Electrolysis hydrogen production low load and parking safe operation process
By diluting the hydrogen and oxygen concentrations during low-load operation of the electrolyzer and diluting and recovering the gases before and after shutdown, the safety and economic issues of the water electrolysis hydrogen production system are solved, achieving higher electrolyzer safety and economic benefits.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SICHUAN GUANJUE CONSTRUCTION TECHNOLOGY CO LTD
- Filing Date
- 2026-04-09
- Publication Date
- 2026-05-29
AI Technical Summary
When the water electrolysis hydrogen production system is running at low load, the cross-permeation of hydrogen and oxygen is severe, which increases the risk of explosion. When the system is shut down, the reverse current affects the life of the electrodes and causes frequent shutdowns, resulting in economic losses and waste of resources.
During low-load operation, preheated circulating hydrogen and circulating oxygen are introduced into the hydrogen and oxygen sides of the electrolyzer to dilute the concentration of impurity gases. The concentration of gases generated by reverse current is diluted before and after shutdown. The gases in the separator are recovered before maintenance, and nitrogen is used for safe replacement and recovery.
It improves the safety of the electrolyzer under low load and the utilization rate of off-grid electricity, reduces the number of downtimes and electrode replacement frequency, saves nitrogen consumption and energy loss, and enhances the economy and safety of the water electrolysis hydrogen production system.
Smart Images
Figure CN122105519A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of water electrolysis hydrogen production technology, specifically to a low-load and safe shutdown operation process for water electrolysis hydrogen production. Background Technology
[0002] In water electrolysis for hydrogen production, medium-pressure alkaline electrolyzers are the most widely used. However, when the electrolyzer operates at low load, the cross-permeability between hydrogen and oxygen increases, leading to a significant increase in either the hydrogen concentration in the oxygen or the oxygen concentration in the hydrogen. When the load drops to a certain level, the hydrogen concentration in the oxygen, in particular, can easily reach the explosive limit, seriously threatening the safe operation of the electrolyzer. Several explosions caused by electrolyzers operating at low loads have occurred in China. To ensure safety, the industry typically sets the minimum safe load for hydrogen production in electrolyzers (safe load generally refers to the oxygen concentration in hydrogen being below 50% of the lower explosive limit, or the hydrogen concentration in oxygen being below 50% of the lower explosive limit) to no less than 20%. For systems using off-grid power such as wind and solar power for hydrogen production, the safety risks of low-load operation are even more pronounced due to the intermittent and unstable nature of the power source itself. As hydrogen production pressure increases, the minimum safe load also increases. When further pressurization of hydrogen is required, it is desirable to have even higher hydrogen production pressure. Currently, for hydrogen production pressures below 3.0 MPa, the minimum load of off-grid hydrogen production systems is usually set to no less than 30%. If the pressure is higher than 3.0 MPa, the minimum load of off-grid hydrogen production systems will be greater than 30%, which will further reduce the off-grid power utilization rate and the efficiency of hydrogen production.
[0003] Furthermore, the electrolyzer generates reverse current during shutdown, severely impacting electrode lifespan. Frequent shutdowns accelerate electrode aging; typically, after 10 shutdowns, the electrode coating shows significant peeling, leading to decreased electrolysis efficiency and necessitating electrode replacement. Simultaneously, the reverse current can generate oxygen on the hydrogen side or hydrogen on the oxygen side, affecting the safe operation of the electrolyzer. In off-grid hydrogen production scenarios, multiple electrolyzers are often used to form a unit. When grid power is insufficient, the common practice is to operate some units at minimum load while the remaining units are completely shut down. For example, in a 500MW off-grid hydrogen production project using wind power, a unit with a hydrogen production capacity of 10,000 Nm³ / h is configured, with 10 units, each equipped with 5 electrolyzers. When wind power generation drops to 15MW, only one unit operates at the minimum load of 30%, while the other nine units are shut down. When wind power falls below 15MW, all units are unable to operate, resulting in significant wind curtailment. If wind power generation time is less than 15MW for 1500 hours per year, averaging 10MW, then the annual wind power curtailment will reach 150 million kWh. At 0.2 yuan / kWh, the economic loss will reach 30 million yuan. Meanwhile, each electrolyzer will shut down approximately 20 times per year, requiring electrode replacement twice, with each replacement costing approximately 500,000 yuan, resulting in an annual cost of 1 million yuan per unit and a total project cost of approximately 50 million yuan, indicating extremely high operation and maintenance costs.
[0004] Meanwhile, after the electrolyzer shuts down, the reverse current will generate oxygen on the hydrogen side or hydrogen on the oxygen side. Simultaneously, the hydrogen and oxygen remaining in the electrolyte will slowly escape into the gas phase space of the separator, causing the concentration of hydrogen in oxygen or oxygen in hydrogen to gradually increase, approaching the explosion limit. To ensure shutdown safety, current technology typically involves opening the vent valve and purging the system with nitrogen after 6 hours of shutdown, followed by venting the mixed gas. Taking the above project as an example, each electrolyzer separator has a gas phase volume of 2 m³, an operating pressure of 1.6 MPa, and experiences more than 20 shutdowns per year due to low airflow. Each unit vents approximately 32 Nm³ of hydrogen per cycle, totaling 640 Nm³ annually. For all 10 units, this amounts to 32,000 Nm³ of hydrogen vented, with the same amount of oxygen vented. The amount of nitrogen used for purging is approximately five times the amount of exhaust gas, consuming 320,000 Nm³ of nitrogen annually. Based on a cost of 1.5 yuan / Nm³ for hydrogen, 0.5 yuan / Nm³ for oxygen, and 0.2 yuan / Nm³ for nitrogen, the annual loss is approximately 160,000 yuan. Furthermore, the losses caused by purging and releasing gas before annual maintenance are even more severe.
[0005] Therefore, there is an urgent need to provide a low-load and safe shutdown operation process for hydrogen production by water electrolysis in order to solve the above problems. Summary of the Invention
[0006] The purpose of this invention is to overcome the shortcomings and defects of the prior art and provide a low-load and safe operation process for hydrogen production by water electrolysis, which increases the hydrogen production pressure of the electrolyzer, reduces the hydrogen production load of the electrolyzer, improves the off-grid power utilization rate, reduces the number of shutdowns, extends electrode life, and simultaneously realizes the recovery and utilization of hydrogen and oxygen, thereby improving the safety and economy of the water electrolysis hydrogen production system.
[0007] The objective of this invention is achieved through the following technical solution: A process for safe operation of hydrogen production via water electrolysis under low load and shutdown conditions includes the following steps: S1: When the load rate of the electrolyzer is lower than a certain load, a certain flow rate of circulating oxygen is introduced into the oxygen side of the electrolyzer after exchanging heat with the electrolyte, so that the hydrogen concentration on the oxygen side is lower than the safe value of the lower explosive limit; at the same time, a certain flow rate of circulating hydrogen is introduced into the hydrogen side of the electrolyzer after exchanging heat with the electrolyte, so that the oxygen concentration on the hydrogen side is lower than the safe value of the lower explosive limit. S2: Before and for a period of time after the electrolyzer is shut down, a certain amount of circulating oxygen is introduced into the oxygen side of the electrolyzer to dilute the hydrogen concentration generated by the reverse current during shutdown. At the same time, the hydrogen dissolved in the electrolyte escapes with the oxygen and enters the downstream oxygen system from the oxygen separator, ensuring that the hydrogen concentration on the oxygen side of the electrolyzer is below the lower explosive limit. Simultaneously, a certain amount of circulating hydrogen is introduced into the hydrogen side of the electrolyzer to dilute the oxygen concentration generated by the reverse current during shutdown. At the same time, the oxygen dissolved in the electrolyte escapes with the hydrogen and enters the downstream hydrogen system from the hydrogen separator, ensuring that the oxygen concentration on the hydrogen side of the electrolyzer is below the lower explosive limit. S3: Recovery and inerting before shutdown and maintenance; Before the electrolyzer is shut down for maintenance, nitrogen is introduced into the oxygen-side outlet pipe and the hydrogen-side outlet pipe of the electrolyzer to replace and recover the hydrogen in the oxygen separator or the oxygen in the hydrogen separator. Nitrogen is then introduced to purge the electrolyzer until the hydrogen concentration or oxygen concentration is lower than the safety threshold.
[0008] Optionally, in step S1, the heat exchange between the circulating hydrogen or circulating oxygen and the electrolyte is a wall-type heat exchange, and after the heat exchange, the temperature of the circulating gas rises to a value within a preset range that is within the difference between the temperature of the circulating gas and the operating temperature of the electrolyzer.
[0009] Optionally, in step S1, the amount of circulating hydrogen or circulating oxygen added is related to the operating pressure and minimum load rate of the electrolyzer. The higher the operating pressure of the electrolyzer and the lower the minimum load rate, the greater the amount of circulating oxygen or circulating hydrogen added; the lower the operating pressure of the electrolyzer and the higher the minimum load rate, the smaller the amount of circulating oxygen or circulating hydrogen added.
[0010] Optionally, in step S2, the amount of circulating hydrogen or circulating oxygen introduced is related to the electrolyzer pressure and the gas phase volume of the separator. The higher the electrolyzer pressure, the larger the gas phase volume of the separator, and the greater the amount of circulating hydrogen or circulating oxygen introduced; the lower the electrolyzer pressure, the smaller the gas phase volume of the separator, and the smaller the amount of circulating hydrogen or circulating oxygen introduced.
[0011] Optionally, in step S3, when nitrogen is introduced, the amount of nitrogen introduced and the valve switching are controlled to push the hydrogen in the hydrogen separator or the oxygen in the oxygen separator to the post-processing system for recovery.
[0012] Optionally, in step S3, the amount of hydrogen or oxygen recovered is related to the electrolyzer pressure and the gas phase volume of the separator. The higher the electrolyzer pressure and the larger the gas phase volume of the separator, the greater the amount of hydrogen or oxygen recovered; the lower the electrolyzer pressure and the smaller the gas phase volume of the separator, the smaller the amount of hydrogen or oxygen recovered.
[0013] Optionally, the circulating oxygen is oxygen after hydrogen has been removed, and the circulating hydrogen is hydrogen after oxygen has been removed.
[0014] Compared with the prior art, the present invention has the following beneficial effects: In this invention, in step S1, during low-load operation, preheated circulating hydrogen and circulating oxygen are introduced into the hydrogen and oxygen sides of the electrolyzer, respectively, to effectively dilute the impurity gases generated during electrolysis. This ensures that the hydrogen concentration on the oxygen side and the oxygen concentration on the hydrogen side of the electrolyzer are always controlled within the lower explosive limit. This allows the electrolyzer to operate at lower loads and higher pressures, improving the utilization rate of off-grid electricity and saving on subsequent hydrogen pressurization and treatment costs. Simultaneously, it reduces the number of electrolyzer shutdowns and the frequency of electrode replacement. In step S2, before and after the electrolyzer is shut down, a certain amount of circulating oxygen or circulating hydrogen is introduced into the electrolyzer. This process dilutes the concentration of explosive gases generated by the reverse current during shutdown, while simultaneously releasing gases dissolved in the electrolyte, thus reducing the gas concentration to a safe level. This prevents the potential for gases generated by the reverse current during electrolytic cell shutdown and for dissolved gases to accumulate to explosive limits during standby, allowing the system to operate safely for extended periods without nitrogen purging or venting, saving nitrogen consumption and facilitating rapid restart. In step S3, before shutdown maintenance, nitrogen is used to safely push hydrogen and oxygen from the separator and pipelines to the downstream system for recovery, saving hydrogen and oxygen consumption and avoiding energy waste. Attached Figure Description
[0015] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation
[0016] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.
[0017] The present invention proposes a process for low-load and safe operation of hydrogen production by water electrolysis.
[0018] Reference Figure 1 In this embodiment, the following steps are included: S1: Low-load operation; Under a certain pressure, when the electrolyzer load rate is lower than a certain load, the circulating oxygen and electrolyte are exchanged in the first heat exchanger and then introduced into the oxygen side of the electrolyzer; at the same time, the circulating hydrogen and electrolyte are exchanged in the second heat exchanger and then introduced into the hydrogen side of the electrolyzer; so that the hydrogen concentration on the oxygen side and the oxygen concentration on the hydrogen side are respectively lower than the safe value of the lower explosion limit. S2: Before and after the electrolyzer is shut down, a certain amount of circulating oxygen is introduced into the oxygen side of the electrolyzer to dilute the hydrogen concentration generated by the reverse current during shutdown. At the same time, the hydrogen dissolved in the electrolyte escapes with the oxygen and enters the downstream oxygen system from the oxygen separator, ensuring that the hydrogen concentration on the oxygen side of the electrolyzer is below the lower explosive limit. Simultaneously, a certain amount of circulating hydrogen is introduced into the hydrogen side of the electrolyzer to dilute the oxygen concentration generated by the reverse current during shutdown. At the same time, the oxygen dissolved in the electrolyte escapes with the hydrogen and enters the downstream hydrogen system from the hydrogen separator, ensuring that the oxygen concentration on the hydrogen side of the electrolyzer is below the lower explosive limit. S3: Recovery and inerting before shutdown and maintenance; Before the electrolyzer is shut down for maintenance, nitrogen is introduced into the oxygen-side outlet pipe and the hydrogen-side outlet pipe of the electrolyzer to replace and recover the hydrogen in the oxygen separator or the oxygen in the hydrogen separator. Nitrogen is then introduced to purge the electrolyzer until the hydrogen concentration or oxygen concentration is lower than the safety threshold.
[0019] Example 1 In the 500MW off-grid hydrogen production project, the hydrogen production capacity is divided into 10 units with a capacity of 10,000 Nm³ / h. Each unit is equipped with 5 electrolyzers with an operating pressure of 1.6 MPa.
[0020] When wind power generation decreases, causing the average load rate of the electrolyzer to fall below 30%, a low-load safe operation procedure is initiated. Specifically, when the electrolyzer load rate drops to 3%, circulating hydrogen and circulating oxygen (after oxygen removal) are introduced into the system. The circulating hydrogen undergoes indirect heat exchange with the hot electrolyte from the electrolyte system in the second heat exchanger, raising its temperature to within 10°C of the electrolyzer's operating temperature (e.g., 90°C). It is then introduced from the bottom of the hydrogen side of the electrolyzer, mixing with the fresh hydrogen produced by electrolysis. The circulating oxygen is treated similarly to the circulating hydrogen: after being heated by heat exchange with the hot electrolyte in the first heat exchanger, it is introduced from the bottom of the oxygen side of the electrolyzer. The amount of circulating hydrogen and circulating oxygen introduced is dynamically adjusted based on the electrolyzer operating pressure (e.g., 1.6 MPa) and the current load rate, ensuring that the amount of circulating hydrogen and hydrogen produced by electrolysis introduced is not less than the minimum safe load, i.e., 30%. The same applies to the oxygen. The lower the load rate, the greater the amount of circulating gas required. In this embodiment, when the electrolyzer operates at the minimum load of 3%, the flow rates of both circulating hydrogen and circulating oxygen exceed 540 Nm³ / h, effectively ensuring that the oxygen concentration on the hydrogen side and the hydrogen concentration on the oxygen side remain below 50% of the lower explosive limit. Compared to the existing technology with a minimum load of 30%, this operation allows the electrolyzer to absorb lower wind power, reducing the available wind power limit from 15MW to below 1.5MW, resulting in an additional annual electricity utilization of approximately 500,000 kWh. Simultaneously, because the electrolyzer does not require frequent start-ups and shutdowns under high-frequency fluctuations, the number of annual shutdowns is reduced from 20 to 8, significantly decreasing the electrode replacement frequency and substantially saving on electrode replacement costs.
[0021] When the electrolyzer needs to be shut down due to insufficient power, it enters a safe standby state. Before shutting down the electrolyzer, a purging procedure is initiated. Approximately one minute before shutdown, 30% circulating oxygen or circulating hydrogen is introduced into the oxygen or hydrogen side, respectively. After shutdown, based on the electrolyzer pressure (1.6 MPa), the gas phase volume of the oxygen separator and hydrogen separator, the required amounts of circulating hydrogen and circulating oxygen are calculated, and the duration of continued circulation of circulating oxygen or circulating hydrogen is determined. This circulating gas effectively dilutes the original gas in the separator, as well as the gas generated by the reverse current during shutdown and the gas subsequently escaping from the electrolyte, ensuring that at any given time, the hydrogen concentration on the oxygen side and the oxygen concentration on the hydrogen side are both below 50% of the lower explosive limit. This operation allows the electrolyzer to remain in safe standby mode for extended periods without the need for traditional methods of nitrogen purging and venting.
[0022] When the electrolyzer needs to be shut down for maintenance, a pre-shutdown recovery and inerting procedure is executed. First, the electrolyzer is stopped and disconnected from the downstream system. Nitrogen gas is introduced into the hydrogen and oxygen outlet pipes of the electrolyzer. By precisely controlling the nitrogen flow rate and the switching sequence of relevant valves, the nitrogen is used to push the hydrogen in the hydrogen separator to the post-processing system for recovery. Similarly, the oxygen in the oxygen separator is pushed to the post-processing system for recovery. The amount of hydrogen and oxygen recovered is related to the system pressure and separator volume. In this embodiment, approximately 32,000 Nm³ of hydrogen and approximately 32,000 Nm³ of oxygen are recovered annually. After gas recovery is completed, nitrogen is continued to purge the entire system until the concentration of residual hydrogen or oxygen in the system is below the safety threshold (e.g., hydrogen concentration below 2%), providing a safe working environment for maintenance operations.
[0023] Compared with existing technologies, this embodiment, by implementing the above process, comprehensively improves the safety and economy of the water electrolysis hydrogen production system in three key stages: low-load operation, shutdown standby, and pre-maintenance replacement. It generates significant economic benefits by saving on electricity costs and electrode replacement costs throughout the year, while also recovering hydrogen and oxygen and reducing nitrogen consumption.
[0024] The embodiments described above merely illustrate implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.
Claims
1. A process for safe operation of hydrogen production via water electrolysis under low load and shutdown conditions, characterized in that, Includes the following steps: S1: When the load rate of the electrolyzer is lower than a certain load, a certain flow rate of circulating oxygen is introduced into the oxygen side of the electrolyzer after exchanging heat with the electrolyte, so that the hydrogen concentration on the oxygen side is lower than the safe value of the lower explosive limit; at the same time, a certain flow rate of circulating hydrogen is introduced into the hydrogen side of the electrolyzer after exchanging heat with the electrolyte, so that the oxygen concentration on the hydrogen side is lower than the safe value of the lower explosive limit. S2: Before and for a period of time after the electrolyzer is shut down, a certain amount of circulating oxygen is introduced into the oxygen side of the electrolyzer to dilute the hydrogen concentration generated by the reverse current during shutdown. At the same time, the hydrogen dissolved in the electrolyte escapes with the oxygen and enters the downstream oxygen system from the oxygen separator, ensuring that the hydrogen concentration on the oxygen side of the electrolyzer is below the lower explosive limit. Simultaneously, a certain amount of circulating hydrogen is introduced into the hydrogen side of the electrolyzer to dilute the oxygen concentration generated by the reverse current during shutdown. At the same time, the oxygen dissolved in the electrolyte escapes with the hydrogen and enters the downstream hydrogen system from the hydrogen separator, ensuring that the oxygen concentration on the hydrogen side of the electrolyzer is below the lower explosive limit. S3: Recovery and inerting before shutdown and maintenance; Before the electrolyzer is shut down for maintenance, nitrogen is introduced into the oxygen-side outlet pipe and the hydrogen-side outlet pipe of the electrolyzer to replace the hydrogen in the oxygen separator or the oxygen in the hydrogen separator and send it for recovery. Nitrogen is then introduced to purge the electrolyzer until the hydrogen concentration or oxygen concentration is lower than the safety threshold.
2. The low-load and safe shutdown operation process for hydrogen production via water electrolysis according to claim 1, characterized in that, In step S1, the heat exchange between the circulating hydrogen or circulating oxygen and the electrolyte is a wall-type heat exchange. After the heat exchange, the temperature of the circulating gas rises to a value within a preset range that is within the difference between the circulating gas temperature and the operating temperature of the electrolyzer.
3. The low-load and shutdown safe operation process for hydrogen production by water electrolysis according to claim 1, characterized in that, In step S1, the amount of circulating hydrogen or circulating oxygen added is related to the electrolyzer operating pressure and minimum load rate. The higher the electrolyzer operating pressure and the lower the minimum load rate, the greater the amount of circulating oxygen or circulating hydrogen added; the lower the electrolyzer operating pressure and the higher the minimum load rate, the smaller the amount of circulating oxygen or circulating hydrogen added.
4. The low-load and shutdown safe operation process for hydrogen production by water electrolysis according to claim 1, characterized in that, In step S2, the amount of circulating hydrogen or circulating oxygen introduced is related to the electrolyzer pressure and the gas phase volume of the separator. The higher the electrolyzer pressure, the larger the gas phase volume of the separator, and the greater the amount of circulating hydrogen or circulating oxygen introduced; the lower the electrolyzer pressure, the smaller the gas phase volume of the separator, and the smaller the amount of circulating hydrogen or circulating oxygen introduced.
5. The low-load and shutdown safe operation process for hydrogen production by water electrolysis according to claim 1, characterized in that, In step S3, when nitrogen is introduced, the amount of nitrogen introduced and the valve switching are controlled to push the hydrogen in the hydrogen separator or the oxygen in the oxygen separator to the post-processing system for recovery.
6. The low-load and shutdown safe operation process for hydrogen production by water electrolysis according to claim 1, characterized in that, In step S3, the amount of hydrogen or oxygen recovered is related to the electrolyzer pressure and the gas phase volume of the separator. The higher the electrolyzer pressure and the larger the gas phase volume of the separator, the greater the amount of hydrogen or oxygen recovered. The lower the electrolyzer pressure and the smaller the gas phase volume of the separator, the smaller the amount of hydrogen or oxygen recovered.
7. The low-load and shutdown safe operation process for hydrogen production by water electrolysis according to claim 1, characterized in that... The circulating oxygen is the oxygen gas after the hydrogen has been removed, and the circulating hydrogen is the hydrogen gas after the oxygen has been removed.