A fuel cell system and its shutdown anode purging method

Abstract

This invention discloses a fuel cell system and its shutdown anode purging method. The shutdown anode purging method includes the following steps: when the fuel cell system is shut down, hydrogen enters the anode of the fuel cell stack for purging; during the anode purging process, a drain and vent valve is periodically opened, with each opening duration of the drain and vent valve being t1 and the interval between two openings being t2; the opening degree of the hydrogen proportional valve is adaptively adjusted to maintain the anode pressure of the fuel cell stack at a specified pressure; the change in the opening degree of the hydrogen proportional valve during each opening of the drain and vent valve is recorded, and the average opening degree of the hydrogen proportional valve during each opening of the drain and vent valve is calculated and recorded; when the average opening degree of the hydrogen proportional valve in the nth time minus the average opening degree in the (n-1)th time is less than a set threshold, the anode purging of the fuel cell stack is stopped. This invention determines whether the anode liquid water has been purged completely by using the opening degree of the hydrogen proportional valve, forming a closed-loop feedback for anode shutdown purging and saving hydrogen purging consumption.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a fuel cell system and a shutdown anode purging method thereof. Background Technology

[0002] Hydrogen fuel is a clean, pollution-free, and renewable energy source that is being used in an increasing number of fields. Hydrogen fuel cells can convert hydrogen into electrical and thermal energy. When operating, hydrogen fuel cells not only have high power generation efficiency but also have advantages such as low noise and zero pollution.

[0003] A fuel cell stack consists of a cathode and an anode. During operation, hydrogen undergoes an electrochemical reaction at the anode, while air undergoes an electrochemical reaction at the cathode. During fuel cell system shutdown, both the cathode and anode of the fuel cell stack need to be purged. Purging the anode removes liquid water from the anode channels and pipes; purging the cathode not only removes liquid water from the cathode channels and pipes but also reduces the water content in the membrane electrode assembly (MEA) in preparation for the next startup. Furthermore, removing liquid water helps prevent ice formation in the channels and pipes at low temperatures, which could block them. Air is used for purging the cathode, while hydrogen is used for purging the anode.

[0004] The duration of hydrogen purging at the anode is difficult to control. Existing technologies often employ excessive purging to prevent residual liquid water at the anode, which wastes hydrogen and reduces its utilization rate. Alternatively, the hydrogen purging time may be too short, resulting in insufficient removal of liquid water at the anode. Summary of the Invention

[0005] To address one of the aforementioned technical problems, this invention provides a fuel cell system and its shutdown anode purging method. The method determines whether the anode liquid water has been purged completely by checking the opening of a hydrogen proportional valve, thus creating a closed-loop feedback for anode shutdown purging, saving hydrogen purging consumption, and consequently reducing costs.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a fuel cell system, including a fuel cell stack, a hydrogen supply unit, a hydrogen proportional valve, a hydrogen ejector, a gas-liquid separator, and a drain and exhaust valve. The fuel cell stack includes an anode inlet and an anode outlet. The hydrogen supply unit, the hydrogen proportional valve, the hydrogen ejector, and the anode inlet of the fuel cell stack are connected in sequence. The anode outlet of the fuel cell stack is connected to the gas-liquid separator, and the gas-liquid separator is connected to the hydrogen ejector and the drain and exhaust valve.

[0007] The fuel cell system also includes a control unit, which is connected to a hydrogen proportioning valve and a drain / vent valve.

[0008] The control unit is used to: periodically open the drain and vent valve during the shutdown and purging process of the fuel cell system, with each opening duration of the drain and vent valve being t1 and the interval between two openings being t2; adaptively adjust the opening degree of the hydrogen proportional valve to maintain the anode pressure of the fuel cell stack at a specified pressure; record the opening degree change of the hydrogen proportional valve during each opening of the drain and vent valve, and calculate and record the average opening degree of the hydrogen proportional valve during each opening of the drain and vent valve; when the average opening degree of the hydrogen proportional valve in the nth time minus the average opening degree in the (n-1)th time is less than a set threshold, the anode purging of the fuel cell stack is stopped.

[0009] Another object of the present invention is to provide a shutdown anode purging method for a fuel cell system, which operates on a fuel cell system and includes the following steps:

[0010] When the fuel cell system is shut down, hydrogen from the hydrogen supply unit is introduced into the anode of the fuel cell stack for purging.

[0011] During the anode purging process, the drain and vent valve is opened periodically. The opening time of each drain and vent valve is t1, and the interval between two openings of the drain and vent valve is t2.

[0012] The opening of the hydrogen proportional valve is adaptively adjusted to maintain the anode pressure of the fuel cell stack at the specified pressure.

[0013] Record the change in the opening degree of the hydrogen proportional valve during each opening of the drain and exhaust valve, and calculate the average opening degree of the hydrogen proportional valve during each opening of the drain and exhaust valve. When the average opening degree of the hydrogen proportional valve in the nth time minus the average opening degree in the (n-1)th time is less than the set threshold, stop the anode purging of the fuel cell stack.

[0014] After adopting the above technical solution, the present invention has at least the following beneficial effects: The present invention determines whether the anode liquid water has been purged completely by the opening of the hydrogen proportional valve, ensuring that the anode water is fully removed, and greatly saving the amount of hydrogen purging, thereby saving costs; In addition, the present invention enables the anode shutdown purging to form a closed-loop feedback. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of a fuel cell system according to the present invention.

[0016] Figure 2 This is a flowchart illustrating the steps of a fuel cell system shutdown anode purging method according to the present invention.

[0017] Figure 3 This is a state diagram showing the change over time of the opening degree of the hydrogen proportional valve 5 and the opening of the drain and exhaust valve 8 in this invention.

[0018] Figure 4 This is a two-phase flow pattern diagram of the anode outlet pipeline of the fuel cell stack of the present invention. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] Example 1

[0021] like Figure 1 As shown, this embodiment discloses a fuel cell system, including a fuel cell stack 1, an air compressor 2, an intercooler 3, an air back pressure valve 4, a hydrogen proportioning valve 5, a hydrogen ejector 6, a gas-liquid separator 7, a drain and vent valve 8, a hydrogen supply unit 9, and a pressure sensor 10. The fuel cell stack 1 includes an anode inlet, an anode outlet, a cathode inlet, and a cathode outlet. The air compressor 2, the intercooler 3, and the cathode inlet of the fuel cell stack 1 are connected in sequence, and the cathode outlet of the fuel cell stack 1 is connected to the air back pressure valve 4. The hydrogen supply unit 9, the hydrogen proportioning valve 5, the hydrogen ejector 6, and the anode inlet of the fuel cell stack 1 are connected in sequence, and the anode outlet of the fuel cell stack 1 is connected to the gas-liquid separator 7. The gas-liquid separator 7 is connected to the hydrogen ejector 6 and the drain and vent valve 8. The pressure sensor 10 is connected to the anode inlet of the fuel cell stack 1.

[0022] The hydrogen supply unit 9 is used to supply hydrogen to the anode side of the fuel cell stack 1;

[0023] The hydrogen proportional valve 5 is used to receive hydrogen from the hydrogen supply unit 9 and, after depressurizing the hydrogen, input the hydrogen into the hydrogen ejector 6.

[0024] The hydrogen is used to receive the hydrogen supplied by the hydrogen proportioning valve 5 and the hydrogen supplied by the gas-water separator 7, and to input the received hydrogen into the anode of the fuel cell stack 1.

[0025] The gas-water separator 7 is used to receive the gas-water mixture emitted from the anode of the fuel cell stack 1 and separate the gas-water mixture. The separated hydrogen is then transported to the hydrogen ejector 6.

[0026] The drain and vent valve 8 is used to discharge water from the gas-water separator 7;

[0027] The fuel cell system further includes a control unit 11, which is connected to a hydrogen proportioning valve 5, a drain and exhaust valve 8, and a pressure sensor 10.

[0028] The control unit 11 is used to: periodically open the drain and exhaust valve 8 during the shutdown and purging process of the fuel cell system, with each opening duration of the drain and exhaust valve 8 being t1 and the interval between two openings of the drain and exhaust valve 8 being t2; adaptively adjust the opening degree of the hydrogen proportional valve 5 to maintain the anode pressure of the fuel cell stack 1 at a specified pressure; record the opening degree change of the hydrogen proportional valve 5 during each opening of the drain and exhaust valve 8, and calculate and record the average opening degree of the hydrogen proportional valve 5 during each opening of the drain and exhaust valve 8; when the average opening degree of the hydrogen proportional valve 5 in the nth time minus the average opening degree in the (n-1)th time is less than a set threshold, the fuel cell system stops the anode purging of the fuel cell stack 1.

[0029] This embodiment mainly determines whether there is still liquid water accumulation at the anode by comparing the change in the opening degree of the hydrogen proportional valve 5 when the drain and exhaust valve 8 is opened. When the judgment condition is met, the anode purging is stopped, so that the anode shutdown purging forms a closed loop feedback, saving the amount of hydrogen purging.

[0030] Example 2

[0031] This embodiment discloses a shutdown anode purging method for a fuel cell system, which is applied to a fuel cell system as described in Embodiment 1. Figure 2 As shown, the specific steps are as follows:

[0032] When the fuel cell system is shut down normally, on the cathode side of the fuel cell stack 1, the air driven by the air compressor 2 is cooled by the intercooler 3 and then enters the cathode of the fuel cell stack 1 for purging. The air back pressure valve 4 controls the air pressure on the cathode side of the fuel cell stack 1. On the anode side of the fuel cell stack 1, the high-pressure hydrogen from the hydrogen supply unit 9 is depressurized by the hydrogen proportional valve 5 and then injected into the anode of the fuel cell stack 1 through the hydrogen ejector 6 for purging. At the same time, the hydrogen ejector 6 absorbs the exhaust gas from the anode outlet of the fuel cell stack 1 to form hydrogen recirculation. The drain and exhaust valve 8 is opened at regular intervals to discharge the gas-water mixture in the gas-water separator 7.

[0033] During anode purging, such as Figure 3 As shown, the drain and vent valve 8 is opened periodically. The opening time of the drain and vent valve 8 is t1 each time, and the interval between two openings of the drain and vent valve 8 is t2. The purpose of this design is to allow the small droplets in the anode channel to re-aggregate into large droplets after each purging. Compared with small droplets, large droplets are easier to purge and discharge, thereby improving purging efficiency.

[0034] The opening of the hydrogen proportional valve 5 is adaptively adjusted to maintain the anode pressure of the fuel cell stack 1 at a specified pressure. Specifically, when the drain and vent valve 8 is open, the gas-liquid two-phase flow rapidly passes through the drain and vent valve 8. Figure 4As shown, this will reduce the anode pressure. Therefore, in order to maintain the anode pressure at the specified level, the fuel cell system needs to open the hydrogen proportional valve 5 more fully to compensate for the anode pressure loss; as... Figure 3 As shown, when the liquid proportion in the gas-liquid two-phase flow on the anode side of fuel cell stack 1 is relatively high, the drain and exhaust valve 8 is opened. Due to the large flow resistance of the gas-liquid two-phase flow at the anode and the very unstable flow of the gas-liquid two-phase flow, the average opening increment of the hydrogen proportional valve 5 is small and the opening fluctuation is large. When the drain and exhaust valve 8 is opened again, due to the reduction of liquid at the anode, that is, the liquid proportion in the gas-liquid two-phase flow is reduced, the flow resistance of the gas-liquid two-phase flow at the anode is reduced, and the liquid disturbance is reduced. Therefore, the average opening increment of the hydrogen proportional valve 5 becomes larger and the opening fluctuation decreases.

[0035] Record the change in the opening degree of the hydrogen proportional valve 5 during each opening of the drain and exhaust valve 8, and calculate the average opening degree of the hydrogen proportional valve 5 during each opening of the drain and exhaust valve 8. When the average opening degree of the hydrogen proportional valve 5 in the nth time minus the average opening degree in the (n-1)th time is less than the set threshold, it is considered that the anode liquid water has been purged and the fuel cell system stops the anode purging of the stack 1.

[0036] During anode purging, cathode is continuously purged with air.

[0037] This embodiment ensures that the water accumulated at the anode is fully removed and greatly saves the amount of hydrogen purging; in addition, this embodiment enables the anode shutdown purging to form a closed-loop feedback.

[0038] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various equivalent changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A purging method for a fuel cell system during shutdown, characterized in that, The fuel cell system includes a stack, a hydrogen supply unit, a hydrogen proportioning valve, a hydrogen ejector, a gas-liquid separator, and a drain / vent valve. The stack includes an anode inlet and an anode outlet. The hydrogen supply unit, hydrogen proportioning valve, hydrogen ejector, and anode inlet of the stack are connected in sequence. The anode outlet of the stack is connected to the gas-liquid separator, which is connected to the hydrogen ejector and the drain / vent valve. The fuel cell system also includes a pressure sensor located at the anode inlet of the stack, and a control unit connected to the hydrogen proportioning valve, drain / vent valve, and pressure sensor. The purging method includes the following steps: when the fuel cell system is normally shut down, a purge is performed on the cathode side of the stack using an air compressor. Air, cooled by an intercooler, enters the cathode of the fuel cell stack for purging. An air back pressure valve controls the air pressure on the cathode side. On the anode side, high-pressure hydrogen from the hydrogen supply unit is depressurized by a hydrogen proportional valve and then injected into the anode through a hydrogen ejector for purging. Simultaneously, the hydrogen ejector absorbs waste gas from the anode outlet, thus recycling hydrogen. A drain and vent valve opens periodically to discharge the gas-water mixture from the gas-water separator. During anode purging, the drain and vent valve is opened periodically. Each opening duration is t1, and the interval between openings is t2. This design aims to allow fine droplets in the anode channel to dissipate after each purging cycle. The liquid re-aggregates into larger droplets, which are easier to purge and remove than smaller droplets, thus improving purging efficiency. The hydrogen proportioning valve opening is adaptively adjusted to maintain the anode pressure of the fuel cell stack at the specified level. Specifically: when the drain / vent valve is open, the gas-liquid two-phase flow passes rapidly through it, reducing the anode pressure. Therefore, to maintain the anode pressure at the specified level, the fuel cell system needs to open the hydrogen proportioning valve more to compensate for the pressure loss. When the liquid component in the gas-liquid two-phase flow on the anode side of the fuel cell stack is higher, the drain / vent valve opens. Due to the high flow resistance at the anode and the highly unstable flow of the gas-liquid two-phase flow, the average opening increment of the hydrogen proportioning valve is small. The fluctuations are relatively large. When the drain and vent valve is reopened, the liquid at the anode decreases, meaning the liquid ratio in the gas-liquid two-phase flow decreases. This reduces the flow resistance of the gas-liquid two-phase flow at the anode and decreases liquid disturbance. Therefore, the average opening increment of the hydrogen proportional valve increases, and the opening fluctuation decreases. The opening change of the hydrogen proportional valve is recorded during each opening of the drain and vent valve, and the average opening of the hydrogen proportional valve during each opening is calculated. When the average opening of the hydrogen proportional valve in the nth time minus the average opening in the (n-1)th time is less than the set threshold, it is considered that the liquid accumulation at the anode has been purged, and the anode purging of the fuel cell system is stopped. During the anode purging, the cathode is continuously purged with air.

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