Electrolysis unit and method for operating the electrolysis unit

Abstract

An electrolysis unit and to a method for electrochemically decomposing water into hydrogen and oxygen. The electrolysis unit has at least two electrolysis modules. The electrolysis unit also has exactly one first gas separation device for a first product gas including oxygen and exactly one second gas separation device for a second product gas including hydrogen. The first gas separation device is connected to the at least two electrolysis modules by respective first lines. The second gas separation device is connected to the at least two electrolysis modules by respective second lines. The at least two first lines have the same first length. The at least two second lines likewise have the same second length.

Claims

1. An electrolysis unit for the electrochemical dissociation of water (H2O) into hydrogen (H2) and oxygen (O2), comprising: at least two electrolysis modules; exactly one first gas separation device for a first product gas comprising oxygen, exactly one second gas separation device for a second product gas comprising hydrogen, wherein the first gas separation device is connected to each of the at least two electrolysis modules by means of a first conduit in each case and the second gas separation device is connected to each of the electrolysis modules by means of a second conduit in each case and the at least two first conduits have the same first length and the at least two second conduits have the same second length.

2. The electrolysis unit as claimed in claim 1, wherein an electrolysis module of the at least two electrolysis modules comprises at least two electrolysis cells and each electrolysis cell comprises an anode space having an anode and a cathode space having a cathode and the anode space is separated from the cathode space by means of a proton exchange membrane and the anode space is suitable for taking up water (H2O) and oxidizing it at the anode to give a first product comprising oxygen (O2) and the cathode space is suitable for taking up water (H2O) and reducing it at the cathode to give a second product comprising hydrogen (H2).

3. The electrolysis unit as claimed in claim 2, wherein the cathode space is connected to the second gas separation device and the anode space is connected to the first gas separation device.

4. The electrolysis unit as claimed in claim 1, wherein the first gas separation device and the second gas separation device are arranged inside one another, with the first or the second gas separation device being configured as an outer shell and a bottom and the other second or first gas separation device projecting as tube into the shell.

5. The electrolysis unit as claimed in claim 4, wherein the tube has a closing face in the direction of the bottom and the closing face is configured as a grid, as a perforated plate, or as a mesh.

6. The electrolysis unit as claimed in claim 4, wherein a cross section of the shell and/or of the tube is round or is a polygon.

7. The electrolysis unit as claimed in claim 1, wherein the first gas separation device is connected to a first pressure maintenance device and the second gas separation device is connected to a second pressure maintenance device.

8. The electrolysis unit as claimed in claim 1, wherein at least one pump is arranged between the first and/or second gas separation device and the electrolysis modules.

9. The electrolysis unit as claimed in claim 4 comprising: at least three electrolysis modules, wherein the electrolysis modules are arranged in a circle and the first and second gas separation devices are arranged centrally in the middle between the modules.

10. The electrolysis unit as claimed in claim 4, wherein the first and/or second gas separation device is connected to exactly one heat exchanger for cooling the water (H2O) which has been separated off.

11. The electrolysis unit as claimed in claim 4, wherein the first or second gas separation device is connected to exactly one water treatment device.

12. The electrolysis unit as claimed in claim 11, wherein the water treatment device comprises a pump, a cooling device, and an ion exchange device.

13. The electrolysis unit as claimed in claim 1, wherein the electrolysis module comprises a module end plate, which has an exterior covering surface, on each of two opposite sides and a first electrolysis module is electrically connected to a second electrolysis module in such a way that a contacting device contacts a covering surface of the first electrolysis module and a covering surface of the second electrolysis module to a large extent.

14. A method for operating an electrolysis unit comprising: providing an electrolysis unit comprising at least two electrolysis modules, with water (H2O) being dissociated into hydrogen (H2) and oxygen (O2) in the electrolysis module, providing only one first gas separation device for a first product gas comprising oxygen, providing only one second gas separation device for a second product gas comprising hydrogen, wherein the first gas separation device is connected to each of the at least two electrolysis modules by means of a first conduit in each case and the second gas separation device is connected to each of the electrolysis modules by means of a second conduit in each case and the at least two first conduits comprise a same first length and the at least two second conduits comprise a same second length.

15. The method as claimed in claim 14, wherein the electrolysis unit is operated at a pressure in the range from 1 bar to 5 bar.

16. The electrolysis unit as claimed in claim 1, wherein the first gas separation device and the second gas separation device are arranged inside one another.

17. The electrolysis unit as claimed in claim 1, further comprising a central gas separation device comprising the first gas separation device and the second gas separation device, wherein a fluid-permeable wall permits fluid communication directly between respective interior volumes of the first gas separation device and the second gas separation device, and wherein the central gas separation device is configured to contain a fluid bath such that when the fluid bath is present the fluid-permeable wall is submerged therein.

18. The electrolysis unit as claimed in claim 1, wherein the central gas separation device is further configured such that when the fluid bath is present: respective portions of the interior volumes of the first gas separation device and the second gas separation device remain above the fluid bath; and no direct fluid communication is provided between the respective portions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features, properties and advantages of the present invention may be derived from the following description with reference to the accompanying figures. The figures schematically show:

(2) FIG. 1 an electrolysis unit according to the prior art comprising two electrolysis cells and first gas separation devices connected to one another;

(3) FIG. 2 an electrolysis cell with proton exchange membrane;

(4) FIG. 3 a plan view of an electrolysis unit having five electrolysis modules and a central gas separation device;

(5) FIG. 4 a sectional view of an electrolysis unit having electrolysis modules and a central gas separation device;

(6) FIG. 5 a plan view of an electrolysis unit having electrolysis modules, a central gas separation device, a heat exchanger and a water treatment device;

(7) FIG. 6 an electrolysis unit having a central gas separation device and areally contacted electrolysis modules.

DETAILED DESCRIPTION OF INVENTION

(8) FIG. 1 shows an electrolysis unit 1 from the prior art having two electrolysis modules 40, with an electrolysis module comprising a plurality of electrolysis cells 2, in particular fifty electrolysis cells. Each of the electrolysis modules 40 has an oxygen-side first gas separation device 20 (20′) and a hydrogen-side second gas separation device 21 (21′). The recirculation of the water is configured in such a way that the back-flowing water streams mix in the heat exchanger and are subsequently conveyed back to the oxygen side in the electrolysis cell. The oxygen-side gas separation devices 20 (20′) are connected to one another via a syphon-like fifth conduit 17. Furthermore, the fifth conduit 17 comprises a feed device 18 for fresh water. This example from the prior art involves single-side circulation operation on the oxygen side.

(9) The connection of a plurality of electrolysis cells via the syphon-like fifth conduit 17 ensures resupply of water, which avoids dropping of the liquid level in the gas separation devices 20, 21. In the prior art, all gas separation devices of the same type, in each case those of the oxygen side and hydrogen side, are thus connected to one another by means of a syphon-like conduit in order to keep the levels in the gas separation devices constant among one another and thus ensure safety.

(10) FIG. 2 shows an electrolysis cell 2 having a proton exchange membrane 3. The electrolysis cell 2 comprises an anode 7 and a cathode 8. The two electrodes 7, 8 are adjoined in each case by bipolar plates 30, 31. The bipolar plates each adjoin a porous support structure 32. The starting material water flows through this support structure 32 in the electrolysis cell 2. The porous support structure 32 in turn adjoins an electrocatalytic layer 33. An electrocatalytic layer 33 is arranged in the anode space 4, and an electrocatalytic layer 33 is arranged in the cathode space 5. The electrocatalytic layer 33 of the anode side typically comprises iridium, while the electrocatalytic layer 33 of the cathode side typically comprises platinum. The proton exchange membrane PEM 3 is located between these two catalytic layers 33. This PEM comprises, in particular, a sulfonated fluoropolymer, particularly comprising perfluorosulfonic acid. An advantage of the PEM electrolysis cell 2 is that pure water can be used as starting material. Thus, no alkali or other liquid components are used as carrier components for the water.

(11) FIG. 3 shows an electrolysis unit 1 having five electrolysis modules 40. Each electrolysis module 40 typically comprises 50 electrolysis cells as depicted in FIG. 2. A central gas separation device is arranged in the middle between the electrolysis modules 40. The central gas separation device comprises a first gas separation device 20 for separating off oxygen. The central gas separation device further comprises a second gas separation device 21 for separating off hydrogen. The first gas separation device 20 is arranged within the second gas separation device 21.

(12) The electrolysis modules 40 are each connected via a first conduit 9 to the second gas separation device 21. The first conduit 9 is advantageously connected to the cathode space in which the hydrogen is formed. A mixture of water and hydrogen is conveyed through the first conduit 9. This mixture is subsequently separated in the second gas separation device 21. The electrolysis modules 40 are each additionally connected via a third conduit 11 to the first gas separation device 20. Accordingly, a mixture of water and oxygen is transported through the third conduit 11. Advantageously, the third conduit 11 is thus connected directly to the anode space 4 of the electrolysis cells 2.

(13) Furthermore, the electrolysis modules 40 are each connected via a second conduit 10 to the second gas separation device 21. Water is conveyed through the second conduit 10 back into the electrolysis modules 40. The second conduit 10 can be connected both to the first gas separation device 20 and also to the second gas separation device 21.

(14) Furthermore, the electrolysis unit 1 comprises an apparatus for performing the process engineering 100. The process engineering 100 comprises, in particular, a heat exchanger 50 for cooling the water.

(15) Advantageously, only one first and one second gas separation device 20, 21 are required for all electrolysis modules 40 in order to separate off all product gases in this structure. Furthermore, it is advantageously very easy to increase the number of electrolysis modules 40. In particular, it is also possible to connect an odd number of electrolysis modules 40 to the central gas separation device and subsequently operate them.

(16) A further advantage of this arrangement can be seen from FIG. 4. FIG. 4 shows a section A-A′ through the electrolysis unit 1. This is the same electrolysis unit 1 as depicted in FIG. 3. Accordingly, the central gas separator with the first gas separation device 20 and the second gas separation device 21 is likewise located in the middle of the electrolysis modules 40. In this view, two of the five electrolysis modules 40 can be seen. The central gas separation device and the electrolysis modules 40 are once again connected to one other in each case via a first conduit 9, a second conduit 10 and a third conduit 11. The conduits are in this example arranged at the same height for each electrolysis module 40. Thus, all conduits advantageously have the same length. This identical nature of the parts allows the plant to be constructed more cheaply.

(17) The level 70 of the water in the central gas separation device can also be seen. Furthermore, it can be seen that the first gas separation device 20 has a closing face 41. This closing face 41 is configured as grid in this example. However, it is likewise possible to use meshes or open hole structures or a complete opening over the cross section of the first gas separation device 20.

(18) The first gas separation device 20 and the second gas separation device 21 communicate with one other via the openly configured closing face 41 of the first gas separation device 20. In other words, this means that the level 70 of the water in the two gas separation devices 20, 21 is virtually identical.

(19) Furthermore, it can be seen in FIG. 4 that the level 70 of the water is arranged above the upper edge of the electrolysis modules 40. This is particularly important for safe operation of the electrolysis unit 1. This level 70 ensures that no product gases can be returned via the second conduit 10 into the electrolysis modules 40. Furthermore, the water forms, as a result of the level 70, a lock between the hydrogen-containing, in this example annular, gas space of the second gas separation device 21 and the oxygen-containing, in this example round, gas space. The water thus prevents, as a result of a syphon-like communication between the two gas separation devices, the hydrogen and the oxygen from being mixed with one another or a hydrogen-oxygen reaction being able to take place.

(20) The gas space for the hydrogen particularly advantageously has a volume twice as great as that of the gas space for the oxygen.

(21) Furthermore, a first safety valve 46 and a second safety valve 47 are arranged directly at the outlets for oxygen and hydrogen. It is thus advantageously possible to arrange the pressure maintenance directly at the positions to be secured on the oxygen side and hydrogen side.

(22) In the case of this structure of the central gas separation devices, level equalization for all electrolysis modules 40 is advantageously achieved. No complex arrangements of conduits for each electrolysis module 40 are necessary. This advantageously simplifies the structure of the electrolysis unit 1.

(23) Gas sampling can also be carried out centrally in one of the two gas separation devices 20, 21 and the sample can then be cooled and analyzed centrally. This further simplifies the structure of the electrolysis unit 1. Gas sampling is not shown in the figures.

(24) FIG. 5 shows an electrolysis unit having a plurality of electrolysis modules 40. The figure shows 3 electrolysis modules 40, but it is likewise possible for at least 4, 5 or 6 electrolysis modules to be arranged around the central gas separation device. In this working example, the second gas separation device 21 is arranged in the middle of the first gas separation device 20. In other words, this means that the first gas separation device 20 is arranged on the outside here. As in the other working examples, the electrolysis modules 40 are each connected via a first conduit 9, a second conduit 10 and a third conduit 11 to the central gas separation device. FIG. 5 also shows a heat exchanger 50 and a water treatment device 60. The heat exchanger 50 is connected via a pump and a second conduit 10 to the first gas separation device 20. Since the first gas separation device 20 communicates with the second gas separation device 21, the water from both gas separation devices is thus transported through this second conduit 10 into the heat exchanger 50. Advantageously, only one heat exchanger 50 is thus required for the total electrolysis unit 1. The type of cooling in the heat exchanger 50 can be chosen freely. It can thus be effected by means of air or water. It is likewise conceivable, depending on the circumstances of the site on which the electrolysis unit is located, to operate an intermediate cooling circuit for a water/glycol mixture using the heat exchanger 50.

(25) Advantageously, only one central pump 48 is required in this example for water exchange in the water treatment device 60. This pump can be adapted individually to the plant conditions. It is conceivable, but not shown in this figure, for the first and second gas separation devices 20, 21 to be positioned on a central support frame. This advantageously makes it possible to arrange a cooling circuit connection underneath the central gas separation device. The one pump 48 of the electrolysis unit 1 is readily accessible as a result.

(26) It is particularly advantageous that the entire thermal mass to be cooled, in particular the water, is arranged centrally between the electrolysis modules 40. As a result, temperature regulation of the process temperature can advantageously be simplified compared to the prior art. In particular, valves in the cooling circuit can be saved, which advantageously leads to cost savings.

(27) After the heat exchanger, the water is fed into a water treatment device 60. The water treatment device is also arranged centrally. Thus, only one device for water treatment is necessary, which constitutes an advantage. Water can advantageously be transported into this water treatment device 60 by means of the same pump 48 used for transport into the heat exchanger 50. Furthermore, the central arrangement of the water treatment device 60 is advantageous since the ion exchangers which are present in the water treatment device 60 are readily accessible. It is also particularly advantageous that the water treatment device can be operated at a low temperature and the ion exchangers can thus advantageously have a longer operating life than in the prior art.

(28) Depending on the process pressure of the electrolysis unit 1, it is likewise possible to provide a second pump for conveying the water through the water treatment device 60.

(29) In all working examples shown in FIGS. 3 to 5, a grating can be arranged between the electrolysis modules 40 and the central gas separation device. This allows ready accessibility of the devices for maintenance purposes.

(30) The central positioning of the gas separation devices 20, 21 in the middle of the electrolysis modules 40 around the gas separation device allows advantageous contacting of the electrolysis modules 40 with one another. This contacting is shown in FIG. 6. As has been shown in the other examples, a first gas separation device 20 and a second gas separation device 21 surrounding this first gas separation device 20 are arranged in the middle of the electrolysis unit 1. This central gas separation device is surrounded by three electrolysis modules 40. It is likewise possible to conceive of a larger number of electrolysis modules 40 which surround the central gas separation device.

(31) The electrolysis modules 40 each have a module end plate 44 at their two end faces. These module end plates 44 are electrically connected from electrolysis module 40 to electrolysis module 40 via contact plates 45. The contact plates 45 can advantageously be arranged over the entire area of the module end plate 44 or at least large parts of the module end plate 44. This advantageously increases the uniformity of the distribution of current between the electrolysis modules 40. A uniform distribution of current over the electrolysis modules 40 increases the life of the individual electrolysis cells 2 with the proton exchange membrane 3, which constitutes an advantage.

LIST OF REFERENCE SYMBOLS

(32) 1 Electrolysis unit 2 Electrolysis cell 3 Proton exchange membrane 4 Anode space 5 Cathode space 6 Heat exchanger 7 Anode 8 Cathode 9 First conduit 10 Second conduit 11 Third conduit 12 Fourth conduit 13 First diameter 14 Second diameter 15 Second riser conduit 16 Connecting conduit 17 Fifth conduit 18 Feed device for water 20 First gas separation device 21 Second gas separation device 30 Bipolar plate of the anode 31 Bipolar plate of the cathode 32 Porous support structure 33 Electrocatalytic layer 40 Electrolysis module 41 Closing face 42 Shell 43 Intermediate space 44 Module end plate 45 Contact plates 46 First safety valve 47 Second safety valve 48 Pump 50 Heat exchanger 60 Water treatment device 70 Level 100 Process engineering H.sub.2O Water H.sub.2 Hydrogen O.sub.2 Oxygen