A multi-stage heat cascade recovery system for a proton exchange membrane fuel cell stack

Abstract

The application provides a multi-stage heat gradient recovery system of a proton exchange membrane fuel cell stack, belonging to the field of air-cooled proton exchange membrane fuel cell stacks, and comprising: an air-cooled fuel cell stack, a cold and hot fluid mixing heat exchanger, a flow control valve, a heat exchanger, a heat exchanger working fluid flow control valve and a stack end plate heater; hot air at the outlet of the last air-cooled fuel cell stack is used to heat the air inlet of the first air-cooled fuel cell stack; for the air-cooled fuel cell stacks in the middle, hot air at the outlet of the air-cooled fuel cell stack is used to heat the air inlet of the adjacent air-cooled fuel cell stack; the cathode exhaust gas of each air-cooled fuel cell stack enters the heat exchanger through the flow control valve; the air-cooled fuel cell stack is provided with the stack end plate heater at both ends; and the heat exchanger absorbs heat from the outlet of the air-cooled fuel cell stack to heat the circulating working fluid. The application improves the environmental adaptability of the air-cooled stack system and the stack output consistency.

Description

Technical Field

[0001] This invention belongs to the field of air-cooled proton exchange membrane fuel cell stacks, and more specifically, relates to a multi-stage heat recovery system for proton exchange membrane fuel cell stacks. Background Technology

[0002] Air-cooled proton exchange membrane fuel cells (PEMFCs) typically feature an open cathode structure, with a fan supplying air to the cathode side. This airflow serves to supply oxidizing gases and dissipate heat from the fuel cell stack. This structure integrates the cathode intake and cooling circuits, simplifying the fuel cell stack's system structure and significantly reducing its weight and size. However, in room temperature environments, compact air-cooled PEMFC stacks often suffer from low endplate temperatures, affecting the performance of cells near the endplates. In low-temperature environments, high cathode airflow velocities can cause excessive heat loss in the fuel cell, limiting its use in cold environments. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a multi-stage heat recovery system for proton exchange membrane fuel cell stacks. This system addresses the problems of existing compact air-cooled proton exchange membrane fuel cell stacks where low endplate temperatures at room temperature affect the performance of cells near the endplates, and high cathode wind speeds at low temperatures can cause excessive heat loss in the fuel cell, thus limiting its use in low-temperature environments.

[0004] To achieve the above objectives, the present invention provides a multi-stage heat recovery system for a proton exchange membrane fuel cell stack, comprising: several air-cooled fuel cell stacks, a hot and cold fluid mixing heat exchanger, a flow control valve, a heat exchanger, a heat exchange medium flow control valve, and a stack endplate heater; wherein the number of air-cooled fuel cell stacks and hot and cold fluid mixing heat exchangers are equal.

[0005] Air-cooled fuel cell stacks are connected in series for air intake; a hot and cold fluid mixing heat exchanger is placed at the air intake of each air-cooled fuel cell stack; the hot air outlet of the last air-cooled fuel cell stack heats the air intake of the first air-cooled fuel cell stack; for intermediate air-cooled fuel cell stacks, the hot air outlet of the air-cooled fuel cell stack in the air intake to air outlet direction heats the air intake of the adjacent next-stage air-cooled fuel cell stack; the cathode outlet air of each air-cooled fuel cell stack enters the heat exchanger with a preset proportion of hot fluid through a flow control valve; a heat exchange medium flow control valve is set between the heat exchanger and each air-cooled fuel cell stack; stack end plate heaters with heat exchange medium flow channels are set at both ends of the air-cooled fuel cell stack; the hot air outlet of the last air-cooled fuel cell stack is introduced into the hot and cold fluid mixing heat exchanger corresponding to the first air-cooled fuel cell stack through a flow control valve, and the remaining hot air outlet of the last air-cooled fuel cell stack is released through a flow control valve.

[0006] The heat exchanger is used to absorb heat from the outlet of the air-cooled fuel cell stack to heat the circulating working fluid. The working fluid heats the stack endplates by flowing through the flow channels of the stack endplate heater.

[0007] More preferably, there are at least two air-cooled fuel cell stacks, and the spacing between adjacent air-cooled fuel cell stacks is 1cm to 200cm.

[0008] More preferably, for each air-cooled fuel cell stack, the proportion of the air flow rate entering the heat exchanger through the flow control valve to heat the end plates is 0% to 100% of the total air flow rate; in low-temperature environments, the proportion of the air flow rate used to heat the end plates of the air-cooled fuel cell stack is 0% to 40% of the total air flow rate, and the remaining air is used to heat the intake air of the adjacent next-stage air-cooled fuel cell stack; in normal-temperature environments, the proportion of the air flow rate used to heat the end plates of the air-cooled fuel cell stack is 50% to 100% of the total air flow rate, and the remaining air is used to heat the intake air of the adjacent next-stage air-cooled fuel cell stack.

[0009] More preferably, the size of the hot and cold fluid mixing heat exchanger is smaller than the distance between the inlet and outlet ports of adjacent air-cooled fuel cell stacks, and the thickness of the hot and cold fluid mixing heat exchanger is 10% to 70% of the distance between the inlet and outlet ports of adjacent air-cooled fuel cell stacks.

[0010] More preferably, the air-cooled fuel cell stack is arranged in a linear or loop pattern.

[0011] More preferably, the air-cooled fuel cell stack includes a first air-cooled fuel cell stack, a second air-cooled fuel cell stack, a third air-cooled fuel cell stack, and a fourth air-cooled fuel cell stack.

[0012] More preferably, when the multi-stage heat recovery system of the proton exchange membrane fuel cell stack is in a normal temperature environment, the exhaust gas from all air-cooled fuel cell stacks is used for heating the stack endplates; the hot air from the fourth stack outlet, the first stack outlet, the second stack outlet, and the third stack outlet is introduced into the heat exchanger through the fourth flow control valve, the first flow control valve, the second flow control valve, and the third flow control valve, respectively, and heated by the circulating working fluid to the first, second, third, and fourth air-cooled fuel cell stacks; when the fourth air-cooled fuel cell stack has excess heat, it is released through the sixth flow control valve.

[0013] More preferably, when the multi-stage heat recovery system of the proton exchange membrane fuel cell stack is in a sub-zero environment, the heat ratio of stack endplate heating and intake air heating is distributed through the first flow control valve, the second flow control valve, the third flow control valve and the fourth flow control valve; and the heat distribution ratio of each stage of stack endplate heating is adjusted through the first heat exchange medium flow control valve, the second heat exchange medium flow control valve, the third heat exchange medium flow control valve and the fourth heat exchange medium flow control valve.

[0014] In summary, compared with the prior art, the above-described technical solutions conceived by this invention have the following advantages:

[0015] Beneficial effects:

[0016] This invention provides a multi-stage heat recovery and cascade utilization system for multiple air-cooled fuel cell stacks. The hot air outlet of the last air-cooled fuel cell stack heats the inlet air of the first air-cooled fuel cell stack. For intermediate air-cooled fuel cell stacks, the hot air outlet of the air-cooled fuel cell stack in the inlet-to-outlet direction heats the inlet air of the adjacent air-cooled fuel cell stack. The cathode outlet air of each air-cooled fuel cell stack enters a heat exchanger via a flow control valve at a preset ratio of hot fluid. A heat exchange medium flow control valve is installed between the heat exchanger and each air-cooled fuel cell stack. As can be seen, the system effectively recovers and utilizes the heat from the cathode outlet of the air-cooled stacks. Part of the recovered heat is used to heat the cathode inlet air of the next stage stack, and the other part is used through the heat exchanger to heat the end plates of each stage stack using the circulating working fluid. This achieves the goal of heating the cathode inlet air of the air-cooled stack while simultaneously heating the stack end plates. The uniform heating of the inlet air and end plates increases the stack temperature, improving the environmental adaptability of the air-cooled stack system, the consistency of stack output, and the overall system output performance. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a multi-stage energy cascade recovery system for a proton exchange membrane fuel cell stack with linear arrangement provided in an embodiment of the present invention;

[0018] Figure 2 This is a schematic diagram of a multi-stage heat recovery system for a proton exchange membrane fuel cell stack with a U-shaped arrangement provided in an embodiment of the present invention;

[0019] Marker explanation:

[0020] 1-First air-cooled fuel cell stack; 2-Second air-cooled fuel cell stack; 3-Third air-cooled fuel cell stack; 4-Fourth air-cooled fuel cell stack; 5-First hot and cold fluid mixing heat exchanger; 6-Second hot and cold fluid mixing heat exchanger; 7-Third hot and cold fluid mixing heat exchanger; 8-Fourth hot and cold fluid mixing heat exchanger; 9-First flow control valve; 10-Second flow control valve; 11-Third flow control valve; 12-Fourth flow control valve; 13-Heat exchanger; 14-First heat exchange medium flow control valve; 15-Second heat exchange medium flow control valve; 16-Third heat exchange medium flow control valve; 17-Fourth 18-Fifth flow control valve for heat exchange medium; 19-Sixth flow control valve; 20-Fourth fuel cell stack outlet hot air; 21-Fresh air introduced into the first hot and cold fluid mixing heat exchanger; 22-First fuel cell stack outlet hot air; 23-Fresh air introduced into the second hot and cold fluid mixing heat exchanger; 24-Second fuel cell stack outlet hot air; 25-Fresh air introduced into the third hot and cold fluid mixing heat exchanger; 26-Third fuel cell stack outlet hot air; 27-Fresh air introduced into the fourth hot and cold fluid mixing heat exchanger; 28-First fuel cell stack end plate heater; 29-Second fuel cell stack end plate heater; 30-Third fuel cell stack end plate heater; 31-Fourth fuel cell stack end plate heater. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] Example 1

[0023] like Figure 1 As shown, the linearly arranged proton exchange membrane fuel cell stack multi-stage heat recovery system, taking a four-stage stack as an example, includes four air-cooled fuel cell stacks. Specifically, the linearly arranged proton exchange membrane fuel cell stack multi-stage heat recovery system includes: a first air-cooled fuel cell stack 1, a second air-cooled fuel cell stack 2, a third air-cooled fuel cell stack 3, a fourth air-cooled fuel cell stack 4, a first hot and cold fluid mixing heat exchanger 5, a second hot and cold fluid mixing heat exchanger 6, and a third hot and cold fluid mixing heat exchanger 7. 8. Fourth hot and cold fluid mixing heat exchanger; 9. First flow control valve; 10. Second flow control valve; 11. Third flow control valve; 12. Fourth flow control valve; 13. Heat exchanger; 14. First heat exchange medium flow control valve; 15. Second heat exchange medium flow control valve; 16. Third heat exchange medium flow control valve; 17. Fourth heat exchange medium flow control valve; 18. Fifth flow control valve; 19. Sixth flow control valve; 28. First fuel cell stack end plate; 29. ​​Second fuel cell stack end plate; 30. Third fuel cell stack end plate; and 31. Fourth fuel cell stack end plate.

[0024] The first air-cooled fuel cell stack 1, the second air-cooled fuel cell stack 2, the third air-cooled fuel cell stack 3, and the fourth air-cooled fuel cell stack 4 are connected in series for air intake; the hot air outlet 20 of the fourth stack heats the air intake of the first air-cooled fuel cell stack 1; the hot air outlet 22 of the first stack heats the air intake of the second air-cooled fuel cell stack 2; the hot air outlet 24 of the second stack heats the air intake of the third air-cooled fuel cell stack 3; the hot air outlet 26 of the third stack heats the air intake of the fourth air-cooled fuel cell stack 4; and the first air-cooled fuel cell stack 1, the second air-cooled fuel cell stack 2, the third air-cooled fuel cell stack 3, and the fourth air-cooled fuel cell stack 4 are respectively equipped with a first air-cooled fuel cell stack 4 before air intake. A hot and cold fluid mixing heat exchanger 5, a second hot and cold fluid mixing heat exchanger 6, a third hot and cold fluid mixing heat exchanger 7, and a fourth hot and cold fluid mixing heat exchanger 8 are provided. The cathode gas of the first air-cooled fuel cell stack 1 exits through the first flow control valve 9, the cathode gas of the second air-cooled fuel cell stack 2 exits through the second flow control valve 10, the cathode gas of the third air-cooled fuel cell stack 3 exits through the third flow control valve 11, and the cathode gas of the fourth air-cooled fuel cell stack 4 exits through the fourth flow control valve 12. The first flow control valve 9, the second flow control valve 10, the third flow control valve 11, and the fourth flow control valve 12 respectively introduce a portion of the hot fluid into the heat exchanger 13 for heat exchange.

[0025] The hot air 20 from the fourth stack outlet of the fourth air-cooled fuel cell stack 4 is introduced into the first hot and cold fluid mixing heat exchanger 5 through the fifth flow control valve 18 and mixed with the fresh air 21 introduced by the first hot and cold fluid mixing heat exchanger to form hot air entering the first air-cooled fuel cell stack 1; the hot air 22 from the first stack outlet of the first air-cooled fuel cell stack 1 is introduced into the second hot and cold fluid mixing heat exchanger 6 and mixed with the fresh air 23 introduced by the second hot and cold fluid mixing heat exchanger to form hot air entering the second air-cooled fuel cell stack 2; the hot air 24 from the second stack outlet is introduced into the third hot and cold fluid mixing heat exchanger 7 and mixed with the fresh air 25 introduced by the third hot and cold fluid mixing heat exchanger to form hot air entering the third air-cooled fuel cell stack 3; the hot air 26 from the third stack outlet is introduced into the fourth hot and cold fluid mixing heat exchanger 8 and mixed with the fresh air 27 introduced by the fourth hot and cold fluid mixing heat exchanger to form hot air entering the fourth air-cooled fuel cell stack 4.

[0026] Heat exchanger 13 absorbs heat from the stack outlet to heat the circulating working fluid. The circulating working fluid heats the first stack end plate heater 28 of the first air-cooled fuel cell stack 1 through the first heat exchange working fluid flow control valve 14, heats the second end plate heater 29 of the second air-cooled fuel cell stack 2 through the second heat exchange working fluid flow control valve 15, heats the third end plate heater 30 of the third air-cooled fuel cell stack 3 through the third heat exchange working fluid flow control valve 16, and heats the fourth end plate heater 31 of the fourth air-cooled fuel cell stack 4 through the fourth heat exchange working fluid flow control valve 17.

[0027] A multi-stack thermal series system contains two or more fuel cell stacks. The distance between the air inlet and outlet of the two stacks should not be too large to avoid heat waste. The distance should be selected reasonably according to the actual power size of the stack, preferably 1cm-200cm.

[0028] The flow rate entering the heat exchanger 13 through the first flow control valve 9, the second flow control valve 10, the third flow control valve 11, and the fourth flow control valve 12 to heat the end plate accounts for 0% to 100% of the total outlet air flow rate. Under low temperature conditions, the flow rate of the end plate heating accounts for 0% to 40% of the total outlet air flow rate, and under normal temperature conditions, the flow rate of the end plate heating accounts for 50% to 100% of the total outlet air flow rate.

[0029] The size of the heat exchanger for mixing hot and cold fluids should be smaller than the distance between the inlet and outlet ports between the two-stage fuel cell stacks to allow sufficient space for fluid mixing. The thickness is preferably 10% to 70% of the distance between the inlet and outlet ports.

[0030] When the system operates in a normal temperature environment, the effect of intake air heating on system power improvement is limited, and all exhaust air can be used for end plate heating. The hot air from the fourth stack outlet 20, the first stack outlet 22, the second stack outlet 24, and the third stack outlet 26 are introduced into the heat exchanger 13 through the fourth flow control valve 12, the first flow control valve 9, the second flow control valve 10, and the third flow control valve 11, respectively. After circulating through the energy-converting working fluid, the first air-cooled fuel cell stack 1, the second air-cooled fuel cell stack 2, the third air-cooled fuel cell stack 3, and the fourth air-cooled fuel cell stack are heated. Stack 4; when the heat of the fourth air-cooled fuel cell stack 4 is excessive, it is released through the sixth flow control valve 19; when the system working environment is a sub-zero temperature environment, the heat ratio of stack end plate heating and intake air heating is reasonably distributed through the first flow control valve 9, the second flow control valve 10, the third flow control valve 11 and the fourth flow control valve 12; the heat distribution ratio of each stage of stack end plate heating can be reasonably adjusted through the first heat exchange medium flow control valve 14, the second heat exchange medium flow control valve 15, the third heat exchange medium flow control valve 16 and the fourth heat exchange medium flow control valve 17.

[0031] Example 2

[0032] like Figure 2 As shown, this is a multi-stage energy cascade recovery system for proton exchange membrane fuel cell stacks arranged in a U-shape. The system includes four stacks. The overall structure and implementation method of this embodiment are similar to those of Embodiment 1, and will not be repeated. The system includes, but is not limited to, linear and U-shaped arrangements, which can make the entire system more compact. This arrangement can be used to reduce the system's footprint when space is limited. The system is rationally configured, and heat is recovered and reused. The allocation and utilization of recovered heat are adjusted through valves at each level, and the heating power at each level is adjusted according to the actual operating conditions and usage of the system.

[0033] In summary, compared with the prior art, the present invention has the following advantages:

[0034] This invention provides a multi-stage heat recovery and cascade utilization system for multiple air-cooled fuel cell stacks. The hot air outlet of the last air-cooled fuel cell stack heats the inlet air of the first air-cooled fuel cell stack. For intermediate air-cooled fuel cell stacks, the hot air outlet of the air-cooled fuel cell stack in the inlet-to-outlet direction heats the inlet air of the adjacent air-cooled fuel cell stack. The cathode outlet air of each air-cooled fuel cell stack enters a heat exchanger via a flow control valve at a preset ratio of hot fluid. A heat exchange medium flow control valve is installed between the heat exchanger and each air-cooled fuel cell stack. As can be seen, the system effectively recovers and utilizes the heat from the cathode outlet of the air-cooled stacks. Part of the recovered heat is used to heat the cathode inlet air of the next stage stack, and the other part is used through the heat exchanger to heat the end plates of each stage stack using the circulating working fluid. This achieves the goal of heating the cathode inlet air of the air-cooled stack while simultaneously heating the stack end plates. The uniform heating of the inlet air and end plates increases the stack temperature, improving the environmental adaptability of the air-cooled stack system, the consistency of stack output, and the overall system output performance.

[0035] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A multi-stage energy cascade recovery system for a proton exchange membrane fuel cell stack, characterized in that, include: The fuel cell stacks include several air-cooled fuel cell stacks, hot and cold fluid mixing heat exchangers, flow control valves, heat exchangers, heat exchange medium flow control valves, and stack end plate heaters; wherein the number of air-cooled fuel cell stacks and hot and cold fluid mixing heat exchangers is equal. The air-cooled fuel cell stacks are connected in series for air intake; a hot and cold fluid mixing heat exchanger is placed at the air intake of each air-cooled fuel cell stack; the outlet hot air of the last air-cooled fuel cell stack heats the inlet air of the first air-cooled fuel cell stack; for the intermediate air-cooled fuel cell stacks, the outlet hot air of the air-cooled fuel cell stack in the air intake to outlet direction heats the inlet air of the adjacent next-stage air-cooled fuel cell stack; the cathode outlet air of each air-cooled fuel cell stack enters the heat exchanger with a preset proportion of hot fluid through a flow control valve; a heat exchange medium flow control valve is provided between the heat exchanger and each air-cooled fuel cell stack; stack end plate heaters with heat exchange medium flow channels are provided at both ends of the air-cooled fuel cell stack; the outlet portion of the hot air of the last air-cooled fuel cell stack is introduced into the hot and cold fluid mixing heat exchanger corresponding to the first air-cooled fuel cell stack through a flow control valve, and the remaining hot air at the outlet of the last air-cooled fuel cell stack is released through a flow control valve. The heat exchanger is used to absorb heat from the outlet of the air-cooled fuel cell stack to heat the circulating working fluid. The working fluid heats the stack endplate by flowing through the flow channel of the stack endplate heater.

2. The multi-stage energy cascade recovery system for a proton exchange membrane fuel cell stack according to claim 1, characterized in that, There are at least two air-cooled fuel cell stacks, and the spacing between adjacent air-cooled fuel cell stacks is 1cm to 200cm.

3. The multi-stage energy cascade recovery system for a proton exchange membrane fuel cell stack according to claim 1 or 2, characterized in that, For each air-cooled fuel cell stack, the proportion of the outflow used to heat the end plates of the heat exchanger through the flow control valve is 0% to 100% of the total outflow. In low-temperature environments, the proportion of the outflow used to heat the end plates of the air-cooled fuel cell stack is 0% to 40% of the total outflow, and the remaining outflow is used to heat the intake air of the adjacent next-stage air-cooled fuel cell stack. In normal-temperature environments, the proportion of the outflow used to heat the end plates of the air-cooled fuel cell stack is 50% to 100% of the total outflow, and the remaining outflow is used to heat the intake air of the adjacent next-stage air-cooled fuel cell stack.

4. The multi-stage energy cascade recovery system for a proton exchange membrane fuel cell stack according to claim 3, characterized in that, The thickness of the hot and cold fluid mixing heat exchanger is 10% to 70% of the distance between the inlet and outlet of adjacent air-cooled fuel cell stacks.

5. The multi-stage energy cascade recovery system for a proton exchange membrane fuel cell stack according to claim 1, characterized in that, The air-cooled fuel cell stack is arranged in a linear or loop pattern.

6. The multi-stage energy cascade recovery system for a proton exchange membrane fuel cell stack according to claim 1 or 5, characterized in that, The air-cooled fuel cell stack includes a first air-cooled fuel cell stack, a second air-cooled fuel cell stack, a third air-cooled fuel cell stack, and a fourth air-cooled fuel cell stack.

7. The multi-stage energy cascade recovery system for a proton exchange membrane fuel cell stack according to claim 6, characterized in that, When the multi-stage heat recovery system of the proton exchange membrane fuel cell stack is in a normal temperature environment, the exhaust gas from all air-cooled fuel cell stacks is used for heating the stack endplates. The hot air from the fourth stack outlet, the first stack outlet, the second stack outlet, and the third stack outlet is introduced into the heat exchanger through the fourth flow control valve, the first flow control valve, the second flow control valve, and the third flow control valve, respectively. After circulating through the energy exchange medium, the first, second, third, and fourth air-cooled fuel cell stacks are heated. When the fourth air-cooled fuel cell stack has excess heat, it is released through the sixth flow control valve.

8. The multi-stage energy cascade recovery system for a proton exchange membrane fuel cell stack according to claim 6, characterized in that, When the multi-stage heat recovery system of the proton exchange membrane fuel cell stack is in a sub-zero environment, the heat ratio of stack endplate heating and intake air heating is distributed through the first, second, third and fourth flow control valves; and the heat distribution ratio of each stage of stack endplate heating is adjusted through the first, second, third and fourth heat exchange medium flow control valves.

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