Drying method for drying fuel cell stack
Through multi-stage drying methods and temperature control, the problem of frozen start-up of the fuel cell system in low-temperature environments is solved, the reliable start-up and normal operation of the fuel cell stack are achieved, freezing and damage are avoided, and the normal operation of the system is ensured under different conditions.
Patent Information
- Application Number
- CN202480012646.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-02-14
- Filing Date
- 2024-02-07
- Publication Date
- 2025-09-23
AI Technical Summary
In low-temperature environments, the freeze start of the fuel cell system causes the fuel cell stack to freeze, resulting in irreversible damage. Existing technologies make it difficult to achieve reliable freeze start under different conditions and avoid freezing, degradation or functional failure of the fuel cell stack.
A multi-stage drying method is adopted to achieve different temperature stages in the fuel cell stack by adjusting the coolant temperature, including the first drying stage to absorb moisture at high temperature and the second drying stage to homogenize the temperature at low temperature. Purge and hydrogen/air flow are combined to avoid over-drying or condensation, and a three-way valve is used to control the coolant flow.
It effectively avoids the freezing of the fuel cell stack during low-temperature startup, ensures reliable system startup, prevents membrane clogging and damage, achieves a fast and uniform drying process, and ensures the normal operation of the fuel cell system under different conditions.
Smart Images
Figure CN120693709A_ABST
Abstract
Description
Technical Field
[0001] The proposed invention relates to a drying method for drying a fuel cell stack and a fuel cell system according to the appended claims. Background Art
[0002] In a fuel cell system, oxygen from ambient air is generally used as an oxidant and hydrogen as a reductant to react with fuel in the fuel cell to generate water or water vapor, thereby providing electrical power through electrochemical conversion.
[0003] A major technical challenge for mobile fuel cell systems is to enable functional startup under all relevant conditions worldwide and after downtimes of varying lengths, while also meeting the respectively prescribed service life requirements.
[0004] During a freeze start, i.e., a start at a low external temperature of, for example, below 4°C, the fuel cell stack needs to be heated to a critical temperature above 0°C as quickly as possible so that the product water generated during the operation of the fuel cell stack does not freeze, especially in critical locations in the fuel cell stack, such as thin pipes or bends.
[0005] In the event of a freeze start failure, the fuel cell stack will suffer severe irreversible damage and the fuel cell system will not be able to start, so the fuel cell system must be brought to a "warm" environment.
[0006] For a successful freeze start, it is crucial to determine how much water the fuel cell stack contains before or at the start of a freeze start. This amount of water must be within a tolerance range so that, on the one hand, the fuel cell stack can store the product water produced during a freeze start in its components capable of storing it, such as the membranes and gas diffusion layers, without causing clogging due to frozen water, and, on the other hand, the fuel cell stack does not dry out to such an extent that the membranes cannot conduct protons or are damaged by excessive drying. Summary of the Invention
[0007] Within the scope of the proposed invention, a drying method for drying a fuel cell stack and a fuel cell system are provided. Further features and details of the invention are derived from the respective dependent claims, the description, and the drawings. Features and details relating to the drying method according to the invention naturally also apply to the fuel cell system according to the invention, and vice versa. Therefore, the disclosures of the various inventive aspects are or can be mutually referenced.
[0008] The proposed invention serves in particular to achieve a reliable frozen start of a fuel cell system.
[0009] Therefore, according to a first aspect of the present invention, a drying method for drying a fuel cell stack is provided. The drying method comprises a first drying phase, in which the coolant temperature of a coolant flowing through the fuel cell stack is set and maintained at a first coolant temperature target value; and a second drying phase, in which the coolant temperature is set to a second coolant temperature target value, wherein the first coolant temperature target value is greater than the second coolant temperature target value.
[0010] The proposed drying method is based on a multi-stage drying process, in which different temperatures are set in the fuel cell stack during the various drying phases. This ensures that the fuel cell stack does not shut down too wet.
[0011] Furthermore, the proposed drying method prevents the fuel cell stack from overheating during shutdown, especially at low ambient temperatures, so that water subsequently evaporates, redistributes, and condenses at unfavorable locations in the fuel cell system during the cooling process. Consequently, the proposed drying method eliminates problems during frozen startups, such as icing, degradation, damage, or malfunctions of the fuel cell stack.
[0012] To set different temperatures in the fuel cell stack, the coolant temperature of the coolant flowing through the fuel cell stack is set, ie, the temperature is varied. To set the coolant temperature, for example, the coolant flow directed to the cooler can be set.
[0013] In the first drying phase of the proposed drying method, the coolant temperature is set or regulated to a high temperature level, for example, 60°C. This high temperature allows the air flowing through the fuel cell stack to absorb a large amount of water until the air is saturated with water or water vapor. This allows for efficient and rapid drying of the fuel cell stack.
[0014] After the first drying phase, the coolant temperature is set or regulated to a lower level for the second drying phase, thereby cooling and homogenizing the temperature of the fuel cell stack. This means that the temperature is ideally the same throughout the fuel cell stack, and critical areas where moisture could accumulate are avoided.
[0015] Another effect of the second drying phase is to carry away the additional condensed water. For this reason, for example, the cathode section can be purged and the anode section can be flowed through with hydrogen and the purge or drain valve can be opened in both the first drying phase and the second drying phase.
[0016] It can be set that the first drying stage is implemented for a predetermined time period; or the first drying stage is implemented until the anode humidity in the anode section of the fuel cell stack and the cathode humidity in the cathode section of the fuel cell stack are lower than a predetermined humidity threshold; or the first drying stage is implemented until the difference between the fluid temperature of the fluid flowing through the fuel cell stack and the coolant temperature is higher than a predetermined first temperature difference threshold.
[0017] The end of the first drying phase on the anode side and on the cathode side can be time-controlled or pre-determined, or determined based on the temperature difference between the fuel cell stack or the anode and cathode segments and the coolant or based on the outlet temperature profile of the fluid flow flowing out of the anode segment or cathode segment.
[0018] In order to set or regulate the coolant temperature to a second coolant temperature target value after the first drying phase, the three-way valve of the cooling system of the fuel cell system can be set so that the entire coolant mass flow passes through the cooler of the cooling system, thereby achieving a rapid reduction in the coolant temperature. For example, to this end, the cooler outlet temperature can be lowered to the minimum permissible temperature by means of a cooler blower during the first drying phase.
[0019] For example, the second drying phase begins when the setpoint value of the coolant temperature, for example, reaches the target value of the ramp function and / or the coolant input temperature measured at the coolant inlet of the fuel cell stack corresponds to the second coolant temperature setpoint value or is within a value formed by the second coolant temperature setpoint value and a permissible variance or a so-called "offset".
[0020] Furthermore, it can be provided that the second drying phase is implemented for a predetermined time period, or that the second drying phase is implemented until the difference between the coolant inlet temperature measured at the coolant inlet of the fuel cell stack and the coolant outlet temperature measured at the coolant outlet of the fuel cell stack is lower than a predetermined second temperature difference threshold value.
[0021] The end of the second drying phase can be time-controlled or time-predetermined, or determined based on the temperature difference between the fuel cell stack or the anode and cathode segments and the coolant or based on the outlet temperature profile of the fluid stream flowing out of the anode or cathode segments.
[0022] In addition, it can be provided that the drying method also includes: flowing an anode fluid flow through the anode section of the fuel cell stack by controlling the purge valve of the fuel cell stack at a predetermined flow rate (controlling the purge valve of the fuel cell stack to achieve a predetermined flow rate); and flowing through the cathode section of the fuel cell stack at a predetermined flow mass flow provided by a blower, wherein the blower is used to supply fluid to the cathode section, wherein the flow rate and the flow mass flow of the controlled purge valve (achieved) are reduced during the transition of the coolant temperature from a first coolant temperature rated value to a second coolant temperature rated value, and wherein the flow rate and the flow mass flow are increased again when the coolant temperature corresponds to the second coolant temperature rated value.
[0023] By reducing the throughflow velocity and the throughflow mass flow between the first drying phase and the second drying phase, a drying pause is provided between the first drying phase and the second drying phase in order to avoid overdrying of the fuel cell stack.
[0024] Furthermore, it can be provided that the coolant temperature of the coolant flowing through the fuel cell stack is adjusted by means of a three-way valve, wherein, in order to reduce the coolant temperature, a greater coolant flow is conducted through a cooler of the fuel cell system.
[0025] The three-way valve allows for the rapid and precise adjustment of the coolant flow through the cooler and, consequently, the removal of heat energy from the coolant through the cooler. For this purpose, the three-way valve can, for example, switch between a cooling path through the cooler and a bypass path that bypasses or passes by the cooler, in particular stepwise or continuously.
[0026] Furthermore, it can be provided that the first coolant temperature target value is gradually reduced to the second coolant temperature threshold value by means of a ramp function.
[0027] In preparation for the second drying phase, lowering the coolant temperature can be performed along a setpoint value ramp. For example, when the setpoint value along the ramp reaches its target value, the second drying phase can be started.
[0028] Furthermore, it can be provided that the second coolant temperature threshold value is formed with the aid of a maximum value of the application parameter, the ambient temperature of the fuel cell system and a predefined variance value.
[0029] If the end of the first drying phase is reached, i.e., if a first coolant temperature target value is detected in the anode and cathode segments, for example, the coolant temperature is adjusted to a second, lower coolant temperature target value. The second coolant temperature target value can be formed by selecting the maximum value between the application parameter and the sum of the ambient temperature and a variance value, or so-called "offset." The sum of the ambient temperature and the variance value represents the lowest coolant temperature achievable in conventional cooling systems.
[0030] Furthermore, it can be provided that the drying method is started in response to a command for shutting down the fuel cell system.
[0031] In order to enable a reliable cold start, the proposed drying method can be initiated when the respective fuel cell system or the respective vehicle is shut down or decommissioned.
[0032] According to a second aspect, the proposed invention relates to a fuel cell system for converting energy.
[0033] The proposed fuel cell system comprises a fuel cell stack having an anode segment and a cathode segment, a purge valve for discharging a fluid from the anode segment, a metering valve for metering a fluid into the anode segment, a blower for supplying a volume flow into the cathode segment, a cooling system, and a computing unit, wherein the computing unit is configured to implement one possible configuration of the proposed drying method.
[0034] It can be provided that the cooling system includes a three-way valve, a coolant pump for supplying coolant to the fuel cell stack, and a heat exchanger in contact with the environment.
[0035] The three-way valve is connected to a line to the outlet of the heat exchanger, a line to the coolant pump, and a bypass line, and the bypass line passes past the pump and the fuel cell stack and is connected to the inlet of the heat exchanger.
[0036] Further advantages, features and details of the invention are apparent from the following description of exemplary embodiments of the invention in conjunction with the accompanying drawings. The features mentioned in the claims and the description may be essential to the invention individually or in any combination. BRIEF DESCRIPTION OF THE DRAWINGS
[0037] The accompanying drawings show:
[0038] Figure 1 shows one possible configuration of the proposed drying method,
[0039] Figure 2 One possible configuration of the proposed fuel cell system is shown. DETAILED DESCRIPTION
[0040] Figure 1 There is shown a drying method 100. The drying method 100 is started in a start step 101 in response to a command for deactivating the fuel cell system.
[0041] In the first drying phase 103 , the cooler outlet temperature is reduced to a minimum, constant conditions are provided in the anode section of the fuel cell system by regularly performing purging or draining processes, and a constant cathode air mass flow with a constant pressure level is established in the cathode section.
[0042] In a check step 105 , it is checked whether a predefined drying duration and / or a temperature-based criterion, for example a first coolant temperature setpoint value, has been reached, so that if not, the first drying phase 103 is continued, and if so, a drying pause 107 is performed.
[0043] During the drying pause 107 , the cathode mass flow is reduced, the purge frequency is lowered and / or the purge duration is shortened, and the coolant temperature of the fuel cell stack is set to a second coolant temperature target value.
[0044] In a check step 109 , it is checked whether the target value of the ramp function for adjusting the coolant temperature is reached and / or whether the measured coolant temperature of the fuel cell stack corresponds to a second coolant temperature setpoint value, so that if not, the drying pause 107 is continued and if so, the second drying phase 111 is started.
[0045] In the second drying phase 111 , hydrogen is again regularly or increasingly flowed through the anode segments, and air is increasingly flowed through the cathode segments.
[0046] In a check step 113, it is checked whether a predetermined drying duration has been reached and / or whether the coolant temperature measured at the output end or coolant outlet of the fuel cell stack corresponds to the coolant temperature measured at the input end or coolant inlet of the fuel cell stack (if necessary plus a predetermined variance value or so-called "Offset"), so that, if not, the second drying stage 111 is continued, if yes, a termination step 115 is introduced.
[0047] Figure 2 A fuel cell system 200 is shown. The fuel cell system 200 comprises a fuel cell stack 201 having an anode section 203 and a cathode section 205, a purge valve 207 for removing fluid from the anode section 203, a metering valve 209 for metering fluid into the anode section 203, a blower 211 for supplying a volume flow into the cathode section 205, a cooling system 213, and a computing unit 215.
[0048] The calculation unit 215 is configured to implement Figure 1 Drying method 100. For this purpose, a computing unit 215 is communicatively connected to a three-way valve 223 of a cooling system 213 in order to divide the coolant flow of a coolant path 217 flowing through the fuel cell stack 201 between a cooling line 219 passing through a cooling system cooler 221 and a bypass line 225 passing past the cooler 221, and thereby adjust the coolant temperature of the coolant or the fuel cell stack temperature of the fuel cell stack 201.
Claims
1. A drying method (100) for drying a fuel cell stack (201), in, The drying method (200) comprises: a first drying phase (103), in which the coolant temperature of the coolant flowing through the fuel cell stack (201) is set and maintained at a first coolant temperature setpoint value, a second drying phase (111), in which the coolant temperature is set to a second coolant temperature setpoint value, The first coolant temperature rating is greater than the second coolant temperature rating.
2. The drying method (100) according to claim 1, It is characterized by: The first drying stage (103) is carried out for a predetermined period of time, or The first drying phase is carried out until the anode humidity in the anode section (203) of the fuel cell stack (201) and the cathode humidity in the cathode section (205) of the fuel cell stack (201) are below a predetermined humidity threshold value, or The first drying phase is carried out until the difference between the fluid temperature of the fluid flowing through the fuel cell stack (201) and the coolant temperature is higher than a predetermined first temperature difference threshold value.
3. The drying method (100) according to claim 1 or 2, It is characterized by: The second drying stage (111) is carried out for a predetermined period of time, or The second drying phase is performed until the difference between the coolant inlet temperature measured at the coolant inlet of the fuel cell stack (201) and the coolant outlet temperature measured at the coolant outlet of the fuel cell stack (201) falls below a predetermined second temperature difference threshold.
4. Drying method (100) according to any one of the preceding claims, It is characterized by: The drying method (100) further comprises: - flowing an anode fluid stream through the anode segment (203) of the fuel cell stack (201) by actuating a purge valve (207) of the fuel cell stack (201) at a predetermined flow rate, - flowing through the cathode segment (205) of the fuel cell stack (201) with a predetermined throughflow mass flow provided by a blower (211), the blower being used to supply the cathode segment (205) with fluid, wherein, during the transition of the coolant temperature from the first coolant temperature target value to the second coolant temperature target value, the throughflow rate and the throughflow mass flow of the actuation of the purge valve (207) are reduced, and In this case, the throughflow rate and the throughflow mass flow are increased again when the coolant temperature corresponds to the second coolant temperature target value.
5. Drying method (100) according to any one of the preceding claims, It is characterized by: The coolant temperature of the coolant flowing through the fuel cell stack (201) is adjusted by means of a three-way valve (223), In order to reduce the coolant temperature, a larger coolant flow is directed through a cooler (221) of the fuel cell system (200).
6. Drying method (100) according to any one of the preceding claims, It is characterized by: The first coolant temperature target value is gradually reduced to the second coolant temperature threshold value by means of a ramp function.
7. Drying method (100) according to any one of the preceding claims, It is characterized by: The second coolant temperature threshold value is formed with the aid of a maximum value of the application parameter, an ambient temperature of the fuel cell system, and a predefined variance value.
8. Drying method (100) according to any one of the preceding claims, It is characterized by: The drying method is initiated in response to a command to shut down the fuel cell system.
9. A fuel cell system (200) for converting energy, in, The fuel cell system (200) comprises: - a fuel cell stack (201) having an anode segment (201) and a cathode segment (203), - a purge valve (207) for draining fluid from the anode segment (203), - a metering valve (209) for metering fluid into the anode segment (203), - a blower (211) for supplying a volume flow into the cathode segment (205), - cooling system (213), - a calculation unit (215), Wherein, the computing unit (215) is configured to implement the drying method (100) according to any one of claims 1 to 8.
10. The fuel cell system (200) according to claim 9, It is characterized by: The cooling system (213) includes a three-way valve (223), a coolant pump for supplying coolant to the fuel cell stack (201), and a heat exchanger in contact with the environment. The three-way valve (223) is connected to the pipeline (219) leading to the output end of the heat exchanger, the pipeline leading to the coolant pump, and the bypass pipeline (225). The bypass line (225) passes beside the coolant pump and the fuel cell stack (201) and is connected to the input end of the heat exchanger.