ALKALINE ELECTROLYSIS ARRANGEMENT WITH DEAERATOR AND METHOD THEREFOR

Abstract

The invention relates to an electrolysis arrangement for alkaline electrolysis and a method for producing hydrogen and oxygen by electrolysis of an alkaline electrolysis medium. According to the invention, an anolyte deaerating means is arranged downstream of an anolyte gas-liquid separator and is arranged upstream of the electrolysis cell stack of the electrolysis arrangement, and/or a catholyte deaerating means is arranged downstream of a catholyte gas-liquid separator and arranged upstream of the electrolysis cell stack of the electrolysis arrangement. By this arrangement, the fact is exploited that many undesirable gas components have a much lower solubility in the alkaline electrolysis medium than in pure deionised water, which is supplied as fresh water to the electrolysis arrangement for compensation of the water consumed by the electrochemical reaction.

Claims

1. An electrolysis arrangement for alkaline electrolysis, comprising an electrolysis cell stack comprising a plurality of electrolysis cells for the electrochemical generation of hydrogen and oxygen from an alkaline electrolysis medium, wherein the electrolysis cell stack comprises an anode section for the generation of oxygen and a cathode section for the generation of hydrogen; an anolyte gas-liquid separator configured for the separation of oxygen gas from an oxygen loaded anolyte portion of the alkaline electrolysis medium; a catholyte gas-liquid separator configured for the separation of hydrogen gas from a hydrogen loaded catholyte portion of the alkaline electrolysis medium; an anolyte cooling means arranged downstream of the anolyte gas-liquid separator and upstream of the electrolysis cell stack, configured to cool an oxygen depleted anolyte withdrawn from the anolyte gas-liquid separator before the oxygen depleted anolyte is supplied to the electrolysis cell stack and/or a catholyte cooling means arranged downstream of the catholyte gas-liquid separator and upstream of the electrolysis cell stack, configured to cool a hydrogen depleted catholyte withdrawn from the catholyte gas-liquid separator before the hydrogen depleted catholyte is supplied to the electrolysis cell stack; an anolyte deaerating means arranged downstream of the anolyte gas-liquid separator and arranged upstream of the electrolysis cell stack and/or a catholyte deaerating means arranged downstream of the catholyte gas-liquid separator and arranged upstream of the electrolysis cell stack.

2. The electrolysis arrangement according to claim 1, wherein the alkaline electrolysis medium is a concentrated lye solution.

3. The electrolysis arrangement according to claim 1, wherein the anolyte deaerating means is arranged downstream of the anolyte gas-liquid separator and is arranged upstream of the anolyte cooling means and/or the catholyte deaerating means is arranged downstream of the catholyte gas-liquid separator and is arranged upstream of the catholyte cooling means.

4. The electrolysis arrangement according to claim 1, wherein an anolyte recirculation pump configured to recirculate anolyte between the anolyte gas-liquid separator and the electrolysis cell stack is arranged downstream of the anolyte deaerating means and upstream of the anolyte cooling means and/or a catholyte recirculation pump configured to recirculate catholyte between the catholyte gas-liquid separator and the electrolysis cell stack is arranged downstream of the catholyte deaerating means and upstream of the catholyte cooling means.

5. The electrolysis arrangement according claim 1, wherein the electrolysis arrangement comprises a hydrogen purification unit configured for the removal of oxygen and water from the hydrogen gas separated in the catholyte gas-liquid separator, whereby a purified hydrogen gas is obtainable by means of the hydrogen purification unit.

6. The electrolysis arrangement according to claim 1, wherein the catholyte deaerating means is configured for the degassing of the hydrogen depleted catholyte by means of hydrogen gas supplied to the catholyte deaerating means.

7. The electrolysis arrangement according to claim 1, wherein the catholyte deaerating means is configured for the degassing of the hydrogen depleted catholyte by means of hydrogen gas supplied to the catholyte deaerating means, wherein the electrolysis arrangement comprises a hydrogen purification unit configured for the removal of oxygen and water from the hydrogen gas separated in the catholyte gas-liquid separator, whereby a purified hydrogen gas is obtainable by means of the hydrogen purification unit, wherein the hydrogen gas supplied to the catholyte deaerating means comprises the purified hydrogen gas obtainable by means of the hydrogen purification unit.

8. The electrolysis arrangement according to claim 1, wherein the anolyte deaerating means is configured for the degassing of the oxygen depleted anolyte by means of oxygen gas supplied to the anolyte deaerating means.

9. The electrolysis arrangement according to claim 1, wherein the anolyte deaerating means and/or the catholyte deaerating means comprises a heating means in order to degas the hydrogen depleted catholyte and/or the oxygen depleted anolyte.

10. A method for producing hydrogen and oxygen by electrolysis of an alkaline electrolysis medium, the method comprising the method steps of electrochemical splitting of water contained in the alkaline electrolysis medium by means of an electrolysis cell stack, whereby a hydrogen loaded catholyte withdrawn from a cathode section of the electrolysis cell stack and an oxygen loaded anolyte withdrawn from an anode section of the electrolysis cell stack are obtained; supplying the hydrogen loaded catholyte to a catholyte gas-liquid separator to separate hydrogen from the hydrogen loaded catholyte, whereby hydrogen gas and a hydrogen depleted catholyte are obtained; supplying the oxygen loaded anolyte to an anolyte gas-liquid separator to separate oxygen from the oxygen loaded anolyte, whereby oxygen gas and an oxygen depleted anolyte are obtained; withdrawing the hydrogen depleted catholyte from the catholyte gas-liquid separator, optionally cooling the hydrogen depleted catholyte and supplying the hydrogen depleted catholyte to the cathode section of the electrolysis cell stack; withdrawing the oxygen depleted anolyte from the anolyte gas-liquid separator, optionally cooling the oxygen depleted anolyte and supplying the oxygen depleted anolyte to the anode section of the electrolysis cell stack; degassing the hydrogen depleted catholyte withdrawn from the catholyte gas-liquid separator by means of a catholyte deaerating means and supplying the degassed hydrogen depleted catholyte to the electrolysis cell stack and/or degassing the oxygen depleted anolyte withdrawn from the anolyte gas-liquid separator by means of an anolyte deaerating means and supplying the degassed oxygen depleted anolyte to the electrolysis cell stack.

11. The method according to claim 10, wherein the alkaline electrolysis medium is a concentrated lye solution.

12. The method according to claim 10, wherein the degassing of the hydrogen depleted catholyte and/or the degassing of the oxygen depleted anolyte is carried out before cooling of the hydrogen depleted catholyte and the oxygen depleted anolyte.

13. The method according to claim 10, wherein the hydrogen gas separated in the catholyte gas-liquid separator is withdrawn from said gas-liquid separator and supplied to a hydrogen purification unit for removal of water and oxygen, to obtain a purified hydrogen gas.

14. The method according to claim 10, wherein the degassing of the hydrogen depleted catholyte is effected by introducing hydrogen gas into the hydrogen depleted catholyte.

15. The method according to claim 1, wherein the degassing of the hydrogen depleted catholyte is effected by introducing hydrogen gas into the hydrogen depleted catholyte, wherein the degassing of the hydrogen depleted catholyte is affected by introducing purified hydrogen gas into the hydrogen depleted catholyte, wherein the hydrogen gas separated in the catholyte gas-liquid separator is withdrawn from said gas-liquid separator and supplied to a hydrogen purification unit for removal of water and oxygen, to obtain a purified hydrogen gas.

16. The method according to claim 10, wherein the degassing of the oxygen depleted anolyte is effected by introducing oxygen gas into the oxygen depleted anolyte.

17. The method according to claim 10, wherein the degassing of the hydrogen depleted catholyte and/or the degassing of the oxygen depleted anolyte is effected by heating the hydrogen depleted catholyte and/or the oxygen depleted anolyte.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0094] The invention will now be detailed by way of an exemplary embodiment with reference to the attached drawing. Unless otherwise stated, the drawing is not to scale.

[0095] In the FIGURE and the accompanying description, equivalent elements are each provided with the same reference marks.

[0096] FIG. 1 depicts a simplified flow diagram of an electrolysis arrangement 1 according to one exemplary embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0097] FIG. 1 depicts one exemplary embodiment of an electrolysis arrangement 1 according to the invention. It is assumed that the electrolysis arrangement 1 performs an alkaline type electrolysis with 30 wt.-% KOH lye solution as the electrolysis medium.

[0098] The electrolysis arrangement 1 comprises an electrolysis cell stack 2, a rectifier 3, a catholyte cooler 12, an anolyte cooler 13, a catholyte recirculation pump 14, an anolyte recirculation pump 15, a catholyte gas-liquid separator 16 with hydrogen cooler 19, an anolyte gas-liquid separator 17 with oxygen cooler 20, a catholyte deaerator 18 and a hydrogen purification unit 21. The aforementioned components are at least partially in fluid communication with each other via the conduits 22 to 35. The electrolysis arrangement further comprises a deionised (DI) water supply (not shown) to compensate for the amount of water consumed by the electrochemical water splitting reaction in electrolysis cell stack 2.

[0099] Direct current 4 is supplied to the electrolysis cell stack 2 by means of the rectifier 3. For the sake of simplification, only one electrolysis cell is shown in regards of electrolysis cell stack 2, but the electrolysis cell stack 2 actually contains a plurality of electrolysis cells. The electrolysis cell shown comprises an anode section 10, which consists of an anode 8 and an anode compartment 9. The electrolysis cell further comprises a cathode section 7, which consists of a cathode 5 and a cathode compartment 6. The anode section 10 and the cathode section 7 are separated by a liquid tight membrane 11 which enables the exchange of hydroxyl ions between the anode section 10 and the cathode section 7.

[0100] By supplying direct current 4 to the electrolysis cell stack 2, water of the electrolyte lye solution is split into hydrogen (cathode side) and oxygen (anode side). This results in the generation of an oxygen loaded anolyte in the anode section 10 of the electrolysis cell stack 2 and a hydrogen loaded catholyte in the cathode section 7 of the electrolysis cell stack 2.

[0101] On the cathode side of the electrolysis arrangement 2, hydrogen loaded catholyte is withdrawn from the cathode section 7 of the electrolysis cell stack and sent via conduit 26 to cathode gas-liquid separator 16. In catholyte gas-liquid separator 16, hydrogen gas is separated from the hydrogen loaded catholyte, whereby an hydrogen depleted catholyte and hydrogen gas is obtained. The hydrogen gas contains uncondensed water. Hence, it is cooled in hydrogen cooler 19 of catholyte gas-liquid separator 16 by indirect cooling. Therefore, hydrogen cooler 19 is supplied with cooling water (not shown). The thereby condensed water is returned to the catholyte gas-liquid separator 16. Heated cooling water is withdrawn from hydrogen cooler 16 and re-cooled by e.g. an air cooler (not shown). Mostly dry hydrogen gas is withdrawn from the hydrogen cooler 19 part of the catholyte gas-liquid separator 16 and is then sent via conduit 27 to the hydrogen purification unit 21. The hydrogen gas withdrawn from hydrogen cooler 19 contains residual amounts of water and oxygen, the latter from oxygen crossover from the anode section 10 to the cathode section 7 of the electrolysis cell stack 2 through membrane 11. In hydrogen purification unit 21, the oxygen contained in the hydrogen gas is first reacted with a small amount of hydrogen on a catalyst bed (not shown) to form water. The formed water and residual water of the hydrogen stream is then removed in an adsorption bed containing molecular sieves. The obtained pure hydrogen stream is withdrawn from the hydrogen purification unit 21 via conduit 28 and is then discharged from the process for further processing.

[0102] Hydrogen depleted catholyte formed in catholyte gas-liquid separator 16 is withdrawn from catholyte gas-liquid separator 16 via conduit 25 and is sent to catholyte deaerator 18. From the purified hydrogen gas main stream of conduit 28, a small side stream is withdrawn and sent via conduit 29 to catholyte deaerator 18. In catholyte deaerator 18, hydrogen depleted catholyte is degassed by the pure hydrogen introduced into deaerator 18 through the principle of displacement. That is, undesired gas components, e.g. Argon, dissolved in the hydrogen depleted catholyte are displaced in catholyte deaerator through the introduction of hydrogen gas into the hydrogen depleted catholyte. The undesired and desorbed gas components are then vented from the catholyte deaerator 18 via conduit 30.

[0103] To make the degassing process in catholyte deaerator 18 more effective, catholyte deaerator 18 can optionally be equipped with a heating device (not shown).

[0104] The degassed hydrogen depleted catholyte is withdrawn from catholyte deaerator 18 via conduits 24 and 23 and sent to catholyte cooler 12. Between conduits 23 and 24, the catholyte recirculation pump is arranged to recirculate the catholyte between the cathode section 7 of the electrolysis cell stack 2, the catholyte gas-liquid separator 16, the catholyte deaerator 18 and the catholyte cooler 12. In catholyte cooler 12, the degassed and hydrogen depleted catholyte is cooled to a pre-determined set temperature and then sent via conduit 22 to the cathode section 7 of the electrolysis cell stack 2 for renewed electrochemical water splitting and formation of hydrogen at the cathode 5.

[0105] On the anode side of the electrolysis arrangement 2, oxygen loaded anolyte is withdrawn from the anode section 10 of the electrolysis cell stack and sent via conduit 34 to anode gas-liquid separator 17. In anolyte gas-liquid separator 17, oxygen gas is separated from the oxygen loaded catholyte, whereby an oxygen depleted anolyte and oxygen gas is obtained. The oxygen gas contains uncondensed water. Hence, it is cooled in oxygen cooler 20 of anode gas-liquid separator 17 by indirect cooling. Therefore, oxygen cooler 16 is supplied with cooling water (not shown). The thereby condensed water is returned to the anolyte gas-liquid separator 17. Heated cooling water is withdrawn from oxygen cooler 20 and re-cooled by e.g. an air cooler (not shown). Mostly dry oxygen gas is withdrawn from the oxygen cooler 20 part of the anolyte gas-liquid separator 17 and is then sent via conduit 35 to a further processing step (not shown).

[0106] Oxygen depleted anolyte formed in anolyte gas-liquid separator 17 is withdrawn from anolyte gas-liquid separator 17 via conduit 33 and is sent via conduit 32 to anolyte cooler 13. Between conduits 33 and 32, the anolyte recirculation pump 15 is arranged to recirculate the anolyte between the anode section 10 of the electrolysis cell stack 2, the anolyte gas-liquid separator 17, and the anolyte cooler 13. anolyte cooler 13, the oxygen depleted anolyte is cooled to a pre-determined set temperature and then sent via conduit 31 to the anode section 10 of the electrolysis cell stack 2 for renewed electrochemical water splitting and formation of oxygen at the cathode 8.

[0107] If there is also a high demand on the purity of the oxygen to be produced, the anode side of the electrolysis arrangement can also be equipped with a corresponding anolyte deaerator, whereby said anolyte deaerator can also be operated with oxygen, in particular purified oxygen, to displace undesired gas components.

LIST OF REFERENCE SIGNS

[0108] 1 electrolysis arrangement [0109] 2 electrolysis cell stack [0110] 3 rectifier [0111] 4 direct current [0112] 5 cathode [0113] 6 cathode compartment [0114] 7 cathode section [0115] 8 anode [0116] 9 anode compartment [0117] 10 anode section [0118] 11 membrane [0119] 12 catholyte cooler [0120] 13 anolyte cooler [0121] 14 catholyte recirculation pump [0122] 15 anolyte recirculation pump [0123] 16 catholyte gas-liquid separator [0124] 17 anolyte gas-liquid separator [0125] 18 catholyte deaerator [0126] 19 hydrogen cooler [0127] 20 oxygen cooler [0128] 21 hydrogen purification unit [0129] 22 conduit (hydrogen depleted catholyte) [0130] 23 conduit (hydrogen depleted catholyte) [0131] 24 conduit (hydrogen depleted catholyte) [0132] 25 conduit (hydrogen depleted catholyte) [0133] 26 conduit (hydrogen loaded catholyte) [0134] 27 conduit (hydrogen gas) [0135] 28 conduit (main stream purified hydrogen gas) [0136] 29 conduit (purified hydrogen gas stream to deaerator) [0137] 30 conduit (undesired gas components) [0138] 31 conduit (oxygen depleted anolyte) [0139] 32 conduit (oxygen depleted anolyte) [0140] 33 conduit (oxygen depleted anolyte) [0141] 34 conduit (oxygen loaded anolyte) [0142] 35 conduit (oxygen gas)

[0143] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.