Air-cooled fuel cell system
The air-cooled fuel cell system addresses the challenge of low-temperature inefficiency by reversing cooling air flow in independent channels, enhancing temperature uniformity and performance without enlarging the casing or adding mechanical structures.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- TOYOTA JIDOSHA KK
- Filing Date
- 2023-07-31
- Publication Date
- 2026-05-19
AI Technical Summary
Existing air-cooled fuel cell systems require larger casings and mechanical structures to circulate cooling air, leading to increased complexity and inefficiency, particularly at low temperatures, where temperature uniformity is challenging.
An air-cooled fuel cell system with independent reaction air and cooling air channels, allowing for reversing the flow of cooling air when predetermined conditions are met, such as low ambient temperature, to achieve temperature uniformity without the need for additional fans or mechanical structures.
The system maintains excellent operating performance at low temperatures by preventing condensation and flooding, reducing the size and complexity of the casing, and improving efficiency through temperature equalization.
Smart Images
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Abstract
Description
Technical Field
[0001] The present disclosure relates to an air-cooled fuel cell system.
Background Art
[0002] Various technologies have been proposed regarding fuel cells (FCs) as disclosed in Patent Documents 1-5.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Patent Document 2
Patent Document 3
Patent Document 4
Patent Document 5
Summary of the Invention
Problems to be Solved by the Invention
[0004] In the prior art, in order to circulate the cooling air, it is necessary to increase the size of the case. Or, it is necessary to add a reversibly rotatable cooling fan or a mechanical structure.
[0005] In view of the above circumstances, the present disclosure is made, and the main object is to provide an air-cooled fuel cell system that suppresses the enlargement and complication of the case and has excellent operating performance of the fuel cell at low temperatures.
Means for Solving the Problems
[0006] In the present disclosure, an air-cooled fuel cell system, The fuel cell system comprises a fuel cell, a hydrogen system for supplying hydrogen to the fuel cell, a reaction air system for supplying reaction air to the fuel cell, and a cooling air system for supplying cooling air to the fuel cell. The fuel cell has a reaction air channel and a cooling air channel, each with an independent flow path structure for the reaction air and the cooling air. The fuel cell system has a case, The case houses the fuel cell, The case has an upstream space and a downstream space in the direction of the flow of the cooling air within the case, with respect to the fuel cell. The cooling air system has a cooling air blowing means that generates the flow of the cooling air in the downstream space, The reaction air system has a reaction air intake port and a reaction air blowing means in the upstream space. The fuel cell system is characterized in that, when a predetermined switching condition occurs, the fuel cell system stops driving the cooling air blowing means and drives the reaction air blowing means to reverse the flow of the cooling air in the case.
[0007] In this disclosure, the predetermined switching condition may be at least one selected from the group consisting of when the ambient temperature is below a predetermined temperature, when the voltage amplitude value of the fuel cell is greater than or equal to a predetermined value, and when the temperature difference between the cooling air inlet temperature and the cooling air outlet temperature in the plane of the fuel cell is greater than or equal to a predetermined value. [Effects of the Invention]
[0008] The fuel cell system disclosed herein offers excellent fuel cell operating performance at low temperatures while suppressing the increase in size and complexity of the case. [Brief explanation of the drawing]
[0009] [Figure 1] This is an exploded perspective schematic diagram showing an example of a single cell of the fuel cell system of the fuel cell system of this disclosure. [Figure 2] This diagram shows an example of a fuel cell system in normal operation as disclosed herein. [Figure 3] This diagram shows an example of a fuel cell system operating under temperature uniformity in accordance with the disclosure. [Figure 4] This is a schematic diagram showing an example of the temperature distribution inside a cell during normal operation. [Figure 5] This is a schematic diagram showing an example of the temperature distribution within a cell during temperature uniformity operation. [Figure 6] This flowchart shows an example of control for a fuel cell system in this disclosure. [Modes for carrying out the invention]
[0010] Embodiments of this disclosure are described below. Matters other than those specifically mentioned herein but necessary for the implementation of this disclosure (e.g., general configurations and manufacturing processes of fuel cell systems not characterizing this disclosure) can be understood as design matters for those skilled in the art based on prior art. This disclosure can be implemented based on the content disclosed herein and common technical knowledge in the art. Furthermore, the dimensions (length, width, thickness, etc.) shown in the diagram do not necessarily reflect the actual dimensions. In this disclosure, the gas supplied to the anode of the fuel cell is the fuel gas (anode gas), and the gas supplied to the cathode of the fuel cell is the oxidizer gas (cathode gas). The fuel gas is a gas mainly containing hydrogen, but may also be hydrogen. The oxidizer gas is a gas containing oxygen, but may also be oxygen, air, etc. In this disclosure, air used as the oxidizer gas is referred to as reaction air, and air used as the cooling gas is referred to as cooling air.
[0011] In this disclosure, an air-cooled fuel cell system is provided. The fuel cell system comprises a fuel cell, a hydrogen system for supplying hydrogen to the fuel cell, a reaction air system for supplying reaction air to the fuel cell, and a cooling air system for supplying cooling air to the fuel cell. The fuel cell has a reaction air flow path and a cooling air flow path with an independent flow path structure for the reaction air and the cooling air. The fuel cell system has a case. The case houses the fuel cell. Based on the fuel cell, the case has an upstream space and a downstream space in the flow direction of the cooling air within the case. The cooling air system has a cooling air blowing means for generating a flow of the cooling air in the downstream space. The reaction air system has a reaction air intake port and a reaction air blowing means in the upstream space. When a predetermined switching condition occurs, the fuel cell system stops driving the cooling air blowing means, drives the reaction air blowing means, and reverses the flow of the cooling air within the case. A fuel cell system is provided characterized by this.
[0012] In the prior art, in order to circulate the cooling air, it is necessary to provide a special fan that can rotate reversely, which requires an increase in the size of the case, an increase in the cost of the device, and a decrease in the efficiency of the cooling fan during normal operation. There are problems such as this. Providing a mechanism for reversing the fan or installing an additional fan for reverse flow requires an increase in the size of the case, an increase in the cost of the device, and other problems. Also, in the prior art, since the temperature adjustment of the fuel cell by the cooling air and the supply of the reaction air to the fuel cell are controlled by the same fan, for example, when it is desired to make the cooling air flow rate very small and supply a large amount of reaction air to the fuel cell, independent control of each cannot be achieved. The present disclosure relates to a method for uniformizing the temperature during effective low-temperature operation of an air-cooled fuel cell. By sucking in reaction air from the intake side compartment, the flow of the cooling air flow path can be reversed to uniformize the temperature within the cell surface. There is no need to provide a special fan that can rotate reversely, the increase in size and complexity of the case can be suppressed, and the operating performance of the fuel cell at low temperatures can be improved.
[0013] The fuel cell system comprises a fuel cell that generates electricity through the reaction of hydrogen and air, a hydrogen system that supplies hydrogen necessary for the fuel cell to generate electricity, a reaction air system that supplies reaction air to the fuel cell, and a cooling air system that supplies cooling air to cool the heat generated by the power generation of the fuel cell.
[0014] A fuel cell may consist of only one single fuel cell, or it may be a fuel cell stack, which is a stack of multiple cells arranged in a single layer. In this disclosure, both cells and fuel cell stacks may be referred to as fuel cells. The number of cells stacked in a fuel cell stack is not particularly limited and may range from 2 to several hundred. The fuel cell stack may have corrugated cooling fins in each cell that serve as cooling air passages. The fuel cell stack may have current collector plates, pressure plates, etc., at its ends in the stacking direction.
[0015] A fuel cell has a reaction air channel (oxidizer gas channel) and a cooling air channel (cooling gas channel) with independent flow path structures for the reaction air and cooling air, and may also have a hydrogen gas channel (fuel gas channel). A flow path structure in which the reaction air and cooling air are independent means that there is no sharing of air between the flow paths, from the supply of air to the fuel cell to the discharge of air from the fuel cell. The flow path for discharging the air discharged from the fuel cell to the outside of the fuel cell system may or may not be independent.
[0016] The cell may have a flow path structure for the reaction air and the cooling air such that, in a plan view, the flow of cooling air and the flow of reaction air intersect. The flow of cooling air and the flow of reaction air may intersect or be perpendicular to each other. The cell may have a power generation unit. The shape of the power generation unit may be rectangular in plan view. The power generation section may be a membrane electrode assembly (MEA) including an electrolyte membrane and two electrodes. The electrolyte membrane may be a solid polymer electrolyte membrane. Examples of solid polymer electrolyte membranes include fluorine-based electrolyte membranes such as a thin film of perfluorosulfonic acid containing water, and hydrocarbon-based electrolyte membranes. The electrolyte membrane may also be, for example, a Nafion membrane (manufactured by DuPont). The two electrodes are the anode (fuel electrode, or hydrogen electrode) and the cathode (oxygen electrode, or air electrode). The electrode includes a catalyst layer and may optionally include a gas diffusion layer, and the power generation section may be a membrane electrode gas diffusion layer assembly (MEGA). The catalyst layer includes a catalyst, which may comprise a catalytic metal that promotes an electrochemical reaction, a proton-conducting electrolyte, and an electron-conducting support, etc. Examples of catalyst metals that can be used include platinum (Pt) and alloys of Pt with other metals (for example, Pt alloys mixed with cobalt and nickel). The catalyst metal used as the cathode catalyst and the catalyst metal used as the anode catalyst may be the same or different. The electrolyte may be a fluororesin or the like. For example, a Nafion solution may be used as the fluororesin. The catalyst metal is supported on a support, and in each catalyst layer, the support on which the catalyst metal is supported (catalyst support) and the electrolyte may be mixed. Examples of carriers for supporting the catalytic metal include commercially available carbon materials such as carbon. The gas diffusion layer may be a conductive material having pores or the like. Examples of conductive materials include carbon porous materials such as carbon cloth and carbon paper, as well as metal porous materials such as metal mesh and foamed metal. The fuel cell may include a separator. Separators collect the current generated by power generation and function as partitions. In a fuel cell cell, separators are typically arranged on both sides of the power generation section in the stacking direction, with a pair of separators sandwiching the power generation section. One of the separators is the anode separator, and the other is the cathode separator. The anode separator may have grooves on the side facing the power generation section that serve as hydrogen gas flow channels. The cathode separator may have grooves on the side facing the power generation section that serve as reaction air channels. The separator may have holes that constitute a manifold, such as supply holes and discharge holes, for circulating fluid in the stacking direction of the cells. The separator may be, for example, dense carbon that has been compressed to be gas-impermeable, or press-formed metal (for example, iron, titanium, and stainless steel). The cell may include an insulating resin frame positioned on the outer (circumferential) side in the planar direction of the membrane electrode assembly between the anode separator and the cathode separator. The resin frame is molded from a thermoplastic resin to form a plate-like or frame-like structure, and seals the space between the anode separator and the cathode separator while holding the membrane electrode assembly in its central region. For example, resins such as PE, PP, PET, and PEN can be used for the resin frame. The resin frame may also be a three-layer sheet composed of three layers with an adhesive layer on the surface.
[0017] The fuel cell system may be equipped with a control device. The control device may control the reaction air system, hydrogen system, cooling air system, etc., and control the entire fuel cell system. Physically, the control device includes, for example, a processing unit such as a CPU (Central Processing Unit), a ROM (Read-Only Memory) that stores control programs and control data processed by the CPU, a storage device such as a RAM (Random Access Memory) used primarily as various work areas for control processing, and an input / output interface. It may also be an ECU (Electronic Control Unit).
[0018] The fuel cell system has a case. The case houses the fuel cell. The case, relative to the fuel cell, has an upstream space (intake side) and a downstream space (exhaust side) in the direction of the cooling air flow within the case. The case has an intake port and an exhaust port for the cooling air system. The upstream space is the partitioned area from the air intake to the fuel cell, while the downstream space is the partitioned area from the fuel cell to the cooling air supply mechanism.
[0019] The reaction air system supplies reaction air to the fuel cell as an oxidizing gas and adjusts the flow rate of the reaction air. The reaction air system has a reaction air intake and a reaction air blowing means in the upstream space within the case. A pressure drop element (air filter) may be installed in the reaction air intake. The reaction air supply means may be an air compressor, air pump, air blower, air fan, etc. The reaction air system may have an inlet sealing valve at the inlet of the reaction air of the fuel cell and an outlet sealing valve at the outlet of the reaction air of the fuel cell. The inlet sealing valve and the outlet sealing valve may be located in the upstream space within the case or in the downstream space within the case. In this disclosure, the fuel cell has a flow channel structure in which the reaction air and cooling air are independent, and valves (inlet sealing valve and outlet sealing valve) are installed at the inlet and outlet of the reaction air of the fuel cell in the reaction air system. This makes it possible to seal the cathode of the fuel cell in a smaller volume compared to the case in which the reaction air and cooling air share a common flow channel structure.
[0020] The cooling air system supplies cooling air to the fuel cell as a cooling gas and adjusts the flow rate of the cooling air. The cooling air system has a means for blowing cooling air to create a flow of cooling air in the downstream space inside the case. The cooling air system has an air intake port for drawing air from the outside. A pressure dropper (air filter) may be installed at the air intake port. The means for supplying cooling air may be an air compressor, air pump, air blower, air fan, etc.
[0021] The hydrogen system supplies hydrogen to the fuel cell as fuel gas and adjusts the flow rate of the hydrogen. The hydrogen system may include a hydrogen tank, a hydrogen inlet valve, an injector, a hydrogen purge valve, a gas-liquid separator, a hydrogen pump for hydrogen circulation, a hydrogen ejector for hydrogen circulation, and hydrogen piping, etc.
[0022] When predetermined switching conditions occur, the fuel cell system performs a cell temperature equalization operation by stopping the operation of the cooling air blowing means and driving the reaction air blowing means to reverse the flow of cooling air inside the case. Since the cooling air inside the fuel cell flows in the opposite direction to that of normal operation, the temperature inside the cell can be equalized. The predetermined switching conditions may be at least one selected from the group consisting of: when the ambient temperature is below a predetermined temperature; when the voltage amplitude value of the fuel cell is greater than or equal to a predetermined value; and when the temperature difference between the cooling air inlet temperature and the cooling air outlet temperature in the plane of the fuel cell is greater than or equal to a predetermined value.
[0023] Figure 1 is an exploded perspective schematic diagram showing an example of a single cell of a fuel cell system provided in the present disclosure. The cell 1 shown in Figure 1 comprises cooling fins (cooling air channels) 2 that serve as flow paths for cooling air (cooling gas) 7, a reaction air inlet 3, a reaction air outlet 4, a hydrogen gas inlet 5, a hydrogen gas outlet 6, two separators 11, and an MEA and resin frame 12 sandwiched between the two separators 11. As shown in Figure 1, the cell 1 of the fuel cell has a flow path structure in which the reaction air 9 and the cooling air 7 are independent of each other.
[0024] Figure 2 is a system configuration diagram showing an example of a fuel cell system under normal operation according to this disclosure. Figure 3 is a system configuration diagram showing an example of the fuel cell system of this disclosure during temperature uniformity operation. Figure 4 is a schematic diagram showing an example of the temperature distribution inside the cell during normal operation. Figure 5 is a schematic diagram showing an example of the temperature distribution inside a cell during temperature uniformity operation. The fuel cell system shown in Figures 2 and 3 comprises a case 50, a fuel cell stack 10, a reaction air system 20, a cooling air system 30, and a hydrogen system. In Figures 2 and 3, the description of the hydrogen system is omitted for convenience. The reaction air system 20 comprises a reaction air intake port 21, an air blower 22, an inlet sealing valve 23, and an outlet sealing valve 24. The cooling air system 30 comprises a cooling fan 31 and an intake port 32. The intake port 32 may be equipped with an intake filter. The fuel cell system shown in Figures 2 and 3 is equipped with sealing valves 23 and 24 at the inlet and outlet of the reaction air system 20, and has independent air blowing means 22 and 31 for the reaction air system 20 and the cooling air system 30. The reaction air intake port 21 may be equipped with an air filter. The fuel cell stack 10 has a flow channel structure in which the reaction air and cooling air are independent. Case 50 has an upstream space 52 and a downstream space 53 separated by a partition wall 51 in the direction of the flow of cooling air 7 within Case 50, relative to the fuel cell stack 10. The upstream space 52 is the partitioned space from the air intake 32 to the fuel cell stack 10, and the downstream space 53 is the partitioned space from the fuel cell stack 10 to the cooling fan 31. In the fuel cell system shown in Figures 2 and 3, the reaction air intake port 21 of the reaction air system 20, the air blower 22, the inlet side sealing valve 23, and the outlet side sealing valve 24 are housed in the upstream space 52 of the cooling air. Because the reaction air intake port 21 is located in the upstream space 52, which is the cooling air intake side, the cooling fan 31 can be stopped and the air blower 22 can be driven to reverse the flow of cooling air inside the case, as shown in Figure 3.
[0025] In air-cooled fuel cell stacks, outside air is directly drawn into the fuel cell stack, so the side where the outside air is drawn in becomes close to the ambient temperature T1 (Figures 2 and 4). Due to the heat generated by the cells, the cooling air is heated, and the temperature at the cell outlet becomes T2, which is higher than T1. For example, if the system is operating at T1=-5°C and T2=50°C, the low-temperature part 61 of the cell will cool down, causing the liquid water to increase too much, leading to flooding and a decrease in power generation performance, or it may freeze and block, making power generation impossible. During this time, temperature equalization operation reverses the flow of cooling air within the cell, transferring heat from the high-temperature section 60 to the low-temperature section 61, thereby equalizing the cell temperature and preventing a decrease in fuel cell performance (Figures 3 and 5). Since the reaction air is exhausted to the outside as in normal operation, moist exhaust gas does not flow back. If the reaction air intake is not located in the upstream space which is the cooling air intake side, or if there is no pressure drop at the intake, backflow of cooling air will not occur. In fuel cells where the reaction air channel and cooling air channel are not independent channel structures, backflow of moist cooling reaction air can cause condensation inside the case, potentially leading to malfunctions in electronic equipment. However, by having independent channel structures for the reaction air channel and cooling air channel of a fuel cell, the above-mentioned problems can be avoided.
[0026] Figure 6 is a flowchart showing an example of the control of the fuel cell system of this disclosure. First, we perform a temperature check. For example, it determines whether the ambient temperature or the temperature T1 inside the fuel cell system is less than a predetermined temperature T0. The predetermined temperature T0 can be set to any value as appropriate; for example, it may be set to the ambient temperature of 0°C. If T1 is equal to or greater than the predetermined temperature T0, the normal mode is executed and the control is terminated. On the other hand, if T1 is less than the predetermined temperature T0, the low-temperature mode is executed. In low-temperature mode, the presence or absence of water accumulation or freezing is determined. The presence or absence of water accumulation or freezing may be determined, for example, if a decrease in cell voltage or voltage fluctuations are detected by a cell voltage monitor. Alternatively, if power generation is performed for a certain period of time or longer in a low-temperature state, a large amount of water accumulation may be determined, and in this case, water accumulation may be determined. Furthermore, a temperature sensor may be installed in the low-temperature part of the fuel cell to directly measure the temperature of the fuel cell, and if the temperature of the fuel cell is below a predetermined temperature, freezing may be determined. If there is no puddle or ice formation, the normal mode is executed and the control is terminated. On the other hand, if there is a puddle or ice formation, the cooling air blowing means is stopped and the reaction air blowing means is driven to perform cell temperature equalization operation. After the temperature equalization operation, a recovery determination is made. Recovery may be determined when the decreased cell voltage rises to the normal voltage using a cell voltage monitor. Alternatively, recovery may be determined when the temperature equalization operation is continued for a certain period of time or longer, indicating that the warm-up is complete. Furthermore, a temperature sensor may be installed in the low-temperature part of the fuel cell to directly measure the fuel cell's temperature, and recovery may be determined when the fuel cell's temperature is above a predetermined temperature. In the recovery determination, if recovery is determined, normal operation is performed and control is terminated. On the other hand, if recovery is not determined in the recovery determination, temperature equalization operation is continued and an interruption determination is made. The interruption determination may be made, for example, when the ambient temperature T1 rises to or above a predetermined temperature T0. Alternatively, it may be determined that the system should be interrupted when the load required for the fuel cell system fluctuates. Furthermore, it may be determined that the system should be interrupted when an interruption from another mode occurs. If the interruption determination is made, normal operation will be performed and the control will be terminated. On the other hand, if the interruption determination is not made, the temperature equalization operation will continue. [Explanation of symbols]
[0027] 1. Cell 2. Cooling fins (cooling air passages) 3. Reaction air inlet 4. Reaction air outlet 5. Hydrogen gas inlet 6. Hydrogen gas outlet 7. Cooling air (cooling gas) 8. Hydrogen gas 9. Reaction air 10. Fuel cell stack 11. Separator 12. MEA, resin frame 20. Reaction air system 21. Reaction air intake 22. Air blower 23. Inlet sealing valve 24. Outlet side sealing valve 30. Cooling air system 31. Cooling fan 32. Air intake 50. Case 51. Bulkhead 52. Upstream space 53. Downstream space 60. High temperature section 61. Low-temperature section
Claims
1. An air-cooled fuel cell system, The fuel cell system comprises a fuel cell, a hydrogen system for supplying hydrogen to the fuel cell, a reaction air system for supplying reaction air to the fuel cell, and a cooling air system for supplying cooling air to the fuel cell. The fuel cell has a reaction air channel and a cooling air channel, each with an independent flow path structure for the reaction air and the cooling air. The fuel cell system has a case, The case houses the fuel cell, The case has an upstream space and a downstream space in the direction of the flow of the cooling air within the case, with respect to the fuel cell. The cooling air system has a cooling air blowing means that generates the flow of the cooling air in the downstream space, The reaction air system has a reaction air intake port and a reaction air blowing means in the upstream space. A fuel cell system characterized in that, when a predetermined switching condition occurs, the fuel cell system stops driving the cooling air blowing means and drives the reaction air blowing means to reverse the flow of the cooling air in the case.
2. The fuel cell system according to claim 1, wherein the predetermined switching condition is at least one selected from the group consisting of when the ambient temperature is below a predetermined temperature, when the voltage amplitude value of the fuel cell is greater than or equal to a predetermined value, and when the temperature difference between the cooling air inlet temperature and the cooling air outlet temperature in the plane of the fuel cell is greater than or equal to a predetermined value.