Water electrolysis system and method for producing compressed hydrogen gas
By integrating a multiphase pump downstream of the water electrolyzer to compress a mixture of hydrogen and deionized water or liquid electrolyte, the high energy consumption and high cost of existing hydrogen compression methods are solved, achieving efficient and safe hydrogen compression and system simplification.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HESTAR CO LTD
- Filing Date
- 2024-09-05
- Publication Date
- 2026-06-02
AI Technical Summary
Existing hydrogen compression technology suffers from high energy consumption and high cost. In particular, when hydrogen is compressed under high pressure, traditional compressors pose safety hazards and have high energy requirements. Existing systems are difficult to integrate efficiently with water electrolyzers for hydrogen compression.
A hydrogen production system is integrated downstream of a water electrolyzer using a multiphase pump. The multiphase pump compresses a mixture of hydrogen and deionized water or liquid electrolyte, and a gas-liquid separator is used to achieve efficient hydrogen compression. Deionized water or liquid electrolyte is circulated during the electrolysis process.
Isothermal compression of hydrogen was achieved, reducing energy consumption, simplifying system structure, lowering costs and maintenance requirements, and improving safety.
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Abstract
Description
Technical Field
[0001] The present invention generally relates to hydrogen production and processing systems, and more specifically to enhancing the performance of integrated hydrogen production and processing systems including a water electrolysis system and a compression subsystem for hydrogen production. Background Technology
[0002] Water electrolysis systems used for hydrogen production include alkaline water electrolysis (AWE), proton exchange membrane electrolysis (PEM), solid oxide electrolysis (SOEC), and anion exchange membrane electrolysis (AEM). All technologies involve a single water electrolysis cell comprising an anode and a cathode, as well as a diaphragm, membrane, or electrolyte. AWE systems use a liquid alkaline electrolyte solution and a diaphragm. AEM systems use a less alkaline liquid electrolyte and an anion exchange membrane. PEM systems do not contain a liquid electrolyte; instead, they use deionized water and a polymer electrolyte membrane, also known as a proton exchange membrane (PEM).
[0003] The development of infrastructure for the low-cost distribution, transport, storage, and use of hydrogen depends on cost-effective and energy-efficient hydrogen compression. Hydrogen is one of the most difficult gases to compress due to its low molecular weight and small size. Various compressors are available, but the final choice of compression technology, associated costs, and energy usage will depend on its location within the supply chain.
[0004] Mechanical compressors are widely used and are designed to directly convert mechanical energy into the energy to compress gas. There are several classifications, but most compressors currently used for compressing gaseous hydrogen are either positive displacement compressors or dynamic compressors.
[0005] Centrifugal compressors are examples of dynamic compressors, most commonly used in applications requiring high flow rates and moderate compression ratios. Centrifugal compressors use a rotating impeller with radial blades to compress process gases, imparting kinetic energy to the gas by increasing its velocity. Unlike reciprocating compressors, the compression ratio in a centrifugal compressor depends heavily on the molecular weight of the gas. Due to the low molecular weight of H2, compared to, for example, compressed natural gas, the impeller velocity must be increased or an additional compression stage added. Increasing current impeller tip velocities is extremely challenging due to material strength limitations and H2 embrittlement issues.
[0006] Reciprocating piston compressors are ideal for low to medium flow and high pressure applications. They are positive displacement machines that operate by compressing and discharging gases. Single-stage reciprocating compressors employ a piston and system design where the piston is driven by a crankshaft, converting rotary motion into linear motion. The cylinder uses two automatic valves—one for intake and one for exhaust—and the energy required for compression is provided by a power source or heat source.
[0007] Another method for producing hydrogen at high pressure for use or storage is through direct water electrolysis at the desired pressure, simultaneously producing hydrogen and oxygen. Alternatively, differential pressure electrolysis can be used, producing hydrogen at high pressure and oxygen at near atmospheric pressure. In state-of-the-art proton exchange membrane (PEM) electrolyzers, a low-pressure pump supplies liquid water at near atmospheric pressure to the anode side of the electrolyzer stack. When direct current is applied, the water is decomposed at the anode into oxygen, protons, and electrons. The oxygen is separated from excess circulating water in a low-pressure gas / water separator. All functions on the anode side are typically performed at near atmospheric pressure. Protons, along with some water, are electrochemically transported through the membrane to the cathode, where they react with externally supplied electrons to produce hydrogen at the required higher operating pressure. The hydrogen is then separated from the supplied water in a high-pressure gas / water separator. After hydrogen and water separation, the hydrogen can be further compressed in a single-phase compressor outside the integrated PEM electrolysis process. The separated water is reintroduced into the electrolysis process.
[0008] To date, high-pressure water electrolyzers have been manufactured, which either simultaneously produce hydrogen and oxygen at pressures up to 200 bar, or produce hydrogen at 200 bar and oxygen at near atmospheric pressure. For example, U.S. Patent 8282811B2 discloses a water electrolyzer that uses a plastic material as a frame and a proton exchange membrane (PEM) as a solid polymer electrolyte, operating at a pressure differential of 2500 psia (H2>O2). However, electrolyzers operating fully or partially at these high pressures are expensive, structurally complex, and pose safety hazards due to the high risk of hydrogen leakage. Such electrolyzers providing outlet pressures above 40 bar have not yet achieved commercial success. Therefore, most PEM electrolyzer manufacturers currently offer electrolyzers with hydrogen output pressures between 15 and 40 bar. Even at these pressures, a significant amount of hydrogen diffuses from the cathode chamber to the anode chamber, resulting in the formation of an H2 / O2 gas mixture in the anode chamber. This hydrogen cross-permeation phenomenon necessitates the use of thicker membranes (>50 μm) to limit the amount of hydrogen mixed with oxygen, thereby preventing the formation of flammable or explosive gas mixtures. Using thicker membranes increases costs and leads to higher ohmic resistance in a single PEM electrolysis cell, thus increasing the energy requirements of the electrolysis process.
[0009] In conventional electrolyzer processes, any additional hydrogen compression exceeding the operating pressure of the water electrolyzer stack is carried out outside the electrolysis process, i.e., after liquid-hydrogen separation in the separator vessel, using a conventional single-phase compressor or wet gas compressor. In addition to the compressor, the process may also include a buffer tank and / or a gas dryer before the compressor.
[0010] Compared to other gases such as natural gas, the energy required to compress hydrogen is relatively high. To adiabatically compress hydrogen from 1 bar to 200 bar, approximately 10 MJ / kg of energy is required, or about 10% of the energy content of the compressed hydrogen. In contrast, ideal isothermal compression requires only about 6 MJ / kg.
[0011] As hydrogen compression presents technical challenges and high energy requirements as described above, there is a need in the art for improved systems and methods to simultaneously compress hydrogen in conjunction with electrolyzer production.
[0012] Multiphase pumps are used in many different industries where it is necessary to transport or compress multiphase process fluids that consist of mixtures of multiple phases, such as liquid and gas phases. A multiphase pump is essentially a hybrid of a pump and a compressor, and is therefore also referred to as a multiphase compressor. In this disclosure, the term "multiphase pump" will be used. The proportion of the gas phase in a multiphase mixture is typically measured by the dimensionless gas volume fraction (GVF), which represents the volume ratio of gas in the multiphase process fluid. Multiphase pumps can be designed to transport multiphase process fluids with GVFs ranging from close to 0% to close to 100%, i.e., all process fluids from pure liquid (GVF = 0%) to pure gas (GVF = 100%). Summary of the Invention
[0013] According to a first aspect of the present invention, a water electrolysis system for producing hydrogen is provided, comprising an electrolyzer stack, a multiphase pump disposed downstream of the electrolyzer stack, and a hydrogen gas-liquid separator, wherein the multiphase pump is disposed between the water electrolyzer stack and the hydrogen gas-liquid separator.
[0014] In one embodiment, the water electrolyzer stack includes a PEM water electrolyzer stack comprising multiple proton exchange membrane (PEM) water electrolyzer cells, each PEM water electrolyzer cell including an anode chamber, a cathode chamber, and a proton exchange membrane; the cathode chamber is configured to be supplied with deionized water through a stack cathode inlet, and the anode chamber is configured to be supplied with air through a stack anode inlet. In this embodiment, a control valve is provided between a hydrogen gas-liquid separator and the stack cathode inlet for controlling the supply of deionized water to the PEM water electrolyzer stack. A humidifier is not required, but it may be included to provide humidified air to the anode chamber.
[0015] In another embodiment, the PEM water electrolyzer stack includes multiple proton exchange membrane water electrolyzer cells, each including an anode chamber and a cathode chamber. The anode chamber is configured to supply deionized water through a stack anode inlet. The cathode chamber includes a cathode outlet through which a mixture of generated hydrogen and entrained water is discharged. This embodiment also includes an oxygen gas-liquid separator for separating the mixture of water and generated oxygen. In this embodiment, at least one control valve is provided between the hydrogen gas-liquid separator and the oxygen gas-liquid separator to control the supply of deionized water to the PEM water electrolyzer stack.
[0016] In another embodiment, the water electrolyzer stack includes an AEM water electrolyzer stack or an AWE water electrolyzer stack, and a pump for supplying liquid alkaline electrolyte to the AEM water electrolyzer stack or the AWE water electrolyzer stack.
[0017] According to a second aspect of the present invention, a method for producing hydrogen in a water electrolysis system is provided, the method comprising: supplying water or liquid electrolyte to a water electrolyzer stack; producing hydrogen in the water electrolyzer stack; compressing the produced hydrogen and a mixture of entrained deionized water or liquid electrolyte in a multiphase pump; and performing gas-liquid separation of the compressed produced hydrogen and the entrained deionized water or liquid electrolyte in a hydrogen gas-liquid separator.
[0018] In one embodiment of the method, the outlet pressure of the multiphase pump is 2 to 100 bar higher than the outlet pressure of the electrolyzer stack, preferably 4 to 50 bar higher. The gas volume fraction in the mixture of the generated hydrogen and deionized water or liquid electrolyte is in the range of 5% to 95%. The deionized water or liquid electrolyte can be circulated from the hydrogen gas-liquid separator to the water electrolyzer stack via a control valve. Attached Figure Description
[0019] Figure 1 A schematic diagram of one embodiment of a PEM water electrolysis system for hydrogen production is shown.
[0020] Figure 2 Another schematic diagram of one embodiment of a PEM water electrolysis system for hydrogen production is shown.
[0021] Figure 3 A schematic diagram of anion exchange membrane or liquid alkaline water electrolysis system for hydrogen production is shown.
[0022] Figure 4 Another configuration of an anion exchange membrane or liquid alkaline water electrolysis system for hydrogen production is shown.
[0023] Figure 5 The energy required to compress hydrogen from ambient conditions to different final pressures is shown. Detailed Implementation
[0024] This invention relates to the use of a multiphase pump integrated into a water electrolysis process for compressing a mixture of hydrogen gas and deionized water or liquid electrolyte, while simultaneously circulating the deionized water or liquid electrolyte in the process.
[0025] Water electrolysis can be a proton exchange membrane (PEM), liquid alkaline (AWE), or anion exchange membrane (AEM) electrolysis process. The multiphase pump functions similarly in different processes, with the main difference being: the circulating liquid in a PEM electrolyzer is ultrapure deionized water; the liquid electrolyte in a liquid alkaline water electrolyzer is an aqueous alkaline electrolyte solution, typically concentrated potassium hydroxide (25-30 wt% KOH); and the liquid electrolyte in an AEM electrolyzer is an aqueous alkaline electrolyte solution, typically a dilute KOH solution (0.01-1 wt%). In specific embodiments of this invention, examples of PEM water electrolysis systems and AEM or liquid alkaline water electrolysis systems will be described.
[0026] An integrated system is disclosed for the combined compression of hydrogen produced by the aforementioned electrolyzer stack, and for the use of a multiphase pump to circulate deionized water or liquid electrolyte in the water electrolyzer stack, thereby enabling the economical and efficient compression of hydrogen produced during electrolysis.
[0027] In one embodiment of the present invention, such as Figure 1 As shown, the system includes a hydrogen gas-liquid separator 10, a PEM water electrolyzer stack 11 connected to the hydrogen gas-liquid separator 10 via a stack cathode inlet 14, a pressure control valve 13a located on the connecting pipeline between the hydrogen gas-liquid separator 10 and the PEM water electrolyzer stack 11, and a multiphase pump 12. The pump inlet 22 of the multiphase pump 12 is connected to the cathode outlet 15 of the PEM water electrolyzer stack 11, and the pump outlet 23 is connected to the hydrogen gas-liquid separator 10.
[0028] The cathode inlet 14 of the PEM water electrolyzer stack is supplied with deionized water via a deionized water supply line 21 and a hydrogen / liquid separator 10, through a pressure control valve 13a. A small portion of the supplied water is converted into oxygen in the anode chamber and into hydrogen in the cathode chamber. Air is supplied through the anode inlet 16. A humidifier 19 is not required, but may be included to supply humidified air to the anode chamber. A mixture of humidified oxygen and air can be led from the anode outlet 17 to the humidifier 19. Typically, hydrogen is generated at pressure levels between ambient pressure (1 bar) and 50 bar, depending on the design of the PEM water electrolyzer stack and system. In one embodiment of the invention, the gas is generated at pressure levels between 1 bar and 10 bar. The remaining water is used as a cooling medium to remove excess heat generated in the electrochemical reaction and is discharged from the PEM water electrolyzer stack 11 as a two-phase flow along with the generated hydrogen. The gas volume fraction in this two-phase flow can vary between 2% and 90% depending on the operating conditions of the PEM water electrolyzer stack.
[0029] A two-phase flow consisting of hydrogen and deionized water enters the hydrogen multiphase pump 12, where it is compressed to a pressure higher than that at the reactor cathode outlet 15. This pressure level can vary from 1 bar to 100 bar higher than the outlet pressure of the electrolyzer reactor, depending on the operating pressure of the PEM water electrolyzer reactor and the desired design pressure of the hydrogen gas-liquid separator 10. In one embodiment of the invention, the outlet pressure of the multiphase pump 12 is 4 bar to 50 bar higher than the outlet pressure of the electrolyzer reactor.
[0030] In another embodiment of the invention, such as Figure 2 As shown, the system includes an oxygen gas-liquid separator 20 and a hydrogen gas-liquid separator 10, a PEM water electrolyzer stack 11 connected to the oxygen gas-liquid separator 20 via a stack anode inlet 16 and connected to the stack anode outlet 17, a multiphase pump 12 (pump inlet 22 connected to the stack cathode outlet 15 of the PEM water electrolyzer stack 11 and pump outlet 23 connected to the hydrogen gas-liquid separator 10), and a pressure control valve 13b located on the connecting pipeline between the hydrogen gas-liquid separator 10 and the oxygen gas-liquid separator 20.
[0031] The anode inlet 16 of the PEM water electrolyzer stack 11 is supplied with deionized water from the oxygen gas-liquid separator 20 via pump 18a, and a small portion of the supplied water is converted into oxygen in the anode chamber and into hydrogen in the cathode chamber. The deionized water is supplied via supply line 21. Typically, hydrogen is generated at pressure levels between ambient pressure (1 bar) and 50 bar, depending on the design of the PEM water electrolyzer stack and system. Some water (2 to 5 water molecules per proton, depending on the membrane material and operating conditions) also migrates through the membrane separating the anode and cathode chambers via electroosmosis. This water, along with the generated hydrogen, is discharged from the cathode chamber of the PEM water electrolyzer stack 11 as a two-phase flow. The gas volume fraction in this two-phase flow can vary between 5% and 95% depending on the operating conditions of the PEM electrolyzer stack. The two-phase flow consisting of hydrogen and deionized water enters the multiphase pump 12, where it is compressed to a pressure 1 to 100 bar higher than the outlet pressure of the PEM water electrolyzer stack 11. The pressure level depends on the operating pressure of the PEM water electrolyzer stack 11 and the desired design pressure of the hydrogen gas-liquid separator 10. In one embodiment of the invention, the outlet pressure of the multiphase pump 12 is 4 to 50 bar higher than the outlet pressure of the PEM water electrolyzer stack 11. Water entering the hydrogen gas-liquid separator 10 from the multiphase pump 12 is reinjected into the oxygen gas-liquid separator via a pressure control valve 13b and a fluid connection line 24. This fluid connection line may optionally include a dedicated degassing chamber for removing dissolved hydrogen from the water before it enters the oxygen gas-liquid separator 20.
[0032] In the third embodiment of the present invention, as Figure 3 As shown, the system includes an oxygen gas-liquid separator 20 and a hydrogen gas-liquid separator 10, an anion exchange membrane or liquid alkaline water electrolyzer stack 11 connected to a liquid electrolyte pump 18b via anode inlet 16 and cathode inlet 14, a liquid electrolyte pump 18b connected to the oxygen gas-liquid separator 20 and the hydrogen gas-liquid separator 10 (with a pressure control valve 13c on the connecting line between the hydrogen gas-liquid separator 10 and the liquid electrolyte pump inlet), and a multiphase pump 12 (pump inlet 22 connected to the cathode outlet 15 of the one or more AEMs or liquid alkaline water electrolyzer stacks 11, and compressor outlet 23 connected to the hydrogen gas-liquid separator 10). A water supply line 21 supplies deionized water to the oxygen gas-liquid separator 20.
[0033] Electrolytes are supplied from oxygen gas-liquid separator 20 and hydrogen gas-liquid separator 10 to the liquid pump inlet, and liquid electrolytes are supplied from pump 18b to the stack anode inlet 16 and cathode inlet 14. A small amount of water in the electrolyte is converted into oxygen in the anode chamber and into hydrogen in the cathode chamber.
[0034] Oxygen and hydrogen are generated at pressure levels between ambient pressure (1 bar) and 50 bar, depending on the design of the AEM or liquid alkaline water electrolyzer stack and system. The liquid electrolyte, along with the generated oxygen, is discharged in a two-phase flow from the anode chamber of the AEM or liquid alkaline water electrolyzer stack 11 and enters the oxygen gas-liquid separator 20.
[0035] The liquid electrolyte, along with the generated hydrogen, is discharged from the cathode chamber of the AEM or liquid alkaline water electrolyzer stack 11 as a two-phase flow. Depending on the operating conditions of the AEM or liquid alkaline water electrolyzer stack 11, the gas volume fraction in this two-phase flow can vary between 5% and 95%. The two-phase flow consisting of hydrogen and liquid electrolyte enters the multiphase pump 12, where it is compressed to a higher pressure. This pressure level can vary between 2 bar and 100 bar, depending on the operating pressure of the AEM or liquid alkaline water electrolyzer stack 11 and the desired design pressure of the hydrogen gas-liquid separator 10. In a preferred embodiment of the invention, the outlet pressure of the multiphase pump 12 is between 4 bar and 50 bar.
[0036] The multiphase pump / compressor 12 used in the embodiments can be of any design and can consist of one or more compression stages depending on the total compression ratio required for the entire compressor. Examples of multiphase pumps that can be used include twin-screw pumps, helical axial flow pumps, progressive cavity pumps, or center reciprocating pumps.
[0037] During PEM electrolysis, at least one pressure control valve (13a, 13b) controls the supply of deionized water to at least one electrolytic cell stack. During liquid alkaline or anion exchange membrane (AEM) electrolysis, at least one pressure control valve (13c) controls the supply of liquid electrolyte (concentrated or dilute KOH) to at least one electrolytic cell stack.
[0038] exist Figure 4 The figure illustrates an alternative configuration for a liquid alkaline or anion exchange membrane electrolysis process. The cathode inlet 14 and anode inlet 16 of the water electrolyzer stack are separate, and pump 18c circulates the liquid electrolyte to the anode side of the AWE or AEM water electrolyzer stack 11. Furthermore, a balancing line 25 exists between the anode inlet 16 and the cathode inlet 14, which serves to balance the electrolyte concentration difference between the anode and cathode sides. Other reference numerals in this figure are consistent with... Figure 3 The corresponding reference numerals in the attached figures correspond to each other.
[0039] In all the above embodiments, but not shown in the figures, more than one water electrolysis cell stack can be used.
[0040] Advantages of this invention: In the PEM water electrolyzer process, using a multiphase pump downstream of the PEM water electrolyzer stack, instead of the traditional single-phase water pump upstream, offers several advantages over existing technologies. For example, when compressing hydrogen in a hydrogen / water two-phase mixture, the cooling effect of the water allows for near-isothermal compression: the high mass fraction of water in the two-phase mixture enables it to absorb the heat generated during gas compression, while the temperature rises only slightly due to water's higher heat capacity.
[0041] In traditional PEM electrolyzer processes, hydrogen compression occurs outside the integrated PEM electrolysis process, after water and gas separation, and the compression process is close to adiabatic compression. For example... Figure 5 As shown, the energy used in isothermal compression is significantly lower than that in adiabatic compression, therefore using a multiphase pump will reduce the overall energy consumption of this process.
[0042] Another advantage is that multiphase pumps replace two other process equipment, namely traditional single-phase liquid pumps and single-phase hydrogen compressors, reducing the overall complexity, cost and maintenance requirements of the system.
[0043] List of reference numerals
Claims
1. A water electrolysis system for producing compressed hydrogen, characterized in that, include Water electrolysis cell stack; A multiphase pump located downstream of the water electrolyzer stack; and Hydrogen gas-liquid separator; The multiphase pump is located between the water electrolyzer stack and the hydrogen gas-liquid separator.
2. The water electrolysis system according to claim 1, characterized in that, The water electrolyzer stack includes a proton exchange membrane (PEM) water electrolyzer stack, an anion exchange membrane (AEM) water electrolyzer stack, or a liquid alkaline (AWE) water electrolyzer stack.
3. The water electrolysis system according to claim 1 or 2, characterized in that, The water electrolyzer stack includes a PEM water electrolyzer stack, which includes multiple PEM water electrolyzer cells, each of which includes an anode chamber, a cathode chamber, and a proton exchange membrane. The cathode chamber is configured to supply deionized water through the stack cathode inlet, and The anode chamber is configured to be supplied with air through the stack anode inlet.
4. The water electrolysis system according to claim 3, characterized in that, A control valve for controlling the supply of deionized water to the cathode chamber is provided between the hydrogen gas-liquid separator and the cathode inlet.
5. The water electrolysis system according to claim 1 or 2, characterized in that, The water electrolyzer stack includes a PEM water electrolyzer stack, which includes multiple proton exchange membrane water electrolyzer cells, each water electrolyzer cell including an anode chamber and a cathode chamber; The anode chamber is configured to supply deionized water through the stack anode inlet; and The cathode chamber includes a cathode outlet through which a mixture of generated hydrogen gas and entrained deionized water is discharged.
6. The water electrolysis system according to claim 5, characterized in that, It also includes an oxygen gas-liquid separator, which is used to separate the mixture of water and generated oxygen into gas and liquid components.
7. The water electrolysis system according to claim 5 or 6, characterized in that, A control valve for controlling the supply of deionized water to the anode is provided between the hydrogen gas-liquid separator and the oxygen gas-liquid separator.
8. The water electrolysis system according to claim 1 or 2, characterized in that, The water electrolyzer stack includes an AEM water electrolyzer stack or an AWE water electrolyzer stack, and a pump for supplying liquid alkaline electrolyte to the AEM water electrolyzer stack or the AWE water electrolyzer stack.
9. A method for producing compressed hydrogen in a water electrolysis system, characterized in that, include: Supply deionized water or liquid electrolyte to the water electrolyzer stack; Hydrogen is produced in the water electrolyzer stack. A mixture of hydrogen gas produced by compression in a multiphase pump and entrained deionized water or liquid electrolyte; and In a hydrogen gas-liquid separator, the compressed hydrogen gas and the entrained mixture of deionized water or liquid electrolyte are separated into gas and liquid components.
10. The method according to claim 9, characterized in that, The water electrolyzer stack includes a proton exchange membrane (PEM) water electrolyzer stack, an anion exchange membrane (AEM) water electrolyzer stack, or a liquid alkaline (AWE) water electrolyzer stack.
11. The method according to claim 9 or 10, characterized in that, The outlet pressure of the multiphase pump is 2 to 100 bar higher than the outlet pressure of the water electrolyzer stack, preferably 4 to 50 bar higher.
12. The method according to any one of claims 9 to 11, characterized in that, The volume fraction of the generated hydrogen gas in the mixture with deionized water or liquid electrolyte is in the range of 5% to 95%.
13. The method according to any one of claims 9 to 12, characterized in that, Also includes Deionized water or liquid electrolyte from the hydrogen gas-liquid separator is circulated to the water electrolysis tank stack through a control valve.