening): 10-120, preferably 20-100, most preferably 30-50. Distance between the waves maxima: given by angle and height. Diameter of circle at top of the wave: given by angle and height.

(33) The present pressure element comprises a combination of mechanical strength, current conductivity, chemical resistance and minimum gas diffusion resistance due to the different optimized geometries as described in more detail in the following. The pressure element is supplied in one piece, which can be manually or automatically inserted between a bipolar plate and an electrode in an electrolysis cell thus simplifying the stacking. When a pressure element according to the present invention is inserted on each side of a bipolar plate, conduction of current is ensured between the bipolar plate and the electrodes, without compromising the mechanical integrity of said bipolar plate. In the present invention, large numbers of points of electrical contact are established leading to uniform current distribution by pressing the pressure element to the electrode surface. The obtained optimized wave function of the present pressure element provides required spring force to keep electrode in intimate contact with a diaphragm regardless of distance variation due to temperature/pressure variation, thus maintaining the zero gap and low ohmic resistance. Further, free transport of the produced gas in both vertical and horizontal direction, thus ensuring an efficient removal of gas from inner electrode-bipolar plate area is achieved according to the present invention.

(34) In an electrolyser of filter-press design, the compression force (force needed to compress the cell stack) is the sum of the force required to seal the stack and the force needed to compress the pressure elements. The compression force is decisive for the design of the end lids of the electrolyser. In case of pressurized systems the design of the end lid would need to take into account the operation pressure.

(35) The compression of the pressure elements, however, acts in concert with the internal pressure and if the compression force of the pressure elements becomes substantial, this will have direct impact on the design of lids and tie rods of an electrolyser. According to the present invention a pressure element comprising specific features and properties has been invented. The present pressure element tolerates a compression pressure in the range 0.001 to 100 bar. In one embodiment the present pressure element withstands a maximum compression pressure of roughly 1 bar, and the typical pressure exerted by the pressure elements is in the range of 0.2-0.5 bar, which constitute about 1-2% of the design pressure of an electrolyser. The impact of the present pressure elements on the design of the end lids of the electrolyser is thus insignificant. Even used under atmospheric conditions, the current pressure elements would have minor impact on the lid design.

(36) In one embodiment of the present invention the different parts can be stacked as follows:

(37) a closed frame defining at least one first opening in which one first element is chosen as a diaphragm, in which said frame is partly covered with a sealing and electric insulating material;

(38) a first electrode;

(39) a first pressure element;

(40) a bipolar plate;

(41) a second pressure element;

(42) a second electrode;

(43) a closed frame defining at least one first opening in which one first element is chosen as a diaphragm, in which said frame is partly covered with a sealing and electric insulating material.

(44) In one embodiment of the present invention the different parts can be stacked as follows:

(45) a closed frame defining at least one first opening in which one first element is chosen as a bipolar plate, in which said frame is partly covered with a sealing and electric insulating material;

(46) a first pressure element;

(47) a first electrode;

(48) a diaphragm;

(49) a second electrode;

(50) a second pressure element;

(51) a closed frame defining at least one first opening in which one first element is chosen as a bipolar plate, in which said frame is partly covered with a sealing and electric insulating material.

(52) In one embodiment of the present invention the different parts can be stacked as follows:

(53) a diaphragm;

(54) a closed frame defining at least one first opening, in which said frame is partly covered with a sealing and electric insulating material;

(55) a first electrode;

(56) a first pressure element;

(57) a bipolar plate,

(58) a second pressure element;

(59) a second electrode;

(60) a closed frame defining at least one first opening, in which said frame is partly covered with a sealing and electric insulating material;

(61) a diaphragm.

(62) In one embodiment of the present invention the different parts can be stacked as follows:

(63) a closed frame defining at least one first opening in which one first element is chosen as a pressure element, in which said frame is partly covered with a sealing and electric insulating material;

(64) a first electrode;

(65) a diaphragm

(66) a second electrode;

(67) a closed frame defining at least one first opening in which one first element is chosen as a pressure element, in which said frame is partly covered with a sealing and electric insulating material;

(68) a bipolar plate.

(69) In one embodiment of the present invention the different parts can be stacked as follows:

(70) a first pressure element;

(71) a closed frame defining at least one first opening in which one first element is chosen as a first electrode, in which said frame is partly covered with a sealing and electric insulating material;

(72) a diaphragm;

(73) a closed frame defining at least one first opening in which one first element is chosen as a second electrode, in which said frame is partly covered with a sealing and electric insulating material;

(74) a second pressure element;

(75) a bipolar plate;

(76) Having described preferred embodiments of the invention it will be apparent to those skilled in the art that other embodiments incorporating the concepts may be used. These and other examples of the invention illustrated above are intended by way of example only and the actual scope of the invention is to be determined from the following claims.

Examples

Example 1

Compressibility Testing

(77) The compressibility was measured on an area of 427 cm.sup.2, first on a sample cut to size, and subsequently on the same area in the middle of the element, two parallels. The results of the compression tests are shown in FIG. 4. It is readily seen from FIG. 4 that the element behaves sinusoidically up to a compression of about 0.6 mm, where after it behaves trapezoidically. The results from the sample cut to size and those from the uncut sample are very similar, and demonstrate that reliable measurements can be made on small samples cut to size as well as on areas on uncut elements.

(78) The sample cut to size was compressed to 1 mm and became permanently deformed. The two parallels on the uncut sample also decompressed as shown in FIG. 5. The first sample was compressed about 0.7 mm and the second about 0.8 mm. As readily seen from FIG. 5, the upper flat part of the curve was completely reversible, even up to 0.8 mm compression. This means that the compression element, behaves like a constant pressure element after compression in the cell stack. For the electrical contacts that the pressure element is designed to maintain, this is the perfect situation. Variations in temperature and compression will have only very minor effects on the pressure on the cell stack components and the electrical contacts will be stable.