Drying method for drying a fuel cell stack
A multi-stage drying method with controlled coolant temperature adjustments addresses the challenge of frozen starts in fuel cell systems, ensuring reliable and damage-free start-up by efficiently removing water and maintaining temperature balance.
Patent Information
- Application Number
- JP2025545034
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-02-14
- Filing Date
- 2024-02-07
- Publication Date
- 2026-01-30
AI Technical Summary
Mobile fuel cell systems face challenges in achieving functional start-up under diverse global conditions and shutdown lengths, particularly during frozen starts at low temperatures, which can cause irreparable damage due to frozen water accumulation and improper drying.
A multi-stage drying method is employed, adjusting coolant temperatures to specific setpoints in the fuel cell stack, ensuring efficient water removal and temperature equalization to prevent damage and ensure reliable start-up.
The method effectively prevents shutdowns and damage by efficiently removing water, ensuring rapid and reliable start-up of fuel cell systems under frozen conditions.
Smart Images
Figure 2026503854000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to a drying method for drying a fuel cell stack and a fuel cell system as claimed in the accompanying claims. [Background technology]
[0002] Fuel cell systems typically utilize oxygen from ambient air as an oxidant and hydrogen as a fuel as a reductant, which react in the fuel cell to form water or water vapor, thus providing electrical power through electrochemical conversion.
[0003] For mobile fuel cell systems, the major technical challenge is to achieve functional start-up under all globally relevant conditions and with different lengths of shutdown, while still achieving the respective pre-defined lifespan requirements.
[0004] During a frozen start, i.e., during start-up at low outside temperatures, for example below 4°C, it is necessary to warm the fuel cell stack above the critical temperature of 0°C as quickly as possible to prevent product water that forms during operation of the fuel cell stack in particularly dangerous locations within the fuel cell stack, such as thin tubes or bends, from freezing.
[0005] A sloppy frozen start can cause irreparable damage to the fuel cell stack or can even render the fuel cell system unable to start, requiring the fuel cell system to be brought into a "hot" environment.
[0006] For a frozen start to be successful, it is important to consider the amount of water the fuel cell stack contains before or at the beginning of the frozen start. This amount must be within a tolerance range. This is necessary to ensure that the fuel cell stack can accumulate the product water generated during a frozen start in storage components such as diaphragms and gas diffusion layers without causing clogging due to frozen water, and to avoid drying the fuel cell stack out to the point where the diaphragms no longer conduct protons or are damaged by excessively dry conditions. Summary of the Invention
[0007] Within the scope of the presented invention, a drying method for drying a fuel cell stack and a fuel cell system are presented. Further features and details of the invention are evident from the respective dependent claims, the description and the drawings. It should be noted that the features and details described in the context of the drying method according to the invention also naturally apply in the context of the fuel cell system according to the invention and vice versa, so that the disclosures of the individual inventive aspects are always mutually associated or can be associated with each other.
[0008] The presented invention is particularly used to enable reliable freeze starting of fuel cell systems.
[0009] Thus, according to a first aspect of the present invention, a drying method for drying a fuel cell stack is presented, the drying method including a first drying stage in which a coolant temperature of a coolant flowing through the fuel cell stack is adjusted and maintained at a first coolant temperature setpoint, and a second drying stage in which the coolant temperature is adjusted to a second coolant temperature setpoint, wherein the first coolant temperature setpoint is greater than the second coolant temperature setpoint.
[0010] The drying method presented is based on a multi-stage drying process, where different temperatures are set within the fuel cell stack at different drying stages, ensuring that the fuel cell stack does not shut down due to excessive humidity.
[0011] Furthermore, the presented drying method prevents the fuel cell stack from overheating and shutting down, especially at low ambient temperatures, which then causes water to evaporate, re-disperse, and condense in undesirable locations within the fuel cell system during the cool-down process. Correspondingly, the presented drying method eliminates frozen start problems, such as icing, degradation, damage, or malfunction 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 adjusted, i.e., varied. To adjust the coolant temperature, for example, the coolant flow directed to the cooler can be adjusted.
[0013] In the first drying stage of the drying method described, the coolant temperature is adjusted or controlled to a high temperature level, for example, 60° C. The high temperature level 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, thus enabling efficient and rapid drying of the fuel cell stack.
[0014] Following the first drying stage, the coolant temperature is adjusted or controlled to a lower temperature level for the second drying stage, thereby achieving cooling and temperature equalization of the fuel cell stack, which means that ideally the same temperature prevails throughout the fuel cell stack, avoiding dangerous spots where moisture can accumulate.
[0015] A further effect of the second drying stage is the release of additional condensed water, for which reason, for example, blowing out the cathode section, flowing through the anode section with hydrogen, and opening the purge or drain valves may be maintained both in the first and in the second drying stage.
[0016] It may be considered to carry out the first drying stage for a predetermined time, or 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 below a predetermined humidity threshold, or until the difference between the fluid temperature of the fluid flowing through the fuel cell stack and the coolant temperature is above a predetermined first temperature difference threshold.
[0017] The end of the first drying stage on the anode and cathode sides may be time-controlled or time-set or may be determined based on the temperature difference of the fuel cell stack or the anode and cathode sections relative to the coolant or based on the course of the discharge temperature of the fluid streams leaving the anode or cathode sections.
[0018] To regulate or control the coolant temperature after the end of the first drying stage to the second coolant temperature setpoint, the three-way valve of the cooling system of the fuel cell system may be adjusted so that the entire cooling mass flow flows through the cooler of the cooling system, so that a rapid reduction in the coolant temperature is achieved, for example, by adjusting the cooler discharge temperature to the permissible minimum temperature already during the first drying stage using a cooler fan.
[0019] The second drying phase may start, for example, when the coolant temperature setpoint reaches a target value, for example a ramp function, and / or when the coolant inlet temperature measured at the coolant inlet of the fuel cell stack corresponds to the second coolant temperature setpoint or is within a range consisting of the second coolant temperature setpoint and an allowable variance value, or so-called "offset."
[0020] It may further be considered to carry out the second drying stage for a predetermined time or until the difference between the coolant intake temperature measured at the coolant intake of the fuel cell stack and the coolant discharge temperature measured at the coolant discharge of the fuel cell stack falls below a predetermined second temperature difference threshold.
[0021] The end of the second drying stage may be time-controlled or time-set, or may be determined based on the temperature difference of the fuel cell stack or the anode and cathode sections relative to the coolant, or based on the course of the discharge temperature of the fluid streams leaving the anode or cathode sections.
[0022] It may also be envisaged that the drying method further comprises flowing an anode fluid flow through the anode section of the fuel cell stack by activating a purge valve of the fuel cell stack at a predetermined flow rate, and flowing a cathode section of the fuel cell stack at a predetermined flow rate provided by a fan to supply fluid to the cathode section, wherein the flow rate and flow rate at which the purge valve is activated are reduced during the transition of the coolant temperature from the first coolant temperature setpoint to the second coolant temperature setpoint, and the flow rate and flow rate are increased again when the coolant temperature corresponds to the second coolant temperature setpoint.
[0023] By reducing the throughflow rate and throughflow mass flow between the first and second drying stages, a drying pause is inserted between the first and second drying stages to avoid over-drying the fuel cell stack.
[0024] Furthermore, it may be possible to regulate the coolant temperature of the coolant flowing through the fuel cell stack using a three-way valve, in which case it may be possible to direct more coolant flow through the cooler of the fuel cell system in order to lower the coolant temperature.
[0025] The three-way valve allows for rapid and precise regulation of the refrigerant flow induced through the cooler and the resulting release of heat energy from the cooler by the cooler, and for this purpose may be switched, in particular stepwise or continuously, between a cooling path through the cooler and a bypass path arranged around or past the cooler.
[0026] Additionally, it may be contemplated that the first coolant temperature setpoint may be continuously reduced to the second coolant temperature threshold using a ramp function.
[0027] The reduction of the coolant temperature in preparation for the second drying stage can occur along a setpoint ramp, with the start of the second drying stage occurring, for example, when the setpoint reaches its target value along the ramp.
[0028] It may be envisaged that the second coolant temperature threshold is formed using the maximum value of the application parameter, the ambient temperature of the fuel cell system and a predetermined variance value.
[0029] When the end of the first drying phase is initiated, i.e., when the first coolant temperature setpoint is detected, for example, in the anode section and the cathode section, the coolant temperature is adjusted to a lower second coolant temperature setpoint, which can be formed by selecting the maximum value between the application parameters and the sum of the ambient temperature and the variance, or so-called "offset," which is the lowest coolant temperature achievable in a typical cooling system.
[0030] Furthermore, it may be contemplated that the drying method may be initiated in response to a command to shut down the fuel cell system.
[0031] To allow for a reliable frozen start, the drying method presented can be initiated by shutting down or disabling the respective fuel cell system or corresponding vehicle.
[0032] According to a second aspect, the presented invention relates to a fuel cell system for converting energy.
[0033] The presented fuel cell system comprises a fuel cell stack including an anode section and a cathode section, a purge valve for draining fluid from the anode section, a metering valve for metering fluid into the anode section, a fan for supplying a volume flow into the cathode section, a cooling system, and a computing unit, wherein the computing unit is configured to implement a possible embodiment of the presented drying method.
[0034] It may be considered that the cooling system includes a three-way valve, a coolant pump that supplies coolant to the fuel cell stack, and a heat exchanger in contact with the surroundings, in which case the three-way valve is connected to a pipe leading to the outlet of the heat exchanger, a pipe leading to the coolant pump, and a bypass pipe, which passes by the pump and the fuel cell stack and is connected to the inlet of the heat exchanger.
[0035] Further advantages, features and details of the invention emerge from the following description in which an embodiment of the invention is described in detail with reference to the drawings, in which the features set out in the claims and in the description may each be essential to the invention either alone or in any combination. [Brief explanation of the drawings]
[0036] [Figure 1] FIG. 1 shows one possible configuration of the drying method presented. [Figure 2] FIG. 1 shows one possible configuration of the fuel cell system presented. DETAILED DESCRIPTION OF THE INVENTION
[0037] 1 illustrates a drying method 100. The drying method 100 begins at a start step 101 in response to a command to disable the fuel cell system.
[0038] In the first drying stage 103, the cooler discharge temperature is reduced to a minimum value and purge or drain processes are performed regularly to create constant conditions in the anode section of the fuel cell system and generate a constant cathode air mass flow with a constant pressure level in the cathode section.
[0039] A test step 105 checks whether a predetermined drying time has been achieved and / or whether a temperature-based criterion has been achieved, e.g., whether a first coolant temperature setpoint has been achieved, and if not, continues with the first drying phase 103, or if yes, introduces a drying pause 107.
[0040] During the dry pause 107, the cathode mass flow is reduced, the purge frequency and / or purge duration is decreased, and the fuel cell stack coolant temperature is adjusted to a second coolant temperature setpoint.
[0041] In test step 109, it is checked whether the target value of the ramp function for regulating the coolant temperature has been achieved and / or whether the measured fuel cell stack coolant temperature corresponds to the second coolant temperature setpoint, and if not, the drying pause 107 is continued, or if yes, the second drying phase 111 is started.
[0042] In the second drying stage 111, hydrogen is again passed through the anode section regularly or more frequently, and air is passed through the cathode section more frequently.
[0043] In a test step 113, it is checked whether a predetermined drying time has been reached and / or whether the coolant temperature measured at the outlet or coolant discharge of the fuel cell stack corresponds to the coolant temperature measured at the inlet or coolant intake of the fuel cell stack, possibly taking into account a predetermined variance value or so-called "offset", and if this is not the case, the second drying phase 111 is continued, or if this is the case, a termination step 115 is introduced.
[0044] 2 illustrates a fuel cell system 200. The fuel cell system 200 includes a fuel cell stack 201 including an anode section 203 and a cathode section 205, a purge valve 207 for evacuating fluid from the anode section 203, a metering valve 209 for metering fluid into the anode section 203, a fan 211 for providing a volumetric flow into the cathode section 205, a cooling system 213, and a computing unit 215.
[0045] The computing unit 215 is configured to perform the drying method 100 according to Fig. 1. To this end, the computing unit 215 is connected in communication with the three-way valve 223 of the cooling system 213 and distributes the coolant flow through the coolant path 217 of the fuel cell stack 201 between a cooling pipe 219 passing through a cooler 221 of the cooling system and a bypass pipe 225 arranged adjacent to the cooler 221, thereby adjusting the coolant temperature of the coolant or the fuel cell stack temperature of the fuel cell stack 201. [Explanation of symbols]
[0046] 100 Drying method 103 First drying stage 111 Second drying stage 200 Fuel Cell System 201 Fuel Cell Stack 203 Anode Section 205 Cathode Section 207 Purge valve 209 Dosing valve 211 Fan 213 Cooling System 215 arithmetic unit 219 Cooling pipe (pipe leading to the outlet of the heat exchanger) 221 Cooler 223 Three-way valve 225 Bypass Pipe
Claims
1. A drying method (100) for drying a fuel cell stack (201), comprising: The drying method (100) a first drying stage (103) in which the coolant temperature of the coolant flowing through said fuel cell stack (201) is adjusted and maintained at a first coolant temperature setpoint; - a second drying stage (111) in which the coolant temperature is adjusted to a second coolant temperature setpoint; Including, the first refrigerant temperature setpoint is greater than the second refrigerant temperature setpoint; Drying method (100).
2. carrying out said first drying step (103) for a predetermined time, or 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; or until the difference between the fluid temperature of the fluid flowing through the fuel cell stack (201) and the coolant temperature is above a predetermined first temperature difference threshold. The drying method (100) according to claim 1, characterized in that
3. carrying out said second drying step (111) for a predetermined time, or until a difference between a coolant intake temperature measured at a coolant intake of the fuel cell stack (201) and a coolant discharge temperature measured at a coolant discharge of the fuel cell stack (201) falls below a second predetermined temperature difference threshold.
3. A drying method (100) according to claim 1 or 2, characterized in that
4. The drying method (100) further comprises: - activating the purge valve (207) of said fuel cell stack (201) at a predetermined flow rate to allow the anode fluid flow through the anode section (203) of said fuel cell stack (201); - flowing through the cathode section (205) of the fuel cell stack (201) with a predetermined throughflow mass flow provided by a fan (211) to supply fluid to the cathode section (205); Including, reducing the once-through mass flow and the once-through rate that activates the purge valve (207) while the refrigerant temperature is transitioning from the first refrigerant temperature setpoint to the second refrigerant temperature setpoint; and increasing the through-flow rate and the through-flow mass flow again when the refrigerant temperature corresponds to the second refrigerant temperature setpoint.
4. A drying method (100) according to any one of claims 1 to 3, characterized in that
5. 5. The drying method (100) according to claim 1, wherein the refrigerant temperature of the refrigerant flowing through the fuel cell stack (201) is adjusted using a three-way valve (223) and more refrigerant flow is directed through a cooler (221) of the fuel cell system (200) to lower the refrigerant temperature.
6. 6. The drying method (100) of any one of claims 1 to 5, characterized in that the first coolant temperature setpoint is continuously decreased to the second coolant temperature threshold using a ramp function.
7. 7. The drying method (100) according to claim 1, wherein the second coolant temperature threshold is formed using a maximum value of an application parameter, an ambient temperature of the fuel cell system, and a predetermined variance value.
8. Drying method (100) according to any one of claims 1 to 7, characterized in that the drying method is started in response to a command to shut down the fuel cell system.
9. A fuel cell system (200) for converting energy, comprising: The fuel cell system (200) a fuel cell stack (201) comprising an anode section (203) and a cathode section (205); - a purge valve (207) for evacuating the fluid from said anode section (203); a metering valve (209) for metering fluid into said anode section (203); a fan (211) for supplying a volumetric flow into said cathode section (205); a cooling system (213), a calculation unit (215), Including, The computing unit (215) is configured to perform the drying method (100) according to any one of claims 1 to 8. A fuel cell system (200).
10. the cooling system (213) includes a three-way valve (223), a coolant pump that supplies coolant to the fuel cell stack (201), and a heat exchanger in contact with the surroundings; The three-way valve (223) is connected to a pipe (219) leading to the outlet of the heat exchanger, a pipe leading to the refrigerant pump, and a bypass pipe (225); The bypass pipe (225) passes by the coolant pump and the fuel cell stack (201) and is connected to the inlet of the heat exchanger.
10. The fuel cell system (200) of claim 9.