NO20230953A1

NO20230953A1 - A water electrolyser system and method for producing compressed hydrogen

Info

Publication number: NO20230953A1
Application number: NO20230953A
Authority: NO
Inventors: Eddy Van Oort; Magnus Thomassen
Original assignee: Hystar As
Priority date: 2023-09-07
Filing date: 2023-09-07
Publication date: 2024-11-11
Also published as: NO348295B1; WO2025053761A1

Description

A WATER ELECTROLYSER SYSTEM AND METHOD FOR PRODUCING

COMPRESSED HYDROGEN

Technical Field

[0001] The invention relates generally to hydrogen production and processing systems and more particularly to enhancement of the performance of an integrated hydrogen production and processing system that includes hydrogen production and compression sub-systems.

Background Art

[0002] The development of infrastructure for low-cost distribution, delivery, storage and use of hydrogen is reliant on cost and energy efficient hydrogen compression. Hydrogen is one of the most challenging gases to compress due to its low molecular weight and small size. There are various compressors that can be used and ultimately the choice of compression technology, associated costs and energy use will depend on where in the supply chain it is used.

[0003] Mechanical compressors are widely used and are designed based on the direct conversion of mechanical energy into compressed gas energy. There are several classifications, but most compressors used today for gaseous H2 compression are either positive displacement compressors or dynamic compressors.

[0004] Centrifugal compressors are examples of dynamic compressors that are most commonly used in applications that require high throughput and moderate compression ratios. They compress the process gas using a rotating impeller with radial blades that imparts kinetic energy to the process gas by increasing its velocity. Unlike reciprocating compressors, the compression ratio largely depends on the molecular weight of the gas in the centrifugal compressor. Because of the low molecular weight of H2, the impeller speed must be increased, or additional compression stages must be added compared to compression of e.g. natural gas. Increasing current impeller tip speeds is very challenging due to material strength limitations and H2 embrittlement issues.

[0005] Reciprocating piston compressors are ideal for low to moderate flow and high-pressure applications. They are positive displacement machines that work via compression and displacement of gases. A single stage reciprocating compressor is designed using a piston and system where the piston is driven by a crankshaft, converting rotary motion into linear motion. The cylinder uses two automatic valves – one for gas suction and the other for gas discharge and the energy needed for compression is provided by either an electrical or thermal source.

[0006] Another option to produce hydrogen for use or storage at high pressure is to perform water electrolysis at the required pressure directly, generating both hydrogen and oxygen at high pressure. Alternatively, differential-pressure electrolysis may be employed to generate hydrogen at high pressure and oxygen at substantially atmospheric pressure. In a state-of-the-art PEM (proton-exchange membrane) electrolyser, a low-pressure pump provides liquid water at near-ambient pressure to the anode side of the electrolyser stack. When DC current is applied, the water is decomposed at the anode to oxygen, protons and electrons. The oxygen is separated from the excess circulating water in a low-pressure gas/water separator. All functions on the anode side are conducted at near-ambient pressure. The protons, along with some water, are electrochemically transported across the membrane to the cathode, where they react with the externally transported electrons to produce hydrogen at the required higher operating pressure. The hydrogen is then separated from the transported water in a high-pressure gas/water separator. The hydrogen may further be compressed in a single-phase compressor outside the integrated PEM electrolysis process.

[0007] To date, high pressure water electrolysers have been fabricated that either generate both hydrogen and oxygen at pressures up to 200 bar or generate hydrogen at 200 bar and oxygen at atmospheric pressure. For example, US8282811B2 discloses a water electrolyser that operates at a differential pressure (H2>O2) of 2500 psia using plastic materials as frames and proton-exchange membranes (PEMs) as solid-polymer electrolytes. Electrolysers operating totally or partially at high pressure is however expensive, involve complex construction, and present safety hazards due to higher risk of hydrogen leaks. Such electrolysers providing outlet pressures above 40 bar have not been a commercial success. Most PEM electrolyser manufacturers today therefore offers electrolysers with a hydrogen output pressure between 15 and 40 bar. Even at these pressures there is a significant amount of hydrogen diffusing from the cathode compartment to the anode compartment causing the formation of a H2/O2 gas mixture in the anode compartment. This hydrogen crossover phenomenon forces the use of thick membranes (> 50µm) to limit the amount of hydrogen that is mixed with the oxygen to prevent flammable or explosive gas mixtures to be formed. The use of thick membranes increases the cost and leads to higher ohmic resistances in the PEM electrolyser cells which increases the energy demand for the electrolyser process.

[0008] In a conventional electrolyser process, any additional hydrogen compression beyond the operating pressure of the electrolyser stack takes place using a conventional single-phase compressor outside the electrolysis process, after the separation of liquid and hydrogen in the separator vessel. In addition to the compressor, the process can also include a buffer tank and/or a gas drier before the compressor.

[0009] The energy needed to compress hydrogen is relatively high compared to other gases such as natural gas. For an adiabatic compression of hydrogen from 1 to 200 bar, the energy need is ~14 MJ/kg, or about 10% of the energy content of the compressed hydrogen. The ideal isothermal compression would in comparison need only ~6 MJ/kg.

[0010] Due to the technical difficulties and the high energy demand for compression of hydrogen as described above, there exists a need in the art for improved systems and methods for compressing hydrogen in combination with production from electrolysers.

[0011] Multiphase pumps are used in many different industries, where it is necessary to convey or compress a multiphase process fluid which comprises a mixture of a plurality of phases, for example a liquid phase and a gaseous phase. A multiphase pump is essentially a hybrid of a pump and a compressor and is also referred to as a multiphase compressor. In the present disclosure, the term multiphase pumps will be used. The ratio of the gaseous phase in the multiphase mixture is commonly measured by the dimensionless gas volume fraction (GVF) designating the volume ratio of the gas in the multiphase process fluid. A multiphase pump may be designed for conveying multiphase process fluids having a GVF from 0% to 100%, i.e. all process fluids from a pure liquid (GVF = 0%) to a pure gas (GVF = 100%).

Summary of invention

[0012] According to a first aspect of the present invention, there is provided a water electrolyser system for hydrogen production, comprising an electrolyser stack, a multiphase pump arranged downstream of the electrolyser stack; and a hydrogen gas/liquid separator, wherein the multiphase pump is arranged between the electrolyser stack and the hydrogen gas/liquid separator.

[0013] In an embodiment, the system includes a control valve controlling supply of water or liquid electrolyte to the electrolyser stack.

[0014] In an embodiment, the electrolyser stack comprises a plurality of polymer electrolyte membrane water electrolyser cells, each water electrolyser cell comprises an anode compartment, a cathode compartment and a polymer electrolyte membrane; the cathode compartment is configured to be supplied with deionised water through a stack cathode inlet, and the anode compartment is configured to be supplied with air through a stack anode inlet. In this embodiment, the control valve is arranged between the hydrogen gas/liquid separator and the stack cathode inlet. A humidifier is not required but may be included to provide humidified air to the anode compartment.

[0015] In another embodiment, the electrolyser stack comprises a plurality of polymer electrolyte membrane water electrolyser cells, each water electrolyser cell comprises an anode compartment, a cathode compartment; the anode compartment is configured to be supplied with deionised water through a stack anode inlet; the cathode compartment comprises a cathode outlet where a mixture of produced hydrogen and entrained water exits. This embodiment further includes an oxygen gas/liquid separator separating a mixture of water and produced oxygen. In this embodiment, the at least one control valve is arranged between the hydrogen gas/liquid separator and the oxygen gas/liquid separator.

[0016] According to a second aspect of the present invention, there is provided a method for production of hydrogen in a water electrolyser system including: supplying water or liquid electrolyte to an electrolyser stack, producing hydrogen in the electrolyser stack, compressing a mixture of produced hydrogen and entrained water or liquid electrolyte in a multiphase pump; separating the compressed mixture of produced hydrogen and entrained water or liquid electrolyte in a hydrogen gas/liquid separator.

[0017] In an embodiment of the method, the outlet pressure from the multiphase compressor is between 2 and 100, preferably 4 and 50 bar above the outlet pressure from the electrolyser stack. The gas volume fraction in the mixture of produced hydrogen and water or liquid electrolyte may be within the range 5 to 95%. Water or liquid electrolyte may be circulated from the hydrogen gas/liquid separator via a control valve to a stack cathode inlet of the electrolyser stack. Alternatively, water or liquid electrolyte may be circulated from the hydrogen gas/liquid separator via a control valve to an oxygen gas/ liquid separator.

Figures

[0018] Figure 1 shows a schematic diagram of one embodiment of PEM water electrolyser system for hydrogen production.

[0019] Figure 2 shows another schematic diagram of one embodiment of PEM water electrolyser system for hydrogen production.

[0020] Figure 3 shows a schematic diagram of an AEM or liquid alkaline electrolyser system for hydrogen production.

[0021] Figure 4 is a diagram showing the energy required to compress hydrogen from ambient conditions to different final pressures.

Detailed description of the invention

[0022] The present invention relates to a use of a multiphase pump integrated in an electrolysis process to compress a mixture of hydrogen and water or liquid electrolyte and simultaneously circulate water or liquid electrolyte in the process.

[0023] The water electrolysis process can be either a PEM, a liquid alkaline or an anion exchange membrane (AEM) electrolysis process. The functionality of the multiphase pump in the different processes is similar, with the main difference being the circulated liquid which in a PEM electrolyser is ultrapure, deionised water, in a liquid alkaline electrolyser is concentrated KOH and in an AEM electrolyser a dilute KOH solution (0.01-1 M KOH). In the present detailed description of the invention, embodiments of PEM electrolyser systems and an AEM or liquid alkaline electrolyser system will be described.

[0024] An integrated system is disclosed for the combined compression of hydrogen produced by an electrolyser as described above and circulation of water through the electrolyser using a multiphase pump, enabling a cost effective and energy efficient compression of hydrogen produced in an electrolysis process.

[0025] In one embodiment of the invention, shown in Fig.1, the system comprises a hydrogen gas/liquid separator 10, a PEM electrolyser stack 11 connected to the hydrogen gas/liquid separator 10 via a stack cathode inlet 14, a pressure control valve 13 on the connection between the hydrogen gas/liquid separator 10 and the PEM electrolyser stacks 11, a multiphase pump 12 with a compressor inlet 22 connected to a cathode outlet 15 of the PEM electrolyser stack 11 and a compressor outlet 23 connected to the hydrogen gas/liquid separator 10.

[0026] The stack cathode inlet 14 of the PEM electrolyser stack may be supplied with deionised water via the deionised water supply line 21 and the hydrogen gas/separator 10 via the pressure control valve 13 and a small amount of the supplied water is converted to oxygen in the anode compartment and hydrogen in the cathode compartment. Generally, the hydrogen gas is produced at a pressure level between ambient pressure (1bar) and 50 bar, depending on the PEM electrolyser stack and system design. In an embodiment of this invention the gas is produced at a pressure level between 1 and 10 bar. The remaining water acts as a coolant medium to remove excess heat formed in the electrochemical reaction and exits the PEM electrolyser stack 11 together with the produced hydrogen as a two-phase flow. The gas volume fraction in this two-phase flow can vary between 2-90%, depending on the operating conditions of the PEM electrolyser stack.

[0027] The two-phase flow consisting of hydrogen and water enters the hydrogen multiphase pump 12 where it is compressed to a higher pressure than the pressure at the electrolyser outlet. The level of this pressure can vary between 2 and 100 bar above the outlet pressure from the electrolyser stack, depending on the operating pressure of the PEM electrolyser stack and the desired design pressure of the hydrogen gas/liquid separator 10. In an embodiment of this invention, the outlet pressure from the multiphase pump 12 is between 4 and 50 bar above the outlet pressure from the electrolyser stack.

[0028] In another embodiment of the invention, shown in Fig 2, the system comprises one oxygen gas/liquid separator 20 and one hydrogen gas/liquid separator 10, a PEM electrolyser stack 11 connected to the first oxygen gas/liquid separator 20 via a stack anode inlet 16 and to a stack anode outlet 17, a multiphase pump 12 with compressor inlet 22 connected to a stack cathode outlet 15 of the PEM electrolyser stack 11 and a compressor outlet 23 connected to the hydrogen gas/liquid separator 10 and the pressure control valve 13 on the connection between the hydrogen gas/liquid separator 10 and the oxygen gas/liquid separator 20.

[0029] The anode inlet 16 of the PEM electrolyser stack 11 is supplied with deionised water from the oxygen gas/separator 20 and a small amount of the supplied water is converted to oxygen in the anode compartment and hydrogen in the cathode compartment. Generally, the hydrogen gas is produced at a pressure level between ambient pressure (1bar) and 50 bar, depending on the PEM electrolyser stack and system design. Some water (between 2 and 5 water molecules per proton, depending on membrane material and operating conditions) is also transferred through the membrane separating the anode compartment and the cathode compartment by electroosmosis. This water exits the cathode compartment of the PEM electrolyser stack 11 together with the produced hydrogen as a two-phase flow. The gas volume fraction in this two-phase flow can vary between 5-95%, depending on the operating conditions of the PEM electrolyser stack. The two-phase flow consisting of hydrogen and water enters the multiphase pump 12 where it is compressed to a pressure between 2 and 100 bar above the outlet pressure from the electrolyser stack. The level of this pressure depends on the operating pressure of the PEM electrolyser stack 11 and the desired design pressure of the hydrogen gas/liquid separator 10. In an embodiment of this invention, the outlet pressure from the multiphase compressor 12 is between 4 and 50 bar above the outlet pressure from the electrolyser stack.

[0030] In a third embodiment of the invention, shown in Fig 3, the system comprises a oxygen gas/liquid separator 20 and a hydrogen gas/liquid separator 10, an AEM or liquid alkaline electrolyser stack 11 connected to a liquid electrolyte pump 18 via a stack anode inlet 16 and a stack cathode inlet 14, the liquid electrolyte pump 18 connected to the oxygen gas/liquid separator 20 and the hydrogen gas/liquid separator 10 with a pressure control valve 13 on the connection between the hydrogen/gas liquid separator 10 and the pump inlet, a multiphase pump 12 with compressor inlet connected to a stack cathode outlet 15 of the one or more AEM or liquid alkaline electrolyser stack(s) 11 and a compressor outlet connected to the hydrogen gas/liquid separator 10.

[0031] The liquid pump inlet is supplied with electrolyte from both the oxygen gas/liquid separator 20 and the hydrogen gas/liquid separator 10, and the stack inlets are supplied with liquid electrolyte from the pump 18 and a small amount of the water in the electrolyte is converted to oxygen in the anode compartment and hydrogen in the cathode compartment.

[0032] The oxygen and hydrogen gas are produced at a pressure level between ambient pressure (1bar) and 50 bar, depending on the AEM or liquid alkaline electrolyser stack and system design. Liquid electrolyte exits the anode compartment of the AEM or liquid alkaline electrolyser stack 11 together with the produced oxygen as a two-phase flow and enters the oxygen gas/liquid separator 20.

[0033] Liquid electrolyte exits the cathode compartment of the AEM or liquid alkaline electrolyser stack 11 together with the produced hydrogen as a two-phase flow. The gas volume fraction in this two-phase flow can vary between 5-95%, depending on the operating conditions of the AEM or liquid alkaline electrolyser stack 11. The twophase flow consisting of hydrogen and water enters the multiphase pump 12 where it is compressed to a higher pressure. The level of this pressure can vary between 2 and 100 bar, depending on the operating pressure of the AEM or liquid alkaline electrolyser stack 11 and the desired design pressure of the hydrogen gas/liquid separator 10. In a preferred embodiment of this invention, the outlet pressure from the multiphase pump 12 is between 4 and 50 bar.

[0034] The multiphase pump compressor 12 used in the described embodiments, can be of any design and can consist of one or more compression stages, depending on the desired total compression ratio over the complete compressor. Twin-screw, helicoaxial progressing-cavity or centric reciprocating pumps are examples of multiphase pumps.

[0035] In a PEM electrolysis process, at least one pressure control valve controls supply of deionised water to at least one electrolyser stack. In a liquid alkaline or an anion exchange membrane (AEM) electrolysis process, at least one pressure control valve controls supply of liquid electrolyte (concentrated or diluted KOH) to at least one electrolyser stack.

[0036] Advantages:

[0037] The use of a multiphase pump downstream of a PEM electrolyser stack in the PEM electrolyser process instead of a conventional single phase water pump upstream of the PEM electrolyser stack provides several advantages over state of the art. For example, the compression of hydrogen in a hydrogen/water two phase mixture enables a close to isothermal compression of the gas due to the cooling effect of the water present. In a conventional PEM electrolyser process, the hydrogen compression takes place outside the integrated PEM electrolysis process, after the separation of water and gas, and the compression process will be close to an adiabatic compression. As shown in Fig 4, the energy use in an isothermal compression process is significantly lower than in an adiabatic process, thus the use of a multiphase compressor will reduce the overall energy consumption of the process.

[0038] Another advantage is that the multiphase compressor replaces two other process equipment, namely the conventional single-phase liquid pump and the single phase hydrogen gas compressor, reducing the overall complexity, cost and service requirements of the system.

List of figure reference signs

Claims

1. A water electrolyser system for production of compressed hydrogen, comprising

an electrolyser stack;

a multiphase pump arranged downstream of the electrolyser stack; and

a hydrogen gas/liquid separator;

wherein the multiphase pump is arranged between the electrolyser stack and the hydrogen gas/liquid separator.

2 The water electrolyser system of claim 1, further comprising a control valve controlling supply of water or liquid electrolyte to the electrolyser stack.

3. The water electrolyser system of claim 1 or 2, wherein the electrolyser stack comprises a PEM, AEM or liquid alkaline electrolyser stack.

4. The water electrolyser system of any of claims 1 to 3, wherein the electrolyser stack comprises a plurality of polymer electrolyte membrane water electrolyser cells, each water electrolyser cell comprises an anode compartment, a cathode compartment and a polymer electrolyte membrane; the cathode compartment is configured to be supplied with deionised water through a stack cathode inlet, and

the anode compartment is configured to be supplied with air through a stack anode inlet.

5. The water electrolyser system of claim 4, wherein the control valve is arranged between the hydrogen gas/liquid separator and the stack cathode inlet.

6. The water electrolyser system of claim 4 or 5, wherein a humidifier provides humidified air to the anode compartment.

7. The water electrolyser system of any of claims 1 to 3, wherein the electrolyser stack comprises a plurality of polymer electrolyte membrane water electrolyser cells, each water electrolyser cell comprises an anode compartment, a cathode compartment;

the anode compartment is configured to be supplied with deionised water through a stack anode inlet;

the cathode compartment comprises a cathode outlet where a mixture of produced hydrogen and entrained water exits.

8. The water electrolyser system of claim 7, further comprising an oxygen gas/liquid separator separating a mixture of water and produced oxygen.

9. The water electrolyser system of claim 2, wherein the control valve is arranged between the hydrogen gas/liquid separator and the oxygen gas/liquid separator.

10. Method for production of compressed hydrogen in a water electrolyser system, including:

supplying water or liquid electrolyte to an electrolyser stack; producing hydrogen in an electrolyser stack;

compressing a mixture of produced hydrogen and entrained water or liquid electrolyte in a multiphase pump; and

separating the compressed mixture of produced hydrogen and entrained water or liquid electrolyte in a hydrogen gas/liquid separator.

11. The method of claim 10, wherein the outlet pressure from the multiphase compressor is between 2 and 100 bar, preferably between 4 and 50 bar, above the outlet pressure from the electrolyser stack.

12 The method of claim 10 or 11, wherein the gas volume fraction in the mixture of produced hydrogen and water or liquid electrolyte is within the range 5 to 95%.

13. The method of any of claims 10 to 12, further comprising

circulating water or liquid electrolyte from the hydrogen gas/liquid separator via a control valve to a stack cathode inlet of the electrolyser stack.

14. The method of any of claims 10 to 12, further comprising controlling supply of water or liquid electrolyte from the hydrogen gas/liquid separator via a control valve to an oxygen gas/ liquid separator.