ELECTROLYSIS UNIT AND ELECTROLYSER

Abstract

An electrolytic device and to a method for operating an electrolysis of water with at least one electrolysis cell, the electrolysis cell having an anode compartment having an anode and a cathode compartment having a cathode. The anode compartment is separated from the cathode compartment by a proton exchange membrane. The anode compartment is suitable for holding water and oxidising the water on the anode to form a first product including oxygen and the cathode compartment is suitable for holding water and reducing the water on the cathode to a second product including hydrogen. Furthermore, the electrolysis device includes a first gas precipitation device for precipitation of oxygen, the first gas precipitation device for carrying out a natural water circulation being arranged above the electrolysis cell.

Claims

1. An electrolysis device for the electrolysis of water, comprising: at least one electrolysis cell, wherein the electrolysis cell comprises an anode space having an anode and a cathode space having a cathode, wherein the anode space is separated from the cathode space by means of a proton exchange membrane, and the anode space is suitable for receiving water and oxidizing it at the anode to give a first product comprising oxygen and the cathode space is suitable for receiving water and reducing it at the cathode to give a second product comprising hydrogen; a first gas separating apparatus for separation of oxygen; wherein the first gas separating apparatus is arranged above the electrolysis cell for performing a natural circulation of water.

2. The electrolysis device as claimed in claim 1, further comprising: a first line which is connected to an upper section of the anode space and to the first gas separating apparatus, and a second line which is connected to the first gas separating apparatus and to a lower section of the anode space.

3. The electrolysis device as claimed in claim 1, further comprising: a second gas separating apparatus for separation of hydrogen; a third line which is connected to an upper section of the cathode space and to the second gas separating apparatus; a fourth line which is connected to the second gas separating apparatus and to a lower section of the anode space and/or cathode space, wherein the second gas separating apparatus is arranged above the electrolysis cell for performing a natural circulation of water.

4. The electrolysis device as claimed in claim 3, wherein a first heat exchanger is arranged in the second line and/or a second heat exchanger is arranged in the fourth line.

5. The electrolysis device as claimed in claim 4, wherein the first heat exchanger and the second heat exchanger are thermally coupled.

6. The electrolysis device as claimed in claim 4, wherein the first heat exchanger and the second heat exchanger are coupled so as to allow transfer of material.

7. The electrolysis device as claimed in claim 3, wherein the second line and the fourth line are connected via a connection line for water equalization.

8. A method for operating an electrolysis device for electrolysis of water as claimed in claim 1, the method comprising: producing in an electrolysis cell an oxygen-comprising first product and a hydrogen-comprising second product by means of electrolysis at a functional membrane from water as a starting material, circulating of the starting material, wherein the first product and/or the second product is effected in the form of a natural water circulation.

9. The method as claimed in claim 8, wherein a prevailing operating pressure is atmospheric pressure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Further features, properties and advantages of the present invention can be found in the following description with reference to the appended figures. In the figures, in each case schematically:

[0035] FIG. 1 shows an electrolysis unit having a first and a second gas separating apparatus;

[0036] FIG. 2 shows an electrolysis cell having a proton exchange membrane;

[0037] FIG. 3 shows an electrolysis unit having a first and a second gas separating apparatus and a water bypass;

[0038] FIG. 4 shows an electrolysis unit comprising two electrolysis cells and interconnected first gas separating apparatuses.

DETAILED DESCRIPTION OF INVENTION

[0039] FIG. 1 shows a first exemplary embodiment of an electrolysis unit 1 having an electrolysis cell 2. The electrolysis cell 2 comprises a proton exchange membrane 3 which separates the anode space 4 from the cathode space 5. The anode space 4 comprises an anode 7. The cathode space 5 comprises a cathode 8. In the anode space 4, water H.sub.2O is oxidized at the anode to oxygen O.sub.2. The oxygen/water mixture forming in the anode space 4 during the electrolysis has a lower density than pure water. As a result, it rises up in the first line 9, also called a riser pipe, into a first gas separating apparatus 20. The first gas separating apparatus 20 is situated above the anode space 4. The oxygen separates from the water in the first gas separating apparatus 20. The oxygen O.sub.2 can be conducted out from the electrolysis unit 1. The water is led via a second line 10 into a heat exchanger 6. In the cathode space, water is reduced at the cathode 8 to hydrogen H.sub.2 during the electrolysis. The hydrogen/water mixture rises up via a third line 11 into a second gas separating apparatus 21 on account of the lower density compared to water. The hydrogen separates from the water in the second gas separating apparatus 21. The hydrogen leaves the electrolysis unit 1. The water can be led via a fourth line 12 into the heat exchanger. The water is subsequently led out from the heat exchanger 6 back into the anode space 4 and the cathode space 5. The heat exchanger is operated with a coolant, in particular water. No mass transfer occurs between this coolant and the water from the electrolysis. For the sake of clarity, the coolant feed stream and discharge stream from the heat exchanger 6 has not been depicted in FIGS. 1, 3 and 4.

[0040] The electrolysis unit 1 is advantageously operable dynamically, that is to say that depending on the load input the electrolysis unit 1 can be operated with an energy density of more than 0 A/cm.sup.2 up to 4 A/cm.sup.2, particularly of more than 1 A/cm.sup.2 to 3 A/cm.sup.2.

[0041] The first and the second gas separating apparatus 20, 21 are at a height h.sub.2. The maximum height of the electrolysis cell is h.sub.1. The height h.sub.2 is above the height h.sub.1. As a result, a natural circulation of the starting materials and products in the electrolyzer can be ensured solely on account of the density differences arising in the electrolyzer. However, both heights must lie above the height h.sub.1 of the electrolysis cell. Additional pumps or other conveying means are advantageously not necessary. As an alternative to the embodiment depicted here, it is also possible to perform the natural circulation exclusively on the oxygen side, that is to say in the anode space 4. The water conveying rate regulates itself as a result of the principle of natural circulation based on the physical parameter of density. That is, given a suitable process design, at an elevated gas production rate the water conveying rate is increased, as a result of which the heat is in turn advantageously conducted away.

[0042] The operation of the natural circulation at atmospheric pressure is particularly advantageous, since here the size of the hydrogen and/or oxygen gas bubbles, and hence the resulting transportability with regard to the gases and the water, is sufficiently great such that pumps can be completely dispensed with.

[0043] The water circuits on the hydrogen side and the oxygen side, that is to say the water in the anode space 4 and in the cathode space 5, are connected to one another via the heat exchanger 6.

[0044] On account of the water cleavage reaction equation it is clear that about double the volume of hydrogen gas compared to oxygen gas is formed during the decomposition of water. Therefore, for an identically configured pipe diameter on the hydrogen side and on the oxygen side, the hydrogen side would exhibit a higher water conveying rate than the oxygen side, provided the conveying rate is not limited by the pipe diameter. If the conveying rate of the water is limited by the riser pipe, the conveying rate may be optimized by adapting the riser pipe diameter. In order thus to optimize the water flow rate on both sides, the first diameter 13 of the first line 9 is dimensioned smaller than the second diameter 14 of the third line 11. Particularly advantageously, the first line 9 has a cross-sectional area of roughly half the cross-sectional area of the third line 11. Compared to a conventional uniform pipe diameter distribution, a higher water conveying rate, particularly on the anode side, can advantageously be achieved.

[0045] FIG. 2 shows an electrolysis cell having a proton exchange membrane. The electrolysis cell comprises an anode 7 and a cathode 8. Bipolar plates 30, 31 in each case adjoin the two electrodes 7, 8. The bipolar plates each adjoin a porous support structure 32. The starting material water flows through the electrolysis cell 2 via this support structure 32. The porous support structure 32 in turn adjoins an electrocatalytic layer 33. One electrocatalytic layer 33 is arranged in the anode space 4, and one electrocatalytic layer 33 is arranged in the cathode space 5. The electrocatalytic layer 33 on the anode side typically comprises iridium; the electrocatalytic layer 33 on the cathode side typically comprises platinum. The proton exchange membrane PEM is situated between these two catalytic layers 33. This comprises in particular a sulfonated fluoropolymer, particularly comprising perfluorosulfonic acid. One advantage of the PEM electrolysis cell is that pure water can be used as the starting material. It is advantageous not to use any alkaline solution or other liquid components as a carrier component for the water.

[0046] In a further exemplary embodiment (not illustrated in the figures) of an electrolysis unit 1 having an electrolysis cell 2, an alternative arrangement of the riser pipes 11 from the cathode space 5 is used. All components are arranged in the same way as in the first exemplary embodiment in FIG. 1. Merely an additional riser pipe connects the cathode space 5 to the second gas separating apparatus 21. If, due to the existing operating conditions and despite the differing cross-sectional areas of riser pipes 10 and 11, the conveying rate is still insufficient, an additional, second riser line 15 may be present on the hydrogen side. This second riser line, in other words seventh line, advantageously guarantees a sufficiently high conveying rate of the water and of the hydrogen into the second gas separating apparatus 21. It is likewise conceivable that the first exemplary embodiment and the second exemplary embodiment can be combined. This means, in other words, that a second riser line is present but is only opened via the use of valves when it is required due to the conveying rate on the hydrogen side.

[0047] FIG. 3 shows a third exemplary embodiment of an electrolysis unit 1 having an electrolysis cell 2 having a first gas separating apparatus 20 and a second gas separating apparatus 21. The gas separating apparatuses 20, 21 are respectively connected via riser pipes 9, 11 to the anode space 4 and cathode space 5, respectively. The gas separating apparatuses 20, 21 are connected to the heat exchanger 6 respectively via a second line 10 and a fourth line 12. The second line 10 in turn connects the heat exchanger 6 to the anode space 4. The fourth line 12 connects the heat exchanger 6. In other words, the heat exchanger 6 is arranged in the second line 10 and the heat exchanger 6′ is likewise arranged in the fourth line 12. No mass transfer takes place here in the heat exchanger 6 and 6′, such that the returned water on the anode side is separated from the returned water on the cathode side. The complete separation of the water circuits in this way would disadvantageously result in a shift in levels in the gas separators, since in the water cleavage reaction, in addition to protons, water is also transported from the oxygen side to the hydrogen side. By means of the pipeline arrangement illustrated in this third exemplary embodiment, which provides a bypass line 16 between the second line 10, that is to say the anode space 4, and the fourth line 12, that is to say the cathode space 5, the water circuits are connected to each other. The returning water streams are advantageously not mixed with each other in the heat exchanger 6 but instead only immediately before entry into the electrolysis cell 2. The connection of the cathode space to the anode side forms a communicating system which advantageously ensures equalization of the water stream from the hydrogen side to the oxygen side. A slight increase in the hydrogen concentration on the oxygen side does not impair the reliable operation of the installation. If the water streams are already mixed with each other in the heat exchanger 6, the residence time of the mixed water streams is markedly higher. As a result of this, there may be a rise in the respective foreign gas concentration in the gas separators. If merely a directed water stream is conducted from the hydrogen to the oxygen side in the form of the bypass connection 16, potentially only the hydrogen concentration in the oxygen in the gas separator increases. The reliability of the installation is thus advantageously further increased.

[0048] It becomes clear in all three exemplary embodiments of FIGS. 1, 3 and 4 that the water/gas mixture is supplied in the gas separating apparatuses 20, 21 close to the phase boundary in the gas separating apparatuses 21 and 22. This is achieved by controlling pressure valves connected to the gas separating apparatuses 20, 21 (not shown in the figures). Since both vessels are hydraulically connected to each other, virtually the same filling level is established in both gas separating apparatuses 20 and 21. The prerequisite for this is that the pressure losses in the pipelines which are connected to the gas separating apparatuses 20, 21 which are caused by the gas stream do not generate any appreciable pressure losses in the gas separating apparatus 20, 21. In other words, the pipe diameters of the pipelines are so great that there is no limiting of the material stream and thus no shift in levels in the gas separating apparatuses 20, 21.

[0049] FIG. 4 shows an electrolysis unit 1 having two electrolysis cells 2. Both electrolysis cells each possess an oxygen-side, first gas separating apparatus 20, 20′ and a hydrogen-side, second gas separating apparatus 21, 21′. The returning of the water has been configured analogously to the first exemplary embodiment such that the water streams flowing back mix in the heat exchanger and are subsequently conducted into the electrolysis cell back toward the oxygen side. As an alternative, it is also conceivable to carry out a bypass according to the third exemplary embodiment. The oxygen-side gas separating apparatuses 20, 20′ are connected to each other via a siphon-like fifth line 17. The fifth line 17 additionally comprises a fresh water supply apparatus 18. This exemplary embodiment involves a one-sided circulating mode on the oxygen side. Connecting a plurality of electrolysis cells via the siphon-like fifth line 17 advantageously ensures the replenishment of water, which avoids the lowering of the liquid level in the gas separating apparatuses 20, 21 in an advantageous manner. The fresh water of the water consumed during the reaction is advantageously supplied into the fifth line 17 connecting the first gas separating apparatuses 20 to each other. This advantageously avoids an additional pipeline to the gas separating apparatuses.

[0050] In order to make the passing through of gas as unlikely as possible, and hence to avoid a failure, the first gas separating apparatuses 20, 20′ on the oxygen side are connected to each other and, separately from this, the second gas separating apparatuses 21, 21′ on the hydrogen side are connected to each other. In other words, the gas separating apparatuses are connected to each other only in such a way that the oxygen side remains separated from the hydrogen side. In addition to the exemplary embodiment shown in FIG. 5, it is therefore possible to also connect the second gas separating apparatuses 21 on the hydrogen side to each other via a siphon-like line. The filling levels between the second gas separating apparatuses 21 are thus advantageously equalized.